Ina Bergheim

Toll‐like receptor 4 is involved in the development of fructose‐induced hepatic steatosis in mice

A link between dietary fructose intake, gut‐derived endotoxemia, and nonalcoholic fatty liver disease (NAFLD) has been suggested by the results of human and animal studies. To further investigate the role of gut‐derived endotoxin in the onset of fructose‐induced NAFLD, Toll‐like receptor (TLR‐) 4‐mutant (C3H/HeJ) mice and wildtype (C3H/HouJ) mice were either fed plain water or water enriched with 30% fructose for 8 weeks. Hepatic steatosis, plasma alanine aminotransferase (ALT), and markers of insulin resistance as well as portal endotoxin levels were determined. Hepatic levels of myeloid differentiation factor 88 (MyD88), interferon regulatory factor (IRF) 3 and 7, and tumor necrosis factor alpha (TNFα) as well as markers of lipid peroxidation were assessed. Chronic intake of 30% fructose solution caused a significant increase in hepatic steatosis and plasma ALT levels in wildtype animals in comparison to water controls. In fructose‐fed TLR‐4 mutant mice, hepatic triglyceride accumulation was significantly reduced by ≈40% in comparison to fructose‐fed wildtype mice and plasma ALT levels were at the level of water‐fed controls. No difference in portal endotoxin concentration between fructose‐fed wildtype and TLR‐4‐mutant animals was detected. In contrast, hepatic lipid peroxidation, MyD88, and TNFα levels were significantly decreased in fructose‐fed TLR‐4‐mutant mice in comparison to fructose‐fed wildtype mice, whereas IRF3 and IRF7 expression remained unchanged. Markers of insulin resistance (e.g., plasma TNFα, retinol binding protein 4, and hepatic phospho‐AKT) were only altered in fructose‐fed wildtype animals. Conclusion: Taken together, these data further support the hypothesis that in mice the onset of fructose‐induced NAFLD is associated with intestinal bacterial overgrowth and increased intestinal permeability, subsequently leading to an endotoxin‐dependent activation of hepatic Kupffer cells. (HEPATOLOGY 2009.)

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

BACKGROUND/AIMSnConsumption 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.nnnMETHODSnFor 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.nnnRESULTSnTotal 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.nnnCONCLUSIONSnThese 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.

Dietary fructose and intestinal barrier: potential risk factor in the pathogenesis of nonalcoholic fatty liver disease

Worldwide, not only the prevalence of obesity has increased dramatically throughout the last three decades but also the incidences of co-morbid conditions such as diabetes type 2 and liver disease have increased. The hepatic manifestation of the metabolic syndrome is called nonalcoholic fatty liver disease (NAFLD) and comprises a wide spectrum of stages of liver disease ranging from simple steatosis to liver cirrhosis. NAFLD of different stages is found in approximately 30% of adults and approximately 20% in the US population. Not just a general overnutrition but also an elevated intake of certain macronutrients such as fat and carbohydrates and herein particularly fructose has been claimed to be risk factors for the development for NAFLD; however, the etiology of this disease is still unknown. The present review outlines some of the potential mechanisms associated with the development of NAFLD and fructose intake with a particular focus on the role of the intestinal barrier functions.

Role of tumor necrosis factor α (TNFα) in the onset of fructose-induced nonalcoholic fatty liver disease in mice

Tumor necrosis factor α (TNFα) is known to be involved in dysregulation of hepatic lipid metabolism and insulin signaling. However, whether TNFα also plays a casual role in the onset of fructose-induced nonalcoholic fatty liver disease (NAFLD) has not yet been determined. Therefore, wild-type and TNFα receptor 1 (TNFR1)-/- mice were fed with either 30% fructose solution or plain tap water. Hepatic triglycerides, markers of inflammation and ATP concentration as well as plasma ALT levels were determined. Hepatic PAI-1, SREBP-1, FAS mRNA expression was assessed by real-time RT-PCR. Furthermore, lipid peroxidation and indices of insulin resistance were determined in liver tissue and plasma. In comparison to water controls, chronic intake of 30% fructose solution caused a significant ∼5-fold increase in triglyceride accumulation and neutrophil infiltration in livers of wild-type mice and a ∼8-fold increase in plasma ALT levels. In TNFR1-/- mice, hepatic steatosis was attenuated and neutrophil infiltration in the liver as well as plasma ALT levels was similar to water controls. The protective effect of the TNFR1 deletion against the onset of fructose-induced steatosis was associated with increased phospho AMPK and Akt levels, decreased SREBP-1 and FAS expression in the liver and decreased RBP4 plasma levels, whereas hepatic lipid peroxidation, iNOS protein and ATP levels were similar between wild-type and TNFR1-/- mice fed fructose. Taken together, these data suggest that TNFα plays a casual role in the onset of fructose-induced liver damage as well as insulin resistance in mice through signaling cascades downstream of TNFR1.

