AGAT, GAMT and SLC6A8 distribution in the central nervous system, in relation to creatine deficiency syndromes: a review

Integration of mult-omics and nucleotide metabolism reprogramming signature analysis reveals gastric cancer immunological and prognostic features

BACKGROUND

Gastric cancer is a frequent and lethal solid tumor that has a poor prognosis and treatment result. Reprogramming of nucleotide metabolism is a characteristic of cancer development and progression.

METHODS

We used a variety of machine learning techniques to create a novel nucleotide metabolism-related index (NMRI) using gastric cancer sample data obtained from the TCGA and GEO databases. This index is based on genes associated to nucleotide metabolism. Gastric cancer patients were categorized into high and low NMRI groups based on NMRI results. The clinical features, tumor immune microenvironment, response to chemotherapy, and response to immunotherapy were then thoroughly examined. In vitro experiments were then used to confirm the biological role of SERPINE1 in gastric cancer.

RESULTS

The four nucleotide metabolism-related genes that make up NMRI (GAMT, ORC1, CNGB3, and SERPINE1) were verified in an external dataset and are a valid predictor of prognosis for patients with gastric cancer. The high NMRI group was more responsive to immunotherapy and had greater levels of immune cell infiltration than the low NMRI group. The proliferation and migration of stomach cancer was shown to be decreased by SERPINE1 knockdown in vitro.

CONCLUSIONS

This study's NMRI can reliably predict a patient's prognosis for stomach cancer and pinpoint the patient group that will benefit from immunotherapy, offering important new information on the clinical treatment of stomach cancer.

Arginine, glycine, and creatine supplementation improves symptoms in a female with creatine transporter deficiency

X-linked creatine transporter deficiency is caused by hemizygous or heterozygous pathogenic variants in SLC6A8 that cause neuropsychiatric symptoms because of impaired uptake of creatine into tissues throughout the body. Small cohorts have suggested that supplementation of creatine, arginine, and glycine can stop disease progression in males, but only six cases of supplementation in females have been published. Here, we present a female with a de-novo pathogenic SLC6A8 variant who had ongoing weight loss, mild intellectual disability, and neuropsychiatric symptoms. Magnetic resonance spectroscopy of the brain showed reduced creatine on all acquired spectra. The patient was started on creatine-monohydrate, l-arginine, and l-glycine supplementation, and she had significant symptomatic improvement within the following 3 weeks. After 8 months of supplementation, magnetic resonance spectroscopy showed improved creatine concentrations with normalizing semiquantitative ratios with other brain metabolites. Current data supports clinicians trialing creatine, arginine, and glycine supplements for female patients with creatine transporter deficiency.

Creatine supplementation research fails to support the theoretical basis for an effect on cognition: Evidence from a systematic review

Creatine supplementation has been put forward as a possible aid to cognition, particularly for vegans, vegetarians, the elderly, sleep deprived and hypoxic individuals. However, previous narrative reviews have only provided limited support for these claims. This is despite the fact that research has shown that creatine supplementation can induce increased brain concentrations of creatine, albeit to a limited extent. We carried out a systematic review to examine the current state of affairs. The review supported claims that creatine supplementation can increases brain creatine content but also demonstrated somewhat equivocal results for effects on cognition. It does, however, provide evidence to suggest that more research is required with stressed populations, as supplementation does appear to significantly affect brain content. Issues with research design, especially supplementation regimens, need to be addressed. Future research must include measurements of creatine brain content.

Clinical Characteristics, Developmental Trajectory, and Caregiver Burden of Patients With Creatine Transporter Deficiency (SLC6A8)

BACKGROUND AND OBJECTIVES

Creatine transporter deficiency (CTD) is a rare X-linked genetic disorder characterized by intellectual disability (ID). We evaluated the clinical characteristics and trajectory of patients with CTD and the impact of the disease on caregivers to identify relevant endpoints for future therapeutic trials.

METHODS

As part of a French National Research Program, patients with CTD were included based on (1) a pathogenic SLC6A8 variant and (2) ID and/or autism spectrum disorder. Families and patients were referred by the physician who ordered the genetic analysis through Reference Centers of ID from rare causes and inherited metabolic diseases. After we informed the patients and their parents/guardians about the study, all of them gave written consent and were included. A control group of age-matched and sex-matched patients with Fragile X syndrome was also included. Physical examination, neuropsychological assessments, and caregiver impact were assessed. All data were analyzed using R software.

RESULTS

Thirty-one patients (27 male, 4 female) were included (25/31 aged 18 years or younger). Most of the patients (71%) had symptoms at <24 months of age. The mean age at diagnosis was 6.5 years. Epilepsy occurred in 45% (mean age at onset: 8 years). Early-onset behavioral disorder occurred in 82%. Developmental trajectory was consistently delayed (fine and gross motor skills, language, and communication/sociability). Half of the patients with CTD had axial hypotonia during the first year of life. All patients were able to walk without help, but 7/31 had ataxia and only 14/31 could walk tandem gait. Most of them had abnormal fine motor skills (27/31), and most of them had language impairment (30/31), but 12/23 male patients (52.2%) completed the Peabody Picture Vocabulary Test. Approximately half (14/31) had slender build. Most of them needed nursing care (20/31), generally 1-4 h/d. Adaptive assessment (Vineland) confirmed that male patients with CTD had moderate-to-severe ID. Most caregivers (79%) were at risk of burnout, as shown by Caregiver Burden Inventory (CBI) > 36 (significantly higher than for patients with Fragile X syndrome) with a high burden of time dependence.

DISCUSSION

In addition to clinical endpoints, such as the assessment of epilepsy and the developmental trajectory of the patient, the Vineland scale, PPVT5, and CBI are of particular interest as outcome measures for future trials.

TRIAL REGISTRATION INFORMATION

ANSM Registration Number 2010-A00327-32.

Epigenetic alterations in creatine transporter deficiency: a new marker for dodecyl creatine ester therapeutic efficacy monitoring

Creatine transporter deficiency (CTD) is an X-linked disease caused by mutations in the Slc6a8 gene. The impaired creatine uptake in the brain leads to developmental delays with intellectual disability. We hypothesized that deficient creatine uptake in CTD cerebral cells impact methylation balance leading to alterations of genes and proteins expression by epigenetic mechanism. In this study, we determined the status of nucleic acid methylation in both Slc6a8 knockout mouse model and brain organoids derived from CTD patients' cells. We also investigated the effect of dodecyl creatine ester (DCE), a promising prodrug that increases brain creatine content in the mouse model of CTD. The level of nucleic acid methylation was significantly reduced compared to healthy controls in both in vivo and in vitro CTD models. This hypo-methylation tended to be regulated by DCE treatment in vivo. These results suggest that increased brain creatine after DCE treatment restores normal levels of DNA methylation, unveiling the potential of using DNA methylation as a marker to monitor the drug efficacy.

