Preparation of Monoclonal Antibody Against Chicken Apolipoprotein B and Development of Enzyme Liked Immunosolvent Assay (ELISA) Method with the Antibody Aiming at the Optimization of Lipid Metabolism in Chickens

Molecular nutrition: Interaction of nutrients, gene regulations and performances

Nutrition deals with ingestion of foods, digestion, absorption, transport of nutrients, intermediary metabolism, underlying anabolism and catabolism, and excretion of unabsorbed nutrients and metabolites. In addition, nutrition interacts with gene expressions, which are involved in the regulation of animal performances. Our laboratory is concerned with the improvement of animal productions, such as milks, meats and eggs, with molecular nutritional aspects. The present review shows overviews on the nutritional regulation of metabolism, physiological functions and gene expressions to improve animal production in chickens and dairy cows.

Regulation of bile acid, cholesterol, and fatty acid synthesis in chicken primary hepatocytes by different concentrations of T0901317, an agonist of liver X receptors

Liver X receptors (LXRs) are members of the nuclear receptor family of transcription factors. They play a crucial role in lipid metabolism processes such as bile acid and fatty acid synthesis, as well as minor or limited roles in the regulation of cholesterol synthesis and uptake in mammals. In avian species, however, little is known about the role of LXRs except for the fact that they are involved in the stimulation of fatty acid synthesis. In this study, we characterize the expression profile of genes related to bile acid, cholesterol, and fatty acid synthesis and VLDL secretion in chicken primary hepatocytes treated with T0901317, a synthetic agonist of LXR. The activity of chicken cholesterol 7α hydroxylase (CYP7A1), a key enzyme in bile acid synthesis, mRNA expression, and bile acid excretion, was stimulated by supplementation of the culture medium with a low concentration (0.01 μM) of T0901317. In contrast, the levels of sterol regulatory element binding protein (SREBP)-1, fatty acid synthase mRNA, and VLDL-triacylglycerol in cells cultured in the presence of a high concentration (10 μM) of T0901317 were higher than those cultured in zero or low concentrations of T0901317. These results suggest that cellular responses to this LXR agonist were similar to those present in mammals. A novel finding of this study concerned changes to the regulation of cholesterol synthesis and uptake in chicken hepatocytes treated with T0901317. Levels of SREBP-2,3-hydroxy-3-methylglutaryl coenzyme A reductase (HMGR) and low-density lipoprotein receptor (LDLr) mRNA expression increased as a function of increasing T0901317 (up to 1.0 μM), but remained similar to those in cells cultured under control conditions when the concentration of T0901317 was increased to 10 μM. These results suggest that LXRs play an important role in cholesterol synthesis and uptake in chicken hepatocytes and, as such, differ to findings in mammals where the effect of LXR agonists on cholesterol synthesis plays only a minor role in the regulation of cellular sterol homeostasis.

Octanoate reduces very low-density lipoprotein secretion by decreasing the synthesis of apolipoprotein B in primary cultures of chicken hepatocytes

Fatty acids of varying lengths and saturation differentially affect plasma apolipoprotein B (apoB) levels. To identify the mechanisms underlying the effect of octanoate on very low-density lipoprotein (VLDL) secretion, chicken primary hepatocytes were incubated with either fatty acid-bovine serum albumin (BSA) complexes or BSA alone. Addition of octanoate to culture medium significantly reduced VLDL-triacylglycerol (TG), VLDL-cholesterol and apoB secretion from hepatocytes compared to both control cultures with BSA only and palmitate treatments, but did not modulate intracellular TG accumulation. However, no differences in cellular microsomal triglyceride transfer protein levels were observed in the cultures with saturated fatty acid. In pulse-chase studies, octanoate treatment resulted in reduced apoB-100 synthesis, in agreement with its promotion of secretion. This characteristic effect of octanoate was confirmed by addition of a protease inhibitor, N-acetyl-leucyl-leucyl-norleucinal (ALLN), to hepatocyte cultures. Analysis showed that the level of apoB mRNA was lower in cultures supplemented with octanoate than in the control cultures, but no significant changes were observed in the levels of apolipoprotein A-I, fatty acid synthase and 3-hydroxy-3-methylglutaryl-CoA reductase mRNA as a result of octanoate treatment. Time-course studies indicate that a 50% reduction in apoB mRNA levels requires 12 h of incubation with octanoate. We conclude that octanoate reduced VLDL secretion by the specific down-regulation of apoB gene expression and impairment of subsequent synthesis of apoB, not by the modulation of intracellular apoB degradation, which is known to be a major regulatory target of VLDL secretion of other fatty acids.

Impairment of VLDL secretion by medium-chain fatty acids in chicken primary hepatocytes is affected by the chain length

To determine the effect of the chain length of medium-chain fatty acids (MCFAs) on VLDL secretion, the media of chicken hepatocyte cultures were supplemented with hexanoate (6:0), octanoate (8:0), decanoate (10:0), or dodecanoate (12:0). The supplementation of palmitate (16:0) or bovine serum albumin (BSA) alone in media was used as the positive control or the control, respectively. Palmitate significantly increased intracellular triacylglycerol (TG) accumulation and VLDL-TG, -cholesterol, and -apolipoprotein (apo)B secretion. On the other hand, the addition of hexanoate did not affect these variables relative to control cultures supplemented with BSA alone, whereas octanoate, decanoate, and dodecanoate decreased apoB secretion from the chicken hepatocytes. ApoB secretion from hepatocytes cultured with 1.0 mmol/L MCFA, in particular decanoate and dodecanoate, in the presence of 0.2 mmol/L palmitate was significantly lower than that obtained with 0.2 mmol/L palmitate alone. Decanoate at 0.25-1.0 mmol/L dose dependently reduced apoB mRNA expression compared with the control (BSA alone). The levels of 3-hydroxy-3-metylglutaryl-CoA reductase and apoA-I mRNA were significantly lower in cultures supplemented with hexanoate, octanoate, and decanoate than in cultures with dodecanoate and palmitate. These changes did not correspond to the reduction in VLDL-apoB secretion. We suggest that MCFAs with different chain lengths differentially affect apoB secretion and mRNA expression, with decanoate being the most effective at decreasing VLDL-apoB secretion by regulating apoB mRNA expression at the transcriptional level.