Title: The effect of docosahexaenoic acid on t10, c12-conjugated linoleic acid-induced changes in fatty acid composition of mouse liver, adipose and muscle Authors
Submitted to: Metabolic Syndrome and Disorders
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: October 20, 2012
Publication Date: February 11, 2013
Citation: Fedor, D.M., Adkins, Y.C., Newman, J.W., Mackey, B.E., Kelley, D.S. 2013. The effect of docosahexaenoic acid on t10, c12-conjugated linoleic acid-induced changes in fatty acid composition of mouse liver, adipose and muscle. Metabolic Syndrome and Disorders. 11(1):63-70. DOI: 10.1089/met.2012.0116. Interpretive Summary: Increase in obesity and metabolic syndrome is usually accompanied by increases in Non-alcoholic fatty liver disease (NAFLD) and insulin resistance (IR). Non-alcoholic fatty liver disease (NAFLD) develops when fatty acid uptake and synthesis in the liver exceeds oxidation and export as triglycerides (TG). It is the number one liver disease in the Western world and if not treated it leads to liver failure. Consumption of diets high in fat, particularly the saturated and trans fatty acids increases the incidence of NAFLD and IR, while consumption of diets high in omega-3 fatty acids prevents the incidence of these metabolic disorders. Conjugated linoleic acid (t10, c12-CLA) CLA is one of the major trans fatty acids found in processed foods and partially hydrogenated vegetable oils; it has been found to cause IR and NAFLD in animal models. We previously reported that docosahexaenoic acid (DHA), one of the long chain omega-3 polyunsaturated fatty acids found in fish oils, prevented the CLA-induced NAFLD and IR in the mouse model. The effects of these fatty acids on individual insulin sensitive tissues (liver, adipose, and muscle), their fatty acid composition and altered gene expression are not known. We tested the effect of CLA (0.5 %) alone and also concomitantly with DHA (1.5%) on the fat mass and fatty acid composition of the insulin sensitive tissues, and also examined the changes in gene expression in adipose tissue of mice fed experimental diets for 4 weeks (changes in liver gene expression have been previously reported; changes in muscle gene expression were not investigated because its fat content did not change). CLA supplementation significantly decreased the fat content of adipose tissue and increased that of liver, but had no effect on muscle fat content. Both CLA and DHA were incorporated into lipids of all three tissues, with highest concentrations in adipose tissue and lowest concentrations in muscle. DHA supplementation along with CLA prevented the increase in liver fat, but not the depletion of adipose tissue fat; it did not alter muscle fat content. CLA exhibited the most dramatic effects on liver fatty acid composition, with a decrease in n-3 polyunsaturated fatty acids (PUFA) and an increase in n-6:n-3 PUFA ratio. DHA increased the n-3 PUFA in all 3 tissues and decreased n-6:n-3 PUFA in all 3 tissues. CLA decreased the expression of adipose tissue genes involved in not only fatty acid synthesis, but also of those involved in fatty acid oxidation, uptake, and lipolysis; it also increased the expression of uncoupling protein 2. DHA failed to prevent the CLA-induced changes in adipose tissue gene expression. Our results show that the insulin sensitive tissues responded differently to dietary treatments with CLA and DHA.
Technical Abstract: Background: Concomitant supplementation of 1.5% docosahexaenoic acid (22:6 n-3; DHA) with 0.5% t10, c12- conjugated linoleic acid (18:2 n-6; CLA) prevented the CLA-induced increase in expression of hepatic genes involved in fatty acid synthesis and the decrease in expression of genes involved in fatty acid oxidation. The effect of CLA on fatty acid compositions of adipose tissue and muscle, and whether DHA can prevent those CLA-induced changes in fatty acid composition is not known. Methods: We investigated if DHA concomitantly fed with CLA for 4 weeks will prevent the CLA-induced changes in fatty acid compositions of liver, adipose, and muscle lipids in C57BL/6N female mice. We also examined changes in expression of adipose tissue genes involved in fatty acid synthesis, oxidation, uptake, and lipolysis. Results: CLA supplementation increased liver fat and decreased total n-3 PUFA concentration. DHA not only prevented the CLA-induced changes in liver fat, but also increased n-3 PUFA by >350% as compared with the control group. CLA decreased adipose weight and the expression of genes involved in fatty acid synthesis, oxidation, and uptake, and increased that of UCP2. Supplementing DHA along with CLA increased adipose n-3 PUFA by >1000% compared with control group, but did not prevent the CLA-induced changes in mass or gene expression. Both CLA and DHA were incorporated into muscle lipids, but had minor effects on FA composition. Conclusions: Liver, adipose tissue, and muscle responded differently to CLA and DHA supplementation. DHA prevented CLA-induced increase in liver fat but not loss of adipose mass.