5-HIAA Concentrations Research Articles

No effect of C1473G polymorphism in the tryptophan hydroxylase 2 gene on the response of the brain serotonin system to chronic fluoxetine treatment in mice.

Selective serotonin reuptake inhibitors (SSRIs) are antidepressants that block serotonin transporter (SERT) and increase serotonin (5-HT) level in the synaptic cleft. The interaction between SERT and the key enzyme of 5-HT synthesis in the brain, tryptophan hydroxylase 2 (TPH2), is essential to maintain the brain 5-HT level. The G allele of C1473G polymorphism in Tph2 gene decreases enzyme activity by half in mouse brain. Here we studied effect of C1473G polymorphism on the reaction of brain 5-HT system to chronic fluoxetine treatment (120mg/l in drinking water, for 3 weeks) in adult males of the congenic B6-1473C and B6-1473G mouse lines with high and low enzyme activity, respectively. The polymorphism did not affect the levels of 5-HT, its metabolite, 5-hydroxyindoleacetic acid (5-HIAA) and Tph2 gene mRNA in the brain. Fluoxetine significantly attenuated 5-HT levels in the cortex and striatum, 5-HIAA concentrations in the cortex, hippocampus, striatum and midbrain, and Tph2 gene expression in the midbrain. However, we did not observed any effect of the genotype x treatment interaction on these neurochemical characteristics. Therefore, C1473G polymorphism does not seem to play an essential role in the reaction of the brain 5-HT system to chronic fluoxetine treatment.

Analgesic effects of JCM-16021 on neonatal maternal separation-induced visceral pain in rats.

To investigate the pharmacological effect of JCM-16021, a Chinese herbal formula, and its underlying mechanisms. JCM-16021 is composed of seven herbal plant materials. All raw materials of the formula were examined according to the quality control criteria listed in the Chinese Pharmacopeia (2005). In a neonatal maternal separation (NMS) model, male Sprague-Dawley rats were submitted to daily maternal separation from postnatal day 2 to day 14, or no specific handling (NH). Starting from postnatal day 60, rats were administered JCM-16021 (2, 4, 8 g/kg per day) orally twice a day for 28 d. Pain threshold pressure and electromyographic activities of external oblique muscles in response to colorectal distention recorded with a Power Lab System (AD Instruments International), were tested as pain indices. Changes in serotonin (5-HT) and 5-hydroxyindoleacetic acid (5-HIAA) concentrations in the colon of rats were analyzed; the enterochromaffin cell numbers and serotonin transporter in the colon of rats were also evaluated with an immunohistochemistry method. NMS treatment significantly reduced pain threshold pressure (37.4 +/- 1.4 mmHg), as compared to that of NH rats (57.7 +/- 1.9 mmHg, P < 0.05). After JCM-16021 treatment, the pain threshold pressure significantly increased when compared to that before treatment (34.2 +/- 0.9 mmHg vs 52.8 +/- 2.3 mmHg in the high dose group, 40.2 +/- 1.6 mmHg vs 46.5 +/- 1.3 mmHg in the middle dose group, and 39.3 +/- 0.7 mmHg vs 46.5 +/- 1.6 mmHg in the low dose group, P < 0.05). Also JCM-16021 significantly and dose-dependently decreased electromyographic activity to the graded colorectal distension (CRD), (the mean DeltaAUC values were: 0.17 +/- 0.03, 0.53 +/- 0.15, 1.06 +/- 0.18, 1.22 +/- 0.24 in the high dose group; 0.23 +/- 0.04, 0.68 +/- 0.17, 1.27 +/- 0.26, 1.8 +/- 0.3 in the middle dose group; and 0.29 +/- 0.06, 0.8 +/- 0.16, 1.53 +/- 0.24, 2.1 +/- 0.21 in the low dose group for the pressures 20, 40, 60, 80 mmHg), as compared to the NMS vehicle group. The mean DeltaAUC values were: 0.57 +/- 0.12, 1.33 +/- 0.18, 2.57 +/- 0.37, 3.08 +/- 0.37 for the pressures 20, 40, 60, 80 mmHg (P < 0.05). JCM-16021 treatment significantly reduced the 5-HT concentrations (from high, middle and low dosage groups: 60.25 +/- 5.98 ng/100 mg, 60.32 +/- 4.22 ng/100 mg, 73.31 +/- 7.65 ng/100 mg), as compared to the NMS vehicle groups (93.11 +/- 9.85 ng/100 mg, P < 0.05); and increased the 5-HIAA concentrations (after treatment, from high, middle and low dosage groups: 54.24 +/- 3.27 ng/100 mg, 50.34 +/- 1.26 ng/100 mg, 51.37 +/- 2.13 ng/100 mg) when compared to that in the NMS vehicle group (51.75 +/- 1.98 ng/100 mg, P < 0.05); but did not change the enterochromaffin cell numbers in the colon of rats. In addition, NMS rats had higher SERT expression (n = 10) than NH rats (n = 8, P < 0.05). JCM-16021 treatment significantly decreased SERT expression when compared to the NMS group (P < 0.01-0.001). JCM-16021 can attenuate visceral hypersensitivity, and this analgesic effect may be mediated through the serotonin signaling pathway in the colon of rats.

