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Biomedical subjects

M E Carr

Publications and source records attributed to M E Carr.

At least 37 records · Page 2Linked to original sources
PubMed1996

Use of TPA-induced clot lysis time (TCLOT) to diagnose abnormal clot structure and fibrinolysis in a patient with spontaneous bleeding into his leg.

Diagnosis and treatment of patients with bleeding due to enhanced fibrinolysis is hampered by the absence of a rapid screen of fibrinolytic potential. The authors have developed a simple assay to assess clot structure and fibrinolysis in patient samples exposed to tissue plasminogen activator (TPA). They present the case of a forty-one-year-old man who presented with spontaneous bleeding despite normal results from coagulation screening tests, platelet count, platelet aggregation studies, platelet force development, and bleeding time. Evaluation of the patient's clot structure revealed a very weak, low-modulus, clot that rapidly dissolved in the presence of TPA. Identification of the abnormality allowed treatment with epsilon-aminocaproic acid with prompt resolution of bleeding.

Adult↗
PubMed1996

Comparison of factor VIII-related antigen and erythrocyte sedimentation rate in outpatient management of vasculitis.

Electroimmunodiffusion (Laurell rocket) determinations of factor VIII-related antigen in plasma were ordered to determine the cost/benefit ratio for factor VIII-related antigen as a putative test for endothelial damage in suspected vasculitis. Twenty-seven consecutive patients referred for vasculitis or suspected vasculitis were identified and followed up for an average of 9.1 +/- months (range: one to thirty-three months) in a prospective, unblinded study performed in a clinic, associated with a 1054-bed inner-city university hospital. There was no difference in Westergren erythrocyte sedimentation rate (WESR) in patients with final diagnosis of systemic vasculitis (SV) (38 +/- 12 mm/hour) compared to those without vasculitis (NV) (27 +/- 7) as the final diagnosis. The mean plasma concentration of factor VIII-related antigen was significantly elevated in SV (344 +/- 100%) when compared with NV (147 +/- 39%) (P < 0.016). The factor VIII-related antigen test in this study was 2.56 times more likely (crude odds ratio) than the WESR to contribute to a change in diagnosis or therapy (P = 0.016). Positive and negative predictive values (PPV and NPV) for factor VIII-related antigen (abnormal at greater than 220% of the normal value) were both 70%. PPV and NPV for WESR were 56% and 86%, respectively. The factor VIII-related test was less cost-effective than the WESR in the follow-up period unless it was important to define complete remission or differentiate vasculitis flare from infection. The authors conclude that factor VIII-related antigen is a useful test in the initial diagnosis of vasculitis.

Ambulatory Care↗
PubMed1996

Heparin ablates force development during platelet mediated clot retraction.

Although snake venom enzymes such as reptilase do not cause viscous metamorphosis, platelet secretion or clot retraction; when batroxobin and calcium are added to citrated blood significant platelet force development occurs. When this batroxobin-calcium system was applied to the study of platelet function during cardiopulmonary bypass (CPB), force development was found to be completely inhibited. After heparin reversal by protamine sulfate, significant recovery of force occurred. The present investigation was performed to evaluate the role of heparin in reducing force development during CPB. At concentrations above 0.10 U/ml, heparin totally suppressed force development in normal plasma. Addition of protamine sulfate to heparinized plasma caused complete recovery of force development. These concentrations of heparin had little effect on platelet aggregation by ADP or collagen. Possible direct effects of heparin on fibrin assembly and structure were studied by adding varying amounts of heparin to plasma and then inducing clot formation with batroxobin. At 1 U/ml, heparin reduced the size of fibrin fibers by 33%. Higher heparin concentrations had no additional effect. These results indicate that heparin may be responsible for a significant component of the decreased platelet force noted during cardiopulmonary bypass. To test whether heparin's effect could be due to suppression of thrombin activity, the effects of the antithrombin hirudin on force development were measured. Hirudin also inhibited force development in a concentration dependent manner. Thus, heparin's reduction of platelet force development may be due, at least in part, to suppression of thrombin activity.

Batroxobin↗
PubMed1995

Aggregatory characteristics and expression of the collagen adhesion receptor in fetal porcine platelets.

