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Inhibition of nitric oxide synthesis in vascular smooth muscle by retinoids
K Hirokawa1, K M O'Shaughnessy, P Ramrakha
1Department of Clinical Pharmacology, Royal Postgraduate Medical School, London.
Abstract:
1. These studies examine the effect of retinoids on interleukin 1 beta (IL-1 beta)-induced nitric oxide synthase (NOS) activity in cultured rat aortic vascular smooth muscle (VSM) cells and isolated rat aortic rings. 2. All-trans-retinoic acid (all-trans-RA, 0.1-10 microM) and its active analogues produced concentration-dependent inhibition of IL-1 beta (0.1-10 ng ml-1)-induced nitrite production in cultured VSM cells. In contrast, the inactive retinoid, Ro 14-6113 (0.1-10 microM), had no effect on IL-1 beta-induced nitrite production. 3. Since some of the actions of retinoids are mediated by induction of transforming growth factor beta (TGF-beta), its effect on inducible NOS activity in VSM cells was examined. TGF-beta produced concentration-dependent (0.1-10 ng ml-1) inhibition of IL-1 beta-induced nitrite production and the maximum effect (approximately 90% inhibition) was significantly greater than that seen with all-trans-RA (approximately 70% with 10 microM). However, an anti-TGF-beta antibody (50 micrograms ml-1) which blocked the effect of exogenous TGF-beta (5 ng ml-1) did not significantly reverse the inhibitory action of all-trans-RA (10 microM). 4. In addition to inhibiting IL-1 beta-induced nitrite production, all-trans-RA (10 microM) reduced substantially inducible NOS mRNA and protein levels in IL-1 beta-induced VSM cells (P < 0.01). 5. Incubation of isolated rat aortic rings with IL-1 beta (10 ng ml-1) caused a progressive resistance of the rings to the vasoconstrictor action of phenylephrine (10 nM to 10 microM). This effect was abolished by the addition of the nitric oxide synthase inhibitor L-NG-monomethyl-L-arginine (L-NMMA, 1 mM). All trans-RA (10 micro M) also markedly and significantly reversed this IL-1p-induced vascular hyporeactivity(P<0.01).6. These data show that all-trans-RA and other active retinoids are able to block cytokine-stimulated expression of inducible NOS in cultured VSM cells and isolated aortic rings.
Insights
Retinoids, like all-trans-retinoic acid, inhibit interleukin-1 beta-induced nitric oxide synthase (NOS) expression and activity in vascular cells. This suggests retinoids may protect against cytokine-induced vascular dysfunction.
Area of Science:
- Biochemistry
- Pharmacology
- Cardiovascular Research
Background:
- Interleukin-1 beta (IL-1 beta) can induce nitric oxide synthase (NOS) activity in vascular smooth muscle (VSM) cells.
- Retinoids are known to modulate cellular functions, and their effects on cytokine-induced responses require investigation.
Purpose of the Study:
- To investigate the effect of retinoids on IL-1 beta-induced nitric oxide synthase (NOS) activity in rat aortic VSM cells and aortic rings.
- To determine if transforming growth factor beta (TGF-beta) mediates the action of retinoids on NOS.
Main Methods:
- Cultured rat aortic VSM cells and isolated rat aortic rings were treated with IL-1 beta and various retinoids.
- Nitrite production, inducible NOS mRNA and protein levels, and vascular reactivity to phenylephrine were measured.
- The role of TGF-beta was assessed using an anti-TGF-beta antibody.
Main Results:
- All-trans-retinoic acid (all-trans-RA) and active retinoids inhibited IL-1 beta-induced nitrite production in a concentration-dependent manner.
- TGF-beta also inhibited nitrite production, but an anti-TGF-beta antibody did not block the effect of all-trans-RA.
- All-trans-RA reduced inducible NOS mRNA and protein levels and reversed IL-1 beta-induced vascular hyporeactivity in aortic rings.
Conclusions:
- Active retinoids, including all-trans-RA, effectively block cytokine-stimulated expression of inducible NOS in VSM cells and aortic rings.
- Retinoids may offer a protective mechanism against inflammatory vascular responses mediated by NOS.