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Biomedical subjects

M B Holmes

Publications and source records attributed to M B Holmes.

12 recordsLinked to original sources
PubMed2001

Quantification by flow cytometry of the efficacy of and interindividual variation of platelet inhibition induced by treatment with tirofiban and abciximab.

BACKGROUND: After exposure of platelets to abciximab and tirofiban in vitro, we have observed variable inhibition of fibrinogen binding and a lack of inhibition of alpha-granule degranulation. DESIGN: To determine whether such changes occur with treatment, platelet reactivity was assayed in blood from 50 patients receiving abciximab or tirofiban. METHODS: Platelet reactivity was determined before and during steady-state infusions of abciximab (0.125 microg/kg/min) or tirofiban, with either the PRISM-PLUS dosage (0.1 microg/kg/min) or the RESTORE dosage (0.15 microg/kg/min). Fibrinogen binding and P-selectin expression were determined by flow cytometry after stimulation of platelets with ADP (0.2 or 1 microM) or thrombin-receptor agonist peptide (TRAP, 25 microM). RESULTS: Both dosages of tirofiban and abciximab reduced fibrinogen binding in response to 0.2 microM ADP comparably. However, fibrinogen binding in response to 1.0 microM ADP or 25 microM TRAP was inhibited to a greater extent by the RESTORE dosage of tirofiban and abciximab than by the PRISM-PLUS dosage of tirofiban (P< 0.05). Furthermore, only the RESTORE dosage of tirofiban and abciximab reduced P-selectin expression in response to ADP. Inhibition with each regimen varied markedly between patients. CONCLUSIONS: The RESTORE dosages of tirofiban and abciximab each inhibit fibrinogen binding and alpha-granule degranulation similarly. However, substantial interindividual variation in inhibition of fibrinogen binding is evident.

Abciximab↗
PubMed2001

Time and dose dependent augmentation of inhibitory effects of abciximab by aspirin.

Aspirin and abciximab independently decrease the incidence of cardiac events. To identify potential interactions, antiplatelet effects of abciximab were characterized in blood from healthy subjects given aspirin. Platelet activation was determined in whole blood with and without abciximab (2 microg/ml) added in vitro. Flow cytometry was used to quantify fibrinogen binding (glycoprotein IIb-IIIa activation). Binding of fluorochrome-labeled and 125I-labeled abciximab was determined before and after exposure to aspirin. In blood from subjects given aspirin for 5 days, abciximab-induced inhibition of the capacity to bind fibrinogen in response to 1 microM ADP was greater when the daily dose had been 325 mg compared with 81 mg (% inhibition: no aspirin 53 +/- 6; 81 mg daily 62 +/- 5; 325 mg daily 69 +/- 6). The effect of 5 daily doses of aspirin was greater than that of one. Larger single doses elicited larger effects (% inhibition 2 h after 325 mg 59 +/- 6; 2 h after 650 mg 78 +/- 5). Neither salicylsalicylic acid nor naproxen sodium potentiated the effect of abciximab. Exposure of platelets to 14C-acetylsalicylic acid led to acetylation of glycoprotein IIb and IIIa. Binding of 125I-abciximab to platelets was increased after 30 and 60 min. Acetylation of glycoprotein IIb-IIIa by aspirin augments inhibitory effects of abciximab in a dose- and time-dependent manner by increasing binding of abciximab to platelets.

Abciximab↗
PubMed2000

Novel, bedside, tissue factor-dependent clotting assay permits improved assessment of combination antithrombotic and antiplatelet therapy.

BACKGROUND: Because optimal use of combinations of antiplatelet and antithrombotic drugs requires improved methods for assessment of therapeutic efficacy, we developed an assay designed to increase sensitivity that is based on initiation of clotting by tissue factor in minimally altered whole blood. METHODS AND RESULTS: Blood samples were obtained from healthy subjects, and the contact pathway of coagulation was inhibited with corn trypsin inhibitor (a specific factor XIIa inhibitor without effect on other coagulation factors). Clotting was initiated with relipidated tissue factor and detected with a Hemochron ACT instrument. Results were reproducible with samples from 25 healthy volunteers (mean time to clot, 125+/-17 seconds). Blood was also exposed to pharmacological concentrations of antithrombotic and antiplatelet agents in vitro. Heparin (0.25 anti-IIa/Xa U/mL) prolonged the time to clot by 2.4-fold (172 seconds, P:<0.05); hirudin (1.0 anti-IIa U/mL), by 3-fold (250 seconds P:<0.05); and enoxaparin (0.6 anti-Xa U/mL), by 2 -fold (123 seconds, P:<0.05). Additive effects of antiplatelet agents were readily detectable with both heparin and hirudin. Thus, addition of 3 microg/mL abciximab to 1.0 anti-IIa/Xa U/mL heparin and to 1.0 anti-IIa U/mL hirudin further prolonged the times to clot by 140 and 67 seconds, respectively (P:<0.05 for each). Addition of abciximab to enoxaparin did not further prolong the time to clot (increment, 13 seconds; P:=NS). CONCLUSIONS: The assay developed should facilitate improved dose selection, titration, and monitoring of combination antithrombotic and antiplatelet treatment regimens.

