ADP-Induced Refractory State of Platelets in Vitro

ADP-induced aggregation was determined at various times of pre-incubation with ADP in unstirred platelet rich plasma to which adenosine deaminase was added. In the early stages of incubation the shape change response was absent, the aggregation response was poor and not reversible. As incubation proceeded, these three parameters returned towards normal while there was still ADP in the system. Log dose response (rate of aggregation) curves for the platelets incubated with 1 μM of ADP had shifted to higher concentrations of ADP and there was a small decrease in the maximal height of the curves. Gelfiltered platelets in calcium-free Tyrode solution were incubated with 1 μM of ADP at 37° C. Log dose response curves obtained at different times of incubation showed a greater shift to higher ADP concentrations than those obtained with platelets in plasma. There was also a pronounced decrease in the maximal height of the curves. These two observations became more apparent as incubation proceeded. Addition of apyrase (0.1 mg/ml) at various times of incubation prevented the progessive impairment of the aggregation response and this even slowly increased towards that of the control. The time of incubation with ADP before addition of apyrase did not have any influence on the ability of the platelets to recover their aggregability towards ADP.

The Role of Prostaglandins in the ADP-Induced Aggregation of Rabbit Platelets Shown by the Use of 15-Hydroxyprostaglandin Dehydrogenase

10.1055/s-0038-1646749 ◽

1978 ◽

Vol 39 (03) ◽

pp. 725-732 ◽

Cited By ~ 2

Author(s):

Robert B Wallis

Keyword(s):

Platelet Rich Plasma ◽

Shape Change ◽

Rabbit Platelet ◽

Direct Role ◽

Initial Shape ◽

Rabbit Platelets ◽

Induced Aggregation ◽

Aggregation Of Platelets

SummaryThe initial shape change and subsequent aggregation of platelets in citrated rabbit platelet-rich plasma caused by ADP in vitro was inhibited by 15-hydroxyprostaglandin dehydrogenase. This inhibition was NAD-dependent and was also seen when shape change and aggregation were initiated by sodium arachidonate or by collagen. The aggregation of gel-filtered rabbit platelets by thrombin was not, however, affected by removal of 15-hydroxyprostaglandins.Indomethacin was found to inhibit ADP-induced aggregation but at a concentration (250 μM) much higher than that required to inhibit collagen-induced aggregation. Moreover the platelet release reaction had not taken place 3 min after ADP stimulation. The direct role 15-hydroxyprostaglandin production in ADP-induced aggregation of rabbit platelets is proposed. The involvement of 15-hydroxyprostaglandins in platelet aggregation caused by other inducers is also discussed.

DIFFERENTIAL INHIBITION OF THE PLATELET ACTIVATION SEQUENCE: SHAPE CHANGE, MICRO- AND MACRO- AGGREGATION, BY A STABLE PROSTACYCLIN ANALOGUE (IL0PR0ST)

10.1055/s-0038-1643451 ◽

1987 ◽

Author(s):

L G Pedvis ◽

T Wong ◽

J Wylie ◽

M M Frojmovic

Keyword(s):

