Mitochondrial genome depletion in human liver cells abolishes bile acid-induced apoptosis: role of the Akt/mTOR survival pathway and Bcl-2 family proteins

Metabolomics and serum pharmacochemistry combined with network pharmacology uncover the potential effective ingredients and mechanisms of Yin-Chen-Si-Ni Decoction treating ANIT-induced cholestatic liver injury

ETHNOPHARMACOLOGICAL RELEVANCE

Yin-Chen-Si-Ni Decoction is a classical traditional Chinese medicine (TCM) prescription that is used clinically for treating cholestatic liver injury (CLI) and other hepatic diseases. However, the material basis and underlying mechanisms of YCSND are not clear.

AIM OF THE STUDY

To investigate effective components and mechanisms of YCSND in the treatment of CLI using serum pharmacochemistry, metabolomics, and network pharmacology.

MATERIALS AND METHODS

Biochemical indicators, liver index, and histopathology analysis were adopted to evaluate the protective effect of YCSND on ANIT-induced CLI rats. Then, a UPLC-Q-Exactive Orbitrap MS/MS analysis of the migrant components in serum and liver including prototype and metabolic components was performed in YCSND. In addition, a study of the endogenous metabolites using serum and liver metabolomics was performed to discover potential biomarkers, metabolic pathways, and associated mechanisms. Further, the network pharmacology oriented by in vivo migrant components was also used to pinpoint the active ingredients, core targets, and signaling pathways of YCSND. Finally, molecular docking and molecular dynamics simulation (MDS) were used to predict the binding ability between components and core targets, and a real-time qPCR (RT-qPCR) experiment was used to measure the mRNA expression of the core target genes.

RESULTS

Pharmacodynamic studies suggest that YCSND could exert obvious hepatoprotective effects on CLI rats. Furthermore, 68 compounds, comprising 32 prototype components and 36 metabolic components from YCSND, were found by serum pharmacochemistry analysis. Network pharmacology combining molecular docking and MDS showed that apigenin, naringenin, 18β-glycyrrhetinic acid, and isoformononetin have better binding ability to 6 core targets (EGFR, AKT1, IL6, MMP9, CASP3, PPARG). Additionally, PI3K, TNF-α, MAPK3, and six core target genes in liver tissues were validated with RT-qPCR. Metabolomics revealed the anti-CLI effects of YCSND by regulating four metabolic pathways of primary bile acid and biosynthesis, phenylalanine, tyrosine and tryptophan biosynthesis, taurine and hypotaurine metabolism, and arachidonic acid metabolism. Integrating metabolomics and network pharmacology identified four pathways related to CLI, including the PI3K-Akt, HIF-1, MAPK, and TNF signaling pathway, which revealed multiple mechanisms of YCSND against CLI that might involve anti-inflammatory and apoptosis.

CONCLUSION

The research based on serum pharmacochemistry, network pharmacology, and metabolomics demonstrates the beneficial hepatoprotective effects of YCSND on CLI rats by regulating multiple components, multiple targets, and multiple pathways, and provides a potent means of illuminating the material basis and mechanisms of TCM prescriptions.

Distinctive metabolic remodeling in TYMP deficiency beyond mitochondrial dysfunction