Fetal wound healing differs significantly from that of the adult by its rapidity, the paucity of an inflammatory response, and the lack of scarring. In the adult, activation and aggregation of platelets at the site of injury result in the release of cytokines and inflammatory mediators that stimulate wound healing by initiating an acute inflammatory response. The aim of this study was to characterize the activity of midtrimester (day 60) and third-trimester (day 95) fetal porcine platelets (full term, 114 days) compared with that of adults in an attempt to understand the lack of inflammation in fetal wounds. The aggregatory capabilities of adult and fetal platelets were analyzed after exposure to adenosine diphosphate (ADP) concentrations of 10 mumol/L and 40 mumol/L concentrations, collagen of 0.19 mg/mL, and arachidonic acid of 0.5 mg/mL. Expression of the alpha 2 subunit of the collagen receptor (alpha 2 beta 1) was evaluated by Western blot analysis. The aggregation of day-60 fetal platelets when exposed to ADP (10 mumol/L and 40mumol/L) and collagen was significantly lower than that of the adult. The aggregation of third-trimester platelets to 10 mumol/L of ADP was similar to that of the adult and significantly greater than that of midtrimester fetuses at higher concentrations (40 mumol/L). Both fetal groups responded suboptimally to collagen, and the response was significantly less than that of adults. In contrast, arachidonic acid caused rapid and complete aggregation of both fetal platelet groups, suggesting that both mid- and late-trimester fetal platelets possessed the ability to fully aggregate with the appropriate stimulus. The different aggregatory responses to collagen could not be explained by differences in collagen receptor expression, because these were found to be similar in adults and midtrimester fetuses. It is concluded that although fetal platelets have the potential to aggregate effectively, they aggregate poorly to collagen and exhibit improved aggregation to ADP with increasing maturity. There is a transition to "adultlike" platelet aggregatory activity in the third trimester, which correlates with the period of transition to adultlike wound healing in utero. Similar expression of the alpha 2 beta 1 collagen receptor in the fetus and adult cannot explain the differences observed in their responses to collagen.

Animals↗
PubMed1995

Reductions in platelet force development by cardiopulmonary bypass are associated with hemorrhage.

Quantitative assessment of platelet dysfunction after cardiopulmonary bypass (CPB) and prediction of excessive microvascular bleeding remain elusive goals. We used a sensitive instrument capable of simultaneously measuring the force generated by platelets during plasma clot retraction and global clot strength. We hypothesized that CPB would significantly reduce these two variables. Platelet-rich plasma was obtained from eight patients undergoing aortocoronary revascularization prior to induction, after 90 min of CPB, and after protamine administration. Platelet force development was measured using a standardized technique that controlled for platelet number and permitted clot formation in the presence of heparin. Despite the presence of a measurable elastic modulus, platelet force development during bypass was abolished. Peak platelet force development after CPB was significantly lower than before CPB (5255 +/- 955 dynes vs 11,600 +/- 780 dynes, P = 0.01). The percent recovery (after/before bypass) of peak platelet force development inversely correlated with tube thoracostomy drainage during the first 24 h after placement (rs = -0.71, P = 0.048). This study demonstrates that CPB has dramatic effects on platelet force development. The correlation between the percent recovery of peak platelet force development and blood loss supports the clinical relevance of this measurement.

Aged↗
PubMed1995

Fibrin structure and concentration alter clot elastic modulus but do not alter platelet mediated force development.

During clot retraction, platelets interact with fibrin resulting in marked reduction of clot volume. Altered fibrin structure has been reported to affect clot retraction as measured by serum expression. This study was performed to test whether such altered retraction was the result of increased resistance to network collapse or due to decreased force development by platelets. Altered fibrin structure was documented as variation of fibre mass/length ratios (mu) and shifts in clot elastic modulus. The force developed by platelets during clotting was measured directly. Increasing the fibrinogen concentration led to thinner fibre formation (decreased mu), and a linear increase in gel elastic modulus. Over a fibrinogen concentration range of 100 to 400 mg/dl, force development was minimally affected. Force development and clot elastic modulus increased in a linear fashion with increasing platelet concentration. Increasing the calcium concentration from 5 to 20 mM caused a 160% increase in fibrin fibre size (mu), and a 52% decline in clot modulus. Force developed at 1200 s declined by 17%. At 15 mg/ml, dextran and hydroxyethyl starch (HES) also increased mu, and decreased clot modulus; however, both agents markedly reduced force development. Increasing ionic strength or the addition of IgG decreased mu and increased gel elastic modulus. Force development increased modestly with increased ionic strength, did not change with addition of IgG in saline and declined with addition of IgG in maltose. This study indicates that force development is primarily dependent on platelet function while clot modulus depends on both fibrin structure and platelet function.(ABSTRACT TRUNCATED AT 250 WORDS)

Blood Coagulation↗
PubMed1995

Effect of fibrin structure on plasmin-mediated dissolution of plasma clots.

