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

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.

Inflammation in the lungs of mice due to methyl methacrylate exposure

Aim:

This study aimed to predict the potential inflammation in lungs caused by exposure to methyl methacrylate (MMA; in silico study) and assess inflammation in lungs in response to MMA inhalation in mice (in vivo study).

Materials and Methods:

In silico and in vivo studies were performed using 24 mice divided into a control group (0 ppm MMA) and five treatment groups, which were exposed to 150 ppm MMA for 40, 80, 120, 160, and 200 min, respectively. Lung tissues were harvested and examined with a light microscope at 400×.

Results:

In silico studies confirmed the existence of one activation bond between MMA and the toll-like receptor 4 (TLR-4), namely, His 228, with a MolDock score of −43.677 kcal/mol. Microscopic examination of lungs confirmed that a greater number of inflammatory cells were found in the treatment group than in the control group and symptoms of inflammation were clearly observable after 120 min of exposure.

Conclusion:

Thus, inflammation occurring due to MMA interaction with TLR-4 receptors can be predicted in silico and exposure to 150 ppm MMA for more than 120 min can cause lung inflammation in mice.

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.