OBJECTIVE— Diabetes and obesity are characterized by a low-grade inflammation whose molecular origin is unknown. We previously determined, first, that metabolic endotoxemia controls the inflammatory tone, body weight gain, and diabetes, and second, that high-fat feeding modulates gut microbiota and the plasma concentration of lipopolysaccharide (LPS), i.e., metabolic endotoxemia. Therefore, it remained to demonstrate whether changes in gut microbiota control the occurrence of metabolic diseases. RESEARCH DESIGN AND METHODS— We changed gut microbiota by means of antibiotic treatment to demonstrate, first, that changes in gut microbiota could be responsible for the control of metabolic endotoxemia, the low-grade inflammation, obesity, and type 2 diabetes and, second, to provide some mechanisms responsible for such effect. RESULTS— We found that changes of gut microbiota induced by an antibiotic treatment reduced metabolic endotoxemia and the cecal content of LPS in both high-fat–fed and ob/ob mice. This effect was correlated with reduced glucose intolerance, body weight gain, fat mass development, lower inflammation, oxidative stress, and macrophage infiltration marker mRNA expression in visceral adipose tissue. Importantly, high-fat feeding strongly increased intestinal permeability and reduced the expression of genes coding for proteins of the tight junctions. Furthermore, the absence of CD14 in ob/ob CD14 − / − mutant mice mimicked the metabolic and inflammatory effects of antibiotics. CONCLUSIONS— This new finding demonstrates that changes in gut microbiota controls metabolic endotoxemia, inflammation, and associated disorders by a mechanism that could increase intestinal permeability. It would thus be useful to develop strategies for changing gut microbiota to control, intestinal permeability, metabolic endotoxemia, and associated disorders.

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Changes in gut microbiota control metabolic endotoxemia-induced inflammation in high-fat diet-induced obesity and diabetes in mice

BACKGROUND AND AIMS: Obese and diabetic mice display enhanced intestinal permeability and metabolic endotoxaemia that participate in the occurrence of metabolic disorders. Our recent data support the idea that a selective increase of Bifidobacterium spp. reduces the impact of high-fat diet-induced metabolic endotoxaemia and inflammatory disorders. Here, we hypothesised that prebiotic modulation of gut microbiota lowers intestinal permeability, by a mechanism involving glucagon-like peptide-2 (GLP-2) thereby improving inflammation and metabolic disorders during obesity and diabetes. METHODS: Study 1: ob/ob mice (Ob-CT) were treated with either prebiotic (Ob-Pre) or non-prebiotic carbohydrates as control (Ob-Cell). Study 2: Ob-CT and Ob-Pre mice were treated with GLP-2 antagonist or saline. Study 3: Ob-CT mice were treated with a GLP-2 agonist or saline. We assessed changes in the gut microbiota, intestinal permeability, gut peptides, intestinal epithelial tight-junction proteins ZO-1 and occludin (qPCR and immunohistochemistry), hepatic and systemic inflammation. RESULTS: Prebiotic-treated mice exhibited a lower plasma lipopolysaccharide (LPS) and cytokines, and a decreased hepatic expression of inflammatory and oxidative stress markers. This decreased inflammatory tone was associated with a lower intestinal permeability and improved tight-junction integrity compared to controls. Prebiotic increased the endogenous intestinotrophic proglucagon-derived peptide (GLP-2) production whereas the GLP-2 antagonist abolished most of the prebiotic effects. Finally, pharmacological GLP-2 treatment decreased gut permeability, systemic and hepatic inflammatory phenotype associated with obesity to a similar extent as that observed following prebiotic-induced changes in gut microbiota. CONCLUSION: We found that a selective gut microbiota change controls and increases endogenous GLP-2 production, and consequently improves gut barrier functions by a GLP-2-dependent mechanism, contributing to the improvement of gut barrier functions during obesity and diabetes.

https://gut.bmj.com/content/gutjnl/58/8/1091.full.pdf

Changes in gut microbiota control inflammation in obese mice through a mechanism involving GLP-2-driven improvement of gut permeability

The role of the endothelium in severe sepsis and multiple organ dysfunction syndrome

