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Zinc: An essential and unheralded nutrient
Zinc: An essential and unheralded nutrient Abbreviation:
p
5'NT = ecto-5'-nucleotidase
rimary human zinc deficiency was discovered nearly 40 years ago by Prasad et al. 1'2 Ever since, a lack of convenient, sensitive indicators of zinc nutriture has slowed the application of knowledge concerning zinc in clinical medicine. Plasma (serum) zinc concentration, the most commonly measured index of zinc status, is insensitive. 3 Therefore Prasad and others searched for other methods for determining zinc status. Approaches include measurement of zinc concentrations in white blood cells, 4 measurement of 5'NT activity in cellular elements of blood 5 and blood plasma, 6 measurement of zinc kinetics, 7'8 and determination of relationships between physiologic functions and zinc nutriture. 9'1° Of these approaches, measurement of zinc or 5'NT in white blood cells (or plasma) appears to be the most applicable to clinical situations. The extreme tediousness of measurements of zinc in white blood cells is reason for another approach. Excessive care is required throughout the isolation of lymphocytes, granulocytes, and platelets to avoid contamination by the ubiquitous element. In addition, matching the matrix of the solutions analyzed by graphite furnace atomic absorption spectrophotometry is extremely important. Hence the solution volume should be adjusted so that equal numbers of cells are present in the injected sample, rather than the dilution of samples so that concentrations fall within the calibrated range (Beck, personal communication). Adequate quality control from batch to batch of samples and checking of all reagents for the absence of zinc contamination must always be practiced. The low standard deviations obtained by Beck et al. ~ for blood cellular zinc concentrations, as compared with those reported by other workers, attest to the high quality of the analysis. Beck et al. ~1 report in this issue an alternative and
J Lab Clin Med 1997;130:116-8. Copyright © 1997 by Mosby-Year Book, Inc. 0022-2143/97 $5.00 + 0 5/1/83003
116
perhaps more clinically useful approach for the assessment of zinc status. The presence of 5'NT in cell membranes requires zinc, and according to Meftah et al., 5 the level of 5'NT is decreased by experimental zinc depletion. That the assay is highly sensitive was suggested by Bales e t al., 6 who found that 15 days of depletion in adults fed 4 mg zinc daily caused a significant decrease in plasma 5'NT. Beck et al. 11 assessed zinc nutriture by using fluorescent antibody measurement of the CD73 antigen that reflects 5'NT in cell membranes. 5'NT is present on subsets of both B and T lymphocytes, with its greatest expression on CD8 + B lymphocytes. 12 Beck's approach utilizes technology routinely available in most modern clinical hematology laboratories for determination of CD4+/CD8 ÷ ratios. Thus it potentially offers a clinically useful means for identifying patients whose zinc nutriture is less than desirable. Beck et al. 11 found associations between low numbers of CD73 lymphocytes and low zinc status, determined by white blood cell zinc concentrations, and associations between increases in CD73 lymphocytes and zinc repletion. Confirmation by others and demonstration that CD73 is indeed a convenient, sensitive, primary indicator of zinc status will lead to its application in clinical care. A second application will be in epidemiologic studies that focus on the prevalence of human zinc deficiency. Since Prasad's 1'2 discovery of primary zinc deficiency, basic and clinical investigations have shown that zinc is involved in many physiologic processes. Stable chemical bonding with macromolecules accounts for zinc's effects on the activity of about 300 enzymes representing all six categories of the International Classification. 13 Zinc nutriture affects cell division, growth, and differentiation14'15; membrane transport of calciumS6; the structure of certain proteins13; and detoxification of certain mitogens. 17 In addition, zinc is essential for certain processes of communication and coordination among ceils that result in physiologic functions such as neuropsychologic performance. 18
