Hepatic stellate cells contain the functional estrogen receptor beta but not the estrogen receptor alpha in male and female rats

Estrogen/estrogen receptor activation protects against DEN-induced liver fibrosis in female rats via modulating TLR-4/NF-kβ signaling

AIM

Men are more susceptible to liver fibrosis (LF) than women. However, the underlying molecular mechanism, especially the role of estrogen/estrogen receptor (ER) activation in this sexual dimorphism is unclear. Therefore, the aim of the current study was to investigate the impact and the underlying molecular mechanisms of estrogen/ER activation on diethyl nitrosamine (DEN)-induced LF.

MAIN METHODS

Thirty ovariectomized (OVX) female rats were randomly allocated into five groups (n = 6), and received no treatment, diethyl nitrosamine (DEN), DEN/fulvestrant, DEN/silymarin or DEN/estradiol benzoate (EB). In addition, three sham groups received no treatment, DEN or DEN/fulvestrant, and one control group that neither ovariectomized nor treated. Directly after treatment, liver injury biomarkers were measured. In addition, hepatic tissue hydroxyproline, TNF- α, TGF- β, and IL-10 were evaluated. Expression of NF-kβ, CD68 (a marker for macrophage infiltration), ER-β and TLR-4 were measured. Finally, liver tissue histopathology was assessed.

KEY FINDINGS

Ovariectomy aggravates DEN-induced LF, as it significantly elevated all liver tissue injury biomarkers. This effect has become even worse after blocking ER by fulvestrant, indicating a protective role of estrogen/ER activation against DEN-induced LF. Inhibition of TLR-4/NF-kβ signaling pathway contributed to this protective effect, as estrogen deprivation or blocking of ER significantly activates this pathway during the onset of LF. While administration of EB or silymarin (selective ER-β activator) improved LF indices and deactivated this pathway.

SIGNIFICANCE

These results provide new insight into the pivotal role of estrogen/ER activation via modulation of TLR-4/NF-kβ, in the alleviation of LF pathogenesis.

Metabolic benefits of 17α-estradiol in liver are partially mediated by ERβ in male mice

Metabolic dysfunction underlies several chronic diseases. Dietary interventions can reverse metabolic declines and slow aging but remaining compliant is difficult. 17α-estradiol (17α-E2) treatment improves metabolic parameters and slows aging in male mice without inducing significant feminization. We recently reported that estrogen receptor α is required for the majority of 17α-E2-mediated benefits in male mice, but that 17α-E2 also attenuates fibrogenesis in liver, which is regulated by estrogen receptor β (ERβ)-expressing hepatic stellate cells (HSC). The current studies sought to determine if 17α-E2-mediated benefits on systemic and hepatic metabolism are ERβ-dependent. We found that 17α-E2 treatment reversed obesity and related systemic metabolic sequela in both male and female mice, but this was partially blocked in female, but not male, ERβKO mice. ERβ ablation in male mice attenuated 17α-E2-mediated benefits on hepatic stearoyl-coenyzme A desaturase 1 (SCD1) and transforming growth factor β1 (TGF-β1) production, which play critical roles in HSC activation and liver fibrosis. We also found that 17α-E2 treatment suppresses SCD1 production in cultured hepatocytes and hepatic stellate cells, indicating that 17α-E2 directly signals in both cell-types to suppress drivers of steatosis and fibrosis. We conclude that ERβ partially controls 17α-E2-mediated benefits on systemic metabolic regulation in female, but not male, mice, and that 17α-E2 likely signals through ERβ in HSCs to attenuate pro-fibrotic mechanisms.

Pre- and Post-Sexual Maturity Liver-specific ERα Knockout Does Not Impact Hepatic Mitochondrial Function

Compared with males, premenopausal women and female rodents are protected against hepatic steatosis and present with higher functioning mitochondria (greater hepatic mitochondrial respiration and reduced H2O2 emission). Despite evidence that estrogen action mediates female protection against steatosis, mechanisms remain unknown. Here we validated a mouse model with inducible reduction of liver estrogen receptor alpha (ERα) (LERKO) via adeno-associated virus (AAV) Cre. We phenotyped the liver health and mitochondrial function of LERKO mice (n = 10-12 per group) on a short-term high-fat diet (HFD), and then tested whether timing of LERKO induction at 2 timepoints (sexually immature: 4 weeks old [n = 11 per group] vs sexually mature: 8-10 weeks old [n = 8 per group]) would impact HFD-induced outcomes. We opted for an inducible LERKO model due to known estrogen-mediated developmental programming, and we reported both receptor and tissue specificity with our model. Control mice were ERαfl/fl receiving AAV with green fluorescent protein (GFP) only. Results show that there were no differences in body weight/composition or hepatic steatosis in LERKO mice with either short-term (4-week) or chronic (8-week) high-fat feeding. Similarly, LERKO genotype nor timing of LERKO induction (pre vs post sexual maturity) did not alter hepatic mitochondrial O2 and H2O2 flux, coupling, or OXPHOS protein. Transcriptomic analysis showed that hepatic gene expression in LERKO was significantly influenced by developmental stage. Together, these studies suggest that hepatic ERα is not required in female protection against HFD-induced hepatic steatosis nor does it mediate sexual dimorphism in liver mitochondria function.

Metabolic benefits of 17α-estradiol in liver are partially mediated by ERβ in male mice

Metabolic dysfunction underlies several chronic diseases. Dietary interventions can reverse metabolic declines and slow aging but remaining compliant is difficult. 17α-estradiol (17α-E2) treatment improves metabolic parameters and slows aging in male mice without inducing significant feminization. We recently reported that estrogen receptor α is required for the majority of 17α-E2-mediated benefits in male mice, but that 17α-E2 also attenuates fibrogenesis in liver, which is regulated by estrogen receptor β (ERβ)-expressing hepatic stellate cells (HSC). The current studies sought to determine if 17α-E2-mediated benefits on systemic and hepatic metabolism are ERβ-dependent. We found that 17α-E2 treatment reversed obesity and related systemic metabolic sequela in both male and female mice, but this was partially blocked in female, but not male, ERβKO mice. ERβ ablation in male mice attenuated 17α-E2-mediated benefits on hepatic stearoyl-coenyzme A desaturase 1 (SCD1) and transforming growth factor β1 (TGF-β1) production, which play critical roles in HSC activation and liver fibrosis. We also found that 17α-E2 treatment suppresses SCD1 production in cultured hepatocytes and hepatic stellate cells, indicating that 17α-E2 directly signals in both cell-types to suppress drivers of steatosis and fibrosis. We conclude that ERβ partially controls 17α-E2-mediated benefits on systemic metabolic regulation in female, but not male, mice, and that 17α-E2 likely signals through ERβ in HSCs to attenuate pro-fibrotic mechanisms.

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.

Astaxanthin Attenuates Nonalcoholic Steatohepatitis with Downregulation of Osteoprotegerin in Ovariectomized Mice Fed Choline-Deficient High-Fat Diet

BACKGROUND

Postmenopausal estrogen decline increases the risk of developing nonalcoholic steatohepatitis (NASH), and it might accelerate progression to cirrhosis and hepatocellular carcinoma.

AIMS

This study aimed to investigate a novel therapy for postmenopausal women who are diagnosed with NASH.

METHODS

Seven-week-old female C57BL/6 J mice were divided into three experimental groups as follows: (1) sham operation (SHAM group), (2) ovariectomy (OVX group), and (3) ovariectomy + 0.02% astaxanthin (OVX + ASTX group). These three groups of mice were fed a choline-deficient high-fat (CDHF) diet for 8 weeks. Blood serum and liver tissues were collected to examine liver injury, histological changes, and hepatic genes associated with NASH. An in vitro study was performed with the hepatic stellate cell line LX-2.

RESULTS

The administration of ASTX significantly improved pathological NASH with suppressed steatosis, inflammation, and fibrosis, in comparison with those in the OVX-induced estrogen deficiency group. As a result, liver injury was also attenuated with reduced levels of alanine aminotransferase and aspartate transaminase. In addition, our study found that ASTX supplementation decreased hepatic osteoprotegerin (OPG) in vivo, a possible factor that contributes to NASH development. In vitro, this study further confirmed that ASTX has an inhibitory effect on the secretion of OPG in LX-2 human hepatic stellate cells.

CONCLUSIONS

Our findings suggest that ASTX alleviates CDHF-OVX-induced pathohistological NASH with downregulated OPG, possibly via suppression of the transforming growth factor beta pathway. ASTX could has promise for use in postmenopausal women diagnosed with NASH.