Practical LC-MS/MS Method for 5-Hydroxyindoleacetic Acid in Urine.

Serotonin, an endogenous biogenic amine found in enterochromaffin cells of the gastrointestinal tract, is produced in excess by carcinoid tumors. The primary urinary metabolite of serotonin, 5-hydroxyindoleacetic acid (5-HIAA), is used in the diagnosis and management of carcinoid disease. This study describes the development and validation of a dilute-and-shoot LC-MS/MS method for the measurement of 5-HIAA in urine. Samples were prepared by dilution in a 96-well format using an automated liquid handler. Chromatographic isolation of the analyte was achieved using a reversed-phase analytical column. A triple quadrupole mass spectrometer with electrospray ionization in positive mode was used for detection and quantification. Data were acquired by multiple reaction monitoring. Two transitions, quantifier (192.1/146.1) and qualifier (192.1/118.1), were monitored for the analyte and its stable isotope-labeled internal standard [5-hydroxyindole-4,6,7-d3-3-acetic-2,2-d2 acid (5-HIAA-d5)]. Chromatography was designed to elute the analyte outside of major suppression zones. Injection-to-injection time was 4 min. The method was validated for linearity, limit of quantification, accuracy, and imprecision. The analytical measurement range was 0.5-100 mg/L. Coefficients of variation for within-run, between-day, and total imprecision ranged from 0.8% to 5.4%. The method produced accurate 5-HIAA concentrations and correlated well (R = 0.9876) with a comparison HPLC method. Matrix effects were evaluated by post-column infusion of urine samples. An analytical specificity study of endogenous compounds, vitamins, medications, and drugs showed minimal interference. A simple, inexpensive LC-MS/MS method was developed for measurement of 5-HIAA in urine. Results from the assay can be used clinically to assess carcinoid tumors.

Simultaneous measurement of monoamine metabolites and 5-methyltetrahydrofolate in the cerebrospinal fluid of children

BackgroundWe describe a new method for simultaneous measurement of monoamine metabolites (3-O-methyldopa [3-OMD], 3-methoxy-4-hydroxyphenylethyleneglycol [MHPG], 5-hydroxyindoleacetic acid [5-HIAA], and homovanillic acid [HVA]) and 5-methyltetrahydrofolate (5-MTHF) and its use on cerebrospinal fluid (CSF) samples from pediatric patients. MethodsMonoamine metabolites and 5-MTHF were measured by high-performance liquid chromatography with fluorescence detection. CSF samples were prospectively collected from children according to a standardized collection protocol in which the first 1-ml fraction was used for analysis. ResultsMonoamine metabolites and 5-MTHF were separated within 10min. They showed linearity from the limit of detection to 1024nmol/l. The limit of quantification of each metabolite was sufficiently low for the CSF sample assay. In 42 CSF samples after excluding cases with possibly altered neurotransmitter profiles, the concentrations of 3-OMD, MHPG, 5-HIAA, HVA, and 5-MTHF showed significant age dependence and their ranges were comparable with the reference values in the literature. The metabolite profiles of aromatic l-amino acid decarboxylase deficiency, Segawa disease, and folate receptor α defect by this method were compatible with those in the literature. ConclusionsThis method is a simple means of measuring CSF monoamine metabolites and 5-MTHF, and is especially useful for laboratories not equipped with electrochemical detectors.

Long-term effects of pre-pubertal fluoxetine on behaviour and monoaminergic stress response in stress-sensitive rats.

