| Background: P-glycoprotein (P-gp) is one of the blood–brain barrier efflux transporters that limit anti-epileptic drugs into the brain in pharmacoresistant epilepsy patients. There was recent evidence that the brain inflammatory response may contribute to the development of drug-resistant epilepsy (DRE), and nuclear factor-kappa B (NF-κB) activation played a central role in this process. Previous studies have shown that the transport activity and expression level of P-gp is up-regulated by NF-κB activation under many brain inflammation conditions, such as carcinoma and human immunodeficiency virus. However, the role of NF-κB in regulating seizure-induced P-gp expression in the rat brain following epileptogenic insults has not been fully elucidated.Objective: This study was aimed to investigate the effect of NF-κB activity and expression on P-gp expression in the brain of epileptic rats, and to explore the association between P-gp overexpression and NF-κB activity. Meanwhile, the effect of NF-κB inhibition on the seizure severity and brain damage of epileptic rats was also focused on.Methods: Male SD rats were divided into saline control-sham group (NS group, n=8), epilepsy model group (EP group, n=14), epilepsy group pretreated with specific NF-κB inhibitor-pyrrolidine dithiocarbamate salt (PDTC group, n=14) and epilepsy group intervened with nonspecific NF-κB inhibitor-dexamethasone (DEX group, n=14). The seizure models were produced by kainic acid (KA) microinjection into hippocampus CA3 area and the rats in PDTC group and DEX group were treated with intraperitoneal injection of PDTC (150 mg/kg) or DEX (0.4 mg/kg) 30 min prior to KA injection. The latencies to grade III seizure and grade V seizure onset of each animal were recorded as well as the interval time of sustained 6 times of≥IVseizure of each rat (an indicator to evaluate the seizure severity). The rats were sacrificed 24 h after the KA injection. H.E. and immuno-histochemical study were performed to detect the brain pathological changes as well as P-gp and NF-κB (including the phosphorylation of p65 as the active form) expression levels. Neuron Specific Nuclear Protein (NeurN) was stained to count the survival neurons. Cells undergoing apoptosis were detected by TUNEL Assay.Results:(1)No seizures were observed in the rats of NS group. PDTC or DEX pre-treatment significantly increased the latency to grade III or V seizure onset compared to EP group. Compared with EP group, the interval time arranged from 1st to 6th≥IV seizure of the rats in PDTC group and DEX group was significantly prolonged. It implied that both PDTC and DEX pretreatment decreased the seizure susceptibility and severity.(2)Compared with that of the EP group, the number of the survival neurons showed a growing trend in rat brain of PDTC group and DEX group; but there were no statistics differences (P>0.05). The number of the apoptotic cells was also no significantly different among 4 groups (P>0.05), meaning the neuron loss was mainly due to necrosis rather than apoptosis. In all, both PDTC and DEX failed to show obvioursly neuron-protective effect.(3)The expression of P-gp and NF-κB p65 subunit in the rat brain of the EP group was significantly enhanced compared with NS group. P-gp expression along with NF-κB activation in the hippocampus CA3 area and amygdala complex of rats in PDTC group was significantly reduced compared with the EP group. It showed a positive rank correlation between the P-gp and NF-κB p65 expression. P-gp expression was also decreased in the DEX group but with no significant changes in NF-κB expression.Conclusions:(1) Both PDTC and DEX reduced the seizure susceptibility and severity of KA induced epileptic rats during the 24 h observation period, with no increasing the rat mortality and brain damage.(2) NF-κB inhibition with PDTC pre-treatment could abolish the P-gp over-expression in hippocampus CA3 and amygdale complex areas of epileptic rats. Although DEX pretreatment lowered the P-gp expression, it did not changed NF-κB activity and expression significantly in the brain of seizure rats. These findings implied that epileptogenic insults induced P-gp over-expression was partly regulated through NF-κB activation and there may be independent NF-κB signaling pathway in the regulation of P-gp expression.
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