Effect of fish and krill oil supplementation on glucose tolerance in rabbits with experimentally induced obesity

Changes in Plasma Pyruvate and TCA Cycle Metabolites upon Increased Hepatic Fatty Acid Oxidation and Ketogenesis in Male Wistar Rats

Altered hepatic mitochondrial fatty acid β-oxidation and associated tricarboxylic acid (TCA) cycle activity contributes to lifestyle-related diseases, and circulating biomarkers reflecting these changes could have disease prognostic value. This study aimed to determine hepatic and systemic changes in TCA-cycle-related metabolites upon the selective pharmacologic enhancement of mitochondrial fatty acid β-oxidation in the liver, and to elucidate the mechanisms and potential markers of hepatic mitochondrial activity. Male Wistar rats were treated with 3-thia fatty acids (e.g., tetradecylthioacetic acid (TTA)), which target mitochondrial biogenesis, mitochondrial fatty acid β-oxidation, and ketogenesis predominantly in the liver. Hepatic and plasma concentrations of TCA cycle intermediates and anaplerotic substrates (LC-MS/MS), plasma ketones (colorimetric assay), and acylcarnitines (HPLC-MS/MS), along with associated TCA-cycle-related gene expression (qPCR) and enzyme activities, were determined. TTA-induced hepatic fatty acid β-oxidation resulted in an increased ratio of plasma ketone bodies/nonesterified fatty acid (NEFA), lower plasma malonyl-CoA levels, and a higher ratio of plasma acetylcarnitine/palmitoylcarnitine (C2/C16). These changes were associated with decreased hepatic and increased plasma pyruvate concentrations, and increased plasma concentrations of succinate, malate, and 2-hydroxyglutarate. Expression of several genes encoding TCA cycle enzymes and the malate-oxoglutarate carrier (Slc25a11), glutamate dehydrogenase (Gdh), and malic enzyme (Mdh1 and Mdh2) were significantly increased. In conclusion, the induction of hepatic mitochondrial fatty acid β-oxidation by 3-thia fatty acids lowered hepatic pyruvate while increasing plasma pyruvate, as well as succinate, malate, and 2-hydroxyglutarate.

Feeds of animal origin in rabbit nutrition – a review

Rabbits are classified as obligate herbivores. However, under natural conditions, some members of the family Leporidae incorporate animal products into their diets. Therefore, it seems biologically justified to supplement the diets of farmed rabbits with feeds of animal origin as sources of protein, fat and minerals. The aim of this review was to describe, from a historical perspective, the use of various feeds of animal origin in rabbit nutrition. The applicability of by-products from mammal, poultry, fish and invertebrate processing for rabbit feeding was evaluated, including the future prospects for their use. A review of the available literature revealed that various animal-based feeds can be valuable protein sources in rabbit diets, but their inclusion levels should not exceed 5-10%. Studies investigating their efficacy have been conducted since the 1970s. In some regions of the world, the use of animal-derived protein in livestock feeds was prohibited due to the risk of spreading bovine spongiform encephalopathy (BSE). However, the interest in animal by-products as protein sources in livestock diets is likely to increase since the above ban has been lifted.

Co-administration of oleic and docosahexaenoic acids enhances glucose uptake rather than lipolysis in mature 3T3-L1 adipocytes cell culture

This study investigated the effect of different types of long-chain fatty acids and their combination on the triglyceride accumulation, glucose utilisation, and lipolysis in already obese adipocytes. 3T3-L1 MBX cells were first differentiated into mature adipocytes using adipogenic inducers (3-isobutyl-1-methylxanthine, dexamethasone, indomethacin, insulin, and high glucose), then 100 µM 0.1% ethanol extracts of palmitic (PA), oleic (OA), or docosahexaenoic acid (DHA) were applied for nine days. Unsaturated fatty acids decreased the intracellular lipid accumulation while maintaining glucose utilisation levels. However, unlike OA, self-administration of DHA only intensified lipolysis by 25% vs induced untreated control (IC), which may have a direct detrimental impact on the whole body’s metabolic state. DHA applied in equal proportion with PA elevated triglyceride accumulation by 10% compared to IC, but applied with OA, enhanced glucose uptake without any significant changes in the lipogenic drive and the lipolytic rate, suggesting that this unsaturated fatty acids combination may offer a considerable advantage in amelioration of obesity-related disorders.

Efficacy of krill oil versus fish oil on obesity-related parameters and lipid gene expression in rats: randomized controlled study

Backround

This study aimed to determine the effects of LC n-3 PUFA supplementation on the prevention and treatment of obesity and obesity-related diseases, and to compare the efficiency of different LC n-3 PUFA sources via biochemical and genetic mechanisms in rats.

