Evidential requirements for the regulatory hazard and risk assessment of respiratory sensitisers: methyl methacrylate as an example.

This review addresses the need for a framework to increase the consistency, objectivity and transparency in the regulatory assessment of respiratory sensitisers and associated uncertainties. Principal issues are considered and illustrated through a case study (with methyl methacrylate). In the absence of test methods validated for regulatory use, formal documentation of the weight-of-evidence for hazard classification both at the level of integration of individual studies within lines of evidence and across a broad range of data streams was agreed to be critical for such a framework. An integrated approach is proposed to include not only occupational studies and clinical evidence for the regulatory assessment of respiratory sensitisers, but also information on structure and physical and chemical factors, predictive approaches such as structure activity analysis and in vitro and in vivo mechanistic and toxicokinetic findings. A weight-of-evidence protocol, incorporating integration of these sources of data based on predefined considerations, would contribute to transparency and consistency in the outcome of the assessment. In those cases where a decision may need to be taken on the basis of occupational findings alone, conclusions should be based on transparent weighting of relevant data on the observed prevalence of occupational asthma in various studies taking into account all relevant information including the range and nature of workplace exposures to the substance of interest, co-exposure to other chemicals and study quality.

Methyl methacrylate and respiratory sensitisation: a comprehensive review.

Methyl methacrylate (MMA) is classified under GHS as a weak skin sensitiser and a skin and respiratory irritant. It has recently been proposed that MMA be classified as a respiratory sensitiser (a designation that in a regulatory context embraces both true respiratory allergens, as well as chemicals that cause asthma through non-immunological mechanisms). This proposal was based primarily upon the interpretation of human data. This review, and a detailed weight of evidence analysis, has led to another interpretation of these data. The conclusion drawn is that persuasive evidence consistent with the designation of MMA as a respiratory sensitiser is lacking. It is suggested that one reason for different interpretations of these data is that occupational asthma poses several challenges with respect to establishing causation. Among these is that it is difficult to distinguish between allergic asthma, non-allergic asthma, and work-related exacerbation of pre-existing asthma. Moreover, there is a lack of methods for the identification of true chemical respiratory allergens. The characterisation and causation of occupational asthma is consequently largely dependent upon interpretation of human data of various types. Recommendations are made that are designed to improve the utility and interpretation of human data for establishing causation in occupational asthma.

Nickel, chromium and methyl methacrylate monomer release from orthopaedic functional appliances.

AIM: This study was purposed to evaluate release of nickel and chromium ions and methyl methacrylate (MMA) monomers from functional appliances and their possible health effects. MATERIALS AND METHODS: Study design: Twin-block appliances and Bionators were immersed in artificial saliva and kept in a thermal incubator. Control group was established as artificial saliva without appliances. Artificial saliva was analysed after 7 days, 30 days and 90 days. Inductively coupled plasma mass spectrometry and gas chromatography-mass spectrometry was used for detection of nickel and chromium ions and MMA monomers. MTT assays and cytokine array were performed. STATISTICS: One way ANOVA with Tukey test and Dunnett's T3 for post-hoc analysis was used for evaluation of time-dependent changes and independent t-test was used for evaluation of MTT assay results. RESULTS: The results revealed that metal ions and MMA monomers are released from the appliances. Metal ion detection pattern was irregular and could not be analysed. Twin-block group showed significantly larger amount of MMA release. MTT assay revealed statistically significant but minimally reduced cellular activity on Bionator and twin-block groups compared to control groups. Cytokine array showed no or less inflammatory cytokine release on Bionator and twin-block groups. CONCLUSION: MMA monomer release was confirmed but the cytotoxic effect of functional appliance material release is minimal or negligible. General toxicity of the functional appliance from the MMA monomer release is likely to be minimal or negligible.

Effect of processing methods on the cytotoxicity of methyl methacrylate-based ocular prostheses: An in vitro study.

