Joris I. Rotmans

Sirolimus-eluting stents to abolish intimal hyperplasia and improve flow in porcine arteriovenous grafts: A 4-week follow-up study

Background—The patency of arteriovenous (AV) expanded polytetrafluoroethylene (ePTFE) hemodialysis grafts is severely compromised by intimal hyperplasia (IH) at the venous anastomosis and in the venous outflow tract. We addressed the potential of primary placement of a sirolimus-eluting stent (SES) in a validated porcine model. Methods and Results—In 25 pigs, ePTFE AV grafts were created bilaterally between the carotid artery and the jugular vein, whereupon a self-expandable nitinol stent (14 SESs and 11 bare-metal stents) was implanted over the venous anastomosis in 1 of the 2 grafts. After exclusion of technical failures and 1 unilateral occlusion, 16 pigs (9 SESs and 7 bare-metal stents) were included for further analysis. After 28 days, we measured graft flow and performed quantitative angiography. The pigs were then euthanized, and grafts with adjacent vessels were excised for histological analysis. Minimal luminal diameter was substantially larger in the SES group compared with unstented controls (5.9±0.2 versus 3.8±0.4 mm, respectively, P=0.01), which was accompanied by more prominent graft flow (SES, 1360±89 mL/min versus unstented, 861±83 mL/min, P=0.05). IH at the venous anastomosis was 77% less in the SES group compared with unstented controls (0.44±0.05 versus 1.92±0.5 mm2, respectively, P=0.01), whereas IH increased markedly when bare-metal stents were used (5.7±1.4 mm2, P=0.05). Conclusions—SESs in the venous outflow of AV grafts significantly reduce IH and increase vessel diameter and graft flow compared with unstented grafts. These findings suggest that SESs have the potential to improve primary patency of AV grafts in hemodialysis patients.

Arteriovenous access failure: more than just intimal hyperplasia?

Haemodialysis vascular access patency is severely compromised by fistula non-maturation and access stenosis. Intimal hyperplasia (IH) is considered the culprit lesion in failed fistulas, resulting in luminal narrowing and stenosis. This review focuses on the biology and pathophysiology of fistula failure and highlights not only the classically associated IH but also some relatively neglected but potentially important contributors such as inadequate outward remodelling. In addition, the complex process and fragile balance of successful fistula maturation might be partially hindered by pre-existent chronic kidney disease-mediated vasculopathy. Further unravelling the (patho)physiology of outward remodelling and IH could contribute to novel therapies and enhance fistula patency.

Effects of CRP infusion on endothelial function and coagulation in normocholesterolemic and hypercholesterolemic subjects

C-reactive protein (CRP) has been suggested to exert direct adverse effects on the vasculature in experimental setups, including endothelial dysfunction and proinflammatory changes. Here, we assessed the consequences of 1.25 mg/kg highly purified recombinant human CRP, administered as an intravenous bolus, in six patients with familial hypercholesterolemia (FH) and six normocholesterolemic subjects. Endothelium-dependent and -independent vasoreactivity to serotonin and nitroprusside, respectively, were assessed using venous occlusion plethysmography before and after CRP infusion. For biochemical analyses, blood was drawn at different time points. At baseline, FH patients showed blunted endothelium-dependent vasodilation (maximum, 89.2 ± 30.0% vs. 117.7 ± 13.1% in normolipidemic subjects; P = 0.037). Procoagulant activity was also higher in FH patients, illustrated by increased prothrombin fragment 1+2 (F1+2) levels (P = 0.030) and plasminogen activator inhibitor type-1 (PAI-1) activity (P = 0.016). Upon CRP challenge, endothelium-dependent vasodilator capacity further deteriorated in FH patients (P = 0.029), whereas no change in vascular reactivity was observed in normolipidemic subjects. Additionally, coagulation activation was augmented in FH patients compared with normolipidemic subjects (P = 0.009 for F1+2 levels; P = 0.018 and P = 0.003 for PAI-1 antigen and activity, respectively). No difference in inflammatory responses was observed between groups. In hypercholesterolemic patients, CRP aggravates endothelial dysfunction and also evokes augmented procoagulant responses. These findings suggest that particularly in hypercholesterolemia, CRP-lowering strategies should be considered in addition to LDL reduction.

