Leukotrienes: biosynthesis, metabolism, and analysis

Role of Human 15-Lipoxygenase-2 in the Biosynthesis of the Lipoxin Intermediate, 5S,15S-diHpETE, Implicated with the Altered Positional Specificity of Human 15-Lipoxygenase-1

The oxylipins, 5S,12S-dihydroxy-6E,8Z,10E,14Z-eicosatetraenoic acid (5S,12S-diHETE) and 5S,15S-dihydroxy-6E,8Z,11Z,13E-eicosatetraenoic acid (5S,15S-diHETE), have been identified in cell exudates and have chemotactic activity toward eosinophils and neutrophils. Their biosynthesis has been proposed to occur by sequential oxidations of arachidonic acid (AA) by lipoxygenase enzymes, specifically through oxidation of AA by h5-LOX followed by h12-LOX, h15-LOX-1, or h15-LOX-2. In this work, h15-LOX-1 demonstrates altered positional specificity when reacting with 5S-HETE, producing 90% 5S,12S-diHETE, instead of 5S,15S-diHETE, with kinetics 5-fold greater than that of h12-LOX. This is consistent with previous work in which h15-LOX-1 reacts with 7S-HDHA, producing the noncanonical, DHA-derived, specialized pro-resolving mediator, 7S,14S-diHDHA. It is also determined that oxygenation of 5S-HETE by h15-LOX-2 produces 5S,15S-diHETE and its biosynthetic kcat/KM flux is 2-fold greater than that of h15-LOX-1, suggesting that h15-LOX-2 may have a greater role in lipoxin biosynthesis than previously thought. In addition, it is shown that oxygenation of 12S-HETE and 15S-HETE by h5-LOX is kinetically slow, suggesting that the first step in the in vitro biosynthesis of both 5S,12S-diHETE and 5S,15S-diHETE is the production of 5S-HETE.

Association of Delta-6-Desaturase Expression with Aggressiveness of Cancer, Diabetes Mellitus, and Multiple Sclerosis: A Narrative Review

Background: The phosphatidylinositol 3-kinase/ protein kinase B /mammalian target of rapamycin (PI3K/Akt/ mTOR) signaling regulates multiple cellular processes and organizes cell proliferation, survival, and differentiation with the available nutrients, in particular, fatty acids. Polyunsaturated fatty acids (PUFAs) are cytotoxic to cancer cells and play a critical role in the treatment of multiple sclerosis (MS) and diabetes mellitus (DM). PUFAs are produced in the body by desaturases and elongases from dietary essential fatty acids (EFAs), primarily involving delta-6-desaturase (D6D). D6D is a rate-limiting enzyme for maintaining many aspects of lipid homeostasis and normal health. D6D is important to recognize the mechanisms that regulate the expression of this enzyme in humans. A lower level of D6D was seen in breast tumors compared to normal tissues. Interestingly, the elevated serum level of D6D was seen in MS and DM, which explains the critical role of D6D in inflammatory diseases. Methods: We searched databases of PubMed, Web of Science (WOS), Google Scholar, Scopus and related studies by predefined eligibility criteria. We assessed their quality and extracted data. Results: Regarding the mTOR signaling pathway, there is remarkable contributions of many inflammatory diseases to attention to common metabolic pathways are depicted. Of course, we need to have the insights into each disorder and their pathological process. The first step in balancing the intake of EFAs is to prevent the disruption of metabolism and expression of the D6D enzyme. Conclusions: The ω6 and ω3 pathways are two major pathways in the biosynthesis of PUFAs. In both of these, D6D is a vital bifunctional enzyme desaturating linoleic acid or alpha-linolenic acid. Therefore, if ω6 and ω3 EFAs are given together in a ratio of 2: 1, the D6D expression will be down-regulated and normalized.

The Sources of Essential Fatty Acids for Allergic and Cancer Patients; a Connection with Insight into Mammalian Target of Rapamycin: A Narrative Review

Background:

Disturbance in essential fatty acids (EFA) metabolism plays a key role in autoimmune diseases, but EFA supplementation with sources of borage, evening primrose, hemp seed and fish oils was not effective in atopic and cancer diseases, as that seen in the case of multiple sclerosis. It seems that two complexes of the mammalian target of rapamycin (mTOR) signaling, mTORC1 and mTORC2, are congruent with the two bases of the Traditional Iranian Medicine (TIM) therapy, Cold and Hot nature, which are essential for the efficacy of functional oils for controlling immune responses in autoimmune diseases.

Methods:

We searched PubMed database, Web of Science (WOS), Google Scholar, Scopus and selected studies by predefined eligibility criteria. We then assessed their quality and extracted data.

Results:

The oils controlled by Cold or Hot nature may be helpful in maintaining homeostasis and preventing autoimmune diseases. In summary, studies of randomized controlled trials for allergy and cancer patients found no improvement in the signs or response to tests, despite a remarkable change in EFA fractions in the blood by supplementation with sources of borage, evening primrose, hemp seed and fish oils. In contrast, portulaca oleracea oil exhibited protective effects by anti-inflammatory properties via the PI3K/Akt/mTORC2 pathway with a deviation immune response to Th1 to treat atopic diseases and cancer.

Conclusions:

According to the concept of Traditional Iranian Medicine therapy, in contrast to Cold-nature oils, EFA supplementation with the sources of Hot-nature oilsis not suitable for the treatment of atopic and cancerous diseases.

