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At least 541 records · Page 30Linked to original sources
PubMedDate not supplied

[On-line haemodiafiltration with sorbent-regenerated ultrafiltrate as replacement fluid: Beta2-microglobulin removal versus filtration fraction].

PURPOSE: In order to encourage the removal of middle molecules in hemodiafiltration (HDF) techniques an attempt is made to maximize convective clearance by increasing the ultrafiltration rate. However, convective clearance is limited by the maximum filtration fraction (FF%) obtainable, by the pre- or post reinfusion method and by the convective surface and the capacity of the filter used. This study aimed to evaluate the effect of the FF% in the removal of Beta2-microglobulin (Beta2-m) during hemodiafiltration reinfusion (HFR) to identify the best ultrafiltration strategies; and therefore, a better removal of medium molecular weight solutes in this hemodiafiltrative technique recently introduced in clinical practice. METHODS: Ten chronic uremic patients (eight males, two females; age 66 +/- 18 yrs) already on renal dialysis therapy (RDT) for 80 +/- 36 months, were subjected to four HFR sessions, with Td=240 +/- 10 min, Qb=312 +/- 18 and Qd=500 mL/min; the reinfusion rates (Qr) used were 43.6 +/- 7.2 mL/min (25-58) with FF% rates varying from 20-34 (24.2 +/- 3.8) for hematocritic levels of 34.6 +/- 4.2% at the start of the dialysis session. For each session the intradialytic reduction rates (RR%) of urea, creatinine (Cr), phosphate, uric acid and Beta2-m and its average clearance (KBeta2-m mL/min) were evaluated. RESULTS: The results obtained gave a RR% for urea of 69.4 +/- 5 (Kt/Veq=1.23 +/- 0.2) and for Cr, phosphate and uric acid values of, respectively, 61.2 +/- 5.4, 47.5 +/- 10 and 75.8 +/- 6.7. The intradialytic reductions in Beta2-m were 49.3 +/- 10.3% with a variability range from 29-69% and with average KBeta2-m values of 63.8 +/- 13.5 mL/min. The RR% of ss2-m and KBeta2-m were inversely correlated (p<0.01) to the FF% rate applied during the treatment; 75% of the HRF sessions in which we observed a reduction in Beta2-m levels >40% were those where a FF% between 20 and 26% was applied. CONCLUSIONS. From our study, it appears that in HFR the best ultrafiltration strategy from the convective sector in removing Beta2-m has FF% values in the range 20-26%. The occurrence of lower intradialytic reductions of Beta2-m with increasing FF% can be interpreted as a consequence of phenomena related to high intradialytic hemoconcentrations, to the excessive increase in the TMP and/or the increase in the protein cake with a consequent reduction in permeability and mass transfer. Although using a limited convective surface with a limited possibility of increasing the FF%, nevertheless, HFR seems capable of ensuring a satisfactory uremic toxin removal of low and medium molecular weight, which combined with the high biocompatibility deriving from the use of reinfused endogen, can be considered an effective dialytic strategy for preventing or retarding the complications in dialytic patients.

Aged↗
PubMed1990

[Effect of serum and ultrafiltrate (less than 50 k DA) of normal serum and uremic serum from chronic hemodialysis children on lipid peroxidation and vitality of fetal rat hepatocytes in vitro].

The influence of ultrafiltrate with a molecular exclusion border of less than 50 kDa of hemodialyzed children on viability and lipid peroxidation (LPO) of hepatocytes was investigated in the model of fetal rat hepatocytes. Viability of cells was estimated by trybanblue test and malondialdehyde equivalents (MDA) were estimated by thiobarbiturate method as parameters of LPO. Ultrafiltrate of uremic patients may lead to a concentration-dependent loss of viability and simultaneous reduction of MDA formation of hepatocytes after incubation of 120 min. Uremic serum may reduce the viability, but not the MDA formation of hepatocytes opposite to uremic ultrafiltrate (p less than 0.01). In uremic serum high molecular substances (greater than 50 kDa) may show a cytotoxic effect, but on the other side low and high molecular substances may increase the antioxidative capacity in comparison with serum of healthy volunteers.

Adolescent↗
PubMed1989

Peritoneal ultrafiltration and fluid reabsorption during peritoneal dialysis.

