A new perspective on the treatment of aromatic L-amino acid decarboxylase deficiency

Transcription profiling reveals tissue-specific metabolic pathways in the fat body and ovary of the diapausing mosquito Culex pipiens

The northern house mosquito, Culex pipiens, employs diapause as an essential survival strategy during winter, inducing important phenotypic changes such as enhanced stress tolerance, lipid accumulation, and extended longevity. During diapause, the cessation of reproductive development represents another distinctive phenotypic change, underlining the need for adjusted modulation of gene expressions within the ovary. Although considerable advancements in screening gene expression profiles in diapausing and non-diapausing mosquitoes, there remains a gap in tissue-specific transcriptomic profiling that could elucidate the complicated formation of diverse diapause features in Cx. pipiens. Here, we filled this gap by utilizing RNA sequencing, providing a detailed examination of gene expression patterns in the fat body and ovary during diapause compared to non-diapause conditions. Functional annotation of upregulated genes identified associations with carbohydrate metabolism, stress tolerance, immunity, and epigenetic regulation. The validation of candidate genes using quantitative real-time PCR verified the differentially expressed genes identified in diapausing mosquitoes. Our findings contribute novel insights into potential regulators during diapause in Cx. pipiens, thereby opening possible avenues for developing innovative vector control strategies.

Effects of an Acute Dose of Zinc Monomethionine Asparate and Magnesium Asparate (ZMA) on Subsequent Sleep and Next-Day Morning Performance (Countermovement Jumps, Repeated Sprints and Stroop Test)

The goal of the present study was to determine whether an acute dose of a zinc-containing nutritional supplement (ZMA) has any effects on sleep and morning performance in recreationally trained males. Nineteen males participated in a repeated-measures within-subjects study to assess objective and subjective measures of sleep, completed counter-movement jumps (CMJ) and repeated sprint morning performance (RSP). Three days of baseline food intake showed no major deficiencies of zinc, magnesium or vitamin B6 for all participants (11.9 ± 3.4, 395 ± 103 and 2.7 ± 0.9 mg.day-1, respectively). Sleep (22:30-06:30 h) was assessed via actimetry, and either a control (no tablets, NoPill), dextrose placebo (PLAC) or ZMA was ingested 30-60 min before retiring to bed for two nights. The participants undertook the three conditions (NoPill, PLAC or ZMA) administered in a counterbalanced order. The data were analyzed using general linear models with repeated measures. In healthy active males who consume diets of adequate micronutrients, sleep normally and maintain good sleep hygiene (time to bed and wake times), ZMA supplementation had no beneficial effect on RSP or performance in the Stroop test (p > 0.05) but did improve CMJ height (p < 0.001) compared to that of PLAC but not NoPill (p > 0.05). Supplementation of ZMA for two nights had no effect on sleep, RSP or cognitive function. The NoPill condition elucidated the effects of the intervention under investigation.

A novel mechanism of idiopathic orthostatic hypotension and hypocatecholaminemia due to autoimmunity against aromatic l-Amino acid decarboxylase

Orthostatic hypotension (OH) is a common condition. Many potential etiologies of OH have been identified, but in clinical practice the underlying cause of OH is often unknown. In the present study, we identified a novel and extraordinary etiology of OH. We describe a first case of acquired severe OH with syncope, and the female patient had extremely low levels of catecholamines and serotonin in plasma, urine and cerebrospinal fluid (CSF). Her clinical and biochemical evidence showed a deficiency of the enzyme aromatic l-amino acid decarboxylase (AADC), which converts l-DOPA to dopamine, and 5-hydroxytryptophan to serotonin, respectively. The consequence of pharmacologic stimulation of catecholaminergic nerves and radionuclide examination revealed her catecholaminergic nerves denervation. Moreover, we found that the patient's serum showed presence of autoantibodies against AADC, and that isolated peripheral blood mononuclear cells (PBMCs) from the patient showed cytokine-induced toxicity against AADC. These observations suggest that her autoimmunity against AADC is highly likely to cause toxicity to adrenal medulla and catecholaminergic nerves which contain AADC, resulting in hypocatecholaminemia and severe OH. Administration of vitamin B6, an essential cofactor of AADC, enhanced her residual AADC activity and drastically improved her symptoms. Our data thus provide a new insight into pathogenesis and pathophysiology of OH.

Lactobacillus melliventris promotes hive productivity and immune functionality in Bombus terrestris performance in the greenhouse

Bumblebees are important pollinators in agricultural ecosystems, but their abundance is declining globally. There is an urgent need to protect bumblebee health and their pollination services. Bumblebees possess specialized gut microbiota with potential to be used as probiotics to help defend at-risk bumblebee populations. However, evidence for probiotic benefits on bumblebees is lacking. Here, we evaluated how supplementation with Lactobacillus melliventris isolated from bumblebee gut affected the colony development of Bombus terrestris. This native strain colonized robustly and persisted long-term in bumblebees, leading to a significantly higher quality of offspring. Subsequently, the tyrosine pathway was upregulated in the brain and fat body, while the Wnt and mTOR pathways of the gut were downregulated. Notably, the field experiment in the greenhouse revealed the supplementation of L. melliventris led to a 2.5-fold increase in the bumblebee survival rate and a more than 10% increase in the number of flowers visited, indicating a better health condition and pollination ability in field conditions. Our study represents a first screening for the potential use of the native gut member, L. melliventris, as probiotic strains in hive supplement for bumblebee breeding, which may be a practical approach to improve immunity and hive health.

Novel presentation of AADC deficiency as a mild phenotype with exercise-induced dystonic crises: A case report

Aromatic l-amino acid decarboxylase (AADC) deficiency is a rare autosomal recessive neurometabolic disorder caused by biallelic pathogenic variants in the DDC gene; approximately 140 patients have been described worldwide. AADC deficiency is characterised by a combined deficiency of dopamine, serotonin, adrenaline and noradrenaline causing a highly variable phenotype with developmental delay, early-onset hypotonia, movement disorders and autonomic symptoms. We expand the phenotype of this neurometabolic disorder by reporting on a paediatric patient with a mild phenotype with atypical exercise-induced dystonic crises, a feature that has not been described in AADC deficiency up till now. Additionally, we also present a second patient with typical characteristics and a severe phenotype. The diagnosis in both patients was confirmed by the presence of a homozygous pathogenic variant in the DDC gene and reduced AADC enzyme plasma activity. The use of whole exome sequencing-based strategies has played a crucial role in diagnosing these two patients.

