Predictivity of standardized and controlled permeation studies: Ex vivo - In vitro - In vivo correlation for sublingual absorption of propranolol.

In preclinical drug development, ex vivo and in vitro permeability studies are a decisive element for specifying subsequent development steps. In this context, reliability, physiological alignment and appropriate in vivo correlation are mandatory for predictivity regarding drug absorption. Especially in oromucosal drug delivery, these prerequisites are not adequately met, which hinders its progressive development and results in the continuous need for animal experiments. To address current limitations, an innovative, standardized, and controlled ex vivo permeation model was applied. It is based on Kerski diffusion cells embedded in automated sampling and coupled to mass spectrometric quantification under physiologically relevant conditions. This study aimed to evaluate the predictivity of the developed model using porcine mucosa (ex vivo) in relation to data of sublingual propranolol absorption (in vivo). In addition, the usefulness of biomimetic barriers (in vitro) as a replacement for porcine mucosa was investigated. Therefore, solubility and permeability studies considering microenvironmental conditions were conducted and achieved good predictivity (R2 = 0.997) for pH-dependent permeability. A multiple level C correlation (R2 ≥ 0.860) between obtained permeability and reported pharmacokinetic animal data (AUC, Cmax) was revealed. Furthermore, a point-to-point correlation was demonstrated for several sublingual formulations. The successful IVIVC confirms the standardized ex vivo model as a viable alternative to animal testing for estimating the in vivo absorption behavior of oromucosal pharmaceuticals.

Synopsis of Barrier Function of Skin and Oral Mucosa-Volume 1.

This is an attempt to make readers of the second edition of International Journal of Molecular Sciences Special Issue on the Barrier Function of Skin and Oral Mucosa aware of the content of the first edition on this same topic [...].

Acute and Chronic Pain from Facial Skin and Oral Mucosa: Unique Neurobiology and Challenging Treatment.

The oral cavity is a portal into the digestive system, which exhibits unique sensory properties. Like facial skin, the oral mucosa needs to be exquisitely sensitive and selective, in order to detect harmful toxins versus edible food. Chemosensation and somatosensation by multiple receptors, including transient receptor potential channels, are well-developed to meet these needs. In contrast to facial skin, however, the oral mucosa rarely exhibits itch responses. Like the gut, the oral cavity performs mechanical and chemical digestion. Therefore, the oral mucosa needs to be insensitive, to some degree, in order to endure noxious irritation. Persistent pain from the oral mucosa is often due to ulcers, involving both tissue injury and infection. Trigeminal nerve injury and trigeminal neuralgia produce intractable pain in the orofacial skin and the oral mucosa, through mechanisms distinct from those seen in the spinal area, which is particularly difficult to predict or treat. The diagnosis and treatment of idiopathic chronic pain, such as atypical odontalgia (idiopathic painful trigeminal neuropathy or post-traumatic trigeminal neuropathy) and burning mouth syndrome, remain especially challenging. The central integration of gustatory inputs might modulate chronic oral and facial pain. A lack of pain in chronic inflammation inside the oral cavity, such as chronic periodontitis, involves the specialized functioning of oral bacteria. A more detailed understanding of the unique neurobiology of pain from the orofacial skin and the oral mucosa should help us develop novel methods for better treating persistent orofacial pain.

Roles of Lipids in the Permeability Barriers of Skin and Oral Mucosa.

