A novel diet-induced murine model of steatohepatitis with fibrosis for screening and evaluation of drug candidates for nonalcoholic steatohepatitis

Albumin-fused thioredoxin ameliorates high-fat diet-induced non-alcoholic steatohepatitis

The pathogenesis of non-alcoholic steatohepatitis (NASH) involves the simultaneous interaction of multiple factors such as lipid accumulation, oxidative stress, and inflammatory response. Here, the effect of human serum albumin (HSA) fused to thioredoxin (Trx) on NASH was investigated. Trx is known to have anti-oxidative, anti-inflammatory, and anti-apoptotic effects. However, Trx is a low molecular weight protein and is rapidly eliminated from the blood. To overcome the low availability of Trx, HSA-Trx fusion protein was produced and evaluated the therapeutic effect on high-fat diet (HFD)-induced NASH model mice. HSA-Trx administered before the formation of NASH pathology showed it to have a preventive effect. Specifically, HSA-Trx was found to prevent the pathological progression to NASH by suppressing lipid accumulation, liver injury markers, and liver fibrosis. When HSA-Trx was administered during the early stage of NASH there was a marked reduction in lipid accumulation, inflammation, and fibrosis in the liver, indicating that HSA-Trx ameliorates NASH pathology. The findings indicate that HSA-Trx influences multiple pathological factors, such as oxidative stress, inflammation, and apoptosis, to elicit a therapeutic benefit. HSA-Trx also inhibited palmitic acid-induced lipotoxicity in HepG2 cells. Taken together, these results indicate that HSA-Trx has potential as a therapeutic agent for NASH pathology.

A New Non-Obese Steatohepatitis Mouse Model with Cardiac Dysfunction Induced by Addition of Ethanol to a High-Fat/High-Cholesterol Diet

Non-obese metabolic dysfunction-associated steatotic liver disease (MASLD) has been associated with cardiovascular-related mortality, leading to a higher mortality rate compared to the general population. However, few reports have examined cardiovascular events in non-obese MASLD mouse models. In this study we created a mouse model to mimic this condition. In this study involving seven-week-old C57BL/6J male mice, two dietary conditions were tested: a standard high-fat/high-cholesterol diet (STHD-01) and a combined diet of STHD-01 and ethanol. Over periods of 6 and 12 weeks, we analyzed the effects on liver and cardiac tissues using various staining techniques and PCR. Echocardiography and blood tests were also performed to assess cardiac function and liver damage. The results showed that mice on the ethanol-supplemented STHD-01 diet developed signs of steatohepatitis and cardiac dysfunction, along with increased sympathetic activity, as early as 6 weeks. At 12 weeks, more pronounced exacerbations accompanied with cardiac dilation, advanced liver fibrosis, and activated myocardial fibrosis with sympathetic activation were observed. This mouse model effectively replicated non-obese MASLD and cardiac dysfunction over a 12-week period using a combined diet of STHD-01 and ethanol. This dietary approach highlighted that both liver inflammation and fibrosis, as well as cardiac dysfunction, could be significantly worsened due to the activation of the sympathetic nervous system. Our results indicate that alcohol, even when completely metabolized on the day of drinking, exacerbates the progression of non-obese MASLD and cardiac dysfunction.

Neonatal streptozotocin treatment rapidly causes different subtype of hepatocellular carcinoma without persistent hyperglycemia in 4CS mice fed on a normal diet

Although diabetes mellitus (DM) is a well-known risk factor for hepatocellular carcinoma (HCC), the underlying mechanisms have not yet to be defined. We previously reported that DIAR mice fed with standard murine diet developed type 1 diabetes and HCC at age of 16 weeks old with a neonatal streptozotocin treatment (n-STZ). Because DIAR mice did not manifest obesity nor develop steatohepatitis, hyperglycemia with streptozotocin trigger or streptozotocin alone might turn on the hepato-carcinogenesis. An insulin-recruitment to DIAR-nSTZ mice showed an increased frequency of HCC during the first 12 weeks of age, although the diabetic indications notably improved. To elucidate the role of hyperglycemia in hepato-carcinogenesis, we performed a head-to-head comparative study by using 4CS mice and DIAR mice with n-STZ treatment. Newborn 4CS mice and DIAR mice were divided into STZ treated group and control group. The blood glucose levels of DIAR-nSTZ mice increased at age of eight weeks, while that of 4CS-nSTZ mice were maintained in the normal range. At eight weeks old, three out of five DIAR-nSTZ mice (60%) and one out of ten 4CS-nSTZ mice (10%) developed multiple liver tumors. At age of 12 weeks old, all eight of DIAR-nSTZ mice (100%) and two of 10 4CS-nSTZ mice (20%) developed multiple liver tumors. At 16 weeks old, all animals of DIAR-nSTZ and 4CS-nSTZ mice occurred liver tumors. DIAR-nSTZ showed hyperglycemia and HCC, and 4CS-nSTZ developed HCC without hyperglycemia. These results were interpreted that the onset of HCC maybe not related to the presence or absence of hyperglycemia but nSTZ treatment. On the other hand, since the carcinogenesis of 4CS-nSTZ is delayed compared to DIAR-nSTZ, hyperglycemia may play a role in the progression of carcinogenesis. Histologically, the liver tumor appeared irregularly trabecular arrangements of hepatocytes with various degrees of nuclear atypia. By immunohistochemical analyses, all liver tumors showed positive staining of glutamine synthetase (GS), an established human HCC marker. The expression pattern of GS was divided into a strong diffuse pattern and weak patchy pattern, respectively. The liver tumor showing the weak GS-patchy pattern expressed biliary/stem markers, EpCAM, and SALL4, partially. Because 4CS-nSTZ mice did not show any metabolic complications such as gaining body weight or high blood glucose level, it is a unique animal model with a simple condition to investigate hepatic carcinogenesis by excluding other factors.

