OCTN2 在内侧血视网膜屏障中对乙酰左旋肉碱的转运作用。

Involvement of OCTN2 in the transport of acetyl-L-carnitine across the inner blood-retinal barrier.

机构信息

Department of Pharmaceutics, Graduate School of Medicine and Pharmaceutical Sciences, University of Toyama, Toyama, Japan.

出版信息

Invest Ophthalmol Vis Sci. 2010 Jan;51(1):430-6. doi: 10.1167/iovs.09-4080. Epub 2009 Aug 13.

DOI:10.1167/iovs.09-4080

PMID:19684012

Abstract

PURPOSE

To elucidate the mechanisms of acetyl-L-carnitine transport across the inner blood-retinal barrier (inner BRB).

METHODS

In vivo integration plot and retinal uptake index (RUI) analyses were used to examine acetyl-L-[(3)H]carnitine transport in the retina across the inner BRB in rats. RUI was determined from the ratio of acetyl-L-[(3)H]carnitine and [(14)C]n-butanol, a freely diffusible internal reference, in the retina divided by the same ratio in the solution injected in the carotid artery. The transport mechanism was characterized in a conditionally immortalized rat retinal capillary endothelial cell line (TR-iBRB2 cells), as an in vitro inner BRB model.

RESULTS

The apparent influx permeability clearance (K(in)) per gram retina of acetyl-L-[(3)H]carnitine was found to be 2.31 microL/(minute . g retina). The K(in) of acetyl-L-[(3)H]carnitine was 3.7-fold greater than that of [(3)H]D-mannitol, a nonpermeable paracellular marker. Acetyl-L-[(3)H]carnitine uptake by the retina was found to be significantly inhibited by L-carnitine and acetyl-L-carnitine, supporting a carrier-mediated influx transport of acetyl-L-carnitine at the inner BRB. L-[(3)H]carnitine and acetyl-L-[(3)H]carnitine uptake by TR-iBRB2 cells was Na(+)- and concentration-dependent, with a K(m) of 29 and 26 microM, respectively. These forms of transport were significantly inhibited by organic cation/carnitine transporter (OCTN) substrates and inhibitors such as L-carnitine and acetyl-L-carnitine, tetraethylammonium, quinidine, and betaine. These transport properties are consistent with those of carnitine transport by OCTN2. OCTN2 was predominantly expressed in TR-iBRB2 cells and isolated rat retinal vascular endothelial cells.

CONCLUSIONS

The findings suggest that OCTN2 is involved in the transport of acetyl-L-carnitine from the circulating blood to the retina across the inner BRB.

摘要

目的

阐明乙酰-L-肉碱通过内血视网膜屏障（内 BRB）的转运机制。

方法

采用体内整合图和视网膜摄取指数（RUI）分析方法，研究大鼠视网膜对内 BRB 中乙酰-L-[(3)H]肉碱的转运。RUI 是通过将乙酰-L-[(3)H]肉碱与 [(14)C]正丁醇（一种可自由扩散的内参）在视网膜中的比值除以颈动脉注射溶液中的相同比值来确定的。在条件性永生化大鼠视网膜毛细血管内皮细胞系（TR-iBRB2 细胞）中作为体外内 BRB 模型，对转运机制进行了表征。

结果

发现乙酰-L-[(3)H]肉碱每克视网膜的表观渗透清除率（K(in)）为 2.31 μL/（min. g 视网膜）。乙酰-L-[(3)H]肉碱的 K(in)是不可渗透的旁细胞标记物 [(3)H]D-甘露醇的 3.7 倍。发现乙酰-L-[(3)H]肉碱的摄取被 L-肉碱和乙酰-L-肉碱显著抑制，支持乙酰-L-肉碱在内 BRB 处通过载体介导的内流转运。L-[(3)H]肉碱和乙酰-L-[(3)H]肉碱摄取由 TR-iBRB2 细胞是 Na(+)-和浓度依赖性的，K(m)分别为 29 和 26 μM。这些形式的转运被有机阳离子/肉碱转运体（OCTN）底物和抑制剂（如 L-肉碱和乙酰-L-肉碱、四乙铵、奎尼丁和甜菜碱）显著抑制。这些转运特性与 OCTN2 介导的肉碱转运特性一致。OCTN2 主要在内 BRB2 细胞和分离的大鼠视网膜血管内皮细胞中表达。