Inhibition of PAF-induced human platelet aggregation by antithrombotic nipecotomides.
Nipecotamides (piperidine-3-carboxamides) are potent inhibitors of platelet aggregation induced by a variety of agonists in vitro and in vivo. The inhibitory effects of six structural types of nipecotamides on human platelet aggregation induced by platelet-activating factor (PAF) in vitro, are studied. Evaluation of 15 racemates and stereoisomers of two nipecotamides showed that bis-nipecotoyl alkanes were more active than their mono congeners. Mono- and bis-nipecotoyl decanes were more potent than the corresponding hexanes. Lipophilicity was found to play a significant role in the antiplatelet activity of these compounds. The stereoselectivity in the PAF-antagonist potential of nipecotamides was less pronounced than that resulting from their action on ADP- or collagen-induced aggregation. Oxidation of the two benzylic carbon atoms of alpha, alpha'-bis[3-(N,N-diethylcarbamoyl)piperidino]-p-xylene.2HBr (A-1) to form 1,4-bis[3-N,N-diethylcarbamoyl) piperidino]benzenedicarboxamide (A-40K), which has a second set of carbonyl oxygens but lacks basic N atoms, resulted in a remarkable loss of ADP-antagonist potency while retaining PAF-antagonist activity. It is suggested that in addition to their membrane effects, nipecotamides act at other sites, including the PAF receptor. Double reciprocal plots of PAF binding to gel-filtered platelets (GFP) in the presence and absence of a typical nipecotamide (A-1C) were indicative of competitive inhibition (Ki = 19.28 microM). Scatchard analysis of 3H-PAF binding to GFP suggested the presence of high, intermediate (I) and low affinity binding sites, of which the I site gave a KD/app of 0.332 nM with an estimated 564 sites/platelet. Key interactions of nipecotamides with the PAF receptor appear to be the following (i) electrostatic interactions of the two amide oxygens with a primary set of electropositive areas spaced at 5-7 A, (ii) in the case of appropriate compounds, electrostatic interactions of the two amide oxygens spaced at 10-12 A with corresponding secondary receptor sites carrying positive electrostatic potential, (iii) a hydrophobic moiety fitting into a hydrophobic pocket in the receptor, and (iv) the cationic piperidine N+ (at pH 7.4) interacting with a counterion, probably aspartic acid.
Herron
D
D
Department of Pharmaceutical Sciences, College of Pharmacy, University of Tennessee, Memphis 38163, USA.
Dillingham
E O
EO
Lyman
B A
BA
Zheng
X
X
Bond
S E
SE
Salgia
S R
SR
Gollamudi
R
R
D000244:Adenosine Diphosphate / Q000494:pharmacology; D000328:Adult; D001667:Binding, Competitive; D001792:Blood Platelets / Q000187:drug effects / Q000378:metabolism; D002850:Chromatography, Gel; D003094:Collagen / Q000494:pharmacology; D005260:Female; D006801:Humans; D008297:Male; D009557:Nipecotic Acids / Q000737:chemistry / Q000494:pharmacology*; D010972:Platelet Activating Factor / Q000378:metabolism / Q000494:pharmacology*; D010974:Platelet Aggregation; D010975:Platelet Aggregation Inhibitors / Q000494:pharmacology*; D013237:Stereoisomerism
D009557:Nipecotic Acids; D010972:Platelet Activating Factor; D010975:Platelet Aggregation Inhibitors; C043099:alpha, alpha'-bis(3-(N,N-diethylcarbamoyl)piperidino)-4-xylene; C077875:alpha,alpha'-bis(3-(N-benzyl-N-methylcarbamoyl)piperidinol)-4-xylene; D000244:Adenosine Diphosphate; D003094:Collagen