Platinum nanoparticles are being utilized in various industrial applications, including in catalysis, cosmetics, and dietary supplements. Although reducing the size of the nanoparticles improves the physicochemical properties and provides useful performance characteristics, the safety of the material remains a major concern. The aim of the present study was to evaluate the biological effects of platinum particles less than 1 nm in size (snPt1). In mice administered with a single intravenous dose of snPt1, histological analysis revealed necrosis of tubular epithelial cells and urinary casts in the kidney, without obvious toxic effects in the lung, spleen, and heart. These mice exhibited dose-dependent elevation of blood urea nitrogen, an indicator of kidney damage. Direct application of snPt1 toin vitrocultures of renal cells induced significant cytotoxicity. In mice administered for 4 weeks with twice-weekly intraperitoneal snPt1, histological analysis of the kidney revealed urinary casts, tubular atrophy, and inflammatory cell accumulation. Notably, these toxic effects were not observed in mice injected with 8-nm platinum particles, either by single- or multiple-dose administration. Our findings suggest that exposure to platinum particles of less than 1 nm in size may induce nephrotoxicity and disrupt some kidney functions. However, this toxicity may be reduced by increasing the nanoparticle size.

With the continued progress in genomic drug discovery, the high-throughput production of drug candidates has become possible, and thus today there are a number of candidates that are extremely effective both in cell-free and in cell models. However, a drug delivery system suitable for the high-throughput production has yet to be fully developed. In tissues, the tight junction (TJ) plays a pivotal role as both a barrier to restrict various substances and in intra-tissue maintenance. Claudin, a ca. 23 kDa transmembrane protein with four transmembrane domains, is responsible for the TJ functions. Interestingly, for each of the 24 members of the claudin family, expression profiles and exact barrier functions differ. Therefore, claudin may be a potential target for use as a drug delivery system via a paracellular route. The C-terminal fragment of Clostridium perfringens enterotoxin (C-CPE) is known to modulate the barrier function of claudin. We found that C-CPE is a potent absorption-enhancer and that this enhancing activity is 400-fold greater than clinically used enhancers. The enhancing activity examined in this study involved an interaction between C-CPE and claudin-4. These findings indicate that claudin might be a novel target for a drug delivery system. In the current review, we describe about background and data on our research about claudin modulator, and we also discuss the possibility of the use of the claudin family in a new approach for developing a drug delivery system.

Efficient vaccine delivery to mucosal tissues including mucosa-associated lymphoid tissues is essential for the development of mucosal vaccine. We previously reported that claudin-4 was highly expressed on the epithelium of nasopharynx-associated lymphoid tissue (NALT) and thus claudin-4-targeting using C-terminal fragment of Clostridium perfringens enterotoxin (C-CPE) effectively delivered fused antigen to NALT and consequently induced antigen-specific immune responses. In this study, we applied the C-CPE-based vaccine delivery system to develop a nasal pneumococcal vaccine. We fused C-CPE with pneumococcal surface protein A (PspA), an important antigen for the induction of protective immunity against Streptococcus pneumoniae infection, (PspA-C-CPE). PspA-C-CPE binds to claudin-4 and thus efficiently attaches to NALT epithelium, including antigen-sampling M cells. Nasal immunization with PspA-C-CPE induced PspA-specific IgG in the serum and bronchoalveolar lavage fluid (BALF) as well as IgA in the nasal wash and BALF. These immune responses were sufficient to protect against pneumococcal infection. These results suggest that C-CPE is an efficient vaccine delivery system for the development of nasal vaccines against pneumococcal infection.

Hepatitis C virus (HCV) entry into host cells is a complex process requiring multiple host factors, including claudin-1 (CLDN1). Safe and effective therapeutic entry inhibitors need to be developed. We isolated a human hepatic Huh7.5.1-derived cell mutant that is nonpermissive to HCV, and comparative microarray analysis showed that the mutant was CLDN1 defective. Four hybridomas were obtained, which produced monoclonal antibodies (MAbs) that interacted with the parental Huh7.5.1 cell but not with the CLDN1-defective mutant. All MAbs produced by these hybridomas specifically bound to human CLDN1 with a very high affinity and prevented HCV infection of Huh7.5.1 cells in a dose-dependent manner, without apparent cytotoxicity. Two selected MAbs also inhibited HCV infection of human liver-chimeric mice without significant adverse effects. CLDN1 may be a potential target to prevent HCV infection in vivo . Anti-CLDN1 MAbs may hence be promising candidates as novel anti-HCV agents. IMPORTANCE Safe and effective therapeutic entry inhibitors against hepatitis C virus (HCV) are very useful for combination therapies with other anti-HCV drugs, such as direct-acting antivirals. In this study, we first showed an effective strategy for developing functional monoclonal antibodies (MAbs) against extracellular domains of a multimembrane-spanning target protein, claudin-1 (CLDN1), by using parental cells expressing the intact target membrane protein and target-defective cells. The established MAbs against CLDN1, which had a very high affinity for intact CLDN1, efficiently inhibited in vitro and in vivo HCV infections. These anti-CLDN1 MAbs are promising leads for novel entry inhibitors against HCV.

A current bottleneck in the development of central nervous system (CNS) drugs is the lack of drug delivery systems targeting the CNS. The intercellular space between endothelial cells of the blood brain barrier (BBB) is sealed by complex protein-based structures called tight junctions (TJs). Claudin-5, a tetra-transmembrane protein is a key component of the TJ seal that prevents the paracellular diffusion of drugs into the CNS. In the present study, to investigate whether CLDN-5 binders can be used for delivery of drugs to the CNS, we generated monoclonal antibodies specific to the extracellular domains of CLDN-5. In an in vitro model of the blood-brain barrier, the anti-CLDN-5 mAbs dose-dependently attenuated TEER and enhanced solute permeation. These anti-CLDN-5 monoclonal antibodies are potential leads for the development of novel drug delivery systems targeting the CNS.