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Biomedical subjects

C J Parker

Publications and source records attributed to C J Parker.

At least 19 recordsLinked to original sources
PubMed1992

Use of low molecular weight heparin in pregnancy.

In a controlled study of 15 pregnant patients undergoing therapeutic termination of pregnancy, seven received subcutaneously 5,000 anti-FXa units of low molecular weight (LMW) heparin 15 and 3 h prior to the termination, and eight patients acted as controls. Paired maternal and fetal blood samples were taken (before or immediately after the termination) for assay of heparin activity by a chromogenic anti-FXa method sensitive to levels of 0.02 anti-FXa U/ml. LMW heparin was detected in all maternal samples of the test patients but was not detected in any of the fetal samples. The use of LMW heparin as a thromboprophylactic agent was then evaluated in 11 patients who were known to have a severe thromboembolic tendency, had suffered recurrent miscarriages and had responded poorly to conventional anticoagulation (oral anticoagulant, conventional heparin). All patients receiving LMW heparin in thromboprophylactic doses completed uneventful pregnancies and gave birth to healthy babies (three for the first time) without complication. Bone density scans performed in all patients shortly after the delivery showed normal mineral mass. We conclude that LMW heparin does not cross the placental barrier, and in addition offers satisfactory antithrombotic protection for both maternal and placental circulation. In addition, this study provides preliminary data from 11 patients suggesting LMWH may not give rise to maternal osteoporosis, a finding that now needs further investigation.

Abortion, Habitual↗
PubMed1992

Estrogenic potential of progestins in oral contraceptives to stimulate human breast cancer cell proliferation.

Most oral contraceptives (OC) contain a progestin in combination with an estrogen, and the progestin component in OC includes one of the following 19-nortestosterone derivatives: norethynodrel; norethindrone; or norgestrel (levonorgestrel). It is well known that estrogens promote the growth of breast cancer. However, progestins have recently also been implicated in the development of breast cancer. We have compared and contrasted the ability of synthetic progestins to stimulate the proliferation of cultured human breast cancer cells and examined their possible mechanism of action. We found that some progestins used in OC were able to stimulate the growth of estrogen receptor-positive (ER+) MCF-7 and T47DA18 human breast cancer cells but not ER- MDA-MB-231, BT-20, and T47DC4 human breast cancer cells. However, two other progestins, MPA and R5020, which are not used in OC, were either not able to stimulate or only slightly stimulated growth. The potency of norethynodrel [median effective dose (EC50) = 4 x 10(-8) M] and norethindrone (EC50 = 3 x 10(-8) M) was greater than norgestrel (EC50 = 2 x 10(-7) M) in MCF-7 cells. E2 (EC50 = 8 x 10(-13) M) was an even more potent stimulator of growth. More importantly, the progestin-induced growth stimulation was blocked by the antiestrogens 4-hydroxytamoxifen and ICI 164,384 but not the antiprogestin 17 beta-hydroxy-11 beta-(4-dimethylaminophenyl)-17 alpha-(1-propynyl)-estra-4, 9-dien-3-one (RU486). To determine whether the proliferative action of progestins was mediated through the ER, cells were transfected with a chloramphenicol acetyltransferase reporter gene containing an estrogen response element derived from vitellogenin 2A gene. The progestins which stimulated the growth of breast cancer cells also increased chloramphenicol acetyltransferase activity. The induction of chloramphenicol acetyltransferase activity was blocked by the addition of the antiestrogens 4-hydroxytamoxifen and ICI 164,384 but not the antiprogestin RU486. This study provides direct evidence that the 19-nortestosterone derivatives in OC have estrogenic properties and suggests that activation of ER, but not progesterone receptor, is the growth-stimulatory mechanism for these synthetic progestins. Our results may help to explain the conflicting evidence linking OC and breast cancer risk. A rigorous evaluation of the "total" estrogenic potential of OC might produce a better correlation with breast cancer risk.

Amino Acid Sequence↗
PubMed1992

Induction of tissue factor activity in endothelial cells and monocytes by a modified form of albumin present in normal human plasma.

