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Biomedical subjects

C A Ward

Publications and source records attributed to C A Ward.

At least 37 records · Page 2Linked to original sources
PubMed1995

Stability and activity of alteplase with injectable drugs commonly used in cardiac therapy.

The stability, activity, and compatibility of alteplase with eight drugs frequently used in cardiovascular disease were studied. Alteplase 1 mg/mL was mixed with each of the following: heparin sodium 80 units/mL in 0.9% sodium chloride injection, dobutamine 10 mg/mL (as the hydrochloride salt) in 0.9% sodium chloride injection or 5% dextrose injection, dopamine hydrochloride 1.6 mg/mL in 0.9% sodium chloride injection or 5% dextrose injection, morphine sulfate 2 mg/mL in 0.9% sodium chloride injection or 5% dextrose injection, lidocaine hydrochloride 8 mg/mL in 0.9% sodium chloride injection or 5% dextrose injection, propranolol hydrochloride 1 mg/mL, metoprolol tartrate 1 mg/mL, or nitroglycerin 0.8 mg/mL in 0.9% sodium chloride injection or 5% dextrose injection. Each mixture was assayed immediately and after storage for 24 hours at 25 degrees C; mixtures containing heparin were also assayed at 4 hours. The alteplase concentration and percentage of the single-chain molecule in each mixture were analyzed by using size-exclusion high-performance liquid chromatography (HPLC). Alteplase bioactivity was determined by a clot-lysis assay. Drug concentrations were assayed by HPLC, pH values of the mixtures were determined, and the mixtures were visually inspected. Instability was defined as a > 10% decrease in concentration; inactivity was defined as a > 10% decrease in activity; incompatibility was defined as detection of a precipitate, opalescence, or color change. Alteplase was not stable in the presence of heparin sodium, morphine sulfate, or dobutamine and was not active in the presence of dopamine hydrochloride. Alteplase was compatible with and stable and active (in vitro) in the presence of lidocaine hydrochloride, propranolol hydrochloride, metoprolol tartrate, or nitroglycerin.(ABSTRACT TRUNCATED AT 250 WORDS)

Cardiotonic Agents↗
PubMed1995

Role of protein kinase C in mediating effects of hydrogen peroxide in guinea-pig ventricular myocytes.

The present study examined the effects of hydrogen peroxide (H2O2) on intracellular calcium transients and unloaded cell shortening in the presence of the protein kinase C (PKC) inhibitors 1-(5-isoquinolinesulfonyl-2-methylpiperazine (H7) or chelerythrine chloride (CHC) or the PKC activator phorbol 12-myristate 13-acetate (PMA). Calcium transient amplitudes and cell shortening were measured simultaneously in single, enzymatically dissociated ventricular myocytes loaded with fura2-AM. Exposure of myocytes to H2O2, 25 microM or 75 microM, for 15 min caused a time- and concentration-dependent increase in calcium transient amplitude, cell shortening and the diastolic 340/380 fluorescence ratio. Significant increases in calcium transient amplitude were observed from 7 to 15 min of superfusion with 25 microM H2O2 and the transient amplitude remained elevated throughout the 10 min washout period. In the presence of 75 microM H2O2, transient amplitude was elevated following 2 min and remained elevated for the remainder of the experiment. Significant increases in cell shortening were also observed from 7 to 15 min in the presence of either 25 or 75 microM H2O2. This effect was reversed upon washout of the lower concentration of H2O2 but persisted during the initial 5 min of washout at the higher concentration. The diastolic 340/380 fluorescence ratio was unaltered in the presence of 25 microM of H2O2, however this parameter was significantly increased from 7 to 15 min following exposure to 75 microM H2O2 and remained elevated throughout the washout period. The H2O2-induced increases in calcium transient amplitude and cell shortening were significantly attenuated in myocytes which were pretreated with either H7 or CHC.(ABSTRACT TRUNCATED AT 250 WORDS)

1-(5-Isoquinolinesulfonyl)-2-Methylpiperazine↗
PubMed1995

Methotrexate loaded acrylic cement in the management of skeletal metastases. Biomechanical, biological, and systemic effect.

