The algal polysaccharide ulvan suppresses growth of hepatoma cells

Treatment for tumors depends on host immune system. The antitumor and immunoregulatory activities of Ulva lactuca polysaccharide (ULP) were evaluated in H22 tumor-bearing mice and cyclophosphamide-induced immunosuppressed mice, respectively. The structural properties of ULP were identified through multi-angle laser light scattering, high-performance liquid chromatography, Fourier-transformed infrared, and nuclear magnetic resonance. It was composed of α-D-Manp-(1→, →2,4)-β-L-Rhap-(1→, β-D-GlcpA-(1→, β-GalpA-(1→, →2,4)-α-D-Glcp-(1→, and →6)-β-D-Galp-(1→ with the molecular weight of 1.46 × 105 Da. Its antioxidant, anti-inflammatory, and antitumor effects were determined. Liver and tumor tissues were collected for histopathological, immunohistochemical, and western blotting analysis. ULP showed the great tumor growth inhibition of 74.41% compared with cyclophosphamide, which has side effects on immune system. ULP enhanced the expression of p53 to inhibit tumorigenesis, promoted the activation of IKKα, and inhibited the activation of p65 within the NF-κB pathway. ULP inhibited the tumor growth through downregulating the expressions of PI3K/Akt and mTOR, and promoting BAX/Bcl-2 ratio. The inhibition of TRAF2/TNF-α and CD31/VEGF achieved a direct killing effect on tumor cells and inhibited tumor proliferation by inhibiting angiogenesis, respectively. Moreover, ULP increased the levels of immunoglobulin M and total superoxide dismutase, decreased the level of methane dicarboxylic aldehyde, and inhibited the activation of PI3K/AKT/mTOR/p70S6k pathways. The results showed that ULP exhibited pronounced antitumor activity and immunoregulatory effect.