Renal tubule-specific Atgl deletion links kidney lipid metabolism to glucagon-like peptide 1 and insulin secretion independent of renal inflammation or lipotoxicity.

OBJECTIVE: Lipotoxic injury from renal lipid accumulation in obesity and type 2 diabetes (T2D) is implicated in associated kidney damage. However, models examining effects of renal ectopic lipid accumulation independent of obesity or T2D are lacking. We generated renal tubule-specific adipose triglyceride lipase knockout (RT-SAKO) mice to determine if this targeted triacylglycerol (TAG) over-storage affects glycemic control and kidney health. METHODS: Male and female RT-SAKO mice and their control littermates were tested for changes in glycemic control at 10-12 and 16-18 weeks of age. Markers of kidney health and blood lipid and hormone concentrations were analyzed. Kidney and blood lysophosphatidic acid (LPA) levels were measured, and a role for LPA in mediating impaired glycemic control was evaluated using the LPA receptor 1/3 inhibitor Ki-16425. RESULTS: All groups remained insulin sensitive, but 16- to 18-week-old male RT-SAKO mice became glucose intolerant, without developing kidney inflammation or fibrosis. Rather, these mice displayed lower circulating insulin and glucagon-like peptide 1 (GLP-1) levels. Impaired first-phase glucose-stimulated insulin secretion was detected and restored by Exendin-4. Kidney and blood LPA levels were elevated in older male but not female RT-SAKO mice, associated with increased kidney diacylglycerol kinase epsilon. Inhibition of LPA-mediated signaling restored serum GLP-1 levels, first-phase insulin secretion, and glucose tolerance. CONCLUSIONS: TAG over-storage alone is insufficient to cause renal tubule lipotoxicity. This work is the first to show that endogenously derived LPA modulates GLP-1 levels in vivo, demonstrating a new mechanism of kidney-gut-pancreas crosstalk to regulate insulin secretion and glucose homeostasis.

Gut microbiota and fermentation-derived branched chain hydroxy acids mediate health benefits of yogurt consumption in obese mice.

Meta-analyses suggest that yogurt consumption reduces type 2 diabetes incidence in humans, but the molecular basis of these observations remains unknown. Here we show that dietary yogurt intake preserves whole-body glucose homeostasis and prevents hepatic insulin resistance and liver steatosis in a dietary mouse model of obesity-linked type 2 diabetes. Fecal microbiota transplantation studies reveal that these effects are partly linked to the gut microbiota. We further show that yogurt intake impacts the hepatic metabolome, notably maintaining the levels of branched chain hydroxy acids (BCHA) which correlate with improved metabolic parameters. These metabolites are generated upon milk fermentation and concentrated in yogurt. Remarkably, diet-induced obesity reduces plasma and tissue BCHA levels, and this is partly prevented by dietary yogurt intake. We further show that BCHA improve insulin action on glucose metabolism in liver and muscle cells, identifying BCHA as cell-autonomous metabolic regulators and potential mediators of yogurt's health effects.

Feeding diversified protein sources exacerbates hepatic insulin resistance via increased gut microbial branched-chain fatty acids and mTORC1 signaling in obese mice.

Animal models of human diseases are classically fed purified diets that contain casein as the unique protein source. We show that provision of a mixed protein source mirroring that found in the western diet exacerbates diet-induced obesity and insulin resistance by potentiating hepatic mTORC1/S6K1 signaling as compared to casein alone. These effects involve alterations in gut microbiota as shown by fecal microbiota transplantation studies. The detrimental impact of the mixed protein source is also linked with early changes in microbial production of branched-chain fatty acids (BCFA) and elevated plasma and hepatic acylcarnitines, indicative of aberrant mitochondrial fatty acid oxidation. We further show that the BCFA, isobutyric and isovaleric acid, increase glucose production and activate mTORC1/S6K1 in hepatocytes. Our findings demonstrate that alteration of dietary protein source exerts a rapid and robust impact on gut microbiota and BCFA with significant consequences for the development of obesity and insulin resistance.

Cholecalciferol Supplementation Does Not Prevent the Development of Metabolic Syndrome or Enhance the Beneficial Effects of Omega-3 Fatty Acids in Obese Mice.

