Losartan Carboxylic Acid (EXP-3174)

In vitro, losartan competes with the binding of angiotensin II to AT1 receptors; the concentration that inhibits 50% of the binding of angiotensin II (IC50) is 20 nmol/L^[2]. Losartan increases AMPK phosphorylation in a time- and dose-dependent manner in VSMCs. It also increases ACC phosphorylation, a major downstream target protein in the AMPK signaling cascade, and LKB1 phosphorylation, which is an upstream kinase of AMPK. Losartan increases p53 and p21 expression in a time-dependent manner, whereas the levels of p27 are not changed. Losartan suppresses Ang II-induced Rb phosphorylation, as well as cyclin D and cyclin E expression which are required for cell cycle progression. The mechanism of growth suppression by losartan is therefore G0/G1 cell cycle arrest which is reversed by AMPK inhibition, such as compound C or AMPK siRNA, but not by apoptosis^[3].

Cells were treated with Ang II or 15% FBS in the presence or absence of indicated concentration of losartan for 48 hrs. Cell proliferation was determined by the MTT assay.

Losartan has a major active metabolite, EXP 3174. Administered intravenously, EXP3174 is 10 to 20 times more potent than losartan and has a longer duration of action than losartan. However, the oral bioavailability of EXP 3174 is very low. Losartan has a bioavailability of about 33%, the half-life averages 2 h (6-9 hours), and the rate of protein binding is 98.7% when dosed at 50-100 mg/d^[2]. Treatment with losartan ameliorates the loss in the number and function of endothelial progenitor cells (EPCs) in hypertensive rats^[4].