Urinary 5-hydroxyindoleacetic acid and whole blood serotonin and tryptophan in autistic and normal subjects

A Systematic Review on Autism and Hyperserotonemia: State-of-the-Art, Limitations, and Future Directions

Hyperserotonemia is one of the most studied endophenotypes in autism spectrum disorder (ASD), but there are still no unequivocal results about its causes or biological and behavioral outcomes. This systematic review summarizes the studies investigating the relationship between blood serotonin (5-HT) levels and ASD, comparing diagnostic tools, analytical methods, and clinical outcomes. A literature search on peripheral 5-HT levels and ASD was conducted. In total, 1104 publications were screened, of which 113 entered the present systematic review. Of these, 59 articles reported hyperserotonemia in subjects with ASD, and 26 presented correlations between 5-HT levels and ASD-core clinical outcomes. The 5-HT levels are increased in about half, and correlations between hyperserotonemia and clinical outcomes are detected in a quarter of the studies. The present research highlights a large amount of heterogeneity in this field, ranging from the characterization of ASD and control groups to diagnostic and clinical assessments, from blood sampling procedures to analytical methods, allowing us to delineate critical topics for future studies.

Intestinal Predictors of Whole Blood Serotonin Levels in Children With or Without Autism

Hyperserotonemia, or elevated levels of whole blood serotonin (WB5-HT), was the first biomarker linked to autism spectrum disorder (ASD). Despite numerous studies investigating the etiology of hyperserotonemia, results have been inconsistent. Recent findings suggest a relationship between the immune system and hyperserotonemia. The current study investigated whether intestinal 5-HT levels, 5-HT gene expression, or intestinal cell types predict WB5-HT. Participants included thirty-one males aged 3-18 who were classified into one of three groups: ASD and functional GI issues, typically developing with GI issues, and typically developing without GI issues. Samples from a lower endoscopy were analyzed to examine the pathways in predicting WB-5HT. Results demonstrated an association between T-Lymphocytes and WB5-HT.

Autism Spectrum Disorders and the Gut Microbiota

In recent years, there has been an emerging interest in the possible role of the gut microbiota as a co-factor in the development of autism spectrum disorders (ASDs), as many studies have highlighted the bidirectional communication between the gut and brain (the so-called "gut-brain axis"). Accumulating evidence has shown a link between alterations in the composition of the gut microbiota and both gastrointestinal and neurobehavioural symptoms in children with ASD. The aim of this narrative review was to analyse the current knowledge about dysbiosis and gastrointestinal (GI) disorders in ASD and assess the current evidence for the role of probiotics and other non-pharmacological approaches in the treatment of children with ASD. Analysis of the literature showed that gut dysbiosis in ASD has been widely demonstrated; however, there is no single distinctive profile of the composition of the microbiota in people with ASD. Gut dysbiosis could contribute to the low-grade systemic inflammatory state reported in patients with GI comorbidities. The administration of probiotics (mostly a mixture of Bifidobacteria, Streptococci and Lactobacilli) is the most promising treatment for neurobehavioural symptoms and bowel dysfunction, but clinical trials are still limited and heterogeneous. Well-designed, randomized, placebo-controlled clinical trials are required to validate the effectiveness of probiotics in the treatment of ASD and to identify the appropriate strains, dose, and timing of treatment.

Serotonin dynamics in and around the central nervous system: is autism solvable without fundamental insights?

Altered serotonin (5-hydroxytryptamine, 5-HT) signaling has been implicated in some developmental abnormalities of autism spectrum disorder (ASD). However, the presumed role of 5-HT in ASD raises new questions in fundamental neuroscience. Specifically, it is not clear if the current piecemeal approach to 5-HT signaling in the mammalian body is effective and whether new conceptual approaches may be required. This review briefly discusses 5-HT production and circulation in the central nervous system and outside of it, especially with regard to ASD, and proposes a more encompassing approach that questions the utility of the "neurotransmitter" concept. It then introduces the idea of a generalized 5-HT packet that may offer insights into possible links between serotonergic varicosities and blood platelets. These approaches have theoretical significance, but they are also well positioned to advance our understanding of some long-standing problems in autism research.

