Early atherosclerosis aggravates renal microvascular loss and fibrosis in swine renal artery stenosis

Detection of microvascular damage of membranous nephropathy by MicroFlow imaging: a novel ultrasound technique

Background

MicroFlow imaging (MFI) is a novel noninvasive ultrasound (US) technique that depicts microcirculatory blood vessels in the kidney while filtering out tissue motion and enhancing blood flow signals. We aimed to investigate the value of MFI for the detection of renal microvascular perfusion in chronic kidney disease caused by stage I-II membranous nephropathy (MN).

Methods

Seventy-six participants including biopsy-proven MN (n=38) and healthy volunteers (n=38) were prospectively examined using MFI from March 2020 to December 2020. In addition, patients with MN were subdivided into a mild group, a moderate group, and a severe group based on the results of vascular pathology evaluation. All MFI images were analyzed by Image Pro Plus to obtain a cortical vascular index (VI). Basic patient information, relative US parameters and laboratory results were then acquired for each participant. Finally, after the univariate analysis among multiple groups, binary logistic regression (forward LR) and ordered logistic regression were used for multivariate analysis. Significance was set at P<0.05.

Results

VI was significantly lower in MN patients compared with that of healthy controls (0.65±0.09 vs. 0.35±0.18, P<0.001). After multivariate analysis, we found that the exploratory diagnostic performance of VI [area under the curve (AUC): 0.94; 95% confidence interval (CI): 0.89-0.99] outperformed that of serum creatinine (Scr) (AUC: 0.87; 95% CI: 0.79-0.95) in identifying MN. We also observed considerable differences among MN groups in parameters including VI (P=0.006), estimated glomerular filtration rate (eGFR) (P=0.037), shape (P=0.013), and impression (P=0.007). In addition, in the group with mild vascular damage, the exploratory diagnostic performance of VI (AUC: 0.79; 95% CI: 0.64-0.94) was better than other parameters, such as eGFR (AUC: 0.63; 95% CI: 0.43-0.84).

Conclusions

MFI detected abnormal renal microvascular perfusion in patients with MN (particularly in those with early vascular damage or preserved renal function) without the use of a contrast agent. Combining MFI with B-mode US can improve the predictive performance of traditional kidney US.

Microvascular remodeling and altered angiogenic signaling in human kidneys distal to occlusive atherosclerotic renal artery stenosis

BACKGROUND

Renal artery stenosis (RAS) is an important cause of chronic kidney disease and secondary hypertension. In animal models, renal ischemia leads to downregulation of growth-factor expression and loss of intrarenal microcirculation. However, little is known about the sequelae of large vessel occlusive disease on the microcirculation within human kidneys.

METHOD

This study included 5 patients who underwent nephrectomy due to renovascular occlusion, and 7 non-stenotic discarded donor kidneys (4 deceased donors). Micro-computed tomography was performed to assess microvascular spatial densities and tortuosity, an index of microvascular immaturity. Renal protein expression, gene expression, and histology were studied in-vitro using immunoblotting, polymerase-chain-reaction, and staining.

RESULTS

RAS demonstrated loss of medium-sized vessels (0.2-0.3mm) compared to donor kidneys (p = 0.037) and increased microvascular tortuosity. RAS kidneys had greater protein expression of angiopoietin-1, hypoxia-inducible factor (HIF)-1α, and thrombospondin (TSP)-1, but lower protein expression of vascular endothelial growth factor (VEGF) than donor kidneys. Renal fibrosis, loss of peritubular capillaries (PTC) and pericyte detachment were greater in RAS, yet they had more newly-formed PTC than donor kidneys. Therefore, our study quantified significant microvascular remodeling in the post-stenotic human kidney. RAS induced renal microvascular loss, vascular remodeling, and fibrosis. Despite downregulated VEGF, stenotic kidneys upregulated compensatory angiogenic pathways related to angiopoietin-1.

CONCLUSIONS

These observations underscore the nature of human RAS as a microvascular disease distal to main vessel stenosis, and support therapeutic strategies directly targeting the post-stenotic kidney microcirculation in patients with RAS.