Leukotriene B4 and Peptido-Leukotriene Levels during Radiographic Contrast Media Infusion

The pathogenic mechanisms of radiographic contrast media (CM) reactions are still not well understood. Recently it has been proposed that leukotrienes (LT) may be involved in CM reactions. We measured plasma LTB4 and peptido-LT levels in 20 subjects undergoing urography with 2 low osmolality CM (ioxaglate and iopamidol) in order to elucidate if CM infusion determines LT release in plasma. LTB4 and peptido-LT did not change significantly during infusion of the 2 CM. Blood pressure, heart rate, and the number of circulating granulocytes were not affected by CM infusions, further evidence that LT release did not occur. We conclude therefore that LT are not released during infusion with the CM studied.

Circulating leukotriene B4 identifies respiratory complications after trauma

Background. Leukotriene B4 (LTB4), a proinflammatory lipid mediator correlates well with the acute phase of Acute Respiratory Distress Syndrome (ARDS). Therefore, LTB4-levels were investigated to determine whether they might be a useful clinical marker in predicting pulmonary complications (PC) in multiply traumatized patients. Methods: Plasma levels of LTB4 were determined in 100 patients on admission (ED) and for five consecutive days (daily). Twenty healthy volunteers served as control. LTB4-levels were measured by ELISA. Thirty patients developed PC (pneumonia, respiratory failure, acute lung injury (ALI), ARDS, pulmonary embolism) and 70 had no PC (ØPC). Results. LTB4-levels in the PC-group [127.8 pg/mL, IQR: 104–200pg/ml] were significantly higher compared to the ØPC-group on admission [95.6 pg/mL, IQR: 55–143 pg/mL] or control-group [58.4 pg/mL, IQR: 36–108 pg/mL]. LTB4 continuously declined to basal levels from day 1 to 5 without differences between the groups. The cutoff to predict PC was calculated at 109.6 pg/mL (72% specificity, 67% sensitivity). LTB4 was not influenced by overall or chest injury severity, age, gender or massive transfusion. Patients with PC received mechanical ventilation for a significantly longer period of time, and had prolonged intensive care unit and overall hospital stay. Conclusion. High LTB4-levels indicate risk for PC development in multiply traumatized patients.

Platelets may inhibit leucotriene biosynthesis by human neutrophils at the integrin level

Polymorphonuclear leucocytes and blood platelets co-operate in several pathophysiological processes, and arachidonic acid (AA) metabolites produced in response to the activation of these cells are potent mediators of their functions. We studied the role of platelets in the formation of 5-lipoxygenase products from AA by autologous neutrophils, especially the chemotactic agent leucotriene (LT) B4. The formation of all products, namely 5-hydroxy-eicosatetraenoic acid (5-HETE), LTB4 and the other LTA4-derived metabolites, in response to the calcium ionophore A23187 was evaluated by high-performance liquid chromatography. All the 5-lipoxygenase products were significantly diminished by physiological concentrations of platelets. This inhibitory effect was lost when platelets were previously degranulated by thrombin in non-aggregating conditions. Peptides containing the Arg-Gly-Asp-Ser or His-His-Leu-Gly-Gly-Ala-Lys-Gln-Ala-Gly-Asp-Val sequence, which prevent the adhesion of platelets to neutrophils via the fibrinogen released from platelet granules and the integrin glycoprotein IIb/IIIa, markedly decreased the inhibitory effect of non-degranulated platelets. The production of transcellular metabolites of AA such as LTC4, the dual 5- and 12-lipoxygenase product 5,12-diHETE and lipoxins could not account for the decreased formation of 5-HETE and LTA4-derived metabolites. It is concluded that platelets may inhibit the neutrophil 5-lipoxygenase activity at the integrin level and in turn may play a role in slowing down the production of LTB4 in the course of inflammation.

The change in leukotrienes and lipoxins in activated mouse peritoneal macrophages

The aim of this study was to investigate to what extent the generation of leukotrienes (LTs) and lipoxins (LXs) was affected by the expression of definite levels of macrophage activation. We used a system of murine peritoneal macrophages at different states of activation consisting in resident macrophages and FCS-, thioglycollate- or Corynebacterium parvum-elicited macrophages. The profile of lipoxygenase metabolites in resident macrophages was characterized by the presence of high levels of 12-HETE, followed by 15-HETE, 5-HETE, LTB(4) and 6-trans-LTB(4), 6-trans-12-epi-LTB(4). A comparable pattern was also found in FCS-elicited macrophages which appeared not to be responsive to the challenge with interferon gamma plus LPS, as measured by the generation of NO and tumor necrosis factor alpha. Resident as well as FCS-elicited macrophages also generated appreciable quantities of LXs (A(4) and B(4)). Thioglycollate-elicited macrophages, which expressed a state of 'responsive' macrophages, showed a block of the LT and LX synthesis. This block was also present in C. parvum-elicited macrophages which expressed a fully 'activated' phenotype, reflected by their capacity of releasing NO and tumor necrosis factor alpha even though they were not challenged. These results provide the first evidence that the level of 'responsive' as well as 'activated' macrophages was associated with of a simultaneous block of LTB(4) and LXs.

