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Biomedical subjects

G M Rodgers

Publications and source records attributed to G M Rodgers.

At least 37 records · Page 2Linked to original sources
PubMed1999

Overview of platelet physiology and laboratory evaluation of platelet function.

Appropriate laboratory testing for the platelet-type bleeding disorders hinges on an adequate assessment in the history and physical examination. Patients with histories and screening laboratory results consistent with coagulation disorders (hemophilia, disseminated intravascular coagulation) are not appropriate candidates for platelet function testing. In contrast, patients with a lifelong history of platelet-type bleeding symptoms and perhaps a positive family history of bleeding would be appropriate for testing. Figure 6 depicts one strategy to evaluate these patients. Platelet morphology can easily be evaluated to screen for two uncommon qualitative platelet disorders: Bernard-Soulier syndrome (associated with giant platelets) and gray platelet syndrome, a subtype of storage pool disorder in which platelet granulation is morphologically abnormal by light microscopy. If the bleeding disorder occurred later in life (no bleeding with surgery or trauma early in life), the focus should be on acquired disorders of platelet function. For those patients thought to have an inherited disorder, testing for vWD should be done initially because approximately 1% of the population has vWD. The complete vWD panel (factor VIII coagulant activity, vWf antigen, ristocetin cofactor activity) should be performed because many patients will have abnormalities of only one particular panel component. Patients diagnosed with vWD should be classified using multimeric analysis to identify the type 1 vWD patients likely to respond to DDAVP. If vWD studies are normal, platelet aggregation testing should be performed, ensuring that no antiplatelet medications have been ingested at least 1 week before testing. If platelet aggregation tests are normal and if suspicion for an inherited disorder remains high, vWD testing should be repeated. The evaluation of thrombocytopenia may require bone marrow examination to exclude primary hematologic disorders. If future studies with thrombopoietin assays confirm preliminary results, however, the bone marrow examination of certain patients may be replaced by a thrombopoietin level.

Blood Platelet Disorders↗
PubMed1998

Disseminated intravascular coagulation: clinical and laboratory aspects.

Disseminated intravascular coagulation (DIC) is a complex acquired coagulopathy resulting from excessive thrombin formation. Abnormal tissue factor (TF) expression is a major mechanism initiating DIC in many disorders, including obstetrical complications, sepsis, cancer, and trauma. Numerous laboratory tests are available to monitor DIC, but most patients are adequately managed using only routine hemostasis screening tests, and assays for fibrinogen and D-dimer. Treatment of DIC should focus on reversing the underlying disorder initiating the coagulopathy. Novel treatments are being investigated for treating DIC; many of these experimental modalities target the excessive TF activity that characterizes DIC.

Disseminated Intravascular Coagulation↗
PubMed1997

Enoxaparin, a low-molecular-weight heparin suppresses prothrombin activation more effectively than unfractionated heparin in patients treated for venous thromboembolism.

Although unfractionated heparin (UFH) is standard therapy for venous thromboembolism, there is a clinical failure rate of up to 10%. Newer treatment strategies include low-molecular-weight heparins (LMWH). As part of an international study comparing the efficacy and safety of enoxaparin, a LMWH versus UFH in patients with venous thromboembolism, we studied the effects of enoxaparin and UFH on the plasma concentrations of two activation peptides, fragment 1 + 2 (F1 + 2), and thrombin-antithrombin III (TAT) complexes. We hypothesized that enoxaparin would be more effective in suppressing activation of coagulation. Intravenous heparin was given by bolus injection followed by infusion. There were 2 enoxaparin treatment groups (1 mg/kg s.c., bid and 1.5 mg/kg s.c. daily). Plasma samples were obtained from 11 patients in the enoxaparin group and 6 patients in the heparin group prior to and at 6 hour intervals after initiating therapy. Clinical characteristics of the enoxaparin and UFH patient groups were similar. TAT concentrations were not statistically different between groups at any treatment interval. However, plasma F1 + 2 concentrations differed significantly (p < 0.05); concentrations in the enoxaparin group were consistently lower over time than in the UFH group. These results suggest that this LMWH is more effective in suppressing ongoing thrombosis in vivo than UFH in patients with venous thrombosis.

Adult↗
PubMed1997

Biochemical characterization of procoagulant albumin.

