Marchi Nicola, Guiso Giovanna, Rizzi Massimo, Pirker Susanne, Novak Klaus, Czech Thomas, Baumgartner Christoph, Janigro Damir, Caccia Silvio, Vezzani Annamaria
Department of Neuroscience, Mario Negri Institute for Pharmacological Research, Milan, Italy.
Epilepsia. 2005 Oct;46(10):1613-9. doi: 10.1111/j.1528-1167.2005.00265.x.
We measured the brain-to-plasma partition of 10,11-dihydro-10-hydroxy-5H-dibenzo(b,f)azepine-5-carboxamide (10-OHCBZ) in epilepsy patients undergoing surgery to alleviate drug-resistant seizures and administered with different oral doses of oxcarbazepine (OXC). We addressed the possible contribution of the multidrug transporter P-glycoprotein (P-gp or MDR1) in determining 10-OHCBZ brain levels by measuring whether this active metabolite is a substrate of P-gp and the relation between the level of expression of MDR1 and the drug concentration in the same brain tissue specimens.
Steady-state plasma and brain concentrations (C(ss)) of 10-OHCBZ were determined intraoperatively in 11 patients by high-performance liquid chromatography (HPLC) with UV detection. The level of expression of MDR1 mRNA was measured in surgically resected brain tissue by reverse transcriptase polymerase chain reaction (RT-PCR). The ability of 10-OHCBZ to act as substate of P-gp was evaluated by measuring its uptake in cell lines expressing different levels of P-gp, in the presence or absence of a selective P-gp inhibitor.
OXC was converted to 10-OHCBZ and to Di-OHCBZ, the two main metabolites measured in plasma. The brain concentrations of the active metabolite 10-OHCBZ did not reflect plasma C(ss). A significant inverse linear correlation was found between 10-OHCBZ brain-to-plasma concentration ratio and the level of brain expression of MDR1 mRNA. In vitro uptake studies demonstrated lower intracellular 10-OHCBZ levels in cells with higher P-gp expression. Intracellular drug concentration was increased by XR9576, a specific P-gp blocker.
Pharmacologic failure of OXC in pharmacoresistant epilepsy is unlikely to be due to alterations in drug metabolism. 10-OHCBZ does not appear to cross the blood-brain barrier by simple diffusion, and it acts as a substrate of P-gp. The level of expression of MDR1 is inversely correlated with 10-OHCBZ concentration in the epileptic tissue. P-gp may play a role in the pharmacoresistance to OXC by determining the attainment of insufficient concentrations of its active metabolite at neuronal targets.
我们测定了接受手术以缓解耐药性癫痫发作且服用不同口服剂量奥卡西平（OXC）的癫痫患者体内10,11-二氢-10-羟基-5H-二苯并[b,f]氮杂䓬-5-甲酰胺（10-OHCBZ）的脑-血浆分配情况。我们通过测量这种活性代谢物是否为P-糖蛋白（P-gp或MDR1）的底物以及同一脑组织标本中MDR1的表达水平与药物浓度之间的关系，探讨了多药转运蛋白P-糖蛋白在决定10-OHCBZ脑内水平方面的可能作用。
通过高效液相色谱（HPLC）结合紫外检测法，术中测定了11例患者体内10-OHCBZ的稳态血浆和脑浓度（C(ss)）。通过逆转录聚合酶链反应（RT-PCR）测定手术切除脑组织中MDR1 mRNA的表达水平。通过在表达不同水平P-gp的细胞系中测量10-OHCBZ的摄取情况，在有或没有选择性P-gp抑制剂的情况下，评估10-OHCBZ作为P-gp底物的能力。
OXC转化为10-OHCBZ和二羟基奥卡西平（Di-OHCBZ），这是血浆中检测到的两种主要代谢物。活性代谢物10-OHCBZ的脑浓度并未反映血浆C(ss)。在10-OHCBZ脑-血浆浓度比与MDR1 mRNA的脑表达水平之间发现了显著的负线性相关性。体外摄取研究表明，P-gp表达较高的细胞内10-OHCBZ水平较低。特异性P-gp阻滞剂XR9576可增加细胞内药物浓度。
OXC在药物难治性癫痫中药物治疗失败不太可能是由于药物代谢改变所致。10-OHCBZ似乎不是通过简单扩散穿过血脑屏障的，并且它是P-gp的底物。MDR1的表达水平与癫痫组织中10-OHCBZ的浓度呈负相关。P-gp可能通过决定其活性代谢物在神经元靶点处达到不足的浓度，在对OXC的药物抵抗中发挥作用。