Molecules that induce tissue factor expression by responsive cells such as endothelial cells and monocytes may be important in the regulation of hemostasis and, perhaps, in mediating certain hemostatic disorders. A constituent of normal human plasma capable of inducing tissue factor activity in human endothelial cells and monocytes has been isolated and identified as a derivative of, or modification associated with albumin. Procoagulant albumin caused a concentration-dependent induction of tissue factor expression by human endothelial cells, but bovine endothelial cells were unresponsive. The dose-response curve developed a plateau phase, indicating that the capacity of endothelial cells to respond to the stimulus was finite. The maximum response induced by the procoagulant albumin was similar to that observed for maximally effective concentrations of endotoxin, interleukin-1, and tumor necrosis factor. Time-course studies showed that procoagulant albumin produced peak activity in 4 to 6 hours. Identification of a procoagulant form of albumin in normal human plasma suggests a potential role for this constituent in regulation of hemostasis.

Barium↗
PubMed1992

Analysis of the effects of activation of the alternative pathway of complement on erythrocytes with an isolated deficiency of decay accelerating factor.

E from individuals with the Inab blood group phenotype have an isolated deficiency of decay accelerating factor (DAF, CD55). DAF is a glycosyl phosphatidylinositol anchored membrane protein that inhibits activation of both the classical and alternative pathways of complement. Deficiency of DAF from the E of paroxysmal nocturnal hemoglobinuria (PNH) is thought to contribute to their greater sensitivity to complement-mediated lysis. Unlike PNH E, however, Inab cells are not susceptible to acidified serum lysis, a process that is mediated through activation of the alternative pathway. This observation led us to hypothesize that membrane constituents other than DAF control susceptibility to acidified serum lysis. To investigate this hypothesis, Inab E were incubated in acidified serum, and hemolysis and C3 deposition (as a measure of alternative pathway activation) were quantitated. C3 deposition of Inab cells was approximately 20 times greater than normal, however, hemolysis was not observed. Inab E expressed a normal amount of membrane inhibitor of reactive lysis (MIRL, CD59), a glycosyl phosphatidylinositol anchored protein that is also deficient in PNH. When MIRL function was blocked with antibody, C3 deposition markedly increased, and 100% of the Inab cells hemolyzed in acidified serum. These studies demonstrate that susceptibility to acidified serum lysis is controlled primarily by MIRL, and that in addition to its regulatory affect on the membrane attack complex, MIRL also modulates the activity of the C3 convertase of the alternative pathway by a mechanism that remains to be determined.

Animals↗
PubMed1992

A new four-parameter threshold model for the plasma atracurium concentration-response relationship.

The plasma concentration of atracurium and the electromyographic depression of the first response of the train-of-four (T1:T0) were measured during and after recovery from a 10-min infusion of atracurium 0.25 mg kg-1 in 14 patients anaesthetized with 66% nitrous oxide and 0.9% isoflurane (end-tidal) in oxygen. A standard pharmaco-dynamic model was fitted to the data; a small but consistent discrepancy was found between the time and rate of onset of depression of the ratio T1:T0 and the predictions of the standard biophase model of best fit to the data. This discrepancy is reduced by the inclusion of a threshold term (CPss theta) in the model to represent the greatest steady state plasma concentration which would just fail to evoke an effect. The values of CPss theta correlated significantly with the values of CPss50 (r = +0.627; P less than 0.02). The estimates of CPss50 and keo from the two models are very similar; the estimate of gamma, the slope of the concentration-response curve, was less in the threshold model. The relationship of the present threshold model to existing knowledge of neuromuscular physiology is discussed.

Adult↗
PubMed1992

Dependence of the neuromuscular blocking effect of atracurium upon its disposition.

We have assessed the profiles of plasma concentration of atracurium and its neuromuscular blocking effect on the first response of the train-of-four measured by electromyography after a short infusion of atracurium 0.25 mg kg-1, in 38 patients anaesthetized by one of three techniques. Measures of the temporal profile of neuromuscular block were found to correlate with pharmacokinetic variables. When anaesthetic technique was taken into account in a multivariate model, the time to onset of 10% deprssion of T1:T0 correlated positively with the central volume of distribution (P less than 0.05). The change in T1:T0 during the 1 min after 10% depression, and the logit of maximum depression were both correlated negatively with the central volume of distribution (P less than 0.05 and P less than 0.01, respectively). Both the times to 20% and 50% recovery of T1:T0 correlated strongly negatively with clearance (P less than 0.0001 for both measures). The findings support the conclusion that the effect of atracurium is dependent upon its disposition.

Adult↗
PubMed1992

Relationship of the train-of-four ratio to plasma atracurium concentration.

