Sirtuin 1 activation alleviates cholestatic liver injury in a cholic acid-fed mouse model of cholestasis

Irisin inhibits microglial senescence via TFAM-mediated mitochondrial metabolism in a mouse model of tauopathy

BACKGROUND

The accumulation of senescent microglia has been highlighted as a critical contributor to the progression of tauopathies. Irisin, a muscle-derived hormone produced by the proteolytic cleavage of Fibronectin-domain III containing 5 (FNDC5), mediates the pleiotropic effects of exercise on the physical body. Herein, we investigate the potential role of irisin in microglial senescence in tauopathies.

METHODS

To model tauopathies both in vivo and in vitro, we utilized P301S tau transgenic mice and tau K18 fibril-treated microglia BV2 cells, respectively. We first examined the expression of the irisin expression and senescence phenotypes of microglia in tauopathies. Subsequently, we investigated the impact of irisin on microglial senescence and its underlying molecular mechanisms.

RESULT

We observed a reduction in irisin levels and an onset of premature microglial senescence both in vivo and in vitro. Irisin administration was found to counteract microglial senescence and ameliorate cognitive decline in P301S mice. Mechanistically, irisin effectively inhibited microglial senescence by stimulating the expression of mitochondrial transcription factor A (TFAM), a master regulator of mitochondrial respiratory chain biogenesis, thereby enhancing mitochondrial oxidative phosphorylation (OXPHOS). Silencing TFAM eliminated the inhibitory effect of irisin on microglial senescence as well as the restorative effect of irisin on mitochondrial OXPHOS. Furthermore, the SIRT1/PGC1α signaling pathway appeared to be implicated in irisin-mediated upregulation of TFAM.

CONCLUSION

Taken together, our study revealed that irisin mitigated microglial senescence via TFAM-driven mitochondrial biogenesis, suggesting a promising new avenue for therapeutic strategies targeting tauopathies.

The role of sirtuin1 in liver injury: molecular mechanisms and novel therapeutic target

Liver disease is a common and serious threat to human health. The progression of liver diseases is influenced by many physiologic processes, including oxidative stress, inflammation, bile acid metabolism, and autophagy. Various factors lead to the dysfunction of these processes and basing on the different pathogeny, pathology, clinical manifestation, and pathogenesis, liver diseases are grouped into different categories. Specifically, Sirtuin1 (SIRT1), a member of the sirtuin protein family, has been extensively studied in the context of liver injury in recent years and are confirmed the significant role in liver disease. SIRT1 has been found to play a critical role in regulating key processes in liver injury. Further, SIRT1 seems to cause divers outcomes in different types of liver diseases. Recent studies have showed some therapeutic strategies involving modulating SIRT1, which may bring a novel therapeutic target. To elucidate the mechanisms underlying the role of sirtuin1 in liver injury and its potentiality as a therapeutic target, this review outlines the key signaling pathways associated with sirtuin1 and liver injury, and discusses recent advances in therapeutic strategies targeting sirtuin1 in liver diseases.

Ginsenoside Rg1 alleviates ANIT-induced cholestatic liver injury by inhibiting hepatic inflammation and oxidative stress via SIRT1 activation

ETHNOPHARMACOLOGICAL RELEVANCE

Ginseng (Panax ginseng C. A. Mey) is a common traditional Chinese medicine used for anti-inflammation, treating colitis, type 2 diabetes, diarrhea, and recovering hepatobiliary function. Ginsenosides, the main active components isolated from ginseng, possess liver and gallbladder diseases therapeutic potential.

AIMS OF THE STUDY

Cholestatic liver injury (CLI) is a liver disease induced by intrahepatic accumulation of toxic bile acids and currently lacks clinically effective drugs. Our previous study found that ginsenosides alleviated CLI by activating sirtuin 1 (SIRT1), but the effective ingredients and the underlying mechanism have not been clarified. This study aimed to identify an effective ingredient with the most significant activation effect on SIRT1 from the five major monomer saponins of ginsenosides: Rb1, Rd, Rg1, 20s-Rg3, and Rc further explore its protective effects on CLI, and elaborate its underlying mechanism.

MATERIALS AND METHODS

Discovery Studio 3.0 was used to conduct molecular docking between monomer saponins and SIRT1, and further detect the influence of monomer saponins on SIRT1 activity in vitro. Finally, it was determined that Rg1 had the most significant stimulative effect on SIRT1, and the hepatoprotective activity of Rg1 in CLI was explored in vivo. Wild-type mice were intragastrically α-naphthylisothiocyanate (ANIT) to establish an experimental model of intrahepatic cholestasis and Rg1 intervention, and then liver injury and cholestasis related indexes were detected. In addition, Liver-specific SIRT1 gene knockout (SIRT1-/-) mice were administered with ANIT and/or Rg1 to further investigate the mechanism of action of Rg1.

RESULTS

The results of molecular docking and in vitro experiments showed that all the five ginsenoside monomers could bind to the active site of SIRT1 and promote SIRT1 activity in HepG2 cells. Among them, Rg1 exhibited the most significant stimulation of SIRT1 activity in cholestasis. Besides, it could ameliorate ANIT-induced inflammation and oxidative stress in HepG2 cells. Therefore, we investigated the hepatoprotective effect and mechanism of Rg1 on CLI. Results showed that Rg1 reversed the ANIT-induced increase in biochemical parameters, improved liver pathological injury, and decreased liver lipid accumulation, reactive oxygen species and pro-inflammatory factor levels. Mechanistically, Rg1 induced SIRT1 expression, followed by promoted the activity of Nrf2 and suppressed the activation of NF-κB. Interestingly, the hepatoprotective effect of Rg1 was blocked in SIRT1-/- mice.

CONCLUSION

Rg1 mitigated ANIT-induced CLI via upregulating SIRT1 expression, and our results suggested that Rg1 is a candidate compound for treating CLI.

Papaverine attenuates the progression of alpha naphthylisothiocyanate induce cholestasis in rats

Cholestasis is a hepatobiliary condition that manifests as acute or chronic and results from disruptions in the bile flow, formation, or secretion processes. The Farnesoid X receptor (FXR) is a vital target for the therapy of cholestasis since it regulates BA homeostasis. Despite the discovery of multiple active FXR agonists, there are still no effective treatments for cholestasis. Papaverine is identified as an FXR agonist.This study investigates papaverine's efficacy and probable mechanism in protecting against alpha naphthylisothiocyanate (ANIT) induced cholestasis. Thirty male albino rats were divided into three groups, each with ten rats. Group I (control) rats were administered 1 mL/kg corn oil 48 h before sacrifice; group II rats were orally administered 100 mg/kg ANIT. Group III received a 200 mg/kg dosage of papaverine over seven consecutive days. A single dose of ANIT at a concentration of 100 mg/kg was orally administered on the fifth day; group II and III animals were euthanized 48 h after inducing cholestasis, and serum concentrations of liver function tests and total bile acid (TBA) were measured. Besides measuring the inflammatory mediator's tumor necrosis factor-alpha (TNF-α) and interleukin 1 (IL-1β), antioxidant markers such as superoxide dismutase (SOD) and glutathione (GSH) were also assessed. The findings indicated the enhancement in the liver function test and total bile acids, as well as in liver histology; papaverine significantly lowered TNF-α and IL-1β while SOD and GSH significantly increased. Additionally, papaverine upregulates Fxr gene expression, bile salt export pump (Besp), small heterodimer partner (shp), hepatocyte nuclear factor 1α (Hnfα), nuclear factor erythroid 2-related factor (Nrf2), heme oxygenase (Ho-1), NAD(P)H quinone oxidoreductase 1 (Nqo1). Furthermore, papaverine increased protein expressions of Sirtuin1. (SIRT 1), FXR, HO-1, and BSEP levels in the rats' livers. The protective effects of papaverine may be attributed to the activation of FXR signaling pathways. These findings revealed that papaverine protects against ANIT-induced Cholestasis.

Bile Acid Application in Cell-Targeting for Molecular Receptors in Relation to Hearing: A Comprehensive Review

Bile acids play important roles in the human body, and changes in their pool can be used as markers for various liver pathologies. In addition to their functional effects in modulating inflammatory responses and cellular survivability, the unconjugated or conjugated, secondary, or primary nature of bile acids accounts for their various ligand effects. The common hydrophilic bile acids have been used successfully as local treatment to resolve drug-induced cell damage or to ameliorate hearing loss. From various literature references, bile acids show concentration and tissue-dependent effects. Some hydrophobic bile acids act as ligands modulating vitamin D receptors, muscarinic receptors, and calcium-activated potassium channels, important proteins in the inner ear system. Currently, there are limited resources investigating the therapeutic effects of bile acid on hearing loss and little to no information on detecting bile acids in the remote ear system, let alone baseline bile acid levels and their prevalence in healthy and disease conditions. This review presents both hydrophilic and hydrophobic human bile acids and their tissue-specific effects in modulating cellular integrity, thus considering the possible effects and extended therapeutic applicability of bile acids to the inner ear tissue.