The Development and Full Validation of a Novel Liquid Chromatography Electrochemical Detection Method for Simultaneous Determination of Nine Catecholamines in Rat Brain

Objectives

Chemical neurotransmission, managed by neurotransmitters, has a crucial role in brain processes such as fear, memory, learning, and pain, or neuropathology such as schizophrenia, epilepsy, anxiety/depression, and Parkinson's disease. The measurement of these compounds is used to elucidate the disease mechanisms and evaluate the outcomes of therapeutic interventions. However, this can be quite difficult because of various matrix effects and the problems of chromatographic separation of analysts. In the current study; for the first time, an optimized and fully validated high-performance liquid chromatography-electrochemical detection (HPLC-EC) method according to Food and Drug Administration and European Medicines Agency Bioanalytical Validation Guidance was developed for the simultaneous analysis of nine neurotransmitter compounds, namely dopamine, homovanilic acid, vanilmandelic acid, serotonin (SER), 5-hydroxyindole-3-acetic acid, 4-hydroxy-3-methoxyphenylglycol, norepinephrine, 3,4 dihydroxyphenylacetic acid, and 3-methoxytyramine and simultaneously determined in rat brain samples.

Materials and Methods

Separation was achieved with 150 mm x 4.6 mm, 2.6 μm Kinetex F5 (Phenomenex, USA) column isocratically, and analysis was carried out by HPLC equipped with a DECADE II EC detector.

Results

The method exhibited good selectivity, and the correlation coefficient values for each analyte's calibration curves were > 0.99. The detection and quantification limits ranged from 0.01 to 0.03 ng/mL and 3.04 to 9.13 ng/mL, respectively. The stability of the analyses and method robustness were also examined in detail in the study, and the obtained results are presented statistically.

Conclusion

The developed and fully validated method has been successfully applied to actual rat brain samples, and important results have been obtained. In the rat brain sample analysis, the lowest number of SER and the highest amount of noradrenaline were found.

Corylin ameliorates chronic ulcerative colitis via regulating the gut-brain axis and promoting 5-hydroxytryptophan production in the colon

BACKGROUND

Chronic ulcerative colitis (UC) is a lifelong disease, patients with chronic UC have a high prevalence of common mental disorders. The increasing interest in the role of gut-brain axis is seen in inflammatory bowel diseases.

PURPOSE

Corylin is a representative flavonoid compound isolated from the Psoraleae Fructus. This study aimed to identify the effects and mechanism of corylin on the inflammation interactions and 5-HT synthesis between the gut and brain in chronic UC.

METHODS

Dextran sulfate sodium (DSS) induced chronic UC mouse model was established to assess the therapeutic effect of corylin on chronic UC symptoms. The expression of inflammatory cytokines was detected in the colon and brain. The expression of tight junction (TJ) proteins of intestinal mucosal barrier and blood-brain barrier (BBB) and the ionized calcium-binding adaptor molecule 1 (Iba1) in the hippocampus were determined by western blotting and immunofluorescence staining. In addition, several tryptophan (Trp) metabolites and related neurotransmitters in faeces, colon, serum, and brain were detected by UPLC-MS/MS. The interaction between corylin and 5-hydroxytryptophan decarboxylase (5-HTPDC) was performed by molecular docking and surface plasmon resonance (SPR). Finally, the changes of gut microbiota composition were analyzed by 16S rRNA sequencing.

RESULTS

Corylin significantly alleviated colitis symptoms and inhibited inflammatory response in the colon and brain of DSS-induced chronic UC mice. The TJ proteins of intestinal mucosal barrier and BBB were improved and the expression of Iba1 in the hippocampus was normalized after corylin treatment. In addition, corylin treatment increased the expression of neurotransmitters in the brain, especially 5-hydroxytryptamine (5-HT) and 5-hydroxytryptophan (5-HTP), but the expression of 5-HT in the colon was inhibited. Further study firstly proved that corylin could bind to the 5-HTDPC, and then inhibit the expression of 5-HTDPC and VB₆, resulting in the 5-HT reduction and 5-HTP accumulation in the colon. Moreover, the intake of corylin transformed the diversity and composition of intestinal microbiota, Bacteroides, Escherichia-Shigella, and Turicibacter were decreased but Dubosiella, Enterorhabdus, and Candidatus_Stoquefichus were increased.

CONCLUSION

Corylin administration ameliorated DSS-induced colitis and inhibited intestinal inflammation and neuroinflammation via regulating the inflammation interactions across gut-brain axis and increasing 5-HTP generation in the colon.

Genipap (Genipa americana L.) juice intake biomarkers after medium-term consumption

Genipap (Genipa americana L.) is an exotic fruit largely consumed and well known, in Amazonian pharmacopeia, to treat anemia, measles and uterine cancer. It is also used as a diuretic, digestive, healing, laxative and antiseptic. The aim of this study was to apply an untargeted metabolomics strategy to determine biomarkers of food intake after short-term consumption of genipap juice. Sixteen healthy adult men were administered jenipap juice (250 mL) twice a day for three weeks. Before and after the three weeks of consumption. the subjects drank a control drink, and they consumed a standard diet. Urine was collected after 0-6 h, 6-12 h and 12-24 h. An ultrahigh-performance liquid chromatography-mass spectrometry (UHPLC-MS)-based metabolomics approach was applied to analyze the urine samples. Principal components analysis (PCA) and partial least squares discriminant analysis (PLS-DA) were performed to highlight experimental differences between groups. The value of the area under the curve (AUC) of the receiver operator characteristic (ROC) curve validated the identified biomarkers. Thirty-one statistically affected urinary metabolites were putatively identified and were mainly related to iridoids family, medium-chain fatty acids, and polyphenols. Also a group of urinary markers including dihydrocaffeic acid (DHCA), 1-(4-hydroxyphenyl)-1,2-propanediol and 3-carboxy-4-methyl-5-propyl-2-furanpropionic acid were established as biomarkers of genipap consumption. Our findings have established a comprehensive panel of changes in the urinary metabolome and provided information to monitor endogenous alterations that are linked to genipap juice intake. These data should be used in further studies to understand the health implications of genipap juice consumption.

Aromatic L-amino acid decarboxylase deficiency in 17 Mainland China patients: Clinical phenotype, molecular spectrum, and therapy overview

Background

Aromatic L‐amino acid decarboxylase deficiency (AADCD) is a rare, autosomal recessive inherited disorder which is characterized by neurological and vegetative symptoms. To date, only 130 patients with AADCD have been reported worldwide.

Methods

We demonstrated 14 previously undescribed patients together with three reportedly patients in Mainland China. Full clinical information was collected, and disease‐causing variants in the DDC gene were detected.

