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J J Cook

Publications and source records attributed to J J Cook.

At least 37 records · Page 2Linked to original sources
PubMed1996

Investigation of (Oxodioxolenyl)methyl carbamates as nonchiral bioreversible prodrug moieties for chiral amines.

The preparation of (oxodioxolenyl)methyl carbamates and their evaluation as novel nonchiral prodrug moieties for chiral primary and secondary amino functional drugs are described. 4-(Carbamoylmethyl)-2-oxo-1,3-dioxolene derivatives of 3,4-dimethoxyphenethylamine with 5-methyl, 5-phenyl, and 5-anisyl substitution (5a, 5b, and 5c) on the dioxolenone ring were prepared as model amine prodrugs by a one step process involving displacement of p-nitrophenol from appropriately substituted ring opening of these carbamates led to a cascade reaction resulting in the rapid and quantitative regeneration of the parent amine drug. Aryl substitution did not significantly alter the hydrolysis rates of these dioxolenone carbamates in buffers at pH 1 and 7.4 or in rat plasma, although the hydrolysis rates of 5-phenyl- (1b) and 5-anisyl- 4-methyl-1,3-dioxol-4-en-2-one (1c) in pH 7.4 phosphate buffer were 2-3 fold faster than that of the 5-methyl-substituted analog (1a). Application of this prodrug strategy to the chiral fibrinogen receptor antagonist L-734,217 resulted in a prodrug that gave quantitative reconversion in rat and dog plasma in vitro and oral bioavailability of 23 +/- 6% in dogs for the parent drug.

Amines↗
PubMed1996

Nonpeptide glycoprotein IIb/IIIa inhibitors. 8. Antiplatelet activity and oral antithrombotic efficacy of L-734,217.

The antiplatelet activity of L-734,217, a nonpeptide platelet GPIIb/IIIa antagonist, was evaluated in the rat, guinea pig and dog. IC50 for inhibition of in vitro platelet aggregation for these species (agonists: adenosine diphosphate, collagen) were rat, 838,000 and > 1,100,000 nM; guinea pig, 124 and 156 nM; dog, 42 and 50 nM. In an in vivo rat/in vitro dog platelet aggregation assay, effective antiaggregatory plasma concentrations of L-734,217 were achieved after 8.0 to 16.0 mg/kg p.o. vs. 0.3 to 1.0 mg/kg i.v. to rats. Delays in platelet-dependent hemostatic plug formation in severed mesenteric arteries were observed after 2.0 to 5.0 mg/kg p.o. vs. 0.1 to 0.2 mg/kg i.v. to guinea pigs. Dose-dependent inhibitions of ex vivo platelet aggregation after 0.3 to 3.0 mg/kg p.o. and 0.03 to 0.3 mg/kg i.v. L-734,217 to conscious dogs yielded estimates of 8 to 16% oral bioavailability. The antiplatelet activity of 3.0 mg/kg p.o. L-734,217 in dogs was unaffected by dosage form or food. In a conscious dog model of left circumflex coronary artery electrolytic lesion, 3.0 mg/kg p.o. L-734,217 q4 to 8 hr reduced thrombus mass, prevented occlusive coronary artery thrombosis and reduced or prevented myocardial infarction and ventricular ectopy. In anesthetized dogs, a dissociation between inhibition of ex vivo platelet aggregation and template bleeding time prolongation was observed with i.v. L-734,217. The results of the coadministration of heparin, aspirin and L-734,217 to anesthetized dogs suggested a synergistic effect on template bleeding time with no effect on plasma L-734,217 concentrations. These findings indicate L-734,217 to be an important lead structure for the development of therapeutically useful oral antiplatelet agents.

Animals↗
PubMed1995

Non-peptide fibrinogen receptor antagonists. 7. Design and synthesis of a potent, orally active fibrinogen receptor antagonist.