Alleviation of colonic inflammation by Lypd8 in a mouse model of inflammatory bowel disease

Dysfunction of the intestinal mucosal barrier causes inflammatory bowel diseases (IBDs). Indeed, mucosal barrier impairment in the gut of IBD patients results from decreased expression of barrier molecules. Ly6/Plaur domain containing 8 (Lypd8) segregates microbiota from the colonic epithelial layer. In this study, we found that Lypd8-/- mice, in which flagellated bacteria invaded the mucosal surface of the colon, developed spontaneous colitis when dysbiosis was induced by a high-fat diet (HFD). On the basis of this finding, we assessed whether the application of human LYPD8 (hLYPD8) protein exhibiting the glycan-dependent inhibition of bacterial motility is effective in a colitis model. Oral and anal treatments with hLYPD8 protein ameliorate dextran sulfate sodium-induced colitis and HFD-induced colitis in Lypd8-/- mice. These results indicate a therapeutic potential of hLYPD8 protein supplementation for IBD.

A novel chicken model of fatty liver disease induced by high cholesterol and low choline diets

Fatty liver diseases, common metabolic diseases in chickens, can lead to a decrease in egg production and sudden death of chickens. To solve problems caused by the diseases, reliable chicken models of fatty liver disease are required. To generate chicken models of fatty liver, 7-week-old ISA female chickens were fed with a control diet (17% protein, 5.3% fat, and 1,300 mg/kg choline), a low protein and high fat diet (LPHF, 13% protein, 9.1% fat, and 1,300 mg/kg choline), a high cholesterol with low choline diet (CLC, 17% protein, 7.6% fat with additional 2% cholesterol, and 800 mg/kg choline), a low protein, high fat, high cholesterol, and low choline diet (LPHFCLC, 13% protein, 12.6% fat with additional 2% cholesterol, and 800 mg/kg choline) for 4 wk. Our data showed that the CLC and LPHFCLC diets induced hyperlipidemia. Histological examination and the content of hepatic lipids indicated that the CLC and LPHFCLC diets induced hepatic steatosis. Plasma dipeptidyl peptidase 4, a biomarker of fatty liver diseases in laying hens, increased in chickens fed with the CLC or LPHFCLC diets. Hepatic ballooning and immune infiltration were observed in these livers accompanied by elevated interleukin 1 beta and lipopolysaccharide induced tumor necrosis factor mRNAs suggesting that the CLC and LPHFCLC diets also caused steatohepatitis in these livers. These diets also induced hepatic steatosis in Plymouth Rock chickens. Thus, the CLC and LPHFCLC diets can be used to generate models for fatty liver diseases in different strains of chickens. In ISA chickens fed with the CLC diet, peroxisome proliferator-activated receptor γ, sterol regulatory element binding transcription factor 1, and fatty acid synthase mRNAs increased in the livers, suggesting that lipogenesis was enhanced by the CLC treatment. Our data show that treatment with CLC or LPHFCLC for 4 wk induces fatty liver disease in chickens. These diets can be utilized to rapidly generate chicken models for fatty liver research.