J Lab Clin Med Volume 130, Number 2
T o d a y the m a j o r causes o f p r i m a r y h u m a n zinc deficiency are known. 19 Flesh foods, particularly red meat, are the best dietary sources o f zinc, w h e r e a s f o o d s b a s e d o n plants are generally p o o r sources o f bioavailable zinc. P h y t a t e and dietary fiber f r o m plants bind zinc and p r e v e n t its absorption by the intestine. H u m a n zinc r e q u i r e m e n t s have b e e n calculated factorially and adjusted for bioavailability f r o m various types o f diets. Risk o f p r i m a r y zinc deficiency is r e l a t e d to life cycle, f o o d selection, and p e r s o n a l habits. G r o w t h increases the n e e d for zinc. T h u s e m b r y o s , fetuses, infants, children, and p e r s o n s w h o are healing are at risk o f zinc deficiency. Individuals with low c o n s u m p t i o n o f n u t r i e n t - d e n s e f o o d s such as the elderly 2° are also at risk. M a j o r clinical effects o f zinc deficiency include fetal g r o w t h failure, 2~ c h i l d h o o d g r o w t h r e t a r d a t i o n , 22 d e l a y e d p u b e r ty, 23 p o o r immunity, 24 p o o r healing, 2s a c r o d e r m a titis, 26 milder f o r m s of dermatitis, a n d i m p a i r e d n e u r o p s y c h o l o g i c p e r f o r m a n c e . 1° Secondary or conditioned zinc deficiency can occur in m a n y conditions. Included are illnesses that increase catabolism, impair intestinal absorption, impair renal retention of cations, increase loss o f amino acids and proteins, or cause r e p e a t e d h e m o lysis. 27 Beck's H a p p r o a c h m a y also be useful in research designed to assess the prevalence of zinc deficiency. However, before such research is started it will be important to c o m p a r e the sensitivity of Beck's m e t h o d to the sensitivity of physiologic responses after zinc r e p l e t i o n - - s u c h as growth, immunity, and neuropsychologic p e r f o r m a n c e - - b y r a n d o m i z e d controlled trial. A l t h o u g h the prevalence of zinc deficiency is uncertain, 28 it appears c o m m o n a m o n g populations of developing countries. 22 Because zinc is most bioavailable f r o m the same foods as iron, it seems likely the prevalence of primary iron deficiency and that of zinc deficiency are similar. S u p p o r t for this idea was provided by a study of the relationship between serum ferritin concentration and zinc kinetics in w o m e n , s Serum ferritin concentrations -<20 ixg/dl were associated with an accelerated disappearance of injected zinc 67 f r o m the blood: T h e m a n y p o t e n t i a l applications of B e c k ' s app r o a c h m a k e c o n f i r m a t i o n o f h e r findings a high priority. T h o s e o f us w h o have b e e n f r u s t r a t e d over the past n e a r l y 40 years by the insensitivity o f p l a s m a zinc as an i n d i c a t o r o f z i n c status l o o k f o r w a r d to the results o f r e s e a r c h that validate B e c k ' s findings.
Editorial
117
H A R O L D H. SANDSTEAD, MD NANCY W. ALCOCK, PhD
Department of Preventive Medicine and Community Health The University of Texas Medical Branch Galveston, TX 77555-1109 REFERENCES
