Enhancement of A23187-induced production of the slow-reacting substance on peripheral leukocytes from subjects with asthma

Effects of systemic glucocorticosteroids on peripheral neutrophil functions in asthmatic subjects: an ex vivo study

In 21 asthmatic subjects, several functions of isolated peripheral neutrophils (chemokinesis and chemotaxis toward 10% E. coli; superoxide anion generation after PMA; leukotriene B(4) (LTB(4)) release from whole blood and isolated neutrophtls, before and after different stimuli) were evaluated during an acute exacerbation of asthma, and after 14 - 54 days of treatment with systemic glucocorticosteroids (GCS). During acute exacerbation, superoxide anion generation was higher in asthmatics than in eleven normal subjects (39.2 +/- 14.1 vs. 25.2 +/- 7.3 nmol, p < 0.05); there was a significant correlation between FEV(1) (% of predicted) and neutrophil chemotaxis (r = -0.52, p = 0.04). After treatment, there was no significant change in all neutrophil functions, except for a decrease in neutrophil chemotaxis in subjects who showed an FEV(1) increase > 20% after GCS treatment (from 131 +/- 18 to 117 +/- 21 mum, p = 0.005). Chemokinesis sicantly decreased in all subjects, and the changes significantly correlated with an arbitrary score of the total administered dose of GCS (r = 0.57, p < 0.05). These data suggest that neutrophil activation plays a minor role in asthma, and that treatment with GCS is not able to modify most functions of peripheral neutrophils in asthmatic subjects; chemotaxis seems to be related only to the severity of the asthma and it could reflect the improvement of the disease.

A study of granulocyte respiratory burst in patients with allergic bronchial asthma

The respiratory burst of phagocytes plays an important role in the tissue damage that accompanies the inflammatory response. One of these conditions is allergic bronchial asthma, therefore, to evaluate the activation state of peripheral granulocytes the generation of reactive oxygen metabolites was evaluated using Luminol-enhanced chemiluminescence (LCL) and reduction of cytochrome C by superoxide. The resting granulocytes of the asthmatic patients under crisis showed a higher LCL compared to the noncrisis patients and control subjects. The granulocytes stimulated with PMA presented a significant increase in the respiratory burst in both groups of asthmatics. The granulocytes of noncrisis asthmatics challenged with Ops-Zym and with fMLP + Ops-Zym showed a higher metabolic activity, whereas the asthmatics under crisis presented no difference between reactive oxygen generation and that of the control group. The quantitative analysis of superoxide generation by granulocytes of the same patients did not show differences among the groups. Our findings suggest that the granulocytes of crisis and noncrisis asthmatics seem to be in a hyperreactive state and with a higher metabolic response when compared to the control group. However, the patients present a different behavior depending on stimulus used to activate cells. This could indicate that in peripheral blood exist different granulocyte populations depending on the inflammatory response taking place in the respiratory tract.

Neutrophils from asthmatics exhibit diminished responsiveness to 2-chloroadenosine which is reversed by theophylline. Evidence for a cyclic-AMP-independent pathway on human neutrophils

We have shown previously that neutrophils (PMNs) from patients with asthma have a more potent stimulated respiratory burst than normals and that their respiratory burst is significantly less suppressed with exposure to 2-chloroadenosine (2-CADO). The present studies investigated the basis of this defect in responsiveness to 2-CADO. PMNs obtained from asthmatics either not on theophylline (minus theophylline) or taking theophylline (plus theophylline) generated significantly more superoxide in response to 2 x 10(-8) M FMLP (2.08 +/- 0.36 nmol/5 x 10(5) PMNs (minus theophylline) (P less than 0.01 compared to controls) vs. 2.16 +/- 0.44 (plus theophylline) (P less than 0.01) as compared to controls (1.05 +/- 0.17 nmol). In the presence of FMLP (2 x 10(-8) M), PMNs from the minus theophylline cohort had less 2-CADO (10(-6) M)-mediated suppression of superoxide generation as compared to controls (38.3 +/- 3.8% vs. 67.1 +/- 3.8%; (P less than 0.001). The plus theophylline group exhibited suppression values similar to controls (64.5 +/- 7.2%). Theophylline, in the presence of a physiological concentration of 2-CADO (0.1 microM) accentuated the suppression of the respiratory burst in normals (74.1 +/- 5.9%, 80.1 +/- 4.9% (P less than 0.02) and 84.7 +/- 3.8% (P less than 0.02) at 0, 10, and 100 microM, respectively). PMNs from asthmatics not taking theophylline demonstrated suppression values of 46.2 +/- 6%, 53.8 +/- 6.6% (P = NS), and 63.2 +/- 7.1% (P less than 0.01), respectively. Resting PMNs from normal controls generated 0.97 +/- 0.20 pmol cAMP/10(7) cells compared to 2.83 +/- 0.75 pmol in the presence of 0.1 microM 2-CADO. The combination of 2-CADO and theophylline (10-100 microM) produced cAMP concentrations not significantly different from that observed with 2-CADO alone. These findings support the existence of a novel cAMP-independent adenosine receptor in PMNs. The specific binding of 10(-8)M 3H-labeled 2-CADO (in delta cpm) was 10,358 +/- 1502 (P less than 0.001 compared to controls), 5468 +/- 843 (NS compared to controls), and 3751 +/- 477 in the plus theophylline group, minus theophylline group, and controls, respectively. Such up-regulation of specific binding may represent the effects of theophylline as shown by the specific binding of [3H]2-CADO in PMNs from normal controls exposed to 10 microM theophylline for 30 min (6013 +/- 969) compared to unexposed PMNs (3768 +/- 656; P less than 0.05).(ABSTRACT TRUNCATED AT 400 WORDS)

