Microvascular disease precedes the decline in renal function in the streptozotocin-induced diabetic rat

Contrast Agent-Free 3D Renal Ultrafast Doppler Imaging Reveals Vascular Dysfunction in Acute and Diabetic Kidney Diseases

To combat the irreversible decline in renal function associated with kidney disease, it is essential to establish non-invasive biomarkers for assessing renal microcirculation. However, the limited resolution and/or vascular sensitivity of existing diagnostic imaging techniques hinders the visualization of complex cortical vessels. Here, a 3D renal ultrafast Doppler (UFD) imaging system that uses a high ultrasound frequency (18 MHz) and ultrahigh frame rate (1 KHz per slice) to scan the entire volume of a rat's kidney in vivo is demonstrated. The system, which can visualize the full 3D renal vascular branching pyramid at a resolution of 167 µm without any contrast agent, is used to chronically and noninvasively monitor kidneys with acute kidney injury (AKI, 3 days) and diabetic kidney disease (DKD, 8 weeks). Multiparametric UFD analyses (e.g., vessel volume occupancy (VVO), fractional moving blood volume (FMBV), vessel number density (VND), and vessel tortuosity (VT)) describe rapid vascular rarefaction from AKI and long-term vascular degeneration from DKD, while the renal pathogeneses are validated by in vitro blood serum testing and stained histopathology. This work demonstrates the potential of 3D renal UFD to offer valuable insights into assessing kidney perfusion levels for future research in diabetes and kidney transplantation.

Endothelial Glycocalyx of Peritubular Capillaries in Experimental Diabetic Nephropathy: A Target of ACE Inhibitor-Induced Kidney Microvascular Protection

Peritubular capillary rarefaction is a recurrent aspect of progressive nephropathies. We previously found that peritubular capillary density was reduced in BTBR ob/ob mice with type 2 diabetic nephropathy. In this model, we searched for abnormalities in the ultrastructure of peritubular capillaries, with a specific focus on the endothelial glycocalyx, and evaluated the impact of treatment with an angiotensin-converting enzyme inhibitor (ACEi). Mice were intracardially perfused with lanthanum to visualise the glycocalyx. Transmission electron microscopy analysis revealed endothelial cell abnormalities and basement membrane thickening in the peritubular capillaries of BTBR ob/ob mice compared to wild-type mice. Remodelling and focal loss of glycocalyx was observed in lanthanum-stained diabetic kidneys, associated with a reduction in glycocalyx components, including sialic acids, as detected through specific lectins. ACEi treatment preserved the endothelial glycocalyx and attenuated the ultrastructural abnormalities of peritubular capillaries. In diabetic mice, peritubular capillary damage was associated with an enhanced tubular expression of heparanase, which degrades heparan sulfate residues of the glycocalyx. Heparanase was also detected in renal interstitial macrophages that expressed tumor necrosis factor-α. All these abnormalities were mitigated by ACEi. Our findings suggest that, in experimental diabetic nephropathy, preserving the endothelial glycocalyx is important in order to protect peritubular capillaries from damage and loss.

Super-Resolution Ultrasound Imaging of Renal Vascular Alterations in Zucker Diabetic Fatty Rats during the Development of Diabetic Kidney Disease

Individuals with diabetes at risk of developing diabetic kidney disease (DKD) are challenging to identify using currently available clinical methods. Prognostic accuracy and initiation of treatment could be improved by a quantification of the renal microvascular rarefaction and the increased vascular tortuosity during the development of DKD. Super-resolution ultrasound (SRUS) imaging is an in vivo technique capable of visualizing blood vessels at sizes below 75 µm. This preclinical study aimed to investigate the alterations in renal blood vessels' density and tortuosity in a type 2 diabetes rat model, Zucker diabetic fatty (ZDF) rats, as a prediction of DKD. Lean age-matched Zucker rats were used as controls. A total of 36 rats were studied, subdivided into ages of 12, 22, and 40 weeks. Measured albuminuria indicated the early stage of DKD, and the SRUS was compared with the ex vivo micro-computed tomography (µCT) of the same kidneys. Assessed using the SRUS imaging, a significantly decreased cortical vascular density was detected in the ZDF rats from 22 weeks of age compared to the healthy controls, concomitant with a significantly increased albuminuria. Already by week 12, a trend towards a decreased cortical vascular density was found prior to the increased albuminuria. The quantified vascular density in µCT corresponded with the in vivo SRUS imaging, presenting a consistently lower vascular density in the ZDF rats. Regarding vessel tortuosity, an overall trend towards an increased tortuosity was present in the ZDF rats. SRUS shows promise for becoming an additional tool for monitoring and prognosing DKD. In the future, large-scale animal studies and human trials are needed for confirmation.

Long-Term Effects of Suramin on Renal Function in Streptozotocin-Induced Diabetes in Rats

In short-term diabetes (3 weeks), suramin, a drug used clinically, affects renal function and the expression of vascular endothelial growth factor A (VEGF-A), which may be involved in the pathogenesis of diabetic nephropathy, the main cause of end-stage renal disease. In the present study, we evaluated the long-term (11 weeks) effects of suramin (10 mg/kg, i.p., once-weekly) in diabetic rats. Concentrations of VEGF-A, albumin, soluble adhesive molecules (sICAM-1, sVCAM-1), nucleosomes, and thrombin-antithrombin complex (TAT) were measured by ELISA, total protein was measured using a biuret reagent. Glomerular expression of VEGF-A was evaluated by Western blot, mRNA for VEGF-A receptors in the renal cortex by RT-PCR. The vasoreactivity of the interlobar arteries to acetylcholine was assessed by wire myography. Long-term diabetes led to an increased concentration of VEGF-A, TAT, and urinary excretion of total protein and albumin, and a decrease in the concentration of sVCAM-1. We have shown that suramin in diabetes reduces total urinary protein excretion and restores the relaxing properties of acetylcholine relaxation properties to non-diabetic levels. Suramin had no effect on glomerular expression VEGF-A expression and specific receptors, and on sICAM-1 and nucleosomes concentrations in diabetic rats. In conclusion, the long-term effect of suramin on the kidneys in diabetes, expressed in the reduction of proteinuria and the restoration of endothelium-dependent relaxation of the renal arteries, can be considered as potentially contributing to the reduction/slowing down of the development of diabetic nephropathy.

Suramin Affects the Renal VEGF-A/VEGFR Axis in Short-Term Streptozotocin-Induced Diabetes

Diabetic nephropathy (DN) accounts for approximately 50% of end-stage renal diseases. Vascular endothelial growth factor A (VEGF-A) is thought to be a critical mediator of vascular dysfunction in DN, but its role is unclear. The lack of pharmacological tools to modify renal concentrations further hinders the understanding of its role in DN. In this study, rats were evaluated after 3 weeks of streptozotocin-induced diabetes and two suramin treatments (10 mg/kg, ip). Vascular endothelial growth factor A expression was evaluated by western blot of glomeruli and immunofluorescence of the renal cortex. RT-PCR for receptors Vegfr1 mRNA and Vegfr2 mRNA quantitation was performed. The soluble adhesive molecules (sICAM-1, sVCAM-1) in blood were measured by ELISA and the vasoreactivity of interlobar arteries to acetylcholine was evaluated using wire myography. Suramin administration reduced the expression and intraglomerular localisation of VEGF-A. Increased VEGFR-2 expression in diabetes was reduced by suramin to non-diabetic levels. Diabetes reduced the sVCAM-1 concentrations. Suramin in diabetes restored acetylcholine relaxation properties to non-diabetic levels. In conclusion, suramin affects the renal VEGF-A/VEGF receptors axis and has a beneficial impact on endothelium-dependent relaxation of renal arteries. Thus, suramin may be used as a pharmacological agent to investigate the potential role of VEGF-A in the pathogenesis of renal vascular complications in short-term diabetes.

