Enzyme Immunoassays of Icosanoids Using Acetylcholinesterase

Abstract

In the early seventies, the need for the development of sensitive and quantitative assay methods for the analysis of the prostanoids became obvious. Two major complementary methods were selected by the scientists: gas-chromatography combined with mass spectrometry and radioimmunoassay (RIA) techniques. Both methods were improved throughout the years in regard of their specificity and sensitivity. The introduction of deuterated carriers for the first one and the use of low-bleeding fused glass capillary column with high efficiency allowed the detection of a few picograms. The RIA techniques improved their specificity after gradually avoiding the classical pitfalls that result from a mishandling of the assay. The gain in sensitivity was related to the increase of specific radioactivity of the tracers. From the early days of (³H) prostaglandins (PG) with 5–10 Ci/mmole (1) these tracers presently range from 50–200 Ci/mmole. In 1975, we introduced the 125_I labeling of these substances after coupling of their carboxyle to the amino group of a potential iodine receptor (e.g. histamine, tyramine or tyrosylmethyl ester) (2). Such an approach allowed us to reach for these tracers the theoretical specific radioactivity of the iodine, i.e. 2,000 Ci/mmole. The gain in sensitivity was x5–10 as compared with the corresponding tritiated systems; further these tracers provided the advantages intrinsic to the iodinated labels (absence of quenching, low cost, rapidity of counting...). More recently, non isotopic immunoassay methods for PG have emerged : they involve enzyme immunoassay (EIA) or chemiluminescence immunoassays. These methods should gain a widespread use due to the reinforcement of the regulation on the use of radioactive substances and because of environmental and pollution requirements. However, until now, these methods are rather disappointing because their sensitivity is still poor (3, 4) especially as compared to iodinated tracers.