Effect of time of restriction on the decrease in mitochondrial H2O2 production and oxidative DNA damage in the heart of food-restricted rats

In the present study, the question if medium-term (4 months) caloric restriction (40%) decreases mitochondrial H2O2 production and oxidative DNA damage was investigated. Caloric restriction (CR) is the only experimental manipulation that increases maximum life span. Previous long-term CR studies have showed that CR decreases the mitochondrial rate of free radical production in diverse tissues and species. Those studies agree with the idea that the superior longevity of the restricted animals can be partly due to their lower mitochondrial rate of free radical generation. However, caloric restriction effects strongly depend on implementation time. Previous studies have shown that the decrease induced by CR on oxygen radical generation and oxidative damage to mitochondrial DNA occurs after 1 year but not after 6 weeks of restriction. In the present investigation, mitochondrial H2O2 production did not change in medium-term (4 months) caloric restricted animals, and, in agreement with that, no differences were found in either mitochondrial or nuclear oxidative DNA damage between restricted and ad libitum-fed animals. These results confirm the importance of the time of CR implementation, and show that time longer than 4 months is needed to decrease the mitochondrial rate of free radical generation and the oxidative damage to mtDNA in the rat heart.

Thyroid hormone-induced oxidative damage on lipids, glutathione and DNA in the mouse heart

Oxygen radicals of mitochondrial origin are involved in oxidative damage. In order to analyze the possible relationship between metabolic rate, oxidative stress and oxidative damage, OF1 female mice were rendered hyper- and hypothyroid by chronic administration of 0.0012% L-thyroxine (T4) and 0.05% 6-n-propyl-2-thiouracil (PTU), respectively, in their drinking water for 5 weeks. Hyperthyroidism significantly increased the sensitivity to lipid peroxidation in the heart, although the endogenous levels of lipid peroxidation were not altered. Thyroid hormone-induced oxidative stress also resulted in higher levels of GSSG and GSSG/GSH ratio. Oxidative damage to mitochondrial DNA was greater than that to genomic DNA. Hyperthyroidism decreased oxidative damage to genomic DNA. Hypothyroidism did not modify oxidative damage in the lipid fraction but significantly decreased GSSG and GSSG/GSH ratio and oxidative damage to mitochondrial DNA. These results indicate that thyroid hormones modulate oxidative damage to lipids and DNA, and cellular redox potential in the mouse heart. A higher oxidative stress in the hyperthyroid group is presumably neutralized in the case of nuclear DNA by an increase in repair activity, thus protecting this key molecule. Treatment with PTU, a thyroid hormone inhibitor, reduced oxidative damage in the different cell compartments.

Mono- and dinuclear five-coordinate cyclometalated palladium(II) compounds

Reaction of cyclometalated halide-bridged Pd(II) complexes 1-4 with the tertiary triphosphine ligand (Ph2PCH2CH2)2PPh (triphos) yielded complexes [((Ph2PCH2CH2)2PPh-P,P,P)Pd(N(Cy)=(H)C)C6H2(C(H)=N(Cy))Pd((Ph2PCH2CH2)2PPh-P,P,P)][ClO4]2 5, [Pd(C6H4-N=NC6H5)((Ph2PCH2CH2)2PPh-P,P,P)][ClO4] 6, and [Pd(R-C6H3C(H)=NCy)((Ph2PCH2CH2)2PPh-P,P,P)][ClO4] (7; R = 4-CHO, 8; 3-CHO). Spectroscopic and analytic data suggest five-coordination on the palladium atom, which, for complexes 5, 6, and 7, was confirmed by X-ray crystallography. The geometry around palladium may be view as a distorted trigonal bipyramid, with the palladium, nitrogen, and terminal phosphorus atoms in the equatorial plane. Compound 5 is the first doubly cyclometalated palladium(II) compound with two pentacoordinated metal centers. The structure of 6 comprises two discrete cations with slightly different geometries, showing the importance of crystal packing forces in order to determine the coordination arrangement.

Effect of short-term caloric restriction on H2O2 production and oxidative DNA damage in rat liver mitochondria and location of the free radical source

Oxygen free radicals (ROS) of mitochondrial origin seem to be involved in aging. Whereas in other tissues complexes I or III of the respiratory chain contain the ROS generators, in this study we find that rat liver mitochondria generate oxygen radicals at complexes I, II, and III. Short-term (6 weeks) caloric restriction significantly decreased H2O2 production in rat liver mitochondria. This decrease in ROS production was located at complex I because it occurred with complex I-linked substrates (pyruvate/malate), but did not reach statistical significance with the complex II-linked substrate succinate. The mechanism responsible for the lowered ROS production was not a decrease in oxygen consumption. Instead, the mitochondria of caloric-restricted animals released less ROS per unit electron flow. This was due to a decrease in the degree of reduction of the complex I generator. Furthermore, oxidative damage to mitochondrial and nuclear DNA was also decreased in the liver by short-term caloric restriction. The results agree with the idea that caloric restriction delays aging, at least in part, by decreasing the rate of mitochondrial ROS generation and thus the rate of attack to molecules, like DNA, highly relevant for the accumulation of age-dependent changes.

