Obeticholic acid ameliorates hepatorenal syndrome in ascitic cirrhotic rats by down-regulating the renal 8-iso-PGF2α-activated COX-TXA2 pathway

Bile cast nephropathy: A systematic review of case reports and case series

BACKGROUND

Bile cast nephropathy (BCN) is suspected in the setting of liver disease and hyperbilirubinemia and is characterized by the formation of tubular bile casts and acute tubular injury. While postmortem studies reveal a high prevalence of BCN, little is known about this orphan acute kidney injury syndrome.

AIM

To address this knowledge gap, we performed a systematic review of case reports and case series of BCN, focusing on risk factors, diagnostic criteria, clinical presentation, kidney biopsy findings, severity, treatment approaches, and outcomes.

METHODS

Electronic databases were searched to identify eligible studies of patients with possible, probable, or definite BCN, using pre-established criteria. Relevant variables were extracted and analyzed. We explored the impact of serum total bilirubin levels and alcoholic liver disease on BCN severity and outcomes by stratifying cases into total bilirubin tertiles and alcoholic vs non-alcoholic liver disease. Univariate and multivariable logistic regression analyses were used to examine factors associated with the composite outcome of dialysis requirement or death.

RESULTS

Sixty-seven case reports and six case series (involving 2 patients each) met the inclusion criteria, totaling 79 cases of BCN. The mean age was 48.3 years, and 83.5% were men. The most common cause of liver disease was drug-induced injury (30.4%), followed by infection (18.9%) and alcoholism (12.7%). BCN diagnosis was deemed definite, probable, and possible in 65.8%, 32.9%, and 1.3% of cases, respectively. Levels of serum creatinine, dialysis requirement, and renal recovery did not differ among the total bilirubin tertile groups. However, both initial and peak serum creatinine were significantly higher in the alcoholic liver disease group compared to the non-alcoholic group (P = 0.011 and P = 0.012, respectively). There was also a non-significant trend toward a higher incidence of dialysis requirement or death in the alcoholic liver disease group (80% vs 52%, P = 0.098). Finally, higher initial serum creatinine (per 1 mg/dL increase) was independently associated with dialysis requirement or death (adjusted odds ratio 1.291, 95% confidence interval: 1.032-1.615, P = 0.025).

CONCLUSION

BCN is a common and potentially serious cause of acute kidney injury in patients with liver disease. The degree of hyperbilirubinemia does not appear to correlate with BCN severity or outcomes. However, in alcoholic liver disease, BCN is associated with a greater rise in serum creatinine and a trend toward worse outcomes compared to non-alcoholic liver disease. Serum creatinine may be a valuable predictor of BCN prognosis. Further studies are needed to develop non-invasive diagnostic tools and establish effective treatments for BCN.

Restoring FXR expression as a novel treatment strategy in liver cancer and other liver disorders

INTRODUCTION

Liver cancer is a leading cause of cancer-associated mortality and is often linked to preexisting liver conditions. Emerging research demonstrates FXR dysregulation, particularly its reduced expression, in the pathogenesis of liver diseases, including inflammation, fibrosis, cholestatic disorders, metabolic dysregulation, and liver cancer. Therefore, this review explores the role of FXR and its agonists in mitigating these conditions.

AREAS COVERED

This article summarizes FXR's involvement in liver disorders, primarily emphasizing on hepatic neoplasms, and examines the potential of FXR agonists in restoring FXR activity in liver diseases, thereby preventing their progression to liver cancer. The information presented is drawn from existing preclinical and clinical studies specific to each liver disorder, sourced from PubMed.

EXPERT OPINION

It is well established that FXR expression is downregulated in liver disorders, contributing to disease progression. Notably, FXR agonists have demonstrated therapeutic potential in ameliorating liver diseases, including hepatocellular carcinoma. We believe that activating or restoring FXR expression with agonists offers significant promise for the treatment of liver cancer and other liver conditions. Therefore, FXR modulation by agonists, particularly in combination with other therapeutic agents, could lead to more targeted treatments, improving efficacy while reducing side effects.