Previous studies in purified systems have demonstrated that fibrin structure influences the rate of conversion of plasminogen to plasmin by t-PA as well as the rate of plasmin-mediated clot digestion. The present study extended these observations to a plasma system in which fibrin structure was altered by varying the thrombin concentration, varying the plasma ionic strength, or by adding dextran 40. The effect of fibrin structure on the rate of fibrinolysis was assessed by adding plasminogen activators (t-PA or urokinase (UK)) either before or after clot formation. Gel formation and dissolution were monitored optically (turbidity) and isotopically (125I-fibrinogen). Clots formed under conditions of high ionic strength and/or high thrombin concentration were composed of thin fibrin fibres that dissolved slowly. Clots formed at lower ionic strengths, at lower thrombin concentrations or in the presence of dextran were composed of thicker fibres and dissolved more rapidly. The difference in fibrinolytic rate between thin and thick fibres was noted when t-PA or UK was added before or after clot formation. These data indicate that even in a plasma milieu fibre diameter is a factor in determining fibrinolytic rate induced by either UK or t-PA. The method by which fibre diameter is altered does not influence the conclusion that fibrinolytic rate is increased with increasing diameter.

Dextrans↗
PubMed1995

A sensitive platelet activation-based functional assay for the antileukemic agent bryostatin 1.

Bryostatin 1, a macrocyclic lactone activator of protein kinase C (PKC) currently in phase I evaluation, is a biologic response modifier which exhibits significant antitumor activity in several experimental systems. Clinical trials have been hampered by the absence of a sensitive assay for bryostatin 1 blood levels. The purpose of these studies was to exploit the exquisite sensitity of human platelets to bryostatin 1-induced aggregation in order to develop an assay capable of detecting plasma bryostatin 1 levels in the nanomolar range. Addition of bryostatin 1 (5-100 nM) to platelet-rich plasma resulted in complete platelet aggregation. A highly linear relationship was observed between low bryostatin 1 concentrations (i.e. 2-25 nM) and (i) reduction in the lag phase prior to aggregation and (ii) maximal rate of aggregation (R = 0.976). At higher bryostatin 1 concentrations (i.e. 10-100 nM), platelet aggregation was accompanied by detectable ATP release; both the extent and maximal rate of ATP secretion were highly linear functions of bryostatin 1 levels (R = 0.992). Bryostatin 1 concentrations in anticoagulated human blood samples could also be determined by mixing platelet poor plasma obtained from such samples with normal platelet-rich plasma. Notably, measurement of the delay in the aggregation lag phase permitted quantitation of bryostatin 1 concentrations of 5 nM or below. The capacity to detect bryostatin 1 plasma levels of 10 nM or lower should facilitate the conduct of pharmacokinetic and pharmacodynamic studies in conjunction with ongoing phase 1 trials.

Adenosine Triphosphate↗
PubMed1995

Glycoprotein IIb/IIIa blockade inhibits platelet-mediated force development and reduces gel elastic modulus.

