Effect of enkephalins on bone marrow cells

Oligopeptide fragments of the enkephalin molecule interfere with hematopoietic cell colony formation

Dipeptide Tyr-Gly and tripeptide Tyr-Gly-Gly representing the NH(2)-end of the Met-enkephalin molecule inhibited the GM-colony formation in clonal cultures of mouse bone marrow cells. Intermediate or C00H-terminal dipeptides Gly-Gly and Phe-Met respectively were inneffective. The suppressive effects were not abolished by opioid receptor blocking agent naloxone and only partly so by depletion of the accessory (adherent) cells. The results are congruent with idea that neuropeptides and products of their enzymatic degradation participate in the regulation of hematopoiesis.

Enkephalins in hematopoiesis

Recent data support the view that neuropeptide mediators, in particular opioid peptides, participate in the control of hematopoiesis. The main arguments are: neuropeptides modulate the functions of lymphoid cells, macrophages and mature granulocytes; they control cell proliferation and differentiation in many tissues, particularly during embryogenesis; lymphoid cells, macrophages, polymorphonuclear granulocytes and bone marrow stromal elements express neuropeptide receptors; bone marrow cells produce opioid-like neuropeptides; the CD10/CALLA marker of lymphoid, myeloid and marrow stromal cells is an enzyme, endopeptidase, which cleaves- and thus activates/inactivates-opioid and other neuropeptides. We have shown that opioid peptides enkephalins, opioid antagonist naloxone, and the inhibitor of enkephalin-degrading endopeptidase, thiorphan, modulate the proliferation and differentiation of hematopoietic cells in clonal and long-term cultures of mouse bone marrow. The effects partly depended on the presence of the accessory hematopoietic elements, and followed a circadian pattern. The dose-responses were irregular, showed strain-dependent and individual variations, and apparently reflected the state of the activity of target cells, cellular interactions and simultaneous signals by other mediators. The enkephalins were shown to bind to specific (opioid) receptors on the target cells, and their signals to be transmitted to the cell interior by a cascade of secondary messengers including diacyl-glycerol (DAG), protein-kinase C (PKC) and Ca++ ions. Neuropeptide regulation of hematopoiesis might belong to a complex immuno-neuroendocrine network including melatonin.

Suppressive effect of met-enkephalin on bone marrow cell proliferation in vitro shows circadian pattern and depends on the presence of adherent accessory cells

The cellularity of femoral bone marrow and the content of the granulocyte-macrophage colony forming cells (GM-CFC) were followed in mice between 0600 h and 1800 h. The cellularity increased at the beginning of the light period, and the GM-CFC content at the end. Opioid pentapeptide methionine-enkephalin reduced the GM colony forming ability of the bone marrow cell suspensions in proportion to the GM-CFC content. Removal of the accessory cells reversed the enkephalin sensitivity pattern of the GM-CFC. The circadian variations have been ascribed to a neuroendocrine regulatory network involving the opioid peptides and affecting the bone marrow accessory cells. The work draws attention to the circadian activity pattern of hemoregulatory oligopeptides applicable as adjuvants to antineoplastic chemotherapy.

Naloxone behaves as opioid agonist/antagonist in clonal cultures of mouse bone marrow cells

The opioid peptide methionine (Met)-enkephalin and the opioid-receptor blocking agent naloxone were added to unseparated or to progenitor-enriched cell suspensions of mouse bone marrow before assay in clonal cultures. Bone marrow samples harvested at 18:00 hours produced more granulocyte-macrophage (GM) colonies than the 06:00 hour samples, and were more sensitive to the proliferation inhibition by both agents. Additive inhibitory effects of naloxone with the enkephalin were occasionally seen. Thus, in this experimental system, naloxone could behave as an opioid agonist. However, there were examples of naloxone diminishing (blocking) the suppressive effect of the enkephalin, as a true opioid antagonist. Significant naloxone/enkephalin interactions occurred in opioid-sensitive (18:00 h) samples of unseparated bone marrow. The interactions were virtually absent in progenitor cell-enriched populations, indicating a significant role of accessory cells in opioidergic regulation of hematopoietic progenitors.

Enkephalinase-blocking agent thiorphan affects cell growth and differentiation in long term culture of mouse bone marrow

Enkephalinase-blocking agent thiorphan was added to long-term cultures of mouse bone marrow cells at the time of culture initiation (time 0) or 2 weeks thereafter, when the stromal layer appears. Cellularity, cell morphology (in cytospin smears) and the yield of granulocyte-macrophage progenitor cells (GM-CFC assay in agar) were recorded. Low concentrations of thiorphan accelerated recovery of the cultures after an initial drop of the cell count. Expansion and maturation of the granulocytic lineage was promoted, with parallel decline of the GM-CFC yield. Thiorphan probably interfered with the activity of enkephalinase (endopeptidase 24.11) in the cultures. That enzyme is the CD10 surface marker (CALLA) of lymphoid, myeloid and stromal elements.

Naloxone interferes with granulocytopoiesis in long-term cultures of mouse bone marrow; buffering by the stromal layer

Long-term cultures of mouse bone marrow cells were treated with naloxone, starting at the time of culture initiation or in the 2nd or 4th week of culture. Cell proliferation was suppressed and the ratio of immature and mature granulocytes to macrophages diminished by naloxone treatment. The effect depended on the timing of naloxone addition to the cultures and on its concentration, with a bell-shaped dose-response curve. High and low concentrations of naloxone (10(-4), 10(-6), 10(-14) M) interfered with hematopoiesis more strongly than the intermediate concentrations (10(-8) to 10(-12) M). Early cultures lacking the stromal layer were more sensitive to naloxone than the cultures with established stroma. The bell-shaped dose-response curve has been attributed to an interplay of specific (opioid-receptor-mediated) and nonspecific mechanisms. Opioidergic mechanisms apparently participate in the regulation of hematopoiesis.

Endogenous opiates: 1992

This paper is the fifteenth installment of our annual review of research concerning the opiate system. It includes papers published during 1992 involving the behavioral, non-analgesic, effects of the endogenous opiate peptides. The specific topics this year include stress; tolerance and dependence; eating; drinking; gastrointestinal and renal function; mental illness and mood; learning, memory, and reward; cardiovascular responses; respiration and thermoregulation; seizures and other neurological disorders; electrical-related activity; general activity and locomotion; sex, pregnancy, and development; immunological responses; and other behaviors.