SUMMARY: Posterior reversible encephalopathy syndrome (PRES) is a neurotoxic state accompanied by a unique brain imaging pattern typically associated with a number of complex clinical conditions including: preeclampsia/eclampsia, allogeneic bone marrow transplantation, solid organ transplantation, autoimmune diseases and high dose cancer chemotherapy. The mechanism behind the developing vasogenic edema and CT or MR imaging appearance of PRES is not known. Two theories have historically been proposed: 1) Severe hypertension leads to failed auto-regulation, subsequent hyperperfusion, with endothelial injury/vasogenic edema and; 2) vasoconstriction and hypoperfusion leads to brain ischemia and subsequent vasogenic edema. The strengths/weaknesses of these hypotheses are reviewed in a translational fashion including supporting evidence and current available imaging/clinical data related to the conditions that develop PRES. While the hypertension/hyperperfusion theory has been most popular, the conditions associated with PRES have a similar immune challenge present and develop a similar state of T-cell/endothelial cell activation that may be the basis of leukocyte trafficking and systemic/cerebral vasoconstriction. These systemic features along with current vascular and perfusion imaging features in PRES appear to render strong support for the older theory of vasoconstriction coupled with hypoperfusion as the mechanism.

http://www.ajnr.org/content/ajnr/29/6/1043.full.pdf

Posterior reversible encephalopathy syndrome, part 2: controversies surrounding pathophysiology of vasogenic edema.

Ischemia-reperfusion injury is, at least in part, responsible for the morbidity associated with liver surgery under total vascular exclusion or after liver transplantation. The pathophysiology of hepatic ischemia-reperfusion includes a number of mechanisms that contribute to various degrees in the overall injury. Some of the topics discussed in this review include cellular mechanisms of injury, formation of pro- and anti-inflammatory mediators, expression of adhesion molecules, and the role of oxidant stress during the inflammatory response. Furthermore, the roles of nitric oxide in preventing microcirculatory disturbances and as a substrate for peroxynitrite formation are reviewed. In addition, emerging mechanisms of protection by ischemic preconditioning are discussed. On the basis of current knowledge, preconditioning or pharmacological interventions that mimic these effects have the greatest potential to improve clinical outcome in liver surgery involving ischemic stress and reperfusion.

Molecular mechanisms of hepatic ischemia-reperfusion injury and preconditioning.

The initial responses to endotoxemia are detectable in the microcirculation as a microvascular inflammatory response characterized by activation of the endothelium stimulating these cells from their normal anticoagulant state to a procoagulant state with increased adhesiveness for leukocytes and platelets. Concomitantly, arteriolar tone is lost and reactivity to a variety of agonists is modified. Tissue damage subsequently results not only from reduced perfusion of the exchange vessels, but also from injurious substances released from activated, sequestered leukocytes as well as activated endothelial cells, macrophages, and platelets. This is the result of endotoxins inducing activation and interaction of a number of effector cells, cascades, and acute-phase responses, such as the complement, coagulation, bradykinin/kinin, and hematopoietic systems accompanied by the release of a myriad of mediators. These include eicosanoids, cytokines, chemokines, adhesion molecules, reactive free radicals, platelet-activating factor, and nitric oxide. This paper briefly reviews the microvascular responses to endotoxemia and discusses some of the mechanisms involved.

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The microcirculation during endotoxemia

Background: Chronic alcohol ingestion leads to endotoxemia which is believed to play an important role in the pathogenesis of alcoholic liver disease (ALD). The purpose of this study was to determine if chronic ethanol consumption, in addition to affecting plasma endotoxin and cytokines, also affects the endotoxin-neutralizing capacity (ENC), sCD14, and sICAM-1, in patients with ALD. A second aim was to identify correlations between these latter parameters, endotoxin, and cytokines, especially IL-10. Methods: Hospitalized patients with various degrees of ALD (n = 59), and 20 healthy volunteers were studied. Plasma endotoxin and ENC were determined using our kinetic Limulus amebocyte lysate test. Cytokines, sCD14, and sICAM-1 were measured by enzyme-linked immunosorbent assay. Results: Patients with ALD exhibited a mild endotoxemia (p < 0.01) and a marked decrease in ENC (p < 0.0002). TNF-a (p < 0.05), IL-6 (p < 0.0001), sICAM (p < 0.005), and sCD14 (p < 0.0005) were significantly elevated in all patients with ALD, and IL-10 (p < 0.05) in patients with cirrhotic ALD. With the exception of IL-10, the cytokines correlated with each other and with sICAM-1. No correlations occurred between endotoxin, ENC, and sCD14, and between these and the cytokines and sICAM-1. Elevated levels of endotoxin correlate with acute excessive alcohol ingestion. No gender differences were observed. Conclusions: Acute alcohol intoxication rather than severe ALD results in significant endotoxemia. The limited capacity of plasma to neutralize endotoxin in liver injury seems to be an important factor in ALD which may be responsible for the release of endotoxin-induced mediators, such as cytokines, as well as s-ICAM-1, that are relevant in the pathogenesis of ALD.

