Dietary trans fatty acid isomers differ in their effects on mammary lipid metabolism as well as lipogenic gene expression in lactating mice.

The biological activities and mechanisms of action of individual transoctadecenoic acids (trans-18:1 FA) have not been completely elucidated. We examined the effects of several individual trans-18:1 FA isomers and trans-10, cis-12 conjugated linoleic acid (CLA) on fat synthesis, and expression of lipogenic genes in mammary and liver tissue in lactating mice. From d 6 to 10 postpartum, 30 lactating C57BL/6J mice were randomly assigned to either a control (CTR) diet containing 20 g/kg oleic acid or diets in which the oleic acid was either completely replaced by partially hydrogenated vegetable oil (PHVO), trans-7 18:1 (T7), trans-9 18:1 (T9), or trans-11 18:1 (T11) or partially replaced with 6.66 g/kg trans-10, cis-12 CLA. Milk fat percentage was decreased by CLA (44%), T7 (27%), and PHVO (23%), compared with CTR. In the mammary gland, CLA decreased the expression of genes related to de novo FA synthesis, desaturation, triacylglycerol formation, and transcriptional regulation. PHVO and T7 diets decreased the expression of 1-acylglycerol-3-phosphate O-acyltransferase and thyroid hormone responsive SPOT14 homolog (THRSP) mRNA. In contrast, dietary trans FA (tFA) did not affect hepatic lipogenic gene expression. However, mice fed CLA, T7, and PHVO diets had increased liver weights due to hepatic steatosis. Trans-7 18:1 was extensively desaturated to trans-7, cis-9 CLA in mammary and liver tissues. Dietary trans-7 18:1 could lead to milk fat depression in lactating mice, possibly through its desaturation product trans-7, cis-9 CLA. Also, the differences between the effects of trans-10, cis-12 CLA and other tFA could be attributed to its effects on carbohydrate response element binding protein and PPARgamma, in addition to sterol regulatory element binding transcription factor 1c and THRSP.

Duodenal and milk trans octadecenoic acid and conjugated linoleic acid (CLA) isomers indicate that postabsorptive synthesis is the predominant source of cis-9-containing CLA in lactating dairy cows.

Duodenal and milk samples obtained from lactating cows in a previous study were analyzed to compare the content and isomer distribution of conjugated linoleic acids (CLA) and trans-18:1 fatty acids (tFA). Four diets containing either low [25 g/100 g dry matter (DM)] or high (60 g/100 g DM) forage were fed with or without 2% added buffer to four multiparous Holstein dairy cows in a 2 x 2 factorial, 4 x 4 Latin square design with 3-wk experimental periods. Duodenal flows of CLA were low (1.02-1.84 g/d), compared with that of tFA (57-120 g/d), regardless of diet. The greatest amounts of CLA and tFA, as well as the greatest proportions of trans-10-18:1 (P < 0.02), and cis-9, trans-11 (P < 0.01) and trans-10, cis-12 CLA (P < 0.01) were in the duodenal flow of cows fed the low forage unbuffered diet. In milk fat, tFA were increased by the low forage unbuffered diet and the trans-10-18:1 (P < 0.02) replaced trans-11-18:1 as the major 18:1 isomer. Milk CLA secretion (7.2-9.1 g/d) was greater (P < 0.001) than that in the duodenal flow with each diet. This was due to the increase in cis-9, trans-11-18:2 and trans-7, cis-9 CLA, resulting most likely from endogenous synthesis via Delta9-desaturation of ruminally derived tFA. For other CLA isomers, duodenal flow was always greater than milk secretion, suggesting that they essentially were produced in the rumen.