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

Objective: The 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.

Methods: Cytochrome P450 subunit 11B2 (aldosterone synthase), extracellular signal-regulated kinase (p44/42) and voltage-gated Cachannel alpha subunit mRNA profiling, aldosterone production, cytosolic calcium and RNA interference were assessed in adrenocarcinoma human cells (H295R).

Safety and tolerability of dalcetrapib.

Efficacy and safety data for dalcetrapib (RO4607381/JTT-705) are presented, following a report of increased mortality and cardiac events with another cholesteryl ester transfer protein inhibitor, torcetrapib, associated with off-target adverse effects (hypertension and the activation of the renin-angiotensin-aldosterone system). The efficacy and clinical safety of dalcetrapib 300, 600, and 900 mg or placebo were assessed (n = 838) in 4 pooled 4-week phase IIa trials (1 monotherapy, n = 193; 3 statin combination, n = 353) and 1 12-week phase IIb trial (with pravastatin, n = 292). Nonclinical safety, assessed by the induction of aldosterone production and aldosterone synthase (cytochrome P450 11B2) messenger ribonucleic acid, was measured in human adrenocarcinoma (H295R) cells exposed to dalcetrapib or torcetrapib.

c-Fos mediates angiotensin II-induced aldosterone production and protein synthesis in bovine adrenal glomerulosa cells.

Angiotensin II (AngII), potassium ion, and ACTH are the main factors controlling aldosterone biosynthesis in adrenal glomerulosa cells. AP-1 response elements for the immediate early gene products, c-Fos and c-Jun, have been identified, among others, in the promoter of the steroidogenic acute regulatory (StAR) protein gene, whose expression is acutely regulated by activators of aldosterone production. In bovine glomerulosa cells, AngII treatment led to a rapid and transient increase in c-fos mRNA expression, c-Fos protein expression, and c-Fos phosphorylation.

Angiotensin II-induced mitogen-activated protein kinase phosphatase-1 expression in bovine adrenal glomerulosa cells: implications in mineralocorticoid biosynthesis.

Angiotensin II (AngII) stimulates aldosterone biosynthesis in the zona glomerulosa of the adrenal cortex. AngII also triggers the MAPK pathways (ERK1/2 and p38). Because ERK1/2 phosphorylation is a transient process, phosphatases could play a crucial role in the acute steroidogenic response.

A novel mutation in the steroidogenic acute regulatory protein gene promoter leading to reduced promoter activity.

We have identified a novel cytosine/thymidine polymorphism of the human steroidogenic acute regulatory (StAR) gene promoter located 3 bp downstream of the steroidogenic factor-1 (SF-1)-binding site and 9 bp upstream of the TATA box (ATTTAAG). Carriers of this mutation have a high prevalence of primary aldosteronism. In transfection experiments, basal StAR promoter activity was unaltered by the mutation in murine Y-1 cells and human H295R cells.

Chicken ovalbumin upstream promoter-transcription factor is a negative regulator of steroidogenesis in bovine adrenal glomerulosa cells.

The octapeptide hormone, angiotensin II (AngII) and ACTH stimulate mineralocorticoid biosynthesis in the zona glomerulosa of the adrenal cortex in part by promoting the transcription of the gene coding for the steroidogenic acute regulatory (StAR) protein. We have examined whether chicken ovalbumin upstream promoter-transcription factor (COUP-TF), a member of the orphan nuclear receptor family of transcription factors, is involved in this transcriptional regulation. We analyzed COUP-TF and StAR mRNA and protein levels in bovine adrenal glomerulosa cells in primary culture.

The control by angiotensin II of cholesterol supply for aldosterone biosynthesis.

In the adrenal glomerulosa cell, aldosterone is synthesized from cholesterol, which is supplied to the cell and stored under the form of cholesterol esters, then hydrolyzed to be transferred to the mitochondrial outer membrane and finally transported to the inner membrane where the P450 side-chain cleavage enzyme will convert it to pregnenolone. Angiotensin II (AngII), one of the major physiological regulators of mineralocorticoid synthesis, appears to affect most of the steps along this cascade and thus to exert a powerful control over the use of cholesterol for aldosterone production.

Angiotensin II activates cholesterol ester hydrolase in bovine adrenal glomerulosa cells through phosphorylation mediated by p42/p44 mitogen-activated protein kinase.

In adrenal glomerulosa cells, the stimulation of aldosterone biosynthesis by angiotensin II (Ang II) occurs via activation of the Ca2+ messenger system, increased expression of the steroidogenic acute regulatory protein, and enhanced transfer of cholesterol to the inner mitochondrial membrane. We examined here whether Ang II affects the activity of cholesterol ester hydrolase (CEH), also named hormone-sensitive lipase, the enzyme recruiting cholesterol from intracellular pools, in bovine adrenal glomerulosa cells. In bovine adrenal tissue, CEH activity was detected with characteristics similar to those reported in other tissues (Michaelis constant = 46.

Expression and modulation of steroidogenic acute regulatory protein messenger ribonucleic acid in rat cardiocytes and after myocardial infarction.

We examined whether the mRNA for steroidogenic acute regulatory (StAR) protein, a crucial factor in the rate-limiting step of aldosterone biosynthesis, is expressed and regulated in rat heart. We performed quantitative RT-PCR for StAR mRNA in an in vitro and an in vivo model: purified rat neonatal cardiomyocytes in primary culture and myocardial infarction (MI) in the rat. StAR mRNA was expressed in cultured cardiomyocytes, and angiotensin II (10 nM) increased it in a time-dependent fashion (132 +/- 2.

Cytosolic calcium oscillations in signal transduction pathways.

The oscillatory nature of the intracellular calcium signal has been recognized as soon as the methodological developments allowed us to record calcium fluctuations at the single cell level. While the principal mechanisms responsible for the generation of these oscillations have been partially resolved, more attention has been recently focused on signal decoding and more particularly on the role of cell structure organization in transducing this signal to the molecular targets of the calcium messenger.

Repression of DAX-1 and induction of SF-1 expression. Two mechanisms contributing to the activation of aldosterone biosynthesis in adrenal glomerulosa cells.

Angiotensin II (Ang II) and adrenocorticotropic hormone stimulate aldosterone biosynthesis in the zona glomerulosa of the adrenal cortex through induction of the expression of the steroidogenic acute regulatory (StAR) protein, which promotes intramitochondrial cholesterol transfer. To understand the mechanism of this induction of the StAR protein, we have examined the effect of Ang II and forskolin, a mimicker of adrenocorticotropic hormone action, on two transcription factors known to modulate StAR gene expression in opposite ways, DAX-1 and SF-1, in bovine adrenal glomerulosa cells in primary culture. Ang II markedly inhibited DAX-1 protein expression in a time- and concentration-dependent manner (to 38.

Regulation of cholesterol supply for mineralocorticoid biosynthesis.

In addition to intracellular cholesterol synthesis, plasma low- and high-density lipoproteins (LDL and HDL, respectively) are the major potential sources of a cholesterol precursor for steroid synthesis in all steroidogenic tissues. LDL- and HDL-cholesterol are taken up by cells through entirely distinct mechanisms. In the case of aldosterone production in the zona glomerulosa of the adrenal cortex, it has been assumed in the past that LDL is the major supplier of cholesterol.