Sports as a cause of oxidative stress and hemolysis

Javier F. Bonilla, M.D.¹, Raúl Narváez, M.D., M.Sc.², Lilian Chuaire, M.Sc.³

1. Assistant Professor, School of Rehabilitation and Human Development, Universidad del Rosario, Bogotá, Colombia. e-mail: jfbonill@urosario.edu.co
2. Principal Professor, Physiology Laboratory Coordinator, Basic Sciences Institute, School of Medicine, Universidad del Rosario, Bogotá, Colombia. e-mail: rnarvaez@urosario.edu.co
3. Principal Professor, Basic Sciences Institute, School of Medicine, Universidad del Rosario, Bogotá, Colombia. e-mail: lchuaire@urosario.edu.co
Received for publication December 3, 2004 Accepted for publication October 26, 2005

SUMMARY

More than three decades ago, it was established that anemia, a cause of tissue oxygenation deficiency, can be caused by exercise. However, this preliminary relationship really corresponds to an event where the plasma is diluted and for this reason the term «sports pseudoanemia» was made. New data relate exercise from moderated to exhaustive, with blood loss through gastrointestinal and urinary tracts, as well as erythrocytes rupture by mechanical, osmotic and oxidative events. Therefore, now the association between chronic exercise and impairment in erythrocytes number and form is clearer, which is evidence in favor of a true anemia in sports. In this anemia it is evident the ferropenic etiology. But recent information opens discussion about whether hemolytic etiology is a co adjuvant factor to anemia, and on the role of oxidative stress in it. This paper is an updated review for a relationship between sports and anemia, and for assessing causes of ferropenic anemia and for sports hemolysis.

Key words: Anemia; Physiology; Exercise.

Anemia could be defined as the status in which the quantity and quality of circulating erythrocytes is below the normal levels for a determined individual, according with the reference ranges for hemoglobin (Hb) and erythrocyte count appropriate to age, sex and sea level as well.

There is a recent number of investigations that inform about changes in the physiological erythrocyte indices as well as in the erythropoyesis itself after a physical training session in general, or a high intensity aerobic exercise¹. This fact leads to postulate the physical exercise as a possible cause for anemia. From this it was derived more than three decades ago the term «sportsmen anemia»^2-4 to define a limit anemic status (borderline) proper for individuals who practice some physical activity on a regular basis, e.g. athletes⁵. Who were found a hemodilutional effect, which should not be considered as a true anemic condition but a reologycal adaptation to exercise⁶.

Several researches indicate that the frequency of this kind of anemia is similar in problem groups constituted by athletes, in respect to control groups. Exercise could affect Hb concentration in an undetermined way, since during and after the exercise session it is possible to find modifications in its values, for example due to hemo-concentration or to changes in the individual hydration grade⁷.

A great part of the difficulty to precisely determine whether there is an anemia due to exercise resides in the existing differences among the researched population, as well as in the diversity of definitions and etiologies proposed for the anemia⁸.

When etiology is associated to dilution, we are not dealing with a true anemia. From this the term pseudo-anemia is derived. Today, when the exercise benefits are every time more controversial (vgr. sportsman sudden death)⁹ and there exist diverse research in favor or against the physical activity whether it is regular or occasional¹⁰, it is important to determine whether exercise is the cause of anemia in the individual, who could be through other etiologies added to the event associated to dilution. From this perspective, the diagnose for a true anemia must be done through the evaluation of clinical aspects but also hematological parameters such as the media corpuscular hemoglobin (CHCM) which is not affected by the hemodilution¹¹.

Whenever the ferropenic etiology is evident, exercise is described as one of the causes of anemia. It is under discussion how much the hemolitical etiology contributes to the sports anemia and therefore the role of the oxidative stress in this anemia is being better understood.

