Vasorelaxation

Background: Vasoconstriction is a major pathological feature of cardiovascular diseases involving endothelium dependent and independent mechanisms. Oxadiazole moiety appeared to be effective in various pathologies. Objective: The aim of the study was to synthesize and evaluate the mechanism of vasorelaxation exhibited by synthesized oxadiazole derivatives. Method: The 2,5-disubstituted-1,3,4-oxadiazole derivatives were synthesized by an efficient and simple method. The derivatives were investigated for their ex-vivo vasorelaxant action on intact/denuded endothelium rat aortic rings precon-tracted with norepinephrine/ phenylephrine/KCl. Results: The contractions induced in the aortic rings by the addition of cumulative concentrations of norepinephrine, phenylephrine, KCl and calcium were significantly antagonized by a derivative, OXD-Z2. In another experiment, verapa-mil pretreatment inhibited phenylephrine and Ca 2+-induced aortic contractions and OXD-Z2 did not alter verapamil-induced inhibition. This indicated the role of L-type Ca 2+-channels in the OXD-Z2-induced vasorelaxation via inhibition of calcium influx. Further, atropine (muscarinic receptor antagonist), L-NAME (NO synthase inhibitor) and methylene blue (non-selective cGMP inhibitor) inhibited OXD-Z2-induced relaxation in other sets of experiments. These results indicate that OXD-Z2 also mediates vasorelaxation through NO release by muscarinic receptor activation. In addition, the molecular docking studies showed that OXD-Z2 interacts with L-type Ca 2+-channel, muscarinic (M 2) receptor and eNOS. Conclusion: Thus, it is deduced from the above findings that the vasorelaxant activity of OXD-Z2 involves muscarinic receptor-mediated nitric oxide release in addition to direct inhibition of L-type Ca 2+-channels.

Despite the mechanisms for endogenous nitroxyl (HNO) production and action being incompletely understood, pharmacological donors show broad therapeutic promise and are in clinical trials. Mass spectrometry and site-directed mutagenesis showed that chemically distinct HNO donors 1-nitrosocyclohexyl acetate or Angeli's salt induced disulfides within cGMP-dependent protein kinase I-alpha (PKGIα), an interdisulfide between Cys42 of the two identical subunits of the kinase and a previously unobserved intradisulfide between Cys117 and Cys195 in the high affinity cGMP-binding site. Kinase activity was monitored in cells transfected with wildtype (WT), Cys42Ser or Cys117/195Ser PKGIα that cannot form the inter- or intradisulfide, respectively. HNO enhanced WT kinase activity, an effect significantly attenuated in inter- or intradisulfide-deficient PKGIα. To investigate whether the intradisulfide modulates cGMP binding, real-time imaging was performed in vascular smooth muscle cells expressing a FRET-biosensor comprising the cGMP-binding sites of PKGIα. HNO induced FRET changes similar to those elicited by an increase of cGMP, suggesting that intradisulfide formation is associated with activation of PKGIα. Intradisulfide formation in PKGIα correlated with enhanced HNO-mediated vasorelaxation in mesenteric arteries in vitro and arteriolar dilation in vivo in mice. HNO induces intradisulfide formation in PKGIα, inducing the same effect as cGMP binding, namely kinase activation and thus vasorelaxation.

