Indication of an involvement of interleukin-1β converting enzyme-like protease in intramedullary apoptotic cell death in the bone marrow of patients with myelodysplastic syndromes

Abstract

Our previous studies using in situ end labeling (ISEL) of fragmented DNA revealed extensive apoptotic cell death in the bone marrows (BM) of patients with myelodysplastic syndromes (MDS) involving both stromal and hematopoietic cells. In the present report we show greater synthesis of interleukin-lβ (IL-1β) in 4 hour cultures of density separated BM aspirate mononuclear (BMAM) cells from MDS patients as compared to the cultures of normal BM from healthy donors or lymphoma patients (1.7 ± 0.37 pg/106 cells, n = 29 v 0.42 ± 0.24 pg/106 cells, n = 11, respectively, P = .049). Further, these amounts of IL-1β in MDS showed a significant correlation with the extent of apoptosis detected by ISEL in corresponding plastic embedded BM biopsies (r = .480, n = 30, P = .007). In contrast normal BMs did not show any correlation between the two (r = .091, n = 12, P = .779). No significant correlation was found between the amounts of IL-lβ and % S-phase cells (labeling index; LI%) in MDS determined in BM biopsies using immunohistochemistry following in vivo infusions of iodo- and/or bromodeoxyuridine. Neither anti-lL-lβ antibody nor IL-1 receptor antagonist blocked the apoptotic death of BMAM cells in 4 hour cultures (n = 5) determined by ISEL (apoptotic index; AI%), although the latter led to a dose-dependent accumulation of active IL-1β in the culture supernatants. On the other hand, a specific tetrapetide-aldehyde inhibitor of ICE significantly retarded the apoptotic death of BMAM cells at 1 μmol/L in 5/6 MDS cases studied (AI% = 2.99 ± 0.30 in controls v 1.58 ± 0.40 with ICE-inhibitor, P = .05) and also reduced the levels of active IL-1β synthesized (5.59 ± 2.63 v 2.24 ± 0.93 pg/106 cells, respectively). In normal cells, neither IL-1 blockers nor the ICE inhibitor showed any effect on the marginal increase in apoptosis observed in 4 hour cultures. Our data thus suggest a possible involvement of an ICE-like protease in the intramedullary apoptotic cell death in the BMs of MDS patients.