Basic And Clinical Research On Association Of Prolyl Oligopeptidase With Metabolic Syndrome

BackgroundMetabolic syndrome(MS) is a clustering of some cardiovascular risk factors,including obesity,hypertension,hyperglycemia and dyslipidemia.With the development of society and changes of life style,the prevalence of MS is increased.It consists of multiple,interrelated risk factors of metabolic origin that appear to directly promote the development of atherosclerotic cardiovascular disease.Recently,studies revealed that metabolic syndrome is associated with cardiac interstitial fibrosis,which has been associated with cardiac remodeling and produced a wide range of alterations in cardiac structure and function.The mechanism of MS is complex.Recently the role of neuroendocrine system in the pathogenesis of MS has received more and more attention.Prolyl oligopeptidase(POP)is a serine peptidase which digests small peptide like hormones,neuroactive peptides,and various cellular factors.The recognition of rennin-angiotensin system(RAS) has been developed as the studies of angiotensin(1-7),a new member of RAS.It was produced by various tissue peptidases including POP.Angiotensin(1-7)has antihypertensive and antithrombolic effects.It not only inhibits proliferation of vascular smooth muscle cells and fibrosis of myocardial cells but also has effects on the regulation of hydro-electrolyte metabolic balance. Angiotensin(1-7)is like an endogenous antagonist of angiotensin II.N-acetyl-serylaspartyl -lysyl-proline(Ac-SDKP)is also the product of POP,which can reverse the fibrosis of cardiac muscle.So the activity of POP is associated with many physiological and pathologic states of cardiovascular system.Doppler ultrasound as the noninvasive diagnostic method has been widely applicated in clinical practice.The high-resolution sonography,providing a direct and dynamic evaluation of artery structure and function,improves the prediction of cardiovascular events greatly.Tissue Doppler imaging,a relatively new echocardiographic technique,offers a more sensitive method for the detection of the left ventricular long-axis myocardial velocity changes,which reflect the alterations in cardiac structure more accurately,and thus for the assessment of cardiac systolic and diastolic function.Objectives(1)To investigate the enzymatic activity levels and the mRNA expression levels of POP in patients with MS and hypertension,and to probe into the potential mechanism underlying these changes;(2)To investigate the alterations in structure and function of the carotid artery,as well as the association of POP with these changes;(3) To investigate the alterations in structure and function of the heart,as well as the association of POP with these changes.Subjects and MethodsAccording to IDF 2005 criteria of MS,we enrolled 103 patients with MS(49 females and 54 males,51.11±6.95 yr of age) and 97 people matched with age and sex (P＞0.05) without MS(51 females and 46 males,48.79±9.67 yr of age).We also enrolled 35 patients with hypertension(19 females and 16 males,54.71±9.69 yr of age)and 60 people without hypertension(39 females and 21 males,50.68±9.36 yr of age).Height,weight,systolic blood pressure,diastolic blood pressure,waist circumference and hip circumference were measured.Pulse pressure,body mass index and waist-hip ratio were calculated.Furthermore,fasting blood sample was collected from each subjects after 12-14 hours fast to determine the total cholesterol,triglycerides,high-density lipoprotein cholesterol,low-density lipoprotein cholesterol,and uric acid(UA),fasting blood glucose,insulin and HOMA-IR.Plasma POP enzymatic activity was determined by a fluorimetric assay.Briefly PBMCs were isolated.Total RNA was extracted using Trizol one-step method.The RT-PCR technique was applied to detect the mRNA expressions of POP.B-mode ultrasonography of the carotid arteries was performed and Ultrasound images were acquired using a 5～10MHz linear array transducer and a commercially available ultrasound machine(Vivid 7 dimension;General Electric Medical Systems, Horten,Norway).ECG data were recorded concurrently.Echocardiograms were obtained with a commercially available ultrasound machine(Vivid 7;GE Vingemed Ultrasound,Horten,Norway)with a 1 to 3MHZ phased array transducer.The M-mode echocardiography,two-dimensional echocardiography,pulsed-Doppler echocardiography and tissue Doppler echocardiography were performed respectively.All statistical analyses were performed using the SPSS 16.0 statistical program. Normally distributed data were expressed as means±SD or±SEM as indicated,and non-normally distributed data are presented as medians(quartile range).Continuous variables were compared between groups by unpaired Student's t test,The associations between categorical ones