Procoagulant albumin (Pro-Alb) is an anionic form of albumin isolated from normal human plasma that regulates vascular endothelial cell hemostatic properties, including induction of tissue factor activity. We investigated the biochemical modification of Pro-Alb that was associated with procoagulant-inducing activity. Tryptic digestion of Pro-Alb identified greatest bioactivity in the carboxy-terminus of the molecule, a region associated with lipid binding sites. Activated charcoal treatment and phopholipase C digestion reduced the procoagulant-inducing activity of Pro-Alb, and Pro-Alb contained 2.3-fold more phosphorus than inactive albumin. We conclude that modification of albumin by phospholipid imparts tissue factor-inducing activity to Pro-Alb.

Amino Acid Sequence↗
PubMed1997

Inherited thrombotic disorders: an update.

Significant advances in identification of etiologies of inherited thrombosis have been recently reported. A point mutation in coagulation factor V (factor V Leiden) results in resistance to activated protein C and probably represents the most common genetic risk factor for venous thrombosis. A metabolic disorder, homocysteinemia, is now known to be an important risk factor for both arterial and venous thrombosis. Many patients with recurrent thrombosis will have more than one genetic risk factor identified. Recognition of these new disorders should permit a diagnosis to be achieved in at least half of patients evaluated for inherited thrombosis.

Antithrombin III Deficiency↗
PubMed1997

Chlamydia species infect human vascular endothelial cells and induce procoagulant activity.

BACKGROUND: Chlamydia pneumoniae infections have been linked with myocardial infarction, stroke, and the development of atherosclerosis by epidemiologic studies, immunohistochemical studies, and electron microscopic studies. The mechanisms underlying this association are unknown. METHODS: Using cultured human venous endothelial cells, we investigated whether C pneumoniae, C trachomatis (types H and L2/434/BU) could infect these cells. The ability of infected cells to express procoagulant (tissue factor) activity was also measured using clotting and chromogenic substrate assays. Adhesion of platelets to chlamydia-infected cells was also quantitated. RESULTS: We found that C pneumoniae, C trachomatis type H, and C trachomatis L2/434/BU could infect cultured human umbilical vein endothelial cells and stimulate a 4-fold increase in expression of tissue factor, which reached a peak 18 hours postinfection. Tissue factor expression was enhanced even in the presence of tetracycline, suggesting that the chlamydial factor responsible for stimulating synthesis of endothelial cell tissue factor was preformed. Platelet adhesion was significantly enhanced when endothelial cells were infected by chlamydia species. CONCLUSIONS: These in vitro studies suggest possible pathogenic mechanisms that may explain the association of thrombotic events with C pneumoniae infection, including pathologically enhanced production of tissue factor by human endothelial cells and enhanced focal platelet deposition.

Cells, Cultured↗
PubMed1996

Characterization of an inducible endothelial cell prothrombin activator.

In vivo prothrombin activation is thought to occur via a factor Xa/factor V-dependent mechanism. We investigated whether human venous endothelial cells (EC) could be induced to express a prothrombin activator. EC treated with lipopolysaccharide (LPS) or interleukin-1 activated prothrombin in the absence of exogenous factors Xa and V. This activity resided in the membrane fraction of EC and was not inhibited by an antibody to factor V. The apparent Km value was 3.3 +/- 0.3 mumol/L. Comparative studies of thrombin generation using a model system of phospholipid and factors Xa/V versus LPS-treated EC were performed to quantitate the effects of known inhibitors to factor Xa. The factor Xa inhibitor DEGR-chloromethyl ketone and an antibody to factor X inhibited prothrombin activation. However, the EC activator did not hydrolyze a factor Xa chromogenic substrate, and recombinant tick anticoagulant peptide did not suppress activity of the prothrombin activator. The apparent molecular weight of the EC activator was approximately 30 kD. Exogenous factor V enhanced the activity of the EC activator, such that in the presence of factor V, the apparent K(m) value was 1.28 +/- 0.10 mumol/L. Additionally, LPS-treated EC activated exogenous factor V. This activator has several characteristics of a previously described inducible murine monocyte prothrombin activator and may contribute to thrombin generation associated with pathologic stimuli.

Animals↗
PubMed1996

Utilization of testing for activated protein C resistance in a reference laboratory.

