- Email: [email protected]
Space flight and oxidative stress
REGULATION OF PHYSIOLOGICAL SYSTEMS BY NUTRIENTS
Space Flight and Oxidative Stress T. P. Stein, PhD From the Department of Surgery, University of Medicine and Dentistry of New Jersey, School of Osteopathic Medicine, Stratford, New Jersey, USA Space flight is associated with an increase in oxidative stress after return to 1g. The effect is more pronounced after long-duration space flight. The effects lasts for several weeks after landing. In humans there is increased lipid peroxidation in erythrocyte membranes, reduction in some blood antioxidants, and increased urinary excretion of 8-iso-prostaglandin F2␣ and 8-oxo-7,8 dihydro-2 deoxyguanosine. Isoprostane 8-iso-prostaglandin F2␣ and 8-oxo-7,8 dihydro-2 deoxyguanosine are markers for oxidative damage to lipids and DNA, respectively. The changes have been attributed to a combination of the energy deficiency that occurs during flight and substrate competition for amino acids occurring between repleting muscle and other tissues during the recovery phase. The observations in humans have been complemented by rodent studies. Most rodent studies showed increased production of lipid peroxidation products postflight and decreased antioxidant enzyme activity postflight. The rodent observations were attributed to the stress associated with reentry into Earth’s gravity. Decreasing the imbalance between the production of endogenous oxidant defenses and oxidant production by increasing the supply of dietary antioxidants may lessen the severity of the postflight increase in oxidative stress. Nutrition 2002;18:867– 871. ©Elsevier Science Inc. 2002 KEY WORDS: space flight, human, rats, antioxidants
INTRODUCTION There is a balance within the body between oxidant production and antioxidant defenses, with the balance shifted slightly in favor of oxidants. The body generates about 5 g of reactive oxygen species (ROS) per day, mostly by leakage from the electron transport chain during oxidative phosphorylation.1 The major product of this “leakage” are the two ROS: the superoxide radical (O2⫺) and H2O2.1 Other ROS include free radicals such as nitric oxide and compounds such as ozone and HOCl. ROS can attack and damage cellular constituents such as DNA, proteins, and membrane lipids. Oxidative damage from free radicals to DNA and lipids has been implicated in the etiology of a wide variety of chronic diseases and acute pathologic states. The chronic diseases range from cancer to cardiovascular disease and neurodegenerative disease including Alzheimer and Parkinson diseases.1–7 Examples of acute states in which oxidative damage is suspected include ischemia-reperfusion injury,7,8 sepsis,9,10 inflammatory diseases,7,11 preeclampsia,12 and strenuous exercise.13–17 With exercise, the threshold for oxidative stress is lower for untrained and elderly subjects.17–19 Other factors that can result in increased oxidative damage include environmental pollutants,20 cigarette smoke,3,21 radiation,22 severe nutritional depletion undernutrition,1,23 and space flight.24 –28 Russian investigators found evidence for increased lipid peroxidation in human erythrocyte membranes and reductions in some blood antioxidants after long-duration space flight.24 –26 A subsequent study28 on the Russian space station Mir assessed the urinary excretion of 8-iso-prostaglandin F2␣ and 8-oxo-7,8 dihydro-2 deoxyguanosine (8-OH dG) in six subjects during and after long-duration space flight (90 to 180 d). Isoprostane 8-isoprostaglandin F2␣ and 8-OH dG are markers for oxidative damage
Supported by NASA contract NAS 9-18775. Correspondence to: T. P. Stein, PhD, Department of Surgery, University of Medicine and Dentistry of New Jersey, SOM, 2 Medical Center Drive, Stratford, NJ, 08084, USA. E-mail: [email protected] Nutrition 18:867– 871, 2002 ©Elsevier Science Inc., 2002. Printed in the United States. All rights reserved.
to lipids and DNA, respectively.29,30 The preflight measurements consisted of two to four 2-d sessions during the year before the mission to establish a baseline. In addition to 24-h urine collections, dietary intake was monitored but not controlled. The 24-h urine and dietary data were also collected in flight and for the 2 wk after landing. To facilitate interpretation of the data, the data from Mir were compared with the results from the 17-d Life and Microgravity Sciences shuttle mission (LMS) and a 17-d, 6-degree head-down tilt bedrest study.31 These flight data sets are inflight data that has been collected to date on either humans or animals.
IN-FLIGHT FINDINGS Urinary isoprostane excretion was decreased in flight by approximately 20% on Mir, by approximately 40% on the Space Shuttle, and unchanged with bedrest28 (Fig. 1). It would appear that oxidative damage to lipids was not increased during space flight. The most likely explanation is that the decrease in isoprostane production on Mir and LMS was due to a downregulation of intermediary metabolism, leading to a decreased flux through the electron transport system in response to the deficit in energy intake. The principal source of free radicals in the body is from free radical leakage (3% to 5% of the electron flux) from the electron transport chain.1 Decreased endogenous free radical production is the expected result if the flux is decreased and there is no increase in free radical generation from radiation. A decreased flux through the electron transport chain will generate fewer free radicals within the mitochondria. Figure 1 shows the trend toward an increase in 8-OH dG excretion in flight. A similar observation was made on the LMS mission. When the excretion rate of 8-OH dG is regressed against the energy deficit for either Mir or LMS, both show correlations that approach significance (P ⬍ 0.1; Fig. 2). The greater the decrease in energy intake, the more extensive free radical propagation because of the diminished protein-based antioxidant defenses. The whole-body protein synthesis rate was measured on Mir but not on LMS. Figure 2 shows that as the whole-body protein 0899-9007/02/$22.00 PII S0899-9007(02)00938-3
868
Stein
Nutrition Volume 18, Number 10, 2002 TABLE I. DISEASE AND THE EXCRETION OF THE PRODUCTS OF DNA AND LIPID OXIDATION32
8-OH dG After space flight on Mir Smoking, 1 pack/d Environmental cigarette smoke Cancer Radiotherapy Isoprostanes After space flight on Mir Smoking Diabetes Liver disease Hepatorenal syndrome
% Increase
Reference
150 200 60 150 400
28 67 68 3 3
200 200 350 500 900
28 21 69 30 70
8-OH dG, 8-oxo-7,8 dihydro-2 deoxyguanosine.
FIG. 1. Oxidative stress during and after space flight or bed rest.28 Data are from the National Aeronautics and Space Administration and Mir program (flight duration, 90 –180 d), the LMS shuttle mission (17 d), and a bedrest study (14 d). *P ⬍ 0.05 versus preflight value. 8-ISO-PGF2␣, 8-isoprostaglandin F2␣; 8-OH dG, 8-oxo-7,8 dihydro-2 deoxyguanosine; LMS, Life and Microgravity Sciences.
synthesis rate on Mir decreased as the energy deficit increased, 8-OH dG production increased. This observation suggests that there is a relationship between the ability to make proteins and the ability to protect DNA from ROS. There were no such correlations with isoprostanes for Mir or LMS (r2 ⫽ 0). The implication is that, for lipid oxidation during space flight, the dominant effect is the flux through the electron transport chain. The potential for radiation damage during long-duration flights (particularly for flights out of low Earth orbit, where the exposure to radiation flux is greater) is currently believed to be the most
FIG. 2. Inverse relationships between the decrease in intake, the decrease in protein synthesis (solid circles), and the increase in 8-OH dG excretion (open circles) during space flight on Mir compared to preflight. 8-OH dG, 8-oxo-7,8 dihydro-2 deoxyguanosine28,31
serious impediment to interplanetary travel. Isoprostane excretion was decreased and 8-OH dG was essentially unchanged during a flight on Mir.28 Any damage incurred from radiation on these near-Earth missions is likely to have been small and masked by the dominant nutritional effect. The effect of radiation damage is additive and depends on orbit and solar cycle activity and may be a major contributing factor to oxidative damage on long-duration missions farther away from Earth.
