Microbial Butyrate Synthesis Indicates Therapeutic Efficacy of Azathioprine in IBD Patients.

BACKGROUND AND AIMS: The microbial ecosystem seems to be an important player for therapeutic intervenption in inflammatory bowel disease [IBD]. We assessed longitudinal microbiome changes in IBD patients undergoing therapy with either azathioprine [AZA] or anti-tumour necrosis factor [anti-TNF] antibodies. We predicted the metabolic microbial community exchange and linked it to clinical outcome. METHODS: Faecal and blood samples were collected from 65 IBD patients at baseline and after 12 and 30 weeks on therapy. Clinical remission was defined as Crohn's Disease Activity Index [CDAI] < 150 in Crohn´s disease [CD], partial Mayo score <2 in ulcerative colitis [UC], and faecal calprotectin values <150 µg/g and C-reactive protein <5 mg/dl. 16S rRNA amplicon sequencing was performed. To predict microbial community metabolic processes, we constructed multispecies genome-scale metabolic network models. RESULTS: Paired Bray-Curtis distance between baseline and follow-up time points was significantly different for UC patients treated with anti-TNF antibodies. Longitudinal changes in taxa composition at phylum level showed a significant decrease of Proteobacteria and an increase of Bacteroidetes in CD patients responding to both therapies. At family level, Lactobacilli were associated with persistent disease and Bacteroides abundance with remission in CD. In-silico simulations of microbial metabolite exchange predicted a 1.7-fold higher butyrate production capacity of patients in remission compared with patients without remission [p = 0.041]. In this model, the difference in butyrate production between patients in remission and patients without remission was most pronounced in the CD group treated with AZA [p = 0.008]. CONCLUSIONS: In-silico simulation identifies microbial butyrate synthesis predictive of therapeutic efficacy in IBD.

Targeting T and B lymphocytes in inflammatory bowel diseases: lessons from clinical trials.

Both innate and adaptive immunity play an important role in the pathogenesis of inflammatory bowel diseases (IBDs). There is strong evidence that especially activated T cells initiate and perpetuate inflammation and tissue destruction. The increased numbers of CD4+ T cells in the intestinal wall of IBD patients may be explained by enhanced influx/activation and decreased apoptosis of these cells. Several studies have demonstrated that the gut-homing receptors CCR9 and α4ß7 are selectively induced on T cells during their priming in intestinal inflamed sites. Whereas targeting of activated CD4+ T cells by specific antibody strategies or neutralization of key T-cell cytokines such as IL-2 or IFN-γ has not been effective in human IBD, blocking migration of activated leukocytes, e.g. T cells into the inflamed tissue by specific antibodies such as vedolizumab, seems highly effective. Recently it could also been demonstrated that administration of antigen-specific regulatory T cells to patients with refractory Crohn's disease was not only well tolerated but showed promising results. The role of B cells in human IBD is less clear. B-cell depletion has so far only been studied in ulcerative colitis where rituximab (anti-CD20) therapy failed. Therefore, although the therapeutic targeting of 'inflammatory' T and B cells was not successful in IBD, especially T cells remain key players in IBD. Targeting either T-cell migration or the use of regulatory T cells appears as the most promising 'T-cell-directed' therapies in the future.

Liver complications in inflammatory bowel diseases.

Diseases of the liver and the biliary tract are commonly observed in patients with inflammatory bowel diseases (IBD). Besides primary sclerosing cholangitis (PSC), drug-induced hepatotoxicity and non-alcoholic fatty liver disease (NAFLD) are the most frequent liver complications in IBD. PSC is a chronic inflammatory and commonly progressive disorder of unknown etiology associated with fibrosis and stricture development in the intrahepatic and extrahepatic biliary tree. Interestingly, this form of liver disease is mainly associated with ulcerative colitis. Development of PSC is highly relevant for IBD patients as cholestasis-associated problems increase over time resulting in biliary strictures, cholangitis, cholangiocarcinoma and importantly these patients also have a higher risk to develop colon cancer. Another major aspect regarding IBD and liver disease refers to drug-induced hepatotoxicity. Clinically, most relevant is liver toxicity caused by immunosuppressants such as azathioprine. Azathioprine and its derivate 6-mercaptopurine can cause a spectrum of liver injuries ranging from asymptomatic elevated liver enzymes to cholestasis and nodular regenerative hyperplasia. The third common IBD-associated liver disease is NAFLD, and first studies suggest that NAFLD might appear in IBD patients independent of classical risk factors such as obesity or insulin resistance. Overall, liver complications are observed in 10-20% of IBD patients, and therefore physicians have to be familiar with these complications to improve and to optimize patient care.

Adiponectin: key player in the adipose tissue-liver crosstalk.

The adipose tissue has recently emerged as an important endocrine organ releasing numerous mediators including adipocytokines, classical cytokines and others. Adiponectin, one of the major products of adipocytes, is a prototypic anti-diabetic adipocytokine, the actions of which are mainly exerted by the activation of AMP-activated kinase and peroxisome proliferator-activated receptor alpha. This adipocytokine is one of the most abundant circulating (adipo)cytokines in health. Non-alcoholic fatty liver disease (NAFLD), the major reason for abnormal liver functions in the western world, is commonly associated with obesity, insulin resistance and decreased adiponectin serum levels. Adiponectin has many anti-inflammatory activities and suppresses tumour necrosis factor-alpha (TNFα), a cytokine of key importance in NAFLD. The anti-inflammatory effects of adiponectin are also exerted by induction of the anti-inflammatory cytokines interleukin-10 (IL-10) or IL-1 receptor antagonist and up-regulation of heme-oxygenase-1. Whereas the liver probably is not a relevant source of circulating adiponectin, it is a major target organ for many adiponectin effects. Adiponectin is able to regulate steatosis, insulin resistance, inflammation and fibrosis. NAFLD is also associated with decreased liver expression of the two adiponectin receptors (AdipoR1 and 2) thereby contributing to a state of hepatic adiponectin resistance. In contrast, most other liver diseases especially in advanced disease states exhibit increased adiponectin serum levels with highest levels observed in cirrhosis. Targeting adiponectin could evolve as a major treatment concept especially for fatty liver diseases in the future.

