Three-Dimensional Oral Mucosal Equivalents as Models for Transmucosal Drug Permeation Studies

Nanoemulsion and nanoemulgel-based carriers as advanced delivery tools for the treatment of oral diseases

Oral diseases rank among the most widespread ailments worldwide posing significant global health and economic challenges affecting around 3.5 billion people, impacting the quality of life for affected individuals. Dental caries, periodontal disease, bacterial and fungal infections, tooth loss and oral malignancies are among the most prevalent global clinical disorders contributing to oral health burden. Traditional treatments for oral diseases often face challenges such as poor drug bioavailability, breakdown of medication in saliva, inconsistent antibiotic levels at the site of periodontal infection as well as higher side effects. However, the emergence of nanoemulgel (NEG) as an innovative drug delivery system offers promising solutions where NEG combines the advantages of both nanoemulsions (NEs) and hydrogels providing improved drug solubility, stability, and targeted delivery. Due to their minuscule size and ability to control drug release, NEGs hold promise for improving treatment of oral diseases, where versatility of these delivery systems makes them suitable for various applications, including topical delivery in dentistry. This review concisely outlines the anatomy of the oral environment and investigates the therapeutic potential of NE-based gels in oral disorder treatment. It thoroughly examines the challenges of drug delivery in the oral cavity and proposes strategies to improve therapeutic efficacy, drawing attention to previous research reports for comparison. Through comprehensive analysis, the review highlights the promising role of NEGs as a novel therapeutic approach for oral health management via research advancements and their clinical translation. Additionally, it provides valuable insights into future research directions and development opportunities in this area.

The Evolution of In Vitro Toxicity Assessment Methods for Oral Cavity Tissues-From 2D Cell Cultures to Organ-on-a-Chip

Since the oral cavity comes into contact with several xenobiotics (dental materials, oral hygiene formulations, drugs, or tobacco products), it is one major site for toxicity manifestation. Multiple parameters are assessed during toxicity testing (cell viability and proliferation, apoptosis, morphological changes, genotoxicity, oxidative stress, and inflammatory response). Due to the complexity of the oral cavity environment, researchers have made great efforts to design better in vitro models that mimic natural human anatomic and functional features. The present review describes the in vitro methods currently used to investigate the toxic potential of various agents on oral cavity tissues and their evolution from simple 2D cell culture systems to complex organ-a-chip designs.

Bioengineering the Junctional Epithelium in 3D Oral Mucosa Models

Two-dimensional (2D) culture models and animal experiments have been widely used to study the pathogenesis of periodontal and peri-implant diseases and to test new treatment approaches. However, neither of them can reproduce the complexity of human periodontal tissues, making the development of a successful 3D oral mucosal model a necessity. The soft-tissue attachment formed around a tooth or an implant function like a biologic seal, protecting the deeper tissues from bacterial infection. The aim of this review is to explore the advancements made so far in the biofabrication of a junctional epithelium around a tooth-like or an implant insert in vitro. This review focuses on the origin of cells and the variety of extracellular components and biomaterials that have been used for the biofabrication of 3D oral mucosa models. The existing 3D models recapitulate soft-tissue attachment around implant abutments and hydroxyapatite discs. Hereby, the qualitative and quantitative assessments performed for evidencing the soft-tissue attachment are critically reviewed. In perspective, the design of sophisticated 3D models should work together for oral immunology and microbiology biofilms to accurately reproduce periodontal and peri-implant diseases.

Tissue-Engineered Oral Epithelium for Dental Material Testing: Toward In Vitro Biomimetic Models

Tissue-engineered oral epithelium (ΤΕΟΕ) was developed after comparing various culture conditions, including submerged (SUB) and air-liquid interface (ALI) human cell expansion options. Barrier formation was evaluated via transepithelial electrical resistance (TEER) and calcein permeation via spectrofluorometry. TEOE was further assessed for long-term viability via live/dead staining and development of intercellular connections via transmission electron microscopy. Tissue architecture was evaluated via histochemistry and the expression of pancytokeratin (pCK) via immunohistochemistry. The effect of two commonly used dental resinous monomers on TEOE was evaluated for alterations in cell viability and barrier permeability. ALI/keratinocyte growth factor-supplemented (ALI-KGS) culture conditions led to the formation of an 8-20-layer thick, intercellularly connected epithelial barrier. TEER values of ALI-KGS-developed TEOE decreased compared with all other tested conditions, and the established epithelium intensively expressed pCK. Exposure to dental monomers affected the integrity and architecture of TEOE and induced cellular vacuolation, implicating hydropic degeneration. Despite structural modifications, the permeability of TEOE was not substantially affected after exposure to the monomers. In conclusion, the biological properties of the TEOE mimicking the physiological functional conditions and its value as biocompatibility assessment tool for dental materials were characterized.

