Delaying Aging with Mitochondrial Micronutrients and Antioxidants.

Abstract

MITOCHONDRIAL DECAY IN AGING. Mitochondria decay with age due to the oxidation of mtDNA, proteins, and lipids. Some of this decay can be reversed in old rats by feeding them normal mitochondrial metabolites at high levels. Aging appears to be in good part due to the oxidants produced as by-products of normal metabolism by mitochondria [1-5]. In old rats mitochondrial membrane potential, cardiolipin levels, respiratory control ratio, and overall cellular O2 consumption are lower than in young rats and the level of oxidants (per unit O2) and mutagenic aldehydes from lipid peroxidation is higher [3]. Ambulatory activity declines markedly in old rats. Spatial memory as measured by the Morris water maze, also declines with age. Feeding old rats the normal mitochondrial metabolites acetyl carnitine and lipoic acid for a few weeks, restores mitochondrial function, lowers oxidants to the level of a young rat, and increases ambulatory activity and spatial memory [6-11]. Thus, these two metabolites can be considered necessary for health in old age and are therefore “conditional micronutrients”. This restoration suggests a plausible mechanism [11]: with age increased oxidative damage to proteins, such as acyl carnitine transferase (whose activity declines with age), and lipid membranes, particularly in mitochondria, causes a deformation of structure of key enzymes, with a consequent lessening of affinity (Km) for the enzyme substrate; an increased level of the substrate restores the velocity of the reaction, and thus restores function. Hepatocytes were isolated from young (3-5 months) and old (24-28 months) rats and incubated with various concentrations of tert-butylhydroperoxide (t-BuOOH) [10]. The t-BuOOH concentration that killed 50% of cells (LC50) in 2 hr declined nearly two-fold from 721 ± 32 µM in cells from young rats to 391 ± 31 µM in cells from old rats. This increased sensitivity of hepatocytes from old rats may be due, in part, to changes in glutathione (GSH) levels, because total cellular and mitochondrial GSH were 37.7% and 58.3% lower, respectively, compared to cells from young rats. Cells from old animals were incubated with either (R)- or (S)-lipoic acid (100 µM) for 30 min prior to the addition of 300 µM t-BuOOH. The physiologically relevant (R)-form, a coenzyme in mitochondria, as opposed to the (S)-form significantly protected hepatocytes against t-BuOOH toxicity. Dietary supplementation of (R)-lipoic acid [0.5% (wt/wt)] for 2 weeks also completely reversed the age-related decline in hepatocellular GSH levels and the increased vulnerability to t-BuOOH as well. An identical supplemental diet fed to young rats did not enhance the resistance to t-BuOOH, indicating that antioxidant protection was already optimal in young rats. Thus, this study shows that cells from old animals are more susceptible to oxidant insult and (R)-lipoic acid, after reduction to an antioxidant in the mitochondria, effectively reverses this age-related increase in oxidant vulnerability.