- Email: [email protected]
Neocytolysis contributes to the anemia of renal disease
Neocytolysis Contributes to the Anemia of Renal Disease Lawrence Rice, MD, Clarence P. Alfrey, MD, PhD, Theda Driscoll, CNT, Carl E. Whitley, MT, David L. Hachey, PhD, and Wadi Suki, MD ● Neocytolysis is a recently described physiological process affecting the selective hemolysis of young red blood cells in circumstances of plethora. Erythropoietin (EPO) depression appears to initiate the process, providing the rationale to investigate its contributions to the anemia of renal disease. When EPO therapy was withheld, four of five stable hemodialysis patients showed chromium 51 (51Cr) –red cell survival patterns indicative of neocytolysis; red cell survival was short in the first 9 days, then normalized. Two of these four patients received oral 13C-glycine and 15N-glycine, and there was a suggestion of pathological isotope enrichment of stool porphyrins when EPO therapy was held, again supporting selective hemolysis of newly released red cells that take up the isotope (one patient had chronic hemolysis indicated by isotope studies of blood and stool). Thus, neocytolysis can contribute to the anemia of renal disease and explain some unresolved issues about such anemia. One implication is the prediction that intravenous bolus EPO therapy is metabolically and economically inefficient compared with lower doses administered more frequently subcutaneously. 娀 1999 by the National Kidney Foundation, Inc. INDEX WORDS: Anemia of renal disease; erythropoietin; hemolytic anemia; neocytolysis.
Editorial, p. 140
W
E HAVE UNCOVERED a physiological process that selectively hemolyzes the youngest circulating red blood cells in situations of red cell excess and have named this process neocytolysis.1 Neocytolysis became manifest while studying mechanisms underlying spaceflight anemia, an adaptation of astronauts to acute plethora in microgravity.2 Individuals acclimated to high altitude who descend to sea level also experience neocytolysis, and we are actively extending these observations to further elucidate the process.3-5 Neocytolysis occurs in situations in which erythropoietin (EPO) secretion is suppressed, creating suspicion that the process is initiated by a decrease in EPO levels to less than a threshold. On descent from altitude, low doses of subcutaneous EPO prevented a rapid adaptive decrease in red cell mass, further implicating low EPO levels in precipitating this process.4-5 Renal insufficiency presents a pathological situation in which EPO production is depressed. We sought to determine whether neocytolysis is present in some patients with renal insufficiency and contributes to their anemia. If so, important implications might extend to optimizing therapy for the anemia of renal disease. METHODS From nine stable dialysis patients screened, five were selected for study and consented to participate in our institutional review board–approved protocol. Patient selection was on the basis of low baseline EPO levels (Eporia; Ramco,
Houston, TX), all less than 25 U/mL drawn at least 3 days after their last EPO injection. Patients were screened for the absence of infection, active inflammatory disease, and iron deficiency (based on serum ferritin levels ⬎80 ng/mL). Patients had stable hematocrits on standard EPO therapy (generally 50 µg/kg three times weekly intravenously). The patients studied were from 36 to 69 years of age, four were men, and renal failure was caused by hypertension in four patients and unknown causes in one patient. The five patients had their red cells labeled with 50 µCi of chromium 51 (51Cr) and survival curves traced by standard methods (corrected for elution) while receiving or not receiving EPO.6 Curves were fitted by the method of least squares. Each patient had EPO therapy held for at least 12 days. The first two patients had red cell mass determinations at the beginning and completion of the study using a standard 