Peritoneal ultrafiltration and fluid reabsorption characteristics for 18 patients undergoing continuous ambulatory peritoneal dialysis (CAPD) were investigated in single dwell studies of 6 h duration with 21 of 3.86% glucose dialysis fluid. Dialysate volumes were determined in situ using radioiodinated serum albumin (RISA) as volume marker with a correction applied for the total elimination of RISA from the peritoneal cavity. The RISA elimination rate was calculated as 2.1 +/- 0.5 ml/min. The true dialysate volume after 360 min was on average 28% less than the apparent volume calculated without correction for the elimination of RISA. The mean maximum true volume plus sampling losses was 3255 ml at 240 min, corresponding to a mean net ultrafiltration volume of 762 ml between 3 min and 240 min. The mean net fluid reabsorption rate between 240 min and 360 min was 1.2 +/- 0.7 ml/min. This study of standard dialysate volume/time curves in clinically stable CAPD patients using hypertonic dialysis fluid shows that about 90% of the total net ultrafiltration is achieved during the first 90 min of the dwell. After an extended period of dialysate isovolaemia, usually lasting as long as between 120 min and 240 min, fluid reabsorption is observed in all patients.

Aged↗
PubMed1989

[Isolated ultrafiltration of the blood in patients with refractory heart failure: the status of the renin-angiotensin-aldosterone system and the secretion of antidiuretic hormone].

Isolated ultrafiltration was performed in 107 patients with refractory heart failure (HF) which developed in the presence of different cardiovascular diseases. The beneficial action of isolated ultrafiltration in 71 patients (68%) with refractory HF was determined by complex interaction of the effects provoked by ultrafiltrate removal. Among those effects of paramount importance was correction of secondary hyperaldosteronism and reduction of the concentration of antidiuretic hormone accompanied by the improvement of liver and heart functions.

Acute Disease↗
PubMed1980

[Growth-stimulating effect of serum ultrafiltrates on BHK-21 cells].

The growth of BHK-21 cells exposed to various bovine serum ultrafiltrates has been studied. The intensity of cell multiplication equal to that seen in the presence of the whole serum was provided only by the ultra filtrate containing all components with molecular weights up to 200 000 dalton. Ultrafiltrates containing components with molecular weight up to 70 000 dalton or from 70 000 to 200 000 dalton provided stretching of cells and their partial multiplication. Ultrafiltrates containing components with molecular weight up to 14 000 dalton stimulated only attachment of cells, without stretching.

Animals↗
PubMedDate not supplied

[Doppler laser interferometry in the determination of ultrafiltrate consumption].

To evaluate the clinical efficiency of hemodialysis and ultrafiltration monitoring, the consumption and volume of an ultrafiltrate should be timely measured. Balance measurement of changes in a patient's body weight during hemodialysis has a significant methodological error made by patient's body weight changes unassociated with ultrafiltration.

Hemofiltration↗
PubMed1993

Testosterone concentration is increased in whole saliva, but not in ultrafiltrate, after toothbrushing.

The concentration of testosterone in whole saliva is significantly increased (by 9%) after toothbrushing. In ultrafiltrates of saliva collected at the same time as the whole saliva, testosterone concentrations after toothbrushing were unchanged. In 88% of the 162 whole-saliva specimens, but not in the ultrafiltrates, we also measured higher hemoglobin concentrations after toothbrushing. We conclude that the increase of testosterone in whole saliva after toothbrushing can be attributed to a protein-bound fraction. For analytes that are bound to serum proteins, salivary measurements can give spurious results. This problem can be avoided by using as a diagnostic medium an ultrafiltrate of saliva collected directly in the mouth.

Adult↗
PubMed1998

Retention and regeneration of native NAD(H) in noncharged ultrafiltration membrane reactors: application to L-lactate and gluconate production.

NAD(H) was retained in a noncharged ultrafiltration membrane reactor for the simultaneous and continuous production of L-lactate and gluconate with coenzyme regeneration. Polyethyleneimine (PEI), a 50-kDa cationic polymer, achieved coenzyme retentions above 0.8 for PEI/NAD(H) molar ratios higher than 5. The ionic strength of the inlet medium caused a decrease of NAD(H) retention that can be counterbalanced by an initial addition of 1% bovine serum albumin (BSA). Continuous reactor performance in the presence of PEI and BSA showed that NAD(H), glucose dehydrogenase, and lactate dehydrogenase were retained by 10-kDa ultrafiltration membranes; L-lactate and gluconate were produced at conversions higher than 95%. PEI enhanced the thermal stability of the enzymes used and increased the catalytic efficiency of glucose dehydrogenase, while no effect was found on the kinetic parameters of lactate dehydrogenase. A model that implements the kinetic equations of the two enzymes describes the reactor behavior satisfactorily. In brief, the use of PEI to retain NAD(H) is a new interesting approach to be widely applied in continuous synthesis with the large number of known dehydrogenases.

