Microbiota and Nod-like receptors balance inflammation and metabolism during obesity and diabetes

Gut microbiota influence host immunity and metabolism during obesity. Bacterial sensors of the innate immune system relay signals from specific bacterial components (i.e., postbiotics) that can have opposing outcomes on host metabolic inflammation. NOD-like receptors (NLRs) such as Nod1 and Nod2 both recruit receptor-interacting protein kinase 2 (RIPK2) but have opposite effects on blood glucose control. Nod1 connects bacterial cell wall-derived signals to metabolic inflammation and insulin resistance, whereas Nod2 can promote immune tolerance, insulin sensitivity, and better blood glucose control during obesity. NLR family pyrin domain containing (NLRP) inflammasomes can also generate divergent metabolic outcomes. NLRP1 protects against obesity and metabolic inflammation potentially because of a bias toward IL-18 regulation, whereas NLRP3 appears to have a bias toward IL-1β-mediated metabolic inflammation and insulin resistance. Targeting specific postbiotics that improve immunometabolism is a key goal. The Nod2 ligand, muramyl dipeptide (MDP) is a short-acting insulin sensitizer during obesity or during inflammatory lipopolysaccharide (LPS) stress. LPS with underacylated lipid-A antagonizes TLR4 and counteracts the metabolic effects of inflammatory LPS. Providing underacylated LPS derived from Rhodobacter sphaeroides improved insulin sensitivity in obese mice. Therefore, certain types of LPS can generate metabolically beneficial metabolic endotoxemia. Engaging protective adaptive immunoglobulin immune responses can also improve blood glucose during obesity. A bacterial vaccine approach using an extract of the entire bacterial community in the upper gut promotes protective adaptive immune response and long-lasting improvements in blood glucose control. A key future goal is to identify and combine postbiotics that cooperate to improve blood glucose control.

Intestinal permeability and peripheral immune cell composition are altered by pregnancy and adiposity at mid- and late-gestation in the mouse

It is clear that the gastrointestinal tract influences metabolism and immune function. Most studies to date have used male test subjects, with a focus on effects of obesity and dietary challenges. Despite significant physiological maternal adaptations that occur across gestation, relatively few studies have examined pregnancy-related gut function. Moreover, it remains unknown how pregnancy and diet can interact to alter intestinal barrier function. In this study, we investigated the impacts of pregnancy and adiposity on maternal intestinal epithelium morphology, in vivo intestinal permeability, and peripheral blood immunophenotype, using control (CTL) and high-fat (HF) fed non-pregnant female mice and pregnant mice at mid- (embryonic day (E)14.5) and late (E18.5) gestation. We found that small intestine length increased between non-pregnant mice and dams at late-gestation, but ileum villus length, and ileum and colon crypt depths and goblet cell numbers remained similar. Compared to CTL-fed mice, HF-fed mice had reduced small intestine length, ileum crypt depth and villus length. Goblet cell numbers were only consistently reduced in HF-fed non-pregnant mice. Pregnancy increased in vivo gut permeability, with a greater effect at mid- versus late-gestation. Non-pregnant HF-fed mice had greater gut permeability, and permeability was also increased in HF-fed pregnant dams at mid but not late-gestation. The impaired maternal gut barrier in HF-fed dams at mid-gestation coincided with changes in maternal blood and bone marrow immune cell composition, including an expansion of circulating inflammatory Ly6Chigh monocytes. In summary, pregnancy has temporal effects on maternal intestinal structure and barrier function, and on peripheral immunophenotype, which are further modified by HF diet-induced maternal adiposity. Maternal adaptations in pregnancy are thus vulnerable to excess maternal adiposity, which may both affect maternal and child health.

Dietary nitrate and corresponding gut microbiota prevent cardiac dysfunction in obese mice

Impaired heart function can develop in diabetic individuals in the absence of coronary artery disease or hypertension, suggesting mechanisms beyond hypertension/increased afterload contribute to diabetic cardiomyopathy. Identifying therapeutic approaches that improve glycemia and prevent cardiovascular disease are clearly required for clinical management of diabetes-related comorbidities. Since intestinal bacteria are important for metabolism of nitrate, we examined if dietary nitrate and fecal microbial transplantation (FMT) from nitrate-fed mice could prevent high-fat diet (HFD)-induced cardiac abnormalities. Male C57Bl/6N mice were fed an 8-week low-fat diet (LFD), HFD, or HFD+Nitrate (4mM sodium nitrate). HFD-fed mice presented with pathological left ventricular (LV) hypertrophy, reduced stroke volume and increased end diastolic pressure, in association with increased myocardial fibrosis, glucose intolerance, adipose inflammation, serum lipids, LV mitochondrial reactive oxygen species (ROS), and gut dysbiosis. In contrast, dietary nitrate attenuated these detriments. In HFD-fed mice, FMT from HFD+Nitrate donors did not influence serum nitrate, blood pressure, adipose inflammation, or myocardial fibrosis. However, microbiota from HFD+Nitrate mice decreased serum lipids, LV ROS, and similar to FMT from LFD donors, prevented glucose intolerance and cardiac morphology changes. Therefore, the cardioprotective effects of nitrate are not dependent on reducing blood pressure, but rather mitigating gut dysbiosis, highlighting a nitrate-gut-heart axis.

Kinase inhibitors for cancer alter metabolism, blood glucose, and insulin

Small molecule kinase inhibitors (SMKIs) are a class of therapeutic drugs that target protein kinases in diseases such as cancer. SMKIs are often designed to inhibit kinases involved in cell proliferation, but these drugs alter cell metabolism and the endocrine control of organismal metabolism. SMKI treatment in diabetic cancer patients reveals that certain SMKIs improve blood glucose levels and can mitigate insulin dependence or diabetic medication requirements in both type 1 diabetes (T1D) and type 2 diabetes (T2D). Certain SMKIs can preserve functional β-cell mass and increase insulin secretion or insulin sensitivity. It is not yet clear why different SMKIs can have opposing effects on insulin and blood glucose. Understanding the therapeutic effects of these drugs in T1D and T2D is complicated by overlapping off-target effects of SMKIs. The potency of inhibition of the intended protein kinase and inhibition of multiple off-target kinases may underpin conflicting reports of how certain SMKIs alter blood glucose and insulin. We summarize the effects of SMKIs on the intended and off-target kinases that can alter blood glucose and insulin, including c-Abl, c-Kit, EGFR, and VEGF. Inhibition of PDGFRβ consistently lowers blood glucose in T1D and T2D. The effects of SMKIs on the kinases that regulate immune pathways, such as BTK and RIPKs, mediate many of the diverse effects of these drugs on metabolism. We highlight that inhibition of RIPK2 by SMKIs is a central node in metabolism that influences key metabolic pathways including lipolysis, blood glucose control, insulin secretion, and insulin resistance.

Chronic exposure to synthetic food colorant Allura Red AC promotes susceptibility to experimental colitis via intestinal serotonin in mice

Chemicals in food are widely used leading to significant human exposure. Allura Red AC (AR) is a highly common synthetic colorant; however, little is known about its impact on colitis. Here, we show chronic exposure of AR at a dose found in commonly consumed dietary products exacerbates experimental models of colitis in mice. While intermittent exposure is more akin to a typical human exposure, intermittent exposure to AR in mice for 12 weeks, does not influence susceptibility to colitis. However, exposure to AR during early life primes mice to heightened susceptibility to colitis. In addition, chronic exposure to AR induces mild colitis, which is associated with elevated colonic serotonin (5-hydroxytryptamine; 5-HT) levels and impairment of the epithelial barrier function via myosin light chain kinase (MLCK). Importantly, chronic exposure to AR does not influence colitis susceptibility in mice lacking tryptophan hydroxylase 1 (TPH1), the rate limiting enzyme for 5-HT biosynthesis. Cecal transfer of the perturbed gut microbiota by AR exposure worsens colitis severity in the recipient germ-free (GF) mice. Furthermore, chronic AR exposure elevates colonic 5-HT levels in naïve GF mice. Though it remains unknown whether AR has similar effects in humans, our study reveals that chronic long-term exposure to a common synthetic colorant promotes experimental colitis via colonic 5-HT in gut microbiota-dependent and -independent pathway in mice.

