The biologically active leukotrienes. Biosynthesis, metabolism, receptors, functions, and pharmacology

Novel pathway for the metabolism of 6-trans-leukotriene B4 by human polymorphonuclear leukocytes

Polymorphonuclear leukocytes convert arachidonic acid to leukotriene B4 as well as to two 6-trans isomers of this substance. Both leukotriene B4 and 6-trans-leukotriene B4 are metabolized by a hydroxylase in human polymorphonuclear leukocytes to 20-hydroxy metabolites. We have now found a second, previously unknown, metabolic pathway for 6-trans-leukotriene B4 involving reduction of either the 6- or the 10- double bond. One of the two major metabolites of 6-trans-leukotriene B4 in human polymorphonuclear leukocytes is formed by the action of this reductase, followed by hydroxylation by leukotriene B4 20-hydroxylase. On the basis of ultraviolet (maximum absorbance at 232 nm) and mass spectral evidence, this product is either 5,12,20-trihydroxy-6,8,14-eicosatrienoic acid or 5,12,20-trihydroxy-8,10,14-eicosatrienoic acid.

Leukotrienes cause eosinophil emigration into conjunctival tissue

The ability of LTB4, LTC4, the 5S,6R and 5R,6S LTD4 stereoisomers, and LTE4 to evoke leukocyte infiltration into the conjunctiva was demonstrated in the guinea pig by histological and light microscopy techniques. LTD4 and LTE4 demonstrated a dose-dependent and predominantly eosinophilic infiltrate over the selected dose range (10 ng to 1000 ng), while there was only a minimal response to LTC4. LTB4 produced marked eosinophil infiltrates only at the highest dose; scattered neutrophil infiltrates were also noted at the high dose of LTB4. The 5R,6S LTD4 stereoisomer did not evoke any leukocyte infiltration. The SRS-A antagonist, FPL 55712, abolished peptidoleukotriene-induced eosinophil emigration, and indomethacin pre-treatment had no inhibitory effect, indicating direct mediation of this response by LTs. Histamine caused a comparable eosinophilia over a dose range of 10 micrograms to 1000 micrograms. LT-induced eosinophil emigration was directed to the conjunctival epithelium; the cells appeared intact and no tissue damage was observed. These results may have relevance in the areas of allergic conjunctivitis and asthma research.

Leukotriene C4 binding sites in the rat central nervous system

Binding sites for [3H]LTC4 were observed in crude membrane preparations of rat central nervous system tissue. Equilibrium binding studies indicated one high affinity [3H]LTC4 binding site with a KD of 31.4 +/- 3.4 nM for whole brain preparations. The binding was highly specific for [3H]LTC4 and could be inhibited by the SRS-A antagonist FPL 55172. Specific binding was increased with both mono- and di-valent ions. Regional distribution studies revealed a three-fold difference in binding capacity within different regions of the brain with the highest binding capacity in the brainstem (94.1 +/- 6.9 fmol/mg of protein) and the lowest in the hypothalamus (29.6 +/- 12.8 fmol/mg of protein). In addition, weak low capacity binding was observed for [3H]LTB4 and [3H]LTE4, while no saturable binding was observed for [3H]LTD4. The order of selectivity in inhibiting [3H]LTC4 binding was LTC4 much greater than LTD4 = LTE4 greater than LTB4.

Inhalation challenge with sulfidopeptide leukotrienes in human subjects

What is the meaning of these findings to the practicing chest physician? First, leukotrienes are potent airway constrictors; they are capable of reproducing the type of airway constriction observed in asthma. The role of leukotrienes in this regard has yet to be established, but experiments to test the importance of these agents in this setting are likely to be performed soon. Specifically, several leukotriene receptor antagonists or synthesis inhibitors have been identified and may provide the tools needed to test this crucial hypothesis. Second, the leukotrienes are unique bronchoactive agents in that the degree of hyperresponsiveness between normal and asthmatic subjects varies markedly with the bronchoconstrictor index used to assess response. When one compares normal subjects to asthmatic subjects, there is substantial overlap in leukotriene sensitivity among groups when V30-P is used as the bronchoconstrictor index. However, when the FEV1 is used as the bronchoconstrictor index, there is little overlap in sensitivity between normal and asthmatic subjects, and the separation between the two groups is even more clearly made than it is with histamine or methacholine challenge. Thus, LTD4 inhalation challenge may replace the histamine and methacholine challenges in the diagnosis of cryptic shortness of breath. Third, the differential sensitivity of various bronchoconstrictor indices in both normal and asthmatic subjects when leukotrienes are used may provide clues as to the locus of airway hyperresponsiveness in asthma. Thus, leukotrienes hold the promise of new ways to treat and diagnose asthma, as well as providing new insights into the pathobiology of the disease itself.

Tissue distribution of leukotriene A4 hydrolase activity in guinea pig

The distribution of the activity of leukotriene A4 hydrolase, an enzyme catalyzing hydrolysis of the allylic epoxide leukotriene A4 to the dihydroxy acid leukotriene B4, was determined in various tissues of guinea pig by using the supernatant fraction (100,000 X g, 60 min) of the homogenates. The activity was ubiquitously distributed in all tissues examined, and the highest specific activity was found in small intestine, followed by lung, aorta, colon, and spleen, in this order. The specific activity in these tissues was higher than that of leukocytes. The physiological roles of this compound in these organs deserve reexamination in this context.

