MRGPRX4 in Cholestatic Pruritus

Taurocholic acid represents an earlier and more sensitive biomarker and promotes cholestatic hepatotoxicity in ANIT-treated rats

Bile acid homeostasis is crucial for the normal physiological functioning of the liver. Disruptions in bile acid profiles are closely linked to the occurrence of cholestatic liver injury. As part of our diagnostic and therapeutic approach, we aimed to investigate the disturbance in bile acid profiles during cholestasis and its correlation with cholestatic liver injury. Before the occurrence of liver injury, alterations in bile acid profiles were detected in both plasma and liver between 8 and 16 h, persisting up to 96 h. TCA, TCDCA, and TUDCA in the plasma, as well as TCA, TUDCA, TCDCA, TDCA, TLCA, and THDCA in the liver, emerged as early sensitive and potential markers for diagnosing ANIT-induced cholestasis at 8-16 h. The distinguishing features of ANIT-induced liver injury were as follows: T-BAs exceeding G-BAs and serum biochemical indicators surpassing free bile acids. Notably, plasma T-BAs, particularly TCA, exhibited higher sensitivity to cholestatic hepatotoxicity compared with serum enzyme activity and liver histopathology. Further investigation revealed that TCA exacerbated ANIT-induced liver injury by elevating liver function enzyme activity, inflammation, and bile duct proliferation and promoting the migration of bile duct epithelial cell. Nevertheless, no morphological changes or alterations in transaminase activity indicative of liver damage were observed in the rats treated with TCA alone. Additionally, there were no changes in bile acid profiles or inflammatory responses under physiological conditions with maintained bile acid homeostasis. In summary, our findings suggest that taurine-conjugated bile acids in both plasma and liver, particularly TCA, can serve as early and sensitive markers for predicting intrahepatic cholestatic drugs and can act as potent exacerbators of cholestatic liver injury progression. However, exogenous TCA does not induce liver injury under physiological conditions where bile acid homeostasis is maintained.

Systematic review: efficacy of therapies for cholestatic pruritus

Background

Pruritus is a symptom of several cholestatic liver diseases (CLDs) that can impair health-related quality of life (HRQoL). Despite evidence-based guideline therapy, managing cholestatic pruritus (CP) remains challenging, thus making the need for newer, more effective therapeutic agents more evident.

Objective

Our study evaluated the efficacy of existing CP therapies.

Design

Systematic review.

Data sources

From inception until March 2023, we conducted a comprehensive search of MEDLINE, Cochrane, EMBASE, Scopus, ClinicalTrial.gov, and other sources, including pharmaceutical webpages and conference proceedings published in English that reported on CP interventions.

Methods

Two reviewers independently conducted screening and full-text review of articles with extraction conducted according to the Preferred Reporting Items for Systematic Reviews and Meta-Analysis (PRISMA) guidelines. The methodological quality of studies included in our qualitative synthesis was assessed by using the Cochrane ROBINS-I and ROBINS-II tools for interventional studies and the National Heart, Lung, and Blood Institute Quality Assessment Tool for Observational Cohort and Cross-Sectional Studies. The primary outcome assessed in our systematic review was the severity of CP after therapy.

Results

Of 3293 screened articles, 92 studies were eligible for inclusion in the qualitative synthesis. Some patients' HRQoL improved with evidence-based standard therapy. Others, particularly those with severe and refractory CP, often required conversion to or addition of experimental noninvasive (e.g., ondansetron) or extracorporeal liver support to alleviate CP. In addition, studies investigating a newer class drug, the ileal bile acid transporter inhibitor (IBATi), demonstrate its effectiveness in reducing serum bile acid and alleviating CP with sustained improvement noted in patients with the inherited childhood cholestatic disorders - progressive familial intrahepatic cholestasis and Alagille syndrome.

Conclusion

Our findings consolidate data on the efficacy of guideline-based approaches and newer therapies for CP. While the initial findings are promising, additional clinical trials will be needed to determine the full extent of IBATi's efficacy and potential use in treating other common CLDs. These results provide a foundation for future research and highlight the need for continued investigation into the management and treatment of CLDs.

Itch receptor MRGPRX4 interacts with the receptor activity-modifying proteins

Cholestatic itch is a severe and debilitating symptom in liver diseases with limited treatment options. The class A G protein-coupled receptor (GPCR) Mas-related GPCR subtype X4 (MRGPRX4) has been identified as a receptor for bile acids, which are potential cholestatic pruritogens. An increasing number of GPCRs have been shown to interact with receptor activity-modifying proteins (RAMPs), which can modulate different aspects of GPCR biology. Using a combination of multiplexed immunoassay and proximity ligation assay, we show that MRGPRX4 interacts with RAMPs. The interaction of MRGPRX4 with RAMP2, but not RAMP1 or 3, causes attenuation of basal and agonist-dependent signaling, which correlates with a decrease of MRGPRX4 cell surface expression as measured using a quantitative NanoBRET pulse-chase assay. Finally, we use AlphaFold Multimer to predict the structure of the MRGPRX4-RAMP2 complex. The discovery that RAMP2 regulates MRGPRX4 may have direct implications for future drug development for cholestatic itch.

Primary biliary cholangitis as a roadmap for the development of novel treatments for cholestatic liver diseases†

The discovery of nuclear receptors and transporters has contributed to the development of new drugs for the treatment of cholestatic liver diseases. Particular progress has been made in the development of second-line therapies for PBC. These new drugs can be separated into compounds primarily targeting cholestasis, molecules targeting fibrogenesis and molecules with immune-mediated action. Finally, drugs aimed at symptom relief (pruritus and fatigue) are also under investigation. Obeticholic acid is currently the only approved second-line therapy for PBC. Drugs in the late phase of clinical development include peroxisome proliferator-activated receptor agonists, norursodeoxycholic acid and NADPH oxidase 1/4 inhibitors.