*3.1. Reagents and Chemicals*

*S. japonica* was harvested in Xiapu coastal area, Fujian province, China. Phosphate-buffered saline (PBS) and fetal bovine serum (FBS) were purchased from Solarbio (Beijing, China). The dimethyl sulfoxide (DMSO), DCFH-DA, 1,3-Bis (diphenylphosphino) propane (DPPP), dimethyl sulfoxide (DMSO), diaminofluorophore 4-amino-5-methylamino-2, 7-difluorofluorescein diacetate (DAF-FM-DA), bovine serum albumin (BSA), 3-(4, 5)-dimethylthiazol-2-yl)-2, 5-diphenyltetrazolium bromide (MTT), acridine orange, and Hoechst 33342 were purchased from Sigma Co. (St. Louis, MO, USA). Penicillin/streptomycin (P/S) and Dulbecco's modified Eagle's medium (DMEM) were purchased from Gibco (Rockville, MD, USA). Antibodies against GAPDH (clone number of ARC0205, catalog number of MA5-35235), Bax (clone number of ARC0164, catalog number of MA5-35342), Bcl-xL (clone number of C.85.1, catalog number of MA5-15142), and cleaved caspase-3 (clone number of ARC0133, catalog number of MA5-35333) were purchased from Thermo Scientific (Waltham, MA, USA). All other reagents used in this study were of analytical grade and purchased from Solarbio (Beijing, China).

#### *3.2. Purification and Monosaccharide Determination of Fucoidan Fractions*

## 3.2.1. Extraction and Purification of Polysaccharides

LJSF4 was prepared according to the method described in our previous study [25]. In brief, the defatted sample of *S. japonica* was extracted by triple volume of distilled water at 120 ◦C for 2 h, and then the supernatant was collected. Then, via adding an equal volume of 2% CaCl2 solution in order to remove the alginate in the supernatant, and the resulting supernatant was finally lyophilized to gain crude fucoidan of LJS. The crude LJS was further purified by an anion exchange chromatography (AKTA Purifier UPC100, GE healthcare, Pittsburgh, PA, USA) to obtain the four fractions of LJSF1, LJSF2, LJSF3, LJSF4. The sulfate content and total sugar of each fraction were determined according to our published work [25]. LJSF4 was collected for further assays in this work.
