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Immune-modulating effects of sulfur-containing nutraceuticals
Nutrition 23 (2007) 514 –516 www.elsevier.com/locate/nut
Nutraceutical column
Immune-modulating effects of sulfur-containing nutraceuticals Ines J. Hardy, B.Pharm., M.R.Pharm.S.*, and Gil Hardy, Ph.D., F.R.S.C. Faculty of Medical and Health Sciences, University of Auckland, Auckland, New Zealand
Introduction The role of immunonutrition and the mechanisms by which individual amino acids or combinations with other nutrients improve immune status and modify disease progression is becoming better understood. The metabolic properties of some key sulfur-containing amino acids and related substrates, namely methionine (Met), cysteine (Cys), N-acetyl cysteine (NAC), taurine (Tau), and the tripeptide glutathione (GSH), provide insights into their important functions as nutraceuticals to formulate strategies for specialized nutrition support.
Methionine Methionine is classified as an essential amino acid; however, only the carbon skeleton and the sulfur are truly essential; the amino group can be provided by transamination and the methyl group by the 1-carbon pool (e.g., dietary choline or tetrahydrofolic acid) through methylation of homocysteine. All proteins contain sulfur, usually in the form of Met or Cys. In mammals Met is synthesized by at least two enzymes that are dependent on vitamin B12 and it is an important methyl donor for some of the reactions involved in DNA synthesis [1]. In the first step of this sequence, Met loses the methylene group attached to its sulfur atom to become homocysteine. This reacts with serine to yield cystathionine, which is cleaved hydrolytically to Cys. Homocysteine accumulation is associated with vascular endothelial damage, myocardial infarction, strokes, and other morbidities. Methylation from amino acid donors suggests sulfur amino acid– enriched diets may have a role in cancer therapy [2]. Moderate deficiencies of the major dietary The data in this paper were presented in part at the IPaNEMA Symposium on Novel Substrates for Specialized Parenteral Nutrition at Clinical Nutrition Week; Phoenix, Arizona, USA; January 28 –31 2007. * Corresponding author. E-mail address: [email protected] (G. Hardy). 0899-9007/07/$ – see front matter © 2007 Elsevier Inc. All rights reserved. doi:10.1016/j.nut.2007.04.008
methyl donors, Met and choline, have markedly enhanced liver tumor formation in rodents. However, Met restriction surprisingly leads to conservation of GSH levels in the extrahepatic tissues and erythrocytes of rats [3].
Cysteine Cysteine is partly converted to cystine in the plasma and is then regenerated intracellularly. Studies of Cys transport activity in T cells have yielded a 10-fold lower rate than for other investigated amino acids and the concentration of the cystine/Cys complex is low in plasma. As a consequence, the lowest intracellular concentration, among the three components of the GSH tripeptide, is Cys, which therefore represents not only the sulfur contributor but also the ratelimiting substrate for GSH synthesis [4]. There may be an inability of biosynthetic pathways for interconversion to provide sufficient supply of non-essential amino acids such as Cys in specific clinical conditions. In the neonate poor conversion of Met to Cys may occur because of low tissue levels of the enzyme cystathionase. Observed Cys deficiencies may be due to increased demand for Tau and GSH [1].
Glutathione Interest in thiols and aminothiols (amino acid molecules possessing an ⫺SH group) is largely focussed on the tripeptide GSH. It is the most abundant antioxidant in the intracellular space and is considered the principal defense within the body against free radicals. It is physiologically responsible for detoxification of reactive oxygen species (ROS), drugs, and metabolites. The major source of GSH is the liver, but it is also present in the kidneys, intestines, blood cells, plasma, and other tissues. GSH deficiency is associated with mitochondrial dysfunction and widespread cell damage. In situations of GSH depletion, vitamin C, vitamin E, and other antioxidants cannot be recycled by the cell, thus rapidly losing their protective effects [5,6].