Citation frequency: A biased measure of research impact significantly influenced by the geographical origin of research articles

AbstractContext. The use of citation frequency and impact factor as measures of research quality and journal prestige is being criticized. Citation frequency is augmented by self-citation and for most journals the majority of citations originate from a minority of papers. We hypothesized that citation frequency is also associated with the geographical origin of the research publication. Objective. We determined whether citations originate more frequently from institutes that are located in the same country as the authors of the cited publication than would be expected by chance. Design. We screened citations referring to 1200 cardiovascular publications in the 7 years following their publication. For the 1200 citation recipient publications we documented the country where the research originated (9 countries/regions) and the total number of received citations. For a selection of 8864 citation donor papers we registered the country/region where the citing paper originated. Results. Self-citation was common in cardiovascular journals (n = 1534, 17.8%). After exclusion of self-citation, however, the number of citations that originated from the same country as the author of the citation recipient was found to be on average 31.6% higher than would be expected by chance (p<0.01 for all countries/regions). In absolute numbers, nation oriented citation bias was most pronounced in the USA, the country with the largest research output (p<0.001). Conclusion. Citation frequency was significantly augmented by nation oriented citation bias. This nation oriented citation behaviour seems to mainly influence the cumulative citation number for papers originating from the countries with a larger research output.

Erythropoietin doping in cycling: lack of evidence for efficacy and a negative risk–benefit

Imagine a medicine that is expected to have very limited effects based upon knowledge of its pharmacology and (patho)physiology and that is studied in the wrong population, with low‐quality studies that use a surrogate end‐point that relates to the clinical end‐point in a partial manner at most. Such a medicine would surely not be recommended. The use of recombinant human erythropoietin (rHuEPO) to enhance performance in cycling is very common. A qualitative systematic review of the available literature was performed to examine the evidence for the ergogenic properties of this drug, which is normally used to treat anaemia in chronic renal failure patients. The results of this literature search show that there is no scientific basis from which to conclude that rHuEPO has performance‐enhancing properties in elite cyclists. The reported studies have many shortcomings regarding translation of the results to professional cycling endurance performance. Additionally, the possibly harmful side‐effects have not been adequately researched for this population but appear to be worrying, at least. The use of rHuEPO in cycling is rife but scientifically unsupported by evidence, and its use in sports is medical malpractice. What its use would have been, if the involved team physicians had been trained in clinical pharmacology and had investigated this properly, remains a matter of speculation. A single well‐controlled trial in athletes in real‐life circumstances would give a better indication of the real advantages and risk factors of rHuEPO use, but it would be an oversimplification to suggest that this would eradicate its use.

Circulating MicroRNAs Associate With Diabetic Nephropathy and Systemic Microvascular Damage and Normalize After Simultaneous Pancreas–Kidney Transplantation

Because microvascular disease is one of the most important drivers of diabetic complications, early monitoring of microvascular integrity may be of clinical value. By assessing profiles of circulating microRNAs (miRNAs), known regulators of microvascular pathophysiology, in healthy controls and diabetic nephropathy (DN) patients before and after simultaneous pancreas–kidney transplantation (SPK), we aimed to identify differentially expressed miRNAs that associate with microvascular impairment. Following a pilot study, we selected 13 candidate miRNAs and determined their circulating levels in DN (n = 21), SPK‐patients (n = 37), healthy controls (n = 19), type 1 diabetes mellitus patients (n = 15) and DN patients with a kidney transplant (n = 15). For validation of selected miRNAs, 14 DN patients were studied longitudinally up to 12 months after SPK. We demonstrated a direct association of miR‐25, ‐27a, ‐126, ‐130b, ‐132, ‐152, ‐181a, ‐223, ‐320, ‐326, ‐340, ‐574‐3p and ‐660 with DN. Of those, miR‐25, ‐27a, ‐130b, ‐132, ‐152, ‐320, ‐326, ‐340, ‐574‐3p and ‐660 normalized after SPK. Importantly, circulating levels of some of these miRNAs tightly associate with microvascular impairment as they relate to aberrant capillary tortuosity, angiopoietin‐2/angiopoietin‐1 ratios, circulating levels of soluble‐thrombomodulin and insulin‐like growth factor. Taken together, circulating miRNA profiles associate with DN and systemic microvascular damage, and might serve to identify individuals at risk of experiencing microvascular complications, as well as give insight into underlying pathologies.