Engineered FGF19ΔKLB protects against intrahepatic cholestatic liver injury in ANIT-induced and Mdr2-/- mice model

BACKGROUND

The major safety concern of the clinical application of wild type FGF19 (FGF19WT) emerges given that its extended treatment causes hepatocellular carcinoma. Therefore, we previously generated a safer FGF19 variant - FGF19ΔKLB, which have same effects on glycemic control and bile acid production but much less mitogenic activity. However, it remains unclear as to whether FGF19ΔKLB ameliorates intrahepatic cholestasis.

RESULTS

We found that, similar to that of FGF19WT, the chronic administration of FGF19ΔKLB protects mice from cholestatic liver injury in these two models. The therapeutic benefits of FGF19ΔKLB on cholestatic liver damage are attributable, according to the following mechanistic investigation, to the reduction of BA production, liver inflammation, and fibrosis. More importantly, FGF19ΔKLB did not induce any tumorigenesis effects during its prolonged treatment.

CONCLUSIONS

Together, our findings raise hope that FGF19ΔKLB may represent a useful therapeutic strategy for the treatment of intrahepatic cholestasis.

Kupffer cell pyroptosis mediated by METTL3 contributes to the progression of alcoholic steatohepatitis

Chronic alcohol consumption is a major risk factor for alcoholic steatohepatitis (ASH). Previous studies have shown that direct injury of hepatocytes is the key factor in its occurrence and development. However, our study shows that the role of Kupffer cells in ASH cannot be ignored. We isolated Kupffer cells from the livers of ASH mice and found that alcohol consumption induced Kupffer cell pyroptosis and increased the release of interleukin-1β (IL-1β). Furthermore, we screened the related m6A enzyme methyltransferase-like 3 (METTL3) from liver Kupffer cells, and found that silencing METTL3 alleviated inflammatory cytokine eruption by Kupffer cell pyroptosis in ASH mice. In vitro, we silenced METTL3 with lentivirus in BMDMs and RAW264.7 cells and confirmed that METTL3 could reduce pyroptosis by influencing the splicing of pri-miR-34A. Together, our results revealed a critical role of KC pyroptosis in ASH and highlighted the mechanism by which METLL3 relieves cell pyroptosis, which could be a promising therapeutic strategy for ASH.

Yinchen decoction protects against cholic acid diet-induced cholestatic liver injury in mice through liver and ileal FXR signaling

ETHNOPHARMACOLOGICAL RELEVANCE

Cholestasis is a pathophysiological syndrome characterized by the accumulation of bile acids (BAs) that leads to severe liver disease. Artemisia capillaris is documented in Chinese Pharmacopoeia as the authentic resources for Yinchen. Although Yinchen (Artemisia capillaris Thunb.) decoction (YCD) has been used in China for thousands of years to treat jaundice, the underlying mechanisms to ameliorate cholestatic liver injury have not been elucidated.

AIM OF THE STUDY

To investigate the molecular mechanism of how YCD protects against 1% cholic acid (CA) diet-induced intrahepatic cholestasis through FXR signaling.

MATERIALS AND METHODS

Wild-type and Fxr-deficient mice were fed a diet containing 1% CA to establish the intrahepatic cholestasis model. The mice received low-, medium-, or high-dose YCD for 10 days. Plasma biochemical markers were analyzed, liver injury was identified by histopathology, and hepatic and plasma BA content was analyzed. Western blot was used to determine the expression levels of transporters and enzymes involved in BA homeostasis in the liver and intestine.

RESULTS

In wild-type mice, YCD significantly improved plasma transaminase levels, multifocal hepatocellular necrosis, and hepatic and plasma BA contents, upregulated the expression of hepatic FXR and downstream target enzymes and transporters. Meanwhile, YCD significantly induced the expressions of intestinal FXR and FGF15 and hepatic FGFR4. In contrast, the hepatic protective effect of YCD on cholestasis was abolished in Fxr-deficient mice.

CONCLUSION

YCD protects against cholestatic liver injury induced by a CA diet by restoring the homeostasis of BAs via activation of the liver FXR/SHP and ileal FXR/FGF15 signaling pathways. Furthermore, chlorogenic acid and caffeic acid may be the pharmacological agents in YCD responsible for protecting against cholestatic liver injury.

Insulin dysregulation drives mitochondrial cholesterol metabolite accumulation: Initiating hepatic toxicity in NAFLD

CYP7B1 catalyzes mitochondria-derived cholesterol metabolites such as (25R)26-hydroxycholesterol (26HC) and 3β-hydroxy-5-cholesten-(25R)26-oic acid (3βHCA) and facilitates their conversion to bile acids. Disruption of 26HC/3βHCA metabolism in the absence of CYP7B1 leads to neonatal liver failure. Disrupted 26HC/3βHCA metabolism with reduced hepatic CYP7B1 expression is also found in nonalcoholic steatohepatitis (NASH). The current study aimed to understand the regulatory mechanism of mitochondrial cholesterol metabolites and their contribution to onset of NASH. We used Cyp7b1^-/- mice fed a normal diet (ND), Western diet (WD), or high-cholesterol diet (HCD). Serum and liver cholesterol metabolites as well as hepatic gene expressions were comprehensively analyzed. Interestingly, 26HC/3βHCA levels were maintained at basal levels in ND-fed Cyp7b1^-/- mice livers by the reduced cholesterol transport to mitochondria, and the upregulated glucuronidation and sulfation. However, WD-fed Cyp7b1^-/- mice developed insulin resistance (IR) with subsequent 26HC/3βHCA accumulation due to overwhelmed glucuronidation/sulfation with facilitated mitochondrial cholesterol transport. Meanwhile, Cyp7b1^-/- mice fed an HCD did not develop IR or subsequent evidence of liver toxicity. HCD-fed mice livers revealed marked cholesterol accumulation but no 26HC/3βHCA accumulation. The results suggest 26HC/3βHCA-induced cytotoxicity occurs when increased cholesterol transport into mitochondria is coupled to decreased 26HC/3βHCA metabolism driven with IR. Supportive evidence for cholesterol metabolite-driven hepatotoxicity is provided in a diet-induced nonalcoholic fatty liver mouse model and by human specimen analyses. This study uncovers an insulin-mediated regulatory pathway that drives the formation and accumulation of toxic cholesterol metabolites within the hepatocyte mitochondria, mechanistically connecting IR to cholesterol metabolite-induced hepatocyte toxicity which drives nonalcoholic fatty liver disease.

SIRT1 activation synergizes with FXR agonism in hepatoprotection via governing nucleocytoplasmic shuttling and degradation of FXR

Farnesoid X receptor (FXR) is widely accepted as a promising target for various liver diseases; however, panels of ligands in drug development show limited clinical benefits, without a clear mechanism. Here, we reveal that acetylation initiates and orchestrates FXR nucleocytoplasmic shuttling and then enhances degradation by the cytosolic E3 ligase CHIP under conditions of liver injury, which represents the major culprit that limits the clinical benefits of FXR agonists against liver diseases. Upon inflammatory and apoptotic stimulation, enhanced FXR acetylation at K217, closed to the nuclear location signal, blocks its recognition by importin KPNA3, thereby preventing its nuclear import. Concomitantly, reduced phosphorylation at T442 within the nuclear export signals promotes its recognition by exportin CRM1, and thereby facilitating FXR export to the cytosol. Acetylation governs nucleocytoplasmic shuttling of FXR, resulting in enhanced cytosolic retention of FXR that is amenable to degradation by CHIP. SIRT1 activators reduce FXR acetylation and prevent its cytosolic degradation. More importantly, SIRT1 activators synergize with FXR agonists in combating acute and chronic liver injuries. In conclusion, these findings innovate a promising strategy to develop therapeutics against liver diseases by combining SIRT1 activators and FXR agonists.

A High Cholesterol Diet During Late Pregnancy Impairs Long-Term Maternal Vascular Function in Mice

BACKGROUND

Gestational dyslipidemia is associated with pregnancy complications including preeclampsia. However, whether gestational dyslipidemia leads postpartum vascular dysfunction, which could increase the risk for cardiovascular complications later in life, is not known. Here, we aimed to determine whether a gestational dyslipidemia affects postpartum vascular health and induces early signs of atherosclerosis.

METHODS

Pregnant C57BL/6 mice received a high cholesterol diet or control diet from gestational day 13.5 until term. After delivery, all mice received the control diet for ≈3 months postpartum (PP). Age-matched nulliparous females were on the same diets for equal periods. After 3 months, all mice were euthanized, serum was collected, and aortas were isolated to assess vascular function (wire myography) and markers of oxidative stress and early atherosclerosis.

RESULTS

PP-high cholesterol diet females had increased circulating cholesterol levels compared with PP-control diet mice, without effect of the diet in nulliparous mice. Methacholine-induced vasodilation was impaired, and nitric oxide contribution reduced, by the high cholesterol diet in aortas of PP mice, but not in nulliparous mice. Exposure to oxidized low-density-protein cholesterol further impaired methylcholine-induced vasodilation in PP-high cholesterol diet aortas only. Compared with PP-control diet mice, aortic inducible nitric oxide synthase expression, reactive oxygen species and nitrotyrosine levels were increased in aortas from PP-high cholesterol diet mice. No differences in aortic lipid deposition and macrophage infiltration were found.