Blood serotonin levels in autism spectrum disorder: a systematic review and meta-analysis

Elevated blood serotonin (5-HT) levels were the first biomarker identified in autism research. Many studies have contrasted blood 5-HT levels in autistic patients and controls, but different measurement protocols, technologies, and biomaterials have been used through the years. We performed a systematic review and meta-analysis to provide an overall estimate of effect size and between-study heterogeneity, while verifying whether and to what extent different methodological approaches influence the strength of this association. Our literature search strategy identified 551 papers, from which 22 studies providing patient and control blood 5-HT values were selected for meta-analysis. Significantly higher 5-HT levels in autistic patients compared to controls were recorded both in whole blood (WB) [O.R.=4.6; (3.1-5.2); P=1.0×10(-12]), and in platelet-rich plasma (PRP) [O.R.=2.6 (1.8-3.9); P=2.7×10(-7)]. Predictably, studies measuring 5-HT levels in platelet-poor plasma (PPP) yielded no significant group difference [O.R.=0.54 (0.2-2-0); P=0.36]. Altogether, elevated 5-HT blood levels were recorded in 28.3% in WB and 22.5% in PRP samples of autistic individuals, as reported in 15 and 4 studies, respectively. Studies employing HPLC vs fluorometric assays yield similar cumulative effect sizes, but the former display much lower variability. In summary, despite some limitations mainly due to small study sample sizes, our results significantly reinforce the reliability of elevated 5-HT blood levels as a biomarker in ASD, providing practical indications potentially useful for its inclusion in multi-marker diagnostic panels for clinical use.

5-HT1A-receptor agonist modified amygdala activity and amygdala-associated social behavior in a valproate-induced rat autism model

Accumulating evidence suggests that dysfunction of the amygdala is related to abnormal fear processing, anxiety, and social behaviors noted in autistic spectrum disorders (ASDs). In addition, studies have shown that disrupted brain serotonin homeostasis is linked to ASD. With a valproate (VPA)-induced rat ASD model, we investigated the possible role of amygdala serotonin homeostasis in autistic phenotypes and further explored the underlying mechanism. We first discovered that the distribution of tryptophan hydroxylase immunoreactivity in the caudal raphe system was modulated on postnatal day (PD) 28 of the VPA-exposed offspring. Then, we found a significantly higher serotonin transporter availability in the amygdala of the VPA-exposed offspring on PD 56 by using single photon emission computed tomography and computed tomography co-registration following injection of (123)I-labeled 2-((2-(dimethylamino)methyl)phenyl)thio)-5-iodophenylamine((123)I[ADAM]). Furthermore, treatment with 8-hydroxy-2-(di-n-propylamino)tetralin (8-OH-DPAT), a 5-HT1A receptor agonist, increased social interaction and improved fear memory extinction in the VPA-exposed offspring. 8-OH-DPAT treatment also reversed the characteristics of miniature excitatory post-synaptic currents as well as paired pulse facilitation observed in lateral amygdala slices. These results provided further evidence to support the role of the amygdala in characteristic behavioral changes in the rat ASD model. The serotonergic projections that modulate the amygdala function might play a certain role in the development and treatment of behavioral symptoms exhibited in individuals with ASD.

A review of candidate urinary biomarkers for autism spectrum disorder

CONTEXT

Autism is a complex, heterogeneous neurodevelopmental condition with a strong genetic component potentially impacted by various environmental factors influencing susceptibility. There are no reliable laboratory tests available to confirm an autism diagnosis.

OBJECTIVE

To examine the published literature and identify putative urinary biomarkers of autism.

METHODS

A comprehensive literature search was conducted using electronic bibliographic databases.

RESULTS

Putative autism biomarkers were identified that could be categorized according to the key theories that exist regarding the etiology of autism: gastrointestinal factors, immune dysregulation, heavy metal toxicity, neurotransmitter abnormalities, and oxidative stress.

CONCLUSION

There is scope for specific urinary biomarkers to be useful for identification of autistic metabolic phenotypes.

