The use of mini-organ cultures of human upper aerodigestive tract epithelia in ecogenotoxicology

Organoids for toxicology and genetic toxicology: applications with drugs and prospects for environmental carcinogenesis

Advances in three-dimensional (3D) cell culture technology have led to the development of more biologically and physiologically relevant models to study organ development, disease, toxicology and drug screening. Organoids have been derived from many mammalian tissues, both normal and tumour, from adult stem cells and from pluripotent stem cells. Tissue organoids can retain many of the cell types and much of the structure and function of the organ of origin. Organoids derived from pluripotent stem cells display increased complexity compared with organoids derived from adult stem cells. It has been shown that organoids express many functional xenobiotic-metabolising enzymes including cytochrome P450s (CYPs). This has benefitted the drug development field in facilitating pre-clinical testing of more personalised treatments and in developing large toxicity and efficacy screens for a range of compounds. In the field of environmental and genetic toxicology, treatment of organoids with various compounds has generated responses that are close to those obtained in primary tissues and in vivo models, demonstrating the biological relevance of these in vitro multicellular 3D systems. Toxicological investigations of compounds in different tissue organoids have produced promising results indicating that organoids will refine future studies on the effects of environmental exposures and carcinogenic risk to humans. With further development and standardised procedures, advancing our understanding on the metabolic capabilities of organoids will help to validate their use to investigate the modes of action of environmental carcinogens.

Organoid culture to study epithelial cell differentiation and barrier formation in the colon: bridging the gap between monolayer cell culture and human subject research

Organoid culture provides a powerful technology that can bridge the gap between monolayer cell culture on the one hand and whole animal or human subject research on the other. Tissues from many different organs from multiple species, including human, have already been successfully adapted to organoid growth. While optimal culture conditions have not yet been established for all tissue types, it seems that most tissues will, ultimately, be amenable to this type of culture. The colon is one of the tissues in which organoid culture was first established as a technology and which has been most successfully employed. The ready availability of histologically normal tissue as well as both premalignant and malignant tissue (often from the same individual) makes this possible. While individual tumors are highly variable relative to one another in organoid culture, a high degree of genotypic consistency exists between the tumor tissue and the histologically normal counterpart from a given source. Further, source material and tumor tissue in organoid culture demonstrate a high degree of genotypic consistency. Even after 6-9 mo in continuous culture, drift in the mutational profile has been shown to be minimal. Colon tissue maintained in organoid culture, thus, provides a good surrogate for the tissue of origin-a surrogate, however, that is as amenable to intervention with molecular, pharmacological, and immunological approaches as are more-traditionally studied cell lines.

Effects of cold atmospheric plasma (CAP) on bacteria and mucosa of the upper aerodigestive tract

OBJECTIVE

Ear, nose and throat infections are among the most common reasons for absence from work. They are usually caused by various bacteria like Haemophilus influenzae, Staphylococcus aureus, Streptococcus pneumoniae and Streptococcus pyogenes. Cold atmospheric plasma (CAP) can effectively eliminate even multi-resistant bacteria and has no cytotoxic or mutagenic effects on the mucosa when applied for less than 60s. Aim of the study was to evaluate the effects of CAP on common ENT bacteria and on the mucosa of the upper aerodigestive tract.

METHODS

The bactericidal effects of CAP against the bacteria most commonly causing ENT infections were investigated using the colony-forming units assay (CFU) on a Müller-Hinton agar plate after applying CAP for 30, 60, 90 and 120s. To evaluate the interaction of CAP with mucosal cells, 3D mini organ cultures were treated for up to 180s, after which cell viability and necrosis induction were evaluated.

RESULTS

Treatment with CAP for 60s or longer induced at least a 3-log₁₀ reduction in the bacterial load (> 99.9%). Treatment times shorter than 60s had only slight cytotoxic effects on cell viability and necrosis whereas treatment times above 60s showed a fast increase of cytotoxic side effects.

CONCLUSION

CAP exhibited strong bactericidal effects on the most common ENT pathogens. Treatment times of up to 60s showed only minimal adverse reactions in healthy mucosa. CAP could be a promising new therapeutic modality for ENT infections.

Use of Single-cell Gel Electrophoresis Assays in Dietary Intervention Trials

The single-cell gel electrophoresis (SCGE) technique has been frequently used to investigate the impact of consumption of complex foods and individual constituents on DNA stability in humans. Since no division or cultivation of the indicator cells (in most studies lymphocytes) is required, this approach is less costly and time consuming than cytogenetic methods. Apart from single- and double-stand breaks and apurinic sites, which can be detected under standard conditions, it is also possible to assess the formation of oxidized DNA bases and alterations of DNA repair as well as protection of the DNA against chemical carcinogens. In total, 93 studies have been published since the first use of the Comet assay in this field in 1997. The results which emerged from these studies show that human foods contain specific highly protective components (e.g. gallic acid, xanthohumol, isoflavones); promising results were also obtained with beverages (coffee and other drinks), while mixed diets with vegetables and fruits conferred no or moderate protection; however, individual plant foods (e.g. kiwis and specific cruciferous vegetables) were highly protective. It is notable that prevention of DNA damage was rarely detected under standard conditions while evidence for reduced formation of oxidized DNA bases was found in approximately 30% of the trials. In some investigations it was possible to identify the modes of action by which specific compounds prevented damage of the genetic material in additional mechanistic experiments. The currently available data show that SCGE assays are a valuable tool for identifying dietary factors which improve the stability of the genetic material and prevent adverse health effects which are causally related to DNA damage.

