Angiotensin-converting enzyme inhibitors limit infarct size in animal models of myocardial ischemia reperfusion injury. This effect has been shown to be due to inhibition of bradykinin degradation rather than inhibition of angiotensin II formation. The purpose of this study was to determine whether angiotensin AT1 receptor blockade by losartan or its active metabolite EXP3174 protects against myocardial ischemia-reperfusion injury in mice and whether this protection is mediated by the kallikrein kinin system. We subjected anesthetized mice to 30 min of coronary artery occlusion followed by 3 h of reperfusion and evaluated infarct size immediately after reperfusion. Losartan (Los) or EXP3174 [2-n-butyl-4-chloro-1-[(2′-(1H-tetrazol-5-yl)biphenyl-4-yI)methyl]imidazole-5-carboxylic acid] were administered 5 min before starting reperfusion at dosages determined by preliminary studies of blood pressure effect and inhibition of angiotensin pressor response. Compared with saline, both drugs significantly reduced myocardial infarct size by roughly 40% (P < 0.001). Pretreatment of mice with the selective AT2 receptor antagonist PD123,319 [S-(+)-1-([4-(dimethylamino)-3-methylphenyl]methyl)-5-(diphenylacetyl)-4,5,6,7-tetrahydro-1H-imidazo(4,5-c)pyridine-6-carboxylic acid] did not affect infarct size in the absence of losartan but abolished the reduction in infarct size provided by losartan. In tissue kallikrein gene-deficient mice (TK^–/–), losartan no longer reduced infarct size. Pretreatment of wild-type mice with the B₂ receptor antagonist icatibant reproduced the effect of TK deficiency. We conclude that AT1 receptor blockade provides cardioprotection against myocardial ischemia-reperfusion injury through stimulation of AT2 receptors. Kallikrein and B₂ receptor are major determinants of this cardioprotective effect of losartan. Our results support the hypothesis of a coupling between AT2 receptors and kallikrein during AT1 receptor blockade, which plays a major role in cardioprotection.

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.

Angiogenesis is a cause of visual impairment and blindness in the wet form of age‐related macular degeneration and in ischemic retinopathies. Current therapies include use of anti‐VEGF agents to reduce choroidal neovascularization (CNV) and edema. These treatments are effective in most cases, but spontaneous or acquired resistance to anti‐VEGF and possible adverse effects of long‐term VEGF inhibition in the retina and choroid highlight a need for additional alternative therapies. Integrins αvβ3 and αvβ5, which regulate endothelial cell proliferation and stabilization, have been implicated in ocular angiogenesis. Lebecetin (LCT) is a 30‐kDa heterodimeric C‐type lectin that is isolated from Macrovipera lebetina venom and interacts with α5β1‐ and αv‐containing integrins. We previously showed that LCT inhibits human brain microvascular endothelial cell adhesion, migration, proliferation, and tubulogenesis. To evaluate the inhibitory effect of LCT on ocular angiogenesis, we cultured aortic and choroidal explants in the presence of LCT and analyzed the effect of LCT on CNV in the mouse CNV model and on retinal neovascularization in the oxygen‐induced retinopathy model. Our data demonstrate that a single injection of LCT efficiently reduced CNV and retinal neovascularization in these models.—Montassar, F., Darche, M., Blaizot, A., Augustin, S., Conart, J.‐B., Millet, A., Elayeb, M., Sahel, J.‐A., Réaux‐Le Goazigo, A., Sennlaub, F., Marrakchi, N., Messadi, E., Guillonneau, X. Lebecetin, a C‐type lectin, inhibits choroidal and retinal neovascularization. FASEB J. 31, 1107–1119 (2017). www.fasebj.org

Coronary endothelial dysfunction is involved in cardiac ischemia–reperfusion (IR) injury. Vascular endothelial growth factor (VEGF) activates endothelial cells and exerts cardioprotective effects in isolated hearts. The recently discovered viper venom protein called increasing capillary permeability protein (ICPP) exerts VEGF-like effects in endothelial cells. We examined whether VEGF or ICPP can influence IR outcome in vivo in mice. Dosages of VEGF and ICPP were determined by preliminary blood pressure study. In IR, both the proteins administered intravenously at reperfusion reduced infarct size (IS) by 57% for VEGF and 52% for ICPP (P < 0.01). Pretreatment with a selective VEGFR2 receptor antagonist abolished the reduction in IS. VEGF and ICPP induced ERK phosphorylation in the myocardium. IR triggered mitochondrial pore opening and impaired mitochondrial respiratory function. These effects of IR were prevented by VEGF or ICPP, which increased mitochondrial calcium retention capacity by 37% compared with saline (P < 0.05) and improved mitochondrial respiratory function (by 71% and 65%, respectively for state 3, and 51% and 38% for state 4, P < 0.01 for VEGF). Thus, intravenous administration of VEGF or ICPP at reperfusion largely reduces IS in IR, through stimulation of VEGFR2 receptors. This effect is mediated, at least in part, by improvement of IR-induced mitochondrial dysfunction.

To elucidate the mechanisms responsible for the adverse renal effects induced by dual blockade of the renin-angiotensin system (RAS) and the role of salt therein. The effects of enalapril, losartan and their combination on blood pressure, renal haemodynamics, renal function and RAS were investigated over a wide range of doses in spontaneously hypertensive rats fed either a low-sodium or a high-sodium diet. In rats fed the low-sodium diet, the losartan-enalapril combination induced the same dose-dependent haemodynamic and hormonal changes as did three- to 10-fold greater doses of enalapril or losartan alone. When a strong decrease (> 50%) in blood pressure was achieved (with 10 mg/kg enalapril plus 10 mg/kg losartan, 100 mg/kg enalapril or 100 mg/kg losartan), a massive renal vasoplegia occurred and renal insufficiency developed. In addition, because of the huge release of renin, angiotensinogen concentrations were reduced, leading to a decrease in intrarenal angiotensins. In rats fed the high-sodium diet, those treated with the enalapril 30 mg/kg plus losartan 30 mg/kg combination, despite complete functional RAS blockade, exhibited smaller decreases in blood pressure and renal resistance, lesser release of renin and angiotensinogen consumption, and a normal renal function. These effects were similar to those produced by 100 mg/kg of enalapril or losartan in rats fed the high-salt diet, or by 10 mg/kg of enalapril or of losartan in rats fed the low-salt diet. Dual RAS blockade could be either beneficial, when sodium intake is unrestricted, or dangerous, when sodium intake is restricted.