Although prescription rates of antidepressants for children and adolescents have increased, concerns have been raised regarding effects on neurodevelopment and long-term outcome. Using a genetic animal model of depression, this study investigated the long-term effects of pre-pubertal administration of fluoxetine (FLX) on depressive-like behaviour in early adulthood, as well as on central monoaminergic response to an acute stressor. We postulated that pre-pubertal FLX will have lasting effects on animal behaviour and monoaminergic stress responses in early adulthood. Flinders sensitive line (FSL) rats received 10 mg/kg/day FLX subcutaneously from postnatal day 21 (PnD21) to PnD34 (pre-pubertal). Thereafter, following normal housing, rats were either subjected to locomotor testing and the forced swim test (FST) on PnD60 (early adulthood), or underwent surgery for microdialysis, followed on PnD60 by exposure to acute swim stress and measurement of stressor-induced changes in plasma corticosterone and pre-frontal cortical monoamine concentrations. Pre-pubertal FLX did not induce a late emergent effect on immobility in FSL rats on PnD60, whereas locomotor activity was significantly decreased. Acute swim stress on PnD60 significantly increased plasma corticosterone levels, and increased pre-frontal cortical norepinephrine (NE) and 5-hydroxyindole-3-acetic acid (5-HIAA) concentrations. Pre-pubertal FLX significantly blunted the pre-frontal cortical NE and 5-HIAA response following swim stress on PnD60. Baseline dopamine levels were significantly enhanced by pre-pubertal FLX, but no further changes were induced by swim stress. Pre-pubertal FLX did not have lasting antidepressant-like behavioural effects in genetically susceptible, stress-sensitive FSL rats. However, such treatment reduced locomotor activity, abrogated noradrenergic and serotonergic stressor responses and elevated dopaminergic baseline levels in adulthood.

Myocardial interstitial levels of serotonin and its major metabolite 5-hydroxyindole acetic acid during ischemia-reperfusion.

By monitoring myocardial interstitial levels of 5-HT and its metabolite, 5-hydroxyindole acetic acid, we investigated 5-HT kinetics during myocardial ischemia-reperfusion. 5-HT accumulates but 5-HT degradation is suppressed during ischemia. After reperfusion, 5-HT degradation is enhanced and this degradation is dependent on monoamine oxidase activity but not fluoxetine-sensitive uptake transporter.

Determination of 5-Hydroxyindole Acetic Acid by Electrochemical Methods with an Oxidized Glassy Carbon Electrode

The concentration of 5-hydroxyindole acetic acid (5-HIAA), the major metabolite of serotonin, might be the diagnosis basis for some cranial nerve pathology. An oxidized glassy carbon electrode (named OGCE) was employed to detect 5-HIAA with electrochemical methods. Multi-peaks appeared from the second cycle in range of 0.10–0.55V (vs. AgCl/Ag) were assigned to the oxidative intermediates and products of 5-HIAA after the electrochemically driven oxidation at over 0.6V in the first cycle. Kinetics studies show that all of these electrode reactions are adsorption-controlled processes, which are contributed to the strong hydrogen-bond interaction of these intermediates with the negatively charged hydroxyl and carboxyl groups on the surface of OGCE. Based on the square wave voltammetry (SWV) method, the linear relationship was shown between the peak current at 0.7V and the concentration of 5-HIAA in range of 1.56–58.6μmol/L, so 5-HIAA could be determined with limit of 0.917μmol/L (S/N=3) even certain interference were co-existed.

Does elevated urinary 5-hydroxyindole acetic acid level predict acute appendicitis in children?

BackgroundAcute appendicitis is the most common abdominal surgical emergency in children, and appendectomy is the most frequent acute abdominal operation. Prompt diagnosis and surgical treatment are required to reduce the...

GABAergic modulation of serotonin release in the rat subfornical organ area

The present study was carried out to examine whether γ–aminobutyric acid (GABA) receptor mechanisms are involved in the release of serotonin (5-hydroxytryptamine, 5-HT) in the subfornical organ (SFO) using intracerebral microdialysis techniques. Perfusion with the GABA receptor antagonists as well as agonists was performed in the region of the SFO through a microdialysis probe and extracellular concentrations of 5-HT and its metabolite 5-hydroxyindoleacetic acid (5-HIAA) were measured in freely moving rats. Perfusion with the GABAA receptor antagonist bicuculline (10 and 50μM), but not the GABAB receptor antagonist phaclofen (10 and 50μM), increased dialysate 5-HT and 5-HIAA concentrations in the SFO area, suggesting that the GABAergic system may tonically inhibit the 5-HT release in the SFO area through GABAA receptors. Higher perfusion with the GABAA receptor agonist muscimol (50μM) or the GABAB receptor agonist baclofen (250μM) decreased extracellular levels of 5-HT and 5-HIAA in the SFO area. Nonhypotensive hypovolemia induced by subcutaneous injection of polyethylene glycol (PEG, 30%, 5ml) significantly enhanced the 5-HT and 5-HIAA concentrations in the SFO area. The enhanced 5-HT and 5-HIAA levels elicited the PEG treatment were reduced by perfusion with muscimol (10μM), but not by baclofen (50μM). These results show the involvement of both GABAA and GABAB receptors in the modulation of the 5-HT release in the SFO area, and imply that the GABAA receptor mechanism may be importance for the serotonergic regulatory system of body fluid balance.

