Pathological study of pulmonary toxicity induced by intratracheally instilled Asian sand dust (Kosa): effects of lowered serum zinc level on the toxicity

Abstract

I: NTRODUCTION: We have previously reported that Asian sand dust (ASD) induced acute and chronic inflammatory changes in the lung of mice. Zinc (Zn) is reported to influence inflammation and wound healing. The purpose of the study was to assess the effects of lowered serum Zn levels on the lung toxicity induced by ASD.

Material and methods: Mice that were fed diets containing normal (group 1) or low (group 2) content of Zn for 8 weeks were intratracheally instilled with 3.0 mg of ASD, followed by sacrifice at 24 hours, 2 weeks, and 1, 2 and 3 months after instillation. Paraffin sections of lung tissues were stained by hematoxylin and eosin and by immunohistochemistry to detect tumor necrosis factor (TNF) and interleukin (IL)-1β as well as inflammasome (NALP3), autophagy (LC-3) and lysosome (LAMP-1) markers. Selected samples of lung tissue were examined by electron microscopy.

Results: Following histological examination of the lung, similar patterns of inflammatory changes were observed in mice with normal and low serum Zn concentrations; however, they were more prominent and persistent in mice with low serum Zn level. These changes were both purulent (acute) and pyogranulomatous (chronic) in nature. In the lung lesions of group 2 mice the changes within the cytoplasmic vacuoles of enlarged ASD-containing macrophages (Mo) were clearly visible. The macrophages expressed TNF and IL-1β, and semi-quantitative analysis revealed a larger number of TNF-positive Mo in mice with normal level of serum Zn and a larger number of IL-1β-positive Mo in mice with low level of serum Zn. Decreased positive LC-3 staining and dilated lysosomes containing ASD particles were observed in the cytoplasm of Mo in mice with low serum Zn concentration.

Conclusions: These findings suggest that low serum zinc concentration may induce the modulation of cytokine expression and lysosomal malfunction by phagocytotic and/or autophagic mechanisms, and may result in interstitial pyogranulomatous inflammation in the lungs of mice treated with ASD.

Keywords: Asian sand lung toxicity; IHC; IL-1; LAMP-1; LC-3; NALP-3; TNF; electron microscopy; low zinc level; mice.