I. J. Hardy and G. Hardy / Nutrition 23 (2007) 514 –516
Synthesis of GSH starts with the bonding of Cys and glutamate (Glu) by the enzyme ␥-glutamylcysteine synthetase. The addition of glycine to the resultant dipeptide, by the enzyme glutathione synthetase, then leads to the tripeptide, L-glutamyl-L-cysteinyl-glycine. Glycine is easily transported into the cells and may have immunomodulating properties related to its role as a GSH precursor. It has been shown to decrease the release of proinflammatory tumor necrosis factor-␣ (TNF-␣) and interleukin-1 and accelerate the anti-inflammatory interleukin-10 secretion in rats after lipopolysaccharide exposure in a dose-dependant manner [7]. Glycine is included in all total parental nutrition (TPN) regimens but has not been extensively used as a nutraceutical for supraphysiologic supplementation. Although a key constituent of GSH, Glu cannot cross cell membranes in sufficient quantities, but glutamine (Gln), which is readily converted to Glu and is the most abundant amino acid in plasma, does act as a GSH substrate. Cell growth is a function of Gln influx, suggesting that the molecule is used for GSH synthesis [8]. In cancer GSH content decreases when cell proliferation and the rate of protein synthesis in the tumor decrease. Glu derived from Gln inhibits GSH uptake by tumor mitochondria and leads to selective depletion of mitochondrial GSH content, which may render tumor cells more susceptible to oxidative stress-induced mediators [9]. In consequence, Gln-enriched nutrition increases TNF-␣–induced tumor cytotoxicity. Gln oxidation and TNF-␣, by causing a change in the GSH redox status within the tumor mitochondria, activate the molecular mechanism of apoptotic cell death. There also is evidence to show that GSH is important immunologically for the initiation and progression of lymphocyte activation for the function of natural killer cells.
515
Taurine Taurine (2-aminoethanesulfonic acid) is an S-containing -amino acid functioning as membrane stabilizer and modulator of transmembrane calcium transport [12]. Tau is also thought to function as a neurotransmitter/neuromodulator [13] and may delay the onset of diabetes mellitus in nonobese diabetic mice [14]. It can be synthesized from Met via Cys, a vitamin B6- and B2-dependent process. There is some evidence to suggest that the in vivo ability of humans to do this may be limited. Urinary loss of Tau is increased in patients undergoing chemotherapy, a combination of increased free radical stress, vitamin deficiencies, and reduced precursor availability in patients after bone marrow transplantation may contribute to the observed Tau deficiency. Pediatric and adult patients on TPN often show evidence of Tau deficiency, thus highlighting the role of Tau as a biologically valuable nutrient involved in a wide range of metabolic responses [15]. Functional retinal impairment in humans on Tau-free TPN is reversed by supplementation. The requirement for Tau in normal development is inferred from its active secretion in milk. Further, Tau may function as a general detoxifier by eliminating excess cholates, removing xenobiotics, and scavenging chlorine oxidants. Tau conjugates bile acids and deficiency can cause cholestasis, a common problem in parenterally fed patients. Normal nutrition provides Cys as the precursor for Tau synthesis. However, due to the poor solubility and instability of Cys, it is not usually included in solutions for TPN. Therefore, the role of Tau as a nutraceutical in TPN appears advantageous, even though it is classified as a “non-essential” nutrient.
Conclusion N-acetyl cysteine Cysteine itself is not ideal for therapeutic use as a nutraceutical because neurologic toxicity has been observed with high doses in rats, mice, and cells in tissue cultures. However, Tau, Met, GSH, and NAC are sulfur substrates with nutritional and pharmacologic applications. N-acetyl cysteine is relatively safe in high doses as a nutraceutical and can play a useful role in GSH synthesis [10]. In a supplementation study with gynecologic patients requiring radiotherapy, the red blood cells and platelets were not significantly changed, and lymphocytopenia tended to be less severe in the group receiving NAC; thus, the antioxidant not only provided hematologic protection but also mitigated the systemic inflammatory reaction initiated by free radicals associated with irradiation therapy [11]. In some countries NAC is also used pharmacologically for its mucolytic properties and as an antidote in paracetamol (acetaminophen) poisoning.