Results

The common clinical manifestation of patients, including intermittent oculogyric crises, retarded movement development, and autonomic symptoms. Notably, a patient showed bone‐density loss which have not been reported and two mildly phenotype patients improved psychomotor function after being prescribed medication. The most common genotype of Mainland Chinese AADCD is the splice‐site variant (IVS6+4A> T; c.714+4A> T), which accounts for 58.8%, followed by c.1234C>T variant. Three novel compound heterozygous variants, c. 565G>T, c.170T>C, and c.1021+1G>A, were firstly reported. It is important to recognize the milder phenotypes of the disease as these patients might respond well to therapy. Besides, we discovered that patients may presented with milder if found to be compound heterozygote or homozygote for one of the following variants c.478C>G, c.853C>T, c.1123C>T, c.387G>A, and c.665T>C.

Discussion

The clinical data of the cohort of 17 patients in Mainland China broaden the clinical, molecular, and treatment spectrum of aromatic L‐amino acid decarboxylase deficiency.

New variants of AADC deficiency expand the knowledge of enzymatic phenotypes

AADC deficiency is a rare genetic disease caused by mutations in the gene of aromatic amino acid decarboxylase, the pyridoxal 5'-phosphate dependent enzyme responsible for the synthesis of dopamine and serotonin. Here, following a biochemical approach together with an in silico bioinformatic analysis, we present a structural and functional characterization of 13 new variants of AADC. The amino acid substitutions are spread over the entire protein from the N-terminal (V60A), to its loop1 (H70Y and F77L), to the large domain (G96R) and its various motifs, i.e. loop2 (A110E), or a core β-barrel either on the surface (P210L, F251S and E283A) or in a more hydrophobic milieu (L222P, F237S and W267R) or loop3 (L353P), and to the C-terminal domain (R453C). Results show that the β-barrel variants exhibit a low solubility and those belonging to the surface tend to aggregate in their apo form, leading to the identification of a new enzymatic phenotype for AADC deficiency. Moreover, five variants of residues belonging to the large interface of AADC (V60A, G96R, A110E, L353P and R453C) are characterized by a decreased catalytic efficiency. The remaining ones (H70Y and F77L) present features typical of apo-to-holo impaired transition. Thus, defects in catalysis or in the acquirement of the correct holo structure are due not only to specific local domain effects but also to long-range effects at either the protein surface or the subunit interface. Altogether, the new characterized enzymatic phenotypes represent a further step in the elucidation of the molecular basis for the disease.

A new common functional coding variant at the DDC gene change renal enzyme activity and modify renal dopamine function

The intra-renal dopamine (DA) system is highly expressed in the proximal tubule and contributes to Na+ and blood pressure homeostasis, as well as to the development of nephropathy. In the kidney, the enzyme DOPA Decarboxylase (DDC) originating from the circulation. We used a twin/family study design, followed by polymorphism association analysis at DDC locus to elucidate heritable influences on renal DA production. Dense single nucleotide polymorphism (SNP) genotyping across the DDC locus on chromosome 7p12 was analyzed by re-sequencing guided by trait-associated genetic markers to discover the responsible genetic variation. We also characterized kinetics of the expressed DDC mutant enzyme. Systematic polymorphism screening across the 15-Exon DDC locus revealed a single coding variant in Exon-14 that was associated with DA excretion and multiple other renal traits indicating pleiotropy. When expressed and characterized in eukaryotic cells, the 462Gln variant displayed lower Vmax (maximal rate of product formation by an enzyme) (21.3 versus 44.9 nmol/min/mg) and lower Km (substrate concentration at which half-maximal product formation is achieved by an enzyme.)(36.2 versus 46.8 μM) than the wild-type (Arg462) allele. The highly heritable DA excretion trait is substantially influenced by a previously uncharacterized common coding variant (Arg462Gln) at the DDC gene that affects multiple renal tubular and glomerular traits, and predicts accelerated functional decline in chronic kidney disease.

A pathogenic S250F missense mutation results in a mouse model of mild aromatic l-amino acid decarboxylase (AADC) deficiency

Homozygous mutations in the aromatic l-amino acid decarboxylase (AADC) gene result in a severe depletion of its namesake protein, triggering a debilitating and often fatal form of infantile Parkinsonism known as AADC deficiency. AADC deficient patients fail to produce normal levels of the monoamine neurotransmitters dopamine and serotonin, and suffer a multi-systemic disorder characterized by movement abnormalities, developmental delay and autonomic dysfunction; an absolute loss of dopamine is generally considered incompatible with life. There is no optimal treatment for AADC deficiency and few truly good models in which to investigate disease mechanisms or develop and refine therapeutic strategies. In this study, we introduced a relatively frequently reported but mildly pathogenic S250F missense mutation into the murine Aadc gene. We show that mutants homozygous for the mutation are viable and express a stable but minimally active form of the AADC protein. Although the low enzymatic activity of the protein resulted in only modestly reduced concentrations of brain dopamine, serotonin levels were markedly diminished, and this perturbed behavior as well as autonomic function in mutant mice. Still, we found no evidence of morphologic abnormalities of the dopaminergic cells in mutant brains. The striatum as well as substantia nigra appeared normal and no loss of dopamine expressing cells in the latter was detected. We conclude that even minute levels of active AADC are sufficient to allow for substantial amounts of dopamine to be produced in model mice harboring the S250F mutation. Such mutants represent a novel, mild model of human AADC deficiency.

Heterozygosis in aromatic amino acid decarboxylase deficiency: Evidence for a positive interallelic complementation between R347Q and R358H mutations

Aromatic amino acid or Dopa decarboxylase (AADC or DDC) is a homodimeric pyridoxal 5'-phosphate (PLP) enzyme responsible for the generation of the neurotransmitters dopamine and serotonin. AADC deficiency is a rare inborn disease caused by mutations of the AADC gene leading to a defect of AADC enzyme and resulting in impaired dopamine and serotonin synthesis. Until now, only the molecular effects of homozygous mutations were analyzed. However, although heterozygous carriers of AADC deficiency were identified, the molecular aspects of their enzymatic phenotypes are not yet investigated. Here, we focus our attention on the R347Q/R358H and R347Q/R160W heterozygous mutations, and report for the first time the isolation and characterization, in the purified recombinant form, of the R347Q/R358H heterodimer and of the R358H homodimer. The results, integrated with those already known of the R347Q homodimeric variant, provide evidence that (i) the R358H mutation strongly reduces the PLP-binding affinity and the catalytic activity, and (ii) a positive interallelic complementation exists between the R347Q and the R358H mutations. Bioinformatics analyses provide the structural basis for these data. Unfortunately, the R347Q/R160W heterodimer was not obtained in a sufficient amount to allow its purification and characterization. Nevertheless, the biochemical features of the R160W homodimer give a contribution to the enzymatic phenotype of the heterozygous R347Q/R160W and suggest the possible relevance of Arg160 in the proper folding of human DDC. © 2018 IUBMB Life, 70(3):215-223, 2018.

