Behavioral discrimination and olfactory bulb encoding of odor plume intermittency

In order to survive, animals often need to navigate a complex odor landscape where odors can exist in airborne plumes. Several odor plume properties change with distance from the odor source, providing potential navigational cues to searching animals. Here, we focus on odor intermittency, a temporal odor plume property that measures the fraction of time odor is above a threshold at a given point within the plume and decreases with increasing distance from the odor source. We sought to determine if mice can use changes in intermittency to locate an odor source. To do so, we trained mice on an intermittency discrimination task. We establish that mice can discriminate odor plume samples of low and high intermittency and that the neural responses in the olfactory bulb can account for task performance and support intermittency encoding. Modulation of sniffing, a behavioral parameter that is highly dynamic during odor-guided navigation, affects both behavioral outcome on the intermittency discrimination task and neural representation of intermittency. Together, this work demonstrates that intermittency is an odor plume property that can inform olfactory search and more broadly supports the notion that mammalian odor-based navigation can be guided by temporal odor plume properties.

Incremental value of cardiovascular magnetic resonance imaging in family screening for hypertrophic cardiomyopathy

Funding Acknowledgements

Type of funding sources: None.

Genetic testing in relatives of hypertrophic cardiomyopathy (HCM) patients can lead to early identification of carriers of pathogenic DNA variants (G+), before onset of left ventricular hypertrophy (LVH). Repeated evaluation by electrocardiography (ECG) and transthoracic echocardiography (TTE) is recommended to detect HCM during follow-up. Cardiovascular magnetic resonance (CMR) imaging has become valuable in the work-up of HCM, although its role in G+ subjects has not been extensively evaluated. In this study, we investigated the value of CMR in the G+/LVH- population.

We included 55 G+ subjects who underwent CMR in addition to ECG and TTE, with a maximal wall thickness (MWT) <15mm on TTE. The CMR imaging protocol consisted at least of steady state free procession imaging and 2-dimensional late gadolinium enhancement (LGE) images. ECGs were considered abnormal in case of pathologic Q waves, T wave inversion or signs of LVH (by voltage criteria including Sokolow-Lyon and a Romhilt-Estes score ≥4). TTEs were abnormal in case of LVH (defined as MWT≥10mm). For both modalities, the diagnosis of HCM was based on a MWT≥13mm. The yield of CMR relative to ECG/TTE was assessed by comparing the proportion of HCM diagnoses and the presence of other phenotypic features. Forward step logistic regression was used to assess whether the presence of TTE/ECG abnormalities could predict reclassifications or abnormalities (crypts and LGE) on CMR.

An overview of ECG/TTE and CMR findings is shown in the Figure. Two of 16 (13%) subjects diagnosed with HCM on TTE were reclassified as having no HCM on CMR, and 8 of 39 (21%) subjects without HCM on TTE were reclassified as HCM on CMR. These 8 subjects had a mean MWT of 15.4 ± 2.6 mm on CMR and a mean MWT difference of 4.5 ± 2.9 mm (range 1.7-9.4) compared to TTE, which in 3 cases was explained by a hook-shaped thickening of the basal anterior wall in the 2 chamber view, not visible on TTE. Compared to subjects without HCM on both modalities, the reclassified group had a significantly higher QRS duration (104 ± 14 vs 93 ± 11 ms, p = 0.03) and anterior mitral valve leaflet length (30 ± 4 vs 26 ± 3 mm, p = 0.01). Of the 13 subjects with normal ECG/TTE results, none were reclassified as HCM using CMR.

The proportion of additional CMR abnormalities was large in subjects with and without abnormal ECG/TTE results (57% vs 38%, p = 0.24). Subjects with poor TTE image quality were equally likely to be reclassified compared to those with sufficient image quality (10% vs 24%, p = 0.19). Logistic regression demonstrated that the presence of TTE/ECG abnormalities (odds ratio [OR] 8.7 [1.3-59.0], p = 0.03) and age (OR 1.1 [1.0-1.2], p < 0.01) independently predicted reclassifications or presence of abnormalities using CMR.

Additional CMR imaging reclassifies 18% of subjects. Subjects with normal ECG and TTE results are not diagnosed as HCM on CMR, but the prevalence of HCM-related abnormalities on CMR was high in subjects with and without ECG/TTE abnormalities.

Abstract Figure. Diagnostic approach and CMR findings

Differences in left ventricular mass and morphology and right ventricular function differentiate phenotype-negative sarcomere gene mutation carriers from healthy volunteers

Funding Acknowledgements

Type of funding sources: None.

Carriers of pathogenic DNA variants (G+) causing hypertrophic cardiomyopathy (HCM) can be identified by genetic testing, before manifestation of left ventricular hypertrophy (LVH). These G+/LVH- subjects are routinely monitored for phenotypic expression, which, alongside LVH, can include other HCM-related abnormalities, including crypts and myocardial fibrosis. Cardiovascular magnetic resonance (CMR) imaging has emerged as a valuable technique in diagnosing and follow-up of HCM. In this study, we identified clinical features of subclinical HCM in a G+/LVH- population compared to healthy subjects.

