Abstract
BACKGROUND: To evaluate the effect of insulin treatment on the incidence and/or severity of hepatocellular carcinoma (HCC) in a mouse model of HCC based on diabetes. METHODS: We recently reported that neonatal streptozotocin (STZ) treatment causes type 1 diabetes and subsequent HCC in ddY, Institute for Animal Reproduction (DIAR) mice. Newborn male DIAR mice were divided into three groups based on STZ and insulin (INS) treatment. STZ was subcutaneously injected (60 mg/g) into the STZ-treated group (DIAR-nSTZ mice, N = 13) and the STZ/insulin-treated group (DIAR-nSTZ/INS mice, N = 20). A physiologic solution was injected into the control group (DIAR-control mice, N = 8) 1.5 days after birth. Insulin was subcutaneously injected into the DIAR-nSTZ/INS mice according to the following protocol: 2 IU/day at 4-5 weeks of age, 3 IU/day at 5-7 weeks of age, and 4 IU/day at 7-12 weeks of age. All mice were fed a normal diet and were subjected to physiological and histopathological assessments at 12 weeks of age. RESULTS: DIAR-nSTZ mice had significantly lower body weight and higher blood glucose levels than DIAR-control mice, whereas no significant differences were observed between DIAR-nSTZ/INS mice and control mice. At 12 weeks of age, lower weight of paratesticular fat and higher levels of total cholesterol, triglyceride, and free fatty acids were observed in DIAR-nSTZ mice compared to DIAR-control mice, whereas there were no significant differences between DIAR-nSTZ/INS mice and DIAR-control mice. In the livers of DIAR-nSTZ mice, HCC was observed in 15% of cases, and dysplastic nodules were observed in 77% of cases. In the livers of DIAR-nSTZ/INS mice, HCC was observed in 39% of cases and dysplastic nodules were observed in 61% of cases (p = 0.011). Moreover, the average tumor size was significantly larger in STZ/INS-treated mice than in STZ-treated mice. Immunohistochemical analysis demonstrated that the expression of ERK1/2, downstream substrates of insulin signaling that activate cell proliferation, was significantly higher in STZ/INS-treated mice compared to STZ-treated mice. CONCLUSIONS: Insulin treatment promoted, rather than inhibited, the progression of liver carcinogenesis in DIAR-nSTZ mice. Hyperinsulinemia rather than hyperglycemia can accelerate the progression of HCC via insulin signaling.