Antioxidant effects of N-acetylserotonin: possible mechanisms and clinical implications

Investigating metabolic dysregulation in serum of triple transgenic Alzheimer's disease male mice: implications for pathogenesis and potential biomarkers

Alzheimer's disease (AD) is a multifactorial neurodegenerative disease that lacks convenient and accessible peripheral blood diagnostic markers and effective drugs. Metabolic dysfunction is one of AD risk factors, which leaded to alterations of various metabolites in the body. Pathological changes of the brain can be reflected in blood metabolites that are expected to explain the disease mechanisms or be candidate biomarkers. The aim of this study was to investigate the changes of targeted metabolites within peripheral blood of AD mouse model, with the purpose of exploring the disease mechanism and potential biomarkers. Targeted metabolomics was used to quantify 256 metabolites in serum of triple transgenic AD (3 × Tg-AD) male mice. Compared with controls, 49 differential metabolites represented dysregulation in purine, pyrimidine, tryptophan, cysteine and methionine and glycerophospholipid metabolism. Among them, adenosine, serotonin, N-acetyl-5-hydroxytryptamine, and acetylcholine play a key role in regulating neural transmitter network. The alteration of S-adenosine-L-homocysteine, S-adenosine-L-methionine, and trimethylamine-N-oxide in AD mice serum can served as indicator of AD risk. The results revealed the changes of metabolites in serum, suggesting that metabolic dysregulation in periphery in AD mice may be related to the disturbances in neuroinhibition, the serotonergic system, sleep function, the cholinergic system, and the gut microbiota. This study provides novel insights into the dysregulation of several key metabolites and metabolic pathways in AD, presenting potential avenues for future research and the development of peripheral biomarkers.

N-Acetylserotonin Protects Rat Nucleus Pulposus Cells Against Oxidative Stress Injury by Activating the PI3K/AKT Signaling Pathway

BACKGROUND

Current studies suggest that the pathogenesis of intervertebral disc degeneration (IDD) is related to oxidative stress damage in nucleus pulposus cells (NPCs). N-acetylserotonin (NAS) is an effective scavenger of reactive oxygen species, but its role in IDD and its underlying mechanisms are not yet clear. Therefore, the aim of this study was to investigate the effect of NAS on oxidative stress injury in NPCs and its mechanism.

METHODS

NP tissue of rat intervertebral disc was collected and NPCs were isolated. NPCs were treated with H2O2 to simulate the state of oxidative stress. The effects of NAS on cell viability, apoptosis, senescence, extracellular matrix (ECM), redox status and PI3K/AKT signal pathway were evaluated by cell counting kit-8, western blot, immunofluorescence, flow cytometry and SA-β-gal staining. Finally, the changes of the above indexes were further observed after the inhibition of PI3K pathway by LY294002.

RESULTS

Flow cytometry showed that NAS reduced H2O2-induced apoptosis of NPCs. SA-β-Gal staining showed that H2O2-induced senescence of NP cells was reversed by NAS. Immunofluorescence staining showed that NAS inhibited H2O2-induced ECM degradation. Western blotting analysis revealed that NAS significantly decreased apoptosis, senescence and ECM degradation. Further analysis showed that NAS treatment activated the PI3K/AKT pathway in H2O2-stimulated NPCs. However, these protected effects were inhibited after LY294002 treatment.

CONCLUSIONS

The results of the present study suggest that NAS inhibits H2O2-induced NPCs degeneration by activating PI3K/AKT pathway, suggesting that NAS has the potential to treat IDD.

Neurobehavioral disorders induced by environmental zinc in female zebrafish (Danio rerio): Insights from brain and intestine transcriptional and metabolic signatures

