Cholestasis-Associated Pruritus and Its Pruritogens

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.

Endogenous Opioid Imbalance as a Potential Factor Involved in the Pathogenesis of Chronic Kidney Disease-Associated Pruritus in Dialysis Patients

Chronic pruritus is one of the most common symptoms of dermatological diseases. It may occur in the course of other disorders, such as kidney disease. Chronic kidney disease-associated pruritus (CKD-aP) most often affects people with end-stage renal disease. The etiology of this condition is still not fully understood, but researchers are currently focusing on a thorough analysis of the association between disturbed opioid balance and increased neuronal signaling leading to pruritus. The aim of this study is to assess the concentration of endogenous opioids in dialysis patients with and without pruritus and in the control group, and to determine the correlation between the concentration of these substances and the occurrence and severity of itching. The study involved 126 dialysis patients and 50 healthy controls. Patients were divided into groups with pruritus (n = 62) and without pruritus (n = 64). The severity of pruritus was assessed using the NRS scale. The concentration of endogenous opioids was determined using the ELISA. The concentration of met-enkephalin was higher in the group of patients with pruritus compared to the control group. Moreover, significantly lower levels of β-endorphin and dynorphin A were observed in the group of dialysis patients compared to the control group. In addition, a statistically significant difference was seen between the β-endorphin concentration in the group of dialysis patients with pruritus compared to the group without pruritus. The ratio of β-endorphin/dynorphin A concentrations was significantly lower in the group of patients with pruritus compared to patients without pruritus and the control group. No correlations were found between serum level of studied opioids and the severity of pruritus. The concentrations of the studied opioids did not correlate with the severity of pruritus. Observed opioid imbalance may affect the occurrence of CKD-aP in dialysis patients, but a thorough understanding of the mechanism of action of these substances in the sensation of pruritus is necessary to assess the possibility of finding a new therapeutic target.

Selected Aspects of the Intricate Background of Immune-Related Cholangiopathies-A Critical Overview

Primary biliary cholangitis (PBC), and primary sclerosing cholangitis (PSC) are rare immune-related cholangiopathies with still poorly explained pathogenesis. Although triggers of chronic inflammation with subsequent fibrosis that affect cholangiocytes leading to obliteration of bile ducts and conversion to liver cirrhosis are unclear, both disorders are regarded to be multifactorial. Different factors can contribute to the development of hepatocellular injury in the course of progressive cholestasis, including (1) body accumulation of bile acids and their toxicity, (2) decreased food intake and nutrient absorption, (3) gut microbiota transformation, and (4) reorganized host metabolism. Growing evidence suggests that intestinal microbiome composition not only can be altered by liver dysfunction, but in turn, it actively impacts hepatic conditions. In this review, we highlight the role of key factors such as the gut-liver axis, intestinal barrier integrity, bile acid synthesis and circulation, and microbiome composition, which seem to be strongly related to PBC and PSC outcome. Emerging treatments and future therapeutic strategies are also presented.

Pruritus in Chronic Liver Disease

Pruritus can be associated with chronic liver disease, particularly cholestatic liver disease. Although the pathophysiology is uncertain, there are a few proposed mechanisms and much is still being discovered. Workup involves an assessment to rule out a dermatologic, neurologic, psychogenic, or other underlying systemic disorder. First-line therapy is cholestyramine, which is generally well tolerated and effective. In those who fail cholestyramine, alternative drugs including rifampicin and μ-opioid receptor antagonists can be considered. If medical therapy is ineffective and pruritus is significant, alternative experimental therapies such as albumin dialysis, photopheresis, plasmapheresis, and biliary diversion can be considered.

Mechanisms of pruritus in cholestasis: understanding and treating the itch

Pruritus in cholestatic liver diseases can be a major burden and dramatically impair the quality of life of those affected. Here, we provide an update on the latest insights into the molecular pathogenesis of and novel therapeutic approaches for cholestasis-associated itch. Endogenous and exogenous small-molecule pruritogen candidates bind to their receptors on unmyelinated itch C-fibres in the skin. Candidate pruritogens in cholestasis include certain lysophospholipids and sulfated progesterone metabolites, among others, whereas total bile acid or bilirubin conjugates seem unlikely to have a dominant role in the pathogenesis of cholestasis-associated pruritus. Transmission of itch signals via primary, secondary and tertiary itch neurons to the postcentral gyrus and activation of scratch responses offer various targets for therapeutic intervention. At present, evidence-based treatment options for pruritus in fibrosing cholangiopathies, such as primary biliary cholangitis and primary sclerosing cholangitis, are the peroxisome proliferator-associated receptor (PPAR) agonist bezafibrate and the pregnane X receptor (PXR) agonist rifampicin. In pruritus of intrahepatic cholestasis of pregnancy, ursodeoxycholic acid is recommended and might be supported in the third trimester by rifampicin if needed. Alternatively, non-absorbable anion exchange resins, such as cholestyramine, can be administered, albeit with poor trial evidence. Liver transplantation for intolerable refractory pruritus has become an extremely rare therapeutic strategy.

Evaluation and Management of Pruritus in Primary Biliary Cholangitis

Chronic pruritus is a classic symptom in patients with primary biliary cholangitis. It affects up to two-thirds of patients in the course of the disease. Efficient therapy consists of topical treatment combined with systemic options such as anion exchangers, rifampicin, bezafibrate, μ-opioid receptor antagonists, selective-serotonin receptor uptake inhibitors, and gabapentinoids. Future therapeutic approaches may contain the selective blockade of the enterohepatic cycle by inhibiting the ileal bile acid transporter, the agonism at κ-opioid receptors, and antagonism of the mas-related G protein-coupled receptor X4. As nondrug treatment, ultraviolet B therapy, albumin dialysis, and biliary drainage are available at specialized centers.

