Cytotoxic effect of hemin and protoporphyrin on chronic lymphocytic leukemia lymphocytes

Hemin and protoporphyrin exerted a cytotoxic effect on lymphocytes from 24 patients with chronic lymphocytic leukemia (CLL). The porphyrins inhibited protein and RNA synthesis in a dose dependent pattern. Exposure of leukemic cells to 15 μM hemin for 10 min reduced leucine incorporation to less than 20%, and 78% of the cells were freely permeable to trypan blue. Hemin at 0.17 μM had to be bound to 10⁶ cells in the dark to produce this killing effect. On the other hand, the control lymphocytes from 20 healthy subjects were relatively resistant to the hemin effect, and cell damage was reversible. Fetal calf serum (FCS) protected most leukemic lymphocytes from porphyrin toxicity. The combination of human hemoglobin with free protoporphyrin showed a synergistic toxicity, and this combination was the most potent inhibitor of protein synthesis in the presence of serum. ⁵⁵Fe-hemin was preferentially bound to leukemic lymphocytes, and the binding site of protoporphyrin was observed to be on the cell surface membrane. The hemin quenching effect of diphenyl hexatriene (DPH) stained cell fluorescence indicated that hemin was apparently bound to the lipid layer of the outer membrane. Scanning electron microscopy (SEM) of hemin treated cells revealed an initial development of membranal blebs, followed by total destruction of the cell surface membrane. Transmission electron microscopy (TEM) of the treated cells showed a profound damage in the cytoplasma and nucleus. Control lymphocytes treated by hemin appeared relatively undamaged and free of membranal blebs.