Pathways underlying the gut-to-brain connection in autism spectrum disorders as future targets for disease management

Autism spectrum disorders (ASDs) are pervasive neurodevelopmental disorders, characterized by impairments in social interaction and communication and the presence of limited, repetitive and stereotyped interests and behavior. Bowel symptoms are frequently reported in children with ASD and a potential role for gastrointestinal disturbances in ASD has been suggested. This review focuses on the importance of (allergic) gastrointestinal problems in ASD. We provide an overview of the possible gut-to-brain pathways and discuss opportunities for pharmaceutical and/or nutritional approaches for therapy.

Discovery of leukotriene A4 hydrolase inhibitors using metabolomics biased fragment crystallography

We describe a novel fragment library termed fragments of life (FOL) for structure-based drug discovery. The FOL library includes natural small molecules of life, derivatives thereof, and biaryl protein architecture mimetics. The choice of fragments facilitates the interrogation of protein active sites, allosteric binding sites, and protein−protein interaction surfaces for fragment binding. We screened the FOL library against leukotriene A4 hydrolase (LTA4H) by X-ray crystallography. A diverse set of fragments including derivatives of resveratrol, nicotinamide, and indole were identified as efficient ligands for LTA4H. These fragments were elaborated in a small number of synthetic cycles into potent inhibitors of LTA4H representing multiple novel chemotypes for modulating leukotriene biosynthesis. Analysis of the fragment-bound structures also showed that the fragments comprehensively recapitulated key chemical features and binding modes of several reported LTA4H inhibitors.

Relationships among body mass, brain size, gut length, and blood tryptophan and serotonin in young wild-type mice

Background

The blood hyperserotonemia of autism is one of the most consistent biological findings in autism research, but its causes remain unclear. A major difficulty in understanding this phenomenon is the lack of information on fundamental interactions among the developing brain, gut, and blood in the mammalian body. We therefore investigated relationships among the body mass, the brain mass, the volume of the hippocampal complex, the gut length, and the whole-blood levels of tryptophan and 5-hydroxytryptamine (5-HT, serotonin) in young, sexually immature wild-type mice.

Results

Three-dimensional reconstructions of the hippocampal complex were obtained from serial, Nissl-stained sections and the gut was allowed to attain its maximal relaxed length prior to measurements. The tryptophan and 5-HT concentrations in the blood were assessed with high-performance liquid chromatography (HPLC) and the sex of mice was confirmed by genotyping. Statistical analysis yielded information about correlative relationships among all studied variables. It revealed a strong negative correlation between blood 5-HT concentration and body mass and a strong negative correlation between the brain mass/body mass ratio and gut length. Also, a negative correlation was found between the volume of the hippocampal complex and blood tryptophan concentration.

Conclusion

The study provides information on the covariance structure of several central and peripheral variables related to the body serotonin systems. In particular, the results indicate that body mass should be included as a covariate in studies on platelet 5-HT levels and they also suggest a link between brain growth and gut length.

Ontogeny of brain and blood serotonin levels in 5-HT receptor knockout mice: potential relevance to the neurobiology of autism

The most consistent neurochemical finding in autism has been elevated group mean levels of blood platelet 5-hydroxytryptamine (5-HT, serotonin). The origin and significance of this platelet hyperserotonemia remain poorly understood. The 5-HT(1A) receptor plays important roles in the developing brain and is also expressed in the gut, the main source of platelet 5-HT. Post-natal tissue levels of 5-HT, 5-hydroxyindoleacetic acid (5-HIAA) and tryptophan were examined in the brain, duodenum and blood of 5-HT(1A) receptor-knockout and wild-type mice. At 3 days after birth, the knockout mice had lower mean brain 5-HT levels and normal mean platelet 5-HT levels. Also, at 3 days after birth, the mean tryptophan levels in the brain, duodenum and blood of the knockout mice were around 30% lower than those of the wild-type mice. By 2 weeks after birth, the mean brain 5-HT levels of the knockout mice normalized, but their mean platelet 5-HT levels became 24% higher than normal. The possible causes of these dynamic shifts were explored by examining correlations between central and peripheral levels of 5-HT, 5-HIAA and tryptophan. The results are discussed in relation to the possible role of 5-HT in the ontogeny of autism.

