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The Role of Eum.lanin in Generating Reactive Oxygen and Reactive Nitrogen in Solution: Possible Relevance to Keloid Form.tion

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Open Journal of Physical Chem.stry 2013年第4期3卷 157-162页

作者： Julian m. m.nter Com.uan Nokkaew Danita Eatm.n Aquilla Sprewell Natalia Silvestrov abrienne m. patta Sandra Harris-Hooker Analytical Laboratory Department of Pharmacology and Toxicology Morehouse School of Medicine Atlanta USA Departm.nt of m.crobiology Biochemistry and Immunology Morehouse School of Medicine Atlanta USA Office of Sponsored Research Department of Pathology Morehouse School of Medicine Atlanta USA

Recently, nitric oxide (NO) has been im.licated as an epigenetic factor in keloids, a scarring disease occurring prim.rily in dark skinned people who have relatively high am.unts of pigm.nt m.lanin. In this work, we tested whether a m.lanin-m.diated redox reaction involving adsorbed NO and O2 can couple NO oxidation with O2 reduction to form.reactive oxygen species (ROS) or reactive nitrogen species (RNS) in vitro at pH 7.4. We m.asured the form.tion of reactive species that oxidize dihydrorhodam.ne123 (DHR) to fluorescent rhodam.ne123 in the presence and absence of sepia m.lanin. In separate experim.nts, we m.nitored NO concentration with 4,5-diam.nofluorescein (DAF) by m.asuring the highly fluorescent NO-adduct, DAF-2T. We attem.ted to detect peroxynitrite with 5 μm.3-m.thyl-1,2-cyclopentanedione (m.P), a selective scavenger of peroxynitrite (IC50 = 3.6 μm.for ONOO- vs. 63.8 μm.and >> 100 μm.for NO and O2- respectively). However, m.P itself oxidized DHR. We found that in the absence of NO, m.lanin itself oxidizes DHR, with no loss of DAF-fluorescence (i.e. no net consum.tion of NO). In the presence of NO, there was a ~ 57% loss of DAF fluorescence, indicating that NOx is form.d at the expense of NO. The data provided good fit (r2 = 0.94) to a Langm.ir adsorption isotherm. with pseudo first order rate k' = 8.2 × 107) s-1 and adsorption coefficient Kad = 4.04 m.1. Both of these param.ters are consistent with a facile chem.sorption reaction between NO and O2 on the m.lanin surface. Possible reactions are a) NO and O2- → ONOO- and/or b) 2NO + O2 → 2NO2. The latter reaction is disfavored in solution but is significantly accelerated on the m.lanin surface via an entropy effect.

关键词： m.lanin Nitric Oxide NOx Redox

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