Sieving Coefficients Research Articles

In vivo Elimination of Clonidine by Continuous Venovenous Hemofiltration in Critically Ill Patients

Background: Clonidine is an α₂-agonist that is commonly used for sedation in the intensive care unit. When patients are on continuous venovenous hemofiltration (CVVH) in the presence of kidney dysfunction, the sieving coefficient of clonidine is required to estimate how much drug is removed by CVVH. In the present study, we measured the sieving coefficient of clonidine in critically ill, ventilated patients receiving CVVH. Methods: A total of 20 samples of plasma and ultrafiltrate of 3 patients on CVVH, using a standard 1.5 m² polyacrylonitrile AN69 membrane, during continuous clonidine infusion were collected. After correction for the effect of predilution, we calculated the sieving coefficient for clonidine. Results: The mean sieving coefficient of clonidine was 0.52 (SD 0.097). Conclusion: Using a polyacrylonitrile AN69 membrane in a CVVH machine, the in vivo sieving coefficient of clonidine was 0.52.

Pharmacokinetics and Pharmacodynamics of Anti-infective Agents during Continuous Veno-venous Hemofiltration in Critically Ill Patients: Lessons Learned from an Ancillary Study of the IVOIRE Trial.

BackgroundHemofiltration rate, changes in blood and ultrafiltration flow, and discrepancies between the prescribed and administered doses strongly influence pharmacokinetics (PK) and pharmacodynamics (PD) of antimicrobial agents during continuous veno-venous hemofiltration (CVVH) in critically ill patients.MethodsAncillary data were from the prospective multicenter IVOIRE (hIgh VOlume in Intensive caRE) study. High volume (HV, 70 mL/kg/h) was at random compared with standard volume (SV, 35 mL/kg/h) CVVH in septic shock patients with acute kidney injury (AKI). PK/PD parameters for all antimicrobial agents used in each patient were studied during five days.ResultsAntimicrobial treatment met efficacy targets for both percentage of time above the minimal inhibitory concentration and inhibitory quotient. A significant correlation was observed between the ultrafiltration flow and total systemic clearance (Spearman test: P < 0.005) and between CVVH clearance and drug elimination half-life (Spearman test: P < 0.005). All agents were easily filtered. Mean sieving coefficient ranged from 38.7% to 96.7%. Mean elimination half-life of all agents was significantly shorter during HV-CVVH (from 1.29 to 28.54 h) than during SV-CVVH (from 1.51 to 33.85 h) (P < 0.05).ConclusionsThis study confirms that CVVH influences the PK/PD behavior of most antimicrobial agents. Antimicrobial elimination was directly correlated with convection rate. Current antimicrobial dose recommendations will expose patients to underdosing and increase the risk for treatment failure and development of resistance. Dose recommendations are proposed for some major antibiotic and antifungal treatments in patients receiving at least 25 mL/kg/h CVVH.

Pharmacokinetics of and maintenance dose recommendations for vancomycin in severe pneumonia patients undergoing continuous venovenous hemofiltration with the combination of predilution and postdilution.

Therapeutic vancomycin levels are difficult to maintain in severe pneumonia patients who are receiving IV vancomycin therapy while on continuous venovenous hemofiltration (CVVH). The objective of this study was to determine the pharmacokinetics and maintenance dose recommendations of vancomycin in severe pneumonia patients receiving CVVH. A prospective study was conducted in the intensive care unit of a university hospital. Ten severe pneumonia patients receiving vancomycin and CVVH treatment were determined the initial and steady-state pharmacokinetics of vancomycin. CVVH was performed in mixed predilution and postdilution mode with a blood flow rate of 180mL/min and an ultrafiltrate flow rate of 30-40mL/kg/h. Group A received an initial dose of 500mg only, whereas group B received 500mg every 12h until steady state is achieved. Serum and ultrafiltrate were collected over 12h after infusion of vancomycin. After initial dosing, the mean sieving coefficient (SC) was 0.72 ± 0.02, and CVVH clearance (CLCVVH, 1.35 ± 0.03L/h) constituted 60.55% ± 13.69% of total vancomycin clearance (CLtot, 2.36 ± 0.72L/h). When steady state was reached, the SC of the patients was 0.71 ± 0.03, and the CLCVVH (1.34 ± 0.06L/h) accounted for 66.96% ± 6.05% of the CLtot (2.03 ± 0.27L/h). The recommended maintenance dose for vancomycin in severe pneumonia patients was 400-650mg every 12h, which was calculated based on CLtot, to achieve a trough concentration of 15-20mg/L at steady state. Single administration or multiple administration does not affect SC and CLCVVH. Owing to therapeutic vancomycin levels is difficult to maintain in severe pneumonia patients who are receiving IV vancomycin therapy while on CVVH, close monitoring of serum trough concentrations is required.

