The possible role of nitric oxide signaling and NMDA receptors in allopurinol effect on maximal electroshock- and pentylenetetrazol-induced seizures in mice.

Allopurinol, a uric-acid-lowering medication, has shown its efficacy in several studies suggesting that allopurinol can be prescribed as adjunctive cure meant for intractable epilepsy. The exact mechanism of allopurinol is still unknown. This study evaluates allopurinol's effect on seizure threshold, seizure incidence, and mortality rate in mice models. Moreover, the possible involvement of nitric oxide (NO) pathway and N-methyl-D-aspartate (NMDA) receptors are investigated. To evaluate the effect of allopurinol on seizure, we used the pentylenetetrazole (PTZ)-induced seizure along with maximal electroshock (MES)-induced seizure. To assess the underlying mechanism behind the allopurinol activity, we used nitric oxide synthase (NOS) substrate (L-arginine), NOS inhibitors (L-NAME, aminoguanidine, 7-nitroindazole), and NMDA receptor antagonist (MK-801). Intraperitoneal allopurinol administration at a dose of 50 mg/kg in mice showed a significant (p < 0.001) anti-convulsant activity in the PTZ-induced seizure. Even though pre-treatment with L-Arginine (60 mg/kg) potentiates allopurinol's anti-convulsant effect in the PTZ-induced seizure, pre-treatment with L-NAME (10 mg/kg), aminoguanidine (100 mg/kg), and 7-nitroindazole (30 mg/kg) reversed the anti-convulsant effect of allopurinol in the PTZ-induced seizure. In addition, pre-treatment with MK-801 also decreased the anti-convulsant effect of allopurinol in the PTZ-induced seizure. While allopurinol at a dose of 50 mg/kg and 100 mg/kg did not induce protection against seizure incidence in the MES-induced seizure, it revealed a remarkable effect in reducing the mortality rate in the MES-induced seizure. Allopurinol increases the seizure threshold in PTZ-induced seizure and enhances the survival rate in MES-induced seizure. Allopurinol exerts its anti-convulsant effect, possibly through targeting NO pathway and NMDA receptors.

1-Methyl tryptophan, an indoleamine 2,3-dioxygenase inhibitor, attenuates cardiac and hepatic dysfunction in rats with biliary cirrhosis.

Kynurenine Pathway (KP) is the dominant metabolic route of tryptophan which is catalyzed by indoleamine-2,3-dioxygenase (IDO). This pathway is upregulated in liver disease where the level of KP metabolites correlates with the severity of disease. Cirrhosis is associated with cardiac dysfunction, which manifests itself during severe physiological challenges such as liver transplantation. Cardiac dysfunction in cirrhosis is linked to systemic inflammation and impaired cardiac beta-adrenergic signaling pathways. The KP pathway is involved in modulation of cardiac signaling and is upregulated by systemic inflammation. Therefore, this study aimed to evaluate the effect of IDO inhibition on development of cardiac dysfunction in an experimental model of cirrhosis. Cirrhosis was induced by bile duct ligation (BDL). Experimental groups were given either 1-methyl tryptophan (1-MT, 1, 3, 9 mg/kg), or saline. 28 days after BDL, cardiac chronotropic response to epinephrine was assessed ex vivo. HPLC was employed to measure hepatic and cardiac levels of tryptophan, kynurenine and kynurenic acid. Cirrhosis in rats was associated with impaired cardiac chronotropic responsiveness to adrenergic stimulation. 1-MT dose-dependently improved cirrhosis-induced chronotropic dysfunction as well as elevated serum levels of CRP and IL-6 in BDL rats. Hepatic and cardiac kynurenine/tryptophan ratio were elevated in cirrhotic rats and were reduced following 1-MT administration. Chronic administration of 1-MT could also reduce hepatic inflammation, fibrosis and ductular proliferation. 1-MT attenuates cardiac dysfunction in rats with biliary cirrhosis. This protective effect is not limited to the cardiac function as liver histopathologic changes were also improved following chronic 1-MT administration.

Protective Effects of Spermidine Against Cirrhotic Cardiomyopathy in Bile Duct-Ligated Rats.