Dietary sugar lowers immunity and microbiota that protect against metabolic disease

Diet influences intestinal microbiota, inflammation, and metabolism. Kawano et al. show that dietary sugar engaged upper gut innate lymphoid cells to replace segmented filamentous bacteria with a pathobiont. Added sugar worsened early metabolic disease by lowering protective Th17 immunity, thereby promoting intestinal lipid absorption and obesity in high-fat-diet-fed mice.

Postbiotics engage IRF4 in adipocytes to promote sex-dependent changes in blood glucose during obesity

Postbiotics are microbial-derived components or metabolites that can influence host immunity and metabolism. Some postbiotics can improve blood glucose control and lower inflammation during bacterial or nutritional stress. Bacterial cell wall-derived muramyl dipeptide (MDP) is a potent insulin-sensitizing postbiotic that engages NOD2, RIPK2, and requires interferon regulatory factor 4 (IRF4) to lower inflammation and improve blood glucose. However, the sex-dependent effects of this postbiotic and the cell type required for IRF4 to cause inflammatory versus glycemic responses to MDP were unknown. Here, we measured how MDP injection altered glucose tolerance and adipose tissue inflammation during low-level endotoxemia and high fat diet (HFD)-induced obesity in male and female adipocyte-specific IRF4 knockout mice (AdipoIRF4fl/fl ) compared to WTfl/fl mice. Adipocyte IRF4 was required for the blood glucose-lowering effects of MDP during endotoxemia and HFD-induced obesity in male mice. However, MDP did not alter blood glucose in female WTfl/fl and AdipoIRF4fl/f mice during endotoxemia. Unexpectedly, female HFD-fed AdipoIRF4fl/f mice had lower blood glucose after MDP treatment compared to WTfl/fl mice. MDP lowered inflammatory gene expression in adipose tissue of HFD-fed WTfl/fl and AdipoIRF4fl/fl mice of both sexes. Therefore, MDP-mediated lowering of adipose inflammation does not require adipocyte IRF4 and was independent of sex. Together, these data show that injection of MDP, an insulin-sensitizing postbiotic, lowers adipose tissue inflammation in male and female mice, but lower adipose inflammation is not always associated with improved blood glucose. The blood glucose-lowering effect of the postbiotic MDP and dependence on adipocyte IRF4 is sex-dependent.

Increased gut serotonin production in response to bisphenol A structural analogs may contribute to their obesogenic effects

Obesogens are synthetic, environmental chemicals that can disrupt endocrine control of metabolism and contribute to the risk of obesity and metabolic disease. Bisphenol A (BPA) is one of the most studied obesogens. There is considerable evidence that BPA exposure is associated with weight gain, increased adiposity, poor blood glucose control, and nonalcoholic fatty liver disease in animal models and human populations. Increased usage of structural analogs of BPA has occurred in response to legislation banning their use in some commercial products. However, BPA analogs may also cause some of the same metabolic impairments because of common mechanisms of action. One key effector that is altered by BPA and its analogs is serotonin, however, it is unknown if BPA-induced changes in peripheral serotonin pathways underlie metabolic perturbations seen with BPA exposure. Upon ingestion, BPA and its analogs act as endocrine-disrupting chemicals in the gastrointestinal tract to influence serotonin production by the gut, where over 95% of serotonin is produced. The purpose of this review is to evaluate how BPA and its analogs alter gut serotonin regulation and then discuss how disruption of serotonergic networks influences host metabolism. We also provide evidence that BPA and its analogs enhance serotonin production in gut enterochromaffin cells. Taken together, we propose that BPA and many BPA analogs represent endocrine-disrupting chemicals that can influence host metabolism through the endogenous production of gut-derived factors, such as serotonin.

Insulin resistance corresponds with a progressive increase in NOD1 in high fat diet-fed mice

PURPOSE

Innate immune components participate in obesity-induced inflammation, which can contribute to endocrine dysfunction during metabolic diseases. However, the chronological activation of specific immune proteins such as Nucleotide-binding oligomerization domain-containing protein 1 (NOD1) and relevance to cellular crosstalk during the progression of obesity-associated insulin resistance (IR) is not known.

METHODS

The NOD1 signaling in various insulin-sensitive metabolic tissues during the progression of diet-insulin resistance was assessed in C57BL/6J mice fed with 60% high-fat diet (HFD) for 4, 8, 12, and 16 weeks. Intestinal permeability was measured using FITC-dextran. NOD1 activating potential was analyzed using HEK-Blue mNOD1 cells.

RESULTS

HFD-fed mice showed progressive induction of glucose intolerance and impairment of insulin signaling in key metabolic tissues. We found a time-dependent increase in intestinal permeability coupled with transport and accumulation of NOD1 activating ligand in the serum of HFD-fed mice. We also observed a progressive accumulation of γ-D-glutamyl-meso-diaminopimelic acid (DAP), a microbial peptidoglycan ligand known to activate NOD1, in serum samples of the HFD-fed mice. There was also a progressive increase in transcripts levels of NOD1 in bone marrow-derived macrophages during HFD-feeding. In addition, skeletal muscle, adipose and liver, the key insulin sensitive metabolic tissues also had a time-dependent increase in transcripts of NOD1 and Rip2 and a corresponding activation of pro-inflammatory responses in these tissues.

CONCLUSION

These data highlight the correlation of inflammation and insulin resistance to NOD1 activation in the bone marrow derived macrophages and insulin responsive metabolic tissues during high fat diet feeding in mice.

Metformin-induced reductions in tumor growth involves modulation of the gut microbiome

Background/Purpose

Type 2 diabetes and obesity increase the risk of developing colorectal cancer. Metformin may reduce colorectal cancer but the mechanisms mediating this effect remain unclear. In mice and humans, a high-fat diet (HFD), obesity and metformin are known to alter the gut microbiome but whether this is important for influencing tumor growth is not known.

Methods

Mice with syngeneic MC38 colon adenocarcinomas were treated with metformin or feces obtained from control or metformin treated mice.

Results

We find that compared to chow-fed controls, tumor growth is increased when mice are fed a HFD and that this acceleration of tumor growth can be partially recapitulated through transfer of the fecal microbiome or in vitro treatment of cells with fecal filtrates from HFD-fed animals. Treatment of HFD-fed mice with orally ingested, but not intraperitoneally injected, metformin suppresses tumor growth and increases the expression of short-chain fatty acid (SCFA)-producing microbes Alistipes, Lachnospiraceae and Ruminococcaceae. The transfer of the gut microbiome from mice treated orally with metformin to drug naïve, conventionalized HFD-fed mice increases circulating propionate and butyrate, reduces tumor proliferation, and suppresses the expression of sterol response element binding protein (SREBP) gene targets in the tumor.

Conclusion

These data indicate that in obese mice fed a HFD, metformin reduces tumor burden through changes in the gut microbiome.

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Oral but not intraperitoneal injection of metformin is associated with changes in the gut microbiome and reductions in MC38 tumor cell growth in mice fed a high-fat diet.

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Transferring feces from mice treated with oral metformin into metformin naïve mice inhibits tumor growth independently of changes in body mass, blood glucose or serum insulin.

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Metformin fecal transfers to metformin naïve mice leads to increased abundance of short chain fatty acid producing microbes.