The design, synthesis, and pharmacological evaluation of L-734,217, a potent, low-molecular weight, orally active fibrinogen receptor antagonist, is reported. A strategy for producing low-molecular weight inhibitors from the peptide c-[(Ac)CRGDC] A, previously reported from these laboratories, is outlined. This strategy combines a retrodesign analysis of the conformationally defined cyclic peptide A with stereochemical information present in the arginine-glycine-aspartic acid (RGD) tripeptide sequence, culminating with the discovery of L-734,217. L-734,217 inhibited the aggregation of human, dog, and chimpanzee platelets at concentrations below 100 nM and was found to be > 15000-fold less effective at inhibiting the attachment of human umbilical vein endothelial cells to fibrinogen, fibronectin, and vitronectin than it was at inhibiting the aggregation of platelets. L-734,217 showed significant ex vivo antiplatelet activity following oral administration in dogs and chimpanzees at doses of 1.0 and 2.0 mg/kg, respectively, and has been selected as a clinical candidate for development as an antithrombotic agent.

Administration, Oral↗
PubMed1995

An antibody against the exosite of the cloned thrombin receptor inhibits experimental arterial thrombosis in the African green monkey.

BACKGROUND: Thrombin inhibitors have been shown to be efficacious in animal models of thrombosis and in initial human clinical trials. It is unknown if their efficacy is due to their prevention of thrombin-mediated fibrin formation or to an inhibitory effect on thrombin-stimulated platelet activation. Appropriate tools to address this question have not been available. Therefore, to evaluate the role of the platelet thrombin receptor in intravascular thrombus formation, a polyclonal antibody was raised against a peptide derived from the thrombin-binding exosite region of the cloned human thrombin receptor. This antibody serves as a selective inhibitor of the thrombin receptor for in vivo evaluation. METHODS AND RESULTS: The immune IgG (IgG 9600) inhibited thrombin-stimulated aggregation and secretion of human platelets. In contrast, it had no effect on platelet activation induced by other agonists including ADP, collagen, or the thrombin receptor-derived peptide SFLLR-NH2. IgG 9600 also inhibited thrombin-induced aggregation of African Green monkey (AGM) platelets. By Western blot analysis, the IgG identified a protein of approximately 64 kD in homogenates of both human and AGM platelets. The effect of thrombin receptor blockade by this antibody on arterial thrombosis was evaluated in an in vivo model of platelet-dependent cyclic flow reductions (CFRs) in the carotid artery of the AGM. The intravenous administration of IgG 9600 (10 mg/kg) abolished CFRs in three monkeys and reduced CFR frequency by 50% in a fourth monkey. Ex vivo platelet aggregation in response to up to 100 nmol/L thrombin was completely inhibited during the 120-minute postbolus observation period in all four animals. There was a twofold increase in bleeding time, which was not statistically different from baseline, and ex vivo clotting time (APTT) was not changed. The glycoprotein IIb/IIIa receptor antagonist MK-0852 and the thrombin inhibitor recombinant hirudin also demonstrated inhibitory effects on CFRs at doses that did not significantly prolong template bleeding time. Control IgG had no effect on CFRs, ex vivo platelet aggregation, bleeding time, or APTT. CONCLUSIONS: These results demonstrate that blockade of the platelet thrombin receptor can prevent arterial thrombosis in this animal model without significantly altering hemostatic parameters and suggest that the thrombin receptor is an attractive antithrombotic target.

Animals↗
PubMed1995

Nonpeptide glycoprotein IIb/IIIa inhibitors. 5. Antithrombotic effects of MK-0383.

