Valentina Volynets

Antibiotics protect against fructose-induced hepatic lipid accumulation in mice: Role of endotoxin

BACKGROUND/AIMS Consumption of refined carbohydrates in soft drinks has been postulated to be a key factor in the development of non-alcoholic fatty liver disease (NAFLD). The aim of the present study was to test the effects of ad libitum access to different sugars consumed in drinking water on hepatic fat accumulation. METHODS For 8 weeks, C57BL/J6 mice had free access to solutions containing 30% glucose, fructose, sucrose, or water sweetened with artificial sweetener (AS) or plain water. Body weight, caloric intake, hepatic steatosis and lipid peroxidation were assessed. RESULTS Total caloric intake and weight gain were highest in mice exposed to glucose. In contrast, hepatic lipid accumulation was significantly higher in mice consuming fructose compared to all other groups. Moreover, endotoxin levels in portal blood and lipid peroxidation as well as TNFalpha expression were significantly higher in fructose fed mice than in all other groups. Concomitant treatment of fructose fed mice with antibiotics (e.g., polymyxin B and neomycin) markedly reduced hepatic lipid accumulation in fructose fed mice. CONCLUSIONS These data support the hypothesis that high fructose consumption may not only lead to liver damage through overfeeding but also may be directly pro-inflammatory by increasing intestinal translocation of endotoxin.

Nutrition, Intestinal Permeability, and Blood Ethanol Levels Are Altered in Patients with Nonalcoholic Fatty Liver Disease (NAFLD)

BackgroundA role of an altered dietary pattern (e.g., a diet rich in sugar) but also alterations at the level of the intestinal barrier have repeatedly been discussed to be involved in the development and progression of nonalcoholic fatty liver disease (NAFLD).AimsTo determine if the nutritional intake, intestinal flora, and permeability and the development of NAFLD are related in humans.MethodsTen controls and 20 patients with NAFLD ranging from simple steatosis to steatohepatitis were included in the study. Bacterial overgrowth, orocecal transit time, and intestinal permeability were assessed. Alcohol, endotoxin, and plasminogen activator inhibitor (PAI-) 1 concentration were determined in plasma. Nutritional intake was assessed using a dietary history.ResultsDespite no differences in the prevalence of bacterial overgrowth and in the orocecal transit time, intestinal permeability, alcohol, and endotoxin levels in plasma were significantly higher in patients with NAFLD than in controls. Similar results were also found for PAI-1 plasma concentrations. Patients with NAFLD had a significantly higher intake of protein, total carbohydrates, and mono- as well as disaccharides than controls. PAI-1, endotoxin, and ALT plasma levels were positively related to total protein and carbohydrate intake.ConclusionsTaken together, our results indicate that intestinal permeability, endogenous alcohol synthesis, and nutritional intake are markedly altered in patients with NAFLD.

Toll-like receptors 1–9 are elevated in livers with fructose-induced hepatic steatosis

Studies in animals and human subjects indicate that gut-derived bacterial endotoxins may play a critical role in the development of non-alcoholic 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-α, 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-α, 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.

Cinnamon Extract Protects against Acute Alcohol-Induced Liver Steatosis in Mice

Acute and chronic consumption of alcohol can cause increased intestinal permeability and bacterial overgrowth, thereby increasing portal endotoxin levels. This barrier impairment subsequently leads to an activation of hepatic Kupffer cells and increased release of reactive oxygen species as well as of tumor necrosis factor-alpha (TNFalpha). Recent studies have suggested that cinnamon extract may have antiinflammatory effects. In the present study, the protective effects of an alcoholic extract of cinnamon bark was assessed in a mouse model of acute alcohol-induced steatosis and in RAW 264.7 macrophages, used here as a model of Kupffer cells. Acute alcohol ingestion caused a >20-fold increase in hepatic lipid accumulation. Pretreatment with cinnamon extract significantly reduced the hepatic lipid accumulation. This protective effect of cinnamon extract was associated with an inhibition of the induction of the myeloid differentiation primary response gene (MyD) 88, inducible nitric oxide (NO) synthase (iNOS), and plasminogen activator inhibitor 1 mRNA expression found in livers of alcohol-treated animals. In vitro prechallenge with cinnamon extract suppressed lipopolysaccharide (LPS)-induced MyD88, iNOS, and TNFalpha expression as well as NO formation almost completely. Furthermore, LPS treatment of RAW 264.7 macrophages further resulted in degradation of inhibitor kappaB; this effect was almost completely blocked by cinnamon extract. Taken together, our data show that an alcohol extract of cinnamon bark may protect the liver from acute alcohol-induced steatosis through mechanisms involving the inhibition of MyD88 expression.