Methods

Male Wistar rats were randomized into four study groups, and fed with a standard diet, High Fat Diet (HFD), HFD+%2.5 Fish Oil (FO-HFD) or HFD+%2.5 Krill Oil (KO-HFD) for eight weeks. Food consumption, weight gain, serum glucose, insulin, ghrelin and leptin concentrations, lipid profile, liver fatty acid composition, and FADS1 and FADS2 mRNA gene expression levels were measured.

Results

Weight gain in each HFD group was significantly higher than control group (p < 0.001), without any differences among them (p < 0.05). LC n-3 PUFAs modified lipid profile, but not glucose tolerance. Serum leptin levels were significantly higher in HFD groups than in the control group, however, no difference in serum ghrelin levels was observed among the groups. Liver n-3 fatty acid desaturation activity was higher (p = 0.74), and liver total lipid content was lower (p = 0.86) in KO-HFD compared to FO-HFD. FADS1 gene expression was highest in the HFD group (p < 0.001) while FADS2 gene expression was highest in the FO-HFD group (p < 0.001).

Conclusion

LC n-3 PUFAs, especially krill oil, had moderate effects on lipid profile, but limited effects on obesity related parameters, suggesting different effects of different sources on gene expression levels. Further randomized controlled trials are needed to determine the efficacy of different LC n-3 PUFA sources in the prevention and treatment of obesity in humans.

Advances in Technologies for Highly Active Omega-3 Fatty Acids from Krill Oil: Clinical Applications

Euphausia superba, commonly known as krill, is a small marine crustacean from the Antarctic Ocean that plays an important role in the marine ecosystem, serving as feed for most fish. It is a known source of highly bioavailable omega-3 polyunsaturated fatty acids (eicosapentaenoic acid and docosahexaenoic acid). In preclinical studies, krill oil showed metabolic, anti-inflammatory, neuroprotective and chemo preventive effects, while in clinical trials it showed significant metabolic, vascular and ergogenic actions. Solvent extraction is the most conventional method to obtain krill oil. However, different solvents must be used to extract all lipids from krill because of the diversity of the polarities of the lipid compounds in the biomass. This review aims to provide an overview of the chemical composition, bioavailability and bioaccessibility of krill oil, as well as the mechanisms of action, classic and non-conventional extraction techniques, health benefits and current applications of this marine crustacean.

Animal Fats in Rabbit Feeding – A Review

The purpose of this article is to overview the history of feeding rabbits with different types of animal fats, and to discuss their effects on rabbit performance and quality of their products. Other aspects of the inclusion of various animal fats in rabbit diets are also described. This article is based on the analysis of relevant scientific literature and presents animal fats fed to rabbits, such as beef tallow, butter, pork lard, poultry fat, fish oil, krill oil, oil extracted from insect larvae, mixtures of various animal fats, and mixtures of animal and vegetable fats. The reported papers describe the effect of fats on growth performance, lactation, rearing performance, meat quality, and health status of rabbits. It is notable that in many cases, various animal fats were often an integral part of numerous diets or were included in control diets. The presented information demonstrates that animal fat can be fed to rabbits at 2–4% of the diet without negative effects on reproductive performance, growth performance and quality of meat obtained. Rabbits were used as model animals in many studies in which fat was added to balance the diets and to increase their energy value, especially when investigating various cardiovascular and obesity-related diseases.

Growth, behavioural, serum biochemical and morphological changes in female rabbits fed high-fat diet

This study aimed to determine whether high-fat diet (HFD) could cause growth, behavioural, biochemical and morphological changes in young female rabbits. Thirty-six female rabbits were randomly divided into two groups fed with either a high-fat diet (HFD) or a standard normal diet (SND) for 5 weeks. Growth and behavioural changes were recorded during the 5-week feeding period. Tissue samples, including blood and adipose tissue, were obtained after slaughter. HFD rabbits weighed more by the end of the feeding period, had a higher percent body weight and adipose tissue weight change and had longer body and bust lengths than SND rabbits. HFD rabbits significantly reduced their feed intake and feeding frequency during the fourth and fifth weeks. HFD rabbits also showed lower frequency of drinking and resting and increased stereotypical behaviour. Besides, HFD rabbits showed significant physiological abnormalities. HFD rabbits had higher serum cholesterol (TC) and triglycerides (TG) levels than SND rabbits at the end of the feeding period, and higher free fatty acid (FFA) levels than rabbits in the SND group after the third week of feeding. Serum thyroxine (T4) increased significantly in week 2 and week 5 and triiodothyronine (T3) increased significantly in week four. However, there was no significant change in serum glucose (GLU) and insulin (INS) levels. Additionally, HFD reduced the area and diameter of perirenal and subcutaneous fat cells and increased their density. Our findings suggest that HFD rabbits had higher weight gains, accumulation of fat, and more behavioural changes than SND rabbits. Although high levels of fat in the diet had a low impact on hyperglycaemia, it could lead to hyperlipidemia and hyperthyroidism. Our results also suggest that sustained HFD may cause the proliferation of adipocytes in young female rabbits.