Some S-containing enzymes (glutathione reductase, glutathione peroxidase, superoxide dismutase, and catalase) and proteins (ceruloplasmin, transferrin, albumin, and heparin) are free radical scavengers protecting against ROS. Thus, in addition to their nutritional value, the S-containing nutraceuticals (Tau, Cys, and NAC) may also act as antioxidants with pharmacologic applications [16] or as precursors to antioxidant peptides (GSH and other thiols). In view of the comparative safety and tolerance of sulfur amino acids and associated compounds at relatively high doses, there are many possibilities in which their pharmacologic properties could be investigated. Selected patients with trauma, sepsis, severe oxidative stress from radiotherapy, or cancer chemotherapy with free radical–producing drugs are obvious candidates. There are now encouraging reports that Tau may upregulate genes implicated in DNA repair and signal transduction, whereas supplementation diminishes ischemia/reperfusion injury from ROS. Stable GSH products and precursors appear to be reasonably compatible with other nutrients and can be admin-
516
I. J. Hardy and G. Hardy / Nutrition 23 (2007) 514 –516
istered safely by most of the common routes, including as a supplement to certain TPN admixtures [17]. Efforts are necessary to fully establish if Gln can be termed a classic signaling molecule rather than an essential substrate for cell metabolism and GSH synthesis, interacting with stress kinase pathways and gene transcription [18]. GSH certainly appears to serve in a “damage limitation” capacity for free radical–mediated damage and Gln is important in the amelioration of the effects of radiation mucositis. Gln and Samino acid supplementation and other treatment strategies that maintain GSH levels or replenish depleted stores may minimize the susceptibility of patients to free radical– mediated tissue injury and help improve outcome in the critically ill. Much research is currently in progress and our knowledge is rapidly improving. As new data and experience broaden our knowledge, changes in clinical practice and therapeutic intervention with the sulfur-containing nutraceuticals may be possible.
References [1] Brosnan JT, Brosnan ME. The sulfur-containing amino acids: an overview. J Nutr 2006;136:1636S40. [2] Grimble RF. The effects of sulfur amino acids intake on immune function in humans. J Nutr 2006;136:1660S5. [3] Richie JP, Komninou D, Leutzinger Y, et al Tissue glutathione and cysteine levels in methionine-restricted rats. Nutrition 2004:20;800 –3. [4] Ishii T, Sugita Y, Bannai S, et al. Regulation of glutathione levels in mouse spleen lymphocytes by transport of cysteine. J Cell Physiol 1987;133:330.
[5] Shaheen AA, Hassan SM. Radioprotection of whole-body-gammairradiation–induced alteration in some haematological parameters by cysteine, vit E combination in rats. Strahlenther Onkol 1991;167:498. [6] Meister A. Glutathione, ascorbate and cellular protection. Cancer Res 1994;54:1969S. [7] Spittler A, Reissner CM, Oehler R, et al. Immunomodulatory effects of glycine on LPS-treated monocytes: reduced TNF-␣ production and accelerated IL-10 expression. FASEB J 1999:13:563–71. [8] Hong RW, Robinson MX, Rounds JD. Glutamine preserves liver glutathione after lethal hepatic injury. Ann Surg 1992;215:114. [9] Carretero J, Obrador E, Pellicer JA, et al. Mitochondrial glutathione depletion by glutamine in growing tumour cells. Free Radic Biol Med 2000;913–23. [10] Dröge W, Gross A, Hack V, et al. Role of cysteine and glutathione in HIV infection and cancer cachexia. Therapeutic intervention with N-acetylcysteine. Adv Pharmacol 1997;38:581. [11] Aguilar PB, Faintuch J, Hardy G. The stability and cytoprotective effects of N-acetylcysteine in cervical cancer patients undergoing radiotherapy. Proc Nut Soc 1998;57;107A. [12] Chesney RW. Taurine its biological role and clinical implications. Adv Pediatr 1985;32:1– 42. [13] Bouckenooghe T, Remacie C, Reusens B. Is taurine a functional nutrient? Curr Opin Clin Nutr Met Care 2006:9;728 –33. [14] Franconi F, Loizzo A, Ghirlanda G, Seghieri G. Taurine supplementation and diabetes mellitus. Curr Opin Clin Nutr Metab Care 2006: 9;3226. [15] Gray GE, Landel AM, Meguid MM. Taurine-supplemented total parenteral nutrition and taurine status of malnourished cancer patients. Nutrition 1994;10:11–5. [16] Atmaca G. Antioxidant effects of sulfur-containing amino acids. Yonsei Med J 2004:45;776 – 88. [17] Valencia E, Hardy G, Practicalities of glutathione supplementation in nutritional support. Curr Opin Clin Nutr Met Care 2002:5;321– 6. [18] Bray TM, Taylor CG. Tissue glutathione, nutrition, and oxidative stress. Can J Phys Pharm 1993;71:746.