Overexpression of estrogen receptor β inhibits cellular functions of human hepatic stellate cells and promotes the anti-fibrosis effect of calycosin via inhibiting STAT3 phosphorylation

BACKGROUND

Estrogen receptor β (ERβ) is the major ER subtype in hepatic stellate cells (HSCs). Previously we reported phytoestrogen calycosin suppressed liver fibrosis progression and inhibited HSC-T6 cell functions, suggesting the effects may be related to ERβ. Here, we explore the effect of overexpressed ERβ on human HSCs and the role of ERβ in pharmacological action of calycosin.

METHODS

LX-2 cells were transfected with lentivirus to overexpress ERβ. In the presence or absence of overexpressed ERβ, the effects of ERβ and calycosin on proliferation, migration, activation, collagen production and degradation of TGF-β1-induced LX-2 cells and the role of ERβ in the inhibition effect of calycosin were investigated. LX-2 cells overexpressed with ERβ or treated with ER non-selective antagonist ICI182,780 were used to investigate the regulation of ERβ on JAK2/STAT3 signaling pathway. CCK-8 method was used to screen effective doses of calycosin and investigate cell proliferation. The cell migration was detected by transwell chamber assay. The expression of α-SMA was detected by immunofluorescence and western blot. The protein expressions of Col-I, MMP1, TIMP1, JAK2, p-JAK2, STAT3 and p-STAT3 were detected by western blot.

RESULTS

ERβ overexpressed lentivirus was successfully transfected into LX-2 cells with high efficiency. Overexpressed ERβ or calycosin alone inhibited the TGF-β1-induced LX-2 cell proliferation and migration, downregulated the protein expressions of α-SMA, Col-I, TIMP-1, p-STAT3 and upregulated MMP-1. Both overexpressed ERβ and calycosin had no significant effect on JAK2, p-JAK2 and STAT3 expressions. ERβ overexpression further enhanced the above effects of calycosin. However, after the cells were treated with ICI182,780, downregulation of STAT3 phosphorylation induced by calycosin was reversed.

CONCLUSIONS

ERβ mediated the inhibition of major functions of LX-2 cell possibly by inhibiting the phosphorylation of STAT3, and was an important pathway through which calycosin exerted anti-liver fibrosis effect.

Saikosaponin d Alleviates Liver Fibrosis by Negatively Regulating the ROS/NLRP3 Inflammasome Through Activating the ERβ Pathway

Background and aims: Saikosaponin d (SSd) has a steroidal structure and significant anti-inflammatory effects. The purpose of this study was to explore the mechanism underlying SSd’s inhibitory effects on liver fibrosis.

Methods: Wild-type and estrogen receptor knockout (ERKO) mice were treated with CCl₄ to establish liver fibrosis mouse models. The effects of SSd on hepatic fibrogenesis were studied in these mouse models. Hepatic stellate cells (HSCs) were activated by H₂O₂ to investigate the potential molecular mechanisms. The establishment of the models and the degrees of inflammation and liver tissue fibrosis were evaluated by detecting changes in serum liver enzymes and liver histopathology. The expression of α-SMA and TGF-β1 was determined by immunohistochemistry. The expression and significance of NLRP3 inflammasome proteins were explored by RT-PCR and Western blotting analyses. The mitochondrial ROS-related indexes were evaluated by MitoSOX Red.

Results: In wild-type and ERKO mice treated with CCl₄, the fluorescence expression of mitochondrial ROS was up-regulated, while the mitochondrial membrane potential and ATP content were decreased, suggesting that the mitochondria were damaged. In addition, the expression of NLRP3 inflammatory bodies and fibrosis markers (α-SMA, TGF-β, TIMP-1, MMP-2, and Vimentin) in liver tissue increased. Furthermore, the above indexes showed the same expression trend in activated HSCs. In addition, the peripheral serum ALT and AST levels increased in CCl₄-induced liver injury model mice. And HE staining showed a large number of inflammatory cell infiltration in the liver of model mice. Picric acid-Sirius staining and Masson staining showed that there was significant collagen fibrous tissue deposition in mice liver sections. IHC and WB detection confirmed that the expression of α-SMA and TGF-β1 increased. Liver fibrosis scores were also elevated. Then, after SSd intervention, the expression of ROS in wild-type mice and αERKO mice decreased, mitochondrial membrane potential recovered, ATP level increased, NLRP3 inflammasome and fibrosis indexes decreased, liver enzyme levels decreased, and liver pathology showed liver inflammation. The damage and collagen deposition were significantly relieved, the expression of α-SMA and TGF-β1 was decreased, and the fibrosis score was also decreased. More importantly, the effect of SSd in alleviating liver injury and liver fibrosis had no effect on βERKO mice.

Conclusion: SSd alleviated liver fibrosis by negatively regulating the ROS/NLRP3 inflammasome through activating the ERβ pathway. By establishing liver fibrosis models using wild-type and ERKO mice, we demonstrated that SSd could alleviate liver fibrosis by inhibiting the ROS/NLRP3 inflammasome axis through activating the ERβ pathway.

Saikosaponins: A Review of Structures and Pharmacological Activities

Radix Bupleuri is a traditional medicine widely used in China and other Asian countries. Phytochemistry and pharmacology study reveal that saikosaponins(SSs) are the main bioactive compounds in Radix Bupleuri. SSs are complex compounds composed of triterpene aglycone and carbohydrate part containing 1-13 monosaccharides, which can be divided into seven types based on their structural characteristics. Many different kinds of SSs have been isolated from plants of Bupleurum L. SSs show a variety of biological activities, such as central nervous system protection, liver protection, antivirus, anti-tumor, anti-inflammation, hormone-like effects, and immune regulation functions. Due to their broad activity and favorable safety profile, SSs attract an increasing amount of attention in recent years. In this review, the structures of 86 SSs are summarized based on the different aglycones due to the diverse structures of saikosaponin(SS). The pharmacological effects and related mechanism of SSs are thoroughly reviewed, and perspectives for future research are further discussed.

Beyond the X Factor: Relevance of Sex Hormones in NAFLD Pathophysiology

Non-alcoholic fatty liver disease (NAFLD) is a major health issue worldwide, being frequently associated with obesity, unbalanced dietary regimens, and reduced physical activity. Despite their greater adiposity and reduced physical activity, women show a lower risk of developing NAFLD in comparison to men, likely a consequence of a sex-specific regulation of liver metabolism. In the liver, sex differences in the uptake, synthesis, oxidation, deposition, and mobilization of lipids, as well as in the regulation of inflammation, are associated with differences in NAFLD prevalence and progression between men and women. Given the major role of sex hormones in driving hepatic sexual dimorphism, this review will focus on the role of sex hormones and their signaling in the regulation of hepatic metabolism and in the molecular mechanisms triggering NAFLD development and progression.

Saikosaponin-d protects against liver fibrosis by regulating Estrogen receptor-β/NLRP3 inflammasome pathway

Liver fibrosis is the ultimate common pathway in most types of chronic liver damage characterized by imbalance of extracellular matrix degradation and synthesis. Saikosaponin-d (SSd) possesses anti-inflammatory and anti-liver fibrosis effects. However, the underlying mechanism of SSd in repressing hepatic stellate cells (HSCs) activation remains unclear. Here we found that SSd alleviated remarkably carbon tetrachloride (CCl4)-induced liver fibrosis, as evidenced by decreased collagen level and profibrotic markers (COl1a1 and α-smooth muscle actin (SMA)) expression. SSd repressed CCl4-induced NOD-like receptor family pyrin-domain-containng-3 (NLRP3) activation in fibrotic livers, as suggested by decreased level of NLRP3, IL-18, and IL-β. The primary HSCs of CCl4 mice exhibited a significant increase in profibrotic markers expression and NLRP3 activation, but SSd treatment reversed the effect. SSd also repressed TGF-β-induced profibrotic markers expression and NLRP3 activation in vitro. Mechanistically, TGF-β decreased the expression of Estrogen receptor-β (ERβ) in HSCs, whereas SSd treatment reversed the effect. ERβ inhibition enhanced NLRP3 activation in HSCs. More important, ERβ or NLRP3 inhibition destroyed partially the function of SSd on anti-liver fibrosis. In summary, the current data suggest that SSd prevents hepatic fibrosis through regulating ERβ/NLRP3 inflammasome pathway, and suggest SSd as a potential agent for treating liver fibrosis.

Sex-Related Differences of Acute and Chronic Pancreatitis in Adults

The incidence of acute and chronic pancreatitis is increasing in the United States. Rates of acute pancreatitis (AP) are similar in both sexes, but chronic pancreatitis (CP) is more common in males. When stratified by etiology, women have higher rates of gallstone AP, while men have higher rates of alcohol- and tobacco-related AP and CP, hypercalcemic AP, hypertriglyceridemic AP, malignancy-related AP, and type 1 autoimmune pancreatitis (AIP). No significant sex-related differences have been reported in medication-induced AP or type 2 AIP. Whether post-endoscopic retrograde cholangiopancreatography pancreatitis is sex-associated remains controversial. Animal models have demonstrated sex-related differences in the rates of induction and severity of AP, CP, and AIP. Animal and human studies have suggested that a combination of risk factor profiles, as well as genes, may be responsible for the observed differences. More investigation into the sex-related differences of AP and CP is desired in order to improve clinical management by developing effective prevention strategies, diagnostics, and therapeutics.

