Piotr Tutka

NG-Nitro-L-arginine differentially affects glutamate- or kainate- induced seizures

The effects of nitric oxide (NO) synthase inhibitor, NG-nitro-L-arginine (NNA) on seizures induced by excitatory amino acids, bicuculline, pentylenetetrazol and pilocarpine were studied in mice. NNA (10 and 40 mg kg-1, i.p.) enhanced the susceptibility to intracerebroventricular (i.c.v.) kainate (KA) which was reflected by a decrease in its convulsant dose 50% (CD50) from 0.66 nmol to 0.38 and 0.29 nmol/mouse, respectively. Also, NNA (40 mg kg-1) increased the KA-induced mortality. Conversely, NNA (40 mg kg-1) produced an anticonvulsant effect against i.c.v. glutamate whose CD50 value was significantly elevated from 0.49 mumol to 0.84 mumol/mouse. The convulsive activity of i.c.v. N-methyl-D-aspartic acid (NDMA), alpha-amino-3-hydroxy-5-methylisoxazole-4-propionic acid (AMPA), and trans-(+/-)-1-amino-1,3-cyclopentanedicarboxylic acid (trans-ACPD) was not affected by the pretreatment with NNA (40 mg kg-1). NNA (5-40 mg kg-1) also potentiated the convulsive action of systematic KA and KA-induced mortality but (up to 40 mg kg-1) remained without effect on seizures produced by bicuculline, N-methyl-D, L-aspartic acid (NMDLA), pentylenetetrazol, and pilocarpine. Only bicuculline-produced lethality was significantly enhanced. It may be concluded that the manipulation of the NO level affects differently seizures arising from a diffuse stimulation of glutamate receptors and seizures resulting from an activation of an individual subtype of these receptors. It is noteworthy that in the majority of convulsive tests used in this study, NNA exerted no modulatory effect.

NG-nitro-L-arginine impairs the anticonvulsive action of ethosuximide against pentylenetetrazol

N(G)-nitro-L-arginine (NNA; an inhibitor of nitric oxide synthase) in a dose of 40 mg/kg impaired the protective activity of ethosuximide against the clonic phase of pentylenetetrazol-induced seizures in mice. The ED50 value of ethosuximide was significantly increased from 108 to 158 mg/kg. NNA (40 mg/kg) was ineffective against the protective effects of diazepam, phenobarbital and valproate against pentylenetetrazol-induced seizures. NNA (40 mg/kg) did not influence the plasma levels of the antiepileptic drugs studied, so a pharmacokinetic interaction is not probable. L-Arginine (500 mg/kg) prevented the NNA-induced reduction of the anticonvulsive activity of ethosuximide. It can be concluded that nitric oxide participates in the expression of the anticonvulsive action of ethosuximide, but not that of diazepam, phenobarbital and valproate, against pentylenetetrazol-induced seizures.

Bupropion-induced convulsions: Preclinical evaluation of antiepileptic drugs

Bupropion, a unique, non-nicotine smoking cessation aid and an effective antidepressant, is well known to produce seizures following overdosing in humans. However, the experimental background for the usefulness of antiepileptic drugs in the protection against bupropion-induced convulsions has not been established yet. Therefore, we tested if the antiepileptic drugs were able to protect mice against clonic convulsions induced by intraperitoneally (i.p.) administered bupropion in the CD97 dose (139.5 mg/kg). Among 13 tested drugs, clonazepam showed the greatest potency (dose-dependent full protection; ED50 = 0.06 mg/kg, i.p.). No signs of locomotor impairment were observed in the rotarod test after anticonvulsive doses of clonazepam, resulting in a broad therapeutic window and favorable protective index (PI) (33.3). Gabapentin produced dose-dependent protection against convulsions at nontoxic doses (up to 1000 mg/kg), having PI>29. Diazepam in a very high dose showed full protection but its PI (1.7) was much less favorable than that of clonazepam. The PI values for ethosuximide, phenobarbital and valproate were slightly higher than unity and lower than 2, and for topiramate and felbamate were lower than unity. Phenytoin, carbamazepine, and lamotrigine as well as tiagabine failed to block the convulsant effects of bupropion even at doses that caused severe motor impairment. Our results encourage clinical testing of clonazepam against seizures developing after bupropion overdose.

