Dietary supplementation with fermentable fiber suppresses adiposity and the associated parameters of metabolic syndrome. Microbiota-generated fiber-derived short-chain fatty acids (SCFAs) and free fatty acid receptors including GPR43 are thought to mediate these effects. We find that while fermentable (inulin), but not insoluble (cellulose), fiber markedly protected mice against high-fat diet (HFD)-induced metabolic syndrome, the effect was not significantly impaired by either inhibiting SCFA production or genetic ablation of GPR43. Rather, HFD decimates gut microbiota, resulting in loss of enterocyte proliferation, leading to microbiota encroachment, low-grade inflammation (LGI), and metabolic syndrome. Enriching HFD with inulin restored microbiota loads, interleukin-22 (IL-22) production, enterocyte proliferation, and antimicrobial gene expression in a microbiota-dependent manner, as assessed by antibiotic and germ-free approaches. Inulin-induced IL-22 expression, which required innate lymphoid cells, prevented microbiota encroachment and protected against LGI and metabolic syndrome. Thus, fermentable fiber protects against metabolic syndrome by nourishing microbiota to restore IL-22-mediated enterocyte function.

SUMMARY Dietary soluble fibers are fermented by gut bacteria into short-chain fatty acids (SCFA), which are considered broadly health-promoting. Accordingly, consumption of such fibers ameliorates metabolic syndrome. However, incorporating soluble fiber inulin, but not insoluble fiber, into a compositionally defined diet, induced icteric hepatocellular carcinoma (HCC). Such HCC was microbiota-dependent and observed in multiple strains of dysbiotic mice but not in germ-free nor antibiotics-treated mice. Furthermore, consumption of an inulin-enriched high-fat diet induced both dysbiosis and HCC in wild-type (WT) mice. Inulin-induced HCC progressed via early onset of cholestasis, hepatocyte death, followed by neutrophilic inflammation in liver. Pharmacologic inhibition of fermentation or depletion of fermenting bacteria markedly reduced intestinal SCFA and prevented HCC. Intervening with cholestyramine to prevent reabsorption of bile acids also conferred protection against such HCC. Thus, its benefits notwithstanding, enrichment of foods with fermentable fiber should be approached with great caution as it may increase risk of HCC.

Macrophages are central to the initiation and progression of atherosclerosis and thus can be very appropriate targets for therapy. Cell adhesion molecules mediating monocytes recruitment to the endothelium are attractive therapy targets and their inhibitors are in clinical trials. Macrophage scavenger receptors like SR-A and CD-36 mediate foam cell formation by facilitating the uptake of modified lipids. Peroxisome proliferator-activated receptors (PPAR), liver X receptor (LXR)-mediated signaling, mitogen-activated protein kinase (MAPK) induced phosphorylation events seem to play an important role in this phenomenon. Proteins affecting macrophage cholesterol metabolism and transport, including ATP-binding cassette (ABC) A1, ABCG1, acylCoA:cholesterol acyltransferase (ACAT), apolipoprotein A-1 (ApoA-1), neutral cholesteryl ester hydrolase (NCEH) also regulate foam cell formation and are being developed as therapeutic targets by many pharmaceutical companies. Macrophage proliferation and apoptosis are important events controlling inflammatory response, plaque vulnerability, and destabilization. Free cholesterol (FC) activates the macrophage endoplasmic reticulum (ER) stress pathway and apoptosis. Free radicals and nitric oxide also modulate macrophage foam cell formation and apoptosis. Various antioxidants like AGI-1067 and BO-653 are in clinical trials for atherosclerosis treatment. Macrophage matrix metalloproteinase's (MMP's) play a significant role in weakening and rupture of plaques. Efforts are on to develop isoform specific MMP inhibitor. CD-14, MMP-3, ABCA1, Toll-like receptor-4 (TLR-4), lectin-like oxidized low-density lipoprotein receptor-1 (LOX-1), arachidonate lipoxygenase-15 (ALOX-15), and Connexin37 polymorphisms and macrophage dysfunction signify their importance in atherosclerosis. Deciphering the role of macrophages in regulating dyslipidemia and inflammation during atherosclerosis is important for developing them as therapeutic targets. ß 2007 Wiley Periodicals, Inc. Med Res Rev, 28, No. 4, 483-544, 2008

SUMMARY The gut microbiota plays a key role in host metabolism. Toll-Like Receptor 5 (TLR5), a flagellin receptor, is required for gut microbiota homeostasis. Accordingly, TLR5 deficient (T5KO) mice are prone to develop microbiota-dependent metabolic syndrome. Here we observed that T5KO mice display elevated neutral lipids with a compositional increase of oleate [C18:1 (n9)] relative to wild-type littermates. Increased oleate contribution to hepatic lipids and liver SCD1 expression were both microbiota-dependent. Analysis of short chain fatty acids (SCFA) and 13C-acetate label incorporation revealed elevated SCFA in ceca and hepatic portal blood and, increased liver de novo lipogenesis in T5KO mice. Dietary SCFA further aggravated metabolic syndrome in T5KO mice. Deletion of hepatic SCD1 not only prevented hepatic neutral lipid oleate enrichment but also ameliorated metabolic syndrome in T5KO mice. Collectively, these results underscore the key role of the gut microbiota-liver axis in the pathogenesis of metabolic diseases.