Mitochondrial neurogastrointestinal encephalomyopathy (MNGIE) is caused by mutations in the TYMP gene, which encodes thymidine phosphorylase (TP). As a cytosolic metabolic enzyme, TP defects affect biological processes that are thought to not be limited to the abnormal replication of mitochondrial DNA. This study aimed to elucidate the characteristic metabolic alterations and associated homeostatic regulation caused by TYMP deficiency. The pathogenicity of novel TYMP variants was evaluated in terms of clinical features, genetic analysis, and structural instability. We analyzed plasma samples from three patients with MNGIE; three patients with m.3243A > G mitochondrial encephalopathy, lactic acidosis, and stroke-like episodes (MELAS); and four healthy controls (HC) using both targeted and untargeted metabolomics techniques. Transcriptomics analysis and bioenergetic studies were performed on skin fibroblasts from participants in these three groups. A TYMP overexpression experiment was conducted to rescue the observed changes. Compared with controls, specific alterations in nucleosides, bile acids, and steroid metabolites were identified in the plasma of MNGIE patients. Comparable mitochondrial dysfunction was present in fibroblasts from patients with TYMP deficiency and in those from patients with the m.3243A > G mutation. Distinctively decreased sterol regulatory element binding protein (SREBP) regulated cholesterol metabolism and fatty acid (FA) biosynthesis as well as reduced FA degradation were revealed in fibroblasts with TYMP deficiency. The restoration of thymidine phosphorylase activity rescued the observed changes in MNGIE fibroblasts. Our findings indicated that more widespread metabolic disturbance may be caused by TYMP deficiency in addition to mitochondrial dysfunction, which expands our knowledge of the biochemical outcome of TYMP deficiency. KEY MESSAGES: Distinct metabolic profiles in patients with TYMP deficiency compared to those with m.3243A > G mutation. TYMP deficiency leads to a global disruption of nucleoside metabolism. Cholesterol and fatty acid metabolism are inhibited in individuals with MNGIE. TYMP is functionally related to SREBP-regulated pathways. Potential metabolite biomarkers that could be valuable clinical tools to improve the diagnosis of MNGIE.

Farnesoid X Receptor (FXR) Regulates mTORC1 Signaling and Autophagy by Inhibiting SESN2 Expression

SCOPE

The mechanistic target of rapamycin complex 1 (mTORC1), as a link between nutrients and autophagy, senses many nutrients in the microenvironment. A growing body of recent literature describes the function of bile acids (BAs) as versatile signaling molecules, while it remains largely unclear whether mTORC1 can sense BAs and the mechanism has not been studied.

METHODS AND RESULTS

After treating LO2 cells with indicated concentration of chenodeoxycholic acid (CDCA) and farnesoid X receptor (FXR) inhibitor/activator for 6 h, it finds that CDCA and FXR significantly accelerate mTORC1 activation. The results of immunofluorescence indicate that CDCA and FXR inhibit cellular autophagy through activating mTORC1 pathway. In particular, these findings show that CDCA and FXR promote the lysosomal translocation and activation of mTORC1 in an amino acid-sensitive manner. Mechanistically, the transcriptomics data indicate that SESN2 is a checkpoint for mTORC1 lysosome translocation and activation induced by FXR, and knockdown SESN2 with siRNA suppresses the regulation of FXR on autophagy.

CONCLUSION

These results indicate that FXR-induced decrease in SESN2 expression and activation of the mTORC1 pathway can control autophagy and be explored as potential therapeutic targets for enterohepatic and metabolic disorders.

mtDNA Maintenance and Alterations in the Pathogenesis of Neurodegenerative Diseases

Considerable evidence indicates that the semiautonomous organelles mitochondria play key roles in the progression of many neurodegenerative disorders. Mitochondrial DNA (mtDNA) encodes components of the OXPHOS complex but mutated mtDNA accumulates in cells with aging, which mirrors the increased prevalence of neurodegenerative diseases. This accumulation stems not only from the misreplication of mtDNA and the highly oxidative environment but also from defective mitophagy after fission. In this review, we focus on several pivotal mitochondrial proteins related to mtDNA maintenance (such as ATAD3A and TFAM), mtDNA alterations including mtDNA mutations, mtDNA elimination, and mtDNA release-activated inflammation to understand the crucial role played by mtDNA in the pathogenesis of neurodegenerative diseases such as Alzheimer's disease, Parkinson's disease, amyotrophic lateral sclerosis, and Huntington's disease. Our work outlines novel therapeutic strategies for targeting mtDNA.

Hepatocellular Carcinoma: How the Gut Microbiota Contributes to Pathogenesis, Diagnosis, and Therapy

The gut microbiota is gaining increasing attention, and the concept of the "gut-liver axis" is gradually being recognized. Leaky gut resulting from injury and/or inflammation can cause the translocation of flora to the liver. Microbiota-associated metabolites and components mediate the activation of a series of signalling pathways, thereby playing an important role in the development of hepatocellular carcinoma (HCC). For this reason, targeting the gut microbiota in the diagnosis, prevention, and treatment of HCC holds great promise. In this review, we summarize the gut microbiota and the mechanisms by which it mediates HCC development, and the characteristic alterations in the gut microbiota during HCC pathogenesis. Furthermore, we propose several strategies to target the gut microbiota for the prevention and treatment of HCC, including antibiotics, probiotics, faecal microbiota transplantation, and immunotherapy.

