Apolipoprotein H, a new mediator in the inflammatory changes ensuing in jeopardised human myocardium

Aim-To investigate the presence of membrane ((flip flop)) in ischaemic huma n myocardium, we assessed depositions of apolipoprotein H (apoH; beta2-glyc oprotein 1) in ischaemic myocardium. Serum protein apoH can bind to negativ ely charged phospholipids and can also inhibit blood coagulation in vitro. We hypothesised that, because of its affinity for phosphatidyl serine, apoH might bind to "flip flopped" cells and would therefore be useful as a mark er for membrane flip flop in vivo. Methods-Myocardial tissue specimens were obtained from patients who had die d within 14 days of acute myocardial infarction. Results-Immunohistochemical analysis of these specimens revealed that apoH was selectively deposited in infarcted areas of human myocardium of at leas t one day's duration. Depositions of apoH were not found in non-ischaemic m yocardial tissue samples obtained from patients who died from other (extrac ardial) causes. In vitro experiments with the human leukaemia T cell line J urkat, subjected to apoptosis by etoposide, showed that apoH was bound to t he membrane of apoptotic cells. However, these experiments also indicated t hat flip flop itself is not sufficient for apoH binding. In addition, Jurka t cells that bound apoH were positive for activated complement complexes, a s was also found in the human heart. Conclusions-These results suggest that apoH is involved in the inflammatory processes that occur in ischaemic myocardium.