AM218, A NEW POLYANIONIC POLYSACCHARIDE, INDUCES RADIOPROTECTION IN MICE WHEN ADMINISTERED SHORTLY BEFORE IRRADIATION

We have shown that the polyanionic polysaccharide AM218 improves the s urvival rate of the potentially lethally irradiated mice. This radiopr otective effect was highly dependent on the administration schedule, t he most efficient protocol being that in which the drug was given shor tly before irradiation. The haematopoietic implications in the pharmac ological action of AM218 were confirmed by the improved recovery in th e three peripheral blood lineages observed in the AM218-treated mice. However, because of a marked increase observed in the number of white blood cells during the period of highest mortality of the control irra diated mice, effects on the neutrophil lineage may account for the eff ects mediated by AM218 in the irradiated mice. Both in vitro and in vi vo treatment with AM218 before irradiation improved the survival rate of CFU-GM progenitors, while no effects were observed on the CFU-S poo l. This led us to postulate that the improved survival rate of the com mitted progenitors, at least the granulocyte-macrophage progenitors, a ccounts for the radioprotective capacity of AM218.