The Role of Mitochondrial DNA Variation in Drug Response: A Systematic Review

Background: The triad of drug efficacy, toxicity and resistance underpins the risk-benefit balance of all therapeutics. The application of pharmacogenomics has the potential to improve the risk-benefit balance of a given therapeutic via the stratification of patient populations based on DNA variants. A growth in the understanding of the particulars of the mitochondrial genome, alongside the availability of techniques for its interrogation has resulted in a growing body of literature examining the impact of mitochondrial DNA (mtDNA) variation upon drug response. Objective: To critically evaluate and summarize the available literature, across a defined period, in a systematic fashion in order to map out the current landscape of the subject area and identify how the field may continue to advance. Methods: A systematic review of the literature published between January 2009 and December 2020 was conducted using the PubMed database with the following key inclusion criteria: reference to specific mtDNA polymorphisms or haplogroups, a core objective to examine associations between mtDNA variants and drug response, and research performed using human subjects or human in vitro models. Results: Review of the literature identified 24 articles reporting an investigation of the association between mtDNA variant(s) and drug efficacy, toxicity or resistance that met the key inclusion criteria. This included 10 articles examining mtDNA variations associated with antiretroviral therapy response, 4 articles examining mtDNA variants associated with anticancer agent response and 4 articles examining mtDNA variants associated with antimicrobial agent response. The remaining articles covered a wide breadth of medications and were therefore grouped together and referred to as "other." Conclusions: Investigation of the impact of mtDNA variation upon drug response has been sporadic to-date. Collective assessment of the associations identified in the articles was inconclusive due to heterogeneous methods and outcomes, limited racial/ethnic groups, lack of replication and inadequate statistical power. There remains a high degree of idiosyncrasy in drug response and this area has the potential to explain variation in drug response in a clinical setting, therefore further research is likely to be of clinical benefit.

Boosting mitochondria activity by silencing MCJ overcomes cholestasis-induced liver injury

BACKGROUND & AIMS

Mitochondria are the major organelles for the formation of reactive oxygen species (ROS) in the cell, and mitochondrial dysfunction has been described as a key factor in the pathogenesis of cholestatic liver disease. The methylation-controlled J-protein (MCJ) is a mitochondrial protein that interacts with and represses the function of complex I of the electron transport chain. The relevance of MCJ in the pathology of cholestasis has not yet been explored.

METHODS

We studied the relationship between MCJ and cholestasis-induced liver injury in liver biopsies from patients with chronic cholestatic liver diseases, and in livers and primary hepatocytes obtained from WT and MCJ-KO mice. Bile duct ligation (BDL) was used as an animal model of cholestasis, and primary hepatocytes were treated with toxic doses of bile acids. We evaluated the effect of MCJ silencing for the treatment of cholestasis-induced liver injury.

RESULTS

Elevated levels of MCJ were detected in the liver tissue of patients with chronic cholestatic liver disease when compared with normal liver tissue. Likewise, in mouse models, the hepatic levels of MCJ were increased. After BDL, MCJ-KO animals showed significantly decreased inflammation and apoptosis. In an in vitro model of bile-acid induced toxicity, we observed that the loss of MCJ protected mouse primary hepatocytes from bile acid-induced mitochondrial ROS overproduction and ATP depletion, enabling higher cell viability. Finally, the in vivo inhibition of the MCJ expression, following BDL, showed reduced liver injury and a mitigation of the main cholestatic characteristics.

CONCLUSIONS

We demonstrated that MCJ is involved in the progression of cholestatic liver injury, and our results identified MCJ as a potential therapeutic target to mitigate the liver injury caused by cholestasis.

LAY SUMMARY

In this study, we examine the effect of mitochondrial respiratory chain inhibition by MCJ on bile acid-induced liver toxicity. The loss of MCJ protects hepatocytes against apoptosis, mitochondrial ROS overproduction, and ATP depletion as a result of bile acid toxicity. Our results identify MCJ as a potential therapeutic target to mitigate liver injury in cholestatic liver diseases.

