Hepatic steatosis: an experimental model for quantification

Non-alcoholic fatty liver disease (NAFLD) has gained extensive research attention, and the relationship with cardiovascular disease is of great clinical interest. Traditionally, diagnosis of NAFLD is dependent on liver biopsy, but the heterogeneous fatty infiltration may confound the diagnosis. The main purpose of this study was to introduce an experimental method to quantify hepatic steatosis in rats, and to provide an alternative experimental model in following researches. Twenty male Sprague-Dawley rats (6-week-old) randomly divided into two groups and were fed by the commercial chow diet and the choline/methionine deficient (CMD) diet for 2 weeks. All rats underwent a complete morphological measurements and blood biochemistry studies at the beginning of study and 2 weeks later. Two Chinese acupuncture needles were inserted percutaneously into the liver of each rat under general anesthesia for bioelectric impedance analysis (BIA). The acupuncture needles were carefully wrapped by non-conducting sheathes, and were inserted at left subcostal margin and the lower limb of the left rib with the depth of 0.5 cm. All rats were sacrificed with their livers isolated, sampled, sliced and well prepared after BIA measurements were completed. All pathological specimens were interpreted by one single hepatopathologist. With similar weight in the beginning of study, CMD rats were significantly lighter in weight, but had significantly higher liver weight/body weight ratio (5.5% (4.5-6.7%) vs. 4.6% (4.2-5.7%), p=0.015) 2 weeks later. Serum levels of ALT: 77 (64-125) vs. 53 (40-167) IU/ml, p=0.019, and AST: 370 (324-420) vs. 282 (217-365) IU/ml, p<0.001, were significantly higher in CMD rats, but not the lipid profile. Hepatic steatosis was more advanced: 3 (0-3) vs. 0 (0-0), p<0.001, in pathological staging, and the BIA readings were significantly lower: 15.3 (12-25) vs. 30.5 (14-66) mΩ, p=0.004, in CMD rats. Steatosis score was significantly correlated with BIA readings (p<0.001, γ=-0.52). In conclusion, this experimental model enables researchers to quantify hepatic steatosis with less concern of heterogeneous fatty infiltration, and providing a continuous but not categorical measurement of hepatic steatosis.