Figure 19.

Consumption of PAM constituents by tumor cells. PAM was generated by CAP treatment of medium for 1 min. PAM was preincubated (stored) either in the absence of cells (open circle) or in the presence of MKN-45 at standard density (closed circles) for 15 min. The preparations were then centrifuged to remove the cells or to perform mock treatment, and the supernatants were added at increasing concentrations to fresh MKN-45 cells. The percentages of apoptotic cells in this fresh group were determined after 3 h (A) and 5.5 h (B). The result shows that pretreatment of PAM with tumor cells substantially lowers the potential of PAM to induce apoptosis in the fresh cells. The most likely explanation is the consumption of H₂O₂ by membrane-associated catalase, and potentially also the oxidation of NO₂⁻ to ^●NO₂ by catalase.