Aromatic L-amino acid decarboxylase: biological characterization and functional role

Exploring the Sublethal Impacts of Cu and Zn on Daphnia magna: a transcriptomic perspective

Metal contamination of aquatic environments remains a major concern due to their persistence. The water flea Daphnia magna is an important model species for metal toxicity studies and water quality assessment. However, most research has focused on physiological endpoints such as mortality, growth, and reproduction in laboratory settings, as well as neglected toxicogenomic responses. Copper (Cu) and zinc (Zn) are essential trace elements that play crucial roles in many biological processes, including iron metabolism, connective tissue formation, neurotransmitter synthesis, DNA synthesis, and immune function. Excess amounts of these metals result in deviations from homeostasis and may induce toxic responses. In this study, we analyzed Daphnia magna transcriptomic responses to IC5 levels of Cu (120 µg/L) and Zn (300 µg/L) in environmental water obtained from a pristine lake with adjusted water hardness (150 mg/L CaCO3). The study was carried out to gain insights into the Cu and Zn regulated stress response mechanisms in Daphnia magna at transcriptome level. A total of 2,688 and 3,080 genes were found to be differentially expressed (DEG) between the control and Cu and the control and Zn, respectively. There were 1,793 differentially expressed genes in common for both Cu and Zn, whereas the number of unique DEGs for Cu and Zn were 895 and 1,287, respectively. Gene ontology and KEGG pathways enrichment were carried out to identify the molecular functions and biological processes affected by metal exposures. In addition to well-known biomarkers, novel targets for metal toxicity screening at the genomic level were identified.

Fermentative production of halogenated tryptophan derivatives with Corynebacterium glutamicum overexpressing tryptophanase or decarboxylase genes

The aromatic amino acid l‐tryptophan serves as a precursor for many valuable compounds such as neuromodulators, indoleamines and indole alkaloids. In this work, tryptophan biosynthesis was extended by halogenation followed by decarboxylation to the respective tryptamines or cleavage to the respective indoles. Either the tryptophanase genes tnaAs from E. coli and Proteus vulgaris or the aromatic amino acid decarboxylase genes AADCs from Bacillus atrophaeus, Clostridium sporogenes, and Ruminococcus gnavus were expressed in Corynebacterium glutamicum strains producing (halogenated) tryptophan. Regarding indoles, final titers of 16 mg L⁻¹ 7‐Cl‐indole and 23 mg L⁻¹ 7‐Br‐indole were attained. Tryptamine production led to a much higher titer of 2.26 g L⁻¹ upon expression of AADC from B. atrophaeus. AADC enzymes were shown to be active with halogenated tryptophan in vitro and in vivo and supported production of 0.36 g L⁻¹ 7‐Br‐tryptamine with a volumetric productivity of 8.3 mg L⁻¹ h⁻¹ in a fed‐batch fermentation.

Symbiont-regulated serotonin biosynthesis modulates tick feeding activity

Ticks are obligate hematophagous arthropods. Blood feeding ensures that ticks obtain nutrients essential for their survival, development, and reproduction while providing routes for pathogen transmission. However, the effectors that determine tick feeding activities remain poorly understood. Here, we demonstrate that reduced abundance of the symbiont Coxiella (CHI) in Haemaphysalis longicornis decreases blood intake. Providing tetracycline-treated ticks with the CHI-derived tryptophan precursor chorismate, tryptophan, or 5-hydroxytryptamine (5-HT; serotonin) restores the feeding defect. Mechanistically, CHI-derived chorismate increases tick 5-HT biosynthesis by stimulating the expression of aromatic amino acid decarboxylase (AAAD), which catalyzes the decarboxylation of 5-hydroxytryptophan (5-HTP) to 5-HT. The increased level of 5-HT in the synganglion and midgut promotes tick feeding. Inhibition of CHI chorismate biosynthesis by treating the colonized tick with the herbicide glyphosate suppresses blood-feeding behavior. Taken together, our results demonstrate an important function of the endosymbiont Coxiella in the regulation of tick 5-HT biosynthesis and feeding.

Molecular Insights into SARS-CoV2-Induced Alterations of the Gut/Brain Axis

For a yet unknown reason, a substantial share of patients suffering from COVID-19 develop long-lasting neuropsychiatric symptoms ranging from cognitive deficits to mood disorders and/or an extreme fatigue. We previously reported that in non-neural cells, angiotensin-1 converting enzyme 2 (ACE2), the gene coding for the SARS-CoV2 host receptor, harbors tight co-expression links with dopa-decarboxylase (DDC), an enzyme involved in the metabolism of dopamine. Here, we mined and integrated data from distinct human expression atlases and found that, among a wide range of tissues and cells, enterocytes of the small intestine express the highest expression levels of ACE2, DDC and several key genes supporting the metabolism of neurotransmitters. Based on these results, we performed co-expression analyses on a recently published set of RNA-seq data obtained from SARS-CoV2-infected human intestinal organoids. We observed that in SARS-CoV2-infected enterocytes, ACE2 co-regulates not only with DDC but also with a specific group of genes involved in (i) the dopamine/trace amines metabolic pathway, (ii) the absorption of microbiota-derived L-DOPA and (iii) the absorption of neutral amino acids serving as precursors to neurotransmitters. We conclude that in patients with long COVID, a chronic infection and inflammation of small intestine enterocytes might be indirectly responsible for prolonged brain alterations.

Biochemical characterization and synthetic application of aromatic L-amino acid decarboxylase from Bacillus atrophaeus

Aromatic L-amino acid decarboxylases (AADCs) are ubiquitously found in higher organisms owing to their physiological role in the synthesis of neurotransmitters and alkaloids. However, bacterial AADC has not attracted much attention because of its rather limited availability and narrow substrate range. Here, we examined the biochemical properties of AADC from Bacillus atrophaeus (AADC-BA) and assessed the synthetic feasibility of the enzyme for the preparation of monoamine neurotransmitters. AADC-BA was expressed in Escherichia coli BL21(DE3) and the purified enzyme showed a specific activity of 2.6 ± 0.4 U/mg for 10 mM L-phenylalanine (L-Phe) at 37 °C. AADC-BA showed optimal pH and temperature ranges at 7-8 and 37-45 °C, respectively. The K_M and k_cat values for L-Phe were 7.2 mM and 7.4 s^-1, respectively, at pH 7.0 and 37 °C. Comparison of the kinetic constants at different temperatures revealed that the temperature dependency of the enzyme was mainly determined by catalytic turnover rather than substrate binding. AADC-BA showed a broad substrate scope for various aromatic amino acids, including L-Phe, L-tryptophan (610% relative to L-Phe), L-tyrosine (12%), 3,4-dihydroxyphenyl-L-alanine (24%), 5-hydroxy-L-tryptophan (L-HTP, 71%), 4-chloro-L-phenylalanine (520%), and 4-nitro-L-phenylalanine (450%). Homology modeling and docking simulations were carried out and were consistent with the observed substrate specificity. To demonstrate the synthetic potential of AADC-BA, we carried out the production of serotonin by decarboxylation of L-HTP. The reaction yield of serotonin reached 98% after 1 h at the reaction conditions of 50 mM L-HTP and 4 U/mL AADC-BA. Moreover, we carried out preparative-scale decarboxylation of L-Phe (100 mM in 40-mL reaction mixture) and isolated the resulting 2-phenylethylamine (51% recovery yield). We expect that the broad substrate specificity of AADC-BA can be exploited to produce various aromatic biogenic amines. KEY POINTS: • AADC-BA showed broad substrate specificity for various aromatic amino acids. • The substrate specificity was elucidated by in silico structural modeling. • The synthetic potential of AADC-BA was demonstrated for the production of biogenic amines.

