Exocytotic release of creatine in rat brain

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.

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.

Is creatine a CNS neurotransmitter?

A range of experiments suggests that creatine, a molecule known for recycling ATP in muscle and brain tissue, may also function as a neurotransmitter in the central nervous system.

Gene therapy for guanidinoacetate methyltransferase deficiency restores cerebral and myocardial creatine while resolving behavioral abnormalities

Creatine deficiency disorders are inborn errors of creatine metabolism, an energy homeostasis molecule. One of these, guanidinoacetate N-methyltransferase (GAMT) deficiency, has clinical characteristics that include features of autism, self-mutilation, intellectual disability, and seizures, with approximately 40% having a disorder of movement; failure to thrive can also be a component. Along with low creatine levels, guanidinoacetic acid (GAA) toxicity has been implicated in the pathophysiology of the disorder. Present-day therapy with oral creatine to control GAA lacks efficacy; seizures can persist. Dietary management and pharmacological ornithine treatment are challenging. Using an AAV-based gene therapy approach to express human codon-optimized GAMT in hepatocytes, in situ hybridization, and immunostaining, we demonstrated pan-hepatic GAMT expression. Serial collection of blood demonstrated a marked early and sustained reduction of GAA with normalization of plasma creatine; urinary GAA levels also markedly declined. The terminal time point demonstrated marked improvement in cerebral and myocardial creatine levels. In conjunction with the biochemical findings, treated mice gained weight to nearly match their wild-type littermates, while behavioral studies demonstrated resolution of abnormalities; PET-CT imaging demonstrated improvement in brain metabolism. In conclusion, a gene therapy approach can result in long-term normalization of GAA with increased creatine in guanidinoacetate N-methyltransferase deficiency and at the same time resolves the behavioral phenotype in a murine model of the disorder. These findings have important implications for the development of a new therapy for this abnormality of creatine metabolism.

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.

Evaluation of chronic toxicity of cyclocreatine in beagle dogs after oral gavage administration for up to 23 weeks

Cyclocreatine (LUM-001) was evaluated for chronic toxicity (23 weeks) in beagle dogs to support clinical development in patients with creatine transporter deficiency (CTD) disorder. Deionized water (vehicle control) or cyclocreatine was administered by oral gavage twice daily (12 ± 1 h apart) at 20, 40 and 75 mg/kg/dose followed by a recovery period. Due to severe toxicity, the study was terminated earlier than the planned 39 weeks of dosing. Animals in the 20, 40 and 75 mg/kg/dose groups completed 160, 106, and 55 days of dosing, respectively, followed by 30, 55 and 106 days of a recovery period, respectively. Three (25%), 7 (58%), and 7 (58%) animals were euthanized and/or found dead in the 40, 80, and 150 mg/kg/day dose groups, respectively. Clinical signs observed were inappetence, frequent emesis, stool abnormalities, weight loss, lethargy and respiratory distress. Histopathological evaluation revealed congestion, edema, cellular infiltration, fibrin, and/or hemorrhage in the lungs of all dose groups. Additionally, animals in all cyclocreatine treatment groups had perinuclear cytoplasmic vacuoles in the heart, kidneys, skeletal and smooth muscles. After the recovery period, the vacuoles were still observed in the cardiac and renal tissues. Cyclocreatine was absorbed rapidly with mean Tmax within 1 to 2 h and half-life ranged between 2.17 and 2.79 h on Day 1, however, on the final day of dosing, it ranged between 5.80 and 8.77 h (males) and 10.3 to 13.1 h (females). To conclude, in this study the lungs, kidneys, heart, skeletal and smooth muscles were identified as the target organs of cyclocreatine toxicity in beagle dogs.

The Role of Preclinical Models in Creatine Transporter Deficiency: Neurobiological Mechanisms, Biomarkers and Therapeutic Development

Creatine (Cr) Transporter Deficiency (CTD) is an X-linked metabolic disorder, mostly caused by missense mutations in the SLC6A8 gene and presenting with intellectual disability, autistic behavior, and epilepsy. There is no effective treatment for CTD and patients need lifelong assistance. Thus, the research of novel intervention strategies is a major scientific challenge. Animal models are an excellent tool to dissect the disease pathogenetic mechanisms and drive the preclinical development of therapeutics. This review illustrates the current knowledge about Cr metabolism and CTD clinical aspects, with a focus on mainstay diagnostic and therapeutic options. Then, we discuss the rodent models of CTD characterized in the last decade, comparing the phenotypes expressed within clinically relevant domains and the timeline of symptom development. This analysis highlights that animals with the ubiquitous deletion/mutation of SLC6A8 genes well recapitulate the early onset and the complex pathological phenotype of the human condition. Thus, they should represent the preferred model for preclinical efficacy studies. On the other hand, brain- and cell-specific conditional mutants are ideal for understanding the basis of CTD at a cellular and molecular level. Finally, we explain how CTD models might provide novel insight about the pathogenesis of other disorders, including cancer.

