Aims/hypothesis We have previously described a strong correlation between pyruvate cycling and insulin secretion. We have also demonstrated a particularly important role for a pyruvate-isocitrate cycling pathway involving the mitochondrial citrate/isocitrate carrier (CIC) and cytosolic NADP-dependent isocitrate dehydrogenase. CIC requires cytosolic malate as a counter-substrate during citrate and isocitrate export. Thus, considering that the mitochondrial dicarboxylate carrier (DIC) provides an important source of cytosolic malate, we investigated the potential role of DIC in control of glucose-stimulated insulin secretion (GSIS). Methods We used pharmacological and small interfering RNA (siRNA) tools to assess the role of DIC in insulin release in clonal insulin-secreting 832/13 cells and isolated rat islets. Results Butylmalonate, an inhibitor of malate transport, reduced cytosolic malate and citrate levels, and inhibited GSIS in a dose-dependent manner in 832/13 cells. Suppression of DIC expression resulted in inhibition of GSIS by 5% to 69%, the extent of inhibition of insulin secretion being proportional to the level of Dic (also known as Slc25a10) gene knockdown. The most effective siRNA duplex against Dic did not affect glucose utilisation, glucose oxidation or ATP/ADP ratio, but did suppress glucose-induced increments of the NADPH/NADP + ratio. Confirmation of our results in primary cultures of isolated rat islets showed that butylmalonate and an adenovirus expressing an siRNA against Dic-inhibited GSIS. Conclusions/interpretation Malate transport by DIC may play an important role in GSIS, possibly by providing cytosolic malate as a counter-substrate for citrate and/or isocitrate export by CIC. These studies also suggest that malate transport by DIC is (1) a critical component of NADPH production mediated by pyruvate-cycling and (2) regulates GSIS.

The therapeutic potential of cannabinoids has been described previously for several inflammatory diseases, but the molecular mechanisms underlying the anti-inflammatory properties of cannabinoids are not well understood. In this study, we investigated the mechanism of action of a novel synthetic cannabinoid, [(ϩ)-(6aS,10aS)-6,6-Dimethyl-3-(1,1-dimethylheptyl)-1-hydroxy-9-(1H-imidazol-2-ylsulfanylmethyl]-6a,7,10,10a-tetrahydro-6H-dibenzo [b,d]pyran 092) that has no psychotropic effects but exhibits immunomodulatory properties. Treatment with PRS-211,092 significantly decreased Concanavalin A-induced liver injury in mice that was accompanied by: 1) promotion of early gene expression of interleukin (IL)-6 and IL-10 that play a protective role in this model; 2) induction of early gene expression of the suppressors of cytokine signaling (SOCS-1 and 3), followed by 3) inhibition of several pro-inflammatory mediators, including IL-2, monocyte chemoattractant protein-1 (MCP-1), IL-1␤, interferon-␥, and tumor necrosis factor ␣. Based on these results, we propose a mechanism by which PRS-211,092 stimulates the expression of IL-6, IL-10 and the SOCS proteins that, in turn, negatively regulates the expression of pro-inflammatory cytokines. Negative regulation by PRS-211,092 was further demonstrated in cultured T cells, where it inhibited IL-2 production and nuclear factor of activated T cells activity. These findings suggest that this cannabinoid derivative is an immunomodulator that could be developed as a potential drug for hepatitis as well as for other short-or long-term inflammatory diseases.The identification of ⌬ 9 -tetrahydrocannabinol as the active component of marijuana (Cannabis sativa) prompted medicinal chemists to develop numerous cannabinoid analogs and opened a new era in research on the pharmaceutical applications of these compounds. Mechoulam (2000) discovered that the undesirable psychotropic effects of cannabinoids lie in a specific configuration of the molecule. This situation was best exemplified with the HU-210 and HU-211 enantiomeric pair of synthetic cannabinoids, HU-210 has the natural configuration and is 100 times more psychoactive than ⌬ 9

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Small interfering RNA (siRNA) shows great therapeutic potential due to its ability to regulate gene expression in a highly selective manner, but this application has been limited by effective delivery, partly because of the low nuclease resistance of siRNA in the presence of serum, and inefficient cellular uptake. We previously reported a library of cell-penetrating and amino acid-pairing peptides that facilitate effective siRNA delivery to mammalian cells without causing cytotoxicity, but they are unstable within serum-containing medium. Here, we investigated the possibility of conjugating the peptide with diethylene glycol to improve its serum stability without compromising its gene-regulation capability. One of the most promising peptides, C6M1, was conjugated with diethylene glycol, and its incorporated siRNA complexes had excellent serum stability and highly efficient cellular uptake with negligible cytotoxicity. The gene-silencing ability of diethylene glycol conjugated-peptide/siRNA complexes was comparable to that of non-conjugated peptide/siRNA at both mRNA and protein levels. Our data demonstrate that conjugating peptides with diethylene glycol is a promising method for improving siRNA delivery by improving its serum stability.