Corticosterone modulates noradrenaline-induced melatonin synthesis through inhibition of nuclear factor kappa B

Systemic administration of propranolol reduces bone resorption and inflammation in apical periodontitis of chronically stressed rats

AIM

To evaluate the effect of systemic administration of propranolol on the severity of apical periodontitis (AP) in chronically stressed rats.

METHODOLOGY

Twenty-four 70-day-old male Wistar rats (Rattus norvegicus, albinus) were distributed into three groups (n = 8): rats with AP without stressful conditions (AP-Control), rats with AP and submitted to a chronic unpredictable stress (CUS) protocol (AP + S) and rats with AP and submitted to a CUS protocol treated with propranolol (AP + S + PRO). Stress procedures were applied daily until the end of the experiment. After 3 weeks of CUS, AP was induced in all groups by exposing the pulpal tissue of mandibular and maxillary first molars to the oral environment. Propranolol treatment was administered orally once a day for the entire period of the experiment. Rats were sacrificed at 42 days, and the blood was collected for stress biomarkers serum dosage by multiplex assay. Mandibles were removed and submitted to microtomography and histopathological analyses. Periapical tissue surrounding the upper first molar was homogenized and subjected to RT-PCR analysis to evaluate the mRNA expression of RANKL, TRAP and OPG. Parametric data were assessed using one-way ANOVA followed by Tukey's test while the nonparametric data were analysed by the Kruskal-Wallis followed by Dunn's test. Significance level was set at 5% (p < .05) for all assessed parameters.

RESULTS

Micro-CT revealed statistically significant differences in bone resorption which was greater in the AP + S group (p < .05), but no differences were observed between the Control and AP + S + PRO groups (p > .05). The AP + S + PRO group had a lower intensity and extent of inflammatory infiltrate compared to the AP + S group with smaller areas of bone loss (p < 0.05). The gene expression of RANKL and TRAP was significantly higher in the stressed group AP + S compared to the control group (p < .05), and a significantly higher OPG expression was observed in AP + S + PRO compared to the AP + S group (p < .05).

CONCLUSIONS

Oral administration of propranolol had a significant effect on the AP severity in stressed rats, suggesting an anti-inflammatory effect and a protective role on bone resorption of AP in stressed animals. Further research is necessary to fully comprehend the underlying mechanisms.

The emerging role of rapid corticosteroid actions on excitatory and inhibitory synaptic signaling in the brain

Over the past two decades, there has been increasing evidence for the importance of rapid-onset actions of corticosteroid hormones in the brain. Here, we highlight the distinct rapid corticosteroid actions that regulate excitatory and inhibitory synaptic transmission in the hypothalamus, the hippocampus, basolateral amygdala, and prefrontal cortex. The receptors that mediate rapid corticosteroid actions are located at or close to the plasma membrane, though many of the receptor characteristics remain unresolved. Rapid-onset corticosteroid effects play a role in fast neuroendocrine feedback as well as in higher brain functions, including increased aggression and anxiety, and impaired memory retrieval. The rapid non-genomic corticosteroid actions precede and complement slow-onset, long-lasting transcriptional actions of the steroids. Both rapid and slow corticosteroid actions appear to be indispensable to adapt to a continuously changing environment, and their imbalance can increase an individual's susceptibility to psychopathology.

IL-10-induced STAT3/NF-κB crosstalk modulates pineal and extra-pineal melatonin synthesis

Immune-pineal axis activation is part of the assembly of immune responses. Proinflammatory cytokines inhibit the pineal synthesis of melatonin while inducing it in macrophages by mechanisms dependent on nuclear factor-κB (NF-κB) activation. Cytokines activating the Janus kinase/signal transducer and activator of transcription (STAT) pathways, such as interferon-gamma (IFN-γ) and interleukin-10 (IL-10), modulate melatonin synthesis in the pineal, bone marrow (BM), and spleen. The stimulatory effect of IFN-γ upon the pineal gland depends on STAT1/NF-κB interaction, but the mechanisms controlling IL-10 effects on melatonin synthesis remain unclear. Here, we evaluated the role of STAT3 and NF-κB activation by IL-10 upon the melatonin synthesis of rats' pineal gland, BM, spleen, and peritoneal cells. The results show that IL-10-induced interaction of (p)STAT3 with specific NF-κB dimmers leads to different cell effects. IL-10 increases the pineal's acetylserotonin O-methyltransferase (ASMT), N-acetylserotonin, and melatonin content via nuclear translocation of NF-κB/STAT3. In BM, the nuclear translocation of STAT3/p65-NF-κB complexes increases ASMT expression and melatonin content. Increased pSTAT3/p65-NF-κB nuclear translocation in the spleen enhances phosphorylated serotonin N-acetyltransferase ((p)SNAT) expression and melatonin content. Conversely, in peritoneal cells, IL-10 leads to NF-κB p50/p50 inhibitory dimmer nuclear translocation, decreasing (p)SNAT expression and melatonin content. In conclusion, IL-10's effects on melatonin production depend on the NF-κB subunits interacting with (p)STAT3. Thus, variations of IL-10 levels and downstream pathways during immune responses might be critical regulatory factors adjusting pineal and extra-pineal synthesis of melatonin.

Gut microbiota regulates host melatonin production through epithelial cell MyD88

Melatonin has various physiological effects, such as the maintenance of circadian rhythms, anti-inflammatory functions, and regulation of intestinal barriers. The regulatory functions of melatonin in gut microbiota remodeling have also been well clarified; however, the role of gut microbiota in regulating host melatonin production remains poorly understood. To address this, we studied the contribution of gut microbiota to host melatonin production using gut microbiota-perturbed models. We demonstrated that antibiotic-treated and germ-free mice possessed diminished melatonin levels in the serum and elevated melatonin levels in the colon. The influence of the intestinal microbiota on host melatonin production was further confirmed by fecal microbiota transplantation. Notably, Lactobacillus reuteri (L. R) and Escherichia coli (E. coli) recapitulated the effects of gut microbiota on host melatonin production. Mechanistically, L. R and E. coli activated the TLR2/4/MyD88/NF-κB signaling pathway to promote expression of arylalkylamine N-acetyltransferase (AANAT, a rate-limiting enzyme for melatonin production), and MyD88 deficiency in colonic epithelial cells abolished the influence of intestinal microbiota on colonic melatonin production. Collectively, we revealed a specific underlying mechanism of gut microbiota to modulate host melatonin production, which might provide novel therapeutic ideas for melatonin-related diseases.

Rat resistance to rheumatoid arthritis induction as a function of the early-phase adrenal-pineal crosstalk

Chronic inflammatory diseases are triggered by causal stimuli that might occur long before the appearance of the symptoms. Increasing evidence suggests that these stimuli are necessary but not always sufficient to induce the diseases. The murine model of type II collagen emulsified in Freund's incomplete adjuvant (collagen-induced arthritis) to induce rheumatoid arthritis (RA) follows this pattern as some animals do not develop the chronically inflamed phenotype. Considering that in the immune-pineal axis (IPA) theory adrenal-pineal cross-talk adjusts early phases of inflammatory processes, we investigated whether differences in IPA activation could explain why some animals are resistant (RES) while others develop RA. We observed a similar increase in 6-sulfatoxymelatonin (aMT6s) excretion from day 3 to 13 in both RES and RA animals, followed by a significant decrease in RA animals. This pattern of aMT6s excretion positively correlated with plasma corticosterone (CORT) in RES animals. Additionally, RA animals presented a lower aMT6s/CORT ratio than saline-injected or RES animals. Plasmatic levels of tumour necrosis factor were similar in both groups, but interleukin (IL)-1β and monocyte chemotactic protein 1 (MCP-1) levels were lower in RES compared to RA animals. IL-2 and IL-4 were decreased in RES animals compared to saline-injected animals. The aMT6s/CORT ratio inversely correlated with the paw thickness and the inflammatory score (levels of IL-1β, MCP-1, IL-2 and IL-4 combined). Thus, adrenocortical-pineal positive interaction is an early defence mechanism for avoiding inflammatory chronification. KEY POINTS: Immune-pineal axis imbalance is observed in early-phase rheumatoid arthritis development. Only resistant animals present a positive association between adrenal and pineal hormones. The 6-sulfatoxymelatonin/corticosterone ratio is decreased in animals that develop rheumatoid arthritis. The inflammatory score combining the levels of nocturnal interleukin (IL)-1β, monocyte chemotactic protein 1, IL-2 and IL-4 presents a very strong positive correlation with the size of inflammatory lesion. The 6-sulfatoxymelatonin/corticosterone ratio presents a strong negative correlation with the inflammatory score and paw oedema size.