1. Prasad AS, Halsted JA, Nadirni M. Syndrome of iron deficiency anemia, hepatosplenomegaly, hypogonadism, dwarfism and geophagia. Am J Med 1961;31:532-46. 2. Prasad A, Miale A Jr, Farid Z, Sandstead H, Schulert A. Zinc metabolism in patients with syndrome of iron deficiency anemia, hepatosplenomegaly, dwarfism and hypogonadism. J Lab Clin Med 1963;61:537-49. 3. Sandstead HH. Assessment of zinc status. J Lab Clin Med 1991;118:299-300. 4. Wang H, Prasad A, Mouchelle E. Zinc in platelets, lymphocytes and granulocytes by flameless atomic absorption spectrophometry. J Micronutr Anal 1989;5:181-90. 5. Meftah S, Prasad A, Lee D, Brewer G. Ecto 5' nucleotidase (5'NT) as a sensitive indicator of human zinc deficiency. J Lab Clin Med 1991;118:309-16. 6. Bales C, DiSilvestro R, Currie K, et al. Marginal zinc deficiency in older adults: responsiveness of zinc status indicators. J Am Coll Nutr 1994;13:455-62. 7. Miller L, Hambridge K, Naake V, Hong Z, Westcott J, Fennessey P. Size of the zinc pools that exchange rapidly with plasma zinc in humans: alternative techniques for measuring and relation to dietary intake. J Nutr 1994;124:268-76. 8. Yokoi K, Alcock N, Sandstead H. Iron and zinc nutriture of premenopausal women: associations of diet with serum ferritin and plasma zinc disappearance, and of serum ferritin with plasma zinc and plasma zinc disappearance. J Lab Clin Med 1994;124:852-61. 9. Wada L, King J. Effect of low zinc intakes on basal metabolic rate, thyroid hormones and protein utilization in adult men. J Nutr 1986;116:1045-53. 10. Penland J, Sandstead H, Alcock N, et al. Preliminary report: effects of zinc and micronutrient repletion on growth and neuropsychological function of urban Chinese children. J Am Coll Nutr 1997;16:268-72. 11. Beck F, Kaplan J, Fine N, Handschu W, Prasad A. Decreased expression of CD73 (ecto-5'-nucleotidase) in the CD8+ subset is associated with zinc deficiency in humans. J Lab Clin Med 1997;130:147-56. 12. Thompson L, Ruedi J, Low M, Clement L. Distribution of ecto-5'-nucleotidase on subsets of human T and B lymphocytes as detected by indirect immunofluorescence using goat antibodies. J Immunol 1987;139:4042-8. 13. Vallee B, Falchuk K. The biochemical basis of zinc physiology. Physiol Rev 1993;73:79-118. 14. Hurley LS, Shrader RE. Abnormal development of preimplantation rat eggs after three days of maternal dietary zinc deficiency. Nature 1974;254:427-9. 15. Dvergsten C, Johnson L, Sandstead H. Alterations in the postnatal development of the cerebellar cortex due to zinc deficiency. III. Impaired dendritic differentiation of basket and stellate cells. Brain Res 1984;318:21-6. 16. Browning J, O'Dell B. Zinc deficiency decreases the concentration of N-methyl-D-aspartate receptors in guinea pig cortical synaptic membranes. J Nutr 1995;125:2083-9. 17. Barch D, Fox C. Dietary zinc deficiency increases the meth-
118
18. 19.
20.
21.
22. 23.
J Lab Clin Med August 1997
Editorial
ylbenzylnitrosamine induced formation of O6-methylguanine in the esophageal DNA of the rat. Carcinogenesis 1987;8: 1461-4. Sandstead HH. Zinc: essentiality for brain development and function. Nutr Rev 1985;43:129-37. Sandstead H, Smith J Jr. Deliberations and evaluations of approaches, endpoints, and paradigms for determining zinc dietary recommendations. J Nutr 1996;126:2410S-8S. Prasad A, Fitzgerald J, Hess J, Kaplan J, Peleu F, Dardenne M. Zinc deficiency in elderly patients. Nutrition 1993;9:21824. Goldenberg R, Tamura T, Neggers Y, et al. The effect of zinc supplementation on pregnancy Outcome. J Am Med Assoc 1995;274:463-8. Gibson R. Zinc nutrition in developing countries. Nutr Res Rev 1994;7:151-73. Sandstead HH, Prasad AS, Schulert AR, Miale A Jr, Bassily S, Darby W. Human zinc deficiency, endocrine manifesta-
24.
25. 26.
27.
28.
tions, and response to treatment. Am J Clin Nutr 1967;20: 422-42. Fraker P, King L, Garvy B, Medina C. The immunopathology of zinc deficiency in humans and rodents, a possible force for programmed cell death. In: Klurfeld D, editor. Human nutrition--a comprehensive treatise (vol 8). New York: Academic Press, 1993:267-83. Haeger K, Lanner E. Oral zinc sulfate and ischemic leg ulcers. J Vasc Dis 1974;3:77-81. Kay R, Tasmin-Jones C, Pybus J. A syndrome of acute zinc deficiency during total parenteral alimentation. Ann Surg 1976;183:331-40. Sandstead H, Vo-Khactu K, Solomons NI. Conditioned zinc deficiencies. In: Prasad A, editor. Trace elements in human health and disease (vol 1). New York: Academic Press, 1976: 33-49. Sandstead HH. Zinc deficiency: a public health problem. Am J Dis Child 1991;145:835-59.