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Metformin fecal transfers reprogram tumor metabolism reducing the expression of SREBP and cholesterol synthesis genes.

Determining the metabolic impact of postbiotics in mice

Postbiotics cooperate to influence immune and metabolic outcomes in the host. Here we describe a protocol for in vivo assessment of blood glucose control following acute administration of lipopolysaccharide (LPS) and peptidoglycan (PGN) in mice. This protocol can be adapted for testing a broad range of microbial molecules and ligands for host immune receptors. Experience with mouse handling is required.

For complete details on the use and execution of this protocol, please refer to Anhê et al. (2021) and Cavallari et al. (2017).

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Postbiotics influence host immunometabolism and change blood glucose control

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Our model tests synergy or tolerance of postbiotics on blood glucose in vivo

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Lipopolysaccharide (LPS) and peptidoglycan (PGN) are used as examples

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A glucose tolerance test (GTT) is one suitable endpoint

Life-long exercise training and inherited aerobic endurance capacity produce converging gut microbiome signatures in rodents

High aerobic endurance capacity can be acquired by training and/or inherited. Aerobic exercise training (AET) and aging are linked to altered gut microbiome composition, but it is unknown if the environmental stress of exercise and host genetics that predispose for higher exercise capacity have similar effects on the gut microbiome during aging. We hypothesized that exercise training and host genetics would have conserved effects on the gut microbiome across different rodents. We studied young sedentary (Y-SED, 2-month-old) mice, old sedentary (O-SED, 26-month-old) mice, old mice with life-long AET (O-AET, 26-month-old), and aged rats selectively bred for high (HCR [High Capacity Runner], 21-month-old) and low (LCR [Low Capacity Runner], 21-month-old) aerobic capacity. Our results showed that O-SED mice had lower running capacity than Y-SED mice. The fecal microbiota of O-SED mice had a higher relative abundance of Lachnospiraceae, Ruminococcaceae, Turicibacteriaceae, and Allobaculum, but lower Bacteroidales, Alistipes, Akkermansia, and Anaeroplasma. O-AET mice had a higher running capacity than O-SED mice. O-AET mice had lower fecal levels of Lachnospiraceae, Turicibacteriaceae, and Allobaculum and higher Anaeroplasma than O-SED mice. Similar to O-AET mice, but despite no exercise training regime, aged HCR rats had lower Lachnospiraceae and Ruminococcaceae and expansion of certain Bacteroidales in the fecal microbiome compared to LCR rats. Our data show that environmental and genetic modifiers of high aerobic endurance capacity produce convergent gut microbiome signatures across different rodent species during aging. Therefore, we conclude that host genetics and life-long exercise influence the composition of the gut microbiome and can mitigate gut dysbiosis and functional decline during aging.

Exploration of BAY 11-7082 as a Potential Antibiotic

Exposure of the Gram-negative pathogen Pseudomonas aeruginosa to subinhibitory concentrations of antibiotics increases the formation of biofilms. We exploited this phenotype to identify molecules with potential antimicrobial activity in a biofilm-based high-throughput screen. The anti-inflammatory compound BAY 11-7082 induced dose-dependent biofilm stimulation, indicative of antibacterial activity. We confirmed that BAY 11-7082 inhibits the growth of P. aeruginosa and other priority pathogens, including methicillin-resistant Staphylococcus aureus (MRSA). We synthesized 27 structural analogues, including a series based on the related scaffold 3-(phenylsulfonyl)-2-pyrazinecarbonitrile (PSPC), 10 of which displayed increased anti-Staphylococcal activity. Because the parent molecule inhibits the NLR Family Pyrin Domain Containing 3 (NLRP3) inflammasome, we measured the ability of select analogues to reduce interleukin-1β (IL-1β) production in mammalian macrophages, identifying minor differences in the structure-activity relationship for the anti-inflammatory and antibacterial properties of this scaffold. Although we could evolve stably resistant MRSA mutants with cross-resistance to BAY 11-7082 and PSPC, their lack of shared mutations suggested that the two molecules could have multiple targets. Finally, we showed that BAY 11-7082 and its analogues synergize with penicillin G against MRSA, suggesting that this scaffold may serve as an interesting starting point for the development of antibiotic adjuvants.

Gut microbiota-based vaccination engages innate immunity to improve blood glucose control in obese mice

Objective

Obesity and diabetes increase circulating levels of microbial components derived from the gut microbiota. Individual bacterial factors (i.e., postbiotics) can have opposing effects on blood glucose.

Methods

We tested the net effect of gut bacterial extracts on blood glucose in mice using a microbiota-based vaccination strategy.

Results

Male and female mice had improved glucose and insulin tolerance five weeks after a single subcutaneous injection of a specific dose of a bacterial extract obtained from the luminal contents of the upper small intestine (SI), lower SI, or cecum. Injection of mice with intestinal extracts from germ-free mice revealed that bacteria were required for a microbiota-based vaccination to improve blood glucose control. Vaccination of Nod1^−/−, Nod2^−/−, and Ripk2^−/− mice showed that each of these innate immune proteins was required for bacterial extract injection to improve blood glucose control. A microbiota-based vaccination promoted an immunoglobulin-G (IgG) response directed against bacterial extract antigens, where subcutaneous injection of mice with the luminal contents of the lower SI elicited a bacterial extract-specific IgG response that is compartmentalized to the lower SI of vaccinated mice. A microbiota-based vaccination was associated with an altered microbiota composition in the lower SI and colon of mice. Lean mice only required a single injection of small intestinal-derived bacterial extract, but high fat diet (HFD)-fed, obese mice required prime-boost bacterial extract injections for improvements in blood glucose control.

Conclusions

Subversion of the gut barrier by vaccination with a microbiota-based extract engages innate immunity to promote long-lasting improvements in blood glucose control in a dose-dependent manner.

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Subcutaneous injection of gut bacterial extracts improved blood glucose control in mice.

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Microbiota-based vaccination engaged NOD1-NOD2-RIPK2 to alter blood glucose.

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Microbiota-based vaccination promoted a proximal gut IgG response.

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Microbiota-based vaccination altered the composition of the gut microbiome.

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Obese mice required prime-boost injections to improve blood glucose control.

Lower brown adipose tissue activity is associated with non-alcoholic fatty liver disease but not changes in the gut microbiota

In rodents, lower brown adipose tissue (BAT) activity is associated with greater liver steatosis and changes in the gut microbiome. However, little is known about these relationships in humans. In adults (n = 60), we assessed hepatic fat and cold-stimulated BAT activity using magnetic resonance imaging and the gut microbiota with 16S sequencing. We transplanted gnotobiotic mice with feces from humans to assess the transferability of BAT activity through the microbiota. Individuals with NAFLD (n = 29) have lower BAT activity than those without, and BAT activity is inversely related to hepatic fat content. BAT activity is not related to the characteristics of the fecal microbiota and is not transmissible through fecal transplantation to mice. Thus, low BAT activity is associated with higher hepatic fat accumulation in human adults, but this does not appear to have been mediated through the gut microbiota.

Metabolic endotoxemia is dictated by the type of lipopolysaccharide

Lipopolysaccharides (LPSs) can promote metabolic endotoxemia, which is considered inflammatory and metabolically detrimental based on Toll-like receptor (TLR)4 agonists, such as Escherichia coli-derived LPS. LPSs from certain bacteria antagonize TLR4 yet contribute to endotoxemia measured by endotoxin units (EUs). We found that E. coli LPS impairs gut barrier function and worsens glycemic control in mice, but equal doses of LPSs from other bacteria do not. Matching the LPS dose from R. sphaeroides and E. coli by EUs reveals that only E. coli LPS promotes dysglycemia and adipose inflammation, delays intestinal glucose absorption, and augments insulin and glucagon-like peptide (GLP)-1 secretion. Metabolically beneficial endotoxemia promoted by R. sphaeroides LPS counteracts dysglycemia caused by an equal dose of E. coli LPS and improves glucose control in obese mice. The concept of metabolic endotoxemia should be expanded beyond LPS load to include LPS characteristics, such as lipid A acylation, which dictates the effect of metabolic endotoxemia.

