Non‐alcoholic fatty liver disease (NAFLD) is believed to be a type of metabolic syndrome. MicroRNA‐122 (miR‐122) is the most abundant microRNA in the liver and is an important factor for the metabolism of glucose and lipids. In the present study, we examined the correlation between the hepatic and serum miR‐122 expression levels and the clinicopathological factors of patients with NAFLD.

We extracted the total RNA, along with preserved miRNAs, from liver biopsy samples of 67 patients with NAFLD. In 52 of these 67 patients, the total RNA was extracted from serum. The miR‐122 that was obtained by quantitative reverse transcription‐polymerase chain reaction was quantified using TaqMan MicroRNA assays.

A significant correlation was detected between serum and hepatic miR‐122 expression (correlation coefficient, 0.461; P = 0.005). Patients with mild steatosis (<33%) showed significantly lower levels of hepatic miR‐122 compared with patients with severe steatosis (>33%) (hepatic miR‐122: mild/severe = 2.158 ± 1.786/4.836 ± 7.506, P = 0.0473; serum miR‐122: mild/severe = 0.002 ± 0.005/0.007 ± 0.001, P = 0.0491). Moreover, hepatic and serum miR‐122 levels were significantly higher in patients with mild fibrosis than in those with severe fibrosis (hepatic miR‐122: mild/severe = 5.201 ± 7.275/2.394 ± 1.547, P = 0.0087; serum miR‐122: mild/severe = 0.008 ± 0.011/0.002 ± 0.004, P = 0.0191).

We found that the hepatic and serum miR‐122 levels were associated with hepatic steatosis and fibrosis. The serum miR‐122 level can be a useful predictive marker of liver fibrosis in patients with NAFLD.