A technique for the study of endocytosis in human oral epithelial cells

Influence of oligospermines architecture on their suitability for siRNA delivery

Spermines are naturally abundant polyamines that partially condense nucleic acids and exhibit the proton-sponge effect in an acidic environment. However, spermines show a limited efficiency for transfecting nucleic acids because of their low molecular weight. Therefore, spermines need to be modified to be used as nonviral vectors for nucleic acids. Here, we synthesized linear bisspermine as well as a linear and dendritic tetraspermine with different molecular architectures. These oligospermines were self-assembled into polyplexes with siRNA. The structure–activity relationship of the oligospermines was evaluated in terms of their efficiency for delivering siRNA into a nonsmall cell lung carcinoma cell line. Oligospermines displayed minimal cytotoxicity but efficient siRNA condensation and showed better stability against polyanions than polyethylenimine. The morphology of the polyplexes was strongly affected by the oligospermine architecture. Linear tetraspermine/siRNA polyplexes showed the best gene-silencing efficiency among the oligospermines tested at both the mRNA and protein expression levels, indicating the most favorable structure for siRNA delivery.

Critical evaluation of biodegradable polymers used in nanodrugs

Use of biodegradable polymers for biomedical applications has increased in recent decades due to their biocompatibility, biodegradability, flexibility, and minimal side effects. Applications of these materials include creation of skin, blood vessels, cartilage scaffolds, and nanosystems for drug delivery. These biodegradable polymeric nanoparticles enhance properties such as bioavailability and stability, and provide controlled release of bioactive compounds. This review evaluates the classification, synthesis, degradation mechanisms, and biological applications of the biodegradable polymers currently being studied as drug delivery carriers. In addition, the use of nanosystems to solve current drug delivery problems are reviewed.

The SRC family tyrosine kinase HCK and the ETS family transcription factors SPIB and EHF regulate transcytosis across a human follicle-associated epithelium model

A critical step in the induction of adaptive mucosal immunity is antigen transcytosis, in which luminal antigens are transported to organized lymphoid tissues across the follicle-associated epithelium (FAE) of Peyer's patches. However, virtually nothing is known about intracellular signaling proteins and transcription factors that regulate apical-to-basolateral transcytosis. The FAE can transcytose a variety of luminal contents, including inert particles, in the absence of specific opsonins. Furthermore, it expresses receptors for secretory immunoglobulin A (SIgA), the main antibody in mucosal secretions, and uses them to efficiently transcytose SIgA-opsonized particles present in the lumen. Using a human FAE model, we show that the tyrosine kinase HCK regulates apical-to-basolateral transcytosis of non-opsonized and SIgA-opsonized particles. We also show that, in cultured intestinal epithelial cells, ectopic expression of the transcription factor SPIB or EHF is sufficient to activate HCK-dependent apical-to-basolateral transcytosis of these particles. Our results provide the first molecular insights into the intracellular regulation of antigen sampling at mucosal surfaces.

Imidazole-grafted chitosan-mediated gene delivery: in vitro study on transfection, intracellular trafficking and degradation

AIM

To study the mechanism of transfection mediated by imidazole-grafted chitosan (CHimi) nanoparticles, to propose new strategies to control and improve the expression of a delivered gene in the context of regenerative medicine.

METHODS

Biochemical and microscopy methods were used to establish transfection efficiency and nanoparticle intracellular trafficking. The role of CHimi and degree of N-acetylation (DA) on transfection was explored.

RESULTS

CHimi was found to promote the expression of a delivered gene during a minimum 7-day period. Additionally, the production of a protein of interest could be upheld by consecutive transfections, without compromising cell viability. Transfection was found to be a time-dependent process, requiring CHimi-DNA complex disassembling. The DA was found to have an impact on transfection kinetics in line with the observation that the rate of lysozyme-mediated nanoparticle degradation increases with the polymer DA.

CONCLUSION

The adjustment of the CH degradation rate can be used as a tool for tuning the expression of a gene delivered by CH-based nanoparticle systems.