p
5'NT = ecto-5'-nucleotidase
rimary human zinc deficiency was discovered nearly 40 years ago by Prasad et al. 1'2 Ever since, a lack of convenient, sensitive indicators of zinc nutriture has slowed the application of knowledge concerning zinc in clinical medicine. Plasma (serum) zinc concentration, the most commonly measured index of zinc status, is insensitive. 3 Therefore Prasad and others searched for other methods for determining zinc status. Approaches include measurement of zinc concentrations in white blood cells, 4 measurement of 5'NT activity in cellular elements of blood 5 and blood plasma, 6 measurement of zinc kinetics, 7'8 and determination of relationships between physiologic functions and zinc nutriture. 9'1° Of these approaches, measurement of zinc or 5'NT in white blood cells (or plasma) appears to be the most applicable to clinical situations. The extreme tediousness of measurements of zinc in white blood cells is reason for another approach. Excessive care is required throughout the isolation of lymphocytes, granulocytes, and platelets to avoid contamination by the ubiquitous element. In addition, matching the matrix of the solutions analyzed by graphite furnace atomic absorption spectrophotometry is extremely important. Hence the solution volume should be adjusted so that equal numbers of cells are present in the injected sample, rather than the dilution of samples so that concentrations fall within the calibrated range (Beck, personal communication). Adequate quality control from batch to batch of samples and checking of all reagents for the absence of zinc contamination must always be practiced. The low standard deviations obtained by Beck et al. ~ for blood cellular zinc concentrations, as compared with those reported by other workers, attest to the high quality of the analysis. Beck et al. ~1 report in this issue an alternative and
J Lab Clin Med 1997;130:116-8. Copyright © 1997 by Mosby-Year Book, Inc. 0022-2143/97 $5.00 + 0 5/1/83003
116
perhaps more clinically useful approach for the assessment of zinc status. The presence of 5'NT in cell membranes requires zinc, and according to Meftah et al., 5 the level of 5'NT is decreased by experimental zinc depletion. That the assay is highly sensitive was suggested by Bales e t al., 6 who found that 15 days of depletion in adults fed 4 mg zinc daily caused a significant decrease in plasma 5'NT. Beck et al. 11 assessed zinc nutriture by using fluorescent antibody measurement of the CD73 antigen that reflects 5'NT in cell membranes. 5'NT is present on subsets of both B and T lymphocytes, with its greatest expression on CD8 + B lymphocytes. 12 Beck's approach utilizes technology routinely available in most modern clinical hematology laboratories for determination of CD4+/CD8 ÷ ratios. Thus it potentially offers a clinically useful means for identifying patients whose zinc nutriture is less than desirable. Beck et al. 11 found associations between low numbers of CD73 lymphocytes and low zinc status, determined by white blood cell zinc concentrations, and associations between increases in CD73 lymphocytes and zinc repletion. Confirmation by others and demonstration that CD73 is indeed a convenient, sensitive, primary indicator of zinc status will lead to its application in clinical care. A second application will be in epidemiologic studies that focus on the prevalence of human zinc deficiency. Since Prasad's 1'2 discovery of primary zinc deficiency, basic and clinical investigations have shown that zinc is involved in many physiologic processes. Stable chemical bonding with macromolecules accounts for zinc's effects on the activity of about 300 enzymes representing all six categories of the International Classification. 13 Zinc nutriture affects cell division, growth, and differentiation14'15; membrane transport of calciumS6; the structure of certain proteins13; and detoxification of certain mitogens. 17 In addition, zinc is essential for certain processes of communication and coordination among ceils that result in physiologic functions such as neuropsychologic performance. 18
