The role of air pollutants in initiating liver disease

Recent episodes of severe air pollution in eastern Asia have been reported in the scientific literature and news media. Therefore, there is growing concern about the systemic effects of air pollution on human health. Along with the other well-known harmful effects of air pollution, recently, several animal models have provided strong evidence that air pollutants can induce liver toxicity and act to accelerate liver inflammation and steatosis. This review briefly describes examples where exposure to air pollutants was involved in liver toxicity, focusing on how particulate matter (PM) or carbon black (CB) may be translocated from lung to liver and what liver diseases are closely associated with these air pollutants.

Spliceosome-Associated Protein 130 Exacerbates Alcohol-Induced Liver Injury by Inducing NLRP3 Inflammasome-Mediated IL-1β in Mice

Excessive alcohol consumption leads to chronic liver diseases. Macrophage-inducible C-type lectin (Mincle) is a C-type lectin receptor that recognizes spliceosome-associated protein 130 (SAP130) known as an endogenous ligand released from dying cells. The aim was to examine the role of Mincle-SAP130 in the pathogenesis of alcoholic liver disease. Alcohol-induced liver injury was induced in wild-type (WT) and Mincle knockout (KO) mice by using a chronic-binge ethanol-feeding model. Mincle KO mice showed significant lower hepatic steatosis, inflammation with neutrophil infiltration, and fibrosis compared with WT mice after alcohol feeding. In contrast, Mincle activation exacerbated alcohol-induced liver injury. Kupffer cells (KCs) are major sources of Mincle. IL-1β expression was significantly down-regulated in Mincle KO mice compared with that in WT mice after alcohol consumption. Interestingly, expression and production of IL-1β were significantly decreased in SAP130-treated KCs isolated from leucine-rich-containing family pyrin domain containing-3-deficient mice compared with those in WT KCs. Such results were also observed in cells treated with SAP130 plus Syk inhibitor. Furthermore, infiltration of invariant natural killer T cells was decreased in livers of Mincle KO mice. Finally, inhibition of Syk signaling ameliorated alcohol-induced liver injury. Collectively, these results demonstrated that interaction between Mincle and SAP130 may promote the progression of alcoholic liver disease by IL-1β production in KCs and consequently increase inflammatory immune cell infiltration.

Therapeutic effects of zerumbone in an alkali-burned corneal wound healing model

Cornea is an avascular transparent tissue. Ocular trauma caused by a corneal alkali burn induces corneal neovascularization (CNV), inflammation, and fibrosis, leading to vision loss. The purpose of this study was to examine the effects of Zerumbone (ZER) on corneal wound healing caused by alkali burns in mice. CNV was induced by alkali-burn injury in BALB/C female mice. Topical ZER (three times per day, 3μl each time, at concentrations of 5, 15, and 30μM) was applied to treat alkali-burned mouse corneas for 14 consecutive days. Histopathologically, ZER treatment suppressed alkali burn-induced CNV and decreased corneal epithelial defects induced by alkali burns. Corneal tissue treated with ZER showed reduced mRNA levels of pro-angiogenic genes, including vascular endothelial growth factor, matrix metalloproteinase-2 and 9, and pro-fibrotic factors such as alpha smooth muscle actin and transforming growth factor-1 and 2. Immunohistochemical analysis demonstrated that the infiltration of F4/80 and/or CCR2 positive cells was significantly decreased in ZER-treated corneas. ZER markedly inhibited the mRNA and protein levels of monocyte chemoattractant protein-1 (MCP-1) in human corneal fibroblasts and murine peritoneal macrophages. Immunoblot analysis revealed that ZER decreased the activation of signal transducer and activator of transcription 3 (STAT3), with consequent reduction of MCP-1 production by these cells. In conclusion, topical administration of ZER accelerated corneal wound healing by inhibition of STAT3 and MCP-1 production.

