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G M Rodgers

Publications and source records attributed to G M Rodgers.

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

Characterization of the interactions between procoagulant albumin and human endothelial cells.

Normal human plasma contains procoagulant albumin (PC-Al), an anionic form of albumin that induces tissue factor (TF) activity in human umbilical vein endothelial cells (HUVEC) and monocytes. In this study, we investigated both the interactions between HUVEC and PC-Al and the mechanism by which PC-Al induces TF activity. Binding of PC-Al to HUVEC was specific and reversible. Further studies indicated that membrane-bound PC-Al was not internalized by HUVEC. A potential receptor on HUVEC was suggested by studies in which the capacity of a variety of reagents to inhibit the activity of PC-Al was quantitated. Induction of TF activity by PC-Al was antagonized by dextran sulfate, heparin, fucoidan, and concanavalin A but not by ovalbumin, polyglutamic acid, or polyvinyl sulfate. This competition profile bears similarities to those reported for scavenger receptors that have been identified on both HUVEC and monocytes. Involvement of protein kinase C (PKC) in the PC-Al-induced enhancement of TF activity was suggested by experiments in which staurosporine, an inhibitor of PKC, suppressed the activity of PC-Al. The induction of TF activity by PC-Al was further characterized by using a quantitative polymerase chain reaction assay. Increased TF mRNA was first seen after 1 hour of incubation with PC-Al. Maximal observed expression occurred at 2 hours, but at 5 hours, expression had significantly decreased. Monocytes could also be induced to express TF mRNA after a 2-hour incubation with PC-Al. These results suggest that the functionally relevant binding of PC-Al to HUVEC may be mediated through interactions with a membrane constituent that has some of the properties of a scavenger receptor and that this interaction augments TF activity by enhancing transcription of TF mRNA, at least in part, by a mechanism that is dependent on activation of PKC.

Base Sequence↗
PubMed1993

Regulation of endothelial cell protein C activation and fibrinolysis by procoagulant albumin.

Endothelial cell regulation of protein C activation and fibrinolysis are important components of the hemostatic response to vascular injury or perturbation. Procoagulant albumin (P-A1), a constituent of normal human plasma has been purified and identified as an inducer of endothelial cell tissue factor activity. The purpose of the studies reported herein was to investigate the effects of P-A1 on human endothelial cell protein C activation and fibrinolysis. P-A1 suppressed protein C activation, enhanced release of plasminogen activator inhibitor-1, but had no effect on tissue-plasminogen activator release. Plasminogen activator inhibitor-1 released by P-A1 was functional as evidenced by the capacity to form a covalent complex with 125I-urokinase. Inactive albumin (isolated during the same purification procedure as P-A1, but without tissue factor-inducing activity) did not suppress protein C activation or increase plasminogen activator inhibitor-1 release. These results indicate that P-A1, a component of human plasma, can modulate multiple vascular hemostatic properties, and support the hypothesis that P-A1 is involved in normal or pathologic hemostasis.

Anions↗
PubMed1993

Induction of endothelial cell tissue factor activity by sera from patients with antiphospholipid syndrome: a possible mechanism of thrombosis.

OBJECTIVE: The hypothesis of our study is that antiphospholipid antibodies predispose to thrombosis by inducing endothelial cell tissue factor expression. STUDY DESIGN: Monolayers of cultured human umbilical vein endothelial cells were incubated for 8 hours in a medium containing 20% serum obtained either from patients with antiphospholipid antibodies (n = 11) or normal subjects (n = 8). Similar incubations were performed with immunoglobulin G fractions from either patients with antiphospholipid antibodies (n = 3) or normal subjects (n = 3). Endothelial cell tissue factor expression was measured with a tissue factor-specific chromogenic substrate assay. The results were analyzed with a two-tailed t test. RESULTS: The mean endothelial cell tissue factor expression induced by antiphospholipid sera was significantly greater than the controls (p < 0.02). Immunoglobulin experiments indicated that the factor(s) responsible for the induction of tissue factor expression resides in the immunoglobulin G fraction of the sera (p < 0.01). CONCLUSIONS: Endothelial cell tissue factor expression is induced by antiphospholipid sera, with activity residing at least in part in the immunoglobulin fraction. The induction of tissue factor by antiphospholipid sera may play a role in the thrombotic tendency observed in patients with antiphospholipid syndrome.