We studied 33 G+ subjects with CMR and a maximal wall thickness (MWT) <13mm, and compared them to an age- and gender-matched group of 35 healthy controls  (44 ± 14 vs 48 ± 10 y, p = 0.17; 11 (33%) vs 12 (34%) men, p = 0.93). The CMR imaging protocol consisted of 1) steady state free procession cine imaging, 2) 2-dimensional late gadolinium enhancement (LGE) images in the G+ patients and 3) pre-contrast T1 mapping using a modified look-locker inverse recovery sequence. We assessed CMR examinations for features of HCM. Forward logistic regression analysis was performed to determine which of the CMR characteristics were predictive of G+ status.

G+ subjects had a higher MWT (10.9 ± 1.6 vs 10.2 ± 1.3 mm, p = 0.04), a similar interventricular septal wall (IVS) thickness (8.8 ± 1.6 vs 8.7 ± 1.6 mm, p = 0.85), a smaller posterior wall (PW) and a higher IVS/PW ratio (6.6 ± 1.2 vs 7.7 ± 1.3mm, p < 0.001; 1.4 ± 0.3 vs 1.1 ± 0.2, p = 0.001). Indexed left ventricular (LV) mass was significantly lower in the G+ group (Table). LV function was similar (63 ± 6 vs. 61 ± 5%, p = 0.12), but right ventricular (RV) function was higher in the G+ group. They often had a characteristic hook-shaped thickening of the basal anterior wall (7 (21%) vs 0, p < 0.004; Figure) and  more frequently exhibited myocardial crypts. Midwall LGE was present in 3 (9%) G+ subjects. Native septal T1 values were elevated in G+ patients compared to controls, although mostly within the normal range (986 ± 31 vs 963 ± 28 ms, p < 0.01). Crypts, indexed LV mass and RV ejection fraction were significant predictors of G+ status in logistic regression analysis (Table).

CMR demonstrates significant morphological differences between the G+/LVH- population and healthy controls. Further studies are needed to assess the prognostic significance of these morphological features.

Predictors of genotype-positive status Variables G+ subjects (n = 33) Controls (n = 35) P value OR for G+ status P value Left ventricular mass/BSA (g/m²) 45 ± 7.4 53 ± 7.9 <0.001 0.86 [0.78-0.95] 0.003 Right ventricular ejection fraction (%) 58 ± 6 53 ± 4 <0.001 1.15 [1.00-1.32] 0.047 Crypts 17 (55%) 4 (11%) <0.001 9.62 [1.93-48.00] 0.006 G+: genotype-positive, OR: odds ratio Abstract Figure. CMR findings

Validation of an Ultrasensitive and Specific Immunofluorometric Assay for Mouse Follicle-Stimulating Hormone1

Sensitive and specific measurement of FSH is critical to research in reproductive biology, and the increasing availability of transgenic mouse models has created a need for a robust, sensitive, and specific mouse (m) FSH assay. The present study evaluated a time-resolved immunofluorometric assay (IFMA) for mFSH using monoclonal antibody to human (h) FSHbeta as a capture antibody and a biotinylated polyclonal antibody to rat alpha subunit as a detection probe, with signaling amplified by europium-labeled streptavidin. The mFSH IFMA lowered the detection limit 34-fold (5 vs. 170 pg/sample) compared with standard mFSH RIA. The mFSH IFMA demonstrated parallelism of response to dilutions of castrated mouse serum and rat FSH but no cross-reactivity with hFSH and mLH or hLH, whereas the RIA demonstrated nonparallel cross-reactivity with hFSH. The IFMA has a wide analytical range, with a good precision profile for within- and between-assay reproducibility. Because the IFMA is a sandwich-type assay with strict dimer-specificity by design, the lower readings and recovery obtained were compared with the RIA when both assays used a pituitary-purified mFSH assay standard that contained isolated or fragmented subunits as well as intact dimeric FSH. When used with mouse serum sample, the mFSH IFMA demonstrated the expected increases following orchidectomy as well as markedly enhanced sensitivity to very low levels of endogenous mFSH in gonadotropin-deficient mice. Furthermore, the IFMA measured mFSH with fidelity in both intact and orchidectomized male mice without any interference from transgenic hFSH. The greatly enhanced sensitivity, specificity, and technical convenience of this mFSH IFMA will allow wider application of FSH measurements to very small blood samples in immature and mature mice as well as transgenic models.

