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Biomedical subjects

R S Labow

Publications and source records attributed to R S Labow.

At least 55 records · Page 3Linked to original sources
PubMed1993

Enzyme-biomaterial interactions: effect of biosystems on degradation of polyurethanes.

Enzyme-induced liberation of hard-segment-containing components from polyurethanes was evaluated using two 14C-labeled polyurethanes. A polyester urea-urethane and polyether urea-urethane were synthesized from toluene-2,4-diisocyanate (TDI)/polycaprolactone diol (PCL) or TDI/polyethylene glycol (PEO) with 14C-labeled ethylene diamine. Both materials were characterized using electron spectroscopy for chemical analysis (ESCA), differential scanning calorimetry (DSC), size exclusion chromatography, and material chemistry by Fourier transform infrared (FTIR) spectroscopy. Biodegradation assays were carried out using cholesterol esterase (CE), collagenase (CO), cathepsin B (CB), and xanthine oxidase (XO) at the pH optimum conditions for each enzyme at 37 degrees C. Biodegradation was analyzed by monitoring the release of radiolabel, by weight change, and by surface analysis using scanning electron microscopy. The polyester urea-urethane was shown to be susceptible to enzymatic degradation above the effect of the buffer control solution by the CE but not by the other enzyme systems as monitored by radiolabel released. In the initial period of incubation, the rate of degradation was increased for all systems, including buffer controls; however, the rates dropped off rapidly by day 28. The change in weight data for the polyester urea-urethane and polyether urea-urethane showed no enzyme-dependent biodegradation above the buffer controls. However, in sodium acetate buffer at pH = 5, the polymers showed a significant weight loss relative to other buffers. In conclusion, this study showed that the biological component responsible for the onset of the biodegradation process is more likely the result of a multitude of biologically mediated compounds acting synergistically, with the process being enhanced by physical parameters such as material dissolution. In addition characterization of surface and bulk chemistry as well as material structure evaluation have been shown to be essential to interpret degradation data.

Biocompatible Materials↗
PubMed1993

Temperature affects human cardiac sarcoplasmic reticulum energy-mediated calcium transport.

Hypothermic cardioplegic solutions are currently used to preserve cardiac function during transportation. However, it has been shown that end-diastolic compliance decreases in donor hearts during reperfusion. Excessively cold temperatures may affect membrane-bound enzymes (Ca2+ ATPase and Ca2+ uptake) which are necessary for calcium homeostasis. To study the effect of temperature on Ca2+ ATPase and Ca2+ uptake activities over the temperature range to which a donor heart is usually exposed (4 degrees-37 degrees C), sarcoplasmic reticulum (SR) was isolated from human atrial appendages. SR was also isolated from atrial appendages which had been stored in saline at 4 degrees C for 4 or 24 h or 24 h in St Thomas' cardioplegic solution (ST). Ca2+ ATPase and Ca2+ uptake from these samples were compared with those found in the SR of unstored appendages. The activity of Ca2+ uptake and Ca2+ ATPase showed great sensitivity at assay temperatures below 22 degrees C, while no such sensitivity was identified in SR NADPH/cytochrome C reductase (NCR). After storage of atrial appendages for only 4 h in saline at 4 degrees C, Ca2+ uptake activity was reduced 50% in the SR when compared to unstored controls (80 +/- 9.9 nmol/mg/min and 155.24 +/- 2.4 nmol/mg/min, respectively; P < 0.02) whereas Ca2+ ATPase was not affected until 24 h of storage, when the activity was also decreased > 50% (P = 0.0002). However, NCR was not affected. In addition, storage at 4 degrees C significantly decreased the SR protein yield (mg/g homogenate protein) at 4 or 24 h in saline as well as 24 h in ST. However, there was no decrease in the enzyme activities (Ca2+ ATPase, 229 +/- 25.3; Ca2+ uptake, 221 +/- 27.1; NCR, 24.9 +/- 0.48 nmol/mg/min). Following exposure to low temperature, alteration of Ca2+ uptake and Ca2+ ATPase may result in disruption of calcium homeostasis, thereby interrupting excitation-contraction coupling and relaxation. The damaging effects of hypothermia should be taken into account when assessing the peri-operative complications and the long-term results of cardiac transplantation.

