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The present study characterizes for the first time a GSH specific transporter in a human intestinal epithelial cell line (I407). GSH metabolism is very important for the antioxidant and detoxifying action of intestine and for the maintenance of the luminal thiol-disulfide ratio involved in regulation mechanisms of the protein activity of epithelial cells. GSH level decreases have been related to physio-pathological alterations either of intestine or other organs. GSH specific transport systems have been identified in membranes of various cell types of rat, mice and rabbit. The presence of a Na+-independent transport system of GSH is confirmed by the similar behaviour of GSH uptake time-courses when Na+ in extracellular uptake medium was replaced with choline+ or K+ as well as by kinetic saturation and by the trans-stimulation effect on GSH uptake in GSH preloaded cells. Moreover, this transporter is activated when cations are present in extracellular medium and it is affected by membrane potential changes with an increase in GSH uptake values when membrane depolarization occurs. The present results also show a remarkable affinity and specificity of this transporter for GSH; in fact, Km value is very low (90 +/- 20 microM) and only compounds strictly related to GSH structure, such as GSH S-conjugates and GSH-ethyl ester, inhibit GSH uptake in 1407 cells. Finally, a possible hormonal control and modulation by the thiol-disulfide status of GSH transporter activity is suggested.

The present study reports data on absorption of orally administered glutathione (GSH) in rat jejunum and in other organs, and the possible role of specific transport systems of GSH and gamma-glutamyltranspeptidase (EC 2.3.2.1; gamma-GT) activity. GSH levels were measured simultaneously in various organs after oral GSH administration to untreated rats and rats treated with L-buthionine sulfoximine (BSO) or acivicin (AT125). BSO selectively inhibits GSH intracellular synthesis and AT125 is a specific inhibitor of gamma-GT activity. GSH levels were also measured after oral administration of an equivalent amount of the constituent amino acids of GSH to untreated and BSO-treated rats. Significant increases in GSH levels were found in jejunum, lung, heart, liver and brain after oral GSH administration to untreated rats. GSH increases were also obtained in all organs, except liver, when GSH was administered to rats previously GHS-depleted by treatment with BSO. The analysis of all results allowed us to distinguish between the increase in GSH intracellular levels due to intact GSH uptake by specific transporters, and that due to GSH degradation by gamma-GT activity and subsequent absorption of degradation products with intracellular resynthesis of GSH; both these mechanisms seemed to be involved in increasing GSH content in heart after oral GSH administration. Jejunum, lung and brain took up GSH mostly intact, by specific transport systems, while in liver GSH uptake occurred only by its breakdown by gamma-GT activity followed by intracellular resynthesis.

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A comprehensive study on glutathione metabolism in rat heart and liver as a function of age was performed. In the heart, reduced glutathione, total glutathione, and the glutathione redox index showed a decrease during aging, while oxidized glutathione levels increased in 5-month-old rats with respect to the young animals and remained quite constant in 14- and 27-month-old rats. In the liver, the highest levels of reduced glutathione were found in the 2-month-old rats, while oxidized glutathione reached a peak at 5 months. Glutathione-associated enzymes showed age-related changes. Glutathione peroxidase, unaffected by aging in the heart, decreased in the liver of the 27-month-old rats. In the heart and the liver, the highest values of glutathione S-transferase were found at 5 months and 27 months, respectively. Glucose-6-phosphate dehydrogenase followed a similar trend in both heart and liver. Glutathione reductase also showed the same behaviour in heart and in liver, increasing in old rats with respect to the other age groups. A decrease in gamma-glutamylcysteine synthetase was found in the heart and liver of 27-month-old rats in comparison with the 2-month-old ones. In conclusion, a decreased antioxidant capability has been demonstrated in both heart and liver of old rats.

Recent studies show that glutathione, while being involved in the well-known physiological processes of amino acid transport and detoxification, can also play a part in cell proliferation events. Cell treatment with l-buthionine sulphoximine, which causes glutathione depletion, is accompanied by a decrease in cell proliferation. At present no precise relationship between this thiol and any critical intermediate of the mitogenic cascade has been proved. In this study, conducted on NIH/3T3 murine fibroblasts, we demonstrate a strict correlation between glutathione levels and platelet-derived growth-factor-receptor activation in response to stimulation and cell proliferation. The receptor autophosphorylation is severely impaired at low glutathione cellular levels. The interaction of glutathione with this growth-factor receptor in vivo, while being rather specific, is complex and may involve both cytosolic and extracellular receptor domains.

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