A Unique Photoreaction of Hypericinate Bound to Human Serum Albumin, Lipids, or Vesicles

Hypericinate bound to human serum albumin is effectively photo-bleached. This reaction occurs to a lesser extent for hypericinate incorporated into dipalmitoyl-phosphatidyl-cholin vesicles or lecithin. Surprisingly, the photo-bleaching was strongly retarded for the complex of hypericinate with bovine serum albumin. In homogeneous solutions in a variety of solvents, micellar systems, and in ethanolic solutions containing additives mimicking possibly active parts of the mentioned hosts, almost no photoreaction was discernible. No products besides hypericin could be recovered from a bleached system. It was concluded that the main photoreaction involves photo-reduction or photo-addition in which the product becomes specifically stabilized by the host, but reverts partly to hypericinate upon destruction of the complex.