Human activities can cause zinc (Zn) contamination of aquatic environments. Zn is an essential trace metal, but effects of environmentally relevant Zn exposure on the brain-intestine axis in fish are poorly understood. Here, six-month-old female zebrafish (Danio rerio) were exposed to environmentally relevant Zn concentrations (0, 1.0, and 1.5 mg/L) for six weeks. Zn significantly accumulated in the brain and intestine, causing anxiety-like behaviors and altered social behaviors. Zn accumulation altered levels of neurotransmitters, including serotonin, glutamate, and γ-aminobutyric acid, in the brain and intestine, and these changes were directly associated with changes in behavior. Zn caused oxidative damage and mitochondrial dysfunction, and impaired NADH dehydrogenase, thereby dysregulating the energy supply in brain Zn exposure resulted in nucleotide imbalance and dysregulation of DNA replication and the cell cycle, potentially impairing the self-renewal of intestinal cells. Zn also disturbed carbohydrate and peptide metabolism in the intestine. These results indicate that chronic exposure to Zn at environmentally relevant concentrations dysregulates the bidirectional interaction of the brain-intestine axis with respect to neurotransmitters, nutrients, and nucleotide metabolites, thereby causing neurological disorder-like behaviors. Our study highlights the necessity to evaluate the negative impacts of chronic environmentally relevant Zn exposure on the health of humans and aquatic animals.

Metabolomic Analyses to Identify Candidate Biomarkers of Cystinosis

Cystinosis is a rare, devastating hereditary disease secondary to recessive CTNS gene mutations. The most commonly used diagnostic method is confirmation of an elevated leukocyte cystine level; however, this method is expensive and difficult to perform. This study aimed to identify candidate biomarkers for the diagnosis and follow-up of cystinosis based on multiomics studies. The study included three groups: newly-diagnosed cystinosis patients (patient group, n = 14); cystinosis patients under treatment (treatment group, n = 19); and healthy controls (control group, n = 30). Plasma metabolomics analysis identified 10 metabolites as candidate biomarkers that differed between the patient and control groups [L-serine, taurine, lyxose, 4-trimethylammoniobutanoic acid, orotic acid, glutathione, PE(O-18:1(9Z)/0:0), 2-hydroxyphenyl acetic acid, acetyl-N-formil-5-metoxikinuramine, 3-indoxyl sulphate]. As compared to the healthy control group, in the treatment group, hypotaurine, phosphatidylethanolamine, N-acetyl-d-mannosamine, 3-indolacetic acid, p-cresol, phenylethylamine, 5-aminovaleric acid, glycine, creatinine, and saccharic acid levels were significantly higher, and the metabolites quinic acid, capric acid, lenticin, xanthotoxin, glucose-6-phosphate, taurine, uric acid, glyceric acid, alpha-D-glucosamine phosphate, and serine levels were significantly lower. Urinary metabolomic analysis clearly differentiated the patient group from the control group by means of higher allo-inositol, talose, glucose, 2-hydroxybutiric acid, cystine, pyruvic acid, valine, and phenylalanine levels, and lower metabolite (N-acetyl-L-glutamic acid, 3-aminopropionitrile, ribitol, hydroquinone, glucuronic acid, 3-phosphoglycerate, xanthine, creatinine, and 5-aminovaleric acid) levels in the patient group. Urine metabolites were also found to be significantly different in the treatment group than in the control group. Thus, this study identified candidate biomarkers that could be used for the diagnosis and follow-up of cystinosis.

EGCG and catechin relative to green tea extract differentially modulate the gut microbial metabolome and liver metabolome to prevent obesity in mice fed a high-fat diet

Green tea extract (GTE) alleviates obesity, in part, by modulating gut microbial composition and metabolism. However, direct evidence regarding the catechin-specific bioactivities that are responsible for these benefits remain unclear. The present study therefore investigated dietary supplementation of GTE, epigallocatechin gallate (EGCG), or (+)-catechin (CAT) in male C57BL6/J mice that were fed a high-fat (HF) diet to establish the independent contributions of EGCG and CAT relative to GTE to restore microbial and host metabolism. We hypothesized that EGCG would regulate the gut microbial metabolome and host liver metabolome more similar to GTE than CAT to explain their previously observed differential effects on cardiometabolic health. To test this, we assessed metabolic and phenolic shifts in liver and fecal samples during dietary HF-induced obesity. Ten fecal metabolites and ten liver metabolites (VIP > 2) primarily contributed to the differences in the metabolome among different interventions. In fecal samples, nine metabolic pathways (e.g., tricarboxcylic acid cycle and tyrosine metabolism) were differentially altered between the GTE and CAT interventions, whereas three pathways differed between GTE and EGCG interventions, suggesting differential benefits of GTE and its distinctive bioactive components on gut microbial metabolism. Likewise, hepatic glycolysis / gluconeogenesis metabolic pathways were significantly altered between GTE and EGCG interventions, while only hepatic tyrosine metabolism was altered between CAT and GTE interventions. Thus, our findings support that purified catechins relative to GTE uniquely contribute to regulating host and microbial metabolic pathways such as central energy metabolism to protect against metabolic dysfunction leading to obesity.

