In vitro induction of apoptosis in U937 cells by perillyl alcohol with sensitization by pentoxifylline: increased BCL-2 and BAX protein expression.

BACKGROUND: Chemotherapy is effective against a wide variety of tumor cells, although its use is limited by side effects. In vitro experiments and phase I and II trials have shown that phytochemicals such as perillyl alcohol (P-OH) have antitumor effects. Pentoxifylline (PTX), a synthetic methylxanthine used mainly to treat pathologies associated with hematological diseases, sensitizes tumor cells to chemotherapy. The aim of this study was to determine whether PTX amplifies the antitumor effects of P-OH in U937 human myelomonocytic leukemia cells. METHODS: Apoptosis was measured by the loss of mitochondrial membrane potential determined by flow cytometry using dihexyloxacarbocyanine iodide (DiOC6) and propidium iodide. Bcl-2 and Bax protein expression was also assessed by Western blot analysis. RESULTS: P-OH and PTX induced loss of the mitochondrial membrane potential in U937 cells in vitro. Culturing the cells in the presence of both compounds caused a significant increase (p < 0.001) in apoptosis and expression of anti-apoptotic Bcl-2 and pro-apoptotic Bax proteins. However, despite their coexistence, Bax expression prevailed in our experiments. These data suggest that the effects of PTX might be attributable to changes in the mitochondrial membrane potential. CONCLUSION: PTX sensitizes tumor cells to the anti-neoplastic action of P-OH. These observations may have clinical relevance in the treatment of cancer patients.

In vivo modification of adriamycin-induced apoptosis in L-5178Y lymphoma cell-bearing mice by (+)-alpha-tocopherol and superoxide dismutase.

Apoptosis was followed in L5178Y lymphoma cell-bearing mice at different times after intraperitoneal injections of adriamycin (ADM). Apoptosis was determined morphologically and confirmed by DNA laddering on electrophoresis. Apoptosis was observed 36h after injection of 5mg/kg ADM (apoptotic cell index 64.2+/-5.6 vs. 1.5+/-2.1 from the untreated group) and confirmed by DNA electrophoresis. However, when the animals were pretreated with (+)-alpha-tocopherol acid succinate or superoxide dismutase before ADM administration apoptotic index significantly diminished (P<0.05) and the DNA electrophoresis did not show fragmentations. We conclude that in ADM-treated mice, tumour cell death occurs in two ways: first by necrosis, then later by apoptosis. These observations are likely to be associated with or caused by the generation of reactive oxygen species.

In vivo inhibition by antioxidants of adriamycin-induced apoptosis in murine peritoneal macrophages.

Adriamycin (ADM) is an oncostatic of the anthracycline family with confirmed experimental and clinical efficiency. This antitumoral drug has been reported to stimulate macrophage activity and is able to induce apoptosis (AP) in some tumour cells. The objective of the present work was to investigate if in vivo administration of ADM to mice induces AP in their peritoneal macrophages (PM). AP was expressed by the apoptotic index (AI) of peritoneal macrophages observed under fluorescence microscope after ethidium bromide and acridine orange staining and confirmed by detection of the ladder pattern on DNA electrophoresis, indicates DNA fragmentation in 80-120 bp characteristic of apoptotic state. 24 hours after i.p. ADM administration, AP was observed in PM. The effect was best visible after the injection of 5 mg/kg ADM. (Al: 76.3+/-8.9 vs untreated control group AI: 2.8+/-1.1). In the ADM treated group a DNA ladder electrophoretic pattern was observed while DNA from normal PM was genomic. Since ADM toxicity has been attributed to reactive oxygen species generation, we investigated its possible participation in AP induction by pretreating mice with antioxidants: (+)-alpha-tocopherol acid succinate (30 IU/mouse per os) for 3 days before ADM administration with E. coli lipopolysacharide (0.15 microg/mouse i.p.) 24 hours before ADM administration or with superoxide dismutase (10,000 IU/mouse i.p.) 1 hour before ADM administration. AI was significantly decreased, with values close to those of the untreated control group (AI: 15+/-5.7, 9.6+/-8.0 and 32.9+/-6.9, respectively). Antioxidants given before ADM treatment significantly increased the live cell index (p < or = 0.001) in PM the groups while inactivated antioxidants no longer protect PM against the ADM AP induction. DNA analysis confirmed the effect: in the untreated control and in the antioxidant protected groups DNA was genomic while in either ADM or inactivated-antioxidants + ADM treated groups, DNA presented the ladder pattern. AP can thus be induced in PM by ADM and inhibited by antioxidants. These observations may have clinical applications.