Melatonin and tryptophan circadian profiles in patients with advanced non-small cell lung cancer
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Accumulating studies indicate that melatonin is a natural oncostatic agent capable of mediating the influence of the psychoneuroendocrine system on cancer growth. Although there is increasing evidence to show that the pineal gland may play a role in human non-small cell lung cancer (NSCLC), there is uncertainty about circadian profiles of melatonin, its precursor tryptophan, and its major metabolite, 6-sulfatoxymelatonin (6-OH-MLT) in NSCLC patients before and after treatment with standard chemotherapy (cisplatin plus vinorelbine). The aim of this study was to investigate the concentration changes of melatonin, tryptophan, and 6-OH-MLT in NSCLC patients treated with standard chemotherapy.
We examined the circadian melatonin, tryptophan, and 6-OH-MLT rhythms in 30 patients suffering from advanced-stage NSCLC and compared them with those of 63 healthy volunteers free from neoplastic disease. Blood samples were collected at 12 noon and 12 midnight. Urine samples were collected at 7 am and 4 pm. The levels of melatonin in serum and of 6-OH-MLT in urine were measured by high-performance liquid chromatography. The concentration of amino acids including tryptophan in serum was measured by amino acid analyzer.
Melatonin, tryptophan, and 6-OH-MLT concentrations were significantly lower in cancer patients, in comparison with healthy subjects. A significant inverse correlation between melatonin and tryptophan was observed. Additionally, after three cycles of standard chemotherapy, there was a tendency of melatonin, tryptophan, and 6-OH-MLT concentrations to progressively decrease in NSCLC patients.
The results of the present study indicate that the presence of NSCLC influences the metabolism of melatonin, and chemotherapy in NSCLC patients may progressively decrease the production of melatonin.
Keywords6-sulfatoxymelatonin circadian rhythm melatonin non-small cell lung cancer tryptophan
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