Effect of tranexamic acid on neutrophil superoxide anion generation

Respiratory burst function of ovine neutrophils

BACKGROUND

Respiratory burst function resulting in the release of reactive oxygen species such as superoxide anion (O2-) from neutrophils is one of the key mechanisms of the innate immune system, and maladaptive control of this mechanism is thought to play a pivotal role in the development of pathologies such as acute lung injury and sepsis. Ovine models of these pathologies are limited by the poor understanding of ovine neutrophil respiratory burst function.

RESULTS

Aspects of ovine neutrophil respiratory burst function to be characterised were: i) the maximum rate of O2- generated (Vmax); ii) the time taken to reach Vmax; iii) the total amount of O2- generated during the reaction; and iv) the duration of the reaction. As well as for unstimulated neutrophils, these aspects were also characterised after incubation with a priming agonist (platelet activating factor [PAF], tumour necrosis factor alpha [TNF-alpha] and lipopolysaccharides [LPS]) activating agonists (N-formylmethionyl-leucyl-phenylalanine [fMLP] and phorbol 12-myristate 13-acetate [PMA]) or a combination of a priming and an activating agonist. In the absence of priming or activating agonists, ovine neutrophils displayed a low level of respiratory burst function which was not enhanced by either PAF, TNF-alpha, LPS or fMLP, but was significantly enhanced by PMA. The PMA-induced respiratory burst function was further enhanced by pre-incubation with PAF, but not with TNF-alpha or LPS. By varying the length of pre-incubation with PAF it was demonstrated that this effect decreased as the duration of pre-incubation with PAF increased, and that PAF was enhancing PMA's effects rather than PMA enhancing PAF's effects.

CONCLUSION

This study successfully adapted a commonly used method of measuring human neutrophil respiratory burst function to characterise different aspects of ovine neutrophil respiratory burst function. This improved understanding of ovine neutrophils will facilitate the validitation of ovine biomedical models of human pathologies in which neutrophils have been implicated.

Aprotinin but not tranexamic acid inhibits cytokine-induced inducible nitric oxide synthase expression

Cell expression of inducible nitric oxide synthase (iNOS) is increased by cytokines, which results in high endogenous concentrations of nitric oxide (NO) and has been implicated in organ injury, including myocardial reperfusion injury. Serine protease inhibitors reduce cytokine-induced iNOS expression. The protease inhibitors aprotinin and tranexamic acid, which are used to reduce blood loss after cardiac surgery, were evaluated in vitro on cytokine-induced iNOS expression and the resulting NO production to demonstrate the relative antiinflammatory effects of each drug. A murine bronchial epithelial cell line (LA-4) was stimulated with cytomix (tumor necrosis factor alpha, interleukin 1beta, and gamma-interferon) with or without aprotinin, tranexamic acid, or N-alpha-tosyl-L-lysine chloromethyl ketone (TLCK; a protease inhibitor). The resultant iNOS expression was measured by using Northern blot analysis and cell supernatant nitrite concentrations (in aqueous media, NO is oxidized primarily to nitrite, NO2-) by chemiluminescence. Nitrite concentrations in the supernatant were significantly increased by cytomix, not affected by any concentration of tranexamic acid, but significantly (P < 0.05) reduced by aprotinin and TLCK. Consistent with the nitrite reduction, aprotinin significantly (P < 0.05) reduced cytokine-induced iNOS expression, while tranexamic acid had no effect. Aprotinin but not tranexamic acid reduces endogenous cytokine-induced NO production by inhibiting iNOS expression. Since increased endogenous NO concentrations secondary to iNOS activation have been implicated in organ injury, aprotinin may have clinical benefits when compared with tranexamic acid.