Crystal structure of Oryza sativa TDC reveals the substrate specificity for TDC-mediated melatonin biosynthesis

Plant tryptophan decarboxylase (TDC) is a type II Pyridoxal-5'-phosphate-dependent decarboxylase (PLP_DC) that could be used as a target to genetically improve crops. However, lack of accurate structural information on plant TDC hampers the understanding of its decarboxylation mechanisms. In the present study, the crystal structures of Oryza sativa TDC (OsTDC) in its complexes with pyridoxal-5'-phosphate, tryptamine and serotonin were determined. The structures provide detailed interaction information between TDC and its substrates. The Y359 residue from the loop gate is a proton donor and forms a Lewis acid-base pair with serotonin/tryptamine, which is associated with product release. The H214 residue is responsible for PLP binding and proton transfer, and its proper interaction with Y359 is essential for OsTDC enzyme activity. The extra hydrogen bonds formed between the 5-hydroxyl group of serotonin and the backbone carboxyl groups of F104 and P105 explain the discrepancy between the catalytic activity of TDC in tryptophan and in 5-hydroxytryptophan. In addition, an evolutionary analysis revealed that type II PLP_DC originated from glutamic acid decarboxylase, potentially as an adaptive evolution of mechanism in organisms in extreme environments. This study is, to our knowledge, the first to present a detailed analysis of the crystal structure of OsTDC in these complexes. The information regarding the catalytic mechanism described here could facilitate the development of protocols to regulate melatonin levels and thereby contribute to crop improvement efforts to improve food security worldwide.

A Study for Therapeutic Treatment against Parkinson's Disease via Chou's 5-steps Rule

The enzyme L-DOPA decarboxylase (DDC), also called aromatic-L-amino-acid decarboxylase, catalyzes the biosynthesis of dopamine, serotonin, and trace amines. Its deficiency or perturbations in expression result in severe motor dysfunction or a range of neurodegenerative and psychiatric disorders. A DDC substrate, L-DOPA, combined with an inhibitor of the enzyme is still the most effective treatment for symptoms of Parkinson's disease. In this review, we provide an update regarding the structures, functions, and inhibitors of DDC, particularly with regards to the treatment of Parkinson's disease. This information will provide insight into the pharmacological treatment of Parkinson's disease.

Intricacies of the Molecular Machinery of Catecholamine Biosynthesis and Secretion by Chromaffin Cells of the Normal Adrenal Medulla and in Pheochromocytoma and Paraganglioma

The adrenal medulla is composed predominantly of chromaffin cells producing and secreting the catecholamines dopamine, norepinephrine, and epinephrine. Catecholamine biosynthesis and secretion is a complex and tightly controlled physiologic process. The pathways involved have been extensively studied, and various elements of the underlying molecular machinery have been identified. In this review, we provide a detailed description of the route from stimulus to secretion of catecholamines by the normal adrenal chromaffin cell compared to chromaffin tumor cells in pheochromocytomas. Pheochromocytomas are adrenomedullary tumors that are characterized by uncontrolled synthesis and secretion of catecholamines. This uncontrolled secretion can be partly explained by perturbations of the molecular catecholamine secretory machinery in pheochromocytoma cells. Chromaffin cell tumors also include sympathetic paragangliomas originating in sympathetic ganglia. Pheochromocytomas and paragangliomas are usually locally confined tumors, but about 15% do metastasize to distant locations. Histopathological examination currently poorly predicts future biologic behavior, thus long term postoperative follow-up is required. Therefore, there is an unmet need for prognostic biomarkers. Clearer understanding of the cellular mechanisms involved in the secretory characteristics of pheochromocytomas and sympathetic paragangliomas may offer one approach for the discovery of novel prognostic biomarkers for improved therapeutic targeting and monitoring of treatment or disease progression.

Similarities and Differences in the Peripheral Actions of Thyroid Hormones and Their Metabolites

Thyroxine (T4) and 3,5,3'-triiodothyronine (T3) are secreted by the thyroid gland, while T3 is also generated from the peripheral metabolism of T4 by iodothyronine deiodinases types I and II. Several conditions like stress, diseases, and physical exercise can promote changes in local TH metabolism, leading to different target tissue effects that depend on the presence of tissue-specific enzymatic activities. The newly discovered physiological and pharmacological actions of T4 and T3 metabolites, such as 3,5-diiodothyronine (3,5-T2), and 3-iodothyronamine (T1AM) are of great interest. A classical thyroid hormone effect is the ability of T3 to increase oxygen consumption in almost all cell types studied. Approximately 30 years ago, a seminal report has shown that 3,5-T2 increased oxygen consumption more rapidly than T3 in hepatocytes. Other studies demonstrated that exogenous 3,5-T2 administration was able to increase whole body energy expenditure in rodents and humans. In fact, 3,5-T2 treatment prevents diabetic nephropathy, hepatic steatosis induced by high fat diet, insulin resistance, and weight gain during aging in Wistar male rats. The regulation of mitochondria is likely one of the most important actions of T3 and its metabolite 3,5-T2, which was able to restore the thermogenic program of brown adipose tissue (BAT) in hypothyroid rats, just as T3 does, while T1AM administration induced rapid hypothermia. T3 increases heart rate and cardiac contractility, which are hallmark effects of hyperthyroidism involved in cardiac arrhythmia. These deleterious cardiac effects were not observed with the use of 3,5-T2 pharmacological doses, and in contrast T1AM was shown to promote a negative inotropic and chronotropic action at micromolar concentrations in isolated hearts. Furthermore, T1AM has a cardioprotective effect in a model of ischemic/reperfusion injury in isolated hearts, such as occurs with T3 administration. Despite the encouraging possible therapeutic use of TH metabolites, further studies are needed to better understand their peripheral effects, when compared to T3 itself, in order to establish their risk and benefit. On this basis, the main peripheral effects of thyroid hormones and their metabolites in tissues, such as heart, liver, skeletal muscle, and BAT are discussed herein.

