Location: Arkansas Children's Nutrition CenterTitle: Application of an in vivo hepatic triacylglycerol production method in the setting of a high fat diet in mice
|Ono-moore, K - Arkansas Children'S Nutrition Research Center (ACNC)|
|Ferguson, M - Arkansas Children'S Nutrition Research Center (ACNC)|
|Blackburn, M - University Arkansas For Medical Sciences (UAMS)|
|Issafras, H - Merck Research Laboratories|
Submitted to: Nutrients
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 12/21/2016
Publication Date: 12/28/2016
Citation: Ono-Moore, K.D., Ferguson, M., Blackburn, M.L., Issafras, H., Adams, S.H. 2016. Application of an in vivo hepatic triacylglycerol production method in the setting of a high fat diet in mice. Nutrients. 9(1):16. doi:10.3390/nu9010016.
Interpretive Summary: High fat, high simple sugar diets can contribute to the development of obesity and obesity related diseases, including diabetes and non-alcoholic fatty liver disease. In addition to the adult population being affected by these diseases, childhood rates are also increasing. Changes in how the body processes triacylglycerides (fat) may contribute to the development of fatty liver, which, over many years, can damage the liver and lead to liver failure. The liver produces triacylglyceride (TAG) from sugar and also from repackaging of fatty acids from the bloodstream. Understanding the specific mechanisms by which specific nutrients impact the liver's fat metabolism is important to determine how dietary changes can improve liver function and overall metabolic health. We used a test called a hepatic TAG production test (HTPT) in mice, applying an inhibitor that prevents the breakdown of liver-derived TAG from the blood, allowing the liver's TAG production rate to be measured. Previous HTPT studies have not reported the effects of the injection of the inhibitor on food intake and weight gain, which can confuse other important test results. The purpose of this study was to measure the changes in food intake and weight gain after the HTPT, and to compare the impact of low fat/low sugar versus a high fat diet on liver fat metabolism in mice. Male C57BL/6J mice were fed a low fat or high fat diet for 7 wk. Body weight and food intake were measured. After 4 wk, the mice underwent the HTPT, and at 7 wk liver TAG content and fat metabolism-relevant gene expression were assessed. As expected, HF fed mice had increased energy intake, weight gain, fat gain, and high insulin levels compared to LF controls. Somewhat unexpectedly, HF fed mice had lower liver production of TAG, reduced plasma TAG and lower fatty acid levels compared to LF fed mice. Weight gain and food intake normalized 7-10 days post-HTPT. HF fed mice showed no differences in liver weight and liver TAG content compared to LF controls. Expression of genes associated with production of fat from sugar was reduced in the livers of mice fed a HF diet, expression of genes related to export of fat from the liver were not affected. The data suggest that investigators using the HTPT test should wait 7-10 days after test to measure other important test results, due to transient changes in body weight and food intake from the HTPT inhibitor treatment. Furthermore, the results question the assumption that short-term intake of high fat diet drives excessive liver fat accumulation and higher blood lipids. Future research should focus on longer-term outcomes from high fat feeding in both animal models and in children and adults.
Technical Abstract: High fat (HF) diets typically promote diet-induced obesity (DIO) and metabolic dysfunction (i.e., insulin resistance, hypertriglyceridemia, and hepatic steatosis). Changes in TAG metabolism contribute to the development of hepatic steatosis including changes in production rate from de novo lipogenesis (DNL) and repackaging of circulating NEFAs. Hepatic TAG production (HTP) rate can be assessed through injecting mice with nonionic detergents that inhibit blood lipoprotein lipase. HTP studies have not reported the potential confounding effects of detergent-based HTP tests (HTPTs) on energy balance and weight gain. This study evaluated changes in energy balance and body weight after HTPTs and HTP in HF fed mice compared to low fat (LF) controls. Male C57BL/6J mice were fed a 10% or 60% kcal from fat diet for 7 wk (n=10/group). Body weight and food intake were assessed. After 4 wk, the mice underwent a HTPT via poloxamer 407 injections. Postabsorptive levels of TAG and NEFA were assessed 1 and 2 wk post HTPT. Liver TAG content and lipid metabolism-relevant gene expression were assessed. We found that HF fed mice had increased energy intake, weight gain, adiposity, and insulin levels compared to LF controls. HF fed mice had reduced HTP, plasma TAG and NEFA levels compared to LF fed mice. Weight gain, energy intake, and postabsorptive TAG levels normalized 7-10 days post-HTPT. HF fed mice exhibited no differences in liver masses and liver TAG content compared to LF controls. Fatty acid synthase expression decreased in the livers of HF fed mice, while microsomal TAG transfer protein expression did not change (LF vs. HF). The post-HTPT recovery of body weight and energy intake in mice suggests that in metabolic phenotyping studies, any additional sample collection should occur at least 7–10 days after the HTPT to reduce confounding effects. Furthermore, our data suggest that HF fed mice have reduced HTP production compared to LF fed mice, due to reduced DNL or NEFA repackaging and not due to impaired hepatic TAG trafficking. In conclusion, the current study highlights the procedural and physiological complexities associated with studying lipid metabolism using a HTPT in the DIO mouse model.