Mohammed Bensaid

Rimonabant reduces obesity-associated hepatic steatosis and features of metabolic syndrome in obese zucker fa/fa rats

This study investigated the effects of rimonabant (SR141716), an antagonist of the cannabinoid receptor type 1 (CB1), on obesity‐associated hepatic steatosis and related features of metabolic syndrome: inflammation (elevated plasma levels of tumor necrosis factor alpha [TNFα]), dyslipidemia, and reduced plasma levels of adiponectin. We report that oral treatment of obese (fa/fa) rats with rimonabant (30 mg/kg) daily for 8 weeks abolished hepatic steatosis. This treatment reduced hepatomegaly, reduced elevation of plasma levels of enzyme markers of hepatic damage (alanine aminotransferase, gamma glutamyltransferase, and alkaline phosphatase) and decreased the high level of local hepatic TNFα currently associated with steatohepatitis. In parallel, treatment of obese (fa/fa) rats with rimonabant reduced the high plasma level of the proinflammatory cytokine TNFα and increased the reduced plasma level of the anti‐inflammatory hormone adiponectin. Finally, rimonabant treatment also improved dyslipidemia by both decreasing plasma levels of triglycerides, free fatty acids, and total cholesterol and increasing the HDLc/LDLc ratio. All the effects of rimonabant found in this study were not or only slightly observed in pair‐fed obese animals, highlighting the additional beneficial effects of treatment with rimonabant compared to diet. These results demonstrate that rimonabant plays a hepatoprotective role and suggest that this CB1 receptor antagonist potentially has clinical applications in the treatment of obesity‐associated liver diseases and related features of metabolic syndrome. (HEPATOLOGY 2007.)

Purification and Characterization of the Human SR 31747A-binding Protein A NUCLEAR MEMBRANE PROTEIN RELATED TO YEAST STEROL ISOMERASE

SR 31747A, defined as a sigma ligand, is a novel immunosuppressive agent that blocks proliferation of human and mouse lymphocytes. Using a radiolabeled chemical probe, we here purified a target of SR 31747A and called it SR 31747A-binding protein (SR-BP). Purified SR-BP retained its binding properties and migrated on SDS-polyacrylamide gel as a M r 28,000 protein. Cloning of the cDNA encoding human SR-BP shows an open reading frame for a 223-amino acid protein, which is homologous to the recently cloned sigma 1 receptor. Interestingly, the deduced amino acid sequence was found to be related to fungal C8-C7 sterol isomerase, encoded by the ERG2 gene. The ERG2 gene product has been identified recently as the molecular target of SR 31747A that mediates antiproliferative effects of the drug in yeast. Northern blot analysis of SR-BP gene expression revealed a single transcript of 2 kilobases which was widely expressed among organs, with the highest abundance in liver and the lowest abundance in brain. Subcellular localization analysis in various cells, using a specific monoclonal antibody raised against SR-BP, demonstrated that this protein was associated with the nuclear envelope. When studying the binding of SR 31747A on membranes from yeast expressing SR-BP, we found a pharmacological profile of sigma 1 receptors; binding was displaced by (+)-pentazocine, haloperidol, and (+)-SKF 10,047, with (+)-SKF 10,047 being a more potent competitor than (−)-SKF 10,047. Scatchard plot analysis revealed K d values of 7.1 nm and 0.15 nm for (+)-pentazocine and SR 31747A, respectively, indicating an affinity of SR-BP 50-fold higher for SR 31747A than for pentazocine. Additionally, we showed that pentazocine, a competitive inhibitor of SR 31747A binding, also prevents the immunosuppressive effect of SR 31747A. Taken together, these findings strongly suggest that SR-BP represents the molecular target for SR 31747A in mammalian tissues, which could be critical for T cell proliferation.

Expression and presence of septal neurokinin-2 receptors controlling hippocampal acetylcholine release during sensory stimulation in rat

We examined the expression and presence of NK2 receptors in the septal area of rat brain, and investigated their functional role in the regulation of the septohippocampal cholinergic system. Using reverse transcription‐polymerase chain reaction (RT‐PCR) analysis, we showed the presence of NK2 receptor mRNA expression in the septal area, and detected septal NK2 binding sites by using a fluorescent‐tagged neurokinin A (NKA) derivative. In vivo microdialysis was employed to explore the functional role of NK2 receptors in the release of hippocampal acetylcholine evoked by tactile stimulation in freely moving rats. Two sessions of stroking of the neck and back of the rat for 30 min, at 90 min intervals, produced a marked and reproducible increase in hippocampal acetylcholine release. This effect was dose‐dependently prevented by intraperitoneal administration of the two selective non‐peptide tachykinin NK2 receptor antagonists SR144190 (0.03–0.3 mg/kg, i.p.) and SR48968 (0.3 and 1 mg/kg, i.p.), but not by the inactive enantiomer of SR48968 (SR48965, 1 mg/kg) nor by the two non‐peptide NK1 receptor antagonists SR140333 (3 mg/kg, i.p.) and GR205171 (1 mg/kg, i.p.). Furthermore, the intraseptal application of SR144190 (10–8m) reduced the sensory response. Finally, intraseptal perfusion of neurokinin A (0.01–10 μm) in anaesthetized rats produced a concentration‐dependent increase in hippocampal acetylcholine release. The response to neurokinin A (0.1 μm) was prevented by SR144190 (0.03–0.3 mg/kg, i.p.) and SR48968 (0.3–1 mg/kg, i.p.). In conclusion, this study provides direct evidence for the role of endogenous NKA/substance P, through the activation of NK2 receptors, in regulating the septohippocampal cholinergic function.

The rat β3‐adrenergic receptor gene contains an intron

We report that the rat β3‐adrenergic receptor (β3‐AR) gene has an intron. The intron starts with an in‐frame stop codon with the result that unspliced transcripts will encode a C‐terminal truncated protein. The reported protein sequences of mouse and human β3‐AR were both deduced from genomic DNA sequences. Given the heterogeneity at the C‐termini of the otherwise highly similar rat, mouse and human sequences, we discuss the intriguing possibility that the β3‐AR gene of the latter two species also contain an intron near the extremity of the open reading frame. A β‐adrenergic receptor (β‐AR) cDNA we have cloned from rat colonic tissue which has a sequence essentially identical to that previously reported for the rat adipose β3‐AR cDNA [(1991) J. Chem. 266, 24053], encodes the spliced version of the β3‐AR.

Expression of tachykinin NK2 receptor mRNA in human brain.

Tachykinin NK2 receptors have been suggested to play an important role in the central nervous system. This study, using reverse transcription-polymerase chain reaction revealed a detectable expression of NK2 receptor mRNA in various human brain regions, including the caudate nucleus, the putamen, the hippocampus, the substantia nigra and the cerebral cortex. The distribution of NK2 receptor expression in the cortex revealed a major expression in frontal and temporal cortex compared to occipital and parietal areas. These results provide a molecular basis for considering a role of NK2 receptors in human pathophysiology.