Retinoic acid attenuates inducible nitric oxide synthase (NOS2) activationin cultured rat cardiac myocytes and microvascular endothelial cells

The inducible NO synthase (NOS2) in cardiac tissue contributes to myocardia l and coronary inflammation and dysfunction. Several natural (endogenous) h ormones such as retinoic acid, the active metabolite of vitamin A. have the ability to attenuate NOS2 activation in inflammatory cells. The aim of thi s study M as to investigate the effect of RA on NOS2 activation in cultured cardiac microvascular endothelial cells (CMEC) and adult rat ventricular m yocytes (ARVM). CMEC were stimulated either with a combination of 10 mug/ml lipopolysaccharide (LPS) and 50 IU/ml interferon-gamma (IFN-gamma) or with a combination of 1 ng/ml interleukin-1 beta (IL-1 beta) +IFN-gamma whereas ARVM cz ere stimulated with 1 ng/ml 1L-1 beta and 50 IU/ml IFN-gamma in th e absence or presence of all-trans retinoic acid (atRA). Activation of the NOS2 pathway was estimated by measurement of mRNA (Northern blot) and prote in (Western blot) expression. enzyme activity by conversion of [H-3] L-argi nine to [H-3] L-citrulline, and nitrite accumulation. NOS2 mRNA half-life M as studied in CMEC and ARVM in the presence of actinomycin D. Tn CMEC and ARVM stimulated with a combination of LPS and:or cytokines. atRA (10(-h),10 (-5) M) significantly (P<0.05) attenuated NOS2 mRNA and protein expression. enzymatic activity and reduced supetnatant nitrite concentration. Upon sti mulation with LPS/IFN-<gamma>, atRA significantly decreased NOS2, mRNA half -life. This cl as not seen after stimulation with IL-I beta /IFN-gamma. The se results document for the first time an effect of RA on NOS2 activation i n cardiac cells. They may contribute to the characterization of the immunom odulatory effects of retinoids ill myocardial and coronary inflammatory dis orders. (C) 2001 Academic Press.