Ferropenic anemia secondary to exercise. Ferropenic anemia is related to a decrease in the sportsmen performance¹². It affects particularly to marathonists and this is the most researched form of anemia¹³. Its causes could be the hemoglobinuria, hematuria, gastrointestinal blood loss and iron loss due to profuse sweat¹⁴.

Hemoglobinuria. The first report about the hemoglobinuria associated to exercise dates from 1881, when Fleischer in Jones and Newhouse¹⁵ described the presence of obscure urine in a young soldier after his participation in a march, and he named it as the marching hemoglobinuria. Hemoglobinuria, sometimes associated to hematuria, could promote an anemic condition in competitive athletes¹⁵ specially those running long distances¹⁶. This anemic condition has been related to hemolysis associated to exercise and to consequent hypohaptoglobinemia and plasmatic Hb increase¹⁷. There is much evidence that hemoglobinuria could be most common than believed, although it seems to be self-limited and benign¹⁸.

Hematuria. Hematuria is documented from contact exercise (football or box) as well as in non-contact ones (swimming or soaking). It could be macro or microscopic. It is frequent, self-limited and benign, since it disappears 48 to 72 hours after exercise¹⁸. It could be related or not to gall bladder and/or renal trauma. Whenever it is not traumatic, it is associated with glomerular ischemia due to the constriction of the renal and splenic vessels or it could also be due to an increase in the filtration pressure secondary to the efferent arterioles constriction. The severity of the hematuria is proportional to the intensity and duration of exercise¹⁹ and could course with dehydration, myoglobinuria and lipid peroxidation in erythrocytes^15,20.

Gastrointestinal blood loss. The digestive blood loss is frequent after a prolonged exercise²¹. In marathon athletes, it is present with a frequency of 8% to 30%, not associated to inflammation nor with gastric blood loss²² and apparently it is independent from age, career time, abdominal symptoms, and recent ingestion of vitamin C or acetylsalicylic acid²³. The digestive blood loss related to the intensity of exercise could induce a decrease in the circulating erythrocytes and therefore increase the iron loss²⁴.

Iron loss for profuse sweat. This form of iron loss has been evaluated in several researches, during and after an exercise session, in trained individuals and non-trained ones as well. Results indicate that this loss depends directly on the amount of sweat, since this is higher in prolonged exercise under high temperatures. There is not a significant difference between women and men. The possible severity of this loss depends on the sportsmen iron reserve (iron status)^25,26.

DOES HEMOLYSIS CONTRIBUTE TO SPORTS ANEMIA?

Several authors have described a significant increase in the destruction of the erythrocytes after intense physical exercise²⁷. In 1943 Gilligan et al.¹⁷ evaluated the hemolysis associated with intense exercise when determined the plasmatic hemoglobinemia and the hemoglobinuria in marathon athletes. The most affected with this condition are athletes, specially those elite athletes who apparently constitute the most susceptible population. The hemolysis intensity depends on the race distance²⁷. Also it has been found hemolysis associated with sports such as swimming²⁸, soaking, triathlon and aerobic dance²⁹ as well as in non-competitive races and in rigorous military training³⁰. One on the causes for this hemolysis is the fact that after a strong exercise the erythrocytes are more susceptible to stress, whether of mechanical, oxidative or osmotic type³¹. The oxidative stress could also alter the ionic homeostasis and facilitate the cellular dehydration. These changes decrease the deformability of the red cell thus impeding its passing through the micro-circulation³².

Telford et al.³³ informed about the large ranges in the increase of the plasmatic Hb concentration and the haptoglobine (Hp) decrease in amateur athletes and cyclists who were taken to the maximum oxygen (VO₂max) consumption and to the same exercise intensity as well. These facts lead to assume the occurrence of hemolysis in both sportsmen groups. The free Hb increases up to 85+35 Hb mg per each plasma liter, with a higher and a more persistent increase in the Hb plasmatic concentration in the athletes.

