Short-term severe thyroid hormone deficiency does not influence sleep parameters.

PURPOSE: The influence of short-term severe thyroid hormone deficiency on sleep is currently still unknown. Several studies have demonstrated an effect of long-term hypothyroidism on sleep disorders due to anatomical changes of the pharynx or body mass. The aim of this preliminary study, however, is to evaluate the changes in sleep patterns of patients with short-term hypothyroidism to elucidate the isolated effect of thyroid hormone withdrawal before anatomical changes can potentially occur. METHODS: Ten patients with differentiated thyroid carcinoma were enrolled in this study. Two patients discontinued the study and one patient was finally excluded due to obesity, so that the datasets of seven patients were available for study analysis. During the course of carcinoma treatment, each patient had previously undergone total thyroidectomy and I-131 remnant ablation. Polysomnographic measurements were performed twice: (1) over the course of two consecutive nights during severe thyroid hormone deficiency after levothyroxine withdrawal and prior to further diagnostics and therapy and (2) during euthyroidism after substitution with levothyroxine. RESULTS: Comparison of the Epworth Sleepiness Scale during hypo- and euthyroidism for each patient revealed no statistically significant difference. Furthermore, the comparison of polysomnographic parameters like (1) apnea-hypopnea index, (2) the duration of various sleep stages, (3) duration of rapid eye movement sleep, (4) latency until rapid eye movement sleep, (5) total sleep time, (6) periodic leg movements, and (7) arousal index showed no statistically significant differences between the hypothyroid or euthyroid state. CONCLUSIONS: We conclude that, in this preliminary experimental setting, short-term severe thyroid hormone deficiency per se does not cause sleep disturbances and a feeling of fatigue as described in other studies may be due to changes in perception or brain metabolism during hypothyroidism.

Bisphosphonate-induced osteonecrosis of the external ear canal: a retrospective study.

In 2003, osteonecrosis of the jaw was described as an intraoral complication of bisphosphonate therapy. More recently, cases of avascular necrosis of the hip were reported in patients with long-lasting bisphosphonate therapy. Thus, it was the aim of the present study to analyze cases of benign osteonecrosis of the external ear canal and to retrospectively identify a possible relationship to long-lasting bisphosphonate therapy. 13 patients with osteonecrosis of the external ear canal operated on between 2005 and 2009 were included. Patient histories were reviewed for possible previous or current bisphosphonate therapy. Three patients with osteonecrosis of the external ear canal and long-term bisphosphonate therapy could be identified. They had been treated either for breast cancer or multiple myeloma. Certainly, the jaw is an area of increased risk for developing osteonecrosis with its high mechanical stress and intraoral bacterial flora. However, osteonecrosis of the hips and the external ear canal in patients receiving long-term bisphosphonate therapy necessitate further investigation of a possible systemic, bisphosphonate-related phenomenon.

Optimization of fibrinogen isolation for manufacturing autologous fibrin glue for use as scaffold in tissue engineering.

Numerous manufacturing techniques for autogenous fibrin glue used as scaffold material have been described. As there is no consensus regarding the influence of chemical additives on cell biology, it was the aim of this study to establish a method for manufacturing autologous fibrin glue without any additives. The serum part was separated from whole blood. After fibrinogen precipitation, centrifugation was performed to obtain the fibrinogen pellet. Various experimental series were run to examine influences of various temperatures or substituting centrifugation for sedimentation. The method as described here is effective, simple, and performed without any additives, which could potentially influence cell biology.

[Effects of nicotine with special consideration given to tumorigenesis in the head and neck region]. / Effekte von Nikotin unter besonderer Berücksichtigung der Tumorentstehung im Kopf-Hals-Bereich.

