Regulatory Mechanisms Underlying The Suppression Of Atherosclerosis Of A Purified Laminaria Japonica Polysaccharide In High Fat Diet Induced LDLr^-/- Mice

Laminaria japonica is an important marine vegetable with great health-benefits for preventing atherosclerosis. Since the foam cell formation is an important hallmark for the initiation of atherosclerosis, we examined the effect and underlying mechanism of a purified L. japonica polysaccharide (LJP61A) on the formation of macrophage foam cell in this study. The main results were obtained follows:(1) Purification and characterization of LJP61A:After extraction, the crude LJP6 was fractionated by DEAE-Cellulose ion-exchange chromatography and further purified by Sephacryl S-500 gel filtration chromatography, giving one homogeneous polysaccharides (LJP61A). The average molecular weight of LJP61A was estimated to be 1.96×106 Da. GC analysis showed that LJP61A was mainly composed of mannose, glucose, galactose in a molar ratio of 1:1.85:2.92. The structure of LJP61A was characterized as a repeating unit consisting of →3,6)-α-D-Man,p-(1→, →4)-α-D-Manp-(1→,→4)-2-O-avetyl-β-D-Glqp-(1→,→4)-β-D-Glcp-(1→, →6)-4O-SO3-β-D-Galp-(1→,→6)β-D-Galp-(1→.→3)-β-D-Galp-(1→ and α-D-Glcp-(1→.(2) Anti-atherosclerosis activity of LJP61A in vivo:Anti-atherosclerosis activity of LJP61A was researched using model of LDL-/- mice induced by high fat diet (HFD). Pathologic observation showed that LJP61A had good potential for preventing the initiation and development of atherosclerosis induced by high fat diet (HFD). When the mice were treated with 200 mg/kg-day LJP61A, the levels of TC, TG, HDL-C and LDL-C were decreased by 73.9%、73.6%,30.4% and 84.1% than those of the model group. Meanwhile, LJP61A could significantly suppress the content and the mRNA expression of TNF-α, IL-1β and IL-6 in the aorta than those of the model group. According to these results, we can conduce that, at least partly, LJP61A inhibited the initiation and development of atherosclerosis induced by HFD via regulation of lipid metabolism and suppression of inflammation.(3) The regulating and mechanism of LJP61A inhibited foam cell formation induced by oxLDL:Using oxidized low-density lipoprotein (ox-LDL)-induced foam cell model, we found that the cellular lipid accumulation was significantly attenuated by 25 μg/mL LJP61A. Meanwhile, LJP61A caused a remarkable decrease in mRNA expression of peroxisome proliferator-activated receptor y which was accompanied by the reduction of CD36 and Acyl coenzyme A:cholesterol acyltransferase-1 mRNA levels, and the enhancement of ATP-binding cassette transporters Al and scavenger receptor B1 mRNA and protein levels. Results showed LJP61A, through PPARy pathway, modulates the expression of genes involved in regulation of the balance between lipoprotein uptake, conversion and efflux, and thus inhibits the conversion of macrophages into foam cells. Moreover, we also found that LJP61A can suppress the ox-LDL induced activation of TLR2/4-mediated MAPK and NFκB signaling pathways and the production of TNF-a and IL-1β via mTOR. Our findings suggest that LJP61A inhibits the conversion of macrophage into foam cell via regulating cellular lipid metabolism and suppressing cellular inflammation.