CONCLUSIONS

Exposure to a high cholesterol diet in pregnancy impairs vascular function postpartum. Our results support the hypothesis that gestational dyslipidemia impacts maternal vascular function after pregnancy, which could potentially predispose these women to future cardiovascular complications.

Role of Hepatocyte Transporters in Drug-Induced Liver Injury (DILI)-In Vitro Testing

Bile acids and bile salts (BA/BS) are substrates of both influx and efflux transporters on hepatocytes. Canalicular efflux transporters, such as BSEP and MRP2, are crucial for the removal of BA/BS to the bile. Basolateral influx transporters, such as NTCP, OATP1B1/1B3, and OSTα/β, cooperate with canalicular transporters in the transcellular vectorial flux of BA/BS from the sinusoids to the bile. The blockage of canalicular transporters not only impairs the bile flow but also causes the intracellular accumulation of BA/BS in hepatocytes that contributes to, or even triggers, liver injury. In the case of BA/BS overload, the efflux of these toxic substances back to the blood via MRP3, MRP4, and OST α/β is considered a relief function. FXR, a key regulator of defense against BA/BS toxicity suppresses de novo bile acid synthesis and bile acid uptake, and promotes bile acid removal via increased efflux. In drug development, the early testing of the inhibition of these transporters, BSEP in particular, is important to flag compounds that could potentially inflict drug-induced liver injury (DILI). In vitro test systems for efflux transporters employ membrane vesicles, whereas those for influx transporters employ whole cells. Additional in vitro pharmaceutical testing panels usually include cellular toxicity tests using hepatocytes, as well as assessments of the mitochondrial toxicity and accumulation of reactive oxygen species (ROS). Primary hepatocytes are the cells of choice for toxicity testing, with HepaRG cells emerging as an alternative. Inhibition of the FXR function is also included in some testing panels. The molecular weight and hydrophobicity of the drug, as well as the steady-state total plasma levels, may positively correlate with the DILI potential. Depending on the phase of drug development, the physicochemical properties, dosing, and cut-off values of BSEP IC₅₀ ≤ 25-50 µM or total C_ss,plasma/BSEP IC₅₀ ≥ 0.1 may be an indication for further testing to minimize the risk of DILI liability.

Farnesoid-X receptor as a therapeutic target for inflammatory bowel disease and colorectal cancer

Farnesoid-X receptor (FXR), as a nuclear receptor activated by bile acids, is a vital molecule involved in bile acid metabolism. Due to its expression in immune cells, FXR has a significant effect on the function of immune cells and the release of chemokines when immune cells sense changes in bile acids. In addition to its regulation by ligands, FXR is also controlled by post-translational modification (PTM) activities such as acetylation, SUMOylation, and methylation. Due to the high expression of FXR in the liver and intestine, it significantly influences intestinal homeostasis under the action of enterohepatic circulation. Thus, FXR protects the intestinal barrier, resists bacterial infection, reduces oxidative stress, inhibits inflammatory reactions, and also acts as a tumor suppressor to impair the multiplication and invasion of tumor cells. These potentials provide new perspectives on the treatment of intestinal conditions, including inflammatory bowel disease (IBD) and its associated colorectal cancer (CRC). Moreover, FXR agonists on the market have certain organizational heterogeneity and may be used in combination with other drugs to achieve a greater therapeutic effect. This review summarizes current data on the role of FXR in bile acid metabolism, regulation of immune cells, and effects of the PTM of FXR. The functions of FXR in intestinal homeostasis and potential application in the treatment of IBD and CRC are discussed.

Role and Regulation of Hepatobiliary ATP-Binding Cassette Transporters during Chemical-Induced Liver Injury

Severity of drug-induced liver injury (DILI) ranges from mild, asymptomatic, and transient elevations in liver function tests to irreversible liver damage, often needing transplantation. Traditionally, DILI is classified mechanistically as high-frequency intrinsic DILI, commonly dose dependent or DILI that rarely occurs and is idiosyncratic in nature. This latter form is not dose dependent and has a pattern of histopathological manifestation that is not always uniform. Currently, a third type of DILI called indirect hepatotoxicity has been described that is associated with the pharmacological action of the drug. Historically, DILI was primarily linked to drug metabolism events; however, the impact of transporter-mediated rates of drug uptake and excretion has gained greater prominence in DILI research. This review provides a comprehensive view of the major findings from studies examining the contribution of hepatic ATP-binding cassette transporters as key contributors to DILI and how changes in their expression and function influence the development, severity, and overall toxicity outcome. SIGNIFICANCE STATEMENT: Drug-induced liver injury (DILI) continues to be a focal point in drug development research. ATP-binding cassette (ABC) transporters have emerged as important determinants of drug detoxification, disposition, and safety. This review article provides a comprehensive analysis of the literature addressing: (a) the role of hepatic ABC transporters in DILI, (b) the influence of genetic mutations in ABC transporters on DILI, and (c) new areas of research emphasis, such as the influence of the gut microbiota and epigenetic regulation, on ABC transporters.

Bile acid metabolism and signaling, the microbiota, and metabolic disease

The diversity, composition, and function of the bacterial community inhabiting the human gastrointestinal tract contributes to host health through its role in producing energy or signaling molecules that regulate metabolic and immunologic functions. Bile acids are potent metabolic and immune signaling molecules synthesized from cholesterol in the liver and then transported to the intestine where they can undergo metabolism by gut bacteria. The combination of host- and microbiota-derived enzymatic activities contribute to the composition of the bile acid pool and thus there can be great diversity in bile acid composition that depends in part on the differences in the gut bacteria species. Bile acids can profoundly impact host metabolic and immunological functions by activating different bile acid receptors to regulate signaling pathways that control a broad range of complex symbiotic metabolic networks, including glucose, lipid, steroid and xenobiotic metabolism, and modulation of energy homeostasis. Disruption of bile acid signaling due to perturbation of the gut microbiota or dysregulation of the gut microbiota-host interaction is associated with the pathogenesis and progression of metabolic disorders. The metabolic and immunological roles of bile acids in human health have led to novel therapeutic approaches to manipulate the bile acid pool size, composition, and function by targeting one or multiple components of the microbiota-bile acid-bile acid receptor axis.

Gene Therapy for Acquired and Genetic Cholestasis

Cholestatic diseases can be caused by the dysfunction of transporters involved in hepatobiliary circulation. Although pharmacological treatments constitute the current standard of care for these diseases, none are curative, with liver transplantation being the only long-term solution for severe cholestasis, albeit with many disadvantages. Liver-directed gene therapy has shown promising results in clinical trials for genetic diseases, and it could constitute a potential new therapeutic approach for cholestatic diseases. Many preclinical gene therapy studies have shown positive results in animal models of both acquired and genetic cholestasis. The delivery of genes that reduce apoptosis or fibrosis or improve bile flow has shown therapeutic effects in rodents in which cholestasis was induced by drugs or bile duct ligation. Most studies targeting inherited cholestasis, such as progressive familial intrahepatic cholestasis (PFIC), have focused on supplementing a correct version of a mutated gene to the liver using viral or non-viral vectors in order to achieve expression of the therapeutic protein. These strategies have generated promising results in treating PFIC3 in mouse models of the disease. However, important challenges remain in translating this therapy to the clinic, as well as in developing gene therapy strategies for other types of acquired and genetic cholestasis.

Angelica keiskei Root Extract Attenuates Bile Duct Ligation-Induced Liver Injury in Mice

Although multiple studies have shown that Angelica keiskei of the Umbelliferae family has potent anti-inflammatory and antioxidative activities and that it reduces the serum bile acids in humans, whether A. keiskei has protective effects against cholestasis-induced liver injury remains unexplored until now. This study tests the hypothesis that Angelica keiskei root extract (AKE) alleviates liver injury, inflammation, and fibrosis in mouse models of acute cholestasis induced by bile duct ligation (BDL). Oral administration of AKE (200 or 500 mg/kg) attenuated hepatocellular necrosis and significantly reduced serum levels of bile acids and bilirubin in BDL mice. The critical enzyme of bile acid synthesis, CYP7A1, was repressed by AKE, suggesting that reduced bile acid production may contribute to liver protection. Moreover, we determined through gene expression and cytokine analysis and histological examination that AKE treatment decreased liver inflammation, oxidative stress, and fibrosis. AKE also suppressed the NF-κB pathway, suggesting this as a possible mediator of its anti-inflammatory effect. Our findings substantiate that AKE may be promising for treating cholestatic liver diseases in the future.

Pterostilbene Alleviates Cholestasis by Promoting SIRT1 Activity in Hepatocytes and Macrophages

Background and purpose: FXR is a promising target for the treatment of human cholestatic liver disease (CLD). SIRT1 is a deacetylase which promotes FXR activity through deacetylating FXR. Pterostilbene (PTE) is an activator of SIRT1. However, the role of PTE in cholestasis has so far not been investigated. We examined whether PTE treatment alleviate liver injury in DDC or ANIT-induced experimental cholestasis, and explored the underlying mechanisms. Experimental approach: Mice with DDC- or ANIT-induced cholestasis were treated with different dose of PTE. Primary hepatocytes and bone marrow derived macrophages were used in vitro to assess the molecular mechanism by which PTE may improve CLD. Identical doses of UDCA or PTE were administered to DDC- or ANIT-induced cholestasis mice. Key results: PTE intervention attenuated DDC or ANIT-induced cholestasis. PTE inhibited macrophage infiltration and activation in mouse liver through the SIRT1-p53 signaling pathway, and it improved hepatic bile metabolism through the SIRT1-FXR signaling pathway. Compare with UDCA, the same doses of PTE was more effective in improving cholestatic liver injury caused by DDC or ANIT. Conclusion and implications: SIRT1 activation in macrophages may be an effective CLD treatment avenue. Using CLD models, we thus identified PTE as a novel clinical candidate compound for the treatment of CLD.

