Melatonin inhibits LPS-induced NO production in rat endothelial cells

• Published in: Journal of pineal research Vol. 46; no. 3; pp. 268 - 274
• Main Authors: Tamura, Eduardo Koji, Cecon, Erika, Monteiro, Alex Willian Arantes, Silva, Cláudia Lúcia Martins, Markus, Regina Pekelmann
• Format: Journal Article
• Language: English
• Published: Oxford, UK Blackwell Publishing Ltd 01.04.2009; Blackwell
• Subjects: Analysis of Variance; Animals; aorta; Aorta - drug effects; Aorta - metabolism; Biological and medical sciences; bradykinin; Cells, Cultured; Endothelial Cells - drug effects; Endothelial Cells - metabolism; endothelium; Fundamental and applied biological sciences. Psychology; lipopolysaccharide; Lipopolysaccharides - immunology; Male; melatonin; Melatonin - pharmacology; NF-kappa B - metabolism; nitric oxide; Nitric Oxide - metabolism; Nitric Oxide Synthase Type II - metabolism; Rats; Rats, Wistar; Vasodilation - drug effects; Vertebrates: endocrinology; Endothelial cell; Melatonin; Rat; Peptide hormone; Rodentia; Neuropeptide; Artery; Endothelium; Vertebrata; Mammalia; Blood vessel; Animal; Bradykinin; Nitric oxide; Lipopolysaccharide; Aorta; Circulatory system; Pineal hormone
• ISSN: 0742-3098; 1600-079X
• DOI: 10.1111/j.1600-079X.2008.00657.x

:  Endothelial cells produce NO by activation of constitutive nitric oxide synthase (NOS) and transcription of inducible NOS (iNOS). We have previously shown that melatonin, in the nanomolar range, inhibits activation of constitutive NOS, and in the present paper, we evaluated whether it could interfere with the expression of iNOS, which is activated by lipopolysaccharide (LPS), a major component of gram‐negative bacteria cell walls. Primary cultures of rat endothelial cells were loaded with fluorescent probe for NO detection. Nuclear factor kappa B (NF‐κB) translocation in endothelial cells elicited by LPS was measured by electromobility shift assay, and the vasodilation of aortic rings was accessed by recording isometric contraction. Melatonin in a micromolar but not in a nanomolar range inhibits the NO production induced by LPS. This effect is not dependent on the activation of G protein‐coupled melatonin receptors. The nuclear NF‐κB translocation is a process necessary for iNOS transcription, and melatonin also inhibits its translocation. LPS induced vasodilation only in endothelium‐intact aortic rings, and melatonin (10 μm) inhibits the vasodilation. Here, we show that concentrations compatible with nocturnal melatonin surge (nm) did not interfere with the activity of iNOS. Considering that micromolar melatonin concentrations could be locally achieved through production by activated immune competent cells, extra‐pineal melatonin could have a protective effect against tissue injury. We propose that melatonin blocked the LPS‐induced vasodilation by inhibiting the NF‐κB pathway. Finally, we propose that the effect of melatonin on vascular reactivity is one of the mechanisms that underlies the protective effect of this indolamine against LPS.