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Ligand-specific glucocorticoid receptor activation in human platelets
Leonardo A Moraes1, Mark J Paul-Clark, Alice Rickman
1The William Harvey Research Institute, Charterhouse Square, London EC1M 6BQ, United Kingdom.
Blood
|September 1, 2005
Summary
Human platelets possess glucocorticoid receptors (GR). Prednisolone inhibits platelet aggregation and thromboxane production via GR, unlike dexamethasone, suggesting differential ligand activation.
Area of Science:
- Biochemistry
- Pharmacology
- Hematology
Background:
- Limited research exists on anti-inflammatory glucocorticoids' impact on platelet function.
- Platelets play a crucial role in hemostasis and thrombosis.
Purpose of the Study:
- To investigate the presence and function of glucocorticoid receptors (GR) in human platelets.
- To determine the effects of specific glucocorticoids on platelet activation.
Main Methods:
- Biochemical and functional assays to identify and characterize GR in platelets.
- Ligand-binding studies using [3H]-dexamethasone.
- Platelet aggregation assays with adenosine diphosphate (ADP) and U46619.
- Measurement of thromboxane B2 levels.
Main Results:
- Human platelets express glucocorticoid receptors (GR), identified through binding and functional studies.
- Prednisolone significantly inhibited ADP- and U46619-induced platelet aggregation and reduced thromboxane B2 levels.
- Dexamethasone did not affect platelet aggregation or thromboxane B2 levels.
- Prednisolone's inhibitory effect was reversed by the GR antagonist mifepristone.
- Platelets contain both GR and mineralocorticoid receptors (MR), which associate, suggesting heterodimer formation.
Conclusions:
- Human platelets possess functional glucocorticoid receptors (GR).
- Prednisolone exerts anti-platelet effects through GR activation, potentially via a heterodimer with the mineralocorticoid receptor.
- Differential activation of the GR-MR complex by specific ligands like prednisolone influences platelet function.