Nutraceutical column
Immune-modulating effects of sulfur-containing nutraceuticals Ines J. Hardy, B.Pharm., M.R.Pharm.S.*, and Gil Hardy, Ph.D., F.R.S.C. Faculty of Medical and Health Sciences, University of Auckland, Auckland, New Zealand
Introduction The role of immunonutrition and the mechanisms by which individual amino acids or combinations with other nutrients improve immune status and modify disease progression is becoming better understood. The metabolic properties of some key sulfur-containing amino acids and related substrates, namely methionine (Met), cysteine (Cys), N-acetyl cysteine (NAC), taurine (Tau), and the tripeptide glutathione (GSH), provide insights into their important functions as nutraceuticals to formulate strategies for specialized nutrition support.
Methionine Methionine is classified as an essential amino acid; however, only the carbon skeleton and the sulfur are truly essential; the amino group can be provided by transamination and the methyl group by the 1-carbon pool (e.g., dietary choline or tetrahydrofolic acid) through methylation of homocysteine. All proteins contain sulfur, usually in the form of Met or Cys. In mammals Met is synthesized by at least two enzymes that are dependent on vitamin B12 and it is an important methyl donor for some of the reactions involved in DNA synthesis [1]. In the first step of this sequence, Met loses the methylene group attached to its sulfur atom to become homocysteine. This reacts with serine to yield cystathionine, which is cleaved hydrolytically to Cys. Homocysteine accumulation is associated with vascular endothelial damage, myocardial infarction, strokes, and other morbidities. Methylation from amino acid donors suggests sulfur amino acid– enriched diets may have a role in cancer therapy [2]. Moderate deficiencies of the major dietary The data in this paper were presented in part at the IPaNEMA Symposium on Novel Substrates for Specialized Parenteral Nutrition at Clinical Nutrition Week; Phoenix, Arizona, USA; January 28 –31 2007. * Corresponding author. E-mail address: [email protected] (G. Hardy). 0899-9007/07/$ – see front matter © 2007 Elsevier Inc. All rights reserved. doi:10.1016/j.nut.2007.04.008
methyl donors, Met and choline, have markedly enhanced liver tumor formation in rodents. However, Met restriction surprisingly leads to conservation of GSH levels in the extrahepatic tissues and erythrocytes of rats [3].
Cysteine Cysteine is partly converted to cystine in the plasma and is then regenerated intracellularly. Studies of Cys transport activity in T cells have yielded a 10-fold lower rate than for other investigated amino acids and the concentration of the cystine/Cys complex is low in plasma. As a consequence, the lowest intracellular concentration, among the three components of the GSH tripeptide, is Cys, which therefore represents not only the sulfur contributor but also the ratelimiting substrate for GSH synthesis [4]. There may be an inability of biosynthetic pathways for interconversion to provide sufficient supply of non-essential amino acids such as Cys in specific clinical conditions. In the neonate poor conversion of Met to Cys may occur because of low tissue levels of the enzyme cystathionase. Observed Cys deficiencies may be due to increased demand for Tau and GSH [1].
Glutathione Interest in thiols and aminothiols (amino acid molecules possessing an ⫺SH group) is largely focussed on the tripeptide GSH. It is the most abundant antioxidant in the intracellular space and is considered the principal defense within the body against free radicals. It is physiologically responsible for detoxification of reactive oxygen species (ROS), drugs, and metabolites. The major source of GSH is the liver, but it is also present in the kidneys, intestines, blood cells, plasma, and other tissues. GSH deficiency is associated with mitochondrial dysfunction and widespread cell damage. In situations of GSH depletion, vitamin C, vitamin E, and other antioxidants cannot be recycled by the cell, thus rapidly losing their protective effects [5,6].
