 to oxidative stress, which cause the endothelial dysfunction and promote the development of many cardiovascular diseases such as atherosclerosis by activating downstream signal molecules such as NF-B [31]. Our previous study also showed that elevating ROS levels triggered apoptosis in HUVECs with nutrition deprivation [18]. Ox-LDL is a potent inducer of ROS, and this was confirmed in the present study; ROS level was increased in HUVECs treated with ox-LDL, whereas both types of propolis could depress ROS level, which lend support to the theory that ROS scavenging could reduce the risk of cardiovascular diseases [32]. Furthermore, transcription factor NF-B is activated by high level of ROS [33]. In present study, ox-LDL induced ROS increase and subsequent activation of NF-B p65 were all attenuated by EECP and EEBP. NF-B signaling pathway is involved in multiple cell processes including apoptosis, proliferation, and gene expression. Moreover, recent studies have suggested that several natural products including propolis suppress inflammatory responses by regulating the NF-B pathway [34, 35]. Atherosclerosis is a kind of chronic inflammatory disease. These findings concur with our finding that the transcriptional inhibition of proinflammatory mediators by propolis is associated with the blockade of NF-B signaling pathway.
Mitochondria are the most important intracellular source of ROS, and elevated ROS levels can also decrease mitochondrial membrane potential [36]. Ox-LDL damages mitochondrial membrane potential, leading the cytochrome c release to induce apoptosis in HUVECs [37]. We previously reported that high concentration of propolis damaged mitochondrial membrane potential in endothelial cells with nutrition deprivation. Here we found that both types of propolis 12.5 g/mL significantly protected mitochondrial membrane potential. Together with these results, we confirmed the protective effect of propolis on HUVECs induced by ox-LDL, and it may be the major mechanisms of propolis modulating atherosclerosis.
Many studies indicate that propolis from different areas has similar biological activity although the chemical constituents are different. Hu et al. (2011) reported that Chinese propolis and Brazilian green propolis had similar biological activities on streptozotocin-induced type 1 diabetes mellitus in rats [38]. And we also previously found that Chinese propolis and Brazilian green propolis had similar protective effects on hepatocytes injury induced by hydrogen peroxide [39]. In current study, we confirmed that both Chinese propolis and Brazilian green propolis had similar activity on ANXA7 expression and PC-PLC activity and other signal molecules in HUVECs induced by ox-LDL. We proposed that it was not a simple chemical constituent in propolis playing crucial role modulating dyslipidemia diseases; it might be a synergy effect of various chemical constituents of propolis. However, in other cells, such as breast cancer MCF-7 and MDA-MB-231 cells, we found that the cytotoxicity of Chinese propolis and Brazilian green propolis was different. So the activities of propolis on different diseases and cells should be further studied.
Altogether, the present findings indicated that both types of propolis 12.5 g/mL significantly increased cell viability and attenuated apoptosis rate, increased the expression of ANXA7, and decreased PC-PLC activity. Both kinds of propolis also inhibited ROS generation as well as the subsequent MMP collapse and NF-B p65 activation induced by ox-LDL in HUVECs, which may be the major mechanisms of propolis protecting endothelial injury and preventing atherosclerosis. Our results also indicated that Chinese propolis and Brazilian green propolis had similar biological activities and prevented ox-LDL induced cellular dysfunction in HUVECs. Both types of propolis may be potent alternative drugs for the prevention of atherosclerosis. However, the mechanism of propolis regulating dyslipidemia should be further studied.
Conflict of Interests
The authors declare that there is no conflict of interests regarding the publication of this paper.
Acknowledgments
This work was supported by the Grant from the National Natural Science Foundation of China (nos. 31201860 and 31272512), Shandong Provincial Natural Science Foundation of China (no. ZR2012CQ003), the Modern Agroindustry Technology Research System from the Ministry of Agriculture of China (CARS-45), and the Doctor Foundation of Liaocheng University of China (no. 31805).
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