Identification of the major endogenous leukotriene metabolite in the bile of rats as N-acetyl leukotriene E4

Mercapturic acid formation, an established pathway in the detoxication of xenobiotics, is demonstrated for cysteinyl leukotrienes generated in rats in vivo after endotoxin treatment. The mercapturate N-acetyl-leukotriene E4 (N-acetyl-LTE4) represented a major metabolite eliminated into bile after injection of [3H]LTC4 as shown by cochromatography with synthetic N-acetyl-LTE4 in four different HPLC solvent systems. The identity of endogenous N-acetyl-LTE4 elicited by endotoxin in vivo was additionally verified by enzymatic deacetylation followed by chemical N-acetylation. The deacetylation was catalyzed by penicillin amidase. Endogenous cysteinyl leukotrienes were quantified by radioimmunoassay after HPLC separation. A N-acetyl-LTE4 concentration of 80 nmol/l was determined in bile collected between 30 and 60 min after endotoxin injection. Under this condition, other cysteinyl leukotrienes detected in bile by radioimmunoassay amounted to less than 5% of N-acetyl-LTE4. The mercapturic acid pathway, leading from the glutathione conjugate LTC4 to N-acetyl-LTE4, thus plays an important role in the deactivation and elimination of these potent endogenous mediators.

Release of leukotrienes into the perfusate of calcium-ionophore stimulated rabbit lungs. Influence of 5-lipoxygenase inhibitors

Arachidonic acid and the calcium ionophore A23187 are known to provoke a pulmonary artery pressor response, edema formation and release of thromboxane B2 (TxB2) and 6-keto prostaglandin-F1 alpha (6-keto PGFl alpha) into the recirculating perfusion fluid of isolated blood-free perfused rabbit lungs. Here we investigated the release of leukotrienes (LTs) by repetitive 0.1 microM A23187 challenge in the presence or absence of cyclooxygenase and 5-lipoxygenase inhibitors. RP-HPLC analysis of perfusion fluid extracts persistently showed peaks with retention times of authentic LTC4, -D4, -E4 and -B4. Fractionated RP-HPLC eluate subjected to radioimmunoassay (RIA) with LTC4 and LTB4 antibodies showed two major peaks of immunoreactivity corresponding to those compounds and minor immunoreactivity with LTD4 and LTE4 in accordance with the stated cross-reactivities of the LTC4 antibody. Good correlation for both LTB4 and LTC4 levels measured by RP-HPLC versus RIA of collected HPLC peaks was found. Five to ten min after A23187 challenge, LTC4, -D4 and -B4 levels ranged from 800 to 1600 pg/ml perfusate. LTC4 reached a maximum level at 20 min whereas LTB4 slightly increased over a 35 min period. Upon repeated A23187 challenge, interrupted by rinsing phases with fresh perfusion fluid, the LT release was reproducible several times with increasing reaction strength. This performed in presence of increasing concentration of the 5-lipoxygenase inhibitors AA-861 or U-60,257 caused a dose-dependent inhibition of the release of all LTs with an IC50 of approximately 10(-8) to 10(-7) M and 10(-6) M, respectively. Cyclooxygenase inhibition with acetylsalicylic acid at doses completely suppressing the A23187 induced pressor response did not inhibit the peptidoleukotriene release and only slightly depressed LTB4 release.

CONCLUSION

using a rapid and sensitive extraction and RP-HPLC method isolated lungs are found to release nanomolar amounts of LTs into the perfusate upon repetitive A23187 challenge, suppressed by 5-lipoxygenase inhibition.

Leukotriene B4 synthesis and metabolism by neutrophils and granule-free cytoplasts

Leukotriene B4 [LTB4, (5S,12R)-hydroxyeicosa-6,14-cis-8,10-trans-tetraenoic acid], a potent mediator of inflammation, is released from neutrophils by agonists that provoke degranulation of the cell. To examine whether degranulation is a necessary requirement for synthesis and metabolism of LTB4 (or of other arachidonate metabolites), we prepared neutrophil-derived cytoplasts (neutroplasts), organelle-depleted vesicles of cytoplasm surrounded by the plasma membrane. In the presence of extracellular Ca2+ with or without exogenous arachidonic acid (150 microM), neutroplasts were exposed to the Ca2+ ionophore A23187 (10 microM) and the resultant lipoxygenation products of arachidonate were determined. Neutrophils metabolize arachidonic acid to 5-HETE greater than 15-HETE greater than LTB4 greater than all-trans-LTB4 isomers. Neutroplast products of arachidonate lipoxygenation were 15-HETE greater than 5-HETE greater than LTB4 greater than all-trans-LTB4 isomers. Neutroplasts, like neutrophils, were capable of converting LTB4 into its 20-hydroxy and 20-carboxy metabolites. Finally, neutroplasts could utilize intrinsic arachidonate, since the neutroplasts synthesized LTB4 (30 pmol/mg of protein) in the absence of added arachidonic acid. The data demonstrate that neutrophil degranulation is not required for synthesis or metabolism of LTB4 by neutrophils.

Development of cyclooxygenase and lipoxygenase metabolites of arachidonic acid after transient cerebral ischemia