Advances in intrahepatic and extrahepatic vascular dysregulations in cirrhotic portal hypertension

Cirrhotic portal hypertension, the most prevalent and clinically significant complication of liver cirrhosis, manifests as elevated portal venous pressure and is associated with severe complications. Although much research on the mechanisms of portal hypertension has focused on liver fibrosis, less attention has been given to the role of intrahepatic and extrahepatic vascular dysfunction, particularly with respect to extrahepatic vasculature. While the role of hepatic fibrosis in cirrhotic portal hypertension is undeniable, the underlying mechanisms involving intrahepatic and extrahepatic vasculature are highly complex. Sinusoidal capillarization and endothelial dysfunction contribute to increased intrahepatic vascular resistance. Hemodynamic changes in the extrahepatic circulation, including splanchnic vasodilation and hyperdynamic circulation, play a significant role in the development of portal hypertension. Additionally, therapeutic strategies targeting these vascular mechanisms are diverse, including improvement of sinusoidal microcirculation, therapies targeting hepatic stellate cells activation, and pharmacological modulation of systemic vascular tone. Therefore, in this review, we will discuss the vascular-related mechanisms and treatment progress of portal hypertension in cirrhosis to provide a new theoretical basis and practical guidance for clinical treatment.

Protective effect of long-chain polyunsaturated fatty acids on hepatorenal syndrome in rats

BACKGROUND

Hepatorenal syndrome (HRS) is the most prevalent form of acute kidney injury in cirrhotic patients. It is characterized by reduced renal blood flow and represents the most severe complication in cirrhotic patients with advanced disease. Previous research has indicated that antioxidants can delay the onset of a hyperdynamic circulatory state in cirrhosis and improve renal function in HRS patients. Regular omega-3 supplementation has significantly reduced the risk of liver disease. This supplementation could represent an additional therapy for individuals with HRS.

AIM

To evaluated the antioxidant effect of omega-3 polyunsaturated fatty acid supplementation on the kidneys of cirrhotic rats.

METHODS

Secondary biliary cirrhosis was induced in rats by biliary duct ligation (BDL) for 28 d. We used 24 male Wistar rats divided into the following groups: I (control); II (treated with omega-3, 1 g/kg of body weight); III (BDL treated with omega-3, 1 g/kg of body weight); and IV (BDL without treatment). The animals were killed by overdose of anesthetic; the kidneys were dissected, removed, frozen in liquid nitrogen, and stored in a freezer at -80℃ for later analysis. We evaluated oxidative stress, nitric oxide (NO) metabolites, DNA damage by the comet assay, cell viability test, and apoptosis in the kidneys. Data were analyzed by one-way analysis of variance, and means were compared using the Tukey test, with P ≤ 0.05.

RESULTS

Omega-3 significantly decreased the production of reactive oxygen species (P < 0.001) and lipoperoxidation in the kidneys of cirrhotic rats treated with omega-3 (P < 0.001). The activity of the antioxidant enzymes superoxide dismutase and catalase increased in the BDL+omega-3 group compared to the BDL group (P < 0.01). NO production, DNA damage, and caspase-9 cleavage decreased significantly in the omega-3-treated BDL group. There was an increase in mitochondrial electrochemical potential (P < 0.001) in BDL treated with omega-3 compared to BDL. No changes in the cell survival index in HRS with omega-3 compared to the control group (P > 0.05) were observed.

CONCLUSION

The study demonstrates that omega-3 can protect cellular integrity and function by increasing antioxidant enzymes, inhibiting the formation of free radicals, and reducing apoptosis.