Single dose creatine improves cognitive performance and induces changes in cerebral high energy phosphates during sleep deprivation

The inverse effects of creatine supplementation and sleep deprivation on high energy phosphates, neural creatine, and cognitive performances suggest that creatine is a suitable candidate for reducing the negative effects of sleep deprivation. With this, the main obstacle is the limited exogenous uptake by the central nervous system (CNS), making creatine only effective over a long-term diet of weeks. Thus far, only repeated dosing of creatine over weeks has been studied, yielding detectable changes in CNS levels. Based on the hypothesis that a high extracellular creatine availability and increased intracellular energy consumption will temporarily increase the central creatine uptake, subjects were orally administered a high single dose of creatinemonohydrate (0.35 g/kg) while performing cognitive tests during sleep deprivation. Two consecutive 31P-MRS scans, 1H-MRS, and cognitive tests were performed each at evening baseline, 3, 5.5, and 7.5 h after single dose creatine (0.35 g/kg) or placebo during sub-total 21 h sleep deprivation (SD). Our results show that creatine induces changes in PCr/Pi, ATP, tCr/tNAA, prevents a drop in pH level, and improves cognitive performance and processing speed. These outcomes suggest that a high single dose of creatine can partially reverse metabolic alterations and fatigue-related cognitive deterioration.

Characterization of seizures and EEG findings in creatine transporter deficiency due to SLC6A8 mutation

Seizures occur in up to 59% of boys with creatine transporter deficiency (CTD). While seizure phenotypes have been previously described, electroencephalogram (EEG) findings have only been reported in several case reports. In this prospective observational study, we report seizure characteristics and EEG findings in combination with neurobehavioral and SLC6A8 pathogenic variants in twenty males with CTD. Eighteen study participants (SP) underwent video-EEG, and seven had follow-up EEG recordings. Seizures typically occurred by age of 2 years. Thirteen (65%) had non-febrile seizures, requiring anti-seizure medications in nine. Four had febrile seizures. Seizures were bilateral tonic-clonic in 7 SP and focal impaired awareness in 5 SP; often responding to 1 to 2 antiseizure medications. EEG showed slowing in 5 SP, beta activity in 6 SP, and focal/multifocal, and/or generalized epileptiform activity in 9 SP. Follow-up EEGs in 7 SP showed emergence of epileptiform activity in 1 SP, and increased activity in 2 SP. In conclusion, seizures were frequent in our cohort but tended to respond to antiseizure medications. Longitudinal follow up provided further insight into emergence of seizures and EEG abnormalities soliciting future studies with long term follow up. Biomarkers of epileptogenicity in CTD are needed to predict seizures in this population.

Probing binding and occlusion of substrate in the human creatine transporter-1 by computation and mutagenesis

In chordates, energy buffering is achieved in part through phosphocreatine, which requires cellular uptake of creatine by the membrane-embedded creatine transporter (CRT1/SLC6A8). Mutations in human slc6a8 lead to creatine transporter deficiency syndrome, for which there is only limited treatment. Here, we used a combined homology modeling, molecular dynamics, and experimental approach to generate a structural model of CRT1. Our observations support the following conclusions: contrary to previous proposals, C144, a key residue in the substrate binding site, is not present in a charged state. Similarly, the side chain D458 must be present in a protonated form to maintain the structural integrity of CRT1. Finally, we identified that the interaction chain Y148-creatine-Na+ is essential to the process of occlusion, which occurs via a "hold-and-pull" mechanism. The model should be useful to study the impact of disease-associated point mutations on the folding of CRT1 and identify approaches which correct folding-deficient mutants.

Suggestion of creatine as a new neurotransmitter by approaches ranging from chemical analysis and biochemistry to electrophysiology

The discovery of a new neurotransmitter, especially one in the central nervous system, is both important and difficult. We have been searching for new neurotransmitters for 12 y. We detected creatine (Cr) in synaptic vesicles (SVs) at a level lower than glutamate and gamma-aminobutyric acid but higher than acetylcholine and 5-hydroxytryptamine. SV Cr was reduced in mice lacking either arginine:glycine amidinotransferase (a Cr synthetase) or SLC6A8, a Cr transporter with mutations among the most common causes of intellectual disability in men. Calcium-dependent release of Cr was detected after stimulation in brain slices. Cr release was reduced in Slc6a8 and Agat mutants. Cr inhibited neocortical pyramidal neurons. SLC6A8 was necessary for Cr uptake into synaptosomes. Cr was found by us to be taken up into SVs in an ATP-dependent manner. Our biochemical, chemical, genetic, and electrophysiological results are consistent with the possibility of Cr as a neurotransmitter, though not yet reaching the level of proof for the now classic transmitters. Our novel approach to discover neurotransmitters is to begin with analysis of contents in SVs before defining their function and physiology.

"Heads Up" for Creatine Supplementation and its Potential Applications for Brain Health and Function

There is emerging interest regarding the potential beneficial effects of creatine supplementation on indices of brain health and function. Creatine supplementation can increase brain creatine stores, which may help explain some of the positive effects on measures of cognition and memory, especially in aging adults or during times of metabolic stress (i.e., sleep deprivation). Furthermore, creatine has shown promise for improving health outcome measures associated with muscular dystrophy, traumatic brain injury (including concussions in children), depression, and anxiety. However, whether any sex- or age-related differences exist in regard to creatine and indices of brain health and function is relatively unknown. The purpose of this narrative review is to: (1) provide an up-to-date summary and discussion of the current body of research focusing on creatine and indices of brain health and function and (2) discuss possible sex- and age-related differences in response to creatine supplementation on brain bioenergetics, measures of brain health and function, and neurological diseases.

Laboratory Diagnosis of Cerebral Creatine Deficiency Syndromes by Determining Creatine and Guanidinoacetate in Plasma and Urine

Cerebral creatine deficiency syndromes are caused by the dysfunctional creatine biosynthesis or transport and comprise three hereditary neurodevelopmental defects including arginine-glycine amidinotransferase (AGAT), guanidinoacetate methyltransferase (GAMT), and creatine transporter deficiencies. All conditions are characterized by seizures, intellectual disability, and behavioral abnormalities. Laboratory diagnosis of these disorders relies on the determination of creatine and guanidinoacetate concentrations in both plasma and urine. Here we describe a rapid quantitative UPLC/MS/MS method for the simultaneous determination of these analytes using a normal-phase HILIC column after analyte derivatization. The approach is suitable for neonatal screening follow-ups and monitoring of the treatment for creatine deficiency syndromes.

Cooperative Binding of Substrate and Ions Drives Forward Cycling of the Human Creatine Transporter-1

Creatine serves as an ATP buffer and is thus an integral component of cellular energy metabolism. Most cells maintain their creatine levels via uptake by the creatine transporter (CRT-1, SLC6A8). The activity of CRT-1, therefore, is a major determinant of cytosolic creatine concentrations. We determined the kinetics of CRT-1 in real time by relying on electrophysiological recordings of transport-associated currents. Our analysis revealed that CRT-1 harvested the concentration gradient of NaCl and the membrane potential but not the potassium gradient to achieve a very high concentrative power. We investigated the mechanistic basis for the ability of CRT-1 to maintain the forward cycling mode in spite of high intracellular concentrations of creatine: this is achieved by cooperative binding of substrate and co-substrate ions, which, under physiological ion conditions, results in a very pronounced (i.e. about 500-fold) drop in the affinity of creatine to the inward-facing state of CRT-1. Kinetic estimates were integrated into a mathematical model of the transport cycle of CRT-1, which faithfully reproduced all experimental data. We interrogated the kinetic model to examine the most plausible mechanistic basis of cooperativity: based on this systematic exploration, we conclude that destabilization of binary rather than ternary complexes is necessary for CRT-1 to maintain the observed cytosolic creatine concentrations. Our model also provides a plausible explanation why neurons, heart and skeletal muscle cells must express a creatine releasing transporter to achieve rapid equilibration of the intracellular creatine pool.