51Cr dilution technique. The last three patients had red cell mass determinations at the time of each sample collection based on measurements of carboxyhemoglobin after carbon monoxide inhalation.7 For each patient, the residual 51Cr remaining in the blood was the product of the radioactivity per milliliter of blood corrected for elution and the red cell mass. The last three patients studied ingested 1 g each of oral 13C-glycine (13C) and 15N-glycine (15N) to label newly synthesized red cells. One isotope was administered during EPO therapy and the second before withholding exogenous EPO. From collected serial stool specimens, stercobilin was From the Methodist Hospital; and Sections of Hematology and Nephrology, Baylor College of Medicine, Houston, TX. Received January 12, 1998; accepted in revised form September 15, 1998. Supported by grant no. TMC/NASA NCC 9-36/24-272223315111 from the Texas Medical Center and the National Aeronautics and Space Administration, Houston, TX. Dr Hatchey is now at Vanderbilt University, Nashville, TN. Address reprint requests to Lawrence Rice, MD, 6565 Fannin, MS 902-Main, Houston, TX 77030. E-mail: [email protected]
娀 1999 by the National Kidney Foundation, Inc. 0272-6386/99/3301-0009$3.00/0
American Journal of Kidney Diseases, Vol 33, No 1 (January), 1999: pp 59-62
59
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RICE ET AL
isolated by ethanol, ether, and chloroform extraction,8 a final thin-layer chromatography step,9 and then specimens were frozen at –20°C. Isotopic measurements of 13C and 15N enrichment were determined by online combustion isotopic analysis using a Tacermass isotope ratio mass spectrometer (Europa Scientific, Crewe, United Kingdom) equipped with a RoboPrep N continuous-flow combustion interface (Europa Scientific).10 A 1- to 2-mg sample of crystalline hemin or stercobilin was placed in tin combustion cups and loaded on the autosampler. The isotopic results were determined as atom percent with a relatively precision of ⫾0.5 milliAtom percent excess (mAPE) (0.0005 Atom%).
RESULTS
Figure 1 shows a composite 51Cr–red cell survival curve representing all five patients. When EPO therapy was held, the slope was steeper (red cells disappeared more quickly) during the first 9 days than afterward, as predicted by our theory (see Discussion). The survival curve slope for the first 9 days off EPO therapy was –3.15% ⫾ 0.30% (standard error) per day and the subsequent slope was –1.32% ⫾ 0.25% per day, statistically shorter in the first 9 days off EPO therapy (P ⬍ 0.02). In the three patients who received oral 13C and 15N, two had some suggestion of abnormal enrichment of their stool with the isotope administered just before EPO was withheld. Figure 2 shows
Fig 2. Isotope enrichment of stool porphyrins is graphed for a healthy subject and two patients. There is a suggestion of increased isotope in stercobilin on day 10 after EPO was withheld from patient 1, compared with the normal or to his results on EPO therapy (patient 2 had a similar suggestion). This is consistent with hemolysis of young red cell precursors. Patient 3 shows persistent elevation of isotope whether on or off EPO therapy, a pattern suggesting chronic hemolytic anemia.
this graphically in patient 1. The results in patient 2 were similar. For comparison, data from a healthy control and from patient 3 are shown. Patient 3 appeared to have abnormal stool enrichment by both isotopes and also had short 51Cr– red cell survival with little improvement in survival after 9 days; thus, this patient appears to have a chronic hemolytic process. DISCUSSION
Fig 1. Composite 51Cr–red cell survival curve for all five patients (corrected for elution and changes in red cell mass). The slope in the first 9 days when EPO was withheld is statistically steeper than the slope of the curve after 9 days (–3.15 v –1.32; P F 0.02). After 9 days, the slope approximates normal. The pattern is consistent with neocytolysis.