Lack of increased numbers of low-density eosinophils in the circulation of asthmatic individuals

The density distribution pattern of eosinophils over discontinuous isotonic Percoll gradients from the blood of normal, asymptomatic allergic and non-allergic asthmatic individuals was investigated. There was a completely identical distribution pattern between the investigated groups. Analysis of the expression of surface markers for complement receptors CR1 and CR3 and immunoglobulin G receptor on eosinophils derived from the density bands 1.080, 1.085 and 1.090 g/ml supported this finding since they did not reveal differences in expression between the bands within one group but also not between the three groups. Eosinophils of the various density bands were further purified and stimulated in vitro to produce leukotriene C4 (LTC4) by the calcium ionophore A23187 or serum treated zymosan. Equal amounts of LTC4 were synthesized by the eosinophils of the various density bands within one group. However, it appeared that the eosinophils of all density bands of allergic and non-allergic asthmatics synthesized significantly more LTC4 than the eosinophils from normal individuals (five- to tenfold). Probably this indicates in vivo priming of the eosinophils in asthmatic individuals which is not reflected by a change in density. Control experiments, dealing with possible artifacts due to the isolation procedure or the patient selection, to find differences in distribution patterns over discontinuous Percoll density gradients of the eosinophils of asthmatic compared to normal individuals failed to show such a difference. Therefore, the density distribution pattern of eosinophils over these gradients does not reflect cell activation, whereas LTC4 formation clearly does. This could mean that LTC4 formation is a more sensitive parameter for cell activation than density distribution or cell surface marker expression.

12-Lipoxygenase from rat basophilic leukemia cells, an oxygenase with leukotriene A4-synthase activity

Rat basophilic leukemia cells exhibit 12-lipoxygenase activity only upon cell disruption. 12-Lipoxygenase may also possess 15-lipoxygenase activity, as is indicated by the formation of low amounts of 15(S)-HETE, in addition to the predominant product 12(S)-HETE, upon incubation of partially purified 12-lipoxygenase with arachidonic acid. With 5(S)-HPETE as substrate not only 5(S), 12(S)-diHETE and 5(S), 15(S)-diHETE are formed, but also LTA4, as was indicated by the presence of LTA4-derived LTB4-isomers. 12-Lipoxygenase from rat basophilic leukemia cells has many features in common with 12-lipoxygenase from bovine leukocytes. As was suggested for the latter enzyme, 12-lipoxygenase from rat basophilic leukemia cells may represent the remaining LTA4-synthase activity of 5-lipoxygenase, of which the 5-dioxygenase activity has disappeared upon cell disruption. Such a possible shift from 5-lipoxygenase activity to 12-lipoxygenase activity could not simply be induced by interaction of cytosolic 5-lipoxygenase with a membrane fraction after cell disruption, but may involve release of membrane-associated 5-lipoxygenase upon disruption of activated rat basophilic leukemia cells.

Effect of lipid hydroperoxide on lipoxygenase kinetics

In order to investigate the activation of lipoxygenase and to clarify the role of the oxygenation product hydroperoxide in this process, the effect of 13-hydroperoxylinoleic acid (P, 0-35 microM) on linoleic acid (S, 1-80 microM) oxygenation catalysis by 12 nM lipoxygenase-1 from soybean was studied at pH 10, 25 degrees C, and 240 microM O2 with rapid kinetic techniques. The following observations were made: (1) Iron(II) and iron(III) lipoxygenases are kinetically different: reactions started with the Fe(II) enzyme form show a lag phase, whereas iron(III) lipoxygenase induces an initial burst. (2) Oxidation of the enzyme alone is not sufficient to abolish the lag phase: at [S] greater than 50 microM, the initial burst in the iron(III) lipoxygenase curves is still followed by a lag. The lag phase disappears completely only in the presence of micromolar quantities of P. (3) The approximate dissociation constants for S and P are 15 and 24 microM, respectively, 1 order of magnitude smaller than the corresponding values in the absence of oxygen. The observed kinetics are predicted by numerical integration of the rate equations of a model based on the single lipid binding site mechanism for the anaerobic lipoxygenase reaction [Ludwig et al. (1987) Eur. J. Biochem. 168, 325-337; Verhagen et al. (1978) Biochim. Biophys. Acta 529, 369-379]. A quasi-steady-state approximation of the model suggests that a high [S]/[P] the fraction of active iron(III) lipoxygenase is small and that, therefore, a lag phase is intrinsic to the mechanism.

Pregnancy in a quadriplegic patient treated with continuous intrathecal baclofen infusion to manage her severe spasticity. Case report

A report on pregnancy in a quadriplegic patient treated with a high dose of 1000 mcg/24 h continuous intrathecal baclofen infusion using an implanted drug delivery system (Synchromed, Medtronic, USA). Spasticity could be managed up to the 35th week of gestation. However, uterine contractions evoke enormous spastic symptoms which we, even with maximum values of the spasticity scales, could not classify. The recurrence of spasticity was associated with autonomic dysregulation. With continuous epidurally infused bupivacaine (11.25 mg/h) adequate relaxation could be reached and gestation was terminated by a primary caesarean section. A healthy girl was born (2040 g, Apgar 9 and 10).