On the other side, recent researches suggest the possible hemolysis in sportsmen³⁴ caused by mechanical effects since they strike erythrocytes and promotes their destruction. The same occurs with long-distance runners when hemolysis occurs as a consequence of the repeated foot impact (footstrike) over the surface³³.

What is the reason why some sportsmen present a higher grade of hemolysis than other, considering that they are under the same conditions of intensity and exercise length? It is necessary to think that hemolysis during and after exercise could be the result of running long distances where erythrocytes are stroke, but it also result from other mechanisms such as the oxidative stress^28,33.

Sportsmen hemolysis caused by oxidative stress. Oxidative stress is described as the event in which the free radicals are over the systemic mechanisms of the antioxidative defense³⁵. In 1978 Dillard et al.³⁶ were the first in demonstrating that physical exercise leads to a lipid peroxidation increase.

It is estimated that at rest, 2% to 5% of electrons flow of the respiratory chain escapes to form reactive oxygen species³⁷ (ROS), such as peroxide (O₂-), hydrogen peroxide (H₂O₂), hydroxyl (OH-) and those associated with nitric oxide (NO)³⁸.

The mitochondria is a source of ROS, although it is not necessarily the most important (at least in vitro) since during exercise it increases the O₂ tissue consumption range. There is an experimental indicating evidence of increase in the ROS production, as well as oxidative stress and tissue damage associated with exercise, whether exhaustive and severe³⁹, or moderate⁴⁰. During exhaustive exercise, the muscle oxygen consumption increases 100 to 200 times if compared to the one under rest status⁴¹. This induces an electron flow increase through the mitochondrial respiratory chain, which at the same time results in an increase of ROS production³⁸. It has been determined recently that mitochondrion also generate NO, which could be a part of the free radicals total production during exercise. When NO reacts with O₂, it forms peroxynitrite (ONOO-), a powerful oxidant. This reaction is believed as the main via to generate reactive nitrogen species (RNS)⁴².

Oxidative stress could occur in individuals whether or not adapted to exercise, thus making them susceptible to present injury in their enzymatic systems, as well as in lipids and membrane receptors and also in their ADN^42,43.

Now, the ROS and RNS actions could occur at the end of the exercise session or hours after it. Available information associates exercise with ROS and RNS production through three evidences related between them, such as:

1. The free radicals production is muscle, liver, heart and blood.
2. The increase in the biomarkers of oxidative damage, such as protein carbonyls and substances reactive to thiobarbituric acid44, and the increase in the exhaled pentane levels, which is a possible result of the lipid oxidative damage (36).
3. The decrease in the antioxidant enzymatic and non-enzymatic levels in heart, blood (45), brain and muscle (46).

Another generating source of ROS is the xanthine-oxidase (XO) via which contributes to the H₂O₂ tissue generation with high xanthine and hypoxanthine concentrations. Tissue hypoxia, through the XO⁴³ via could generate oxidative stress during exercise⁴⁷. This occurs also after events of ischemia-reperfusion in organs such as heart⁴⁸.

XO activation is produced during exhausting exercise thus allowing ROS generation in different tissues^42,49. For example, in the skeletal muscle the hypo-xanthine is liberated to blood, thus the XO enzyme is activated⁵⁰. Radak et al.⁵¹ demonstrated that the XO via is also committed in the O₂ generation.

The third source of ROS is the peroxisomes. In physiological conditions these organelles produce H₂O₂ but not peroxide. Peroxisomal oxidation of the fat acids is an important source of H₂O₂. Since fat acids are a source of energy for heart and for skeletal muscle during exhaustive exercise, it is probable that peroxisomes contributes to the oxidative stress in sportsmen³⁸.