Chitosan-based gene delivery vectors targeted to the peripheral nervous system

A non-toxic, targeted, simple and efficient system that can specifically transfect peripheral sensorial neurons can pave the way towards the development of new therapeutics for the treatment of peripheral neuropathies. In this study chitosan (CH), a biodegradable polymer, was used as the starting material in the design of a multicomponent vector targeted to the peripheral nervous system (PNS). Polycation-DNA complexes were optimized using imidazole- and thiol-grafted CH (CHimiSH), in order to increase transfection efficiency and allow the formation of ligand conjugated nanocomplexes, respectively. The 50 kDa non-toxic fragment from the tetanus toxin (HC), shown to interact specifically with peripheral neurons and undergo retrograde transport, was grafted to the binary complex via a bi-functional poly(ethylene glycol) (HC-PEG) reactive for the thiol moieties present in the complex surface. The targeting of the developed nanocomplexes was assessed by means of internalization and transfection studies in the ND7/23 (neuronal) vs. NIH 3T3 (fibroblast) cell lines. Targeted transfection was further confirmed in dorsal root ganglion dissociated primary cultures. A versatile, multi-component nanoparticle system that successfully targets and transfects neuronal cell lines, as well as dorsal root ganglia (DRG) primary neuron cultures was obtained for the 1.0 (w/w) HC-PEG/DNA formulation.

Nanoparticles for local drug delivery to the oral mucosa: proof of principle studies

Purpose

To determine if solid lipid nanoparticles represent a viable strategy for local delivery of poorly water soluble and unstable chemopreventive compounds to human oral tissues.

Methods

Nanoparticle uptake and compound retention evaluations employed monolayer-cultured human oral squamous cell carcinoma (OSCC) cell lines and normal human oral mucosal explants. Feasibility of nanoparticle delivery was also evaluated with respect to the presence of phase-III efflux transporters in normal oral mucosal tissue and OSCC tissues.

Results

Functional uptake assays confirmed significantly greater internalization of nanoparticle-delivered fluorescent probe relative to free-fluorescent probe delivery, while concurrently demonstrating nanoparticle uptake rate differences among the OSCC cell lines and the phagocytic control human monocyte cell line. Mucosal explants exhibited nanoparticle penetration and internalization in the spinous and basal epithelial layers (7/10 specimens), and also exhibited the presence of the phase-III efflux transporters multidrug resistance-associated protein 1 (MRP1) and breast cancer resistance protein (BCRP).

Conclusions

These data confirm nanoparticle internalization by OSCC cells and support the premise that nanoparticle-based delivery provides higher final intracellular levels relative to bolus administration. Furthermore, the penetration and subsequent internalization of nanoparticles within the proliferating basal layer cells demonstrates the feasibility of nanoparticle formulations for local delivery and stabilization of oral chemopreventive compounds.

Quantitative mechanics of endothelial phagocytosis of silicon microparticles

Endothelia, once thought of as a barrier to the delivery of therapeutics, is now a major target for tissue-specific drug delivery. Tissue- and disease-specific molecular presentations on endothelial cells provide targets for anchoring or internalizing delivery vectors. Porous silicon delivery vectors are phagocytosed by vascular endothelial cells. The rapidity and efficiency of silicon microparticle uptake lead us to delineate the kinetics of internalization. To discriminate between surface-attached and -internalized microparticles, we developed a double fluorescent/FRET flow cytometric approach. The approach relies on quenching of antibody-conjugated fluorescein isothiocyanate covalently attached to the microparticle surface by attachment of a secondary antibody labeled with an acceptor fluorophore, phycoerythrin. The resulting half-time for microparticle internalization was 15.7 min, with confirmation provided by live confocal imaging as well as transmission electron microscopy.

