Butyrate Rescues Oxidative Stress-Induced Transport Deficits of Tryptophan: Potential Implication in Affective or Gut-Brain Axis Disorders.

INTRODUCTION: Butyrate is a short-chain fatty acid metabolite produced by microbiota in the colon. With its antioxidant properties, butyrate has also been shown to alter the neurological functions in affective disorder models, suggesting it as a key mediator in gut-brain interactions. OBJECTIVE: Here, we evaluated the negative effect of oxidative stress on the transport of the serotonin precursor tryptophan as present in affective disorders. Butyrate was hypothesized to be able to rescue these deficits due to its antioxidative capacities and its effect on transmembrane transport of tryptophan. Human skin-derived fibroblasts were used as cellular models to address these objectives. METHODS: Human fibroblasts were treated with hydrogen peroxide to induce oxidative stress. Stressed as well as control cells were treated with different concentrations of butyrate. Tryptophan (3H) was used as a tracer to measure the transport of tryptophan across the cell membranes (n = 6). Furthermore, gene expression profiles of different amino acid transporters were analyzed (n = 2). RESULTS: As hypothesized,oxidative stress significantly decreased the uptake of tryptophan in fibroblast cells, while butyrate counteracted this effect. Oxidative stress did not alter the gene expression profile of amino acid transporters. However, treatment of stressed and control cells with different concentrations of butyrate differentially regulated the gene expression of large amino acid transporters 1 and 2, which are the major transporters of tryptophan. CONCLUSIONS: Gut microbiota-derived butyrate may have therapeutic potential in affective disorders characterized by either aberrant serotonergic activity or neuroinflammation due to its role in rescuing the oxidative stress-induced perturbations of tryptophan transport.

Aberrant tryptophan transport in cultured fibroblast from patients with Male Idiopathic Osteoporosis: An in vitro study.

It has been demonstrated, that long-term chronic tryptophan deficiency, results in decreased serotonin synthesis, which may lead to low bone mass and low bone formation. Findings from studies in male patients with idiopathic osteoporosis suggested a decreased transport of tryptophan in erythrocytes of osteoporotic patients, indicating that serotonin system defects may be involved in the etiology of low bone mass. Tryptophan is the precursor of serotonin, and a disturbed transport of tryptophan is implicated in altered serotonin synthesis. However, no study has investigated the tryptophan transport kinetics in MIO patients. The aim of this study is to investigate the kinetic parameters of tryptophan transport in fibroblasts derived from MIO patients compared to age and sex matched controls. Fibroblast cells were cultured from skin biopsies obtained from 14 patients diagnosed with Male Idiopathic Osteoporosis and from 13 healthy age-sex matched controls, without a diagnosis of osteoporosis. Transport of the amino acid tryptophan across the cell membrane was measured by the cluster tray method. The kinetic parameters, maximal transport capacity (Vmax) and affinity constant (Km) were determined by using the Lineweaver-Burke plot equation. The results of this study have shown a significantly lower mean value for Vmax (p = 0.0138) and lower Km mean value (p = 0.0009) of tryptophan transport in fibroblasts of MIO patients compared to the control group. A lower Vmax implied a decreased tryptophan transport availability in MIO patients. In conclusion, reduced cellular tryptophan availability in MIO patients might result in reduced brain serotonin synthesis and its endogenous levels in peripheral tissues, and this may contribute to low bone mass/formation. The findings of the present study could contribute to the etiology of idiopathic osteoporosis and for the development of novel approaches for diagnosis, treatment and management strategies of MIO.

Probing the lithium-response pathway in hiPSCs implicates the phosphoregulatory set-point for a cytoskeletal modulator in bipolar pathogenesis.

