In this study, we demonstrated that the serum vasohibine-1 levels in patients with clinically diagnosed diabetic nephropathy were not different from those diabetic patients without nephropathy and healthy subjects. We also demonstrated that serum vasohibine-1 levels were not associated with clinical or laboratory findings related with nephropathy such as daily protein excretion, glomerular filtration rate and blood pressure.
It is well known that there is an increase in glomerular filtration rate in the early stages of diabetes. In addition to hemodynamic factors, glomerular neoangiogenesis contributes to this increase. Abnormal vascular structures have been described in the glomeruli both of rats and humans with diabetic nephropathy [5, 6, 16–19]. Moreover, in rodents, an increase in glomerular filtration surface area due to slight elongation in new generated and also the existing capillaries has been shown [5–6]. Angiogenesis is a physiological event that is defined as the formation of new vessels from existing vessels and is regulated by the balance between proangiogenic and antiangiogenic factors. The most important proangiogenic agent is VEGF-A. It is known that there is an increase in levels of VEGF-A, and its receptor VEGFR-2, in both humans with diabetic nephropathy and animal experiments [8, 9, 20, 21]. In experimental models, overexpression of VEGF-A has been shown to lead to basal membrane thickening and mesangial expansion similar to diabetic nephropathy [7]. On the other hand, VEGF-A not only stimulates angiogenesis but also shows an increase in vascular permeability and chemotactic properties for monocytes [22, 23].
Vasohibine-1 is an antiangiogenic factor discovered for the first time during cDNA microarray assays to detect gene upregulation occurring against VEGF-A administration. It is synthesized by endothelial cells and acts as a negative feedback regulator that inhibits angiogenesis. Hence, vasohibine-1 can be expected to antagonize the deleterious effects of VEGF-A in the development of diabetic nephropathy and hence prevent nephropathy. In type 1 diabetic mice, treatment with vasohibine-1 expressing adenoviral vector increased serum vasohibine-1 levels, resulting in significant reduction in pathological changes, such as renal hypertrophy, glomerular hypertrophy and hyperfiltration, albuminuria, type 4 collagen deposition, and mesangial enlargement [11]. Also inflammatory cell infiltration, TGF B1 level and MCP levels decreased. Treatment with vasohibine-1 resulted in a reduction in the number of receptors for high glucose-induced TGF beta, MCP-1 and advanced glycosylation end products in cultured mesangial cells. The same authors obtained similar results in obese type 2 diabetic mice and also demonstrated that treatment with vasohibine-1 reduced VEGF-A expression in podocytes incubated in a high glucose medium [12]. On the other hand, nephropathic changes due to streptozotocin-induced diabetes mellitus, such as diabetes-induced mesangial matrix enlargement, inflammatory infiltration, and albuminuria were more severe in vasohibine-1 gene heterozygous knockout mice than in vasohibine-1 wild-type mice [24]. These findings suggest that vasohibine-1 possesses inhibitory properties against diabetic changes not only through antiangiogenic pathways, but also through direct effect on mesangial cells and inflammatory cascade.
Unfortunately, the relationship between vasohibine-1 and diabetic nephropathy has not been adequately studied in humans. Recently, a unique human study that investigates serum Vasohibin-1 levels in diabetic patients, Ren et al. have shown that urinary albumin/creatinine ratio positively correlated with serum vasohibine-1 levels in 697 type 2 DM patients. They demonstrated in diabetic patients that those with macroalbuminuria had higher levels of vasohibine-1 than those with microalbuminuria, and that those with microalbuminuria had higher levels of vasohibine-1 than healthy individuals [25]. In our study, we could not demonstrate such a relationship between the presence and severity of proteinuria, and serum vasohibine-1 levels. During angiogenesis, vasohibine-1 is secreted from endothelial cells in the termination zone, which inhibits excessive vessel formation. Vasohibine-1 has autocrine and paracrine effects on tissue locally. In our study, the most plausible reason for the lack of correlation between clinical nephropathy parameters and serum vasohibine-1 levels was that the local paracrine effects of vasohibine-1 may be more important than the vasohibine-1 levels in the blood. The systemic and local activity of vasohibine-1 may be different, similar to the difference between systemic and tissue-level RAS activity. Hinamoto et al., evaluated the renal biopsy findings and serum vasohibine-1 levels of 67 patients with chronic kidney disease caused mostly by etiologies other than diabetic nephropathy, and 22 healthy control patients [26]. Their results showed that serum vasohibine-1 levels were inversely correlated with systolic blood pressure, diastolic blood pressure and age, and were not associated with GFR and proteinuria, suggesting that high urine and serum vasohibine-1 levels were associated with poor renal outcomes. In our study, serum vasohibine-1 levels were inversely correlated with systolic blood pressure in patients with diabetic nephropathy, however, we did not find any significant relationship between vasohibin-1 levels and other parameters such as age, sex, GFR and proteinuria. On the other hand, cisplatin-induced acute renal failure in vasohibine-1 knockout mice has been shown to be more severe than in wild-type mice [27]. It was observed in renal biopsies taken from patients with kidney disease that vasohibine-1 was expressed in a glomerular crescent and interstitial inflammatory cells, as well as in endothelial cells [28]. This finding suggests that vasohibine-1 may be associated with the progression of inflammation and renal damage and that the kidneys respond to cellular stressors with an increase in vasohibine-1 expression.
Our study has some limitations. First, the diagnosis of DM is usually a clinical diagnosis and absence of proteinuria does not mean that there are no histologically nephropathic changes in the kidney. Although studies show that the results of spot protein/cretinine and spot albümin/creatinine are highly correlated, current guidelines use spot albumin /creatinine for the diabetic nephropathy diagnosis. Evaluation of vasohibine-1 activity at tissue level may yield different results. Second, our study was conducted with a relatively small number of patients. We showed that diabetic patients have slightly lower vasohibin-1 levels but it was not statistically significant. This difference may reach more significant magnitude with larger patient numbers. A larger study in which more patients are included is needed.