Hyperserotoninemia and Altered Immunity in Autism

One of the most consistent biological findings in autism is elevated whole blood serotonin (5-HT) levels found in about 1/3 of cases. Immune abnormalities are also commonly observed in this disorder. Given 5-HT's role as an immunomodulator, possible connections between 5-HT and immune abnormalities in autism are explored in this review. Areas of focus include hyperserotoninemia and cellular immune function, autoantibodies to 5-HT receptors, and 5-HT's role in autoimmunity. Further research is needed to determine the interactions between neuropsychiatric and immune dysfunction in autism and related disorders.

Automated On-Line Solid-Phase Extraction Coupled with HPLC for Measurement of 5-Hydroxyindole-3-acetic Acid in Urine

Background: Quantification of 5-hydroxyindole-3-acetic acid (5-HIAA) in urine is useful in diagnosing and monitoring of patients with carcinoid tumors and in the study of serotonin (5-hydroxytryptamine) metabolism in various disorders. We describe an automated method that incorporates on-line solid-phase extraction (SPE) and HPLC to measure urinary 5-HIAA.

Methods: Automated prepurification of urine was accomplished with HySphere-resin GP SPE cartridges containing strong hydrophobic polystyrene resin. The analyte (5-HIAA) and internal standard [5-hydroxyindole-3-carboxylic acid (5-HICA)] were eluted from the SPE cartridge, separated by reversed-phase HPLC, and detected fluorometrically with a total cycle time of 20 min. Urinary excretion of 5-HIAA was measured in a group of patients with known and suspected carcinoid tumors (n = 63) and in 20 patients with autism.

Results: The internal standard (5-HICA) and 5-HIAA were recovered in high yields (87.2%–114%). Within- and between-series CVs for the measurement of 5-HIAA in urine ranged from 1.2% to 3.9% and 3.2% to 7.6%, respectively. For urine samples from patients with known or suspected carcinoid tumors, results obtained by the automated method were highly correlated (r = 0.988) with those from an established manual extraction method. For samples from autistic patients, urinary excretion of 5-HIAA was similar to that reported for healthy individuals.

Conclusion: This SPE-HPLC method demonstrated lower imprecision and time per analysis than the manual solvent extraction method.

Statistical distribution of blood serotonin as a predictor of early autistic brain abnormalities

BACKGROUND

A wide range of abnormalities has been reported in autistic brains, but these abnormalities may be the result of an earlier underlying developmental alteration that may no longer be evident by the time autism is diagnosed. The most consistent biological finding in autistic individuals has been their statistically elevated levels of 5-hydroxytryptamine (5-HT, serotonin) in blood platelets (platelet hyperserotonemia). The early developmental alteration of the autistic brain and the autistic platelet hyperserotonemia may be caused by the same biological factor expressed in the brain and outside the brain, respectively. Unlike the brain, blood platelets are short-lived and continue to be produced throughout the life span, suggesting that this factor may continue to operate outside the brain years after the brain is formed. The statistical distributions of the platelet 5-HT levels in normal and autistic groups have characteristic features and may contain information about the nature of this yet unidentified factor.

RESULTS

The identity of this factor was studied by using a novel, quantitative approach that was applied to published distributions of the platelet 5-HT levels in normal and autistic groups. It was shown that the published data are consistent with the hypothesis that a factor that interferes with brain development in autism may also regulate the release of 5-HT from gut enterochromaffin cells. Numerical analysis revealed that this factor may be non-functional in autistic individuals.

CONCLUSION

At least some biological factors, the abnormal function of which leads to the development of the autistic brain, may regulate the release of 5-HT from the gut years after birth. If the present model is correct, it will allow future efforts to be focused on a limited number of gene candidates, some of which have not been suspected to be involved in autism (such as the 5-HT4 receptor gene) based on currently available clinical and experimental studies.

