A. De Sarro

Systemic cytokine administration can affect blood-brain barrier permeability in the rat

The aim of the present study was to clarify the effect of intracarotid injection of interleukin-1 beta (IL-1 beta), interleukin-2 (IL-2), interleukin-6 (IL-6) and tumor necrosis factor-alpha (TNF-alpha) on the permeability of the blood-brain barrier (BBB) in the rat. A regional blood-to-brain transfer constant (Ki) for [14C] alpha-aminoisobutyric acid ([14C]AIB) and the cerebral residual blood volume were calculated 10 min following administration of cytokines (CKs; 1000 U/rat). The injection of IL-2 and IL-6 (but not of IL-1 beta) induced a significant enhancement of Ki values for [14C]AIB within several brain areas; conversely, when the rats were given TNF-alpha, a striking decrease in BBB permeability was observed. The cerebral regional blood volumes appeared significantly lower in the rats injected with IL-6 than in the control animals, but markedly increased following TNF-alpha administration. Our findings confirm the ability of some CKs to affect the permeability of the BBB and/or to act, probably indirectly, as vasomodulator agents of the cerebral microvessel endothelium.

Relationship between structure and convulsant properties of some beta-lactam antibiotics following intracerebroventricular microinjection in rats.

The epileptogenic activities of several beta-lactam antibiotics were compared following their intracerebroventricular administration in rats. Different convulsant potencies were observed among the various beta-lactam antibiotics tested, but the epileptogenic patterns were similar. The patterns consisted of an initial phase characterized by wet-dog shakes followed by head tremor, nodding, and clonic convulsions. After the largest doses of beta-lactam antibiotics injected, clonus of all four limbs and/or the trunk, rearing, jumping, falling down, escape response, transient tonic-clonic seizures, and sometimes generalized seizures were observed, followed by a postictal period with a fatal outcome. At a dose of 0.033 mumol per rat, cefazolin was the most powerful epileptogenic compound among the drugs tested. It was approximately three times more potent than benzylpenicillin in generating a response and much more potent than other cephalosporins, such as ceftriaxone, cefoperazone, and cefamandole. No epileptogenic signs were observed with equimolar doses of cefotaxime, cefonicid, cefixime, and ceftizoxime in this model. The more convulsant compounds (i.e., cefazolin and ceftezole) are both characterized by the presence of a tetrazole nucleus at position 7 and show a marked chemical similarity to pentylenetetrazole. Imipenem and meropenem, the two carbapenems tested, also showed epileptogenic properties, but imipenem was more potent than meropenem, with a convulsant potency similar to those of ceftezole and benzylpenicillin. In addition, the monobactam aztreonam possessed convulsant properties more potent than those of cefoperazone and cefamandole. This suggest that the beta-lactam ring is a possible determinant of production of epileptogenic activity, with likely contributory factors in the substitutions at the 7-aminocephalosporanic or 6-aminopenicillanic acid that may increase or reduce the epileptogenic properties of the beta-lactam antibiotics. While the structure-activity relationship was also investigated, there seem to be no convincing correlations among the rank order of lipophilicities and the convulsant potencies of the compounds studied. The lack of marked convulsant properties of cefixime, cefonicid, cefuroxime, and cephradine suggests that these antibiotics may interact with a binding site which is different from that by which the beta-lactam antibiotics exert their convulsant effects or may demonstrate a reduced affinity for the relevant site(s).

Effects of tempol, a membrane-permeable radical scavenger, in a gerbil model of brain injury.

There is evidence that the excessive generation of reactive-oxygen radicals contributes to the brain injury associated with transient, cerebral ischemia. This study investigates the effects of tempol, a small, water-soluble molecule, that crosses biological membranes, on the brain injury caused by bilateral occlusion and reperfusion of both common carotid arteries in the gerbil (BCO). Treatment of gerbils with tempol (30 mg/kg i.p. at 30 min prior to reperfusion and at 1 and 6 h after the onset of reperfusion) reduced the formation of post-ischemic brain oedema. Tempol also attenuated the increase in the cerebral levels of malondialdehyde (MDA) and the hippocampal levels of myeloperoxidase (MPO) caused by cerebral ischemia and reperfusion. The immunohistochemical analysis of the hippocampal region of brains subjected to ischemia-reperfusion exhibited positive staining for nitrotyrosine (an indicator of the generation of peroxynitrite) and poly(ADP-ribose) synthetase (PARS) (an indicator of the activation of this nuclear enzyme secondary to single strand breaks in DNA). In gerbils subjected to BCO, which were treated with tempol, the degree of staining for nitrotyrosine and PARS was markedly reduced. Tempol increased survival and reduced the hyperactivity (secondary to the ischemia-induced neurodegeneration) caused by cerebral ischemia and reperfusion. The loss of neurons from the pyramidal layer of the CA1 region caused by ischemia and reperfusion was also attenuated by treatment of gerbils with tempol. This is the first evidence that the membrane-permeable, radical scavenger tempol reduces the cerebral injury caused by transient, cerebral ischemia in vivo.

