The functional interrelationship between gap junctions and fenestrae in endothelial cells of the liver organoid

On-Chip Construction of Liver Lobules with Self-Assembled Perfusable Hepatic Sinusoid Networks

Although various liver chips have been developed using emerging organ-on-a-chip techniques, it remains an enormous challenge to replicate the liver lobules with self-assembled perfusable hepatic sinusoid networks. Herein we develop a lifelike bionic liver lobule chip (LLC), on which the perfusable hepatic sinusoid networks are achieved using a microflow-guided angiogenesis methodology; additionally, during and after self-assembly, oxygen concentration is regulated to mimic physiologically dissolved levels supplied by actual hepatic arterioles and venules. This liver lobule design thereby produces more bionic liver microstructures, higher metabolic abilities, and longer lasting hepatocyte function than other liver-on-a-chip techniques that are able to deliver. We found that the flow through the unique micropillar design in the cell coculture zone guides the radiating assembly of the hepatic sinusoid, the oxygen concentration affects the morphology of the sinusoid by proliferation, and the oxygen gradient plays a key role in prolonging hepatocyte function. The expected breadth of applications our LLC is suited to is demonstrated by means of preliminarily testing chronic and acute hepatotoxicity of drugs and replicating growth of tumors in situ. This work provides new insights into designing more extensive bionic vascularized liver chips, while achieving longer lasting ex-vivo hepatocyte function.

Multichannel AC Biosusceptometry System to Map Biodistribution and Assess the Pharmacokinetic Profile of Magnetic Nanoparticles by Imaging

In this paper, the application of a technique to evaluate in vivo biodistribution of magnetic nanoparticles (MNP) is addressed: the Multichannel AC Biosusceptometry System (MC-ACB). It allows real-time assessment of magnetic nanoparticles in both bloodstream clearance and liver accumulation, where a complex network of inter-related cells is responsible for MNP uptake. Based on the acquired MC-ACB images, we propose a mathematical model which helps to understand the distribution and accumulation pharmacokinetics of MNP. The MC-ACB showed a high time resolution to detect and monitor MNP, providing sequential images over the particle biodistribution. Utilizing the MC-ACB instrument, we assessed regions corresponding to the heart and liver, and we determined the MNP transfer rates between the bloodstream and the liver. The pharmacokinetic model resulted in having a strong correlation with the experimental data, suggesting that the MC-ACB is a valuable and accessible imaging device to assess in vivo and real-time pharmacokinetic features of MNP.

Microfluidic-Based Multi-Organ Platforms for Drug Discovery

Development of predictive multi-organ models before implementing costly clinical trials is central for screening the toxicity, efficacy, and side effects of new therapeutic agents. Despite significant efforts that have been recently made to develop biomimetic in vitro tissue models, the clinical application of such platforms is still far from reality. Recent advances in physiologically-based pharmacokinetic and pharmacodynamic (PBPK-PD) modeling, micro- and nanotechnology, and in silico modeling have enabled single- and multi-organ platforms for investigation of new chemical agents and tissue-tissue interactions. This review provides an overview of the principles of designing microfluidic-based organ-on-chip models for drug testing and highlights current state-of-the-art in developing predictive multi-organ models for studying the cross-talk of interconnected organs. We further discuss the challenges associated with establishing a predictive body-on-chip (BOC) model such as the scaling, cell types, the common medium, and principles of the study design for characterizing the interaction of drugs with multiple targets.

In vivo delivery, pharmacokinetics, biodistribution and toxicity of iron oxide nanoparticles

Iron oxide nanoparticles (IONPs) have been extensively used during the last two decades, either as effective bio-imaging contrast agents or as carriers of biomolecules such as drugs, nucleic acids and peptides for controlled delivery to specific organs and tissues. Most of these novel applications require elaborate tuning of the physiochemical and surface properties of the IONPs. As new IONPs designs are envisioned, synergistic consideration of the body's innate biological barriers against the administered nanoparticles and the short and long-term side effects of the IONPs become even more essential. There are several important criteria (e.g. size and size-distribution, charge, coating molecules, and plasma protein adsorption) that can be effectively tuned to control the in vivo pharmacokinetics and biodistribution of the IONPs. This paper reviews these crucial parameters, in light of biological barriers in the body, and the latest IONPs design strategies used to overcome them. A careful review of the long-term biodistribution and side effects of the IONPs in relation to nanoparticle design is also given. While the discussions presented in this review are specific to IONPs, some of the information can be readily applied to other nanoparticle systems, such as gold, silver, silica, calcium phosphates and various polymers.

