Human peritoneal macrophages synthesize leukotrienes B4 and C4

Uncoupled regulation of leukotriene C4 synthase in platelets from aspirin-intolerant asthmatics and healthy volunteers after aspirin treatment

BACKGROUND

We have reported that thromboxane A2 induces suppression of leukotriene (LT) C4 synthase activity in human platelets.

AIM

In the present study, we describe a mechanism whereby aspirin treatment can lead to increased formation of LTC4, which is a potent bronchoconstrictor and inflammatory mediator. This mechanism is also demonstrated to be present in platelets from aspirin-intolerant asthmatics (AIA).

METHODS

The effect of arachidonic acid or platelet agonists on LTC4 synthase activity was investigated in platelets obtained from healthy volunteers, aspirin-intolerant asthmatics or aspirin-tolerant asthmatics after in vivo treatment or in vitro pre-incubation with aspirin.

RESULTS

Incubation of normal platelets with arachidonic acid or collagen provoked approximately 50% reduction of platelet LTC4 synthase activity, as determined by the conversion of LTA4 to LTC4. However, the inhibitory effect of arachidonic acid or collagen was not observed after oral administration of aspirin prior to collection of the platelets. Arachidonic acid-induced inhibition of LTC4 synthase activity was totally abolished in platelets collected from peripheral blood already 30 min after aspirin ingestion but was fully restored in platelets collected 3 to 7 days after the administration of aspirin. Treatment of platelet suspensions with aspirin in vitro dose-dependently counteracted the suppressive effect of arachidonic acid on LTC4 formation, with total reversal at approximately 40 microm. In contrast, the major aspirin metabolite, salicylic acid did not alter arachidonic acid-induced reduction of LTC4 synthase activity. Similarly, LTC4 synthase activity in platelets from AIA and aspirin-tolerant asthmatics (ATA) was reduced by approximately 50% after pre-treatment with arachidonic acid in vitro. Again the inhibitory effect was abolished when platelets were pre-incubated in the presence of aspirin.

CONCLUSION

The results indicate that oral aspirin administration can lead to uncoupling of thromboxane A2-dependent negative feedback mechanisms, which may normally restrict the production of cysteinyl leukotrienes. This mechanism can be of potential interest in aspirin-induced asthma.

Pathophysiological role of leukotrienes in dermatological diseases: potential therapeutic implications

In vitro and in vivo data have demonstrated that leukotrienes play a key role not only in allergic airway diseases but also in inflammatory reactions of the skin. Antileukotriene drugs, i.e. leukotriene receptor antagonists and synthesis inhibitors, are a new class of anti-inflammatory drugs that have shown clinical efficacy in the management of asthma, allergic rhinitis and inflammatory bowel disease. To address the question of the validity and applicability of published evidence of the use of antileukotriene drugs in dermatological diseases, we reviewed data concerning the pathophysiological effect of leukotrienes in the skin and in skin diseases, and the experience with antileukotriene treatment that has been published. In vivo and in vitro data suggest that antileukotriene treatment may have efficacy in atopic dermatitis, different types of urticaria or psoriasis and other skin diseases such as bullous skin diseases, collagenoses, Sjogren-Larsson syndrome or Kawasaki disease. Nevertheless, published evidence is very limited and before any conclusions can be drawn, additional basic research needs to be performed with regard to the role of different leukotrienes and leukotriene receptors in skin diseases. On the basis of these data, randomised and placebo-controlled clinical trials with leukotriene antagonists and synthesis inhibitors should be performed. Moreover, future studies investigating the additive benefit of antileukotriene drugs are warranted, e.g. in combination with antihistamines, corticosteroids or other anti-inflammatory drugs.

Identification and characterization of a novel human microsomal glutathione S-transferase with leukotriene C4 synthase activity and significant sequence identity to 5-lipoxygenase-activating protein and leukotriene C4 synthase

5-Lipoxygenase-activating protein (FLAP) and leukotriene C4 (LTC4) synthase, two proteins involved in leukotriene biosynthesis, have been demonstrated to be 31% identical at the amino acid level. We have recently identified and characterized a novel member of the FLAP/LTC4 synthase gene family termed microsomal glutathione S-transferase II (microsomal GST-II). The open reading frame encodes a 16.6-kDa protein with a calculated pI of 10.4. Microsomal GST-II has 33% amino acid identity to FLAP, 44% amino acid identity to LTC4 synthase, and 11% amino acid identity to the previously characterized human microsomal GST (microsomal GST-I). Microsomal GST-II also has a similar hydrophobicity pattern to FLAP, LTC4 synthase, and microsomal GST-I. Fluorescent in situ hybridization mapped microsomal GST-II to chromosomal localization 4q28-31. Microsomal GST-II has a wide tissue distribution (at the mRNA level) and was specifically expressed in human liver, spleen, skeletal muscle, heart, adrenals, pancreas, prostate, testis, fetal liver, and fetal spleen. In contrast, microsomal GST-II mRNA expression was very low (when present) in lung, brain, placenta, and bone marrow. This differs from FLAP mRNA, which was detected in lung, various organs of the immune system, and peripheral blood leukocytes, and LTC4 synthase mRNA, which could not be detected in any tissues by Northern blot analysis. Microsomal GST-II and LTC4 synthase were expressed in a baculovirus insect cell system, and microsomes from Sf9 cells containing microsomal GST-II or LTC4 synthase were both found to catalyze the production of LTC4 from LTA4 and reduced glutathione. Microsomal GST-II also catalyzed the formation of another product, displaying a conjugated triene UV absorption spectra with a maximum at 283 nm, suggesting less catalytic stereospecificity compared with LTC4 synthase. Also, the apparent Km for LTA4 was higher for microsomal GST-II (41 microM) than LTC4 synthase (7 microM). In addition, unlike LTC4 synthase, microsomal GST-II was able to catalyze the conjugation of 1-chloro-2, 4-dinitrobenzene with reduced glutathione. Therefore, it is proposed that this novel membrane protein is a member of the microsomal glutathione S-transferase family, also including LTC4 synthase, with significant sequence identities to both LTC4 synthase and FLAP.

