Mechanisms underlying off-target effects of the cholesteryl ester transfer protein inhibitor torcetrapib involve L-type calcium channels

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ObjectiveThe increased mortality observed with the cholesteryl ester transfer protein inhibitor torcetrapib is partly due to increased aldosterone production and blood pressure. The mechanisms underlying these effects were investigated.MethodsCytochrome P450 subunit 11B2 (aldosterone synthase), extracellular signal-regulated kinase (p44/42) and voltage-gated Ca2+channel alpha subunit mRNA profiling, aldosterone production, cytosolic calcium and RNA interference were assessed in adrenocarcinoma human cells (H295R). Telemetry was conducted in spontaneously hypertensive rats.ResultsTorcetrapib and angiotensin II (Ang II) but not dalcetrapib (a structurally different cholesteryl ester transfer protein inhibitor) elevated both cytochrome P450 subunit 11B2 mRNA and aldosterone production in H295R cells at 6 h. At days 1–5, torcetrapib produced a sustained increase of cytochrome P450 subunit 11B2 mRNA, unlike Ang II. Although torcetrapib and Ang II potentiated the effect of 25-OH cholesterol and raised pregnenolone levels, torcetrapib increased neither cytosolic Ca2+ at 5 min nor extracellular signal-regulated kinase1/2 phosphorylation, suggesting initially divergent pathways. Unlike Ang II, torcetrapib steroidogenesis was not affected by Ang II type 1 receptor antagonism or voltage-gated T-type Ca2+ channel antagonism, but was blocked by several L-type Ca2+channel antagonists. In unbiased genome-wide screening, Ang II and torcetrapib modulated an overlapping but distinct set of genes in H295R cells. Torcetrapib, but not Ang II, upregulated mRNA levels of the L-type Ca2+ channel alpha 1C subunit. In spontaneously hypertensive rat, torcetrapib had a potent hypertensive effect mediated by the L-type Ca2+ channel.ConclusionThe unique steroidogenic and hypertensive side effects of torcetrapib may be linked and involve voltage-gated L-type Ca2+ channels. Structurally unrelated cholesteryl ester transfer protein inhibitors such as dalcetrapib do not share this effect.

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