Cerebrospinal Fluid Melatonin Research Articles

Brain washing and neural health: role of age, sleep, and the cerebrospinal fluid melatonin rhythm.

The brain lacks a classic lymphatic drainage system.How it is cleansed of damaged proteins, cellular debris, and molecular by-products has remained a mystery for decades. Recent discoveries have identified ahybrid system that includes cerebrospinal fluid (CSF)-filled perivascular spaces and classic lymph vessels in the dural covering of the brain and spinal cord that functionally cooperate to remove toxic and non-functional trash from the brain. These two components functioning together are referred to as the glymphatic system. We propose that the high levels of melatonin secreted by the pineal gland directly into the CSF play a role in flushing pathological molecules such as amyloid-β peptide (Aβ) from the brain via this network. Melatonin is a sleep-promoting agent, with waste clearance from the CNS being highest especially during slow wave sleep. Melatonin is also a potent and versatile antioxidant that prevents neural accumulation of oxidatively-damaged molecules which contribute to neurological decline. Due to its feedback actions on the suprachiasmatic nucleus, CSF melatonin rhythm functions to maintain optimal circadian rhythmicity, which is also critical for preserving neurocognitive health. Melatonin levels drop dramatically in the frail aged, potentially contributing to neurological failure and dementia. Melatonin supplementation in animal models of Alzheimer's disease (AD) defers Aβ accumulation, enhances its clearance from the CNS, and prolongs animal survival. In AD patients, preliminary data show that melatonin use reduces neurobehavioral signs such as sundowning. Finally, melatonin controls the mitotic activity of neural stem cells in the subventricular zone, suggesting its involvement in neuronal renewal.

Blast Exposure Dysregulates Nighttime Melatonin Synthesis and Signaling in the Pineal Gland: A Potential Mechanism of Blast-Induced Sleep Disruptions.

Blast-induced traumatic brain injury (bTBI) frequently results in sleep-wake disturbances. However, limited studies have investigated the molecular signaling mechanisms underlying these sleep disturbances, and potentially efficacious therapies are lacking. We investigated the levels of melatonin and genes involved in melatonin synthesis pathway in the pineal glands of Sprague Dawley rats exposed to single and tightly coupled repeated blasts during the night and daytime. Rats were exposed to single and tightly coupled repeated blasts using an advanced blast simulator. The plasma, cerebrospinal fluid (CSF), and pineal gland were collected at 6 h, 24 h, or 1 month postblast at two different time points: one during the day (1000 h) and one at night (2200 h). Differential expressions of genes involved in pineal melatonin synthesis were quantified using quantitative real-time polymerase chain reaction (qRT-PCR). Plasma and CSF melatonin levels were assessed using a commercial melatonin ELISA kit. The plasma and CSF melatonin levels showed statistically significant decreases at 6 h and 24 h in the blast-exposed rats euthanized in the night (in dim light), with no significant alterations noted in rats euthanized in the morning (daylight) at all three-time points. Blast-exposed rats showed statistically significant decreases in Tph1, Aanat, Asmt, and Mtnr1b mRNA levels, along with increased Tph2 mRNA, in the pineal gland samples collected at night at 6 h and 24 h. No significant changes in the mRNA levels of these genes were noted at 1 month. These findings imply that the melatonin circadian rhythm is disrupted following blast exposure, which may be a factor in the sleep disturbances that blast victims frequently experience.

Neural glymphatic system: Clinical implications and potential importance of melatonin

The central nervous system was thought to lack a lymphatic drainage until the recent discovery of the neural glymphatic system. This highly specialized waste disposal network includes classical lymphatic vessels in the dura that absorb fluid and metabolic by-products and debris from the underlying cerebrospinal fluid (CSF) in the subarachnoid space. The subarachnoid space is continuous with the Virchow-Robin peri-arterial and peri-vascular spaces which surround the arteries and veins that penetrate into the neural tissue, respectively. The dural lymphatic vessels exit the cranial vault via an anterior and a posterior route and eventually drain into the deep cervical lymph nodes. Aided by the presence of aquaporin 4 on the perivascular endfeet of astrocytes, nutrients and other molecules enter the brain from peri-arterial spaces and form interstitial fluid (ISF) that baths neurons and glia before being released into peri-venous spaces. Melatonin, a pineal-derived secretory product which is in much higher concentration in the CSF than in the blood, is believed to follow this route and to clear waste products such as amyloid-β from the interstitial space. The clearance of amyloid-β reportedly occurs especially during slow wave sleep which happens concurrently with highest CSF levels of melatonin. Experimentally, exogenously-administered melatonin defers amyloid-β buildup in the brain of animals and causes its accumulation in the cervical lymph nodes. Clinically, with increased age CSF melatonin levels decrease markedly, co-incident with neurodegeneration and dementia. Collectively, these findings suggest a potential association between the loss of melatonin, decreased glymphatic drainage and neurocognitive decline in the elderly.