The antiaggregatory and antithrombotic actions of MK-0383, a low molecular weight, nonpeptide antagonist of the platelet glycoprotein IIb/IIIa, were evaluated in a variety of canine models. Inhibition of ex vivo platelet aggregation responses to ADP and collagen were observed after the acute sequential i.v. administrations of 10 to 500 micrograms/kg or 360-min continuous i.v. infusions of 1 to 10 micrograms/kg/min of MK-0383. Hemostatic function normalized within 30 (platelet response to collagen, template bleeding times) to 90 min (platelet response and sensitivity to ADP) after the termination of 360-min i.v. MK-0383 infusions, suggesting no protracted, direct effects on platelet function. With acute sequential i.v. administrations of MK-0383, platelet response to ADP was abolished without significant extension of bleeding time. In a model of platelet-dependent cyclic flow reductions in injured, stenosed left circumflex coronary artery, the bolus i.v. administrations of 300 and 1000 micrograms/kg of MK-0383 totally abolished cyclic flow reductions for periods of 18 +/- 1 and 37 +/- 5 min, respectively. In a model of electrically induced left circumflex coronary artery occlusive thrombosis, 10 micrograms/kg/min i.v. of MK-0383 initiated 15 min before electrical injury prevented occlusive thrombosis in three of six preparations despite continued electrical stimulation of the vessel for 300 min, delayed occlusion in three of six preparations (160.3 +/- 5.5 min) and reduced thrombus mass (5.1 +/- 1.3 mg), compared to the development of occlusive thrombosis in six of six saline-treated preparations (50.5 +/- 8.7 min; 19.1 +/- 3.0 mg). When administered as an adjunct to thrombolytic agents in the presence of background heparin for lysis of electrically induced left circumflex coronary artery occlusive thrombus, 10 micrograms/kg/min i.v. of MK-0383 initiated 15 min before tissue-type plasminogen activator or streptokinase increased the incidence of (tissue-type plasminogen activator: eight of nine MK-0383 vs. three of eight saline; streptokinase: eight of eight MK-0383 vs. two of eight saline) and accelerated reperfusion, and reduced the incidence of acute thrombotic reocclusion during continued MK-0383 infusion. These findings indicate significant antithrombotic potential for MK-0383 alone or as an adjunct to thrombolytic therapy in the treatment of coronary artery ischemic syndromes.

Adenosine Diphosphate↗
PubMed1994

Species variability in platelet and other cellular responsiveness to thrombin receptor-derived peptides.

The aggregation of platelets from a variety of animal species in response to thrombin receptor-derived activating peptides was evaluated. A series of 14-(SFLLRNPNDKYEPF), 7-(SFLLRNP-NH2), 6-(SFLLRN-HN2) or 5-(SFLLR-NH2) residue peptides, the structures of which were based on the deduced amino acid sequence of the human thrombin receptor, promoted full aggregation of platelets in plasma from humans, African Green and Rhesus monkeys, baboons and guinea pigs at 4-50 microM depending on the peptide used. Platelets in plasma from rabbit, dog, pig, and hamster underwent a shape change but failed to aggregate in response to these peptides over 3 log units of peptide up to 800 microM, despite being fully responsive to human thrombin. However, because the receptor peptides induced shape change in the platelets from these non-aggregating species, they apparently can activate some of the intracellular signaling system(s) usually initiated by thrombin in these platelets. In contrast, platelets from rats did not undergo shape change or aggregate in response to the peptides. A 7-residue receptor-derived peptide based on the deduced amino acid sequence of the clone of the hamster thrombin receptor (SFFLRNP-N2) was nearly as efficacious as the corresponding human receptor-derived 7-residue peptide to promote aggregation of human platelets. However, the hamster peptide could not promote aggregation of hamster platelets in plasma at up to 800 microM peptide, while a shape change response was elicited. Platelets from rats, rabbits and pigs also did not aggregate in response to this peptide derived from the hamster thrombin receptor, but all species except the rat underwent a shape change.(ABSTRACT TRUNCATED AT 250 WORDS)

Amino Acid Sequence↗
PubMed1993

Mouse antithrombotic assay. Inhibition of platelet thromboembolism by disintegrins.

