Background and objectives ESRD is accompanied by endothelial dysfunction. Because the endothelial glycocalyx (endothelial surface layer) governs interactions between flowing blood and the vessel wall, perturbation could influence disease progression. This study used a novel noninvasive sidestream-darkfield imaging method, which measures the accessibility of red blood cells to the endothelial surface layer in the microcirculation (perfused boundary region), to investigate whether renal function is associated with endothelial surface layer dimensions.Design, setting, participants, & measurements Perfused boundary region was measured in control participants (n=10), patients with ESRD (n=23), participants with normal kidney function after successful living donor kidney transplantation (n=12), and patients who developed interstitial fibrosis/tubular atrophy after kidney transplantation (n=10). In addition, the endothelial activation marker angiopoietin-2 and shed endothelial surface layer components syndecan-1 and soluble thrombomodulin were measured using ELISA.Results Compared with healthy controls (1.8260.16 mm), ESRD patients had a larger perfused boundary region (+0.23; 95% confidence interval, 0.46 to ,0.01; P,0.05), which signifies loss of endothelial surface layer dimensions. This large perfused boundary region was accompanied by higher circulating levels of syndecan-1 (+57.71; 95% confidence interval, 17.38 to 98.04; P,0.01) and soluble thrombomodulin (+12.88; 95% confidence interval, 0.29 to 25.46; P,0.001). After successful transplantation, the perfused boundary region was indistinguishable from healthy controls (without elevated levels of soluble thrombomodulin or syndecan-1). In contrast, however, patients who developed interstitial fibrosis and tubular atrophy showed a large perfused boundary region (+0.36; 95% confidence interval, 0.09 to 0.63; P,0.01) and higher levels of endothelial activation markers. In addition, a significant correlation between perfused boundary region, angiopoietin-2, and eGFR was observed (perfused boundary region versus GFR: Spearman's r=0.31; P,0.05; perfused boundary region versus angiopoietin-2: Spearman's r=20.33; P,0.05).Conclusion Reduced renal function is strongly associated with low endothelial surface layer dimensions. After successful kidney transplantation, the endothelial surface layer is indistinguishable from control.

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Ischemia/reperfusion injury (IRI) is a central phenomenon in kidney transplantation and AKI. Integrity of the renal peritubular capillary network is an important limiting factor in the recovery from IRI. facilitates vascular regeneration by functioning as an angiomiR and by modulating mobilization of hematopoietic stem/progenitor cells. We hypothesized that overexpression of miR-126 in the hematopoietic compartment could protect the kidney against IRI via preservation of microvascular integrity. Here, we demonstrate that hematopoietic overexpression of miR-126 increases neovascularization of subcutaneously implanted Matrigel plugs in mice. After renal IRI, mice overexpressing miR-126 displayed a marked decrease in urea levels, weight loss, fibrotic markers, and injury markers (such as kidney injury molecule-1 and neutrophil gelatinase-associated lipocalin). This protective effect was associated with a higher density of the peritubular capillary network in the corticomedullary junction and increased numbers of bone marrow-derived endothelial cells. Hematopoietic overexpression of miR-126 increased the number of circulating Lin 2 /Sca-1 + /cKit + hematopoietic stem and progenitor cells. Additionally, miR-126 overexpression attenuated expression of the chemokine receptor CXCR4 on Lin 2 /Sca-1 + /cKit + cells in the bone marrow and increased renal expression of its ligand stromal cell-derived factor 1, thus favoring mobilization of Lin 2 /Sca-1 + /cKit + cells toward the kidney. Taken together, these results suggest overexpression of miR-126 in the hematopoietic compartment is associated with stromal cell-derived factor 1/CXCR4-dependent vasculogenic progenitor cell mobilization and promotes vascular integrity and supports recovery of the kidney after IRI.

