The role of vascular endothelial growth factor (VEGF) in renal pathophysiology

Autocrine VEGF-VEGF-R loop on podocytes during glomerulonephritis in humans

BACKGROUND

Vascular endothelial growth factor (VEGF) is the most important and tightly regulated angiogenic cytokine in the kidney. Its activity is critical for capillary/glomerular preservation and repair, and recent studies have also demonstrated its relevance for the preservation of podocytes.

METHODS

The present study investigated a large number (n = 153) of renal biopsies from patients with glomerulonephritis (GN) and evaluated the expression and activity of the glomerular VEGF system [VEGF, VEGF-R1, VEGF-R2 and biologically active VEGF as identified by VEGF-VEGF receptor complexes (VEGF-VEGF-R)] in parallel with markers of renal function, injury and repair.

RESULTS

Whereas glomerular VEGF expression was clearly elevated, VEGF-R expression levels were widely unchanged. In parallel to the overall VEGF expression, the biological activity of VEGF on its receptors was uniformly significantly enhanced. Interestingly, the expression pattern of VEGF-R1 and VEGF-R2 significantly changed during GN where a very prominent podocytic pattern appeared, which was also detected for receptor-bound VEGF. VEGF expression and activity could be linked with indicators of renal injury such as glomerular proliferation and creatinine, respectively.

CONCLUSIONS

This study shows, for the first time, increased podocytic VEGF-VEGF-R binding during human GN, suggesting not only the existence of a glomerular paracrine proangiogenic, but also an autocrine role of the VEGF-VEGF-R system in diseased podocytes.

Transgenic overexpression of GLUT1 in mouse glomeruli produces renal disease resembling diabetic glomerulosclerosis

Previous work identified an important role for hyperglycemia in diabetic nephropathy (The Diabetes Control and Complications Trial Research Group. N Engl J Med 329: 977-986, 1993; UK Prospective Diabetes Study Group. Lancet 352: 837-853, 1998), and increased glomerular GLUT1 has been implicated. However, the roles of GLUT1 and intracellular glucose have not been determined. Here, we developed transgenic GLUT1-overexpressing mice (GT1S) to characterize the roles of GLUT1 and intracellular glucose in the development of glomerular disease without diabetes. GLUT1 was overexpressed in glomerular mesangial cells (MC) of C57BL6 mice, a line relatively resistant to diabetic nephropathy. Blood pressure, blood glucose, glomerular morphometry, matrix proteins, cell signaling, transcription factors, and selected growth factors were examined. Kidneys of GT1S mice overexpressed GLUT1 in glomerular MCs and small vessels, rather than renal tubules. GT1S mice were neither diabetic nor hypertensive. Glomerular GLUT1, glucose uptake, mean capillary diameter, and mean glomerular volume were all increased in the GT1S mice. Moderately severe glomerulosclerosis (GS) was established by 26 wk of age in GT1S mice, with increased glomerular type IV collagen and fibronectin. Modest increases in glomerular basement membrane thickness and albuminuria were detected with podocyte foot processes largely preserved, in the absence of podocyte GLUT1 overexpression. Activation of glomerular PKC, along with increased transforming growth factor-beta1, VEGFR1, VEGFR2, and VEGF were all detected in glomeruli of GT1S mice, likely contributing to GS. The transcription factor NF-kappaB was also activated. Overexpression of glomerular GLUT1, mimicking the diabetic GLUT1 response, produced numerous features typical of diabetic glomerular disease, without diabetes or hypertension. This suggested GLUT1 may play an important role in the development of diabetic GS.

Overexpression of VEGF-A in podocytes of adult mice causes glomerular disease

We sought to examine the pathogenic role of excessive VEGF-A expression in podocytes, since it has been reported that diabetic nephropathy and other glomerular diseases are associated with increased VEGF-A expression. The induction of podocyte-specific VEGF164 overexpression in adult transgenic mice led to proteinuria, glomerulomegaly, glomerular basement membrane thickening, mesangial expansion, loss of slit diaphragms, and podocyte effacement. When doxycycline-mediated VEGF164 was stopped, these abnormalities reversed. These findings were associated with reversible downregulation of metalloproteinase 9 and nephrin expression. Using transmission electron microscopy, we established that VEGF-A receptor-2 (VEGFR2) was expressed in podocytes and glomerular endothelial cells. We also found that VEGF164 induced VEGFR2 phosphorylation in podocytes. Further, we were able to co-immunoprecipitate VEGFR2 and nephrin using whole kidney lysates, confirming interaction in vivo. This implies that autocrine and paracrine VEGF-A signaling through VEGFR2 occurs in podocytes and may mediate the glomerular phenotype caused by VEGF164 overexpression. Thus, we suggest that podocyte VEGF164 overexpression in adult mice is sufficient to induce glomerular filtration barrier structural and functional abnormalities similar to those present in murine diabetic nephropathy.

VEGF signalling inhibition-induced proteinuria: Mechanisms, significance and management

Proteinuria is a dose-related side-effect occurring after inhibition of vascular endothelial growth factor (VEGF) signalling and may reflect severe glomerular damage. The inhibition of the VEGF signalling axis induces downexpression or suppression of nephrin, an important protein for the maintenance of the glomerular slit diaphragm, sometimes leading to nephritic syndrome and/or glomerular thrombotic microangiopathy, the main-associated kidney disease. A MEDLINE search was carried out using the following criteria: (1) all MEDLINE listings as of 01-01-2000 with abstracts; (2) English language; and (3) Humans. The following phrases were used to query the database: (proteinuria) AND (anti-VEGF OR VEGF inhibition OR bevacizumab OR sunitinib OR sorafenib OR VEGF Trap OR axitinib OR pazopanib OR AZ 2171). The references of each article identified were carefully reviewed for additional reference. The incidence of mild and asymptomatic proteinuria ranges from 21% up to 63%, but heavy proteinuria has been reported in up to 6.5% of renal cell carcinoma patients. Although discontinuation of anti-VEGF agent induced significant reduction, persistence of proteinuria is common. Although angiotensinconverting-enzyme inhibitors and/or angiotensin receptor blockers seem to be preferred, no specific recommendation for an antiproteinuric agent can be made in this context because there are no controlled studies addressing the subject. Periodic monitoring of urinary protein should be carried out in anti-VEGF-treated patients and patients showing proteinuria need special referral to nephrologists.

Role of renal microcirculation in experimental renovascular disease

BACKGROUND

Renal artery stenosis (RAS) causes renal injury partly via microvascular (MV) endothelial dysfunction and damage. Vascular endothelial growth factor (VEGF) is crucial for preservation of microvasculature and promotes vascular proliferation and endothelial repair. We have previously shown that MV rarefaction is associated with decreased VEGF in the kidney exposed to chronic RAS, accompanied by deteriorated renal function and fibrosis. We hypothesized that preserving the renal microcirculation in the stenotic kidney will halt the progression of renal damage.