Pharmacokinetics and Pharmacodynamics of Extended-Infusion Cefepime in Critically Ill Patients Receiving Continuous Renal Replacement Therapy: A Prospective, Open-Label Study.

To evaluate extended-infusion (EI) cefepime pharmacokinetics (PK) and pharmacodynamic target attainment in critically ill patients receiving continuous venovenous hemofiltration (CVVH) or continuous venovenous hemodialysis (CVVHD). Prospective, open-label, PK study. Intensive care units at a large, academic, tertiary-care medical center. Ten critically ill adults who were receiving cefepime 2g intravenously every 8hours as a 4-hour infusion while receiving CVVH (eight patients) or CVVHD (two patients). Two sets of five serum cefepime concentrations were collected for each patient to assess pharmacokinetics before and during presumed steady state. Concurrent serum and CRRT effluent samples were collected at hours 1, 2, 3, 4, and 8 after the first cefepime dose and after either the fourth, fifth, or sixth (steady-state) cefepime doses. Reversed-phase high-performance liquid chromatography was used to determine free cefepime concentrations. PK analyses included CRRT clearance, half-life, and sieving coefficient or saturation coefficient. Cefepime peak (4 hrs) concentrations, trough (8 hrs) concentrations (Cmin ), and minimum inhibitory concentration breakpoint of 8µg/ml for the pathogen (MIC8 ) were used to evaluate attainment of pharmacodynamic targets: 100% of the dosing interval that free drug remains above MIC8 (100% fT>MIC8 ), 100% fT>4×MIC8 (optimal), percentage of time fT>4×MIC8 (%fT>4×MIC8 ) at steady state, and ratio of Cmin to MIC8 (fCmin /MIC8 ). Total CRRT effluent flow rate was a mean±SD of 30.1±5.4ml/kg/hr, CRRT clearance was 39.6±9.9ml/min, and half-life was 5.3±1.7hours. Sieving coefficient or saturation coefficient were 0.83±0.13 and 0.69±0.22, respectively. First and steady-state dose Cmin were 23.4±10.1µg/ml and 45.2±14.6µg/ml, respectively. All patients achieved 100% fT>MIC8 on first and steady-state doses. First and steady-state dose 100% fT>4×MIC8 were achieved in 22% (2/9 patients) and 87.5% (7/8 patients) of patients, respectively. The mean %fT>4×MIC8 at steady state was 97.5%. The fCmin /MIC8 was 2.92±1.26 for the first dose and 5.65±1.83 at steady state. Extended-infusion cefepime dosing in critically ill patients receiving CRRT successfully attained 100% fT>MIC8 in all patients and an appropriate fCmin /MIC8 for both first and steady-state doses. All but one patient achieved 100% fT>4×MIC8 at steady state. No significant differences were observed in PK properties between first and steady-state doses among or between patients. It may be reasonable to initiate an empiric or definitive regimen of EI cefepime in critically ill patients receiving concurrent CRRT who are at risk for resistant organisms. Further research is needed to identify the optimal dosing regimen of EI cefepime in this patient population.

Two-pore physiologically based pharmacokinetic model with de novo derived parameters for predicting plasma PK of different size protein therapeutics.