Epithelial cells as alternative human biomatrices for comet assay

The comet assay is a valuable experimental tool aimed at mapping DNA damage in human cells in vivo for environmental and occupational monitoring, as well as for therapeutic purposes, such as storage prior to transplant, during tissue engineering, and in experimental ex vivo assays. Furthermore, due to its great versatility, the comet assay allows to explore the use of alternative cell types to assess DNA damage, such as epithelial cells. Epithelial cells, as specialized components of many organs, have the potential to serve as biomatrices that can be used to evaluate genotoxicity and may also serve as early effect biomarkers. Furthermore, 80% of solid cancers are of epithelial origin, which points to the importance of studying DNA damage in these tissues. Indeed, studies including comet assay in epithelial cells have either clear clinical applications (lens and corneal epithelial cells) or examine genotoxicity within human biomonitoring and in vitro studies. We here review improvements in determining DNA damage using the comet assay by employing lens, corneal, tear duct, buccal, and nasal epithelial cells. For some of these tissues invasive sampling procedures are needed. Desquamated epithelial cells must be obtained and dissociated prior to examination using the comet assay, and such procedures may induce varying amounts of DNA damage. Buccal epithelial cells require lysis enriched with proteinase K to obtain free nucleosomes. Over a 30 year period, the comet assay in epithelial cells has been little employed, however its use indicates that it could be an extraordinary tool not only for risk assessment, but also for diagnosis, prognosis of treatments and diseases.

Nicotine causes genotoxic damage but is not metabolized during long-term exposure of human nasal miniorgan cultures

Human nasal miniorgan cultures (MOC) are a useful tool in ecogenotoxicology. Repetitive exposure to nicotine showed reversible DNA damage, and stable CYP2A6 expression was demonstrated in nasal MOC in previous investigations. The aim of the present study was to evaluate the genotoxic effect of nicotine in nasal MOC after chronic nicotine exposure, and to monitor possible metabolism capacities. MOC were dissected from human nasal mucosa and cultured under standard cell culture conditions. MOC were exposed to nicotine for 3 weeks at concentrations of 1 μM and 1 mM. The concentrations were chosen based on nicotine plasma levels in heavy smokers, and possible concentrations used in topical application of nicotine nasal spray. DNA damage was assessed by the comet assay at days 7, 14 and 21. Concentrations of nicotine and cotinine were analyzed in cell culture medium by gas chromatography/mass spectrometry to determine a possible metabolism of nicotine by MOC. Distinct DNA damage in MOC could be demonstrated after 1 week of exposure to 1 μM and 1 mM nicotine. This effect decreased after 2 and 3 weeks with no statistically relevant DNA migration. No nicotine metabolism could be detected by changes in nicotine and cotinine concentrations in the supernatants. This is the first time genotoxic effects have been evaluated in nasal MOC after chronic nicotine exposure for up to 3 weeks. Genotoxic effects were present after 1 week of culture with a decrease over time. Down-regulation of nicotinic acetylcholine receptors, which are expressed in nasal mucosa, may be a possible explanation. The lack of nicotine metabolism in this model could be explained by the functional loss of CYP2A6 during chronic nicotine exposure. Further investigations are necessary to provide a more detailed description of the underlying mechanisms involved in DNA damage by nicotine.

Dexamethasone Induces Apoptosis of Nasal Polyp-Derived Tissue Cultures Through JNK and p38 MAPK Activation

Objectives

Glucocorticoids, such as dexamethasone (DEX), increase apoptosis in a variety of white cells in nasal polyps and apoptosis is an important factor in the resolution of inflammation. However, the mechanism of glucocorticoids induced apoptosis in nasal polyp remains unclear. In this study the authors evaluated which pathways were engaged in apoptosis induced by DEX in an ex vivo model of nasal polyps.

Methods

Nasal polyp tissues were cultured using an air-liquid interface method. Cultures were maintained in the absence or presence of DEX (10 or 100 µM) for 24 hours. To investigate the involvement of the apoptotic signaling pathways in nasal polyp, such as caspase cascades, Fas-FasL signaling pathway, mitochondrial pathway and p38 mitogen-activated protein kinase (MAPK)/JNK pathway, the authors performed reverse transcription-polymerase chain reaction and Western blotting.

