Formaldehyde cytotoxicity in three human cell types assessed in three different assays

Antioxidants as Protection against Reactive Oxygen Stress Induced by Formaldehyde (FA) Exposure: A Systematic Review

BACKGROUND AND OBJECTIVES

Formaldehyde induces oxidative stress and is carcinogenic, particularly squamous cell carcinoma of the nasopharyngeal area. Around us, in exhaust gases, cigarette smoke, and various industrial products, FA primarily affects the respiratory tract and other organs like the cornea, liver, kidneys, brain, and cardiovascular system. This study aims to determine if antioxidants can mitigate FA's harmful effects.

MATERIALS AND METHODS

Several databases, including PubMed, Science Direct, Springer, and Wiley, were systematically searched. Research publications on antioxidants mitigating FA-induced oxidative damage were included, but reviews and articles lacking complete texts were excluded. SYRCLE's risk of bias tool for animal studies has been used. Tables were used for data synthesis. Out of 8790 articles, 35 publications detailing tissue homogenate for biochemical analysis, standard hematoxylin-eosin staining, and immunohistochemistry markers for histopathological and immunohistochemical diagnosis were selected. Most studies were case-control studies, utilizing rat or mouse models. Additionally, one cohort study on industrial workers was analyzed.

CONCLUSIONS

Antioxidants, including plant extracts, vitamins, and pigments, can prevent or heal FA-induced lesions. However, human studies, particularly biopsies, remain challenging, and animal trials are limited. Further research is needed to confirm FA's long-term effects and optimize antioxidant dosages.

The Cytotoxic Effect of Thermoplastic Denture Base Resins: A Systematic Review

Partial or complete dentures are constructed from thermoplastic resins that are thermally processed and molded. This review examines the presently available evidence for the cytotoxicity of thermoplasticized denture base resins on human gingival epithelial cells, adipose cells, and fibroblasts; human amnion fibroblasts; and mouse fibroblasts. Electronic searches were performed on PubMed, Scopus, Web of Science, and Google Scholar databases to identify relevant articles to be included in the review until September 2022. Clinical, in vivo, and in vitro studies in English language were searched for. The quality of the studies was assessed using the Toxicological data Reliability Assessment tool (ToxRTool) developed by the European Commission's Joint Research Centre. GRADE assessment was used to evaluate the certainty of evidence. Seven in vitro studies were included in the review. The overall risk of bias was determined to be high, with the majority of studies assessed found to be reliable with restrictions or not reliable. Only two studies were considered reliable without restrictions based on ToxRTool assessment. The effect of thermoplastic denture base resins on viability and cell adherence of human gingival or amnion fibroblasts and mouse fibroblasts (L929s) is not significant. Conditioned media from unpolished specimens of resins were significantly more toxic to cultured cells than those from polished specimens. This may be of concern in cases of poor post-processing of dentures. Based on the limited evidence available, there is low-certainty evidence that thermoplastic denture base resins appear to be biocompatible and show insignificant cytotoxicity. Further well-designed trials adhering to standard reporting guidelines and using objective measures are necessary before outlining universal guidelines for best practice. Long-term in vivo and clinical assessment is necessary to corroborate laboratory findings with clinical outcomes. Denture base resins are in constant contact with oral tissues, and cytotoxic components released by the resins may irritate or inflame the tissues or provoke an allergic response.

