Sebastian Nowak

The intrinsic renal compartment syndrome: new perspectives in kidney transplantation.

Purpose. Inflammatory edema after ischemia-reperfusion may impair renal allograft function after kidney transplantation. This study examines the effect of edema-related pressure elevation on renal function and describes a simple method to relieve pressure within the renal compartment. Methods. Subcapsular pressure at 6, 12, 24, 48 hr, and 18 days after a 45 min warm ischemia was determined in a murine model of renal ischemia-reperfusion injury. Renal function was measured by 99mTc-MAG3 scintigraphy and laser Doppler perfusion. Structural damage was assessed by histologic analysis. As a therapeutic approach, parenchymal pressure was relieved by a standardized circular 0.3 mm incision at the lower pole of the kidney capsule. Results. Compared with baseline (0.9±0.3 mm Hg), prolonged ischemia was associated with a sevenfold increase in subcapsular pressure 6 hr after ischemia (7.0±1.0 mm Hg; P<0.001). Pressure levels remained significantly elevated for 24 hr. Without therapy, a significant decrease in functional parameters was found with considerably reduced tubular excretion rate (33±3.5%, P<0.001) and renal perfusion (64.5±6.8%, P<0.005). Histologically, severe tissue damage was found. Surgical pressure relief was able to significantly prevent loss of tubular excretion rate (62.5±6.8%, P<0.05) and renal blood flow (96.2±4.8%; P<0.05) and preserved the integrity of renal structures. Conclusions. Our data support the hypothesis of the existence of a renal compartment syndrome as a consequence of ischemia-reperfusion injury. Surgical pressure relief effectively prevented functional and structural renal impairment, and we speculate that this approach might be of value for improving graft function after renal transplantation.

Uptake and binding of the serotonin 5-HT1A antagonist [18F]-MPPF in brain of rats: Effects of the novel P-glycoprotein inhibitor tariquidar

We used microPET to map the dose-response to the novel P-glycoprotein (P-gp) inhibitor tariquidar (TQD) of the initial influx of the P-gp substrate [(18)F]-MPPF in rat brain, and to test for effects of P-gp inhibition on the subsequent binding of [(18)F]-MPPF to serotonin 5-HT(1A) receptors. Summation maps of [(18)F]-MPPF uptake during the first 100 seconds after intravenous injection were calculated in groups of rats with vehicle (glucose 5%) pretreatment, or following pretreatment with TQD at doses of 5, 15, or 30 mg/kg. The early summation image (K(1)-weighted), were validated as a surrogate marker for the physiological blood-brain clearance (K(1); ml g(-)(1) min(-1)) by linear graphic analysis of the unidirectional blood-brain clearance relative to an image-based arterial input measured in the left ventricle of the heart. In the same animals, parametric maps of the [(18)F]-MPPF binding potential (BP(ND)) were calculated from the entire 60-minute emission recordings using conventional reference tissue methods. All [(18)F]-MPPF recordings were followed by an [(18)F]-FDG emission recording, the summation of which was used for spatial normalization to a rat brain atlas. Test-retest variability of K(1)-weighted uptake and BP(ND) was 25%. TQD treatment evoked a global dose-dependent increase in K(1)-weighted summation, which increased 2.5-fold with TQD (30 mg/kg), suggesting an IC(50) of 5 mg/kg TQD. All TQD doses increased the apparent [(18)F]-MPPF BP(ND) calculated by the Logan method by 30%-40%, a bias likely arising due to increased free [(18)F]-MPPF concentrations in brain. TQD (15 mg/kg) evoked a 45% global increase in [(18)F]-FDG uptake, suggesting perturbation of brain energy metabolism due to P-gp blockade.

Endogenous competition against binding of [(18)F]DMFP and [(18)F]fallypride to dopamine D(2/3) receptors in brain of living mouse.