The role of apolipoprotein A5 in non-alcoholic fatty liver disease.

BACKGROUND: Apolipoprotein A5 (apoA5) is a recently described liver-specific protein that has been shown to influence triglyceride (TG) metabolism. ApoA5 transgenic mice display dramatically reduced TG levels, while in contrast apoA5 deficiency in humans was reported to result in marked hypertriglyceridemia. ApoA5 exerts its extracellular effects by increasing lipolysis of TG-rich lipoproteins, while in vitro data suggest additional intrahepatic effects. METHODS: In this study the authors set out to investigate a possible role of apoA5 in non-alcoholic fatty liver disease (NAFLD). We thus determined hepatic apoA5 expression in 15 obese subjects with histologically proven NAFLD undergoing bariatric surgery. In addition, the authors established a hepatic cell culture model of apoA5 knockdown by transfecting human hepatoma cells (HepG2) with apoA5 small interfering (si) RNA, and determined intracellular TG content and expression levels of key enzymes and transcription factors of intrahepatic lipid metabolism in these cells. RESULTS: Pronounced weight loss and associated histologically verified improvement of hepatic steatosis were accompanied by significant reductions of hepatic apoA5 mRNA expression levels. Significant apoA5 knockdown in HepG2 cells resulted in a marked decrease of intracellular TG content. When HepG2 cells were co-transfected with apoA5 and peroxisome proliferator-activated receptor gamma (PPARγ), reductions in hepatic TG accumulation were significantly less pronounced when compared to apoA5 siRNA transfected HepG2 cells. CONCLUSIONS: In obese subjects, hepatic apoA5 mRNA expression decreases after weight loss and improvements in hepatic steatosis. The authors' in vitro data demonstrate that apoA5 influences intrahepatic TG metabolism and that these intracellular effects of apoA5 are accompanied by changes in PPARγ mRNA expression. In summary, the data suggest that as well as several other factors, apoA5 might be involved in the pathogenesis of hepatic steatosis.

Gut, inflammation and osteoporosis: basic and clinical concepts.

Chronic inflammatory disorders such as inflammatory bowel diseases (IBD) affect bone metabolism and are frequently associated with the presence of osteoporosis. Bone loss is regulated by various mediators of the immune system such as the pro-inflammatory cytokines tumour necrosis factor-alpha (TNF-alpha), interleukin-1 beta (IL-1 beta), IL-6, or interferon-gamma. TNF-alpha, a master cytokine in human IBD, causes bone erosions in experimental models and these effects are exerted by osteoclasts. Other TNF-related cytokines such as receptor activator of nuclear factor kappa B (RANK), its ligand, RANKL, and osteoprotegerin are important mediators in inflammatory processes in the gut and are critically involved in the pathophysiology of bone loss. The awareness and early diagnosis of osteoporosis in states of chronic inflammation, together with applied therapies such as bisphosphonates, may be beneficial in inflammation-associated osteoporosis. Although several mechanisms may contribute to osteoporosis in patients with IBD and coeliac disease, inflammation as an important factor has so far been neglected. As key inflammatory mediators in IBD such as TNF-alpha are involved in the disease process both in gut and bone, we hypothesise that neutralisation of TNF-alpha could prove an efficient strategy in the treatment of inflammation-related osteoporosis in the future.

The RANKL/OPG system is activated in inflammatory bowel disease and relates to the state of bone loss.

BACKGROUND AND AIMS: A substantial proportion of patients with inflammatory bowel disease (IBD) develops osteopenia and osteoporosis in the course of disease. Recent data from a mouse model of colitis suggest that the receptor activator of nuclear factor kappa B (RANKL)/osteoprotegerin (OPG) system may be responsible for bone loss. METHODS: We investigated the activation state of the RANKL/OPG system and its association with bone loss in human IBD. Plasma levels of OPG and RANKL were correlated with bone mineral density and current IBD therapy. Colonic secretion of OPG and RANKL and cell types responsible for such secretion were determined. RESULTS: OPG plasma levels were elevated 2.4-fold in Crohn's disease (CD) and 1.9-fold in ulcerative colitis (UC) whereas soluble RANKL (sRANKL) levels were not significantly different in IBD patients compared with healthy controls. High levels of OPG were released from colonic explant cultures (CEC) derived from inflamed IBD specimens, and colonic macrophages and dendritic cells costained for OPG. sRANKL levels from CEC were low both in IBD patients and healthy controls. Interestingly, increased expression of RANKL was mainly confined to cells in the lamina muscularis. A significant negative correlation was found between OPG plasma levels and femoral neck/lumbar spine bone mineral density. CONCLUSIONS: We have demonstrated that IBD is associated with alterations in the RANKL/OPG system. Applying results from a murine model of colitis associated bone loss, the constellation of OPG and sRANKL regulation observed in our study raises the possibility that RANKL/OPG may contribute to the development of bone loss in IBD.