Abstract 3618: No Increase in the In Vitro Production of Aldosterone or the Expression of CYP11B2 with the CETP Modulator Dalcetrapib (RO4607381/JTT-705), in Contrast with Torcetrapib
Background: Contrary to dalcetrapib (RO4607381/JTT-705), torcetrapib (TOR), a cholesteryl ester transfer protein inhibitor, has been shown to increase blood pressure in clinical and preclinical studies, and expression of some RAAS-related genes in rat adrenal tissue. We investigated the effects of TOR and dalcetrapib on aldosterone secretion and on expression of the aldosterone synthase gene CYP11B2 in the human adrenocortical carcinoma cell line H295R.
Methods: Aldosterone and pregnenolone, an aldosterone precursor, were measured by direct radioimmunoassay in media of H295R cells exposed to 0.1% DMSO (control), TOR (0.001–2.5 μM) or dalcetrapib (1–10 μM). Quantitative real-time PCR was used to measure CYP11B2 mRNA. Angiotensin II (Ang II) 100 nM was used as positive control
Results: TOR concentration-dependently increased 24-hour aldosterone secretion (EC50: 10 nM) to a maximum of 396±87.8% of control (mean±SEM; n=3) (Ang II: 392.1±14.2%, n=3). TOR increased CYP11B2 mRNA 11.1 fold (SE=1.99) versus control and maintained this effect over 24 hours. In the presence of trilostane, an inhibitor of 3β-HSD, pregnenolone production was increased to 287.1±30.6 % and 276±15.4 % of control by TOR and Ang II, respectively, suggesting also an upstream TOR effect on steroidogenesis. The addition of 25-OH cholesterol, a membrane permeant precursor of steroidogenesis, further increased the amount of aldosterone secreted in the presence of TOR. In contrast to Ang II, TOR had no acute effect on cytosolic [Ca2+], as measured with the fluorescent probe, fura-2. None of the TOR-induced changes were observed with dalcetrapib up to 10 μM.
Conclusion: These studies provide evidence that TOR is a potent steroidogenic agent on adrenal glomerulosa cells. These effects, with differences from Ang II, were compound specific, unrelated to CETP inhibition, and not observed with dalcetrapib. Additional investigations are required to understand the relationship between the effects of TOR on RAAS and its pharmacochemical properties.