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PubMed2003

Evaluation of microspheres as surrogates for Cryptosporidium parvum oocysts in filtration experiments.

The size and surface characteristics of a surrogate particle and Cryptosporidium parvum oocysts are important in determining the ability of the particle to mimic the behavior of C. parvum oocysts in filtration and particle transport experiments. The zeta potential, hydrophobicity, and filterability of a surrogate particle, 5 microm carboxylated latex microspheres, and oocysts were compared for a variety of solution conditions. C. pervum oocysts had a slightly negative zeta potential (-1.5 to -12.5 mV) at pH 6.7 over a wide range of calcium concentration (10(-6)-10(-1) M), while the fluorescent microspheres were more negatively charged under the same conditions (-7.4 to -50.2 mV). After exposure to 5 mg of C/L of Suwanee River natural organic matter (NOM), the ; potentials of both particles became significantly more negative, with the microspheres consistently maintaining a more negative zeta potential than the oocysts. Alum was able to neutralize the negative zeta potentials of both particles when in the presence of NOM, but nearly twice the dosage was required for the microspheres. NOM also affected the hydrophobicity of the particles by increasing the hydrophobicity of the relatively hydrophilic oocysts and decreasing the hydrophobicity of the relatively hydrophobic microspheres. A bench-scale filtration system removed less microspheres (40.3 +/- 1.5%) than oocysts (49.7 +/- 2.9%) when 0.01 M CaCl2 was supplied as coagulant. After preexposure to 5 mg of C/L of NOM, the removals of both particles declined significantly, and the removals of microspheres (13.7 +/- 1.5%) and oocysts (16.3 +/- 1.5%) were similar. Finally, the removal efficiencies of microspheres and oocysts in the presence of NOM increased to 69.3 +/- 3.5% and 67.7 +/- 6.4%, respectively, when alum was supplied as coagulant at the optimum dosage needed to destabilize the oocysts. These experimental results suggest that microspheres can be used to provide a conservative estimate of oocyst removal in filters containing hydrophilic negatively charged filter media.

Animals↗
PubMed2003

Syringe filtration methods for examining dissolved and colloidal trace element distributions in remote field locations.

It is well-established that sampling and sample processing can easily introduce contamination into dissolved trace element samples if precautions are not taken. However, work in remote locations sometimes precludes bringing bulky clean lab equipment into the field and likewise may make timely transport of samples to the lab for processing impossible. Straightforward syringe filtration methods are described here for collecting small quantities (15 mL) of 0.45- and 0.02-microm filtered river water in an uncontaminated manner. These filtration methods take advantage of recent advances in analytical capabilities that require only small amounts of waterfor analysis of a suite of dissolved trace elements. Filter clogging and solute rejection artifacts appear to be minimal, although some adsorption of metals and organics does affect the first approximately 10 mL of water passing through the filters. Overall the methods are clean, easy to use, and provide reproducible representations of the dissolved and colloidal fractions of trace elements in river waters. Furthermore, sample processing materials can be prepared well in advance in a clean lab and transported cleanly and compactly to the field. Application of these methods is illustrated with data from remote locations in the Rocky Mountains and along the Yukon River. Evidence from field flow fractionation suggests that the 0.02-microm filters may provide a practical cutoff to distinguish metals associated with small inorganic and organic complexes from those associated with silicate and oxide colloids.

Colloids↗
PubMed2005

Comparison of centrifugation and filtration techniques for the size fractionation of colloidal material in soil suspensions using sedimentation field-flow fractionation.

Sedimentation field-flow fractionation (SdFFF) with UV detection is used to systematically investigate the effect of traditional membrane filtration and centrifugation procedures on the isolation of specific size fractions from soil suspensions. Both procedures were used to isolate the nominal <0.45 and <0.2 microm fractions from a clay soil suspension. Results showed that the membrane filtration approach seriously underestimated the total mass of particulate matter present as compared to the centrifugation approach. This has serious implications forthe interpretation of results for "colloidal" and "soluble" fractions from soil suspensions and other environmental matrices obtained using the standard membrane approach. The results also show that sedimentation FFF has great potential as a robust and relatively mild technology for studying size distributions in the "colloidal" range for soil suspensions and other aquatic matrices.

