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Biomedical subjects

R R Montgomery

Publications and source records attributed to R R Montgomery.

At least 73 records · Page 4Linked to original sources
PubMed1991

The rapid differentiation of type IIb von Willebrand's disease from platelet-type (pseudo-) von Willebrand's disease by the "neutral" monoclonal antibody binding assay.

The differentiation of type IIb von Willebrand's disease from other variants of von Willebrand's disease, especially platelet-type (pseudo-) von Willebrand's disease, poses a significant clinical problem because, although they are similar in the clinical and diagnostic laboratory settings, the therapy of type IIb von Willebrand's disease is different from the therapy of platelet-type von Willebrand's disease. This discrimination has required cumbersome assays using fresh platelet-rich plasma that often yielded equivocal results. Because it was shown by other researchers that type IIb von Willebrand factor binds to normal platelets with increased avidity at low concentrations of ristocetin, it was reasoned that von Willebrand factor from patients with type IIb von Willebrand's disease would also bind to formalin-fixed washed platelets at low concentrations of ristocetin. Using the radiolabeled "neutral" monoclonal antibody AVW1 to label plasma von Willebrand factor, the binding of von Willebrand factor to formalin-fixed washed platelets was studied as a function of ristocetin concentration. These studies demonstrated that the 125I-AVW1 von Willebrand factor from 13 patients with type IIb von Willebrand's disease binds to formalin-fixed washed platelets at significantly lower concentrations of ristocetin than plasma von Willebrand factor from 18 normal individuals, 3 patients with platelet-type von Willebrand's disease and 8 patients with other variant forms of von Willebrand's disease. This radiolabeled "neutral" monoclonal antibody technique provides a rapid, simple method for the differentiation on frozen plasma samples of type IIb von Willebrand's disease from platelet-type and other variants of von Willebrand's disease.

Antibodies, Monoclonal↗
PubMed1990

Evaluation of merocyanine 540-sensitized photoirradiation as a means to inactivate enveloped viruses in blood products.

Dry or wet heat, solvents, and detergents combined with ultraviolet irradiation provide effective means of sterilizing soluble blood products such as albumin or factor VIII. For obvious reasons, these procedures are not applicable to cellular blood components. We have recently shown that simultaneous exposure to the photosensitizer, merocyanine 540 (MC 540) and white light rapidly inactivates the Friend erythroleukemia virus complex and Friend virus-transformed cells, but causes relatively little damage to pluripotent hematopoietic stem cells. In this communication, we show that several lipid-enveloped human pathogenic viruses are also highly susceptible to MC 540-sensitized photoirradiation, and we report on an initial evaluation of the ability of MC 540-sensitized photoirradiation to sterilize blood products.

2,3-Diphosphoglycerate↗
PubMed1989

Endocytic and secretory repertoire of the lipid-loaded macrophage.

We have studied the effects of intracellular lipid storage on macrophage function. Mouse peritoneal macrophages were lipid loaded by three regimens modeling loading through the scavenger receptor [acetylated low density lipoprotein (Ac-LDL) cells], by extracellular matrix-bound LDL [low density lipoprotein complexed with dextran sulfate (DS-LDL) cells], and by conditions of reduced cholesterol acceptors in the medium [low serum, oleic acid, Ac-LDL (LS/OI) cells]. Significantly increased cholesterol levels in all three regimens were measured by cholesterol determination and Oil Red O staining of fixed cells. Lipid-laden cells were equal to control macrophages in binding and ingesting immunoglobulin-coated sheep erythrocytes, reflecting Fc-mediated endocytosis. The lipid-laden cells were compared to control cells for secretory functions of macrophages that could be important in the atherosclerotic artery. They were still capable of producing all secretory products examined, but the quantities of H2O2 and arachidonic acid metabolites were reduced in some cases, and fibrinolytic activity appeared to be increased. Western blot analysis showed a five-fold increase in the release of tumor necrosis factor by DS-LDL-loaded cells. We suggest that the location of intracellular lipid pools as well as the type of lipids (and/or lipid complexes) ingested may determine the extent of functional changes.