p-Coumaric Acid Nanoparticles Ameliorate Diabetic Nephropathy via Regulating mRNA Expression of KIM-1 and GLUT-2 in Streptozotocin-Induced Diabetic Rats

Diabetic nephropathy (DN) has become a leading cause of end-stage renal failure worldwide. The goal of the current study was to examine the protective effects of chitosan-loaded p-Coumaric acid nanoparticles (PCNPs) in nephrotoxicity induced by streptozotocin (STZ). Because of the antidiabetic, anti-inflammatory, and antioxidant properties of PCNPs, the development of DN may be considerably decreased. In this study, the rats received a single intraperitoneal injection (i.p.) of STZ (45 mg/kg) to induce DN. PCNPs were given orally 80 mg/kg b.w to the rats for a duration of four weeks. Body weight, kidney weight, blood glucose, and insulin levels were measured at the end of the experiment. Serum and urine parameters were also examined, along with the histological, immunobiological, and tumor necrosis factor (TNF) and interleukin-6 (IL-6) expression of the nephrotic rats. To comprehend the impact of PCNPs, the expression patterns of the kidney injury molecule (KIM-1) and glucose transporter-2 (GLUT-2) were evaluated. Administration of PCNPs significantly increased body weight, decreased kidney weight and also ameliorated blood glucose levels in the nephropathic rats. The administration of PCNPs also reverted the levels of urea, serum creatinine, urinary NAG, β-glucuronidase and albumin to near-normal levels. The administration of PCNPs also caused the levels of serum and urine parameters to return to near-normal levels. Additionally, the PCNP-treated rats had markedly reduced TNF-α, IL-6, and KIM-1 expressions as well as enhanced GLUT-2 mRNA expression. Our findings clearly showed that PCNP administration prevents the onset of DN in rats by lowering hyperglycemia, decreasing inflammation, and improving the expression of GLUT-2 mRNA in nephropathic rats.

Unravelling the Inflammatory Processes in the Early Stages of Diabetic Nephropathy and the Potential Effect of (Ss)-DS-ONJ

Inflammatory processes play a central role in the pathogenesis of diabetic nephropathy (DN) in the early stages of the disease. The authors demonstrate that the glycolipid mimetic (S_s)-DS-ONJ is able to abolish inflammation via the induction of autophagy flux and provokes the inhibition of inflammasome complex in ex vivo and in vitro models, using adult kidney explants from BB rats. The contribution of (S_s)-DS-ONJ to reducing inflammatory events is mediated by the inhibition of classical stress kinase pathways and the blocking of inflammasome complex activation. The (S_s)-DS-ONJ treatment is able to inhibit the epithelial-to-mesenchymal transition (EMT) progression, but only when the IL18 levels are reduced by the treatment. These findings suggest that (S_s)-DS-ONJ could be a novel, and multifactorial treatment for DN.

Super-Resolution Ultrasound Imaging Provides Quantification of the Renal Cortical and Medullary Vasculature in Obese Zucker Rats: A Pilot Study

Obesity is a risk factor of chronic kidney disease (CKD), leading to alterations in the renal vascular structure. This study tested if renal vascular density and tortuosity was quantifiable in vivo in obese rats using microbubble-based super-resolution ultrasound imaging. The kidneys of two 11-week-old and two 20-week-old male obese Zucker rats were compared with age-matched male lean Zucker rats. The super-resolution ultrasound images were manually divided into inner medulla, outer medulla, and cortex, and each area was subdivided into arteries and veins. We quantified vascular density and tortuosity, number of detected microbubbles, and generated tracks. For comparison, we assessed glomerular filtration rate, albumin/creatinine ratio, and renal histology to evaluate CKD. The number of detected microbubbles and generated tracks varied between animals and significantly affected quantification of vessel density. In areas with a comparable number of tracks, density increased in the obese animals, concomitant with a decrease in glomerular filtration rate and an increase in albumin/creatinine ratio, but without any pathology in the histological staining. The results indicate that super-resolution ultrasound imaging can be used to quantify structural alterations in the renal vasculature. Techniques to generate more comparable number of microbubble tracks and confirmation of the findings in larger-scale studies are needed.

In Vivo Ultrasound Localization Microscopy Imaging of the Kidney's Microvasculature With Block-Matching 3-D Denoising

Structural abnormalities and functional changes of renal microvascular networks play a significant pathophysiologic role in the occurrence of kidney diseases. Super-resolution ultrasound imaging has been successfully utilized to visualize the microvascular network and provide valuable diagnostic information. To prevent the burst of microbubbles, a lower mechanical index (MI) is generally used in ultrasound localization microscopy (ULM) imaging. However, high noise levels lead to incorrect signal localizations in relatively low-MI settings and deep tissue. In this study, we implemented a block-matching 3-D (BM3D) image-denoising method, after the application of singular value decomposition filtering, to further suppress the noise at various depths. The in vitro flow-phantom results show that the BM3D method helps the significant reduction of the error localizations, thus improving the localization accuracy. In vivo rhesus macaque experiments help conclude that the BM3D method improves the resolution more than other image-based denoising techniques, such as the nonlocal means method. The obtained clutter-filtered images with fewer incorrect localizations can enable robust ULM imaging, thus helping in establishing an effective diagnostic tool.

The role of microRNA-155 in glomerular endothelial cell injury induced by high glucose

Objective

To investigate the role of microRNA-155-5p on apoptosis and inflammatory response in human renal glomerular endothelial cells (HRGEC) cultured with high glucose.

Methods

The primary HRGEC were mainly studied, light microscopy was used to detect changes in cell morphology. Quantitative Real Time-Polymerase Chain Reaction, Western Blot, immunofluorescence were aimed to observe the mRNA and protein expression levels of target gene ETS-1, downstream factors VCAM-1, MCP-1 and cleaved caspase-3 in each group after high glucose treatment as well as transfection with miR-155 mimics or inhibitor.

Results

The expression of inflammatory factors and apoptosis of HRGEC cells increased under high glucose treatment. Compared with normal-glucose treatment, the expression of microRNA-155 markedly increased in HRGECs treated with high-glucose, as well as the mRNA and protein levels of ETS-1, VCAM-1, MCP-1 and cleaved caspase-3. Overexpression of microRNA-155 remarkably downregulated mRNA and protein levels of ETS-1, VCAM-1, MCP-1 and cleaved caspase-3, whereas miRNA-155 knockdown upregulated their levels. In addition, HRGEC cells were transfected with miR-155 mimics and ETS-1 siRNA with high glucose stimulation. The expression of ETS-1 was positively correlated with the expression of downstream factors VCAM-1 and MCP-1. These results suggest that ETS-1 can mediate endothelial cell inflammation by regulating VCAM-1 and MCP-1.

Conclusion

MiR-155 can negatively regulate the expression of target gene ETS-1 and its downstream factors VCAM-1, MCP-1 and cleaved caspase-3, thus mediating the inflammatory response and apoptosis of HRGEC.

Supplementary Information

The online version contains supplementary material available at 10.1007/s11033-021-07106-1.