Metabolic Basis of Creatine in Health and Disease: A Bioinformatics-Assisted Review

Creatine (Cr) is a ubiquitous molecule that is synthesized mainly in the liver, kidneys, and pancreas. Most of the Cr pool is found in tissues with high-energy demands. Cr enters target cells through a specific symporter called Na⁺/Cl⁻-dependent Cr transporter (CRT). Once within cells, creatine kinase (CK) catalyzes the reversible transphosphorylation reaction between [Mg²⁺:ATP⁴⁻]²⁻ and Cr to produce phosphocreatine (PCr) and [Mg²⁺:ADP³⁻]⁻. We aimed to perform a comprehensive and bioinformatics-assisted review of the most recent research findings regarding Cr metabolism. Specifically, several public databases, repositories, and bioinformatics tools were utilized for this endeavor. Topics of biological complexity ranging from structural biology to cellular dynamics were addressed herein. In this sense, we sought to address certain pre-specified questions including: (i) What happens when creatine is transported into cells? (ii) How is the CK/PCr system involved in cellular bioenergetics? (iii) How is the CK/PCr system compartmentalized throughout the cell? (iv) What is the role of creatine amongst different tissues? and (v) What is the basis of creatine transport? Under the cellular allostasis paradigm, the CK/PCr system is physiologically essential for life (cell survival, growth, proliferation, differentiation, and migration/motility) by providing an evolutionary advantage for rapid, local, and temporal support of energy- and mechanical-dependent processes. Thus, we suggest the CK/PCr system acts as a dynamic biosensor based on chemo-mechanical energy transduction, which might explain why dysregulation in Cr metabolism contributes to a wide range of diseases besides the mitigating effect that Cr supplementation may have in some of these disease states.

Creatine Supplementation, Physical Exercise and Oxidative Stress Markers: A Review of the Mechanisms and Effectiveness

Oxidative stress is the result of an imbalance between the generation of reactive oxygen species (ROS) and their elimination by antioxidant mechanisms. ROS degrade biogenic substances such as deoxyribonucleic acid, lipids, and proteins, which in turn may lead to oxidative tissue damage. One of the physiological conditions currently associated with enhanced oxidative stress is exercise. Although a period of intense training may cause oxidative damage to muscle fibers, regular exercise helps increase the cells' ability to reduce the ROS over-accumulation. Regular moderate-intensity exercise has been shown to increase antioxidant defense. Endogenous antioxidants cannot completely prevent oxidative damage under the physiological and pathological conditions (intense exercise and exercise at altitude). These conditions may disturb the endogenous antioxidant balance and increase oxidative stress. In this case, the use of antioxidant supplements such as creatine can have positive effects on the antioxidant system. Creatine is made up of two essential amino acids, arginine and methionine, and one non-essential amino acid, glycine. The exact action mechanism of creatine as an antioxidant is not known. However, it has been shown to increase the activity of antioxidant enzymes and the capability to eliminate ROS and reactive nitrogen species (RNS). It seems that the antioxidant effects of creatine may be due to various mechanisms such as its indirect (i.e., increased or normalized cell energy status) and direct (i.e., maintaining mitochondrial integrity) mechanisms. Creatine supplement consumption may have a synergistic effect with training, but the intensity and duration of training can play an important role in the antioxidant activity. In this study, the researchers attempted to review the literature on the effects of creatine supplementation and physical exercise on oxidative stress.

High serum creatinine is associated with reduction of psychiatric symptoms in female patients with anti-NMDAR encephalitis

OBJECTIVE

Serum creatinine (SCR) has been shown to be associated with many neurodegenerative diseases. In this study, we investigated the relationship between SCR levels and the incidence of psychiatric symptoms in patients with anti-N-methyl-d-aspartate receptor (anti-NMDAR) encephalitis.

METHODS

The SCR levels were tested in 69 patients with anti-NMDAR encephalitis at admission. Clinical characteristics and blood and CSF parameters were compared between the group of patients with psychiatric symptoms (P + group) and the group of those without psychiatric symptoms (P- group). The association between SCR and the incidence of psychiatric symptoms was determined by multivariate-adjusted linear regression analyses.

RESULTS

The SCR levels in the P + group were significantly lower than those in the P- group (P < 0.001). In the female subgroup, the SCR levels in the P + group were significantly lower compared to the P- group (P < 0.001), whereas in the male subgroup, the SCR levels did not differ between the two groups (P = 0.084). Furthermore, the highest SCR tercile overall had a significantly lower incidence of psychiatric symptoms than the lowest tercile (P < 0.001), and a significant negative correlation between the SCR levels and the occurrence of psychiatric symptoms was observed (r = -0.392, P < 0.001). Multivariate logistic regression analysis showed that the association was independent after adjusting for age, cystatin C and the modified Rankin Scale (mRS) score (P = 0.001). A similar result was found in the female subgroup (P = 0.010), but not in the male subgroup (P = 0.225).

CONCLUSION

Our study indicated that the SCR level was negatively correlated with incidence of psychiatric symptoms in female patients, and higher SCR level could be a protective factor for psychiatric symptoms in female patients with anti-NMDAR encephalitis.

Metabolite activity in the anterior cingulate cortex during a painful stimulus using functional MRS

To understand neurochemical brain responses to pain, proton magnetic resonance spectroscopy (1H-MRS) is used in humans in vivo to examine various metabolites. Recent MRS investigations have adopted a functional approach, where acquisitions of MRS are performed over time to track task-related changes. Previous studies suggest glutamate is of primary interest, as it may play a role during cortical processing of noxious stimuli. The objective of this study was to examine the metabolic effect (i.e., glutamate) in the anterior cingulate cortex during noxious stimulation using fMRS. The analysis addressed changes in glutamate and glutamate + glutamine (Glx) associated with the onset of pain, and the degree by which fluctuations in metabolites corresponded with continuous pain outcomes. Results suggest healthy participants undergoing tonic noxious stimulation demonstrated increased concentrations of glutamate and Glx at the onset of pain. Subsequent reports of pain were not accompanied by corresponding changes in glutamate of Glx concentrations. An exploratory analysis on sex revealed large effect size changes in glutamate at pain onset in female participants, compared with medium-sized effects in male participants. We propose a role for glutamate in the ACC related to the detection of a noxious stimulus.