An Innovative Ultrasound Technique for Early Detection of Kidney Dysfunction: Superb Microvascular Imaging as a Reference Standard

Background: Superb microvascular imaging (SMI) is an innovative ultrasound image processing technique that provides greater detail and better visualization of small branching vessels. We assume that SMI will provide sufficient information regarding the severity of chronic kidney disease (CKD) and reflecting histological changes. Aims: The aims was to assess the capabilities of SMI imaging regarding the early detection of kidney dysfunction and renal fibrosis in comparison to the reference standard renal biopsy for the early diagnosis of kidney fibrosis. Methods: SMI was performed in patients (n = 52) with CKD stage 2–5, where some of them underwent biopsy proven CKD and fibrosis as part of the diagnosis. In addition, biochemical tests were performed, including kidney function tests, urine collection for proteinuria, and the estimation of GFR by MDRD or CKD-EPI eGFR in CKD patients and healthy controls (n = 17). All subjects underwent SMI, where vascularity is expressed as the SMI index (a low index reflects low vascularity/fibrosis and vice versa). Results: The SMI vascular index was significantly lower in CKD patients as compared with healthy controls (72.2 ± 12.9 vs. 49.9 ± 16.7%, p < 0.01). Notably, a moderate correlation between the SMI index and eGFR was found among the CKD patients (r = 0.56, p < 0.001). Similarly, a strong correlation was found between SCr and the SMI index of the diseased subjects (r = −0.54, p < 0.001). In patients who underwent renal biopsy, the SMI index corresponded with the histological alterations and CKD staging. Conclusions: This study demonstrated that SMI imaging may be utilized in CKD patients of various stages for the evaluation of chronic renal morphological changes and for differentiation between CKD grades.

Cell-based regenerative medicine for renovascular disease

Renal artery stenosis (RAS) elicits the development of hypertension and post-stenotic kidney damage, which may become irresponsive to restoration of arterial patency. Rather than mere losses of blood flow or oxygen supply, irreversible intrarenal microvascular rarefaction, tubular injury, and interstitial fibrosis are now attributed to intrinsic pathways activated within the kidney, focusing attention on the kidney parenchyma as a therapeutic target. Several regenerative approaches involving the delivery of reparative cells or products have achieved kidney repair in experimental models of RAS and the delivery of mesenchymal stem/stromal cells (MSCs) has already been translated to human subjects with RAS with promising results. The ongoing development of innovative approaches in kidney disease awaits application, validation, and acceptance as routine clinical treatment to avert kidney damage in RAS.

Superimposition of metabolic syndrome magnifies post-stenotic kidney injury in dyslipidemic pigs

BACKGROUND

Dyslipidemia aggravates kidney injury distal to atherosclerotic renal artery stenosis (ARAS). Besides dyslipidemia, metabolic syndrome (MetS) also involves development of obesity and insulin-resistance (IR). We hypothesized that concurrent obesity and IR magnify swine stenotic-kidney damage beyond dyslipidemia.

METHODS

Pigs with unilateral RAS were studied after 16 weeks of atherogenic diets without (ARAS) or with (MetS + RAS) development of obesity/IR (n=6 each). Additional pigs on normal diet served as normal or non-dyslipidemic RAS controls (n=6 each). Stenotic-kidney renal blood flow (RBF), glomerular filtration rate (GFR), and microvascular architecture were studied using CT, and oxygenation was studied using blood oxygen level-dependent magnetic-resonance-imaging. We further compared kidney adiposity, oxidative stress, inflammation, apoptosis, fibrosis, and systemic levels of oxidative and inflammatory cytokines.

RESULTS

ARAS and MetS + RAS developed hypertension and dyslipidemia, and MetS + RAS also developed obesity and IR. RBF and GFR were similarly decreased in all post-stenotic pig kidneys compared to normal pig kidneys, yet MetS + RAS aggravated and expanded medullary hypoxia and microvascular loss. RAS and ARAS increased systemic levels of tumor necrosis factor (TNF)-α, which were further elevated in MetS + RAS. Renal oxidative stress and TNF-α expression increased in ARAS and further in MetS + RAS, which also upregulated expression of anti-angiogenic angiostatin, and magnified apoptosis, tubular injury, and fibrosis.

CONCLUSION

Beyond dyslipidemia, obesity and insulin-resistance aggravate damage in the post-stenotic kidney in MetS, despite relative hyperfiltration-related preservation of renal function. These observations underscore the need to control systemic metabolic disturbances in order to curb renal damage in subjects with ischemic kidney disease.

