Heparin can liberate high molecular weight DNA from secondary necrotic cells

Abstract

The border-line between necrosis and apoptosis is not sharp, but the distinction between types of cell death is important, because necrosis may lead to local inflammation, while apoptosis usually does not. In certain autoimmune disorders, the inhibition of cell death is crucial, since macromolecules released from dead cells, may accelerate the autoimmune processes. In our study we used various cell death inhibitors to block N-(4-hydroxyphenil)-retinamide induced cell death in BL41 and U937 cell lines. VD-fmk, a general caspase inhibitor, inhibited DNA fragmentation induced by N-(4-hydroxyphenil)-retinamide, but not propidium-iodide uptake and necrosis. Interestingly heparin, a serine-protease inhibitor, lowered the propidium-iodide fluorescence of the dead cell population and increased the subG1 population measured by flow cytometry. We investigated the cause of these changes and found that heparin did not actually increase DNA fragmentation, it merely liberated high molecular weight DNA fragments from the dead cells. The exact mechanism is unclear, but we believe, that during secondary necrosis, heparin can enter the cells, bind ribonucleoproteins, and pull them out of the cells with the attached DNA where they are sensitive to enzymatic degradation. Our results suggest that heparin treatment may help the clearance of cell debris and decreases the immunogenity of secondary necrotic cells.