Sex Differences ◽

Dose Response ◽

Platelet Rich Plasma ◽

Shape Change ◽

Adenosine Monophosphate ◽

Differential Inhibition ◽

Response Curves ◽

Healthy Human ◽

Intracellular Signals ◽

The Relationship

The relative sensitivities of ADP-induced activation, and prostaglandin-mediated inhibition, were determined for rates of platelet shape change (SC), early platelet recruitment measured by electronic particle counting (PA), and turbidometrically-measured aggregation (TA). Studies were performed in stirred citrated platelet-rich plasma from 7 healthy human donors. The [ADP]½ ([ADP] giving half maximal rate) was determined for the sequence of activation steps expanding on Holmsen’s classical scheme: unactivated platelets → SC → PA → TA. Distinct ADP sensitivities were obtained from log dose-response studies, with a relative dose dependency in the order of [ADP] ½ TA → [ADP] ½ PA → [ADP]> SC of 4:3:1. Sex differences in ADP sensitivities ([ADP]½), for rates of early platelet recruitment measured at 3 seconds were studied from a pool of 20 females and 19 males. Values obtained between the two sexes were comparable (p > 0.05) and independent of hematocrit. Differential inhibition of the above activation scheme was evaluated with Iloprost (ZK 36 374), a stable carbacyclin analogue of prostacyclin (PGI2), with similar potency as PGI2 for the same platelet receptors. Log dose - response curves for inhibition were measured at one high [ADP] (> 1.5 μM) for all 3 parameters, or at respective [ADP]½ values for each parameter. IC5u values ([ZK J causing 50% of inhibition) for inhibition of TA:PA:SC were found in the relative ratios of ∽ 1:3:5, when normalized and expressed as nM ZK per pM ADP used as activator. Thus, ∽ 3x and ∽ 5x more ZK, and likely PGI2, is required to respectively inhibit PA and SC, than that needed to inhibit TA. As observed above for activation, no sex differences in ZK sensitivities were observed (p > 0.1) for 6 males and 6 females. The range of ZK used in this study was below the threshold (∽ 3 nM) generally reported for measurable increases in total basal cyclic 3’ ,5’ adenosine monophosphate (cAMP). This suggests that for each parameter, any increase in cAMP may be associated with selective intracellular pools. The relationship between ZK or PGI2 and intracellular signals remains to be determined.

Reaction of Acetaldehyde with Human Platelets

10.1055/s-0038-1648393 ◽

1992 ◽

Vol 67 (01) ◽

pp. 126-130 ◽

Cited By ~ 8

Author(s):

Olivier Spertini ◽

Jacques Hauert ◽

Fedor Bachmann

Keyword(s):

Platelet Aggregation ◽

Inhibitory Action ◽

Ex Vivo ◽

Platelet Rich Plasma ◽

Shape Change ◽

Reaction Medium ◽

Human Platelets ◽

Membrane Glycoproteins ◽

Neutral Ph

SummaryPlatelet function defects observed in chronic alcoholics are not wholly explained by the inhibitory action of ethanol on platelet aggregation; they are not completely reproduced either in vivo by short-term ethanol perfusion into volunteers or in vitro by the addition of ethanol to platelet-rich plasma. As acetaldehyde (AcH) binds to many proteins and impairs cellular activities, we investigated the effect of this early degradation product of ethanol on platelets. AcH formed adducts with human platelets at neutral pH at 37° C which were stable to extensive washing, trichloracetic acid hydrolysis and heating at 100° C, and were not reduced by sodium borohydride. The amount of platelet adducts formed was a function of the incubation time and of the concentration of AcH in the reaction medium. At low AcH concentrations (<0.2 mM), platelet bound AcH was directly proportional to the concentration of AcH in the reaction medium. At higher concentrations (≥0.2 mM), AcH uptake by platelets tended to reach a plateau. The amount of adducts was also proportional to the number of exposures of platelets to pulses of 20 pM AcH.AcH adducts formation severely impaired platelet aggregation and shape change induced by ADP, collagen and thrombin. A positive correlation was established between platelet-bound AcH and inhibition of aggregation.SDS-PAGE analysis of AcH adducts at neutral pH demonstrated the binding of [14C]acetaldehyde to many platelet proteins. AcH adduct formation with membrane glycoproteins, cytoskeleton and enzymes might interfere with several steps of platelet activation and impair platelet aggregation.This in vitro study shows that AcH has a major inhibitory action on platelet aggregation and may account for the prolonged ex vivo inhibition of aggregation observed in chronic alcoholics even in the absence of alcoholemia.

Dipyridamole Inhibits Platelet Aggregation in Whole Blood

10.1055/s-0038-1665327 ◽

1983 ◽

Vol 50 (04) ◽

pp. 852-856 ◽

Cited By ~ 104

Author(s):

P Gresele ◽

C Zoja ◽

H Deckmyn ◽

J Arnout ◽

J Vermylen ◽

...