Evaluation of chronic toxicity of cyclocreatine, a creatine analog, in Sprague Dawley rat after oral gavage administration for up to 26 weeks

Cyclocreatine (LUM-001), a creatine analog, was evaluated for its nonclinical toxicity in Sprague Dawley (SD) rats. Deionized water as a vehicle control article or cyclocreatine was administered by oral gavage twice daily (approximately 12 ± 1 h apart) at 30, 100 and 300 mg/kg/dose levels in rats up to 26 weeks followed by a 28-day recovery period. Due to an increased incidence of seizures, the 600 mg/kg/day dose group males were dosed only for 16-weeks followed by a 14-week recovery period. Thirteen males and four females from 600 mg/kg/day dose group were sacrificed at interim on Day 113 to study plausible brain lesions and not due to moribundity. There was a dose dependent increase in the number of seizure incidences in ≥60 mg/kg/day males and 600 mg/kg/day females. Microscopically, higher incidences of vacuoles in the brain at 600 mg/kg/day in both sexes, thyroid follicular atrophy and follicular cell hypertrophy at ≥200 mg/kg/day in males and 600 mg/kg/day in females, and seminiferous tubular degeneration and/or interstitial edema in testes at ≥200 mg/kg/day were observed. Mean plasma half-life of cyclocreatine was between 3.5 and 6.5 h. In conclusion, chronic administration of cyclocreatine by oral gavage in Sprague Dawley rats induced the seizures and microscopic lesions in the brain, testes and thyroid. Based on the results of this study the highest tested dose of 600 mg/kg/day (mean C_max of 151.5 μg/mL; AUC_0-24 of 1970 h*μg/mL) was considered the maximum tolerated dose (MTD) in SD rats.

Magnetic resonance imaging reveals specific anatomical changes in the brain of Agat- and Gamt-mice attributed to creatine depletion and guanidinoacetate alteration

Arginine:glycine amidinotransferase- and guanidinoacetate methyltransferase deficiency are severe neurodevelopmental disorders. It is not known whether mouse models of disease express a neuroanatomical phenotype. High-resolution magnetic resonance imaging (MRI) with advanced image analysis was performed in perfused, fixed mouse brains encapsulated with the skull from male, 10-12 week old Agat ^-exc and B6J.Cg-Gamt ^tm1Isb mice (n = 48; n = 8 per genotype, strain). T2-weighted MRI scans were nonlinearly aligned to a 3D atlas of the mouse brain with 62 structures identified. Local differences in brain shape related to genotype were assessed by analysis of deformation fields. Creatine (Cr) and guanidinoacetate (GAA) were measured with high-performance liquid chromatography (HPLC) in brain homogenates (n = 24; n = 4 per genotype, strain) after whole-body perfusion. Cr was decreased in the brain of Agat- and Gamt mutant mice. GAA was decreased in Agat^-/- and increased in Gamt^-/- . Body weight and brain volume were lower in Agat^-/- than in Gamt^-/- . The analysis of entire brain structures revealed corpus callosum, internal capsule, fimbria and hypothalamus being different between the genotypes in both strains. Eighteen and fourteen significant peaks (local areas of difference in relative size) were found in Agat- and Gamt mutants, respectively. Comparing Agat^-/- with Gamt^-/- , we found changes in three brain regions, lateral septum, amygdala, and medulla. Intra-strain differences in four brain structures can be associated with Cr deficiency, while the inter-strain differences in three brain structures of the mutant mice may relate to GAA. Correlating these neuroanatomical findings with gene expression data implies the role of Cr metabolism in the developing brain and the importance of early intervention in patients with Cr deficiency syndromes.

Creatine for the Treatment of Depression

Depressed mood, which can occur in the context of major depressive disorder, bipolar disorder, and other conditions, represents a serious threat to public health and wellness. Conventional treatments are not effective for a significant proportion of patients and interventions that are often beneficial for treatment-refractory depression are not widely available. There is, therefore, an immense need to identify novel antidepressant strategies, particularly strategies that target physiological pathways that are distinct from those addressed by conventional treatments. There is growing evidence from human neuroimaging, genetics, epidemiology, and animal studies that disruptions in brain energy production, storage, and utilization are implicated in the development and maintenance of depression. Creatine, a widely available nutritional supplement, has the potential to improve these disruptions in some patients, and early clinical trials indicate that it may have efficacy as an antidepressant agent.

Effects of the antidepressant medication duloxetine on brain metabolites in persistent depressive disorder: A randomized, controlled trial

Background

To assess whether patients with Persistent Depressive Disorder (PDD) have abnormal levels of N-acetyl-aspartate (NAA) and whether those levels normalize following treatment with the antidepressant medication duloxetine. Furthermore, we conducted post hoc analyses of other important brain metabolites to understand better the cellular and physiological determinants for changes in NAA levels.

Methods

We acquired proton (1H) magnetic resonance spectroscopic imaging (MRSI) data on a 3 Tesla (3T), GE Magnetic Resonance Imaging (MRI) scanner in 41 patients (39.9±10.4 years, 22 males) with PDD at two time points: before the start and at the end of a 10-week, placebo-controlled, double-blind, randomized controlled trial (RCT) of the antidepressant medication duloxetine. Patients were randomized such that 21 patients received the active medication and 20 patients received placebo during the 10 week period of the trial. In addition, we acquire 1H MRSI data once in 29 healthy controls (37.7±11.2 years, 17 males).

Findings

Patients had significantly higher baseline concentrations of NAA across white matter (WM) pathways and subcortical gray matter, and in direct proportion to the severity of depressive symptoms. NAA concentrations declined in duloxetine-treated patients over the duration of the trial in the direction toward healthy values, whereas concentrations increased in placebo-treated patients, deviating even further away from healthy values. Changes in NAA concentration did not mediate medication effects on reducing symptom severity, however; instead, changes in symptom severity partially mediated the effects of medication on NAA concentration, especially in the caudate and putamen.

