| BackgroundThe incidence of hyperuricemia has been increasing,which has reached 10%,and even reached 25%in coastal economically developed cities in our country.At present,China's economic development,changes in diet and other factors have aggravated the increase.As hyperuricemia closely related to gout,metabolic diseases,cardiovascular diseases,hypertension,kidney disease,type 2 diabetes,it has become the fourth most common metabolic disease after high blood sugar,high blood pressure,high blood lipids.Hyperuricemia(HUA)is a pathological condition in which serum urate levels are abnormally high or oversaturated.Serum urate levels are controlled through the balance among dietary purines,purine catabolism,and urate excretion.Therefore,hyperuricemia can result from the excessive intake of purines,the increase in purine catabolism,the decrease in urate excretion,or combinations of them.Currently,two types of therapeutic drugs are available for the treatment of hyperuricemia,including xanthine oxidase inhibitors and the tubular reabsorption of urate.Febuxostat,topiroxostat,allopurinol can inhibit xanthine oxidase,while benzbromarone,probenecid,RDEA-594,UR-1102 can increase uric acid excretion.However,no therapeutic drug focused on the dietary purine.A large number of epidemiological studies have shown that high purine intake is a risk factor for hyperuricemia,and experiments have shown that ingesting yeast nucleic acid can induce hyperuricemia in healthy subjects within a few days.At the same time,experiments have shown that low purine diet can reduce serum uric acid levels in patients with hyperuricemia.So it can be seen that increased purine intake can increase blood uric acid levels and inhibit its gastrointestinal absorption as a role in the prevention and treatment of hyperuricemia.Purine are mainly absorbed in the small intestine.The main forms of absorption are nucleosides,transmembrane transport of nucleosides requires nucleoside transporters.There are two main types of nucleoside transporters:concentrative nucleoside transporters(CNTs or SLC28)and equilibbrative nucleoside transporters(ENTs or SLC29).CNTs are Na+-dependent carriers and are active transporters.Reversible concentrations of CNTs transport extracellular substrates into cells and distribute in the apical membrane of intestinal epithelial cells.ENTs are mainly distributed in the basolateral membrane of intestinal epithelial cells,and transport pyrimidines and purines through facilitated diffusion.CNT2 plays a central role in the gastrointestinal absorption of purines.CNT2 is a purine nucleoside-preferring transporter,also largely distributed in the stomach,jejunum,ileum.It has been found that the protein and mRNA levels of CNT2 are increased and the amount of exogenously added nucleotides transported by the carrier is increased.It has also been experimentally confirmed that oral administration of a selective inhibitor of CNT2 in monkeys can significantly reduce blood uric acid levels by inhibiting intestinal purine nucleoside uptake.At the same time,21 compounds including caffeic acid,flavonoids and sesquiterpenes contained in chicory which can be combined with CNT2 were preliminarily screened in our laboratory,among which of cichoric acid with high content and relatively high specificity can inhibit CNT2 transporting adenosine in IEC-6 cell.Does the chicory extract affect purine nucleoside uptake in the small intestine by interfering with CNT2?What is the effect of purine uptake on the key synthesis of endogenous nucleotides and the catabolism of purines and blood uric acid?It still need be studied.Based on these problems in life and clinics,the following hypothesis was proposed:One of the causes of hyperuricemia is the increased expression of the purine transporter CNT2 in the intestine,resulting in increased purine absorption,activation of purine metabolic enzymes,and increased uric acid production.Chinese herbs chicory can play a role in the mechanism of uric acid lowering through the regulation of intestinal CNT2.To test this hypothesis,we used rat and quail as model animals for experimental studies.ObjectiveFirstly,to clarify the pathological basis of hyperuricemia rats and quails by investigated the relationship between the intestinal purine transporter CNT2 and hyperuricemia via intestinal purine uptake pathway and observing purine metabolic enzymes related CNT2.Secondly,to explore the lowering uric acid action of chicory by analyzing influences of CNT2 in hyperuricemia rats and quails.MethodsThis paper consists of literature review and experimental research.Literature review includes the epidemiological characteristics,TCM treatment of hyperuricemia,intestinal nucleosides transporters,especially CNT2,and its association with hyperuricemia by consulting literature at home and abroad for the past decade.In the experimental study,animal models are duplicated by etiology-inducing method.A certain amount of yeast induces HUA quail model,and the same dose of yeast combined with a small dose of adenine induce HUA rat model.Experimental studies take advantage of various methods,including biochemical detection,real-time fluorescence PCR,Western Blotting,immunohistochemistry,and high-performance liquid chromatography,to explore the change of intestinal nucleosides transporters and the effect of chicory on the hyperuricemia rats and quails.Experimental research content is mainly divided into two chapters.The first chapters:observe the expression of intestinal CNT2 in Model Animals with Hyperuricemia.Combining the results of pre-laboratory experiments and literature search,copy the hyperuricemia model induced by increased purine intake,observe the changes of serum uric acid and the expression of CNT2 in the intestine of model animal with hyperuricemia.The second chapters:investigate the effect of extract of Chicory on the expression of Intestinal CNT2 in hyperuricemia rats and quails.clarify the intervention of chicory extract of intestinal CNT2 gene and protein expression on hyperuricemia rats and quails and nucleosides absorption of the quail everted intestinal sacs model,explain the possible role and mechanism of chicory extract lowering uric acid action.ResultsResearch of Model screening:Oral administration of yeast only produced rats short-term hyperuricemia.but also did harm to rats.The dose of 50mg/kg adenine with yeast is safe enough but without High blood uric acid status.Therefore,we chose combination of yeast and 80mg/kg adenine which could produce rats long-term hyperuricemia while rats were in good condition at the same time.Investigation of the changes of CNT2 expression in the intestine of hyperuricemia rats and quail:?Yeast combined with adenine made rats long-term hyperuricemia,while large ofyeast made quails serum UA increase.? CNT2 mRNA expression in duodenum,jejunum and ileum of hyperuricemia rats increased compared with normal group and the expression of CNT2 mRNA in jejunum increased significantly.? CNT2 expression in jejunum of hyperuricemia quails increased significantly compared with normal group.Effect of chicory extract on Hyperuricemia rats and quails:?Chicory extract can stably reduce serum uric acid levels in model animals and reduce purine metabolic enzyme activity in serum and liver.?Chicory extract could down-regulate the expression of CNT2 gene and protein significantly in hyperuricemia rats and down-regulate the expression of CNT2 protein significantly in quails.? In the quail everted intestinal sacs experient,chicory extract can reduce the amount of substrate transport volume in jejunal of hyperuricemia quails.Conclusions? There are pathological relations between increased Intestinal nucleoside transporter CNT2 and hyperuricemia on rats and quails.The increased purine absorption mediated by the up-regulate CNT2 expression may be one of the pathological mechanism of hyperuricemia quails.? Chicory extract can down-regulate mRNA and protein expression of nucleoside transporter CNT2 on hyperuricemia rats,and protein expression of CNT2 on hyperuricemia quails,and reduce purine metabolic enzyme activity in model animals,so as to achieve the mechanism of uric acid lowering.Innovation points:? From the point of view of purine absorption,to explore the pathological relationship between the hyperuricemia rat,quail model and intestinal purine transporter CNT2 expression.? The study demonstrated that one of the mechanisms of chicory extract uric acid lowering effect is to downregulate the expression of CNT2 in the intestine of model animals and reduce the purine absorption. |
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