POSTFLIGHT FINDINGS Human Both 8-OH dG and 8-iso-prostaglandin F2␣ were increased by more than two-fold after more than 3 mo on Mir (Fig. 1). The implication is that oxidative damage after an extended period in orbit is increased after landing. There is other evidence for increased oxidative damage after space flight. Spot blood analyses by Russian investigators on cosmonauts after long-duration flights showed a non-statistically significant trend for an increase in the accumulation of lipid oxidation products in the serum and erythrocyte membranes.25 The erythrocyte membrane compositional changes were a combination of membrane lipid peroxidation and increased rigidity. The changes persisted for up to 6 mo after long-duration flight (up to 1 y) on Mir.25 Thus a number of independent studies have concluded that recovery after space flight is associated with an increase in oxidative damage. It is of interest to ask: How physiologically significant is this increase in oxidative damage? The answer depends on two factors, the magnitude of the increase and its duration. Table I compares the postflight urinary isoprostane and 8-OH dG excretion values against some well-known clinical conditions. Long-duration space flight appears to rank with cigarette smoking.32,33 The simplest explanation for the increased oxidative damage postflight in humans is that the increase is due to a combination of 1) the consequences of the loss of protein secondary to the in-flight reductive remodeling of skeletal muscle from the decreased work load on the antigravity muscles, 2) the in-flight protein depletion from inadequate dietary intake, and 3) the increased anabolism associated with protein repletion. With increased generation of adenosine triphosphate, leakage of ROS from the mitochondrial electron transport chain will be increased.1 Negative energy balance in humans has been a frequent finding during space flight.28,31,32,34 The LMS astronauts lost 2.6 ⫾ 0.4
Nutrition Volume 18, Number 10, 2002
Oxidative Stress
TABLE II. ENERGY INTAKE IS NOT INCREASED POSTFLIGHT EVEN THOUGH INTAKE IS DECREASED IN FLIGHT33* Intake (kcal 䡠 kg⫺1 䡠 d⫺1) Mission
Weight loss during flight (kg)
Preflight
In flight
Postflight
SLS1/2 LMS Mir
1.0 ⫾ 0.4† 3.6 ⫾ 0.4† 4.3 ⫾ 1.2†
39.6 ⫾ 2.4 35.6 ⫾ 2.1 34.8 ⫾ 3.3
31.5 ⫾ 1.5† 24.3 ⫾ 1.2† 26.3 ⫾ 2.3†
40.0 ⫾ 1.9 37.1 ⫾ 2.8 32.8 ⫾ 2.2
* Data presented as mean ⫾ standard error of the mean. † P ⬍ 0.05 versus preflight for weight and versus pre- and postflight for energy intake. LMS, Life and Microgravity Sciences; SLS1/2, Space Life Sciences 1 and 2.
kg, of which 1.5 ⫾ 0.6 kg was fat, and the Mir astronauts lost 4.3 ⫾ 1.2 kg. The reason for the weight loss was the very low dietary intake rather than an increase in energy expenditure. Energy intakes 24.6 ⫾ 3.3 kcal · kg⫺1 · d⫺1 on LMS and 26.3 ⫾ 2.3 kcal · kg⫺1 · d⫺1 on Mir.33 These values are substantially less than energy expenditure during space flight. There have been three independent measurements of energy expenditure during flight: on Skylab by the intake balance method (43.7 ⫾ ⬃1 kcal · kg⫺1 · d⫺1),35 across several shuttle missions by the doublelabeled water method (36.2 ⫾ 5.8 1 kcal · kg⫺1 · d⫺1),36 and by the double-labeled water and intake balance methods (40.8 ⫾ 1.6 1 kcal · kg⫺1 · d⫺1)34 on the LMS shuttle mission. Indeed, the energy deficit on Mir was enough to reduce the whole-body protein synthesis rate. Figure 2 shows that the greater the energy deficit, the greater the reduction in the whole-body protein synthesis rate. Two alternative explanations are increases in free radical production from 1) damage incurred from the reimposition of gravity on the atrophied muscles or 2) a large increase in metabolic activity. Explanation 1 is unlikely. On the ground, when there is increased oxidative damage after exercise,19,37 there is also an increase in 3-methylhistidine excretion.38,39 3-Methylhistidine excretion was not increased postflight on Mir and was not increased after flight on Skylab40 (Fig. 2). Explanation 2 is also improbable. Energy intake after flight is about the same as that before flight; there is no dramatic anabolic increase in intake. The observations make it improbable that there was a large increase in energy expenditure postflight in the absence of a parallel increase in dietary intake (Table II). A deficit in energy intake of the magnitude that occurred on Mir or LMS is not sustainable in the long term without some metabolic accommodation, one manifestation of which was a reduction in protein synthesis.31 On Mir, the greater the apparent energy deficit, the larger the decrease in the in-flight whole-body protein synthesis rate31 (Fig. 2). The downregulation of protein turnover leads to the loss of protein systems of lower priority to spare systems that are of higher priority. High-priority proteins are protected because of the high costs associated with their loss; nevertheless, some loss of protein antioxidants is likely, and these losses persist into the early postflight recovery phase.28 After long-duration space flight, protein metabolism is compromised due to the in-flight undernutrition. There is another factor that can lead to decreased production of antioxidant defenses postflight, which is the suboptimal synthesis of host (defense) proteins. There is some evidence that the synthesis of host antioxidant protein defenses could be suboptimal due to competition for amino acids occurring between repleting muscle and other tissues.41
869
Postflight, the Americans and the Russians found the plasma amino acids to be decreased.42– 46 The most consistent findings have concerned methionine and the branched-chain amino acids. Plasma methionine and branched-chain amino acid levels are reduced in the immediate postflight phase, and this decrease persists for the first week of recovery.41,43,47 The amino acids are needed to support the postflight anabolic replacement of proteins lost during space flight. There is other evidence, which is suggestive rather than conclusive, that protein synthesis is suboptimal postflight. First, whole-body protein synthesis should be increased postflight because the recovery period is anabolic. Except for the day of landing, no consistent evidence for an increase in protein synthesis was found after short-duration space flight on the Shuttle or long-duration space flight on Mir.33 Second, Russian investigators have reported that the synthesis of plasma proteins of hepatic origin is decreased a week after landing.46 Collectively, these observations are suggestive of amino acids being limiting postflight, possibly due to competition for substrates secondary to increased demand by repleting muscle and the requirements of the other tissues.48 Rodent Most,24,27 but not all,49 rodent studies showed increased production of lipid peroxidation products postflight and decreased antioxidant enzyme activity postflight. In rats flown on an 8-d Shuttle mission, Hollander et al.27 found space flight to simultaneously downregulate antioxidant defense capacity and elicit an oxidative stress in the liver. There was an approximately 50% increase in liver malondialdehyde concentration with space flight. Space flight significantly decreased catalase, glutathione reductase, glutathione sulfur-transferase, and ␥-glutamyl transpeptidase activities in the livers of flight rats when compared with those of ground controls. The relative abundance of mRNA for Cu-Zn superoxide dismutase and catalase were significantly decreased. Also decreased were liver glutathione and glutathione disulfide. The rodent observations were attributed to the stress associated with reentry into Earth’s gravity.24,27 Undernutrition is not likely to have been a factor in the postflight rodent response. Rats, unlike humans, are able to maintain intake and energy balance during space flight.50 However, substrate competition is still likely to occur after landing because repleting muscle and other tissues compete for the same amount of substrates. Consistent with substrate competition is a rat hindlimb suspension study by Tucker et al.51 During immobilization, muscle protein synthesis is reduced. After immobilization, protein synthesis in the gastrocnemius muscle returned to the preimmobilization baseline within 6 h, remained unchanged for the next 2 d, and then doubled on day 4.51
