Zhen-Yu Du

The information on binding capacity of different fatty acids (FAs) to albumin is incomplete, however, in the majority of in vitro experiments, FAs and albumin were simply mixed and their affinity believed to be complete. In this study, seven [1‐¹⁴C] FAs were mixed with albumin and assayed for β‐oxidation in rat liver homogenates. In the process of identifying the radioactive background of control assay by LCMS/MS, the results indicated different binding capacity of FAs to albumin. The percentage of unbound FAs recovered in clarified acidic solution was lower than 2% with 16:0 and 18:1n‐9, nearly 5% with EPA, 7% with 18:2n‐6, 18:3n‐3 and 20:4n‐6, and surprisingly high to 41% with DHA. Various FA/albumin molar ratios as well as different types of albumin only marginally affected these data. Thus, the big mass of unbound free DHA led to a high blank value, which is 60 times higher than the real value in the procedure of β‐oxidation measurement in vitro. In the design of future FA research in vitro, the binding capacity of FA to albumin or other proteins must be considered, especially for DHA research.

We investigated whether the hypolipidaemic effect of fenofibrate and fasting observed in most omnivorous mammals may also apply to herbivorous fish. Grass carp (Ctenopharyngodon idella) fed a high-fat (8 %) diet exhibited a marked increase in blood lipids and body fat after 6 weeks. They were then treated with fenofibrate (100 mg/kg body weight) in the same high-fat diet for 2 weeks, followed by fasting for 1 week. Plasma lipid concentration, body fat amount, fatty acid composition, plasma thiobarbituric acid-reactive substances and some parameters related to hepatic fatty acid oxidation were measured, and liver samples were stained for histological examination. Fenofibrate treatment decreased TAG and cholesterol concentrations in plasma, total lipids of the whole body and liver, and EPA and DHA contents in tissues. Further, a mobilisation of mesenteric fat concomitant with an increase in hepatic peroxisomal fatty acid oxidation and lipid peroxidation was observed. Compared with fenofibrate treatment, fasting decreased body weight and plasma TAG, but not plasma cholesterol. It also reduced the fat content of the whole body and increased the EPA and DHA contents in the liver and other tissues. Fatty acid oxidation was stimulated by fasting in mitochondria, but not in peroxisomes. These data suggest that fenofibrate and fasting regulate the lipid metabolism in grass carp through different metabolic pathways. The grass carp is moderately responsive to a fibrate derivative in comparison with the well-known excess responsiveness of the rat model, and so it could be used for the study of lipid abnormalities as a herbivorous model.

Herbivorous grass carp (Ctenopharyngodon idella) has been reported to exhibit low capacity to utilize high dietary lipid, but different lipid sources might affect this limited capacity. In order to compare the effects of different lipid sources with different lipid levels, juvenile grass carp were fed one of nine diets containing three oils [lard, plant oil mixed by maize and linseed oil, and n-3 high unsaturated fatty acid-enriched (HUFA-enriched) fish oil] at three lipid levels (20, 60 and 100 g kg⁻¹ dry diet) for 8 weeks. Decreased feed intake, poor growth performance, hepatic pathology and higher blood lipid peroxidation were found in 60 and 100 g kg⁻¹ fish oil groups. Conversely, in lard and plant oil groups, even at 100 g kg⁻¹ dietary lipid level, feed intake and growth performance did not decrease, despite histological observation revealed hepatic pathology in these groups. Plasma triglyceride and cholesterol contents increased significantly in all 100 g kg⁻¹ dietary lipid groups. In the comparison of hepatic FA β-oxidation among three oil groups at 60 g kg⁻¹ dietary lipid level, impaired mitochondrial and peroxisomal FA oxidation capacity was observed in fish oil group. The results confirmed the relatively low capacity of grass carp to utilize high dietary lipid, and furthermore excess HUFA intake will result in more serious adverse effects than other FA.