Metabolic cleavage and translocation efficiency of selected cell penetrating peptides: a comparative study with epithelial cell cultures

We investigated the metabolic stability of four cell penetrating peptides (CPPs), namely SAP, hCT(9-32)-br, [Palpha] and [Pbeta], when in contact with either subconfluent HeLa, confluent MDCK or Calu-3 epithelial cell cultures. Additionally, through analysis of their cellular translocation efficiency, we evaluated possible relations between metabolic stability and translocation efficiency. Metabolic degradation kinetics and resulting metabolites were assessed using RP-HPLC and MALDI-TOF mass spectrometry. Translocation efficiencies were determined using fluorescence-activated cell sorting (FACS) and confocal laser scanning microscopy (CLSM). Between HeLa, MDCK and Calu-3 we found the levels of proteolytic activities to be highly variable. However, for each peptide, the individual degradation patterns were quite similar. The metabolic stability of the investigated CPPs was in the order of CF-SAP = CF-hCT(9-32)-br > [Pbeta]-IAF > [Palpha] and we identified specific cleavage sites for each of the four peptides. Throughout, we observed higher translocation efficiencies into HeLa cells as compared to MDCK and Calu-3, corresponding to the lower state of differentiation of HeLa cell cultures. No direct relation between metabolic stability and translocation efficiency was found, indicating that metabolic stability in general is not a main limiting factor for efficient cellular translocation. Nevertheless, translocation of individual CPPs may be improved by structural modifications aiming at increased metabolic stability.

Proline-rich, amphipathic cell-penetrating peptides

Proline-rich peptides are a chemically and structurally diverse family of cell-penetrating vectors characterised by the presence of pyrrolidine rings from prolines. Amphipathic Pro-rich peptides are particularly effective, demonstrating efficient cellular uptake and non-cytotoxicity. Derivatives with hydrophobic moieties, such as fatty acids or silaproline, have shown highly improved internalisation efficiency; an all D-amino acid version of the CPP SAP was shown to be completely protease resistant and was evaluated in a preliminary in vivo study. CD and TEM studies regarding the self-assembly properties of this family of peptides highlight the possible role of aggregated species in the internalisation process. Finally, these CPPs were shown to be internalised via caveolae or lipid-rafts mediated endocytosis, which circumvents the lysosomal route of degradation.

Cellular delivery of small interfering RNA by a non-covalently attached cell-penetrating peptide: quantitative analysis of uptake and biological effect

Cell-penetrating peptides (CPPs) have evolved as promising new tools to deliver nucleic acids into cells. So far, the majority of these delivery systems require a covalent linkage between carrier and cargo. To exploit the higher flexibility of a non-covalent strategy, we focused on the characterisation of a novel carrier peptide termed MPGα, which spontaneously forms complexes with nucleic acids. Using a luciferase-targeted small interfering RNA (siRNA) as cargo, we optimised the conditions for MPGα-mediated transfection of mammalian cells. In this system, reporter gene activity could be inhibited up to 90% with an IC₅₀ value in the sub-nanomolar range. As a key issue, we addressed the cellular uptake mechanism of MPGα/siRNA complexes applying various approaches. First, transfection of HeLa cells with MPGα/siRNA complexes in the presence of several inhibitors of endocytosis showed a significant reduction of the RNA interference (RNAi) effect. Second, confocal laser microscopy revealed a punctual intracellular pattern rather than a diffuse distribution of fluorescently labelled RNA-cargo. These data provide strong evidence of an endocytotic pathway contributing significantly to the uptake of MPGα/siRNA complexes. Finally, we quantified the intracellular number of siRNA molecules after MPGα-mediated transfection. The amount of siRNA required to induce half maximal RNAi was 10 000 molecules per cell. Together, the combination of methods provided allows for a detailed side by side quantitative analysis of cargo internalisation and related biological effects. Thus, the overall efficiency of a given delivery technique as well as the mechanism of uptake can be assessed.