Keyword(s):

Platelet Aggregation ◽

Whole Blood ◽

Ex Vivo ◽

Platelet Rich Plasma ◽

Significant Negative Correlation ◽

Significant Inhibition ◽

Oral Drug ◽

Human Blood Samples ◽

SummaryDipyridamole possesses antithrombotic properties in the animal and in man but it does not inhibit platelet aggregation in plasma. We evaluated the effect of dipyridamole ex vivo and in vitro on platelet aggregation induced by collagen and adenosine- 5’-diphosphate (ADP) in human whole blood with an impedance aggregometer. Two hundred mg dipyridamole induced a significant inhibition of both ADP- and collagen-induced aggregation in human blood samples taken 2 hr after oral drug intake. Administration of the drug for four days, 400 mg/day, further increased the antiplatelet effect. A significant negative correlation was found between collagen-induced platelet aggregation in whole blood and dipyridamole levels in plasma (p <0.001). A statistically significant inhibition of both collagen (p <0.0025) and ADP-induced (p <0.005) platelet aggregation was also obtained by incubating whole blood in vitro for 2 min at 37° C with dipyridamole (3.9 μM). No such effects were seen in platelet-rich plasma, even after enrichment with leukocytes. Low-dose adenosine enhanced in vitro inhibition in whole blood.Our results demonstrate that dipyridamole impedes platelet aggregation in whole blood by an interaction with red blood cells, probably involving adenosine.

Decreased Platelet Vitamin C in Diabetes Mellitus; Possible Role in Peraggregatoon

10.1055/s-0039-1687640 ◽

1979 ◽

Author(s):

K.E. Sarji ◽

J. Gonzalez ◽

H. Hempling ◽

J.A. Colwell

Keyword(s):

Ascorbic Acid ◽

Arachidonic Acid ◽

Platelet Aggregation ◽

Vitamin C ◽

Platelet Rich Plasma ◽

Solution Ph ◽

Dose Dependent Fashion ◽

Insulin Dependent Diabetic ◽

To determine whether Vitamin C might relate to the increased platelet sensitivity in the diabetic, we have measured levels of platelet Vitamin C and studied the effects of Vitamin C on platelet aggregation. Ascorbic acid levels in washed platelets from diabetics were significantly lower than from normals (4s.2±3 μg/1010 platelets vs. 2s.s±2 μg/1010 platelets, p<.001). The effects of ascorbic acid on platelet aggregation in vitro were studied by adding ascorbic acid in buffered solution (pH 7.35) prior to-aggregating agents. Ascorbic acid in platelet-rich plasma consistently inhibited platelet aggregation with threshold concentrations of ADP, epinephrine, and collagen. With washed platelets, ascorbic acid inhibited arachidonic, acid-induced aggregation. When platelets were incubated at 37°C for 10 minutes with varying concentrations of ascorbic acid, rewashed, and aggregation with arachidonic acid tested, aggregation was inhibited in a linear dose-dependent fashion. Oral ingestion of ascorbic acid (2 gm/day) for seven days by normal non-smoking males produced a marked inhibition of aggregation. In a similar study, platelets from an insulin-dependent diabetic showed no change in aggregation. These results suggest that platelet levels of ascorbic acid may relate to the hyperaggregat ion of platelets from diabetics.