BACKGROUND: Cholecalciferol (D3) may improve inflammation, and thus provide protection from cardiometabolic diseases (CMD), although controversy remains. Omega-3 fatty acids (ω-3FA) may also prevent the development of CMD, but the combined effects of ω-3FA and D3 are not fully understood. OBJECTIVES: We determined the chronic independent and combined effects of D3 and ω-3FA on body weight, glucose homeostasis, and markers of inflammation in obese mice. METHODS: We gave 8-week-old male C57BL/6J mice, which had been fed a high-fat, high-sucrose (HF) diet (65.5% kcal fat, 19.8% kcal carbohydrate, and 14% kcal protein) for 12 weeks, either a standard D3 dose (+SD3; 1400 IU D3/kg diet) or a high D3 dose (+HD3; 15,000 IU D3/kg diet). We fed 1 +SD3 group and 1 +HD3 group with 4.36% (w/w) fish oil (+ω-3FA; 44% eicosapentaenoic acid, 25% docosahexaenoic acid), and fed the other 2 groups with corn oil [+omega-6 fatty acids (ω-6FA)]. A fifth group was fed a low-fat (LF; 15.5% kcal) diet. LF and HF+ω-6+SD3 differences were tested by a Student's t-test and HF treatment differences were tested by a 2-way ANOVA. RESULTS: D3 supplementation in the +HD3 groups did not significantly increase plasma total 25-hydroxyvitamin D and 25-hydroxyvitamin D3 [25(OH)D3] versus the +SD3 groups, but it increased 3-epi-25-hydroxyvitamin D3 levels by 3.4 ng/mL in the HF+ω-6+HD3 group and 4.0 ng/mL in the HF+ω-3+HD3 group, representing 30% and 70%, respectively, of the total 25(OH)D3 increase. Energy expenditure increased in those mice fed diets +ω-3FA, by 3.9% in the HF+ω-3+SD3 group and 7.4% in the HF+ω-3+HD3 group, but it did not translate into lower body weight. The glucose tolerance curves of the HF+ω-3+SD3 and HF+ω-3+HD3 groups were improved by 11% and 17%, respectively, as compared to the respective +ω-6FA groups. D3 supplementation, within the ω-3FA groups, altered the gut microbiota by increasing the abundance of S24-7 and Lachnospiraceae taxa compared to the standard dose, while within the ω-6FA groups, D3 supplementation did not modulate specific taxa. CONCLUSIONS: Overall, D3 supplementation does not prevent CMD or enhance the beneficial effects of ω-3FA in vitamin D-sufficient obese mice.

Dietary fat and low fiber in purified diets differently impact the gut-liver axis to promote obesity-linked metabolic impairments.

Selecting the most relevant control diet is of critical importance for metabolic and intestinal studies in animal models. Chow and LF-purified diet differentially impact metabolic and gut microbiome outcomes resulting in major changes in intestinal integrity in LF-fed animals which contributes to altering metabolic homeostasis. Dietary fat and low fiber both contribute to the deleterious metabolic effect of purified HF diets through both selective and overlapping mechanisms.

Fish oil replacement prevents, while docosahexaenoic acid-derived protectin DX mitigates end-stage-renal-disease in atherosclerotic diabetic mice.

Diabetic nephropathy (DN) remains the major cause of end-stage renal disease (ESRD). We used high-fat/high-sucrose (HFHS)-fed LDLr-/- /ApoB100/100 mice with transgenic overexpression of IGFII in pancreatic ß-cells (LRKOB100/IGFII) as a model of ESRD to test whether dietary long chain omega-3 polyunsaturated fatty acids LCω3FA-rich fish oil (FO) could prevent ESRD development. We further evaluated the potential of docosahexaenoic acid (DHA)-derived pro-resolving lipid mediators, 17-hydroxy-DHA (17-HDHA) and Protectin DX (PDX), to reverse established ESRD damage. HFHS-fed vehicle-treated LRKOB100/IGFII mice developed severe kidney dysfunction leading to ESRD, as revealed by advanced glomerular fibrosis and mesangial expansion along with reduced percent survival. The kidney failure outcome was associated with cardiac dysfunction, revealed by reduced heart rate and prolonged diastolic and systolic time. Dietary FO prevented kidney damage, lean mass loss, cardiac dysfunction, and death. 17-HDHA reduced podocyte foot process effacement while PDX treatment alleviated kidney fibrosis and mesangial expansion as compared to vehicle treatment. Only PDX therapy was effective at preserving the heart function and survival rate. These results show that dietary LCω3FA intake can prevent ESRD and cardiac dysfunction in LRKOB100/IGFII diabetic mice. Our data further reveals that PDX can protect against renal failure and cardiac dysfunction, offering a potential new therapeutic strategy against ESRD.