A fourth source of ROS is the polymorphonuclears leukocytes (PMN). When neutrophile PMN are activated (respiratory burst) they liberate O₂-. Therefore, if does exist tissue damage caused by exhaustive exercise, the subsequent neutrophile activation becomes a source of ROS^38,52. These activated cells could cause lipid peroxidation in closer cells, and in erythrocytes⁵³, since their products are able to cross the cellular membrane and produce Hb oxidation⁵⁴ which will initiate the hemolysis process. Moreover, the ROS oxidizing action over low density lipoproteins (LDL)⁵⁶ and over the lipids of the erythrocyte membrane are associated with hemolysis^53,57.

The neutrophile PMN could infiltrate the muscle tissue damaged by high-density exercise. When this occurs, the O₂– generated through oxidase NADPH associated with the membrane, reacts and leads to H₂O₂ formation. This last has become a hipochlorosus acid (HOCl) for a hemoproteic myeloperoxidase secreted by neutrophiles and monocytes. HOCl is an inflammatory mediator, powerful oxidant and chlorinate, since at the same time it generates other reactive metabolites such as nitryle chloride (NO₂Cl) in presence of nitrite. Nitrite could become, through the myeloperoxidase and H₂O₂, the radical nitrogen dioxide (NO₂) that facilitates the formation of other high injuring substances⁴². Since neutrophiles infiltration in the tissue injured by exercise is secondary to production and liberation of proinflammatories, this via may not be the first source of ROS production during exercise. However, it could certainly serve as an important source during the recovery period after exhaustive exercise⁵⁸. A fifth source of ROS is the catecholamines, although their contribution to the free radicals has not been quantified³⁸. For example, it has been proposed that in oxidative lesion of the myocardial ischemia-reperfusion, it occurs the epinephrine autooxidation in adrenochrome, associated with O₂ formation.

There has been established that the iron and the hemo group of hemoglobin and myoglobin are potential sources of ROS⁴², but it is not clear yet how much they participate in the oxidative stress during or after exhaustive exercise⁵⁹.

Several researches in vitro discard mitochondria as the main producer of ROS during exercise, since they sustain that these Hb-Mb system is not only capable to generate it but also to increase the reactivity of those produced by other via. Within the radicals generated there is O₂-, ferryl iron (Fe+4=O₂-) and free radicals joined with proteins⁵⁹.

The Hb-Mb system causes injuries in different ways. Thus, following Hb liberation to intravascular space, as a consequence of hemolysis, there is the formation of Hp/Hb complex. But an intense hemolysis saturates the Hp capability to alloy Hb, which takes Hb to remain free in plasma⁶⁰. In the same way, Mb could be free in plasma due to processes such as the rhabdomyolysis, usually associated with exhaustive exercise. When free Hb and Mb are oxidized, they become citotoxic substances and could injury the endothelia (atherosclerosis, vasculitis) and also the erythrocyte itself (intravascular hemolysis)⁶¹.

Hb and Mb oxidation is associated with the ROS liberated from activated leukocytes, during exhaustive exercise and hypoxia. The methemyoglobin (metHb) and metmyoglobin (metMb) thus generated, as well as their derivatives are capable to produce more ROS, besides lipid peroxidation, with formation of hydroperoxides^59,62. Other researchers have found that hemo group is related with membrane protein oxidation and with formation of surface antigens in senescent red blood cells⁶³.

Therefore there are established direct and indirect injury mechanisms from Hb and Mb and from their derivatives. One example of the direct one is the primary cytolysis caused by ROS from the type ferryl iron. As an example of indirect mechanisms is the sensibilization to the damage caused by hydroperoxides from the oxidizing LDL type. These mechanisms receive feedback in a way that origins vicious circles: the exercise is a hypoxemic process that generates hemolysis and thus liberates Hb and Mb and their derivatives, which facilitates more hemolysis and more hypoxemia⁵⁹.

There exist two control ways that limit the action of the free hemo: the cellular via in which Hp and hemopexin take part and the intracellular one, where hemooxygenase and ferritin participate. These ways are rebased with a defect in the control ways, or if there is an excessive elevation of the free hemo⁶¹.