Analysis of Variance↗
PubMed1993

Magnesium enhances function of postischaemic human myocardial tissue.

OBJECTIVES: The effect of Mg2+ on the developed force and concentrations of high energy phosphate metabolites in isolated human atrial trabeculae has been investigated. METHODS: Human atrial trabeculae, obtained from right atrial appendages of patients undergoing cardiac surgery requiring cardiopulmonary bypass, were dissected at room temperature in modified Krebs-Henseleit buffer containing 1.2 or 16 mM Mg2+, mounted on muscle stands, and rewarmed to 34 degrees C in the same buffer. After 30 minutes, their mechanical function was assessed. At the end of the protocol, trabeculae were fast frozen for measurement of concentrations of metabolites of high energy phosphates. RESULTS: Trabeculae collected and rewarmed in 16 mM Mg2+ Krebs-Henseleit buffer showed significantly higher mean developed force (0.59(SEM 0.10) g, p < 0.01) than those rewarmed in 1.2 mM Mg2+ Krebs-Henseleit buffer (0.32(0.03) g). Trabeculae that had a developed force > or = 0.8 g, a resting force < or = 0.7 g, and a cross sectional area < or = 1 mm2 ("functional" trabeculae) were selected for further comparison. New reverse phase high performance liquid chromatography techniques developed for the analysis of small samples (0.5-5 mg dry weight) were used to measure nucleotide, nucleoside, and creatine compounds. Total adenylate (ATP+ADP+AMP) concentrations in trabeculae revived in the presence of 16 mM Mg2+ (15.4(1.1) mumol.g-1 dry weight) were significantly higher (p < 0.01) than in those revived with 1.2 mM Mg2+ (11.8(1.0) mumol.g-1), but lower (p < 0.01) than in trabeculae fast frozen immediately after removal from the patient (22.6(1.0) mumol.g-1). There were no significant differences in NAD and total creatine (phosphocreatine+creatine) concentrations between the three groups. CONCLUSIONS: The presence of high Mg2+ during the rewarming of human atrial trabecular preparations maintains a significantly higher developed force and a significantly higher total adenylate pool than does collection and rewarming with normal concentrations of Mg2+.

Aged↗
PubMed1993

A comparison of intracellular solutions for donor heart preservation.

Numerous solutions have been advocated for the preservation of donor hearts, and there has been much interest in universal and intracellular preservation solutions. This study compared the effects of Euro-Collins, University of Wisconsin, and Bretschneider's solutions with the use of an in vitro human right atrial muscle preparation to assess recovery of function after a 24-hour period of simulated cardiac arrest. There were no statistically significant differences among groups in length, weight, cross-sectional area, initial developed force, or resting force of muscles, including those muscles that were contracted in Krebs-Henseleit solution and served as a control. After the 24-hour arrest period at either 4 degrees or 12 degrees C, the solution was changed back to Krebs-henseleit at 34 degrees C and recovery was assessed over 30 minutes. At 30 minutes, developed forces for muscles that were cooled to 4 degree C were 58.9%, 76.6%, and 60.7% of the control for Euro-Collins, University of Wisconsin, and Bretschneider's solutions, respectively (p = not significant). For those cooled to 12 degrees C, developed forces were 9.5%, 30.5%, and 95.6% of the control for Euro-Collins, University of Wisconsin, and Bretschneider's solutions (p = 0.0001). Bretscheider's solution resulted in greatly improved recovery compared with both Euro-Collins and University of Wisconsin solutions (p = 0.005), and University of Wisconsin solution was better than Euro-Collins solution (p = 0.02). Recovery of developed force was affected by temperature for Euro-Collins and University of Wisconsin solutions (p = 0.005 and p = 0.001, respectively) but not for Bretschneider's solution. Resting force was elevated in muscles that were cooled in both Euro-Collins and University of Wisconsin solutions at 12 degrees C compared with almost normal values for Bretschneider's solution at either temperature (p = 0.07). Bretschneider's solution has a very high buffering capacity, which may be beneficial for long-term preservation. In conclusion, Bretschneider's solution resulted in the best recovery of human atrial myocardial function after a 24-hour preservation period compared with Euro-Collins and University of Wisconsin solutions and should be considered for use in donor heart transportation. The variability in quality of preservation at different temperatures with either Euro-Collins or University of Wisconsin solution make them less desirable as preservation solutions because uniform temperatures are seldom obtained during donor heart transplantation.

