Acrolein: a potent modulator of lung macrophage arachidonic acid metabolism

Effect of acrolein on human alveolar macrophage NF-kappaB activity

Acrolein is an environmental pollutant that is known to suppress respiratory host defense against infections; however, the mechanism of the decrease in host defense is not yet clear. We have previously reported that acrolein inhibited endotoxin-induced cytokine release and induced apoptosis in human alveolar macrophages, suggesting that the inhibition of cytokine release and/or cytotoxicity to alveolar macrophages may, in part, be responsible for acrolein-induced immunosuppression in the lung. Because nuclear factor-kappaB (NF-kappaB) is an important transcription factor for a number of cytokine genes and is also an important regulator of apoptosis, the effect of acrolein on NF-kappaB activity was examined by electrophoresis mobility shift assay. Acrolein caused a dose-dependent inhibition of endotoxin-induced NF-kappaB activation as well as an inhibition of basal level NF-kappaB activity. Because IkappaB is a principal regulator of NF-kappaB activity in the nucleus, changes in IkappaB were determined by Western blotting. Acrolein-inhibited IkappaB phosphorylation leads to an increase in cellular IkappaB levels preventing NF-kappaB nuclear translocation and is likely the mechanism of acrolein-induced inhibition of NF-kappaB activity. The role of basal level NF-kappaB in acrolein-induced apoptosis was also examined. An NF-kappaB inhibitor (MG-132) also induced apoptosis in human alveolar macrophages, suggesting that a certain basal level NF-kappaB activity may be required for macrophage cell survival. Taken together, our results suggest that the acrolein-inhibited endotoxin-induced NF-kappaB activation decreased the basal level NF-kappaB activity, which may be responsible for the inhibition of cytokine release and the induction of apoptosis in human alveolar macrophages.

Regulation of human airway mucins by acrolein and inflammatory mediators

Bronchitis, asthma, and cystic fibrosis, marked by inflammation and mucus hypersecretion, can be caused or exacerbated by airway pathogens or irritants including acrolein, an aldehyde present in tobacco smoke. To determine whether acrolein and inflammatory mediators alter mucin gene expression, steady-state mRNA levels of two airway mucins, MUC5AC and MUC5B, were measured (by RT-PCR) in human lung carcinoma cells (NCI-H292). MUC5AC mRNA levels increased after >/=0.01 nM acrolein, 10 microM prostaglandin E2 or 15-hydroxyeicosatetraenoic acid, 1.0 nM tumor necrosis factor-alpha (TNF-alpha), or 10 nM phorbol 12-myristate 13-acetate (a protein kinase C activator). In contrast, MUC5B mRNA levels, although easily detected, were unaffected by these agonists, suggesting that irritants and associated inflammatory mediators increase mucin biosynthesis by inducing MUC5AC message levels, whereas MUC5B is constitutively expressed. When transcription was inhibited, TNF-alpha exposure increased MUC5AC message half-life compared with control level, suggesting that transcript stabilization is a major mechanism controlling increased MUC5AC message levels. Together, these findings imply that irritants like acrolein can directly and indirectly (via inflammatory mediators) increase airway mucin transcripts in epithelial cells.

Acrolein-induced cell death in human alveolar macrophages

Acrolein is an environmental air pollutant that is known to suppress respiratory host defense against infections. The mechanism of the decrease in host defense is not yet clear. In this study, the effects of acrolein on human alveolar macrophages and their function were examined. Acrolein caused dose-dependent cytotoxicity to alveolar macrophages as demonstrated by the induction of apoptosis and necrosis. In addition, at lower doses, acrolein caused induction of heme oxygenase 1 protein; however, stress protein 72 (SP72) was not induced. These findings demonstrated that acrolein caused a dose-dependent selective induction of a stress response, apoptosis, and necrosis in human alveolar macrophages. Macrophage function was assessed by release of cytokines in response to endotoxin stimulation. Acrolein caused a dose-dependent inhibition of release of IL-1beta, TNF-alpha, and IL-12. The inhibition of cytokine release and cytotoxicity to alveolar macrophages may in part be responsible for acrolein-induced immunosuppression of the lung.