Vasoactive arachidonic acid metabolites are postulated to play a role in the pathogenesis of cerebral ischemia. In order to characterize the local generation of cyclooxygenase and lipoxygenase metabolites of arachidonic acid in transient ischemia with reperfusion, Mongolian gerbils were studied for regional cerebral blood flow (CBF), using the hydrogen clearance technique, and for cerebral levels of the thromboxane metabolite TXB2, and prostaglandins 6-keto-PGF1 alpha and PGE2, as well as the leukotriene LTB4. The gerbils were anesthetized with pentobarbital, and half of the animals were pretreated with the cyclooxygenase inhibitor indomethacin. All received 10 or 20 minutes of dense forebrain ischemia followed by reperfusion of 10 minutes, 50 minutes, or 100 minutes. A separate control group received no ischemic lesion. Regional CBF decreased significantly from 23.7 +/- 2.6 to 4.3 +/- 1.7 cc/100 gm/min during ischemia (p less than 0.01). Reperfusion resulted in initially normal flows (22.5 +/- 5.1 cc/100 gm/min) followed by a progressive hypoperfusion (11.3 +/- 2.7 cc/100 gm/min). All metabolites showed parallel significant (p less than 0.05) increases after transient ischemia and reperfusion compared to baseline levels (values (in pg/mg protein) were: TXB2 45.5 +/- 7.1 vs 23.3 +/- 3.6; 6-keto-PGF1 alpha 262.8 +/- 47.9 vs 175.8 +/- 26.8; PGE2 256.5 +/- 35.6 vs 112.5 +/- 11.2; and LTB4 37.8 +/- 4.6 vs 24.6 +/- 6). These levels were all significantly decreased (p less than 0.05) by pretreatment with indomethacin except for the leukotriene LTB4, which was increased. Transient cerebral ischemia results in a reperfusion abnormality and the local generation of cyclooxygenase products, which are reduced by pretreatment with indomethacin; however, cyclooxygenase inhibition may result in increased substrate availability for the lipoxygenase system. Studies of such an interaction may lead to new understandings of the pharmacological modification of detrimental vascular changes after transient cerebral ischemia.

The eosinophilic leukocyte: structure and function

The evidence reviewed here indicates that the eosinophil has the ability to kill many species of helminths and likely does so during worm infection. This toxic ability appears to be regulated by several other cells including mast cells, monocytes, and T lymphocytes. Eosinophils kill helminths through their ability to generate potent oxidants and through their content of cationic proteins, which likely achieve high concentrations at points of granule deposition. Eosinophils also participate in inflammation in human disease especially asthma, skin diseases, and heart disease. Though present concepts hold that the mast cell is the cornerstone of the allergic inflammatory response (450), the findings that eosinophils bind IgE and are activated by antigen-IgE complexes and that the eosinophil can elaborate many inflammatory mediators raise the possibility that the eosinophil might also be involved in the initiation of inflammatory responses. Finally, an eosinophil-related protein appears to play an undefined role in human reproduction.

Sotalol potentiates the leukotriene C4-induced contractions and thromboxane A2 release of guinea pig lung parenchymal strips

The leukotriene C4 (LTC4)-induced contraction and thromboxane A2 (TxA2) release of the guinea pig lung parenchymal (GPLP) strip are both inhibited by the beta 2-adrenergic agent salbutamol. The effect of LTC4 is restored to nearly normal by the beta-adrenergic antagonist sotalol. The latter substance alone also induces a contraction in the GPLP strip and potentiates the contractions and the TxA2 release of LTC4. During the sotalol-induced contractions, no TxA2 release occurs. An antihistaminic, mepyramine had no effect on the sotalol-induced contraction. When sotalol is added repeatedly to a GPLP strip, only the first time a contraction occurs.

Helminth-induced intestinal inflammation

Gastrointestinal inflammation is a prominent feature of protective reactions in animals immune against helminths. Infiltration into the inflamed mucosa of various cells and their subsequent activation result in the elaboration of an array of pharmacologically and biologically active substances. The release of mediators is also associated with alterations in the epithelial layer. Furthermore, increased smooth muscle reactivity and enhanced secretory function of the mucosal tissue contribute to the development of an unfavourable environment and lead to worm expulsion. Mediators elaborated from inflammatory cells, whether associated with cell granules (i.e., preformed) or de novo-generated from membrane phospholipids, possess a number of potent vasoactive and spasmogenic properties which may contribute to events leading to worm elimination. The lipoxygenase metabolites of arachidonic acid (leukotrienes) derived from cell membranes probably contribute to the state of intestinal hypersensitivity against helminths. The measurement of elevated levels of these lipid mediators following worm challenge of immune, but not control, rats suggests that leukotrienes may play a role in amplifying and augmenting the inflammatory process associated with worm expulsion.

Pharmacology of platelet inhibition in humans: implications of the salicylate-aspirin interaction

The current dispute over the effects of "low" vs "high" doses of aspirin should take into consideration the pharmacokinetics of this drug. In fact, different pharmaceutical formulations of aspirin may deliver little or no aspirin to the systemic blood. This was the case, for instance, in healthy volunteers taking 320 mg of compressed aspirin or 800 mg of enteric-coated aspirin. In all instances thromboxane B2 generation in serum was fully inhibited. Platelet cyclooxygenase might therefore be effectively acetylated by exposure to aspirin in the portal circulation, whereas vascular cyclooxygenase could be spared. Thus aspirin formulations ensuring complete first-pass deacetylation should be sought rather than "low" or "high" doses of unspecified aspirin formulations. Regardless of the type and dose of aspirin administered, salicylate is formed and accumulates in the circulation. It may antagonize the effects of aspirin on cyclooxygenase, at least in acute conditions. As an example, after administration of 1 g of salicylate to healthy volunteers, when plasma levels of the drug were about 75 micrograms/ml, the effect of 40 mg iv aspirin (given 40 min later) on platelet cyclooxygenase and aggregation was significantly diminished. In contrast, in patients undergoing saphenectomy, the same dose of salicylate (1 g) gave plasma drug levels of about 25 micrograms/ml; salicylate was unable to prevent the inhibitory effect on platelets of 40 mg iv aspirin (given 1 hr later) but did act on vascular prostacyclin. Thus the combination of salicylate with aspirin at an appropriate dose and blood level ratio may result in almost complete dissociation of the drug's effect on platelets and vessels in man.(ABSTRACT TRUNCATED AT 250 WORDS)

