Angiotensin-(1-7): Pharmacological properties and pharmacotherapeutic perspectives

Therapeutic modulation of the renin-angiotensin system is not complete without taking into consideration the beneficial effects of angiotensin-(1-7) in cardiovascular pathology. Various pharmacological pathways are already exploited to involve this heptapeptide in therapy as both inhibitors of angiotensin-converting enzyme and angiotensin II type 1 receptor blockers increase its levels. These drugs and administered angiotensin-(1-7) elicit various common effects, and some effects of the drugs are partially mediated by angiotensin-(1-7). The pharmacodynamic profile of angiotensin-(1-7) is rather complex, and in vitro and in vivo studies demonstrated a wide palette of effects for angiotensin-(1-7), some of them potentially beneficial for cardiovascular disease. Using various animal models to study cardiovascular physiology and disease it was shown that angiotensin-(1-7) has antihypertensive, antihypertrophic, antifibrotic and antithrombotic properties, all properties that may prove beneficial in a clinical setting. We also observed a novel action of angiotensin-(1-7), namely its capacity to stimulate the proliferation of endothelial progenitor cells. Access of angiotensin-(1-7) to the clinic, however, is restricted due to its unfavorable pharmacokinetic properties. In order to benefit of the therapeutic potential of angiotensin-(1-7) it is crucial to increase its half-life, either by using more stable analogues, which are now under development, or specific delivery methods. We here review the pharmacological characteristics and therapeutic potential of angiotensin-(l-7), implementing the experimental strategies taken to exploit the pharmacological mechanism of this heptapeptide in a clinical setting, and present our contribution to this field of research. (C) 2008 Elsevier B.V. All rights reserved

Bradykinin Protects Against Oxidative Stress-Induced Endothelial Cell Senescence

Premature aging (senescence) of endothelial cells might play an important role in the development and progression of hypertension and atherosclerosis. We hypothesized that bradykinin, a hormone that mediates vasoprotective effects of angiotensin-converting enzyme inhibitors, protects endothelial cells from oxidative stress-induced senescence. Bradykinin treatment (0.001 to 1 nmol/L) dose-dependently decreased senescence induced by 25 mu mol/L of H2O2 in cultured bovine aortic endothelial cells, as witnessed by a complete inhibition of increased senescent cell numbers and a 34% reduction of the levels of the senescence-associated cell cycle protein p21. Because H2O2 induces senescence through superoxide-induced DNA damage, single-cell DNA damage was measured by comet assay. Bradykinin reduced DNA damage to control levels. The protective effect of bradykinin also resulted in a significant increase in the migration of H2O2-treated bovine aorta endothelial cells in an in vitro endothelial injury model, or "scratch" assay. The protective effect of bradykinin was abolished by the bradykinin B2 receptor antagonist HOE-140 and the NO production inhibitor N-omega-methyl-L-arginine acetate salt. Therefore, we conclude that bradykinin protects endothelial cells from superoxide-induced senescence through bradykinin B2 receptor-and NO-mediated inhibition of DNA damage. (Hypertension. 2009; 53[part 2]: 417-422.

Human OATP1B1, OATP1B3 and OATP1A2 can mediate the in vivo uptake and clearance of docetaxel

Organic anion transporting polypeptides (human: OATPs and mouse: Oatps) are uptake transporters with important roles in drug pharmacokinetics and toxicity. We aimed to study the in vivo impact of mouse and human OATP1A/1B transporters on docetaxel plasma clearance and liver and intestinal uptake. Docetaxel was administered to Oatp1a/1b knockout and liver-specific humanized OATP1B1, OATP1B3 and OATP1A2 transgenic mice. Experiments were conducted with a low polysorbate 80 (2.8%) formulation, as 8% polysorbate somewhat inhibited docetaxel plasma clearance after intravenous administration. After intravenous administration (10 mg/kg), Oatp1a/1b knockout mice had an approximately threefold higher plasma area under the curve (AUC). Impaired liver uptake was evident from the significantly reduced (approximately threefold) liver-to-plasma AUC ratios. Absence of mouse Oatp1a/1b transporters did not affect the intestinal absorption of orally administered docetaxel (10 mg/kg), while the systemic exposure of docetaxel was again substantially increased owing to impaired liver uptake. Most importantly, liver-specific expression of each of the human OATP1B1, OATP1B3 and OATP1A2 transporters provided a nearly complete rescue of the increased plasma levels of docetaxel in Oatp1a/1b-null mice after intravenous administration. Our data show that one or more of the mouse Oatp1a/1b transporters and each of the human OATP1A/1B transporters can mediate docetaxel uptake in vivo. This might be clinically relevant for OATP1A/1B-mediated tumor uptake of docetaxel and for docetaxel clearance in patients in whom the transport activity of OATP1A/1B transporters is reduced owing to genetic variation or pharmacological inhibition, leading to potentially altered toxicity and therapeutic efficacy of this drug