Evaluation of 2D super-resolution ultrasound imaging of the rat renal vasculature using ex vivo micro-computed tomography

Super-resolution ultrasound imaging (SRUS) enables in vivo microvascular imaging of deeper-lying tissues and organs, such as the kidneys or liver. The technique allows new insights into microvascular anatomy and physiology and the development of disease-related microvascular abnormalities. However, the microvascular anatomy is intricate and challenging to depict with the currently available imaging techniques, and validation of the microvascular structures of deeper-lying organs obtained with SRUS remains difficult. Our study aimed to directly compare the vascular anatomy in two in vivo 2D SRUS images of a Sprague-Dawley rat kidney with ex vivo μCT of the same kidney. Co-registering the SRUS images to the μCT volume revealed visually very similar vascular features of vessels ranging from ~ 100 to 1300 μm in diameter and illustrated a high level of vessel branching complexity captured in the 2D SRUS images. Additionally, it was shown that it is difficult to use μCT data of a whole rat kidney specimen to validate the super-resolution capability of our ultrasound scans, i.e., validating the actual microvasculature of the rat kidney. Lastly, by comparing the two imaging modalities, fundamental challenges for 2D SRUS were demonstrated, including the complexity of projecting a 3D vessel network into 2D. These challenges should be considered when interpreting clinical or preclinical SRUS data in future studies.

The renal microcirculation in chronic kidney disease: novel diagnostic methods and therapeutic perspectives

Chronic kidney disease (CKD) affects 8–16% of the population worldwide and is characterized by fibrotic processes. Understanding the cellular and molecular mechanisms underpinning renal fibrosis is critical to the development of new therapeutics. Microvascular injury is considered an important contributor to renal progressive diseases. Vascular endothelium plays a significant role in responding to physical and chemical signals by generating factors that help maintain normal vascular tone, inhibit leukocyte adhesion and platelet aggregation, and suppress smooth muscle cell proliferation. Loss of the rich capillary network results in endothelial dysfunction, hypoxia, and inflammatory and oxidative effects and further leads to the imbalance of pro- and antiangiogenic factors, endothelial cell apoptosis and endothelial-mesenchymal transition. New techniques, including both invasive and noninvasive techniques, offer multiple methods to observe and monitor renal microcirculation and guide targeted therapeutic strategies. A better understanding of the role of endothelium in CKD will help in the development of effective interventions for renal microcirculation improvement. This review focuses on the role of microvascular injury in CKD, the methods to detect microvessels and the novel treatments to ameliorate renal fibrosis.

A dose-escalating toxicology study of the candidate biologic ELP-VEGF

Vascular Endothelial Growth Factor (VEGF), a key mediator of angiogenesis and vascular repair, is reduced in chronic ischemic renal diseases, leading to microvascular rarefaction and deterioration of renal function. We developed a chimeric fusion of human VEGF-A₁₂₁ with the carrier protein Elastin-like Polypeptide (ELP-VEGF) to induce therapeutic angiogenesis via targeted renal VEGF therapy. We previously showed that ELP-VEGF improves renal vascular density, renal fibrosis, and renal function in swine models of chronic renal diseases. However, VEGF is a potent cytokine that induces angiogenesis and increases vascular permeability, which could cause undesired off-target effects or be deleterious in a patient with a solid tumor. Therefore, the current study aims to define the toxicological profile of ELP-VEGF and assess its risk for exacerbating tumor progression and vascularity using rodent models. A dose escalating toxicology assessment of ELP-VEGF was performed by administering a bolus intravenous injection at doses ranging from 0.1 to 200 mg/kg in Sprague Dawley (SD) rats. Blood pressure, body weight, and glomerular filtration rate (GFR) were quantified longitudinally, and terminal blood sampling and renal vascular density measurements were made 14 days after treatment. Additionally, the effects of a single administration of ELP-VEGF (0.1-10 mg/kg) on tumor growth rate, mass, and vascular density were examined in a mouse model of breast cancer. At doses up to 200 mg/kg, ELP-VEGF had no effect on body weight, caused no changes in plasma or urinary markers of renal injury, and did not induce renal fibrosis or other histopathological findings in SD rats. At the highest doses (100-200 mg/kg), ELP-VEGF caused an acute, transient hypotension (30 min), increased GFR, and reduced renal microvascular density 14 days after injection. In a mouse tumor model, ELP-VEGF did not affect tumor growth rate or tumor mass, but analysis of tumor vascular density by micro-computed tomography (μCT) revealed significant, dose dependent increases in tumor vascularity after ELP-VEGF administration. ELP-VEGF did not induce toxicity in the therapeutic dosing range, and doses one hundred times higher than the expected maximum therapeutic dose were needed to observe any adverse signs in rats. In breast tumor-bearing mice, ELP-VEGF therapy induced a dose-dependent increase in tumor vascularity, demanding caution for potential use in a patient suffering from kidney disease but with known or suspected malignancy.

Super-Resolution Imaging with Ultrasound for Visualization of the Renal Microvasculature in Rats Before and After Renal Ischemia: A Pilot Study

In vivo monitoring of the microvasculature is relevant since diseases such as diabetes, ischemia, or cancer cause microvascular impairment. Super-resolution ultrasound imaging allows in vivo examination of the microvasculature by detecting and tracking sparsely distributed intravascular microbubbles over a minute-long period. The ability to create detailed images of the renal vasculature of Sprague-Dawley rats using a modified clinical ultrasound platform was investigated in this study. Additionally, we hypothesized that early ischemic damage to the renal microcirculation could be visualized. After a baseline scan of the exposed kidney, 10 rats underwent clamping of the renal vein (n = 5) or artery (n = 5) for 45 min. The kidneys were rescanned at the onset of clamp release and after 60 min of reperfusion. Using a processing pipeline for tissue motion compensation and microbubble tracking, super-resolution images with a very high level of detail were constructed. Image filtration allowed further characterization of the vasculature by isolating specific vessels such as the ascending vasa recta with a 15–20 μm diameter. Using the super-resolution images alone, it was only possible for six assessors to consistently distinguish the healthy renal microvasculature from the microvasculature at the onset of vein clamp release. Future studies will aim at attaining quantitative estimations of alterations in the renal microvascular blood flow using super-resolution ultrasound imaging.

Microrheology, microcirculation and structural compensatory mechanisms of a chronic kidney disease rat model. A preliminary study

BACKGROUND

Chronic kidney disease (CKD) models are known to study pathophysiology and various treatment methods. Renal dysfunction could influence erythrocytes through several pathways. However, hemorheological and microcirculatory relation of CKD models are not completely studied yet.

OBJECTIVE

To evaluate erythrocyte micro-rheology, microcirculatory and structural compensatory mechanisms in a rat model of CKD.

METHODS

Female Sprague-Dawley rats were subjected to nephrectomy group (NG, n = 6) or sham-operated group (SG, n = 6). NG rats were subjected to 5/6 nephrectomy in two stages. In SG no intervention was made on kidneys. Hemorheological and hematological measurements were carried out after each stage, and 5 weeks after the last operation. Histological and microcirculatory studies were done on the remaining kidney and compared with sham rats.

RESULTS

Serum creatinine increased in NG (p = 0.008), accompanied with decrease of red blood cell count (p = 0.028) and hemoglobin (p = 0.015). Erythrocyte aggregation parameters slightly increased in NG, while the elongation index didn't show significant changes. Microcirculation was intact in the remnant kidney of NG. However, in comparison with SG, the diameter of glomeruli increased significantly (p < 0.01).

CONCLUSIONS

Erythrocyte mass was influenced more than micro-rheological properties in this model. The main compensation mechanism was rather structural than at microcirculatory level.