Edaravone and obeticholic acid protect against cisplatin-induced heart toxicity by suppressing oxidative stress and inflammation and modulating Nrf2, TLR4/p38MAPK, and JAK1/STAT3/NF-κB signals

Cardiotoxicity is a significant adverse effect of cisplatin (CIS) that necessitates extensive medical care. The current study examines the cardioprotective effects of edaravone (EDV), obeticholic acid (OCA), and their combinations on CIS-induced cardiac damage. Rats were allocated into five groups: the normal control group, the remaining four groups received CIS (7.5 mg/kg, i.p.) as a single dose on the fifth day and were assigned to CIS, OCA (10 mg/kg/day) + CIS, EDV (20 mg/kg/day) + CIS, and the (EDV + OCA) + CIS group. Compared to the CIS-treated group, co-treating rats with EDV, OCA, or their combinations significantly decreased ALP, AST, LDH, CK-MB, and troponin-I serum levels and alleviated histopathological heart abnormalities. Biochemically, EDV, OCA, and EDV plus OCA administration mitigated cardiac oxidative stress as indicated by a marked decrease in heart MDA content with a rise in cardiac antioxidants SOD and GSH associated with upregulating Nrf2, PPARγ, and SIRT1 expression. Besides, it dampened inflammation by decreasing cardiac levels of TNF-α, IL-1β, and IL-6, mediated by suppressing NF-κB, JAK1/STAT3, and TLR4/p38MAPK signal activation. Notably, rats co-administered with EDV plus OCA showed noticeable protection that exceeded that of EDV and OCA alone. In conclusion, our study provided that EDV, OCA, and their combinations effectively attenuated CIS-induced cardiac intoxication by activating Nrf2, PPARγ, and SIRT1 signals and downregulating NF-κB, JAK1/STAT3, and TLR4/p38MAPK signals.

Cholemic Nephropathy: Role in Acute Kidney Injury in Cholestasis and Cirrhosis

The concept of structural kidney damage and renal dysfunction as a result of jaundice attracted attention in the medical community in the early and mid-20th century. The postulated doctrine of the time was that the excretion of elevated concentrations of bile results in bile-stained casts occupying collecting and distal convoluted tubules, degeneration of tubular epithelium, and decreased renal function. Compared to the hepatorenal syndrome, the poster child of hepatology and nephrology collaboration, the notion of structural kidney damage and renal dysfunction as a result of cholemia lost its traction and has almost disappeared from modern textbooks. Today, cholemic nephropathy is experiencing a renaissance, with multiple case reports and case series of jaundiced patients with kidney dysfunction and evidence of bile acid casts upon histologic examination. Published cases include acute hepatitis, chronic liver injury, cirrhosis, and obstructive etiologies. Diagnosis of cholemic nephropathy is based on histological examination, typically showing intraluminal bile casts predominantly located in the distal tubules. In common bile duct-ligated mice, the histomorphological and functional alterations of cholemic nephropathy mimic those seen in humans. Some argue against the concept of cholemic nephropathy and postulate that bile casts are a secondary phenomenon. What we need are carefully designed trials to establish diagnostic criteria and subsequently translate this knowledge into evidence-based therapies.

Bile Acids and Farnesoid X Receptor in Renal Pathophysiology

BACKGROUND

Bile acids (BAs) act not only as lipids and lipid-soluble vitamin detergents but also function as signaling molecules, participating in diverse physiological processes. The identification of BA receptors in organs beyond the enterohepatic system, such as the farnesoid X receptor (FXR), has initiated inquiries into their organ-specific functions. Among these organs, the kidney prominently expresses FXR.

SUMMARY

This review provides a comprehensive overview of various BA species identified in kidneys and delves into the roles of renal apical and basolateral BA transporters. Furthermore, we explore changes in BAs and their potential implications for various renal diseases, particularly chronic kidney disease. Lastly, we center our discussion on FXR, a key BA receptor in the kidney and a potential therapeutic target for renal diseases, providing current insights into the protective mechanisms associated with FXR agonist treatments.

KEY MESSAGES

Despite the relatively low concentrations of BAs in the kidney, their presence is noteworthy, with rodents and humans exhibiting distinct renal BA compositions. Renal BA transporters efficiently facilitate either reabsorption into systemic circulation or excretion into the urine. However, adaptive changes in BA transporters are evident during cholestasis. Various renal diseases are accompanied by alterations in BA concentrations and FXR expression. Consequently, the activation of FXR in the kidney could be a promising target for mitigating kidney damage.