Two-pore PBPK models have been used for characterizing the PK of protein therapeutics since 1990s. However, widespread utilization of these models is hampered by the lack of a priori parameter values, which are typically estimated using the observed data. To overcome this hurdle, here we have presented the development of a two-pore PBPK model using de novo derived parameters. The PBPK model was validated using plasma PK data for different size proteins in mice. Using the "two pore theory" we were able to establish the relationship between protein size and key model parameters, such as: permeability-surface area product (PS), vascular reflection coefficient (σ), peclet number (Pe), and glomerular sieving coefficient (θ). The model accounted for size dependent changes in tissue extravasation and glomerular filtration. The model was able to a priori predict the PK of 8 different proteins: IgG (150kDa), scFv-Fc (105kDa), F(ab)2 (100kDa, minibody (80kDa), scFv2 (55kDa), Fab (50kDa), diabody (50kDa), scFv (27kDa), and nanobody (13kDa). In addition, the model was able to provide unprecedented quantitative insight into the relative contribution of convective and diffusive pathway towards trans-capillary mass transportation of different size proteins. The two-pore PBPK model was also able to predict systemic clearance (CL) versus Molecular Weight relationship for different size proteins reasonably well. As such, the PBPK model proposed here represents a bottom-up systems PK model for protein therapeutics, which can serve as a generalized platform for the development of truly translational PBPK model for protein therapeutics.

In-vitro adsorption and sieving coefficient of ticarcillin-clavulanate during continuous haemofiltration

There are very limited data on ticarcillin-clavulanate elimination by haemofiltration. We measured in vitro ticarcillin-clavulanate adsorption to polyacrylonitrile (PAN) filters and the sieving coefficient using a well-described bench model of haemofiltration. The dose of ticarcillin-clavulanate was 60/2 mg or 180/3 mg, and 0 or 12 g albumin was added to the 1 L of circulating blood-crystalloid mixture to produce four different experimental conditions. The experiment was repeated four times under each condition. Median (interquartile range [IQR] ) ticarcillin adsorption varied from 28 (27-30) mg to 85 (78-90) mg. Adsorption was increased when the dose of ticarcillin was higher (P<0.001), but was not affected by the addition of albumin. Median (IQR) adsorption of clavulanate ranged from 0.67 (0.55-0.75) mg to 1.8 (0.33-3.5) mg and was neither dose dependent (P = 0.505) nor significantly affected by the addition of albumin. Median (IQR) ticarcillin sieving coefficient ranged from 0.73 (0.67-0.75) to 0.99 (0.97-1.03). It was significantly higher with a higher dose of ticarcillin (P = 0.021) and without addition of albumin (P = 0.015). Median (IQR) clavulanate sieving coefficient ranged from 1.03 (1.00-2.24) to 2.0 (1.98-2.47). Clavulanate sieving coefficient was not significantly affected by dose or the addition of albumin.These data indicate that significant adsorption of both ticarcillin and clavulanate occurs in vitro; however, this requires confirmation by clinical pharmacokinetic studies. The sieving coefficient data may help guide appropriate dosing of critically ill patients receiving haemofiltration until more extensive clinical pharmacokinetic data are available.

Sustained, delayed, and small increments in glomerular permeability to macromolecules during systemic ET-1 infusion mediated via the ETA receptor.

Emerging evidence indicates that endogenous production of endothelin (ET)-1, a 21-amino acid peptide vasoconstrictor, plays an important role in proteinuric kidney disease. Previous studies in rats have shown that chronic administration of ET-1 leads to increased glomerular albumin leakage. The underlying mechanisms are, however, currently not known. Here, we used size-exclusion chromatography to measure glomerular sieving coefficients for neutral FITC-Ficoll (molecular Stokes-Einstein radius: 15-80 Å, molecular weight: 70 kDa/400 kDa) in anesthetized male Sprague-Dawley rats (n = 12) at baseline and at 5, 15, 30, and 60 min after intravenous administration of ET-1. In separate experiments, ET-1 was given together with the selective ET type A (ETA) or ET type B (ETB) receptor antagonists JKC-301 and BQ-788, respectively. At both 15 and 30 min postadministration, the glomerular sieving coefficient for macromolecular Ficoll (70 Å) was significantly increased to 4.4 × 10-5 ± 0.7 × 10-5 (P = 0.024) and 4.5 × 10-5 ± 0.8 × 10-5 (P = 0.007), respectively, compared with baseline (2.2 × 10-5 ± 0.4 ×10-5). Decreased urine production after ET-1 prevented the use of higher doses of ET-1. Data analysis using the two-pore model indicated changes in large-pore permeability after ET-1, with no changes in the small-pore pathway. Administration of ETA blocker abrogated the permeability changes induced by ET-1 at 30 min, whereas blockade of ETB receptors was ineffective. Mean arterial pressure was only significantly increased at 60 min, being 123 ± 4 mmHg compared with 111 ± 2 mmHg at baseline (P = 0.02). We conclude that ET-1 evoked small, delayed, and sustained increases in glomerular permeability, mediated via the ETA receptor.

