Abstract
Subcritical water can effectively hydrolyze pectin into smaller molecules while still maintaining its functional regions. Pectic heteropolysaccharide can mediate immune regulation; however, the possible effects of subcritical water-hydrolyzed citrus pectin (SCP) on the immune response remain unclear. Therefore, the effects of SCP on immunomodulatory functions and intestinal microbial dysbiosis were investigated using a cyclophosphamide-induced immunosuppressed mouse model. In this research, immunosuppressed ICR mice were administrated with SCP at dosages of 300/600/1200 mg/kg.bw by oral gavage, and body weight, immune organ indexes, cytokines, and gut microbiota were determined. The results showed that subcritical water treatment decreased the molecular mass and increased the content of galacturonic acid in citrus pectin hydrolysates. Meanwhile, the treatment with SCP improved immunoregulatory functional properties and bioactivities over the original citrus pectin. For example, SCP protected immune organs (accelerated recovery of immune organ indexes) and significantly enhanced the expression of immune-related cytokines (IL-2, IL-6, IFN-γ, and TNF-α). The results of the 16S rDNA sequencing analysis on an IlluminaMiSeq platform showed that SCP normalized Cy-induced gut dysbiosis. SCP ameliorated Cy-dependent changes in the relative abundance of several taxa, shifting the balance back to normal status (e.g., SCP increased beneficial Muribaculaceae, Ruminococcaceae, Bacteroidaceae, and Prevotellaceae while decreasing pathogenic Brevundimonas and Streptococcus). The results of this study suggest an innovative application of citrus pectin as an immunomodulator.
Highlights
Immunosuppression is a state of temporary or permanent immune disorder, which can affect or destroy the immune functional balance, causing an immunocompromised state [1].Immunosuppression is closely associated with upper respiratory tract infection, urinary tract infection, sepsis, and meningitis [2]
The molecular mass of the original citrus pectin (CP) and the products of subcritical water treatment using a high-pressure pump was measured by size exclusion chromatography
The weight-average molecular weight (Mw) and number-average molecular weight (Mn) of citrus pectin were remarkably reduced within 40 min of heat treatment, indicating that subcritical water treatment resulted in a decrease in the molecular weight of pectin
Summary
Immunosuppression is a state of temporary or permanent immune disorder, which can affect or destroy the immune functional balance, causing an immunocompromised state [1].Immunosuppression is closely associated with upper respiratory tract infection, urinary tract infection, sepsis, and meningitis [2]. A recent study indicated that an imbalance of immune function was closely related to dysbiosis of the intestinal microbiota [3], as the gut barrier was disrupted and digestive system complications developed in the immunocompromised group [4]. Cyclophosphamide-induced immunosuppressed mice exhibited a decrease in the richness of bacterial species and an increase in the proportion of Bacteroidetes, while the proportion of Firmicutes and Proteobacteria increased [1,3,5]. This suggests that an imbalance of the immune system causes dysbiosis of the intestinal microbiota. Optimizing the structure of gut microbiota may be an alternative target for ameliorating an imbalance in immunity
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