Increased urinary excretion of hedgehog interacting protein (uHhip) in early diabetic kidney disease

Glomerular endothelial cell (GEC) dysfunction occurs in diabetic kidney disease (DKD) and generally precedes albuminuria. We recently reported that hedgehog interacting protein (Hhip), highly expressed in GECs, contributes to DKD development in diabetic mice. Here, we hypothesized that urinary Hhip (uHhip) could identify early DKD; we tested uHhip in mice and humans with diabetes (DM). In both type 1 (Akita) and type 2 (db/db) DM mice, uHhip is elevated prior to the development of albuminuria, while non-DM controls excrete minimal amount of uHhip. In 87 type 2 DM patients and 39 healthy controls, the uHhip/creatinine (Cr) ratio provides a significant discrimination between non-DM and DM groups; 0 [0-69.5] in non-DM, 9.9 [1.7-39.5] in normoalbuminuric DM, 167.7 [95.7-558.7] in microalbuminuric DM, and 207.9 [0-957.2] in macroalbuminuric DM (median [IQR] ng/mmol, P < 0.0001). The log-uHhip/Cr is positively correlated with urine albumin/Cr ratio (UACR) (spearman correlation coefficient 0.47, P < 0.0001). The log-uHhip/Cr is also associated with eGFR, pulse pressure, and urinary cytokines (IL-1β, IL-6, IL-8, and TGFβ1) independent of UACR. By immunostaining, Hhip is localized in glomeruli and tubules, and is increased in human DM kidneys compared with non-DM kidneys. TGFβ1 shares the similar staining pattern as Hhip in human DM kidneys. Thus, uHhip appears to be a novel indicator of diabetic GEC injury and is elevated in early DKD before the development of microalbuminuria in mice and humans. Clinical value for detecting early DKD warrants further investigation.

Id1 expression in kidney endothelial cells protects against diabetes-induced microvascular injury

The inhibitor of differentiation (Id) transcription regulators, which are induced in response to oxidative stress, promote cell proliferation and inhibit senescence. Inhibitor of differentiation 1 (Id1) expression is limited to endothelial cells (EC) in the normal mouse kidney and is required for a normal response to injury. Endothelial dysfunction leads to the development of diabetic nephropathy, and so, we hypothesized that endothelial Id1 may help protect against hyperglycemia-induced microvascular injury and nephropathy. Here, we tested this hypothesis by using streptozotocin to induce diabetes in Id1 knockout (KO) mice and WT B6;129 littermates and examining the mice at 3 months. Expression of Id1 was observed to be increased 15-fold in WT kidney EC, and Id1 KO mice exhibited increased mesangial and myofibroblast proliferation, matrix deposition, and albuminuria compared with WT mice. Electron microscopy demonstrated peritubular capillary EC injury and lumen narrowing, and fluorescence microangiography showed a 45% reduction in capillary perfusion area with no reduction in CD31-stained areas in Id1 KO mice. Microarray analysis of EC isolated from WT and KO control and diabetic mice demonstrated activation of senescence pathways in KO cells. Kidneys from KO diabetic mice showed increased histological expression of senescence markers. In addition, premature senescence in cultured KO EC was also seen in response to oxidative stress. In conclusion, endothelial Id1 upregulation with hyperglycemia protects against microvascular injury and senescence and subsequent nephropathy.

A Boolean Model of Microvascular Rarefaction to Predict Treatment Outcomes in Renal Disease

Despite advances in renovascular disease (RVD) research, gaps remain between experimental and clinical outcomes, translation of results, and the understanding of pathophysiological mechanisms. A predictive tool to indicate support (or lack of) for biological findings may aid clinical translation of therapies. We created a Boolean model of RVD and hypothesized that it would predict outcomes observed in our previous studies using a translational swine model of RVD. Our studies have focused on developing treatments to halt renal microvascular (MV) rarefaction in RVD, a major feature of renal injury. A network topology of 20 factors involved in renal MV rarefaction that allowed simulation of 5 previously tested treatments was created. Each factor was assigned a function based upon its interactions with other variables and assumed to be “on” or “off”. Simulations of interventions were performed until outcomes reached a steady state and analyzed to determine pathological processes that were activated, inactivated, or unchanged vs. RVD with no intervention. Boolean simulations mimicked the results of our previous studies, confirming the importance of MV integrity on treatment outcomes in RVD. Furthermore, our study supports the potential application of a mathematical tool to predict therapeutic feasibility, which may guide the design of future studies for RVD.

Osmotic diuresis by SGLT2 inhibition stimulates vasopressin-induced water reabsorption to maintain body fluid volume

Most of the filtered glucose is reabsorbed in the early proximal tubule by the sodium-glucose cotransporter SGLT2. The glycosuric effect of the SGLT2 inhibitor ipragliflozin is linked to a diuretic and natriuretic effect that activates compensatory increases in fluid and food intake to stabilize body fluid volume (BFV). However, the compensatory mechanisms that are activated on the level of renal tubules remain unclear. Type 2 diabetic Goto-Kakizaki (GK) rats were treated with vehicle or 0.01% (in diet) ipragliflozin with free access to fluid and food. After 8 weeks, GK rats were placed in metabolic cages for 24-hr. Ipragliflozin decreased body weight, serum glucose and systolic blood pressure, and increased fluid and food intake, urinary glucose and Na+ excretion, urine volume, and renal osmolar clearance, as well as urine vasopressin and solute-free water reabsorption (TcH2O). BFV, measured by bioimpedance spectroscopy, and fluid balance were similar among the two groups. Urine vasopressin in ipragliflozin-treated rats was negatively and positively associated with fluid balance and TcH2O, respectively. Ipragliflozin increased the renal membrane protein expression of SGLT2, aquaporin (AQP) 2 phosphorylated at Ser269 and vasopressin V2 receptor. The expression of SGLT1, GLUT2, AQP1, and AQP2 was similar between the groups. In conclusion, the SGLT2 inhibitor ipragliflozin induced a sustained glucosuria, diuresis, and natriuresis, with compensatory increases in fluid intake and vasopressin-induced TcH2O in proportion to the reduced fluid balance to maintain BFV. These results indicate that the osmotic diuresis induced by SGLT2 inhibition stimulates compensatory fluid intake and renal water reabsorption to maintain BFV.

The double edge of anti-CD40 siRNA therapy: It increases renal microcapillar density but favours the generation of an inflammatory milieu in the kidneys of ApoE -/- mice

Background

Chronic kidney disease (CKD) is associated with endothelial dysfunctions thus prompting links between microcirculation (MC), inflammation and major cardiovascular risk factors.

Purpose of the study

We have previously reported that siRNA-silencing of CD40 (siCD40) reduced atherosclerosis (ATH) progression. Here, we have deepened on the effects of the siCD40 treatment by evaluating retrospectively, in stored kidneys from the siCD40 treated ApoE^−/− mice, the renal microcirculation (measured as the density of peritubular capillaries), macrophage infiltration and NF-κB activation.

Methods

Kidneys were isolated after 16 weeks of treatment with the anti-CD40 siRNA (siCD40), with a scrambled control siRNA (siSC) or with PBS (Veh. group). Renal endothelium, infiltrating macrophages and activated NF-κB in endothelium were identified by immunohistochemistry, while the density of stained peritubular capillaries was quantified by image analysis.

Results

ATH was associated with a reduction in renal MC, an effect reversed by the anti-CD40 siRNA treatment (3.8 ± 2.7% in siCD40; vs. 1.8 ± 0.1% in siSC; or 1.9 ± 1.6% in Veh.; p < 0.0001). Furthermore, siCD40 treatment reduced the number of infiltrating macrophages compared to the SC group (14.1 ± 5.9 cells/field in siCD40; vs. 37.1 ± 17.8 cells/field in siSC; and 1.3 ± 1.7 cells/field in Veh.; p = 0.001). NF-κB activation also peaked in the siSC group, showing lower levels in the siCD40 and Veh. groups (63 ± 60 positive cells/section in siCD40; vs. 152 ± 44 positive cells/section in siSC; or 26 ± 29 positive cells/section in veh.; p = 0.014). Lastly, serum creatinine was also increased in the siCD40 (3.4 ± 3.3 mg/dL) and siSC (4.6 ± 3.0 mg/dL) groups when compared with Veh. (1.1 ± 0.9 mg/dL, p = 0.1).

