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Glutathione: A marker and antioxidant for aging

      Abstract

      J Lab Clin Med 2002;140:380-1.

      Abbreviations:

      GR (glutathione reductase), GSH (reduced glutathione), GSSCy (mixed disulfide with cysteine), HPLC (high-pressure liquid chromatography), SOD (superoxide dismutase)
      Aging individuals form an ever increasing percentage of the population, and the maintenance of quality of life in later years utilizes a significant proportion of the nation's medical monetary expenditures. In the etiology of aging, Parkinson's disease, Alzheimer's disease, amyotrophic lateral sclerosis, trauma, and other diseases, oxidative stress has been implicated.
      • Knight JA
      The biochemistry of aging.
      Oxidative stress implies imbalance in the neutralization of oxygen related free radicals (eg, superoxide anion [O2−•], hydroxyl [OH], and nitrogen dioxide [NO2]). As a consequence, there is enhancement in the deleterious effects of these radicals on cellular functions. The body has multiple antioxidant defenses, of which SOD and GSH seem especially important. GSH scavenges free radicals and is converted to GSSG or GSSCy which is reduced back to GSH by the enzymatic activity of GR. GSH protects cells from oxidative stress. The detoxification capability of GSH is directly related to its reduced thiol group. The enzymatic activity of glutathione-peroxidases and glutathione-transferases is also dependent on reduced thiol group of GSH. GSH and other reduced thiols are important for the ability of the body to resist oxidant stress. It has been postulated that decreased levels of reduced GSH would be a marker for increased susceptibility to oxidant injury and also indicating depletion of reserves due to oxidative stress. The use of GSH as an anti-aging drug has recently increased remarkably, but this use is unsubstantiated by clinical data. GSH homeostasis has been reported to be altered in a wide variety of human diseases. In order to understand the mechanism of its action, the measurement of the steady state levels of GSH and the rate of synthesis of GSH has been reported in various diseases.
      In a study of 176 healthy individuals negative correlations were observed between age and GSH, GSH/GSSG molar ratio or GR activity.
      • Erden-Inal M
      • Sunal E
      • Kanbak G
      Age-related changes in the glutathione redox system.
      There were positive correlations between age and glutathione-peroxidase and GSSG levels. A different study of 74 patients with chronic illnesses reported that one third of these patients had GSH levels below the lower limit of normal and GSSG levels were similar to those in control subjects. In another study the GSH levels in 60-79 year old group were 17% lower than the reference group.
      • Lang CA
      • Naryshkin S
      • Schneider DL
      • Mills BJ
      • Lindeman RD
      Low blood glutathione levels in healthy aging adults.
      In a representative study of community-based elderly group (N = 33), higher glutathione levels were associated with fewer illnesses, better self-rated health, lower cholesterol, lower body mass index, and lower blood pressures.
      • Julius M
      • Lang CA
      • Gleiberman L
      • Harburg E
      • DiFranceisco W
      • Schork A
      Glutathione and morbidity in a community-based sample of elderly.
      In the current issue of Journal, a study by Lang et al
      • Lang CA
      • Mills BJ
      • Lang HL
      • Liu MC
      • Riche Jr, JP
      • Mastropaolo W
      • et al.
      High blood glutathione levels accompany excellent physical and mental health in women 60 to 103 years old.
      reports that GSH status in non-diseased aged individuals with better psychosocial or mental health is similar to healthy young individuals. The conclusion of the study is that total GSH levels in whole blood correlated very well with the physical health irrespective of the age. According to the study, the well-being of healthy females > 60 years old can be predicted by their GSH levels. This is an important finding and needs to be supported by other studies that monitor the levels of reduced GSH and GSSG in elderly populations. Studies like these are difficult to complete and require a lot of planing and resources to validate the hypothesis. Therefore the selection of patient population, endpoints, methods of analysis, and biochemical markers of oxidative stress that are compatible with the hypothesis is very crucial. All these are necessary for the validation of the hypothesis that minimal GSH levels are indispensable in aging and various other diseases. Recent improvements in technology enable the development of methods that precisely and accurately measure reduced GSH concentrations in humans. In the analysis of blood or serum samples, the fractionation of GSH and GSSG concentrations is essential in understanding the role of reduced GSH in aging and other diseases. Recently, the use a novel approach of estimation of redox potential of GSH has suggested that in age-related pathologies, oxidation of GSH may be more important in aging than a decrease in total GSH.
      • Adams Jr, JD
      • Klaidman LK
      • Chang ML
      • Yang J
      Brain oxidative stress-analytical chemistry and thermodynamics of glutathione and NADPH.
      But in specific diseases such as diabetes, both oxidation and a deficiency in total GSH may be observed.
      For quantitative analysis of reduced GSH, enzymatic, spectrophotometric, fluorometric, and HPLC-based methods have been used in numerous reports and all of these methods have used derivitization of GSH and GSSG. These reports lack validation and method comparison data and don't help in the selection of the best method for use in clinical laboratories. HPLC methods with various detectors (eg, ultraviolet, fluorometric, and electrochemical detection) have been developed and are relatively more specific.
      • Stempak D
      • Dallas S
      • Klein J
      • Bendayan R
      • Koren G
      • Baruchel S
      Glutathione stability in whole blood: effects of various deproteinizing acids.
      The recent invention of electrospray interface, enabling the coupling of HPLC to mass spectrometers, has helped in the development of a method with increased specificity and sensitivity in comparison to the spectrophotometric- or fluorescence-based detection methods. State of the art tandem mass spectrometers offer several advantages over single stage instruments, which can target molecular ions of GSH and GSSG in the first mass analyzer and a characteristic fragment of GSH and GSSG in the second mass analyzer offering greater specificity.
      • Norris RL
      • Eaglesham GK
      • Shaw GR
      • Smith MJ
      • Chiswell RK
      • Seawright AA
      • et al.
      A sensitive and specific assay for glutathione with potential application to glutathione disulphide, using high-performance liquid chromatography-tandem mass spectrometry.
      Further studies in large different populations with a uniform method of quantitation of GSH are needed to support that GSH is a potential health risk factor for morbidity among the aging population.

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