Centrifugation↗
PubMed2005

Hexavalent chromium removal by reduction with ferrous sulfate, coagulation, and filtration: a pilot-scale study.

A flow-through pilot-scale system was tested for removal of Cr(VI) from contaminated groundwater in Glendale, California. The process consisted of the reduction of Cr(VI) to Cr(lll) using ferrous sulfate followed by coagulation and filtration. Results indicated that the technology could reduce influent Cr(VI) concentrations of 100 microg L(-1) to below detectable levels and also remove total Cr (Cr(VI) plus Cr(lll)) to very low concentrations (< 5 microg L(-1)) under optimized conditions. Complete reduction of Cr(VI) to Cr(lll) was accomplished with Fe(ll) doses of 10-50 times the Cr(Vl) concentration even in the presence of significant dissolved oxygen levels. The overall Cr removal efficiency was largely determined by the filterability of Cr(lll) and Fe(lll) precipitates, of which a relatively high filtration pH (7.5-7.6) and high filter loading rate (6 gpm ft(-2)) had negative impacts. The pilot system was able to operate for an extended time period (23-46 h depending on the Fe:Cr mass ratio) before turbidity breakthrough or high head loss. Backwash water was effectively settled with low doses (0.2-1.0 mg L(-1)) of high molecular weight polymer. Backwash solids were found to be nonhazardous bythe toxicity characteristic leaching procedure but hazardous by the California waste extraction test.

California↗
PubMed2006

Understanding the size and character of fouling-causing substances from effluent organic matter (EfOM) in low-pressure membrane filtration.

Stirred cell tests with microfiltration (MF) and ultrafiltration (UF) membranes show high flux decline for WWTP effluents. For the MF membrane, for example, the flux declines within 15 min to 70-80% of the initial flux (J0 is in the range of 1000 L/m2h to 1500 L/m2h). This time corresponds to the filtration of a cumulative volume of 110 L/m2. Feed and permeate samples of the stirred cell tests are analyzed by size-exclusion chromatography (SEC) with on-line organic carbon and UVA254 detection. The resulting chromatograms exhibit a clear difference between the feed and permeate samples in the so-called polysaccharide (PS) peak. The substances eluting in the PS peak (organic colloids, polysaccharides, and proteins) are retained completely by UF membranes and partly by MF membranes, and are responsible for the observed fouling. By sequential filtration experiments the sizes of these macromolecules are determined to be in the range of 10 to 100 nm.

Chromatography, Gel↗
PubMed2006

Time-resolved luminescence screening of antibiotics in tissue matrices without centrifugation and filtration: spiked recovery studies.

Analyses of chemical residues in animal tissue matrices require multistep sample preparation. To simplify this process, a methodology was developed that combines sorbent extraction and solid-matrix time-resolved luminescence (TRL); it was applied to tetracycline screening in milk. Reported here is an effort to extend its application to tissue matrices, illustrated by oxytetracycline (OTC) screening in catfish muscle. Extraction and enrichment are accomplished by immersing small C18 sorbent strips into tissue homogenates for 20 min, followed by a 3 min rinse in water and a 2 min dip in a reagent solution. After desiccation, TRL is measured directly on the sorbent surface. Tissue particulates no longer interfere via attenuation or scattering, rendering centrifugation and filtration unnecessary. The integrated TRL intensity shows a linear dependence on OTC concentration in the 0-8 microg/g range (R2 = 0.9992) with a 0.026 microg/g limit of detection. To screen OTC at 2 microg/g, the U.S. regulatory tolerance level, a threshold is established at x2-3sigma2, where x2 and sigma2 are the mean and standard deviation, respectively, of the TRL signals from 15 samples fortified at 2 microg/g. Among 45 blind samples randomly fortified at 0-4 microg/g, 41 were screened correctly and 4 negative samples were presumed positive. This method has the potential to improve throughput and save assay costs by eliminating acids, organic solvents, centrifugation, and filtration.

Animals↗
PubMed2005

Effects of clarification and filtration processes on the removal of fungicide residues in red wines (var. Monastrell).