Obeticholic acid treatment of mice to promote fertilization and reproduction

Obeticholic acid (OCA), a farnesoid X receptor (FXR) agonist, has been demonstrated to ameliorate the histopathological characteristics of liver damage. Nonetheless, the systemic safety profile of OCA with regard to reproduction and development remains poorly understood. In the present study, we conducted a dose-response experiment by administering OCA at doses of 5 mg/kg, 10 mg/kg, or 20 mg/kg through tube feeding to investigate its effect on reproductive development and fertilization rate in both male and female mice. Furthermore, we evaluated the levels of protein and mitochondrial function in the placenta through western blot, qPCR, and scanning electron microscopy. The results showed that 10 mg/kg and 20 mg/kg OCA doses significantly reduced the rate of placental implantation (P < 0.05). Also, OCA increased maternal body weight. In addition, OCA increased levels of FXR and TGR5 and produced changes in oxidative stress levels (P < 0.05). Mitochondrial activity result found that 10 mg/kg and 20 mg/kg of OCA significantly reduced the mitophagy autosomes/nucleus compared with the normal control group (P < 0.05). What is more, there was no significant difference in sperm count after OCA intervention in either C57BL/10 mice or BALB/c mice. Overall, we demonstrated that OCA treatment protected against placental implantation by suppressing placental oxidative stress and mitochondrial activity.

Farnesoid X receptor prevents neutrophil extracellular traps via reduced sphingosine-1-phosphate in chronic kidney disease

Farnesoid X receptor (FXR) activation reduces renal inflammation, but the underlying mechanisms remain elusive. Neutrophil extracellular traps (NETs) are webs of DNA formed when neutrophils undergo specialized programmed cell death (NETosis). The signaling lipid sphingosine-1-phosphate (S1P) stimulates NETosis via its receptor on neutrophils. Here, we identify FXR as a negative regulator of NETosis via repressing S1P signaling. We determined the effects of the FXR agonist obeticholic acid (OCA) in mouse models of adenosine phosphoribosyltransferase (APRT) deficiency and Alport syndrome, both genetic disorders that cause chronic kidney disease. Renal FXR activity is greatly reduced in both models, and FXR agonism reduces disease severity. Renal NETosis and sphingosine kinase 1 (Sphk1) expression are increased in diseased mice, and they are reduced by OCA in both models. Genetic deletion of FXR increases Sphk1 expression, and Sphk1 expression correlates with NETosis. Importantly, kidney S1P levels in Alport mice are two-fold higher than controls, and FXR agonism restores them back to baseline. Short-term inhibition of sphingosine synthesis in Alport mice with severe kidney disease reverses NETosis, establishing a causal relationship between S1P signaling and renal NETosis. Finally, extensive NETosis is present in human Alport kidney biopsies (six male, nine female), and NETosis severity correlates with clinical markers of kidney disease. This suggests the potential clinical relevance of the newly identified FXR-S1P-NETosis pathway. In summary, FXR agonism represses kidney Sphk1 expression. This inhibits renal S1P signaling, thereby reducing neutrophilic inflammation and NETosis.NEW & NOTEWORTHY Many preclinical studies have shown that the farnesoid X receptor (FXR) reduces renal inflammation, but the mechanism is poorly understood. This report identifies FXR as a novel regulator of neutrophilic inflammation and NETosis via the inhibition of sphingosine-1-phosphate signaling. Additionally, NETosis severity in human Alport kidney biopsies correlates with clinical markers of kidney disease. A better understanding of this signaling axis may lead to novel treatments that prevent renal inflammation and chronic kidney disease.