Results

The expression ratios of FasL, activated form of caspase-8, caspase-9, and caspase-3 were significantly higher in DEX-treated polyps (P<0.01). In the Bcl-2 family expression, the anti-apoptotic molecules, Bcl-2 and Bcl-XL decreased, but pro-apoptotic molecules, Bax increased, and Bid and Bad were activated. In the conventional MAPKs, JNK, and the phospho-p38 MAPK were significantly higher, but phospho-extracellular signal-regulated kinase (ERK)1/2 was significantly lower in DEX-treated polyps (P<0.01).

Conclusion

DEX induces apoptosis of nasal polyp via caspase cascades, Fas-FasL signaling pathway, mitochondrial pathway and p38 MAPK/JNK pathway.

Nitrogen dioxide is genotoxic in urban concentrations

In the discussion on toxic and genotoxic thresholds of air pollutants such as nitrogen dioxide (NO2), realistically low urban concentration ranges are of major interest. For NO2, the WHO defines the annual limit value as corresponding to 0.02 ppm. In the present study, the toxicity and genotoxicity of NO2 is set at a concentration under this limit value and examined in human nasal epithelium at different exposure durations in vitro. Nasal epithelial mucosa samples of 10 donors were harvested during nasal air passage surgery and cultured as an air-liquid interface. Exposure to 0.01 ppm NO2 or synthetic air as a control was performed for 0.5, 1, 2 and 3 h. Analysis included the caspase-3 ELISA, the single cell microgel electrophoresis (comet) assay and the micronucleus assay. The caspase-3 activity was not influenced by NO2 exposure, DNA strand fragmentation correlated with exposure durations to NO2 at 0.01 ppm NO2, and no cytotoxic effects such as apoptosis, necrosis or disturbances of cell proliferation were present. However, micronucleus induction as a sign of genotoxicity at an exposure duration of 3 h could be shown. Shorter exposures did not induce micronucleus formation. In summary, genotoxicity of NO2 could be demonstrated at a common urban concentration in vitro, but a threshold of NO2 genotoxicity could not be defined based on the present experiments.

Determination of genotoxicity by the Comet assay applied to murine precision-cut lung slices

Precision-cut lung slices (PCLSs) are an organotypic lung model that is widely used in pharmacological, physiological, and toxicological studies. Genotoxicity testing, as a pivotal part of early risk assessment, is currently established in vivo in various organs including lung, brain, or liver, and in vitro in cell lines or primary cells. The aim of the present study was to provide the three-dimensional organ culture PCLS as a new ex vivo model for determination of genotoxicity using the Comet assay. Murine PCLS were exposed to increasing concentrations of ethyl methane sulfonate 'EMS' (0.03-0.4%) and formalin (0.5-5mM). Tissue was subsequently dissociated, and DNA single-strand breaks were quantified using the Comet assay. Number of viable dissociated lung cells was between 4×10(5) and 6.7×10(5)cells/slice. Even treatment with EMS did not induce toxicity compared to untreated tissue control. As expected, DNA single-strand breaks were increased dose-dependently and significantly after exposure to EMS. Here, tail length rose from 24μm to 75μm. In contrast, formalin resulted in a significant induction of DNA cross-links. The effects induced by EMS and formalin demonstrate the usefulness of PCLS as a new ex vivo lung model for genotoxicity testing in the early risk assessment of airborne substances in the future.

Assessment of nicotine-induced DNA damage in a genotoxicological test battery

The role of the tobacco-alkaloid nicotine in tumour biology is widely discussed in the literature. Due to a strong capacity to induce angiogenesis, a pro-mutagenic potential in non-tumour and cancer cells, and a pro- and anti-apoptotic influence, nicotine seems to promote the growth of established tumours. However, results indicating DNA damage and genetic instability associated with nicotine have been contradictory thus far. A variety of markers and endpoints of genotoxicity are required to characterize the genotoxic potential of nicotine. Induction of DNA single- and double-strand breaks, the formation of micronuclei, and the induction of sister chromatid exchange and chromosome aberrations represent possible genotoxicological endpoints at different cellular levels. Human lymphocytes were exposed to nicotine concentrations between 1μM and 1mM for 24h in vitro. The comet assay, the cytokinesis-block micronucleus test, the chromosome aberration (CA) test, and the sister chromatid exchange (SCE) test were then applied. Viability and apoptosis were measured by flow cytometry in combination with the annexin V-propidium iodide staining test. In this test setting, no enhanced DNA migration was measured by the comet assay. An increase in the micronucleus frequency was detected at a concentration of 100μM nicotine without affecting the frequency of apoptotic cells. A distinct genotoxic effect was determined by the CA test and the SCE test, with a significant increase in CA and SCE at a concentration of 1μM. In the annexin V test, nicotine did not influence the proportion of apoptotic or necrotic cells. The current data indicating the induction of CA by nicotine underscore the necessity of ongoing investigations on the potential of nicotine to initiate mutagenesis and tumour promotion. Taking into account the physiological nicotine plasma levels in smokers or in nicotine-replacement therapy, particularly the long-term use of nicotine should be critically discussed.

