Background: Animal models of hepatic steatosis have improved our understanding of the pathogenesis of non-alcoholic fatty liver disease (NAFLD). Two models, normal rats fed methionine and choline deficient (MCD) diet and genetically Obese Zucker rats, have been particularly informative. Previous results demonstrated a relationship between fatty acid composition and desaturase activity as major factors involved in the development and progression of liver steatosis (Park et al, 2010). The aim of this study was to investigate the modifications in liver fatty acid delta-9, delta-6 and delta-5 desaturase (D9D, D6D and D5D, respectively) in two rat models of NAFLD such as the MCD diet model and Obese Zucker rats. Methods: Eight-week-old male Wistar rats fed for 3-week with MCD diet and relative control diet were used as nutritional model of NAFLD. Twelve-week-old Obese and Lean male Zucker rats were used as genetic model of NAFLD. Serum levels of hepatic enzymes (AST, ALT, Alkaline Phosphatase) were quantified. Hepatic TBARS and ROS were evaluated as index of oxidative stress. Liver fatty acid profiling was performed by Gas Chromatography-Mass Spectrometry analysis (GC-MS). The estimated desaturase activities were calculated using ratios of 16:1n-7/16:0 (D9-16D), 18:1n-9/18:0 (D9-18D), 18:3n-6/18:2n-6 (D6D) and 20:4n-6/20:3n-6 (D5D). The anti-inflammatory fatty acid index (AIFAI) was also quantified as the ratio of 20:5n-3, 22:6n-3, and 20:3n-6 divided by of 20:4n-6. Results: Liver D9-18D activity increased both in MCD and Obese Zucker rats but it was considerably upregulated in MCD rats. No changes in D9-16D occurred in MCD group while an increase was found in Obese Zucker rats. Four and two fold decrease in hepatic D5D activity occurred in MCD and Obese Zucker rats, respectively. About four fold increase in D6D occurred in MCD rats as well as significant positive correlation comparing tissue levels of D6D and oxidative stress assessed by TBARS and ROS (r=0.74, P<0.01 and r=0.87, P<0.001, respectively). Conversely, no D6D was detectable in Obese Zucker rats. Liver docosahexaenoic acid (DHA; 22:6n-3) and AIFAI were lower in MCD when compared with Obese Zucker rats. No significant difference in serum AST, ALT and Alkaline Phosphatase were found comparing the two NAFLD animal models. Conclusion: Extensive changes in D9-18D, D6D and D5D occurred in MCD rats when compared with Obese Zucker rats. These events were associated with marked oxidative stress and decrease in AIFAI and DHA, this last recently found to protect against the progression to steatohepatitis that spontaneously occurs only in MCD rats. These results may contribute to the understanding of NAFLD pathogenesis and progression and provide the basis for the identification of potential therapeutic targets able to counteract this common disorder.
Pathogenesis of NAFLD: changes in liver fatty acid delta-9, delta-6 and delta-5 desaturase activities in two animal models of hepatic steatosis
CROCE AC;
2018
Abstract
Background: Animal models of hepatic steatosis have improved our understanding of the pathogenesis of non-alcoholic fatty liver disease (NAFLD). Two models, normal rats fed methionine and choline deficient (MCD) diet and genetically Obese Zucker rats, have been particularly informative. Previous results demonstrated a relationship between fatty acid composition and desaturase activity as major factors involved in the development and progression of liver steatosis (Park et al, 2010). The aim of this study was to investigate the modifications in liver fatty acid delta-9, delta-6 and delta-5 desaturase (D9D, D6D and D5D, respectively) in two rat models of NAFLD such as the MCD diet model and Obese Zucker rats. Methods: Eight-week-old male Wistar rats fed for 3-week with MCD diet and relative control diet were used as nutritional model of NAFLD. Twelve-week-old Obese and Lean male Zucker rats were used as genetic model of NAFLD. Serum levels of hepatic enzymes (AST, ALT, Alkaline Phosphatase) were quantified. Hepatic TBARS and ROS were evaluated as index of oxidative stress. Liver fatty acid profiling was performed by Gas Chromatography-Mass Spectrometry analysis (GC-MS). The estimated desaturase activities were calculated using ratios of 16:1n-7/16:0 (D9-16D), 18:1n-9/18:0 (D9-18D), 18:3n-6/18:2n-6 (D6D) and 20:4n-6/20:3n-6 (D5D). The anti-inflammatory fatty acid index (AIFAI) was also quantified as the ratio of 20:5n-3, 22:6n-3, and 20:3n-6 divided by of 20:4n-6. Results: Liver D9-18D activity increased both in MCD and Obese Zucker rats but it was considerably upregulated in MCD rats. No changes in D9-16D occurred in MCD group while an increase was found in Obese Zucker rats. Four and two fold decrease in hepatic D5D activity occurred in MCD and Obese Zucker rats, respectively. About four fold increase in D6D occurred in MCD rats as well as significant positive correlation comparing tissue levels of D6D and oxidative stress assessed by TBARS and ROS (r=0.74, P<0.01 and r=0.87, P<0.001, respectively). Conversely, no D6D was detectable in Obese Zucker rats. Liver docosahexaenoic acid (DHA; 22:6n-3) and AIFAI were lower in MCD when compared with Obese Zucker rats. No significant difference in serum AST, ALT and Alkaline Phosphatase were found comparing the two NAFLD animal models. Conclusion: Extensive changes in D9-18D, D6D and D5D occurred in MCD rats when compared with Obese Zucker rats. These events were associated with marked oxidative stress and decrease in AIFAI and DHA, this last recently found to protect against the progression to steatohepatitis that spontaneously occurs only in MCD rats. These results may contribute to the understanding of NAFLD pathogenesis and progression and provide the basis for the identification of potential therapeutic targets able to counteract this common disorder.I documenti in IRIS sono protetti da copyright e tutti i diritti sono riservati, salvo diversa indicazione.
