Cyp3a11 is not essential for the formation of murine bile acids

Humans and mice differ substantially in their bile acid profiles as mice in addition to cholic acid (CA) predominantly synthesize 6β-hydroxylated muricholic acids (MCAs) whereas humans produces chenodeoxycholic acid (CDCA) and CA as primary bile acids. Identifying the gene performing 6β-hydroxylation would be useful for ‘humanizing’ the bile acid profile in mice for studies of the interaction between bile acids, gut microbiota, and host metabolism. We investigated the formation of MCAs in primary murine hepatocytes and found that αMCA is synthesized from CDCA and βMCA from UDCA. It is commonly assumed that the P450-enzyme CYP3A11 catalyzes 6β-hydroxylation of bile acids, thus we hypothesized that mice without the Cyp3a11 gene would lack MCAs. To test this hypothesis, we analyzed bile acid profiles in Cyp3a deficient mice, which lack 7 genes in the Cyp3a gene cluster including Cyp3a11, and compared them with wild-type littermate controls. Bile acid composition in liver, gallbladder, caecum and serum from Cyp3a knock out mice and wild-type littermate controls was analyzed with UPLC-MS/MS and revealed no major differences in bile acid composition. We conclude that Cyp3a11 is not necessary for 6β-hydroxylation and the formation of MCAs

Deficiency of SARS-CoV-2 T-cell responses after vaccination in long-term allo-HSCT survivors translates into abated humoral immunity

Recipients of allogeneic hematopoietic stem cell transplantation (allo-HSCT) for hematological diseases are at risk of severe disease and death from COVID-19. To determine the safety and immunogenicity of BNT162b2 and mRNA-1273 COVID-19 vaccines, samples from 50 infection-naive allo-HSCT recipients (median, 92 months from transplantation, range, 7-340 months) and 39 healthy controls were analyzed for serum immunoglobulin G (IgG) against the receptor binding domain (RBD) within spike 1 (S1) of severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2; anti–RBD-S1 IgG) and for SARS-CoV-2–specific T-cell immunity, reflected by induction of T-cell–derived interferon-g in whole blood stimulated ex vivo with 15-mer SI-spanning peptides with 11 amino acid overlap S1-spanning peptides. The rate of seroconversion was not significantly lower in allo-transplanted patients than in controls with 24% (12/50) and 6% (3/50) of patients remaining seronegative after the first and second vaccination, respectively. However, 58% of transplanted patients lacked T-cell responses against S1 peptides after 1 vaccination compared with 19% of controls (odds ratio [OR] 0.17; P 5 .009, Fisher’s exact test) with a similar trend after the second vaccination where 28% of patients were devoid of detectable specific T-cell immunity, compared with 6% of controls (OR 0.18; P 5 .02, Fisher’s exact test). Importantly, lack of T-cell reactivity to S1 peptides after vaccination heralded substandard levels (,100 BAU/mL) of anti–RBD-S1 IgG 5 to 6 months after the second vaccine dose (OR 8.2; P 5 .007, Fisher’s exact test). We conclude that although allo-HSCT recipients achieve serum anti–RBD-S1 IgG against SARS-CoV-2 after 2 vaccinations, a deficiency of SARS-CoV-2–specific T-cell immunity may subsequently translate into insufficient humoral responses

Understanding the molecular mechanisms of bile acid receptor activation for the treatment of human liver disease

Farnesoid X receptor (FXR) is a nuclear transcription factor that is activated by bile acids and regulates bile acid homeostasis, glucose and lipid metabolism. FXR activation by a ligand has been identified as a therapeutic modality for a range of liver and metabolic diseases. Although bile acids and FXR are known to be key players in the interplay between the liver, gastrointestinal tract, lipid and glucose metabolism, the interactions are complex and not well understood. To date, FXR activation studies to decipher the underlying molecular mechanisms of its action have almost exclusively been conducted in mouse models, which are of limited human relevance due to interspecies differences between mice and humans in bile acid composition, metabolism and FXR activation patterns. Looking at bile acid homeostasis from another angle; the apical sodium-dependent bile acid transporter (ASBT; also known as ileal bile acid transporter (IBAT)) is an important FXR target gene and it is pivotal for the physiological reabsorption of conjugated bile acids from the ileum back to the liver. IBAT inhibition results in an increased bile acid load in the colon and subsequently a lower bile acid pool. To date, IBAT inhibitors have been used in animal models for the treatment of non-alcoholic steatohepatitis (NASH), and in humans they have been sparsely tested in clinical trials for the treatment of chronic constipation and severe itch that is associated with cholestatic liver diseases, such as primary biliary cholangitis (PBC) and pediatric liver disease. Paper I presents a prospective open-label phase IIa pilot study with IBAT inhibitor A4250 to assess the safety and efficacy of this compound in alleviating itch in patients with PBC. In this study, 10 patients with PBC were treated with A4250 for four weeks. Despite some subjective improvements in pruritus severity, the study needed to be stopped prematurely because of abdominal side effects. Paper II examines how the FXR agonist obeticholic acid (OCA) may increase the risk of gallstone formation in susceptible patients. In this randomized, double-blinded placebo control trial Obeticholic Acid in Gallstone Surgery (OCAGS), 20 patients were randomised to either OCA 25 mg/day or a matching placebo for 3 weeks prior to undergoing a laparoscopic cholecystectomy. Bile acids, fibroblast growth factor 19 (FGF19) and lipids were measured both in serum and gallbladder bile before and after treatment. The index of cholesterol saturation and bile acid pool hydrophobicity were calculated and both were higher in the OCA treated group, implying a higher risk of cholelithiasis. Gene analysis suggested a biliary origin of FGF19. We concluded that treatment with OCA leads to a higher risk of gallstone formation. Paper III investigates how bile acids and FXR interactions modulate metabolic phenotypes in humans. In this double-blinded randomized control trial Obeticholic Acid in Bariatric Surgery & Gallstone Surgery OCABSGS, we explored the effects of FXR activation on bile acid turnover. We found by performing ChIP-Seq that the expression of FXR-DNA binding sites was not related to OCA-treatment; rather, it seems to be predetermined by the phenotype (obese vs non-obese). In contrast, RNA-Seq indicated induction of FXR target genes by OCA as compared to placebo. In conclusion, our experiments explore a novel treatment modality for pruritus patients with cholestatic liver disease. However, given the side effects, the clinical applicability of this compound is doubtful. Our studies also offer a unique insight into gallbladder pathophysiology and the mechanisms leading to the formation of gallstones in susceptible populations during treatment with FXR agonists. We have also shown that FXR transcriptional signalling in human DNA is altered in the obese phenotype, which may underlie aberrant metabolism and liver function in obesity