The effects of chronic sidestream cigarette smoke exposure on eicosanoid production by tracheal epithelium

Environmental exposure to sidestream cigarette smoke (SSCS) has been associated with an increased incidence of pulmonary infection and bronchospasm. Chronic exposure to SSCS could modify the release of bronchoreactive eicosanoids by tracheal epithelium, the site of initial contact by lung with inhaled toxins. To assess this possibility, New Zealand white rabbits were placed in an environmental chamber flushed with 3 L of SSCS, 15 min/day for 20 days. Eighteen hours after the last exposure the animals were sacrificed and the tracheas were explanted. At 7 days, the epithelial cell outgrowths were exposed to media containing endotoxin (10 micrograms/mL) or acrolein (50 microM), an aldehyde commonly found in smoke, or to control media. After a 2-h exposure, media were assayed for eicosanoids by radioimmunoassay. PGE2 was produced in epithelium from normal animals (5.7 +/- 1.3 ng/10(6) cells), and was not significantly different in SSCS-exposed epithelium. When incubated in medium containing acrolein, PGE2 production increased significantly in SSCS-exposed epithelium (14.9 +/- 2.5, p < .05) but not in control groups. Endotoxin also increased PGE2 production in SSCS-exposed cells (12.6 +/- 3.3 ng/10(6), p < .05). Baseline production of 6-keto PGF1 alpha was 10.8 +/- 3.2 ng/10(6) cells in non-SSCS controls and did not change significantly in these cells with the addition of endotoxin or acrolein. In acrolein plus SSCS-exposed cells, 6-keto PGF1 alpha increased, in a dose-dependent manner, to 88.1 +/- 26.1 ng/10(6) (p < .05 compared to all normals, SSCS-exposed controls, and SSCS plus LPS). TxB2 release in control, non-SSCS-exposed cells was 13.3 +/- 2.8 ng/10(6) cells and was significantly increased (P < .05) only in the SSCS plus acrolein group (60.7 +/- 16.2 ng/10(6) cells). The results indicate that even brief, recurrent exposure to SSCS can change the production of cyclooxygenase products, particularly PGE2, 6- keto PGF1 alpha, and TxB2. This may reflect an altered ability of SSCS-exposed tracheal epithelium to respond to environmental (e.g., acrolein) or bacterial (e.g., endotoxin) insults.

Release of arachidonic acid metabolites from isolated human alveolar type II cells

Human alveolar type II cells are thought to play a role in the pathogenesis of lung injury. Patterns of mediator release of arachidonic acid metabolism by type II cells were therefore studied after challenge with calcium ionophore A23187, opsonized zymosan and hydrogen peroxide. A time- and concentration dependent release of cyclooxygenase products was observed, with release of PGE2 greater than 6-keto-PGF1 alpha greater than TxB2. Addition of glutathione or bicarbonate further increased the production of PGE2. N-ethylmaleimide, a sulfhydryl (SH) reactant, induced a dose-dependent increase in the release of TxB2 and 6-keto-PGF1 alpha, but not of PGE2. This relates most likely to the SH-dependency and glutathione requirement of the PGE2 isomerase and SH-independence of thromboxane and prostacyclin isomerase.

Cysteine isopropylester protects against paracetamol-induced toxicity

Cysteine isopropylester (CIPE), a novel ester of cysteine, has been synthesized in order to evaluate its potential as a chemoprotectant. The increased lipophilicity of the ester relative to cysteine should facilitate its entry into cells where, following hydrolysis, it should act as an intracellular source of cysteine or be utilized for the synthesis of glutathione so protecting the cell against various types of chemical insult. In this study, we evaluate the ability of CIPE to protect against paracetamol-induced hepatotoxicity in mice. When administered to mice, CIPE produced a rapid but transient elevation of levels of non-protein sulphydryls (NPSH) in liver, lung, kidney and spleen. The greatest increase in NPSH was seen in the lung, but after 60 min all NPSH values had returned to control levels, demonstrating the capacity of the mouse to rapidly metabolize both CIPE and cysteine. In mice pretreated with benzo(a)pyrene, CIPE protected against paracetamol-induced toxicity as measured by the prevention of mortality, the fall in hepatic NPSH and the decreased elevation of serum transaminases. CIPE (1.5 mmol/kg) appeared as effective as N-acetylcysteine (1.5 mmol/kg). Higher doses of CIPE (3.0 mmol/kg) alone were toxic to mice induced with benzo(a)pyrene but not to control or phenobarbitone-induced mice. The mechanism of this increased toxicity is unclear. CIPE has a short in vivo half life but was capable of protecting against paracetamol-induced toxicity. The potential of CIPE and other related cysteine esters to act as chemoprotectants merits further investigation.

