David V. Godin

Parkinson's disease: A disorder due to nigral glutathione deficiency?

Amino acid analysis of autopsied human brain showed reduced glutathione (GSH) content significantly lower in the substantia nigra than in other brain regions. GSH was virtually absent in the nigra of patients with Parkinsons disease. Oxidative degradation of L-DOPA and dopamine in vivo may generate reactive oxygen species (hydrogen peroxide, superoxide, hydroxyl radical, or singlet oxygen) which can damage membranes and other cellular components. Since GSH is an important natural antioxidant, a deficiency of GSH in the substantia nigra could make this region vulnerable to oxidative injury. If confirmed, the hypothesis that loss of nigrostriatal dopaminergic neurons results from a regional GSH deficiency could have important therapeutic implications for the management and prevention of Parkinsons disease.

Alterations in Free Radical Tissue-Defense Mechanisms in Streptozocin-Induced Diabetes in Rat: Effects of Insulin Treatment

We investigated the possible involvement of reactive oxygen radical-related processes in chronic (12-wk) diabetes induced in rats by streptozocin (STZ). Diabetes was associated with significantly increased activities of catalase (CAT), glutathione reductase (GSSG-RD), and CuZn-superoxide dismutase (SOD) in the pancreas and of CAT and GSSG-RD in the heart. On the other hand, the liver of diabetic rats showed a generalized decrease in CAT, glutathione peroxidase (GSH-PX), and SOD as well as in the levels of reduced glutathione (GSH). Diabetic kidney also showed decreases in CAT and SOD, but the activities of GSH-PX were increased. Insulin treatment (9–12 U/kg body wt) that was started after 8 wk of diabetes and continued for 4 wk reversed all of the foregoing alterations in tissue antioxidant status. Our results suggest the presence of increased oxidative stress in uncontrolled diabetes as manifested by the marked alterations in tissue antioxidant enzyme activities, the magnitude of which increased with the degree of emaciation. The complex patterns of changes observed in the various tissues examined are believed to be the result of compensatory increases in enzyme activities (usually involving enzymes whose activity in control tissues is low) and direct inhibitory effects, possibly resulting from an increased tissue-oxidant activity. Our findings support the view that tissue antioxidant status may be an important factor in the etiology of diabetes and its complications.

Antioxidant enzyme alterations in experimental and clinical diabetes

Previous studies from our laboratory have demonstrated the presence of complex alterations in the activities of antioxidant enzymes in various tissues of rats with streptozotocin (STZ)-induced diabetes. In the present investigation, it is shown that rats made diabetic with alloxan (ALX), an agent differing from STZ both chemically and in its mechanism of diabetogenesis, show virtually identical tissue antioxidant enzyme changes which, as is the case with STZ, are preventable by insulin treatment. The finding that the patterns of antioxidant enzyme alterations in chemically-induced diabetes are independent of the diabetogenic agent used and the presence of similar abnormalities in tissues of spontaneously diabetic (BB) Wistar rats (particularly when diabetic control is less than optimal) suggest that the changes observed are a characteristic feature of the uncontrolled diabetic state and that these may be responsible for (or predispose to) the development of secondary complications in clinical diabetes. Comparative studies involving red cells of diabetic rats and human diabetics revealed a number of common changes, namely an increase in glutathione reductase activity, a decreased susceptibility to oxidative glutathione depletion (which was related to the presence of hyperglycemia) and an increased production of malondialdehyde (an indirect index of lipid peroxidation) in response to in vitro challenge with hydrogen peroxide. In the diabetic patients, the extent of this increase in susceptibility of red cell lipids to oxidation paralleled the severity of diabetic complications. Our results suggest that increased (or uncontrolled) oxidative activity may play an important role in the pathogenesis of complications associated with the chronic diabetic state.

Nigrostriatal dopaminergic neurons remain undamaged in rats given high doses of L-DOPA and carbidopa chronically.