Aim. Molecular imaging studies with benzamide radioligands can reveal competition from endogenous binding at D2/3‐receptors in living brain. However, single photon emission computed tomography (SPECT) methods suffer from limited spatial resolution, and [11C]‐labeled ligands are only available at positron emission tomography (PET) research sites with cyclotron‐radiochemistry facilities, whereas [18F] can be transported, due to its longer physical half‐life. Therefore, we endeavored to characterize the vulnerabilities of the benzamide antagonist [18F]desmethoxyfallypride (DMFP) and its high‐affinity congener [18F]fallypride (FP) to competition from endogenous dopamine in living mouse brain. Methods. Groups of awake mice were pretreated with saline, amphetamine (10 mg/kg), or reserpine (5 mg/kg), followed by i.v. tracer injections. Mice were killed at 2.5–90 min (DMFP) or 2.5–180 min (FP) circulation times. Brains were dissected and regional radioactivity concentration measured by gamma counting. Other groups of mice were anesthetized for dynamic microPET recordings with DMFP or FP. Binding potentials (BPND) were calculated using cerebellum as reference region. Results. With 90‐min circulation, DMFP BPND in striatum was 2.4 by dissection and 2.2 by microPET, which showed a 62% decrease in response to amphetamine‐evoked dopamine release and a 33% increase after reserpine‐evoked dopamine depletion. With 120‐min circulation, FP BPND in striatum was 24.1 by dissection and 9.2 by microPET, which showed a 31% decrease in the amphetamine group, but no effect of reserpine. Dissection showed similar sensitivities for FP binding, but only a 29% amphetamine‐evoked reduction for DMFP. Conclusions. Relative to gold standard ex vivo results, microPET estimates of DMFP BPND were unbiased, whereas FP BPND in striatum was substantially underestimated. Both tracers proved suitable for revealing pharmacologically evoked changes in competition at D2/3‐receptors in striatum of living mice. Synapse 64:313–322, 2010.

DIFFERENTIAL EFFECTS OF IMMUNOSUPPRESSIVE AGENTS ON RENAL FUNCTION AFTER ISCHEMIA-REPERFUSION INJURY: NEW INSIGHTS BY USING 99MTC-MAG3 IMAGING: 1684

Introduction: Ischemia-reperfusion (I/R) injury after kidney transplantation has not only acute effects on renal function, but may also determine long-term outcomes after transplantation. This study differentially investigates acute functional consequences of commonly used immunosuppressive agents on renal function of kidneys after I/R and non-ischemic control kidneys. Methods: In Balb/C wt mice unilateral warm ischemia was induced by vascular clamping of the kidney hilum for 45 min. Immunosuppressive doses of cyclosporine A (CsA,40mg/kg b.w./d), sirolimus (SRL,1.5mg/ kg b.w./d) and dexamethasone (DEX,10mg/kg b.w./d) were administered beginning 2 h before surgery. Tubular excretion function characterized by renal function peak and tubular excretion rate was examined using 99mTc-MAG3 scintigraphy 48 h post ischemia. Tubular function was simultanously and separately recorded in both the ischemic and the contralateral non-ischemic kidney. Results: Without treatment tubular function was severely compromised after I/R compared to contralateral control kidneys. A significant reduction of renal function peak (85.9%±3.8%;p<0.01) indicating maximum uptake of the radioactive compound and tubular excretion rate (35.1%±5.2%;p<0.01) indicating the elimination capacity was found. Renal function in postischemic kidneys decreased even further with immunosuppressive doses of CsA (peak 52.1%±8.0%,p<0.01; tubular excretion rate 7.2%±1.0%), SRL (peak 78.6%±2.4%,n.s.; tubular excretion rate 11.1%±3.4%,p<0.01), and DEX (peak 61.69%±1.24%,p<0.01); tubular excretion rate 6.1%±1.9%,p<0.01) However, in contralateral control kidneys, immunosuppressive agents elicited a more differential effect on renal function. A compensatory increase in peak was seen without treatment (145.6%±8.5%) and when treated with DEX (114.0%±15.1%) and SRL (115.7%±7.5%), respectively. SRL was found to protect renal function and showed no significant change in tubular excretion rate (86.6%±15.4%,n.s.) compared to non-treated kidneys subjected to I/R (86.3%±12.1%). DEX led to a moderate decrease in tubular excretion function (32.3%±12.3%;p<0.05). In contrast, CsA did significantly impair renal function, as seen in marked reduction of peak level (42.8%±4.3%,p<0.01) and tubular excretion rate (5.8%±0.8%,p<0.01). Conclusions: This model using 99mTc-MAG3 imaging measures and simulates renal function in both severely injured and healthy nephrons. While in reality both entities will coexsist after I/R injury and transplantation and commonly used parameters will only detect the net effect (e.g.s-creatinine), this technique allows for differential observation of these effects. Reflecting clinical experience CsA significantly impaired renal function of the healthy kidney. This was not the case for SRL. Both CsA and DEX affected recovery of renal function of kidneys after I/R injury, whereas SRL was unexpectedly inert. The results of this study suggest that delayed CsA strategies may help both renal recovery and the protection of not or lightly injured nephrons. In contrast, our data does not provide any rationale to withhold SRL immediately after transplantation in order to facilitate renal recovery. Disclosure: All authors have declared no conflicts of interest.

