Largest recent impact craters on Mars: Orbital imaging and surface seismic co-investigation.

Two >130-meter-diameter impact craters formed on Mars during the later half of 2021. These are the two largest fresh impact craters discovered by the Mars Reconnaissance Orbiter since operations started 16 years ago. The impacts created two of the largest seismic events (magnitudes greater than 4) recorded by InSight during its 3-year mission. The combination of orbital imagery and seismic ground motion enables the investigation of subsurface and atmospheric energy partitioning of the impact process on a planet with a thin atmosphere and the first direct test of martian deep-interior seismic models with known event distances. The impact at 35°N excavated blocks of water ice, which is the lowest latitude at which ice has been directly observed on Mars.

Three-dimensional growth of human hepatoma C3A cells within alginate beads for fluidized bioartificial liver.

OBJECTIVES: Alginate beads allow cultivation of cells in a 3-dimensional environment. The aim of our study was to assess the influence of a 3-dimensional culture in alginate microbeads, on hepatic cell metabolism. METHODS: We used 2 types of alginate: low viscosity (LV) and medium viscosity (MV). The hepatic cell line C3A was encapsulated in alginate beads. Cells were cultured for 2 weeks. Using scanning electron microscopy, the morphology of 3D structures and the surfaces of cells were analyzed. Fluidized bed bioartificial liver experiments were performed 24 hours, 7, and 14 days after bead formation. RESULTS: Two different cell growth types in alginate beads were observed: channel-like structures and spherical aggregates characteristic of LV and MV alginate, respectively. A significant increase in albumin synthesis was observed in long-term culture. Formation of characteristic hepatic cell microvilli on cell surfaces was observed under scanning electron microscopy for both types of alginate. Prolonged static cultivation of C3A cells within the alginate beads in both types of alginates caused significant increases in albumin production in the fluidized bioreactor. CONCLUSIONS: Cultivation of the hepatic C3A cells within the alginate microbeads significantly improved bioreactor effectiveness in albumin production. The presence of extensions of cell membranes on the surface of hepatoma cells in 3-dimensional culture within the alginate beads indicated formation of microvilli-like structures characteristic of normal hepatocytes.

Culture of C3A cells in alginate beads for fluidized bed bioartificial liver.

Extracorporeal bioartificial liver has been designed to sustain the detoxification and synthetic function of the failed liver in patients suffering from acute liver failure until the time of liver allotransplantation or regeneration of their own. A fluidized bed, bioartificial liver improves the mass transfer velocity between the medium and the hepatocytes. Detoxification functions of the liver could be replaced by completely artificial systems, but the synthetic functions of hepatocytes may be obtained only by metabolically active cells. The aim of our study was to investigate the influence of C3A cell culture in alginate beads on synthetic function in a fluidized bed, bioartificial liver. Cells in alginate beads were prepared using an electrostatic droplet generator of our own design using low-viscosity alginate. Beads were cultured for 24 hours then 7 days in static conditions and then 24 hours of fluidization in the bioreactor to assess albumin production. We observed significantly increased albumin production by C3A cells entrapped in alginate beads during static culture. Fluidization increased albumin production compared with static culture. Fluidization performed after 7 days of static culture resulted in a significant increase in albumin synthesis. In conclusion, static culture of alginate beads hosting hepatic cells facilitates restoration of cell function.

Three-dimensional culture of hepatocytes on spongy polyethersulfone membrane developed for cell transplantation.

Implantable bioartificial liver has been investigated for patients suffering from liver insufficiency after mass liver resection or acute liver failure. Liver cells are implanted as free cell suspension, in microencapsulation systems or using microcarriers. To exhibit their typical functions, hepatic cells need a three-dimensional environment that is much more physiological than a flat one. The aim of our study was in vivo evaluation of spongy polyethersulfone membranes as a synthetic support for hepatic cells grown three dimensionally and transplanted to SCID/NOD mice. Spongy membranes were prepared using phase inversion from membrane-forming mixtures containing the following: polyethersulfone (based polymer), dimethylformamide (solvent), polyvinylpyrrolidone MW 10000 (small pore precursor), and cellulose (large pore precursor). We observed that polyethersulfone membranes were well tolerated by C3A cells and we did not observe any toxic effect, resulting in viability of cells >95%. Use of collagen gel as a support for cells on the scaffold gives the opportunity to increase 10 times the number of cells seeded on the membrane. Heparin addition to collagen gel did not influence albumin production in SCID/NOD mice. We observed an increase of albumin production after 7 and 14 days after implantation. Use of collagen gels in combination with polymer scaffolds allows preparation of bioartificial organs possessing high cell concentration for transplantation purposes.

