Raman spectroscopic evaluation of aging and long-wave UV exposure in the guinea pig lens: A possible model for human aging

The laser Raman optical dissection technique makes it possible to study individual points of minute volumes (2×10^-3μl) in the intact living lens in vitro. This technique was used to measure the sulfhydryl and disulfide content of 21 distinct points along the visual axis of the guinea-pig lens after aging and long-wave ultraviolet exposure (9-month duration in vivo). To facilitate comparison between different lenses, data was compiled as the intensity ratio of sulfhydryl (2580 cm^-1) to a protein reference signal (2731 cm^-1) or disulfide (508 cm^-1) to phenylalanine (622 cm^-1). These 21 ratios for each experiment were plotted as a function of the distance of the point from the nuclear center of the lens to give a visual axis profile. From these profiles we have found that the loss of sulfhydryl can be accelerated in the guinea-pig lens by in vivo ultraviolet exposure (353 nm peak from an incoherent source) for nine months. There is also a subsequent uniform increase in the disulfide content across the visual axis after UV exposure suggesting a direct sulfhydryl to disulfide conversion in the guinea-pig lens.