Effect of thyroid hormones on mitochondrial oxygen free radical production and DNA oxidative damage in the rat heart

Mitochondria seem to be involved in oxygen radical damage and aging. However, the possible relationships between oxygen consumption and oxygen radical production by functional mitochondria, and oxidative DNA damage, have not been studied previously. In order to analyze these relationships, male Wistar rats of 12 weeks of age were rendered hyper- and hypothyroid by chronic T(3) and 6-n-propyl-2-thiouracil treatments, respectively. Hypothyroidism decreased heart mitochondrial H(2)O(2) production in States 4 (to 51% of controls; P<0.05) and 3 (to 21% of controls; P<0.05). In agreement with this, 8-oxo-7,8-dihydro-2'-deoxyguanosine (8-oxodG) decreased in the heart genomic DNA of hypothyroid animals to 40% of controls (P<0.001). Studies with respiratory inhibitors showed that the decrease in oxygen radical generation observed in hypothyroidism occurred at Complex III (mainly) and at Complex I; that decrease was due to the presence of a lower free radical leak in the respiratory chain (P<0.05). Hyperthyroidism did not significantly change heart mitochondrial H(2)O(2) production since the increase in State 4 oxygen consumption in comparison with control and hypothyroid animals (P<0.05) was compensated by a decrease in the free radical leak in relation to control animals (P<0.05). In agreement with this, heart 8-oxodG was not changed in hyperthyroid animals. The lack of increase in H(2)O(2) production per unit of mitochondrial protein will protect mitochondria themselves against self-inflicted damage during hyperthyroidism.

Low fatty acid unsaturation: a mechanism for lowered lipoperoxidative modification of tissue proteins in mammalian species with long life spans

Carbonyl compounds generated by the nonenzymatic oxidation of polyunsaturated fatty acids react with nucleophilic groups in proteins, leading to their modification. It has not been tested whether fatty acid unsaturation is related to steady-state levels of lipoxidation-derived protein modification in vivo. A low fatty acid unsaturation, hence a low protein lipoxidation, in tissues of longevous animals would be consistent with the free radical theory of aging, because membrane lipids increase their sensitivity to oxidative damage as a function of their degree of unsaturation. To evaluate the relationship between fatty acid composition, protein lipoxidation, and maximum life span (MLSP), we analyzed liver fatty acids and proteins from seven mammalian species, ranging in MLSP from 3.5 to 46 years. The results show that the peroxidizability index of fatty acids and the sensitivity to in vitro lipid peroxidation are negatively correlated with the MLSP. Based on gas chromatography and mass spectroscopy analyses, liver proteins of all these species contain malondialdehyde-lysine and Nepsilon-carboxymethyllysine adducts, two biomarkers of protein lipoxidation. The steady-state levels of malondialdehyde-lysine and Nepsilon-carboxymethyl lysine are directly related to the peroxidizability index and inversely related to the MLSP. We propose that a low degree of fatty acid unsaturation may have been selected in longevous mammals to protect their tissue lipids and proteins against oxidative damage while maintaining an appropriate environment for membrane function.

Thyroid status modulates glycoxidative and lipoxidative modification of tissue proteins

Steady state protein modification by carbonyl compounds is related to the rate of carbonyl adduct formation and the half-life of the protein. Thyroid hormones are physiologic modulators of both tissue oxidative stress and protein degradation. The levels of the glycation product N(epsilon)-fructoselysine (FL) and those of the oxidation products, N(epsilon)-(carboxymethyl)lysine (CML) and malondialdehyde-lysine (MDA-lys), identified by GC/MS in liver proteins, decreased significantly in hyperthyroid rats, as well as (less acutely) in hypothyroid animals. Immunoblotting of liver proteins for advanced glycation end-products (AGE) is in agreement with the results obtained by GC/MS. Cytosolic proteolytic activity against carboxymethylated foreign proteins measured in vitro was significantly increased in hypo- and hyperthyroidism. Oxidative damage to DNA, estimated as 8-oxo-7,8-dihydro-2'-deoxyguanosine (8oxodG), did not show significant differences between groups. The results suggests that the steady state levels of these markers depend on the levels of thyroid hormones, presumably through their combined effects on the rates of protein degradation and oxidative stress, whereas DNA is more protected from oxidative damage.

Effect of thyroid status on lipid composition and peroxidation in the mouse liver

In order to analyze the possible relationship between metabolic rate and oxidative stress, OF1 female mice were rendered hyper- or hypothyroid for 4-5 weeks by administration of 0.0012% L-thyroxine (T4) or 0.05% 6-n-propyl-2-thiouracil (PTU), respectively, in their drinking water. Treatment with T4 resulted in increased basal metabolic rate measured by oxygen consumption and liver cytochrome oxidase activity without altering the glutathione redox system. Endogenous lipid peroxidation, sensitivity to lipid peroxidation and fatty acid unsaturation were decreased in the hyperthyroid group. Hypothyroidism also decreased phosphatidylcholine and cardiolipin fatty acid unsaturation but not in total lipids, and thus lipid peroxidation was not altered. Cardiolipin, a mainly mitochondrial lipid, was the most profoundly altered fraction by both hyper- and hypothyroidism. It is suggested that the lipid changes observed in hyperthyroid animals can protect them against an increased oxidative attack to tissue lipids due to their increased mitochondrial activities.