Isolation and characterization of leukotriene C4 synthetase of rat basophilic leukemia cells

When leukotriene (LT) A4 was incubated with subcellular fractions of sonicated rat basophilic leukemia (RBL) cells in the presence of glutathione, the enzyme producing LTC4, designated LTC4 synthetase, was found in the 105,000 X g pellet (microsomes) with a 3-fold enrichment in specific activity over that of the sonicate. The identification of the reaction product as LTC4 was confirmed by its identical retention time on reverse-phase HPLC to that of synthetic LTC4, the incorporation of [3H]glutathione into the product, its reactivity in a radioimmunoassay, and its UV absorption spectrum. In contrast, glutathione S-transferase activity, measured spectrophotometrically with 1-chloro-2,4-dinitrobenzene, was detected predominantly in the 105,000 X g supernatant (89%) and also in the microsomes (7%). The microsomal glutathione S-transferase and LTC4 synthetase were solubilized with 0.4% Triton X-102 and separated by DEAE-Sephacel chromatography; the former appeared in the effluent and the latter in the eluate after the addition of 0.16 M NaCl to the equilibration buffer. Solubilized, microsomal glutathione S-transferase was inhibited by S-hexylglutathione with an IC50 of 36 microM and was stable at 40 degrees C for 5 min, whereas LTC4 synthetase was only slightly inhibited (IC50, 2.3 mM) by S-hexylglutathione and retained no activity after incubation at 40 degrees C for 5 min. The partially purified LTC4 synthetase showed a specific activity of 1.34 +/- 0.51 nmol of LTC4 per 10 min per mg of protein (mean +/- SD, n = 9), representing a 10-fold purification from the sonicate and catalyzed the dose- and time-dependent production of LTC4 from LTA4 and glutathione. The apparent Km values for LTA4 and glutathione were estimated by Lineweaver-Burk plots to be 5-10 microM and 3-6 mM, respectively. These results indicate that the conjugation of LTA4 with glutathione to form LTC4 is catalyzed by a unique microsomal enzyme.

Reduction in blood flow in normal and narrowed coronary arteries of dogs by leukotriene C4

The hemodynamic effects of intracoronary leukotriene C4 (0.3 to 10.0 micrograms) in seven anesthetized dogs with normal and severely narrowed coronary arteries were examined. Intracoronary leukotriene C4 caused a significant dose-related reduction in coronary blood flow in both normal and narrowed coronary arteries with no effect on heart rate or mean arterial pressure. However, left ventricular end-diastolic pressure increased at the 10.0 micrograms dose. The reduction of blood flow in normal and narrowed coronary arteries in response to leukotriene C4 was similar. At the peak effects of leukotriene C4, there was evidence of intracoronary thromboxane A2 release. To examine the contribution of thromboxane A2 release to the coronary vasoconstrictor effects of leukotriene C4, dogs were administered leukotriene C4 after indomethacin pretreatment. The decrease in coronary blood flow was not significantly affected by pretreatment of the animals with indomethacin. However, indomethacin lowered baseline levels of thromboxane B2 and blocked the release of thromboxane A2 after leukotriene C4 administration. Thus, intracoronary leukotriene C4 causes direct dose-dependent decrease in coronary blood flow of similar magnitude in both normal and narrowed coronary arteries. These coronary hemodynamic effects of leukotriene C4 in dogs are not mediated by release of thromboxane A2. Leukotriene C4 released from activated leukocyte in the intracoronary thrombus or in the injured myocardium may reduce coronary blood flow and adversely influence the fate of the affected myocardial tissue.

Increased generation of leukotriene C4 from eosinophils in asthmatic patients

Human eosinophils with a density of over 1.095 were isolated from peripheral blood by dextran sedimentation, centrifugation with Lymphoprep and density gradients with Percoll. After the cells (1 X 10(5)/ml) were incubated with 1 microgram/ml calcium ionophore A23187 for 20 min, leukotriene C4 (LTC4) content in the supernatant was measured by radioimmunoassay. The generation of LTC4 was significantly higher in the cells from extrinsic asthmatics (23.5 +/- 14.8 ng/10(6) cells, mean +/- SD, n = 26, P less than 0.01) and intrinsic asthmatics (24.6 +/- 20.6 ng/10(6) cells, n = 27, P less than 0.01 as compared with normal healthy subjects (8.3 +/- 7.7 ng/10(6) cells, n = 10). There was no significant difference in the generation of LTC4 between intrinsic and extrinsic asthmatics. These observations indicate that eosinophils from asthmatic patients have increased ability to release LTC4.

Leukotrienes as mediators in tissue trauma

A significant increase in the production of cysteinyl leukotrienes was observed after mechanical or thermal trauma in the anesthesized rat. The amount of biliary N-acetyl-leukotriene E4, which represents a suitable indicator for blood plasma leukotrienes, was used as a measure of leukotriene generation. Cysteinyl leukotrienes were rapidly eliminated from blood plasma into bile where N-acetyl-leukotriene E4 was the major metabolite. Leukotrienes were at a much lower concentration in blood plasma than in bile and differed in the pattern of metabolites. The detected amounts of leukotrienes were sufficient to induce known phenomena associated with trauma, such as tissue edema and circulatory and respiratory dysfunction. Increased leukotriene generation appears to play an important role in the pathophysiology of tissue trauma.