Heterogenic Distribution of Aromatic L-Amino Acid Decarboxylase Neurons in the Rat Spinal Cord

Aromatic L-amino acid decarboxylase (AADC) is an essential enzyme in the synthesis of serotonin, dopamine, and certain trace amines and is present in a variety of organs including the brain and spinal cord. It is previously reported that in mammalian spinal cord AADC cells (called D-cells) were largely confined to a region around the central canal and that they do not produce monoamines. To date, there has not been a detailed description of their distribution and morphology in mammals. In the present study this issue is systematically investigated using immunohistochemistry. We have found that AADC cells in the rat spinal cord are both more numerous and more widely distributed than previously reported. In the gray matter, AADC neurons immunolabeled for NeuN were not only found in the region around the central canal but also in the dorsal horn, intermediate zone, and ventral horn. In the white matter a large number of glial cells were AADC-immunopositive in different spinal segments and the vast majority of these cells expressed oligodendrocyte and radial glial phenotypes. Additionally, a small number of AADC neurons labeled for NeuN were found in the white matter along the ventral median fissure. The shapes and sizes of AADC neurons varied according to their location. For example, throughout cervical and lumbar segments AADC neurons in the intermediate zone and ventral horn tended to be rather large and weakly immunolabeled, whereas those in comparable regions of sacrocaudal segments were smaller and more densely immunolabeled. The diverse morphological characteristics of the AADC cells suggests that they could be further divided into several subtypes. These results indicate that AADC cells are heterogeneously distributed in the rat spinal cord and they may exert different functions in different physiological and pathological situations.

Thyronamines and Derivatives: Physiological Relevance, Pharmacological Actions, and Future Research Directions

Thyronamines (3-T₁AM, T₀AM) are endogenous compounds probably derived from L-thyroxine or its intermediate metabolites. Combined activities of intestinal deiodinases and ornithine decarboxylase generate 3-T₁AM in vitro. Alternatively, 3-T₁AM might be formed by the thyroid gland and secreted into the blood. 3-T₁AM and T₀AM concentrations have been determined by liquid chromatography-tandem mass spectrometry analysis (LC-MS/MS) in tissues, serum, and cell lines. However, large variations of 3-T₁AM concentrations in human serum were reported by LC-MS/MS compared with a monoclonal antibody-based immunoassay. These differences might be caused by strong binding of the highly hydrophobic 3-T₁AM to apolipoprotein B100. Pharmacological administration of 3-T₁AM results in dose-dependent reversible effects on body temperature, cardiac function, energy metabolism, and neurological functions. The physiological relevance of these actions is unclear, but may occur at tissue concentrations close to the estimated endogenous concentrations of 3-T₁AM or its metabolites T₀AM or thyroacetic acid (TA₁). A number of putative receptors, binding sites, and cellular target molecules mediating actions of the multi-target ligand 3-T₁AM have been proposed. Among those are members of the trace amine associated receptor family, the adrenergic receptor ADRα2a, and the thermosensitive transient receptor potential melastatin 8 channel. Preclinical studies employing various animal experimental models are in progress, and more stable receptor-selective agonistic and antagonistic analogues of 3-T₁AM are now available for testing. The potent endogenous thyroid hormone-derived biogenic amine 3-T₁AM exerts marked cryogenic, metabolic, cardiac and central actions and represents a valuable lead compound linking endocrine, metabolic, and neuroscience research to advance development of new drugs.

Common Variation in the DOPA Decarboxylase (DDC) Gene and Human Striatal DDC Activity In Vivo

The synthesis of multiple amine neurotransmitters, such as dopamine, norepinephrine, serotonin, and trace amines, relies in part on DOPA decarboxylase (DDC, AADC), an enzyme that is required for normative neural operations. Because rare, loss-of-function mutations in the DDC gene result in severe enzymatic deficiency and devastating autonomic, motor, and cognitive impairment, DDC common genetic polymorphisms have been proposed as a source of more moderate, but clinically important, alterations in DDC function that may contribute to risk, course, or treatment response in complex, heritable neuropsychiatric illnesses. However, a direct link between common genetic variation in DDC and DDC activity in the living human brain has never been established. We therefore tested for this association by conducting extensive genotyping across the DDC gene in a large cohort of 120 healthy individuals, for whom DDC activity was then quantified with [(18)F]-FDOPA positron emission tomography (PET). The specific uptake constant, Ki, a measure of DDC activity, was estimated for striatal regions of interest and found to be predicted by one of five tested haplotypes, particularly in the ventral striatum. These data provide evidence for cis-acting, functional common polymorphisms in the DDC gene and support future work to determine whether such variation might meaningfully contribute to DDC-mediated neural processes relevant to neuropsychiatric illness and treatment.

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.

Investigation of a substrate-specifying residue within Papaver somniferum and Catharanthus roseus aromatic amino acid decarboxylases

Plant aromatic amino acid decarboxylases (AAADs) catalyze the decarboxylation of aromatic amino acids with either benzene or indole rings. Because the substrate selectivity of AAADs is intimately related to their physiological functions, primary sequence data and their differentiation could provide significant physiological insights. However, due to general high sequence identity, plant AAAD substrate specificities have been difficult to identify through primary sequence comparison. In this study, bioinformatic approaches were utilized to identify several active site residues within plant AAAD enzymes that may impact substrate specificity. Next a Papaver somniferum tyrosine decarboxylase (TyDC) was selected as a model to verify our putative substrate-dictating residues through mutation. Results indicated that mutagenesis of serine 372 to glycine enables the P. somniferum TyDC to use 5-hydroxytryptophan as a substrate, and reduces the enzyme activity toward 3,4-dihydroxy-L-phenylalanine (dopa). Additionally, the reverse mutation in a Catharanthus roseus tryptophan decarboxylase (TDC) enables the mutant enzyme to utilize tyrosine and dopa as substrates with a reduced affinity toward tryptophan. Molecular modeling and molecular docking of the P. somniferum TyDC and the C. roseus TDC enzymes provided a structural basis to explain alterations in substrate specificity. Identification of an active site residue that impacts substrate selectivity produces a primary sequence identifier that may help differentiate the indolic and phenolic substrate specificities of individual plant AAADs.

Enhanced synthesis of 5-hydroxy-l-tryptophan through tetrahydropterin regeneration

5-Hydroxy-l-tryptophan (5-HTP) is a naturally occurring aromatic amino acid present in the seeds of the African plant Griffonia simplicifolia. Although 5-HTP has therapeutic effects in various symptoms, efficient method of producing 5-HTP has not been established. In this study, we developed a novel cofactor regeneration process to achieve enhanced synthesis of 5-HTP by using modified l-phenylalanine 4-hydroxylase of Chromobacterium violaceum. For the synthesis of 5-HTP using Escherichia coli whole cell bioconversion, l-tryptophan and 5-HTP degradation by E. coli endogenous catabolic enzymes should be considered. The tryptophanase gene was disrupted using the λ red recombination system, since tryptophanase is postulated as an initial enzyme for the degradation of l-tryptophan and 5-HTP in E. coli. For regeneration of the cofactor pterin, we screened and investigated several key enzymes, including dihydropteridine reductase from E. coli, glucose dehydrogenase from Bacillus subtilis, and pterin-4α-carbinolamine dehydratase from Pseudomonas syringae. Genes encoding these three enzymes were overexpressed in an E. coli tryptophanase-deficient host, resulting in the synthesis of 0.74 mM 5-HTP in the presence of 0.1 mM pterin and the synthesis of 0.07 mM 5-HTP in the absence of regeneration of pterin. These results clearly indicated the successful regeneration of pterin. Following optimization of the reaction conditions, 2.5 mM 5-HTP was synthesized with cofactor regeneration, while 0.8 mM 5-HTP was recovered without cofactor regeneration under the same reaction conditions, suggesting that the principle described here provides a new method for cofactor regeneration.