Single-Step Rapid Diagnosis of Dopamine and Serotonin Metabolism Disorders

Early diagnosis of dopamine and serotonin metabolic defects is of importance notably because of the availability of therapeutic strategies able to prevent the associated progressive brain dysfunction. The diagnosis of these diseases relies on the determination of monoamine metabolites and pterins in cerebrospinal fluid (CSF). Current methods involve at least two high-performance liquid chromatography runs of CSF analysis. The first one is devoted to the quantification of dopamine and serotonin metabolites and the second one to the quantification of pterins. Here, we describe a single-step method to measure monoamine neurotransmitter metabolites and pterins of interest in less than 10 min by ultrahigh-performance liquid chromatography coupled to sequential coulometric oxidation and fluorescence detections. All target compounds were quantified in CSF with a small volume (50 μL) and a single filtration step for sample preparation and analysis. After validation, the proposed method was applied to the determination of age-related reference ranges in the CSF of target compounds from a series of 1372 samples collected in France from 2008 to 2014. In the same period, the results obtained for 19 CSF samples from patients with known neurotransmitter disorders and 115 CSF samples with known immune system activation confirmed the expected pattern of changes in monoamine metabolites and pterins.

Pterin determination in cerebrospinal fluid: state of the art

The analysis of pterins in the cerebrospinal fluid (CSF) is mandatory for the etiologic diagnosis of inborn errors of dopamine and serotonin metabolism. The success of the available therapeutic strategies for preventing the ongoing brain dysfunction is tightly dependent of the early diagnosis of these neurotransmitter disorders. Previous methods of pterins determination in the CSF have in common at least one reversed phase HPLC step coupled to electrochemical or fluorescence detection (FD). They differ in the oxidation procedure of the reduced forms of pterins into their oxidized fluorescent counterparts. Most of the methods using the FD include at least one offline chemical oxidation procedure and cannot allow the direct quantification of tetrahydrobiopterin (BH4). A recent method proposed a single step simultaneous quantification of all forms of pterins including BH4 by HPLC coupled to FD after post-column coulometric oxidation. Nowadays, recent advances in mass spectrometry (MS), notably in term of sensitivity, allow the direct unambiguous determination of all forms of pterins in the CSF by LC-MS/MS.

[Feeding difficulty and developmental delay for 8 months and nystagmus for 4 months in an infant]

Aromatic L-amino acid decarboxylase (AADC) deficiency is a rare autosomal recessive hereditary disease and is a congenital metabolic disorder of neurotransmitter biosynthesis. It is mainly manifested as hypotonia, oculogyric crisis, autonomic dysfunction, and developmental delay. This article reports a boy manifested as delayed motor development, hypotonia, and oculogyric crisis. Gene screening for metabolic disorders revealed new compound heterozygous mutations, c.1063dupA (p.I355fs) and c.250A>C (p.S84R), in the exon of DDC gene. The boy had a significant increase in 3-O-methyldopa as measured by dried blood spot. Therefore, he was diagnosed with AADC deficiency. After treatment with the dopamine receptor agonist pramipexole dihydrochloride, the catechol-O-methyltransferase inhibitor entacapone, and vitamin B6, the boy showed mild improvements in hypotonia, blepharoptosis, and oculogyric crisis. Clinical physicians should enhance their ability for identifying AADC deficiency, so as to facilitate early diagnosis and treatment of this disorder. Genetic counseling for birth health and prenatal diagnosis should be performed for parents in need.

A Systematic Review of Treatment Outcome in Patients with Dopa-responsive Dystonia (DRD) and DRD-Plus

Background

Dopa-responsive dystonia (DRD) and DRD-plus are inherited metabolic disorders of the dopamine synthetic pathway that have considerable clinical, biochemical, and genetic heterogeneity. Dopamine is the main deficient neurotransmitter; however, a deficiency in norepinephrine and serotonin can coexist, depending on the gene and its degree of defect. Therefore, even though levodopa is the mainstay of therapy, response to levodopa can be suboptimal and, thus, other drugs are tried.

Methods and Results

The authors searched for reports of DRD and DRD-plus and reviewed the drugs used, their response and side effects, and neurologic outcomes, including motor and cognition. Based on the current results, a recommended treatment plan is presented according to the type of enzyme defect in patients with DRD and DRD-plus.

Conclusions

It is important to recognize the features of DRD and DRD-plus, because many of them have a good clinical response to the appropriate treatment. The aim of this review is to help guide clinicians with planning treatment for patients with DRD and DRD-plus.

Chronic Diarrhea in L-Amino Acid Decarboxylase (AADC) Deficiency: A Prominent Clinical Finding Among a Series of Ten French Patients

Aromatic L-amino acid decarboxylase (AADC) deficiency is an autosomal recessive inborn error of metabolism, affecting catecholamines and serotonin biosynthesis. Cardinal signs consist in psychomotor delay, hypotonia, oculogyric crises, dystonia, and extraneurological symptoms.

PATIENTS AND METHODS

We present a retrospective descriptive multicentric study concerning ten French children with a biochemical and molecular confirmed diagnosis of AADC deficiency.

RESULTS

Clinical presentation of most of our patients was consistent with the previous descriptions from the literature (hypotonia (nine children), autonomic signs (nine children), sleep disorders (eight children), oculogyric crises (eight children), motor disorders like hypertonia and involuntary movements (seven children)). We described however some phenotypic particularities. Two patients exhibited normal intellectual abilities (patients already described in the literature). We also underlined the importance of digestive symptoms like diarrhea, which occurred in five among the ten patients. We report in particular two children with chronic diarrhea, complicated by severe failure to thrive. Vanillactic acid (VLA) elevation in urines of one of these two patients led to suspect the diagnosis of AADC deficiency, as in two other patients from our population.

CONCLUSION

Some symptoms like chronic diarrhea were atypical and have been poorly described in the literature up to now. Diagnosis of the AADC deficiency is sometimes difficult because of the phenotypic heterogeneity of the disease and VLA elevation in urines should suggest the diagnosis.

