Effects of benzofuran and seven benzofuran derivatives including four carbamate insecticides in the in vitro porcine brain tubulin assembly assay and description of a new approach for the evaluation of the test data.

The influence of benzofuran and 7 benzofuran derivatives, including the carbamate insecticides benfuracarb, carbofuran, carbosulfan, and furathiocarb, on the in vitro assembly kinetics of porcine brain tubulin was investigated. A new approach to the evaluation of the raw data was made based on polynomial regression and the calculation of a polynomial function of the 11th degree fitting the raw data. By this procedure it is possible to calculate the parameters defining the shape of the absorbance curves and more parameters than those used so far can be included in the analysis of substance effects. In detail, the following curve parameters of the dependence of optical absorption on time were included in the evaluation of the substances of interest: the difference between maximum and minimum absorbance as a measure for the polymerization degree, the coordinates of the turning point of the curve, the slope of the tangent at the turning point which represents the maximum reaction velocity, the mean slope between the points with 10% absorbance increase and 90% absorbance increase and the duration of the lag phase. Out of the eight compounds tested, only the carbamate insecticides had distinct effects on the in vitro polymerization of tubulin, whereas benzofuran and the three 2,3-dihydro-2,2-dimethylbenzofuran derivatives without a carbamate function were inactive. Benfuracarb, carbofuran, carbosulfan, and furathiocarb led to a dose-dependent reduction of the polymerization degree of tubulin as well as to reduction of the maximum and mean reaction velocities. The strongest effects were obtained with furathiocarb and benfuracarb.