Quantification and study of the L-DOPA decarboxylase expression in gastric adenocarcinoma cells treated with chemotherapeutic substances

3,4-Dihydroxy-L-phenylalanine decarboxylase (DDC) is an enzyme implicated in the biosynthetic pathways of the neurotransmitters dopamine and probably serotonin. DDC gene expression has been studied in numerous malignancies and the corresponding data have shown remarkable alterations in the mRNA and/or protein levels encoded by the gene. The aim of this study was to examine any modulations in the DDC mRNA levels in gastric cancer cells after their treatment with the chemotherapeutic agents 5-fluorouracil, leucovorin, irinotecan, etoposide, cisplatin, and taxol. The sensitivity of the AGS gastric adenocarcinoma cells to the antineoplastic drugs was evaluated using the MTT assay. Total RNA was extracted and reverse transcribed into cDNA. A highly sensitive quantitative real-time PCR methodology was developed for the quantification of DDC mRNA. GAPDH was used as a housekeeping gene. Relative quantification analysis was carried out using the comparative C T method ((Equation is included in full-text article.)). The treatment of AGS cells with several concentrations of various broadly used anticancer drugs resulted in significant modulations of the DDC mRNA levels compared with those in the untreated cells in a time-specific and drug-specific manner. Generally, DDC expression levels appeared to decrease after three time periods of exposure to the selected chemotherapeutic agents, suggesting a characteristic DDC mRNA expression profile that is possibly related to the mechanism of each drug. Our experimental data show that the DDC gene might serve as a new potential molecular biomarker predicting treatment response in gastric cancer cells.

Complexity of dopamine metabolism

: Parkinson's disease (PD) coincides with a dramatic loss of dopaminergic neurons within the substantia nigra. A key player in the loss of dopaminergic neurons is oxidative stress. Dopamine (DA) metabolism itself is strongly linked to oxidative stress as its degradation generates reactive oxygen species (ROS) and DA oxidation can lead to endogenous neurotoxins whereas some DA derivatives show antioxidative effects. Therefore, DA metabolism is of special importance for neuronal redox-homeostasis and viability.In this review we highlight different aspects of dopamine metabolism in the context of PD and neurodegeneration. Since most reviews focus only on single aspects of the DA system, we will give a broader overview by looking at DA biosynthesis, sequestration, degradation and oxidation chemistry at the metabolic level, as well as at the transcriptional, translational and posttranslational regulation of all enzymes involved. This is followed by a short overview of cellular models currently used in PD research. Finally, we will address the topic from a medical point of view which directly aims to encounter PD.

l-DOPA Decarboxylase (DDC) Expression Status as a Novel Molecular Tumor Marker for Diagnostic and Prognostic Purposes in Laryngeal Cancer

l-DOPA decarboxylase (DDC) plays an essential role in the enzymatic synthesis of dopamine and alterations in its gene expression have been reported in several malignancies. Our objective was to analyze DDC messenger RNA (mRNA) and protein expression in laryngeal tissues and to evaluate the clinical implication of this molecule in laryngeal cancer. In this study, total RNA was isolated from 157 tissue samples surgically removed from 100 laryngeal cancer patients. A highly sensitive real-time polymerase chain reaction methodology based on SYBR Green I fluorescent dye was developed for the quantification of DDC mRNA levels. In addition, Western blot analysis was performed for the detection of DDC protein. DDC mRNA expression was revealed to be significantly downregulated in primary laryngeal cancer samples compared with their nonmalignant counterparts (P = .001). A significant negative association was also disclosed between DDC mRNA levels and TNM staging (P = .034). Univariate analysis showed that patients bearing DDC-positive tumors had a significantly decreased risk of death (hazard ratio = 0.23, P = .012) and local recurrence (hazard ratio = 0.32, P =.006), whereas DDC expression retained its favorable prognostic significance in the multivariate analysis. Kaplan-Meier curves further demonstrated that DDC-positive patients experienced longer overall and disease-free survival periods (P = .006 and P = .004, respectively). Moreover, DDC protein was detected in both neoplastic and noncancerous tissues. Therefore, our results suggest that DDC expression status could qualify as a promising biomarker for the future clinical management of laryngeal cancer patients.

Carbidopa enhances antitumoral activity of bicalutamide on the androgen receptor-axis in castration-resistant prostate tumors

BACKGROUND

Response to bicalutamide after castration failure is not durable and treatment options at this stage are limited. Carbidopa, an L-dopa decarboxylase (AR-coactivator) inhibitor, has been shown to retard prostate tumor growth/PSA production in xenografts. Here, we hypothesize that pharmacological targeting of the AR-axis by combination treatment with bicalutamide plus carbidopa significantly enhances antitumoral activity in vitro and in vivo compared to monotherapy with either drug.

METHODS

Carbidopa was tested for its ability to enhance the effects of bicalutamide on cell viability, apoptosis and PSA transactivation in LNCaP and C4-2 cells. The castration-resistant prostate cancer (CRPC) LNCaP xenograft tumor model was used in vivo. After CRPC progression, mice were treated with carbidopa (50 mg/kg) and bicalutamide (50 mg/kg) as monotherapy or in combination. Tumor volume and serum PSA were evaluated weekly.

RESULTS

Combination treatment of carbidopa plus bicalutamide significantly inhibited cell viability in both cell lines and induced apoptosis. The combination treatment also decreased androgen-induced PSA transactivation by 62.6% in LNCaP cells and by 55.6% in C4-2 cells compared to control, while bicalutamide monotherapy reduced PSA levels by 27.5% and 29.1% in LNCaP and C4-2 cells. In vivo, bicalutamide monotherapy delayed LNCaP CRPC tumor growth rate by 72.2%, while combination treatment reduced tumor growth by 84.4% compared to control. Serum PSA was also reduced 70.6% with bicalutamide monotherapy, while combination therapy reduced PSA levels by 76.7% compared to control.

CONCLUSIONS

This study demonstrates preclinical proof-of-principle that pharmacological targeting of prostate tumors by combination treatment of bicalutamide plus carbidopa significantly reduces AR activity, and thereby delays CRPC tumor progression in vivo.

Does the aromatic L-amino acid decarboxylase contribute to thyronamine biosynthesis?

