| Background:Hyperuricaemia(HUA)is a syndrome of metabolic abnormalities caused by disturbances in purine metabolism.It is associated with the development of hypertension,atherosclerosis,chronic kidney disease and disorders of glucose metabolism.The mechanisms of glucose metabolism disorders due to hyperuricemia have been investigated,mainly in the pancreatic islets,liver and skeletal muscle,to investigate the effect of hyperuric acid on insulin synthesis and secretion and insulin resistance.As the "second brain",the intestine not only participates in the absorption and metabolism of nutrients,but also plays an important role in regulating secretion and inflammation in the body.At present,there is a lack of research on the mechanism of glucose metabolism disorders caused by high uric acid with a focus on the intestinal tract.Objective:By constructing a hyperuric acid rat model and using the gut as a starting point,this study analyses the effects of hyperuric acid on glucose metabolism,explores the relationship between the gut and glucose metabolism disorders in a hyperuric acid environment,clarifies the role of the gut flora and its metabolites in disease development,investigates the specific mechanisms of glucose metabolism disorders caused by hyperuric acid,and provides new strategies for the treatment of hyperuricemia and its complications as well as the development of new clinical drugs.Methods:(1)Construction of hyperuricemia model: Rats were divided into normal and hyperuric acid groups and constructed using adenine gavage combined with intraperitoneal injection of potassium oxytetracycline.The effect of hyperuricemia on glucose metabolism was assessed by measuring serum uric acid,fasting glucose,serum insulin and oral glucose tolerance test(OGTT).Pancreatic islet HE staining was performed to observe changes at high uric acid levels.The expression of glucose transporter protein 2(GLUT2)-related genes and proteins(HNF1A,GLUT2,SGLT1,T1R2,T1R3,PLC β II,PKC β II)was examined by immunofluorescence,q PCR and western blot to explore the effect of hyperuric acid on the regulation of intestinal GLUT2 proteins.(2)Glucose uptake in rat intestinal epithelial cells(IEC-6)under high uric acid environment: The exogenous uric acid concentration used for cell treatment was determined using CCK-8 assay,and the uptake of fluorescent glucose analog(2-NBDG)under high uric acid environment was observed by adding exogenous uric acid.The expression of glucose transporter protein 2(GLUT2)-related genes and proteins(HNF1A,GLUT2,SGLT1,T1R2,T1R3,PLCβII,PKCβII)in rat intestinal epithelial cells was examined by immunofluorescence,q PCR and western blot to explore the regulatory role.CCK-8 assay was used to determine the concentration of faecal supernatant used for cell treatment to investigate the regulation of GLUT2-related protein expression by the intestinal environment under high uric acid.(3)Observation of glucose metabolism indexes in clinically normal,hyperuricemic and uric acid-lowering populations: After excluding the effects of age,body mass index(BMI),liver function,blood lipids and renal function on glucose metabolism indexes according to the inclusion and exclusion criteria,16 normal subjects and 13 hyperuricemic subjects were selected and 13 cases were treated with febuxostat uric acid-lowering therapy to observe blood uric acid,fasting blood glucose,insulin and glycosylated haemoglobin levels and assess the effects of uric acid-lowering therapy on glucose metabolism.The effect of uric acid-lowering treatment on glucose metabolism was assessed.(4)Improvement of glucose metabolism by uric acid-lowering treatment: On the basis of the original animal model,interventions were made with uric acid-lowering drugs,serum uric acid,fasting blood glucose,serum insulin(INS)and serum glucagon-like peptide-1(GLP-1)levels were measured,and the effect of febuxostat uric acid-lowering treatment on glucose metabolism was assessed by OGTT and insulin tolerance test(ITT),and the effect of febuxostat uric acid-lowering treatment on glucose metabolism was measured by mass spectrometry.GLP-1,GLP-1R,FFAR2,FFAR3,immunofluorescence for islet cell mass apoptosis.western blot technique to detect changes in the expression of apoptosis-related proteins(Bax,Bcl-2,Cleaved-caspase3)in pancreatic tissue.Results:(1)Compared to normal rats,Hua rats showed signs of glucose metabolism disorders such as elevated fasting glucose,reduced serum insulin and impaired glucose tolerance.HE staining of the pancreas showed that hyperuricemia led to islet cell mass damage;GLUT2 protein expression was reduced.In the intestine,HNF1 A and GLUT2 protein expression was upregulated and SGLT1 expression was not different.GLUT2 translocation signals T1R2,T1R3,PLCβII and PKCβII were significantly enhanced,GLUT2 expression was increased on the apical membrane of the intestinal epithelium and GLUT2 underwent significant translocation.