The metabolism "in vitro" of leukotriene B4 in blood of normal subjects and asthmatic patients

Persistent increase in plasma and urinary leukotrienes after acute asthma

Leukotrienes may mediate bronchoconstriction in asthma. Cysteinyl leukotriene production rises in vivo after allergen challenge, but few reports describe leukotriene concentrations in clinical asthma or in children. Using high performance liquid chromatography/radioimmunoassay, plasma and urinary leukotrienes in asthmatic children (aged 5-10 years) were measured during an acute exacerbation (peak expiratory flow (PEF) < 65%, n = 10) and one month later (PEF 74-169%, n = 9), and in non-atopic normal children (aged 1.3-13.2 years). In the asthmatics, geometric mean (95% confidence interval) plasma leukotriene B4 (LTB4) was 746 pg/ml (398 to 1403) acutely and 1026 pg/ml (662 to 1593) in remission, compared with 369 pg/ml (167 to 728) in the normal children (n = 14). Plasma cysteinyl leukotrienes were low or undetectable, but urinary leukotriene E4 (LTE4) was higher in the asthmatics during an acute episode (210 pmol/mmol creatinine, 101 to 454) and at follow up (179 pmol/mmol, 110 to 293), compared with the normal children (98 pmol/mmol, 81 to 118, n = 41). This persistent increase in plasma LTB4 and urinary LTE4 concentrations one month after a severe asthmatic episode suggests leukotriene production is related to chronic inflammation rather than to acute bronchoconstriction.

A specific assay for leukotriene B4 in human whole blood

Leukotrienes (LTs) are potent mediators of inflammatory and allergic responses, and are present in biological fluids in minute amounts, that is, in the picogram range. The aim of this study was to develop and validate a method for determination of LTB4 synthesized in vitro in human whole blood. Heparinized blood was stimulated with calcium-ionophore A23187 at 37 degrees C. After 30 min cells were separated by centrifugation. LTB4 was analyzed by radioimmunoassay (RIA). When sample preparation was restricted to protein precipitation with acetone, interference was demonstrated by lack of parallelism between standard and sample dilution curves. Purification was, therefore, extended by combinations of the following steps: 1) protein precipitation, 2) lipid extractions, and 3) high-performance liquid chromatography (HPLC). One of two commercially available LTB4 standards was found to contain multiple components, several of which were immunoreactive in RIA. Even for the standard containing pure LTB4, interference was demonstrated by lack of parallelism between sample and standard dilution curves. Testing eight combinations of varying purification steps, we found that only a three-step purification procedure, including 1) solid-phase extraction, 2) protein precipitation at -20 degrees C, and 3) HPLC, was able to eliminate interference in RIA. Using this procedure, the recovery was 78%. Stimulation of whole blood from normal subjects with calcium-ionophore showed optimal LTB4 production at 10 microM ionophore, yielding 6.6 ng LTB4/mL blood.

Serum leukotriene B4 levels in patients with obstructive pulmonary disease

Leukotriene B4 has been found to be increased in the serum of cigarette smokers and some patients with bronchial asthma, as well as in the sputum of patients with cystic fibrosis and COPD. Corticosteroids supposedly may block the formation of LTB4. To determine if the effect of CS on airway disease is by reduction in LTB4, we studied serum LTB4 levels in clinically stable patients with asthma or COPD who were treated with or without CS. The LTB4 was extracted from serum and assayed by radioimmunoassay. Serum LTB4 concentrations, expressed as the mean +/- SD, were 0.36 +/- 0.15 ng/ml in ten normal controls, 0.56 +/- 0.18 ng/ml in nine asthmatic subjects, 0.67 +/- 0.2 ng/ml in eight asthmatic subjects receiving CS, 0.81 +/- 0.19 ng/ml in seven patients with COPD, and 0.97 +/- 0.29 ng/ml in eight patients with COPD receiving CS. Serum LTB4 levels in normal controls differed significantly from all groups with COPD or asthma (p less than 0.01). Levels of LTB4 in asthmatic subjects differed from levels in patients with COPD (p less than 0.03), and levels in asthmatic subjects receiving CS differed from subjects with COPD receiving CS (p less than 0.03). Concentrations of LTB4 within either the COPD or the asthmatic groups were not lower in the patients treated with CS. We conclude that serum LTB4 concentrations are higher in COPD than in asthma or normal controls and that administration of CS is not associated with low LTB4 levels. The beneficial effects of CS in obstructive airway disease appear to be mediated by mechanisms other than reduction of LTB4.

Leukotriene metabolism and hypersensitivity in man and mouse

The relative rates of cysteinyl-leukotriene metabolism were analyzed in fresh human and mouse serum. Human serum contained higher gamma-glutamyl-transpeptidase activity than mouse serum, and a higher percentage of the metabolized leukotriene C4 was recovered as leukotriene D4 in the human serum than in the mouse serum. The results suggest that the patterns of metabolism of the cysteinyl-leukotrienes could be an important factor in determining the relative sensitivity of an animal to the development of hypersensitivity reactions.