A new microimmunoassay for apolipoprotein B in arterial tissue. Studies on peroperative human biopsies

An immuno-radiometric assay (IRMA) for determination of apolipoprotein B (apo B) in arterial intima is described. Intima was dissected from aortic biopsies obtained peroperatively. The tissue was first incubated in buffer to release a 'buffer extractable' pool of apo B. A 'tightly bound' fraction was then released by incubating the tissue in collagenase for 6 h. 'Buffer extractable' and 'tightly bound' apo B were then determined with IRMA. The IRMA is an immunological method based on the primary reaction between antigen and antibody, and it was found to be reproducible and sensitive enough for determination of apo B even in small tissue samples. In aortic intimal specimens without obvious atherosclerotic lesions, total apo B content was found to be 223 +/- 213.2 micrograms/g wet weight or 30 +/- 32.8 micrograms/mm2 intimal area (mean +/- SD). The majority of the biopsies contained 100-300 micrograms/g wet weight of apo B. This concentration corresponds to approximately 25% of the serum concentration. Duplicate tissue samples were obtained from 26 patients. The 2 samples were analysed separately and there was a highly significant correlation between apo B content in the 2 biopsies (rs = +0.89). About 20% of the tissue apo B was buffer extractable, and there was a strong positive correlation between buffer extractable and tightly bound apo B (rs = +0.76). The total amount of apo B found in non-atherosclerotic intima, is considerably lower than in previous reports. This difference might at least partly be due to different quantitation techniques but may also be due to differences between autopsy material and peroperatively obtained biopsies. The lower level reported here is more in agreement with studies on the kinetics of apo B into the arterial wall, as well as reported levels of apo B in interstitial fluid and in lymph.