The mouse antithrombotic assay represents a model of fatal pulmonary thromboembolism induced by intravenous injection of collagen and epinephrine. Mice were protected by low doses of two disintegrins, albolabrin (10 micrograms/mouse) and eristostatin (0.6 micrograms/mouse), whereas high doses of a thrombin inhibitor and an inhibitor of von Willebrand Factor binding to glycoprotein Ib were not effective. Injection of collagen and epinephrine resulted in the drop of platelet count and accumulation of platelet aggregates in the lung that appears to be the immediate cause of death. Albolabrin or eristostatin administration did not prevent the decrease of platelet count. Injection of albolabrin resulted in the formation of smaller and reversible platelet aggregates in the lungs and decreased accumulation of 51Cr-labeled platelets in the lung suggesting that this disintegrin decreases formation of platelet aggregates in vivo. We compared the effects of albolabrin and erisostatin on platelet aggregation, tail bleeding time, and survival of challenged animals. Eristostatin was about 5 times more potent in inhibiting platelet aggregation in vitro than albolabrin and 38 times more potent than albolabrin in protecting animals from sudden death. Both disintegrins, at the same doses (0.6-5 micrograms/mouse), caused similar dose-dependent prolongation of the bleeding time; however, only eristostatin exerted a protective effect. In conclusion, a) the mouse antithrombotic assay is a suitable model to screen and to evaluate the potency of platelet fibrinogen receptor antagonists in vivo; b) the results of the antithrombotic assay correlate better with the inhibition of platelet aggregation in vitro than with the prolongation of bleeding time.

Amino Acid Chloromethyl Ketones↗
PubMed1992

Binding of glycoprotein IIIa-derived peptide 217-231 to fibrinogen and von Willebrand factors and its inhibition by platelet glycoprotein IIb/IIIa complex.

Based on previous reports in the literature and the high homology between platelet glycoprotein (GP) IIIa 217-231 and similar portions of other beta subunits of integrin receptors, we hypothesized that this region may participate in ligand binding. Using a polyclonal antibody against GPIIIa 217-231(YC), we tested the interaction of a synthetic peptide representing this region with fibrinogen (Fg), in the enzyme-linked immunosorbent assay (ELISA) system. Results show a calcium-independent, dose-related, direct interaction between GPIIIa 217-231(Y) and immobilized Fg. This peptide also bound to von Willebrand Factor (vWF) and fibronectin (Fn), but did not attach to a 50 kDa Fn fragment which is deficient in the cell attachment site. In addition, purified GPIIb/IIIa displaced GPIIIa 217-231(Y) from Fg and vWF. Binding of 125I-GPIIIa 217-231(Y) to Fg coated tubes was inhibited by soluble Fg and by the GPIIb/IIIa complex. We synthesized this peptide with several alterations; similar peptides with Pro-219 replaced with an Ala showed significantly reduced binding to Fg and vWF. The decreased binding of the peptides with Pro-219 substitutes suggests that the confirmation of GPIIIa 217-230 is important for its ability to bind to adhesive ligands. In conclusion, the amino acid residues between 217 and 231 of GPIIIa appear to be involved in ligand binding and Pro-219 probably plays a significant role in this interaction.

Amino Acid Sequence↗
PubMed1992

Age-related alterations in the arterial microvasculature of skeletal muscle.

This study investigated the possibility that the aging process results in alterations in the structure and/or functional reactivity of the microvessels that could contribute to increased resistance to blood flow in working skeletal muscle. Initially, latex casts were made of the cremaster muscle microvasculature in adult (12 mo) and senescent (24 mo) male Fischer 344 rats. Although the average diameter was not different between age groups, segmental length (distance between adjacent branches) increased significantly (3rd order) during aging. Additionally, in vivo experiments were performed to determine the response of the vessels to the topical application of norepinephrine and adenosine. There was no increase in vasoconstriction produced by norepinephrine; however, the vasodilation in response to adenosine declined dramatically (1st and 2nd order) with advancing age. It can be concluded that the increase in skeletal muscle vascular resistance during contraction in aged male rats could be explained by morphological changes and/or the diminished vasodilation elicited by adenosine.

