Vascular catabolism of bradykinin in the isolated perfused rat kidney

Neprilysin Inhibitors and Bradykinin

Bradykinin has important physiological actions related to the regulation of blood vessel tone and renal function, and protection from ischemia reperfusion injury. However, bradykinin also contributes to pathological states such as angioedema and inflammation. Bradykinin is metabolized by many different peptidases that play a major role in the control of bradykinin levels. Peptidase inhibitor therapies such as angiotensin converting enzyme (ACE) and neprilysin inhibitors increase bradykinin levels, and the challenge for such therapies is to achieve the beneficial cardiovascular and renal effects without the adverse consequences such as angioedema that may result from increased bradykinin levels. Neprilysin also metabolizes natriuretic peptides. However, despite the potential therapeutic benefit of increased natriuretic peptide and bradykinin levels, neprilysin inhibitor therapy has only modest efficacy in essential hypertension and heart failure. Initial attempts to combine neprilysin inhibition with inhibition of the renin angiotensin system led to the development of omapatrilat, a drug that combines ACE and neprilysin inhibition. However, omapatrilat produced an unacceptably high incidence of angioedema in patients with hypertension (2.17%) in comparison with the ACE inhibitor enalapril (0.68%), although angioedema incidence was less in patients with heart failure with reduced ejection fraction (HFrEF) treated with omapatrilat (0.8%), and not different from that for enalapril therapy (0.5%). More recently, LCZ696, a drug that combines angiotensin receptor blockade and neprilysin inhibition, was approved for the treatment of HFrEF. The approval of LCZ696 therapy for HFrEF represents the first approval of long-term neprilysin inhibitor administration. While angioedema incidence was acceptably low in HFrEF patients receiving LCZ696 therapy (0.45%), it remains to be seen whether LCZ696 therapy for other conditions such as hypertension is also accompanied by an acceptable incidence of angioedema.

Elevated Aminopeptidase P Attenuates Cerebral Arterial Responses to Bradykinin in Fawn-Hooded Hypertensive Rats

Cerebral arterial myogenic and autoregulatory responses are impaired in Fawn Hooded hypertensive (FHH) rats. Cerebral autoregulatory responses are restored in the congenic rat strain in which a segment of chromosome 1 from the Brown Norway (BN) rat was transferred into the FHH genetic background (FHH.1BN). The impact of this region on cerebral arterial dilator responses remains unknown. Aminopeptidase is a gene that was transferred into the FHH genetic background to generate the FHH.1BN rats and is responsible for degradation of the vasodilator bradykinin. Thus, we hypothesized that FHH rats will have increased aminopeptidase P levels with impaired cerebral arterial responses to bradykinin compared to BN and FHH.1BN rats. We demonstrated higher cerebral arterial expression of aminopeptidase P in FHH compared to BN rats. Accordingly, we demonstrated markedly impaired cerebral arterial dilation to bradykinin in FHH compared to BN rats. Interestingly, aminopeptidase P expression was lower in FHH.1BN compared to FHH rats. Decreased aminopeptidase P levels in FHH.1BN rats were associated with increased cerebral arterial bradykinin-induced dilator responses. Aminopeptidase P inhibition by apstatin improved cerebral arterial bradykinin dilator responses in FHH rats to a level similar to FHH.1BN rats. Unlike bradykinin, cerebral arterial responses to acetylcholine were similar between FHH and FHH.1BN groups. These findings indicate decreased bradykinin bioavailability contributes to impaired cerebral arterial dilation in FHH rats. Overall, these data indicate an important role of aminopeptidase P in the impaired cerebral arterial function in FHH rat.