BACKGROUND: Tumorigenesis is based on initiation, promotion, and progression, whereas tobacco smoke is a decisive predisposing factor for squamous cell carcinomas of the upper aerodigestive tract. A variety of tobacco smoke compounds is known to potentially initiate tumors, but the alkaloid nicotine is generally considered to induce addiction only. However, there is growing evidence that nicotine may also contribute to early stages of tumorigenesis. In the present study, a possible direct genotoxic potential of nicotine is investigated. MATERIAL AND METHODS: Lymphatic tissue of the tonsilla palatina of eight donors was harvested during surgery and incubated with nicotine. DNA damage was measured with the comet assay. RESULTS: Genotoxic effects of nicotine could be demonstrated. DISCUSSION: The results suggest a direct contribution of nicotine to tumor initiation and carcinogenesis.

[Does nicotine add to the carcinogenic strain of tobacco smoke?]. / Trägt Nikotin zur Krebsentstehung im oberen Aerodigestivtrakt bei?

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.

[Mini-organ cultures of human nasal mucosa. A model for eco-genotoxicological investigations]. / Miniorgankulturen humaner nasaler Mukosa. Ein Modell für ökogenotoxikologische Untersuchungen.

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.

[Carcinogenic and co-carcinogenic effects of metals and ethanol on human salivary gland tissue]. / Karzinogene und kokarzinogene Effekte von Metallen und Ethylalkohol in humanen Speicheldrüsenzellen.

BACKGROUND: The etiology of malignomas of human salivary glands is examined. MATERIAL AND METHODS: Macroscopic, healthy salivary gland tissue from 46 donors was harvested during surgery. Single cells were isolated by enzymatic digestion. These were then incubated for 60 min with Na(2)Cr(2)O(7), NiSO(4), CdSO(4), ZnCl(2) and ethanol. Additionally, incubation with Na(2)Cr(2)O(7) was combined with NiSO(4), CdSO(4), ZnCl(2) and ethanol. The influence of CdSO(4) was analyzed by altered combinations with Na(2)Cr(2)O(7) during incubation and by the DNA-repair period. Evaluation was performed using fluorescent staining and digital analysis. RESULTS: Of all of the substances tested, only Na(2)Cr(2)O(7) showed genotoxic effects. NiSO(4), ZnCl(2) and ethanol had neither genotoxic nor cofactorial impacts. CdSO(4), however, caused additional genotoxic effects in combination with Na(2)Cr(2)O(7), although it lacked direct genotoxic potential. A reduction of DNA-repair of Na(2)Cr(2)O(7)-induced oxidative damage by CdSO(4) could be demonstrated. CONCLUSIONS: In this investigation, sodium dichromate was identified as genotoxic in association with human salivary gland tissue. These effects could be increased by CdSO(4), reinforcing DNA damage based on oxidative stress.

Toxicological assessment of noxious inhalants.

In the past centuries mankind has been exposed to various forms of air pollution not only at his occupational but also in his social environment. He mainly gets exposed with these pollutants through the respiratory organs and partially absorbs them into the body. Many of these airborne substances can be harmful for humans and some of them may account for tumorigenic effects.The following essay describes the main features of toxicological assessment of inhalative environmental and workplace xenobiotics. The essay also explains relevant characteristics and limit values of noxious compounds and gases and depicts modern testing methods. To this end, emphasis is given on methods characterizing the different stages of tumorigenic processes. Various test systems have been developed which can be used in vivo, ex vivo or in vitro. They are to a great part based on the evidence of changes in DNA or particular genes of cells. Among others they have highlighted the impact of interindividual variability on enzymatic activation of xenobiotics and on susceptibility of the host to tumor diseases.Unfortunately, for many inhalative environmental noxious agents no sufficient risk profiles have been developed. The completion of these profiles should be the goal of toxicological assessment in order to allow reasonable socioeconomic or individual-based risk reduction.

[Preservation of mucosal specimens before processing in the alkaline single cell microgel electrophoresis assay]. / Lagerung humaner nasaler Mukosa für die Einzelzell-Mikrogelelektrophorese.

