ABCB11 deficiency presenting as transient neonatal cholestasis: Correlation with genotypes and BSEP expression

Fluorescence-based methods for studying activity and drug-drug interactions of hepatic solute carrier and ATP binding cassette proteins involved in ADME-Tox

In humans, approximately 70% of drugs are eliminated through the liver. This process is governed by the concerted action of membrane transporters and metabolic enzymes. Transporters mediating hepatocellular uptake of drugs belong to the SLC (Solute carrier) superfamily of transporters. Drug efflux either toward the portal vein or into the bile is mainly mediated by active transporters of the ABC (ATP Binding Cassette) family. Alteration in the function and/or expression of liver transporters due to mutations, disease conditions, or co-administration of drugs or food components can result in altered pharmacokinetics. On the other hand, drugs or food components interacting with liver transporters may also interfere with liver function (e.g., bile acid homeostasis) and may even cause liver toxicity. Accordingly, certain transporters of the liver should be investigated already at an early stage of drug development. Most frequently radioactive probes are applied in these drug-transporter interaction tests. However, fluorescent probes are cost-effective and sensitive alternatives to radioligands, and are gaining wider application in drug-transporter interaction tests. In our review, we summarize our current understanding about hepatocyte ABC and SLC transporters affected by drug interactions. We provide an update of the available fluorescent and fluorogenic/activable probes applicable in in vitro or in vivo testing of these ABC and SLC transporters, including near-infrared transporter probes especially suitable for in vivo imaging. Furthermore, our review gives a comprehensive overview of the available fluorescence-based methods, not directly relying on the transport of the probe, suitable for the investigation of hepatic ABC or SLC-type drug transporters.

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.

Role of Drug Transporters in Elucidating Inter-Individual Variability in Pediatric Chemotherapy-Related Toxicities and Response

Pediatric cancer treatment has evolved significantly in recent decades. The implementation of risk stratification strategies and the selection of evidence-based chemotherapy combinations have improved survival outcomes. However, there is large interindividual variability in terms of chemotherapy-related toxicities and, sometimes, the response among this population. This variability is partly attributed to the functional variability of drug-metabolizing enzymes (DME) and drug transporters (DTS) involved in the process of absorption, distribution, metabolism and excretion (ADME). The DTS, being ubiquitous, affects drug disposition across membranes and has relevance in determining chemotherapy response in pediatric cancer patients. Among the factors affecting DTS function, ontogeny or maturation is important in the pediatric population. In this narrative review, we describe the role of drug uptake/efflux transporters in defining pediatric chemotherapy-treatment-related toxicities and responses. Developmental differences in DTS and the consequent implications are also briefly discussed for the most commonly used chemotherapeutic drugs in the pediatric population.

Overview of Progressive Familial Intrahepatic Cholestasis

Bile acid transport is a complex physiologic process, of which disruption at any step can lead to progressive intrahepatic cholestasis (PFIC). The first described PFIC disorders were originally named as such before identification of a genetic cause. However, advances in clinical molecular genetics have led to the identification of additional disorders that can cause these monogenic inherited cholestasis syndromes, and they are now increasingly referred to by the affected protein causing disease. The list of PFIC disorders is expected to grow as more causative genes are discovered. Here forth, we present a comprehensive overview of known PFIC disorders.

MYO5B-associated diseases: Novel liver-related variants and genotype-phenotype correlation

BACKGROUND & AIMS

Biallelic pathogenic variants in MYO5B cause microvillus inclusion disease (MVID), or familial intrahepatic cholestasis (FIC). The reported FIC patients are scarce and so the genotype-phenotype correlation has not been fully characterised. This study aimed to report more MYO5B-associated FIC patients and correlate genotypes to phenotypes in more detail.

METHODS

The phenotype and genetic data of 12 newly diagnosed MYO5B-associated (including 11 FIC) patients, as well as 118 previously reported patients with available genotypes, were summarised. Only patients with biallelic MYO5B variants were enrolled. Nonsense, frameshift, canonical splice sites, initiation codon loss, and single exon or multiexon deletion were defined as null MYO5B variants.