Thyronamines (TAM), recently described endogenous signaling molecules, exert metabolic and pharmacological actions partly opposing those of the thyromimetic hormone T(3). TAM biosynthesis from thyroid hormone (TH) precursors requires decarboxylation of the L-alanine side chain and several deiodination steps to convert e.g. L-thyroxine (T(4)) into the most potent 3-T(1)AM. Aromatic L-amino acid decarboxylase (AADC) was proposed to mediate TAM biosynthesis via decarboxylation of TH. This hypothesis was tested by incubating recombinant human AADC, which actively catalyzes dopamine production from DOPA, with several TH. Under all reaction conditions tested, AADC failed to catalyze TH decarboxylation, thus challenging the initial hypothesis. These in vitro observations are supported by detection of 3-T(1)AM in plasma of patients with AADC-deficiency at levels (46 ± 18 nM, n=4) similar to those of healthy controls. Therefore, we propose that the enzymatic decarboxylation needed to form TAM from TH is catalyzed by another unique, perhaps TH-specific, decarboxylase.

L-amino acid decarboxylase- and tyrosine hydroxylase-immunoreactive cells in the extended olfactory amygdala and elsewhere in the adult prairie vole brain

Neurons synthesizing dopamine (DA) are widely distributed in the brain and implicated in a tremendous number of physiological and behavioral functions, including socioreproductive behaviors in rodents. We have recently been investigating the possible involvement of sex- and species-specific TH-immunoreactive (TH-ir) cells in the male prairie vole (Microtus ochrogaster) principal bed nucleus of the stria terminalis (pBST) and posterodorsal medial amygdala (MeApd) in the chemosensory control of their monogamous pairbonding and parenting behaviors. These TH-ir cells are not immunoreactive for dopamine-beta-hydroxylase (DBH), suggesting they are not noradrenergic but possibly DAergic. A DAergic phenotype would require them to contain aromatic L-amino acid decarboxylase (AADC) and here we examined the existence of cells immunoreactive for both TH and AADC in the pBST and MeApd of adult virgin male and female prairie voles. We also investigated the presence of TH/AADC cells in the anteroventral periventricular nucleus (AVPV), medial preoptic area (MPO), arcuate nucleus (ARH), zona incerta (ZI), substantia nigra (SN) and ventral tegmental area (VTA). Among our findings were: (1) the pBST and MeApd each contained completely non-overlapping distributions of TH-ir and AADC-ir cells, (2) the AVPV contained surprisingly few AADC-ir cells and almost no TH-ir cells contained AADC-ir, (3) approximately 60% of the TH-ir cells in the MPO, ARH, and ZI also contained AADC-ir, (4) unexpectedly, only about half of TH-ir cells in the SN and VTA contained AADC-ir, and (5) notable populations of AADC-ir cells were found outside traditional monoamine-synthesizing regions, including some sites that do not contain AADC-ir cells in adult laboratory rats or cats (medial septum and cerebral cortex). In the absence of the chemical requirements to produce DA, monoenzymatic TH-ir cells in the virgin adult prairie vole pBST, MeApd, and elsewhere in their brain may instead produce L-DOPA as an end product and use it as a neurotransmitter or neuromodulator, similar to what has been observed for monoenzymatic TH-synthesizing cells in the laboratory rat brain.

Carbidopa abrogates L-dopa decarboxylase coactivation of the androgen receptor and delays prostate tumor progression

The androgen receptor (AR) plays a central role in prostate cancer progression to the castration-resistant (CR) lethal state. L-Dopa decarboxylase (DDC) is an AR coactivator that increases in expression with disease progression and is coexpressed with the receptor in prostate adenocarcinoma cells, where it may enhance AR activity. Here, we hypothesize that the DDC enzymatic inhibitor, carbidopa, can suppress DDC-coactivation of AR and retard prostate tumor growth. Treating LNCaP prostate cancer cells with carbidopa in transcriptional assays suppressed the enhanced AR transactivation seen with DDC overexpression and decreased prostate-specific antigen (PSA) mRNA levels. Carbidopa dose-dependently inhibited cell growth and decreased survival in LNCaP cell proliferation and apoptosis assays. The inhibitory effect of carbidopa on DDC-coactivation of AR and cell growth/survival was also observed in PC3 prostate cancer cells (stably expressing AR). In vivo studies demonstrated that serum PSA velocity and tumor growth rates elevated ∼2-fold in LNCaP xenografts, inducibly overexpressing DDC, were reverted to control levels with carbidopa administration. In castrated mice, treating LNCaP tumors, expressing endogenous DDC, with carbidopa delayed progression to the CR state from 6 to 10 weeks, while serum PSA and tumor growth decreased 4.3-fold and 5.4-fold, respectively. Our study is a first time demonstration that carbidopa can abrogate DDC-coactivation of AR in prostate cancer cells and tumors, decrease serum PSA, reduce tumor growth and delay CR progression. Since carbidopa is clinically approved, it may be readily used as a novel therapeutic strategy to suppress aberrant AR activity and delay prostate cancer progression.

First evidence of a membrane-bound, tyramine and beta-phenylethylamine producing, tyrosine decarboxylase in Enterococcus faecalis: a two-dimensional electrophoresis proteomic study

The soluble and membrane proteome of a tyramine producing Enterococcus faecalis, isolated from an Italian goat cheese, was investigated. A detailed analysis revealed that this strain also produces small amounts of beta-phenylethylamine. Kinetics of tyramine and beta-phenylethylamine accumulation, evaluated in tyrosine plus phenylalanine-enriched cultures (stimulated condition), suggest that the same enzyme, the tyrosine decarboxylase (TDC), catalyzes both tyrosine and phenylalanine decarboxylation: tyrosine was recognized as the first substrate and completely converted into tyramine (100% yield) while phenylalanine was decarboxylated to beta-phenylethylamine (10% yield) only when tyrosine was completely depleted. The presence of an aspecific aromatic amino acid decarboxylase is a common feature in eukaryotes, but in bacteria only indirect evidences of a phenylalanine decarboxylating TDC have been presented so far. Comparative proteomic investigations, performed by 2-DE and MALDI-TOF/TOF MS, on bacteria grown in conditions stimulating tyramine and beta-phenylethylamine biosynthesis and in control conditions revealed 49 differentially expressed proteins. Except for aromatic amino acid biosynthetic enzymes, no significant down-regulation of the central metabolic pathways was observed in stimulated conditions, suggesting that tyrosine decarboxylation does not compete with the other energy-supplying routes. The most interesting finding is a membrane-bound TDC highly over-expressed during amine production. This is the first evidence of a true membrane-bound TDC, longly suspected in bacteria on the basis of the gene sequence.

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

The final step in production of the neurotransmitters dopamine and serotonin is catalyzed by aromatic l-amino acid decarboxylase (AADC). AADC deficiency is a debilitating genetic condition that results in a deficit in these neurotransmitters, and manifests in infancy as a severe movement disorder with developmental delay. Response to current treatments is often disappointing. We have reviewed the literature to look for improvements to the current treatment strategy and also for new directions for AADC deficiency treatment. There may be differences in the mode of action, side-effect risk and effectiveness between different dopamine agonists and monoamine oxidase inhibitors currently used for AADC deficiency treatment. The range of these drugs used requires re-evaluation as some may have greater efficacy than others. Pyridoxal 5'-phosphate, the AADC cofactor may stabilize AADC and could increase AADC activity. Pyridoxal 5'-phosphate could have advantages as a treatment instead of pyridoxine. Atypical neuroleptics and peripheral AADC inhibitors both increase AADC activity in vivo and could be a future direction for AADC deficiency treatment and related conditions. Parkinson's disease gene therapy to deliver and express the human AADC gene in striatum is being tested in humans. Consequently gene therapy for AADC deficiency could be a realistic aim however an animal model of AADC deficiency is important for further progression.