BACKGROUND: Human mucosal biopsies are established in ecogenotoxicological studies, but up until now they have demanded immediate processing after harvesting. We report our experience with the preservation of specimens either for 24 h at 4 degrees C or for longer periods at -80 degrees C and compare the results with fresh specimens using the alkaline single cell microgel electrophoresis assay. PATIENTS AND METHODS: Nasal mucosa was harvested from ten patients, transferred to the laboratory and divided into groups for immediate processing,24 h preservation at 4 degrees C and cryopreservation at -80 degrees C. Alkaline single cell microgel electrophoresis assays were performed after separating the specimens into single cells and after exposure to benzo[a]pyrene,benzo[a]pyrene-diolepoxide, N-nitrosodiethylamine, or sodium dichromate. The trypan blue exclusion test was used to assess cytotoxicity. RESULTS: Despite of the fact that cell viability remained stable, after cryopreservation DNA-migration increased significantly for the negative control and benzo[a]pyrene. Although an increase was also seen for sodium dichromate, this was not significant. For benzo[a]pyrene-diolepoxide, N-nitrosodiethylamine and N-methyl-N'-nitro-N-nitrosoguanidine there were no significant changes in DNA-migration. After 24 h in cell medium at 4 degrees C,DNA-migration did not rise compared to the samples which were immediately processed. CONCLUSIONS: Preservation of mucosal specimens at 4 degrees C for 24 h may be legitimate in order to facilitate laboratory practice. However, cryopreservation should not be applied because it leads to higher rates of DNA migration in some tested substances in the alkaline single cell microgel electrophoresis assay.

[The single cell microgelelectrophoresis technique in ecogenotoxicology]. / Stellenwert der Einzelzell Mikrogelelektrophorese in der Okogenotoxikologie.

BACKGROUND: The development of carcinoma in the upper aerodigestive tract is often associated with exposure to xenobiotics. Therefore, the identification of such tumor initiating substances is relevant. Most genotoxicity test systems require mammalian cells, human lymphocytes or cell cultures to detect genotoxicity caused by carcinogens. The single cell microgelelectrophoresis technique (Comet assay) is presented, being a sensitive method, identifying DNA strand breaks, alkali labile sites and DNA repair in human epithelial cells of the upper aerodigestive tract. It is compared to other common techniques for the identification of genotoxic damage. Future applications and contributions of the method are introduced. GENOTOXICITY TEST SYSTEMS: Using the alkaline microgel electrophoresis assay, freshly isolated single epithelial cells are incubated with xenobiotics causing DNA strand breaks and alkali labile sites. Data are examined using a digital computer analysis. The method is described for the application of epithelial cells of the upper aerodigestive tract and compared to other procedures for the monitoring of genotoxicity. These are the Ames test identifying mutagenicity in bacteria, the sister chromatid exchange and the micronucleus test demonstrating genomic instability in lymphocytes and cultured mammalian cells. CONCLUSIONS: The microgel electrophoresis technique is a sensitive method to detect genotoxic effects and DNA repair in human epithelia of the upper aerodigestive tract. The assay offers considerable advantages to other common genotoxicity tests. However, combining of the Comet assay with mini organ cultures allows to use repetitive incubations with xenobiotics. Furthermore, signalling selected chromosomal material by the combination of the assay with the fluorescence in situ hybridisation, DNA-damage and -repair mechanisms within comets can be identified.

[Voice disorders, dyspnea, aspiration. A laryngeal injury can be the cause]. / Stimmstörungen, Luftnot, Aspiration. Hier kann eine Kehlkopfverletzung vorliegen.

Injuries to the larynx may have extracorporeal (external), or endolaryngeal (internal), causes and are here classified on the basis of traumatic mechanisms. External trauma may be due to the action of blunt force or sharp objects--also including ruptures. Internal injuries may occur as a result of endotracheal intubation (also for anesthesia), long-term intubation and mechanical ventilation, ingestion of foreign bodies, surgical or nonsurgical interventions. In some cases, laryngeal injuries may be difficult to diagnose and evaluate. If the patient survives the primary traumatic event and his vital functions are preserved and stable, a careful laryngoscopic exploration--where indicated also such imaging procedure as high-resolution CT, direct microlaryngoscopy and laryngometry--should be applied to establish the diagnosis and decide on appropriate treatment.