Adenosine↗
PubMed1991

An NMR probe to study function and metabolism simultaneously in isolated human cardiac tissue.

Trabeculae isolated from human atrial appendages have been used to study preservation of donor hearts for cardiac transplantation. We have developed a perifusion system equipped with a fiber optic strain gauge to study mechanical performance of human atrial trabeculae (10-20 mg) while simultaneously observing the energetic compounds by 31P NMR spectroscopy. The NMR probe consists of an eight-turn solenoid coil (2.3 mm i.d. x 5 mm length, 24-gauge wire) double tuned to allow observation of 1H and 31P nuclei. The probe and the perifusion system are temperature regulated and permit preservation studies using a variety of small muscles at low temperatures (down to 4 degrees C) as well as at physiological temperature (37 degrees C). 31P NMR spectra suitable for quantification can be obtained from approximately 10 mg of human atrial trabeculae in 15 min. Spectra of 8- to 12-mg mouse extensor digitalis longus or soleus muscle can be obtained in less than 10 min.

Animals↗
PubMed1991

The human atrial trabecula: effects of calcium and temperature.

The human atrial trabecular preparation is an in vitro model which has been used to evaluate drugs and conditions to which cardiac muscle is exposed perioperatively. During its development, modifications have been made to this preparation. Two important components affecting myocardial muscle contraction are temperature and calcium concentration of the muscle bath medium. Previously, these parameters were determined independently of one another and found to be 34 degrees C and 2.5 mM calcium in a minimal Tyrode's buffer with glucose. This study was undertaken to define the optimal temperature and calcium concentration which would result in the highest yield of muscles that satisfied rigorous criteria for acceptability: developed force (DF) greater than 0.8 g, resting force (RF) less than 0.7 g, cross-sectional area less than or equal to 1.0 mm2). A total of 134 trabeculae were tested using a modified Krebs-Henseleit buffer, enriched with Eagles' medium and containing either 1.25 or 2.5 mM calcium at 34 or 37 degrees C. The trabeculae contracting in 2.5 mM calcium at 37 degrees C resulted in the highest yield of 26% while those maintained at 34 degrees C in either 1.25 or 2.5 mM calcium led to 20 and 15% useful preparations respectively (P = N.S.). Trabeculae contracting at 37 degrees C in 1.25 mM calcium resulted in the poorest yield of 8% (P = 0.002). There is a small (5 to 7%), but significant (P = 0.02), decrease in DF in 1 h when all groups were analyzed together. The exclusion criteria which are applied eliminate variability due to disease and/or treatment, therefore only 20 to 25% are acceptable for study. In summary, with well-defined and stringently applied criteria, the human right atrial trabecular preparation can be a reliable and reproducible model functioning at 37 degrees C and 2.5 mM calcium for a variety of studies.

Calcium↗
PubMed1991

Validation of a human atrial trabecular preparation for evaluation of inotropic substances.

