Quantitation of plasma levels of 8-methoxypsoralen by competitive enzyme-linked immunosorbent assay

Suppression of delayed-type hypersensitivity and hemolysis induced by previously photooxidized psoralen: effect of fluence rate and psoralen concentration

The kinetics of the formation of biologically active psoralen photooxidation (POP) products were analyzed by the biological effects produced. Effects of the UV light fluence rate and psoralen concentration during the preirradiation were investigated to assess the yield of POP products, which were active in vivo (inducing suppression of delayed-type hypersensitivity [DTH] reaction to sheep red blood cells) and in vitro (altering the human erythrocyte membrane permeability). It was shown that the reciprocity law of the irradiation fluence rate and time was not valid in the case of POP-induced hemolysis and DTH suppression. Immunosuppressive POP products were more efficiently formed at low fluence rate (20.8 W/m2), whereas POP hemolysins were more efficiently produced at a high fluence rate (180 W/m2) of UV light. The yield of immunosuppressive POP products was enhanced in dilute psoralen solutions, while the POP hemolysins yield increased with increasing psoralen concentration. A kinetic scheme for psoralen photoproduct formation was proposed. Kinetic analysis showed that a labile intermediate was produced as the result of excitation of psoralen. This intermediate was either converted to a stable immunosuppressive POP product, or two intermediates combined to form a POP hemolysin. It is proposed that PUVA therapy conditions are more favorable for the formation of immunosuppressive rather than membrane-damaging psoralen photooxidation products.

Cell membrane, a target for PUVA therapy

The photochemical reactions occurring in the cell membranes, sensitized photo-oxidation and psoralen photoaddition to lipids, are briefly reviewed. Phospholipid dynamics in the membrane structure, based on erythrocyte lipid organization, are described. Evidence for alterations of cell membrane functions under psoralen plus UVA radiation (PUVA) treatment in a variety of mammalian cells is presented. Cell receptor dysfunctions under PUVA treatment are demonstrated in a number of biological investigations. The purpose of this survey is to illustrate the feasibility of studying psoralen photobiology with phospholipids. The reaction of psoralens with phospholipids is considered to be one of the triggering mechanisms of the subsequent physiological responses, which may be relevant to PUVA photochemotherapy.