The effects of GPIIb/IIIa blockade on clot retraction were studied utilizing an instrument which directly measures force produced by platelets. GPIIb/IIIa disruption by calcium chelation, and GPIIb/IIIa blockade by peptides and anti-GPIIb/IIIa antibodies were investigated. One mM EDTA suppressed ADP-induced platelet aggregation by 72% and reduced force developed at 1200 s by 33%. At 234 microM, the tetrapeptide Arg-Gly-Asp-Ser (RGDS) suppressed platelet aggregation by 74%, reduced force at 1200 s by 45% and reduced gel elastic modulus by 19%. At 10 microM, the peptide D-Arg-Gly-L-Asp-L-Try (D-RGDW) completely suppressed platelet aggregation, reduced force development by 38% and reduced gel elastic modulus by 29%. At 0.133 microM, monoclonal anti-GPIIIa antibody (AP-3) reduced force development by 74% and reduced gel modulus by 60%. Murine antiGPIIb/IIIa antibodies 10E5 and 7E3 markedly suppressed force development. At 0.133 microM, 10E5 reduced force by 89% and reduced gel modulus by 67%. At 0.053 microM, 7E3 completely stopped force development and reduced gel modulus by 46%. Platelet aggregation was blocked by 0.027 microM 7E3. Selective GPIIb blockade by antibodies did not affect force development. None of the agents studied altered fibrin structure as monitored by effects of fibrin mass/length ratios. Suppression of platelet aggregation occurred at inhibitor concentrations substantially lower than those required to suppress force development. Complete suppression of platelet aggregation did not assure inhibition of clot retraction probably due to profound platelet activation by thrombin.(ABSTRACT TRUNCATED AT 250 WORDS)

Amino Acid Sequence↗
PubMed1994

At high heparin concentrations, protamine concentrations which reverse heparin anticoagulant effects are insufficient to reverse heparin anti-platelet effects.

Combined effects of heparin and protamine on plasma clot structure and platelet function were studied. Anticoagulant effects were monitored as changes in aPTT. Clot structure was defined in terms of fibrin fiber mass/length ratio (mu) and clot elastic modulus (EM). Platelet function was studied utilizing platelet aggregation and platelet force development (PFD) measurements. Heparin (1 U/ml) prolonged the aPTT from 30 to > 300 seconds, reduced PFD from 5,100 to 0 dynes, decreased mu (in batroxobin-induced gels) from 1.36 to 1.08 x 10(13) daltons/cm and decreased clot EM from 9,600 to 2000 dynes/cm2. Varying amounts of protamine reversed these effects: 16 micrograms/ml normalized the aPTT, 20 micrograms/ml normalized PFD, 32 micrograms/ml corrected mu, and 20 micrograms/ml returned EM to baseline. At high heparin concentrations (4 U/ml), protamine concentrations which corrected anticoagulant effects were inadequate to reverse antiplatelet effects. A protamine concentration of 40 micrograms/ml normalized the aPTT and mu, but 140 micrograms/ml of protamine was required to reverse heparin suppression of force development and clot elastic modulus. Excess protamine inhibited clotting and platelet function. In plasma containing 1 u heparin/ml, 140 micrograms protamine/ml reduced PFD by 83%, prolonged the aPTT by 63%, and reduced clot EM by 75%. In heparin free plasma, > 75 micrograms protamine/ml prolonged the aPTT. Thus, platelet function and clot structure are sensitive to protamine during heparin neutralization, and anti-platelet effects of heparin may persist when the aPTT is completely corrected. Excess protamine inhibits platelet function and compromises clot structure.

Blood Coagulation↗
PubMed1994

Quantitative assessment of platelet function and clot structure in patients with severe coronary artery disease.

The prothrombotic state of patients with coronary artery disease (CAD) can be attributed partially to platelet activity. Management of such patients is hindered by a lack of techniques to assess hemostatic function. This study used a sensitive technique to monitor platelet function by measuring platelet force development during clot retraction. This technique allowed simultaneous measurement of clot elastic modulus on the same sample. Fibrin mass-length ratio (mu), fibrinopeptide A, D-Dimer, von Willebrand's factor, thromboxane A2, platelet aggregation studies, and bleeding times also were performed. Fourteen patients with CAD were compared with 10 healthy volunteers. Despite more than 95% suppression of thromboxane B2 and prolongation bleeding times in patients taking aspirin, force development remained significantly elevated over healthy control patients (8,279 +/- 476 dynes versus 4,857 +/- 380 dynes, p < 0.0006). Patients not taking aspirin had normal bleeding times and force development of 19,110 +/- 3,700 dynes. Clot elastic moduli were enhanced in patients with CAD whether taking or not taking aspirin. Adenosine diphosphate and ristocetin-induced platelet aggregation were insensitive to the effect of aspirin in patients with CAD. Fibrinopeptide A, von Willebrand's factor, and D-Dimer levels were significantly elevated, and fibrin mass-length ratios were significantly larger in patients with CAD. Therefore, despite aspirin therapy, patients with severe CAD have evidence of persistent platelet activation and rigid clot structure. Monitoring of platelet force development may prove useful in delineating enhanced platelet function.

