Resistance to carbon tetrachloride-induced hepatotoxicity in mice which lack CYP2E1 expression

Contributing roles of mitochondrial dysfunction and hepatocyte apoptosis in liver diseases through oxidative stress, post-translational modifications, inflammation, and intestinal barrier dysfunction

This review provides an update on recent findings from basic, translational, and clinical studies on the molecular mechanisms of mitochondrial dysfunction and apoptosis of hepatocytes in multiple liver diseases, including but not limited to alcohol-associated liver disease (ALD), metabolic dysfunction-associated steatotic liver disease (MASLD), and drug-induced liver injury (DILI). While the ethanol-inducible cytochrome P450-2E1 (CYP2E1) is mainly responsible for oxidizing binge alcohol via the microsomal ethanol oxidizing system, it is also responsible for metabolizing many xenobiotics, including pollutants, chemicals, drugs, and specific diets abundant in n-6 fatty acids, into toxic metabolites in many organs, including the liver, causing pathological insults through organelles such as mitochondria and endoplasmic reticula. Oxidative imbalances (oxidative stress) in mitochondria promote the covalent modifications of lipids, proteins, and nucleic acids through enzymatic and non-enzymatic mechanisms. Excessive changes stimulate various post-translational modifications (PTMs) of mitochondrial proteins, transcription factors, and histones. Increased PTMs of mitochondrial proteins inactivate many enzymes involved in the reduction of oxidative species, fatty acid metabolism, and mitophagy pathways, leading to mitochondrial dysfunction, energy depletion, and apoptosis. Unique from other organelles, mitochondria control many signaling cascades involved in bioenergetics (fat metabolism), inflammation, and apoptosis/necrosis of hepatocytes. When mitochondrial homeostasis is shifted, these pathways become altered or shut down, likely contributing to the death of hepatocytes with activation of inflammation and hepatic stellate cells, causing liver fibrosis and cirrhosis. This review will encapsulate how mitochondrial dysfunction contributes to hepatocyte apoptosis in several types of liver diseases in order to provide recommendations for targeted therapeutics.

Increased expression of phosphodiesterase 4 in activated hepatic stellate cells promotes cytoskeleton remodeling and cell migration

Activation and transdifferentiation of hepatic stellate cells (HSC) into migratory myofibroblasts is a key process in liver fibrogenesis. Cell migration requires an active remodeling of the cytoskeleton, which is a tightly regulated process coordinated by Rho-specific guanine nucleotide exchange factors (GEFs) and the Rho family of small GTPases. Rho-associated kinase (ROCK) promotes assembly of focal adhesions and actin stress fibers by regulating cytoskeleton organization. GEF exchange protein directly activated by cAMP 1 (EPAC1) has been implicated in modulating TGFβ1 and Rho signaling; however, its role in HSC migration has never been examined. The aim of this study was to evaluate the role of cAMP-degrading phosphodiesterase 4 (PDE4) enzymes in regulating EPAC1 signaling, HSC migration, and fibrogenesis. We show that PDE4 protein expression is increased in activated HSCs expressing alpha smooth muscle actin and active myosin light chain (MLC) in fibrotic tissues of human nonalcoholic steatohepatitis cirrhosis livers and mouse livers exposed to carbon tetrachloride. In human livers, TGFβ1 levels were highly correlated with PDE4 expression. TGFβ1 treatment of LX2 HSCs decreased levels of cAMP and EPAC1 and increased PDE4D expression. PDE4 specific inhibitor, rolipram, and an EPAC-specific agonist decreased TGFβ1-mediated cell migration in vitro. In vivo, targeted delivery of rolipram to the liver prevented fibrogenesis and collagen deposition and decreased the expression of several fibrosis-related genes, and HSC activation. Proteomic analysis of mouse liver tissues identified the regulation of actin cytoskeleton by the kinase effectors of Rho GTPases as a major pathway impacted by rolipram. Western blot analyses confirmed that PDE4 inhibition decreased active MLC and endothelin 1 levels, key proteins involved in cytoskeleton remodeling and contractility. The current study, for the first time, demonstrates that PDE4 enzymes are expressed in hepatic myofibroblasts and promote cytoskeleton remodeling and HSC migration. © 2023 The Pathological Society of Great Britain and Ireland.

Evaluation of the carcinogenicity of carbon tetrachloride

Carbon tetrachloride (CCl4) has been extensively used and reported to produce toxicity, most notably involving the liver. Carbon tetrachloride metabolism involves CYP450-mediated bioactivation to trichloromethyl and trichloromethyl peroxy radicals, which are capable of macromolecular interaction with cell components including lipids and proteins. Radical interaction with lipids produces lipid peroxidation which can mediate cellular damage leading to cell death. Chronic exposure with CCl4 a rodent hepatic carcinogen with a mode of action (MOA) exhibits the following key events: 1) metabolic activation; 2) hepatocellular toxicity and cell death; 3) consequent regenerative increased cell proliferation; and 4) hepatocellular proliferative lesions (foci, adenomas, carcinomas). The induction of rodent hepatic tumors is dependent upon the dose (concentration and exposure duration) of CCl4, with tumors only occurring at cytotoxic exposure levels. Adrenal benign pheochromocytomas were also increased in mice at high CCl4 exposures; however, these tumors are not of relevant importance to human cancer risk. Few epidemiology studies that have been performed on CCl4, do not provide credible evidence of enhanced risk of occurrence of liver or adrenal cancers, but these studies have serious flaws limiting their usefulness for risk assessment. This manuscript summarizes the toxicity and carcinogenicity attributed to CCl4, specifically addressing MOA, dose-response, and human relevance.

17α-estradiol, a lifespan-extending compound, attenuates liver fibrosis by modulating collagen turnover rates in male mice

Estrogen signaling is protective against chronic liver diseases, although men and a subset of women are contraindicated for chronic treatment with 17β-estradiol (17β-E2) or combination hormone replacement therapies. We sought to determine if 17α-estradiol (17α-E2), a naturally occurring diastereomer of 17β-E2, could attenuate liver fibrosis. We evaluated the effects of 17α-E2 treatment on collagen synthesis and degradation rates using tracer-based labeling approaches in male mice subjected to carbon tetrachloride (CCl4)-induced liver fibrosis. We also assessed the effects of 17α-E2 on markers of hepatic stellate cell (HSC) activation, collagen cross-linking, collagen degradation, and liver macrophage content and polarity. We found that 17α-E2 significantly reduced collagen synthesis rates and increased collagen degradation rates, which was mirrored by declines in transforming growth factor β1 (TGF-β1) and lysyl oxidase-like 2 (LOXL2) protein content in liver. These improvements were associated with increased matrix metalloproteinase 2 (MMP2) activity and suppressed stearoyl-coenzyme A desaturase 1 (SCD1) protein levels, the latter of which has been linked to the resolution of liver fibrosis. We also found that 17α-E2 increased liver fetuin-A protein, a strong inhibitor of TGF-β1 signaling, and reduced proinflammatory macrophage activation and cytokines expression in the liver. We conclude that 17α-E2 reduces fibrotic burden by suppressing HSC activation and enhancing collagen degradation mechanisms. Future studies will be needed to determine if 17α-E2 acts directly in hepatocytes, HSCs, and/or immune cells to elicit these benefits.

Ubiquitin ligase E3 HUWE1/MULE targets transferrin receptor for degradation and suppresses ferroptosis in acute liver injury

Hepatic ischemia followed by reperfusion (I/R), a major clinical problem during liver surgical procedures, can induce liver injury with severe cell death including ferroptosis which is characterized by iron-dependent accumulation of lipid peroxidation. The HECT domain-containing ubiquitin E3 ligase HUWE1 (also known as MULE) was initially shown to promote apoptosis. However, our preliminary study demonstrates that high expression of HUWE1 in the liver donors corelates with less injury and better hepatic function after liver transplantation in patients. Thus, we investigate the role of HUWE1 in acute liver injury, and identify HUWE1 as a negative ferroptosis modulator through transferrin receptor 1(TfR1). Deficiency of Huwe1 in mice hepatocytes (HKO) exacerbated I/R and CCl4-induced liver injury with more ferroptosis occurrence. Moreover, Suppression of Huwe1 remarkably enhances cellular sensitivity to ferroptosis in primary hepatocytes and mouse embryonic fibroblasts. Mechanistically, HUWE1 specifically targets TfR1 for ubiquitination and proteasomal degradation, thereby regulates iron metabolism. Importantly, chemical and genetic inhibition of TfR1 dramatically diminishes the ferroptotic cell death in Huwe1 KO cells and Huwe1 HKO mice. Therefore, HUWE1 is a potential protective factor to antagonize both aberrant iron accumulation and ferroptosis thereby mitigating acute liver injury. These findings may provide clinical implications for patients with the high-expression Huwe1 alleles.