Quantification of serotonin and eight of its metabolites in plasma of healthy volunteers by mass spectrometry

Serotonin is transformed into melatonin under the control of the light/dark cycle, representing a cornerstone of circadian rhythmicity. Serotonin also undergoes extensive metabolism to produce 5-hydroxyindoleacetic acid (5-HIAA), a biomarker for the diagnosis and monitoring of serotonin secreting neuroendocrine tumors (NETs). While serotonin, melatonin and their metabolites are part of an integrated comprehensive system, human observations about their respective plasma concentrations are still limited. We report here for the first time a multiplex UHPLC-MS/MS assay for the quantification of serotonin, 5-HIAA, 5-hydroxytryptophol (5-HTPL), N-acetyl-serotonin (NAS), Mel, 6-OH-Mel, 5-methoxytryptamine (5-MT), 5-methoxytryptophol (5-MTPL), and 5-methoxyindoleacetic acid (5-MIAA) in human plasma. Analytes were extracted by protein precipitation and solid phase extraction. Plasma concentrations for these analytes were determined in 102 healthy volunteers. The LLOQ of the assay ranges from 2.2 nM for serotonin to 1.0 pM for 6-OH-Mel. This sensitivity enables the quantification of circulating serotonin, 5-HIAA, NAS, Mel, and 5-MIAA, even at their lowest diurnal concentrations. This assay will enable specific, precise and accurate measurement of serotonin, Mel and their metabolites to draw a detailed picture of this complex pineal metabolism, allowing a dynamic understanding of these pathways and providing promising biomarkers and a metabolic signature for serotonin-secreting NETs.

A Tropomycin-Related Kinase B Receptor Activator for the Management of Ocular Blast-Induced Vision Loss

Pressure waves from explosions or other traumatic events can damage the neurons of the eye and visual centers of the brain, leading to functional loss of vision. There are currently few treatments for such injuries that can be deployed rapidly to mitigate damage. Brain-derived neurotrophic factor (BDNF) and activation of its receptor tropomycin-related kinase B (TrkB) have neuroprotective effects in a number of degeneration models. Small molecule activators of TrkB, such as N-[2-(5-hydroxy-1H-indol-3-yl)ethyl]-2-oxopiperidine-3-carboxamide (HIOC), cross the blood-brain and blood-retina barriers after systemic administration. We characterize the effects of blast-induced ocular trauma on retinal and visual function. We show that systemic administration of HIOC, a potent small molecule activator of the BDNF/TrkB receptor, preserves visual function in mice exposed to ocular blast injury. The HIOC treatment for one week preserves visual function for at least four months. The HIOC treatment effectively protected vision when the initial dose was administered up to 3 h after blast, but not if the initial treatment was delayed for 24 h. We provide evidence that the therapeutic effect of HIOC is mediated by activation of BDNF/TrkB receptors. The results indicate that HIOC may be useful for managing ocular blast injury and other forms of traumatic optic neuropathy.

Serotonin and its metabolites reduce oxidative stress in murine RAW264.7 macrophages and prevent inflammation

In this study, we focused on comparing the effects of serotonin and its metabolites on the functions of RAW264.7 cells (emphasis on oxidative burst and production of nitric oxide and cytokines), thereby expanding the scope of existing knowledge with advent of novel findings in this field. Changes in production of reactive oxygen species (ROS) by RAW264.7 cells after treatment with serotonin, N-acetylserotonin and melatonin were determined using the chemiluminescence (CL) assay. To exclude the direct scavenging effects of the studied compounds on the CL response, the antioxidant properties of all respective compounds were measured using TRAP and amperometrical method. Nitric oxide (NO) production was measured by Griess reagent and inducible NO synthase (iNOS) expression by Western blot. Cytokine production was assessed using the Mouse Cytokine Panel A Array kit and ELISA. We showed that all tested compounds were able to reduce oxidative stress, as well as inhibit production of inflammatory cytokines by macrophages. Of the tested compounds, serotonin and N-acetylserotonin were markedly better antioxidants than melatonin. In comparison, other effects of tested compounds were very similar. It can be concluded that antioxidant capacity of tested compounds is a major advantage in the early stages of inflammation. Since plasma concentrations of N-acetylserotonin and melatonin are lower than serotonin, it can be deduced that serotonin plays a key role in modulation of inflammation and the regulatory functions of immune cells, while also protecting cells against oxidative stress.

