Study Of P38MAPK On The Drug Resistance Mediated By P-glycoprotein In Rats With Medically Intractable Epilepsy

About30%of epileptic patients are refractory to treatment using more than one AEDs, which is called medically intractable epilepsy. P-glycoprotein (PGP) is one of the early discovered multidrug transporters and plays a key role in resistance to AEDs. The high expressed PGP is involved in drug resistance. It is able to use the AEDs as a substrate and pump AEDs out of the brain tissue or brain cells, leading to the decrease in the concentration of AEDs in the brain extracellular fluid, which may account for multidrug resistance in medically intractable epilepsy. The molecular mechanism of PGP expression is unclear. The p38mitogen-activated protein kinase (MAPK) signaling pathway mediates multiple cellular events, including proliferation, differentiation, migration, adhesion and apoptosis, in response to various extracellular stimuli, such as growth factors, hormones, inflammatory cytokines and stresses. A series of researches demonstrate that PGP expression can be induced by several factors, including cytotoxic drugs, irradiation, heat shock, and other stresses. These factors also activate the p38MAPK signaling pathway, suggesting that the p38MAPK signaling pathway may be involved in the regulation of PGP expression.In this study, the effect of p38MAPK on the expression of PGP was detected by Western blot and immunochemistry. Whether the inhibition of p38MAPK affects the concentration of two AEDs, lamotrigine (LTG) and Sodium Valproate (VPA), in hippocampal extracellular fluid of medically intractable epilepsy was also evaluated by microdialysis, high performance liquid chromatography (HPLC). And p38MAPK inhibitor-SB202190was applied to epileptic rats, while seizure activity was observed in PTZ-induced kindled rats.This task comprised of two parts below.Part I:The effect of p38MAPK on the expression of PGP in the brain and behavior in rats of epilepsy.After the esabilshment of PTZ-induced kindling model in rats, SB202190was administrated in hippocampal of rats by microdialysis, then to observe the behavior in epileptic rats. The effect of p38MAPK on the expression of PGP was observed by western blot and immunofluorescence. Part Ⅱ:The effect of p38MAPK on the concentration of AEDs in hippocampal extracellular fluid in rats of epilepsy.After the esabilshment of PTZ-induced kindling model in rats, VPA and LTG were injected. At the same time, SB202190was administrated in hippocampal of rats by microdialysis. The concentration of AEDs in hippocampal extracellular fluid in rats was detected by high performance liquid chromatography (HPLC).ResultsThe experimental results of Part I:Compared with the normal group, the expression of PGP and p38MAPK in brain of epileptic rats were significantly increased (p<0.01), which could be down-regulated with SB202190(p<0.05). In addition, seizures level and frequency were decreased in the SB202190group (p<0.05).The experimental results of Part Ⅱ:(1) Compared with the normal group, the concentration of VPA in hippocampal extracellular fluid in the epilepsy group were lower during30-120min after i.p.(p<0.05), while there was no significant difference at150min after i.p.(p>0.05); Compared with the epilepsy group, the concentration of VPA in hippocampal extracellular fluid in the SB202190group were higher during30-120min after i.p.(p<0.05), while there was no significant difference at150min after i.p.(p>0.05).(2) Compared with the normal group, the concentration of lamotrigine in hippocampal extracellular fluid in the epilepsy group were lower during30-90min after i.p., and also at150min after i.p.(p<0.05), while there was no significant difference at120min after i.p.(p>0.05); Compared with the epilepsy group, the concentration of lamotrigine in hippocampal extracellular fluid in the SB202190group were higher during30-150min after i.p.(p<0.05).(3) Time of peak concentration of sodium valproate of the epilepsy group is that60min after the administration, same with the SB202190group, both were failed behind the normal group with the time at30min after the administration.(4) Time of peak concentration of lamotrigine of the epilepsy group is that90min after the administration, same with the SB202190group, both were failed behind the normal group with the time at60min after the administration.Conclusions1. p38MAPK specific antagonist SB202190could reduce the expression of PGP in brain in rats with epilepsy. p38MAPK signaling pathways may concerned with the expression of PGP. Blocking p38MAPK signaling pathways could reduce the classification of seizure after kindling.2. p38MAPK specific antagonist SB202190could increase the concentration of VPA and LTG in hippocampal extracellular fluid in rats with epilepsy.3. p38MAPK might be involved in the mechanisms of drug resistance in intractable epilepsy by up-regulation of PGP.