The effects of six clarification agents (egg albumin, blood albumin, bentonite plus gelatin, charcoal, PVPP, and silica gel) on the removal of residues of four fungicides (cyprodinil, fludioxonil, pyrimethanil, and quinoxyfen) applied directly to a racked red wine, elaborated from Monastrell variety grapes from the D.O. region of Jumilla (Murcia, Spain), are studied. The clarified wines were filtered with 0.45 microm nylon filters to determine the influence of this winemaking process in the disappearance of fungicide residues. Analytical determination of cyprodinil, fludioxonil and pyrimethanil was performed by gas chromatography with an alkaline thermoionic detector (NPD), whereas that of quinoxyfen using an electron captor detector (ECD). In general, and for all of the fungicides except quinoxyfen, blood albumin has proved to be the most effective clarifying agent in the removal of residues, whereas silica gel proved to be ineffective against all of the pesticides with the exception of fludioxonil. Quinoxyfen is the least persistent fungicide in the clarified wines and that which appears with highest frequency in the lees. In general, filtration is not an effective step in the elimination of wine residues. The greatest elimination after filtration is obtained in wines clarified with charcoal and the lowest in those clarified with PVPP.

Charcoal↗
PubMed1992

Sterile filtration of a parenteral emulsion.

The Syntex adjuvant formulation (SAF) containing [thr1]-muramyldipeptide in an oil-in-water emulsion has proven to be an effective adjuvant eliciting both cell-mediated and humoral immune response. As a parenteral emulsion, sterility of the final product was a concern, and various methods of achieving sterility were considered. For emulsions, most conventional sterilization methods are not viable, requiring the more cumbersome technique of sterilizing individual components and assembling/manufacturing under sterile conditions. Emulsion vehicles were manufactured with various models in the Microfluidizer M110 series. All equipment examined was capable of reducing the average dispersed oil droplet size to approximately 160 nm, with varying size ranges. Operating at an internal equipment pressure of greater than 16,000 psi, with at least five cycles through the interaction chamber, the resulting emulsion had a narrow droplet size range distribution, with the largest droplets being small enough to enable sterile filtration. Under specific-manufacturing conditions, the adjuvant emulsion becomes easily filtered through a 0.22-micron cartridge filter, thus yielding a sterile end product. This is the first published example of emulsion sterilization being achieved by terminal filtration.

Chemistry, Pharmaceutical↗
PubMed2001

Long-term infusion of atrial natriuretic peptide (ANP) improves renal blood flow and glomerular filtration rate in clinical acute renal failure.

BACKGROUND: Short-term infusion of atrial natriuretic peptide (ANP) increases renal blood flow (RBF) and glomerular filtration rate (GFR) in patients with acute renal dysfunction. In the present study we evaluated the effects of long-term infusion (>48 h) of ANP on (RBF) and (GFR) in 11 postcardiac surgical patients requiring pharmacological circulatory support and with acute renal impairment. METHODS: Urinary clearance of Cr-EDTA and PAH as well as central hemodynamic measurements were performed for 2-3 consecutive 30-min periods during ANP infusion (50 ng. kg-1. min-1), one hour after abrupt discontinuation of ANP and again immediately after reinstitution of ANP infusion. RESULTS: During ANP infusion, urine flow (UF), GFR, RBF and renal vascular resistance (RVR) were 6.4+/-1.1 ml. min-1, 19.9+/-3.1 ml. min-1, 408+/-108 ml. min-1 and 0.286+/-0.054 mmHg. min. ml-1, respectively. UF, GFR and RBF decreased significantly by 28% (P<0.001), 32% (P<0.01) and 31% (P<0.05), respectively when ANP infusion was discontinued. RVR increased by 93% (P<0.05) while there was no change in filtration fraction. After reinstitution of ANP infusion, all measured renal variables returned to baseline. There was no significant correlation between the number of ANP treatment days and the percentage decrease in GFR (r=0.18) or RBF (r=0.22) during ANP withdrawal. Central hemodynamic variables were not affected by ANP withdrawal. CONCLUSIONS: ANP infusion improves RBF and GFR in patients with acute renal impairment after cardiac surgery. This renal vasodilatory effect is maintained during a long-term infusion and seems to be hemodynamically safe.

