Inhibition of xanthine oxidase by theaflavin: Possible mechanism for anti-hyperuricaemia effect in mice

Xanthine oxidase (XO) catalyzes the oxidation of hypoxanthine to xanthine and then to uric acid. Excessive production of uric acid leads to hyperuricaemia. Due to the serious side effects of allopurinol, it is an urgent need to explore new XO inhibitors. Herein, the effects of theaflavin (TF1) on XO and anti-hyperuricaemia effect in hyperuricemic mice were investigated. Kinetic analysis indicate that TF1 is a reversible competitive inhibitor and has a significant inhibitory effect on XO with an IC₅₀ value of 63.17 ± 0.13 μmol/L. Analysis of fluorescence spectra suggests that TF1 causes the obvious fluorescence quenching of XO, which is mainly driven by hydrophobic interactions and hydrogen bonds. Docking studies demonstrate that TF1 interacts with dozens of amino acid residues surrounded in the active cavity of XO, including Glu-879, Pro-1012, Thr-1010, Val-1011, Lys-771, Glu-802, Pro-1076, Leu-873, Leu-1014, Asn-768, Leu-648 and Phe-649. The inhibitory mechanism may be the insertion of TF1 into the active site of XO, which hinders the substrate xanthine to enter into the site. Furthermore, the results from animal experiments demonstrate that TF1 is effective in reducing serum uric acid in mice. These findings suggest that TF1 may be a potential drug candidate for the treatment of hyperuricaemia.     

Teratogenic effect of ketamine and cocaine in CF-1 mice

Pregnant CF-1 mice were used to study the teratogenic effect of ketamine and cocaine, alone and in combination. The dose of ketamine was 50 mg/kg and that of cocaine was 20 mg/kg, given intravenously (tail) once daily (these doses of ketamine and cocaine are comparable to doses used by addicted humans). Treatment was started from day 6 to day 15 of gestation, and dams were sacrificed on day 18. There were significant decreases in the fetal weight and length in the combined group. Skeletal defects such as incomplete ossification of skull bones and vertebrae were observed in both the cocaine and combined group, compared with the control. An increased frequency of cerebral and abdominal hemorrhages as well as hydrocephalus and hydronephrosis was observed in the combined group. This study showed that fetal exposure to ketamine and cocaine in combination was more teratogenic than each drug alone in CF-1 mice.     

Possible involvement of GABAergic mechanism in protective effect of melatonin against sleep deprivation-induced behavior modification and oxidative damage in mice

Sleep deprivation for 72 h caused anxiety like behavior, weight loss, impaired locomotor activity and oxidative damage as indicated by increase in lipid peroxidation, nitrite level and depletion of reduced glutathione and catalase activity in sleep deprived mice brain. Treatment with melatonin (5 and 10 mg/kg, ip) significantly improved locomotor activity, weight loss and antianxiety effect as compared to control (sleep deprived). Biochemically, melatonin treatment significantly restored depleted reduced glutathione, catalase activity, attenuated lipid peroxidation and nitrite level as compared to control (72 h sleep-deprived) animals. A combination of flumazenil (0.5 mg/kg, ip) and picrotoxin (0.5 mg/kg, ip) with lower dose of melatonin (5 mg/kg, ip) significantly antagonized the protective effect of melatonin. However, combination of muscimol (0.05 mg/kg, ip) with melatonin (5 mg/kg, ip) potentiated protective effect of melatonin as compared to their effect per se. The results suggest that melatonin may produce its protective effect by involving GABAergic system against sleep deprivation-induced anxiety like behavior and related oxidative damage.     

Increasing anticonvulsant effect of AD-810 (zonisamide) in aging BDF1 mice

The anticonvulsant efficacy of a newly developed anticonvulsant, AD-810 (zonisamide, 3-sulfamoylmethyl-1,2-benzisoxazole) was examined in relation to mouse age in three different age groups of female BDF1 mice (7-, 25- and 29-month-old). The minimal effective concentration (MEC) of AD-810 in both plasma and brain for abolishing the electroshock-induced maximal seizure steadily decreased with age, the 25- and 29-month values being 50 and 30% of respective 7-month values. The observation in the present study was almost identical to previous observations by the authors on phenytoin, phenobarbital and oxazepam. The present results support our previous contention that the dose and plasma concentration of anticonvulsants can (and probably should) be reduced in the elderly regardless of the drug. Since the anticonvulsant mechanism of AD-810 has been reported to differ from those of previously examined drugs (phenobarbital and oxazepam), the results also suggest that the apparent increase in the pharmacological effect of these anticonvulsants may be due to old animals' lowered response capability for seizures rather than a specific age effect on the pharmacological reaction sites for individual anticonvulsants.     

