Autoxidation of Fish Oil Blended with Rice Bran Oil.

Effects of rice bran oil on the oxidative and flavor stability of fish oil were investigated by the gas liquid chromatography-head space method. When fish oil blending with different ratio of rice bran oils was oxidized at room temperature in the dark, volatile compounds produced during autoxidation was measured by gas liquid chromatography. The amounts of volatile compounds were decreased with increased the ratio of blended rice bran oil as well as peroxide value. The level of propanal and acrolein which gave unpleasant flavor was also decreased with increased the ratio of blended rice bran oil. Especially, the level of propanal and acrolein and peroxide value were remarkably decreased when blending more than 75% of rice bran oil. Blending of rice bran oil improved the oxidative and flavor stabilities of fish oil.

Down Regulation of Asparagine Synthetase and 3-Phosphoglycerate Dehydrogenase, and the Up-Regulation of Serine Dehydratase in Rat Liver from Intake of Excess Amount of Leucine Are Not Related to Leucine-Caused Amino Acid Imbalance.

Asparagine synthetase (ASNS), 3-phosphoglycerate dehydrogenase (PHGDH) and serine dehydratase (SDS) in rat liver are expressed in response to protein and amino acid intake. In the present study, we examined the expression of these enzymes in relation to amino acid imbalance caused by leucine. Rats were subjected to leucine administration in the diet or orally between meals. Consumption of more than 2% leucine in a 6% casein diet suppressed food intake and caused growth retardation in a dose-dependent manner, but this was not seen in a 12% or 40% casein diet. ASNS and PHGDH expression in the liver was significantly induced by the 6% casein diet and was suppressed by leucine in a dose-dependent manner, whereas the SDS expression was induced. These effects were leucine specific and not seen with ingestion of isoleucine or valine. However, leucine orally administered between meals did not change the food intake or growth of rats fed a 6% casein die, though it similarly affected the expression of ASNS, PHGDH and SDS in the liver. These results suggest that the growth retardation caused by leucine imbalance was mainly because of the suppression of food intake, and demonstrated that there are no causal relationships between ASNS, PHGDH and SDS expression and amino acid imbalance caused by leucine.

Further validation of unsaturated long-chain fatty acids as inhibitors for oxidized low-density lipoprotein binding to CD36 via assays with synthetic CD36 peptide-cross-linked plates.

We recently obtained evidence that unsaturated long-chain fatty acids (LCFAs) (e.g. oleic acid) inhibit binding of oxidized low-density lipoproteins (oxLDLs) to CD36. In the present study, we validated this prediction by examining inhibition by unsaturated LCFAs of Alexa-fluor-labeled oxLDL binding to multiwell plates onto which a synthetic CD36 peptide is covalently immobilized via thiol-maleimide coupling.

Unsaturated long-chain fatty acids inhibit the binding of oxidized low-density lipoproteins to a model CD36.

Transmembrane protein CD36 binds multiple ligands, including oxidized low-density lipoproteins (oxLDLs) and long-chain fatty acids (LCFAs). Our aim was to determine whether LCFAs compete with oxLDLs for binding to CD36. We addressed this issue by examining the inhibitory effect of LCFAs against the binding of Alexa-fluor-labeled oxLDLs (AFL-oxLDL) to a synthetic peptide representing the oxLDL-binding site on CD36 (3S-CD36150₋168). All of the unsaturated LCFAs tested, inhibited the binding of AFL-oxLDL to 3S-CD36150₋168, albeit to varying degrees. For instance, the concentrations required for 50% inhibition of binding for oleic, linoleic, and α-linolenic acids were 0.25, 0.97, and 1.2 mM, respectively. None of the saturated LCFAs tested (e.g. stearic acid) exhibited inhibitory effects. These results suggest that at least unsaturated LCFAs can compete with oxLDLs for binding to CD36. The study also provides information on the structural requirements of LCFAs for inhibition of oxLDLs-CD36 binding.

Assessment of key amino-acid residues of CD36 in specific binding interaction with an oxidized low-density lipoprotein.

CD36 binds oxidized low-density lipoprotein (oxLDL). A synthetic peptide comprising amino-acid residues 149-168 of mouse CD36 was recently found to bind fluorescence-labeled oxLDL particles. Based on our oxLDL-binding analysis of various synthetic CD36 peptides, we suggest that not only hydrophilic residues (e.g., Lys164 and Lys166) but also hydrophobic ones (e.g., Phe153, Leu158, and Leu161) are critical to binding.

Adverse effects of excessive leucine intake depend on dietary protein intake: a transcriptomic analysis to identify useful biomarkers.

The present study was conducted to identify reliable gene biomarkers for the adverse effects of excessive leucine (Leu) in Sprague-Dawley rats by DNA microarray. It has long been known that the adverse effects of excessive amino acid intake depend on dietary protein levels. Male rats were divided into 12 groups (n=6) and fed for 1 wk a diet containing low (6%), moderate (12%) or high (40%) protein. Different levels of Leu (0, 2, 4, and 8%) were added to the diets. Consumption of diets containing more than 4% Leu in 6% protein resulted in growth retardation and reduced liver weight, whereas the administration of the same dose of Leu with 12% or 40% protein did not affect them. By a process of systematic data extraction, 6 candidate gene markers were identified. The liver gene expression data obtained from another experiment with 0, 2, 3, 4, and 8% Leu in a low-protein diet was used to examine the validity of these biomarker candidates with receiver operating characteristic (ROC) curve analysis. All of AUC values of the biomarker candidates were more than 0.700, suggesting the effectiveness of the marker candidates as the indices of Leu excess. The cut-off value for the ROC curve of the gene-marker panel, which was obtained by multiple regression analysis of gene markers, indicated that Leu levels higher than 3% have adverse effects. In conclusion, the gene-marker panel suggested that for male rats dietary Leu supplementation of 2% is the NOAEL dose in low-protein (6%) diets.

A synthetic peptide-based assay system for detecting binding between CD36 and an oxidized low-density lipoprotein.

CD36 is an integral membrane protein that mediates the cellular uptake of oxidized low-density lipoprotein (oxLDL) through recognition of the oxidized glycerophospholipids (oxPLs) formed during LDL oxidation. We aimed to devise an assay system to detect binding between CD36 and oxLDL/oxPL without using recombinant proteins. A peptide corresponding to amino-acid residues 149-168 of mouse CD36 with biotin at its N-terminus (named biotin-CD36(149-168)) and variants of it were synthesized and immobilized onto streptavidin-coated plates. oxLDL labeled with Alexa-Fluor-488 bound specifically and saturably to immobilized biotin-CD36(149-168), but poorly or not at all to the variants, such as that with a scrambled amino-acid sequence. The binding of fluorescence-labeled oxLDL to biotin-CD36(149-168) was inhibited efficiently by an oxPL species, but not by a nonoxidized glycerophospholipid. This assay system using biotin-CD36(149-168) provides a convenient means not only of characterizing binding profiles between CD36 and oxLDL/oxPL but also of finding competitors for the binding.