The Effects Of Insulin Resistance On Cardiovascular Lesions In Early Chronic Kidney Disease And Its Mechanisms

Background:Cardiovascular disease (CVD) is the most common complication and the major cause of death in patients with chronic kidney disease (CKD). Recent studies have found that even in early CKD patients, the risk of CVD increased obviously, not only in those with end stage renal disease (ESRD). But the mechanism of CVD development in early CKD is still uncertain. Our previous study found that: compared with the normal population, patients with CKD1-3 had significant higher level of fasting plasma glucose (FPG),2-hour postprandial blood glucose (2hPG), fasting insulin (FINS),2-hour postprandial insulin (2hINS), and significant higher insulin resistance index (homeostasis model assessment of insulin resistance, Homa-IR) value. This phenomenon was accompanied by a higher incidence of left ventricular hypertrophy (LVH), and Homa-IR value was positively correlated with left ventricular mass index (LVMI) and entered its multiple stepwise regression analysis equation. It shows that insulin resistance (IR) exists in early CKD patients and may play an important role in the development of CVD in patients with early CKD. Is there any relation between IR and wider cardiovascular lesions, such as endothelial dysfunction, atherosclerosis and so on, in early CKD? What is the realation? And what are the mechanisms? By establishing early CKD animal model, we are going to research the effects of IR on the cardiovascular lesions and its mechanisms.Objective:Using the method of unilateral nephrectomy, we try to establish the early CKD animal models to study the effects of IR on the cardiovascular lesions and its mechanisms in rats with early CKD.Methods:By right-side nephrectomy and feeding with standard food for 12 weeks, we try to establish the animal model of early CKD. In the end of the study, left kidney weight, left kidney/body weight ratio and heart/body weight ratio are tested; hemoglobin (Hb) and hematocrit (Hct) are measured with BC-3003 Plus automated blood cell analyzer; biochemical indicators such as serum creatinine (Scr), blood urea nitrogen (BUN), blood uric acid (UA), cystamine-C (Cys-C), fasting plasma glucose (FPG) and serum albumin (Alb) are tested with Beckman CX9 analyzer; fasting insulin (FINS), serum angiotensinⅡ(AngⅡ), serum endothelial nitric oxide synthase (eNOS), endothelin-1 (ET-1), serum high-sensitivity C-reactive protein (hsCRP), serum malondialdehyde (MDA) and serum superoxide dismutase (SOD) are measured with enzyme-linked immunosorbent assay method and Homa-IR is counted. The pathological changes of the kidneys (detected with hematoxylin and eosin staining and periodic acid-Schiff staining), hearts and vessels (detected with hematoxylin and eosin staining) and the deposition of typeⅠcollagen (ColⅠ, detected with immunohistochemical method) in the myocardial interstitium and vascular wall are observed under light microscope. Then, the differences of these data between the experiment group (group A) and the control group (group C) are compared with t test and the effects of IR on the cardiovascular lesions and its mechanisms are analyzed with single-factor linear correlation analysis and multiple stepwise regression analysis further.1. In our study, there is no obvious pathological change in the left kidney of group C. The main pathological changes in group A are glomerular mesangial proliferation and inflammatory cell infiltration. Compared with group C, group A has significant higher level of left kidney weight, left kidney/body weight ratio and Cys-C (all P<0.05), but there are no obvious differences in Scr, BUN, UA, Hb, Hct and Alb between the two groups.2. There is no obvious pathological change in the heart of group C. There are no obvious differences in both heart weight and heart/body weight between the two groups. However, in group A, myocytes proliferate and disarrange; a large number of inflammatory cells infiltrate in local myocardium; muscle fibroblasts and perivascular fibrosis surround coronary. Compared with group C, the group A has higher level of the percentage of collagenⅠpositive area in myocardial interstitium (P<0.05)3. There is no obvious pathological change in the artery of the group C. However, in group A, edema exists in both vascular endothelium and interstitium; the endothelial cells partly drops from the artery; and the gap between them broadens; the vascular smooth muscle cells proliferate and disarrange, and their shape are irregular; inflammatory cells infiltrate around the endothelium; fibrosis occurs in intima. Compared with group C, the group A has higher level of the percentage of collagenⅠpositive area in vascular wall and serum ET-1 (both P<0.05), but lower level of serum eNOS(P< 0.05). 4. There is no significant difference in FPG level between the two groups. However, compared with group C, group A has significant higher level of FINS and higher Homa-IR value (both P<0.05).5. Compared with group C, the group A has higher level of serum AngⅡ, MDA and hsCRP (all P<0.05), but lower level of serum SOD (P<0.05).6. Single-factor linear correlation analysisHoma-IR has no significant correlation with Cys-C (P>0.05), but has significant positive correlations with the level of left kidney weight, left kidney/body weight ratio and glomerular mesangial proliferation (all P<0.05).Homa-IR has no significant correlation with both heart weight and heart/body weight ratio (both P>0.05), but has significant positive correlation with the level of the percentage of collagenⅠpositive area in myocardial interstitium (P<0.05).Homa-IR has significant positive correlations with both the level of serum ET-1 and the percentage of collagenⅠpositive area in vascular wall (both P<0.05), but has significant negative correlation with the level of serum eNOS (P<0.05).Homa-IR has significant positive correlations with level of serum AngⅡ, MDA and hsCRP (all P<0.05), but has significant negative correlation with the level of serum SOD (P<0.05).The percentage of collagen I positive area in myocardial interstitium has significant positive correlations with level of Homa-IR, serum ET-1, AngⅡ, MDA, hsCRP, left kidney weight, left kidney/body weight ratio and glomerular mesangial proliferation (all P<0.05), but has significant negative correlations with the level of serum eNOS and SOD (both P<0.05).The percentage of collagen I positive area in vascular wall has significant positive correlations with level of Homa-IR, serum ET-1, AngⅡ, MDA, hsCRP, left kidney weight, left kidney/body weight ratio and glomerular mesangial proliferation (all P<0.05), but has significant negative correlations with the level of serum eNOS and SOD (both P<0.05).7. Multiple stepwise regression analysisMultiple stepwise regression analysis shows that glomerular mesangial proliferation and left kidney/body weight ratio enter the equation, in which the percentage of collagenⅡpositive area in myocardial interstitium is a dependent variable. The equation is y=6.736x1±9.286x2-18.962 (y= the percentage of collagenⅠpositive area in myocardial interstitium; X1=glomerular mesangial proliferation, t=8.950, P=0.000; x2= left kidney/body weight ratio,t=6.330, P=0.000;-18.962 is a constant,t=4.577, P=0.000).Multiple stepwise regression analysis shows that glomerular mesangial proliferation and left kidney/body weight ratio enter the equation, in which the percentage of collagen I positive area in vascular wall is a dependent variable. The equation is y=7.308x1+10.457x2-17.474 (y=the percentage of collagen I positive area in vascular wall; x1=glomerular mesangial proliferation, t=9.142, P=0.000; x2= left kidney/body weight ratio,t=6.711, P=0.000;-17.474 is a constant, t=-3.971, P=0.001).Conclusions:By right-side nephrectomy and feeding with standard food for 12 weeks, we successfully establish the animal model of early CKD. We find that obvious cardiovascular lesions exist in rats with early CKD; kidney damage is an independent risk factor of cardiovascular lesions in early CKD, and IR may be one of the mechanisms of the cardiovascular lesions in early CKD; kidney damage may cause IR which lead to cardiovascular lesions through such mechanisms as endothelial dysfunction, high activity of renin-angiotensin system, micro-inflammatory state and oxidative stress.