Receptors for the 5-oxo class of eicosanoids in neutrophils

5-Hydroxy- and 5-oxo-eicosatetraenoate (5-HETE and 5-oxoETE) activate polymorphonuclear neutrophils (PMNs) through a common, receptor-like recognition system. To define this system, we examined the interaction of these eicosanoids with human PMNs. PMNs esterified 5-[3H]HETE to glycerolipids at 37 and 4 degreesC. At 37 but not 4 degreesC, the cells also hydroxylated the label to 5, 20-[3H]diHETE. The acyl:CoA synthetase blocker, triacsin C, inhibited esterification but also led to an increase in the hydroxylation of the label. PMNs processed 5-[3H]oxoETE through the same pathways but only or principally after reducing it to 5-[3H]HETE (37 or 4 degreesC). In the presence of these varying metabolic reactions, PMNs (37 or 4 degreesC; +/- triacsin C) could not be shown to receptor bind either radiolabel. Plasma membranes isolated from PMNs esterified but unlike whole cells did not reduce or hydroxylate 5-[3H]oxoETE. Triacsin C blocked esterification, thereby rendering the membranes unable to metabolize this radiolabel. Indeed, triacsin C-treated membranes bound (Kd = 3.8 nM) 5-[3H]oxoETE specifically and reversibly to 86 pmol of sites per 25 micrograms of membrane protein. 5-OxoETE, 5-HETE, and 5,15-diHETE displaced this binding at concentrations correlating with their potency in eliciting PMN Ca2+ transients. GTP and GTPgammaS, but not ATP or ATPgammaS, also reduced 5-[3H]oxoETE binding, whereas 15-HETE, leukotriene B4, platelet-activating factor, IL-8, C5a, and N-formyl-Met-Leu-Phe lacked this effect. We conclude that PMNs and their plasma membranes use an acyl:CoA synthetase-dependent route to esterify 5-HETE and 5-oxoETE into lipids. Blockade of the synthetase uncovers cryptic plasmalemma sites that bind 5-oxoETE with exquisite specificity. These sites apparently mediate responses to the 5-oxo class of eicosanoids and are likely members of the serpentine superfamily of G protein-linked receptors.

Release of leukotriene A4 versus leukotriene B4 from human polymorphonuclear leukocytes

The reactive intermediate formed by 5-lipoxygenase metabolism of arachidonic acid, leukotriene A4, is known to be released from cells and subsequently taken up by other cells for biochemical processing. The objective of this study was to determine the relative amount of leukotriene A4 synthesized by human polymorphonuclear leukocytes (PMNL) that is available for transcellular biosynthetic processes. This was accomplished by diluting cell suspensions and measuring the relative amounts of enzymatic versus nonenzymatic leukotriene A4-derived metabolites after challenge with the Ca2+ ionophore A23187. Nonenzymatic leukotriene A4-derived metabolites were used as a quantitative index of the amount of leukotriene A4 released into the extracellular milieu. The results obtained demonstrated that in human PMNL, the relative amounts of nonenzymatic versus enzymatic leukotriene A4-derived metabolites increased with decreasing cell concentrations. After a 20-fold dilution of PMNL in cell preparations, a doubling in the amount of nonenzymatic leukotriene A4-derived metabolites was observed following challenge (from 53.9 +/- 1.3 to 110.4 +/- 8.9 pmol/10(6) PMNL, p < 0.01). Reduction of possible cell-cell interactions by dilution suggested that over 50% of leukotriene A4 synthesized is released from the PMNL. These data provide evidence that, in human PMNL preparations, transfer of leukotriene A4 to neighboring PMNL is taking place, resulting in additional formation of leukotriene B4 and its omega-oxidized metabolites 20-hydroxy- and 20-carboxy-leukotriene B4. Neutrophil reuptake of extracellular leukotriene A4 leads to an underestimation of the fraction of leukotriene A4 that is in fact available for transcellular metabolism when tight cell-cell interactions occur, such as during PMNL adhesion to the microvascular endothelium and diapedesis.

Leukotriene A4, and not leukotriene B4, is the main 5-lipoxygenase metabolite released by bovine leukocytes

The production of leukotriene A4 (LTA4)-derived metabolites, analysed by RP-HPLC, was studied in purified bovine polymorphonuclear leukocyte (PMNL) preparations and in PMNL-platelet coincubations after challenge with the calcium ionophore A23187. The results obtained show that in bovine PMNL LTB4 represents the main LTA4 metabolite. When washed platelets were added to PMNL, LTC4 was the main enzymatic metabolite observed, indicating a substantial transfer of PMNL-derived LTA4 to platelets. The synthesis of LTC4 was accompanied by a significant decrease in LTB4, suggesting that a quota of the LTB4 synthesized in PMNL preparations is the result of transcellular metabolism of released LTA4 by neighbouring PMNL. Reduction of PMNL-PMNL interactions through dilution of cell incubates allowed us to estimate that most of the leukotriene A4 synthesized by PMNL is indeed released from the cell. LTA4, and not LTB4, represents the main 5-lipoxygenase metabolite released by bovine PMNL.

Alpha-linolenic acid in the treatment of rheumatoid arthritis. A double-blind, placebo-controlled and randomized study: flaxseed vs. safflower seed

In rheumatoid arthritis various pro-inflammatory metabolites of arachidonic acid (AA), such as leukotriene B4 (LTB4) and prostaglandin E2 (PGE2), contribute to tissue destruction and pain. In contrast to AA, which is an omega-6 fatty acid, the omega-3 fatty acids, after having been liberated from the cell membrane phospholipids, are further converted into the non- or anti-inflammatory eicosanoids LTB5 and PGI3. AA concentration is an important regulatory step in the synthesis of both prostanoids and leukotriens. Dietary supplementation with eicosapentaenoic acid (EPA) and docosahexaenoic acid (DHA) has therefore been used to decrease the ratio of AA to EPA or DHA to obtain beneficial clinical effects. EPA and DHA are found in animal fat and are quite expensive compared to their precursor alpha-linolenic acid (alpha-LNA) found in flaxseed oil. We, therefore, performed a placebo-controlled trial with alpha-LNA in 22 patients with rheumatoid arthritis, using a linoleic acid preparation as a placebo. After a 3-month follow-up, the treatment group showed an increased bleeding time, but the clinical, subjective (global assessment, classification of functional status, joint score index, visual analogue scale, pain tenderness score) and laboratory parameters (haemoglobin, erythrocyte sedimentation rate, C-reactive protein) did not show any statistical alterations. AA, EPA and DHA did not change either in spite of a significant increase in alpha-LNA in the treatment group. Thus, 3-month's supplementation with alpha-LNA did not prove to be beneficial in rheumatoid arthritis.

