Evaluation of buccal damage associated with acute inhalation exposure to 2,4-dichlorophenoxyacetic acid (2,4-D) in mice

Abstract

Background: The herbicide dichlorophenoxyacetic acid (2,4-D) is one of the most widely used crop spraying products in the world. Some pesticides induce the degranulation of mast cells and increase allergic responses. This is the first study to evaluate the damage to the oral mucosa after an experimental simulation of environmental inhalation exposure to the 2,4-D herbicide. The aim of this study was evaluate the possible oral damage caused by acute inhalation exposure to the herbicide 2,4-D.

Results: There was a difference between the exposure concentrations in relation to tissue congestion intensity (p = 0.002) and mast cell counts (p = 0.002), a difference in the evaluation of the interaction between the exposure concentrations and nebulization time in the dorsum epithelium thickness (p = 0.013), and a significant correlation between the epithelial thickness and the number of nucleoli organizing regions on the dorsum of the tongue (p = 0.048).

Conclusions: Even after acute exposure, the herbicide 2,4-D had the potential to damage the oral epithelium, especially at higher doses.

Keywords: Environmental exposure; Inflammation; Leukoplakia; Mast cells; Pesticide exposure; oral.

Fig. 1

Photomicroscopy of the tongue with inflammatory foci in the submucosa (arrow). Hematoxylin-eosin, 400x magnification (100 µm bar for scale)

Fig. 2

Intensity (percentage ± standard error) of congestion in the tongue of the animals per study group regardless the time of exposure. Groups: SG: saline group; LCG: low 2,4-D concentration group; MCG: middle 2,4-D concentration group; HCG: high 2,4-D concentration group. (HCG, MCG) x (SG, LCG): p < 0.05

Fig. 3

Photomicroscopy of the tongue with congestion. Note the dilated capillaries that are full of plasma and/ or red blood cells (*): a – Slightly dilated capillaries featuring mild tissue congestion (Animal of the SG group after 1 inhalation exposure of 2,4-D). b - Slightly dilated capillaries featuring mild tissue congestion (Animal of the LCG group after 1 inhalation exposure of 2,4-D). c - Very dilated capillaries featuring moderate tissue congestion (Animal of the MCG group after 3 inhalation exposures of 2,4-D). d - Very dilated capillaries featuring moderate tissue congestion (Animal of the HCG group after 2 inhalation exposures of 2,4-D). Hematoxylin-eosin, 100x magnification (100 µm bar for scale)

Fig. 4

Mean number (± standard error) of mast cells (per mm²) per study group regardless the time of exposure. Groups: SG saline group, LCG low 2,4-D concentration group, MCG middle 2,4-D concentration group, HCG high 2,4-D concentration group. HCG x (SG, LCG, MCG): p < 0.05

Fig. 5

Photomicroscopy of the tongue showing mast cells (arrows). a - Large number of mast cells in the tissue (Animal of the SG group after 2 inhalation exposures of 2,4-D). b - Large number of mast cells in the tissue (Animal of the LCG group after 2 inhalation exposures of 2,4-D). c - Large number of mast cells in the tissue (Animal of the MCG group after 2 inhalation exposures of 2,4-D). d - Few mast cells in the tissue (Animal of the HCG group eight days after three nebulizations of 2,4-D). Hematoxylin-eosin, 400x magnification (100 µm bar for scale)

Fig. 6

Correlation between the epithelial thickness (in microns) and the number of nucleoli organizing regions (NORs) (per mm²) in the epithelium of the dorsum of the tongue by study group and time of exposue (p = 0.048). Groups: SG: saline group; LCG: low 2,4-D concentration group; MCG: middle 2,4-D concentration group; HCG: high 2,4-D concentration group; 1D: one nebulization; 2D: two nebulizations; 3D: three nebulizations; 8D: eight days after three nebulizations

Fig. 7

Experimental study design. SG: saline group; LCG: low 2,4-D concentration group; MCG: middle 2,4-D concentration group; HCG: high 2,4-D concentration group; 1D: one nebulization; 2D: two nebulizations; 3D: three nebulizations; 8D: eight days after three nebulizations