Skeletal metastases occur commonly, and frequently are complicated by the development of an impending or pathologic fracture. In the majority of instances, these patients are best treated by internal stabilization, frequently supplemented by methylmethacrylate, to relieve pain and maintain the patient's mobility. The underlying tumor may continue to grow, and if this occurs the progressive lysis may result in loosening and subsequent failure of the implant. To prevent additional local growth, postoperative radiotherapy is recommended, and many patients also receive endocrine or chemotherapy, but the adjuvant therapy is not always successful in preventing progressive local tumor induced osteolysis. It is possible that the addition of chemotherapeutic agents to the methylmethacrylate may inhibit local growth. This study was performed to determine the biomechanical, biologic, and systemic effects of adding methotrexate to methylmethacrylate. The results show that the addition of methotrexate in as much as a concentration of 2 g methotrexate per 40 g cement did not significantly alter the biomechanical characteristics of the bone cement. The incorporated methotrexate was released continuously from the loaded bone cement, and in the amount and concentration used did not have any toxic effects on the host animal. The methotrexate did not appear to be affected by the heat of polymerization and had a significant systemic effect. There was a significant reduction in pulmonary metastases with methotrexate loaded cement as compared with unloaded cement, the effect being dependent on the concentration of methotrexate in the cement. The results of these studies indicate that methotrexate loaded cement may have an important role to play as part of the orthopaedic management of impending and pathologic fractures.

Animals↗
PubMed1995

Modulation of sodium-hydrogen exchange activity in cardiac myocytes during acidosis and realkalinisation: effects on calcium, pHi, and cell shortening.

OBJECTIVE: The aim was to examine the effects of the Na+/H+ exchange inhibitor methylisobutylamiloride (MIA) as well as protein kinase C, a putative regulator of Na+/H+ exchange, on intracellular calcium, intracellular pH, and unloaded cell shortening in isolated guinea pig cardiac myocytes subjected to lactic acid induced acidosis followed by realkalinisation. METHODS: Calcium transient amplitude and cell shortening were measured simultaneously in single isolated myocytes loaded with fura2-AM. Intracellular pH was measured in cells loaded with BCECF-AM. RESULTS: Exposure of cells to 5 min of lactate (20 mM) acidosis (pH 6.8) caused an increase in calcium transient amplitude and a decrease in cell shortening and intracellular pH. During realkalinisation (pH 7.3), the calcium transient gradually decreased while intracellular pH became more alkaline than pre-acidosis values. The cells underwent transient hypercontractility as evidenced by a marked increase in systolic cell shortening and a decrease in diastolic cell length. Inhibition of sodium/hydrogen exchange with MIA (1 microM) caused a significant attenuation of the increase in calcium transient amplitude during acidosis and further depressed cell shortening as well as intracellular pH. In addition, MIA significantly attenuated hypercontractility and abolished cell contracture upon realkalinisation. In contrast, phorbol 12-myristate 13-acetate (10(-12) M) exerted no effects on the response to acidosis; however, this treatment exacerbated cell hypercontractility and reduced functional recovery upon realkalinisation. CONCLUSIONS: Inhibition of Na+/H+ exchange activity during acidosis/realkalinisation enhances recovery of cell function.

Acidosis↗
PubMed1993

Pump and exchanger mechanisms in a model of smooth muscle.

A novel approach to modelling pump and exchanger mechanisms is presented. In this approach, new thermodynamic expressions for the calcium pump, sodium-calcium exchanger and sodium-potassium pump are developed using statistical rate theory (SRT). This theory is well-defined and is not derived empirically. This is in contrast to previous thermodynamic pump expressions which used a simple linear relationship or relied on empirical data for their functional form. The functional form of these new expressions does not require assumptions of steady state or particular forms of voltage dependencies in specific steps. Also, the explicit reaction scheme is not required. Instead, assumptions of a rate-limiting step in the scheme and a near-equilibrium ratio of intermediate substrates are required. These expressions are incorporated into an overall model of gastric smooth muscle. This model presents a novel approach whereby thermodynamic representations for calcium pumps, sodium-calcium exchangers and sodium-potassium pumps have been included together in a model of ionic transport mechanisms for smooth muscle. Variations in basal metabolic concentrations are used to explain the observed amplitude variation in the transmembrane voltage of gastric smooth muscle. The interaction of the various mechanisms are used to illustrate the large depolarization obtained in smooth muscle with ouabain as well as the forward and reverse modes of the sodium-calcium exchanger.

Animals↗
PubMed1993

Permeation in ionic channels: a statistical rate theory approach.