Current and potential new treatment strategies for creatine deficiency syndromes

Creatine deficiency syndromes (CDS) are inherited metabolic disorders caused by mutations in GATM, GAMT and SLC6A8 and mainly affect central nervous system (CNS). AGAT- and GAMT-deficient patients lack the functional brain endogenous creatine (Cr) synthesis pathway but express the Cr transporter SLC6A8 at blood-brain barrier (BBB), and can thus be treated by oral supplementation of high doses of Cr. For Cr transporter deficiency (SLC6A8 deficiency or CTD), current treatment strategies benefit one-third of patients. However, as their phenotype is not completely reversed, and for the other two-thirds of CTD patients, the development of novel more effective therapies is needed. This article aims to review the current knowledge on Cr metabolism and CDS clinical aspects, highlighting their current treatment possibilities and the most recent research perspectives on CDS potential therapeutics designed, in particular, to bring new options for the treatment of CTD.

Analysis of Host Jejunum Transcriptome and Associated Microbial Community Structure Variation in Young Calves with Feed-Induced Acidosis

Diet-induced acidosis imposes a health risk to young calves. In this study, we aimed to investigate the host jejunum transcriptome changes, along with its microbial community variations, using our established model of feed-induced ruminal acidosis in young calves. Eight bull calves were randomly assigned to two diet treatments beginning at birth (a starch-rich diet, Aci; a control diet, Con). Whole-transcriptome RNA sequencing was performed on the jejunum tissues collected at 17 weeks of age. Ribosomal RNA reads were used for studying microbial community structure variations in the jejunum. A total of 853 differentially expressed genes were identified (402 upregulated and 451 downregulated) between the two groups. The cell cycle and the digestion and absorption of protein in jejunal tissue were affected by acidosis. Compared to the control, genera of Campylobacter, Burkholderia, Acidaminococcus, Corynebacterium, and Olsenella significantly increased in abundance in the Aci group, while Lachnoclostridium and Ruminococcus were significantly lower in the Aci group. Expression changes in the AXL gene were associated with the abundance variations of a high number of genera in jejunum. Our study provided a snapshot of the transcriptome changes in the jejunum and its associated meta-transcriptome changes in microbial communities in young calves with feed-induced acidosis.

An Electrochemical Approach for the Selective Detection of Cancer Metabolic Creatine Biomarker with Porous Nano-Formulated CMNO Materials Decorated Glassy Carbon Electrode

The facile wet-chemical technique was used to prepare the low-dimensional nano-formulated porous mixed metal oxide nanomaterials (CuO.Mn2O3.NiO; CMNO NMs) in an alkaline medium at low temperature. Detailed structural, morphological, crystalline, and functional characterization of CMNO NMs were performed by X-ray photoelectron spectroscopy (XPS), powder X-ray diffraction (XRD), ultraviolet-visible spectroscopy (UV-vis), Fourier-transform infrared spectroscopy (FTIR), field emission scanning electron microscopy (FESEM), and energy-dispersive X-ray spectroscopy (EDS) analyses. An efficient and selective creatine (CA) sensor probe was fabricated by using CMNO NMs decorated onto glassy carbon electrode (GCE) as CMNO NMs/GCE by using Nafion adhesive (5% suspension in ethanol). The relation of current versus the concentration of CA was plotted to draw a calibration curve of the CMNO NMs/GCE sensor probe, which was found to have a very linear value (r2 = 0.9995) over a large dynamic range (LDR: 0.1 nM~0.1 mM) for selective CA detection. The slope of LDR by considering the active surface area of GCE (0.0316 cm2) was applied to estimate the sensor sensitivity (14.6308 µAµM-1 cm-2). Moreover, the detection limit (21.63 ± 0.05 pM) of CMNO MNs modified GCE was calculated from the signal/noise (S/N) ratio at 3. As a CA sensor probe, it exhibited long-term stability, good reproducibility, and fast response time in the detection of CA by electrochemical approach. Therefore, this research technique is introduced as a promising platform to develop an efficient sensor probe for cancer metabolic biomarker by using nano-formulated mixed metal oxides for biochemical as well as biomedical research for the safety of health care fields.

The Creatine Transporter Unfolded: A Knotty Premise in the Cerebral Creatine Deficiency Syndrome

Creatine provides cells with high-energy phosphates for the rapid reconstitution of hydrolyzed adenosine triphosphate. The eponymous creatine transporter (CRT1/SLC6A8) belongs to a family of solute carrier 6 (SLC6) proteins. The key role of CRT1 is to translocate creatine across tissue barriers and into target cells, such as neurons and myocytes. Individuals harboring mutations in the coding sequence of the human CRT1 gene develop creatine transporter deficiency (CTD), one of the pivotal underlying causes of cerebral creatine deficiency syndrome. CTD encompasses an array of clinical manifestations, including severe intellectual disability, epilepsy, autism, development delay, and motor dysfunction. CTD is characterized by the absence of cerebral creatine, which implies an indispensable role for CRT1 in supplying the brain cells with creatine. CTD-associated variants dramatically reduce or abolish creatine transport activity by CRT1. Many of these are point mutations that are known to trigger folding defects, leading to the retention of encoded CRT1 proteins in the endoplasmic reticulum and precluding their delivery to the cell surface. Misfolding of several related SLC6 transporters also gives rise to detrimental pathologic conditions in people; e.g., mutations in the dopamine transporter induce infantile parkinsonism/dystonia, while mutations in the GABA transporter 1 cause treatment-resistant epilepsy. In some cases, folding defects are amenable to rescue by small molecules, known as pharmacological and chemical chaperones, which restore the cell surface expression and transport activity of the previously non-functional proteins. Insights from the recent molecular, animal and human case studies of CTD add toward our understanding of this complex disorder and reveal the wide-ranging effects elicited upon CRT1 dysfunction. This grants novel therapeutic prospects for the treatment of patients afflicted with CTD, e.g., modifying the creatine molecule to facilitate CRT1-independent entry into brain cells, or correcting folding-deficient and loss-of-function CTD variants using pharmacochaperones and/or allosteric modulators. The latter justifies a search for additional compounds with a capacity to correct mutation-specific defects.

Locus heterogeneity in two siblings presenting with developmental delay, intellectual disability and autism spectrum disorder

Correct diagnosis of children presenting with developmental delay and intellectual disability remains challenging due to the complex and heterogeneous etiology. High throughput sequencing technologies like exome sequencing have become more commonly available and are significantly improving genetic testing. We present two siblings - a 14-year old male and an 8-year old female patient - with a similar clinical phenotype that was characterized by combined developmental delay primarily affecting speech, mild to moderate intellectual disability, behavioral abnormalities, and autism spectrum disorder, but with no congenital anomalies. The sister showed additional muscular hypotonia and more pronounced dysmorphic features compared to her brother. Both parents had psychiatric disorders and mild to moderate intellectual disability. A common genetic etiology in the siblings was suspected. Metabolic, psychological and neuroradiological examinations were complemented by basic genetic testing including chromosome analysis and array comparative genomics hybridization analysis (CGH), followed by exome sequencing and combined data analysis of the family. Exome sequencing identified two different underlying genetic conditions: in the sister, a maternally inherited pathogenic variant c.1661C > T, p.Pro554Leu in SLC6A8 (NM_005629.4) was identified causing cerebral creatine deficiency syndrome 1 (MIM #300352) which was confirmed by MR spectroscopy and treated accordingly. In the brother, a paternally inherited 16p13.11 duplication was identified by exome sequencing and considered to be likely associated with his and possibly his father's phenotype. The 16p13.11 duplication had been previously identified in an array CGH but had not been prioritized due to the lack of segregation in the siblings. In conclusion, we report a case of intra-familial locus heterogeneity of developmental delay in two siblings. We advocate for the need of unbiased and comprehensive genetic testing to provide accurate diagnosis despite locus heterogeneity.