The molecular pathogenesis of bipolar disorder (BPD) is poorly understood. Using human-induced pluripotent stem cells (hiPSCs) to unravel such mechanisms in polygenic diseases is generally challenging. However, hiPSCs from BPD patients responsive to lithium offered unique opportunities to discern lithium's target and hence gain molecular insight into BPD. By profiling the proteomics of BDP-hiPSC-derived neurons, we found that lithium alters the phosphorylation state of collapsin response mediator protein-2 (CRMP2). Active nonphosphorylated CRMP2, which binds cytoskeleton, is present throughout the neuron; inactive phosphorylated CRMP2, which dissociates from cytoskeleton, exits dendritic spines. CRMP2 elimination yields aberrant dendritogenesis with diminished spine density and lost lithium responsiveness (LiR). The "set-point" for the ratio of pCRMP2:CRMP2 is elevated uniquely in hiPSC-derived neurons from LiR BPD patients, but not with other psychiatric (including lithium-nonresponsive BPD) and neurological disorders. Lithium (and other pathway modulators) lowers pCRMP2, increasing spine area and density. Human BPD brains show similarly elevated ratios and diminished spine densities; lithium therapy normalizes the ratios and spines. Consistent with such "spine-opathies," human LiR BPD neurons with abnormal ratios evince abnormally steep slopes for calcium flux; lithium normalizes both. Behaviorally, transgenic mice that reproduce lithium's postulated site-of-action in dephosphorylating CRMP2 emulate LiR in BPD. These data suggest that the "lithium response pathway" in BPD governs CRMP2's phosphorylation, which regulates cytoskeletal organization, particularly in spines, modulating neural networks. Aberrations in the posttranslational regulation of this developmentally critical molecule may underlie LiR BPD pathogenesis. Instructively, examining the proteomic profile in hiPSCs of a functional agent-even one whose mechanism-of-action is unknown-might reveal otherwise inscrutable intracellular pathogenic pathways.

Proinflammatory Cytokines and Oxidative Stress Decrease the Transport of Dopamine Precursor Tyrosine in Human Fibroblasts.

BACKGROUND: Proinflammatory cytokines and oxidative stress responses have been extensively implicated in the pathophysiology of neuropsychiatric disorders over the past 2 decades. Moreover, disturbed transport of the dopamine precursor (i.e., the amino acid tyrosine) has been demonstrated, in different studies, across fibroblast cell membranes obtained from neuropsychiatric patients. However, the role and influences of proinflammatory cytokines and oxidative stress, and the reasons for disturbed tyrosine transport in neuropsychiatric disorders, are still not evaluated. AIMS: The present study aimed to assess the role of proinflammatory cytokines and oxidative stress, indicated in many neuropsychiatric disorders, in tyrosine transportation, by using human skin-derived fibroblasts. METHODS: Fibroblasts obtained from a healthy control were used in this study. Fibroblasts were treated with proinflammatory cytokines (IL-1ß, IFN-γ, IL-6, TNF-α), their combinations, and oxidative stress, optimized for concentrations and incubation time, to analyze the uptake of 14C-tyrosine compared to untreated controls. RESULTS AND CONCLUSION: This study demonstrates that proinflammatory cytokines and oxidative stress decrease the transport of tyrosine (47% and 33%, respectively), which can alter dopamine synthesis. The functionality of the tyrosine transporter could be a new potential biomarker to target for discovering new drugs to counteract the effects of proinflammatory cytokines and oxidative stress in the pathophysiology of neuropsychiatric disorders.

Genetic and Functional Study of L-Type Amino Acid Transporter 1 in Schizophrenia.

Schizophrenia involves neural catecholaminergic dysregulation. Tyrosine is the precursor of catecholamines, and its major transporter, according to studies on fibroblasts, in the brain is the L-type amino acid transporter 1 (LAT1). The present study assessed haplotype tag single-nucleotide polymorphisms (SNPs) of the SLC7A5/LAT1 gene in 315 patients with psychosis within the schizophrenia spectrum and 233 healthy controls to investigate genetic vulnerability to the disorder as well as genetic relationships to homovanillic acid (HVA) and 3-methoxy-4-hydroxyphenylglycol (MHPG), the major catecholamine metabolites in the cerebrospinal fluid (CSF). Moreover, the involvement of the different isoforms of the system L in tyrosine uptake and LAT1 tyrosine kinetics were studied in fibroblast cell lines of 10 patients with schizophrenia and 10 healthy controls. The results provide suggestive evidence of individual vulnerability to schizophrenia related to the LAT1 SNP rs9936204 genotype. A number of SNPs were nominally associated with CSF HVA and MHPG concentrations but did not survive correction for multiple testing. The LAT1 isoform was confirmed as the major tyrosine transporter in patients with schizophrenia. However, the kinetic parameters (maximal transport capacity, affinity of the binding sites, and diffusion constant of tyrosine transport through the LAT1 isoform) did not differ between patients with schizophrenia and controls. The present genetic findings call for independent replication in larger samples, while the functional study seems to exclude a role of LAT1 in the aberrant transport of tyrosine in fibroblasts of patients with schizophrenia.