Cirrhotic cardiomyopathy is a critical factor that causes morbidity and mortality in crucial conditions such as liver transplantation. In animal model, the common pathophysiologic mechanisms of cirrhotic cardiomyopathy are similar to those associated with bile duct ligation (BDL). Overproduction of inflammatory and oxidant markers plays a crucial role in cirrhotic cardiomyopathy. Spermidine, a multifunctional polyamine, is known for its antioxidant and anti-inflammatory effects. In this study, we investigated the effects of spermidine on development of cirrhotic cardiomyopathy in BDL rats. Rats were randomly housed in 6 groups. Except the normal and sham groups, BDL was performed for all the control and spermidine groups. Seven days after operation, 3 different doses of spermidine (5, 10 and 50 mg/kg) were administrated until day 28, in spermidine groups. At the end of the fourth week, the electrocardiography (ECG) and papillary muscle isolation were performed. The serum level of tumor necrosis factor-a (TNF-α), interleukin-1ß (IL-1ß), and IL-10 and cardiac level of superoxide dismutase, glutathione (GSH). and malondialdehyde (MDA) were assessed. Furthermore, the nuclear factor-κB (NF-κB) expression was assessed by western blot. Cardiac histopathological changes were monitored. The serum levels of magnesium (Mg) and potassium (K) were investigated. Control group, exhibited exaggerated signs of cirrhotic cardiomyopathy in comparison with the sham group. Co-administration of spermidine at the dose of 10 mg/kg in BDL rats significantly improved the cardiac condition, reduced the inflammatory mediators, and increased antioxidant enzymes. In addition, the histopathologic findings were in accordance with the other results of the study. Besides, there was no significant alteration in serum levels of Mg and K. This study demonstrates that spermidine at the dose of 10 mg/kg significantly improved the cirrhotic cardiomyopathy in BDL model in rats.

Anticonvulsant Effects of Thalidomide on Pentylenetetrazole-Induced Seizure in Mice: A Role for Opioidergic and Nitrergic Transmissions.

Although accumulating evidence indicates that the immunomodulatory medication thalidomide exerts anticonvulsant properties, the mechanisms underlying such effects of thalidomide are still unknown. Our previous preclinical study suggested that nitric oxide (NO) signaling may be involved in the anticonvulsant effects of thalidomide in a mouse model of clonic seizure. Additionally, several studies have shown a modulatory interaction between thalidomide and opioids in opioids intolerance, nociception and neuropathic pain. However, it is unclear whether opioidergic transmission or its interaction with NO signaling is involved in the anticonvulsant effects of thalidomide. Given the fact that both opioidergic and nitrergic transmissions have bimodal modulatory effects on seizure thresholds, in the present study we explored the involvement of these signaling pathways in the possible anticonvulsant effects of thalidomide on the pentylenetetrazole (PTZ)-induced clonic seizure in mice. Our data showed that acute administration of thalidomide (5-50 mg/kg, i.p., 30 min prior PTZ injection) dose-dependently elevated PTZ-induced clonic seizure thresholds. Acute administration of low doses (0.5-3 mg/kg, i.p., 60 min prior PTZ) of morphine exerted anticonvulsant effects (P < 0.001), whereas higher doses (15-60 mg/kg, 60 min prior PTZ) had proconvulsant effects (P < 0.01). Acute administration of a non-effective anticonvulsant dose of morphine (0.25 mg/kg) prior non-effective dose of thalidomide (5 mg/kg) exerted a robust (P < 0.01) anticonvulsant effect. Administration of a non-effective proconvulsant dose of morphine (7.5 mg/kg) prior thalidomide (5 mg/kg) didn't affect clonic seizure thresholds. Acute administration of a non-effective dose of the opioid receptor antagonist naltrexone (1 mg/kg, i.p.) significantly prevented anticonvulsant effects of thalidomide (10 mg/kg, i.p.). Pretreatment with non-effective dose of the NO precursor L-arginine (60 mg/kg, i.p.) significantly (P < 0.01) reduced the anticonvulsant effects of combined low doses of morphine (0.25 mg/kg) and thalidomide (5 mg/kg). Conversely, pretreatment with non-effective doses of either non-selective (L-NAME, 5 mg/kg, i.p.) or selective neuronal (7-nitroindazole, 30 mg/kg, i.p.) NO synthase (NOS) inhibitors significantly augmented the anticonvulsant effects of combined low doses of thalidomide and morphine, whereas the inducible NOS inhibitor aminoguanidine (100 mg/kg, i.p.) did not exert such effect. Our results indicate that opioidergic transmission and its interaction with neuronal NO signaling may contribute to the anti-seizure activity of thalidomide in the mice PTZ model of clonic seizure.