CONCLUSIONS

Sportsmen pseudoanemia is related with a plasma expansion. In individuals who practice frequent aerobic sport activity it could coexist associated events such hematuria, gastrointestinal blood loss, as well as an increase in the intravascular hemolysis. These factors link exercise with the deterioration of corporal iron reserve and the erythrocyte number and morphology. Likewise there are foreseen much more etiological possibilities not only of entities like anemia, but of a great number of other diseases related to exhaustive and competitive exercise with damaging responses to the organism.

It is necessary to deeply study the reasons why some sportsmen present higher grades of hemolysis than others, even when they are submitted to similar conditions of intensity and work terms. For this, it must be considered that hemolysis in exercise could result not only from running long distances where erythrocytes are stroke, but also from other mechanisms such as the oxidative stress. To thoroughly understand the mechanisms of action of the oxidative stress and the mechanisms of response of the erythrocyte constitutes an important challenge within the sports physiological field.

REFERENCES

1. Fallon K. Utility of hematological and iron-related screening in elite athletes. Clin J Sport Med 2004; 14: 145-152.
2. Yoshimura H. Anemia during physical training (sports anemia). Nutr Rev 1970; 28: 251-255.
3. Schumacher Y, Schmid A, Grathwohl D, et al. Hematological indices and iron status in athletes of various sports and performances. Med Sci Sports Exerc 2002; 34: 869-875.
4. Wim H, Senden J, Brouns F. What is a normal red-blood cell mass for professional cyclists? Lancet 1998; 352: 1758-1761.
5. Carlson D, Mawdsley R. Sports anemia: a review of the literature. Am J Sports Med 1986; 14: 109-112.
6. Weigth L, Klein M, Noakes T, Jacobs P. Sports anemia: a real or apparent phenomenon in endurance-trained athletes? Int J Sports Med 1992; 13: 344-347.
7. Balaban E, Cox J, Snell P, et al. The frequency of anemia and iron deficiency in the runner. Med Sci Sports Exerc 1989; 21: 643-648.
8. Shaskey D, Green G. Sports haematology. Sports Med 2000; 29: 27-38.
9. Cava J, Danduran M, Fedderly R, et al. Exercise recommendations and risk factors for sudden cardiac death. Pediatr Clin North Am 2004; 51: 1401-1420.
10. Melzer K, Kayser B, Pichard C. Physical activity: the health benefits outweigh the risks. Curr Opin Clin Nutr Metab Care 2004; 7: 641-647.
11. Dang C. Runner´s anemia. JAMA 2001; 286: 714-716.
12. Dubnov G, Constantini N. Prevalence of iron depletion and anemia in top-level basketball players. Int J Sport Nutr Exerc Metab 2004; 14: 30-37.
13. Bartsch P, Mairbaurl H, Friedmann B. Pseudo-anemia caused by sports. Ther Umsch 1998; 55: 251-255.
14. Beard J, Tobin B. Iron status and exercise. Am J Clin Nutr 2000; 72: 594-597.
15. Fleischer citado en Jones G. Newhouse I. Sport-related hematuria: a review. Clin J Sports Med 1997; 7: 119-125.
16. Siegel A, Hennekens C, Solomon H, et al. Exercise-related hematuria. Findings in a group of marathon runners. JAMA 1979; 26: 391-392.
17. Gilligan D, Altschule M, Katersky E. Physiological intravascular hemolysis of exercise. Hemoglobinemia and hemoglobinuria following cross-country runs. J Clin Invest 1943; 22: 859-869.
