Ueda M, Masu Y, Ando A, Maeda H, Del Monte M A, Uyama M, Ito S
Department of Ophthalmology, Kansai Medical University, Osaka, Japan.
Invest Ophthalmol Vis Sci. 1998 Apr;39(5):820-7.
To investigate the relationship between ornithine-delta-aminotransferase (OAT) deficiency and ornithine accumulation and the specific degeneration of retinal pigment epithelial (RPE) cells in gyrate atrophy.
Human RPE cells, human hepatoma cells, and human fibroblast cells were treated with 5-fluoromethylornithine (5-FMOrn), a specific irreversible inhibitor of OAT. Ornithine cytotoxicity was determined by using a [3H]thymidine incorporation assay and immunohistochemical staining for cytokeratin. The effects of various metabolites of ornithine and arginine, such as creatine, creatine phosphate, I-delta 1-pyrroline-5-carboxylic acid (L-P5C), and proline, which may be deficient in gyrate atrophy on RPE cell damage by ornithine, were determined by the same procedures.
When the human RPE cells, HepG2 hepatoma cells, and WI-38 fibroblast cells were treated with 0.5 mM 5-FMOrn for 30 minutes, which inactivated OAT, ornithine exhibited severe time- and dose-dependent inhibition of DNA synthesis in the human RPE cells but not in the HepG2 hepatoma cells or WI-38 fibroblast cells. The inhibition of DNA synthesis was accompanied by drastic changes in morphologic appearance, disorganization of the cytoskeleton, and cell death. Ornithine or 5-FMOrn alone did not exhibit such cytotoxicity to the RPE cells. Proline prevented the cytotoxicity of ornithine.
These findings suggest that an elevated level of ornithine combined with an increased sensitivity to ornithine as a result of OAT deficiency may be crucial to the specific RPE degeneration in gyrate atrophy. They suggest also that abnormalities of proline metabolism may be involved in the progress of gyrate atrophy.
研究鸟氨酸 - δ - 氨基转移酶（OAT）缺乏与鸟氨酸蓄积以及视网膜色素上皮（RPE）细胞在回旋状萎缩中的特异性变性之间的关系。
用人RPE细胞、人肝癌细胞和人成纤维细胞，用OAT的特异性不可逆抑制剂5 - 氟甲基鸟氨酸（5 - FMOrn）进行处理。通过[³H]胸腺嘧啶核苷掺入试验和细胞角蛋白免疫组化染色来测定鸟氨酸的细胞毒性。通过相同程序测定鸟氨酸和精氨酸的各种代谢产物，如肌酸、磷酸肌酸、I - δ¹ - 吡咯啉 - 5 - 羧酸（L - P5C）和脯氨酸，这些在回旋状萎缩中可能缺乏的物质对鸟氨酸所致RPE细胞损伤的影响。
当人RPE细胞、HepG2肝癌细胞和WI - 38成纤维细胞用0.5 mM 5 - FMOrn处理30分钟使OAT失活时，鸟氨酸对人RPE细胞的DNA合成表现出严重的时间和剂量依赖性抑制，但对HepG2肝癌细胞或WI - 38成纤维细胞无此作用。DNA合成的抑制伴随着形态外观的剧烈变化、细胞骨架的紊乱和细胞死亡。单独的鸟氨酸或5 - FMOrn对RPE细胞未表现出这种细胞毒性。脯氨酸可预防鸟氨酸的细胞毒性。
这些发现表明，鸟氨酸水平升高以及由于OAT缺乏导致对鸟氨酸敏感性增加，可能对回旋状萎缩中RPE细胞的特异性变性至关重要。它们还表明脯氨酸代谢异常可能参与了回旋状萎缩的进展。
