The Effects Of Uric Acid On Cardiac Pathology In Rats During Early Chronic Kidney Disease And Pharmacologic Interventions

BackgroundCardiovascular disease (CVD) is the most common complication and the major cause of death in patients with chronic kidney disease (CKD). There are about fifty percent patients with end stage renal disease(ESRD) dying from CVD. Recent studies have found that even in early CKD patients, the risk of CVD increased obviously, such as left ventricular hypertrophy (LVH), not only in those with ESRD. The risk factors of CVD in CKD patients include traditional risk factors and untraditional risk factors, which associated with uremia. Late years abundant exprimental and clinical researches have confirmed that UA is the independent risk factor for CVD. It can induce endothelial function disorders,oxidative stress, inflammatory reaction and so on, leading to CVD. CKD as well as hyperuricemia (HUA) can increase the mortality of CVD patients. But the mechanisms of CVD in early CKD is still uncertain. Our earlier clinical study found that serum uric acid increased significantly and was associated with the severity of LVH in patients with stage2-3CKD, and left ventricular matrix index (LVMI) has a positive correlation with serum uric acid (SUA), indicating that HUA has some definited effects on CVD in patients with early CKD. But there are still controversies that whether UA is the independent risk factor of CVD in early CKD patients. It is unclear how UA causes CVD. What will happen if allopurinol and losartan be used in early CKD? What are the mechanisms? All these questions are waiting for resolved. This research is going to study the relationship between uric acid and cardiac lesion in early CKD rats, as well as its mechanisms. At the same time, we also plan to research the influence of allopurinol and losartan on cardiac lesion, including its mechanisms.Objective:By establishing the early CKD animal model with HUA, we studied the relation between UA and cardiac lesion in early CKD and its mechanisms. Moreover, we intervene in the cardiac lesion with allopurinol and losartan, studying the potential mechanisms, which can give aid to clinical practice.Methods:The early CKD Sprague Dawley rat animal model was established by right-side nephrectomy. The rats are divided into five groups randomly, including group A (sham operation group), group B(CKD group), group C(CKD group with elevated UA level:CKD group fed with potassium oxonate(OXO)), group D(CKD group with elevated UA leve and allopurinol fed:CKD group fed with0X0and allopurinol),group E(CKD group with elevated UA level and losartan fed:CKD group fed with0X0and losartan). Each group has fifteen rats. Groups C、D、E were given the drug treatment through gastric lavage (oxo,800mg/Kg/time, two times a day;allopurinol,25mg/Kg/time, two times a day; losartan,20mg/Kg/time,once a day), while groups A and B were fed with drinking water by gavage.16weeks later the rats were sacrificed, and blood samples, kidney and heart tissue specimens were collected. Biochemical assay was used for the detection of serum creatinine(Scr), serum uric acid (SUA), low density lipoprotein(LDL) and fasting plasma glucose(FPG), while ELISA method for the detection of serum fasting insulin(FINS), endothelial nitric oxide synthase(eNOS) endothelin-1(ET-1), high-sensitivity C-reactive protein(hsCRP), interleukin-6(IL-6) and oxidative modified low density lipoprotein (ox-LDL), as well as plasma aldosterone(ALD) detected by radioinmunoassay, super oxide dismutase(SOD) detected by colorimetry. In addition, we also measured the pathological changes of kidney and heart, type I collagen expression of myocardiol tissue.Results:(1) In our study, the pathological change was not obvious in the kidney of group A, and it was slight in the remaining four groups, only part of the existence of mild glomerular mesangial proliferation, in the kidney of group C、D and E the pathological change in the renal tubules and renal interstitium was not obvious. And there was no urate crystal calm in all five groups. Compared with the other four groups, group C had significant higher level of serum uric acid, but there was no obvious difference in Scr level among the five groups. It indicated that the model of early CKD accompanied with HUA was established successfully. (2)There was no statistical difference of heart weight in each group. However, the group C had higher level of heart/body weight than group A. HE staining of the