Membrane surface-associated helices promote lipid interactions and cellular uptake of human calcitonin-derived cell penetrating peptides

hCT(9-32) is a human calcitonin (hCT)-derived cell-penetrating peptide that has been shown to translocate the plasma membrane of mammalian cells. It has been suggested as a cellular carrier for drugs, green fluorescent protein, and plasmid DNA. Because of its temperature-dependent cellular translocation resulting in punctuated cytoplasmatic distribution, its uptake is likely to follow an endocytic pathway. To gain insight into the molecular orientation of hCT(9-32) when interacting with lipid models, and to learn more about its mode of action, various biophysical techniques from liposome partitioning to high-resolution NMR spectroscopy were utilized. Moreover, to establish the role of individual residues for the topology of its association with the lipid membrane, two mutants of hCT(9-32), i.e., W30-hCT(9-32) and A23-hCT(9-32), were also investigated. Although unstructured in aqueous solution, hCT(9-32) adopted two short helical stretches when bound to dodecylphosphocholine micelles, extending from Thr10 to Asn17 and from Gln24 to Val29. A23-hCT(9-32), in which the helix-breaking Pro23 was replaced by Ala, displayed a continuous alpha-helix extending from residue 12 to 26. Probing with the spin label 5-doxylstearate revealed that association with dodecylphosphocholine micelles was such that the helix engaged in parallel orientation to the micelle surface. Moreover, the Gly to Trp exchange in W30-hCT(9-32) resulted in a more stable anchoring of the C-terminal segment close to the interface, as reflected by a twofold increase in the partition coefficient in liposomes. Interestingly, tighter binding to model membranes was associated with an increase in the in vitro uptake in human cervix epithelial adenocarcinoma cell line cells. Liposome leakage studies excluded pore formation, and the punctuated fluorescence pattern of internalized peptide indicated vesicular localization and, in conclusion, strongly suggested an endocytic pathway of translocation.

Size-dependent internalization of particles via the pathways of clathrin- and caveolae-mediated endocytosis

Non-phagocytic eukaryotic cells can internalize particles <1 microm in size, encompassing pathogens, liposomes for drug delivery or lipoplexes applied in gene delivery. In the present study, we have investigated the effect of particle size on the pathway of entry and subsequent intracellular fate in non-phagocytic B16 cells, using a range of fluorescent latex beads of defined sizes (50-1000 nm). Our data reveal that particles as large as 500 nm were internalized by cells via an energy-dependent process. With an increase in size (50-500 nm), cholesterol depletion increased the efficiency of inhibition of uptake. The processing of the smaller particles was significantly perturbed upon microtubule disruption, while displaying a negligible effect on that of the 500 nm beads. Inhibitor and co-localization studies revealed that the mechanism by which the beads were internalized, and their subsequent intracellular routing, was strongly dependent on particle size. Internalization of microspheres with a diameter <200 nm involved clathrin-coated pits. With increasing size, a shift to a mechanism that relied on caveolae-mediated internalization became apparent, which became the predominant pathway of entry for particles of 500 nm in size. At these conditions, delivery to the lysosomes was no longer apparent. The data indicate that the size itself of (ligand-devoid) particles can determine the pathway of entry. The clathrin-mediated pathway of endocytosis shows an upper size limit for internalization of approx. 200 nm, and kinetic parameters may determine the almost exclusive internalization of such particles along this pathway rather than via caveolae.

Phagocytosis of titanium particles and necrosis in TNF-alpha-resistant mouse sarcoma L929 cells

In the oral cavity, titanium is an excellent biocompatible material. However, it is reported that high ratios of intracellular titanium particles can cause cell apoptosis or necrosis by as-yet unknown mechanisms. The purpose of this study was to investigate the response of tumor necrosis factor alpha (TNF-alpha)-resistant L929 fibroblasts to titanium particles. Cells were cultured in Eagle's medium supplemented with fetal bovine serum and L-glutamine. Titanium particle sizes were less than 9 micro. Cytotoxicity was assayed by a cell counting kit, trypan blue dye exclusion test and lactate dehydrogenase (LDH) leakage. The production of reactive oxygen species (ROS) was detected by a confocal laser scanning microscope (CLSM) using dichlorofluorescein diacetate as a fluorescent probe. Morphology was viewed by a CLSM and with an X-ray microanalyser (XMA). When titanium particles were added to cells, the viability decreased to around 50% at a particle concentration of 2.0%. The number of dead cells and LDH activity in the culture media increased significantly between 1 and 2 days. However, formation of active oxygen species did not occur, since no dichlorofluorescein fluorescence was observed. A scanning electron photomicrograph (SEM) revealed a large number of particles covering or adhering to cellular components in lysed cells compared with flattened control cells attached to the substrate. The XMA showed that the titanium accumulation was coincident with the deformed cell shape. The CLSM also confirmed that particles were within the cells. From these results it was concluded that titanium particles ingested in large quantities into the cell induced necrosis by a pathway other than by producing ROS.