Low dietary fiber promotes enteric expansion of a Crohn's disease-associated pathobiont independent of obesity

Obesity is associated with metabolic, immunological, and infectious disease comorbidities, including an increased risk of enteric infection and inflammatory bowel disease such as Crohn's disease (CD). Expansion of intestinal pathobionts such as adherent-invasive Escherichia coli (AIEC) is a common dysbiotic feature of CD, which is amplified by prior use of oral antibiotics. Although high-fat, high-sugar diets are associated with dysbiotic expansion of E. coli, it is unknown if the content of fat or another dietary component in obesogenic diets is sufficient to promote AIEC expansion. Here, we found that administration of an antibiotic combined with feeding mice an obesogenic low-fiber, high-sucrose, high-fat diet (HFD) that is typically used in rodent-obesity studies promoted AIEC intestinal expansion. Even a short-term (i.e., 1 day) pulse of HFD feeding before infection was sufficient to promote AIEC expansion, indicating that the magnitude of obesity was not the main driver of AIEC expansion. Controlled-diet experiments demonstrated that neither dietary fat nor sugar were the key determinants of AIEC colonization, but that lowering dietary fiber from approximately 13% to 5%-6% was sufficient to promote the intestinal expansion of AIEC when combined with antibiotics in mice. When combined with antibiotics, lowering fiber promoted AIEC intestinal expansion to a similar extent as widely used HFDs in mice. However, lowering dietary fiber was sufficient to promote AIEC intestinal expansion without affecting body mass. Our results show that low dietary fiber combined with oral antibiotics are environmental factors that promote the expansion of Crohn's disease-associated pathobionts in the gut.NEW & NOTEWORTHY It is commonly thought that obesity or a high-fat diet alters pathogenic bacteria and promotes inflammatory gut diseases. We found that lower dietary fiber is a key factor that expands a gut pathobiont linked to Crohn's disease, independent of obesity status in mice.

Micronutrients impact the gut microbiota and blood glucose

Micronutrients influence hormone action and host metabolism. Dietary minerals, trace elements, and vitamins can alter blood glucose and cellular glucose metabolism, and several micronutrients are associated with the risk and progression of type 2 diabetes. Dietary components, microbes, and host immune, endocrine, and metabolic responses all interact in the intestine. There has been a focus on macronutrients modifying the host-microbe relationship in metabolic disease. Micronutrients are positioned to alter host-microbe symbiosis that participates in host endocrine control of glucose metabolism. Minerals and trace elements can alter the composition of the intestinal microbiota, gut barrier function, compartmentalized metabolic inflammation, cellular glucose transport, and endocrine control of glucose metabolism, including insulin and thyroid hormones. Dietary vitamins also influence the composition of the intestinal microbiota and vitamins can be biotransformed by gut microbes. Host-microbe regulation of vitamins can alter immunity, lipid and glucose metabolism, and cell fate and function of pancreatic beta cells. Causal effects of micronutrients in host-microbe metabolism are still emerging, and the mechanisms linking dietary excess or deficiency of specific micronutrients to changes in gut microbes directly linked to metabolic disease risk are not yet clear. Dietary fiber, fat, protein, and carbohydrates are key dietary factors that impact how microbes participate in host glucose metabolism. It is possible that micronutrient and microbiota-derived factors also participate in host-microbe responses that tip the balance in the endocrine control of host glucose metabolism. Dietary micronutrients should be considered, tested, and controlled in pre-clinical and clinical studies investigating host-microbe factors in metabolic diseases.

Effects of Obesity-Associated Chronic Inflammation on Peripheral Blood Immunophenotype Are Not Mediated by TNF in Female C57BL/6J Mice

Chronic low-grade systemic inflammation in obesity contributes to the development and progression of aspects of metabolic syndrome. In obese male mice, expanded adipose tissue releases proinflammatory cytokines, including TNF, which promotes an increase in immature, proinflammatory, peripheral blood Ly-6C^high monocytes. The aim of this study was to characterize how TNF alters circulating cellular immunity in female mice with diet-induced obesity. We initially quantified peripheral blood immune cells by flow cytometry in female wild-type C57BL/6J mice after 3-30 wk of allocation to a high-fat (HF) or standard chow diet. We assessed effects of diet and time on neutrophil, monocyte, B cell, NK cell, CD4⁺ T cell, and CD8⁺ T cell populations. There was a significant interaction of the effects of diet type and time on the numbers and prevalence of circulating total monocytes and Ly-6C^high, Ly-6C^low, and Ly-6C^- subsets. Circulating monocytes, in particular Ly-6C^high monocytes, were increased in HF-fed mice compared with chow-fed mice. Ly-6C^high monocytes from HF-fed mice also had a more immature phenotype yet were highly responsive to the chemotactic ligand CCL2 and had greater intracellular production of TNF. Comparisons of the effects of HF diet feeding in littermate wild-type (TNF^+/+) and TNF^-/- female mice showed that genetic ablation of TNF did not protect from higher adiposity or an increase in circulating, immature, proinflammatory Ly-6C^high monocytes during HF diet-induced obesity. These data emphasize the importance of considering biological sex when determining the mechanisms of TNF action in obesity-induced cellular inflammation and in other chronic inflammatory conditions.

Metabolic flexibility determines human NK cell functional fate in the tumor microenvironment

NK cells are central to anti-tumor immunity and recently showed efficacy for treating hematologic malignancies. However, their dysfunction in the hostile tumor microenvironment remains a pivotal barrier for cancer immunotherapies against solid tumors. Using cancer patient samples and proteomics, we found that human NK cell dysfunction in the tumor microenvironment is due to suppression of glucose metabolism via lipid peroxidation-associated oxidative stress. Activation of the Nrf2 antioxidant pathway restored NK cell metabolism and function and resulted in greater anti-tumor activity in vivo. Strikingly, expanded NK cells reprogrammed with complete metabolic substrate flexibility not only sustained metabolic fitness but paradoxically augmented their tumor killing in the tumor microenvironment and in response to nutrient deprivation. Our results uncover that metabolic flexibility enables a cytotoxic immune cell to exploit the metabolic hostility of tumors for their advantage, addressing a critical hurdle for cancer immunotherapy.

Iron Reshapes the Gut Microbiome and Host Metabolism

Compelling studies have established that the gut microbiome is a modifier of metabolic health. Changes in the composition of the gut microbiome are influenced by genetics and the environment, including diet. Iron is a potential node of crosstalk between the host-microbe relationship and metabolic disease. Although iron is well characterized as a frequent traveling companion of metabolic disease, the role of iron is underappreciated because the mechanisms of iron's influence on host metabolism are poorly characterized. Both iron deficiency and excessive amounts leading to iron overload can have detrimental effects on cardiometabolic health. Optimal iron homeostasis is critical for regulation of host immunity and metabolism in addition to regulation of commensal and pathogenic enteric bacteria. In this article we review evidence to support the notion that altering composition of the gut microbiome may be an important route via which iron impacts cardiometabolic health. We discuss reshaping of the microbiome by iron, the physiological significance and the potential for therapeutic interventions.

Bacterial Postbiotics as Promising Tools to Mitigate Cardiometabolic Diseases

Gut microbes dictate critical features of host immunometabolism. Certain bacterial components and metabolites (termed postbiotics) mitigate cardiometabolic diseases whereas others potentiate pathological processes. In this review, we discuss key aspects related to the usefulness of bacterial-related molecules strategically positioned as promising treatment strategies for cardiometabolic diseases.

