Melatonin Levels in Age-Related Macular Degeneration Patients as Measured by Urinary 6-Sulfatoxymelatonin Level

Abstract

Purpose: : Melatonin is a potent antioxidant and free radical scavenger. It has been reported that serum melatonin level is relevant to certain aging diseases. In order to capture peak melatonin levels, which occur late at night, and avoid the need for hospitalization, melatonin levels can be determined by measuring the urinary 6-sulfatoxymelatonin level (the main metabolite of melatonin), which correlates well with the melatonin level in the blood. In our preliminary study (ARVO 2008, # 3423), urinary 6-sulfatoxymelatonin level in a small group of AMD patients was lower than that from normal controls. The significance of this difference was difficult to evaluate because of the small number of specimens. The purpose of this study was to extend this experiment to a larger group of AMD patients and normal controls to investigate whether urinary 6-sulfatoxymelatonin level in AMD is statistically different from the normal controls.

Methods: : The first urine of the morning was collected from 44 AMD patients (17 cases of dry type and 25 cases of wet type) and 12 age-and gender-matched normal controls. Specimens were stored at -70 C until measurement. Level of 6-sulfatoxymelatonin in specimens was measured by a commercial 6-sulfatoxymelatonin ELISA kit (ALPCO Diagnostics, Windham, NH). The measurement was performed by researchers that were masked to the information of these specimens. This study complied with the tenets of the Declaration of Helsinki and was approved by the Institutional Review Board of New York Eye and Ear Infirmary. Informed consent was obtained from each enrolled individual.

Results: : The levels of urinary 6-sulfatoxymelatonin (mean ± SD) in AMD (7.20 ± 4.23 ng/ml) were significantly lower than those of controls (11.1 ± 5.6 ng/ml. P < 0.05). In the subgroups of AMD, the urinary 6-sulfatoxymelatonin levels (mean ± SD) in wet AMD (6.46 ± 4.14 ng/ml) and dry AMD (8.29 ± 4.28 ng/ml) were both lower than those of controls. The difference in the levels of 6-sulfatoxymelatonin was statistically significant (P < 0.05) between wet AMD (P < 0.05) and the controls but not between dry AMD and the controls (P > 0.05).

Conclusions: : Urinary 6-sulfatoxymelatonin levels in AMD patients measured 25-40% lower than those of the age/gender matched normal controls. This difference between AMD and control subjects was statistically significant. The clinical significance of these results and the role of melatonin in the occurrence of AMD require further investigation.

Keywords: age-related macular degeneration • antioxidants • retinal degenerations: cell biology