Receptor-mediated regulation of leukotriene C4 synthase activity in human platelets

Human platelets possess a specific membrane-bound leukotriene (LT) C4 synthase, which catalyzes the conversion of LTA4 to LTC4. Stimulation of the receptors for thrombin, collagen or thromboxane A2 provoked inhibition of this enzyme, as judged by suppressed transformation of exogenous LTA4 to LTC4. Similarly, direct activation of protein kinase (PK) C with nanomolar concentrations of 4 beta-phorbol 12-myristate 13-acetate (PMA) inhibited the production of LTC4. Kinetic studies demonstrated that the inhibition induced by thrombin and PMA was non-competitive. Elevation of intracellular cAMP levels with carbacyclin did not affect basal LTC4 formation, but abolished the attenuation of platelet LTC4 synthase activity induced by the thromboxane receptor agonist U-46619. The unselective protein kinase inhibitor staurosporine prevented both receptor-mediated and PMA-induced suppression of LTC4 formation. In contrast, two selective PKC inhibitors, Ro 31-8220 and GF 109203X, reversed the inhibitory effect provoked by PMA, but failed to prevent thrombin-induced inhibition. Furthermore, the protein tyrosine phosphatase inhibitor, sodium orthovanadate, induced dose-dependent inhibition of LTC4 production in platelet sonicates. In conclusion, receptor-mediated activation of human platelets leads to decreased LTC4 synthase activity via phosphoregulation. Although the present results demonstrate that platelet LTC4 synthase can be regulated via PKC-dependent events, alternative mechanisms appears to be involved in the physiological regulation of this enzyme. The findings suggest the possible importance of protein tyrosine phosphorylations in this process.

In human monocytes interleukin-1 stimulates a phospholipase C active on phosphatidylcholine and inactive on phosphatidylinositol

Interleukin-1 (IL-1) can initiate the synthesis of prostaglandins which in turn act as endogenous modulators of IL-1 production. The human monocyte/macrophage synthesizes various eicosanoids through the activation of the cellular phospholipase system. Cell stimulation results in the activation of phospholipase A2 (PLA2) whose major substrate is phosphatidylcholine (PC) and the release of the eicosanoid precursor arachidonic acid (AA) from PC. Another pathway is the stimulation of a phospholipase C (PLC) mainly active on phosphoinositides and the resulting formation of inositol phosphates (IPs) and diacylglycerol (DAG). Phospholipids other than phosphoinositides can also be hydrolysed by PLC to give rise to DAG. Studies have shown that IL-1 does not activate the IP pathway, but it primarily stimulates a PLC linked to phosphatidylethanolamine in cultured rat mesangial cells, and a PLC linked to PC in Jurkart cells. We have stimulated human monocytes with IL-1 and calcium ionophore A23187 and we have observed their effect on the phospholipase system. The results indicate that IL-1 does not activate the formation of IPs in cells labeled with [3H]myo-inositol. In contrast, in cells labeled with [3H]AA, IL-1 causes the formation of DAG associated with the hydrolysis of PC. Moreover, after stimulation with IL-1 there is no accumulation of free AA which would indicate that there has been no activation of PLA2, which occurs instead with A23187 stimulation. These data suggest that, in monocytes, IL-1 does not directly stimulate a PLA2 or a PLC active on phosphatidylinositol; instead it primarily stimulates a PLC active on PC.

Time-dependent alterations of leukotriene production and catabolism in rat peritoneal macrophages following intraperitoneal injection of thioglycollate broth

Alterations of leukotriene (LT) productivity in peritoneal macrophages (PM) from untreated rats (control) as well as from rats treated i.p. with thioglycollate broth (TG) were investigated on days 3, 7 and 14 after TG administration. The resident PM from the untreated rats produced mainly LTB4 and 5-HETE with small amounts of 12-HETE and LTD4 with only a trace of LTC4 when stimulated with the calcium ionophore A23187. The PM elicited from rats on days 3 and 7 produced more LTC4 than did the resident PM but fewer other lipoxygenase metabolites. On day 14, however, the elicited PM resembled the resident PM in terms of lipoxygenase metabolite production. Similar results were achieved in the presence of arachidonic acid and A23187. A decrease in lipoxygenase metabolism in the elicited PM was also suggested by using opsonized zymosan. Catabolism studies indicated a reduction in r-glutamyl transpeptidase activity in the elicited PM and suggested a reduction in catabolism for LTB4 in the former cells. The authors conclude that the TG-elicited PM generate fewer lipoxygenase metabolites than the resident PM following stimulation, but show a preferential conversion of LTA4 to sulfidopeptide LTs rather than to LTB4. The elicited PM also show a reduced catabolism for LTC4 and LTB4.