The study evaluated the influence of cycles and methods of an ocular prosthesis resin on cytotoxicity toward human conjunctival cells. Resins were polymerized by water bath (WB, 74 °C or 100 °C for 30 min to 9 h), microwave (MW, 1200 W, 3 to 14 min and 30 s at 0 to 720 W), or autopolymerization (AP, room temperature for 20 min ± 60 °C for 30 min). Degree of conversion (DC), cytotoxicity, level of inflammatory mediators, gene expression of different markers, and apoptosis were evaluated. Data were submitted to ANOVA and Tukey test (p < 0.05). WB with longer processing time at higher temperature had highest DC (85.6%) and higher TGF ß1-gene expression (1.39); long cycle low power MW showed lowest DC (69.6%), lower cell proliferation (85.4%, MTT), and large IL-2 release (39,297 ng/mL). AP with additional processing time showed lower cell proliferation (75.3%, Alamar Blue), and AP polymerized at room temperature showed higher CASP 9-gene expression (1.21). AP methods showed higher IL-6 release (>277 pg/mL). Short cycle medium power MW had higher IL-23 release (534.2 pg/mL). MW (long and short cycles) and AP polymerizations have triggered a more intense inflammatory response. Among methods recommended by the manufacturer, WB showed high DC and less cytotoxicity.

Occupational exposure of dental technicians to methyl methacrylate: Genotoxicity assessment.

Dental technicians may be chronically exposed to methyl methacrylate (MMA), used in the production of dental prostheses. We have studied whether occupational exposure to MMA affects genotoxicity biomarkers such as 8-OHdG formation, comet assay, and buccal micronucleus frequency. MMA exposure was assessed via ambient air analysis. Although no significant differences between exposed and non-exposed individuals were seen with respect to blood genotoxicity measurements, we found a higher level of buccal-cell anomalies in the exposed group.

Label-free toxicology screening of primary human mesenchymal cells and iPS-derived neurons.

The high-throughput, label-free Corning Epic assay has applications in drug discovery, pharmacogenomics, cell receptor signaling, cell migration, and viral titration. The utility of Epic technology for biocompatibility testing has not been well established. In manufacturing of medical devices, in vitro and in vivo biocompatibility assessments are mandatory, according to ISO 10993. The new medical device regulation MDR 745/2017 specifies that ex vivo assays that can closely recapitulate in vivo scenarios are needed to better evaluate biomedical devices. We propose herein that Epic technology-which enables detection of variations in cell mass distribution-is suitable for biocompatibility screening of compounds. In this study, we challenged primary human osteoblasts, endothelial cells, and neurons derived from induced pluripotent stem cells with specific concentrations of methyl methacrylate (MMA). Polymeric MMA has long been applied in cranioplasty, where it makes contact with multiple cell types. Application of Epic technology yielded real-time cytotoxicity profiles for all considered cell types. The results were compared with those from microscopic observation of the same culture plate used in the Epic analyses. The Epic assay should be further examined for its utility for cell biology, genomics, and proteomics companion assays. Our results suggest that Epic technology can be applied to biocompatibility evaluation of human cells in medical device development.

[Dangerous cosmetic products in Germany : Analysis of the RAPEX database of the European Commission]. / Gefährliche Kosmetikprodukte in Deutschland : Analyse der RAPEX-Datenbank der Europäischen Kommission.

BACKGROUND: Cosmetic products are subject to the European Cosmetics Regulation: They shall not harm human health when used under "normal or reasonably foreseeable conditions". Hazardous cosmetic products are reported by the EU Member States to the EU Commission and are listed in the database of the European Rapid Alert System RAPEX. MATERIAL AND METHODS: The reports from Germany on dangerous cosmetic products from the years 2005-3/2017 in the European RAPEX database were systematically analyzed. RESULTS: During the study period, 157 dangerous cosmetic products were reported from Germany. The most common product categories were bleaching creams (24.2%) because of the content of hydroquinone, mercury or corticosteroids, creams/lotions/gels (10.8%) mainly due to microbiological contamination, henna products (10.2%) because of sensitizing concentrations of paraphenylene diamine, and nail adhesives (8.9%) because of high levels of methyl methacrylate. CONCLUSIONS: Hazardous cosmetic products appear to be rare in view of the high market volume of cosmetics, even though the total number of official investigations the RAPEX reports based on is not known. Dermatologists should inform the competent monitoring authorities in case of a suspected harm to health caused by dangerous cosmetic products so that the products can be examined and, if necessary, withdrawn from the market.