Preparation and Characterization of Microemulsions Based on Antarctic Krill Oil

Antarctic krill oil is high in nutritional value and has biological functions like anti-inflammation and hypolipidemic effects. But it has and unpleasant smell, and unsaturated fatty acids are prone to oxidative deterioration. Its high viscosity and low solubility in water make it difficult for processing. Microemulsion can be a new promising route for development of krill oil product. We determined a formula of krill oil-in-water microemulsion with krill oil: isopropyl myristate = 1:3 as oil phase, Tween 80:Span 80 = 8:2 as surfactant, ethanol as co-surfactant and the mass ratio of surfactant to co-surfactant of 3:1. After screening the formula, we researched several characteristics of the prepared oil-in-water microemulsion, including electrical conductivity, microstructure by transmission electron microscope and cryogenic transmission electron microscope, droplet size analysis, rheological properties, thermal behavior by differential scanning calorimeter and stability against pH, salinity, and storage time.

Egg oil from Portunus trituberculatus alleviates insulin resistance through activation of insulin signaling in mice

Marine bioactive lipids have been utilized to overcome insulin resistance. However, oil from swimming crab has never been studied. Here, we analyzed the constituents of egg oil from Portunus trituberculatus (Pt-egg oil) and investigated its protective effects against insulin resistance in mice on a high-fat diet. The results showed that Pt-egg oil contained 52.05% phospholipids, 8.61% free fatty acids (especially eicosapentaenoic acid and docosahexaenoic acid), 32.38% triglyceride, 4.79% total cholesterol, and ditissimus astaxanthin. Animal experiments showed that Pt-egg oil significantly mitigated insulin resistance and was associated with reductions in blood glucose, insulin, glucose tolerance, insulin tolerance, serum lipids, and hepatic glycogen. Pt-egg oil activated the phosphatidylinositol 3-hydroxy kinase (PI3K)/protein kinase B (Akt)/glucose transporter 4 pathway in skeletal muscle both at the transcriptional level and at the translational level. Pt-egg oil also promoted hepatic glycogen synthesis through activation of the PI3K/Akt/glycogen synthase kinase-3 beta pathway. These indicate that Pt-egg oil can be used as an alternative to marine bioactive lipids to improve insulin resistance.

Effect of fish oil supplementation and restricted feeding on body fat distribution and blood lipid profile in a rabbit model of castration-induced obesity

This study investigates the effect of fish oil supplementation and restricted feeding on body fat distribution and blood lipid profile in experimentally induced obesity in rabbits. The trial was carried out with 30 male rabbits, divided into 5 groups of 6 animals each (NC - non-castrated, non-treated, full-diet fed; C100 - castrated, non-treated, full-diet fed; FO100 - castrated, treated with fish oil, full-diet fed; C50 - castrated, non-treated, 50% restricted fed; FO50 - castrated, treated with fish oil, 50% restricted fed). At the end of the experiment, plasma lipids measurement and quantification of fat distribution was performed. The results of this study indicate that fish oil supplementation reduces obesity-associated abnormalities in lipid profile (high-density lipoprotein cholesterol to low-density lipoprotein cholesterol ratio and non-esterified fatty acids) and in body fat distribution in full-diet fed rabbits. Restricted feeding (C50) alone and the combination of restricted feeding and fish oil supplementation (FO50) in particular, has a detrimental effect on the lipid profile despite the marked reduction in intra-abdominal fat.

Antarctic Krill (Euphausia superba) Oil: A Comprehensive Review of Chemical Composition, Extraction Technologies, Health Benefits, and Current Applications