Plant protein diet-induced hypoimmunity by affecting the spiral valve intestinal microbiota and bile acid enterohepatic circulation in Amur sturgeon (Acipenser schrenckii)

An 8-week growth trial was conducted to study enterohepatic recirculation of bile acid metabolism and the intestinal microbiota of Amur sturgeon (Acipenser schrenckii) fed with three diets, including 540 g/kg, 270 g/kg or 0 g/kg fishmeal, which was correspondingly replaced by a plant protein blend (named P0, P50 and P100, respectively). The diets were designed to be isonitrogenous, isoenergetic and essential nutrients balanced. With rising levels of dietary plant protein, disruption of the spiral valve intestinal microbiota and more morbidity with liver disease were observed in the P100 group, although there were no haematological abnormalities observed. An obvious bile acids enterohepatic circulation disorder was found with phenotypes of increased liver bile acids compensatory synthesis, and reduced expression of bile acid receptors (FXR and TGR5), which induced BA accumulative toxicity. Accompanied by increased oxidative stress, it further induced hepatic lesions and hypoimmunity, which were non-negligible reasons for the high mortality and low utilization ability of plant protein by Amur sturgeon.

Mitochondrial DNA Mutation, Diseases, and Nutrient-Regulated Mitophagy

A wide spectrum of human diseases, including cancer, neurodegenerative diseases, and metabolic disorders, have been shown to be associated with mitochondrial dysfunction through multiple molecular mechanisms. Mitochondria are particularly susceptible to nutrient deficiencies, and nutritional intervention is an essential way to maintain mitochondrial homeostasis. Recent advances in genetic manipulation and next-generation sequencing reveal the crucial roles of mitochondrial DNA (mtDNA) in various pathophysiological conditions. Mitophagy, a term coined to describe autophagy that targets dysfunctional mitochondria, has emerged as an important cellular process to maintain mitochondrial homeostasis and has been shown to be regulated by various nutrients and nutritional stresses. Given the high prevalence of mtDNA mutations in humans and their impact on mitochondrial function, it is important to investigate the mechanisms that regulate mtDNA mutation. Here, we discuss mitochondrial genetics and mtDNA mutations and their implications for human diseases. We also examine the role of mitophagy as a therapeutic target, highlighting how nutrients may eliminate mtDNA mutations through mitophagy.

Mito-Nuclear Communication in Hepatocellular Carcinoma Metabolic Rewiring

As the main metabolic and detoxification organ, the liver constantly adapts its activity to fulfill the energy requirements of the whole body. Despite the remarkable adaptive capacity of the liver, prolonged exposure to noxious stimuli such as alcohol, viruses and metabolic disorders results in the development of chronic liver disease that can progress to hepatocellular carcinoma (HCC), which is currently the second leading cause of cancer-related death worldwide. Metabolic rewiring is a common feature of cancers, including HCC. Altered mito-nuclear communication is emerging as a driving force in the metabolic reprogramming of cancer cells, affecting all aspects of cancer biology from neoplastic transformation to acquired drug resistance. Here, we explore relevant aspects (and discuss recent findings) of mito-nuclear crosstalk in the metabolic reprogramming of hepatocellular carcinoma.

Lithocholic acid activates mTOR signaling inducing endoplasmic reticulum stress in placenta during intrahepatic cholestasis of pregnancy

AIMS

Intrahepatic cholestasis of pregnancy (ICP) is a pregnancy-specific disorder, which increases risks of adverse fetal outcomes. However, the pathophysiology is not fully understood. Here, we explored the roles of mTOR signaling and ER stress in placenta during ICP.

MATERIALS AND METHODS

Placental tissues were collected from normal and ICP pregnancies. mTOR signaling and endoplasmic reticulum stress were detected by immunohistochemistry in the placenta. The human placenta trophoblast cell line HTR-8/SVneo was used in vitro experiment.