Production of Dopamine by Aromatic l-Amino Acid Decarboxylase Cells after Spinal Cord Injury

Aromatic l-amino acid decarboxylase (AADC) cells are widely distributed in the spinal cord, and their functions are largely unknown. We have previously found that AADC cells in the spinal cord could increase their ability to produce serotonin (5-hydroxytryptamine) from 5-hydroxytryptophan after spinal cord injury (SCI). Because AADC is a common enzyme catalyzing 5-hydroxytryptophan to serotonin and l-3,4-dihydroxyphenylalanine (l-dopa) to dopamine (DA), it seems likely that the ability of AADC cells using l-dopa to synthesize DA is also increased. To prove whether or not this is the case, a similar rat sacral SCI model and a similar experimental paradigm were adopted as that which we had used previously. In the chronic SCI rats (> 45 days), no AADC cells expressed DA if there was no exogenous l-dopa application. However, following administration of a peripheral AADC inhibitor (carbidopa) with or without a monoamine oxidase inhibitor (pargyline) co-application, systemic administration of l-dopa resulted in ∼94% of AADC cells becoming DA-immunopositive in the spinal cord below the lesion, whereas in normal or sham-operated rats none or very few of AADC cells became DA-immunopositive with the same treatment. Using tail electromyography, spontaneous tail muscle activity was increased nearly fivefold over the baseline level. When pretreated with a central AADC inhibitor (NSD-1015), further application of l-dopa failed to increase the motoneuron activity although the expression of DA in the AADC cells was not completely inhibited. These findings demonstrate that AADC cells in the spinal cord below the lesion gain the ability to produce DA from its precursor in response to SCI. This ability also enables the AADC cells to produce 5-HT and trace amines, and likely contributes to the development of hyperexcitability. These results might also be implicated for revealing the pathological mechanisms underlying l-dopa-induced dyskinesia in Parkinson's disease.

AAV viral vector delivery to the brain by shape-conforming MR-guided infusions

Gene transfer technology offers great promise as a potential therapeutic approach to the brain but has to be viewed as a very complex technology. Success of ongoing clinical gene therapy trials depends on many factors such as selection of the correct genetic and anatomical target in the brain. In addition, selection of the viral vector capable of transfer of therapeutic gene into target cells, along with long-term expression that avoids immunotoxicity has to be established. As with any drug development strategy, delivery of gene therapy has to be consistent and predictable in each study subject. Failed drug and vector delivery will lead to failed clinical trials. In this article, we describe our experience with AAV viral vector delivery system, that allows us to optimize and monitor in real time viral vector administration into affected regions of the brain. In addition to discussing MRI-guided technology for administration of AAV vectors we have developed and now employ in current clinical trials, we also describe ways in which infusion cannula design and stereotactic trajectory may be used to maximize the anatomical coverage by using fluid backflow. This innovative approach enables more precise coverage by fitting the shape of the infusion to the shape of the anatomical target.

Monoamine neurotransmitter disorders--clinical advances and future perspectives

The monoamine neurotransmitter disorders are important genetic syndromes that cause disturbances in catecholamine (dopamine, noradrenaline and adrenaline) and serotonin homeostasis. These disorders result in aberrant monoamine synthesis, metabolism and transport. The clinical phenotypes are predominantly neurological, and symptoms resemble other childhood neurological disorders, such as dystonic or dyskinetic cerebral palsy, hypoxic ischaemic encephalopathy and movement disorders. As a consequence, monoamine neurotransmitter disorders are under-recognized and often misdiagnosed. The diagnosis of monoamine neurotransmitter disorders requires detailed clinical assessment, cerebrospinal fluid neurotransmitter analysis and further supportive diagnostic investigations. Prompt and accurate diagnosis of neurotransmitter disorders is paramount, as many are responsive to treatment. The treatment is usually mechanism-based, with the aim to reverse disturbances of monoamine synthesis and/or metabolism. Therapeutic intervention can lead to complete resolution of motor symptoms in some conditions, and considerably improve quality of life in others. In this Review, we discuss the clinical features, diagnosis and management of monoamine neurotransmitter disorders, and consider novel concepts, the latest advances in research and future prospects for therapy.

Functional constituents of a local serotonergic system, intrinsic to the human coronary artery smooth muscle cells

Human coronary artery smooth muscle cells (HCASMCs) play an important role in the pathogenesis of coronary atherosclerosis and coronary artery diseases (CAD). Serotonin is a mediator known to produce vascular smooth muscle cell mitogenesis and contribute to coronary atherosclerosis. We hypothesize that the HCASMC possesses certain functional constituents of the serotonergic system such as: tryptophan hydroxylase and serotonin transporter. Our aim was to examine the presence of functional tryptophan hydroxylase-1 (TPH1) and serotonin transporter (SERT) in HCASMCs. The mRNA transcripts by qPCR and protein expression by Western blot of TPH1 and SERT were examined. The specificity and accuracy of the primers were verified using DNA gel electrophoresis and sequencing of qPCR products. The functionality of SERT was examined using a fluorescence dye-based serotonin transporter assay. The enzymatic activity of TPH was evaluated using UPLC. The HCASMCs expressed both mRNA transcripts and protein of SERT and TPH. The qPCR showed a single melt curve peak for both transcripts and in sequence analysis the amplicons were aligned with the respective genes. SERT and TPH enzymatic activity was present in the HCASMCs. Taken together, both TPH and SERT are functionally expressed in HCASMCs. These findings are novel and represent an initial step in examining the clinical relevance of the serotonergic system in HCASMCs and its role in the pathogenesis of coronary atherosclerosis and CAD.

The Parkinson's disease death rate: carbidopa and vitamin B6

The only indication for carbidopa and benserazide is the management of L-3,4-dihydroxyphenylalanine (L-dopa)-induced nausea. Both drugs irreversibly bind to and permanently deactivate pyridoxal 5'-phosphate (PLP), the active form of vitamin B6, and PLP-dependent enzymes. PLP is required for the function of over 300 enzymes and proteins. Virtually every major system in the body is impacted directly or indirectly by PLP. The administration of carbidopa and benserazide potentially induces a nutritional catastrophe. During the first 15 years of prescribing L-dopa, a decreasing Parkinson's disease death rate was observed. Then, in 1976, 1 year after US Food and Drug Administration approved the original L-dopa/carbidopa combination drug, the Parkinson's disease death rate started increasing. This trend has continued to the present, for 38 years and counting. The previous literature documents this increasing death rate, but no hypothesis has been offered concerning this trend. Carbidopa is postulated to contribute to the increasing Parkinson's disease death rate and to the classification of Parkinson's as a progressive neurodegenerative disease. It may contribute to L-dopa tachyphylaxis.