The rate of free radical production as a determinant of the rate of aging: evidence from the comparative approach

The relationship of oxidative stress with maximum life span (MLSP) in different vertebrate species is reviewed. In all animal groups the endogenous levels of enzymatic and non-enzymatic antioxidants in tissues negatively correlate with MLSP and the most longevous animals studied in each group, pigeon or man, show the minimum levels of antioxidants. A possible evolutionary reason for this is that longevous animals produce oxygen radicals at a low rate. This has been analysed at the place where more than 90% of oxygen is consumed in the cell, the mitochondria. All available work agrees that, across species, the longer the life span, the lower the rate of mitochondrial oxygen radical production. This is true even in animal groups that do not conform to the rate of living theory of aging, such as birds. Birds have low rates of mitochondrial oxygen radical production, frequently due to a low free radical leak in their respiratory chain. Possibly the low rate of mitochondrial oxygen radical production of longevous species can decrease oxidative damage at targets important for aging (like mitochondrial DNA) that are situated near the places of free radical generation. A low rate of free radical production can contribute to a low aging rate both in animals that conform to the rate of living (metabolic) theory of aging and in animals with exceptional longevities, like birds and primates. Available research indicates there are at least two main characteristics of longevous species: a high rate of DNA repair together with a low rate of free radical production near DNA. Simultaneous consideration of these two characteristics can explain part of the quantitative differences in longevity between animal species.

Effect of dietary vitamin E levels on fatty acid profiles and nonenzymatic lipid peroxidation in the guinea pig liver

Guinea pigs were fed for five weeks with three diets containing different levels of vitamin E: LOW (but nondeficient, 15 mg of vitamin E/kg diet), MEDIUM (150 mg/kg diet), and HIGH (1,500 mg/kg diet). Dietary vitamin E supplementation did not change oxidative stress indicators in the hydrophilic compartment but increased liver alpha-tocopherol in a dose-dependent way and strongly decreased sensitivity to nonenzymatic in vitro liver lipid peroxidation. This last effect was already observed in group MEDIUM, and no further decrease in in vitro lipid peroxidation occurred from group MEDIUM to group HIGH. The protective effect of vitamin E against in vitro lipid peroxidation was observed even though an optimum dietary concentration of vitamin C for this animal model was present in the three different vitamin E diets. Both HIGH and LOW vitamin E decreased percentage fatty acid unsaturation in all phospholipid fractions from membrane origin in relation to group MEDIUM. The results, together with previous information, show that both vitamin E and vitamin C at intermediate concentrations are needed for optimal protection against lipid peroxidation and loss of fatty acid unsaturation even in normal nonstressful conditions. These protective concentrations are higher than those needed to avoid deficiency syndromes.

Increase in heart glutathione redox ratio and total antioxidant capacity and decrease in lipid peroxidation after vitamin E dietary supplementation in guinea pigs

Dietary treatment with three diets differing in vitamin E, Low E (15 mg of vitamin E/kg diet), Medium E (150 mg/kg), or High E (1,500 mg/kg), resulted in guinea pigs with low (but nondeficient), intermediate, or high heart alpha-tocopherol concentration. Neither the antioxidant enzymes superoxide dismutase, catalase, glutathione peroxidase, and reductase, nor the nonenzymatic antioxidants, GSH, ascorbate, and uric acid were homeostatically depressed by increases in heart alpha-tocopherol. Protection from both enzymatic (NADPH dependent) and nonenzymatic (ascorbate-Fe2+) lipid peroxidation was strongly increased by vitamin E supplementation from Low to Medium E whereas no additional gain was obtained from the Medium E to the High E group. The GSH/GSSG and GSH/total glutathione ratios increased as a function of the vitamin E dietary concentration closely resembling the shape of the dependence of heart alpha-tocopherol on dietary vitamin E. The results show the capacity of dietary vitamin E to increase the global antioxidant capacity of the heart and to improve the heart redox status in both the lipid and water-soluble compartments. This capacity occurred at levels six times higher than the minimum daily requirement of vitamin E, even in the presence of optimum dietary vitamin C concentrations and basal unstressed conditions. The need for vitamin E dietary supplementation seems specially important in this tissue due to the low constitutive levels of endogenous enzymatic and nonenzymatic antioxidants present of the mammalian heart in comparison with those of other internal organs.

Vitamin E protects guinea pig liver from lipid peroxidation without depressing levels of antioxidants

Oxidative stress is considered a pathogenic factor in many disorders. The capacity of dietary vitamin E to increase global antioxidant capacity and to decrease lipid peroxidation was studied in the guinea pig, an animal that cannot synthesize ascorbate. Male guinea pigs were subjected for 5 weeks to three diets differing in vitamin E content in the presence of optimum levels of vitamin C: group 15 (15 mg vitamin E/kg diet), group 150 (150 mg/kg), and group 1500 (1500 mg/kg). Hepatic vitamin E increased in the three groups in relation to the level of vitamin E in the diet. The increase in vitamin E between groups 15 and 150 was accompanied by a reduction in sensitivity to enzymatic lipid peroxidation. This did not occur between groups 150 and 1500. The different liver vitamin E concentrations did not affect the antioxidant enzymes superoxide dismutase, catalase, GSH-peroxidase and GSH-reductase, nor the non-enzymatic antioxidants vitamin C, GSH and ascorbate. It is concluded that dietary supplementation with vitamin E, at a level 6 times higher than the minimum daily requirement for guinea pigs, increases protection against hepatic lipid peroxidation without depressing endogenous antioxidant defences. Further increases in vitamin E to megadose levels did not provide additional protection from oxidative stress. The results also suggest that optimum levels of both vitamin C and vitamin E, simultaneously needed for protection against oxidative stress, are much higher than the minimum daily requirements.

