S. A. Schoonderwoerd

In vivo PHOTODEGRADATION OF CHLORPROMAZINE

Abstract— The in vivo photodegradation of chlorpromazine (CPZ) in the skin was investigated after systemic administration of 3H‐CPZ to shaven Wistar rats and exposure to UV‐A. Promazine (PZ) and 2‐hydroxy‐promazine (2‐OH‐PZ) appeared to be formed in irradiated rats, but not in the skin of rats kept in the dark. This indicates that upon irradiation with UV‐A the PZ‐radical is formed which can be held responsible for the photobinding to eye and skin constituents as observed earlier [Schoonder‐woerd and Beijersbergen von Henegouwen (1987) Photochem. Photobiol. 46, 501–505]. Chlorpromaz‐ine‐sulfoxide (CPZSO) is a major metabolite of CPZ. Less CPZSO was found in the skin of irradiated rats compared to those kept in the dark. As this appeared not to be caused by photobinding or photodegradation of CPZSO it can be concluded that CPZSO is not a photoproduct of CPZ under these experimental conditions. This study shows that the in vivo photodegradation of CPZ proceeds via the promazinyl radical rather than via the radical cation.

Effect of alpha-tocopherol and di-butyl-hydroxytoluene (BHT) on UV-A-induced photobinding of 8-methoxypsoralen to Wistar rat epidermal biomacromolecules in vivo

The possible formation of singlet oxygen via photoexcited psoralens has been associated with the occurrence of, amongst others, erythema. Therefore it has been suggested to combine PUVA with the topical or systemic administration of antioxidants. However, the effect of these antioxidants on the photobinding of psoralens to DNA, which is held responsible for the anti-proliferative effect, should be taken into account. In the present study the effect of two phenolic antioxidants, alpha-tocopherol (AT) and butylated hydroxytoluene (BHT), on the in vivo photobinding of 8-methoxypsoralen (8-MOP) to not only epidermal DNA, but also proteins and lipids was determined. After topical application of an ethanolic antioxidant solution onto the shaven skin of Wistar rats, labeled 8-MOP was applied using the same solvent. After this the rats were exposed to UV-A. By separating epidermal lipids, DNA/RNA and proteins by a selective extraction method, irreversible binding of 8-MOP to each of these biomacromolecules was determined. Both AT and BHT caused a decrease in the photobinding of 8-MOP to epidermal DNA and proteins. To investigate the underlying mechanism of this protection, the effect of AT was compared with that of AT-acetate. It also proved helpful to study the effects of the antiooxidants on the photobinding of another photosensitizer, namely chlorpromazine. From these experiments it was concluded that AT and BHT affect 8-MOP photobinding by quenching reactive 8-MOP intermediates, involving the phenolic hydroxyl group of the antioxidants. BHT offered protection against lipid binding of 8-MOP but AT, especially at high concentrations, enhanced the UV-A-induced binding of 8-MOP to lipids. This is noteworthy with respect to the current interest in the role of 8-MOP-lipid adducts in PUVA therapy.

Irreversible photobinding to skin constituents after systemic administration of chlorpromazine to Wistar rats.

From in vitro experiments it is known that chlorpromazine binds to protein and DNA/ RNA upon UV‐irradiation. In the present study the possible photobinding of chlorpromazine (or its metabolites) in vivo was examined. Tritium labeled drug was administered intraperitoneally to female albino Wistar rats after which they were irradiated with light with maximum intensity at 310, 370 or 420 nm. After homogenization, unbound radioactivity in tissue of several organs was removed by dialysis. In the ears, eyes and skin of the back irreversibly bound radioactivity could be detected after irradiation with 310‐ and 370‐ but not with 420 nm light. Binding in the skin of the back after UVA irradiation was examined in more detail by separating epidermal lipids, DNA/RNA and proteins by a selective extraction/precipitation method. Radioactivity appeared to be bound to lipids and proteins but not to DNA/RNA.

PHOTOBINDING OF CHLORPROMAZINE AND ITS SULFOXIDE IN VITRO AND IN VIVO

Abstract— Photosensitivity as observed after chlorpromazine (CPZ) treatment is enhanced in the UVA‐ rather than the UVB region, whereas CPZ has its absorption maximum at 305 nm. This long wavelength sensitivity has sometimes been ascribed to CPZ‐sulfoxide (CPZSO) which has an absorption maximum at 340 nm. We compared the photobinding properties of CPZSO and CPZ under both in vitro and in vivo conditions.

Singlet Oxygen Mediated Photobinding of 8-Methoxypsoralen to DNA and Genotoxicity in E. coli

Abstract Although oxygen dependent photoreactions of 8-methoxypsoralen (8-MOP) are known, damage to DNA is mostly considered to proceed via photocycloaddition to this biomacromolecule. In this study the survival of colony forming ability of E. coli K 12/343, which is deficient in DNA-repair capability, appeared to be lower in D2O than in H2O after exposure to the combination of 8-MOP and UV-A . Photobinding to bacterial DNA was ∼40% higher in D2O than in H2O. How ever this last difference was found only when the bacteria were kept in the reaction medium for 1 h at 37 °C after the irradiation was stopped and not when they were plated out immediately afterwards. The results indicate that in this bacterial test system 1O2 mediated photobinding of 8-MOP to DNA contributes to the genotoxic effect observed.

UVA-induced genetic effects of thioridazine, mesoridazine and sulforidazine: an in vitro study.

Abstract This in vitro study focuses on the UVA-induced reactions with DNA of thioridazine (TRZ), and two of its major metabolites (TRZ-2-sulfoxide or mesoridazine, MRZ ; and TRZ- 2-sulfone or sulforidazine, SRZ). TRZ binds covalently to DNA upon UVA-irradiation. Under comparable irradiation conditions, MRZ binds to a lesser extent and almost no binding was observed with SRZ. Besides, photo-induced genetic effects were investigated by means of a differential DNA repair test in E. coli. The photo-induced genetic effects in E. coli decreased from TRZ, MRZ to SRZ, which corresponds with their capacity for UVA-induced binding to DNA. TRZ, MRZ and SRZ differed in their rate of photodecomposition rather than in the intrinsic reactivity towards DNA of the instable intermediates formed. Irreversible binding to DNA was also observed upon treatment with peroxidase, which is known to oxidize phenothiazines via the formation of reactive radical cation species. As both the colour of the intermediate and its reactivity towards DNA were comparable for peroxidase treatment and exposure to UVA, we assume that the radical cation is the reactive species in the latter case as well.

Systemic Photobiological Effects of Xenobiotics

The conversion of 7-dehydrocholesterol into vitamin D3 and that of bilirubin into more water-soluble products, upon exposure of the body to UV-B (290–320 nm) and to visible light respectively, are two examples of systemic photo-biological effects of endogenous compounds. Vitamin D3 is essential for proper bone calcification and the photoconversion of bilirubin in the visible light therapy for neonatal jaundice results in a decrease of brain-damaging effects. That simultaneous exposure to (sun)light and a xenobiotic may also result in systemic effects is indicated by results from animal experiments.

Systemic Reactions in Phototoxicity

The conversion of 7-dehydrocholesterol into vitamin D3 and that of bilirubin into more water soluble products, upon exposure of the body to UV-B (290–320 nm) and to visible light respectively, are two examples of systemic photobiological effects by endogenous compounds. Vitamin D3 is essential for proper bone calcification and the photoconversion of bilirubin in the visible light therapy of neonatal jaundice results in a decrease of brain-damaging effects. That simultaneous exposure to (sun)light and a xenobiotic may also result in systemic effects is indicated by results from animal experiments.