Peripheral and central regulation of insulin by the intestine and microbiome

Blood glucose and insulin homeostasis is disrupted during the progression of type 2 diabetes. Insulin levels and action are regulated by both peripheral and central responses that involve the intestine and microbiome. The intestine and its microbiota process nutrients and generate molecules that influence blood glucose and insulin. Peripheral insulin regulation is regulated by gut-segment-dependent nutrient sensing and microbial factors such as short-chain fatty acids and bile acids that engage G-protein-coupled receptors. Innate immune sensing of gut-derived bacterial cell wall components and lipopolysaccharides also alter insulin homeostasis. These bacterial metabolites and postbiotics influence insulin secretion and insulin clearance in part by altering endocrine responses such as glucagon-like peptide-1. Gut-derived bacterial factors can promote inflammation and insulin resistance, but other postbiotics can be insulin sensitizers. In parallel, activation of small intestinal sirtuin 1 increases insulin sensitivity by reversing high fat-induced hypothalamic insulin resistance through a gut-brain neuronal axis, whereas high fat-feeding alters small intestinal microbiome and increases taurochenodeoxycholic acid in the plasma and the dorsal vagal complex to induce insulin resistance. In summary, emerging evidence indicates that intestinal molecular signaling involving nutrient sensing and the host-microbe symbiosis alters insulin homeostasis and action. Gut-derived host endocrine and paracrine factors as well as microbial metabolites act on the liver, pancreas, and the brain, and in parallel on the gut-brain neuronal axis. Understanding common nodes of peripheral and central insulin homeostasis and action may reveal new ways to target the intestinal host-microbe relationship in obesity, metabolic disease, and type 2 diabetes.

NOD1 activation induces oxidative stress via NOX1/4 in adipocytes

Activation of innate immune components promotes cell autonomous inflammation in adipocytes. Oxidative stress links pattern recognition receptor-mediated detection of inflammatory ligands and the immune response. Reactive oxygen species (ROS) may mediate the effect of nucleotide-binding oligomerization domain protein-1 (NOD1) activation on inflammation in adipocytes. Here, we define the potential role of NADPH oxidase (NOX)-derived ROS in NOD1-mediated inflammatory response in adipocytes. Differentiated 3T3-L1 adipocytes were treated with NOD1 activating ligand D-gamma-Glu-meso-diaminopimelic acid (iE-DAP) to evaluate the oxidative stress and contribution of NOX as source of intracellular ROS. NOD1 activation potently induced ROS generation in 3T3-L1 adipocytes. Of the NOX family members, expression of NOX1 and NOX4 was increased upon NOD1 activation, in a PKCδ-dependent manner. siRNA-mediated down-regulation of NOX1 or NOX4 inhibited NOD1-mediated ROS production and increased the expression of antioxidant defense enzyme catalase and superoxide dismutase (SOD). siRNA-mediated lowering of NOX1 or NOX4 also suppressed NOD1-mediated activation of JNK1/2 and NF-κB, and consequent activation of inflammatory response in 3T3-L1 adipocytes. In summary, our findings demonstrate that NOD1 activation provokes oxidative stress in adipocytes via NOX1/4 and that oxidative stress, at least in part, contributes to induction of inflammatory response. Defining the source of ROS after immune response engagement may lead to new therapeutic strategies for adipose tissue inflammation.

Gut microbiota impairs insulin clearance in obese mice

Objective

Hyperinsulinemia can be both a cause and consequence of obesity and insulin resistance. Hyperinsulinemia can result from increased insulin secretion and/or reduced insulin clearance. While many studies have focused on mechanisms triggering insulin secretion during obesity, the triggers for changes in insulin clearance during obesity are less defined. In this study, we investigated the role of the microbiota in regulating insulin clearance during diet-induced obesity.

Methods

Blood glucose and insulin clearance were tested in conventional male mice treated with antibiotics and germ-free mice colonized with microbes from mice that were fed a control (chow) diet or an obesogenic high-fat diet (HFD). The composition of the fecal microbiota was analyzed using 16S rRNA sequencing.

Results

Short-term HFD feeding and aging did not alter insulin clearance in the mice. Oral antibiotics mitigated impaired blood insulin clearance in the mice fed an HFD for 12 weeks or longer. Germ-free mice colonized with microbes from HFD-fed donor mice had impaired insulin but not C-peptide clearance. Microbe-transmissible insulin clearance impairment was only observed in germ-free mice after more than 6 weeks post-colonization upon HFD feeding. Five bacterial taxa predicted >90% of the variance in insulin clearance. Mechanistically, impaired insulin clearance was associated with lower levels of hepatic Ceacam-1 but increased liver and skeletal muscle insulin-degrading enzyme (IDE) activity.

Conclusions

Gut microbes regulate insulin clearance during diet-induced obesity. A small cluster of microbes or their metabolites may be targeted for mitigating defects in insulin clearance and hyperinsulinemia during the progression of obesity and type 2 diabetes.

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Obesity impairs insulin clearance in mice, which is mitigated by antibiotics.

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The gut microbiota contributes to impaired insulin but not C-peptide clearance.

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The gut microbiota is a stand-alone factor that impairs insulin clearance.

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A cluster of related bacteria predict >90% of the variance in insulin clearance.

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Impaired insulin clearance is associated with lower hepatic Ceacam-1.

Adipose Tissue Inflammation Is Directly Linked to Obesity-Induced Insulin Resistance, while Gut Dysbiosis and Mitochondrial Dysfunction Are Not Required

Obesity is associated with adipose tissue hypertrophy, systemic inflammation, mitochondrial dysfunction, and intestinal dysbiosis. Rodent models of high-fat diet (HFD)-feeding or genetic deletion of multifunctional proteins involved in immunity and metabolism are often used to probe the etiology of obesity; however, these models make it difficult to divorce the effects of obesity, diet composition, or immunity on endocrine regulation of blood glucose. We, therefore, investigated the importance of adipose inflammation, mitochondrial dysfunction, and gut dysbiosis for obesity-induced insulin resistance using a spontaneously obese mouse model. We examined metabolic changes in skeletal muscle, adipose tissue, liver, the intestinal microbiome, and whole-body glucose control in spontaneously hyperphagic C57Bl/6J mice compared to lean littermates. A separate subset of lean and obese mice was subject to 8 weeks of obesogenic HFD feeding, or to pair feeding of a standard rodent diet. Hyperphagia, obesity, adipose inflammation, and insulin resistance were present in obese mice despite consuming a standard rodent diet, and these effects were blunted with caloric restriction. However, hyperphagic obese mice had normal mitochondrial respiratory function in all tissues tested and no discernable intestinal dysbiosis relative to lean littermates. In contrast, feeding mice an obesogenic HFD altered the composition of the gut microbiome, impaired skeletal muscle mitochondrial bioenergetics, and promoted poor glucose control. These data show that adipose inflammation and redox stress occurred in all models of obesity, but gut dysbiosis and mitochondrial respiratory dysfunction are not always required for obesity-induced insulin resistance. Rather, changes in the intestinal microbiome and mitochondrial bioenergetics may reflect physiological consequences of HFD feeding.