An oxygenated metabolite of benzo[a]pyrene increases hepatic ß-oxidation of fatty acids in chick embryos.

Polycyclic aromatic hydrocarbons (PAHs) are well-known carcinogens to humans and ecotoxicological effects have been shown in several studies. However, PAHs can also be oxidized into more water soluble-oxygenated metabolites (Oxy-PAHs). The first purpose of the present project was to (1) assess the effects of a mixture containing three parent PAHs: anthracene, benz[a]anthracene, and benzo[a]pyrene versus a mixture of their oxygenated metabolites, namely: anthracene-9,10-dione, benz[a]anthracene-7,12-dione, and 9,10-dihydrobenzo[a]pyrene-7-(8H)-one on the hepatic fatty acid ß-oxidation in chicken embryos (Gallus gallus domesticus) exposed in ovo. The second and also main purpose of the project was to (2) assess the effects of the parent PAHs versus their oxy-PAHs analogues when injected individually, followed by (3) additional testing of the individual oxy-PAHs. The hepatic ß-oxidation was measured using a tritium release assay with [9,10-(3)H]-palmitic acid (16:0) as substrate. The result from the first part (1) showed reduced hepatic ß-oxidation after exposure in ovo to a mixture of three PAHs, however, increased after exposure to the mixture of three oxy-PAHs compared to control. The result from the second part (2) and also the follow-up experiment (3) showed that 9,10-dihydrobenzo[a]pyrene-7-(8H)-one was the causative oxy-PAH. The implication of this finding on the risk assessment of PAH metabolite exposure in avian wildlife remains to be determined. To the best of our knowledge, no similar studies have been reported.

A comparative genomic study in schizophrenic and in bipolar disorder patients, based on microarray expression profiling meta-analysis.

Schizophrenia affecting almost 1% and bipolar disorder affecting almost 3%-5% of the global population constitute two severe mental disorders. The catecholaminergic and the serotonergic pathways have been proved to play an important role in the development of schizophrenia, bipolar disorder, and other related psychiatric disorders. The aim of the study was to perform and interpret the results of a comparative genomic profiling study in schizophrenic patients as well as in healthy controls and in patients with bipolar disorder and try to relate and integrate our results with an aberrant amino acid transport through cell membranes. In particular we have focused on genes and mechanisms involved in amino acid transport through cell membranes from whole genome expression profiling data. We performed bioinformatic analysis on raw data derived from four different published studies. In two studies postmortem samples from prefrontal cortices, derived from patients with bipolar disorder, schizophrenia, and control subjects, have been used. In another study we used samples from postmortem orbitofrontal cortex of bipolar subjects while the final study was performed based on raw data from a gene expression profiling dataset in the postmortem superior temporal cortex of schizophrenics. The data were downloaded from NCBI's GEO datasets.

Decreased binding capacity (Bmax) of muscarinic acetylcholine receptors in fibroblasts from boys with attention-deficit/hyperactivity disorder (ADHD).