A polyphenol-rich cranberry extract protects against endogenous exposure to persistent organic pollutants during weight loss in mice.

The dramatic rise in the global occurrence of obesity and associated diseases calls for new strategies to promote weight loss. However, while the beneficial effects of weight loss are well known, rapid loss of fat mass can also lead to the endogenous release of liposoluble molecules with potential harmful effects, such as persistent organic pollutants (POP). The aim of this study was to evaluate the impact of a polyphenol-rich cranberry extract (CE) on POP release and their potential deleterious effects during weight loss of obese mice. C57BL/6 J mice were fed an obesogenic diet with or without a mixture of POP for 12 weeks and then changed to a low-fat diet to induce weight loss and endogenous POP release. The POP-exposed mice were then separated in two groups during weight loss, receiving either CE or the vehicle. Unexpectedly, despite the higher fat loss in the CE-treated group, the circulating levels of POP were not enhanced in these mice. Moreover, glucose homeostasis was further improved during CE-induced weight loss, as revealed by lower fasting glycemia and improved glucose tolerance as compared to vehicle-treated mice. Interestingly, the CE extract also induced changes in the gut microbiota after weight loss in POP-exposed mice, including blooming of Parvibacter, a member of the Coriobacteriaceae family which has been predicted to play a role in xenobiotic metabolism. Our data thus suggests that the gut microbiota can be targeted by polyphenol-rich extracts to protect from increased POP exposure and their detrimental metabolic effects during rapid weight loss.

Differential Effects of Chronic Ingestion of Refined Sugars versus Natural Sweeteners on Insulin Resistance and Hepatic Steatosis in a Rat Model of Diet-Induced Obesity.

While the detrimental effect of refined sugars on health has been the subject of many investigations, little is known about the long-term impact of natural sweeteners on metabolic disorders. In this study we compared the metabolic responses to chronic ingestion of refined sugars compared to various natural sweeteners in diet-induced obese rats. Wistar rats were fed a high-fat high-sucrose diet (HFHS) for 8 weeks and daily gavaged with a solution containing 1 g of total carbohydrates from refined sugar (sucrose or fructose) or six different natural sugar sources, followed by assessment of glucose homeostasis, hepatic lipid accumulation, and inflammation. While glucose tolerance was similar following treatments with refined and natural sugars, lowered glucose-induced hyperinsulinemia was observed with fructose. Consumption of fructose and all-natural sweeteners but not corn syrup were associated with lower insulin resistance as revealed by reduced fasting insulin and homeostatic model assessment of insulin resistance (HOMA-IR) compared to sucrose treatment of HFHS-fed rats. All-natural sweeteners and fructose induced similar liver lipid accumulation as sucrose. Nevertheless, maple syrup, molasses, agave syrup, and corn syrup as well as fructose further reduced hepatic IL-1ß levels compared to sucrose treatment. We conclude that natural sweeteners and especially maple syrup, molasses, and agave syrup attenuate the development of insulin resistance and hepatic inflammation compared to sucrose in diet-induced obese rats, suggesting that consumption of those natural sweeteners is a less harmful alternative to sucrose in the context of obesity.

Blueberry proanthocyanidins and anthocyanins improve metabolic health through a gut microbiota-dependent mechanism in diet-induced obese mice.

Blueberry consumption can prevent obesity-linked metabolic diseases, and it has been proposed that the polyphenol content of blueberries may contribute to these effects. Polyphenols have been shown to favorably impact metabolic health, but the role of specific polyphenol classes and whether the gut microbiota is linked to these effects remain unclear. We aimed to evaluate the impact of whole blueberry powder and blueberry polyphenols on the development of obesity and insulin resistance and to determine the potential role of gut microbes in these effects by using fecal microbiota transplantation (FMT). Sixty-eight C57BL/6 male mice were assigned to one of the following diets for 12 wk: balanced diet (Chow); high-fat, high-sucrose diet (HFHS); or HFHS supplemented with whole blueberry powder (BB), anthocyanidin (ANT)-rich extract, or proanthocyanidin (PAC)-rich extract. After 8 wk, mice were housed in metabolic cages, and an oral glucose tolerance test (OGTT) was performed. Sixty germ-free mice fed HFHS diet received FMT from one of the above groups biweekly for 8 wk, followed by an OGTT. PAC-treated mice were leaner than HFHS controls although they had the same energy intake and were more physically active. This observation was reproduced in germ-free mice receiving FMT from PAC-treated mice. PAC- and ANT-treated mice showed improved insulin responses during OGTT, and this finding was also reproduced in germ-free mice following FMT. These results show that blueberry PAC and ANT polyphenols can reduce diet-induced body weight and improve insulin sensitivity and that at least part of these beneficial effects are explained by modulation of the gut microbiota.