Influence of combined treatment with NMDA and non-NMDA receptor antagonists on electroconvulsions in mice

alpha-Amino-3-hydroxy-5-methyl-isoxazole-4-propionate/kainate (AMPA/kainate) receptor antagonists (at subthreshold doses against electroconvulsions), 1-(4-aminophenyl)-4-methyl-7,8-methylenedioxy-5H-2,3-benzodiazepine (GYKI 52466 at maximally 5 mg/kg) and 2,3-dihydroxy-6-nitro-7-sulfamoylbenzo(F)quinoxaline (NBQX at maximally 20 mg/kg) enhanced the protective effects of NMDA receptor antagonists, MK-801 (dizocilpine) or 2-(2-carboxypiperazine-4-yl)-1-propenyl-1-phosphonic acid (D-CPP-ene), against electroconvulsions. Similarly, MK-801 or D-CPP-ene reduced the ED50 values of both NBQX and GYKI 52466 against maximal electroshock. The adverse effects of D-CPP-ene, evaluated in the chimney and rotorod tests, were potentiated by both GYKI 52466 (2.5 mg/kg) and NBQX (10 mg/kg). Also, D-CPP-ene (0.1 mg/kg) worsened the motor performance of mice pretreated with GYKI 52466 in the rotorod test. Neither MK-801 (0.025 mg/kg) nor D-CPP-ene (0.1 mg/kg) affected the NBQX-induced impairment of motor coordination. Similarly, GYKI 52466 (2.5 mg/kg) or NBQX (10 mg/kg) did not influence the performance of mice treated with MK-801 (0.2 mg/kg). It may be concluded that the blockade of more than one subtype of glutamate receptors leads to a more pronounced anticonvulsive effect when compared with the effect of blockade of an individual receptor subtype. In some cases more efficient seizure protection was not associated with increased adverse effects.

Synthetic cannabinoid WIN 55,212-2 mesylate enhances the protective action of four classical antiepileptic drugs against maximal electroshock-induced seizures in mice☆

The aim of this study was to determine the effect of WIN 55,212-2 mesylate (WIN--a non-selective cannabinoid CB1 and CB2 receptor agonist) on the protective action of four classical antiepileptic drugs (carbamazepine, phenytoin, phenobarbital, and valproate) in the mouse maximal electroshock seizure (MES) model. The results indicate that WIN (10 mg/kg, i.p.) significantly enhanced the anticonvulsant action of carbamazepine, phenytoin, phenobarbital and valproate in the MES test in mice. WIN (5 mg/kg) potentiated the anticonvulsant action of carbamazepine and valproate, but not that of phenytoin or phenobarbital in the MES test in mice. However, WIN administered alone and in combination with carbamazepine, phenytoin, phenobarbital and valproate significantly reduced muscular strength in mice in the grip-strength test. In the passive avoidance task, WIN in combination with phenobarbital, phenytoin and valproate significantly impaired long-term memory in mice. In the chimney test, only the combinations of WIN with phenobarbital and valproate significantly impaired motor coordination in mice. In conclusion, WIN enhanced the anticonvulsant action of carbamazepine, phenytoin, phenobarbital and valproate in the MES test. However, the utmost caution is advised when combining WIN with classical antiepileptic drugs due to impairment of motor coordination and long-term memory and/or reduction of skeletal muscular strength that might appear during combined treatment.

Nicotinic receptor partial agonists as novel compounds for the treatment of smoking cessation

Nicotine addiction and the neurobiological mechanisms explaining nicotine reinforcement, withdrawal, and relapse involve α4β2 nicotinic acetylcholine receptors (nAChRs). This review updates readers on the preclinical and clinical pharmacology, as well as the therapeutic efficacy and safety of cytisine and varenicline, the two partial agonists of nAChRs for smoking cessation. Cytisine has been used for several decades; yet despite its surprising popularity in some parts of the world, it has been absent from almost all existing reviews of smoking cessation drugs. If safe and sufficiently efficacious, an obvious advantage would be its low cost, which could make cytisine an attractive treatment available to millions of smokers. Varenicline was recently introduced to the drug market and has been found to be more efficacious than existing treatments. Very encouraging results of early human trials and strong theoretical background for their use make the nAChRs partial agonists a promising alternative for currently available antismoking treatments.

Molsidomine enhances the protective activity of valproate against pentylenetetrazole-induced seizures in mice

Summary. Molsidomine (25 mg kg−1), a donor of nitric oxide, commonly used in the treatment of coronary artery disease, enhanced the protective activity of valproate against the clonic phase of pentylenetetrazole-induced seizures in mice, significantly reducing the ED50 of valproate from 123.5 to 78 mg kg−1. Molsidomine was found to be ineffective with respect to the protective action of clonazepam, ethosuximide and phenobarbital. Alone, molsidomine in a dose of 25 mg kg−1 was ineffective in this model of seizures. Since NG-nitro-L-arginine, an inhibitor of nitric oxide synthase, failed to reverse the effect of molsidomine on valproate, an involvement of nitric oxide in the mechanism of the anticonvulsive efficacy of valproate does not seem to be probable. Molsidomine (25 mg kg−1) significantly elevated the free plasma level of valproate from 33.8 to 46.2 μg ml−1. Therefore, we conclude that the interaction of molsidomine with valproate is at the pharmacokinetic level.The combination of valproate with molsidomine appears beneficial because is free from adverse effects, in terms of motor impairment and long-term memory deficit. Our results suggest that the dosage of valproate in patients with coronary artery disease treated with molsidomine should be decreased. It would allow us to reduce adverse effects of valproate.