Serum Daytime Melatonin Levels Reflect Cerebrospinal Fluid Melatonin Levels in Alzheimer's Disease but Are Not Correlated with Cognitive Decline.

Background:Nocturnal cerebrospinal fluid (CSF) and blood melatonin levels are altered in Alzheimer’s disease (AD). However, literature remains inconclusive on daytime blood melatonin levels. A positive correlation between melatonin levels and Mini-Mental State Examination (MMSE) scores in AD subjects has been evidenced following cross-sectional analyses. Whereas a correlation between serum and spinal CSF melatonin has been shown in healthy volunteers, an equal investigation in AD patients still has to be undertaken.Objective:1) To evaluate whether serum melatonin levels correlate with spinal CSF melatonin levels in AD. 2) To compare daytime CSF and serum melatonin levels between patients with AD dementia, mild cognitive impairment due to AD, and healthy controls, and to evaluate whether melatonin can affect cognitive decline in AD.Methods:Subjects with AD and healthy controls included in two existing cohorts, of whom a CSF and serum sample was available at the neurobiobank and had at least 6 months of neuropsychological follow-up, were included in the present study. Melatonin concentrations were measured with liquid chromatography-mass spectrometry.Results:Daytime serum melatonin levels correlated with spinal CSF melatonin levels in AD (r = 0.751, p < 0.001). No significant differences regarding daytime melatonin levels were found between patients and controls. No correlations were observed between daytime melatonin levels and MMSE score changes.Conclusion:Daytime serum melatonin accurately reflects CSF melatonin levels in AD, raising the possibility to assess melatonin alterations by solely performing blood sampling if also confirmed for night-time values. However, daytime melatonin levels are not associated with changes of cognitive impairment.

Elevated serum melatonin under constant darkness enhances neural repair in spinal cord injury through regulation of circadian clock proteins expression

We investigated the effects of environmental lighting conditions regulating endogenous melatonin production on neural repair, following experimental spinal cord injury (SCI). Rats were divided into three groups randomly: the SCI + L/D (12/12‐h light/dark), SCI + LL (24‐h constant light), and SCI + DD (24‐h constant dark) groups. Controlled light/dark cycle was pre‐applied 2 weeks before induction of spinal cord injury. There was a significant increase in motor recovery as well as body weight from postoperative day (POD) 7 under constant darkness. However, spontaneous elevation of endogenous melatonin in cerebrospinal fluid was seen at POD 3 in all of the SCI rats, which was enhanced in SCI + DD group. Augmented melatonin concentration under constant dark condition resulted in facilitation of neuronal differentiation as well as inhibition of primary cell death. In the rostrocaudal region, elevated endogenous melatonin concentration promoted neural remodeling in acute phase including oligodendrogenesis, excitatory synaptic formation, and axonal outgrowth. The changes were mediated via NAS‐TrkB‐AKT/ERK signal transduction co‐regulated by the circadian clock mechanism, leading to rapid motor recovery. In contrast, exposure to constant light exacerbated the inflammatory responses and neuroglial loss. These results suggest that light/dark control in the acute phase might be a considerable environmental factor for a favorable prognosis after SCI.Support or Funding InformationNational Research Foundation (NRF‐2013R1A2A2A01067169, NRF‐2015R1C1A2A01055691, NRF‐2017R1D1A1B03029565), Korea.

