Quantitative determination by bioassay of photoactive 8-methoxypsoralen in serum.

Photoactive 8-methoxypsoralen (8-MOP) levels in human and animal sera were determined by bioassay with Staphylcoccus aureus serving as the test organism. 8-MOP was extracted from sera with as 9:1 (V/V) ethyl acetate-n-hexane mixture and reconstituted in an aqueous medium following evaporation of the extractant. Bacterial suspensions containing extracted 8-MOP were irradiated for predetermined intervals with longwave ultraviolet light (UVA) at an intensity of 2.1 mw/cm2. Cultures containing known amounts of 8-MOP were used as standards and cytotoxicity (i.e., drug levels) determined by colony counts. The detection limit for 8-MOP was 5 ng/ml with an accuracy of +/- 10% above 10 ng/ml. Concomitant determinations of 8-MOP levels by high pressure liquid chromatography (HPLC) were in excellent agreement with the bioassay results.

Kinetics of [14C-5] 8-methoxypsoralen distribution in rabbits.

Distribution, kinetics and localization of 8-methoxypsoralen (8-MOP) was determined in rabbits over 24 h following i.v. administration of [14C-5] labeled and carrier 8-MOP at respective concentration of 50 muCi and 5 mg/kg. Peak levels were reached by kidneys at 1 h (18,500 ng/g) at 2 h by liver (2,470 ng/g) and at 8 h by bile (64,000 ng/g). Muscles, lymphatic tissues and brain showed low drug uptake (800 ng/g). Endocrine organs also had low drug concentration. In gastrointestinal tract the maximum level of 8-MOP was 1,500 mg/g at 1 h in jejunum. Plasma 8-MOP concentration was 3,700 ng/ml at 5 min post injection with 100 ng/ml still detectable at 24 h. Urine label concentration peaked at 1 h (4 x 10(5) cpm/ml) and was 2 x 10(2) cpm/ml at 24 h. The intact skin concentration was at the maximum during the first 30 min (1,958 ng/g) declining progressively thereafter to 155 ng/g at 24 h. The UVA irradiated skin (320-380 nm at the rate of 14.2 mW/cm2 x s-1 for 1 h) had a higher 8-MOP concentration (2,834 ng/g at 1 h and 280 ng/g at 24 h).

Photochemotherapy and the eye: photoprotective factors.

The photosensitizer, 8-Methoxypsoralen, binds reversibly to a greater extent to human serum albumin than to human lens in the absence of UVA irradiation. Since experimental and clinical evidence suggests that peak levels in skin exceed those in plasma, which in turn exceed those in the lens, 5 to 10 fold more UVA is required to induce lenticular injury than to produce a threshold skin effect. To prevent the potential photoactivation of residual of 8-MOP in the lens, UVA opaque wraparound sunglasses should be worn for 24 hours after drug ingestion. Glasses with limited UVA transmission but good visible transmission should be worn after the 24 hour period following drug ingestion or indoors during the first 24 hours as a substitute for the wraparound. Every effort should be made to insure complete compliance in the wearing of UVA photoprotective lenses by all psoralen photosensitized patients.

Kinetics of [14C-5] 8-methoxypsoralen uptake by UVA irradiated and non-irradiated rabbit eye tissues.

Total 8-methoxypsoralen (8-MOP) in intact and UVA irradiated rabbit eye tissues and its unaltered fraction in aqueous and eye lenses were determined over the 24 hours after i.v. injection of [14-C-5] and carrier 8-MOP at the concentration of 50 microCi and 5 mg/kg. No 8-MOP was detected at the end of 24 hours in intact and irradiated aqueous, vitreous and retina in contrast to one hour when the respective levels were congruent to 220, greater than 0 and congruent to 160 ng/g. Eye-plasma drug concentration ratios were less than 0.5 initially, but increased thereafter. While the average lens 8-MOP levels of congruent to 140 ng/g remained unchanged for 24 hours, no unaltered drug was detected beyond eight hours. Measurable amounts of label at the end of 24 hours also persisted in the cornea, iris, sclera and conjunctiva.