Strain‐specific altered nicotine metabolism in 3,3′‐diindolylmethane (DIM) exposed mice

Abstract

Two indole compounds, indole‐3‐carbinol (I3C) and its acid condensation product, 3,3′‐diindolymethane (DIM), have been shown to suppress the expression of flavin‐containing monooxygenases (FMO) and to induce some hepatic cytochrome P450s (CYPs) in rats. In liver microsomes prepared from rats fed I3C or DIM, FMO‐mediated nicotine N‐oxygenation was decreased, whereas CYP‐mediated nicotine metabolism to nicotine iminium and subsequently to cotinine was unchanged. Therefore, it was hypothesized that in mice DIM would also suppress nicotine N‐oxygenation without affecting CYP‐mediated nicotine metabolism. Liver microsomes were produced from male and female C57BL/6 J and CD1 mice fed 2500 parts per million (ppm) DIM for 14 days. In liver microsomes from DIM‐fed mice, FMO‐mediated nicotine N‐oxygenation did not differ from the controls, but CYP‐mediated nicotine metabolism was significantly increased, with results varying by sex and strain. To confirm the effects of DIM in vivo, control and DIM‐fed CD1 male mice were injected subcutaneously with nicotine, and the plasma concentrations of nicotine, cotinine and nicotine‐N‐oxide were measured over 30 minutes. The DIM‐fed mice showed greater cotinine concentrations compared with the controls 10 minutes following injection. It is concluded that the effects of DIM on nicotine metabolism in vitro and in vivo differ between mice and rats and between mouse strains, and that DIM is an effective inducer of CYP‐mediated nicotine metabolism in commonly studied mouse strains.

Identification of 5-Hydroxycotinine in the Plasma of Nicotine-Treated Mice: Implications for Cotinine Metabolism and Disposition in Vivo

“…Recently, the vitro rate of CYP2A5-catalyzed oxidation of nicotine to nicotine-iminium ion (Fig. 1) was shown to exhibit a higher median, as well as a larger inter-animal variability, in female than in male nicotine-injected C57BL/6 mice (Bloom et al, 2019). Our present finding that CYP2A5 activity is higher in female than in male mice (N = 8 for each sex) is in accord with these recent reports.…”

The Impact of Sex on Changes in Plasma Corticosterone and Cotinine Levels Induced by Nicotine in C57BL/6J Mice

“…In females, an additional mechanism of regulation of CYP2A5/CYP2A4, viz by female hormones, may occur. It has been suggested that the observed wider ranges of CYP2A5/CYP2A4 protein levels and of the in vitro C-oxidation rates in female C57BL/6 mice compared to male mice [ 14 , 15 ] is due to the effect of female sex hormones, estradiol and progesterone, whose concentrations vary during the estrous cycle of 3–4 days [ 25 , 26 ]. Although we did not examine possible effects of the estrous cycle on the rate of cotinine formation, the current result is less likely to be largely affected by fluctuations in female hormone levels because we collected samples from five mice that received nicotine for seven days, which encompass most if not all phases of the estrous cycle.…”

“…The formation of nicotine-∆5′(1′)-iminium ion, mediated by CYP2A5, is the first step in the formation of cotinine. The in vitro rate of iminium ion formation is significantly faster in female-derived liver microsomes than in their male counterparts [ 9 , 14 ]. These observations strongly suggest that, in vitro, nicotine is metabolized to cotinine at a faster rate in female than in male C57BL mice.…”