Consumption of salmon fishmeal increases hepatic cholesterol content in obese C57BL/6 J mice

Abstract

Purpose By-products from farmed fish contain large amounts of proteins and may be used for human consumption. The purpose of this study was to investigate cardiometabolic effects and metabolic tolerance in mice consuming fishmeal from salmon by-products, salmon filet or beef. Methods Female C57BL/6J mice were fed chow, as a healthy reference group, or a high-fat diet for 10 weeks to induce obesity and glucose intolerance. Obese mice were subsequently given isocaloric diets containing 50% of the dietary protein from salmon fishmeal, salmon filet or beef for 10 weeks. Mice were subjected to metabolic phenotyping, which included measurements of body composition, energy metabolism in metabolic cages and glucose tolerance. Lipid content and markers of hepatic toxicity were determined in plasma and liver. Hepatic gene and protein expression was determined with RNA sequencing and immunoblotting. Results Mice fed fishmeal, salmon filet or beef had similar food intake, energy consumption, body weight gain, adiposity, glucose tolerance and circulating levels of lipids and hepatic toxicity markers, such as p-ALT and p-AST. Fishmeal increased hepatic cholesterol levels by 35–36% as compared to salmon filet (p = 0.0001) and beef (p = 0.005). This was accompanied by repressed expression of genes involved in steroid and cholesterol metabolism and reduced levels of circulating Pcsk9. Conclusion Salmon fishmeal was well tolerated, but increased hepatic cholesterol content. The high cholesterol content in fishmeal may be responsible for the effects on hepatic cholesterol metabolism. Before introducing fishmeal from salmon by-products as a dietary component, it may be advantageous to reduce the cholesterol content in fishmeal.

Altered hepatic lipid droplet morphology and lipid metabolism in fasted Plin2-null mice

“…A week before euthanasia, mice were placed in an indirect calorimetry system consisting of 20 individual cages (PhenoMaster, TSE Systems, Germany). Indirect calorimetric measurements were performed as described previously ( 45 ). Gas flow was 0.42 l/min, with gas exchange measured for 10 s per cage in 20 min intervals.…”

“…The RNA samples had RIN values between 7.6 and 8.9. Total RNA samples were subjected to Strand-Specific TruSeq TM mRNA-Seq library preparation, and 50 bp paired-end reads were sequenced at the Norwegian Sequencing Centre (Oslo University Hospital, Ullevål, Oslo) as described before ( 45 ) on an Illumina Novaseq 600 instrument. BBDuk (BBMap v34.56 was used to remove/trim low-quality reads and adapter sequences sourceforge.net/projects/bbmap/ ).…”

Can dietary proteins selectively reduce either the visceral or subcutaneous adipose tissues?

“…In rodents, only two studies used females but, in both cases, there were no effects of the tested protein (glycomacropeptide and salmon) on the two depots. 115,132 Despite this, there are some interesting observations that need to be highlighted. For instance, while above studies show that whey proteins reduce sWAT in both male and female subjects that were obese when tested together as a group, studies undertaken with only females show that whey proteins reduced only the vWAT (Table 1).…”

“…Of note, only six studies tested the effects of dietary proteins on both sexes (together) in humans, whereas three undertook similar work only recruiting females and one with only males (Table 1). In rodents, only two studies used females but, in both cases, there were no effects of the tested protein (glycomacropeptide and salmon) on the two depots 115,132 . Despite this, there are some interesting observations that need to be highlighted.…”