Interpretation

These findings, taken together, suggest that PDD is not a direct consequence of elevated NAA concentrations, but that a more fundamental pathophysiological process likely causes PDD and determines the severity of its symptoms. The findings also suggest that although duloxetine normalized NAA concentrations in patients, it did so by modulating the severity of depressive symptoms. Medication presumably reduced depressive symptoms through other, as yet unidentified, brain processes.

Trial registration

ClinicalTrials.gov NCT00360724.

Beyond sports: Efficacy and safety of creatine supplementation in pathological or paraphysiological conditions of brain and muscle

Creatine is pivotal in energy metabolism of muscle and brain cells, both in physiological and in pathological conditions. Additionally, creatine facilitates the differentiation of muscle and neuronal cells. Evidence of effectiveness of creatine supplementation in improving several clinical conditions is now substantial, and we review it in this paper. In hereditary diseases where its synthesis is impaired, creatine has a disease-modifying capacity, especially when started soon after birth. Strong evidence, including a Cochrane meta-analysis, shows that it improves muscular strength and general well-being in muscular dystrophies. Significant evidence exists also of its effectiveness in secondary prevention of statin myopathy and of treatment-resistant depression in women. Vegetarians and vegans do not consume any dietary creatine and must synthesize all they need, spending most of their methylation capacity. Nevertheless, they have a lower muscular concentration of creatine. Creatine supplementation has proved effective in increasing muscular and neuropsychological performance in vegetarians or vegans and should, therefore, be recommended especially in those of them who are athletes, heavy-duty laborers or who undergo intense mental effort. Convincing evidence also exists of creatine effectiveness in muscular atrophy and sarcopenia in the elderly, and in brain energy shortage (mental fatigue, sleep deprivation, environmental hypoxia as in mountain climbing, and advanced age). Furthermore, we review more randomized, placebo-controlled trials showing that creatine supplementation is safe up to 20 g/d, with a possible caveat only in people with kidney disease. We trust that the evidence we review will be translated into clinical practice and will spur more research on these subjects.

Rescue by 4-phenylbutyrate of several misfolded creatine transporter-1 variants linked to the creatine transporter deficiency syndrome

Diseases arising from misfolding of SLC6 transporters have been reported over recent years, e.g. folding-deficient mutants of the dopamine transporter and of the glycine transporter-2 cause infantile/juvenile Parkinsonism dystonia and hyperekplexia, respectively. Mutations in the coding sequence of the human creatine transporter-1 (hCRT-1/SLC6A8) gene result in a creatine transporter deficiency syndrome, which varies in its clinical manifestation from epilepsy, mental retardation, autism, development delay and motor dysfunction to gastrointestinal symptoms. Some of the mutations in hCRT-1 occur at residues, which are highly conserved across the SLC6 family. Here, we examined 16 clinically relevant hCRT-1 variants to verify the conjecture that they were misfolded and that this folding defect was amenable to correction. Confocal microscopy imaging revealed that the heterologously expressed YFP-tagged mutant CRTs were trapped in the endoplasmic reticulum (ER), co-localised with the ER-resident chaperone calnexin. In contrast, the wild type hCRT-1 reached the plasma membrane. Preincubation of transiently transfected HEK293 cells with the chemical chaperone 4-phenylbutyrate (4-PBA) restored ER export and surface expression of as well as substrate uptake by several folding-deficient CRT-1 mutants. A representative mutant (hCRT-1-P544L) was expressed in rat primary hippocampal neurons to verify pharmacochaperoning in a target cell: 4-PBA promoted the delivery of hCRT-1-P544L to the neurite extensions. These observations show that several folding-deficient hCRT-1 mutants can be rescued. This proof-of-principle justifies the search for additional pharmacochaperones to restore folding of 4PBA-unresponsive hCRT-1 mutants. Finally, 4-PBA is an approved drug in paediatric use: this provides a rationale for translating the current insights into clinical trials. This article is part of the issue entitled 'Special Issue on Neurotransmitter Transporters'.

The possible beneficial effects of creatine for the management of depression

Depression, a highly prevalent neuropsychiatric disorder worldwide, causes a heavy burden for the society and is associated with suicide risk. The treatment of this disorder remains a challenge, since currently available antidepressants provide a slow and, often, incomplete response and cause several side effects that contribute to diminish the adhesion of patients to treatment. In this context, several nutraceuticals have been investigated regarding their possible beneficial effects for the management of this neuropsychiatric disorder. Creatine stands out as a supplement frequently used for ergogenic purpose, but it also is a neuroprotective compound with potential to treat or mitigate a broad range of central nervous systems diseases, including depression. This review presents preclinical and clinical evidence that creatine may exhibit antidepressant properties. The focus is given on the possible molecular mechanisms underlying its effects based on the results obtained with different animal models of depression. Finally, evidence obtained in animal models of depression addressing the possibility that creatine may produce rapid antidepressant effect, similar to ketamine, are also presented and discussed.

Novel Targets for Fast Antidepressant Responses: Possible Role of Endogenous Neuromodulators

The available medications for the treatment of major depressive disorder have limitations, particularly their limited efficacy, delayed therapeutic effects, and the side effects associated with treatment. These issues highlight the need for better therapeutic agents that provide more efficacious and faster effects for the management of this disorder. Ketamine, an N-methyl-D-aspartate receptor antagonist, is the prototype for novel glutamate-based antidepressants that has been shown to cause a rapid and sustained antidepressant effect even in severe refractory depressive patients. Considering the importance of these findings, several studies have been conducted to elucidate the molecular targets for ketamine's effect. In addition, efforts are under way to characterize ketamine-like drugs. This review focuses particularly on evidence that endogenous glutamatergic neuromodulators may be able to modulate mood and to elicit fast antidepressant responses. Among these molecules, agmatine and creatine stand out as those with more published evidence of similarities with ketamine, but guanosine and ascorbic acid have also provided promising results. The possibility that these neuromodulators and ketamine have common neurobiological mechanisms, mainly the ability to activate mechanistic target of rapamycin and brain-derived neurotrophic factor signaling, and synthesis of synaptic proteins in the prefrontal cortex and/or hippocampus is presented and discussed.

