The in vivo and in vitro effects of melatonin (N-acetyl-5-methoxytryptamine) on lipid peroxidation of long chain polyunsaturated fatty acids (PUFA) located in rat liver microsomes were determined. The effect of intraperitoneal administration of melatonin (10 mg/kg weight/24 hr) on ascorbate-Fe++ induced lipid peroxidation of isolated rat liver microsomes was first examined. The ascorbate induced light emission in hepatic microsomes was inhibited by melatonin treatment [control group: 10.714 +/- 0.894; melatonin group: 3.162 +/- 0.515, counts per minute (cpm) x 10(-5)]. Significant differences in the content of arachidonic C20:4 n-6 and docosahexaenoic acid C22:6 n-3 were observed when control microsomes were lipid peroxidized in the presence of ascorbic acid. These changes were less pronounced in liver microsomes isolated from melatonin treated rats. In vitro assays showed that after incubation of rat liver microsomes in an ascorbate-Fe++ system, at 37 degrees C for 210 min, the total cpm originated from light emission (chemiluminescence) was found to be lower in those membranes incubated in the presence of melatonin. The fatty acid composition of total lipids isolated from rat liver microsomes was substantially modified when subjected to nonenzymatic lipid peroxidation with a considerable decrease of docosahexaenoic acid 22:6 n-3 and arachidonic acid 20:4 n-6. The inhibition of the lipid peroxidation process evaluated as chemiluminescence (total cpm at selected times) was melatonin concentration dependent. Melatonin, at a concentration 1.2 mm, inhibited almost completely the lipid peroxidation process. Arachidonic and docosahexaenoic acids were more affected than docosapentaenoic acid during the lipid peroxidation process. Not all fatty acids were equally protected after the addition of melatonin to the incubation medium. Our results indicate that melatonin may act in vivo and in vitro as an antioxidant protecting long chain PUFA present in rat liver microsomes from the deleterious effect by a selective mechanism that reduces the loss of docosahexaenoic and arachidonic acids.

Melatonin (N-acetyl-5-methoxytryptamine), the main secretory product of the pineal gland, is a free radical scavenger that has been found to protect against lipid peroxidation in many experimental models. In the present study the effect of melatonin on lipid peroxidation of long chain polyunsaturated fatty acids located in rat liver, kidney and brain microsomes was determined using gas chromatography and a chemiluminescence assay. In vitro assays showed that after incubation of rat liver, kidney or brain microsomes in an ascorbate-Fe++ system, at 37 degrees C for 180 min, the total cpm originated from light emission (chemiluminescence) was found to be lower in those membranes incubated in the presence of melatonin. The incubation of rat liver, kidney or brain microsomes in the presence of ascorbate-Fe2+ resulted in lipid-peroxidation of membranes as evidenced by light emission and decrease of docosahexaenoic acid 22:6 n-3 and arachidonic acid 20:4 n-6. In the presence of melatonin (0.5, 1.0, 1.5 mm), light emission percent inhibition of microsomes was: (liver - 3.33, 9.98, 39.40) (kidney - 46.79, 61.88, 68.36) and (brain - 33.36, 28.89, 43.32). Not all fatty acids were equally protected after the addition of melatonin to the incubation medium. Our results indicate a selective protection of C20:4 n6 and C22:6 n3 by melatonin during non-enzymatic lipid peroxidation of rat liver, kidney and brain microsomes.

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Reactive Oxygen Species (ROS) participate in the induction and progression of damage in many human pathologies, such as: heart attack, cerebral ischemia, diabetic neuropathy and Alzheimer's disease, among others. Alpha Lipoic Acid (ALA, also called thioctic acid) is a sulfur compound that acts as a growth factor in some microorganisms and as a coenzyme or prosthetic group in mammalian tissues. The beneficial action of ALA is due to its high antioxidant power that allows it to capture numerous free radicals such as Hydroxyl Radicals (OH•), Hypochlorous (HClO-) and oxygen (O•). ALA easily crosses cell membranes acting in both lipophilic and hydrophilic media, so it can act against oxidative stress and prevent cell damage at many levels. In the study reported here the effect of ALA on chemiluminescence of mitochondria isolated from liver and kidney rat was analyzed. After incubation of both mitochondria in an ascorbate (0.4mM)-Fe++ (2.15μM) system (120min at 37°C), non-enzymatic peroxidation, it was observed that the total cpm/mg protein originated from light emission: chemiluminescence was lower in liver and kidney mitochondria obtained from ALA group than in the control group (without ALA). Moreover, it was observed that the ALA was reduced, concentration dependent (0.05 mg, 0.15 mg and 0.25 mg of solution), of chemiluminescence, measured as total cpm. The analyses of chemiluminescence indicate that ALA may act as antioxidant protecting rat liver and kidney mitochondria from peroxidative damage.

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