Walther H. Boer

Progenitor cells and vascular function are impaired in patients with chronic kidney disease

BACKGROUND Endothelial dysfunction contributes to accelerated atherosclerosis in chronic kidney disease (CKD). Bone marrow-derived endothelial progenitor cells (EPC) constitute an endogenous vascular repair system protecting against atherosclerosis. Smooth muscle progenitor cells (SPC) may stimulate atherosclerosis development. We hypothesized that an imbalance in EPC and SPC occurs in CKD, which may contribute to the increased cardiovascular disease (CVD) risk. METHODS EPC and SPC outgrowth from mononuclear cells (MNC), EPC migratory function and circulating CD34(+)KDR(+)-EPC were measured in 49 patients with varying degrees of CKD on regular therapy and 33 healthy volunteers. Renal function, CKD cause, CVD history and endothelial dysfunction parameters were determined as factors of influence on progenitor cells. RESULTS Patients had reduced EPC outgrowth compared to controls [9 (2-22) vs 12 (1-38) cells/10(3) MNC, P = 0.026], independent of CKD cause and degree, whereas SPC outgrowth levels were higher in patients with more impaired kidney function (r = -0.397, P = 0.008). Patients had lower CD34(+)KDR(+)-EPC compared to controls [9 (0-52) vs 19 (4-110) cells/10(5) granulocytes, P = 0.004]. CVD history and increased endothelial dysfunction markers were related to lower EPC levels. Progenitor cell outgrowth was shifted towards SPC with progression of endothelial damage. Reduction in EPC could not be attributed to decreases in progenitor cell-mobilizing factors SDF-1 alpha and VEGF as levels increased with progressive kidney and endothelial dysfunction, while EPC remained low. CONCLUSIONS Our data suggest that, already in mild CKD, EPC-mediated endogenous vascular regeneration is impaired, while SPC levels increase with declining kidney function.

Lithium clearance during variations in sodium intake in man: effects of sodium restriction and amiloride

Abstract. Assuming that lithium is exclusively reabsorbed in the proximal tubules in proportion to sodium and water, the lithium clearance (CLi) has been advanced as an index of filtrate delivery from the proximal tubules. However, studies in the rat and dog showed that CLi drops sharply at fractional sodium excretion rates (FELi) below 0·4% due to lithium reabsorption in the amiloride‐sensitive segment of the distal nephron, which disqualified CLi as an index of distal filtrate delivery during sodium restriction in these animals. In order to investigate whether this phenomenon also occurs in man, we studied CLi in 103 normal subjects at varying sodium intakes, including marked sodium restriction. In contrast to findings in the rat and dog, no sharp drop but a gradual fall in CLi was observed at decreasing FENa values down to 0·02%. Maximum urine flow, another index of filtrate delivery from the proximal tubules, decreased proportionally, suggesting that the fall in CLi was due to enhanced proximal and not distal lithium reabsorption. Amiloride (15 mg p.o.) did not affect CLi despite unequivocal effects in the distal nephron in eight normal subjects at a mean FENa of 0·1%. In conclusion, a low FENa due to severe sodium restriction in man is not accompanied by strongly enhanced distal lithium reabsorption sensitive to amiloride. Thus, in contrast to the rat and dog, a low FENa forms no objection to use CLi as an index of sodium and filtrate delivery from the proximal tubules in humans.

Variant of Bartter’s Syndrome with a Distal Tubular Rather than Loop of Henle Defect

A 19-year-old normotensive patient had all of the clinical features of Bartter’s syndrome: hypokalemia, elevated renin and aldosterone levels and increased excretion of prostaglandin E. In contrast to

Sodium profiling, but not cool dialysate, increases the absolute plasma refill rate during hemodialysis.

Intradialytic hypotension is often caused by a discrepancy between ultrafiltration and plasma refilling. Increasing the plasma refill rate could therefore reduce intradialytic hypotension. We used a recently developed method to measure the effect of cool dialysate and sodium (Na) profiling on refill during hemodialysis (HD). Using a Gambro AK200 with blood volume (BV) sensor plus computer-guided external pump, a high ultrafiltration rate quickly induced a preset BV reduction. A software feedback mechanism subsequently adjusted the ultrafiltration rate continuously to maintain BV between very narrow preset boundaries. The continuously changing, software-generated ultrafiltration rate then quantitatively equalled refill. Absolute plasma refill rate was measured in six stable patients without intradialytic hypotension, undergoing HD without intervention, with cool dialysate (1°C below core temperature), and with Na profiling (gradually declining from 150 to 140 mmol/l). Baseline refill rate was 20.1 ± 4.0 ml/min (mean ± SD). Although cool dialysate did not affect refill (22.2 ± 4.1 ml/min, p = 0.27 vs. baseline), Na profiling induced a significant improvement (26.8 ± 3.7 ml/min, p = 0.006 vs. baseline). Using our method to measure absolute plasma refill rate during HD, we demonstrated that Na profiling indeed improves the plasma refill rate. A potential effect of cool dialysate could not be established.

