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.

Keywords: DIM; IC3; metabolism; mouse; nicotine.

Figure 1.

Nicotine-N-oxide produced by liver microsomes from DIM-fed and control mice. Each column represents microsomes from five mice. The boxplots provide summaries of the data distributions for each group. A box represents the interquartile range, which includes 50% of values. The line across the box indicates the median. The whisker lines extend to the highest and lowest values that are within 1.5x the interquartile range. Further outliers are marked with circles.

Figure 2.

Nicotine iminium produced by liver microsomes from DIM-fed and control mice. Each column represents microsomes from five mice. The boxplots provide summaries of the data distributions for each group. A box represents the interquartile range, which includes 50% of values. The line across the box indicates the median. The whisker lines extend to the highest and lowest values that are within 1.5x the interquartile range. Further outliers are marked with circles. * p<0.01, ** p<0.0001.

Figure 3.

Plasma cotinine concentrations in DIM-fed and control CD1 male mice subcutaneously injected with 0.35 mg/kg nicotine. Each data point represents the mean ± standard deviation of 5 mice. * p<0.03.

Figure 4.

Plasma nicotine concentrations in DIM-fed and control CD1 male mice subcutaneously injected with 0.35 mg/kg nicotine. Each data point represents the mean ± standard deviation of 5 mice. * p<0.01.