Involvement of orexin A in nocturnal melatonin secretion into the cerebrospinal fluid and the blood plasma in seasonal sheep

In sheep, differences in orexin A (OXA) gene expression and activity are related to changes in energy demand and seasonal reproduction. However, the mechanism by which and the key place where the OXA signal is integrated with photoperiod, whose main biochemical expression is melatonin (MEL), remain unknown. We examined the effects of cisterna magna injections of OXA (0.3 μg/kg body weight) on nocturnal cerebrospinal fluid (CSF) and plasma MEL concentrations; mRNA and protein expression of two rate-limiting enzymes for MEL biosynthesis, tryptophan 5-hydroxylase-1 (TPH1) and arylalkylamine-N-acetyltransferase (AA-NAT); and OXA receptor (OX1R, OX2R) expression in the pineal gland (PG) obtained from twenty ewes during the short-day (SD) and long-day (LD) seasons. OXA increased (P < 0.001) CSF and plasma MEL concentrations regardless of the season. Plasma MEL was positively correlated (P < 0.001) with CSF MEL in the OXA-treated sheep in both seasons. OXA had no effect (P > 0.05) on TPH1 transcript or protein level but upregulated (P < 0.05) AA-NAT mRNA and protein expression in both seasons. OXA enhanced (P < 0.05) OX1R mRNA level only during the LD season. Our results show that the endocrine activity of the ovine PG is regulated by day length and non-photic signals via hypothalamic OXA. These results are important for understanding the work of the biological clock and recognizing mechanisms responsible for the adaptation of seasonal animals to the changing external environment conditions. OXA and MEL are both involved in the regulation of the sleep-wakefulness system, therefore our results can be used in the study on the circadian rhythm disorders in humans (e.g. jet lag, insomnia, seasonal depression).

Origin of cerebrospinal fluid melatonin and possible function in the integration of photoperiod

Melatonin, which is synthesized at night by the pineal gland, is present in the cerebrospinal fluid (CSF), but its entry site and its role in this compartment are not known. Using several approaches, we tested the hypothesis that melatonin enters the CSF through the pineal recess, an evagination of the third ventricle. CSF melatonin concentrations are higher near the pineal gland than in the anterior part of the third ventricle, and decrease markedly (80%) after sealing off the pineal recess. Moreover, ultrastructure and permeability analyses of the pineal-CSF interface showed that melatonin could reach the CSF either via delivery in situ by protruding pinealocytes that make direct contact with the CSF or via extracellular secretion and interstitial fluid draining into the ventricular lumen. These data indicate that melatonin in the CSF probably originates from a few pinealocytes of the basal part of the pineal gland neighbouring the pineal recess. Melatonin carried to the brain by the blood appears to be able to mediate the effects of photoperiod on reproduction, but it is unclear whether melatonin in CSF may fine-tune this response both in terms of timing and amplitude. It is critical to determine which pathway, blood or CSF, allows melatonin to reach its central targets more efficiently.

Elevated Serum Melatonin under Constant Darkness Enhances Neural Repair in Spinal Cord Injury through Regulation of Circadian Clock Proteins Expression.

We investigated the effects of environmental lighting conditions regulating endogenous melatonin production on neural repair, following experimental spinal cord injury (SCI). Rats were divided into three groups randomly: the SCI + L/D (12/12-h light/dark), SCI + LL (24-h constant light), and SCI + DD (24-h constant dark) groups. Controlled light/dark cycle was pre-applied 2 weeks before induction of spinal cord injury. There was a significant increase in motor recovery as well as body weight from postoperative day (POD) 7 under constant darkness. However, spontaneous elevation of endogenous melatonin in cerebrospinal fluid was seen at POD 3 in all of the SCI rats, which was enhanced in SCI + DD group. Augmented melatonin concentration under constant dark condition resulted in facilitation of neuronal differentiation as well as inhibition of primary cell death. In the rostrocaudal region, elevated endogenous melatonin concentration promoted neural remodeling in acute phase including oligodendrogenesis, excitatory synaptic formation, and axonal outgrowth. The changes were mediated via NAS-TrkB-AKT/ERK signal transduction co-regulated by the circadian clock mechanism, leading to rapid motor recovery. In contrast, exposure to constant light exacerbated the inflammatory responses and neuroglial loss. These results suggest that light/dark control in the acute phase might be a considerable environmental factor for a favorable prognosis after SCI.