Targeted Metabolomics Analysis of Bile Acids in Patients with Idiosyncratic Drug-Induced Liver Injury

Drug-induced liver injury (DILI) is rare but clinically important due to a high rate of mortality. However, specific biomarkers for diagnosing and predicting the severity and prognosis of DILI are lacking. Here, we used targeted metabolomics to identify and quantify specific types of bile acids that can predict the severity of DILI. A total of 161 DILI patients were enrolled in this prospective cohort study, as well as 31 health controls. A targeted metabolomics method was used to identify 24 types of bile acids. DILI patients were divided into mild, moderate, and severe groups according to disease severity. A multivariate analysis was performed to identify characteristic bile acids. Then the patients were divided into severe and non-severe groups, and logistic regression was used to identify bile acids that could predict DILI severity. Among the enrolled DILI patients, 32 were in the mild group, 90 were in the moderate group, and 39 were in the severe group. Orthogonal partial least squares-discriminant analysis (OPLS-DA) modeling clearly discriminated among the different groups. Among the four groups, glycochenodeoxycholate (GCDCA), taurochenodeoxycholate (TCDCA), deoxycholic acid (DCA), Nor Cholic acid (NorCA), glycocholic acid (GCA), and taurocholic acid (TCA) showed significant differences in concentration between at least two groups. NorCA, GCDCA, and TCDCA were all independent risk factors that differentiated severe DILI patients from the other groups. The area under the receiver operating characteristic curve (AUROC) of GCDCA, TCDCA, and NorCA was 0.856, 0.792, and 0.753, respectively. Together, these three bile acids had an AUROC of 0.895 for predicting severe DILI patients. DILI patients with different disease severities have specific bile acid metabolomics. NorCA, GCDTA, and TCDCA were independent risk factors for differentiating severe DILI patients from less-severe patients and have the potential to predict DILI severity.

Paeoniflorin Protects against ANIT-Induced Cholestatic Liver Injury in Rats via the Activation of SIRT1-FXR Signaling Pathway

Paeoniflorin (PF), a water-soluble monoterpene glycoside, is initially isolated from the dried roots of Paeonia lactiflora Pall., which has effects on ameliorating cholestasis in our previous study. However, comprehensive approaches for understanding the protective effects and mechanisms underlying cholestatic liver injury from the regulating of bile acid metabolism have not been sufficiently elucidated. This study was aimed to explore the effectiveness as well as potential mechanism of PF on alpha-naphthylisothiocyanate (ANIT)-induced cholestatic liver injury. Rats with cholestasis induced by ANIT was used to evaluate the protective effects and mechanism of PF by regulating SIRT1/FXR and NF-κB/NLRP3 signaling pathway. Rats were intragastrically administrated with ANIT to establish cholestatic liver injury model. Serum levels of ALT, AST, TBA, TBIL, ALP, γ-GT and ALB in rats were detected. The histopathology of the liver of rats was analyzed in vivo. The relative mRNA expression and protein expression levels of IL-18, IL-1β, TNF-α, HO-1, Nrf2, TLR4, NLRP3, Caspase-1, ASC, NF-κB, FXR, and SIRT1 in liver of rats were investigated. The results showed that the serum indexes and the liver histopathology were significantly improved by PF. The overexpression of IL-18, IL-1β, TNF-α, NLRP3, ASC, and Caspase-1 in liver was markedly reduced by PF. Furthermore, PF dramatically increased the mRNA and protein expressions of SIRT1, FXR, HO-1, and Nrf2, but decreased NF-κB p65 and TLR4 levels in liver of rats. Taken together, the protective effects of PF on cholestatic liver injury were possibly related to the activation of the SIRT1/FXR and inhibition of NF-κB/NLRP3 inflammasome signaling pathway. These findings might provide a potential protection for cholestatic liver injury.

Advances in the role of silence information regulator family in pathological pregnancy

Aberrant maternal inflammation and oxidative stress are the two main mechanisms of pathological pregnancy. The silence information regulator (sirtuin) family is a highly conserved family of nicotinamide adenine dinucleotide (NAD)-dependent deacylases. By regulating the post-translational modification of proteins, sirtuin is involved in various biological processes including oxidative stress and inflammation. Nowadays, emerging evidence indicates that sirtuin may be closely related to the occurrence and development of pathological pregnancy. The down-regulation of sirtuin can cause spontaneous preterm delivery by promoting uterine contraction and rupture of fetal membranes, cause gestational diabetes mellitus through promoting oxidative stress and affecting the activity of key enzymes in glucose metabolism, cause preeclampsia by reducing the proliferation and invasion ability of trophoblasts, cause intrahepatic cholestasis of pregnancy by promoting the production of bile acids and T helper 1 cell (Th1) cytokines, and cause intrauterine growth restriction through inducing mitochondrial dysfunction. Moreover, the expression and activation of sirtuin can be modulated through dietary interventions, thus sirtuin is expected to become a new target for the prevention and treatment of pregnancy complications. This article reviews the role of the sirtuin family in the occurrence and development of pathological pregnancy and its influence on the development of the offspring.

Bidirectional Role of NLRP3 During Acute and Chronic Cholestatic Liver Injury

BACKGROUND AND AIMS

Cholestatic liver injury leads to cell death and subsequent inflammation and fibrosis. As shown for primary biliary cholangitis (PBC), the mechanisms and circuits between different cell death pathways leading to disease progression are incompletely defined. Common bile duct ligation (BDL) is a well-established murine model to mimic cholestatic liver injury. Here, we hypothesized that pyroptotic cell death by the Nucleotide-Binding Domain, Leucine-Rich-Containing Family, Pyrin Domain-Containing-3 (Nlrp3) inflammasome plays an essential role during human and murine cholestasis.

APPROACH AND RESULTS

NLRP3 activation was analyzed in humans with cholestatic liver injury. Wild-type (WT) and Nlrp3^-/- mice were subjected to BDL for 2 or 28 days. Chronic cholestasis in humans and mice is associated with NLRP3 activation and correlates with disease activity. Acute BDL in Nlrp3-deficient mice triggered increased inflammation as well as liver injury, associated with stronger apoptotic and necroptotic cell death. In contrast, NLRP3 deletion led to decreased liver injury and inflammation in chronic cholestasis. Moreover, bridging fibrosis was observed in WT, but not in NLRP3 knockout, mice 28 days after BDL. In contrast, lack of NLRP3 expression attenuated kidney injury and fibrosis after acute and chronic BDL. Importantly, administration of MCC950, an NLRP3 small molecule inhibitor, reduced BDL-induced disease progression in WT mice.

CONCLUSIONS

NLRP3 activation correlates with disease activity in patients with PBC. NLRP3 has a differential role during acute and chronic cholestatic liver injury in contrast to kidney injury. Disease progression during chronic cholestasis can be targeted through small molecules and thus suggests a potential clinical benefit for humans, attenuating liver and kidney injury.

The protective role of hydrophilic tetrahydroxylated bile acids (THBA)

Bile acids are key components of bile required for human health. In humans and mice, conditions of reduced bile flow, cholestasis, induce bile acid detoxification by producing tetrahydroxylated bile acids (THBA), more hydrophilic and less cytotoxic than the usual bile acids, which are typically di- or tri-hydroxylated. Mice deficient in the Bile Salt Export Pump (Bsep, or Abcb11), the primary bile acid transporter in liver cells, produce high levels of THBA, and avoid the severe liver damage typically seen in humans with BSEP deficiencies. THBA can suppress bile acid-induced liver damage in Mdr2-deficient mice, caused by their lack of phospholipids in bile exposing their biliary tracts to unbound bile acids. Here we review THBA-related works in both animals and humans, and discuss their potential relevance and applications as a class of functional bile acids.

TUDCA Ameliorates Liver Injury Via Activation of SIRT1-FXR Signaling in a Rat Hemorrhagic Shock Model

OBJECTIVE

The aim of this study was to investigate the changes of bile acids in the liver during hemorrhagic shock (HS) and their potential to attenuate liver injury via activation of SIRT1 (sirtuin 1)-FXR (farnesoid X receptor) signaling.

METHODS

A Sprague-Dawley (SD) rat HS model was established, whereas HepG2 cells were hypoxically cultured to simulate HS in vitro. Liver bile acids (BA) were profiled with ultraperformance liquid chromatography-tandem mass spectrometry (UPLC-MS/MS). FXR expression was detected by western blot and immunohistochemistry. The mRNA levels of SIRT1 and FXR were detected by polymerase chain reaction. Protein expression of SIRT1, FoxM1, NF-κB, acetyl-NF-κB, p53, and acetyl-p53 was analyzed by western blot. Hepatocyte apoptosis and proliferation were measured by TUNEL assay and Ki-67 staining, respectively. Serum and supernatant cytokines were analyzed using ELISA assays. Liver injury was also assessed. To investigate the possible mechanisms, SIRT1 agonist (SRT1720), SIRT1 inhibitor (EX527), and FXR inhibitor (Z-guggulsterone) were used.