Improvement in histology, enzymatic activity, and redox state of the liver following administration of Cinnamomum zeylanicum bark oil in rats with established hepatotoxicity

Formaldehyde (FA) is an environmentally-available pollutant. Since the liver acts as a detoxifier in the human body, it is the first and most affected organ in individuals exposed to higher-than-normal amounts of FA. FA mainly alters oxidant/antioxidant status and initiates oxidative stress, and by means, causes functional damage to the liver. Thus, it is important to identify natural bioactive compounds with antioxidant properties in order to be used as food additives. Cinnamon (Cinnamomum zeylanicum) is a popular flavor and also a medicinal plant with a variety of beneficial effects. In the present original study, cinnamon essential oil (CEO) has been administrated at doses of 10, 20, and 100 mg/kg, orally, to hepatotoxicity rat models caused by FA (10 mg/kg, intraperitoneally). Liver enzymes and its histology were assessed and oxidative stress biomarkers in the liver tissue were also examined. CEO administration caused a significant increase in superoxide dismutase, glutathione peroxidase, and catalase and a prominent decrease in nitric oxide levels in the liver tissue. Also, in serum samples, CEO significantly reduced the elevated amounts of alanine aminotransferase, aspartate aminotransferase, and alkaline phosphatase. When assessed histologically, portal area and central vein fibrosis alongside with the hepatocytes' hypereosinophilia and swelling, focal inflammation, and necrotic areas were found to be prominently decreased in the CEO group. In conclusion, our study suggested that the CEO may have the potential for being used against FA-induced hepatotoxicity.

In-vitro cytocompatibility and growth factor content of GBR/GTR membranes

OBJECTIVE

To assess the cytocompatibility of five commercially available xenogenic barrier membranes used for oral regenerative procedures and to determine the growth factor content of these membranes in-vitro.

METHODS

Human mesenchymal stem cells (hMSCs) and immortalized periodontal ligament stem cells (PDL-hTERTs) were used to determine the cytocompatibility of xenogenic barrier membranes made of collagen (Biogide, BG, Geistlich Pharma AG, Switzerland; Biomend, BM, Zimmer Biomet, USA; Osseoguard OG, Zimmer Biomet, USA; OssixPlus, OX, Datum Dental, Israel) or extracellular matrix (ECM) (Dynamatrix, DM, Keystone Dental, USA) and of their eluates obtained by washing. Cells were cultured with previously washed and unwashed membranes (n=4) and in the medium used for washing (eluate). Cell proliferation at 3 days (eluates) and at 7 days (membranes) was assessed using the WST-1 cell proliferation kit. Growth factor content of the membranes was measured using multiplex ELISA.

RESULTS

The eluate of BG and BM significantly inhibited proliferation of hMSCs, whereas DM and OX showed stimulating effects. The highest impact was observed for DM, its eluate doubled the cell proliferation of adherent cells when compared to the control (p<0.001). The eluate of OG did not influence eluate cell cultures (p>0.05). The presence of membranes had different impact on hMSCs and PDLs. hMSCs seem to be more resistant to the inhibitory effects of BG, OG and BM. hMSCs are only affected by OX, which actually stimulates hMSCs when the specimens are not washed previously. PDLs however proliferate significantly less once they are placed into culture with BM and OG as well as BG-not washed. Once BG is washed no inhibitory effect on PDLs was observed, however overall the washing of membrane samples prior to the placement into the cell culture did hardly have any effect on the outcome. The strongest inhibition of proliferation was shown with the BM and OG membrane in PDL-hTERTs (p<0.001). Growth factor contents were quite similar quantitatively and qualitatively among the tested membranes with concentrations in the range of 50-500 pg/ml. Intriguingly DM contained considerably higher amounts of bFGF with up to 8000 pg/ml.

SIGNIFICANCE

The collagen membranes cross-linked with aldehydes show poor outcomes in PDLs while the collagen membrane cross-linked with polysaccharides generally shows promising results similar to the ECM-membrane DM in both membrane and eluate tests. The findings may be due to various factors, especially differences observed in composition, processing and bFGF content.

Formaldehyde produced from d-ribose under neutral and alkaline conditions

Formaldehyde is toxic and has been implicated in the pathologies of various diseases, such as cognitive impairment and cancer. Though d-ribose is widely studied and provided as a supplement to food such as flavor and drinks, no laboratories have reported that d-ribose is involved in the formaldehyde production. Here, we show that formaldehyde is produced from d-ribose in lysine or glycine solution and Tris-HCl buffer under neutral and alkaline conditions. Intraperitoneal injection of C57BL/6J mice with d-ribose significantly increased the concentration of brain formaldehyde, compared to the injection with d-glucose or saline. These data suggest that formaldehyde levels should be monitored for the people who take d-ribose as a supplement.

