Melatonin protects against pro‐oxidant enzymes and reduces lipid peroxidation in distinct membranes induced by the hydroxyl and ascorbyl radicals and by peroxynitrite

Abstract

: We have investigated the action of melatonin against lipid peroxidation in membranes including brain homogenates (BH), brain and liver microsomes (MIC), and phosphatidylcholine (PC) liposomes, as well as its effect on the activity of pro‐oxidant enzymes such as constitutive neuronal nitric oxide synthase (cnNOS), xanthine oxidase (XO) and myeloperoxidase (MPO). The liposomes were reconstituted by a dialysis method, lipid peroxidation was monitored using the thiobarbituric reactive substances (TBARS) method and enzyme activities were measured spectrophotometrically. The ascorbyl and hydroxyl free radicals were generated by the reaction of ascorbic acid + FeSO4 and H2O2 + FeCl2, respectively, and peroxynitrite using a mixture of NaNO2 in an alkaline medium. Melatonin protected against lipid peroxidation induced by distinct reactive oxygen species (ROS) in all membranes tested although with different potency, in the following order BH < MIC < PC. The K0.5 for enzyme inhibition by melatonin was determined for nNOS (2.0 ± 0.1 mm), for XO (0.8 ± 0.1 mm) and for MPO (0.063 ± 0.003 mm), the latter one with high affinity. Melatonin showed a weak effect as a nitrogen monoxide (NO) scavenger in the presence of sodium nitroprusside (NO donor) and low reactivity with 1,1–diphenyl‐2‐picryl hydrazyl (DPPH). These results demonstrate the antioxidant action of melatonin, principally that related to the activity of pro‐oxidant enzymes such as XO and MPO.

The effects of prophylactic zinc and melatonin application on experimental spinal cord ischemia–reperfusion injury in rabbits: experimental study

“…*Po 0.05 compared to groups 1, [3][4][5] other hand, it is stated that melatonin treatment, affecting pro-oxidant enzyme activity, has a protective role against lipid peroxidation. 11 As similar results were obtained in our study, it is compatible with the mentioned study. The fact that lower XO levels were obtained in the group with combined zinc and melatonin showed that the effect created by zinc was made more distinct by melatonin.…”

“…A significant increase in the XO levels following the I/R was reported also by other researchers. 11,30,31 On the Figure 7 Intact ganglion cell numbers in the groups (n/ 0.1 mm 2 ). Data were analyzed with one-way ANOVA (group 1: control, group 2: I/R, group 3: I/R þ zinc, group 4: I/R þ mel, group 5: I/R þ zinc þ mel).…”

“…In a study similar to the current one, it was reported that MPO activity increased as the result of spinal injury, but melatonin treatment improved the increased MPO activity by suppressing it. 8,11 Although there are no studies that investigated the effects of spinal cord injury and zinc application on XO levels, there are studies that have investigated the effects of zinc on the levels of damage in different organs. These studies state that zinc supplementation functions as an antioxidant.…”

“…10 It was also stated that melatonin treatment had a protective role against lipid peroxidation by affecting pro-oxidant enzyme activity like XO and MPO. 11 Nitric oxide (NO) acts as an important mediator in glutamate toxicity, which develops after cerebral I/R. However, melatonin treatment reduces brain NO production by suppressing NO synthetase activity.…”

Protective Effects of Antioxidants on the Experimental Liver and Kidney Toxicity in Mice

“…The MPO activity was measured in kidney and liver tissues using a procedure similar to that reported by Teixeira et al (13). The samples were centrifuged at 12,000 g at 4 0 C for 20 min.…”