RESULTS

Tauroursodeoxycholic acid (TUDCA) in the liver decreased significantly after HS. SIRT1 and FXR expression was time-dependently downregulated by HS or hypoxia condition. TUDCA upregulated SIRT1-FXR activity, which inhibited expression and acetylation of NF-κB and p53 and increased FoxM1 expression, leading to decreased inflammatory response and apoptosis and increased proliferative capacity in hepatocytes, and attenuation of liver injury. EX527 pretreatment reversed the protective effect of TUDCA. Moreover, Z-guggulsterone supplementation decreased the protective effect of TUDCA in vitro.

CONCLUSION

TUDCA in the liver decreased during HS. TUDCA supplementation might attenuate HS-induced liver injury by upregulating SIRT1-FXR signaling.

Activation of the AMPK-SIRT1 pathway contributes to protective effects of Salvianolic acid A against lipotoxicity in hepatocytes and NAFLD in mice

Background: Salvianolic acid A (Sal A), a natural polyphenol compound extracted from Radix Salvia miltiorrhiza (known as Danshen in China), possesses a variety of potential pharmacological activities. The aim of this study is to determine mechanisms of hepatoprotective effects of Sal A against lipotoxicity both in cultured hepatocytes and in a mouse model of fatty liver disease. Methods: High-fat and high-carbohydrate diet (HFCD)-fed C57BL/6J mice were employed to establish hepatic lipotoxicity in a mouse model. Two doses of Sal A were administered every other day via intraperitoneal injection (20 and 40 mg/kg BW, respectively). After a 10-week intervention, liver injury was detected by immunohistochemical and biochemical analyses. For in vitro studies, we used HepG2, a human hepatoma cell line, and exposed them to palmitic acid to induce lipotoxicity. The protective effects of Sal A on palmitic acid-induced lipotoxicity were examined in Sal A-pretreated HepG2 cells. Results: Sal A treatments attenuated body weight gain, liver injury, and hepatic steatosis in mice exposed to HFCD. Sal A pretreatments ameliorated palmitic acid-induced cell death but did not reverse effects of HFCD- or palmitate-induced activations of JNK, ERK1/2, and PKA. Induction of p38 phosphorylation was significantly reversed by Sal A in HFCD-fed mice but not in palmitate-treated HepG2 cells. However, Sal A rescued hepatic AMP-activated protein kinase (AMPK) suppression and sirtuin 1 (SIRT1) downregulation by both HFCD feeding in mice and exposure to palmitate in HepG2 cells. Sal A dose-dependently up-regulated p-AMPK and SIRT1 protein levels. Importantly, siRNA silencing of either AMPK or SIRT1 gene expression abolished the protective effects of Sal A on lipotoxicity. Moreover, while AMPK silencing blocked Sal A-induced SIRT1, silencing of SIRT1 had no effect on Sal A-triggered AMPK activation, suggesting SIRT1 upregulation by Sal A is mediated by AMPK activation. Conclusion: Our data uncover a novel mechanism for hepatoprotective effects of Sal A against lipotoxicity both in livers from HFCD-fed mice and palmitic acid-treated hepatocytes.

SIRT2 modulates VEGFD-associated lymphangiogenesis by deacetylating EPAS1 in human head and neck cancer

Sirtuin 2 (SIRT2) is one of seven mammalian homologs of silent information regulator 2 (Sir2) and an NAD⁺ -dependent deacetylase; however, its critical role in lymphangiogenesis remains to be explored. We investigate SIRT2 mediated regulation of vascular endothelial growth factor D (VEGFD) expression and lymphangiogenesis by deacetylating endothelial PAS domain protein 1 (EPAS1) in head and neck cancer (HNC) in vitro and in vivo. In this study, we report that SIRT2, rather than other members of the Sir2 family, reduces the expression of VEGFD and lymphangiogenesis in hypoxia-induced HNC cells and transplanted HNC mice models by reducing EPAS1 acetylation at Lys674 and decreasing the transcriptional activity of EPAS1 target genes. The expression of SIRT2 was closely related to the expression of VEGFD, lymphangiogenesis in subcutaneously transplanted mice models, and lymphangiogenesis in patients with HNC. Our results suggest that SIRT2 plays a central role in tumor lymphangiogenesis via deacetylating EPAS1 protein. Reagents targeting the NAD⁺ -dependent deacetylase activity of SIRT2 would be beneficial for inhibiting tumor lymphangiogenesis and treating other hypoxia-related diseases.

ERRγ suppression by Sirt6 alleviates cholestatic liver injury and fibrosis

Orphan nuclear receptor estrogen-related receptor γ (ERRγ) stimulates bile acid production; however, the role and the regulatory mechanism of ERRγ in cholestatic liver disease are largely unknown. This study identifies that Sirt6 is a deacetylase of ERRγ and suggests a potentially novel mechanism by which Sirt6 activation alleviates cholestatic liver damage and fibrosis through regulating ERRγ. We observed that hepatic expression of Sirt6 is repressed, whereas hepatic expression of ERRγ is upregulated in murine cholestasis models. Hepatocyte-specific Sirt6-KO mice were more severely injured after a bile duct ligation (BDL) than WT mice, and adenoviral reexpression of Sirt6 reversed liver damage and fibrosis as demonstrated by biochemical and histological analyses. Mechanistically, Sirt6 deacetylated ERRγ, thereby destabilizing ERRγ and inhibiting its transcriptional activity. Elimination of hepatic ERRγ using Ad-shERRγ abolished the deleterious effects of Sirt6 deficiency, whereas ERRγ overexpression aggravated cholestatic liver injury. Administration of a Sirt6 deacetylase activator prevented BDL-induced liver damage and fibrosis. In patients with cholestasis, Sirt6 expression was decreased, whereas total ERRγ and acetylated ERRγ levels were increased, confirming negative regulation of ERRγ by Sirt6. Thus, Sirt6 activation represents a potentially novel therapeutic strategy for treating cholestatic liver injury.

Sirt6 activation alleviates cholestatic liver damage and fibrosis in murine cholestasis models by deacetylation of ERRγ.

Mechanism of Hydrophobic Bile Acid-Induced Hepatocyte Injury and Drug Discovery

Cholestatic liver disease is caused by the obstruction of bile synthesis, transport, and excretion in or outside the liver by a variety of reasons. Long-term persistent cholestasis in the liver can trigger inflammation, necrosis, or apoptosis of hepatocytes. Bile acid nuclear receptors have received the most attention for the treatment of cholestasis, while the drug development for bile acid nuclear receptors has made considerable progress. However, the targets regulated by bile acid receptor drugs are limited. Thus, as anticipated, intervention in the expression of bile acid nuclear receptors alone will not yield satisfactory clinical results. Therefore, this review comprehensively summarized the literature related to cholestasis, analyzed the molecular mechanism that bile acid damages cells, and status of drug development. It is hoped that this review will provide some reference for the research and development of drugs for cholestasis treatment in the future.

Apigenin Prevents Acetaminophen-Induced Liver Injury by Activating the SIRT1 Pathway

Acetaminophen (APAP) overdose is the main cause of acute liver failure. Apigenin (API) is a natural dietary flavonol with high antioxidant capacity. Herein, we investigated protection by API against APAP-induced liver injury in mice, and explored the potential mechanism. Cell viability assays and mice were used to evaluate the effects of API against APAP-induced liver injury. Western blotting, immunofluorescence staining, RT-PCR, and Transmission Electron Microscope were carried out to determine the signalling pathways affected by API. Analysis of mouse serum levels of alanine/aspartate aminotransferase (ALT/AST), malondialdehyde (MDA), liver myeloperoxidase (MPO) activity, glutathione (GSH), and reactive oxygen species (ROS) revealed that API (80 mg/kg) owned protective effect on APAP-induced liver injury. Meanwhile, API ameliorated the decreased cell viability in L-02 cells incubated by APAP with a dose dependent. Furthermore, API promoted SIRT1 expression and deacetylated p53. Western blotting showed that API promoted APAP-induced autophagy, activated the NRF2 pathway, and inhibited the transcriptional activation of nuclear p65 in the presence of APAP. Furthermore, SIRT1 inhibitor EX-527 reduced protection by API against APAP-induced hepatotoxicity. Molecular docking results indicate potential interaction between API and SIRT1. API prevents APAP-induced liver injury by regulating the SIRT1-p53 axis, thereby promoting APAP-induced autophagy and ameliorating APAP-induced inflammatory responses and oxidative stress injury.

Sirt6 opposes glycochenodeoxycholate-induced apoptosis of biliary epithelial cells through the AMPK/PGC-1α pathway

Background

Induction of biliary epithelial cell apoptosis by toxic bile acids is involved in the development of cholestatic disease, but the underlying molecular mechanism is not clear. The purpose of this study was to investigate the molecular mechanisms involved in Sirt6 protection against the apoptosis of human intrahepatic biliary epithelial cells (HiBEC) induced by the bile acid glycochenodeoxycholate (GCDC).

