METHODS: The extract was analyzed quantitatively by performing a validated reversed phase high performance liquid chromatography (RP-HPLC). Zerumbone was isolated by chromatographic technique while the essential oil was acquired through hydro-distillation of the rhizomes and further analyzed by gas chromatography (GC) and GC-MS. Chemotaxis assay was assessed by using a 24-well cell migration assay kit, while CD18 integrin expression and phagocytic engulfment were measured using flow cytometry. The reactive oxygen species (ROS) production was evaluated by applying lucigenin- and luminol-enhanced chemiluminescence assays.
RESULTS: Zerumbone was found to be the most abundant compound in the extract (242.73 mg/g) and the oil (58.44%). Among the samples tested, the oil revealed the highest inhibition on cell migration with an IC50 value of 3.24 μg/mL. The extract, oil and zerumbone showed moderate inhibition of CD18 integrin expression in a dose-dependent trend. Z. zerumbet extract showed the highest inhibitory effect on phagocytic engulfment with percentage of phagocytizing cells of 55.43% for PMN. Zerumbone exhibited strong inhibitory activity on oxidative burst of zymosan- and PMA-stimulated neutrophils. Zerumbone remarkably inhibited extracellular ROS production in PMNs with an IC50 value of 17.36 μM which was comparable to that of aspirin.
CONCLUSION: The strong inhibition on the phagocytosis of neutrophils by Z. zerumbet extract and its essential oil might be due the presence of its chemical components particularly zerumbone which was capable of impeding phagocytosis at different stages.
METHODS: Chemotaxis was evaluated using a modified Boyden chamber and phagocytosis was determined by flowcytometer. Respiratory burst was investigated by luminol-based chemiluminescence assay while MPO activity was determined by colorimetric assay.
KEY FINDINGS: Artocarpanone and artocarpin strongly inhibited all steps of phagocytosis. Artocarpanone and artocarpin showed strong chemotactic activity with IC50 values of 6.96 and 6.10 μm, respectively, which were lower than that of ibuprofen (7.37 μm). Artocarpanone was the most potent compound in inhibiting ROS production of polymorphonuclear leucocytes and monocytes with IC50 values comparable to those of aspirin. Artocarpin at 100 μg/ml inhibited phagocytosis of opsonized bacteria (28.3%). It also strongly inhibited MPO release with an IC50 value (23.3 μm) lower than that of indomethacin (69 μm). Structure-activity analysis indicated that the number of hydroxyl group, the presence of prenyl group and variation of C-2 and C-3 bonds might contribute towards their phagocytosis.
CONCLUSIONS: Artocarpanone and artocarpin were able to suppress strongly the phagocytosis of human phagocytes at different steps and have potential to be developed into potent anti-inflammatory agents.
METHODOLOGY/PRINCIPAL FINDINGS: PA exerted selective cytotoxicity on human umbilical vein endothelial cells (HUVECs) with IC(50) value of 6.91 ± 0.85 µM when compared to human normal fibroblast and normal liver epithelial cells. Assessment of the growth kinetics by cell impedance-based Real-Time Cell Analyzer showed that PA induced both cytotoxic and cytostatic effects on HUVECs, depending on the concentration used. Results also showed that PA suppressed VEGF-induced survival and proliferation of HUVECs. Furthermore, endothelial cell migration, invasion, and morphogenesis or tube formation demonstrated significant time- and dose-dependent inhibition by PA. PA also suppressed matrix metalloproteinase-2 (MMP-2) secretion and attenuated its activation to intermediate and active MMP-2. In addition, PA suppressed F-actin stress fiber formation to prevent migration of the endothelial cells. More importantly, anti-angiogenic potential of PA was also evidenced in two in vivo models. PA inhibited neo-vessels formation in murine Matrigel plugs, and angiogenesis in zebrafish embryos.
CONCLUSIONS/SIGNIFICANCE: Taken together, our study demonstrated the distinctive anti-angiogenic properties of PA, both in vitro and in vivo. This report thus reveals another biological activity of PA in addition to its reported anti-inflammatory and anti-cancer activities, suggestive of PA's potential for development as an anti-angiogenic agent for cancer therapy.