Wnt/beta-catenin signaling and its modulators in nonalcoholic fatty liver diseases

Nonalcoholic fatty liver disease(NAFLD)is a global health concern associated with significant morbidity and mortality.NAFLD is a spectrum of diseases originating from simple steatosis,progressing through nonalcoholic steatohepatitis(NASH),fibrosis,and cirrhosis that may lead to hepatocellular carcinoma(HCC).The pathogenesis of NAFLD is mediated by the triglyceride accumulation followed by proinflam-matory cytokines expression leading to inflammation,oxidative stress,and mitochondrial dysfunction de-noted as“two-hit hypothesis”,advancing with a“third hit”of insufficient hepatocyte proliferation,lead-ing to the increase in hepatic progenitor cells contributing to fibrosis and HCC.Wnt/β-catenin signaling is responsible for normal liver development,regeneration,hepatic metabolic zonation,ammonia and drug detoxification,hepatobiliary development,etc.,maintaining the overall liver homeostasis.The key regula-tors of canonical Wnt signaling such as LRP6,Wnt1,Wnt3a,β-catenin,GSK-3β,and APC are abnormally regulated in NAFLD.Many experimental studies have shown the aberrated Wnt/β-catenin signaling dur-ing the NAFLD progression and NASH to hepatic fibrosis and HCC.Therefore,in this review,we have em-phasized the role of Wnt/β-catenin signaling and its modulators that can potentially aid in the inhibition of NAFLD.

Reply to“Wnt/beta-catenin signaling inhibitors and nonalcoholic fatty liver disease:Potential therapeutic implications”

The Author Reply:We sincerely appreciated the interest of Polyzos et al.,in our review article and sharing their improvised thoughts regarding the Wnt signaling modulators for the treatment of postmenopausal women with osteoporosis and nonalcoholic fatty liver disease(NAFLD).Several experimental studies have showed that the aberrant Wnt/β-catenin signaling promotes the development and/or progression of a variety of chronic liver diseases including NAFLD[1,2].Therefore,our review emphasized on the modulation of Wnt/β-catenin signaling and the role of its mediators in NAFLD progression.Given that NAFLD prevalence is constantly increas-ing,and that osteoporosis is associated with women over 50 years of age with NAFLD[3],there is an unmet need for an effective treatment.Sclerostin blocks the canonical Wnt signaling pathway of bone formation.Therefore,romosozumab,a humanized anti-sclerostin monoclonal antibody,was approved for the treatment of osteoporosis.Romosozumab binds to sclerostin,permitting the en-gagement of Wnt ligands with their co-receptors,resulting in an increase in bone formation and bone mineral density.

Hepatic fibrosis： It is time to go with hepatic stellate cell-specifictherapeutic targets

Hepatic fibrosis is a pathological lesion, characterized by the progressive accumulation of extracellularmatrix （ECM） in the perisinusoidal space and it is a major problem in chronic liver diseases. Phenotypicactivation of hepatic stellate cells （HSC） plays a central role in the progression of hepatic fibrosis. Retardation of proliferation and clearance of activated HSCs from the injured liver is an appropriate therapeuticstrategy for the resolution and treatment of hepatic fibrosis. Clearance of activated HSCs from the injuredliver by autophagy inhibitors, proapoptotic agents and senescence inducers with the high affinity towardthe activated HSCs may be the novel therapeutic strategy for the treatment of hepatic fibrosis in the nearfuture.

Silibinin induces hepatic stellate cell cycle arrest via enhancing p53/p27 and inhibiting Akt downstream signaling protein expression

BACKGROUND： Proliferation of hepatic stellate cells （HSCs） plays a pivotal role in the progression of liver fibrosis conse- quent to chronic liver injury. Silibinin, a flavonoid compound, has been shown to possess anti-fibrogenic effects in animal models of liver fibrosis. This was attributed to an inhibition of cell proliferation of activated HSCs. The present study was to gain insight into the molecular pathways involved in silibinin anti-fibrogenic effect. METHODS： The study was conducted on LX-2 human stellate cells treated with three concentrations of silibinin （10, 50 and 100 μmol/L） for 24 and 96 hours. At the end of the treatment cell viability and proliferation were evaluated. Protein expression of p27, p21, p53, Akt and phosphorylated-Akt was evaluated by Western blotting analysis and Ki-67 protein expression was by immunocytochemistry. Sirtuin activity was evaluated by chemiluminescence based assay. RESULTS： Silibinin inhibits LX-2 cell proliferation in doseand time-dependent manner; we showed that silibinin upregulated the protein expressions of p27 and p53. Such regulation was correlated to an inhibition of both downstream Akt and phosphorylated-Akt protein signaling and Ki-67 protein expression. Sirtuin activity also was correlated to silibinin- inhibited proliferation of LX-2 cells. CONCLUSION： The anti-proliferative effect of silibinin on LX-2 human steUate cells is via the inhibition of the expres- sions of various cell cycle targets including p27, Akt and sir- tuin signaling.

