The influence of AT1002 on the nasal absorption of molecular weight markers and therapeutic agents when co-administered with bioadhesive polymers and an AT1002 antagonist, AT1001

A comprehensive review of advanced nasal delivery: Specially insulin and calcitonin

Peptide drugs through nasal mucous membrane, such as insulin and calcitonin have been widely used in the medical field. There are always two sides to a coin. One side, intranasal drug delivery can imitate the secretion pattern in human body, having advantages of physiological structure and convenient use. Another side, the low permeability of nasal mucosa, protease environment and clearance effect of nasal cilia hinder the intranasal absorption of peptide drugs. Researchers have taken multiple means to achieve faster therapeutic concentration, lower management dose, and fewer side effects for better nasal preparations. To improve the peptide drugs absorption, various strategies had been explored via the nasal mucosa route. In this paper, we reviewed the achievements of 18 peptide drugs in the past decade about the perspectives of the efficacy, mechanism of enhancing intranasal absorption and safety. The most studies were insulin and calcitonin. As a result, absorption enhancers, nanoparticles (NPs) and bio-adhesive system are the most widely used. Among them, chitosan (CS), cell penetrating peptides (CPPs), tight junction modulators (TJMs), soft NPs and gel/hydrogel are the most promising strategies. Moreover, two or three strategies can be combined to prepare drug vectors. In addition, spray freeze dried (SFD), self-emulsifying nano-system (SEN), and intelligent glucose reaction drug delivery system are new research directions in the future.

Modulating the paracellular pathway at the blood-brain barrier: current and future approaches for drug delivery to the CNS

The blood-brain barrier (BBB) is the tightly regulated point of entry by which any neuro-targeting therapy must pass through. BBB modulation is a means to loosen the size exclusion properties of the barrier by temporarily interfering with the formation of intercellular tight junction (TJ) or adheren junction (AJ) complexes, allowing for diffusion of small molecule therapeutics from blood to brain. Several technologies, such as RNAi, peptidomimetics, high frequency ultrasound and nanoparticles, have been developed and refined over the years, paving the way for barrier modulation to become an effective part of conventional central nervous system therapies. Here, we review the current and future approaches aimed at facilitating enhanced drug delivery to the central nervous system (CNS).

Paracellular permeation-enhancing effect of AT1002 C-terminal amidation in nasal delivery

BACKGROUND

The identification of permeation enhancers has gained interest in the development of drug delivery systems. A six-mer peptide, H-FCIGRL-OH (AT1002), is a tight junction modulator with promising permeation-enhancing activity. AT1002 enhances the transport of molecular weight markers or agents with low bioavailability with no cytotoxicity. However, AT1002 is not stable in neutral pH or after incubation under physiological conditions, which is necessary to fully uncover its permeation-enhancing effect. Thus, we increased the stability or mitigated the instability of AT1002 by modifying its terminal amino acids and evaluated its subsequent biological activity.

METHODS

C-terminal-amidated (FCIGRL-NH2, Pep1) and N-terminal-acetylated (Ac-FCIGRL, Pep2) peptides were analyzed by liquid chromatography-mass spectrometry. We further assessed cytotoxicity on cell monolayers, as well as the permeation-enhancing activity following nasal administration of the paracellular marker mannitol.

RESULTS

Pep1 was nontoxic to cell monolayers and showed a relatively low decrease in peak area compared to AT1002. In addition, administration of mannitol with Pep1 resulted in significant increases in the area under the plasma concentration-time curve and peak plasma concentration at 3.63-fold and 2.68-fold, respectively, compared to mannitol alone. In contrast, no increase in mannitol concentration was shown with mannitol/AT1002 or mannitol/Pep2 compared to the control. Thus, Pep1 increased the stability or possibly reduced the instability of AT1002, which resulted in an increased permeation-enhancing effect of AT1002.

CONCLUSION

These results suggest the potential usefulness of C-terminal-amidated AT1002 in enhancing nasal drug delivery, which may lead to the development of a practical drug delivery technology for drugs with low bioavailability.

Trends in drug delivery through tissue barriers containing tight junctions

A limitation in the uptake of many drugs is the restricted permeation through tissue barriers. There are two general ways to cross barriers formed by cell layers: by transcytosis or by diffusion through the intercellular space. In the latter, tight junctions (TJs) play the decisive role in the regulation of the barrier permeability. Thus, transient modulation of TJs is a potent strategy to improve drug delivery. There have been extensive studies on surfactant-like absorption enhancers. One of the most effective enhancers found is sodium caprate. However, this modulates TJs in an unspecific fashion. A novel approach would be the specific modulation of TJ-associated marvel proteins and claudins, which are the main structural components of the TJs. Recent studies have identified synthetic peptidomimetics and RNA interference techniques to downregulate the expression of targeted TJ proteins. This review summarizes current progress and discusses the impact on TJs' barrier function.

Recent progress in tight junction modulation for improving bioavailability

INTRODUCTION

Currently, there are many novel drugs that belong to class III or IV of the Biopharmaceutics Classification System, showing low bioavailability. Tight junction (TJ) modulation offers an approach to increase bioavailability of pharmaceutical compounds. Furthermore, some diseases are accompanied by disturbed barrier function or TJ dysregulation and thus represent a second application for TJ modulators.

AREAS COVERED

This review contains a summary of three different TJ modulators: AT1002, PN159 and labradimil. Within this summary, the authors provide a description of their effects on TJs, their adverse effects and their success in clinical trials. Furthermore, the authors present the current understanding of TJ regulation and highlight opportunities to develop new TJ modulators; they also review the problems that might occur.

EXPERT OPINION

The development of new mechanism-based (MB) TJ modulators is a very promising field of research. MB approaches are expected to have the best future prospects. Further elucidation of signaling pathways and TJ regulation will be necessary for advancing MB TJ modulator research.

The impact of AT1002 on the delivery of ritonavir in the presence of bioadhesive polymer, carrageenan

New insights into the modification of the tight junctions theoretically offer the opportunity to regulate the diffusion barrier and then make it possible to investigate a permeation enhancer of low-bioavailability therapeutic agents. AT1002, a minimum biologically active fragment of zonula occludens toxin which reversibly opens intercellular tight junctions after binding to the Zonulin receptor, increased the transport of various molecular weight markers or low-bioavailability agents. The objective of this study was continuously to evaluate the permeation-enhancing ability of AT1002 in the presence of the bioadhesive agent, carrageenan after intranasal administration of the antiretroviral drug, ritonavir, and the permeation enhancement ratio compared with the previous results. The permeation-enhancing effect of AT1002 was significantly promoted by the bioadhesive agent, carrageenan. The administration of ritonavir with AT1002 and carrageenan resulted in a 2.55-fold increase in AUC(0-240min) and a 2.48-fold increase in C(max) compared with the control group. However, AT1002 in the absence of carrageenan did not produce a statistic enhancement in the absorption of ritonavir. Hence, AT1002 together with the addition of carrageenan may open a new approach of research in the tight junction modulated permeation enhancer, and allow the development of the mucosal drug delivery of therapeutic agents.