Monoaminergic dysregulation is implicated in attention-deficit/hyperactivity disorder (ADHD), and methylphenidate and amphetamines are the most frequently prescribed pharmacological agents for treating ADHD. However, it has recently been proposed that the core symptoms of the disorder might be due to an imbalance between monoaminergic and cholinergic systems. In this study, we used fibroblast cell homogenates from boys with and without ADHD as an extraneural cell model to examine the cholinergic receptor density, that is, muscarinic acetylcholine receptors (mAChRs). We found that the binding capacity (Bmax) of [³H] Quinuclidinyl benzilate (³H-QNB) to mAChRs was decreased by almost 50 % in the children with ADHD (mean = 30.6 fmol/mg protein, SD = 25.6) in comparison with controls [mean = 63.1 fmol/mg protein, SD = 20.5, p ≤ 0.01 (Student's unpaired t test)]. The decreased Bmax indicates a reduced cholinergic receptor density, which might constitute a biomarker for ADHD. However, these preliminary findings need to be replicated in larger ADHD and comparison cohorts.

Polycyclic aromatic hydrocarbons (PAHs) reduce hepatic ß-oxidation of fatty acids in chick embryos.

Polycyclic aromatic hydrocarbons (PAHs) are widespread fused-ring contaminants formed during incomplete combustion of almost all kind of organic materials from both natural and anthropogenic sources. Some PAHs have been shown to be carcinogenic to humans, and a wide range of PAHs are found in wildlife all around the globe including avian species. The purpose of this project was to assess the effects of a standard mixture of 16 PAHs (United States Environmental Protection Agency) on the hepatic fatty acid ß-oxidation in chicken embryos (Gallus gallus domesticus) exposed in ovo. The hepatic ß-oxidation was measured using a tritium release assay with [9,10-(3)H]-palmitic acid (16:0) as substrate. Treated groups were divided into groups of 0.05, 0.1, 0.3, 0.5, and 0.8 mg PAHs/kg egg weight. The hepatic ß-oxidation was reduced after exposure in ovo to the 16 PAHs mixture compared to control. The mechanisms causing reduced fatty acid oxidation in the present study are unclear, however may be due to deficient membrane structure, the functionality of enzymes controlling the rate of fatty acid entering into the mitochondria, or complex pathways connected to endocrine disruption. To the best of our knowledge, this is the first time a PAH-caused reduction of hepatic ß-oxidation of fatty acids in avian embryos has been observed. The implication of this finding on risk assessment of PAH exposure in avian wildlife remains to be determined.

Perfluorooctane sulfonate increases ß-oxidation of palmitic acid in chicken liver.

PURPOSE: Perfluorooctane sulfonate (PFOS) belongs to a group of chemicals called perfluoroalkyl acids that have been extensively used in various applications such as stain and oil resistant treatments for fabrics, fire-fighting foams, and insecticides. These chemicals present an environmental and health risk being present in many samples both in wildlife and humans. In this study, we investigate the effect of PFOS on fatty acid ß-oxidation in developing chicken embryos. METHODS: Fertilized chicken eggs were exposed in ovo to PFOS at day 4 of incubation. On day 10, the eggs were dissected and livers were incubated in vitro with (3)H-palmitic acid for 2 h. The media were collected, and after clean up, the amount of tritiated water was measured with liquid scintillation counting to determine the rate of palmitic acid ß-oxidation. RESULTS: PFOS was found to induce fatty acid ß-oxidation at doses starting from a lowest observed effect level (LOEL) of 0.1 µg/g egg weight. Maximum induction of 77% compared to control was seen at 0.3 µg/g. CONCLUSIONS: The administered doses in which effects are seen are around and even lower than the levels that can be found in wild populations of birds. General population human levels are a factor of two to three times lower than the LOEL value of this study. The environmental contamination of PFOS therefore presents a possibility of effects in wild populations of birds.

Tryptophan transport in human fibroblast cells-a functional characterization.