Bioreactors↗
PubMed1999

Fractionation of sugar beet pulp into pectin, cellulose, and arabinose by arabinases combined with ultrafiltration.

Incubation of beet pulp with two arabinases (alpha-L-arabinofuranosidase and endo-arabinase), used singularly or in combination at different units of activity per gram of beet pulp, caused the hydrolysis of arabinan, which produced a hydrolyzate consisting mainly of arabinose. Pectin and a residue enriched with cellulose were subsequently separated from the incubation mixture. The best enzymatic hydrolysis results were obtained when 100 U/g of beet pulp of each enzyme worked synergistically with yields of 100% arabinose and 91.7% pectin. These yields were higher than those obtained with traditional chemical hydrolysis. The pectin fraction showed a low content of neutral sugar content and the cellulose residue contained only a small amount of pentoses. Semicontinuous hydrolysis with enzyme recycling in an ultrafiltration unit was also carried out to separate arabinose, pectin, and cellulose from beet pulp in 7 cycles of hydrolysis followed by ultrafiltration. The yields of separation were similar to those obtained in batch experiments, with an enzyme consumption reduced by 3.5 times and some significant advantages over batch processes.

Arabinose↗
PubMed2000

Purification of lysozyme using ultrafiltration.

This article examines the separation of lysozyme from chicken egg white by ultrafiltration with 25 kDa and 50 kDa MWCO polysulfone membranes. The effects of pH, system hydrodynamics, feed concentration, and transmembrane pressure on permeate flux, lysozyme transmission, purification factor, and productivity have been discussed. With both types of membranes, higher permeate flux and lysozyme transmission were observed at higher pH. Higher lysozyme purity was generally obtained with the 25 kDa MWCO membrane. Purity of lysozyme decreased when the feed concentration was increased. With the 50 kDa MWCO membrane permeate flux, productivity and the purity of lysozyme were found to increase with increase in transmembrane pressure. The possibility of using a two-step ultrafiltration process for achieving high productivity along with high purity of lysozyme was also investigated.

Animals↗
PubMed1996

Endotoxin rejection by ultrafiltration through high-flux, hollow fiber filters.

The efficacy of endotoxin (ET) rejection of four hollow fiber membranes with comparable sieving properties was evaluated in an ultrafiltration experiment. The solution conditioned with type I lipopolysaccharide (LPS) from Escherichia coli, 80,000 endotoxin units (EU)/L, was filtered through polyesterpolymer alloy (PEPA), polymethyl methacrylate (PMMA), polyacrylonitrile (PAN), and polysulfone (PS) membranes. The ET activity of the filtrate was not detectable in PEPA and PMMA, 6.4 +/- .04 (mean +/- SD) EU/L in PAN, and 10.3 +/- 1.1 EU/L in PS. The ET activity of the filtrate of type II LPS from Acinetobacter solution, 80,000 EU/L, was not detectable in PEPA, 3.7 +/- 0.4 EU/L in PMMA, 16.5 +/- 1.5 EU/L in PAN, and 20.7 +/- 1.4 EU/L in the PS filter. The order of the rejection capability coincided with the adsorptive capacity as shown by the decrement in ET levels of solutions filled within the filter modules in the adsorption equilibrium experiment. In conclusion complete rejection of ET molecules can be achieved by ultrafiltration through hydrophobic membranes having a high adsorptive capacity in addition to an appropriate sieving property for ET molecules.

Acinetobacter↗
PubMed2001

Proteomic analysis of human plasma: failure of centrifugal ultrafiltration to remove albumin and other high molecular weight proteins.

