No abstract

Results of animal experiments suggest that consumption of refined carbohydrates (e.g. fructose) can result in small intestinal bacterial overgrowth and increased intestinal permeability, thereby contributing to the development of nonalcoholic fatty liver disease (NAFLD). Furthermore, increased plasminogen activator inhibitor (PAI)-1 has been linked to liver damage of various etiologies (e.g. alcohol, endotoxin, nonalcoholic). The aim of the present pilot study was to compare dietary factors, endotoxin, and PAI-1 concentrations between NAFLD patients and controls. We assessed the dietary intake of 12 patients with NAFLD and 6 control subjects. Plasma endotoxin and PAI-1 concentrations as well as hepatic expression of PAI-1 and toll-like receptor (TLR) 4 mRNA were determined. Despite similar total energy, fat, protein, and carbohydrate intakes, patients with NAFLD consumed significantly more fructose than controls. Endotoxin and PAI-1 plasma concentrations as well as hepatic TLR4 and PAI-1 mRNA expression of NAFLD patients were significantly higher than in controls. The plasma PAI-1 concentration was positively correlated with the plasma endotoxin concentration (Spearman r = 0.83; P < 0.005) and hepatic TLR4 mRNA expression (Spearman r = 0.54; P < 0.05). Hepatic mRNA expression of PAI-1 was positively associated with dietary intakes of carbohydrates (Spearman r = 0.67; P < 0.01), glucose (Spearman r = 0.58; P < 0.01), fructose (Spearman r = 0.58; P < 0.01), and sucrose (Spearman r = 0.70; P < 0.01). In conclusion, our results suggest that dietary fructose intake, increased intestinal translocation of bacterial endotoxin, and PAI-1 may contribute to the development of NAFLD in humans.

No abstract

The intestinal microbiota is involved in many physiological processes and it is increasingly recognized that differences in community composition can influence the outcome of a variety of murine models used in biomedical research. In an effort to describe and account for the variation in intestinal microbiota composition across the animal facilities of participating members of the DFG Priority Program 1656 "Intestinal Microbiota", we performed a survey of C57BL/6J mice from 21 different mouse rooms/facilities located at 13 different institutions across Germany. Fresh feces was sampled from five mice per room/facility using standardized procedures, followed by extraction and 16S rRNA gene profiling (V1-V2 region, Illumina MiSeq) at both the DNA and RNA (reverse transcribed to cDNA) level. In order to determine the variables contributing to bacterial community differences, we collected detailed questionnaires of animal husbandry practices and incorporated this information into our analyses. We identified considerable variation in a number of descriptive aspects including the proportions of major phyla, alpha- and beta diversity, all of which displayed significant associations to specific aspects of husbandry. Salient findings include a reduction in alpha diversity with the use of irradiated chow, an increase in inter-individual variability (beta diversity) with respect to barrier access and open cages and an increase in bacterial community divergence with time since importing from a vendor. We further observe a high degree of facility-level individuality, which is likely due to each facility harboring its own unique combination of multiple varying attributes of animal husbandry. While it is important to account and control for such differences between facilities, the documentation of such diversity may also serve as a valuable future resource for investigating the origins of microbial-driven host phenotypes.