The Effect of Serum Neutrophil Gelatinase-Associated Lipocalin on the Discontinuation of Continuous Renal Replacement Therapy in Critically Ill Patients with Acute Kidney Injury

Background: To determine the optimal time for discontinuing continuous renal replacement therapy (CRRT) by evaluating serum neutrophil gelatinase-associated lipocalin (NGAL) in critically ill patients with acute kidney injury (AKI). Methods: A prospective observational study was conducted from September 2015 to March 2018. AKI patients treated with CRRT for at least 24 h were divided into “success” and “failure” groups according to their RRT requirement within 7 days after the initial discontinuation of CRRT. The prefilter and effluent NGAL concentrations were measured to calculate the sieving coefficient (SC) of NGAL in all included subjects from 0 to 72 h. Results: In total, 110 patients were divided into success (n = 78) and failure groups (n = 32). The mean SC of NGAL during CRRT was less than 0.05. The patients in the failure group were associated with higher mortality compared with patients in the success group (37.5 vs. 12.8%, respectively, p = 0.013). There were significant differences in serum NGAL, creatinine, and urine output at discontinuation. In patients without sepsis (n = 70), serum NGAL and urine output were significant predictors of successful cessation. The area under the receiver operating characteristic to predict the successful discontinuation of CRRT was 0.88 for NGAL and 0.86 for urine output. An NGAL level of 403 ng/mL had the highest sensitivity (81%) and specificity (89%) and a urine output of 695 mL/day had the highest sensitivity (83%) and specificity (88%). However, in septic patients (n = 40), urine output but not serum NGAL (OR 0.999, p = 0.69) was a significant variable (OR 1.002, p = 0.005), with a cutoff of 796 mL/day (sensitivity 83%, specificity 88%). Conclusions: Serum NGAL was a significant factor for predicting successful CRRT discontinuation in nonseptic AKI patients. However, urine output, rather than serum NGAL, was a significant predictor in septic AKI patients.

Effect of diabetes mellitus on the recovery of changes in renal functions and glomerular permeability following reversible 24-hour unilateral ureteral obstruction.

Following reversal of short periods of ureteral obstruction (UO), glomerular and tubular renal dysfunction recovers with time. Diabetes mellitus (DM) affects glomerular function; thus, the ability of diabetic kidneys to recover from UO may be impaired. This study investigated the effects of long-term DM on the recovery of glomerular and tubular function, as well as permeability of the glomerular filtration barrier (GFB), after unilateral UO (UUO) reversal. Diabetes mellitus was induced in Wistar rats by intraperitoneal streptozotocin. All diabetic and age-matched control rats underwent reversible 24-hour left UUO. The renal function of both kidneys was measured using clearance techniques 3 hours and 7 and 30 days after UUO reversal. Glomerular permeability was assessed by measuring the glomerular sieving coefficients for fluorescein isothiocyanate-conjugated Ficoll (molecular radius: 20-90 Å). Unilateral UO induced transient changes in the size selectivity of GFB small pores. However, the size selectivity function of large pores had not returned to baseline even 30 days after UUO reversal. Diabetes mellitus caused exaggerated early alterations in glomerular hemodynamic and tubular function, as well as size selectivity dysfunction of both small and large pores. At 30 days after UUO reversal, despite glomerular hemodynamic and tubular function and the size selectivity of small pores returning to normal in both diabetic and non-diabetic rats, the residual size selectivity dysfunction of large pores was more severe in diabetic rats. Unilateral UO caused long-term dysfunction in the size selectivity of large pores of the GFB. In addition, DM significantly exaggerated this dysfunction, indicating a more ominous outcome in diabetic kidneys following UUO.

The effects of alternating tangential flow (ATF) residence time, hydrodynamic stress, and filtration flux on high-density perfusion cell culture.

