Enzymatic Preparation and Immunomodulatory Mechanism of Oligosaccharide from Caulerpa racemosa var. peltate

In this study, oligosaccharide from Caulerpa racemosa var. peltate (CRVO-G) was prepared by sequential enzymatic hydrolysis with lactase, membrane filtration, dialysis, and freeze-drying, and the relative molecular mass and monosaccharide composition of CRVO-G were measured. Meanwhile, the immunoregulatory activity of CRVO-G was evaluated and its mechanism of action was studied. The results showed that CRVO-G was a mixture of two tetrasaccharides and one hexasaccharide with relative molecular masses of 617.115, 621.081, and 995.368, and was mainly composed of galactose (51.0%), mannose (21.3%), glucose (11.5%), xylose (6.5%), rhamnose (2.3%), glucuronic acid (2.0%), glucosamine hydrochloride (1.8%), fucose (0.8%), glucosamine hydrochloride (0.7%), galacturonic acid (0.7%), mannuronic acid (0.7%), and arabinose (0.6%). In addition, CRVO-G had good immunomodulatory activity, as manifested by increased release of nitric oxide and cytokines (interleukin (IL)-1β, IL-6 and tumor necrosis factor (TNF)-α). The results of metabolomics analysis and Western blot showed that CRVO-G could promote the synthesis of thromboxane A2 (TXA2) and 15-keto prostaglandin F2α (15-keto-PGF2α) in the arachidonic acid pathway of macrophages, and increase the expression levels of cyclooxygenase-2 (COX-2), inducible nitric oxide synthase (iNOS), and the phosphorylation of nuclear factor κB (NF-κB). In summary, CRVO-G exerts immunomodulatory effects by the NF-κB/iNOS/COX-2 pathway in RAW264.7 macrophages.