Serotonergic paradoxes of autism replicated in a simple mathematical model

The biological causes of autism are unknown. Since the early 1960s, the most consistent pathophysiological finding in autistic individuals has been their statistically elevated blood 5-hydroxytryptamine (5-HT, serotonin) levels. However, many autistic individuals have normal blood 5-HT levels, so this finding has been difficult to interpret. The serotonin transporter (SERT) controls 5-HT uptake by blood platelets and has been implicated in autism, but recent studies have found no correlation between SERT polymorphisms and autism. Finally, autism is considered a brain disorder, but studies have so far failed to find consistent serotonergic abnormalities in autistic brains. A simple mathematical model may account for these paradoxes, if one assumes that autism is associated with the failure of a molecular mechanism that both regulates 5-HT release from gut enterochromaffin cells and mediates 5-HT signaling in the brain. Some 5-HT receptors may play such a dual role. While the failure of such a mechanism may lead to consistent abnormalities of synaptic transmission with no alteration of brain 5-HT levels, its effects on blood 5-HT levels may appear paradoxical.

Psychopharmacology in autism

Autism is a neurobiological disorder. The core clinical features of autism include impairment in social interaction, impairments in verbal and nonverbal communication, and restricted, repetitive, and stereotyped patterns of behavior, interests, and activities. Autism often has coexisting neuropsychiatric disorders, including seizure disorders, attention deficit hyperactivity disorder, affective disorders, anxiety disorder, obsessive-compulsive disorder, and Tourette disorder. No etiology-based treatment modality has been developed to cure individuals with autism. However, comprehensive intervention, including parental counseling, behavior modification, special education in a highly structured environment, sensory integration training, speech therapy, social skill training, and medication, has demonstrated significant treatment effects in many individuals with autism. Findings from preliminary studies of major neurotransmitters and other neurochemical agents strongly suggest that neurochemical factors play a major role in autism. The findings also provide the rationale for psychopharmacotherapy in individuals with autism. This article reviews studies of neurochemical systems and related psychopharmacological research in autism and related neuropsychiatric disorders. Clinical indications for pharmacotherapy are described, and uses of various medications are suggested. This article also discusses new avenues of investigation that may lead to the development of more effective medication treatments in persons with autism.

Childhood autism: the need for physical investigations

In this paper the results of an extensive medical investigation of 25 children with childhood autism are presented and compared with those found in a group of non-autistic individuals matched for sex, age and intellectual level, all referred for developmental deviancy of unknown etiology. The examination included a psychiatric assessment and a neurological examination in addition to neurophysiological, chromosomal, metabolic and neuroimaging evaluation. In the clinical examination macrocephaly was found only among the autistic individuals, while the frequency of pathological cerebral CT and clinical parameters such as tendon reflexes and mobility problems was significantly greater in the control group. All the other pathological findings were found to occur with the same frequency in the two groups. Except for research purposes this study did not lend support to those who argue for extensive medical examinations for all children with autism. Based on the present findings, ordinary procedures for assessment of developmentally delayed children should be followed. This should include a systematic clinical neuropaediatric examination, an assessment of vision and hearing and a chromosome study, including that for fragile X.

Human brain serotonin synthesis capacity measured in vivo with alpha-[C-11]methyl-L-tryptophan