In this study, we investigated the effects of alternating tangential flow (ATF) cell separation on high-density perfusion cultures. We have developed methods to estimate theoretical residence times of cells in the ATF system and discovered that long residence times (above 75 s) correlate with decreased growth, metabolism, and productivity. We have calculated energy dissipation rates in the ATF transfer line and filter and empirically studied the impacts of increased exchange rates on cell culture, determining that increased hydrodynamic stress can lead to decreased cell size, lactate production, and specific productivity. Finally, we have conducted experiments to understand the relationship between filtration fluxes and ATF membrane fouling, finding that at fluxes above 60 L·m-2 ·day -1 , protein sieving coefficients see significant rates of decrease (greater than 1% per day). While most of these studies have been conducted with one cell line at one target viable cell density (40 million cells/ml), the general, directional knowledge arising from this study should be applicable to other conditions and programs, ultimately leading to more robust and well-designed perfusion processes.

High Efficiency Removal of Cytokines and HMGB-1 by Continuous Hemofiltration With a Dual Layered Polyethersulfone Membrane: An Ex Vivo Study.

Cytokines and high mobility group box chromosomal protein-1 (HMGB-1) play key roles in inflammatory conditions. While hemofiltration has been shown to remove cytokines, removal of cytokines and HMGB-1 by hemofiltration using a polyethersulfone membrane has not been reported. This study aimed to test the hypothesis that the polyethersulfone membrane will achieve higher removal performance for substances including inflammatory cytokines compared to other hemofilters, while retaining low albumin removal capacity. Subjects were eight healthy volunteers. We collected 400 mL each of blood samples into containers with heparin and added 30 mg of lipopolysaccharide to spike cytokines and HMGB-1. After incubation at 39ºC for 12 h, each blood sample was circulated through a hemofiltration circuit with a polyethersulfone hemofilter (2.1 m2 or 1.1 m2 ) at a filtration flow rate of 2 L/h. Measurement samples were collected from arterial, venous, and ultrafiltrate sampling points. Concentrations of cytokines (IL-1ß, IL-4, IL-6, IL-8, IL- 10, and tumor necrosis factor [TNF-a]), HMGB-1, and albumin were determined at each time point (1, 4, 8, 12, and 24h). High sieving coefficients (SCs) above 0.8 were obtained for all cytokines except for TNF-a as well as HMGB-1, whereas the SC for albumin was less than 0.04 with both hemofilters. The hemofilter with a larger membrane area achieved significantly higher clearances for TNF-a and HMGB-1, and slower decreases in SCs over time for IL-1ß, IL-6, IL-8, TNF-a, and albumin. Continuous hemofiltration with a polyethersulfone membrane achieved high efficiency removal of cytokines and HMGB-1, without excessive removal of albumin.

Aldosterone induces albuminuria via matrix metalloproteinase–dependent damage of the endothelial glycocalyx

Aldosterone contributes to end-organ damage in heart failure and chronic kidney disease. Mineralocorticoid-receptor inhibitors limit activation of the receptor by aldosterone and slow disease progression, but side effects, including hyperkalemia, limit their clinical use. Damage to the endothelial glycocalyx (a luminal biopolymer layer) has been implicated in the pathogenesis of endothelial dysfunction and albuminuria, but to date no one has investigated whether the glomerular endothelial glycocalyx is affected by aldosterone. Invitro, human glomerular endothelial cells exposed to 0.1 nM aldosterone and 145 mMol NaCl exhibited reduced cell surface glycocalyx components (heparan sulfate and syndecan-4) and disrupted shear sensing consistent with damage of the glycocalyx. Invivo, administration of 0.6 μg/g/d of aldosterone (subcutaneous minipump) and 1% NaCl drinking water increased glomerular matrix metalloproteinase 2 activity, reduced syndecan 4 expression, and caused albuminuria. Intravital multiphoton imaging confirmed that aldosterone caused damage of the glomerular endothelial glycocalyx and increased the glomerular sieving coefficient for albumin. Targeting matrix metalloproteinases 2 and 9 with a specific gelatinase inhibitor preserved the glycocalyx, blocked the rise in glomerular sieving coefficient, and prevented albuminuria. Together these data suggest that preservation of the glomerular endothelial glycocalyx may represent a novel strategy for limiting the pathological effects of aldosterone.

