title: Induction of rat hepatic drug metabolizing enzymes by dimethylcyclosiloxanes.
abstract: Low molecular weight dimethylcyclosiloxanes (DMCS) are important precursors in the synthesis of polydimethysiloxane polymers widely used in industry, and in medical and personal care products. The objective of this study was to characterize the ability of two DMCS, octamethylcyclosiloxane (D4) and decamethylcyclopentasiloxane (D5) to induce drug metabolizing enzymes in rats. Male and female Sprague-Dawley rats were administered 1, 5, 20, or 100 mg/kg D4 or D5 in corn oil daily by gavage for 4 days. Changes in the levels of activity and/or immunoreactivity of CYP1A1/2, CYP2B1/2, CYP3A1/2 and NADPH cytochrome P450 reductase in liver microsomes were examined. Significant increases were observed in the liver to body weight ratio in female rats administered either D4 or D5 at doses > or = 20 mg/kg. Increases in the liver to body weight ratio were observed in male rats treated with > or = 100 mg/kg D5 but not with D4. Relatively large increases in CYP2B1/2 enzymatic activity and immunoreactive protein were observed with increasing concentrations of both D4 and D5. Significant increases in 7-pentoxyresorufin O-depentylase (PROD) activity were also detected in male and female rats given D4 at doses > or = 5 mg/kg. D5 increased PROD activity in male rats at doses > or = 20 mg/kg and in female rats at doses > or = 5 mg/kg. 7-Ethoxyresorufin O-deethylase (EROD) activity was increased in both male and female rats receiving > or = 20 mg/kg D4 or > or = 5 mg/kg D5; however, no changes were detected in CYP1A1/2 immunoreactive protein in rats of either sex. D4 and D5 caused significant increases in CYP3A1/2 immunoreactive protein in only male rats treated with 100 mg/kg of either compound. However, significant increases were detected in CYP3A1/2 immunoreactive protein in female rats at D4 doses > or = 20 mg/kg and D5 doses > or = 5 mg/kg. Induction of NADPH cytochrome P-450 reductase immunoreactive protein was observed with D4 in female rats and in both male and female rats with D5. Induction of CYP2B/1/2, CYP3A1/2 and NADPH cytochrome P450 reductase was observed in rats treated with 50 mg/kg phenobarbital by intraperitoneal injection. Maximal CYP2B induction detected with D4 was approximately 50% of the increase observed with phenobarbital. In summary, D4 and D5 induced CYP2B1/2 in adult rat liver in a manner similar to that observed with phenobarbital; however, differences were observed between D4 and D5 in their ability to induce CYP3A1/2 and NADPH cytochrome P450 reductase. Female rats were more sensitive to the inductive properties of low doses of both DMCS than male rats whereas male rats were more responsive to phenobarbital induction.
authors.affiliation: Department of Pharmacology and Toxicology, University of Alabama at Birmingham, 35294, USA.
authors.forename: J
authors.initials: J
authors.lastname: Zhang
authors.forename: J L
authors.initials: JL
authors.lastname: Falany
authors.forename: X
authors.initials: X
authors.lastname: Xie
authors.forename: C N
authors.initials: CN
authors.lastname: Falany
mesh_terms: D000818:Animals; D001189:Aryl Hydrocarbon Hydroxylases; D001672:Biocompatible Materials / Q000633:toxicity; D019363:Cytochrome P-450 CYP1A1 / Q000096:biosynthesis; D019362:Cytochrome P-450 CYP2B1 / Q000096:biosynthesis; D051544:Cytochrome P-450 CYP3A; D003577:Cytochrome P-450 Enzyme System / Q000096:biosynthesis; D004790:Enzyme Induction / Q000187:drug effects; D005260:Female; D008297:Male; D008862:Microsomes, Liver / Q000187:drug effects* / Q000201:enzymology*; D006899:Mixed Function Oxygenases / Q000096:biosynthesis; D009251:NADPH-Ferrihemoprotein Reductase / Q000096:biosynthesis; D051381:Rats; D017207:Rats, Sprague-Dawley; D012727:Sex Characteristics; D012833:Siloxanes / Q000633:toxicity*; D013250:Steroid Hydroxylases / Q000096:biosynthesis
chemical_list: D001672:Biocompatible Materials; D012833:Siloxanes; C114768:decamethylcyclopentasiloxane; D003577:Cytochrome P-450 Enzyme System; C024064:octamethylcyclotetrasiloxane; D006899:Mixed Function Oxygenases; D013250:Steroid Hydroxylases; D001189:Aryl Hydrocarbon Hydroxylases; C104464:CYP3A protein, human; C465138:Cyp3a23-3a1 protein, rat; D019363:Cytochrome P-450 CYP1A1; D019362:Cytochrome P-450 CYP2B1; D051544:Cytochrome P-450 CYP3A; C025619:steroid 16-beta-hydroxylase; C022657:steroid hormone 6-beta-hydroxylase; D009251:NADPH-Ferrihemoprotein Reductase