Nitric oxide and convulsions in 4-aminopyridine-treated mice.

We studied whether N(G)-nitro-L-arginine (NNA), an inhibitor of nitric oxide (NO) synthase as well as L-arginine and molsidomine, two agents elevating NO, influenced convulsions caused by 4-aminopyridine, a K+ channel blocker in mice. NNA, in a dose known to decrease level of NO (40 mg x kg(-1)), enhanced the seizure susceptibility to intraperitoneal (i.p.) and intracerebroventricular (i.c.v.) 4-aminopyridine. L-arginine (500 mg x kg(-1)) and molsidomine (20 mg x kg(-1)) alone did not influence 4-aminopyridine-induced seizure activity. Surprisingly, the proconvulsant effect of NNA upon clonic and tonic seizures was potentiated by molsidomine (20 mg x kg(-1)). No influence of L-arginine on the proconvulsant effect of NNA was found. Taking into account the proconvulsant effect of NNA, an involvement of NO-mediated events in the mechanism of convulsive activity of 4-aminopyridine might be postulated. However, the ineffectiveness of L-arginine and molsidomine to suppress the convulsive activity of 4-aminopyridine as well as a paradoxical potentiation of the proconvulsant effect of NNA by molsidomine seem to exclude the impact of NO pathway on 4-aminopyridine-induced convulsions in mice. Our data suggest that the proconvulsant effect of NNA in this seizure model is caused by other, not related to NO, mechanisms.

Effects of cigarette smoking, metabolic syndrome and dehydroepiandrosterone deficiency on intima-media thickness and endothelial function in hypertensive postmenopausal women

Summary Background Cigarette smoking is a major risk factor of atherosclerosis. The aim of this study was to assess the relationship between smoking and arterial hypertension as well as endothelial dysfunction in postmenopausal women without clinically manifested symptoms of atherosclerosis. Material/Methods The study groups consisted of 35 current smokers and 45 nonsmokers. The thickness of intima-media complex (IMT), a marker of atherosclerosis, was measured in carotid arteries. Plasma concentrations of fasting glucose, insulin, lipoproteins, inflammatory markers (tumor necrosis factor-alpha, intercellular adhesion molecule-1), matrix metalloproteinases (metalloproteinase-9, tissue inhibitor of metalloproteinase-1), insulin, and dehydroepiandrosterone sulfate (DHEA-S) were measured. Results Smokers compared with nonsmokers showed lower fasting glucose levels in blood (87.0±10.9 and 93.2±13.6 mg/dl, p<0.05), higher mean systolic (131.1±15.9 vs. 123.0±10.9 mm Hg, p<0.05) and diastolic (81.7±11.4 vs. 75.2±9.2 mm Hg, p<0.05) blood pressure during daytime, and higher average heart rate during the daytime (78.2±9.3/min vs. 71.5±9.5/min, p<0.01) and at night (67.2±10.6/min vs. 61.7±7.7/min, p<0.05), respectively. The IMT in the right carotid artery was significantly higher in smokers than in nonsmokers (0.96±0.16 mm vs. 0.82±0.21, p<0.05) and was positively correlated with smoking intensity (R=0.36) and habit duration (R=0.35). The comparison of inflammatory markers, metalloproteinases, and DHEA-S concentrations in plasma did not reveal significant differences between the 2 groups. A significant negative correlation between DHEA-S concentration in plasma and IMT in right carotid artery was found in smokers. Conclusions Smoking in hypertensive postmenopausal women is associated with lower fasting blood glucose and BMI values, but higher arterial pressure and heart rate, and increases in IMT in right carotid artery.

Low dose of bupropion significantly enhances the anticonvulsant activity of felbamate, lamotrigine and topiramate in mice

Experimental evidence indicates that bupropion hydrochloride, an antidepressant and a first-line smoking cessation aid, exerts dose-dependently anticonvulsant and convulsant effects. In this study, chronic bupropion pretreatment intraperitoneally (i.p.) for 14 days in a dose of 5 mg/kg reduced the ED(50) (i.e. the dose protecting 50% of mice against electroconvulsions) of lamotrigine, topiramate, and felbamate from 4.58, 60.95, and 48.79 (antiepileptic+vehicle) to 3.01, 41.68, and 37.28 mg/kg (antiepileptic+bupropion), respectively, against maximal electroshock-induced seizures in mice. Bupropion significantly increased the plasma and brain concentrations of lamotrigine. Plasma concentration of topiramate was elevated, however, the brain concentration of the drug was not affected. Neither plasma nor brain concentrations of felbamate were elevated by bupropion administration. Bupropion did not exacerbate motor coordination impairment caused by the antiepileptic drugs in the rotarod test. Chronic administration of bupropion significantly potentiates the protective activity of lamotrigine, topiramate, and felbamate against maximal electroshock-induced seizures. A pharmacokinetic interaction is responsible for the effect of bupropion co-administered with lamotrigine.