Age dependence and distribution of green and blue fluorophores in human lens homogenates

Abstract

This is comprehensive study of the age dependence and regional distribution of the blue and the green fluorophores, per unit protein, (specific fluorescence) in the human lens. Spectroscopic measurements were obtained using fiber optic sensors that considerably improved upon techniques used in the past because inner-filter and scattering effects were minimized. An increase in the specific green and blue fluorescence was observed with increasing age in the soluble and insoluble nuclear fractions. In the cortical fractions, an increase with age was observed in lenses of donors under 30 yr old. No significant variations in the specific fluorescence were measured beyond the third/fourth decade of life in the cortical fractions. The specific fluorescence was about twice as high in samples from the cortex compared to those from the nucleus. The insoluble protein fractions also exhibited twice as much specific fluorescence compared to the soluble ones. At older ages, the fluorescence level of insoluble proteins was always greater than that in soluble ones, but the specific fluorescence of insoluble fractions from young lenses was less than that of soluble older lenses. The greater fluorescence per unit protein may be just a manifestation or marker of the insolubilization process. Furthermore, because a threshold level of specific fluorescence was observed in the cortical fraction of clear lenses, it is likely that fluorophor formation is not a marker of aging in this region, as it is in the nuclear region in which the specific fluorescence increases with increasing age, perhaps reaching a threshold level beyond which cataractogenesis may occur.