Alteration of leukotriene release by macrophages ingesting Toxoplasma gondii

Mouse resident peritoneal macrophages incubated with ionophore A23187 or opsonized zymosan released leukotrienes (LT) B4 and C4 (LTB4 and LTC4) and LTC4 and LTD4, respectively. In contrast, incubation with Toxoplasma gondii, an obligate intracellular protozoan, led to the formation of 11-, 12-, and 15-hydroxyicosatetraenoic acids (HETEs), together with an unidentified compound, designated compound X. Each of these compounds incorporated [3H]arachidonic acid from the macrophage during phagocytosis of T. gondii. Compound X migrated immediately prior to 15-HETE by reverse-phase HPLC and was distinct from authentic monoHETE, monohydroperoxyicosatetraenoic acid (mono-HPETE), and dihydroxyicosatetraenoic acid (diHETE) standards. The generation of compound X by macrophages correlated with the extent of phagocytosis of T. gondii and with intracellular survival of the organisms. Prior antibody-coating of T. gondii or activation of macrophages, either of which inhibited survival and replication of ingested organisms, was associated with production of LTD4 but not compound X. Killed organisms also stimulated LTD4 release only. Although T. gondii concentrated arachidonic acid, they did not metabolize the compound to identifiable lipoxygenase products. Preincubation of macrophages with the relative lipoxygenase inhibitors nordihydroguaiaretic acid or 5,8,11,14-icosatetraynoic acid inhibited the formation of compound X. The absence of leukotriene production by macrophages ingesting T. gondii may explain the relative lack of a neutrophil inflammatory response in diseases due to obligate intracellular organisms. Alternatively, compound X may have functional activities that might mediate some of the host responses to cellular parasitism.

Oxidative transformations of arachidonic acid in human dispersed lung cells: disparity between the utilization of endogenous and exogenous substrate

Eicosanoid release from human dispersed lung cells (HDLC) containing ca 5% mast cells was studied before and after cell activation with ionophore A23187 or anti-IgE. Basal release of eicosanoids synthesized from endogenous arachidonate was measured by radioimmunoassay. In descending order of abundance the products were: 5-hydroxyeicosatetraenoic acid (5-HETE) greater than thromboxane B2 (TXB2) greater than prostaglandin F2 alpha (PGF2 alpha) approximately immunoreactive (i)-PGE2 greater than PGD2 greater than 6-keto-PGF1 alpha approximately i-LTC4. Stimulation of HDLC with ionophore A23187 or, after passive sensitization, with anti-IgE resulted in 2-10 fold increases in the generation of individual eicosanoids. In terms of net generation the most abundant products were PGD2 and TXB2 with either stimulus. Activation with A23187 caused net release of i-LTC4 and 5-HETE, but these products were not measured after immunological activation. A more complete profile of lipoxygenase products released from HDLC dispersed from one lung was obtained after separation by high performance liquid chromatography combined with ultra violet spectroscopy and bioassay. The major products released from the cells from this lung with ionophore stimulation were 13-hydroxylinoleic acid greater than LTB4 greater than 5-HETE greater than 12-HETE greater than LTC4 greater than 15-HETE greater than 11-HETE approximately 9-HETE. When the utilization of exogenous [14C]-arachidonic acid for prostanoid biosynthesis was compared to that of endogenous unlabelled arachidonate the formation of TXB2 was consistently underestimated. These results imply compartmentalization of arachidonic acid utilization in Ca2+-activated HDLC. In unstimulated cells the proportional formation of PGD2 was overestimated when exogenous arachidonic acid was substrate. After activation with A23187 the proportions of PGD2 were similar with both substrate sources. The large proportions of PGD2 and TXB2 generated by HDLC further supports the view that these eicosanoids may be important inflammatory mediators in lung tissue.

Long-term effects of dietary marine omega-3 fatty acids upon plasma and cellular lipids, platelet function, and eicosanoid formation in humans

We studied the incorporation and metabolism of eicosapentanoic (EPA) and docosahexaenoic acid in six human volunteers who supplemented their normal Western diet for 5 mo daily with 10-40 ml of cod liver oil, rich in omega-3 polyunsaturated fatty acids. EPA and docosahexaenoic acid were incorporated into the total phospholipids of plasma, platelets, and erythrocytes in a dose- and time-dependent manner. During omega-3 fatty acid ingestion serum triacylglycerols were lowered and platelet aggregation upon low doses of collagen was reduced. Concomitantly, formation and excretion of prostanoids showed a characteristic change. As measured in serum from whole clotted blood, thromboxane A3 was formed in small amounts, whereas thromboxane A2 formation was reduced to 50% of control values. Excretion of the main urinary thromboxane A metabolites was unaltered in subjects with low basal excretion rates, but decreased markedly in two subjects with high control values. As determined from the main urinary metabolite, prostaglandin I3 was formed from EPA at rates up to 50% of unaltered prostaglandin I2 formation. The biochemical and functional changes observed lasted for the entire supplementation period of 5 mo and were reversible within 12 wk after cessation of cod liver oil intake. Favorable changes induced by long-chain omega-3 fatty acids include a dose-related and sustained shift of the prostaglandin I/thromboxane A balance to a more antiaggregatory and vasodilatory state.

Leukotriene C4 production by murine mast cells: evidence of a role for extracellular leukotriene A4

The glutathione-containing leukotriene C4 (LTC4) is a major mediator of smooth muscle contraction and is released by mast cells when antigen interacts with cell-bound IgE. Antigen-stimulated mast cells undergo phospholipase activation. We report a pathway of LTC4 production by mast cells that does not require phospholipase activation but depends on the interaction of activated neutrophils with unstimulated mast cells, using as an intermediate extracellular leukotriene A4 (LTA4). The epoxide LTA4 is released by neutrophils and, together with leukotriene B4 and 5-hydroxyeicosatetraenoic acid, constitutes the major lipoxygenase metabolites found in supernatants of stimulated neutrophils. Five minutes after activation of neutrophils by calcium ionophore A23187 we measured 136 pmol of extracellular LTA4 per 10(7) neutrophils (range 40-300, n = 7) by trapping the epoxide with alcohols. Therefore, we conclude that LTA4 is not just an intracellular leukotriene precursor but is released as a lipoxygenase metabolite. LTA4 is known to be stabilized by albumin and is efficiently converted by mast cells into LTC4 even at low LTA4 concentrations. The LTA4 complexed to albumin is converted into LTC4 rapidly and completely within 10-15 min. More than 50% of the LTA4 presented to mast cells is metabolized to LTC4 at concentrations of LTA4 between 0.2 and 2 nmol of LTA4 per 10(7) mast cells. This observation establishes a potential physiologic role for extracellular LTA4. Therefore, interactions between various cell types that release or utilize LTA4 may provide an important metabolic pathway for the production of leukotrienes.

