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Tissue plasminogen activator (tPA) inhibits human neutrophil superoxide anion production in vitro
K A Stringer1, J Lindenfeld, A J Repine
1Department of Pharmacy Practice, University of Colorado Health Sciences Center, Denver 80262, USA.
Abstract:
Because neutrophils contribute to reperfusion injury associated with acute myocardial infarction (MI), and because tissue plasminogen activator (tPA) is often used in the management of MI, we evaluated the effect of tPA on superoxide (O2.-) production by human neutrophils in vitro. We found that adding increasing amounts of tPA significantly (r = 0.89, P < 0.025) and progressively reduced O2.- generation by neutrophils treated with phorbol myristate acetate (PMA) in vitro. Furthermore, adding tPA that had been previously treated with the protease inhibitor, D-Phe-Pro-Arg-chloromethyl ketone HCl (PPACK), also decreased neutrophil O2.- generation in vitro (P < 0.05). In contrast, adding L-arginine, a component of the tPA preparation and a precursor of nitric oxide (NO), did not inhibit PMA-induced neutrophil O2.- production. Also, adding increasing concentrations of tPA did not reduce (P > 0.05) the concentrations of O2.- produced by xanthine oxidase (XO) in vitro. Our findings suggest that tPA reduces neutrophil O2.- generation by a mechanism that is not related to L-arginine, is not dependent on tPA proteolytic activity, and is not a function of direct scavenging. This property may account for some of the effectiveness of tPA in the treatment of MI and/or make tPA valuable for treating acute respiratory distress syndrome (ARDS) or other inflammatory disorders involving neutrophil O2.- production.
Insights
Tissue plasminogen activator (tPA) reduces superoxide production by neutrophils, a key factor in reperfusion injury after heart attack. This finding suggests tPA may have broader therapeutic applications beyond heart attack treatment.
Area of Science:
- Biochemistry
- Immunology
- Cardiology
Background:
- Neutrophils play a significant role in reperfusion injury following acute myocardial infarction (MI).
- Tissue plasminogen activator (tPA) is a common treatment for MI.
- Understanding tPA's effect on neutrophil function is crucial for optimizing MI treatment and exploring new therapeutic avenues.
Purpose of the Study:
- To investigate the in vitro effect of tissue plasminogen activator (tPA) on superoxide (O2.-) production by human neutrophils.
- To elucidate the mechanism by which tPA influences neutrophil superoxide generation.
Main Methods:
- Human neutrophils were stimulated with phorbol myristate acetate (PMA) in the presence of varying concentrations of tPA.
- Neutrophil superoxide production was measured.
- Experiments were conducted using tPA pre-treated with a protease inhibitor (PPACK) and with L-arginine to assess the role of proteolytic activity and L-arginine.
Main Results:
- Increasing concentrations of tPA significantly and progressively reduced superoxide generation by PMA-stimulated neutrophils in vitro.
- tPA that had been inactivated by PPACK also reduced neutrophil superoxide production, indicating the effect is not dependent on tPA's proteolytic activity.
- L-arginine and xanthine oxidase-generated superoxide did not show inhibition by tPA, suggesting the mechanism is not related to L-arginine or direct scavenging.
Conclusions:
- Tissue plasminogen activator (tPA) effectively reduces neutrophil superoxide production through a mechanism independent of its proteolytic activity and L-arginine.
- This inhibitory effect on neutrophil superoxide generation may contribute to tPA's efficacy in treating myocardial infarction.
- tPA's ability to modulate neutrophil superoxide production suggests potential therapeutic value in other inflammatory conditions like acute respiratory distress syndrome (ARDS).