Bruno Hagenbuch

Human induced pluripotent stem cells (hiPSCs) possess broad differentiation potential; however, efficient maturation into functional hepatocytes remains challenging, in part because conventional differentiation strategies rely on 2D culture or partially defined 3D systems that fail to recapitulate key developmental microenvironmental cues. Although 3D culture has been shown to promote hepatic specification and maturation, a fully defined platform that supports the entire differentiation process from hiPSCs in 3D has not been established. Here, we report a scalable synthetic peptide hydrogel (PepGel) platform that enables hiPSCs to self-organize into long-term, proliferative luminal cavity (LC) architectures within 3D colonies (LC-hiPSCs). These LC-hiPSCs exhibited markedly enhanced differentiation efficiency compared to hiPSC aggregates generated via scaffold-free suspension methods. Using a shear-thinning, self-healing hydrogel configuration optimized for suspension culture, we produced large quantities of LC-hiPSCs and directed their differentiation into PepGel-derived hiPSC-derived hepatocyte-like cells (PG-hiHs). PG-hiHs formed polarized, multi-luminal organoid-like structures and exhibited robust expression of hepatocyte-specific genes and proteins, high cytochrome P450 activity, and in vitro metabolic functions comparable to primary human hepatocytes (PHHs). Following live shipment and transplantation into immunocompromised mouse livers, PG-hiHs engrafted efficiently and maintained human-specific albumin and alpha-1 antitrypsin secretion at PHH-equivalent levels. Furthermore, both LC-hiPSCs and PG-hiHs retained viability, structural organization, and phenotype in complex 3D bioprinted constructs for at least 14 days. Together, this work establishes a fully defined, reproducible, and scalable 3D platform that supports the entire differentiation process, overcoming limitations in hiPSC-derived hepatic maturation and enables physiologically relevant hepatocyte-like tissues for disease modeling, regenerative medicine, and biofabrication.

The Concise Guide to Pharmacology 2025/26 marks the seventh edition in this series of biennial publications in the British Journal of Pharmacology. Presented in landscape format, the guide provides a comparative overview of the pharmacology of drug target families. The concise nature of the Concise Guide refers to the style of presentation, being clear, accessible, and well‐structured, rather than the scope of the content, which spans approximately 500 pages. The Concise Guide summarises the key pharmacological properties of around 1900 human drug targets, and nearly 7000 interactions, involving around 4400 ligands. While the content is a substantially condensed version of the more detailed information and links available at the www.guidetopharmacology.org website, the printed guide serves as a permanent, citable, point‐in‐time record, that remains stable despite ongoing updates to the online database. The full contents of this publication can be found at https://bpspubs.onlinelibrary.wiley.com/doi/10.1111/bph.70235 . The Concise Guides provide expert‐curated recommendations of ‘Gold Standard’ selective pharmacological tools, available either commercially or as donations, which enable the identification of individual drug targets or families of drug targets. While the Concise Guide offers a more streamlined overview, more comprehensive information, including detailed pharmacological profiles and links to multiple online databases, is available through the Guide to Pharmacology website. The 2025/26 edition of the Concise Guide is based on material current as of mid‐2025, and supersedes all previous editions, including the 2023/24 Guide, and earlier Guides to Receptors and Channels. It is produced in close conjunction with the Nomenclature and Standards Committee of the International Union of Basic and Clinical Pharmacology (NC‐IUPHAR), and as such provides official IUPHAR classification and nomenclature for human drug targets, where applicable. Transporters are one of the six major pharmacological targets into which the Guide is divided, with the others being: G protein‐coupled receptors, ion channels, nuclear hormone receptors, catalytic receptors and enzymes. Each section includes nomenclature guidance, concise summaries, information of the best available pharmacological tools, key references, and suggestions for further reading.

In the human Na ⁺ /taurocholate cotransporting polypeptide (NTCP), several non‐synonymous SNPs are known to have positive or negative medical consequences, and hundreds more are “variants of unknown significance.” One reason outcomes remain unknown is that computational predictions are not yet reliable. Such predictions are especially problematic for “rheostat” positions, where amino acid substitutions have widely varied outcomes. We previously predicted that NTCP contains multiple rheostat positions for substrate transport. To test this, we selected two positions that—by classical assumptions—would not be rheostat positions. Position G102 is highly conserved and buried deep in the substrate channel; as such, most substitutions are expected to be catastrophic. In contrast, position Y146 is non‐conserved with a solvent‐exposed side chain near the channel opening; thus, most substitutions are expected to be well‐tolerated. At each position, we made all 19 substitutions and assessed the effects on substrate transport and cell surface expression. Position G102 tolerated more substitutions than expected and acted as a rheostat position for both parameters; nevertheless, correlations with side chain properties showed that glycine best met the simultaneous and different requirements of surface expression and substrate transport. While most substitutions at position Y146 were neutral, two substitutions unexpectedly abolished cellular expression. Along with previously studied rheostat positions 267 and 271, results suggest that the substrate channel of NTCP is lined with rheostat positions that contribute to multiple NTCP characteristics with pleiotropic effects. Thus, integrating contributions of rheostat positions to function and/or stability computations should improve prediction of NTCP substitution outcomes.