PubMed searches reveal much literature regarding lipids in barrier function of skin and less literature on lipids in barrier function of the oral mucosa. In terrestrial mammals, birds, and reptiles, the skin's permeability barrier is provided by ceramides, fatty acids, and cholesterol in the outermost layers of the epidermis, the stratum corneum. This layer consists of about 10-20 layers of cornified cells embedded in a lipid matrix. It effectively prevents loss of water and electrolytes from the underlying tissue, and it limits the penetration of potentially harmful substances from the environment. In the oral cavity, the regions of the gingiva and hard palate are covered by keratinized epithelia that much resemble the epidermis. The oral stratum corneum contains a lipid mixture similar to that in the epidermal stratum corneum but in lower amounts and is accordingly more permeable. The superficial regions of the nonkeratinized oral epithelia also provide a permeability barrier. These epithelial regions do contain ceramides, cholesterol, and free fatty acids, which may underlie barrier function. The oral epithelial permeability barriers primarily protect the underlying tissue by preventing the penetration of potentially toxic substances, including microbial products. Transdermal drug delivery, buccal absorption, and lipid-related disease are discussed.

Cells/colony motion of oral keratinocytes determined by non-invasive and quantitative measurement using optical flow predicts epithelial regenerative capacity.

Cells/colony motion determined by non-invasive, quantitative measurements using the optical flow (OF) algorithm can indicate the oral keratinocyte proliferative capacity in early-phase primary cultures. This study aimed to determine a threshold for the cells/colony motion index to detect substandard cell populations in a subsequent subculture before manufacturing a tissue-engineered oral mucosa graft and to investigate the correlation with the epithelial regenerative capacity. The distinctive proliferating pattern of first-passage [passage 1 (p1)] cells reveals the motion of p1 cells/colonies, which can be measured in a non-invasive, quantitative manner using OF with fewer full-screen imaging analyses and cell segmentations. Our results demonstrate that the motion index lower than 40 µm/h reflects cellular damages by experimental metabolic challenges although this value shall only apply in case of our culture system. Nonetheless, the motion index can be used as the threshold to determine the quality of cultured cells while it may be affected by any different culture conditions. Because the p1 cells/colony motion index is correlated with epithelial regenerative capacity, it is a reliable index for quality control of oral keratinocytes.

Effects of adding a commercial capsaicin fertilizer on the feeding behavior of sika deer (Cervus nippon).

We investigated the inhibitory effect of capsaicin fertilizer on feeding in deer. We tested four captive adult female deer. In Experiment 1, in addition to the treatment (intact) containing only a solid feed (HC), we mixed the fertilizer not containing capsaicin (F) or the capsaicin fertilizer (CF) in the solid feed. In addition, the solid feed was put on a wire net that capsaicin fertilizer was placed 5 cm below (SCF). We investigated their feeding behavior response. In Experiment 2, we changed the amount of substance (fertilizer and capsaicin fertilizer) mixed in the HC. We mixed different amounts (0, 50, 100, and 200 g) of the treatments other than the intact with HC and presented them to the deer, and investigated their feeding behavior response. In Experiment 1, intake in the F and CF decreased (p < .05). In Experiment 2, HC intake was significantly lower in the 100 and 200 g CF (p < .05). However, HC intake relatively increased by the last day in the CF 200 g too. The capsaicin fertilizer decreased the feeding behavior of deer by directly touching the mucous membranes of the deer nose and lips. However, the effects were decreased over time.

Targeting lncRNA H19/miR-29b/COL1A1 Axis Impedes Myofibroblast Activities of Precancerous Oral Submucous Fibrosis.

Oral submucous fibrosis (OSF) is known as a potentially malignant disorder, which may result from chemical irritation due to areca nuts (such as arecoline). Emerging evidence suggests that fibrogenesis and carcinogenesis are regulated by the interaction of long noncoding RNAs (lncRNAs) and microRNAs. Among these regulators, profibrotic lncRNA H19 has been found to be overexpressed in several fibrosis diseases. Here, we examined the expression of H19 in OSF specimens and its functional role in fibrotic buccal mucosal fibroblasts (fBMFs). Our results indicate that the aberrantly overexpressed H19 contributed to higher myofibroblast activities, such as collagen gel contractility and migration ability. We also demonstrated that H19 interacted with miR-29b, which suppressed the direct binding of miR-29b to the 3'-untranslated region of type I collagen (COL1A1). We showed that ectopic expression of miR-29b ameliorated various myofibroblast phenotypes and the expression of α-smooth muscle actin (α-SMA), COL1A1, and fibronectin (FN1) in fBMFs. In OSF tissues, we found that the expression of miR-29b was downregulated and there was a negative correlation between miR-29b and these fibrosis markers. Lastly, we demonstrate that arecoline stimulated the upregulation of H19 through the transforming growth factor (TGF)-ß pathway. Altogether, this study suggests that increased TGF-ß secretion following areca nut chewing may induce the upregulation of H19, which serves as a natural sponge for miR-29b and impedes its antifibrotic effects.

