Gene/Protein Disease Symptom Drug Enzyme Compound
Pivot Concepts:   Target Concepts:
Query: EC:3.1.4.3 (phospholipase C)
 18,461 document(s) hit in 31,850,051 MEDLINE articles (0.00 seconds)

We have shown earlier that phospholipase C (PLC) from Clostridium perfringens causes platelet activation possibly by inducing turnover of phosphoinositides and phosphorylation of a 47,000 Dalton protein (P47). Moreover, only 15 microM and 11 microM flurazepam inhibits PLC-induced platelet aggregation and serotonin secretion by 50% respectively. This study was conducted to better understand the mechanism of platelet activation by PLC and its inhibition by flurazepam. Incubation of (14C)-arachidonic acid labelled platelets with PLC produced diacylglycerol in a time- and concentration-dependent manner. Flurazepam did not inhibit diacylglycerol production by PLC. Paranitrophenolphosphorylcholine and prostaglandin E1 inhibited diacylglycerol production by 75% and 20% respectively. In a platelet-free system PLC hydrolyzed 14C-choline-phosphatidylcholine (14C-PC) in a time- and calcium ions-dependent manner. Flurazepam had no effect on PLC-induced hydrolysis of 14C-PC. Platelet cytosolic fraction (PCF), containing phosphatidylinositol-specific PLC (PI-PLC), hydrolyzed (3H-inositol)-phosphatidylinositol (3H-PI) in a platelet-free system. Flurazepam did not inhibit hydrolysis of 3H-PI by PCF. Phospholipase C caused phosphorylation of P47 in 32P-labelled platelets. Flurazepam did not block phosphorylation of P47 in the first three minutes and had very little inhibitory effect by five minutes. However, flurazepam completely blocked phosphorylation of P47 by seven minutes. Platelet aggregation induced by ionomycin, a calcium ionophore, was completely inhibited by 100 microM flurazepam whereas platelet aggregation induced by 12-O-Tetradecanoylphorbol-13-acetate (TPA), which mimics the action of diacylglycerol, was partially inhibited by 300 microM flurazepam. These findings suggest that PLC induced platelet activation depends, at least in part, on diacylglycerol production and phosphorylation of P47. These data also suggest that flurazepam does not inhibit PLC-induced platelet activation by inhibiting: (a) the production of diacylglycerol from phosphatidylcholine; and (b) the action of PI-PLC on phosphatidylinositol. The ability of flurazepam to inhibit ionomycin-induced platelet aggregation indicates that flurazepam is able to block platelet activation by inhibiting the increase in free cytosolic calcium ions in platelets or by inhibiting a step subsequent to the rise in intraplatelet calcium ions.
 ...
PMID:Human platelet activation by bacterial phospholipase C: mechanism of inhibition by flurazepam. 289 97

These studies were undertaken to examine the effects and the mechanism of action of flurazepam and diazepam on human platelet activation. One minute preincubation with flurazepam (3-300 microM) or diazepam (3-300 microM) inhibited platelet aggregation, serotonin secretion and prostaglandin synthesis induced by ADP (1-5 microM), epinephrine (1-5 microM), and arachidonic acid (600-1000 microM). However, 357% higher concentration of diazepam (265 microM) as compared to flurazepam (58 microM), was required to inhibit arachidonic acid induced production of malondialdehyde (MDA) by 50%. In addition, flurazepam and not diazepam inhibited the release of arachidonic acid from platelet phospholipids in a concentration dependent manner. In other experiments flurazepam but not diazepam also blocked aggregation and secretion induced by U46619 (2 microM), a stable analog of prostaglandin H2. Platelet aggregation and serotonin secretion induced by collagen (40-300 micrograms/ml) was inhibited by flurazepam with an IC-50 of 153 microM and 136 microM respectively, whereas higher than 300 microM diazepam was required to inhibit collagen-induced aggregation and secretion by 50%. Flurazepam and diazepam both exhibited their most potent antiplatelet effects against phospholipase C-induced aggregation which is mediated by prostaglandin-independent mechanisms. Only 15 microM and 11 microM flurazepam and 31 microM and 27 microM diazepam were needed to inhibit PLC-induced aggregation and secretion of serotonin by 50% respectively. Effects of these benzodiazepines on platelet cyclic AMP and cyclic GMP were also examined. Neither flurazepam nor diazepam caused any significant change in cyclic AMP or cyclic GMP levels in platelets. These findings suggest that: (a) flurazepam, as compared to diazepam, is 106% - 357% more effective in inhibiting platelet aggregation and serotonin secretion induced by arachidonic acid, collagen and phospholipase C; (b) flurazepam inhibits platelet activation by inhibiting the release of arachidonic acid, its conversion into prostaglandins and by blocking the action of prostaglandins on platelets; (c) diazepam does not inhibit thrombin-induced release of arachidonic acid, conversion of exogenously added arachidonic acid into MDA, or the action of prostaglandins; (d) both flurazepam and diazepam inhibit PLC-mediated activation of platelets; and (e) neither diazepam nor flurazepam achieve their antiplatelet actions by affecting platelet cyclic nucleotide levels.
 ...
PMID:Benzodiazepines inhibit human platelet activation: comparison of the mechanism of antiplatelet actions of flurazepam and diazepam. 299 62