The effects of several steroids and their metabolites were examined for their ability to rapidly alter intracellular free calcium ([Ca2+]i) in the anucleate human platelet. Earlier studies suggested that steroids had direct and rapid non-genomic effects to alter platelet physiology. The rationale for performing this study was to investigate the signal transduction events being activated by steroids. Super-physiologic concentrations (1.0–10.0 μM) of β-estradiol and several estradiol metabolites and analogs potentiated (approximately twofold) the action of thrombin to elevate [Ca2+]i in platelets, whereas 10.0 μM progesterone inhibited the action of human thrombin by 10–15%. Progesterone and β-estradiol by themselves did not affect [Ca2+]i. Progesterone metabolites can achieve high blood concentrations. Some progesterone metabolites, particularly those in the β-conformation, were potent stimulators of Ca2+ influx and intracellular Ca2+ mobilization in platelets. They activated phospholipase C because their ability to increase [Ca2+]i was inhibited by the phospholipase C inhibitor U-73122. The ability of pregnanediol and collagen to increase [Ca2+]i was inhibited by the src tyrosine kinase inhibitor PP1, whereas the actions of thrombin and thapsigargin to increase [Ca2+]i were not affected by PP1. The effects of progesterone metabolites to increase [Ca2+]i were observed with concentrations as low as 0.1 μM. Pregnanolone synergized with thrombin to increase [Ca2+]i. It is hypothesized that human platelets possess receptors for progesterone metabolites. These receptors when stimulated will activate platelets by causing a rapid increase in [Ca2+]i. Pregnanolone, isopregnanediol and pregnanediol were the most effective stimulators of this newly identified src-dependent signal transduction system in platelets. Progesterone metabolites may regulate platelet aggregation and hence thrombosis in vivo.
ARTICLE
Showing posts with label human. Show all posts
Showing posts with label human. Show all posts
Monday
Friday
FDA Approves Human Thrombin for Topical Use in Surgery
The U.S. Food and Drug Administration approved Evithrom (Human Thrombin), a blood-clotting protein used to help control bleeding during surgery.
Evithrom is the first human thrombin approved since 1954 and is the only product currently licensed. It is derived from human plasma obtained from carefully screened and tested U.S. donors and has undergone steps to further reduce the risk for transfusion-transmitted diseases.
Evithrom is indicated as an aid to stop oozing and minor bleeding from capillaries and small veins and when control of bleeding by standard surgical techniques is ineffective or impractical. The product is applied to the surface of bleeding tissue and may be used in conjunction with an absorbable gelatin sponge. Evithrom must not be injected into blood vessels, which would result in serious clinical complications and may even be fatal.
"The approval of Evithrom offers an important additional option for surgeons and their patients to help control surgical bleeding," said Jesse L. Goodman, M.D., M.P.H., director of FDA's Center for Biologics Evaluation and Research. "Surgeons will now be able to choose between human thrombin and thrombin derived from cattle plasma."
In a clinical trial involving several hundred subjects, Evithrom was found comparable to cattle-derived thrombin in both safety and effectiveness.
Evithrom is manufactured by Omrix Biopharmaceuticals, Ltd., Ramat Gan, Israel, and will be distributed by Johnson & Johnson Wound Management, a division of Ethicon, Inc., Somerville, N.J.
Evithrom is the first human thrombin approved since 1954 and is the only product currently licensed. It is derived from human plasma obtained from carefully screened and tested U.S. donors and has undergone steps to further reduce the risk for transfusion-transmitted diseases.
Evithrom is indicated as an aid to stop oozing and minor bleeding from capillaries and small veins and when control of bleeding by standard surgical techniques is ineffective or impractical. The product is applied to the surface of bleeding tissue and may be used in conjunction with an absorbable gelatin sponge. Evithrom must not be injected into blood vessels, which would result in serious clinical complications and may even be fatal.
"The approval of Evithrom offers an important additional option for surgeons and their patients to help control surgical bleeding," said Jesse L. Goodman, M.D., M.P.H., director of FDA's Center for Biologics Evaluation and Research. "Surgeons will now be able to choose between human thrombin and thrombin derived from cattle plasma."
In a clinical trial involving several hundred subjects, Evithrom was found comparable to cattle-derived thrombin in both safety and effectiveness.
Evithrom is manufactured by Omrix Biopharmaceuticals, Ltd., Ramat Gan, Israel, and will be distributed by Johnson & Johnson Wound Management, a division of Ethicon, Inc., Somerville, N.J.
Monday
Role of the Endothelium in the Vascular Effects of the Thrombin Receptor (Protease-Activated Receptor Type 1) in Humans
Objectives
The purpose of this study was to determine the role of the endothelium in the vascular actions of protease-activated receptor type 1(PAR-1) activation in vivo in man.
Background
Thrombin is central to the pathophysiology of atherothrombosis. Its cellular actions are mediated via PAR-1. Protease-activated receptor type 1 activation causes arterial vasodilation, venoconstriction, platelet activation, and tissue-type plasminogen activator release in man.
