Effects of arachidonyl-2'-chloroethylamide (ACEA) on the protective action of various antiepileptic drugs in the 6-Hz corneal stimulation model in mice.

Accumulating evidence indicates that cannabinoid CB1 receptor ligands play a pivotal role in seizures, not only in preclinical studies on animals, but also in clinical settings. This study was aimed at characterizing the influence of arachidonyl-2'-chloroethylamide (ACEA-a selective cannabinoid CB1 receptor agonist) co-administered with phenylmethylsulfonyl fluoride (PMSF) on the anticonvulsant potency of various antiepileptic drugs (clobazam, lacosamide, levetiracetam, phenobarbital, tiagabine and valproate) in the 6-Hz corneal stimulation model. Psychomotor seizures in male albino Swiss mice were evoked by a current (32 mA, 6 Hz, 3 s stimulus duration) delivered via corneal electrodes. Potential adverse effects produced by the antiepileptic drugs in combination with ACEA+PMSF were assessed using the chimney test (motor performance), passive avoidance task (remembering and acquisition of learning), and grip-strength test (muscular strength). Brain concentrations of antiepileptic drugs were measured by HPLC to exclude any pharmacokinetic contribution to the observed effect. ACEA (5 mg/kg, i.p.) + PMSF (30 mg/kg, i.p.) significantly potentiated the anticonvulsant potency of levetiracetam (P<0.05), but not that of clobazam, lacosamide, phenobarbital, tiagabine or valproate in the 6-Hz corneal stimulation model. Moreover, ACEA+PMSF did not significantly affect total brain concentrations of levetiracetam in mice. No behavioral side effects were observed in animals receiving combinations of the studied antiepileptic drugs with ACEA+PMSF. In conclusion, the combined administration of ACEA+PMSF with levetiracetam is associated with beneficial anticonvulsant pharmacodynamic interaction in the 6-Hz corneal stimulation model. The selective activation of cannabinoid CB1 receptor-mediated neurotransmission in the brain may enhance levetiracetam-related suppression of seizures in epilepsy patients, contributing to the efficacious treatment of epilepsy in future.

Influence of xanthotoxin (8-methoxypsoralen) on the anticonvulsant activity of various novel antiepileptic drugs against maximal electroshock-induced seizures in mice.

The aim of this study was to determine the effects of xanthotoxin (8-methoxypsoralen) on the protective action of 5 various second- and third-generation antiepileptic drugs (i.e., lacosamide, lamotrigine, oxcarbazepine, pregabalin and topiramate) in the mouse maximal electroshock-induced seizure model. Seizure activity was evoked in adult male albino Swiss mice by a current (25mA, 500V, 0.2s stimulus duration) delivered via auricular electrodes. Drug-related adverse effects were determined in the chimney, grip-strength and passive avoidance tests. Total brain antiepileptic drug concentrations were measured to confirm pharmacodynamic nature of observed interactions with xanthotoxin. Results indicate that xanthotoxin (100mg/kg, i.p.) significantly enhanced the anticonvulsant action of lacosamide (P<0.01), oxcarbazepine (P<0.05), pregabalin (P<0.01), and topiramate (P<0.001), but not that of lamotrigine in the maximal electroshock-induced seizure test. Moreover, xanthotoxin (50mg/kg) still significantly potentiated the anticonvulsant action of lacosamide (P<0.05), pregabalin (P<0.05), and topiramate (P<0.001) in this seizure test. Xanthotoxin had no significant impact on total brain concentrations of the studied antiepileptic drugs in mice. Furthermore, combinations of xanthotoxin with oxcarbazepine or topiramate produced no adverse effects. However, xanthotoxin in combination with lacosamide, lamotrigine or pregabalin significantly reduced muscular strength in mice in the grip-strength test. In the chimney test, only the combinations of xanthotoxin with pregabalin significantly impaired motor coordination in mice. In conclusion, the combinations of xanthotoxin with oxcarbazepine and topiramate produce beneficial anticonvulsant pharmacodynamic interactions in the maximal electroshock-induced seizure test. A special caution is advised when combining xanthotoxin with pregabalin due to appearance of acute adverse effects.

Role of polyisoprenoids in tobacco resistance against biotic stresses.

Infection with avirulent pathogens, tobacco mosaic virus (TMV) or Pseudomonas syringae pv. tabaci induced accumulation of polyisoprenoid alcohols, solanesol and a family of polyprenols [from polyprenol composed of 14 isoprene units (Pren-14) to -18, with Pren-16 dominating] in the leaves of resistant tobacco plants Nicotiana tabacum cv. Samsun NN. Upon TMV infection, solanesol content was increased seven- and eight-fold in the inoculated and upper leaves, respectively, while polyprenol content was increased 2.5- and 2-fold in the inoculated and upper leaves, respectively, on the seventh day post-infection. Accumulation of polyisoprenoid alcohols was also stimulated by exogenously applied hydrogen peroxide but not by exogenous salicylic acid (SA). On the contrary, neither inoculation of the leaves of susceptible tobacco plants nor wounding of tobacco leaves caused an increase in polyisoprenoid content. Taken together, these results indicate that polyisoprenoid alcohols might be involved in plant resistance against pathogens. A putative role of accumulated polyisoprenoids in plant response to pathogen attack is discussed. Similarly, the content of plastoquinone (PQ) was increased two-fold in TMV-inoculated and upper leaves of resistant plants. Accumulation of PQ was also stimulated by hydrogen peroxide, bacteria (P. syringae) and SA. The role of PQ in antioxidant defense in cellular membranous compartments is discussed in the context of the enzymatic antioxidant machinery activated in tobacco leaves subjected to viral infection. Elevated activity of several antioxidant enzymes (ascorbate peroxidase, guaiacol peroxidase, glutathione reductase and superoxide dismutase, especially the CuZn superoxide dismutase isoform) and high, but transient elevation of catalase was found in inoculated leaves of resistant tobacco plants but not in susceptible plants.