Absolute oral bioavailability and metabolic turnover of ß-sitosterol in healthy subjects.

The metabolic turnover, absolute oral bioavailability, clearance, and volume of distribution for ß-sitosterol were measured in healthy subjects. [(14)C]ß-Sitosterol was used as an isotopic tracer to distinguish pulse doses from dietary sources and was administered by both oral and intravenous routes. The administered doses of [(14)C]ß-sitosterol were in the region of 3 to 4 µg, sufficiently low as not to perturb the kinetics of ß-sitosterol derived from the diet. Because the plasma concentrations of [(14)C]ß-sitosterol arising from such low doses were anticipated to be very low, the ultrasensitive isotope ratio analytical method of accelerator mass spectrometry was used. The limit of quantification for [(14)C]ß-sitosterol was approximately 0.1 pg/ml, the oral absolute bioavailability was just 0.41%, clearance was 85 ml/h, volume of distribution was 46 L, and the turnover was 5.8 mg/day. Given the steady-state concentrations of ß-sitosterol (2.83 µg/ml), then the dietary load was calculated to be approximately 1400 mg/day.

Interlaboratory assessment of the GreenScreen HC GADD45a-GFP genotoxicity screening assay: an enabling study for independent validation as an alternative method.

Sixteen coded compounds were blind-tested at 4 laboratories using the recently described GADD45a-GFP genotoxicity assay. The compounds were chosen to include non-genotoxic compounds as well as weak and strong genotoxins. None of the compounds required metabolic activation in order to exhibit genotoxic effects. The participating laboratories included 2 global pharmaceutical companies, a global consumer goods company and the Gentronix laboratory in Manchester. Each compound was tested 4 times on different days following a protocol previously described. The tests were carried out after a 3-day training period from the parent lab (Manchester). Following the exclusion of data from tests with positive control failures and data series with 'spikes', 92% of assays gave the correct result: non-genotoxins giving negative results and genotoxins giving positive results. There were no randomly distributed problems suggesting that differences between the results from different sites reflected the use of different instruments, procedural differences and operator experience. In naïve operator laboratories the quality of data improved with operator practice. It was concluded that simple clarification of the protocol would provide the level of reliability required for widespread use of the assay in hazard assessment.