Primary creatine deficiency syndrome as a potential missed diagnosis in children with psychomotor delay and seizure: case presentation with two novel variants and literature review

Creatine is the main source of energy for the brain. Primary creatine deficiency syndromes (PCDSs) are inborn error of metabolism of creatine synthesis. Symptoms of central nervous system involvement are the most common clinical manifestations in these disorders. We reviewed medical records of all genetically confirmed patients diagnosed by whole exome sequencing who were referred to Myelin and Neurodegenerative Disorders Clinic, Children's Medical Center, Tehran, Iran, from May 2016 to Dec 2018. A literature review was conducted on clinical and genomic variability of PCDS to compare our patients with previously reported cases. We report two patients with creatine deficiency among a cohort of 550 registered cases out of which 200 patients had a genetically confirmed neurodegenerative disorder diagnosis. The main complain in the first patient with creatine transporter (CRTR) deficiency was seizure and genetic study in this patient identified a novel hemizygote variant of "c.92 > T; p.Pro31Leu" in the first exon of SLC6A8 gene. The second patient with guanidinoacetate methyltransferase (GAMT) deficiency had an unknown motor and speech delay as the striking manifestation and molecular assay revealed a novel homozygote variant of "c.134G > A; p.Trp45*" in the first exon of GAMT gene. PCDSs usually are associated with nonspecific neurologic symptoms. The first presented case had a mean delayed diagnosis of 5 years. Therefore, in children with unexplained neurologic features including developmental delay and/or regression, mental disability and repeated seizures without any significant findings in metabolic studies, PCDSs can be considered as a differential diagnosis and molecular analysis can be helpful for the precise diagnosis and treatment.

Creatine as a Neuroprotector: an Actor that Can Play Many Parts

Creatine is a nitrogenous organic acid that plays a central role as an energy buffer in high energy demanding systems, including the muscular and the central nervous system. It can be acquired from diet or synthesized endogenously, and its main destination is the system creatine/phosphocreatine that strengthens cellular energetics via a temporal and spatial energy buffer that can restore cellular ATP without a reliance on oxygen. This compound has been proposed to possess secondary roles, such as direct and indirect antioxidant, immunomodulatory agent, and possible neuromodulator. However, these effects may be associated with its bioenergetic role in the mitochondria. Given the fundamental roles that creatine plays in the CNS, several preclinical and clinical studies have tested the potential that creatine has to treat degenerative disorders. However, although in vitro and in vivo animal models are highly encouraging, most clinical trials fail to reproduce positive results suggesting that the prophylactic use for neuroprotection in at-risk populations or patients is the most promising field. Nonetheless, the only clearly positive data of the creatine supplementation in human beings are related to the (rare) creatine deficiency syndromes. It seems critical that future studies must establish the best dosage regime to increase brain creatine in a way that can relate to animal studies, provide new ways for creatine to reach the brain, and seek larger experimental groups with biomarkers for prediction of efficacy.

Oligodendrocyte Bioenergetics in Health and Disease

The human brain weighs approximately 2% of the body; however, it consumes about 20% of a person’s total energy intake. Cellular bioenergetics in the central nervous system involves a delicate balance between biochemical processes engaged in energy conversion and those responsible for respiration. Neurons have high energy demands, which rely on metabolic coupling with glia, such as with oligodendrocytes and astrocytes. It has been well established that astrocytes recycle and transport glutamine to neurons to make the essential neurotransmitters, glutamate and GABA, as well as shuttle lactate to support energy synthesis in neurons. However, the metabolic role of oligodendrocytes in the central nervous system is less clear. In this review, we discuss the energetic demands of oligodendrocytes in their survival and maturation, the impact of altered oligodendrocyte energetics on disease pathology, and the role of energetic metabolites, taurine, creatine, N-acetylaspartate, and biotin, in regulating oligodendrocyte function.

Functional assessment of creatine transporter in control and X-linked SLC6A8-deficient fibroblasts

Creatine transporter is currently the focus of renewed interest with emerging roles in brain neurotransmission and physiology, and the bioenergetics of cancer metastases. We here report on amendments of a standard creatine uptake assay which might help clinical chemistry laboratories to extend their current range of measurements of creatine and metabolites in body fluids to functional enzyme explorations. In this respect, short incubation times and the use of a stable-isotope-labeled substrate (D₃-creatine) preceded by a creatine wash-out step from cultured fibroblast cells by removal of fetal bovine serum (rich in creatine) from the incubation medium are recommended. Together, these measures decreased, by a first order of magnitude, creatine concentrations in the incubation medium at the start of creatine-uptake studies and allowed to functionally discriminate between 4 hemizygous male and 4 heterozygous female patients with X-linked SLC6A8 deficiency, and between this cohort of eight patients and controls. The functional assay corroborated genetic diagnosis of SLC6A8 deficiency. Gene anomalies in our small cohort included splicing site (c.912G > A [p.Ile260_Gln304del], c.778-2A > G and c.1495 + 2 T > G), substitution (c.407C > T) [p.Ala136Val] and deletion (c.635_636delAG [p.Glu212Valfs*84] and c.1324delC [p.Gln442Lysfs*21]) variants with reduced creatine transporter function validating their pathogenicity, including that of a previously unreported c.1324delC variant. The present assay adaptations provide an easy, reliable and discriminative manner for exploring creatine transporter activity and disease variations. It might apply to drug testing or other evaluations in the genetic and metabolic horizons covered by the emerging functions of creatine and its transporter, in a way, however, requiring and completed by additional studies on female patients and blood-brain barrier permeability properties of selected compounds. As a whole, the proposed assay of creatine transporter positively adds to currently existing measurements of this transporter activity, and determining on a large scale the extent of its exact suitability to detect female patients should condition in the future its transfer in clinical practice.

Cognitive deficits and increases in creatine precursors in a brain-specific knockout of the creatine transporter gene Slc6a8

Creatine transporter (CrT; SLC6A8) deficiency (CTD) is an X-linked disorder characterized by severe cognitive deficits, impairments in language and an absence of brain creatine (Cr). In a previous study, we generated floxed Slc6a8 (Slc6a8 ^flox ) mice to create ubiquitous Slc6a8 knockout (Slc6a8^-/y ) mice. Slc6a8^-/y mice lacked whole body Cr and exhibited cognitive deficits. While Slc6a8^-/y mice have a similar biochemical phenotype to CTD patients, they also showed a reduction in size and reductions in swim speed that may have contributed to the observed deficits. To address this, we created brain-specific Slc6a8 knockout (bKO) mice by crossing Slc6a8^flox mice with Nestin-cre mice. bKO mice had reduced cerebral Cr levels while maintaining normal Cr levels in peripheral tissue. Interestingly, brain concentrations of the Cr synthesis precursor guanidinoacetic acid were increased in bKO mice. bKO mice had longer latencies and path lengths in the Morris water maze, without reductions in swim speed. In accordance with data from Slc6a8 ^-/y mice, bKO mice showed deficits in novel object recognition as well as contextual and cued fear conditioning. bKO mice were also hyperactive, in contrast with data from the Slc6a8 ^-/y mice. The results show that the loss of cerebral Cr is responsible for the learning and memory deficits seen in ubiquitous Slc6a8^-/y mice.

