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We examined the involvement of apoptosis with myelodysplastic syndrome (MDS) accompanied by peripheral cytopenias despite normo-hypercellular bone marrow.Bone marrow smears from 31 patients with MDS-refractory anemia (RA) and five normal controls were stained using the in situ end labeling (ISEL) method. Next, the inhibitory effects of a caspase-3 inhibitor, matrix metalloproteinase inhibitor (MMPI), anti-tumor necrosis factor (TNF)-α or anti-Fas antibody upon the apoptosis induction in overnight cultures of bone marrow cells from the patients were examined. Further, TNF-α, transforming growth factor (TGF)-β and soluble Fas ligand (sFasL) concentrations in culture supernatants of the cells were assessed by enzyme-linked immunosorbent assay (ELISA).The incidence of ISEL-positive cells among MDS patients was significantly higher than in normal controls (50.8 ± 14.0% vs. 11.3 ± 2.4%; P < 0.0001). A caspase-3 inhibitor reduced significantly the ISEL-positive rates (32.6 ± 15.2% vs. 50.2 ± 16.5%; P < 0.0001). Anti-TNF-α or anti-Fas antibody reduced the ISEL-positive rates significantly (28.2 ± 6.0%, 29.2 ± 5.8%, vs. 44.2 ± 3.4%, P < 0.001, P = 0.001, respectively). KB-R7785 also significantly decreased the ISEL-positive rates (18.0 ± 9.3% vs. 43.6 ± 14.0%; P < 0.0001). The concentration of TNF-α was significantly reduced by KB-R7785 (P < 0.05), whereas that of TGF-β was not. Concentration of sFasL was under detectable level in the present assay system. The derivatives of KB-R7785 that can be administrated orally showed inhibitory effect on apoptosis induction as well.These findings suggest that MMPIs inhibits the apoptosis induction of MDS bone marrow cells via the inhibition of TNF-α and probably sFasL secretion, and that MMPIs can be used to control the abnormal induction of apoptosis in MDS.