I. J. Hardy and G. Hardy / Nutrition 23 (2007) 514 –516
Synthesis of GSH starts with the bonding of Cys and glutamate (Glu) by the enzyme ␥-glutamylcysteine synthetase. The addition of glycine to the resultant dipeptide, by the enzyme glutathione synthetase, then leads to the tripeptide, L-glutamyl-L-cysteinyl-glycine. Glycine is easily transported into the cells and may have immunomodulating properties related to its role as a GSH precursor. It has been shown to decrease the release of proinflammatory tumor necrosis factor-␣ (TNF-␣) and interleukin-1 and accelerate the anti-inflammatory interleukin-10 secretion in rats after lipopolysaccharide exposure in a dose-dependant manner [7]. Glycine is included in all total parental nutrition (TPN) regimens but has not been extensively used as a nutraceutical for supraphysiologic supplementation. Although a key constituent of GSH, Glu cannot cross cell membranes in sufficient quantities, but glutamine (Gln), which is readily converted to Glu and is the most abundant amino acid in plasma, does act as a GSH substrate. Cell growth is a function of Gln influx, suggesting that the molecule is used for GSH synthesis [8]. In cancer GSH content decreases when cell proliferation and the rate of protein synthesis in the tumor decrease. Glu derived from Gln inhibits GSH uptake by tumor mitochondria and leads to selective depletion of mitochondrial GSH content, which may render tumor cells more susceptible to oxidative stress-induced mediators [9]. In consequence, Gln-enriched nutrition increases TNF-␣–induced tumor cytotoxicity. Gln oxidation and TNF-␣, by causing a change in the GSH redox status within the tumor mitochondria, activate the molecular mechanism of apoptotic cell death. There also is evidence to show that GSH is important immunologically for the initiation and progression of lymphocyte activation for the function of natural killer cells.
515
Taurine Taurine (2-aminoethanesulfonic acid) is an S-containing -amino acid functioning as membrane stabilizer and modulator of transmembrane calcium transport [12]. Tau is also thought to function as a neurotransmitter/neuromodulator [13] and may delay the onset of diabetes mellitus in nonobese diabetic mice [14]. It can be synthesized from Met via Cys, a vitamin B6- and B2-dependent process. There is some evidence to suggest that the in vivo ability of humans to do this may be limited. Urinary loss of Tau is increased in patients undergoing chemotherapy, a combination of increased free radical stress, vitamin deficiencies, and reduced precursor availability in patients after bone marrow transplantation may contribute to the observed Tau deficiency. Pediatric and adult patients on TPN often show evidence of Tau deficiency, thus highlighting the role of Tau as a biologically valuable nutrient involved in a wide range of metabolic responses [15]. Functional retinal impairment in humans on Tau-free TPN is reversed by supplementation. The requirement for Tau in normal development is inferred from its active secretion in milk. Further, Tau may function as a general detoxifier by eliminating excess cholates, removing xenobiotics, and scavenging chlorine oxidants. Tau conjugates bile acids and deficiency can cause cholestasis, a common problem in parenterally fed patients. Normal nutrition provides Cys as the precursor for Tau synthesis. However, due to the poor solubility and instability of Cys, it is not usually included in solutions for TPN. Therefore, the role of Tau as a nutraceutical in TPN appears advantageous, even though it is classified as a “non-essential” nutrient.
Conclusion N-acetyl cysteine Cysteine itself is not ideal for therapeutic use as a nutraceutical because neurologic toxicity has been observed with high doses in rats, mice, and cells in tissue cultures. However, Tau, Met, GSH, and NAC are sulfur substrates with nutritional and pharmacologic applications. N-acetyl cysteine is relatively safe in high doses as a nutraceutical and can play a useful role in GSH synthesis [10]. In a supplementation study with gynecologic patients requiring radiotherapy, the red blood cells and platelets were not significantly changed, and lymphocytopenia tended to be less severe in the group receiving NAC; thus, the antioxidant not only provided hematologic protection but also mitigated the systemic inflammatory reaction initiated by free radicals associated with irradiation therapy [11]. In some countries NAC is also used pharmacologically for its mucolytic properties and as an antidote in paracetamol (acetaminophen) poisoning.