RIPK2 Dictates Insulin Responses to Tyrosine Kinase Inhibitors in Obese Male Mice

Tyrosine kinase inhibitors (TKIs) used in cancer are also being investigated in diabetes. TKIs can improve blood glucose control in diabetic cancer patients, but the specific kinases that alter blood glucose or insulin are not clear. We sought to define the role of Receptor Interacting Serine/Threonine Kinase 2 (RIPK2) in mouse models of insulin resistance. We tested the TKI gefitinib, which inhibits RIPK2 activity, in wild-type (WT), Nod1-/-, Nod2-/-, and Ripk2-/- mice fed an obesogenic high-fat diet. Gefitinib lowered blood glucose during a glucose tolerance test (GTT) in a nucleotide-binding oligomerization domain (NOD)-RIPK2-independent manner in all obese mice. However, gefitinib lowered glucose-stimulated insulin secretion only in obese Ripk2-/- mice. Gefitinib had no effect on insulin secretion in obese WT, Nod1-/-, or Nod2-/- mice. Hence, genetic deletion of Ripk2 promoted the insulin-sensitizing potential of gefitinib, since this TKI lowered both blood glucose and insulin only in Ripk2-/- mice. Gefitinib did not alter the inflammatory profile of pancreas, adipose, liver, or muscle tissues in obese Ripk2-/- mice compared with obese WT mice. We also tested imatinib, a TKI that does not inhibit RIPK2 activity, in obese WT mice. Imatinib lowered blood glucose during a GTT, consistent with TKIs lowering blood glucose independently of RIPK2. However, imatinib increased glucose-stimulated insulin secretion during the glucose challenge. These data show that multiple TKIs lower blood glucose, where actions of TKIs on RIPK2 dictate divergent insulin responses, independent of tissue inflammation. Our data show that RIPK2 limits the insulin sensitizing effect of gefitinib, whereas imatinib increased insulin secretion.

NOD2 in hepatocytes engages a liver-gut axis to protect against steatosis, fibrosis, and gut dysbiosis during fatty liver disease in mice

Obesity promotes nonalcoholic fatty liver disease (NAFLD). The intestinal microbiota contributes to NAFLD progression through a gut-to-liver pathway that promotes inflammation and fibrosis. Gut microbiota-derived factors can travel to the liver and activate immune responses in liver resident cells to promote inflammation and NAFLD. Little is known about bacterial sensors or immune responses that can protect against NAFLD. We tested whether the bacterial cell wall sensor nucleotide-binding oligomerization domain-containing (NOD)2 protects against diet-induced NAFLD in mice. Whole body deletion of NOD2 exacerbated liver steatosis and fibrosis in mice fed a NAFLD-promoting diet. Mice with a hepatocyte-specific deletion of NOD2 (Nod2^-/-HKO) also had higher liver steatosis and fibrosis compared with littermate wild-type mice (WT) fed a NAFLD-promoting diet. Hepatocyte-specific NOD2 deletion altered the composition of the gut microbiome. Nod2^-/-HKO mice had increased relative abundance of Clostridiales and lower Erysipelotrichaceae among other changes in cecal bacteria compared with littermate WT mice. Hepatocyte-specific NOD2 deletion altered a transcriptional program of liver inflammation, metabolism, and fibrosis. Nod2^-/-HKO mice had higher levels of transcripts involved in lipid and cholesterol metabolism. Nod2^-/-HKO mice had higher transcript levels of transforming growth factor-β and collagen isoforms, which coincided with higher levels of liver collagen compared with WT mice. These data show that bacterial cell wall sensing within hepatocytes can engage retrograde cross-talk from the liver to the gut, where liver immunity communicates with the gut to influence the intestinal host-microbe relationship during diet-induced NAFLD, and NOD2 within the hepatocyte confers protection from liver steatosis and fibrosis.

Statins activate the NLRP3 inflammasome and impair insulin signaling via p38 and mTOR

Statins lower cholesterol and risk of cardiovascular disease. Statins can increase blood glucose and risk of new-onset diabetes. It is unclear why statins can have opposing effects on lipids versus glucose. Statins have cholesterol-independent pleiotropic effects that influence both insulin and glucose control. Statin lowering of isoprenoids required for protein prenylation promotes pancreatic β-cell dysfunction and adipose tissue insulin resistance. Protein prenylation influences immune function and statin-mediated adipose tissue insulin resistance involves the NLR family pyrin domain-containing 3 (NLRP3) inflammasome and IL-1β. However, the intracellular cues that statins engage to activate the NLRP3 inflammasome and those responsible for IL-1β-mediated insulin resistance in adipose tissue have not been identified. We hypothesized that stress kinases or components of the insulin signaling pathway mediated statin-induced insulin resistance. We tested the associations of p38, ERK, JNK, phosphatase, and tensin homolog (PTEN), and mTOR in statin-exposed adipose tissue from WT and IL-1β^-/- mice. We found that statins increased phosphorylation of p38 in WT and IL-1β^-/- mice. Statin activation of p38 upstream of IL-1β led to priming of this NLRP3 inflammasome effector in macrophages. We found that mTORC1 inhibition with low doses of rapamycin (2 or 20 nM) lowered macrophage priming of IL-1β mRNA and secretion of IL-1β caused by multiple statins. Rapamycin (20 nM) or the rapalog everolimus (20 nM) prevented atorvastatin-induced lowering of insulin-mediated phosphorylation of Akt in mouse adipose tissue. These results position p38 and mTOR as mediators of statin-induced insulin resistance in adipose tissue and highlight rapalogs as candidates to mitigate the insulin resistance and glycemic side effects of statins.

Chronically Elevating Circulating Ketones Can Reduce Cardiac Inflammation and Blunt the Development of Heart Failure

BACKGROUND

Previous studies have shown beneficial effects of acute infusion of the primary ketone body, β-hydroxybutyrate, in heart failure (HF). However, whether chronic elevations in circulating ketones are beneficial remains unknown.

METHODS

To chronically elevate circulating ketones in mice, we deleted the expression of the ketolytic, rate-limiting-enzyme, SCOT (succinyl-CoA:3-ketoacid-CoA transferase 1; encoded by Oxct1), in skeletal muscle. Tamoxifen-inducible skeletal muscle-specific Oxct1^Muscle-/- knockout (n=32) mice and littermate controls (wild type; WT; n=35) were subjected to transverse aortic constriction (TAC) surgery to induce HF.

RESULTS

Deletion of SCOT in skeletal, but not cardiac muscle resulted in elevated concentrations of fasted circulating β-hydroxybutyrate in knockout mice compared with WT mice (P=0.030). Five weeks following TAC, WT mice progressed to HF, whereas knockout mice with elevated fasting circulating ketones were largely protected from the TAC-induced effects observed in WT mice (ejection fraction, P=0.011; mitral E/A, P=0.012). Furthermore, knockout mice with TAC had attenuated expression of markers of sterile inflammation and macrophage infiltration, which were otherwise elevated in WT mice subjected to TAC. Lastly, addition of β-hydroxybutyrate to isolated hearts was associated with reduced NLRP3 (nucleotide-binding domain-like receptor protein 3)-inflammasome activation, which has been previously shown to play a role in contributing to HF-induced cardiac inflammation.

CONCLUSIONS

These data show that chronic elevation of circulating ketones protects against the development of HF that is associated with the ability of β-hydroxybutyrate to directly reduce inflammation. These beneficial effects of ketones were associated with reduced cardiac NLRP3 inflammasome activation, suggesting that ketones may modulate cardiac inflammation via this mechanism.