Curcumin and other polyphenolic compounds in head and neck cancer chemoprevention

Despite clear results of observational studies linking a diet rich in fruits and vegetables to a decreased cancer risk, large interventional trials evaluating the impact of dietary micronutrient supplementation, mostly vitamins, could not show any beneficial effects. Today it has become clear that a single micronutrient, given in supernutritional doses, cannot match cancer preventive effects of whole fruits and vegetables. In this regard polyphenols came into focus, not only because of their antioxidant potential but also because of their ability to interact with molecular targets within the cells. Because polyphenols occur in many foods and beverages in high concentration and evidence for their anticancer activity is best for tissues they can come into direct contact with, field cancerization predestines upper aerodigestive tract epithelium for cancer chemoprevention by polyphenols. In this paper, we summarize cancer chemopreventive attempts with emphasis on head and neck carcinogenesis and discuss some methodological issues. We present data regarding antimutagenic effects of curcumin and epigallocatechin-3-gallate in human oropharyngeal mucosa cultures exposed to cigarette smoke condensate.

The impact of EGFR stimulation and inhibition on BPDE induced DNA fragmentation in oral/oropharyngeal mucosa in vitro

Still, the vast majority of head and neck squamous cell carcinoma (HNSCC) can be linked to the "traditional" risk factors tobacco smoke and alcohol consumption. These tumors are believed to be the results of multiple years of carcinogenic impact on upper aerodigestive tract mucosa. The frequent observation, that one patient suffers from several synchronous cancers, multiple local recurrences, and second primary tumors led to the concept of field cancerization, first introduced by Slaughter and colleagues in 1953. As underlying molecular events, genetic instability, loss of heterozygosity, amplification, deletion, up- and down-regulation of oncogenes and/or tumor suppressor genes were revealed. One of the best studied oncogenic features of head and neck carcinogenesis are high expression levels of epidermal growth factor receptor (EGFR). Enhanced expression of the receptor was detected in histologically normal mucosa from HNSCC patients and increasing levels during the progress from hyperplasia to dysplastic lesion and invasive carcinoma were demonstrated. Whereas nearly all of our knowledge about EGFR biology in HNSCC is based on preclinical and clinical studies investigating receptor inhibitors, little is known about cause and function of EGFR in premalignant mucosa. In this study we show, that EGFR stimulation significantly decreases carcinogen induced DNA damage in normal mucosa from HNSCC patients and that this effect is completely abrogated adding an anti-EGFR antibody before stimulation, while there was no effect in non-tumor controls. The effect of EGFR inhibition was contrary. In non-tumor controls, blocking the receptor with an antibody significantly decreased DNA damage, whereas in cases no effect was seen. Our results indicate an important role of the receptor during chemical carcinogenesis. On the basis of this study we suppose, that increasing EGFR levels during head and neck carcinogenesis can be interpreted as a physiological response to permanent carcinogen impact on the mucosa.

Repetitive exposure to zinc oxide nanoparticles induces dna damage in human nasal mucosa mini organ cultures

Data on the toxicological properties of zinc oxide nanoparticles (ZnO-NPs) is incomplete. ZnO-NPs may enter humans via inhalation or ingestion. The aim of the current study was to evaluate ZnO-NP-induced genotoxicity in three-dimensional (3D) mini organ cultures (MOCs) of human nasal mucosa following repeated exposure to ZnO-NP and regeneration. Nasal MOCs of 10 patients and ZnO-NPs were cultivated for one week and then characterized by electron microscopy. Nasal MOCs were partially covered by ciliated epithelium after one week of cultivation. ZnO-NPs were distributed to the cytoplasm and the nucleus. MOCs were exposed once, twice, or three times to 0.1 or 5 μg/ml of ZnO-NPs for 1 hr per exposure and were then evaluated for cytotoxicity and genotoxicity. MOCs were cultivated for 24 hr after the triple ZnO-NP exposure to allow for regeneration. ZnO-NP exposure did not result in significant cytotoxicity or apoptosis, as determined by trypan blue exclusion and caspase-3 activity, respectively. A significant increase in DNA damage was detected following repetitive exposure compared to single exposure to ZnO-NPs at 5 μg/ml, but not 0.1 μg/ml ZnO-NPs. At both concentrations of ZnO-NP, DNA fragmentation increased after 24 hr of regeneration. In contrast, DNA damage which was induced by the positive control, methyl methanesulfonate, was significantly reduced after 24-hr regeneration. Thus, our results suggest that repetitive exposure to low concentrations of ZnO-NPs results in persistent or ongoing DNA damage.