Renoprotektive Effekte der Zelltherapie mit Progenitorzellen beim renalen Ischämie-Reperfusionsschaden: Die Notwendigkeit der Dekompressionstherapie

Purpose: Cell therapy represents a promising therapeutic approach in kidney transplantation. This study examines the precise potentials and limits of cell therapy in renal ischemia-reperfusion injury. Methods: The effects of endothelial progenitor cell therapy following a 45 min warm ischemia were investigated in a murine model of renal ischemia-reperfusion injury alone and in combination with surgical decompression of the renal compartment. Renal function was measured by 99mTc-MAG3 scintigraphy and laser Doppler perfusion. Structural damage was assessed by histological/ immunohistochemical analysis. Results: Warm ischemia of 45 min was associated with severe tissue damage and led to a significant decrease in tubular excretion rate (46.4 % ± 12.5 %, p < 0.05) and renal perfusion (67.7 % ± 3.9 %, p < 0.001). Cell therapy potently enhanced vascular regeneration with increased perfusion (112.5 % ± 3.1 %, p < 0.001) and excellent tissue vitality, while tubular excretion remained impaired (33.3 % ± 8.8 %, p < 0.001). Most importantly, combination of cell-based and decompression therapy enabled significant recovery of renal function (103.3 % ± 16.0 %, p < 0.05) and perfusion (116.7 % ± 2.5 %; p < 0.001) and preserved the integrity of renal structures. Conclusion: Progenitor cell therapy alone promotes vascular regeneration and preserves organ integrity following renal ischemia-reperfusion injury, but lacks beneficial effects on renal function. Combining cellular and decompressive therapy results in enhanced functional recovery and may improve the outcome of renal allografts.

Cell-based therapy using endothelial progenitor cells rescues kidney from ischemia-reperfusion injury

In the past years, optimization of immunosuppressive protocols considerably reduced the incidence of acute rejection after kidney transplantation. In contrast, very little progress has been achieved in the field of long-term transplant function and survival. Chronic allograft dysfunction still represents a major cause of graft loss and the underlying multi-factorial reasons involving both immunological and non-immunological aspects remain poorly understood. In the clinical setting prevention of ischemia-reperfusion injury as a non-immunological factor is achieved by cold preservation and particular perfusion solutions, whereas effective renoprotective treatment options after transplantation are still lacking. As prolonged ischemia not only leads to early tissue damage with reduced graft function, but also exhibits deteriorating long-term effects on the transplant kidney by increasing immunogenicity and predisposition to fibrosis, we aimed to identify new treatment strategies to counter or even reverse this clinical disease pattern. The precise part of different renal structures and components in kidney dysfunction and the effects of endothelial progenitor cell therapy were analyzed in a murine model of ischemia-reperfusion injury using 99mTc-MAG3 scintigraphy, assessment of laser Doppler perfusion, examination of kidney-relevant parameters in blood and urine, as well as histological analysis. Without treatment, ischemia-reperfusion injury exhibited a substantial reduction of renal function with no evidence for regeneration, considerable tissue damage, and marked impairment of organ perfusion. Progenitor cell therapy potently enhanced vascular regeneration with increased perfusion and excellent tissue vitality, but had only limited beneficial effect on functional impairment. Histological analysis conclusively confirmed functional findings. Here, we show that cell-based therapy using endothelial progenitor cells represents a promising strategy to suspend the deteriorating cascade of events following ischemia-reperfusion injury. This novel treatment modality may aid to prolong allograft function and survival after kidney transplantation.