J Lab Clin Med Volume 130, Number 2
T o d a y the m a j o r causes o f p r i m a r y h u m a n zinc deficiency are known. 19 Flesh foods, particularly red meat, are the best dietary sources o f zinc, w h e r e a s f o o d s b a s e d o n plants are generally p o o r sources o f bioavailable zinc. P h y t a t e and dietary fiber f r o m plants bind zinc and p r e v e n t its absorption by the intestine. H u m a n zinc r e q u i r e m e n t s have b e e n calculated factorially and adjusted for bioavailability f r o m various types o f diets. Risk o f p r i m a r y zinc deficiency is r e l a t e d to life cycle, f o o d selection, and p e r s o n a l habits. G r o w t h increases the n e e d for zinc. T h u s e m b r y o s , fetuses, infants, children, and p e r s o n s w h o are healing are at risk o f zinc deficiency. Individuals with low c o n s u m p t i o n o f n u t r i e n t - d e n s e f o o d s such as the elderly 2° are also at risk. M a j o r clinical effects o f zinc deficiency include fetal g r o w t h failure, 2~ c h i l d h o o d g r o w t h r e t a r d a t i o n , 22 d e l a y e d p u b e r ty, 23 p o o r immunity, 24 p o o r healing, 2s a c r o d e r m a titis, 26 milder f o r m s of dermatitis, a n d i m p a i r e d n e u r o p s y c h o l o g i c p e r f o r m a n c e . 1° Secondary or conditioned zinc deficiency can occur in m a n y conditions. Included are illnesses that increase catabolism, impair intestinal absorption, impair renal retention of cations, increase loss o f amino acids and proteins, or cause r e p e a t e d h e m o lysis. 27 Beck's H a p p r o a c h m a y also be useful in research designed to assess the prevalence of zinc deficiency. However, before such research is started it will be important to c o m p a r e the sensitivity of Beck's m e t h o d to the sensitivity of physiologic responses after zinc r e p l e t i o n - - s u c h as growth, immunity, and neuropsychologic p e r f o r m a n c e - - b y r a n d o m i z e d controlled trial. A l t h o u g h the prevalence of zinc deficiency is uncertain, 28 it appears c o m m o n a m o n g populations of developing countries. 22 Because zinc is most bioavailable f r o m the same foods as iron, it seems likely the prevalence of primary iron deficiency and that of zinc deficiency are similar. S u p p o r t for this idea was provided by a study of the relationship between serum ferritin concentration and zinc kinetics in w o m e n , s Serum ferritin concentrations -<20 ixg/dl were associated with an accelerated disappearance of injected zinc 67 f r o m the blood: T h e m a n y p o t e n t i a l applications of B e c k ' s app r o a c h m a k e c o n f i r m a t i o n o f h e r findings a high priority. T h o s e o f us w h o have b e e n f r u s t r a t e d over the past n e a r l y 40 years by the insensitivity o f p l a s m a zinc as an i n d i c a t o r o f z i n c status l o o k f o r w a r d to the results o f r e s e a r c h that validate B e c k ' s findings.
Editorial
117
H A R O L D H. SANDSTEAD, MD NANCY W. ALCOCK, PhD
Department of Preventive Medicine and Community Health The University of Texas Medical Branch Galveston, TX 77555-1109 REFERENCES
1. Prasad AS, Halsted JA, Nadirni M. Syndrome of iron deficiency anemia, hepatosplenomegaly, hypogonadism, dwarfism and geophagia. Am J Med 1961;31:532-46. 2. Prasad A, Miale A Jr, Farid Z, Sandstead H, Schulert A. Zinc metabolism in patients with syndrome of iron deficiency anemia, hepatosplenomegaly, dwarfism and hypogonadism. J Lab Clin Med 1963;61:537-49. 3. Sandstead HH. Assessment of zinc status. J Lab Clin Med 1991;118:299-300. 4. Wang H, Prasad A, Mouchelle E. Zinc in platelets, lymphocytes and granulocytes by flameless atomic absorption spectrophometry. J Micronutr Anal 1989;5:181-90. 