KEY FINDINGS

ICP placenta displayed histological abnormalities with fewer trophoblasts. Moreover, the expression of Bip and the phosphorylation of pS6(S235/236) or pAkt(S473) were higher comparing with normal placenta. In in vitro studies, the bile acids specifically to lithocholic acid rather than taurocholic acid or ursodeoxycholic acid, drastically increased the phosphorylation of pS6K1(T389), pS6(S235/236), or pAkt(S473), whereas the mTOR inhibitor can prohibit the upregulation. Similarly, the expressions of IRE1α and BiP increased sharply under lithocholic acid (20 μM) administration, while the same inhibitor can also decrease the expression. Additionally, transmission electron microscopy showed enlarged endoplasmic reticulum lumen under the lithocholic acid treatment. Furthermore, the cell viability reduced sharply under treatment with different dose of lithocholic acid. The mTOR inhibitor can reverse the decrease of cell viability to some extent.

SIGNIFICANCE

Bile acid can activate mTOR signaling which resulted in endoplasmic reticulum stress, leading to trophocyte viability decrease. mTOR pathway activation may be associated with the pathophysiology of ICP.

α‑lipoic acid protects against carbon tetrachloride‑induced liver cirrhosis through the suppression of the TGF‑β/Smad3 pathway and autophagy

α-lipoic acid (ALA) is a naturally occurring antioxidant with protective effects against various hepatic injuries. The aim of the present study was to investigate the mechanisms by which ALA protects the liver from carbon tetrachloride (CCl₄)-induced liver cirrhosis. The widely used liver cirrhosis rat model was established via an intraperitoneal injection of 2 mg/kg 50% CCl_4, three times/week for 8 weeks. Simultaneously, 50 or 100 mg/kg ALA was orally administrated to the rats every day for 8 weeks. The activity of alanine aminotransferase (ALT) and aspartate aminotransferase (AST) was detected in the serum. The pathological liver injuries were analyzed using hematoxylin and eosin and Masson's trichrome staining. The principal factors involved in the transforming growth factor-β (TGF-β)/mothers against decapentaplegic homolog 9 (Smad3) and protein kinase B (AKT)/mammalian target of rapamycin (mTOR) pathways and in autophagy were examined using reverse transcription-quantitative polymerase chain reaction or western blot analysis. The results demonstrated that the administration of ALA alleviated CCl₄-induced liver injury, as demonstrated by decreased ALT and AST activity, improved pathological injuries and reduced collagen deposition. The CCl4-induced increase in TGF-β and phosphorylated-Smad3 expression levels was additionally inhibited by treatment with ALA. Furthermore, the administration of ALA reversed the CCl₄-induced upregulation of light chain 3II and Beclin-1, and downregulation of p62. The CCl₄-induced suppression of the AKT/mTOR pathway was additionally restored following treatment with ALA. In combination, the results of the present study demonstrated that ALA was able to protect CCl₄-induced liver cirrhosis, an effect that may be associated with inactivation of the TGF-β/Smad3 pathway and suppression of autophagy.

Dysregulation of autophagy in rat liver with mitochondrial DNA depletion induced by the nucleoside analogue zidovudine

The nucleoside reverse transcriptase inhibitor zidovudine (AZT), used in HIV infection treatment, induces mitochondrial DNA (mtDNA) depletion. A cause-effect relationship between mtDNA status alterations and autophagy has been reported. Both events are common in several liver diseases, including hepatocellular carcinoma. Here, we have studied autophagy activation in rat liver with mtDNA depletion induced by AZT administration in drinking water for 35 days. AZT at a concentration of 1 mg/ml, but not 0.5 mg/ml in the drinking water, decreased mtDNA levels in rat liver and extrahepatic tissues. In liver, mtDNA-encoded cytochrome c oxidase 1 protein levels were decreased. Although serum biomarkers of liver and kidney toxicity remained unaltered, β-hydroxybutyrate levels were increased in liver of AZT-treated rats. Moreover, autophagy was dysregulated at two levels: (i) decreased induction signalling of this process as indicated by increases in autophagy inhibitors activity (AKT/mTOR), and absence of changes (Beclin-1, Atg5, Atg7) or decreases (AMPK/ULK1) in the expression/activity of pro-autophagy proteins; and (ii) reduced autophagosome degradation as indicated by decreases in the lysosome abundance (LAMP2 marker) and the transcription factor TFEB controlling lysosome biogenesis. This resulted in increased autophagosome abundance (LC3-II marker) and accumulation of the protein selectively degraded by autophagy p62, and the transcription factor Nrf2 in liver of AZT-treated rats. Nrf2 was activated as indicated by the up-regulation of antioxidant target genes Nqo1 and Hmox-1. In conclusion, rat liver with AZT-induced mtDNA depletion presented dysregulations in autophagosome formation and degradation balance, which results in accumulation of these structures in parenchymal liver cells, favouring hepatocarcinogenesis.

