Metabolism-dependent induction of DNA and chromosome damage by orally administered carbamazepine in adult male C57BL/6J mice, Cyp2b being major activating enzymes

Carbamazepine is a commonly applied anti-neurosis drug, which meanwhile severely pollutes the global environment. It induced DNA/chromosome damage and gene mutations in vitro following metabolic activation, however, evidence for its genotoxicity in intact mammalians remains absent. In this study, 6-week old male C57BL/6J mice were exposed to carbamazepine by gastric gavage at doses of 8, 20, and 50 mg/kg/d for 7 consecutive days, followed by a micronucleus test in bone marrow polychromatic erythrocytes, a comet assay in hepatocytes, and Western blot assay of hepatic proteins, including a phosphorylated histone 2AX (γ-H2AX, indicator of double-strand DNA breaks), aryl hydrocarbon receptor (AhR), pregnane X receptor (PXR), constitutive androstane receptor (CAR), and several Cyp enzymes. In some experiments, ticlopidine (4 mg/kg/d, specific inhibitor of Cyp2b) was used as a modulator. The results demonstrated no obvious toxicity of carbamazepine to the liver or bone marrow, while it induced micronucleus formation in the bone marrow and hepatic DNA damage (indicated by positive comet assay results and elevated γ-H2AX protein) at 20 and/or 50 mg/kg/d doses, all of which were nevertheless abolished or alleviated by ticlopidine. Meanwhile, carbamazepine induced hepatic AhR and CAR at 50 mg/kg/d, and PXR, Cyp2b10 and Cyp3a11 at doses ≥ 20 mg/kg/d, with no effect on Cyp1a2; furthermore, coexposure of ticlopidine blocked the induction of PXR, Cyp3a11 and Cyp2b10 by carbamazepine, while enhanced that of AhR. This study provides evidence for the genotoxicity of carbamazepine in mammalians in vivo, its dependence on Cyp2b activity, and the activation of relevant nuclear receptor/Cyp-regulating pathway.