Conclusions

Anti-CD40 siRNA therapy significantly increased the density of peritubular capillaries and decreased renal inflammation in the ATH model. These data provide a physiological basis for the development of renal diseases in patients with ATH. Furthermore, our results also highligth renal off-target effects of the siRNA treatment which are discussed.

Graphical abstract

Biopolymer-delivered vascular endothelial growth factor improves renal outcomes following revascularization

Renal angioplasty and stenting (PTRAs) resolves renal artery stenosis, but inconsistently improves renal function, possibly due to persistent parenchymal damage. We developed a bioengineered fusion of a drug delivery vector (elastin-like polypeptide, ELP) with vascular endothelial growth factor (VEGF), and showed its therapeutic efficacy. We tested the hypothesis that combined ELP-VEGF therapy with PTRAs improves renal recovery more efficiently than PTRAs alone, by protecting the stenotic renal parenchyma. Unilateral renovascular disease (RVD) was induced by renal artery stenosis in 14 pigs. Six weeks later, stenotic kidney blood flow (RBF) and glomerular filtration rate (GFR) were quantified in vivo using multidetector CT. Blood and urine were collected during in vivo studies. All pigs underwent PTRAs and then were randomized into single intrarenal ELP-VEGF administration or placebo (n = 7 each) groups. Pigs were observed for four additional weeks, in vivo CT studies were repeated, and then pigs were euthanized for ex vivo studies to quantify renal microvascular (MV) density, angiogenic factor expression, and morphometric analysis. Renal hemodynamics were similarly blunted in all RVD pigs. PTRAs resolved stenosis but modestly improved RBF and GFR. However, combined PTRAs+ ELP-VEGF improved RBF, GFR, regional perfusion, plasma creatinine, asymmetric dimethlyarginine (ADMA), and albuminuria compared with PTRAs alone, accompanied by improved angiogenic signaling, MV density, and renal fibrosis. Greater improvement of renal function via coadjuvant ELP-VEGF therapy may be driven by enhanced MV proliferation and repair, which ameliorates MV rarefaction and fibrogenic activity that PTRAs alone cannot offset. Thus, our study supports a novel strategy to boost renal recovery in RVD after PTRAs.

Understanding and managing atherosclerotic renovascular disease: still a work in progress

Atherosclerotic renovascular disease (ARVD) is an unresolved therapeutic dilemma despite extensive pre-clinical and clinical studies. The pathophysiology of the disease has been widely studied, and many factors that may be involved in progressive renal injury and cardiovascular risk associated with ARVD have been identified. However, therapies and clinical trials have focused largely on attempts to resolve renal artery stenosis without considering the potential need to treat the renal parenchyma beyond the obstruction. The results of these trials show a staggering consistence: although nearly 100% of the patients undergoing renal angioplasty show a resolution of the vascular obstruction, they do not achieve significant improvements in renal function or blood pressure control compared with those patients receiving medical treatment alone. It seems that we may need to take a step back and reconsider the pathophysiology of the disease in order to develop more effective therapeutic strategies. This mini-review discusses potential therapeutic alternatives that focus on the renal parenchyma distal to the vascular obstruction and may provide additional tools to enhance current treatment of ARVD.

High-fat diet-induced kidney alterations in rats with metabolic syndrome: endothelial dysfunction and decreased antioxidant defense

INTRODUCTION

This study aimed to investigate changes in renal function and the AGE-RAGE axis in the kidney of a non-genetic animal model of metabolic syndrome (MetS) induced by high-fat diet (HFD). Additionally, we evaluated the protective effect of pyridoxamine (PM), a vitamin B6 analog with anti-AGE effects, in the context of diet-related renal endothelial dysfunction.

METHODOLOGY

In Wistar rats, the MetS animal model was induced by 20 or 28 weeks of HFD feeding. When indicated, a subgroup of animals was treated daily with PM (60 mg/kg) for 2 months. Tissue perfusion in renal microcirculation was examined by laser speckle contrast imaging. Oxidative stress was analyzed by thiobarbituric acid reactive species and the inflammatory markers by ELISA (TNF-α and IL-1β). Reverse transcription polymerase chain reaction was used to analyze eNOs, IL-6, vascular cell adhesion molecule (VCAM), NADPH oxidase subunit 47 (N47), catalase, and receptor for AGE (RAGE) gene expression.

RESULTS

Wistar rats fed a HFD showed negligible alteration in renal function, decrease in catalase mRNA transcripts and catalase enzyme activity compared to control (CTL) animals. Increased levels of IL-1β were observed in the kidney of MetS-induced rats. HFD-fed rats exhibited kidney endothelial dysfunction, with no significant differences in basal microvascular blood flow. PM significantly improved kidney vasorelaxation in HFD-fed rats. eNOS, VCAM, and RAGE gene expression and AGE content were not altered in kidneys of HFD-induced MetS rats in comparison to CTLs.

CONCLUSIONS

Our findings suggest that HFD-induced microvascular dysfunction precedes the decline in renal function, and could be related to antioxidant machinery defects and inflammation activation in the kidney. PM showed a vasoprotective effect, and thus, could be an important contributory factor in ameliorating diet-induced renal damage.

Unmasking a sustained negative effect of SGLT2 inhibition on body fluid volume in the rat

The chronic intrinsic diuretic and natriuretic tone of sodium-glucose cotransporter 2 (SGLT2) inhibitors is incompletely understood because their effect on body fluid volume (BFV) has not been fully evaluated and because they often increase food and fluid intake at the same time. Here we first compared the effect of the SGLT2 inhibitor ipragliflozin (Ipra, 0.01% in diet for 8 wk) and vehicle (Veh) in Spontaneously Diabetic Torii rat, a nonobese type 2 diabetic model, and nondiabetic Sprague-Dawley rats. In nondiabetic rats, Ipra increased urinary excretion of Na+ (UNaV) and fluid (UV) associated with increased food and fluid intake. Diabetes increased these four parameters, but Ipra had no further effect, probably because of its antihyperglycemic effect, such that glucosuria and, as a consequence, food and fluid intake were unchanged. Fluid balance and BFV, determined by bioimpedance spectroscopy, were similar among the four groups. To study the impact of food and fluid intake, nondiabetic rats were treated for 7 days with Veh, Ipra, or Ipra+pair feeding+pair drinking (Pair-Ipra). Pair-Ipra maintained a small increase in UV and UNaV versus Veh despite similar food and fluid intake. Pair-Ipra induced a negative fluid balance and decreased BFV, whereas Ipra or Veh had no significant effect compared with basal values. In conclusion, SGLT2 inhibition induces a sustained diuretic and natriuretic tone. Homeostatic mechanisms are activated to stabilize BFV, including compensatory increases in fluid and food intake.

A translational model of chronic kidney disease in swine

Animal models of chronic kidney disease (CKD) are critical for understanding its pathophysiology and for therapeutic development. The cardiovascular and renal anatomy and physiology of the pig are virtually identical to humans. This study aimed to develop a novel translational model of CKD that mimics the pathological features of CKD in humans. CKD was induced in seven domestic pigs by bilateral renal artery stenosis and diet-induced dyslipidemia. Animals were observed for a total of 14 wk. Renal hemodynamics and function were quantified in vivo using multi-detector CT after 6, 10, and 14 wk of CKD. Urine and blood were collected at each time-point, and blood pressure was continuously measured (telemetry). After completion of in vivo studies, pigs were euthanized, kidneys were removed, and microvascular (MV) architecture (μCT), markers of renal injury, inflammation, and fibrosis were evaluated ex vivo. Additional pigs were used as controls ( n = 7). Renal blood flow and glomerular filtration were reduced by 50% in CKD, accompanied by hypertension and elevated plasma creatinine, albumin-to-creatinine ratio and increased urinary KIM-1 and NGAL, suggesting renal injury. Furthermore, 14 wk of CKD resulted in cortical and medullary MV remodeling and loss, inflammation, glomerulosclerosis, tubular atrophy, and tubule-interstitial fibrosis compared with controls. The current study characterizes a novel model of CKD that mimics several of the pathological features observed in human CKD, irrespective of the etiology. Current approaches only slow rather than halt CKD progression, and this novel model may offer a suitable platform for the development of new treatments in a translational fashion.