Adenosine↗
PubMed1992

Platelet factor 4 efficiently reverses heparin anticoagulation in the rat without adverse effects of heparin-protamine complexes.

BACKGROUND: It has been observed that the reversal of heparin anticoagulation in humans by protamine sulfate (PS) results in various adverse reactions including leukopenia, thrombocytopenia, activation of complement, increased vascular permeability, systemic hypotension, pulmonary vasoconstriction, and pulmonary edema. The purpose of this study was to compare the efficacy and effects of native platelet factor 4 (PF4) and recombinant platelet factor 4 (rPF4) with those of PS in heparin neutralization in vivo, using a rat model. METHODS AND RESULTS: Sprague-Dawley rats were anesthetized with sodium pentobarbital, and the right femoral vein and carotid artery were cannulated. For determination of activated partial thromboplastin time, platelet count, white blood cell count, and complement titer, arterial blood samples were taken before and immediately after heparin (10 units/100 g) infusion and at several time points after the infusion of the neutralizing agent (PS, 0.1 mg/100 g; PF4, 0.5 mg/100 g). In separate groups of animals, mean arterial blood pressure was monitored throughout identical protocols and the lungs were prepared for histological examination. The anticoagulant activity of heparin was effectively reversed by all of the neutralizing agents (PS, PF4, and rPF4). Platelet count (48% of initial), white blood cell count (52% of initial), complement titer (60% of initial), and mean arterial pressure (20% decrease) decreased significantly in heparinized animals receiving PS but not in those receiving PF4 or rPF4. Lung interstitium appeared normal when heparin was followed by PF4; however, interstitial edema and hemorrhage were observed with heparin-PS. CONCLUSIONS: These results suggest that PF4 efficiently reverses heparin anticoagulation in the rat without the adverse effects of heparin-protamine complexes. Therefore, rPF4 may be an appropriate substitute for PS in patients undergoing cardiovascular surgery and other procedures that require heparin anticoagulation.

Animals↗
PubMed1991

Identification of the disulfide bond pattern in albolabrin, an RGD-containing peptide from the venom of Trimeresurus albolabris: significance for the expression of platelet aggregation inhibitory activity.

Albolabrin is a 73 amino acid peptide isolated from the venom of Trimeresurus albolabris. It contains an RGD sequence and 12 cysteines and is a potent inhibitor of both platelet aggregation and fibrinogen binding to the GPIIb/IIIa complex. This protein shows a high degree of analogy (primarily due to the alignment of all cysteines and the RGD) with a number of other viper venom proteins which inhibit cell adhesion and platelet aggregation and are referred to as disintegrins: rhodostomin, trigramin, flavoridin, applagin, elegantin, and batroxostatin. In this study, we found that the reduction and vinylpyridylethylation of albolabrin and flavoridin decreased their platelet aggregation inhibitory activity approximately 40-50 times. It can be postulated that the higher potency of native and reduced flavoridin as compared to albolabrin depends on the substitution of the Asp of albolabrin with a Phe at the C-terminal end of the RGD in flavoridin. The activity of a synthetic C-terminal peptide derived from flavoridin (residues 35-65) containing four cysteines was about 75 times lower than that of the original flavoridin. The substitution of a pair of cysteine residues with alanines in this peptide resulted in further loss of activity. In order to identify the disulfide bonds in albolabrin, the molecule was digested consecutively by trypsin and porcine pancreatic elastase. Peptides resulting from this digestion were isolated by reverse-phase HPLC and identified by amino acid composition and mass spectrometry.(ABSTRACT TRUNCATED AT 250 WORDS)

Adenosine Diphosphate↗
PubMed1991

Cyclosporin A augments human platelet sensitivity to aggregating agents by increasing fibrinogen receptor availability.