Enhanced leukotriene synthesis in leukocytes of atopic and asthmatic subjects

1. We have investigated the capacities of peripheral leukocytes from atopic asthmatic (AA) (n = 7), atopic non-asthmatic (AN) (n = 7), and normal (N) (n = 7) subjects to generate the bronchoconstrictor and proinflammatory mediators leukotrienes (LTs) B4 and C4. 2. Mixed leukocyte preparations containing 61-84% neutrophils, 2.4-15% eosinophils, and 13-29% mononuclear cells were incubated in vitro at 37 degrees C in the presence of calcium ionophore A23187. Synthesis of LTB4 and LTC4 was quantitated by radioimmunoassay. 3. Both in dose-response experiments (0-10 microM A23187 for 5 min), and in time-course investigations (2 microM A23187 for 0-30 min), the mixed leukocytes of the AA and AN subjects generated on average 4- to 5-fold more LTB4 and 3- to 5-fold more LTC4 than the normal leukocytes (P less than 0.01 in all cases; ANOVA). 4. This enhanced LT synthesis by the AN and AA leukocytes was not due to differences in the counts of leukocyte sub-types, or to altered rates of LT catabolism between the subject groups. 5. LTB4 synthesis correlated significantly with LTC4 synthesis in the leukocytes of the AN and AA subjects (r = 0.81, n = 14, P less than 0.01), but not in those of the normal subjects (r = 0.19, n = 7, P greater than 0.05). 6. Our results demonstrate an up-regulation of the leukotriene synthetic pathway in the circulating leukocytes of atopic non-asthmatic and atopic asthmatic subjects, which may have important implications in the pathophysiology of asthma and allergy.

The role of free radicals in airway obstruction in asthmatic patients

Neutrophils from asthmatic patients seem to be in an activated state. This study demonstrated that superoxide radical (O2-) production was enhanced in asthmatic patients compared with healthy control subjects. Production of (O2-) also increased with progression of disease and with disease duration. In addition, (O2-) release was inversely correlated with FEV1 and midflows and was greater in neutrophils from patients with exacerbated disease than in those from patients with stable disease. These findings suggest that oxygen metabolites may play a direct or indirect role in the modulation of airway inflammation.

The metabolism of leukotrienes, detoxification of reactive oxygen species and the activity of the cytochrome P450 mixed function oxidase system in sensitised guinea-pig lungs

In sensitised guinea-pig lungs alterations in leukotriene (LT) metabolism occurred which resulted in an increase in LTD4 synthesis and a reduction in its catabolism. This may lead to an increase in the concentration of this potent spasmogen in the sensitised lungs. The LTs may cause hyperreactivity of bronchial smooth muscle by stimulating formation of toxic oxygen species. Thus, the activities of the enzymes responsible for detoxifying reactive oxygen metabolites were measured in the sensitised lung tissue. Superoxide dismutase activity was decreased in sensitised lungs. The activity of the selenium-independent glutathione peroxidase was increased, whereas those of catalase, glutathione reductase and the selenium-dependent glutathione peroxidase were unaffected. As a result of these alterations, sensitised guinea pig lungs may be more sensitive to the effects of superoxide, but are able to detoxify the products of any resulting lipid peroxidation more efficiently. The cytochrome P450 content of the lung and the activity of the associated mixed function oxidase (MFO) system was significantly decreased in sensitised guinea-pigs. This will lead to altered arachidonate metabolism, particularly generation of epoxyeicosatrienoic acids, decreased capacity to terminate the action of cysteinyl LTs and also compromised xenobiotic metabolising ability.