Gut microbial metabolites in depression: understanding the biochemical mechanisms

Gastrointestinal and central function are intrinsically connected by the gut microbiota, an ecosystem that has co-evolved with the host to expand its biotransformational capabilities and interact with host physiological processes by means of its metabolic products. Abnormalities in this microbiota-gut-brain axis have emerged as a key component in the pathophysiology of depression, leading to more research attempting to understand the neuroactive potential of the products of gut microbial metabolism. This review explores the potential for the gut microbiota to contribute to depression and focuses on the role that microbially-derived molecules – neurotransmitters, short-chain fatty acids, indoles, bile acids, choline metabolites, lactate and vitamins – play in the context of emotional behavior. The future of gut-brain axis research lies is moving away from association, towards the mechanisms underlying the relationship between the gut bacteria and depressive behavior. We propose that direct and indirect mechanisms exist through which gut microbial metabolites affect depressive behavior: these include (i) direct stimulation of central receptors, (ii) peripheral stimulation of neural, endocrine, and immune mediators, and (iii) epigenetic regulation of histone acetylation and DNA methylation. Elucidating these mechanisms is essential to expand our understanding of the etiology of depression, and to develop new strategies to harness the beneficial psychotropic effects of these molecules. Overall, the review highlights the potential for dietary interventions to represent such novel therapeutic strategies for major depressive disorder.

The influence of ageing on the extrapineal melatonin synthetic pathway

Ageing affects various physiological and metabolic processes in a body and a progressive accumulation of oxidative damage stands out as often used explanation. One of the most powerful scavenger of reactive oxygen species (ROS) in all organs is melatonin. A majority of melatonin supplied to the body via blood originates from the pineal gland. However, we have been interested in a locally produced melatonin. We have used 2.5- and 36-months-old Wistar rats. Tissues were collected and gene expression of AA-NAT and ASMT, the two key enzymes in a synthesis of melatonin, was determined in brain, liver, kidney, heart, skin, and intestine. Since melatonin can influence antioxidant enzymes, the activity of superoxide dismutase (SOD) and catalase (CAT), and the level of GSH were measured in liver. In addition, Copper (Cu), Zinc (Zn), and Manganese (Mn) were also determined in liver since these microelements might affect the activity of antioxidant enzymes. The expression of AA-NAT and ASMT was increased in liver and skin of old animals. A positive correlation in AA-NAT and ASMT expression was observed in liver, intestine and kidney. Moreover, the activity of CAT enzyme in liver was increased while SOD activity was decreased. SOD and CAT were probably affected by the observed decreased amount of Cu, Zn, and Mn in liver of old animals. In our model, extrapineal melatonin pathway in ageing consisted of complex interplay of locally produced melatonin, activities of SOD and CAT, and adequate presence of Cu, Zn and Mn microelements in order to defend organs against oxidative damage.

Seasonal Reproduction in Vertebrates: Melatonin Synthesis, Binding, and Functionality Using Tinbergen's Four Questions

One of the many functions of melatonin in vertebrates is seasonal reproductive timing. Longer nights in winter correspond to an extended duration of melatonin secretion. The purpose of this review is to discuss melatonin synthesis, receptor subtypes, and function in the context of seasonality across vertebrates. We conclude with Tinbergen's Four Questions to create a comparative framework for future melatonin research in the context of seasonal reproduction.

Social defeat stress causes depression-like behavior with metabolite changes in the prefrontal cortex of rats