The electromyographic response to a short infusion of atracurium 0.25 mg kg-1 was recorded using the train-of-four (TOF) technique, and the plasma atracurium concentration profile measured, in 10 healthy patients. The TOF ratio (T4:T1) was depressed over a time course which did not conform to the predictions of an effect compartment model; the fit of such a model, when possible, was associated with large residual errors. In contrast, the absolute height of the fourth response of the TOF (T4:T0) may be fitted by a standard effect compartment model with smaller errors. This residual error was reduced further on fitting a threshold effect compartment model to the data set T4:T0. The parameter values of such a model were related closely to those for the first response (T1:T0). The kinetics of the effect compartments for the first and fourth response of the TOF were similar, whilst the CPss50 for the fourth response was approximately 67% that for the first response.

Adolescent↗
PubMed1992

Effect of age, sex and anaesthetic technique on the pharmacokinetics of atracurium.

We have defined the pharmacokinetics of atracurium besylate 0.25 mg kg-1 in 41 patients anaesthetized with 0.9% isoflurane end-tidal, 0.5% halothane end-tidal or midazolam 3-10 mg as a supplement to 66% nitrous oxide in oxygen. The pharmacokinetic profile was affected by age, sex and anaesthetic technique. Advancing age was associated with a reduced clearance and a longer elimination half-time; clearance was greater and elimination half-time was shorter in males than in females. Clearance was also greater in patients anaesthetized with isoflurane than with the two other techniques. Age, sex and anaesthetic technique did not significantly affect the volume of distribution.

Adolescent↗
PubMed1992

Bacterial evasion of the antibody response: human IgG antibodies neutralize soluble but not bacteria-associated group B streptococcal C5a-ase.

Most strains of group B streptococci (GBS) possess an enzyme that inactivates the human anaphylatoxin C5a by cleaving a heptapeptide from the carboxyl terminus of C5a. This enzyme, called GBS C5a-ase, has been purified to homogeneity and cleaves and inactivates C5a in physiologic buffer. The enzymatic activity of soluble C5a-ase is completely inhibited, however, in the presence of plasma or serum from normal human adults. The neutralization of soluble C5a-ase by plasma and serum results largely from naturally occurring IgG antibodies directed against C5a-ase. IgG does not neutralize C5a-ase present on intact encapsulated type III GBS but does neutralize the C5a-ase activity associated with a transposon-induced mutant strain of type III GBS that lacks capsule. The location of GBS C5a-ase on the surface of encapsulated type III GBS permits the C5a-ase to inactivate C5a while evading neutralization by IgG antibodies.

Adhesins, Bacterial↗
PubMed1992

Cell-surface regulation of the human alternative pathway of complement. Sheep but not rabbit erythrocytes express factor I-dependent cofactor activity.

When incubated in normal human serum, rabbit erythrocytes are haemolysed as a result of activation of the alternative pathway of complement (APC), but sheep erythrocytes do not spontaneously activate the human APC under physiological conditions. The mechanism for this difference has been attributed to differences in the relative affinity of membrane-bound C3b for its natural ligands, factor B and factor H, that favour the formation and stability of the APC C3 convertase on rabbit erythrocytes and inhibit convertase activity on sheep erythrocytes. Previous studies have also suggested that factor I inactivated C3b on sheep erythrocytes more effectively than on rabbit erythrocytes. Further, sheep erythrocytes have recently been shown to have a membrane protein that associates non-covalently with cell-bound C3b, but rabbit erythrocytes lack a predominant C3b binding protein. Together, these results suggested the possibility that sheep but not rabbit erythrocytes have a membrane constituent with factor I cofactor activity. To investigate this hypothesis, rabbit and sheep erythrocytes bearing radiolabelled C3b were treated either with factor I or with factor I and factor H, and conversion to iC3b was assessed by autoradiography. Factor I caused a concentration-dependent conversion of C3b to iC3b on sheep erythrocytes; however, only trace amounts of C3b on rabbit erythrocytes were degraded even when high concentrations of factor I (83 micrograms/ml) were used. While C3b on rabbit erythrocytes was converted to iC3b by the combination of factor H and factor I, much less factor H was required for the same degree of conversion of C3b on sheep erythrocytes. Treatment of sheep erythrocytes with neuraminidase had no effect on either factor I-dependent cofactor activity or the capacity of factor H to serve as a factor I cofactor. Sheep erythrocytes did not manifest decay accelerating activity, however, suggesting that the factor I cofactor constituent is a functional analogue of the human membrane cofactor protein.

Animals↗
PubMed1992

Modulation of complement activation on hemodialysis membranes by immobilized heparin.

