Peripheral blood leukocyte alterations in mice induced by a hemoregulatory pentapeptide (HP 5b)

Selectivity of hemoregulatory peptide (HP5b) action in culture

A synthetic analog of a hemoregulatory peptide associated with mature human granulocytes (HP5b) has been investigated for inhibitory effects on various cell types in culture as compared to inhibitory action on mouse and human myelopoietic colonies (CFU-gm), which occurs from 1 X 10(-13) to 1 X 10(-6) M in vitro. This includes colony formation by lymphoid T and B cells in capillary cultures, as well as mitogen activation of T, B and NK cells. At higher concentrations, i.e., above 1 X 10(-7) M, an inhibitory effect was found on colony formation. Neither the production of interleukin (IL) 3 by mitogen-activated T cells, nor the proliferation of the IL-3-dependent L/B cell line were affected by the peptide up to 1 X 10(-5) M. A slight inhibitory effect was found above 1 X 10(-9) M on mouse 3T3 fibroblasts. A series of malignant cell lines was also tested. No effect was seen between 1 X 10(-11) and 1 X 10(-7) M on human mammary carcinoma cells in culture. On Ehrlich ascites mouse mammary carcinoma cells a 30% inhibition was seen at 10(-6) M. On a human glioblastoma cell line (GaMg) no effect was seen, and on a rat glioma cell line (BT5C) an inhibitory effect was seen at 1 X 10(-7) M and above. No significant inhibition of cell growth was seen on SC1 mouse lymphoma cells from 1 X 10(-9) to 1 X 10(-5) M during 7 days of culture. The investigated normal and malignant cell types in culture were thus not inhibited in very low concentrations which act on CFU-gm. However, a variable inhibitory effect was found at higher concentrations where the inhibition of myelopoiesis was maximal and at concentrations where the inhibition is released. The hemoregulatory peptide thus seems to be a concentration-dependent selective inhibitor of myelopoiesis. The finding that various malignant cells do not respond at lower concentrations supports the possibility of using the peptide as a protector of normal cells during cancer chemotherapy.

A synthetic hemoregulatory peptide (HP5B) inhibits human myelopoietic colony formation (CFU-GM) but not leukocyte phagocytosis in vitro

A synthetic analog of a hemoregulatory peptide associated with mature human granulocyte (HP5B) has been investigated for inhibitory effects on human myelopoietic stem cells in vitro. In addition, it has been tested for effects on phagocytosis by human granulocytes and monocytes by use of an automatic flow cytometric method. A dose-dependent inhibition of colony formation was found after preincubation of bone marrow cells for 1 h at 37 degrees C in the range 10(7) -10(-11) mol/l. Above or below these concentrations, no inhibitory effects were seen. The degree of inhibition varied from experiment to experiment, indicating variable responsiveness of the donor cells. Maximal effect was of magnitude 90% inhibition, and the optimal dose was 10(7) mol/l. The peptide had no effect on the kinetics of phagocytosis by measurements of the uptake of fluorescent Zymosan particles or Staphylococcus aureus. This may indicate a selective effect on the precursor cells, with no effect on the functional state of their progeny, the granulocytes and monocytes.

Effects of a hemoregulatory peptide (HP5b) on erythroid and myelopoietic colony formation in vitro

A hemoregulatory peptide (HP5b) associated with mature human granulocytes has been investigated for inhibitory effects on murine hemopoietic stem cells in vitro. Both highly purified peptide from natural sources and a synthetic analog peptide have been investigated in parallel. Strong inhibitory effects were found on myelopoietic colony formation in the dose range 10(-13)-10(-5) mol/l. On exceeding this dose, the inhibitory effect disappeared. Moderate to slight inhibitory effects on erythroid colony formation (BFU-E and CFU-E) from adult animals were only seen in 1,000 X the optimal doses for myelopoiesis. No effect was found on CFU-E from fetal liver. The peptide thus has a selective effect on myelopoiesis in a certain dose range. A regulatory mechanism for the peptide on hemopoiesis is proposed.

Modification of mouse hemopoietic cell proliferation in vivo by a hemoregulatory pentapeptide (HP 5b). Relation to circadian rhythms

The effects on murine hemopoietic cell proliferation of hemoregulatory peptide 5b, a synthetic factor which inhibits granulopoiesis, have been studied in vivo by 3H-thymidine labeling, cell cycle analyses by flow cytometry and total cell counts per femur. Single injections of the peptide seemed to obliterate the normal circadian rhythm of bone marrow cell proliferation. By autoradiography, the main effect was an inhibition of myelopoietic cell proliferation, although erythropoiesis was also affected. This occurred in two ways: a) an immediate effect observed in the first 24 h after a single injection, and b) a delayed effect observed 6-12 days after a week of peptide infusion which could be a result of stem cell inhibition. A secondary accumulation of cells with G2 phase DNA content was seen regularly. Thus the hemoregulatory peptide seems to influence hemopoietic cell proliferation and has its main effect on myelopoiesis. However, inhibition is less marked than observed previously in stem cells.