Effects of aldosterone and related steroids on LPS-induced increased expression of inducible NOS in rat aortic smooth muscle cells

BACKGROUND AND PURPOSE

Expression of inducible NOS (iNOS) is important in certain inflammatory diseases. We determined if the hormone aldosterone, a mineralocorticoid receptor (MR) agonist, affects LPS activation of iNOS expression in rat aortic smooth muscle cells (RASMC).

EXPERIMENTAL APPROACH

Cultured RASMC were treated with LPS, with or without agonists/antagonists of steroid receptors. iNOS expression was determined by nitrite assays on culture medium removed from treated cells and by immunoblotting of cell protein extracts.

KEY RESULTS

LPS (1 µg·mL^?1) increased nitrite and iNOS protein above that in control (untreated) cells. These effects of LPS were reduced by aldosterone (0.1–10 µM). The MR antagonists, eplerenone (10 µM) and spironolactone (10 or 50 µM), did not inhibit these actions of 1 µM aldosterone, but the latter were prevented by 10 µM mifepristone, a glucocorticoid (GR) and progestogen receptor (PR) antagonist. Mifepristone also prevented the reduction of LPS-induced nitrite increase produced by 1 µM dexamethasone (GR agonist) and 10 µM progesterone (PR agonist). Spironolactone (10–50 µM) by itself decreased LPS-induced increases in nitrite and iNOS protein. Mifepristone (10 µM) partially reversed these effects of 10 µM spironolactone, but not those of 50 µM; the effects of 50 µM spironolactone were also unchanged when mifepristone was increased to 50 µM.

CONCLUSIONS AND IMPLICATIONS

This pharmacological profile suggests that aldosterone, and possibly 10 µM spironolactone, use mechanisms that are dependent on PR and/or GR, but not MR, to inhibit iNOS induction in RASMC. With 50 µM spironolactone, other inhibitory mechanisms requiring further investigation may become predominant.