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.