Improved purification of 12-lipoxygenase from rat basophilic leukemia cells and conditions for optimal enzyme activity

12-Lipoxygenase from rat basophilic leukemia cells was purified about 300-fold by protein-HPLC in a single run. Maximal 12-lipoxygenase activity was observed at pH 7.5, while the enzyme became almost inactive at pH 6 and 9. Although Ca2+ was not essential for 12-lipoxygenase activity, the partially purified enzyme was stimulated approx. 2-fold in the presence of 0.1-5.0 mM Ca2+. Contrary to 5-lipoxygenase from RBL-1 cells, 12-lipoxygenase was not inactivated by preincubation with Ca2+ for 1-10 min, nor was it stimulated by 0.1-10 mM ATP.

12-Lipoxygenase from rat basophilic leukemia cells: separation from 5-lipoxygenase and temperature-dependent inactivation by hydroperoxy fatty acid

12-Lipoxygenase and 5-lipoxygenase from rat basophilic leukemia cells were separated by protein-HPLC in a single step. Upon incubation in the presence of Ca2+, 12-lipoxygenase converted arachidonic acid into 12(S)-hydroxyeicosatetraenoic acid and linoleic acid into 13(S)-hydro(pero)xyoctadecadienoic acid. The reaction products were analyzed by reversed-phase and chiral straight-phase HPLC with ultraviolet-detection. Using the cytosolic fraction of rat basophilic leukemia cells, optimal 12-lipoxygenase activity was observed at 10 degrees C. At 37 degrees C 12-lipoxygenase was very rapidly inactivated by its own product, hydroperoxy fatty acid, at low concentrations (10-100 nM).

Leukotriene C4 formation by purified human eosinophils can be induced by arachidonic acid in the absence of calcium-ionophore A23187

Addition of arachidonic acid (50 microM) to purified human eosinophils leads to the formation of considerable amounts of LTC4 [11.3 +/- 1.3) x 10(6) molecules/cell, mean +/- SEM, n = 10), 15-HETE [412 +/- 142) x 10(6) molecules/cell, mean +/- SEM, n = 3) and 15-series leukotrienes [35 +/- 15) x 10(6) molecules/cell, mean +/- SEM, n = 3). The ratio of the amounts of LTC4 and 15-lipoxygenase products was found to be strongly dependent on the arachidonic acid concentration, being relatively large at low arachidonic acid concentrations and very small at high arachidonic acid concentrations. Platelet activating factor (1 microM) was able to enhance significantly the production of LTC4 but not that of 15-lipoxygenase products. As arachidonic acid was found to be capable of inducing a fast, transient rise in the cytosolic free Ca2+ concentration, this explains, at least partly, its ability to induce the Ca2+-dependent formation of LTC4.

The possible role of particular leukotrienes in the allergen-induced late-phase asthmatic reaction

Challenge with allergen may provoke an early-phase and late-phase asthmatic reaction in allergic asthmatic individuals. Although the pathogenesis of the allergen-induced late-phase asthmatic reaction (LAR) is still poorly understood, the cell types and mediators involved in this reaction are considered to be of extreme importance for the understanding of the pathogenesis of asthma. Evidence has been provided that predominantly eosinophils penetrate into the bronchioli at the beginning of the LAR. The mobilization of those eosinophils into the lung tissue is caused by the release of chemotactic factors of protein or lipid nature, most likely platelet activating factor (PAF). How these cells are finally activated to release their mediators, when they have infiltrated into the bronchioli, remains obscure. They may, however, actively contribute to the occurrence of the LAR by the release of the strongly bronchoconstrictive compound leukotriene C4 (LTC4). Our investigations have shown that eosinophils do possess the capacity to synthesize this mediator upon in-vitro challenge with the calcium ionophore A23187, zymosan particles coated with IgG and C3b (C3bi) or PAF at relatively high concentrations. As to demonstrating the possible in-vivo formation of leukotrienes, studies have been undertaken to demonstrate the excretion of a stable metabolite of LTC4, i.e. LTE4, into human urine. In our first series of investigations normal individuals were challenged via inhalation of high amounts of LTD4. Besides a bronchoconstrictive reaction and an increase in the level of maximal airway narrowing to challenge with methacholine, significant LTE4 excretion could be demonstrated in the urine. Similar studies concerning allergen provocation in allergic asthmatic individuals are now in progress.(ABSTRACT TRUNCATED AT 250 WORDS)

Arachidonic acid can induce leukotriene C4 formation by purified human eosinophils in the absence of other stimuli

Stimulation of purified human eosinophils with 50 microM arachidonic acid leads to the production of leukotriene C4, 15-hydroxy-eicosatetraenoic acid and 15-series leukotrienes. The ratio of the amounts of leukotriene C4 and 15-lipoxygenase products was found to be strongly dependent on the arachidonic acid concentration, being relatively large at low arachidonic acid concentrations and very small at high arachidonic acid concentrations. In the presence of 1 microM platelet-activating factor a significant elevation of leukotriene C4 formation is observed, whereas the formation of 15-lipoxygenase products remains unaltered. As arachidonic acid was found to be capable of inducing a fast, transient rise in the cytosolic free Ca2+ concentration, this explains at least partly its ability to induce the Ca2+-dependent formation of leukotriene C4.