Abstract: Rats were fed maximally tolerated doses of l‐3,4‐Dihydroxyphenylalanine (l‐DOPA) and carbidopa daily for 120 days in order to achieve a sustained elevation in brain dopamine levels. Some animals were also given buthionine sulfoximine, a γ‐glutamylcysteine synthetase inhibitor, in an unsuccessful effort to reduce brain glutathione contents. l‐DOPA‐ and carbidopa‐treated animals displayed no behavioral changes suggestive of nigrostriatal dopaminergic neuronal loss. When sacrificed 60 days after L‐DOPA treatment ended, all rats had normal tyrosine hydroxylase activities and dopamine contents in their striata, and cell counts were normal in the substantia nigra. It therefore seems unlikely that a model of Parkinsons disease, suitable for exploring the etiological importance of glutathione deficiency, can be produced in rats merely by administering the largest tolerable doses of l‐DOPA.

Pathophysiology of apolipoprotein E deficiency in mice: relevance to apo E-related disorders in humans

Apolipoprotein E (apo E) deficiency (or its abnormalities in humans) is associated with a series of pathological conditions including dyslipidemia, atherosclerosis, Alzheimers disease, and shorter life span. The purpose of this study was to characterize these conditions in apo E‐deficient C57BL/6J mice and relate them to human disorders. Deletion of apo E gene in mice is associated with changes in lipoprotein metabolism [plasma total cholesterol (TC) (>+400%), HDL cholesterol (‐80%), HDL/TC, and HDL/LDL ratios (‐93% and ‐96%, respectively), esterification rate in apo B‐depleted plasma (+ 100%), plasma triglyceride (+200%), hepatic HMG‐CoA reductase activity (‐50%), hepatic cholesterol content (+30%)], decreased plasma homocyst(e)ine and glucose levels, and severe atherosclerosis and cutaneous xanthomatosis. Hepatic and lipoprotein lipase activities, hepatic LDL receptor function, and organ antioxidant capacity remain unchanged. Several histological/immunohistological stainings failed to detect potential markers for neurodegenerative disease in the brain of 37‐wk‐old male apo E‐KO mice. Apo E‐KO mice may have normal growth and development, but advanced atherosclerosis and xanthomatosis may indirectly reduce their life span. Apo E plays a crucial role in regulation of lipid metabolism and atherogene‐sis without affecting lipase activities, endogenous anti‐oxidant capacity, or appearance of neurodegenerative markers in 37‐wk‐old male mice.—Moghadasian M. H., McManus B. M., Nguyen, L. B., Shefer, S., Nadji M., Godin D. V., Green, T. J., Hill, J., Yang, Y., Scud‐amore C. H., Frohlich J. J. Pathophysiology of apoli‐poprotein E deficiency in mice: relevance to apo E‐related disorders in humans. FASEB J. 15, 2623–2630 (2001)

Starvation-Related Alterations in Free Radical Tissue Defense Mechanisms in Rats

Alterations in endogenous free radical-scavenging defense mechanisms of rat tissues after body weight loss (induced by starvation for 72 h) associated with hypoinsulinemia were investigated. The activities of catalase (CAT), superoxide dismutase (SOD), glutathione peroxidase (GSH-PX), and glutathione (GSSG) reductase as well as levels of reduced glutathione (GSH) were examined in several tissues and in erythrocytes. A complex pattern of changes was observed. CAT activities were increased in the heart and pancreas and decreased in the liver. SOD levels were decreased in the heart and increased in the kidney and pancreas. GSH-PX activities were increased only in the kidney, and levels of GSH were decreased only in the liver of starved animals. Erythrocytes from starved animals showed no alterations in the levels of major free radical-scavenging enzymes. However, GSSG reductase levels were lower in erythrocytes from starved animals, and this was associated with an increased susceptibility to H2O2-induced GSH depletion. Paradoxically, H2O2-induced malondialdehyde (MDA) production in erythrocytes from starved animals was lower than that in control erythrocytes. Our results suggest that, in studies of experimental diabetes, attention must be given to the influence of body weight loss per se on the biochemical alterations associated with this disease.