Assessment of cardioactive substances is usually performed using animal tissue, with the effects being extrapolated to humans, thereby potentially introducing errors due to species differences. In order to validate the use of human atrial tissue, known positive and negative inotropic agents were tested on trabeculae obtained from patients' atrial appendages at the time of cardiac surgery requiring, cardiopulmonary bypass. Trabeculae were selected according to strict criteria: cross-sectional area less than 1.0 mm2, resting force (RF) less than 0.7 g, and developed force (DF) greater than 0.8 g. Each trabecula received only one drug in a cumulative dose manner. Where necessary, the vehicle used to dissolve or stabilize the drug solution was also tested. In addition, the relative DF of "no-drug," "time-only" controls were measured during the same time period. After adjusting for the effect of time on the preparation, relative DF was increased to 157% by dobutamine (1.5 x 10(-5) M), to 136% by amrinone (5.6 x 10(-4) M), and to 117% by ouabain (2 x 10(-7) M). The relative DF decreased with nifedipine and propranolol, with 50% inhibition for both drugs being 1.5 x 10(-7) M. Although human ventricular muscles might be more appropriate to use in order to determine the effects observed with the whole heart, they are extremely difficult to obtain on a regular basis. The results of this study show that the atrial trabecular preparation offers an acceptable alternative.

Cardiotonic Agents↗
PubMed1991

An assessment of crystalloid solutions for donor heart preservation.

The optimal technique for donor heart protection remains controversial. One component of preservation is the transport solution. Although saline solution is most frequently used as a transport medium, other crystalloid solutions may be superior. Accordingly, human right atrial trabeculae contracting isometrically in vitro were used to assess five crystalloid solutions at two different temperatures (12 degrees and 4 degrees C): St. Thomas' Hospital solution, modified Krebs-Henseleit (K+ = 16 mEq/L), Krebs-Henseleit (K+ = 4.5 mEq/L, saline, and Euro-Collins. After a 24-hour preservation period the muscles were restimulated at 34 degrees C and recovery of function was monitored for 30 minutes. Recovery of developed force was not affected by temperature (p = 0.13 by two-way analysis of variance). However, St. Thomas' Hospital solution provided the best recovery of developed force (103.3 +/- 6.2% of control) compared with saline, which had the worst developed force (2.8% +/- 1.3%) (p less than 0.002). Modified Krebs-Henseleit, Krebs-Henseleit, and Euro-Collins demonstrated intermediate performance. Although there were no differences between groups in recovery of resting force, it was greater in all groups with muscles cooled to 4 degrees C (238.7% +/- 17.6% of control) (p less than 0.001). Dry/wet weight ratios did not demonstrate statistically significant differences between groups. We conclude that, of the solutions tested, St. Thomas' Hospital solution provides the best preservation of atrial myocardium. Storage in crystalloid solutions leads to impaired relaxation, which is more apparent in tissue cooled to 4 degrees C and does not appear to be solely due to increased tissue swelling.

Evaluation Studies as Topic↗
PubMed1990

Atropine inhibition of the cardiodepressive effect of mono(2-ethylhexyl)phthalate on human myocardium.

Di(2-ethylhexyl)phthalate (DEHP) is a commonly used plasticizer in polyvinylchloride (PVC)-derived plastic. Mono(2-ethylhexyl)phthalate (MEHP), the major metabolite of DEHP, had a reversible, concentration-dependent (15-200 micrograms/ml) negative inotropic effect on a human in vitro atrial trabecular isometric preparation with an IC50 of 85 micrograms/ml. When atropine (22-32 micrograms/ml) was included in the atrial preparation the IC50 was shifted to greater than 120 micrograms/ml, suggesting that MEHP acts in part through the cholinergic receptors.

Adult↗
PubMed1990

Transfer of arachidonic acid from phosphatidylcholine to phosphatidylethanolamine during storage of human platelets for 5 days.

