Oxidative stress is thought to be one of the mechanisms leading to the initiation or progression of specific diseases as well as to the general process of aging. Glutathione (GSH), a tripeptide present in high concentrations in all mammalian cells, is the body's major endogenous antioxidant and plays a vital role in detoxification reactions and in the protection of cells from the toxic effects of oxidants. Maintenance of body GSH stores is a complex, integrated phenomenon, and there has been a resurgence of interest in potential interventions that may modulate GSH levels in the whole body and in specific tissues and cells. Advancing age, known to be associated with increased oxidative stress, is also reported to be associated with low GSH concentrations. In addition, aging is associated with an increased prevalence of cardiovascular disease, impaired glucose tolerance, and diabetes mellitus; the latter has also been shown to be accompanied by lower GSH concentrations. The mechanisms that could be responsible for a compromised GSH status include decreased synthesis and/or increased utilization relative to synthetic capacity. Ideally, one would like to measure in vivo rates of both GSH synthesis and utilization. Unfortunately, the multitude of pathways consuming GSH, as well as tissue variation, makes it impossible to have meaningful simultaneous measurements of utilization by all of the different pathways in the human. Hence, the focus of this proposal will be on GSH synthesis rates. We plan to test the hypotheses that 1) older men and women (age 60+ years) will have lower GSH synthesis rates and lower GSH levels compared to younger (<35 years) subjects and these differences will be exacerbated by diabetes mellitus in the old and 2) the provision of precursors for cysteine, the rate-limiting amino acid in GSH synthesis, will attenuate these differences.
The specific aims are to determine: 1) Rates of GSH synthesis in younger and older groups of non-diabetic men and women using stable isotope tracer methodology, and GSH concentrations in plasma and erythrocytes of these volunteers. 2)The effect of diabetes mellitus on GSH synthesis rates and concentrations in older men and women. 3)The effect of GSH depletion by acetaminophen on rates of GSH synthesis in young and old non-diabetics. 4) The effect of GSH depletion by acetaminophen on rates of GSH synthesis in older non-diabetics and diabetics. 5) Whether acute administration of the cysteine precursor, L-2-oxothiazolidine-4-carboxylic acid (OTZ), will increase rates of GSH synthesis and GSH levels in young and old non-diabetic volunteers. 6) Whether acute administration of the cysteine precursor, OTZ, will increase rates of GSH synthesis and GSH levels 7 older nondiabetic and diabetic men and women. Data obtained in these in vivo studies will help to integrate in humans the diverse findings obtained in experiments conducted in animals and from in vitro cell culture systems and to improve our fundamental understanding of the effect of aging on GSH homeostasis in humans. It is hoped that the data will lay the groundwork for future studies examining the efficacy of nutritional supplements aimed at modulating an individual's GSH status and potentially ameliorating the deleterious effects of oxidative stress. ? ?
