Disease relevance of Leukotriene A4

• The capacity to convert exogenous leukotriene A4 to lipoxins (LXs) was investigated in platelet suspensions from patients with myeloproliferative disorders (MPD) (n = 22) and healthy control subjects (n = 14) [1].
• Although there was limited inter-study concordance of important loci, two gene variants in the leukotriene pathway (ALOX5AP and LTA4) have emerged as susceptibility factors for myocardial infarction (MI) [2].
• In the model of pulmonary leukostasis, no nonenzymatic LTA4-derivatives were detected, coincident with a predominance of cysteinyl-LT [3].
• 5-Lipoxygenase is the first committed enzyme in the leukotriene biosynthetic pathway and is known to catalyze not only the first oxygenation of arachidonate to form 5(S)-hydroperoxyeicosatetraenoic acid (5(S)-HPETE), but also dehydration of this intermediate into leukotriene A4 (LTA4) by an activity termed leukotriene A4 synthase [4].
• The cytosolic enzymes displayed activity with leukotriene A4, but their specific activities and intracellular concentrations were too low to account for the leukotriene C4 formation in the mastocytoma cells [5].

High impact information on Leukotriene A4

• The initial enzymatic step in the formation of leukotrienes is the oxidation of arachidonic acid by 5-lipoxygenase (5-LO) to leukotriene A4 [6].
• Arachidonic acid is released from membrane phospholipids upon cell stimulation (for example, by immune complexes and calcium ionophores) and converted to leukotrienes by a 5-lipoxygenase that also has leukotriene A4 synthetase activity [7].
• Exposure of HAM to leukotriene A4 (LTA4) resulted in a 2-fold increase in LXA4 and 10-fold increase in LXB4 [8].
• In contrast, neutrophils did not transform LTA4 to lipoxins [9].
• IC50 values for the inhibition of the conjugation of 20 microM LTA4-me with 5 mM GSH were 2.1 microM and 0.3 microM for LTC4 and LTC3, respectively [10].

Chemical compound and disease context of Leukotriene A4

• Our results suggest that epidermal cells could cooperate in leukotriene B4 biosynthesis by transcellular metabolism of leukotriene A4 in lesions of psoriasis, and possibly other inflammatory dermatoses characterized by increased leukotriene B4 levels and prominent polymorphonuclear leukocyte infiltrates [11].
• The first step consists of the oxidation of arachidonic acid to the unstable intermediate 5-hydroperoxyeicosatetraenoic acid (5-HPETE), and the second step is the dehydration of 5-HPETE to form LTA4 [12].
• To investigate the role of LTB4 in dermatitis, we used S-(4-dimethylaminobenzyl)-N-[(2S)-3-mercapto-2-methylpropionyl]-L- cysteine (SA6541), a potent leukotriene A4 (LTA4) hydrolase inhibitor [13].
• These results indicate that the enzyme responsible for the conversion of LTA4 to LTC4 in human melanoma cells is LTC4 synthase rather than a nonspecific or microsomal glutathione-S-transferase [14].
• Human melanoma cells generate leukotrienes B4 and C4 from leukotriene A4 [14].

Biological context of Leukotriene A4

• The conversion of LTA4-me to LTC4-me was competitively inhibited by LTA3, LTA4, and LTA5, with respective Ki values of 1.5, 3.3, and 2.8 microM, suggesting that these substrates were recognized by a common active site [10].
• The recombinant 5-lipoxygenase in 10,000 x g supernatant fractions was able to synthesize large amounts of 5-hydroperoxy-6,8,10,14-icosatetraenoic acid, together with smaller amounts of the nonenzymatic hydrolysis products of leukotriene A4, and exhibited a dependence on Ca2+ and ATP for maximal activity [15].
• A sensitive fluorescence-linked immunoassay for LTC4 was used to screen a KG-1 cDNA expression library for LTC4 synthase activity after transfection of COS cells and addition of substrate LTA4 [16].
• The enzymatic reaction obeyed Michaelis-Menten saturation kinetics with respect to varying concentrations of leukotriene A4 [17].
• They also demonstrate a specific PMNL-endothelial cell interaction in which endothelial cell LTC4 synthesis results from the intercellular transfer of LTA4 produced by PMNL [18].