In vitro models for investigating itch

Itch (pruritus) is a sensation that drives a desire to scratch, a behavior observed in many animals. Although generally short-lasting and not causing harm, there are several pathological conditions where chronic itch is a hallmark symptom and in which prolonged scratching can induce damage. Finding medications to counteract the sensation of chronic itch has proven difficult due to the molecular complexity that involves a multitude of triggers, receptors and signaling pathways between skin, immune and nerve cells. While much has been learned about pruritus from in vivo animal models, they have limitations that corroborate the necessity for a transition to more human disease-like models. Also, reducing animal use should be encouraged in research. However, conducting human in vivo experiments can also be ethically challenging. Thus, there is a clear need for surrogate models to be used in pre-clinical investigation of the mechanisms of itch. Most in vitro models used for itch research focus on the use of known pruritogens. For this, sensory neurons and different types of skin and/or immune cells are stimulated in 2D or 3D co-culture, and factors such as neurotransmitter or cytokine release can be measured. There are however limitations of such simplistic in vitro models. For example, not all naturally occurring cell types are present and there is also no connection to the itch-sensing organ, the central nervous system (CNS). Nevertheless, in vitro models offer a chance to investigate otherwise inaccessible specific cell–cell interactions and molecular pathways. In recent years, stem cell-based approaches and human primary cells have emerged as viable alternatives to standard cell lines or animal tissue. As in vitro models have increased in their complexity, further opportunities for more elaborated means of investigating itch have been developed. In this review, we introduce the latest concepts of itch and discuss the advantages and limitations of current in vitro models, which provide valuable contributions to pruritus research and might help to meet the unmet clinical need for more refined anti-pruritic substances.

Serum Bile Acid Profiling and Mixed Model Analysis Reveal Biomarkers Associated with Pruritus Reduction in Maralixibat-Treated Patients with BSEP Deficiency

Progressive familial intrahepatic cholestasis (PFIC) is a debilitating disease manifest by severe cholestasis, intractable pruritus and growth delay that ultimately leads to liver failure or transplantation. Maralixibat (MRX) was recently approved for the treatment of cholestatic pruritus in patients with Alagille syndrome. The aim of this study was to determine whether specific changes in the composition of the serum bile acid metabolome could predict pruritus response to treatment. Serum BAs (sBA) and 7α-hydroxy-4-cholesten-3-one (7α-C4), a surrogate marker of BA synthesis, were monitored by ultrahigh-performance liquid chromatography coupled with tandem mass spectrometry over 72 weeks in PFIC patients with mild to moderate non-truncating bile salt export pump (BSEP) mutations (n = 19) treated with MRX. The weekly itch reported outcome observer (ItchRO[Obs]) score measured pruritus severity. Linear mixed models (LMM) were applied to explore the effects of individual sBA profiles and their relationship to pruritus response. Changes in the composition of sBA correlated with pruritus improvement. Notably, the trajectory of serum total and individual BA species and 7α-C4 were significantly associated with ItchRO[Obs] score (p < 0.05). These results reveal that beyond simple total sBA concentrations, specific changes to the BA metabolome are associated with pruritus reduction in patients with BSEP deficiency, thus providing further insight into causal relationship of bile acids and pruritus.

Guidelines for the Management of Cholestatic Liver Diseases (2021)

In 2015, the Chinese Society of Hepatology and the Chinese Society of Gastroenterology issued a consensus statement on the diagnosis and management of cholestatic liver diseases. More clinical data on this topic have appeared during recent years. The Autoimmune Liver Disease Group of the Chinese Society of Hepatology organized an expert group to review recent evidence and provide an update to these previous guidelines. Herein, we provide 22 recommendations as a working reference for the management of cholestatic liver diseases by clinical practitioners.

Acupuncture for the Treatment of Itch: Peripheral and Central Mechanisms

Despite the widespread clinical use of acupuncture in the treatment of pruritus caused by psoriasis, urticaria, uremic, and other diseases, insights into the mechanism of action of acupuncture are still emerging. For the above reasons, a beneficial effect of acupuncture on pruritus was not recommended or reported in recent clinical practice guidelines. Acupuncture is a kind of physical stimulation, which has the characteristics of multi-channel and multi-target effects. The biomechanical stimulation signal of acupuncture needling can be transformed into bioelectric and chemical signals; interfere with kinds of cells and nerve fibers in the skin and muscle; alter signaling pathways and transcriptional activity of cells, mediators, and receptors; and result in inhibition of peripheral and central transmission of pruritus. Available mechanistic data give insights into the biological regulation potency of acupuncture for pruritus and provide a basis for more in-depth and comprehensive mechanism research.

Doxycycline-induced cholestatic liver injury

Doxycycline-induced liver injury is a rare phenomenon, with an unclear clinical course and etiopathogenesis. The onset of injury may be acute-to-subacute, with a pattern ranging from hepatocellular or cholestatic to mixed, and it often lasts up to several weeks. We present a case of cholestatic liver injury secondary to doxycycline use in a middle-aged woman. In patients with a history of doxycycline exposure and subsequent hepatic injury, an adverse drug reaction due to doxycycline should remain on the differential, and immediate removal of the offending agent with close monitoring of the clinical condition should be pursued.