Activated protein C (APC) resistance is a newly described thrombotic disorder accounting for the majority of patients with inherited thrombosis. The authors prospectively evaluated laboratory testing of this disorder over a 1-year period in their reference laboratory, which draws samples from a large number of community and academic hospitals throughout the United States. Testing for other inherited thrombotic disorders (antithrombin III deficiency, protein C and S deficiencies) occurred at a six-fold greater rate than that for APC resistance. Previously published studies have indicated a prevalence of up to 60% for APC resistance in populations with thrombosis; however, the prevalence rate in this study was only 12%. Of patient samples submitted for APC resistance assays, 37% were not evaluable because of concomitant anticoagulant therapy. Clinical pathologists and practitioners need to be made aware of APC resistance and of optimal sample collection to improve the efficiency of laboratory testing for thrombosis.

Adolescent↗
PubMed1996

Sensitivity of the activated partial thromboplastin time, the dilute Russell's viper venom time, and the kaolin clotting time for the detection of the lupus anticoagulant: a direct comparison using plasma dilutions.

Increasing dilutions of lupus anticoagulant (LA) plasmas from twelve patients were used to directly compare the sensitivity of four tests for LA. The tests evaluated were the modified Bell and Alton activated partial thromboplastin time (APTT), an APTT using a commercially prepared partial thromboplastin (Platelin LS APTT), a modified dilute Russell's viper venom time (DRVVT), and a modified kaolin clotting time (KCT). LAs were detected in all twelve plasmas by each of three tests and eleven of twelve plasmas in a fourth test when undiluted patient plasma was used. Repeating the tests after diluting the LA plasmas with normal platelet-free plasma (PFP) showed that the KCT was the most sensitive test for LA, detecting eleven of twelve LAs at a dilution of 10% patient plasma and ten of twelve LAs at a dilution of 5% patient plasma. The modified Bell and Alton APTT and the modified DRVVT had similar sensitivities at a patient plasma concentration of 10%, detecting seven of twelve and eight of twelve LAs, respectively. The Platelin LS APTT detected only four of twelve LAs at a patient plasma concentration of 10%. Our results indicate that the modified KCT is a sensitive method for the detection of LAs. The modified Bell and Alton APTT and the DRVVT were less sensitive.

Humans↗
PubMed1995

Pyrrolidine dithiocarbamate abrogates tissue factor (TF) expression by endothelial cells: evidence implicating nuclear factor-kappa B in TF induction by diverse agonists.

Tissue factor (TF), a 46-kD glycoprotein receptor for coagulation factors VII and VIIa, is expressed on the surface of endothelial cells in response to a variety of agonists and is thought to play an important role in initiating the thrombosis associated with inflammation during infection, sepsis, and organ transplant rejection. The induction of TF activity by lipopolysaccharide (LPS) is regulated, at least partially, at a transcriptional level and an LPS response element containing two activator protein-1 sites and a nuclear factor-kappa B (NF kappa B)-like site has been localized to the 5' flanking region of the TF gene by transfection studies of TF promoter/reporter gene constructs. We have examined the effect of pyrrolidine dithiocarbamate (PDTC), a specific inhibitor of the NF kappa B pathway on the expression of the endogenous TF gene in human umbilical vein endothelial cells (HUVEC). Preincubation of HUVEC for 60 minutes with PDTC inhibited LPS induction of TF activity on the cell surface in a dose-dependent manner, with 50% inhibition occurring at 10 mumol/L PDTC and 100% inhibition at higher concentrations (> or = 100 mumol/L). Furthermore, PDTC inhibited TF expression in response to tumor necrosis factor-alpha, interleukin-1 beta, and phorbol 12-myristate 13-acetate. The effect of PDTC was at the mRNA level, as seen by the complete abrogation of the large increase in TF mRNA observed in LPS-treated HUVEC. These results suggest that endothelial cell activation by diverse agonists initiates intracellular signaling events that converge upon a common pathway involving NF kappa B and, furthermore, that NF kappa B activation is an obligatory step induction of TF.

Base Sequence↗
PubMed1995

Procoagulant albumin increases vascular endothelial cell prostacyclin secretion.