Cannabinoid-1 receptor deletion in podocytes mitigates both glomerular and tubular dysfunction in a mouse model of diabetic nephropathy

AIMS

To determine the specific role of podocyte-expressed cannabinoid-1 receptor (CB₁ R) in the development of diabetic nephropathy (DN), relative to CB₁ R in other renal cell types.

MATERIAL AND METHODS

We developed a mouse model with a podocyte-specific deletion of CB₁ R (pCB1Rko) and challenged this model with streptozotocin (STZ)-induced type-1 DN. We also assessed the podocyte response to high glucose in vitro and its effects on CB₁ R activation.

RESULTS

High glucose exposure for 48 hours led to an increase in CB₁ R gene expression (CNR1) and endocannabinoid production in cultured human podocytes. This was associated with podocyte injury, reflected by decreased podocin and nephrin expression. These changes could be prevented by Cnr1-silencing, thus identifying CB1R as a key player in podocyte injury. After 12 weeks of chronic hyperglycaemia, STZ-treated pCB1Rko mice showed elevated blood glucose similar to that of their wild-type littermates. However, they displayed less albuminuria and less podocyte loss than STZ-treated wild-type mice. Unexpectedly, pCB1Rko mice also have milder tubular dysfunction, fibrosis and reduction of cortical microcirculation compared to wild-type controls, which is mediated, in part, by podocyte-derived endocannabinoids acting via CB₁ R on proximal tubular cells.

CONCLUSIONS

Activation of CB₁ R in podocytes contributes to both glomerular and tubular dysfunction in type-1 DN, which highlights the therapeutic potential of peripheral CB₁ R blockade.

VEGF therapy for the kidney: emerging strategies

Renovascular disease (RVD), which is prevalent in the elderly, significantly increases cardiovascular risk and can progressively deteriorate renal function. The loss of renal function in patients with RVD is associated with a progressive dysfunction, damage, and loss of renal microvessels, which can be combined with decreased renal bioavailability of vascular endothelial growth factor (VEGF) and a defective vascular repair and proliferation. This association has been the impetus for recent efforts that have focused on developing methods to stop the progression of renal injury by protecting the renal microvasculature. This mini-review focuses on recent studies supporting potential applications of VEGF therapy for the kidney and discusses underlying mechanisms of renoprotection.

Endothelial cell apoptosis in angiogenesis and vessel regression

Blood vessel regression is an essential process for ensuring blood vessel networks function at optimal efficiency and for matching blood supply to the metabolic needs of tissues as they change over time. Angiogenesis is the major mechanism by which new blood vessels are produced, but the vessel growth associated with angiogenesis must be complemented by remodeling and maturation events including the removal of redundant vessel segments and cells to fashion the newly forming vasculature into an efficient, hierarchical network. This review will summarize recent findings on the role that endothelial cell apoptosis plays in vascular remodeling during angiogenesis and in vessel regression more generally.

Endothelial marker-expressing stromal cells are critical for kidney formation

Kidneys are highly vascularized and contain many distinct vascular beds. However, the origins of renal endothelial cells and roles of the developing endothelia in the formation of the kidney are unclear. We have shown that the Foxd1-positive renal stroma gives rise to endothelial marker-expressing progenitors that are incorporated within a subset of peritubular capillaries; however, the significance of these cells is unclear. The purpose of this study was to determine whether deletion of Flk1 in the Foxd1 stroma was important for renal development. To that end, we conditionally deleted Flk1 (critical for endothelial cell development) in the renal stroma by breeding-floxed Flk1 mice (Flk1fl/fl ) with Foxd1cre mice to generate Foxd1cre; Flk1fl/fl (Flk1ST-/- ) mice. We then performed FACsorting, histological, morphometric, and metabolic analyses of Flk1ST-/- vs. control mice. We confirmed decreased expression of endothelial markers in the renal stroma of Flk1ST-/- kidneys via flow sorting and immunostaining, and upon interrogation of embryonic and postnatal Flk1ST-/- mice, we found they had dilated peritubular capillaries. Three-dimensional reconstructions showed reduced ureteric branching and fewer nephrons in developing Flk1ST-/- kidneys vs.

CONTROLS

Juvenile Flk1ST-/- kidneys displayed renal papillary hypoplasia and a paucity of collecting ducts. Twenty-four-hour urine collections revealed that postnatal Flk1ST-/- mice had urinary-concentrating defects. Thus, while lineage-tracing revealed that the renal cortical stroma gave rise to a small subset of endothelial progenitors, these Flk1-expressing stromal cells are critical for patterning the peritubular capillaries. Also, loss of Flk1 in the renal stroma leads to nonautonomous-patterning defects in ureteric lineages.

Reduced Microvascular Density in Omental Biopsies of Children with Chronic Kidney Disease

BACKGROUND

Endothelial dysfunction is an early manifestation of cardiovascular disease (CVD) and consistently observed in patients with chronic kidney disease (CKD). We hypothesized that CKD is associated with systemic damage to the microcirculation, preceding macrovascular pathology. To assess the degree of "uremic microangiopathy", we have measured microvascular density in biopsies of the omentum of children with CKD.

PATIENTS AND METHODS

Omental tissue was collected from 32 healthy children (0-18 years) undergoing elective abdominal surgery and from 23 age-matched cases with stage 5 CKD at the time of catheter insertion for initiation of peritoneal dialysis. Biopsies were analyzed by independent observers using either a manual or an automated imaging system for the assessment of microvascular density. Quantitative immunohistochemistry was performed for markers of autophagy and apoptosis, and for the abundance of the angiogenesis-regulating proteins VEGF-A, VEGF-R2, Angpt1 and Angpt2.

RESULTS

Microvascular density was significantly reduced in uremic children compared to healthy controls, both by manual imaging with a digital microscope (median surface area 0.61% vs. 0.95%, p<0.0021 and by automated quantification (total microvascular surface area 0.89% vs. 1.17% p = 0.01). Density measured by manual imaging was significantly associated with age, height, weight and body surface area in CKD patients and healthy controls. In multivariate analysis, age and serum creatinine level were the only independent, significant predictors of microvascular density (r2 = 0.73). There was no immunohistochemical evidence for apoptosis or autophagy. Quantitative staining showed similar expression levels of the angiogenesis regulators VEGF-A, VEGF-receptor 2 and Angpt1 (p = 0.11), but Angpt2 was significantly lower in CKD children (p = 0.01).

CONCLUSIONS

Microvascular density is profoundly reduced in omental biopsies of children with stage 5 CKD and associated with diminished Angpt2 signaling. Microvascular rarefaction could be an early systemic manifestation of CKD-induced cardiovascular disease.

Role of the Renal Microcirculation in Progression of Chronic Kidney Injury in Obesity

BACKGROUND

Obesity is largely responsible for the growing incidence and prevalence of diabetes, cardiovascular and renal diseases. Current strategies to prevent and treat obesity and its consequences have been insufficient to reverse the ongoing trends. Lifestyle modification or pharmacological therapies often produce modest weight loss which is not sustained and recurrence of obesity is frequently observed, leading to progression of target organ damage in many obese subjects. Therefore, research efforts have focused not only on the factors that regulate energy balance, but also on understanding mechanisms of target organ injury in obesity. Summary and Key Message: Microvascular (MV) disease plays a pivotal role in progressive kidney injury from different etiologies such as hypertension, diabetes, and atherosclerosis, which are all important consequences of chronic obesity. The MV networks are anatomical units that are closely adapted to specific functions of nutrition and removal of waste in every organ. Damage of the small vessels in several tissues and organs has been reported in obesity and may increase cardio-renal risk. However, the mechanisms by which obesity and its attendant cardiovascular and metabolic consequences interact to cause renal MV injury and chronic kidney disease are still unclear, although substantial progress has been made in recent years. This review addresses potential mechanisms and consequences of obesity-induced renal MV injury as well as current treatments that may provide protection of the renal microcirculation and slow progressive kidney injury in obesity.