Evidence for lipoxin formation by bovine polymorphonuclear leukocytes via triple dioxygenation of arachidonic acid

Incubation of bovine polymorphonuclear leukocytes (PMNs) with arachidonic acid leads to the formation of four lipoxins. The same lipoxins are also formed upon incubation of bovine PMNs with 5(S)-hydroperoxy-6-trans-8,11,14-cis-eicosatetraenoic acid, 5-hydroxy-6-trans-8,11,14-cis-eicosatetraenoic acid, 5(S)-hydroperoxy, 15(S)-hydroxy-6,13-trans-8,11-cis-eicosatetraenoic acid or 5(S),15(S)-dihydroxy-6,13-trans-8,11-cis-eicosatetraenoic acid. A 5,6-epoxide as intermediate in lipoxin formation in the bovine PMN is highly improbable because the 5-hydroxy compounds are as good substrates as the 5-hydroperoxy compounds. Moreover, the two main lipoxins were found to coelute with the two lipoxins produced via a triple dioxygenation of arachidonic acid by soybean lipoxygenase-1. Hence the bovine PMN is the first cell for which evidence is presented that the formation of lipoxins proceeds mainly via triple dioxygenation and not via 15-hydroxy-leukotriene A4 as is proposed for human and porcine PMNs.

12-Lipoxygenase from bovine polymorphonuclear leukocytes, an enzyme with leukotriene A4-synthase activity

Bovine polymorphonuclear leukocytes exhibit a 12-lipoxygenase activity upon sonication. In contrast to bovine platelet 12-lipoxygenase and other 12-lipoxygenases, this enzyme is unable to convert 5(S)-HETE (5(S)-hydroxy,6-trans-8,11,14-cis-eicosatetraenoic acid) or 5(S)-HPETE (5(S)-hydroperoxy,6-trans-8,11,14-cis-eicosatetraenoic acid) into 5(S),12(S)-dihydroxy-6,10-trans,8,14-cis-eicosatetraenoic acid. Surprisingly, the formation of leukotriene A4-derived products namely leukotriene B4 and the leukotriene B4-isomers 12-epi,6-trans- leukotriene B4 and 6-trans-leukotriene B4, was observed upon incubation of this enzyme with 5(S)-HPETE. Hence, the 12-lipoxygenase from bovine polymorphonuclear leukocytes possesses leukotriene A4-synthase activity.

The excretion of leukotriene E4 into urine following inhalation of leukotriene D4 by human individuals

Healthy volunteers underwent bronchial challenge with increasing doses of nebulized leukotriene D4 (0.007 - 200 nmol) at 15 min intervals. Total amounts of 200 nmol (females) and 400 nmol (males) were inhaled, corresponding to approximately 100 nmol and 200 nmol deposited in the lung, respectively. Of the latter amounts 3 +/- 1% (mean +/- S.E.M., n = 5) was found to be excreted as leukotriene E4 into the urine within 12 h. No further excretion after this period was observed. Approximately 50% of the total urinary leukotriene E4 was excreted during the first 2 h. These results suggest that a possible formation of sulfidopeptide leukotrienes in the lung in vivo can be monitored by measuring leukotriene E4 excretion into the urine.

Demonstration of a 12-lipoxygenase activity in bovine polymorphonuclear leukocytes

In this study we present evidence for the existence of an intrinsic 12-lipoxygenase in the bovine polymorphonuclear leukocyte which differs from the well-known platelet 12-lipoxygenase. Intact bovine polymorphonuclear leukocytes synthesize predominantly 5-lipoxygenase products. However, this 5-lipoxygenase activity disappears completely upon sonication of the cells, whereas a 12-lipoxygenase activity then becomes apparent. This 12-lipoxygenase resembles the platelet 12-lipoxygenase in metabolizing arachidonic acid into 12(S)-hydroxyeicosatetraenoic acid and in being independent of Ca2+ as well as of ATP. The most striking difference between the two 12-lipoxygenases is their behaviour towards linoleic acid. While the platelet 12-lipoxygenase does not convert linoleic acid, the 12-lipoxygenase from bovine polymorphonuclear leukocytes, apparent only in the cell-free system, converts linoleic acid into 13-hydroxyoctadecadienoic acid as efficiently as it converts arachidonic acid into 12-hydroxyeicosatetraenoic acid. This provides a convenient method to distinguish both 12-lipoxygenase activities. The fact that this new 12-lipoxygenase is able to metabolize linoleic acid into 13-hydroxyoctadecadienoic acid suggests that this enzyme, in contrast to platelet 12-lipoxygenase, resembles 5-lipoxygenases in showing a preference for hydrogen abstraction at a position which is determined by the distance to the carboxylic end of the fatty acid.