Inhibition of mitochondrial complex 1 by the S6K1 inhibitor PF-4708671 partly contributes to its glucose metabolic effects in muscle and liver cells.

mTOR complex 1 (mTORC1) and p70 S6 kinase (S6K1) are both involved in the development of obesity-linked insulin resistance. Recently, we showed that the S6K1 inhibitor PF-4708671 (PF) increases insulin sensitivity. However, we also reported that PF can increase glucose metabolism even in the absence of insulin in muscle and hepatic cells. Here we further explored the potential mechanisms by which PF increases glucose metabolism in muscle and liver cells independent of insulin. Time course experiments revealed that PF induces AMP-activated protein kinase (AMPK) activation before inhibiting S6K1. However, PF-induced glucose uptake was not prevented in primary muscle cells from AMPK α1/2 double KO (dKO) mice. Moreover, PF-mediated suppression of hepatic glucose production was maintained in hepatocytes derived from AMPK α1/2-dKO mice. Remarkably, PF could still reduce glucose production and activate AMPK in hepatocytes from S6K1/2 dKO mice. Mechanistically, bioenergetics experiments revealed that PF reduces mitochondrial complex I activity in both muscle and hepatic cells. The stimulatory effect of PF on glucose uptake was partially reduced by expression of the Saccharomyces cerevisiae NADH:ubiquinone oxidoreductase in L6 cells. These results indicate that PF-mediated S6K1 inhibition is not required for its effect on insulin-independent glucose metabolism and AMPK activation. We conclude that, although PF rapidly activates AMPK, its ability to acutely increase glucose uptake and suppress glucose production does not require AMPK activation. Unexpectedly, PF rapidly inhibits mitochondrial complex I activity, a mechanism that partially underlies PF's effect on glucose metabolism.

Loss of OcaB Prevents Age-Induced Fat Accretion and Insulin Resistance by Altering B-Lymphocyte Transition and Promoting Energy Expenditure.

The current demographic shift toward an aging population has led to a robust increase in the prevalence of age-associated metabolic disorders. Recent studies have demonstrated that the etiology of obesity-related insulin resistance that develops with aging differs from that induced by high-calorie diets. Whereas the role of adaptive immunity in changes in energy metabolism driven by nutritional challenges has recently gained attention, its impact on aging remains mostly unknown. Here we found that the number of follicular B2 lymphocytes and expression of the B-cell-specific transcriptional coactivator OcaB increase with age in spleen and in intra-abdominal epididymal white adipose tissue (eWAT), concomitantly with higher circulating levels of IgG and impaired glucose homeostasis. Reduction of B-cell maturation and Ig production-especially that of IgG2c-by ablation of OcaB prevented age-induced glucose intolerance and insulin resistance and promoted energy expenditure by stimulating fatty acid utilization in eWAT and brown adipose tissue. Transfer of wild-type bone marrow in OcaB-/- mice replenished the eWAT B2-cell population and IgG levels, which diminished glucose tolerance, insulin sensitivity, and energy expenditure while increasing body weight gain in aged mice. Thus these findings demonstrate that upon aging, modifications in B-cell-driven adaptive immunity contribute to glucose intolerance and fat accretion.

Arctic berry extracts target the gut-liver axis to alleviate metabolic endotoxaemia, insulin resistance and hepatic steatosis in diet-induced obese mice.