Choroid plexus is an additional source of melatonin in the brain.

The cerebrospinal fluid melatonin is released from the pineal gland, directly into the third ventricle, or produced de novo in the brain from extrapineal melatonin sources leading to a melatonin concentration gradient in the cerebrospinal fluid. Despite the interest on this topic, the brain areas capable of producing melatonin are not yet clear. Bearing this in mind, we hypothesized that the choroid plexus (CP) could be one of these melatonin sources. We analyzed and confirmed the presence of the four enzymes required for melatonin synthesis in rat CP and demonstrated that arylalkylamine N-acetyltransferase shows a circadian expression in female and male rat CP. Specifically, this enzyme colocalizes with mitochondria in rat CP epithelial cells, an organelle known to be involved in melatonin function and synthesis. Then, we demonstrated that melatonin is synthesized by porcine CP explants, although without a circadian pattern. In conclusion, our data show that the CP is a local source of melatonin to the central nervous system, probably contributing to its high levels in the cerebrospinal fluid. We believe that in the CP, melatonin might be regulated by its endogenous clock machinery and by the hormonal background.

Evaluation of human pineal gland acetylserotonin O-methyltransferase immunoreactivity in suicide: A preliminary study.

Disorders of the serotonergic system are especially known to be present in the neurobiology of suicidal behavior. Studies investigating melatonin levels show that changes in pineal gland functions may also play a role in the pathogenesis of suicide. However, to our knowledge, there are no studies evaluating the activity of pinealocytes responsible for melatonin synthesis in suicide. This preliminary study aimed to investigate the relationship among pinealocyte, acetylserotonin O-methyltransferase (ASMT) immunoreactivity, and suicide. Samples of pineal gland, cerebrospinal fluid, blood, and urine were obtained from 21 suicide and 21 non-suicide cases on which medicolegal autopsies were performed. Expression of ASMT in human pineal gland was evaluated by immunohistochemical methods. A scoring system was used to define the anti-ASMT-positive staining in the sections. Enzyme-linked immunosorbent assays were employed to assess serum and cerebrospinal fluid melatonin levels and blood and urine noradrenaline levels. The ASMT-immunopositive pinealocyte count was observed to be lower in suicide cases compared to the non-suicide cases. With the exception of two cases (with moderate staining), all graded scores were 3 (strong staining) in non-suicide group, whereas scores were 1 (mild staining) or 2 (moderate staining) in the suicide group. Melatonin levels in the blood were lower among the suicide victims. These results support decreased pineal gland activity in suicide. However, further studies are needed to assess whether these changes are related to a psychiatric disorder.

Preoperative CSF Melatonin Concentrations and the Occurrence of Delirium in Older Hip Fracture Patients: A Preliminary Study.

BackgroundDelirium is characterized by disturbances in circadian rhythm. Melatonin regulates our circadian rhythm. Our aim was to compare preoperative cerebrospinal fluid (CSF) melatonin levels in patients with and without postoperative delirium.MethodsProspective cohort study with hip fracture patients ≥ 65 years who were acutely admitted to the hospital for surgical treatment and received spinal anaesthesia. CSF was collected after cannulation, before administering anaesthetics. Melatonin was measured by radioimmunoassay (RIA). Data on delirium was obtained from medical and nursing records. Nurses screened every shift for delirium using the Delirium Observation Screening Scale (DOSS). If the DOSS was ≥3, a psychiatrist was consulted to diagnose possible delirium using the DSM-IV criteria. At admission, demographic data, medical history, and information on functional and cognitive status was obtained.ResultsSeventy-six patients met the inclusion criteria. Sixty patients were included in the analysis. Main reasons for exclusion were technical difficulties, insufficient CSF or exogenous melatonin use. Thirteen patients (21.7%) experienced delirium during hospitalisation. Baseline characteristics did not differ between patients with and without postoperative delirium. In patients with and without postoperative delirium melatonin levels were 12.88 pg/ml (SD 6.3) and 11.72 pg/ml (SD 4.5) respectively, p-value 0.47. No differences between patients with and without delirium were found in mean melatonin levels in analyses stratified for cognitive impairment or age.ConclusionPreoperative CSF melatonin levels did not differ between patients with and without postoperative delirium. This suggests that, if disturbances in melatonin secretion occur, these might occur after surgery due to postoperative inflammation.

