Fucoidan Oligosaccharide Supplementation Relieved Kidney Injury and Modulated Intestinal Homeostasis in D-Galactose-Exposed Rats

Abstract

Background/Objectives: A fucoidan oligosaccharide (FOS), a potent compound derived from algae, is known for its diverse biological activities, including prebiotic activity, anticancer activity, and antioxidative properties, and has demonstrated supportive therapeutic effects in treating kidney ailments. This study was conducted to explore the protective influence of FOS on kidney damage due to aging induced by D-galactose in Sprague Dawley (SD) rats. Methods: The low-dose FOS group was administered FOS (100 mg/kg) by gavage, and the high-FOS group received FOS (200 mg/kg) by gavage. Results: The findings showed that FOS could effectively mitigate kidney damage and improve the pathological condition of kidney tissues caused by D-gal and enhance kidney function. Intervention with FOS significantly reduced serum creatinine, serum uric acid, and serum urea nitrogen levels, compared to the model group. The protective mechanism of FOS on D-gal-induced kidney injury may be to inhibit oxidative stress and improve impaired mitochondrial function by downregulating the AMPK/ULK1 signaling pathway. FOS could also modulate the expression of mitochondrial autophagy-related proteins (Beclin-1, P62, and LC3II/LC3I), thereby mitigate D-gal-induced excessive mitophagy in the kidney. Furthermore, FOS may protect against kidney injury by preserving intestinal homeostasis. FOS decreased serum lipopolysaccharide levels and enhanced intestinal mucosal barrier function. FOS upregulated the abundances of Bacteroidota, Muribaculaceae, and Lactobacillus, while it decreased the abundances of Firmicutes, NK4A136_group, and Lachnospiraceae_NK4A136_group. FOS supplementation modulated gut microbiota composition, increasing beneficial bacteria and reducing detrimental ones, potentially contributing to improved kidney function. Conclusions: FOS may safeguard against renal injury in D-gal-exposed rats by inhibiting kidney excessive mitophagy, preserving mitochondrial function, and regulating intestinal homeostasis.

Keywords: fucoidan oligosaccharide; kidney injury; mitochondrial autophagy.

Figure 1

FOS attenuated D-gal-induced renal impairment. (A) Body weight; (B) daily food consumption; (C) kidney index; (D) serum creatinine; (E) serum uric acid; (F) serum urea nitrogen. All data are presented as mean ± SEM (n = 10). ^a p < 0.05 vs. CON group, ^b p < 0.05 vs. MOD group, ^c p < 0.05 vs. LF group.

Figure 2

FOS alleviated D-gal-induced kidney histopathological changes and SA-β-gal staining positive cell rate. (A) Representative HE staining (×200, bar = 50 µm; ×400, bar = 20 µm). (B) Representative SA-β-gal staining (×100, bar = 100 µm; ×200, bar = 50 µm). (C) Percentage of SA-β-gal staining positive cells in each group. All data are presented as mean ± SEM (n = 3). ^a p < 0.05 vs. CON group, ^b p < 0.05 vs. MOD group, ^c p < 0.05 vs. LF group.

Figure 3

FOS declined the ROS level in D-gal-exposed rats. (A) The levels of ROS; (B) the fluorescence intensity of the probe. All data are presented as the mean ± SEM (n = 3). ^a p < 0.05 vs. CON group, ^b p < 0.05 vs. MOD group, ^c p < 0.05 vs. LF group.

Figure 4

FOS attenuated oxidative stress in D-gal-exposed rats. Levels of (A) CAT, (B) SOD, (C) GSH-PX, and (D) MDA in serum; levels of (E) CAT, (F) SOD, (G) GSH-PX, and (H) MDA in kidney tissues. All data are presented as mean ± SEM (n = 10). ^a p < 0.05 vs. CON group, ^b p < 0.05 vs. MOD group, ^c p < 0.05 vs. LF group.

Figure 5

FOS improved mitochondrial damage in D-gal-exposed rats. (A) Representative TEM images (bar = 1 µm). Black arrow: mitochondrial cristae. Stemless arrows: mitophagosomes. Kidney ATP (B) and AMP (C) levels. AMP/ATP ratio (D). All data are presented as mean ± SEM (n = 3). ^a p < 0.05 vs. CON group, ^b p < 0.05 vs. MOD group, ^c p < 0.05 vs. LF group.

Figure 6

FOS downregulated p-AMPK and p-ULK1 protein levels of kidney tissue in D-gal-exposed rats. (A) Protein expression levels of AMPK, P-AMPK, ULK1, and P-ULK1 were measured by Western blotting; semi-quantification of (B) AMPK and ULK1, and (C) P-AMPK/AMPK and P-ULK1/ULK1, protein expression. All data are presented as mean ± SEM (n = 3). ^a p < 0.05 vs. CON group, ^b p < 0.05 vs. MOD group, ^c p < 0.05 vs. LF group.

Figure 7

FOS inhibited excessive mitophagy by downregulating autophagy-related protein levels of kidney tissue in D-gal-exposed rats. (A) The protein expression levels of Beclin-1, P62, and LC3II/LC3I. (B) The semi-quantification of Beclin-1, P62, and LC3II/LC3I protein expression. All data are presented as the mean ± SEM (n = 3). ^a p < 0.05 vs. CON group, ^b p < 0.05 vs. MOD group, ^c p < 0.05 vs. LF group.

Figure 8

FOS improved ileal structural damage and increased tight junction protein expression levels in D-gal-exposed rats. (A) Pathological changes in intestine tissues by H&E staining. Scale bar = 100 µm (100×); (B) villus height and (C) crypt depth; (D) serum LPS level; (E) protein expression levels of ZO-1 and Claudin1; semi-quantification of ZO-1 (F) and Claudin1 (G) protein expression. All data are presented as mean ± SEM (n = 3). ^a p < 0.05 vs. CON group, ^b p < 0.05 vs. MOD group, ^c p < 0.05 vs. LF group.

Figure 9

α-Diversity analysis of D-gal-exposed rats’ gut microbiota, including ACE (A), Chao1 (B), Simpson index (C), and Shannon index (D). All data are presented as mean ± SD (n = 6). ^a p < 0.05 vs. CON group.

Figure 10

The β-diversity analysis of gut microbiota in D-gal-exposed rats. (A) The principal coordinate analysis between the three groups (PCoA); (B) ANOSIM assessed gut microbiota differences among three groups, and + shows an outlier value; (C) the β-diversity heatmap represents three groups’ gut microbiota variation.

Figure 11

Gut microbiota community composition in each group. (A) Phylum; (B) genus; (C) Firmicutes abundance; (D) Bacteroidota abundance; (E) F/B ratios; (F) unclassified_Muribaculaceae abundance; (G) NK4A214 group abundance. ^a p < 0.05 vs. CON group, ^b p < 0.05 vs. MOD group.

Figure 12

Correlation heatmap between biological index and gut microbiota. (A) Correlation heatmap between biological index and phylum level; (B) correlation heatmap between biological index and genus level. Correlations between biochemical parameters and gut microbiota are positively correlated in red, while being negatively correlated in blue. Correlations are stronger with darker colors. * p < 0.05 and ** p < 0.01 show significant correlations.

Figure 13

Potential alleviation mechanisms of FOS on kidney damage in D-gal-exposed rats. The upward arrow indicates increase, and the downward arrow indicates decrease.