Chen Xiaomei, Keep Richard F, Liang Yan, Zhu Hao-Jie, Hammarlund-Udenaes Margareta, Hu Yongjun, Smith David E
Department of Pharmaceutical Sciences, College of Pharmacy, University of Michigan, Ann Arbor, MI, USA.
Department of Neurosurgery, University of Michigan Health System, Ann Arbor, MI, USA.
Biochem Pharmacol. 2017 May 1;131:89-97. doi: 10.1016/j.bcp.2017.02.005. Epub 2017 Feb 10.
Peptide transporter 2 (PEPT2) is a high-affinity low-capacity transporter belonging to the proton-coupled oligopeptide transporter family. Although many aspects of PEPT2 structure-function are known, including its localization in choroid plexus and neurons, its regional activity in brain, especially extracellular fluid (ECF), is uncertain. In this study, the pharmacokinetics and regional brain distribution of cefadroxil, a β-lactam antibiotic and PEPT2 substrate, were investigated in wildtype and Pept2 null mice using in vivo intracerebral microdialysis. Cefadroxil was infused intravenously over 4h at 0.15mg/min/kg, and samples obtained from plasma, brain ECF, cerebrospinal fluid (CSF) and brain tissue. A permeability-surface area experiment was also performed in which 0.15mg/min/kg cefadroxil was infused intravenously for 10min, and samples obtained from plasma and brain tissues. Our results showed that PEPT2 ablation significantly increased the brain ECF and CSF levels of cefadroxil (2- to 2.5-fold). In contrast, there were no significant differences between wildtype and Pept2 null mice in the amount of cefadroxil in brain cells. The unbound volume of distribution of cefadroxil in brain was 60% lower in Pept2 null mice indicating an uptake function for PEPT2 in brain cells. Finally, PEPT2 did not affect the influx clearance of cefadroxil, thereby, ruling out differences between the two genotypes in drug entry across the blood-brain barriers. These findings demonstrate, for the first time, the impact of PEPT2 on brain ECF as well as the known role of PEPT2 in removing peptide-like drugs, such as cefadroxil, from the CSF to blood.
肽转运体2（PEPT2）是一种高亲和力、低容量的转运体，属于质子偶联寡肽转运体家族。尽管PEPT2的结构功能在很多方面已为人所知，包括其在脉络丛和神经元中的定位，但其在脑内的区域活性，尤其是细胞外液（ECF）中的活性尚不确定。在本研究中，使用体内脑微透析技术，对野生型和Pept2基因敲除小鼠中头孢羟氨苄（一种β-内酰胺类抗生素及PEPT2底物）的药代动力学和脑内区域分布进行了研究。以0.15mg/（min·kg）的速度静脉输注头孢羟氨苄4小时，采集血浆、脑ECF、脑脊液（CSF）和脑组织样本。还进行了通透表面积实验，以0.15mg/（min·kg）的速度静脉输注头孢羟氨苄10分钟，采集血浆和脑组织样本。我们的结果表明，PEPT2基因敲除显著提高了头孢羟氨苄在脑ECF和CSF中的水平（2至2.5倍）。相比之下，野生型和Pept2基因敲除小鼠脑细胞中头孢羟氨苄的含量没有显著差异。Pept2基因敲除小鼠中头孢羟氨苄在脑内的非结合分布容积降低了60%，表明PEPT2在脑细胞中具有摄取功能。最后，PEPT2不影响头孢羟氨苄的流入清除率，因此排除了两种基因型在药物通过血脑屏障进入方面的差异。这些发现首次证明了PEPT2对脑ECF的影响，以及PEPT2在将肽类药物（如头孢羟氨苄）从CSF清除到血液中的已知作用。