Bile acid receptors and renal regulation of water homeostasis

The kidney is the key organ responsible for maintaining the body's water and electrolyte homeostasis. About 99% of the primary urine filtered from the Bowman's capsule is reabsorbed along various renal tubules every day, with only 1-2 L of urine excreted. Aquaporins (AQPs) play a vital role in water reabsorption in the kidney. Currently, a variety of molecules are found to be involved in the process of urine concentration by regulating the expression or activity of AQPs, such as antidiuretic hormone, renin-angiotensin-aldosterone system (RAAS), prostaglandin, and several nuclear receptors. As the main bile acid receptors, farnesoid X receptor (FXR) and membrane G protein-coupled bile acid receptor 1 (TGR5) play important roles in bile acid, glucose, lipid, and energy metabolism. In the kidney, FXR and TGR5 exhibit broad expression across all segments of renal tubules, and their activation holds significant therapeutic potential for numerous acute and chronic kidney diseases through alleviating renal lipid accumulation, inflammation, oxidative stress, and fibrosis. Emerging evidence has demonstrated that the genetic deletion of FXR or TGR5 exhibits increased basal urine output, suggesting that bile acid receptors play a critical role in urine concentration. Here, we briefly summarize the function of bile acid receptors in renal water reabsorption and urine concentration.

Effects and mechanisms of Xiaochaihu Tang against liver fibrosis: An integration of network pharmacology, molecular docking and experimental validation

ETHNOPHARMACOLOGICAL RELEVANCE

Liver fibrosis is a potentially harmful chronic liver disease caused by various etiologies. There is currently no specific drug for liver fibrosis. Xiaochaihu Tang (XCHT) is a traditional formula combined of seven herbs, which was first recorded in the Treatise on Febrile Diseases in Han Dynasty of ancient China. It is widely used in clinic to hepatic protection, analgesic, antipyretic and anti-inflammatory treatment. And it has been recommended for treating chronic hepatitis and chronic cholecystitis in the latest guidelines for the diagnosis and treatment of liver fibrosis with integrated traditional and western medicine. However, the underlying regulatory mechanisms remain elusive.

AIM OF THE STUDY

This study aims to explore the therapeutic effects of XCHT on liver fibrosis and its underlying molecular mechanisms from the perspective of network pharmacology and experimental research.

MATERIALS AND METHODS

Carbon tetrachloride (CCl₄) induced and bile duct ligation (BDL) induced liver fibrosis models in mice were established to evaluate the anti-fibrosis effects of XCHT in vivo. Potential anti-fibrosis targets of XCHT were screened via network establishment. The underlying mechanisms were uncovered through GO and pathway enrichment analysis. Then, the core targets were identified from protein-protein interaction network by means of the Cytohubba plug-in of Cytoscape. Furthermore, two effective monomer components of XCHT were recognized by molecular docking. Moreover, the predicted components and pathways were verified by in vitro experiments.

RESULTS

When treated with XCHT, liver fibrosis was alleviated in both mice models, showing as the improvement of liver function, the protection of hepatocytes, the inhibition of HSC activation and the reduction of hepatic collagen accumulation. 540 monomer components, 300 therapeutic targets, 109 signaling pathways, 246 GO biological processes, 77 GO cellular components, 107 GO molecular functions items and core targets were identified by network analysis. Then, 6-gingerol and baicalein were identified as the core components of anti-fibrosis effects of XCHT via leptin or Nrf2 signaling pathway. Furthermore, the experiment in vitro also validated the results.

CONCLUSIONS

Our study suggests XCHT could alleviate liver fibrosis through multi-targets and multi-pathways; 6-gingerol and baicalein are its core components which may play an important role via leptin or Nrf2 signaling pathway.

Role of FXR in Renal Physiology and Kidney Diseases

Farnesoid X receptor, also known as the bile acid receptor, belongs to the nuclear receptor (NR) superfamily of ligand-regulated transcription factors, which performs its functions by regulating the transcription of target genes. FXR is highly expressed in the liver, small intestine, kidney and adrenal gland, maintaining homeostasis of bile acid, glucose and lipids by regulating a diverse array of target genes. It also participates in several pathophysiological processes, such as inflammation, immune responses and fibrosis. The kidney is a key organ that manages water and solute homeostasis for the whole body, and kidney injury or dysfunction is associated with high morbidity and mortality. In the kidney, FXR plays an important role in renal water reabsorption and is thought to perform protective functions in acute kidney disease and chronic kidney disease, especially diabetic kidney disease. In this review, we summarize the recent advances in the understanding of the physiological and pathophysiological function of FXR in the kidney.