Acute Kidney Injury↗
PubMed2001

Double filtration plasmapheresis in the treatment of myasthenic crisis--analysis of prognostic factors and efficacy.

OBJECTIVES: To examine the prognostic factors and outcome of myasthenia gravis (MG) patients in crisis with double filtration plasmapheresis (DFP) treatment. MATERIAL AND METHODS: A total of 15 patients experienced 20 episodes of crisis during the study period. Plasmapheresis was carried out using a double filtration METHOD: Demographic information, clinical features of crisis, and associated complications were analyzed. RESULTS: The median duration of crisis was 9 days. Chest infection was the most common precipitant of crisis. Twelve out of the 20 episodes (60%) responded well to DFP and mechanical ventilation was discontinued after the third session of DFP in 8 of them. Three significant predictors for prolonged crisis were shorter intervals between the onset of MG and the first crisis (P=0.04), higher serum bicarbonate levels at baseline (P=0.03) and the thymic pathology of thymoma (P=0.03). CONCLUSION: DFP can ameliorate the profound weakness in crisis and seems to be a rational therapy for patients with myasthenic crisis.

Adolescent↗
PubMed2001

Crossflow filtration in suspension-feeding fishes.

Rows of comb-like or tufted gill rakers in the oral cavity of suspension-feeding fishes (for example, herring, anchovies and tilapia) have been thought to serve as (1) non-porous barriers that direct particle-laden water to the sticky oral roof, where particles are retained as water exits from the oral cavity, (2) conventional dead-end filters that sieve particles from water exiting between rakers, or (3) sticky filters that retain particles encountered by a hydrosol filtration mechanism. Here we present data from computational fluid dynamics and video endoscopy in suspension-feeding fish indicating that the rakers of three distantly related species function instead as a crossflow filter. Particles are concentrated inside the oral cavity as filtrate exits between the rakers, but particles are not retained on the rakers. Instead, the high-velocity crossflow along the rakers carries particles away from the raker surfaces and transports the particles towards the oesophagus. This crossflow prevents particles from clogging the gaps between the rakers, and solves the mystery of particle transport from the rakers to the oesophagus.

Animals↗
PubMed1977

Micropuncture studies of the filtration and absorption of albumin by nephrotic rats.

The proximal tubular fluid albumin concentration of rats with immunologically induced nephrotic syndrome rose from 0.60 +/- 0.11 (SEM) mg/100 ml to 7.42 to 0.87 mg/100 ml. The glomerular filtration rate (GFR) was slightly depressed (P less than 0.001) and fractional water absorption unchanged (P greater than 0.45). Urinary albumin excretion rose from 0.18 +/- 0.03 (SEM) mg/100 g of body wt/24 hr to 78.5 +/- 39.5 mg/100 g/100 g of body wt/24 hr (P less than 0.001). The concentration of albumin in glomerular filtrate, calculated as the product of proximal tubular albumin concentration and fractional water absorption (4.53 +/- 0.60 mg [SEM]/100 ml), equalled that calculated from urine albumin concentration and whole kidney water absorption (4.14 +/- 0.84 mg/100 ml, P greater than 0.30). The data are interpreted to reflect a significant increase in filtered albumin and only a modest (if any) tubular albumin absorption in this study. Thus, the concept that tubular absorption plays a major role in the catabolism of albumin and the genesis of hypoalbuminemia in the nephrotic syndrome could not be confirmed.

Absorption↗
PubMed1984

Evaluation of the micropuncture determination of single nephron filtration fraction.

Spontaneous and aspirated blood samples were collected from the welling points of surface efferent arterioles in the rat kidney. The amount of tubular reabsorbate in each sample was calculated from measurements of the inulin concentration in the sample and systemic arterial plasma. Both spontaneous and aspirated samples contained substantial amounts of tubular reabsorbate (4% +/- 1% and 11% +/- 1%, respectively). Accordingly, the single nephron filtration fraction values derived from measurements of albumin concentrations alone were significantly lower than those calculated considering the addition of the amount of tubular reabsorbate in each sample (0.26 +/- 0.01 vs. 0.30 +/- 0.01 and 0.25 +/- 0.01 vs. 0.34 +/- 0.01 for the spontaneous and aspirated samples, respectively). Increasing the rate of blood collection from the welling point by aspiration was associated with a significant decrease in the hydraulic pressure in the same vessel. The efferent arteriolar blood samples were therefore probably contaminated with tubular reabsorbate as a result of retrograde flow from the peritubular capillaries. It was confirmed that single nephron filtration fractions derived from hematocrit measurements were significantly higher than those based on albumin concentration measurements, supporting that the hematocrit of afferent arteriolar blood of the superficial nephrons is higher than that of systemic arterial blood.

