Cardiovascular disease was recognized as a major cause of death in children with chronic kidney disease CKD. Similar to adults, children with CKD have an extremely high prevalence of traditional and uremia-related CVD risk factors as hypertension, dyslipidemia, hyperglycemia, uremia, hypoalbuminemia, anemia, and hyperparathyroidism. Early markers of cardiomyopathy include left ventricular hypertrophy, systolic and diastolic dysfunction to be followed with cardiac dilatation and valvular regurge . Subclinical forms of atherosclerosis are reported in children and its early markers include increased carotid arterial intima-media thickness and coronary artery calcification. Cardiovascular disease is particularly evident in those on maintenance hemodialysis as they are very much exposed to altered hemodynamics.
Contributing to CKD and/or CVD has been recently on focus. Apolipoprotein E and plasminogen activator inhibitor 1-related genes are common examples. The first one is highly involved in lipid metabolism and the latter blocks fibrinolytic pathway and thus promotes vascular thrombosis. The aim of this work is to study the two mentioned gene polymorphisms in children with CKD associated with CVD, with special consideration to those on hemodialysis, looking for special allele patterns. As dyslipidemia is a common sequence for CKD, a major risk factor for CVD and genetically controlled by the Apolipoprotein E gene; therefore, it has been also extensively studied. Links between gene results with dyslipidemia and between each of them with echocardiography findings and thrombosis will be discussed.
Altered serum lipid profile (dyslipidemia) secondary to renal insufficiency is well known since early time. In this study, it was reported in each group and in the total patient sample with different patterns and frequency. Total patient sample with CKD showed that high triglycerides (TG) and high low-density lipoproteins (LDL) as the most frequent pattern recording incidence of 46% and 44% respectively, next followed by low HDL, high cholesterol, and high CHO/HDL recording incidence of (28%, 20%, 16%) (Table 3). Cases et al. reported high TG, normal to high total CHO, low HDL, normal to high LDL, and high VLDL dyslipidemic patterns to associate CRI and described it as atherogenic dyslipidemia . The mean level of TG in this study showed the non-significant difference between predialytic compared to those on hemodialysis. Group III showed a lower mean of triglycerides after renal transplantation (Table 3). Aser also reported no particular effect of hemodialysis on TG as compared to predialytic patients . Pattern and frequency of dyslipidemia in CKD, as well as its relation with hemodialysis and peritoneal dialysis have been extensively discussed in the literature. Normal to high total cholesterol, normal LDL, low HDL, high VLDL in predialytic, and hemodialysis patients were reported by Bregman et al. . Possible mechanisms include postprandial dyslipidemia as the intestine is the site of synthesis of APO-A1 and A2, APO-B48, and APO-E . Also, Charlesworth JA related the greater and prolonged postprandial rise of TG in CRI to be due to impaired clearance of chylomicron remnants . Hepatic role for dyslipidemia in CRI is related to the role of the liver in the synthesis of APO-B100. AP0-C11, APO-C111, AP0–1, and AP0–11, and the role of the liver in expression of receptors for all lipoprotein classes and so its ability to synthesize HDL and VLDL . Other mechanisms for dyslipidemia in CRI include insulin resistance , proteinuria , and increased oxidative stress with increase LDL . LDL has a high atherogenic effect.
Relation between dyslipidemia and CVD
The relation between dyslipidemia and CVD in this study showed non-significant relation with echocardiography changes in total cases, HD, and post-transplantation. It was only significant in the predialytic group as high TG was most evident in this group (Table 10). Dyslipidemia by itself accelerates glomerular injury to mesangium, endothelium, and podocytes through lipid mediators of oxidative stress, this contributes to the development of hypertension, uremic toxins, hypervolemia, and anemia with their impact on cardiac changes . In adults, dyslipidemia is a high-risk factor for atherosclerosis. Such finding is milder or lacking in children and young adults . Subclinical atherosclerosis begins in childhood and is likely accelerated in children with CKD . As for the association between dyslipidemia and thrombosis (Table 12), there was a significant association between dyslipidemia and the severity of thrombosis among patients on HD. High VLDL triglyceredemia, in particular, is a very important stimulant to express a high level of PAI-1 that promotes thrombosis through its antifibrinolytic effect. HD by itself is a major contributor to vascular thrombosis through vascular access trauma and the release of endothelin, thrombin, and Tpa. It may also be related to the inflammatory response that may happen on the contact of blood with the dialyzer and dialysate through activation of kallikrein-kinin system and generation of cytokines, expression of PAI-1 in high plasma levels that promotes thrombosis .