Choline and choline-related nutrients in regular and preterm infant growth

BACKGROUND

Choline is an essential nutrient, with increased requirements during development. It forms the headgroup of phosphatidylcholine and sphingomyelin in all membranes and many secretions. Phosphatidylcholine is linked to cell signaling as a phosphocholine donor to synthesize sphingomyelin from ceramide, a trigger of apoptosis, and is the major carrier of arachidonic and docosahexaenoic acid in plasma. Acetylcholine is important for neurodevelopment and the placental storage form for fetal choline supply. Betaine, a choline metabolite, functions as osmolyte and methyl donor. Their concentrations are all tightly regulated in tissues.

CLINCAL IMPACT

During the fetal growth spurt at 24-34-week postmenstrual age, plasma choline is higher than beyond 34 weeks, and threefold higher than in pregnant women [45 (36-60) µmol/L vs. 14 (10-17) µmol/L]. The rapid decrease in plasma choline after premature birth suggests an untimely reduction in choline supply, as cellular uptake is proportional to plasma concentration. Supply via breast milk, with phosphocholine and α-glycerophosphocholine as its major choline components, does not prevent such postnatal decrease. Moreover, high amounts of liver PC are secreted via bile, causing rapid hepatic choline turnover via the enterohepatic cycle, and deficiency in case of pancreatic phospholipase A2 deficiency or intestinal resection. Choline deficiency causes hepatic damage and choline accretion at the expense of the lungs and other tissues.

CONCLUSION

Choline deficiency may contribute to the impaired lean body mass growth and pulmonary and neurocognitive development of preterm infants despite adequate macronutrient supply and weight gain. In this context, a reconsideration of current recommendations for choline supply to preterm infants is required.

1H MR spectroscopy of the motor cortex immediately following transcranial direct current stimulation at 7 Tesla

Transcranial direct current stimulation (tDCS) is a form of non-invasive brain stimulation that may modulate cortical excitability, metabolite concentration, and human behaviour. The supplementary motor area (SMA) has been largely ignored as a potential target for tDCS neurorehabilitation but is an important region in motor compensation after brain injury with strong efferent connections to the primary motor cortex (M1). The objective of this work was to measure tissue metabolite changes in the human motor cortex immediately following tDCS. We hypothesized that bihemispheric tDCS would change levels of metabolites involved in neuromodulation including N-acetylaspartate (NAA), glutamate (Glu), and creatine (tCr). In this single-blind, randomized, cross-over study, fifteen healthy adults aged 21–60 participated in two 7T MRI sessions, to identify changes in metabolite concentrations by magnetic resonance spectroscopy. Immediately after 20 minutes of tDCS, there were no significant changes in metabolite levels or metabolite ratios comparing tDCS to sham. However there was a trend toward increased NAA/tCr concentration (p = 0.08) in M1 under the stimulating cathode. There was a strong, positive correlation between the change in the absolute concentration of NAA and the change in the absolute concentration of tCr (p<0.001) suggesting an effect of tDCS. Both NAA and creatine are important markers of neurometabolism. Our findings provide novel insight into the modulation of neural metabolites in the motor cortex immediately following application of bihemispheric tDCS.

Altered brain high-energy phosphate metabolism in mild Alzheimer's disease: A 3-dimensional 31P MR spectroscopic imaging study

In Alzheimer's disease (AD), defects in essential metabolic processes for energy supply and phospholipid membrane function have been implicated in the pathological process. However, post-mortem investigations are generally limited to late stage disease and prone to tissue decay artifacts. In vivo assessments of high energy phosphates, tissue pH and phospholipid metabolites are possible by phosphorus MR spectroscopy (³¹P–MRS), but so far only small studies, mostly focusing on single brain regions, have been performed. Therefore, we assessed phospholipid and energy metabolism in multiple brain regions of 31 early stage AD patients and 31 age- and gender-matched controls using ³¹P–MRS imaging. An increase of phosphocreatine (PCr) was found in AD patients compared with controls in the retrosplenial cortex, and both hippocampi, but not in the anterior cingulate cortex. While PCr/inorganic phosphate and pH were also increased in AD, no changes were found for phospholipid metabolites. This study showed that PCr levels are specifically increased in regions that show early degeneration in AD. Together with an increased pH, this indicates an altered energy metabolism in mild AD.

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Phosphocreatine and pH are increased in mild Alzheimer's disease.

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Phosphocreatine increase occurs in early affected brain regions.

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Brain energy metabolism may be altered in mild Alzheimer's disease.

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Phospholipid and energy metabolites as well as pH, differ across brain regions.

Biochemical and behavioral phenotype of AGAT and GAMT deficient mice following long-term Creatine monohydrate supplementation

The creatine/phosphocreatine system is essential for cellular phosphate coupled energy storage and production. We investigated the utility of creatine monohydrate supplementation in two different creatine deficient knockout mouse models. Following weaning, female Arginine: Glycine Amidinotransferase (AGAT) and Guanidinoacetate: methyltransferase (GAMT) knockouts and wild type mice were studied based on their genotypes and dietary supplementation (creatine free or 2% creatine monohydrate supplemented diet) for 10 weeks, using a series of behavioral tests and biochemical analyzes. An improved Rota rod performance was observed in both AGAT (p = 0.02) and GAMT knockout mice (p < 0.001) supplemented with 2% creatine. During Morris water maze probe trial, creatine supplemented AGAT knockout mice took less time to reach virtual platform (p = 0.03) and more frequently crossed this area (p = 0.001) than mice on creatine free diet. Similar observations were recorded for GAMT knockout mice. Urinary creatinine concentrations for AGAT (p = 0.001) and GAMT (p = 0.05) knockout mice were increased following creatine supplementation. Creatine supplementation has a potential to improve neuro-muscular coordination, spatial learning in both AGAT and GAMT knockout mice. Long term Creatine supplementation results in increased urine creatinine concentrations indicating improved creatine metabolism in knockout mice.

