Ionizing radiation promotes, whereas calorie restriction suppresses, NASH and hepatocellular carcinoma in mice

Abstract

The pathological conditions of nonalcoholic fatty liver disease and nonalcoholic steatohepatitis (NASH) are the major risk factors for hepatocellular carcinoma (HCC). Exposure to DNA‐damaging agents such as ionizing radiation is another risk factor for HCC; calorie restriction (CR), however, effectively delays the onset of radiation‐induced HCC. We investigated whether NASH is relevant to radiation‐induced HCC and the cancer‐preventing effect of CR. Eight‐day‐old male B6C3F1 mice were irradiated with 3.8 Gy of X‐rays and then fed a standard diet or 30% CR diet from 49 days of age until necropsy, which was performed from 56 to 600 days with ~100‐day intervals to assess both pathological changes and gene expression levels. We found that early‐life exposure to radiation accelerated lipid accumulation and NASH‐like histopathological changes in the liver, accompanied by accelerated development of HCC. CR ameliorated the changes in lipid metabolism in the liver and reversed the NASH‐like pathology, which effectively delayed HCC development. Gene‐expression profiling revealed the radiation‐related activation and CR‐related suppression of the peroxisome proliferator‐activated receptor gamma/Cd36 pathway of transmembrane fatty‐acid translocation before development of the NASH‐like state. Thus, early‐life exposure to radiation affects lipid metabolism and induces a steatoinflammatory microenvironment that favors HCC development. Therefore, targeting this pathway by CR (or measures that mimic CR) may be a promising strategy for preventing HCC caused by either radiation or other DNA‐damaging agents.