Neocytolysis has been observed with physiological EPO suppression in astronauts and in polycythemic individuals descending from high altitude, and it can be prevented by administration of low doses of EPO.1-5 This mandated the study of a situation in which there is pathological EPO suppression, the anemia of renal insufficiency. When five dialysis patients with low baseline EPO levels had their EPO therapy withheld, a pattern of neocytolysis emerged in four (the fifth showed a pattern of chronic hemolytic anemia). 51Cr–red cell survival curves showed a statistically significant steeper slope in the first 9 days after EPO was withheld. This is a pattern consistent with neocytolysis (discussed next). Stool porphyrins were studied in two of the four
NEOCYTOLYSIS IN RENAL ANEMIA
patients with a pattern of neocytolysis. In both, there was a suggestion of abnormal stool enrichment of the isotope administered just before EPO was withheld. Because only young red cells take up the label, this is in keeping with selective hemolysis of these cells. Neocytolysis first became apparent in trying to understand the anemia that invariably is found in astronauts returning from spaceflights of even a few days.1,2 On entering microgravity, blood pools centrally from the extremities. The total blood volume and red cell mass are suddenly inappropriately elevated for the new environment. For some time, investigators were confused by the facts that 51Cr–red cell survival was repeatedly normal in astronauts and ferrokinetic measurements of red cell production also remained normal during the first days in space, during which time there is a 10% to 15% decrease in red cell mass. This became understandable when we considered that the 51Cr label had been applied 12 days before launch, leading to the inescapable conclusion that young red cells (⬍12 days old) are selectively hemolyzed. We have confirmed neocytolysis in another situation in which red cell mass is suddenly inappropriately elevated for a changed environment, which is the rapid descent of acclimated individuals from very high altitude to sea level.3-5 In these situations, there is rapid profound endogenous EPO suppression, and our belief that suppression of EPO to less than a threshold nadir initiates the process is supported by the fact that low doses of subcutaneous EPO prevented the rapid decrease in red cell mass in those descending from high altitude. We know that neocytolysis begins in less than 24 hours, that the process is limited to reducing red cell mass by 10% to 15%, and the process is completed within 7 to 10 days (this is why we analyzed survival curves before and after 9 days of EPO withdrawal).1,5 If further adaptation is necessary, it proceeds more slowly through changes in red cell production. Among the unknowns about the process are how low EPO levels must be suppressed and for how long. We are attempting to address these questions by creating models of neocytolysis in exhypoxic mice and in healthy humans temporarily administered EPO injections. The mechanism by which low EPO levels can initiate neocytolysis is also under study. Our working theory is that
61
endothelial cells (which have been shown to express messenger RNA for EPO receptors) secrete cytokines influencing adhesive interactions between young red blood cells and reticuloendothelial (RE) phagocytes. The anemia of renal disease was long regarded as a multifactorial process, but the extraordinary clinical efficacy of recombinant EPO clearly establishes EPO deficiency as paramount.11 Too quickly disregarded have been studies showing a consistent hemolytic component of variable degree in the anemia of renal insufficiency,12-14 an extracorpuscular hemolytic component that has never been fully explained.15 Neocytolysis can explain this hemolytic component without negating the therapeutic efficacy of EPO; after all, prevention of neocytolysis appears to be a newly recognized action of EPO.1,4,5 Further support for this concept comes from observations that EPO therapy prolongs red cell survival in patients with renal disease.16,17 Neocytolysis predicts the inefficiency of intravenous bolus dosing schedules of recombinant EPO. The EPO peak would effect commitment and proliferation of erythroid progenitors, but the nadir would bring about neocytolysis of newly released red cells. This phenomenon might contribute to the metabolic toxicities of hyperkalemia and hyperphosphatemia that have been observed with bolus EPO therapy.11 Quite a number of empiric studies have shown that subcutaneous EPO injections are more effective than intravenous boluses at considerably lower total dose and cost.18-20 Investigators have been unable to satisfactorily explain the basis of the increased efficiency of subcutaneous therapy, but avoidance of nadirs that precipitate neocytolysis explains it nicely. In summary, neocytolysis is a physiological process allowing rapid adaptation to plethora by selectively hemolyzing young red blood cells, apparently precipitated by EPO depression. We now show its occurrence in four of five studied dialysis patients. In the anemia of renal disease, neocytolysis helps explain (1) the often demonstrable hemolytic component, (2) worse hemolysis with more advanced renal disease,13 (3) responsiveness of hemolysis to EPO therapy, and (4) increased efficiency of daily subcutaneous EPO. Having shown that neocytolysis can contribute to anemia in renal failure patients with
62
RICE ET AL
low baseline EPO levels when the exogenous hormone is withheld, we would endorse studies of the intensity of neocytolysis in patients receiving intravenous bolus versus low-dose daily subcutaneous EPO therapy. ACKNOWLEDGMENT We appreciate the logistic support at different phases of this project from Dr Juan Olivero and renal fellows, Drs Millie Samaniego, Katherine Timmins, Mario Assouad, and Bashar Mourad.