18. Reid R, Hoshing D, Ramsey E. Haematuria following a marathon run: source and significance. Br J Urol 1987; 59: 133-136.
19. McInnis M, Newhouse I, von Duvillard S, et al. The effect of exercise intensity on hematuria in healthy male runners. Eur J Appl Physiol Occup Physiol 1998; 79: 99-105.
20. Ota M, Ozono S, Ikeda T, et al. Analysis of sports hematuria after running in summer. Nippon Hinyokika Gakkai Zasshi 2004; 95: 705-710.
21. Simons S, Kennedy R. Gastrointestinal problems in runners. Curr Sports Med Rep 2004; 3: 112-116.
22. Zoller H, Vogel W. Iron supplementation in athletes-first do no harm. Nutrition 2004; 20: 615-619.
23. McCabe M, Peura D, Kadakia S, et al. Gastrointestinal blood loss associated with running a marathon. Dig Dis Sci 1986; 31: 1229-1232.
24. Rudzki S, Hazard H, Collinson D. Gastrointestinal blood loss in triathletes: its etiology and relationship to sports anemia. Aust J Sci Med Sport 1995; 27: 3-8.
25. Weaver C, Rajaram S. Exercise and iron status. J Nutr 1992; 123: 782-787.
26. DeRuisseau K, Cheuvront S, Haymes E, et al. Sweat iron and zinc losses during prolonged exercise. Int J Sport Nutr Exerc Metab 2002; 12: 428-437.
27. O´Toole M, Hiller W, Roalstad M, et al. Hemolysis during triathlon races: its relation to race distance. Med Sci Sports Exerc 1988; 20: 272-275.
28. Selby G, Eichner E. Endurance swimming, intravascular hemolysis, anemia, and iron depletion. Am J Med 1986; 81: 791-794.
29. Wolf P, Lott J, Nitti G. Changes in serum enzymes, lactate, and haptoglobin following acute physical stress and type of routine. Clin Biochem 1987; 20: 73-77.
30. Kehat I, Shupak A, Goldenberg I, et al. Long-term hematological effects in Special Forces trainers. Mil Med 2003; 168: 116-119.
31. Smith J, Kolbuch-Braddon M, Gillam I, et al. Changes in the susceptibility of red blood cells to oxidative and osmotic stress following submaximal exercise. Eur J Appl Occup Physiol 1995; 70: 427-436.
32. Smith J. Exercise, training and RBC turnover. Sports Med 1995; 19: 9-31.
33. Telford R, Sly G, Hahn A, et al. Footstrike is the major cause of hemolysis during running. J Appl Physiol 2003; 94: 38-42.
34. Weight L, Byrne M, Jacobs P. Haemolytic effects of exercise. Clin Sci (Lond) 1991; 81: 147-152.
35. Rousseau AS, Hininger I, Palazzetti S, et al. Antioxidant vitamin status in high exposure to oxidative stress in competitive athletes. Br J Nutr 2004; 92: 461-468.
36. Dillard C, Litov R, Savin W, et al. Effect of exercise, vitamin E and ozone on pulmonary function and lipid peroxidation. J Appl Physiol 1978; 45: 927-932.
37. Carrell R, Winterbourn C, Rachmilewtz E. Activated oxygen and hemolysis. Br J Haematol 1975; 30: 259-264.
38. Ji L. Exercise, oxidative stress, and antioxidants. Am J Sports Med 1996; 24: 20-24.
39. Chevion S, Moran D, Heled Y, et al. Plasma antioxidant status and cell injury after severe physical exercise. Proc Natl Acad Sci USA 2003; 100: 5119-5123.
40. Inayama T, Oka J, Kashiba M, et al. Moderate physical exercise induces the oxidation of human blood protein thiols. Life Sci 2000; 70: 2039-2046.
41. Sjodin B, Hellsten W, Apple F. Biochemical mechanism for oxygen free radical formation during exercise. Sports Med 1990; 10: 236-254.
42. Leeuwenburgh C, Heinecke J. Oxidative stress and antioxidants in exercise. Curr Med Chem 2001; 8: 829-838.
