Correlation of tumor necrosis factor α (TNFα) with high Caspase 3-like activity in myelodysplastic syndromes

Increased intramedullary apoptotic death of hematopoietic cells is thought to contribute to the ineffective hematopoiesis in myelodysplastic syndromes (MDS). Furthermore, high amounts of tumor necrosis factor α (TNFα) have previously been correlated with apoptosis in MDS marrows. The present studies were undertaken to examine the status of two key downstream effectors of TNFα signaling, i.e. Caspase 1 and Caspase 3 enzymes, using a fluorometric assay in the bone marrow aspirate mononuclear cells (BMMNC) in relation to apoptotic DNA fragmentation detected by in situ end-labeling (ISEL) of DNA and with localization of TNFα in the corresponding biopsies from 14 MDS patients. Both Caspase 1 and 3 were detectable in freshly harvested BMMNC, albeit median Caspase 3 levels (47.5 units/mg protein) being almost 10 times higher than Caspase 1 (4.0 units/mg protein). Upon short-term culture for 4 h in a serum-supplemented medium in vitro a significant increase was seen in Caspase 3 activity (58.8±13.9 at 0 h vs. 177.8±55.2 units/mg protein at 4 h, n=14, P=0.017) and in percent cells labeled by ISEL (apoptotic index or AI%: 0.76%±0.25% vs. 3.99%±1.1%, n=14, P=0.004, respectively). Caspase 1 activity increased after 15 min in culture. Interestingly, TNFα levels measured by immunohistochemistry correlated with the net increase in Caspase 3 activity after 4 h (ρ=0.517, n=13, P=0.07) and the starting levels of Caspase 1 at 0 h correlated with the Caspase 3 levels attained at 4 h (ρ=0.593, n=13, P=0.033). Additionally when TNFα-positive bone marrows (8/14) were compared with the negative marrows (6/14) the Caspase 3 levels were significantly higher in the TNFα-positive marrows (189.6±66.2 vs. 25.0±14.6 units/mg protein, respectively, P=0.043). The increase in AI%, though not statistically significant, was also higher in the TNFα-positive marrows. Finally in HL60 cells the effects of different Caspase inhibitors and pentoxifylline (PTX) (interferes with lipid signaling of cytokines) on TNFα-induced apoptosis were evaluated. TNFα treatment significantly increased AI% (P<0.003) as compared to the untreated controls. A co-treatment with three Caspase inhibitors, zVAD.FMK (inhibitor of Caspases 1 and 3, 10 μM/l), Ac.YVAD.FMK (Caspase 1 inhibitor, 1 μM/l), Ac.DEVD.FMK (Caspase 3 inhibitor, 10 μM/l) as well as PTX (250 μM/l) significantly curtailed the AI% induced by TNFα The present studies thus identify the downstream effectors of TNFα-inducible apoptosis in MDS and so also the suppressors of TNFα apoptotic signaling. These results may have significant clinical implications in the therapy of MDS in the future.