Lack of mitochondrial DNA impairs chemical hypoxia-induced autophagy in liver tumor cells through ROS-AMPK-ULK1 signaling dysregulation independently of HIF-1α

Alterations in mitochondrial DNA (mtDNA) and autophagy activation are common events in tumors. Here we have investigated the effect of mitochondrial genome depletion on chemical hypoxia-induced autophagy in liver tumor cells. Human SK-Hep-1 wild-type and mtDNA-depleted (Rho) cells were exposed to the hypoxia mimetic agents CoCl₂ and deferoxamine (DFO). Up-regulation of HIF-1α, but not HIF-2α was observed. The expression of several HIF-1α target genes was also found. In human SK-Hep-1 and mouse Hepa 1-6 liver tumor cells, but not in the counterpart Rho derived lines, chemical hypoxia increased the abundance of autophagosomes and autolysosomes. In wild-type and Rho cells, chemical hypoxia induced down-regulation of HIF-1α-dependent autophagy inhibitors Bcl-2 and mTOR, whereas activation of AMPK/ULK1-mediated pro-autophagy pathway occurred only in wild-type cells. Chemical (compound C) and genetic (shRNA) inhibition of AMPK activation resulted in reduced autophagy. ATP levels were similar in both cell types, whereas constitutive and chemical hypoxia-induced reactive oxygen species (ROS) generation was lower in Rho cells. In wild-type cells, the antioxidant N-acetylcysteine blocked CoCl₂- and DFO-induced AMPK and autophagy activation, but not endoplasmic reticulum stress induced by CoCl₂. Enhanced Bax-α/Bcl-2 ratio and cell death was induced by hypoxia mimetic agents more markedly in wild-type than in Rho cells. Upon blocking autophagy activation with 3-methyladenine, DFO-induced cell death was partially prevented whereas that induced by CoCl₂ was increased, but only in wild-type cells. These results suggest that mitochondrial dysfunction associated with the lack of mtDNA impairs the signaling pathways mediated by ROS, controlling autophagy activation in liver tumor cells, which may contributes to cancer development.

Regulatory Effects and Mechanism of Adenovirus-Mediated PTEN Gene on Hepatic Stellate Cells

BACKGROUND

Tension homology deleted on chromosome ten (PTEN) is important in liver fibrosis.

AIMS

The purpose of this study was to evaluate the PTEN gene effects and mechanism of action on hepatic stellate cells (HSCs).

METHODS

The rat primary HSCs and human LX-2 cells were transfected by an adenovirus containing cDNA constructs encoding the wild-type PTEN (Ad-PTEN), the PTEN mutant G129E gene (Ad-G129E) and RNA interference targeting the PTEN sequence PTEN short hairpin RNA (PTEN shRNA), to up-regulate and down-regulate PTEN expression, respectively. The HSCs were assayed with a fluorescent microscope, real time PCR, Western blot, MTT, flow cytometry and Terminal-deoxynucleoitidyl transferase mediated nick end labeling. In addition, the CCl4 induced rat hepatic fibrosis model was also established to check the in vivo effects of the recombinant adenovirus with various levels of PTEN expression.

RESULTS

The data have shown that the over-expressed PTEN gene led to reduced HSCs activation and viability, caspase-3 activity and cell cycle arrest in the G0/G1 and G2/M phases, as well as negative regulation of the PI3K/Akt and FAK/ERK signaling pathways in vitro. The over-expressed PTEN gene improved liver function, inhibited proliferation and promoted apoptosis of HSCs both in vitro and in vivo.

CONCLUSIONS

These data have shown that gene therapy using the recombinant adenovirus encoding wild-type PTEN inhibits proliferation and induces apoptosis of HSCs, which is a potential treatment option for hepatic fibrosis.