Endocrine regulation of aging and reproduction in Drosophila

Hormonal signals can modulate lifespan and reproductive capacity across the animal kingdom. The use of model organisms such as worms, flies and mice has been fundamentally important for aging research in the discovery of genetic alterations that can extend healthy lifespan. The effects of mutations in the insulin and insulin-like growth factor-like signaling (IIS) pathways are evolutionarily conserved in that they can increase lifespan in all three animal models. Additionally, steroids and other lipophilic signaling molecules modulate lifespan in diverse organisms. Here we shall review how major hormonal pathways in the fruit fly Drosophila melanogaster interact to influence reproductive capacity and aging.

Thyronamines are isozyme-specific substrates of deiodinases

3-Iodothyronamine (3-T 1 AM) and thyronamine (T AM) are novel endogenous signaling molecules that exhibit great structural similarity to thyroid hormones but apparently antagonize classical thyroid hormone (T(3)) actions. Their proposed biosynthesis from thyroid hormones would require decarboxylation and more or less extensive deiodination. Deiodinases (Dio1, Dio2, and Dio3) catalyze the removal of iodine from their substrates. Because a role of deiodinases in thyronamine biosynthesis requires their ability to accept thyronamines as substrates, we investigated whether thyronamines are converted by deiodinases. Thyronamines were incubated with isozyme-specific deiodinase preparations. Deiodination products were analyzed using a newly established method applying liquid chromatography and tandem mass spectrometry (LC-MS/MS). Phenolic ring deiodinations of 3,3',5'-triiodothyronamine (rT3AM), 3',5'-diiodothyronamine (3',5'-T2AM), and 3,3'-diiodothyronamine (3,3'-T2AM) as well as tyrosyl ring deiodinations of 3,5,3'-triiodothyronamine (T3AM) and 3,5-diiodothyronamine (3,5-T2AM) were observed with Dio1. These reactions were completely inhibited by the Dio1-specific inhibitor 6n-propyl-2-thiouracil (PTU). Dio2 containing preparations also deiodinated rT(3)AM and 3',5'-T2AM at the phenolic rings but in a PTU-insensitive fashion. All thyronamines with tyrosyl ring iodine atoms were 5(3)-deiodinated by Dio3-containing preparations. In functional competition assays, the newly identified thyronamine substrates inhibited an established iodothyronine deiodination reaction. By contrast, thyronamines that had been excluded as deiodinase substrates in LC-MS/MS experiments failed to show any effect in the competition assays, thus verifying the former results. These data support a role for deiodinases in thyronamine biosynthesis and contribute to confining the biosynthetic pathways for 3-T 1 AM and T 0 AM.

Androgen-regulated genes differentially modulated by the androgen receptor coactivator L-dopa decarboxylase in human prostate cancer cells

Background

The androgen receptor is a ligand-induced transcriptional factor, which plays an important role in normal development of the prostate as well as in the progression of prostate cancer to a hormone refractory state. We previously reported the identification of a novel AR coactivator protein, L-dopa decarboxylase (DDC), which can act at the cytoplasmic level to enhance AR activity. We have also shown that DDC is a neuroendocrine (NE) marker of prostate cancer and that its expression is increased after hormone-ablation therapy and progression to androgen independence. In the present study, we generated tetracycline-inducible LNCaP-DDC prostate cancer stable cells to identify DDC downstream target genes by oligonucleotide microarray analysis.

Results

Comparison of induced DDC overexpressing cells versus non-induced control cell lines revealed a number of changes in the expression of androgen-regulated transcripts encoding proteins with a variety of molecular functions, including signal transduction, binding and catalytic activities. There were a total of 35 differentially expressed genes, 25 up-regulated and 10 down-regulated, in the DDC overexpressing cell line. In particular, we found a well-known androgen induced gene, TMEPAI, which wasup-regulated in DDC overexpressing cells, supporting its known co-activation function. In addition, DDC also further augmented the transcriptional repression function of AR for a subset of androgen-repressed genes. Changes in cellular gene transcription detected by microarray analysis were confirmed for selected genes by quantitative real-time RT-PCR.

Conclusion

Taken together, our results provide evidence for linking DDC action with AR signaling, which may be important for orchestrating molecular changes responsible for prostate cancer progression.

5-Hydroxy-L-[beta-11C]tryptophan versus alpha-[11C]methyl-L-tryptophan for positron emission tomography imaging of serotonin synthesis capacity in the rhesus monkey brain

The purpose of this study was to compare two positron emission tomography (PET) tracers that were developed to follow serotonin (5HT) synthesis by performing sequential PET scanning of the same rhesus monkey (n=4) on the same day. alpha-[11C]Methyl-L-tryptophan ([11C]AMT) and 5-Hydroxy-L-[beta-11C]tryptophan ([11C]HTP) are substrates in the first and second enzymatic steps, respectively, in the biosynthesis of 5HT. Regional net accumulation rate constants were derived from kinetic (two-tissue compartment model with irreversible tracer trapping) and graphic (Patlak) analyses, using the arterial plasma concentrations as input. The kinetic data analysis showed that the rate constant for the transfer of [11C]HTP into the brain (K1) was higher than that for [11C]AMT in the striatum and thalamus but was similar in other brain regions. The rate constant for tracer trapping (k3) was also higher for [11C]HTP than for [11C]AMT in the striatum (0.046+/-0.024 versus 0.019+/-0.006 min(-1)) and thalamus (0.039+/-0.013 versus 0.016+/-0.007 min(-1)). In agreement with previously reported regional HTP accumulation rates, the net accumulation rate constant (K(acc)) for [11C]HTP was also higher in these regions than in other brain regions; this is in contrast to the uniform distribution of [11C]AMT K(acc) values. This suggests that the regional net accumulation rates obtained with these two PET tracers will be of different magnitude, which might be related to the activity of each targeted enzyme.

Epitope mapping of human aromatic l-amino acid decarboxylase

Autoimmune polyendocrine syndrome type I (APS I) is a rare hereditary condition considered a model disease for organ specific autoimmunity. A wide range of autoantibodies targeting antigens present in the affected organs have been identified. Autoantibodies against aromatic L-amino acid decarboxylase (AADC) are present in about 50% of APS I patients. In order to increase our understanding of autoantibody specificity in APS I, the aim of the present study was to localize target regions on AADC recognized by sera from APS I patients. Using several complementing strategies, we have shown that autoantibodies against AADC mainly recognize conformational epitopes. The major antigenic determinants were detected N-terminally to amino acid residue 237. Replacement of amino acids 227-230 (ERDK) with alanine residues reduced the reactivity towards AADC by >80% in all patient sera tested, suggesting that amino acids 227-230 are an important part of an immunodominant epitope.