AIMS/HYPOTHESIS: There is growing evidence that fruit polyphenols exert beneficial effects on the metabolic syndrome, but the underlying mechanisms remain poorly understood. In the present study, we aimed to analyse the effects of polyphenolic extracts from five types of Arctic berries in a model of diet-induced obesity. METHODS: Male C57BL/6 J mice were fed a high-fat/high-sucrose (HFHS) diet and orally treated with extracts of bog blueberry (BBE), cloudberry (CLE), crowberry (CRE), alpine bearberry (ABE), lingonberry (LGE) or vehicle (HFHS) for 8 weeks. An additional group of standard-chow-fed, vehicle-treated mice was included as a reference control for diet-induced obesity. OGTTs and insulin tolerance tests were conducted, and both plasma insulin and C-peptide were assessed throughout the OGTT. Quantitative PCR, western blot analysis and ELISAs were used to assess enterohepatic immunometabolic features. Faecal DNA was extracted and 16S rRNA gene-based analysis was used to profile the gut microbiota. RESULTS: Treatment with CLE, ABE and LGE, but not with BBE or CRE, prevented both fasting hyperinsulinaemia (mean ± SEM [pmol/l]: chow 67.2 ± 12.3, HFHS 153.9 ± 19.3, BBE 114.4 ± 14.3, CLE 82.5 ± 13.0, CRE 152.3 ± 24.4, ABE 90.6 ± 18.0, LGE 95.4 ± 10.5) and postprandial hyperinsulinaemia (mean ± SEM AUC [pmol/l × min]: chow 14.3 ± 1.4, HFHS 31.4 ± 3.1, BBE 27.2 ± 4.0, CLE 17.7 ± 2.2, CRE 32.6 ± 6.3, ABE 22.7 ± 18.0, LGE 23.9 ± 2.5). None of the berry extracts affected C-peptide levels or body weight gain. Levels of hepatic serine phosphorylated Akt were 1.6-, 1.5- and 1.2-fold higher with CLE, ABE and LGE treatment, respectively, and hepatic carcinoembryonic antigen-related cell adhesion molecule (CEACAM)-1 tyrosine phosphorylation was 0.6-, 0.7- and 0.9-fold increased in these mice vs vehicle-treated, HFHS-fed mice. These changes were associated with reduced liver triacylglycerol deposition, lower circulating endotoxins, alleviated hepatic and intestinal inflammation, and major gut microbial alterations (e.g. bloom of Akkermansia muciniphila, Turicibacter and Oscillibacter) in CLE-, ABE- and LGE-treated mice. CONCLUSIONS/INTERPRETATION: Our findings reveal novel mechanisms by which polyphenolic extracts from ABE, LGE and especially CLE target the gut-liver axis to protect diet-induced obese mice against metabolic endotoxaemia, insulin resistance and hepatic steatosis, which importantly improves hepatic insulin clearance. These results support the potential benefits of these Arctic berries and their integration into health programmes to help attenuate obesity-related chronic inflammation and metabolic disorders. DATA AVAILABILITY: All raw sequences have been deposited in the public European Nucleotide Archive server under accession number PRJEB19783 ( https://www.ebi.ac.uk/ena/data/view/PRJEB19783 ).

Treatment with a novel agent combining docosahexaenoate and metformin increases protectin DX and IL-6 production in skeletal muscle and reduces insulin resistance in obese diabetic db/db mice.

AIMS: To compare the therapeutic potential of TP-113, a unique molecular entity linking DHA with metformin, for alleviating insulin resistance in obese diabetic mice through the PDX/IL-6 pathway. MATERIAL AND METHODS: We utilized the generically obese diabetic db/db mouse model for all experiments. Initial studies investigated both a dose and time course response. These results were then utilized to design a long-term (5 week) treatment protocol. Mice were gavaged twice daily with 1 of 3 treatments: 200 mg/kg BW TP113, an equivalent dose of metformin alone (70 mg/kg BW) or water. Whole-body insulin sensitivity was measured using the hyperinsulinaemic-isoglycaemic clamp procedure in awake unrestrained mice. RESULTS: We first confirmed that acute TP-113 treatment raises PDX and IL-6 levels in skeletal muscle. We next tested the long-term glucoregulatory effect of oral TP-113 in obese diabetic db/db mice and compared its effect to an equivalent dose of metformin. A 5-week oral treatment with TP-113 reduced insulin resistance compared to both vehicle treatment and metformin alone, revealed by the determination of whole-body insulin sensitivity for glucose disposal using the clamp technique. This insulin-sensitizing effect was explained primarily by improvement of insulin action to suppress hepatic glucose production in TP-113-treated mice. These effects of TP-113 were greater than that of an equivalent dose of metformin, indicating that TP-113 increases metformin efficacy for reducing insulin resistance. CONCLUSION: We conclude that TP-113 improves insulin sensitivity in obese diabetic mice through activation of the PDX/IL-6 signaling axis in skeletal muscle and improved glucoregulatory action in the liver.

Pharmacological inhibition of S6K1 increases glucose metabolism and Akt signalling in vitro and in diet-induced obese mice.