5H-[1,2,4]Oxadiazolo[5,4-d][1,5]benzothiazepines as anticonvulsant agents in DBA/2 mice

Summary A series of 3 a ,4-dihydro-5 H -[1,2,4]oxadiazolo[5,4- d ][1,5]benzothiazepines have been synthesized by 1,3-dipolar cycloaddition reaction of benzonitriloxide to the C N double bond of 1,5-benzothiazepine derivatives, and the stereochemical features of compounds obtained have been determined by NMR spectroscopy. The results of evaluation of their activity in preventing seizures induced by audiogenic stimulation in DBA/2 mice are also reported and discussed. The 5-(4-bromophenyl)-1,3-diphenyl derivative 3b , the most active compound of the series, is over 20 times more active than the parent benzothiazepine 1b and shows an activity comparable to clobazam and better than desmethylclobazam.

Anticonvulsant properties of non-competitive antagonists of the N-methyl-D-aspartate receptor in genetically epilepsy-prone rats: comparison with CPPene.

Abstract Some non-competitive antagonists of N- methyl- D -aspartate (NMDA) were evaluated for potency to antagonize audiogenic seizures in genetically epilepsy-prone rats, following intraperitoneal administration. Phencyclidine (PCP), dizocilpine (MK-801), ketamine, ifenprodil and dextromethorphan, displayed anticonvulsant activity at doses similar to those which impaired performance in the rotarod equilibrium procedure. The noncompetitive NMDA receptor antagonists, at doses which slightly overlapped with the doses required for a full anticonvulsant protection against audiogenic seizures in genetically epilepsy-prone rats, induced profound untoward behavioural effects. This behavioural syndrome was characterized by marked ataxia, hyperactivity, stereotypes and wet dog shakes. In contrast, the effective anticonvulsant dose of 3-(2-carboxypiperazin-4-yl)propenyl-1-phosphonic acid (CPPene) was less than that required to impair rotarod performance and did not produce the PCP-like syndrome. A potential use in antiepileptic therapy, of CPPene or other new selective NMDA antagonists, with fewer neurotoxic effects but not for non-competitive antagonists such as MK-801, is suggested.

Effects of interleukin-10 on water intake, locomotory activity, and rectal temperature in rat treated with endotoxin

Intracerebroventricular (i.c.v.) interleukin-10 (25, 50, and 100 ng/rat) effects on water intake, exploratory behaviour, and rectal temperature were evaluated in rats treated intraperitoneally (i.p.) with lipopolysaccharide (0.32, 0.64, and 0.96 mg/kg). Endotoxin administration induced fever and inhibition of thirst in water-deprived rats, and a decrease in lococomotory activity in normohydrated and water-deprived animals. Our data show that interleukin-10 during lipopolysaccharide administration controlled fever, increases exploratory behaviour, but did not reverse lipopolysaccharide inhibition of thirst. These effects suggest that fever, depression in locomotory activity but not inhibition of thirst, induced by endotoxin are influenced by interleukin-10 levels.

Convulsant effects of some xanthine derivatives in genetically epilepsy-prone rats

The behavioural and electrocorticographic (ECoG) convulsant effects of several xanthine derivatives injected intraperitoneally (i.p.) were studied in genetically-epilepsy prone rats. The aim of the study was to evaluate the relationship among convulsant potency, molecular structure and lipophilicity of some xanthines. Animals were injected i.p. with various doses (250-1000 mmol/kg) and a different convulsant potency was observed among the various xanthines tested. IBMX (3-isobutyl-1-methylxanthine), theophylline (1,3-dimethylxanthine) and caffeine (1,3,7-trimethylxanthine) induced an epileptogenic pattern that consisted in an initial phase characterized by wet-dog shakes followed by head tremor, nodding, clonic convulsion and they appeared to be the most potent xanthines among those studied. During seizures, the electrocortical activity was usually characterized by single or multiple sharp- or spike-wave episodes followed by polyspike discharges. After the highest doses of IBMX, theophylline and caffeine, the animals react with falling down, transient tonic clonic seizures, escape response and generalized seizures followed by post-ictal period. Equimolar doses of 8-chlorotheophylline and theobromine (3,7-dimethylxanthine) produced less evident epileptic responses in comparison to previous compounds, whereas no epileptic signs were observed following the administration of enprofylline (3-propylxanthine), etofylline [7-(2-hydroxyethyl)theo-phylline], diprophylline [7-(2,3-dihydroxy-propyl)theo-phylline] and doxofylline [7-(1,3-dioxolan-2-ylmethyl) theophylline]. Lipophylicity of the compounds was determined, but no convincing correlations were found between the rank order of lipophilicities and the convulsant potencies of the compounds studied. On the other hand, structure-activity relationship was also investigated. We suggest that the substitution pattern on the xanthine nucleus may explain, in part, the different convulsant potency of the compounds studied. Furthermore, a selective antagonism of adenosine subtype receptors should be considered.

