2-Aminochromones block human platelet aggregation by inhibiting cyclic AMP-dependent phosphodiesterase leading to reduced platelet phospholipase C activity

J Pharmacol Exp Ther. 1993 Apr;265(1):457-62.

Abstract

We examined a series of 2-aminochromone analogs typified by U-84569 [8-methyl-2-(4-morpholinyl)-7-(1-naphthylenylmethoxy)-4H-1- benzopyran-4-one] as potential antithrombotic agents. U-84569 proved to be a potent inhibitor of human platelet aggregation regardless of the agonist used. Subsequent experiments showed that U-84569 increased platelet cyclic AMP (cAMP) levels in intact cells, but U-84569 did not directly stimulate adenylate cyclase. Our experiments showed that U-84569 was a potent inhibitor of the low Km cAMP-dependent phosphodiesterase with an IC50 of 300 nM in platelet cytosol. Isobutylmethylxanthine had an IC50 of 10 microM in the same system. Although U-84569 elevated cAMP by inhibiting cAMP metabolism, we were interested in the mechanism by which cAMP blocked aggregation. Our first experiments showed that U-84569 concentration-dependently blocked agonist-stimulated, but not phorbol myristate acetate-dependent, phosphorylation of the 47 kDa protein kinase C substrate in platelets. These data suggested that U-84569 could interrupt receptor-mediated signal transduction. In support of this hypothesis, U-84569 proved to be a potent inhibitor of thrombin-stimulated inositol phosphate synthesis, diacylglycerol formation and Ca++ mobilization in intact cells. These data indicate that agonist-stimulated phospholipase C activity was reduced in U-84569-treated cells. There was no direct influence of U-84569 on either basal or thrombin-stimulated phospholipase C activity in broken cells, suggesting that U-84569 (by inhibiting phosphodiesterase and elevating cAMP), indirectly blocked receptor-mediated phospholipase C activation and aggregation in platelets. The 2-aminochromones represent a new class of potent antithrombotic agents.

MeSH terms

  • 1-Methyl-3-isobutylxanthine / pharmacology
  • 3',5'-Cyclic-AMP Phosphodiesterases / antagonists & inhibitors*
  • Blood Platelets / drug effects*
  • Blood Platelets / enzymology
  • Blood Platelets / metabolism
  • Calcium / metabolism
  • Chromones / chemistry
  • Chromones / pharmacology*
  • Cyclic AMP / metabolism
  • Humans
  • In Vitro Techniques
  • Molecular Structure
  • Morpholines / chemistry
  • Morpholines / pharmacology
  • Platelet Aggregation Inhibitors / pharmacology*
  • Type C Phospholipases / antagonists & inhibitors*

Substances

  • Chromones
  • Morpholines
  • Platelet Aggregation Inhibitors
  • U 84569
  • Cyclic AMP
  • Type C Phospholipases
  • 3',5'-Cyclic-AMP Phosphodiesterases
  • Calcium
  • 1-Methyl-3-isobutylxanthine