Aging results in iron accumulations in the non-human primate choroid of the eye without an associated increase in zinc, copper or sulphur

We present further analyses of a previous experiment published in 2016 where the distribution, concentration and correlation of iron, zinc, copper and sulphur in the choroid of the eye in young and aged old world primates (Macaca fascicularis) was studied with synchrotron X-ray fluorescence with a 2 μm resolution. The results indicate that iron accumulates in hotspots in the choroid with age with fluorescence intensity ranging from 2- to 7-fold (1002–3752 ppm) the mean level in the choroidal stroma (500 ppm) and maximum iron levels in blood vessel lumina. Iron hotspots with iron ppm > 1000 preferentially contained Fe(3+) as demonstrated by Perls staining. There was a strong spatial co-localisation and correlation between copper and zinc (Pearson’s correlation coefficient 0.97), and both elements with sulphur in the choroid of young animals. However, these are reduced in the choroid of aged animals and lost in the iron hotspots. The lack of proportional co-distribution suggests that iron accumulation does not induce a concomitant increase in zinc, copper or zinc-, copper-metalloproteins. It is possible that the iron hotspots are ferritin or hemosiderin molecules loaded with Fe(3+) in stable, insoluble, non-toxic complexes without a significant oxidative environment.