Growth regulation of serum-free cultures of epithelial cells from normal human buccal mucosa

Patients with oral lichen planus display lower levels of salivary acidic glycoproteins than individuals without oral mucosal disease

OBJECTIVES

Salivary proteins, acidic glycoproteins, and free calcium might take part in oral mucosal defence against inflammation in oral lichen planus (OLP). The study aimed to investigate whether the levels of sulfated and sialylated glycoproteins, total protein, and free calcium in saliva from patients with OLP differ from those of individuals without oral mucosal diseases.

MATERIAL AND METHODS

Patients diagnosed with OLP (n = 25) and two control groups without any oral mucosal disease; age- and gender-matched controls (n = 25, 65.6 ± 2.9 years), and younger controls (n = 25, 41.8 ± 2.5 years) were included. Subjective dry mouth (xerostomia) was assessed by asking a single-item question. Chew-stimulated whole saliva was collected to measure sulfated and sialylated glycoproteins by the Alcian Blue method. The total protein was determined spectrophotometrically, and the free calcium measured using an electrode.

RESULTS

The output of salivary sulfated and sialylated glycoproteins in the OLP group (21.8 ± 2.4 µg/min) was lower than in the age- and gender-matched controls (43.0 ± 2.9 µg/min, p = 0.0002), whereas the total protein and calcium output did not differ between the three groups (p > 0.05). The prevalence of xerostomia was significantly higher in the OLP group compared to both control groups (p = 0.038).

CONCLUSIONS

Patients with OLP showed a high prevalence of xerostomia and lower levels of salivary acidic type glycoproteins compared to the individuals without oral mucosa disease.

CLINICAL RELEVANCE

It is relevant to investigate the role of acidic glycoproteins in the pathogenesis of OLP.

GMP compliant isolation of mucosal epithelial cells and fibroblasts from biopsy samples for clinical tissue engineering

Engineered epithelial cell sheets for clinical replacement of non-functional upper aerodigestive tract mucosa are regulated as medicinal products and should be manufactured to the standards of good manufacturing practice (GMP). The current gold standard for growth of epithelial cells for research utilises growth arrested murine 3T3 J2 feeder layers, which are not available for use as a GMP compliant raw material. Using porcine mucosal tissue, we demonstrate a new method for obtaining and growing non-keratinised squamous epithelial cells and fibroblast cells from a single biopsy, replacing the 3T3 J2 with a growth arrested primary fibroblast feeder layer and using pooled Human Platelet lysate (HPL) as the media serum supplement to replace foetal bovine serum (FBS). The initial isolation of the cells was semi-automated using an Octodissociator and the resultant cell suspension cryopreservation for future use. When compared to the gold standard of 3T3 J2 and FBS containing medium there was no reduction in growth, viability, stem cell population or ability to differentiate to mature epithelial cells. Furthermore, this method was replicated with Human buccal tissue, providing cells of sufficient quality and number to create a tissue engineered sheet.

Towards a defined, serum- and feeder-free culture of stratified human oral mucosal epithelium for ocular surface reconstruction

PURPOSE

Ocular surface reconstruction with cultivated oral mucosal epithelial transplantation technique is a viable treatment option for severe ocular surface injuries and diseases with limbal stem cell deficiency. Currently, this technique is based on utilization of xenogenic, allogenic or undefined components such as murine 3T3 feeders, serum and amniotic membrane. In this study, we aimed to find a more defined culture method to generate stratified human oral mucosal epithelium.

METHODS

In this study, we have examined the formation of stratified cell sheets from human oral mucosal epithelial cells under serum-free culture environment both in the absence and presence of fibroblast-conditioned culture medium and elevated epidermal growth factor (EGF) concentration.

RESULTS

In all examined culture conditions, the cultivated oral epithelial cells formed a stratified tissue, which was positive for keratins K3/12, K4 and K13. The tissue-engineered oral epithelia also expressed proliferation and progenitor markers Ki67 and p63 in the basal layer of the cell sheets, suggesting that the epithelia still had regenerative capacity. The cultures presented expression of tight junction proteins ZO-1 and occludin and high transepithelial electrical resistance values.

