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The nocturnal surge of melatonin is the endocrine expression of the circadian system and is essential for organizing the timing of various endogenous processes. Previous works suggest that, in the beginning of a defense response, the increase in circulating tumor necrosis factor-α (TNF-α) leads to a transient block of nocturnal melatonin production and promotes a disruption of internal time organization. In the present paper, the concentration of melatonin and cytokines [TNF-α, interferon-γ (IFN-γ), interleukin (IL)-2, IL-4, IL-5, IL-10, IL-12] in the colostrum (postdelivery day 3) and in the milk (postdelivery days 10, 15, 20 and 30) obtained at midday and midnight from mothers who gave birth by vaginal or cesarean section were compared. The nocturnal melatonin surge observed 3 days after vaginal delivery was absent after cesarean section. IL-12 presented no daily variation in either case, while daily variations in IFN-γ, IL-10, IL-4 and IL-5 were observed after vaginal delivery and cesarean section. On the other hand, the increase in TNF-α after cesarean section resulted in suppression of the nocturnal melatonin surge. Daily variation of IL-2 was only observed after recovery of the nocturnal melatonin surge, 30 days after cesarean section. The present paper supports the hypothesis of a cross-talk between the pineal gland and the immune system, which could represent a putative immune–pineal axis. [ABSTRACT FROM AUTHOR]

Control of the acute phase of Trypanosoma cruzi infection is critically dependent on cytokine-mediated macrophage activation to intracellular killing, natural killer (NK) cells, CD4+ T cells, CD8+ T cells and B cells. Cell-mediated immunity in T. cruzi infection is also modulated by cytokines, but in addition to parasite-specific responses, autoimmunity can be also triggered. Importantly, cytokines may also play a role in the cell-mediated immunity of infected subjects. Here we studied the role of cytokines in the regulation of innate and adaptive immunity during the acute phase of T. cruzi infection in Wistar rats. Melatonin is an effective regulator of the immune system. Macrophages and T lymphocytes, which have melatonin receptors, are target cells for the immunomodulatory function of melatonin. In this paper melatonin was orally given via two protocols: prior to and concomitant with infection. Both treatments were highly effective against T. cruzi with enhanced action for the concomitant treatment. The data suggest an up-regulation of the TH-1 immune response as all analyzed parameters, interleukin (IL)-4, IL-10, transforming growth factor-β1 and splenocyte proliferation, displayed reduced levels as compared with the untreated counterparts. However, the direct effects of melatonin on immune cells have not been fully investigated during T. cruzi infection. We conclude that in light of the current results, melatonin exerted important therapeutic benefits through its immune regulatory effects. [ABSTRACT FROM AUTHOR]

A large number of data show that melatonin has immunomodulatory properties and is produced by immunocompetent cells; also, some evidence suggests a ‘feedback’ of the activated immune system on the pineal gland. In this paper, we studied immune–pineal interactions in colostrum obtained from healthy puerperae and mothers with mastitis taking into account that, (a) melatonin levels in milk reflects pineal activity and (b) colostrum quiescent mononuclear and polymorphonuclear phagocytes from healthy mothers in culture are adequate for evaluating the ability of immunocompetent cells to produce melatonin. Here we compared the diurnal and nocturnal melatonin levels in colostrum from healthy puerperae and mothers with mastitis; this is a unique noninvasive model for determining pineal activity in the proinflammatory phase of a defense response. In addition, we determined the ‘in vitro’ production of melatonin by colostrum immunocompetent cells stimulated by enteropathogenic Escherichia coli or zymosan. Suppression of nocturnal melatonin rise in mothers with mastitis was highly correlated with increased tumor necrosis factor- α (TNF- α) secretion. This result, interpreted taking into account the presence of the transcription factor nuclear factor kappa B in pineal gland, suggest that the proinflammatory cytokine can inhibit nocturnal pineal melatonin production. On the other hand, stimulated, but not quiescent, immunocompetent cells secreted in the colostrum produced melatonin in vitro. In addition, this production ceases after bacteria killing. These results suggest that during the response to an injury the production of melatonin can be transiently shifted from an endocrine (pineal) to a paracrine (immunocompetent cells) source. [ABSTRACT FROM AUTHOR]

The pineal hormone melatonin exhibits immunomodulatory activity well documented in mammals and birds. The mechanism of melatonin action within the immune system is, however, poorly understood. In mammalian immune cells in vitro, melatonin acts mainly as an antiapoptotic, oncostatic and antiproliferative agent, and these effects are exertedviaspecific receptors or are related to its free radical scavenging activity. In previous studies we have found that in short-term chicken splenocyte cultures in vitro melatonin stimulated basil proliferation and inhibited that stimulated with phytohemagglutinin, a T-cell mitogen. This paper is devoted to the involvement of membrane receptors, previously characterised by us as MT2 (Mel1b) and Mel1c subtypes, in the above mentioned melatonin effects in chicken splenocyte cultures. For this purpose, in present study a nonselective melatonin receptor antagonist, luzindole, and the selective MT2 blocker, 4P-PDOT, were used. The effect of melatonin on second messengers, cyclic adenosine-3′,5′-monophosphate (cAMP) and inositol-1,4,5-trisphosphate (IP3), involved in the regulation of proliferation, was examined. We have found that the stimulation of proliferation occursviaMel1c receptor and is associated with the changes in intracellular second messengers concentration: a decrease in cAMP and an increase in IP3. In contrast, in mitogen-activated splenocytes, melatonin-induced inhibition of proliferation is mediated by MT2 receptors and is related to cAMP accumulation, as well as a decrease in IP3. In conclusion, we have demonstrated that the stimulatory and inhibitory effect of melatonin on chicken splenocytes in vitro, dependent on the magnitude of cell stimulation, resulted from two different subtypes of membrane receptors. [ABSTRACT FROM AUTHOR]