REFERENCES 1. Alfrey CP, Rice L, Udden M, Driscoll T: Neocytolysis: A physiologic down-regulator of red blood cell mass. Lancet 349:1389-1390, 1997 2. Alfrey CP, Udden MM, Leach-Huntoon CS, Driscoll T, Pickett MH: Control of red blood cell mass in spaceflight. J Appl Physiol 81:98-104, 1996 3. Rice L, Udden M, Driscoll T, Whitley C, Alfrey CP: Neocytolysis in the adaptation of red cell mass on descent from altitude. Acta Andina 6:17-20, 1997 4. Rice L, Alfrey C, Ruiz W, Driscoll T, Whitley C, Gonzales G: Neocytolysis on descent from altitude. Blood 90:8b, 1997 (suppl 1; abstr) 5. Rice L, Alfrey C, Ruiz W, Driscoll T, Whitley C, Gonzales G: Neocytolysis on descent from altitude. (manuscript in preparation) 1998 6. International Committee for Standardization in Haematology: Recommended method for radioisotope red cell survival studies. Brit J Haematol 45:659-666, 1980 7. Burge CM, Skinner SL: Determination of hemoglobin mass and blood volume with CO: Evaluation and application of a method. J Appl Physiol 79:623-631, 1995 8. Rothuizen J, van den Brom WE, Fevery J: The origins and kinetics of bilirubin in healthy dogs, in comparison with man. J Hepatol 15:25-34, 1992 9. Samson D, Halliday D, Nicholson DC, Chanarin I: Quantitation of ineffective erythropoiesis from the incorpo-
ration of [15N]delta-aminolevulinic acid and [13C]glycine into early labeled bilirubin. Brit J Haematol 34:33-44, 1976 10. Barrie A, Prosser SJ: Automated analysis of lightelement stable isotopes ratio mass spectrometry, in Boutton TW, Yamasaki S (eds): Mass Spectrometry of Soils. New York, NY, Marcel Dekker, 1996, pp 1-46 11. Eschbach JW, Egrie JC, Downing MR, Brown JK, Adamson JW: Correction of the anemia of end-stage renal disease with recombinant human erythropoietin. N Engl J Med 316:73-78, 1987 12. Eschbach JW, Funk D, Adamson JW, Kuhn I, Scribner BH, Finch CA: Erythropoiesis in patients with renal failure undergoing chronic dialysis. N Engl J Med 276:653658, 1967 13. Shaw AB: Haemolysis in chronic renal failure. BMJ 2:213-216, 1967 14. Adamson JW, Eschbach J, Finch C: The kidney and erythropoiesis. Blood 44:725-733, 1968 15. Caro J, Erslev AJ: Anemia of chronic renal failure, in Williams WJ (ed): Hematology (ed 5). New York, NY, McGraw Hill, 1995, pp 456-462 16. Eschbach JW: The anemia of chronic renal failure: Pathophysiology and the effects of recombinant erythropoietin. Kidney Int 35:134-148, 1989 17. Polenakovic M, Sikole A: Is erythropoietin a survival factor for red blood cells? J Am Soc Nephrol 7:1178-1182, 1996 18. Granolleras C, Branger B, Beau MC, DeSchodt G, Alsabadani D, Shaldon S: Subcutaneous erythropoietin: A comparison of daily and thrice-weekly administration. Contrib Nephrol 88:143-148, 1991 19. Paganini EP, Eschbach JW, Lazarus JM, Van Stone JC, Gimenez LF, Egrie JC, Okamoto DM, Goodkin DA: Intravenous versus subcutaneous dosing of epoetin alpha in hemodialysis patients. Am J Kidney Dis 26:331-340, 1995 20. Kaufman JS, Domenic JR, Fye CL, Goldfarb DS, Henderson WG, Kleinman JG, Vaamonde CA: Subcutaneous compared with intravenous Epoetin in patients receiving hemodialysis. N Engl J Med 339:578-83, 1998
Editorial, p. 140
W
E HAVE UNCOVERED a physiological process that selectively hemolyzes the youngest circulating red blood cells in situations of red cell excess and have named this process neocytolysis.1 Neocytolysis became manifest while studying mechanisms underlying spaceflight anemia, an adaptation of astronauts to acute plethora in microgravity.2 Individuals acclimated to high altitude who descend to sea level also experience neocytolysis, and we are actively extending these observations to further elucidate the process.3-5 Neocytolysis occurs in situations in which erythropoietin (EPO) secretion is suppressed, creating