Suppression of Delayed‐type Hypersensitivity and Hemolysis Induced by Previously Photooxidized Psoralen: Effect of Fluence Rate and Psoralen Concentration

Abstract

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.

<title>Mechanism of photobiological effects of psoralens: the involvement of photo-oxidized psoralens as reactive intermediate species in induction of photosensitized hemolysis and skin erythema</title>

“…the Bunsen-Roscoe law was not fulfilled. It agrees with the data of Schalla et al [37] for 8-MOP-sensitized erythema and correlates with the results obtained for PUVA-and POP-hemolysis [23,28].…”

“…I , while concentration dependence of production of POP-immunosuppressors agrees with curve I in Fig. I [23]. POP-immunosuppressors are more efficiently produced under small fluence rates, while POP-hemolysins under high fluence rate conditions ofirradiation [23].…”

“…Time of incubation, mm 2.6. Effects of fluence rate of UVA irradiation and cation chelators on PUVA-induced erythema It was shown that the reciprocity law of fluence rate and duration of UVA-irradiation (Bunsen-Roscoe law) was not fulfilled for PUVA-hemolysis [28] and POP-hemolysis [23]. It supports a proposal about different mechanisms of HFR and LFR PUVA-hemolysis [4].…”

“…I [23]. POP-immunosuppressors are more efficiently produced under small fluence rates, while POP-hemolysins under high fluence rate conditions ofirradiation [23]. One can conclude that the formation of membrane-damaging and immunosuppressive POP-products are competitive processes, i.e.…”

“…Thus it remains to be important to study the biological effects of crude mixtures of psoralen photoproducts. Externally added POP was found to induce oxidation of unsaturated lipids [12,13], bind covalently to proteins [14], induce conversions of hemoproteins [1 5], inactivate enzymes [16], damage plasma membranes of erythrocytes [17][18][19] and leukocytes [20], modulate superoxide radical production by phagocytes [20], inhibit hemotactic activity of polymorphonuclear neutrophils [21], induce mutagenic and lethal effects in microorganisms [17,18], modulate T-cell immune system in mice [22,23], and induce therapeutic effects in patients with skin diseases [24,25].…”