Human milk extracellular vesicles target nodes in interconnected signalling pathways that enhance oral epithelial barrier function and dampen immune responses.

Maternal milk is nature's first functional food. It plays a crucial role in the development of the infant's gastrointestinal (GI) tract and the immune system. Extracellular vesicles (EVs) are a heterogeneous population of lipid bilayer enclosed vesicles released by cells for intercellular communication and are a component of milk. Recently, we discovered that human milk EVs contain a unique proteome compared to other milk components. Here, we show that physiological concentrations of milk EVs support epithelial barrier function by increasing cell migration via the p38 MAPK pathway. Additionally, milk EVs inhibit agonist-induced activation of endosomal Toll like receptors TLR3 and TLR9. Furthermore, milk EVs directly inhibit activation of CD4+ T cells by temporarily suppressing T cell activation without inducing tolerance. We show that milk EV proteins target key hotspots of signalling networks that can modulate cellular processes in various cell types of the GI tract.

A mussel-inspired film for adhesion to wet buccal tissue and efficient buccal drug delivery.

Administration of drugs via the buccal route has attracted much attention in recent years. However, developing systems with satisfactory adhesion under wet conditions and adequate drug bioavailability still remains a challenge. Here, we propose a mussel-inspired mucoadhesive film. Ex vivo models show that this film can achieve strong adhesion to wet buccal tissues (up to 38.72 ± 10.94 kPa). We also demonstrate that the adhesion mechanism of this film relies on both physical association and covalent bonding between the film and mucus. Additionally, the film with incorporated polydopamine nanoparticles shows superior advantages for transport across the mucosal barrier, with improved drug bioavailability (~3.5-fold greater than observed with oral delivery) and therapeutic efficacy in oral mucositis models (~6.0-fold improvement in wound closure at day 5 compared with that observed with no treatment). We anticipate that this platform might aid the development of tissue adhesives and inspire the design of nanoparticle-based buccal delivery systems.

Rebalancing the Oral Microbiota as an Efficient Tool in Endocrine, Metabolic and Immune Disorders.

The current treatment and prevention procedures of oral disorders follow a very targeted approach considering mouth and its structures as a system that is completely independent, than the rest of the body. The main therapeutic approach is to keep the levels of oral bacteria and hygiene in an acceptable range compatible with oral-mouth health, completely separated from systemic microbial homeostasis (eubiosis vs dysbiosis). This can negatively impact the diagnosis of a more complex systemic disease and its progression. Dysbiosis occurs as a consequence of imbalance in oral and gut microbiota which leads to cardiovascular diseases, diabetes mellitus, rheumatoid arthritis, and Alzheimer's disease, as reported in current literature. Likewise, there is a need to highlight and develop a novel philosophical approach in the treatments for oral diseases that will necessarily involve nonconventional approaches.

Response of human oral mucosal epithelial cells to different storage temperatures: A structural and transcriptional study.

