Sulforaphane-mediated reduction of aflatoxin B₁-N⁷-guanine in rat liver DNA: impacts of strain and sex

Abstract

Aflatoxin B₁ (AFB₁) is a DNA-binding toxin that contributes to the burden of liver cancer in tropical areas. AFB₁-DNA adducts are powerful biomarkers that discern individual and population risk from exposure to this carcinogen. The discovery of concordance between the metabolic pathways of the male Fischer rat and humans allowed data from rats to guide the development of chemoprevention strategies employed in clinical trials in high-risk regions. In this study, the variables of strain and sex are studied in the rat model, as a step toward understanding how ethnic differences and sex influence DNA adduct formation and the induction of enzymes by chemoprotective agents. Sulforaphane (SF), which induces phase II enzymes including glutathione S-transferases (GSTs), was evaluated for its ability to induce GST activity and reduce the AFB₁-DNA adducts in livers of both sexes of two rat strains that differ in susceptibility to AFB₁ hepatocarcinogenesis. A dose-dependent relationship was found for SF for both induction of GST and reduction in of AFB₁-N⁷-guanine in both Fischer (sensitive to AFB₁) and Sprague-Dawley rats (relatively resistant). Sprague-Dawley rats exhibited the greatest increase in GST levels and the largest reduction in AFB₁-N⁷-guanine in liver DNA. Males and females of each strain were also compared to determine if the ability of SF to induce GST and reduce AFB₁-N⁷-guanine correlated with gender differences in sensitivity to AFB₁ carcinogenesis. No gender-specific responses to SF were observed. These results support the view that SF induction of liver GST activity may play a role in its chemoprotective activity.

FIG. 1.

Experimental protocol. SF and D3T were evaluated for their effects on GST activity and levels of AFB₁-N⁷-guanine in liver DNA of male and female Fischer and Sprague-Dawley rats. “•” Indicates start of AIN-76A diet; “↓” indicates gavage with SF or D3T; “*” indicates treatment with AFB₁. Each group consisted of 10 animals per strain, 5 males and 5 females.

FIG. 2.

Effect of SF and D3T on liver GST levels. Rats were treated with as described in Materials and Methods and cytosolic GST activity determined 24 h after the last dose. “*” Indicates significantly different from vehicle treated (p< 0.05).

FIG. 3.

Effect of SF or D3T on the levels of AFB₁-N⁷-guanine in liver DNA isolated from Sprague-Dawley (A) or Fischer (B) rats. Animals received SF or D3T prior to administration of AFB₁ as described in Materials and Methods. SF was dissolved in corn oil and D3T was dissolved in PBS/DMSO/Cremophor (D3T vehicle), both were administered via gavage.