Innate immune regulatory networks in hepatic lipid metabolism. J Mol Med (Berl). 2019;97:593-604. [PMID: 30891617 DOI: 10.1007/s00109-019-01765-1]

COVID-19 and non-alcoholic fatty liver disease: Two intersecting pandemics

BACKGROUND

Initial evidence from China suggests that most vulnerable subjects to COVID-19 infection suffer from pre-existing illness, including metabolic abnormalities. The pandemic characteristics and high-lethality rate of COVID-19 infection have raised concerns about interactions between virus pathobiology and components of the metabolic syndrome.

METHODS

We harmonized the information from the recent existing literature on COVID-19 acute pandemic and mechanisms of damage in non-alcoholic fatty liver disease (NAFLD), as an example of chronic (non-communicable) metabolic pandemic.

RESULTS

COVID-19-infected patients are more fragile with underlying metabolic illness, including hypertension, cardiovascular disease, type 2 diabetes, chronic lung diseases (e.g. asthma, chronic obstructive pulmonary disease and emphysema) and metabolic syndrome. During metabolic abnormalities, expansion of metabolically active fat ('overfat condition') parallels chronic inflammatory changes, development of insulin resistance and accumulation of fat in configuring NAFLD. The deleterious interplay of inflammatory pathways chronically active in NAFLD and acutely in COVID-19-infected patients, can explain liver damage in a subgroup of patients and might condition a worse outcome in metabolically compromised NAFLD patients. In a subgroup of patients with NAFLD, the underlying liver fibrosis might represent an additional and independent risk factor for severe COVID-19 illness, irrespective of metabolic comorbidities.

CONCLUSIONS

NAFLD can play a role in the outcome of COVID-19 illness due to frequent association with comorbidities. Initial evidences suggest that increased liver fibrosis in NAFLD might affect COVID-19 outcome. In addition, long-term monitoring of post-COVID-19 NAFLD patients is advisable, to document further deterioration of liver damage. Further studies are required in this field.

Liver Steatosis, Gut-Liver Axis, Microbiome and Environmental Factors. A Never-Ending Bidirectional Cross-Talk

The prevalence of non-alcoholic fatty liver disease (NAFLD) is increasing worldwide and parallels comorbidities such as obesity, metabolic syndrome, dyslipidemia, and diabetes. Recent studies describe the presence of NAFLD in non-obese individuals, with mechanisms partially independent from excessive caloric intake. Increasing evidences, in particular, point towards a close interaction between dietary and environmental factors (including food contaminants), gut, blood flow, and liver metabolism, with pathways involving intestinal permeability, the composition of gut microbiota, bacterial products, immunity, local, and systemic inflammation. These factors play a critical role in the maintenance of intestinal, liver, and metabolic homeostasis. An anomalous or imbalanced gut microbial composition may favor an increased intestinal permeability, predisposing to portal translocation of microorganisms, microbial products, and cell wall components. These components form microbial-associated molecular patterns (MAMPs) or pathogen-associated molecular patterns (PAMPs), with potentials to interact in the intestine lamina propria enriched in immune cells, and in the liver at the level of the immune cells, i.e., Kupffer cells and stellate cells. The resulting inflammatory environment ultimately leads to liver fibrosis with potentials to progression towards necrotic and fibrotic changes, cirrhosis. and hepatocellular carcinoma. By contrast, measures able to modulate the composition of gut microbiota and to preserve gut vascular barrier might prevent or reverse NAFLD.

Role of oxidative stress in the pathogenesis of nonalcoholic fatty liver disease

Nonalcoholic fatty liver disease (NAFLD) has emerged as the most common chronic liver disease worldwide and is strongly associated with the presence of oxidative stress. Disturbances in lipid metabolism lead to hepatic lipid accumulation, which affects different reactive oxygen species (ROS) generators, including mitochondria, endoplasmic reticulum, and NADPH oxidase. Mitochondrial function adapts to NAFLD mainly through the downregulation of the electron transport chain (ETC) and the preserved or enhanced capacity of mitochondrial fatty acid oxidation, which stimulates ROS overproduction within different ETC components upstream of cytochrome c oxidase. However, non-ETC sources of ROS, in particular, fatty acid β-oxidation, appear to produce more ROS in hepatic metabolic diseases. Endoplasmic reticulum stress and NADPH oxidase alterations are also associated with NAFLD, but the degree of their contribution to oxidative stress in NAFLD remains unclear. Increased ROS generation induces changes in insulin sensitivity and in the expression and activity of key enzymes involved in lipid metabolism. Moreover, the interaction between redox signaling and innate immune signaling forms a complex network that regulates inflammatory responses. Based on the mechanistic view described above, this review summarizes the mechanisms that may account for the excessive production of ROS, the potential mechanistic roles of ROS that drive NAFLD progression, and therapeutic interventions that are related to oxidative stress.

