Plant natural products calycosin and gallic acid synergistically attenuate neutrophil infiltration and subsequent injury in isoproterenol-induced myocardial infarction: a possible role for leukotriene B4 12-hydroxydehydrogenase?

Abstract

Background and aims: Leukotriene B4 12-hydroxydehydrogenase (LTB4DH) catalyzes the oxidation of pro-inflammatory lipid mediator leukotriene B4 (LTB4) into less bioactive 12-oxo-LTB4. We recently discovered that LTB4DH expression was induced by the combination of two different plant natural products: gallic acid from Radix Paeoniae and the other uncharacterized ones from Radix Astrgali. The purpose of this study was to test the hypothesis that LTB4DH inducers may suppress neutrophil-mediated inflammation in myocardial infarction. Methods and results: The active compounds were isolated from Radix Astrgali extract following the bioactivity-guided fractionation strategy, and subsequently identified by high performance liquid chromatography-electronic spray ionization-mass spectrometry (HPLC-ESI-MS) technique. LTB4DH induction was detected in human HepG2 cells and neutrophils by RT-PCR technique. LTB4DH inducers (i.e., calycosin and gallic acid) in combination were first evaluated for the in vitro effects on the survival and chemotaxis of human neutrophils. Calycosin and gallic acid in combination were further assessed for the in vivo cardioprotection in isoproterenol-induced mice model of myocardial infarction. We found that calycosin and gallic acid in combination exhibited the following activities: 1) antagonized the effects of LTB4 on the survival and chemotaxis of human neutrophils; 2) suppressed neutrophil infiltration into cardiac tissue; 3) reduced MPO activity and MDA production in mouse heart tissues; 4) attenuated neutrophil-mediated cardiac injury in isoproterenol-induced myocardial infarction. Conclusion: Plant natural products calycosin and gallic acid synergistically attenuated neutrophil infiltration and subsequent cardiac injury in isoproterenol-induced myocardial infarction. Thus, LTB4DH inducers represent a novel combined therapy for the treatment of neutrophil-mediated myocardial injury. Acknowledgements: This work was supported by a General Research Fund (GRF) grant (HKU774307 M) from the Research Grants Council of Hong Kong (to J.R.) and two internal Seed Funds for Basic Research Programme from University of Hong Kong.