Human platelets are routinely stored for 5 days prior to transfusion, but they deteriorate during storage. Since very little information is available concerning the effect of storage on platelet phospholipid metabolism, the biosynthesis and remodelling of platelet phospholipids were studied. Platelets were incubated separately with [14C]glycerol, [14C]arachidonic acid, or a mixture of [14C]glycerol and [3H]arachidonic acid, and stored in a platelet storage medium at 22 degrees C. Maximum glycerol uptake (20%) was attained after 6 h. [14C]Glycerol was incorporated into phosphatidylcholine, phosphatidylethanolamine, and phosphatidylinositol, and to a much lesser extent phosphatidylserine, under storage conditions for 5 days. The distribution of the initial arachidonic acid uptake was not as would be expected based on the molar composition of endogenous phospholipids. The arachidonic acid (75%) which was taken up within 10 min of incubation distributed 55% into the phosphatidylcholine and only 14% into the phosphatidylethanolamine; the molar composition is actually 18% phosphatidylcholine and 47% phosphatidylethanolamine. During storage, there was a continuous transfer of the radiolabelled arachidonic from phosphatidylcholine to phosphatidylethanolamine until, after 5 days, the distribution of arachidonic acid was identical to the endogenous distribution. In contrast, no change in the glycerol incorporation pattern was detected during storage. This suggested that the mechanism for arachidonic acid redistribution was not through exchange of polar head groups, but through acyl transfer of arachidonic acid from phosphatidylcholine to phosphatidylethanolamine.

Arachidonic Acid↗
PubMed1990

The effect of mono(2-ethylhexyl)phthalate on an isolated perfused rat heart-lung preparation.

Di(2-ethylhexyl)phthalate (DEHP), the plasticizer used in the biomedical production of blood storage bags, hemodialysis systems, cardiopulmonary bypass (CPB) circuitry, and intubation tubes, is extracted from the plastic material when it comes into contact with biological fluids and is converted to its principal metabolite, mono(2-ethylhexyl)phthalate (MEHP). We have shown that MEHP causes cardiac and respiratory arrest, as well as hypotension, when infused into anesthetized rats. Using a well-ventilated in vitro rat heart-lung preparation, we investigated the effect of MEHP on pulmonary artery pressure (PAP) and found that MEHP had a hypertensive effect on the pulmonary vasculature ending in constriction and edema. There was a significant increase of 0.58 mm Hg/min in the PAP of isolated rat lungs when perfused with MEHP dissolved in Krebs-Henseleit (K-H) buffer (p = 0.0003). The rat lungs that were perfused with K-H buffer only increased 0.094 mm Hg/min during the same perfusion time of 20 min. The water gained during this time was 0.22 g/min with MEHP in the buffer compared to 0.04 g/min with buffer alone. The pO2 in the effluent did not decrease during the perfusion time. The concentration of MEHP in the rat lungs after perfusion varied from 20 to 40 micrograms/g. Although the mechanism of action of MEHP on PAP is too complex to be fully elucidated by this model, the increase in PAP which we have demonstrated is significant and adds yet another toxic effect of this major metabolite of the ubiquitous plasticizer, DEHP.

Animals↗
PubMed1989

Perioperative exposure to plasticizers in patients undergoing cardiopulmonary bypass.

Di(2-ethylhexyl)phthalate and its principal metabolite, mono(2-ethylhexyl)phthalate, are contaminants of blood that are extracted on contact with polyvinylchloride surfaces, such as blood collection bags and tubing used in cardiopulmonary bypass. In this study, levels of the two plasticizers were measured in patients who underwent coronary artery bypass grafting, orthotopic transplantation, implantation of the Jarvik 7-70 total artificial heart during bridge-to-transplant procedures, and in infants who underwent corrective operations for congenital defects. In all adult patients the levels of di(2-ethylhexyl)phthalate increased tenfold by the end of cardiopulmonary bypass, whereas the levels of mono(2-ethylhexyl)phthalate increased ninefold. In infants, levels of di(2-ethylhexyl)phthalate rose seven times by the end of bypass and mono(2-ethylhexyl)phthalate rose significantly as well. In most of the patients having coronary bypass, the two plasticizers declined to preoperative levels within 24 hours. However, in some of the patients having orthotopic transplantation and in those in whom the Jarvik 7-70 total artificial heart was used as a bridge to transplant, the levels were still detectable 120 hours postoperatively. Circulating levels of mono(2-ethylhexyl)phthalate are only 20- to 35-fold lower in patients undergoing cardiac operations than the level of mono(2-ethylhexyl)phthalate causing a 50% reduction in developed contractile force and arrhythmias in an in vitro human atrial trabecular preparation. This study shows that patients with multisystem failure and infants may be at risk for this acute exposure to mono(2-ethylhexyl)phthalate.