High cut-off membrane for in-vivo dialysis of free plasma hemoglobin in a patient with massive hemolysis

BackgroundThe possibility of clearing Cell-free Plasma Hemoglobin (CPH) from human plasma may appear attractive, especially when considering the noxious effects that CPH has on the immune function and the renal damage caused by its filtration. The existence of the so-called High Cut-Off (HCO) filters, possessing pores as big as 60 kDa, could potentially allow the clearance of the αβ dimers (31.3 kDa), the form in which the α2β2 hemoglobin tetramers (62.6 kDa) physiologically dissociate in plasma. We present herein the first reported case in which such an attempt was made.Case presentationThe patient was a 51-year-old man with hemolytic crisis due to glucose-6-phosphate dehydrogenase deficiency, further complicated by pigment-induced nephropathy. He underwent a 48-h CVVHD session, in which a HCO filter was used. The Sieving Coefficient (SC) for CPH was initially 0.08 and decreased to 0.02 after 24 h. This unexpected low SC was due to the initial high concentration of CPH (4.24 g/L). At such concentrations, the α2β2 tetramer poorly dissociates into the αβ dimer; but increases exponentially at concentrations lower than 1 g/L.ConclusionsClearance of CPH through a HCO filter is technically feasible but its performance markedly relies on the initial concentration of CPH. Critically ill patients with smoldering hemolysis, as it happens during septic shock or ECMO treatment, may benefit the most from the use of this membrane in order to clear CPH.

Requirements and Pitfalls of Dialyzer Sieving Coefficients Comparisons.

Sieving coefficients reported in dialyzer data sheets and instructions for use (IFUs) indicate the potential of different solutes to pass across a particular membrane. Despite being measured in vitro, sieving coefficient data are often used as a predictor of the clinical performance of dialyzers. Although standards for the measurement of sieving coefficients exist, the stated methodologies do not offer sufficient guidance to ensure comparability of test results between different dialyzers. The aim of this work was to investigate the relationship between sieving coefficients and published clinical performance indicators for two solutes, albumin loss and beta‐2 microglobulin (β2M) reduction ratio (RR), and to assess the impact of different in vitro test parameters on sieving coefficient values for albumin, β2M, and myoglobin. Clinical albumin loss and β2M RR for commercially available dialyzers used in hemodialysis (HD) and post‐dilution hemodiafiltration (HDF) were extracted from the literature and plotted against sieving coefficients reported in data sheets and IFUs. Albumin, β2M, and myoglobin sieving coefficients of a selection of dialyzers were measured per the ISO 8637 standard. The impact of in vitro testing conditions was assessed by changing blood flow rate, ultrafiltration (UF) rate, sampling time, and origin of test plasma. Results showed variation in albumin loss and β2M RR for the same sieving coefficient across different dialyzers in HD and HDF. Changes in blood flow rates, UF rates, sampling time, and test plasma (bovine vs. human) caused marked differences in sieving coefficient values for all investigated solutes. When identical testing conditions were used, sieving coefficient values for the same dialyzer were reproducible. Testing conditions have a marked impact on the measurement of sieving coefficients, and values should not be compared unless identical conditions are used. Further, variability in observed clinical data in part reflects the lack of definition of test conditions.

Cyclic sieving and plethysm coefficients

A combinatorial expression for the coefficient of the Schur function s λ s_{\lambda } in the expansion of the plethysm p n / d d ∘ s μ p_{n/d}^d \circ s_{\mu } is given for all d d dividing n n for the cases in which n = 2 n=2 or λ \lambda is rectangular. In these cases, the coefficient ⟨ p n / d d ∘ s μ , s λ ⟩ \langle p_{n/d}^d \circ s_{\mu }, s_{\lambda } \rangle is shown to count, up to sign, the number of fixed points of an ⟨ s μ n , s λ ⟩ \langle s_{\mu }^n, s_{\lambda } \rangle -element set under the d d th power of an order- n n cyclic action. If n = 2 n=2 , the action is the Schützenberger involution on semistandard Young tableaux (also known as evacuation), and, if λ \lambda is rectangular, the action is a certain power of Schützenberger and Shimozono’s jeu-de-taquin promotion. This work extends results of Stembridge and Rhoades linking fixed points of the Schützenberger actions to ribbon tableaux enumeration. The conclusion for the case n = 2 n=2 is equivalent to the domino tableaux rule of Carré and Leclerc for discriminating between the symmetric and antisymmetric parts of the square of a Schur function.