Variability of Creatine Metabolism Genes in Children with Autism Spectrum Disorder

Creatine deficiency syndrome (CDS) comprises three separate enzyme deficiencies with overlapping clinical presentations: arginine:glycine amidinotransferase (GATM gene, glycine amidinotransferase), guanidinoacetate methyltransferase (GAMT gene), and creatine transporter deficiency (SLC6A8 gene, solute carrier family 6 member 8). CDS presents with developmental delays/regression, intellectual disability, speech and language impairment, autistic behaviour, epileptic seizures, treatment-refractory epilepsy, and extrapyramidal movement disorders; symptoms that are also evident in children with autism. The objective of the study was to test the hypothesis that genetic variability in creatine metabolism genes is associated with autism. We sequenced GATM, GAMT and SLC6A8 genes in 166 patients with autism (coding sequence, introns and adjacent untranslated regions). A total of 29, 16 and 25 variants were identified in each gene, respectively. Four variants were novel in GATM, and 5 in SLC6A8 (not present in the 1000 Genomes, Exome Sequencing Project (ESP) or Exome Aggregation Consortium (ExAC) databases). A single variant in each gene was identified as non-synonymous, and computationally predicted to be potentially damaging. Nine variants in GATM were shown to have a lower minor allele frequency (MAF) in the autism population than in the 1000 Genomes database, specifically in the East Asian population (Fisher’s exact test). Two variants also had lower MAFs in the European population. In summary, there were no apparent associations of variants in GAMT and SLC6A8 genes with autism. The data implying there could be a lower association of some specific GATM gene variants with autism is an observation that would need to be corroborated in a larger group of autism patients, and with sub-populations of Asian ethnicities. Overall, our findings suggest that the genetic variability of creatine synthesis/transport is unlikely to play a part in the pathogenesis of autism spectrum disorder (ASD) in children.

High serum creatinine is associated with reduction of vision impaired in patients with NMOSD

Serum creatinine (SCR) has been found to be neuroprotective in neurodegenerative disease. However, whether SCR is a protective factor for vision impaired in neuromyelitis optica spectrum disorder (NMOSD) is unclear. This study to determine the relationship between SCR level and vision impaired in NMOSD patients through multivariate-adjusted linear regression analyses. Our result showed that high level of SCR was associated with a low occurrence of vision impaired, and the association was independent after adjustment for confounding risk factors and hierarchical analysis. Therefore, these results demonstrated that higher SCR level is a protective factor of vision impaired in male NMOSD patients.

Variable White Matter Atrophy and Intellectual Development in a Family With X-linked Creatine Transporter Deficiency Despite Genotypic Homogeneity

BACKGROUND

The X-linked creatine transporter deficiency (CRTD) caused by an SLC6A8 mutation represents the second most common cause of X-linked intellectual disability. The clinical phenotype ranges from mild to severe intellectual disability, epilepsy, short stature, poor language skills, and autism spectrum disorders. The objective of this study was to investigate phenotypic variability in the context of genotype, cerebral creatine concentration, and volumetric analysis in a family with CRTD.

PATIENTS AND METHODS

The clinical phenotype and manifestations of epilepsy were assessed in a Caucasian family with CRTD. DNA sequencing and creatine metabolism analysis confirmed the diagnosis. Cerebral magnetic resonance imaging (cMRI) with voxel-based morphometry and magnetic resonance spectroscopy was performed in all family members.

RESULTS

An SLC6A8 missense mutation (c.1169C>T; p.Pro390Leu, exon 8) was detected in four of five individuals. Both male siblings were hemizygous, the mother and the affected sister heterozygous for the mutation. Structural cMRI was normal, whereas voxel-based morphometry analysis showed reduced white matter volume below the first percentile of the reference population of 290 subjects in the more severely affected boy compared with family members and controls. Normalized creatine concentration differed significantly between the individuals (P < 0.005).

CONCLUSIONS

There is a broad phenotypic variability in CRTD even in family members with the same mutation. Differences in mental development could be related to atrophy of the subcortical white matter.

Effect of creatine monohydrate supplementation on learning, memory and neuromuscular coordination in female albino mice

BACKGROUND

Research findings made over the last few years have highlighted the important role of creatine (Cr) in health and disease. However, limited information is available regarding the effect of Cr supplementation on cognation. Present study was designed to determine the effect of variable doses of Cr (1% and 3%) on selected parameters of female albino mice behaviour.

METHODS

Following weaning, on 20th postnatal day, female albino mice were divided into three groups on the basis of dietary supplementation. Control group were was fed with normal rodent diet, whereas treated groups received diet supplemented with 1% and 3% Creatine monohydrate (Ssniff, Germany) for 10 weeks. Morris water maze (MWM), Rota rod and open field (OF) tests were carried out at the end of diet supplementation for neurofunctional assessment in all the groups.

RESULTS

Data analysis showed that Cr supplementation did not affect the muscular activity and during rota rod test as well as locomotor and exploratory behaviour during OF test. Results of MWM probe trial indicated that mice supplemented with 3% Cr had significantly more entries in platform area than other two treatments (p=0.03) indicating improved spatial memory. Body weight remained unaffected (p>0.05) when compared between three experimental treatments.