[Organic changes of the vocal cords. Phonosurgery helps here]. / Organische Veränderungen an den Stimmlippen. Hier hilft die Phonochirurgie.

Surgical interventions aimed at preserving, improving or restoring vocal function define the term phonosurgery. Options include endolaryngeal microscopic techniques and extralaryngeal approaches for the treatment of vocal cord polyps, Reinke's edema, nodules and cysts, treatment of injuries to the larynx, and partial resection of malignant tumors. Further indications are deficits in vocal cord closure resulting from impaired laryngeal nerve function. Of particular importance in this connection are augmentation and medialization of the vocal cords. Additional possibilities are modification (higher/lower) of the pitch of the voice to improve the quality of life of transsexuals. Provided the indications are carefully established and concomitent voice training is offered, phonosurgical interventions may be a good means of ameliorating morphological and functional deficits of the larynx. Patient information on the possibilities of phonosurgery, careful selection of the appropriate surgical technique, adequate experience on the part of the surgeon, and good anesthesiological management, all impact on the outcome of this form of treatment.

[Cytotoxicity and genotoxicity of fluorides in human mucosa and lymphocytes]. / Zytotoxizität und Genotoxizität von Fluoriden in humaner Mukosa und Lymphozyten.

BACKGROUND: Fluorides are widely used in dental health products and drinking water, due to their beneficial effects in caries-prophylaxis and -treatment. Nevertheless, irritation of the gingiva and oropharyngeal mucosa as well as in gastric mucosa is observed since neither local nor systemic application is restricted to the teeth. These effects may partly be attributed to a known cytotoxicity of fluorides. Whether fluorides also have genotoxic effects on human mucosa or lymphocytes as a possible factor in tumor initiation was investigated in this study. MATERIAL AND METHODS: Human oropharyngeal epithelial cells and peripheral lymphocytes were incubated after single cell preparation with the aminefluoride Olaflur at concentrations of 2 ppm, 21 ppm, 35 ppm, 71 ppm and 213 ppm. The extent of cytotoxicity was investigated using the trypan blue exclusion test. Following incubation, electrophoresis for migration of DNA fragments, fluorescence staining and digital image analysis according to a standard protocol of the single cell microgel electrophoresis assay (Comet assay) followed. DNA damage was characterized using the Olive Tail Moment (OTM). RESULTS: For fluoride concentrations of 2 ppm to 35 ppm, non vital cells of less than 10% could be shown. After incubation with 71 ppm and 213 ppm Olaflur, there were 15% and 43% of damaged cells, respectively. Weak genotoxic effects on mucosal cells as well as on lymphocytes could be demonstrated at all concentrations tested. In fluoride concentrations of 213 ppm genotoxicity increased to max. OTM-levels of 23. CONCLUSIONS: Beside the cytotoxic effect of fluorides, also a minor genotoxic impact on human mucosa and on peripheral lymphocytes could be demonstrated using the Comet assay. Further investigations are warranted to examine fluorides in a model allowing for repeated or long term incubations on structurally intact human mucosa in vitro. Such a model will help to distinguish between DNA damage that may be repaired successfully and other impairments that may show an additive character in repetitive or chronic exposure in vivo.

[Genotoxicity of phthalates. On the discussion of plasticizers in children's toys]. / Genotoxizität von Phthalaten. Zur Diskussion über Weichmacher in Kinderspielzeug.