Investigation of the oxidative stress condition for occupational exposure to methyl methacrylate.

The purpose of this study is the evaluation of possible toxicological effects on dental personnel, who are exposed to the production materials of prostheses during their entire working life. In this study, the level of methyl methacrylate (MMA) in ambient air was measured as an indicator of external exposure on the personnel. In order to evaluate the possible toxic effects of oxidative stress, which is thought to play an important role in the formation process of many diseases such as cancer, blood samples of volunteers were examined via the ultraviolet-spectroscopic determination of superoxide dismutase (SOD), catalase (CAT) and glutathione peroxidase antioxidant enzyme activities, comparing occupationally MMA-exposed ( n = 69) and control ( n = 67) groups. In these groups, malondialdehyde (MDA) and glutathione levels were also determined by the same method. The results showed that SOD activity and MDA and glutathione levels were significantly higher in the exposed group when compared with the control group ( p < 0.001). A significant decrease was determined in the glutathione peroxidase activities of the exposed group ( p < 0.05). No significant difference in CAT activities between the groups has been found. When the results obtained in the study are considered, it is suggested that an adaptive response might be developed by dental technicians against low-level MMA exposure.

Uptake and toxicity of methylmethacrylate-based nanoplastic particles in aquatic organisms.

The uptake and toxicity of 2 poly(methylmethacrylate)-based plastic nanoparticles (PNPs) with different surface chemistries (medium and hydrophobic) were assessed using aquatic organisms selected for their relevance based on the environmental behavior of the PNPs. Pure poly(methylmethacrylate) (medium; PMMA PNPs) and poly(methylmethacrylate-co-stearylmethacrylate) copolymer (hydrophobic; PMMA-PSMA PNPs) of 86 nm to 125 nm were synthesized using a miniemulsion polymerization method. Fluorescent analogs of each PNP were also synthesized using monomer 7-[4-(trifluoromethyl)coumarin]acrylamide and studied. Daphnia magna, Corophium volutator, and Vibrio fischeri were employed in a series of standard acute ecotoxicity tests, being exposed to the PNPs at 3 different environmentally realistic concentrations (0.01 mg/L, 0.1 mg/L, and 1.0 mg/L) and a high concentration 500 mg/L to 1000 mg/L. In addition, sublethal effects of PNPs in C. volutator were determined using a sediment reburial test, and the uptake and depuration of fluorescent PNPs was studied in D. magna. The PNPs and fluorescent PNPs did not exhibit any observable toxicity at concentrations up to 500 mg/L to 1000 mg/L in any of the tests except for PMMA-PSMA PNPs and fluorescent PNPs following 48-h exposure to D. magna (median lethal concentration values of 879 mg/L and 887 mg/L, respectively). No significant differences were observed between labeled and nonlabeled PNPs, indicating the suitability of using fluorescent labeling. Significant uptake and rapid excretion of the fluorescent PNPs was observed in D. magna. Environ Toxicol Chem 2016;35:1641-1649. © 2015 SETAC.

No acute effects of an exposure to 50 ppm methyl methacrylate on the upper airways.