Non-parametric analysis of neurochemical effects and Arc expression in amphetamine-induced 50-kHz ultrasonic vocalization

A number of studies have identified the importance of dopaminergic, opioid, serotonergic, noradrenergic and glutamatergic neurotransmission in amphetamine-induced “50-kHz” ultrasonic vocalizations (USVs). Amphetamine became a topic of interest for many researchers interested in USVs due to its ability to induce 50-kHz USVs. To date, it has been difficult to identify the neurotransmitters responsible for this phenomenon. The aim of this study was to determine the following: (i) concentrations of neurotransmitters in selected structures of the rat brain after re-exposure of the rats to amphetamine administration; (ii) changes in Arc in the medial prefrontal cortex, striatum, nucleus accumbens core and shell, hippocampus, amygdala and ventral tegmental area; and (iii) a biological basis for differences in 50-kHz USV emissions in response to amphetamine administration. Re-exposure to amphetamine increased 50-kHz USVs. This parameter do not correlate with distance covered by the investigated animals. An increased concentration of noradrenaline in the nucleus accumbens (NAcc) strongly correlated with the number of 50-kHz USVs. We found that NAcc noradrenaline concentrations negatively correlated with the concentration of dopamine and dopamine metabolites and positively correlated with the concentration of GABA and 5-HIAA (serotonin metabolite) in this structure. We have also identified a positive correlation between striatal 3-MT (dopamine metabolite) concentrations and Arc expression in the hippocampal DG as well as a negative correlation between the concentration of GABA in the amygdala and Arc expression in the central amygdala. Thus, the relationship between the emission of 50-kHz USVs and the neurochemical changes that occur after re-exposure to amphetamine indicates cross-talk between NA, DA, 5-HT and GABA neurotransmission in the NAcc.

Serotonin release in the subfornical organ area induced by sodium and water intake in the rat

Previous studies have shown that the subfornical organ (SFO) is involved in the modulation of sodium intake in rats. To clarify whether serotonergic mechanisms in the SFO participate in the modulatory system, the present study was carried out to examine the effects of sodium and water intake on serotonin (5-hydroxytryptamine, 5-HT) release in the subfornical organ (SFO) in freely moving rats. The ingestion of 0.3M NaCl and water was induced by subcutaneous injections of the diuretic furosemide (FURO, 10mg/kg) and the angiotensin converting enzyme inhibitor captopril (CAP, 5mg/kg), and extracellular concentrations of 5-HT and its metabolite 5-hydroxyindoleacetic acid (5-HIAA) in the region of the SFO were measured using intracerebral microdialysis techniques. The combined treatment with FURO and CAP elicited significant decreases in the 5-HT and 5-HIAA levels in the SFO area. The 0.3M NaCl and water intake caused by the treatment significantly enhanced the 5-HT and 5-HIAA concentrations in the SFO area compared with the basal levels. No significant changes in the 5-HT and 5-HIAA levels caused by either the FURO and CAP treatment or water and NaCl intake were observed in the sites away from the SFO. These results suggest that the serotonergic mechanism in the SFO may be important for the control of sodium appetite and thirst.

Editorial: serotonin and irritable bowel syndrome – reconciling pharmacological effects with basic biology; authors' reply