Comparison of kinetic characteristics of amino acid-based and dipeptide-based peritoneal dialysis solutions.

UNLABELLED: A mixture of dipeptides (DP) has been proposed as alternatives (to glucose and amino acids, (AA)) osmotic agent in peritoneal dialysis (PD) solutions. DP based solutions may have metabolic and nutritional advantages compared to AA based solutions, as some sources of AA (such as tyrosine) are poorly soluble in water. In a previous study, we compared the kinetic characteristics of DP and AA based solutions; however, the amount of AA differed substantially. The aim of the present study was to compare solutions with almost equal amounts of AA. METHODS: The following solutions were used: (1) amino acid (AA) solution containing leucine, valine, lysine, isoleucine, threonine, phenylalanine and histidine (tyrosine was omitted because of its poor solubility), (2) dipeptide (DP) solution containing leucyl-valine, lysyl-isoleucine, threonyl-phenylalanine and histidyl-tyrosine. Sixteen Sprague-Dawley rats were divided in two groups and were subjected to intraperitoneal injection of either 25 mL of AA (n=8) or DP solution. Dialysate and blood samples were taken frequently postinfusion for measurement of AA and DP concentrations as well as AA from DP. RESULTS: Kinetic models were developed for estimation of diffusive mass transport coefficient between peritoneal cavity and blood (K BD), DP hydrolysis rate coefficient (K H) and AA clearance in the body (K C). Calculations showed that K H is about ten times lower than K BD. Thus, hydrolysis rate in peritoneal cavity is much lower than the diffusive transport rate of DP. K BD for AA appeared to be similar to K BD for dipeptides. K C was much higher than K BD for AA. This finding explains the rapid clearance of amino acids from blood. Nevertheless, the AA-based solution resulted in much higher peak concentrations of AA in blood after 120 min of the dwell than AA concentrations achieved following the use of the DP-based solution. CONCLUSIONS: Peritoneal transport characteristics of AA and DP were similar; however their kinetics in blood differs substantially. The DP solution resulted in a less pronounced increase in AA concentrations in blood, suggesting that DP solution could provide AA in a more physiological way.

Survival analysis of Escherichia coli encapsulated in a hollow fiber membrane in vitro and in vivo: preliminary report.

The purpose of the observations was the viability and quality evaluation of E. coli bacteria encapsulated in hollow fiber membranes (HF) in short in vivo and in vitro experiments. A polypropylene, surface-modified hollow fiber was applied for immunoisolation of E. coli bacteria transfected with a green fluorescent protein (E. coli GFPI). The presence of GFP fluorescence of organisms was assessed with the use of flow cytometry. The E. coli GFPIs were then observed for the period of 5 days in in vitro experiments in the culture medium. A single IPTG (isopropyl beta-D-1-thiogalactopyranoside) induction of GFP gene appeared to be adequate for an expression of GFP protein for 5 days. The GFP expression values observed for E. coli GFPs encapsulated in HF during culture in different culture media were comparable. The survival of E. coli GFPIs encapsulated in HF after 1, 2, 4, or 5 days of subcutaneous implantation into mice was evaluated. The explanted E. coli GFPIs exhibited mean expression 603 +/- 17 (n = 32) units of fluorescence during the implantation period. The values obtained were comparable for selected days of observation. It was observed that the membranes applied ensured the bacteria growth within the HF's space only.

Fluid and solute transport in CAPD patients before and after permanent loss of ultrafiltration capacity.