There are indications that serotonergic neurotransmission is disturbed in several psychiatric disorders. One explanation may be disturbed transport of tryptophan (precursor for serotonin synthesis) across cell membranes. Human fibroblast cells offer an advantageous model to study the transport of amino acids across cell membranes, since they are easy to propagate and the environmental factors can be controlled. The aim of this study was to functionally characterize tryptophan transport and to identify the main transporters of tryptophan in fibroblast cell lines from healthy controls.Tryptophan kinetic parameters (V(max) and K(m)) at low and high concentrations were measured in fibroblasts using the cluster tray method. Uptake of (3)H (5)-L-tryptophan at different concentrations in the presence and absence of excess concentrations of inhibitors or combinations of inhibitors of amino acid transporters were also measured. Tryptophan transport at high concentration (0.5 mM) had low affinity and high V(max) and the LAT1 isoform of system-L was responsible for approximately 40% of the total uptake of tryptophan. In comparison, tryptophan transport at low concentration (50 nM) had higher affinity, lower V(max) and approximately 80% of tryptophan uptake was transported by system-L with LAT1 as the major isoform. The uptake of tryptophan at the low concentration was mainly sodium (Na(+)) dependent, while uptake at high substrate concentration was mainly Na(+) independent. A series of different transporter inhibitors had varying inhibitory effects on tryptophan uptake.This study indicates that tryptophan is transported by multiple transporters that are active at different substrate concentrations in human fibroblast cells. The tryptophan transport trough system-L was mainly facilitated by the LAT1 isoform, at both low and high substrate concentrations of tryptophan.

Altered tryptophan and alanine transport in fibroblasts from boys with attention-deficit/hyperactivity disorder (ADHD): an in vitro study.

BACKGROUND: The catecholaminergic and serotonergic neurotransmitter systems are implicated in the pathophysiology of attention-deficit/hyperactivity disorder (ADHD). The amino acid tyrosine is the precursor for synthesis of the catecholamines dopamine and norepinephrine, while tryptophan is the precursor of serotonin. A disturbed transport of tyrosine, as well as other amino acids, has been found in a number of other psychiatric disorders, such as schizophrenia, bipolar disorder and autism, when using the fibroblast cell model. Hence, the aim of this study was to explore whether children with ADHD may have disturbed amino acid transport. METHODS: Fibroblast cells were cultured from skin biopsies obtained from 14 boys diagnosed with ADHD and from 13 matching boys without a diagnosis of a developmental disorder. Transport of the amino acids tyrosine, tryptophan and alanine across the cell membrane was measured by the cluster tray method. The kinetic parameters, maximal transport capacity (V(max)) and affinity constant (K(m)) were determined. Any difference between the two groups was analyzed by Student's unpaired t-test or the Mann Whitney U test. RESULTS: The ADHD group had significantly decreased V(max) (p = 0.039) and K(m) (increased affinity) (p = 0.010) of tryptophan transport in comparison to controls. They also had a significantly higher V(max)of alanine transport (p = 0.031), but the Km of alanine transport did not differ significantly. There were no significant differences in any of the kinetic parameters regarding tyrosine transport in fibroblasts for the ADHD group. CONCLUSIONS: Tryptophan uses the same transport systems in both fibroblasts and at the blood brain barrier (BBB). Hence, a decreased transport capacity of tryptophan implies that less tryptophan is being transported across the BBB in the ADHD group. This could lead to deficient serotonin access in the brain that might cause disturbances in both the serotonergic and the catecholaminergic neurotransmitter systems, since these systems are highly interconnected. The physiological importance of an elevated transport capacity of alanine to the brain is not known to date.

Aberrant tyrosine transport across the fibroblast membrane in patients with schizophrenia--indications of maternal inheritance.

BACKGROUND: In previous studies of the present patients with schizophrenia, aberrant tyrosine transport across the fibroblast membrane was found. A low K(m), a kinetic factor indicating high affinity between tyrosine and the binding site at the cell membrane, was found to be associated with poor cognitive functions in patients. The present study aimed at investigating possible relationships between patients with schizophrenia and their first-degree relatives in aberrant tyrosine transport indicating that it may be a biological marker for the genetic susceptibility. METHODS: Thirty-three parents, 13 fathers and 20 mothers, from 23 families with a schizophrenic patient agreed to enter the study. They underwent skin biopsies for fibroblast cultivation, neuropsychological and psychiatric investigations and were classified as family history positive or negative. Tyrosine transport kinetics (K(m) and V(max)) were calculated from in vitro trials of gradients of extracellular tyrosine concentrations in fibroblast cultures. RESULTS: An association between patients with schizophrenia and their mothers were found for a low K(m) indicating maternal inheritance. Mothers displaying a low K(m) performed worse on the neuropsychological tests compared to mothers with normal K(m). Corresponding relationships between a low K(m) and neurocognitive dysfunction had previously been found for the patients. CONCLUSIONS: An aberrant tyrosine transport across plasma membrane may constitute a biological marker for an endophenotype within the schizophrenia spectrum with low cognitive functioning. A plausible mode for genetic transmission is maternal inheritance.