Biological Evaluation of Oral Care Products Using 3D Tissue-Engineered In Vitro Models of Plaque-Induced Gingivitis

BACKGROUND

The aim of this study was to investigate and visualize the anti-inflammatory and anti-bacterial effects of different oral care products using an infected and inflamed 3D tissue-engineered gingival mucosal model.

METHODS

A 3D full-thickness oral mucosal model was engineered inside tissue culture inserts using collagen hydrogels populated with human gingival fibroblasts and THP-1 monocytes and layered with oral epithelial cell lines. Oral saliva bacteria were cultured and added to the surface of the models and inflammation was further simulated with lipopolysaccharide (LPS) of Escherichia coli. The 3D models were exposed to three different types of toothpastes, a chlorhexidine antiseptic mouthwash, different antibiotics, and a mechanical rinse with phosphate-buffered saline (PBS) prior to biological evaluation using the PrestoBlue tissue viability assay, histology, optical coherence tomography (OCT), confocal microscopy, and measurement of the release of the inflammatory markers IL-1β, IL-6, and IL-8 with ELISA.

RESULTS

Multiple-endpoint analyses of the infected oral mucosal models treated with different anti-bacterial agents showed consistent outcomes in terms of tissue viability, histology, OCT, and confocal microscopy findings. In terms of anti-inflammatory testings, the positive control group showed the highest level of inflammation compared with all other groups. Depending on the anti-bacterial and anti-inflammatory potential of the test groups, different levels of inflammation were observed in the test groups.

CONCLUSIONS

The inflamed 3D oral mucosal model developed in this study has the potential to be used as a suitable in vitro model for testing the biocompatibility, anti-inflammatory, and anti-bacterial properties of oral care products including mouthwashes and toothpastes. The results of this study indicate that the chlorhexidine mouthwash has both anti-bacterial and cytotoxic effects on the 3D oral mucosal model. Hyaluronic-acid-containing toothpaste has significant anti-bacterial and anti-inflammatory effects on the 3D oral mucosal model.

Inhalable porous particles as dual micro-nano carriers demonstrating efficient lung drug delivery for treatment of tuberculosis

Inhalation therapy treating severe infectious disease is among the more complex and emerging topics in controlled drug release. Micron-sized carriers are needed to deposit drugs into the lower airways, while nano-sized carriers are of preference for cell targeting. Here, we present a novel and versatile strategy using micron-sized spherical particles with an excellent aerodynamic profile that dissolve in the lung fluid to ultimately generate nanoparticles enabling to enhance both extra- and intra-cellular drug delivery (i.e., dual micro-nano inhalation strategy). The spherical particles are synthesised through the condensation of nano-sized amorphous silicon dioxide resulting in high surface area, disordered mesoporous silica particles (MSPs) with monodispersed size of 2.43 μm. Clofazimine (CLZ), a drug shown to be effective against multidrug-resistant tuberculosis, was encapsulated in the MSPs obtaining a dry powder formulation with high respirable fraction (F.P.F. <5 μm of 50%) without the need of additional excipients. DSC, XRPD, and Nitrogen adsorption-desorption indicate that the drug was fully amorphous when confined in the nano-sized pores (9-10 nm) of the MSPs (shelf-life of 20 months at 4 °C). Once deposited in the lung, the CLZ-MSPs exhibited a dual action. Firstly, the nanoconfinement within the MSPs enabled a drastic dissolution enhancement of CLZ in simulated lung fluid (i.e., 16-fold higher than the free drug), increasing mycobacterial killing than CLZ alone (p = 0.0262) and reaching concentrations above the minimum bactericidal concentration (MBC) against biofilms of M. tuberculosis (i.e., targeting extracellular bacteria). The released CLZ permeated but was highly retained in a Calu-3 respiratory epithelium model, suggesting a high local drug concentration within the lung tissue minimizing risk for systemic side effects. Secondly, the micron-sized drug carriers spontaneously dissolve in simulated lung fluid into nano-sized drug carriers (shown by Nano-FTIR), delivering high CLZ cargo inside macrophages and drastically decreasing the mycobacterial burden inside macrophages (i.e., targeting intracellular bacteria). Safety studies showed neither measurable toxicity on macrophages nor Calu-3 cells, nor impaired epithelial integrity. The dissolved MSPs also did not show haemolytic effect on human erythrocytes. In a nutshell, this study presents a low-cost, stable and non-invasive dried powder formulation based on a dual micro-nano carrier to efficiently deliver drug to the lungs overcoming technological and practical challenges for global healthcare.

