Flaxseed Oil Attenuates Hepatic Steatosis and Insulin Resistance in Mice by Rescuing the Adaption to ER Stress

Beneficial Effects of Dietary Flaxseed Oil through Inflammation Pathways and Gut Microbiota in Streptozotocin-Induced Diabetic Mice

Flaxseed oil (FO) has displayed potential anti-diabetes properties by providing a high content of α-linolenic acid. However, the effects and mechanisms of FO on type 1 diabetes are still unclear. The present study aims to explore the effects of different doses of FO feeding on hepatic inflammation and gut microbiota in streptozotocin-induced diabetic mice. Forty-eight six-week-old C57BL/6J male mice were divided into a control group (CON), a diabetic group (MOD), a diabetes with 7.0% w/w FO feeding group (FO-L), and a diabetes with 10.5% w/w FO feeding group (FO-H) for six weeks. The 7.0% w/w and 10.5% w/w FO feeding groups exhibited potential recovery of the number and size of pancreas tissues. The fasting blood glucose level was significantly decreased only after 4 weeks of feeding with 10.5% w/w FO in diabetic mice. The 10.5% w/w FO feeding group significantly decreased the postprandial blood glucose level of mice in the OGTT test. Hepatic glycogen levels were dramatically upregulated in the mice fed with both 7.0% w/w and 10.5% w/w FO. FO feeding significantly attenuated hepatic LPS, TNF-α, and IL-1β levels. In addition, we observed that 7.0% w/w and 10.5% w/w FO feedings notably downregulated hepatic gene and protein expressions of TLR4, MyD88, and P65. Furthermore, only 10.5% FO regulated fecal microbiota by increasing the relative abundance of the Bacteroidetes phylum, Lactococcus family, and Muribaculaceae and Streptococcaceae family and genus in streptozotocin-induced diabetic mice. Therefore, we conclude that FO feeding plays a role in anti-inflammation via the regulation of hepatic LPS/TLR4/MyD88 pathways and gut microbiota. In addition, different doses of FO supplementation may exhibit varying mechanisms in streptozotocin-induced mice.

Beneficial Effects of Flaxseed and/or Mulberry Extracts Supplementation in Ovariectomized Wistar Rats

Low endogenous estrogen action causes several injuries. Medicinal plants, such as flaxseed and mulberry, contain substances that have been shown to be effective to the organism. The aim was to verify the effects of flaxseed and/or mulberry extracts on ovariectomized Wistar rats. The animals received supplements of extracts and estrogen or saline by gavage for 60 days and were weighed weekly. Vaginal wash, blood, pituitary, uterus, liver, and kidneys were collected. Phenolic compounds and the antioxidant activity of the extracts, lipid profile, uric acid, liver enzymes, and pituitary weight were measured. Histomorphometric for uterine wall and histopathological analyses for liver and kidney were performed. Flaxseed and mulberry extracts showed great antioxidant activity and large amounts of phenolic compounds. The treatment with extracts had less weight gain, increased pituitary weight, the predominance of vaginal epithelial cells, and reduced TC, LDL-c and lipase activity, similar to estrogen animals. Estrogen or flaxseed + mulberry animals reduced VLDL-c and TAG. HDL-c, uric acid, and liver enzymes did not differ. Estrogen or extracts demonstrated trophic action on the endometrial thickness and have not shown hepatotoxicity or nephrotoxicity. We suggested the beneficial effects of flaxseed and mulberry extract as an alternative to reduce and/or prevent the negative effects caused by low estrogenic action.

Plant sterol ester of α-linolenic acid improved non-alcoholic fatty liver disease by attenuating endoplasmic reticulum stress-triggered apoptosis via activation of the AMPK

Apoptosis is a feature of progressions steatosis to nonalcoholic steatohepatitis (NASH) and can be explained by endoplasmic reticulum stress (ERS). The present study aimed to investigate the protective effects of plant sterol ester of α-linolenic acid (PS-ALA) on ERS-triggered apoptosis in high fat diet-fed mice and oleic acid-induced hepatocytes, and further explore the underlying mechanisms. Our results showed that PS-ALA improved NAFLD in both in vivo and in vitro models. Moreover, PS-ALA treatment can attenuate ERS and associated apoptosis via inhibiting IRE1α/TRAF2/JNK signal pathway. Furthermore, we found that the protective effect of PS-ALA on ERS-triggered apoptosis was mediated by activation of AMPK as pretreatment with Compound C, an AMPK inhibitor, abolished the anti-apoptotic effect of PS-ALA. Taken together, our results illustrate that PS-ALA attenuating ERS-mediated apoptosis via activating AMPK, which provided new insights into the protective effect of PS-ALA in NAFLD.