Extract of Jasminum grandiflorum L. alleviates CCl4-induced liver injury by decreasing inflammation, oxidative stress and hepatic CYP2E1 expression in mice

Jasminum grandiflorum L. (JG) is a medicinal plant containing many bioactive ingredients. Herein, we analyzed the effects of four different extracts and two compounds of JG on acute liver injury caused by carbon tetrachloride (CCl₄) and underlying molecular mechanisms. 7 weeks old C57BL/6 male mice were used to establish a liver injury model by injecting with 1% CCl₄, 10 mL/kg ip. Four different extracts and two compounds of JG were given to mice by gavage for 3 days. Clinical and histological chemistry assays were performed to assess liver injury. Moreover, hepatic oxidative stress and inflammation related markers were determined by immunohistochemistry and western blotting. As a result, JG extracts and two functional components showed different degree of protect effects against CCl₄-induced liver injury by the decrease of elevated serum transaminases and liver index, and the attenuation of histopathological changes in mice, among which JG extracted with petroleum ether (PET) had the most significant effect. In addition, PET remarkably alleviated hepatic oxidative stress and inflammation. Further studies revealed that PET significantly inhibited the TNF-α expression, signal pathway expression, NF-κB p65 and inflammatory factors IL-1β and IL-6 expression in CCl₄-induced liver injury mice. Nevertheless, hydroxytyrosol (HT) alleviated liver injury by reducing oxidative stress. Apart from PET extract, other extracts of JG can inhibit cytochrome CYP2E1 expression to protect liver tissue. These findings suggest that the extracts and its components of JG possesses the potential protective effects against CCl₄-induced liver injury in mice by exerting antioxidative stress and anti-inflammation.

Assessing cytochrome P450 function using genetically engineered mouse models

The ability to knock out and/or humanize different genes in experimental animals, globally or in cell- and tissue-specific patterns, has revolutionized scientific research in many areas. Genetically engineered mouse models, including knockout models, transgenic models, and humanized models, have played important roles in revealing the in vivo functions of various cytochrome P450 (CYP) enzymes. These functions are very diverse, ranging from the biotransformation of drugs and other xenobiotics, events that often dictate their pharmacokinetic or toxicokinetic properties and the associated therapeutic or adverse actions, to the metabolism of endogenous compounds, such as steroid hormones and other bioactive substances, that may determine susceptibility to many diseases, such as cancer and metabolic diseases. In this review, we provide a comprehensive list of Cyp-knockout, human CYP-transgenic, and CYP-humanized mouse models that target genes in the CYP1-4 gene families, and highlight their utility in assessing the in vivo metabolism, bioactivation, and toxicity of various xenobiotic compounds, including therapeutic agents and chemical carcinogens. We aim to showcase the advantages of utilizing these mouse models for in vivo drug metabolism and toxicology studies, and to encourage and facilitate greater utility of engineered mouse models to further improve our knowledge of the in vivo functions of various P450 enzymes, which is integral to our ability to develop safer and more effective therapeutics and to identify individuals predisposed to adverse drug reactions or environmental diseases.

Novel Deep Eutectic Solvent-Hydrogel Systems for Synergistic Transdermal Delivery of Chinese Herb Medicine and Local Treatments for Rheumatoid Arthritis

In this study, a novel hydrogel system incorporating an amino acid-based deep eutectic solvent (DES) was prepared, and the skin-permeation enhancement of traditional Chinese herb medicine was evaluated using "sanwujiaowan" extract as the model formula. Briefly, a DES-extract complex was constructed by co-heating the herb formula extracts with the amino acid as the hydrogen receptor and citric acid as the hydrogen donor. The DES-extract complex demonstrated excellent dissolution and skin permeability of the complicated ingredients in the extracts. Consequently, the DES-extract complex was introduced to a hydrogel system, which showed better mechanical properties and viscoelasticity performance. Using a collagen-induced arthritis rat model, the DES-hydrogels exerted an enhanced therapeutic effect that significantly reduced the inflammatory response with systemic toxicity of the extracts. Therefore, our work suggests a novel strategy for synergistic transdermal delivery of Chinese herb medicine and local treatments for rheumatoid arthritis.

A noninvasive iRFP713 p53 reporter reveals dynamic p53 activity in response to irradiation and liver regeneration in vivo

Genetically encoded probes are widely used to visualize cellular processes in vitro and in vivo. Although effective in cultured cells, fluorescent protein tags and reporters are suboptimal in vivo because of poor tissue penetration and high background signal. Luciferase reporters offer improved signal-to-noise ratios but require injections of luciferin that can lead to variable responses and that limit the number and timing of data points that can be gathered. Such issues in studying the critical transcription factor p53 have limited insight on its activity in vivo during development and tissue injury responses. Here, by linking the expression of the near-infrared fluorescent protein iRFP713 to a synthetic p53-responsive promoter, we generated a knock-in reporter mouse that enabled noninvasive, longitudinal analysis of p53 activity in vivo in response to various stimuli. In the developing embryo, this model revealed the timing and localization of p53 activation. In adult mice, the model monitored p53 activation in response to irradiation and paracetamol- or CCl4-induced liver regeneration. After irradiation, we observed potent and sustained activation of p53 in the liver, which limited the production of reactive oxygen species (ROS) and promoted DNA damage resolution. We propose that this new reporter may be used to further advance our understanding of various physiological and pathophysiological p53 responses.

Polystyrene microplastics induce hepatotoxicity and disrupt lipid metabolism in the liver organoids

Microplastic particles (MP) has been detected in the environment widespread. Human beings are inevitably exposed to MP via multiple routines. However, the hazard identifications, as direct evidence of exposure and health risk, have not been fully characterized in human beings. Many studies suggest the liver is a potential target organ, but currently no study regarding the MP on human liver has been reported. In this study, we used a novel in vitro 3D model, the liver organoids (LOs) generated from human pluripotent stem cells, as an alternative model to the human liver, to explore the adverse biological effect of 1 μm polystyrene-MP (PS-MP) microbeads applying a non-static exposure approach. When the LOs were exposed to 0.25, 2.5 and 25 μg/mL PS-MP (the lowest one was relevant to the environmental concentrations, calculated to be 102 ± 7 items/mL). The potential mechanisms of PS-MP induced hepatotoxicity and lipotoxicity, in aspects of cytotoxicity, levels of key molecular markers, ATP production, alteration in lipid metabolism, ROS generation, oxidative stress and inflammation response, were determined. Specifically, it has been firstly observed that PS-MP could increase the expression of hepatic HNF4A and CYP2E1. Based on these findings, the potential adverse outcome pathways (AOPs) relevant to PS-MP were proposed, and the potential risks of PS-MP on liver steatosis, fibrosis and cancer were implicated. The combined application of novel LOs model and AOPs framework provides a new insight into the risk assessment of MP. Further studies are anticipated to validate the hepatotoxic molecular mechanism of PS-MP based on HNF4A or CYP2E1, and to investigate the MP-induced physical damage and its relationship to hepatic adverse effect for human beings. CAPSULE: Microplastics cause hepatotoxicity and disrupt lipid metabolism in the human pluripotent stem cells-derived liver organoids, providing evidence for human implication.

Hepatoprotective Potential of Pomegranate in Curbing the Incidence of Acute Liver Injury by Alleviating Oxidative Stress and Inflammatory Response

Hepatitis is an inflammatory disease of the liver and is considered one of the leading causes of death worldwide. Due to its scavenging activity, Punica granatum may be used for the treatment and prevention of liver diseases. The current study investigated the protective mechanism underlying the effects of pomegranate against a rat model of carbon tetrachloride–induced liver injury. Intraperitoneal injection of CCl₄ resulted in liver inflammation, oxidative stress, and accumulation of lipid in hepatocytes. CCl₄ induced a downregulation of superoxide dismutase (SOD), glutathione (GSH), and melonaldehyde (MDA). Pomegranate protection was assessed in terms of biochemical parameters, histopathology, and immunohistochemistry. Promegranate administration decreased inflammation, elevated serum enzymes and ROS production, and countered the debilitating effects caused by CCl₄. In addition, CCl₄-induced histological changes were absent in the crude pomegranate extract group, which also enhanced the scavenging activity of reactive oxygen species by enhancing the antioxidant defense mechanism as confirmed by detecting MDA, SOD, and GSH expressions. The migration of CD68⁺ macrophages was halted at the injured area of the central vein and the number of macrophages was reduced to the normal control by the crude extract compared to the positive control silymarin group. Likewise, protective effects of ethylacetate and the aqueous fraction of the crude extract were also observed. However, the butanol and n-hexane fractions displayed increased levels of ALT, AST, and ALP as compared to silymarin. About 25% damage to hepatocytes was observed in the butanol and n-hexane group by histopathological examination, which is a little better compared to the CCl₄-treated group. The crude extract and its ethyl acetate and aqueous fractions may be accountable for the hepatoprotective potential of Punica granatum, which was further confirmed by in vivo experiments. Together, these findings confirm that pomegranate exerts hepatoprotective activity against CCl₄-induced oxidative stress and liver damage.

Therapeutic HNF4A mRNA attenuates liver fibrosis in a preclinical model

BACKGROUND & AIMS

Therapeutic targeting of injuries that require transient restoration of proteins by mRNA delivery is an attractive approach that, until recently, has remained poorly explored. In this study, we examined the therapeutic utility of mRNA delivery for liver fibrosis and cirrhosis. Specifically, we aimed to demonstrate the therapeutic efficacy of human hepatocyte nuclear factor alpha (HNF4A) mRNA in mouse models of fibrosis and cirrhosis.