METHODS

Unilateral RAS was induced in 16 pigs. In eight, VEGF (0.05 micrograms/kg) was infused intra-renally at the onset of RAS. After 6 weeks, single-kidney haemodynamics and function were assessed using in vivo multi-detector computed tomography (CT). Renal microvessels, angiogenic pathways and morphology were investigated ex vivo using micro-CT, real-time PCR and histology.

RESULTS

Blood pressure and degree of RAS was similar in RAS and RAS + VEGF pigs. Single-kidney renal blood flow (RBF) and glomerular filtration rate (GFR) were reduced in RAS compared to Normal (221.1 +/- 46.5 and 29.9 +/- 3.8 vs. 522.5 +/- 60.9 and 49.3 +/- 3.4 mL/min, respectively, P < 0.05), accompanied by decreased cortical MV density and increased renal fibrosis. Pre-emptive administration of VEGF preserved MV architecture, attenuated fibrosis and normalized RBF and GFR (510.8 +/- 50.9 and 39.9.1 +/- 4.1 mL/min, P = not significant vs. Normal).

CONCLUSIONS

This study underscores the importance of the renal microcirculation in renovascular disease. Intra-renal administration of VEGF preserved renal MV architecture and function of the stenotic kidney, which in turn preserved renal haemodynamics and function and decreased renal fibrosis. These observations suggest that preventing renal MV loss may be a potential target for therapeutic approaches for patients with chronic renovascular disease.

Vascular endothelial growth factor inhibition by dRK6 causes endothelial apoptosis, fibrosis, and inflammation in the heart via the Akt/eNOS axis in db/db mice

OBJECTIVE

Vascular endothelial growth factor (VEGF), which is associated with the stimulation of angiogenesis and collateral vessel synthase, is one of the crucial factors involved in cardiac remodeling in type 2 diabetes.

RESEARCH DESIGN AND METHODS

We investigated VEGF inhibition by dRK6 on the heart in an animal model of type 2 diabetes. Male db/db and db/m mice either were treated with dRK6 starting at 7 weeks of age for 12 weeks (db/db-dRK6 and db/m-dRK6) or were untreated.

RESULTS

Cardiac dysfunction and hypertrophy were noted by echocardiogram and molecular markers in the db/db-dRK6 mice. The presence of diabetes significantly suppressed the expression of VEGF receptor (VEGFR)-1 and VEGFR-2, phospho-Akt, and phospho-endothelial nitric oxide synthase (eNOS) in the heart. In db/db-dRK6 mice, dRK6 completely inhibited VEGFR-2, phospho-Akt, and phospho-eNOS expression, whereas no effect on VEGFR-1 was observed. Cardiac fibrosis, microvascular scarcity associated with an increase in apoptotic endothelial cells, and inflammation were prominent, as well as increase in antiangiogenic growth factors. Cardiac 8-hydroxy-deoxyguanine and hypoxia-inducible factor-1alpha expression were significantly increased. No such changes were found in the other groups, including the db/m-dRK6 mice. The number of apoptotic human umbilical vein endothelial cells was increased by dRK6 in a dose-dependent manner only at high glucose concentrations, and this was associated with a decrease in phospho-Akt and phospho-eNOS related to oxidative stress.

CONCLUSIONS

Our results demonstrated that systemic blockade of VEGF by dRK6 had deleterious effects on the heart in an animal model of type 2 diabetes; dRK6 induced downregulation of the VEGFR-2 and Akt-eNOS axis and enhancement of oxidative stress.

Effects of increased renal tubular vascular endothelial growth factor (VEGF) on fibrosis, cyst formation, and glomerular disease

The role of vascular endothelial growth factor (VEGF) in renal fibrosis, tubular cyst formation, and glomerular diseases is incompletely understood. We studied a new conditional transgenic mouse system [Pax8-rtTA/(tetO)(7)VEGF], which allows increased tubular VEGF production in adult mice. The following pathology was observed. The interstitial changes consisted of a ubiquitous proliferation of peritubular capillaries and fibroblasts, followed by deposition of matrix leading to a unique kind of fibrosis, ie, healthy tubules amid a capillary-rich dense fibrotic tissue. In tubular segments with high expression of VEGF, cysts developed that were surrounded by a dense network of peritubular capillaries. The glomerular effects consisted of a proliferative enlargement of glomerular capillaries, followed by mesangial proliferation. This resulted in enlarged glomeruli with loss of the characteristic lobular structure. Capillaries became randomly embedded into mesangial nodules, losing their filtration surface. Serum VEGF levels were increased, whereas endogenous VEGF production by podocytes was down-regulated. Taken together, this study shows that systemic VEGF interferes with the intraglomerular cross-talk between podocytes and the endocapillary compartment. It suppresses VEGF secretion by podocytes but cannot compensate for the deficit. VEGF from podocytes induces a directional effect, attracting the capillaries to the lobular surface, a relevant mechanism to optimize filtration surface. Systemic VEGF lacks this effect, leading to severe deterioration in glomerular architecture, similar to that seen in diabetic nephropathy.

Glomerular collapse associated with subtotal renal infarction in kidney transplant recipients with multiple renal arteries

Collapsing glomerulopathy is an aggressive kidney disease with rapid progression toward end-stage renal disease. Rare cases of de novo collapsing glomerulopathy have been reported during the post-transplant course and, in some instances, have been associated with renal graft vascular lesions. This finding raises the important question of whether ischemia could induce podocyte transdifferentiation, a hypothesis supported by evidence of hypoxia-inducible factor-dependent podocyte proliferation in HIV-associated nephropathy. We describe here 3 HIV-negative kidney transplant recipients in whom early graft biopsy performed in the vicinity of segmental graft infarction disclosed the typical features of glomerular collapse. Podocyte transdifferentiation was characterized by hallmark lesions, such as loss of mature podocyte phenotype, podocyte proliferation, and acquisition of a macrophage-like phenotype. Together, these data suggest that acute glomerular ischemia may lead to glomerular collapse in kidney transplants.

Rapamycin has dual opposing effects on proteinuric experimental nephropathies: is it a matter of podocyte damage?

BACKGROUND

In clinical renal transplantation, an increase in proteinuria after conversion from calcineurin inhibitors to rapamycin has been reported. In contrast, there are studies showing a nephro-protective effect of rapamycin in proteinuric diseases characterized by progressive interstitial inflammatory fibrosis.

METHODS

Because of the contradictory reports concerning rapamycin on proteinuria, we examined proteinuria and podocyte damage markers on two renal disease models, with clearly different pathophysiological mechanisms: a glomerular toxico-immunological model induced by puromycin aminonucleoside, and a chronic hyperfiltration and inflammatory model by mass reduction, both treated with a fixed high rapamycin dose.