Results

Sirt6 was either overexpressed or knocked down in HiBEC, with or without GCDC pretreatment. The CCK-8 assay was used to assess cell viability and, Hoechst 33258 staining was used to determine apoptotic rate. Mitochondrial DNA (mtDNA) copy number, malondialdehyde (MDA) and reactive oxygen species (ROS) production were detected to evaluate the severity of the mitochondrial dysfunction and oxidative stress. The mRNA and protein levels of PGC-1α, Nrf1, and Nrf2 were analyzed using RT-qPCR and western blot assay. The results showed that Sirt6 opposed GCDC-induced apoptosis in HiBEC via up-regulating PGC-1α expression and stabilizing mtDNA. We used agonists and inhibitors of AMPK to demonstrate that Sirt6 increased PGC-1α expression through the AMPK pathway whereas GCDC had the opposite effect. Finally, western blot, luciferase assay, and co-immunoprecipitation were used to describe a direct interaction and acetylation modification of PGC-1α by Sirt6.

Conclusion

Our data illuminated that Sirt6 ameliorated GCDC-induced HiBEC apoptosis by upregulating PGC-1α expression through the AMPK pathway and its deacetylation effect.

Sirtuin 1 activation alleviates primary biliary cholangitis via the blocking of the NF-κB signaling pathway

This report sought to establish the mechanistic role of sirtuin-1 (Sirt1), a NAD⁺-dependent deacetylase in the modulation of primary biliary cholangitis (PBC) pathogenesis. 64 PBC patients (diagnosed based on practice guidelines for American Association for the Study of Liver Diseases) and 60 healthy controls were included in this study. Clinically, the mRNA expression level of Sirt1 in macrophages differentiated from peripheral blood mononuclear cells (PBMCs) of PBC subjects substantially decreased when compared with the healthy controls but not in other Sirt family genes (Sirt2-7). Consistent with clinical results, a PBC murine model showed that levels of Sirt1 significantly decreased in the liver and Kupffer cells of mice treated with polyinosinic/polycytidylic acid (poly I:C) for 16 weeks. A TAK1 inhibitor (NG25) prevented the poly I:C-induced Sirt1 protein level decreasing in Kupffer cells but not MAPK inhibitor. Sirt1 activators resveratrol (RSV) and SRT1720 (SRT) ameliorated poly I:C-induced hepatic injury observed via histopathologic analysis and decreased aspartate aminotransferase (AST) and alanine aminotransferase (ALT) levels in the PBC murine model. Furthermore, Sirt1 activators significantly reduced pro-inflammatory cytokines levels such as interleukin-1 beta (IL-1β), IL-6, interferon-gamma (IFN-γ) and tumor necrosis factor alpha (TNF-α) in serum in poly I:C-induced mice. In addition, Sirt1 activators significantly inhibited the phosphorylated and acetylated levels of the RelA/p65 subunit of the nuclear transcription factor (NF-κB) but not the interferon regulatory factor (IRF) 3 in poly I:C-injured mice livers. Significantly, RSV improved the interaction between Sirt1 and p65, which may contribute to the decreased activity of NF-κB. In summary, the Sirt1 signaling pathway plays an essential role in the development of PBC and this may represent a novel approach and target for the treatment of PBC.

A Change in Bile Flow: Looking Beyond Transporter Inhibition in the Development of Drug-induced Cholestasis

BACKGROUND

Drug-induced Liver Injury (DILI) has received increasing attention over the past decades, as it represents the leading cause of drug failure and attrition. One of the most prevalent and severe forms of DILI involves the toxic accumulation of bile acids in the liver, known as Drug-induced Cholestasis (DIC). Traditionally, DIC is studied by exploring the inhibition of hepatic transporters such as Bile Salt Export Pump (BSEP) and multidrug resistance-associated proteins, predominantly through vesicular transport assays. Although this approach has identified numerous drugs that alter bile flow, many DIC drugs do not demonstrate prototypical transporter inhibition, but rather are associated with alternative mechanisms.

METHODS

We undertook a focused literature search on DIC and biliary transporters and analyzed peer-reviewed publications over the past two decades or so.

RESULTS

We have summarized the current perception regarding DIC, biliary transporters, and transcriptional regulation of bile acid homeostasis. A growing body of literature aimed to identify alternative mechanisms in the development of DIC has been evaluated. This review also highlights current in vitro approaches used for prediction of DIC.

CONCLUSION

Efforts have continued to focus on BSEP, as it is the primary route for hepatic biliary clearance. In addition to inhibition, drug-induced BSEP repression or the combination of these two has emerged as important alternative mechanisms leading to DIC. Furthermore, there has been an evolution in the approaches to studying DIC including 3D cell cultures and computational modeling.

Baicalin Protects Against 17α-Ethinylestradiol-Induced Cholestasis via the Sirtuin 1/Hepatic Nuclear Receptor-1α/Farnesoid X Receptor Pathway

Estrogen-induced cholestasis (EIC) is characterized by impairment of bile flow and accumulated bile acids (BAs) in the liver, always along with the liver damage. Baicalin is a major flavonoid component of Scutellaria baicalensis, and has been used in the treatment of liver diseases for many years. However, the role of baicalin in EIC remains to be elucidated. In this study, we demonstrated that baicalin showed obvious hepatoprotective effects in EIC rats by reducing serum biomarkers and increasing the bile flow rate, as well as by alleviating liver histology and restoring the abnormal composition of hepatic BAs. In addition, baicalin protected against estrogen-induced liver injury by up-regulation of the expression of hepatic efflux transporters and down-regulation of hepatic uptake transporters. Furthermore, baicalin increased the expression of hepatic BA synthase (CYP27A1) and metabolic enzymes (Bal, Baat, Sult2a1) in EIC rats. We showed that baicalin significantly inhibited hepatic inflammatory responses in EIC rats through reducing elevated levels of TNF-α, IL-1β, IL-6, and NF-κB. Finally, we confirmed that baicalin maintains hepatic BA homeostasis and alleviates inflammation through sirtuin 1 (Sirt1)/hepatic nuclear receptor-1α (HNF-1α)/farnesoid X receptor (FXR) signaling pathway. Thus, baicalin protects against estrogen-induced cholestatic liver injury, and the underlying mechanism involved is related to activation of the Sirt1/HNF-1α/FXR signaling pathway.

Mechanism of Hydrophobic Bile Acid-Induced Hepatocyte Injury and Drug Discovery

Cholestatic liver disease is caused by the obstruction of bile synthesis, transport, and excretion in or outside the liver by a variety of reasons. Long-term persistent cholestasis in the liver can trigger inflammation, necrosis, or apoptosis of hepatocytes. Bile acid nuclear receptors have received the most attention for the treatment of cholestasis, while the drug development for bile acid nuclear receptors has made considerable progress. However, the targets regulated by bile acid receptor drugs are limited. Thus, as anticipated, intervention in the expression of bile acid nuclear receptors alone will not yield satisfactory clinical results. Therefore, this review comprehensively summarized the literature related to cholestasis, analyzed the molecular mechanism that bile acid damages cells, and status of drug development. It is hoped that this review will provide some reference for the research and development of drugs for cholestasis treatment in the future.

Pharmaceutical Intervention of Aging

The aging population represents a significant worldwide socioeconomic challenge. Aging is an inevitable and multifactorial biological process and primary risk factor for most age-related diseases, such as cardiovascular diseases, cancers, type 2 diabetes mellitus (T2DM), and neurodegenerative diseases. Pharmacological interventions targeting aging appear to be a more effective approach in preventing age-related disorders compared with the treatments targeted to specific disease. In this chapter, we focus on the latest findings on molecular compounds that mimic caloric restriction (CR), supplement nicotinamide adenine dinucleotide (NAD⁺) levels, and eliminate senescent cells, including metformin, resveratrol, spermidine, rapamycin, NAD⁺ boosters, as well as senolytics. All these interventions modulate the determinants and pathways responsible for aging/longevity, such as the kinase target of rapamycin (TOR), AMP-activated protein kinase (AMPK), sirtuins, and insulin-like growth factor (IGF-1) signaling (Fig. 15.1).

microRNA-141 is associated with hepatic steatosis by downregulating the sirtuin1/AMP-activated protein kinase pathway in hepatocytes

Sirtuin1 (SIRT1) is a crucial regulator of metabolism and it is implicated in the metabolic pathophysiology of several disorders inclusive of Type 2 diabetes and fatty liver disease (NAFLD). The aim of this study was to investigate the role of miR-141 in hepatic steatosis via regulation of SIRT1/AMP-activated protein kinase (AMPK) pathway in hepatocytes. Liver hepatocellular cells (HepG2) were treated with high concentration of glucose to be subsequently used for the assessment of miR-141 and SIRT1 levels in a model of hepatic steatosis. On the other hand, cells were transfected with miR-141 to investigate its effect on hepatocyte steatosis and viability as well as SIRT1 expression and activity along with AMPK phosphorylation. Targeting of SIRT1 by miR-141 was evaluated by bioinformatics tools and confirmed by luciferase reporter assay. Following the intracellular accumulation of lipids in HepG2 cells, the level of miR-141 was increased while SIRT1 mRNA and protein levels, as well as AMPK phosphorylation, was decreased. Transfection with miR-141 mimic significantly downregulated SIRT1 expression and activity while miR-141 inhibitor had the opposite effects. Additionally, modulation of miR-141 levels significantly influenced AMPK phosphorylation status. The results of luciferase reporter assay verified SIRT1 to be directly targeted by miR-141. miR-141 could effectively suppress SIRT1 and lead to decreased AMPK phosphorylation in HepG2 cells. Thus, miR-141/SIRT1/AMPK signaling pathway may be considered a potential target for the therapeutic management of NAFLD.