Enhanced leukotriene C4 synthase activity in thioglycollate-elicited peritoneal macrophages

The utilization of LTA4 by peritoneal macrophages (MO) obtained from untreated rats (control) as well as by those elicited from rats was investigated at designated intervals (on days 3, 7, and 14) following the intraperitoneal injection of thioglycollate (TG). On day 7 following the injection the elicited MO converted LTA4 to LTC4 at the highest rate while the resident MO showed the lowest rate. The conversion of LTA4 to LTC4 and LTB4 was next examined by using each MO lysate. The apparent LTC4 synthase activity was significantly higher in the MO lysate both on day 3 and day 7, with the latter being the highest value obtained. The GSH S-transferase activity in each lysate using as the substrate, DNCB was significantly lower on day 3 but significantly higher on day 7 as compared to control values. However, this elevated activity was less variable than that observed with LTC4 synthase. The possible implication for these observations is discussed.

Eicosanoid synthesis in human peritoneal macrophages stimulated with S. epidermidis

Peritoneal macrophages isolated from CAPD patients phagocytosed S. epidermidis in a time dependent manner. Coincident with a maximum phagocytic uptake of 56% by 12 hours, there was secretion of a significant amount of neutral protease (1.37 +/- 0.2 mg [3H]-casein degraded/10(6) cells, P = 0.05). In contrast to these delayed effects, coincubation of PMO with S. epidermidis resulted in a significant increase in both LTB4 and LTC4 synthesis above that of controls, with 6.33 +/- 1.20 ng LTB4/10(6) cells (P less than 0.01) and 2.06 +/- 0.68 ng LTC4/10(6) cells (P = 0.014) being generated by three hours. The generation of these lipoxygenase products was both time and dose dependent, and the rapid production and release of the potently chemotactic LTB4 is consistent with the observed clinical response, where a rapid influx of PMN into the peritoneal cavity occurs during episodes of peritonitis, while the generation of LTC4 may contribute to the hyperemia and interstitial edema. In contrast, although there was a time dependent rise in cyclooxygenase product generation by unstimulated cells, a dose dependent inhibition of synthesis was clearly demonstrated when cells were incubated with bacteria, with a mean 40% reduction in generation of PGE2 and a mean 34% reduction in TXB2 generation (P = 0.01 and P less than 0.025, respectively). It was demonstrated that the inhibition was not due to lack of available substrate and that the generation of eicosanoids was unrelated to phagocytosis, bacterial/PMO contact or bacterial surface characteristics. Instead, the observed effect of S. epidermidis on the PMO was attributable to a secreted bacterial product.

Leukotriene C4 is an essential 5-lipoxygenase intermediate in A23187-induced macrophage cytostatic activity against P815 tumor cells

Resident peritoneal macrophages incubated with 3.5 x 10(-7) M Calcium ionophore A23187 in tumor cell growth medium (TGM) release large amounts of leukotriene (LT)E4 and an unidentified 5-lipoxygenase product, whereas A23187-stimulated macrophages produce in serum free medium LTD4, predominately. LTC4 and 3H-LTC4 incubated for 20 min at 37 degree C in serum containing TGM, convert into LTE4 and 3H-LTE4, respectively. Thus, LTC4 released from A23187-stimulated macrophages is an intermediate in TGM which rapidly converts into LTE4, probably because of the presence of gamma-glutamyl transpeptidase and cystenylglycinase in TGM. Macrophages express antitumor cytostatic activity towards P815 cells (49-53%) in a cocultured ratio (macrophage: tumor cell) 2:1 when stimulated with 3.5 x 10(-7) M A23187 in TGM. The 5-lipoxygenase inhibitor AA861 reverses the cytostatic activity by 42-58% and it inhibits also the formation of A23187-induced 5-lipoxygenase products from macrophages. Restoration of 38% macrophage- antitumor cytostatic activity by exogenous LTC4 (10(-8) M) indicates that LTC4 is an essential 5-lipoxygenase intermediate in the pathway of required signals underlying A23187-induced macrophage antitumor cytostatic activity. Macrophages not stimulated by A23187 do not express cytostatic activity in the presence of LTC4. This implies that besides LTC4, increased cytosolic [Ca2+] is required for A23187 induction of macrophage cytostatic activity.

Mononuclear phagocytes and eicosanoids: aspects of their synthesis and biological activities

Mononuclear phagocytes convert arachidonic acid and other unsaturated fatty acids from intracellular sources to a variety of oxygenated metabolites such as prostaglandins and leukotrienes which are secreted into the surrounding medium. Other oxidative products such as hydroxylinoleic acids are reacylated into cellular constituents. The underlying metabolic pathways are activated by numerous stimuli of exogenous or endogenous origin. Depending on the state of activation and cell differentiation, the organ of origin and the nature of the stimulus used, macrophages elaborate a distinct spectrum of oxidative arachidonic acid metabolites. The contribution of these metabolites to the proinflammatory properties of macrophages is twofold: As autocrine signals they modulate the synthesis of diverse macrophage products and they influence cellular functions of other cells such as T-lymphocytes.