RESULTS

In puromycin groups, rapamycin provoked significant increases in proteinuria, together with a significant fall in podocin immunofluorescence, as well as clear additional damage to podocyte foot processes. Conversely, after mass reduction, rapamycin produced lower levels of proteinuria and amelioration of inflammatory and pro-fibrotic damage. In contrast to the puromycin model, higher glomerular podocin and nephrin expression and amelioration of glomerular ultrastructural damage were found.

CONCLUSIONS

We conclude that rapamycin has dual opposing effects on subjacent renal lesion, with proteinuria and podocyte damage aggravation in the glomerular model and a nephro-protective effect in the chronic inflammatory tubulointerstitial model. Rapamycin produces slight alterations in podocyte structure when acting on healthy podocytes, but it clearly worsens those podocytes damaged by other concomitant injury.

Angiogenesis in the kidney: a new therapeutic target?

PURPOSE OF REVIEW

The prevalence of chronic kidney disease has been growing consistently for the past decades. Renal failure is often associated with defective angiogenesis, and recognition of the contribution of the renal microcirculation to the progression of chronic renal disease may aid in the development of therapeutic interventions.

RECENT FINDINGS

Intra-renal proliferation, remodeling, and/or rarefaction of microvessels in response to injury can all aggravate nephron damage, and experimental evidence suggests that they may constitute the early steps in the complex pathways involved in progressive renal injury. Recent studies showed the benefits of targeted interventions deemed to promote neovascularization (e.g. progenitor cells, growth factors) on the ischemic myocardium and brain and in a few models of renal disease.

SUMMARY

Evidence of aberrant renal microvascular architecture in various forms of renal disease provides the impetus to attempt modulating the renal microcirculation to interfere with the disease process. Targeted interventions to preserve the renal microcirculation may not only decrease the evolving injury in renal vascular disease but also potentially constitute a coadjuvant intervention to become part of a comprehensive management plan to improve the success of parallel strategies to preserve renal function, such as revascularization.

Adverse effects of anticancer agents that target the VEGF pathway

Antiangiogenesis agents that target the VEGF/VEGF receptor pathway have become an important part of standard therapy in multiple cancer indications. With expanded clinical experience with this class of agents has come the increasing recognition of the diverse adverse effects related to disturbance of VEGF-dependent physiological functions and homeostasis in the cardiovascular and renal systems, as well as wound healing and tissue repair. Although most adverse effects of VEGF inhibitors are modest and manageable, some are associated with serious and life-threatening consequences, particularly in high-risk patients and in certain clinical settings. This Review examines the toxicity profiles of anti-VEGF antibodies and small-molecule inhibitors. The potential mechanisms of the adverse effects, risk factors, and the implications for selection of patients and management are discussed.

Autologous and allogeneic marrow stromal cells are safe and effective for the treatment of acute kidney injury

Acute kidney injury (AKI) is a major clinical problem associated with high morbidity and mortality. Likely due to its complex pathophysiology, therapies with a single pharmacological agent have generally failed to improve outcomes. In contrast, stem cell-based interventions utilize these cells' ability to simultaneously target multiple pathophysiological components of AKI and thus represent a promising new tool for the treatment of AKI. The aims of the this study were to investigate the long-term outcome and safety of treatment with autologous and allogeneic mesenchymal stem cells (MSCs) after AKI and the role of vascular endothelial growth factor (VEGF) as one of the principal paracrine mediators of renoprotection of MSCs. MSC administration after AKI was not associated with adverse events and proved to be renoprotective in animals with severe renal failure. Identical doses of autologous MSC were more effective than allogeneic. At 3 months, MSCs were not engrafted in any tissues except in the bone marrow in 50% of animals given the highest allogeneic cell dose. There was no long-term fibrotic response in the kidneys attributable to MSC therapy, and animals with severe AKI were protected from development of fibrotic lesions after AKI. Furthermore, this study establishes VEGF as a critical factor mediating renal recovery. VEGF knockdown by small-interfering RNA reduced effectiveness of MSCs significantly and decreased survival. In summary, our results show that both autologous and allogeneic MSC are safe and effective in AKI, and importantly, reduce late renal fibrosis and loss of renal function in surviving animals and that VEGF is a critical factor in renoprotection by MSCs. Together, we posit that these data provide further justification for the conduct of clinical trails in which AKI is treated with MSC.

Vascular endothelial growth factor receptor inhibitor enhances dietary salt-induced hypertension in Sprague-Dawley rats

Clinical evidence links the inhibition of VEGF to hypertension. However, the mechanisms by which VEGF affects the pathogenesis of hypertension remain in question. We determined 1) whether administration of VEGF receptor inhibitor SU5416 enhances dietary salt-induced hypertension in Sprague-Dawley (SD) rats, and 2) whether VEGF or SU5416 directly affects proliferation of cultured human renal proximal tubular epithelial cells (HRPTEC) and endothelial nitric oxide synthase (eNOS) expression in cultured human glomerular microvessel endothelial cells (HGMEC). Ten 10-wk-old male SD rats received a high sodium diet (HS; 8%) and the other 10 SD rats received a normal sodium diet (NS; 0.5%) for 4 wks. After 2 wks of the dietary program, five rats were administered with SU5416 at 10 mg x kg(-1) x day(-1) ip or DMSO (vehicle) for 14 days in HS and NS groups. Mean arterial pressure was significantly higher in rats treated with SU5416, as opposed to those treated with DMSO and fed with HS for 4 wk (157.6 +/- 3.9 vs. 125.9 +/- 4.3 mmHg, P < 0.01). Increased proteinuria and albuminuria were associated with marked renal histological abnormalities in HS group with SU5416 administration, compared with those in the vehicle HS group. 3H-thymidine incorporation assay showed that SU5416 blocked the actions of both exogenous and endogenous VEGF on the proliferation of HRPTEC. VEGF (10 ng/ml) significantly increased eNOS protein levels by 29% in cultured HGMEC, but its action was completely abolished by SU5416. These results suggest that VEGF receptor inhibition enhances dietary salt-induced hypertension and kidney injury, possibly by direct damage on renal cells and decreasing NO production by eNOS.

Drug-induced Kidney Disease – Pathology and Current Concepts

The kidneys can be damaged by a large number of therapeutic agents. The aim of this article is to discuss the pathological features of drug-induced renal disease as diagnosed by kidney biopsy. The literature is reviewed and cases seen by the authors that have a known drug association are analysed. Mechanisms of injury are varied and all renal structures may be affected. The tubulointerstitial compartment is most frequently involved, but glomerular and vascular lesions are seen in a significant proportion of cases. Key words: Drug, Kidney, Nephrotoxicity, Pathology

Intricacies of bevacizumab-induced toxicities and their management

OBJECTIVE

To review the serious and common toxicities of bevacizumab and describe their incidence, risk factors, presentation, pathophysiology, and management.