The generation and metabolism of leukotrienes in the ionophore-stimulated blood of normal and asthmatic subjects

The generation and metabolism of leukotrienes (LTs) B4, C4, D4, and E4 were studied in vitro in the A23187-stimulated whole blood of normal (N) and atopic asthmatic (AA) human subjects. Using a combination of reversed-phase high performance liquid chromatography and radioimmunoassay, we have demonstrated that the blood cells of atopic asthmatic patients have an enhanced ability to release LTB4 and LTC4 when compared to those of normal subjects. The release of LTB4 and LTC4 in response to ionophore is dose- and time-dependent. Half-maximal doses of ionophore caused the generation of high, sustained levels of LTB4, which are significantly higher in the AA blood than in N blood. Incubations of 3H-LTB4 in ionophore-stimulated N and AA blood revealed a slow metabolism to 20-OH-LTB4 and 20-COOH-LTB4. LTC4 is generated in smaller amounts than LTB4, with an early peak after 10 min which is significantly higher (p less than 0.01) in the AA blood compared to the N blood. Subsequent metabolism of LTC4 elicits significantly greater amounts of LTD4, and consistently higher levels of LTE4, in the AA blood. Parallel incubations of 3H-LTC4 in ionophore-stimulated N and AA blood demonstrated rapid metabolism of LTC4 by the glutathione detoxification pathway. The elevated production of LTB4 and LTC4 in AA blood was not accounted for by differences in leukocyte sub-type counts in the two groups, nor by differences in their rates of catabolism. The novel, selective 5-lipoxygenase inhibitor BW A4C [N-(3-phenoxycinnamyl) acetohydroxamic acid] caused dose-dependent inhibition of LTB4 and LTC4 generation and was equipotent in N and AA blood.

Asthmatic patients have neutrophils that exhibit diminished responsiveness to adenosine

Activation of neutrophils (PMN) within the airways results in the secretion of a number of products such as reduced oxygen metabolites that could contribute to the inflammatory response associated with asthma. However, mediators of allergy, such as histamine, prostaglandin E2 (PGE2), isoproterenol, and adenosine, may serve to mitigate this inflammation through feedback inhibition of neutrophil function. To test the hypothesis that PMN activation and feedback inhibition mechanisms may be abnormal in asthmatics, we compared both superoxide production and adenosine-induced suppression of superoxide production in 12 matched pairs of asthmatics and control subjects. PMN obtained from asthmatic patients generated significantly more superoxide in response to f-met-leu-phe (fMLP) than controls (2.94 +/- 55 nmol/5 x 10(5) PMN/5 min versus 1.38 +/- 0.35 at 2 x 10(-8) M fMLP and 3.81 +/- 0.68 nmol versus 2.04 +/- 0.45 nmol at 10(-7) M; p less than 0.01 for both). In contrast, the respiratory burst generated by two receptor-independent stimuli, the calcium ionophore A23187 and phorbol myristate acetate, was equivalent between control and asthmatic subjects. At 10(-6) M, 2-chloroadenosine induced a 19.5 +/- 5.1% inhibition of fMLP-stimulated superoxide production in PMN from patients with asthma as compared to 55.6 +/- 24.6% inhibition in PMN from control subjects (p less than 0.01).(ABSTRACT TRUNCATED AT 250 WORDS)

The biotransformation in vitro of cysteinyl leukotrienes in blood of normal and asthmatic subjects

The metabolism of exogenous leukotriene C4 (LTC4), LTD4 and LTE4 (10(-8) M) was studied in vitro in blood of normal and asthmatic subjects for up to 2 hr by reverse-phase high performance liquid chromatography. In whole blood, incubation of LTC4 (T1/2 = 11.5 min) resulted in the formation of LTD4 and LTE4 whose biosynthesis was inhibited by serine borate (30 mM). Similar experiments performed with LTD4 (T1/2 = 5 min) produced a single metabolite (LTE4) which was inhibited by L-cysteine (10 mM). On the other hand, LTE4 represented a highly stable product in our in vitro system. The bioconversion of LTC4 or LTD4 was slower in plasma but this effect appeared more pronounced for the cysteinylglycinyl derivative. The bioconversion of LTD4 in whole blood or plasma was almost twice as rapid as LTC4. Experiments performed with asthmatic blood showed no significant difference in the survival of LTC4. These results suggest that blood may play a role in regulating the bioavailability of cysteinyl-containing LTs which could be of relevance to their excretion in man.