Hepatoprotective effect and possible mechanism of phytoestrogen calycosin on carbon tetrachloride-induced liver fibrosis in mice

The study was to explore the hepatoprotective effect and possible mechanism of calycosin on carbon tetrachloride (CCl4)-induced liver fibrosis in mice. Hepatic fibrosis was induced by intraperitoneal injection of CCl4 in C57BL/6 male mice. Serum alanine aminotransferase (ALT) and aspartate transaminase (AST) activity, superoxide dismutase (SOD) activity, and hydroxyproline (Hyp) and malondialdehyde (MDA) levels were determined by biochemical assays. Liver histopathology was assessed by H&E and Masson trichrome staining. The mRNA expressions of α-smooth muscle actin (α-SMA), collagen-I (Col-I), Janus kinase 2 (JAK2) and signal transducer and activator of transcription 3 (STAT3) were determined using qRT-PCR. The protein levels of α-SMA, Col-I, estrogen receptor α (ERα), estrogen receptor β (ERβ), tissue inhibitor of metalloproteinase-1 (TIMP-1), matrix metalloproteinase-1 (MMP-1), JAK2, phospho-JAK2 (p-JAK2), STAT3, and phospho-STAT3 (p-STAT3) were detected by Western blotting. The levels of α-SMA and ERβ were measured by immunohistochemistry. Calycosin significantly reduced liver index, MDA level, and ALT and AST activity and increased SOD activity. The α-SMA, Col-I, and Hyp of the calycosin group were significantly lower than those of the model group. Calycosin increased MMP-1 and inhibited TIMP-1 expression resulting in the improvement of MMP-1/TIMP-1 ratio. Importantly, calycosin improved ERβ protein expression, JAK2 and STAT3 mRNA expressions, p-JAK2/JAK2, and p-STAT3/STAT3 relative protein expressions. However, ERα, JAK2, and STAT3 protein expressions were relatively unchanged. Calycosin significantly inhibits liver fibrosis in mice, and its mechanism may involve the following: calycosin inhibits oxidative stress; calycosin inhibits collagen synthesis and balances MMP-1/TIMP-1 system; calycosin increases ERβ expression and activates JAK2-STAT3 pathway.

Estrogen receptor agonists protect against acetaminophen-induced hepatorenal toxicity in rats

AIMS

Acetaminophen-induced hepatorenal toxicity varies among sexes with controversial results among species. The aim was to compare the impact of sex and ovarian hormones on hepatorenal toxicity and to elucidate protective effects of estrogen and estrogen receptor (ER) agonists.

MAIN METHODS

Under anesthesia, female rats underwent ovariectomy (OVX) or sham-OVX. Starting at postsurgical 40th day, OVX-rats received subcutaneously (each, 1 mg/kg/day) 17β-estradiol (E₂), ERβ-agonist (DPN) or ERα-agonist (PPT) for 10 days, while male and sham-OVX rats received vehicle for 10 days. Then, rats received either acetaminophen (3 g/kg) or saline by orogastric gavage and were decapitated at 24th h. Blood samples were obtained to measure serum ALT, AST, BUN, creatinine levels. Liver and kidney samples were obtained for histopathologic examination and for analyzing levels of luminol- and lucigenin-chemiluminescence, glutathione and myeloperoxidase activity.

KEY FINDINGS

Compared to their control groups, levels of AST, ALT, BUN, creatinine, hepatic and renal myeloperoxidase activity and chemiluminescence levels were increased, and hepatic glutathione level was decreased in acetaminophen-administered male groups, while ALT and hepatic chemiluminescence levels were not elevated in sham-OVX-rats. Both ER-agonists and E₂ reduced BUN, creatinine and reversed all oxidative parameters in renal tissues of OVX-rats. Additionally, ERα-agonist reversed all hepatic injury parameters, while ERβ-agonist elevated hepatic glutathione level.

SIGNIFICANCE

Acetaminophen toxicity in female rats presented with a more preserved hepatic function, while renal toxicity was not influenced by sex or by the lack of ovarian hormones. Pretreatment with estrogen or ER agonists, via their antioxidant actions, provided protective effects on acetaminophen-induced hepatorenal toxicity.

Non-alcoholic Fatty Liver Disease as a Canonical Example of Metabolic Inflammatory-Based Liver Disease Showing a Sex-Specific Prevalence: Relevance of Estrogen Signaling

There is extensive evidence supporting the interplay between metabolism and immune response, that have evolved in close relationship, sharing regulatory molecules and signaling systems, to support biological functions. Nowadays, the disruption of this interaction in the context of obesity and overnutrition underlies the increasing incidence of many inflammatory-based metabolic diseases, even in a sex-specific fashion. During evolution, the interplay between metabolism and reproduction has reached a degree of complexity particularly high in female mammals, likely to ensure reproduction only under favorable conditions. Several factors may account for differences in the incidence and progression of inflammatory-based metabolic diseases between females and males, thus contributing to age-related disease development and difference in life expectancy between the two sexes. Among these factors, estrogens, acting mainly through Estrogen Receptors (ERs), have been reported to regulate several metabolic pathways and inflammatory processes particularly in the liver, the metabolic organ showing the highest degree of sexual dimorphism. This review aims to investigate on the interaction between metabolism and inflammation in the liver, focusing on the relevance of estrogen signaling in counteracting the development and progression of non-alcoholic fatty liver disease (NAFLD), a canonical example of metabolic inflammatory-based liver disease showing a sex-specific prevalence. Understanding the role of estrogens/ERs in the regulation of hepatic metabolism and inflammation may provide the basis for the development of sex-specific therapeutic strategies for the management of such an inflammatory-based metabolic disease and its cardio-metabolic consequences.

Sex differences in non-alcoholic fatty liver disease: hints for future management of the disease

Non-alcoholic fatty liver disease (NAFLD) remains a major cause of chronic liver disease worldwide. Despite extensive studies, the heterogeneity of the risk factors as well as different disease mechanisms complicate the goals toward effective diagnosis and management. Recently, it has been shown that sex differences play a role in the prevalence and progression of NAFLD. In vitro, in vivo, and clinical studies revealed that the lower prevalence of NAFLD in premenopausal as compared to postmenopausal women and men is mainly due to the protective effects of estrogen and body fat distribution. It has been also described that males and females present differential pathogenic features in terms of biochemical profiles and histological characteristics. However, the exact molecular mechanisms for the gender differences that exist in the pathogenesis of NAFLD are still elusive. Lipogenesis, oxidative stress, and inflammation play a key role in the progression of NAFLD. For NAFLD, only a few studies characterized these mechanisms at the molecular level. Therefore, we aim to review the reported differential molecular mechanisms that trigger such different pathogenesis in both sexes. Differences in lipid metabolism, glucose homeostasis, oxidative stress, inflammation, and fibrosis were discussed based on the evidence reported in recent publications. In conclusion, with this review, we hope to provide a new perspective for the development of future practice guidelines as well as a new avenue for the management of the disease.

Estrogen Receptor beta (ERβ) Regulation of Lipid Homeostasis-Does Sex Matter?

In this communication, we aim to summarize the role of estrogen receptor beta (ERβ) in lipid metabolism in the main metabolic organs with a special focus on sex differences. The action of ERβ is tissue-specific and acts in a sex-dependent manner, emphasizing the necessity of developing sex- and tissue-selective targeting drugs in the future.

Potential Therapeutic Application of Estrogen in Gender Disparity of Nonalcoholic Fatty Liver Disease/Nonalcoholic Steatohepatitis

Nonalcoholic fatty liver disease (NAFLD) caused by fat accumulation in the liver is globally the most common cause of chronic liver disease. Simple steatosis can progress to nonalcoholic steatohepatitis (NASH), a more severe form of NAFLD. The most potent driver for NASH is hepatocyte death induced by lipotoxicity, which triggers inflammation and fibrosis, leading to cirrhosis and/or liver cancer. Despite the significant burden of NAFLD, there is no therapy for NAFLD/NASH. Accumulating evidence indicates gender-related NAFLD progression. A higher incidence of NAFLD is found in men and postmenopausal women than premenopausal women, and the experimental results, showing protective actions of estradiol in liver diseases, suggest that estrogen, as the main female hormone, is associated with the progression of NAFLD/NASH. However, the mechanism explaining the functions of estrogen in NAFLD remains unclear because of the lack of reliable animal models for NASH, the imbalance between the sexes in animal experiments, and subsequent insufficient results. Herein, we reviewed the pathogenesis of NAFLD/NASH focused on gender and proposed a feasible association of estradiol with NAFLD/NASH based on the findings reported thus far. This review would help to expand our knowledge of the gender differences in NAFLD and for developing gender-based treatment strategies for NAFLD/NASH.