In vitro cytotoxic evaluation of novel fast-setting calcium silicate cement compositions and dental materials using colorimetric methyl-thiazolyl-tetrazolium assay

A novel fast-setting calcium silicate cement with fluoride (CSC) has been developed for potential application in tooth crowns. This study compared the cytotoxicity of CSC compositions and a variety of dental materials. We tested CSC compositions (Protooth), MTA, Biodentine, Ketac Molar, Fuji II LC, Vitrebond, DeTrey Zinc, Dycal, and IRM, DMEM (negative control) and 1% NaOCl (positive control). After setting of cements for 24 h, specimens were immersed in DMEM for 24 h to obtain material elutes. The elutes were serially diluted in serum-free DMEM to obtain three dilutions. L929 mouse fibroblast cells (1 × 10⁴ cells per well) were treated for 24 h with elute dilutions (n = 3). Cytotoxicity was determined using methyl-thiazolyl-tetrazolium assay in triplicate. CSC compositions, MTA, and Biodentine showed no significant reduction in cell viability compared to DMEM. There was no significant difference in cell viability, at any of three dilutions, between CSC compositions and either MTA or Biodentine. Cytotoxicity was significantly lower for CSC compositions than for Vitrebond, DeTrey Zinc, Dycal, IRM, and 1% NaOCl, at all three dilutions, and undiluted Fuji II LC elute. In contrast to resin-modified glass ionomers, zinc phosphate cements, Dycal, and IRM, the CSC compositions showed no cytotoxic potential.

Endodontic-related inferior alveolar nerve injuries: A review and a therapeutic flow chart

INTRODUCTION

Inferior alveolar nerve (IAN) lesions related to endodontic treatments can be explained by the anatomical proximity between the apices of the mandibular posterior teeth and the mandibular canal. The aim of this article is to review the management of inferior alveolar nerve lesions due to endodontic treatments and to establish a therapeutic flow chart.

METHODS

A review of publications reporting IAN damage related to endodontic treatment over the past 20 years has been conducted, using the Preferred Reporting Items for Systematic Reviews and Meta-Analyses checklist; it combines an electronic search of the Pubmed^® and Google Scholar^® databasis. Forty-two full-text articles corresponding to 115 clinical cases have been selected. Two personal clinical cases were additionally reported.

RESULTS

IAN lesions due to endodontic treatments require urgent management. Early surgical removal of the excess of endodontic material, in contact with the nerve allows the best recovery prognosis (72h). Beyond this delay, irreversible nervous lesions prevail and a medical symptomatic treatment, most of the time with pregabalin, must be/can be carried out. A delayed surgical procedure shows some good benefits for patients. However, the healing prognosis remains poorly predictable.

Investigation of the cytotoxicity of thermoplastic denture base resins

PURPOSE

The purpose of this study was to investigate the in vitro cytotoxicity of thermoplastic denture base resins and to identify the possible adverse effects of these resins on oral keratinocytes in response to hot water/food intake.

MATERIALS AND METHODS

Six dental thermoplastic resin materials were evaluated: three polyamide materials (Smile tone, ST; Valplast, VP; and Luciton FRS, LF), two acrylic materials (Acrytone, AT; and Acryshot, AS), and one polypropylene resin material (Unigum, UG). One heat-polymerized acrylic resin (Vertex RS, RS) was chosen for comparison. After obtaining extracts from specimens of the denture resin materials (Φ=10 mm and d=2 mm) under different extraction conditions (37℃ for 24 hours, 70℃ for 24 hours, and 121℃ for 1 hour), the extracts (50%) or serial dilutions (25%, 12.5%, and 6.25%) in distilled water were co-cultured for 24 hours with immortalized human oral keratinocytes (IHOKs) or mouse fibroblasts (L929s) for the cytotoxicity assay described in ISO 10993.