Major depressive disorder is a serious mental disorder with high morbidity and mortality. The role of social stress in the development of depression remains unclear. Here, we used the social defeat stress paradigm to induce depression-like behavior in rats, then evaluated the behavior of the rats and measured metabolic changes in the prefrontal cortex using gas chromatography-mass spectrometry. Within the first week after the social defeat procedure, the sucrose preference test (SPT), open field test (OFT), elevated plus maze (EPM) and forced swim test (FST) were conducted to examine the depressive-like and anxiety-like behaviors. For our metabolite analysis, multivariate statistics were applied to observe the distribution of all samples and to differentiate the socially defeated group from the control group. Ingenuity pathway analysis was used to find the potential relationships among the differential metabolites. In the OFT and EPM, there were no significant differences between the two experimental groups. In the SPT and FST, socially defeated rats showed less sucrose intake and longer immobility time compared with control rats. Metabolic profiling identified 25 significant variables with good predictability. Ingenuity pathways analysis revealed that “Hereditary Disorder, Neurological Disease, Lipid Metabolism” was the most significantly altered network. Stress-induced alterations of low molecular weight metabolites were observed in the prefrontal cortex of rats. Particularly, lipid metabolism, amino acid metabolism, and energy metabolism were significantly perturbed. The results of this study suggest that repeated social defeat can lead to metabolic changes and depression-like behavior in rats.

Phenolic Melatonin-Related Compounds: Their Role as Chemical Protectors against Oxidative Stress

There is currently no doubt about the serious threat that oxidative stress (OS) poses to human health. Therefore, a crucial strategy to maintain a good health status is to identify molecules capable of offering protection against OS through chemical routes. Based on the known efficiency of the phenolic and melatonin (MLT) families of compounds as antioxidants, it is logical to assume that phenolic MLT-related compounds should be (at least) equally efficient. Unfortunately, they have been less investigated than phenols, MLT and its non-phenolic metabolites in this context. The evidence reviewed here strongly suggests that MLT phenolic derivatives can act as both primary and secondary antioxidants, exerting their protection through diverse chemical routes. They all seem to be better free radical scavengers than MLT and Trolox, while some of them also surpass ascorbic acid and resveratrol. However, there are still many aspects that deserve further investigations for this kind of compounds.

Phenotypic characterization of nanshi oral liquid alters metabolic signatures during disease prevention

This paper was designed to investigate the phenotypic characterization of Nanshi Oral Liquid (NOL) alters metabolic signatures of the ‘Kidney Yang Deficiency syndrome’ (KYDS). Urine metabolites were profiled by UPLC-ESI-Q-TOF-HDMS. The significantly changed metabolites such as xanthurenic acid, 4,8-dihydroxyquinoline, 3-methyldioxyindole, 4,6-dihydroxyquinoline, kynurenic acid, hippuric acid, taurine, tyramine, and 3-metanephrine, had been identified, and were related to the disturbance in tyrosine metabolism, steroid hormone biosynthesis, taurine and hypotaurine metabolism, tryptophan metabolism, phenylalanine metabolism and lysine degradation, which were helpful to further understanding the KYDS and intervention mechanism of NOL. The biochemical result showed that NOL can alleviate the kidney impairment induced by KYDS. Metabolomics results indicated the significantly changed metabolites were found to be reasonable in explaining the action mechanism of NOL. Interestingly, the effectiveness of NOL against KYDS was proved using the established metabolomics method and regulated the biomarkers as well as adjusted the metabolic disorder pathways. NOL had potentially pharmacological effect through regulating multiple perturbed pathways to normal state. This work showed that the metabolomics method was a powerful approach for studying the phenotypic characterization of disease’s syndrome during disease prevention and its intervention mechanism.

N-acetyl-serotonin protects HepG2 cells from oxidative stress injury induced by hydrogen peroxide

Oxidative stress plays an important role in the pathogenesis of liver diseases. N-Acetyl-serotonin (NAS) has been reported to protect against oxidative damage, though the mechanisms by which NAS protects hepatocytes from oxidative stress remain unknown. To determine whether pretreatment with NAS could reduce hydrogen peroxide- (H₂O₂-) induced oxidative stress in HepG2 cells by inhibiting the mitochondrial apoptosis pathway, we investigated the H₂O₂-induced oxidative damage to HepG2 cells with or without NAS using MTT, Hoechst 33342, rhodamine 123, Terminal dUTP Nick End Labeling Assay (TUNEL), dihydrodichlorofluorescein (H2DCF), Annexin V and propidium iodide (PI) double staining, immunocytochemistry, and western blot. H₂O₂ produced dramatic injuries in HepG2 cells, represented by classical morphological changes of apoptosis, increased levels of malondialdehyde (MDA) and intracellular reactive oxygen species (ROS), decreased activity of superoxide dismutase (SOD), and increased activities of caspase-9 and caspase-3, release of cytochrome c (Cyt-C) and apoptosis-inducing factor (AIF) from mitochondria, and loss of membrane potential (ΔΨ_m). NAS significantly inhibited H₂O₂-induced changes, indicating that it protected against H₂O₂-induced oxidative damage by reducing MDA levels and increasing SOD activity and that it protected the HepG2 cells from apoptosis through regulating the mitochondrial apoptosis pathway, involving inhibition of mitochondrial hyperpolarization, release of mitochondrial apoptogenic factors, and caspase activity.