BACKGROUND AND OBJECTIVE: Recently, health hazards caused by phthalates, which are added as softeners to plastic materials, have been subject to discussion. The aim of the present study was to measure possible genotoxic impacts on mucosal cells of the upper aerodigestive tract. PATIENTS AND METHODS: Genotoxicity tests for dibutyl phthalate (DBP) and diisobutyl phthalate (DiBP) on human oropharyngeal mucosa in vitro were performed using the alkaline comet assay. Specimens (n = 50) were harvested from the surface of ectomized tonsils. RESULTS: DBP and DiBP caused significant DNA damage in human mucosal cells of the upper aerodigestive tract. The impact of DiBP was higher than that of DBP. CONCLUSIONS: A genotoxic impact of phthalates on human epithelial cells as a hazard to babies and children chewing these materials cannot be excluded and demands further investigation. The DNA damage measured in this study may represent one factor in the complex genesis of neoplasms in the upper aerodigestive tract.

Genotoxicity of nitroso compounds and sodium dichromate in a model combining organ cultures of human nasal epithelia and the comet assay.

Genotoxic effects of xenobiotics are a possible step in tumor initiation in the mucosa of the upper aerodigestive tract. Using the comet assay, detecting genotoxicity in human tissue has been restricted to single incubations in vitro, but in vivo most xenobiotics harm their target in a repetitive or chronic manner. Therefore, we propose a model, which provides repetitive incubations in human upper aerodigestive tract mucosa cultures. Samples of human inferior nasal turbinate mucosa (n = 25) were cultured according to a modified version of a technique originally described by Steinsvåg. On day 1 fresh samples and on days 7, 9 and 11 organ cultures were incubated with N-nitrosodiethylamine (NDEA), sodium dichromate (Na2Cr2O7) and N'-methyl-N-nitro-N-nitrosoguanidine (MNNG). Mucosa samples and organ cultures, respectively, underwent a modified comet assay on days 1, 7 and 11. Genotoxicity could be shown for NDEA, Na2Cr2O7 and MNNG on days 1, 7 and 11. Duration of tissue culture and repetitive incubations did not significantly influence the results for NDEA. Nevertheless, Na2Cr2O7 and MNNG caused higher genotoxic effects on cultures subjected to the comet assay on day 11. This model may help to assess genotoxic hazards posed by environmental pollutants that have a cumulative character in repetitive or chronic exposure in vivo.

Mutagen sensitivity of nasopharyngeal cancer patients.

Primary nasopharyngeal carcinomas (NPCs) may be of various types, including squamous cell carcinomas, undifferentiated carcinomas, and lymphoepitheliomas. Tumor initiation has been linked to the Epstein-Barr virus and, in some geographical regions, to alimentary factors. Possible hereditary components for the appearance of NPCs have not yet been clearly identified. In this study, genetic sensitivity to the genotoxic effects of carcinogenic xenobiotics as an endogenous risk factor of tumor initiation was investigated. The single cell microgel electrophoresis assay was used to quantify chemically-induced DNA damage in lymphocytes of 30 NPC patients and 30 non-tumor donors. The xenobiotics investigated were N'-nitrosodiethylamine, sodium dichromate, and nickel sulphate, with N-methyl-N'-nitro-N-nitrosoguanidine (MNNG) and dimethyl sulfoxide (DMSO) as positive and negative controls, respectively. The extent of DNA migration in the solvent control cultures was not significantly different between the two groups (1.2+/-0.5 mean Olive tail moment and standard deviation of 30 individuals for NPC patients; 1.1+/-0.4 for non-tumor donors). With constant exposure and electrophoretic conditions, genotoxic effects of varying degrees were induced by the different xenobiotics in tumor and non-tumor patients (nickel sulphate: 7.1+/-2.5 for NPC patients and 5.9+/-1.6 for non-tumor donors; sodium dichromate: 18.1+/-5.3 for NPC patients and 16.2+/-5.4 for non-tumor donors; MNNG: 47.8+/-13.3 for NPC patients and 52.7+/-13.6 for non-tumor donors). Only N'-nitrosodiethylamine proved to induce significantly more DNA migration in lymphocytes of tumor patients (9.8+/-3.1) as compared to non-tumor patients (8.2+/-2.3). Although for sodium dichromate the degree of DNA migration did not significantly differ, variability in migration patterns proved to be lower in the tumor group. Mutagen sensitivity of NPC patients was shown to be elevated for a selected xenobiotic, whereas a general elevation of DNA fragility was not present. Further studies on mutagen sensitivity as an endogenous risk factor influencing the susceptibility of patients at the time of first diagnosis of nasopharyngeal carcinomas are warranted.