Plasminogen activator inhibitor-1 results
4G in its homozygous 4G/4G and its heterozygous 4G/5G forms constitute the most common within the total patient sample (Table 6 and 7, Fig. 4). The statistical comparison regarding PAI-1 gene polymorphism between the total patient sample and healthy control showed a significant difference, as 4G in its homozygous and heterozygous forms represent the most prevalent pattern (Tables 6 and 7). PAI-1 plasma level is highly determined by PAI-1 genotype in addition to other factors. Higher plasma levels are correlated with polymorphic variance in the number of guanine bases 4G/5G in the promoter at position − 675. 4G is associated with higher plasma levels. 4G/4G shows the highest level, 5G/5G shows the lowest level, and 4G/5G is intermediate . Other factors that determine its level include the balance between agonists and inhibitors. Suppressors include interferon-y, nitric oxide, natriuretic factors, and lipid-lowering drugs . Factors that increase its level include growth factors; coagulation factors as fibrin fragments, thrombin, and Tpa; metabolic factors as glucose, LDL, and APO-A; hormones as aldosterone, angiotensin, renin, and erythropoietin; and environmental factors as endothelial stretch, hypoxia, and endothelin .
PAI-1 contributes much to many acute and chronic kidney diseases such as acute thrombotic microangiopathy with fibrin deposition in glomeruli and arterioles as reported in hemolytic uremic syndrome (HUS), scleroderma, and antiphospholipid renal vasculitis . This is also reported in crescentic glomerulonephritis, and antiglomerular basement membrane disease (antiGBM) . Chronic kidney disease associated with high PAI-1 includes focal sclerosis glomerulonephritis (FSGS), diabetic nephropathy, focal necrotizing glomerulonephritis, membranous nephropathy, cyclosporine-induced glomerulosclerosis, and chronic allograft nephropathy . 4G polymorphism was reported with a high incidence among CKD and also in those with high risk of posttransplant rejection . PAI-1 expression is stimulated in CKD through transforming growth factor-beta (TGF-B), angiotensin II, tissue growth factors, cytokines, endothelin − 1, glucose-insulin resistance, LDL, hormones, acute phase response, oxidative stress, endotoxins. PAI-1, as it reduces plasmin activity it promotes thrombotic and necrotizing glomerular lesions that end with sclerosis and it also can directly induce migration of macrophages, trans-differentiated tubular epithelium, and myofibroblasts that end with interstitial fibrosis .
Association between presence of G4 and dyslipidemia (Table 10)
There was non-significant association between each form of dyslipidemia with the presence of 4G mutation within each of the patient groups and within total patient sample. The literature reported that PAI-1 plasma level correlates positively with very low-density lipoprotein triglycerides , such combination is well evident in CKD with renal dysfunction and is independent on the presence of 4G polymorphism as evident in this study.
