Inhibition of mural thrombus formation by novel nipecotoylpiperazine antiplatelet agents

1992 ALZA Distinguished Lecture: bioengineering and vascular biology

The vascular system is naturally dynamic; fluid mechanics and mass transfer are closely integrated with blood and vascular cell function. We are beginning to understand how local wall shear stress and strain modulate endothelial cell metabolism at the gene level. This knowledge may help explain the focal nature of many vascular pathologies, including atherosclerosis. Understanding mechanical control of gene regulation at the level of specific promoter elements and transcription factors involved will lead to development of novel constructs for localized delivery of specific gene products in regions of high or low shear stress or strain in the vascular system. In addition, recent research has shown how local fluid mechanics can alter receptor specificity in cell-to-cell and cell-to-matrix protein adhesion and aggregation. Knowledge of the specific molecular sequences involved in cell-to-cell recognition will allow development of targeted therapeutics, with applications in thrombosis, inflammation, cancer metastasis, and sickle-cell anemia. Bioengineers are uniquely qualified to be leaders in this field, because advances require a synthesis of cell and molecular biology with systems analysis, transport phenomena, and quantitative modeling. Rapid progress in tissue engineering applications will require this new kind of biomedical engineer, which represents both a challenge and an opportunity for our profession.

Enantioselective antiplatelet actions of nipecotamides

Two synthetic racemic nipecotamides, 1-decyl-3-(N,N- diethylcarbamoyl)piperidine hydrobromide (1) and alpha, alpha'-bis[3-(N-benzyl-N-methylcarbamoyl)piperidino]-p-xylene dihydrobromide (2) were resolved on a chiral alpha 1-acid glycoprotein semipreparative HPLC column. Thus, rac.1 was resolved into two enantiomers 1A-(+) and 1B-(-); rac.2 was separated into the optical antipodes 2A-(-) and 2C-(+), and the meso diastereomer 2B-(0). Also on a preparative scale, 97% pure 2C was obtained via diastereomeric salt formation using dibenzoyl-L-(-)-tartaric acid. The individual isomers were evaluated for their platelet aggregation inhibitory potency. In inhibiting ADP-induced aggregation of human platelets in vitro, 1B-(-) was 4 times more potent than its optical antipode 1A-(+), and 2C-(+) was 6 times as active as 2A-(-); the meso diastereomer 2B-(0) had intermediate activity. With collagen as the 1B-(-) was twice as active as 1A-(+), and 2C-(+), the most active compound in this series (IC50 = 0.96 microM), was 10 times more potent than its antipode 2A-(-). Again, the meso diastereomer 2B-(0) had intermediate activity. These results demonstrate the enantioselective antiplatelet actions of mono- and bis- nipecotamide derivatives.

Inhibition of platelet adhesion and thrombus formation on a collagen-coated surface by novel carbamoylpiperidine antiplatelet agents

The inhibitory effect of two novel antiplatelet agents, 1,10-bis[3-(N,N-diethylcarbamoyl)piperidino]decane dihydrobromide (G-110) and 1,6-bis[3-(N,N-diethylcarbamoyl)piperidino]hexane dihydrobromide (G-112), on platelet adhesion and subsequent aggregation on collagen-coated surface was evaluated under controlled flow. Glass coverslips coated with bovine fibrillar collagen type I were exposed to heparinized human whole blood that had been preincubated with either aqueous solutions of one of the two carbamoylpiperidine congeners or corresponding amounts (1.0-4.0 microliters/ml blood) of distilled water, at a wall shear rate of 1000 s-1, in a parallel-plate perfusion chamber. Epifluorescence video microscopy with a microphotometric measurement technique was used to visualize and quantify deposition of fluorescently-labeled platelets from flowing whole blood onto the collagen-coated surface. At concentrations of 100 and 200 microM, G-110 inhibited platelet accumulation by 30 +/- 9% (+/- S.E.) and 63 +/- 3% (+/- S.E.), respectively; while G-112 reduced platelet deposition by 19 +/- 3% (+/- S.E.) and 31 +/- 2% (+/- S.E.) at concentrations of 200 and 400 microM, respectively. Digital image processing techniques were used to analyze the dynamics of thrombus growth on the collagen-coated surfaces. It was found that the compounds reduced the rate of thrombus growth by impeding both surface coverage and the number of platelets per thrombus in a concentration-dependent manner. This study, together with others on related compounds GT-12, BPAT-117 and BPAT-143, corroborates the nature of pivotal features in the molecular structure of carbamoylpiperidine and nipecotoylpiperazine derivatives which enhance desirable antithrombotic effects, e.g. intramolecular distance between two tertiary amines (ring nitrogens) and levels of hydrophobicity.