Animals↗
PubMed1989

Diagnosis and treatment of homozygous protein C deficiency. Report of the Working Party on Homozygous Protein C Deficiency of the Subcommittee on Protein C and Protein S, International Committee on Thrombosis and Haemostasis.

This report summarizes the documented cases of homozygous protein C deficiency in the United States and Europe. Procedures for diagnosing and treating this disorder (both initially and over the long term) have been compiled by a working party on homozygous protein C deficiency of the Subcommittee on Protein C of the International Committee on Thrombosis and Haemostasis. Homozygous protein C deficiency is an autosomal recessive disorder that usually manifests itself by purpura fulminans and, less commonly, by massive large vein thrombosis; severe diffuse intravascular coagulation also develops in these infants, and there is evidence of intrauterine thrombosis. For confirmation of homozygous protein C deficiency in a neonate with purpura fulminans or massive venous thrombosis, the infant should have undetectable protein C activity and both parents should be heterozygous for protein C deficiency. At the onset of symptoms, the initial treatment should be plasma (8 to 12 ml/kg every 12 hours) until all lesions have healed. Two modalities for long-term treatment are accepted as useful in these children: oral anticoagulant therapy or protein C replacement (fresh frozen plasma or prothrombin complex concentrate). Liver transplantation has been performed in only one child, with success. Oral anticoagulation (vitamin K antagonists, maintaining the prothrombin time from one and one-half to two times control values or at the International Normalized Ratio of 2.5 to 4.4) is our recommendation of choice for long-term treatment. With appropriate care, these children are able to be free of coagulopathy and live relatively normal lives.

Anticoagulants↗
PubMed1989

Molecular basis of human von Willebrand disease: analysis of platelet von Willebrand factor mRNA.

von Willebrand disease (vWD), the most common inherited bleeding disorder in humans, can result from either a quantitative or a qualitative defect in the adhesive glycoprotein, von Willebrand factor (vWF). Molecular studies of vWD have been limited by the large size of the vWF gene and difficulty in obtaining the vWF mRNA from patients. By use of an adaptation of the polymerase chain reaction, vWF mRNA was amplified and sequenced from peripheral blood platelets. A silent vWF allele was identified, resulting from a cis defect in vWF mRNA transcription or processing. In two type IIA vWD patients, two different but adjacent missense mutations were identified, the locations of which may identify an important vWF functional domain. Expression in heterologous cells of recombinant vWF containing one of these latter mutations reproduced the characteristic structural abnormality seen in type IIA vWD plasma.

Alleles↗
PubMed1988

Effects of monoclonal antibodies against the platelet glycoprotein IIb/IIIa complex on thrombosis and hemostasis in the baboon.

To assess the hemostatic consequences and antithrombotic effectiveness of blocking the platelet glycoprotein (GP) IIb/IIIa receptor for fibrinogen and other adhesive glycoproteins in vivo, well characterized murine monoclonal antibodies against the platelet GP IIb/IIIa complex, AP-2 and LJ-CP8, were infused intravenously into baboons. Four animals each received doses of 0.2, 0.4, and 1.0 mg/kg of purified AP-2 IgG, and three animals were given 1.0 mg/kg of the F(ab)2 fragment of AP-2. Five additional animals were given 10 mg/kg LJ-CP8 IgG. At the highest dose, radiolabeled AP-2 IgG bound to an average of 33,000 sites on the circulating platelets. Serial measurements included platelet count, bleeding time, platelet aggregation (induced by ADP, collagen, and gamma-thrombin), and 111In-platelet deposition onto Dacron vascular grafts. Bleeding times were markedly prolonged after injection of 1.0 mg/kg AP-2 IgG (19.2 +/- 3.4 min), 1.0 mg/kg AP-2 F(ab)2 (16.5 +/- 1.8 min), and 10 mg/kg LJ-CP8 (greater than 30 min) vs. control studies (4.6 +/- 0.2 min), and remained prolonged for 48 h. With each antibody platelet aggregation was initially reduced or absent, with partial recovery over 48 h in a manner that was inversely related to dose. AP-2, both whole IgG and F(ab)2 fragment, but not LJ-CP8, caused a dose-dependent reduction (20-46%) in the circulating platelet count over 24 h. Neither AP-2 nor LJ-CP8 caused a reduction in intraplatelet platelet factor 4, beta-thromboglobulin, or [14C]serotonin. Graft-associated platelet thrombus formation was reduced by 73% (1.0 mg/kg AP-2 IgG and 10 mg/kg LJ-CP8) and 53% (1.0 mg/kg AP-2 F(ab)2) relative to control values. In contrast, neither heparin (100 U/kg) nor aspirin (32.5 mg/kg twice a day) showed antithrombotic efficacy in this model. Thus, antibodies that functionally alter the platelet GP IIb/IIIa complex may produce immediate, potent, and transient, antihemostatic, and antithrombotic effects.

