The in vivo localization of porphyrins.

Abstract

A series of porphyrins with varying side chains was synthesized and tested in the rat for hard and soft tissue binding and photosensitization. It was found that for combination with either type of tissue there was a requirement for groups capable of ionic or hydrogen bonding at more than one edge of the tetrapyrrole nucleus. Thus binding to keratin, collagen and growing bone occurred with purified haematopophyrin, commercial “haematoporphyrin” and haematoporphyrin “derivative”. Little or no binding with these tissues occurred with deuteroporphyrin, deuteroporphyrin dimethyl ester disulphonic acid, haematoporphyrin dimethylether and unexpectedly, porphyrin c and N,N′-diacetyl porphyrin c. Incorporation of iron into the last two named is thought to account for their apparent lack of binding. In the case of growing bone, the same pattern was apparent with the exception that porphyrin c and N,N′-diacetyl porphyrin c were very strong labels. Combination to bone was with the organic rather than with the inorganic component. All soluble porphyrins tested induced a potential photosensitivity on intraperitoneal injection. Using intravenous colloidal carbon as an indicator of an increase in vascular permeability, the photoresponse following excitation with sunlight, mercury vapour lamp or carbon arc was found to be biphasic, with the delayed response altered by dosage and binding ability of porphyrins, and the amount of light absorbed.