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Effect of enkephalins on bone marrow cells
L Krizanac-Bengez1, M Boranic, N G Testa
1Department of Experimental Biology and Medicine, Ruder Boskovic Institute, Zagreb, Croatia.
Abstract:
Mouse bone marrow cells were incubated with methionine- or leucine-enkephalin (10(-15)-10(-6) M) before seeding into soft agar cultures. In marrow samples harvested at different times, enkephalins decreased GM colony count on average by 30-40%. In individual experiments, however, the same concentration of enkephalins caused even stimulation, or at other times had effect. In view of the circadian periodicity of neuroendocrine functions and hematopoietic activity, the enkephalin effect on bone marrow cells was tested on marrow samples harvested at fixed time points (6 am, 6 pm), using enkephalin concentrations in the physiological range (10(-12)-10(-9) M). The seeding efficiency of the 6-pm cell population was on average 50% above that of the 6-am population. The 6-pm cell population was also more susceptible to the inhibitory effect of the enkephalins (35% inhibition) than the 6-am population (15% inhibition), and the variability in response was considerably reduced. With progenitor cell-enriched population, obtained by fluorescence-activated cell sorting (FACS) of 6-am bone marrow samples, in 3 out of 6 experiments Met- and Leu-enkephalin showed 30-35% inhibition of GM colony formation over a wide range of concentrations (10(-15)-10(-6)). In the other 3 experiments, suppression as well as stimulation or no alteration in colony count were observed. This variability probably reflected quality (purity) of the progenitor cell population, and may indicate that the enkephalins affected hematopoietic cells via a population of accessory cells.
Insights
Enkephalins, naturally occurring peptides, can inhibit mouse bone marrow cell growth. Their effect varies, but they show greater inhibitory impact on cells collected in the evening, suggesting a role in regulating hematopoiesis.
Area of Science:
- Hematology
- Neuroendocrinology
- Cell Biology
Background:
- Enkephalins are endogenous opioid peptides with diverse physiological roles.
- Hematopoiesis, the formation of blood cellular components, exhibits circadian rhythms.
- The interaction between neuroendocrine factors and hematopoietic activity is an area of ongoing research.
Purpose of the Study:
- To investigate the effect of methionine-enkephalin and leucine-enkephalin on mouse bone marrow cell growth.
- To explore the influence of circadian timing on enkephalin's impact on hematopoiesis.
- To determine if enkephalins affect hematopoietic progenitor cells directly or indirectly.
Main Methods:
- Mouse bone marrow cells were incubated with varying concentrations of methionine- or leucine-enkephalin.
- Cells were cultured in soft agar to assess colony-forming unit-granulocyte-macrophage (CFU-GM) counts.
- Experiments were conducted on cells harvested at different times of day (6 am and 6 pm) and on progenitor cell-enriched populations obtained via fluorescence-activated cell sorting (FACS).
Main Results:
- Enkephalins generally decreased CFU-GM counts, with an average reduction of 30-40%.
- Bone marrow cells harvested at 6 pm showed significantly higher seeding efficiency and greater susceptibility to enkephalin-induced inhibition (35%) compared to 6 am cells (15%).
- Variability in enkephalin's effect was observed, particularly in experiments using enriched progenitor cell populations, suggesting the involvement of accessory cells.
Conclusions:
- Enkephalins can modulate hematopoietic progenitor cell function, with effects potentially influenced by circadian rhythms.
- The timing of bone marrow cell collection impacts their response to enkephalins.
- The observed variability suggests that enkephalins may exert their effects on hematopoietic cells through accessory cells within the bone marrow microenvironment.