Distribution of lead and transthyretin in human eyes

Background: The retinal pigment epithelium serves as a defensive barrier to the retina in the same way that the choroid plexus functions in the brain. Previous studies have shown that lead sequestration in the choroid plexus reduces the production and secretion of transthyretin by the choroid plexus. The purpose of this study was to investigate the distribution of lead and transthyretin in human eyes and to explore the potential effect of lead on transthyretin in human eyes. Methods: Eight pairs of human eyes were obtained from the New York City Eyebank within 24 hours of postmortem. The eyes were dissected to obtain the aqueous, vitreous, retina, and choroid. Lead and transthyretin concentrations in ocular tissues and liquids were determined by atomic absorption spectrophotometry for lead and radioimmunoassay for transthyretin. Lead accumulated in the retina at concentrations that were 166, 739, and 5 times higher than those in the aqueous, vitreous, and choroid, respectively (p < 0.05 for all comparisons). Lead concentrations in ocular tissues or intraocular liquids did not change as a function of age or gender. The concentration of transthyretin in the vitreous (14.4 ± 5.1SE μg/mL) was twice as much as in the aqueous (7.0 ± 1.1SE μg/mL) and was significantly correlated to that in the retina (r = 0.93, p < 0.005). Conclusions: This study indicates that lead accumulates in human ocular tissues, particularly in the retina. The markedly elevated retina lead level and its relationship to ocular transthyretin and other macromolecules bear further investigation.