PURPOSE: The German MAK value of methyl methacrylate has been fixed at 50 ppm. The aim of this study was to evaluate possible acute effects of an exposure to 50 ppm methyl methacrylate on the upper airways of human subjects. METHODS: Twenty healthy subjects were exposed to 50 ppm methyl methacrylate and to air (sham) in an exposure chamber for 4 h according to a crossover design. Symptoms were assessed by the SPES questionnaire. Olfactory thresholds for n-butanol and mucociliary transport time were measured before and after exposure. Concentrations of interleukin 1ß and interleukin 8 were determined in nasal secretions taken after exposure. mRNA levels of interleukins 1ß, 6 and 8, tumor necrosis factor α, granulocyte-macrophage colony-stimulating factor, monocyte chemotactic protein 1, and cyclooxygenases 1 and 2 were measured in nasal epithelial cells, obtained after exposure. Possible effects were investigated by semiparametric and parametric crossover analyses. RESULTS: The score of the item "irritation to the nose" was slightly elevated following exposure to methyl methacrylate (p ≤ 0.01). Olfactory functioning was not impaired. Mucociliary transport time did not change. Neither concentrations of interleukins in nasal secretions nor mRNA levels were elevated. CONCLUSION: Only minor irritating effects on the nose were observed. The acute exposure to 50 ppm methyl methacrylate did not cause any adverse effects. However, the results cannot be extrapolated to chronic exposure.

Occupational hazards for pregnant or lactating women in the orthopaedic operating room.

Pregnant or lactating staff working in the orthopaedic operating room may be at risk of occupational exposure to several hazards, including blood-borne pathogens, anesthetic gases, methylmethacrylate, physical stress, and radiation. Because the use of proper personal protective equipment is mandatory, the risk of contamination with blood-borne pathogens such as hepatitis B, hepatitis C, and HIV is low. Moreover, effective postexposure prophylactic regimens are available for hepatitis B and HIV. In the 1960s, concerns were raised about occupational exposure to harmful chemicals in the operating room such as anesthetic gases and methylmethacrylate. Guidelines on safe levels of exposure to these chemicals and the use of personal protective equipment have helped to minimize the risks to pregnant or lactating staff. Short periods of moderate physical activity are beneficial for pregnant women, but prolonged strenuous activity can lead to increased pregnancy complications. The risk of prenatal radiation exposure during orthopaedic procedures is of concern, as well. However, proper lead protection and contamination control can minimize the risk of occupational exposure to radiation.

Allergic contact dermatitis from two-component acrylic resin in a manicurist and a dental hygienist.

BACKGROUNDS: Two-component acrylic resin used in nail art and dentistry can cause allergic contact dermatitis (ACD), but only a few reports from Japan have been published. CASES: A 35-year-old female manicurist (case 1) and 30-year-old female dental hygienist (case 2) were diagnosed with ACD caused by ethyl methacrylate and methyl methacrylate in a liquid monomer of two-component acrylic resin respectively. Case 1 was sensitized from direct skin contact with nail art acrylic products, which could have been avoided, and gave up both being a manicurist and a user. Onset in case 2 occurred when she started to work as an apprentice. She had believed that the cause of her symptoms was use of disposable natural rubber gloves, not a liquid monomer penetrating through her gloves, until she was patch tested positive to (meth)acrylates and liquid monomer. CONCLUSIONS: To prevent sensitization, it should be emphasized in occupational training in both specialties that there should be no direct contact with acrylic products and that disposable gloves do not have sufficient protecting properties.

2-diethylaminoethyl-dextran methyl methacrylate copolymer nonviral vector: still a long way toward the safety of aerosol gene therapy.

Revealing the lung tumor genome has directed the current treatment strategies toward targeted therapy. First line treatments targeting the genome of lung tumor cells have been approved and are on the market. However, they are limited by the small number of patients with the current investigated genetic mutations. Novel treatment administration modalities have been also investigated in an effort to increase the local drug deposition and disease control. In the current study, we investigated the safety of the new nonviral vector 2-diethylaminoethyl-dextran methyl methacrylate copolymer (DDMC; Ryujyu Science), which belongs to the 2-diethylaminoethyl-dextran family by aerosol administration. Thirty male BALBC mice, 2 month old, were included and divided into three groups. However, pathological findings indicated severe emphysema within three aerosol sessions. In addition, the CytoViva technique was applied for the first time to display the nonviral particles within the pulmonary tissue and emphysema lesions, and a spectral library of the nonviral vector was also established. Although our results in BALBC mice prevented us from further investigation of the DDMC nonviral vector as a vehicle for gene therapy, further investigation in animals with larger airways is warranted to properly evaluate the safety of the vector.