Clinical features and pharmacotherapy of childhood monoamine neurotransmitter disorders

Childhood neurotransmitter disorders are increasingly recognised as an expanding group of inherited neurometabolic syndromes. They are caused by disturbance in synthesis, metabolism, and homeostasis of the monoamine neurotransmitters, including the catecholamines (dopamine, norepinephrine, and epinephrine) and serotonin. Disturbances in monoamine neurotransmission will lead to neurological symptoms that often overlap with clinical features of other childhood neurological disorders (such as hypoxic ischaemic encephalopathy, cerebral palsy, other movement disorders, and paroxysmal conditions); consequently, neurotransmitter disorders are frequently misdiagnosed. The diagnosis of neurotransmitter disorders is made through detailed clinical assessment, analysis of cerebrospinal fluid neurotransmitters, and further supportive diagnostic investigations. Early and accurate diagnosis of neurotransmitter disorders is important, as many are amenable to therapeutic intervention. The principles of treatment for monoamine neurotransmitter disorders are mainly directly derived from understanding these metabolic pathways. In disorders characterized by enzyme deficiency, we aim to increase monoamine substrate availability, boost enzyme co-factor levels, reduce monoamine breakdown, and replace depleted levels of monoamines with pharmacological analogs as clinically indicated. Most monoamine neurotransmitter disorders lead to reduced levels of central dopamine and/or serotonin. Complete amelioration of motor symptoms is achievable in some disorders, such as Segawa's syndrome, and, in other conditions, significant improvement in quality of life can be attained with pharmacotherapy. In this review, we provide an overview of the clinical features and current treatment strategies for childhood monoamine neurotransmitter disorders.

Widening Phenotypic Spectrum of AADC Deficiency, a Disorder of Dopamine and Serotonin Synthesis

OBJECTIVES

Aromatic amino acid decarboxylase deficiency presents with prominent extrapyramidal and autonomic features and CSF monoamine deficiency with increased 3-O-methyldopa, a by-product of accumulated L-DOPA. Less than 100 cases have been identified. The disease is typically associated with a severe phenotype and worse prognosis in females. Gene transfer technology has been implemented using an adeno-associated virus encoding AADC in the putamen bilaterally.

METHODS

We describe the phenotype/genotype in a cohort of five cases showing a heterogeneous phenotype and variably intact response to pharmacologic therapy.

RESULTS

Five patients (age range 2-10 years, mean 5 years, 3M/2F) with confirmed AADC deficiency are described. Four (3M/1F) have had improvement on combinations of dopaminergic agonists, MAO inhibitors, pyridoxine/P5P, and folinic acid. Each presented with hypotonia, decreased voluntary movement, dystonia, irritability, and oculogyric crises. Two (1M/1F) are independently ambulatory and are not dependent on gastrostomy tube feedings; the 9-year-old girl is reading single words. One female has a severe phenotype including recurrent hypoglycemic events associated with bradycardia, although the latter have resolved with chronic anticholinergic therapy. One Taiwanese boy had the common homozygous mutation, and otherwise we describe five new DDC mutations.

CONCLUSIONS

We report a wider phenotypic spectrum including intact response to pharmacologic management and milder outcome in a female, as well as five new mutations. Four of five patients have improved on combination therapy including a dopamine agonist, MAO inhibitor, pyridoxal-5'-phosphate, and folinic acid. The advent of viral-mediated gene therapy in AADC deficiency renders expanded knowledge of the outcome increasingly important.

What is new for monoamine neurotransmitter disorders?

The monoamine neurotransmitter disorders are increasingly recognized as an expanding group of inherited neurometabolic syndromes caused by disturbances in the synthesis, transport and metabolism of the biogenic amines, including the catecholamines (dopamine, norepinephrine, and epinephrine) and serotonin. Disturbances in monoamine metabolism lead to neurological syndromes that frequently mimic other conditions, such as hypoxic ischemic encephalopathy, cerebral palsy, parkinsonism-dystonia syndromes, primary genetic dystonia and paroxysmal disorders. As a consequence, neurotransmitter disorders are frequently misdiagnosed. Early and accurate diagnosis of these neurotransmitter disorders is important, as many are highly amenable to, and some even cured by, therapeutic intervention. In this review, we highlight recent advances in the field, particularly the recent extensive characterization of known neurotransmitter disorders and identification of novel neurotransmitter disorders. We also provide an overview of current and future research in the field focused on developing novel treatment strategies.

Aromatic amino Acid decarboxylase deficiency not responding to pyridoxine and bromocriptine therapy: case report and review of response to treatment

Aromatic L-amino acid decarboxylase (AADC) deficiency (MIM #608643) is an autosomal recessive inborn error of monoamines. It is caused by a mutation in the DDC gene that leads to a deficiency in the AADC enzyme. The clinical features of this condition include a combination of dopamine, noradrenaline, and serotonin deficiencies, and a patient may present with hypotonia, oculogyric crises, sweating, hypersalivation, autonomic dysfunction, and progressive encephalopathy with severe developmental delay. We report the case of an 8-month-old boy who presented with the abovementioned symptoms and who was diagnosed with AADC deficiency based on clinical, biochemical, and molecular investigations. Treatment with bromocriptine and pyridoxine showed no improvement. These data support the findings observed among previously reported cohorts that showed poor response of this disease to current regimens. Alternative therapies are needed to ameliorate the clinical complications associated with this disorder.

S250F variant associated with aromatic amino acid decarboxylase deficiency: molecular defects and intracellular rescue by pyridoxine

Dopa or aromatic amino acid decarboxylase (DDC, AADC) is a pyridoxal 5'-phosphate-dependent enzyme that catalyses the production of the neurotransmitters dopamine and serotonin. Among the so far identified mutations associated with AADC deficiency, an inherited rare neurometabolic disease, the S250F mutation is the most frequent one. Here, for the first time, the molecular basis of the deficit of the S250F variant was investigated both in vitro and in cellular systems. Ser250 is not essential for the catalytic activity of the enzyme. However, its mutation to Phe causes a ~7-fold reduction of catalytic efficiency and a conformational change in the proximity of the mutated residue that is transmitted to the active site. In cellular extracts of E. coli and mammalian cells, both the specific activity and the protein level of the variant decrease with respect to the wild-type. The results with mammalian cells indicate that the mutation does not affect intracellular mRNA levels, and are consistent with a model where S250F undergoes a degradation process via the proteasome, possibly through an ubiquitination process occurring faster than in the wild-type. Overall, biochemical and cell biology experiments show that loss of function of S250F occurs by two distinct but not exclusive mechanisms affecting activity and folding. Importantly, 4-phenylbutirric acid (4-PBA) or, to a major extent, pyridoxine increase the expression level and, in a dose-dependent manner, the decarboxylase specific activity of mutant-expressing cells. This strongly suggests that 4-PBA and/or pyridoxine administration may be of important value in therapy of patients bearing the S250F mutation.