Cardioprotective effects of dapsone against doxorubicin-induced cardiotoxicity in rats.

PURPOSE: It has been supposed that cardiac toxicity of doxorubicin is due to its production of free radicals and inflammatory cytokines. Dapsone, an antibiotic drug which is the principal in a multidrug regimen for the treatment of leprosy, is a sulfone with anti-inflammatory and antioxidant immunosuppressive properties. Therefore, we designed this study to investigate the possible effects of dapsone on doxorubicin-induced cardiotoxicity. METHODS: Male rats were administrated doxorubicin (2.5 mg/kg) and dapsone (1, 3, 10 mg/kg) intraperitoneally six times in 2 weeks. Then electrocardiographic (ECG) parameters (QRS complexes, RR and QT intervals) alternation, papillary muscle contraction and excitation, and histopathological changes were assessed. Also, the heart tissue levels of malondialdehyde (MDA) as oxidant factor and superoxide dismutase (SOD) as antioxidant enzyme, tumor necrosis factor-alpha (TNF-α) and serum level of CK-MB were analyzed. RESULTS: Administration of dapsone with doxorubicin significantly reversed alterations induced by doxorubicin in serum levels of CK-MB, ECG parameters, papillary muscle contractility and excitation. Furthermore, the measurement of MDA, SOD and TNF-α tissue level indicated that dapsone significantly reduced oxidative stress and inflammation. These findings were consistent with histopathological analysis. CONCLUSION: Dapsone exerts cardioprotective effects on doxorubicin-induced cardiotoxicity through its anti-inflammatory and antioxidant mechanism.

Modulatory effect of opioid ligands on status epilepticus and the role of nitric oxide pathway.

Epilepsy is a chronic disorder that causes unprovoked, recurrent seizures. Status epilepticus (SE) is a medical emergency associated with significant morbidity and mortality. Morphine has been the cornerstone of pain controlling medicines for a long time. In addition to the analgesic and opioid responses, morphine has also revealed anticonvulsant effects in different epilepsy models including pentylenetetrazole (PTZ)-induced seizures threshold. Some authors suggest that nitric oxide (NO) pathway interactions of morphine explain the reason for its pro or anticonvulsant activities. To induce SE, injection of a single dose of lithium chloride (127 mg/kg, intraperitoneal (i.p.)) 20 h before pilocarpine (60 mg/kg, i.p.) was used. Administration of morphine (15 mg/kg, i.p.) inhibited the SE and decreased the mortality in rats when injected 30 min before pilocarpine. On the other hand, injection of L-NG-nitro arginine methyl ester (L-NAME, a nonselective NO synthase (NOS) blocker; 10 mg/kg, i.p.), 7-nitroindazole (7-NI, a neuronal NOS (nNOS) blocker; 30 mg/kg, i.p.), and aminoguanidine (AG, an inducible NOS (iNOS) blocker; 50 mg/kg, i.p.) 15 min before morphine, significantly reversed inhibitory effect of morphine on SE. Subsequently, measurement of nitrite metabolite levels in the hippocampus of SE-induced rats displayed high levels of nitrite metabolite for the control group. However, after injection of morphine in SE-induced rats, nitrite metabolite levels reduced. In conclusion, these findings demonstrated that NO pathway (both nNOS and iNOS) interactions are involved in the anticonvulsant effects of morphine on the SE signs and mortality rate induced by lithium-pilocarpine in rats.

Nitric oxide and glutamate are contributors of anti-seizure activity of rubidium chloride: A comparison with lithium.