Serotonin reuptake transporter (SERT) plays a critical role in the onset of fructose-induced hepatic steatosis in mice

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.

Protective effect of bile acids on the onset of fructose-induced hepatic steatosis in mice.

Fructose intake is being discussed as a key dietary factor in the development of nonalcoholic fatty liver disease (NAFLD). Bile acids have been shown to modulate energy metabolism. We tested the effects of bile acids on fructose-induced hepatic steatosis. In C57BL/6J mice treated with a combination of chenodeoxycholic acid and cholic acid (100 mg/kg body weight each) while drinking water or a 30% fructose solution for eight weeks and appropriate controls, markers of hepatic steatosis, portal endotoxin levels, and markers of hepatic lipogenesis were determined. In mice concomitantly treated with bile acids, the onset of fructose-induced hepatic steatosis was markedly attenuated compared to mice only fed fructose. The protective effects of the bile acid treatment were associated with a downregulation of tumor necrosis factor (TNF)α, sterol regulatory element-binding protein (SREBP)1, FAS mRNA expression, and lipid peroxidation in the liver, whereas hepatic farnesoid X receptor (FXR) or short heterodimer partner (SHP) protein concentration did not differ between groups fed fructose. Rather, bile acid treatment normalized occludin protein concentration in the duodenum, portal endotoxin levels, and markers of Kupffer cell activation to the level of water controls. Taken together, these data suggest that bile acids prevent fructose-induced hepatic steatosis in mice through mechanisms involving protection against the fructose-induced translocation of intestinal bacterial endotoxin.

Gut permeability is related to body weight, fatty liver disease, and insulin resistance in obese individuals undergoing weight reduction

BACKGROUND Obesity and associated metabolic disorders are related to impairments of the intestinal barrier. OBJECTIVE We examined lactulose:mannitol (Lac:Man) permeability in obese individuals with and without liver steatosis undergoing a weight-reduction program to test whether an effective weight-loss program improves gut barrier function and whether obese patients with or without liver steatosis differ in this function. DESIGN Twenty-seven adult, nondiabetic individuals [mean ± SD body mass index (BMI; in kg/m2): 43.7 ± 5.2; 78% with moderate or severe liver steatosis] were included in the follow-up intervention study (n = 13 by month 12). All patients reduced their weight to a mean ± SD BMI of 36.4 ± 5.1 within 12 mo. We assessed barrier functions by the oral Lac:Man and the fecal zonulin tests. Insulin resistance was assessed by the homeostatic model assessment index (HOMA), and liver steatosis by sonography and the fatty liver index (FLI). RESULTS The Lac:Man ratio and circulating interleukin (IL) 6 concentration decreased during intervention from 0.080 (95% CI: 0.073, 0.093) to 0.027 (95% CI: 0.024, 0.034; P < 0.001) and from 4.2 ± 1.4 to 2.8 ± 1.6 pg/mL (P < 0.01), respectively. At study start, the Lac:Man ratio was higher in patients with moderate or severe steatosis than in those without any steatosis (P < 0.001). The Lac:Man ratio tended to correlate with HOMA (ρ = 0.55, P = 0.052), which correlated with FLI (ρ = 0.75, P < 0.01). A multiple-regression analysis led to a final model explaining FLI best through BMI, waist circumference, and the Lac:Man ratio. CONCLUSIONS 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.

