Activation of the aryl hydrocarbon receptor by clozapine induces preadipocyte differentiation and contributes to endothelial dysfunction.

BACKGROUND: The superior therapeutic benefit of clozapine is often associated with metabolic disruptions as obesity, insulin resistance, tachycardia, higher blood pressure, and even hypertension. AIMS: These adverse vascular/ metabolic events under clozapine are similar to those caused by polycyclic aromatic hydrocarbons (PAHs), and clozapine shows structural similarity to well-known ligands of the aryl hydrocarbon receptor (AhR). Therefore, we speculated that the side effects caused by clozapine might rely on AhR signaling. METHODS: We examined clozapine-induced AhR activation by luciferase reporter assays in hepatoma HepG2 cells and we proved upregulation of the prototypical AhR target gene Cyp1A1 by realtime-PCR (RT-PCR) analysis and enzyme activity. Next we studied the physiological role of AhR in clozapine's effects on human preadipocyte differentiation and on vasodilatation by myography in wild-type and AhR-/- mice. RESULTS: In contrast to other antipsychotic drugs (APDs), clozapine triggered AhR activation and Cyp1A1 expression in HepG2 cells and adipocytes. Clozapine induced adipogenesis via AhR signaling. After PGF2α-induced constriction of mouse aortic rings, clozapine strongly reduced the maximal vasorelaxation under acetylcholine in rings from wild-type mice, but only slightly in rings from AhR-/- mice. The reduction was also prevented by pretreatment with the AhR antagonist CH-223191. CONCLUSION: Identification of clozapine as a ligand for the AhR opens new perspectives to explain common clozapine therapy-associated adverse effects at the molecular level.

Generation of two iPSC clones (MHHi021-A and MHHi021-B) from a patient with hypertrophic cardiomyopathy with p.Arg723Gly mutation in the MYH7 gene.

Hypertrophic cardiomyopathy (HCM) is the most common form of genetic heart disease and is characterized by abnormal thickening of the left ventricular wall and interventricular septum. Here we describe the generation of two induced pluripotent stem cell (iPSC) clones from a HCM patient, heterozygous for the p.Arg723Gly (c.2169C > G) mutation in the MYH7 gene. The generated iPSC clones may provide a useful resource for disease modelling to study the mechanisms underlying HCM pathogenesis in iPSC derived progenies, in particular cardiomyocytes.

Long-term effects of CCK-agonist and -antagonist on food intake and body weight in Zucker lean and obese rats.

The present study evaluates long-term effects of the CCK-agonist caerulein and the CCK-A antagonist loxiglumide in obese and lean Zucker rats. Caerulein and loxiglumide altered food intake neither in obese nor in lean rats. By as yet unknown mechanisms, however, weight increase was accelerated by loxiglumide and reduced by caerulein in obese and lean rats. Caerulein increased pancreatic weight only in lean but not in obese rats. Thus, obese rats show a resistance of pancreatic CCK-A receptors. The failure of CCK-agonist and -antagonist to alter food intake suggests that this CCK-resistance is not responsible for obesity in the genetically altered rats.

Cell volume changes modulate cholecystokinin- and carbachol-stimulated amylase release in isolated rat pancreatic acini.

BACKGROUND & AIMS: Changes in cell volume have been recently identified as modulators of cell function and gene expression. This study evaluated the regulation of exocrine secretion by pancreatic acini on the basis of changes in cell hydration. METHODS: Acini were exposed to hypotonicity or hypertonicity. The effects of corresponding changes in cell volume on various cell functions were analyzed. RESULTS: Hypertonicity and hypotonicity caused a stepwise cell shrinkage and swelling, respectively. Cell shrinkage decreased and cell swelling increased amylase secretion stimulated by cholecystokinin (CCK) and carbachol but not by secretin. Changes in cell volume did not alter basal or CCK-stimulated calcium concentrations or CCK-stimulated inositol triphosphate generation. The regulation of secretion by cell volume is not mediated via changes in CCK receptor binding or protein kinase C. The increase of amylase release caused by hypotonicity was completely inhibited by cytochalasin B, colchicine, and genistein. Hypotonicity as well as CCK caused activation of mitogen-activated protein kinases. CONCLUSIONS: Changes in cell volume regulate exocrine secretion of pancreatic acini. The effects were found only for secretagogues that act via the calcium/inositol-trisphosphate pathway. However, the mechanisms involved are located at luminal parts of the signal-transduction cascade and involve the cytoskeleton, protein phosphorylation, and activation of mitogen-activated protein kinases.

CCK-resistance in Zucker obese versus lean rats.

Obese Zucker rats are less sensitive to the satiety effect of CCK than lean litter mates. The present studies further characterised this CCK resistance. Subcutaneous injection of the CCK agonist caerulein dose-dependently decreased food intake in Zucker obese and lean rats whereas the CCK-B agonist gastrin-17 did not. Caerulein at 4 microg/kg, which resulted in CCK plasma bioactivity slightly above postprandial levels, decreased food intake in lean rats but not in obese rats. The decrease in food intake was also more marked at higher caerulein doses (20-100 microg/kg) in lean versus obese rats. In lean animals the satiety effects of the "near physiological" 4 microg/kg caerulein dose was abolished after blockade of vagal afferents with capsaicin, whereas the effects of higher caerulein doses were not. CCK-stimulated amylase secretion from pancreatic acini and binding capacity of 125I-labelled CCK-8 were decreased in obese versus lean rats. The CCK-A antagonist loxiglumide at 20 mg/kg, a dose which abolished the action of all caerulein doses on food intake, failed to alter the food intake either in obese or in lean rats when given without an agonist. The results suggest that the satiety effects of "near physiological" doses of caerulein in lean rats are mediated by vagal afferents whereas pharmacological doses act via non-vagal mechanisms. The differences in CCK's satiety effect between lean and obese rats may be due to differences in CCK-receptor binding and action at peripheral vagal sites. However, the failure of the CCK-A antagonist to increase food intake questions whether any of the effects of exogenous CCK are of physiological relevance.