Effect of vitamin C on antioxidants, lipid peroxidation, and GSH system in the normal guinea pig heart

Male guinea pigs were fed during 5 weeks with diets differing only in vitamin C content: low (33 mg/kg diet), medium (660 mg/kg), and high (13,200 mg/kg). Heart vitamin C was strongly dependent on dietary vitamin C and heart vitamin E showed a trend to increase as a function of the vitamin C level in the diet. The low vitamin C diet decreased body weight gain, food intake, and heart malondialdehyde without changing lipid peroxidation, whereas the high vitamin C increased oxidized glutathione and glutathione peroxidase and decreased body growth. A tendency to show higher levels of all the first-line antioxidants reduced glutathione, uric acid, superoxide dismutase, catalase, and glutathione peroxidase at extreme (high or low) dietary levels of vitamin C was observed. The guinea pig heart showed capacity for enzymatic but not for non-enzymatic in vitro lipid peroxidation. It is concluded that dietary vitamin C supplementation is able to increase the global antioxidant capacity of the heart tissue.

Low mitochondrial free radical production per unit O2 consumption can explain the simultaneous presence of high longevity and high aerobic metabolic rate in birds

Birds are unique since they can combine a high rate of oxygen consumption at rest with a high maximum life span (MLSP). The reasons for this capacity are unknown. A similar situation is present in primates including humans which show MLSPs higher than predicted from their rates of O2 consumption. In this work rates of oxygen radical production and O2 consumption by mitochondria were compared between adult male rats (MLSP = 4 years) and adult pigeons (MLSP = 35 years), animals of similar body size. Both the O2 consumption of the whole animal at rest and the O2 consumption of brain, lung and liver mitochondria were higher in the pigeon than in the rat. Nevertheless, mitochondrial free radical production was 2-4 times lower in pigeon than in rat tissues. This is possible because pigeon mitochondria show a rate of free radical production per unit O2 consumed one order of magnitude lower than rat mitochondria: bird mitochondria show a lower free radical leak at the respiratory chain. This result, described here for the first time, can possibly explain the capacity of birds to simultaneously increase maximum longevity and basal metabolic rate. It also suggests that the main factor relating oxidative stress to aging and longevity is not the rate of oxygen consumption but the rate of oxygen radical production. Previous inconsistencies of the rate of living theory of aging can be explained by a free radical theory of aging which focuses on the rate of oxygen radical production and on local damage to targets relevant for aging situated near the places where free radicals are continuously generated.

Dietary vitamin C decreases endogenous protein oxidative damage, malondialdehyde, and lipid peroxidation and maintains fatty acid unsaturation in the guinea pig liver

Guinea pigs were fed during 5 weeks with three different levels of vitamin C in the diet: 33 (marginal deficiency), 660, or 13,200 mg of vitamin C per kg of diet. The group fed 660 mg of vitamin C/kg of diet showed strongly reduced levels of protein carbonyls (46% decrease), malondialdehyde (HPLC; 72% decrease), and in vitro production of TBARS (both stimulated with ascorbate-Fe2+ and with NADPH-ADP-Fe2+; 68% and 71% decrease), increased glutathione reductase activity, and increased vitamin C content (48 times higher) in the liver in relation to the group fed 33 mg/kg. The treatment with 660 mg of vitamin C/kg did not decrease any of the antioxidant defenses studied: superoxide dismutase, catalase, glutathione peroxidase, glutathione reductase, GSH, vitamin E, or uric acid. Further supplementation with 13,200 mg vitamin C/kg also reduced protein and lipid peroxidation, but decreased hepatic glutathione reductase and uric acid and resulted in a lower body weight of the animals. Both low (33 mg/kg) and very high (13,200 mg/kg) levels of vitamin C decreased body weight, glutathione reductase, and unsaturation of fatty acids in membrane lipids. The results show that a diet supplying an amount of vitamin C 40 times higher than the minimum daily requirement to avoid scurvy increases the global antioxidant capacity and is of protective value against endogenous lipid and protein oxidation in the liver under normal nonstressful conditions.

A decrease of free radical production near critical targets as a cause of maximum longevity in animals

A comprehensive study was performed on the brains of various vertebrate species showing different life energy potentials in order to find out if free radicals are important determinants of species-specific maximum life span. Brain superoxide dismutase, catalase, Se-dependent and independent GSH-peroxidases, GSH-reductase, and ascorbic acid showed significant inverse correlations with maximum longevity, whereas GSH, uric acid, GSSG/GSH, in vitro peroxidation (thiobarbituric acid test), and malondialdehyde (measured by HPLC), did not correlate with maximum life span. Superoxide dismutase, catalase, GSH-peroxidase, GSH and ascorbate results agree with those previously reported in various independent works using different animal species. GSSG/GSH, and true malondialdehyde (HPLC) results are reported for the first time in relation to maximum longevity. The results suggest that longevous species simultaneously show low antioxidant concentrations and low levels of in vivo free radical production (a low free radical turnover) in their tissues. The "free radical production hypothesis of aging" is proposed: a decrease in oxygen radical production per unit of O2 consumption near critical DNA targets (mitochondria or nucleus) increases the maximum life span of extraordinarily long-lived species like birds, primates, and man. Free radical production near these DNA sites would be a main factor responsible for aging in all the species, in those following Pearl's (Rubner's) metabolic rule as well as in those not following it.