Is there an association between peripheral immune markers and structural/functional neuroimaging findings?

OBJECTIVES

There is mounting evidence that inflammatory processes play a key role in emotional as well as cognitive dysfunctions. In this context, research employing magnetic resonance imaging (MRI) and magnetic resonance spectroscopy (MR spectroscopy) suggests a possible link between structural/functional anomalies in the brain and an increase of circulating inflammation markers. The present paper reviews this research, with particular focus on major depressive disorder (MDD), cognitive impairment in older adults, Alzheimer's disease (AD) and schizophrenia.

RESULTS

In MDD, cognitive impairment and AD, inflammatory processes have been found to be associated with both structural and functional anomalies, perhaps under the influence of environmental stress. Not enough research can suggest similar considerations in schizophrenia, although studies in mice and non-human primates support the belief that inflammatory responses generated during pregnancy can affect brain development and contribute to the etiology of schizophrenia.

CONCLUSIONS

The present review suggests a link between inflammatory processes and MRI detected anomalies in the brain of individuals with MDD, older adults with cognitive impairment as well as of individuals with AD and schizophrenia.

N-acetylserotonin: circadian activation of the BDNF receptor and neuroprotection in the retina and brain

TrkB is the cognate receptor for brain-derived neurotrophic factor (BDNF), a member of the neurotrophin family involved in neuronal survival, neurogenesis and synaptic plasticity. BDNF has been shown to protect photoreceptors from light-induced retinal degeneration (LIRD) and to improve ganglion cell survival following optic nerve damage. However, the utility of BDNF as a retinal neuroprotectant is limited by its short half-life, inability to cross the blood-brain and blood-retinal barriers, and activation of the proapoptotic p75 neurotrophin receptor. N-Acetylserotonin (NAS) is a naturally occurring chemical intermediate in the melatonin biosynthetic pathway in the pineal gland and retina. Its synthesis occurs in a circadian fashion with high levels at night and is suppressed by light exposure. Until recently, NAS was thought to function primarily as a melatonin precursor with little or no biological function of its own. We have now shown that TrkB activation in the retina and hippocampus is circadian in C3H/f(+/+) mice, which synthesize NAS, but not in C57BL/6 mice, which have a mutation in the gene encoding the enzyme that converts serotonin to NAS. In addition, treatment of mice exogenous NAS, but not with serotonin or melatonin, activates TrkB during the daytime in a BDNF-independent manner. NAS appears to have neuroprotective properties and its administration reduces caspase 3 activation in the brain in response to kainic acid, a neurotoxic glutamate analog. We have developed structural analogs of NAS that activate TrkB. One of these derivatives, N- [2-(-indol-3-yl)ethyl]-2-oxopiperideine-3-carboximide (HIOC), selectively activates TrkB with greater potency than NAS and has a significantly 5-hydroxy-1Hlonger biological half-life than NAS after systemic administration. HIOC administration results in long-lasting activation of TrkB and downstream signaling kinases. The compound can pass the blood-brain and blood-retinal barriers when administered systemically and reduces kainic acid-induced neuronal cell death in a TrkB-dependent manner. Systemic administration of HIOC mitigates LIRD, assessed electrophysiologically and morphometrically. Hence, NAS may function as an endogenous circadian neurotrophin-like compound and HIOC is a good lead compound for further drug development for treatment of retinal degenerative diseases.

