Effects of Conjugated Linoleic Acid Isomers on Lipid Metabolism and Gluconeogenesis in Monolayer Cultures of Bovine Hepatocytes

Diacylglycerol O-acyltransferase (DGAT) isoforms play a role in peridroplet mitochondrial fatty acid metabolism in bovine liver

Hepatocellular lipid accumulation characterizes fatty liver in dairy cows. Lipid droplets (LD), specialized organelles that store lipids and maintain cellular lipid homeostasis, are responsible for the ectopic storage of lipids associated with several metabolic disorders. In recent years, non-ruminant studies have reported that LD-mitochondria interactions play an important role in lipid metabolism. Due to the role of diacylglycerol acyltransferase isoforms (DGAT1 and DGAT2) in LD synthesis, we explored mechanisms of mitochondrial fatty acid transport in ketotic cows using liver biopsies and isolated primary hepatocytes. Compared with healthy cows, cows with fatty liver had massive accumulation of LD and high protein expression of the triglyceride (TAG) synthesis-related enzymes DGAT1 and DGAT2, LD synthesis-related proteins perilipin 2 (PLIN2) and perilipin 5 (PLIN5), and the mitochondrial fragmentation-related proteins dynamin-related protein 1 (DRP1) and fission 1 (FIS1). In contrast, factors associated with fatty acid oxidation, mitochondrial fusion and mitochondrial electron transport chain complex were lower compared with those in the healthy cows. In addition, transmission electron microscopy revealed significant contacts between LD-mitochondria in liver tissue from cows with fatty liver. Compared with isolated cytoplasmic mitochondria, expression of carnitine palmitoyl transferase 1A (CPT1A) and DRP1 was lower, but mitofusin 2 (MFN2) and mitochondrial electron transport chain complex was greater in isolated peridroplet mitochondria from hepatic tissue of cows with fatty liver. In vitro data indicated that exogenous free fatty acids (FFA) induced hepatocyte LD synthesis and mitochondrial dynamics consistent with in vivo results. Furthermore, DGAT2 inhibitor treatment attenuated the FFA-induced upregulation of PLIN2 and PLIN5 and rescued the impairment of mitochondrial dynamics. Inhibition of DGAT2 also restored mitochondrial membrane potential and reduced hepatocyte reactive oxygen species production. The present in vivo and in vitro results indicated there are functional differences among different types of mitochondria in the liver tissue of dairy cows with ketosis. Activity of DGAT2 may play a key role in maintaining liver mitochondrial function and lipid homeostasis in dairy cows during the transition period.

Biological models for phytochemical research: from cell to human organism

Nutrigenomics represents a shift of nutrition research from epidemiology and physiology to molecular biology and genetics. Nutrigenomics seeks to understand nutrition influences on homeostasis, the mechanism of genetic predispositions for diseases, to identify the genes influencing risk of diet related diseases. This review presents somein vitromodels applicable in nutrigenomic studies, and discuses the use of animal models, their advantages and limitations and relevance for human situation.In vitroandin vivomodels are suitable for performance of DNA microarrays, proteomic and transcriptomic analyses.In vitromodels (intracellular organelles and suborganellar compartments, cell cultures, or tissue samples/cultures) give insight in metabolic pathways and responses to test stimuli on cellular and molecular levels. Animal models allow evaluation of the biological significance of the effects recordedin vitroand testing of the hypothesis on how a specific factor affects specific species under specific circumstances. Therefore, the evaluation of the data in relation to human organism should be done carefully, considering the species differences. The use ofin vitroandin vivomodels is likely to continue as the effects of nutrition on health and disease cannot be fully explained without understanding of nutrients action at nuclear level and their role in the intra- and intercellular signal transduction. Through advances in cell and molecular biology (including genomic and proteomic), the use of these models should become more predictively accurate. However, this predictive value relies on an underpinning knowledge of the advantages and limitations of the model in nutrigenomic research as in other fields of biomedical research.

Conjugated linoleic acid supplementation alters the 6-mo change in fat oxidation during sleep

BACKGROUND

Conjugated linoleic acid (CLA) is a family of positional and geometric isomers with 2 conjugated double bonds formed from linoleic acid and linolenic acid. CLA has a wide range of biological effects, including body fat reduction.