The consumption of a Western-style diet (WSD) and high fructose intake are risk factors for metabolic diseases. The underlying mechanisms are largely unclear. To unravel the mechanisms by which a WSD and fructose promote metabolic disease, we investigated their effects on the gut microbiome and barrier function. Adult female C57BL/6J mice were fed a sugar- and fat-rich WSD or control diet (CD) for 12 wk and given access to tap water or fructose-supplemented water. The microbiota was analyzed with the use of 16S rRNA gene sequencing. Barrier function was studied with the use of permeability tests, and endotoxin, mucus thickness, and gene expressions were measured. The WSD increased body weight gain but not endotoxin translocation compared with the CD. In contrast, high fructose intake increased endotoxin translocation 2.6- and 3.8-fold in the groups fed the CD + fructose and WSD + fructose, respectively, compared with the CD group. The WSD + fructose treatment also induced a loss of mucus thickness in the colon (-46%) and reduced defensin expression in the ileum and colon. The lactulose:mannitol ratio in the WSD + fructose mice was 1.8-fold higher than in the CD mice. Microbiota analysis revealed that fructose, but not the WSD, increased the Firmicutes:Bacteroidetes ratio by 88% for CD + fructose and 63% for WSD + fructose compared with the CD group. abundance was greater in the WSD mice than in the CD mice (63-fold) and in the WSD + fructose mice than in the CD + fructose mice (330-fold). The consumption of a WSD or high fructose intake differentially affects gut permeability and the microbiome. Whether these differences are related to the distinct clinical outcomes, whereby the WSD primarily promotes weight gain and high fructose intake causes barrier dysfunction, needs to be investigated in future studies.

Intestinal permeability is increased in obese patients with steatosis compared with obese patients without. The increased permeability fell to within the previously reported normal range after weight reduction. The data suggest that a leaky gut barrier is linked with liver steatosis and could be a new target for future steatosis therapies. This trial was registered at clinicaltrials.gov as NCT01344525.

Studies in animals and human subjects indicate that gut-derived bacterial endotoxins may play a critical role in the development of nonalcoholic fatty liver disease (NAFLD). In the present study, we investigated if the liver is also sensitised by other microbial components during the onset of fructose-induced steatosis in a mouse model. C57BL/6 mice were either fed with 30 % fructose solution or tap water (control) with or without antibiotics for 8 weeks. Expression of toll-like receptors (TLR)1-9, TNF-a, inducible NO synthase (iNOS), myeloid differentiation factor 88 (MyD88) and number of F4/80 positive cells in the liver were assessed. Occludin protein, DNA of microbiota in the small and large intestine and retinol binding protein 4 (RBP4) in plasma were analysed using Western blot, DNA fingerprinting and ELISA, respectively. F4/80 positive cells were determined by immunohistochemistry. The accumulation of TAG found in the livers of fructose-fed mice was associated with a significant induction of TLR 1 -4 and 6-8. Plasma RBP4 concentration and hepatic mRNA expression levels of TNF-a, iNOS, MyD88 and number of F4/80 positive cells of fructose-fed animals were significantly higher than those of controls; however, these effects of fructose were attenuated in antibiotic-treated mice. Whereas protein concentration of occludin was lower in the duodenum of fructose-treated mice, no systematic alterations of microbiota were found in this part of the intestine. Taken together, these data support the hypothesis that (1) an increased intestinal translocation of microbial components and (2) an increased number of F4/80 positive cells and induction of several TLR and dependent pathways (e.g. MyD88 and iNOS) may be involved in the onset of fructose-induced NAFLD.

Elevated dietary fructose intake, altered intestinal motility, and barrier function may be involved in the development of nonalcoholic fatty liver disease (NAFLD). Because intestinal motility and permeability are also regulated through the bioavailability of serotonin (5-HT), we assessed markers of hepatic injury in serotonin reuptake transporter knockout (SERT(-/-)) and wild-type mice chronically exposed to different monosaccharide solutions (30% glucose or fructose solution) or water for 8 wk. The significant increase in hepatic triglyceride, TNF-alpha, and 4-hydroxynonenal adduct as well as portal endotoxin levels found in fructose-fed mice was associated with a significant decrease of SERT and the tight-junction occludin in the duodenum. Similar effects were not found in mice fed glucose. In contrast, in SERT(-/-) mice fed glucose, portal endotoxin levels, concentration of occludin, and indices of hepatic damage were similar to those found in wild-type and SERT(-/-) mice fed fructose. In fructose-fed mice treated with a 5-HT3 receptor antagonist, hepatic steatosis was significantly attenuated. Our data suggest that a loss of intestinal SERT is a critical factor in fructose-induced impairment of intestinal barrier function and subsequently the development of steatosis.