Functional characterization of tyrosine transport in fibroblast cells from healthy controls.

Human fibroblast cells are an advantageous model to study the transport of amino acids across cell membranes, since one can control the environmental factors. A major problem in all earlier studies is the lack of precise and detailed knowledge regarding the expression and functionality of tyrosine transporters in human fibroblasts. This motivated us to perform a systematic functional characterization of the tyrosine transport in fibroblast cells with respect to the isoforms of system-L (LAT1, LAT2, LAT3, LAT4), which is the major transporter of tyrosine. Ten (n=10) fibroblast cell lines from healthy volunteers were included in the study. Uptake of L-[U-14C] tyrosine in fibroblasts was measured using the cluster tray method in the presence and absence of excess concentrations of various combinations of inhibitors. This study demonstrated that LAT1 is involved in 90% of total uptake of tyrosine and also around 51% of alanine. Not more than 10% can be accounted for by LAT2, LAT3 and LAT4 isoforms. LAT2 seems to be functionally weak in uptake of tyrosine while LAT3 and LAT4 contributed around 7%. 10% could be contributed by system-A (ATA2 isoform). Alanine consequently inhibited the tyrosine transport by up to 60%. Tyrosine transport through the LAT1 isoform has a higher affinity compared to system-L. In conclusion, the LAT1 isoform is the major transporter of tyrosine in human fibroblast cells. Competition between tyrosine and alanine for transport is shown to exist, probably between LAT1 and LAT2 isoforms. This study established fibroblast cells as a suitable experimental model for studying amino acid transport defects in humans.

Aberrant amino acid transport in fibroblasts from children with autism.

Autism is a developmental, cognitive disorder clinically characterized by impaired social interaction, communication and restricted behaviours. The present study was designed to explore whether an abnormality in transport of tyrosine and/or alanine is present in children with autism. Skin biopsies were obtained from 11 children with autism (9 boys and 2 girls) fulfilling the DSM-IV diagnostic criteria for autistic disorder and 11 healthy male control children. Transport of amino acids tyrosine and alanine across the cell membrane of cultured fibroblasts was studied by the cluster tray method. The maximal transport capacity, V(max) and the affinity constant of the amino acid binding sites, K(m), were determined. Significantly increased V(max) for alanine (p=0.014) and increased K(m) for tyrosine (p=0.007) were found in children with autism. The increased transport capacity of alanine across the cell membrane and decreased affinity for transport sites of tyrosine indicates the involvement of two major amino acid transport systems (L- and A-system) in children with autism. This may influence the transport of several other amino acids across the blood-brain-barrier. The significance of the findings has to be further explored.

Coagulase-negative staphylococci isolated from sternal wound infections after cardiac surgery: attachment to and accumulation on sternal fixation stainless steel wires.

Sternal wound infection (SWI) is a serious complication after cardiac surgery. Coagulase-negative staphylococci (CoNS) have been found to be the most common pathogen involved in this postoperative infection related to implanted foreign materials, i.e. sternal fixation wires made from stainless steel. In this study a rapid and simple assay was developed for studying attachment and accumulation of CoNS on stainless steel wires in vitro using [(3)H] thymidine. The method showed a potential to detect differences in the dynamics of the adherence patterns among various CoNS isolates. However, no differences in attachment and accumulation were found between isolates causing deep SWI after cardiac surgery and contaminant isolates. In addition, there were no differences in the distribution of the ica operon between the two groups, as determined by polymerase chain reaction (PCR). Nevertheless, the ability to produce biofilm was found to be present significantly more frequently among SWI isolates than among contaminants.

