Age Impacts Pulmonary Inflammation and Systemic Bone Response to Inhaled Organic Dust Exposure

Abstract

Agricultural workers have high rates of airway and skeletal health disease. Studies recently demonstrated that inhaled agricultural organic dust extract (ODE) induced-airway injury is associated with bone deterioration in an animal model. However, the effect of age in governing these responses to organic dusts is unclear, but might be important in future approaches. Young (7–9 weeks) and older (12–14 months) male C57BL/6 mice received intranasal (i.n.) inhalation exposure to ODE from swine confinement facilities once or daily for 3 weeks. Acute ODE-induced neutrophil influx and cytokine and chemokine (TNF-α, IL-6, CXCL1, CXCL2) airway production was reduced in older compared to young mice. Repetitive ODE treatment, however, increased lymphocyte recruitment and alveolar compartment histopathologic inflammatory changes in older mice. Whole lung cell infiltrate analysis revealed that young, but not older mice, repetitively treated with ODE demonstrated an elevated CD4:CD8 lymphocyte response. Acute inhalant ODE exposure resulted in a 4-fold and 1.5-fold rise in blood neutrophils in young and older mice, respectively. Serum IL-6 and CXCL1 levels were elevated in young and older mice i.n. exposed once to ODE, with increased CXCL1 levels in younger compared to older mice. Although older mice displayed reduced bone measurements compared to younger mice, younger rodents demonstrated ODE-induced decrease in bone mineral density, bone volume and bone micro-architecture quality as determined by CT analysis. Collectively, age impacts the airway injury, and systemic inflammatory and bone loss response to inhalant ODE, suggesting an altered and enhanced immunologic response in younger as compared to older counterparts.

Combined Collagen-Induced Arthritis and Organic Dust-Induced Airway Inflammation to Model Inflammatory Lung Disease in Rheumatoid Arthritis

“…Thus, in the present study, we chose to use high‐resolution µCT of the trabecular bone in the tibia and calcaneus to assess the effects of CIA, ODE, and coexposure on systemic bone quantity and quality. Following euthanization, hind limbs (calcaneus and tibia) were isolated and processed for µCT scanning and analysis . Bones were scanned using high‐resolution µCT (Skyscan 1172; Bruker, Kontich, Belgium) with bone position corrected using Dataviewer (Skyscan) to assure proper orientation .…”

“…Following euthanization, hind limbs (calcaneus and tibia) were isolated and processed for µCT scanning and analysis. (32) Bones were scanned using high-resolution µCT (Skyscan 1172; Bruker, Kontich, Belgium) with bone position corrected using Dataviewer (Skyscan) to assure proper orientation. (33) For tibias, resolution was acquired at 6.07 μm, the X-ray source set at 48 kV and 187 μA, and scanning was done at 0.4-degree intervals with four average frames/rotation.…”

Toll-Like Receptor 4 Signaling Pathway Mediates Inhalant Organic Dust-Induced Bone Loss

“…The right hind limbs from exposed mice were excised, processed, and prepared for micro-computed tomography (CT) scanning and analysis as previously described [ 13 , 14 , 35 ]. Briefly, the proximal tibia was scanned using high-resolution micro-CT (Skyscan 1172; Skyscan, Aartselaar, Belgium) with images acquired at a resolution of 6.07 μm, source set at 48 kV and 187 μ with 0.5-mm-thick aluminum filter with an exposure time of 620 ms. Scanning performed at 0.4° intervals, and 6 average frames were obtained for each rotation.…”

“…Briefly, the proximal tibia was scanned using high-resolution micro-CT (Skyscan 1172; Skyscan, Aartselaar, Belgium) with images acquired at a resolution of 6.07 μm, source set at 48 kV and 187 μ with 0.5-mm-thick aluminum filter with an exposure time of 620 ms. Scanning performed at 0.4° intervals, and 6 average frames were obtained for each rotation. NRecon (Skyscan) software was used to reconstruct scanned images, and analysis was conducted on stacked reconstructed images using CTAn (Skyscan) software as previously described [ 35 ]. To ensure proper orientation along the longitudinal axis, growth plates were identified as the reference point and tibial position was corrected using Dataviewer (Skyscan).…”

The Effect of Inhalant Organic Dust on Bone Health

“…IL-6 has also been shown to impact RANKL expression and influence osteoclastogenesis (18). In addition, IL-6 is a key cytokine that is consistently associated with organic dust induced airway injury (31,49,50,51), and murine serum levels of IL-6 have been detected following inhalant ODE exposure (30,52). Therefore, it was hypothesized that systemic IL-6 could be responsible for mediating inhalant-ODE induced bone loss.…”