Treatment with the 5-HT3 antagonist tropisetron modulates glucose-induced obesity in mice

Objective:Sugar consumption has increased markedly over the last few decades and parallels the dramatic increase in overweight and obesity. Data obtained from animal studies suggest that the intestinal serotonergic system and herein particularly the serotonin receptor 3 (5-HT3R) may be involved in sugar detection and short-term control of food intake. Using a mouse model, we tested the hypothesis that blocking 5-HT3R prevents the development of sugar-induced obesity.Design:For 8 weeks, C57BL/J6 mice were offered either water containing 30% glucose or plain water in addition to normal chow. The effect of oral treatment with the 5-HT3R antagonist, tropisetron (0.2 mg kg−1 body weight), on body weight and caloric intake was studied.Results:Total caloric intake and weight gain were significantly increased in mice fed glucose compared with the control group. Tropisetron treatment reduced intestinal motility and almost completely blocked weight gain associated with glucose feeding; however, total caloric intake was not affected. The effect of tropisetron was not associated with a decreased expression of the intestinal and hepatic glucose transporters, SGLT1 (sodium-dependent glucose cotransporter) and Glut2 (glucose transporter 2); instead, the expression of these transporters was slightly increased by the 5-HT3R antagonist. However, expressions of carbohydrate responsive element binding protein and fatty acid synthase, as well as triglyceride levels in the liver were only enhanced in mice fed glucose, but remained unchanged at the level of the control group when mice were treated concomitantly with tropisetron. At the same time, β-hydroxybutyrate dehydrogenase mRNA expression and plasma levels of ketone bodies were significantly increased.Conclusion:Our results suggest that 5-HT3R is a new target for the modulation of hepatic glucose metabolism and for the prevention of obesity.

Intestinal Barrier Function and the Gut Microbiome Are Differentially Affected in Mice Fed a Western-Style Diet or Drinking Water Supplemented with Fructose

Background: The consumption of a Western-style diet (WSD) and high fructose intake are risk factors for metabolic diseases. The underlying mechanisms are largely unclear.Objective: To unravel the mechanisms by which a WSD and fructose promote metabolic disease, we investigated their effects on the gut microbiome and barrier function.Methods: 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.Results: 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. Bifidobacterium 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).Conclusions: 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 barrier analysis by assessment of mucins, tight junctions, and α-defensins in healthy C57BL/6J and BALB/cJ mice

ABSTRACT The intestinal barrier is gaining increasing attention because it is related to intestinal homeostasis and disease. Different parameters have been used in the past to assess intestinal barrier functions in experimental studies; however most of them are poorly defined in healthy mice. Here, we compared a number of barrier markers in healthy mice, established normal values and correlations. In 48 mice (24 C57BL/6J, 24 BALB/cJ background), we measured mucus thickness, and expression of mucin-2, α-defensin-1 and -4, zonula occludens-1, occludin, junctional adhesion molecule-A, claudin-1, 2 and -5. We also analyzed claudin-3 and fatty acid binding protein-2 in urine and plasma, respectively. A higher expression of mucin-2 protein was found in the colon compared to the ileum. In contrast, the α-defensins-1 and -4 were expressed almost exclusively in the ileum. The protein expression of the tight junction molecules claudin-1, occludin and zonula occludens-1 did not differ between colon and ileum, although some differences occurred at the mRNA level. No age- or gender-related differences were found. Differences between C57BL/6J and BALB/cJ mice were found for α-defensin-1 and -4 mRNA expression, and for urine and plasma marker concentrations. The α-defensin-1 mRNA correlated with claudin-5 mRNA, whereas α-defensin-4 mRNA correlated with claudin-3 concentrations in urine. In conclusion, we identified a number of murine intestinal barrier markers requiring tissue analyses or measurable in urine or plasma. We provide normal values for these markers in mice of different genetic background. Such data might be helpful for future animal studies in which the intestinal barrier is of interest.