X-ray microanalysis of melanin granules of retinal pigment epithelium and choroid in hereditary copper deficient mice (macular mice)

The role of trace elements in vivo has not been completely clarified. Trace elements were studied in melanin granules in the retinal pigment epitheliu m (RPE) and choroid of hereditary copper-deficient macular mice as a model of Menkes' disease. The analysis of elements in these melanin granules was done by new methods: freeze-embedding and an energy dispersive X-ray microa nalysis (EDX). Mie used 14-day- and 1-month-old male hemizygote macular mic e for the experiments and normal litter-mates as controls. Melanin granules in RPE and choroid contained sulfur, chloride, calcium, iron, copper and z inc. Calcium and copper were especially abundant in 14-day-old hemizygote m acular mice, although there were few melanin granules in their RPE. The fac t that copper was most abundant in the melanin granules in the RPE of 14-da y-old macular mice suggests that the synthesis of melanin granules in the R PE and choroid of the hemizygote macular mice cannot be completed because o f the lower activity of copper-containing enzymes such as tyrosinase and th e abnormal copper distribution in various organs. Therefore, the melanin gr anules in the RPE and choroid of hemizygote macular mice are irregular in s hape and few in number. Large amounts of copper concentrated in melanin gra nules in the RPE and choroid of hemizygote macular mice might induce quanti tative abnormalities of trace elements. (C) 1999 Academic Press.