We thank Professor Quigley for his interest in our recent publication.1, 2 In that study, we investigated plasma concentrations of serotonin and its principal metabolite 5-HIAA for differences between IBS patients and healthy controls.1 Due to the prominent role of serotonin in both gut and brain function, different pharmacological therapies aimed at serotonergic targets, including 5HT3 antagonists, 5HT4 agonists and in particular SSRIs have traditionally been administered for IBS with a high variability in treatment efficacy. The Cochrane review from 2011 reports on a significant effect of SSRIs with regard to global improvement but not abdominal pain.3 In a recent meta-analysis, Ford et al. concluded that the relative risk of remaining symptomatic after therapy for SSRIs vs. placebo was 0.68 (95% CI = 0.51–0.91).4 On the other hand, Xie et al. recently showed that SSRIs have no benefit in alleviating symptoms or improving quality of life in IBS patients.5 The contradicting conclusions are probably based on differences in inclusion criteria and thereby in number of studies included in the meta-analyses. Furthermore, it has to be noted that comparing outcomes of trials in IBS patients remains difficult due to a large variety in the definition of study endpoints, as we have shown in a recent systematic review.6 In addition, it remains controversial whether a benefit from SSRI treatment arises from the treatment of co-existent psychopathologies,7 as Ladabaum et al. found no effect of citalopram in nondepressed IBS patients.8 The discrepancy in the evidence for efficacy of SSRIs could also be explained by the heterogeneity of the IBS population. Probably a more selective subgroup for serotonin-targeted therapy could be the solution. Patients could be selected based on psychological comorbidity,8, 9 but pre-treatment assessment of plasma and/or mucosal serotonin metabolism may aid patient selection in the future.1, 10 In this respect, measurement of plasma 5-HIAA appears attractive, as 5-HIAA is less sensitive to oxidative breakdown, compared with 5-HT, and therefore can be measured more reliably. It should however be noted that mere plasma measurements are probably unable to reflect the complexity of serotonergic biology in the gut and brain. Furthermore, Professor Quigley acknowledges the interesting differences in 5-HIAA concentrations between IBS-subtypes, particularly with respect to distinct low 5-HIAA concentrations in the IBS-M subtype in our study.1, 2 He also suggests that the shift of subtypes observed in IBS patients in longitudinal studies would speak against the hypothesis for a role of altered serotonin metabolism in IBS-M.2 Indeed about 50% of IBS patients tend to shift from one subtype to the other, mostly from IBS-M to IBS-D or IBS-C, or vice versa.11 However, this may not contradict our hypothesis. Serotonin is found to affect both gut motility and secretion.12 Therefore, one could speculate that the poorly understood changes in bowel pattern over time may be caused by changes in serotonin metabolism, reflected by plasma 5-HIAA concentrations. A study with a longitudinal design is needed to correlate plasma 5-HIAA concentrations with bowel pattern over time in IBS patients. Declaration of personal and funding interests: None.

Design, Synthesis, and Potential Antidepressant-like Activity of 7-prenyloxy-2,3-dihydroflavanone Derivatives.

A series of 7-prenyloxy-2, 3-dihydroflavanone derivatives were synthesized and screened for their antidepressant-like activity. Among them, it was observed that compounds 5j and 5k were found to be the most antidepressant-like activity. In addition, it was found that compounds 5j and 5k significantly increased the concentrations of the main neurotransmitters 5-HT and NE in the hippocampus, hypothalamus, and cortex. Compounds 5j and 5k also significantly increased the contents of 5-HIAA in the hippocampus and cortex, shut down 5-HT metabolism compared with mice treated with stress vehicle. These results suggested that compounds 5j and 5k displayed potent antidepressant-like properties that were mediated via neurochemical systems.

Bromide-Assisted Anisotropic Growth of Gold Nanoparticles as Substrates for Surface-Enhanced Raman Scattering

We report herein a one-step synthesis of gold nanoparticles (Au NPs) of various shapes such as triangles, hexagons, and semispheres, using 5-hydroxyindoleacetic acid (5-HIAA) as the reducing agent in the presence of potassium bromide (KBr). Anisotropic Au NPs have received ever-increasing attention in various areas of research due to their unique physical and chemical properties. Numerous synthetic methods involving either top-down or bottom-up approaches have been developed to synthesize Au NPs with deliberately varied shapes, sizes, and configurations; however, the production of templateless, seedless, and surfactant-free singular-shaped anisotropic Au NPs remains a significant challenge. The concentrations of hydrogen tetrachloroaurate (HAuCl4), 5-HIAA, and KBr, as well as the reaction temperature, were found to influence the resulting product morphology. A detailed characterization of the resulting Au NPs was performed using ultraviolet-visible (UV-Vis) spectroscopy, scanning electron microscopy (SEM), and Raman spectroscopy. The as-prepared Au NPs exhibited excellent surface-enhanced Raman scattering (SERS) properties, which make them very attractive for the development of SERS-based chemical and biological sensors.

Dietary tryptophan depletion in humans using a simplified two amino acid formula – a pilot study