Effect of dietary vitamin C and catalase inhibition of antioxidants and molecular markers of oxidative damage in guinea pigs

Guinea pigs were fed for five weeks with two diets with different levels of vitamin C, low (33 mg of Vit C/Kg diet) and high (13,200 mg of Vit C/Kg of diet). Catalase was inhibited with 3-amino-1,2,4-triazole (AT) in half of the animals from each dietary group. AT caused an almost complete depletion of liver catalase activity (90%) in both dietary groups. Vitamin C supplementation increased total glutathione peroxidase activity and tissue vitamin C level and decreased levels of protein carbonyls and malondialdehyde (MDA) in both treated and non-treated animals. This vitamin C supplementation did not change any of the other antioxidant defences studied. Our results show that dietary vitamin C supplementation increases global antioxidant capacity and decreases endogenous oxidative damage in the guinea pig liver under normal non-stressful conditions. This supports the protective value of dietary antioxidant supplementation.

Longevity and antioxidant enzymes, non-enzymatic antioxidants and oxidative stress in the vertebrate lung: a comparative study

It has been proposed that antioxidants can be longevity determinants in animals. However, no comprehensive study has been conducted to try to relate free radicals with maximum life span. This study compares the lung tissue of various vertebrate species--amphibia, mammals and birds--showing very different and well known maximum life spans and life energy potentials. The lung antioxidant enzymes superoxide dismutase, catalase, Se-dependent and non-Se-dependent glutathione peroxidases, and glutathione reductase showed significantly negative correlations with maximum life span. The same was observed for the lung antioxidants, reduced glutathione and ascorbate. It is concluded that a generalized decrease in tissue antioxidant capacity is a characteristic of longevous species. It is suggested that a low rate of free radical recycling (free-radical generation and scavenging) can be an important factor involved in the evolution of high maximum animal longevities. A low free-radical production could be responsible for a low rate of damage at critical sites such as mitochondrial DNA.

Caloric and carbohydrate restriction in the kidney: effects on free radical metabolism

Carbohydrate restriction and caloric restriction (60% restriction of calories in relation to controls in both cases) were imposed on OF1 mice during 8 weeks in their growing phase. The three groups of animals ingested the same amount of vitamins and minerals. Kidney ascorbate strongly decreased in both restriction groups. Nevertheless, global caloric restriction significantly increased kidney antioxidant glutathione (GSH)/oxidized glutathione (GSSG) ratio, a sign of a reduced kidney oxidative stress. Increased glutathione peroxidase and cytochrome oxidase activities and decreased in vivo peroxidation were found in the kidney when the restriction was performed by substituting carbohydrates by nonnutritive bulk. No significant changes were observed for superoxide dismutase, catalase, glutathione reductase, glutathione, uric acid, malondialdehyde (HPLC), or in vitro sensitivity to peroxidation in the kidney. The results, reported for the first time in this tissue, show that short-term caloric restriction can increase the capacity for enzymatic decomposition of hydroperoxides and can decrease oxidative stress in the kidney, thus suggesting a role for free radical metabolism in the caloric restriction phenomenon.

Relationship between lipid peroxidation, fatty acid composition, and ascorbic acid in the liver during carbohydrate and caloric restriction in mice

Growing OF1 mice were treated on a short-term basis with ad libitum, caloric-restricted, or carbohydrate-restricted diets, maintaining the same intake of vitamins and minerals in the three groups. Caloric intake was 60% of controls both in the caloric-restricted and in the carbohydrate-restricted groups. Neither global nor carbohydrate restriction changed liver superoxide dismutase, catalase, glutathione peroxidase, glutathione reductase, cytochrome oxidase, GSH, uric acid, or malondialdehyde (HPLC). Ascorbate was decreased in both restricted groups. Carbohydrate restriction, but not caloric restriction, increased unsaturation indexes of fatty acids in all lipid classes analyzed and increased sensitivity to peroxidation by one order of magnitude. It is concluded that short-term caloric restriction does not seem to increase antioxidants and decrease peroxidation in the mouse liver whereas long-term restriction can avoid decreases of antioxidants and increases of peroxidation during aging. Our experiments support the prevailing view that the caloric restriction phenomenon is due to a reduction in calories themselves instead of to a reduction in carbohydrates. This last manipulation strongly increases sensitivity to peroxidative damage in the liver. The results show that in vivo fatty acid unsaturation is a main factor in determining the sensitivity to lipid peroxidation.

Effect of early maternal adrenalectomy on antioxidant enzymes, GSH, ascorbate, and uric acid in the rat fetal lung at term

Previous studies have shown that the increase of the enzymatic antioxidant defense that takes place in the fetal rat lung at the end of gestation can be accelerated by the synthetic glucocorticoid dexamethasone and diminished by metyrapone, a blocker of glucocorticoid synthesis. Since it is known that the fetal adrenal does not start to synthesize corticosterone until the last 20% of gestation, pregnant rats were bilaterally adrenalectomized on the first day of gestation in order to clarify the role of the endogenous maternal hormone on the development of the enzymatic and nonenzymatic antioxidant systems of fetal lung. This early adrenalectomy did not change fetal lung catalase, glutathione peroxidase, glutathione reductase, cytochrome oxidase, GSH, ascorbate, and uric acid at term. The presence of the maternal glands is not essential for lung antioxidant development in the fetus and that the stimulus of fetal corticosterone during the last 20% of gestation is enough to achieve a normal maturation of the fetal lung enzymatic and nonenzymatic antioxidant systems.

