Fucoidan is a sulfated polysaccharide extracted from brown algae; according to previous studies, it has been found to have many beneficial physiological effects. For example, it exhibits antioxidant, anti-inflammatory, and anticancer effects. However, the mechanisms of endoplasmic reticulum (ER) stress-mediated fucoidan-induced apoptosis are still unexplored.

Therefore, in this blog, I would like to introduce the study, “Fucoidan induces Toll-like receptor 4-regulated reactive oxygen species and promotes endoplasmic reticulum stress-mediated apoptosis in lung cancer” by Hsien-Yeh Hsu et al. This study is the first to identify a new mechanism of Fucoidan’s anti-tumor activity, demonstrating that Fucoidan prevents tumorigenesis and reduces tumor size in LLC1 xenografted male C57BL/6 mice.

First, to investigate the effects of Fucoidan feeding on LLC1-bearing mice in vivo, mice were fed Fucoidan (24 mg/kg/day) for 14 days, followed by subcutaneous dorsal inoculation of LLC1 cells on day 14. Fucoidan was also given daily, and the tumor growth rate was assessed over 23 days. Fucoidan-fed mice significantly reduced tumor volume. (See Figure. 1A, B)

They then collected tumor lesions from mice and analyzed the expression of ER stress-related proteins. Figures 1D and E show that ATF4 and CHOP (involved in proliferation, differentiation and expression, and energy metabolism) protein levels were increased in fucoidan-fed LLC1-bearing mice compared with mice in the control group.

Hence, the study established that Fucoidan inhibited the growth of LLC1 cells in a dose- and time-dependent manner using the MTT assay. Specifically, they found that Fucoidan induced the expression of endoplasmic reticulum stress-related proteins such as GRP78, ATF4, and CHOP in a time- and dose-dependent manner.

Furthermore, they showed that Fucoidan inhibited the phosphorylation of AKT and ERK, which are associated with cancer cell viability and proliferation. These results indicate that induction of ER stress and inhibition of AKT/ERK signaling are involved in preventing and suppressing fucoidan-mediated tumorigenesis in vitro and in vivo.

Next, they investigated whether Fucoidan induces apoptosis in A549 and CL1-5 lung cancer cells. As shown in Figure. 3A and Supplementary Figure. 1A, B, apoptotic cells increased after fucoidan treatment for 48 h. Moreover, using Western blot assay and FACS analysis, they also found that Fucoidan activated caspase-3 and PARP and induced apoptosis in LLC-1 cells

CHOP (a chemotherapy combination) expression is upregulated by endoplasmic reticulum stress and triggers apoptosis. CHOP expression is upregulated by endoplasmic reticulum stress and triggers apoptosis. To further investigate, they confirmed the role of CHOP in fucoidan-induced apoptosis based on the western blotting analysis. The study found that CHOP knockdown decreased TG-induced ER stress-mediated CHOP expression. These results indicate that CHOP is essential in fucoidan-induced ER stress-mediated apoptosis in lung cancer cells.

Also, the induction of intracellular ROS generation can trigger cell apoptosis via the ER stress pathway. Therefore, the study used H2DCFDA to measure intracellular ROS production in fucoidan-treated lung cancer cells. As shown in Figure 3A, a time-dependent increase in DCF fluorescence was observed after cells were treated with Fucoidan. It indicates that Fucoidan induced intracellular ROS generation in A549 cells.

Here, H2DCFDA was used to measure intracellular ROS production in fucoidan-treated lung cancer cells. As shown in Figure 6A, a time-dependent increase in DCF fluorescence was observed after cells were treated with Fucoidan. It indicates that Fucoidan induced intracellular ROS generation in A549 cells.

They performed TLR4 knockdown experiments and found that knockdown of TLR4 expression (shTLR4) abolished fucoidan-induced ROS compared to the ‘scrambled’ TLR4 control group. Second, They found that the knockdown of TLR4 expression dose-dependently abolished fucoidan-induced ROS. Third, they analyzed the fluorochromes’ mean fluorescence intensity (MFI) (H2DCFHDA and DCF) and observed that fucoidan treatment reduced ROS in TLR4-knockdown cells by 40%. It proves that TLR4 plays a partial role in fucoidan-induced ROS and promotes ER stress and stress-mediated apoptotic gene expression.

In conclusion, these results indicate that Fucoidan is a potential preventive and therapeutic agent for lung cancer that acts via the activation of ROS-dependent ER stress pathways.