| Alginate is a naturally acidic polysaccharide composed alternately ofβ-D-mannuronic acid and its C-5 epimer α-L-guluronic acid with 1,4-glycosidic linkages and widely exists in the cell walls of various brown seaweeds.Alginate and its derivatives exert a variety of biological and pharmaceutical activities.This study focuses on the mechanisms of the phagocytosis-promotion of alginate,anti-inflammation of seleno-polymannuronate(Se-PM)and anti-Alzheimer’s disease(AD)of unsaturated mannuronate oligosaccharide(MOS).This thesis is divided into four chapters as follows:(1)The effect of alginate on the promotion of macrophage phagocytosis and the corresponding molecular mechanisms were investigated in murine RAW264.7 cells.Alginate could enhance the intracellular phagocytosis of gold nanoparticles(AuNPs),fluorescent microspheres and immunoglobulin G(IgG)-opsonized Staphylococcus aureus(S.aureus).Moreover,alginate increased Toll-like receptor 4(TLR4)expression and activated the Akt/nuclear factor-κB(NF-κB)and p38mitogen-activated protein kinase(MAPK)signalling pathways.Alginate-promoted phagocytosis was suppressed by the addition of inhibitors of TLR4,NF-κB and p38 MAPK and by TLR4 gene knockdown,indicating the involvement of these key components.(2)The anti-inflammatory activity of Se-PM and the corresponding molecular mechanisms were investigated.Se-PM could significantly attenuate the production of nitric oxide(NO),prostaglandin E2(PGE2)and reactive oxygen species(ROS),the expression of inducible nitric oxide synthase(iNOS)and cyclooxygenase-2(COX-2),and the secretion of pro-inflammatory cytokines in lipopolysaccharide(LPS)-activated murine macrophage RAW264.7 cells.Moreover,Se-PM could remarkably inhibit the LPS-induced activation of nuclear factor(NF)-κB and mitogen-activated protein(MAP)kinase pathways in RAW264.7 cells.A similar trend was observed for above influences in primary macrophages.Additionally,Se-PMcould inhibit the production of pro-inflammatory cytokines in ascites and serum of septic shock mice and in fluid air pouch and serum of mouse air pouch model.(3)The effect of MOS on anti-AD was investigated.MOS could decrease levels of amyloid-β(Aβ),amyloid precursor protein(APP)and γ-secretase(BACE1)in N2a-sw-APP695 cells and in primary cortex neurons in 3×Transgene(3×Tg,APPswe/PS1M146V/TauP301L)mice.Additionally,MOS could reduce phosphorylation levels of protein kinase B(Akt)and mammalian target of rapamycin(mTOR),upregulate the expression of Beclin-1,microtubule associated protein II light chain3(LC3-II)and mature cathepsin D(Cat-D),and decrease the expression of p62.These results indicated that MOS could effectively increase the autophagy level and inhibit Aβ production in AD model.(4)The inhibitory effect of MOS on Tau phosphorylation through autophagy was investigated.MOS could decrease phosphorylation levels of Tau protein on the sites of Ser202,Ser262,Ser396 and Ser404,reduce Tau level,and inhibit glycogen synthase kinase 3β(GSK3β)in HEK293/Tau cells and in primary cortex neurons in3×Tg mice.Additionally,MOS could reduce phosphorylation levels of mTOR,upregulate the expression of Beclin-1,LC3-II and mature Cat-D,and decrease the expression of p62 in 3×Tg mice.These results indicated that MOS could increase the level of autophagy in 3×Tg mice.Taken together,alginate and its derivatives exert various pharmacological activities,including the phagocytosis enhancement,anti-inflammation and anti-neurodegeneration.Therefore,alginate and its derivatives might be promising functional foods and therapeutic candidates to improve health. |
