Storming the gate: New approaches for targeting the dynamic tight junction for improved drug delivery

A short guide to the tight junction

Tight junctions (TJs) are specialized regions of contact between cells of epithelial and endothelial tissues that form selective semipermeable paracellular barriers that establish and maintain body compartments with different fluid compositions. As such, the formation of TJs represents a critical step in metazoan evolution, allowing the formation of multicompartmental organisms and true, barrier-forming epithelia and endothelia. In the six decades that have passed since the first observations of TJs by transmission electron microscopy, much progress has been made in understanding the structure, function, molecular composition and regulation of TJs. The goal of this Perspective is to highlight the key concepts that have emerged through this research and the future challenges that lie ahead for the field.

Evaluation of Drug Blood-Brain-Barrier Permeability Using a Microfluidic Chip

The blood-brain-barrier (BBB) is made up of blood vessels whose permeability enables the passage of some compounds. A predictive model of BBB permeability is important in the early stages of drug development. The predicted BBB permeabilities of drugs have been confirmed using a variety of in vitro methods to reduce the quantities of drug candidates needed in preclinical and clinical trials. Most prior studies have relied on animal or cell-culture models, which do not fully recapitulate the human BBB. The development of microfluidic models of human-derived BBB cells could address this issue. We analyzed a model for predicting BBB permeability using the Emulate BBB-on-a-chip machine. Ten compounds were evaluated, and their permeabilities were estimated. Our study demonstrated that the permeability trends of ten compounds in our microfluidic-based system resembled those observed in previous animal and cell-based experiments. Furthermore, we established a general correlation between the partition coefficient (Kp) and the apparent permeability (Papp). In conclusion, we introduced a new paradigm for predicting BBB permeability using microfluidic-based systems.

Tight junction proteins and biliary diseases

PURPOSE OF REVIEW

In the pathophysiological context of cholangiopathies and more broadly of hepatopathies, while it is conceptually clear that the maintenance of inter-cholangiocyte and inter-hepatocyte tight junction integrity would be crucial for liver protection, only scarce studies have been devoted to this topic. Indeed, in the liver, alteration of tight junctions, the intercellular adhesion complexes that control paracellular permeability would result in leaky bile ducts and bile canaliculi, allowing bile reflux towards hepatic parenchyma, contributing to injury during the disease process.

RECENT FINDINGS

Last decades have provided a great deal of information regarding both tight junction structural organization and signaling pathways related to tight junctions, providing clues about potential intervention to modulate paracellular permeability during cholangiopathies pathogenesis. Interestingly, several liver diseases have been reported to be associated with abnormal expression of one or several tight junction proteins. However, the question remains unanswered if these alterations would be primarily involved in the disease pathogenesis or if they would occur secondarily in the pathological course.

SUMMARY

In this review, we provide an overview of tight junction disruptions described in various biliary diseases that should pave the way for defining new therapeutic targets in this field.

Nanotechnology for enhanced nose-to-brain drug delivery in treating neurological diseases

Despite the increasing global incidence of brain disorders, achieving sufficient delivery towards the central nervous system (CNS) remains a formidable challenge in terms of translating into improved clinical outcomes. The brain is highly safeguarded by physiological barriers, primarily the blood-brain barrier (BBB), which routinely excludes most therapeutics from entering the brain following systemic administration. Among various strategies investigated to circumvent this challenge, intranasal administration, a noninvasive method that bypasses the BBB to allow direct access of drugs to the CNS, has been showing promising results. Nanotechnology-based drug delivery systems, in particular, have demonstrated remarkable capacities in overcoming the challenges posed by nose-to-brain drug delivery and facilitating targeted drug accumulation within the brain while minimizing side effects of systemic distribution. This review comprehensively summarizes the barriers of nose-to-brain drug delivery, aiming to enhance our understanding of potential physiological obstacles and improve the efficacy of nasal delivery in future trials. We then highlight cutting-edge nanotechnology-based studies that enhance nose-to-brain drug delivery in three key aspects, demonstrating substantial potential for improved treatment of brain diseases. Furthermore, the attention towards clinical studies will ease the regulatory approval process for nasal administration of nanomedicines targeting brain disease.