Activation of liver X receptors inhibits pancreatic islet beta cell proliferation through cell cycle arrest.

AIMS/HYPOTHESIS: Liver X receptors (LXRs) are important transcriptional regulators of lipid homeostasis and proliferation in several cell types. However, the roles of LXRs in pancreatic beta cells have not been fully established. The aim of this study was to investigate the effects of LXRs on pancreatic beta cell proliferation. METHODS: Gene expression was analysed using real-time RT-PCR. Transient transfection and reporter gene assays were used to determine the transcriptional activity of LXRs in pancreatic beta cells. Cell viability and proliferation were analysed using 3-(4,5-dimethylthiazol-2-yl)-2,5-diphenyltetrazolium bromide (MTT), DNA fluorometric, BrdU labelling and [(3)H]thymidine incorporation assays. Cell cycle distribution was investigated by flow cytometry analysis. Adenovirus-based RNA interference was used to knockdown LXRalpha, LXRbeta and p27 in MIN6 cells and mouse islets. RESULTS: We found that both Lxralpha (also known as Nr1h3) and Lxrbeta (also known as Nr1h2) were expressed and transactivated the LXR response element in HIT-T15 and MIN6 cells. Activation of LXRs dose-dependently inhibited pancreatic beta cell viability and proliferation. This was accompanied by beta cell cycle arrest at the G1 phase. Furthermore, LXR activation increased levels of the p27 protein by inhibiting its degradation. Knockdown of p27 reversed these effects of LXR activation on growth inhibition and cell cycle arrest. CONCLUSIONS/INTERPRETATION: Our observations indicate that LXR activation inhibits pancreatic beta cell proliferation through cell cycle arrest. A well-known regulator of pancreatic beta cell cycle progression, p27, is upregulated and mediates the effects of LXRs on growth inhibition in beta cells. These observations suggest the involvement of aberrant activation of LXR in beta cell mass inadequacy, which is an important step in the development of type 2 diabetes.

Prostaglandin E2 regulates Foxo activity via the Akt pathway: implications for pancreatic islet beta cell dysfunction.

AIMS/HYPOTHESIS: Prostaglandin E(2) (PGE(2)) is a well-recognised inhibitor of glucose-stimulated insulin secretion (GSIS). The aim of this study was to investigate the signalling pathway of PGE(2) in beta cell function regulation in HIT-T15 cells and isolated rat islets. MATERIALS AND METHODS: mRNA levels of the prostaglandin E receptor 3 (Ptger3) were measured by real-time PCR. Western blot analysis was used to detect changes in the levels of PTGER3, phosphorylated and total Akt, phosphorylated and total forkhead box 'Other' (Foxo). Transient transfection and reporter assays were used to measure Foxo transcriptional activity. The biological significance of PGE(2) in beta cell function was analysed using MTT, flow cytometry and GSIS assays. RESULTS: We found that treating HIT-T15 cells with exogenous PGE(2) stimulated Ptger3 gene expression specifically, and diminished cAMP generation. These were accompanied by the downregulation of Akt and Foxo phosphorylation in HIT-T15 cells and isolated rat islets. Moreover, PGE(2) upregulated basal and partially reversed constitutively active Akt-inactivated Foxo transcriptional activity. Furthermore, GSIS was impaired in PGE(2)-treated HIT-T15 cells and isolated islets. However, the dosage used in the above experiments did not affect beta cell viability and apoptosis. In addition, insulin-like growth factor 1 (IGF-1) pretreatment reversed the effects of PGE(2), and wortmannin treatment abolished the preventive effects of IGF-1. CONCLUSIONS/INTERPRETATION: Our observations strongly suggest that PGE(2) can induce pancreatic beta cell dysfunction through the induction of Ptger3 gene expression and inhibition of Akt/Foxo phosphorylation without impacting beta cell viability. These results shed light on the mechanisms of PGE(2) actions in pancreatic beta cell dysfunction.

Incidence of deep vein thrombosis after laparoscopic vs minilaparotomy cholecystectomy.

OBJECTIVES: To determine the frequency of deep vein thrombosis (DVT) associated with minimally invasive cholecystectomy and to determine, using minilaparotomy cholecystectomy as a control operation, the influence of the laparoscopic pneumoperitoneum on DVT formation. DESIGN: Prospective nonrandomized control trial. SETTING: Tertiary care university hospital. PATIENTS: One hundred consecutive patients intended to undergo either laparoscopic cholecystectomy (59 patients) or minilaparotomy cholecystectomy (41 patients) with either of 2 surgeons were prospectively enrolled between April 1996 and April 1997. The minilaparotomy cholecystectomy group served as controls to isolate the effect of the pneumoperitoneum. Patient details, operative details, and any thromboembolic or bleeding complications were recorded. The same thromboprophylaxis regimen was prescribed for each group; namely, preoperative and postoperative subcutaneous low-molecular-weight heparin (LMWH), graduated compression stockings, and intraoperative intermittent calf compression. INTERVENTION: Minimally invasive cholecystectomy. MAIN OUTCOME MEASURE: Frequency of DVT. Bilateral lower limb venous color duplex scanning was used to detect DVT. Scans were performed on 3 occasions: (1) preoperatively on admission to hospital, (2) on the first postoperative day, and (3) between 2 and 4 weeks postoperatively. RESULTS: Three patients in the laparoscopic group and 2 patients in the minilaparotomy group underwent conversion to conventional open cholecystectomy. There were no significant differences between patients in the 2 groups for age, sex, body mass index, preoperative white blood cell count, platelet count, prothrombin time, or activated partial thromboplastin time. There were no significant differences between the 2 groups for elective vs emergency operations, public hospital vs private hospital admissions, or consultant vs resident surgeon. Macroscopic gallbladder pathology grades for both groups were not significantly different, and there was no significant difference in the duration of postoperative hospital stay. Operative cholangiography was performed in a significantly larger proportion of laparoscopic cases (86% vs 66% in the minilaparotomy group; chi(2) test, P=.002), and the duration of anesthesia was significantly longer for the laparoscopic operation (118 minutes vs 98 minutes; t test, P=.05). Ninety-seven patients received preoperative LMWH and all patients received graduated compression stockings, intraoperative intermittent calf compression, and postoperative LMWH. Two of the 100 patients had postoperative DVT, 1 after laparoscopic cholecystectomy and 1 after minilaparotomy cholecystectomy. Both DVTs were detected by duplex examination on the first postoperative day. The DVT found after laparoscopic cholecystectomy was in 1 of the 3 patients who did not receive preoperative LMWH. There were no DVTs in any of the 40 patients who had an additional duplex scan between 2 and 4 weeks after operation. CONCLUSIONS: Despite the theoretical risk of thromboembolic disease due to use of the laparoscopic pneumoperitoneum, the frequency of DVT after either laparoscopic cholecystectomy or minilaparotomy cholecystectomy is low if adequate thromboprophylaxis is provided.

Sustained inhibition of acetylcholinesterase activity does not disrupt early geniculocortical ingrowth to developing rat visual cortex.

Esterase activity of endogenous transiently expressed acetylcholinesterase was locally suppressed in visual cortex of infant rats for 2-5 days by the irreversible inhibitor phospholine iodide, delivered from Elvax implants. Tissue processed for anterograde movement of the carbocyanine dye DiI or anterograde transneuronal transport of wheat germ agglutinin-horseradish peroxidase revealed normal geniculocortical growth into layer IV of visual cortex. These results suggest that the catalytic activity of transiently expressed acetylcholinesterase may play little, if any, role in early development of thalamocortical systems.