Heparin induces apoptosis in lymphocytes from B-cell chronic lymphocytic leukemia

It has been shown that glycosaminoglycans play a role in the regulation of immune response. In particular, heparin exerts an antiproliferative and apoptotic action in different cellular systems. In this study we evaluate whether heparin can also induce a naturally occurring programmed cell death in lymphocytes from B-chronic lymphocytic leukemia (B-CLL), a neoplastic lineage where apoptosis is blocked by the expression of the proto-oncogene bcl-2. Peripheral blood lymphocytes (PBL) from 7 cases of B-CLL patients in different stages were cultured with three different heparin sodium concentrations for 4 days. Apoptosis was evaluated by agarose gel electrophoresis and by cytofluorimetric analysis. Bcl-2 expression was tested by flow cytometric analysis and immunohistochemistry on cytospin preparations. Agarose gel electrophoresis showed the characteristic DNA fragmentation pattern of apoptosis in all the cases of B-CLL stage III and IV after heparin incubation. DNA from normal and neoplastic lymphocytes cultured without heparin did not undergo spontaneous apoptosis. Cytofluorimetric analysis confirmed the agarose gel pattern and found a level of apoptosis over 50% after culture of neoplastic PBL with heparin. In these cases bcl-2 expression was found to be significantly reduced after heparin incubation when comparing to bcl-2 level before incubation. Our data adds further evidence regarding the potential role of heparin in oncogene inhibition and in apoptosis induction. In particular, the induction of apoptosis in neoplastic lymphocytes by heparin may have a role in the complicated field of interactions between the immune system and the blood vessels by glycosaminoglycans.