Metabolism of cysteinyl leukotrienes to novel polar metabolites in the rat and endogenous formation of leukotriene D4 during systemic anaphylaxis in the guinea pig

Asthma therapy with agents preventing leukotriene synthesis or action

Elucidation of the biochemistry of leukotriene production and the pharmacology of its actions has led to the development of a number of therapeutic agents shown to be of value in the treatment of asthma. These agents either prevent the synthesis of the leukotrienes, by preventing the action of the 5-lipoxygenase-activating protein or the catalytic action of the 5-lipoxygenase, or by inhibiting the action of leukotrienes at the CysLT1 receptor. Numerous clinical trials in exercise-induced asthma, allergen-induced asthma, aspirin-induced asthma, and spontaneously occurring asthmatic episodes have indicated that these agents are safe and effective asthma treatments.

Leukotrienes as mediators of airway obstruction

The cysteinyl leukotrienes are potent mediators of airway narrowing derived from the lipoxygenation of arachidonic acid and the adduction of glutathione to this eicosanoid backbone. In lower animals and humans, the cysteinyl leukotrienes are among the most potent airway contractile substances ever identified. Furthermore, these moieties can be recovered from the urine during induced or spontaneous asthma attacks. Most important, inhibition of the synthesis of the leukotrienes or prevention of their action at the CysLT1 receptor is associated with an improvement in the airway dysfunction that occurs in both induced and spontaneous asthma. These data indicate that the cysteinyl leukotrienes have a clinically significant role in the airway obstruction that characterizes asthma.

Posttreatment with eicosatetraynoic acid decreases lung edema in guinea pigs exposed to phosgene: the role of leukotrienes

Acetylenic acids such as 5,8,11,14-eicosatetraynoic acid (ETYA), have been shown to be effective in preventing pulmonary edema formation (PEF). In phosgene-exposed guinea pigs, we examined the effects of ETYA on PEF, measured as real time lung weight gain (lwg). Pulmonary artery pressure (Ppa), airway pressure (Paw), perfusate leukotrienes (LT) C4/D4/E4/B4, and lung tissue lipid peroxidation (TBARS) were measured using the isolated, buffer-perfused lung model. Guinea pigs were challenged to 175 mg/m3 (44 ppm) phosgene for 10 minutes giving a concentration x time product of 1750 mg.min/m3 (437 ppm.min). Five minutes after removal from the exposure chamber, guinea pigs were treated, i.p., with 200 microL of 100 microM ETYA. 200 microL of 50 microM ETYA was added to the perfusate every 40 minutes, beginning at 60 minutes after start of exposure (t = 0). There were four groups in this study: air-treated, phosgene-exposed, ETYA-posttreated + phosgene, and ETYA-posttreated + air ETYA-posttreated + phosgene guinea pigs had significantly lower Ppa (P = .006), Paw (P = .009), and lwg (P = .016) compared with phosgene-exposed animals. Phosgene exposure reduced LTB4 compared with air-treated controls (P = .09). ETYA-posttreatment + phosgene had significantly increased perfusate LTB4 (P = .0006) compared with phosgene exposure only group. Total perfusate, LTC4 + LTD4 + LTE4, was not different between phosgene-exposed, air-treated or ETYA-posttreatment + phosgene over time. Posttreatment with ETYA significantly lowered TBARS formation, 206 +/- 13 versus 285 +/- 23 nmol/mg protein (P = .016), compared with phosgene-exposed lungs. Paradoxically, ETYA posttreatment decreased PEF and lipid peroxidation, but increased sulfidopeptide LT release from the lung during perfusion. We conclude that LTC4/D4/E4, and B4, may play different roles than previously thought for PEF in the isolated perfused lung model.

Hyperpnea-induced bronchoconstriction is dependent on tachykinin-induced cysteinyl leukotriene synthesis

The purpose of the study was to test the hypothesis that tachykinins mediate hyperpnea-induced induced bronchoconstriction indirectly by triggering cysteinyl leukotriene (LT) synthesis in the airways. Guinea pigs (350-600 g) were anesthetized with xylazine and pentobarbital sodium and received hyperpnea challenge (tidal volume 3.5-4.0 ml, frequency 150 breaths/min) with either humidified isocapnic gas (n = 6) or dry gas (n = 7). Dry gas challenge was performed on animals that received MK-571 (LTD4 antagonist; 2 mg/kg i.v.; n = 5), capsaicin (n = 4), neurokinin (NK) antagonists [NK1 (CP-99994) + NK2 (SR-48968) (1 mg/kg i.v.); n = 6], or the H1 antihistamine pyrilamine (2 mg/kg i.v.; n = 5). We measured the tracheal pressure and collected bile for 1 h before and 2 h after hyperpnea challenge. We examined the biliary excretion of cysteinyl LTs; the recovery of radioactivity in bile after instillation of 1 microCi [3H]LTC4 intratracheally averaged 24% within 4 h (n = 2). The major cysteinyl LT identified was LTD4 (32% recovery of radioactivity). Cysteinyl LTs were purified from bile of animals undergoing hyperpnea challenge by using reverse-phase high-pressure liquid chromatography and quantified by radioimmunoassay. There was a significant increase in the peak value of tracheal pressure after challenge, indicating bronchoconstriction in dry gas-challenged animals but not after humidified gas challenge. MK-571, capsaicin, and NK antagonists prevented the bronchoconstriction; pyrilamine did not. Cysteinyl LT levels in the bile after challenge were significantly increased from baseline in dry gas-challenged animals (P < 0.05) and were higher than in the animals challenged with humidified gas or dry gas-challenged animals treated with capsaicin or NK antagonists (P < 0.01). The results indicate that isocapnic dry gas hyperpnea-induced bronchoconstriction is LT mediated and the role of tachykinins in the response is indirect through release of LTs. Endogenous histamine does not contribute to the response.

Tissue distribution, elimination and metabolism of [3H]-leukotriene C4 in the American bullfrog, Rana catesbeiana

Tissue distribution, elimination, and metabolism of [3H]-leukotriene C4 were studied at 2.5 hours after injection in the conscious and anesthetized American bullfrog, Rana catesbeiana. Conscious frogs were injected via the dorsal lymph sac or the sciatic vein. Anesthetized frogs were injected via the abdominal vein. The organs containing the greatest percent of injected radioactivity at 2.5 hours after injection were liver, small intestine and kidney. Route of injection and anesthesia appears to alter distribution and elimination of leukotrienes. [3H]-leukotrienes were eliminated into bladder water and bile. In addition, 7.8 +/- 2.2 and 5.2 +/- 2.5 percent of the injected radioactivity was found in the pan water bathing the ventral surface of the venously and dorsally injected conscious frogs, respectively, suggesting transfer of radioactivity across the skin. At 2.5 hours, polar metabolites represented 50% of the radioactivity found in liver, bile, and bladder water. These polar metabolites were determined to be 18-carboxy-19,20-dinor-leukotriene E4, 20-carboxy-leukotriene E4, and 20-hydroxy-leukotriene E4. Of the non-oxidized leukotrienes, bile contained mainly LTD4 while bladder water contained primarily LTE4. N-acetyl LTE4 was not detected in any samples. The tissue distribution, elimination and metabolism of leukotrienes in the bullfrog was similar to mammalian studies and suggests evolutionary conservation of leukotriene processing.