BackgroundAcute tryptophan depletion (ATD) is a well-established dietary method in translational brain research used to briefly lower central nervous serotonin (5-hydroxytryptamine (5-HT)) synthesis. A simplified two amino acid ATD formula (ATDPHE/LEU) was developed while reducing the overall amount of amino acids (AAs), with the objective of administration especially in children and adolescents in future studies.ObjectiveThis study investigated tryptophan (TRP) influx rates across the blood-brain barrier (BBB) after dietary ATDPHE/LEU administration relative to the ATD Moja-De protocol that has been established for use in children and adolescents.DesignSeventy-two healthy adults (50% females) were randomized into four groups and administered ATD Moja-De, its TRP-balanced control condition (BAL), ATDPHE/LEU, or its respective control mixture (BALPHE/LEU) in a counterbalanced, double-blind, between-subjects design. Blood samples were collected at baseline and at hourly intervals for 6 h after AA intake. Questionnaires about mood, taste, and challenge tolerance were completed at fixed time points.ResultsBoth challenge mixtures significantly reduced central nervous TRP influx as calculated by Michaelis–Menten kinetics relative to baseline and the respective control conditions with only mild and comparable side effects. A greater decline in TRP influx over the BBB after ATDPHE/LEU administration when compared with ATD Moja-De was detected without group effects for taste, challenge tolerance, and mood. There was unintended initial short increase in plasma TRP concentrations observed after ATDPHE/LEU intake, and a possible redistribution between free and protein-bound TRP triggered by protein synthesis stimulated by the ingested AAs may account for this finding. Moreover, a decline in TRP influx after BALPHE/LEU administration over a 6-h period was observed, and the large amount of PHE in the BALPHE/LEU mixture may be a possible explanation for this particular phenomenon, which could have led to an unexpected increase in displacement of TRP at the BBB in this control condition.ConclusionsThis pilot study provides preliminary evidence for the possibility of lowering TRP influx as calculated by Michaelis–Menten kinetics into the brain by using a simplified ATD protocol in humans. The simplified composition of only two AAs, the lower overall AA amount, and the appropriate tolerance are characteristics of the newly developed ATDPHE/LEU protocol. Future studies focusing on the effects of the ATDPHE/LEU protocol and its respective control condition on CSF 5-HIAA concentrations, as well as neurochemical studies in rodents, are needed to further validate this newly developed AA mixture before definite conclusions about its usability in ATD-related research in humans, its specificity, and additional effects can be made.

Commentary: Clinical Correlates of Raphe Serotonergic Dysfunction in Early Parkinson's Disease.

Growing and clinical evidence supports the conclusion that Parkinson’s Disease (PD) is a complex multisystem disorder not exclusively affecting the dopaminergic circuits. In fact, the dopaminergic neuronal loss does not cover all the clinical aspects of PD. Therefore, different non-dopaminergic neurotransmitter systems have been invoked as playing a role in the PD clinical picture. Principally, the inefficiency of serotonergic circuitry has been demonstrated in PD animal models, as well as in post-mortem and in vivo human studies. In the recent article published in Brain, Zahi Qamhawi and colleagues interrogated 123I-FP-CIT single-photon emission computed tomography documenting raphe serotonergic dysfunction in a large group of early PD patients compared to a subset of possible PD patients without evidence of dopaminergic deficit (SWEDD) and a population of healthy controls (1). This paper combined an accurate clinical evaluation with a sophisticated neuroimaging protocol and documented in PD patients a mean raphe serotonin (5-HT) transporter availability significantly lower than both SWEDD patients and controls. These findings, achieved in a large cohort of PD patients, enforced previous autoptic examinations documenting serotonergic neurons loss due to Lewy body pathology in the raphe nuclei of PD patients (2). Accordingly, neuroimaging studies have shown the progressive 5-HT transporter availability reduction in the raphe nuclei as PD pathology progresses (3–5). It is well accepted that concentration of 5-HT and its metabolite 5-hydroxyindolacetic acid (5-HIAA) in CSF reflects the serotonergic metabolism and turnover in the CNS (6, 7). We performed a case-control study investigating CSF levels of 5-HT and 5-HIAA in a cohort of PD patients, after a 3-day dopaminergic therapy withdrawal and in absence of serotonergic agents (8). We demonstrated the significant reduction of CSF 5-HT and 5-HIAA concentrations in PD patients compared to controls. We also found the significant reduction of CSF 5-HT and 5-HIAA in the PD population with respect to Alzheimer’s Disease patients (8), thus highlighting that the impairment of serotonergic system could represent a specific effect of synuclein-mediated neurodegeneration (8). As a matter of fact, novel experimental studies in alpha-synuclein (α-syn) mouse model of PD showed the impairment of serotonergic system owing to the intracellular accumulation of α-syn in serotonergic neurons coupled with the reduction of 5-HT levels in lower brainstem (9). Based on the clinical presentation, Qamhawi and collegues divided PD patients into two subgroups corresponding to patients with and without resting tremor. Remarkably, patients with tremor had lower mean raphe 5-HT transporter availability than patients unaffected by tremor. Since tremor amplitude, constancy, and severity negatively correlated with raphe 5-HT transporter availability in the whole PD cohort, authors suggested that the serotonergic system inefficiency could be responsible for parkinsonian tremor. This finding was consistent with previous studies detecting an association between 5-HT receptor availability in the raphe nuclei and severity of parkinsonian tremor (10). However, in our CSF study, we found no differences in CSF 5-HT and 5-HIAA levels between tremor dominant and non-tremor dominant patients. This discrepancy could be ascribed to the fact that Qamhawi and collegues studied de novo early PD patients, whereas we investigated patients with higher Hoehn and Yahr stage and greater motor disability at the Unified PD Rating Scale-motor section. It could be of interest to evaluate in follow-up studies how the serotonergic transmission damage may influence PD motor symptoms along with the progression of the disease. Concurrently, the reliability of the proposed difference in raphe 5-HT transporter availability found by Qamhawi and coworkers in early PD patients should be also analyzed in more advanced PD patients. Remarkably, Qamhawi and coauthors documented that raphe 5-HT transporter availability did not correlate with PD non-motor symptoms, such as fatigue, depression, and sleep-wake cycle disturbances. In agreement with this finding, we did not identify mutual interplays linking CSF 5-HT and 5-HIAA concentrations to depression, apathy, and sleep disturbances. Although our report sustained Qamhawi and coworkers results, literature proposes controversial data regarding the involvement of serotonergic pathways breakage in the pathophysiology of PD non-motor symptoms (11), thus requiring further investigations. All considering, we suppose that the reduced 5-HT transporter availability, as shown by Qamhawi and collegues, and the 5-HT synthesis, metabolism, and turnover impairment, resulting in reduced CSF levels of 5-HT and 5-HIAA (8) may both contribute to the serotonergic transmission dysfunction evident in PD. Hence, serotonin circuitry inefficiency could represent the fitting partner of the dopaminergic deficit in PD.

