Not all light transmission aggregation assays are created equal: qualitative differences between light transmission and 96-well plate aggregometry.

In this short article, submitted as part of the review on platelet function testing, we illustrate the quantitative and qualitative differences between classical light transmission aggregometry (LTA) and 96-well plate aggregometry. We show that responses to platelet agonists and antagonists differ depending upon the method of aggregation testing. For example, in 96-well aggregometry, responses to collagen are strongly inhibited by P2Y12 receptor antagonists while in LTA they are much less affected. Furthermore, we explore the importance of differences in the mechanical environment upon platelet aggregation. We emphasize that LTA and 96-well aggregometry are not interchangeable assays. These two assays are best used as complementary tests to explore platelet function in depth.

Cyclooxygenase-1, not cyclooxygenase-2, is responsible for physiological production of prostacyclin in the cardiovascular system.

Prostacyclin is an antithrombotic hormone produced by the endothelium, whose production is dependent on cyclooxygenase (COX) enzymes of which two isoforms exist. It is widely believed that COX-2 drives prostacyclin production and that this explains the cardiovascular toxicity associated with COX-2 inhibition, yet the evidence for this relies on indirect evidence from urinary metabolites. Here we have used a range of experimental approaches to explore which isoform drives the production of prostacyclin in vitro and in vivo. Our data show unequivocally that under physiological conditions it is COX-1 and not COX-2 that drives prostacyclin production in the cardiovascular system, and that urinary metabolites do not reflect prostacyclin production in the systemic circulation. With the idea that COX-2 in endothelium drives prostacyclin production in healthy individuals removed, we must seek new answers to why COX-2 inhibitors increase the risk of cardiovascular events to move forward with drug discovery and to enable more informed prescribing advice.