Structure Characterization Of Selenium-containing Polysaccharide From Spirulina Platensis And Its Protective Effect Against Cadmium-induced Toxicity

Selenium polysaccharides are a new type of functional polysaccharide.Previous studies have demonstrated that selenium polysaccharides possess better biological activities than either polysaccharides or inorganic selenium.Selenium polysaccharides have gradually become a research topic of interest for the development of functional foods and pharmaceutical products.Currently,Spirulina platensis has the largest scale of cultivation and processing among edible microalgae,which has high medical and health value.The bio-activities of the polysaccharide isolated from Spirulina platensis have been proved,including antioxidant,antitumour,antiviral,antiradiation and other functional activities.At present,there have been researches on selenium-enriched Spirulina.However,the investigate related to selenium polysaccharide from Spirulina platensis focused on its antioxidant or anti-tumor activities,and lacked of research on its specific molecular structure.Due to the extensive biological half-life and high toxicity,the impact of cadmium(Cd)pollution on human health requires special attention.Polysaccharides derived from various natural products possess good potential in protective effect against cadmium toxicity.At the same time,inorganic selenium also plays role in alleviating cadmium-induced damage.The selenium-containing polysaccharide from selenium-enriched Spirulina may replace polysaccharides as potential natural products to attenuate cadmium toxicity.In order to investigate the structure characteristics,protective effect against cadmium toxicity and its mechanism of selenium polysaccharides form Spirulina platensis,this study was carried out.The main research content,methods and conclusions are as follows:(1)By adjusting the addition of selenite,original and selenium-enriched Spirulina platensis were harvested.And then the original polysaccharide(SPP,0.01±0.01?g/g Se content)and selenium polysaccharide(Se-SPP,14.12±1.41?g/g Se content)were isolated.The chemical composition,molecular weight and monosaccharide composition of SPP and Se-SPP were almost the same.Therefore,it was inferred that the bonding of a small amount of Se element did not influence on the structure properties of the polysaccharide.(2)Se-SPP-1(molecular weight 44.0 k Da)was separated from Se-SPP.The results of structure analysis illustrated that Se-SPP-1 was a homogeneous glucan.The backbone of Se-SPP-1 was composed of?4)-?-Glcp-(1?sugar residues.As well as,there were branches linked with?3,4)-?-Glcp-(1?and?4,6)-?-Glcp-(1?sugar residues at the C-3 andC-6 positions.The spatial structure of Se-SPP-1 was a stretched,multi-branched long chain structure.(3)CdCl₂was utilized to buildCd-intoxicated HL-7702 and HEK293 cells model in vitro.After 24 hours of Cd²⁺exposure,compared to the cell viability of Cd group,those in the Na₂Se O₃,SPP and Se-SPP groups increased significantly(p<0.05).Among them,the protective effect of Se-SPP group was superior to Na₂Se O₃and SPP groups.Furthermore,CdCl₂was also utilized to buildCd-intoxicated SD rats model in vivo.The analysis of organ coefficients,contents of Cd in liver and kidney,biochemical indicators of hepatorenal function and histopathology examination showed that Se-SPP appeared better protective effect on relieving liver and kidney damage than Na₂Se O3 or SPP.(4)So as to investigate the long-term protective effect of selenium polysaccharide from Spirulina platensis(Se-SPP-1,for short SeP)against cadmium toxicity,a 28-day long-term Cd exposure C57BL/6J mouse model was established.The results of Biochemical indicators of liver function and histopathology examination revealed that long-term Cd exposure caused apparent liver damage,and the degree of damage is positively correlated with the accumulation of Cd in the liver.The oral administration of SeP obviously reducedCd toxicity.(5)Evaluating from liver oxidative stress,it can be seen that long-term Cd exposure activated the oxidative stress in body,which lead to inflammation and apoptosis of liver.SeP substantially mitigatedCd-induced hepatotoxicity by enhancing the activities of SOD,GSH-Px andCAT and inhibiting nitrosification and inflammation.By measuring the expression of inflammation-related genes,it can be found that SeP can reduce the gene expression of NF-?B,c-FLIP,JNK,ERK,and P38 m RNA,while increasing the gene expression of XIAP m RNA,which indicating that SeP inhibited the NF-?B/MAPK pathway to reduce Cd-induced liver damage in treated mice.(6)Evaluating from intestinal barrier protection,it can be suggested that long-term oral administration of CdCl₂damaged the intestinal structure of mice,and SeP effectively alleviated the intestinal injury.Meanwhile,the expression of tight junction protein claudin-4 and ZO-1 in intestinal barrier were determined by western bolt method.The results exhibited that SeP maintained the expression of claudin-4 and ZO-1,thereby repairing the damage to intestinal barrier.Furthermore,the results of 16S sequencing showed that Cd caused changes in the gut microbiota of mice at the phylum and genus levels.Na₂Se O₃and SeP substantially affected the composition of the gut microbiota of experimental mice,thus maintaining the integrity of the intestinal barrier.Finally,the the levels of SCFAs in mouse feces revealed that Cd exposure caused a sharp drop in the level of total SCFAs and acetic acid?propanoic acid?isobutyric acid?butyric acid?isovaleric acid?valeric acid?hexanoic acid in feces.SeP increased the concentration of short-chain fatty acids to varying degrees,and 100mg/kg.b.w was the best dose.In summary,the biological selenium enrichment method was utilized to prepare selenium polysaccharide from Spirulina platensis.The combination of Se hardly influenced on the original structure of polysaccharide,but significantly enhanced its protective effect against cadmium toxicity.In addition,two mechanisms of attenuating the toxicity of cadmium have been studied:inhibiting oxidative stress in the liver and protecting the intestinal barrier.The research broadened the application of Spirulina platensis,and provided an experimental and theoretical basis for the associated research of selenium polysaccharides.As well as,the research of polysaccharides from daily dietary sources to decrease heavy metal toxicity can be referenced from this paper.