Renal Microvascular Disease Predicts Renal Function in Diabetes

Microvascular Dysfunction as a Systemic Disease: A Review of the Evidence

Microvascular dysfunction describes a varied set of conditions that includes vessel destruction, abnormal vasoreactivity, in situ thrombosis, and fibrosis, which ultimately results in tissue damage and progressive organ failure. Microvascular dysfunction has a wide array of clinical presentations, ranging from ischemic heart disease to renal failure, stroke, blindness, pulmonary arterial hypertension, and dementia. An intriguing unifying hypothesis suggests that microvascular dysfunction of specific organs is an expression of a systemic illness that worsens with age and is accelerated by vascular risk factors. Studying relationships across a spectrum of microvascular diseases affecting the brain, retina, kidney, lung, and heart may uncover shared pathologic mechanisms that could inform novel treatment strategies. We review the evidence that supports the notion that microvascular dysfunction represents a global pathologic process. Our focus is on studies reporting concomitant microvascular dysfunction of the heart with that of the brain, kidney, retina, and lung.

The Role of Vascular Lesions in Diabetes Across a Spectrum of Clinical Kidney Disease

Introduction

The clinical-histologic correlation in diabetic nephropathy is not completely known.

Methods

We analyzed nephrectomy specimens from 90 patients with diabetes and diverse degrees of proteinuria and glomerular filtration rate (GFR).

Results

Thirty-six (40%) subjects had normoalbuminuria, 33 (37%) microalbuminuria, and 21 (23%) non-nephrotic proteinuria. Mean estimated GFR (eGFR) was 65±23 (40% <60 ml/min per 1.73 m²). About 170 glomeruli per patient were analyzed, and all samples included vascular tissue. Six subjects (7%) were classified in diabetic nephropathy class I, 61 (68%) in class II-a, 13 (14%) in class II-b, 9 (10%) class III, and 1 (1%) in class IV. Eighty percent to 90% of those with normoalbuminuria or microalbuminuria were classified in class II-a or II-b and <10% in class III; 52% of those with proteinuria were in class II-a, 15% in class II-b, and 19% in class III. Nodular sclerosis (57%) and mesangial expansion (15%) were more frequent in cases with proteinuria than in normoalbuminuria (28% and 8%; P = 0.028 and 0.017). About 20% to 30% of all cases, regardless the level of albuminuria or proteinuria or the histologic class had tubular atrophy, interstitial fibrosis, or inflammation in >10% to 20% of the sample. Moderate hyalinosis and arteriolar sclerosis were observed in 80% to 100% of cases with normoalbuminuria, microalbuminuria, proteinuria, as well as in class I, II, or III.

Conclusions

Weak correspondence between analytical parameters and kidney histology was found. Thus, disease may progress undetected from the early clinical stages of the disease. Finally, vascular damage was a very common finding, which highlights the role of ischemic intrarenal disease in diabetes.

Recovery of Renal Function following Kidney-Specific VEGF Therapy in Experimental Renovascular Disease

BACKGROUND

Chronic renovascular disease (RVD) can lead to a progressive loss of renal function, and current treatments are inefficient. We designed a fusion of vascular endothelial growth factor (VEGF) conjugated to an elastin-like polypeptide (ELP) carrier protein with an N-terminal kidney-targeting peptide (KTP). We tested the hypothesis that KTP-ELP-VEGF therapy will effectively recover renal function with an improved targeting profile. Further, we aimed to elucidate potential mechanisms driving renal recovery.

METHODS

Unilateral RVD was induced in 14 pigs. Six weeks later, renal blood flow (RBF) and glomerular filtration rate (GFR) were quantified by multidetector CT imaging. Pigs then received a single intrarenal injection of KTP-ELP-VEGF or vehicle. CT quantification of renal hemodynamics was repeated 4 weeks later, and then pigs were euthanized. Ex vivo renal microvascular (MV) density and media-to-lumen ratio, macrophage infiltration, and fibrosis were quantified. In parallel, THP-1 human monocytes were differentiated into naïve macrophages (M0) or inflammatory macrophages (M1) and incubated with VEGF, KTP-ELP, KTP-ELP-VEGF, or control media. The mRNA expression of macrophage polarization and angiogenic markers was quantified (qPCR).

