Localization of rate-limiting barrier to penetration of endotoxin through nonkeratinized oral mucosa in vitro

Recent advances in oral delivery of biologics: nanomedicine and physical modes of delivery

INTRODUCTION

Research into oral delivery of biologics has a long and rich history but has not produced technologies used in the clinic. The area has evolved in terms of strategies to promote oral biologics delivery from early chemical absorption enhancers to nanomedicine to devices. Continued activity in this area is justifiable considering the remarkable proliferation of biologics.

AREAS COVERED

The article discusses some physiological barriers to oral delivery of biologics, with a special focus on less characterized barriers such as the basement membrane. Recent progress in oral delivery of biologics via nanomedicine is subsequently covered. Finally, the emerging field of device-mediated gastrointestinal delivery of biotherapeutics is discussed

EXPERT OPINION

Oral delivery of biologics is considered a 'panacea' in drug delivery. Almost century-old approaches of utilizing chemical absorption enhancers have not produced clinically translated technologies. Nanomedicine for oral biologics delivery has demonstrated potential, but the field is relatively new, and technologies have not progressed to the clinic. Device-mediated oral biologics delivery (e.g. ultrasound or microneedles) is in its infancy. However, this space is likely to intensify owing to advances in electronics and materials, as well as the challenges and history related to clinical translation of alternative approaches.

Basement membrane influences intestinal epithelial cell growth and presents a barrier to the movement of macromolecules

This work examines the potential drug delivery barrier of the basement membrane (BM) by assessing the permeability of select macromolecules and nanoparticles. The study further extends to probing the effect of BM on intestinal epithelial cell attachment and monolayer characteristics, including cell morphology. Serum-free cultured Caco-2 cells were grown on BM-containing porous supports, which were obtained by prior culture of airway epithelial cells (Calu-3), shown to assemble and deposit a BM on the growth substrate, followed by decellularisation. Data overall show that the attachment capacity of Caco-2 cells, which is completely lost in serum-free culture, is fully restored when the cells are grown on BM-coated substrates, with cells forming intact monolayers with high electrical resistance and low permeability to macromolecules. Caco-2 cells cultured on BM-coated substrates displayed strikingly different morphological characteristics, suggestive of a higher level of differentiation and closer resemblance to the native intestinal epithelium. BM was found to notably hinder the diffusion of macromolecules and nanoparticles in a size dependent manner. This suggests that the specialised network of extracellular matrix proteins may have a significant impact on transmucosal delivery of certain therapeutics or drug delivery systems.

Keratinized Gingiva Determines a Homeostatic Behavior of Gingival Sulcus through Transudation of Gingival Crevice Fluid

Objective. To shed light on the role of KG, its influence on periodontal behavior was investigated. Methods. Tissue fluid transudation was assessed in alveolar mucosa (P1A), outer gingival margin (P1B), at entrance of (P2) and within gingival sulcus (P3), before and after chewing of fibrous food in 16 patients portraying ≥2 mm KG at one tooth (group 1), and <2 mm at another homologous tooth (group 2). Results. There was a significant increase in GCF after chewing at P1B and P3 in group 1 and at P1A in group 2 (t-test, P < 0.05). Conclusions. The results suggest that KG plays a role in marginal periodontal homeostasis.

Transbuccal delivery of 2',3'-dideoxycytidine: in vitro permeation study and histological investigation

Permeation of 2',3'-dideoxycytidine (ddC), an ionic compound, through buccal mucosa was investigated in this in vitro study to identify the major permeation barrier within the epithelium of buccal mucosa and explore the feasibility of transbuccal delivery of ddC. In vitro permeation of ddC across porcine buccal mucosa was conducted in isotonic McIlvaine buffer solution (IMB) using in-line flow through diffusion cells at 37 degrees C. Sodium glycodeoxycholate (GDC) was used as the permeation enhancer in the permeation enhancement studies. Light microscopy was used in the histological studies of buccal tissue. The steady-state flux of ddC permeating through buccal mucosa increased linearly (R(2)=0.96, P<0.05) as the donor concentration of ddC was increased from 1 to 20 mg/ml. The permeabilities for the full thickness buccal mucosa, the epithelium, and the connective tissue were determined to be 1.75+/-0.74x10(-7), 2.90+/-1.86x10(-7), and 3.49+/-1.19x10(-6) cm/s, respectively. The permeability of ddC was significantly (P<0.05) enhanced by GDC at a concentration of 4 mM. The histological study revealed that the thickness of epithelium was greatly reduced after buccal tissues were immersed in IMB for 12 and 24 h but the basal lamina remained intact even after 24 h. A bilayer diffusion model was established to quantitatively describe the contributions of the epithelium and the connective tissue to the permeation barrier. In conclusion, ddC permeated through buccal mucosa by passive diffusion over the range of concentrations examined. The basal lamina layer within the epithelium of buccal mucosa acted as an important barrier to the permeation of ddC. GDC effectively enhanced the buccal permeability of ddC. The transbuccal delivery is a potential route for the administration of ddC.