DATA SOURCES

Literature for this review article was collected from PubMed, MEDLINE, and the proceedings of the American Society of Clinical Oncology (2000-November 2008). The key terms used in the search were: bevacizumab, vascular endothelial growth factor, angiogenesis inhibitors, toxicity, toxicity management, and adverse event.

STUDY SELECTION AND DATA EXTRACTION

Review articles, preclinical studies, and all published Phase 1-3 clinical trials were reviewed. The references listed in identified articles were examined for additional publications.

DATA SYNTHESIS

The biomedical literature from 2000 to 2008 confirms that bevacizumab carries serious and potentially life-threatening toxicity risks and emphasizes the importance of early recognition, continuous monitoring, and prompt management of these toxicities. Such toxicities include hemorrhage/bleeding, wound healing complications, gastrointestinal perforation, arterial thromboembolism, congestive heart failure, hypertension, proteinuria/nephrotic syndrome, infusion-related hypersensitivity reactions, and reversible posterior leukoencephalopathy syndrome. Patients at the highest risk for these toxicities are individuals with a history of hypertension, thromboembolism, bleeding, cardiovascular disease, or preexisting proteinuria, as these conditions may be exacerbated by bevacizumab use. Additionally, particular tumor types correlate with risk for individual toxicities; for example, patients with squamous non-small-cell lung cancer or rectal cancer have a higher risk of bleeding, those with renal cell carcinoma have a higher proteinuria risk, and patients with colorectal cancer have a higher risk of gastrointestinal perforation. Further investigation is warranted to develop effective management strategies for these toxicities.

CONCLUSIONS

As bevacizumab is becoming widely used in general oncology practice, it is important to understand the toxicities that can arise and to develop practice guidelines for their management.

Hypoxia response and VEGF-A expression in human proximal tubular epithelial cells in stable and progressive renal disease

Proteinuria, inflammation, chronic hypoxia, and rarefaction of peritubular capillaries contribute to the progression of renal disease by affecting proximal tubular epithelial cells (PTECs). To study the transcriptional response that separates patients with a stable course from those with a progressive course of disease, we isolated PTECs by laser capture microdissection from cryocut tissue sections of patients with proteinuric glomerulopathies (stable n=20, progressive n=11) with a median clinical follow-up of 26 months. Gene-expression profiling and a systems biology analysis identified activation of intracellular vascular endothelial growth factor (VEGF) signaling and hypoxia response pathways in progressive patients, which was associated with upregulation of hypoxia-inducible-factor (HIF)-1alpha and several HIF target genes, such as transferrin, transferrin-receptor, p21, and VEGF-receptor 1, but downregulation of VEGF-A. The inverse expression levels of HIF-1alpha and VEGF-A were significantly superior in predicting clinical outcome as compared with proteinuria, renal function, and degree of tubular atrophy and interstitial fibrosis at the time of biopsy. Interactome analysis showed the association of attenuated VEGF-A expression with the downregulation of genes that usually stimulate VEGF-A expression, such as epidermal growth factor (EGF), insulin-like growth factor-1 (IGF-1), and HIF-2alpha. In vitro experiments confirmed the positive regulatory effect of EGF and IGF-1 on VEGF-A transcription in human proximal tubular cells. Thus, in progressive but not in stable proteinuric kidney disease, human PTECs show an attenuated VEGF-A expression despite an activation of intracellular hypoxia response and VEGF signaling pathways, which might be due to a reduced expression of positive coregulators, such as EGF and IGF-1.

Peritubular capillaries are rarefied in congenital nephrotic syndrome of the Finnish type

Congenital nephrotic syndrome of the Finnish type (NPHS1) is associated with the rapid development of glomerular and tubulointerstitial fibrosis. Here we measured morphologic and molecular changes in the peritubular capillaries of the kidney in patients with NPHS1. Immunohistochemical analysis for the endothelial cell marker CD31 showed marked narrowing and a moderate but significant reduction in peritubular capillary density, especially in areas of increased collagen I and alpha-smooth muscle actin content. No evidence of endothelial-mesenchymal transformation was found. There was increased expression (up to 43-fold) of hypoxia inducible factor-1alpha suggesting tubulointerstitial hypoxia. Double-labeling for CD31 and vimentin showed small foci of peritubular capillary loss and tubular cell damage. While the amount of intercellular adhesion molecule-1 was upregulated in endothelial cells, other adhesion molecules were only modestly expressed. Vascular endothelial growth factor expression was reduced by up to half and decreased endothelial progenitor cell marker CD34 expression indicated lack of vascular repair. Our results suggest that hypoxia in the tubulointerstitium caused by hypoperfusion of glomerular and tubulointerstitial capillaries and rarefaction of the latter may be important for the rapid progression of fibrosis in the kidneys of patients with NPHS1.

Pathogenesis of HIV-associated nephropathy

Human immunodeficiency virus-associated nephropathy (HIVAN) is a leading cause of end-stage renal disease in the HIV-1-seropositive population. HIVAN, which is characterized by heavy proteinuria and a rapid decline in renal function, is caused by infection and subsequent expression of viral genes in renal epithelial cells, although the exact mechanism of viral entry into these cells is unknown. The infected renal epithelium is a distinct compartment that supports the evolution of viral strains that may diverge from those found in the patient's blood. Research using animal models and in vitro studies has shown that vpr and nef are the HIV-1 genes most responsible for inducing the characteristic clinical and histopathologic syndrome of HIVAN. Dysregulation of several host factors, including mediators of inflammation, apoptosis, proliferation, transcription, and cell-cell interactions, are also critical factors in determining whether infection of the renal epithelium will lead to HIVAN. Additional research is required to delineate the mechanisms of HIVAN pathogenesis further so that more effective interventions can be implemented to prevent and treat this disease.

Thrombotic microangiopathy secondary to VEGF pathway inhibition by sunitinib

BACKGROUND

Drugs targeting the VEGF pathway are associated with renal adverse events, including proteinuria, hypertension and thrombotic microangiopathy (TMA). Most cases of TMA are reported secondary to bevacizumab. It was shown recently that sunitinib, a small molecule inhibiting several tyrosine kinase receptors, including VEGF receptors, can also induce proteinuria, hypertension and biological features of TMA. Case. A 44-year-old woman with a history of malignant skin hidradenoma was started on sunitinib for refractory disease. She developed hypertension after 2 weeks and low-grade proteinuria after 4 weeks. Renal function remained normal, and biological signs of TMA were absent. A renal biopsy was performed 6 months later as proteinuria persisted, demonstrating typical features of TMA. The patient was given irbesartan, and sunitinib was continued for 3 months after diagnosis. Over this period, blood pressure and renal function remained stable and proteinuria became undetectable.