Postbiotics for NOD2 require nonhematopoietic RIPK2 to improve blood glucose and metabolic inflammation in mice

Defining the host receptors and metabolic consequences of bacterial components can help explain how the microbiome influences metabolic diseases. Bacterial peptidoglycans that activate nucleotide-binding oligomerization domain-containing (NOD)1 worsen glucose control, whereas NOD2 activation improves glycemia. Receptor-interacting serine/threonine-protein kinase 2 (RIPK2) is required for innate immunity instigated by NOD1 and NOD2. The role of RIPK2 in the divergent effects of NOD1 versus NOD2 on blood glucose was unknown. We found that whole body deletion of RIPK2 negated all effects of NOD1 or NOD2 activation on blood glucose during an acute, low level endotoxin challenge in mice. It was known that NOD1 in hematopoietic cells participates in insulin resistance and metabolic inflammation in obese mice. It was unknown if RIPK2 in hematopoietic cells is required for the glucose-lowering and anti-inflammatory effects of NOD2 activation. We hypothesized that RIPK2 in nonhematopoietic cells dictated the glycemic effects of NOD2 activation. We found that whole body deletion of RIPK2 prevented the glucose-lowering effects of repeated NOD2 activation that were evident during a glucose tolerance test (GTT) in high-fat diet (HFD)-fed wild-type (WT) mice. NOD2 activation lowered glucose during a GTT and lowered adipose tissue inflammation in mice with RIPK2 deleted in hematopoietic cells. We conclude that RIPK2 in nonhematopoietic cells mediates the glucose lowering and anti-inflammatory effects of NOD2-activating postbiotics. We propose a model where lipopolysaccharides and NOD1 ligands synergize in hematopoietic cells to promote insulin resistance but NOD2 activation in nonhematopoietic cells promotes RIPK2-dependent immune tolerance and lowering of inflammation and insulin resistance.

Type 2 diabetes influences bacterial tissue compartmentalisation in human obesity

Visceral obesity is a key risk factor for type 2 diabetes (T2D). Whereas gut dysbiosis appears to be instrumental for this relationship, whether gut-associated signatures translocate to extra-intestinal tissues and how this affects host metabolism remain elusive. Here we provide a comparative analysis of the microbial profile found in plasma, liver and in three distinct adipose tissues of individuals with morbid obesity. We explored how these tissue microbial signatures vary between individuals with normoglycaemia and those with T2D that were matched for body mass index. We identified tissue-specific signatures with higher bacterial load in the liver and omental adipose tissue. Gut commensals, but also environmental bacteria, showed tissue- and T2D-specific compartmentalisation. T2D signatures were most evident in mesenteric adipose tissue, in which individuals with diabetes displayed reduced bacterial diversity concomitant with fewer Gram-positive bacteria, such as Faecalibacterium, as opposed to enhanced levels of typically opportunistic Gram-negative Enterobacteriaceae. Plasma samples of individuals with diabetes were similarly enriched in Enterobacteriaceae, including the pathobiont Escherichia-Shigella. Our work provides evidence for the presence of selective plasma and tissue microbial signatures in individuals with severe obesity and identifies new potential microbial targets and biomarkers of T2D.

Glucose alters the symbiotic relationships between gut microbiota and host physiology

Bacteria and mammals exhibit all aspects of symbiosis. Metabolic flux in bacteria and in specific host cells can influence host-microbe symbiotic relationships and tip the balance between mutualism, commensalism, and parasitism. The relationship between microbes and host metabolism is bidirectional: microbes can influence host blood glucose, but glucose levels can influence the microbiota and host response to specific bacteria. A key consideration determining symbiotic relationships is compartmentalization of bacterial niches by mucosal, chemical, and physical barriers of the gut. We propose that compartmentalization of glucose levels in the blood versus the intestinal lumen is another important factor dictating host-microbe symbiosis. Host glucose and specific bacteria can modify the intestinal barrier, immune function, and antimicrobial defenses, which can then break down compartmentalization of microbes, alter glucose levels and impact symbiosis. Determining how glucose metabolism promotes mutualistic, commensal, and parasitic relationships within the entire microbiota community is relevant to glucose control in diabetes and enteric infections, which occur more often and have worse outcomes in diabetics.

Statins Promote Interleukin-1β-Dependent Adipocyte Insulin Resistance Through Lower Prenylation, Not Cholesterol

Statins lower cholesterol and adverse cardiovascular outcomes, but this drug class increases diabetes risk. Statins are generally anti-inflammatory. However, statins can promote inflammasome-mediated adipose tissue inflammation and insulin resistance through an unidentified immune effector. Statins lower mevalonate pathway intermediates beyond cholesterol, but it is unknown whether lower cholesterol underpins statin-mediated insulin resistance. We sought to define the mevalonate pathway metabolites and immune effectors that propagate statin-induced adipose insulin resistance. We found that LDL cholesterol lowering was dispensable, but statin-induced lowering of isoprenoids required for protein prenylation triggered NLRP3/caspase-1 inflammasome activation and interleukin-1β (IL-1β)-dependent insulin resistance in adipose tissue. Multiple statins impaired insulin action at the level of Akt/protein kinase B signaling in mouse adipose tissue. Providing geranylgeranyl isoprenoids or inhibiting caspase-1 prevented statin-induced defects in insulin signaling. Atorvastatin (Lipitor) impaired insulin signaling in adipose tissue from wild-type and IL-18^-/- mice, but not IL-1β^-/- mice. Atorvastatin decreased cell-autonomous insulin-stimulated lipogenesis but did not alter lipolysis or glucose uptake in 3T3-L1 adipocytes. Our results show that statin lowering of prenylation isoprenoids activates caspase-1/IL-1β inflammasome responses that impair endocrine control of adipocyte lipogenesis. This may allow the targeting of cholesterol-independent statin side effects on adipose lipid handling without compromising the blood lipid/cholesterol-lowering effects of statins.

Host-Microbe Interplay in the Cardiometabolic Benefits of Dietary Polyphenols

Polyphenols are nonessential phytonutrients abundantly found in fruits and vegetables. A wealth of data from preclinical models and clinical trials consistently supports cardiometabolic benefits associated with dietary polyphenols in murine models and humans. Furthermore, a growing number of studies have shown that specific classes of polyphenols, such as proanthocyanidins (PACs) and ellagitannins, as well as the stilbenoid resveratrol, can alleviate several features of the metabolic syndrome. Moreover, mounting evidence points to the gut microbiota as a key mediator of the health benefits of polyphenols. In this review we summarize recent findings supporting the beneficial potential of polyphenols against cardiometabolic diseases, with a focus on the role of host-microbe interactions.

TNF, but not hyperinsulinemia or hyperglycemia, is a key driver of obesity-induced monocytosis revealing that inflammatory monocytes correlate with insulin in obese male mice

Inflammation contributes to obesity-related hyperinsulinemia and insulin resistance, which often precede type 2 diabetes. Inflammation is one way that obesity can promote insulin resistance. It is not clear if the extent of obesity, hyperinsulinemia, or hyperglycemia, underpins changes in cellular immunity during diet-induced obesity. In particular, the requirement for obesity or directionality in the relationship between insulin resistance and monocyte characteristics is poorly defined. Inflammatory cytokines such as tumor necrosis factor (TNF) can contribute to insulin resistance. It is unclear if TNF alters monocytosis or specific markers of cellular immunity in the context of obesity. We measured bone marrow and blood monocyte characteristics in WT and TNF-/- mice that were fed obesogenic, high fat (HF) diets. We also used hyperglycemic Akita mice and mice implanted with insulin pellets in order to determine if glucose or insulin were sufficient to alter monocyte characteristics. We found that diet-induced obesity in male mice increased the total number of monocytes in blood, but not in bone marrow. Immature, inflammatory (Ly6Chigh ) monocytes decreased within the bone marrow and increased within peripheral blood of HF-fed mice. We found that neither hyperinsulinemia nor hyperglycemia was sufficient to induce the observed changes in circulating monocytes in the absence of diet-induced obesity. In obese HF-fed mice, antibiotic treatment lowered insulin and insulin resistance, but did not alter circulating monocyte characteristics. Fewer Ly6Chigh monocytes were present within the blood of HF-fed TNF-/- mice in comparison to HF-fed wild-type (WT) mice. The prevalence of immature Ly6Chigh monocytes in the blood correlated with serum insulin and insulin resistance irrespective of the magnitude of adipocyte or adipose tissue hypertrophy in obese mice. These data suggest that diet-induced obesity instigates a TNF-dependent increase in circulating inflammatory monocytes, which predicts increased blood insulin and insulin resistance independently from markers of adiposity or adipose tissue expansion.