suspicion that the process is initiated by a decrease in EPO levels to less than a threshold. On descent from altitude, low doses of subcutaneous EPO prevented a rapid adaptive decrease in red cell mass, further implicating low EPO levels in precipitating this process.4-5 Renal insufficiency presents a pathological situation in which EPO production is depressed. We sought to determine whether neocytolysis is present in some patients with renal insufficiency and contributes to their anemia. If so, important implications might extend to optimizing therapy for the anemia of renal disease. METHODS From nine stable dialysis patients screened, five were selected for study and consented to participate in our institutional review board–approved protocol. Patient selection was on the basis of low baseline EPO levels (Eporia; Ramco,
Houston, TX), all less than 25 U/mL drawn at least 3 days after their last EPO injection. Patients were screened for the absence of infection, active inflammatory disease, and iron deficiency (based on serum ferritin levels ⬎80 ng/mL). Patients had stable hematocrits on standard EPO therapy (generally 50 µg/kg three times weekly intravenously). The patients studied were from 36 to 69 years of age, four were men, and renal failure was caused by hypertension in four patients and unknown causes in one patient. The five patients had their red cells labeled with 50 µCi of chromium 51 (51Cr) and survival curves traced by standard methods (corrected for elution) while receiving or not receiving EPO.6 Curves were fitted by the method of least squares. Each patient had EPO therapy held for at least 12 days. The first two patients had red cell mass determinations at the beginning and completion of the study using a standard 51Cr dilution technique. The last three patients had red cell mass determinations at the time of each sample collection based on measurements of carboxyhemoglobin after carbon monoxide inhalation.7 For each patient, the residual 51Cr remaining in the blood was the product of the radioactivity per milliliter of blood corrected for elution and the red cell mass. The last three patients studied ingested 1 g each of oral 13C-glycine (13C) and 15N-glycine (15N) to label newly synthesized red cells. One isotope was administered during EPO therapy and the second before withholding exogenous EPO. From collected serial stool specimens, stercobilin was From the Methodist Hospital; and Sections of Hematology and Nephrology, Baylor College of Medicine, Houston, TX. Received January 12, 1998; accepted in revised form September 15, 1998. Supported by grant no. TMC/NASA NCC 9-36/24-272223315111 from the Texas Medical Center and the National Aeronautics and Space Administration, Houston, TX. Dr Hatchey is now at Vanderbilt University, Nashville, TN. Address reprint requests to Lawrence Rice, MD, 6565 Fannin, MS 902-Main, Houston, TX 77030. E-mail: [email protected]
娀 1999 by the National Kidney Foundation, Inc. 0272-6386/99/3301-0009$3.00/0
American Journal of Kidney Diseases, Vol 33, No 1 (January), 1999: pp 59-62
59
60
RICE ET AL
isolated by ethanol, ether, and chloroform extraction,8 a final thin-layer chromatography step,9 and then specimens were frozen at –20°C. Isotopic measurements of 13C and 15N enrichment were determined by online combustion isotopic analysis using a Tacermass isotope ratio mass spectrometer (Europa Scientific, Crewe, United Kingdom) equipped with a RoboPrep N continuous-flow combustion interface (Europa Scientific).10 A 1- to 2-mg sample of crystalline hemin or stercobilin was placed in tin combustion cups and loaded on the autosampler. The isotopic results were determined as atom percent with a relatively precision of ⫾0.5 milliAtom percent excess (mAPE) (0.0005 Atom%).