AIMS/HYPOTHESIS: The mammalian target of rapamycin complex 1 (mTORC1)/p70 ribosomal S6 kinase (S6K)1 pathway is overactivated in obesity, leading to inhibition of phosphoinositide 3-kinase (PI3K)/Akt signalling and insulin resistance. However, chronic mTORC1 inhibition by rapamycin impairs glucose homeostasis because of robust induction of liver gluconeogenesis. Here, we compared the effect of rapamycin with that of the selective S6K1 inhibitor, PF-4708671, on glucose metabolism in vitro and in vivo. METHODS: We used L6 myocytes and FAO hepatocytes to explore the effect of PF-4708671 on the regulation of glucose uptake, glucose production and insulin signalling. We also treated high-fat (HF)-fed obese mice for 7 days with PF-4708671 in comparison with rapamycin to assess glucose tolerance, insulin resistance and insulin signalling in vivo. RESULTS: Chronic rapamycin treatment induced insulin resistance and impaired glucose metabolism in hepatic and muscle cells. Conversely, chronic S6K1 inhibition with PF-4708671 reduced glucose production in hepatocytes and enhanced glucose uptake in myocytes. Whereas rapamycin treatment inhibited Akt phosphorylation, PF-4708671 increased Akt phosphorylation in both cell lines. These opposite effects of the mTORC1 and S6K1 inhibitors were also observed in vivo. Indeed, while rapamycin treatment induced glucose intolerance and failed to improve Akt phosphorylation in liver and muscle of HF-fed mice, PF-4708671 treatment improved glucose tolerance and increased Akt phosphorylation in metabolic tissues of these obese mice. CONCLUSIONS/INTERPRETATION: Chronic S6K1 inhibition by PF-4708671 improves glucose homeostasis in obese mice through enhanced Akt activation in liver and muscle. Our results suggest that specific S6K1 blockade is a valid pharmacological approach to improve glucose disposal in obese diabetic individuals.

Low-Molecular-Weight Peptides from Salmon Protein Prevent Obesity-Linked Glucose Intolerance, Inflammation, and Dyslipidemia in LDLR-/-/ApoB100/100 Mice.

BACKGROUND: We previously reported that fish proteins can alleviate metabolic syndrome (MetS) in obese animals and human subjects. OBJECTIVES: We tested whether a salmon peptide fraction (SPF) could improve MetS in mice and explored potential mechanisms of action. METHODS: ApoB(100) only, LDL receptor knockout male mice (LDLR(-/-)/ApoB(100/100)) were fed a high-fat and -sucrose (HFS) diet (25 g/kg sucrose). Two groups were fed 10 g/kg casein hydrolysate (HFS), and 1 group was additionally fed 4.35 g/kg fish oil (FO; HFS+FO). Two other groups were fed 10 g SPF/kg (HFS+SPF), and 1 group was additionally fed 4.35 g FO/kg (HFS+SPF+FO). A fifth (reference) group was fed a standard feed pellet diet. We assessed the impact of dietary treatments on glucose tolerance, adipose tissue inflammation, lipid homeostasis, and hepatic insulin signaling. The effects of SPF on glucose uptake, hepatic glucose production, and inducible nitric oxide synthase activity were further studied in vitro with the use of L6 myocytes, FAO hepatocytes, and J774 macrophages. RESULTS: Mice fed HFS+SPF or HFS+SPF+FO diets had lower body weight (protein effect, P = 0.024), feed efficiency (protein effect, P = 0.018), and liver weight (protein effect, P = 0.003) as well as lower concentrations of adipose tissue cytokines and chemokines (protein effect, P ≤ 0.003) compared with HFS and HFS+FO groups. They also had greater glucose tolerance (protein effect, P < 0.001), lower activation of the mammalian target of rapamycin complex 1/S6 kinase 1/insulin receptor substrate 1 (mTORC1/S6K1/IRS1) pathway, and increased insulin signaling in liver compared with the HFS and HFS+FO groups. The HFS+FO, HFS+SPF, and HFS+SPF+FO groups had lower plasma triglycerides (protein effect, P = 0.003; lipid effect, P = 0.002) than did the HFS group. SPF increased glucose uptake and decreased HGP and iNOS activation in vitro. CONCLUSIONS: SPF reduces obesity-linked MetS features in LDLR(-/-)/ApoB(100/100) mice. The anti-inflammatory and glucoregulatory properties of SPF were confirmed in L6 myocytes, FAO hepatocytes, and J774 macrophages.