Trace amine-associated receptors and their ligands

Classical biogenic amines (adrenaline, noradrenaline, dopamine, serotonin and histamine) interact with specific families of G protein-coupled receptors (GPCRs). The term 'trace amines' is used when referring to p-tyramine, beta-phenylethylamine, tryptamine and octopamine, compounds that are present in mammalian tissues at very low (nanomolar) concentrations. The pharmacological effects of trace amines are usually attributed to their interference with the aminergic pathways, but in 2001 a new gene was identified, that codes for a GPCR responding to p-tyramine and beta-phenylethylamine but not to classical biogenic amines. Several closely related genes were subsequently identified and designated as the trace amine-associated receptors (TAARs). Pharmacological investigations in vitro show that many TAAR subtypes may not respond to p-tyramine, beta-phenylethylamine, tryptamine or octopamine, suggesting the existence of additional endogenous ligands. A novel endogenous thyroid hormone derivative, 3-iodothyronamine, has been found to interact with TAAR1 and possibly other TAAR subtypes. In vivo, micromolar concentrations of 3-iodothyronamine determine functional effects which are opposite to those produced on a longer time scale by thyroid hormones, including reduction in body temperature and decrease in cardiac contractility. Expression of all TAAR subtypes except TAAR1 has been reported in mouse olfactory epithelium, and several volatile amines were shown to interact with specific TAAR subtypes. In addition, there is evidence that TAAR1 is targeted by amphetamines and other psychotropic agents, while genetic linkage studies show a significant association between the TAAR gene family locus and susceptibility to schizophrenia or bipolar affective disorder.

Different effects of 7-nitroindazole in reserpine-induced hypolocomotion in two strains of mice

There are a number of reasons for believing that nitric oxide participates in motor control in the striatum. Therefore, effects of neuronal nitric oxide synthase inhibitor 7-nitroindazole (7-NI) were studied on the reserpine model of Parkinson's disease in Swiss and C57BL/6 mice using the open-field test. Mice received reserpine (1 mg/kg administered intraperitoneally). A significant hypolocomotion was observed 24 h and 48 h after reserpine injection. The treatment with 7-nitroindazole (25 mg/kg, administered intraperitoneally, 30 min after reserpine) attenuated reserpine-induced hypolocomotion 24 h and 48 h after the treatment in Swiss mice, but not completely in C57BL/6 mice. These results suggest that nitric oxide functions as an intercellular messenger in motor circuits in the brain. Moreover, our data suggests that the comparison of such mouse strains may provide information on genetic basis for strain differences in different sensitivity to these drugs.

Anesthesia management in a young child with aromatic l-amino acid decarboxylase deficiency

Aromatic l-amino acid decarboxylase (AADC) deficiency is characterized by an almost complete absence of sympathetic autoregulation, because of very low levels of circulating catecholamines. Here, we report the successful management of four consecutive anesthesia procedures in a young child presenting with AADC deficiency. Our experience suggests that, with appropriate anticipation of the potential autonomic disturbances, anesthesia, at least for minor surgical and diagnostic procedures, can be conducted safely in patients with AADC deficiency.

Current concepts in neuroendocrine cancer metabolism

Neuroendocrine (NE) cancers occur in multiple anatomic locations and range in prognosis from indolent to aggressive. In addition, adenocarcinomas can express gene products associated with NE cells, referred to as NE differentiation (NED), which correlates with poor prognosis and aggressive disease. Several metabolites and peptides produced by NE cells have been discovered that engage in cellular signaling and have autocrine and paracrine effects on cancer cell proliferation. This review focuses on the current knowledge of small molecule metabolism in NE cancers involving the synthesis of biogenic amine, polyamine, and amino acid neurotransmitters. Systems biology-directed approaches to NE cancer metabolism using gene expression profiling, liquid chromatography/mass spectrometry (LC/MS) and nuclear magnetic resonance (NMR) are also discussed. Furthermore, knowledge of metabolic and signaling pathways in NE cancers has led to the successful implementation of therapeutic regimens in cell culture and animal models of NE carcinogenesis.

Portal 5-hydroxytryptophan infusion enhances glucose disposal in conscious dogs

Intraportal serotonin infusion enhances net hepatic glucose uptake (NHGU) during glucose infusion but blunts nonhepatic glucose uptake and can cause gastrointestinal discomfort and diarrhea at high doses. Whether the serotonin precursor 5-hydroxytryptophan (5-HTP) could enhance NHGU without gastrointestinal side effects during glucose infusion was examined in conscious 42-h-fasted dogs, using arteriovenous difference and tracer ([3-3H]glucose) techniques. Experiments consisted of equilibration (-120 to -30 min), basal (-30 to 0 min), and experimental (EXP; 0-270 min) periods. During EXP, somatostatin, fourfold basal intraportal insulin, basal intraportal glucagon, and peripheral glucose (to double the hepatic glucose load) were infused. In one group of dogs (HTP, n = 6), saline was infused intraportally from 0 to 90 min (P1), and 5-HTP was infused intraportally at 10, 20, and 40 microg x kg(-1) x min(-1) from 90 to 150 (P2), 150 to 210 (P3), and 210 to 270 (P4) min, respectively. In the other group (SAL, n = 7), saline was infused intraportally from 0 to 270 min. NHGU in SAL was 14.8 +/- 1.9, 18.5 +/- 2.3, 16.3 +/- 1.4, and 19.7 +/- 1.6 micromol x kg(-1) x min(-1) in P1-P4, whereas NHGU in 5-HTP averaged 16.4 +/- 2.6, 18.5 +/- 1.4, 20.8 +/- 2.0, and 27.6 +/- 2.6 micromol x kg(-1) x min(-1) (P < 0.05 vs. SAL). Nonhepatic glucose uptake (micromol x kg(-1) x min(-1)) in SAL was 30.2 +/- 4.3, 36.8 +/- 5.8, 44.3 +/- 5.8, and 54.6 +/- 11.8 during P1-P4, respectively, whereas in HTP the corresponding values were 26.3 +/- 6.8, 44.9 +/- 10.1, 47.5 +/- 11.7, and 51.4 +/- 13.2 (not significant between groups). Intraportal 5-HTP enhances NHGU without significantly altering nonhepatic glucose uptake or causing gastrointestinal side effects, raising the possibility that a related agent might have a role in reducing postprandial hyperglycemia.