Organic anion-transporting polypeptide 2B1 knockout and humanized mice; insights into the handling of bilirubin and drugs

Organic anion transporting polypeptide 2B1 (OATP2B1/SLCO2B1) facilitates uptake transport of structurally diverse endogenous and exogenous compounds. To investigate the roles of OATP2B1 in physiology and pharmacology, we established and characterized Oatp2b1 knockout (single Slco2b1-/- and combination Slco1a/1b/2b1-/-) and humanized hepatic and intestinal OATP2B1 transgenic mouse models. While viable and fertile, these strains exhibited a modestly increased body weight. In males, unconjugated bilirubin levels were markedly reduced in Slco2b1-/- compared to wild-type mice, whereas bilirubin monoglucuronide levels were modestly increased in Slco1a/1b/2b1-/- compared to Slco1a/1b-/- mice. Single Slco2b1-/- mice showed no significant changes in oral pharmacokinetics of several tested drugs. However, markedly higher or lower plasma exposure of pravastatin and the erlotinib metabolite OSI-420, respectively, were found in Slco1a/1b/2b1-/- compared to Slco1a/1b-/- mice, while oral rosuvastatin and fluvastatin behaved similarly between the strains. In males, humanized OATP2B1 strains showed lower conjugated and unconjugated bilirubin levels than control Slco1a/1b/2b1-deficient mice. Moreover, hepatic expression of human OATP2B1 partially or completely rescued the impaired hepatic uptake of OSI-420, rosuvastatin, pravastatin, and fluvastatin in Slco1a/1b/2b1-/- mice, establishing an important role in hepatic uptake. Expression of human OATP2B1 in the intestine was basolateral and markedly reduced the oral availability of rosuvastatin and pravastatin, but not of OSI-420 and fluvastatin. Neither lack of Oatp2b1, nor overexpression of human OATP2B1 had any effect on fexofenadine oral pharmacokinetics. While these mouse models still have limitations for human translation, with additional work we expect they will provide powerful tools to further understand the physiological and pharmacological roles of OATP2B1

Organic Anion-Transporting Polypeptides 1a/1b Control the Hepatic Uptake of Pravastatin in Mice

Organic anion-transporting polypeptides (OATPs) mediate the hepatic uptake of many drugs. Hepatic uptake is crucial for the therapeutic effect of pravastatin, a cholesterol-lowering drug and OATP1A/1B substrate. We aimed to gain empirical insight into the relationship between OATPs and pravastatin pharmacokinetics and toxicity. We therefore compared the distribution and toxicity of pravastatin in wild-type and Oatp1a/1b-null mice. Intestinal absorption of pravastatin was not affected by Oatp1a/1b absence, but systemic plasma exposure (AUC) increased up to 30-fold after oral bolus administration. This increased plasma exposure resulted from reduced hepatic uptake, as evident from 10 to 100-fold lower liver-to-plasma concentration ratios. However, the reductions in liver exposure were far smaller (<2-fold) than the increases in plasma exposure. Reduced pravastatin liver uptake in Oatp1a/1b-null mice was more obvious shortly after intravenous administration, with 8-fold lower biliary pravastatin excretion. Although mice chronically exposed to pravastatin for 60 days evinced little muscular toxicity, Oatp1a/1b-null mice displayed 10-fold higher plasma concentrations and 8-fold lower liver concentrations than wild-type mice. Thus, Oatp1a/1b transporters importantly control the hepatic uptake of pravastatin. Activity-reducing human OATP1B polymorphisms may therefore both reduce pravastatin therapeutic efficacy in the liver and increase systemic toxicity risks, thus compromising its therapeutic index in a two-edged way