Physiological and pharmacological perspectives of melatonin

The pineal gland is a interface between light-dark cycle and shows neuro-endocrine functions. Melatonin is the primary hormone of pineal gland, secreted at night. The night-time melatonin peak regulates the physiological functions at dark. Melatonin has several unique features as it synchronises internal rhythm with daily and seasonal variations, regulates circadian rhythm and sleep-wake cycle. Physiologically melatonin involves in detoxification of free radicals, immune functions, neuro-protection, oncostatic effects, cardiovascular functions, reproduction, and foetal development. The precise functions of melatonin are exhibited by specific receptors. In relation to pathophysiology, impaired melatonin secretion promotes sleep disorder, cancer progression, type-2 diabetes, and neurodegenerative diseases. Several reports have highlighted the therapeutic benefits of melatonin specially related to cancer protection, sleep disorder, psychiatric disorders, and jet lag problems. This review will touch the most of the area of melatonin-oriented health impacts and its therapeutic aspects.

New insights into the role of melatonin in diabetic cardiomyopathy

Diabetic cardiovascular complications and impaired cardiac function are considered to be the main causes of death in diabetic patients worldwide, especially patients with type 2 diabetes mellitus (T2DM). An increasing number of studies have shown that melatonin, as the main product secreted by the pineal gland, plays a vital role in the occurrence and development of diabetes. Melatonin improves myocardial cell metabolism, reduces vascular endothelial cell death, reverses microcirculation disorders, reduces myocardial fibrosis, reduces oxidative and endoplasmic reticulum stress, regulates cell autophagy and apoptosis, and improves mitochondrial function, all of which are the characteristics of diabetic cardiomyopathy (DCM). This review focuses on the role of melatonin in DCM. We also discuss new molecular findings that might facilitate a better understanding of the underlying mechanism. Finally, we propose potential new therapeutic strategies for patients with T2DM.

Daily and LPS-induced variation of endocrine mediators in cururu toads (Rhinella icterica)

Increased plasma glucocorticoids (corticosterone - CORT, in amphibians) and melatonin (MEL) are associated with the daily activity phase and with environmental darkness, respectively. Besides, CORT and MEL also play pivotal immunomodulatory roles in several vertebrates. Herein we described the daily profile of plasma MEL and CORT for Rhinella icterica toads in captivity. Thereafter, we investigated the effects of lipopolysaccharide (LPS)-induced systemic inflammation on the production of CORT and MEL in the R. icterica. Captive toads showed CORT and MEL diurnal variation typical of nocturnal species, with increased values for CORT at ZT12 (18 h) and MEL peak at ZT18 (24 h). LPS-induced hormonal changes included increased plasma CORT and decreased ocular and plasma MEL when compared to those from toads treated with saline 2 h post-injection. Our results demonstrated the presence of a diurnal CORT and MEL variation in toads. We also showed the crosstalk between CORT and MEL during the toad's systemic inflammation in response to an immune challenge with LPS. Additionally, our results demonstrated that anuran eyes' MEL production might be regulated during the inflammatory processes.

Corticoid-like anti-inflammatory effect of Vochysia bifalcata Warm.: Preclinical evidence of efficacy and safety

ETHNOPHARMACOLOGICAL RELEVANCE

Vochysia bifalcata is a Brazilian native tree commonly used for economic purpose in the reforestation and in the manufacture of products. However, the potential usage of other parts of the plant is usually wasted. Besides, other species of Vochysia are well known for its anti-inflammatory action.

AIM OF THE STUDY

In this study we evaluate the possible anti-inflammatory activity of the hydroethanolic extract from the leaves of V. bifalcata in models of mice skin inflammation.

MATERIALS AND METHODS

Effects of V. bifalcata were evaluated in croton oil-induced acute and chronic skin inflammation. The role of glucocorticoid receptors in the extract effect was assessed by using a glucocorticoid receptor antagonist and by a specific binding assay. Possible adverse effects were evaluated after multiple treatments with the extract in a skin atrophy model.

RESULTS

Topical application of V. bifalcata reduced ear edema formation, cell infiltration and interleukin (IL)-6 and tumor necrosis factor (TNF)-α levels. In the chronic model, besides edema formation and cell infiltration, the extract inhibited epidermal hyperproliferation and Proliferating Cell Nuclear Antigen expression. V. bifalcata seems to act by biding to corticoid receptors, however it did not induce corticoid related undesirable effects.

CONCLUSION

Hydroethanolic extract from leaves of V. bifalcata could be an interesting tool in the search for new anti-inflammatory and antiproliferative agents for the treatment of skin disorders.

Immune-pineal axis protects rat lungs exposed to polluted air

Environmental pollution in the form of particulate matter <2.5 μm (PM_2.5 ) is a major risk factor for diseases such as lung cancer, chronic respiratory infections, and major cardiovascular diseases. Our goal was to show that PM_2.5 eliciting a proinflammatory response activates the immune-pineal axis, reducing the pineal synthesis and increasing the extrapineal synthesis of melatonin. Herein, we report that the exposure of rats to polluted air for 6 hours reduced nocturnal plasma melatonin levels and increased lung melatonin levels. Melatonin synthesis in the lung reduced lipid peroxidation and increased PM_2.5 engulfment and cell viability by activating high-affinity melatonin receptors. Diesel exhaust particles (DEPs) promoted the synthesis of melatonin in a cultured cell line (RAW 264.7 cells) and rat alveolar macrophages via the expression of the gene encoding for AANAT through a mechanism dependent on activation of the NFκB pathway. Expression of the genes encoding AANAT, MT1, and MT2 was negatively correlated with cellular necroptosis, as disclosed by analysis of Gene Expression Omnibus (GEO) microarray data from the human alveolar macrophages of nonsmoking subjects. The enrichment score for antioxidant genes obtained from lung gene expression data (GTEx) was significantly correlated with the levels of AANAT and MT1 but not the MT2 melatonin receptor. Collectively, these data provide a systemic and mechanistic rationale for coordination of the pineal and extrapineal synthesis of melatonin by a standard damage-associated stimulus, which activates the immune-pineal axis and provides a new framework for understanding the effects of air pollution on lung diseases.

Inflammation and tissue homeostasis: the NF-κB system in physiology and malignant progression

Disruption of tissue function activates cellular stress which triggers a number of mechanisms that protect the tissue from further damage. These mechanisms involve a number of homeostatic modules, which are regulated at the level of gene expression by the transactivator NF-κB. This transcription factor shifts between activation and repression of discrete, cell-dependent gene expression clusters. Some of its target genes provide feedback to NF-κB itself, thereby strengthening the inflammatory response of the tissue and later terminating inflammation to facilitate restoration of tissue homeostasis. Disruption of key feedback modules for NF-κB in certain cell types facilitates the survival of clones with genomic aberrations, and protects them from being recognized and eliminated by the immune system, to enable thereby carcinogenesis.

Rhythmic expression of the melatonergic biosynthetic pathway and its differential modulation in vitro by LPS and IL10 in bone marrow and spleen

Daily oscillation of the immune system follows the central biological clock outputs control such as melatonin produced by the pineal gland. Despite the literature showing that melatonin is also synthesized by macrophages and T lymphocytes, no information is available regarding the temporal profile of the melatonergic system of immune cells and organs in steady-state. Here, the expression of the enzymes arylalkylamine-N-acetyltransferase (AA-NAT), its phosphorylated form (P-AA-NAT) and acetylserotonin-O-methyltransferase (ASMT) were evaluated in phagocytes and T cells of the bone marrow (BM) and spleen. We also determined how the melatonergic system of these cells is modulated by LPS and the cytokine IL-10. The expression of the melatonergic enzymes showed daily rhythms in BM and spleen cells. Melatonin rhythm in the BM, but not in the spleen, follows P-AA-NAT daily variation. In BM cells, LPS and IL10 induced an increase in melatonin levels associated with the increased expressions of P-AA-NAT and ASMT. In spleen cells, LPS induced an increase in the expression of P-AA-NAT but not of melatonin. Conversely, IL10 induced a significant increase in melatonin production associated with increased AA-NAT/P-AA-NAT expressions. In conclusion, BM and spleen cells present different profiles of circadian production of local melatonin and responses to immune signals.