ObjectiveDiets rich in fermentable fibres provide an array of health benefits; however, many patients with IBD report poor tolerance to fermentable fibre-rich foods. Intervention studies with dietary fibres in murine models of colonic inflammation have yielded conflicting results on whether fibres ameliorate or exacerbate IBD. Herein, we examined how replacing the insoluble fibre, cellulose, with the fermentable fibres, inulin or pectin, impacted murine colitis resulting from immune dysregulation via inhibition of interleukin (IL)-10 signalling and/or innate immune deficiency (Tlr5KO).DesignMice were fed with diet containing either cellulose, inulin or pectin and subjected to weekly injections of an IL-10 receptor (αIL-10R) neutralising antibody. Colitis development was examined by serological, biochemical, histological and immunological parameters.ResultsInulin potentiated the severity of αIL10R-induced colitis, while pectin ameliorated the disease. Such exacerbation of colitis following inulin feeding was associated with enrichment of butyrate-producing bacteria and elevated levels of caecal butyrate. Blockade of butyrate production by either metronidazole or hops β-acids ameliorated colitis severity in inulin-fed mice, whereas augmenting caecal butyrate via tributyrin increased colitis severity in cellulose containing diet-fed mice. Elevated butyrate levels were associated with increased IL-1β activity, while inhibition of the NOD-like receptor protein 3 by genetic, pharmacologic or dietary means markedly reduced colitis.ConclusionThese results not only support the notion that fermentable fibres have the potential to ameliorate colitis but also caution that, in some contexts, prebiotic fibres can lead to gut dysbiosis and surfeit colonic butyrate that might exacerbate IBD.

During an inflammatory response in the gut, some commensal bacteria such as E. coli can thrive and contribute to disease. Here we demonstrate that enterobactin (Ent), a catecholate siderophore released by E. coli, is a potent inhibitor of myeloperoxidase (MPO), a bactericidal enzyme of the host. Glycosylated Ent (salmochelin) and non-catecholate siderophores (yersiniabactin and ferrichrome) fail to inhibit MPO activity. An E. coli mutant (ΔfepA) that overproduces Ent, but not an Ent-deficient double mutant (ΔaroB/ΔfepA), inhibits MPO activity and exhibits enhanced survival in inflamed guts. This survival advantage is counter-regulated by lipocalin 2, a siderophore-binding host protein, which rescues MPO from Ent-mediated inhibition. Spectral analysis reveals that Ent interferes with compound I [oxoiron, Fe(IV)=O] and reverts the enzyme back to its native ferric [Fe(III)] state. These findings define a fundamental mechanism by which E. coli surpasses the host innate immune responses during inflammatory gut diseases and gains a distinct survival advantage.

BACKGROUND & AIMS Lipocalin 2 (Lcn2) is a multifunctional innate immune protein whose expression closely correlates with extent of intestinal inflammation. However, whether Lcn2 plays a role in the pathogenesis of gut inflammation is unknown. Herein, we investigated the extent to which Lcn2 regulates inflammation and gut bacterial dysbiosis in mouse models of IBD. METHODS Lcn2 expression was monitored in murine colitis models and upon microbiota ablation/restoration. WT and Lcn2 knockout (Lcn2KO) mice were analyzed for gut bacterial load, composition by 16S rRNA gene pyrosequencing and, their colitogenic potential by co-housing with Il-10KO mice. Acute (dextran sodium sulfate) and chronic (IL-10R neutralization and T-cell adoptive transfer) colitis was induced in WT and Lcn2KO mice with or without antibiotics. RESULTS Lcn2 expression was dramatically induced upon inflammation and was dependent upon presence of a gut microbiota and MyD88 signaling. Use of bone-marrow chimeric mice revealed non-immune cells are the major contributors of circulating Lcn2. Lcn2KO mice exhibited elevated levels of entA-expressing gut bacteria burden and, moreover, a broadly distinct bacterial community relative to WT littermates. Lcn2KO mice developed highly colitogenic T-cells and exhibited exacerbated colitis upon exposure to DSS or neutralization of IL-10. Such exacerbated colitis could be prevented by antibiotic treatment. Moreover, exposure to the microbiota of Lcn2KO mice, via cohousing, resulted in severe colitis in Il-10KO mice. CONCLUSION Lcn2 is a bacterially-induced, MyD88-dependent, protein that play an important role in gut homeostasis and a pivotal role upon challenge. Hence, therapeutic manipulation of Lcn2 levels may provide a strategy to help manage diseases driven by alteration of the gut microbiota.

Dietary salt reduction and exercise are lifestyle modifications for salt‐sensitive hypertensives. While exercise has prominent metabolic effects, salt has an adverse effect on metabolic syndrome, of which hypertension is a hallmark. We hypothesized that dietary salt impacts metabolism in a salt‐sensitive model of hypertension. An untargeted metabolomics approach demonstrates lower circulating levels of the ketone body, beta‐hydroxybutyrate (βOHB), in high salt‐fed hypertensive rats. Despite the high salt intake, specific rescue of βOHB levels by nutritional supplementation of its precursor, 1,3‐butanediol, attenuates hypertension and protects kidney function. This beneficial effect of βOHB was likely independent of gut‐microbiotal and Th17‐mediated effects of salt and instead facilitated by βOHB inhibiting the renal Nlrp3 inflammasome. The juxtaposed effects of dietary salt and exercise on salt‐sensitive hypertension, which decrease and increase βOHB respectively, indicate that nutritional supplementation of a precursor of βOHB provides a similar benefit to salt‐sensitive hypertension as exercise. Support or Funding Information Funding from this work to BJ from the NHLBI (NIH) (HL143082) is gratefully acknowledged. Declaration of interests: Bina Joe and Saroj Chakraborty have an interest in U.S. Patent Application Serial No.: 62/665,690 filed on May 2, 2018 in this paper regarding nutritional intervention for salt‐sensitive hypertension for 1,3‐butanediol. This abstract is from the Experimental Biology 2019 Meeting. There is no full text article associated with this abstract published in The FASEB Journal.