The effect of age on the adaptation of the brain to the anticonvulsant effect of phenobarbital in mice

The anticonvulsant effect of phenobarbital was examined in young (6 month old) and old (24 month old) BDF1 female mice consisting of three groups each (one control and two chronically dosed phenobarbital groups), using the abolition of the tonic hindlimb extensor component of maximal electroshock seizure as the index. The minimal effective concentrations (MEC) of phenobarbital in plasma and brain in old control mice that were given a vehicle (tragacanth) for one week were significantly lower in comparison to the respective values in young adult control mice with the same treatment, confirming our previous findings. In young mice chronically treated with phenobarbital for one week (20 mg/kg daily for two days followed by daily dose of 50 mg/kg for 5 days), the MECs in both plasma and brain were significantly higher compared with respective control values. The 3 week treatment also produced an increase in MEc comparable to the one-week treatment. The same one-week treatment with phenobarbital in old mice similarly caused significantly higher plasma and brain MEC values but 3-week-treatment values were not significantly different from corresponding control values. It is concluded that the development of brain adaptation to phenobarbital is almost equal for young and old mice, so that the reduction in MEC with age indicates the need for lowered dosages for the aged, even when the age effect on brain adaptation developed to chronic dosing is taken into consideration.     

Possible mechanism of the protective effect of phosphocreatine on the ischemic myocardium

The uptake of 32P-phosphocreatine by control and ischemic isolated perfused rat hearts has been studied. The rate of phosphocreatine (PCr) uptake by the hearts after 35 minutes of ischemia was two times that in control hearts at 0.5-10 mM PCr in the perfusate. At 10 mM PCr in the perfusate, this rate was 182 nmoles/min/g dry weight. The 5'-nucleotidase and phosphatase activities were found in the crude plasma membrane fraction of rat heart. The pH-dependence of these enzymes was examined. The 5'-nucleotidase activity decreased with a drop in pH from 8.0 to 6.0. The phosphatase activity in the crude plasma membrane fraction of rat heart was increased 2-fold with a decrease in pH from 8.0 to 6.0. The 5'-nucleotidase activity was inhibited by 10 mM PCr in the presence of 5 mM Mg2+. This inhibition was pH-dependent with a maximum (58%) at pH 6.0. The inhibition of phosphatase activity by PCr was independent of pH and reached 20% in the presence of 10 mM PCr. Some feasible mechanisms of the protective effect of PCr on ischemic myocardium are discussed.     

Selenium induced anticonvulsant effect: A potential role of prostaglandin E1 receptor activation linked mechanism

ProjectSelenium deficiency has been associated with enhanced propensity of seizures in man and laboratory animals. Therefore, the present study has been designed to investigate the anti-convulsant effect of sodium selenite and seleno-dl-methionine on pentylenetetrazole induced seizures in mice and the role of prostaglandin receptor activation in the proposed anticonvulsant effect of sodium selenite.ProcedureSodium selenite (1, 3 and 10 mg kg^?1, i.p.) and seleno-dl-methionine (0.3, 1 and 3 mg kg^?1, i.p.) was used to evaluate the potential effect on pentylenetetrazole induced seizures in mice. Pentylenetetrazole induced seizures were assessed in terms of onset time of straub's tail phenomenon, jerky movements of the whole body and convulsions. Additionally, an isobolographic study design was used to examine the interaction between sodium selenite and celecoxib (a cyclooxygenase-2 inhibitor). Sodium selenite and seleno-dl-methionine significantly attenuated pentylenetetrazole induced seizures in mice.ResultsPrior administration of misoprostol (a selective agonist of prostaglandin E₁ receptors) markedly attenuated the anticonvulsant effect of sodium selenite as well as seleno-dl-methionine in mice. However, the administration of misoprostol per se did not produce any behavioral changes. Further, sodium selenite was observed to exert a synergistic interaction with celecoxib.ConclusionsSelenium induced reduction in seizure like behavior might be ascribed to the activation of a prostaglandin E₁ receptor activation linked mechanism. It is further proposed that sodium selenite exerts a synergistic anti-convulsant effect with celecoxib indicating the therapeutic usefulness of combining the two agents to treat epilepsy.     

Possible mechanism of membrane fusion

The stalker mechanism of membrane fusion was considered. Initiation and evolution of monolayer and bilayer bridges-stalks between the membranes were studied. From the expression of elastic energy of the stalk the value of spontaneous curvature of its membrane Ks at which the bridge may appear, was found. It was shown that in terms of the stalker mechanism formation of the stalk of the final radius or complete fusion were possible Ks values for realizing this or that variant were found. The energetic barrier of hydrophobic interaction and the barrier of elastic energy which the membranes had to overcome for stalker formation were found. The experimental data on the fusion of small and large liposomes were analysed.     

Possible mechanism of long-term anti-arrhythmia and local anesthetic effect of quaternary ammonium compounds

In experiments with dialized neurons of L. stagnalis mollusc the recovery of Na-current (INa) after its depression by local anesthetic trimecaine and its quaternary derivative N-ethyltrimecaine (G-88) was studied. A full recovery of INa within tens of seconds after washing off trimecaine but not G-88 was observed. The half-time for vanishing of INa use-dependent depression by G-88 was 17 minutes, and there was no substantial vanishing of tonic INa block even after an hour of G-88 washing off. A hypothesis is advanced that the long recovery time of INa is one of the mechanisms providing long pharmacological action of quaternary antiarrhythmic and local anesthetic ammonium compounds.