Ultrafiltration behavior of partially retained proteins and completely retained proteins using equally-staged single pass tangential flow filtration membranes.

This work examines the ultrafiltration behavior of partially retained proteins like lysozyme and completely retained proteins like monoclonal antibodies using single pass tangential flow filtration (SPTFF) modules with different screen channels and molecular weight cut-offs. When the staging of the SPTFF used the same membrane area in each stage, there was no impact of the module screened channel or the buffer matrix on the final concentration achieved for completely retained monoclonal antibodies. A hybrid configuration containing 30 kDa membranes and 50 kDa membranes increased the maximum achievable concentration for both the monoclonal antibodies used in this work, at the same time, allowing a two-fold to four-fold increase in normalized feed flow-rate through the system compared to only the 30 kDa or only the 50 kDa membranes. The sieving coefficient of lysozyme measured and calculated using SPTFF was lower than those measured during conventional recirculation TFF indicating a more complicated concentration polarization effect than conventional recirculation TFF. Moreover, the sieving coefficients of lysozyme were the same for the 10 kDa regenerated cellulose and 50 kDa PES membranes while it was higher for the 30 kDa regenerated cellulose membrane. The difference in TFF and SPTFF behavior is important when the product of interest is desired to be permeated. This work presents the first body of data for partially and completely retained solutes together in the SPTFF mode and provides a strategy to increase protein concentration at higher feed flow rates. © 2018 American Institute of Chemical Engineers Biotechnol. Prog., 2018 © 2018 American Institute of Chemical Engineers Biotechnol. Prog., 34:1137-1148, 2018.

Thrombogenicity and long-term cytokine removal capability of a novel asymmetric triacetate membrane hemofilter

Hemofilters applied in continuous renal replacement therapies (CRRTs) for the treatment of acute kidney injury must meet high standards in biocompatibility and permeability for middle and large molecules over extended treatment times. In general, cellulose-based membranes exhibit good biocompatibility and low fouling, and thus appear to be beneficial for CRRT. In this in vitro study, we compared a novel asymmetric cellulose triacetate (ATA) membrane with three synthetic membranes [polysulfone (PS), polyethersulfone (PES), and polyethylenimine-treated acrylonitrile/sodium methallyl sulfonate copolymer (AN69 ST)] regarding thrombogenicity and cytokine removal. For thrombogenicity assessment, we analyzed the thrombin-antithrombin complex (TAT) generation in human whole blood during 5h recirculation and filtration. Sieving coefficients of interleukin-6 (IL-6), IL-8, IL-10, and tumor necrosis factor-alpha (TNF-α) were determined using human plasma as test fluid. ATA and AN69 ST membrane permeability were determined also during long-term experiments (48.5h). ATA exhibited the lowest TAT generation (6.3µg/L at 5h), while AN69 ST induced a pronounced concentration increase (152.1µg/L) and filter clogging during 4 out of 5 experiments. ATA (IL-8: 1.053; IL-6: 1.079; IL-10: 0.898; TNF-α: 0.493) and PES (0.973; 0.846; 0.468; 0.303) had the highest sieving coefficients, while PS (0.697; 0.100; 0.014; 0.012) and AN69 ST (N/A; 0.717; 0; 0.063) exhibited lower permeability. Long-term experiments revealed stronger fouling of the AN69 ST compared to the ATA membrane. We observed the highest permeability for the tested cytokines, the lowest thrombogenicity, and the lowest fouling with the ATA membrane. In CRRT, these factors may lead to increased therapy efficacy and lower incidence of coagulation-associated events.

Effects of Plasma Proteins on the Transport and Surface Characteristics of Polysulfone/Polyethersulfone and Asymmetric Cellulose Triacetate High Flux Dialyzers.