Effects of acrolein on human platelet aggregation

Acrolein, a component of tobacco smoke, potentiated platelet aggregation and increased thromboxane A2 (TXA2) formation caused by thrombin and arachidonic acid (AA). Acrolein produced these effects at concentrations in the range 50-5000 microM. Acrolein had no effect on platelet responses to ADP, epinephrine, collagen or the ionophore A23187. Acrolein increased the mobilization of [3H]arachidonic acid from prelabelled platelets in response to thrombin and arachidonic acid. The increased availability of substrate could partly explain the enhanced production of TXA2 and increased aggregation observed in the presence of acrolein. These findings could provide an explanation for the increased incidence of vascular disease in cigarette smokers.

Alterations of arachidonate metabolism in cardiovascular system by cigarette smoking

Male rats were exposed to freshly generated cigarette smoke once daily for various lengths of time. Inhalation of smoke was verified by elevated levels of carboxyhemoglobin. Metabolism of arachidonate in the cardiovascular system to thromboxane and prostacyclin through the cyclooxygenase pathway and their further metabolism to 15-keto-derivatives, and to 12-hydroxyeicosatetraenoic acid (12-HETE) through lipoxygenase pathway was investigated. Synthesis of thromboxane and prostacyclin in platelets and aortas respectively was not changed within 8 weeks of smoke exposure. However, formation of 12-HETE in platelets was significantly increased after 4 weeks of smoke exposure. Catabolism of thromboxane and prostacyclin as determined by NAD(+)-dependent 15-hydroxyprostaglandin dehydrogenase activity was greatly decreased in lung but not in kidney and stomach following 4 weeks of smoke exposure. Increased 12-lipoxygenase activity in platelets may lead to stimulation of migration and proliferation of smooth muscle cells and to increased synthesis of leukotrienes in neutrophils. Decreased pulmonary prostaglandin catabolic activity may result in increase in circulating thromboxane/prostacyclin ratio and subsequently alteration of vascular homeostasis. The consequence of these biochemical changes may contribute to the development of atherosclerosis, thromboembolism and emphysema commonly found in smokers.

Negative correlation of cigarette smoking and dysmenorrhea: reduced prostaglandin synthesis due to beta-endorphin, nicotine, or acrolein antagonism

It is suggested that the mechanism for decreased incidence of dysmenorrhea in female cigarette smokers may lie in the possible inhibition of algesic prostaglandins smoking induced stimulation of beta-endorphin, nicotine, or acrolein.

The oral gold compound auranofin triggers arachidonate release and cyclooxygenase metabolism in the alveolar macrophage

We examined the effect of in vitro incubation with the oral gold compound auranofin (AF) on arachidonic acid (AA) release and metabolism by rat alveolar macrophages (AMs). AF stimulated dose- and time-dependent release of 14C-AA from prelabeled AMs, which reached 4.7 +/- 0.3% (mean +/- SEM) of incorporated radioactivity at 10 micrograms/ml for 90 min, as compared to 0.5 +/- 0.1% release following control incubation for 90 min (p less than 0.001). Similar dose- and time-dependent synthesis of thromboxane (Tx) A2 (measured as TxB2) and prostaglandin (PG) E2 was demonstrated by radioimmunoassay of medium from unlabeled cultures, reaching 18-fold and 9-fold, respectively, of the control values at 10 micrograms/ml AF for 90 min (p less than 0.001 for both). AF-induced TxB2 and PGE2 synthesis was inhibited by indomethacin as well as by pretreatment with methylprednisolone. No increase in the synthesis of immunoreactive leukotrienes (LT) B4 or C4 was noted at any dose or time of AF. High performance liquid chromatographic separation of 14C-eicosanoids synthesized by prelabeled AMs confirmed that AF induced the release of free AA and its metabolism to cyclooxygenase, but not 5-lipoxygenase, metabolites. The ability of AF to trigger macrophage AA metabolism may be relevant to the exacerbation of certain inflammatory processes which sometimes accompany gold therapy.