Eicosanoid production in rheumatoid synovitis

Leukotriene B4 (LTB4) synthesis in rheumatoid synovitis was studied using peripheral and synovial fluid polymorphonuclear leukocytes (PMNs) and rheumatic synovial lining cells. No differences were found in LTB4 synthesis between peripheral PMNs from healthy volunteers and rheumatoid arthritis patients. When peripheral and synovial PMNs from the same RA patient were compared, arachidonic acid-induced LTB4 synthesis in synovial fluid PMNs was increased 1.7-7.2 fold, whereas the response to Ca ionophore A23187 stimulation was similar. This suggests 5-lipoxygenase stimulating factor(s) in inflamed joints. Rheumatic synovial lining cells in a primary cell culture produced small amounts of LTB4, the concentrations being less than 0.1 per cent of those of prostaglandin E2 (PGE2). PGE2 synthesis in synovial cells was increased when arachidonic acid or interleukin-1 was added to the culture, whereas LTB4 production remained unaltered. The present results suggest that in inflamed joints LTB4 originates mainly from PMNs whereas synovial lining cells are the source for PGE2.

Leukotrienes. Biology and role in disease

Leukotrienes are a novel group of chemical messengers derived from arachidonic acid. They are produced by several different tissues by processes linked to phospholipid flux in response to specific stimuli. The leukotrienes interact with specific receptors in target cell membranes to initiate a response. Most of these responsive cells are derived from bone marrow, skin, smooth muscle, and vascular endothelium. Leukotrienes are powerful mediators of inflammation and smooth muscle contraction, and there is increasing evidence that they are important factors in immune-mediated disease. Several available effective antiinflammatory drugs may act partially by inhibiting the production of leukotrienes.

IgG-, IgA-, and IgE-induced release of leukotriene C4 by monocytes isolated from patients with atopic dermatitis

Purified peripheral blood monocytes isolated from patients with atopic dermatitis (AD) and from nonallergic normal donors were compared for their abilities to release leukotriene C4 (LTC4), leukotriene B4 (LTB4) and beta-glucuronidase in response to challenge with aggregated immunoglobulins or anti-immunoglobulins. The relationship between mediator release and the number of monocytes that formed rosettes with immunoglobulin-coated indicator cells was examined. Patients with AD had twice as many IgA- and three times as many IgE-rosetting monocytes as normal donors (48 +/- 12% versus 27 +/- 10% and 40 +/- 15% versus 14 +/- 3%, respectively), and yet the amounts of IgA- and IgE-induced LTC4 released were similar for both groups. This apparent discrepancy did not result from a decreased capacity for arachidonate metabolism via the C5-lipoxygenase pathway, since stimulation of monocytes from patients and normal donors with the calcium ionophore A23187 induced similar amounts of LTC4 and LTB4 release (LTC4, 3.0 +/- 1.7 versus 3.0 +/- 1.0 ng/10(6) cells; LTB4, 5.3 +/- 0.7 versus 5.2 +/- 0.5 ng/10(6) cells, respectively). In addition, aggregated IgG-induced LTC4 release by monocytes of both groups was similar, concomitant with an equivalent number of IgG-rosetting cells. Determination of cytophilically bound IgG and IgE by flow cytometry demonstrated that monocytes from atopic patients had more IgG bound than monocytes from normal donors. Similar amounts of IgE were detected on most monocytes from both groups, despite the higher serum IgE levels of patients. However, approximately 3% to 8% of monocytes from atopic but not normal donors stained brightly for IgE, suggesting that relatively large amounts of cytophilic IgE were bound to a small percentage of the patients' monocytes. Challenge of monocytes with anti-IgE or anti-IgG induced release of similar amounts of LTC4 for both groups, despite the presence of more cytophilic IgG on monocytes from atopic donors. These data indicate that monocytes from patients with AD release LTC4 and LTB4 in response to challenge with aggregated IgE or anti-IgE, as well as aggregated IgG, IgA, and anti-IgG. However, under our in vitro conditions, stimulation of patients' monocytes with aggregated IgA or IgE was not associated with increased mediator release, despite higher percentages of IgA- and IgE-rosetting cells compared to normal donors.

Comparison of the production of eicosanoids by human and rat peritoneal macrophages and rat Kupffer cells

Human and rat peritoneal macrophages and rat Kupffer cells were labelled with [1-14C] arachidonic acid and stimulated with the calcium ionophore A23187. The metabolites formed were separated by high pressure liquid chromatography (HPLC). Human peritoneal macrophages formed especially leukotriene B4, 5-hydroxy-6,8,11,14 eicosatetraenoic acid and small amounts of leukotriene C4 and thromboxane B2, 12-hydroxy-5,8,10 heptadecatrienoic acid and 6-keto-prostaglandin F1 alpha, whereas rat peritoneal macrophages mainly produced cyclooxygenase products and in particular thromboxane B2 and 12-hydroxy-5,8,10 heptadecatrienoic acid. Rat Kupffer cells synthesized mainly cyclooxygenase products such as prostaglandin F2 alpha, prostaglandin D2 and prostaglandin E2. These results indicate that the profile of eicosanoids production by macrophages is dependent both on the species and on the tissue from which the macrophage is derived.