RESULTS

Greater than 70% viability was detected under all test conditions. Significantly lower IHOK and L929 viability was detected in the 50% extract from the VP (70℃) and AT (121℃) samples (P<.05), but only L929 showed reduced viability in the 50% and 25% extract from LF (37℃) (P<.05).

CONCLUSION

Extracts obtained from six materials under different extraction conditions (37℃, 70℃, and 121℃) did not exhibit severe cytotoxicity (less than 70% viability), although their potential risk to oral mucosa at high temperatures should not be ignored.

Cytotoxicity and proinflammatory cytokine expression induced by interim resin materials in primary cultured human dental pulp cells

STATEMENT OF PROBLEM

Acrylic resin materials for interim restoration may adversely affect pulp tissue during the polymerization phase.

PURPOSE

The purpose of this in vitro study was to determine the cytotoxic and proinflammatory cytokine production effects induced by interim resin materials in primary cultured human dental pulp cells (hDPCs).

MATERIAL AND METHODS

Five interim resin materials were evaluated: 3 types of chemically activated products, 1 light-activated product, and 1 computer-aided design and computer-aided manufacturing (CAD-CAM) product. After obtaining eluates from interim resin materials that either were in the process of polymerizing or were already polymerized, these extracts were cocultured with hDPCs under serially diluted conditions (50%, 25%, 12.5%, 6.25%, and 3.125%) for 24 hours with positive (1% phenol) and negative (distilled water) controls. A cell viability assay with tetrazolium was used to evaluate toxic effects on the cells, and images of both live and dead cells were captured using confocal microscopy. Proinflammatory cytokine levels were measured using cytokine antibody arrays. All experiments were independently repeated 3 times, and data were analyzed using 1-way ANOVA and post hoc Tukey honest significant differences test (α=.05).

RESULTS

Cell viabilities less than 70% were observed from the eluates of the 3 chemically activated products under the 50% conditions. Among the chemically activated products, the adverse effects were significantly greater with eluates derived from the polymerizing phase compared than those that had already polymerized, as shown by confocal microscopy images of live and dead cells. However, the light-activated and CAD-CAM-fabricated products did not adversely affect the hDPCs. Significantly increased levels of proinflammatory cytokines were not detected in 12.5% of extract from polymerizing compared with distilled water control.

CONCLUSIONS

The 50% eluates derived from chemically activated interim resin during the polymerizing phase were cytotoxic to hDPCs and may adversely affect pulp tissue. Recommendations such as excess washing are necessary during fabrication.

In vitro cytotoxicity testing of airborne formaldehyde collected in serum-free culture media

The purpose of this study was to identify a suitable sampling model for on-site toxicity assessment of soluble air contaminants such as formaldehyde, a well known industrial and indoor air contaminant. The in vitro cytotoxicity of formaldehyde, the selected model for soluble air contaminants, was studied using the MTS (tetrazolium salt) assay in two carcinoma cell lines, A549 epithelial lung and HepG2 hepatocarcinoma, and in skin fibroblasts. The cytotoxic effects of airborne formaldehyde were evaluated using test atmospheres in concentrations below 10 ppm (12.3 mg/m3), generated by a dynamic diffusion method and bubbled (0.3 L/min) through serum-free culture media for one or four hours. Human cells were treated with formaldehyde air samples, and cell viability was determined after four hours incubation. In parallel, the concentration of airborne formaldehyde was monitored, using the 3500 NIOSH method. Cell viability of the HepG2 cells exposed to formaldehyde air samples (8.75 ppm-4 h) was reduced to less than 50% (31.69/1.24%). The HepG2 cell lines were found to be more sensitive (IC50=103.799/23.55 mg/L) to formaldehyde than both A549 cell lines (IC50=198.369/9.54 mg/L) and skin fibroblasts (IC50=196.689/36.73 mg/L) (PB/0.01). An average of 96.8% was determined for collection efficiency of formaldehyde in serum-free culture media. The results of this study suggest that absorption of soluble air contaminants, such as formaldehyde, in serum-free culture media can be used as a suitable sampling model for on-site toxicity assessments.

