**4. Conclusions**

In this paper, a native fucoidan (SC) was extracted from *S. crassifolium* pretreated by single-screw extrusion. The extrusion pretreatment process augmented the extraction yield of fucoidan as compared to the non-extruded sample. Three degraded fucoidans (SCA, SCH, and SCAH) were obtained by degrading SC with different combinations of degradation reagents. Among SC, SCA, SCH, and SCAH, the chemical compositions varied but their structural features were similar, as illustrated by the results of FTIR and NMR analyses. In vitro anti-lung cancer studies revealed that SC, SCA, SCH, and SCAH decreased MMP, decreased Bcl-2 expression, increased the release of cytochrome c, increased activation of caspase-9 and -3, and increased late apoptosis of A-549 cells. In general, SCA has a high amount of low-molecular-weight fraction and the highest fucose content, is highly cytotoxic to A-549 cells, and shows a high ability to suppress Bcl-2 expression, to induce cytochrome c release, to promote activation of caspase-9, and to induce late apoptosis of A-549 cells. Therefore, SCA demonstrated excellent potential for development as an adjuvant treatment of lung cancer. Additional in vitro experiments showed that the Akt/mTOR signaling pathway is involved in SC-, SCA-, SCH-, and SCAH-induced apoptosis of A-549 cells. Further experiments are warranted to elucidate the precise signaling mechanisms involved, especially using in vivo studies.

**Supplementary Materials: <sup>1</sup>**H-NMR spectra and 13C-NMR spectra for SC, SCA, SCH, and SCAH are available online at http://www.mdpi.com/1660-3397/18/6/334/s1.

**Author Contributions:** Conceptualization, T.-C.W. and C.-H.K.; methodology, Y.-H.T.; software, S.-L.H.; validation, R.-H.H., Y.-H.H., and C.-Y.H.; formal analysis, R.-H.H. and Y.-H.H.; investigation, Y.-H.T., C.-H.K., and Y.-H.H.; resources, C.-H.K. and S.-L.H.; data curation, R.-H.H. and T.-C.W.; writing—original draft preparation, T.-C.W., Y.-H.H., and C.-H.K.; writing—review and editing, C.-H.K. and C.-Y.H.; supervision, Y.-H.H.; project administration, C.-Y.H.; funding acquisition, T.-C.W., Y.-H.H., and C.-Y.H. All authors read and agreed to the published version of the manuscript.

**Funding:** This research received no external funding.

**Acknowledgments:** This study was supported by a gran<sup>t</sup> from the Kaohsiung Medical University Hospital (KMUH107-M729) to Tien-Chiu Wu, as well as by the Ministry of Science and Technology, Taiwan, gran<sup>t</sup> number MOST 107-2320-B-992-001, which was awarded to Chun-Yung Huang. The authors thank the Ministry of Education, Taiwan, for supporting this study (grant number MOE-RSC-108RSN0005), awarded to Yong-Han Hong.

**Conflicts of Interest:** The authors declare no conflicts of interest.