Animals↗
PubMed1988

Homozygous protein C deficiency: observations on the nature of the molecular abnormality and the effectiveness of warfarin therapy.

An infant with severe homozygous protein C deficiency was brought to medical attention because of purpura fulminans and severe bilateral vitreous hemorrhages in the neonatal period. Infusions of fresh frozen plasma were given for 8 months. On two occasions, attempts to decrease the frequency of fresh frozen plasma infusions to less than twice a day led to episodes of microangiopathic hemolysis, fibrinolysis, and acute renal failure. Infarction of skin and subcutaneous tissues did not recur. Both episodes were controlled after reinstitution of fresh frozen plasma. Complications of therapy with fresh frozen plasma included hyperproteinemia and hypertension. Warfarin therapy was instituted when the baby was 8 months of age, followed by a gradual withdrawal of fresh frozen plasma therapy. The dose of warfarin required to maintain the prothrombin time in a range of 1.8 to 2.2 times normal varied considerably during short periods, a phenomenon that may have been due to several factors: hypercatabolism of the drug with prolonged administration, abnormality of liver function, variation in levels of serum albumin, fluctuations in drug dosage secondary to oral administration, and variations in dietary vitamin K. Protein C determinations by immunologic and functional assays consistently showed detectable but reduced protein C antigen levels with undetectable activity levels, suggesting that a dysproteinemia rather than a deficiency of synthesis is responsible for the child's coagulopathy.

Blood Coagulation Disorders↗
PubMed1987

Protein C deficiency.

Severe homozygous protein C deficiency is a rare but serious problem in the newborn, with a clinical presentation of purpura fulminans. We have presented such a case in an 1,870 gm female neonate. Salient clinical findings in this case include DIC associated with extensive ecchymosis and subsequent gangrene of the skin, thrombotic complications that began on the third day of life. There was no precipitating infection. The progressive gangrenous necrosis of heel and toes was refractory to heparin therapy, but there was clinical improvement after treatment with fresh frozen plasma. Our patient's level of protein C antigen was less than 3% (normal 70% to 130%). Levels of other vitamin-K-dependent factors, as well as factor V, factor VIIIC, and antithrombin III were normal. A heterozygous protein C deficiency was documented in the mother and father. Presently the child is receiving warfarin sodium (Coumadin) therapy and is clinically stable.

Adolescent↗
PubMed1987

Endothelial cell processing of von Willebrand proteins.

The endothelial regulation of vWF synthesis, storage, regulated and constitutive release, and now binding are the focus of numerous research laboratories. The understanding of these phenomena is important to the pathophysiology of local hemostasis. Although the structural understanding of the relationship of vW AgII to vWF is now known, its functional role in synthesis, release, or function is yet to be clearly defined.

Amino Acid Sequence↗
PubMed1987

The effect of ABO blood group on the diagnosis of von Willebrand disease.