Prostaglandins, thromboxanes and leukotrienes in clinical medicine

Although prostaglandin research began about 50 years ago, many of the most important advances in understanding the biochemistry, physiology and pharmacology have taken place within the past five to ten years. There is great potential for the extension of this research to the clinical practice of medicine. At this time, the most common interaction that clinicians have with the prostaglandin field is in administering nonsteroidal anti-inflammatory drugs, which function by inhibiting prostaglandins. The uses of these drugs include treating not only inflammation, but also dysmenorrhea, some renal disease, thrombotic diseases and some metabolic disorders. Prostaglandin analogs, with their potent effects on uterine contraction, are in common use in obstetrics. Other analogs, with gastric and duodenal cytoprotective effects are useful in treating peptic ulcer disease. Future benefits from prostaglandin and leukotriene research may include new therapy for inflammatory and hypersensitivity diseases such as asthma, inflammatory bowel diseases and dermatitis.

The uncertain role of the neutrophil in increased permeability pulmonary edema

The intrapulmonic accumulation of neutrophils is a relatively common finding in certain animal models of increased permeability pulmonary edema and in humans with the adult respiratory distress syndrome. The release of toxic oxygen radicals from these cells can result in acute lung injury. Whether these cells mediate the increased permeability in all models of increased permeability pulmonary edema remains controversial. This review will examine the role of the neutrophils in various models of increased permeability pulmonary edema.

New insights into the cellular mechanisms of vasospasm

Previous attempts to define the etiology of coronary artery spasm have focused on such mechanisms as autonomic nervous system dysfunction or enhanced platelet activation leading to high levels of circulating vasoconstrictors. More recent evidence, however, suggests that the basic abnormality may be hypercontractility of the arterial wall associated with the atherosclerotic process itself. Results of both animal experiments and clinical studies support a role for certain cellular events in atherogenesis, including endothelial injury, presence of mitogenic factors and leukotrienes generated by platelets and macrophages, changes in histamine and serotonin receptor density of vascular smooth muscle and neovascularization of atherosclerotic plaque. The mechanisms postulated to underlie coronary vasospasm are discussed, relative to the clinical characteristics of vasospastic angina and the possible therapeutic implications.

Leukotriene B4 omega-hydroxylase in human polymorphonuclear leukocytes. Partial purification and identification as a cytochrome P-450

Human polymorphonuclear leukocytes (PMN) not only synthesize and respond to leukotriene B4 (LTB4), but also catabolize this mediator of inflammation rapidly and specifically by omega-oxidation. To characterize the enzyme(s) responsible for omega-oxidation of LTB4, human PMN were disrupted by sonication and subjected to differential centrifugation to yield membrane, granule, and cytosol fractions (identified by biochemical markers). LTB4 omega-hydroxylase activity was concentrated (together with NADPH cytochrome c reductase activity) only in the membrane fraction (specific activity increased 10-fold as compared to whole sonicates, 41% recovery). Negligible activity was detected in granule or cytosol fractions. LTB4 omega-hydroxylase activity in isolated PMN membranes was linear with respect to duration of incubation and protein concentration, was maximal at pH 7.4, had a Km for LTB4 of 0.6 microM, and was dependent on oxygen and on reduced pyridine nucleotides (apparent Km for NADPH = 0.5 microM; apparent Km for NADH = 223 microM). The LTB4 omega-hydroxylase was inhibited significantly by carbon monoxide, ferricytochrome c, SKF-525A, and Triton X-100, but was not affected by alpha-naphthoflavone, azide, cyanide, catalase, and superoxide dismutase. Finally, isolated PMN membranes exhibited a carbon monoxide difference spectrum with a peak at 452 nm. Thus, we have partially purified the LTB4 omega-hydroxylase in human PMN and identified the enzyme as a membrane-associated, NADPH-dependent cytochrome P-450.

Mechanisms of glucocorticoid action in pulmonary disease

This article reviews the multiple mechanisms by which glucocorticoids influence the pathophysiology of pulmonary disease. Particular emphasis is given to the influence of glucocorticoids on the release and action of mediators that promote inflammation and that modulate other pathophysiologic processes in the lung. The time course and mechanisms of action that contribute to glucocorticoid effects on pulmonary function are also discussed.

