Melatonin and N-acetyl serotonin inhibit selectively enzymatic and non-enzymatic lipid peroxidation of rat liver microsomes.
Melatonin (N-acetyl-5-methoxytryptamine) and its immediate precursor N-acetyl serotonin in the metabolism of tryptophan are free radical scavengers that have been found to protect against non-enzymatic lipid peroxidation in many experimental models. By contrast, little is known about the antioxidant ability of these indoleamines against NADPH enzymatic lipid peroxidation. The light emission produced by rat-liver microsomes, expressed as total cpm during 180 min of incubation at 37 degrees C, was two-fold greater in the presence of ascorbate (0.4mM) when compared with NADPH (0.2 mM). Maximal peaks of light emission produced by microsomes lipid peroxidized with ascorbic-Fe(2+) or NADPH and expressed as cpm were 354,208 (at 60 min) and 135,800 (at 15 min), respectively. During non-enzymatic lipid peroxidation a decrease of total chemiluminescence (inhibition of lipid peroxidation) was observed when increasing concentrations of melatonin were added to liver microsomes. The protective effect was concentration-dependent. The inhibition observed in light emission was coincident with the protection of the most PUFAs. Preincubation of microsomes with N-acetyl serotonin reduced these changes very dramatically. Thus, in the presence of both antioxidants (0.36, 0.75, 1.5 mM), light emission percent inhibition during non-enzymatic (ascorbate-Fe(2+)) lipid peroxidation of rat liver microsomes was for melatonin: 6.12, 16.20, 34.88 and for N-acetyl serotonin: 85.10, 88.48, 84.4 respectively. The incubation of rat liver microsomes in the presence of NADPH (0.36, 0.75, 1.5 mM) produce a sudden increase of chemiluminescence that gradually increased and reached a maximal value at about 15 min; however, N-acetyl serotonin reduced these changes very efficiently.
Cátedra de Bioquímica, Facultad de Ciencias Veterinarias, Argentina.
Patricio J
PJ
Leaden
Angel
A
Catalá
D000818:Animals; D001205:Ascorbic Acid / Q000378:metabolism; D005260:Female; D005296:Ferrous Compounds / Q000378:metabolism; D050356:Lipid Metabolism; D015227:Lipid Peroxidation / Q000187:drug effects*; D008550:Melatonin / Q000494:pharmacology*; D008862:Microsomes, Liver / Q000187:drug effects / Q000201:enzymology / Q000378:metabolism*; D009249:NADP / Q000378:metabolism; D051381:Rats; D012701:Serotonin / Q000031:analogs & derivatives* / Q000494:pharmacology; D013997:Time Factors
D005296:Ferrous Compounds; D012701:Serotonin; D009249:NADP; D008550:Melatonin; C006389:N-acetylserotonin; D001205:Ascorbic Acid