Platelet-activating factor induces leukotriene C4 synthesis by purified human eosinophils

Platelet-activating factor, at a concentration of 10 microM, was capable of inducing leukotriene C4 synthesis by eosinophils of healthy donors, i.e. (3.1 +/- 0.3) x 10(6) molecules leukotriene C4/cell (n = 31, mean +/- SEM, cell purity 87 +/- 2%). Reversed-phase high performance liquid chromatography analysis demonstrated the exclusive synthesis of leukotriene C4. At a concentration of 1 microM, platelet-activating factor was capable of significantly enhancing the calcium ionophore A23187, the opsonized zymosan or the arachidonic acid induced leukotriene C4 synthesis by eosinophils. These results show that PAF is capable of inducing and enhancing the leukotriene C4 formation by human eosinophils.

Platelet-activating factor (PAF-acether) induced leukotriene C4 formation and luminol dependent chemiluminescence by human eosinophils

Human eosinophils are capable of synthesizing almost exclusively the strongly spasmogenic compound LTC4 when stimulated with either the calcium ionophore A 23187 or opsonized zymosan (OZ). Although PAF-acether in concentrations ranging from 10 nM to 1 microM is hardly capable of inducing significant LTC4 synthesis itself, it significantly enhances the OZ-induced LTC4 formation at a concentration of 1 microM. However, at a concentration of 10 microM, PAF-acether itself is capable of inducing LTC4 formation comparable with that induced by OZ. PAF-acether, at a concentration of 10 microM (and not at a concentration of 1 microM) is also capable of inducing a luminol dependent chemiluminescent response by eosinophils. The PAF-acether antagonist BN 52021 at a concentration of 0.1 mM not only partially inhibited the PAF-acether induced LTC4 formation but also the OZ induced LTC4 formation. Since an equal inhibition is found the inhibitory mode of action of BN 52021 is most likely directed towards a common pathway. Taken together, these results suggest that eosinophils may be triggered by high locally reached concentrations of PAF-acether to release inflammatory and bronchoconstrictive mediators. This may be of importance for the pathogenesis of the allergen induced late phase asthmatic reaction.

Leukotrienes and their possible significance for the pathogenesis of asthma

Six years ago the structure of slow reacting substance of anaphylaxis (SRS-A), a strongly bronchoconstrictive substance, has been unravelled SRS-A proved to be a mixture of different closely related compounds, now denominated as sulfidopeptide Leukotrienes. Leukotrienes possess a conjugated triene system and one or more oxygen functions. They are formed from membrane derived arachidonic acid by an initial oxygenation by the enzyme lipoxygenase. Sofar the following leukotrienes have been characterized leukotriene A4, B4, C4, D4, E4 and F4. Leukotrienes possess important biological properties. Leukotriene B4 is strongly chemotactic for leukocytes, whereas the sulfidopeptide leukotrienes C4, D4 and E4 are strongly spasmogenic. In this review the formation and the different biological activities of leukotrienes and the possible role of leukotrienes in the asthmatic process will be discussed.

On the optimal conditions of LTC4 formation by human eosinophils in vitro

The optimal conditions for the -in vitro- LTC4 formation by the human eosinophil, isolated from peripheral blood, have been investigated in detail. LTC4 formation was found strongly Ca2+ and ionophore dependent and was complete after 20 min. Maximal LTC4 production was observed in the presence of 2 mM Ca2+, 10 microM ionophore A23187 and 5 mM glutathione. Addition of arachidonic acid resulted in a significant inhibition of the LTC4-synthesis by human eosinophils. In contrast, the formation of 15-HETE was strongly stimulated by the addition of arachidonic acid. As the LTC4 synthesis was found to be strongly inhibited by the addition of 15(S)-HETE to the incubation medium, this monohydroxy acid may be responsible for the inhibitory activity of arachidonic acid.