Benefits and drawbacks of guanidinoacetic acid as a possible treatment to replenish cerebral creatine in AGAT deficiency

Arginine-glycine amidinotransferase (AGAT) deficiency is a rare inherited metabolic disorder that severely affects brain bioenergetics. Characterized by mental retardation, language impairment, and behavioral disorders, AGAT deficiency is a treatable condition, where long-term creatine supplementation usually restores brain creatine levels and improves its clinical features. In some cases of AGAT deficiency, creatine treatment might be somewhat limited due to possible shortcomings in performance and transport of creatine to the brain. Guanidinoacetic acid (GAA), a direct metabolic precursor of creatine, has recently been suggested as a possible alternative to creatine to tackle brain creatine levels in experimental medicine. AGAT patients might benefit from oral GAA due to upgraded bioavailability and convenient utilization of the compound, while possible drawbacks (e.g. brain methylation issues, neurotoxicity, and hyperhomocysteinemia) should be accounted as well.

First reported Chinese case of guanidinoacetate methyltransferase deficiency in a 4-year-old child

Guanidinoacetate methyltransferase (GAMT) deficiency is a rare inherited disorder characterized by creatine (Cr) depletion and guanidinoacetate (GAA) accumulation in body fluids. We report the first identified Chinese case, diagnosed in a 4-year-old girl with onset of global developmental. Low Cr and high GAA levels were detected in her serum and urine, and low Cr level in her brain. Compound heterozygous variants in GAMT gene were found, including a previously reported variant at c.491dupG which was inherited from her mother and a novel variant at c.564G>T, which was inherited from her father. The Cr and GAA levels returned back to normal after 3 months of treatment. After one year of treatment, the patient stopped taking antiepileptic drugs and her electroencephalogram (EEG) was also back to normal. The girl was followed up for five years and exhibited good results beyond our expectation. The results have shown that protein restriction with high-dose ornithine and creatine supplements have strong therapeutic potential for our patient.

Microphthalmia-associated transcription factor ensures the elongation of axons and dendrites in the mouse frontal cortex

Long interspersed element-1 (LINE-1) is a mammalian transposable element, and its genomic insertion could cause neurological disorders in humans. Incidentally, LINE-1 is present in intron 3 of the microphthalmia-associated transcription factor (Mitf) gene of the black-eyed white mouse (Mitf^mi-bw allele). Mice homozygous for the Mitf^mi-bw allele show the white coat color with black eye and deafness. Here, we explored the functional consequences of the LINE-1 insertion in the Mitf gene using homozygous Mitf^mi-bw mice on the C3H background (C3H-bw mice) or on the C57BL/6 background (bw mice). The open-field test showed that C3H-bw mice moved more irregularly in an unfamiliar environment during the 20-min period, compared to wild-type mice, suggesting the altered emotionality. Moreover, C3H-bw mice showed the lower serum creatinine levels, which may reflect the creatine deficiency. In fact, morphologically abnormal neurons and astrocytes were detected in the frontal cortex of bw mice. The immunohistochemical analysis of bw mouse tissues showed the lower intensity for expression of guanidinoacetate methyltransferase, a key enzyme in creatine synthesis, in neurons of the frontal cortex and in glomeruli and renal tubules. Thus, Mitf may ensure the elongation of axons and dendrites by maintaining creatine synthesis in the frontal cortex.

Creatine in the central nervous system: From magnetic resonance spectroscopy to creatine deficiencies

Creatine (Cr) is an important organic compound acting as intracellular high-energy phosphate shuttle and in energy storage. While located in most cells where it plays its main roles in energy metabolism and cytoprotection, Cr is highly concentrated in muscle and brain tissues, in which Cr also appears to act in osmoregulation and neurotransmission. This review discusses the basis of Cr metabolism, synthesis and transport within brain cells. The importance of Cr in brain function and the consequences of its impaired metabolism in primary and secondary Cr deficiencies are also discussed. Cr and phosphocreatine (PCr) in living systems can be well characterized using in vivo magnetic resonance spectroscopy (MRS). This review describes how ¹H MRS allows the measurement of Cr and PCr, and how ³¹P MRS makes it possible to estimate the creatine kinase (CK) rate constant and so detect dynamic changes in the Cr/PCr/CK system. Absolute quantification by MRS using creatine as internal reference is also debated. The use of in vivo MRS to study brain Cr in a non-invasive way is presented, as well as its use in clinical and preclinical studies, including diagnosis and treatment follow-up in patients.

Creatine Defects and Central Nervous System

Creatine deficiency syndromes are a group of disorders of creatine (Cr) synthesis and transport characterized by intellectual disability, language delay, epilepsy, autism spectrum disorder, and movement disorders secondary to decrease of Cr concentration in the brain. Synthesis defects are treatable, therefore an early diagnosis and treatment is essential. The aim of this article is to review the Cr metabolism and function in the central nervous system. We describe the optimal diagnostic protocol in Cr deficiency syndromes based on biochemical methods, neuroradiological (1H-MRS), and molecular analysis. Finally, a treatment approach of the different Cr deficiency syndromes is described.

Creatine synthesis and exchanges between brain cells: What can be learned from human creatine deficiencies and various experimental models?

While it has long been thought that most of cerebral creatine is of peripheral origin, the last 20 years has provided evidence that the creatine synthetic pathway (AGAT and GAMT enzymes) is expressed in the brain together with the creatine transporter (SLC6A8). It has also been shown that SLC6A8 is expressed by microcapillary endothelial cells at the blood-brain barrier, but is absent from surrounding astrocytes, raising the concept that the blood-brain barrier has a limited permeability for peripheral creatine. The first creatine deficiency syndrome in humans was also discovered 20 years ago (GAMT deficiency), followed later by AGAT and SLC6A8 deficiencies, all three diseases being characterized by creatine deficiency in the CNS and essentially affecting the brain. By reviewing the numerous and latest experimental studies addressing creatine transport and synthesis in the CNS, as well as the clinical and biochemical characteristics of creatine-deficient patients, our aim was to delineate a clearer view of the roles of the blood-brain and blood-cerebrospinal fluid barriers in the transport of creatine and guanidinoacetate between periphery and CNS, and on the intracerebral synthesis and transport of creatine. This review also addresses the question of guanidinoacetate toxicity for brain cells, as probably found under GAMT deficiency.

Genetic diversity and natural selection footprints of the glycine amidinotransferase gene in various human populations

The glycine amidinotransferase gene (GATM) plays a vital role in energy metabolism in muscle tissues and is associated with multiple clinically important phenotypes. However, the genetic diversity of the GATM gene remains poorly understood within and between human populations. Here we analyzed the 1,000 Genomes Project data through population genetics approaches and observed significant genetic diversity across the GATM gene among various continental human populations. We observed considerable variations in GATM allele frequencies and haplotype composition among different populations. Substantial genetic differences were observed between East Asian and European populations (F_ST = 0.56). In addition, the frequency of a distinct major GATM haplotype in these groups was congruent with population-wide diversity at this locus. Furthermore, we identified GATM as the top differentiated gene compared to the other statin drug response-associated genes. Composite multiple analyses identified signatures of positive selection at the GATM locus, which was estimated to have occurred around 850 generations ago in European populations. As GATM catalyzes the key step of creatine biosynthesis involved in energy metabolism, we speculate that the European prehistorical demographic transition from hunter-gatherer to farming cultures was the driving force of selection that fulfilled creatine-based metabolic requirement of the populations.

