ABSTRACT
OBJECTIVES.
The aim of this research consisted in studying the effects
of tetrapeptide Epitalon on both thymocyte proliferation and
interleukin-1b (IL-1b)
signal transduction via sphingomyelin pathway in the cerebral
cortex membranes of mice exposed to stresses exerting diverse
effects upon humoral immune response.
DESIGN
AND SETTING: The experiments were performed on male (CBAxC57BL6)F1
mice aged 8-10 weeks. Two models of experimental stress were
used: immune-stimulatory rotation stress and immune-suppressive
combined stress (cooling followed by immobilization). The
combined effect of Epitalon was determined according to its
influence on thymocyte proliferation stimulated by concanavalin
A at a sub-optimal dose and recombinant IL-1b.
The activity of membrane neutral sphingomyelinase (nSMase),
the key enzyme of sphingomyelin signal transduction pathway,
was assayed according to modified Rao and Spence's method
(1976).
RESULTS.
The investigation demonstrated that Epitalon increased thymocyte
proliferative activity, both enhanced under rotation stress
and suppressed under combined one. It also increased IL-1b
combined effect. These findings corresponded to Epitalon effect
on diverse stress-induced changes in nSMase activity in cerebral
cortex fraction P2. Epitalon activated nSMase in the cerebral
cortex membranes of intact mice and increased IL-1b
stimulatory effect on the enzyme activity.
CONCLUSIONS.
The obtained results provided a conclusive evidence of Epitalon
stress-protective effect at the level of IL-1b signal transduction
via sphingomyelin pathway in the nerve tissue, as well as
at the level of target thymocyte proliferation.
List
of abbreviations
AB
- antibodies
PFC - plaque forming cells
IL-1 - interleukin-1
Con A - concanavalin A
nSMase - neutral sphingomyelinase
RTBT - reaction of thymocyte blast transformation
rIL-1ß - recombinant interleukin-1ß
SM - sphingomyelin
c.p.m. - counts per minute
INTRODUCTION
The
maintenance of the organism resistance to damaging factors
and diseases of various etiology, as well as the prospects
of active life prolongation and inhibition of aging much depend
upon the preservation of both innate and acquired (immunological)
defense functions and the mechanisms of their regulation.
Hence, experimental investigations and subsequent clinical
application of substances modulating the activity of these
mechanisms and promoting their functional safety are of high
priority today.
Tetrapeptide
Epitalon (Ala-Glu-Asp-Gly) belongs to the most promising medications.
It has been synthesized at the St. Petersburg Institute of
Bioregulation and Gerontology on the basis of the amino acid
analysis of Epithalamin, a complex peptide substance extracted
from the pineal gland. High biological activity of these bioregulators
has been confirmed experimentally [4, 6, 7].
As
it has been shown before, small peptides administered intramuscularly
or intravenously do not only modulate immunological reactions
but also influence brain functions and, thus, participate
in the interactions of neuroendocrine and immune systems.
Epitalon is found capable to restore some disturbed neuroendocrine
processes and, namely, to stimulate melatonin synthesis and
normalize cortisol secretion circadian rhythm in senescent
monkeys [6].
Especially interesting are the effects of Epitalon on the
indices of defense functions changed (increased or lowered),
for instance, under stress of various origin, intensity and
duration, and the modulating effect of this peptide on the
activity of natural endogenous bioregulators.
Cytokine interleukine-1 (IL-1) is one of the key endogenous
regulators of defense functions. It is the most important
mediator of neuroimmune interactions indispensable in the
development of stress reaction [1, 2, 9]. Over the recent
years, the sphingomyelin (SM) pathway has been found to play
the principal role in intracellular IL-1b signal transduction.
This pathway is initiated by the hydrolysis of membrane SM
to the secondary cellular messenger ceramide under the effect
of membrane enzyme nSMase, the key enzyme of the sphingomyelin
cascade [3, 8, 11, 12, 13].
This research has been designed to study Epitalon effects
on IL-1b signal transduction via SM pathway in the membranes
of cerebral cortex nerve cells and on the blast transformation
reaction of murine thymocytes under stress impacts diversely
affecting humoral immune response.
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