Dysregulation of arachidonic acid release and metabolism by atopic mononuclear cells

We studied the ability of monocytes to metabolize [3H]arachidonic acid (AA) provided exogenously by activated T cells, and the extent to which dexamethasone suppressed eicosanoid production by normal and atopic cells. [3H]AA metabolites were identified using a reverse-phase high pressure liquid chromatography system (HPLC). Unstimulated and PHA-stimulated T cells from normal and atopic subjects exhibited a similar uptake and time-dependent release of radiolabel, 90% of which was identified as free AA. The addition of autologous normal and atopic monocytes to these cultures enhanced the release of radiolabel, even in the absence of stimulation with mitogen. Atopic T cell/monocyte cultures released significantly (P = 0.046) more radiolabel than normal cells when stimulated with PHA. Furthermore, the monocytes from both normal and atopic subjects metabolized T cell derived [3H]AA into cyclo-oxygenase (CO) and lipoxygenase (LO) products. Under unstimulated conditions, atopic cells produced significantly (P = 0.04) less CO products than normal cells. In contrast, under PHA and calcium ionophore-stimulated conditions, the atopic cells produced significantly (P = 0.048) more prostaglandins than normal donor cells. Furthermore, although the total release of radioactivity was comparable in both groups, significantly less (P = 0.02) free AA remained in ionophore-stimulated culture supernatants from atopic cells. In order to study the regulation of AA release by normal and atopic T cells, dexamethasone (1 microM) was added to T cell cultures. Dexamethasone inhibited the release of [3H]AA from normal T cells to a significantly (P = 0.003) greater extent than it did to atopic cells.(ABSTRACT TRUNCATED AT 250 WORDS)

Enhanced generation of leukotriene B4 by neutrophils stimulated by unopsonized zymosan and by calcium ionophore after exercise-induced asthma

The generation of LTB4 by peripheral blood neutrophils (PMN) isolated before and for as long as 6 h after exercise-induced asthma (EIA) has been analyzed. Three and 6 h after the development of EIA, PMN isolated from 10 asthmatic subjects and stimulated in vitro by 2 x 10(8) and 4 x 10(8) zymosan particles per 2 x 10(6) PMN demonstrated a 12- and 4-fold enhancement, respectively, in the production of immunoreactive LTB4 as compared with PMN isolated before exercise. At 6 h after EIA, there was a redistribution of generated LTB4 such that 30 to 40% of LTB4 produced by zymosan-activated PMN was released extracellularly as compared with 10% before exercise. There was no significant enhancement in the generation of LTB4 by unstimulated PMN at any time point after exercise. Resolution by reverse-phase high performance liquid chromatography (HPLC) of products from [3H]arachidonic-acid-labeled and zymosan-activated PMN demonstrated that, in addition to LTB4, there was enhanced metabolism to 6-trans-LTB4, omega-oxidation metabolites of LTB4 and 5-HETE. Stimulation of PMN with 10 microM A23187 revealed a 2-, 6-, and 5-fold enhancement in the production of LTB4, 6-trans-LTB4, and 5-HETE, respectively, at 6 h after EIA, as measured by integrated ultraviolet absorbance after HPLC. There was no significant enhancement in LTB4 generation by PMN in 6 asthmatic subjects after methacholine-induced bronchospasm, and after exercise in 6 subjects who did not develop asthma. The augmentation of PMN LTB4 generation in EIA correlated with the extent of the early decrease in SGaw.(ABSTRACT TRUNCATED AT 250 WORDS)

The inflammatory theory of asthma

In summary, these observations suggest a model for asthma which is summarized in Table III. Initially, mast cells and possibly other bronchial cells, e.g., alveolar macrophages, are activated either in an IgE-dependent or, in intrinsic asthma, in an IgE-independent fashion. These cells release two sets of mediators which may be either preformed or newly synthesized. One set of mediators is responsible for the immediate bronchospastic response. This bronchospasm is transient, readily reversible, and not associated with either airway inflammation or bronchial hyperreactivity. The second set of mediators, however, promote chemotaxis and activation of neutrophils and eosinophils. The subsequent bronchial inflammation causes damage and desquamation of the respiratory epithelium. The increased exposure of irritant receptors results in hyperreactive airways. In addition, these inflammatory cells induce mast cell degranulation and recurrent bronchospasm. Thus, after the initial exposure to allergen, a vicious cycle of inflammation, hyperreactivity and recurrent mast cell degranulation develops, ultimately leading to the pathological picture of chronic asthma.