Enhancement of eicosanoid synthesis in mouse peritoneal macrophages by the organic mercury compound thimerosal

Availability of the common precursor arachidonic acid represents the fundamental prerequisite of the cellular eicosanoid synthesis. The amount of free arachidonic acid is regulated not only by phospholipases, which liberate this polyunsaturated fatty acid from lipid pools, but also by the reacylating enzyme acylCoA:lysophosphatide acyltransferase. We have previously shown (Goppelt-Strübe, G., C.-F. Körner, G. Hausmann, D. Gemsa, and K. Resch. Control of Prostanoid Synthesis: Role of Reincorporation of Released Precursor Fatty Acids. Prostaglandins 32:373. 1986.) that the organic mercury compound thimerosal in murine peritoneal macrophages inhibits arachidonic acid reincorporation into cellular lipids, thereby leading to an enhanced prostanoid synthesis. In this report we show that the production of leukotriene C4 was also increased after the addition of thimerosal to mouse peritoneal macrophages in a time and dose dependent manner. Concomitantly, thimerosal led to a significant rise of the intracellular calcium concentration as measured by fura-2 fluorescence. Simultaneous addition of thimerosal and indomethacin or exogeneous arachidonic acid to the cells resulted in a synergistic enhancement of leukotriene C4 synthesis. On the other hand, another sulfhydryl group blocking agent, ethacrynic acid, was found to be ineffective in increasing leukotriene C4 levels even in combination with exogeneous arachidonic acid. Thimerosal therefore provides a helpful tool in studying the basic regulatory mechanisms of the cellular leukotriene synthesis.

The pathologic and immunologic effects of inhaled acrolein in rats

Four groups of 40 male Sprague-Dawley rats each were exposed by inhalation to target concentrations of 0, 0.1, 1.0, and 3.0 ppm of acrolein 6 h/day, 5 days/week for 3 weeks. Subsequent changes in local pulmonary immunity were determined by examining the number of antibody plaque-forming cells in the lung-associated lymph nodes following intratracheal immunization with sheep red blood cells. Separate groups of rats were evaluated for blastogenic responsiveness to phytohemagglutinin-P and Salmonella typhimurium antigen using spleen- and lung-associated lymph node cells. In vivo resistance was evaluated utilizing acrolein-exposed rats subsequently challenged with intravenous Listeria monocytogenes. Local pulmonary antibody responsiveness was not affected by acrolein exposure. Lymphocyte blastogenesis and resistance to Listeria challenge were not altered. Body weights and spleen weights were decreased in the 3 ppm-exposed group only. Microscopic examination of the nasal turbinates revealed acrolein-induced exfoliation, erosion, and necrosis of the respiratory epithelium as well as squamous metaplasia, however, lung histology was not affected. Thus at environmental concentrations, acrolein toxicity appeared to be confined to local nasal pathologic changes with no alterations in lung histology or immune function.

Influence of immune complexes on macrophage membrane fluidity: a nanosecond fluorescence anisotropy study

Time-resolved fluorescence anisotropy (TRFA) and steady-state anisotropy measurements and fluorescence intensification microscopic observations were made on RAW264 macrophages labeled with 1,6-diphenyl-1,3,5-hexatriene (DPH) or 1-[4-(trimethylammonio)phenyl]-6-phenyl-1,3,5-hexatriene (TMA-DPH). Microscopic analysis revealed that the fluorescent probe DPH was found in association with plasma membranes and small vesicles. Macrophages treated with immune complexes could not be distinguished from untreated cells, indicating that the same membrane compartments were labeled. The probe TMA-DPH was exclusively localized to the plasma membrane. Steady-state anisotropy measurements indicated that in vitro culture conditions did not significantly affect membrane fluidity. TRFA measurements were conducted to determine the physical properties of macrophage membranes during immune recognition and endocytosis. Data were analyzed by iterative deconvolution to yield phi, the rotational correlation time, and r infinity, the limiting anisotropy. These parameters may be interpreted as the "fluidity" and order parameter of the membrane environment, respectively. Typical values for untreated macrophages were phi = 7.8 ns and r infinity = 0.12. Binding and endocytosis of immune complexes prepared in 4-fold antigen excess increase these values to phi = 22.1 ns and r infinity = 0.15. However, receptor-independent phagocytosis of latex beads decreases these values to phi = 2.2 ns and r infinity = 0.10. Addition of catalase before, but not after, immune complex incubation with cells diminishes the effect upon membrane structure, suggesting that H2O2 participates in fluidity changes. Pretreatment of macrophages with the membrane-impermeable sulfhydryl blocker p-(chloromercuri)benzenesulfonic acid also diminished these effects.(ABSTRACT TRUNCATED AT 250 WORDS)

Increase in thromboxane B2 and decrease in prostaglandin E2 and 6-keto-prostaglandin F1 alpha release into rat bronchoalveolar fluid as a consequence of cigarette smoking

Rats were exposed to cigarette smoke once daily for 4 to 8 weeks. Bronchoalveolar lavage fluid was obtained from each animal and assayed for immunoreactive PGE2, TXB2 and 6-Keto-PGF1 alpha. Significant increase in TXB2 and decrease in PGE2 and 6-Keto-PGF1 a release into bronchoalveolar fluid as a consequence of cigarette smoking were observed. These changes of arachidonate metabolites in lung alveoli may account in part for bronchoconstriction induced by cigarette smoking.

