Investigations on cell proliferation and enzyme induction in male rat kidney and female mouse liver caused by tetrahydrofuran.

To elucidate possible mechanism(s) of carcinogenic action of tetrahydrofuran (THF) that had been demonstrated in previous inhalation studies, groups of male F344 rats and female B6C3F(1) mice were exposed to dynamic atmospheric concentrations of 0, 600, 1800, or 5400 mg/m(3) for 6 h per day, either for 5 consecutive days or for a period of 4 weeks (5 days per week). The reversibility of treatment-related changes was investigated in rats and mice exposed for 5 days and sacrificed 21 days after the last exposure. Female B6C3F(1) mice exposed to 5400 mg/m(3) showed significantly increased cytochrome P450 content, increased ethoxyresorufin-O-deethylase and pentoxyresorufin-O-depentylase activities, increased cell proliferation (5-bromo-2'-deoxyuridine-method) and an increased mitotic index in liver zones 2 (midzonal region) and 3 (central vein region). The changes were found to be reversible after a 3-week treatment-free period (cell proliferation examined, only). Male F344 rats showed dose-related alpha2u-globulin (alpha2u) accumulation in the renal cortex after 5 or 20 exposures, and there were no signs of reversal after a 3-week treatment-free period. After 20 exposures at 5400 mg/m(3), the alpha2u accumulation was found to be associated with increased cell proliferation in "hot spots" of the renal cortex and increased apoptosis. Increased cell proliferation was also detected after 20 exposures at 1800 mg/m(3). There were no effects at 600 mg/m(3). It is concluded that THF enhances tumor formation in male rat kidney and female mouse liver via induction of cell proliferation. These features present essential elements that should be taken into account for the carcinogenic risk assessment of THF.

Structure-activity relationships in toxicology and ecotoxicology: An assessment.

A critical assessment of the scope, applicability and limitations of structure-activity relationships (QSARs) in toxicology and ecotoxicology opens with a general explanation of QSARs and a description of the components of a QSAR (chemical descriptors, biological descriptors and the techniques used to seek a relationship between them). The main statistical terms used to assess the validity of certain types of QSAR are briefly explained and attention is drawn to a number of common errors in the statistical assessments. This is followed by a detailed analysis of 18 typical QSAR publications, which were chosen to represent the main types of chemical and biological descriptors that have been studied and a range of techniques for deriving the structure-activity relationships. A discussion of the strengths, weaknesses, applicability and limitations of QSARs is based on the above analysis, and some conclusions and recommendations are offered. The most important recommendation is that, at present, QSARs should not be used in isolation for making decisions that affect the health of humans or other species.