CONCLUSION

We report on the first case of histologically documented TMA secondary to sunitinib and provide detailed description of renal histological involvement. This suggests that all anti-VEGF drugs may share a common risk for developing renal adverse events, including TMA. Our case highlights the possible discrepancy between mild clinical manifestation on one hand and severe TMA features on renal biopsy on the other hand and pleads for large indication of renal biopsy in this setting. The renin-angiotensin system blockers may be considered in patients with mild clinical manifestations and in the absence of therapeutic alternative to anti-VEGF drugs.

The alternatively spliced anti-angiogenic family of VEGF isoforms VEGFxxxb in human kidney development

BACKGROUND/AIM

Vascular endothelial growth factor (VEGF), required for renal development, is generated by alternative splicing of 8 exons to produce two families, pro-angiogenic VEGF(xxx), formed by proximal splicing in exon 8 (exon 8a), and anti-angiogenic VEGF(xxx)b, generated by distal splicing in exon 8 (exon 8b). VEGF(165)b, the first described exon 8b-containing isoform, antagonises VEGF(165) and is anti-angiogenic in vivo.

METHODS

Using VEGF(xxx)b-specific antibodies, we investigated its expression quantitatively and qualitatively in developing kidney, and measured the effect of VEGF(165)b on renal endothelial and epithelial cells.

RESULTS

VEGF(xxx)b formed 45% of total VEGF protein in adult renal cortex, and VEGF(165)b does not increase glomerular endothelial cell permeability, it inhibits migration, and is cytoprotective for podocytes. During renal development, VEGF(xxx)b was expressed in the condensed vesicles of the metanephros, epithelial cells of the comma-shaped bodies, invading endothelial cells and epithelial cells of the S-shaped body, and in the immature podocytes. Expression reduced as the glomerulus matured.

CONCLUSION

These results show that the anti-angiogenic VEGF(xxx)b isoforms are highly expressed in adult and developing renal cortex, and suggest that the VEGF(xxx)b family plays a role in glomerular maturation and podocyte protection by regulating the pro-angiogenic pro-permeability properties of VEGF(xxx) isoforms.

Renal hypoxia and dysoxia after reperfusion of the ischemic kidney

Ischemia is the most common cause of acute renal failure. Ischemic-induced renal tissue hypoxia is thought to be a major component in the development of acute renal failure in promoting the initial tubular damage. Renal oxygenation originates from a balance between oxygen supply and consumption. Recent investigations have provided new insights into alterations in oxygenation pathways in the ischemic kidney. These findings have identified a central role of microvascular dysfunction related to an imbalance between vasoconstrictors and vasodilators, endothelial damage and endothelium-leukocyte interactions, leading to decreased renal oxygen supply. Reduced microcirculatory oxygen supply may be associated with altered cellular oxygen consumption (dysoxia), because of mitochondrial dysfunction and activity of alternative oxygen-consuming pathways. Alterations in oxygen utilization and/or supply might therefore contribute to the occurrence of organ dysfunction. This view places oxygen pathways' alterations as a potential central player in the pathogenesis of acute kidney injury. Both in regulation of oxygen supply and consumption, nitric oxide seems to play a pivotal role. Furthermore, recent studies suggest that, following acute ischemic renal injury, persistent tissue hypoxia contributes to the development of chronic renal dysfunction. Adaptative mechanisms to renal hypoxia may be ineffective in more severe cases and lead to the development of chronic renal failure following ischemia-reperfusion. This paper is aimed at reviewing the current insights into oxygen transport pathways, from oxygen supply to oxygen consumption in the kidney and from the adaptation mechanisms to renal hypoxia. Their role in the development of ischemia-induced renal damage and ischemic acute renal failure are discussed.

Renal hypoxia and dysoxia after reperfusion of the ischemic kidney

Ischemia is the most common cause of acute renal failure. Ischemic-induced renal tissue hypoxia is thought to be a major component in the development of acute renal failure in promoting the initial tubular damage. Renal oxygenation originates from a balance between oxygen supply and consumption. Recent investigations have provided new insights into alterations in oxygenation pathways in the ischemic kidney. These findings have identified a central role of microvascular dysfunction related to an imbalance between vasoconstrictors and vasodilators, endothelial damage and endothelium-leukocyte interactions, leading to decreased renal oxygen supply. Reduced microcirculatory oxygen supply may be associated with altered cellular oxygen consumption (dysoxia), because of mitochondrial dysfunction and activity of alternative oxygen-consuming pathways. Alterations in oxygen utilization and/or supply might therefore contribute to the occurrence of organ dysfunction. This view places oxygen pathways' alterations as a potential central player in the pathogenesis of acute kidney injury. Both in regulation of oxygen supply and consumption, nitric oxide seems to play a pivotal role. Furthermore, recent studies suggest that, following acute ischemic renal injury, persistent tissue hypoxia contributes to the development of chronic renal dysfunction. Adaptative mechanisms to renal hypoxia may be ineffective in more severe cases and lead to the development of chronic renal failure following ischemia-reperfusion. This paper is aimed at reviewing the current insights into oxygen transport pathways, from oxygen supply to oxygen consumption in the kidney and from the adaptation mechanisms to renal hypoxia. Their role in the development of ischemia-induced renal damage and ischemic acute renal failure are discussed.

1,25-dihydroxyvitamin D3 regulates VEGF production through a vitamin D response element in the VEGF promoter

In previous studies we have demonstrated that the active form of vitamin D (1,25(OH)(2)D(3)) increases vascular endothelial growth factor (VEGF) expression and release in vascular smooth muscle cells (VSMC) in vitro. However, the mechanism by which 1,25(OH)(2)D(3) increases VEGF production is currently unknown. In this work, we demonstrated binding of vitamin D receptor to two response elements in the VEGF promoter. We performed promoter transactivation analysis and we observed that, in 293T cells, VEGF promoter was activated after vitamin D treatment. Using site-directed mutagenesis we have shown that both response elements are important for VEGF promoter activity. Therefore, the increase in VEGF expression and secretion induced by 1,25(OH)(2)D(3) in VSMC in vitro could be explained by direct binding of the vitamin D receptor, as a transcription factor, to VEGF promoter. These results could explain part of the beneficial effects of vitamin D treatment in renal patients by a possible VEGF-mediated improvement of the endothelial dysfunction.

A case of Castleman's disease complicated with nephrotic syndrome due to glomerulopathy mimicking membranoproliferative glomerulonephritis

Castleman's disease is a rare atypical lymphoproliferative disorder. Renal manifestations, such as proteinuria, hematuria, and renal dysfunction, are common in Castleman's disease; however, a nephrotic syndrome rarely occurs. We have encountered an unusual case of Castleman's disease of the plasma cell type characterized by nephrotic syndrome because of glomerulopathy mimicking membranoproliferative glomerulonephritis. Our patient showed higher levels of circulating cytokines (interleukin-6/vascular endothelial cell-derived growth factor), the glomerular lesions not associated with immunocomplex deposition, and the resolution of nephrotic syndrome after successful corticosteroids therapy resulting in a decline in cytokines levels, thereby implicating a cytokine-induced glomerular cell injury/activation as a possible cause of the glomerular pathological changes in this case.