Simultaneous induction of sod, glutathione reductase, GSH, and ascorbate in liver and kidney correlates with survival during aging

Catalase was continuously inhibited with aminotriazole in the liver and kidney during 33 months in large populations of old and young frogs in order to study the effects of the modification of the tissue antioxidant/prooxidant balance on the life span of a vertebrate species showing an oxygen consumption rate similar to that of humans. Free-radical-related parameters were measured during three consecutive years at 2.5, 14.5, and 26.5 months of experimentation. Aging per se did not decrease antioxidant enzymes and did not increase peroxidation (thiobarbituric acid positive substances, or high-pressure liquid chromatography [HPLC]-malondialdehyde), either cross sectionally or longitudinally. Long-term catalase inhibition leads to time-dependent increases (100-900%) of endogenous superoxide dismutase, GSH, ascorbate, and especially glutathione reductase at 2.5 and 14.5 months of experimentation. This was positively correlated with a higher survival of treated animals (91% in treated versus 46% in controls at 14.5 months of experimentation). The loss of those inductions after 26.5 months leads to a sharp increase in mortality rate. The results show for the first time that simultaneous induction of various tissue antioxidant enzymes and nonenzymatic antioxidants can increase the mean life span of a vertebrate animal. It is concluded that the tissue antioxidant/prooxidant balance is a strong determinant of mean life span.

A comparative study of free radicals in vertebrates--II. Non-enzymatic antioxidants and oxidative stress

1. The three main non-enzymatic endogenous soluble antioxidants and three estimators of oxidative stress were measured in the liver, lung and brain of seven animal species of different vertebrate classes. 2. The more concentrated antioxidant was GSH, followed by ascorbate and finally by uric acid. Liver showed higher levels of GSH and uric acid than the other two organs in the majority of the species. 3. GSSG/GSH ratio was highest in lung, probably due to the high pO2 prevalent in the tissue. Nevertheless, this did not result in higher tissue peroxidation, suggesting that the lung antioxidants are capable of coping with a high tissue pO2. 4. Tissue peroxidation was maximal in the brain when assayed by the TBA test, but this was not confirmed by HPLC of malondialdehyde (MDA). HPLC resulted in much lower MDA values than TBA.

A comparative study of free radicals in vertebrates--I. Antioxidant enzymes

1. Five antioxidant enzymes and cytochrome oxidase were measured in three vital organs of seven animal species of different vertebrate classes. 2. Minimal superoxide dismutase activities were found in the brain of homeotherms and in the lung of amphibia. Catalase (CAT) was maximal in liver and minimal in brain. 3. Possession of both Se dependent and independent glutathione peroxidase (GPx) is widespread in vertebrate organs. Similarities in tissue distribution were found among enzymes which use hydroperoxides (Se and non-Se GPx and CAT) or glutathione (both GPx and glutathione reductase) as substrates. 4. The results also suggest that the high aerobic capacity of the liver strongly influences the activities of the antioxidant enzymes in this tissue across vertebrate species, whereas other factors such as tissue pO2 can be more important in the lung.

Brain glutathione reductase induction increases early survival and decreases lipofuscin accumulation in aging frogs

Brain catalase was continuously depleted throughout the life span starting with a large population of initially young and old frogs. Free radical-related parameters were measured in the brain tissue once per year after 2.5, 14.5, and 26.5 months of experimentation. Brain lipofuscin accumulation was observed after 14.5 and 26.5 months, and survival was continuously followed during 33 months. The age of the animal did not decrease endogenous antioxidants nor increase tissue peroxidation either in cross-sectional or longitudinal comparisons. Continuous catalase depletion similarly affected young and old animals, inducing glutathione reductase, tending to decrease oxidized glutathione/reduced glutathione (GSSG/GSH) ratio, decreasing lipofuscin accumulation in the brain, and increasing survival from 46% to 91% after 14.5 months. At 26.5 months of experimentation the loss of the glutathione reductase induction in catalase-depleted animals was accompanied by the presence of higher lipofuscin deposits than in controls and was followed by a great increase in mortality rate. Even though the maximal life span (7 years) was the same in the control and treated animals which were already old (4.2 years) at the beginning of the experiment, the treated animals showed a strong reduction in the rates of early death. It is proposed that the maintenance of a high antioxidant/prooxidant balance in the vertebrate brain greatly increases the probability of the individual to reach the final segments of its species-specific life span.

Sensitivity to in vitro lipid peroxidation in liver and brain of aged rats

Lipid peroxidation in rat liver and brain has been studied to see if it increases with old age. No significant differences in the level of endogenous, nonstimulated lipid peroxidation (TBA-RS) is found between 9 month-old (mature adults) and 28 month-old animals in liver or cerebral cortex. Liver homogenates subjected in vitro to an oxidative stress (ascorbate-Fe++), show a clearly slower peroxidation rate in old than in young animals. On the other hand, the in vitro peroxidation rate of cerebral homogenates was similar in young and old animals. The in vitro peroxidation rate was much higher in brain than in liver tissue. These results do not support the view that old rats liver and brain are more susceptible to free radical oxidative damage than those of young ones.