Epigallocatechin-3-gallate reduces DNA damage induced by benzo[a]pyrene diol epoxide and cigarette smoke condensate in human mucosa tissue cultures

Although epidemiological studies indicate cancer preventive effects of diets rich in fruit and vegetables, large clinical intervention studies conducted to evaluate dietary supplementation with micronutrients, mostly vitamins, showed disappointing results in large parts. In contrast, there is encouraging epidemiologic data indicating great chemopreventive potential of a large group of phytochemicals, namely polyphenols. This study shows the DNA protective effect epigallocatechin-3-gallate, a tea catechin, and one of the best-studied substances within this group, on carcinogen-induced DNA fragmentation in upper aerodigestive tract cells. Cell cultures from fresh oropharyngeal mucosa biopsies were preincubated with epigallocatechin-3-gallate in different concentrations before DNA damage was introduced with the metabolically activated carcinogen benzo[a]pyrene-7,8-dihydrodiol-9,10-epoxide or cigarette smoke condensate. Effects on resulting DNA fragmentation were measured using the alkaline single-cell microgel electrophoresis (comet assay). Epigallocatechin-3-gallate significantly reduced benzo[a]pyrene-7,8-dihydrodiol-9,10-epoxide-induced DNA damage by up to 51% (P<0.001). Fragmentation induced by cigarette smoke condensate could be lowered by 47% (P<0.001). Data suggest a cancer preventive potential of epigallocatechin-3-gallate as demonstrated on a subcellular level. An additional mechanism of tea catechin action is revealed by using a primary mucosa culture model.

Chemopreventive action of dexamethasone and alpha-tocopherol in oxidative stressed cells

INTRODUCTION

Recent research indicates a close connection of inflammation and cancer as presumed by Virchow in 1893. The growing understanding of cellular signalling and regulatory pathways reveals multiple links between inflammation and cancer. This study was designed to evaluate the influence of the anti-inflammatory drug dexamethasone and the antioxidant alpha-tocopherol on oxidative induced DNA damage, a major factor in the development of malignancies.

MATERIAL AND METHODS

Miniorgan cultures (MOC) of fresh biopsied human nasal mucosa were used to keep cells in their microenvironment and thus to mimic in vivo conditions. MOC were pretreated with dexamethasone and alpha-tocopherol in different concentrations on 1 or on 5 days before oxidative DNA damage was introduced by hydrogen peroxide. The effect of these substances on DNA damage was evaluated using the alkaline single cell microgel electrophoresis (Comet Assay).

RESULTS

Dexamethasone induced slight, but considerable DNA fragmentation by itself. It effectively protected cells from hydrogen peroxide induced DNA damage, leading to a maximum decrease of about 45% when preincubated on 5 days at 20 microM. alpha-Tocopherol most effectively reduced oxidative DNA fragmentation by about 38% when MOC were pretreated 5 days at 20 microM.

DISCUSSION

Our experimental data clearly shows the DNA protective action of dexamethasone and alpha-tocopherol with regard to oxidatively induced DNA damage, a major pathogenetic factor that inflammation and cancer have in common.

Cytochrome P4502A6 stability in a mini organ culture model of human nasal mucosa for genotoxicology studies as detected by flow cytometry

Three dimensional mini organ cultures (MOCs) of human nasal turbinate epithelia have been shown to be a relevant tool in genotoxicology studies. MOCs allow repetitive or chronic exposure of cells in an organ specific mucosal architecture for an extended period of time and monitoring of possible adverse effects with, e.g., the comet assay. It is the aim to demonstrate whether the proteins of key enzymes of xenobiotic metabolism, represented by cytochrome P450 2A6 (CYP2A6), remain on a stable level for a culture period that allows repetitive or chronic exposure to xenobiotics. Culture of mini organs was performed by cutting pieces of 1 mm(3) from fresh specimens of human nasal turbinates. MOCs of five tissue donors were incubated on multi-well plates with BEBM, on days 0, 4, 7, 9, and 11 aliquots were transmitted to flow cytometric quantification of the CYP2A6 protein. The CYP2A6 protein could be demonstrated on all days of culture investigated. Interindividual differences were more pronounced on day 0 than at later stages of culture. Although there appeared to be a slight decrease over the culture period, flow cytometric analysis did not reveal a significant loss of the signals up to day 11. The present data could show a pre-requisite of metabolic competence of MOCs that is in contrast to single cell cultures. Thus, this type of organ culture provides an in vitro model suitable for the assessment of genotoxic effects of environmental pollutants mimicking the in vivo situation with target cells of carcinogens in their functional organ specific architecture.