Cardiac Surgical Procedures↗
PubMed1988

Inhibition of human platelet phospholipase A2 by mono(2-ethylhexyl)phthalate.

There is evidence that the carcinogenic and teratogenic effects attributed to the plasticizer di(2-ethylhexyl)phthalate (DEHP) are due to its major metabolite mono(2-ethylhexyl)phthalate (MEHP). MEHP is also formed ex vivo by a plasma enzyme in blood products stored in polyvinyl chloride (PVC) DEHP plastic containers. People who receive large amounts of blood products, such as hemophiliacs or patients undergoing hemodialysis, cardiopulmonary bypass, or massive transfusion, are exposed to significant levels of plasticizer. In this study, the platelet was used to show that MEHP inhibits phospholipase A2 (PLA2), one of enzymes important in the release of arachidonic acid from membrane phospholipids. Arachidonate is the parent molecule for the synthesis of prostaglandins, thromboxanes, leukotrienes, and lipoxins that are made by a wide variety of cells. PLA2 was measured by the liberation of 14C-arachidonic acid from 1-stearoyl-2-[1-14C]arachidonyl-L-3-phosphatidylcholine. MEHP inhibits PLA2 activity noncompetitively in intact human platelets and lysates with a Ki of 3.7 x 10(-4) M. DEHP does not inhibit PLA2 in whole platelets. Inhibition of PLA2 by MEHP occurs at only three times the circulating level of MEHP measured in neonates undergoing exchange transfusion and 20-fold the levels experienced by patients during cardiopulmonary bypass. Therefore, infants and adult patients with multisystem failure who accumulate MEHP in their blood may be at risk for decreased platelet function.

Blood Platelets↗
PubMed1987

The effect of the plasticizer di(2-ethylhexyl)phthalate on red cell deformability.

Red cell concentrates (RCC) are stored for 35 to 42 days in plastic containers manufactured with the liquid plasticizer di(2-ethylhexyl)phthalate (DEHP). DEHP leaches from the polyvinylchloride (PVC) plastic bag, then binds to and stabilizes the RC membrane. This study was undertaken to determine the deformability of the RC membrane using an osmotic gradient ektacytometer and to relate these measurements to the concentration of DEHP in the stored RCC. Pooled RCC was aliquoted into PL146 (PVC), PL732 (polyolefin), and PL732 (with added DEHP) bags with samples removed weekly for analysis of osmotic fragility, deformability, and DEHP concentration. The adenosine triphosphate (ATP) content was also measured. The increase in osmotic fragility during storage was greater when RCC was stored without DEHP. In addition, there was a decrease in the maximum elongation index (El max) when there was decreased DEHP in the storage bag. The osmolarity (Omax) at which El max occurred, as well as the Omin, the osmolarity at which minimum elongation (El min) occurred was higher in the PL732 container than in the PL146 or in the PL732 to which DEHP had been added. These changes could be reversed by addition of DEHP at the beginning of the storage period, showing a direct correlation between DEHP concentration during storage and RC membrane flexibility. By a better understanding of the mechanism of DEHP protection, it might be possible to substitute a less toxic stabilizing compound.

Adenosine Triphosphate↗