Non-alcoholic steatohepatitis-associated hepatic fibrosis and hepatocellular carcinoma in a combined mouse model of genetic modification and dietary challenge

Mechanisms of tumor-associated macrophages affecting the progression of hepatocellular carcinoma

Tumor-associated macrophages (TAMs) are essential components of the immune cell stroma of hepatocellular carcinoma. TAMs originate from monocytic myeloid-derived suppressor cells, peripheral blood monocytes, and kupffer cells. The recruitment of monocytes to the HCC tumor microenvironment is facilitated by various factors, leading to their differentiation into TAMs with unique phenotypes. TAMs can directly activate or inhibit the nuclear factor-κB, interleukin-6/signal transducer and signal transducer and activator of transcription 3, Wnt/β-catenin, transforming growth factor-β1/bone morphogenetic protein, and extracellular signal-regulated kinase 1/2 signaling pathways in tumor cells and interact with other immune cells via producing cytokines and extracellular vesicles, thus affecting carcinoma cell proliferation, invasive and migratory, angiogenesis, liver fibrosis progression, and other processes to participate in different stages of tumor progression. In recent years, TAMs have received much attention as a prospective treatment target for HCC. This review describes the origin and characteristics of TAMs and their mechanism of action in the occurrence and development of HCC to offer a theoretical foundation for further clinical research of TAMs.

Spontaneous Occurrence of Various Types of Hepatocellular Adenoma in the Livers of Metabolic Syndrome-Associated Steatohepatitis Model TSOD Mice

Male Tsumura-Suzuki Obese Diabetes (TSOD) mice, a spontaneous metabolic syndrome model, develop non-alcoholic steatohepatitis and liver tumors by feeding on a standard mouse diet. Nearly 70% of liver tumors express glutamine synthetase (GS), a marker of hepatocellular carcinoma. In contrast, approximately 30% are GS-negative without prominent nuclear or structural atypia. In this study, we examined the characteristics of the GS-negative tumors of TSOD mice. Twenty male TSOD mice were sacrificed at 40 weeks and a total of 21 tumors were analyzed by HE staining and immunostaining of GS, liver fatty acid-binding protein (L-FABP), serum amyloid A (SAA), and beta-catenin. With immunostaining for GS, six (29%) tumors were negative. Based on the histological and immunohistological characteristics, six GS-negative tumors were classified into several subtypes of human hepatocellular adenoma (HCA). One large tumor showed generally similar findings to inflammatory HCA, but contained small atypical foci with GS staining and partial nuclear beta-catenin expression suggesting malignant transformation. GS-negative tumors of TSOD mice contained features similar to various subtypes of HCA. Different HCA subtypes occurring in the same liver have been reported in humans; however, the diversity of patient backgrounds limits the ability to conduct a detailed, multifaceted analysis. TSOD mice may share similar mechanisms of HCA development as in humans. It is timely to review the pathogenesis of HCA from both genetic and environmental perspectives, and it is expected that TSOD mice will make further contributions in this regard.

A trans fatty acid substitute enhanced development of liver proliferative lesions induced in mice by feeding a choline-deficient, methionine-lowered, L-amino acid-defined, high-fat diet

Background

Nonalcoholic steatohepatitis (NASH) is a form of liver disease characterized by steatosis, necroinflammation, and fibrosis, resulting in cirrhosis and cancer. Efforts have focused on reducing the intake of trans fatty acids (TFAs) because of potential hazards to human health and the increased risk for NASH. However, the health benefits of reducing dietary TFAs have not been fully elucidated. Here, the effects of TFAs vs. a substitute on NASH induced in mice by feeding a choline-deficient, methionine-lowered, L-amino acid-defined, high-fat diet (CDAA-HF) were investigated.

Methods

Mice were fed CDAA-HF containing shortening with TFAs (CDAA-HF-T(+)), CDAA-HF containing shortening without TFAs (CDAA-HF-T(−)), or a control chow for 13 or 26 weeks.

Results

At week 13, NASH was induced in mice by feeding CDAA-HF-T(+) containing TFAs or CDAA-HF-T(−) containing no TFAs, but rather mostly saturated fatty acids (FAs), as evidenced by elevated serum transaminase activity and liver changes, including steatosis, inflammation, and fibrosis. CDAA-HF-T(−) induced a greater extent of hepatocellular apoptosis at week 13. At week 26, proliferative (preneoplastic and non-neoplastic) nodular lesions were more pronounced in mice fed CDAA-HF-T(−) than CDAA-HF-T(+).

Conclusions

Replacement of dietary TFAs with a substitute promoted the development of proliferation lesions in the liver of a mouse NASH model, at least under the present conditions. Attention should be paid regarding use of TFA substitutes in foods for human consumption, and a balance of FAs is likely more important than the particular types of FAs.

Supplementary Information

The online version contains supplementary material available at 10.1186/s12944-020-01423-3.