Examining the link between coronary heart disease and the elimination of chronic dental infections

BACKGROUND

While it has been suggested that periodontal disease may be associated with coronary heart disease, or CHD, there are no data to suggest that the elimination of chronic dental infections actually lowers the risk of developing chronic CHD. The goal of this study was to determine whether people with a definitive elimination of all potential dental infections--edentulous people, who are at the optimum endpoint of dental infection elimination from a CHD perspective--lower their CHD risk over time when compared with people who have a specific dental infection, periodontitis.

METHODS

The authors examined data from a prospective cohort of 4,027 people who participated in the First National Health and Nutrition Examination Survey, or NHANES I, Epidemiologic Follow-up Study. The primary outcome measure was the first CHD event.

RESULTS

During a mean follow-up of 17 years, there were 1,238 CHD events (538 fatal). The confirmed elimination of chronic dental infections did not lead to a decreased risk of experiencing a CHD event (relative risk, 1.02; 95 percent confidence interval, 0.86-1.21). The CHD risk among people with and without chronic dental infections remained constant over time with respect to each other (test for increasing or decreasing trend over time: not significant, chi2(1) = 0.48; P = .93).

CONCLUSIONS

People who had a complete, definitive and long-term elimination of all potential dental infections through extraction of all teeth did not have lower CHD risk when compared with people with diagnosed periodontitis.

CLINICAL IMPLICATIONS

Until evidence is found to the contrary, the authors suggest that prevention of CHD should not be used as the basis for recommending treatment to eliminate chronic dental infections.

Possible role of monkey gingival fibroblasts in external basement membrane maintenance

Morphological and immunocytochemical investigations were made of the interface between the junctional epithelium and connective tissue in gingiva from young monkeys (Macaca fuscata). Some fibroblasts with conspicuous cytoplasmic organelles, including the elements of rough endoplasmic reticulum, the Golgi apparatus, and mitochondria, were found close to the external basement membrane in the connective tissue underlying the junctional epithelium. Occasionally, cytoplasmic cell processes either made contact with the lamina densa of the basement membrane or came into direct contact with the plasma membrane of the basal layer of junctional epithelium cells. Fragments of a structure like that of the basement membrane were observed between the process and the basal cells. Fibroblasts could be seen very close to the disrupted portion created by the passage of leukocytes migrating into the junctional epithelium through the external basement membrane. Immunoperoxidase methods demonstrated a positive reaction product for laminin on the external basement membrane. This product was observed in the rough endoplasmic reticulum of junctional epithelium cells and of gingival connective tissue fibroblasts located close to the junctional epithelium basement membrane. The cytoplasm of fibroblasts distant from the epithelium, however, demonstrated no immunoreactivity. These results suggest that, in cooperation with epithelial cells, some fibroblasts located near the junctional epithelium can produce such basement membrane components as laminin and that these components may serve to stabilize and/or restore previously assembled basement membrane.