Perspectives on the Role of Magnetic Resonance Imaging (MRI) for Noninvasive Evaluation of Diabetic Kidney Disease

Renal magnetic resonance imaging (MRI) techniques are currently in vogue, as they provide in vivo information on renal volume, function, metabolism, perfusion, oxygenation, and microstructural alterations, without the need for exogenous contrast media. New imaging biomarkers can be identified using these tools, which represent a major advance in the understanding and study of the different pathologies affecting the kidney. Diabetic kidney disease (DKD) is one of the most important diseases worldwide due to its high prevalence and impact on public health. However, its multifactorial etiology poses a challenge for both basic and clinical research. Therefore, the use of novel renal MRI techniques is an attractive step forward in the comprehension of DKD, both in its pathogenesis and in its detection and surveillance in the clinical practice. This review article outlines the most promising MRI techniques in the study of DKD, with the purpose of stimulating their clinical translation as possible tools for the diagnosis, follow-up, and monitoring of the clinical impacts of new DKD treatments.

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.

Magnetization Transfer Imaging Predicts Porcine Kidney Recovery After Revascularization of Renal Artery Stenosis

MATERIALS AND METHODS

Stenotic kidney (STK) and contralateral kidney magnetization transfer ratios (MTRs; Mt/M0) were measured at 3.0-T magnetic resonance imaging, at offset frequencies of 600 and 1000 Hz, before and 1 month post-PTRA in 7 RVD pigs. Stenotic kidney MTR was correlated to renal perfusion, renal blood flow (RBF), and glomerular filtration rate (GFR), determined using multidetector computed tomography and with ex vivo renal fibrosis (trichrome staining). Untreated RVD (n = 6) and normal pigs (n = 7) served as controls.

RESULTS

Renovascular disease induced hypertension and renal dysfunction. Blood pressure and renal perfusion were unchanged post-PTRA, but GFR and RBF increased. Baseline cortical STK-MTR predicted post-PTRA renal perfusion and RBF, and MTR changes associated inversely with changes in perfusion and normalized GFR. Stenotic kidney MTR at 600 Hz showed closer association with renal parameters, but both frequencies predicted post-PTRA cortical fibrosis.

CONCLUSIONS

Renal STK-MTR, particularly at 600 Hz offset, is sensitive to hemodynamic changes after PTRA in swine RVD and capable of noninvasively predicting post-PTRA kidney perfusion, RBF, and fibrosis. Therefore, STK-MTR may be a valuable tool to predict renal hemodynamic and functional recovery, as well as residual kidney fibrosis after revascularization in RVD.

The Value of Contrast-Enhanced Ultrasound versus Doppler Ultrasound in Grading Renal Artery Stenosis

Objective

This study is aimed at exploring the accuracy of contrast-enhanced ultrasound (CEUS) in grading renal artery stenosis.

Methods

122 renal arteries with suspected renal artery stenosis were selected. DSA, DUS, and CEUS were performed for all patients with suspected renal artery stenosis in the research. DSA was selected as the gold standard. The sensitivity, specificity, accuracy, positive predictive value (PPV), and negative predictive value (NPV) of CEUS or Doppler ultrasound (DUS) in the diagnosis of renal artery stenosis were analyzed. The consistency between CEUS and digital subtraction angiography (DSA) was compared. The accuracy of DUS or CEUS in grading renal artery stenosis was assessed by the area under the receiver operating characteristic (ROC) curves and compared between groups.

Results

The sensitivity, specificity, accuracy, positive predictive value, and negative predictive value of CEUS in the diagnosis of renal artery stenosis were 88.9%, 87.8%, 88.5%, 93.5%, and 80.0%, respectively. There was no significant difference in grading renal artery stenosis between CEUS and DSA (X² = 0.643, P = 0.424). 77 of the 122 renal arteries were diagnosed with the stenosis rate more than 30% by CEUS. Compared with the results of DSA, the kappa value of CEUS was 0.749 (P < 0.05).

Conclusion

CEUS is accurate in grading renal artery stenosis, and it may represent the method of choice in diagnosing renal artery stenosis.