In order to firmly establish a normal range for von Willebrand factor antigen (vWF:Ag), we determined plasma vWF:Ag concentrations in 1,117 volunteer blood donors by quantitative immunoelectrophoresis. The presence of the ABO blood group has a significant influence on vWF:Ag values; individuals with blood group O had the lowest mean vWF:Ag level (74.8 U/dL), followed by group A (105.9 U/dL), then group B (116.9 U/dL), and finally group AB (123.3 U/dL). Multiple regression analysis revealed that age significantly correlated with vWF:Ag levels in each blood group. We then performed reverse ABO typing on stored plasma from 142 patients with the diagnosis of von Willebrand disease (vWd). Of 114 patients with type I vWd, blood group O was found in 88 (77%), group A in 21 (18%), group B in 5 (4%), and group AB in none (0%), whereas the frequency of these blood groups in the normal population is significantly different (45%, 45%, 7% and 3%, respectively) (P less than .001). Patients with type II or III vWd had ABO blood group frequencies that were not different from the expected distribution. There may be a subset of symptomatic vWd patients with decreased concentrations of structurally normal vWf (vWd, type I) on the basis of blood group O. Some individuals of blood group AB with a genetic defect of vWF may have the diagnosis overlooked because vWF levels are elevated due to blood type.

ABO Blood-Group System↗
PubMed1987

Low-dose aspirin protects against lipid accumulation in primate vein bypass grafts.

Platelet inhibition with high-dose aspirin combined with dipyridamole reduces lipid accumulation and improves early patency of coronary artery bypass grafts. However, recent evidence suggests that platelet inhibition can be achieved with substantially lower aspirin doses than have been conventionally prescribed. To evaluate whether low-dose aspirin protects against lipid accumulation in bypass grafts, we studied 15 stump-tailed macaque monkeys in which autologous cephalic veins were grafted into the femoral arteries. A control group received no treatment, a second group was treated with a low, single daily dose of aspirin (12 mg), and a third group was given a higher dosage of aspirin (80 mg/day) combined with dipyridamole (50 mg/day) divided into two daily doses. A special diet was fed that resulted in plasma cholesterol levels (224 +/- 50 mg/dl, mean +/- standard deviation) and plasma lipoprotein distributions that mimic the profile in humans. Cholesterol concentration in grafts removed 3 months after insertion was 0.47 +/- 0.12 mg/100 mg tissue in the control group; it was reduced to 0.23 +/- 0.04 mg/100 mg (p less than 0.001) by low-dose aspirin and to 0.17 +/- 0.05 mg/100 mg (p less than 0.001) by combined aspirin and dipyridamole therapy. Graft apolipoprotein B concentration was 66 +/- 19 micrograms/100 mg in control group; it was reduced to 40 +/- 8 micrograms/100 mg (p less than 0.05) by low-dose aspirin and to 23 +/- 7 micrograms/100 mg (p less than 0.001) with the combination treatment. There were no differences between groups in either cholesterol concentration (0.09 +/- 0.02 mg/100 mg) or apolipoprotein B concentration (10 +/- 3 micrograms/100 mg) in normal ungrafted vein. Platelet function tests demonstrated platelet aggregation in all control monkeys, in none of the combined therapy group, and in two of five monkeys receiving low-dose aspirin. This study indicates that low-dose aspirin is protective against graft lipid accumulation in monkeys. The mechanism of this antilipid effect and its relation to any antithrombotic effect remain to be elucidated.

Animals↗
PubMed1986

HTLV-III serology in hemophilia: relationship with immunologic abnormalities.

We investigated the relationship of the presence of antibodies to HTLV-III and immunologic abnormalities in patients with hemophilia. Serum antibodies to HTLV-III were analyzed by ELISA assay, immunoprecipitation of labeled cell extracts, and immunoprecipitation of purified HTLV-III p24. Thirty-four (61%) of the total group (n = 56) had antibody to HTLV-III; 34 (76%) of 45 patients given commercial factor VIII preparations were seropositive, compared with none of 11 patients treated exclusively with cryoprecipitate obtained from volunteer blood donors. Of patients who were seropositive for HTLV-III antibody, 94% had abnormal T4/T8 ratios, and 33% of those whose serum was antibody negative had abnormal T4/T8 ratios; five patients, each antibody positive, have lymphadenopathy syndrome. Sequential studies in a subset of patients indicate that there is a changing pattern of antibody production to HTLV-III antigens after seroconversion.

Acquired Immunodeficiency Syndrome↗
PubMed1986

Effects of reagent and cell-generated hydrogen peroxide on the properties of low density lipoprotein.