RESULTS
Figure 1 shows a composite 51Cr–red cell survival curve representing all five patients. When EPO therapy was held, the slope was steeper (red cells disappeared more quickly) during the first 9 days than afterward, as predicted by our theory (see Discussion). The survival curve slope for the first 9 days off EPO therapy was –3.15% ⫾ 0.30% (standard error) per day and the subsequent slope was –1.32% ⫾ 0.25% per day, statistically shorter in the first 9 days off EPO therapy (P ⬍ 0.02). In the three patients who received oral 13C and 15N, two had some suggestion of abnormal enrichment of their stool with the isotope administered just before EPO was withheld. Figure 2 shows
Fig 2. Isotope enrichment of stool porphyrins is graphed for a healthy subject and two patients. There is a suggestion of increased isotope in stercobilin on day 10 after EPO was withheld from patient 1, compared with the normal or to his results on EPO therapy (patient 2 had a similar suggestion). This is consistent with hemolysis of young red cell precursors. Patient 3 shows persistent elevation of isotope whether on or off EPO therapy, a pattern suggesting chronic hemolytic anemia.
this graphically in patient 1. The results in patient 2 were similar. For comparison, data from a healthy control and from patient 3 are shown. Patient 3 appeared to have abnormal stool enrichment by both isotopes and also had short 51Cr– red cell survival with little improvement in survival after 9 days; thus, this patient appears to have a chronic hemolytic process. DISCUSSION
Fig 1. Composite 51Cr–red cell survival curve for all five patients (corrected for elution and changes in red cell mass). The slope in the first 9 days when EPO was withheld is statistically steeper than the slope of the curve after 9 days (–3.15 v –1.32; P F 0.02). After 9 days, the slope approximates normal. The pattern is consistent with neocytolysis.
Neocytolysis has been observed with physiological EPO suppression in astronauts and in polycythemic individuals descending from high altitude, and it can be prevented by administration of low doses of EPO.1-5 This mandated the study of a situation in which there is pathological EPO suppression, the anemia of renal insufficiency. When five dialysis patients with low baseline EPO levels had their EPO therapy withheld, a pattern of neocytolysis emerged in four (the fifth showed a pattern of chronic hemolytic anemia). 51Cr–red cell survival curves showed a statistically significant steeper slope in the first 9 days after EPO was withheld. This is a pattern consistent with neocytolysis (discussed next). Stool porphyrins were studied in two of the four
NEOCYTOLYSIS IN RENAL ANEMIA
patients with a pattern of neocytolysis. In both, there was a suggestion of abnormal stool enrichment of the isotope administered just before EPO was withheld. Because only young red cells take up the label, this is in keeping with selective hemolysis of these cells. Neocytolysis first became apparent in trying to understand the anemia that invariably is found in astronauts returning from spaceflights of even a few days.1,2 On entering microgravity, blood pools centrally from the extremities. The total blood volume and red cell mass are suddenly inappropriately elevated for the new environment. For some time, investigators were confused by the facts that 51Cr–red cell survival was repeatedly normal in astronauts and ferrokinetic measurements of red cell production also remained normal during the first days in space, during which time there is a 10% to 15% decrease in red cell mass. This became understandable when we considered that the 51Cr label had been applied 12 days before launch, leading to the inescapable conclusion that young red cells (⬍12 days old) are selectively hemolyzed. We have confirmed neocytolysis in another situation in which red cell mass is suddenly inappropriately elevated