Endotoxin, endotoxin-neutralizing-capacity, sCD14, sICAM-1, and cytokines in patients with various degrees of alcoholic liver disease.

High-resolution in vivo microscopic methods have been used to explore the responses to endotoxin of Kupffer cells in the livers of anesthetized mice, rats, hamsters, and guinea pigs under a variety of experimental conditions. These include studies of normal animals as well as of animals sensitized or tolerant to endotoxin, C3H/HeJ mice with a low response to endotoxin, mice rendered septic by cecal ligation and puncture, mice with Kupffer cells selectively destroyed by frog virus 3, and rats with portacaval shunts. The functional state of Kupffer cells was evaluated by measuring both the number of these cells per microscopic field that phagocytosed 1.0-micron latex particles and the rate at which individual Kupffer cells phagocytosed single latex particles. The intrahepatic density and level of activation of Kupffer cells were found to play a role in determining endotoxin sensitivity and to be involved, in conjunction with endotoxin, in the development of tolerance. All of these studies support the concept of a central role for Kupffer cells in host defense mechanisms and of the possible modulation and of this role by gut-derived endotoxins contained in the portal blood.

Kupffer cell function in host defense.

The relative species sensitivity to Escherichia coli O111:B4 endotoxin was found to be guinea pig greater than hamster greater than mouse greater than rat. The 50% lethal dose of this endotoxin correlated with both the rate at which single latex particles were phagocytosed by individual Kupffer cells and the number of Kupffer cells in hepatic lobules that phagocytosed latex. The results suggests that the intrahepatic density and the level of activation of Kupffer cells participate in determining endotoxin sensitivity.

Species differences in Kupffer cells and endotoxin sensitivity.

Hepatic fibrosis in alcoholic liver disease often heralds progression to cirrhosis and, therefore, noninvasive parameters are required for early diagnosis and follow-up. Collagens VI and XIV, procollagen-III-N-propeptide, hyaluronic acid, and active transforming growth factor-β1 (TGF-β1) were measured in healthy volunteers, patients with alcoholic cirrhosis, and heavy drinkers without cirrhosis. Noncirrhotic alcoholics were assigned to two groups with either normal aspartate aminotransferase or levels ≥2 normal. Collagens VI and XIV were elevated in all alcoholic patients compared to controls (P < 0.0001, all instances). Procollagen-III-N-propeptide and hyaluronic acid levels were higher in alcoholic patients with elevated liver enzymes and in cirrhotics as compared to controls. Procollagen-III-N-propeptide revealed a significant correlation with serum levels of TGF-β1
(P < 0.0001). Collagens VI, and XIV, procollagen-III-N-propeptide, and hyaluronic acid appear to be sensitive markers indicating fibrotic transformation in alcoholics. The correlation between procollagen-III-N-propeptide and TGF-β1 emphasizes its role in hepatic fibrogenesis.

Renate Urbaschek

Papers

The microcirculation during endotoxemia

Endotoxin, endotoxin-neutralizing-capacity, sCD14, sICAM-1, and cytokines in patients with various degrees of alcoholic liver disease.

Kupffer cell function in host defense.

Species differences in Kupffer cells and endotoxin sensitivity.

Serum collagen type VI and XIV and hyaluronic acid as early indicators for altered connective tissue turnover in alcoholic liver disease.