[Involvement of the Free Fatty Acid Receptor GPR120/FFAR4 in the Development of Nonalcoholic Steatohepatitis]

Nonalcoholic fatty liver disease (NAFLD) is characterized by the pathological accumulation of fat in the liver in the absence of any other disease related to liver steatosis, which includes a wide spectrum ranging from mild asymptomatic fatty liver to nonalcoholic steatohepatitis (NASH) and cirrhosis. However, the pathogenesis of NASH has not been established. In this study, we investigated the involvement of the G-protein-coupled receptor 120/free fatty acid receptor 4 (GPR120/FFAR4) in the pathogenesis of NASH. Mice fed a 0.1% methionine- and choline-deficient l-amino acid-defined, high-fat (CDAHF) diet showed a significant increase in plasma aspartate aminotransferase and alanine aminotransferase levels, fatty deposition, inflammatory cell infiltration, and slight fibrosis. Docosahexanoic acid (DHA, a GPR120/FFAR4 agonist) suppressed the inflammatory cytokines in hepatic tissues and prevented liver fibrosis. On the other hand, GPR120/FFAR4-deficient CDAHF-fed mice showed increments in the number of hepatic crown-like structures and immunoreactivity to F4/80-positive cells compared with wild-type mice. Furthermore, the levels of hepatic TNF-α mRNA expression increased in GPR120-deficient mice. These findings suggest that the GPR120/FFAR4-mediating system could be a key signaling pathway to prevent the development of NASH. In this review, we describe our recent data showing that GPR120/FFAR4 could be a therapeutic target in NASH/NAFLD.

Disease Progression and Pharmacological Intervention in a Nutrient-Deficient Rat Model of Nonalcoholic Steatohepatitis

BACKGROUND

There is a marked need for improved animal models of nonalcoholic steatohepatitis (NASH) to facilitate the development of more efficacious drug therapies for the disease.

METHODS

Here, we investigated the development of fibrotic NASH in male Wistar rats fed a choline-deficient L-amino acid-defined (CDAA) diet with or without cholesterol supplementation for subsequent assessment of drug treatment efficacy in NASH biopsy-confirmed rats. The metabolic profile and liver histopathology were evaluated after 4, 8, and 12 weeks of dieting. Subsequently, rats with biopsy-confirmed NASH were selected for pharmacological intervention with vehicle, elafibranor (30 mg/kg/day) or obeticholic acid (OCA, 30 mg/kg/day) for 5 weeks.

RESULTS

The CDAA diet led to marked hepatomegaly and fibrosis already after 4 weeks of feeding, with further progression of collagen deposition and fibrogenesis-associated gene expression during the 12-week feeding period. Cholesterol supplementation enhanced the stimulatory effect of CDAA on gene transcripts associated with fibrogenesis without significantly increasing collagen deposition. Pharmacological intervention with elafibranor, but not OCA, significantly reduced steatohepatitis scores, and fibrosis-associated gene expression, however, was unable to prevent progression in fibrosis scores.

CONCLUSION

CDAA-fed rats develop early-onset progressive NASH, which offers the opportunity to probe anti-NASH compounds with potential disease-modifying properties.

Pharmacological evaluation of pioglitazone and candesartan cilexetil in a novel mouse model of non-alcoholic steatohepatitis, modified choline-deficient, amino acid-defined diet fed low-density lipoprotein receptor knockout mice

AIM

Low-density lipoprotein receptor knockout (LDLR-KO) mice fed a modified choline-deficient and amino acid-defined (mCDAA) diet show non-alcoholic steatohepatitis (NASH)-like pathophysiology. In order to pharmacologically benchmark this model, effects of pioglitazone (a thiazolidinedione) and candesartan cilexetil (an angiotensin II type 1 receptor blocker) on steatosis and liver fibrosis were examined.

METHODS

Pioglitazone (10 mg/kg) and candesartan cilexetil (3 mg/kg) were given orally once daily to LDLR-KO mice under mCDAA diet for 7 weeks. Blood biochemistry and hepatic histology were assessed, and hepatic gene expression levels and triglyceride content were measured.

RESULTS

Pioglitazone suppressed hepatic COL1A1 gene expression by 43% and attenuated hepatic fibrosis areas by 49%. Pioglitazone also decreased plasma alanine aminotransferase levels, liver weight, hepatic triglyceride content, and hepatic expression of other fibrosis-related genes such as TGFB1, SPP1, TIMP1, and IL6. Candesartan cilexetil suppressed hepatic COL1A1 gene expression by 33%, whereas the other end-points including hepatic fibrosis areas were not affected.

CONCLUSIONS

Pioglitazone showed anti-fibrotic effects accompanied by improving hepatic transaminase activity and hepatic lipid accumulation, but the effect of candesartan cilexetil was only limited, unlike previous reports for angiotensin II type 1 receptor blockers. As the pharmacological effects of pioglitazone in the current animal model are similar to those reported in patients with NASH, this model may represent some aspects of the pathophysiology of NASH. Further profiling using other agents or mechanisms that have been tested in the clinic will better clarify the utility of the animal model.