POSSIBLE COUNTERMEASURES The phenomenon of increased oxidative stress during the recovery process has not been reproduced in a relevant ground-based model. At this time no suitable models have been described. Increased oxidative stress does not occur after short-term bedrest by otherwise healthy people.28 The appropriate human ground-based model would probably be long-term bedrest on a hypocaloric diet, possibly with chronic supplemental chronic cortisol administration, a model that is ethically not tenable. The potential applicability of the rodent hindlimb suspension model has not been explored. All conceivable mechanisms point to an imbalance between oxidant stress and antioxidant defenses. Almost irrespective of what any ground studies might show, evaluation of antioxidant vitamins as a dietary supplement is likely to be the first countermeasure tested because it is so obvious and risk free. Taking more (antioxidant) vitamins as a dietary intervention is simple, safe, and
870
Stein
acceptable, so it is not likely to encounter resistance from the astronaut corps. The alternative, ensuring that astronauts maintain energy balance during space flight, might be very difficult. Astronauts are routinely encouraged to eat, but on US and Russian missions energy intake routinely falls short of needs.31,34,52,53 Postflight substrate competition may not be so easy to correct, either. A priori, one would expect dietary intake by nutritionally depleted astronauts to be greater after than before flight; it is not (Table II). Table II shows that dietary intake is not increased over the preflight period after short-term minor protein losses (Space Life Sciences 1 and 2), short-term major losses (LMS), and longterm major losses (Mir). Most intervention studies with the antioxidant vitamins have been directed at chronic disease states such as cancer and atherosclerosis. The vitamins with antioxidant properties are A, C, and E. Vitamin E is the primary chain-breaking antioxidant in cell membranes.16,54,55 Like vitamin E, carotenoids are located in cell membranes and can function as scavengers for ROS.15,56 The protective role of vitamin C seems to lie in its ability to reduce the oxidized form of vitamin E, thereby making it reusable by the cell.16,57–59 At very high doses (⬃1 mM), vitamin C also can function as a pro-oxidant in the presence of transition metals.15 A recent report from the Food and Nutrition Board of the National Academy of Sciences reviewed the role of antioxidants in chronic disease prevention.6 The study noted the potential involvement of ROS in the etiology of these chronic diseases but was unable to resolve the question of whether supplemental antioxidants are of benefit. Most recent randomized trials (as opposed to observational studies) for various chronic diseases attributed to oxidative stress have been negative or inconclusive (see reviews by the National Research Council,6 Brown et al.,60 and Willett and Stampfer61). Nevertheless, the committee recommended increases in the recommended dietary intakes of vitamins C and E,6 as did a recent review by Willett and Stampfer for vitamin E.61 The use of supplemental vitamin antioxidant preparations as prophylaxis against future chronic disease in populations who are already taking vitamin supplements is an inappropriate analogy to the space-flight situation. Clinical trials of supplemental dietary antioxidants after chronic damage (e.g., cancer and cardiovascular disease) has occurred also is not an appropriate model. The postflight situation is different. It is concerned with an acute situation in which there is a relatively short-term increase in free radical generation from a physiologic perturbation. Numerous studies have shown that exercise can lead to an increase in oxidative damage from actual muscle damage precipitating an inflammatory response or the increased oxidative metabolism in the working muscle.13–17 Most studies in the physically fit have found no benefit from antioxidant supplementation, possibly because endogenous antioxidant levels were already high enough.7,16,62– 64 The benefits from antioxidant supplementation (as defined by decreased production of markers for oxidative stress) after exercise appear to be in less fit individuals.19,56,62– 65 The combination of muscle decompensation and nutritional depletion would place astronauts in this category. The principal difference between the ground-based exercise studies and the space-flight situation is that the ground-based studies lack the undernutrition component. Another difference between the space-flight situation and the groundbased exercise studies is that the concerns of the latter are directed toward performance, whereas for the astronauts the concern is for long-term damage. Antioxidant intervention is not likely to prevent muscle injury resulting from physical damage, but it could decrease the ability of free radicals to attack other sites within the cell.16,66 The postflight situation is more analogous to increased oxidative metabolism and diminished host defenses secondary to undernutrition rather than muscle damage because there is no increase in 3-methylhistidine excretion.28,32 Decreasing the imbalance between the production of endogenous oxidant defenses and oxidant production by in-
Nutrition Volume 18, Number 10, 2002 creasing the supply of dietary antioxidants may well decease the risks. In summary, rodent and human studies have shown that oxidative damage is increased after space flight. There are three causes. 1) Substrate competition between repleting muscle and host defense mechanisms diminishes host endogenous antioxidant defense production. 2) In humans, the problem of protein depletion is compounded by the additional protein losses from the in-flight undernutrition. 3) Anabolism increases during the recovery phase. With increased anabolism comes oxidative phosphorylation and the associated leakage of ROS from the electron transport chain. Providing additional dietary antioxidants during the recovery process may decrease the oxidative damage.
REFERENCES 1. Halliwell B. Anti-oxidants and human disease: a general introduction. Nutr Rev 1997;55:S44 2. Ames BN. Endogenous oxidative DNA damage, aging, and cancer. Free Radic Res Commun 1989;7:121 3. Loft S, Poulsen HE. Estimation of oxidative DNA damage in man from urinary excretion of repair products. Acta Biochim Pol 1998;45:133 4. Morrow JD, Roberts LJ. The isoprostanes: unique bioactive products of lipid peroxidation. Prog Lipid Res 1997;36:1 5. Rokach J, Khanapure SP, Hwang SW, et al. The isoprostanes: a perspective. Prostaglandins 1997;54:823 6. National Research Council, Food and Nutrition Board. Dietary reference intakes for vitamin C, vitamin E, selenium and carotenoids. Washington, DC: National Academy Press, 2000 7. Maxwell SR. Prospects for the use of anti-oxidant therapies. Drugs 1995;49:345 8. McCord JM. Oxygen-derived free radicals in postischemic tissue injury. N Engl J Med 1985;312:159 9. Goode HF, Webster NR. Free radicals and anti-oxidants in sepsis. Crit Care Med 1993;21:1770 10. Gutteridge JM, Mitchell J. Redox imbalance in the critically ill. Br Med Bull 1999;55:49 11. Henson PM, Johnston RB Jr. Tissue injury in inflammation. Oxidants, proteinases, and cationic proteins. J Clin Invest 1987;79:669 12. Walsh SW. Maternal-placental interactions of oxidative stress and anti-oxidants in preeclampsia. Semin Reprod Endocrinol 1998;16:93 13. Borzone G, Zhao B, Merola AJ, Berliner L, Clanton TL. Detection of free radicals by electron spin resonance in rat diaphragm after resistive loading. J Appl Physiol 1994;77:812 14. Davies KJ, Quintanilha AT, Brooks GA, Packer L. Free radicals and tissue damage produced by exercise. Biochem Biophys Res Commun 1982;107:1198 15. Powers SK, Hamilton K. Anti-oxidants and exercise. Clin Sports Med 1999;18: 525 16. Sen CK. Oxidants and anti-oxidants in exercise. J Appl Physiol 1995;79:675 17. Viguie CA, Frei B, Shigenaga MK, et al. Anti-oxidant