BACKGROUND: Two major types of permanent loss of ultrafiltration capacity (UFC) were previously distinguished among patients treated with CAPD: 1) type HDR with high diffusive peritoneal transport rate of small solutes and low osmotic conductance,but with normal fluid absorption rate, and 2) type HAR with high fluid absorption rate, but with normal diffusive peritoneal transport rate of small solutes and normal osmotic conductance. However, the detailed pattern of changes in peritoneal transport parameters in patients developing loss of ultrafiltration capacity is not known. OBJECTIVE: Analysis of solute and fluid transport parameters in the same patient before and after UFC loss. PATIENTS: Seven CAPD patients who had undergone repeated dwell studies,which were carried out before and/or after the onset of UFC loss. METHODS: Dialysis fluids (2 L) with glucose or a mixture of amino acids as osmotic agent at three basic tonicities were applied during 6 hour dwell studies. Fluid and solute transport parameters were previously shown not to be affected by these dialysis solutions (except by hypertonic amino acid-based solution). Intraperitoneal dialysate volume and fluid absorption rate were assessed using radiolabeled human serum albumin (RISA). Osmotic conductance (a(OS))was estimated by a mathematical model as ultrafiltration rate induced by unit osmolality gradient. Diffusive mass transport coefficients, K(BD), for glucose,urea,and creatinine were estimated using the modified Babb-Randerson-Farrell model. RESULTS: Five patients had increased K(BD) for small solutes after the onset of UFC loss,and three of them had decreased a(OS),whereas two patients had normal a(OS). In one of them, a(OS) decreased with time after the onset of UFC loss with concomitant normalization of glucose absorption. In all studies of these five patients the fluid absorption rate was within the normal range. Two other patients had increased fluid absorption rate (about 5 ml/min),and one of them also had increased K(BD) for small solutes,in two consecutive dwell studies in each patient with the second study being carried out at 1 and 7 months respectively after the first one. In all four studies in these two patients, the a(OS) was within the normal range. The sodium dip during dialysis with 3.86% glucose-based solution was lost, not only among most patients with UFC loss related to reduced osmotic conductance, but also in patients with increased K(BD). CONCLUSIONS: The occurrence of two major types of UFC loss was confirmed. However, a case of a mixed type of UFC loss with high fluid absorption rate and high K(BD) for small solutes, but normal osmotic conductance, and with normalization of initially high K(BD) for small solutes, linked with decreasing initially normal osmotic conductance,was also found. As a reduced sodium dip with hypertonic glucose solution is not only seen in patients with reduced osmotic conductance, it cannot reliably be used as a single measure of decreased aquaporin function. Permanent ultrafiltration capacity loss may be a dynamic phenomenon with a variety of alterations in peritoneal transport characteristics.

Evaluation of a system producing the hemopoietic factor. WEHI-3B cell line function, when encapsulated in a polypropylene hollow fibre.

The purpose of our study was evaluation of functioning of WEHI-3B (an mouse cell line producing IL-3) cells encapsulated in hollow fibers (HF). In vitro: the WEHI-3B cells were encapsulated in HF of polypropylene K600 silikonized, and cultured over two weeks. In vivo: the encapsulated WEHI-3B after weeks culture, were implanted subcutaneously into mice for 1 week. After explantation encapsulated WEHI 3-B were cultured again in culture medium for one week. The production of IL-3 by encapsulated WEHI-3B cells was assessed by evaluation of IL-3 dependent, BaF3 cells viability. The percent number of one day survival of BaF3 cells in the culture medium supplemented with 15% of encapsulated WEHI-3B in vitro or encapsulated WEHI-3B after in vivo conditioned medium was comparable with positive control. Possible replacement of recombinant cytokines with HF encapsulated cytokine-producing cells may be a chance for continous supplementation of the factors for hematopoietic stem cells differentiation.

Encapsulation of parathyroid cells in hollow fibers: a preliminary report.