Relationship between antioxidants, lipid peroxidation and aging

Experiments performed on species as different as flies, rats and frogs are not conclusive about the possibility that antioxidant defenses decrease in old animals. Even when these decreases are found, their physiological meaning is far from clear. Furthermore, a constancy of antioxidant capacity in old age is consistent with the fact that aging is a progressive phenomenon which occurs at a rather constant rate from the mature young to the very old animal, without showing a great acceleration rate in the aged. Nevertheless, experimental results strongly suggest that the maintenance of an appropriate antioxidant/prooxidant balance does have an important role in maintaining health in the aging animal. It is possible that the continuous presence of small amounts of free radicals in the adult tissues of both mature adults and old animals is an important factor in aging (a progressive phenomenon) and susceptibility to disease. Since, similarly to what occurs in procariota, the whole antioxidant system seems to be under homeostatic control in vertebrates, it is imperative to perform comprehensive and detailed studies on the effects of carefully controlled doses of antioxidants on biomarkers of health as well as on the different endogenous cellular antioxidant and prooxidant systems. These studies should have as a final goal the knowledge of which doses of antioxidants are high enough to increase antioxidant protection but low enough to avoid feedback depression of other endogenous antioxidants; this could further improve the health state of humans situated in the middle and last phases of their life span.

Simultaneous determination of two antioxidants, uric and ascorbic acid, in animal tissue by high-performance liquid chromatography

A rapid and simple method for the simultaneous analysis of uric and ascorbic acid in extracts of animal tissue is described. The method uses reversed-phase ion-pair chromatography with ultraviolet detection. The technique allows efficient separation of both acids while showing high selectivity, recovery, reproducibility, and sample stability. Calculated levels of both substances in mouse liver tissue were 1.00 +/- 0.05 mumol ascorbic acid/g and 130 +/- 5 nmol uric acid/g.

Effect of cold acclimation on GSH, antioxidant enzymes and lipid peroxidation in brown adipose tissue

Cold acclimation increased the activities of superoxide dismutase, catalase, total and selenium (Se)-dependent glutathione peroxidases (GPx) and glutathione reductase by 2-4-fold in the brown adipose tissue (BAT) of cold-acclimated rats. Nevertheless, when expressed per unit protein, the antioxidant enzyme activities were unaltered. Sensitivity to lipid peroxidation and GSH levels both increased by one order of magnitude in the cold on a per weight basis and were still 3-5 times greater in the cold when expressed per mg of protein. We suggest that activation of BAT leads to a large increase in the potential for lipid peroxidation and that the tissue responds to this challenge by increasing practically all of its antioxidant defences. Nevertheless, GSH, and possibly GPx activity, seem to be the principal defences involved in adaptation of the tissue to a higher sensitivity to peroxidative damage after activation.

Effect of natural ageing and antioxidant inhibition on liver antioxidant enzymes, glutathione system, peroxidation, and oxygen consumption in Rana perezi

A study of the physiological role of oxygen free radicals in relation to the ageing process was performed using the liver of Rana perezi, an animal with a moderate rate of oxygen consumption and a life span substantially longer than that of laboratory rodents. Among the five different antioxidant enzymes only superoxide dismutase (SOD) showed an age-dependent decrease. Cytochrome oxidase (COX), glutathione status, in vivo and in vitro liver peroxidation, and metabolic rate did not vary as a function of age. Long-term (2.5 months) treatment with aminotriazole and diethyldithiocarbamate depleted catalase (CAT) activity and did not change both glutathione peroxidases (GPx), COX, reduced (GSH) and oxidized (GSSG) glutathione, or metabolic rate. This treatment resulted in great compensatory increases in SOD (to 250-460% of controls) and glutathione reductase (GR) (to 200%) which are possibly responsible for the lack of increase of in vivo and in vitro liver peroxidation and for the absence of changes in survival rate. The comparison of these results with previous data from other species suggests the possibility that decreases in antioxidant capacity in old age are restricted to animal species with high metabolic rates. Nevertheless, ageing can still be due to the continuous presence of small concentrations of O2 radicals in the tissues throughout life in animals with either high or low metabolic rates, because radical scavenging can not be 100% effective. Compensatory homeostasis among antioxidants seems to be a general phenomenon in different species.

Lung antioxidant enzymes, peroxidation, glutathione system and oxygen consumption in catalase inactivated young and old Rana perezi frogs

In the lung of Rana perezi no differences as a function of age have been found for any of the five major antioxidant enzymes, reduced (GSH), oxidized (GSSG) or glutathione ratio (GSSG/GSH), oxygen consumption (VO2) and for in vivo or in vitro stimulated tissue peroxidation. This frog shows a moderate rate of oxygen consumption and a life span substantially longer than that of rats and mice. Chronic (2.5 months) catalase depletion in the lung did not affect survival or any additional antioxidant enzyme, GSH, GSSG or in vivo and in vitro lung peroxidation in any age group. Only the GSSG/GSH ratio and the VO2 were elevated in catalase depleted old but not young frogs. After comparison of these results with those obtained in other animal species by other authors we suggest the possibility that decreases in antioxidant capacity in old age be restricted to species with high basal metabolic rates. Nevertheless, scavenging of oxygen radicals can not be 100% effective in any species. Thus, aging can still be due to the continuous presence of small concentrations of O2 radicals in the tissues throughout the life span in animals with either high or low metabolic rates.

