Study On The Antiandrogenic Activity And Mechanism Of Dimethachlon

[Objective] Structure related fungicides including vinclozolin(VIN), procymidone(PRO), iprodione(IPR) and dimethachlon(DIM) are widely used in China and the potential for human exposure to this class of compounds is significant. Recently the antiandrogenic activity of VIN, PRO and IPR, but not DIM, has been reported. The antiandrogenic activity and mechanism of DIM was investigated using in vivo and in vitro assays, and the antiandrogenic potency of VIN, PRO, IPR and flutamide was compared with DIM.[Methods] Hershberger assay was used to determine the antiandrogenic potential of DIM in vivo. Six-week-old castrated male SD rats were randomly divided into 11 groups, each of which consisted of 6 rats. Ten groups of rats were administrated once daily for 7 days with testosterone propionate (TP, 100μg/d, sc) plus gavage doses of corn oil vehicle or DIM (50, 100 or 200 mg/kg/d) or 3,5-dichloroaniline (3,5-DCA, 100 or 200 mg/kg/d) or PRO (150 or 300 mg/kg/d) or IPR (100mg/kg/d) or flutamide (50 mg/kg/d). An additional group of rats was not treated with TP as hormone deficient control. After 7-day treatment, all rats were euthanized and liver, kidneys, spleen, adrenals, pituitary, ventral prostate, dorsolateral prostate, glans penis, seminal vesicle (with coagulating glands and fluid), and levator ani plus bulbocavernosus muscles were weighed. Transcriptional activation assay was used to determine the mechanism of antiandrogenic activity of DIM. In this assay HepG2 human hepatoma liver cells were transiently cotransfected with human AR, AR-dependent luciferase reporter gene and β -galactosidase gene (transfected control). Transfected cells were treated with various concentrations of DIM or known antiandrogens with or without adding DHT. After incubation, cells were lysed, and then luciferase activity and β -galactosidase activity were measured. Finally the ratio of the former to the latter is luciferase activity value, which represents antiandrogenic potency. [Results] In in vivo, (1) DIM and antiandrogens (flutamide, PRO and IPR) caused significantdecrease in total weight of prostate and seminal vesicle, levator ani plus bulbocavernosus muscles (p<0.05). The order of their antiandrogem'c potencies was flutamide>>PRO>DIM> IPR; (2) 3,5-DCA had no effect on the weight of these tissues; (3) The antiandrogenic activity of DIM occurred at dose of 50 mg/kg while the general toxic responses including reduction on body weight gain and kidney swollen occurred at higher dose of 200 mg/kg.In in vitro, DHT increased the AR activity and induced the expression of luciferase reporter gene in a concentration-dependent manner. DIM can concentration-dependently block DHT-induced AR activity in transiently transfected HepG2 cells. The in vitro potency of DIM as AR antagonist is lower than that of flutamide (about 1/100 of flutamide). DIM did not increase AR activity in the absense of DHT.[Conclusion] (1) DIM has antiandrogenic activity, and acts as an AR antagonist both in vivo and in vitro; (2) Its antiandrogenic potency is lower than that of flutamide and PRO, but higher than that of IPR; (3) Its antiandrogenic activity occurs at dose level below that exerts significant general toxicity; (4) It seems that the antiandrogenic activity of DIM is not derived by its metabolite 3,5-DCA.