Exclusive leukotriene C4 synthesis by purified human eosinophils induced by opsonized zymosan

Purified human eosinophils were challenged with N-formyl-methionyl-leucyl-phenylalanine, leukotriene B4, platelet-activating-factor, valyl-glycyl-seryl-glutamic acid, phorbol myristate acetate, zymosan, opsonized zymosan and the calcium ionophore A23187 to induce leukotriene synthesis. Reversed-phase high performance liquid chromatography analysis demonstrated the almost exclusive synthesis of leukotriene C4 by eosinophils of 11 healthy donors after challenge with opsonized zymosan [(22 +/- 4) X 10(6) molecules LTC4/cell, mean +/- SE] or the calcium ionophore A23187 [(54 +/- 7) X 10(6) molecules LTC4/cell, mean +/- SE]. The other agents were not capable of inducing leukotriene formation. When in addition to opsonized zymosan N-formyl-methionyl-leucyl-phenylalanine or platelet-activating factor were added a significant increase of the leukotriene C4 synthesis by eosinophils was observed. These results suggest that eosinophils might be triggered to produce considerable amounts of the spasmogenic leukotriene C4 in vivo by C3b- and/or IgG-mediated mechanisms e.g. phagocytosis.

Leukotriene formation by bovine polymorphonuclear leukocytes

The leukotriene production by bovine polymorphonuclear leukocytes isolated from peripheral blood has been studied. Cells were incubated in the presence of arachidonic acid, glutathione, calcium ionophore A23187 and Ca2+. The leukotrienes then formed are leukotriene C4, leukotriene B4, two all-trans isomers of leukotriene B4 and the double dioxygenation product 12-epi-6-trans-8-cis-leukotriene B4. Leukotriene C4 is formed in such a large quantity by the bovine polymorphonuclear leukocyte that it might constitute an excellent and inexpensive source for the biosynthetic preparation of this spasmogenic leukotriene.

Specific leukotriene formation by purified human eosinophils and neutrophils

Human granulocytes isolated from peripheral blood have been described to synthesize both LTB4 and LTC4 from arachidonic acid. We have observed that the amount of LTC4 produced by human granulocyte preparations is strongly dependent on the relative amount of eosinophils. To investigate a possibly significant difference in leukotriene synthesis of the eosinophilic and neutrophilic granulocytes, we developed a purification method to isolate both cell types from granulocytes obtained from the blood of healthy donors. Leukotrienes were generated by incubation of the purified cells with arachidonic acid, calcium ionophore A23187, calcium-chloride and reduced glutathione. Surprisingly, eosinophils were found to produce almost exclusively the spasmogenic LTC4. In contrast, neutrophils produce almost exclusively the chemotactic LTB4, its omega-hydroxylated metabolite 20-hydroxy-LTB4 and two non-enzymically formed LTB4 isomers.

Separation and quantitation of leukotrienes by reversed-phase high-performance liquid chromatography

A rapid and sensitive reversed-phase HPLC procedure is reported which allows the simultaneous separation and quantitation of LTC4, 11t-LTC4, LTD4, LTB4, 12epi,6t,8c-LTB4, 6t-LTB4 + 12epi,6t-LTB4, two trihydroxy-eicosatetraenoic acids tentatively identified as 20-OH-LTB4 and 20-OH,12epi,6t,8c-LTB4 and several not yet identified 15-series leukotrienes produced by the cytosol of porcine polymorphonuclear leukocytes.

Double dioxygenation of arachidonic acid by soybean lipoxygenase-1. Kinetics and regio-stereo specificities of the reaction steps

The kinetic parameters of the first and second oxygenation of arachidonic acid by soybean lipoxygenase-1 were determined and found to be for the first step at pH 10.0, Km (arachidonic acid) = 8.5 +/- 0.5 microM; kcat = 225 +/- 7 s-1 and for the second step at pH 8.7 Km (15-HPETE) = 440 +/- microM; kcat = 25 +/- 1 s-1. In the second oxygenation for which 15-Ls-hydroperoxy 5-cis, 8-cis, 11-cis 13-trans-eicosatetraenoic acid is a substrate, two isomeric dihydroperoxy fatty acids are formed. After separation of the corresponding dihydroxy esters by high-performance liquid chromatography, they were identified by mass-spectrometry, 1H- and 13C-NMR spectroscopy as 8-DS, 15-LS-dihydroperoxy 5-cis, 9-trans, 11-cis, 13-trans-eicosatetraenoic acid and 5-DS, 15-LS-dihydroperoxy 6-trans, 8-cis, 11-cis, 13-trans-eicosatetraenoic acid. Independent evidence for the absolute configurations was obtained by capillary gas-liquid chromatography of diastereomeric R-(-)-2-butyl esters of the acetylated 2-hydroxy carboxylic acids produced by oxidative ozonolysis of the acetylated dihydroxy fatty acids. It is concluded that soybean lipoxygenase-1 produces hydroperoxides with predominantly the S-configuration irrespective of the position in the fatty acid which is oxygenated.