Maternal creatine supplementation affects the morpho-functional development of hippocampal neurons in rat offspring

Creatine supplementation has been shown to protect neurons from oxidative damage due to its antioxidant and ergogenic functions. These features have led to the hypothesis of creatine supplementation use during pregnancy as prophylactic treatment to prevent CNS damage, such as hypoxic-ischemic encephalopathy. Unfortunately, very little is known on the effects of creatine supplementation during neuron differentiation, while in vitro studies revealed an influence on neuron excitability, leaving the possibility of creatine supplementation during the CNS development an open question. Using a multiple approach, we studied the hippocampal neuron morphological and functional development in neonatal rats born by dams supplemented with 1% creatine in drinking water during pregnancy. CA1 pyramidal neurons of supplemented newborn rats showed enhanced dendritic tree development, increased LTP maintenance, larger evoked-synaptic responses, and higher intrinsic excitability in comparison to controls. Moreover, a faster repolarizing phase of action potential with the appearance of a hyperpolarization were recorded in neurons of the creatine-treated group. Consistently, CA1 neurons of creatine exposed pups exhibited a higher maximum firing frequency than controls. In summary, we found that creatine supplementation during pregnancy positively affects morphological and electrophysiological development of CA1 neurons in offspring rats, increasing neuronal excitability. Altogether, these findings emphasize the need to evaluate the benefits and the safety of maternal intake of creatine in humans.

Chronic high-dose creatine has opposing effects on depression-related gene expression and behavior in intact and sex hormone-treated gonadectomized male and female rats

Creatine is an antioxidant, neuromodulator and key regulator of energy metabolism shown to improve depressive symptoms in humans and animals, especially in females. To better understand the pharmacological effects of creatine, we examined its influence on depression-related hippocampal gene expression and behaviors in the presence and absence of sex steroids. Sham-operated and gonadectomized male and female rats were fed chow alone or chow blended with either 2% or 4% w/w creatine monohydrate for five weeks before forced swim, open field, and wire suspension tests, or seven weeks total. Before supplementation, males were chronically implanted with an empty or a testosterone-filled (T) capsule (10-mm surface release), and females were administered progesterone (P, 250 μg), estradiol benzoate (EB, 2.5 μg), EB+P, or sesame oil vehicle weekly. Relative to non-supplemented shams, all hippocampal plasticity-related mRNAs measured, including brain-derived neurotrophic factor (BDNF), tyrosine kinase B, doublecortin, calretinin, and calbindin, were downregulated in sham males given 4% creatine, and BDNF, doublecortin, and calbindin mRNAs were downregulated in sham females given 4% creatine. In contrast, combined 4% creatine+T in castrates prevented downregulation of BDNF, doublecortin, and calretinin mRNAs. Similarly, combined 4% creatine+EB+P in ovariectomized females attenuated downregulation of BDNF and calbindin mRNA levels. Moderate antidepressant and anxiolytic-like behaviors were observed in EB+P-treated ovariectomized females fed creatine, with similar trends in T-treated castrates fed creatine. Altogether, these data show that chronic, high-dose creatine has opposing effects on neuroplasticity-related genes and depressive behavior in intact and gonadectomized male and female rats. The dose and schedule of creatine used negatively impacted hippocampal neuronal integrity in otherwise healthy brains, possibly through negative compensatory changes in energy metabolism, whereas combined creatine and sex steroids acted in a neuroprotective manner in gonadectomized rats, potentially by reducing metabolic complications associated with castration or ovariectomy.

Negative regulation of the creatine transporter SLC6A8 by SPAK and OSR1

BACKGROUND/AIMS

Transport regulation involves several kinases including SPAK (SPS1-related proline/alanine-rich kinase) and OSR1 (oxidative stress-responsive kinase 1), which are under control of WNK (with-no-K[Lys]) kinases. The present study explored whether SPAK and/or OSR1 participate in the regulation of the creatine transporter CreaT (SLC6A8), which accomplishes Na+ coupled cellular uptake of creatine in several tissues including kidney, intestine, heart, skeletal muscle and brain.

METHODS

cRNA encoding SLC6A8 was injected into Xenopus laevis oocytes with or without additional injection of cRNA encoding wild-type SPAK, constitutively active (T233E)SPAK, WNK insensitive (T233A)SPAK, catalytically inactive (D212A)SPAK, wild-type OSR1, constitutively active (T185E)OSR1, WNK insensitive (T185A)OSR1 and catalytically inactive (D164A)OSR1. Transporter activity was determined from creatine (1 mM) induced current utilizing dual electrode voltage clamp.

RESULTS

Coexpression of wild-type SPAK and of (T233E)SPAK, but not of (T233A)SPAK or of (D212A)SPAK was followed by a significant decrease of creatine induced current in SLC6A8 expressing oocytes. Coexpression of SPAK significantly decreased maximal transport rate. Coexpression of wild-type OSR1, (T185E)OSR1 and (T185A)OSR1 but not of (D164A)OSR1 significantly negatively regulated SLC6A8 activity. OSR1 again decreased significantly maximal transport rate.

CONCLUSIONS

Both, SPAK and OSR1, are negative regulators of the creatine transporter SLC6A8.

Upregulation of the creatine transporter Slc6A8 by Klotho

BACKGROUND/AIMS

The transmembrane Klotho protein contributes to inhibition of 1,25(OH)2D3 formation. The extracellular domain of Klotho protein could function as an enzyme with e.g. β-glucuronidase activity, be cleaved off and be released into blood and cerebrospinal fluid. Klotho regulates several cellular transporters. Klotho protein deficiency accelerates the appearance of age related disorders including neurodegeneration and muscle wasting and eventually leads to premature death. The main site of Klotho protein expression is the kidney. Klotho protein is also appreciably expressed in other tissues including chorioid plexus. The present study explored the effect of Klotho protein on the creatine transporter CreaT (Slc6A8), which participates in the maintenance of neuronal function and survival.

METHODS

To this end cRNA encoding Slc6A8 was injected into Xenopus oocytes with and without additional injection of cRNA encoding Klotho protein. Creatine transporter CreaT (Slc6A8) activity was estimated from creatine induced current determined by two-electrode voltage-clamp.

RESULTS

Coexpression of Klotho protein significantly increased creatine-induced current in Slc6A8 expressing Xenopus oocytes. Coexpression of Klotho protein delayed the decline of creatine induced current following inhibition of carrier insertion into the cell membrane by brefeldin A (5 µM). The increase of creatine induced current by coexpression of Klotho protein in Slc6A8 expressing Xenopus oocytes was reversed by β-glucuronidase inhibitor (DSAL). Similarly, treatment of Slc6A8 expressing Xenopus oocytes with recombinant human alpha Klotho protein significantly increased creatine induced current.

CONCLUSION

Klotho protein up-regulates the activity of creatine transporter CreaT (Slc6A8) by stabilizing the carrier protein in the cell membrane, an effect requiring β-glucuronidase activity of Klotho protein.