Dietary zerumbone, a sesquiterpene, ameliorates hepatotoxin-mediated acute and chronic liver injury in mice

Acute liver injury (ALI) is a life-threatening clinical syndrome. Long-lasting liver injury can lead to chronic hepatic inflammation and fibrogenic responses. Zerumbone (ZER), the main constituent of rhizomes of Zingiber zerumbet Smith, has a variety of functions including anticancer activity. We investigated the role of ZER on the progression of hepatotoxin-induced liver injury. Single or repeated injection of CCl₄ was used to induce acute or chronic liver injury, respectively. Mice were orally administered with ZER (10, 50 mg/kg) during the experimental period. Histopathologic analysis and serum biochemical levels revealed that ZER had hepatoprotective activities against ALI. Similar effects of ZER on injured livers were confirmed by analyses of inflammation and apoptosis-related genes. Western blot analysis showed that protein levels of apoptotic molecules were decreased, whereas antiapoptotic protein levels were conversely increased in injured livers treated with ZER. Furthermore, chronic liver injury and its associated fibrogenesis in mice were reduced by ZER treatment. These findings from our in vivo experiments further indicate that ZER could alleviate hepatocellular toxicity and inhibit activation of primary hepatic stellate cells. Our results suggest that ZER might have potential as a safe and prophylactic alternative to prevent acute and chronic liver injury.

Effects of nicotine on corneal wound healing following acute alkali burn

Epidemiological studies have indicated that smoking is a pivotal risk factor for the progression of several chronic diseases. Nicotine, the addictive component of cigarettes, has powerful pathophysiological properties in the body. Although the effects of cigarette smoking on corneal re-epithelialization have been studied, the effects of nicotine on corneal wound healing-related neovascularization and fibrosis have not been fully demonstrated. The aim of this study was to evaluate the effects of chronic administration of nicotine on corneal wound healing following acute insult induced by an alkali burn. BALB/C female mice randomly received either vehicle (2% saccharin) or nicotine (100 or 200 μg/ml in 2% saccharin) in drinking water ad libitum. After 1 week, animals were re-randomized and the experimental group was subjected to a corneal alkali burn, and then nicotine was administered until day 14 after the alkali burn. A corneal alkali burn model was generated by placing a piece of 2 mm-diameter filter paper soaked in 1N NaOH on the right eye. Histopathological analysis and the expression level of the pro-angiogenic genes vascular endothelial growth factor (VEGF) and matrix metalloproteinase-9 (MMP9) revealed that chronic nicotine administration enhanced alkali burn-induced corneal neovascularization. Furthermore, the mRNA expression of the pro-fibrogenic factors α-smooth muscle actin (αSMA), transforming growth factor-β (TGF-β), and collagen α1 (Col1) was enhanced in the high-concentration nicotine-treated group compared with the vehicle group after corneal injury. Immunohistochemical analysis also showed that the αSMA-positive area was increased in chronic nicotine-treated mice after corneal alkali burn. An in vitro assay found that expression of the α3, α7, and β1 nicotinic acetylcholine receptor (nAChR) subunits was significantly increased by chemical injury in human corneal fibroblast cells. Moreover, alkali-induced fibrogenic gene expression and proliferation of fibroblast cells were further increased by treatment with nicotine and cotinine. The proliferation of such cells induced by treatment of nicotine and cotinine was reduced by inhibition of the PI3K and PKC pathways using specific inhibitors. In conclusion, chronic administration of nicotine accelerated the angiogenic and fibrogenic healing processes in alkali-burned corneal tissue.

Cigarette smoking differentially regulates inflammatory responses in a mouse model of nonalcoholic steatohepatitis depending on exposure time point

