The uptake, location and fluorescence of hypericin in bovine intact lens

Purpose. To determine the uptake, location and fluorescence of hypericin, t he active ingredient in St. John's Wort, in situ in the isolated intact cal f lens. Methods. The absorption and fluorescence spectra of hypericin 10(-5) M were measured in DMSO/phosphate buffer, pH 7.4) [PBS] (1/10 in volume) in the p resence of alpha -crystallin (0.5 and 1.1 mg/ml). Bovine lenses were incuba ted in the dark for 24 hours in 10(-4) M hypericin in a DMSO/PBS (1/10 in v olume) mixture. Diffused hypericin fluorescence emission was detected with a fluorescence stereomicroscope from the PBS washed lens surface. A lens-ho lder specially built for front-surface excitation-detection was used to mea sure fluorescence emission and excitation spectra of intact lenses incubate d with hypericin solutions. Results. As increasing concentrations of alpha -crystallin were added, the absorption and fluorescence spectra of hypericin in DMSO/PBS (1/10 in volum e) changed, indicating a binding between the chromophore and the lens prote in. Fluorescence emission spectra detected from the lens surface (lambda (c m) = 601 and 651 nm; lambda (exc) = 550 nm) confirmed that hypericin does b ind to the ocular tissues. Conclusions. The results we obtained in simplified model systems can provid e dues to investigate the effects of hypericin on lens properties in physio logical conditions. Hypericin could in fact bind to lens protein thus incre asing the retention time of hypericin in the eye and possibly altering alph a -crystallin properties as a chaperone. Should therefore hypericin be take n up by the lens, this can be detected, non-invasively by its fluorescence. Therefore, ophthalmologists may use a slit-lamp or scanning fluorometry to monitor the uptake of hypericin in the eyes of patients using St. John's W ort or receiving high doses of hypericin while undergoing photodynamic ther apy.