CONCLUSION

In this culture method, we have been able to produce stratified cell sheets successfully without serum, conditioning of the medium or increased EGF concentration. We provide a novel protocol to produce tight multi-layered epithelium with proliferative potential, which can be easily adapted for cultivated oral mucosal epithelial transplantation.

Oral and pharyngeal epithelial keratinocyte culture

Primary human oral epithelial cells are readily available and have been recently employed for tissue engineering. These cells are currently being widely utilized in multiple research efforts, ranging from the study of oral biology, mucosal immunity, and carcinogenesis to stem cell biology and tissue engineering. This chapter describes step-by-step protocols for the successful isolation and culture of human oral epithelial cells and fibroblasts, and techniques for their use in two-dimensional and three-dimensional culture systems. The described methods will enable to generate reconstituted tissues that resemble epithelial like structures in vitro, which can recapitulate some of the key features of the oral epithelium in vivo.

The application of normal, SV40 T-antigen-immortalised and tumour-derived oral keratinocytes, under serum-free conditions, to the study of the probability of cancer progression as a result of environmental exposure to chemicals

In vitro models are currently not considered to be suitable replacements for animals in experiments to assess the multiple factors that underlie the development of cancer as a result of environmental exposure to chemicals. An evaluation was conducted on the potential use of normal keratinocytes, the SV40 T-antigen-immortalised keratinocyte cell line, SVpgC2a, and the carcinoma cell line, SqCC/Y1, alone and in combination, and under standardised serum-free culture conditions, to study oral cancer progression. In addition, features considered to be central to cancer development as a result of environmental exposure to chemicals, were analysed. Genomic expression, and enzymatic and functional data from the cell lines reflected many aspects of the transition of normal tissue epithelium, via dysplasia, to full malignancy. The composite cell line model develops aberrances in proliferation, terminal differentiation and apoptosis, in a similar manner to oral cancer progression in vivo. Transcript and protein profiling links aberrations in multiple gene ontologies, molecular networks and tumour biomarker genes (some proposed previously, and some new) in oral carcinoma development. Typical specific changes include the loss of tumour-suppressor p53 function and of sensitivity to retinoids. Environmental agents associated with the aetiology of oral cancer differ in their requirements for metabolic activation, and cause toxic effects to cells in both the normal and the transformed states. The results suggest that the model might be useful for studies on the sensitivity of cells to chemicals at different stages of cancer progression, including many aspects of the integrated roles of cytotoxicity and genotoxicity. Overall, the properties of the SVpgC2a and SqCC/Y1 cell lines, relative to normal epithelial cells in monolayer or organotypic culture, support their potential applicability to mechanistic studies on cancer risk factors, including, in particular, the definition of critical toxicity effects and dose-effect relationships.

The phenotype of in vitro reconstituted normal human oral epithelium is essentially determined by culture medium

OBJECTIVE

To evaluate the role of various culture media and serum supplement on growth of oral cells in monolayer, and on morphogenesis of in vitro reconstituted normal human oral epithelium.

METHODS

Primary keratinocytes and fibroblasts were isolated from normal human buccal mucosa. The monolayers were assessed by growth curve analysis and morphology. The organotypic cultures were evaluated by morphometry, immunohistochemistry, and TUNEL.

RESULTS

FAD medium (a 3:1 mixture of Dulbecco's modified Eagle's medium and Ham's F12 medium) was able to support fibroblast growth in defined conditions, and to diminish the negative effect of physiological Ca concentration on keratinocytes in monolayers. Medium type had a profound influence on morphogenesis of in vitro reconstituted human oral epithelium. FAD medium was superior to other types of medium tested in supporting both epithelial growth and differentiation. Defined conditions supported epithelial morphogenesis equally well as serum-containing medium.