The purpose of experiments was to evaluate the survival and functioning of human parathyroid cells after encapsulation in hollow fibers (HFs). The polypropylene HFs K600(PP Accurel (Akzo-Nobel, Germany) of inner diameter 0.6 mm, wall thickness 0.2 mm, original or surface modified were used for encapsulation. Production of parathormone (PTH) by encapsulated cells was measured in vitro. HF were filled with parathyroid cell suspension and tightly closed. Encapsulated cells were cultured for 9 or 33 days in RPMI 1640 containing 10% FCS or in Chang's medium. The level of PTH, produced by encapsulated cells was evaluated in the culture medium with radioimmunoassay test (RIA). The assays were performed every 2-4 days. The result of PTH assay was similar in both types of tested media as well as with unmodified and modified HFs, being 2-4 pg/ml of culture medium per 10(3) encapsulated cells. In conclusion, encapsulation in original or modified HFs ensures diffusion of nutrients from culture medium to encapsulated cells and allows for functioning of cells for at least 33 days in vitro.

Paradoxes in peritoneal transport of small solutes.

Analysis of kinetic studies of peritoneal solute transport involves the need for discrimination between three transport components: diffusion, convective transport, and peritoneal absorption. The description of convective transport in standard clinical conditions of continuous ambulatory peritoneal dialysis (CAPD), as well as in isochratic measurements, has met some problems related to the paradoxical and often anomalous values of sieving coefficient, a parameter that characterizes solute drag with the flow of ultrafiltrate. A possible explanation of some of these results is the time dependence of the transport parameters, which is in contrast to their assumed steadiness. These anomalies as well as the time dependence of the transport parameters are confined more to the standard glucose-based dialysis fluid than to some alternative dialysis fluids. Furthermore, the most striking anomalies have been found for small electrolytes as well as for osmotic agents, which are applied in high, unphysiological concentrations. These solutes may be involved in the transport between intracellular and extracellular compartments within the peritoneal membrane, which phenomena are not included in the current modeling.

Methods for estimation of peritoneal dialysate volume and reabsorption rate using macromolecular markers.

Reabsorption of fluid and solutes from the peritoneal cavity poses several problems for the correct estimation of peritoneal dialysate volume and ultrafiltration rate with macromolecular volume markers. Although physiological mechanisms of peritoneal reabsorption (direct lymphatic absorption vs reabsorption to the peritoneal tissue) are being currently discussed, many experimental and clinical studies have demonstrated that peritoneal reabsorption of the marker is mainly a bulk "backflow" out of the peritoneal cavity. Theoretical bases for the estimation of peritoneal dialysate volume and cumulative ultrafiltration of fluid including the correction for peritoneal reabsorption are reviewed. A widely applied simplified method which, however, neglects the impact of ultrafiltration on marker concentration is also discussed. The systematic errors involved in the application of the simplified method are usually less than 10% in the standard conditions; however, in specific cases they may be much higher. Therefore, the correct method is suggested for practical applications.

Discriminative impact of ultrafiltration on peritoneal protein transport.

OBJECTIVE: The dialysate concentration of large proteins increases, on average, linearly during the whole peritoneal dialysis dwell, and this linear pattern seems to be independent of the rate of ultrafiltration induced by dialysis fluid. However, we observed a high variability of protein kinetics in individual dwell studies. Therefore, we studied the details of the kinetic pattern of peritoneal transport. DESIGN AND METHODS: Kinetics of beta2-microglobulin, albumin, and total protein was examined in 23 clinically stable continuous ambulatory peritoneal dialysis patients using Dianeal 3.86% (15 dwell studies) or Dianeal 1.36% (9 dwell studies) dialysis fluid. Dialysate volume was measured using radioisotopically labeled albumin as a volume marker, with corrections for sample volume and absorption of fluid and marker from the peritoneal cavity. The generalized version of the Babb-Randerson-Farrell model was applied to estimate diffusive mass transport coefficient (K(BD)) and sieving coefficient (S) for proteins and small solutes (urea, creatinine, glucose, sodium, potassium). To quantify deviations from the linear pattern of protein dialysate concentration increase, the ratio (SR) of the slope of the linear regression line for the initial 3-30 minutes, divided by the slope for the next 60 - 360 minutes, was evaluated for albumin. RESULTS: In 5 dwell studies with Dianeal 3.86% fluid, SR was lower than 1 [low albumin transport (LAT) group, median SR = 0.49, range -4.39 - 0.71], while in the other 10 dwell studies with this solution, SR was higher than 1 [high albumin transport (HAT) group, median SR = 2.77, range 1.32 - 7.56]. Clearances of albumin up to 120 minutes were higher in the HAT group than in the LAT group. The transport of fluid, beta2-microglobulin, and small solutes did not differ between the LAT and the HAT groups. K(BD) values for proteins did not differ between the groups, but S values for albumin and total protein were lower for the LAT group than for the HAT group. A similar diversity was found in the dwell studies with Dianeal 1.36%: In three dwell studies, SR for albumin was lower than 1 (median SR = 0.95, range 0.70 - 0.97), and in six dwells it was higher than 1 (median SR = 1.55, range 1.23 - 1.98). In general, the SR values observed with Dianeal 1.36% were closer to 1 than those for Dianeal 3.86%. CONCLUSIONS: Ultrafiltration may affect the initial kinetic patterns of large protein (such as albumin) transport in two opposing ways: (1) by slowing the increase of protein concentration in dialysate (due to a low sieving coefficient, LAT group), and (2) by speeding up the increase of protein concentration in dialysate (due to a high sieving coefficient, HAT group). The average pattern in a non-selected group of studies is, however, close to a steady (linear) increase.