Evaluation of the cytotoxicity of different root canal sealers on L929 cell line by MTT assay

The purpose of this study was to evaluate the cytotoxic effects of commercially available root canal sealers [Sealite Ultra (SU), Tubli-Seal (TS), Tubli-Seal EWT (TS-EWT), Pulp Canal Sealer (PCS), Pulp Canal Sealer EWT (PCS-EWT), Endomethasone N (En N), and Apexit Plus (AP)] on L929 cells by using MTT assay. After incubation with each sealer's extract at 37°C in a humidified air atmosphere containing 5% CO(2 )for 24 h, MTT (5 mg/mL) in saline was added into each well and further incubated at 37°C for 4 h. Formazan precipitate was dissolved in a buffer containing 23% sodium dodecyl sulfate and 50% N, N-dimethylformamide (pH 4.7). Optical densities of dissolved formazan were read using a microplate spectrophotometer. AP, TS, and TS-EWT showed no cytotoxicity at any dilution tested. Other sealers exhibited some degree of cytotoxicity at the 1/4 and 1/2 dilutions. PCS-EWT and SU exerted more potent cytotoxicity at 1/2 dilution than the other sealers.

Cytotoxicity of ammonium hexafluorosilicate on human gingival fibroblasts

Ammonium hexafluorosilicate (SiF), which is claimed to significantly improve occlusion of dentinal tubules, was proposed as a novel desensitizer for dentine hypersensitivity (DH). However, the cytotoxicity of SiF on oral cells is lacking. The purpose of this study was to investigate the cytotoxicity of SiF on human gingival fibroblasts (hGFs) under different dosages (0.001%, 0.01%, 0.1%, and 1%) and treatment durations (1, 5, 10, and 30min). Cell proliferation, mitochondrial membrane potential (MMP) and cell cycle were tested by MTT assay, JC-1 staining and flow cytometry, respectively. Glutathione (GSH) depletion was analyzed to further investigate the underlying mechanism of SiF-induced cytotoxicity. MTT assay showed that there was significantly lower number of viable cells when the hGFs were treated with 0.01% (10min), 0.1% (10 and 30min) and 1% (5, 10, and 30min) SiF than the control group (p<0.05). MMP decreased and GSH depletion increased dramatically along with higher concentrations (0.1% and 1% SiF) and prolonged times (10 and 30min). DNA synthesis [S (%)] of cells treated with 0.1% and 1% SiF (5, 10, and 30min) was significantly lower than the control group (p<0.05). Our results indicate exposure to up to 0.01% SiF for less than 5min causes low or no cytotoxicity in vitro.

Effects of formalin on some biomarker activities of earthworms pre-exposed to temephos

Despite its negative effects, formalin has been often used for the expulsion of earthworms due to its high efficiency; however it is not known whether it will affect any significant measurable molecular processes in sampled earthworms. The aim of this research was to investigate effects of formalin on the activities of chosen molecular biomarkers in Eisenia andrei earthworms previously exposed to temephos. Additionally, the inhibitory effect of temephos, hitherto evaluated only on laboratory-bred earthworm species, was confirmed on two earthworm species obtained from their natural environment -Dendrobaena octaedra and Lumbricus rubellus. Earthworms were first exposed to the sub-lethal concentration of temephos for 2h and then to formalin 15 min in order to simulate the sampling procedure. Besides acetylcholinesterase (AChE) inhibition - a known biomarker of exposure to organophosphate insecticides - the concentration of oximes and the activities of catalase (CAT) and efflux pump were measured. Results showed that in all species temephos caused inhibition of AChE and CAT activity. Exposure of E. andrei to formalin caused inhibition of AChE, however after post-exposure to formalin for 15 min significant increase in AChE activity was recorded. Similar results were obtained with the measurement of oximes concentrations. Exposure to only formalin and combination of temephos (2h) and formalin (15 min) led to an increase in the CAT activity. The obtained results showed that exposure to formalin during the sampling could affect measured molecular biomarkers and also may change effects caused by exposure to temephos.