was analyzed using the chi-square test.Correlation coefficients between the variables were determined using the Pearson's or Spearman's method,meanwhile multiple regression analysis was performed to determine relationships between variables of interest.A P value＜0.05 was considered statistically significant.Results(1)Analysis of clinical and biochemical characteristics with MS①Comparison of clinical and biochemical characteristics of the subjectsThere were no significant differences in age or gender between MS group and control group(P＞0.05).Compared with the controls,the MS group showed significantly higher SBP,DBP,PP,W,BMI,WC,HC,WHR,TC,TG,LDL-c,FBG,FINS, HOMA-IR,UA but lower POP enzymatic activity and HDL-c(P＜0.001).②Correlation of POP enzymatic activity level with clinical and biochemical characteristics:POP enzymatic activity level was significantly correlated with SBP, DBP,BMI,W,WC,HC,TG,HDL-c,UA,FINS and HOMA-IR(P＜0.05～0.01). ③Stepwise multiple linear regression model for SBP was as follows: SBP=-0.135×POP+0.407×WC+0.241×TG-0.133×smoking,The POP(P=0.030), WC(P=0.000),TG(P=0.000),smoking(P=0.039) were enrolled,suggesting the association of SBP and POP,WC,TG and smoking.④Stepwise multiple linear regression model for DBP was as follows: DBP=-0.157×POP+0.415×WC+0.253×TG,The POP(P=0.012),WC(P=0.000), TG(P=0.000) were enrolled,suggesting the association of DBP and POP,WC and TG.(2)Analysis of carotid ultrasonic parameters with MS①Comparison of carotid ultrasonic parameters of the subjectsIMT_mean,IMT_max,D_d,Ds,plaque index of the MS group were significantly higher than those of the control group(P＜0.05～0.001).Furthermore the MS group showed significantly decreases in Vs,Vd,Vm,RI and AC(P＜0.05～0.001),with significantly increases in PI,Ep,Ep^* andβ(P＜0.001).②Correlation of POP enzymatic activity level with carotid ultrasonic parametersPOP enzymatic activity level was significantly correlated with IMT_mean,IMT_max, PI,Ep,Ep^*,βand AC(P＜0.05)(3)Analysis of cardiac ultrasonic parameters with MS①Comparison of cardiac ultrasonic parametersThe IVS,LVPW,LVM,LVMI,LA and AO of the MS group were significantly higher than those of the control group(P＜0.001).Furthermore the MS group showed significantly decreases in E/A,TVIE,TVIE/A,TVIS,LA-S,LA-SSR and LA-ESR with significantly increases in A,E/TVIE(P＜0.001).②Correlation of POP enzymatic activity level with cardiac ultrasonic parametersPOP enzymatic activity level was significantly correlated with TVIE,LA-ESR, IVS(P＜0.05～0.01).(4)Analysis of clinical and biochemical characteristics with hypertension①Comparison of clinical and biochemical characteristics of the subjectsCompared with the non-HT group,the HT group showed significantly higher POP mRNA expression level,SBP,DBP,PP,age,W,BMI,WC,HC,WHR,TC,TG,LDL-c, FBG,FINS,HOMA-IR and UA but lower HDL-c(P＜0.001). ②Correlation of POP mRNA expression level with clinical and biochemical characteristics:POP mRNA expression level was significantly correlated with age, SBP,DBP,PP,WC,HC,HDL-cx,UA.(P＜0.05～0.01)(5)Analysis of carotid ultrasonic parameters with hypertension①Comparison of carotid ultrasonic parameters of the subjectsIMT_mean,IMT_max,D_d,,plaque index of the HT group were significantly higher than those of the non-HT group(P＜0.01～0.001).Furthermore the HT group showed significantly decreases in Vs,Vd,Vm,RI and AC(P＜0.05～0.001),with significantly increases in PI,Ep,Ep^* andβ(P＜0.001).②Correlation of POP mRNA expression level with carotid ultrasonic parameters:POP mRNA expression level was significantly correlated with IMT,IMT_max,Ep,βand AC(P＜0.05)(6)Analysis of cardiac ultrasonic parameters with hypertension①Comparison of cardiac ultrasonic parametersThe IVS,LVPW,LVM,LVMI,LA,LA-index and AO of the HT group were significantly higher than those of the non-HT group(P＜0.05～0.001).Furthermore the HT group showed significantly decreases in E/A,TVIE,TVIE/A,TVIS,LA-S,LA-SSR and LA-ESR with significantly increases in A,TVIA,E/TVIE(P＜0.001).②Correlation of POP mRNA expression level with cardiac ultrasonic parametersPOP mRNA expression level was significantly correlated with LA,IVS,E/A, TVIE,TVIE/A(P＜0.05～0.01).③Stepwise multiple linear regression model for E/TVIE was as follows: E/TVIE=0.320×POP+0.332×TG-0.384×H,The POP(P=0.003),TG(P=0.002), H(P=0.000) were enrolled,suggesting the association of E/TVIE and POP,TG and H.Conclusions(1)The Plasma POP enzymatic activity of the MS group was obviously decreased. The decrease of POP enzymatic activity was independent risk factor for blood pressure.That indicated that POP may play an important role in the pathogenesis of hypertension.(2) The mRNA expression level of POP in the hypertension group was obviously increased.This is a mechanism of compensation.