Bidirectional solute transport in peritoneal dialysis.

OBJECTIVE: Three transport components are involved in solute transport in peritoneal dialysis: diffusion, convective transport, and peritoneal reabsorption of dialysate (fluid and solutes). The relative impact of these components on measureable transport characteristics (dialysate-to-plasma concentration ratio, diffusive mass transport coefficient, unidirectional clearances) may depend on the direction of solute transport, that is, from blood to dialysate or vice versa. The application of the bidirectional characteristics for the assessment of fluid and solute transport in peritoneal dialysis is reviewed and evaluated. DATA SOURCES: Theoretical analysis as well as computer simulations were applied to discuss available data from our own studies on peritoneal transport as well as from published clinical, experimental, and theoretical studies in the same field. STUDY SELECTION: Thirty-three relevant clinical and experimental studies as well as theoretical analyses derived from the literature were reviewed. DATA EXTRACTION: Data were extracted to highlight current controversies in the literature concerning the assessment of peritoneal reabsorption rate based on transport of macromolecules, middle molecules, and small solutes. RESULTS: Peritoneal reabsorption is the main component of the transport of macromolecules infused into the peritoneal cavity, and these solutes are currently being used for the assessment of the rate of reabsorption. In contrast, diffusive transport and peritoneal reabsorption cannot be experimentally discriminated for small solutes which exhibit negligible sieving through the membrane in convective transport (i.e., solutes with sieving coefficient equal to 1). For middle molecules each transport component may be of importance and may have an independent impact on bidirectional transport characteristics. CONCLUSIONS: Middle molecules, with sieving coefficients substantially less than 1, may be applied for estimation of peritoneal reabsorption rate using bidirectional transport characteristics, as apparent diffusive mass transport coefficients or unidirectional clearances. However, an independent measurement of sieving coefficient is necessary for this method.

The effect of dialysate acidity on peritoneal solute transport in the rat.