CONCLUSION

Female mice supplemented with 3% Cr showed improved spatial memory than mice fed on 1% Cr-supplemented diet and mice on normal rodent diet.

Laboratory diagnosis of creatine deficiency syndromes: a technical standard and guideline of the American College of Medical Genetics and Genomics

Disclaimer: These ACMG Standards and Guidelines are intended as an educational resource for clinical laboratory geneticists to help them provide quality clinical laboratory genetic services. Adherence to these standards and guidelines is voluntary and does not necessarily assure a successful medical outcome. These Standards and Guidelines should not be considered inclusive of all proper procedures and tests or exclusive of others that are reasonably directed to obtaining the same results. In determining the propriety of any specific procedure or test, clinical laboratory geneticists should apply their professional judgment to the specific circumstances presented by the patient or specimen. Clinical laboratory geneticists are encouraged to document in the patient's record the rationale for the use of a particular procedure or test, whether or not it is in conformance with these Standards and Guidelines. They also are advised to take notice of the date any particular guideline was adopted, and to consider other relevant medical and scientific information that becomes available after that date. It also would be prudent to consider whether intellectual property interests may restrict the performance of certain tests and other procedures.Cerebral creatine deficiency syndromes are neurometabolic conditions characterized by intellectual disability, seizures, speech delay, and behavioral abnormalities. Several laboratory methods are available for preliminary and confirmatory diagnosis of these conditions, including measurement of creatine and related metabolites in biofluids using liquid chromatography-tandem mass spectrometry or gas chromatography-mass spectrometry, enzyme activity assays in cultured cells, and DNA sequence analysis. These guidelines are intended to standardize these procedures to help optimize the diagnosis of creatine deficiency syndromes. While biochemical methods are emphasized, considerations for confirmatory molecular testing are also discussed, along with variables that influence test results and interpretation.Genet Med 19 2, 256-263.

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.

Prevalence of Creatine Deficiency Syndromes in Children With Nonsyndromic Autism

BACKGROUND AND OBJECTIVE

Creatine deficiency may play a role in the neurobiology of autism and may represent a treatable cause of autism. The goal of the study was to ascertain the prevalence of creatine deficiency syndromes (CDSs) in children with autism spectrum disorder (ASD).

METHODS

In a prospective multicenter study, 443 children were investigated after a confirmed diagnosis of ASD. Random spot urine screening for creatine metabolites (creatine, guanidinoacetate, creatinine, and arginine) with liquid chromatography-tandem mass spectrometry and second-tier testing with high-performance liquid chromatography methodology was followed by recall testing in 24-hour urines and confirmatory testing by Sanger-based DNA sequencing of GAMT, GATM, and SLC6A8 genes. Additional diagnostic tests included plasma creatine metabolites and in vivo brain proton magnetic resonance spectroscopy. The creatine metabolites in spot urine in the autism group were compared with 128 healthy controls controlled for age.

RESULTS

In 443 subjects with ASD investigated for CDS, we had 0 events (event: 0, 95% confidence interval 0-0.0068), therefore with 95% confidence the prevalence of CDS is <7 in 1000 children with ASD. The autism and control groups did not vary in terms of creatine metabolites (P > .0125) in urine.

CONCLUSION

Our study revealed a very low prevalence of CDS in children with nonsyndromic ASD and no obvious association between creatine metabolites and autism. Unlike our study population, we expect more frequent CDS among children with severe developmental delay, speech impairment, seizures, and movement disorders in addition to impairments in social communication, restricted interests, and repetitive behaviors.

A pilot study to estimate incidence of guanidinoacetate methyltransferase deficiency in newborns by direct sequencing of the GAMT gene

BACKGROUND

GAMT deficiency is an autosomal recessive disorder of creatine biosynthesis causing developmental delays or intellectual disability in untreated patients as a result of irreversible brain damage occurring prior to diagnosis. Normal neurodevelopmental outcome has been reported in patients treated from neonatal period highlighting the importance of early treatment.

METHODS

Five hundred anonymized newborns from the National Newborn Screening Program of The Netherlands were included into this pilot study. Direct sequencing of the coding region of the GAMT gene was applied following DNA extraction. The disease causing nature of novel missense variants in the GAMT gene was studied by overexpression studies. GAA and creatine was measured in blood dot spots.

RESULTS

We detected two carriers, one with a known common (c.327G>A) and one with a novel mutation (c.297_309dup (p.Arg105Glyfs*) in the GAMT gene. The estimated incidence of GAMT deficiency was 1:250,000. We also detected five novel missense variants. Overexpression of these variants in GAMT deficient fibroblasts did restore GAMT activity and thus all were considered rare, but not disease causing variants including the c.131G>T (p.Arg44Leu) variant. Interestingly, this variant was predicted to be pathogenic by in silico analysis. The variants were included in the Leiden Open Variation Database (LOVD) database (www.LOVD.nl/GAMT). The average GAA level was 1.14μmol/L±0.45 standard deviations. The average creatine level was 408μmol/L±106. The average GAA/creatine ratio was 2.94±0.136.

CONCLUSION

The estimated incidence of GAMT deficiency is 1:250,000 newborns based on our pilot study. The newborn screening for GAMT deficiency should be implemented to identify patients at the asymptomatic stage to achieve normal neurodevelopmental outcome for this treatable neurometabolic disease. Biochemical investigations including GAA, creatine and GAMT enzyme activity measurements are essential to confirm the diagnosis of GAMT deficiency. According to availability, all missense variants can be assessed functionally, as in silico prediction analysis of missense variants is not sufficient to confirm the pathogenicity of missense variants.

Creatine as a booster for human brain function. How might it work?