The neuro-protective effects of rubidium and lithium as alkali metals have been reported for different central nervous system dysfunctions including mania and depression. The aim of this study was evaluating as well as comparing the effects of rubidium chloride (RbCl) and lithium chloride (LiCl) on different seizures paradigms in mice and determining the involvement of NMDA receptors and nitrergic pathway. To assess the seizures threshold, animals received intravenous pentylenetetrazole (PTZ, 0.5%; 1 mL/min). Male NMRI mice (6-8 weeks) received intraperitoneal (i.p.) injections of different doses of RbCl and LiCl. Doses greater than 10 mg/kg of RbCl showed a significant anticonvulsant activity 60 min after administration; the anticonvulsant effects of LiCl was observed at the doses more than 5 mg/kg and after 30 min in PTZ-induced seizure threshold. But, RbCl (10, 20 mg/kg, i.p) or LiCl (5, 10 mg/kg, i.p) injection did not induce protection against maximal electroshock (MES) or intraperitoneal injection of PTZ lethal dose (80 mg/kg)-induced seizure models. Pre-treatment with L-NAME (non-selective nitric oxide synthase (NOS) inhibitor, 10 mg/kg; i.p.) and 7-nitroindazole (selective neuronal NOS inhibitor, 30 mg/kg; i.p.) enhanced the anticonvulsive effects of both RbCl (5 mg/kg, i.p.) and LiCl (1 mg/kg, i.p.) in PTZ-induced seizure threshold model. Injection of MK-801 (NMDA receptor antagonist, 0.05 mg/kg; i.p.) before RbCl (5 mg/kg, i.p.; P < 0.001) and LiCl (1 mg/kg, i.p.; P < 0.001) administration increased the anti-seizure activity. But, treatment with L-arginine (precursor of nitric oxide, 100 mg/kg; i.p.) decreased the seizure threshold of both RbCl (20 mg/kg, i.p.; P < 0.001) and LiCl (10 mg/kg, i.p.; P < 0.001). Measurement of nitrite levels in hippocampus of animals revealed a remarkable reduction after treatment with RbCl (20 mg/kg, i.p; P < 0.05) and LiCl (10 mg/kg, i.p; P < 0.01). To conclude, rubidium may protect central nervous system against seizures in PTZ-induced seizures threshold model through NMDA/nitrergic pathways with a similarity to lithium effects in mice.

Sumatriptan protects against myocardial ischaemia-reperfusion injury by inhibition of inflammation in rat model.

Ischemic heart disease is a leading cause of death on a global scale, placing major socio-economic burdens on health systems worldwide. Myocardial ischaemia and reperfusion (I/R)-induced tissue injury is associated with alteration in activity of inflammatory system and nitric oxide pathway. Sumatriptan, which is mainly used to relieve migraine headache, has recently been shown to exert anti-inflammatory properties. In this study, we aimed to assess the possible cardioprotective effect of sumatriptan in a rat model of I/R injury. Male Wistar rats were subjected to 30-min ligation of left anterior descending coronary artery and 120-min reperfusion. Animals were randomly divided into five groups: (1) Sham (2) I/R (3) I/R treated with sumatriptan (0.3 mg/kg i.p.) 20 min after induction of I/R rats, (4) GR127935 (a selective antagonist of 5-HT1B/D serotonin receptors; 0.3 mg/kg) 20 min after induction of I/R, and (5) GR127935 (0.3 mg/kg) 15 min before administration of sumatriptan. Post-infarct treatment with sumatriptan increased left ventricular function, which was damaged in I/R animal's heart. Sumatriptan (0.3 mg/kg) decreased lipid peroxidation, CK-MB and lactate dehydrogenase levels; tumor necrosis factor concentration; and Nf-Ò¡B' protein production. Treatment with sumatriptan significantly increased the endothelial nitric oxide synthase (eNOS) expression consequences nitric oxide metabolites' level in I/R rats. Also, injection of sumatriptan remarkably decreased myocardial tissue injury assessed by histopathological study. These findings suggest that sumatriptan may attenuate I/R injury via modulating the inflammatory responses and endothelial NOS activity. But therapeutic index of sumatriptan is narrow according to the result of this study.