Mitochondria: A critical hub for hepatic stellate cells activation during chronic liver diseases

Background: Upon liver injury, quiescent hepatic stellate cells(q HSCs), reside in the perisinusoidal space, phenotypically transdifferentiate into myofibroblast-like cells(MFBs). The q HSCs in the normal liver are less fibrogenic, migratory, and also have less proliferative potential. However, activated HSCs(a HSCs) are more fibrogenic and have a high migratory and proliferative MFBs phenotype. HSCs activation is a highly energetic process that needs abundant intracellular energy in the form of adenosine triphosphate(ATP) for the synthesis of extracellular matrix(ECM) in the injured liver to substantiate the injury. Data sources: The articles were collected through Pub Med and EMBASE using search terms "mitochondria and hepatic stellate cells", "mitochondria and HSCs", "mitochondria and hepatic fibrosis", "mitochondria and liver diseases", and "mitochondria and chronic liver disease", and relevant publications published before September 31, 2020 were included in this review. Results: Mitochondria homeostasis is affected during HSCs activation. Mitochondria in a HSCs are highly energetic and are in a high metabolically active state exhibiting increased activity such as glycolysis and respiration. a HSCs have high glycolytic enzymes expression and glycolytic activity induced by Hedgehog(Hh) signaling from injured hepatocytes. Increased glycolysis and aerobic glycolysis(Warburg effect) endproducts in a HSCs consequently activate the ECM-related gene expressions. Increased Hh signaling from injured hepatocytes downregulates peroxisome proliferator-activated receptor-γ expression and decreases lipogenesis in a HSCs. Glutaminolysis and tricarboxylic acid cycle liberate ATPs that fuel HSCs to proliferate and produce ECM during their activation. Conclusions: Available studies suggest that mitochondria functions can increase in parallel with HSCs activation. Therefore, mitochondrial modulators should be tested in an elaborate manner to control or prevent the HSCs activation during liver injury to subsequently regress hepatic fibrosis.

Critical role of estrogen in the progression of chronic liver diseases

Background:Estrogens regulate sexual function and also have a significant role in various pathophysiological processes.Estrogens have a non-reproductive role as the modulators of the immune system,growth,neuronal function,and metabolism.Estrogen receptors are expressed in the liver and their impaired expression and function are implicated with obesity and liver associated metabolic dysfunctions.The purpose of the current review is to discuss the disparity role of estrogens on several forms of liver diseases.Data sources:A comprehensive search in PubMed and EMBASE was conducted using the keywords“estrogens and liver diseases”,“estradiol and liver diseases”,“hormones and liver diseases”,“endocrine function in liver diseases”,and“female hormones in liver diseases”.Relevant papers published before September 30,2019 were included.Results:The present review confirms the imperative role of estrogen in various forms of chronic liver diseases.Estrogens play a key role in maintaining homeostasis and make the liver less susceptible to several forms of chronic liver diseases in healthy premenopausal individuals.In contrast,clinical studies also showed increased estrogen levels with chronic liver diseases.Conclusions:Several studies reported the protective role of estrogens in chronic liver diseases and this has been widely accepted and confirmed in experimental studies using ovariectomized rat models.However,in a few clinical studies,increased estrogen levels are also implicated in chronic liver diseases.Therefore,further studies are warranted at molecular level to explore the role of estrogen in various forms of chronic liver diseases.

Silibinin alleviates N-nitrosodimethylamine-induced glutathione dysregulation and hepatotoxicity in rats

The present study was designed to evaluate the hepatoprotective and antioxidant potentials of silibinin(SBN)against N-nitrosodimethylamine(DMN)-induced toxic insults in the rat liver.The liver damage was induced in Wistar albino rats by repeated administration of DMN(10 mg·kg-1 b.w.,i.p.)on 3 consecutive days per week for 3 weeks.SBN(100 mg·kg-1 b.w.,p.o.)was given daily to the DMN treated rats for two weeks.The marker enzymes of liver toxicity and second-line enzymic and non-enzymic antioxidants were evaluated in serum and liver tissues before and after SBN treatment.Histopathology of the liver was evaluated by H & E staining.The DMN treatment produced a progressive increase in all the serum marker enzymes(AST,ALT,ALP,LDH,and γ-GT),peaking on Day 21.This treatment produced highly significant decreases in all the second-line antioxidant parameters(GSH,GST,GR,GPx,and vitamins C and E).The SBN treatment significantly reversed the DMN-induced damages,towards normalcy.Histopathological studies confirmed the development of liver toxicity in DMN-treated rats,which was reversed by SBN treatment in corroboration with the aforementioned biochemical results,indicating the hepatoprotective and antioxidant properties of SBN.In conclusion,the DMN-induced degenerative changes in the liver were alleviated by SBN treatment and this protective ability may be attributed to its antioxidant,free radical scavenging,and membrane stabilizing properties.

Plant derived antioxidants and antifibrotic drugs:past,present and future

Hepatic fibrosis occurs as a wound-healing process after several forms of chronic hepatic injury.Activation and proliferation of hepatic stellate cells play pivotal role in the pathogenesis of hepatic fibrosis.Many researchers,from the therapeutic perspective,have focused their attention on searching for novel agents with inhibitory effects on hepatic stellate cells proliferation and activation to prevent hepatic fibrogenesis and a number of plant derived antioxidants have been tested as anti-fibrogenic agents,they generally suppress proliferation and collagen synthesis.Plants remain an imperative source of novel drugs,novel drug leads and new chemical entities.The plant based drug discovery resulted primarily in the development of antioxidant,anti-cancer and other anti-infectious agents and continues to contribute to the new leads in clinical trials.This review summarizes some of those most important plant derived anti-fibrotic drugs and their beneficial effects on experimentally induced hepatic fibrosis in vitro and in vivo.The plant derived antioxidant compounds described herein are curcumin,silymarin,silibinin,baicalein,resveratrol,salvianolic acids,tetrandine,quercetin and berberine.Studies from ours and as demonstrated by pervious workers much information has been accumulated over the past two decades through in vivo and in vitro.In light of those studies,it has been confirmed that plants derived antioxidants,particularly flavanoids,show a significant influence to block hepatic fibrosis regardless of any etiology.This review outlines recent progress in the use of plant derived drugs against experimentally induced liver fibrosis by in vitro and in vivo studies and summarizes the possible mechanisms anti-fibrotic effects of these compounds.