Genotoxicity of di-butyl-phthalate and di-iso-butyl-phthalate in human lymphocytes and mucosal cells.

The genotoxicity of phthalates, widely used plasticizers, has been shown previously for di-butyl-phthalate (DBP) and di-iso-butyl-phthalate (DBP) in human mucosal cells of the upper aerodigestive tract in a previous study using the Comet assay. Furthermore, higher genotoxic sensitivities of patients with squamous cell carcinomas of either the larynx or the oropharynx compared to non-tumor patients were described. Other authors have demonstrated DNA damage by a different phthalate in human lymphocytes. It was the aim of the present study to determine whether there is a correlation between the genotoxic sensitivities to DBP and its isomer DiBP in either mucosal cells or lymphocytes. The single-cell microgel electrophoresis assay (Comet assay) was applied to detect DNA strand breaks in human epithelial cells of the upper aerodigestive tract (n=132 specimens). Human mucosa was harvested from the oropharynx in non-tumor patients and patients with squamous cell carcinomas of the oropharynx. Laryngeal mucosa of patients with laryngeal squamous cell carcinomas was harvested as well. Peripheral lymphocytes (n=49 specimens) were separated from peripheral blood. Xenobiotics investigated were DBP, DiBP, and N'methyl-N'-nitro-N-nitrosoguanidine (MNNG) as positive control, respectively. For statistical analysis, the SPSS correlation analysis according to Pearson and the Wilcoxon test were performed. Genotoxicity was found for DBP and DiBP in epithelial cells and lymphocytes (P<0.001). MNNG caused severe DNA damage. In analyzing DBP and DiBP results, genotoxic impacts in mucosal cells showed an intermediate correlation (r=0.570). Correlation in lymphocytes was the same (r=0.570). Phthalates have been investigated as a potential health hazard for a variety of reasons, including possible xenoestrogenic impact, peroxisome proliferation, and membrane destabilization. The present investigation suggests a correlated DNA-damaging impact of DBP and DiBP in human mucosal cells and in lymphocytes, respectively.

[DNA repair if mucous membrane cells and lymphocytes with the comet assay]. / Untersuchungen zur DNA-Reparatur von Schleimhautzellen und Lymphozyten mit dem Comet Assay.

BACKGROUND: Exogenous and endogenous risk factors are involved in human carcinogenesis of the head and neck. Noteworthy hereditary factors include mutagen sensitivity and the individual's capacity for DNA repair. Repair mechanisms influence different phases of mutation and malignant transformation. The present study introduces a highly sensitive method for evaluating the repair capacity of human mucosal cells and lymphocytes. METHOD: Human epithelia of the nose and peripheral lymphocytes were incubated with the tobacco-related carcinogen N'nitrosodiethylamine (NDEA). The solvent dimethylsulfoxide (DMSO) served as negative control. Following repair times of 0 min, 15 min and 30 min, the cells were subjected to a modified version of the alkaline microgel electrophoresis technique (Comet assay). The data were digitally analyzed after fluorescent staining. RESULTS: Using the Comet assay, DNA repair could be quantified in human mucosal cells and in lymphocytes. The majority of DNA strand breaks induced by NDEA were repaired within 15 min in both cell types. CONCLUSIONS: Up to now, the Comet assay has been the preferred method for demonstrating substance-induced DNA damage. It has been used in repair studies involving lymphocytes, bacterial systems and animal-derived cells. A modified version of this method, however, can be used to quantify DNA repair in human mucosal cells and peripheral lymphocytes targeted by carcinogens. It is thus possible to evaluate an endogenous factor involved in the development of malignant transformations in mucosal cells of the upper aerodigestive tract.