Zinc uptake and storage: the role of fundus pigmentation.

BACKGROUND

Age-related macular degeneration (AMD) is associated with lower melanin pigmentation and is more prevalent among the elderly Caucasian population than among Africans. A correlation between light iris colour, fundus pigmentation and the incidence of AMD is reported. Moreover, melanin represents the main storage of zinc in the eye. Zinc enhances antioxidant capacity through its function as a cofactor of important enzymes or by influencing gene expression of regulatory elements in the eye. In this study, we investigated the uptake and storage of zinc in the human choroid/retinal pigment epithelium (RPE) complexes in dependence on the fundus pigmentation as judged by the iris colour.

MATERIAL AND METHODS

Choroid/RPE complexes of blue and brown human eyes were used. Tissues without any substitution served as controls. Specimens from choroid/RPE complexes were incubated with 100 microM zinc chloride for 24 h. After incubation, pieces of the complexes were stored to investigate the uptake of zinc. The rest of the tissues were kept for 3 and 7 days in culture medium (DMEM) for storage examination. The concentration of zinc was measured by inductively coupled plasma mass spectrometry.

RESULTS

After 24 h of zinc treatment the concentration of zinc in the choroid/RPE complexes of blue eyes was not significantly increased. The concentration of zinc in highly pigmented tissues (brown eyes) was increased by the factor 5.1 after 24 h and remained at high levels after 3 days (factor 4.4) and 7 days (factor 2.8).

CONCLUSIONS

Zinc uptake in the choroid/RPE complex correlates to the iris colour. Alterations of the degree of iris pigmentation result in differences of zinc uptake and storage in the choroids. A potential protective role of zinc may be more prominent in dark- than in light-coloured eyes.