Clozapine-induced myocarditis: role of catecholamines in a murine model.

Clozapine, an atypical antipsychotic, is very effective in the treatment of resistant schizophrenia. However, cardiotoxicity of clozapine, particularly in young patients, has raised concerns about its safety. Increased catecholamines have been postulated to trigger an inflammatory response resulting in myocarditis, dilated cardiomyopathy, and death, although this has not yet been thoroughly studied. Here, we used the mouse to study whether clozapine administration could cause adverse myocarditis associated with an increase in catecholamines. Male Balb/C mice, age ~6 weeks, were administered 5, 10 or 25 mg/kg clozapine daily for 7 and 14 days; one group was administered 25 mg/kg clozapine plus 2 mg/kg propranolol for 14 days. Saline-treated mice served as controls. Heart sections were stained with hematoxylin and eosin for histopathological examination. Plasma catecholamines were measured with HPLC. Myocardial TNF-alpha concentrations were determined by ELISA. Histopathology of clozapine-treated mice showed a significant dose-related increase in myocardial inflammation that correlated with plasma catecholamine levels and release of TNF-alpha. Propranolol significantly attenuated these effects. A hypercatecholaminergic state induced by clozapine could explain the occurrence of myocarditis in some patients. Our data suggest that a beta-adrenergic blocking agent may be effective in reducing the incidence and severity of clozapine-induced myocarditis.

Evidence of increased flux to n-6 docosapentaenoic acid in phospholipids of pancreas from cftr-/- knockout mice.

An association has been reported between alterations in fatty acid metabolism and cystic fibrosis (CF). We hypothesized that these alterations are specific for a particular lipid component(s) and are the result of a specific metabolic defect. The different lipid classes were examined for fatty acid changes by using pancreatic homogenates and primary cultures of pancreatic acini from cftr(-/-) (CF) and wild-type mice. Lipid classes and phospholipids were separated by aminopropyl column chromatography and high-performance liquid chromatography, and fatty acid methyl esters were analyzed. The results indicate that in CF mice (1) linoleate was decreased in phospholipids but not in neutral lipids; (2) there was an increase in dihomo-gamma-linolenate and in docosapentaenoate, the terminal fatty acid of the n-6 pathway, in total lipids and total phospholipids, but not in the neutral lipid class; and (3) the docosapentaenoate (n-6)/docosahexaenoate (n-3) ratio was significantly elevated in neutral phospholipids. This suggests an enhanced flux through the n-6 pathway beyond arachidonate. This study provides a more in-depth understanding of the fatty acid alterations found in CF, as reflected by the cftr(-/-) mouse model.

Intracellular accumulation of mercury enhances P450 CYP1A1 expression and Cl- currents in cultured shark rectal gland cells.

The effects of acute and subchronic exposure to mercury on the Cl- current (ICl) were investigated in cultured shark rectal gland (SRG) cells. The effects of intracellular accumulation of mercury on cytochrome P450 (P450) were also assessed. Bath perfusion of a cocktail solution containing forskolin, 1-isobutyl-3-methylxanthine, and 8-bromoadenosine monophosphate enhanced ICl. Addition of 10 microM HgCl2 significantly inhibited the cAMP-activated ICl (p < 0.05, n = 11). Intracellular dialysis with ATP gamma S did not prevent the inhibitory effect of mercury on ICl. In contrast, incubation of SRG cells with 10 microM HgCl2 for 48 hrs markedly increased ICl (p < 0.01, n = 12). Dephosphorylation of the channel by intracellular dialysis with phosphatase I and II abolished the mercury-incubated increase in ICl. The P450-mediated metabolite of arachidonic acid, 11,12-epoxyeicosatrienoic acid (11,12-EET), significantly increased ICl. However, application of 11,12-dihydroxyeicosatrienoic acid (11,12-DHT) did not alter ICl. Mercury incubation for 48 hrs did not alter the protein expression of Cl- channels, but caused an induction of CYP1A1 in cultured SRG cells. In addition, co-incubation of SRG cells with mercury and the P450 inhibitor clotrimazole prevented the mercury-incubated increase in ICl. Our results demonstrate that acute and subchronic application of mercury has opposing effects on ICl in cultured SRG cells. The acute effect of mercury on ICl may result from mercury blockade of Cl- channels. The subchronic effect of mercury on ICl may be due to an induction of P450 CYP1A1 and its mediated metabolites, but not due to an over-expression of Cl- channels.