Omega-3 fatty acids protect from diet-induced obesity, glucose intolerance, and adipose tissue inflammation through PPARγ-dependent and PPARγ-independent actions.

SCOPE: We tested herein the hypothesis that peroxisome proliferator activated receptor γ (PPARγ) is a major mediator of omega-3 (n-3) protective actions against high-fat diet (HFD) induced obesity, glucose intolerance, and adipose tissue inflammation. METHODS AND RESULTS: C57BL6 wild-type and fat-1 transgenic (fat-1) mice were fed a low-fat diet (LFD) or HFD, treated or not with PPARγ antagonist, and evaluated for energy balance, adiposity, glucose tolerance, and adipose tissue inflammation. Fat-1 mice were protected from obesity, fasting hyperglycemia, glucose intolerance, and adipose tissue inflammation. PPARγ inhibition completely abolished fat-1 protection against HFD-induced glucose intolerance, but not obesity or adipose tissue inflammation. To investigate the role of myeloid cell as mediator of n-3 beneficial metabolic actions, mice with deletion (LyzM-PPARγ(KO)) or nondeletion (LyzM-PPARγ(WT)) of PPARγ in myeloid cells were fed either LFD or HFD (lard) or an HFD rich in n-3 (fish oil). Our findings indicate that myeloid cell associated PPARγ is not involved in the attenuation of HFD-induced glucose intolerance and adipose tissue inflammation induced by n-3. CONCLUSION: High endogenous n-3 fatty acid levels protect from HFD obesity, glucose intolerance, and adipose tissue inflammation. Among these, only protection against glucose intolerance is mediated by non-myeloid cell PPARγ.

Protectin DX alleviates insulin resistance by activating a myokine-liver glucoregulatory axis.

We previously demonstrated that low biosynthesis of ω-3 fatty acid-derived proresolution mediators, termed protectins, is associated with an impaired global resolution capacity, inflammation and insulin resistance in obese high-fat diet-fed mice. These findings prompted a more direct study of the therapeutic potential of protectins for the treatment of metabolic disorders. Herein we show that protectin DX (PDX) exerts an unanticipated glucoregulatory activity that is distinct from its anti-inflammatory actions. We found that PDX selectively stimulated the release of the prototypic myokine interleukin-6 (IL-6) from skeletal muscle and thereby initiated a myokine-liver signaling axis, which blunted hepatic glucose production via signal transducer and activator of transcription 3 (STAT3)-mediated transcriptional suppression of the gluconeogenic program. These effects of PDX were abrogated in Il6-null mice. PDX also activated AMP-activated protein kinase (AMPK); however, it did so in an IL-6-independent manner. Notably, we demonstrated that administration of PDX to obese diabetic db/db mice raises skeletal muscle IL-6 levels and substantially improves their insulin sensitivity without any impact on adipose tissue inflammation. Our findings thus support the development of PDX-based selective muscle IL-6 secretagogues as a new class of therapy for the treatment of insulin resistance and type 2 diabetes.

PPARγ activation attenuates glucose intolerance induced by mTOR inhibition with rapamycin in rats.

mTOR inhibition with rapamycin induces a diabetes-like syndrome characterized by severe glucose intolerance, hyperinsulinemia, and hypertriglyceridemia, which is due to increased hepatic glucose production as well as reduced skeletal muscle glucose uptake and adipose tissue PPARγ activity. Herein, we tested the hypothesis that pharmacological PPARγ activation attenuates the diabetes-like syndrome associated with chronic mTOR inhibition. Rats treated with the mTOR inhibitor rapamycin (2 mg·kg(-1)·day(-1)) in combination or not with the PPARγ ligand rosiglitazone (15 mg·kg(-1)·day(-1)) for 15 days were evaluated for insulin secretion, glucose, insulin, and pyruvate tolerance, skeletal muscle and adipose tissue glucose uptake, and insulin signaling. Rosiglitazone corrected fasting hyperglycemia, attenuated the glucose and insulin intolerances, and abolished the increase in fasting plasma insulin and C-peptide levels induced by rapamycin. Surprisingly, rosiglitazone markedly increased the plasma insulin and C-peptide responses to refeeding in rapamycin-treated rats. Furthermore, rosiglitazone partially attenuated rapamycin-induced gluconeogenesis, as evidenced by the improved pyruvate tolerance and reduced mRNA levels of phosphoenolpyruvate carboxykinase and glucose-6-phosphatase. Rosiglitazone also restored insulin's ability to stimulate glucose uptake and its incorporation into glycogen in skeletal muscle of rapamycin-treated rats, which was associated with normalization of Akt Ser(473) phosphorylation. However, the rapamycin-mediated impairments of adipose tissue glucose uptake and incorporation into triacylglycerol were unaffected by rosiglitazone. Our findings indicate that PPARγ activation ameliorates some of the disturbances in glucose homeostasis and insulin action associated with chronic rapamycin treatment by reducing gluconeogenesis and insulin secretion and restoring muscle insulin signaling and glucose uptake.