Antibodies, Antiphospholipid↗
PubMed1993

Homocysteine, a risk factor for premature vascular disease and thrombosis, induces tissue factor activity in endothelial cells.

Elevated blood levels of homocysteine represent an independent risk factor for premature arterial vascular disease and thrombosis. We investigated whether homocysteine could induce tissue factor (TF) procoagulant activity in cultured human endothelial cells. Homocysteine increased cellular TF activity in a time- and concentration-dependent manner. Low concentrations of homocysteine (0.1 to 0.6 mmol/L), similar to those found in the blood of patients with homocystinuria, enhanced TF activity by 25% to 100%. Other sulfur-containing amino acids (cystine, homocystine, cysteine, and methionine) induced less TF activity than did homocysteine; however, beta-mercaptoethanol and dithiothreitol were more effective than homocysteine in increasing TF activity. Preincubation of homocysteine with a sulfhydryl inhibitor such as N-ethylmaleimide prevented homocysteine induction of TF activity. A quantitative polymerase chain reaction method indicated that homocysteine increased TF mRNA in endothelial cells. These results indicate that an atherogenic amino acid, homocysteine, can initiate coagulation by the TF pathway through a mechanism involving the free thiol group of the amino acid and by TF gene transcription. These data support the hypothesis that perturbation of vascular coagulant mechanisms may contribute to the thrombotic tendency seen in patients with homocystinuria.

Base Sequence↗
PubMed1993

Novel antithrombotic therapy.

The prospects for more effective and safe antithrombotic therapy appear promising. I have presented only a portion of all novel antithrombotic agents currently under basic and clinical investigations. A discussion of additional new antithrombotic drugs is presented elsewhere.

Fibrinolytic Agents↗
PubMed1992

Platelet dysfunction in a patient with the Opitz (BBBG) syndrome.

An 11-year-old girl with Opitz (BBBG) syndrome presented with a bleeding disorder. Studies showed an immune-mediated qualitative platelet dysfunction in the absence of thrombocytopenia. This is the first report of hemostatic dysfunction in a patient with the Opitz (BBBG) syndrome. This report considers the possible relationship of the platelet dysfunction to the Opitz (BBBG) syndrome and its treatment.

Abnormalities, Multiple↗
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

Laboratory and clinical aspects of inherited thrombotic disorders.

The laboratory evaluation of patients with recurrent thrombosis is frequently frustrating, with a low diagnostic yield obtained despite extensive testing. The likelihood of reaching a diagnosis in these patients can be increased by considering diagnostic possibilities usually overlooked and by using assays optimal for their detection. This review summarizes clinical and laboratory issues important in inherited thrombotic disease and discusses practical aspects and a strategy for laboratory testing. New information is provided on the fibrinolytic disorders that may be a common cause of recurrent thrombosis.

Homocystinuria↗
PubMed1992

Regulation of endothelial cell protein C activation by native and oxidized low density lipoprotein.

The effects of native LDL and Ox-LDL and HDL on endothelial cell protein C activation were examined. Ox-LDL, which is postulated to contribute to cardiovascular disease, markedly suppressed activation of protein C, an important vascular anticoagulant activity. This effect was seen with both human venous and arterial endothelial cells. Endothelial cells modified LDL to a form that reduced protein C activation, an effect prevented by the anti-oxidant, probucol. Endothelial cells are known to express the acetyl LDL (scavenger) receptor, which binds chemically modified and Ox-LDL. The effect of Ox-LDL on protein C activation does not appear to result from uptake via the acetyl LDL receptor, since a known scavenger receptor antagonist (fucoidin) did not inhibit the oxidized LDL effect. In contrast to the results with Ox-LDL, native LDL and both native and oxidized HDL increased protein C activation. These data indicate that native and modified lipoproteins regulate blood coagulation by affecting vascular anticoagulant activity and suggest mechanisms that may link modified lipoproteins with both vascular disease and thrombosis.