Comparative structural and techno-functional elucidation of full-fat and defatted flaxseed extracts: implication of atmospheric pressure plasma jet

BACKGROUND

The relatively inferior techno-functionality of flaxseed protein/polysaccharide complexes, especially regarding emulsifying and antioxidant activities, has partially limited their implication in the health food system. The present study aimed to investigate the effects of an atmospheric pressure plasma jet (APPJ) on the physicochemical, structural and selected techno-functional properties of flaxseed extracts.

RESULTS

The results obtained showed that the full-fat and defatted flaxseed extract solutions (5 mg mL^-1 ) displayed a sustainable decline in pH (-54.06%, -48.80%, P < 0.05) and zeta potential values (-29.42%, -44.28%, P < 0.05), but a gradual increase in particle sizes, as visualised by an optical microscope, during 0-120 s of APPJ treatment. Moreover, the APPJ led to initial decrease but subsequent increase in protein carbonyls and secondary lipid oxidation products, and concurrently changed the spatial conformation and microstructure of flaxseed extracts, as indicated by endogenous fluorescence properties and scanning electron microscopy (SEM). Additionally, the protein subunit remodeling and gum polysaccharides depolymerization were different for full-fat and defatted flaxseed extracts after 30 s of APPJ exposure. Importantly, the emulsifying and antioxidant activities of defatted flaxseed extract were particularly improved, as assessed by cyro-SEM and 2,2-diphenyl-1-picrylhydrazyl radical scavenging activity following 15-30 s of APPJ treatment, as a result of the changing interactions between protein and gum polysaccharides, as well as the release of specific phenolic compounds.

CONCLUSION

APPJ could serve as a promising strategy for tailoring the specific techno-functionality of flaxseed extracts based on mild structural modification. © 2021 Society of Chemical Industry.

The quality and antioxidant elucidation of germinated flaxseed treated with acidic electrolyzed water

The endogenous fortification of antioxidant lipid concomitants in flaxseed was imperative to improve the oxidative stability of α-linolenic acid (ALA) in flaxseed and flaxseed oil upon processing, storage and gastrointestinal digestion. The comparative effects of acidic electrolyzed water (ACEW) and tap water (TW) on the triglyceride configuration, typical lipid concomitants, and antioxidant properties of flaxseed were conducted during 0-5 days of germination. The results showed that ACEW enhanced the germination rate of flaxseed by 18.25% and simultaneously suppressed the dynamic depletion of ALA by 5.32% when compared with TW (p < .05). The total phenolic acids, lignans, and flavonoids were effectively accumulated in flaxseed following ACEW-mediated germination with the further increase by 4.82%, 15.48%, and 8.22% in comparison with those induced by TW (p < .05). The total contents of cyclolinopeptides in flaxseed progressively dropped following either ACEW or TW treatment, a slighter decrease by 5.59% for flaxseed treated by ACEW than that by TW. Notably, the maximum accumulation of tocopherols and phytosterols had been early obtained for flaxseed treated with ACEW for 2-3 days due to the de novo synthesis or intermolecular conformational transition (p < .05). Most importantly, ACEW-mediated germination led to higher increment of the thermal oxidative stability and antioxidant properties of flaxseed and flaxseed oil in comparison to TW. In brief, the initial oxidation temperature increased by 7.09% and 3.06% (p < .05), and the antioxidant activities as evaluated by DPPH, ABTS, and FRAP values raised by 3.86%-28.07% and 4.21%-9.18% (p < .05), respectively. These findings clarify that the germination especailly mediated by ACEW could be an effective method to further optimize the nutritional and functional properties of flaxseed through reconstructing the endogenous antioxidant system.