Creatine metabolism differs between mammals and rainbow trout (Oncorhynchus mykiss)

Creatine plays an important role in the cell as an energy buffer. As the energy system is a basic element of the organism it may possibly contribute to differences between rainbow trout strains selected for the traits growth and robustness, respectively. The cDNA sequences of creatine-related genes encoding glycine amidinotransferase (GATM), guanidinoacetate N-methyltransferase (GAMT), creatine kinase muscle-type (CKM) and creatine transporter 1 (CT1, encoded by gene solute carrier family 6, member 8 (SLC6A8)) were characterized in rainbow trout. Transcripts of the respective genes were quantified in kidney, liver, brain and skeletal muscle in both trout strains that had been acclimated to different temperatures. Several differences between the compared trout strains were found as well as between temperatures indicating that the energy system may contribute to differences between both strains. In addition to that, the expression data showed clear differences between the creatine system in rainbow trout and mammals, as the spatial distribution of the enzyme-encoding gene expression was clearly different from the patterns described for mammals. In rainbow trout, creatine synthesis seems to take place to a big extent in the skeletal muscle.

X-linked creatine transporter deficiency: clinical aspects and pathophysiology

Creatine transporter deficiency was discovered in 2001 as an X-linked cause of intellectual disability characterized by cerebral creatine deficiency. This review describes the current knowledge regarding creatine metabolism, the creatine transporter and the clinical aspects of creatine transporter deficiency. The condition mainly affects the brain while other creatine requiring organs, such as the muscles, are relatively spared. Recent studies have provided strong evidence that creatine synthesis also occurs in the brain, leading to the intriguing question of why cerebral creatine is deficient in creatine transporter deficiency. The possible mechanisms explaining the cerebral creatine deficiency are discussed. The creatine transporter knockout mouse provides a good model to study the disease. Over the past years several treatment options have been explored but no treatment has been proven effective. Understanding the pathogenesis of creatine transporter deficiency is of paramount importance in the development of an effective treatment.

Creatine and guanidinoacetate reference values in a French population

Creatine and guanidinoacetate are biomarkers of creatine metabolism. Their assays in body fluids may be used for detecting patients with primary creatine deficiency disorders (PCDD), a class of inherited diseases. Their laboratory values in blood and urine may vary with age, requiring that reference normal values are given within the age range. Despite the long known role of creatine for muscle physiology, muscle signs are not necessarily the major complaint expressed by PCDD patients. These disorders drastically affect brain function inducing, in patients, intellectual disability, autistic behavior and other neurological signs (delays in speech and language, epilepsy, ataxia, dystonia and choreoathetosis), being a common feature the drop in brain creatine content. For this reason, screening of PCDD patients has been repeatedly carried out in populations with neurological signs. This report is aimed at providing reference laboratory values and related age ranges found for a large scale population of patients with neurological signs (more than 6 thousand patients) previously serving as a background population for screening French patients with PCDD. These reference laboratory values and age ranges compare rather favorably with literature values for healthy populations. Some differences are also observed, and female participants are discriminated from male participants as regards to urine but not blood values including creatine on creatinine ratio and guanidinoacetate on creatinine ratio values. Such gender differences were previously observed in healthy populations; they might be explained by literature differential effects of testosterone and estrogen in adolescents and adults, and by estrogen effects in prepubertal age on SLC6A8 function. Finally, though they were acquired on a population with neurological signs, the present data might reasonably serve as reference laboratory values in any future medical study exploring abnormalities of creatine metabolism and transport.

Synthesis of guanidinoacetate and creatine from amino acids by rat pancreas

Creatine is an important molecule involved in cellular energy metabolism. Creatine is spontaneously converted to creatinine at a rate of 1·7% per d; creatinine is lost in the urine. Creatine can be obtained from the diet or synthesised from endogenous amino acids via the enzymes arginine:glycine amidinotransferase (AGAT) and guanidinoacetate N-methyltransferase (GAMT). The liver has high GAMT activity and the kidney has high AGAT activity. Although the pancreas has both AGAT and GAMT activities, its possible role in creatine synthesis has not been characterised. In the present study, we examined the enzymes involved in creatine synthesis in the pancreas as well as the synthesis of guanidinoacetate (GAA) and creatine by isolated pancreatic acini. We found significant AGAT activity and somewhat lower GAMT activity in the pancreas and that pancreatic acini had measurable activities of both AGAT and GAMT and the capacity to synthesise GAA and creatine from amino acids. Creatine supplementation led to a decrease in AGAT activity in the pancreas, though it did not affect its mRNA or protein abundance. This was in contrast with the reduction of AGAT activity and mRNA and protein abundance in the kidney, suggesting that the regulatory mechanisms that control the expression of this enzyme in the pancreas are different from those in the kidney. Dietary creatine increased the concentrations of GAA, creatine and phosphocreatine in the pancreas. Unexpectedly, creatine supplementation decreased the concentrations of S-adenosylmethionine, while those of S-adenosylhomocysteine were not altered significantly.

Screening for primary creatine deficiencies in French patients with unexplained neurological symptoms

A population of patients with unexplained neurological symptoms from six major French university hospitals was screened over a 28-month period for primary creatine disorder (PCD). Urine guanidinoacetate (GAA) and creatine:creatinine ratios were measured in a cohort of 6,353 subjects to identify PCD patients and compile their clinical, 1H-MRS, biochemical and molecular data. Six GAMT [N-guanidinoacetatemethyltransferase (EC 2.1.1.2)] and 10 X-linked creatine transporter (SLC6A8) but no AGAT (GATM) [L-arginine/glycine amidinotransferase (EC 2.1.4.1)] deficient patients were identified in this manner. Three additional affected sibs were further identified after familial inquiry (1 brother with GAMT deficiency and 2 brothers with SLC6A8 deficiency in two different families). The prevalence of PCD in this population was 0.25% (0.09% and 0.16% for GAMT and SLC6A8 deficiencies, respectively). Seven new PCD-causing mutations were discovered (2 nonsense [c.577C > T and c.289C > T] and 1 splicing [c.391 + 15G > T] mutations for the GAMT gene and, 2 missense [c.1208C > A and c.926C > A], 1 frameshift [c.930delG] and 1 splicing [c.1393-1G > A] mutations for the SLC6A8 gene). No hot spot mutations were observed in these genes, as all the mutations were distributed throughout the entire gene sequences and were essentially patient/family specific. Approximately one fifth of the mutations of SLC6A8, but not GAMT, were attributed to neo-mutation, germinal or somatic mosaicism events. The only SLC6A8-deficient female patient in our series presented with the severe phenotype usually characterizing affected male patients, an observation in agreement with recent evidence that is in support of the fact that this X-linked disorder might be more frequent than expected in the female population with intellectual disability.

Patterns of brain injury in inborn errors of metabolism

Many inborn errors of metabolism (IEMs) are associated with irreversible brain injury. For many, it is unclear how metabolite intoxication or substrate depletion accounts for the specific neurologic findings observed. IEM-associated brain injury patterns are characterized by whether the process involves gray matter, white matter, or both, and beyond that, whether subcortical or cortical gray matter nuclei are involved. Despite global insults, IEMs may result in selective injury to deep gray matter nuclei or white matter. This manuscript reviews the neuro-imaging patterns of neural injury in selected disorders of metabolism involving small molecule and macromolecular disorders (ie, Phenylketonuria, urea cycle disorders, and maple syrup urine disease) and discusses the contribution of diet and nutrition to the prevention or exacerbation of injury in selected inborn metabolic disorders. Where known, a review of the roles of individual differences in blood-brain permeability and transport mechanisms in the etiology of these disorders will be discussed.

