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Background and PurposeThe circadian rhythm of melatonin in saliva or plasma, or of the melatonin metabolite 6-sulfatoxymelatonin (a6MTs) in urine, is a defining feature of suprachiasmatic nucleus (SCN) function, the body’s endogenous oscillatory pacemaker. The primary objective of this review is to ascertain the clinical benefits and limitations of current methodologies employed for detection and quantification of melatonin in biological fluids and tissues.Data IdentificationA search of the English-language literature (Medline) and a systematic review of published articles were carried out.Study SelectionArticles that specified both the methodology for quantifying melatonin and indicated the clinical purpose were chosen for inclusion in the review.Data ExtractionThe authors critically evaluated the methodological issues associated with various tools and techniques (e.g. standards, protocols, and procedures).Results of Data SynthesisMelatonin measurements are useful for evaluating problems related to the onset or offset of sleep and for assessing phase delays or advances of rhythms in entrained individuals. They have also become an important tool for psychiatric diagnosis, their use being recommended for phase typing in patients suffering from sleep and mood disorders. Additionally, there has been a continuous interest in the use of melatonin as a marker for neoplasms of the pineal region. Melatonin decreases such as found with aging are or post pinealectomy can cause alterations in the sleep/wake cycle. The development of sensitive and selective methods for the precise detection of melatonin in tissues and fluids has increasingly been shown to have direct relevance for clinical decision making.ConclusionsDue to melatonin’s low concentration, as well as the coexistence of numerous other compounds in the blood, the routine determination of melatonin has been an analytical challenge. The available evidence indicates however that these challenges can be overcome and consequently that evaluation of melatonin's presence and activity can be an accessible and useful tool for clinical diagnosis.

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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 and N1-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.

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