Mechanism Of Lipid Metabolism Disorder Induced By High Uric Acid And The Intervention Effect Of Insulin-like Growth Factor-1

Objectives:Hyperuricemia is the leading cause in the pathogenesis of gout.The disorder of lipid metabolism associated with high uric acid(HUA)can seriously affect the prognosis of gout patients.However,the mechanism of lipid metabolism disorder induced by hyperuricemia remains unclear.Hence,the present study will explore the relationship between serum uric acid(SUA)level and other metabolic factors such as insulin-like growth factor-1(IGF-1)and triglyceride in patients with gout.On this basis,the key enzymes,transcription factors and insulin receptor substrate 1(IRS1)/phosphatidylinositol 3-kinase(PI3K)in the process of triglyceride synthesis and fatty acid oxidative decomposition induced by uric acid were further investigated in cell model and mouse model of lipid metabolism disorder induced by high uric acid.The PI3K/Akt signaling pathway involved in these processes was also determined.The data of the present study will provide theoretical and experimental basis for the development of targeted treatment strategies for gout,hyperuricemia,and hypertriglyceridemia.Methods:The main characteristics of each indicators,the relationship between serum uric acid level and other indexes,and the relationship between serum IGF-1 level and other indicators were analyzed for the involved 221 gout patients.A cell model of lipid metabolism disorder induced by uric acid stimulation of LO2 cells was established.And a mouse model of hyperuricemia with lipid metabolism disorder was also established.The effect of uric acid stimulation on triglyceride level,the effect of uric acid stimulation on ketone body level,the effect of uric acid stimulation on lipid metabolism enzymes,the effect of uric acid on intracellular lipid metabolism related signaling pathways,and lipid metabolism regulatory transcription factors were investigated.On this basis,we further used the LO2 cell model of lipid metabolism disorder and the mouse model of hyperuricemia with lipid metabolism disorder to explore the intervention effect of IGF-1 on related metabolic indicators through IRS1/PI3K Akt signaling pathway.Results:(1)Serum uric acid level was positively correlated with triglyceride(r=0.305,P<0.001),serum insulin and creatinine levels were also positively correlated,and negatively correlated with age.Serum uric acid was no correlation with insulin-like growth factor-1(IGF-1),low density lipoprotein cholesterol(LDL-C),high density lipoprotein cholesterol(HDL-C),fasting blood glucose,and C-reactive protein(CRP)in all patients.(2)Serum IGF-1 level was negatively correlated with age and positively correlated with HDL-C.There was no correlation between IGF-1 and triglyceride levels in all patients included in this study.There was a negative correlation between serum triglyceride level and age(r=0.161,P=0.017).The correlation analysis after age stratification showed that there was a negative correlation between serum IGF-1 and triglyceride levels in the group of≤38 years old,but there was no correlation between IGF-1 and triglyceride levels in the group of>38 years old.(3)High concentration of uric acid(15 mg/dL)for 72 h could significantly increase the content of triglyceride in LO2 cells.The serum triglyceride level of hyperuricemic mice increased gradually at the end of 1～4 weeks,and reached the highest level at the end of 4 weeks.(4)High concentration of uric acid(15 mg/dL)for 72 h could significantly reduce the level of ketone bodies in the supernatant of LO2 cells,which indicated that uric acid could inhibit the process of fatty acid decomposition.The serum ketone body concentration of hyperuricemic mice decreased gradually with the prolongation of hyperuricemic diet from 1 to 4 weeks,and reached the lowest level at the end of the 4th week.(5)High concentration of uric acid(15 mg/dL)for 72 h increased the levels of fatty acid synthase(FAS)and acetyl CoA carboxylase(ACC)in LO2 cells,decreased levels of arnitine palmitoyltransferase 1A(CPT1A)and acyl-CoA dehydrogenase C-4 to C-12 straight chain(ACADM).Among the four lipid metabolism enzymes,uric acid has the most obvious effect on FAS.At the end of the 4th week,the expression of lipid metabolizing enzymes in liver tissue of hyperuricemic mice showed the same trend as that of LO2 cell experiment.