A dynamic system for single and repeated exposure of airway epithelial cells to gaseous pollutants

In vitro models are promising approaches to investigate the adverse effects and the mode of action of air pollutants on the respiratory tract. We designed a dynamic system that allows the single or repeated exposure of cultured cells to two major indoor air gaseous pollutants, formaldehyde (HCHO) and nitrogen dioxide (NO2), alone or as a mixture. In this system, the Calu-3 human bronchial epithelial cell line was exposed at the air-liquid interface (ALI) or submerged by culture medium to synthetic air or to target concentrations of HCHO and/or NO2 once or on 4 consecutive days before assessment of cell viability and necrosis, IL-6 and IL-8 release and trans-epithelial electrical resistance. Our data showed that whereas the ALI method can be used for single short-term exposures only, the submerged method provides the possibility to expose Calu-3 cells in a repeated manner. As well, we found that repeated exposures of the cells to HCHO and NO2 at concentrations that can be found indoors triggered a significant decrease in cell metabolism and an increase in IL-8 release that were not evoked by a single exposure. Thus, our work highlights the fact that the development of systems and methods that allow repeated exposures of cultured cells to gaseous compounds in mixtures is of major interest to evaluate the impact of air pollution on the respiratory tract.

Formaldehyde interferes with airway epithelium integrity and functions in a dose- and time-dependent manner

Formaldehyde (HCHO) is a common indoor air pollutant. To assess its potential role and mechanism of action in asthma, we exposed the bronchial epithelial cell lines Calu-3 and 16HBE to HCHO (70-7000 μM) according to two exposure schedules (30 min and 24 h), before measuring cell viability, necrosis and apoptosis, reactive oxygen species production, cytokine release, as well as trans-epithelial electrical resistance (TEER) of cell monolayers. Whereas exposure to HCHO for 30 min had a limited effect on cell viability, exposure for 24h to 1400-7000 μM HCHO induced a pronounced dose-dependent cell death. The important decrease in cell viability observed after 24h exposure to the highest concentrations of HCHO (1400-7000 μM) was accompanied by important LDH release and ROS production, whereas a 4h exposure to lower HCHO concentrations (350 μM) induced cell apoptosis. Also, exposure to HCHO for 30 min dose-dependently inhibited basal and lipopolysaccharide-induced interleukin-6 (IL-6) and IL-8 production by bronchial epithelial cells. As well, HCHO triggered a dose- and time-dependent decrease in TEER of Calu-3 cell monolayers. The present work demonstrates that HCHO interferes with airway epithelium integrity and functions, and may thus modulate the onset and the severity of asthma. However, importantly, conditions of exposure to HCHO, e.g. level and duration, are determinant in the nature of the effects triggered by the pollutant.

