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.
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).
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