METHODS

We investigated restoration of hepatocyte functions by HNF4A mRNA transfection in vitro, and analyzed the attenuation of liver fibrosis and cirrhosis in multiple mouse models, by delivering hepatocyte-targeted biodegradable lipid nanoparticles (LNPs) encapsulating HNF4A mRNA. To identify potential mechanisms of action, we performed microarray-based gene expression profiling, single-cell RNA sequencing, and chromatin immunoprecipitation. We used primary liver cells and human liver buds for additional functional validation.

RESULTS

Expression of HNF4A mRNA led to restoration of the metabolic activity of fibrotic primary murine and human hepatocytes in vitro. Repeated in vivo delivery of LNP-encapsulated HNF4A mRNA induced a robust inhibition of fibrogenesis in 4 independent mouse models of hepatotoxin- and cholestasis-induced liver fibrosis. Mechanistically, we discovered that paraoxonase 1 is a direct target of HNF4A and it contributes to HNF4A-mediated attenuation of liver fibrosis via modulation of liver macrophages and hepatic stellate cells.

CONCLUSION

Collectively, our findings provide the first direct preclinical evidence of the applicability of HNF4A mRNA therapeutics for the treatment of fibrosis in the liver.

LAY SUMMARY

Liver fibrosis and cirrhosis remain unmet medical needs and contribute to high mortality worldwide. Herein, we take advantage of a promising therapeutic approach to treat liver fibrosis and cirrhosis. We demonstrate that restoration of a key gene, HNF4A, via mRNA encapsulated in lipid nanoparticles decreased injury in multiple mouse models of fibrosis and cirrhosis. Our study provides proof-of-concept that mRNA therapy is a promising strategy for reversing liver fibrosis and cirrhosis.

Splicing Factor SLU7 Prevents Oxidative Stress-Mediated Hepatocyte Nuclear Factor 4α Degradation, Preserving Hepatic Differentiation and Protecting From Liver Damage

BACKGROUND AND AIMS

Hepatocellular dedifferentiation is emerging as an important determinant in liver disease progression. Preservation of mature hepatocyte identity relies on a set of key genes, predominantly the transcription factor hepatocyte nuclear factor 4α (HNF4α) but also splicing factors like SLU7. How these factors interact and become dysregulated and the impact of their impairment in driving liver disease are not fully understood.

APPROACH AND RESULTS

Expression of SLU7 and that of the adult and oncofetal isoforms of HNF4α, driven by its promoter 1 (P1) and P2, respectively, was studied in diseased human and mouse livers. Hepatic function and damage response were analyzed in wild-type and Slu7-haploinsufficient/heterozygous (Slu7^+/- ) mice undergoing chronic (CCl₄ ) and acute (acetaminophen) injury. SLU7 expression was restored in CCl₄ -injured mice using SLU7-expressing adeno-associated viruses (AAV-SLU7). The hepatocellular SLU7 interactome was characterized by mass spectrometry. Reduced SLU7 expression in human and mouse diseased livers correlated with a switch in HNF4α P1 to P2 usage. This response was reproduced in Slu7^+/- mice, which displayed increased sensitivity to chronic and acute liver injury, enhanced oxidative stress, and marked impairment of hepatic functions. AAV-SLU7 infection prevented liver injury and hepatocellular dedifferentiation. Mechanistically we demonstrate a unique role for SLU7 in the preservation of HNF4α1 protein stability through its capacity to protect the liver against oxidative stress. SLU7 is herein identified as a key component of the stress granule proteome, an essential part of the cell's antioxidant machinery.

CONCLUSIONS

Our results place SLU7 at the highest level of hepatocellular identity control, identifying SLU7 as a link between stress-protective mechanisms and liver differentiation. These findings emphasize the importance of the preservation of hepatic functions in the protection from liver injury.

Comparison of the Effects of Intraperitoneal Injection with Carbon Tetrachloride on Acute Liver Toxicity in Male and Female Kunming Mice

Background

Acute chemical liver injury needs to be further explored. The present study aimed to compare the effects of intraperitoneal injection with carbon tetrachloride on acute liver toxicity after 24 h in male and female Kunming mice.

Material/Methods

In this study, female and male mice were simultaneously divided into 3 different groups. Each group was treated differently, and after 24 h, blood samples were collected to check for changes in the activity of alanine aminotransferase (ALT) and aspartate aminotransferase (AST), which were used to assess liver toxicity. Liver samples were used for hematoxylin-eosin staining, and periodic acid Schiff reagent staining was performed to detect the pathological changes of each group. The expression level of biomarker molecules in liver cells was also systematically analyzed.

Results

Our results showed that, compared with male mice, female mice showed more serious damage: reduced glycogen and higher degree of necrosis, and the levels of heatshock protein 27 (HSP27), heat-shock protein 70 (HSP70), proliferating cell nuclear antigen (PCNA) and B cell lymphoma/lewkmia-2 (Bcl-2) were significantly lower than in the male group (P<0.05 or P<0.01), while the results of Bcl-2-associated X protein (Bax), cysteinyl aspartate specific proteinase 3 (Caspase3), and cytochrome P450 2E1 (CYP2E1) were the opposite (P<0.05 or P<0.01).

Conclusions

The findings from this study showed that, compared with male mice, at 24 h after CCl₄ toxicity, female mice showed more severe changes of hepatocyte necrosis and PAS-positivity, with significantly reduced expression of HSP27, HSP70, PCNA, and Bcl-2, and significantly increased expression of Bax, caspase-3, and CYP2E1.

Antioxidant properties of Klunzinger's mullet (Liza klunzingeri) protein hydrolysates prepared with enzymatic hydrolysis using a commercial protease and microbial hydrolysis with Bacillus licheniformis

Antioxidant activity of Klunzinger's mullet (Liza klunzingeri) muscle hydrolysates obtained using Bacillus licheniformis fermentation and enzymatic hydrolysis was determined. Hydrolysates obtained after 6 days of fermentation with B. licheniformis showed the highest free radical scavenging activity, metal chelating ability and ferric reducing antioxidant power (FRAP) (P ≤ 0.05). Microbial fermentation led to a higher percentage of small peptides and higher solubility compared with Alcalase hydrolysis (P ≤ 0.05). Hydrolysates showing the highest antioxidant properties attenuated serum, liver, and kidney oxidative stress biomarkers in male Wister rats stressed by carbon tetrachloride (P ≤ 0.05). At 300 mg/kg oral administration, hydrolysates increased serum, renal, and hepatic total antioxidant capacity (TAC) (P ≤ 0.05) and reduced their elevated levels of malondialdehyde (MDA), nitric oxide (NO^•), and serum liver enzymes (AST, ALP, and ALT) (P ≤ 0.05). The hydrolysates were able to ameliorate hepatic damage by reducing necrosis, fatty changes, and inflammation. Results showed the antioxidant and hepato-toxic protective activities of Klunzinger's mullet muscle hydrolysates obtained using microbial fermentation, which may, therefore, potentially be considered as a functional food ingredient.

Thermoresponsive polysaccharides with tunable thermoresponsive properties via functionalisation with alkylamide groups

Polysaccharides have been used widely in many industries, from food technology and mining to cosmetics and biomedical applications. Over recent years there has been growing interest in the development of responsive polysaccharides with unique and switchable properties, particularly systems that display lower-critical solution temperatures (LCSTs). Therefore, in this study we aimed to investigate a novel strategy that would allow the conversion of non-responsive polysaccharides into thermoresponsive polysaccharides with tuneable LCSTs. Through the functionalisation of dextran with alkylamide groups (isopropyl amide, diethyl amide, piperidinyl and diisobutyl amide) using a carbodiimide coupling approach in conjunction with amic acid derivatives, we prepared a library of novel dextrans with various degrees of substitution (DS), which were characterised via nuclear magnetic resonance (NMR) spectroscopy and gel permeation chromatography (GPC). The alkylamide-functionalised dextrans were found to have good solubility in aqueous solutions, with the exception of those having a high DS of large hydrophobic substituents. Determination of the thermoresponsive characteristics of the polymer solutions via UV-vis spectroscopy revealed that the LCST of the alkylamide-functionalised dextrans was highly dependent on the type of alkylamide group and the DS and could be tuned over a large range (5-35 °C). Above the LCST, all of the thermoresponsive alkylamide-functionalised dextrans formed colloidal dispersions with particles sizes ranging from 400 -600 nm, as determined by dynamic light scattering (DLS). In addition, the polymers were found to exhibit a fast and reversible phase transition in solution with narrow hysteresis (∼ 1-5 °C). Finally, the injectability and biocompatibility of the novel thermoresponsive dextrans was confirmed in vivo via subcutaneous and intracranial ventricle injections, with no local or systemic toxicity noted over a 14 d period. Overall, the alkylamide-functionalised dextrans display interesting thermoresponsive properties and trends that may make them useful in biomedical applications, such as drug-delivery.