Cigarette smoke (CS) is a risk factor for the development of nonalcoholic fatty liver disease. However, the role of mainstream CS (MSCS) in the pathogenesis of nonalcoholic steatohepatitis (NASH) remains unclear. During the first (early exposure) or last (late exposure) three weeks of methionine-choline deficient with high fat diet feeding (6 weeks), each diet group was exposed to MSCS (300 or 600 μg/L). Hepatic or serum biochemical analysis showed that MSCS differentially modulated hepatic injury in NASH milieu, depending on exposure time points. Consistently, NASH-related hepatocellular apoptosis and fibrosis were increased in the early exposure group, but decreased in the late exposure group, except for steatosis. Ex vivo experiments showed that CS extract differentially regulated inflammatory responses in co-cultured hepatocytes and macrophages isolated from steatohepatitic livers after 10 days or 3 weeks of diet feeding. Furthermore, CS differentially up- and down-regulated the expression levels of M1/M2 polarization markers and peroxisome proliferator-activated receptor-gamma (PPARγ) in livers (29% and 38%, respectively) or co-cultured macrophages (2 and 2.5 fold, respectively). Collectively, our findings indicate that opposite effects of MSCS on NASH progression are mediated by differential modulation of PPARγ and its-associated M1/M2 polarization in hepatic macrophages, depending on exposure time points.

Evaluating the Influence of Side Stream Cigarette Smoke at an Early Stage of Non-Alcoholic Steatohepatitis Progression in Mice

Side stream cigarette smoke (SSCS) is known to be as harmful and hazardous to human health as is active smoking. In this study, we investigated the relationship between the exposure to SSCS and its stimulatory and subacute effects on the progression of non-alcoholic steatohepatitis (NASH). A methionine and choline-deficient plus high fat (MCDHF) diet was administered to C57BL/6 mice for 6 weeks. During the first three weeks of MCDHF diet feeding, each diet group was exposed to SSCS (0, 20, 40 μg/L) or fresh air for 2 hrs per day and 5 days per week. Additional experiments were performed by increasing the concentration (0, 30, 60 μg/L) and exposure time (6 hours per day) of SSCS. According to histopathologic analysis and serum levels of Alanine Aminotransferase (ALT) and Aspartate Aminotransferase (AST), there were no differences in hepatic fat deposition, fibrosis, apoptosis or liver damage in MCDHF-fed mice based on SSCS exposure. There were also no differences in the expression of inflammation-, oxidative stress- or fibrosis-related genes between MCDHF-fed mice with or without SSCS exposure. Therefore, it is concluded that SSCS with current exposure amounts does not have additive detrimental effects on the early stage of NASH.

Heme-thiolate monooxygenase cytochrome P450 1B1, an old dog with many new tricks

Cytochrome P450 CYP1B1 is a heme-thiolate monooxygenase traditionally recognized for its xenobiotic functions and extrahepatic expressions. Recent studies have suggested that CYP1B1 is also expressed in hepatic stellate cells, immune cells, endothelial cells, and fibroblasts within the tumor microenvironment, as well as tumor cells themselves. CYP1B1 is responsible for the metabolism of a wide range of substrates, including xenobiotics such as drugs, environmental chemicals, and endobiotics such as steroids, retinol, and fatty acids. Consequently, CYP1B1 and its associated exogenous and endogenous metabolites have been critically implicated in the pathogenesis of many diseases. Understanding the mode of action of CYP1B1 in different pathophysiological conditions and developing pharmacological inhibitors that allow for systemic or cell type-specific modulation of CYP1B1 may pave the way for novel therapeutic opportunities. This review highlights the significant role of CYP1B1 in maintaining physiological homeostasis and provides a comprehensive discussion of recent advancements in our understanding of CYP1B1's involvement in the pathogenesis of diseases such as fibrosis, cancer, glaucoma, and metabolic disorders. Finally, the review emphasizes the therapeutic potential of targeting CYP1B1 for drug development, particularly in the treatment and prevention of cancers and liver fibrosis. SIGNIFICANCE STATEMENT: CYP1B1 plays a critical role in various physiological processes. Dysregulation or genetic mutations of the gene encoding this enzyme can lead to health complications and may increase the risk of diseases such as cancer and liver fibrosis. In this review, we summarize recent preclinical and clinical evidence that underscores the potential of CYP1B1 as a therapeutic target.