Differential melatonin alterations in cerebrospinal fluid and serum of patients with major depressive disorder and bipolar disorder

BackgroundMelatonin, which plays an important role for regulation of circadian rhythms and the sleep/wake cycle has been linked to the pathophysiology of major depressive and bipolar disorder. Here we investigated melatonin levels in cerebrospinal fluid (CSF) and serum of depression and bipolar patients to elucidate potential differences and commonalities in melatonin alterations across the two disorders. MethodsUsing enzyme-linked immunosorbent assays, CSF and serum melatonin levels were measured in 108 subjects (27 healthy volunteers, 44 depressed and 37 bipolar patients). Covariate adjusted multiple regression analysis was used to investigate group differences in melatonin levels. ResultsIn CSF, melatonin levels were significantly decreased in bipolar (P<0.001), but not major depressive disorder. In serum, we observed a significant melatonin decrease in major depressive (P=0.003), but not bipolar disorder. No associations were found between serum and CSF melatonin levels or between melatonin and measures of symptom severity or sleep disruptions in either condition. ConclusionThis study suggests the presence of differential, body fluid specific alterations of melatonin levels in bipolar and major depressive disorder. Further, longitudinal studies are required to explore the disease phase dependency of melatonin alterations and to mechanistically explore the causes and consequences of site-specific alterations.

P-176: Are preoperative cerebrospinal fluid melatonin concentrations associated with postoperative delirium?

P-176: Are preoperative cerebrospinal fluid melatonin concentrations associated with postoperative delirium?

Melatonin from Cerebrospinal Fluid but Not from Blood Reaches Sheep Cerebral Tissues Under Physiological Conditions

The pineal gland secretes melatonin (MLT) that circulates in the blood and cerebrospinal fluid (CSF). We provide data to support the hypothesis that, in sheep and possibly in humans, only the CSF MLT, and not the blood MLT, can provide most of MLT to the cerebral tissue in high concentrations, particularly in the periventricular area. The MLT content of sheep brain, our chosen animal model, was found in significant concentration gradients oriented from the ventricle (close to the CSF) to the cerebral tissue, with concentrations varying by a factor of 1-125. The highest concentrations were observed close to the ventricle wall, whereas the lowest concentrations were furthest from the ventricles (407.0 ± 71.5 pg/ml compared to 84.7 ± 5.2 pg/ml around the third ventricle). This concentration gradient was measured in brain tissue collected at mid-day and at the end of the night. Nocturnal concentrations were higher than daytime concentrations, reflecting the diurnal variation in the pineal gland. The concentration gradient was not detected when MLT was delivered to the brain via the bloodstream. The diffusion of MLT to cerebral tissues via CSF was supported by in vivo scintigraphy and autoradiography. 2-[(123)I]-MLT infused into the CSF quickly and efficiently diffused into the brain tissues, whereas [(123)I]-iodine (control) was mostly washed away by the CSF flow and [(123)I]-bovine serum albumin remained mostly in the CSF. Taken together, these data support a critical role of CSF in providing the brain with MLT.

Delivery of pineal melatonin to the brain and SCN: role of canaliculi, cerebrospinal fluid, tanycytes and Virchow–Robin perivascular spaces

Historically, the direct release of pineal melatonin into the capillary bed within the gland has been accepted as the primary route of secretion. Herein, we propose that the major route of melatonin delivery to the brain is after its direct release into the cerebrospinal fluid (CSF) of the third ventricle (3V). Melatonin concentrations in the CSF are not only much higher than in the blood, also, there is a rapid nocturnal rise at darkness onset and precipitous decline of melatonin levels at the time of lights on. Because melatonin is a potent free radical scavenger and antioxidant, we surmise that the elevated CSF levels are necessary to combat the massive free radical damage that the brain would normally endure because of its high utilization of oxygen, the parent molecule of many toxic oxygen metabolites, i.e., free radicals. Additionally, the precise rhythm of CSF melatonin provides the master circadian clock, the suprachiasmatic nucleus, with highly accurate chronobiotic information regarding the duration of the dark period. We predict that the discharge of melatonin directly into the 3V is aided by a number of epithalamic structures that have heretofore been overlooked; these include interpinealocyte canaliculi and evaginations of the posterodorsal 3V that directly abut the pineal. Moreover, the presence of tanycytes in the pineal recess and/or a discontinuous ependymal lining in the pineal recess allows melatonin ready access to the CSF. From the ventricles melatonin enters the brain by diffusion and by transport through tanycytes. Melatonin-rich CSF also circulates through the aqueduct and eventually into the subarachnoid space. From the subarachnoid space surrounding the brain, melatonin penetrates into the deepest portions of the neural tissue via the Virchow-Robin perivascular spaces from where it diffuses into the neural parenchyma. Because of the high level of pineal-derived melatonin in the CSF, all portions of the brain are better shielded from oxidative stress resulting from toxic oxygen derivatives.

