Abstract
Melatonin is a potent scavenger of reactive oxygen species or free radicals like superoxide and hydroxyl radicals. The oxidation of hemoglobin to methemoglobin (meth-Hb) by oxidizing compounds has been widely studied. The present work was designed to evaluate the ability of different concentrations of melatonin to inhibit nitrite–induced oxidation of hemoglobin. Blood samples were obtained from apparently healthy individuals from which erythrocyte hemolysate was prepared. Different concentrations of melatonin (10-9-1.0 mg/ml) were incubated for 10 min with the hemolysate, then to the resultant mixture 1 ml of sodium nitrite (final concentration 0.6 mM) was added, and the formation of meth-Hb was measured by monitoring absorbance of light at 631 nm each min for 30 min. Control samples without melatonin were utilized for comparison. Nitrite caused rapid oxidation of hemoglobin to meth-Hb in control samples; in the presence of melatonin, the oxidation process was delayed in a dose–dependent manner. The effect of melatonin on the time course of nitrite-induced oxidation of Hb showed that melatonin has a protective effect initiated early after addition along with nitrite. Melatonin also affect the time required for the formation of meth-Hb, the time required to convert 50% of the available Hb to meth-Hb was 4 min in the absence of melatonin, and became 17, 22, 26, 30, 114 and 383 min with increasing melatonin concentrations (10-9, 10-6, 0.001, 0.01, 0.1, and 1.0 mg/ml respectively). In conclusion, melatonin in a concentration and time dependent manner can protect Hb from oxidation by nitrite; melatonin delays the onset of autocatalytic stage and the protective effect extended over long period of time.
 Key words: melatonin, erythrocytes oxidation
Highlights
اى عولية اكسدة الهيوغلىبيي وتحىله الً هيتهيوغلوىبيي دود توو رااتوتهب بلووا واتوته وتهودر الدااتوة الحبليوة الوً تريوين هروداة تن الحصوى علوً عيٌوبم رم هوي.تراكيز هختلفة هي هبرة الويلاتىًيي علً هٌت أو تأخير حدوث عولية الأكسدة بوبرة ًبيتراي الصىريىم
The oxidation of Hb to Meth-Hb by nitrite has been widely studied, [7,8,9] formation of Meth-Hb occurs in two stages; there is a slow initial stage followed by a rapid autocatalytic stage, which carries the reaction to completion
(10) The present study has shown that melatonin can protect hemoglobin from oxidation by sodium nitrite in hemolysate, and there are two suggested theories for the mechanism through which melatonin produces this protective role; erythrocytes are utilized as a traditional target for studying oxidative damage, when exposed to high oxygen tensions and in presence of high iron contents oxidative damage occur due to both endogenous and exogenous insults
Summary
اى عولية اكسدة الهيوغلىبيي وتحىله الً هيتهيوغلوىبيي دود توو رااتوتهب بلووا واتوته وتهودر الدااتوة الحبليوة الوً تريوين هروداة تن الحصوى علوً عيٌوبم رم هوي.تراكيز هختلفة هي هبرة الويلاتىًيي علً هٌت أو تأخير حدوث عولية الأكسدة بوبرة ًبيتراي الصىريىم. [2] These it behaves in vitro as an electron donor, many studies prompted research on physiological antioxidant systems and molecules, and electrophilic compounds, such as the hydroxyl radical, Fe+3, or carbon centered radicals may stimulated the development of natural or act as acceptors in one-electron transfer synthetic compounds that prevent oxidative stress and damage mediated by an enhanced reactions, which convert the indolamine to the indolyl cation radical. The exact relationship between such activity and the concentrations required to perform it is not clarified, its ability to scavenge a broad spectrum of radicals could allow melatonin to behave as an antioxidant in various and possibly complex ways. [6] This study was designed to investigate the antioxidant activity of melatonin in different concentrations using an in vitro model of nitrite-induced hemoglobin oxidation The exact relationship between such activity and the concentrations required to perform it is not clarified, its ability to scavenge a broad spectrum of radicals could allow melatonin to behave as an antioxidant in various and possibly complex ways. [6] This study was designed to investigate the antioxidant activity of melatonin in different concentrations using an in vitro model of nitrite-induced hemoglobin oxidation
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