Serotonin-kynurenine hypothesis of depression: historical overview and recent developments

This mini-review focuses on the studies of late Prof. IP Lapin (1903 - 2012) and his research team on the role of methoxyindole and kynurenine (KYN) pathways of tryptophan (TRP) metabolism in the pathogenesis of depression and action mechanisms of antidepressant effect. In the late 60s of the last century Prof. IP Lapin suggested that "intensification of central serotoninergic processes is a determinant of the thymoleptic (mood elevating) component" while "activation of noradrenergic processes is responsible for psychoenergetic and motor-stimulating component of the clinical antidepressant effect". The cause of serotonin deficiency in depression was attributed to the shunt of TRP "metabolism away from serotonin production towards KYN production" due to cortisol-induced activation of liver enzyme, tryptophan 2,3- dioxygenase, the rate-limiting enzyme of TRP - KYN pathway. Prof. Lapin suggested and discovered that KYN and its metabolites affect brain functions, and proposed the role of neurokynurenines in pathogenesis of depression and action mechanisms of antidepressant effect (kynurenine hypothesis). Further research suggested the antidepressant and cognition- enhancing effects of post-serotonin metabolite, N-acetylserotonin (NAS), an agonist to tyrosine kinase B (TrkB) receptor; and link between depression and chronic inflammation-associated disorders (e.g., insulin resistance, hepatitis C virus) via inflammation-induced activation of indoleamine 2,3- dioxygenase, brain located rate-limiting enzyme of TRY - KYN metabolism. NAS and kynurenines might be the targets for prevention and treatment of depression and associated conditions.

N-acetylserotonin: neuroprotection, neurogenesis, and the sleepy brain

N-Acetylserotonin (NAS) is a naturally occurring chemical intermediate in biosynthesis of melatonin. Previous studies have shown that NAS has different brain distribution patterns from those of serotonin and melatonin, suggesting that NAS might have functions other than as a precursor or metabolite of melatonin. Indeed, several studies have now shown that NAS may play an important role in mood regulation and may have antidepressant activity. Additional studies have shown that NAS stimulates proliferation of neuroprogenitor cells and prevents some of the negative effects of sleep deprivation. It is believed that the antidepressant and neurotrophic actions of NAS are due at least in part to the capability on this molecule to activate the TrkB receptor in a brain-derived neurotrophic factor-independent manner. Emerging evidence also indicates that NAS and its derivatives have neuroprotective properties and protect retinal photoreceptor cells from light-induced degeneration. In this review, the authors discuss the literature about this exciting and underappreciated molecule.

Circadian regulation of pineal gland rhythmicity

The pineal gland is a neuroendocrine organ of the brain. Its main task is to synthesize and secrete melatonin, a nocturnal hormone with diverse physiological functions. This review will focus on the central and pineal mechanisms in generation of mammalian pineal rhythmicity including melatonin production. In particular, this review covers the following topics: (1) local control of serotonin and melatonin rhythms; (2) neurotransmitters involved in central control of melatonin; (3) plasticity of the neural circuit controlling melatonin production; (4) role of clock genes in melatonin formation; (5) phase control of pineal rhythmicity; (6) impact of light at night on pineal rhythms; and (7) physiological function of the pineal rhythmicity.

Interferon-gamma-inducible kynurenines/pteridines inflammation cascade: implications for aging and aging-associated psychiatric and medical disorders

This review of literature and our data suggests that up-regulated production of interferon-gamma (IFNG) in periphery and brain triggers a merger of tryptophan (TRY)-kynurenine (KYN) and guanine-tetrahydrobiopterin (BH4) metabolic pathways into inflammation cascade involved in aging and aging-associated medical and psychiatric disorders (AAMPD) (metabolic syndrome, depression, vascular cognitive impairment). IFNG-inducible KYN/pteridines inflammation cascade is characterized by up-regulation of nitric oxide synthase (NOS) activity (induced by KYN) and decreased formation of NOS cofactor, BH4, that results in uncoupling of NOS that shifting arginine from NO to superoxide anion production. Superoxide anion and free radicals among KYN derivatives trigger phospholipase A2-arachidonic acid cascade associated with AAMPD. IFNG-induced up-regulation of indoleamine 2,3-dioxygenase (IDO), rate-limiting enzyme of TRY-KYN pathway, decreases TRY conversion into serotonin (substrate of antidepressant effect) and increases production of KYN associated with diabetes [xanthurenic acid (XA)], anxiety (KYN), psychoses and cognitive impairment (kynurenic acid). IFNG-inducible KYN/pteridines inflammation cascade is impacted by IFNG (+874) T/A genotypes, encoding cytokine production. In addition to literature data on KYN/TRY ratio (IDO activity index), we observe neopterin levels (index of activity of rate-limiting enzyme of guanine-BH4 pathway) to be higher in carriers of high (T) than of low (A) producers alleles; and to correlate with AAMPD markers (e.g., insulin resistance, body mass index, mortality risk), and with IFN-alpha-induced depression in hepatitis C patients. IFNG-inducible cascade is influenced by environmental factors (e.g., vitamin B6 deficiency increases XA formation) and by pharmacological agents; and might offer new approaches for anti-aging and anti-AAMPD interventions.

