Elsevier

Advanced Drug Delivery Reviews

Volume 60, Issues 13–14, October–November 2008, Pages 1545-1552
Advanced Drug Delivery Reviews

Pro-oxidant shift in glutathione redox state during aging

https://doi.org/10.1016/j.addr.2008.06.001Get rights and content

Abstract

The GSH:GSSG ratio, which is the primary determinant of the cellular redox state, becomes progressively more pro-oxidizing during the aging process due to an elevation in the GSSG content and a decline in the ability for de novo GSH biosynthesis. The Km of glutamate-cysteine ligase (GCL), the rate-limiting enzyme in de novo GSH biosynthesis, significantly increases during aging, which would adversely affect the ability for rapid GSH biosynthesis, especially under stressful conditions. Experimental studies suggest that age-related accumulation of homocysteine, an intermediate in the trans-sulfuration pathway, may be responsible for causing the loss of affinity between GCL and its substrates. Over-expression of GCL has been shown to prolong the life span of Drosophila by up to 50%, suggesting that perturbations in glutathione metabolism play a causal role in the aging process.

Introduction

An invariable feature of the life cycle of all multi-cellular organisms is that following a period of growth and reproduction there is a gradual decline in physiological fitness, and the ability to maintain homeostasis is progressively whittled, which inevitably culminates in the death of the organism. The nature of the mechanisms causing the various age-associated physiological decrements or those that determine the vast differences in the maximum life spans of various species are presently poorly understood. Among the many candidate causal hypotheses, one that has gained considerable interest postulates that senescent physiological changes emanate from the deleterious effects of reactive oxygen species (ROS), generated during cellular metabolism. This hypothesis, often referred to as the “oxidative stress hypothesis”, was originally advanced in 1956 [1], an era when there was relatively little understanding of the mechanisms of ROS production or the nature of their interactions with biomacromolecules. Nevertheless, considerable progress has since been made in understanding the role of ROS in the aging process, primarily due to the contemporaneous advances in the biochemistry of ROS. The main focus of current investigations is the elucidation of the mechanism by which ROS cause attenuations in specific cellular functions, which govern the progression of senescence and determine the species-specific maximum life spans.

Section snippets

Oxidative stress, redox state and the aging process

Historically, ROS were generally regarded as potentially toxic and physiologically costly products of aerobic metabolism [2], [3]. Their formation was assigned to some intrinsic biochemical and/or structural flaws(s), requiring considerable expenditure of metabolic resources for their detoxification. In this view, ROS served no useful function, and if not totally eliminated by the anti-oxidant defenses, they would inflict random macromolecular damage, whose accumulation with age would cause

Glutathione homeostasis

The intra-cellular concentration of GSH (γ-l-glutamylcysteinylglycine), a tripeptide, often approaches millimolar amounts in mammals; however, GSH concentration varies in different cellular compartments, implying that distinct intra-cellular redox microenvironments exist within different organelles. For instance, GSH levels are much lower in the nucleus than in the cytoplasm, but the nuclear GSH content increases during cell division [13]. There is increasing realization that intra-cellular

Analytical procedures for measurement of glutathione and estimation of the redox potential

Measurements of GSH and GSSG in biological specimens can be erroneously affected during procedural handling due to the artificial oxidation of GSH. Analytical procedures in earlier studies, employing colorimetric, fluorimetric, and enzymatic assays were eventually found to have low sensitivity, inadequate specificity and/or low reproducibility [10], [12], [30]. Later procedures employing high-performance liquid chromatography, in combination with UV-absorbance or fluorescence detection, were

Effect of age on glutathione redox state in mice

Comparisons of the amounts of GSH, GSSG and protein–glutathione (protein–SSG) disulfides and GSH:GSSG ratios in homogenates and mitochondria of different tissues (liver, kidney, heart, brain, eye, and testis) were made between 4-, 10-, 22- and 26-month-old C57BL/6 mice [26]. In 4-month-old mice, GSH content of tissue homogenates varied ~ 10-fold among different tissues, with the rank order: liver = testis > brain = heart > eye > kidney. GSSG content of tissue homogenates also varied ~ 10-fold. The GSH:

Mechanisms of age-related oxidizing shift in glutathione redox state

The two main factors affecting the glutathione redox state during the aging process in the mouse seemed to be an increase in GSSG concentration and a decrease in the GSH pool size. In virtually all tissues, GSSG concentration is elevated during the last trimester of life. This is accompanied by an increase in the rates of mitochondrial superoxide and hydrogen peroxide production [34], [35], [36]. These two ROS are progenitors of a variety of other, some highly reactive, ROS. Age-related

Effects of caloric restriction on glutathione redox state in mouse

A decrease in the amount of food consumption, relative to the ad libitum (AL) fed level, has been shown to extend life span of certain laboratory strains of mice and rats [39], [40]. There is also some evidence that caloric restriction (CR) retards the onset and progression of some age-associated changes linked to oxidative stress. A comparison between 22-month-old AL mice and those fed a diet containing 40% fewer calories than the AL group since the age of 4 months, indicated that CR had no

Effects of dietary anti-oxidants on glutathione

The question whether intake of low molecular weight anti-oxidants causes a lowering of the level of oxidative stress has been intensely debated in the literature [36], [41], [42]. We addressed this issue by determining the effect of long term (8–10 months) dietary supplementation with two different mixtures of anti-oxidants on the glutathione redox state in senescence-accelerated mice (SAM-P8) [29]. Diet I was enriched with vitamin E, vitamin C, l-carnitine, and lipoic acid, while Diet II

Glutathione redox state in aging Drosophila melanogaster

The fruit fly (Drosophila melanogaster) provides several relative advantages as an experimental model for investigating the relationship between oxidative stress and aging, such as: i) relatively short life span (~ 8 weeks), ii) ability to manipulate the metabolic rate and life expectancy of flies by varying the ambient temperature, iii) availability of mutants and transformants (over-expressors). Glutathione redox state, amounts of the redox sensitive aminothiols (cysteine, Cys–Gly and

Role of glutathione in disease and toxicity

Depletion of glutathione or a disturbance in its redox state can lead not only to the disruption of a variety of cellular activities, but also to sensitization of cells to toxicants, thereby causing drug-induced cell toxicity. Indeed, some drugs have been shown to affect glutathione redox couple and mitochondrial function; e.g., usnic acid, a key constituent of LipoKinetix (a dietary supplement marketed as a weight-loss agent), can induce hepatic necrosis, triggered by GSH depletion and

Acknowledgements

Our research has been supported by grants RO1 AG 13563 and RO1 AG 7657 from National Institutes of Health—National Institute on Aging.

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    This review is part of the Advanced Drug Delivery Reviews theme issue on “Mitochondrial Medicine and Mitochondrion-Based Therapeutics”.

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