43. Oostenburg G, Mensink R, Hardemen M, et al. Exercise performance red blood cell deformability and lipid peroxidation: effects of fish oil and vitamin E. J Appl Physiol 1997; 83: 746-752.
44. Sen C, Atalay M, Agren J, et al. Fish oil and vitamin E supplementation in oxidative stress at rest and after physical exercise. J Appl Physiol 1997; 83: 189-195.
45. Viguie C, Frei B, Shigenaga K, et al. Antioxidant status and indexes of oxidative stress during consecutive days of exercise. J Appl Physiol 1993; 75: 566-572.
46. Sen C, Marin E, Kretzschmar M, et al. Skeletal muscle and liver glutathione homeostasis in response to training, exercise, and immobilization. J Appl Physiol 1992; 73: 1265-1272.
47. Moller P, Loft S, Lundby G, et al. Acute hypoxia and hypoxic exercise induce DNA strand breaks and oxidative DNA damage in humans. FASEB J 2001; 15: 1181-1186.
48. Simpson P, Lucchesi P. Free radicals and myocardial ischemia and reperfusion injury. J Lab Clin Med 1987; 110: 13-30.
49. Koyama K, Kaya M, Ishigaki T, et al. Role of xanthine oxidase in delayed lipid peroxidation in rat liver induced by acute exhausting exercise. Eur J Appl Physiol Occup Physiol 1999; 80: 28-33.
50. Vina J, Gimeno V, Sastre J, et al. Mechanism of free radical production in exhaustive exercise in humans and rats; role of xanthine oxidase and protection by allopurinol. IUBMB Life 2000; 49: 539-544.
51. Radak Z, Asano K, Inoue M. Superoxide dismutase derivate reduces oxidative damage in skeletal muscle of rats during exhaustive exercise. J Appl Physiol 1995; 79: 129-135.
52. Peake J, Wilson G, Hordern M, et al. Changes in neutrophil surface receptor expression, degranulation, and respiratory burst activity after moderate- and high-intensity exercise. J Appl Physiol 2004; 97: 612-618.
53. Claster S, Chiu D., Quintanilha A, et al. Neutrophils mediate lipid peroxidation in human red cells. Blood 1984; 64: 1079-1084.
54. Weiss S. Neutrophil-mediated methemoglobin formation in the erythrocyte. J Biol Chem 1982; 257: 2947-2953.
55. Weiss S. The role of superoxide in the destruction of erythrocyte targets by human neutrophils. J Biol Chem 1980; 255: 9912-9917.
56. Liu M, Berghol R, Mäkimattila S, et al. A marathon run increases the susceptibility of LDL to oxidation in vitro and modifies plasma antioxidants. Am J Physiol 1999; 39: 1083-1091.
57. Azizova O, Piryazev A, Nikitina N, et al. Effect of oxidized LDL on hemolytic resistance erythrocyte. Bull Exp Biol Med 2002; 134: 137-138.
58. Kuo C, Fattor JA, Henderson GC, Brooks GA. Lipid oxidation in fit young adults during postexercise recovery. J Appl Physiol 2005; 99: 349-356.
59. Cooper C, Vollaard J, Choueiri T, et al. Exercise, free radical and oxidative stress. Biochem Soc Trans 2002; 30: 280-285.
60. Lee R. Enfermedades hemolíticas: consideraciones generales. Capítulo 32. In: Wintrobe MM (ed.). Hematología clínica. 9ª ed. Buenos Aires: Editorial Intermédica; 1994.
61. Balla J, Vercelloti G, Nath K, et al. Haem, haem oxygenase and ferritin in vascular endothelial cell injury. Nephrol Dial Transplant 2003; 18: 8-12.
62. Murakami K, Mawatari S. Oxidation of hemoglobin to methemoglobin in intact erythrocyte by a hydroperoxide induces formation of glutathionyl hemoglobin and binding of ±-hemoglobin to membrane. Arch Biochem Bhioph 2003; 417: 244-250.
63. Comporti M, Signorini C, Buonocore G, et al. Iron release, oxidative stress and erythrocyte ageing. Free Radic Biol Med 2002; 32: 568-576.