Lack of initiation activity of 4-oxo-2-hexenal, a peroxidation product generated from ω-3 polyunsaturated fatty acids, in an in vivo five-week liver assay

Peroxidation products formed from polyunsaturated lipids have DNA damaging potential. 4-oxo-2-hexenal (4-OHE), generated by the oxidation of ω-3 fatty acids, has been demonstrated to be mutagenic in vitro as assessed in the Ames test. To examine the carcinogenic risk of 4-OHE in vivo, initiation activity was investigated in a five-week liver assay, established to be effective for screening of carcinogenic potential of mutagens. Sevenweek- old male F344 rats underwent two-thirds partial hepatectomy (PH) and were administered 4-OHE intragastrically at doses of 128, 80, 64, 40, 32, 20, or 0 mg/kg body weight (b.w.) at 18 hours thereafter, then being fed on diet containing 0.015% 2-acetylaminofluorene from weeks 2 to 4. All rats were given with 0.8 ml/kg b.w. CCl₄ at week 3. At week 5, all survivors were sacrificed and initiation activity was assessed with reference to induction of glutathione S-transferase placental form (GST-P) positive foci in the liver. Mortality was significantly increased to 72.7% in the 128 mg/kg b.w. dose group compared with 0.9% in the control group. However, the average number of GST-P positive foci in the "128" dose group was 3.26±1.66 foci/cm2, not significantly different from the control value (2.78±1.33). Areas of GST-P positive foci were also similar (1.11±0.5 and 1.53±1.33 mm²cm² in "128" and the control groups, respectively). These results showed 4-OHE to have no significant initiation activity in vivo.