A novel way to model permeation through ionic channels is formulated. Our method does not require that equilibrium exists in the channel or at the channel interfaces. In addition, the potential profile does not need to be specified and the assumption of constant field across the membrane does not need to be made. Our formulation relies on statistical rate theory for its development and uses a form of the electrochemical potential which assumes that the ions are in solution. We show that the conductance and the degree of nonlinearity are dependent on the relative equilibrium exchange rates in the channel and at the interfaces. Nonlinear current-voltage plots can be obtained in symmetric solutions as well as a nonunity exponent for the Ussing flux ratio. Due to the dependence of the partition coefficient on solubility, it is highly unlikely that the intracellular and extracellular partition coefficients are the same. A manifestation of unequal partition coefficients is a current reversal at a membrane voltage that is different from the Nernst potential of the current-carrying ionic species.

Electrophysiology↗
PubMed1993

Effects of epoxyeicosatrienoic acids on isolated hearts and ventricular myocytes.

Effects of cytochrome P-450 metabolites of arachidonic acid, epoxyeicosatrienoic acids (EETS; 5,6-EET, 8,9-EET, 11,12-EET, and 14,15-EET), were examined in isolated guinea pig hearts and ventricular myocytes. Addition of 1-16 ng/ml EETs to normal isolated hearts produced no effects on contractility or coronary pressure. In hearts subjected to 60 min of low-flow ischemia, impairment of contractility and declines in heart rate and coronary perfusion pressure were similar in the presence or absence of 1 ng/ml EETs. However, in the presence of either 5,6- or 11,12-EET, recovery was delayed for the first 10 min only. No significant differences were found in any group regarding heart rate, coronary perfusion pressure, or energy metabolite content after 30 min of reperfusion. In myocytes, both 5,6- and 11,12-EET (100 pg/ml, 1.0 ng/ml, and 20 ng/ml) significantly increased cell shortening as well as intracellular calcium concentrations, whereas 8,9- or 14,15-EET was without effect on these parameters. These results describe for the first time the direct effects of various EETs on cardiac cell function as well as their ability to modulate some of the myocardial responses to postischemic reperfusion. The results suggest a potential role for these substances in the response of the heart to pathological insult.

8,11,14-Eicosatrienoic Acid↗
PubMed1992

Positive and negative inotropic effects of phorbol 12-myristate 13-acetate: relationship to PKC-dependence and changes in [Ca2+]i.

The present study examined the concentration-dependent effects of phorbol 12-myristate 13-acetate (PMA), a PKC-activating phorbol ester, on contractile force and [Ca2+]i in guinea-pig hearts and isolated cardiac myocytes, respectively. Contractile force was measured using isolated Langendorff-perfused hearts while [Ca2+]i was measured independently in isolated cardiac myocytes loaded with fura2-AM. Phorbol 12-myristate 13-acetate, as well as another PKC-activating phorbol, phorbol dibutyrate (PDBu), and two non-PKC-activating phorbols, alpha-phorbol didecanoate (alpha PDD) and 4 alpha-phorbol, exerted time- and concentration-dependent effects on contractility. A significant positive inotropic response was observed with either PMA (10(-12) M; 5-15 min of perfusion) or PDBu (10(-12) M; 5 min of perfusion). In contrast, 10(-10) M PMA caused a significant negative inotropic effect following 30 min of perfusion while 10(-8) M PMA produced a significant negative inotropic effect which occurred earlier (10 min) and was sustained throughout the 30 min perfusion period. A similar negative inotropic effect was seen with 10(-8) M of either PDBu or alpha PDD. In addition, 4 alpha-phorbol (10(-8) M) exerted a modest, but significant negative inotropic effect following 25 and 30 min of perfusion. Both concentration-dependent increases and decreases of +dF/dt and -dF/dt were observed in the presence of PMA. In addition, both PMA and PDBu caused a concentration-dependent increase in coronary perfusion pressure. The positive inotropic responses and coronary perfusion pressure effects elicited by PMA and PDBu were largely prevented by the addition of the PKC inhibitors H7 (6 nM) or HAG (10 nM); however, these drugs were without effect on the negative inotropic response to higher concentrations of both PKC-activating (PMA, PDBu) and non-PKC-activating (alpha PDD, 4 alpha-phorbol) phorbol compounds. The lowest concentration of either PMA or PDBu (10(-12) M) increased the 340/380 fluorescence ratio of isolated cardiac myocytes loaded with fura2-AM on a time scale similar to that at which the positive inotropic response was seen in the whole heart. However, in contrast to results in the isolated heart, PDBu elicited a greater and sustained increase in the fluorescence ratio measured in isolated cardiac myocytes. The higher concentration of either PMA or PDBu (10(-8) M), resulted in a decrease in the 340/380 ratio.(ABSTRACT TRUNCATED AT 400 WORDS)

Animals↗
PubMed1992

Determining the optimum residual moisture in lyophilized protein pharmaceuticals.