Potential role for a carbohydrate moiety in anti-Candida activity of human oral epithelial cells

Candida albicans is both a commensal and a pathogen at the oral mucosa. Although an intricate network of host defense mechanisms are expected for protection against oropharyngeal candidiasis, anti-Candida host defense mechanisms at the oral mucosa are poorly understood. Our laboratory recently showed that primary epithelial cells from human oral mucosa, as well as an oral epithelial cell line, inhibit the growth of blastoconidia and/or hyphal phases of several Candida species in vitro with a requirement for cell contact and with no demonstrable role for soluble factors. In the present study, we show that oral epithelial cell-mediated anti-Candida activity is resistant to gamma-irradiation and is not mediated by phagocytosis, nitric oxide, hydrogen peroxide, and superoxide oxidative inhibitory pathways or by nonoxidative components such as soluble defensin and calprotectin peptides. In contrast, epithelial cell-mediated anti-Candida activity was sensitive to heat, paraformaldehyde fixation, and detergents, but these treatments were accompanied by a significant loss in epithelial cell viability. Treatments that removed existing membrane protein or lipid moieties in the presence or absence of protein synthesis inhibitors had no effect on epithelial cell inhibitory activity. In contrast, the epithelial cell-mediated anti-Candida activity was abrogated after treatment of the epithelial cells with periodic acid, suggesting a role for carbohydrates. Adherence of C. albicans to oral epithelial cells was unaffected, indicating that the carbohydrate moiety is exclusively associated with the growth inhibition activity. Subsequent studies that evaluated specific membrane carbohydrate moieties, however, showed no role for sulfated polysaccharides, sialic acid residues, or glucose- and mannose-containing carbohydrates. These results suggest that oral epithelial cell-mediated anti-Candida activity occurs exclusively with viable epithelial cells through contact with C. albicans by an as-yet-undefined carbohydrate moiety.

Fluid phase endocytosis within buccal mucosal cells of alcohol misusers

The structure of the oral mucosa is now well characterised, although studies on oral epithelial cell function have received less attention. The aims of this study were to see whether endocytosis could be demonstrated in cells from oral smears and if so, to assess the effect of chronic high alcohol intake on such uptake. Buccal mucosal smears were collected from 135 patients (91 non- or social drinkers, and 44 patients with harmful alcohol use). Name, age, sex, and alcohol history (for alcohol problem patients) were recorded. Cell suspensions were incubated in a solution of bovine serum albumin (BSA)-coated fluorescently labelled latex microspheres (0.02 micron diameter) in Ham's F-10 culture medium for 1 h at 37 degrees C as a marker of fluid phase endocytosis. Uptake of microspheres was confirmed by confocal microscopy, and mean endocytosed fluorescence levels determined by flow cytometry. A repeat smear from 11 of the alcohol patients was taken 9-14 days later. Endocytosis was significantly reduced in both male (P < 0.01) and female (P < 0.01) alcohol problem patients compared to controls. Units of alcohol consumed and cigarettes smoked per day did not show a dose-response correlation with endocytosis in the alcohol problem patients. Apparent abstinence from alcohol had no further effect on endocytic uptake at days 9-14. This study shows that normal oral squamous cells removed as buccal smears readily endocytose fluorescent microspheres and that this capacity can be affected by alcohol. Chronic high alcohol intake would appear to down regulate endocytosis in buccal cells even up to 14 days of abstinence. This may have implications for the pathogenesis of oral mucosal disorders in long-term users.