Agmatine ameliorates acetic acid-induced colitis in rats: involvement of nitrergic system.

Aim: The aim of the present study is to investigate the anti-inflammatory effect of agmatine through the inhibition of iNOS enzyme in acetic acid-induced rat colitis. Methods: Acute colitis was induced by administration of 2 mL of diluted acetic acid (4%) solution rectally. Two hours after colitis induction, animals were treated with normal saline, dexamethasone (2 mg/kg), agmatine (2, 5, 10 mg/kg), L-NAME (30 mg/kg), Aminoguanidine (20 mg/kg), agmatine (2 mg/kg) with L-NAME (30 mg/kg) and agmatine (2 mg/kg) with aminoguanidine (20 mg/kg) intraperitoneally and continued for 3 consecutive days. Assessment of macroscopic and microscopic damage was performed. MPO activity was evaluated by biochemical method. Furthermore, the tissue level of TNF-α was determined by ELISA and the expression level of iNOS protein was detected by immunohistochemistry (IHC). Results: Dexamethasone (2 mg/kg) and agmatine (5, 10 mg/kg) and subeffective doses of agmatine (2 mg/kg) with aminoguanidine (20 mg/kg) improved macroscopic and microscopic damage compared to acetic acid group (p < .001). In addition, these drugs reduced the activity of MPO (p < .001) and the level of TNF-α (p < .001) in colon tissue compared to acetic acid group. Furthermore, they decreased acetic acid-induced expression of iNOS protein in colon tissue (p < .01, p < .001). Conclusion: It is suggested that the anti-inflammatory activity of agmatine on acetic acid-induced rat colitis may involve the inhibition of iNOS enzyme.

The Possible Role of Nitric Oxide Pathway in Pentylenetetrazole Preconditioning Against Seizure in Mice.

Preconditioning is defined as an induction of adaptive response in organs against lethal stimulation provoked by subsequent mild sublethal stress. Several chemical agents have been demonstrated to cause brain tolerance through preconditioning. The aim of the present study is to test the hypothesis that preconditioning with pentylenetetrazole (PTZ) may have protective effect against seizure induced by i.v. infusion of PTZ. Mice were preconditioned by low-dose administration of PTZ (25 mg/kg) for 5 consecutive days, and the threshold of seizure elicited by i.v. infusion of PTZ was measured. To investigate the possible role of nitric oxide, NOS inhibitor enzymes, including L-NG-nitro-L-arginine methyl ester hydrochloride (L-NAME) (10 mg/kg), aminoguanidine (AG) (50 mg/kg), 7-nitroindazole (7-NI) (15 mg/kg), and L-arginine (L-arg) (60 mg/kg), were administered concomitantly with PTZ in both acute and chronic phases. Determination of seizure threshold revealed significant enhancement after preconditioning with low dose of PTZ. While the protective effect of PTZ preconditioning was enhanced after the administration of L-arg, it was reversed following administration of L-NAME and 7NI, suggesting the involvement of nitric oxide pathway as an underlying mechanism of PTZ-induced preconditioning. Preconditioning with PTZ led to brain tolerance and adaptive response in animal model of PTZ-induced seizure. This effect is in part due to the involvement of nitric oxide pathway.

Anti-inflammatory effects of Metformin improve the neuropathic pain and locomotor activity in spinal cord injured rats: introduction of an alternative therapy.

