Interactions of Prostaglandin H2 and Thromboxane A2 with Human Serum Albumin

Abstract

The present report describes the interactions of human plasma proteins with the unstable endoperoxide, prostaglandin H₂ and thromboxane A₂, generated by incubation of platelets with prostaglandin H₂ or arachidonic acid. It was found that both compounds reacted very rapidly with plasma proteins to form covalently bound derivatives. The major reacting plasma protein was human serum albumin. Depending on conditions, 20–40% of added prostaglandin H₂ and 50–80% of generated thromboxane were bound to proteins. This reaction of both prostaglandin H₂ and thromboxane A₂ prevents their detection by classical analytical methods. The protein binding of thromboxane was more pH-sensitive than the binding of prostaglandin H₂. The reactions cause reduced levels of both endoperoxide and thromboxane B₂ in suspensions of washed platelets using human serum albumin as compared to buffer. It was also shown that the half-life of prostaglandin H₂ was considerably reduced in the presence of albumin.