Metabolism of exogenous arachidonic acid by mouse peritoneal macrophages

On incubation of resident mouse peritoneal macrophages with arachidonic acid several hydroxyacyl derivatives detectable in cellular supernatants are formed. As main products monohydroxyarachidonic acids (monoHETE's) were identified. In addition, smaller amounts of dihydroxyarachidonic acids (diHETE's) were formed. A detailed analysis of cell culture supernatants by reversed phase HPLC, normal phase HPLC in combination with UV-spectroscopy and combined gas-chromatography/masspectrometry revealed the presence of 5-, 8-, 12- and 15- monoHETE's, two distinct 5,12-diHETE's, several 8,15-diHETE's and 14,15-diHETE. Among the 5,12-diHETE's, only small amounts of a compound with the characteristics of LTB4 were detected. Under the conditions employed, the cyclooxygenase products PGE2 and PGI2 (as 6-keto-PGF1 alpha) were only minor metabolites. In contrast, when macrophage cultures were stimulated with the phagocytic stimulus zymosan, PGI2, PGE2 and LTC4 were found as the major conversion products of arachidonic acid, whereas mono- and diHETE's were not formed in detectable amounts.

Formation of leukotriene B4, 20-hydroxy leukotriene B4 and other arachidonic acid metabolites by macrophages during peritonitis in patients with continuous ambulatory peritoneal dialysis

Macrophages, isolated from dialysis fluid of three patients with continuous ambulatory peritoneal dialysis (CAPD) at different times during peritonitis were labelled with 14C-arachidonic acid and stimulated with the calcium ionophore A23187. The main metabolites formed by 5-lipoxygenase activity were leukotriene B4 (LTB4) and 5-hydroxy-6, 9, 11, 14-eicosatetraenoic acid (5-HETE). Smaller amounts of cyclooxygenase metabolites were present and also a major compound with an elution time between 6-keto-prostaglandin F1 alpha (6-keto-PGF1 alpha) and thromboxane B2 (TxB2). This substance was isolated, analyzed by GC-MS and identified as 20-hydroxy-leukotriene B4 (20-OH-LTB4). This indicates that human peritoneal macrophages obtained from CAPD not only produce leukotrienes and prostaglandins, but also the omega-hydroxylase product of LTB4, which has been demonstrated to be present in polymorphonuclear leucocytes. The activity of this enzyme was not correlated with the severity of the peritonitis.

Blood leukotriene levels during the acute asthma attack in children

Leukotrienes (LT) have been proposed to be important mediators in the etiology of the acute asthma attack (AAA). We therefore studied blood LT levels in 18 children having AAA. Heparinized blood samples were obtained before and after treatment with epinephrine injections and/or metaproterenol inhalations in the emergency room. The samples were acidified and subjected to Sep-pak chromatography. Reverse phase high performance liquid chromatography (RP-HPLC), ultraviolet (UV) spectroscopy and bioassay on guinea pig ileum were used to identify the LT based on comparison to data produced by standard synthetic LT samples. Radioimmunoassay (RIA) was used to further confirm the presence of LT. LT C, D and E were detected in the plasma of children having AAA. Only LT C levels were significantly elevated over control values. The mean blood LT C level of control patients was 1.6 +/- 1.2 nanograms per milliliter (ng/ml, mean +/- SEM) while that of the asthma patients was 73.8 +/- 18.2 ng/ml prior to treatment. After emergency room treatment the asthma patients had a mean blood LT C level of 22.5 +/- 11.7 ng/ml. Lowered levels of LT C accompanied improved clinical condition of the patients. This finding indicates that the AAA in children is associated with elevated blood levels of LT C.

Increase in the formation of leukotriene B4 and other lipoxygenase products in peritoneal macrophages of adrenalectomized rats

The effect of adrenalectomy on the formation of cyclooxygenase and lipoxygenase products by activated peritoneal rat macrophages was determined. After isolation, the cells were incubated with [1-14C]arachidonic acid and the calcium ionophore A23187 and the metabolites isolated by HPLC chromatography. The main components formed in the controls are 6-keto-prostaglandin F1 alpha, thromboxane B2 and 12-HETE. One peak represents 5,12-di-HETE. Smaller amounts of prostaglandin F2 alpha, prostaglandin E2, prostaglandin D2, leukotriene B4 and 15-HETE are also present. After adrenalectomy, a considerable increase occurs in the amounts of leukotriene B4, 15-HETE and 12-HETE. The increase in the prostaglandins is smaller. The compounds formed from endogenous arachidonic acid are also determined. In the cells of the controls, 6-keto-prostaglandin F1 alpha and thromboxane B2 are produced in higher amounts than leukotriene B4. After adrenalectomy, the formation of leukotriene B4 is much more increased than that of 6-keto-prostaglandin F1 alpha. These effects are most probably related to a diminished amount or inactivation of lipocortin, a glucocorticosteroid-induced peptide with phospholipase A2 inhibitory activity in adrenalectomized animals.