Herbal formulation MIT ameliorates high-fat diet-induced non-alcoholic fatty liver disease

Background

Non-alcoholic fatty liver disease (NAFLD) is one of the most common liver diseases and is caused by obesity, diabetes, high blood pressure, and insulin resistance. Many studies have explored novel candidates to treat NAFLD using herbal medicines owing to their fewer side effects. In this study, we examined the effect of MIT, an herbal formula comprising Ephedra sinica, Panax ginseng, and Alisma orientale, on the murine model of NAFLD.

Methods

To evaluate the effect of MIT on NAFLD, we used the high-fat diet (HFD)-induced NAFLD mice model. The mice were divided into four groups: control, HFD, HFD with metformin administration, and HFD with MIT administration. Freeze-dried MIT was dissolved in phosphate buffered saline and orally administered for 8 weeks to MIT-treated mice (60 mg/kg) after feeding them with HFD for 16 weeks.

Results

MIT treatment significantly attenuated fat accumulation, serum glucose levels, and excessive cholesterol. It also reduced the activation of NF-κB, JNK, ERK, mammalian target of rapamycin, and peroxisome proliferator-activated receptor γ in the HFD-induced NAFLD mice. The expression level of enzymes involved in the synthesis and oxidation of fatty acids, acetyl-coA carboxylase and CYP2E1, were clearly reduced by MIT treatment. Reactive oxygen species (ROS) production and subsequent liver damage were effectively reduced by MIT treatment.

Conclusion

We suggest that MIT is a potent herbal formula that can be used for the prevention and treatment of obesity-related NAFLD via regulating the levels of serum glucose and free fatty acids, inflammation, lipid accumulation, and ROS-mediated liver damage.

Herbal Medicine in the Treatment of Non-Alcoholic Fatty Liver Diseases-Efficacy, Action Mechanism, and Clinical Application

Non-alcoholic fatty liver disease (NAFLD) is a common chronic liver disease with high prevalence in the developed countries. NAFLD has been considered as one of the leading causes of cryptogenic cirrhosis and chronic liver disease. The individuals with obesity, insulin resistance and diabetes mellitus, hyperlipidaemia, and hypertension cardiovascular disease have a high risk to develop NAFLD. The related critical pathological events are associated with the development of NAFLD including insulin resistance, lipid metabolism dysfunction, oxidative stress, inflammation, apoptosis, and fibrosis. The development of NAFLD range from simple steatosis to non-alcoholic steatohepatitis (NASH). Hepatic steatosis is characterized by fat accumulation, which represents the early stage of NAFLD. Then, inflammation triggered by steatosis drives early NAFLD progression into NASH. Therefore, the amelioration of steatosis and inflammation is essential for NAFLD therapy. The herbal medicine have taken great effects on the improvement of steatosis and inflammation for treating NAFLD. It has been found out that these effects involved the multiple mechanisms underlying lipid metabolism and inflammation. In this review, we pay particular attention on herbal medicine treatment and make summary about the research of herbal medicine, including herb formula, herb extract and naturals compound on NAFLD. We make details about their protective effects, the mechanism of action involved in the amelioration steatosis and inflammation for NAFLD therapy as well as the clinical application.

TNFAIP3 Interacting Protein 3 Overexpression Suppresses Nonalcoholic Steatohepatitis by Blocking TAK1 Activation

Nonalcoholic steatohepatitis (NASH) is an unmet clinical challenge due to the rapid increase in its occurrence but the lack of approved drugs to treat it. Further unraveling of the molecular mechanisms underlying NASH may identify potential successful drug targets for this condition. Here, we identified TNFAIP3 interacting protein 3 (TNIP3) as a novel inhibitor of NASH. Hepatocyte-specific TNIP3 transgenic overexpression attenuates NASH in two dietary models in mice. Mechanistically, this inhibitory effect of TNIP3 is independent of its conventional role as an inhibitor of TNFAIP3. Rather, TNIP3 directly interacts with TAK1 and inhibits its ubiquitination and activation by the E3 ligase TRIM8 in hepatocytes in response to metabolic stress. Notably, adenovirus-mediated TNIP3 expression in the liver substantially blocks NASH progression in mice. These results suggest that TNIP3 may be a promising therapeutic target for NASH management.

