Okatani Y, Wakatsuki A, Reiter R J
Department of Obstetrics and Gynecology, Kochi Medical School, Japan.
Biochem Biophys Res Commun. 2000 Oct 22;277(2):470-5. doi: 10.1006/bbrc.2000.3687.
Hyperhomocysteinemia is a major and independent risk factor for vascular disease. Oxidative stress is a possible mechanism for homocysteine (Hcy)-induced endothelial dysfunction. Herein, we evaluated the antioxidant property of melatonin (MLT) in relation to the vasoconstrictive effect of Hcy on the human umbilical artery. In an initial experiment in a cell-free system, a micromolar concentration of iron was found to catalyze oxygen-dependent oxidation of Hcy. MLT (10 or 100 microM) did not affect oxygen-dependent oxidation of Hcy. Next, smooth muscle contraction induced by prostaglandin F(2alpha) (10 microM) was measured in arterial strips. Hcy (10 to 500 microM) increased this vascular tension in a concentration-dependent manner (P < 0.0001). Addition of Fe(2+) (10 microM) significantly potentiated the Hcy effect. Removal of endothelium (P < 0.05), pretreatment with a nitric oxide (NO) synthesis inhibitor (l-N(G)-monomethylarginine, 200 microM, P < 0.001), or pretreatment with a hydroxyl radical (()OH) scavenger (mannitol, 10 mM, P < 0.001) significantly attenuated contraction potentiated by Hcy plus Fe(2+). At a much lower concentration than mannitol, MLT (1 to 100 microM) significantly reduced the contractile effect of Hcy and Fe(2+) in a concentration-dependent manner. Hcy plus Fe(2+) significantly impaired calcium ionophore A 23187-induced relaxation (P < 0.0001), while MLT restored this relaxation in a concentration-dependent manner. These findings suggest that Hcy potentiates vascular tension in human umbilical artery, possibly by suppressing bioavailable NO. MLT protects against the vasoconstrictive effect of Hcy, most likely by scavenging ()OH arising from Hcy autooxidation.
高同型半胱氨酸血症是血管疾病的一个主要且独立的危险因素。氧化应激是同型半胱氨酸（Hcy）诱导内皮功能障碍的一种可能机制。在此，我们评估了褪黑素（MLT）的抗氧化特性及其与Hcy对人脐动脉血管收缩作用的关系。在无细胞系统的初始实验中，发现微摩尔浓度的铁可催化Hcy的氧依赖性氧化。MLT（10或100微摩尔）不影响Hcy的氧依赖性氧化。接下来，在动脉条中测量前列腺素F2α（10微摩尔）诱导的平滑肌收缩。Hcy（10至500微摩尔）以浓度依赖性方式增加这种血管张力（P < 0.0001）。添加Fe2 +（10微摩尔）显著增强了Hcy的作用。去除内皮（P < 0.05）、用一氧化氮（NO）合成抑制剂（L-N(G)-单甲基精氨酸，200微摩尔，P < 0.001）预处理或用羟基自由基（OH）清除剂（甘露醇，10毫摩尔，P < 0.001）预处理可显著减弱Hcy加Fe2 +增强的收缩。在比甘露醇低得多的浓度下，MLT（1至100微摩尔）以浓度依赖性方式显著降低Hcy和Fe2 +的收缩作用。Hcy加Fe2 +显著损害钙离子载体A 23187诱导的舒张（P < 0.0001），而MLT以浓度依赖性方式恢复这种舒张。这些发现表明，Hcy可能通过抑制生物可利用的NO来增强人脐动脉的血管张力。MLT可防止Hcy的血管收缩作用，很可能是通过清除Hcy自氧化产生的OH。