Decreased arachidonic acid metabolism in human platelets by autologous neutrophils: possible role of cell adhesion

The amount of the 12-lipoxygenase and cyclo-oxygenase products, 12(S)-hydroxy-(Z,Z,E,Z)-5,8,10,14-eicosatetraenoic acid (12-HETE) and 12(S)-hydroxy-(E,E,Z)-5,8,10-heptadecatrienoic acid (HHT), in human platelets stimulated by thrombin (0.1 and 2.5 units/ml), was studied in the presence of autologous neutrophils. A decreased formation of both products was induced by unstimulated neutrophils or neutrophils challenged with N-formylmethionyl- leucyl-phenylalanine (0.1 microM) or Ca2+ ionophore A23187 (0.15 microM). The effect of neutrophils was observed only in the presence of Ca2+. 12-HETE and HHT were also produced in platelets stimulated with thrombin in the absence of Ca2+ and/or Mg2+, but their level was not altered by neutrophils. 12(S),20-Dihydroxy-(Z,Z,E,Z)-5,8,10,14-eicosatetraenoic acid (12,20-DHETE), the cytochrome P-450 product from 12-HETE in neutrophils, was hardly detected, and its level did not compensate for the decrease in 12-HETE observed after platelet and neutrophil co-incubation. 5(S),12(S)-Dihydroxy-(E,Z,E,Z)- 6,8,10,14-eicosatetraenoic acid (5(S),12(S)-DHETE), the 5-lipoxygenase product of 12-HETE in neutrophils, was never detectable. In addition, the inhibition of 12-HETE and HHT formations appeared not to be due to degradation or thrombin uptake by neutrophils, nor was the decrease observed when the two cell populations were physically separated. A monoclonal antibody against the human platelet glycoprotein GMP140 (CD62), mediating Ca(2+)-dependent platelet-neutrophil adhesion, mimicked the inhibitory effect of neutrophils in a dose-dependent fashion. Furthermore, the 12-HETE and HHT productions were not affected when platelets were stimulated in the presence of neutrophils previously incubated with sialidase, which removes the sialic acid from a sialyl Lewis(x) structure assumed to be the neutrophil receptor for platelet GMP140. We conclude that the decrease in thrombin-stimulated 12-HETE and HHT formation observed when platelets were co-incubated with autologous neutrophils might be the consequence of platelet-neutrophil adherence, presumably through platelet GMP140.

Lipid analysis

The analysis of lipids remains at the periphery of the biotechnology arena. Methods for analysis of lipids still center around the proven methods of thin layer chromatography, gas chromatography, gas chromatography-mass spectrometry and, more recently, high performance liquid chromatography. Advances have been made recently in understanding the biological role of lipid-conjugated molecules. Encapsulation of active substances in lipids is receiving more attention in order to achieve cellular penetration.

Evidence for Kupffer cell activation by burn injury and Pseudomonas exotoxin A

Postburn metabolic and immunological alterations may in part be due to translocation of gut exotoxin and endotoxin, which can result in tumour necrosis factor (TNF) and prostaglandin E (PGE) production by macrophages. We evaluated the effect of burn injury, plus exotoxin and endotoxin on TNF-alpha and PGE production by Kupffer cells, and peritoneal macrophages. Adult Wistar rats underwent 30 per cent TBSA burn or sham burn. Kupffer cells were harvested from rat livers and peritoneal macrophages from the abdominal cavity 24 h postburn. They were cultured overnight at 1 x 10(6) cells/ml and stimulated with saline, 5 micrograms/ml of Pseud. aeruginosa Exotoxin A (Exo-A), 5 micrograms/ml of Pseud. aeruginosa Endotoxin (Endo), Exo-A + Endo, or Exo-A + Endo + the PGE derivative 16,16 dimethyl-PGE (dPGE) (10 micrograms/ml). The supernatants were harvested after 4, 24 and 48 h of culture and assayed for TNF-alpha and PGE. Results showed that burn injury induced an increase in TNF-alpha and PGE production by Kupffer cells stimulated with Exo-A, Endo, and both Exo-A + Endo (P < 0.05). The release of TNF-alpha by Kupffer cells was downregulated by exogenous PGE (P < 0.05). The increased TNF-alpha production was inversely related to PGE levels. In conclusion, both burn injury and Exo-A potentiate the responsiveness of Kupffer cells and peritoneal macrophages to endotoxin as measured by the rate of production of TNF-alpha and PGE. PGE may locally downregulate the immune response by limiting Kupffer cells' and peritoneal macrophages' TNF-alpha production.

New isoflavonoids as inhibitors of porcine 5-lipoxygenase

The inhibitory activity of new isoflavonoids on 5-lipoxygenase of porcine leukocytes was investigated. Isoflavans (I) proved to be stronger inhibitors than isoflavones (II). The isoflavans containing ortho-hydroxy groups in ring A showed the lowest Ki values (0.8-50 microM). In comparison, isoflavans with meta-dihydroxy groups exhibited Ki values higher than 150 microM. The effect of commercial antioxidants was tested also on porcine 5-lipoxygenase. Butylated hydroxyanisole (Ki: 25 microM) and butylated hydroxytoluene (Ki: 55 microM) revealed moderate inhibitory activity, whereas L-ascorbic acid, L-ascorbyl palmitate, dl-alpha-tocopherol and n-propyl gallate showed weak inhibitory activities (Ki: 100-260 microM).