Sandalwood seed oil ameliorates hepatic insulin resistance by regulating the JNK/NF-κB inflammatory and PI3K/AKT insulin signaling pathways

Sandalwood (santalum spicatum) seed oil (SSO) is rich in ximenynic acid. The aim of the present study was to investigate the effect of SSO on high-fat/high-sucrose diet (HFHSD) induced insulin resistance (IR) in comparison with fish oil (FO), sunflower oil (SO) and linseed oil (LO). Fifty male Sprague-Dawley rats were randomly divided into five dietary groups: standard chow diet (controls), HFHSD plus 7% SSO, HFHSD plus 7% FO, HFHSD plus 7% SO and HFHSD plus 7% LO. After 12 weeks of feeding, the rats were sacrificed, and the serum parameters, hepatic lipids and underlying molecular mechanisms were studied. SSO, FO or LO significantly prevented glucose intolerance, hyperglycaemia, obesity, and hepatic lipid accumulation, and decreased the homeostasis model assessment of IR (HOMA-IR) and the serum levels of pro-inflammatory factors (IL-6, IL-1β and TNF-α) compared with SO. In addition, SSO activated the PI3K/AKT insulin signaling pathway and down-regulated the JNK/NF-κB inflammatory signaling pathway in the liver. In summary, our results proved that SSO exerted an ameliorative effect on IR by regulating the hepatic inflammation related blockage of the insulin signaling pathway in the rats.

Methionine sulfoxide reductase B3 deficiency inhibits the development of diet-induced insulin resistance in mice

Oxidative and endoplasmic reticulum (ER) stress are involved in mediating high-fat diet (HFD)-induced insulin resistance. As the ER-localized methionine sulfoxide reductase B3 (MsrB3) protects cells against oxidative and ER stress, we hypothesized that MsrB3 might be associated with HFD-induced insulin resistance. To test this hypothesis, we examined the effect of MsrB3 deficiency on HFD-induced insulin resistance using MsrB3 knockout (KO) mice. Mice were fed a control diet or HFD for 12 weeks and insulin sensitivity was measured using a hyperinsulinemic-euglycemic clamp. HFD consumption increased the body weight of both wild-type and MsrB3 KO mice, and no significant difference was observed between the genotypes. The HFD increased oxidative stress and induced insulin resistance in the skeletal muscle of wild-type mice, but did not affect either in MsrB3 KO mice. The unfolded protein response (UPR) was increased in MsrB3 KO mice upon consumption of HFD, but not in wild-type mice. Mitochondrial oxidative phosphorylation proteins and the levels of superoxide dismutase 2 and glutathione peroxidase 1 were increased in MsrB3 KO mice upon HFD consumption. The respiratory control ratio was reduced in wild-type mice consuming HFD but not in MsrB3 KO mice. The levels of calcium/calmodulin-dependent protein kinase kinase β, phosphorylated AMP-activated protein kinase, and peroxisome proliferator-activated receptor gamma coactivator 1α were increased in MsrB3 KO mice following HFD consumption. These results suggest that MsrB3 deficiency inhibits HFD-induced insulin resistance, and the increased mitochondrial biogenesis and antioxidant induction might be the mechanisms underlying this phenomenon.

Dietary α-Linolenic Acid Counters Cardioprotective Dysfunction in Diabetic Mice: Unconventional PUFA Protection

Whether dietary omega-3 (n-3) polyunsaturated fatty acid (PUFA) confers cardiac benefit in cardiometabolic disorders is unclear. We test whether dietary -linolenic acid (ALA) enhances myocardial resistance to ischemia-reperfusion (I-R) and responses to ischemic preconditioning (IPC) in type 2 diabetes (T2D); and involvement of conventional PUFA-dependent mechanisms (caveolins/cavins, kinase signaling, mitochondrial function, and inflammation). Eight-week male C57Bl/6 mice received streptozotocin (75 mg/kg) and 21 weeks high-fat/high-carbohydrate feeding. Half received ALA over six weeks. Responses to I-R/IPC were assessed in perfused hearts. Localization and expression of caveolins/cavins, protein kinase B (AKT), and glycogen synthase kinase-3 β (GSK3β); mitochondrial function; and inflammatory mediators were assessed. ALA reduced circulating leptin, without affecting body weight, glycemic dysfunction, or cholesterol. While I-R tolerance was unaltered, paradoxical injury with IPC was reversed to cardioprotection with ALA. However, post-ischemic apoptosis (nucleosome content) appeared unchanged. Benefit was not associated with shifts in localization or expression of caveolins/cavins, p-AKT, p-GSK3β, or mitochondrial function. Despite mixed inflammatory mediator changes, tumor necrosis factor-a (TNF-a) was markedly reduced. Data collectively reveal a novel impact of ALA on cardioprotective dysfunction in T2D mice, unrelated to caveolins/cavins, mitochondrial, or stress kinase modulation. Although evidence suggests inflammatory involvement, the basis of this "un-conventional" protection remains to be identified.