PURPOSE: Seeking to improve the access to regenerative medicine, this study investigated the structural and transcriptional effects of storage temperature on human oral mucosal epithelial cells (OMECs). METHODS: Cells were stored at four different temperatures (4°C, 12°C, 24°C and 37°C) for two weeks. Then, the morphology, cell viability and differential gene expression were examined using light and scanning electron microscopy, trypan blue exclusion test and TaqMan gene expression array cards, respectively. RESULTS: Cells stored at 4°C had the most similar morphology to non-stored controls with the highest viability rate (58%), whereas the 37°C group was most dissimilar with no living cells. The genes involved in stress-induced growth arrest (GADD45B) and cell proliferation inhibition (TGFB2) were upregulated at 12°C and 24°C. Upregulation was also observed in multifunctional genes responsible for morphology, growth, adhesion and motility such as EFEMP1 (12°C) and EPHA4 (4°C-24°C). Among genes used as differentiation markers, PPARA and TP53 (along with its associated gene CDKN1A) were downregulated in all temperature conditions, whereas KRT1 and KRT10 were either unchanged (4°C) or downregulated (24°C and 12°C; and 24°C, respectively), except for upregulation at 12°C for KRT1. CONCLUSIONS: Cells stored at 12°C and 24°C were stressed, although the expression levels of some adhesion-, growth- and apoptosis-related genes were favourable. Collectively, this study suggests that 4°C is the optimal storage temperature for maintenance of structure, viability and function of OMECs after two weeks.

Reducing the Number of Mismatches between Hairs and Buccal References When Analysing mtDNA Heteroplasmic Variation by Massively Parallel Sequencing.

In forensics, mitochondrial DNA (mtDNA) analysis is foremost applied to rootless hairs often lacking detectable nuclear DNA. Sanger sequencing is the routine mtDNA method in most forensic laboratories, even though interpretation of mixed samples and heteroplasmic sites can be challenging. Individuals may hold cells with low-level heteroplasmy variants below the detection threshold and other cells where this minor variant is the major one. This difference may be interpreted as a mismatch between reference and evidentiary trace samples, such as buccal specimens and rootless hairs. Such mismatches may be solved by Massively Parallel Sequencing (MPS), allowing more sensitive quantitative analysis for mixed positions than Sanger. The mtDNA control region was analysed in buccal reference samples from 26 individuals and 475 corresponding hairs by MPS and compared to Sanger sequencing data generated on the same samples. With MPS, mixed contributions down to 3% were regarded, leading to a substantial increase in the frequency of heteroplasmy. Our results demonstrate that previously reported mismatches between buccal reference and hair shaft samples by Sanger are detected as low-level heteroplasmy by MPS. A detailed overview of buccal and hair heteroplasmy is provided and implications for MPS-based mtDNA analysis in the context of forensic cases are discussed.

Synthetic peptide SVVYGLR upregulates cell motility and facilitates oral mucosal wound healing.

Osteopontin-derived SVVYGLR (SV) 7-amino-acid sequence is a multifunctional and synthetic SV peptide implicated in angiogenesis, production of collagen III, and fibroblast differentiation into myofibroblasts. This study investigated the effect of the SV peptide on mucosal wound healing activity. Normal human-derived gingival fibroblasts (NHGF) and human oral mucosa keratinocytes (HOMK) were used for in vitro experiments. In addition, an oral punch wound was prepared at the buccal mucosa in male rats aged 11 weeks, and we evaluated the effect of local injection of SV peptide on wound healing. The synthetic SV peptide showed no influence on the proliferation and adhesion properties of NHGF and HOMK, but it enhanced the cell motility and migration activities. TGF-ß1 receptor inhibitor, SB431542 or SB505124, substantially suppressed the SV peptide-induced migration activity, suggesting an involvement of TGF-ß1 receptor activation. Furthermore, SV peptide accelerated the healing process of an in vivo oral wound model, compared with control groups. Further immunohistological staining of wound tissue revealed that an increase in capillary growth and the greater number of fibroblasts and myofibroblasts that migrated into the wound area might contribute to the facilitation of the healing process produced by the SV peptide. The SV peptide has beneficial effects on oral wound healing through enhancement of the earlier phase consisting of angiogenesis and remodeling with granulation tissue. The synthetic SV peptide can be a useful treatment option, particularly for intractable mucosal wounds caused by trauma or surgery for progressive lesions such as oral cancer.

