Comparative Study on the Mode of Action of Chlorinated Ethylenes on the Expression of Rat CYP Forms.

Abstract

Many environmental chemicals (xenobiotics), including polychlorinated ethylenes (CEs), are known to be metabolically intoxicated via the formation of hazardous intermediates (referred to as biological activation), while the expression of metabolic enzymes might be interfered with by xenobiotics at various stages in a system to minimize their adverse biological effects on the host animals. Three CEs, i.e., tetrachloroethylene (PCE), trichloroethylene (TCE) and 1,1-dichloroethylene (1,1-DCE), were comparatively studied for their effects on the in vivo expression of CYP forms, which are responsible for their metabolic activation, as well as organospecificities between the liver and lung. Furthermore, their effects on the expression of CYP forms were studied in the animals simultaneously administered with phenobarbital (PB), known as an inducer of CYP2B. Individual CEs were administered intraperitoneally at 0.5 g/kg alone or simultaneously with PB (80 mg/kg/d) to 7-week-old male Wistar rats weighing about 200 g. The testosterone hydroxylase activities, CYP2B-and 2E1-mRNA, and CYP2B-and 2E1-proteins were measured 24 hr after the treatment. Testosterone 2β-hydroxylase (2βTSH) and 16βTSH activities are attributable to the functions of CYP3A2, and CYP2B plus CYP3A2, respectively. The induction of hepatic CYP2B in the PB-treated animals might be masked by the suppressive effect of CYP3A2 in terms of the 16βTSH activity, while the pulmonary 16βTSH activity was confined to the function of CYP2B, which was insensitive to the inducing effect of PB. The inhibition of hepatic 16βTSH activity was observed exclusively in the presence of 1,1-DCE, especially in PBcoadministered animals, suggesting the preferable suppression of CYP2B. In the lung, however, PCE suppressed the 16βTSH activity in the absence of PB. The expression levels of hepatic CYP2B mRNA and protein were significantly lowered by 1,1-DCE in the presence of PB. Concerning hepatic CYP2E1, no alternation was observed in the levels of mRNA and protein by any of the CEs in the absence or presence of PB, except for a marked decrease in the amount of mRNA when the rats were treated with 1,1-DCE in combination with PB. In the lung, both mRNA and protein were not detected under the given assay conditions, as in our previous studies. Based on these results, it is suggested that 1,1-DCE suppresses the induction of hepatic CYP2B and 2E1 in advance of the transcriptional stage. The expression of pulmonary CYP2B was obstructed by PCE posttranslationally in the absence of PB.

Effect of Chlorinated Ethylenes on the Expression of Rat CYP2C.

“…11) In the present study, the PB-dependent potentiation of hepatic 2α-TSH activity was confirmed to be completely reversed to the basal level when the rats were treated with 1,1-DCE, although the details of the mechanisms controlling these findings remain to be elucidated. …”

“…10) On the contrary, chlorinated ethylenes (CEs) have been studied extensively for their effects on the expression of CYP1A, 2B, and 2E1 in animal models. 5,[11][12] Although CYP2C is reportedly one of the major P450 forms by which CEs are metabolized, 13) the effects of CEs on the expression of CYP2C have not been studied extensively. Therefore the present study focuses on the in vivo effects of CEs including TCE and PCE, both under stringent legislative control as environmental pollutants, on the expression of CYP2C in rat liver and lung.…”

Comparative Study on Correlation between Chemical Structure and Effect on Expression of Cytochrome P450 mRNAs in Rat among Chlorinated Ethylenes, Tetrachloroethylene, Trichloroethylene, 1, 1-Dichloroethylene.

“…5) In rat hepatocyte primary culture, CEs including 1,1-DCE were apt to work as inducers of CYP forms (Nakahama et al, unpublished). Therefore, the suppressive effects of CEs, particularly 1,1-DCE, observed in the whole animals were not really considered to be direct effects.…”

“…The membrane was hybridized separately with either a CYP2B, CYP2E1 or G3PDH cDNA probe as described previously. 5) The membrane was exposed to an Imaging Plate and analyzed by Storm TM830. Statistics ---Statistical significance was determined using a Student's t-test.…”

“…[5][6][7][8][9] When the animals were treated with 1,1-DCE for 24 hr, severe suppressive effects on the expression of phenobarbital (PB)-induced mRNAs of hepatic CYP2B and 2E1 were observed. In addition to mRNA, the PB-induced apoprotein of hepatic CYP2B was found to be highly susceptible to the suppressive effect of 1,1-dichloroethylene (DCE).…”