Improved renal outcomes after revascularization of the stenotic renal artery in pigs by prior treatment with low-energy extracorporeal shockwave therapy

BACKGROUND

Revascularization does not restore renal function in most patients with atherosclerotic renal artery stenosis (RAS), likely because of inflammation and fibrosis within the stenotic kidney. Low-energy shockwave therapy (LE-SWT) stimulates angiogenesis in the stenotic kidney, but its ability to improve renal function and structure after revascularization remains unexplored. We tested the hypothesis that a LE-SWT regimen before percutaneous transluminal renal angioplasty (PTRA) would enable PTRA to restore renal function in hypercholesterolemic pigs with RAS (HC+RAS), and that this would be associated with attenuation of renal inflammation and fibrosis.

METHODS AND RESULTS

Twenty-six pigs were studied after 16 weeks of HC+RAS, HC+RAS treated with PTRA with or without a preceding LE-SWT regimen (bi-weekly for 3 weeks), and controls. Single-kidney renal blood flow (RBF), glomerular filtration rate (GFR), and oxygenation were assessed in vivo using imaging 4 weeks after PTRA, and then inflammation and fibrosis ex vivo.Four weeks after successful PTRA, blood pressure fell similarly in both revascularized groups. Yet, stenotic-kidney GFR remained lower in HC+RAS and HC+RAS+PTRA (P < 0.01 vs. normal), but was improved in HC+RAS+PTRA+SW (P > 0.05 vs. normal). Furthermore, reduced inflammation, medullary fibrosis, and cortical hypoxia were only shown in swine stenotic kidneys pretreated with LE-SWT before PTRA 4 weeks later.

CONCLUSION

LE-SWT delivery before revascularization permitted PTRA to improve function and decrease cortical and medullary damage in the stenotic swine kidney. This study, therefore, supports the use of an adjunct SW pretreatment to enhance the success of PTRA in blunting loss of kidney function in experimental HC+RAS.

Renal Artery Stenosis in the Patient with Hypertension: Prevalence, Impact and Management

Atherosclerosis is the primary cause of renal artery stenosis. Atherosclerotic renal artery stenosis (ARAS) is associated with three clinical problems: renovascular hypertension, ischemic nephropathy and cardiac destabilization syndrome which pose huge healthcare implications. There is a significant rate of natural disease progression with worsening severity of renal artery stenosis when renal revascularization is not pursued in a timely manner. Selective sub-groups of individuals with ARAS have had good outcomes after percutaneous renal artery stenting (PTRAS). For example, individuals that underwent PTRAS and had improved renal function were reported to have a 45% survival advantage compared to those without improvement in their renal function. Advances in the imaging tools have allowed for better anatomic and physiologic measurements of ARAS. Measuring translesional hemodynamic gradients has allowed for accurate assessment of ARAS severity. Renal revascularization with PTRAS provides a survival advantage in individuals with significant hemodynamic renal artery stenosis lesions. It is important that we screen, diagnosis, intervene with invasive and medical treatments appropriately in these high-risk patients.

Losartan protects against intermittent hypoxia-induced peritubular capillary loss by modulating the renal renin-angiotensin system and angiogenesis factors

Obstructive sleep apnea is characterized by chronic intermittent hypoxia (CIH), which is a risk factor for renal peritubular capillary (PTC) loss, and angiotensin II receptor blockers can alleviate PTC loss. However, the mechanism by which losartan (an angiotensin II receptor blocker) reduces CIH-induced PTC loss and attenuates kidney damage is still unknown. Thus, in this study, we examined the protective effects of losartan against CIH-induced PTC loss and explored the underlying mechanisms in rat CIH model. The immunohistochemical staining of CD34 and morphological examination showed that CIH reduced PTC density and damaged tubular epithelial cells. Immunohistochemistry, enzyme-linked immunosorbent assay (ELISA), real-time quantitative PCR, and western blot analysis results revealed that CIH increased the expression of hypoxia inducible factor-1α (HIF-1α), angiotensin II (Ang II), angiotensin II type 1 receptor (AT1R), pro-angiogenesis factor vascular endothelial growth factor (VEGF), and anti-angiogenesis factor thrombospondin-1 (TSP-1) in the renal cortex of rats. CIH may up-regulate VEGF expression and simultaneously increase TSP-1 production. By histopathological, immunohistochemistry, ELISA, RT-qPCR, and western blot analysis, we found that the expressions of renal renin-angiotensin system (RAS), HIF-1α, VEGF, and TSP-1 were decreased, and PTC loss and tubular epithelial cell injury were attenuated with losartan treatment. Losartan ameliorated CIH-induced PTC loss by modulating renal RAS to improve the crosstalk between endothelial cells and tubular epithelial cells and subsequently regulate the balance of angiogenesis factors. Our study provided novel insights into the mechanisms of CIH-induced kidney damage and indicated that losartan could be a potential therapeutic agent for renal protection by alleviating CIH-induced PTC loss.