Period1 mediates rhythmic metabolism of toxins by interacting with CYP2E1

The biological clock is an endogenous biological timing system, which controls metabolic functions in almost all organs. Nutrient metabolism, substrate processing, and detoxification are circadian controlled in livers. However, how the clock genes respond to toxins and influence toxicity keeps unclear. We identified the clock gene Per1 was specifically elevated in mice exposed to toxins such as carbon tetrachloride (CCl₄). Mice lacking Per1 slowed down the metabolic rate of toxins including CCl₄, capsaicin, and acetaminophen, exhibiting relatively more residues in the plasma. Liver injury and fibrosis induced by acute and chronic CCl₄ exposure were markedly alleviated in Per1-deficient mice. These processes involved the binding of PER1 protein and hepatocyte nuclear factor-1alpha (HNF-1α), which enhances the recruitment of HNF-1α to cytochrome P450 2E1 (Cyp2e1) promoter and increases Cyp2e1 expression, thereby promoting metabolism for toxins in the livers. These results indicate that PER1 mediates the metabolism of toxins and appropriate suppression of Per1 response is a potential therapeutic target for toxin-induced hepatotoxicity.

Dietary Iron Overload Differentially Modulates Chemically-Induced Liver Injury in Rats

Hepatic iron overload is well known as an important risk factor for progression of liver diseases; however, it is unknown whether it can alter the susceptibility to drug-induced hepatotoxicity. Here we investigate the pathological roles of iron overload in two single-dose models of chemically-induced liver injury. Rats were fed a high-iron (Fe) or standard diet (Cont) for four weeks and were then administered with allyl alcohol (AA) or carbon tetrachloride (CCl₄). Twenty-four hours after administration mild mononuclear cell infiltration was seen in the periportal/portal area (Zone 1) in Cont-AA group, whereas extensive hepatocellular necrosis was seen in Fe-AA group. Centrilobular (Zone 3) hepatocellular necrosis was prominent in Cont-CCl₄ group, which was attenuated in Fe-CCl₄ group. Hepatic lipid peroxidation and hepatocellular DNA damage increased in Fe-AA group compared with Cont-AA group. Hepatic caspase-3 cleavage increased in Cont-CCl₄ group, which was suppressed in Fe-CCl₄ group. Our results showed that dietary iron overload exacerbates AA-induced Zone-1 liver injury via enhanced oxidative stress while it attenuates CCl₄-induced Zone-3 liver injury, partly via the suppression of apoptosis pathway. This study suggested that susceptibility to drugs or chemical compounds can be differentially altered in iron-overloaded livers.

The Genetic Architecture of Carbon Tetrachloride-Induced Liver Fibrosis in Mice

BACKGROUND & AIMS

Liver fibrosis is a multifactorial trait that develops in response to chronic liver injury. Our aim was to characterize the genetic architecture of carbon tetrachloride (CCl₄)-induced liver fibrosis using the Hybrid Mouse Diversity Panel, a panel of more than 100 genetically distinct mouse strains optimized for genome-wide association studies and systems genetics.

METHODS

Chronic liver injury was induced by CCl₄ injections twice weekly for 6 weeks. Four hundred thirty-seven mice received CCl₄ and 256 received vehicle, after which animals were euthanized for liver histology and gene expression. Using automated digital image analysis, we quantified fibrosis as the collagen proportionate area of the whole section, excluding normal collagen.

RESULTS

We discovered broad variation in fibrosis among the Hybrid Mouse Diversity Panel strains, demonstrating a significant genetic influence. Genome-wide association analyses revealed significant and suggestive loci underlying susceptibility to fibrosis, some of which overlapped with loci identified in mouse crosses and human population studies. Liver global gene expression was assessed by RNA sequencing across the strains, and candidate genes were identified using differential expression and expression quantitative trait locus analyses. Gene set enrichment analyses identified the underlying pathways, of which stellate cell involvement was prominent, and coexpression network modeling identified modules associated with fibrosis.

CONCLUSIONS

Our results provide a rich resource for the design of experiments to understand mechanisms underlying fibrosis and for rational strain selection when testing antifibrotic drugs.

A single pretreatment with clofibric acid attenuates carbon tetrachloride-induced necrosis, but not steatosis, in rat liver

The present study investigated whether a single pretreatment with clofibric acid suppresses liver injury in rats after CCl₄ intoxication. Rats received a single pretreatment with clofibric acid (100 mg/kg, i.p.) 1 h prior to a CCl₄ (1 mL/kg, p.o.) challenge, and were euthanized 24 h after the CCl₄ administration. A single pretreatment with clofibric acid effectively suppressed increases in the serum aminotransferase activities and the severity of necrosis following the CCl₄ challenge, whereas the pretreatment did not protect against CCl₄-induced fatty liver. The clofibric acid pretreatment did not affect blood concentrations of CCl₄ in the early stage after CCl₄ dosing, or the level of the CCl₄ reaching the liver 1 h after the CCl₄ challenge. Moreover, the clofibric acid pretreatment did not affect the intensity of the covalent binding of the [¹⁴C]CCl₄ metabolite to microsomal proteins and lipids. The clofibric acid pretreatment did not alter microsomal cytochrome P450 2E1 activity. Based on these results, we conclude that protection against CCl₄-induced hepatocellular necrosis by a clofibric acid pretreatment does not require its repeated administration, and that a single and brief pre-exposure to clofibric acid prior to CCl₄ dosing markedly suppresses necrosis without affecting the development and progression of steatosis.

Crocin attenuates CCl4-induced liver fibrosis via PPAR-γ mediated modulation of inflammation and fibrogenesis in rats

BACKGROUND

Liver fibrosis is a chronic pathological condition with a leading cause of liver-related mortality worldwide. In the present study, we have evaluated the antifibrotic effect of crocin, a carotenoid present in the stigma of Crocus sativus, and also explored its putative mechanism of action.

METHODS

Liver fibrosis was induced by intraperitoneal administration of 30% carbon tetrachloride (CCl₄). The crocin was administered orally at 20, 40 and 80 mg/kg body weight along with CCl₄ up to 8 weeks.

RESULTS

Chronic exposure to CCl₄ resulted in elevated levels of liver enzymes and reduced cytochrome P450 2E1 (CYP2E1) activity in the liver. The liver tissue showed cellular swelling, vacuolization, necrosis, infiltration of inflammatory cells and fibrotic changes. The crocin treatment significantly lowered the levels of liver enzymes in serum and improved the liver CYP2E1 mRNA levels. The pathological changes in the liver were also lowered by crocin treatment. The level of pro-inflammatory cytokines, nuclear factor-kappa B, interleukin-6 and tumor necrosis factor α and fibrogenic factor, transforming growth factor β, and α-smooth muscle actin were elevated by the CCl₄ in the liver tissue. However, crocin treatment at different doses significantly reduced the expression of these factors. The increased caspase 3/7 activity was also lowered by crocin. CCl₄ administration decreased the expression of peroxisome proliferator-activated receptor γ (PPAR-γ) in liver tissue. The improved PPAR-γ expression in the liver by crocin treatment indicates its role in the therapeutic effect of crocin.

CONCLUSIONS

Crocin attenuated the various events in the progression of liver fibrosis via PPAR-γ mediated modulation of inflammatory and fibrogenic pathways.

Dendrobium nobile Lindl. alkaloids-mediated protection against CCl4-induced liver mitochondrial oxidative damage is dependent on the activation of Nrf2 signaling pathway

The activation of nuclear factor erythroid 2-related factor 2 (Nrf2)-mediated signaling pathway has been involved in the mechanisms of a variety of protective agents against cellular oxidative stress. We recently demonstrated that Dendrobium nobile Lindl. alkaloids (DNLA), the active ingredients of Dendrobium, protects mice from CCl₄-induced liver injury, dependent on the Nrf2 signaling pathway. The present study was aimed to determine whether the protection against mitochondrial oxidative damage plays a role in the mode of action of DNLA on CCl₄-induced liver injury, and to further investigate whether the DNLA-conferred mitochondrial beneficial effects is dependent on the activation of Nrf2 signaling. The CCl₄-induced acute liver injury model was employed in both wild-type (WT) and Nrf2-knockout (Nrf2^-/-) mice. The results showed that in WT mice DNLA reduced CCl₄-induced liver injury, accompanied by a significant reduction in CCl₄-induced mitochondrial oxidative stress as evidenced by a decrease in mitochondrial H₂O₂ content and MDA production, and a marked increase in GSH level and Mn-SOD activity. However, these protective effects were significantly attenuated in Nrf2^-/- mice. Furthermore, the administration of DNLA improved mitochondrial oxygen consumption, elevated ATP production, and decreased CCl₄-induced apoptosis in the WT mice, whereas the DNLA-mediated protections on mitochondrial function were diminished in the Nrf2 null mice. These results demonstrate that the improvement of mitochondrial oxidative stress and mitochondrial dysfunction is implicated in the mechanism of DNLA-mediated protection on CCl₄-induced liver injury, and this DNLA-modulated mode of action is dependent on the activation of Nrf2 signaling pathway.