Influence of labor and oxytocin on in vitro leukotriene release by human fetal membranes and uterine decidua at term gestation

OBJECTIVE

The purpose of this study was to determine whether labor and oxytocin influence in vitro leukotriene release by human fetal membranes and uterine decidua at term gestation.

STUDY DESIGN

All women (N = 21) were studied in an academic clinical research environment. They were delivered either vaginally or before labor by cesarean section. Tissues were incubated with calcium ionophore A23187 alone or with calcium ionophore A23187 after preincubation with either oxytocin, BW755c, or cycloheximide. Leukotrienes in culture medium were determined by high-performance liquid chromatography. Statistical analysis was performed with analysis of variance.

RESULTS

Tissues obtained after vaginal delivery released significantly higher (p less than 0.05) quantities of leukotrienes LTB4, LTD4, and delta-6-trans-LTB4 than did tissues obtained during cesarean section. Leukotriene release was stimulated by oxytocin and was inhibited by both BW755c and cycloheximide.

CONCLUSION

These results suggest an activation of the arachidonate lipoxygenase pathway in these tissues during labor. Oxytocin could play a regulatory role in this process.

Reduced neutrophil LTB4 release in atopic dermatitis patients despite normal fatty acid composition

Propositions about an abnormal fatty acid metabolism in atopic dermatitis patients prompted us to compare the phospholipid fatty acid composition and LTB4 release of neutrophils from 15 atopic dermatitis patients, as well as the adipose tissue triglyceride fatty acid composition, to that of 15 healthy controls matched by age, gender, and smoking habits. We found no differences in the tissue fatty acid composition between the two groups. The release of leukotriene B4 from Ca-ionophore-stimulated neutrophils in patients was on the average only 42% (p less than 0.001) of that measured in the control group, despite the very similar arachidonic acid contents of these cells. Our study does not support the assumption of an abnormal fatty acid desaturation in atopic dermatitis patients. Rather, the capacity to release and/or convert arachidonic acid into leukotrienes in neutrophils appears to be affected by this disease.

Biosynthesis and biological activity of leukotriene B4

The leukotrienes are a family of biologically active molecules derived from arachidonic acid. While prostaglandins and thromboxanes are products of the cyclooxygenase pathway of arachidonic acid metabolism, the leukotrienes are formed by arachidonate 5-lipoxygenase, an enzyme present in phagocytes, mast cells, and basophils. Inflammatory stimuli, such as chemotactic peptides, platelet-activating factor, phagocytic particles, and immunological stimuli, which activate phagocytes and mast cells, stimulate leukotriene synthesis. Leukotriene B4, a dihydroxy derivative of arachidonic acid, has a unique stimulatory activity on important functional responses of phagocytes; leukotriene B4 exerts chemotactic and chemokinetic activity towards phagocytes in vitro and in vivo, and it is a putative mediator of inflammation.

Inhibitory effects of MK-886 on arachidonic acid metabolism in human phagocytes

1. We have investigated the inhibitory activity of compound MK-886 (formerly L-663,536), an indole derivative, on 5-lipoxygenase product synthesis in various human phagocytes stimulated with either the ionophore A23187, in the presence and absence of exogenous arachidonic acid, or platelet-activating factor (PAF). The lipoxygenase products were analysed by reversed-phase h.p.l.c. 2. MK-886 inhibited the formation of 5-hydroxy-eicosatetraenoic acid (5-HETE), leukotriene B4 (LTB4), its omega-oxidation products and 6-trans-isomers with an IC50 value of 10-14 nM in A23187-stimulated neutrophils. In the same system, nordihydroguaiaretic acid (NDGA), AA-861 and L-655,240 showed IC50 values of 250-510, 110-420 nM and 1.7-3.9 microM, respectively. 3. MK-886 inhibited 5-lipoxygenase product synthesis in A23187-stimulated blood eosinophils and monocytes, and in neutrophils primed with granulocyte-macrophage colony-stimulating factor and stimulated with PAF with IC50 values of 1-13 nM. 4. The inhibitory activity of MK-886 was not reversed by addition of 10 microM arachidonic acid to A23187-stimulated neutrophils. 5. Compound MK-886 had no effect on 15-lipoxygenase product synthesis in blood eosinophils and neutrophils up to a concentration of 1 microM. 6. At 100 nM compound MK-886 had no significant effects on calcium ion mobilization, superoxide anion production and actin polymerization in neutrophils. 7. In conclusion, MK-886 is a very potent and specific inhibitor of both LTB4 and LTC4 synthesis in various types of human phagocytes.