Determination of specific low abundance proteins, usually by radiolabelled or enzyme-linked immunoassays in serum or plasma is widely used in diagnostic medicine. Substitution of these assays by a proteomic approach has been suggested, but this methodology has far from realised its potential as a diagnostic tool. The main protein fractions of plasma represent more than 80% of total protein, making the hundreds or even thousands of other proteins difficult to detect by two-dimensional electrophoresis (2-DE). Thus, loading sufficient sample to detect trace proteins invariably means excessive loading of albumin and other high abundance proteins. The aim of this study was to determine whether centrifugal ultrafiltration of whole plasma could be used to eliminate proteins exceeding a desired molecular weight cut-off. Cellulose filters with a 30 kDa molecular weight cut-off were used with whole plasma, and total protein was determined before and after ultrafiltration. Samples were processed by routine methods for 2-DE using 18 cm, pH 3-10 isoelectric focusing strips for the first dimension and 7-15% gradient gels for the second dimension followed by silver staining. Gel analysis of the retentate fraction (> 30 kDa) revealed a typical 2-DE plasma profile with most of the major landmark proteins in place and as expected, the gels lacked many of the smaller (< 30 kDa) proteins. Comparison with gels of the filtrate fraction (> 30 kDa) revealed very little difference. Not only were many of the higher molecular weight proteins still present, but some of the smaller < 30 kDa landmark proteins were absent. Overall, gels of both the retentate and filtrate fractions were less informative than gels of whole plasma.

Blood↗
PubMedDate not supplied

Ceforanide pharmacokinetics in haemodialysis: the effect of ultrafiltration.

The kinetics of ceforanide in plasma and dialysate was studied in 8 patients with terminal renal impairment after undergoing haemodialysis sessions lasting between 4 and 5 h. All patients received a single i.v. dose of 15 mg kg-1 of the drug at the start of the session. The dialysers used in this study were Spiraflow capillar 1.3 m2, Travenol plates 1.4 m2, and PAN plates. Blood flow ranged between 200 and 300 ml min-1 and dialysate flow between 500-650 ml min-1. Plasma ceforanide levels were measured at the input and output of the dialyser and the antibiotic levels in dialysate were determined coinciding with the withdrawal times of the blood samples. A microbiologic plate diffusion method was used to determine the antibiotic concentrations. The mean values of some pharmacokinetic parameters of ceforanide calculated with a non-linear regression program from the data obtained from arterial blood were the following: alpha (h-1) = 4.14 +/- 1.32; beta (h-1) = 0.26 +/- 0.07; t1/2 beta (h) = 2.82 +/- 0.82; Vdss (1) = 10.24 +/- 2.14. From the relationships between the antibiotic concentrations at the input and output of the dialyser it was possible to calculate an extraction coefficient of 0.11 +/- 0.06. The dialysis clearance of ceforanide was calculated from the determination of the extraction coefficient and from the measuring of antibiotic in dialysate, though different results were obtained with the two methods. Dialysis clearance calculated from the extraction coefficient showed a mean value of 18.68 +/- 12.16 ml min-1, significantly lower (p less than 0.01) than that established by analysis of the antibiotic in dialysate, which was 41.55 +/- 15.83 ml min-1. These differences may be attributed to problems related to the determination of blood flow and to the ultrafiltration capacity of the dialysis membranes. A linear relationship was established between the percentage error in the observed and predicted extraction coefficients and the ultrafiltration rate. The results obtained suggest that the simultaneous measurement of the antibiotic in plasma and dialysate is the most suitable method for predicting the dialysis clearance of the drug. The amount of antibiotic extracted over a 4-hour dialysis session proved to be equal to 57.85 +/- 15.62 per cent of the dose administered.

Adult↗
PubMed2002

Affinity ultrafiltration: effects of ligand binding on selectivity and process optimization.

The effective design of affinity ultrafiltration processes using a selective macroligand requires a detailed understanding of the effects of ligand-binding interactions on product yield and purification. Theoretical calculations were performed to evaluate the performance of affinity diafiltration separations with both competitive and independent binding interactions for the product and impurity. The intrinsic selectivity for independent binding decreased during the diafiltration due to the increase in fractional impurity binding as the impurity is selectively removed. The opposite behavior was seen for competitive binding because the strongly bound product displaces the impurity from the binding sites. Purification-yield diagrams were used to examine the effects of affinity-ligand concentration and binding constants on the separation. Model calculations were in excellent agreement with experimental data for the separation of tryptophan isomers using bovine serum albumin as the steroselective macroligand. Simulations with a fixed number of diavolumes show a clear optimum in product yield and purification factor at an intermediate ligand concentration due to the competing effects of the intrinsic selectivity and the rate of impurity removal. These results provide an appropriate framework for the design and optimization of affinity ultrafiltration systems.