5. Meftah S, Prasad A, Lee D, Brewer G. Ecto 5' nucleotidase (5'NT) as a sensitive indicator of human zinc deficiency. J Lab Clin Med 1991;118:309-16. 6. Bales C, DiSilvestro R, Currie K, et al. Marginal zinc deficiency in older adults: responsiveness of zinc status indicators. J Am Coll Nutr 1994;13:455-62. 7. Miller L, Hambridge K, Naake V, Hong Z, Westcott J, Fennessey P. Size of the zinc pools that exchange rapidly with plasma zinc in humans: alternative techniques for measuring and relation to dietary intake. J Nutr 1994;124:268-76. 8. Yokoi K, Alcock N, Sandstead H. Iron and zinc nutriture of premenopausal women: associations of diet with serum ferritin and plasma zinc disappearance, and of serum ferritin with plasma zinc and plasma zinc disappearance. J Lab Clin Med 1994;124:852-61. 9. Wada L, King J. Effect of low zinc intakes on basal metabolic rate, thyroid hormones and protein utilization in adult men. J Nutr 1986;116:1045-53. 10. Penland J, Sandstead H, Alcock N, et al. Preliminary report: effects of zinc and micronutrient repletion on growth and neuropsychological function of urban Chinese children. J Am Coll Nutr 1997;16:268-72. 11. Beck F, Kaplan J, Fine N, Handschu W, Prasad A. Decreased expression of CD73 (ecto-5'-nucleotidase) in the CD8+ subset is associated with zinc deficiency in humans. J Lab Clin Med 1997;130:147-56. 12. Thompson L, Ruedi J, Low M, Clement L. Distribution of ecto-5'-nucleotidase on subsets of human T and B lymphocytes as detected by indirect immunofluorescence using goat antibodies. J Immunol 1987;139:4042-8. 13. Vallee B, Falchuk K. The biochemical basis of zinc physiology. Physiol Rev 1993;73:79-118. 14. Hurley LS, Shrader RE. Abnormal development of preimplantation rat eggs after three days of maternal dietary zinc deficiency. Nature 1974;254:427-9. 15. Dvergsten C, Johnson L, Sandstead H. Alterations in the postnatal development of the cerebellar cortex due to zinc deficiency. III. Impaired dendritic differentiation of basket and stellate cells. Brain Res 1984;318:21-6. 16. Browning J, O'Dell B. Zinc deficiency decreases the concentration of N-methyl-D-aspartate receptors in guinea pig cortical synaptic membranes. J Nutr 1995;125:2083-9. 17. Barch D, Fox C. Dietary zinc deficiency increases the meth-
118
18. 19.
20.
21.
22. 23.
J Lab Clin Med August 1997
Editorial
ylbenzylnitrosamine induced formation of O6-methylguanine in the esophageal DNA of the rat. Carcinogenesis 1987;8: 1461-4. Sandstead HH. Zinc: essentiality for brain development and function. Nutr Rev 1985;43:129-37. Sandstead H, Smith J Jr. Deliberations and evaluations of approaches, endpoints, and paradigms for determining zinc dietary recommendations. J Nutr 1996;126:2410S-8S. Prasad A, Fitzgerald J, Hess J, Kaplan J, Peleu F, Dardenne M. Zinc deficiency in elderly patients. Nutrition 1993;9:21824. Goldenberg R, Tamura T, Neggers Y, et al. The effect of zinc supplementation on pregnancy Outcome. J Am Med Assoc 1995;274:463-8. Gibson R. Zinc nutrition in developing countries. Nutr Res Rev 1994;7:151-73. Sandstead HH, Prasad AS, Schulert AR, Miale A Jr, Bassily S, Darby W. Human zinc deficiency, endocrine manifesta-
24.
25. 26.
27.
28.
tions, and response to treatment. Am J Clin Nutr 1967;20: 422-42. Fraker P, King L, Garvy B, Medina C. The immunopathology of zinc deficiency in humans and rodents, a possible force for programmed cell death. In: Klurfeld D, editor. Human nutrition--a comprehensive treatise (vol 8). New York: Academic Press, 1993:267-83. Haeger K, Lanner E. Oral zinc sulfate and ischemic leg ulcers. J Vasc Dis 1974;3:77-81. Kay R, Tasmin-Jones C, Pybus J. A syndrome of acute zinc deficiency during total parenteral alimentation. Ann Surg 1976;183:331-40. Sandstead H, Vo-Khactu K, Solomons NI. Conditioned zinc deficiencies. In: Prasad A, editor. Trace elements in human health and disease (vol 1). New York: Academic Press, 1976: 33-49. Sandstead HH. Zinc deficiency: a public health problem. Am J Dis Child 1991;145:835-59.