Two functional but noncomplementing Drosophila tyrosine decarboxylase genes: distinct roles for neural tyramine and octopamine in female fertility

The trace biogenic amine tyramine is present in the nervous systems of animals ranging in complexity from nematodes to mammals. Tyramine is synthesized from tyrosine by the enzyme tyrosine decarboxylase (TDC), a member of the aromatic amino acid family, but this enzyme has not been identified in Drosophila or in higher animals. To further clarify the roles of tyramine and its metabolite octopamine, we have cloned two TDC genes from Drosophila melanogaster, dTdc1 and dTdc2. Although both gene products have TDC activity in vivo, dTdc1 is expressed nonneurally, whereas dTdc2 is expressed neurally. Flies with a mutation in dTdc2 lack neural tyramine and octopamine and are female sterile due to egg retention. Although other Drosophila mutants that lack octopamine retain eggs completely within the ovaries, dTdc2 mutants release eggs into the oviducts but are unable to deposit them. This specific sterility phenotype can be partially rescued by driving the expression of dTdc2 in a dTdc2-specific pattern, whereas driving the expression of dTdc1 in the same pattern results in a complete rescue. The disparity in rescue efficiencies between the ectopically expressed Tdc genes may reflect the differential activities of these gene products. The egg retention phenotype of the dTdc2 mutant and the phenotypes associated with ectopic dTdc expression contribute to a model in which octopamine and tyramine have distinct and separable neural activities.

Function and evolution of the serotonin-synthetic bas-1 gene and other aromatic amino acid decarboxylase genes in Caenorhabditis

Background

Aromatic L-amino acid decarboxylase (AADC) enzymes catalyze the synthesis of biogenic amines, including the neurotransmitters serotonin and dopamine, throughout the animal kingdom. These neurotransmitters typically perform important functions in both the nervous system and other tissues, as illustrated by the debilitating conditions that arise from their deficiency. Studying the regulation and evolution of AADC genes is therefore desirable to further our understanding of how nervous systems function and evolve.

Results

In the nematode C. elegans, the bas-1 gene is required for both serotonin and dopamine synthesis, and maps genetically near two AADC-homologous sequences. We show by transformation rescue and sequencing of mutant alleles that bas-1 encodes an AADC enzyme. Expression of a reporter construct in transgenics suggests that the bas-1 gene is expressed, as expected, in identified serotonergic and dopaminergic neurons. The bas-1 gene is one of six AADC-like sequences in the C. elegans genome, including a duplicate that is immediately downstream of the bas-1 gene. Some of the six AADC genes are quite similar to known serotonin- and dopamine-synthetic AADC's from other organisms whereas others are divergent, suggesting previously unidentified functions. In comparing the AADC genes of C. elegans with those of the congeneric C. briggsae, we find only four orthologous AADC genes in C. briggsae. Two C. elegans AADC genes – those most similar to bas-1 – are missing from C. briggsae. Phylogenetic analysis indicates that one or both of these bas-1-like genes were present in the common ancestor of C. elegans and C. briggsae, and were retained in the C. elegans line, but lost in the C. briggsae line. Further analysis of the two bas-1-like genes in C. elegans suggests that they are unlikely to encode functional enzymes, and may be expressed pseudogenes.

Conclusions

The bas-1 gene of C. elegans encodes a serotonin- and dopamine-synthetic AADC enzyme. Two C. elegans AADC-homologous genes that are closely related to bas-1 are missing from the congeneric C. briggsae; one or more these genes was present in the common ancestor of C. elegans and C. briggsae. Despite their persistence in C. elegans, evidence suggests the bas-1-like genes do not encode functional AADC proteins. The presence of the genes in C. elegans raises questions about how many 'predicted genes' in sequenced genomes are functional, and how duplicate genes are retained or lost during evolution. This is another example of unexpected retention of duplicate genes in eukaryotic genomes.

Age-Dependent Effects of Severe Traumatic Brain Injury on Cerebral Dopaminergic Activity in Newborn and Juvenile Pigs

There is evidence that the dopaminergic system is sensitive to traumatic brain injury (TBI). However, the age-dependency of this sensitivity has not been studied together with brain oxidative metabolism. We postulate that the acute effects of severe TBI on brain dopamine turnover are age-dependent. Therefore 18F-labelled 6-fluoro-L-3,4-dihydroxyphenylalanine (FDOPA) together with Positron-Emission-Tomography (PET) was used to estimate the activity of the aromatic amino acid decarboxylase (AADC) in the brain of 11 newborn piglets (7-10 days old) and nine juvenile pigs (6-7 weeks old). Six newborn and five juvenile animals were subjected to a severe fluid-percussion (FP) induced TBI. The remaining animals were used as sham operated untreated control groups. Simultaneously, the regional cerebral blood flow (CBF) was measured with colored microspheres and the cerebral metabolic rates of oxygen and glucose were determined. At 1 h after FP-TBI, [18F]FDOPA was infused and PET scanning was performed for 2 h. At 2 h after FP-TBI administration, a second series of measurements of physiological values including CBF and brain oxidative metabolism data had been obtained. Severe FP-TBI elicited a marked increase in the rate constant for fluorodopamine production (k3FDOPA) in all brain regions of newborn piglets studied by between 97% (mesencephalon) and 143% (frontal cortex) (p < 0.05). In contrast, brain hemodynamics and cerebral oxidative metabolism remained unaltered after TBI. Furthermore, the permeability-surface area product of FDOPA (PSFDOPA) was unchanged. In addition, regional blood flow differences between corresponding ipsi- and contralateral brain regions did not occur after TBI. Thus, it is suggested that severe FP-TBI induces an upregulation of AADC activity of newborn piglets that is not related to alterations in brain oxidative metabolism.

The effect of oral 5-HTP administration on 5-HTP and 5-HT immunoreactivity in monoaminergic brain regions of rats

5-Hydroxytryptophan (5-HTP), which is the rate-limiting precursor in serotonin (5-hydroxytryptamine (5-HT)) biosynthesis, is used as an oral supplement to enhance serotonin levels in humans. To evaluate its effects on serotonin levels and localization, 5-hydroxytryptophan was administered to Sprague-Dawley rats either orally or via intraperitoneal injection. 5-Hydroxytryptophan-immunoreactivity was co-localized with serotonin-immunoreactivity in the serotonergic dorsal raphe nucleus of control animals and this was not changed in animals given 5-hydroxytryptophan. Oral 5-HTP administration increased the intensity of both 5-HTP and serotonin immunoreactivity in raphe neurons. However, 5-HTP treatment also caused ectopic 5-hydroxytryptophan-immunoreactivity and serotonin-immunoreactivity in normally dopaminergic neurons of the substantia nigra par compacta. Serotonin-immunoreactivity was confined to neurons that also displayed amino acid decarboxylase immunoreactivity, but in a small percentage of substantia nigra neurons, serotonin immunoreactivity was not co-localized with tyrosine hydroxylase-immunoreactivity. The intensity of the immunoreactivity to serotonin and 5-hydroxytryptophan in the substantia nigra was maximal within 2h of 5-hydroxytryptophan administration and returned to control levels by 24h. This time course mirrored changes in HPLC measurements of 5-hydroxytryptophan, serotonin, and the metabolite 5-hydroxyindoleacetic acid (5-HIAA) in the urine. 5-Hydroxytryptophan administration did not cause ectopic appearance of either serotonin or 5-hydroxytryptophan in the noradrenergic locus coeruleus. These results suggest that a single oral dose of 5-HTP increases the 5-HTP and serotonin content of serotonergic neurons and causes the transient ectopic appearance of serotonin in some normally non-serotonergic neurons.