Background: We have previously demonstrated that the function and expression of the Na⁺/taurocholate cotransporting polypeptide (NTCP) and the organic cation transporter 1 (OCT1) are affected by increasing free or unesterified cholesterol in the plasma membrane by an acute incubation with cholesterol for 30 min. In the current study we wanted to extend these findings to a more chronic condition to mimic what would be seen in obese patients. Methods: We incubated HEK293 cells that stably express NTCP or OCT1 for 24 h with 0.05 mM cholesterol and determined their function by measuring uptake of radioactive taurocholate or MPP⁺. Expression at the plasma membrane was quantified with a biotinylation assay combined with Western blots. Results: Incubation with cholesterol increased the cholesterol content of the cells by about 2-fold. Transport mediated by NTCP and OCT1 was decreased. Membrane expression for both transporters showed a slight decrease, and when kinetics were normalized for the membrane expression, the V_max for NTCP-mediated taurocholate uptake slightly decreased, but the V_max and the capacity (V_max/K_m) for OCT1-mediated MPP⁺ uptake increased by 2.5-fold and 3-fold, respectively. Acyl-Coenzyme A acyltransferase inhibitors enhanced the decrease in transport function, potentially due to retention of more free cholesterol in the plasma membrane. Conclusions: Chronic increases in free cholesterol in the plasma membrane can result in increased or decreased transporter function and expression. In the case of OCT1, which is involved in the uptake of the anti-diabetic drug metformin into hepatocytes, the 3-fold increase in transport capacity might affect drug therapy.

Background: We have previously demonstrated that the function and expression of the Na+/taurocholate cotransporting polypeptide (NTCP) and the organic cation transporter 1 (OCT1) are affected by increasing free cholesterol in the plasma membrane by an acute incubation with cholesterol for 30 minutes. In the current study we wanted to extend these findings to a more chronic condition to mimic what would be seen in obese patients. Methods: We incubated HEK293 cells that stably express NTCP or OCT1 for 24 hours with 0.05 mM cholesterol and determined their function by measuring uptake of radioactive taurocholate or MPP+. Expression at the plasma membrane was quantified with a biotinylation assay combined with Western blots. Results: Incubation with cholesterol increased the cholesterol content of the cells by about 2-fold. Transport mediated by NTCP and OCT1 was decreased. Membrane expression for both transporters showed a slight decrease and when kinetics were normalized for the membrane expression, the Vmax for NTCP-mediated taurocholate uptake slightly decreased but the Vmax and the capacity (Vmax/Km) for OCT1-mediated MPP+ uptake increased by 2.5-fold and 3-fold, respectively. Acyl-Coenzyme A acyltransferase inhibitors enhanced the decrease in transport function, potentially due to retention of more free cholesterol in the plasma membrane. Conclusions: Chronic increases in free cholesterol in the plasma membrane can result in increased or decreased transporter function and expression. In the case of OCT1, which is involved in the uptake of the anti-diabetic drug metformin into hepatocytes, the 3-fold increase in transport capacity suggests that patients might benefit from dose adjustments.

Human organic anion transporting polypeptide 1B1 (OATP1B1) and 1B3 are two highly homologous liver-specific uptake transporters. However, 29,79-dichlorofluorescein (DCF) is preferably transported by OATP1B1. In the current study, the molecular mechanisms for the selective transport of DCF by OATP1B1 were investigated by constructing and characterizing an array of OATP1B1/1B3 chimeras and site-directed mutagenesis. Our results show that transmembrane domain 10 (TM10) is crucial for the surface expression and function of OATP1B1, in which Q541 and L545 play the most important roles in DCF transport. Replacement of TM10 in OATP1B1 with its OATP1B3 counterpart led to OATP1B19s complete intracellular retention. Q541 and L545 may interact with DCF directly via hydrogen bonding and hydrophobic interactions. The decrease of DCF uptake by Q541A and L545S was due to their reduced binding affinity for DCF as compared to OATP1B1. In addition, Q541 and L545 are also crucial for the transport of estradiol-17β-glucuronide (E17βG) but not for the transport of estrone-3-sulfate (E3S), indicating different interaction modes between DCF/E17βG and E3S in OATP1B1. Taken together, Q541 and L545 in TM10 are critical for OATP1B1-mediated DCF uptake, but their effect is substrate-dependent. Significance Statement The key transmembrane domains (TMs) and amino acid residues for the selective transport of DCF by OATP1B1 were identified. TM10 is crucial for the surface expression and function of OATP1B1. Within TM10, Q541 and L545 played the most significant roles and affected the function of OATP1B1 in a substrate-dependent manner. This information is crucial for a better understanding of the mechanism of the multispecificity of OATP1B1 and as a consequence the mechanism of OATP1B1-mediated drug-drug interactions.

Organic anion-transporting polypeptides (OATPs) 1B1 and 1B3 are two highly homologous transport proteins. However, OATP1B1- and 1B3-mediated estradiol-17β-glucuronide (E17βG) uptake can be differentially affected by clotrimazole. In this study, by functional characterization on chimeric transporters and single mutants, we find that G45 in transmembrane domain 1 (TM1) and V386 in TM8 are critical for the activation of OATP1B3-mediated E17βG uptake by clotrimazole. However, the effect of clotrimazole on the function of OATP1B3 is substrate-dependent as clotrimazole does not stimulate OATP1B3-mediated uptake of 4',5'-dibromofluorescein (DBF) and rosuvastatin. In addition, clotrimazole is not transported by OATP1B3, but it can efficiently permeate the plasma membrane due to its lipophilic properties. Homology modeling and molecular docking indicate that E17βG binds in a substrate binding pocket of OATP1B3 through hydrogen bonding and hydrophobic interactions, among which its sterol scaffold forms hydrophobic contacts with V386. In addition, a flexible glycine residue at position 45 is essential for the activation of OATP1B3. Finally, clotrimazole is predicted to bind at an allosteric site, which mainly consists of hydrophobic residues located at the cytoplasmic halves of TMs 4, 5, 10, and 11.