Release of arachidonic acid metabolites during acute pancreatitis in pigs

The pancreatic release of arachidonic acid metabolites was studied in a porcine model of acute pancreatitis. In situ isolation of the pancreatic gland enabled selective collection of pancreatic venous blood, pancreatic lymph, and ascites fluid. Three experimental groups were studied: 1) control (n = 9); 2) hemorrhagic pancreatitis induced by injection of 5% bile salt (sodium taurocholate) into the pancreatic duct (n = 10); and 3) edematous pancreatitis induced by injection of free fatty acid (FFA) into the pancreatic artery (n = 10). Determinations of cyclooxygenase metabolites were performed by radioimmunoassay; lipoxygenase metabolites (LTC4, LTD4) were measured by radioimmunoassay after purification by high-performance liquid chromatography. Prostaglandin (PG)F1 alpha, thromboxane B2, and PGF2 alpha concentrations were almost doubled in the lymph of the FFA group during pancreatitis, as were PGF1 alpha levels in pancreatic venous blood. However, concentrations of cyclooxygenase metabolites remained unchanged in the control group and in the bile salt group. Concentrations of LTC4 and LTD4 in lymph and ascites fluid of both pancreatitis groups increased from about 50 pg/ml to a mean level of 600 pg/ml at 6 h. Leukotriene concentrations in the control group were consistently below 50 pg/ml. The results of this study indicate that above all LTC4 and LTD4 are released from the organ and that these arachidonic acid metabolites may be also involved in the events following acute pancreatitis contributing to the systemic effects of the disease.

Release of 15-hydroxyeicosatetraenoic acid (15-HETE) and prostaglandin E2 (PGE2) by cultured human bronchial epithelial cells

Human bronchial epithelial cells were isolated from macroscopically normal bronchi obtained from lobectomy specimens. Cells were grown in nutrient F12 medium, and after the third or fourth subculture they were stimulated with arachidonic acid, histamine, leukotrienes (LT) C4, D4, or E4, prostaglandin (PG) D2, anti-IgE, acetylcholine, bradykinin, or phorbol myristate acetate (PMA). Neither mast cell mediators (i.e., histamine, LTC4, LTD4, LTE4, or PGD2) nor anti-IgE stimulated the release of arachidonic acid metabolites from the epithelial cells. However, arachidonic acid, acetylcholine, bradykinin, and PMA stimulated the release of 15-hydroxyeicosatetraenoic acid (15-HETE) as major and prostaglandin E2 (PGE2) as minor products. The maximal release of 15-HETE and PGE2 occurred in 1 h with arachidonic acid stimulation and in 2 h with other stimuli. Arachidonic acid at 30 microM caused the release of 258 +/- 76 ng and 29 +/- 15 ng (n = 12) of 15-HETE and PGE2, respectively, from 10 x 10(6) epithelial cells, whereas acetylcholine, bradykinin, or PMA caused the release of approximately 2- to 10-fold less 15-HETE and PGE2. These results demonstrate that human bronchial epithelial cells selectively generate 15-HETE as the predominant arachidonic acid product and PGE2 as a minor metabolite. The role of bronchial epithelial cells and their mediators in the pathogenesis of bronchial hyperresponsiveness needs further study.

In vitro ovulation, prostaglandin synthesis, and proteolysis in isolated ovarian components of yellow perch (Perca flavescens): effects of 17 alpha,20 beta-dihydroxy-4-pregnen-3-one and phorbol ester

The present study investigated the effects of 17 alpha,20 beta-dihydroxy-4-pregnen-3-one (17,20 B-P) on (1) ovulation of isolated perch follicles in which the extrafollicular (EF) ovarian tissue had been removed; (2) prostaglandin F (PGF) and prostaglandin E (PGE) synthesis in EF tissue and intact (= follicles attached to EF tissue) and isolated follicles by radioimmunoassay and [14C]arachidonic acid incorporation; and (3) proteolysis in EF tissue and intact and isolated follicles by substrate sodium dodecyl sulfate-polyacrylamide gel electrophoresis. In addition, the ovulatory and proteolytic effects of the phorbol ester, phorbol-12-myristate-13-acetate (PMA), and the calcium ionophore A23187 on 17,20B-P-stimulated follicles were also studied in the presence/absence of indomethacin (IM) and nordihydroguaiaretic acid (NDGA). Ultrastructural analyses revealed that the preparation of isolated follicles also removed the surface epithelium of the follicle. While 17,20B-P stimulated ovulation and an increase in PGF and PGE in incubates of intact perch follicles, it did not in incubates of isolated follicles. In contrast, PMA, A23187, and a combination of PMA and A23187 stimulated ovulation of these isolated follicles. PMA/A23187-induced ovulation could be blocked by NDGA but not IM, and two hydroxyeicosatetraenoic acids (11- and 15-HETEs) were capable of partially reversing the NDGA block. Incorporations with [14C]arachidonic acid revealed that the EF tissue had a significant potential to produce PGF; however, 17,20B-P did not stimulate an increase in PGF or PGE (measured by RIA) in incubates of EF tissue alone. In addition, neither ovulation nor an increase in prostaglandins was observed in cocultures of isolated follicles and EF tissue. One major protease (66 kDa) was observed in the medium during incubation of intact and isolated perch follicles. No protease activity was present in incubates of EF tissue alone. Protease activity in 17,20B-P-stimulated incubates of intact tissue was significantly higher than in steroid-stimulated incubates of isolated follicles. Protease activity increased in the medium during incubation with PMA or a combination of PMA and A23187. This activity was blocked by NDGA but not IM. The NDGA block was partially reversed by 11-HETE. The combined results suggest that there is an interaction of EF tissue and follicle that is necessary, particularly for the stimulation of ovulation and prostaglandin production. Further, the results with phorbol esters and NDGA suggest that the follicular control of ovulation in perch may involve protein kinase C acting through the production of a lipoxygenase product.