The effect of cyclooxygenase inhibition on vasomotion of proximal coronary arteries with endothelial damage

Vasomotion of the proximal branches of the left coronary artery was studied in an intact anesthetized canine preparation after injury to the endothelium of the left anterior descending branch of the left coronary artery (LAD) with a balloon angioplasty catheter. The dimensions of the left coronary artery were examined by quantitative angiography and LAD flow was measured by determining intracoronary 133Xe washout. Thirty minutes after endothelial damage alone dimensions of the LAD remained unchanged. In five dogs continued observation for a total of 120 min revealed no significant change in dimensions of the LAD. In another group of five dogs, after the administration of 5 mg/kg indomethacin there was a progressive reduction in cross-sectional area of the LAD by 60, 90, and 105 min (37%, 42%, and 50%, respectively, p less than .05). No significant change in the dimensions of the undamaged left circumflex artery was noted after the administration of indomethacin. The effect of another cyclooxygenase inhibitor (4 mg/kg meclofenamate) on endothelial damage to the LAD in an additional four dogs was also examined. Again significant reduction of the cross-sectional area of the LAD was seen at 60 and 120 min (40% and 44%, respectively, p less than .05). Heart rate and blood pressure were unchanged throughout the experiment in control and indomethacin-treated dogs. Mean blood pressure rose slightly after administration of meclofenamate (from 80 +/- 5 to 98 +/- 7 at 120 min, p less than .05). These data indicate that the combination of endothelial injury and cyclooxygenase inhibition with indomethacin or meclofenamate results in proximal coronary artery vasoconstriction.(ABSTRACT TRUNCATED AT 250 WORDS)

Accumulation of leukotriene C4 and histamine in human allergic skin reactions

To determine whether lipoxygenase products of arachidonic acid metabolism are released in vivo during human allergic cutaneous reactions, we serially assayed chamber fluid placed over denuded skin sites for the presence of both C-6 peptide leukotrienes (e.g., LTC4, LTD4, and LTE4) and leukotriene B4 (LTB4), using radioimmune assay and HPLC separation, and compared it to histamine (assayed radioenzymatically) in 13 atopic and two nonatopic volunteers. Skin chamber sites challenged with ragweed or grass pollen antigen (250-750 protein nitrogen units/ml) for the first hour and phosphate-buffered saline (PBS) for the next 3 h were assayed hourly and compared to sites challenged with PBS alone. As assessed by HPLC, LTC4 composed greater than 85% of the C-6 peptide leukotriene released at any skin site, whereas little LTD4 or LTE4 was detected. LTC4 was present in significantly greater concentrations at antigen sites as compared to PBS-challenged sites throughout the 4-h period. Minimal concentrations of LTB4 were found throughout this time period and were not different at antigen or PBS sites. Histamine was present in significantly greater concentrations at antigen rather than PBS sites, but the pattern of release was different from that of LTC4. Peak histamine release invariably occurred during the first hour and decreased progressively thereafter, whereas the greatest amounts of LTC4 were detected during the 2nd to 4th hours. The amount of LTC4 accumulating at the site was dependent upon the dosage of antigen used in the epicutaneous challenge. We have demonstrated in this study that of the leukotrienes assessed LTC4 is released in the greatest quantity in situ during in vivo allergic cutaneous reactions and that it is present at such sites for at least 4 h after antigen challenge. Since intradermal injection of LTC4 in humans induces wheal and flare responses that persist for hours, our findings support the hypothesis that LTC4 is an important mediator of human allergic skin reactions.

A presumptive role for leukotrienes in obstructive airways diseases

The likelihood that the leukotriene products derived from the 5-lipoxygenase pathway mediate aspects of obstructive airways diseases is strongly suggested by their documented capacities to effect airway spasmogenicity, airway hyperreactivity, tissue edema formation, mucus secretion, and tissue infiltration by leukocytes. That the various leukotriene components of SRS-A have unique receptors on responding tissues and are recoverable from airway surfaces in several inflammatory lung diseases and that several resident and infiltrating cell types have significant potential for leukotriene biosynthesis lend further support to their postulated pathobiologic roles. To fulfill Koch's postulates for proof of leukotrienes' etiologic role, it remains to be shown that inhibition of their biosynthesis or specific antagonism at their end-organ receptors can greatly ameliorate these disease states.

Leukotriene C4 binds to human glomerular epithelial cells and promotes their proliferation in vitro

In human and experimental glomerulonephritis, glomerular hypercellularity results both from accumulation of macrophages and proliferation of resident glomerular cells. The recent identification of macrophage-derived factors that stimulate mesangial and epithelial cell proliferation suggests that these factors might contribute to the hypercellularity. To determine the identity of such macrophage-derived growth factors, we studied the effect of leukotrienes (LTs), products that are released from macrophages and leukocytes, on proliferation of human glomerular epithelial cells in culture. Dose-dependent (1-100 nM) stimulation of [3H]thymidine incorporation, an index of cell proliferation, was observed in cells incubated with the sulfidopeptide LTs, LTC4 and LTD4, but not with LTB4. The response was 248 and 172% of control values at 100 nM LTC4 and LTD4, respectively. This effect of LTC4 was abolished by FPL 55712. Subsequent binding studies demonstrated that glomerular epithelial cells possess specific receptors for LTC4. [3H]LTC4 bound rapidly at 8 degrees C to the cells. There was a plateau after 40 min incubation. Maximum specific binding was 70-90% of total binding. Specific binding was totally reversible with addition of an excess of unlabeled LTC4. Analysis of time-course association slopes at two concentrations of [3H]LTC4 and of the competition between a single concentration of [3H]LTC4 and increasing concentrations of unlabelled LTC4 allowed calculation of dissociation constants (Kd) of 220 and 217 nM, respectively. Both LTD4 and LTE4 exhibited ED50 values that were at least one order of magnitude higher than for LTC4. Thus, our findings suggest that LTC4 binds to specific receptors of glomerular epithelial cells, promotes proliferation of these cells, and could contribute to epithelial hypercellularity found in glomerulonephritis.