Animals↗
PubMed1986

Interglomerular heterogeneity of filtration fraction among superficial nephrons: fact or artifact.

The variance (S2inter-G) in protein concentration (CE) of plasma samples collected by micropuncture from randomly chosen surface efferent arterioles was compared to the variance (S2intra-G) of samples collected and re-collected from the same efferent arterioles in 23 Munich-Wistar rats. During efferent arteriolar blood collection, an oil droplet was maintained with gentle suction downstream to the collection pipette to avoid disturbance of natural glomerular blood outflow. S2inter-G averaged 0.067 +/- 0.014 (SE), a value comparable to mean S2intra-G (0.075 +/- 0.016, P greater than 0.50), indicating that the degree of interglomerular heterogeneity in the value of filtration fraction is too small to detect with this micropuncture technique. When ten additional samples were collected using uncontrolled suction pressure, S2inter-G averaged 1.15 +/- 1.30, a value markedly greater than that obtained with controlled pressure. In six nephrons which possessed both glomeruli and efferent arterioles on the surface of the kidney, glomerular capillary pressure (PGC) was monitored during efferent arteriolar blood collection. Applying widely varied suction pressure, PGC changed as much as 42 mmHg, suggesting that improper suction pressure can alter glomerular pressures and flows, hence filtration fraction and CE. Thus, unlike renal proximal tubules, some of the rat renal efferent arterioles do not function as Starling resistors, which may, in turn, account for the wide variability in CE values reported recently by some investigators.

Animals↗
PubMed1988

Serial assessment of glomerular filtration rate in lupus nephropathy.

In patients with lupus nephropathy (LN), previous studies have shown that creatinine clearance (CCr) overestimates true glomerular filtration rate as measured by inulin clearance (CIn), and that among patients the degree of overestimation is highly variable. We sought to determine whether the discrepancy between CCr and CIn remains constant over time (months, years) in each individual patient, and therefore whether serial measurements of CCr reliably reflect the direction and magnitude of change in CIn. Twenty-five patients with LN underwent simultaneous determinations of CCr and CIn performed two to four (mean 3.3) times over three years. In a given patient, it was found that the ratio of CCr/CIn changed substantially over time (mean SD 0.16 with 95% confidence interval of 0.12 to 0.20). Thus, in about 32% of cases the ratio of CCr/CIn will vary more than +/- 16% from a previously measured value of CCr/CIn. Patients with both high and low values of CIn showed similar variability in CCR/CIn over time. Variability in CCr/CIn was found regardless of whether CIn was increasing, decreasing, or constant over time. In nearly one-half of all measurements of CCr, the corresponding change in CIn was directionally discordant. Iothalamate and technetium-DTPA renal clearances correlated highly with CIn (R2 = 0.99). We conclude that the discrepancy between CCr and CIn can vary greatly over time in an individual patient. Consequently, serial CCr does not accurately measure the direction or magnitude of change in glomerular filtration rate in lupus nephropathy.

Adult↗
PubMed1993

Somatostatin antagonizes angiotensin II effects on mesangial cell contraction and glomerular filtration.