Adult↗
PubMed1994

Abnormal clot retraction, altered fibrin structure, and normal platelet function in multiple myeloma.

Clot retraction, measured by serum expression, is absent in some cases of multiple myeloma. Decreased clot retraction has been attributed to platelet dysfunction. A new instrument allows simultaneous measurement of platelet-mediated force development during clot retraction and of clot elastic modulus. We report 10 patients with immunoglobulin (Ig) G myeloma in whom the abnormalities of fibrin structure were quantitatively defined and platelet-fibrin interactions were assessed. Fiber mass-to-length ratios were calculated from gel turbidity. Platelet force development and clot elastic modula were measured in platelet-rich plasma gels. Fiber mass-to-length ratios for IgG myeloma patients were smaller (means +/- SE) (0.98 +/- 0.19 x 10(13) Da/cm) than for normal controls (1.36 +/- 0.06 x 10(13) Da/cm), indicating thinner fiber formation. Elastic modula of myeloma clots (51,013 +/- 14,660 dyn/cm2) were strikingly larger than modula for normal controls (23,355 +/- 1,887 dyn/cm2), indicating that such clots are mechanically less flexible. Platelet force development 1,200 s after thrombin addition was not diminished in myeloma patients (8,315 +/- 1,155 dyn) vs. controls (6,906 +/- 606 dyn). Abnormal clot retraction in myeloma appears to be primarily due to altered clot structure rather than platelet dysfunction.

Aged↗
PubMed1994

Pain relief and clinical improvement temporally related to the use of pentoxifylline in a patient with documented cholesterol emboli--a case report.

A sixty-six-year-old man with known severe atherosclerosis was admitted with painful feet and nonblanching purpuric lesions of his toes. He had undergone cardiac catheterization and coronary artery bypass five and three months, respectively, prior to admission. Initial treatment included: stopping the patient's lisinopril, increasing his nifedipine dose, and adding pentoxifylline 400 mg po tid. Within twenty-four hours pain was markedly decreased. Skin biopsy confirmed a diagnosis of cholesterol embolism. Pentoxifylline was stopped and intravenous heparin therapy was initiated. Within twenty-four hours, pain returned. Nitrol paste applied to the top of each foot had no effect. After forty-eight hours, pentoxifylline was restarted. Once again, pain relief was noted within twenty-four hours, and after forty-eight hours both feet were visibly improved. Heparin and analgesics were discontinued. On the ninth hospital day, the patient was able to walk and was discharged to home. The innocuous nature of the intervention combined with the prompt nature of the therapeutic response support a short trial of pentoxifylline in patients with cholesterol emboli who are not responding to other therapy.

Aged↗
PubMed1993

Protein S levels during the normal menstrual cycle and during estrogen therapy for premature ovarian failure.

Protein S levels have been reported to be decreased in pregnancy and with oral contraceptive use. This study monitored the effects of estrogen shifts on protein S levels. Four patients with premature ovarian failure were treated with either oral or transdermal patch estrogen replacement. Blood drawn on days 1, 14, and 28 of therapy was analyzed for estradiol, estrone, free and total protein S, and C4b-binding protein (C4b-BP) levels. Similar studies were performed on six normally cycling control patients and seven postmenopausal women. In healthy females, total levels of protein S fell from 22.1 +/- 0.73 micrograms/mL on day 1 to 19.2 +/- 1.29 micrograms/mL on day 14 (p < 0.023). Free protein S levels declined from 6.45 +/- 0.70 micrograms/mL to 5.59 +/- 0.69 micrograms/mL (p < 0.016). C4b-BP levels did not change during the normal menstrual cycle. Baseline total protein S (44.1 +/- 7.0 micrograms/mL) and C4b-BP (193 +/- 18%) levels were elevated in patients with premature ovarian failure. On oral therapy, there was a strong, negative correlation (r = -0.979, p < 0.021) between C4b-BP and estradiol levels. C4b-BP levels did not change in patients with the patch. Both estrogen therapies produced similar declines (44 to 26 micrograms/mL) in total protein S levels. In all cases, total protein S levels changed as a reciprocal function of estradiol. C4b-BP (128 +/- 6.5%) and total protein S (32.2 +/- 3.0 micrograms/mL) levels were higher in postmenopausal women than in nonmenopausal females. Free protein S levels in postmenopausal women (9.6 +/- 0.6 micrograms/mL) were normal.(ABSTRACT TRUNCATED AT 250 WORDS)

Adult↗
PubMed1992

Effect of plasminogen activator inhibitor-1 on tissue-type plasminogen activator-induced fibrinolysis.