status and indexes of oxidative stress during consecutive days of exercise. J Appl Physiol 1993;75:566 18. Fielding RA, Evans WJ. Aging and the acute phase response to exercise: implications for the role of systemic factors on skeletal muscle protein turnover. Int J Sports Med 1997;18(suppl 1):S22 19. Meydani M, Evans WJ, Handelman G, et al. Protective effect of vitamin E on exercise-induced oxidative damage in young and older adults. Am J Physiol 1993;264:R992 20. Ames BN. Dietary carcinogens and anticarcinogens. Oxygen radicals and degenerative diseases. Science 1983;221:1256 21. Morrow JD, Frei B, Longmire AW, et al. Increase in circulating products of lipid peroxidation (F2-isoprostanes) in smokers. Smoking as a cause of oxidative damage. N Engl J Med 1995;332:1198 22. Bergtold DS, Berg CD, Simic MG. Urinary biomarkers in radiation therapy of cancer. Adv Exp Med Biol 1990;264:311 23. Golden MH. Oedematous malnutrition. Br Med Bull 1998;54:433 24. Markin AA, Zhuravleva OA. Lipid peroxidation and anti-oxidant defense system in rats after a 14-day space flight in the “Space-2044” spacecraft. Aviakosm Ekolog Med 1993;27:47 25. Markin AA, Popova IA, Vetrova EG, Zhuravleva OA, Balashov OI. Lipid peroxidation and activity of diagnostically significant enzymes in cosmonauts after flights of various durations. Aviakosm Ekolog Med 1997;31:14 26. Markin AA, Zhuravleva OA. Lipid peroxidation and indicators of anti-oxidant defence system in plasma and blood serum of rats during 14-day spaceflight on-board orbital laboratory “Spacelab-2.” Aviakosm Ekolog Med 1998;32:53
Nutrition Volume 18, Number 10, 2002 27. Hollander J, Gore M, Fiebig R, et al. Spaceflight downregulates anti-oxidant defense systems in rat liver. Free Radic Biol Med 1998;24:385 28. Stein TP, Leskiw MJ. Oxidant damage during and after space flight. Am J Physiol Endocrinol Metab 2000;278:E375 29. Loft S, Poulsen HE. Markers of oxidative damage to DNA: anti-oxidants and molecular damage. Methods Enzymol 1999;300:166 30. Awad JA, Roberts LJ II, Burk RF, Morrow JD. Isoprostanes—prostaglandin-like compounds formed in vivo independently of cyclooxygenase: use as clinical indicators of oxidant damage. Gastroenterol Clin North Am 1996;1996:409 31. Stein TP, Leskiw MJ, Schluter MD, Donaldson MR, Larina I. Protein kinetics during and after long term space flight on MIR. Am J Physiol Endocrinol Metab 1999;276:E1014 32. Stein TP. The relationship between dietary intake, exercise, energy balance and the space craft environment. Pflugers Arch 2000;441:R21 33. Stein TP. Nutrition in the space station era. Nutr Res Rev 2001;14:87 34. Stein TP, Leskiw MJ, Schluter MD, et al. Energy expenditure and balance during space flight on the shuttle: the LMS mission. Am J Physiol Endocrinol Metab 1999;276:R1739 35. Rambaut PC, Leach CS, Leonard JI. Observations in energy balance in man during spaceflight. Am J Physiol Endocrinol Metab 1977;233:R208 36. Lane HW, Gretebeck RJ, Schoeller DA, et al. Comparison of ground-based and space flight energy expenditure and water turnover in middle-aged healthy male US astronauts. Am J Clin Nutr 1997;65:4 37. Cannon JG, Meydani SN, Fielding RA, et al. Acute phase response in exercise. II. Associations between vitamin E, cytokines, and muscle proteolysis. Am J Physiol 1991;260:R1235 38. Fielding RA, Meredith CN, O’Reilly KP, et al. Enhanced protein breakdown after eccentric exercise in young and older men. J Appl Physiol 1991;71:674 39. Evans WJ, Meredith CN, Cannon JG, et al. Metabolic changes following eccentric exercise in trained and untrained men. J Appl Physiol 1986;61:1864 40. Leach CS, Rambaut PC, DiFerrante N. Amino aciduria in weightlessness. Acta Aeronaut 1979;6:1323 41. Stein TP, Schluter MD. Plasma amino acids during human space flight. Aviat Space Environ Med 1998;70:250 42. Phillips RW. Food and nutrition during spaceflight. In: Churchill S, ed. Fundamentals of space life sciences. Vol 1. Malabar, FL: Krieger Publishing Co, 1997:135 43. Popov IG, Latskevich AA. Blood amino acids in astronauts before and after a 211-day space flight. Kosm Biol Aviakosm Med 1984;18:10 44. Popov IG, Latskevich AA. Free amino acid content in the blood plasma of cosmonauts before and after a 175-day flight on Salyut-6. Kosm Biol Aviakosm Med 1984;18:26 45. Ushakov AS, Vlasova TF. Free amino acids in human blood plasma during space flights. Aviat Space Environ Med 1976;47:1061 46. Vorobyov EI, Gazenko OG, Genin AM, Egorov AD. Medical results of Salyut-6 manned space flights. Aviat Space Environ Med 1983;54:S31 47. Vlasova TF, Miroshnika EB, Ushakov AS. Various aspects of amino acid metabolism in humans exposed to 120 day anti-orthostatic hypokinesia. Kosm Biol Aviakosm Med 1985:35 48. Popova IA, Grigor’ev AI. The effect of space flight on metabolism: the results of biochemical research in rat experiments on the Kosmos biosatellites. Aviakosm Ekol Med 1992;26:4
Oxidative Stress
871
49. Lee MD, Tuttle R, Girten B. Effect of spaceflight on oxidative and anti-oxidant enzyme activity in rat diaphragm and intercostal muscles. J Gravit Physiol 1995;2:68 50. Wade CE, Miller MM, Baer LA, et al. Body mass, energy intake and water consumption of rats and humans during space flight. Nutrition 2002;18:829 51. Tucker KR, Seider MJ, Booth FW. Protein synthesis rates in atrophied gastrocnemius muscles after limb immobilization. J Appl Physiol 1981;51:73 52. Kas’yan II, Makarov GF. External respiration, gas exchange, and energy expenditure in zero-G. Kosm Biol Aviakosm Med 1984;18:4 53. Heer M, Boerger A, Kamps N, et al. Nutrient supply during recent European missions. Pflugers Arch 2000;441:R8 54. Burton GW, Joyce A, Ingold KU. First proof that vitamin E is major lipidsoluble, chain-breaking anti-oxidant in human blood plasma. Lancet 1982;2:327 55. Janero DR, Hreniuk D, Sharif HM. Hydrogen peroxide-induced oxidative stress to the mammalian heart-muscle cell (cardiomyocyte): lethal peroxidative membrane injury. J Cell Physiol 1991;149:347 56. Goldfarb AH. Nutritional anti-oxidants as therapeutic and preventive modalities in exercise-induced muscle damage. Can J Appl Physiol 1999;24:249 57. Ji LL. Exercise, oxidative stress, and anti-oxidants. Am J Sports Med 1996;24: S20 58. Burton GW, Traber MG. Vitamin E: anti-oxidant activity, biokinetics, and bioavailability. Annu Rev Nutr 1990;10:357 59. Packer JE, Slater TF, Willson RL. Direct observation of a free radical interaction between vitamin E and vitamin C. Nature 1979;278:737 60. Brown BG, Zhao X-Q, Chait A, et al. Simisatatin and Niacin, antrioxidant vitamins, or the combination for the prevention of coronary heart disease. N Engl J Med 2001;345:1583 61. Willett WC, Stampfer MJ. What vitamins should I be taking, Dr? N Engl J Med 2001;345:1919 62. Sharpe P. Oxidative stress and exercise: need for anti-oxidant supplementation? Br J Sports Med 1999;33:298 63. Clarkson PM, Thompson HS. Anti-oxidants: what role do they play in physical activity and health. Am J Clin Nutr 2000;72:637S 64. Evans WJ. Vitamin E, vitamin C, and exercise. Am J Clin Nutr 2000;72:647S 65. Vina J, Gomez-Cabrera MC, Lloret A, et al. Free radicals in exhaustive physical exercise: mechanism of production, and protection by anti-oxidants. IUBMB Life 2000;50:271 66. Warren JA, Jenkins RR, Packer L, Witt EH, Armstrong RB. Elevated muscle vitamin E does not attenuate eccentric exercise-induced muscle injury. J Appl Physiol 1992;72:2168 67. Suzuki J, Inoue Y, Suzuki S. Changes in the urinary excretion level of 8-hydroxyguanine by exposure to reactive oxygen-generating substances. Free Radic Biol Med 1995;18:431 68. Howard DJ, Ota RB, Briggs LA, Hampton M, Pritsos CA. Environmental tobacco smoke in the workplace induces oxidative stress in employees, including increased production of 8-hydroxy-2⬘-deoxyguanosine. Cancer Epidemiol Biomarkers Prev 1998;7:141 69. Gopaul NK, Anggard EE, Mallet AI, et al. Plasma 8-epi-PGF2 alpha levels are elevated in individuals with non-insulin dependent diabetes mellitus. FEBS Lett 1995;368:225 70. Roberts LJ II, Morrow JD. The generation and actions of isoprostanes. Biochim Biophys Acta 1997;1345:121