Methods
Dorsal hand vein diameter was measured in 6 healthy volunteers before and after endothelial denudation. Forearm arterial blood flow, plasma fibrinolytic factors, and platelet activation were measured in 24 healthy volunteers during venous occlusion plethysmography. The effects of inhibition of prostacyclin, nitric oxide (NO), and endothelium-derived hyperpolarizing factor on PAR-1 responses were assessed during coadministration of aspirin, the “NO clamp” (L-NG-monomethyl arginine and sodium nitroprusside), and tetraethylammonium ion, respectively.
Results
Endothelial denudation did not affect PAR-1–evoked venoconstriction (SFLLRN; 0.05 to 15 nmol/min). Although aspirin had no effect, SFLLRN-induced vasodilation (5 to 50 nmol/min) was attenuated by the NO clamp (p < 0.0001) and tetraethylammonium ion (p < 0.05) and abolished by their combination (p < 0.01). The NO clamp augmented SFLLRN-induced tissue-type plasminogen activator and plasminogen activator inhibitor type 1 antigen (p < 0.0001) release, but tetraethylammonium ion and aspirin had no effect. SFLLRN-induced platelet activation was unaffected by NO or prostacyclin inhibition.
Conclusions
Acting via PAR-1, thrombin causes contrasting effects in the human vasculature and has a major interaction with the endothelium. This highlights the critical importance of endothelial function during acute arterial injury and intravascular thrombosis, as occurs in cardiovascular events including myocardial infarction and stroke.
Role of the Endothelium in the Vascular Effects of the Thrombin Receptor (Protease-Activated Receptor Type 1) in Humans
Thrombin is central to the pathophysiology of atherothrombosis and exerts its vascular effects via protease activated receptor type 1 (PAR-1). We report the contrasting role of the endothelium in PAR-1 activation in vivo in man, where it mediates arterial PAR-1–induced vasodilation and tissue plasminogen activator release but does not provide a major contribution to venous tone or plasminogen activator inhibitor type 1 release. Our findings provide evidence of a major interaction between the endothelium and thrombin in vivo. This highlights the critical importance of endothelial function during acute arterial injury and thrombosis, as occurs in acute coronary syndromes.
Ingibjörg J. Gu mundsdóttir, Ninian N. Lang, Nicholas A. Boon, Christopher A. Ludlam, David J. Webb, Keith A. Fox, David E. Newby
The purpose of this study was to determine the role of the endothelium in the vascular actions of protease-activated receptor type 1(PAR-1) activation in vivo in man.
Background
Thrombin is central to the pathophysiology of atherothrombosis. Its cellular actions are mediated via PAR-1. Protease-activated receptor type 1 activation causes arterial vasodilation, venoconstriction, platelet activation, and tissue-type plasminogen activator release in man.
Methods
Dorsal hand vein diameter was measured in 6 healthy volunteers before and after endothelial denudation. Forearm arterial blood flow, plasma fibrinolytic factors, and platelet activation were measured in 24 healthy volunteers during venous occlusion plethysmography. The effects of inhibition of prostacyclin, nitric oxide (NO), and endothelium-derived hyperpolarizing factor on PAR-1 responses were assessed during coadministration of aspirin, the “NO clamp” (L-NG-monomethyl arginine and sodium nitroprusside), and tetraethylammonium ion, respectively.
Results
Endothelial denudation did not affect PAR-1–evoked venoconstriction (SFLLRN; 0.05 to 15 nmol/min). Although aspirin had no effect, SFLLRN-induced vasodilation (5 to 50 nmol/min) was attenuated by the NO clamp (p < 0.0001) and tetraethylammonium ion (p < 0.05) and abolished by their combination (p < 0.01). The NO clamp augmented SFLLRN-induced tissue-type plasminogen activator and plasminogen activator inhibitor type 1 antigen (p < 0.0001) release, but tetraethylammonium ion and aspirin had no effect. SFLLRN-induced platelet activation was unaffected by NO or prostacyclin inhibition.
Conclusions
Acting via PAR-1, thrombin causes contrasting effects in the human vasculature and has a major interaction with the endothelium. This highlights the critical importance of endothelial function during acute arterial injury and intravascular thrombosis, as occurs in cardiovascular events including myocardial infarction and stroke.
Role of the Endothelium in the Vascular Effects of the Thrombin Receptor (Protease-Activated Receptor Type 1) in Humans
Thrombin is central to the pathophysiology of atherothrombosis and exerts its vascular effects via protease activated receptor type 1 (PAR-1). We report the contrasting role of the endothelium in PAR-1 activation in vivo in man, where it mediates arterial PAR-1–induced vasodilation and tissue plasminogen activator release but does not provide a major contribution to venous tone or plasminogen activator inhibitor type 1 release. Our findings provide evidence of a major interaction between the endothelium and thrombin in vivo. This highlights the critical importance of endothelial function during acute arterial injury and thrombosis, as occurs in acute coronary syndromes.
Ingibjörg J. Gu mundsdóttir, Ninian N. Lang, Nicholas A. Boon, Christopher A. Ludlam, David J. Webb, Keith A. Fox, David E. Newby
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