Sleep deprivation in humans: Effects on melatonin in cerebrospinal fluid and serum

Blood, urinary and saliva melatonin levels have been found to be associated with sleep disturbances and sleep deprivation. Melatonin responses to sleep deprivation have not been examined in cerebrospinal fluid (CSF) of healthy individuals. In this study, we measured CSF and serum melatonin before and after one night of sleep deprivation using enzyme linked immunosorbent assay. Melatonin levels increased in both CSF (+142%) as well as serum (+75%) after sleep deprivation but lacked correlation between both body fluids. These findings support melatonin’s central role for regulating sleep processes.

The effect of neuroleptic drugs on serum and cerebrospinal fluid melatonin concentrations in psychiatric subjects.

Journal Article The effect of neuroleptic drugs on serum and cerebrospinal fluid melatonin concentrations in psychiatric subjects Get access J A Smith, J A Smith Department of Pharmaceutical Chemistry, University of Bradford Correspondence: Ida Darwin Hospital, Fulbourn, Cambridge, U.K. Search for other works by this author on: Oxford Academic Google Scholar J L Barnes, J L Barnes Department of Pharmaceutical Chemistry, University of BradfordIda Darwin Hospital, Fulbourn, Cambridge, UK Search for other works by this author on: Oxford Academic Google Scholar T J Mee T J Mee Department of Pharmaceutical Chemistry, University of Bradford Search for other works by this author on: Oxford Academic Google Scholar Journal of Pharmacy and Pharmacology, Volume 31, Issue 1, September 1979, Pages 246–248, https://doi.org/10.1111/j.2042-7158.1979.tb13488.x Published: 12 April 2011 Article history Received: 19 May 1978 Published: 12 April 2011

Significance of High Levels of Endogenous Melatonin in Mammalian Cerebrospinal Fluid and in the Central Nervous System

Levels of melatonin in mammalian circulation are well documented; however, its levels in tissues and other body fluids are yet only poorly established. It is obvious that melatonin concentrations in cerebrospinal fluid (CSF) of mammals including humans are substantially higher than those in the peripheral circulation. Evidence indicates that melatonin produced in pineal gland is directly released into third ventricle via the pineal recess. In addition, brain tissue is equipped with the synthetic machinery for melatonin production and the astrocytes and glial cells have been proven to produce melatonin. These two sources of melatonin may be responsible for its high levels in CNS. The physiological significance of the high levels of melatonin in CNS presumably is to protect neurons and glia from oxidative stress. Melatonin as a potent antioxidant has been reported to be a neuroprotector in animals and in clinical studies. It seems that long term melatonin administration which elevates CSF melatonin concentrations will retard the progression of neurodegenerative disorders, for example, Alzheimer disease.