Kynurenine produced by indoleamine 2,3-dioxygenase 2 exacerbates acute liver injury by carbon tetrachloride in mice

Kynurenine (Kyn) plays an important role as an immune check-point molecule and regulates various immune responses through its aryl hydrocarbon receptor (Ahr). Kyn is synthesized by indoleamine 2,3-dioxygenase (Ido) and tryptophan 2,3-dioxygenase (Tdo). Ido contributes approximately 90% of tryptophan catabolism. Although Kyn is increased in various liver disorders, the roles of Kyn in liver injury are complicated because Ido1, Ido2, and Tdo are activated in different cell types. In this study, the roles of Ido2 in carbon tetrachloride (CCl₄; 1 ml/kg, i.p.)-induced acute liver injury were examined using Ido2 knockout mice and Ido2 inhibitor. After CCl₄ treatment, the ratio of Kyn to tryptophan and levels of Kyn in the liver were increased, accompanied by activation of Ahr-mediated signaling, as revealed by increased nuclear Ahr and Cyp1a1 mRNA. Knockout of Ido2 (Ido2^-/-) and treatment with Ido2 inhibitor 1-methyl-D-tryptophan (D-1MT; 100 mg/kg, i.p.) attenuated CCl₄-induced liver injury, with decreased induction of Ahr-mediated signaling. Administration of D-Kyn (100 mg/kg, i.p.) to Ido2^-/- mice canceled the effect of Ido2 deficiency and exacerbated acute liver damage by CCl₄ treatment. In addition, liver fibrosis induced by repeated CCl₄ administration was suppressed in Ido2^-/- mice. In conclusion, the action of Ido2 and Kyn in the liver may prevent severe hepatocellular damage and liver fibrosis.

Interaction of Lipoplex with Albumin Enhances Gene Expression in Hepatitis Mice

Understanding the in vivo fate of lipoplex, which is composed of cationic liposomes and DNA, is an important issue toward gene therapy. In disease conditions, the fate of lipoplex might change compared with the normal condition. Here, we examined the contribution of interaction with serum components to in vivo transfection using lipoplex in hepatitis mice. Prior to administration, lipoplex was incubated with serum or albumin. In the liver, the interaction with albumin enhanced gene expression in hepatitis mice, while in the lung, the interaction with serum or albumin enhanced it. In normal mice, the interaction with albumin did not enhance hepatic and pulmonary gene expression. Furthermore, hepatic and pulmonary gene expression levels of albumin-interacted lipoplex were correlated with serum transaminases in hepatitis mice. The albumin interaction increased the hepatic accumulation of lipoplex and serum tumor necrosis factor-α level. We suggest that the interaction with albumin enhanced the inflammation level after the administration of lipoplex in hepatitis mice. Consequently, the enhancement of the inflammation level might enhance the gene expression level. Information obtained in the current study will be valuable toward future clinical application of the lipoplex.

Naringenin Ameliorate Carbon Tetrachloride-Induced Hepatic Damage Through Inhibition of Endoplasmic Reticulum Stress and Autophagy in Rats

Hepatic fibrosis emerges upon exposure of liver to various chemicals and if not treated, it develops various diseases such as cirrhosis and cancer. Carbon tetrachloride (CCl₄) is a widely used toxin in animal models to develop hepatic fibrosis. Accumulation of unfolded proteins in cells causes stress in the endoplasmic reticulum (ER) and various mechanisms are involved in the cell to reduce the damage caused by these unfolding proteins. The most well known of these is the unfolded protein response. Further, autophagy works to remove these proteins if the damage cannot be repaired and is permanent. In our study, we investigated the effects of naringenin (NRG), a flavanon abundant in citrus fruits, on ER stress and autophagy in CCl₄-injured rat liver. The animals were given 0.2 mL/kg of CCl₄ for 10 days and treatment group was administered 100 mg/kg of NRG for 14 days. Histopathological examination was performed to show liver damage and to determine the therapeutic properties of the active substance. Transmission electron microscopy (TEM) analysis was carried out to establish cell level damage and effect of treatment. In addition, levels of ER stress and autophagy markers of liver were measured. According to our findings, TEM demonstrated positive effect of NRG and histological examinations reported ameliorative effects. In addition, NRG reduced levels of ER stress markers and inhibited autophagy significantly compared to CCl₄-treated group. As a result, NRG significantly reduced damage in hepatocytes and provided a significant amelioration.

Weaning Mice and Adult Mice Exhibit Differential Carbon Tetrachloride-Induced Acute Hepatotoxicity

Age is a risk factor for drug-induced liver injury (DILI). However, there is a limited understanding of pediatric DILI. Here, 2-week-old weaning and 8-week-old adult male ICR mice were intraperitoneally injected with CCl₄ (0.1 mmol/kg equal to 15.4 mg/kg) to comparatively evaluate the time-dependent liver damage and cellular events. CCl₄ significantly enhanced the serum alanine aminotransferase/aspartate aminotransferase levels and hepatic centrilobular necrosis in the weaning mice, whereas it induced mild liver injury in the adult mice. CCl₄-treated weaning mice exhibited higher hepatic levels of pro-apoptotic proteins (Bax, cleaved caspase-3, -7, and -9), activated MAPKs (p-JNK and p-Erk), and endoplasmic reticulum stress indicators (ATF6 and CHOP) and lower hepatic anti-apoptotic Bcl-2 levels than the adult mice. The weaning mice exhibited enhanced basal hepatic glutathione (GSH) levels due to high glutamate cysteine ligase (GCL) and low anti-cysteine dioxygenase (CDO) enzyme levels. However, CCl₄ markedly reduced the hepatic GSH levels only in the weaning mice. Furthermore, higher hepatic levels of oxidative stress-induced malondialdehyde, 4-hydroxynonenal, nitrotyrosine-protein adducts, and oxidized proteins were observed in CCl₄-treated weaning mice than in CCl₄-treated adult mice. The enhanced levels of hepatic cytochrome P450 (CYP) 2E1 and CYP3A, and decreased hepatic GSH S-transferase (GST)-π and GSH reductase (GR) levels in the weaning mice may contribute to their enhanced susceptibility to liver damage.

The protective effect of Liza klunzingeri protein hydrolysate on carbon tetrachloride-induced oxidative stress and toxicity in male rats

Objective(s):

Today, consumers are looking for food products providing health benefits in addition to meeting the basic nutritional needs of the body. This study aimed to evaluate the antioxidant and cytotoxic effects of Liza klunzingeri protein hydrolysate both in vivo and in vitro.

Materials and Methods:

Fish protein hydrolysate (FPH) was prepared using enzymatic hydrolysis with papain. In vitro antioxidant activity was assessed using five different antioxidant assays. The cytotoxic effect on 4T1 cell line was evaluated using the MTT assay. The distribution of the molecular weight of FPH was measured using HPLC. In the in vivo study, CCl4-exposed Wistar rats were orally treated with FPH (150, 300, and 600 mg/kg) or gallic acid (50 mg/kg) for 28 consecutive days.

Results:

Enzymatic hydrolysis gave hydrolysate rich in low molecular weight peptides (<1000 Da) with strong free radicals (ABTS, DPPH, and OH) scavenging activity and cytotoxicity. Treatment of CCl4-exposed rats with all doses of FPH significantly lowered serum aspartate aminotransferase (AST) and alanine aminotransferase (ALT). FPH at doses of 300 and 600 mg/kg significantly decreased lipid peroxidation and improved total antioxidant capacity in serum, liver, and kidney of the CCl4 exposed rats. All doses of L.klunzingeri protein hydrolysate reduced CCl4-induced nitric oxide production of the kidney. Liver histopathological damage caused by CCl4 also ameliorated with all doses of FPH.

Conclusion:

L. klunzingeri protein hydrolysate can be considered as a functional food to alleviate oxidative stress

Mediator MED23 regulates inflammatory responses and liver fibrosis

Liver fibrosis, often associated with cirrhosis and hepatocellular carcinomas, is characterized by hepatic damage, an inflammatory response, and hepatic stellate cell (HSC) activation, although the underlying mechanisms are largely unknown. Here, we show that the transcriptional Mediator complex subunit 23 (MED23) participates in the development of experimental liver fibrosis. Compared with their control littermates, mice with hepatic Med23 deletion exhibited aggravated carbon tetrachloride (CCl4)-induced liver fibrosis, with enhanced chemokine production and inflammatory infiltration as well as increased hepatocyte regeneration. Mechanistically, the orphan nuclear receptor RAR-related orphan receptor alpha (RORα) activates the expression of the liver fibrosis-related chemokines C-C motif chemokine ligand 5 (CCL5) and C-X-C motif chemokine ligand 10 (CXCL10), which is suppressed by the Mediator subunit MED23. We further found that the inhibition of Ccl5 and Cxcl10 expression by MED23 likely occurs because of G9a (also known as euchromatic histone-lysine N-methyltransferase 2 [EHMT2])-mediated H3K9 dimethylation of the target promoters. Collectively, these findings reveal hepatic MED23 as a key modulator of chemokine production and inflammatory responses and define the MED23-CCL5/CXCL10 axis as a potential target for clinical intervention in liver fibrosis.

Animal Models of Hepatocellular Carcinoma Prevention

Hepatocellular carcinoma (HCC) is a deadly disease and therapeutic efficacy in advanced HCC is limited. Since progression of chronic liver disease to HCC involves a long latency period of a few decades, a significant window of therapeutic opportunities exists for prevention of HCC and improve patient prognosis. Nonetheless, there has been no clinical advancement in instituting HCC chemopreventive strategies. Some of the major challenges are heterogenous genetic aberrations of HCC, significant modulation of tumor microenvironment and incomplete understanding of HCC tumorigenesis. To this end, animal models of HCC are valuable tools to evaluate biology of tumor initiation and progression with specific insight into molecular and genetic mechanisms involved. In this review, we describe various animal models of HCC that facilitate effective ways to study therapeutic prevention strategies that have translational potential to be evaluated in a clinical context.

