Role of vascular endotheliar growth factor in the pathogenesis of nephrotic syndrome in children

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Role of vascular endotheliar growth factor in the pathogenesis of nephrotic syndrome in children

Сiuntu A.O.

Study presents the assessment of the concentration of the vascular endotheliar growth factor (VEGF) in the urine of 50 children with various types of primary glomerulonephritis. The VEGF levels in the urine of children with steroid-sensitive nephrotic syndrome (SSNS) during clinical manifestations increased significantly by 1.5 times compared to the control group. In the group of steroid-resistant nephrotic syndrome (SRNS) the VEGF levels in the urine was increased by 3.2 times. During remission in patients with SSNS and SRNS the levels of VEGF does not differ from those of the control group. At the same time a growth of VEGF levels by 4.5 times in the urine of patients with chronic glomerulonephritis (CGN) mixed form, exacerbation period was identified. Biochemical investigation of VEGF may be a new element specifying the diagnosis, especially in terms of its etiopathology with direct involvement on medicamentous treatment, patient follow-up and early prognosis.

Keywords: nephrotic syndrome, children, vascular endothelial growth factor, urine.

Представлены результаты определения концентрации эндотелиального сосудистого фактора роста (VEGF) в моче у 50 детей с различными вариантами первичного гломерулонефрита. Уровень VEGF в моче у детей был в 1,5 раза выше при стероид-чувствительным нефротическим синдромом (СЧНС), и в 3,2 раза выше при стероид-резистентным нефротическим синдромом (СРНС), по сравнению с контрольной группой. В период ремиссии у детей с СЧНС и СРНС уровень VEGF не отличался от контрольной группы. При хроническом гломерулонефритe (ХГН) смешанной формы в период обострения уровень VEGF в моче превышал в 4,5 раза значения контрольной группы. Определение концентрации VEGF в моче может быть значимым маркером для определения тяжести, эффективности применяемой терапии и прогноза заболевания.

Ключевые слова: нефротический синдром, дети, эндотелиальный сосудистый фактор роста (VEGF), мочa.

Glomerulonephritis has a particular position in reno-urinary pathology due to continued growth of morbidity, clinical course dominated by the severity of nephrotic syndrome (NS), functional, morphological and biochemical changes, tendency to relapse, frequent exacerbations, high percentage of chronicity and disabilitation, difficulties in treatment and prevention.

In present, according to data from the scientific medical literature based on a vast clinical material the annual incidence of NS in children in the USA and in Europe has been estimated to be 2-7 per 100,000 children, with a cumulative prevalence of 16 per 100,000 children [1,8,10].

Nephrotic syndrome in children generates a range of problems in clinical practice: early diagnosis, identification of prognostic indicators, recurrence prediction and response to therapy.

Thus, a particular interest constitutes vascular endothelial markers which proved to poses a significant sensitivity and specificity compared with other biochemical markers. Among these markers special attention goes to vascular endothelial growth factor (VEGF-A or VEGF) previously called “vasculotropin” or “vascular permeability factor (VPF)” and belongs to a family of multipotent cytokines which include besides VEGF-A and VEGF-B also C, D, E and placental growth factor [3,11].

VEGF stimulates proliferation and differentiation of endothelial cells, increases vascular permeability, mediates endothelium-dependent vasodilation and ensures the prevention of apoptosis in vascular endothelial cells. At kidney level, VEGF expression is more prominent in glomerular podocytes and in tubular epithelial cells while VEGF receptors are found primarily on preglomerular, glomerular and peritubular endothelial cells [6].

VEGF is the main angiogenic factor and a potent mitogen for endothelial cells. It is mainly produced in kidney by podocytes and exerts its biological activities by binding to its receptors (VEGFRs) [9].

Clinical observations revealed that plasma VEGF levels in diabetic nephropathy (DN) patients are increased and blocking VEGF improved DN in animal models. Increased plasma VEGF levels have been reported in chronic kidney disease (CKD) patients [2].

Despite numerous studies carried out in this field, the role of VEGF in the pathogenesis of kidney disease remains insufficiently elucidated. So far, there is insufficient information on VEGF manifestation related to renal glomerular diseases in children at different clinical-evolutionary stages of the disease. Therefore, the study of changes in VEGF concentration in urine of children with various forms of glomerulonephritis is extremely important.

The aim of the study is to evaluate the concentration of vascular endothelial growth factor in the urine of children with glomerulonephritis at different clinical-evolutionary stages of the disease.

Material and methods. Research was conducted at Paediatrics National Institute of Health Care for Mother and Child, and in the Laboratory of Biochemistry of IP State University of Medicine and Pharmacy “Nicolae Testemiюanu”, based on biological samples collected according to the principles of contemporary research, approved by the Ethics Committee of Research of IP State University of Medicine and Pharmacy “Nicolae Testemiюanu”, (favorable opinion of 13.05.2015, minutes No. 55). Study included 50 children with primary glomerulonephritis, 25 children with steroid-sensitive nephrotic syndrome (SSNS) and 15 children with steroid-resistant nephrotic syndrome (SRNS), 10 children with chronic glomerulonephritis (CGN) mixed form. Control group constituted 20 basically healthy children. nephrotic syndrome vascular endothelial

Clinical symptomatology of NS was dominated by the presence of edema, massive proteinuria (> 40 mg/mІ/h or the ratio of protein/urinary creatinine > 2.0 mg/mg) and hypoalbuminemia (<2.5 g/dl). Steroid-sensitive nephrotic syndrome (SSNS) was based on normalization of summary urine volume within 4 weeks, rarely 8 weeks after administration of glucocorticoids and installation of complete remission [5].