Antarctic krill (Euphausia superba) oil has been receiving increasing attention due to its nutritional and functional potentials. However, its application as a novel food ingredient has not yet been fully explored. This review summarizes the chemical composition, extraction technologies, potential health benefits, and current applications of krill oil, with the aim of providing suggestions for its exploitation. Krill oil is a unique lipid consisting of diverse lipid classes and is characterized by a high concentration (39.29% to 80.69%) of phospholipids (PLs) associated with eicosapentaenoic acid (EPA) and docosahexaenoic acid (DHA). It also contains considerable amounts of bioactive minor components such as astaxanthin, sterols, tocopherols, vitamin A, flavonoids, and minerals. The current technologies used in krill oil production are solvent extraction, nonsolvent extraction, super/subcritical fluid extraction, and enzyme-assisted pretreatment extraction, which all greatly influence the yield and quality of the end-product. In addition, krill oil has been documented to have various health benefits, including anti-inflammatory effects, cardiovascular disease (CVD) prevention, women's health, neuroprotection, and anticancer activities. Although krill oil products used for dietary supplements have been commercially available, few studies have attempted to explore the underlying molecular mechanisms to elucidate how exactly the krill oil exerts different biological activities. Further studies should focus on this to improve the development of krill oil products for human consumption.

Effects of fish and krill oil on gene expression in peripheral blood mononuclear cells and circulating markers of inflammation: a randomised controlled trial

Marine n-3 (omega-3) fatty acids alter gene expression by regulating the activity of transcription factors. Krill oil is a source of marine n-3 fatty acids that has been shown to modulate gene expression in animal studies; however, the effect in humans is not known. Hence, we aimed to compare the effect of intake of krill oil, lean and fatty fish with a similar content of n-3 fatty acids, and high-oleic sunflower oil (HOSO) with added astaxanthin on the expression of genes involved in glucose and lipid metabolism and inflammation in peripheral blood mononuclear cells (PBMC) as well as circulating inflammatory markers. In an 8-week trial, healthy men and women aged 18–70 years with fasting TAG of 1·3–4·0 mmol/l were randomised to receive krill oil capsules (n 12), HOSO capsules (n 12) or lean and fatty fish (n 12). The weekly intakes of marine n-3 fatty acids from the interventions were 4654, 0 and 4103 mg, respectively. The mRNA expression of four genes, PPAR γ coactivator 1A (PPARGC1A), steaoryl-CoA desaturase (SCD), ATP binding cassette A1 (ABCA1) and cluster of differentiation 40 (CD40), were differently altered by the interventions. Furthermore, within-group analyses revealed that krill oil down-regulated the mRNA expression of thirteen genes, including genes involved in glucose and cholesterol metabolism and β-oxidation. Fish altered the mRNA expression of four genes and HOSO down-regulated sixteen genes, including several inflammation-related genes. There were no differences between the groups in circulating inflammatory markers after the intervention. In conclusion, the intake of krill oil and HOSO with added astaxanthin alter the PBMC mRNA expression of more genes than the intake of fish.

The Protective Effect of Antarctic Krill Oil on Cognitive Function by Inhibiting Oxidative Stress in the Brain of Senescence-Accelerated Prone Mouse Strain 8 (SAMP8) Mice

Alzheimer's disease (AD) is a common neurodegenerative disorder, and oxidative stress plays a vital role in its progression. Antarctic krill oil (AKO) is rich in polyunsaturated fatty acids, which has various biological activities, such as improving insulin sensitivity, alleviating inflammation and ameliorating oxidative stress. In this study, the protective effect of AKO against AD were investigated in senescence-accelerated prone mouse strain 8 (SAMP8) mice. Results showed that treatment with AKO could effectively ameliorate learning and memory deficits and ease the anxiety in SAMP8 mice by Morris water maze, Barnes maze test and open-field test. Further analysis indicated that AKO might reduce β-amyloid (Aβ) accumulation in hippocampus through decreasing the contents of malondialdehyde (MDA) and 7,8-dihydro-8-oxoguanine (8-oxo-G), increasing the superoxide dismutase (SOD) and glutathione peroxidase (GSH-Px) activities in the brain of SAMP8 mice.

PRACTICAL APPLICATION

The results of Morris water maze, Barnes maze test and open-field test indicated that Antarctic krill oil (AKO) improved the cognitive function and anxiety of SAMP8 mice. AKO reduced the Aβ₄₂ level in hippocampus of SAMP8 mice. AKO ameliorated oxidative stress in brain rather than in serum and liver of SAMP8 mice.