Major involvement of mTOR in the PPARγ-induced stimulation of adipose tissue lipid uptake and fat accretion.

Evidence points to a role of the mammalian target of rapamycin (mTOR) signaling pathway as a regulator of adiposity, yet its involvement as a mediator of the positive actions of peroxisome proliferator-activated receptor (PPAR)γ agonism on lipemia, fat accretion, lipid uptake, and its major determinant lipoprotein lipase (LPL) remains to be elucidated. Herein we evaluated the plasma lipid profile, triacylglycerol (TAG) secretion rates, and adipose tissue LPL-dependent lipid uptake, LPL expression/activity, and expression profile of other lipid metabolism genes in rats treated with the PPARγ agonist rosiglitazone (15 mg/kg/day) in combination or not with the mTOR inhibitor rapamycin (2 mg/kg/day) for 15 days. Rosiglitazone stimulated adipose tissue mTOR complex 1 and AMPK and induced TAG-derived lipid uptake (136%), LPL mRNA/activity (2- to 6-fold), and fat accretion in subcutaneous (but not visceral) white adipose tissue (WAT; 50%) and in brown adipose tissue (BAT; 266%). Chronic mTOR inhibition attenuated the upregulation of lipid uptake, LPL expression/activity, and fat accretion induced by PPARγ activation in both subcutaneous WAT and BAT, which resulted in hyperlipidemia. In contrast, rapamycin did not affect most of the other WAT lipogenic genes upregulated by rosiglitazone. Together these findings demonstrate that mTOR is a major regulator of adipose tissue LPL-mediated lipid uptake and a critical mediator of the hypolipidemic and lipogenic actions of PPARγ activation.

Nobiletin attenuates VLDL overproduction, dyslipidemia, and atherosclerosis in mice with diet-induced insulin resistance.

OBJECTIVE: Increased plasma concentrations of apolipoprotein B100 often present in patients with insulin resistance and confer increased risk for the development of atherosclerosis. Naturally occurring polyphenolic compounds including flavonoids have antiatherogenic properties. The aim of the current study was to evaluate the effect of the polymethoxylated flavonoid nobiletin on lipoprotein secretion in cultured human hepatoma cells (HepG2) and in a mouse model of insulin resistance and atherosclerosis. RESEARCH DESIGN AND METHODS: Lipoprotein secretion was determined in HepG2 cells incubated with nobiletin or insulin. mRNA abundance was evaluated by quantitative real-time PCR, and Western blotting was used to demonstrate activation of cell signaling pathways. In LDL receptor-deficient mice (Ldlr(-/-)) fed a Western diet supplemented with nobiletin, metabolic parameters, gene expression, fatty acid oxidation, glucose homeostasis, and energy expenditure were documented. Atherosclerosis was quantitated by histological analysis. RESULTS: In HepG2 cells, activation of mitogen-activated protein kinase-extracellular signal-related kinase signaling by nobiletin or insulin increased LDLR and decreased MTP and DGAT1/2 mRNA, resulting in marked inhibition of apoB100 secretion. Nobiletin, unlike insulin, did not induce phosphorylation of the insulin receptor or insulin receptor substrate-1 and did not stimulate lipogenesis. In fat-fed Ldlr(-/-) mice, nobiletin attenuated dyslipidemia through a reduction in VLDL-triglyceride (TG) secretion. Nobiletin prevented hepatic TG accumulation, increased expression of Pgc1α and Cpt1α, and enhanced fatty acid ß-oxidation. Nobiletin did not activate any peroxisome proliferator-activated receptor (PPAR), indicating that the metabolic effects were PPAR independent. Nobiletin increased hepatic and peripheral insulin sensitivity and glucose tolerance and dramatically attenuated atherosclerosis in the aortic sinus. CONCLUSIONS: Nobiletin provides insight into treatments for dyslipidemia and atherosclerosis associated with insulin-resistant states.