In vitro models in biocompatibility assessment for biomedical-grade chitosan derivatives in wound management

One of the ultimate goals of wound healing research is to find effective healing techniques that utilize the regeneration of similar tissues. This involves the modification of various wound dressing biomaterials for proper wound management. The biopolymer chitosan (beta-1,4-D-glucosamine) has natural biocompatibility and biodegradability that render it suitable for wound management. By definition, a biocompatible biomaterial does not have toxic or injurious effects on biological systems. Chemical and physical modifications of chitosan influence its biocompatibility and biodegradability to an uncertain degree. Hence, the modified biomedical-grade of chitosan derivatives should be pre-examined in vitro in order to produce high-quality, biocompatible dressings. In vitro toxicity examinations are more favorable than those performed in vivo, as the results are more reproducible and predictive. In this paper, basic in vitro tools were used to evaluate cellular and molecular responses with regard to the biocompatibility of biomedical-grade chitosan. Three paramount experimental parameters of biocompatibility in vitro namely cytocompatibility, genotoxicity and skin pro-inflammatory cytokine expression, were generally reviewed for biomedical-grade chitosan as wound dressing.

Bcl-2 expression and apoptosis induction in human HL60 leukaemic cells treated with a novel organotellurium(IV) compound RT-04

Organotellurium(IV) compounds have been reported to have multiple biological activities including cysteine protease-inhibitory activity, mainly cathepsin B. As cathepsin B is a highly predictive indicator for prognosis and diagnosis of cancer, a possible antitumor potential for these new compounds is expected. In this work, it was investigated the effectiveness of organotellurium(IV) RT-04 to produce lethal effects in the human promyelocytic leukaemia cell line HL60. Using the MTT tetrazolium reduction test, and trypan blue exclusion assay, the IC50 for the compound after 24 h incubation was 6.8 and 0.35 microM, respectively. Moreover, the compound was found to trigger apoptosis in HL60 cells, inducing DNA fragmentation and caspase-3, -6, and -9 activations. The apoptsosis-induced by RT-04 is probably related to the diminished Bcl-2 expression, observed by RT-PCR, in HL60-treated cells. In vivo studies demonstrated that the RT-04 treatment (2.76 mg/kg given for three consecutive days) produces no significant toxic effects for bone marrow and spleen CFU-GM. However, higher doses (5.0 and 10 mg/kg) produced a dose-dependent reduction in the number of CFU-GM of RT-04-treated mice. These results suggest that RT-04 is able to induce apoptosis in HL60 cells by Bcl-2 expression down-modulation. Further studies are necessary to better clarify the effects of this compound on bone marrow normal cells.

Pulp cell cultures obtained with two different methods for in vitro cytotoxicity tests

AIM

To describe two different protocols for obtaining primary pulp cell cultures, one derived from explants and the other following dissociation into single cell suspension by enzyme digestion.

METHODS

Human pulp tissue was obtained from three healthy premolars. The harvested pulp tissue was prepared for culture using physical methods (one of the premolars) and enzyme, type XI collagenase, (the two remaining premolars).

RESULTS

In the case of explant based culture, only limited growth was observed in some cases. However, by enzyme digestion, after two weeks cell growth was evident, and differences in cell type were observed according to the tooth involved.

CONCLUSION

It has been possible to obtain abundant biological material using an enzyme digestion-based protocol for testing purposes, with low experimental variability, as all cells originated from the same individual.

Cytotoxicity of materials used in perforation repair tested using the V79 fibroblast cell line and the granulocyte-macrophage progenitor cells

AIM

To compare the cytotoxicity of materials used to repair perforations using permanent V79 fibroblasts and murine granulocyte-macrophage progenitor cells (CFU-GM).

METHODOLOGY

Set specimens from amalgam, glass-ionomer, SuperEBA, N-Rickert, MTA and gutta-percha were eluted with culture medium for 72 h and their cytotoxicities were assessed by incubating the extracts with V79 and bone marrow-derived progenitors for 24 h and 7 days, respectively. Cytotoxicity on V79 cells was judged using the total nucleic acid content (NAC), neutral red uptake (NRU) and reduction of the tetrazolium salt (MTT). The number of bone marrow CFU-GM colonies determined in clonal cultures stimulated with recombinant murine granulocyte-macrophage colony-stimulating factor was used to assess cytotoxicity to progenitor cells. Statistical analyses were conducted using the one-way analysis of variance and Tukey's test where appropriate.