Space Flight and Oxidative Stress T. P. Stein, PhD From the Department of Surgery, University of Medicine and Dentistry of New Jersey, School of Osteopathic Medicine, Stratford, New Jersey, USA Space flight is associated with an increase in oxidative stress after return to 1g. The effect is more pronounced after long-duration space flight. The effects lasts for several weeks after landing. In humans there is increased lipid peroxidation in erythrocyte membranes, reduction in some blood antioxidants, and increased urinary excretion of 8-iso-prostaglandin F2␣ and 8-oxo-7,8 dihydro-2 deoxyguanosine. Isoprostane 8-iso-prostaglandin F2␣ and 8-oxo-7,8 dihydro-2 deoxyguanosine are markers for oxidative damage to lipids and DNA, respectively. The changes have been attributed to a combination of the energy deficiency that occurs during flight and substrate competition for amino acids occurring between repleting muscle and other tissues during the recovery phase. The observations in humans have been complemented by rodent studies. Most rodent studies showed increased production of lipid peroxidation products postflight and decreased antioxidant enzyme activity postflight. The rodent observations were attributed to the stress associated with reentry into Earth’s gravity. Decreasing the imbalance between the production of endogenous oxidant defenses and oxidant production by increasing the supply of dietary antioxidants may lessen the severity of the postflight increase in oxidative stress. Nutrition 2002;18:867– 871. ©Elsevier Science Inc. 2002 KEY WORDS: space flight, human, rats, antioxidants
INTRODUCTION There is a balance within the body between oxidant production and antioxidant defenses, with the balance shifted slightly in favor of oxidants. The body generates about 5 g of reactive oxygen species (ROS) per day, mostly by leakage from the electron transport chain during oxidative phosphorylation.1 The major product of this “leakage” are the two ROS: the superoxide radical (O2⫺) and H2O2.1 Other ROS include free radicals such as nitric oxide and compounds such as ozone and HOCl. ROS can attack and damage cellular constituents such as DNA, proteins, and membrane lipids. Oxidative damage from free radicals to DNA and lipids has been implicated in the etiology of a wide variety of chronic diseases and acute pathologic states. The chronic diseases range from cancer to cardiovascular disease and neurodegenerative disease including Alzheimer and Parkinson diseases.1–7 Examples of acute states in which oxidative damage is suspected include ischemia-reperfusion injury,7,8 sepsis,9,10 inflammatory diseases,7,11 preeclampsia,12 and strenuous exercise.13–17 With exercise, the threshold for oxidative stress is lower for untrained and elderly subjects.17–19 Other factors that can result in increased oxidative damage include environmental pollutants,20 cigarette smoke,3,21 radiation,22 severe nutritional depletion undernutrition,1,23 and space flight.24 –28 Russian investigators found evidence for increased lipid peroxidation in human erythrocyte membranes and reductions in some blood antioxidants after long-duration space flight.24 –26 A subsequent study28 on the Russian space station Mir assessed the urinary excretion of 8-iso-prostaglandin F2␣ and 8-oxo-7,8 dihydro-2 deoxyguanosine (8-OH dG) in six subjects during and after long-duration space flight (90 to 180 d). Isoprostane 8-isoprostaglandin F2␣ and 8-OH dG are markers for oxidative damage
Supported by NASA contract NAS 9-18775. Correspondence to: T. P. Stein, PhD, Department of Surgery, University of Medicine and Dentistry of New Jersey, SOM, 2 Medical Center Drive, Stratford, NJ, 08084, USA. E-mail: [email protected] Nutrition 18:867– 871, 2002 ©Elsevier Science Inc., 2002. Printed in the United States. All rights reserved.
to lipids and DNA, respectively.29,30 The preflight measurements consisted of two to four 2-d sessions during the year before the mission to establish a baseline. In addition to 24-h urine collections, dietary intake was monitored but not controlled. The 24-h urine and dietary data were also collected in flight and for the 2 wk after landing. To facilitate interpretation of the data, the data from Mir were compared with the results from the 17-d Life and Microgravity Sciences shuttle mission (LMS) and a 17-d, 6-degree head-down tilt bedrest study.31 These flight data sets are inflight data that has been collected to date on either humans or animals.
IN-FLIGHT FINDINGS Urinary isoprostane excretion was decreased in flight by approximately 20% on Mir, by approximately 40% on the Space Shuttle, and unchanged with bedrest28 (Fig. 1). It would appear that oxidative damage to lipids was not increased during space flight. The most likely explanation is that the decrease in isoprostane production on Mir and LMS was due to a downregulation of intermediary metabolism, leading to a decreased flux through the electron transport system in response to the deficit in energy intake. The principal source of free radicals in the body is from free radical leakage (3% to 5% of the electron flux) from the electron transport chain.1 Decreased endogenous free radical production is the expected result if the flux is decreased and there is no increase in free radical generation from radiation. A decreased flux through the electron transport chain will generate fewer free radicals within the mitochondria. Figure 1 shows the trend toward an increase in 8-OH dG excretion in flight. A similar observation was made on the LMS mission. When the excretion rate of 8-OH dG is regressed against the energy deficit for either Mir or LMS, both show correlations that approach significance (P ⬍ 0.1; Fig. 2). The greater the decrease in energy intake, the more extensive free radical propagation because of the diminished protein-based antioxidant defenses. The whole-body protein synthesis rate was measured on Mir but not on LMS. Figure 2 shows that as the whole-body protein 0899-9007/02/$22.00 PII S0899-9007(02)00938-3
868
Stein
Nutrition Volume 18, Number 10, 2002 TABLE I. DISEASE AND THE EXCRETION OF THE PRODUCTS OF DNA AND LIPID OXIDATION32
8-OH dG After space flight on Mir Smoking, 1 pack/d Environmental cigarette smoke Cancer Radiotherapy Isoprostanes After space flight on Mir Smoking Diabetes Liver disease Hepatorenal syndrome
% Increase
Reference
150 200 60 150 400
28 67 68 3 3
200 200 350 500 900
28 21 69 30 70
8-OH dG, 8-oxo-7,8 dihydro-2 deoxyguanosine.
FIG. 1. Oxidative stress during and after space flight or bed rest.28 Data are from the National Aeronautics and Space Administration and Mir program (flight duration, 90 –180 d), the LMS shuttle mission (17 d), and a bedrest study (14 d). *P ⬍ 0.05 versus preflight value. 8-ISO-PGF2␣, 8-isoprostaglandin F2␣; 8-OH dG, 8-oxo-7,8 dihydro-2 deoxyguanosine; LMS, Life and Microgravity Sciences.
synthesis rate on Mir decreased as the energy deficit increased, 8-OH dG production increased. This observation suggests that there is a relationship between the ability to make proteins and the ability to protect DNA from ROS. There were no such correlations with isoprostanes for Mir or LMS (r2 ⫽ 0). The implication is that, for lipid oxidation during space flight, the dominant effect is the flux through the electron transport chain. The potential for radiation damage during long-duration flights (particularly for flights out of low Earth orbit, where the exposure to radiation flux is greater) is currently believed to be the most
FIG. 2. Inverse relationships between the decrease in intake, the decrease in protein synthesis (solid circles), and the increase in 8-OH dG excretion (open circles) during space flight on Mir compared to preflight. 8-OH dG, 8-oxo-7,8 dihydro-2 deoxyguanosine28,31
serious impediment to interplanetary travel. Isoprostane excretion was decreased and 8-OH dG was essentially unchanged during a flight on Mir.28 Any damage incurred from radiation on these near-Earth missions is likely to have been small and masked by the dominant nutritional effect. The effect of radiation damage is additive and depends on orbit and solar cycle activity and may be a major contributing factor to oxidative damage on long-duration missions farther away from Earth.