Sex Differences in Nonalcoholic Fatty Liver Disease: State of the Art and Identification of Research Gaps

Despite tremendous research advancements in nonalcoholic fatty liver disease (NAFLD), our understanding of sex differences in NAFLD remains insufficient. This review summarizes the current knowledge on sex differences in NAFLD, identifies gaps, and discusses important considerations for future research. The prevalence and severity of NAFLD are higher in men than in women during the reproductive age. However, after menopause, NAFLD occurs at a higher rate in women, suggesting that estrogen is protective. Sex differences also exist for the major risk factors of NAFLD. In general, animal models of NAFLD recapitulate the sex differences observed in patients, with more severe steatosis and steatohepatitis, more proinflammatory/profibrotic cytokines, and a higher incidence of hepatic tumors in male than female subjects. Based on computer modeling, female and male livers are metabolically distinct with unique regulators modulating sex-specific metabolic outcomes. Analysis of the literature reveals that most published clinical and epidemiological studies fail to examine sex differences appropriately. Considering the paucity of data on sex differences and the knowledge that regulators of pathways relevant to current therapeutic targets for NAFLD differ by sex, clinical trials should be designed to test drug efficacy and safety according to sex, age, reproductive stage (i.e., menopause), and synthetic hormone use. Conclusion: Sex differences do exist in the prevalence, risk factors, fibrosis, and clinical outcomes of NAFLD, suggesting that, while not yet incorporated, sex will probably be considered in future practice guidelines; adequate consideration of sex differences, sex hormones/menopausal status, age, and other reproductive information in clinical investigation and gene association studies of NAFLD are needed to fill current gaps and implement precision medicine for patients with NAFLD.

Beneficial and Deleterious Effects of Female Sex Hormones, Oral Contraceptives, and Phytoestrogens by Immunomodulation on the Liver

The liver is considered the laboratory of the human body because of its many metabolic processes. It accomplishes diverse activities as a mixed gland and is in continuous cross-talk with the endocrine system. Not only do hormones from the gastrointestinal tract that participate in digestion regulate the liver functions, but the sex hormones also exert a strong influence on this sexually dimorphic organ, via their receptors expressed in liver, in both health and disease. Besides, the liver modifies the actions of sex hormones through their metabolism and transport proteins. Given the anatomical position and physiological importance of liver, this organ is evidenced as an immune vigilante that mediates the systemic immune response, and, in turn, the immune system regulates the hepatic functions. Such feedback is performed by cytokines. Pro-inflammatory and anti-inflammatory cytokines are strongly involved in hepatic homeostasis and in pathological states; indeed, female sex hormones, oral contraceptives, and phytoestrogens have immunomodulatory effects in the liver and the whole organism. To analyze the complex and interesting beneficial or deleterious effects of these drugs by their immunomodulatory actions in the liver can provide the basis for either their pharmacological use in therapeutic treatments or to avoid their intake in some diseases.

Reproductive Endocrinology of Nonalcoholic Fatty Liver Disease

The liver and the reproductive system interact in a multifaceted bidirectional fashion. Sex steroid signaling influences hepatic endobiotic and xenobiotic metabolism and contributes to the pathogenesis of functional and structural disorders of the liver. In turn, liver function affects the reproductive axis via modulating sex steroid metabolism and transport to tissues via sex hormone-binding globulin (SHBG). The liver senses the body's metabolic status and adapts its energy homeostasis in a sex-dependent fashion, a dimorphism signaled by the sex steroid milieu and possibly related to the metabolic costs of reproduction. Sex steroids impact the pathogenesis of nonalcoholic fatty liver disease, including development of hepatic steatosis, fibrosis, and carcinogenesis. Preclinical studies in male rodents demonstrate that androgens protect against hepatic steatosis and insulin resistance both via androgen receptor signaling and, following aromatization to estradiol, estrogen receptor signaling, through regulating genes involved in hepatic lipogenesis and glucose metabolism. In female rodents in contrast to males, androgens promote hepatic steatosis and dysglycemia, whereas estradiol is similarly protective against liver disease. In men, hepatic steatosis is associated with modest reductions in circulating testosterone, in part consequent to a reduction in circulating SHBG. Testosterone treatment has not been demonstrated to improve hepatic steatosis in randomized controlled clinical trials. Consistent with sex-dimorphic preclinical findings, androgens promote hepatic steatosis and dysglycemia in women, whereas endogenous estradiol appears protective in both men and women. In both sexes, androgens promote hepatic fibrosis and the development of hepatocellular carcinoma, whereas estradiol is protective.

Inhibition effect of phytoestrogen calycosin on TGF-β1-induced hepatic stellate cell activation, proliferation, and migration via estrogen receptor β

The present study was designed to investigate the effects of calycosin on hepatic stellate cell (HSC) function and to explore whether the drug exerts its effect through the estrogen receptor. HSC proliferation and migration were measured by MTT assay and transwell chamber assay, respectively. The mRNA and protein expression of α-SMA, COL-I, and ERβ were detected by real-time PCR and Western blotting. The co-localization and expression of α-SMA and ERβ protein were detected by immunofluorescence. All the studies were investigated in the absence or presence of ICI 182,780. The results showed that calycosin inhibited the proliferation of activated HSCs and remarkably inhibited HSC migration. Calycosin significantly reduced the expression of α-SMA and COL-I in activated HSCs. However, with co-treatment with ICI 182,780, the inhibitory effect of calycosin against the above effects was strongly negated. Importantly, calycosin significantly downregulated the expression of ERβ protein, while co-treatment with ICI 182,780 partially reversed the ERβ downregulation. In addition, α-SMA decreased with the decrease of ERβ expression and the subtype of ERβ on HSC is ERβ5. In conclusion, calycosin inhibits proliferation, activation, and migration of TGF-β1-induced HSCs. The effect may be related to binding and downregulation of ERβ5.

Estrogen receptor β selective agonist ameliorates liver cirrhosis in rats by inhibiting the activation and proliferation of hepatic stellate cells

BACKGROUND AND AIM

The aim of this study is to explore the roles of estrogen receptor (ER) subtypes and corresponding agonists/antagonists on the development of cirrhosis and activation and proliferation of hepatic stellate cells (HSCs).

METHODS

Carbon tetrachloride (CCl₄ )-induced cirrhotic ovariectomized rats were administered non-selective ER agonist (β-estradiol, E2), ER selective agonists (ERα agonist, propylpyrazoletriol; ERβ agonist, diarylpropionitrile [DPN]; and G-protein-coupled ER [GPER] agonist, G1), or E2 + ER selective antagonists (ERα antagonist, MPP; ERβ antagonist, PHTPP; and GPER antagonist, G15) for 12 weeks. The expression of the three ER subtypes in livers and HSCs and the effects of the drugs on hepatic fibrosis, isolated HSCs, and uteri were evaluated.

RESULTS

Selective ER agonists/antagonists had various effects on CCl₄ -induced cirrhosis. The cirrhotic rats in the CCl₄  + E2, CCl₄  + DPN, CCl₄  + E2 + MPP, and CCl₄  + E2 + G15 groups presented reduced fibrosis scores, compared with those in the CCl₄ group. The cirrhotic rats in the E2 + PHTPP group presented increased fibrosis scores that similar to those in the CCl₄ group. The ovariectomized rats had enlarged uteri with increased uterus indexes after E2 administration; however, the proliferative effects of E2 were partially blocked by MPP or G15, but not PHTPP. In the in vitro study, DPN attenuated the transformation of quiescent HSCs to activated phenotype, suppressed collagen I, and α-smooth muscle actin expression. DPN also suppressed platelet-derived growth factor-induced proliferation in cultured HSCs, which was reversed by PHTPP.

CONCLUSIONS

The antifibrogenic effects of estrogen were mediated by ERβ but not ERα or GPER. The ERβ selective agonist exerted a fibrosuppressive effect by inhibiting the activation and proliferation of HSCs, but did not induce uterine hyperplasia.

