| Abstract: | A synthetic analogue of a pentapeptide associated with mature granulocytes has been investigated for biological effects on stem cell activity in vitro and in vivo. When tested on bone marrow cells from female C3H mice, a short incubation in vitro in doses from 10(-9) to 10(-5) M inhibited myelopoietic colony formation (CFU-C). A maximum of 80% reduction of colony yield was found at 10(-7) M. An oxidized form of the molecule had a stimulatory effect on colony formation, but the inhibitory effect was restored by treatment with a reducing substance (mercaptoethanol). The peptide was nontoxic during continuous exposure of liquid cultures of bone marrow cells for up to 24 h at a dose range of 10(-11) to 10(-4) M. When injected into mice, a dose-dependent inhibitory effect on CFU-C was seen. Maximal effect was obtained by continuous infusion of 1.4 micrograms/h for six days, where only one-fifth of the normal CFU-C number per femur could be retrieved. Prolonged exposure to the same dose level resulted in less reduction. A significant, but less pronounced reduction of spleen colony formation (CFU-S) per femur was seen in the same dose range. Inhibition of both CFU-S and CFU-C was in all cases reversible and mostly accompanied by an overshoot of up to 75% above normal level. In addition, primarily noninhibitory doses led to a secondary increase in the numbers of CFU-S. The total cell number per femur was moderately but significantly reduced, and a prolonged reduction of granulocyte numbers in peripheral blood resulted. No direct toxic effects were seen in vivo on 271 mice given up to 9 mg of the peptide. The results indicate that the peptide may have a regulatory function for stem cell activity in vivo. |