Micronutrients and antioxidants in the progression of diabetes

Evidence for changes in trace mineral and vitamin metabolism as a consequence of diabetes pathophysiology is reviewed. Emphasis is on those micronutrients which have a recognized antioxidant or prooxidant function in vivo, with consideration of the relevance of these changes to current hypotheses regarding the onset of secondary complications in the progression of diabetes. Prospects for re-defining micronutrient requirements specific to diabetic individuals are discussed.

Propofol enhances red cell antioxidant capacity in swine and humans

PurposeTo determine the effect of an anaesthetic with antioxidant potential, propofol, on red blood cell (RBC) antioxidant enzyme activities and RBC susceptibility to peroxidative challenge.MethodsPropofol was administered by intravenous bolus (2.5 mg·kg−1) and continuous infusion (36 and 72 ml·hr−1 in nine swine; 216 ml·hr−1 in two swine), to achieve serum concentrations between 5 and 30μg·ml−1 for two hours at each rate. Arterial blood sampling was at 0,10, 30, 60, and 120 min for each rate of infusion, for measurement of plasma propofol concentration, activities of plasma and RBC Superoxide dismutase, glutathione peroxidase, gluthathione reductase, RBC catalase, and RBC malondialdehyde (MDA) formation in response to exvivo oxidative challenge with t-butyl hydrogen peroxide (tBHP; 1.5mM). Antioxidant mechanisms were determined byin vitro study of MDA formation, GSH depletion, and oxidation of haemoglobin to methaemoglobin in human erythrocytes exposed to propofol 0–75 μM. The antioxidant potential of propofol was compared with that of alpha-tocopherol utilising the reaction with 2,4,6-tripyridyl-s-triazine (TPTZ).ResultsPropofol had no effect on plasma or RBC antioxidant enzyme activities. It inhibited RBC MDA production over the range of 0–20 μg·ml−1 (y = −18.683x + 85.431 ; R2 = 0.8174). Effective propofol concentrations for 25% and 50% reductions in MDA levels were 7–12 and 12–20 μg·ml−1, respectively. Propofol has a similar effect on human erythrocytesin vitro (R2 = 0.98).ConclusionPropofol antagonises the effects of forced peroxidation of red cells at anaesthetic and sub-anaesthetic concentrations in swine. Its actions include scavenging of oxygen derived free radicals in a tocopherol-like manner.RésuméObjectifDéterminer l’effet d’un agent anesthésique possédant un potentiel antioxydant, le propofol, sur l’activité d’un enzyme antioxydant des globules rouges (GR) et sur la susceptibilité des GR à une provocation peroxydative.MéthodesLe propofol a été administré en bolus intraveineux (2,5 mg·kg−1) et en infusions continues (36 et 72 ml·h−1 chez 9 porcs; 216 ml·h−1 chez 2 porcs) pour obtenir des concentrations sériques entre 5 et 30 μg·ml−1 durant deux heures à chaque vitesse d’infusion. Des prélèvements sanguins par voie artérielle ont été réalisés à 0, 10, 30, 60 et 120 min. pour chaque vitesse d’infusion; on a mesuré la concentration de propofol, l’activité de la superoxyde dismutase du plasma et des GR, de la peroxydase du glutathion, de la réductase du glutathion, de la catalase du GR, ainsi que de la formation dans le GR de la malondialdehyde (MDA) en réponse à une provocation oxydative exvivo avec le peroxyde d’hydrogène t-butylique (tBHP, 1,5 mM). Les mécanismes antioxydants ont été déterminés par l’étudein vitro de la formation de MDA, de la déplétion de GSH ainsi que de l’oxydation de l’hémoglobine en methémoglobine dans des GR humains exposés au propofol 0–75 μM. Le potentiel antioxydant du propofol a été comparé à celui de l’alpha-tocophérol en utilisant la réaction avec le 2,4,6-tripyridyl-s-triazine (TPTZ).RésultatsLe propofol n’a pas eu d’effet sur l’activité de l’enzyme antioxydant du plasma ou des GR. Il a inhibé la production de MDA par les GR pour tout le spectre de 0–20 μg·ml−1 (y = −18.683x + 85.431 ; R2 = 0,8174). Les concentrations de propofol efficaces pour obtenir une réduction des taux de MDA de 25 et de 50% étaient respectivement de 7–12 et de 12–20 μg·ml−1. Le propofol a un effet analogue sur les globules rouges humainsin vitro (R2 = 0,98).ConclusionLe propofol, à des concentrations anesthésiques et subanesthésiques chez le porc, antagonise les effets d’une peroxydation forcée des globules rouges. Son mode d’action comporte l’épuration des radicaux libres provoqués par l’oxygène comme le fait le tocophérol.