Renal ischemia-reperfusion induces a dysbalance of angiopoietins, accompanied by proliferation of pericytes and fibrosis

Endothelial cells (ECs) are highly susceptible to hypoxia and easily affected upon ischemia-reperfusion (I/R) during renal transplantation. Pericytes and angiopoeitins play important role in modulating EC function. In the present study, we investigate the effect of renal I/R on the dynamics of angiopoietin expression and its association with pericytes and fibrosis development. Male Lewis rats were subjected to unilateral renal ischemia for 45 min followed by removal of the contralateral kidney. Rats were killed at different time points after reperfusion. Endothelial integrity (RECA-1), pericytes [platelet-derived growth factor receptor-β (PDGFR-β)], angiopoietin-2 (Ang-2)/angiopoietin-1 (Ang-1) expression, and interstitial collagen deposition (Sirius red and α-smooth muscle actin) were assessed using immunohistochemistry and RT-PCR. Our study shows an increase in protein expression of Ang-2 starting at 5 h and remaining elevated up to 72 h, with a consequently higher Ang-2/Ang-1 ratio after renal I/R (P < 0.05 at 48 h). This was accompanied by an increase in protein expression of the pericytic marker PDGFR-β and a loss of ECs (both at 72 h after I/R, P < 0.05). Nine weeks after I/R, when renal function was restored, we observed normalization of the Ang-2/Ang-1 ratio and PDGFR-β expression and increase in cortical ECs, which was accompanied by fibrosis. Renal I/R induces a dysbalance of Ang-2/Ang-1 accompanied by proliferation of pericytes, EC loss, and development of fibrosis. The Ang-2/Ang-1 balance was reversed to baseline at 9 wk after renal I/R, which coincided with restoration of cortical ECs and pericytes. Our findings suggest that angiopoietins and pericytes play an important role in renal microvascular remodeling and development of fibrosis.

Vascular remodeling and intimal hyperplasia in a novel murine model of arteriovenous fistula failure

OBJECTIVE The arteriovenous fistula (AVF) still suffers from a high number of failures caused by insufficient outward remodeling and intimal hyperplasia (IH) formation from which the exact mechanism is largely unknown. A suitable animal model is of vital importance in the unraveling of the underlying pathophysiology. However, current murine models of AVF failure do not incorporate the surgical configuration that is commonly used in humans. Because the hemodynamic profile is one of the key determinants that play a role in vascular remodeling in the AVF, it is preferable to use this same configuration in an animal model. Here we describe a novel murine model of AVF failure in which the configuration (end-to-side) is similar to what is most frequently performed in humans. METHODS An AVF was created in 45 C57BL/6 mice by anastomosing the end of a branch of the external jugular vein to the side of the common carotid artery with interrupted sutures. The AVFs were harvested and analyzed histologically at days 7, 14, and 28. Identical veins of unoperated-on mice served as controls. Intravenous near-infrared fluorescent fluorophores were used to assess the patency of the fistula. RESULTS The patency rates at days 7, 14, and 28 days were 88%, 90%, and 50%, respectively. The mean circumference increased up to day 14, with a maximum 1.4-fold increase at day 7 compared with the control group (1.82 ± 0.7 vs 1.33 ± 0.3 mm; P = .443). Between days 14 and 28, the circumference remained constant (2.36 ± 0.2 vs 2.45 ± 0.2 mm; P = .996). At 7 days after surgery, the intimal area consisted mainly of an acellular layer that was structurally analogous to a focal adherent thrombus. Starting at 14 days after surgery, venous IH increased significantly compared with the unoperated-on group (14 days: 115,090 ± 22,594 μm(2), 28 days: 234,619 ± 47,828 μm(2), unoperated group: 2368 ± 1056 μm(2); P = .001 and P < .001, respectively) and was mainly composed of cells positive for α-smooth muscle actin. We observed leukocytes in the adventitial side of the vein at all time points. CONCLUSIONS Our novel murine AVF model, which incorporates a clinically relevant configuration of the anastomosis, displays similar features that are characteristic of failing human AVFs. Moreover, our findings suggest that coagulation and inflammation could both potentially play an important role in the formation of IH and subsequent AVF failure. Near-infrared fluoroscopy was a suitable alternative for conventional imaging techniques. This murine AVF-model is a valuable addition to the AVF animal model arsenal.

Human polyomavirus 9 infection in kidney transplant patients.

This virus is frequently found within the first year after transplantation and in association with BK polyomavirus infection.

Microvascular Damage in Type 1 Diabetic Patients Is Reversed in the First Year After Simultaneous Pancreas–Kidney Transplantation

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.