Steroid-resistant nephrotic syndrome (SRNS) was diagnosed in case of persistent proteinuria up to <3 g/dl over the course of 6-8 weeks of treatment with prednisolone at a dose of 2 mg/kg/24 h, followed by pulse-dose therapy with prednisolone 20-30 mg/kg/24h N 3 (not more than 1 g during a course) [5].

Complete remission was noticed in the case of solving edema, normalization of serum albumin up to 3,5 g/dl proteinuria and reduction of <4 mg/m2/h (100 mg/m2/24 h) in 3 consecutive urine volume [5].

Relapse was defined as a recurrence of massive proteinuria (> 40 mg/m2/h or the ratio of protein/urinary creatinine > 2.0 mg/mg or ? 2+ albuminuria during 3 consecutive days, usually with recurrence of edema [5].

Urinary excretion of VEGF was determined using mini-ELISA kit of analysis of the PeproTech Company (USA) according to the attached instructions. To appreciate the important difference among studied indices of compared lots were used statistical methods with assessment of arithmetic mean [X], average square deviation and error of average mean [± m]. Also have been used nonparametric statistical test “Mann-Whitney U” and the threshold of significance p <0.05 (StatsDirect statistical software, version 1.9.5, 2001).

Results

Results presented in the table 1 reveal that VEGF levels in the urine of children with SSNS during clinical manifestations period increased by 1.5 times, these alterations didn't show any statistical significance. Whereas in children with SRNS these levels increased significantly by 3.2 times compared to the control group.

Table 1 - Level of VEGF in the urine of children with glomerulonephritis

Note: AGN- acute glomerulonephritis, CGN - chronic glomerulonephritis. Statistically significant difference compared to the control group values: * P <0.05; ** P <0.01; *** P <0.001; p1-authenticity compared with the parameters registered under the acute phase; p2-authenticity of comparison between SSNS and SRNS.

During the period of remission in patients with SSNS and SRNS the cytokine level doesn't differ from the control one. Thus was identified a significant increase by 4.5 times of the level of VEGF in patients with mixed form of CGN during exacerbation. During remission VEGF levels in the urine continues to be increased compared to the control values.

Discussions. In this study was evaluated the VEGF concentration in the urine of children with glomerulonephritis at clinical-evolutionary stages of the disease. Obtained results indicate the presence of a high level of VEGF in urine in all patient groups with GN during exacerbation of the disease. Therewith, over the period of remission it was found the decrease of VEGF with the return to the normal level only in case of SSNS and SRNS. Growth of VEGF concentrations in the urine of children with different variants of GN established by us are undoubtedly one of the factors contributing to the development and progression of this disease. Similar results have also highlighted other researchers. Thus, Matsumoto and Kanmatsuse obtained increased levels of VEGF in urine of patients with nephrotic syndrome with minimal changes and in patients with IgA nephropathy with nephrotic syndrome as compared to patients without nephrotic syndrome and patients from the control group, correlated with the degree of proteinuria. Research results show that urinary VEGF levels decreased gradually after steroid therapy [7].

VEGF can play both beneficial and deleterious roles in renal diseases. Thus, the impaired angiogenesis and decreased VEGF expression were recently documented in the remnant kidney (RK) model of progressive renal failure. In this case the VEGF treatment reduces fibrosis and stabilizes renal function [4].

While VEGF is considered an important growth factor for maintaining glomerular capillary integrity and function, increased action of VEGF in diabetic renal disease may carry adverse consequences. Studies suggest that the effects of VEGF are amplified in the setting of endothelial dysfunction and low nitric oxide (NO) levels, which are a common feature in the diabetic state. The lack of NO may amplify the effects of VEGF to induce inflammation (via effects on the macrophage) and may lead to dysregulation of the vasculature, exacerbating features of diabetic renal disease [14].

The complexity of VEGF-A in renal disease could in part be accounted for by the distinct roles of its two receptors; VEGFR1 is involved in the inflammatory responses, whereas VEGFR2 predominantly mediates angiogenesis. Because nondiabetic chronic renal disease is associated with capillary loss, it was hypothesized that selective stimulation of VEGFR2 could be beneficial in this setting. However, VEGFR2 activation may be deleterious in the presence of NO deficiency and prestimulation of VEGFR2, in this case, can potentiate subsequent renal injury [12].

The finding of the high urinary excretion of the angiogenesis regulator VEGF-A, and it association with that of kidney injury markers in the patients with the proteinuric forms of CGN suggest that this excretion may be considered as an integral index that displays glomerular injury and indicates tubulointerstitial proteinuric/hypoxic remodeling [13].

Moreover, the mechanisms controlling the release and activity of VEGF in acute and chronic kidney diseases which provide modulation of damage induced by this factor remain insufficiently clarified. Further studies are necessary in order to achieve effective and differentiated therapeutic strategy in these patients.

Determination of VEGF in urine of GN can be a clinically relevant marker for determining the severity of pathological process, complications and effectiveness of treatment.

Conclusions

We can conclude that biochemical investigation of vascular endothelial growth factor may represent a new element specifying the diagnosis, especially in terms of its etiopathology with direct involvement on drug treatment, patients follow-up, early and long term prognosis.

References

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