The essential role of CYP2E1 in metabolism and hepatotoxicity of N,N-dimethylformamide using a novel Cyp2e1 knockout mouse model and a population study

N,N-Dimethylformamide (DMF) is a widespread contaminant of leather factories and their surrounding environment. There is a lack of direct in vivo evidence supporting CYP2E1 as a primary enzyme responsible for DMF metabolism and hepatotoxicity. In this study, a novel Cyp2e1 knockout (KO) mouse model was generated and used to assess whether DMF metabolism and hepatotoxicity is CYP2E1 dependent using an acute toxicity protocol with a single dose of 1500 mg DMF/kg. An epidemiological study in 698 DMF-exposed workers and 188 non-DMF-exposed controls was conducted to investigate the associations between functional polymorphisms of CYP2E1 (rs6413432/rs2031920) and DMF metabolite (N-methylcarbmoylated-hemoglobin [NMHb]). We successfully established Cyp2e1 KO mice with evidence from DNA sequence analysis, which showed 1-bp insertion at 65 bp (C) site of Cyp2e1 Exon 1. In addition, western blot and in vivo pharmacokinetic study also showed a complete absence of CYP2E1 protein and a 92% and 88% reduction in CYP2E1 activity among males and females, respectively. DMF metabolism as evidenced by increased blood NMHb, and hepatotoxicity as evidenced by elevated liver/body weight ratio, activity of liver enzymes and massive liver necrosis were detected in wild-type (WT) mice but were completely abrogated in KO mice, strongly supporting a CYP2E1-dependent pattern of DMF metabolism and hepatotoxicity. Moreover, variant allele of CYP2E1-rs6413432 was also significantly associated with higher NMHb levels in DMF-exposed workers (P = 0.045). The increase of glucose-regulated protein 94 detected in WT mice but not in KO mice suggested CYP2E1-dependent endoplasmic reticulum stress may be a key mechanism underlying DMF-induced hepatotoxicity.

Metformin prevents liver tumourigenesis by attenuating fibrosis in a transgenic mouse model of hepatocellular carcinoma

Metformin is a hypoglycaemic agent used to treat type 2 diabetes mellitus (DM2) patients, with a broad safety profile. Since previous epidemiological studies had shown that the incidence of hepatocellular carcinoma (HCC) decreased significantly in metformin treated DM2 patients, we hypothesised that intervention with metformin could reduce the risk of neoplastic transformation of hepatocytes. HCC is the most common primary liver malignancy and it generally originates in a background of liver fibrosis and cirrhosis. In the present study, we took advantage of a transgenic mouse (TG221) characterized by microRNA-221 overexpression, with cirrhotic liver background induced by chronic administration of carbon tetrachloride (CCl4). This mouse model develops fibrosis, cirrhosis and liver tumours that become visible in 100% of mice at 5-6 months of age. Our results demonstrated that metformin intervention improves liver function, inhibits hepatic stellate cell (HSC) activation, reduces liver fibrosis, depletes lipid accumulation in hepatocytes, halts progression to decompensated cirrhosis and abrogates development HCC in CCl4 challenged transgenic mouse model. The study establishes the rationale for investigating metformin in cirrhotic patients regardless of concomitant DM2 status.

Hepatoprotective effects of an Acer tegmentosum Maxim extract through antioxidant activity and the regulation of autophagy

ETHNOPHARMACOLOGICAL RELEVANCE

Acer tegmentosum Maxim (AT), the East Asian stripe maple, is an herb used to treat liver disease and is approved as a functional food in Korea. AT protects against hepatic disorders, atopic dermatitis, and diabetes mellitus.

AIM OF THE STUDY

We explored the mechanism of the hepatoprotective effects of AT extract in in vitro and in vivo levels.

MATERIALS AND METHODS

AT extract from Acer tegmentosum Maxim was extracted by hot water. Hepatoprotective effects of AT extract were confirmed using carbon tetrachloride (CCl₄)- or alcohol-induced mouse model, and H₂O₂- or alcohol-induced HepG2 (liver hepatocellular carcinoma cell line) cells by measuring GOT, GPT, TG, and MDA levels. Hematoxylin and eosin (H&E) staining was used to observe the pathological analysis. Cytotoxicity or protective effect of AT extract was confirmed using MTT assay in HepG2 cells. Antioxidant effect of AT extract was measured using DPPH or H₂DCFDA assay. Mechanism study of antioxidant and autophagy was carried out using western blotting and immunofluorescence analysis.

RESULTS

AT extract increased the viability of HepG2 cells treated with H₂O₂ and ethanol, and protected the liver against damage induced by CCl₄ and alcohol. The AT extract increased the levels of nuclear respiratory factor 2 (Nrf2) and heme oxygenase-1 (HO-1). The level of microtubule-associated protein light chain 3 (LC3)-Ⅱ, beclin-1, autophagy-related genes (Atg) such as Atg3 and Atg12-5 as markers of autophagy activation was also increased. Moreover, the AT extract increased activation of mitogen-activated protein kinase (MAPK), which regulated autophagy and HO-1.

CONCLUSION

Therefore, these results indicate that the AT extract has a hepatoprotective effect by increasing antioxidant activity and inducing autophagy.

Induction of Nrf2 pathway by Dendrobium nobile Lindl. alkaloids protects against carbon tetrachloride induced acute liver injury

Dendrobium nobile Lindl. alkaloids (DNLA), the active ingredients of Dendrobium, has been shown to possess anti-oxidative effects. The nuclear factor erythroid 2-related factor 2 (Nrf2) antioxidant signaling pathway plays a critical role in the cellular response to oxidative stress. Oxidative damage has been implicated in the mechanism of various hepatotoxins induced liver injury. The present study aimed to examine the protective effects of DNLA on CCl₄-induced acute liver injury, and to explore the role of the Nrf2 pathway in the protective action of DNLA. Wild-type (WT) and Nrf2-knockout (Nrf2^-/-) mice were administrated with DNLA (20 mg/kg/day, ig) for 7 days, and then challenged with CCl₄ (20 μL/kg, ip). In WT mice, DNLA reduced CCl₄ induced liver injury, as evidenced by the reduction in the serum levels of alanine aminotransferase (ALT) and aspartate aminotransferase (AST), attenuation of malondialdehyde (MDA) production, and improved ultrastructural morphology in hepatocytes. However, the protective effect was diminished in Nrf2^-/- mice, indicating an essential role of Nrf2 in DNLA-mediated protection over CCl₄ liver injury. Furthermore, it was found that DNLA enhanced Nrf2 expression and nuclear accumulation and increased the expression of Nrf2 regulated downstream proteins. These results demonstrate that DNLA protects mice from CCl₄ induced liver injury, probably through the activation of the Nrf2 signaling pathway.

Engineered Animal Models Designed for Investigating Ethanol Metabolism, Toxicity and Cancer

Excessive consumption of alcohol is a leading cause of lifestyle-induced morbidity and mortality worldwide. Although long-term alcohol abuse has been shown to be detrimental to the liver, brain and many other organs, our understanding of the exact molecular mechanisms by which this occurs is still limited. In tissues, ethanol is metabolized to acetaldehyde (mainly by alcohol dehydrogenase and cytochrome p450 2E1) and subsequently to acetic acid by aldehyde dehydrogenases. Intracellular generation of free radicals and depletion of the antioxidant glutathione (GSH) are believed to be key steps involved in the cellular pathogenic events caused by ethanol. With continued excessive alcohol consumption, further tissue damage can result from the production of cellular protein and DNA adducts caused by accumulating ethanol-derived aldehydes. Much of our understanding about the pathophysiological consequences of ethanol metabolism comes from genetically-engineered mouse models of ethanol-induced tissue injury. In this review, we provide an update on the current understanding of important mouse models in which ethanol-metabolizing and GSH-synthesizing enzymes have been manipulated to investigate alcohol-induced disease.

Hepatocyte-specific suppression of microRNA-221-3p mitigates liver fibrosis

BACKGROUND & AIMS

Fibrosis, a cardinal feature of a dysfunctional liver, significantly contributes to the ever-increasing mortality due to end-stage chronic liver diseases. The crosstalk between hepatocytes and hepatic stellate cells (HSCs) plays a key role in the progression of fibrosis. Although ample efforts have been devoted to elucidate the functions of HSCs during liver fibrosis, the regulatory functions of hepatocytes remain elusive.

METHODS

Using an unbiased functional microRNA (miRNA) screening, we investigated the ability of hepatocytes to regulate fibrosis by fine-tuning gene expression via miRNA modulation. The in vivo functional analyses were performed by inhibiting miRNA in hepatocytes using adeno-associated virus in carbon-tetrachloride- and 3,5-di-diethoxycarbonyl-1,4-dihydrocollidine-induced liver fibrosis.

RESULTS

Blocking miRNA-221-3p function in hepatocytes during chronic liver injury facilitated recovery of the liver and faster resolution of the deposited extracellular matrix. Furthermore, we demonstrate that reduced secretion of C-C motif chemokine ligand 2, as a result of post-transcriptional regulation of GNAI2 (G protein alpha inhibiting activity polypeptide 2) by miRNA-221-3p, mitigates liver fibrosis.

