Inhibition of phagocytic and intracellular killing activity of human neutrophils by aqueous and methanolic leaf extracts of Ixora coccinea.
BACKGROUND
Ixora coccinea is widely used in Ayurveda and traditional medicinal practices in Sri Lanka and in Asia for acute bronchitis, reddened eyes and eruptions and dermatological disorders. The aim of this study was to determine the underling mechanism of anti-inflammatory activity of Ixora coccinea with respect to its inhibitory activity on human neutrophils.


METHODS
Freeze-dried products of aqueous and methanolic leaf extracts (ALE and MLE) prepared from mature fresh leaves of Ixora coccinea and total human leukocytes purified by Dextran sedimentation were used in this study. Three in vitro functional assays were developed and used to assess the inhibitory effects of ALE and MLE on human neutrophils, (i) assay for change-in-shape (CIS) for inhibitory effects on neutrophil polarization, (ii) yeast phagocytosis assay to investigate phagocytic activity of neutrophils and (iii) an optimized quantitative NBT assay to detect the production of reactive oxygen species (ROS).


RESULTS
Both ALE and MLE demonstrated maximum inhibition at 500 µg/ml for CIS (75% and 79% respectively; IC₅₀ values 44.5 and 24.0 µg/ml respectively), yeast phagocytosis (100%; IC₅₀ values 18.0 and 30.0 µg/ml respectively) and ROS production (47% and 67% respectively; IC₅₀ values 248 and 360 µg/ml respectively). All three inhibitory effects of both ALE and MLE were dose-dependent (P<0.05).


CONCLUSIONS
This study has shown that both ALE and MLE of Ixora coccinea exhibit potent anti-neutrophil activity that inhibits its intracellular killing which was demonstrated by the significant inhibition of neutrophil activation, phagocytosis, and production of ROS. MLE showed more potent anti-neutrophil activity compared to ALE reflecting a higher anti-inflammatory activity.
Institute of Biochemistry Molecular Biology and Biotechnology, University of Colombo, Colombo 03, Sri Lanka. Electronic address: rachithaw@yahoo.com.
Rachitha
R
Wickramasinghe
Institute of Biochemistry Molecular Biology and Biotechnology, University of Colombo, Colombo 03, Sri Lanka. Electronic address: rrkumara@gmail.com.
R R
RR
Kumara
Department of Chemistry, Faculty of Science, University of Colombo, Sri Lanka. Electronic address: edilip.desilva@gmail.com.
E Dilip
ED
De Silva
Department of Zoology, Faculty of Science, University of Colombo, Sri Lanka. Electronic address: wdr@zoology.cmb.ac.lk.
W D
WD
Ratnasooriya
Institute of Biochemistry Molecular Biology and Biotechnology, University of Colombo, Colombo 03, Sri Lanka. Electronic address: shiromah@gmail.com.
Shiroma
S
Handunnetti
D000328:Adult; D002478:Cells, Cultured; D006801:Humans; D000432:Methanol / Q000737:chemistry; D009504:Neutrophils / Q000166:cytology / Q000187:drug effects* / Q000502:physiology; D010587:Phagocytosis / Q000187:drug effects; D010936:Plant Extracts / Q000494:pharmacology*; D018515:Plant Leaves; D017382:Reactive Oxygen Species / Q000378:metabolism; D019666:Rubiaceae; D012441:Saccharomyces cerevisiae; D012997:Solvents / Q000737:chemistry; D014867:Water / Q000737:chemistry; D055815:Young Adult
D010936:Plant Extracts; D017382:Reactive Oxygen Species; D012997:Solvents; D014867:Water; D000432:Methanol
Anti-inflammatory; Ixora coccinea; Neutrophil; Phagocytosis; Reactive oxygen species (ROS); Sri Lanka