CONCLUSIONS

This study points to an essential role of medium composition for optimized growth and differentiation of primary organotypic cultures.

Optimizing DNA yield from buccal swabs in the elderly: attempts to promote buccal cell growth in culture

Participation in genetic studies is often limited by a volunteer's reluctance to donate blood samples. We wished to determine if alternate, less painful, methods to venipuncture could be used to collect cells to provide DNA for genotyping, and whether the cells could be grown in culture for extraction of DNA. Volunteers in the study were comprised of two groups. Nine individuals from a university campus were recruited to provide samples for initial experiments. A second group of 710 twins and singletons from North Carolina and of African-American descent were a part of an ongoing study of age-related traits and participated in collection of buccal swabs via the mail. A protocol was generated that maximizes the recovery of DNA from buccal swabs, which are easier to handle than saline rinses. The DNA recovered is stable over several years, allowing genotype tests at a future date. Attempts to encourage growth of buccal epithelial cells recovered from swabs in tissue culture proved unsuccessful. Buccal swabs work well for the collection of DNA, especially from nonclinic-based volunteers, and can be sent via the mail to the laboratory for DNA extraction. Thus, an inexpensive and efficient method exists for genetic studies of population-based samples.

Uniform expression of alcohol dehydrogenase 3 in epithelia regenerated with cultured normal, immortalised and malignant human oral keratinocytes

The human oral epithelium is a target for damage from the inhalation of formaldehyde. However, most experimental studies on this chemical have relied on laboratory animals that are obligatory nose breathers, including rats and mice. Therefore, in vitro model systems that mimic the structure of the human oral epithelium and which retain normal tissue-specific metabolic competence are desirable. Based on the established role of alcohol dehydrogenase 3 (ADH3), also known as glutathione-dependent formaldehyde dehydrogenase, as the primary enzyme catalysing the detoxification of formaldehyde, the aim of this study was to investigate the expression of ADH3 in organotypic epithelia regenerated with normal (NOK), immortalised (SVpgC2a) and malignant (SqCC/Y1) human oral keratinocytes. Organotypic epithelia, usually consisting of 5-10 cell layers, were produced at the air-liquid interface of collagen gels containing human oral fibroblasts, after culture for 10 days in a standardised serum-free medium. Immunochemical staining demonstrated uniform expression of ADH3 in these organotypic epithelia, as well as in the epithelial cells of oral tissue. The specificity of the ADH3 antiserum was ascertained from the complete neutralisation of the immunochemical reaction with purified ADH3 protein. Assessment of the staining intensities indicated that the expression levels were similar among the regenerated epithelia. Furthermore, the regenerated epithelia showed similar ADH3 expression to the epithelium in oral tissue. Therefore, a tissue-like expression pattern for ADH3 can be generated from the culture of various oral keratinocyte lines in an organotypic state. Similar expression levels among the various cell lines indicate the preservation of ADH3 during malignant transformation, and therefore that NOK, SVpgC2a and SqCC/Y1 represent functional models for in vitro studies of formaldehyde metabolism in human oral mucosa.

Innate cellular fluorescence reflects alterations in cellular proliferation

BACKGROUND AND OBJECTIVE

The objective of this study was to examine the question of whether unique spectral patterns were associated with cell proliferation and could be identified by comparing the fluorescence pattern of slow to rapid growing cells.

STUDY DESIGN/MATERIALS AND METHODS

Three in vitro model systems, (A431 cells inhibited by EGF, serum-starved 3T3 fibroblasts, and normal oral epithelial cells exposed to TGF beta), were analyzed using fluorescence spectroscopy. Growth status was monitored by cell number, 3H-thymidine incorporation, and flow cytometry.

