br Material and methods br Results

Material and methods
Results
Discussion Although we were not able to detect 12/15-LOX mRNA in the lungs of 12/15-LOX knockout mice substantial amounts of 15-HETE could be detected in BALF. In fact, significant synthesis of 15-HETE in 12/15-LOX mice have been already reported [17]. The redundant systems involved in oxidation of arachidonic 16,16-Dimethyl Prostaglandin E2 are likely to be responsible for this phenomenon. Lipoxygenases, which facilitate oxygenation of C12 and/or C15, are characterized by high promiscuity reflected by participation of each of these LOXs in synthesis of both 12- and 15-HETE [19]. Moreover, nonspecific oxygenation of arachidonic acid may be responsible for, at least, baseline 15-HETE production. However, induction of allergic airway inflammation was associated with significantly attenuated production of 15-HETE in 12/15-LOX knockout mice as compared with wild type littermates. This indicates that in the lungs 12/15-LOX is indispensable for allergen-induced rather than baseline 15-HETE synthesis and that in a model of allergic airway inflammation the redundant mechanisms are not able to compensate for 12/15-LOX deficiency. Indeed, in 12/15-LOX knockout mice no detectable level of 12/15-LOX mRNA could be demonstrated after development of allergen-induced airway inflammation either. On the contrary, we were able to demonstrate 9-fold up-regulation of 15-LOX expression in wide type mice in which allergic airway inflammation was induced. This finding is in line with the previously reported data [17]. Also, it has been shown that Th2 cytokines involved in the pathogenesis of asthma, such as IL-4 and IL-13 belong to the most potent 12/15-LOX inducers [20,21]. Moreover, the deficiency of 12/15-LOX had also effect on expression of other enzymes involved in metabolism of arachidonic acid including COX-2, 5-LOX and FLAP. This, in combination with lack of 12/15-LOX, led to altered synthesis of other eicosanoids which was particularly evident in mice in which allergic airway inflammation was mounted. Our results are consistent with previous reports which showed strong increase in production of cysLT in ovalbumin (OVA) induced airway inflammation in 12/15-LOX mice [16]. We have not demonstrated however the cellular source of enhanced cysLT production, which we recognize as a limitation of the current study. In contrast to the previously published reports, which did not demonstrate altered PGE2 synthesis in 12/15-LOX mice, we were able to show elevated concentration of PGE2 in BALF of 12/15-LOX knockout mice after induction of allergic airway inflammation. Although in allergen challenged wild type mice only a tendency toward greater production of PGE2 could be shown, the difference did not reach statistical significance. It is difficult to argue whether the differences in PGE2 synthesis between the present and other authors’ reports are due to methodological differences between our and already published models of allergic airway inflammation. In contrast to previously published reports, in the current study we sensitized mice intraperitoneally before allergen challenges were introduced. Moreover, the allergen exposure lasted longer than in previously published studies [16,17]. Our findings in BALF are supported by demonstration of a strong up-regulation of COX-2 in the lung tissue of allergen challenged 12/15-LOX knockout mice in comparison with wild type mice. Moreover, 15-HPETE and 15-HETE can inhibit COX-2-dependent PGE2 production [15]. The insufficient production of 15-HETE in response to allergen challenge can therefore be responsible for exaggerated production of PGE2 in 12/15-LOX knockout mice.
Conclusion
Conflict of interest
Financial disclosure The study was supported by a grant from Polish National Science Center to Krzysztof Kowal (N N401 597440).
The mammalian lipoxygenases belong to a family of structurally related lipid peroxidizing enzymes that are implicated in the pathogenesis of asthma and other inflammatory diseases. Human cells express three main types of lipoxygenases, which catalyse the insertion of molecular oxygen into arachidonic acid (AA) at carbon 5, 12 and 15, and hence are usually named 5-, 12- and 15-lipoxygenase, respectively. 5-Lipoxygenase is the key enzyme in leukotriene (LT) synthesis, and together with the 5-lipoxygenase-activating protein (FLAP), it catalyses the first step in the conversion of arachidonic acid to leukotrienes ().