Melatonin as an adjuvant therapy in patients with rheumatoid arthritis

Because of its antioxidant effects, Forrest et al. 1 used melatonin (10 mg daily for 6 months) as an add-on therapy to treat rheumatoid arthritis (RA) and showed that the indolamine had minor beneficial effects. Maestroni et al. 2, however, opposed using melatonin in RA patients. They claimed that melatonin should be referred as a chronological pacemaker and immune enhancer rather than a potent free radical scavenger. As a justification of this, they claimed that a search with the keywords ‘melatonin’ and ‘radical scavenger’ yielded 338 items including 69 reviews, and the keywords ‘melatonin’ and ‘immune’ resulted in 495 items, of which 157 were reviews. On this basis, they implied that melatonin is not an antioxidant. Pubmed searches, however, using the key words ‘melatonin’ and ‘antioxidant’ (or ‘melatonin’ and ‘free radical scavenger’), yielded >11 000 published papers, and since melatonin was discovered as an antioxidant in 1993, thousands of investigations have confirmed the antioxidative actions of melatonin. There is no doubt that not only melatonin itself but also several of its derivatives have strong free radical scavenging and antioxidative capacities 3. Maestroni et al. 2 expected that melatonin would worsen the outcome of RA patients, but in fact it was not harmful; they actually seemed disappointed that melatonin treatment did not worsen RA. Consistently, published reports have documented that melatonin is an immune modulatory agent with multiple anti-inflammatory effects 4. Maestroni et al. 2 referred to melatonin as a hormone. Although melatonin has hormonal properties, in many cases it functions in other capacities, e.g. as an autocoid, paracoid or direct free radical scavenger 5. Also, whereas melatonin is produced in the pineal gland, the concentration of melatonin in the gut surpasses blood levels by 10–100 times and there is estimated to be at least 400× more melatonin in the gut than in the pineal gland. Thus, melatonin is not a conventional hormone, since it has both receptor-mediated and receptor-independent actions, and virtually all cells are its target whether or not they possess receptors for the indolamine. In relation to the high blood melatonin levels in RA patients as reported by Forrest et al. 1, the increased levels may have been a compensatory response to the inflammation of RA. Also, although the blood levels of melatonin reported by Forrest et al. 1 may seem high, they are comparable to the seemingly much higher levels of melatonin in cerebrospinal fluid 6 and its metabolites in patients with meningitis 7 and as shown in paediatric patients with epilepsy 8. Forrest et al. 1 have performed a highly valuable study documenting that melatonin could be an effective add-on therapy in the treatment of RA. Melatonin is known to have substantial anti-inflammatory properties, which have been documented in studies using known inflammatory agents, e.g. zymosan, lipopolysaccharide and carrageenan 9. Thus, Forrest et al. 1 were perfectly justified in performing this study. These authors should be encouraged concerning the emerging role of epigenetic dysregulation in the pathogenesis of RA 10, since nontoxic melatonin (maternal lowest observed adverse effect level 200 mg kg−1 day−1, developmental no observed adverse effect level ≥200 mg kg−1 day−1) 11 is a strong candidate for epigenetic regulation 12.

Endogenous Melatonin Increases in Cerebrospinal Fluid of Patients after Severe Traumatic Brain Injury and Correlates with Oxidative Stress and Metabolic Disarray

Oxidative stress plays a significant role in secondary damage after severe traumatic brain injury (TBI); and melatonin exhibits both direct and indirect antioxidant effects. Melatonin deficiency is deleterious in TBI animal models, and its administration confers neuroprotection, reducing cerebral oedema, and improving neurobehavioural outcome. This study aimed to measure the endogenous cerebrospinal fluid (CSF) and serum melatonin levels post-TBI in humans and to identify relationships with markers of oxidative stress via 8-isoprostaglandin-F2alpha (isoprostane), brain metabolism and neurologic outcome. Cerebrospinal fluid and serum samples of 39 TBI patients were assessed for melatonin, isoprostane, and various metabolites. Cerebrospinal fluid but not serum melatonin levels were markedly elevated (7.28+/-0.92 versus 1.47+/-0.35 pg/mL, P<0.0005). Isoprostane levels also increased in both CSF (127.62+/-16.85 versus 18.28+/-4.88 pg/mL, P<0.0005) and serum (562.46+/-50.78 versus 126.15+/-40.08 pg/mL (P<0.0005). A strong correlation between CSF melatonin and CSF isoprostane on day 1 after injury (r=0.563, P=0.002) suggests that melatonin production increases in conjunction with lipid peroxidation in TBI. Relationships between CSF melatonin and pyruvate (r=0.369, P=0.049) and glutamate (r=0.373, P=0.046) indicate that melatonin production increases with metabolic disarray. In conclusion, endogenous CSF melatonin levels increase after TBI, whereas serum levels do not. This elevation is likely to represent a response to oxidative stress and metabolic disarray, although further studies are required to elucidate these relationships.