Some S-containing enzymes (glutathione reductase, glutathione peroxidase, superoxide dismutase, and catalase) and proteins (ceruloplasmin, transferrin, albumin, and heparin) are free radical scavengers protecting against ROS. Thus, in addition to their nutritional value, the S-containing nutraceuticals (Tau, Cys, and NAC) may also act as antioxidants with pharmacologic applications [16] or as precursors to antioxidant peptides (GSH and other thiols). In view of the comparative safety and tolerance of sulfur amino acids and associated compounds at relatively high doses, there are many possibilities in which their pharmacologic properties could be investigated. Selected patients with trauma, sepsis, severe oxidative stress from radiotherapy, or cancer chemotherapy with free radical–producing drugs are obvious candidates. There are now encouraging reports that Tau may upregulate genes implicated in DNA repair and signal transduction, whereas supplementation diminishes ischemia/reperfusion injury from ROS. Stable GSH products and precursors appear to be reasonably compatible with other nutrients and can be admin-
516
I. J. Hardy and G. Hardy / Nutrition 23 (2007) 514 –516
istered safely by most of the common routes, including as a supplement to certain TPN admixtures [17]. Efforts are necessary to fully establish if Gln can be termed a classic signaling molecule rather than an essential substrate for cell metabolism and GSH synthesis, interacting with stress kinase pathways and gene transcription [18]. GSH certainly appears to serve in a “damage limitation” capacity for free radical–mediated damage and Gln is important in the amelioration of the effects of radiation mucositis. Gln and Samino acid supplementation and other treatment strategies that maintain GSH levels or replenish depleted stores may minimize the susceptibility of patients to free radical– mediated tissue injury and help improve outcome in the critically ill. Much research is currently in progress and our knowledge is rapidly improving. As new data and experience broaden our knowledge, changes in clinical practice and therapeutic intervention with the sulfur-containing nutraceuticals may be possible.
References [1] Brosnan JT, Brosnan ME. The sulfur-containing amino acids: an overview. J Nutr 2006;136:1636S40. [2] Grimble RF. The effects of sulfur amino acids intake on immune function in humans. J Nutr 2006;136:1660S5. [3] Richie JP, Komninou D, Leutzinger Y, et al Tissue glutathione and cysteine levels in methionine-restricted rats. Nutrition 2004:20;800 –3. [4] Ishii T, Sugita Y, Bannai S, et al. Regulation of glutathione levels in mouse spleen lymphocytes by transport of cysteine. J Cell Physiol 1987;133:330.
[5] Shaheen AA, Hassan SM. Radioprotection of whole-body-gammairradiation–induced alteration in some haematological parameters by cysteine, vit E combination in rats. Strahlenther Onkol 1991;167:498. [6] Meister A. Glutathione, ascorbate and cellular protection. Cancer Res 1994;54:1969S. [7] Spittler A, Reissner CM, Oehler R, et al. Immunomodulatory effects of glycine on LPS-treated monocytes: reduced TNF-␣ production and accelerated IL-10 expression. FASEB J 1999:13:563–71. [8] Hong RW, Robinson MX, Rounds JD. Glutamine preserves liver glutathione after lethal hepatic injury. Ann Surg 1992;215:114. [9] Carretero J, Obrador E, Pellicer JA, et al. Mitochondrial glutathione depletion by glutamine in growing tumour cells. Free Radic Biol Med 2000;913–23. [10] Dröge W, Gross A, Hack V, et al. Role of cysteine and glutathione in HIV infection and cancer cachexia. Therapeutic intervention with N-acetylcysteine. Adv Pharmacol 1997;38:581. [11] Aguilar PB, Faintuch J, Hardy G. The stability and cytoprotective effects of N-acetylcysteine in cervical cancer patients undergoing radiotherapy. Proc Nut Soc 1998;57;107A. [12] Chesney RW. Taurine its biological role and clinical implications. Adv Pediatr 1985;32:1– 42. [13] Bouckenooghe T, Remacie C, Reusens B. Is taurine a functional nutrient? Curr Opin Clin Nutr Met Care 2006:9;728 –33. [14] Franconi F, Loizzo A, Ghirlanda G, Seghieri G. Taurine supplementation and diabetes mellitus. Curr Opin Clin Nutr Metab Care 2006: 9;3226. [15] Gray GE, Landel AM, Meguid MM. Taurine-supplemented total parenteral nutrition and taurine status of malnourished cancer patients. Nutrition 1994;10:11–5. [16] Atmaca G. Antioxidant effects of sulfur-containing amino acids. Yonsei Med J 2004:45;776 – 88. [17] Valencia E, Hardy G, Practicalities of glutathione supplementation in nutritional support. Curr Opin Clin Nutr Met Care 2002:5;321– 6. [18] Bray TM, Taylor CG. Tissue glutathione, nutrition, and oxidative stress. Can J Phys Pharm 1993;71:746.