RESULTS

Intrarenal KTP-ELP-VEGF improved RBF, GFR, and MV density and attenuated MV media-to-lumen ratio and renal fibrosis compared to placebo, accompanied by augmented renal M2 macrophages. In vitro, exposure to VEGF/KTP-ELP-VEGF shifted M0 macrophages to a proangiogenic M2 phenotype while M1s were nonresponsive to VEGF treatment.

CONCLUSIONS

Our results support the efficacy of a new renal-specific biologic construct in recovering renal function and suggest that VEGF may directly influence macrophage phenotype as a possible mechanism to improve MV integrity and function in the stenotic kidney.

The Value of d-Dimer Level in Predicting Contrast-Induced Acute Kidney Injury in Patients With Acute ST-Segment Elevation Myocardial Infarction After PCI

Contrast-induced acute kidney injury (CI-AKI) is a serious complication of percutaneous coronary intervention (PCI) in patients with acute ST-segment elevation myocardial infarction (STEMI). Early identification of high-risk patients has an essential role in preventing CI-AKI. This study was designed to evaluate the predictive value of d-dimer, a marker of thrombosis and hypercoagulable state, for CI-AKI and prognosis in patients with STEMI. We included 400 patients with STEMI who underwent PCI. The patients were subdivided into 4 groups according to d-dimer level using the 4-quantile method. Contrast-induced acute kidney injury occurred in 66 (16.5%) patients. The incidence of CI-AKI in the highest quartile of the d-dimer groups (29.0%) was higher than that in the other 3 groups. Multivariable logistic regression showed that a low d-dimer level was significantly associated with a decreased risk of CI-AKI independent of confounding factors, with an odds ratio (OR) of 0.487 (95% CI: 0.178-0.931, P = 0.041) for those in the first quartile compared with those in the highest quartile. Age (OR: 1.047, 95% CI: 1.003-1.092), diabetes mellitus (OR: 5.896, 95% CI: 2.496-13.927), anemia (OR: 3.488, 95% CI: 1.308-9.306), and total bilirubin (OR: 0.946, 95% CI: 0.904-0.992) were independent predictors of CI-AKI. The incidence of major adverse cardiovascular and cerebral events and all-cause mortality within 30 days, 6 months, and 1 year after PCI in the highest quartile of the d-dimer groups were higher than those in the other 3 groups. In conclusion, increasing d-dimer levels were independently associated with the incidence of CI-AKI and adverse outcomes in patients with STEMI after PCI.

Targeted VEGF (Vascular Endothelial Growth Factor) Therapy Induces Long-Term Renal Recovery in Chronic Kidney Disease via Macrophage Polarization

Chronic kidney disease (CKD) universally associates with renal microvascular rarefaction and inflammation, but whether a link exists between these 2 processes is unclear. We designed a therapeutic construct of VEGF (vascular endothelial growth factor) fused to an ELP (elastin-like polypeptide) carrier and show that it improves renal function in experimental renovascular disease. We test the hypothesis that ELP-VEGF therapy will improve CKD, and that recovery will be driven by decreasing microvascular rarefaction partly via modulation of macrophage phenotype and inflammation. CKD was induced in 14 pigs, which were observed for 14 weeks. At 6 weeks, renal blood flow and filtration were quantified using multidetector computed tomography, and then pigs received single intrarenal ELP-VEGF or placebo (n=7 each). Renal function was quantified again 4 and 8 weeks later. Pigs were euthanized and renal microvascular density, angiogenic and inflammatory markers, fibrosis, macrophage infiltration, and phenotype were quantified. Loss of renal hemodynamics in CKD was progressively recovered by ELP-VEGF therapy, accompanied by improved renal microvascular density, fibrosis, and expression of inflammatory mediators. Although renal macrophage infiltration was similar in both CKD groups, ELP-VEGF therapy distinctly shifted their phenotype from proinflammatory M1 to VEGF-expressing M2. Our study unravels potential mechanisms and feasibility of a new strategy to offset progression of CKD using drug-delivery technologies. The results indicate that renal recovery after ELP-VEGF therapy was largely driven by modulation of renal macrophages toward VEGF-expressing M2 phenotype, restoring VEGF signaling and sustaining improvement of renal function and microvascular integrity in CKD.