A novel model of non-alcoholic steatohepatitis with fibrosis and carcinogenesis in connexin 32 dominant-negative transgenic rats

Non-alcoholic steatohepatitis (NASH) is a recognized risk factor for liver fibrosis and malignancies, and is associated with features of metabolic syndrome, such as obesity and insulin resistance (IR). We previously demonstrated that the disturbance of connexin 32 (Cx32), a gap junctional protein of hepatocytes, exacerbated NASH in Cx32 dominant-negative transgenic (Cx32ΔTg) rats fed methionine choline-deficient diet (MCDD). MCDD is well-established means of inducing NASH in rodents; however, the Cx32ΔTg-MCDD NASH model does not reproduce obesity and IR. In this study, we aimed to establish an improved NASH model. Eight-week-old male Cx32ΔTg and wild-type (Wt) rats received a high-fat diet (HFD) with dimethylnitrosamine (DMN) for 12 weeks. The HFD with DMN led to gains in body, liver, and visceral fat weights in both genotypes. IR was significantly greater in Cx32ΔTg than in Wt rats. Elevation of serum hepatic enzymes (AST, ALT), inflammatory cytokine expressions (Tnfα, Il-6, Tgf-β1, Il-1β, Timp2, and Col1a1), steatohepatitis, and fibrosis were significantly greater in Cx32ΔTg as compared with Wt rats. Regarding carcinogenesis, the number and area of glutathione S-transferase placental form (GST-P)-positive preneoplastic hepatic foci were significantly increased in Cx32ΔTg versus Wt rats. Moreover, activation of NF-κB and JNK contributed to the progression of NASH in Cx32ΔTg rats. These results suggest that Cx32 dysfunction promoted the progression of NASH, metabolic syndrome, and carcinogenesis. Therefore, the novel Cx32ΔTg-HFD-DMN NASH model may be a rapid and useful tool for evaluating the progression of NASH.

[1,2,5]Oxadiazolo[3,4-b]pyrazine-5,6-diamine Derivatives as Mitochondrial Uncouplers for the Potential Treatment of Nonalcoholic Steatohepatitis

Small molecule mitochondrial uncouplers are emerging as a new class of molecules for the treatment of nonalcoholic steatohepatitis. We utilized BAM15, a potent protonophore that uncouples the mitochondria without depolarizing the plasma membrane, as a lead compound for structure-activity profiling. Using oxygen consumption rate as an assay for determining uncoupling activity, changes on the 5- and 6-position of the oxadiazolopyrazine core were introduced. Our studies suggest that unsymmetrical aniline derivatives bearing electron withdrawing groups are preferred compared to the symmetrical counterparts. In addition, alkyl substituents are not tolerated, and the N-H proton of the aniline ring is responsible for the protonophore activity. In particular, compound 10b had an EC₅₀ value of 190 nM in L6 myoblast cells. In an in vivo model of NASH, 10b decreased liver triglyceride levels and showed improvement in fibrosis, inflammation, and plasma ALT. Taken together, our studies indicate that mitochondrial uncouplers have potential for the treatment of NASH.

Outside the liver box: The gut microbiota as pivotal modulator of liver diseases

The gut microbiota affects host physiology and has evolved as an important contributor to health and disease. Gut and liver are closely connected and communicate via the portal vein and the biliary system so the liver is constantly exposed to gut-derived bacterial products and metabolites. The intestinal barrier is important for maintaining physical and functional separation between microbes in the gut and the interior of the host and disruption of the barrier function can lead to bacterial translocation and increased leakage of bacterial metabolites. Liver diseases have been associated with dysbiotic changes in the gut microbiota and impaired gut barrier integrity, thus a future strategy to treat liver disease may be to target the gut microbiota and thereby restore the gut barrier function. This review will summarize and discuss studies that have shown a link between the gut microbiota and liver disease with the main focus on non-alcoholic fatty liver disease and alcoholic liver disease.

Nrf2-mediated anti-oxidant effects contribute to suppression of non-alcoholic steatohepatitis-associated hepatocellular carcinoma in murine model

The exact mechanisms of hepatocellular carcinoma development in non-alcoholic steatohepatitis remain unclear. In this study, we used a new class of high-fat diet, which could induce hepatocellular carcinoma development without the use of general chemical carcinogens or knockout mice. We investigated the correlation between hepatocellular carcinoma and oxidative stress/anti-oxidant effects after depletion of the gut microbiota by treatment with antibiotics. Mice fed with the steatohepatitis-inducing high-fat diet (STHD-01) for 41 weeks developed hepatocellular carcinoma. Antibiotic-treatment in mice fed with STHD-01 significantly depleted the gut microbiota and significantly ameliorated liver injury/histology. The tumor numbers of hepatocellular carcinoma were dramatically decreased by the antibiotics-treatment. We analyzed the factors involved in oxidative stress and anti-oxidant effects. Oxidative stress was elevated in mice fed with STHD-01, whereas some anti-oxidant factors were significantly elevated after antibiotics treatment. These results suggest that the gut microbiota is a key factor in improving oxidative stress induced by STHD-01 feeding.