OBJECTIVE

The aim of our study was to determine CLA's effects on energy expenditure, macronutrient utilization, and dietary fat oxidation in overweight adults after 6 mo of supplementation.

DESIGN

We recruited 23 subjects from our main CLA efficacy study who were receiving either 4 g/d of 78% active CLA isomers (3.2 g/d: 39.2% cis-9,trans-11 and 38.5% trans-10,cis-12) or 4 g/d of safflower oil. Energy expenditure and substrate utilization were measured before and after 6 mo of CLA supplementation by using whole-room indirect calorimetry. Dietary fat oxidation was measured by using stable isotope-labeled oleate and palmitate.

RESULTS

Our substudy detected a difference in the change in fat utilization between the CLA (4 +/- 8 g) and placebo (-7 +/- 11 g) groups during sleep after 6 mo of supplementation. In addition, the percentage of energy from protein was reduced during sleep in the CLA group (CLA: -3.3 +/- 2.6%; placebo: 0.3 +/- 5.7%). We also detected a difference in the change in energy expenditure during sleep (CLA: 0 +/- 38 kcal; placebo: -43 +/- 90 kcal). We did not detect a change in labeled dietary fat oxidation after 6 mo of CLA supplementation given with a breakfast meal.

CONCLUSION

Mixed isomer CLA supplementation, but not placebo, positively altered fat oxidation and energy expenditure during sleep.

In vitro metabolism of rumenic acid in bovine liver slices

Ruminant products are the major source of CLA for humans. However, during periods of fat mobilization, the liver might play an important role in CLA metabolism which would limit the availability of the latter for muscles and milk. In this context, rumenic acid (cis-9, trans-11 CLA) metabolism in the bovine liver (n = 5) was compared to that of oleic acid (n = 3) by using the in vitro liver slice method. Liver slices were incubated for 17 h in a medium containing 0.75 mM of FA mixture and 55 microM of either [1-(14)C] rumenic acid or [1-(14)C] oleic acid at 37 degrees C under an atmosphere of 95% O(2)-5% CO(2). Rumenic acid uptake by liver slices was twice (P = 0.009) that of oleic acid. Hepatic oxidation of both FA (> 50% of incorporated FA) led essentially to the production of acid-soluble products and to a lower extent to CO(2) production. Rumenic acid was partly converted (> 12% of incorporated rumenic acid) into conjugated C18:3. CLA and its conjugated derivatives were mainly esterified into polar lipids (71.7%), whereas oleic acid was preferentially esterified into neutral lipids (59.8%). Rumenic acid secretion as part of VLDL particles was very low and was one-fourth lower than that of oleic acid. In conclusion, rumenic acid was highly metabolized by bovine hepatocytes, especially by the oxidation pathway and by its conversion into conjugated C18:3 for which the biological properties need to be elucidated.

Effects of structural changes of fatty acids on lipid accumulation in adipocytes and primary hepatocytes

Conjugated linoleic acids (CLAs), tetradecylthioacetic acid (TTA), eicosapentaenoic acid (EPA) and docosahexaenoic acid (DHA) are all shown to differently affect lipid homeostasis. Additionally, previous studies have shown that introducing a methyl group in the molecule potentiates the hypolipidemic effect of EPA. The objective of this study was to determine how cis9,trans11 CLA, trans10,cis12 CLA, TTA, EPA and DHA affect lipid accumulation in 3T3-L1 adipocytes and in cultured primary rat hepatocytes, and to what extent changes in cis/trans configuration or introducing a methyl group in the molecules influence their way of affecting lipid accumulation in these cells. Our results show that trans10,cis12 CLA is highly specific in preventing lipid accumulation in adipocytes, and that small structural changes in the molecule (changing to trans/trans or introducing an alpha-methyl group) totally abolish this effect and up-regulate the expression levels of adipogenic marker genes towards control levels. Furthermore, all the fatty acids increased hepatic lipid accumulation, whereas the lipid content was normalized after adding an alpha-methyl group into the molecules. Taken together, our data demonstrate that the various fatty acids are highly specialized molecules, and that small structural changes markedly alter their way of affecting lipid accumulation in adipocytes and hepatocytes.