Nonalcoholic Fatty Liver Disease: An Emerging Driver of Hypertension

Hypertension, a multifactorial disorder resulting from the interplay between genetic predisposition and environmental risk factors, affects ≈30% of adults. Emerging evidence has shown that nonalcoholic fatty liver disease (NAFLD), as an underestimated metabolic abnormality, is strongly associated with an increased risk of incident prehypertension and hypertension. However, the role of NAFLD in the development of hypertension is still obscure and is highly overlooked by the general public. Herein, we highlight the epidemiological evidence and putative mechanisms focusing on the emerging roles of NAFLD in hypertension, with the purpose of reinforcing the notion that NAFLD may serve as an independent risk factor and an important driving force in the development and progression of hypertension. Finally, we also briefly summarize the current potential treatments for NAFLD that might also be beneficial approaches against hypertension.

The hepatic lipidome: From basic science to clinical translation

The liver is the key organ involved in lipid metabolism and transport. Excessive lipid accumulation due to dysregulated lipid metabolism predisposes the liver to steatosis, cirrhosis, and hepatocellular carcinoma. Lipids are generally compartmentalized in specialized organelles called lipid droplets that enable cells to store and release lipids in a regulated manner. However, during flux-in and flux-out of droplets, lipids are converted into toxic species leading to lipid-mediated liver damage. Lipids are categorized into 'toxic' or 'healthy' lipids that are involved in liver disease pathogenesis or resolution, respectively. Lipidomic analysis have revealed unique lipid signature that correlates with the disease progression therefore being used for disease diagnosis. In this comprehensive review, we provide an overview on hepatic lipid homeostasis, lipid compartmentalization mechanisms and lipidomic profiles in different liver diseases. We further discuss promising therapeutics targeting the hepatic lipidome including pro-resolving lipids, liposomes, and small-molecule inhibitors for the treatment of liver diseases.

Emerging Molecular Targets for Treatment of Nonalcoholic Fatty Liver Disease

In parallel with the obesity epidemic, nonalcoholic fatty liver disease (NAFLD) has emerged as the most common chronic liver disease worldwide. Disequilibrium of lipid metabolism and the subsequent metabolic-stress-induced inflammation are believed to be central in the pathogenesis of NAFLD. Of note, metabolic inflammation is primarily mediated by innate immune signaling, which is increasingly recognized as a driving force in NAFLD progression. Currently, a series of agents targeting one or more of these pathomechanisms have shown encouraging results in preclinical models and clinical trials. This review summarizes the emerging molecular targets involved in signaling in the lipid metabolism and innate immunity aspects of NAFLD, focusing on their mechanistic roles and translational potentials.

Tanshinone IIA ameliorates non-alcoholic fatty liver disease through targeting peroxisome proliferator-activated receptor gamma and toll-like receptor 4

Objective

To investigate the cellular mechanisms of action of tanshinone IIA on the fatty liver disease induced by a high-fat diet in an animal model of non-alcoholic fatty liver disease (NAFLD).

Methods

Adult male Sprague Dawley rats were randomized into one of three groups: regular rat diet (CON group) for 4 months; high-fat diet (HFD group) for 4 months; HFD for 2 months followed by tanshinone IIA treatment plus HFD (TAN group) for a further 2 months. A range of physical and biochemical markers of lipid accumulation and fatty liver disease were measured and compared between the groups.

Results

Tanshinone IIA treatment significantly reduced fat accumulation in the liver and plasma lipid levels that had been increased by HFD. The toll-like receptor (TLR4)/nuclear factor kappa B (NF-κB) signalling pathway was silenced by tanshinone IIA treatment. Tumour necrosis factor-α and interleukin-6 were reduced by tanshinone IIA. Hepatocyte apoptosis was inhibited by tanshinone IIA. Tanshinone IIA upregulated peroxisome proliferator-activated receptor gamma (PPAR-γ), which resulted in an improvement in the oxidative status.

Conclusion

Tanshinone IIA ameliorates NAFLD by targeting PPAR-γ and TLR4, resulting in decreased plasma lipids and oxidative stress, suggesting this strategy may form the basis of novel NAFLD therapies.