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Porphyrias are defined as either inborn or acquired diseases related to enzymatic deficiencies in the heme biosynthetic pathway. Lead poisoning, hereditary tyrosinemia, and acute intermittent porphyria (AIP) are characterized by the absence of photosensitivity and the accumulation of 5-aminolevulinic acid (ALA) together with its increased urinary excretion. The main clinical manifestations of AIP are intermittent attacks of abdominal pain, neuromuscular weaknesses and neuropsychiatry alterations, and also an association with primary liver cancer, in which may be involved the oxidative potential of ALA which is able to cause DNA damage. The use of antioxidants in the treatment of ALA-induced oxidative stress is not well established. In the current work, we show the antioxidant efficacy of several compounds including melatonin, quercetin, resveratrol andN1-acetyl-N2-formyl-5-methoxykynuramine (AFMK), a melatonin oxidation product, in terms of their ability to limit DNA damage induced by ALA/Fe2+ in an in vitro system. Damage was measured by plasmid DNA strand breaks and detection of 8-oxo, 7-8-dihydro,2′-deoxyguanosine (8-oxodGuo) by high-performance liquid chromatography coupled with electrochemical detection. All compounds tested showed a dose-dependent protective action against free radical damage. These results could be the first step toward studies of the possible use of these antioxidants in oxidative stress promoted by ALA or other pro-oxidants. [ABSTRACT FROM AUTHOR]

Melatonin ( N-acetyl-5-methoxytryptamine) is implicated in physiologic changes related to light–dark cycles and has been recently found to display antioxidant properties. It is known that the reaction of melatonin with certain reactive oxygen and nitrogen species, such as hydrogen peroxide and singlet oxygen, produces N1-acetyl- N2-formyl-5-methoxykynuramine (AFMK). We report herein on the development of a new liquid chromatography/tandem mass spectrometry (LC/ESI/MS-MS) assay to quantitatively determine melatonin and AFMK. The stable isotopic internal standard of melatonin-D3 was synthesized by the reaction of 5-methoxytryptamine with deuterated acetyl chloride (CD3COCl). Labeled AFMK (AFMK-D3) was obtained after photooxidation of melatonin-D3. The predominant ion [M + H]+ in the full scan mass spectra of melatonin, melatonin-D3, AFMK and AFMK-D3 were located, respectively, at m/ z = 233, 236, 265 and 268. The collision-induced dissociation of the molecules revealed a predominant fragment at m/ z = 174 for melatonin and melatonin-D3 (loss of the N-acetyl group), and at m/ z = 178 for AFMK and AFMK-D3 (loss of both the N-acetyl and the N-formyl groups). The m/ z transitions from 233 to 174 (melatonin), from 236 to 174 (melatonin-D3), from 265 to 178 (AFMK), and from 268 to 178 (AFMK-D3) were therefore chosen for the multiple reaction monitoring detection experiments, ensuring a high specificity and an accurate quantification of melatonin and AFMK in human plasma. [ABSTRACT FROM AUTHOR]

It has been shown that melatonin exhibits antioxidant properties. Chemical structures of some of the products formed by the interaction of melatonin with reactive oxygen and nitrogen species have been elucidated. Despite some evidence that the reaction of melatonin with singlet molecular oxygen (O2 (1 Δg )) produces N 1 -acetyl-N 2 -formyl-5-methoxykynurenine (AFMK), it has not been fully documented. In this investigation, melatonin was oxidized by photosensitization with methylene blue or by a clean chemical source of O2 (1 Δg ), the thermodecomposition of N ,N ′-di(2,3-dihydroxypropyl)-1,4-naphtalenedipropanamide (DHPNO2 ). The resulting product was characterized by high performance liquid chromatography, coupled to electrospray ionization mass spectrometry and also by 1 H, 13 C and dept135 nuclear magnetic resonance spectroscopy. An isotopically labeled DHPN18 O2 was also prepared and used as a chemical source of labeled 18 [O2 (1 Δg )] to unequivocally characterize the end product. The results uncovered by this work confirm the hypothesis that oxidation of melatonin by O2 (1 Δg ) produces AFMK. [ABSTRACT FROM AUTHOR]