Effects of cyclo-oxygenase inhibition on ozone-induced respiratory inflammation and lung function changes

Abstract

Inhalation of O3 causes airways neutrophilic inflammation accompanied by other changes including increased levels of cyclo-oxygenase products of arachidonic acid in bronchoalveolar lavage fluid (BALF). Ozone O3 exposure also causes decreased forced vital capacity (FVC) and forced expiratory volume after 1 s (FEV(1)), associated with cough and substernal pain on inspiration, and small increases in specific airway resistance (SRAW). The spirometric decrements are substantially blunted by pretreatment with indomethacin. Since the O3-induced decrement in FVC is due to involuntary inhibition of inspiration, a role for stimulation of nociceptive respiratory tract afferents has been suggested and cyclo-oxygenase products have been hypothesized to mediate this stimulation. However, the relation (if any) between the O3-induced neutrophilic airways inflammation and decreased inspiratory capacity remains unclear. We studied the effects of pharmacologic inhibition of O3-induced spirometric changes on the inflammatory changes. Each of ten healthy men was exposed twice (5-week interval) to 0.4 ppm O3 for 2 h, including 1 h of intermittent exercise (ventilation 601*min(-1)). One-and-a-half hours prior to and midway during each exposure the subject ingested 800 mg and 200 mg, respectively, of the non-steroidal anti-inflammatory drug ibuprofen (IBU), or placebo [PLA (sucrose)], in randomized, double-blind fashion. Spirometry and body plethysmography were performed prior to drug administration, and before and after O3 exposure. Immediately following postexposure testing, fiberoptic bronchoscopy with bronchoalveolar lavage (BAL) was performed. Neither IBU nor PLA administration changed pre-exposure lung function. O3 exposure (with PLA) caused a significant 17 percent mean decrement in FEV(1) (P <0.01) and a 56 percent increase in mean SRAW. Following IBU pretreatment, O3 exposure induced a significantly lesser mean decrement in FEV(1) (7 percent) but still a 50 percent increase in mean SRAW. IBU pretreatment significantly decreased post-O3 BAL levels of prostaglandin E2 (PGE2) by 60.4 percent (P <0.05) and thromboxane B(2) (TxB(2)) by 25.5 percent (P <0.05). Of the proteins, only interleukin-6 was significantly reduced (45 percent, P <0.05) by IBU as compared to PLA pretreatment. As expected, O3 exposure produced neutrophilia in BALF. There was, however, no effect of IBU on this finding. None of the major cell types in the BALF differed significantly between pretreatments. We found no association between post-exposure changes of BALF components and pulmonary function decrements. We conclude that IBU causes significant inhibition of O3-induced increases in respiratory tract PGE(2) and TxB(2) levels concomitant with a blunting of the spirometric response. This is consistent with the hypothesis that the products of AA metabolism mediate inhibition of inspiration. However, IBU did not alter the modest SRAW response to O3.

Regulation of caveolin-1 expression, nitric oxide production and tissue injury by tumor necrosis factor-α following ozone inhalation

“…TNFα receptor binding activates several downstream signaling molecules including the transcription factor NF-κB, which regulates the activity of inflammatory genes implicated in ozone toxicity including nitric oxide synthase-2 and cyclooxygenase-2 (Hazucha et al, 1996;Fakhrzadeh et al, 2002). We have previously shown that alveolar macrophages from mice with a targeted disruption of NF-κB p50 do not generate reactive nitrogen intermediates and that these mice are protected from ozone toxicity (Fakhrzadeh et al, 2004b).…”

“…A number of biochemical signaling molecules have been implicated in TNFα-induced activation of NF-κB including PI3K and its downstream target, PKB (Hazucha et al, 1996;Wallach et al, 1999;Grivennikov et al, 2006), and expression of these proteins was analyzed next. Alveolar macrophages from air-exposed wild type mice were found to express low levels of PI3K and PKB as determined by western blotting and immunocytochemistry (Fig.…”

Antioxidant consumption and repletion kinetics in nasal lavage fluid following exposure of healthy human volunteers to ozone

“…Cyclo-oxygenase products of arachidonic acid stimulate these receptors which are released on exposure to ozone [30,31]. Vitamins C and E have been shown to affect this arachidonic acid metabolism, but the role of antioxidants in this mechanism is not fully understood [32,33].…”

CXCR2 is essential for maximal neutrophil recruitment and methacholine responsiveness after ozone exposure

“…IN HUMANS, EXPOSURE TO OZONE (O 3 ), a common air pollutant and powerful oxidant, causes substernal irritation, cough, decrements in pulmonary function, and airway hyperresponsiveness (AHR) to nonspecific bronchoconstricting agonists such as methacholine (MCh) (6,10,25,33). Even O 3 concentrations below the current U.S. Environmental Protection Agency standard are sufficient to initiate symptoms in children with asthma (30).…”

“…Molecular changes include an increase in the production and/or expression of prostaglandins (PGE 2 , PGF 2␣ , 6-keto-PGF 1␣ , and 8-epi-PGF 2␣ ) (3,32,33,36), cytokines (IL-1␤, IL-6, and TNF-␣) (4,39,54,55,59,60), and chemokines [eotaxin, interferon-␥-inducible protein (IP-10), monocyte chemoattractant protein (MCP)-1, MCP-3, macrophage inflammatory protein (MIP)-1␣, KC, and MIP-2] (20,38,39,49,59,60,69). Cellular changes include sloughing of epithelial cells and neutrophil emigration into the air spaces (5, 12, 16, 20, 22, 49, 59 -61, 69).…”