Effects of Intestinal FXR-Related Molecules on Intestinal Mucosal Barriers in Biliary Tract Obstruction

Background: The farnesoid X receptor (FXR) is a key factor regulating hepatic bile acid synthesis and enterohepatic circulation. Repression of bile acid synthesis by the FXR is a potential strategy for treating cholestatic liver disease. However, the role of intestinal FXR on the intestinal barrier and intestinal microbiota needs further investigation.

Materials: Intestinal tissues were collected from patients with biliary atresia or without hepatobiliary disease. Then, intestinal mRNA levels of FXR-related molecules were determined. To investigate the effect of FXR activation, bile-duct-ligation rats were treated with obeticholic acid [OCA (5 mg/kg/day)] or vehicle (0.5% methyl cellulose) per oral gavage for 14 days. The mRNA levels of intestinal FXR, SHP, TNF-α, FGF15 and bile acid transporter levels were determined. In addition, the intestinal permeability, morphologic changes, and composition of the intestinal microbiota were evaluated. Gut Microbiome was determined by 16S rDNA MiSeq sequencing, and functional profiling of microbial communities was predicted with BugBase and PICRUSt2. Finally, the role of OCA in injured intestinal epithelial cell apoptosis and proliferation was examined by pretreatment with lipopolysaccharide (LPS) in Caco-2 cells.

Results: The downstream of the FXR in ileum tissues was inhibited in biliary obstruction. Activation of the FXR signaling pathway by OCA significantly reduced liver fibrosis and intestinal inflammation, improved intestinal microbiota, and protected intestinal mucosa in BDL rats. OCA also altered the functional capacities of ileum microbiota in BDL rats. Significant differences existed between the controls and BDL rats, which were attenuated by OCA in the alpha diversity analysis. Principal coordinates analysis showed that microbial communities in BDL rats clustered separately from controls, and OCA treatment attenuated the distinction. Bugbase and PICRUSt2 analysis showed that OCA changed the composition and structure of the intestinal microbiota and improved the metabolic function of the intestinal microbiota by increasing the relative abundance of beneficial bacteria and reducing the relative abundance of harmful bacteria. Moreover, OCA reduced the apoptosis induced by LPS in Caco-2 cells.

Conclusion: The FXR agonist, OCA, activates the intestinal FXR signaling pathway and improves the composition and structure of the intestinal microbiota and intestinal barrier in BDL rats.

Intestinal SIRT1 Deficiency-Related Intestinal Inflammation and Dysbiosis Aggravate TNFα-Mediated Renal Dysfunction in Cirrhotic Ascitic Mice

In advanced cirrhosis, the TNFα-mediated intestinal inflammation and bacteria dysbiosis are involved in the development of inflammation and vasoconstriction-related renal dysfunction. In colitis and acute kidney injury models, activation of SIRT1 attenuates the TNFα-mediated intestinal and renal abnormalities. This study explores the impacts of intestinal SIRT1 deficiency and TNFα-mediated intestinal abnormalities on the development of cirrhosis-related renal dysfunction. Systemic and renal hemodynamics, intestinal dysbiosis [cirrhosis dysbiosis ratio (CDR) as marker of dysbiosis], and direct renal vasoconstrictive response (renal vascular resistance (RVR) and glomerular filtration rate (GFR)) to cumulative doses of TNFα were measured in bile duct ligated (BDL)-cirrhotic ascitic mice. In SIRT1^IEC-KO-BDL-ascitic mice, the worsening of intestinal dysbiosis exacerbates intestinal inflammation/barrier dysfunction, the upregulation of the expressions of intestinal/renal TNFα-related pathogenic signals, higher TNFα-induced increase in RVR, and decrease in GFR in perfused kidney. In intestinal SIRT1 knockout groups, the positive correlations were identified between intestinal SIRT1 activity and CDR. Particularly, the negative correlations were identified between CDR and RVR, with the positive correlation between CDR and GFR. In mice with advanced cirrhosis, the expression of intestinal SIRT1 is involved in the linkage between intestinal dysbiosis and vasoconstriction/hypoperfusion-related renal dysfunction through the crosstalk between intestinal/renal TNFα-related pathogenic inflammatory signals.