RESULTS

The excitation spectra (lambda ex 240-430 nm, lambda em 450 nm) effectively distinguished slow and rapid growing cells in all three systems. Statistical analysis of the ratios of the main broad peak (320-350 nm) to a point on the down-slope of the curve at 370 nm was statistically significant. Ratios in the emission scan (lambda ex 340 nm, lambda em 360-660 nm) could separate slow and rapid growing A431 and oral epithelial cells (P = 0.0001 and P = 0.023, respectively), but not slow and fast growing 3T3 cells (P = 0.56).

CONCLUSION

Innate cellular fluorescence has the potential to discriminate proliferating and nonproliferating cell populations.

Toxicity of formaldehyde to human oral fibroblasts and epithelial cells: influences of culture conditions and role of thiol status

The toxicity of formaldehyde, a monomer released from certain polymeric dental materials, was studied in cultured human oral fibroblasts and epithelial cells. The influences of growth conditions were evaluated for both cell types, as well as the role of the internal and external thiol states. A one-hour exposure to formaldehyde decreased the colony-forming efficiency (CFE) of both cell types in a concentration-dependent manner, although the toxicity varied up to 100-fold with the conditions. Clearly, the presence of serum and the thiol cysteine counteracted the toxicity in fibroblasts. Similarly, pituitary extract and cysteine, or a mixture of amino acids and ethanolamines, counteracted the formaldehyde toxicity in serum-free cultures of epithelial cells. In contrast, a growth-promoting surface matrix of fibronectin and collagen did not influence the formaldehyde toxicity, as shown by both the CFE assay and a dye reduction assay. Further, a short-term change to the various growth media per se with or without the supplements serum or cysteine did not significantly alter the CFE. Analysis of the thiol state demonstrated significant differences between epithelial cells and fibroblasts, i.e., comparatively lower cellular levels of the free low-molecular-weight thiols glutathione and cysteine in fibroblasts. This result correlated to significantly higher formaldehyde toxicity in the fibroblasts than in the epithelial cells. Taken together, the results indicated the cytoprotective function of both intracellular and extracellular thiols toward formaldehyde, as well as the usefulness of thiol-free and chemically defined conditions for toxicity assessments in oral epithelial cells and fibroblasts. We conclude that the combined use of a controlled external milieu and the presumed target cell type may be advantageous in evaluations of oral toxicity mechanisms or the toxic potency of dental materials, particularly those which, like formaldehyde, may react with thiols or amines.

A technique for the culture of Barrett's oesophageal cells

Establishment of cells in tissue culture from Barrett's columnar epithelium has been difficult. The aim of this study was to develop a successful tissue culture method employing a serum-free medium for cultivation of Barrett's epithelial cells. Fragments of Barrett's mucosal tissue were explanted in a 3:1 mixture of Dulbecco's modification of Eagle's medium and Ham's F12, to initiate the outgrowth of epithelial cells. Subsequently, a commercial serum-free medium (formulated for the growth of keratinocytes) was used for the propagation of Barrett's oesophagus cells without fibroblast growth. Cells established in culture retained their epithelial morphology, stained positive for cytokeratin, and contained Alcian blue (pH 2.5) and periodic acid-Schiff reagent-positive/diastase-resistant vacuoles, confirming their origin from Barrett's epithelium. Electron microscopy showed tonofilaments, microvilli and desmosomes. Coating the surface of culture vessels was not required and four cell strains could be passaged up to 20 times with no fibroblast growth, in the keratinocyte serum-free medium.

An Ultrastructural Evaluation of the SKIN2™ ZK1200 System as an in Vitro Model of the Human Oral Mucosa

At present, there are no validated experimental models for the preclinical oral mucosa irritancy screening of dental materials and oral hygiene products. Standardised in vitro models for the assessment of skin irritancy have been marketed, and have made possible the application of such models in preclinical skin irritancy testing. Some of these are currently undergoing international interlaboratory validation. The aim of the present study was to evaluate the histology of the commercially available SKIN2™ ZK1200 system as a potential in vitro model of the human oral mucosa. Histological evaluation by light microscopy and transmission electron microscopy over 6 days revealed a fibroblast-rich matrix covered by an 8–12 cell layer of stratifying epithelium, which shared a number of basic characteristics with non-keratinised human oral mucosa (for example, desmosomes, dispersed tonofilaments, glycogen deposits, membrane-coating granules, and keratohyalin granules, both the spherical and ribosome-associated types). Exposure to a methacrylate-based dental fissure sealant for 24 hours caused structural changes in the epithelium which were not reflected by a cytochemical cytotoxicity assay (MTT).