CONCLUSIONS

Collectively, miRNA modulation in hepatocytes, an easy-to-target cell type in the liver, may serve as a potential therapeutic approach for liver fibrosis.

LAY SUMMARY

Liver fibrosis majorly contributes to mortality resulting from various liver diseases. We discovered a small RNA known as miRNA-221-3p, whose downregulation in hepatocytes results in reduced liver fibrosis. Thus, inhibition of miRNA-221-3p may serve as one of the therapeutic approaches for treatment of liver fibrosis.

Role of CYP2E1 in Mitochondrial Dysfunction and Hepatic Injury by Alcohol and Non-Alcoholic Substances

Alcoholic fatty liver disease (AFLD) and non-alcoholic fatty liver disease (NAFLD) are two pathological conditions that are spreading worldwide. Both conditions are remarkably similar with regard to the pathophysiological mechanism and progression despite different causes. Oxidative stressinduced mitochondrial dysfunction through post-translational protein modifications and/or mitochondrial DNA damage has been a major risk factor in both AFLD and NAFLD development and progression. Cytochrome P450-2E1 (CYP2E1), a known important inducer of oxidative radicals in the cells, has been reported to remarkably increase in both AFLD and NAFLD. Interestingly, CYP2E1 isoforms expressed in both endoplasmic reticulum (ER) and mitochondria, likely lead to the deleterious consequences in response to alcohol or in conditions of NAFLD after exposure to high fat diet (HFD) and in obesity and diabetes. Whether CYP2E1 in both ER and mitochondria work simultaneously or sequentially in various conditions and whether mitochondrial CYP2E1 may exert more pronounced effects on mitochondrial dysfunction in AFLD and NAFLD are unclear. The aims of this review are to briefly describe the role of CYP2E1 and resultant oxidative stress in promoting mitochondrial dysfunction and the development or progression of AFLD and NAFLD, to shed a light on the function of the mitochondrial CYP2E1 as compared with the ER-associated CYP2E1. We finally discuss translational research opportunities related to this field.

Chemical induction of hepatic apoptosis in rodents

The urge of identifying new pharmacological interventions to prevent or attenuate liver injury is of critical importance and needs an expanded experimental toolbox. Hepatocyte injury and cellular death is a prominent feature behind the pathology of liver diseases. Several research activities focused on identifying chemicals and hepatotoxicants that induce cell death by apoptosis, in addition to presenting its corresponding signaling pathway. Although such efforts provided further understanding of the mechanisms of cell death, it has also raised confusion concerning identifying the involvement of several modes of cell death including apoptosis, necrosis and fibrosis. The current review highlights the ability of several chemicals and potential hepatotoxicants to induce liver damage in rodents by means of apoptosis while the probable involvement of other modes of cell death is also exposed. Thus, several chemical substances including hepatotoxins, mycotoxins, hyperglycemia inducers, metallic nanoparticles and immunosuppressant drugs are reviewed to explore the hepatic cytotoxic spectrum they could exert on hepatocytes of rodents. In addition, the current review address the mechanism by which hepatotoxicity is initiated in hepatocytes in different rodents aiding the researcher in choosing the right animal model for a better research outcome.

Confounding influence of tamoxifen in mouse models of Cre recombinase-induced gene activity or modulation

Tamoxifen (TAM) is commonly used for cell type specific Cre recombinase-induced gene inactivation and in cell fate tracing studies. Inducing a gene knockout by TAM and using non-TAM exposed mice as controls lead to a situation where differences are interpreted as consequences of the gene knockout but in reality result from TAM-induced changes in hepatic metabolism. The degree to which TAM may compromise the interpretation of animal experiments with inducible gene expression still has to be elucidated. Here, we report that TAM strongly attenuates CCl₄-induced hepatotoxicity in male C57Bl/6N mice, even after a 10 days TAM exposure-free period. TAM decreased (p < 0.0001) the necrosis index and the level of aspartate- and alanine transaminases in CCl₄-treated compared to vehicle-exposed mice. TAM pretreatment also led to the downregulation of CYP2E1 (p = 0.0045) in mouse liver tissue, and lowered its activity in CYP2E1 expressing HepG2 cell line. Furthermore, TAM increased the level of the antioxidant ascorbate, catalase, SOD2, and methionine, as well as phase II metabolizing enzymes GSTM1 and UGT1A1 in CCl₄-treated livers. Finally, we found that TAM increased the presence of resident macrophages and recruitment of immune cells in necrotic areas of the livers as indicated by F4/80 and CD45 staining. In conclusion, we reveal that TAM increases liver resistance to CCl₄-induced toxicity. This finding is of high relevance for studies using the tamoxifen-inducible expression system particularly if this system is used in combination with hepatotoxic compounds such as CCl₄.

Neutrophils alleviate fibrosis in the CCl4-induced mouse chronic liver injury model

Tribbles pseudokinase 1 (Trib1) is a negative regulator of CCAAT/enhancer binding protein α (C/EBPα) and is known to induce granulopoiesis while suppressing monocyte differentiation. Loss of Trib1 was previously shown to increase the neutrophil population in the spleen but lead to M2-like macrophage reduction. Because M2 macrophages are anti-inflammatory and promote tissue repair by producing fibrogenic factors, we investigated liver fibrosis in Trib1-deficient mice. Interestingly, loss of Trib1 suppressed fibrosis in the CCl4-induced chronic liver injury model. Trib1 knockout increased neutrophils but had a minimal effect on the macrophage population in the liver. Hepatic expressions of neutrophil matrix metalloproteinases (Mmp)8 and Mmp9 were increased, but the production of fibrogenic factors, including transforming growth factor β1, was not affected by loss of Trib1. These results suggest that neutrophils are responsible for the suppression of fibrosis in Trib1-deficient liver. Consistently, transplantation of Trib1-deficient bone marrow cells into wild-type mice alleviated CCl4-induced fibrosis. Furthermore, expression of chemokine (C-X-C motif) ligand 1 (Cxcl1) by adeno-associated viral vector in the normal liver recruited neutrophils and suppressed CCl4-induced fibrosis; infusion of wild-type neutrophils in CCl4-treated mice also ameliorated fibrosis. Using recombinant adeno-associated virus-mediated expression of Mmp8 and Mmp9 alleviated liver fibrosis. Finally, neutrophil depletion by infusion of Ly6G antibody significantly enhanced CCl4-induced fibrosis. Conclusion: While neutrophils are well known to exacerbate acute liver injury, our results demonstrate a beneficial role of neutrophils in chronic liver injury by promoting fibrolysis. (Hepatology Communications 2018;2:703-717).

Molecular mechanism for the influence of gender dimorphism on alcoholic liver injury in mice

It is known that women develop alcoholic liver injury more rapidly and have a lower alcohol toxic threshold than men. However, the detailed molecular mechanisms remain unclear. The precise mechanism responsible for the sex difference needs to be determined. Female and male mice were given ethanol by intragastric infusion every day for 4 weeks. The pathological changes were detected by hematoxylin-eosin, Sirius red, oil red O, periodic acid-Schiff, and Hochest33258 staining in the liver of female and male mice. The related gene and protein expression of hepatocytes stress, proliferation and apoptosis, glycogen synthesis, lipid metabolism, and hepatic fibrosis were also systematically analyzed in the female and male mice. Livers from ethanol-treated female mice had more serious hepatocyte necrosis, liver fibrosis ( P < 0.01), substantial micro/macrovesicular steatosis ( p < 0.01), glycogen consumption ( p < 0.05), and hepatocytes apoptosis ( p < 0.05) than ethanol-treated male mice. The expression of heat shock protein 27 (HSP27), HSP70, proliferating cell nuclear antigen, B-cell lymphoma/leukemia-2 (Bcl-2), and phosphorylated signal transducer and activators of transcription 3 (p-STAT3) was higher in ethanol-treated male mice than ethanol-treated female mice ( P < 0.05 or P < 0.01). But, the expression of Bax (Bcl-2-associated X protein), Caspase 3, CYP2E1 (cytochrome P4502E1), and transforming growth factor βl had the contrary results. Our study suggested that ethanol treatment induced more expression of HSP27 and HSP70, faster hepatocyte proliferation, higher level of glycogen, and interleukin-6 signaling pathway activation, but less hepatocyte apoptosis and CYP2E1 expression in male mice than female mice, which could be helpful to understand the molecular mechanism for the influence of sex difference on alcoholic liver injury.

Mitochondrial Effects of Teucrium Polium and Prosopis Farcta Extracts in Colorectal Cancer Cells

Background:

Teucrium Polium and Prosopis Farcta have been traditionally employed in cancer treatment. In this study we evaluated the effects of methanolic extracts of these two plants in HT-29 cells.

Methods:

IC50s of extracts were obtained via MTT assay and the levels of ROS production, cell death, collapse of mitochondrial membrane potential and Sirt3 enzyme activity were determined.

Results:

After 48 hours exposure, IC50s for Teucrium and Prosopis extracts were 3 and 2µg/ml, respectively. Extracts induced higher ROS production after 6 hours than after 12 hours. Mitochondrial membrane potential collapse and cell death rate were also increased; Teucrium caused greater cell death than Prosopis. Extracts from both plants increased Sirt3 activity in its normal form, but only Teucrium extract caused a significant increase in activity of Sirt3 enzyme isolated from cancer cells.