Comet assay: a reliable tool for the assessment of DNA damage in different models

New chemicals are being added each year to the existing burden of toxic substances in the environment. This has led to increased pollution of ecosystems as well as deterioration of the air, water, and soil quality. Excessive agricultural and industrial activities adversely affect biodiversity, threatening the survival of species in a particular habitat as well as posing disease risks to humans. Some of the chemicals, e.g., pesticides and heavy metals, may be genotoxic to the sentinel species and/or to non-target species, causing deleterious effects in somatic or germ cells. Test systems which help in hazard prediction and risk assessment are important to assess the genotoxic potential of chemicals before their release into the environment or commercial use as well as DNA damage in flora and fauna affected by contaminated/polluted habitats. The Comet assay has been widely accepted as a simple, sensitive, and rapid tool for assessing DNA damage and repair in individual eukaryotic as well as some prokaryotic cells, and has increasingly found application in diverse fields ranging from genetic toxicology to human epidemiology. This review is an attempt to comprehensively encase the use of Comet assay in different models from bacteria to man, employing diverse cell types to assess the DNA-damaging potential of chemicals and/or environmental conditions. Sentinel species are the first to be affected by adverse changes in their environment. Determination of DNA damage using the Comet assay in these indicator organisms would thus provide information about the genotoxic potential of their habitat at an early stage. This would allow for intervention strategies to be implemented for prevention or reduction of deleterious health effects in the sentinel species as well as in humans.

Evaluation of direct transport pathways of glycine receptor antagonists and an angiotensin antagonist from the nasal cavity to the central nervous system in the rat model

PURPOSE

The aim of this study was to investigate and quantify drug movement to the brain via the neuro-olfactory system after intranasal dosing of four model drugs; three glycine receptor antagonists and one angiotensin antagonist.

METHODS

The drugs were dosed to rats via intranasal or intravenous administration, after which a quantitative method for tissue distribution was utilised to determine drug distribution to the olfactory lobes, brain sections and the blood over 30 min. Autoradiography was used to visualise and quantify drug distribution throughout the brain and in the CSF. Micro-autoradiography was used to examine drug distribution throughout the olfactory nerve apparatus.

RESULTS

The three glycine receptor antagonist compounds were transported to the CNS to differing degrees although they had similar molecular structures and similar physicochemical characteristics. All three compounds were shown to exploit a direct route of transport from nose to brain with Direct Transport Percentages (DTP) of 99.99%, 96.71% and 51.95%, respectively, although for the last molecule a major part of the brain content originated from systemic transport across the BBB. Intranasal administration of GR138950 resulted in over 3.5 times more drug in the olfactory lobes at 1 min post-dose compared to intravenous administration; and 5 times more drug was delivered to the olfactory lobes over 30 min. Micro-autoradiography showed that GR138950 could be found throughout the olfactory nerve apparatus. Autoradiography illustrated drug distribution throughout the brain and CSF, with drug concentrations in the CSF being equal or higher than in the brain tissue. It was determined that approximately 0.8% of the administered dose moved into the brain and CSF via the olfactory pathway over 30 min.

CONCLUSIONS

Intranasal administration resulted in greater delivery of the model drugs to the olfactory lobes and brain as compared to intravenous dosing. It is proposed that the drug moved through the neuro-olfactory system, primarily via paracellular pathways.

Organ culture at the air-liquid interface maintains structural and functional integrities of inflammatory and fibrovascular cells of nasal polyps

BACKGROUND

Both inflammatory and fibrovascular cells play an important role in development of nasal polyps (NPs). In this study, we have developed a culture system to maintain structural and functional integrities of submucosal cells in vitro.

METHODS

NP tissue was cultured on a gelatin sponge at air-liquid (AL) interface or was cultured in submerging. Tissues were analyzed for survival, structural integrity, and vascular endothelial growth factor (VEGF) expression.

RESULTS

Most cells of NPs cultured in submerging died within 3 days. In culture at the AL interface, epithelium as well as submucosa kept structural integrity during the culture period. RT-PCR and immunohistochemistry showed that submucosa cells displayed VEGF expression, which is a major inducer of angiogenesis and edema of NPs.

CONCLUSION

Our study is the first demonstration that organ culture of NPs at the AL interface retains integrity of both epithelium and submucosa and this culture method possibly will be used to study the pathogenesis of NPs.

[Does nicotine add to the carcinogenic strain of tobacco smoke?]

BACKGROUND

It is accepted that nicotine in tobacco smoke causes addiction via nicotinic acetylcholine receptors in the central nervous system. For a long time, the tumorigenic potential of smoking was attributed to compounds other than nicotine. However, more recently data have accumulated which suggest that nicotine may add to the cancer risk by stimulating cellular growth via non-neuronal acetylcholine receptors, by suppressing apoptosis, and by inducing angiogenesis not only in atheromatous plaques but also in tumors. In the present study the possible direct genotoxic effects of nicotine on DNA were investigated in human target cells of carcinogenesis in the upper aerodigestive tract.