Clinical use of cyclosporin A (CsA) has been associated with platelet hypersensitivity and an increased incidence of thrombotic and vasoactive events. The purpose of this study was (1) to confirm that CsA enhances platelet sensitivity to the soluble agonists, adenosine diphosphate (ADP) and epinephrine (EPI), and (2) to determine if this enhancement is mediated by alteration in the availability of platelet surface fibrinogen receptors, a final mediator of platelet activation. Mean log dose of ADP required to achieve complete second-wave platelet aggregation in vitro decreased from 1.90 to 1.49 microM (n = 19, paired t test, P less than 0.05) and 2.86 to 2.11 microM (n = 16, P less than 0.05) following a 15-min and 3-hr incubation in the absence (saline) and presence of CsA (1000 ng/ml), respectively. At the threshold dose of ADP, concurrent thromboxane B2 levels at 15 min were 245 +/- 44 ng/ml (n = 12, saline) and 265 +/- 54 ng/ml (n = 9, CsA; P greater than 0.05). At 3 hr respective levels were 333 +/- 57 and 442 +/- 81 ng/ml (P greater than 0.05). Similar results were obtained with EPI. The number of fibrinogen binding sites in response to 50 microM ADP was determined in washed platelets in the absence and presence of CsA by radioligand binding. In 6 of 7 volunteers, CsA increased fibrinogen receptors from 26,635 +/- 4841 to 35,925 +/- 7290 sites/platelet (means +/- SEM; P less than 0.05). No change in receptor affinity was noted. In conclusion, cyclosporine does augment platelet reactivity.(ABSTRACT TRUNCATED AT 250 WORDS)

Adenosine Diphosphate↗
PubMed1991

Characterization of an antibody raised against reduced glycoprotein IIIa of human platelets.

A polyclonal antibody against reduced and vinylpyridylethylated human glycoprotein IIIa was raised in rabbits. Its reactivity with reduced GPIIIa was about 500 times higher than that of the antibody against native GPIIIa. The lowest amounts of purified reduced and native GPIIIa recognized by the antibody against reduced GPIIIa were 25 and 400 ng, respectively. The antibody did not recognize native GPIIIa (about 1-2 micrograms) in platelet extracts and chymotryptic degradation products of GPIIIa. It inhibited ADP-induced platelet aggregation but it did not inhibit fibrinogen binding to ADP-stimulated platelets. Our experiments suggest that the antigenicity of GPIIIa (beta 3 integrin) depends on the conformation of the molecule determined by numerous S-S bridges between cysteine residues.

Antibodies↗
PubMed1990

Microalbuminuria in adolescents with insulin-dependent diabetes mellitus.

Two hundred ten adolescents aged 12 to 18 years with insulin-dependent diabetes mellitus were screened for microalbuminuria (albumin excretion rate of 15 to 300 micrograms/min). Sixteen (7.6%) showed persistent microalbuminuria (mean albumin excretion rate of 70.9 +/- 56.2 micrograms/min). There were no significant differences between those with and without microalbuminuria with respect to age, sex, disease duration, and blood pressure over the previous 9 months and hemoglobin A1c level measured over the preceding 3 years. Within the group with microalbuminuria, there was no correlation between albumin excretion rate and blood pressure. However, there was a significant positive correlation between log albumin excretion rate and mean hemoglobin A1c values measured over the preceding 3 years. Our findings suggest that when microalbuminuria has developed, poorer metabolic control is associated with a higher albumin excretion rate. An actual rise in systemic blood pressure may not always precede the development of microalbuminuria.

Adolescent↗
PubMed1990

Inhibition of platelet adhesion to surfaces of extracorporeal circuits by disintegrins. RGD-containing peptides from viper venoms.

