Melatonin protects against oxidized low-density lipoprotein-induced inhibition of nitric oxide production in human umbilical artery

We evaluated the antioxidative effect of melatonin on the oxidized low-dens ity lipoprotein (LDL)-induced impairment of nitric oxide (NO) production in human umbilical artery, which may be the prime cause of endothelial dysfun ction in pre-eclampsia. Umbilical artery sections with intact endothelium w ere obtained from healthy pregnant women who were delivered between 37 and 40 wk of gestation. The production of NO in the umbilical arteries was stim ulated by adding L-arginine followed by incubation for 60 min. NO concentra tions were estimated by measuring nitrite ions (NO2-) using high-performanc e liquid chromatography. LDL was oxidized by incubation with 5 muM CuSO4 at 37 degreesC for 4 hr, followed by dialysis at 4 degreesC for 24 hr. Prior to the addition Of L-arginine, the segments were treated with native or oxi dized LDL (0, 50, 100, 200, 400 mug/mL), or were pre-treated with either ma nnitol (50 mM) or melatonin (20, 100, 500 muM) before adding oxidized LDL. Changes in L-arginine-induced NOT production were expressed as a percentage of NO2- production at the end of pre-incubation. Treatment with oxidized L DL significantly reduced L-arginine-induced NOT production (P < 0.05), whil e NO2- production did not change by incubation with native LDL. Pre-treatme nt with melatonin significantly increased NO2- production that had been dec reased by oxidized LDL (P < 0.05). Similarly, pre-treatment with mannitol r eversed the oxidized LDL-induced reduction in NO2- production (P < 0.05). T hese results indicate that melatonin protects against oxidized LDL-induced inhibition of NO production in the endothelium of human umbilical arteries, most likely through its ability to scavenge hydroxyl radicals.