AADC deficiency: occurring in humans, modeled in rodents

Aromatic l-amino acid decarboxylase (AADC) is a homodimeric pyridoxal phosphate-dependent enzyme responsible for the syntheses of dopamine and serotonin. Defects in the AADC gene result in neurotransmitter deficiencies. Patients with AADC deficiency have severe motor and autonomic dysfunctions. A mouse model of AADC deficiency was recently established. These mice grow poorly and move awkwardly during infancy. They also show high anxiety when they grow up. Because drug therapy provides little or no benefit for many patients with AADC deficiency, a gene therapy has been attempted. The gene therapy employed an adeno-associated virus viral vector that can express the human AADC protein. The vector was injected to the brain of several children with AADC deficiency. The therapy was well tolerated, and all treated patients showed improvement. In the future, the mouse model will also help the development of treatments for AADC deficiency.

Monoamine neurotransmitter deficiencies

Pediatric neurotransmitter disorders refer to a constellation of inherited neurometabolic syndromes attributable to disturbances of neurotransmitter synthesis, degradation, or transport. Monoamine deficiencies represent defects in synthesis of dopamine, serotonin, norepinephrine, and epinephrine or in availability of tetrahydrobiopterin, an important cofactor for monoamine synthesis. Some disorders do not manifest peripheral hyperphenyalaninemia and require CSF neurotransmitter metabolite assay for diagnosis. These include Segawa dopa-responsive dystonia and enzymatic deficiencies of aromatic amino acid decarboxylase, tyrosine hydroxylase, and sepiapterin reductase. The first, autosomal dominantly inherited GTP cyclohydrolase deficiency, has a satisfying response to therapy at any age with benefits maintained over time. The others have more severe and treatment-refractory phenotypes, typically with manifestations well beyond movement disorders. Disorders detectable by elevated serum phenylalanine are deficiencies of GTP cyclohydrolase (homozygous), pterin-carbinolamine dehydratase, dihydropteridine reductase, and pyruvoyl-tetrahydropterin synthase. The latter is the most prevalent and heterogeneous but typically has infantile onset with extrapyramidal as well as bulbar, hypothalamic, limbic, and epileptic manifestations. There are therapeutic roles for neurotransmitter supplementation, and dopaminergic agonists. Basal ganglia calcifications in dihydropteridine reductase deficiency are reversible with folinic acid. Deficiencies of monoamine degradation lead to cognitive, behavioral, and autonomic disorders.

Gene therapy for aromatic L-amino acid decarboxylase deficiency

Aromatic L-amino acid decarboxylase (AADC) is required for the synthesis of the neurotransmitters dopamine and serotonin. Children with defects in the AADC gene show compromised development, particularly in motor function. Drug therapy has only marginal effects on some of the symptoms and does not change early childhood mortality. Here, we performed adeno-associated viral vector-mediated gene transfer of the human AADC gene bilaterally into the putamen of four patients 4 to 6 years of age. All of the patients showed improvements in motor performance: One patient was able to stand 16 months after gene transfer, and the other three patients achieved supported sitting 6 to 15 months after gene transfer. Choreic dyskinesia was observed in all patients, but this resolved after several months. Positron emission tomography revealed increased uptake by the putamen of 6-[(18)F]fluorodopa, a tracer for AADC. Cerebrospinal fluid analysis showed increased dopamine and serotonin levels after gene transfer. Thus, gene therapy targeting primary AADC deficiency is well tolerated and leads to improved motor function.

Biochemical and computational approaches to improve the clinical treatment of dopa decarboxylase-related diseases: an overview

Dopa decarboxylase (DDC) is a pyridoxal 5’-phosphate (PLP)-dependent enzyme that by catalyzing the decarboxylation of L-Dopa and L-5-hydroxytryptophan produces the neurotransmitters dopamine and serotonin. The functional properties of pig kidney and human DDC enzymes have been extensively characterized, and the crystal structure of the enzyme in the holo- and apo-forms has been elucidated. DDC is a clinically relevant enzyme since it is involved in Parkinson’s disease (PD) and in aromatic amino acid decarboxylase (AADC) deficiency. PD, a chronic progressive neurological disorder characterized by tremor, bradykinesia, rigidity and postural instability, results from the degeneration of dopamine-producing cells in the substantia nigra of the brain. On the other hand, AADC deficiency is a rare debilitating recessive genetic disorder due to mutations in AADC gene leading to the inability to synthesize dopamine and serotonin. Development delay, abnormal movements, oculogyric crises and vegetative symptoms characterize this severe neurometabolic disease. This article is an up to date review of the therapies currently used in the treatment of PD and AADC deficiency as well as of the recent findings that, on one hand provide precious guidelines for the drug development process necessary to PD therapy, and, on the other, suggest an aimed therapeutic approach based on the elucidation of the molecular defects of each variant associated with AADC deficiency.

Diet promotes sleep duration and quality

Sleep, much like eating, is an essential part of life. The mechanisms of sleep are only partially clear and are the subject of intense research. There is increasing evidence showing that sleep has an influence on dietary choices. Both cross-sectional and epidemiologic studies have demonstrated that those who sleep less are more likely to consume energy-rich foods (such as fats or refined carbohydrates), to consume fewer portions of vegetables, and to have more irregular meal patterns. In this narrative review, we pose the opposite question: can ingested food affect sleep? The purpose of this review is to discuss the evidence linking diet and sleep and to determine whether what we eat and what kind of nutrients we obtain from the food consumed before bedtime matter. In addition, scientific evidence behind traditional sleep-promoting foods such as milk and some herbal products is briefly described. These are reviewed using data from clinical trials, mostly in healthy subjects. In addition, we discuss the possible mechanisms behind these observations. Lastly, we summarize our findings that emerging evidence confirms a link between diet and sleep. Overall, foods impacting the availability of tryptophan, as well as the synthesis of serotonin and melatonin, may be the most helpful in promoting sleep. Although there are clear physiological connections behind these effects, the clinical relevance needs to be studied further.