Deregulated immune cell recruitment orchestrated by FOXM1 impairs human diabetic wound healing.

Diabetic foot ulcers (DFUs) are a life-threatening disease that often result in lower limb amputations and a shortened lifespan. However, molecular mechanisms contributing to the pathogenesis of DFUs remain poorly understood. We use next-generation sequencing to generate a human dataset of pathogenic DFUs to compare to transcriptional profiles of human skin and oral acute wounds, oral as a model of "ideal" adult tissue repair due to accelerated closure without scarring. Here we identify major transcriptional networks deregulated in DFUs that result in decreased neutrophils and macrophages recruitment and overall poorly controlled inflammatory response. Transcription factors FOXM1 and STAT3, which function to activate and promote survival of immune cells, are inhibited in DFUs. Moreover, inhibition of FOXM1 in diabetic mouse models (STZ-induced and db/db) results in delayed wound healing and decreased neutrophil and macrophage recruitment in diabetic wounds in vivo. Our data underscore the role of a perturbed, ineffective inflammatory response as a major contributor to the pathogenesis of DFUs, which is facilitated by FOXM1-mediated deregulation of recruitment of neutrophils and macrophages, revealing a potential therapeutic strategy.

In-vivo usefulness of optical coherence tomography in atrophic-erosive oral lichen planus: Comparison between histopathological and ultrastructural findings.

Oral lichen planus (OLP) is a common premalignant chronic inflammatory disorder. Optical Coherence Tomography (OCT) provides a real-time, non-invasive, and in-situ optical signature using light of varying wavelengths to examine tissue. Aim of the present study was to assess the possible role of OCT as diagnostic tool for atrophic-erosive OLP by examining OCT scans of healthy buccal mucosa, and comparing their ultrastructural features with those of a buccal mucosa affected by atrophic-erosive OLP, using their histopathological counterparts as the gold standard. Through grayscale (enface scan) and an application in which the vascularization of the tissue is visible (dynamic scan), it was possible to distinguish the healthy from the lichenoid pattern from 20 controls (12 M; 8 F; mean age: 41.32 years) and 20 patients with histologically confirmed atrophic-erosive OLP (7 M; 13 F; mean age: 64.27 years). In detail, mean width of stratified squamous epithelium (EP) and lamina propria (LP) were evaluated. Among controls, EP and LP showed a mean width of 300 (±50) and of 600 (±50) µm respectively; among cases, disruption of membrane basement prevented from any measurement. Furthermore, a differential pattern of EP and LP emerged between the two groups: a light-grayish, hypo-reflective, homogeneous area of EP recurring in controls turned into a hyper-reflective, non-homogeneous area among cases. Dynamic scan showed a differential profile of LP vascularization, varying from a hypo-reflective red area with small blood vessels in the control group, to a hypo/hyper-reflective area, completely overrun by a denser, wider blood flow amid OLP cases. Although histopathological examination remains the gold standard for OLP diagnosis, OCT could be a potentially helpful tool for the clinician and the pathologist, since it allows analysis of the vascularization of the sample without adversely affecting histological processing.

Mechanical properties of human oral mucosa tissues are site dependent: A combined biomechanical, histological and ultrastructural approach.