RESULTS

Phenotypically, 50 were isolated MVID, 47 involved both liver and intestine (combined), and 33 were isolated FIC (9 persistent, 15 recurrent, 3 transient, and 6 un-sub-classified) patients. The severity of intestinal manifestation was positively correlated to an increased number of null variants (ρ = 0.299, P = .001). All FIC patients carried at least one non-null variant, and the severity of cholestasis was correlated to the presence of a null variant (ρ = 0.420, P = .029). The proportion of FIC patients (16/29, 55%) harbouring missense/in-frame variants affecting the non-motor regions of MYO5B was significantly higher than that of MVID (3/25, 12%, P = .001) and combined patients (3/31, 10%, P = .000). 10 of the 29 FIC patients harboured missense/in-frame variants at the IQ motifs comparing to none in the 56 MVID and combined patients (P = .000).

CONCLUSIONS

The phenotype of MYO5B deficiency was associated with MYO5B genotypes, the nullity or the domain affected.

Recent updates on progressive familial intrahepatic cholestasis types 1, 2 and 3: Outcome and therapeutic strategies

Recent evidence points towards the role of genotype to understand the phenotype, predict the natural course and long term outcome of patients with progressive familial intrahepatic cholestasis (PFIC). Expanded role of the heterozygous transporter defects presenting late needs to be suspected and identified. Treatment of pruritus, nutritional rehabilitation, prevention of fibrosis progression and liver transplantation (LT) in those with end stage liver disease form the crux of the treatment. LT in PFIC has its own unique issues like high rates of intractable diarrhoea, growth failure; steatohepatitis and graft failure in PFIC1 and antibody-mediated bile salt export pump deficiency in PFIC2. Drugs inhibiting apical sodium-dependent bile transporter and adenovirus-associated vector mediated gene therapy hold promise for future.

Identification of ABCC5 Among ATP-Binding Cassette Transporter Family as a New Biomarker for Hepatocellular Carcinoma Based on Bioinformatics Analysis

Purpose

Liver cancer is the fifth most common type of cancer worldwide, and the ATP-binding cassette (ABC) transporter family has been widely accepted as a cause of multidrug resistance. This study was conducted to explore the potential value and mechanisms of the ABC transporter gene family in the liver hepatocellular carcinoma (LIHC).

Materials and Methods

Data were collected from different public databases. UALCAN, ONCOMINE, and GEPIA were used to retrieve a selection of differently expressed and pathological stage-related genes among the ABC family. Principal component analysis (PCA) was utilized for grouping, and its prognostic value was evaluated by univariate and multivariate Cox analyses. The co-expression pattern was constructed with UALCAN, and the functional analyses were carried out with DAVID. The correlation between the biomarker and immune infiltration, genetic alteration frequency, and drug sensitivity were explored with TIMER, cBioPortal, GDSC and CTRP, respectively. Finally, tSNE algorithm was used to explore the distribution of ABCC5 expressed cells.

Results

Among the ABC transporter family members, ABCC5 was differently expressed and strongly related to the pathological stage of LIHC. PCA divided patients of LIHC into two groups, and Cox analyses demonstrated that ABCC5 was an independent risk factor of LIHC. Functional analyses indicated that the genes were enriched in the pathways of transmembrane transporter, ATPase activity, and bile secretion. ABCC5 is also associated with immune infiltration of cells like macrophages, neutrophils, and dendritic cells. The genetic alteration frequency of ABCC5 confirmed its potential value in LIHC. In addition, several drugs were explored and found to be relevant to LIHC. The t-SNE showed that expression of ABCC5 was most concentrated in macrophages, followed by hepatocytes.

Conclusion

ABCC5 may facilitate LIHC progression through different mechanisms and be a potential biomarker and target for diagnosis, prognosis, and therapy of LIHC.

Combined Mutations of Canalicular Transporter Proteins Causing Low Phospholipid-Associated Cholelithiasis and Transient Neonatal Cholestasis in an Infant

Low phospholipid-associated cholelithiasis syndrome is characterized by the development of cholelithiasis in early adulthood (<40 years of age) but is rarely diagnosed in childhood. It is associated with gene sequence variants in the ABCB4 gene encoding the multidrug resistance protein 3 which are mostly heterozygous. Transient neonatal cholestasis has been reported with heterozygous mutations in both ABCB4 and ABCB11 (Bile Salt Exporter Protein). We report a 3-month-old male with cholelithiasis and transient neonatal cholestasis in the setting of combined pathogenic heterozygous mutations in the genes ABCB4 and ABCB11. Initiation of ursodeoxycholic acid therapy led to a resolution of the cholestasis and gall stones. Our case highlights the complex nature of the genetics of cholestatic disorders.