Increased sulfation of bile acids in mice and human subjects with sodium taurocholate cotransporting polypeptide deficiency

Sodium taurocholate cotransporting polypeptide (NTCP, encoded by Slc10a1/SLC10A1) deficiency can result in hypercholanemia but no obvious symptoms in both mice and humans. However, the consequence of and response to long-term hypercholanemia caused by NTCP deficiency remain largely unexplored. Here, we analyzed lifelong dynamics of serum total bile acid (TBA) levels in Slc10a1 ^-/- mice, and we also assessed changes of TBA levels in 33 young individuals with SLC10A1 loss-of-function variant p.Ser267Phe. We found that overall serum TBA levels tended to decrease gradually with age in both Slc10a1 ^-/- mice and p.Ser267Phe individuals. Liver mRNA profiling revealed notable transcription alterations in hypercholanemic Slc10a1 ^-/- mice, including inhibition of bile acid (BA) synthesis, enhancement of BA detoxification, and altered BA transport. Members of the sulfotransferase (SULT) family showed the most dramatic increases in livers of hypercholanemic Slc10a1 ^-/- mice, and one of their BA sulfates, taurolithocholic acid 3-sulfate, significantly increased. Importantly, consistent with the mouse studies, comprehensive profiling of 58 BA species in sera of p.Ser267Phe individuals revealed a markedly increased level of BA sulfates. Together, our findings indicate that the enhanced BA sulfation is a major mechanism for BA detoxification and elimination in both mice and humans with Slc10a1/SLC10A1 deficiency.

SIRT1 Modulators in Experimentally Induced Liver Injury

This article is directed at highlighting the involvement of the endogenous stress sensor SIRT1 (silent information regulator T1) as a possible factor involved in hepatoprotection. The selective SIRT1 modulators whether activators (STACs) or inhibitors are being tried experimentally and clinically. We discuss the modulation of SIRT1 on cytoprotection or even cytotoxicity in the liver chemically injured by hepatotoxic agents in rats, to shed light on the crosstalk between SIRT1 and its modulators. A combination of D-galactosamine and lipopolysaccharide (D-GalN/LPS) downregulated SIRT1 expression, while SIRT1 activators, SRT1720, resveratrol, and quercetin, upregulated SIRT1 and alleviated D-GalN/LPS-induced acute hepatotoxicity. Liver injury markers exhibited an inverse relationship with SIRT1 expression. However, under subchronic hepatotoxicity, quercetin decreased the significant increase in SIRT1 expression to lower levels which are still higher than normal ones and mitigated the liver-damaging effects of carbon tetrachloride. Each of these STACs was hepatoprotective and returned the conventional antioxidant enzymes to the baseline. Polyphenols tend to fine-tune SIRT1 expression towards normal in the liver of intoxicated rats in both acute and subchronic studies. Together, all these events give an impression that the cytoprotective effects of SIRT1 are exhibited within a definite range of expression. The catalytic activity of SIRT1 is important in the hepatoprotective effects of polyphenols where SIRT1 inhibitors block and the allosteric SIRT1 activators mimic the hepatoprotective effects of polyphenols. Our findings indicate that the pharmacologic modulation of SIRT1 could represent both an important move in alleviating hepatic insults and a future major step in the treatment of xenobiotic-induced hepatotoxicity.

Celastrol Protects From Cholestatic Liver Injury Through Modulation of SIRT1-FXR Signaling

Celastrol, derived from the roots of the Tripterygium Wilfordi, shows a striking effect on obesity. In the present study, the role of celastrol in cholestasis was investigated using metabolomics and transcriptomics. Celastrol treatment significantly alleviated cholestatic liver injury in mice induced by α-naphthyl isothiocyanate (ANIT) and thioacetamide (TAA). Celastrol was found to activate sirtuin 1 (SIRT1), increase farnesoid X receptor (FXR) signaling and inhibit nuclear factor-kappa B and P53 signaling. The protective role of celastrol in cholestatic liver injury was diminished in mice on co-administration of SIRT1 inhibitors. Further, the effects of celastrol on cholestatic liver injury were dramatically decreased in Fxr-null mice, suggesting that the SIRT1-FXR signaling pathway mediates the protective effects of celastrol. These observations demonstrated a novel role for celastrol in protecting against cholestatic liver injury through modulation of the SIRT1 and FXR.

SRT1720 retards renal fibrosis via inhibition of HIF1α /GLUT1 in diabetic nephropathy

Renal fibrosis is a major pathological characteristic of diabetic nephropathy (DN). Reportedly, increased SIRT1 expression played a renal protective role in animal models of DN. This study was designed to elucidate the molecular mechanisms underlying the protective effects of SRT1720, an SIRT1 activator, against diabetes-induced renal fibrosis. Type 2 diabetic mice (db/db) were treated with SRT1720 (50 mg/kg/d) by gavage for 10 weeks. Renal proximal tubular epithelial cells (HK-2 cells) were treated with high glucose (HG, 30 mM) in the presence or absence of SRT1720 (2.5 µM) for 48 h. We observed that impaired SIRT1 expression and activity were restored by SRT1720 administration in db/db mice as well as in HG-treated HK-2 cells. Moreover, SRT1720 administration improved renal function, attenuated glomerular hypertrophy, mesangial expansion, glomerulosclerosis and interstitial fibrosis, and inhibited TGFB1 and CTGF expressions and nuclear factor κB (NF-κB) activation in db/db mice. Similarly, HG-induced epithelial-to-mesenchymal transformation (EMT), and collagen IV and fibronectin expressions were inhibited in SRT1720 treated HK-2 cells. Mechanistic studies demonstrated that SRT1720 suppressed HIF1α, GLUT1 and SNAIL expressions both in vivo and in vitro. Furthermore, Hif1α or Glut1 knockdown effectively abrogated HG-induced EMT and collagen IV and fibronectin expressions in HK-2 cells. These findings suggest that SRT1720 prevented diabetes-induced renal fibrosis via the SIRT1/HIF1α/GLUT1/SNAIL pathway.

Fine-Tuning of Sirtuin 1 Expression Is Essential to Protect the Liver From Cholestatic Liver Disease

Cholestasis comprises aetiologically heterogeneous conditions characterized by accumulation of bile acids in the liver that actively contribute to liver damage. Sirtuin 1 (SIRT1) regulates liver regeneration and bile acid metabolism by modulating farnesoid X receptor (FXR); we here investigate its role in cholestatic liver disease. We determined SIRT1 expression in livers from patients with cholestatic disease, in two experimental models of cholestasis, as well as in human and murine liver cells in response to bile acid loading. SIRT1-overexpressing (SIRT^oe ) and hepatocyte-specific SIRT1-KO (knockout) mice (SIRT^hep-/- ) were subjected to bile duct ligation (BDL) and were fed with a 0.1% DDC (3,5-diethoxycarbonyl-1,4-dihydrocollidine) diet to determine the biological relevance of SIRT1 during cholestasis. The effect of NorUDCA (24-norursodeoxycholic acid) was tested in BDL/SIRT^oe mice. We found that SIRT1 was highly expressed in livers from cholestatic patients, mice after BDL, and Mdr2 knockout mice (Mdr2^-/- ) animals. The detrimental effects of SIRT1 during cholestasis were validated in vivo and in vitro. SIRT^oe mice showed exacerbated parenchymal injury whereas SIRT^hep-/- mice evidenced a moderate improvement after BDL and 0.1% DDC feeding. Likewise, hepatocytes isolated from SIRT^oe mice showed increased apoptosis in response to bile acids, whereas a significant reduction was observed in SIRT^hep-/- hepatocytes. Importantly, the decrease, but not complete inhibition, of SIRT1 exerted by norUDCA treatment correlated with pronounced improvement in liver parenchyma in BDL/SIRT^oe mice. Interestingly, both SIRT1 overexpression and hepatocyte-specific SIRT1 depletion correlated with inhibition of FXR, whereas modulation of SIRT1 by NorUDCA associated with restored FXR signaling. Conclusion: SIRT1 expression is increased during human and murine cholestasis. Fine-tuning expression of SIRT1 is essential to protect the liver from cholestatic liver damage.