The de-sulfinylation enzyme sulfiredoxin-1 attenuates hepatic stellate cell activation and liver fibrosis by modulating the PTPN12-NLRP3 axis

BACKGROUND AIMS

Liver fibrosis is characterized by the progressive scarring of liver tissue. Oxidative stress is a critical causal factor of hepatic stellate cell (HSC) activation and the subsequent liver fibrogenesis, but the mechanism is not fully understood. Cysteine sulfinic acid (Cys-SO2H), a modification of reactive cysteine residues, is a unique form of oxidative response that alters the structure and function of proteins. Sulfiredoxin 1 (SRXN1) is responsible for ATP-dependent reduction of the Cys-SO2H to sulfenic acid (Cys-SOH).

APPROACH RESULTS

We found that the expression of SRXN1 was increased in activated HSCs and in human and mouse fibrotic livers. HSC-specific ablation of Srxn1 or pharmacological inhibition of Srxn1 exacerbated HSC activation and sensitized mice to liver fibrosis. Mechanistically, SRXN1 inhibited HSC activation by de-sulfinylating the phosphatase protein tyrosine phosphatase non-receptor type 12 (PTPN12), which enhanced its phosphatase activity and protein stability, leading to decreased tyrosine phosphorylation and reduced activation of the pro-fibrotic inflammasome protein NLRP3. The anti-fibrotic effect of SRXN1 was abolished when NLRP3 was inhibited. In contrast, overexpression of PTPN12 attenuated NLRP3 activation, and this effect was further amplified by the C164A S-sulfinylation resistant mutant of PTPN12.

CONCLUSIONS

Our findings have uncovered an important role of SRXN1 and protein S-sulfinylation in HSC activation and liver fibrosis. The SRXN1-PTPN12-NLRP3 axis represents potential therapeutic targets for liver fibrosis.

Cholesin and GPR146 in Modulating Cholesterol Biosynthesis

BACKGROUND

Cholesterol homeostasis in the human body is a crucial process that involves a delicate balance between dietary cholesterol absorption in the intestine and de novo cholesterol synthesis in the liver. Both pathways contribute significantly to the overall pool of cholesterol in the body, influencing plasma cholesterol levels and impacting cardiovascular health. Elevated absorption of cholesterol in the intestines has a suppressive impact on the synthesis of cholesterol in the liver, serving to preserve cholesterol balance. Nonetheless, the precise mechanisms driving this phenomenon remain largely unclear.

SUMMARY

This review aimed to discuss the previously unrecognized role of cholesin and GPR146 in the regulation of cholesterol biosynthesis, providing a novel conceptual framework for understanding cholesterol homeostasis.

KEY MESSAGES

The discovery of cholesin, a novel protein implicated in the regulation of cholesterol homeostasis, represents a significant advancement in our understanding of cholesterol biosynthesis and its associated pathways. The cholesin-GPR146 axis could have profound implications across various therapeutic areas concerning abnormal cholesterol metabolism, offering new hope for patients and improving overall healthcare outcomes.

The evidence-based multifaceted roles of hepatic stellate cells in liver diseases: A concise review

Hepatic stellate cells (HSCs) play central roles in liver disease pathogenesis, spanning steatosis to cirrhosis and hepatocellular carcinoma. These cells, located in the liver's sinusoidal space of Disse, transition from a quiescent, vitamin A-rich state to an activated, myofibroblast-like phenotype in response to liver injury. This activation results from a complex interplay of cytokines, growth factors, and oxidative stress, leading to excessive collagen deposition and liver fibrosis, a hallmark of chronic liver diseases. Recently, HSCs have gained recognition for their dynamic, multifaceted roles in liver health and disease. Attention has shifted toward their involvement in various liver conditions, including acute liver injury, alcoholic and non-alcoholic fatty liver disease, and liver regeneration. This review aims to explore diverse functions of HSCs in these acute or chronic liver pathologies, with a focus on their roles beyond fibrogenesis. HSCs exhibit a wide range of actions, including lipid storage, immunomodulation, and interactions with other hepatic and extrahepatic cells, making them pivotal in the hepatic microenvironment. Understanding HSC involvement in the progression of liver diseases can offer novel insights into pathogenic mechanisms and guide targeted therapeutic strategies for various liver conditions.