STAT1-NFκB crosstalk triggered by interferon gamma regulates noradrenaline-induced pineal hormonal production

Melatonin production by pineal glands is modulated by several immune signals. The nuclear translocation of nuclear factor kappa-B (NFκB) homodimers, lacking transactivation domains, once induced by lipopolysaccharide (LPS) or tumor necrosis factor (TNF), inhibits the expression of Aanat gene and the synthesis of noradrenaline (NA)-induced melatonin. Interferon gamma (IFN-γ), on the other hand, increases melatonin synthesis. Furthermore, this cytokine activates the signal transducer as well as the activator of transcription 1 (STAT1) pathway, which was never evaluated as a melatonin synthesis modulator before. Reports demonstrated that IFN-γ might also activate NFκB. The present study evaluated the role of STAT1-NFκB crosstalk triggered by IFN-γ regarding the regulation of NA-induced pineal glands' hormonal production. Moreover, IFN-γ treatment increased NA-induced Aanat transcription, in addition to the synthesis of N-acetylserotonin (NAS) and melatonin. These effects were associated with STAT1 nuclear translocation, confirmed by the co-immunoprecipitation of STAT1 and Aanat promoter. Pharmacological STAT1 enhancement augmented NA-induced Aanat transcription as well as NAS and melatonin production. Additionally, IFN-γ induced the nuclear translocation of RelA-NFκB subunits. The blockade of this pathway prevented IFN-γ effects on the pineal function. The present data show that STAT1 and NFκB crosstalk controls melatonin production through a synergistic mechanism, disclosing a new integrative mechanism regarding pineal hormonal activity control.

Pineal gland dysfunction in Alzheimer's disease: relationship with the immune-pineal axis, sleep disturbance, and neurogenesis

Alzheimer’s disease (AD) is a globally common neurodegenerative disease, which is accompanied by alterations to various lifestyle patterns, such as sleep disturbance. The pineal gland is the primary endocrine organ that secretes hormones, such as melatonin, and controls the circadian rhythms. The decrease in pineal gland volume and pineal calcification leads to the reduction of melatonin production. Melatonin has been reported to have multiple roles in the central nervous system (CNS), including improving neurogenesis and synaptic plasticity, suppressing neuroinflammation, enhancing memory function, and protecting against oxidative stress. Recently, reduced pineal gland volume and pineal calcification, accompanied by cognitive decline and sleep disturbances have been observed in AD patients. Here, I review current significant evidence of the contribution of pineal dysfunction in AD to the progress of AD neuropathology. I suggest new insights to understanding the relationship between AD pathogenesis and pineal gland function.

Chronic treatment with dexamethasone alters clock gene expression and melatonin synthesis in rat pineal gland at night

BACKGROUND

Melatonin is a neuroendocrine hormone that regulates many functions involving energy metabolism and behavior in mammals throughout the light/dark cycle. It is considered an output signal of the central circadian clock, located in the suprachiasmatic nucleus of the hypothalamus. Melatonin synthesis can be influenced by other hormones, such as insulin and glucocorticoids in pathological conditions or during stress. Furthermore, glucocorticoids appear to modulate circadian clock genes in peripheral tissues and are associated with the onset of metabolic diseases. In the pineal gland, the modulation of melatonin synthesis by clock genes has already been demonstrated. However, few studies have shown the effects of glucocorticoids on clock genes expression in the pineal gland.

RESULTS

We verified that rats treated with dexamethasone (2 mg/kg body weight, intraperitoneal) for 10 consecutive days, showed hyperglycemia and pronounced hyperinsulinemia during the dark phase. Insulin sensitivity, glucose tolerance, melatonin synthesis, and enzymatic activity of arylalkylamine N-acetyltransferase, the key enzyme of melatonin synthesis, were reduced. Furthermore, we observed an increase in the expression of Bmal1, Per1, Per2, Cry1, and Cry2 in pineal glands of rats treated with dexamethasone.

CONCLUSION

These results show that chronic treatment with dexamethasone can modulate both melatonin synthesis and circadian clock expression during the dark phase.

Disturbances of diurnal phase markers, behavior, and clock genes in a rat model of depression; modulatory effects of agomelatine treatment

Major depressive disorder (MDD) is a growing problem worldwide. Though, the etiology remains unresolved, circadian rhythm disturbances are frequently observed in MDD and thus is speculated to play a key role herein. The present study focuses on circadian rhythm disturbances in the chronic mild stress (CMS) animal model of depression and examined whether the atypical antidepressant, agomelatine, which is mediating its action via melatonergic and serotonergic receptors, is capable of resynchronizing the perturbed rhythm. Melatonin is often used as a marker of the circadian phase, but the functional and behavioral output is dictated on a cellular level by the molecular clock, driven by the clock genes. We applied in situ hybridization histochemistry to measure the expression levels of the core clock genes, period (Per) 1 and 2 and bone and muscle ARNT-like protein 1 (Bmal1), in multiple brain regions believed to be implicated in depression. Agomelatine showed an antidepressant-like effect in the sucrose consumption test and an anxiolytic-like profile in the elevated zero maze. We found that CMS increased nighttime melatonin release in rats and that agomelatine attenuated this effect. Stress was shown to have a time and region-specific effect on clock gene expression in the brain. Treatment with agomelatine failed to normalize clock gene expression, and the observed modifying effect on gene expression did not associate with the antidepressant-like effect. This suggests that the antidepressant actions of agomelatine are mainly independent of circadian rhythm synchronization and, in this regard, not superior to traditional antidepressants tested in our model.

Immune-pineal axis - acute inflammatory responses coordinate melatonin synthesis by pinealocytes and phagocytes

Melatonin is well known for its circadian production by the pineal gland, and there is a growing body of data showing that it is also produced by many other cells and organs, including immune cells. The chronobiotic role of pineal melatonin, as well as its protective effects in vitro and in vivo, have been extensively explored. However, the interaction between the chronobiotic and defence functions of endogenous melatonin has been little investigated. This review details the current knowledge regarding the coordinated shift in melatonin synthesis from the pineal gland (circadian and monitoring roles) to the regulation of acute immune responses via immune cell production and autocrine effects, producing systemic interactions termed the immune-pineal axis. An acute inflammatory response drives the transcription factor, NFκB, to switch melatonin synthesis from pinealocytes to macrophages/microglia and, upon acute inflammatory resolution, back to pinealocytes. The potential pathophysiological relevance of immune-pineal axis dysregulation is highlighted, with both research and clinical implications, across several medical conditions, including host/parasite interaction, neurodegenerative diseases and cancer. LINKED ARTICLES: This article is part of a themed section on Recent Developments in Research of Melatonin and its Potential Therapeutic Applications. To view the other articles in this section visit http://onlinelibrary.wiley.com/doi/10.1111/bph.v175.16/issuetoc.

Agomelatine, venlafaxine, and running exercise effectively prevent anxiety- and depression-like behaviors and memory impairment in restraint stressed rats

Several severe stressful situations, e.g., natural disaster, infectious disease out break, and mass casualty, are known to cause anxiety, depression and cognitive impairment, and preventive intervention for these stress complications is worth exploring. We have previously reported that the serotonin-norepinephrine-dopamine reuptake inhibitor, venlafaxine, as well as voluntary wheel running are effective in the treatment of anxiety- and depression-like behaviors in stressed rats. But whether they are able to prevent deleterious consequences of restraint stress in rats, such as anxiety/depression-like behaviors and memory impairment that occur afterward, was not known. Herein, male Wistar rats were pre-treated for 4 weeks with anti-anxiety/anti-depressive drugs, agomelatine and venlafaxine, or voluntary wheel running, followed by 4 weeks of restraint-induced stress. During the stress period, rats received neither drug nor exercise intervention. Our results showed that restraint stress induced mixed anxiety- and depression-like behaviors, and memory impairment as determined by elevated plus-maze, elevated T-maze, open field test (OFT), forced swimming test (FST), and Morris water maze (MWM). Both pharmacological pre-treatments and running successfully prevented the anxiety-like behavior, especially learned fear, in stressed rats. MWM test suggested that agomelatine, venlafaxine, and running could prevent stress-induced memory impairment, but only pharmacological treatments led to better novel object recognition behavior and positive outcome in FST. Moreover, western blot analysis demonstrated that venlafaxine and running exercise upregulated brain-derived neurotrophic factor (BDNF) expression in the hippocampus. In conclusion, agomelatine, venlafaxine as well as voluntary wheel running had beneficial effects, i.e., preventing the restraint stress-induced anxiety/depression-like behaviors and memory impairment.