The effect of fibrin on the interaction of human recombinant single-chain tissue plasminogen activator (t-PA) and plasminogen activator inhibitor-1 (PAI-1) was studied in normal rabbit plasma and in plasma with high levels of native PAI-1. t-PA was added to diluted plasma containing calcium (10 mM) and 125I-fibrinogen at 37 degrees C. Clotting was initiated with human thrombin, and lysis was monitored both turbidimetrically and by release of 125I-fibrin degradation products (fdp). The activity of t-PA (50 IU/ml) was rapidly reduced to 15% of the initial value in plasma containing PAI-1 (23 AU/ml). When thrombin and t-PA were added simultaneously to the plasma, more than 70% of the activity was retained through incorporation of t-PA into the fibrin clot. t-PA-induced fibrinolysis in PAI-1 enriched plasma was further delayed when the temperature was reduced from 37 to 25 degrees C. Turbidimetric and 125I-fdp release data provided complementary information. The former technique traced fiber dissolution, while the latter reflected network integrity. These results indicate that t-PA-induced fibrinolysis in PAI-1 enriched plasma is modulated by the presence of fibrin and by temperature.

Animals↗
PubMed1992

Case report: a novel form of free protein S deficiency in an HIV-positive patient on hemodialysis.

Investigation of repetitive thrombotic episodes in an HIV-positive patient on maintenance hemodialysis revealed extraordinarily high levels of total (free plus protein bound) protein S antigen but severe reductions in free (interactive) protein S antigen. Patients with the nephrotic syndrome or chronic renal failure have shown elevations of total protein S antigen, associated with increased levels of the specific C4b-binding protein, yet have had normal free protein S antigen levels. Based on the fall in total and free protein S levels during hemodialysis treatments, the presence of normal levels of C4b-binding protein, and the coexistence of a polyclonal gammopathy, the authors infer the presence of a unique protein that binds protein S in this patient and that is not apparent in normal plasma. The anomalous association of protein S with this binding protein resulted in levels of free protein S antigen in the range of those reported in hereditary deficiencies of the anticoagulant.

Adult↗
PubMed1992

Fibrin coating of bladder tumor cells (T24) is not protective against LAK cell cytotoxicity.

Certain evidence indicates that tumor cells in the circulation may be enshrouded with a coat of fibrin. It has been suggested that this fibrin coat protects tumor cells from attack by the immune system. This study compared the interaction of lymphokine activated killer (LAK) cells with tumor cells alone and with fibrin coating. LAK cell killing of cultured human bladder tumor cells (T24) was measured by a 4-hour chromium release assay. Tumor cells (3 x 10(6] were incubated with Na51CrO4 for 2 hours at 37 degrees C and 5% CO2 in serum-free medium. After washing, one half of the cells were coated with fibrin by exposure to recalcified platelet-poor plasma. Fibrin coating was confirmed by immunofluorescence with anti-human-fibrinogen-fluorescein-conjugated antibodies. LAK cells were prepared from peripheral blood lymphocytes by incubation with interleukin-2 at a concentration of 1000 units of interleukin-2/1 ml serum-free medium/1 million cells for 5 days at 37 degrees C, 5% CO2. Five thousand tumor cells with or without fibrin were incubated with varying concentrations of either LAK or peripheral blood lymphocytes (10,000 to 100,000 cells). After 4 hours the supernatants were harvested and counted in a gamma counter for 1 minute. Over a range of effector-to-target cell ratios of 10:1 to 100:1 (LAK to T24), no difference was seen in percentage of specific lysis for T24 alone versus fibrin-coated T24 cells. At a ratio of 100:1 (LAK to T24), percentage of specific lysis was 83.3% versus 87.7% for uncoated and coated T24 cells, respectively. This suggests that fibrin coating of tumor cells is insufficient to provide protection from LAK cell killing.

Cytotoxicity, Immunologic↗