Rapid inhibition by sodium azide of the phosphoinositide-mediated calcium response to serotonin stimulation in human platelets: preservation in Alzheimer's disease

Sodium azide, a bacteriostatic preservative contained in commercially available laboratory reagents, influences the responses of human platelets via the cGMP/PKG/VASP pathway

OBJECTIVE

The bacteriostatic preservative sodium azide (NaN(3)) activates soluble guanylate cyclase (sGC) in vascular tissues, thus elevating cellular 3',5'-cyclic guanosine monophosphate (cGMP). Because the sGC/cGMP pathway is involved in the control of platelet aggregation, we investigated whether in human platelets NaN(3) influences the responses to agonists, cGMP levels and cGMP-regulated pathways.

DESIGN AND METHOD

Concentration- and time-dependent effects of NaN(3) (1-100 micromol/L; 5-60 min incubation) on ADP- and collagen-induced aggregation, NO synthase (NOS) activity, cGMP synthesis and vasodilator-stimulated phosphoprotein (VASP) phosphorylation at Ser239 were investigated in platelets from 21 healthy individuals.

RESULTS

NaN(3) exerted concentration- and time-dependent antiaggregatory effects starting from 1 micromol/L (IC(50) with 5-min incubation: 2.77+/-0.35 micromol/L with ADP and 4.64+/-0.48 micromol/L with collagen) and significantly increased intraplatelet cGMP levels and phosphorylation of VASP at Ser239 at 1-100 micromol/L; these effects were prevented by sGC inhibition, but not by NOS inhibition.

CONCLUSIONS

NaN(3) exerts antiaggregatory effects in human platelets via activation of the sGC/cGMP/VASP pathway. This biological effect must be considered when azide-containing reagents are used for in vitro studies on platelet function.

Effects of staurosporine, U-73122, wortmannin, 4-hydroxynonenal and sodium azide upon the release of secreted beta-amyloid precursor protein from human platelets in response to thrombin stimulation

In the present study, the release of secreted beta-amyloid precursor protein (AbetaPPs) in response to thrombin stimulation in platelets has been investigated. Incubation of platelets with thrombin produced a concentration-dependent release of AbetaPPs with a concomitant reduction in the AbetaPP remaining in the lysates. The response to thrombin was not affected by pretreatment for 15 min with the phospholipase C inhibitor U-73122, with the protein kinase C inhibitor staurosporine, or with hydrogen peroxide (which at the concentrations used affects the phosphoinositide signalling system in human platelets). In contrast, pretreatment with wortmannin and sodium azide reduced the responses to thrombin. These data would suggest that thrombin may cause the release of AbetaPPs from human platelets via an activation of a phospholipase C-independent pathway. Thrombin-stimulated AbetaPPs release was also reduced by 4-hydroxynonenal. This finding, if it is a phenomenon also found for CNS cells, could be of relevance to the pathogenesis of Alzheimer's disease, given that an accumulation of 4-hydroxynonenal is found in this disease.