Pre-clinical efficacy assessment of Malva sylvestris on chronic skin inflammation

In the search for improved quality of life, the treatment of skin diseases like psoriasis (hyperproliferative disease) is valid, since it causes huge social discomfort to the patient. In this context, earlier studies showed that Malva sylvestris L. has anti-inflammatory activity demonstrated by acute animal models of skin inflammation, becoming a promising target for further studies. The present investigation aimed to verify the effect of hydroalcoholic extract of M. sylvestris (HEMS) on the chronic inflammatory and hyperproliferative response caused by multiple applications of 12-O-tetradecanoylphorbol-13-acetate (TPA) on mouse ears. Topical application of HEMS reduced oedema, leukocyte migration (mono- and polymorphonuclear cells) and keratinocyte hyperproliferation, confirmed by histology and proliferating cell nuclear antigen (PCNA) immunostaining. It was found that the anti-inflammatory effects of the extract did not involve the glucocorticoid system, and its incubation with HaCaT keratinocytes caused low toxicity and reduced cell proliferation by apoptosis. Thus, HEMS proved to be effective as an anti-psoriatic therapy, with the ability to prevent keratinocyte hyperproliferation and with low toxicity by topical application.

Daily corticosterone rhythm modulates pineal function through NFκB-related gene transcriptional program

Melatonin and glucocorticoids are key hormones in determining daily rhythmicity and modulating defense responses. In nocturnal animals, corticosterone peaks at light/dark transition,while melatonin peaks at the middle of the night in both nocturnal and diurnal animals. The crosstalk between adrenal and pineal glands under inflammatory conditions indicates that corticosterone potentiates nocturnal melatonin synthesis by reducing the activity of NFκB. This transcription factor, which modulates the expression of a key enzyme in melatonin synthesis, is sharply reduced at the entrance of darkness in the rat pineal gland. In this study, we established the basis for understanding the crosstalk between adrenal and pineal glands in physiological conditions. Here we show that the expression of 70 out of 84 genes implied in defense responses exhibit a sharp reduction exactly at the entrance of darkness. Mifepristone impair the changes of 13 out of 84 genes, suggesting that the rhythm of corticosterone modulates pineal phenotype, as mifepristone also reduces the expression of Aanat and the nocturnal synthesis of melatonin. Therefore, darkness-induced synthesis of the pineal hormone, besides being controlled by the central clock located in the hypothalamus, is also influencedby glucocorticoids through the regulation of NFκB transcriptional program.

Dual Effect of Catecholamines and Corticosterone Crosstalk on Pineal Gland Melatonin Synthesis

BACKGROUND/AIM

The nocturnal production of melatonin by the pineal gland is triggered by sympathetic activation of adrenoceptors and may be modulated by immunological signals. The effect of glucocorticoids on nocturnal melatonin synthesis is controversial; both stimulatory and inhibitory effects have been reported. During pathophysiological processes, an increased sympathetic tonus could result in different patterns of adrenoceptor activation in the pineal gland. Therefore, in this investigation, we evaluated whether the pattern of adrenergic stimulation of the pineal gland drives the direction of the glucocorticoid effect on melatonin production.

METHODS

The corticosterone effect on the pineal hormonal production induced by β-adrenoceptor or β+α1-adrenoceptor activation was evaluated in cultured glands. We also investigated whether the in vivo lipopolysaccharide (LPS)-induced inhibition of melatonin is dependent on the interaction of glucocorticoids and the α1-adrenoceptor in adrenalectomized animals and on the in vivo blockade of glucocorticoid receptors (GRs) or the α1-adrenoceptor.

RESULTS

Corticosterone potentiated β-adrenoceptor-induced pineal melatonin synthesis, whilst corticosterone-dependent inhibition was observed when melatonin production was induced by β+α1-adrenoceptors agonists. The inhibitory effect of corticosterone is mediated by GR, as it was abolished in the presence of a GR antagonist. Moreover, LPS-induced reduction in melatonin nocturnal plasma content was reversed by adrenalectomy and by antagonizing GR or α1-adrenoceptors.

CONCLUSIONS

The dual effect of corticosterone on pineal melatonin synthesis is determined by the activation pattern of adrenoceptors (β or β+α1) in the gland during GR activation, suggesting that increased activation of the sympathetic system and the hypothalamic-pituitary-adrenal axis are necessary for the control of melatonin production during defense responses.

Melatonin regulates catecholamine biosynthesis by modulating bone morphogenetic protein and glucocorticoid actions

Melatonin is functionally involved in the control of circadian rhythm and hormonal secretion. In the present study, we investigated the roles of melatonin in the interaction of catecholamine synthesis with adrenocortical steroids by focusing on bone morphogenetic protein (BMP)-4 expressed in the adrenal medulla using rat pheochromocytoma PC12 cells. Melatonin treatment significantly reduced the mRNA expression of catecholamine synthases, including the rate-limiting enzyme tyrosine hydroxylase (Th), 3,4-dihydroxyphenylalanine decarboxylase and dopamine-β-hydroxylase expressed in PC12 cells. In accordance with changes in the expression levels of enzymes, dopamine production and cAMP synthesis determined in the culture medium and cell lysate were also suppressed by melatonin. The MT1 receptor, but not the MT2 receptor, was expressed in PC12 cells, and luzindole treatment reversed the inhibitory effect of melatonin on Th expression, suggesting that MT1 is a functional receptor for the control of catecholamine synthesis. Interestingly, melatonin enhanced the inhibitory effect of BMP-4 on Th mRNA expression in PC12 cells. Melatonin treatment accelerated BMP-4-induced phosphorylation of SMAD1/5/8 and transcription of the BMP target gene Id1. Of note, melatonin significantly upregulated Alk2 and Bmpr2 mRNA levels but suppressed inhibitory Smad6/7 expression, leading to the enhancement of SMAD1/5/8 signaling in PC12 cells, while BMP-4 did not affect Mt1 expression. Regarding the interaction with adrenocortical steroids, melatonin preferentially enhanced glucocorticoid-induced Th mRNA through upregulation of the glucocorticoid receptor and downregulation of Bmp4 expression, whereas melatonin repressed Th mRNA expression induced by aldosterone or androgen without affecting expression levels of the receptors for mineralocorticoid and androgen. Collectively, the results indicate that melatonin plays a modulatory role in catecholamine synthesis by cooperating with BMP-4 and glucocorticoid in the adrenal medulla.

ACTH modulation on corticosterone, melatonin, testosterone and innate immune response in the tree frog Hypsiboas faber

The modulation exerted by glucocorticoids in physiological responses to stressors is essential for maintaining short-term homeostasis. However, highly frequent and/or prolonged activation of the hypothalamic-pituitary-adrenal/interrenal axis may inhibit processes that are important to long-term fitness and health, including reproduction and immunocompetence. The present study evaluates the response to adrenocorticotropic hormone (ACTH) injection in the adult male tree frog, Hypsiboas faber, as indicated by levels of plasma corticosterone (CORT), plasma testosterone (T), ocular melatonin (MEL), hematocrit and immune functioning (total leukocyte count and bacterial killing ability against Escherichia coli). All levels were measured 1, 3 and 6h after treatment. ACTH increased CORT levels whilst decreasing T and MEL levels at 1h post-treatment. 6h after ACTH injection, hematocrit and MEL levels increased. ACTH treatment did not significantly modulate the immune measures over the time-range sampled. The hormonal changes observed in response to ACTH treatment suggest that stressors could act as inhibitors of reproductive activity, as well as differentially modulating melatonin levels at different time-points.