Hypothesis-based weight-of-evidence evaluation of methyl methacrylate olfactory effects in humans and derivation of an occupational exposure level.

Over 40 years of scientific evidence indicates that methyl methacrylate (MMA) causes olfactory effects in rodents that are relevant to humans. More recent scientific studies have focused on understanding the apparent lack of species concordance between the rodent and human studies. Toxicokinetic studies and a physiologically based pharmacokinetic (PBPK) model describing inhalation dosimetry of MMA in the upper respiratory tract (URT) of rats and humans point to differences in nasal morphology and biochemistry that could explain and reconcile these differences as species-specific manifestations of a common toxicological process. We have applied the hypothesis-based weight-of-evidence (HBWoE) approach to evaluate the concordance of the available data and the hypothesis that the observed difference in sensitivity between rats and humans may be the expected result of physiological and biochemical differences. Our WoE analysis indicates that when the several lines of evidence (i.e., animal, human, mode-of-action, and toxicokinetics data) are integrated, they inform interpretation of one another and, overall, support use of the human data for derivation of an MMA occupational exposure level (OEL) of 50 ppm.

Assessment of methyl methacrylate genotoxicity by the micronucleus test

The aim of this study was to evaluate the genotoxic potential of methyl methacrylate (MMA) vapor by simulating standard occupational exposure of 8 hours per day and using the micronucleus test. We used 32 adult male Wistar rats divided into three groups: A - 16 rats exposed to MMA for 8 hours a day, B - Eight rats receiving single subcutaneous doses of cyclophosphamide on the first day of the experiment (positive control), C - Eight rats receiving only water and food ad libitum (negative control). Eight rats from group A and all of the rats from groups B and C were sacrificed 24 hours after beginning the experiment (acute exposure in group A). The remaining animals in group A were sacrificed 5 days after the experiment began (repeated exposure assessment in group A, simulating occupational exposure 40 hours/week). Femoral bone marrow was collected from each rat at the time of sacrifice for use in the micronucleus test. Two slides were completed per animal and were stained with Giemsa staining. Two thousand polychromatic erythrocytes were counted per animal. The Kruskal-Wallis test followed by a multiple comparisons test (Dunn test) was used for statistical analysis. The median number of micronuclei was 7.00 in the group exposed to MMA for 1 day, 2.00 in the group exposed to MMA for 5 days, 9.00 in the group exposed to cyclophosphamide (positive control) and 0.756 in the negative control group (p < 0.0001). MMA was genotoxic when measured after 1 day of exposure but was not evidently genotoxic after 5 days.

Assessment of methyl methacrylate genotoxicity by the micronucleus test.

The aim of this study was to evaluate the genotoxic potential of methyl methacrylate (MMA) vapor by simulating standard occupational exposure of 8 hours per day and using the micronucleus test. We used 32 adult male Wistar rats divided into three groups: A - 16 rats exposed to MMA for 8 hours a day, B - Eight rats receiving single subcutaneous doses of cyclophosphamide on the first day of the experiment (positive control), C - Eight rats receiving only water and food ad libitum (negative control). Eight rats from group A and all of the rats from groups B and C were sacrificed 24 hours after beginning the experiment (acute exposure in group A). The remaining animals in group A were sacrificed 5 days after the experiment began (repeated exposure assessment in group A, simulating occupational exposure 40 hours/week). Femoral bone marrow was collected from each rat at the time of sacrifice for use in the micronucleus test. Two slides were completed per animal and were stained with Giemsa staining. Two thousand polychromatic erythrocytes were counted per animal. The Kruskal-Wallis test followed by a multiple comparisons test (Dunn test) was used for statistical analysis. The median number of micronuclei was 7.00 in the group exposed to MMA for 1 day, 2.00 in the group exposed to MMA for 5 days, 9.00 in the group exposed to cyclophosphamide (positive control) and 0.756 in the negative control group (p < 0.0001). MMA was genotoxic when measured after 1 day of exposure but was not evidently genotoxic after 5 days.