(3)Significant alterations to carotid arteries of the MS patients include thickened IMT.Multiple linear regressions show no correlation between POP and parameters of carotid arteries.(4)Cardiac structure and function were impaired in patients with metabolic syndrome.The increase of POP mRNA expression level in PBMCs was an independent risk factor for left ventricular diastolic dysfunction,which indicated that POP may play an significant role in the improvement of cardiac diastolic function. Background:The metabolic syndrome has received increased attention in the past few years.It consists of multiple,interrelated risk factors of metabolic origin that appear to directly promote the development of atherosclerotic cardiovascular disease.Insulin resistance has intense relationship with metabolic syndrome.A number of new approaches to diabetes therapy are currently undergoing clinical trials, including those involving stimulation of the pancreaticβ-cell with the gut-derived insulinotropic hormones(incretins),GIP and GLP-1.The current review focuses on an approach based on the inhibition of dipeptidyl peptidaseⅣ(DPPⅣ),the major enzyme responsible for degrading the incretins in vivo.So is DPPⅣenzymatic activity different bwtween MS and the control?What's the influence DPPⅣhave on cardiovascular system?Nowadays,there are few studies referring to these questions. Therefore,we carried out the present study and tried to find satisfying answers to all the above problems.Objectives:(1)To investigate the enzymatic activity levels of DPPⅣin patients with MS,and to probe into the potential mechanism underlying these changes;(2)To investigate the alterations in structure and function of the carotid artery and the heart,as well as the association of DPPⅣwith these changes.Subjects and Methods:The studied population were the same as described previously.We used colorimetric assay to measure DPPⅣenzymatic activity.The clinical and biochemical indicator were measured the same as described previously. Ultrasonography of the carotid arteries and the heart were performed the same as described previously.Results(1)Analysis of clinical and biochemical characteristics with MS①Comparison of clinical and biochemical characteristics of the subjectsThere were no significant differences in age or gender between MS group and control group(P＞0.05).Compared with the controls,the MS group showed significantly higher SBP,DBP,PP,W,BMI,WC,HC,WHR,TC,TG,LDL-c,FBG,FINS, HOMA-IR,UA but lower HDL-c(P＜0.001),the DPPⅣenzymatic activity have no difference between MS and control.②Correlation of DPPⅣenzymatic activity level with clinical and biochemical characteristics:DPPⅣenzymatic activity level was significantly correlated with HDL-c.③Stepwise multiple linear regression model for FBG was as follows:FBG =0.181×DPPⅣ+0.232×TG+0.189×SBP,The DPPⅣ(P=0.009),TG(P=0.009),SBP (P=0.039) were enrolled,suggesting the association of FBG and DPPⅣ,TG and SBP.④Stepwise multiple linear regression model for FINS was as follows:FINS =0.233×DPPⅣ+0.227×SBP+-0.206×HDL-c,The DPPⅣ(P=0.001),SBP(P=0.004), HDL-c(P=0.010) were enrolled,suggesting the association of FINS and DPPⅣ,SBP and HDL-c.⑤Stepwise multiple linear regression model for DPPⅣwas as follows: DPPⅣ=-0.188×SBP+0.195×HDL-c+0.182×FBG+0.251×FINS,The SBP(P=0.030), HDL-c(P=0.029),FBG(P=0.022),FINS(P=0.002) were enrolled,suggesting the association of DPPⅣand SBP,HDL-c,FBG and FINS.(2)Analysis of carotid ultrasonic parameters with MS①Comparison of carotid ultrasonic parameters of the subjectsIMT_mean,IMT_max,D_d,Ds,plaque index of the MS group were significantly higher than those of the control group(P＜0.05～0.001).Furthermore the MS group showed significantly decreases in Vs,Vd,Vm,RI and AC(P＜0.05～0.001),with significantly increases in PI,Ep,Ep^* andβ(P＜0.001). ②Correlation of DPPⅣenzymatic activity level with carotid ultrasonic parametersDPPⅣenzymatic activity level was significantly correlated with Vd,Vm,PI (P＜0.05～0.01).(3)Analysis of cardiac ultrasonic parameters with MS①Comparison of cardiac ultrasonic parametersThe IVS,LVPW,LVM,LVMI,LA and AO of the MS group were significantly higher than those of the control group(P＜0.001).Furthermore the MS group showed significantly decreases in E/A,TVIE,TVIE/A,TVIS,LA-S,LA-SSR and LA-ESR with significantly increases in A,E/TVIE(P＜0.001).②Stepwise multiple linear regression model for AO was as follows: AO=-0.148×DPPⅣ+0.229×SBP+0.252×HDL-c,The DPPⅣ(P=0.036), SBP(P=0.004),HDL-c(P=0.006) were enrolled,suggesting the association of AO and DPPⅣ,SBP and HDL-c.Conclusions(1)The Plasma DPPⅣenzymatic activity of the MS group has no obviously difference with the control.(2) The increase of DPPⅣenzymatic activity was independent risk factor for the increase of FBG and FINS.(3) The increase of DPPⅣenzymatic activity was independent risk factor for the decrease of AO.