Inhibition of Cholesteatoma Migration in vitro with all-Trans Retinoic Acid

Retinoids have recently become of interest to clinicians because of their ability to inhibit migration and proliferation of premalignant squamous cells while enhancing growth and proliferation of normal cells. An in vitro investigation was undertaken to determine whether retinoic acid exhibits similar inhibitory effects on cholesteatoma cells. Cholesteatoma specimens were obtained intraoperatively from 10 patients undergoing mastoidectomy or revision mastoidectomy for chronic ear disease. Cholesteatoma explant growth and en mass migration were observed daily, and topographic maps were constructed at various time intervals to quantify rate and direction of expiant migration in the presence or absence of all- trans retinoic acid. Before all- trans retinoic acid administration, explants migrated very rapidly (1 to 2 mm/day). A maximum threefold inhibition of migratory rate occurred, with explants exposed to 0.1 μmol/L retinoic acid when compared with controls. A sixfold maximum inhibition was observed at higher retinoic acid concentrations (5 μmol/L). On removal of all- trans retinoic acid, twofold and fourfold increases in migratory rates were observed. The direction of explant migration varied significantly for long periods of time and appeared not to be affected by retinoic acid. This investigation suggests that all- trans retinoic acid has an inhibitory effect on cholesteatoma cell migration. Retinoids may have a role in controlling cholesteatoma disease in the future.

Cell, tissue and organ culture as in vitro models to study the biology of squamous cell carcinomas of the head and neck

In vitro models are currently being used to study head and neck squamous cell carcinoma (HNSCC). Several hundred HNSCC cell lines have been established by various investigators and used to study a broad spectrum of questions related to head and neck cancer. The head and neck model with respect to multistage carcinogenesis is now complete. Several techniques exist for the culture of normal epithelial cells from the upper aerodigestive tract (UADT). The biology of these UADT cells (oral cavity, oropharynx, hypopharynx and larynx) is being studied. Successful culture of premalignant lesions (dysplastic mucosa, leukoplakia, erythroplakia) has resulted in establishment of a limited number of premalignant cell lines and cell cultures. HPV infection of normal oral epithelial cells for immortalization (approximately premalignant cells) coupled with transformation with carcinogens (malignant cells) has established an experimental model for progression. Two in vivo models for oral carcinogenesis, the 7,12 dimethylbenz(a)anthracene-induced hamster cheek pouch model and the 4-nitroquinoline-N-oxide rat oral model, have been established in culture. Thus, multistage carcinogenesis models have been established from both human tissues and animal models and include cultures of normal, premalignant and malignant cells. Culture techniques for growing dissociated primary tumor cells for short term experimental analysis are being used. The culture of normal or tumor tissue as organ/explant cultures allows for the maintenance of normal cell-cell and cell-matrix interaction, but limits experimentation since these cultures cannot be propagated. Several three dimensional model systems are being used to obtain this histological complexity but allow for experimentation. The ability to culture normal, premalignant and malignant cells coupled with the use of a variety of culture techniques, should allow for the continued growth and experimentation in head and neck cancer research.