Activated rat neutrophils. Correlation of arachidonate products with enzyme secretion but not with O(2)- generation

Functional responses (enzyme secretion and generation of O2-) have been studied in rat neutrophils with the use of a variety of different agonists which vary in their ability to activate neutrophils. Concomitantly, the authors have analyzed the cells for production of cyclooxygenase (PGE2, PGF2 alpha, and TXB2) and lipoxygenase (monoHETEs and LTB4) products in order to determine whether there is a correlation between functional responses and arachidonate products in stimulated neutrophils. The studies indicate that enzyme secretion is closely correlated with generation of arachidonate (cyclooxygenase as well as lipoxygenase) products. These responses are dependent on the dose of agonist employed, but there does not appear to be a unique pattern of arachidonate products that can be attributed to a specific agonist. With respect to monohydroxyeicosatetraenoic acid (monoHETE) generation, we demonstrate that stimulated rat neutrophils selectively produce 5-HETE, to the virtual exclusion of 12-HETE and 15-HETE. The production of O2- from stimulated rat neutrophils is correlated neither with enzyme secretion nor with the generation of arachidonate products. These studies suggest that enzyme secretion and O2- generation are mediated by two fundamentally different intracellular pathways, even though these functional responses probably derive from common agonist-receptor interactions on the plasma membrane.

Effects of specific nutrients on the immune response. Selected clinical applications

The importance of diet in multiple aspects of the immune response is inescapable. Although only a few trials have attempted to apply knowledge derived from in-vitro and animal data to humans, the ability to modulate or "reset" the immune response by manipulating dietary intake will surely continue to be studied in the future. The role of various nutrients in immunity is reviewed and clinical applications are noted.

Effects of LTB4 and Ca++ ionophore A23187 on the release by human alveolar macrophages of factors controlling fibroblast functions

Cultured human alveolar macrophages from smokers with lung cancer produced spontaneously variable amounts of factors stimulating fibroblast proliferation and production of prostaglandin E2 and collagenase by fibroblasts. These biological activities belong to molecules similar or identical to interleukin 1. Exogenous leukotriene B4 added to alveolar macrophage cultures increased the production of these factors. The Ca++ ionophore A23187 was found to have similar effects. By the control of monokine production, leukotriene B4 locally released by inflammatory cells may modulate lung fibroblast functions.

Inhibition of leukotriene B4 formation in human neutrophils after oral nafazatrom (Bay g 6575)

Three grams of nafazatrom (Bay g 6575), given orally to healthy male volunteers in a single dose, significantly reduce the formation of leukotriene B4 in polymorphonuclear leukocytes. LTB4 synthesis fell from 57.1 +/- 17.0 ng/10(7) PMNL, mean +/- S.D., in control to 34.3 +/- 14.4 ng/10(7) PMNL 3 hr after nafazatrom (2 P less than 0.001). In vitro, nafazatrom inhibited LTB4 formation in human PMNL in a dose dependent manner. At 1 microM nafazatrom LTB4 formation was reduced to 65% of the control value. Nafazatrom had no effect on the excretion of 2,3-dinor-6-keto-PGF1 alpha and 2,3-dinor-TXB2, the major urinary metabolites of endogenously synthesized PGI2 and TXA2, respectively. Serum levels of TXB2 in clotted whole blood also remained unchanged. The inhibitory effect of nafazatrom on leukotriene biosynthesis in human PMNL suggests a therapeutic potential of this drug in processes like allergy and chronic inflammation, where leukotrienes play a pathogenetic role.

Effect of dietary enrichment with eicosapentaenoic and docosahexaenoic acids on in vitro neutrophil and monocyte leukotriene generation and neutrophil function

The effects of dietary fish-oil fatty acids on the function of the 5-lipoxygenase pathway of peripheral-blood polymorphonuclear leukocytes and monocytes were determined in seven normal subjects who supplemented their usual diet for six weeks with daily doses of triglycerides containing 3.2 g of eicosapentaenoic acid and 2.2 g of docosahexaenoic acid. The diet increased the eicosapentaenoic acid content in neutrophils and monocytes more than sevenfold, without changing the quantities of arachidonic acid and docosahexaenoic acid. When the neutrophils were activated, the release of [3H]arachidonic acid and its labeled metabolites was reduced by a mean of 37 per cent, and the maximum generation of three products of the 5-lipoxygenase pathway was reduced by more than 48 per cent. The ionophore-induced release of [3H]arachidonic acid and its labeled metabolites from monocytes in monolayers was reduced by a mean of 39 per cent, and the generation of leukotriene B4 by 58 per cent. The adherence of neutrophils to bovine endothelial-cell monolayers pretreated with leukotriene B4 was inhibited completely, and their average chemotactic response to leukotriene B4 was inhibited by 70 per cent, as compared with values determined before the diet was begun and six weeks after its discontinuation. We conclude that diets enriched with fish-oil-derived fatty acids may have antiinflammatory effects by inhibiting the 5-lipoxygenase pathway in neutrophils and monocytes and inhibiting the leukotriene B4-mediated functions of neutrophils.

Late asthmatic responses: inquiry into mechanisms and significance

Late asthmatic responses are common, simulate a chronic phase of asthma, and are associated with an influx of inflammatory cells. The precise sequence of events leading to late inflammatory responses and increased hyperresponsiveness of the airways is uncertain, but likely begins with the triggering of mediator release from local (luminal or interstitial) mast cells or, conceivably, alveolar macrophages. Consequent influx and activation of granulocytes, including eosinophils and neutrophils, possibly T lymphocytes, basophils, and platelets, and subsequently later-arriving monocytes and macrophages, may be responsible for a continuing inflammatory reaction, airways hyperresponsiveness, and continuing active bronchial asthma. Identification of the relative importance of responsible cells and mediators will help clarify pathogenesis of bronchial asthma and should lead to a better understanding and design of therapeutic regimens and preventive measures in the management of this common and important disease.