Opposite effects of adrenalectomy on eicosanoid release in rat peritoneal macrophages and spleen

The effect of adrenalectomy on the formation of cyclo-oxygenase and lipoxygenase products by activated peritoneal rat macrophages was determined and compared with that of the spleen. After isolation, the cells and tissues were incubated with [1-14C] arachidonic acid and the Ca-ionophore A23187 and the metabolites isolated by HPLC chromatography. The main components formed in the macrophages of the controls are 6-keto-PGF1 alpha, TxB2 and 12-HETE. One peak represents 5, 12 di HETE. Smaller amounts of PGF2 alpha, PGE2, PGD2, LTB4 and 15-HETE are also present. After adrenalectomy, a considerable increase occurs in the amounts of LTB4, 15-HETE and 12-HETE. The increase in the PG is smaller. The compounds formed from endogenous arachidonic acid are also determined. In the cells of the controls, the formation of LTB4 is considerably increased after adrenalectomy. In the spleen, PGD2 and 12-HETE are decreased after adrenalectomy. The effect of the macrophages is most probably related to a diminished amount or inactivation of lipocortin, a glucocorticosteroid induced peptide with PlA2 inhibitory activity in adrenalectomized animals. In the decrease in formation in the spleen, the absence of the permissive effect of glucocorticosteroids on the hormone-induced lipolysis may play a role.

Human peritoneal eosinophils and formation of arachidonate cyclooxygenase products

Human peritoneal eosinophils were obtained from the waste dialysis bags of patients undergoing continuous ambulatory peritoneal dialysis. The number of eosinophils obtained from each bag varied from 3 X 10(7) to 288 X 10(7). The cells were incubated for 1 h in tissue culture medium and prostaglandin E2 (PGE2), 6-keto-prostaglandin F1 (6-keto-PGF1), and thromboxane B2 (TXB2) were determined by radioimmunoassay of the supernatant. The basal release as well as the stimulated release from the purified eosinophils of TXB2 were five times greater than the release of PGE2 and thirty times greater than the release of 6-keto-PGF1. A dose-response curve was achieved for all three cyclooxygenase products with the calcium ionophore A23187. The release of TXB2 was inhibited in a dose-dependent manner by the specific thromboxane A2 (TXA2) synthase inhibitor OKY-1581 and a corresponding increase in PGE2 and 6-keto-PGF1 was obtained. Indomethacin (5.6 X 10(-6) M) inhibited the cyclooxygenase products to almost undetectable levels.

Modulation of phagocytic cell function

Phagocytosis is an important factor in the defense of the host against all kinds of microorganisms. The process of phagocytosis of microorganisms by phagocytes can be separated into distinct but interrelated phases: adherence, chemotaxis, opsonization, attachment, ingestion, degranulation and killing. Phagocytosis is accompanied by an increase in oxygen metabolism in which H2O2 and activated oxygen species are generated. Modulation of phagocytic cell function can be brought about by a variety of substances. Microorganisms produce and contain components which influence the process of phagocytosis. Surrounding tissue cells and the phagocytes themselves produce biologically active molecules that modulate phagocytosis.

Generation of hydroxyeicosatetraenoic acids by human inflammatory cells: analysis by thermospray liquid chromatography-mass spectrometry

Arachidonic acid was converted to a series of hydroxyeicosatetraenoic acids (HETEs) by mixed human inflammatory cells following stimulation with the calcium ionophore A23187. HETEs were purified by a simple one-step extraction procedure followed by HPLC. The HPLC was coupled to a Finnigan quadrupole mass spectrometer using the now commercially available thermospray liquid chromatography-mass spectrometry interface. The HPLC eluant was monitored 'on line' by the mass spectrometer. Soft ionisation occurs, generating intense molecular ion species in the negative ion mode (M - H-:m/z 319) for each of the isomeric HETEs. The (M + H+ - H2O) ion at m/z 303 is the major species in the positive ion spectra of HETEs. Mass spectra were obtained on-line post-HPLC for HETEs formed by the human cells, and the HPLC-MS profile compared with that obtained from standards; species corresponding to the 11-, 9- and 5-HETEs were observed.

Skin levels of arachidonic acid-derived inflammatory mediators and histamine in atopic dermatitis and psoriasis

Since the biochemical events leading to cutaneous inflammation in atopic dermatitis and psoriasis are unknown, we studied the levels of arachidonic acid-derived mediators of inflammation as well as histamine in the suction blister fluid obtained from lesional and nonlesional skin of patients with these dermatoses. Mediator levels were determined radioimmunologically. Skin from healthy controls and uninvolved skin from patients contained very low or unmeasurable levels of the 5-lipoxygenase metabolite of arachidonic acid, leukotriene (LT) B4. In contrast, higher levels of LTB4-like immunoreactivity were detected in suction blister fluid from lesional atopic dermatitis skin, and even higher concentrations occurred in psoriasis lesions. LTB4-like immunoreactivity from atopic dermatitis suction blister fluid cochromatographed on reverse-phase high-pressure liquid chromatography with authentic LTB4, thus excluding cross-reaction of the LTB4-antibody with arachidonic acid or monohydroxyeicosatetraenoic acids. In contrast, suction blister concentrations of the cyclooxygenase metabolite of arachidonic acid prostaglandin (PG) E2 showed no significant differences between lesional and nonlesional patient skin and healthy control skin. PGD2 determined as a stable metabolite could not be detected in these samples. Histamine concentrations in lesional skin were within normal range. The elevated levels of the potent proinflammatory and immunomodulating mediator LTB4 could be involved in the pathogenesis of cutaneous inflammation in atopic dermatitis and psoriasis. In addition, they might explain the therapeutic efficiency of glucocorticosteroids, which among other actions inhibit the release of arachidonic acid from phospholipid stores by blocking the enzyme phospholipase A2. However, the specificity of disease expression in atopic dermatitis and psoriasis must be due to factors other than cutaneous LTB4 elevation.