Parathyroid hormone-related protein interacts with vascular endothelial growth factor to promote fibrogenesis in the obstructed mouse kidney

Parathyroid hormone-related protein (PTHrP) interacts with vascular endothelial growth factor (VEGF) in osteoblasts. Since both PTHrP and VEGF have both proinflammatory and profibrogenic features, we assessed here whether these factors might act in concert to promote fibrogenesis in the obstructed kidney. VEGF receptor (VEGFR)-1 was upregulated, while VEGFR-2 was downregulated (at both mRNA and protein levels) in the mouse kidney within 2-6 days after ureteral obstruction. VEGF protein levels also increased in the obstructed kidney at the latter time. Moreover, this VEGF and VEGFR-1 upregulation was higher in mice overexpressing PTHrP in the proximal tubule than in control littermates. These changes were associated with higher fibronectin mRNA expression and alpha-smooth muscle actin (alpha-SMA) and integrin-linked kinase (ILK) immunostaining and lower apoptotic tubulointerstitial cells in the mouse obstructed kidney than in control littermates. Pretreatment with a neutralizing anti-VEGF antibody reversed these responses in the obstructed kidney of both types of mice. In vitro, PTHrP-(1-36) increased (maximal 2-fold vs. basal, at 100 nM) alpha-SMA and ILK protein expression and decreased E-cadherin protein levels in renal tubuloepithelial mouse cortical tubule and normal rat kidney (NRK) 52E cells. PTHrP-(1-36) also decreased cyclosporine A- and/or osmotic stress-induced apoptosis in these cells and in renal fibroblastic NRK 49F cells. These effects elicited by PTHrP-(1-36) were associated with both VEGF and VEGFR-1 upregulation, and abolished by the anti-VEGF antibody. Collectively, these findings strongly suggest that VEGF acts as an important mediator of PTHrP to promote fibrogenesis in the obstructed kidney.

Overexpression of calmodulin in pancreatic beta cells induces diabetic nephropathy

Recently, endothelial dysfunction induced by an uncoupling of vascular endothelial growth factor (VEGF) and nitric oxide has been implicated in the pathogenesis of diabetic nephropathy (DN). Investigating the pathogenesis of DN has been limited, however, because of the lack of animal models that mimic the human disease. In this report, pancreatic beta cell-specific calmodulin-overexpressing transgenic (CaMTg) mice, a potential new model of DN, are characterized with particular emphasis on VEGF and related molecules. CaMTg mice developed hyperglycemia at 3 wk and persistent proteinuria by 3 mo. Morphometric analysis showed considerable increases in the glomerular and mesangial areas with deposition of type IV collagen. Moreover, the pathologic hallmarks of human DN (mesangiolysis, Kimmelstiel-Wilson-like nodular lesions, exudative lesions, and hyalinosis of afferent and efferent arteries with neovascularization) were observed. In addition, increased VEGF expression was associated with an increased number of peritubular capillaries. Expression of endothelial nitric oxidase synthase was reduced and that of VEGF was markedly elevated in CaMTg mice kidney compared with nontransgenic mice. No differences in VEGF receptor-1 or VEGF receptor-2 expression were observed between CaMTg mice and nontransgenic kidneys. In summary, CaMTg mice develop most of the distinguishing lesions of human DN, and the elevated VEGF expression in the setting of diminished endothelial nitric oxide synthase expression may lead to endothelial proliferation and dysfunction. This model may prove useful in the study of the pathogenesis and treatment of DN.

Different renal toxicity profiles in the association of cyclosporine and tacrolimus with sirolimus in rats

BACKGROUND

The association of calcineurin inhibitors (CNIs) with mTOR inhibitors (mTORi) is still a problem in clinical practice and there is substantial interest in better understanding the impact of these associations on kidney toxicity. We aimed to analyse the functional and histological profiles of damage and to define the contribution of inflammatory and pro-fibrotic mediators in the association of cyclosporine (CsA) and/or tacrolimus (Tac) with sirolimus (SRL).

METHODS

A well-defined model of nephrotoxicity in salt-depleted male rats was used. Monotherapy groups were distributed as a non-treated control group with saline solution (n = 12), the Tac group (n = 16) (tacrolimus 6 mg/kg/day) and the CsA group (n = 13) (CsA 15 mg/kg/day). The groups with different associations were scattered as the Tac + SRL group (n = 14) (tacrolimus 6 mg/kg/day and rapamycin 3 mg/kg/day) and the CsA + SRL group (n = 7) (CsA 15 mg/kg/day and rapamycin 3 mg/kg/day). Groups were divided into 30 and 70 days of follow-up, but the CsA + SRL group was only studied for 30 days because animals became sick.

RESULTS

Rats with the CsA + SRL association were the only ones which showed a significant reduction in body weight, impairment of renal function and severe and diffuse tubular vacuolization and tubular atrophy following a striped distribution, and scarce areas of the kidney were still preserved. The Tac + SRL association did not produce renal function impairment, and mild histological damage including enhanced periglomerular tubular atrophy was observed. This local damage affected the distal convoluted tubule involving macula densa and juxtaglomerular apparatus. Pro-inflammatory mediators paralleled functional and structural data. ED-1 and TNF-alpha were noticeably higher in the CsA + SRL than in the Tac + SRL association. Only in the CsA + SRL association an important increase in alpha-SMA+ cells was seen, mainly found in the areas with tubular atrophy. TGF-beta1 was also markedly enhanced in the CsA + SRL association whilst monotherapy or Tac + SRL groups at 30 days TGF-beta1 did not show any changes. However, at 70 days of treatment TGF-beta1 was significantly increased in the Tac + SRL group. Animals receiving SRL showed a decrease in renal vascular endothelial growth factor (VEGF) expression. This growth factor was significantly down-regulated in both CNI associations than in SRL monotherapy. P-glycoprotein (Pgp) was overexpressed in CsA and CsA + SRL therapy whilst Tac and TAC + SRL showed a middle increase Pgp expression but higher than the control and SRL group.

CONCLUSION

We conclude that the association of SRL with high doses of CsA or Tac produces a different functional, histological, inflammatory and pro-fibrogenic pattern. Thus, the addition of SRL to high doses of CsA leads to severe renal injury. Combination with high doses of Tac is clearly less deleterious in the short term. However, there is a low grade of pro-fibrotic inflammatory expression when this association is prolonged.

Endothelial dysfunction and oxidative stress in type 1 and type 2 diabetic patients without clinical macrovascular complications

AIMS

To evaluate the relationship between oxidative stress and endothelial dysfunction (ED) in diabetic patients without clinical macrovascular complications.