RESULTS

All materials were cytotoxic in both cell systems; however, CFU-GM was more sensitive to the extracts than V79 cells. A similar rank order of toxicity was observed in V79 cells using the NAC and the MTT assays: glass-ionomer > N-Rickert congruent with SuperEBA > gutta-percha > amalgam congruent with MTA (P < 0.05). In contrast, the NRU test exhibited a lower sensitivity to MTA, gutta-percha and amalgam extracts. In the clonal culture assay, the toxicity was less pronounced in the presence of gutta-percha, SuperEBA and MTA. Similar cellular responses were found by placing the set specimens directly in the clonal culture dishes.

CONCLUSIONS

The sensitivity of toxicity depended on the choice of the endpoint and the cell-culture system. Nevertheless, MTA was ranked as the least cytotoxic cement in both cell systems.

Tooth slice organ culture and established cell line culture models for cytotoxicity assessment of dental materials

The aim was to compare the use of different cell-material contact test methods with two different biological systems (cell line and tooth slice cultures) for cytotoxicity assessment of dental materials. Cytotoxicity of composites polymerized with two halogen-based and two light-emitting diode (LED) light-curing units (LCUs) served as the basis for comparison. Disk shaped specimens (7 x 2 mm) were fabricated using the four light sources. Composites were tested using L-929 cell line using direct/indirect/extract tests in accordance to standard protocols. Cytotoxicity was assessed using neutral red uptake. Tooth slice organ cultures were also employed to test the dental materials using direct/indirect test methods. Histomorphometric cell counting of intact odontoblasts and pulp fibroblasts and the use of tetrazolium salt 3-(4,5-dimethylthiazol-2-yl)-2,5-diphenyltetrazolium bromide (MTT) assays were applied for cytotoxicity evaluation. Discrepancy in result presentation was observed in the different tests used with L-929. Sensitivity levels of the L-929 tests ranked as follows: extract test < direct contact test < indirect contact test. Tooth slice tests confirmed that L-929 direct contact test proved to be the most reliable test among the three. In conclusion, this study highlights the risk involved when relying on a single test method for cytotoxicity assessment. It would be advisable to test different culture models and then proceed using more clinically relevant biological system that stimulate the in vivo situation for confirmation.

In vitro assessment of copper-induced toxicity in the human hepatoma line, Hep G2

Copper, though essential, is highly toxic when present in excess, as in Wilson disease, a genetic disorder of hepatic copper metabolism. We hypothesized that mitochondria are a major target of copper-induced cytotoxicity in Wilson disease. We used the human hepatoma line Hep G2 to examine copper-mediated cytotoxicity and three different methods to assess organelle damage: MTT assay (mitochondria), neutral red (NR; lysosomes) and Trypan blue exclusion assay (TB; plasma membrane). For all assays, cells at approximately 60% confluence in microtitre plates were incubated with CuCl(2) (concentration range: 50-100-150-200 microM) for 24 or 48 h. Results were expressed as percent of untreated control. At 24 h, cytotoxicity as detected by NR assay was significantly higher at all concentrations of copper than for MTT or TB ( p<0.005 at all concentrations). Cytotoxicity as detected by MTT was higher than that detected by TB at all concentrations except at 200 microM (p<0.05 for 50 microM, p<0.005 for 100 microM, p = 0.001 for 150 microM). Results at 48 h were similar (NR versus others: p <0.001 MTT versus TB: NS except at 150 microM where p<0.01). We investigated reactive oxygen species (ROS) production in copper-associated hepatocytoxicity by incubating sub-confluent cells with 2('),7(')-dichlorodihydrofluorescein diacetate dye plus copper (concentration range: 0-200 microM) for 1-1.5 h. Copper, but not zinc, produced significant increases in ROS (p<0.001). In summary, Hep G2 lysosomes appeared more susceptible to Cu-mediated damage than mitochondria; the cell membrane was highly resistant to damage.