On the relationship between leukotriene and lipoxin production by human neutrophils: evidence for differential metabolism of 15-HETE and 5-HETE

Lipoxygenase (LO) products generated by human PMN were examined utilizing a gradient-HPLC and rapid spectral detector which permitted continuous UV-spectral monitoring of leukotrienes, lipoxins and related oxygenated products of arachidonic acid. When exposed to the ionophore A23187, PMN generated LTB4 and its omega-oxidation products as well as LXA4, LXB4, and 7-cis-11-trans-LXA4 from endogenous sources. Addition of 15-HETE changed the profile of products generated by activated PMN and led to a time- and dose-dependent increase in lipoxins and related compounds while the production of LTB4 and its omega-oxidation products was inhibited. Results of time-course and radiolabel studies revealed that 15-HETE is rapidly transformed within 15 s to 5,15-DHETE and conjugated tetraene-containing products, and that the inhibition of leukotriene formation followed a similar time-course. In contrast, PMN did not generate either lipoxins or related products from 5-[3H]HETE, nor did 5-HETE block leukotriene formation. Stimulated PMN generated 5,15-DHETE from exogenous 5-HETE, while in the absence of ionophore, 5-HETE was transformed to 5,20-HETE. These results indicate that PMN can generate lipoxins and related products from endogenous sources and that 15-HETE and 5-HETE are transformed by different routes.

Arachidonic acid-induced mobilization of calcium in human neutrophils: evidence for a multicomponent mechanism of action

1. The mechanism(s) involved in the mobilization of calcium induced by arachidonic acid in human neutrophils was investigated. 2. The addition of arachidonic acid to a suspension of human neutrophils led to a time- and concentration-dependent mobilization of calcium which was the result of two separate and experimentally differentiable processes. The latter consisted of a rapid and transient phase followed by a slower and more sustained response. 3. The initial phase of calcium mobilization elicited by arachidonic acid was decreased in the presence of EGTA, inhibited by pertussis toxin as well as by nordihydroguaiaretic acid (NDGA), and diminished following a pre-incubation with leukotriene B4, but not platelet-activating factor. 4. The characteristics of the first phase of the mobilization of calcium were consistent with an interaction of the fatty acid with the leukotriene B4 receptors, either directly or indirectly following the synthesis of leukotriene B4, as well as with a release of internal calcium. 5. The second, slower and more sustained phase of calcium mobilization was more apparent at high concentrations (greater than or equal to 8-16 microM) of arachidonic acid, and was relatively insensitive to pertussis toxin, EGTA or NDGA. 6. The characteristics of the 'slow' phase of calcium mobilization by arachidonic acid are consistent with its being associated primarily with a release of calcium from internal storage pools. 7. The data presented indicate that the mechanism of mobilization of calcium by arachidonic acid in human neutrophils is complex and involves specific activation pathways employed, in part at least, by other neutrophil agonists. These findings may have relevance to various inflammatory situations in which the elevated levels of extracellular arachidonic acid known to be present could modulate the functional responsiveness of the neutrophils to other stimuli.

Synthesis of leukotriene B and other conjugated triene lipoxygenase products by blood cells of the rainbow trout, Salmo gairdneri

Stimulation of whole blood from rainbow trout with the calcium ionophore, A23187 (20 microM), produced leukotrienes B4 and B5 at concentrations in the range 22-30 ng.ml-1 and 8-24 ng.ml-1, respectively. Their identification and quantification was achieved using reverse-phase high-performance liquid chromatography, combined capillary column gas chromatography-electron capture chemical ionization mass spectrometry and ultraviolet spectroscopy. A number of other lipoxygenase products were also detected, but only partially analysed. The fatty acid composition of the leucocytes, which are presumed to be the site of leukotriene synthesis, was determined by thin-layer and gas-liquid chromatography to enable a comparison of the relative levels of the polyunsaturated fatty acids, which act as substrates for the synthesis of these lipoxygenase products. Arachidonic (20:4(n - 6)), eicosapentaenoic (20:5(n - 3)) and docosahexaenoic (22:6(n - 3)) acids represented approx. 6, 5 and 40%, respectively, of the total fatty acid content.

The release of tumor necrosis factor from endotoxin-stimulated rat Kupffer cells is regulated by prostaglandin E2 and dexamethasone

Evidence is presented that upon stimulation with endotoxin (lipopolysaccharide, LPS), Kupffer cells, the body's largest pool of sessile macrophages, synthesize and liberate a factor whose immunological, cytotoxic and chemical properties are those described for tumor necrosis factor (TNF)-alpha. Hepatocytes and sinusoidal endothelial cells do not produce detectable amounts of this protein. Ten nanograms of LPS per ml medium are sufficient to stimulate a substantial release of this mediator. Recombinant interferon-gamma (rIFN gamma) per se is a poor inducer of TNF release. Costimulation with endotoxin and rIFN gamma shows only a slight increment in the release of this cytotoxic factor, relative to LPS alone. Exposure of Kupffer cells to the Ca2+ ionophore A23187 or to elicitors of the oxidative burst and superoxide production, e.g. zymosan or phorbol 12-myristate 13-acetate, stimulates only a fraction (20%) of the TNF release seen after endotoxin challenge. Prostaglandin E2, the synthesis of which is strongly enhanced after challenge of rat Kupffer cells with LPS, suppresses the release of TNF by these cells. This autoregulatory mechanism may explain the kinetics of TNF production by stimulated Kupffer cells. Dexamethasone is another important mediator capable of reducing the LPS-elicited TNF formation. An effect of the glucocorticoid hormone can still be provoked if it is added simultaneously with or shortly after LPS. This rapid action requires a mechanism that is different from the time-consuming one leading to the inhibition of prostaglandin synthesis in Kupffer cells.