Low density lipoprotein (LDL) isolated from human plasma anticoagulated with EDTA (EDTA/LDL) was 4-fold more resistant to oxidation by reagent H2O2, as assayed by the thiobarbituric acid (TBA) assay, than LDL prepared from plasma anticoagulated with citrate (CDP/LDL). The LDLs required 1-3 mM H2O2 for maximal oxidation by this assay, and ED50S were 1.7 X 10(-3) M for EDTA/LDL and 4.5 X 10(-4) M for CDP/LDL. Oxidation was enhanced 2.3-fold by Cu2+ ions. Rabbit endothelial cell line monolayers released two orders of magnitude less H2O2 than was required to oxidize LDL and failed to induce TBA reactivity in either EDTA/LDL or CDP/LDL after a 24-hr coincubation. However, this LDL was subsequently degraded by mouse macrophages more rapidly than untreated LDL. Freshly isolated human monocytes (2 X 10(6) cells per ml), with or without phorbol myristate acetate (100 ng/ml) to trigger the respiratory burst, did not oxidize LDL in the TBA assay, despite producing large amounts of reactive oxygen intermediates. EDTA/LDL, CDP/LDL, and acetoacetylated LDL failed to trigger H2O2 release from human monocytes or macrophages. These results separate oxidation of LDL as measured by TBA assay from the modification of LDL by rabbit aortic endothelial cell line that leads to its subsequent enhanced degradation by macrophages.

Animals↗
PubMed1986

Synthesis by cultured human umbilical vein endothelial cells of two proteins structurally and immunologically related to platelet membrane glycoproteins IIb and IIIa.

Human platelets participate in a number of adhesive interactions, including binding to exposed subendothelium after vascular injury, and platelet-platelet cohesion to form large aggregates. Platelet membrane glycoproteins (GP) IIb and IIIa constitute a receptor for fibrinogen that, together with fibrinogen and calcium, is largely responsible for mediating the formation of the primary hemostatic plug. Using highly specific polyclonal and monoclonal antibodies as probes, we could detect the presence of both of these glycoproteins in cultured human umbilical vein endothelial cells. Western-blot analysis showed that the endothelial cell analogues were similar in size to their platelet counterparts, and were present in cells that had been in culture for over 2 mo. Metabolic labeling of endothelium with [35S]methionine demonstrated that both GPIIb and GPIIIa were actively synthesized in culture. Using the technique of crossed immunoelectrophoresis, evidence was obtained that the endothelial cell forms of GPIIb and GPIIIa may exist complexed to one another after solubilization in Triton X-100. The presence of GPIIb-IIIa analogues in cultured endothelial cells may provide an opportunity to examine the structure, function, and synthesis of these two membrane glycoproteins, as well as provide a source of genetic material with which to begin detailed molecular genetic studies.

Antibodies, Monoclonal↗
PubMed1986

Loss of the largest von Willebrand factor multimers from the plasma of patients with congenital cardiac defects.

We identified a consecutive series of 12 children with noncyanotic congenital cardiac lesions with loss of the largest plasma von Willebrand factor (vWF) multimers determined by SDS-agarose electrophoresis. Seven had previous histories of mucocutaneous hemorrhage; ten had a prolonged bleeding time. Analysis of the factor VIII molecular complex revealed that six patients had reduced vWF measured both immunologically (vW:Ag) and by ristocetin cofactor assay (vW:rist). All had normal or borderline normal factor VIII procoagulant (F VIII) concentrations. Three children had prolonged partial thromboplastin times due to concurrent factor XII deficiency; none had laboratory evidence of intravascular coagulation. Five of the children were restudied after surgical correction of their cardiac lesions. Four had normalization of vWF multimers; the fifth, whose vWF was abnormal postoperatively, had a residual pressure gradient across a previous pulmonary artery banding site. Multimeric abnormalities were not found in the parents of three patients. Thus some patients with noncyanotic congenital heart disease may have an acquired abnormality of vWF that is normalized with correction of the abnormal hemodynamic state.

Blood Coagulation↗