PATIENTS AND METHODS

Human nasal mucosa, lymphatic tissue of the palatine tonsils, supraglottic epithelium of the larynx, and peripheral lymphocytes were exposed to rising concentrations of nicotine. DNA damage was investigated by alkaline single-cell microgel electrophoresis (Comet) assay. Cytotoxicity was assessed by trypan blue exclusion.

RESULTS

Nicotine induced dose-dependent DNA damage in all cell types at low cytotoxic concentrations that allowed viabilities well above 80%. The lowest nicotine concentrations eliciting a significant increase in DNA migration were 1 mM for tonsillar cells and 0.25 mM for all other cell types.

CONCLUSION

Nicotine induces genotoxic effects in human target cells of carcinogenesis in the upper aerodigestive tract at relevant concentrations. Thus, nicotine may contribute directly to tumor initiation resulting from smoking.

Mercuric dichloride induces DNA damage in human salivary gland tissue cells and lymphocytes

Amalgam is still one of the most frequently used dental filling materials. However, the possible adverse effects especially that of the mercuric component have led to continued controversy. Considering that mercury may be released from amalgam fillings into the oral cavity and also reach the circulating blood after absorption and resorption, it eventually may contribute to tumorigenesis in a variety of target cells. The present investigation focuses on genotoxic effects below a cytotoxic dose level of mercuric dichloride (HgCl(2)) in human samples of salivary glands and lymphocytes to elucidate a possible role in tumor initiation. DNA migration due to single strand breaks, alkali labile sites and incomplete excision repair was quantified with the aid of the single cell microgel electrophoresis (Comet) assay. The concepts of Olive Tail Moment, percentage of DNA in the Tail and Tail Length were used as measures of DNA damage. To control for cytotoxic effects, the trypan blue exclusion test was applied. Human samples of the parotid salivary gland and lymphocytes of ten donors were exposed to HgCl(2)concentrations from 1 to 50 microM. N-methyl-N'-nitro-N-nitrosoguanidine (MNNG) and dimethyl sulfoxide (DMSO) served as controls. Increasing dose-dependent DNA migration could be demonstrated after exposure to HgCl(2) in cells of the salivary glands and lymphocytes. In both cell types a significant increase in DNA migration could be shown starting from HgCl(2)concentrations of 5 microM in comparison to the negative control. The viability of the cell systems was not affected except at the highest concentration (50 microM) tested. These data indicate genotoxic effects of mercuric dichloride in human salivary glands and lymphocytes at concentrations not leading to cytotoxic effects or cell death. Consequently, a contributory role in oral salivary gland tumor initiation warrants further investigation.

Cumulative genotoxic and apoptotic effects of xenobiotics in a mini organ culture model of human nasal mucosa as detected by the alkaline single cell microgel electrophoresis assay and the annexin V-affinity assay

Three-dimensional mini organ cultures of human inferior nasal turbinate epithelia have proved to be a useful tool in genotoxicology studies. They allow repetitive or chronic exposure of cells to xenobiotics in a well-preserved organ-specific mucosal architecture for an extended period of time. It is the aim of the present study to concurrently monitor cumulative genotoxic and apoptotic effects of sodium dichromate, N-nitrosodiethylamine (NDEA) and N-methyl-N-nitro-N-nitroso-guanidine (MNNG). Mini organs were raised by separating fresh specimens of human inferior nasal turbinates (n=11) into 1 mm3 sized pieces and culturing them on multiwell plates with bronchial epithelial basal medium for 6 days. Aliquots of the mini organs were subsequently exposed to sodium dichromate (1.0 mM, 1h), NDEA (50 mM, 1h) or MNNG (0.07 mM, 1h) on days 7, 9 and 11 versus a single exposure on day 11 only. DNA fragmentation and apoptotic events were assessed on day 11 using the alkaline single cell microgel electrophoresis assay (comet assay) and the annexin V-affinity assay. Significant DNA fragmentation could be demonstrated after a single exposure of the mini organs to sodium dichromate. Following three subsequent incubations, there was a further increase in the genetic damage observed, accompanied by an increase in the rate of apoptotic cells. In contrast, after single and triple incubation with NDEA there was neither an increase in genetic damage nor in the fraction of apoptotic cells detectable. Repetitive exposure to MNNG resulted in an accumulation of DNA damage without an observable increase in apoptosis. The results verify the need to assess apoptosis in genotoxicology research and to investigate cumulative effects of xenobiotics. Three-dimensional mini organ cultures of human upper aerodigestive tract epithelia have shown to be well-suited for improving the ability to distinguish between cumulative genotoxic and apoptotic effects.

[Mini-organ cultures of human nasal mucosa. A model for eco-genotoxicological investigations]

BACKGROUND

Volatile and ingestive xenobiotics may induce cancer in the mucosa of the upper aerodigestive tract. A new model is presented combining mini-organ cultures of human mucosa and the Comet assay that allows investigation of tumor initiation steps in vitro.