Hydroalcoholic extract of Sapium glandulatum (Vell.) Pax displays potent anti-inflammatory activities through a glucocorticoid receptor-dependent pathway

BACKGROUND

Ethnobotanical studies of the Sapium genus reveal that many species are widely used in several countries as therapeutic drugs and they are widely used in folk medicine for treatment of different diseases, including skin inflammation. This raises interest in the study of the pharmacological properties and phytochemical composition of these plants. The biological properties of Sapium glandulatum, a native species of southern Brazil, has not been reported in the literature.

PURPOSE

The aim of the present study was to investigate the anti-inflammatory action of the hydroalcoholic extract of Sapium glandulatum (EHSG) leaves in mouse models of acute or chronic skin inflammation.

STUDY DESIGN/METHODS

Topical effects of EHSG were evaluated in 12-O-tetradecanoylphorbol-13-acetate (TPA)-induced edema in the ear. Systemic effects of the extract were studied in a TPA-induced ear edema model, as well as in a carrageenan-induced paw edema model. To gain insight into the mechanism by which EHSG blocked inflammation, we evaluated the role of glucocorticoid receptors (GR) using the TPA-induced ear edema model and also measured specific binding in a glucocorticoid assay. Possible adverse effects of EHSG were evaluated after multiple treatments with the extract in the skin atrophy model on the ear and with the alkaline comet assay.

RESULTS

EHSG presented potent anti-inflammatory activity when applied topically in acute and chronic models, inhibiting edema formation and leukocyte migration as well as expression pro-inflammatory cytokines IL-1β, IL-6 and TNF-α in the tissue. Similar anti-inflammatory effects were found following oral treatment in both ear and paw edema models. Strikingly, the EHSG-induced blockade of leukocyte migration was reversed by mifepristone, a GR antagonist. Additionally, a specific binding assay revealed that ESGH interacts with GR. Multiple treatments with EHSG failed to induce adverse effects when evaluated in the skin atrophy model and bone marrow genotoxicity test.

CONCLUSION

Taken together, our data suggest that EHSG is a potential source of anti-inflammatory tool compounds for the treatment of pro-inflammatory-derived skin diseases, and its mechanism of action may be, at least in part, via the GR pathway.

Melatoninergic System in Parkinson's Disease: From Neuroprotection to the Management of Motor and Nonmotor Symptoms

Melatonin is synthesized by several tissues besides the pineal gland, and beyond its regulatory effects in light-dark cycle, melatonin is a hormone with neuroprotective, anti-inflammatory, and antioxidant properties. Melatonin acts as a free-radical scavenger, reducing reactive species and improving mitochondrial homeostasis. Melatonin also regulates the expression of neurotrophins that are involved in the survival of dopaminergic neurons and reduces α-synuclein aggregation, thus protecting the dopaminergic system against damage. The unbalance of pineal melatonin synthesis can predispose the organism to inflammatory and neurodegenerative diseases such as Parkinson's disease (PD). The aim of this review is to summarize the knowledge about the potential role of the melatoninergic system in the pathogenesis and treatment of PD. The literature reviewed here indicates that PD is associated with impaired brain expression of melatonin and its receptors MT₁ and MT₂. Exogenous melatonin treatment presented an outstanding neuroprotective effect in animal models of PD induced by different toxins, such as 6-hydroxydopamine (6-OHDA), 1-methyl-4-phenyl-1,2,3,6-tetrahydropyridine (MPTP), rotenone, paraquat, and maneb. Despite the neuroprotective effects and the improvement of motor impairments, melatonin also presents the potential to improve nonmotor symptoms commonly experienced by PD patients such as sleep and anxiety disorders, depression, and memory dysfunction.

The RelA/cRel nuclear factor-κB (NF-κB) dimer, crucial for inflammation resolution, mediates the transcription of the key enzyme in melatonin synthesis in RAW 264.7 macrophages

Lipopolysaccharide (LPS) modulates the transcription of the gene that codifies the enzyme arylalkylamine-N-acetyltransferase (AA-NAT) through nuclear translocation of the transcription factor nuclear factor-κ-light-chain-enhancer of activated B cells (NF-κB). AA-NAT converts serotonin to N-acetylserotonin, the ultimate precursor of melatonin. Activation of kappa B elements (aa-nat-κB), localized in the promoter (nat-κB1 and nat-κB2), leads to Aa-nat transcription in RAW 264.7 macrophages. Competitive electrophoretic mobility shift assay (EMSA) with oligonucleotide probes corresponding to each of the two elements, as well as a NF-κB consensus corresponding probe, revealed different specificities for each κB element. In addition, activator protein-1 (AP-1) as well as signal transducers and activator of transcription-1 and 3 (STAT-1; STAT-3) competed with NF-κB for binding to nat-κB1, while only STAT-3 competed with NF-κB for binding to nat-κB2. According to co-immunoprecipitation (ChiP) assays, these two sites are able to distinguish NF-κB subunits. The sequence nat-κB1 bound dimers containing p52, RelA, and cRel, while nat-κB2 bound preferentially p50, p52, and RelA, and did not bind cRel. The expression of RelA and cRel is essential for the induction of Aa-nat expression and melatonin synthesis. Considering that the expression of cRel is induced by the earlier expressed p50/RelA, the differential effects of NF-κB dimers may be intimately associated with the temporal regulation of inflammatory responses, with the resolution phase being associated with paracrine and autocrine melatonin effects. Such data suggest that the proven effects of exogenous melatonin in the resolution phase of inflammation are paralleled by the effects of locally synthesized melatonin in immune cells.

Central Interleukin-1β Suppresses the Nocturnal Secretion of Melatonin

In vertebrates, numerous processes occur in a rhythmic manner. The hormonal signal reliably reflecting the environmental light conditions is melatonin. Nocturnal melatonin secretion patterns could be disturbed in pathophysiological states, including inflammation, Alzheimer's disease, and depression. All of these states share common elements in their aetiology, including the overexpression of interleukin- (IL-) 1β in the central nervous system. Therefore, the present study was designed to determine the effect of the central injection of exogenous IL-1β on melatonin release and on the expression of the enzymes of the melatonin biosynthetic pathway in the pineal gland of ewe. It was found that intracerebroventricular injections of IL-1β (50 µg/animal) suppressed (P < 0.05) nocturnal melatonin secretion in sheep regardless of the photoperiod. This may have resulted from decreased (P < 0.05) synthesis of the melatonin intermediate serotonin, which may have resulted, at least partially, from a reduced expression of tryptophan hydroxylase. IL-1β also inhibited (P < 0.05) the expression of the melatonin rhythm enzyme arylalkylamine-N-acetyltransferase and hydroxyindole-O-methyltransferase. However, the ability of IL-1β to affect the expression of these enzymes was dependent upon the photoperiod. Our study may shed new light on the role of central IL-1β in the aetiology of disruptions in melatonin secretion.

Disturbed diurnal rhythm of three classical phase markers in the chronic mild stress rat model of depression

Disturbances of circadian rhythms have been suggested to be a causal factor in the development of major depressive disorder. However, the mechanisms underlying the association between circadian rhythm abnormalities and mood disorders are still unknown. In the current study the association between diurnal pattern of key phase markers (melatonin, corticosterone, and core body temperature) and anhedonic-like behavior was investigated using the highly validated rat chronic mild stress (CMS) model of depression. Phase marker measurements were done after 3.5 weeks of CMS in 48 control rats and 48 anhedonic-like rats at 6 time points within 24h. The results showed that anhedonic-like behavior associates with changes in all three phase markers: an increased dark phase melatonin secretion, an additional peak in corticosterone level in the beginning of the light phase, and hypothermia in the dark phase. The result adds to the validity of the CMS model in general and in particular to be adequate as a model for studying the chronobiology of depressive disorder.