heart had no obvious morphological change in group A.The myocardial cells arranged in neat rows, conformation in shape,no inflammatory cells infiltration and interstitial congestion as well as fibrosis.The vessel wall was normal, with no fibroblasts appearing and degeneration. Immunohistochemistry suggested there was a small amount of collagen I deposition. There was only a bit of sporadic inflammatory cells among myocardial cells in group B, and the large vessel walls can be seen a few fibroblasts accidentally. Compared with group A and group B, group C myocardial cells had apparent inflammatory cells infiltration,with interstitial congestion.fibrosis.The small vessel walls can be seen as the emergence of fibroblasts and myocardial collagen I deposition was significantly increased. Cardiac lesions of group D and group E were similar to group C,but to a lesser extent. It was only visible to a small amount of inflammatory cells infiltration. No interstitial congestion and fibrosis can be seen. Around the vessel wall was some filaments. Inflammatory cells were visible occasionally, but no fibroblast cells. Meanwhile, the deposition of collagen I was only a little increase than group A. Statistical analysis showed that compared with group A and B, group C had higher level of the percentage of collagen I positive area, and the percentage of collagen I positive area of group D and E was lower than group C. Linear regression analysis showed that the level of SUA had significant positive correlations with the percentage of collagen I positive area.(3)The level of serum endothelial nitric oxide synthase in group C decreased significantly than group A. And the level of serum super oxide dismutase in group C was significantly lower than group A and B, while group D and E had higher level of serum super oxide dismutase than group C. The group C had higher level of serum endothelin-1than group A and group B, and compared with group C,group D had lower level of serum endothelin-1. however, compared with group E and group C,there was no difference. The endothelin-1level of group E was remarkablely higher than that in group A. Furthermore, the group C had higher level of serum interleukin-6, and higher level of serum high-sensitivity C-reactive protein, higher level of serum oxidatively modified low density lipoprotein, higher level of serum fasting insulin, higher level of homeostasis model assessment of insulin resistance,and higher level of plasma aldosterone than group A and B, while group D and E had lower level of serum interleukin-6, serum high-sensitivity C-reactive protein, serum oxidatively modified low density lipoprotein, serum fasting insulin, homeostasis model assessment of insulin resistance, plasma aldosterone than group C. There was no significant difference among five groups for the level of serum low density lipoprotein and serum fasting plasma glucose.Linear regression analysis found that the level of SUA had significant positive correlations with serum ET-1, serum hsCRP, serum IL-6, serum ox-LDL, serum FINS, Homa-IR and plasma ALD, but negative correlations with serum eNOS, serum SOD, and no significant correlations with serum FPG.Linear regression analysis found the percentage of collagen I positive area had significant positive correlations with SUA、serum ET-1, serum hsCRP, serum IL-6, serum ox-LDL, serum FINS, serum Homa-IR and serum ALD, but negative correlation with serum SOD, and no significant correlations with serum eNOS, serum FPG, or serum LDL. Multiple stepwise regression analysis showed that SUA、serum FINS entered the equation, and the equation were y=-9.692+0.111x1+3.176x2(y=the percentage of collagen Ⅰ positive area, x1=SUA, x2=FINS,-9.692was constant)Conclusions:In this study, by right-side nephrectomy and feeding the rats with0X0for16weeks, we successfully established the model of early CKD with HUA. Early CKD rats with elevated SUA level had cardiac lesions, and its severity was positively correlated with the SUA level. We found that UA may play a role in cardiac disease through endothelial dysfunction, oxidative stress, the micro-inflammatory state, insulin resistance, depression of serum aldosterone and other mechanisms. Allopurinol and losartan can alleviate the cardiac lesions of early CKD rats by reducing the level of SUA, as well as protecting vascular endothelial function, inhibition of oxidative stress, mitigating inflammation, repressing insulin resistance, reducing the formation of plasma aldosterone and so on.