Blood Coagulation↗
PubMed2000

Increased platelet reactivity in patients given orbofiban after an acute coronary syndrome: an OPUS-TIMI 16 substudy. Orbofiban in Patients with Unstable coronary syndromes. Thrombolysis In Myocardial Infarction.

Patients receiving the oral glycoprotein IIb-IIIa inhibitor orbofiban in the OPUS -TIMI 16 trial had a paradoxical increase in platelet reactivity with respect to both fibrinogen binding and alpha-granule degranulation, suggesting a mechanism for the lack of efficacy of orbofiban in the trial. Thus, sensitive assays of platelet reactivity may be helpful in the design of further clinical studies and implementation of antiplatelet therapy in patients.

Acute Disease↗
PubMed1999

Variable responses to inhibition of fibrinogen binding induced by tirofiban and eptifibatide in blood from healthy subjects.

Antiplatelet therapy with glycoprotein IIb-IIIa inhibitors reduces the incidence of cardiac events in patients with acute coronary syndromes. A lack of universal efficacy may result from interindividual variation in the inhibition of fibrinogen binding after exposure to tirofiban and eptifibatide. Accordingly, accurate monitoring of platelet function in individual subjects may be needed. To assess this possibility, blood was drawn from 15 healthy volunteers into syringes containing corn trypsin inhibitor (an anticoagulant that is a specific inhibitor of factor XIIa) and selected concentrations of tirofiban and eptifibatide. Platelets were then activated with adenosine diphosphate (ADP) and thrombin receptor agonist peptide. Flow cytometry was used to assess activation with respect to glycoprotein IIb-IIIa activation as reflected by fibrinogen binding and alpha-granule degranulation as reflected by P-selectin expression. In platelets activated with 1 microM ADP, clinically relevant concentrations of tirofiban caused inhibition of fibrinogen binding ranging from 17% to 88%. Similarly, eptifibatide caused inhibition of fibrinogen binding ranging from 32% to 74%. The highest concentration of eptifibatide tested enhanced agonist-induced degranulation, an effect not seen with tirofiban at concentrations tested. Flow cytometry in minimally altered whole blood can discriminate variation in the response to glycoprotein IIb-IIIa inhibitors with respect to specific components of platelet activation. Thus, the approach developed should facilitate definition of optimal platelet inhibition and individualized tailoring of therapy to induce optimal effects.

Adenosine Diphosphate↗
PubMed1999

Differences between activation thresholds for platelet P-selectin glycoprotein IIb-IIIa expression and their clinical implications.

Increased platelet reactivity is a descriptor of the risk of cardiovascular events in healthy men and in patients with overt coronary artery disease. We sought to determine if differential thresholds exist for activation of platelets with respect to alpha-granule degranulation and fibrinogen binding in healthy volunteers and in patients with acute coronary syndromes. We also sought to characterize the effect of aspirin on activation. Platelet activation was assessed with flow cytometry in whole blood anticoagulated with corn trypsin inhibitor and incubated with fluorescein isothiocyanate conjugated fibrinogen (to define activation of glycoprotein IIb-IIIa), a phycoerythrin conjugated antibody to P-selectin (a marker of alpha-granule degranulation), and selected concentrations of adenosine diphosphate (ADP) or thrombin receptor agonist peptide. ADP-induced fibrinogen binding was found to be a low threshold activation event (40% of platelets bound fibrinogen in response to 0.2 microM ADP). Alpha-granule degranulation was a higher threshold event (33% of platelets expressed P-selectin in response to 1.0 microM ADP). Intra- and interindividual variability were most apparent with low concentrations of agonist (0.2 microM ADP). Patients with acute coronary syndromes (on aspirin) had significantly increased P-selectin expression in response to ADP compared with healthy subjects (on aspirin), but no difference in ADP-induced fibrinogen binding was observed. Daily ingestion of 325 mg of aspirin had no effect on either P-selectin expression or fibrinogen binding in healthy subjects. Analysis of platelet reactivity with flow cytometry characterizes activation with respect to specific components of the process and should facilitate development and optimal titration of antiplatelet therapy.