In vitro permeation of nicotine and tobacco specific nitrosamines from smokeless tobacco product extracts in a 3D buccal tissue model

Tobacco product use is a risk factor in the development of oral cancer, although epidemiology studies show this risk is far less with smokeless tobacco product use than cigarette smoking. While smokeless tobacco contains harmful and potentially harmful constituents (HPHCs), the oral permeation of HPHCs in oral tobacco products is not completely understood. To improve the understanding, three different extract concentrations of the CORESTA reference products (CRP) for snus (CRP1.1) and moist snuff (CRP2.1) were applied to cellular tissue derived from two donors of EpiOral™ model, a 3D human buccal model, and permeation of nicotine and tobacco-specific nitrosamines (TSNAs) were measured over two hours. Permeation of 0.15% caffeine in complete artificial saliva and cell viability were also measured. Results showed that a consistent and concentration dependent cumulative permeation of nicotine and TSNAs was observed with high percent recovery in all conditions. A high degree of sensitivity was seen for all analytes, with minimal cytotoxicity for both CRPs. The data presented here show the EpiOral™ model is fit-for-purpose to evaluate the permeation of nicotine and TSNAs in nicotine-containing snus and moist snuff oral tobacco.

Evaluating the antioxidant potential of resveratrol-gold nanoparticles in preventing oxidative stress in endothelium on a chip

Vascular endothelial cells play a vital role in the health and maintenance of vascular homeostasis, but hyperglycemia disrupts their function by increasing cellular oxidative stress. Resveratrol, a plant polyphenol, possesses antioxidant properties that can mitigate oxidative stress. Addressing the challenges of its limited solubility and stability, gold nanoparticles (GNps) were utilized as carriers. A microfluidic chip (MFC) with dynamic flow conditions was designed to simulate body vessels and to investigate the antioxidant properties of resveratrol gold nanoparticles (RGNps), citrate gold nanoparticles (CGNps), and free Resveratrol on human umbilical vein endothelial cells (HUVEC). The 2, 2-diphenyl-1-picrylhydrazyl (DPPH) assay was employed to measure the extracellular antioxidant potential, and cell viability was determined using the Alamar Blue test. For assessing intracellular oxidative stress, the 2',7'-dichlorodihydrofluorescein diacetate (DCFH-DA) assay was conducted, and results from both the cell culture plate and MFC were compared. Free Resveratrol demonstrated peak DPPH scavenging activity but had a cell viability of about 24-35%. RGNPs, both 3.0 ± 0.5 nm and 20.2 ± 4.7 nm, consistently showed high cell viability (more than about 90%) across tested concentrations. Notably, RGNPs (20 nm) exhibited antioxidative properties through DPPH scavenging activity (%) in the range of approximately 38-86% which was greater than that of CGNps at about 21-32%. In the MFC,the DCFH-DA analysis indicated that RGNPs (20 nm) reduced cellular oxidative stress by 57-82%, surpassing both CGNps and free Resveratrol. Morphologically, cells in the MFC presented superior structure compared to those in traditional cell culture plates, and the induction of hyperglycemia successfully led to the formation of multinucleated variant endothelial cells (MVECs). The MFC provides a distinct advantage in observing cell morphology and inducing endothelial cell dysfunction. RGNps have demonstrated significant potential in alleviating oxidative stress and preventing endothelial cell disorders.