Conclusion:

Teucrium and Prosopis extracts exert anticancer activity via mitochondrial alterations, as exemplified by increased ROS levels, Sirt3 activity and cell death in HT-29 colorectal cancer cells.

Neoboutonia melleri var velutina Prain: in vitro and in vivo hepatoprotective effects of the aqueous stem bark extract on acute hepatitis models

BACKGROUND

Hepatitis is a liver inflammation caused by different agents and remains a public health problem worldwide. Medicinal plants are an important source of new molecules being considered for treatment of this disease. Our work aims at evaluating the hepatoprotective properties of Neoboutonia velutina, a Cameroonian medicinal plant.

METHODS

The aqueous extract has been prepared using phytochemical methods. HepG2 cells were used to assess anti-inflammatory properties of the extract at different concentrations. Acute hepatitis models (Carbon tetrachloride and Concanavalin A) were performed in mice receiving or not receiving, different extract doses by gavage. Liver injury was assessed using histology, transaminases and pro-inflammatory markers. Extract antioxidant and radical scavenging capacities were evaluated.

RESULTS

The extract led to a significant decrease in pro-inflammatory cytokine expression in vitro and to a remarkable protection of mice from carbon tetrachloride-induced liver injury, as shown by a significant decrease in dose-dependent transaminases level. Upon extract treatment, inflammatory markers were significantly decreased and liver injuries were limited as well. In the Concanavalin A model, the extract displayed weak effects.

CONCLUSIONS

Taking into account underlying mechanisms in both hepatitis models, we demonstrate the extract's radical scavenging capacity. Neoboutonia velutina displays a potent hepatoprotective effect mediated through radical scavenging properties.

Cytochrome P450s and Alcoholic Liver Disease

Alcohol consumption causes liver diseases, designated as Alcoholic Liver Disease (ALD). Because alcohol is detoxified by alcohol dehydrogenase (ADH), a major ethanol metabolism system, the development of ALD was initially believed to be due to malnutrition caused by alcohol metabolism in liver. The discovery of the microsomal ethanol oxidizing system (MEOS) changed this dogma. Cytochrome P450 enzymes (CYP) constitute the major components of MEOS. Cytochrome P450 2E1 (CYP2E1) in MEOS is one of the major ROS generators in liver and is considered to be contributive to ALD. Our labs have been studying the relationship between CYP2E1 and ALD for many years. Recently, we found that human CYP2A6 and its mouse analog CYP2A5 are also induced by alcohol. In mice, the alcohol induction of CYP2A5 is CYP2E1-dependent. Unlike CYP2E1, CYP2A5 protects against the development of ALD. The relationship of CYP2E1, CYP2A5, and ALD is a major focus of this review.

The role of human cytochrome P450 2E1 in liver inflammation and fibrosis

Cytochrome P450 2E1 (CYP2E1) plays an important role in alcohol and toxin metabolism by catalyzing the conversion of substrates into more polar metabolites and producing reactive oxygen species. Reactive oxygen species-induced oxidative stress promotes hepatocyte injury and death, which in turn induces inflammation, activation of hepatic stellate cells, and liver fibrosis. Here, we analyzed mice expressing only the human CYP2E1 gene (hCYP2E1) to determine differences in hCYP2E1 versus endogenous mouse Cyp2e1 function with different liver injuries. After intragastric alcohol feeding, CYP2E1 expression was induced in both hCYP2E1 and wild-type (Wt) mice. hCYP2E1 mice had greater inflammation, fibrosis, and lipid peroxidation but less hepatic steatosis. In addition, hCYP2E1 mice demonstrated increased expression of fibrogenic and proinflammatory genes but decreased expression of de novo lipogenic genes compared to Wt mice. Lipidomics of free fatty acid, triacylglycerol, diacylglycerol, and cholesterol ester species and proinflammatory prostaglandins support these conclusions. Carbon tetrachloride-induced injury suppressed expression of both mouse and human CYP2E1, but again hCYP2E1 mice exhibited greater hepatic stellate cell activation and fibrosis than Wt controls with comparable expression of proinflammatory genes. By contrast, 14-day bile duct ligation induced comparable cholestatic injury and fibrosis in both genotypes. Conclusion: Alcohol-induced liver fibrosis but not hepatic steatosis is more severe in the hCYP2E1 mouse than in the Wt mouse, demonstrating the use of this model to provide insight into the pathogenesis of alcoholic liver disease. (Hepatology Communications 2017;1:1043-1057).

Hepatoprotective properties of Penthorum chinense Pursh against carbon tetrachloride-induced acute liver injury in mice

Background

Penthorum chinense Pursh (Penthoraceae, PCP), a well-known Miao ethnomedicine, has been traditionally used to treat several liver-related diseases, such as jaundice and viral hepatitis. The aims of the present study were to evaluate the probable properties of the aqueous extract of PCP on carbon tetrachloride (CCl₄)—induced acute liver injury in mice.

Methods

C57BL/6 mice were orally administered an aqueous extract of PCP (5.15 and 10.3 g/kg BW) or silymarin (100 mg/kg) once daily for 1 week prior to CCl₄ exposure. Silymarin serves as a positive drug to validate the effectivenes of PCP.

Results

A single dose of CCl₄ exposure caused severe acute liver injury in mice, as evidenced by the elevated serum levels of alanine aminotransferase (ALT), aspartate aminotransferase (AST) and alanine phosphatase (ALP), and the increased TUNEL-positive cells in liver, which were remarkably ameliorated by the pretreatment of PCP. PCP was also found to decrease the levels of malondialdehyde (MDA), restore the glutathione (GSH) and enhance the activities of superoxide dismutase (SOD) and catalase (CAT) in the liver. In addition, the pretreatment of PCP inhibited the degradation of hepatic cytochrome P450 2E1 (CYP2E1), up-regulated the expression of nuclear factor erythroid 2-related factor 2 (Nrf2) and its target proteins in CCl₄-treated mice.

Conclusion

Results indicated that the pretreatment of PCP (10.3 g/kg BW) effectively protected against CCl₄-induced acute liver injury, which was comparable to efficacy of silymarin (100 mg/kg). This hepatoprotective effects might be attributed to amelioration of CCl₄-induced oxidative stress via activating Nrf2 signaling pathway.

Electronic supplementary material

The online version of this article (10.1186/s13020-017-0153-x) contains supplementary material, which is available to authorized users.

Deferoxamine alleviates liver fibrosis induced by CCl4 in rats

Several chronic liver diseases can lead to the occurrence of hepatic fibrosis through the accumulation of iron, which causes induction of oxidative stress and consequently activation of fibrogenesis. The present study was designed to investigate the potential antifibrotic and anti-oxidant effects of deferoxamine (DFO), a well-known iron chelator in an experimental rat model of liver injury using carbon tetrachloride (CCl4 ). First, the potential effective dose of DFO was screened against CCl4 -induced acute hepatotoxicity. Then, rats were co-treated with DFO (300 mg/kg, i.p.) for 6 weeks starting from the third week of CCl4 induction of chronic hepatotoxicity. Liver function was assessed in addition to histopathological examination. Furthermore, oxidative stress and fibrosis markers were assessed. It was found that treatment of animals with DFO significantly counteracted the changes in liver function; histopathological lesions and hepatic iron deposition that were induced by CCl4 . DFO also significantly counteracted the CCl4 -induced lipid peroxidation increase and reduction in antioxidant activities of superoxide dismutase and glutathione peroxidase enzymes. In addition, DFO ameliorated significantly liver fibrosis markers including hydroxyproline, collagen accumulation, and the expression of the hepatic stellate cells (HSCs) activation marker; alpha smooth muscle actin and transforming growth factor-beta (TGF-β). Together, these findings indicate that DFO possesses a potent antifibrotic effect due to its antioxidant properties that counteracted oxidative stress and lipid peroxidation and restored antioxidant enzymes activities as well as reducing HSCs activation and fibrogenesis.

Alcohol and Cancer: Mechanisms and Therapies

Several scientific and clinical studies have shown an association between chronic alcohol consumption and the occurrence of cancer in humans. The mechanism for alcohol-induced carcinogenesis has not been fully understood, although plausible events include genotoxic effects of acetaldehyde, cytochrome P450 2E1 (CYP2E1)-mediated generation of reactive oxygen species, aberrant metabolism of folate and retinoids, increased estrogen, and genetic polymorphisms. Here, we summarize the impact of alcohol drinking on the risk of cancer development and potential underlying molecular mechanisms. The interactions between alcohol abuse, anti-tumor immune response, tumor growth, and metastasis are complex. However, multiple studies have linked the immunosuppressive effects of alcohol with tumor progression and metastasis. The influence of alcohol on the host immune system and the development of possible effective immunotherapy for cancer in alcoholics are also discussed here. The conclusive biological effects of alcohol on tumor progression and malignancy have not been investigated extensively using an animal model that mimics the human disease. This review provides insights into cancer pathogenesis in alcoholics, alcohol and immune interactions in different cancers, and scope and future of targeted immunotherapeutic modalities in patients with alcohol abuse.