Estrogen receptor‑β‑dependent effects of saikosaponin‑d on the suppression of oxidative stress‑induced rat hepatic stellate cell activation

Saikosaponin-d (SSd) is one of the major triterpenoid saponins derived from Bupleurum falcatum L., which has been reported to possess antifibrotic activity. At present, there is little information regarding the potential target of SSd in hepatic stellate cells (HSCs), which serve an important role in excessive extracellular matrix (ECM) deposition during the pathogenesis of hepatic fibrosis. Our recent study indicated that SSd may be considered a novel type of phytoestrogen with estrogen-like actions. Therefore, the present study aimed to investigate the effects of SSd on the proliferation and activation of HSCs, and the underlying mechanisms associated with estrogen receptors. In the present study, a rat HSC line (HSC-T6) was used and cultured with dimethyl sulfoxide, SSd, or estradiol (E₂; positive control), in the presence or absence of three estrogen receptor (ER) antagonists [ICI-182780, methylpiperidinopyrazole (MPP) or (R,R)-tetrahydrochrysene (THC)], for 24 h as pretreatment. Oxidative stress was induced by exposure to hydrogen peroxide for 4 h. Cell proliferation was assessed by MTT growth assay. Malondialdehyde (MDA), CuZn-superoxide dismutase (CuZn-SOD), tissue inhibitor of metalloproteinases-1 (TIMP- 1), matrix metalloproteinase-1 (MMP-1), transforming growth factor-β1 (TGF-β1), hydroxyproline (Hyp) and collagen-1 (COL1) levels in cell culture supernatants were determined by ELISA. Reactive oxygen species (ROS) was detected by flow cytometry. Total and phosphorylated mitogen-activated protein kinases (MAPKs) and α-smooth muscle actin (α-SMA) were examined by western blot analysis. TGF-β1 mRNA expression was determined by RT-quantitative (q)PCR. SSd and E₂ were able to significantly suppress oxidative stress-induced proliferation and activation of HSC-T6 cells. Furthermore, SSd and E₂ were able to reduce ECM deposition, as demonstrated by the decrease in transforming growth factor-β1, hydroxyproline, collagen-1 and tissue inhibitor of metalloproteinases-1, and by the increase in matrix metalloproteinase-1. These results suggested that the possible molecular mechanism could involve downregulation of the reactive oxygen species/mitogen-activated protein kinases signaling pathway. Finally, the effects of SSd and E₂ could be blocked by co-incubation with ICI-182780 or THC, but not MPP, thus indicating that ERβ may be the potential target of SSd in HSC-T6 cells. In conclusion, these findings suggested that SSd may suppress oxidative stress-induced activation of HSCs, which relied on modulation of ERβ.

The stellate cell system (vitamin A-storing cell system)

Past, present, and future research into hepatic stellate cells (HSCs, also called vitamin A-storing cells, lipocytes, interstitial cells, fat-storing cells, or Ito cells) are summarized and discussed in this review. Kupffer discovered black-stained cells in the liver using the gold chloride method and named them stellate cells (Sternzellen in German) in 1876. Wake rediscovered the cells in 1971 using the same gold chloride method and various modern histological techniques including electron microscopy. Between their discovery and rediscovery, HSCs disappeared from the research history. Their identification, the establishment of cell isolation and culture methods, and the development of cellular and molecular biological techniques promoted HSC research after their rediscovery. In mammals, HSCs exist in the space between liver parenchymal cells (PCs) or hepatocytes and liver sinusoidal endothelial cells (LSECs) of the hepatic lobule, and store 50-80% of all vitamin A in the body as retinyl ester in lipid droplets in the cytoplasm. SCs also exist in extrahepatic organs such as pancreas, lung, and kidney. Hepatic (HSCs) and extrahepatic stellate cells (EHSCs) form the stellate cell (SC) system or SC family; the main storage site of vitamin A in the body is HSCs in the liver. In pathological conditions such as liver fibrosis, HSCs lose vitamin A, and synthesize a large amount of extracellular matrix (ECM) components including collagen, proteoglycan, glycosaminoglycan, and adhesive glycoproteins. The morphology of these cells also changes from the star-shaped HSCs to that of fibroblasts or myofibroblasts.

Role of estrogen receptor β selective agonist in ameliorating portal hypertension in rats with CCl4-induced liver cirrhosis

AIM: To investigate the role of diarylpropionitrile (DPN), a selective agonist of estrogen receptor β (ERβ), in liver cirrhosis with portal hypertension (PHT) and isolated hepatic stellate cells (HSCs).

METHODS: Female Sprague-Dawley rats were ovariectomized (OVX), and liver cirrhosis with PHT was induced by CCl₄ injection. DPN and PHTPP, the selective ERβ agonist and antagonist, were used as drug interventions. Liver fibrosis was assessed by hematoxylin and eosin (HE) and Masson’s trichrome staining and by analyzing smooth muscle actin expression. Hemodynamic parameters were determined in vivo using colored microspheres technique. Protein expression and phosphorylation were determined by immunohistochemical staining and Western blot analysis. Messenger RNA levels were analyzed by quantitative real-time polymerase chain reaction (qRT-PCR). Collagen gel contraction assay was performed using gel lattices containing HSCs treated with DPN, PHTPP, or Y-27632 prior to ET-1 addition.

RESULTS: Treatment with DPN in vivo greatly lowered portal pressure and improved hemodynamic parameters without affecting mean arterial pressure, which was associated with the attenuation of liver fibrosis and intrahepatic vascular resistance (IHVR). In CCl₄-treated rat livers, DPN significantly decreased the expression of RhoA and ROCK II, and even suppressed ROCK II activity. Moreover, DPN remarkedly increased the levels of endothelial nitric oxide synthase (eNOS) and phosphorylated eNOS, and promoted the activities of protein kinase G (PKG), which is an NO effector in the liver. Furthermore, DPN reduced the contractility of activated HSCs in the 3-dimensional stress-relaxed collagen lattices, and decreased the ROCK II activity in activated HSCs. Finally, in vivo/in vitro experiments demonstrated that MLC activity was inhibited by DPN.

CONCLUSION: For OVX rats with liver cirrhosis, DPN suppressed liver RhoA/ROCK signal, facilitated NO/PKG pathways, and decreased IHVR, giving rise to reduced portal pressure. Therefore, DPN represents a relevant treatment choice against PHT in cirrhotic patients, especially postmenopausal women.

Raloxifene Ameliorates Liver Fibrosis of Nonalcoholic Steatohepatitis Induced by Choline-Deficient High-Fat Diet in Ovariectomized Mice

BACKGROUND AND AIM

The prevalence of nonalcoholic fatty liver disease (NAFLD) is higher in men than in women, but according to some epidemiological studies, this gender difference disappears after menopause. Estrogen therapy protects against NAFLD and nonalcoholic steatohepatitis (NASH) after menopause. We investigated the therapeutic effect of raloxifene, a second-generation selective estrogen-receptor modulator, on NASH induced by a choline-deficient high-fat (CDHF) diet in female ovariectomized (OVX) mice.

METHODS

Seven-week-old female C57BL/6J mice were divided into three experimental groups as follows: (1) sham operation (SHAM group), (2) ovariectomy (OVX group), and (3) ovariectomy + raloxifene (intraperitoneal injection, 3 mg/kg body weight/day; OVX + RLX group). These three groups of mice were fed a CDHF diet for 8 weeks; choline-sufficient high-fat (CSHF) diet was used as control diet. Serum biochemical indicators of hepatic function and liver histological changes were evaluated.

RESULTS

Compared with CSHF diet, ovariectomy enhances liver injury and fibrosis in CDHF diet-fed mice. Serum alanine aminotransferase (ALT) levels were significantly lower in the OVX + RLX group than in the OVX group. The OVX group developed extensive steatosis with inflammation and fibrosis. Lobular inflammatory scores and fibrosis staging in the OVX + RLX group were significantly lower than in the OVX group. Furthermore, the OVX + RLX group exhibited significantly higher expression of hepatic estrogen receptor-α, which was significantly lower in the OVX group than in the SHAM group.

CONCLUSIONS

Raloxifene may ameliorate progression of liver fibrosis of NASH induced by CDHF diet in ovariectomized female mice, and up-regulation of estrogen receptor-α may play an important role in the beneficial effects of raloxifene on NASH.

Sex-specific association of estrogen receptor 2 polymorphisms with hepatitis C virus infection outcomes in a high-risk Chinese Han population

Hepatitis C virus (HCV) has different clinical and biological characteristics in women versus men, which suggests the potential involvement of estrogen. Estrogen signaling is mediated by the estrogen receptor, and genetic variations in the estrogen receptor gene might affect the pathology of HCV infection. We performed logistic regression analysis to explore the associations between rs1256049, rs4986938 and rs944459 polymorphisms of the estrogen receptor 2 gene (ESR2) and HCV infection outcomes. The variant A allele of rs4986938 was associated with an increased HCV infection susceptibility in the males (additive model: adjusted OR=1.493, P=0.010) and a significantly reduced risk of HCV infection in the female subgroup (GA vs. GG: adjusted OR=0.710, P=0.012; dominant model: adjusted OR=0.686, P=0.004; additive model: adjusted OR=0.703, P=0.002). In addition, females carrying the rs4986938 AA genotype appeared to clear HCV spontaneously more readily (adjusted OR=0.237, P=0.011), and additive model analyses showed that each additional allele contributed a decreased risk of approximately 34% for HCV chronicity (adjusted OR=0.659, P=0.006). Furthermore, a significant multiplicative interaction between the combined rs1256049 and rs4986938 genotypes was found to decrease HCV infection risk (adjusted OR=0.583, P=3.000×10(-4)). The area under the curve, based on the model and including age, gender, HCV genotypes and the three SNPs, was significantly related to the clearance of HCV (P=0.003). We provide here the first report that rs4986938 in the ESR2 gene played a potential sex-specific role in the etiology of HCV infection in a high-risk Chinese Han population, suggesting that ESR2 is a candidate susceptibility gene for HCV infection and viral clearance.