Blood-membrane interactions can have a large impact on the performance of hemodialysis membranes, particularly for high flux membranes in which the membrane itself provides very low resistance to solute transport. The objective of this study was to examine the effects of exposure to serum on the solute clearance and convective sieving characteristics of high flux polysulfone (Optiflux F250NR), polyethersulfone (ELISIO-25H), and asymmetric cellulose triacetate (SOLACEA-25H) hemodialyzers using both vitamin B12 and a range of polydisperse dextrans. Zeta potential measurements were used to obtain additional insights into the changes in membrane surface properties. Exposure to serum in a simulated dialysis session caused a significant reduction in both solute clearance and sieving coefficients for the polysulfone/polyethersulfone dialyzers, particularly for the larger molecular weight solutes. In contrast, the transport characteristics of the asymmetric cellulose triacetate dialyzers were almost unchanged after exposure to serum. The zeta potential of the cellulose triacetate membrane became slightly more negative after exposure to serum, consistent with an adsorbed protein layer composed largely of albumin. The net result is that the asymmetric cellulose triacetate dialyzer had dramatically higher clearance of the larger dextrans after exposure to serum, with the clearance and sieving coefficient for a 10 kDa molecular weight dextran being more than an order of magnitude greater than that of the polysulfone/polyethersulfone membranes. These results provide important insights into the expected clinical performance of these high flux dialyzers.

Glomerular hyperpermeability after acute unilateral ureteral obstruction: effects of Tempol, NOS, RhoA, and Rac-1 inhibition.

It is well known that proteinuria following urinary tract obstruction is mainly of a tubular nature. However, it is unknown whether there are also changes in glomerular permeability. In this study, we compared glomerular sieving coefficients (θ) of polydisperse fluorescein isothiocyanate (FITC)-Ficoll 70/400 following a 120- or 180-min unilateral ureteral obstruction (UUO) in anesthetized Sprague-Dawley rats. Samples were collected from the obstructed kidney at 5, 15, and 30 min postrelease and analyzed by means of high-pressure size-exclusion chromatography. After 120-min UUO, mean θ for Ficoll70Å was increased ( P < 0.01) from 2.2 ± 0.5 × 10-5 (baseline) to 10.6 ± 10 × 10-5 15 min postrelease (highest value). After 180-min UUO, mean θ for Ficoll70Å was further increased ( P < 0.001) from 1.4 ± 0.5 × 10-5 (baseline) to 40 ± 10 × 10-5 at 5 min postrelease (highest value). Administration of a reactive oxygen species (ROS) scavenger (Tempol; 1 mg·kg-1·min-1) partly abrogated the permeability effects following 120-min UUO but not after 180 min. Moreover, administration of the RhoA kinase inhibitor Y-27632, the nitric oxide synthase inhibitor NG-nitro-l-arginine methyl ester, or Rac-1 inhibition did not ameliorate glomerular hyperpermeability following 180-min UUO. We show, for the first time, that acute UUO results in marked elevations in glomerular permeability. In addition, our data suggest a time-dependent pathophysiology of UUO-induced hyperpermeability, where reactive oxygen species generation may play an important role in the early stages.

Super High-Flux Continuous Venovenous Hemodialysis Using Regional Citrate Anticoagulation: Long-Term Stability of Middle Molecule Clearance.

Continuous renal replacement therapy is a standard treatment in critically ill patients with acute kidney injury. All CRRT techniques provide a high low-molecular weight clearance but even with hemofiltration, clearance of middle molecules is low. We investigated whether a new super high-flux hemofilter provides effective and sustained middle molecule clearance during citrate-anticoagulated continuous venovenous hemodialysis for up to 72 h. We included 14 critically ill patients with AKI-KDIGO-III in a prospective observational trial. We measured/calculated blood and urine concentrations, clearances and sieving coefficients of eight molecules with molecular weights from 60 to 66 kDa, hemodynamic parameters and SAPS-II scores. All filters were patent at 72 h. Clearance and sieving coefficients of small solutes were high and sustained over time, those for larger solutes decreased over 72 h but remained high enough to decrease blood concentrations of solutes up to 25 kDa. Albumin serum levels remained unaffected. Catecholamine doses and SAPS-II scores decreased significantly. This new hemofilter may improve blood purification in critically ill patients with AKI.