Propofol enhances ischemic tolerance of middle-aged rat hearts: effects on 15-F2t-isoprostane formation and tissue antioxidant capacity

OBJECTIVE Experimental study has shown that myocardial ischemic tolerance is reduced during middle-age. We investigated the effect of propofol on ischemic tolerance of middle-aged rat hearts. METHODS Hearts of young adult (10 weeks old, Y) and middle-aged rats (20 weeks old, M) were assigned to propofol (P-Y, P-M) and control (C-Y, C-M) groups (n=6 each). Hearts were perfused using a Langendorff preparation with Krebs-Henseleit solution (KH) at constant flow rates. We applied propofol (P-Y, P-M) for 10 min at 12 microg/ml before inducing 40 min global ischemia. During ischemia, saline (C-Y, C-M) or propofol (P-Y, P-M) in saline was perfused through the aorta at 60 microl/min. Propofol in KH was perfused at 12 microg/ml for the first 15 min of reperfusion and subsequently reduced to 5 microg/ml in propofol treatment groups. Coronary effluent was assayed for 15-F(2t)-isoprostane after equilibration, during ischemia (T(1)) and at 0.5 (T(2)) and 5 (T(3)) min of reperfusion. After 90 min of reperfusion (T(4)), hearts were harvested to assess tissue antioxidant capacity. RESULTS In P-Y, we observed an increased latency to ischemic-contracture and a significantly reduced contracture after 35 min ischemia compared to control groups. No ischemic contracture was observed in P-M. There were significantly lower 15-F(2t)-isoprostane levels in P-M and P-Y than in C-M and C-Y at T(1). At T(4), the recovery of left ventricular developed pressure in P-M was greater than in P-Y (P<0.05); both were greater than in C-M and C-Y. CONCLUSION Propofol enhanced ischemic tolerance of middle-aged hearts, primarily by inhibiting lipid peroxidation.

Nutritional deficiency, starvation, and tissue antioxidant status

Tissue antioxidant status may be compromised under conditions of dietary restriction, either as the result of a deficiency in a specific cofactor required by a particular antioxidant enzyme or of more complex alterations of a generalized nature triggered by metabolic responses to starvation. Many similarities exist between insulin-reversible abnormalities in tissue antioxidant enzyme activities seen in experimental diabetes and in animals subjected to food deprivation-induced weight loss which is associated with hypoinsulinemia. The complex alterations in tissue antioxidant enzyme activities resulting from nutritional deficiency states, disease or drug administration may have important clinical consequences. Free radical-related processes have been implicated in the pathology of certain conditions in which weight loss is frequently recommended (e.g., diabetes and atherosclerosis). It will be important to investigate the possible adverse effects of this intervention on the underlying disease process involved. Glutathione-dependent hepatic detoxification processes are impaired under conditions of nutritional deficiency. This finding not only has important clinical implications but the standard practice of fasting small laboratory animals overnight to ensure reliable drug absorption can markedly influence the results of pharmacological/toxicological experiments. Further studies of the influence of nutritional status on free radical-related processes are likely to yield valuable information which may be applicable to a variety of research and clinical problems.