Vasomodulatory effect of novel peroxovanadate compounds on rat aorta: role of rho kinase and nitric oxide/cGMP pathway

Abstract

The present study was undertaken to assess the role of reactive oxygen species (ROS) in rat aortic ring vasoreactivity and integrity by using various peroxovanadate (pV) compounds. All the pV compounds (1 nM-300 µM) used in the present study exerted concentration-dependent contractions on endothelium intact rat aortic rings. All compounds with an exception of DPV-asparagine (DPV-asn) significantly altered vascular integrity as shown by diminished KCl responses. Phenylephrine (PE)-mediated contractions (3 nM-300 µM) were unaltered in the presence of these compounds. Acetylcholine (Ach)-mediated relaxation in PE (1 µM) pre-contracted rings was significantly reduced in presence of diperoxovanadate (DPV), poly (sodium styrene sulfonate-co-maleate)-pV (PSS-CoM-pV) and poly (sodium styrene 4-sulfonate)-pV (PSS-pV). However, no significant change in Ach-mediated responses was observed in the presence of poly (acrylate)-pV (PAA-pV) and DPV-asn. DPV-asn was thus chosen to further elucidate mechanism involved in peroxide mediated modulation of vasoreactivity. DPV-asn (30 nM-300 µM) exerted significantly more stable contractions, that was found to be catalase (100 U/ml) resistant in comparison with H2O2 (30 nM-300 µM) in endothelium intact aortic rings. These contractile responses were found to be dependent on extracellular Ca²⁺ and were significantly inhibited in presence of ROS scavenger N-acetylcysteine (100 µM). Intracellular calcium chelation by BAPTA-AM (10 µM) had no significant effect on DPV-asn (30 nM-300 µM) mediated contraction. Pretreatment of aortic rings by rho-kinase inhibitor Y-27632 (10 µM) significantly inhibited DPV-asn-mediated vasoconstriction indicating role of voltage-dependent Ca²⁺ influx and downstream activation of rho-kinase. The small initial relaxant effect obtained on addition of DPV-asn (30 nM−1 µM) in PE (1 µM) pre-contracted endothelium intact rings, was prevented in the presence of guanylate cyclase inhibitor, methylene blue (10 µM) and/or nitric oxide synthase (NOS) inhibitor, l-NAME (100 µM) suggesting involvement of nitric oxide and cGMP. DPV-asn, like H2O2, exerted a response of vasoconstriction in normal arteries and vasodilation at low concentrations (30 nM−1 µM) in PE-pre contracted rings with overlapping mechanisms. These findings suggest usefulness of DPV-asn having low toxicity, in exploring the peroxide-mediated effects on various vascular beds. The present study also convincingly demonstrates role of H₂O₂ in the modulation of vasoreactivity by using stable peroxide DPV-asn and warrants future studies on peroxide mediated signaling from a newer perspective.