Open conformation of human DOPA decarboxylase reveals the mechanism of PLP addition to Group II decarboxylases

DOPA decarboxylase, the dimeric enzyme responsible for the synthesis of neurotransmitters dopamine and serotonin, is involved in severe neurological diseases such as Parkinson disease, schizophrenia, and depression. Binding of the pyridoxal-5'-phosphate (PLP) cofactor to the apoenzyme is thought to represent a central mechanism for the regulation of its activity. We solved the structure of the human apoenzyme and found it exists in an unexpected open conformation: compared to the pig kidney holoenzyme, the dimer subunits move 20 Å apart and the two active sites become solvent exposed. Moreover, by tuning the PLP concentration in the crystals, we obtained two more structures with different conformations of the active site. Analysis of three-dimensional data coupled to a kinetic study allows to identify the structural determinants of the open/close conformational change occurring upon PLP binding and thereby propose a model for the preferential degradation of the apoenzymes of Group II decarboxylases.

Molecular insights into the pathogenicity of variants associated with the aromatic amino acid decarboxylase deficiency

Dopa decarboxylase (DDC or AADC) is a pyridoxal 5'-phosphate (PLP)-dependent enzyme that catalyzes the decarboxylation of L-aromatic amino acids into the corresponding aromatic amines. AADC deficiency is an inborn error of neurotransmitters biosynthesis with an autosomal recessive inheritance. About 30 pathogenic mutations have been identified, but the enzymatic phenotypes causing AADC deficiency are unknown, and the therapeutic management is challenging. Here, we report biochemical and bioinformatic analyses of the human wild-type DDC and the pathogenic variants G102S, F309L, S147R and A275T whose mutations concern amino acid residues at or near the active site. We found that the mutations cause, even if to different extents, a decreased PLP binding affinity (in the range 1.4-170-fold), an altered state of the bound coenzyme and of its microenvironment, and a reduced catalytic efficiency (in the range 17-930-fold). Moreover, as compared to wild-type, the external aldimines formed by the variants with L-aromatic amino acids exhibit different spectroscopic features, do not protect against limited proteolysis, and lead to the formation, in addition to aromatic amines, of cyclic-substrate adducts. This suggests that these external Schiff bases are not properly oriented and anchored, i.e., in a conformation not completely productive for decarboxylation. The external aldimines that the variants form with D-Dopa also appear not to be correctly located at their active site, as suggested by the rate constants of PLP-L-Dopa adduct production higher than that of the wild-type. The possible therapeutic implications of the data are discussed in the light of the molecular defects of the pathogenic variants.

Validity of urinary monoamine assay sales under the "spot baseline urinary neurotransmitter testing marketing model"

Spot baseline urinary monoamine assays have been used in medicine for over 50 years as a screening test for monoamine-secreting tumors, such as pheochromocytoma and carcinoid syndrome. In these disease states, when the result of a spot baseline monoamine assay is above the specific value set by the laboratory, it is an indication to obtain a 24-hour urine sample to make a definitive diagnosis. There are no defined applications where spot baseline urinary monoamine assays can be used to diagnose disease or other states directly. No peer-reviewed published original research exists which demonstrates that these assays are valid in the treatment of individual patients in the clinical setting. Since 2001, urinary monoamine assay sales have been promoted for numerous applications under the "spot baseline urinary neurotransmitter testing marketing model". There is no published peer-reviewed original research that defines the scientific foundation upon which the claims for these assays are made. On the contrary, several articles have been published that discredit various aspects of the model. To fill the void, this manuscript is a comprehensive review of the scientific foundation and claims put forth by laboratories selling urinary monoamine assays under the spot baseline urinary neurotransmitter testing marketing model.

Pyridoxal 5'-phosphate deficiency causes a loss of aromatic L-amino acid decarboxylase in patients and human neuroblastoma cells, implications for aromatic L-amino acid decarboxylase and vitamin B(6) deficiency states

Pyridoxal 5'-phosphate, the active form of vitamin B(6), is an essential cofactor for multiple enzymes, including aromatic l-amino acid decarboxylase that catalyses the final stage in the production of the neurotransmitters dopamine and serotonin. In two patients with inherited disorders of vitamin B(6) metabolism, we observed reductions in plasma aromatic l-amino acid decarboxylase activity. In one patient, this change was related to an increase in K(m) for pyridoxal 5'-phosphate. Furthermore, pyridoxal 5'-phosphate-deficient human SH-SY5Y neuroblastoma cells were found to exhibit reduced levels of aromatic l-amino acid decarboxylase activity and protein but with no alteration in expression. Further reductions in activity and protein were observed with the addition of the vitamin B(6) antagonist 4-deoxypyridoxine, which also reduced aromatic l-amino acid decarboxylase mRNA levels. Neither pyridoxal 5'-phosphate deficiency nor the addition of 4-deoxypyridoxine affected aromatic l-amino acid decarboxylase stability over 8 h with protein synthesis inhibited. Increasing extracellular availability of pyridoxal 5'-phosphate was not found to have any significant effect on intracellular pyridoxal 5'-phosphate concentrations or on aromatic l-amino acid decarboxylase. These findings suggest that maintaining adequate pyridoxal 5'-phosphate availability may be important for optimal treatment of aromatic l-amino acid decarboxylase deficiency and l-dopa-responsive conditions.

Behavioral disinhibition and reduced anxiety-like behaviors in monoamine oxidase B-deficient mice

Monoamine oxidase (MAO) B catalyzes the degradation of beta-phenylethylamine (PEA), a trace amine neurotransmitter implicated in mood regulation. Although several studies have shown an association between low MAO B activity in platelets and behavioral disinhibition in humans, the nature of this relation remains undefined. To investigate the impact of MAO B deficiency on the emotional responses elicited by environmental cues, we tested MAO B knockout (KO) mice in a set of behavioral assays capturing different aspects of anxiety-related manifestations, such as the elevated plus maze, defensive withdrawal, marble burying, and hole board. Furthermore, MAO B KO mice were evaluated for their exploratory patterns in response to unfamiliar objects and risk-taking behaviors. In comparison with their wild-type (WT) littermates, MAO B KO mice exhibited significantly lower anxiety-like responses and shorter latency to engage in risk-taking behaviors and exploration of unfamiliar objects. To determine the neurobiological bases of the behavioral differences between WT and MAO B KO mice, we measured the brain-regional levels of PEA in both genotypes. Although PEA levels were significantly higher in all brain regions of MAO B KO in comparison with WT mice, the most remarkable increments were observed in the striatum and prefrontal cortex, two key regions for the regulation of behavioral disinhibition. However, no significant differences in transcript levels of PEA's selective receptor, trace amine-associated receptor 1 (TAAR1), were detected in either region. Taken together, these results suggest that MAO B deficiency may lead to behavioral disinhibition and decreased anxiety-like responses partially through regional increases of PEA levels.