Transplantation of liver organoids in the omentum and kidney

Liver organoids were reconstructed by mouse-immortalized hepatocytes and nonparenchymal cells (sinusoidal endothelial cells and hepatic stellate cells) in a radial-flow bioreactor (RFB). A biodegradable apatite-fiber scaffold (AFS) was used as a scaffold packed in the RFB, which enables three-dimensional cell cultures. The organoids cocultured in the RFB showed a liver-like structure with high-density layers of hepatocytes and the formation of vessel-like structures. A liver organoid consisting of three cocultured cells was transplanted under the kidney capsule (kidney group) or into the omentum (omentum group) using BALB/c nude mice. Transplanted liver organoids survived in the kidney or omentum. The expression of mRNAs of albumin, connexin 26 and 32, hepatocyte nuclear factor 4α, and glucose-6-phosphatase was increased in both groups at 8 weeks after transplantation in comparison to the pretransplant status. Tyrosine aminotransferase appeared only in the omentum group. The results suggested that the functions of liver organoids differed depending on the transplanted site in the recipient animals.

Glomerular endothelial cell fenestrations: an integral component of the glomerular filtration barrier

Glomerular endothelial cell (GEnC) fenestrations are analogous to podocyte filtration slits, but their important contribution to the glomerular filtration barrier has not received corresponding attention. GEnC fenestrations are transcytoplasmic holes, specialized for their unique role as a prerequisite for filtration across the glomerular capillary wall. Glomerular filtration rate is dependent on the fractional area of the fenestrations and, through the glycocalyx they contain, GEnC fenestrations are important in restriction of protein passage. Hence, dysregulation of GEnC fenestrations may be associated with both renal failure and proteinuria, and the pathophysiological importance of GEnC fenestrations is well characterized in conditions such as preeclampsia. Recent evidence suggests a wider significance in repair of glomerular injury and in common, yet serious, conditions, including diabetic nephropathy. Study of endothelial cell fenestrations is challenging because of limited availability of suitable in vitro models and by the requirement for electron microscopy to image these sub-100-nm structures. However, extensive evidence, from glomerular development in rodents to in vitro studies in human GEnC, points to vascular endothelial growth factor (VEGF) as a key inducer of fenestrations. In systemic endothelial fenestrations, the intracellular pathways through which VEGF acts to induce fenestrations include a key role for the fenestral diaphragm protein plasmalemmal vesicle-associated protein-1 (PV-1). The role of PV-1 in GEnC is less clear, not least because of controversy over existence of GEnC fenestral diaphragms. In this article, the structure-function relationships of GEnC fenestrations will be evaluated in depth, their role in health and disease explored, and the outlook for future study and therapeutic implications of these peculiar structures will be approached.

Molecular mechanisms and therapeutic targets in steatosis and steatohepatitis

Steatosis of the liver may arise from a variety of conditions, but the molecular basis for lipid droplet formation is poorly understood. Although a certain amount of lipid storage may even be hepatoprotective, prolonged lipid storage can result in an activation of inflammatory reactions and loss of metabolic competency. Apart from drug-induced steatosis, certain metabolic disorders associated with obesity, insulin resistance, and hyperlipidemia give also rise to nonalcoholic fatty liver diseases (NAFLD). It is noteworthy that advanced stages of nonalcoholic hepatic steatosis and steatohepatitis (NASH) result ultimately in fibrosis and cirrhosis. In this regard, the lipid droplets (LDs) have been discovered to be metabolically highly active structures that play major roles in lipid transport, sorting, and signaling cascades. In particular, LDs maintain a dynamic communication with the endoplasmic reticulum (ER) and the plasma membrane via sphingolipid-enriched domains of the plasma membrane-the lipid rafts. These microdomains frequently harbor receptor tyrosine kinases and other signaling molecules and connect extracellular events with intracellular signaling cascades. Here, we review recent knowledge on the molecular mechanisms of drug and metabolically induced hepatic steatosis and its progression to steatohepatitis (NASH). The contribution of cytokines and other signaling molecules, as well as activity of nuclear receptors, lipids, transcription factors, and endocrine mediators toward cellular dysfunction and progression of steatotic liver disease to NASH is specifically addressed, as is the cross-talk of different cell types in the pathogenesis of NAFLD. Furthermore, we provide an overview of recent therapeutic approaches in NASH therapy and discuss new as well as putative targets for pharmacological interventions.

New insights into the dynamics of sinusoidal endothelial fenestrae in liver sinusoidal endothelial cells

Ultrastructural studies have shown that liver sinusoidal endothelial cells (LSECs) contain a cytoskeletal framework of filamentous actin, and that the presence of actin in the form of a calmodulin-actomyosin complex is responsible for regulation of the diameter of sinusoidal endothelial fenestrae (SEF). Rho has emerged as an important regulator of the actin cytoskeleton and consequently of cell morphology. We investigated actin filaments in relation to SEF in LSEC using heavy meromyosin decorated reaction and elucidated the roles of Rho and actin cytoskeleton in morphological and functional alterations of SEF. Second, according to intracytoplasmic Ca2+ concentration, plasma membrane Ca2+Mg2+-ATPase activities were clearly demonstrated on the outer surface of the labyrinth-like SEF in the isolated LSECs. Furthermore, by investigating intracytoplasmic Ca2+ concentration, we have demonstrated plasma membrane Ca2+Mg2+-ATPase activities on the outer surface of the labyrinth-like SEF in the isolated LSECs. Currently, the majority of fenestral studies are focused on finding ways to increase the liver sieve's porosity, which is reduced through pathological mechanisms.