Detection and possible biological role of chondroitinase and heparitinase enzymes produced by Porphyromonas gingivalis W50

Gingival crevicular fluid levels of the glycosaminoglycan (GAG) chondroitin-4-sulphate (C-4-S) have received increased attention as potential indicators of periodontal tissue turnover. However, little is known about the relationship between crevicular fluid connective tissue metabolites and microbial factors. In this study Porphyromonas gingivalis, a periodontopathogen, was investigated for its ability to degrade the GAGs C-4-S, dermatan sulphate (DS) and heparan sulphate (HS) in vitro. The effect of P. gingivalis extracts on the proteoglycans (PG) derived from human gingiva were also investigated. The presence of chondroitinase and heparitinase eliminase enzymes were identified from the vesicle fraction of P. gingivalis W50. These enzymes were extracted from the vesicle fraction by a differential centrifugation technique and partially purified by non-denaturing gel filtration chromatography which revealed heparitinase enzyme peaks at 200 and 150 kDa and chondroitinase at 70 kDa. Gingival proteoglycans for use as substrates were purified using 4 M guanidinium chloride extraction and anion exchange chromatography; these proteoglycans contained 48% DS, 27% C-4-S and 13% HS P. gingivalis chondroitinase and heparitinase enzymes were capable of the degradation of C-4-S and HS but not DS GAGs. The presence of chondroitinase enzymes produced by P. gingivalis may influence levels of connective tissue metabolites in crevicular fluid. Furthermore these enzymes, particularly the heparitinase, may be involved in the initial permeation of the gingival epithelium, permitting the ingress of further microbial virulence factors.

Multilayer culture of periodontal ligament epithelial cells: a model for junctional epithelium

The unique features of junctional epithelium involve lack of keratinization, limited differentiation and a relatively permeable structure. In order to study the relationship between differentiation and permeability of stratified epithelium a model system was developed. Porcine periodontal ligament epithelial cells were cultured on the polycarbonate nucleopore membrane of the Transwell two-compartment culture system. Within 5 days of culture the cells formed a confluent multilayered structure. Subsequently, maturation of the structure and differentiation of surface cells took place. Transmission electron microscopy showed that the cells were arranged into basal and suprabasal layers with sparse desmosomal attachments and wide intercellular spaces resembling the organization of junctional epithelium. The basal cells attached to a subepithelial basal lamina through numerous hemidesmosomes. The cytokeratin profile of the cultured epithelium (K5, 6, 14, 16, 19) resembled that of the cells of junctional epithelium attached to the tooth surface. The older cultures expressed differentiation markers, K4, K13 and involucrin, thereby resembling sulcular epithelium. The epithelial permeability, measured by diffusion of phenol red, radioactive dextran or methionine tracers, and as transepithelial electrical resistance, decreased with the increased cell number and maturation of the cultures. The new model provides an organotypic culture system which allows to control differentiation of a multilayered periodontal epithelium. It thus may serve as a valuable new tool for studies on the permeability and behaviour of periodontal epithelium under the influence of exogenous and endogenous factors.

Drug delivery via the mucous membranes of the oral cavity

The delivery of drugs via the mucous membranes lining the oral cavity (i.e., sublingual and buccal), with consideration of both systemic delivery and local therapy, is reviewed in this paper. The structure and composition of the mucosae at different sites in the oral cavity, factors affecting mucosal permeability, penetration enhancement, selection of appropriate experimental systems for studying mucosal permeability, and formulation factors relevant to the design of systems for oral mucosal delivery are discussed. Sublingual delivery gives rapid absorption and good bioavailability for some small permeants, although this site is not well suited to sustained-delivery systems. The buccal mucosa, by comparison, is considerably less permeable, but is probably better suited to the development of sustained-delivery systems. For these reasons, the buccal mucosa may have potential for delivering some of the growing number of peptide drugs, particularly those of low molecular weight, high potency, and/or long biological half-life. Development of safe and effective penetration enhancers will further expand the utility of this route. Local delivery is a relatively poorly studied area; in general, it is governed by many of the same considerations that apply to systemic delivery.

Effects of surfactants on the permeability of canine oral mucosa in vitro

The effect of 3 cationic, 1 anionic, and 1 non-ionic surfactant on the permeability of oral frenulum removed from anesthetized dogs was determined in vitro. Permeability to 12 organic compounds was measured in the presence and absence of surfactant. Cetylpyridinium chloride, cetyltrimethylammonium bromide, benzalkonium chloride and sodium lauryl sulfate, at concentrations from 0.025-1.0% caused dose-related increases in permeability to each of the solutes tested, whereas polysorbate 80 caused an increase in permeability to only 3 solutes, and this occurred only at the highest surfactant concentration employed.

