The in vitro effects of niacin on platelet aggregation when added to aspirin in normal volunteers

Objectives:   A poor pharmacodynamic response to aspirin has been associated with adverse outcomes in patients with cardiovascular disease. This has inspired investigation of alternative and/or adjunct agents to intensify platelet inhibition. Niacin is a dyslipidemia agent used to raise high-density lipoprotein cholesterol. Niacin may also inhibit platelet thromboxane A2 production and directly inhibit platelet reactivity. Therefore, it may work synergistically with aspirin and could be used to improve the aspirin response. The objective of this study was to test whether niacin increases platelet inhibition when added to aspirin.

Methods:   Four collection tubes of blood were obtained from 5 healthy volunteers. Appropriate amounts of aspirin and/or niacin were added to blood samples and incubated for 30 minutes at room temperature: tube 1 contained 10mM aspirin, tube 2 contained 3mM niacin, tube 3 contained 10mM aspirin and 3mM niacin, tube 4 was control. Platelet aggregation was measured using whole blood impedance aggregometry (measured in ohms) with collagen and arachidonic acid (AA).  Data were analyzed with a paired t-test.

Results:

Collagen Induced Platelet Aggregation
Control (mean ± 1SD)	Aspirin	Niacin	Aspirin + Niacin
13.6 ± 3.1	5.4 ± 2.9	11.4 ± 3.1	4.5 ± 5.4
AA Induced Platelet Aggregation
Control	Aspirin	Niacin	Aspirin + Niacin
5.1 ± 3.7	0	2.7 ± 3.8	0

Aspirin significantly inhibited collagen induced platelet aggregation and completely inhibited AA induced platelet aggregation. Preincubation with niacin resulted in a significant inhibition of collagen-induced (p= 0.007) platelet aggregation, but not AA induced platelet aggregation (p= 0.108).  The addition of niacin to aspirin did not significantly inhibit collagen (p= 0.67) or AA induced platelet aggregation compared to aspirin alone.  

Conclusion:  Preliminary results show that niacin does not augment platelet inhibition when added to aspirin in normal volunteers. The study is ongoing. Final results will be presented during the poster symposium.