Local cerebral serotonin synthesis capacity was measured with alpha-[C-11]methyl-L-tryptophan ([C-11]AMT) in normal adult human brain (n = 10; five males, five females; age range, 18-38 years, mean 28.3 years) by using positron emission tomography (PET). [C-11]AMT is an analog of tryptophan, the precursor for serotonin synthesis, and is converted to alpha-[C-11]methyl-serotonin ([C-11]AM-5HT), which is trapped in serotonergic neurons because [C-11]AM-5HT is not degraded by monoamine oxidase. Kinetic analysis of [C-11] activity in brain after injection of [C-11]AMT confirmed the presence of a compartment with unidirectional uptake that represented approximately 40% of the activity in the brain at 50 min after tracer administration. The undirectional rate constant K, which represents the uptake of [C-11]AMT from the plasma to brain tissue followed by the synthesis and physiologic trapping of [C-11]AM-5HT, was calculated using the Patlak graphic approach on a pixel-by-pixel basis, thus creating parametric images. The rank order of K values for different brain regions corresponded well to the regional concentrations of serotonin in human brain (P < .0001). High serotonin synthesis capacity values were measured in putamen, caudate, thalamus, and hippocampus. Among cortical regions, the highest values were measured in the rectal gyrus of the inferior frontal lobe, followed by transverse temporal gyrus; anterior and posterior cingulate gyrus; middle, superior, and inferior temporal gyri; parietal cortex; occipital cortex, in descending order. Values in women were 10-20% higher (P < .05, MANOVA) throughout the brain than those measured in men. Differences in the serotonin synthesis capacity between men and women measured in this study may reflect gender differences of importance to both normal and pathologic behavior. This study demonstrates the suitability of [C-11]AMT as a tracer for PET scanning of serotonin synthesis capacity in human brain and provides normal adult values for future comparison with patient groups.

Serotonin and autism: biochemical and molecular biology features

Whole blood and urinary levels of serotonin (5-hydroxytryptamine; 5-HT) and the derivative urinary 5-hydroxyindoleacetic acid (5-HIAA) were measured in normal and autistic subjects. An association was tested between autism and a marker coding for the 5-HT2A serotonergic receptor gene. Significant group (high urinary 5-HT and low whole blood 5-HT in autism) and age effects (urinary 5-HT decrease with age) were found. Moreover, whole blood 5-HT levels were correlated with clinical state. No differences in allele and genotype frequencies for the 5-HT2A receptor marker were found in this autistic population compared with age-matched healthy students.

Separation of tryptophan and related indoles by micellar electrokinetic chromatography with KrF laser-induced fluorescence detection

Micellar electrokinetic chromatography (MEKC) was applied for the separation of tryptophan and related indoles. Using a 5 mM sodium borate buffer (pH 9.2) containing 50 mM sodium dodecyl sulfate and 5% acetonitrile, eleven indoles were baseline separated in under 17 min. Most of the indoles were detected at the nM level by native fluorescence using KrF laser-induced fluorescence (LIF), which was approximately 100 times more sensitive than UV absorption detection at 200 nm. Preliminary results show that the MEKC-LIF with direct sample injection is a feasible method for assessing indole profiles in diluted urine and serum.

Serotonin-degradative pathways in the toad (Bufo bufo japonicus) brain: clues to the pharmacological analysis of human psychiatric disorders

Bufotenine (BUTN) is a hallucinogen with psychotropic effects. High levels of BUTN and its precursor, N-methylserotonin are shown for the first time to occur and to accumulate mainly in the brain during the degradation of serotonin in the central nervous system of the toad, Bufo bufo japonicus. These compounds are concentrated in the hindbrain, which includes the cerebellum and medulla oblongata. BUTN can also be detected in blood and urine specimens from the toad. In humans, autism is a subtype of schizophrenia that appears to be a functional disease of the brain. BUTN can be detected in urine specimens from infant autistic patients. Analysis by three-dimensional HPLC suggests that the presence and levels of BUTN may be important markers for the diagnosis of autism. It appears, therefore, that some aspects of the central nervous system of Bufo may provide useful pharmacological clues to the etiology of human psychiatric diseases, such as autism, that are known to be linked to the methylation of serotonin.

Investigation of whole blood and urine monoamines in autism

Levels of serotonin (5-HT), dopamine (DA), norepinephrine (NE) and epinephrine (E) were determined in the whole blood and urine of 23 children with autism and compared to those of normal children. Very significant group effects (low whole blood 5-HT, high urinary 5-HT and high NE+E in autism) and age effects (urinary 5-HT and DA decrease with age) were found. Moreover, the urinary DA and the whole blood E levels were correlated with clinical findings. The results suggest a maturation defect of noradrenergic systems, possibly disturbed dopaminergic and serotoninergic metabolism, and a functional imbalance among these neurotransmitters in autism.

