Activation of endothelial guanylate cyclase inhibits cellular reactivity

Lebetin 2, a Snake Venom-Derived Natriuretic Peptide, Attenuates Acute Myocardial Ischemic Injury through the Modulation of Mitochondrial Permeability Transition Pore at the Time of Reperfusion

Cardiac ischemia is one of the leading causes of death worldwide. It is now well established that natriuretic peptides can attenuate the development of irreversible ischemic injury during myocardial infarction. Lebetin 2 (L2) is a new discovered peptide isolated from Macrovipera lebetina venom with structural similarity to B-type natriuretic peptide (BNP). Our objectives were to define the acute cardioprotective actions of L2 in isolated Langendorff-perfused rat hearts after regional or global ischemia-reperfusion (IR). We studied infarct size, left ventricular contractile recovery, survival protein kinases and mitochondrial permeability transition pore (mPTP) opening in injured myocardium. L2 dosage was determined by preliminary experiments at its ability to induce cyclic guanosine monophosphate (cGMP) release without changing hemodynamic effects in normoxic hearts. L2 was found to be as effective as BNP in reducing infarct size after the induction of either regional or global IR. Both peptides equally improved contractile recovery after regional IR, but only L2 increased coronary flow and reduced severe contractile dysfunction after global ischemia. Cardioprotection afforded by L2 was abolished after isatin or 5-hydroxydecanote pretreatment suggesting the involvement of natriuretic peptide receptors and mitochondrial K_ATP (mitoK_ATP) channels in the L2-induced effects. L2 also increased survival protein expression in the reperfused myocardium as evidenced by phosphorylation of signaling pathways PKCε/ERK/GSK3β and PI3K/Akt/eNOS. IR induced mitochondrial pore opening, but this effect was markedly prevented by L2 treatment. These data show that L2 has strong cardioprotective effect in acute ischemia through stimulation of natriuretic peptide receptors. These beneficial effects are mediated, at least in part, by mitoK_ATP channel opening and downstream activated survival kinases, thus delaying mPTP opening and improving IR-induced mitochondrial dysfunction.

Arteriolar dilation to endotoxin is increased in copper-deficient rats

We have previously reported that there is an altered response to mast cell-mediated inflammation in copper-deficient rats. In the current study we determined the microvascular reactivity to inflammatory stimuli with lipopolysacccharide (LPS) during dietary copper restriction. Male Sprague-Dawley rats were fed purified diets which were either copper-adequate (CuA, 6 micrograms Cu/g) or copper-deficient (CuD, 0.4 micrograms Cu/g) for 4 weeks. Rats were anesthetized and the cremaster muscle was prepared for in vivo television microscopy. Arteriolar diameters were measured and then 2.5 mg/kg LPS was injected i.p. In separate groups, animals were pretreated with the NO-synthase inhibitor L-NAME (2 x 10(-4) M), the cyclooxygenase inhibitor ibuprofen (9.6 x 10(-5) M) or the histamine receptor antagonist diphenhydramine (DPH, 10(-6) M). LPS caused arteriolar dilation in both dietary groups with the response being significantly greater in the CuD group. Ibuprofen and DPH but not L-NAME, each significantly reduced but did not block the dilation in the CuD group. Ibuprofen and DPH together blocked the dilation. These results suggest that dietary copper deficiency increases arteriolar dilation to LPS. The mechanism appears to involve a greater response to arachidonic acid metabolites and histamine but not NO.