Chemical nature and immunotoxicological properties of arachidonic acid degradation products formed by exposure to ozone.

Abstract

Ozone (O3) exposure in vivo has been reported to degrade arachidonic acid (AA) in the lungs of rodents. The O3-degraded AA products may play a role in the responses to this toxicant. To study the chemical nature and biological activity of O3-exposed AA, we exposed AA in a cell-free, aqueous environment to air, 0.1 ppm O3, or 1.0 ppm O3 for 30-120 min. AA exposed to air was not degraded. All O3 exposures degraded > 98% of the AA to more polar products, which were predominantly aldehydic substances (as determined by reactivity with 2,4-dinitrophenylhydrazine and subsequent separation by HPLC) and hydrogen peroxide. The type and amount of aldehydic substances formed depended on the O3 concentration and exposure duration. A human bronchial epithelial cell line (BEAS-2B, S6 subclone) exposed in vitro to either 0.1 ppm or 1.0 ppm O3 for 1 hr produced AA-derived aldehydic substances, some of which eluted with similar retention times as the aldehydic substances derived from O3 degradation of AA in the cell-free system. In vitro, O3-degraded AA induced an increase in human peripheral blood polymorphonuclear leukocyte (PMN) polarization, decreased human peripheral blood T-lymphocyte proliferation in response to mitogens, and decreased human peripheral blood natural killer cell lysis of K562 target cells. The aldehydic substances, but not hydrogen peroxide, appeared to be the principal active agents responsible for the observed effects. O3-degraded AA may play a role in the PMN influx into lungs and in decreased T-lymphocyte mitogenesis and natural killer cell activity observed in humans and rodents exposed to O3.

Comparison of the Toxic Effects of Hydrogen Peroxide and Ozone on Cultured Human Bronchial Epithelial Cells

“…Measurement of DNA damage. To measure DNA single-strand breaks, we prelabeled cells with 3H-thymidine, 10 pCi/mM, for 24-48 hr before exposure to agents. At the termination of exposure, cells were rinsed, scraped off the dishes in chilled HBSS, and placed onto filters for the alkaline elution procedure of Kohn et al (5).…”

Disruption of tracheobronchial airway growth following postnatal exposure to ozone and ultrafine particles

“…As reviewed by Madden et al (2000), ozone has the potential to react with constituents on particles such as PAHs, resulting in additional adverse effects on the lung. Duration of contact between ozone and particles may be an important factor that determines synergistic toxicity, because chemical alterations in the particles will increase with reaction time and the more functionalized organic compounds that result may be more toxic (Madden et al, 1993(Madden et al, , 2000. In this study, simple co-exposure to ozone and particles with short interaction time prior to exposure may explain why synergies were minor.…”

Modulation of Bronchial Epithelial Cell Barrier Function by in vitro Ozone Exposure

“…Exposure of primary human bronchial cells and bronchial cell lines to ozone has been shown to result in the release of a wide range of mediators including interleukins, fibronectin, and platelet activating factor and to stimulate release of arachidonic acid with subsequent synthesis of prostaglandins, leukotrienes, and arachidonate-derived aldehydes (11)(12)(13). Furthermore, it has been reported that the increased tracheal permeability observed in vivo after ozone exposure may decrease or be lost after excision of the tissues (14), suggesting that chemical mediators may be important in the permeability response.…”

“…Ozone-induced injury is recognized to be associated with peroxidation of lipids within lung tissues, including those of the airway epithelial cell membranes (11,18,20). To determine if a similar mechanism mediated the increase in CBE permeability, cultures were grown for 2 days before exposure in the presence of lipid-soluble vitamins A and E. Vitamin E is well known as a biological free-radical scavenger capable of providing antioxidant protection against the effects of ozone (20,21).…”

“…Despite the observation that increased airway permeability is associated with the transit of inflammatory cells, principally neutrophils, into the airway lumen (4-6), a causal role for these cells is brought into question by the demonstration that ozone-induced permeability is not affected by neutrophil depletion (7,8) and that increased permeability and cellular influx can exhibit temporal separation (9). Alternatively, ozone may affect barrier integrity through direct action on epithelial cells by causing oxidation of membrane lipids or other cellular components (10,11), leading, in some cases, to the release of mediators (12,13). Some data suggest that perturbation of contractile cytoskeletal elements may also be involved in increasing paracellular movement through the cell layer (14).…”