Secoisolariciresinol diglucoside alleviates hepatic lipid metabolic misalignment involving the endoplasmic reticulum-mitochondrial axis

Secoisolariciresinol diglucoside (SDG) has positive effects on obesity and its complications. We investigated the effects and mechanism of SDG on high-fat and high-fructose diet (HFFD)-induced hepatic lipid metabolic disorders. Supplementation with 40 mg kg^-1 d^-1 SDG for 12 weeks significantly reduced the body weight and the ratio of liver and adipose tissue to body weight in HFFD-fed mice. Serum and hepatic TG, TC, HDL-C, and LDL-C levels became normalized, and hepatic lipid metabolic disorders lessened because of the downregulation of lipid synthesis genes and upregulation of lipid oxidation genes. SDG also alleviated endoplasmic reticulum (ER) stress and mitochondrial dysfunction by regulating the ER stress factors Bip, IRE1α, Xbp1, Atf6, Perk, and Chop and mitochondrial function-related genes Cox5b, Cox7a1, Cox8b, and Cycs. Results with HepG2 cells confirmed that SDG regulated lipid metabolic disorders by the ER stress-Ca²⁺-mitochondrial-associated pathway. Our study provides a strategy for the treatment of obesity and its related comorbidities.

Plant Sterol Ester of α-Linolenic Acid Attenuates Nonalcoholic Fatty Liver Disease by Rescuing the Adaption to Endoplasmic Reticulum Stress and Enhancing Mitochondrial Biogenesis

Nonalcoholic fatty liver disease (NAFLD) is becoming more common in the world and is presenting a great challenge concerning prevention and treatment. Plant sterol ester of α-linolenic acid (PS-ALA) has a potential benefit to NAFLD. To examine the effect of PS-ALA on NAFLD, C57BL/6J mice were given a control diet, high fat and high cholesterol diet (HFD), and HFD plus 2% PS, 1.3% ALA, or 3.3% PS-ALA for 16 weeks. Our results showed that PS-ALA treatment suppressed hepatic steatosis, ameliorated lipid disorder, attenuated inflammatory response, and inhibited oxidative stress. In the molecular level, PS-ALA downregulated high transcriptional and translational levels of endoplasmic reticulum (ER) stress markers (Grp78 and Chop) leading to decreased protein expression of transcription factor and key enzymes involved in de novo lipogenesis (Srebp-1c and Fas) and cholesterol synthesis (Srebp-2 and Hmgcr). In parallel, PS-ALA blocked Nlrp3 activation and reduced release of IL-1β and IL-18 via inhibiting ER stress-induced sensitization of unfolded protein response sensors (Ire1α and Xbp1s). Finally, PS-ALA improved HFD-induced mitochondrial damage and fatty acid accumulation as exhibited by higher protein and mRNA expression of key genes administering mitochondrial biogenesis (Pgc-1α, Nrf1, and Tfam) and fatty acid β-oxidation (Pparα and Cpt1a). In conclusion, our study originally demonstrated that PS-ALA rescued ER stress, enhanced mitochondrial biogenesis, and thus ameliorated NAFLD.

