Ling Binbing, Alcorn Jane
College of Pharmacy and Nutrition, University of Saskatchewan, Saskatoon, SK, S7N 5C9 Canada.
J Nutr. 2008 Jul;138(7):1317-22. doi: 10.1093/jn/138.7.1317.
Our study investigated the potential for important in vivo drug-nutrient transport interactions at the lactating mammary gland using the L-carnitine transporter substrates, cefepime and L-carnitine, as proof-of-concept. On d 4 (n = 6/treatment) and d 10 (n = 6/treatment) of lactation, rats were administered cefepime (250 mg/h) or saline by continuous i.v. infusion (4 h). Serum and milk L-carnitine and cefepime concentrations were quantified by HPLC-UV. In whole mammary gland, organic cation/carnitine transporter (OCTN)1, OCTN2, OCTN3, amino acid transporter B(0,+) (ATB(0,+)), and L-carnitine transporter 2 expression were determined by quantitative RT-PCR and by western blot and immunohistochemistry when possible. Cefepime caused a 56% decrease in milk L-carnitine concentrations on lactation d 4 (P = 0.0048) but did not affect milk L-carnitine at lactation d 10 or serum L-carnitine concentrations at either time. The mean L-carnitine and cefepime milk:serum ratios (M/S) decreased from 9.1 +/- 0.4 to 4.9 +/- 0.6 (P < 0.0001) and 0.89 +/- 0.3 to 0.12 +/- 0.02 (P = 0.0473), respectively, between d 4 and d 10 of lactation. In both groups, OCTN2 (P < 0.0001), OCTN3 (P = 0.0039), and ATB(0,+) (P = 0.004) mRNA expression and OCTN2 protein (P < 0.0001) were higher in mammary glands at d 4 of lactation compared with d 10. Immunohistochemistry revealed OCTN1 and OCTN2 localization in the mammary alveolar epithelium and OCTN3 expression in the interstitial space and blood vessel endothelium. In conclusion, cefepime significantly decreased milk L-carnitine concentrations only at d 4 of lactation. Relative to d 10, enhanced expression of OCTN2 and ATB(0,+) in mammary glands at d 4 of lactation and higher M/S (L-carnitine and cefepime) suggests cefepime competes with L-carnitine for L-carnitine transporters expressed in the lactating mammary gland to adversely affect L-carnitine milk concentrations and these effects depend upon lactation stage.
我们的研究以L-肉碱转运体底物头孢吡肟和L-肉碱作为概念验证，调查了哺乳期乳腺中体内重要的药物-营养物质转运相互作用的可能性。在哺乳期第4天（每组n = 6）和第10天（每组n = 6），通过静脉持续输注（4小时）给大鼠注射头孢吡肟（250mg/h）或生理盐水。通过高效液相色谱-紫外检测法定量血清和乳汁中L-肉碱和头孢吡肟的浓度。在整个乳腺中，尽可能通过定量逆转录-聚合酶链反应、蛋白质免疫印迹法和免疫组织化学法测定有机阳离子/肉碱转运体（OCTN）1、OCTN2、OCTN3、氨基酸转运体B(0,+)（ATB(0,+)）和L-肉碱转运体2的表达。头孢吡肟使哺乳期第4天乳汁中L-肉碱浓度降低了56%（P = 0.0048），但在哺乳期第10天不影响乳汁中L-肉碱浓度，在两个时间点均不影响血清中L-肉碱浓度。哺乳期第4天和第10天之间，L-肉碱和头孢吡肟的平均乳汁:血清比值（M/S）分别从9.1±0.4降至4.9±0.6（P < 0.0001）和从0.89±0.3降至0.12±0.02（P = 0.0473）。在两组中，哺乳期第4天乳腺中OCTN2（P < 0.0001）、OCTN3（P = 0.0039）和ATB(0,+)（P = 0.004）的mRNA表达以及OCTN2蛋白（P < 0.0001）均高于第10天。免疫组织化学显示OCTN1和OCTN2定位于乳腺腺泡上皮，OCTN3表达于间质空间和血管内皮。总之，头孢吡肟仅在哺乳期第4天显著降低乳汁中L-肉碱浓度。相对于第10天，哺乳期第4天乳腺中OCTN2和ATB(0,+)表达增强以及更高的M/S（L-肉碱和头孢吡肟）表明头孢吡肟与L-肉碱竞争哺乳期乳腺中表达的L-肉碱转运体，从而对乳汁中L-肉碱浓度产生不利影响，且这些影响取决于哺乳期阶段。
