Impact of dietary docosahexaenoic acid and conjugated linoleic acid from naturally enriched milk fat on expression of key genes for fatty acid metabolism
The purpose of the current study was to investigate the impact of milk fat, naturally enriched with docosahexaenoic acid (DHA) and/or conjugated linoleic acid (CLA), on young rats. Changes in body weight, food intake, blood cholesterol, hepatic fatty acid profile and hepatic expression of key genes regulating fatty acid metabolism were measured. DHA and CLA are fatty acids that have been shown to induce certain health benefits. Enrichment of dairy products with DHA and CLA provides consumers with alternative dietary sources to meet the recommendations and/or requirements for DHA and CLA. In the first experiment milk fat, naturally enriched or fortified with 4x lelves enriched with DHA supported normal growth in young Sprague-Dawley rats. Both levels of DHA altered hepatic fatty acid profile and decreased hepatic mRNA level for fatty acid synthase (FAS). Young rats fed DHA-fortified diet had a decreased in total cholesterol level in serum and in hepatic mRNA abundance for acyl-CoA oxidase (ACO). The results indicated that DHA-enriched milk fat was potent enough to induce biological effects in young rats, therefore suggesting the potential as functional food. In the second experiment, CLA-enriched milk fat supported normal growth in young rats and induced alteration in hepatic fatty acid profile without affecting serum cholesterol levels. CLA-enriched milk fat increased hepatic mRNA level of FAS and ACO. The results indicated that CLA level in naturally enriched milk fat was well-tolerated and adequate to induce biological effects in young rats, therefore suggesting the potential as functional food. Because the fatty acid profile of milk fat was inevitably modified when milk fat was enriched with a specific fatty acid of interest by manipulating the diets of dairy cows, what was observed in the first two experiments could be the result of an altered dietary fatty acid profile rather than dietary levels of a specific fatty acid. In the third experiment, we investigated the individual and combined effects of long-chain fatty acids including DHA, CLA, stearic acid and trans-vaccenic acid on expression of key genes for fatty acid metabolism in H-4-II-E rat hepatoma cells. The results indicated that these fatty acids had differential effects on gene expression of key enzymes such as FAS, carnitine palmitoytransferase, phosphoenolpyruvate carboxykinase and peroxisome proliferator-activated receptor-γ coactivator-1α and interactions between different fatty acids at different concentrations. Taken together, the results of these experiments indicate that milk fats naturally enriched with DHA and/or CLA can induce biological effects in young rats, therefore have the potential as functional foods. The biological effects induced in these experiments resulted from altered dietary fatty acid profile.^
Shawn S. Donkin, Purdue University.
Health Sciences, Nutrition
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