The Effect of Flaxseed Enriched Yogurt on the Glycemic Status and Cardiovascular Risk Factors in Patients with Type 2 Diabetes Mellitus: Randomized, Open-labeled, Controlled Study

Flaxseed is one of the rich sources of α-linolenic acid and lignan. Flaxseed and its components have antioxidant, hypolipidemic and hypoglycemic effects. The study aimed to investigate the effect of flaxseed enriched yogurt on glycemic control, lipid profiles and blood pressure in patients with type 2 diabetes. A randomized, open-labeled, controlled clinical trial was conducted on 57 patients with type 2 diabetes. Participants were assigned to receive 200 g 2.5% fat yogurt containing 30-g flaxseed or plain yogurt daily for 8 weeks. Anthropometrics and biochemical parameters were evaluated at the beginning and end of the study. After 8 weeks of supplementation, Hemoglobin A1c was significantly decreased in the intervention group compared to control (p = 0.007). Also, at the end of the study, significant differences were seen between the flaxseed enriched yogurt and control groups in triglycerides and total cholesterol concentrations (p = 0.04 and p = 0.01), systolic blood pressure and diastolic blood pressure (p = 0.02 and p = 0.002, respectively). However, we did not find any difference between 2 groups in low-density lipoprotein, high-density lipoprotein, body weight and waist circumference (p > 0.05). Our results showed that the addition of flaxseed to yogurt can be effective in the management of type 2 diabetes.

Trial Registration

ClinicalTrials.gov Identifier: NCT02436369.

Effect of flaxseed polyphenols on physical stability and oxidative stability of flaxseed oil-in-water nanoemulsions

Recent studies have shown that the high susceptibility of flaxseed oil nanoemulsions to lipid oxidation limits their incorporation into functional foods and beverages. For this reason, the impact of various flaxseed phenolic extracts on the physical and oxidative stability of flaxseed oil nanoemulsions was investigated. Flaxseed lignan extract (FLE) and secoisolariciresinol (SECO) exhibited antioxidant activity whereas secoisolariciresinol diglucoside (SDG) and p-coumaric acid (CouA) exhibited prooxidant activity in the flaxseed oil nanoemulsions. The antioxidant potential of flaxseed phenolics in the nanoemulsions was as follows: SECO < CouA < SDG ≈ FLE. Moreover, the antioxidant/prooxidant activity of the phenolics was also related to their free radical scavenging activity and partitioning in the nanoemulsions. Our results suggested that both SECO and FLE were good plant-based antioxidants for improving the stability of flaxseed oil nanoemulsions.

Effect of Early and Late Interventions with Dietary Oils on Vascular and Neural Complications in a Type 2 Diabetic Rat Model

AIMS

Determine the effect of dietary oils enriched in different mono- or polyunsaturated fatty acids, i.e., olive oil (18 : 1, oleic acid), safflower oil (18 : 2 n-6, linoleic acid), flaxseed oil (18 : 3 n-3, alpha linolenic acid), evening primrose oil (18 : 3 n-6, gamma linolenic acid), or menhaden oil (20:5/22 : 6 n-3 eicosapentaenoic/docosahexaenoic acids), on vascular and neural complications in high-fat-fed low-dose streptozotocin-treated Sprague-Dawley rats, an animal model for late-stage type 2 diabetes.

MATERIALS AND METHODS

Rats were fed a high-fat diet (45% kcal as fat primarily derived from lard) for 8 weeks and then treated with a low dose of streptozotocin (30 mg/kg) in order to induce hyperglycemia. After an additional 8 (early intervention) or 20 (late intervention) weeks, the different groups of rats were fed diets with 1/2 of the kcal of fat derived from lard replaced by the different dietary oils. In addition, a control group fed a standard diet (4.25% kcal as fat) and a diabetic group maintained on the high-fat diet were maintained. The treatment period was approximately 16 weeks. The endpoints evaluated included vascular reactivity of epineurial arterioles, motor and sensory nerve conduction velocity, thermal and corneal sensitivity, and innervation of sensory nerves in the cornea and skin.

RESULTS

Our findings show that menhaden and flaxseed oil provided the greatest benefit for correcting peripheral nerve damage caused by diabetes, whereas enriching the high-fat diet with menhaden oil provided the most benefit to acetylcholine-mediated vascular relaxation of epineurial arterioles of the sciatic nerve. Enriching the diets with fatty acids derived from the other oils provided none to partial improvements.

CONCLUSIONS

These studies imply that long-chain n-6 and n-3 polyunsaturated fatty acids could be an effective treatment for diabetic peripheral neuropathy with n-3 polyunsaturated fatty acids derived from fish oil being the most effective.