Estrogen receptor α and β in the normal immune system and in lymphoid malignancies

Estrogens regulate various normal and pathophysiological processes including cancers. Cellular signaling by estrogens is mediated by estrogen receptor α (ERα) and β (ERβ), respectively. Binding of agonists to the ERs affects gene transcription. The main endogenous estrogen, 17β-estradiol (E2), binds to both ERα and ERβ with similar affinity. However, the ligand-binding pocket of ERα and ERβ are slightly different which has allowed the development of selective ER ligands. Importantly, while estrogens via ERα stimulate proliferation, signaling via ERβ inhibits proliferation and promotes apoptosis. In both normal and cancer cells the ERs are co-expressed with ER splice variants which may modify the transcriptional activity of the wild-type receptors. Estrogens have prominent effects on immune functions and both ERα and ERβ are expressed in immune cells and lymphoid malignancies. With regard to lymphoid malignancies, most show estrogen influence as several epidemiological studies of lymphoid cancers demonstrate gender differences in incidence and prognosis with males being more affected. In line with these findings, recent results generated by us have shown that ERβ selective agonists inhibit growth and induce apoptosis in human and murine lymphomas in vivo in xenograft experiments. This suggests that ERβ selective agonists in the future may be useful in the treatment of lymphomas.

Estrogen derivatives: novel therapeutic agents for liver cirrhosis and portal hypertension

Sex differences in the incidence of liver cirrhosis and portal hypertension have been reported by epidemiological studies. Previous studies have indicated that estrogen therapy improved hepatic fibrosis, inhibited the activation of hepatic stellate cells, and reduced portal pressure, whereas the administration of exogenous estrogens resulted in some potential risks, limiting their clinical use. However, the biological actions of estrogens are mediated by three subtypes of estrogen receptors (ERs): ERα, ERβ, and G-protein-coupled ER. These ER subtypes act in distinct ways and exert different biological effects that mediate genomic and nongenomic events, resulting in tissue-specific responses. In addition, active estrogen metabolites, with little or no affinity for ERs, could mediate the fibrosuppressive effect of estrogens through an ER-independent pathway. Taken together, such specific estrogen derivatives as ER selective agonists, or active estrogen metabolites, would provide novel therapeutic opportunities, stratifying this hormonal treatment, thereby reducing undesired side-effects in the treatment of liver cirrhosis and portal hypertension.

Protective effect of sodium ferulate on acetaldehyde-treated precision-cut rat liver slices

Activated hepatic stellate cells (HSCs) play a key role in hepatic fibrogenesis, and inhibition of HSC activation may prevent liver fibrosis. Acetaldehyde, the most deleterious metabolite of alcohol, triggers HSC activation in alcoholic liver injury. In the present study, we investigated the protective effect of sodium ferulate (SF), a sodium salt of ferulic acid that is rich in fruits and vegetables, on acetaldehyde-stimulated HSC activation using precision-cut liver slices (PCLSs). Rat PCLSs were co-incubated with 350 μM acetaldehyde and different concentrations of SF. Hepatotoxicity was assessed by measuring enzyme leakage and malondialdehyde content in tissue. α-Smooth muscle actin, transforming growth factor-β(1), and hydroxyproline were determined to assess the activation of HSCs. In addition, matrix metalloproteinase (MMP)-1 and the tissue inhibitor of metalloproteinase (TIMP-1) were determined to evaluate collagen degradation. SF prominently prevented the enzyme leakage in acetaldehyde-treated slices and also inhibited HSC activation and collagen production stimulated by acetaldehyde. In addition, SF increased MMP-1 expression and decreased TIMP-1 expression. These results showed that SF protected PCLSs from acetaldehyde-stimulated HSC activation and liver injury, which may be associated with the attenuation of oxidative injury and acceleration of collagen degradation.

Nuclear receptors as new perspective for the management of liver diseases

Nuclear receptors (NRs) are ligand-activated transcription factors that act as sensors for a broad range of natural and synthetic ligands and regulate several key hepatic functions including bile acid homeostasis, bile secretion, lipid and glucose metabolism, as well as drug deposition. Moreover, NRs control hepatic inflammation, regeneration, fibrosis, and tumor formation. Therefore, NRs are key for understanding the pathogenesis and pathophysiology of a wide range of hepatic disorders. Finally, targeting NRs and their alterations offers exciting new perspectives for the treatment of liver diseases.

Hepatic stellate cell (vitamin A-storing cell) and its relative--past, present and future

HSCs (hepatic stellate cells) (also called vitamin A-storing cells, lipocytes, interstitial cells, fat-storing cells or Ito cells) exist in the space between parenchymal cells and liver sinusoidal endothelial cells of the hepatic lobule and store 50-80% of vitamin A in the whole body as retinyl palmitate in lipid droplets in the cytoplasm. In physiological conditions, these cells play pivotal roles in the regulation of vitamin A homoeostasis. In pathological conditions, such as hepatic fibrosis or liver cirrhosis, HSCs lose vitamin A and synthesize a large amount of extracellular matrix components including collagen, proteoglycan, glycosaminoglycan and adhesive glycoproteins. Morphology of these cells also changes from the star-shaped SCs (stellate cells) to that of fibroblasts or myofibroblasts. The hepatic SCs are now considered to be targets of therapy of hepatic fibrosis or liver cirrhosis. HSCs are activated by adhering to the parenchymal cells and lose stored vitamin A during hepatic regeneration. Vitamin A-storing cells exist in extrahepatic organs such as the pancreas, lungs, kidneys and intestines. Vitamin A-storing cells in the liver and extrahepatic organs form a cellular system. The research of the vitamin A-storing cells has developed and expanded vigorously. The past, present and future of the research of the vitamin A-storing cells (SCs) will be summarized and discussed in this review.

Sex differences in nuclear receptor-regulated liver metabolic pathways

Liver metabolism is markedly sex-dimorphic; accordingly, the prevalence of liver diseases is different between sexes. The superfamily of nuclear receptors (NRs) governs the proper expression of key liver metabolism genes by sensing lipid-soluble hormones and dietary lipids. When the expression of those genes is deregulated, disease development is favored. However, we lack a comprehensive picture of the differences between NR actions in males and females. Here, we reviewed explorative studies that assessed NR functions in both sexes, and we propose a first map of sex-dimorphic NR expression in the liver. Our analysis suggested that NRs in the female liver exhibited cross-talk with more liver-protective potential than NRs in male liver. This study provides empirical support to the hypothesis that women are more resilient to some liver diseases than men, based on a more compensative NR network. This article is part of a Special Issue entitled: Translating nuclear receptors from health to disease.

Role of estrogen in liver cancer

Liver cancer is the fifth most common cancer worldwide and despite increasing implementation of ultrasonographic surveillance strategies, its incidence is rising, especially in western countries. A universal characteristic of hepatocellular carcinoma is the striking male prevalence that is found, with few exceptions, both in animals and in humans. Many different hypotheses have been put forward in an attempt to explain this finding, which is not a simple epidemiological oddity but could also have pathogenetic implications. An obvious trail to follow, as gender susceptibility is implicated, is the role played by sex hormones, namely estrogens. Estrogens are not simply involved in reproductive mechanisms; instead, it is increasingly evident that they have a role in such an enormous variety of cellular processes that their implication in liver carcinogenesis may be manifold. The purpose of this review is to provide an overview of the available data, with a special focus on the hormonal mechanisms potentially implicated in the development of liver cancer.