Adenosine triphosphate inhibits melatonin synthesis in the rat pineal gland

Adenosine triphosphate (ATP) is released onto the pinealocyte, along with noradrenaline, from sympathetic neurons and triggers P2Y1 receptors that enhance β-adrenergic-induced N-acetylserotonin (NAS) synthesis. Nevertheless, the biotransformation of NAS into melatonin, which occurs due to the subsequent methylation by acetylserotonin O-methyltransferase (ASMT; EC 2.1.1.4), has not yet been evaluated in the presence of purinergic stimulation. We therefore evaluated the effects of purinergic signaling on melatonin synthesis induced by β-adrenergic stimulation. ATP increased NAS levels, but, surprisingly, inhibited melatonin synthesis in an inverse, concentration-dependent manner. Our results demonstrate that enhanced NAS levels, which depend on phospholipase C (PLC) activity (but not the induction of gene transcription), are a post-translational effect. By contrast, melatonin reduction is related to an ASMT inhibition of expression at both the gene transcription and protein levels. These results were independent of nuclear factor-kappa B (NF-kB) translocation. Neither the P2Y1 receptor activation nor the PLC-mediated pathway was involved in the decrease in melatonin, indicating that ATP regulates pineal metabolism through different mechanisms. Taken together, our data demonstrate that purinergic signaling differentially modulates NAS and melatonin synthesis and point to a regulatory role for ATP as a cotransmitter in the control of ASMT, the rate-limiting enzyme in melatonin synthesis. The endogenous production of melatonin regulates defense responses; therefore, understanding the mechanisms involving ASMT regulation might provide novel insights into the development and progression of neurological disorders since melatonin presents anti-inflammatory, neuroprotective, and neurogenic effects.

Effects of acute restraint stress, prolonged captivity stress and transdermal corticosterone application on immunocompetence and plasma levels of corticosterone on the cururu Toad (Rhinella icterica)

Glucocorticoid steroids modulate immunocompetence in complex ways with both immunoenhancing and immunosuppressive effects in vertebrates exposed to different stressors. Such bimodal effects have been associated with variation in duration and intensity of the stress response. Given that natural populations have been exposed to a multitude of stressors, a better understanding of the functional association between duration and intensity of the stress response, the resulting changes in glucocorticoid plasma levels and their impact on different aspects of immunocompetence emerges as a cornerstone for vertebrate conservation strategies. We investigated the effects of a restraint challenge (with and without movement restriction), long-term captivity, and transdermal corticosterone application on plasma levels of corticosterone (hereinafter referred to as CORT) and different parameters of innate immunocompetence in the male cururu toads (Rhinella icterica). We show that for R. icterica restraint for 24h proved to be a stressful condition, increasing CORT by 3-fold without consistent immunological changes. However, the application of a more intense stressor (restraint with movement restriction), for the same period, potentiated this response resulting in a 9-fold increase in CORT, associated with increase Neutrophil/Lymphocyte ratio (N:L) and a lower bacterial killing ability (BKA). Transdermal application of corticosterone efficiently mimics repeated acute stress response events, without changing the immune parameters even after 13 days of treatment. Interestingly, long-term captivity did not mitigate the stress response, since the toads maintained 3-fold increased CORT even after 3 months under these conditions. Moreover, long-term captivity in the same condition increased total leukocyte count (TLC) and generated an even greater decrease in BKA, suggesting that consequences of the stress response can be aggravated by time in captivity.

The cellular state determines the effect of melatonin on the survival of mixed cerebellar cell culture

The constitutive activation of nuclear factor-κB (NF-κB), a key transcription factor involved in neuroinflammation, is essential for the survival of neurons in situ and of cerebellar granule cells in culture. Melatonin is known to inhibit the activation of NF-κB and has a cytoprotective function. In this study, we evaluated whether the cytoprotective effect of melatonin depends on the state of activation of a mixed cerebellar culture that is composed predominantly of granule cells; we tested the effect of melatonin on cultured rat cerebellar cells stimulated or not with lipopolysaccharide (LPS). The addition of melatonin (0.1 nM–1 µM) reduced the survival of naïve cells while inhibiting LPS-induced cell death. Melatonin (100 nM) transiently (15 min) inhibited the nuclear translocation of both NF-κB dimers (p50/p50, p50/RelA) and, after 60 min, increased the activation of p50/RelA. Melatonin-induced p50/RelA activity in naïve cells resulted in the transcription of inducible nitric oxide synthase (iNOS) and the production of NO. Otherwise, in cultures treated with LPS, melatonin blocked the LPS-induced activation of p50/RelA and the reduction in p50/p50 levels and inhibited iNOS expression and NO synthesis. Therefore, melatonin in vehicle-treated cells induces cell death, while it protects against LPS-induced cytotoxicity. In summary, we confirmed that melatonin is a neuroprotective drug when cerebellar cells are challenged; however, melatonin can also lead to cell death when the normal balance of the NF-κB pathway is disturbed. Our data provide a mechanistic basis for understanding the influence of cell context on the final output response of melatonin.

Protein kinase A mediates adenosine A2a receptor modulation of neurotransmitter release via synapsin I phosphorylation in cultured cells from medulla oblongata

Synaptic transmission is an essential process for neuron physiology. Such process is enabled in part due to modulation of neurotransmitter release. Adenosine is a synaptic modulator of neurotransmitter release in the Central Nervous System, including neurons of medulla oblongata, where several nuclei are involved with neurovegetative reflexes. Adenosine modulates different neurotransmitter systems in medulla oblongata, specially glutamate and noradrenaline in the nucleus tractussolitarii, which are involved in hypotensive responses. However, the intracellular mechanisms involved in this modulation remain unknown. The adenosine A2a receptor modulates neurotransmitter release by activating two cAMP protein effectors, the protein kinase A and the exchange protein activated by cAMP. Therefore, an in vitro approach (cultured cells) was carried out to evaluate modulation of neurotransmission by adenosine A2a receptor and the signaling intracellular pathway involved. Results show that the adenosine A2a receptor agonist, CGS 21680, increases neurotransmitter release, in particular, glutamate and noradrenaline and such response is mediated by protein kinase A activation, which in turn increased synapsin I phosphorylation. This suggests a mechanism of A2aR modulation of neurotransmitter release in cultured cells from medulla oblongata of Wistar rats and suggest that protein kinase A mediates this modulation of neurotransmitter release via synapsin I phosphorylation.

'Chronomics' in ICU: circadian aspects of immune response and therapeutic perspectives in the critically ill

Complex interrelations exist between the master central clock, located in the suprachiasmatic nuclei of the hypothalamus, and several peripheral clocks, such as those found in different immune cells of the body. Moreover, external factors that are called ‘timekeepers’, such as light/dark and sleep/wake cycles, interact with internal clocks by synchronizing their different oscillation phases. Chronobiology is the science that studies biologic rhythms exhibiting recurrent cyclic behavior. Circadian rhythms have a duration of approximately 24 h and can be assessed through chronobiologic analysis of time series of melatonin, cortisol, and temperature. Critically ill patients experience severe circadian deregulation due to not only the lack of effective timekeepers in the intensive care unit (ICU) environment but also systemic inflammation. The latter has been found in both animal and human studies to disrupt circadian rhythmicity of all measured biomarkers. The aims of this article are to describe circadian physiology during acute stress and to discuss the effects of ICU milieu upon circadian rhythms, in order to emphasize the value of considering circadian-immune disturbance as a potential tool for personalized treatment. Thus, besides neoplastic processes, critical illness could be linked to what has been referred as ‘chronomics’: timing and rhythm. In addition, different therapeutic perspectives will be presented in association with environmental approaches that could restore circadian connection and hasten physical recovery.

Modulation of pineal melatonin synthesis by glutamate involves paracrine interactions between pinealocytes and astrocytes through NF-κB activation

The glutamatergic modulation of melatonin synthesis is well known, along with the importance of astrocytes in mediating glutamatergic signaling in the central nervous system. Pinealocytes and astrocytes are the main cell types in the pineal gland. The objective of this work was to investigate the interactions between astrocytes and pinealocytes as a part of the glutamate inhibitory effect on melatonin synthesis. Rat pinealocytes isolated or in coculture with astrocytes were incubated with glutamate in the presence of norepinephrine, and the melatonin content, was quantified. The expression of glutamate receptors, the intracellular calcium content and the NF-κB activation were analyzed in astrocytes and pinealocytes. TNF-α's possible mediation of the effect of glutamate was also investigated. The results showed that glutamate's inhibitory effect on melatonin synthesis involves interactions between astrocytes and pinealocytes, possibly through the release of TNF-α. Moreover, the activation of the astrocytic NF-κB seems to be a necessary step. In astrocytes and pinealocytes, AMPA, NMDA, and group I metabotropic glutamate receptors were observed, as well as the intracellular calcium elevation. In conclusion, there is evidence that the modulation of melatonin synthesis by glutamate involves paracrine interactions between pinealocytes and astrocytes through the activation of the astrocytic NF-κB transcription factor and possibly by subsequent TNF-α release.