Physiologically based kinetic modelling based prediction of in vivo rat and human acetylcholinesterase (AChE) inhibition upon exposure to diazinon

Archives of Toxicology ◽

10.1007/s00204-021-03015-1 ◽

2021 ◽

Author(s):

Shensheng Zhao ◽

Sebastiaan Wesseling ◽

Bert Spenkelink ◽

Ivonne M. C. M. Rietjens

Keyword(s):

Dose Response ◽

Kinetic Modelling ◽

Ache Inhibition ◽

Response Curves ◽

Alternative Testing ◽

Dose Response Curves ◽

Physiologically Based Kinetic Modelling ◽

Point Of Departure

AbstractThe present study predicts in vivo human and rat red blood cell (RBC) acetylcholinesterase (AChE) inhibition upon diazinon (DZN) exposure using physiological based kinetic (PBK) modelling-facilitated reverse dosimetry. Due to the fact that both DZN and its oxon metabolite diazoxon (DZO) can inhibit AChE, a toxic equivalency factor (TEF) was included in the PBK model to combine the effect of DZN and DZO when predicting in vivo AChE inhibition. The PBK models were defined based on kinetic constants derived from in vitro incubations with liver fractions or plasma of rat and human, and were used to translate in vitro concentration–response curves for AChE inhibition obtained in the current study to predicted in vivo dose–response curves. The predicted dose–response curves for rat matched available in vivo data on AChE inhibition, and the benchmark dose lower confidence limits for 10% inhibition (BMDL10 values) were in line with the reported BMDL10 values. Humans were predicted to be 6-fold more sensitive than rats in terms of AChE inhibition, mainly because of inter-species differences in toxicokinetics. It is concluded that the TEF-coded DZN PBK model combined with quantitative in vitro to in vivo extrapolation (QIVIVE) provides an adequate approach to predict RBC AChE inhibition upon acute oral DZN exposure, and can provide an alternative testing strategy for derivation of a point of departure (POD) in risk assessment.

Effects of Ethanol on Pathways of Platelet Aggregation In Vitro

10.1055/s-0038-1647500 ◽

1988 ◽

Vol 59 (03) ◽

pp. 383-387 ◽

Cited By ~ 42

Author(s):

Margaret L Rand ◽

Marian A Packham ◽

Raelene L Kinlough-Rathbone ◽

J Fraser Mustard

Keyword(s):

Arachidonic Acid ◽

Platelet Aggregation ◽

Platelet Rich Plasma ◽

Secondary Phase ◽

Primary Phase ◽

Rabbit Platelet ◽

Membrane Phospholipids ◽

Rabbit Platelets ◽

SummaryEthanol, at physiologically tolerable concentrations, did not affect the primary phase of ADP-induced aggregation of human or rabbit platelets, which is not associated with the secretion of granule contents. Potentiation by epinephrine of the primary phase of ADP-induced aggregation of rabbit platelets was also not inhibited by ethanol. However, ethanol did inhibit the secondary phase of ADP-induced aggregation which occurs with human platelets in citrated platelet-rich plasma and is dependent on the formation of thromboxane A2. Inhibition by ethanol of thromboxane production by stimulated platelets is likely due to inhibition of the mobilization of arachidonic acid from membrane phospholipids, as ethanol had little or no effect on aggregation and secretion induced by arachidonic acid or the thromboxane mimetic U46619. Rabbit platelet aggregation and secretion in response to low concentrations of collagen, thrombin, or PAF were inhibited by ethanol. Inhibition of the effects of thrombin and PAF was also observed with aspirin-treated platelets. Thus, in addition to inhibiting the mobilization of arachidonate for thromboxane formation that occurs with most agonists, ethanol can also inhibit aggregation and secretion through other effects on platelet responses.

Modelling the population-level protection conferred by COVID-19 vaccination

10.1101/2021.03.16.21253742 ◽

2021 ◽

Author(s):

Pranesh Padmanabhan ◽

Rajat Desikan ◽

Narendra M Dixit

Keyword(s):

Mathematical Model ◽

Severe Acute Respiratory Syndrome ◽

Dose Response ◽

Neutralizing Antibodies ◽

Population Level ◽

Response Curves ◽

Post Vaccination ◽

Dose Response Curves ◽

Vaccine Availability

Although severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) vaccines work predominantly by eliciting neutralizing antibodies (NAbs), how the protection they confer depends on the NAb response to vaccination is unclear. Here, we collated and analysed in vitro dose-response curves of >70 NAbs and constructed a landscape defining the spectrum of neutralization efficiencies of NAbs elicited. We mimicked responses of individuals by sampling NAb subsets of known sizes from the landscape and found that they recapitulated responses of convalescent patients. Combining individual responses with a mathematical model of within-host SARS-CoV-2 infection post-vaccination, we predicted how the population-level protection conferred would increase with the NAb response to vaccination. Our predictions captured the outcomes of vaccination trials. Our formalism may help optimize vaccination protocols, given limited vaccine availability.