Epileptogenic activity of some β-lactam derivatives: Structure-activity relationship

The epileptogenic activity of several derivatives of beta-lactam was compared following their intracerebroventricular administration in rats. At a dose of 0.033 mumol/kg cefazolin was the most powerful epileptogenic compound among the drugs tested; dramatic seizure signs (nodding, clonic convulsions and sometimes escape responses) were observed repeatedly. It was approximately three times more potent than benzylpenicillin and other similar compounds, such as ceftriaxone, cefoperazone and cefamandole. No epileptogenic signs were observed with equimolar doses of cefotaxime, cefonicid and ceftizoxime. All these derivatives differ from the substitution at position 3 and at position 7 of 7-aminocephalosporanic acid. The more convulsant compounds (i.e. cefazolin and ceftezole) are both derivatives of tetrazol and show a marked similarity with pentylentetrazol. In addition, aztreonam, a compound having only the beta-lactam ring substituted with a heterocyclic ring at the 4 position, possessed convulsant properties like those of cefoperazone and cefamandole. This suggests that the beta-lactam ring is able to produce epileptogenic activity and it seems likely that substitutions at the 7-aminocephalosporanic or 6-aminopenicillanic acid may increase or reduce the epileptogenic properties of beta-lactam derivatives.

Lamotrigine potentiates the antiseizure activity of some anticonvulsants in DBA/2 mice

Lamotrigine [0.5-10 mg/kg, intraperitoneally (i.p.)] was able to antagonize the audiogenic seizures in DBA/2 mice in a dose-dependent manner. Lamotrigine at doses of 0.5 and 1.25 mg/kg i.p., which per se did not significantly affect the occurrence of audiogenic seizures in DBA/2 mice, markedly potentiated the anticonvulsant activity of carbamazepine, diazepam, phenytoin, phenobarbital and valproate against sound induced seizures in DBA/2 mice. The degree of potentiation by lamotrigine was greatest for diazepam and valproate, lower for phenobarbital, and least for phenytoin and carbamazepine. The increase in anticonvulsant activity was associated with a comparable increase in motor impairment. However, the therapeutic index of combined treatment of diazepam + lamotrigine or valproate + lamotrigine was more favourable than the diazepam + saline or valproate + saline treatment. Since lamotrigine did not significantly influence the plasma levels of the anticonvulsant drugs studied we might suggest that pharmacokinetic interactions, in terms of total plasma levels, are not probable. However, the possibility that lamotrigine alters protein binding and increases the relative free vs protein bound ratio may not be excluded. Lamotrigine did not significantly affect the hypothermic effects of the anticonvulsant compounds studied. Lamotrigine showed an additive effect when administered in combination with some classical anticonvulsants, most notably valproate and diazepam.

Effects of some excitatory amino acid antagonists on imipenem-induced seizures in DBA/2 mice

The behavioural and convulsant effects of imipenem (Imi), a carbapenem derivative, were studied after intraperitoneal (i.p.) or intracerebroventricular (i.c.v.) administration in DBA/2 mice, a strain genetically susceptible to sound-induced seizures. The anticonvulsant effects of some excitatory amino acid antagonists and muscimol (Msc), a GABAA agonist, against seizures induced by i.p. or i.c.v. administration of Imi were also evaluated. The present study demonstrated that the order of anticonvulsant activity in our epileptic model, after i.p. administration, was (+)-5-methyl-10,11-dihydro-5H-dibenzo(a,d)-cyclohepten-5,10-imine maleate (MK-801) > (+/-)(E)-2-amino-4-methyl-5-phosphono-3-pentenoate ethyl ester (CGP 39551) > 3-((+/-)-2-carboxypiperazin-4-yl)propenyl-1-phosphonic acid (CPPene) > 3-((+/-)-2-carboxypiperazin-4-yl)-propyl-1-phosphonic acid (CCP) > 2,3-dihydroxy-6-nitro-7-sulfamoylbenzo(F)-quinoxaline (NBQX). Ifenprodil, a compound acting on the polyamine site of NMDA receptor complex was unable to protect against seizures induced by Imi, suggesting that the poliamine site did not exert a principal role in the genesis of seizures induced by Imi. In addition, the order of anticonvulsant potency in our epileptic model, after i.c.v. administration, was CPPene > MK-801 > Msc > (-)-2-amino-7-phosphonic acid (AP7) > gamma-D-glutamylaminomethylsulphonate (gamma-D-GAMS) > NBQX > kynurenic acid (KYNA) > 6-cyano-7-nitro-quinoxaline-2,3-dione (CNQX). The relationship between the different site of action and the anticonvulsant activity of these derivatives was discussed. Although the main mechanism of Imi induced seizures cannot be easily determined, potential interactions with the receptors of the excitatory amino acid neurotransmitters exists. In fact, antagonists of excitatory amino acids are able to increase the threshold for the seizures or to prevent the seizures induced by Imi. In addition, Imi acts on the central nervous system by inhibition of GABA neurotransmission and Msc, a selective GABAA agonist, was able to protect against seizures induced by Imi.