ROLE OF ALDEHYDE DEHYDROGENASE IN THE PROTECTION OF HEMATOPOIETIC PROGENITOR CELLS FROM 4-HYDROPEROXYCYCLOPHOSPHAMIDE BY INTERLEUKIN-1-BETAAND TUMOR-NECROSIS-FACTOR

Preincubation of human bone marrow cells with interleukin 1-beta (IL-1 ) and tumor necrosis factor-alpha (TNF-alpha) for 20 h can protect ear ly progenitor cells from 4-hydroperoxycyclophosphamide (4-HC) toxicity . In this report, we have studied the mechanism for such protection. W e examined the effect of the length of incubation time and found that preincubation for at least 20 h with IL-1 and TNF-alpha is needed for significant protection. The addition of 2-mu-g/ml cycloheximide, a pro tein synthesis inhibitor, during the 20-h preincubation completely abo lished the protection observed for all colony-forming cells. In order to study the role of aldehyde dehydrogenase (ALDH), an enzyme which in activates 4-HC, we used diethylaminobenzaldehyde, an inhibitor of ALDH . Diethylaminobenzaldehyde was added during the last 10 min of the 20- h preincubation with IL-1 and TNF-alpha. Diethylaminobenzaldehyde prev ented the protection of colony-forming cells from 4-HC. Finally, using the same protection assay system, we showed that a 20-h preincubation with IL-1 and TNF-alpha can also protect early progenitor cells from phenylketophosphamide, an analogue of 4-HC which is resistant to inact ivation by ALDH. From these studies, we conclude that preincubation wi th IL-1 and TNF-alpha for at least 20 h is required for the protection of early progenitor cells from 4-HC. During that time period, protein synthesis, specifically aldehyde dehydrogenase synthesis, is critical for the protection from 4-HC. Preincubation with IL-1 and TNF-alpha a lso protects early progenitors from phenylketophosphamide. Because phe nylketophosphamide cannot be metabolized by ALDH, the reason for this protection must be due to other, as yet unidentified, mechanisms.