Advancing risk assessment: mechanistic dose–response modelling of Listeria monocytogenes infection in human populations

Royal Society Open Science ◽

10.1098/rsos.180343 ◽

2018 ◽

Vol 5 (8) ◽

pp. 180343 ◽

Cited By ~ 5

Author(s):

Ashrafur Rahman ◽

Daniel Munther ◽

Aamir Fazil ◽

Ben Smith ◽

Jianhong Wu

Keyword(s):

Listeria Monocytogenes ◽

Dose Response ◽

Geometric Interpretation ◽

Human Populations ◽

Response Curves ◽

Future Experimentation ◽

Limited Power ◽

Mechanistic Basis ◽

Response Modelling

The utility of characterizing the effects of strain variation and individual/subgroup susceptibility on dose–response outcomes has motivated the search for new approaches beyond the popular use of the exponential dose–response model for listeriosis. While descriptive models can account for such variation, they have limited power to extrapolate beyond the details of particular outbreaks. By contrast, this study exhibits dose–response relationships from a mechanistic basis, quantifying key biological factors involved in pathogen–host dynamics. An efficient computational algorithm and geometric interpretation of the infection pathway are developed to connect dose–response relationships with the underlying bistable dynamics of the model. Relying on in vitro experiments as well as outbreak data, we estimate plausible parameters for the human context. Despite the presence of uncertainty in such parameters, sensitivity analysis reveals that the host response is most influenced by the pathogen–immune system interaction. In particular, we show how variation in this interaction across a subgroup of the population dictates the shape of dose–response curves. Finally, in terms of future experimentation, our model results provide guidelines and highlight vital aspects of the interplay between immune cells and particular strains of Listeria monocytogenes that should be examined.

Prostaglandin Synthesis Inhibitors

Histamine tachyphylaxis in canine airways despite prostaglandin synthesis inhibition

Journal of Applied Physiology ◽

10.1152/jappl.1988.65.5.1944 ◽

1988 ◽

Vol 65 (5) ◽

pp. 1944-1949 ◽

Cited By ~ 7

Author(s):

P. J. Antol ◽

S. J. Gunst ◽

R. E. Hyatt

Keyword(s):

Smooth Muscle ◽

Dose Response ◽

Prostaglandin Synthesis ◽

Response Curves ◽

Synthesis Inhibition ◽

High Concentrations ◽

Alpha Chloralose ◽

Tachyphylaxis to aerosolized histamine was studied in dogs anesthetized with thiamylal after pretreatment with prostaglandin synthesis inhibitors. Three consecutive histamine dose-response curves were obtained in nine dogs pretreated with 5 mg/kg indomethacin; two of these nine were also pretreated with 10 mg/kg indomethacin. Seven of the nine dogs were pretreated with 4 mg/kg sodium meclofenamate; four of these seven were also pretreated with 12 mg/kg. All dogs had tachyphylaxis at high concentrations of histamine regardless of inhibitor used. Pretreatment with indomethacin while the dogs were under alpha-chloralose-urethan anesthesia gave similar results. Histamine tachyphylaxis was also studied both in the presence and in the absence of indomethacin in tracheal smooth muscle strips obtained from seven additional dogs. A decrease in the median effective dose to histamine was observed in the indomethacin-treated strips, but tachyphylaxis to histamine remained. We conclude that prostaglandin synthesis inhibition does not reverse histamine tachyphylaxis either in vivo or in vitro. Thus the mechanism of histamine tachyphylaxis remains unexplained.