Effect of hydrogen sulfide and methyl mercaptan on the permeability of oral mucosa

Hydrogen sulfide (H2S) and methyl mercaptan (CH3SH) are the volatile sulfur compounds (VSC) that were investigated for a possible role in the etiology of periodontal disease. The results show that the permeability of porcine non-keratinized sublingual mucosa is increased by up to 75% or 103% following exposure to H2S and CH3SH, respectively. The effect may be attributed to VSC reaction with tissue components resulting in alteration in the integrity of the tissue barrier. The increase in permeability of the mucosa to [35S]-Na2SO4 was dependent on both the time of exposure and concentration of VSC in the head-space. The [35S]-H2S was retained by the mucosal tissue and was able to penetrate the intact layers consisting of non-keratinized epithelium, basal membrane, and connective tissue. Treatment of the mucosa with 0.22% ZnCl2, either prior to or after exposure to CH3SH, nullified the effect of CH3SH and restored the permeability to a state similar to that observed in control 95% air/5% CO2 systems.

Permeability of the rat oral mucosa to organic solutes measured in vivo

The permeability of the oral mucosa to organic solutes of different molecular volumes, oil-to-water distribution coefficients, and pKa was studied in an in-vivo system. The calculated permeability coefficients were independent of time of application and the concentration of the solutes, a finding consistent with transport by simple diffusion. The permeability of organic acids was pH dependent whereas permeability to compounds with a degree of ionization that did not change over the pH range was not affected by pH. Increasing the chain length from two to eight carbons in an organic acid series resulted in an increase of both the oil-to-water distribution coefficient and the permeability coefficient; the permeability coefficient was decreased by the addition of oxygen in the form of hydroxyl groups. These results indicate that there is similarity in the way that lipid-soluble substances diffuse across oral mucosa and other lipid membranes. Results using compounds with oil-to-water distribution coefficients less than that of water suggest that these compounds traverse the oral mucosa by two additional routes. One, for compounds with molar volumes less than 80 cm3/ml, is via pores; whereas, the second, utilized by larger compounds, is probably by an intercellular route.

Degradation of basement membrane collagen by proteinases from human gingiva, leukocytes and bacterial plaque

Basement membranes in human gingiva are found in dento-epithelial junction, epithelial-connective tissue junction and endothelium-connective-tissue junction where they have important attachment and filtering functions. The ability of plaque and gingiva-derived proteinases to degrade Type IV collagen, the major protein of basement membranes, was examined in vitro. The basement membrane collagen (Type IV) isolated from bovine lens capsules was incubated in the presence of enzyme samples. The degradation was assayed by the release of hydroxyproline from the insoluble substrate and by examining the peptide pattern of the residue by polyacrylamide gel electrophoresis. Salt extracts of inflamed gingival specimens degraded basement membrane collagen into soluble form and produced degradation products that were similar to those produced by human leukocyte extracts. Gingival crevicular fluid collected from patients with severe adult periodontitis also digested the substrate but the degradation pattern was different from the leukocyte and gingival extract samples. The pattern closely resembled the degradation produced by bacterial plaque extracts. A third type of cleavage was observed when collagenase from Clostridium histolyticum was incubated with basement membrane collagen. Crevicular fluid and the extracts from gingiva, leukocytes and plaque also contained gelatinase and elastase-like enzyme activities that have earlier been shown to be potent in degrading basement membrane. It was concluded that enzymes capable of degrading basement membrane collagen in gingivitis and periodontal disease may originate from both plaque bacteria and human leukocytes. It also appeared that the enzymes responsible are more likely to be gelatinase and elastase-like enzymes than specific collagenases.

Permeability of gingival sulcular epithelium in the development of scorbutic gingivitis

Young adult nonhuman primates were initially fed an ascorbic-acid free diet and, subsequently, a diet with a suboptimal level of the vitamin. Following approximately 12 weeks of this dietary regime, five of seven experimental animals of the gingival sulcular epithelium to 3H-inulin, but not to 14C-butyric acid or 14C-urea, had increased significantly (+86%, P less than 0.01) in the experimental group as compared to ad libitum or pair-fed controls. This defect in the intercellular permeability barrier of the sulcular epithelium could have contributed to the pathogenesis of scorbutic gingivitis.