Increased plasma serotonin metabolite 5-hydroxyindole acetic acid concentrations are associated with impaired systolic and late diastolic forward flows during cardiac cycle and elevated resistive index at popliteal artery and renal insufficiency in type 2 diabetic patients with microalbuminuria.

Although lower extremity arterial disease is frequently accompanied by diabetes mellitus, the association of circulating biomarkers with flow components during the cardiac cycle in lower-leg arteries has yet to be fully elucidated. We enrolled 165 type 2 diabetic patients with normal ankle-brachial index (ABI 1.0-1.4), comprising 106 normoalbuminuric and 59 microalbuminuric patients, and 40 age-matched nondiabetic subjects consecutively admitted to our hospital. Serum high sensitivity C-reactive protein (hsCRP) level and plasma von Willebrand factor ristocetin cofactor activity (VWF) and vasoconstrictor serotonin metabolite 5-hydroxyindole acetic acid (5-HIAA) concentrations were measured. An automatic device was used to measure ABI and brachial-ankle pulse wave velocity (baPWV). Flow components during the cardiac cycle, total flow volume, and resistive index at popliteal artery were evaluated using gated magnetic resonance imaging. Although estimated glomerular filtration rate (eGFR), early diastolic flow reversal, heart rate, and ABI were similar between the groups, diabetic patients had higher log hsCRP (p<0.001), VWF (p<0.001), 5-HIAA (p=0.002), resistive index (p<0.001) and baPWV (p<0.001) and lower systolic (p=0.026) and late diastolic (p<0.001) forward flows and total flow volume (p<0.001) than nondiabetic subjects. Multivariate analyses demonstrated that 5-HIAA in microalbuminuric patients showed higher associations with systolic and late diastolic forward flows during the cardiac cycle, total flow volume and resistive index at popliteal artery, and eGFR compared to normoalbuminuric patients. In microalbuminuric patients, 5-HIAA was a significant independent determinant among these factors. Thus, increased plasma 5-HIAA levels are involved in the pathogenesis of impaired blood flow in lower extremities and renal insufficiency in diabetic patients with microalbuminuria.

Alterations in serotonin metabolism in the irritable bowel syndrome.