(6)High concentration of uric acid(15 mg/dL)stimulated LO2 cells for 48 h,the expression level of pIRS1(Ser312)was significantly increased,while the expression level of pAkt(ser473)was significantly decreased.The expression levels of SREBP1c mRNA and PPARy mRNA were significantly increased,while the expression levels of PIK3R3 mRNA and PPARa mRNA were significantly decreased.The expression of IRS1/PI3K/Akt signaling molecules and transcription factors of lipid metabolism in liver tissue of hyperuricemic mice at the end of 4 weeks were consistent with the results of cytological experiment.(7)IGF-1 could reverse the accumulation of intracellular triglycerides induced by hyperuricemia in LO2 cells at 72 h and liver tissues of hyperuricemic mice at the end of 4 weeks.This effect of IGF-1 could be blocked by PI3K inhibitor LY294002.(8)In LO2 cells and liver tissue of hyperuricemic mice,IGF-1 could improve the Ketone body level induced by hyperuricemia,but LY294002,a PI3K inhibitor,had no effect on IGF-1.(9)In LO2 cells,IGF-1 reversed the upregulation of FAS and ACC induced by high uric acid.The effect of IGF-1 on FAS expression was the most significant,and LY294002 could also inhibit the effect of IGF-1 on FAS expression.The effect of IGF-1 on ACC expression was not obvious.LY294002 did not show the effect of blocking IGF-1.IGF-1 could improve the down-regulation of fatty acid oxidative enzymes CPT1A and ACADM induced by high uric acid,but LY294002 did not show the effect of intervening IGF-1.At the end of the 4th week,the expression of lipid metabolizing enzymes in liver tissue of hyperuricemic mice was detected by immunohistochemistry,and the change trend was consistent with the result of LO2 cell experiment.(10)The results of LO2 cell experiment showed that IGF-1 could reverse the upregulation of SREBPlc mRNA and PPARγ mRNA caused by high uric acid stimulation.This effect was inhibited by LY294002.IGF-1 also alleviated the decrease of PPARαexpression induced by high uric acid,but this effect was not affected by LY294002.The results of animal experiments showed that the expression levels of SREBP1c,PPARy,and PPARa in liver tissues of hyperuricemia mice were consistent with the change trend of LO2 cells.(11)The results of LO2 cell experiment showed that IGF-1 could reverse the effect of high uric acid on the expression of pIRS1 and pAkt,while LY294002 blocked the effect of IGF-1.IGF-1 could alleviate the low expression of PIK3R3 mRNA in LO2 cells stimulated by high uric acid,but LY294002 had no effect on the effect of IGF-1.At the end of the 4th week.RNA and protein were extracted from liver tissue of hyperuricemic mice to detect the related signal molecules,and the change trend was consistent with that of LO2 cells.Conclusions:(1)The incidence of male patients with gout tends to younger.The highest blood lipid disorder incidence of gout is hypertriglyceridemia.Serum uric acid was positively correlated with fasting triglyceride,insulin,and creatinine levels in gout patients,and negatively correlated with age.There was a negative correlation between serum IGF-1 and triglyceride in young male patients with gout.Although the correlation coefficient between serum uric acid level and other indicators is not very high,after all,serum uric acid level has a correlation with multiple metabolic indicators.This also reflects the complexity of metabolic disorders associated with elevated uric acid levels,which involves a variety of molecular mechanisms.(2)High uric acid can induce the triglyceride metabolism disorder in a dose-dependent manner.Under the stimulation of high concentration of uric acid,in addition to the increased expression of fat synthetase,the level of ketone body decreased,and the expression levels of CPT1A and AC ADM,the key enzymes of fatty acid oxidation metabolism,also decreased.(3)Under the stimulation of high concentration of uric acid,the expression of many signaling molecules changes in IRS1/PI3K/Akt signaling pathway system,which has the function of regulating fat metabolism.The expression of pIRS1(Ser312/307)was up-regulated,while the expression of pAkt(ser473)was down regulated.The expression of PIK3R3/PPARa related to fatty acid oxidation was down regulated.(4)IRSI/PI3K/Akt signaling pathway plays an important role in triglyceride metabolism disorder induced by high uric acid.IGF-1 inhibits the expression of SREBPlc,PPARγ,and adipose synthetase related to triglyceride synthesis by activating IRS1/PI3K/Akt signaling pathway,then reduces triglyceride accumulation.IGF-1 could also act on PIK3R3/PPARα,improve the fatty acid oxidation disorder caused by high uric acid,and improve the disorder of lipid metabolism.The results of the present study deepened the understanding of the pathogenesis of gout and hyperuricemia combined with lipid metabolism disorder,and provided a new theoretical and experimental basis for the formulation of the overall clinical treatment strategy of gout and hyperuricemia.