Melatonin mediates a variety of biological processes ranging from the control of circadian rhythms to immune regulation. Melatonin also influences bone formation and osteointegration of dental implants. However, the effects of melatonin on dentine formation have not been examined. This study investigated the effects of melatonin on the proliferation and differentiation of rat dental papilla cells ( r DPCs) in vitro and dentine formation in vivo. We found that melatonin (0, 10−12, 10−10,10−8 m) induced a dose-dependent reduction in rDPCs proliferation, increased alkaline phosphatase ( ALP) activity, the expression of dentine sialoprotein ( DSP), and mineralized matrix formation in vitro. In vivo melatonin (50 mg/kg, BW, i.p.) inhibited dentine formation. Melatonin (10−8 m) suppressed the activity of complex I and IV in the basal medium ( OS−) and enhanced the activity of complex I and complex IV in osteogenic medium ( OS+). These results demonstrate that melatonin suppresses the proliferation and promotes differentiation of rDPCs, the mechanisms of which may be related to activity of mitochondrial complex I and complex IV. [ABSTRACT FROM AUTHOR]

Melatonin production is not restricted to the pineal gland. Several extrapineal sources of this indole such as retina, Harderian gland, and immune system are well documented. Melatonin of pineal origin is not present in the rat at early stages of development. To assess the potential capacity of local melatonin synthesis by the immature brain and to gain insight into the relationship between melatonin production by the brain (without the pineal gland) and pineal gland during rat development, the melatonin content as well as the expression and activity of the melatonin-synthesizing enzymes, N-acetyltransferase (NAT) and hydroxyindole- O-methyltransferase (HIOMT), were studied at fetal and postnatal stages. Moreover, melatonin-membrane receptor (MT1) expression was also analyzed. Both, the expression and activity of NAT and HIOMT were found in the brain with significant day/night differences in enzymes activities. Additionally, melatonin content was detected in all stages showing day/night differences depending on the stage of development. The brain nocturnal melatonin content was higher than diurnal content on postnatal day 16 and in adult rats which is in accordance with the pineal melatonin synthesis. To investigate the origin of this brain melatonin, pinealectomized rats were used and we found that the developing brain produced its own melatonin. Also, MT1 expression was detected in brain during development. These results demonstrate that, when the pineal is not yet producing melatonin, there is melatonin synthesis by the brain that could be used as protection from free radical damage and/or could exert some actions through MT1 receptors. [ABSTRACT FROM AUTHOR]

The immunomodulatory action of melatonin in different animal species is already well known, although the mechanism(s) by which the indoleamine influences the immune system have yet to be fully elucidated. Previously, we have shown both anti-inflammatory and opioid-mediated influence of exogenous melatonin on thioglycollate-induced peritonitis in young chickens. In the present study, the kinetics of peritonitis and splenocyte proliferation were compared in chickens reared in both seasons under the same L:D 12:12 conditions. These two aspects of the immune response were correlated with the diurnal rhythm of pineal gland function, measured by the activity of N-acetyltransferase (NAT), a key enzyme in melatonin biosynthesis. The results revealed seasonal changes in the circadian rhythm of pineal NAT activity occurring in parallel to the natural local geophysical seasons. These changes appeared to influence the development of peritonitis and splenocyte responsiveness to mitogenic stimulation in vitro. Moreover, the existence of bidirectional communication between the pineal gland and the activated immune system was supported by the decreased activity of pineal NAT in chickens with peritonitis compared with control birds. [ABSTRACT FROM AUTHOR]

Melatonin is an immune modulator that displays both pro‐ and anti‐inflammatory properties. Proinflammatory actions, which are well documented by many studies in isolated cells or leukocyte‐derived cell lines, can be assumed to enhance the resistance against pathogens. However, they can be detrimental in autoimmune diseases. Anti‐inflammatory actions are of particular medicinal interest, because they are observed in high‐grade inflammation such as sepsis, ischemia/reperfusion, and brain injury, and also in low‐grade inflammation during aging and in neurodegenerative diseases. The mechanisms contributing to anti‐inflammatory effects are manifold and comprise various pathways of secondary signaling. These include numerous antioxidant effects, downregulation of inducible and inhibition of neuronal NO synthases, downregulation of cyclooxygenase‐2, inhibition of high‐mobility group box‐1 signaling and toll‐like receptor‐4 activation, prevention of inflammasome NLRP3 activation, inhibition of NF‐κB activation and upregulation of nuclear factor erythroid 2‐related factor 2 (Nrf2). These effects are also reflected by downregulation of proinflammatory and upregulation of anti‐inflammatory cytokines. Proinflammatory actions of amyloid‐β peptides are reduced by enhancing α‐secretase and inhibition of β‐ and γ‐secretases. A particular role in melatonin's actions seems to be associated with the upregulation of sirtuin‐1 (SIRT1), which shares various effects known from melatonin and additionally interferes with the signaling by the mechanistic target of rapamycin (mTOR) and Notch, and reduces the expression of the proinflammatory lncRNA‐CCL2. The conclusion on a partial mediation by SIRT1 is supported by repeatedly observed inhibitions of melatonin effects by sirtuin inhibitors or knockdown. [ABSTRACT FROM AUTHOR]