Alterations in serotonin (5-HT) metabolism have been postulated to play a role in the pathogenesis of irritable bowel syndrome (IBS). However, previous reports regarding 5-HT metabolism in IBS are contradicting. To compare platelet poor plasma (PPP) 5-HT and 5-hydroxyindole acetic acid (5-HIAA) levels and their ratio in a large cohort of IBS patients and healthy controls (HC), including IBS-subgroup analysis. Irritable bowel syndrome patients and HC were evaluated for fasting PPP 5-HT and 5-HIAA levels. Furthermore, GI-symptom diary, GSRS, quality of life, anxiety and depression scores were assessed in the 2 weeks before blood sampling. One hundred and fifty four IBS patients and 137 HC were included. No differences were detected in plasma 5-HT between groups. The 5-HIAA concentrations and 5-HIAA/5-HT ratio were significantly lower in IBS compared to HC: 24.6 ± 21.9 vs. 39.0 ± 29.5 μg/L (P < 0.001) and 8.4 ± 12.2 vs. 13.5 ± 16.6 (P < 0.01), respectively. Subtype analysis for 5-HIAA showed all IBS subtypes to be significantly different from HC. The 5-HIAA/5-HT ratio was significantly lower in the IBS-M subtype vs. HC. Linear regression analysis points to an influence of gender but not of GI-symptoms, psychological scores or medication use. We demonstrated that fasting 5-HT plasma levels are not significantly different in IBS patients compared to controls. However, decreased 5-HIAA levels and 5-HIAA/5-HT ratio in IBS patients may reflect altered serotonin metabolism in IBS. Gender affects 5-HIAA levels in IBS patients, but no effects of drugs, such as SSRIs, or higher GI-symptom or psychological scores were found.

Association Of Peripheral 5-Hydroxyindole-3-Acetic Acid, A Serotonin Derivative, with Metabolic Syndrome and Low-Grade Inflammation

The constellation of metabolic abnormalities seen in metabolic syndrome (MetS) has been linked to atherosclerosis and adverse cardiovascular outcomes due to heightened inflammation. Accumulating evidence suggests that peripheral 5-hydroxyindole-3-acetic acid (5-HIAA), the derivative end-product of serotonin (5-HT), might be involved in the pathogenesis of obesity, and abnormal lipid and glucose metabolism. We examined the association between serum 5-HIAA concentrations and MetS and also highly sensitive C-reactive protein (hsCRP). We assessed 180 healthy adults (110 males and 70 females) in a cross-sectional setting. Anthropometric indices and blood pressure were measured, as were laboratory parameters including fasting 5-HIAA concentrations. The associations between 5-HIAA and individual components of MetS, as well as MetS as a single entity, were investigated with bivariate correlation and logistic regression analyses. Eighty-nine individuals (49.4%) were diagnosed with MetS. Significant correlations were found between 5-HIAA concentrations and age (r = 0.184), waist circumference (r = 0.415), high-density lipoprotein (HDL) cholesterol (r = -0.148), systolic blood pressure (r = 0.374), diastolic blood pressure (r = 0.355), homeostasis model assessment of insulin resistance (r = 0.201), and hsCRP (r = 0.453) were found (P<.05 in all tests). In logistic regression, 5-HIAA was significantly associated with 4 MetS components including central obesity, raised triglycerides, raised blood pressure, and raised fasting plasma glucose (FPG) (P<.05). Moreover, 5-HIAA was a predictor of MetS as a single entity, and the relationship persisted after adjusting for hsCRP (odds ratio [OR] = 4.41, 95% confidence interval [CI]: 2.58-7.67, P<.001). Elevated concentrations of 5-HIAA are seen in individuals with MetS. Increased 5-HIAA is also associated with hsCRP, a marker of chronic low-grade inflammation underlying MetS.

Cerebrospinal fluid monoamine metabolite concentrations as intermediate phenotypes between glutamate-related genes and psychosis

Glutamate-related genes have been associated with schizophrenia, but the results have been ambiguous and difficult to replicate. Homovanillic acid (HVA), 5-hydroxyindoleacetic acid (5-HIAA) and 3-methoxy-4-hydroxyphenylglycol (MHPG) are the major degradation products of the monoamines dopamine, serotonin and noradrenaline, respectively, and their concentrations in the cerebrospinal fluid (CSF), mainly HVA, have been associated with schizophrenia. In the present study, we hypothesized that CSF HVA, 5-HIAA and MHPG concentrations represent intermediate phenotypes in the association between glutamate-related genes and psychosis. To test this hypothesis, we searched for association between 238 single nucleotide polymorphisms (SNPs) in ten genes shown to be directly or indirectly implicated in glutamate transmission and CSF HVA, 5-HIAA and MHPG concentrations in 74 patients with psychotic disease. Thirty-eight nominally significant associations were found. Further analyses in 111 healthy controls showed that 87% of the nominal associations were restricted to the patients with psychosis. Some of the psychosis-only-associated SNPs found in the d-amino acid oxidase activator (DAOA) and the kynurenine 3-monooxygenase (KMO) genes have previously been reported to be associated with schizophrenia. The present results suggest that CSF monoamine metabolite concentrations may represent intermediate phenotypes in the association between glutamate-related genes and psychosis.