Previous studies indicate that exposure of fibrinogen receptors associated with glycoprotein IIb/IIIa complex contributes to platelet loss during cardiopulmonary bypass. Recently, we isolated a number of RGD (Arg-Gly-Asp)-containing, low molecular weight, cysteine-rich peptides from viper venoms. These peptides, which we propose to call "disintegrins," block platelet-fibrinogen interaction and platelet aggregation. We compared the effect of RGDS (Arg-Gly-Asp-Ser) and four disintegrins (echistatin, flavoridin, albolabrin, and bitistatin) on platelet behavior in a membrane oxygenator. During simulated extracorporeal circulation for 2 hours, platelet count decreased to about 30% of initial values. Addition of echistatin (60-200 nM), albolabrin (60-200 nM), bitistatin (60 nM), and flavoridin (45 nM) significantly inhibited platelet loss in the circuit. RGDS (33 microM) did not show any significant inhibitory effect. ADP-induced platelet aggregation was inhibited in samples of platelet-rich plasma taken from the circuits containing disintegrins. However, echistatin appeared to be a more potent inhibitor of platelet aggregation, whereas albolabrin and flavoridin interfered more selectively with platelet loss from the circuit. Echistatin prevented the accumulation of glycoprotein IIIa on the surface of the circuit. Echistatin (60-200 nM), flavoridin (45 nM), bitistatin (60 nM), and albolabrin (200 nM) significantly inhibited the loss of beta-thromboglobulin from platelets into circulating plasma. Electron microscopy studies demonstrated shape change but not degranulation in platelets circulating in the presence of 200 nM echistatin. On the other hand, this peptide (up to 1,000 nM) did not prevent loss of alpha granules and beta-thromboglobulin from thrombin-stimulated platelets, although it prevented their aggregation. In conclusion, disintegrins protect platelets in the circuit by preventing their adhesion to surfaces and, therefore, preventing fragmentation of adhered platelets under the shear stress of flowing blood. This study indicates that disintegrins may be potential candidates for platelet protection during cardiopulmonary bypass.

Amino Acid Sequence↗
PubMed1990

Disintegrins: a family of integrin inhibitory proteins from viper venoms.

Disintegrins represent a new class of low molecular weight, RGD-containing, cysteine-rich peptides isolated from the venom of various snakes. They interact with the beta 1 and beta 3 families of integrins and their potency is at least 500-2000 times higher than short RGDX peptides. Analysis of the amino acid sequences of 14 different disintegrins suggests that the RGD sequence, in the spatial configuration determined by the appropriate pairing of the cysteine residues, functions as a cell recognition site. However, certain nonconserved amino acids appear to modify the activity of disintegrins, their specificity for various receptors, and their ability to compete specifically with various ligands.

Amino Acid Sequence↗
PubMed1989

Inhibition of platelet hemostatic plug formation by trigramin, a novel RGD-peptide.

Trigramin, a cysteine rich, RGD (Arg-Gly-Asp)-containing peptide from Trimeresurus gramineus snake venom (Mr 7,500) has been previously reported to inhibit fibrinogen binding to ADP-activated platelets and platelet aggregation (disassociation constant 10(-8) M). The present study demonstrates that the infusion of trigramin (17-212 micrograms/100 g body wt) significantly prolonged the bleeding time of severed mesenteric arteries in hamsters (anesthetized with 65 mg/kg pentobarbital), whereas the infusion of RGDS (Arg-Gly-Asp-Ser, 0.45-1.0 mg/100 g body wt) failed to increase the bleeding time in this model. The bleeding time immediately returned to normal after cessation of trigramin infusion. The pattern of the disappearance of 125I-labeled trigramin from the circulation fit a two-compartment model with the half-life for the fast component between 0.7 and 2.0 min and with the half-life for the slow component between 31 and 105 min. It appeared that the kidney and liver are major routes of elimination of trigramin from the circulation. The ability of trigramin to prolong bleeding time, as well as its rapid disappearance from the circulation, indicates that this peptide may be a useful compound to transiently prevent the ability of platelets to form thromboemboli without impairing their long-term hemostatic function.

Animals↗