OBJECTIVE: To investigate the possible effect of unphysiologically low pH in dialysis fluid on peritoneal transport. DESIGN: A 4-hour single-cycle experimental session of peritoneal dialysis was performed in six Sprague-Dawley rats using Dianeal 3.86% solution modified by adding 5 mmol/L of sodium hydroxide, neutral pH solution (NpHS) (pH 7.4). The intraperitoneal volume (VD) and peritoneal bulk fluid reabsorption (Qa) were calculated using a marker, 131I-labeled human serum albumin (RISA). The diffusive mass transport coefficient (KBD) as well as sieving coefficient (S) for glucose, urea, sodium, and potassium were calculated using the Babb-Randerson-Farrell model. The same study was performed in seven rats using Dianeal 3.86% solution, acidic pH solution (ApHS) (pH 5.7) to provide control values. RESULTS: The dialysate pH was stable with NpHS; 45 min after the infusion of ApHS it increased rapidly and reached the physiological value 7.4. Dialysate volume and KBD values for sodium and potassium with NpHS were significantly higher than with ApHS, while the KBD values for glucose and urea did not differ between the two solutions. S values for sodium and urea did not differ between the two solutions, while the values for glucose and potassium with NpHS were significantly higher and lower, respectively, than the values with ApHS (0.92 +/- 1.04 vs 0.04 +/- 0.63 and 0.56 +/- 060 vs 1.15 +/- 0.39, p < 0.05). The absorption of glucose from the dialysis solution expressed as a percentage of the initial amount of dialysate glucose was significantly lower with NpHS than with ApHS at 30 min (17.3 +/- 1.7% vs 29.7 +/- 2.0%, p < 0.05). CONCLUSION: We conclude that the peritoneal transport of fluid and small solutes might to some extent be influenced by the acidity of the dialysis solution. The vasodilatory effect of acidic dialysis solution might be the most important mechanism for these differences. However, a larger KBD value and a lower S value for potassium and higher S values for glucose during dialysis with the neutral dialysis solution may indicate that transport mechanisms other than simple passive transport are involved in peritoneal transport for glucose and electrolytes.

Peritoneal transport of glucose in rat.

OBJECTIVE: To evaluate the convective transport characteristics of glucose and the effect of high glucose and insulin during experimental peritoneal dialysis in rat. METHODS: Male Sprague-Dawley rats weighing 300-400 g were used in this study. Mannitol (5%) was used as osmotic agent. Glucose was added to dialysis solution to yield a concentration of 100 mg/dL (group 1) or 300 mg/dL (group 2). Mannitol solution (5%) containing the same concentration of electrolytes and lactate but without glucose was used as control (group 3). In group 2, blood sugar was maintained at approximately 300 mg/dL by continuous intravenous infusion of 25% glucose solution and 0.9% NaCl solution. A 2-hour dwell study was performed with 30 mL of test solutions. Intraperitoneal volume was calculated by volume marker (18.5 kBq of 131I-human radioiodinated serum albumin, RISA) dilution with corrections made for the elimination of RISA from the peritoneal cavity (K(E)) and sample volume. The diffusive mass transport coefficient (K(BD)) and sieving coefficient (S(BRF)) were calculated by using the Babb-Randerson-Farrell model. S was also calculated directly by using isocratic methods (S(I)). The peritoneal fluid absorption rate (K(E)) was taken into account for the calculation of S(I). RESULTS: Intraperitoneal volume was significantly higher in group 2 compared with groups 1 and 3. Peritoneal fluid absorption rate, K(E), was similar in all three groups. S(BRF) and S(I) for glucose were significantly lower in group 2 compared with groups 1 and 3. S(BRF) for glucose in group 2 was below zero and S(I) near zero. K(BD) for glucose was significantly higher in group 2 than in groups 1 and 3. Plasma and dialysate concentrations of insulin increased during the initial hour and then decreased to the baseline value in groups 1 and 3, while in group 2 it continuously increased. CONCLUSION: Significantly lower sieving coefficients for glucose in the high glucose and high insulin group suggest that transport mechanisms other than simple passive transport are involved in peritoneal glucose transport, and that high glucose per se and/or high insulin may be important factors that determine glucose transport characteristics.

Peritoneal transport during dialysis with amino acid-based solutions.