Melatonin as a therapeutic tool in ophthalmology: implications for glaucoma and uveitis

Several lines of evidence support the view that increased free radical generation and altered nitric oxide (NO) metabolism play a role in the pathogenesis of highly prevalent ocular diseases, such as glaucoma and uveitis. Data are discussed indicating that melatonin, being an efficient antioxidant that displays antinitridergic properties, has a promising role in the treatment of these ocular dysfunctions. Melatonin synthesis occurs in the eye of most species, and melatonin receptors are localized in different ocular structures. In view of the fact that melatonin lacks significant adverse collateral effects even at high doses, the application of melatonin could potentially protect ocular tissues by effectively scavenging free radicals and excessive amounts of NO generated in the glaucomatous or uveitic eye.

Quinone reductase 2 and antidepressant effect of melatonin derivatives

Melatonin and its immediate precursor, N-acetylserotonin (NAS), exert antidepressant effects in experimental models and clinical studies. We reported that melatonin and NAS decreased immobility time (an indicator of antidepressant activity) in the mouse tail suspension test. Melatonin type 3 receptor (MT3) was identified as the same protein as quinone reductase 2 (QR2) detoxifying and antioxidant enzyme. To further elucidate the role of QR2/MT3 in antidepressant action of NAS and melatonin, we studied the effect of QR2/MT3 agonist and antagonist in a tail suspension test. QR2/MT3 agonist 5-MCA-NAT decreased, while the QR2/MT3 antagonist prazosin increased the duration of immobility in the tail suspension test in a dose-dependent manner. Prazosin, in a dose that did not affect the duration of immobility, attenuated the antidepressant-like effect of NAS, melatonin, and typical tricyclic antidepressant, amitriptyline, in the tail suspension test. Our results suggest that the modulation of QR2/MT3 might contribute to mechanism(s) of antidepressant effect. New antidepressants might be searched among the agonists of QR2/MT3.

[Is there any scientific evidence supporting antiaging medicine?]

The objective of antiaging medicine is to interfere in the normal human biological aging process. Is there any scientific basis to justify classifying antiaging medicine as a medical specialty and not a branch of basic biological science? This review evaluated 110 papers, nine of which (8.2% of the total) reported studies involving human subjects. Only one of these studies was randomized and double-blinded (Jadad 2). In accordance with their classification of recommendations and level of evidence, these studies were considered CII. Three of the nine articles were published in journals with an impact factor over 1.110. Therefore, there does not appear to be any solid scientific and/or clinical evidence that would justify the application of antiaging medicine in current medical practice.

Effect of methyl derivatives of dopamine on tumor necrosis factor alpha and lipid peroxidation

We recently demonstrated that melatonin, N-acetylserotonin (NAS), and N-acetyldopamine (NAD) attenuate the synthesis of lipopolysaccharide (LPS)-stimulated tumor necrosis factor-alpha (TNF-alpha) and the generation of oxidant radicals. In this study, we examined whether acetyl and methyl derivatives of dopamine modulate LPS-stimulated TNF-alpha synthesis and LPS- and iron-induced lipid peroxidation. Differentiated THP-1-derived human monocytes were coincubated with Escherichia coli and rising concentrations of NAS, NAD, N-methyldopamine (NMD), or 4-O-methyldopamine (4-O-MD). After 24 h, TNF-alpha was measured in cell supernatants. In addition, lipid peroxidation was induced by adding FeCl(2) solution to mouse brain tissue homogenates in the presence of rising concentrations of NAS, NAD, NMD, or 4-O-MD. Incubating THP-1-derived monocytes with rising concentrations of NAS, NAD, NMD, or 4-O-MD markedly decreased LPS-stimulated TNF-alpha production, which was dose dependent and on the order of 96%-98%. Rising concentrations of NMD markedly inhibited lipid peroxidation by 59%-98%. Our results indicated that the inhibitory effect of NAS, NAD, NMD, or 4-O-MD on LPS-induced TNF-alpha production and FeCl(2)-stimulated lipid peroxidation is robust and dose dependent.