Advancements in Vaccine Strategies for Chronic Liver Disease Patients: Navigating Post-COVID Challenges and Opportunities

This review addresses the vital role of vaccinations in managing patients with chronic liver disease (CLD), especially in the context of the post-COVID-19 landscape. The pandemic has highlighted the unique vulnerabilities of CLD patients, including those awaiting liver transplantation and post-transplant individuals, who face heightened risks of infection due to compromised immune responses. Recent advancements in vaccine technology, such as mRNA platforms, novel adjuvants, and advanced delivery systems, have significantly accelerated vaccine development, enhancing both speed and efficacy. Moreover, the emergence of personalized vaccines, tailored to everyone’s unique immunological profile, presents new opportunities, particularly for those with chronic conditions. This review synthesizes the current state of evidence regarding vaccine recommendations for CLD patients, focusing on their response to vaccinations and proposing effective strategies to protect this vulnerable group from vaccine-preventable diseases. It also explores the challenges in implementing these strategies and considers the impact of emerging vaccine delivery systems on improving outcomes for CLD patients. The paper aims to provide nuanced guidance on vaccination in the rapidly evolving healthcare landscape, addressing both technological innovations and comprehensive patient care strategies

Ileal Bile Acid Transporter Inhibition for the Treatment of Chronic Constipation, Cholestatic Pruritus, and NASH

Bile acids are synthesized from cholesterol in the liver, excreted with bile into the duodenum, almost completely taken up again in the distal ileum and finally returned to the liver with portal blood in a process termed enterohepatic circulation. Bile acid synthesis, excretion, and reuptake are tightly regulated. The apical sodium-dependent bile acid transporter [ASBT; also known as ileal bile acid transporter (IBAT) and SLC10A2] is pivotal for the almost complete reabsorption of conjugated bile acids in the ileum. Dysfunctional IBAT may be the cause of bile acid diarrhea. Pharmacological IBAT inhibition results in an increased bile acid load in the colon and subsequently a lower bile acid pool, which is associated with improved liver histology in animal models of cholestatic liver disease and non-alcoholic steatohepatitis (NASH). In humans, IBAT inhibitors have been tested in clinical trials with widely different indications: in patients with idiopathic chronic constipation, an increased number of bowel movements was observed. In adult and pediatric cholestatic liver diseases with pruritus, various IBAT inhibitors showed potential to improve itching. Adverse events of IBAT inhibitors, based on their mode of action, are abdominal pain and diarrhea which might patients to withdraw from study medications. So far, no data are available of a study of IBAT inhibitors in patients with NASH. In this review we summarize the preclinical and most recent clinical studies with various IBAT inhibitors and discuss the difficulties that should be addressed in future studies

Pilot study with IBAT inhibitor A4250 for the treatment of cholestatic pruritus in primary biliary cholangitis

Pruritus is a common complication of cholestatic liver diseases. Inhibition of the ileal bile acid transporter (IBAT/ASBT) may emerge as treatment option. Our aim was to assess tolerability and effect on pruritus of the selective IBAT inhibitor A4250 in patients with primary biliary cholangitis (PBC). Ten patients with PBC and bile acid sequestrant treatment of cholestatic pruritus were after a two-week wash out of the bile acid sequestrant treated with either 0.75 mg (n = 4) or 1.5 mg (n = 5) of A4250 for four weeks. Patients' pruritus was assessed by Visual Analogue Scale (VAS), 5-D itch scale and the pruritus module of the PBC40 questionnaire. Plasma bile acids and 7α-hydroxy-4-cholesten-3-one were measured by UPLC-MS/MS, plasma fibroblast growth factor 19 by ELISA, and serum autotaxin activity by homemade assay. All nine patients exposed to A4250 reported a remarkable improvement in pruritus, until none or mild according to 5-D itch, VAS and PBC40 pruritus. Five patients finished the study prematurely due to abdominal pain (5/5) and diarrhoea (4/5). The high incidence of probably bile acid malabsorption-related diarrhoea and abdominal pain in the bile acid sequestrant pre-Treated population indicates that the start dose of A4250 may have been too high for adult patients