Experimental Metabolic Syndrome Model Associated with Mechanical and Structural Degenerative Changes of the Aortic Valve

The purpose of this study was to test the hypothesis that an experimental high fat (HF) animal with metabolic syndrome results in structural degeneration of the aortic valve. Domestic pigs were divided (n = 12) and administered either a normal or HF diet. After 16-weeks, the HF diet group had increased weight (p ≤ 0.05), total cholesterol (p ≤ 0.05), and systolic and diastolic pressure (p ≤ 0.05). The aortic valve extracellular matrix showed loss of elastin fibers and increased collagen deposition in the HF diet group. Collagen was quantified with ELISA, which showed an increased concentration of collagen types 1 and 3 (p ≤ 0.05). In the HF diet group, the initial stages of microcalcification were observed. Uniaxial mechanical testing of aortic cusps revealed that the HF diet group expressed a decrease in ultimate tensile strength and elastic modulus compared to the control diet group (p ≤ 0.05). Western blot and immunohistochemistry indicated the presence of proteins: lipoprotein-associated phospholipase A2, osteopontin, and osteocalcin with an increased expression in the HF diet group. The current study demonstrates that experimental metabolic syndrome induced by a 16-week HF diet was associated with a statistically significant alteration to the physical architecture of the aortic valve.

Approach to atherosclerotic renovascular disease: 2016

The management of atherosclerotic renal artery stenosis in patients with hypertension or impaired renal function remains a clinical dilemma. The current general consensus, supported by the results of the Angioplasty and Stenting for Renal Atherosclerotic Lesions and Cardiovascular Outcomes for Renal Artery Lesions trials, argues strongly against endovascular intervention in favor of optimal medical management. We discuss the limitations and implications of the contemporary clinical trials and present our approach and formulate clear recommendations to help with the management of patients with atherosclerotic narrowing of the renal artery.

Low-Energy Shockwave Therapy Improves Ischemic Kidney Microcirculation

Microvascular rarefaction distal to renal artery stenosis is linked to renal dysfunction and poor outcomes. Low-energy shockwave therapy stimulates angiogenesis, but the effect on the kidney microvasculature is unknown. We hypothesized that low-energy shockwave therapy would restore the microcirculation and alleviate renal dysfunction in renovascular disease. Normal pigs and pigs subjected to 3 weeks of renal artery stenosis were treated with six sessions of low-energy shockwave (biweekly for 3 consecutive weeks) or left untreated. We assessed BP, urinary protein, stenotic renal blood flow, GFR, microvascular structure, and oxygenation in vivo 4 weeks after completion of treatment, and then, we assessed expression of angiogenic factors and mechanotransducers (focal adhesion kinase and β1-integrin) ex vivo A 3-week low-energy shockwave regimen attenuated renovascular hypertension, normalized stenotic kidney microvascular density and oxygenation, stabilized function, and alleviated fibrosis in pigs subjected to renal artery stenosis. These effects associated with elevated renal expression of angiogenic factors and mechanotransducers, particularly in proximal tubular cells. In additional pigs with prolonged (6 weeks) renal artery stenosis, shockwave therapy also decreased BP and improved GFR, microvascular density, and oxygenation in the stenotic kidney. This shockwave regimen did not cause detectable kidney injury in normal pigs. In conclusion, low-energy shockwave therapy improves stenotic kidney function, likely in part by mechanotransduction-mediated expression of angiogenic factors in proximal tubular cells, and it may ameliorate renovascular hypertension. Low-energy shockwave therapy may serve as a novel noninvasive intervention in the management of renovascular disease.