A new and potent calmodulin antagonist, HF-2035, which inhibits vascular relaxation induced by nitric oxide synthase

Involvement of Ca2+/calmodulin-dependent protein kinase II in endothelial NO production and endothelium-dependent relaxation

Nitric oxide (NO) is synthesized from l-arginine by the Ca(2+)/calmodulin-sensitive endothelial NO synthase (NOS) isoform (eNOS). The present study assesses the role of Ca(2+)/calmodulin-dependent protein kinase II (CaMK II) in endothelium-dependent relaxation and NO synthesis. The effects of three CaMK II inhibitors were investigated in endothelium-intact aortic rings of normotensive rats. NO synthesis was assessed by a NO sensor and chemiluminescence in culture medium of cultured porcine aortic endothelial cells stimulated with the Ca(2+) ionophore A23187 and thapsigargin. Rat aortic endothelial NOS activity was measured by the conversion of l-[(3)H]arginine to l-[(3)H]citrulline. Three CaMK II inhibitors, polypeptide 281-302, KN-93, and lavendustin C, attenuated the endothelium-dependent relaxation of endothelium-intact rat aortic rings in response to acetylcholine, A23187, and thapsigargin. None of the CaMK II inhibitors affected the relaxation induced by NO donors. In a porcine aortic endothelial cell line, KN-93 decreased NO synthesis and caused a rightward shift of the concentration-response curves to A23187 and thapsigargin. In rat aortic endothelial cells, KN-93 significantly decreased bradykinin-induced eNOS activity. These results suggest that CaMK II was involved in NO synthesis as a result of Ca(2+)-dependent activation of eNOS.

Inter-isoformal regulation of nitric oxide synthase through heteromeric dimerization

Biochemical characterization of neuronal nitric oxide synthase (nNOS) has demonstrated a unique complexity with the native protein being a homodimer. To cast light on its enzyme structure-activity relationship, inactive nNOS, generated by mutation of (Lys732-Lys-Leu) to (Asp732-Asp-Glu) (Watanabe et al., FEBS Lett., 403 (1997) 75-78), and active nNOS were co-expressed using the Sf9 and COS-7 cell expression system. Co-transfectants of active and inactive nNOS resulted in attenuation of Ca2+/calmodulin (CaM) dependent NOS enzyme activity to a level 46.4+/-4.30% as much as active homomeric enzyme. Dimerization between active and inactive nNOS was observed by low temperature SDS-PAGE in the co-transfectants. The dimerization and attenuation of Ca2+/CaM dependent activity were not observed when active and inactive nNOS were combined in vitro, indicating that nNOS dimerization occurs intracellularly to form an active enzyme. Furthermore, we co-expressed inactive nNOS with active inducible NOS (iNOS) to analyze inter-isoformal regulation of NOSs. Interestingly, inactive nNOS also showed similar effects on enzyme activity and heteromeric dimerization against iNOS, thus indicating that inter-isoformal regulation of the two isoforms might also be involved in control of neuron function.

Selective inhibitors of neuronal nitric oxide synthase--is no NOS really good NOS for the nervous system?

It is now ten years since NO was shown to account for the biological activity of endothelium-derived relaxing factor (EDRF). It is also the tenth anniversary of the identification of L-NG monomethyl arginine (L-NMMA) as the very first inhibitor of NO biosynthesis. That EDRF and NO were one and the same sparked an explosion of interest in the biochemistry and pharmacology of NO which has yet to subside. In contrast, the first ever nitric oxide synthase (NOS) inhibitor slipped seamlessly into the literature virtually without comment at the time. Over the following decade, L-NMMA (and like NOS inhibitors) have proved invaluable as tools for probing the biological roles of NO in health and disease and, in particular, have increased our understanding of the function of NO in the nervous system. Further advances in this important area now require the development of inhibitors selective for the neuronal isoform of NOS (nNOS). Here, Philip Moore and Rachel Handy provide an up-to-date account of the literature regarding the biochemical and pharmacological characterization of NOS inhibitors with particular reference to compounds with greater selectivity for the nNOS isoform.

Inhibition of nitric oxide synthase does not affect survival in a rat model of abdominal sepsis

The effect of inhibiting nitric oxide (NO) synthesis during sepsis was studied in a caecal perforation model on Wistar rats. This model induces severe abdominal sepsis with a 48-h mortality > 90% in untreated animals. The survival time in hours (median values with the 95% confidence intervals in parentheses) for the control group was 15 (11.5-27.0) h. Treatment with the inhibitors of NO synthesis, NG-monomethyl-L-arginine (LNMMA), 30 mg kg-1 body weight (BW) or S-(2-aminoethyl)-isothiourea (AET), 3 mg kg-1 BW, given either once or twice after sepsis induction did not affect survival in this model. Survival time when LNMMA was given once was 13 (11-22) h and when given twice it was 14 (8-41) h. The corresponding survival times were 9 (4-28) h and 11 (5-27) h for treatment with AET. In conclusion, this study demonstrates that survival in the present model of live multiplying bacterial sepsis is not affected by either LNMMA or AET. Testing the potential clinical effects of inhibition of NO synthesis during sepsis should not be confined to short-term studies of haemodynamic changes induced by lipopolysaccharide.