Role of sex steroid receptors in pathobiology of hepatocellular carcinoma

The striking gender disparity observed in the incidence of hepatocellular carcinoma (HCC) suggests an important role of sex hormones in HCC pathogenesis. Though the studies began as early as in 1980s, the precise role of sex hormones and the significance of their receptors in HCC still remain poorly understood and perhaps contribute to current controversies about the potential use of hormonal therapy in HCC. A comprehensive review of the existing literature revealed several shortcomings associated with the studies on estrogen receptor (ER) and androgen receptor (AR) in normal liver and HCC. These shortcomings include the use of less sensitive receptor ligand binding assays and immunohistochemistry studies for ERα alone until 1996 when ERβ isoform was identified. The animal models of HCC utilized for studies were primarily based on chemical-induced hepatocarcinogenesis with less similarity to virus-induced HCC pathogenesis. However, recent in vitro studies in hepatoma cells provide newer insights for hormonal regulation of key cellular processes including interaction of ER and AR with viral proteins. In light of the above facts, there is an urgent need for a detailed investigation of sex hormones and their receptors in normal liver and HCC. In this review, we systematically present the information currently available on androgens, estrogens and their receptors in normal liver and HCC obtained from in vitro, in vivo experimental models and clinical studies. This information will direct future basic and clinical research to bridge the gap in knowledge to explore the therapeutic potential of hormonal therapy in HCC.

Genistein and phycocyanobilin may prevent hepatic fibrosis by suppressing proliferation and activation of hepatic stellate cells

Hepatic fibrosis reflects hepatotoxin-mediated activation of hepatic stellate cells, resulting in their proliferation and transformation to myofibroblasts that secrete collagen. This activation is suppressed by estrogen, an effect which explains the decreased risk for hepatic fibrosis enjoyed by premenopausal women and by postmenopausal women receiving hormone replacement therapy. Since stellate cells have been found to express the beta but not the alpha isoform of the estrogen receptor, it can be predicted that nutritional intakes of the soy isoflavone genistein - a selective agonist for ERbeta in the low nanomolar plasma concentrations achievable with these intakes - have potential for suppressing hepatic fibrosis, in both men and women. The antiproliferative impact of estrogen on stellate cells is mediated at least in part by suppression of NADPH oxidase activity; oxidant production by this enzyme complex plays a crucial role in stellate cell activation. Alternatively, it may be feasible to inhibit NADPH oxidase with phycocyanobilin (PCB), a biliverdin homolog found in spirulina that has recently been shown to inhibit the NADPH oxidase activity of human cell cultures in low micromolar concentrations. Joint administration of soy isoflavones and PCB in appropriate doses might have considerable potential for prevention of hepatic fibrosis in at-risk subjects.

Opposing effects of estradiol and progesterone on the oxidative stress-induced production of chemokine and proinflammatory cytokines in murine peritoneal macrophages

In inflammatory and oxidative liver injury, virus proteins and reactive oxygen species are involved in the regulation of proinflammatory cytokine production by macrophages. This study investigated the effects of estradiol (E2) and progesterone on the unstimulated and oxidative stress-stimulated production of tumor necrosis factor (TNF)-alpha, interleukin (IL)-1beta, macrophage inflammatory protein (MIP)-2, and macrophage chemotactic protein (MCP)-1 by peritoneal macrophages isolated from male and female mice. E2 inhibited the cytokine production of TNF-alpha, IL-1beta, MIP-2, and MCP-1 by the unstimulated macrophages from males and females, which was then further stimulated by progesterone. The exposure to hydrogen peroxide in the macrophages from both sexes induced the production of cytokine. The hydrogen peroxide-stimulated cytokine production was suppressed by E2 and enhanced by progesterone. The sex hormone effects on the unstimulated and stimulated macrophages were blocked by their receptor antagonists and showed no significant difference between male and female subjects. These findings suggest that E2 may play a favorable role in the course of persistent liver injury, by inhibiting proinflammatory cytokine production, which, in addition, progesterone may counteract the favorable E2 effects through their receptors.

Female hepatology: Favorable role of estrogen in chronic liver disease with hepatitis B virus infection

Chronic hepatitis B virus (HBV) infection is the most common cause of hepatic fibrosis and hepatocellular carcinoma (HCC), mainly as a result of chronic necroinflammatory liver disease. A characteristic feature of chronic hepatitis B infection, alcoholic liver disease and nonalcoholic fatty liver disease (NAFLD) is hepatic steatosis. Hepatic steatosis leads to an increase in lipid peroxidation in hepatocytes, which, in turn, activates hepatic stellate cells (HSCs). HSCs are the primary target cells for inflammatory and oxidative stimuli, and these cells produce extracellular matrix components. Chronic hepatitis B appears to progress more rapidly in males than in females, and NAFLD, cirrhosis and HCC are predominately diseases that tend to occur in men and postmenopausal women. Premenopausal women have lower hepatic iron stores and a decreased production of proinflammatory cytokines. Hepatic steatosis has been observed in aromatase-deficient mice, and has been shown to decrease in animals after estradiol treatment. Estradiol is a potent endogenous antioxidant which suppresses hepatic fibrosis in animal models, and attenuates induction of redox sensitive transcription factors, hepatocyte apoptosis and HSC activation by inhibiting a generation of reactive oxygen species in primary cultures. Variant estrogen receptors are expressed to a greater extent in male patients with chronic liver disease than in females. These lines of evidence suggest that the greater progression of hepatic fibrosis and HCC in men and postmenopausal women may be due, at least in part, to lower production of estradiol and a reduced response to the action of estradiol. A better understanding of the basic mechanisms underlying the sex-associated differences in hepatic fibrogenesis and carciogenesis may open up new avenues for the prevention and treatment of chronic liver disease.

Protection of estrogens against the progression of chronic liver disease

Hepatitis C virus infections are recognized as a major causative factor of chronic liver disease. A characteristic feature of chronic hepatitis C, alcoholic liver disease and non-alcoholic fatty liver disease is hepatic steatosis. Hepatic steatosis leads to an increase in lipid peroxidation in hepatocytes, which, in turn, activates hepatic stellate cells (HSCs). HSCs are also thought to be the primary target cells for inflammatory and oxidative stimuli, and to produce extracellular matrix components. Based on available clinical information, chronic hepatitis C appears to progress more rapidly in men than in women, and cirrhosis is predominately a disease of men and postmenopausal women. Estradiol is a potent endogenous antioxidant. Hepatic steatosis was reported to become evident in an aromatase-deficient mouse and was diminished in animals after treatment with estradiol. Our previous studies showed that estradiol suppressed hepatic fibrosis in animal models, and attenuated HSC activation by suppressing the generation of reactive oxygen species in primary cultures. Variant estrogen receptors were found to be expressed to a greater extent in male patients with chronic liver disease than in female subjects. A better understanding of the basic mechanisms underlying the gender-associated differences observed in the progression of chronic liver disease would provide valuable information relative to the search for effective antifibrogenic therapies.

Does estrogen contribute to the hepatic regeneration following portal branch ligation in rats?

The aim of this study was to determine whether estrogen plays any role in the hepatic regeneration of nonligated lobe following portal branch ligation (PBL). Male rats were subjected to PBL on the left and middle lobes. Two and 7 days after PBL, the rats were killed and blood and liver samples were analyzed. Sham animals underwent only laparotomy. The serum estradiol levels were significantly elevated on day 2 following PBL and returned to normal levels on day 7. The expression of estrogen receptors (ER) in the liver evaluated by Western blotting did not show any change in the nonligated lobe compared with shams. Immunohistochemical study for ER showed a predominant ER expression in the hepatocyte nucleus in periportal area (zone 1), although there was no apparent difference in the amount and expression pattern between sham and PBL. However, chronic inhibition of ER by an ER antagonist (ICI 182,780) showed a significantly lower regeneration rate of the nonligated lobe compared with vehicle treatment. Liver regeneration-associated genes also were less activated in the ICI group. Moreover, portal venous flow, determined by fluorescent microsphere injection, was significantly lower in the ICI group compared with vehicle group. These changes correlated with the attenuated expression of endothelial nitric oxide synthase mRNA in both superior mesenteric arteries and veins. In conclusion, these results indicate that the estrogen's contribution on hepatic regeneration following PBL is at least partly mediated through maintaining mesenteric blood flow by mesenteric endothelial nitric oxide synthase upregulation rather than directly activating liver regeneration in the liver.

Effects of estradiol and progesterone on tumor necrosis factor alpha-induced apoptosis in human hepatoma HuH-7 cells

Oxidative stress, including the generation of reactive oxygen species (ROS), is known to be involved in apoptosis. Preventing apoptosis may thereby induce a malignant transformation of liver tumor cells. Estradiol (E2) is a potent endogenous antioxidant. We examined the proapoptotic role of progesterone as well as the antiapoptotic role of E2 in human hepatoma HuH-7 cells in a state of early apoptosis induced by tumor necrosis factor (TNF) alpha. The TNF alpha-induced ROS generation, lipid peroxidation, antioxidant enzyme consumption, a proapoptotic predominant expression of Bcl-2 family proteins, and a disruption of mitochondrial membrane potential were all inhibited by E2, and then they were further stimulated by progesterone in HuH-7 cells. The inhibitory effects of E2 were blocked by coincubation with progesterone. Treatment with the progesterone receptor antagonist RU486 led to the blockage of the progesterone-mediated responses to E2 pretreatment in TNF alpha-induced apoptosis. These findings demonstrate that E2 inhibits the TNF alpha-induced early apoptosis in hepatoma cells, by suppressing the oxidative stress processes, whereas progesterone acts in a manner opposite from the effects of E2, and the inhibitory effects of E2 were blocked by progesterone, thus leading to the apoptosis of hepatoma cells.