The effect of modification of sulfhydryl groups in soybean lipoxygenase-1

Soybean lipoxygenase-1 was found to contain five free sulfhydryl groups and no disulfide bridges. Three sulfhydryl groups react readily with methylmercuric halides. This modification results in significant changes of the catalytic properties of the enzyme. Comparison of modified and native lipoxygenase-1 shows the following: 1. The catalytic constant of the oxygenation of linoleic acid is reduced by approximately 50%, whereas the affinity towards linoleic acid remains unaltered. 2. At high concentrations of substrate and low concentrations of enzyme the kinetic lag phase in the oxygenation is considerably longer. 3. The regio- and stereospecificities of the oxygenation are significantly lower. 4. Besides hydroperoxides, oxo-octadecadienoic acids (4%) are formed during the oxygenation. 5. The cooxidation capacity is considerably enhanced. Treatment of methylmercury-modified lipoxygenase-1 with NaHS results in the complete recovery of the sulfhydryl groups and of the catalytic properties.

Properties of a complex of Fe(III)-soybean lipoxygenase-1 and 4-nitrocatechol

Fe(III)-soybean lipoxygenase-1 yields with 4-nitrocatechol a green coloured 1 : 1 complex, which shows at pH 7.0 absorption maxima at 385 nm and 650 nm. The formation of this complex is reversible. The circular dichroism spectrum of the complex of Fe(III)-lipoxygenase-1 and 4-nitrocatechol has a positive band at around 380 nm and a negative band at around 450 nm and is significantly different from that of the Fe(III)-enzyme as such. 4-Nitrocatechol can be displaced from the green complex by 13-L-hydroperoxy-cis-9, trans-11-octadecadienoic acid, resulting in the formation of the blue complex between the Fe(III)-enzyme and 13-L-hydroperoxy-cis-9,trans-11-octadecadienoic acid both under aerobic and anaerobic conditions. Also linoleic acid competes with 4-nitrocatechol for the binding site on the Fe(III)-enzyme, as can be demonstrated under anaerobic conditions, ultimately leading to reduction of the Fe(III)-enzyme. The oxygenation of linoleic acid by Fe(III)-lipoxygenase-1 is inhibited by 4-nitrocatechol. From steady-state kinetics a non-competitive inhibition pattern is obtained. Probably it has to be considered as pseudo non-competitive because of the slow establishment of the complex equilibrium. An inhibition constant (K4NC) of 16.3 microM is found. On prolonged incubation of Fe(III)-lipoxygenase-1 and 4-nitrocatechol the green complex converts into a brown species. This conversion is found to be coupled with a change in the nature of the inhibition from reversible to irreversible. A complex between native lipoxygenase-1 and 4-nitrocatechol is found to be unlikely.

Micelle and acid-soap formation of linoleic acid and 13-L-hydroperoxylinoleic acid being substrates of lipoxygenase-1

Surface tension measurements of linoleic acid solutions in 0.1 M sodiumborate buffer pH 10 at 23 degrees C showed that at increasing the linoleic acid concentration a sharp transition from monomers to micelles occurs at 167 micrometer. At pH 9 and 8 formation of acid-soap dimers from monomers starts at 60 micrometer and 21 micrometer respectively. The concentration range at which only monomers exist is therefore markedly reduced. For 13-L-hydroperoxylinoleic acid at pH 10 acid-soap formation still takes place, starting at approx. 220 micrometer. The total lipid concentration at which acid-soap or micelle formation starts in mixtures of linoleic acid and 13-L-hydroperoxylinoleic acid has been determined in relation to the molar ratio of both acids.

Steady-state kinetics of the anaerobic reaction of soybean lipoxygenase-1 with linoleic acid and 13-L-hydroperoxylinoleic acid

The steady-state kinetics of the anaerobic reaction of soybean lipoxygenase-1 with linoleic acid and 13-L-hydroperoxylinoleic acid were studied. Initial rates of the formation of oxodienoic acids**, absorbing at 285 nm, were measured at pH 10. About 50% of the consumed 13-L-hydroperoxylinoleic acid was converted into oxodienoic acids regardless of the initial ratio of the two substrates. A linear inhibition by both linoleic acid and 13-L-hydroperoxylinoleic acid was observed in the concentration range studied, which is on the upper side limited by the concentrations at which micelle- or acid-soap formation starts. A kinetic scheme is proposed based on one active site in lipoxygenase-1 which alternately binds the two substrates. Values for the kinetic constants were calculated by fitting simultaneously the complete set of data to the appropriate rate equation.

Conversion of 9-D- and 13-L-hydroperoxylinoleic acids by soybean lipoxygenase-1 under anaerobic conditions

Soybean lipoxygenase-1 reacts with both 9-D and 13-L-hydroperoxylinoleic acids under anaerobic conditions. Approximately 40% of the hydroperoxide is converted into oxodienes, absorbing at 285 nm. Concomitantly, more polar compounds are formed, tentatively identified as being mainly epoxy-hydroxy-octadecenoic acids. When oxygen is present, the reaction is strongly inhibited, until in a very slow reaction the oxygen has been depleted. This accounts for the occurrence of a lag period.