Contrast-enhanced CT imaging in patients with chronic kidney disease

Renal microvascular rarefaction characterizes chronic kidney disease (CKD). In murine models of CKD, micro-CT imaging reflected capillary rarefaction using quantification of renal relative blood volume (rBV). In addition, micro-CT imaging revealed morphological alterations of the intrarenal vasculature including reduced vascular branching and lumen diameter. Here, we retrospectively quantified rBV in contrast-enhanced CT angiography in patients and found that, compared to non-CKD patients, those with CKD and renal fibrosis had significantly reduced rBV in the renal cortex. rBV values closely mirrored capillary rarefaction in the corresponding nephrectomy specimens. In patients with follow-up CT angiography, reduction of renal function was paralleled by a decline in rBV. Using virtual autopsy, i.e., postmortem CT angiography, morphometry of intrarenal arteries in 3D-rendered CT images revealed significantly reduced arterial diameter and branching in CKD compared to non-CKD cases. In conclusion, in CKD patients, contrast-enhanced CT imaging with quantification of rBV correlates with functional renal vasculature, whereas virtual autopsy allows morphometric analyses of macrovascular changes. Importantly, the observed vascular alterations in CKD patients mirror those in animals with progressive CKD, suggesting a high relevance of animal models for studying vascular alterations in CKD and renal fibrosis.

Fat and Sucrose Intake Induces Obesity-Related Bone Metabolism Disturbances: Kinetic and Reversibility Studies in Growing and Adult Rats

Metabolic and bone effects were investigated in growing (G, n = 45) and mature (M, n = 45) rats fed a high-fat/high-sucrose diet (HFS) isocaloric to the chow diet of controls (C, n = 30 per group). At week 19, a subset of 15 rats in each group (HFS or C, at both ages) was analyzed. Then one-half of the remaining 30 HFS rats in each groups continued HFS and one-half were shifted to C until week 27. Although no serum or bone marrow inflammation was seen, HFS increased visceral fat, serum leptin and insulin at week 19 and induced further alterations in lipid profile, serum adiponectin, and TGFβ1, TIMP1, MMP2, and MMP9, suggesting a prediabetic phenotype and cardiovascular dysfunction at week 27 more pronounced in M than G. These events were associated with dramatic reduction of osteoclastic and osteoid surfaces with accelerated mineralizing surfaces in both HFS age groups. Mineral metabolism and its major regulators were disturbed, leading to hyperphosphatemia and hypocalcemia. These changes were associated with bone alterations in the weight-bearing tibia, not in the non-weight-bearing vertebra. Indeed in fat rats, tibia trabecular bone accrual increased in G whereas loss of trabecular bone in M was alleviated. At diaphysis cortical porosity increased in G and even more in M at week 27. After the diet switch, metabolic and bone cellular disturbances fully reversed in G, but not in M. Trabecular benefit of the obese was preserved in both age groups and in M the age-related bone loss was even lighter after the diet switch than in prolonged HFS. At the diaphysis, cortical porosity normalized in G but not in M. Hypocalcemia in G and M was irreversible. Thus, the mild metabolic syndrome induced by isocaloric HFS is able to alter bone cellular activities and mineral metabolism, reinforce trabecular bone, and affect cortical bone porosity in an irreversible manner in older rats.

Renal allograft fibrosis: biology and therapeutic targets

Renal tubulointerstitial fibrosis is the final common pathway of progressive renal diseases. In allografts, it is assessed with tubular atrophy as interstitial fibrosis/tubular atrophy (IF/TA). IF/TA occurs in about 40% of kidney allografts at 3-6 months after transplantation, increasing to 65% at 2 years. The origin of renal fibrosis in the allograft is complex and includes donor-related factors, in particular in case of expanded criteria donors, ischemia-reperfusion injury, immune-mediated damage, recurrence of underlying diseases, hypertensive damage, nephrotoxicity of immunosuppressants, recurrent graft infections, postrenal obstruction, etc. Based largely on studies in the non-transplant setting, there is a large body of literature on the role of different cell types, be it intrinsic to the kidney or bone marrow derived, in mediating renal fibrosis, and the number of mediator systems contributing to fibrotic changes is growing steadily. Here we review the most important cellular processes and mediators involved in the progress of renal fibrosis, with a focus on the allograft situation, and discuss some of the challenges in translating experimental insights into clinical trials, in particular fibrosis biomarkers or imaging modalities.

Chronic blockade of endothelin A and B receptors using macitentan in experimental renovascular disease

BACKGROUND

Emerging research has identified the endothelin (ET)-1 pathway as a potential target for novel renoprotective therapies. We recently showed that selective ET-A receptor antagonism in chronic renovascular disease (RVD) improves renal function and reduces renal injury. Although ET-A and -B have opposing roles, in some clinical situations they may induce similar effects. Thus, we hypothesized that simultaneous blockade of the ET-A and -B receptors would protect the kidney during RVD.

METHODS

Unilateral RVD was induced in pigs. After 6 weeks, single-kidney function was quantified in vivo using multi-detector computer tomography. Pigs were subsequently divided into untreated (RVD, n = 7) or daily-treated with the dual ET-A/B receptor antagonist macitentan (RVD + macitentan, n = 6) for 4 weeks. At 10 weeks, in vivo studies were repeated, then pigs were euthanized and ex vivo studies performed in the stenotic kidney to quantify inflammation, fibrosis, microvascular density and remodeling.

RESULTS

Four weeks of macitentan therapy modestly improved renal blood flow (29%, P = 0.06 versus pre-treatment) and showed protective effects on the renal parenchyma by attenuating inflammation and glomerulosclerosis, reducing apoptosis and tubular casts and improving albuminuria and cortical microvessel density. No overt adverse effects were observed.

CONCLUSION

Possibly by inducing a pro-survival renal microenvironment, macitentan increased renal microvascular density, promoted cell survival and decreased injury, which in turn improved stenotic kidney hemodynamics in our model. Our results further support the safety of using macitentan in patients with concomitant chronic renal disease and supported the feasibility of a new strategy that may preserve the stenotic kidney in RVD.

Nephron Deficiency and Predisposition to Renal Injury in a Novel One-Kidney Genetic Model

Some studies have reported up to 40% of patients born with a single kidney develop hypertension, proteinuria, and in some cases renal failure. The increased susceptibility to renal injury may be due, in part, to reduced nephron numbers. Notably, children who undergo nephrectomy or adults who serve as kidney donors exhibit little difference in renal function compared with persons who have two kidneys. However, the difference in risk between being born with a single kidney versus being born with two kidneys and then undergoing nephrectomy are unclear. Animal models used previously to investigate this question are not ideal because they require invasive methods to model congenital solitary kidney. In this study, we describe a new genetic animal model, the heterogeneous stock-derived model of unilateral renal agenesis (HSRA) rat, which demonstrates 50%-75% spontaneous incidence of a single kidney. The HSRA model is characterized by reduced nephron number (more than would be expected by loss of one kidney), early kidney/glomerular hypertrophy, and progressive renal injury, which culminates in reduced renal function. Long-term studies of temporal relationships among BP, renal hemodynamics, and renal function demonstrate that spontaneous single-kidney HSRA rats are more likely than uninephrectomized normal littermates to exhibit renal impairment because of the combination of reduced nephron numbers and prolonged exposure to renal compensatory mechanisms (i.e., hyperfiltration). Future studies with this novel animal model may provide additional insight into the genetic contributions to kidney development and agenesis and the factors influencing susceptibility to renal injury in individuals with congenital solitary kidney.