POSTFLIGHT FINDINGS Human Both 8-OH dG and 8-iso-prostaglandin F2␣ were increased by more than two-fold after more than 3 mo on Mir (Fig. 1). The implication is that oxidative damage after an extended period in orbit is increased after landing. There is other evidence for increased oxidative damage after space flight. Spot blood analyses by Russian investigators on cosmonauts after long-duration flights showed a non-statistically significant trend for an increase in the accumulation of lipid oxidation products in the serum and erythrocyte membranes.25 The erythrocyte membrane compositional changes were a combination of membrane lipid peroxidation and increased rigidity. The changes persisted for up to 6 mo after long-duration flight (up to 1 y) on Mir.25 Thus a number of independent studies have concluded that recovery after space flight is associated with an increase in oxidative damage. It is of interest to ask: How physiologically significant is this increase in oxidative damage? The answer depends on two factors, the magnitude of the increase and its duration. Table I compares the postflight urinary isoprostane and 8-OH dG excretion values against some well-known clinical conditions. Long-duration space flight appears to rank with cigarette smoking.32,33 The simplest explanation for the increased oxidative damage postflight in humans is that the increase is due to a combination of 1) the consequences of the loss of protein secondary to the in-flight reductive remodeling of skeletal muscle from the decreased work load on the antigravity muscles, 2) the in-flight protein depletion from inadequate dietary intake, and 3) the increased anabolism associated with protein repletion. With increased generation of adenosine triphosphate, leakage of ROS from the mitochondrial electron transport chain will be increased.1 Negative energy balance in humans has been a frequent finding during space flight.28,31,32,34 The LMS astronauts lost 2.6 ⫾ 0.4
Nutrition Volume 18, Number 10, 2002
Oxidative Stress
TABLE II. ENERGY INTAKE IS NOT INCREASED POSTFLIGHT EVEN THOUGH INTAKE IS DECREASED IN FLIGHT33* Intake (kcal 䡠 kg⫺1 䡠 d⫺1) Mission
Weight loss during flight (kg)
Preflight
In flight
Postflight
SLS1/2 LMS Mir
1.0 ⫾ 0.4† 3.6 ⫾ 0.4† 4.3 ⫾ 1.2†
39.6 ⫾ 2.4 35.6 ⫾ 2.1 34.8 ⫾ 3.3
31.5 ⫾ 1.5† 24.3 ⫾ 1.2† 26.3 ⫾ 2.3†
40.0 ⫾ 1.9 37.1 ⫾ 2.8 32.8 ⫾ 2.2
* Data presented as mean ⫾ standard error of the mean. † P ⬍ 0.05 versus preflight for weight and versus pre- and postflight for energy intake. LMS, Life and Microgravity Sciences; SLS1/2, Space Life Sciences 1 and 2.
kg, of which 1.5 ⫾ 0.6 kg was fat, and the Mir astronauts lost 4.3 ⫾ 1.2 kg. The reason for the weight loss was the very low dietary intake rather than an increase in energy expenditure. Energy intakes 24.6 ⫾ 3.3 kcal · kg⫺1 · d⫺1 on LMS and 26.3 ⫾ 2.3 kcal · kg⫺1 · d⫺1 on Mir.33 These values are substantially less than energy expenditure during space flight. There have been three independent measurements of energy expenditure during flight: on Skylab by the intake balance method (43.7 ⫾ ⬃1 kcal · kg⫺1 · d⫺1),35 across several shuttle missions by the doublelabeled water method (36.2 ⫾ 5.8 1 kcal · kg⫺1 · d⫺1),36 and by the double-labeled water and intake balance methods (40.8 ⫾ 1.6 1 kcal · kg⫺1 · d⫺1)34 on the LMS shuttle mission. Indeed, the energy deficit on Mir was enough to reduce the whole-body protein synthesis rate. Figure 2 shows that the greater the energy deficit, the greater the reduction in the whole-body protein synthesis rate. Two alternative explanations are increases in free radical production from 1) damage incurred from the reimposition of gravity on the atrophied muscles or 2) a large increase in metabolic activity. Explanation 1 is unlikely. On the ground, when there is increased oxidative damage after exercise,19,37 there is also an increase in 3-methylhistidine excretion.38,39 3-Methylhistidine excretion was not increased postflight on Mir and was not increased after flight on Skylab40 (Fig. 2). Explanation 2 is also improbable. Energy intake after flight is about the same as that before flight; there is no dramatic anabolic increase in intake. The observations make it improbable that there was a large increase in energy expenditure postflight in the absence of a parallel increase in dietary intake (Table II). A deficit in energy intake of the magnitude that occurred on Mir or LMS is not sustainable in the long term without some metabolic accommodation, one manifestation of which was a reduction in protein synthesis.31 On Mir, the greater the apparent energy deficit, the larger the decrease in the in-flight whole-body protein synthesis rate31 (Fig. 2). The downregulation of protein turnover leads to the loss of protein systems of lower priority to spare systems that are of higher priority. High-priority proteins are protected because of the high costs associated with their loss; nevertheless, some loss of protein antioxidants is likely, and these losses persist into the early postflight recovery phase.28 After long-duration space flight, protein metabolism is compromised due to the in-flight undernutrition. There is another factor that can lead to decreased production of antioxidant defenses postflight, which is the suboptimal synthesis of host (defense) proteins. There is some evidence that the synthesis of host antioxidant protein defenses could be suboptimal due to competition for amino acids occurring between repleting muscle and other tissues.41
869
Postflight, the Americans and the Russians found the plasma amino acids to be decreased.42– 46 The most consistent findings have concerned methionine and the branched-chain amino acids. Plasma methionine and branched-chain amino acid levels are reduced in the immediate postflight phase, and this decrease persists for the first week of recovery.41,43,47 The amino acids are needed to support the postflight anabolic replacement of proteins lost during space flight. There is other evidence, which is suggestive rather than conclusive, that protein synthesis is suboptimal postflight. First, whole-body protein synthesis should be increased postflight because the recovery period is anabolic. Except for the day of landing, no consistent evidence for an increase in protein synthesis was found after short-duration space flight on the Shuttle or long-duration space flight on Mir.33 Second, Russian investigators have reported that the synthesis of plasma proteins of hepatic origin is decreased a week after landing.46 Collectively, these observations are suggestive of amino acids being limiting postflight, possibly due to competition for substrates secondary to increased demand by repleting muscle and the requirements of the other tissues.48 Rodent Most,24,27 but not all,49 rodent studies showed increased production of lipid peroxidation products postflight and decreased antioxidant enzyme activity postflight. In rats flown on an 8-d Shuttle mission, Hollander et al.27 found space flight to simultaneously downregulate antioxidant defense capacity and elicit an oxidative stress in the liver. There was an approximately 50% increase in liver malondialdehyde concentration with space flight. Space flight significantly decreased catalase, glutathione reductase, glutathione sulfur-transferase, and ␥-glutamyl transpeptidase activities in the livers of flight rats when compared with those of ground controls. The relative abundance of mRNA for Cu-Zn superoxide dismutase and catalase were significantly decreased. Also decreased were liver glutathione and glutathione disulfide. The rodent observations were attributed to the stress associated with reentry into Earth’s gravity.24,27 Undernutrition is not likely to have been a factor in the postflight rodent response. Rats, unlike humans, are able to maintain intake and energy balance during space flight.50 However, substrate competition is still likely to occur after landing because repleting muscle and other tissues compete for the same amount of substrates. Consistent with substrate competition is a rat hindlimb suspension study by Tucker et al.51 During immobilization, muscle protein synthesis is reduced. After immobilization, protein synthesis in the gastrocnemius muscle returned to the preimmobilization baseline within 6 h, remained unchanged for the next 2 d, and then doubled on day 4.51