Antimicrobial properties and cytotoxicity of an antimicrobial monomer for application in prosthodontics.

PURPOSE: This study aimed to investigate the antimicrobial properties and cytotoxicity of the monomer methacryloyloxyundecylpyridinium bromide (MUPB), an antiseptic agent capable of copolymerizing with denture base acrylic resins. MATERIALS AND METHODS: The antimicrobial activity of MUPB was tested against the species Candida albicans, Candida dubliniensis, Candida glabrata, Lactobacillus casei, Staphylococcus aureus, and Streptococcus mutans. The minimum inhibitory and fungicidal/bactericidal concentrations (MIC, MFC/MBC) of MUPB were determined by serial dilutions in comparison with cetylpyridinium chloride (CPC). The cytotoxic effects of MUPB at concentrations ranging from 0.01 to 1 g/L were assessed by MTT test on L929 cells and compared with methyl methacrylate (MMA). The antimicrobial activity of copolymerized MUPB was tested by means of acrylic resin specimens containing three concentrations of the monomer (0, 0.3, 0.6% w/w). Activity was quantified by means of a disc diffusion test and a quantification of adhered planktonic cells. Statistical analysis employed the Mann-Whitney test for MIC and MFC/MBC, and ANOVA for the microbial adherence test (α = 0.05). RESULTS: MUBP presented lower MIC values when compared with CPC, although differences were significant for C. dubliniensis and S. mutans only (p= 0.046 and 0.043, respectively). MFC/MBC values were similar for all species except C. albicans; in that case, MUPB presented significantly higher values (p = 0.046). MUPB presented higher cytotoxicity than MMA for all tested concentrations (p < 0.001) except at 0.01 g/L. Irrespective of the concentration incorporated and species, there was no inhibition halo around the specimens. The incorporation of MUPB influenced the adhesion of C. albicans only (p = 0.003), with lower CFU counts for the 0.6% group. CONCLUSIONS: It was concluded that non-polymerized MUPB has an antimicrobial capacity close to that of CPC and high cytotoxicity when compared with MMA. The antimicrobial activity of MUPB after incorporation within a denture base acrylic resin did not depend on its elution, but was shown to be restricted to C. albicans.

An in vitro investigation into the cytotoxicity of methyl methacrylate monomer.

Aim of this study was to assess the cytotoxicity of monomer. An in vitro study was designed to study the growth inhibitory effect of monomer (Stellon, Denture Material Improved, Type I, Class I, Dental Products of India Limited) on cells seeded in petri dishes and maintained in an incubator with 5% carbon dioxide at 37 °C. The growth of V79 cells (fibroblast cells) maintained in a culture medium to which monomer was added was studied for a period of 5 days. Results of this study pointed out that even at a concentration of 1 µl of monomer, the cell growth was significantly inhibited, when compared to the control group. The number of viable cells decreased dramatically whereas dead cells increased in the culture groups treated with the monomer. The cytotoxic effect was dose dependent. As the concentration increased from 1 to 10 µl there was a marked inhibition of cell growth and a corresponding increase in dead cell count. Results of this study proved beyond doubt that monomer is indeed cytotoxic even in very low concentrations. Thus, it becomes imperative to adopt every possible means to minimize residual monomer content in heat cured resins. Also precautions to minimize tissue contact should be taken while handling monomer by the dentist and dental personnel in the laboratory.

Occupational hazards to the pregnant orthopaedic surgeon.

The number of female orthopaedic residents and orthopaedic surgeons has increased substantially. Concerns have been raised regarding the effect of the work environment on the health of the female orthopaedic surgeon and her fetus or neonate. Occupational risks, and specifically risks to the pregnant orthopaedic surgeon, are becoming an important issue in medicine. Such risks include exposure to methylmethacrylate (MMA), anesthetic gases, blood-borne pathogens, radiation, emotional stress, and physical stress. Awareness of and knowledge about such exposures are needed for the pregnant orthopaedic surgeon to make informed decisions about her occupational exposures and to be proactive about her own and her child's health.