The effect of aspirin on circulating netrin-1 levels in humans is dependent on the inflammatory status of the vascular endothelium

In atherosclerotic animal models, the cyclo-oxygenase (COX)-inhibitor aspirin counteracts downregulation of endothelial-derived netrin-1, thus reducing arterial inflammation. We here explored the effect of aspirin on netrin-1 in healthy subjects undergoing influenza immunisation, which is an established experimental model of inflammation-related endothelial dysfunction. Our data showed that netrin-1 undergoes reduction (-29.25% from baseline; p=0.0017) in the presence of endothelial activation (VCAM-1 rose by 9.98% 2-days post-vaccination; p=0.0022). Aspirin counteracted vaccine-induced endothelial activation and reduction of netrin-1 in a dose-dependent manner (-3.06% and -17.03% from baseline at a dose of 300mg and 75mg respectively; p=0.0465 and p>0.05 vs untreated). Clopidogrel, which was used as a comparator due to its similar anti-platelet activity, also reduced endothelial activation but, unlike aspirin, enhanced netrin-1 levels (+20.96% from baseline; p=0.0033 vs untreated). A correlation analysis incorporating cytokines, hs-CRP, VCAM-1, TXB(2) and PGE(2), showed that changes in netrin-1 were directly related to PGE(2) variations only (r=0.6103; p=0.0002). In a separate population of 40 healthy unimmunised volunteers, 28-day treatment with aspirin 300mg reduced netrin-1 (-18.76% from baseline; p=0.0012) without affecting endothelial markers or hs-CRP; as expected, aspirin suppressed TXB(2) and PGE(2). Netrin-1 and PGE(2) levels were directly related (r=0.358; p=0.0015), but other parameters including TXB(2), hs-CRP and endothelial markers, were not. In conclusion, aspirin counteracts downregulation of netrin-1 following endothelial dysfunction due to its anti-inflammatory effect on the activated endothelium. However, inhibition of COX-dependent prostanoids negatively modulates netrin-1 synthesis in healthy subjects, and this could give rise to aspirin-dependent reduction in netrin-1 under steady state conditions.