Vascular endothelium regulates multiple aspects of platelet function through secretion of a variety of substances, including von Willebrand factor, nitric oxide, and prostacyclin (PGI2). The objective of this study was to determine whether procoagulant albumin (P-A1), a modified form of albumin present in normal human plasma could modulate endothelial cell secretion of these substances. P-A1 did not affect constitutive secretion of von Willebrand factor or nitric oxide, but did increase PGI2 secretion in a time- and concentration-dependent manner. Pre-treatment of endothelial cells with aspirin, or use of suramin, a broad-specificity inhibitor, prevented the response to P-A1. Prostaglandin H synthase-2 contributed to the P-A1-induced PGI2 secretion. These results indicate that in addition to inducing tissue factor activity and reducing protein C activation and fibrinolysis, P-A1 also modulates vascular endothelial cell PGI2 secretion, and potentially, platelet function.

Aspirin↗
PubMed1994

The skin bleeding time test as a predictor of brain bleeding time in a rat model.

Previous studies have indicated that the skin bleeding time test does not accurately reflect visceral bleeding time (BT). The present study examines the predictive value of the skin bleeding time for brain bleeding tendency. Sixteen Sprague-Dawley rats were divided into equal groups. The first group (controls) underwent standardized skin and brain bleeding time tests under general anesthesia. Mean skin BT was found to be 168.8 sec with a standard deviation of +/- 20.8 sec. Mean brain BT was found to be 172.5 sec with a standard deviation of +/- 19.6 sec. The second group was given 23.2 mg/kg of aspirin per day for five days prior to skin and brain BT testing. Mean skin BT in this group was 315 seconds with a standard deviation of +/- 72.2 sec which proved to be significantly different from the control skin BT (P = 0.0005). Brain BT in the aspirin treated group was 155.6 sec with a standard deviation of +/- 22.6 sec. Brain BT in both control and aspirin treated groups was not significantly different (P = 0.13). All animals were euthanized 30 minutes after brain BT and their brains harvested. One animal in the control group showed evidence of a small subcortical hemorrhage upon brain sectioning. Sectioned brains in the aspirin-treated group showed no evidence of subcortical hematoma. The results indicate that skin BT is prolonged by aspirin administration, but brain bleeding time is unaffected. Brain hemostasis is likely more dependent on intrinsic procoagulant than platelet function. The skin BT test may therefore be of little utility as a preoperative screening test for neurosurgical patients.

Animals↗
PubMed1994

Bioassay of procoagulant albumin in human plasma.

Procoagulant albumin (P-Al) is present in normal human plasma and increases monocyte and endothelial cell expression of tissue factor activity. To develop a bioassay for P-Al, we partially purified plasma from healthy volunteers and several patient groups using BaCl2 and (NH4)2SO4 precipitation. The samples were assayed for tissue factor (TF) inducing activity, expressed as a percentage increase compared to a serum-free media control. Over six months, the assay was reproducible in stored samples and in serial samples from normal volunteers. The plasma P-Al activities of 35 volunteers averaged 141 +/- 8.2% (SEM). There was no diurnal variation. There was no difference in the P-Al activity after a 12 hour fast and 2 hours after a large meal in 4 healthy volunteers. There was no increase in activity (r = 0.16) with the subject's age. The average activity from 16 poorly-controlled diabetics was 131 +/- 11% (SEM). No alteration in activity was seen with samples from patients with uremia, liver dysfunction, hemophilia, thrombotic events, or adenocarcinoma. These results indicate that P-Al activity can be bioassayed in individual patient samples; however, pathologic states associated with abnormal P-Al-induced tissue factor activity presently remain unidentified.

Adult↗
PubMed1994

Laboratory monitoring of warfarin therapy in Utah.

Accurate laboratory monitoring of oral anticoagulation has been emphasized as an important factor in providing safe and effective therapy for patients with thromboembolism. However, recent reports indicate that coagulation laboratories may not be providing optimal clinical information to clinicians who treat these patients. We surveyed all hospital coagulation laboratories in Utah to determine their format for reporting prothrombin time results in patients receiving oral anticoagulants. We found that less than 50% of laboratories used the reliable reporting format, i.e., the International Normalized Ratio (INR), and that many of the laboratories using the INR format may be reporting incorrect values. Our survey also found a significant lack of interest by physicians in requesting that their laboratories adopt reliable reporting methods. These results indicate a substantial lack of understanding by laboratories and clinicians of the importance of using reliable methods to monitor oral anticoagulation. Significant educational efforts will be required to correct this problem.

Drug Monitoring↗