Antioxidative effects of melatonin in Drosophila melanogaster: antagonization of damage induced by the inhibition of catalase.

In Drosophila melanogaster strain Canton S, the catalase inhibitor 3-amino-1,2,4-triazole was used to enhance oxidative stress from endogenous sources. This treatment was chosen as an alternative to direct administration of oxidants, which would cause damage and interact with melatonin already in the extracellular space before they reach the intracellular compartments. Male flies were kept in constant darkness and fed 1% sucrose as the only diet, with or without additions of melatonin (2 mM), inhibitor (100 mM), or combinations of both. After 20 or 24 hr, most of the animals exposed to 3-amino-1,2,4-triazole only had died, whereas a large number of flies had survived the inhibitor treatment in the presence of melatonin. Protein carbonyl, an indicator of oxidative protein modification, and lipid peroxidation, as determined by the formation of malondialdehyde and 4-hydroxyalkenal, were measured in flies treated for 20 hr. Melatonin alone did not substantially change these parameters, but prevented the increase in protein carbonyl caused by the catalase inhibitor. The effect of 3-amino-1,2,4-triazole on lipid peroxidation was relatively minor, but a clear-cut inhibition was found after simultaneous administration of melatonin. The preferential suppression of oxidative damage of proteins, as compared to lipids, indicates a particular protective role for melatonin in the aqueous phase of cellular compartments.