Expression of melatonin synthesizing enzymes in Helicobacter pylori infected gastric mucosa

Helicobacter pylori colonization of gastric mucosa causes pain of unknown etiology in about 15-20% of infected subjects. The aim of the present work was to determine the level of expression of enzymes involved in the synthesis of melatonin in gastric mucosa of asymptomatic and symptomatic H. pylori infected patients. To diagnose H. pylori infection, histological analysis and the urea breath test (UBT C13) were performed. The levels of mRNA expression of arylalkylamine-N-acetyltransferase (AA-NAT) and acetylserotonin methyltransferase (ASMT) were estimated in gastric mucosa with RT-PCR. The level of AA-NAT expression and AMST was decreased in H. pylori infected patients and was increased after H. pylori eradication. We conclude that decreased expression of melatonin synthesizing enzymes, AA-NAT and ASMT, in patients with symptomatic H. pylori infection returns to normal level after H. pylori eradication.

Immune-pineal axis: nuclear factor κB (NF-kB) mediates the shift in the melatonin source from pinealocytes to immune competent cells

Pineal gland melatonin is the darkness hormone, while extra-pineal melatonin produced by the gonads, gut, retina, and immune competent cells acts as a paracrine or autocrine mediator. The well-known immunomodulatory effect of melatonin is observed either as an endocrine, a paracrine or an autocrine response. In mammals, nuclear translocation of nuclear factor κ-light-chain-enhancer of activated B cells (NF-κB) blocks noradrenaline-induced melatonin synthesis in pinealocytes, which induces melatonin synthesis in macrophages. In addition, melatonin reduces NF-κB activation in pinealocytes and immune competent cells. Therefore, pathogen- or danger-associated molecular patterns transiently switch the synthesis of melatonin from pinealocytes to immune competent cells, and as the response progresses melatonin inhibition of NF-κB activity leads these cells to a more quiescent state. The opposite effect of NF-κB in pinealocytes and immune competent cells is due to different NF-κB dimers recruited in each phase of the defense response. This coordinated shift of the source of melatonin driven by NF-κB is called the immune-pineal axis. Finally, we discuss how this concept might be relevant to a better understanding of pathological conditions with impaired melatonin rhythms and hope it opens new horizons for the research of side effects of melatonin-based therapies.

Zebrafish Expression Ontology of Gene Sets (ZEOGS): a tool to analyze enrichment of zebrafish anatomical terms in large gene sets

The zebrafish (Danio rerio) is an established model organism for developmental and biomedical research. It is frequently used for high-throughput functional genomics experiments, such as genome-wide gene expression measurements, to systematically analyze molecular mechanisms. However, the use of whole embryos or larvae in such experiments leads to a loss of the spatial information. To address this problem, we have developed a tool called Zebrafish Expression Ontology of Gene Sets (ZEOGS) to assess the enrichment of anatomical terms in large gene sets. ZEOGS uses gene expression pattern data from several sources: first, in situ hybridization experiments from the Zebrafish Model Organism Database (ZFIN); second, it uses the Zebrafish Anatomical Ontology, a controlled vocabulary that describes connected anatomical structures; and third, the available connections between expression patterns and anatomical terms contained in ZFIN. Upon input of a gene set, ZEOGS determines which anatomical structures are overrepresented in the input gene set. ZEOGS allows one for the first time to look at groups of genes and to describe them in terms of shared anatomical structures. To establish ZEOGS, we first tested it on random gene selections and on two public microarray datasets with known tissue-specific gene expression changes. These tests showed that ZEOGS could reliably identify the tissues affected, whereas only very few enriched terms to none were found in the random gene sets. Next we applied ZEOGS to microarray datasets of 24 and 72 h postfertilization zebrafish embryos treated with beclomethasone, a potent glucocorticoid. This analysis resulted in the identification of several anatomical terms related to glucocorticoid-responsive tissues, some of which were stage-specific. Our studies highlight the ability of ZEOGS to extract spatial information from datasets derived from whole embryos, indicating that ZEOGS could be a useful tool to automatically analyze gene expression pattern features of any large zebrafish gene set.

Endothelial cell adhesiveness is a function of environmental lighting and melatonin level

The endothelial layer regulates the traffic of cells and substances between the blood and tissues and plays a central role in the mounting of an inflammatory response. We have recently shown that inhibition of the nocturnal melatonin surge during the mounting of an inflammatory response primes endothelial cells to a highly reactive state, increasing the expression of adhesion molecules and inducible nitric oxide synthase (iNOS) as well as the in vitro adherence of leukocytes. Here, we investigated whether physiological variations in the plasma melatonin levels owing to the light/dark environmental cycle could also prime the reactive state of endothelial cells. Cultured endothelial cells (16-20 days) obtained from rats killed during the daytime adhere more neutrophils, expressed more adhesion molecules and iNOS, and had a higher content of the transcription factor nuclear factor kappa B (NF-kB) translocated to the nuclei. We also evaluated the expression of 84 genes (using real-time PCR array) related to the innate inflammatory response and observed a higher expression of 19 genes in cultures obtained during the daytime. In addition, the only gene that was highly expressed in cells obtained from rats killed during nighttime was one that encodes a protein that negatively modulates inflammatory response. In conclusion, the daily rhythm of melatonin also primes the ability of endothelial cells to adhere to neutrophils. This new approach for evaluating the influence of the donor on cells maintained in culture should have applications for the standardization of cell banks.

An agent-based model of cellular dynamics and circadian variability in human endotoxemia

As cellular variability and circadian rhythmicity play critical roles in immune and inflammatory responses, we present in this study an agent-based model of human endotoxemia to examine the interplay between circadian controls, cellular variability and stochastic dynamics of inflammatory cytokines. The model is qualitatively validated by its ability to reproduce circadian dynamics of inflammatory mediators and critical inflammatory responses after endotoxin administration in vivo. Novel computational concepts are proposed to characterize the cellular variability and synchronization of inflammatory cytokines in a population of heterogeneous leukocytes. Our results suggest that there is a decrease in cell-to-cell variability of inflammatory cytokines while their synchronization is increased after endotoxin challenge. Model parameters that are responsible for IκB production stimulated by NFκB activation and for the production of anti-inflammatory cytokines have large impacts on system behaviors. Additionally, examining time-dependent systemic responses revealed that the system is least vulnerable to endotoxin in the early morning and most vulnerable around midnight. Although much remains to be explored, proposed computational concepts and the model we have pioneered will provide important insights for future investigations and extensions, especially for single-cell studies to discover how cellular variability contributes to clinical implications.

The concept of the immune-pineal axis tested in patients undergoing an abdominal hysterectomy

OBJECTIVE

Activation of the immune-pineal axis induces a transient reduction in nocturnal melatonin in the plasma during the proinflammatory phase of an innate immune response to allow the proper migration of leukocytes to the lesion site. This transient reduction should be regulated by inflammatory mediators, which are responsible for the fine-tuning of the process. In the present study, we measured the pre- and postoperative serum concentrations of melatonin, tumor necrosis factor (TNF) and cortisol in women who underwent an elective hysterectomy and correlated the variation in melatonin with postoperative pain.

METHODS

We evaluated 12 women who had an abdominal hysterectomy. Blood was collected at 10.00 and 22.00 h 1 week and 1 day before the surgery, on the 1st and 2nd days after the surgery and at 22.00 h on the day of the surgery.

RESULTS

On the night after the surgery, there was no melatonin detected at 22.00 h. High TNF levels were accompanied by a lower nocturnal melatonin output, higher postoperative pain according to a visual analog scale and the request of higher doses of analgesics. In addition, low cortisol levels were accompanied by a lower nocturnal melatonin output.

CONCLUSION

Our results confirm that the same antagonistic pattern between TNF and glucocorticoids observed in cultured pineal glands also occurs in humans. This integrative pattern suggests that the cross talk between the immune and endocrine system orchestrates longitudinal changes in pineal activity, reinforcing the hypothesis of an immune-pineal axis.