Human peritoneal macrophages: clinical models of inflammation and potential targets of antiinflammatory drugs

Human peritoneal macrophages have been obtained from patients with renal disease undergoing chronic peritoneal dialysis, patients with ascites and at laparoscopy. These macrophages in general have both morphological and enzymatic characteristics of activated macrophages, as judged by criteria derived from animal experiments. Human peritoneal macrophages produce a variety of eicosanoids, including leukotriene B4 and leukotriene C4. These cells are suitable for studies on in vitro and in vivo effects of drugs, and for investigation of changes in macrophage activity occurring in human diseases.

Cyclooxygenase inhibitors promote the leukotriene C4 induced release of beta-glucuronidase from rat peritoneal macrophages: prostaglandin E2 suppresses

The effects of leukotriene C4, indomethacin, aspirin and prostaglandin E2 on macrophage activity were investigated, whereby the release of the lysosomal enzyme beta-glucuronidase was taken as a criterion for cell activity. Leukotriene C4 enhanced the release of beta-glucuronidase as well as the production of prostaglandin E2. Blocking the production of endogenous prostaglandins by adding indomethacin or aspirin resulted in an augmented effect of leukotriene C4. Exogenous prostaglandin E2 could reverse the leukotriene C4 and/or indomethacin induced beta-glucuronidase release. These results support the postulated interaction between leukotriene C4 and prostaglandin E2 with respect to the regulation of macrophage activity, leukotriene C4 being stimulatory, prostaglandin E2 suppressive.

Heterogeneity in the metabolism of the arachidonoyl molecular species of glycerophospholipids of rabbit alveolar macrophages. The interrelationship between metabolic activities and chemical structures of the arachidonoyl molecular species

The relative incorporation of [3H]arachidonic acid (20:4) into individual molecular species containing 20:4 at the 2 position (18:1-20:4, 16:0-20:4 and 18:0-20:4 species) of diacyl and ether-linked glycerophosphocholine, glycerophosphoethanolamine and glycerophosphoinositol of rabbit alveolar macrophages has been measured by reversed-phase high-performance liquid chromatography (HPLC). The rate of incorporation of [3H]20:4 into the molecular species of glycerophospholipids was greatly influenced by their structures. The reversed-phase HPLC analysis allowed elucidation of the influence of structural differences, such as the nature of the polar head group, the fatty chain at the 1 position and the chemical form of the bond of the fatty chain attached at the 1 position on the uptake of [3H]20:4 by comparison of the specific radioactivities of arachidonoyl molecular species having the same structures, except that one of the three kinds of moiety was different. The specific radioactivities of the molecular species containing choline head groups were significantly higher than those containing ethanolamine and inositol moieties. The specific radioactivities of diacyl molecular species were considerably higher than those of ether-linked molecular species. The nature of the fatty chain attached at the 1 position also influenced the uptake of [3H]20:4 into glycerophospholipids. The arachidonoyl molecular species containing 18:1 at the 1 position were preferentially labelled with [3H]20:4 as compared to the corresponding 16:0-20:4 and 18:0-20:4 species either of diacyl or ether-linked glycerophospholipids. The present results suggest that the acyltransferase involved in the incorporation of 20:4 into glycerophospholipids has selectivity for the structures of glycerophospholipids and the order of selectivity of this enzyme for the arachidonoyl molecular species, deduced in the present experiments, was as follows: choline head group greater than ethanolamine and inositol groups, acyl bond greater than ether and vinyl ether bonds, 18:1 fatty chain greater than 16:0 and 18:0 fatty chains at the 1 position. Comparison of the metabolic activities of all major arachidonoyl molecular species of glycerophospholipids having a single structure is reported here for the first time.

Production of leukotrienes and prostaglandins by human ascites cells

Ascites was collected from six patients with liver cirrhosis and the cells isolated. These cells, mainly macrophages, were labelled with 14C-arachidonic acid and stimulated with the calcium ionophore A23187. The metabolites formed were separated by HPLC. The main substances formed by the ascites cells were leukotriene B4, 5-hydroxy-6,8,11,14 eicosatetraenoic acid and leukotriene C4. Smaller amounts of thromboxane B2, 12-hydroxy-5,8,10 heptodecatrienoic acid and 6-keto-prostaglandin F1 alpha were isolated. Human peritoneal macrophages are therefore capable of producing leukotrienes and prostaglandins. Production of these substances might play a role in some of the complications of patients with liver cirrhosis and ascites.