for a changed environment, which is the rapid descent of acclimated individuals from very high altitude to sea level.3-5 In these situations, there is rapid profound endogenous EPO suppression, and our belief that suppression of EPO to less than a threshold nadir initiates the process is supported by the fact that low doses of subcutaneous EPO prevented the rapid decrease in red cell mass in those descending from high altitude. We know that neocytolysis begins in less than 24 hours, that the process is limited to reducing red cell mass by 10% to 15%, and the process is completed within 7 to 10 days (this is why we analyzed survival curves before and after 9 days of EPO withdrawal).1,5 If further adaptation is necessary, it proceeds more slowly through changes in red cell production. Among the unknowns about the process are how low EPO levels must be suppressed and for how long. We are attempting to address these questions by creating models of neocytolysis in exhypoxic mice and in healthy humans temporarily administered EPO injections. The mechanism by which low EPO levels can initiate neocytolysis is also under study. Our working theory is that
61
endothelial cells (which have been shown to express messenger RNA for EPO receptors) secrete cytokines influencing adhesive interactions between young red blood cells and reticuloendothelial (RE) phagocytes. The anemia of renal disease was long regarded as a multifactorial process, but the extraordinary clinical efficacy of recombinant EPO clearly establishes EPO deficiency as paramount.11 Too quickly disregarded have been studies showing a consistent hemolytic component of variable degree in the anemia of renal insufficiency,12-14 an extracorpuscular hemolytic component that has never been fully explained.15 Neocytolysis can explain this hemolytic component without negating the therapeutic efficacy of EPO; after all, prevention of neocytolysis appears to be a newly recognized action of EPO.1,4,5 Further support for this concept comes from observations that EPO therapy prolongs red cell survival in patients with renal disease.16,17 Neocytolysis predicts the inefficiency of intravenous bolus dosing schedules of recombinant EPO. The EPO peak would effect commitment and proliferation of erythroid progenitors, but the nadir would bring about neocytolysis of newly released red cells. This phenomenon might contribute to the metabolic toxicities of hyperkalemia and hyperphosphatemia that have been observed with bolus EPO therapy.11 Quite a number of empiric studies have shown that subcutaneous EPO injections are more effective than intravenous boluses at considerably lower total dose and cost.18-20 Investigators have been unable to satisfactorily explain the basis of the increased efficiency of subcutaneous therapy, but avoidance of nadirs that precipitate neocytolysis explains it nicely. In summary, neocytolysis is a physiological process allowing rapid adaptation to plethora by selectively hemolyzing young red blood cells, apparently precipitated by EPO depression. We now show its occurrence in four of five studied dialysis patients. In the anemia of renal disease, neocytolysis helps explain (1) the often demonstrable hemolytic component, (2) worse hemolysis with more advanced renal disease,13 (3) responsiveness of hemolysis to EPO therapy, and (4) increased efficiency of daily subcutaneous EPO. Having shown that neocytolysis can contribute to anemia in renal failure patients with
62
RICE ET AL
low baseline EPO levels when the exogenous hormone is withheld, we would endorse studies of the intensity of neocytolysis in patients receiving intravenous bolus versus low-dose daily subcutaneous EPO therapy. ACKNOWLEDGMENT We appreciate the logistic support at different phases of this project from Dr Juan Olivero and renal fellows, Drs Millie Samaniego, Katherine Timmins, Mario Assouad, and Bashar Mourad.