Creatine and guanidinoacetate transport at blood-brain and blood-cerebrospinal fluid barriers

While it was thought that most of cerebral creatine is of peripheral origin, AGAT and GAMT are well expressed in CNS where brain cells synthesize creatine. While the creatine transporter SLC6A8 is expressed by microcapillary endothelial cells (MCEC) at blood-brain barrier (BBB), it is absent from their surrounding astrocytes. This raised the concept that BBB has a limited permeability for peripheral creatine, and that the brain supplies a part of its creatine by endogenous synthesis. This review brings together the latest data on creatine and guanidinoacetate transport through BBB and blood-CSF barrier (BCSFB) with the clinical evidence of AGAT-, GAMT- and SLC6A8-deficient patients, in order to delineate a clearer view on the roles of BBB and BCSFB in the transport of creatine and guanidinoacetate between periphery and CNS, and on brain synthesis and transport of creatine. It shows that in physiological conditions, creatine is taken up by CNS from periphery through SLC6A8 at BBB, but in limited amounts, and that CNS also needs its own creatine synthesis. No uptake of guanidinoacetate from periphery occurs at BBB except under GAMT deficiency, but a net exit of guanidinoacetate seems to occur from CSF to blood at BCSFB, predominantly through the taurine transporter TauT.

Creatine metabolism and psychiatric disorders: Does creatine supplementation have therapeutic value?

Athletes, body builders, and military personnel use dietary creatine as an ergogenic aid to boost physical performance in sports involving short bursts of high-intensity muscle activity. Lesser known is the essential role creatine, a natural regulator of energy homeostasis, plays in brain function and development. Creatine supplementation has shown promise as a safe, effective, and tolerable adjunct to medication for the treatment of brain-related disorders linked with dysfunctional energy metabolism, such as Huntington's Disease and Parkinson's Disease. Impairments in creatine metabolism have also been implicated in the pathogenesis of psychiatric disorders, leaving clinicians, researchers and patients alike wondering if dietary creatine has therapeutic value for treating mental illness. The present review summarizes the neurobiology of the creatine-phosphocreatine circuit and its relation to psychological stress, schizophrenia, mood and anxiety disorders. While present knowledge of the role of creatine in cognitive and emotional processing is in its infancy, further research on this endogenous metabolite has the potential to advance our understanding of the biological bases of psychopathology and improve current therapeutic strategies.

In vitro study of uptake and synthesis of creatine and its precursors by cerebellar granule cells and astrocytes suggests some hypotheses on the physiopathology of the inherited disorders of creatine metabolism

BACKGROUND

The discovery of the inherited disorders of creatine (Cr) synthesis and transport in the last few years disclosed the importance of blood Cr supply for the normal functioning of the brain. These putatively rare diseases share a common pathogenetic mechanism (the depletion of brain Cr) and similar phenotypes characterized by mental retardation, language disturbances, seizures and movement disorders. In the effort to improve our knowledge on the mechanisms regulating Cr pool inside the nervous tissue, Cr transport and synthesis and related gene transcripts were explored in primary cultures of rat cerebellar granule cells and astrocytes.

METHODS

Cr uptake and synthesis were explored in vitro by incubating monotypic primary cultures of rat type I astrocytes and cerebellar granule cells with: a) D3-Creatine (D3Cr) and D3Cr plus β-guanidinopropionate (GPA, an inhibitor of Cr transporter), and b) labelled precursors of Guanidinoacetate (GAA) and Cr (Arginine, Arg; Glycine, Gly). Intracellular D3Cr and labelled GAA and Cr were assessed by ESI-MS/MS. Creatine transporter (CT1), L-arginine:glycine amidinotransferase (AGAT), and S-adenosylmethionine:guanidinoacetate N-methyltransferase (GAMT) gene expression was assessed in the same cells by real time PCR.

RESULTS

D3Cr signal was extremely high in cells incubated with this isotope (labelled/unlabelled Cr ratio reached about 10 and 122, respectively in cerebellar granule cells and astrocytes) and was reduced by GPA. Labelled Arg and Gly were taken up by the cells and incorporated in GAA, whose concentration paralleled that of these precursors both in the extracellular medium and inside the cells (astrocytes). In contrast, the increase of labelled Cr was relatively much more limited since labelled Cr after precursors' supplementation did not exceed 2,7% (cerebellar granule cells) and 21% (astrocytes) of unlabelled Cr. Finally, AGAT, GAMT and SLC6A8 were expressed in both kind of cells.

CONCLUSIONS

Our results confirm that both neurons and astrocytes have the capability to synthesize and uptake Cr, and suggest that at least in vitro intracellular Cr can increase to a much greater extent through uptake than through de novo synthesis. Our results are compatible with the clinical observations that when the Cr transporter is defective, intracellular Cr is absent despite the brain should be able to synthesize it. Further research is needed to fully understand to what extent our results reflect the in vivo situation.

Long-term follow-up and treatment in nine boys with X-linked creatine transporter defect

The creatine transporter (CRTR) defect is a recently discovered cause of X-linked intellectual disability for which treatment options have been explored. Creatine monotherapy has not proved effective, and the effect of treatment with L-arginine is still controversial. Nine boys between 8 months and 10 years old with molecularly confirmed CRTR defect were followed with repeated (1)H-MRS and neuropsychological assessments during 4-6 years of combination treatment with creatine monohydrate, L-arginine, and glycine. Treatment did not lead to a significant increase in cerebral creatine content as observed with H(1)-MRS. After an initial improvement in locomotor and personal-social IQ subscales, no lasting clinical improvement was recorded. Additionally, we noticed an age-related decline in IQ subscales in boys affected with the CRTR defect.

Creatine affects in vitro electrophysiological maturation of neuroblasts and protects them from oxidative stress

Creatine (Cr) is a very popular ergogenic molecule that has recently been shown to have antioxidant properties. The effectiveness of Cr supplementation in treating neurological diseases and Cr deficiency syndromes has been demonstrated, and experimental reports suggest that it plays an important role in CNS development. In spite of this body of evidence, the role of Cr in functional and structural neuronal differentiation is still poorly understood. Here we used electrophysiological, morphological, and biochemical approaches to study the effects of Cr supplementation on in vitro differentiation of spinal neuroblasts under standard conditions or subjected to oxidative stress, a status closely related to perinatal hypoxia-ischemia, a severe condition for developing brain. Cr supplementation (10 and 20 mM) completely prevented the viability decrease and neurite development impairment induced by radical attack, as well as nonprotein sulphydryl antioxidant pool depletion. Similar results were obtained using the antioxidant trolox. Furthermore, Cr supplementation induced a significant and dose-dependent anticipation of Na(+) and K(+) current expression during the period of in vitro network building. Consistently with the latter finding, higher excitability, expressed as number of spikes following depolarization, was found in supplemented neuroblasts. All effects were dependent on the cytosolic fraction of Cr, as shown using a membrane Cr-transporter blocker. Our results indicate that Cr protects differentiating neuroblasts against oxidative insults and, moreover, affects their in vitro electrophysiological maturation, suggesting possibly relevant effects of dietary Cr supplementation on developing CNS.