STUDY DESIGN: This is an animal study. OBJECTIVES: Metformin is a safe drug for controlling blood sugar in diabetes. It has been shown that metformin improves locomotor recovery after spinal cord injury (SCI). Neuropathic pain is also a disturbing component of SCI. It is indicated that metformin has neuroprotective and anti-inflammatory effects, which attenuate neuropathic pain and hyperalgesia in injured nerves. Thus, we evaluated metformin's therapeutic effects on SCI neuroinflammation and its sensory and locomotor complications. Meanwhile, results were compared to minocycline, an anti-neuroinflammation therapy in SCI. SETTING: Experimental Medicine Research Center, Tehran University of Medical Sciences, Iran METHODS: In an animal model of SCI, 48 male rats were subjected to T9 vertebra laminectomy. Animals were divided into a SHAM-operated group and five treatment groups. The treatments included normal saline as a vehicle control group, minocycline 90 mg/kg and metformin at the doses of 10, 50 and 100 mg/kg. Locomotor scaling, behavioral tests for neuropathic pain and weight changes were evaluated and compared through a 28-days period. At the end of the study, tissue samples were taken to assess neuroinflammatory changes. RESULTS: Metformin 50 mg/kg improved the locomotors ability (p < 0.001) and decreased sensitivity to mechanical and thermal allodynia (p < 0.01). These results were compatible with minocycline effect on SCI (p > 0.05). While metformin led to weight loss, both metformin and minocycline significantly decreased neuroinflammation in the assessment of cord tissue histopathology, and levels of TNF-α and interleukin-1ß (p < 0.001). CONCLUSIONS: Metformin could be considered as an alternative therapeutic agent for SCI, as it potentially attenuates neuroinflammation, sensory and locomotor complications of cord injury.

The expression, localization and function of α7 nicotinic acetylcholine receptor in rat corpus cavernosum.

OBJECTIVES: Alpha7 nicotinic acetylcholine receptor (α7-nAChR), an emerging pharmacological target for a variety of medical conditions, is expressed in the most mammalian tissues with different effects. So, this study was designed to investigate the expression, localization and effect of α7-nAChR in rat corpus cavernosum (CC). METHODS & KEY FINDINGS: Reverse transcription polymerase chain reaction (RT-PCR) revealed that α7-nAChR was expressed in rat CC and double immunofluorescence studies demonstrated the presence of α7-nAChR in corporal neurons. The rat CC segments were mounted in organ bath chambers and contracted with phenylephrine (0.1 µm -300 µm) to investigate the relaxation effect of electrical field stimulation (EFS,10 Hz) assessed in the presence of guanethidine (adrenergic blocker, 5 µm) and atropine (muscarinic cholinergic blocker, 1 µm) to obtain non-adrenergic non-cholinergic (NANC) response. Cumulative administration of nicotine significantly potentiated the EFS-induced NANC relaxation (-log EC50 = 7.5 ± 0.057). Whereas, the potentiated NANC relaxation of nicotine was significantly inhibited with different concentrations of methyllycaconitine citrate (α7-nAChR antagonist, P < 0.05) in preincubated strips. L-NAME (non-specific nitric oxide synthase inhibitor, 1 µm) completely blocked the neurogenic relaxation induced by EFS plus nicotine. CONCLUSION: To conclude α7-nAChR is expressed in rat CC and modulates the neurogenic relaxation response to nicotine.

Protective effects of agmatine on doxorubicin-induced chronic cardiotoxicity in rat.

The detrimental cardio-toxic effect of doxorubicin, an effective chemotherapeutic agent, limited its clinical use. It has been claimed that doxorubicin cardio-toxicity occurs through calcium ions (Ca2+) overload and reactive oxygen species production. Agmatine, an endogenous imidazoline receptor agonist, induce uptake of cytosolic Ca2+ and cause an increase in activity of calcium pumps, including Ca2+-ATPase. Also it shows self-scavenging effect against reactive oxygen species production. Therefore, present study was designed to investigate the effects of agmatine against chronic cardio-toxicity of doxorubicin in rats. Male wistar rats were intraperitoneally injected with doxorubicin and agmatine four times a week for a month. Agmatine significantly alleviate the adverse effect of doxorubicin on left ventricular papillary muscle stimulation threshold and contractibility. Chronic co-administration of agmatine with doxorubicin blocked electrocardiographic changes induced by doxorubicin. In addition, agmatine improved body weight and decreased the mortality rate of animals by doxorubicin. Moreover, reversing the doxorubicin induced myocardial lesions was observed in animals treated by agmatine. A significant rise in the total antioxidant capacity of rat plasma was achieved in agmatine-treated animals in comparison to doxorubicin. To conclude, agmatine may improve therapeutic outcomes of doxorubicin since it exerts protective effects against doxorubicin-induced chronic cardiotoxicity in rats.