Hydrogen-rich saline protects against mitochondrial dysfunction and apoptosis in mice with obstructive jaundice

Previous studies have demonstrated that hydrogen-rich saline (HS) protects against bile duct ligation (BDL)-induced liver injury by suppressing oxidative stress and inflammation. Mitochondria, which are targets of excessive reactive oxygen species and central mediators of apoptosis, have a pivotal role in hepatic injury during obstructive jaundice (OJ); however, the implications of HS in the hepatic mitochondria of BDL mice remain unknown. The present study investigated the hypothesis that HS could reduce OJ‑induced liver injury through the protection of mitochondrial structure and function, as well as inhibition of the mitochondrial apoptotic pathway. Male C57BL/6 mice were randomly divided into three experimental groups: Sham operation group, BDL injury with normal saline (NS) treatment group, and BDL‑injury with HS treatment group. Mitochondrial damage and apoptotic parameters were determined 3 days post‑BDL injury and treatment. The results demonstrated that mitochondria isolated from the livers of NS-treated BDL mice exhibited increased mitochondrial swelling, cytochrome c release, and oxidative damage. In addition, liver samples from NS‑treated BDL mice exhibited significant increases in B‑cell lymphoma 2 (Bcl‑2)‑associated X protein expression, caspase activities, and hepatocyte apoptosis compared with livers from sham‑operated controls. Notably, treatment with HS reduced the levels of these markers and alleviated morphological defects in the mitochondria following injury. In addition, HS markedly increased the antioxidant potential of mitochondria, as evidenced by elevated adenosine triphosphate levels, mitochondrial respiratory function, and increased levels of active Bcl‑2. In conclusion, HS attenuates mitochondrial oxidative stress and dysfunction, and inhibits mitochondrial-mediated apoptosis in the livers of BDL mice.

Mitochondrial (dys)function - a factor underlying the variability of efavirenz-induced hepatotoxicity?

BACKGROUND AND PURPOSE

The non-nucleoside analogue reverse transcriptase inhibitor efavirenz is associated with hepatic toxicity and metabolic disturbances. Although the mechanisms involved are not clear, recent evidence has pinpointed a specific mitochondrial action of efavirenz accompanied by the induction of an endoplasmic reticulum (ER) stress/unfolded protein response in human hepatic cells. The aim of this study was to further investigate the involvement of this organelle by evaluating efavirenz's effects in cells lacking functional mitochondria (rho°) and comparing them with those of the typical mitotoxic agent rotenone, a standard complex I inhibitor, and the ER stress inducer thapsigargin.

EXPERIMENTAL APPROACH

Hep3B rho(+) and rho° cells were treated with clinically relevant concentrations of efavirenz, then mitochondrial function and cytotoxicity were studied using standard cell biology techniques.

KEY RESULTS

Efavirenz-treated rho° cells exhibited a substantial reduction in parameters indicative of mitochondrial interference, such as increased superoxide production, mitochondrial mass/morphology alterations and enhanced expression of LONP, a highly conserved mitochondrial protease. In line with these results, the cytotoxic effect (cell number, chromatin condensation, cell cycle alterations and induction of apoptosis) of efavirenz was less pronounced in Hep3B respiration-depleted cells than in wild-type cells. The effect of efavirenz was both similar and different from those of two distinct mitochondrial stressors, thapsigargin and rotenone.

CONCLUSIONS AND IMPLICATIONS

Cells lacking normal mitochondria (rho°) are less vulnerable to efavirenz. Our results provide further evidence that the hepatic damage induced by efavirenz involves acute interference with mitochondria and extend our knowledge of the response of mitochondria/ER to a stress stimulus.

Up-regulation of nerve growth factor in cholestatic livers and its hepatoprotective role against oxidative stress

The role of nerve growth factor (NGF) in liver injury induced by bile duct ligation (BDL) remains elusive. This study aimed to investigate the relationship between inflammation and hepatic NGF expression, to explore the possible upstream molecules up-regulating NGF, and to determine whether NGF could protect hepatocytes from oxidative liver injury. Biochemical and molecular detection showed that NGF was up-regulated in cholestatic livers and plasma, and well correlated with systemic and hepatic inflammation. Conversely, systemic immunosuppression reduced serum NGF levels and resulted in higher mortality in BDL-treated mice. Immunohistochemistry showed that the up-regulated NGF was mainly localized in parenchymal hepatocytes. In vitro mechanistic study further demonstrated that TGF-β1 up-regulated NGF expression in clone-9 and primary rat hepatocytes. Exogenous NGF supplementation and endogenous NGF overexpression effectively protected hepatocytes against TGF-β1- and oxidative stress-induced cell death in vitro, along with reduced formation of oxidative adducted proteins modified by 4-HNE and 8-OHdG. TUNEL staining confirmed the involvement of anti-apoptosis in the NGF-exhibited hepatoprotection. Moreover, NGF potently induced Akt phosphorylation and increased Bcl-2 to Bax ratios, whereas these molecular alterations by NGF were only seen in the H₂O₂-, but not TGF-β1-treated hepatocytes. In conclusion, NGF exhibits anti-oxidative and hepatoprotective effects and is suggested to be therapeutically applicable in treating cholestatic liver diseases.