Anatomical context of Leukotriene A4

• Single protein from human leukocytes possesses 5-lipoxygenase and leukotriene A4 synthase activities [19].
• Studies on the mechanism of leukotriene B4 biosynthesis in suspensions composed of neutrophils plus erythrocytes indicate that human erythrocytes convert neutrophil-derived leukotriene A4 into leukotriene B4 [20].
• Leukotriene A4 synthase was purified from the cytosolic fraction of murine mast cells [21].
• Metabolism of leukotriene A4 by an enzyme in blood plasma: a possible leukotactic mechanism [22].
• BACKGROUND: The peptido-leukotrienes (LTs) and lipoxins (LX) are produced by platelets through the transcellular conversion of leukocyte-derived LTA4 at sites of vascular inflammation and injury, such as during coronary artery balloon angioplasty [23].

Associations of Leukotriene A4 with other chemical compounds

• Expression cloning of a cDNA for human leukotriene C4 synthase, an integral membrane protein conjugating reduced glutathione to leukotriene A4 [16].
• Leukotriene C4 production by murine mast cells: evidence of a role for extracellular leukotriene A4 [24].
• 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 [24].
• Several experiments, including those with lipoxygenase inhibitors, heat treatment, and competitive inhibition, indicated that both the 5-lipoxygenase and leukotriene A4 synthase activities resided in the same protein and that the formation of leukotriene A4 from 5-HPETE was catalyzed by the 8-lipoxygenase activity of the enzyme [25].
• Leukocyte preparations convert the hydroperoxy icosatetraenoic acids 5(S)-HPETE and 15(S)-HPETE to the unstable leukotriene epoxides LTA4 and 14,15-LTA4 [26].

Gene context of Leukotriene A4

• Also, the apparent Km for LTA4 was higher for microsomal GST-II (41 microM) than LTC4 synthase (7 microM) [27].
• The acid 14b is highly selective as an inhibitor of 5-LO activity when compared to the inhibition of ram seminal vesicle cyclooxygenase (IC50 > 5 microM) or human leukocyte leukotriene A4 (LTA4) hydrolase (IC50 > 20 microM) [28].
• The metal-binding motif in the sequence of leukotriene A4 (LTA4) (EC 3.3.2.6), a bifunctional zinc metalloenzyme, contains a glutamic acid that is conserved in several zinc hydrolases [29].
• It exhibits 33% identity and 48% similarity with leukotriene-A4 hydrolase, a relation further supported by the capacity of Ap-B to hydrolyze leukotriene A4 [30].
• We have previously cloned an LTA4 hydrolase from Saccharomyces cerevisiae with a primitive epoxide hydrolase activity and a Leu aminopeptidase activity, which is stimulated by LTA4 [31].

Analytical, diagnostic and therapeutic context of Leukotriene A4

• Three mutants of recombinant mouse leukotriene A4 (LTA4) hydrolase (3.3.2.6) were produced by site-directed mutagenesis on cDNA [32].
• Enzyme activity determinations and differential peptide mapping, before and after repeated exposure to LTA4, revealed that wild-type enzyme and the mutants [S379A] and [S380A]LTA4hydrolase were equally susceptible to suicide inactivation whereas the mutants in position 378 were no longer inactivated or covalently modified by LTA4 [33].
• This novel enzymatic metabolite of leukotriene A4 was characterized by physical means including ultraviolet spectroscopy, high performance liquid chromatography, and gas chromatography-mass spectrometry [34].
• Molecular cloning and functional expression of a Caenorhabditis elegans aminopeptidase structurally related to mammalian leukotriene A4 hydrolases [35].
• Bronchoalveolar lavage fluid cells obtained from asthmatic patients, primarily alveolar macrophages, contained mRNA for bACT, LTA, 5LX, cyclooxygenase, and 15LX (in decreasing order) [36].

References