POSSIBLE COUNTERMEASURES The phenomenon of increased oxidative stress during the recovery process has not been reproduced in a relevant ground-based model. At this time no suitable models have been described. Increased oxidative stress does not occur after short-term bedrest by otherwise healthy people.28 The appropriate human ground-based model would probably be long-term bedrest on a hypocaloric diet, possibly with chronic supplemental chronic cortisol administration, a model that is ethically not tenable. The potential applicability of the rodent hindlimb suspension model has not been explored. All conceivable mechanisms point to an imbalance between oxidant stress and antioxidant defenses. Almost irrespective of what any ground studies might show, evaluation of antioxidant vitamins as a dietary supplement is likely to be the first countermeasure tested because it is so obvious and risk free. Taking more (antioxidant) vitamins as a dietary intervention is simple, safe, and
870
Stein
acceptable, so it is not likely to encounter resistance from the astronaut corps. The alternative, ensuring that astronauts maintain energy balance during space flight, might be very difficult. Astronauts are routinely encouraged to eat, but on US and Russian missions energy intake routinely falls short of needs.31,34,52,53 Postflight substrate competition may not be so easy to correct, either. A priori, one would expect dietary intake by nutritionally depleted astronauts to be greater after than before flight; it is not (Table II). Table II shows that dietary intake is not increased over the preflight period after short-term minor protein losses (Space Life Sciences 1 and 2), short-term major losses (LMS), and longterm major losses (Mir). Most intervention studies with the antioxidant vitamins have been directed at chronic disease states such as cancer and atherosclerosis. The vitamins with antioxidant properties are A, C, and E. Vitamin E is the primary chain-breaking antioxidant in cell membranes.16,54,55 Like vitamin E, carotenoids are located in cell membranes and can function as scavengers for ROS.15,56 The protective role of vitamin C seems to lie in its ability to reduce the oxidized form of vitamin E, thereby making it reusable by the cell.16,57–59 At very high doses (⬃1 mM), vitamin C also can function as a pro-oxidant in the presence of transition metals.15 A recent report from the Food and Nutrition Board of the National Academy of Sciences reviewed the role of antioxidants in chronic disease prevention.6 The study noted the potential involvement of ROS in the etiology of these chronic diseases but was unable to resolve the question of whether supplemental antioxidants are of benefit. Most recent randomized trials (as opposed to observational studies) for various chronic diseases attributed to oxidative stress have been negative or inconclusive (see reviews by the National Research Council,6 Brown et al.,60 and Willett and Stampfer61). Nevertheless, the committee recommended increases in the recommended dietary intakes of vitamins C and E,6 as did a recent review by Willett and Stampfer for vitamin E.61 The use of supplemental vitamin antioxidant preparations as prophylaxis against future chronic disease in populations who are already taking vitamin supplements is an inappropriate analogy to the space-flight situation. Clinical trials of supplemental dietary antioxidants after chronic damage (e.g., cancer and cardiovascular disease) has occurred also is not an appropriate model. The postflight situation is different. It is concerned with an acute situation in which there is a relatively short-term increase in free radical generation from a physiologic perturbation. Numerous studies have shown that exercise can lead to an increase in oxidative damage from actual muscle damage precipitating an inflammatory response or the increased oxidative metabolism in the working muscle.13–17 Most studies in the physically fit have found no benefit from antioxidant supplementation, possibly because endogenous antioxidant levels were already high enough.7,16,62– 64 The benefits from antioxidant supplementation (as defined by decreased production of markers for oxidative stress) after exercise appear to be in less fit individuals.19,56,62– 65 The combination of muscle decompensation and nutritional depletion would place astronauts in this category. The principal difference between the ground-based exercise studies and the space-flight situation is that the ground-based studies lack the undernutrition component. Another difference between the space-flight situation and the groundbased exercise studies is that the concerns of the latter are directed toward performance, whereas for the astronauts the concern is for long-term damage. Antioxidant intervention is not likely to prevent muscle injury resulting from physical damage, but it could decrease the ability of free radicals to attack other sites within the cell.16,66 The postflight situation is more analogous to increased oxidative metabolism and diminished host defenses secondary to undernutrition rather than muscle damage because there is no increase in 3-methylhistidine excretion.28,32 Decreasing the imbalance between the production of endogenous oxidant defenses and oxidant production by in-
Nutrition Volume 18, Number 10, 2002 creasing the supply of dietary antioxidants may well decease the risks. In summary, rodent and human studies have shown that oxidative damage is increased after space flight. There are three causes. 1) Substrate competition between repleting muscle and host defense mechanisms diminishes host endogenous antioxidant defense production. 2) In humans, the problem of protein depletion is compounded by the additional protein losses from the in-flight undernutrition. 3) Anabolism increases during the recovery phase. With increased anabolism comes oxidative phosphorylation and the associated leakage of ROS from the electron transport chain. Providing additional dietary antioxidants during the recovery process may decrease the oxidative damage.
REFERENCES 1. Halliwell B. Anti-oxidants and human disease: a general introduction. Nutr Rev 1997;55:S44 2. Ames BN. Endogenous oxidative DNA damage, aging, and cancer. Free Radic Res Commun 1989;7:121 3. Loft S, Poulsen HE. Estimation of oxidative DNA damage in man from urinary excretion of repair products. Acta Biochim Pol 1998;45:133 4. Morrow JD, Roberts LJ. The isoprostanes: unique bioactive products of lipid peroxidation. Prog Lipid Res 1997;36:1 5. Rokach J, Khanapure SP, Hwang SW, et al. The isoprostanes: a perspective. Prostaglandins 1997;54:823 6. National Research Council, Food and Nutrition Board. Dietary reference intakes for vitamin C, vitamin E, selenium and carotenoids. Washington, DC: National Academy Press, 2000 7. Maxwell SR. Prospects for the use of anti-oxidant therapies. Drugs 1995;49:345 8. McCord JM. Oxygen-derived free radicals in postischemic tissue injury. N Engl J Med 1985;312:159 9. Goode HF, Webster NR. Free radicals and anti-oxidants in sepsis. Crit Care Med 1993;21:1770 10. Gutteridge JM, Mitchell J. Redox imbalance in the critically ill. Br Med Bull 1999;55:49 11. Henson PM, Johnston RB Jr. Tissue injury in inflammation. Oxidants, proteinases, and cationic proteins. J Clin Invest 1987;79:669 12. Walsh SW. Maternal-placental interactions of oxidative stress and anti-oxidants in preeclampsia. Semin Reprod Endocrinol 1998;16:93 13. Borzone G, Zhao B, Merola AJ, Berliner L, Clanton TL. Detection of free radicals by electron spin resonance in rat diaphragm after resistive loading. J Appl Physiol 1994;77:812 14. Davies KJ, Quintanilha AT, Brooks GA, Packer L. Free radicals and tissue damage produced by exercise. Biochem Biophys Res Commun 1982;107:1198 15. Powers SK, Hamilton K. Anti-oxidants and exercise. Clin Sports Med 1999;18: 525 16. Sen CK. Oxidants and anti-oxidants in exercise. J Appl Physiol 1995;79:675 17. Viguie