Simultaneous pancreas-kidney transplantation (SPK)is an advanced treatment option for type 1 diabetes mellitus (DM) patients with microvascular disease including nephropathy. Sidestreamdarkfield (SDF) imaging has emerged as a noninvasive tool to visualize the human microcirculation. This study assessed the effect of SPK in diabetic nephropathy (DN) patients on microvascular alterations using SDF and correlated this with markers for endothelial dysfunction. Microvascular morphology was visualized using SDF of the oral mucosa in DN (n = 26) and SPK patients (n = 38), healthy controls (n = 20), DM1 patients (n = 15, DM ≥ 40 mL/min) and DN patients with a kidney transplant (KTx, n = 15). Furthermore, 21 DN patients were studied longitudinally up to 12 months after SPK. Circulating levels of angiopoietin-1 (Ang-1), angiopoietin-2 (Ang-2) and soluble thrombomodulin (sTM) were measured using ELISA. Capillary tortuosity in the DN (1.83 ± 0.42) and DM ≥ 40 mL/min (1.55 ± 0.1) group was increased and showed reversal after SPK (1.31 ± 0.3, p < 0.001), but not after KTx (1.64 ± 0.1). sTM levels were increased in DN patients and reduced in SPK and KTx recipients (p < 0.05), while the Ang-2/Ang-1 ratio was normalized after SPK and not after KTx alone (from 0.16 ± 0.04 to 0.08 ± 0.02, p < 0.05). Interestingly, in the longitudinal study, reversal of capillary tortuosity and decrease in Ang-2/Ang-1 ratio and sTM was observed within 12 months after SPK. SPK is effective in reversing the systemic microvascular structural abnormalities in DN patients in the first year after transplantation.Key words: Endothelial dysfunction, microvascular injury, simultaneous pancreas-kidney transplantation, type 1 diabetes mellitus Abbreviations:Ang-1, angiopoietin-1; Ang-2, angiopoietin-2; AUC, area under the curve; BMI, body mass index; CAD, coronary artery disease; DM, diabetes mellitus type 1; DN, diabetic nephropathy; ELISA, enzyme-linked immuno sorbent assay; eGFR, estimated glomerular filtration rate; KTx, kidney transplantation; MDRD, modification of diet in renal disease; MMF, mycophenolatemofetil; SDF, sidestreamdarkfield; SEM, standard error of the mean; SPK, simultaneous pancreas-kidney transplantation; SPKFU, simultaneous pancreas-kidney transplantation follow-up; sTM, soluble thrombomodulin.

Background Immune checkpoint inhibitors, approved for the treatment of various types of cancer, are known to cause a unique spectrum of side effects, including acute kidney injury (AKI). The aim of this study was to describe the incidence, risk factors, renal outcomes, and mortality of AKI in patients receiving checkpoint inhibitors. Methods Patients receiving checkpoint inhibitors between January 2013 and May 2020 at the University Medical Center Utrecht, the Netherlands, were identified using the Utrecht Patient Oriented Database. AKI was defined as an increase in serum creatinine of ≥1.5 times the baseline value, based on the Kidney Disease: Improving Global Outcomes criteria. Cox proportional hazard regression analysis was used to assess risk factors for AKI and to evaluate the relationship between AKI and mortality. Persistent renal dysfunction was diagnosed in AKI patients with a final serum creatinine measurement of >1.3 times the baseline value. Results Among 676 patients receiving checkpoint inhibitors, the overall incidence of AKI was 14.2%. Baseline variables independently associated with AKI were a gynecologic malignancy, monotherapy with ipilimumab, and the use of a diuretic, angiotensin-converting enzyme inhibitor or angiotensin-receptor blocker, or proton pump inhibitor at baseline. AKI was checkpoint inhibitor-associated in one third of all patients with AKI. Checkpoint inhibitor-associated AKI was mostly low-grade, occurred a median of 15 weeks after checkpoint inhibitor initiation, and resulted in persistent renal dysfunction in approximately 40% of the patients. Patients with all-cause AKI had a twofold increased mortality risk, but checkpoint inhibitor-associated AKI was not associated with increased mortality. Conclusions In this study, patients receiving checkpoint inhibitors frequently developed AKI due to various etiologies. AKI directly related to the effect of checkpoint inhibitor toxicity did not increase mortality. However, AKI not related to the effect of checkpoint inhibitor toxicity was associated with increased mortality.