Dung biomass smoke activates inflammatory signaling pathways in human small airway epithelial cells

Abstract

Animal dung is a biomass fuel burned by vulnerable populations who cannot afford cleaner sources of energy, such as wood and gas, for cooking and heating their homes. Exposure to biomass smoke is the leading environmental risk for mortality, with over 4,000,000 deaths each year worldwide attributed to indoor air pollution from biomass smoke. Biomass smoke inhalation is epidemiologically associated with pulmonary diseases, including chronic obstructive pulmonary disease (COPD), lung cancer, and respiratory infections, especially in low and middle-income countries. Yet, few studies have examined the mechanisms of dung biomass smoke-induced inflammatory responses in human lung cells. Here, we tested the hypothesis that dung biomass smoke causes inflammatory responses in human lung cells through signaling pathways involved in acute and chronic lung inflammation. Primary human small airway epithelial cells (SAECs) were exposed to dung smoke at the air-liquid interface using a newly developed, automated, and reproducible dung biomass smoke generation system. The examination of inflammatory signaling showed that dung biomass smoke increased the production of several proinflammatory cytokines and enzymes in SAECs through activation of the activator protein (AP)-1 and arylhydrocarbon receptor (AhR) but not nuclear factor-κB (NF-κB) pathways. We propose that the inflammatory responses of lung cells exposed to dung biomass smoke contribute to the development of respiratory diseases.

Comparison of in vitro toxicological effects of biomass smoke from different sources of animal dung

“…African elephant, domestic goat, and white rhinoceros dung were collected from animals exhibited at Rochester’s Seneca Park Zoo fed timothy hay and commercial grain. The dung was dried overnight at 50°C, ground up, and packed into cigarettes as previously described by McCarthy et al (8). Briefly, dried dung was broken down using a food processor, passed through a sieve to obtain pieces between 850 μm and 420 μm, mixed with 2% glycerol, and rolled into cigarette tubes (Zen) using a cigarette packing machine.…”

“…Primary human small airway epithelial cells (SAECs; Lonza, Walkersville, MD) and SAECs with an NF-κB reporter (SABiosciences, Valencia, CA) were cultured as previously described (8, 21, 22). For dung smoke exposures, SAECs were plated onto culture inserts (1 μm pore size; Millipore), moved to the air-liquid interface (ALI) for 24 hours, and exposed to air or whole dung smoke for 10–30 minutes.…”

“…We used primers for 18S RNA (22), cytochrome P450 (CYP)1A1 (8), interferon (IFN)-β (forward: 5′-AACTGCAACCTTTCGAAGCC-3′; reverse: 5′-TGTCGCCTACTACCTGTTGTGC-3′) and IFN-λ (forward: 5′-GGTGACTTTGGTGCTAGGCT-3′; reverse: 5′-GGCCTTCTTGAAGCTCGCT-3′).…”

“…Epidemiological evidence associates biomass smoke exposure with lung diseases, including Chronic Obstructive Pulmonary Disease (COPD), lung cancer, and respiratory infections (1, 4, 5). Similarly, in vitro studies have shown that human lung cells exposed to certain types of biomass smoke have heightened inflammatory responses and impaired immune defenses (6–8). Biomass smoke exerts toxic effects on the lung, leading to human health problems.…”

“…We and others have reported the pro-inflammatory effects of dung biomass smoke in vitro and in vivo , which was generated by burning selected types of animal dung (6, 8–11). However, the type of animal dung burned in households varies depending on local geography, climate, and agricultural practices.…”