REFERENCES 1. Alfrey CP, Rice L, Udden M, Driscoll T: Neocytolysis: A physiologic down-regulator of red blood cell mass. Lancet 349:1389-1390, 1997 2. Alfrey CP, Udden MM, Leach-Huntoon CS, Driscoll T, Pickett MH: Control of red blood cell mass in spaceflight. J Appl Physiol 81:98-104, 1996 3. Rice L, Udden M, Driscoll T, Whitley C, Alfrey CP: Neocytolysis in the adaptation of red cell mass on descent from altitude. Acta Andina 6:17-20, 1997 4. Rice L, Alfrey C, Ruiz W, Driscoll T, Whitley C, Gonzales G: Neocytolysis on descent from altitude. Blood 90:8b, 1997 (suppl 1; abstr) 5. Rice L, Alfrey C, Ruiz W, Driscoll T, Whitley C, Gonzales G: Neocytolysis on descent from altitude. (manuscript in preparation) 1998 6. International Committee for Standardization in Haematology: Recommended method for radioisotope red cell survival studies. Brit J Haematol 45:659-666, 1980 7. Burge CM, Skinner SL: Determination of hemoglobin mass and blood volume with CO: Evaluation and application of a method. J Appl Physiol 79:623-631, 1995 8. Rothuizen J, van den Brom WE, Fevery J: The origins and kinetics of bilirubin in healthy dogs, in comparison with man. J Hepatol 15:25-34, 1992 9. Samson D, Halliday D, Nicholson DC, Chanarin I: Quantitation of ineffective erythropoiesis from the incorpo-
ration of [15N]delta-aminolevulinic acid and [13C]glycine into early labeled bilirubin. Brit J Haematol 34:33-44, 1976 10. Barrie A, Prosser SJ: Automated analysis of lightelement stable isotopes ratio mass spectrometry, in Boutton TW, Yamasaki S (eds): Mass Spectrometry of Soils. New York, NY, Marcel Dekker, 1996, pp 1-46 11. Eschbach JW, Egrie JC, Downing MR, Brown JK, Adamson JW: Correction of the anemia of end-stage renal disease with recombinant human erythropoietin. N Engl J Med 316:73-78, 1987 12. Eschbach JW, Funk D, Adamson JW, Kuhn I, Scribner BH, Finch CA: Erythropoiesis in patients with renal failure undergoing chronic dialysis. N Engl J Med 276:653658, 1967 13. Shaw AB: Haemolysis in chronic renal failure. BMJ 2:213-216, 1967 14. Adamson JW, Eschbach J, Finch C: The kidney and erythropoiesis. Blood 44:725-733, 1968 15. Caro J, Erslev AJ: Anemia of chronic renal failure, in Williams WJ (ed): Hematology (ed 5). New York, NY, McGraw Hill, 1995, pp 456-462 16. Eschbach JW: The anemia of chronic renal failure: Pathophysiology and the effects of recombinant erythropoietin. Kidney Int 35:134-148, 1989 17. Polenakovic M, Sikole A: Is erythropoietin a survival factor for red blood cells? J Am Soc Nephrol 7:1178-1182, 1996 18. Granolleras C, Branger B, Beau MC, DeSchodt G, Alsabadani D, Shaldon S: Subcutaneous erythropoietin: A comparison of daily and thrice-weekly administration. Contrib Nephrol 88:143-148, 1991 19. Paganini EP, Eschbach JW, Lazarus JM, Van Stone JC, Gimenez LF, Egrie JC, Okamoto DM, Goodkin DA: Intravenous versus subcutaneous dosing of epoetin alpha in hemodialysis patients. Am J Kidney Dis 26:331-340, 1995 20. Kaufman JS, Domenic JR, Fye CL, Goldfarb DS, Henderson WG, Kleinman JG, Vaamonde CA: Subcutaneous compared with intravenous Epoetin in patients receiving hemodialysis. N Engl J Med 339:578-83, 1998