Selective inhibition of 5-lipoxygenase pathway in rat pulmonary alveolar macrophages by cigarette smoking

Pulmonary alveolar macrophages from sham or cigarette-smoke-exposed rats were examined for their ability to transform exogenously added arachidonate to metabolites of lipoxygenase and cyclooxygenase pathways. Synthesis of 5-HETE and leukotriene B4 was selectively inhibited by cigarette smoke exposure, whereas the formation of prostaglandin E2 and thromboxane B2 remained unchanged. Selective inhibition of the lipoxygenase pathway was further reflected by the reduced content of leukotriene B4 in bronchoalveolar fluid of smoke-exposed rats. These results suggest that lipoxygenase-derived products may play a unique role in smoking-induced pulmonary diseases.

Effects of the lipid peroxidation product 4-hydroxynonenal on the aggregation of human platelets

The stimulation by ADP or arachidonic acid of the aggregation of human platelets in plasma was inhibited by 4-hydroxynonenal (HNE). This reduction of aggregation was time related, and was increased by prolonged preincubation of the platelets with the aldehyde. HNE was more potent than its homologue 4-hydroxypentenal (HPE). HNE was less active in decreasing the aggregation induced by calcium ionophore A23187 or collagen in comparison with ADP. HNE was inactive against aggregation of platelet-rich plasma (PRP) stimulated by thrombin whereas it potently inhibited the aggregation of washed platelets in response to both thrombin and collagen. Platelets were found to degrade HNE, and mechanisms additional to covalent binding to glutathione are indicated by the results obtained. The aldehydes, including HNE, generated by platelets originated principally from arachidonic acid metabolism.

Control of prostanoid synthesis: role of reincorporation of released precursor fatty acids

Prostanoid synthesis is limited by the availability of free arachidonic acid. This polyunsaturated fatty acid is liberated by phospholipases and usually is an intermediate of the deacylation-reacylation cycle of membrane phospholipids. In rat peritoneal macrophages, ethylmercurisalicylate (merthiolate) or N-ethylmaleimide (NEM) dose dependently inhibited the incorporation of arachidonic acid into cellular phospholipids, at lower concentrations specifically into phosphatidylcholine. Furthermore, merthiolate could be shown to be a rather selective inhibitor of lysophosphatidylcholine acyltransferase. In contrast, phospholipase A2 activity was not affected over a wide dose range. Consequently, macrophages showed a large increase in prostanoid synthesis (prostaglandin E, prostacyclin and thromboxane) in the presence of both lysophosphatide acyltransferase inhibiting agents. Similar results were obtained with human platelets, in which merthiolate increased the release of thromboxane. Addition of free arachidonic acid also enhanced prostanoid synthesis in macrophages. At optimal concentrations, merthiolate had no further augmenting effect. It is concluded that the rate of prostanoid synthesis is not only controlled by phospholipase A2 activity, but rather by the activity of the reacylating enzymes, mainly lysophosphatide acyltransferase.

Inactivation of pulmonary NAD+-dependent 15-hydroxyprostaglandin dehydrogenase by acrolein

Acrolein, a highly reactive aldehyde found in cigarette smoke, was shown to induce time-dependent inactivation of NAD+-linked 15-hydroxyprostaglandin dehydrogenase from porcine lung. The inactivation process followed pseudo-first-order kinetics and was irreversible. Inactivation by acrolein can be prevented by prior incubation of the enzyme with GSH but not by subsequent addition of GSH during assay. Inactivation can be also protected fully by prior incubation of the enzyme with NAD+, but only partially with prostaglandin E1. The results suggest that acrolein alkylates the enzyme at the coenzyme binding site and inactivates the enzyme. Inactivation of pulmonary NAD+-linked 15-hydroxyprostaglandin dehydrogenase by acrolein may alter cellular and circulating thromboxane/prostacyclin ratios and subsequently disturb vascular homeostasis and augment inflammatory and anaphylactic responses in smokers.