*2.1. Chemical Properties*

Fucoidan was extracted from *S. japonica* by hot-water extraction. The yield of fucoidan was 1.2%. Fucoidan was further degraded into low-molecular-weight fucoidan (LMWF) by oxidant degradation by the combination of hydrogen peroxide and ascorbic acid at room temperature. The average molecular weights of fucoidan and its depolymerized fragment LMWF were 136 and 9.5 kDa, respectively.

It is reported that ascorbate and hydrogen peroxide could induce scission of plant cell wall polysaccharides [21]. In this study, this method was used for the degradation of native fucoidan, and the changes of molecular mass indicated that fucoidan was successfully degraded into depolymerized fragment.

The chemical properties of fucoidan and its depolymerized fragment are shown in Table 1. The results indicated that both fucoidan and its depolymerized fragment had similar chemical constituents. The fucose content of fucoidan and LMWF were 31.6% and 29.6%, respectively. Their sulfate contents were 33.58% and 32.66%, respectively. Besides fucose, other monosaccharides including galactose, mannose, glucose, rhamnose, and xylose were present in fucoidan and LMWF, and they also had similar neutral monosaccharide ratios.

**Table 1.** Chemical constituents of fucoidan and low-molecular-weight fucoidan (LMWF) prepared from *S. japonica.*


The IR spectra of fucoidan and LMWF are shown in Figure 1. Both samples had same infrared absorption properties, suggesting that both fucoidan and its depolymerized fragment contained the same functional groups. As shown in Figure 1, the band at 3600-3000 cm<sup>−</sup><sup>1</sup> was assigned to the deformation of O-H. The strong band around 1251 cm<sup>−</sup><sup>1</sup> was attributed to the asymmetric stretching of S=O, the absorption band around 835 cm<sup>−</sup><sup>1</sup> indicated the presence of sulfate groups. The strong absorption at approximately 1020–1050 cm<sup>−</sup><sup>1</sup> corresponded to the C-O-C/C-OH stretching frequency. Meanwhile, from the spectra, it was found that the band around 1251 cm<sup>−</sup><sup>1</sup> of fucoidan and LMWF had similar intensity, which means their sulfate contents were similar, which was consistent to the results of chemical analysis. The results indicated that oxidation degradation had no damage to the backbone structure of fucoidan.

**Figure 1.** Infrared spectra of fucoidan and low molecular weight fucoidan (LMWF). FPS—fucoidan; DFPS:—low-molecular-weight fucoidan.

Based on the above analysis, it can be concluded that after degradation, the chemical constituents of fucoidan and its depolymerized fragment had no significant changes, only the molecular weight was greatly decreased.

## *2.2. Evaluation of Rats Weight Alteration*

The adriamycin-induced nephrotic syndrome is a classical nephrotic syndrome model. In this study, the general condition of the animals was observed during the experiments. Compared with the normal rats, rats treated with adriamycin showed abnormal behavioral activities, including reduced feed intake, easy tiredness, emaciation, tarnish, and depilation. Some animals had obvious diarrhea.

Body weight changes of all rats were examined once a week during the experiment; the weight changes before and after drug administration are shown in Table 2. Significant changes in body weight were observed among the normal and other groups during the treatment period. The body weight of the model group was significantly lower (*p* < 0.01) than that of the normal group. Compared with the model group, the body weight of rats in positive control group administrated with dexamethasone was much lower, while rats treated with fucoidan and LMWF at the dose of 100 mg/kg gained weight significantly. Rats treated with LMWF at the dose of 100 mg/kg gained a higher weight than fucoidan-treated rats at two weeks after drug administration (*p* < 0.05). LMWF treatment at the dose of 50 and 25 mg/kg also increased the body weight of rats, but had no statistical difference.

**Table 2.** Effect of fucoidan and low molecular weight fucoidan (LMWF) treatment on body weight of rats (*X* ± *S*, g).


: *p* < 0.05, : *p* < 0.01 (vs normal group); \*: *p* < 0.05, \*\*: *p* < 0.01 (vs model group).

The daily feed intake of rats was significantly reduced after adriamycin treatment (Table 3). Compared with the model group, rats treated with fucoidan and LMWF at the dose of 100 mg/kg had much higher feed intake. It partly explains why these rats had higher body weight.


**Table 3.** Effect of fucoidan and low molecular weight fucoidan (LMWF) treatment on feed intake of rats (*X* ± *S*, g).

: *p* < 0.05 (vs normal group); \*: *p* < 0.05 (vs model group).