A novel eicosanoid is the major arachidonic acid metabolite of cultured human monocytes

Human peripheral blood monocyte-macrophages (M phi) generate a novel eicosanoid during in vitro culture. The metabolite is generated during incubation of the cells with 14C - arachidonic acid (AA). Lack of prior recognition of this metabolite probably results from the facts that: 1) on thin-layer chromatography (TLC) in two standard solvent systems, the novel metabolite co-chromatographed with either prostaglandin D2 or thromboxane B2, and 2) its generation, under the conditions studied, does not occur until between 90 and 180 minutes after culture initiation which is a time period beyond that used for most leukocyte studies. The generation of the metabolite is inhibited by nordihydroguaiaretic acid (NDGA) but not by indomethacin. Base hydrolysis did not alter its migration on TLC. On both reversed phase and straight phase high pressure liquid chromatography (HPLC), the novel peak isolated by TLC elutes as a single major peak of radioactivity with a retention time different from the known leukotrienes, hydroxy acids, or their metabolites. Furthermore, the peak isolated on HPLC has a single ultraviolet absorption maximum at 270 nm. M phi cultured for 1 week prior to a 24 hour incubation with 14C-AA generated proportionally less of the novel eicosanoid (roughly 68% of total radiolabeled product) than did M phi cultured for 3 weeks prior to a similar incubation with 14C-AA (roughly 86% of total radiolabeled product). Under the conditions studied, the novel eicosanoid is the major AA metabolite generated from exogenous AA by cultured M phi and it appears to be generated in increasing quantity as the M phi differentiate.

Leukotrienes C4 and D4 in psoriatic skin lesions

Chemoattractant arachidonate lipoxygenase products have been recovered from the skin lesions of psoriasis, and may play a role in eliciting the intra-epidermal neutrophil infiltrate that characterises this disease. In view of evidence for lipoxygenase activity in psoriasis, the characteristic vasodilation in psoriatic lesions, and the vasodilator properties of leukotriene (LT) C4 and D4 in human skin, the presence of these LTs in psoriatic lesions has been investigated. Skin chamber fluid from abraded psoriatic lesions contained significantly greater amounts of immunoreactive material than that from clinically normal skin, as determined by a double antibody radioimmunoassay (RIA) that uses antiserum cross-reacting with both LTC4 and LTD4. Purification of lesional chamber fluid and scale extracts by high performance liquid chromatography (HPLC) and RIA of fractions showed immunoreactivity which co-eluted with standard LTC4 and LTD4. These findings suggest that LTC4 and LTD4 may play a role in mediating the vasodilation and increased blood flow that characterise psoriatic skin lesions.

Formation of prostaglandins, leukotrienes and paf-acether by macrophages

Prostaglandins (PG) and leukotrienes (LT)--arachidonic acid-dependent metabolites--and paf-acether (platelet-activating factor)--an ether phospholipid--are potent mediators of allergic and inflammatory reactions. Their structures, chemical synthesis and biosynthetic pathways have been recently described. These mediators are produced by various cells with proinflammatory activities including the macrophages upon interaction with a specific secretagogue stimulus (phagocytosis of zymosan particles, immune-complexes); in IgE-dependent hypersensitivity reactions; upon interaction with one of these mediators. Formation of these mediators by macrophages depends upon their local environment. Qualitative and/or quantitative variations in their synthesis are observed depending on the tissue they are derived from (alveole or peritoneum) and on the type of inflammation (immunologic specific or not). Their potent biological activities (increase of vascular permeability, smooth muscle contraction, cardiac and vascular effects and/or chemotactism) suggest a role for these mediators in various pathologies.

Determination of leukotrienes and prostaglandins in [14C] arachidonic acid labelled human lung tissue by high-performance liquid chromatography and radioimmunoassay

A liquid chromatographic method for the determination of 14C-labelled prostaglandins, leukotrienes and other lipoxygenase products formed by human lung tissue is described. In this paper we report our problems identifying these substances when 3H- or 14C-labelled compounds are compared with measurements of the mass by absorption or radioimmunoassay. Furthermore, some preliminary results of [14C] arachidonic acid labelled human lung tissue, stimulated by the Ca-ionophore A23187, show that, of the lipoxygenase products, mostly leukotriene B4 like compounds are formed and less leukotriene C4, E4 and D4. Relatively large amounts of hydroxyeicosatetraenoic acids are present. The main cyclooxygenase products are thromboxane B2, 6-ketoprostaglandin F1 alpha and prostaglandin D2.

Leukotrienes: clinical significance

The leukotrienes, so named because of their initial identification in leukocyte preparations and the presence of three conjugated double bonds (a conjugated triene), are metabolites of the same polyunsaturated fatty acids (e.g., arachidonic acid) that give rise to the prostaglandins, thromboxanes, and several other families of biologically active lipids. Their potential clinical importance derives from their effects on vascular and other smooth muscle reactivity and on leukocyte function. Several leukotrienes may markedly influence the cellular and vascular responses that constitute an integral part of hypersensitivity and inflammatory reactions of the skin. Preliminary data from several laboratories have been presented that implicate a specific leukotriene in the evolution of the lesions of psoriasis.

A routine source of human peritoneal macrophages

The routine availability of nucleated human cells for experimental use in limited in the absence of venipuncture. In this paper we have demonstrated that macrophages may be harvested routinely from the waste dialysis bags of patients undergoing continuous ambulatory peritoneal dialysis. These cells were identified as macrophages by morphology, adherence, phagocytosis, chemotaxis, non-specific esterase staining and peroxidase staining. Macrophages from patients with end-stage renal disease produced arachidonate cyclo-oxygenase products in a pattern similar to that of ascites macrophages obtained from patients with normal kidney function. Arachidonate metabolism was shown to be manipulatable. Thus, indomethacin blocked synthesis of cyclooxygenase products, and OKY-1581, a specific thromboxane synthase inhibitor, increased the release of prostaglandin E2 and prostacyclin, measured as its stable breakdown product 6-keto-prostaglandin F1, whereas the thromboxane B2 synthesis was effectively inhibited.