Aspirin↗
PubMed1999

Optimizing antiplatelet therapy in patients with acute coronary syndromes: a role for monitoring platelet reactivity.

Platelet activation is seminal in the thrombosis underlying acute coronary syndromes. Furthermore, high levels of platelet reactivity are associated with an increased risk of future cardiovascular events both in apparently healthy subjects and men with overt coronary artery disease. We have developed a sensitive and specific assay of platelet reactivity using minimally altered whole blood to assess activation of glycoprotein IIb/IIIa and expression of P-selectin (a measure of alpha granule degranulation). This assay reliably identifies subjects with increased platelet reactivity who may benefit from more aggressive inhibition of platelet function on a long-term basis. In addition, this assay is sensitive to the effects of antiplatelet agents such as glycoprotein IIb/IIIa inhibitors. Abciximab, tirofiban and eptifibatide all inhibit fibrinogen binding in a concentration of dependent manner. However, marked variation in the extent of inhibition was seen between individuals. We have postulated that greater inhibition of agonist-induced fibrinogen binding in some and limited inhibition in others may account, in part, for tendencies to bleeding and recurrent thrombosis. This type of assay should allow for determination of platelet reactivity and titration of dosage to the needs of each individual. The assay has the potential to improve the care of patients with acute coronary syndromes and of those undergoing percutaneous coronary intervention as well as assist in the design of clinical trials utilizing antiplatelet drugs.

Platelet Aggregation Inhibitors↗
PubMed1985

Pasteurized milk as a vehicle of infection in an outbreak of listeriosis.

Between June 30th and August 30th, 1983, 49 patients in Massachusetts acquired listeriosis. Seven cases occurred in fetuses or infants and 42 in immunosuppressed adults; 14 patients (29 per cent) died. Of 40 Listeria monocytogenes isolates available for testing, 32 were serotype 4b. Two case-control studies, one matching for neighborhood of residence and the other for underlying disease, revealed that the illness was strongly associated with drinking a specific brand of pasteurized whole or 2 per cent milk (odds ratio = 9, P less than 0.01 for the neighborhood-matched study; odds ratio = 11.5, P less than 0.001 for the illness-matched study). The association with milk was further substantiated by four additional analyses that suggested the presence of a dose-response effect, demonstrated a protective effect of skim milk, associated cases with the same product in an independent study in another state, and linked a specific phage type with the disease associated with milk. The milk associated with disease came from a group of farms on which listeriosis in dairy cows was known to have occurred at the time of the outbreak. Multiple serotypes of L. monocytogenes were isolated from raw milk obtained from these farms after the outbreak. At the plant where the milk was processed, inspections revealed no evidence of improper pasteurization. These results support the hypothesis that human listeriosis can be a foodborne disease and raise questions about the ability of pasteurization to eradicate a large inoculum of L. monocytogenes from contaminated raw milk.

Adult↗
PubMed1982

Molecular epidemiology of antibiotic resistance in salmonella from animals and human beings in the United States.

We collected serotyped isolates of salmonella from reference laboratories in the United States, tested their susceptibility to antibiotics, and extracted plasmids from isolates that were resistant to a different combination of antibiotics from each of three serotypes. Restriction-endonuclease digestion showed that within each of the three groups, plasmid molecules from animal and human isolates were often identical or nearly identical. One serotype-plasmid combination appeared to be endemic in cattle in 20 states and infected 26 persons in two states. The human cases, which were not recognizably related except for their common plasmids, appeared to be clustered in time but geographically dispersed, like cases in previous outbreaks spread by food products. These findings suggest that resistance plasmids may be extensively shared between animal and human bacteria, and that spread of multiresistant strains of salmonella among animals and human beings, as observed in Britain, may have been undetected in the United States for lack of comparable surveillance.

Animals↗
PubMed1981

Vitamilk 20.

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Animals↗