Photoinduced effect of hypericin on collagen and tissues with high collagen content

The photoinduced effect of hypericin, a polycyclic quinone, on collagen has been investigated. It was found that after laser irradiation at both 532nm and 337nm, the spectral form of triple helix structure collagen fluorescence, changed to a spectral profile bearing resemblance to that of its polypeptide single chain counterpart gelatin, or heated collagen. The effect of Chlorin e(6) on collagen was also investigated and proved to be dissimilar to that of hypericin and not indicative of profound structural alterations. Second Harmonic Generation (SHG) of 1064nm-nanosecond laser radiation in collagen was studied. While it was very efficient for pure collagen, the signal intensity was found to diminish blv at least an order of magnitude after hypericin photosensitisation or heating. The above noted fluorescence spectral form alteration was also observed in a smaller scale in collagen rich chicken tissue (tendon). Non sensitised chicken tendon tissue exhibited very efficient SHG, unlike skin and artery samples.