Binding, Competitive↗
PubMed2005

Tangential flow microfiltration and ultrafiltration for human influenza A virus concentration and purification.

Large scale purification of viruses and viral vectors for gene therapy applications and viral vaccines is a major separation challenge. Here tangential flow microfiltration and ultrafiltration using flat sheet membranes has been investigated for concentration of human influenza A virus. Ultrafiltration membranes with molecular weight cutoffs of 100 and 300 kDa as well as 0.1, 0.2 and 0.45 microm microfiltration membranes have been tested. The results indicate that use of 300 kDa membranes not only concentrate the virus particles but also lead to a significant removal of host cell proteins and DNA in the permeate. Tangential flow filtration may be used to fractionate virus particles. Human influenza A virus particles are spherical with an average size of 100 nm. Use of a 0.1 microm membrane leads to passage of virus particles less than 100 nm into the permeate and an increase of larger particles in the retentate. These results suggest that control of the transmembrane pressure, membrane pore size and pore size distribution could enable isolation of intact virus particles from damaged virions. Isolation of the virus particles of interest from viral fragments and other particulate matter could result in simplification of subsequent purification steps. Larger pore size membranes such as 0.45 microm that allow the passage of all virus particles may be used to remove host cell fragments. In addition virus particles attached to these fragments will be removed. Careful selection of membrane morphology and operating conditions will be essential in order to maximize the benefit of tangential flow filtration steps in the purification of viral products from cell cultures.

Animals↗
PubMed2004

Ultrafiltration for proteomic sample preparation.

Proteome analysis represents significant challenges to the existing sample preparation techniques. Traditional methods, such as two-dimensional electrophoresis, typically separate high-molecular-weight proteins while discarding low-molecular-weight species. This approach is well justified considering the complexity of any proteome. However, it is desirable to extract the maximum amount of information from each sample to investigate the entire range of biomolecules. We have demonstrated that ultrafiltration not only improves two-dimensional electrophoresis (2-DE) resolution of the protein fraction but also yields the low-molecular-weight fraction amenable for further analysis by high-resolution mass spectrometry. This approach was successfully adapted to the variety of biological samples including cell and tissue lysates and serum. Therefore, ultrafiltration offers an alternative sample preparation technique that enables more thorough analysis of a proteome.

Animals↗
PubMed1990

Recovery of biosurfactants by ultrafiltration.

Ultrafiltration was used in a one-step method to purify and concentrate biosurfactants--surfactin and rhamnolipids--from culture supernatant fluids. The ability of surfactant molecules to form micelles at concentrations above the critical micelle concentration allows these aggregates to be retained by relatively high molecular weight cut-off membranes. Lower molecular weight impurities such as salts, free amino acids, peptides and small proteins are easily removed. Various molecular weight cut-off membranes were examined for the retention of surfactin and rhamnolipids (mol. wts 1036 and 802 respectively). Amicon XM 50 was the superior membrane for retention of surfactin and a 160-fold purification was rapidly achieved. The YM 10 membrane was the most appropriate for rhamnolipid recovery. Ultrafiltration can play an important role in biosurfactant purification as large volumes of media can be processed rapidly at extremely low cost.

Amino Acid Sequence↗
PubMed1992

Ultrafiltration membranes for the separation of catalyst and products in homogeneous catalysis systems.

Results of preliminary studies on concentration by ultrafiltration and reuse of a Ru(III)EDTA complex in homogeneous catalysis are reported. A method of preparation and selection of conditions of making cellulose acetate membranes for concentrating Ru(III)EDTA is described. At an operating pressure of 75 psig (517 kPa), the above catalyst can be concentrated to seven to eight times its initial concentration. The membrane used exhibits a separation of about 97.5% for the complex with a permeate flow rate of about 3-6 gallons per sq. ft per day. The catalyst activities were determined for two reactions, viz. hydroformylation of 1-hexene and carbonylation of ammonia for five cycles of concentration followed by reuse. The experimental data indicated that the catalyst concentration by ultrafiltration for subsequent reuse is simple and attractive and can provide potentially energy saving alternative to the cumbersome conventional separation processes associated with the recovery of catalysts in homogeneous catalysis.

Biotechnology↗