To determine the effects of surface-associated heparin on the capacity of hemodialysis membranes to activate complement, cellulose acetate (CA) membranes that were untreated and CA membranes that had been coated with heparin (HCA) were incubated with C3-depleted serum repleted with radio-labeled C3. Next, the proteins in the supernatant and those eluted from the membranes were subjected to sodium dodecyl sulfate-polyacrylamide gel electrophoresis. C3 activation was quantified by determining the radioactivity of the C3a-containing band in the gel. Total C3a generation (fluid phase C3a plus membrane-associated C3a) was three times greater in the presence of HCA compared with CA. Most (88%) of the C3a generated in the presence of HCA, however, was adsorbed onto the membrane surface. Consequently, there was more C3a in the CA supernatant than in the HCA supernatant. To determine the mechanism by which heparin enhanced alternative pathway activity, binding studies with radiolabeled factor B and factor H were performed. HCA bound 3.4 times more factor B and 20 times more factor H than did CA. The binding of these proteins, however, was not dependent on complement activation. Studies designed to test the functional activity of isolated factor H and factor B that had been adsorbed to the membrane showed that factor H was active on both CA and HCA, whereas factor B was active only on HCA. These data demonstrate that heparin immobilized onto CA hemodialysis membrane enhances C3 activation but produces low levels of C3a in the fluid phase because of high surface adsorption of the anaphylatoxin. Heparin appears to augment alternative pathway activity by favoring the interactions of factor B with other constituents of the amplification C3 convertase of the alternative pathway of complement.

Biocompatible Materials↗
PubMed1991

Purification of the proteinase from group B streptococci that inactivates human C5a.

We previously reported that group B streptococci (GBS) possess a cell-associated activity that inactivates the chemotactic activity generated in zymosan-activated serum by cleaving a specific site within the carboxy termini of C5a and C5adesarg. This inactivates the major chemoattractants for neutrophils that are generated when serum complement is activated. We now report the isolation of the enzyme responsible for the proteolytic cleavage of C5a. Treatment of GBS with mutanolysin, an endo-N-acetyl muramidase, released activity from GBS which destroyed the functional activity of C5a. The soluble activity was purified to homogeneity by hydroxyapatite, ion-exchange and gel-filtration chromatography. Analysis by SDS-PAGE showed that the enzyme (GBS C5a-ase) has an Mr of approx. 120,000. The GBS C5a-ase appears to be a serine esterase on the basis of its sensitivity to di-isopropyl fluorophosphate. This enzyme is distinct from the C5a-cleaving enzyme produced by group A streptococci, since the two bacterial products migrate differently on SDS-PAGE, and lack antigenic cross reactivity. This enzyme may play a role in the pathogenesis of group B streptococcal disease through its ability to rapidly inactivate the potent neutrophil agonist, C5a, at sites of infection.

Adhesins, Bacterial↗
PubMed1991

Molecular basis of the enhanced susceptibility of the erythrocytes of paroxysmal nocturnal hemoglobinuria to hemolysis in acidified serum.

When incubated in acidified serum, the erythrocytes of paroxysmal nocturnal hemoglobinuria (PNH) are hemolyzed through activation of the alternative pathway of complement (APC), but normal erythrocytes are resistant to this process. PNH cells are deficient in decay-accelerating factor (DAF), a complement regulatory protein that inhibits the activity of both the classical and the alternative pathways. However, deficiency of DAF alone does not account entirely for the aberrant effects of acidified serum on PNH cells. Recently, we have shown that PNH erythrocytes are also deficient in another complement control protein called membrane inhibitor of reactive lysis (MIRL) that restricts complement-mediated lysis by blocking formation of the membrane attack complex (MAC). To determine the effects of the DAF and MIRL on susceptibility to acidified serum lysis, PNH cells were repleted with the purified proteins. DAF partially inhibited acidified serum lysis by blocking the activity of the amplification C3 convertase. MIRL inhibited acidified serum lysis both by blocking the activity of the MAC and by inhibiting the activity the C3 convertase. When DAF function was blocked with antibody, normal erythrocytes became partially susceptible to acidified serum lysis. By blocking MIRL, cells were made completely susceptible to lysis, and control of C3 convertase activity was partially lost. When both DAF and MIRL were blocked, the capacity of normal erythrocytes to control the activity of the APC and the MAC was destroyed, and the cells hemolyzed even in unacidified serum. These studies demonstrate that DAF and MIRL act in concert to control susceptibility to acidified serum lysis; of the two proteins, MIRL is the more important. In addition to its regulatory effects on the MAC, MIRL also influences the activity of the C3 convertase of the APC. Further, in the absence of DAF and MIRL, the plasma regulators (factor H and factor I) lack the capacity to control membrane-associated activation of the APC.

