Alcohol Decreases Organic Dust‐Stimulated Airway Epithelial TNF‐Alpha Through a Nitric Oxide and Protein Kinase‐Mediated Inhibition of TACE

Abstract

Background Farm workers in rural areas consume more alcohol than those who reside in urban areas. Occupational exposures such as agricultural work can pose hazards on the respiratory system. It is established that hog barn dust induces inflammation in the airway, including the release of cytokines such as tumor necrosis factor alpha (TNFα), interleukin-6 (IL-6) and interleukin-8 (IL-8). We have shown that alcohol alters airway epithelial innate defense through changes in both nitric oxide (NO) and cAMP-dependent protein kinase (PKA). Simultaneous exposure to hog barn dust and alcohol decreases inflammatory mediators, TNFα, IL-6 and IL-8, in mice. Previously, mice exposed to both alcohol and hog barn dust showed a depleted amount of lymphocytes compared to mice exposed only to hog barn dust. Weakening of the innate immune response could lead to enhanced susceptibility to disease. In addition, mice that were co-exposed to hog barn dust and alcohol also experienced increased mortality. Methods Because we recently demonstrated that PKA activation inhibits the TNFα sheddase, TNF-α converting enzyme (TACE), we hypothesized that an alcohol-mediated PKA pathway blocks TACE activity and prevents the normative inflammatory response to hog barn dust exposure. To delineate these effects, we used PKA pathway inhibitors (adenylyl cyclase, cAMP and PKA) to modulate the effects of alcohol on dust-stimulated TNFα release in the bronchial epithelial cell line, BEAS-2B. Alcohol pretreatment blocked TACE activity and TNFα release in hog barn dust-treated cells. Results Alcohol continued to block hog barn dust-mediated TNFα release in the presence of the particulate adenylyl cyclase inhibitor, SQ22,536. The soluble adenylyl cyclase (sAC) inhibitor, KH7, however, significantly increased the inflammatory response to hog barn dust. PDE4 inhibitors significantly elevated cAMP and enhanced alcohol-mediated inhibition of dust-stimulated TNFα release. In addition, the nitric oxide synthase inhibitor, L-NMMA, also reversed the alcohol-blocking effect on dust-stimulated TNFα. Conclusions These data suggest that alcohol requires a soluble cyclase-generated cAMP-PKA pathway that is dependent upon the action of NO to inhibit TACE and TNFα release. These findings support our observations that alcohol functions through a dual NO and PKA pathway in bronchial epithelial cells.

Sorrel Extract Reduces Oxidant Production in Airway Epithelial Cells Exposed to Swine Barn Dust Extract In Vitro

“…We observed increases of NO · in response to 5% DE exposure in vitro . This result falls in line with findings from Gerald et al, that NF- κ B activity is increased in BEAS2B cell cultures with a 5% hog barn dust exposure [5]. NF- κ B is an upstream transcription factor that codes for the gene inducible nitric oxide synthase (iNOS).…”

“…Many of these occupational lung diseases are mediated by proinflammatory cytokines including interleukin-6 (IL-6) and IL-8, whose levels are known to increase in respiratory cells and tissues following swine dust exposure [5]. IL-8 is a potent recruiter of neutrophils and other granulocytes, and it promotes phagocytosis, a process that contributes to oxidative stress by releasing free radicals to neutralize bacteria.…”

Alcohol Inhibits Organic Dust-Induced ICAM-1 Expression on Bronchial Epithelial Cells

“…We previously showed that alcohol can block ADAM-17 mediated release of TNFα in HDE-stimulated epithelium [ 16 ]. Thus, we investigated the role of TACE and TNFα in the down regulation of HDE-induced ICAM-1 epithelial expression and neutrophil adhesion.…”

“…This effect is rapid and not the result of TACE down-regulation. This is particularly important in the context of alcohol exposure as an ethanol-sensitive adenylyl cyclase in airway epithelium [ 46 ] can also lead to the inhibition of dust-stimulated TACE activity [ 16 ]. Such alcohol-mediated alterations in response to swine barn dust may explain the significant lack of inflammatory cell aggregates in the lungs of mice fed alcohol prior to nasal inhalation of swine barn dust [ 17 ].…”

“…Recently, we have demonstrated that cytokine release in response to HDE can be blunted by cAMP-dependent protein kinase inhibition of ADAM-17, the sheddase responsible for TNFα release [ 15 ]. Furthermore, we have shown that alcohol-stimulated increases in cAMP can lead to a blunted PKC-mediated cytokine response in HDE-exposed airway epithelium [ 16 ]. These observations provide the mechanistic basis for the dysfunctional lung inflammatory response observed in alcohol-fed mice exposed to swine barn dust [ 17 ].…”