AIM: To investigate load-deformation properties of Thiel-embalmed human oral mucosa tissues and to compare three different anatomical regions in terms of mechanical, histological and ultrastructural characteristic with focus on the extracellular matrix. MATERIALS AND METHODS: Thirty specimens from three different regions of the oral cavity: attached gingiva, buccal mucosa and the hard palate were harvested from two Thiel-embalmed cadavers. Mechanical properties were obtained, combining strain evaluation and digital image correlation in a standardised approach. Elastic modulus, tensile strength, strain at maximum load and strain to failure were computed and analysed statistically. Subsamples were also analysed using scanning electron microscopy (SEM) and histological analysis. RESULTS: The highest elastic modulus of 37.36 ± 17.4 MPa was found in the attached gingiva group, followed by the hard palate and buccal mucosa. The elastic moduli of attached gingiva differed significantly to the buccal mucosa (p = .01) and hard palate (p = .021). However, there was no difference in the elastic moduli between the buccal mucosa and hard palate (p > .22). The tensile strength of the tissue samples ranged from 1.54 ± 0.5MPa to 3.81 ± 0.9 MPa, with a significant difference between gingiva group and buccal mucosa or hard palate (p = .001). No difference was found in the mean tensile strength between the buccal mucosa and hard palate (p = .92). Ultrastructural imaging yielded a morphological basis for the various mechanical properties found intraorally; the attached gingiva showed unidirectional collagen fibre network whereas the buccal mucosa and hard palate showed multi-directional network, which was more prone to tension failure and less elasticity. CONCLUSION: This is the first study assessing the various morphological-mechanical relationships of intraoral soft tissues, utilising Thiel-embalmed tissues. The findings of this study suggest that the tissues from different intraoral regions showed various morphological-mechanical behaviour which was also confirmed under the SEM and in the histological analysis.

How Thick Is the Oral Mucosa around Implants after Augmentation with Different Materials: A Systematic Review of the Effectiveness of Substitute Matrices in Comparison to Connective Tissue Grafts.

This systematic review aimed to assess the effectiveness of xenogeneic collagen matrices (XCMs) and acellular dermal matrices (ADMs) in comparison to connective tissue grafts (CTGs) for the augmentation of oral mucosa around dental implants. MEDLINE and the Web of Science were searched for clinical studies that compared substitute materials for the augmentation of oral mucosa to the subepithelial connective tissue graft around dental implants during or after implantation. The review was conducted according to the recommendations of the PRISMA statement. From an initial search result set of 1050 references, seven articles were included in the review. The study designs were heterogeneous, so no meta-analysis could be performed. Both the CTG and either type of substitute material resulted in increased mucosal thickness. Four studies showed no significant difference, while three demonstrated a significant difference, favoring the CTGs over alternative materials. Soft tissue augmentation around dental implants is a safe procedure and leads to thicker mucosal tissue. The subepithelial connective tissue graft can still be regarded as the gold standard, but substitute materials may be an acceptable alternative in some situations, such as for pain-sensitive patients, among inexperienced surgeons, and for sites with an already thick biotype.

Dentoskeletal and soft-tissue changes comparison between the Jasper Jumper and Twin Force Bite Corrector in Class II malocclusion patients: A retrospective study.

OBJECTIVE: This retrospective study aimed to compare the dentoskeletal and soft-tissue changes in Class II malocclusion patients treated with Jasper Jumper and Twin Force Bite Corrector associated with fixed orthodontic appliances. MATERIAL AND METHODS: The sample comprised 60 subjects divided into 3 groups. Patients with Class II malocclusion, mandibular retrusion, slight or no crowding and with no previous orthodontic treatment were eligible. Group 1 comprised 20 patients treated with the Jasper Jumper (JJ), with an initial age of 12.39 years. Group 2 comprised 20 patients treated with the Twin Force (TF), with an initial age of 11.83 years. The control group consisted of 20 untreated Class II subjects with an initial age of 12.13 years. Intergroup pretreatment comparisons were performed with One-way analysis of variance and intergroup treatment changes were compared with the Analysis of Covariance, both followed by Tukey test. RESULTS: The TF group showed greater increase in mandibular length (6.23mm±4.64, P=0.004) than the control group (2.94mm±1.75). The mandibular incisors in the experimental groups presented significantly greater labial inclination and protrusion than the control (Md1.NB; JJ: 4.19°±2.09; TF: 4.46°±6.83; control: 1.13°±2.08, P=0.000/Md1-NB; JJ: 1.95mm±1.45; TF: 1.74mm±1.79; control: 0.31mm±0.81, P=0.000). In addition, the treated groups also showed significantly improvement of the dental relationships (Overjet; JJ: -4.05mm±4.64; TF: -3.80mm±2.12; control: 0.05mm±1.12, P=0.000/Overbite; JJ: -2.52mm±1.46; TF: -2.93mm±2.13; control: -0.63mm±1.35, P=0.000). CONCLUSION: The Jasper Jumper and Twin Force associated to fixed appliances were effective in correcting Class II malocclusion with a combination of skeletal and dentoalveolar changes. However, the TF seems to provide more skeletal effects with greater maxillary growth restriction and mandibular length increase when compared to the JJ.