(2)At higher concentrations of uric acid(100 mg/L),2-NBDG uptake by intestinal epithelial cells was significantly increased.HNF1 A and GLUT2 protein expression was upregulated in intestinal epithelial cells.Further studies by immunofluorescence showed a significant increase in GLUT2 expression on the cell membrane and enhanced expression of the translocation key factor PKC β II protein.administration of PKC β II inhibitor resulted in a decrease in GLUT2 protein expression on the cell membrane and a decrease in 2-NBDG uptake.Finally,the changes in HNF1 A,GLUT2 and PKC β II protein expression after treatment of cells using Hua rat faecal supernatant were consistent with the results of high concentration uric acid treatment.(3)Uric acid was significantly reduced after uric acid-lowering treatment and was not statistically different from normal human blood uric acid values.Fasting blood glucose was elevated in the hyperuricemic group and decreased but not significantly different after uric acid lowering.Insulin levels were not significantly different between the three groups.And,with the effect of uric acid-lowering,glycated haemoglobin level further increased.(4)After uric acid-lowering treatment,fasting blood glucose elevation caused by high uric acid was improved,serum insulin and GLP-1 were elevated,and glucose metabolism was improved.After uric acid-lowering treatment,the level of propionic acid in faeces was increased and serum levels of isobutyric acid and 2-methylbutyric acid were increased.The results of the flora analysis showed that uric acid-lowering treatment further aggravated the reduction in alpha diversity at the gate level induced by hyperuricemia,and there was a significant difference in beta diversity at the gate level between the three groups of rats.Analysis of gate levels showed that uric acid-lowering treatment further resulted in increased Firmicute abundance and decreased Bacteroidota abundance caused by hyperuricemia.Urate-lowering treatment resulted in significantly higher levels of Roseburia,a genus associated with short-chain fatty acid production.Correlation analysis showed that Roseburia was closely associated with the production of faecal propionic acid.The expression levels of FFAR2 and FFAR3 proteins in the colon and GLP-1 and GLP-1R proteins in the pancreas were increased in the rats in the uric acid-reduced group.The islet β-cell apoptosis was improved by uric acid-lowering treatment,which suppressed the high expression of Bax and Cleaved-caspase3 protein levels induced by high uric acid.Conclusion:High uric acid causes disorders of glucose metabolism with elevated fasting glucose and impaired glucose tolerance as the main symptoms,which may be achieved by regulating intestinal GLUT2 expression and translocation and increasing glucose uptake by the intestinal epithelium.This process is accompanied by an increase in the abundance of the short-chain fatty acid-producing bacterium Roseburia and an increase in faecal propionic acid levels,which promotes the expression of colonic short-chain fatty acid receptors and enhances pancreatic GLP-1 signalling,thereby improving islet cell apoptosis.Significance:(1)High uric acid causes disorders of glucose metabolism in the body;the symptoms of elevated fasting blood glucose caused by high uric acid can be improved through uric acid-lowering therapy,therefore,for patients with hyperuricemia combined with disorders of glucose metabolism,uric acid-lowering therapy is beneficial to improving blood glucose and should be given sufficient attention.(2)Intestinal flora and short-chain fatty acids play an important role in the process of improving glucose metabolism by lowering uric acid,which lays the foundation for flora intervention or related metabolite modulation in patients with hyperuricemia combined with glucose metabolism disorders. |
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