1The contribution of haeme oxygenase-derived carbon monoxide (CO) to the regulation of vascular tone in thoracic aorta was investigated following induction of the inducible isoform of haeme oxygenase (HO-1).2Isometric smooth muscle contractions were recorded in isolated rat aortic ring preparations. Rings were incubated in the presence of the nitric oxide (NO) donor S-nitroso-N-acetyl penicillamine (SNAP, 500 μm) for 1 h, then repetitively washed and maintained for a further 4 h prior to producing a concentration-response curve to phenylephrine (PE, 1–3000 nm).3Treatment with SNAP resulted in increased mRNA and protein expression of aortic HO-1 and was associated with a significant suppression of the contractile response to PE (P<0.05 vs control). Immunohistochemical staining procedures revealed marked HO-1 expression in the endothelial layer and, to a lesser extent, in smooth muscle cells.4Induction of HO-1 in SNAP-treated rings was associated with a higher 14CO release compared to control, as measured by scintillation counting after incubation of aortas with [2-14C]-L-glycine, the precursor of haeme. Guanosine 3′,5′-monophosphate (cyclic GMP) content was also greatly enhanced in aortas expressing high levels of HO-1.5Incubation of aortic rings with the NO synthase inhibitor, NG-monomethyl-L-arginine (100 μm), significantly (P<0.05) increased the contractile response to PE in controls but failed to restore PE-mediated contractility in SNAP-treated rings. In contrast, the selective inhibitor of haeme oxygenase, tin protoporphyrin IX (SnPP-IX, 10 μm), restored the pressor response to PE in SNAP-treated rings whilst markedly reducing CO and cyclic GMP production.6We conclude that up-regulation of the HO-1/CO pathway significantly contributes to the suppression of aortic contractility to PE. This effect appears to be mediated by the elevation of cyclic GMP levels and can be reversed by inhibition of the haeme oxygenase pathway.The contribution of haeme oxygenase-derived carbon monoxide (CO) to the regulation of vascular tone in thoracic aorta was investigated following induction of the inducible isoform of haeme oxygenase (HO-1).Isometric smooth muscle contractions were recorded in isolated rat aortic ring preparations. Rings were incubated in the presence of the nitric oxide (NO) donor S-nitroso-N-acetyl penicillamine (SNAP, 500 μm) for 1 h, then repetitively washed and maintained for a further 4 h prior to producing a concentration-response curve to phenylephrine (PE, 1–3000 nm).Treatment with SNAP resulted in increased mRNA and protein expression of aortic HO-1 and was associated with a significant suppression of the contractile response to PE (P<0.05 vs control). Immunohistochemical staining procedures revealed marked HO-1 expression in the endothelial layer and, to a lesser extent, in smooth muscle cells.Induction of HO-1 in SNAP-treated rings was associated with a higher 14CO release compared to control, as measured by scintillation counting after incubation of aortas with [2-14C]-L-glycine, the precursor of haeme. Guanosine 3′,5′-monophosphate (cyclic GMP) content was also greatly enhanced in aortas expressing high levels of HO-1.Incubation of aortic rings with the NO synthase inhibitor, NG-monomethyl-L-arginine (100 μm), significantly (P<0.05) increased the contractile response to PE in controls but failed to restore PE-mediated contractility in SNAP-treated rings. In contrast, the selective inhibitor of haeme oxygenase, tin protoporphyrin IX (SnPP-IX, 10 μm), restored the pressor response to PE in SNAP-treated rings whilst markedly reducing CO and cyclic GMP production.We conclude that up-regulation of the HO-1/CO pathway significantly contributes to the suppression of aortic contractility to PE. This effect appears to be mediated by the elevation of cyclic GMP levels and can be reversed by inhibition of the haeme oxygenase pathway.British Journal of Pharmacology (1998) 125, 1437–1444; doi:10.1038/sj.bjp.0702212

""1 Carbon monoxide (CO), one of the end products of heme catabolism by heme oxygenase, possesses antihypertensive and vasodilatory characteristics. We have recently discovered that certain transition metal carbonyls are capable of releasing CO in biological fluids and modulate physiological functions via the delivery of CO. Because the initial compounds identified were not water soluble, we have synthesized new CO-releasing molecules that are chemically modified to allow solubility in water. The aim of this study was to assess the vasoactive properties of tricarbonylchloro(glycinato)ruthenium(II) (CORM-3) in vitro and in vivo.
2 CORM-3 produced a concentration-dependent relaxation in vessels precontracted with phenylephrine, exerting significant vasodilatation starting at concentrations of 25–50 µM. Inactive CORM-3, which does not release CO, did not affect vascular tone.
3 Blockers of ATP-dependent potassium channels (glibenclamide) or guanylate cyclase activity (ODQ) considerably reduced CORM-3-dependent relaxation, confirming that potassium channels activation and cGMP partly mediate the vasoactive properties of CO. In fact, increased levels of cGMP were detected in aortas following CORM-3 stimulation.
4 The in vitro and in vivo vasorelaxant activities of CORM-3 were further enhanced in the presence of YC-1, a benzylindazole derivative which is known to sensitize guanylate cyclase to activation by CO. Interestingly, inhibiting nitric oxide production or removing the endothelium significantly decreased vasodilatation by CORM-3, suggesting that factors produced by the endothelium influence CORM-3 vascular activities.
5 These results, together with our previous findings on the cardioprotective functions of CORM-3, indicate that this molecule is an excellent prototype of water-soluble CO carriers for studying the pharmacological and biological features of CO.""