METHOD

Specimens of human mucosa of the inferior nasal turbinates were cultured as mini-organs and exposed to xenobiotics once, twice or three times with consecutive repair intervals. The cultures were monitored for structural integrity (inverse microscopy, histology), DNA fragmentation and repair activity (Comet assay), induction of apoptosis (annexin V assay), and production of IL-8 and GM-CSF (ELISA).

RESULTS

Mini-organ cultures showed a good structural integrity during the whole culture period. Exposure to N-nitrosodiethylamine (NDEA) and benzo[a]pyrene-7,8-dihydrodiol-9,10-epoxide (BPDE) induced significant DNA fragmentation. Sodium dichromate (Na2Cr2O7) had an additive DNA fragmentation effect with repetitive exposure. Significant DNA repair was seen after strand break induction by Na2Cr2O7, only. Apoptosis was seen after three exposures to BPDE und Na2Cr2O7, but not NDEA. Inflammatory cytokine release was unaltered by NDEA. However, BPDE and Na2Cr2O7 reduced GM-CSF and Na2Cr2O7 reduced IL-8 excretion.

CONCLUSION

This three dimensional mini-organ culture system proved to be very helpful in characterizing volatile and ingestive xenobiotics potentially hazardous to humans. Beside the information concerning genotoxicity, it allows cytological and immunological studies. In contrast to investigations with fresh specimens, repetitive or chronic exposure to xenobiotics is possible in mucosal cells with their epithelial structural integrity. Therefore, mini-organ cultures of human upper aerodigestive tract epithelia represent a model closely resembling the in vivo situation.

Genotoxicity of nicotine in mini-organ cultures of human upper aerodigestive tract epithelia

The direct role of nicotine in tobacco carcinogenesis is still controversial. Recently, DNA damage by nicotine has been demonstrated in isolated human tonsillar tissue cells. Presently, these effects were investigated using mini-organ cultures (MOC) of human nasal epithelia. Intact MOC were repeatedly exposed to 2 and 4 mM nicotine for 1 h on culture days 7, 9, and 11. N-Methyl-N'-nitro-N-nitrosoguanidine (MNNG) served as a positive control. DNA damage was examined by Comet assay either directly after exposure or following a 24-h recovery period. Cell viability was not reduced by any treatment. On day 7, 1 h exposure to 2 and 4 mM nicotine caused a significant dose-dependent 3.3- and 5.6-fold increase in DNA damage compared to solvent controls. Although there was no evidence of significant repair within 24 h recovery, DNA damage was not further increased by nicotine on days 9 and 11. After double and triple exposure to 4 mM nicotine a significant reduction in DNA damage following 24 h recovery was observed. In contrast, treatment with MNNG resulted in a highly significant and cumulative increase in DNA migration up to 110-fold compared to controls. During recovery periods, MNNG-induced DNA damage was significantly repaired, leading to a 1.5- to 1.8-fold reduction in DNA migration within 24 h. These results confirm genotoxic effects of nicotine on human nasal epithelia. Further studies are needed to explain the lack of cumulative DNA-damaging effects of nicotine and the absence of significant DNA repair. These studies should include a battery of assays with multiple end points.

The tobacco alkaloid nicotine demonstrates genotoxicity in human tonsillar tissue and lymphocytes

Recent studies suggest a direct contribution of nicotine, the addictive component of tobacco and tobacco smoke, to human carcinogenesis. To assess the genotoxicity of nicotine, the DNA-damaging effect on human lymphocytes and target cells from lymphatic tissue of the palatine tonsils from 10 healthy patients was tested with the alkaline single-cell microgel electrophoresis (Comet) assay. The degree of DNA migration, a measure of possible DNA single strand breaks, alkali labile sites, and incomplete excision repair sites, was expressed as the Olive tail moment, the percentage of DNA in the tail, and the tail length. One hour exposure to nicotine at 0.125, 0.25, 0.5, 1, 2, and 4 mM induced a statistically significant dose-dependent increase of DNA migration up to 3.8-fold and 3.2-fold in tonsillar cells and lymphocytes, respectively. The lowest concentration eliciting significant DNA damage was 0.5 mM nicotine. The genotoxic effect was confirmed in a second series of experiments using nicotine of high purity from two different suppliers. There were no significant differences between the two series, excluding artifacts from the source of nicotine. Finally, DNA damage by nicotine was compared in cells incubated in medium strictly adjusted to neutral pH, with non-adjusted medium becoming alkaline with increasing nicotine concentrations. Again no differences in DNA migration were observed. The data indicate that nicotine expresses significant direct genotoxic effects in human target cells in vitro. However, no differences in DNA damage were observed in cells from smokers and nonsmokers incubated without nicotine. The lack of higher DNA damage in smokers compared to nonsmokers could be a question of nicotine dose, rapid DNA repair, or interactions with other smoke constituents. These results require further investigations on the contribution of nicotine to tobacco carcinogenesis.