Effects of aging and methionine restriction applied at old age on ROS generation and oxidative damage in rat liver mitochondria

Abstract

It is known that a global decrease in food ingestion (dietary restriction, DR) lowers mitochondrial ROS generation (mitROS) and oxidative stress in young immature rats. This seems to be caused by the decreased methionine ingestion of DR animals. This is interesting since isocaloric methionine restriction in the diet (MetR) also increases, like DR, rodent maximum longevity. However, it is not known if old rats maintain the capacity to lower mitROS generation and oxidative stress in response to MetR similarly to young immature animals, and whether MetR implemented at old age can reverse aging-related variations in oxidative stress. In this investigation the effects of aging and 7 weeks of MetR were investigated in liver mitochondria of Wistar rats. MetR implemented at old age decreased mitROS generation, percent free radical leak at the respiratory chain and mtDNA oxidative damage without changing oxygen consumption. Protein oxidation, lipoxidation and glycoxidation increased with age, and MetR in old rats partially or totally reversed these age-related increases. Aging increased the amount of SIRT1, and MetR decreased SIRT1 and TFAM and increased complex IV. No changes were observed in the protein amounts of PGC1, Nrf2, MnSOD, AIF, complexes I, II and III, and in the extent of genomic DNA methylation. In conclusion, treating old rats with isocaloric short-term MetR lowers mitROS production and free radical leak and oxidative damage to mtDNA, and reverses aging-related increases in protein modification. Aged rats maintain the capacity to lower mitochondrial ROS generation and oxidative stress in response to a short-term exposure to restriction of a single dietary substance: methionine.

The Mitochondrial Free Radical Theory of Aging

“…83 In addition, we have recently found that 40% MetR also decreases mtROSp, %FRL, and 8-oxodG in mtDNA and reverses aging-related increases in protein modification when implemented at old age (during 7 weeks in 24-month-old rats). 82 All those results, taken together, indicate that the lowered ingestion of methionine during MetR (and PR and DR) is responsible for the decreases in mitochondrial ROSp and oxidative stress observed in MetR (and PR and DR), and possibly for all (during PR and MetR) or part (during DR) of the life-extension effect observed during these dietary manipulations. Moreover, the extraordinary capacity of a "single dietary molecule" to induce the decrease in mtROSp is still present when the animals reach old age.…”

“…In agreement with that, we have recently detected that MetR induces a small but statistically significant decrease in global genomic DNA methylation in rat heart of young immature rats, 81 whereas when this manipulation was performed in old rats, the decrease in this parameter was not statistically significant in the liver. 82 Concerning mechanism "iii": decreased NADH, it is more likely in DR than in MetR, due to the large number of metabolites than can potentially be decreased because of the lower caloric ingestion. In fact, there is a published study in which it was shown that pyruvate, malate, and succinate, as well as NADH and the NADH/NAD+ ratio, are decreased in the tissues of rodents subjected to DR. 32 Summarizing the described results, DR, PR, and MetR are nutritional interventions that increase longevity in rodents, although the magnitude of the longevity extension of MetR and PR in rodents is around 50% that of DR.…”

Mitohormesis: Promoting Health and Lifespan by Increased Levels of Reactive Oxygen Species (ROS)

“…Increasing mitochondrial biogenesis and function, energy expenditure, stress resistance, aerobic capacity, insulin sensitivity, glutathione (GSH) and expression of glutathione-S-transferase (GST) as well as a decrease of oxidative stress and cell damage due to adaptive changes in methionine and GSH metabolism were also observed (Zimmerman et al 2003, Miller et al 2005, Perrone et al 2010, Richie et al 1994, Malloy et al 2006, Sanz et al 2006, Perrone et al 2012, Tsai et al 2010, Caro et al 2008. Interestingly, co-treatment with an antioxidant, N-acetylcysteine, blocks some of the health-promoting effects of methionine restriction, accentuating a critical role for ROS with mitohormetic adaption processes in this regard (Elshorbagy et al 2012, Sanchez-Roman et al 2012). …”

Age-associated decrease in global DNA methylation in patients with major depression

“…Increased methylation in the white matter of the brain of aged rhesus monkeys was also reported 51. Meanwhile, there is more and more evidence indicating increased methylation during aging, which might be, at least partially, caused by oxidative stress 52,53. These findings indicate that loss of genomic methylation may be involved in aging process.…”