Long term but not short term exposure to obesity related microbiota promotes host insulin resistance

The intestinal microbiota and insulin sensitivity are rapidly altered after ingestion of obesogenic diets. We find that changes in the composition of the fecal microbiota precede changes in glucose tolerance when mice are fed obesogenic, low fiber, high fat diets (HFDs). Antibiotics alter glycemia during the first week of certain HFDs, but antibiotics show a more robust improvement in glycemic control in mice with protracted obesity caused by long-term feeding of multiple HFDs. Microbiota transmissible dysglycemia and glucose intolerance only occur when germ-free mice are exposed to obesity-related microbes for more than 45 days. We find that sufficient host exposure time to microbiota derived from HFD-fed mice allows microbial factors to contribute to insulin resistance, independently from increased adiposity in mice. Our results are consistent with intestinal microbiota contributing to chronic insulin resistance and dysglycemia during prolonged obesity, despite rapid diet-induced changes in the taxonomic composition of the fecal microbiota.

Gut microbiota impact host metabolism and gut microbiome composition reflects dietary habits. Here the authors show that, in animals fed obesogenic diets, changes in gut microbiota precede changes in glucose homeostasis. Importantly, long term exposure of the host to the changed microbiota is required to impair glucose homeostasis.

Targeting macrophage scavenger receptor 1 promotes insulin resistance in obese male mice

Immune components can bridge inflammatory triggers to metabolic dysfunction. Scavenger receptors sense lipoproteins, but it is not clear how different scavenger receptors alter carbohydrate metabolism during obesity. Macrophage scavenger receptor 1 (MSR1) and macrophage receptor with collagenous structure (MARCO) are scavenger receptors that have been implicated in lipoprotein metabolism and cardiovascular disease. We assessed glucose control, tissue-specific insulin sensitivity, and inflammation in Msr1- and Marco-deficient mice fed with obesogenic diets. Compared to wild-type (WT) mice, Msr1-/- mice had worse blood glucose control that was only revealed after diet-induced obesity, not in lean mice. Obese Msr1-/- mice had worse insulin-stimulated glucose uptake in the adipose tissue, which occurred in the absence of overt differences in adipose inflammation compared to obese WT mice. Msr1 deletion worsened dysglycemia independently from bacterial cell wall insulin sensitizers, such as muramyl dipeptide. MARCO was dispensable for glycemic control in obese mice. Oral administration of the polysaccharide fucoidan worsened glucose control in obese WT mice, but fucoidan had no effect on glycemia in obese Msr1-/- mice. Therefore, MSR1 is a scavenger receptor responsible for changes in glucose control in response to the environmental ligand fucoidan. Given the interest in dietary supplements and natural products reducing inflammation or insulin resistance in metabolic disease during obesity, our results highlight the importance of understanding which ligand-receptor relationships promote versus those that protect against metabolic disease factors. Our results show that ligand or gene targeting of MSR1 exacerbates insulin resistance in obese mice.

Fecal transplant from resveratrol-fed donors improves glycaemia and cardiovascular features of the metabolic syndrome in mice

Oral administration of resveratrol attenuates several symptoms associated with the metabolic syndrome, such as impaired glucose homeostasis and hypertension. Recent work has shown that resveratrol can improve glucose homeostasis in obesity via changes in the gut microbiota. Studies involving fecal microbiome transplants (FMTs) suggest that either live gut microbiota or bacterial-derived metabolites from resveratrol ingestion are responsible for producing the observed benefits in recipients. Herein, we show that obese mice receiving FMTs from healthy resveratrol-fed mice have improved glucose homeostasis within 11 days of the first transplant, and that resveratrol-FMTs is more efficacious than oral supplementation of resveratrol for the same duration. The effects of FMTs from resveratrol-fed mice are also associated with decreased inflammation in the colon of obese recipient mice. Furthermore, we show that sterile fecal filtrates from resveratrol-fed mice are sufficient to improve glucose homeostasis in obese mice, demonstrating that nonliving bacterial, metabolites, or other components within the feces of resveratrol-fed mice are sufficient to reduce intestinal inflammation. These postbiotics may be an integral mechanism by which resveratrol improves hyperglycemia in obesity. Resveratrol-FMTs also reduced the systolic blood pressure of hypertensive mice within 2 wk of the first transplant, indicating that the beneficial effects of resveratrol-FMTs may also assist with improving cardiovascular conditions associated with the metabolic syndrome.

Statin Therapy Negatively Impacts Skeletal Muscle Regeneration and Cutaneous Wound Repair in Type 1 Diabetic Mice

Those with diabetes invariably develop complications including cardiovascular disease (CVD). To reduce their CVD risk, diabetics are generally prescribed cholesterol-lowering 3-hydroxy-methylglutaryl coenzyme A reductase inhibitors (i.e., statins). Statins inhibit cholesterol biosynthesis, but also reduce the synthesis of a number of mevalonate pathway intermediates, leading to several cholesterol-independent effects. One of the pleiotropic effects of statins is the reduction of the anti-fibrinolytic hormone plasminogen activator inhibitor-1 (PAI-1). We have previously demonstrated that a PAI-1 specific inhibitor alleviated diabetes-induced delays in skin and muscle repair. Here we tested if statin administration, through its pleiotropic effects on PAI-1, could improve skin and muscle repair in a diabetic rodent model. Six weeks after diabetes onset, adult male streptozotocin-induced diabetic (STZ), and WT mice were assigned to receive control chow or a diet enriched with 600 mg/kg Fluvastatin. Tibialis anterior muscles were injured via Cardiotoxin injection to induce skeletal muscle injury. Punch biopsies were administered on the dorsal scapular region to induce injury of skin. Twenty-four days after the onset of statin therapy (10 days post-injury), tissues were harvested and analyzed. PAI-1 levels were attenuated in statin-treated diabetic tissue when compared to control-treated tissue, however no differences were observed in non-diabetic tissue as a result of treatment. Muscle and skin repair were significantly attenuated in Fluvastatin-treated STZ-diabetic mice as demonstrated by larger wound areas, less mature granulation tissue, and an increased presence of smaller regenerating muscle fibers. Despite attenuating PAI-1 levels in diabetic tissue, Fluvastatin treatment impaired cutaneous healing and skeletal muscle repair in STZ-diabetic mice.

Intrapartum antibiotics for GBS prophylaxis alter colonization patterns in the early infant gut microbiome of low risk infants

Early life microbial colonization and succession is critically important to healthy development with impacts on metabolic and immunologic processes throughout life. A longitudinal prospective cohort was recruited from midwifery practices to include infants born at full term gestation to women with uncomplicated pregnancies. Here we compare bacterial community succession in infants born vaginally, with no exposure to antibiotics (n = 53), with infants who were exposed to intrapartum antibiotic prophylaxis (IAP) for Group B Streptococcus (GBS; n = 14), and infants born by C-section (n = 7). Molecular profiles  of the 16 S rRNA genes indicate that there is a delay in the expansion of Bifidobacterium, which was the dominate infant gut colonizer, over the first 12 weeks and a persistence of Escherichia when IAP for GBS exposure is present during vaginal labour. Longer duration of IAP exposure increased the magnitude of the effect on Bifidobacterium populations, suggesting a longer delay in microbial community maturation. As with prior studies, we found altered gut colonisation following C-section that included a notable lack of Bacteroidetes. This study found that exposure of infants to IAP for GBS during vaginal birth affected aspects of gut microbial ecology that, although dramatic at early time points, disappeared by 12 weeks of age in most infants.