Regulation of human organic anion transporter 3 by peptide hormone bradykinin

Human organic anion transporter (hOAT) 3 belongs to a family of organic anion transporters that play critical roles in the body disposition of numerous clinically important drugs. In the current study, we examined the regulation of hOAT3 by peptide hormone bradykinin (BK) in COS-7 cells. BK (<or=500 nM) induced a concentration- and time-dependent stimulation of hOAT3 activity, kinetically revealed as an increased V(max). Such an increase in V(max) resulted from an increased cell surface expression without a change in total cell expression of the transporter. BK-induced stimulation of hOAT3 activity could be prevented by treating hOAT3-expressing cells with staurosporine, a general inhibitor for protein kinase C (PKC). To obtain further information on which PKC isoform mediates BK regulation of hOAT3 activity, cellular distribution of various PKC isoforms was examined in cells treated with BK. We showed that BK treatment resulted in a significant translocation of PKCdelta, PKCepsilon, and PKCzeta from cytosol to membrane. We further showed that BK treatment enhanced association of hOAT3 with PKCdelta, PKCepsilon, and PKCzeta and that isoform-specific inhibitor for PKCdelta, PKCepsilon, and PKCzeta reversed BK effect on hOAT3 activity. We therefore concluded that BK stimulated hOAT3 activity through activation of PKCdelta, PKCepsilon, and PKCzeta, which then led to the redistribution of hOAT3 from the intracellular compartments to the cell surface and to the up-regulation of hOAT3 activity.

The mechanism of the angiotensin-converting enzyme inhibitor quinapril is not related to bradykinin level in heart tissue

In order to examine the effect of the angiotensin-converting enzyme inhibitor (ACEi) quinapril, we performed a sensitive and specific radioimmunoassay (RIA) to quantify bradykinin, BK-(1-9), in heart and kidney tissues. The BK-(1-9) level was unaffected in the heart of sham and water-deprived rats treated for 2h with quinapril (10mg/kg), but was significantly higher in the kidneys in the two groups. In these conditions, circulating and tissue angiotensin II (Ang II) levels were significantly decreased by quinapril. Moreover, our results indicated that acute treatment with this dose of quinapril induced kinin-mediated effects which were not related to its action on bradykinin degradation in rat hearts.

Signal transduction pathways involved in kinin B(2) receptor-mediated vasodilation in the rat isolated perfused kidney

The signal transduction pathways involved in kinin B(2) receptor-related vasodilation were investigated in rat isolated perfused kidneys. During prostaglandin F(2alpha) or KCl-induced constriction, the vasodilator response to a selective B(2) receptor agonist, Tyr(Me)(8)bradykinin (Tyr(Me)(8)BK), was assessed. Tyr(Me)(8)BK produced a concentration- and endothelium-dependent relaxation that was decreased by about 30 - 40% after inhibition of nitric oxide (NO) synthase by N(G)-nitro-L-arginine (L-NOARG) or of cyclo-oxygenase by indomethacin; a greater decrease (about 40 - 50%) was observed after concomitant inhibition of the two pathways. High extracellular K(+) diminished Tyr(Me)(8)BK-induced relaxation by about 75% suggesting a major contribution of endothelium-derived hyperpolarization. The residual response was almost completely suppressed by NO synthase and cyclo-oxygenase inhibition. The K(+) channel inhibitors, tetrabutylammonium (non-specific) and charybdotoxin (specific for Ca(2+)-activated K(+) channel), suppressed Tyr(Me)(8)BK-induced relaxation resistant to L-NOARG and indomethacin. Inhibition of cytochrome P450 (clotrimazole or 7-ethoxyresorufin) decreased the NO/prostanoids-independent relaxation to Tyr(Me)(8)BK by more than 60%, while inhibition of the cannabinoid CB(1) receptor (SR 141716A) had only a moderate effect. Acetylcholine induced a concentration-dependent relaxation with characteristics nearly similar to the response to Tyr(Me)(8)BK. In contrast, the relaxation elicited by sodium nitroprusside was potentiated in the absence of NO (L-NOARG or removal of endothelium) but remained unchanged otherwise. These results indicate that the activation of kinin B(2) receptors in the rat isolated kidney elicits an endothelium-dependent vasorelaxation, mainly dependent on the activation of charybdotoxin-sensitive Ca(2+)-activated K(+) channels. In addition, cytochrome P450 derivatives appear to be involved.