The effects of somatostatin (ST) on the regulation of the glomerular filtration rate have not been extensively studied. The present experiments were designed to analyze this possible relationship. ST alone did not modify the planar cell surface area (PCSA) of cultured rat mesangial cells (CRMC), but it prevented and reversed the reduction in PCSA induced by 10 nM angiotensin II (Ang II) in a dose- and time-dependent manner. ST (1 microM) completely prevented and reversed the increase in the myosin light chain phosphorylation induced by 10 nM Ang II. Incubation with pertussis toxin (PT, 0.5 micrograms/ml) inhibited the effect of ST on the Ang II-dependent changes in PCSA, but this effect was not inhibited by the blockade of the vasodilatory prostaglandins (indomethacin, 10 microM) or nitric oxide (L-N-methyl-arginine, 0.2 mM) synthesis. 2',5'-dideoxyadenosine (DDA, 0.1 mM), an adenylate cyclase blocker, and methylene blue (MB, 30 microM), a soluble guanylate cyclase blocker, did not interfere with the ST inhibitory effect on the Ang II-dependent reduction in PCSA of rat mesangial cells. ST also blocked the reduction in PCSA induced by phorbol myristate acetate (PMA, 300 nM). ST was also able to prevent and revert the Ang II dependent reduction in glomerular cross-sectional area of isolated rat glomeruli, also in a dose- and time-dependent fashion. Finally, intravenous administration of ST (200 ng/kg body wt as a bolus plus a continuous injection of 25 ng/min/kg body wt) partially blocked the reduction in GFR (measured as CIn) and RPF (measured as CPAH) and the increase in filtration fraction induced by the intravenous administration of Ang II (1.7 micrograms/min/kg body wt) in anesthetized rats. In summary, these results suggest that ST could antagonize the renal actions of Ang II, increasing the GFR and RPF decreased by Ang II, and this effect could be dependent, at least partially, on a direct relaxing effect of ST on mesangial cells.

Adenylate Cyclase Toxin↗
PubMed1996

Structural continuity of filtration slit (slit diaphragm) to plasma membrane of podocyte.

Murine monoclonal antibody 5-1-6 was reported to bind to the slit membrane and closely related structures in rat renal glomeruli; it induced heavy, reversible proteinuria and appeared to redistribute onto the plasma membrane of epithelial cells after binding at the original target sites. This phenomenon of antigenic movement has not been analyzed in detail to date. In addition to normal kidneys we also studied localization of the antigen recognized by monoclonal antibody 5-1-6 in protamine sulfate-perfused rat kidneys, in which slit diaphragms are known to be functionally modified. Isolated glomeruli as well as ultrathin kidney cryosections were labeled by the immunogold technique to clarify the relation between this antigen and the slit diaphragm. Sequential localization of injected monoclonal antibody was visualized using a post-embedding immunogold method in rats 2 hours to 12 days after injection of antibody. Ultrastructural immunogold labeling demonstrated that under normal conditions antigenic molecules were expressed mainly in the area beneath the slit diaphragms. Occasionally labeling was found at the base of the foot process, facing the glomerular basement membrane. After protamine sulfate treatment antigenic sites were dislocated due to the lifting and disruption of slit diaphragms, indicating that this antigen is associated with slit diaphragms. Injected antibody was localized at the filtration slits at 2 hours, and by 12 hours it had moved onto the apical plasma cell membrane of foot process. In addition, from 3 days onwards patch or cap-like formation on the plasma cell membrane of podocytes was seen. Possible shedding of antibody from podocyte cell surface membrane was occasionally encountered, but internalization of antibody was a minor event. Elution experiments in isolated glomeruli at day 3 indicated that antigen and antibody were both localized on the podocyte cell surface membrane, suggesting redistribution of immune complexes. In conclusion, filtration slits (slit diaphragms) and the apical membrane of foot process of podocytes demonstrate structural continuity, as revealed by the movement of the antigen recognized by monoclonal antibody 5-1-6 as antigen-antibody complexes.

Animals↗
PubMed2000

Clinical retroviral vector production: step filtration using clinically approved filters improves titers.

Production of retroviral vectors for clinical use requires removal of cells and cellular debris. We combined a series of filters of decreasing pore size using commercially available blood banking filters approved for clinical use. The collection bag and filters can be connected to create a sterile, closed system using clinically approved tubing and sealing systems. Even when challenged with a large number of vector producer cells (2.38 x 10(9)cells), no viable cells are passed through the system. The step filtration system developed minimizes the titer reduction associated with filtration, provides rapid flow rates, and was cost effective when filtering volumes in excess of 2 liters.

Filtration↗