Evaluation of Renalase Gene Polymorphism in Egyptian Patients with Chronic Kidney Disease

Abstract

C hronic kidney disease is one of the most problematic diseases in our country. Hypertension is a global health problem; it is the major risk factor for development and progression of non-diabetic and diabetic CKD. The combination of CKD and hypertension is a major public health issue. Hypertension is present in approximately 80% to 85% of patients with CKD. It plays a key role in progressive deterioration of renal function and in the exceedingly high rate of cardiovascular events, which represent the primary cause of morbidity and mortality in these patients. Over the last few years the genetic susceptibility to hypertension has been a special focus of attention and many candidate genes have been studied so far. The renalase pathway is a novel mechanism for regulating cardiac function and blood pressure. Renalase is a novel flavin adenine dinucleotide-dependent amine oxidase that is secreted mainly by the kidney. It circulates in the blood and modulates the cardiac function and systemic blood pressure. It metabolizes the circulating catecholamines. Low serum levels of renalase was observed in patients with chronic kidney disease and ESRD which leads to impaired degradation of catecholamines with elevation of their circulating levels causing increased tone of the sympathetic nervous system. This may explain the frequent occurrence of hypertension among these patients. The human renalase gene showed high renal expression, especially in the proximal tubules, it resides on chromosome 10 at q23.33 and encodes a 342–amino acid protein with a calculated molecular mass of 38 kDa. Many isolated single –nucleotide polymorphisms (SNPs) in the renalase gene were found to be associated with essential hypertension and hypertension with CKD. In view of the previous observations, the aim of the present work was to study the potential involvement of renalase gene polymorphism in the development of hypertension in patients with chronic kidney disease. To achieve this aim, the study was conducted on four age and sex matched groups of 80 subjects; group 1 (ESRD with HTN, n=25), group 2 (CKD with HTN, n=25), group 3 (hypertensive pathological control, n=15) and group 4 (normotensive healthy control group, n=15). Exclusion criteria included the presence of diabetes mellitus, stroke, coronary artery disease, peripheral vascular disease and congestive heart failure. All individuals included in this study were subjected to full history taking focusing on previous symptoms of CKD and its complications, thorough clinical examination with special emphasis on measurement of SBP, DBP and MAP. ECG and Echocardiography were also done only for Patients’ group and pathological control group. Routine laboratory investigations: BUN, creatinine, sodium, potassium, uric acid, serum total and ionized calcium, serum phosphorus, fasting and 2 hours postprandial blood glucose (to exclude DM) and lipid profile (serum cholesterol, triglycerides, HDL-C were done. Estimation of glomerular filtration rate using MDRD formula. Determination of genotype distribution and G allele frequencies of rs10887800 polymorphism of renalase gene in different studied groups by DNA extraction from peripheral blood leukocyte, PCR amplification of the target gene followed by allele specific restriction enzyme digestion (PCR-RFLP technique). In group 1, the homotypic allelic frequency of renalase gene was 4 GG (16%), the heterotypic allelic frequency of renalase gene was 17 AG (68%) and the wild (normal) allelic frequency of renalase gene was 4 AA (16%). In group 2, the homotypic allelic frequency of renalase gene was 5 GG (20%), the heterotypic allelic frequency of renalase gene was 15 AG (60%) and the wild (normal) allelic frequency of renalase gene was 5 AA (20%). In group 3, the homotypic allelic frequency of renalase gene was 1 GG (7%), the heterotypic allelic frequency of renalase gene was 8 AG (53%) and the wild (normal) allelic frequency of renalase gene was 6 AA (40%). In group 4, the homotypic allelic frequency of renalase gene was 1 GG (7%), the heterotypic allelic frequency of renalase gene was 3 AG (20%) and the wild (normal) allelic frequency of renalase gene was 11 AA (73%). Regarding the heterotypic gene distribution (heterozygous, AG) between different studied groups, it was significantly higher in group 1, group 2 and group 3 compared to group 4. The comparison between group 1, group 2, and group 3 with each other showed a non-significant difference between these groups regarding the heterotypic gene distribution. Moreover, a non-significant difference was observed when these groups were compared with each other regarding the homotypic renalase gene distribution (homozygous, GG) .Regarding the normal renalase gene distribution (wild type AA), control group showed a significantly higher normal renalase gene distribution when compared to group 1, group 2 and group 3. In addition, our results revealed that SBP, DBP and MAP were significantly higher in homotypic (GG) subgroup compared to heterotypic (AG) subgroup in CKD patients with HTN. Moreover, we found that, in group 1, duration of dialysis was significantly higher in homotypic (GG) and heterotypic (AG) subgroups compared to normal (AA) renalase gene distribution subgroup. Regarding group 3 and group 4, comparative statistics between heterotypic (AG) renalase gene distribution and normal (AA) renalase gene distribution as regard age, SBP, DBP, MAP and showed a non-significant difference.