HPLC studies on leukotriene A4 obtained from the hydrolysis of its methyl ester

Alkaline hydrolysis of leukotriene A4 methyl ester to leukotriene A4 was studied in either methanol or acetone. Hydrolysis in acetone yielded larger amounts of leukotriene A4 than similar hydrolysis in methanol. The maximum amount was obtained 60 minutes after the beginning of the hydrolysis. Leukotriene A4, as well as leukotriene B4 methoxy isomers were obtained from hydrolysis of leukotriene A4 methyl ester in methanol. It was found that initial leukotriene A4 methyl ester concentration affected the amount of LTA4 produced during the hydrolysis. The maximum concentration of leukotriene A4 was obtained by hydrolyzing solutions of 0.25 mg/ml leukotriene methyl ester in acetone. Spontaneous degradation of leukotriene A4 occurred when it was diluted with tris buffer. Addition of bovine serum albumin to the tris buffer significantly prolonged the half life of leukotriene A4.

Effects of antirheumatic drugs on leukotriene B4 and prostanoid synthesis in human polymorphonuclear leukocytes in vitro

The effects of D-penicillamine, sodium aurothiomalate, indomethacin, timegadine and tolfenamic acid on the lipoxygenase and cyclo-oxygenase pathways of arachidonic acid metabolism were studied in human polymorphonuclear leukocytes (PMNs) in vitro. In short-term incubations, D-penicillamine and aurothiomalate did not affect leukotriene B4 (LTB4), prostaglandin E2 (PGE2) or thromboxane B2 (TXB2) production. Each of the three non-steroidal anti-inflammatory drugs (NSAIDs) used were potent inhibitors of prostanoid synthesis. In higher concentrations they also reduced LTB4 production; timegadine and tolfenamic acid were effective in concentrations comparable to those measured in plasma during drug therapy, whereas indomethacin was needed in ten times higher concentrations. The different effects of NSAIDs on 5-lipoxygenase activity may be of importance in their therapeutic actions as well as in the appearance of some side-effects, e.g. gastric irritation and "aspirin-induced" asthma.

Rearrangement of 5S, 12S-dihydroxy-6,8,10,14-(E,Z,E,Z)-eicosatetraenoic acid during gas chromatography: formation of a cyclohexadiene derivative

The 5S, 12S-dihydroxy-6,8,10,14-(E,Z,E,Z,)-eicosatetraenoic acid, a product of double dioxygenation of arachidonic acid by lipoxygenases, undergoes severe decomposition during gas chromatography-mass spectrometric (GC-MS) analysis of the trimethylsilyl ether methyl ester derivative. The decomposition product was studied by GC-MS and identified as a cyclohexadiene derivative of the parent compound formed by ring closure at C6 and C11. Under identical GC conditions, two stereoisomers, i.e. 5S,12R-dihydroxy-6,8,10,14-(Z,E,E,Z)-eicosatetraenoic acid (leukotriene B4), and 6-trans-leukotriene B4 showed excellent chromatographic properties. These data indicated that the 5,12-dihydroxy derivative of arachidonic acid carrying the trans-cis-trans triene unit selectively undergoes cyclization during GC. These studies also provided an explanation to the controversial GC-MS data reported for this lipoxygenase product.

Release of leukotrienes and histamine by the isolated anaphylactic heart

The purpose of this study was to demonstrate the ability of heart tissue to release the mediators of anaphylaxis after antigenic challenges. Guinea pigs were sensitized with ovalbumin. Hearts were excised, perfused in a langendorff apparatus, and challenged with a bolus injection of ovalbumin. Analysis of the perfusates demonstrated the presence of histamine as determined by radioenzymatic assay. Histamine release was observed to be maximum after 2 min (8 +/- 1 nmol) of perfusion, then decreased to baseline level. The heart also released LTB4, LTC4, LTD4, and LTE4 as determined by high performance liquid chromatography and bioassays. The release of LTC4 occurred rapidly, reaching maximum after 2 min (4.2 +/- 1 pmol) and then returned to baseline level. Although the release of LTD4 paralleled the release of LTC4, it reached a maximum after 5 min (7.7 +/- 2 pmol). LTE4 was detected after 10 min and was undetectable after 15 min. Maximum release of LTB4 was observed after 5-10 min (15 +/- 3 pmol) and was no longer detectable after 15 min. These results indicate that the isolated sensitized heart undergoing antigenic challenge releases leukotrienes and histamine suggesting the cardiac anaphylaxis might occur by the locally released mediators.

Modulation of rat polymorphonuclear leukocyte 5-lipoxygenase activity by 5-HPETE and NADH-dependent flavin inhibition

The effect of nicotinamide and flavin coenzymes on the 5-lipoxygenase activity has been determined in cell-free extracts from rat polymorphonuclear leukocytes. 5-lipoxygenase was assayed in the presence of 5-hydroperoxyeicosatetraenoic acid (5-HPETE), which caused a 3 to 4-fold stimulation in the maximal conversion of radiolabeled arachidonic acid to 5-hydroxyeicosatetraenoic acid (5-HETE) and 5,12-dihydroxyeicosatetraenoic acid (5,12-di-HETE). Addition of FMN or FAD to the assay mixture had little effect on the 5-lipoxygenase activity and caused inhibition only at high concentrations (IC50 greater than 100 microM). NADH markedly potentiated the inhibition of lipoxygenase by flavins with a 100-fold decrease in the FMN concentration required to inhibit the enzyme (IC50 approximately equal to 2 microM). Similar effects were observed for FAD although this flavin derivative was slightly less potent than FMN (IC50 congruent to 10 microM). NADH could be substituted by NADPH but not by NAD or NADP, indicating that the inhibition was not due to the production of the oxidized forms of these co-factors. These results show that the 5-lipoxygenase activity is stimulated by 5-HPETE and inhibited by flavin-dependent redox transformations.