Effect of methionine dietary supplementation on mitochondrial oxygen radical generation and oxidative DNA damage in rat liver and heart.

Methionine restriction without energy restriction increases, like caloric restriction, maximum longevity in rodents. Previous studies have shown that methionine restriction strongly decreases mitochondrial reactive oxygen species (ROS) production and oxidative damage to mitochondrial DNA, lowers membrane unsaturation, and decreases five different markers of protein oxidation in rat heart and liver mitochondria. It is unknown whether methionine supplementation in the diet can induce opposite changes, which is also interesting because excessive dietary methionine is hepatotoxic and induces cardiovascular alterations. Because the detailed mechanisms of methionine-related hepatotoxicity and cardiovascular toxicity are poorly understood and today many Western human populations consume levels of dietary protein (and thus, methionine) 2-3.3 fold higher than the average adult requirement, in the present experiment we analyze the effect of a methionine supplemented diet on mitochondrial ROS production and oxidative damage in the rat liver and heart mitochondria. In this investigation male Wistar rats were fed either a L-methionine-supplemented (2.5 g/100 g) diet without changing any other dietary components or a control (0.86 g/100 g) diet for 7 weeks. It was found that methionine supplementation increased mitochondrial ROS generation and percent free radical leak in rat liver mitochondria but not in rat heart. In agreement with these data oxidative damage to mitochondrial DNA increased only in rat liver, but no changes were observed in five different markers of protein oxidation in both organs. The content of mitochondrial respiratory chain complexes and AIF (apoptosis inducing factor) did not change after the dietary supplementation while fatty acid unsaturation decreased. Methionine, S-AdenosylMethionine and S-AdenosylHomocysteine concentration increased in both organs in the supplemented group. These results show that methionine supplementation in the diet specifically increases mitochondrial ROS production and mitochondrial DNA oxidative damage in rat liver mitochondria offering a plausible mechanism for its hepatotoxicity.

Radicales libres de origen mitocondrial y longevidad / Mitochondrial free radicals and longevity

Desde los inicios del siglo XX se han propuesto muchas teorías diferentes sobre las causas del envejecimiento. Hoy en día, la teoría de los radicales libres de origen mitocondrial es la que disfruta de más apoyos a su favor en la literatura científica. En el presente artículo se revisan los trabajos publicados sobre la relación entre la longevidad máxima de las distintas especies animales y sus niveles endógenos de antioxidantes y de generación mitocondrial de radicales de oxígeno. La mayoría de los estudios sobre suplementación experimental con antioxidantes indican que pueden aumentar la esperanza de vida pero no cambian la longevidad máxima. Además, los antioxidantes endógenos correlacionan de forma negativa con la longevidad máxima. Sin embargo, la intensidad de producción mitocondrial de radicales de oxígeno y el daño oxidativo al ADN mitocondrial son menores en los animales longevos que en los de vida corta. Los animales longevos también muestran un menor grado de insaturación de los ácidos grasos de sus membranas tisulares que las especies de vida corta. Por otra parte, la restricción calórica, la manipulación experimental mejor conocida que disminuye la velocidad del envejecimiento, también disminuye la producción mitocondrial de radicales libres y el daño oxidativo al ADN mitocondrial. Este descenso ocurre en el complejo I. Estos resultados sugieren que se han utilizado mecanismos similares para aumentar la longevidad tanto en la restricción calórica como durante la evolución de especies animales con distinta velocidad de envejecimiento, y que dichos mecanismos incluyen un descenso en la intensidad de generación de radicales libres en la mitocondria

Since the beginning of the XXth century many theories have been proposed to explain aging. Nowadays, the mitochondrial free radical theory is strongly supported by the available scientific evidence. In this article published studies on the relationship between the maximum longevity of animals and their levels of endogenous antioxidants and mitochondrial rates of oxygen radical generation are reviewed. Most studies of antioxidant supplementation indicate that these chemicals can increase mean but not maximum longevity. In addition, endogenous antioxidant levels negatively correlate with maximum longevity. However, the rate of production of oxygen radicals at mitochondria and the steady-state levels of oxidative damage in mitochondrial DNA are lower in long-lived than in short-lived animal species. Long-lived species also have lower levels of fatty acid unsaturation in their cellular membranes. On the other hand, caloric restriction, the best know manipulation that decreases the rate of aging, also lowers mitochondrial free radical production and oxidative damage to mitochondrial DNA. This decrease occurs at complex I. These results suggest that common mechanisms have been used to increase longevity in caloric restriction and during the evolution of animal species with different aging rates. These mechanisms include a decrease in the rate of generation of free radicals at mitochondria

Influence of aging and long-term caloric restriction on oxygen radical generation and oxidative DNA damage in rat liver mitochondria.

The effect of long-term caloric restriction and aging on the rates of mitochondrial H2O2 production and oxygen consumption as well as on oxidative damage to nuclear (nDNA) and mitochondrial DNA (mtDNA) was studied in rat liver tissue. Long-term caloric restriction significantly decreased H2O2 production of rat liver mitochondria (47% reduction) and significantly reduced oxidative damage to mtDNA (46% reduction) with no changes in nDNA. The decrease in ROS production was located at complex I because it only took place with complex I-linked substrates (pyruvate/malate) but not with complex II-linked substrates (succinate). The mechanism responsible for that decrease in ROS production was not a decrease in mitochondrial oxygen consumption because it did not change after long-term restriction. Instead, the caloric restricted mitochondria released less ROS per unit electron flow, due to a decrease in the reduction degree of the complex I generator. On the other hand, increased ROS production with aging in state 3 was observed in succinate-supplemented mitochondria because old control animals were unable to suppress H2O2 production during the energy transition from state 4 to state 3. The levels of 8-oxodG in mtDNA increased with age in old animals and this increase was abolished by caloric restriction. These results support the idea that caloric restriction reduces the aging rate at least in part by decreasing the rate of mitochondrial ROS production and so, the rate of oxidative attack to biological macromolecules like mtDNA.

Membrane fatty acid unsaturation, protection against oxidative stress, and maximum life span: a homeoviscous-longevity adaptation?

Aging is a progressive and universal process originating endogenously that manifests during postmaturational life. Available comparative evidence supporting the mitochondrial free radical theory of aging consistently indicates that two basic molecular traits are associated with the rate of aging and thus with the maximum life span: the presence of low rates of mitochondrial oxygen radical production and low degrees of fatty acid unsaturation of cellular membranes in postmitotic tissues of long-lived homeothermic vertebrates in relation to those of short-lived ones. Recent research shows that steady-state levels of free radical-derived damage to mitochondrial DNA (mtDNA) and, in some cases, to proteins are lower in long- than in short-lived animals. Thus, nonenzymatic oxidative modification of tissue macromolecules is related to the rate of aging. The low degree of fatty acid unsaturation in biomembranes of long-lived animals may confer advantage by decreasing their sensitivity to lipid peroxidation. Furthermore, this may prevent lipoxidation-derived damage to other macromolecules. Taking into account the fatty acid distribution pattern, the origin of the low degree of membrane unsaturation in long-lived species seems to be the presence of species-specific desaturation pathways that determine membrane composition while an appropriate environment for membrane function is maintained. Mechanisms that prevent or decrease the generation of endogenous damage during the evolution of long-lived animals seem to be more important than trying to intercept those damaging agents or repairing the damage already inflicted. Here, the physiological meaning of these findings and the effects of experimental manipulations such as dietary stress, caloric restriction, and endocrine control in relation to aging and longevity are discussed.