Theoretical and experimental mechanistic study of water molecule involvement in the Prilezhaev reaction.

The Prilezhaev reaction produces epoxides using alkenes and peroxy acids such as m-chloroperoxybenzoic acid (mCPBA). The reaction proceeds via a concerted mechanism in one step. Although the mCPBA used in organic syntheses contains water because of its explosive nature, the effects of water on the reaction have not been considered. To investigate the effects of water on the reaction mechanism, we determined the thermodynamic parameters for the Prilezhaev reaction between styrene and mCPBA. The activation free energies, including solvent effects, were calculated using the SMD and QM/MC/FEP methods. The calculated thermodynamic parameters for the reaction directly involving two water molecules were in better agreement with the experimental data than those for the concerted mechanism. This result indicated that water molecules are involved in the progression of the mCPBA-mediated Prilezhaev reaction in solvents containing water molecules.

[Comparison of two methods of local anesthetic administration using three phantom tissue models].

BACKGROUND: Local anesthetic is often administered around surgical wounds to reduce pain. It remains unknown, however, how the agent diffuses into tissue, or whether the method of administration has any impact on the drug diffusion. We evaluated drug-diffusion areas around wounds after administering a dummy agent by needle injection (NI) and direct infiltration (DI) using three phantom tissue models : agar, sponge, and pork rib. METHODS: Blue-colored water, a dummy substitute for local anesthetic, was administered in the vicinity of surgical wounds simulated by three tissue models. After the administration, blue-stained cross sectional areas and diffusion capacities were compared. RESULTS: The stained cross sections of the DI tissue were uniform, while those of the NI tissue were globular and centered around the needle point. The sectional area and diffusion capacity were significantly greater in the DI tissue than in the NI tissue in the agar model, though no significant differences between the administration methods were observed in the other models. CONCLUSIONS: The direct infiltration method is likely to diffuse local anesthetic into tissue more uniformly and more extensively than the needle injection method.

Voltage-dependent metabolic regulation of Kv2.1 channels in pancreatic beta-cells.

Voltage-gated potassium channels (Kv channels) play a crucial role in formation of action potentials in response to glucose stimulation in pancreatic beta-ells. We previously reported that the Kv channel is regulated by glucose metabolism, particularly by MgATP. We examined whether the regulation of Kv channels is voltage-dependent and mechanistically related with phosphorylation of the channels. In rat pancreatic beta-cells, suppression of glucose metabolism with low glucose concentrations of 2.8mM or less or by metabolic inhibitors decreased the Kv2.1-channel activity at positive membrane potentials, while increased it at potentials negative to -10 mV, suggesting that modulation of Kv channels by glucose metabolism is voltage-dependent. Similarly, in HEK293 cells expressing the recombinant Kv2.1 channels, 0mM but not 10mM MgATP modulated the channel activity in a manner similar to that in beta-cells. Both steady-state activation and inactivation kinetics of the channel were shifted toward the negative potential in association with the voltage-dependent modulation of the channels by cytosolic dialysis of alkaline phosphatase in beta-cells. The modulation of Kv-channel current-voltage relations were also observed during and after glucose-stimulated electrical excitation. These results suggest that the cellular metabolism including MgATP production and/or channel phosphorylation/dephosphorylation underlie the physiological modulation of Kv2.1 channels during glucose-induced insulin secretion.

α-Lipoic acid protects against arsenic trioxide-induced acute QT prolongation in anesthetized guinea pigs.

Clinical use of arsenic trioxide (As2O3), which can induce the remission of relapsed or refractory acute promyelocytic leukemia, is often limited because of its cardiotoxicity. Symptoms of cardiotoxicity include acute cardiac conduction disturbances, such as QT prolongation. The present study was undertaken to evaluate the effects of α-lipoic acid (LA) on acute As2O3-induced ECG abnormalities (QTc interval prolongation) in anesthetized guinea pigs. Intravenous injection of As2O3 in guinea pigs caused QTc interval prolongation, which was significantly attenuated by co-treatment with LA (0.35, 3.5 and 35 mg/kg) in a dose-dependent manner. In isolated guinea pig cardiomyocytes, the decrease in IKs current induced by As2O3 (1 µM) was rapidly restored to the basal level by the addition of LA (10 µM). Consistent with this finding, the As2O3-induced QTc interval prolongation was also improved rapidly by post-treatment with LA in guinea pigs. Electrospray ionization time-of-flight mass spectrometry analysis detected an expected peak of arsenic-LA complex in vitro, indicating that LA and As2O3 form a new compound in vivo. In addition, pre-treatment with a chelating agent, British anti-Lewisite (BAL, 3.5 or 35 mg/kg), also attenuated the As2O3-induced QTc interval prolongation. In this study, co- and post-treatments with LA and pre-treatment with BAL ameliorated As2O3-induced acute QT prolongation in anesthetized guinea pigs. Because LA and probably BAL may bind to As2O3, these agents may exert protective effects through their chelating activity. Further studies are needed to determine whether LA is beneficial as a prophylactic or rescue agent for acute promyelocytic leukemia patients treated with As2O3.

Regulation of voltage-gated K+ channels by glucose metabolism in pancreatic beta-cells.

Regulation of delayed rectifier-type K(+) channels (Kv-channels) by glucose was studied in rat pancreatic beta-cells. The Kv-channel current was increased in amplitudes by increasing glucose concentration from 2.8 to 16.6mM, while it was decreased by 2.8mM glucose in a reversible manner (down-regulation) in both perforated and conventional whole-cell modes. The current was decreased by FCCP, intrapipette 0mM ATP or AMPPNP. Glyceraldehyde, pyruvic acid, 2-ketoisocaproic acid, and 10mM MgATP prevented the down-regulation induced by 2.8mM or less glucose. The residual current after treatment with Kv2.1-specific blocker, guangxitoxin-1E, was unchanged by lowering or increasing glucose concentration. We conclude that glucose metabolism regulates Kv2.1 channels in rats beta-cells via altering MgATP levels.