The Beneficial Roles of SIRT1 in Drug-Induced Liver Injury

Drug-induced liver injury (DILI) is a major cause of acute liver failure (ALF) as a result of accumulated drugs in the human body metabolized into toxic agents and helps generate heavy oxidative stress, inflammation, and apoptosis, which induces necrosis in hepatocytes and ultimately damages the liver. Sirtuin 1 (SIRT1) is said to have multiple vital roles in cell proliferation, aging, and antistress systems of the human body. The levels of SIRT1 and its activation precisely modulate its critical role in the interaction between multiple step procedures of DILI. The nuclear factor kappa-light-chain-enhancer of activated B cell- (NF-κB-) mediated inflammation signaling pathway, reactive oxygen species (ROS), DNA damage, mitochondrial membrane potential collapse, and endoplasmic reticulum (ER) stress also contribute to aggravate DILI. Apoptosis is regarded as the terminal reaction followed by multiple signaling cascades including caspases, p53, and mitochondrial dysfunction which have been said to contribute in DILI. The SIRT1 activator is regarded as a potential candidate for DILI, because the former could inhibit signaling of p53, NF-κB, and ER stress. On the other hand, overexpression of SIRT1 also enhances the activation of antioxidant responses via Kelch-like ECH-associated protein 1- (Keap1-) nuclear factor- (erythroid-derived 2-) like 2 (Nrf2) signaling. The current manuscript will highlight the mechanism of DILI and the interaction of SIRT1 with various cytoplasmic factors leading to DILI along with the summary of potent SIRT1 agonists.

18β-Glycyrrhetinic acid protects against alpha-naphthylisothiocyanate-induced cholestasis through activation of the Sirt1/FXR signaling pathway

Cholestasis is a common feature of liver injury, which manifests as bile acid excretion and/or enterohepatic circulation disorders. However, very few effective therapies exist for cholestasis. Recently, 18β-Glycyrrhetinic acid (18b-GA), a major metabolic component of glycyrrhizin, which is the main ingredient of licorice, was reported to protect against alpha-naphthylisothiocyanate (ANIT)-induced cholestasis. However, its protective mechanism remains unclear. We hypothesized that 18b-GA may stimulate the signaling pathway of bile acid (BA) transportation in hepatocytes, resulting its hepatoprotective effect. According to the results, 18b-GA markedly attenuated ANIT-induced liver injury as indicated the hepatic plasma chemistry index and histopathology examination. In addition, the expression levels of nuclear factors, including Sirt1, FXR and Nrf2, and their target efflux transporters in the liver, which mainly mediate bile acid homeostasis in hepatocytes, significantly increased. Furthermore, we first revealed that 18b-GA treatment significantly activated FXR, and which can be significantly reduced by EX-527 (a potent and selective Sirt1 inhibitor), indicating that 18b-GA activates FXR through Sirt1. Taken together, 18b-GA confers hepatoprotection against ANIT-induced cholestasis by activating FXR through Sirt1, which promotes gene expression of the efflux transporter, and consequently attenuates dysregulation of bile acid homeostasis in hepatocyte compartments.

Advances in drug-induced cholestasis: Clinical perspectives, potential mechanisms and in vitro systems

Despite growing research, drug-induced liver injury (DILI) remains a serious issue of increasing importance to the medical community that challenges health systems, pharmaceutical industries and drug regulatory agencies. Drug-induced cholestasis (DIC) represents a frequent manifestation of DILI in humans, which is characterised by an impaired canalicular bile flow resulting in a detrimental accumulation of bile constituents in blood and tissues. From a clinical point of view, cholestatic DILI generates a wide spectrum of presentations and can be a diagnostic challenge. The drug classes mostly associated with DIC are anti-infectious, anti-diabetic, anti-inflammatory, psychotropic and cardiovascular agents, steroids, and other miscellaneous drugs. The molecular mechanisms of DIC have been investigated since the 1980s but they remain debatable. It is recognised that altered expression and/or function of hepatobiliary membrane transporters underlies some forms of cholestasis, and this and other concomitant mechanisms are very likely in DIC. Deciphering these processes may pave the ways for diagnosis, prognosis and prevention, for which currently major gaps and caveats exist. In this review, we summarise recent advances in the field of DIC, including clinical aspects, the potential mechanisms postulated so far and the in vitro systems that can be useful to investigate and identify new cholestatic drugs.

H19 Is Expressed in Hybrid Hepatocyte Nuclear Factor 4α+ Periportal Hepatocytes but Not Cytokeratin 19+ Cholangiocytes in Cholestatic Livers

Long noncoding RNA (lncRNA) H19 is abundantly expressed in fetal liver. Its expression is significantly diminished in adult healthy liver but is re‐induced in chronic liver diseases, including cholestasis. In this study, we developed a new method with combined in situ hybridization (ISH) and immunofluorescence (IF) colabeling to establish an H19 expression profile with both parenchymal and nonparenchymal cell‐specific markers in the livers of cholestatic mouse models and patients with cholestasis. H19RNA⁺ cells showed no colocalization with biliary epithelial cell marker cytokeratin 19 (CK19)⁺ cholangiocytes but were immediately adjacent to biliary structures in bile duct ligation (BDL), 3,5‐diethoxycarbony1‐1,4‐dihydrocollidine (DDC), and multidrug‐resistant gene 2 knockout (Mdr2^–/–) mouse models and in human primary biliary cholangitis (PBC) and primary sclerosing cholangitis (PSC) liver specimens. In contrast, double‐positive H19RNA⁺/sex‐determining region Y (SRY)‐box 9 (SOX9)⁺ ductal progenitor cells, H19RNA⁺/hepatocyte nuclear factor 4α (HNF4α)⁺ hepatocytes, H19RNA⁺/F4/80⁺ Kupffer cells, HNF4α⁺/SOX9⁺ hybrid hepatocytes, as well as triple‐positive H19RNA⁺/HNF4α⁺/SOX9⁺ periportal hepatocytes were identified. In addition, H19RNA could not be detected in mesenchymal cell marker desmin⁺ cells. Furthermore, H19RNA was predominately detected in cytoplasm with a small amount at the interspace with neighboring cells. Conclusion:H19RNA is localized in HNF4α⁺ periportal hepatocytes, SOX9⁺ ductal progenitor cells, and F4/80⁺ Kupffer cells but not in CK19⁺ cholangiocytes and desmin⁺ stellate cells in cholestatic livers.

Update on FXR Biology: Promising Therapeutic Target?

Farnesoid X receptor (FXR), a metabolic nuclear receptor, plays critical roles in the maintenance of systemic energy homeostasis and the integrity of many organs, including liver and intestine. It regulates bile acid, lipid, and glucose metabolism, and contributes to inter-organ communication, in particular the enterohepatic signaling pathway, through bile acids and fibroblast growth factor-15/19 (FGF-15/19). The metabolic effects of FXR are also involved in gut microbiota. In addition, FXR has various functions in the kidney, adipose tissue, pancreas, cardiovascular system, and tumorigenesis. Consequently, the deregulation of FXR may lead to abnormalities of specific organs and metabolic dysfunction, allowing the protein as an attractive therapeutic target for the management of liver and/or metabolic diseases. Indeed, many FXR agonists have been being developed and are under pre-clinical and clinical investigations. Although obeticholic acid (OCA) is one of the promising candidates, significant safety issues have remained. The effects of FXR modulation might be multifaceted according to tissue specificity, disease type, and/or energy status, suggesting the careful use of FXR agonists. This review summarizes the current knowledge of systemic FXR biology in various organs and the gut–liver axis, particularly regarding the recent advancement in these fields, and also provides pharmacological aspects of FXR modulation for rational therapeutic strategies and novel drug development.

Precise theranostic nanomedicines for inhibiting vulnerable atherosclerotic plaque progression through regulation of vascular smooth muscle cell phenotype switching

Coronary heart disease is a prevalent and fatal killer caused by vulnerable atherosclerotic plaques (VASPs). However, the precise detection and treatment of VASPs remains a difficult challenge. Here, we present the development of noninvasive human serum albumin (HSA)-based theranostic nanomedicines (NMs) for the specific diagnosis and effective therapy of VASPs.

Methods: The ICG/SRT@HSA-pept NMs were formulated to contain payloads of the near-infrared (NIR) fluorescent dye indocyanine green (ICG) and the sirtuin 1 (Sirt1) activator SRT1720, and modified with a peptide moiety targeting osteopontin (OPN). The in vivo atherosclerotic mouse model was established with the high-fat diet (HFD). The in vitro vascular smooth muscle cells (VSMCs) phenotypic switching was induced using the ox-LDL stimulation.

Results: Due to the overexpression of OPN in activated VSMCs and VASPs, the targeted NMs specifically accumulated within the VASPs region after intravenous injection into the atherosclerotic mice, achieving the precise detection of VASPs. In addition, in the presence of SRT1720, the NMs could activate intracellular Sirt1 and activate an antiatherogenesis effect by inhibiting the phenotypic switching of VSMCs, which is an essential contributor to the vulnerability and progression of atherosclerotic plaques. After therapeutic administration of the ICG/SRT@HSA-pept NMs for two weeks, the physiological sizes and plaque compositions of VASPs were markedly improved. Furthermore, ICG/SRT@HSA-pept NMs-treated mice presented a more favorable plaque phenotype than that was observed in free SRT1720-treated mice, suggesting the enhanced delivery of pharmaceutical agents to the atherosclerotic lesions and improved therapeutic efficacy of NMs compared with free SRT1720.

Conclusions: The theranostic ICG/SRT@HSA-pept NMs showed great potential for the precise identification and targeted treatment of atherosclerotic diseases.