الفهرس 
INTRODUCTIONOnly 14 pages are availabe for public view
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Abstract
Worldwide, epilepsy is a common serious neurological disorder. Of all types of epilepsy, Temporal lobe epilepsy (TLE) is the most common form of partial epilepsy and is often resistant to the well-known pharmacological interventions. TLE can be triggered by different initial insults including traumatic brain injury, brain infections such as encephalitis and meningitis, hypoxic brain injury, stroke, cerebral tumors, genetic syndromes and status epilepticus. The occurrence of acute seizures is common during CNS infections which may result in late development of epilepsy.
To test potential antiepileptic treatments in rodents, the SE model triggered by the cholinergic agonist pilocarpine or its variant (in combination with lithium) has proven its usefulness as a model to study the pathophysiology and progression of TLE. This model resembles the behavioral, electrographic and neuropathological features of human TLE. Pilocarpine administration leads to SE and after a seizure-free latent period known as epileptogenesis, finally develops into a chronic condition characterized by spontaneous recurrent seizures.
Several neuronal alterations, which are involved in the pathophysiology of TLE, are also evident in the pilocarpine model of SE including: oxidative stress, neuro-inflammation hippocampal neurodegeneration and neuronal reorganization of certain brain areas especially those involving limbic structures. Moreover, Cognitive dysfunction, which is commonly frequent among TLE patient, has been demonstrated in pilocarpine epileptic animals.
Many antibiotics are now particularly interesting in the research field because they exert in addition to their immanent antibiotic activity, an array of brain protective functions. Of these antibiotics, rifampicin represents a promising neuro-protective candidate. Rifampicin is a semi-synthetic derivative of rifamycins which are the fermentation products of Nocardia meditterranei. The structure of rifamycins is characterized by a napthohydroquinone moiety extended by an aliphatic ansa chain, the lipophilicity of the ansa chain is mainly responsible for the drug transport across the blood-brain barrier (BBB). Rifampicin with its good lipophilic properties can permeate BBB and reach maximal serum concentration in 1–4 h after administration with plasma half-life of 2–5 h. Besides its well-known antibiotic activity, rifampicin was reported to exert potential neuroprotective effects in different CNS diseases such as cerebral ischemia, Alzheimer and Parkinson. The potential neuroprotective effect of rifampicin can be related to its antioxidant, anti-inflammatory and anti-apoptotic effects in various neuro-experimental models. Rifampicin can reduce ROS production, mitochondrial oxidative stress and function as a free radical scavenger with its naphthohydroquinone ring. It has been demonstrated that rifampicin can improve neuron survival against inflammation, suppress NF-kB pathways and reduce the release of pro-inflammatory cytokines and bacterial compounds; this may suggest the potential role of rifampicin as novel anti-inflammatory drug. Furthermore, rifampicin has been shown to suppress apoptotic pathways which play important role in different neurological disorders.
One of the clinically approved indications of rifampicin is chemoprophylaxis of bacterial meningitis. Meningitis is a common serious CNS infection. Various antibiotics are clinically approved for the management of meningitis. Nonetheless, bacterial meningitis is still associated with high mortality rates and permanent neurological sequelae that include epilepsy.
Considering the neuroprotective properties of rifampicin and that seizures are possible serious consequences of meningitis, this has directed this research towards testing the potential beneficial effects of rifampicin against seizures using lithium-pilocarpine model of SE.
In the present study, 4 groups of male albino rats in were adopted:
a) Control group: received saline and vehicle [PEG 400: distilled water (2:3)]
b) SE group: received pilocarpine (30 mg/kg, i.p) and vehicle
c) SE+RIF group: received pilocarpine (30 mg/kg, i.p) and two rifampicin doses (20mg/kg, i.p)
d) RIF group: received saline and two rifampicin doses (20mg/kg, i.p)
All animal groups received the following treatments:
1- Lithium chloride (127mg/kg, i.p) 24h prior to saline or pilocarpine injection.
2- Atropine sulphate (1mg/kg, i.p) 30 min prior to saline or pilocarpine injection
3- Diazepam (10mg/kg, i.p) one hour after experiencing SE
The following experiments were carried out:
1-Seizure assessment (seizure score, latency to develop SE, % animals developed SE) and mortality rate.
2- Histopathological examination.
3- Oxidative stress markers: Lipid peroxidation, reduced glutathione (GSH), Catalase activity.
4- Inflammatory markers: TNF-alpha, IL-1β, NF-κB and COX-2.
5- Apoptosis markers: e.g. Caspase 3 activity/level, Cytochrome C expression level.
6- Behavioral tests during latent period: locomotor activity and Morris Water Maze test.
In this study, rifampicin pretreatment (20 mg/kg, i.p) significantly reduced the percentage of rats reaching the SE, reduced the severity of seizures based on racine scale, delayed the onset of the SE and significantly decreased mortality rate at 24 hr after SE introduction.
HE staining of brain sections from SE rats showed significant neuronal damage in the hippocampal CA1 and CA3 areas at 24 hr after SE induction. However, rifampicin pretreatment exerted an obvious protective effect against pilocarpine induced hippocampal damage.
Regarding Oxidative damage markers assessment after SE induction; Our study demonstrated increased lipid peroxidation via MDA level as well as decreased GSH content at 24 h after pilocarpine induced seizures in the hippocampus. However, rifampicin pretreatment protected against MDA elevation and GSH depletion in hippocampus suggesting its antioxidant potential. Moreover, our results showed significant elevation in CAT activity at 24 h after SE, suggesting that CAT has an important cytoprotective role during acute seizures. Hippocampal CAT activity in rifampicin pretreated SE rats was slightly but non significantly higher than untreated SE rats.
Regarding apoptosis biomarkers; pilocarpine induced apoptosis was proved by significant increase in the expression of hippocampal cytochrome c and caspase 3 activity in SE rats. However, rifampicin prevented the induction of apoptosis in the hippocampus at 24hr after SE in this study. This indicate the potential anti apoptotic properties of rifampicin
Regarding the effect of lithium-pilocarpine induced seizures on different inflammatory markers in our present work, we found significant increase in tissue levels of IL-1β, TNF-α, NF-ĸB and COX-2 in the hippocampus at 24 hr after SE induction. In contrast, rifampicin pretreatment was able to inhibit the induction of IL-1β, TNF-α, NF-ĸB and COX-2 in the hippocampus suggesting the potential anti-inflammatory effect of rifampicin which may contribute to its neuroprotective effect against seizures.
In this study, MWM test results showed that SE rats suffered from significant memory impairment during the latent period. However, rifampicin alleviated memory impairment in SE rats, probably due to its potential neuroprotective effect against pilocarpine-induced hippocampal damage as demonstrated by H&E staining. Additionally, the results of locomotor activity testing revealed no significant effects of pilocarpine treatment on the motor ability of the rats indicating that impairment in MWM task in the SE rats was not attributed to abnormal movements
In this study, there was no statistical difference between the group treated with rifampicin alone and the control group concerning histopathological examination, oxidative stress, apoptosis, neuroinflammation and behavioral tests.