Effects of krill oil and lean and fatty fish on cardiovascular risk markers: a randomised controlled trial

Fish consumption and supplementation with n-3 fatty acids reduce CVD risk. Krill oil is an alternative source of marine n-3 fatty acids and few studies have investigated its health effects. Thus, we compared krill oil supplementation with the intake of fish with similar amounts of n-3 fatty acids on different cardiovascular risk markers. In an 8-week randomised parallel study, thirty-six healthy subjects aged 18–70 years with fasting serum TAG between 1·3 and 4·0 mmol/l were randomised to receive either fish, krill oil or control oil. In the fish group, subjects consumed lean and fatty fish, according to dietary guidelines. The krill and control group received eight capsules per d containing 4 g oil per d. The weekly intake of marine n-3 fatty acids from fish given in the fish group and from krill oil in the krill group were 4103 and 4654 mg, respectively. Fasting serum TAG did not change between the groups. The level of total lipids (P = 0·007), phospholipids (P = 0·015), cholesterol (P = 0·009), cholesteryl esters (P = 0·022) and non-esterified cholesterol (P = 0·002) in the smallest VLDL subclass increased significantly in response to krill oil supplementation. Blood glucose decreased significantly (P = 0·024) in the krill group and vitamin D increased significantly in the fish group (P = 0·024). Furthermore, plasma levels of marine n-3 fatty acids increased significantly in the fish and krill groups compared with the control (all P ≤ 0·0003). In conclusion, supplementation with krill oil and intake of fish result in health-beneficial effects. Although only krill oil reduced fasting glucose, fish provide health-beneficial nutrients, including vitamin D.

Effects of Antarctic krill oil on lipid and glucose metabolism in C57BL/6J mice fed with high fat diet

Background

Obesity and other metabolic diseases have become epidemic which greatly affect human health. Diets with healthy nutrition are efficient means to prevent this epidemic occurrence. Novel food resources and process technology were needed for these purpose. In this study, Antarctic krill oil (KO) extracted from a dry krill by a procedure of hot pump dehydration in combined with freezing-drying was used to investigate health effect in animals including the growth, lipid and glucose metabolism.

Methods

C57BL/6J mice were fed with a lard based high fat (HF) diet and substituted with KO for a period of 12 weeks in comparison with low fat normal control (NC) diet. Mice body weight and food consumption were recorded. Serum lipid metabolism - of C57BL/6J mice serum was measured. A glucose tolerance tests (GTTs) and pathology analysis of mice were performed at the end of the experiment.

Results

The KO fed mice had less body weight gain, less fat accumulation in tissue such as adipose and liver. Dyslipidemia induced by high fat diet was partially improved by KO feeding with significant reduction of serum low density lipoprotein-cholesterol (LDL-C) content. Furthermore, KO feeding also improved glucose metabolism in C57BL/6J mice including a glucose tolerance of about 22% vs. 32% of AUC (area under the curve) for KO vs HF diet and the fast blood glucose level of 8.5 mmol/L, 9.8 mmol/L and 9.3 mmol/L for NC, HF and KO diet groups, respectively. In addition, KO feeding also reduced oxidative damage in liver with a decrease of malondialdehyde (MDA) content and increase of superoxide dismutase (SOD) content.

Conclusion

This study provided evidence of the beneficial effects of KO on animal health from the processed technology, particularly on lipid and glucose metabolism. This study confirmed that as the Antarctic krill was extracted with a procedure of efficient energy, it might make it possible for Krill oil to be available for food industry.

Convergent evolution of marine mammals is associated with distinct substitutions in common genes

Phenotypic convergence is thought to be driven by parallel substitutions coupled with natural selection at the sequence level. Multiple independent evolutionary transitions of mammals to an aquatic environment offer an opportunity to test this thesis. Here, whole genome alignment of coding sequences identified widespread parallel amino acid substitutions in marine mammals; however, the majority of these changes were not unique to these animals. Conversely, we report that candidate aquatic adaptation genes, identified by signatures of likelihood convergence and/or elevated ratio of nonsynonymous to synonymous nucleotide substitution rate, are characterized by very few parallel substitutions and exhibit distinct sequence changes in each group. Moreover, no significant positive correlation was found between likelihood convergence and positive selection in all three marine lineages. These results suggest that convergence in protein coding genes associated with aquatic lifestyle is mainly characterized by independent substitutions and relaxed negative selection.

Krill products: an overview of animal studies

Many animal studies have been performed with krill oil (KO) and this review aims to summarize their findings and give insight into the mechanism of action of KO. Animal models that have been used in studies with KO include obesity, depression, myocardial infarction, chronic low-grade and ulcerative inflammation and are described in detail. Moreover, studies with KO in the form of krill powder (KP) and krill protein concentrate (KPC) as a mix of lipids and proteins are mentioned and compared to the effects of KO. In addition, differences in tissue uptake of the long-chain omega-3 polyunsaturated fatty acids eicosapentaenoic acid (EPA) and docosahexaenoic acid (DHA), when delivered in either phospholipid or triglyceride form, are addressed and the differential impact the delivery form has on gene expression profiles is explained. In our outlook, we try to highlight the potential of KO and KP supplementation in clinical settings and discuss health segments that have a high potential of showing krill product specific health benefits and warrant further clinical investigations.