Translocation of Bax in rat hepatocytes cultured with ferric nitrilotriacetate

Hepatic fibrosis occurs after many years of iron overload in liver. An effective iron deposition model induced by ferric nitrilotriacetate (FeNTA) in cultured rat hepatocytes was assumed. It has been shown that treatment of rat hepatocytes with FeNTA lead to oxidative stress and hepatocyte apoptosis. Hepatocyte apoptosis can promote liver fibrosis. The mechanisms of hepatocyte apoptosis induced by FeNTA have not yet been fully elucidated. The present study demonstrated that FeNTA-induced hepatocyte apoptosis was related to Bax translocation, cytochrome c release, and caspase-3 activation.

Improvement of portal hypertension and hepatic blood flow in cirrhotic rats by oestrogen

BACKGROUND

In this study, we investigated the effects of oestrogen on nitric oxide synthase activity and nitric oxide production using the cirrhotic rat liver.

MATERIAL AND METHODS

Cirrhosis was induced by dimethylnitrosamine. Estradiol valerate was subcutaneously injected twice at week 4 after dimethylnitrosamine treatment. Furthermore, subcutaneous injection of an oestrogen receptor antagonist, ICI-182.780, was performed 2 days before administration of estradiol valerate. Portal pressure and hepatic blood flow were measured. Nitric oxide synthase activity was assessed by l-citrulline generation. Sinusoidal endothelial cells were isolated from the cirrhotic rat liver and cultured. The cells were incubated with estradiol and/or ICI-182.780 for 24 h. Images for nitric oxide in sinusoidal endothelial cells were obtained using diaminofluorescein-2 diacetate.

RESULTS

Cirrhotic rats treated with estradiol valerate showed a significant decrease in portal pressure and a significant increase in hepatic blood flow compared with those of control cirrhosis rats. However, in cirrhotic rats treated with ICI-182.780, the reduction of portal pressure and elevation of hepatic blood flow were completely inhibited. In cirrhotic rats treated with estradiol valerate, nitric oxide synthase activity was increased compared with that in control cirrhotic rats. The fluorescent level of intracellular nitric oxide in estradiol-stimulated, cultured, sinusoidal endothelial cells was higher than that in nontreated sinusoidal endothelial cells.

CONCLUSIONS

The present study indicated that oestrogen plays an important role in the enhancement of nitric oxide production in sinusoidal endothelial cells of cirrhotic liver and reduces the portal pressure in cirrhotic rats.

Effect of rat serum containing Biejiajian oral liquid on proliferation of rat hepatic stellate cells

AIM: Liver fibrosis is a common pathological process of chronic liver diseases. Activation of hepatic stellate cells (HSCs) is the key issue in the occurrence of liver fibrosis. In this study, we observed the inhibitory action of rat serum containing Biejiajian oral liquid (BOL), a decoction of turtle shell, on proliferation of rat HSCs, and to explore the anti-hepatofibrotic mechanisms of BOL.

METHODS: A rat model of hepatic fibrosis was induced by subcutaneous injection of CCl₄. Serum containing low, medium and high dosages of BOL was prepared respectively. Normal and fibrotic HSCs were isolated and cultured. The effect of sera containing BOL on proliferation of HSCs was determined by ³H-TdR incorporation.

RESULTS: The inhibitory rate of normal rat HSC proliferation caused by 100 mL/mL sera containing medium and high dosages of BOL showed a remarkable difference as compared with that caused by colchicine (medium dosage group: 34.56% ± 4.21% vs 29.12% ± 2.85%, P < 0.01; high dosage group: 37.82% ± 1.32% vs 29.12% ± 2.85%, P < 0.01). The inhibitory rate of fibrotic rat HSC proliferation caused by 100 mL/L serum containing medium and high dosages of BOL showed a remarkable difference as compared with that caused by colchicine (medium dosage group: 51.31% ± 3.14% vs 38.32% ± 2.65%, P < 0.01; high dosage group: 60.15% ± 5.36% vs 38.32% ± 2.65%, P < 0.01). The inhibitory rate of normal rat HSC proliferation caused by 100 mL/L and 200 mL/L sera containing a medium dosage of BOL showed a significant difference as compared with that caused by 50 mL/L (100 mL/L group: 69.02% ± 9.96% vs 50.82% ± 9.28%, P < 0.05; 200 mL/L group: 81.78% ± 8.92% vs 50.82% ± 9.28%, P < 0.01). The inhibitory rate of fibrotic rat HSC proliferation caused by 100 mL/L and 200 mL/L sera containing a medium dosage of BOL showed a significant difference as compared with that caused by 50 mL/L (100 mL/L group: 72.19% ± 10.96% vs 61.38% ± 7.16%, P < 0.05; 200 mL/L group: 87.16% ± 8.54% vs 61.38% ± 7.16%, P < 0.01).

CONCLUSION: Rat serum containing BOL can inhibit proliferation of rat HSCs, and the inhibition depends on the dosage and concentration of BOL. The inhibitory effect on HSC proliferation is one of the main anti-hepatofibrotic mechanisms of BOL.

Estrogen and neuroprotection: higher constitutive expression of glutaredoxin in female mice offers protection against MPTP-mediated neurodegeneration

Incidence of Parkinson's disease is lower in women as compared with men. Although neuroprotective effect of estrogen is recognized, the underlying molecular mechanisms are unclear. MPTP (1-methyl-4-phenyl-1, 2, 3, 6, tetrahydro-pyridine), a neurotoxin that causes Parkinson's disease-like symptoms acts through inhibition of mitochondrial complex I. Administration of MPTP to male mice results in loss of dopaminergic neurons in substantia nigra, whereas female mice are unaffected. Oxidation of critical thiol groups by MPTP disrupts mitochondrial complex I, and up-regulation of glutaredoxin (a thiol disulfide oxidoreductase) is essential for recovery of complex I. Early events following MPTP exposure, such as increased AP1 transcription, loss of glutathione, and up-regulation of glutaredoxin mRNA is seen only in male mice, indicating that early response to neurotoxic insult does not occur in females. Pretreatment of female mice with ICI 182,780, estrogen receptor (ER) antagonist sensitizes them to MPTP-mediated complex I dysfunction. Constitutive expression of glutaredoxin is significantly higher in female mice as compared with males. ICI 182,780 down-regulates glutaredoxin activity in female mouse brain regions (midbrain and striatum), indicating that glutaredoxin expression is regulated through estrogen receptor signaling. Higher constitutive expression of glutaredoxin could potentially contribute to the neuroprotection seen in female mouse following exposure to neurotoxins, such as MPTP.

Antioxidant and antiapoptotic activities of idoxifene and estradiol in hepatic fibrosis in rats

Oxidative stress plays a causative role in the development of hepatic fibrosis and apoptosis. Estradiol (E2) is an antioxidant, and idoxifene is a tissue-specific selective estrogen receptor modulator. We have previously demonstrated that E2 inhibits hepatic fibrosis in a rat model of hepatic fibrosis induced with dimethylnitrosamine (DMN), and suppresses activation of the nuclear factor (NF)-kappaB proinflammatory transcription factor in cultured rat hepatocytes undergoing oxidative stress. This study reports on the antioxidant and antiapoptotic role of idoxifene and E2 in the DMN model of hepatic fibrosis. The DMN model rats were administered with idoxifene or E2, and were examined activity of superoxide dismutase (SOD) and glutathione peroxidase (GPx) and expression of Bcl-2 family proteins in the liver. During the course of hepatofibrogenesis after DMN treatment, serum levels of lactate dehydrogenase (LDH), a biomarker for necrosis, and hepatic levels of malondialdehyde (MDA), an end product of lipid peroxidation, increased rapidly for 3 days. On day 14, serum LDH levels normalized, and hepatic fibrosis developed with increased levels of MDA and collagen and decreased production of SOD and GPx in the liver. Fibrotic liver also showed downregulation of Bcl-2 and Bcl-X(L) expression and upregulation of Bad expression. Idoxifene and E2 suppressed DMN-mediated necrosis, lipid peroxidation, the loss of antioxidant enzyme activity, and proapoptotic status in Bcl-2 family protein expression as well as hepatic fibrosis. These findings indicate that, in addition to their antiinflammatory and antifibrotic action, idoxifene and E2 could enhance antioxidant and antiapoptotic activity in hepatic fibrosis in rats.