Tart cherry (Prunus cerasus L.) fractions inhibit biofilm formation and adherence properties of oral pathogens and enhance oral epithelial barrier function.

Dental caries, candidiasis, and periodontal disease are the most common oral infections affecting a wide range of the population worldwide. The present study investigated the effects of two tart cherry (Prunus cerasus L.) fractions on important oral pathogens, including Candida albicans, Streptococcus mutans, and Fusobacterium nucleatum, as well as on the barrier function of oral epithelial cells. Procyanidins and quercetin and its derivatives were the most important constituents found in the tart cherry fractions. Although the fractions showed poor antimicrobial activity, they inhibited biofilm formation by the three oral pathogens in a dose-dependent manner. The tart cherry fractions also attenuated the adherence of C. albicans and S. mutans to a hydroxylapatite surface as well as the adherence of F. nucleatum to oral epithelial cells. Treating oral epithelial cells with the tart cherry fractions significantly enhanced the barrier function as determined by monitoring the transepithelial electrical resistance. In conclusion, this study showed that the tart cherry fractions and their bioactive constituents could be promising antiplaque compounds by targeting biofilm formation and adherence properties of oral pathogens. Furthermore, its property of increasing the epithelial barrier function may protect against microbial invasion of the underlying connective tissue.

Is rat a good model for assessment of particulate-based taste-masked formulations?

Recently there has been an increased interest to develop specialised dosage forms that are better suited to specific patient populations, such as paediatrics and geriatrics. In these patient populations the acceptability of the oral dosage form can be paramount to the products success. However, many Active Pharmaceutical Ingredients (APIs) are known to cause an aversive taste response. One way to increase the acceptability and to enhance the palatability of the formulation is to design coated taste-masked particulate-based dosage forms. The masking of poorly tasting drugs with physical barriers such as polymer coatings can be utilised to prevent the release of drug within the oral cavity, thus preventing a taste response. However, currently, there are few assessment tools and models available to test the efficiency of these particulate-based taste-masked formulations. The rat brief access taste aversion model has been shown to be useful in assessment of taste for liquid dosage forms. However, the applicability of the rat model for particulate-based taste masked formulations is yet to be assessed. It is not understood whether dissolution, solubility and thus exposure of the drug to taste receptors would be the same in rat and human. Therefore, rat saliva must be compared to human saliva to determine the likelihood that drug release would be similar within the oral cavity for both species. In this study rat saliva was characterised for parameters known to be important for drug dissolution, such as pH, buffer capacity, surface tension, and viscosity. Subsequently dissolution of model bitter tasting compounds, sildenafil citrate and efavirenz, in rat saliva was compared to dissolution in human saliva. For all parameters characterised and for the dissolution of both drugs in rat saliva, a substantial difference was observed when compared to human saliva. This discrepancy in saliva parameters and dissolution of model drugs suggests that preclinical taste evaluation of particulate-based taste-masked formulations suggests rat is not a good model for predicting taste of solid dosage forms or undissolved drug where dissolution is required. Alternative preclinical in vivo models in other species, or improved biorelevant in vitro models should be considered instead.