A general concern in the lyophilization of protein pharmaceuticals is how dry a product should be in order to maintain its stability during storage. This paper presents our exploratory studies on determining if there is an optimal residual moisture content for lyophilized recombinant protein products. The proteins used in this study were methionyl human growth hormone (met-hGH) and tissue type plasminogen activator (tPA). The amount of water adsorbed on each protein can be determined and approximated as a monolayer by the Brunauer-Emmett-Teller method. The result was in good agreement with the theoretical value calculated from the total number of strong polar groups in the molecule without regard to the conformation of the protein. This approach suggests that each protein may have a minimum moisture content that is necessary to shield the polar groups, and that over-drying will lead to exposure of these groups. The effect of residual moisture content on the stability of tPA in lyophilized excipient-free powder was studied. Samples that were dried to a water content below the calculated monolayer exhibited opalescence upon reconstitution, while those that were dried to either monolayer or multilayer water content tended to show a greater loss in biological stability upon storage under temperature stress conditions. The results of our studies reveal that the generally accepted concept "the drier the better" may not be appropriate for tPA. An optimum residual moisture content is required to balance the physical stability and the biological stability. These observations may apply to other protein products as well.

Amino Acid Sequence↗
PubMed1991

Improved biocompatibility of silicone rubber by removal of surface entrapped air nuclei.

Biomaterials activate the complement system which is important since C3a promotes platelet aggregation and release, and C5a activates neutrophils that may augment coagulation. Tiny air nuclei (microbubbles) are found in the surface roughness of biomaterials on exposure to a liquid, therefore two interfaces exist: (a) a blood/biomaterial, and (b) a blood/air interface. Experiments were carried out that documented that air bubbles activate complement and augment in vitro platelet aggregation in human plasma. The air nuclei were removed from the surface of silicone rubber by a technique termed denucleation to determine if complement activation and platelet aggregation could be reduced. We observed a significant reduction in C3a and C5a in the plasma samples incubated with denucleated silicone rubber as compared to the control samples (p less than 0.001, ANOVA). The plasma incubated with the denucleated silicone caused reduced platelet aggregation as compared to the plasma incubated with the control silicone when added to a platelet suspension (p less than 0.001, ANOVA). Surface chemical analysis by x-ray photo-electron spectroscopy (XPS) showed no change in the silicone rubber surface after the denucleation procedure.

Air↗
PubMed1990

Evacuation of microscopic air bubbles from Dacron reduces complement activation and platelet aggregation.

Complement activation by biomaterials may play an important role in vascular graft failure since the physiologically active polypeptides, C3a and C5a, have several relevant properties. C3a promotes platelet aggregation and release, and C5a activates neutrophils, which may stimulate platelet aggregation by liberation of platelet activating factor or by a direct neutrophil platelet interaction. Microscopic air bubbles (nuclei) are found in the surface roughness or pores of most biomaterials, and their number and size are related to the surface tension of the material. Therefore two interfaces can be postulated to exist when Dacron is exposed to blood: (1) a blood/biomaterial, and (2) a blood/air interface. These air nuclei in the surface and the biomaterial itself are capable of activating complement. The purpose of these experiments was to eliminate these surface nuclei from Dacron by a process termed denucleation and subsequently to determine the effect of this intervention on complement activation and platelet aggregation in vitro. Dacron was denucleated by pretreatment that involved serial rinsing with ethanol and degassed buffer that results in replacement of the air nuclei by buffer. Both control and denucleated pieces of Dacron (2, 4, and 6 cm2) were then incubated in human plasma. Each plasma sample was assayed for complement activation products (C3a, C5a, and C4a) by means of radioimmunoassays, and the degree of autologous platelet aggregation that resulted from the addition of a portion of each incubated plasma sample to an autologous platelet suspension was measured. There was a significant reduction in C3a and C5a in the plasma samples incubated with denucleated Dacron as compared to control Dacron (p less than 0.001, analysis of variance [ANOVA]).(ABSTRACT TRUNCATED AT 250 WORDS)

Adult↗
PubMed1990

Complement activation involvement in decompression sickness of rabbits.