Bile acid metabolism regulated by the gut microbiota promotes non-alcoholic steatohepatitis-associated hepatocellular carcinoma in mice

Gut microbiota plays a significant role in the development of hepatocellular carcinoma (HCC) in non-alcoholic steatohepatitis (NASH). However, understanding of the precise mechanism of this process remains incomplete. A new class steatohepatitis-inducing high-fat diet (HFD), namely STHD-01, can promote the development of HCC without the administration of chemical carcinogens. Using this diet, we comprehensively analyzed changes in the gut microbiota and its metabolic functions during the development of HCC in NASH. Mice fed the STHD-01 developed NASH within 9 weeks. NASH further progressed into HCC by 41 weeks. Treatment with antibiotics significantly attenuated liver pathology and suppressed tumor development, indicating the critical role of the gut microbiota in tumor development in this model. Accumulation of cholesterol and bile acids in the liver and feces increased after feeding the mice with STHD-01. Treatment with antibiotics did not reverse these phenotypes. In contrast, accumulation of secondary bile acids was dramatically reduced after the treatment with antibiotics, suggesting the critical role of the gut microbiota in the conversion of primary bile acids to secondary bile acids. Secondary bile acids such as deoxycholic acid activated the mTOR, pathway in hepatocytes. Activation of mTOR was observed in the liver of mice fed STHD-01, and the activation was reduced when mice were treated with antibiotics. Collectively, bile acid metabolism by the gut microbiota promotes HCC development in STHD-01-induced NASH.

Gut microbiota-mediated generation of saturated fatty acids elicits inflammation in the liver in murine high-fat diet-induced steatohepatitis

Background

The gut microbiota plays crucial roles in the development of non-alcoholic steatohepatitis (NASH). However, the precise mechanisms by which alterations of the gut microbiota and its metabolism contributing to the pathogenesis of NASH are not yet fully elucidated.

Methods

Mice were fed with a recently reported new class of high-fat diet (HFD), steatohepatitis-inducing HFD (STHD)-01 for 9 weeks. The composition of the gut microbiota was analyzed by T-RFLP. Luminal metabolome was analyzed using capillary electrophoresis and liquid chromatography time-of-flight mass spectrometry (CE- and LC-TOFMS).

Results

Mice fed the STHD-01 developed NASH-like pathology within a short period. Treatment with antibiotics prevented the development of NASH by STHD-01. The composition of the gut microbiota and its metabolic activities were markedly perturbed in the STHD-01-fed mice, and antibiotic administration normalized these changes. We identified that long-chain saturated fatty acid and n-6 fatty acid metabolic pathways were significantly altered by STHD-01. Of note, the changes in gut lipidome caused by STHD-01 were mediated by gut microbiota, as the depletion of the gut microbiota could reverse the perturbation of these metabolic pathways. A saturated long-chain fatty acid, palmitic acid, which accumulated in the STHD-01 group, activated liver macrophages and promoted TNF-α expression.

Conclusions

Lipid metabolism by the gut microbiota, particularly the saturation of fatty acids, affects fat accumulation in the liver and subsequent liver inflammation in NASH.

Electronic supplementary material

The online version of this article (10.1186/s12876-017-0689-3) contains supplementary material, which is available to authorized users.

A novel diet-induced murine model of steatohepatitis with fibrosis for screening and evaluation of drug candidates for nonalcoholic steatohepatitis

Many animal models of nonalcoholic steatohepatitis have been reported. While these models exhibit mild onset of hepatitis and fibrosis, induction is often slow. For faster screening of drug candidates, there is a compelling need for convenient animal models of steatohepatitis and nonalcoholic steatohepatitis in which fatty liver and hepatitis are stably induced within a short period. Here, we analyzed the hepatic lipid composition in nonalcoholic steatohepatitis, and used this information to successfully establish a murine model where steatohepatitis is induced within only 1 week using a novel diet (steatohepatitis‐inducing high‐fat diet, STHD‐01) high in saturated fatty acids and cholesterol. After receiving STHD‐01 for 1 week, normal mice (C57BL/6J) showed elevated markers of fatty liver and hepatitis, including hepatic triglycerides and plasma alanine aminotransferase; the administration of angiotensin receptor blockers reduced these symptoms. Furthermore, we confirmed that STHD‐01 administration for 36 weeks induced not only sustained elevation of hepatic triglyceride and plasma alanine aminotransferase levels, but also fibrosis and tumor formation. Pretreatment with the carcinogen diethylnitrosamine accelerated tumor formation, and hepatic lesions were observed within 30 weeks of STHD‐01 feeding following diethylnitrosamine pretreatment. Finally, branched‐chain amino acids, known to reduce the risk for hepatocellular carcinoma in preclinical models, were effective in reducing the progression of liver fibrosis induced by STHD‐01 feeding after diethylnitrosamine pretreatment. We concluded that STHD‐01 administration successfully induces steatohepatitis within a short period of time. The proposed murine model is suitable for studying the long‐term effects of pharmaceutical agents targeting steatohepatitis, fibrosis, and tumor formation.