Clinical review: Medical differential diagnosis and treatment of the autistic syndrome

Autism, like mental retardation, is not a definitive diagnosis. This paper discusses the medical differential diagnosis to consider when patients present with autistic symptoms. Summarizing the medical literature, the known infectious, metabolic, chromosomal and structural lesions are reviewed. Autism also can be associated with sensory handicaps, such as blindness and deafiness. When the autistic syndrome is associated with a second syndrome, this produces a "double syndrome" in the patient. A thorough medical evaluation of all individuals with autism is suggested.

The use of platelets as models for neurons: possible applications to the investigation of eating disorders

The pathogenesis of eating disorders is still unclear. However, there is evidence that neurotransmitters may be involved in the control of satiety/appetite. Investigating these disorders could be facilitated if a readily available human cell model were to reflect central nervous system (CNS) function. Platelets may satisfy, at least partially, this requirement. We discuss here the use of platelets as neuronal models with an emphasis on eating disorders.

Plasma and urinary levels of biopterin, neopterin, and related pterins and plasma levels of folate in infantile autism

Tetrahydrobiopterin is essential for brain cells to make monoamine neurotransmitters. It has been reported that the concentrations of tetrahydrobiopterin in plasma and urine are low in certain mental disorders and that oral supplements are beneficial. A group of Japanese investigators have been conducting clinical trials of the effect of administration of tetrahydrobiopterin to autistic children and reported that it is beneficial with no significant side effects. We, therefore, initiated a study to assess plasma and urinary levels of tetrahydrobiopterin in infantile autism to see if they are reduced. Besides tetrahydrobiopterin, we also determined plasma and urinary levels of neopterin and monapterin in these individuals in order to evaluate the status of dihydroneopterin triphosphate, a key biosynthetic precursor of tetrahydrobiopterin. Sixteen autistic children and 12 healthy controls were included in this study. Results indicated that the plasma and urinary levels of tetrahydrobiopterin are not statistically different between the two groups and, therefore, no simple explanation for the beneficial effects of administration of tetrahydrobiopterin on autistic children can be offered at the present time. In contrast, plasma and urinary levels of neopterin were depressed (.01 less than p less than .05) and plasma monapterin was also significantly depressed (p less than .01) in autistic subjects compared with controls. Levels of other pterins, including folate, were not statistically different between the two groups. The basis for this depression in neopterin and monapterin is unknown. It does not seem likely that this depression could be attributed to a difference in age or T-lymphocyte/macrophage activity. However, further studies are needed to investigate these possibilities.

Signal-to-noise optimization of HPLC-fluorometric systems and their application to the analysis of indoles

The signal-to-noise optimization of high performance liquid chromatographic (HPLC) flow-cell fluorometric systems is described and the possibilities for further improving limits of detection for indoles is discussed. Application of HPLC-fluorometry to analyses in rat cerebrospinal fluid (CSF), human lumbar CSF, and human blood is presented. Finally, the intriguing clinical finding of hyperserotonemia in autism is discussed.

Autism: review of neurochemical investigation

The neurochemistry of autism, the most well-validated childhood neuropsychiatric disorder, has been studied extensively over the past three decades. Autism is of interest neurochemically because it represents a relatively homogeneous disorder with a triad of social, communicative, and intellectual developmental disturbance. Because a sufficient animal model has been lacking and relatively few diagnosed people with autism have died, most investigation has been of peripheral fluids and tissues. The most consistent finding has been that over 25% of autistic children and adolescents are hyperserotonemic. However, after 29 years of investigation, the mechanism of hyperserotonemia has not been determined. Hyperserotonemia has been found to be familial. Elevated plasma norepinephrine has also been a replicated finding. Cerebrospinal fluid (CSF) opiate activity has been found to be elevated in two studies. Plasma cyclic adenosine monophosphate (cAMP) has been found to be elevated in autistic children. A high rate of nonsuppression after dexamethasone and blunted or delayed growth hormone response to L-dopa have been found. Abnormal cell-mediated immunity has been replicated consistently in autism. Although several pharmacological trials have been conducted and shown promise in initial open trials, only "typical" antipsychotic drugs have shown replicable chronic ameliorating effects in double-blind trials. However, chronic neurotoxicity (tardive dyskinesia) has also been revealed. Findings of morphological changes in the cerebellum have been replicated. Findings in need of replication include diminished platelet function, increased baseline CSF homovanillic acid, decreased nerve cell adhesion molecule serum fragment, blunted prolactin response to fenfluramine, amelioration of symptoms by naltrexone and bromocriptine, reduced electroretinographic (ERG) b-wave amplitude, and morphological changes in the hippocampus, amygdala, and septal nuclei. In addition to refining and replicating past findings, future directions that may be fruitful include investigation of neurochemical aspects of platelet function, of interactions between monoaminergic systems, of phosphatidylinositides, and of pharmacological response to "atypical" antipsychotic agents and relatively selective serotonin receptor subtype agonists or antagonists.

