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

The inducible NO synthase (NOS2) in cardiac tissue contributes to myocardial and coronary inflammation and dysfunction. Several natural (endogenous) hormones such as retinoic acid, the active metabolite of vitamin A, have the ability to attenuate NOS2 activation in inflammatory cells. The aim of this study was to investigate the effect of RA on NOS2 activation in cultured cardiac microvascular endothelial cells (CMEC) and adult rat ventricular myocytes (ARVM). CMEC were stimulated either with a combination of 10 μg/ml lipopolysaccharide (LPS) and 50 IU/ml interferon-γ (IFN-γ) or with a combination of 1 ng/ml interleukin-1β (IL-1β) + IFN-γ whereas ARVM were stimulated with 1 ng/ml IL-1β and 50 IU/ml IFN-γ in the absence or presence of all-trans retinoic acid (atRA). Activation of the NOS2 pathway was estimated by measurement of mRNA (Northern blot) and protein (Western blot) expression, enzyme activity by conversion of [³H] L-arginine to [³H] L-citrulline, and nitrite accumulation, NOS2 mRNA half-life was studied in CMEC and ARVM in the presence of actinomycin D. In CMEC and ARVM stimulated with a combination of LPS and/or cytokines, atRA (10^-6, 10^-5 M) significantly (P<0.05) attenuated NOS2 mRNA and protein expression, enzymatic activity and reduced supernatant nitrite concentration. Upon stimulation with LPS/IFN-γ, atRA significantly decreased NOS2 mRNA half-life. This was not seen after stimulation with IL-1β/IFN-γ. These results document for the first time an effect of RA on NOS2 activation in cardiac cells. They may contribute to the characterization of the immunomodulatory effects of retinoids in myocardial and coronary inflammatory disorders.