Oxidative stress induced by L-buthionine-(S,R)-sulfoximine, a selective inhibitor of glutathione metabolism, abrogates mouse kidney mineralocorticoidreceptor function

In vitro studies have demonstrated that cysteine groups present in most of the steroid receptors play an essential role in the steroid binding process as well as in the ability of this superfamily of signaling proteins to fun ction as transcription factors. However, there is poor experimental evidenc e, if any, which demonstrates that under conditions of oxidative stress the steroid receptors in general, and the mineralocorticoid receptor in partic ular, are affected in vivo in a similar fashion as has been described for c ell-free systems or cells in culture. In the present work we report that wh en mice are exposed to oxidative stress by treatment with L-buthionine-(S,R )-sulfoximine (L-(S,R)-BSO), a glutathione depleting agent, the aldosterone -dependent mineralocorticoid biological response (measured as sodium retent ion and potassium elimination) was diminished in a directly proportional ma nner with respect to the depletion of renal glutathione. Accordingly, the s teroid binding capacity of the mineralocorticoid receptor was also abrogate d, whereas the receptor protein level remained unchanged. The harmful effec ts observed in mice after glutathione depletion were efficiently prevented by co-treatment with glutathione monoethyl ester. Similar inhibition in the steroid binding capacity was also generated in vitro by receptor alkylatio n and receptor oxidation, an effect which was prevented in the presence of reducing agents. Since the glutathione deficit generated in vivo by treatme nt with L-(S,R)-BSO did not significantly affect other renal proteins which are known to be required for the mineralocorticoid mechanism of action, we suggest that in renal cells a low redox potential exerts drastic and uncom pensated inhibition of the receptor-mediated mineralocorticoid biological r esponse. This effect was ascribed to the loss of steroid binding capacity o f oxidized receptor, most likely by modification of essential cysteines as supported by experiments where a decreased number of reactive thiols and re duced covalent binding of thiol-reactive ligand were evidenced on immunopur ified receptor after in vivo treatment with L-(S,R)-BSO. (C) 2000 Elsevier Science B.V. All rights reserved.