OBJECTIVE: To evaluate the potential clinical role of amino acids as an osmotic agent. DESIGN: The peritoneal transport of fluid, amino acids, and other solutes was investigated during a 6-hour single-cycle peritoneal dialysis with PDA 1% versus 1.36% glucose (n = 6) or PDA 2.7% versus 3.86% glucose solution (n = 9). PATIENTS: Fifteen stable nondiabetic continuous ambulatory peritoneal dialysis (CAPD) patients. RESULTS: The fractional absorption of the osmotic agents at 6 hours was higher with PDA 2.7% versus glucose 3.86% (p < 0.005). The diffusive mass transport coefficient, KBD, calculated for a period of dialysate isovolemia was higher with PDA 2.7% versus PDA 1% for essential, nonessential (p < 0.005), and total (p < 0.05) amino acids. The intraperitoneal volume-over-time curves and KBD values for urea, creatinine, glucose, albumin, beta 2-microglobulin, and total protein did not differ between the amino acid solutions and the corresponding glucose solutions. KBD for urea was significantly higher during the dwell with PDA 2.7% versus PDA 1% (p < 0.05). Plasma amino acid concentrations increased substantially during the first 1-2 hours and then decreased gradually. Valine and methionine rose to 792% and 1119% of baseline values, respectively. CONCLUSIONS: We conclude that the peritoneal transport of fluid and investigated solutes, except amino acids, was not different with the amino acid solutions compared with the corresponding equimolar glucose solutions. However, ultrafiltration tended to be lower with amino acid solutions. Furthermore, the fractional absorption of amino acids and KBD values for amino acids was higher with PDA 2.7% versus PDA 1%, suggesting an effect of the hypertonic amino acid solution on the peritoneal membrane transport properties. Also, the hypertonic PDA 2.7% solution yielded nonphysiologically high plasma levels of several amino acids. We therefore consider this solution not to be safe enough for long-term clinical use.

A simple and fast method to estimate peritoneal membrane transport characteristics using dialysate sodium concentration.

BACKGROUND: The peritoneal equilibration test (PET) is widely used to classify a patient's peritoneal transport characteristics. However, PET is laborious and the prediction of fluid removal based on PET is generally poor. It is believed that osmosis by glucose occurs partially through transcellular water channels, resulting in sieving of sodium and decrease of dialysate sodium concentration when using hypertonic glucose dialysate. OBJECTIVE: In this study, we investigated the possibility of using dialysate sodium concentration to classify the patient's peritoneal transport characteristics. METHODS: A 6-hour dwell study with frequent dialysate and plasma sampling was performed in 46 patients using 2 L of 3.86% glucose dialysate with 131I-albumin as an intraperitoneal volume (IPV) marker. The peritoneal transport of sodium, creatinine, glucose, and fluid was evaluated. RESULTS: The dialysate sodium concentration at 240 min (D(Na240)) significantly correlated with D/P creatinine (r = 0.76, p < 0.001) and D/D0 glucose (r = -0.83, p < 0.001) at 240 min of the dwell (better than dialysate sodium concentration at any other time of the dwell). DNa240 also significantly correlated with IPV at 240 min of the dwell (r = -0.61, p < 0.001)(better than D/P creatinine and D/D0 glucose). There were significant correlations between D(Na240) and the sodium-sieving coefficient (r = 0.71, p < 0.001) and the diffusive mass transfer coefficient for sodium (r = 0.50, p < 0.001). When using D(Na240) to divide the patients into four groups, as in the PET method, no significant difference was found between the two methods. CONCLUSION: Using 3.86% glucose solution, D(Na240) can be used instead of D/P creatinine to classify patients into different transport groups. D(Na240) provides a better prediction of peritoneal fluid transport and reflects both the diffusive and convective transport properties of the membrane. As only one dialysate sample (and no blood sample) is needed, D(Na240) may offer important clinical advantages compared with PET.

Simple membrane models for peritoneal dialysis. Evaluation of diffusive and convective solute transport.

Currently used mathematical models to estimate parameters describing diffusive (diffusive mass transport coefficient, KBD) and convective (sieving coefficient, S) solute transport during peritoneal dialysis, as proposed by Pyle, Popovich, and Moncrief (PPM model) and Babb, Randerson, and Farrell (BRF model), require nonlinear regression and advanced numerical methods for parameter estimation. In this study, a simplified approach to the evaluation of KBD and S, using the same transport equation used in the PPM and BRF models but based on two-dimensional linear regression, is proposed. This new approach can be extended to generate a family of membrane models that differ in assumption concerning the average solute concentration (c) inside the peritoneal membrane. In particular, c was assumed to be equal to the arithmetic mean value of the dialysate and blood concentrations (PPM model), the blood concentration (BRF model), or the dialysate concentration (D model). The investigated family of models was used to study the transport of urea, creatinine, glucose, sodium, potassium, and total protein in 20 single, 6 hr dwell studies carried out in 20 nondiabetic patients in stable clinical condition using hypertonic (3.86%) glucose solution. For the PPM model, the linear and nonlinear regressions were able to provide almost identical values of KBD and S. The theoretical dialysate to plasma concentration ratio (D/P) was adequately fitted to experimental D/P for both the PPM and BRF models, but the fit was worse for the D model. However, unphysiologic (i.e., out of the 0-1 range) values of S were found for urea, potassium, and glucose independent of the version of the model used.