NF-κB drives the synthesis of melatonin in RAW 264.7 macrophages by inducing the transcription of the arylalkylamine-N-acetyltransferase (AA-NAT) gene

We demonstrate that during inflammatory responses the nuclear factor kappa B (NF-κB) induces the synthesis of melatonin by macrophages and that macrophage-synthesized melatonin modulates the function of these professional phagocytes in an autocrine manner. Expression of a DsRed2 fluorescent reporter driven by regions of the aa-nat promoter, that encodes the key enzyme involved in melatonin synthesis (arylalkylamine-N-acetyltransferase), containing one or two upstream κB binding sites in RAW 264.7 macrophage cell lines was repressed when NF-κB activity was inhibited by blocking its nuclear translocation or its DNA binding activity or by silencing the transcription of the RelA or c-Rel NF-κB subunits. Therefore, transcription of aa-nat driven by NF-κB dimers containing RelA or c-Rel subunits mediates pathogen-associated molecular patterns (PAMPs) or pro-inflammatory cytokine-induced melatonin synthesis in macrophages. Furthermore, melatonin acts in an autocrine manner to potentiate macrophage phagocytic activity, whereas luzindole, a competitive antagonist of melatonin receptors, decreases macrophage phagocytic activity. The opposing functions of NF-κB in the modulation of AA-NAT expression in pinealocytes and macrophages may represent the key mechanism for the switch in the source of melatonin from the pineal gland to immune-competent cells during the development of an inflammatory response.

Pineal arylalkylamine N-acetyltransferase (Aanat) gene expression as a target of inflammatory mediators in the chicken

Previously, we demonstrated that experimental peritonitis in chickens was attenuated by treatment with exogenous melatonin, while the developing inflammation decreased pineal AANAT activity. This suggested the existence of a bidirectional relationship between the activated immune system and pineal gland function. The aim of the present study was to identify the step(s) in the chicken pineal melatonin biosynthetic pathway that are affected by inflammation. Peritonitis was evoked by i.p. injection of thioglycollate solution, either 2h after the start, or 2h before the end of the light period, and the animals were sacrificed 4h later. The effect of inflammation on the expression of genes encoding enzymes participating in melatonin biosynthesis in the pineal gland, i.e. tryptophan hydroxylase 1 (Tph1), dopa decarboxylase (Ddc), arylalkylamine N-acetyltransferase (Aanat) and acetylserotonin O-methyltransferase (Asmt), was evaluated by qPCR. The pineal and serum melatonin concentration as well as the content of its precursors in the pineal gland were measured, along with the activity of the relevant biosynthetic enzymes. Developing peritonitis caused an increase in the pineal levels of the Tph1 mRNA during the night and the Asmt mRNA during the day, while nocturnal Aanat transcription was reduced. Both the pineal and serum melatonin level and the pineal content of N-acetylserotonin (NAS) were decreased during the night in birds with peritonitis. The amount and activity of pineal AANAT were significantly reduced, while the activity of HIOMT was increased under these experimental conditions. These results indicate that the observed decrease in MEL biosynthesis in chickens with developing inflammation is a result of transcriptional downregulation of the Aanat gene, followed by reduced synthesis and activity of the encoded enzyme.

Plasma corticosterone elevation inhibits the activation of nuclear factor kappa B (NFKB) in the Syrian hamster pineal gland

We evaluated how the mild stress-induced increase in endogenous corticosterone affected the pineal gland in Syrian hamsters (Mesocricetus auratus). The animals were maintained under constant light for 1 day, instead of a cycle of 14:10-h, to increase the circulating corticosterone levels during the daytime. The nuclear translocation of nuclear factor kappa B (NFKB), which is the pivotal transcription factor for stress and injury, presented a daily rhythm in normal animals. NFKB nuclear content increased linearly from the onset of light [Zeitgeber Time 0 (ZT0)] until ZT11 and decreased after ZT12 when the plasma corticosterone peak was detected in normal animals. However, the 24-h profiles of the two curves were different, and they did not clearly support an exclusive relationship between corticosterone levels and NFKB content. Therefore, we tested the effect of increased endogenous corticosterone through inducing mild stress by maintaining daytime illumination for one night. This stressful condition, which increased daytime corticosterone levels, resulted in a daytime decrease in NFKB nuclear content, and this was inhibited by mifepristone. Overall, this study shows that NFKB has a daily rhythm in Syrian hamster pineal glands and, by increasing endogenous corticosterone with a stressful condition, NFKB activity is regulated. Therefore, this study suggests that the pineal gland in the Syrian hamster is a sensor of stressful conditions.

Neuroimmune endocrine effects of antidepressants

Antidepressant pharmacotherapy is to date the most often used treatment for depression, but the exact mechanism of action underlying its therapeutic effect is still unclear. Many theories have been put forward to account for depression, as well as antidepressant activity, but none of them is exhaustive. Neuroimmune endocrine impairment is found in depressed patients; high levels of circulating corticosteroids along with hyperactivation of the immune system, high levels of proinflammatory cytokines, low levels of melatonin in plasma and urine, and disentrainment of circadian rhythms have been demonstrated. Moreover, antidepressant treatment seems to correct or at least to interfere with these alterations. In this review, we summarize the complex neuroimmune endocrine and chronobiological alterations found in patients with depression and how these systems interact with each other. We also explain how antidepressant therapy can modify these systems, along with some possible mechanisms of action shown in animal and human models.

Molecular basis for defining the pineal gland and pinealocytes as targets for tumor necrosis factor

The pineal gland, the gland that translates darkness into an endocrine signal by releasing melatonin at night, is now considered a key player in the mounting of an innate immune response. Tumor necrosis factor (TNF), the first pro-inflammatory cytokine to be released by an inflammatory response, suppresses the translation of the key enzyme of melatonin synthesis (arylalkylamine-N-acetyltransferase, Aanat). Here, we show that TNF receptors of the subtype 1 (TNF-R1) are expressed by astrocytes, microglia, and pinealocytes. We also show that the TNF signaling reduces the level of inhibitory nuclear factor kappa B protein subtype A (NFKBIA), leading to the nuclear translocation of two NFKB dimers, p50/p50, and p50/RelA. The lack of a transactivating domain in the p50/p50 dimer suggests that this dimer is responsible for the repression of Aanat transcription. Meanwhile, p50/RelA promotes the expression of inducible nitric oxide synthase (iNOS) and the production of nitric oxide, which inhibits adrenergically induced melatonin production. Together, these data provide a mechanistic basis for considering pinealocytes a target of TNF and reinforce the idea that the suppression of pineal melatonin is one of the mechanisms involved in mounting an innate immune response.

Long-lasting priming of endothelial cells by plasma melatonin levels

Background

Endothelial cells are of great interest for cell therapy and tissue engineering. Understanding the heterogeneity among cell lines originating from different sources and culture protocols may allow more standardized material to be obtained. In a recent paper, we showed that adrenalectomy interferes with the expression of membrane adhesion molecules on endothelial cells maintained in culture for 16 to 18 days. In addition, the pineal hormone, melatonin, reduces the adhesion of neutrophils to post-capillary veins in rats. Here, we evaluated whether the reactivity of cultured endothelial cells maintained for more than two weeks in culture is inversely correlated to plasma melatonin concentration.

Methodology/Principal Findings

The nocturnal levels of melatonin were manipulated by treating rats with LPS. Nocturnal plasma melatonin, significantly reduced two hours after LPS treatment, returned to control levels after six hours. Endothelial cells obtained from animals that had lower nocturnal melatonin levels significantly express enhanced adhesion molecules and iNOS, and have more leukocytes adhered than cells from animals that had normal nocturnal levels of melatonin (naïve or injected with vehicle). Endothelial cells from animals sacrificed two hours after a simultaneous injection of LPS and melatonin present similar phenotype and function than those obtained from control animals. Analyzing together all the data, taking into account the plasma melatonin concentration versus the expression of adhesion molecules or iNOS we detected a significant inverse correlation.

Conclusions/Significance

Our data strongly suggest that the plasma melatonin level primes endothelial cells “in vivo,” indicating that the state of the donor animal is translated to cells in culture and therefore, should be considered for establishing cell banks in ideal conditions.