Association between G4 polymorphism and severity of echocardiography changes
There was a non-significant association between severity of echocardiography changes with the presence of 4G polymorphism within each of the patient groups and within total patient sample (Table 11). CKD and renal dysfunction per se contribute to the development of CVD through many mechanisms. Primary traditional factors include arterial hypertension, hyperuricemia, diabetes, dyslipidemia particularly high TG, and low HDL-CHO. Non-traditional risk factors include hyperparathyroidism, anemia, hyper homocysteinemia, increased oxidative stress, endothelial dysfunction, apolipoprotein A, inflammatory procoagulant activity . Left ventricular hypertrophy is common in the early stages of CKD greater than would be expected for the degree of hypertension. Left diastolic and systolic dysfunction, cardiac dilatation soon follow and are highly related to uremic myopathy. Some degree of coronary atherosclerosis was found in 80% of a series of autopsies for children on HD . 4G/5G polymorphism in PAI-1 gene in some studies showed association with arterial ischemic strokes, and others showed a significant high level for plasma PAI-1 that was not influenced by the 4G/5G polymorphism . The homozygous or heterozygous carriage of 4G allele had been associated with higher PAI-1 levels and increased risk for CVD .
Association between G4 polymorphism and thrombotic changes (Table 12)
There was a non-significant association between the severity of thrombosis with the presence of 4G polymorphism within each of the patient groups and within the total patient sample. Kidney dysfunction itself may generate a thrombotic milieu indirectly through electrolytes, acid-base imbalance, and uremic toxins through their actions on enzymes involved in coagulation . Patients on hemodialysis show leucocyte activation and generation of cytokines that affect the fibrinolytic system. Many studies reported rise in PAI-1 in HD patients and attributed this to endothelial dysfunction and proinflammatory effect of bradykinines; however, the rise may be transient as it drops after dialysis due to bradykinine B2 receptor blockade .
Apolipoprotein E results
E3E3 was the most common pattern among HD and predialytic groups and among total sample reporting 75%, 70%, and 60% incidence for each. It was not reported in the control group (Tables 8 and 9 - Fig. 5). E3E3 showed a significant difference among the total patient group (50 cases) as compared to healthy control (60%, 0%) (Tables 8 and 9). APO-E polymorphism associating with renal insufficiency, in multiple studies, showed different data. Prevalence of E2 was reported among Japanese with renal insufficiency , E3/E4 among Sweden patients , and E3/4 and E4/4 in end-stage renal disease secondary to IgA nephropathy . Guz et al. coincides with this study as no difference in E pattern was reported between hemodialysis and predialytic stage . The study of the relation between dyslipidemia and E pattern in this work (Table 8) showed non-significant association between E3E3 pattern and hypertriglyceridemia, hypercholesterolemia, high LDL, low HDL, and high CHO/HDL among each group and among total sample. This was also reported by Guz G . However, Keane W F et al., reported an association between APO-E and its different patterns with renal disease and progress of renal failure. He attributed this to the role of APO-E in altered lipids, lupoid glomerulosclerosis, dialysis-related amyloidosis, and autocrine role of APO-E as a modulator of glomerular and mesangial proliferation . Eto confirmed the role of E2 in particular in renal disease and renal failure and reported high APO-E polymorphism among patients with ESRD with the secondary rise to APO-A . The relation between E3E3 and echocardiography changes (Table 9) reflects a significant association between E3E3 and severity score for echocardiography changes among total cases. E3E3 pattern represents about 70% incidence in groups 1 and 2 who constitute the major part of the total sample and also that patients who show high incidence and severity of high-risk factors contributing to CVD and echocardiography changes, in other way CV changes is multifactorial and not only associated with APO-E3E3 pattern.
The literature reported the prevalence of APO-A among those with coronary heart disease as they show atherogenic lipid profile and even independently on dyslipidemia. AP0-E enhances APO-A which contributes to CVD and directly contributes to the development of atherosclerosis . Association between apolipoprotein E3E3 and thrombotic grading as evident in (Table 10) shows that thrombotic grade severity was not associated with APO-E3E3 pattern. As thrombosis showed association with dyslipidemia, whereas dyslipidemia did not show significant association with APO-E3E3 presence, we can say that renal insufficiency (RI)-induced dyslipidemia is more influential in promoting thrombosis than APO-E role. The role of dyslipidemia in promoting thrombosis is well known.