Removal of urea in a wearable dialysis device: a reappraisal of electro-oxidation

A major challenge for a wearable dialysis device is removal of urea, as urea is difficult to adsorb while daily production is very high. Electro-oxidation (EO) seems attractive because electrodes are durable, small, and inexpensive. We studied the efficacy of urea oxidation, generation of chlorine by-products, and their removal by activated carbon (AC). EO units were designed. Three electrode materials (platinum, ruthenium oxide, and graphite) were compared in single pass experiments using urea in saline solution. Chlorine removal by AC in series with EO by graphite electrodes was tested. Finally, urea-spiked bovine blood was dialyzed and dialysate was recirculated in a dialysate circuit with AC in series with an EO unit containing graphite electrodes. Platinum electrodes degraded more urea (21 ± 2 mmol/h) than ruthenium oxide (13 ± 2 mmol/h) or graphite electrodes (13 ± 1 mmol/h). Chlorine generation was much lower with graphite (13 ± 4 mg/h) than with platinum (231 ± 22 mg/h) or ruthenium oxide electrodes (129 ± 12 mg/h). Platinum and ruthenium oxide electrodes released platinum (4.1 [3.9-8.1] umol/h) and ruthenium (83 [77-107] nmol/h), respectively. AC potently reduced dialysate chlorine levels to < 0.10 mg/L. Urea was removed from blood by EO at constant rate (9.5 ± 1.0 mmol/h). EO by graphite electrodes combined with AC shows promising urea removal and chlorine release complying with Association for the Advancement of Medical Instrumentation standards, and may be worth further exploring for dialysate regeneration in a wearable system.

Solid renal tumours of collecting duct origin in patients on chronic lithium therapy

Background Lithium (Li) is an invaluable drug for the treatment of bipolar disorder. Long-term Li use is associated with renal complications including the formation of uncomplicated renal cysts caused by proliferation and expansion of collecting duct (CD) cells. We report six patients with complicated renal cysts in the context of Li nephropathy. Methods Over a time period of 15 years, we have identified six patients with one or more solid renal tumours in our population of approximately 50 patients with chronic Li nephropathy. In this study we describe the clinical and pathological characteristics of these Li-related tumours. Results All patients were on Li therapy for over 10 years and suffered from varying degrees of Li nephropathy. The tumours were all of CD origin and comprised both oncocytomas and collecting duct carcinomas. The CD carcinomas differed from the very rare “classical” CD cell carcinomas in histological appearance, multifocal presentation and non-aggressive clinical behaviour Conclusions The increased incidence of CD derived tumours and atypical presentation of CD cell carcinomas in patients with chronic Li nephropathy suggests that Li predisposes to the development of these tumours. We hypothesize that prolonged stimulation of CD cell proliferation and expansion by Li not only causes cyst formation, but can eventually induce the formation of adenomas and carcinomas. Increased awareness of a possible relationship between chronic Li therapy and renal neoplasms, will enhance the knowledge on epidemiology, clinical behavior and optimal therapy for the Li-related renal neoplasms.

Renal haemodynamics and sodium handling after hyperoncotic albumin infusion in sodium‐restricted normal man

Abstract. The effect of plasma volume expansion with hyperoncotic albumin (HA) on renal haemodynamics and segmental tubular sodium (Na) handling was studied in eight water‐loaded normal men. Clearance studies were performed before, during and after a 60‐min infusion of 300 ml 20% HA. Sodium intake was restricted (20 mmol day‐1) to mimic clinical conditions of relative hypovolaemia in which HA is often applied. Plasma volume rose by 740±160 ml after infusion and colloid oncotic pressure (COP) by 3·6±1·3 mm Hg. No natriuresis was induced. In fact, Na output fell from 43±29 to 28±25 μmol min‐1 during infusion, returning to 41±36 μmol min‐1 afterwards. Corresponding clearances of inulin were 121±19, 110±19 and 117±21 ml min‐1 and of p‐aminohippurate (CPAH) 602±87, 637±100 and 751±148 ml min‐1. Fractional reabsorption of sodium in the proximal tubules (FPRNa), assessed from maximal free‐water and lithium clearance, rose consistently during infusion but diverging patterns (further rise, no change or fall) were seen afterwards. Fractional distal reabsorption remained unchanged both during and after HA infusion. Changes in plasma volume and CPAH in the post‐infusion period were correlated. These results indicate that, despite considerable plasma volume expansion, HA infusion does not enhance Na excretion in Na‐restricted subjects. This is mainly due to elevation of plasma COP, which reduces glomerular filtration and enhances proximal reabsorption. The biphasic response in FPRNa, an initial increase during infusion that abates afterwards, can be explained from a secondary rise in peritubular capillary hydrostatic pressure related to an increased renal perfusion.