Support for limited brain availability of tyrosine in patients with schizophrenia.

Several mechanisms have been suggested to account for altered dopaminergic neurotransmission in schizophrenia. The brain is the only organ for which amino-acid transport is limited and competition for transport over the blood-brain barrier (BBB) occurs at physiological plasma concentrations. One line of research suggests that patients with schizophrenia have altered brain levels of the essential amino acid tyrosine, the precursor for the synthesis of dopamine. The most common hypothesis is that less tyrosine is available because of competition with elevated levels of other amino acids. By consequence, the synthesis of dopamine in the brain will decrease. In contrast, another line of evidence suggests a change in the affinity for one of the transport proteins. A limitation of this research has been that the systems for amino-acid transport across the BBB have not been fully characterized at a molecular or functional level. The L system is the major system for transport of tyrosine across cell membranes including the BBB. The A system is also involved in this transport. Earlier in-vitro studies using fibroblasts have demonstrated a normal L system in schizophrenia but nevertheless reduced tyrosine transport. The combination of molecular research, fibroblast techniques, and brain imaging provides a new basis for clinical research on the role of amino-acid membrane transport in schizophrenia.

Tyrosine transport in fibroblasts from healthy volunteers and patients with schizophrenia.

Aberrant tyrosine transport across the fibroblast membrane, as measured by lower Vmax and/or lower Km is a repeated finding in patients with schizophrenia. The aim of this study was to investigate the importance of two major transporters, the L- and A-systems and tyrosine transport in fibroblast cell lines from patients with schizophrenia and healthy volunteers. Fibroblast cell lines, n=6 from healthy volunteers and n=6 from patients with schizophrenia, were included in the study. Uptake of [14-C] L-tyrosine in fibroblasts was measured using the cluster tray method in absence and presence of inhibitors. The uptake of tyrosine by the L-system was evaluated with the inhibitor 2-aminobicyclo heptane-2-carboxylic acid (BCH) and the A-system with the inhibitor nonmetabolized methyl-aminoisobutyric acid (MeAIB). Using [14-C] MeAIB the functionality of system A isoform 2, ATA2, was tested. BCH inhibited the uptake of tyrosine with 90%, showing that tyrosine transport in fibroblasts is mainly transported by the L-system. Not more than 10% could be contributed by the A-system. Excess of MeAIB did not influence tyrosine kinetics. Moreover, MeAIB kinetics did not differ between the patients and the controls. In conclusion, aberrant tyrosine transport observed in patients with schizophrenia is probably linked to the one of the L-systems and does not seem to involve the ATA2 transporter.

Kinetics of tyrosine transport and cognitive functioning in schizophrenia.

BACKGROUND: Tyrosine supplementation in humans has been shown to improve cognitive functioning. Several studies have demonstrated a decreased maximal transport capacity of tyrosine (Vmax) across the cell membrane and an increased affinity (Km) of tyrosine to membrane binding sites in schizophrenic patients. A lack of tyrosine for dopamine synthesis with impairment of dopaminergic transmission could impair cognitive functioning. Aberrant tyrosine kinetics in patients with schizophrenia might therefore be associated with cognitive dysfunction--a core feature of schizophrenia. METHODS: Tyrosine kinetics was determined in cultured fibroblasts from 36 schizophrenic patients. The kinetic parameters Vmax and Km were calculated and then the patients were divided into two groups according to the median of the kinetic parameters. A comprehensive neuropsychological test battery was used to evaluate cognitive functioning. RESULTS: Patients with low Km (below the median) had poorer cognitive performance than patients with high Km (above the median). Vmax did not discriminate schizophrenic patients with cognitive dysfunction to the same extent. CONCLUSIONS: Changes in tyrosine transport probably influence cognitive functioning via the dopamine system. However, our findings of a relation between low Km and cognitive dysfunction may have a more complex background. It is suggested that the connection is related to genetically determined membrane factors that disturb communication/transmission among neurons.