METHODS

In 27 type 1, 56 type 2 diabetic patients and 35 healthy controls the redox state (GSH, GSSG; enzymatic method), endothelin-1 (ET-1; ELISA) and von Willebrand factor (vWF; ELISA) plasma levels, urinary vascular endothelial growth factor (VEGF; ELISA) were measured.

RESULTS

Decreased GSH levels (p<0.05, type 1 and type 2), GSH/GSSG ratio (p<0.05 type 1, p<0.001 type 2) and elevated vWF levels (p<0.001, type 1 and type 2) were observed in diabetic patients in comparison with controls. A negative correlation between GSH and vWF (p<0.02 and p<0.001, in type 1 and type 2, respectively) and GSH and BMI (p<0.02 in type 1 and type 2) was observed. ET-1 was positively correlated to age (p<0.05) and diabetes duration (p<0.03) in type 1, while vWF was correlated to systolic blood pressure (p<0.05) in type 2 diabetic patients. Urinary VEGF was higher in type 2 (p<0.05) in comparison with type 1 diabetic patients and was correlated to glycemia (p<0.05) and systolic blood pressure (p<0.05).

CONCLUSIONS

These data might indicate that markers of oxidative stress and ED are altered in diabetic patients without clinical macrovascular complications.

The relationship between the VEGF levels and VEGF mRNA expression and clinical course in different glomerulonephritis

In this study, serum and urinary VEGF levels and VEGF expression in PBMNC were correlated with daily proteinuria, renal function tests, and renal histopathologic findings in untreated patients with different glomerulonephritis and with the course of renal function and proteinuria for one year. Forty-five untreated patients with different glomerulonephritis and 11 healthy persons comprised the study and control groups, respectively. VEGF mRNA expression was detected by RT- PCR in peripheral blood mononuclear cells (PBMNC), and VEGF levels were measured by ELISA in serum and urine samples simultaneously. Male/female ratio was 24/21 and mean ages were 34.49 +/- 14.98. Serum and urinary VEGF levels, VEGF expressions in PBMNC, and the ratios of urine VEGF/urine creatinine were found to be similar in patients and controls. There were important correlations between urinary VEGF levels and baseline serum Cr (p = 0.035) and ESR (p = 0.022). There was also a marginal correlation between urinary VEGF levels and baseline CCr (p = 0.072). There was no correlation between serum and urinary VEGF levels and PBMNC mRNA expression and pathological findings such as with or without glomerular sclerosis, tubulointerstitial fibrosis (TIF), periglomerular fibrosis, and mesangial cell proliferation in renal biopsy. Serum and urinary VEGF levels or VEGF expression in PBMNC in patients with renal amyloidosis or proliferative or nonproliferative glomerulonephritis were similar with that of healthy controls and each other. Serum and urinary VEGF levels and PBMNC VEGF mRNA expression in untreated patients with different glomerulonephritis and controls were similar. We found only one important correlation, that between urinary VEGF levels and baseline serum creatinine levels in patients with different glomerulonephritis. Urinary VEGF can be an important pathogenesis of glomerular disease or a simple proteinuria. Serum and urinary VEGF levels and PBMNC VEGFmRNA did not change by periglomerular sclerosis, periglomerular fibrosis, or tubulointerstitial fibrosis on renal biopsy. PBMNC VEGF mRNA expression decreased in patients undergoing remission. In addition to the important correlation between urinary VEGF and serum creatinine, we also found an important correlation between erythrocyte sedimentation rate and urinary VEGF. This finding was interesting because we could not find a similar conclusion in other studies.

The role of vascular endothelial growth factor, tumor necrosis factor alpha and interleukin-6 in pathogenesis of diabetic retinopathy

The aim of the study was to analyze the relation between early diabetic retinopathy and the pro-inflammatory cytokines tumor necrosis factor alpha (TNF-alpha), interleukin-6 (IL-6), vascular endothelial growth factor (VEGF) in children with diabetes mellitus type 1. Two hundred and two children with diabetes mellitus type 1 aged 13.2+/-3.83 years and 85 healthy controls were analyzed. Patients were divided into two subgroups: children with retinopathy (Group 1, n=39) and children without retinopathy (Group 2, n=163). All the children had 24h urine albumin secretion rate, glycosylated hemoglobin HbA1c level, and C-reactive protein level measured, underwent 24h blood pressure monitoring and had ophthalmologic examination performed. Additionally, all the children had serum TNF-alpha, IL-6 and VEGF level measured using an ELISA test (Quantikine High Sensitivity Human). Statistically significant higher blood serum levels of HbA1c, VEGF, TNF-alpha and IL-6 were found in the Group 1 in comparison with the Group 2. Additionally, the children of the Group 1 showed statistically significant correlation between serum VEGF and serum TNF-alpha (R=0.35, p=0.000), CRP level (R=0.23, p=0.006), 24h albumin urine secretion rate (R=0.45, p=0.000) and duration of the disease (R=0.26, p=0.002). The results of the current study suggest that there is a relationship between VEGF, TNF-alpha, IL-6 and the development of the diabetic retinopathy in children with diabetes mellitus type 1.

Vascular endothelial growth factor protein expression in a renal ablation rabbit model under prolonged warm and cold ischemia

BACKGROUND/AIMS

To establish a potential correlation between renal and systemic production of vascular endothelial growth factor (VEGF) protein after prolonged ischemia in a renal ablation model under normothermic and hypothermic conditions.

METHODS

38 uninephrectomized New Zealand rabbits were divided into 5 groups. The rabbits of each group underwent partial nephrectomy under 90 and 60 min of warm and 90 and 120 min of cold ischemia, except for the sham group (S), which served as control. Serum creatinine (SCr) and blood-urea-nitrogen (BUN) levels were assessed. On the 15th postoperative day (POD), the animals were euthanized and the remaining kidneys were evaluated. VEGF immunohistochemistry and serum Western blot analysis were performed.

RESULTS

In comparison to the control group, groups 60W, 90C and 120C showed 1.6-, 1.14- and 1.75-fold decreases, respectively, while the production of VEGF was significantly declined by 7.4-fold in group 90W (p < 0.05). Immunohistochemistry revealed prominent VEGF staining in the above-mentioned three groups, while in group 90W staining was negative. Serum biochemistry and microscopic evaluation verified the same differentiation.

CONCLUSION

Renal and serum VEGF seem to have an analogous expression under conditions of prolonged ischemia. VEGF is overexpressed in hypothermic conditions compared to warm ischemia exceeding 60 min. Hypothermia can be more advantageous in a procedure applying prolonged ischemia.