Renal lithium handling during water loading and subsequent d‐DAVP‐induced anti‐diuresis

Abstract. Assuming that lithium is exclusively reabsorbed in the proximal tubules pari passu with sodium (Na), the lithium clearance (CLi) has been advanced as an index of filtrate delivery from the proximal tubules. In order to determine whether water loads in a range commonly given during clearance studies affect CLi, we studied nine normal subjects (Na intake 150 mmol day‐1) on three water loads resulting in stable urine flow rates of 2·2 ± 0·9, 6·1 ± 0·7 and 11·7 ± 3·0 ml min‐1, respectively. We also studied the effect of acute anti‐diuresis (urine flow <1 ml min‐1) induced by d‐DAVP given i.v. at the end of all studies. Water loading up to induction of maximum water diuresis did not significantly affect absolute or fractional CLi‐Sodium and chloride excretion were reduced at the highest water intake level. Administration of d‐DAVP caused a 50% reduction in fractional Na excretion and a small but significant rise in fractional lithium reabsorption from 75·5 ± 3·9 to 77·5 ± 3·6%. We conclude that CLi is hardly affected over a wide range of water intakes and urine flow rates, despite concomitant changes in Na excretion. The finding that d‐DAVP, which probably enhances Na reabsorption in the thick ascending limb of Henles loop, also enhanced lithium reabsorption, suggests that lithium may be partly reabsorbed in this nephron segment. Thus, lithium may not be the exact, quantitative marker of Na reabsorption in the proximal tubules that it is purported to be.

Denosumab for treatment of immobilization-related hypercalcaemia in a patient with advanced renal failure

We describe the case of a young adult with immobilization-related hypercalcaemia and advanced renal insufficiency. Because of the uncertain safety profile of bisphosphonates in such patients, only a low dose of pamidronate was administered twice. This did not result in a sufficient decrease in the serum calcium concentration nor was the decrease sustained. We decided to administer a single dose of denosumab, a monoclonal antibody against the receptor activator of nuclear factor-κB ligand, a new antiresorptive agent registered for use in osteoporosis. This resulted in rapid and sustained decrease in the serum calcium concentration. Transient hypocalcaemia ensued with normalization after vitamin D supplementation. Furthermore, we summarize what is known about hypercalcaemia caused by immobilization.

Patients with Encapsulating Peritoneal Sclerosis Have Increased Peritoneal Expression of Connective Tissue Growth Factor (CCN2), Transforming Growth Factor-β1, and Vascular Endothelial Growth Factor

Introduction Encapsulating peritoneal sclerosis (EPS) is a devastating complication of peritoneal dialysis (PD). The pathogenesis is not exactly known and no preventive strategy or targeted medical therapy is available. CCN2 has both pro-fibrotic and pro-angiogenic actions and appears an attractive target. Therefore, we studied peritoneal expression of CCN2, as well as TGFβ1 and VEGF, in different stages of peritoneal fibrosis. Materials and methods Sixteen PD patients were investigated and compared to 12 hemodialysis patients and four pre-emptively transplanted patients. Furthermore, expression was investigated in 12 EPS patients in comparison with 13 PD and 12 non-PD patients without EPS. Peritoneal tissue was taken during kidney transplantation procedure or during EPS surgery. In a subset of patients, CCN2 protein levels in peritoneal effluent and plasma were determined. Samples were examined by qPCR, histology, immunohistochemistry, and ELISA. Results Peritoneal CCN2 expression was 5-fold higher in PD patients compared to pre-emptively transplanted patients (P<0.05), but did not differ from hemodialysis patients. Peritoneal expression of TGFβ1 and VEGF were not different between the three groups; neither was peritoneal thickness. Peritoneum of EPS patients exhibited increased expression of CCN2 (35-fold, P<0.001), TGFβ1 (24-fold, P<0.05), and VEGF (77-fold, P<0.001) compared to PD patients without EPS. In EPS patients, CCN2 protein was mainly localized in peritoneal endothelial cells and fibroblasts. CCN2 protein levels were significantly higher in peritoneal effluent of EPS patients compared to levels in dialysate of PD patients (12.0±4.5 vs. 0.91±0.92 ng/ml, P<0.01), while plasma CCN2 levels were not increased. Conclusions Peritoneal expression of CCN2, TGFβ1, and VEGF are significantly increased in EPS patients. In early stages of peritoneal fibrosis, only CCN2 expression is slightly increased. Peritoneal CCN2 overexpression in EPS patients is a locally driven response. The potential of CCN2 as biomarker and target for CCN2-inhibiting agents to prevent or treat EPS warrants further study.