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.

Type 1 and type 2 diabetes mellitus and risk of acute kidney injury after coronary artery bypass grafting

BACKGROUND

Our objective was to investigate the association between type 1 diabetes mellitus (T1DM), type 2 diabetes mellitus (T2DM), and acute kidney injury (AKI) in patients who underwent coronary artery bypass grafting (CABG).

METHODS

We included all patients (n = 36,106) from the SWEDEHEART register who underwent primary isolated CABG in Sweden from 2003 to 2013. Information on type of diabetes was retrieved from the Swedish National Diabetes Register. Acute kidney injury was defined as an absolute increase by 0.3 mg/dL (26 μmol/L) or a relative increase by at least 50% in postoperative serum creatinine compared with preoperative levels. Odds ratios with 95% CIs for AKI in patients with T1DM and T2DM were compared with those patients without diabetes using logistic regression.

RESULTS

In total, there were 457 patients (1.3%) with T1DM and 5124 (14%) with T2DM. Among patients with T1DM and T2DM, 145 (32%) and 1037 (20%), respectively, developed AKI, compared with 4017 (13%) in patients without diabetes. The adjusted odds ratio for AKI was 4.89 (95% CI 3.82-6.25) in patients with T1DM and 1.27 (95% CI 1.16-1.40) in patients with T2DM, in comparison with patients without diabetes.

CONCLUSIONS

Both T1DM and T2DM were associated with an increased risk of AKI after CABG. The risk was markedly higher in patients with T1DM than in those with T2DM and was independent of preoperative renal function.

Early stage of vascular disease and diabetic kidney disease: an under-recognized entity

Early stage of vascular disease and diabetic kidney disease (DKD stages 1 and 2) has been under-recognized, under common practice worldwide. The lack of sensitive diagnostic marker leads to late diagnosis and a progression of underlying vascular disease associated with chronic renal ischemia, which eventually intensifies the magnitude of DKD damage. Treatment at this late stage fails to correct the renal ischemia, or restore renal function, due to the altered vascular homeostasis associated with an impaired nitric oxide production. In contrast to the above information, early recognition of vascular disease and DKD with sensitive diagnostic markers would be able to implement an effective prevention of progression of vascular disease and DKD. Treatment at early stage under environment favorable for adequate vascular homeostasis is able to correct the renal ischemia and improve the renal function.

Intraoperative hypotension - a neglected causative factor in hospital-acquired acute kidney injury; a Mayo Clinic Health System experience revisited

Acute kidney injury (AKI) is a relatively common complication of cardiothoracic surgery and has both short- and long-term survival implications, even when AKI does not progress to severe renal failure. Given that currently, there are no active effective treatments for AKI, other than renal replacement therapy when indicated, the focus of clinicians ought to be on prevention and risk factor management. In the AKI-surgery literature, there exists this general consensus that intraoperative hypotension (IH) following hypotensive anesthesia (HA) or controlled hypotension (CH) in the operating room has no significant short-term and long-term impacts on renal function. In this review, we examine the basis for this consensus, exposing some of the flaws of the clinical study data upon which this prevailing consensus is based. We then describe our experiences in the last decade at the Mayo Clinic Health System, Eau Claire, in Northwestern Wisconsin, USA, with two selected case presentations to highlight the contribution of IH as a potent yet preventable cause of post-operative AKI. We further highlight the causative although neglected role of IH in precipitating postoperative AKI in chronic kidney disease (CKD) patients. We show additional risk factors associated with this syndrome and further make a strong case for the elimination of IH as an achievable mechanism to reduce overall, the incidence of hospital acquired AKI. We finally posit that as the old saying goes, prevention is indeed better than cure.

Preliminary study of renal hemodynamic alteration in early childhood diabetes mellitus

Renal hemodynamic study was performed in eight patients associated with type 1, early childhood diabetes mellitus (DM) and seven patients associated with type 2, early childhood DM. The results in both types of DM revealed a significant reduction in peritubular capillary flow and a high value of glomerular filtration rate (GFR) in the presence of reduced renal perfusion characteristic of glomerular hyperfiltration. These findings imply that renal ischemia has already developed in both types of early stage childhood DM and GFR is overestimated in DM, which may mislead to improper interpretation of renal function.