Diffusive mass transport coefficients are not constant during a single exchange in continuous ambulatory peritoneal dialysis.

Mass transport coefficients usually are assumed to be constant during single 6 hr exchanges of dialysis fluid in continuous ambulatory peritoneal dialysis (CAPD). To check this assumption, the authors estimated diffusive mass transport coefficients, KBD, for five low molecular weight solutes in 34 dwell studies with glucose 3.86% (20 studies), glucose 2.27% (nine studies), and glucose 1.36% (nine studies) dialysis fluids for time periods 3-30, 30-60, 60-90, 90-120, 120-180, 180-240, and 240-360 min. Dialysate volume and the rate of fluid reabsorption were measured using radiolabeled serum albumin (RISA) as a marker. Convective transport was described using a sieving coefficient of 0.55 for all solutes. The KBD values were constant for sodium, but higher at the beginning (3-30 min) than at the end (180-360 min) of the exchanges by an average of approximately 50% for urea, creatinine, and glucose, and by approximately 120% for potassium with all three dialysis fluids. This initial increment did not depend upon the concentration of glucose in dialysis fluid, except for urea. The steady state value of KBD was reached at 120 min for all solutes. The time patterns of KBD values for urea, creatinine, glucose, and potassium were well described by an exponential decay function, with the decay constant approximately 0.02 min-1. The patterns were similar for electrically neutral solutes, but different for electrolytes. The initial increments in KBD values mean that clearances during short dwell time (30-60 min) may be higher by 5-15% than clearances calculated from the steady state KBD values.

Encapsulation of OKT3 cells in hollow fibers.

Encapsulation of an OKT3 cell line in hollow fibers was evaluated in vitro and in vivo. The cell line is a mouse hybridoma producing immunoglobulin G2a (IgG2a) against CD3 human T lymphocytes and thus may function as a nonspecific activation system of a subpopulation of human T lymphocytes. For encapsulation purpose, hollow fibers of polypropylene K600 PP Accurel (Akzo, Germany) were selected. Hollow fibers were siliconized to improve membrane biocompatibility for in vivo experiments. The siliconized hollow fibers exhibited acceptable diffusive permeability (P) [ml/min/m2] for small solutes (for creatinine, p = 63.9 +/- 2.0, n = 3) and larger solutes (for albumin, p = 16.9 +/- 1.9, n = 3; for IgG, p = 1.0 +/- 0.2, n = 3). The 12 cm long hollow fibers were filled with a suspension of OKT3 cells of an average density of 10(6) cells/ ml, and both ends were sealed. The encapsulated cells were cultivated in RPMI 1640/10% CS medium at 37 degrees C, 5% CO2 for a period of 3 to 4 days. After the culture period, the medium was tested on human peripheral blood lymphocytes for the presence of anti-CD3 antibody and read in a flow FACS-trac cytometer (Becton Dickinson Immunocytochemistry Systems, San Diego, CA). The tightness of hollow fiber sealing was tested with a bubble point method. The number of cells increased after cultivation by four- to nine-fold on average (n = 11). Ten experiments were performed in vivo with OKT3 cells encapsulated in hollow fibers and implanted subcutaneously into mice for 3 days. In 50% of the experiments, some anti-CD3 antigens on human lymphocytes were found; however, the difference, in comparison with control, in percent of CD3+ was insignificant. In conclusion, the hollow fiber method for cultivation of hybridoma cells in vitro allows for separation of cells from the medium containing secreted anti-CD3 antibodies and is effective in maintaining cell viability. In vivo application needs additional study.