Changes on cerebral antioxidant enzymes, peroxidation, and the glutathione system of frogs after aging and catalase inhibition

The five major antioxidant enzymes, glutathione, and in vivo or in vitro stimulated (Fe(++)-ascorbate) peroxidation were similar in old and young Rana perezi frogs. Long-term (2.5 months) treatment with aminotriazole strongly decreased cerebral catalase (CAT) activity and increased in vivo but not in vitro peroxidation in the brain. This suggests that the increase in endogenous brain peroxidation after CAT inhibition is due to an increased free-radical attack on cerebral membranes, and not to a possible increase in their sensitivity to peroxidative damage. The increase of in vivo peroxidation is especially remarkable taking into account the low levels of CAT present in the vertebrate brain. On the other hand, these changes were not accompanied by any effect on the survival of the animals. Comparison of these results with those obtained in other species suggests the possibility that O2-free radicals be of minor importance in relation to brain aging in animals with low rates of oxygen consumption.

Aminotriazole effects on lung and heart H2O2 detoxifying enzymes and TBA-RS at two pO2

In order to clarify the physiological role in vivo of H2O2-detoxifying enzymes at low and high levels of O2 tension we studied catalase (CAT), glutathione peroxidases (GP), and in vivo peroxidation (TBA-RS) in the lung and heart of Rana perezi frogs chronically treated with hyperoxia, aminotriazole (AT) -a CAT inhibitor-, or both. Hyperoxia did not change CAT, GP or TBA-RS. Aminotriazole caused an almost complete depletion of CAT, a 30% decrease of GP and a 132% (lung) to 200% (heart) increase of TBA-RS. Changes similar to these were found in the group treated with AT in hyperoxia. No mortality or changes in total or organ weight occurred in the experimental groups. Main conclusions are: (1) The maximal hyperoxia tolerance showed by frogs among vertebrates does not need antioxidant enzyme induction from lung or heart and is probably related to the presence of high constitutive levels of GP in relation to metabolic rate. (2) Even in normoxia the tissues present significant amounts of H2O2, and CAT is needed to avoid oxidative damage. GP does not compensate its absence. The implications of these results in relation to oxygen toxicity in man is discussed.

Catalase is needed to avoid tissue peroxidation in Rana perezi in normoxia

1. In order to clarify the relative role of catalase (CAT) and glutathione peroxidases (GSH-Px) at normal and high O2 tensions, Rana perezi frogs were chronically treated with aminotriazole (AT), hyperoxia, or both. 2. A 100% survival was observed with both treatments. Hyperoxia increased liver catalase and kidney TBA-RS and decreased GSH-Px. 3. AT caused quantitatively higher alterations than hyperoxia in both organs: CAT was depleted, TBA-RS increased (114% in kidney) and GSH-Px decreased. 4. It is concluded that in Rana perezi (a) CAT, in spite of its much higher KM and Vmax in relation to GSH-Px, is needed to avoid oxidative stress even in normoxia; (b) normoxic tissues have significative amounts of H2O2; (c) GSH-Px does not compensate the lack of CAT.

Effect of hyperoxia acclimation on catalase and glutathione peroxidase activities and in vivo peroxidation products in various tissues of the frog Rana ridibunda perezi

Among vertebrates, adult amphibians are known to be especially tolerant to exposure to high environmental oxygen tensions. To clarify the basis for this high O2 tolerance, adult Rana ridibunda perezi frogs were acclimated for 15 days to water-air phases with either 149 mm Hg O2 (normoxia) or 710 mm Hg O2 (hyperoxia). At the end of the acclimation, various morphometric and biochemical parameters related to oxidative stress were measured in seven organs and tissues. Hyperoxia acclimation did not change either the total weight of the animals or the total and relative wet weights of the organs studied, except for the brain, which showed weight increases in the hyperoxic group. In vivo tissue peroxidation increased in the kidney; decreased in the skeletal muscle and skin; and did not change in the liver, lung, brain, and heart after hyperoxic exposures. Whereas liver, lung, and skin showed glutathione peroxidase (GSH-Px) activities with both cumene hydroperoxide (cumene-OOH) and H2O2 as substrates, skeletal muscle only showed H2O2 GSH-Px activity. Hyperoxia acclimation did not change either catalase (CAT) or GSH-Px activities in any organ, except for the liver in which CAT activity was induced by hyperoxia. Thus hyperoxia tolerance in this species does not need the induction of H2O2-detoxifying enzymes in the majority of the organs. It is suggested that the high O2 tolerance of this amphibian species is related to its comparatively high constitutive GSH-Px activities.

Physiological significance of catalase and glutathione peroxidases, and in vivo peroxidation, in selected tissues of the toad Discoglossus pictus (Amphibia) during acclimation to normobaric hyperoxia

1. Various parameters related to oxidative stress were measured in adult Discoglossus pictus acclimated for 15 days to either normoxia or hyperoxia (PO2 = 710 mmHg). 2. Total weight of the toads and total and relative wet weight of liver, kidneys, lungs and heart were not changed by hyperoxic acclimation. 3. In vivo tissue peroxidation increased in lung, decreased in skeletal muscle, and was not changed in liver, kidney, heart and skin after hyperoxic exposure. 4. Hyperoxic acclimation increased catalase activities in the lung, liver, kidney and heart but not in skeletal muscle and skin. 5. Liver showed higher GSH-peroxidase activity with cumene-OOH than with H2O2 as substrate, whereas lung, skeletal muscle and skin presented similar GSH-peroxidase activities with both substrates. 6. GSH-peroxidase activities did not change between hyperoxic and normoxic animals in liver, lung, skeletal muscle and skin. 7. These results show that catalase, not GSH-peroxidase, is the principal H2O2 detoxifying enzyme involved in the adaptation of D. pictus to hyperoxia.