Renal vascular structure and rarefaction

An intact microcirculation is vital for diffusion of oxygen and nutrients and for removal of toxins of every organ and system in the human body. The functional and/or anatomical loss of microvessels is known as rarefaction, which can compromise the normal organ function and have been suggested as a possible starting point of several diseases. The purpose of this overview is to discuss the potential underlying mechanisms leading to renal microvascular rarefaction, and the potential consequences on renal function and on the progression of renal damage. Although the kidney is a special organ that receives much more blood than its metabolic needs, experimental and clinical evidence indicates that renal microvascular rarefaction is associated to prevalent cardiovascular diseases such as diabetes, hypertension, and atherosclerosis, either as cause or consequence. On the other hand, emerging experimental evidence using progenitor cells or angiogenic cytokines supports the feasibility of therapeutic interventions capable of modifying the progressive nature of microvascular rarefaction in the kidney. This overview will also attempt to discuss the potential renoprotective mechanisms of the therapeutic targeting of the renal microcirculation.

Assessment of renal function; clearance, the renal microcirculation, renal blood flow, and metabolic balance

Historically, tools to assess renal function have been developed to investigate the physiology of the kidney in an experimental setting, and certain of these techniques have utility in evaluating renal function in the clinical setting. The following work will survey a spectrum of these tools, their applications and limitations in four general sections. The first is clearance, including evaluation of exogenous and endogenous markers for determining glomerular filtration rate, the adaptation of estimated glomerular filtration rate in the clinical arena, and additional clearance techniques to assess various other parameters of renal function. The second section deals with in vivo and in vitro approaches to the study of the renal microvasculature. This section surveys a number of experimental techniques including corticotomy, the hydronephrotic kidney, vascular casting, intravital charge coupled device videomicroscopy, multiphoton fluorescent microscopy, synchrotron-based angiography, laser speckle contrast imaging, isolated renal microvessels, and the perfused juxtamedullary nephron microvasculature. The third section addresses in vivo and in vitro approaches to the study of renal blood flow. These include ultrasonic flowmetry, laser-Doppler flowmetry, magnetic resonance imaging (MRI), phase contrast MRI, cine phase contrast MRI, dynamic contrast-enhanced MRI, blood oxygen level dependent MRI, arterial spin labeling MRI, x-ray computed tomography, and positron emission tomography. The final section addresses the methodologies of metabolic balance studies. These are described for humans, large experimental animals as well as for rodents. Overall, the various in vitro and in vivo topics and applications to evaluate renal function should provide a guide for the investigator or physician to understand and to implement the techniques in the laboratory or clinic setting.

C-peptide preserves the renal microvascular architecture in the streptozotocin-induced diabetic rat

AIMS

C-peptide is renoprotective in type 1 diabetes, however, the mechanisms of its actions are not completely understood. We hypothesized that C-peptide attenuates diabetes-associated renal microvascular injury.

METHOD

After 4 or 8weeks of streptozotocin (STZ)-induced diabetes, rats received either vehicle or C-peptide in the presence of low or high doses of insulin. Urine albumin excretion (UAE) was measured prior to initiation of treatment (baseline) and 2 or 4weeks after treatment (sacrifice). Glomerular hypertrophy, glomerular filtration rate (GFR) and renal microvascular density, quantified ex vivo by 3D micro-CT reconstruction, were measured at sacrifice.

RESULTS

In rats receiving low doses of insulin, treatment with C-peptide reduced HbA1c levels by 24%. In these rats, the 107% increase in UAE rate from baseline to sacrifice in vehicle-treated rats was largely prevented with C-peptide. C-peptide also reduced diabetes-associated glomerular hyperfiltration by 30%, glomerular hypertrophy by 22% and increased the density of microvessels between 0 and 500μm in diameter by an average of 31% compared with vehicle-treated groups. Similar renoprotective effects of C-peptide were observed in rats treated with higher doses of daily insulin, despite no differences in HbA1c levels.

CONCLUSIONS

The study suggests that C-peptide is renoprotective by preserving the integrity of the renal microvasculature irrespective of glucose regulation.

Renal lipids and oxygenation in diabetic mice: noninvasive quantification with MR imaging

PURPOSE

To determine the relationship between renal lipid content and intrarenal oxygenation in diabetic nephropathy by using noninvasive chemical shift-selective (CSS) imaging and blood oxygen level-dependent (BOLD) magnetic resonance (MR) imaging.

MATERIALS AND METHODS

The study was approved by the institutional Committee on Animal Research. Lipid and water phantoms for CSS imaging were made, and BOLD MR imaging phantoms from arterial and venous blood samples were collected from rats. CSS imaging and BOLD imaging were performed to measure lipid contents and T2* in phantoms and kidneys of diabetic gene (db) db/db mice and wild-type mice after exposure to nitrogen (four per group) and injection of furosemide (four per group). Results of MR imaging-measured lipid contents and oxygen tension were compared with known values in phantoms and reference standard from mice with histologic data. Statistical analysis was performed with independent sample and paired sample t tests and Pearson correlation test.

RESULTS

Renal lipid content in db/db mice was significantly higher compared with that in control mice (9.40% ± 1.89 and 3.11% ± 0.57, respectively; P < .001). In addition, the lipid content in the cortex of db/db mice was significantly higher than that in medulla (12.73% ± 0.94 and 3.16% ± 0.50, respectively; P < .001). Correlation was significant between T2* measured with BOLD and oxygen tension in blood phantoms (r = 0.958; P < .001). Lower baseline T2* in diabetic kidney suggested lower oxygenation that reserved excess oxygen supply. Lower oxygenation in diabetic kidney cortex was observed after nitrogen exposure and furosemide injection.

CONCLUSION

Noninvasive CSS imaging and MR imaging of db/db diabetic mice revealed the relationship between the renal lipid content and intrarenal oxygenation in diabetic kidney. Lipid accumulation in diabetic kidney compromises the oxygenation of the renal tissue and made it more susceptible to renal hypoxia. Online supplemental material is available for this article.

Neutrophil-to-lymphocyte ratio as a predictor of worsening renal function in diabetic patients (3-year follow-up study)

BACKGROUND

Previous studies have demonstrated the role of inflammation in diabetic nephropathy (DN). Neutrophil to lymphocyte ratio (NLR) rather than other white cell parameters was found to be a useful inflammatory marker to predict adverse outcomes in medical and surgical conditions. Nevertheless, the value of NLR in predicting DN has not been elucidated.

METHOD

An observational study included 338 diabetic patients, who were followed at our clinic between 2007 and 2009. We arranged our patients into tertiles according to their 2007 NLR. The primary outcome was continuous decrease of GFR >12 mL/min between 2007 and 2009 with the last GFR <60 mL/min.

RESULT

The lowest NLR tertile had fewer patients (2.7%) with primary outcome (i.e., worsening renal function) compared with middle and highest NLR tertiles, which had more patients with primary outcomes (8.7% and 11.5%, respectively) with a significant p-value 0.0164. When other potential confounders were individually analyzed with NLR tertile, the NLR tertiles remained a significant predictor of poor GFR outcome in the presence of other variables (hemoglobin A1C, systolic blood pressure, diastolic blood pressure, age, and congestive heart failure with p-values 0.018, 0.019, 0.017, 0.033, and 0.022, respectively).

CONCLUSION

NLR predicted the worsening of the renal function in diabetic patients. Further studies are needed to confirm this result.