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.

Metformin Prevents Endotoxin-Induced Liver Injury after Partial Hepatectomy

Metformin [2-(N,N-dimethylcarbamimidoyl)guanidine] is a drug used in the treatment of type 2 diabetes. Recent studies have suggested that metformin may have effects in addition to lowering serum glucose concentrations (e.g., anti-inflammatory). The aim of the present study was to determine whether metformin prevents the inflammatory reaction and liver damage in a model of postsurgical sepsis. Accordingly, rats underwent 2/3 partial hepatectomy (PH; or sham surgery); 48 h after surgery, animals were administered endotoxin (LPS; 1.5 mg/kg i.v.). Both PH and LPS alone caused some minor liver damage. However, their combined effect (PH/LPS) was synergistic, leading to robust hepatic damage, as indicated by plasma enzymes and histological assessment. Although metformin treatment did not alter changes caused by PH alone, it almost completely blunted the effects of LPS in the PH/LPS group. Increases in biomarkers of inflammation (e.g., interleukin 6, interferon γ, and neutrophil number) were also blunted by metformin treatment. Furthermore, PH/LPS caused a >200× increase in hepatic plasminogen activator inhibitor 1 (PAI-1) mRNA expression and plasma PAI-1 protein. These increases were associated with inhibition of hepatic urokinase plasminogen activator activity and an increase in fibrin deposition, indicative of local thrombosis. These effects were markedly reduced by metformin treatment. In conclusion, these data demonstrate that metformin prevents liver damage in a model of postsurgical sepsis in rats by decreasing proinflammatory and hemostatic responses.

Lactobacillus casei Shirota protects from fructose-induced liver steatosis: a mouse model.

To test the hypothesis that Lactobacillus casei Shirota (Lcs) protects against the onset of non-alcoholic fatty liver disease (NAFLD) in a mouse model of fructose-induced steatosis, C57BL/6J mice were either fed tap water or 30% fructose solution +/- Lcs for 8 weeks. Chronic consumption of 30% fructose solution led to a significant increase in hepatic steatosis as well as plasma alanine-aminotransferase (ALT) levels, which was attenuated by treatment with Lcs. Protein levels of the tight junction protein occludin were found to be markedly lower in both fructose treated groups in the duodenum, whereas microbiota composition in this part of the intestine was not affected. Lcs treatment markedly attenuated the activation of the Toll-like receptor (TLR) 4 signalling cascade found in the livers of mice only treated with fructose. Moreover, in livers of fructose fed mice treated with Lcs peroxisome proliferator-activated receptor (PPAR)-γ activity was markedly higher than in mice only fed fructose. Taken together, the results of the present study suggest that the dietary intake of Lcs protects against the onset of fructose-induced NAFLD through mechanisms involving an attenuation of the TLR-4-signalling cascade in the liver.

Treatment of Alcoholic Liver Disease

Alcoholic liver disease (ALD) remains a major cause of morbidity and mortality worldwide. For example, the Veterans Administration Cooperative Studies reported that patients with cirrhosis and superimposed alcoholic hepatitis had a 4-year mortality of >60% (worse than many common cancers such as breast and prostate). The cornerstone for therapy for ALD is lifestyle modification, including drinking cessation and treatment of decompensation, if appropriate. Nutrition intervention has been shown to play a positive role on both an in-patient and out-patient basis. Corticosteroids are effective in selected patients with alcoholic hepatitis, and treatment with pentoxifylline appears to be a promising anti-inflammatory therapy. Recent studies have indicated anti-TNFα therapy, at least for alcoholic hepatitis. Some complementary and alternative medicinal agents, such as milk thistle and S-adenosylmethionine, may be effective in alcoholic cirrhosis. Treatment of the complications of ALD can improve the quality of life and, in some cases, decrease short-term mortality.