| Background: Epilepsy, one of the most common neurological disorders, its pathophysiological alterations are abnormal discharges originating simultaneously in partial or both hemispheres of the brain, characterized by the periodic and unpredictable occurrence of seizures. Accompanied by considerable progress in understanding the pathogenesis and drug therapy in epilepsy, the majority of patients have good prognosis and be free from seizures. But in about 30% patients are refractory to treatment, and seizures can not be controlled by more than one first-line antiepileptic drugs, which we called refractory epilepsy. Refractory epilepsy is with increased morbidity and mortality and poor prognosis, it has been always a difficult problem to neurological doctors. Therefore to investigate the drug resistance mechanism of refractory epilepsy, and develop new strategies for treatment may have the deep influence in future. Researchers found that many patients who got cancer would yield resistance to anticancer drugs after a period of treatment, the growth of cancer cells would not be suppressed by chemotherapy in this condition. The following research indicate that membrane of cancer cells express multi-drug transporters, they act as drug efflux pump and restrict penetration of anticancer drug into cell, which produce chemotherapy-resistance in cancer. Whether there are the same pathophysiological mechanisms of drug resistance in both epilepsy and cancer arouse wide interests, and a series of research concerning the relationship between multi-drug transporters and drug resistance in epilepsy have been done. The results suggest that several kinds of multi-drug transporters are expressed in the capillary endothelial cells of blood-brain barrier in normal human being. In surgically resected epileptogenic human brain specimens of patients with refractory epilepsy, multi-drug transporters are increasingly expressed in blood brain barrier, and over expression of multi-drug transporters are found in reactive astrocytes in epileptogenic tissue. To investigate its function find that multi-drug transporters are ATP-binding cassette superfamily, they can accept a wide range of antiepileptic drugs with different mechanisms as their potential substrates, and actively efflux drugs out of the brain. It is suggest that multi-drug transporters are increasingly expressed in brain of refractory epileptic patients, limiting penetration of antiepileptic drugs into the brain, lowering the concentration of drugs in the vicinity of epileptogenic focus, this mechanisms maybe involved in the drug resistance in refractory epilepsy. PGP and MRP are recognized as the most important multi-drug transporters expressed in brain. In this article, we investigated the expression of PGP and MRP inbrain of temporal lobe epileptic model, and the influence of PGP and MRP on the penetration of antiepileptic drugs through the blood-brain barrier. In view of its form and function , we intended to explore the role of PGP and MRP on the drug resistance mechanisms of refractory epilepsy.Materials and methods: We divided this research into two parts. In the first part, temporal lobe epileptic model by intracerebroventricular injection of KA was used. The expression of PGP mRNA and MRP mRNA was investigated in cortex and hippocampus in rats of control group^ KA injection 6 hour group? KA injection 24 hour group^ KA injecton 1 week group by RT-PCR technique. The expression of PGP and MRP was investigated in cortex and hippocampus in rat of control group ^ KA injection 6 hour group ^ KA injection 24 hour group > KA injecton 1 week group by immunohistochemistry staining. In the second part, we used microdialysis and high-performance liquid chromatography (HPLC), after i.p. injection of carbamazepine 20 mg/kg and 40 mg/kg, characterized the pharmacokinetics of carbamazepine in cortex and hippocampus regions of brain in rats. After i.p. injection of phenytoin 50 mg/kg and 100 mg/kg, characterized the pharmacokinetics of phenytoin in cortex and hippocampus regions of brain in rats. In the subsequent experiments, we choose carbamazepine 20 mg/kg and phenytoin 50 mg/kg as i.p. injection dose, local application of PGP inhibitor-verapamil in brain through microdialysis probe, to study whether the concentration of carbamazepine and phenytoin in extracellular fluid of cortex in rats were enhanced by verapamil . Local application of MRP inhibitor-probenecid through microdialysis probe, to study whether the concentration of carbamazepine and phenytoin in extracellular fluid of cortex in rats were enhanced by probenecid.Results: The results of first part of experiments elucidated that: 1, Compared with control group, PGP mRNA was relatively little increased in cortex in rats 6 hours after intracerebroventricular injection of KA, but did not have significant difference; PGP mRNA was significantly increased in cortex 24 hour after intracerebroventricular injection of KA (p<0.05), and returned to normal level lweek after KA injection; there was no difference in PGP mRNA expression in hippocampus in rats among each group. Agreed with PGP mRNA expression, immunohistochemistry experiments found that PGP immunopositive staining was significantly increased 24 hour after intracerebroventricular injection of KA(p<0.05), increased PGP was observed in neurons^ astrocytes and microvessel endothelial cells, not only on membrane but also in cytosol. The increased PGP expression could not be detected 1 week after KA injection. The expression of PGP in hippocampus in rats showed no significant difference among each group. 2, Compared with control group, MRP mRNA was relatively little increased in cortex in rats 6 hours after intracerebroventricular injection of KA, but did not have significant difference; MRP mRNA was significantly increased in cortex 24 hour after intracerebroventricular injection of KA...
|
PDF Full Text Request