A hypothesis has been proposed that claims much of the phenomena of decompression sickness (DCS) are mediated by the complement system of blood plasma. This "complement hypothesis" can be used to explain the variation in susceptibility of individuals to DCS, including the phenomena of acclimatization and de-acclimatization. In this study, certain predictions of the complement hypothesis were examined by exposing rabbits to a particular pressure profile; some were observed to have symptoms of DCS and some showed none. Those that were observed to have symptoms were also found to have native complement systems that were activated by air bubbles, and those that did not show symptoms of DCS when exposed to the same pressure profile had native complement systems that were not activated by air bubbles. Rabbits that had shown symptoms of DCS the first 2 times that they were exposed to the pressure profile could be acclimatized to the pressure profile by pharmacologically decomplementing them in vivo. After being decomplemented, they showed no symptoms of DCS when they were exposed to the same pressure profile for a third time. When the decomplemented rabbits were allowed to remain inactive for a period of time that was sufficient to allow their complement systems to return to normal, after having been decomplemented, and were then subjected to the pressure profile for the fourth time, they were each again observed to have symptoms of DCS, i.e., they became de-acclimatized when their complement systems had returned to their native sensitivity. These results provide further experimental support for the complement hypothesis.

Animals↗
PubMed1989

Complement activation mediates cellular adhesion to synthetic biomaterials.

The possibility has arisen that it is the complement proteins of blood plasma that mediates cellular adhesion following the exposure of a synthetic material to blood. There are two means of investigating this possibility. One is by pharmacologically rendering the complement system of an animal incapable of being activated before its blood is exposed to a material and determining the effect on the degree of cellular adhesion that results. The second is to leave the hemostasis system fully in tact but to modify the material so that the material activates less complement when it is exposed to blood and to determine if this also reduces the degree of cellular adhesion. We review the results of a series of studies that involve both of these approaches. The evidence from both indicate that the complement system mediates cellular adhesion to synthetic materials.

Animals↗
PubMed1987

Relation between complement activation and susceptibility to decompression sickness.

The consequences of complement activation and the symptoms of decompression sickness are similar. Consequently, the relation between the sensitivity of individuals to complement activation by air bubbles and their susceptibility to decompression sickness has been examined. Plasma samples from 34 individuals were incubated with air bubbles, and the concentration of the fluid phase metabolites of complement activation C3a, C4a, and C5a were measured with radioimmunoassays. It was found that both the anaphylatoxins C3a and C5a were produced by the presence of air bubbles but that the anaphylatoxin C4a was not. This finding indicates that air bubbles activate the complement system by the alternate pathway. One group of individuals was found to be particularly sensitive to complement activation by this pathway. They produced 3.3 times more C3a and 5.3 times more C5a in their plasma samples incubated with air bubbles as did the other group. Sixteen individuals were subjected to a series of pressure profiles that were severe enough to produce bubbles in their circulatory system that could be detected by Doppler ultrasonic monitoring. The group of individuals that had been identified as being more sensitive to complement activation by the alternate pathway was also found to be more susceptible to decompression sickness.

Adult↗
PubMed1986

ANSIM: an anesthesia simulator for the IBM PC.

Simulations based on physiologic modeling have been used for over twenty years to clarify the pharmacokinetics of inhaled anesthetics. We describe ANSIM, an anesthesia simulator for the IBM PC. ANSIM uses established modeling techniques to create a life-like anesthesia simulator. ANSIM is useful as an educational tool for demonstrating classic concepts of uptake and distribution of inhaled anesthetics.

Anesthesia↗
PubMed1986

Primary DNA sequence determines sites of maintenance and de novo methylation by mammalian DNA methyltransferases.

Analysis of the enzymatic methylation of oligodeoxynucleotides containing multiple C-G groups showed that hemimethylated sites in duplex oligomers are not significantly methylated by human or murine DNA methyltransferase unless those sites are capable of being methylated de novo in the single- or double-stranded oligomers. Thus, the primary sequence of the target strand, rather than the methylation pattern of the complementary strand, determines maintenance methylation. This suggests that de novo and maintenance methylation are the same process catalyzed by the same enzyme. In addition, the study revealed that complementary strands of oligodeoxynucleotides are methylated at different rates and in different patterns. Both primary DNA sequence and the spacing between C-G groups seem important since in one case studied, maximal methylation required a specific spacing of 13 to 17 nucleotides between C-G pairs.

Animals↗