Cardioprotective effect of VEGF and venom VEGF-like protein in acute myocardial ischemia in mice: effect on mitochondrial function.

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.

Selective kinin receptor agonists as cardioprotective agents in myocardial ischemia and diabetes.

Cardiac ischemia is a leading cause of death, especially in diabetic patients. The diabetic ischemic heart is resistant experimentally to established cardioprotective treatments. New pharmacological approaches to cardiac protection are warranted. The kallikrein-kinin system is involved in myocardial protection in ischemia. Respective roles of B1 (B1R) and B2 (B2R) receptors remain controversial. We tested whether pharmacological activation of kinin receptors may have therapeutic effect in cardiac ischemia-reperfusion in nondiabetic (NDiab) and diabetic (Diab) mice. We assessed effect on infarct size (IS) and signaling pathways involved in myocardial protection of potent selective pharmacological agonists of B1R or B2R given at reperfusion. In NDiab mice, a B2R agonist reduced IS significantly by 47%, similarly to ramiprilat or ischemic postconditioning, via activation of phosphoinositide 3 kinase/Akt pathway leading to inhibition of glycogen synthase kinase-3ß (GSK-3ß). B1R agonist had no effect on IS. In contrast, in Diab mice, the B2R agonist, ramiprilat, or ischemic postconditioning failed to reduce IS but a B1R agonist significantly reduced IS by 44% via activation of phosphoinositide 3 kinase/Akt and extracellular signal-regulated kinase 1/2, both leading to GSK-3ß inhibition. Differential effect of B2R or B1R agonists in NDiab and Diab mice can be linked to inactivation of B2R signaling and induction of B1R in heart of Diab mice. Thus, a pharmacological B2R agonist is cardioprotective in acute ischemia in nondiabetic animals. B1R agonist overcomes resistance of diabetic heart to cardioprotective treatments. Pharmacological activation of B1R and B2R may become a treatment for diabetic and nondiabetic patients, respectively, in acute coronary syndromes.

Tissue kallikrein is essential for invasive capacity of circulating proangiogenic cells.

RATIONALE: Homing of proangiogenic cells (PACs) is guided by chemoattractants and requires proteases to disrupt the extracellular matrix. The possibility that PAC recruitment involves an interaction between proteases and chemotactic factor receptors remains largely unexplored. OBJECTIVE: To determine the role of human tissue kallikrein (hK1) in PAC invasion and its dependency on kinin receptor signaling. METHODS AND RESULTS: Human mononuclear cells (MNCs) and culture-selected PACs express and release mature hK1 protein. HK1 gene (KLK1) silencing reduced PACs migratory, invasive, and proangiogenic activities. KLK1-knockout mouse bone marrow-derived MNCs showed similar impairments and were unable to support reparative angiogenesis in a mouse model of peripheral ischemia. Conversely, adenovirus-mediated KLK1 (Ad.KLK1) gene transfer enhanced PAC-associated functions, whereas the catalytically inactive variant R53H-KLK1 was ineffective. HK1-induced effects are mediated by a kinin B(2) receptor (B(2)R)-dependent mechanism involving inducible nitric oxide synthase and metalloproteinase-2 (MMP2). Lower hK1 protein levels were observed in PACs from type 2 diabetic (T2D) patients, whereas KLK1 mRNA levels were similar to those of healthy subjects, suggesting a post-transcriptional defect. Furthermore, B(2)R is normally expressed on T2D-PACs but remains uncoupled from downstream signaling. Importantly, whereas Ad.KLK1 alone could not restore T2D-PAC invasion capacity, combined KLK1 and B(2)R expression rescued the diabetic phenotype. CONCLUSIONS: This study reveals new interactive components of the PACs invasive machinery, acting via protease- and kinin receptor-dependent mechanisms.

Genetically determined angiotensin converting enzyme level and myocardial tolerance to ischemia.

Angiotensin I-converting enzyme (ACE; kininase II) levels in humans are genetically determined. ACE levels have been linked to risk of myocardial infarction, but the association has been inconsistent, and the causality underlying it remains undocumented. We tested the hypothesis that genetic variation in ACE levels influences myocardial tolerance to ischemia. We studied ischemia-reperfusion injury in mice bearing 1 (ACE1c), 2 (ACE2c, wild type), or 3 (ACE3c) functional copies of the ACE gene and displaying an ACE level range similar to humans. Infarct size in ACE1c was 29% lower than in ACE2c (P<0.05). Pretreatment with a kinin B2 receptor antagonist suppressed this reduction. In ACE3c, infarct size was the same as in ACE2c. But ischemic preconditioning, which reduced infarct size in ACE2c (-63%, P<0.001) and ACE1c (-52%, P<0.05), was not efficient in ACE3c (-2%, NS, P<0.01 vs. ACE2c). In ACE3c, ischemic preconditioning did not decrease myocardial inflammation or cardiomyocyte apoptosis. Pretreatment with a renin inhibitor had no cardioprotective effect in ACE2c, but in ACE3c partially restored (38%) the cardioprotection of ischemic preconditioning. Thus, a modest genetic increase in ACE impairs myocardial tolerance to ischemia. ACE level plays a critical role in cardiac ischemia, through both kinin and angiotensin mediated mechanisms.

Tissue kallikrein deficiency and renovascular hypertension in the mouse.

The kallikrein kinin system (KKS) is involved in arterial and renal functions. It may have an antihypertensive effect in both essential and secondary forms of hypertension. The role of the KKS in the development of two-kidneys, one-clip (2K1C) hypertension, a high-renin model, was investigated in mice rendered deficient in tissue kallikrein (TK) and kinins by TK gene inactivation (TK-/-) and in their wild-type littermates (TK+/+). Four weeks after clipping the renal artery, blood flow was reduced in the clipped kidney (2K1C-TK+/+: -90%, 2K1C-TK-/-: -93% vs. sham-operated mice), and the kidney mass had also decreased (2K1C-TK+/+: -65%, 2K1C-TK-/-: -66%), whereas in the unclipped kidney, blood flow (2K1C-TK+/+: +19%, 2K1C-TK-/-: +17%) and kidney mass (2K1C-TK+/+: +32%, 2K1C-TK-/-: +30%) had both increased. The plasma renin concentration (2K1C-TK+/+: +78%, 2K1C-TK-/-: +65%) and renal renin content of the clipped kidney (2K1C-TK+/+: +58%, 2K1C-TK-/-: +65%) had increased significantly. There was no difference for these parameters between 2K1C-TK+/+ and 2K1C-TK-/- mice. Blood pressure monitored by telemetry and by plethysmography, rose immediately after clipping in both genotypes, and reached similar levels (2K1C-TK+/+: +24%, 2K1C-TK-/-: +21%). 2K1C-TK+/+ and 2K1C-TK-/- mice developed similar concentric left ventricular hypertrophy (+24% and +17%, respectively) with normal cardiac function. These findings suggest that in the context of chronic unilateral reduction in renal blood flow, TK and kinins do not influence the trophicity of kidneys, the synthesis and secretion of renin, blood pressure increase, and cardiac remodeling due to renin angiotensin system activation.

Tissue kallikrein is involved in the cardioprotective effect of AT1-receptor blockade in acute myocardial ischemia.

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.