Fenfluramine treatment of twenty children with autism

The effects of fenfluramine were examined on 20 children with autism over a 48-week period utilizing a double-blind placebo-controlled crossover design. Blood and urine samples and psychological tests (Griffith's Developmental Scales and Real Life Rating Scale) were obtained at each crossover period. The only significant improvement was a decrease in abnormal motor behavior. We did not find any significant improvement in intellectual functioning or any correlation between good clinical response and low baseline serotonin levels or high baseline IQ. Serotonin decreased 53% after fenfluramine treatment and rebounded to a level 35% higher than baseline following a placebo period. Fenfluramine and the active metabolite norfenfluramine were determined in plasma samples.

Review of fenfluramine in the treatment of the developmental disabilities

Fenfluramine, a serotonin reducing agent, has been the subject of intense research effort in recent years. A variety of biochemical studies summarized suggest that some autistic children and many nonautistic severely retarded individuals have elevated blood serotonin concentrations. The research on fenfluramine's clinical efficacy is thoroughly reviewed from a methodological perspective. All studies assessing the drug's effects on blood serotonin have observed reductions in whole blood serotonin to about 50% of baseline concentrations. Although there were early reports of drug enhancement of IQ, there is no good evidence that this is the case. However, there are data to suggest that fenfluramine may enhance social relatedness, reduce stereotypic behavior, lessen overactivity, and improve attention span in some autistic children, although these results do not appear consistently across studies. The animal literature on the neurotoxicity of fenfluramine is reviewed, and a number of limitations in this research are identified that raise questions about its relevance to the pharmacotherapy of children.

Whole blood serotonin and tryptophan in autism: temporal stability and the effects of medication

Whole blood serotonin (5-HT) was significantly increased in a drug-free autistic group (n = 17) compared to age- and sex-matched normal control (n = 20). Blood tryptophan (TRP) values and platelet counts were similar in unmedicated autistics and normal subjects; but whole blood concentrations of TRP were significantly lower, and 5-HT values tended to be lower in the medicated group compared to unmedicated autistics. Highly significant intraclass correlation coefficients and low mean percentage differences were found for repeated measures over a year's period of whole blood 5-HT and the platelet count in the unmedicated but not in the medicated group. Blood TRP values were highly variable over time in both the medicated and drug-free autistic groups.

Neurochemical study of dopamine functioning in autistic and normal subjects

Plasma prolactin (PRL) and homovanillic acid (HVA) levels, and urinary HVA and dopamine (DA) excretion, were measured in groups of unmedicated autistics, medicated autistics, and normal controls. No significant differences were found between unmedicated autistics and normal controls in plasma PRL and HVA levels. Excretion rates of urinary HVA and DA were also similar in the unmedicated autistic and normal subjects. Plasma PRL and HVA, as well as urinary HVA excretion, were significantly increased in the autistics on neuroleptic medication compared to the unmedicated autistics. A significant correlation (r = 0.46, p = less than 0.05) was observed between dose of neuroleptics and plasma PRL values; the correlation (r = 0.42) between neuroleptic dose and plasma HVA levels approached significance (p = 0.06). In contrast, no differences were observed in urinary DA excretion between medicated and unmedicated autistics. In general, the findings indicate that peripheral indices of dopamine functioning are normal in autistic subjects.