Ethanol extract of propolis protects vascular endothelial cells from oxidized low-density lipoprotein-induced apoptosis by inhibiting C/EBP homologous protein expression

AIM: To investigate the inhibitory effect of ethanol extract of propolis (EEP) on oxidized low-density lipoprotein (ox-LDL)-induced vascular endothelial cell apoptosis and the underlying molecular mechanisms.METHODS: Human umbilical vein endothelial cells (HUVECs) were pretreated with EEP (7.5, 15 and 30 mg/L) or 4-phenylbutyric acid (PBA, 4 mmol/L) for 1 h and then treated with ox-LDL (100 mg/L) or tunicamycin (TM, 4 mg/L) for 24 h. The cell viability and apoptosis were determined by MTT assay and Annexin V-FITC/PI double staining, respectively. The activities of lactic dehydrogenase (LDH) in the medium and caspase-3 in the HUVECs were measured. The protein and mRNA levels of C/EBP homologous protein (CHOP), a proapoptotic molecule under endoplasmic reticulum stress (ERS), and its downstream Bcl-2 were examined by Western blot and real-time PCR, respectively.RESULTS: Like PBA (an ERS inhibitor), EEP protected HUVECs from ox-LDL-induced injury in a dose-dependent manner, as assessed by the increased cell viability and the decreased LDH release, apoptotic rate and caspase-3 activation. The decrease in cell viabi-lity and the increases in LDH release, apoptotic rate and caspase-3 activation induced by TM, an ERS inducer, were also attenuated by EEP. Moreover, EEP suppressed ox-LDL-induced CHOP upregulation and Bcl-2 downregulation, and this effect was similar to that of PBA. Similarly, EEP significantly suppressed TM-induced CHOP upregulation both at the protein and mRNA levels.CONCLUSION: EEP may protect HUVECs from ox-LDL-induced apoptosis, and the mechanism is at least partially involved in suppressing CHOP-mediated ERS-associated apoptotic pathway.