Objective: To investigate the potential preventive effects of metformin on non-alcoholic fatty liver disease (NAFLD) and roles of phospholipase A2/lysophosphatidylcholine pathway in hepatocyte lipoapoptosis in a rat NAFLD model induced by high-fat diet.
Method: Male SD rats (n = 36) were randomly divided into three groups with 12 rats in each and treated with different diet and drugs: group I: ordinary diet, group II: high-fat diet, group III: high-fat diet and metformin. Ten weeks later, the rats were sacrificed and their body weight and liver weight were obtained, serum lipid metabolic indexes, insulin resistance indexes and secretory phospholipase A2 (sPLA2), lysophosphatidylcholine (LPC) levels and other parameters were measured. Phospholipase A2 mRNA expression levels were measured by quantitative reverse transcription-polymerase chain reaction (RT-PCR). In addition, the histological changes of liver tissue were analyzed.
Result: Compared to ordinary diet group, the rat's liver weight (g) (16.92 ± 2.49 vs. 12.16 ± 0.82), hepatic exponent (0.034 ± 0.004 vs. 0.026 ± 0.002), serum alanine aminotransferase (U/L) (45.43 ± 9.73 vs. 29.42 ± 6.73), triglyceride (mmol/L) (1.22 ± 0.24 vs. 0.85 ± 0.19), cholesterol (mmol/L) (2.00 ± 0.37 vs. 1.49 ± 0.33), lipoprotein(a) (mmol/L) (743.86 ± 32.19 vs. 648.42 ± 78.87), low-density lipoprotein (mmol/L) (1.31 ± 0.35 vs. 0.65 ± 0.22), insulin (mmol/L) (22.16 ± 5.16 vs. 16.86 ± 5.35), insulin resistance index(5.10 ± 1.45 vs. 3.59 ± 0.99), free fatty acid (mEq/L) (0.57 ± 0.10 vs. 0.35 ± 0.07), sPLA2 [µmol/(min·ml)] (0.130 ± 0.016 vs. 0.098 ± 0.024), lysophosphatidylcholine (µmol/L) (707.26 ± 92.48 vs. 508.87 ± 96.50), leptin (pg/ml (80.08 ± 17.73 vs. 65.11 ± 14.09), liver triglyceride (mg/g) (13.57 ± 0.65 vs. 12.03 ± 1.14), cholesterol (mg/g) (2.19 ± 0.15 vs. 1.94 ± 0.12) (P < 0.05) were significantly increased in high-fat diet group. Moreover, degree of hepatic steatosis was significantly higher and sPLA2 mRNA expression was also significantly increased. Secondly, in comparison with high-fat diet group, early metformin treatment significantly reduced the rat's body weight (g) (394.40 ± 33.10 vs. 491.86 ± 26.45), liver weight (g) (13.24 ± 1.16 vs. 16.92 ± 2.49), serum alanine aminotransferase (U/L) (30.40 ± 4.50 vs. 45.43 ± 9.73), triglyceride (mmol/L) (0.75 ± 0.19 vs. 1.22 ± 0.24), cholesterol (mmol/L) (1.61 ± 0.38 vs. 2.00 ± 0.37), insulin (mmol/L) (16.96 ± 5.60 vs. 22.16 ± 5.16), insulin resistance index (3.75 ± 1.41 vs. 5.10 ± 1.45), sPLA2 [µmol/(min·ml)] (0.101 ± 0.009 vs. 0.130 ± 0.016), lysophosphatidylcholine (µmol/L) (549.92 ± 90.78 vs. 707.26 ± 92.48), liver triglyceride (mg/g) (11.23 ± 1.70 vs. 13.57 ± 0.65), cholesterol (mg/g) (1.97 ± 0.20 vs. 2.19 ± 0.15) (P < 0.05). Moreover, degree of hepatic steatosis was significantly lower and sPLA2 mRNA expression was also significantly decreased by metformin. Thirdly, when compared to ordinary diet group, metformin could also significantly increase hepatic exponent (0.034 ± 0.004 vs. 0.026 ± 0.002) and low-density lipoprotein level (mmol/L) (0.96 ± 0.34 vs. 0.65 ± 0.22) (P < 0.05). However, it had no impact on hepatic steatosis and sPLA2 expression (P > 0.05).
Conclusion: It was indicated that metformin has potent effects on improving lipid metabolism and insulin resistance in high-fat diet induced non-alcoholic fatty liver disease rat model. The liver protective mechanisms of metformin in non-alcoholic fatty liver disease may be contributed to down-regulation of secretory phospholipase A2 mRNA expression, decrease in serum secretory phospholipase A2, lysophosphatidylcholine, lower inflammatory response and protect mitochondrial function.