Cells, Cultured↗
PubMed1992

The preparation of a sensitive partial thromboplastin reagent from bovine brain.

Commercial partial thromboplastin reagents markedly differ in their sensitivity to factor deficiency, heparin, or the lupus anticoagulant. These differences may be partly due to the variable phospholipid content of different commercially available reagents. For over 15 years, we have routinely used a partial thromboplastin prepared from human brain. In the past four years, we have been using a similarly prepared bovine partial thromboplastin reagent. This report describes the preparation of our partial thromboplastin reagent, as well as an analysis of the phospholipid composition of both the human and bovine thromboplastin reagents. Four separate brain preparations produced consistent percentages of the anionic phospholipids, phosphatidylserine, and phosphatidylinositol. The bovine reagent was also compared with commercial partial thromboplastin reagents in the detection of coagulation factor deficiency, heparin, and the lupus anticoagulant.

Animals↗
PubMed1992

Hypoprothrombinemia associated with interleukin-2 therapy: correction with vitamin K.

We noted that patients treated with high-dose interleukin (IL)-2 (600,000 IU/kg every 8 h by intravenous bolus) at our institution frequently developed prolongation of their prothrombin time (PT). We therefore performed a prospective study of coagulation function during IL-2 treatment. Since IL-2 treated individuals are known to develop cholestatic liver dysfunction, we hypothesized that the hypoprothrombinemia was due to deficiency of liver-synthesized clotting factors and could be prevented by vitamin K replacement. Alternating patients served as controls or received prophylactic subcutaneous subcutaneous vitamin K. While the nine control patients did not exhibit a significant increase (mean +/- SD) in PT (13.6 +/- 0.6 s pretreatment, 15.0 +/- 2.2 on day 4, and 15.0 +/- 2.5 on day 7, p = 0.77 by repeated measures analysis), three patients developed marked increases in PT (greater than 18 s). Changes in partial thromboplastin time (PTT) over this interval were also not statistically significant. Factor VII levels decreased in all patients from 106 +/- 22 to 59 +/- 16 and 52 +/- 26% on days 4 and 7 (p = 0.0002). Factor VII levels in four patients dropped below the lower limit of normal. Prophylactic treatment of seven patients with vitamin K on days 1-8 of the IL-2 therapy protocol resulted in diminished changes in PT and factor VII compared to control patients (p = 0.02 and 0.003 respectively). No vitamin K-treated patient developed PT or Factor VII levels significantly outside the normal range. Prophylactic vitamin K can prevent hypoprothrombinemia in patients treated with IL-2. This may be of importance in patients with decreased hepatic vitamin K stores, who may be at risk for bleeding complications.

Blood Coagulation↗
PubMed1991

Oxidized low-density lipoprotein increases cultured human endothelial cell tissue factor activity and reduces protein C activation.

Increasing evidence suggests that the formation of oxidized low-density lipoprotein (Ox-LDL) in vivo is associated with the development of atherosclerotic vascular disease. We investigated the effects of Ox-LDL on two vascular endothelial cell coagulant properties, tissue factor expression, and protein C activation. The Ox-LDL increased human arterial and venous endothelial cell tissue factor activity, with 100 micrograms/ml of Ox-LDL increasing factor activity fourfold. Native LDL modified by incubation with cultured human arterial and venous endothelial cells also induced endothelial cell tissue factor activity. This modification was blocked by coincubation with the antioxidants, probucol or ascorbic acid. It was determined, based on inhibition by known scavenger receptor antagonists (fucoidin, dextran sulfate), that binding of Ox-LDL via the acetyl LDL (scavenger) receptor was partially responsible for the increase in tissue factor expression. Whereas endothelial cell tissue factor expression was increased by incubation with Ox-LDL, protein C activation was reduced approximately 80% by incubating cultured endothelial cells with Ox-LDL. The effect of Ox-LDL on protein C activation was not inhibited by antagonists to the scavenger receptor. These data indicating that an atherogenic lipoprotein can regulate key vascular coagulant activities provide an additional link between vascular disease and thrombosis.

Anticoagulants↗