Animals↗
PubMed1991

Induction of the paroxysmal nocturnal hemoglobinuria phenotype in normal human erythrocytes: effects of 2-aminoethylisothiouronium bromide on membrane proteins that regulate complement.

To investigate the mechanism by which treatment of normal human erythrocytes with the sulfhydryl reagent 2-aminoethylisothiouronium bromide (AET) induces susceptibility to complement mediated lysis, the effects of AET on the structural and functional integrity of decay accelerating factor (DAF), membrane inhibitor of reactive lysis (MIRL), and complement receptor type 1 (CR1) were examined. Following treatment with AET, erythrocyte MIRL and CR1 were no longer recognized in situ by antibodies, and antibody binding to DAF was diminished by approximately 50%. These studies indicated that the structural integrity of the three complement regulatory proteins was either partially (DAF) or completely (MIRL and CR1) disrupted by AET. Subsequent experiments showed that functional inactivation paralleled the structural disruption. Treatment of normal erythrocytes with AET induced susceptibility to cobra venom factor-initiated hemolysis, indicating that the functional activity of MIRL had been destroyed. The capacity of erythrocyte CR1 to serve as a cofactor for factor I-mediated cleavage of iC3b to C3c and C3dg was lost following treatment with AET. C3 convertase activity increase markedly following treatment of erythrocytes with AET, but convertase activity on AET cells was approximately 50% less than that observed when DAF function on normal cells was completely inhibited by antibody. Susceptibility of AET cells to acidified serum lysis was shown to be due primarily to inactivation of MIRL. Unexpectedly, in acidified serum the activity of the amplification C3 convertase of the APC was found to be controlled by MIRL as well as by DAF. These studies show that AET induces susceptibility to complement-mediated lysis by disrupting the structural and functional integrity of membrane constituents that regulate the activity of both the C3 convertases and the membrane attack complex of complement.

Antibodies↗
PubMed1991

Detection of the membrane inhibitor of reactive lysis (CD59) in diseased neurons of Alzheimer brain.

The membrane inhibitor of reactive lysis (MIRL) protects host cells from complement-mediated lysis. It was detected immunohistochemically in tangled neurons and dystrophic neurites of Alzheimer disease (AD) tissue in a pattern highly similar to that observed for the membrane attack complex of complement, C5b-9. MIRL was also detected in cultured IMR-32 neuroblastoma cells. The mRNA for MIRL was detected in RNA extracts of both AD and normal brain. These data provide the first evidence of brain neuronal expression of MIRL and its upregulation in neurons exposed to complement attack. They are consistent with the previously advanced hypothesis that complement-mediated neuronal injury may play a role in AD.

Alzheimer Disease↗
PubMed1991

Activated macrophage conditioned medium: identification of the soluble factors inducing cytotoxicity and the L-arginine dependent effector mechanism.

Conditioned medium (CM) from cultures of cytotoxic activated macrophages causes inhibition of mitochondrial respiration, DNA synthesis, and aconitase activity in murine EMT-6 mammary adenocarcinoma cells by an L-arginine dependent effector mechanism. CM induces cytotoxicity and nitrite synthesis in EMT-6 cells in a dose dependent manner. We have identified the soluble factors in CM that induce cytotoxicity and synthesis of inorganic nitrogen oxides from L-arginine by EMT-6 cells. Using functional inhibition experiments, the activity of lipopolysaccharide (LPS), tumor necrosis factor alpha (TNF alpha), and interferon gamma (IFN gamma) in CM was investigated. The LPS inhibitor polymyxin B and TNF alpha antibody produced a modest decrease in nitrite production, while IFN gamma antibody markedly inhibited both nitrite production and cytostasis. Simultaneous treatment with polymyxin B, TNF alpha antibody, and IFN gamma antibody reduced EMT-6 cell nitrite production by 81%, and cytostasis by 74%. By Western blot, IFN gamma and TNF alpha were shown to be present in CM. When CM was subjected to hydrophobic interaction chromatography, a single peak of activity was eluted, and Western blot showed that the active fractions contained IFN gamma. Furthermore, IFN gamma antibody neutralized the activity in these chromatographic fractions. We conclude that induction of inorganic nitrogen oxide synthesis from L-arginine by the synergistic combination of IFN gamma, TNF alpha, and LPS accounts for most of the biologic activity of CM, and that IFN gamma is the major priming factor.

Aconitate Hydratase↗