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Human recombinant chromogranin A-derived vasostatin-1 mimics preconditioning via an adenosine/nitric oxide signaling mechanism

¹Department of Neuroscience, Physiology Division, University of Turin, Turin; Departments of ²Pharmaco-Biology and ³Cell Biology, University of Calabria, Arcavacata di Rende (CS); ⁴Department of Clinical and Biological Sciences, University of Turin, ASO San Luigi, Orbassano; and ⁵Department of Biological and Technological Research, San Raffaele H Scientific Institute, Milan, Italy

Submitted 12 December 2006 ; accepted in final form 3 April 2007

The acidic protein chromogranin A (CgA) is the precursor of several regulatory peptides generated by specific proteolytic processes. Human recombinant CgA NH₂-terminal fragment STA-CgA_1-78 (hrSTA-CgA_1-78), containing vasostatin-1 (CgA_1-76) domain, exerts a negative inotropic effect and counteracts the -adrenergic positive inotropic effect on the rat heart. We hypothesized an involvement of nitric oxide (NO)-dependent pathway in both cardiodepression and cardioprotection by hrSTA-CgA_1-78. We also hypothesized an involvement of adenosine A₁ receptor and protein kinase C (PKC) in cardioprotection by hrSTA-CgA_1-78. Therefore, we evaluated whether 1) the cardioinhibition mediated by hrSTA-CgA_1-78 involves the G_i/o proteins/NO-dependent signal transduction cascade, 2) hrSTA-CgA_1-78 induces ischemic preconditioning-like protective effects on the myocardium, and 3) inhibition of NO synthase (NOS), adenosine A₁ receptor, or PKC affects hrSTA-CgA_1-78 protection. Using the isolated rat heart, we found that the reduction of left ventricular pressure (LVP), rate-pressure product, and maximal values of the first derivative of LVP elicited by hrSTA-CgA_1-78 at 33 nM is abolished by blocking G_i/o proteins with pertussis toxin, scavenging NO with hemoglobin, and blocking NOS activity with N^G-monomethyl-L-arginine or N⁵-(iminoethyl)-L-ornithine, soluble guanylate cyclase with 1H-[1,2,4]oxadiazole-[4,4-a]quinoxalin-1-one, and protein kinase (PKG) with KT5823. Data suggest the involvement of the G_i/o proteins/NO-cGMP-PKG pathway in the hrSTA-CgA_1-78-dependent cardioinhibition. When given before 30 min of ischemia, hrSTA-CgA_1-78 significantly reduced the size of the infarct from 64 ± 4 to 32 ± 3% of the left ventricular mass. This protective effect was abolished by either NOS inhibition or PKC blockade and was attenuated, but not suppressed, by the blockade of A₁ receptors. These results suggest that hrSTA-CgA_1-78 activity triggers two different pathways: one of these pathways is mediated by A₁ receptors, and the other is mediated by NO release. As with repeated brief preconditioning ischemia, hrSTA-CgA_1-78 may be considered a stimulus strong enough to trigger both pathways, which may converge on PKC.

vasostatin; contractility

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