Growth and gene expression in diploid epithelial cell lines derived from normal human parotid gland

Secretions of salivary glands are essential for the maintenance of oral health. Due to the lack of suitable in vitro models, studies to examine biochemical and molecular mechanisms of the cellular secretions have been difficult. Furthermore, adequate quantities of human epithelial cells could not be obtained, because normal diploid cells are believed to exhibit a limited lifespan of two to three passages (40-50 population doublings). This report describes for the first time the development of two diploid epithelial acinar cell lines, HPAM1 and HPAF1, derived from the normal human parotid gland. The cell lines are propagated in serum-free medium comprised of keratinocyte basal medium supplemented with insulin (5 micrograms/ml), hydrocortisone (0.5 micrograms/ml), epidermal growth factor (EGF, 10 ng/ml), bovine pituitary extract (25 micrograms/ml), and antibiotics. The HPAM1 cell line has been passaged more than 50 times (> 189 population doublings) and HPAF1 more than 40 times (> 185 population doublings). Both cell lines exhibit normal diploid karyotypes, lack transformed phenotypes and are non-tumorigenic in nude mice. Both cell lines produce tissue-specific proteins, i.e. alpha-amylase 1, basic proline-rich protein, and cystatins; and express the corresponding genes as determined by RT-PCR analyses. These results demonstrate that normal diploid human cells do not inherently exhibit limited life-span in vitro and can, under optimum conditions, be propagated indefinitely.

Squamous cell differentiation markers in normal, premalignant, and malignant epithelium: effects of retinoids

Vitamin A and some of its analogs (retinoids) maintain normal differentiation of epithelial tissues by preventing aberrant squamous differentiation of cells in nonkeratinizing epithelia. They can also reverse squamous metaplasia, which develops in vivo during vitamin A deficiency. These effects are the result of the ability of retinoids to suppress the expression of genes associated with squamous differentiation (e.g., transglutaminase type I, loricrin, involucrin, filaggrin, and keratin K1). In addition, retinoids reverse keratinizing premalignant lesions in the oral cavity, and inhibit the growth and squamous differentiation of head and neck squamous cell carcinomas (HNSCCs) in vitro. Nuclear retinoic acid receptors, which function as DNA-binding, trans-acting, transcription-modulating factors, are considered to be the proximate mediators of the effects of retinoids on gene expression and may mediate the re-regulation of aberrant differentiation and growth of premalignant and some malignant cells, thereby suppressing the development of head and neck cancer.

Effects of areca nut on growth, differentiation and formation of DNA damage in cultured human buccal epithelial cells

Because the high incidence of oral cancers in South-East Asia is causally linked to the common habit of betel quid chewing, the effects of an aqueous extract of areca nut, one of the main ingredients of the quid, on growth, differentiation, morphology and DNA damage were studied in cultured human buccal epithelial cells. An acute exposure (3 hr) of the cells to the extract altered their morphology and induced ridges in the plasma membrane, with indications of internalization of extract particles. Such exposure also caused formation of DNA single-strand breaks which accumulated during post-treatment culture, indicating continuous exposure to residual particles and/or the possibility of inhibited DNA repair. The extract accelerated terminal differentiation of the cells, measured as involucrin expression at relatively non-toxic levels. The extract caused similar loss of colony-forming efficiency in normal cells and in a buccal carcinoma cell line (SqCC/YI) which was defective in its ability to undergo differentiation, indicating that extract toxicity could occur independently from this response. Finally, the genotoxicity of the salivary areca-nut-specific carcinogen 3-(N-nitrosomethyl-amino)propionaldehyde, was demonstrated by the formation of DNA protein cross-links and DNA single-strand breaks in normal buccal epithelial cells. These findings in vitro suggest that betel quid carcinogenesis in the human oral cavity may involve cytopathic alterations of normal cell morphology, growth and differentiation, as well as formation of DNA damage by areca-nut-related agents extracted or formed in saliva.

Serum-free cell culture

Cell culture is one important tool when studying cellular functions and molecular biology. It is also a basic method in most virological investigations. Serum has been an obligatory component in most cell culture media. During the last decades serum-free, chemically defined media have been developed, that are supplemented with a number of substances with specific cellular activities. The main developments of defined media are presented. Examples are given of investigations with different cell types.