ERYTHROPOIETIN ENHANCES ANGIOGENESIS IN AN EXPERIMENTAL CYCLOSPORINE A-INDUCED NEPHROTOXICITY MODEL IN THE RAT

1. Erythropoietin (EPO) is a hormone regulating the proliferation and differentiation of erythroid precursor cells. The hypothesis that haematopoietic and endothelial cells share a common haemanglioblast progenitor among others is based on the finding that both cell lineages express cell surface antigens, such as CD31 and CD34. 2. In the present study, we investigated the angiogenic potential of recombinant human erythropoietin on cyclosporine A (CsA)-induced nephrotoxicity in the rat kidney and compared it with the effect of basic fibroblast growth factor (bFGF), a well-known angiogenic factor. 3. Rats were divided into five groups: A (control), B (EPO treated), C (CsA treated), D (CsA + EPO treated) and E (CsA + bFGF treated). Mouse anti-human CD31 and CD34 antibodies were used to evaluate the kidney vessels present in histological preparations. 4. Glomerular and peritubular capillaries in Group B (EPO) were increased compared with the control (Group A; P < 0.05). Reduction of the same kidney vessels (glomerular and peritubular capillaries) in Group C (CsA; P < 0.05) compared with controls was observed, whereas in Groups D (CsA + EPO treated) and E (CsA + bFGF treated), capillaries were increased compared with Group C (CsA; P < 0.05). 5. Erythropoietin has a significant angiogenic effect in rat kidney with CsA-induced nephrotoxicity, similar to the effect of the other angiogenic factor bFGF.

Alteration of glomerulogenesis- and podocyte structure-related gene expression in early diabetic nephropathy

Diabetic nephropathy is a leading cause of end-stage renal disease. Several pathways, including the renin-angiotensin system, have been postulated as potential mechanisms of diabetic nephropathy. In addition, glomerulogenesis-related molecules are involved in the pathogenesis of diabetic nephropathy, especially at the early stage. They can be divided into three groups by function, that is, fibrosis-related, podocyte differentiation-related and angiogenesis-related molecules. Most of the molecules are expressed in the podocyte and upregulated, even during the normoalbuminuric stage. Expression of several podocyte structure-related molecules are also altered at the normoalbuminuric stage. They can contribute to the structural alteration of the podocyte in diabetic nephropathy. Thus, normalization of the expression of glomerulogenesis-related molecules could be a new target for preventing the initiation and progression of diabetic nephropathy.

Role of VEGF in maintaining renal structure and function under normotensive and hypertensive conditions

Inhibiting the actions of VEGF is a new therapeutic paradigm in cancer management with antiangiogenic therapy also under intensive investigation in a range of nonmalignant diseases characterized by pathological angiogenesis. However, the effects of VEGF inhibition on organs that constitutively express it in adulthood, such as the kidney, are mostly unknown. Accordingly, we examined the effect of VEGF inhibition on renal structure and function under physiological conditions and in the setting of the common renal stressors: hypertension and activation of the renin-angiotensin system. When compared with normotensive Sprague-Dawley (SD) rats, glomerular VEGF mRNA was increased 2-fold in transgenic (mRen-2)27 rats that overexpress renin with spontaneously hypertensive rat (SHR) kidneys showing VEGF expression levels that were intermediate between them. Administration of either an orally active inhibitor of the type 2 VEGF receptor (VEGFR-2) tyrosine kinase or a VEGF neutralizing antibody to TGR(mRen-2)27 rats resulted in loss of glomerular endothelial cells and transformation to a malignant hypertensive phenotype with severe glomerulosclerosis. VEGFR-2 kinase inhibition treatment was well tolerated in SDs and SHRs; although even in these animals there was detectable endothelial cell loss and rise in albuminuria. Mild mesangial expansion was also noted in hypertensive SHR, but not in SD rats. These studies illustrate: (i) VEGF has a role in the maintenance of glomerular endothelial integrity under physiological circumstances, (ii) glomerular VEGF is increased in response to hypertension and activation of the renin-angiotensin system, and (iii) VEGF signaling plays a protective role in the setting of these renal stressors.

The management of CKD: a look into the future

The increasing global prevalence of chronic kidney disease (CKD) and end-stage renal disease with the associated spiraling cost has profound public health and economic implications. This has made slowing the progression of CKD, a major health-care priority. CKD is invariably characterized by progressive kidney fibrosis and at present, treatment aiming to slow the progression of CKD is limited to aggressive blood pressure control, with few therapies targeting the fibrotic process itself. In this review, we explore the potential of experimental therapeutic strategies, based on preventing or reversing the pathophysiologic steps of kidney remodeling that lead to fibrosis.

Uncoupling of the VEGF-endothelial nitric oxide axis in diabetic nephropathy: an explanation for the paradoxical effects of VEGF in renal disease

In many forms of experimental kidney diseases, renal VEGF is low, and administering VEGF can be shown to be protective. A paradox occurs in diabetes, in which renal VEGF levels are high and a deleterious effect of VEGF on kidney disease has been shown. We have hypothesized that endothelial dysfunction induced by hyperglycemia or other factors may underlie the pathogenic mechanisms of a high VEGF state. VEGF normally stimulates endothelial nitric oxide (NO) release and acts in concert with elevated NO levels as a trophic factor for vascular endothelium. The increased NO derived from the endothelial cell acts as an inhibitory factor that prevents excess endothelial cell proliferation, vascular smooth muscle cell proliferation, and macrophage infiltration. In the setting where NO bioavailability is reduced in diabetes, high levels of VEGF lead to excessive endothelial cell proliferation, stimulation of macrophage chemotaxis, and vascular smooth muscle cell activation. Consistent with this hypothesis is our recent observation that diabetes induced in endothelial NO-deficient mice results in clinical and histological features identical to human diabetic nephropathy. The discovery of the key role for impaired endothelial NO bioavailability in the stimulation of VEGF and VEGF-dependent disease may provide key insights into not only the pathogenesis of diabetic nephropathy but also the utility and hazard of administering VEGF as a treatment for kidney disease.

Proteinuria in a patient receiving anti-VEGF therapy for metastatic renal cell carcinoma

BACKGROUND

A 59-year-old man who had undergone a left nephrectomy for renal cell carcinoma was found to have metastatic disease during a restaging examination. The patient was started on treatment with interferon alpha2b plus bevacizumab, a humanized monoclonal anti-vascular endothelial growth factor antibody. After 9 months of this therapy, the patient developed proteinuria, which gradually increased to over 6 g/day.

INVESTIGATIONS

Physical examination, urine and blood analysis, biopsy of the right kidney, and histologic evaluation of the non-neoplastic portion of the left nephrectomy specimen.

DIAGNOSIS

Thrombotic microangiopathy and IgA immune-complex deposition in the glomerular capillary walls and mesangium.

MANAGEMENT

Discontinuation of interferon alpha2b and bevacizumab, control of blood pressure with an angiotensin-converting-enzyme inhibitor and an angiotensin-receptor blocker.