Tissue Kallikrein Elicits Cardioprotection by Direct Kinin B2 Receptor Activation Independent of Kinin Formation

Abstract

Abstract-Tissue kallikrein exerts various biological functions through kinin formation with subsequent kinin B2 receptor activation. Recent studies showed that tissue kallikrein directly activates kinin B2 receptor in cultured cells expressing human kinin B2 receptor. In the present study, we investigated the role of tissue kallikrein in protection against cardiac injury through direct kinin B2 receptor activation using kininogen-deficient Brown Norway Katholiek rats after acute myocardial infarction. Tissue kallikrein was injected locally into the myocardium of Brown Norway Katholiek rats after coronary artery ligation with and without coinjection of icatibant (a kinin B2 receptor antagonist) and N -nitro-Larginine methylester (an NO synthase inhibitor). One day after myocardial infarction, tissue kallikrein treatment significantly improved cardiac contractility and reduced myocardial infarct size and left ventricle end diastolic pressure in Brown Norway Katholiek rats. Kallikrein attenuated ischemia-induced apoptosis and monocyte/macrophage accumulation in the ischemic myocardium in conjunction with increased NO levels and reduced myeloperoxidase activity. Icatibant and N -nitro-L-arginine methylester abolished kallikrein's effects, indicating a kinin B2 receptor NO-mediated event. Moreover, inactive kallikrein had no beneficial effects in cardiac function, myocardial infarction, apoptosis, or inflammatory cell infiltration after myocardial infarction. In primary cardiomyocytes derived from Brown Norway Katholiek rats under serum-free conditions, active, but not inactive, kallikrein reduced hypoxia/reoxygenation-induced apoptosis and caspase-3 activity, and the effects were mediated by kinin B2 receptor/nitric oxide formation. This is the first study to demonstrate that tissue kallikrein directly activates kinin B2 receptor in the absence of kininogen to reduce infarct size, apoptosis, and inflammation and improve cardiac performance of infarcted hearts. Key Words: apoptosis Ⅲ cardiac function Ⅲ infarct size Ⅲ kinin B2 receptor Ⅲ tissue kallikrein T issue kallikrein is a serine proteinase that specifically processes low-molecular-weight kininogen to produce the potent vasoactive kinin peptides bradykinin and Lys-bradykinin (kallidin), 1 which bind to and activate the kinin B2 receptor. 2 Kinins have been shown to protect against cardiac injury through kinin B2 receptor activation. 3,4 Yang and coworkers 5 demonstrated that the cardioprotective effect of preconditioning was abolished in kinin B2 receptor knockout mice and in kininogendeficient rats. The cardioprotective response to inhibition of angiotensin-converting enzyme (ACE) and angiotensin II type 1 receptor was diminished in B2 receptor-deficient mice. 6 Similarly, kinins appear to play an important role in the cardioprotective effect of ACE inhibition in kininogen-deficient rats. 7 However, recent studies from Erdös' group demonstrated that tissue kallikrein directly activates the kinin B2 receptor in cultured Chinese hamster ovary cells. 8,9 This nove...

Kallistatin attenuates endothelial apoptosis through inhibition of oxidative stress and activation of Akt-eNOS signaling

“…Moreover, the cells were transfected with scrambled siRNA, eNOS-siRNA, FOXO1-siRNA, or Bim-siRNA for 24 h or transduced with Ad.Null or Ad.DN-Akt for 16 h. The cells were then incubated in the presence or absence of kallistatin (0.2 M) for 30 min, followed by the addition of TNF-␣ (10 ng/ml) for 16 h. The cells were incubated with Hoechst 33342 (0.4 mg/ml) for 5 min and examined under a fluorescence microscope to detect apoptotic nuclei. Caspase-3 activity was measured by incubating cell lysates with caspase-3 substrate (10 M) as described (6). The fluorescence of the cleaved substrate was measured by a spectrofluorometer with excitation and emission wavelengths of 380 and 460 nm, respectively.…”

Hypertension and the bradykinin system

“…It is also known that bradykinin B2 receptor stimulation causes production of cyclic guanosine monophosphate (cyclic GMP) in cultured porcine aortic endothelial cells. The formation of cyclic GMP may be an important step for biologic actions as well as the release of NO evoked by bradykinin in the endothelial cells and in the vascular smooth muscles [3,6].…”

Bradykinin System and Type 2 Diabetes

“…Plasma levels of tissue kallikreinhave been reported to be increased in type 2 diabetes as previously reported [23] In the present study however, we also observed high concentrations of plasma tissue kallikrein , which presumably be due to the hyperactivity of the BK-forming system to induce systemic metabolic abnormalities. It has been reported that tissue kallikrein activates B2R directly without BK generation [24]. Furthermore, diabetic rats have been shown to have the glomerular B1R and B2R expression in the diabetic state [25].…”