The expression of genes involved in hepatocellular carcinoma chemoresistance is affected by mitochondrial genome depletion

Deletions and mutations in mitochondrial DNA (mtDNA), which are frequent in human tumors, such as hepatocellular carcinoma (HCC), may contribute to enhancing their malignant phenotype. Here we have investigated the effect of mtDNA depletion in the expression of genes accounting for mechanisms of chemoresistance (MOC) in HCC. Using human HCC SK-Hep-1 cells depleted of mtDNA (Rho), changes in gene expression in response to antitumor drugs previously assayed in HCC treatment were analyzed. In Rho cells, a decreased sensitivity to doxorubicin-, SN-38-, cisplatin (CDDP)-, and sorafenib-induced cell death was found. Both constitutive and drug-induced reactive oxygen species generation were decreased. Owing to activation of the NRF2-mediated pathway, MDR1, MRP1, and MRP2 expression was higher in Rho than in wild-type cells. This difference was maintained after further upregulation induced by treatment with doxorubicin, SN-38, or CDDP. Topoisomerase-IIa expression was also enhanced in Rho cells before and after treatment with these drugs. Moreover, the ability of doxorubicin, SN-38 and CDDP to induce proapoptotic signals was weaker in Rho cells, as evidenced by survivin upregulation and reductions in Bax/Bcl-2 expression ratios. Changes in these genes seem to play a minor role in the enhanced resistance of Rho cells to sorafenib, which may be related to an enhanced intracellular ATP content together with the loss of expression of the specific target of sorafenib, tyrosine kinase receptor Kit. In conclusion, these results suggest that mtDNA depletion may activate MOC able to hinder the efficacy of chemotherapy against HCC.

The role of mitochondrial DNA damage and repair in the resistance of BCR/ABL-expressing cells to tyrosine kinase inhibitors

Chronic myeloid leukemia (CML) is a hematological malignancy that arises from the transformation of stem hematopoietic cells by the fusion oncogene BCR/ABL and subsequent clonal expansion of BCR/ABL-positive progenitor leukemic cells. The BCR/ABL protein displays a constitutively increased tyrosine kinase activity that alters many regulatory pathways, leading to uncontrolled growth, impaired differentiation and increased resistance to apoptosis featured by leukemic cells. Current CML therapy is based on tyrosine kinase inhibitors (TKIs), primarily imatinib, which induce apoptosis in leukemic cells. However, some patients show primary resistance to TKIs while others develop it in the course of therapy. In both cases, resistance may be underlined by perturbations in apoptotic signaling in leukemic cells. As mitochondria may play an important role in such signaling, alteration in mitochondrial metabolism may change resistance to pro-apoptotic action of TKIs in BCR/ABL-positive cells. Because BCR/ABL may induce reactive oxygen species and unfaithful DNA repair, it may affect the stability of mitochondrial DNA, influencing mitochondrial apoptotic signaling and in this way change the sensitivity of CML cells to TKIs. Moreover, cancer cells, including BCR/ABL-positive cells, show an increased level of glucose metabolism, resulting from the shift from oxidative phosphorylation to glycolysis to supply ATP for extensive proliferation. Enhanced level of glycolysis may be associated with TKI resistance and requires change in the expression of several genes regulated mostly by hypoxia-inducible factor-1α, HIF-1α. Such regulation may be associated with the impaired mitochondrial respiratory system in CML cells. In summary, mitochondria and mitochondria-associated molecules and pathways may be attractive targets to overcome TKI resistance in CML.