CA, Frei B, Shigenaga MK, et al. Anti-oxidant status and indexes of oxidative stress during consecutive days of exercise. J Appl Physiol 1993;75:566 18. Fielding RA, Evans WJ. Aging and the acute phase response to exercise: implications for the role of systemic factors on skeletal muscle protein turnover. Int J Sports Med 1997;18(suppl 1):S22 19. Meydani M, Evans WJ, Handelman G, et al. Protective effect of vitamin E on exercise-induced oxidative damage in young and older adults. Am J Physiol 1993;264:R992 20. Ames BN. Dietary carcinogens and anticarcinogens. Oxygen radicals and degenerative diseases. Science 1983;221:1256 21. Morrow JD, Frei B, Longmire AW, et al. Increase in circulating products of lipid peroxidation (F2-isoprostanes) in smokers. Smoking as a cause of oxidative damage. N Engl J Med 1995;332:1198 22. Bergtold DS, Berg CD, Simic MG. Urinary biomarkers in radiation therapy of cancer. Adv Exp Med Biol 1990;264:311 23. Golden MH. Oedematous malnutrition. Br Med Bull 1998;54:433 24. Markin AA, Zhuravleva OA. Lipid peroxidation and anti-oxidant defense system in rats after a 14-day space flight in the “Space-2044” spacecraft. Aviakosm Ekolog Med 1993;27:47 25. Markin AA, Popova IA, Vetrova EG, Zhuravleva OA, Balashov OI. Lipid peroxidation and activity of diagnostically significant enzymes in cosmonauts after flights of various durations. Aviakosm Ekolog Med 1997;31:14 26. Markin AA, Zhuravleva OA. Lipid peroxidation and indicators of anti-oxidant defence system in plasma and blood serum of rats during 14-day spaceflight on-board orbital laboratory “Spacelab-2.” Aviakosm Ekolog Med 1998;32:53
Nutrition Volume 18, Number 10, 2002 27. Hollander J, Gore M, Fiebig R, et al. Spaceflight downregulates anti-oxidant defense systems in rat liver. Free Radic Biol Med 1998;24:385 28. Stein TP, Leskiw MJ. Oxidant damage during and after space flight. Am J Physiol Endocrinol Metab 2000;278:E375 29. Loft S, Poulsen HE. Markers of oxidative damage to DNA: anti-oxidants and molecular damage. Methods Enzymol 1999;300:166 30. Awad JA, Roberts LJ II, Burk RF, Morrow JD. Isoprostanes—prostaglandin-like compounds formed in vivo independently of cyclooxygenase: use as clinical indicators of oxidant damage. Gastroenterol Clin North Am 1996;1996:409 31. Stein TP, Leskiw MJ, Schluter MD, Donaldson MR, Larina I. Protein kinetics during and after long term space flight on MIR. Am J Physiol Endocrinol Metab 1999;276:E1014 32. Stein TP. The relationship between dietary intake, exercise, energy balance and the space craft environment. Pflugers Arch 2000;441:R21 33. Stein TP. Nutrition in the space station era. Nutr Res Rev 2001;14:87 34. Stein TP, Leskiw MJ, Schluter MD, et al. Energy expenditure and balance during space flight on the shuttle: the LMS mission. Am J Physiol Endocrinol Metab 1999;276:R1739 35. Rambaut PC, Leach CS, Leonard JI. Observations in energy balance in man during spaceflight. Am J Physiol Endocrinol Metab 1977;233:R208 36. Lane HW, Gretebeck RJ, Schoeller DA, et al. Comparison of ground-based and space flight energy expenditure and water turnover in middle-aged healthy male US astronauts. Am J Clin Nutr 1997;65:4 37. Cannon JG, Meydani SN, Fielding RA, et al. Acute phase response in exercise. II. Associations between vitamin E, cytokines, and muscle proteolysis. Am J Physiol 1991;260:R1235 38. Fielding RA, Meredith CN, O’Reilly KP, et al. Enhanced protein breakdown after eccentric exercise in young and older men. J Appl Physiol 1991;71:674 39. Evans WJ, Meredith CN, Cannon JG, et al. Metabolic changes following eccentric exercise in trained and untrained men. J Appl Physiol 1986;61:1864 40. Leach CS, Rambaut PC, DiFerrante N. Amino aciduria in weightlessness. Acta Aeronaut 1979;6:1323 41. Stein TP, Schluter MD. Plasma amino acids during human space flight. Aviat Space Environ Med 1998;70:250 42. Phillips RW. Food and nutrition during spaceflight. In: Churchill S, ed. Fundamentals of space life sciences. Vol 1. Malabar, FL: Krieger Publishing Co, 1997:135 43. Popov IG, Latskevich AA. Blood amino acids in astronauts before and after a 211-day space flight. Kosm Biol Aviakosm Med 1984;18:10 44. Popov IG, Latskevich AA. Free amino acid content in the blood plasma of cosmonauts before and after a 175-day flight on Salyut-6. Kosm Biol Aviakosm Med 1984;18:26 45. Ushakov AS, Vlasova TF. Free amino acids in human blood plasma during space flights. Aviat Space Environ Med 1976;47:1061 46. Vorobyov EI, Gazenko OG, Genin AM, Egorov AD. Medical results of Salyut-6 manned space flights. Aviat Space Environ Med 1983;54:S31 47. Vlasova TF, Miroshnika EB, Ushakov AS. Various aspects of amino acid metabolism in humans exposed to 120 day anti-orthostatic hypokinesia. Kosm Biol Aviakosm Med 1985:35 48. Popova IA, Grigor’ev AI. The effect of space flight on metabolism: the results of biochemical research in rat experiments on the Kosmos biosatellites. Aviakosm Ekol Med 1992;26:4
Oxidative Stress
871
49. Lee MD, Tuttle R, Girten B. Effect of spaceflight on oxidative and anti-oxidant enzyme activity in rat diaphragm and intercostal muscles. J Gravit Physiol 1995;2:68 50. Wade CE, Miller MM, Baer LA, et al. Body mass, energy intake and water consumption of rats and humans during space flight. Nutrition 2002;18:829 51. Tucker KR, Seider MJ, Booth FW. Protein synthesis rates in atrophied gastrocnemius muscles after limb immobilization. J Appl Physiol 1981;51:73 52. Kas’yan II, Makarov GF. External respiration, gas exchange, and energy expenditure in zero-G. Kosm Biol Aviakosm Med 1984;18:4 53. Heer M, Boerger A, Kamps N, et al. Nutrient supply during recent European missions. Pflugers Arch 2000;441:R8 54. Burton GW, Joyce A, Ingold KU. First proof that vitamin E is major lipidsoluble, chain-breaking anti-oxidant in human blood plasma. Lancet 1982;2:327 55. Janero DR, Hreniuk D, Sharif HM. Hydrogen peroxide-induced oxidative stress to the mammalian heart-muscle cell (cardiomyocyte): lethal peroxidative membrane injury. J Cell Physiol 1991;149:347 56. Goldfarb AH. Nutritional anti-oxidants as therapeutic and preventive modalities in exercise-induced muscle damage. Can J Appl Physiol 1999;24:249 57. Ji LL. Exercise, oxidative stress, and anti-oxidants. Am J Sports Med 1996;24: S20 58. Burton GW, Traber MG. Vitamin E: anti-oxidant activity, biokinetics, and bioavailability. Annu Rev Nutr 1990;10:357 59. Packer JE, Slater TF, Willson RL. Direct observation of a free radical interaction between vitamin E and vitamin C. Nature 1979;278:737 60. Brown BG, Zhao X-Q, Chait A, et al. Simisatatin and Niacin, antrioxidant vitamins, or the combination for the prevention of coronary heart disease. N Engl J Med 2001;345:1583 61. Willett WC, Stampfer MJ. What vitamins should I be taking, Dr? N Engl J Med 2001;345:1919 62. Sharpe P. Oxidative stress and exercise: need for anti-oxidant supplementation? Br J Sports Med 1999;33:298 63. Clarkson PM, Thompson HS. Anti-oxidants: what role do they play in physical activity and health. Am J Clin Nutr 2000;72:637S 64. Evans WJ. Vitamin E, vitamin C, and exercise. Am J Clin Nutr 2000;72:647S 65. Vina J, Gomez-Cabrera MC, Lloret A, et al. Free radicals in exhaustive physical exercise: mechanism of production, and protection by anti-oxidants. IUBMB Life 2000;50:271 66. Warren JA, Jenkins RR, Packer L, Witt EH, Armstrong RB. Elevated muscle vitamin E does not attenuate eccentric exercise-induced muscle injury. J Appl Physiol 1992;72:2168 67. Suzuki J, Inoue Y, Suzuki S. Changes in the urinary excretion level of 8-hydroxyguanine by exposure to reactive oxygen-generating substances. Free Radic Biol Med 1995;18:431 68. Howard DJ, Ota RB, Briggs LA, Hampton M, Pritsos CA. Environmental tobacco smoke in the workplace induces oxidative stress in employees, including increased production of 8-hydroxy-2⬘-deoxyguanosine. Cancer Epidemiol Biomarkers Prev 1998;7:141 69. Gopaul NK, Anggard EE, Mallet AI, et al. Plasma 8-epi-PGF2 alpha levels are elevated in individuals with non-insulin dependent diabetes mellitus. FEBS Lett 1995;368:225 70. Roberts LJ II, Morrow JD. The generation and actions of isoprostanes. Biochim Biophys Acta 1997;1345:121