Creatine, a naturally occurring nitrogenous organic acid found in animal tissues, has been found to play key roles in the brain including buffering energy supply, improving mitochondrial efficiency, directly acting as an anti-oxidant and acting as a neuroprotectant. Much of the evidence for these roles has been established in vitro or in pre-clinical studies. Here, we examine the roles of creatine and explore the current status of translation of this research into use in humans and the clinic. Some further possibilities for use of creatine in humans are also discussed.

Estimated carrier frequency of creatine transporter deficiency in females in the general population using functional characterization of novel missense variants in the SLC6A8 gene

Creatine transporter deficiency (CRTR-D) is an X-linked inherited disorder of creatine transport. All males and about 50% of females have intellectual disability or cognitive dysfunction. Creatine deficiency on brain proton magnetic resonance spectroscopy and elevated urinary creatine to creatinine ratio are important biomarkers. Mutations in the SLC6A8 gene occur de novo in 30% of males. Despite reports of high prevalence of CRTR-D in males with intellectual disability, there are no true prevalence studies in the general population. To determine carrier frequency of CRTR-D in the general population we studied the variants in the SLC6A8 gene reported in the Exome Variant Server database and performed functional characterization of missense variants. We also analyzed synonymous and intronic variants for their predicted pathogenicity using in silico analysis tools. Nine missense variants were functionally analyzed using transient transfection by site-directed mutagenesis with In-Fusion HD Cloning in HeLa cells. Creatine uptake was measured by liquid chromatography tandem mass spectrometry for creatine measurement. The c.1654G>T (p.Val552Leu) variant showed low residual creatine uptake activity of 35% of wild type transfected HeLa cells and was classified as pathogenic. Three variants (c.808G>A; p.Val270Met, c.942C>G; p.Phe314Leu and c.952G>A; p.Ala318Thr) were predicted to be pathogenic based on in silico analysis, but proved to be non-pathogenic by our functional analysis. The estimated carrier frequency of CRTR-D was 0.024% in females in the general population. We recommend functional studies for all novel missense variants by transient transfection followed by creatine uptake measurement by liquid chromatography tandem mass spectrometry as fast and cost effective method for the functional analysis of missense variants in the SLC6A8 gene.

Creatine, similarly to ketamine, affords antidepressant-like effects in the tail suspension test via adenosine A₁ and A2A receptor activation

The benefits of creatine supplementation have been reported in a broad range of central nervous systems diseases, including depression. A previous study from our group demonstrated that creatine produces an antidepressant-like effect in the tail suspension test (TST), a predictive model of antidepressant activity. Since depression is associated with a dysfunction of the adenosinergic system, we investigated the involvement of adenosine A1 and A2A receptors in the antidepressant-like effect of creatine in the TST. The anti-immobility effect of creatine (1 mg/kg, po) or ketamine (a fast-acting antidepressant, 1 mg/kg, ip) in the TST was prevented by pretreatment of mice with caffeine (3 mg/kg, ip, nonselective adenosine receptor antagonist), 8-cyclopentyl-1,3-dipropylxanthine (DPCPX) (2 mg/kg, ip, selective adenosine A1 receptor antagonist), and 4-(2-[7-amino-2-{2-furyl}{1,2,4}triazolo-{2,3-a}{1,3,5}triazin-5-yl-amino]ethyl)-phenol (ZM241385) (1 mg/kg, ip, selective adenosine A2A receptor antagonist). In addition, the combined administration of subeffective doses of creatine and adenosine (0.1 mg/kg, ip, nonselective adenosine receptor agonist) or inosine (0.1 mg/kg, ip, nucleoside formed by the breakdown of adenosine) reduced immobility time in the TST. Moreover, the administration of subeffective doses of creatine or ketamine combined with N-6-cyclohexyladenosine (CHA) (0.05 mg/kg, ip, selective adenosine A1 receptor agonist), N-6-[2-(3,5-dimethoxyphenyl)-2-(methylphenyl)ethyl]adenosine (DPMA) (0.1 mg/kg, ip, selective adenosine A2A receptor agonist), or dipyridamole (0.1 μg/mouse, icv, adenosine transporter inhibitor) produced a synergistic antidepressant-like effect in the TST. These results indicate that creatine, similarly to ketamine, exhibits antidepressant-like effect in the TST probably mediated by the activation of both adenosine A1 and A2A receptors, further reinforcing the potential of targeting the purinergic system to the management of mood disorders.

Distribution of the creatine transporter throughout the human brain reveals a spectrum of creatine transporter immunoreactivity

Creatine is a molecule that supports energy metabolism in cells. It is carried across the plasma membrane by the creatine transporter. There has been recent interest in creatine for its neuroprotective effects in neurodegenerative diseases and its potential as a therapeutic agent. This study represents the first systematic investigation of the distribution of the creatine transporter in the human brain. We have used immunohistochemical techniques to map out its location and the intensity of staining. The transporter was found to be strongly expressed, especially in the large projection neurons of the brain and spinal cord. These include the pyramidal neurons in the cerebral cortex, Purkinje cells in the cerebellar cortex, and motor neurons of the somatic motor and visceromotor cranial nerve nuclei and the ventral horn of the spinal cord. Many other neurons in the brain also had some degree of creatine transporter immunoreactivity. By contrast, the medium spiny neurons of the striatum and the catecholaminergic neurons of the substantia nigra and locus coeruleus, which are implicated in neurodegenerative diseases, showed a very low to almost absent level of immunoreactivity for the transporter. We propose that the distribution may reflect the energy consumption by different cell types and that the extent of creatine transporter expression is proportional to the cell's energy requirements. Furthermore, the distribution indicates that supplemented creatine would be widely taken up by brain cells, although possibly less by those cells that degenerate in Huntington's and Parkinson's diseases.

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.

Thirteen new patients with guanidinoacetate methyltransferase deficiency and functional characterization of nineteen novel missense variants in the GAMT gene

Guanidinoacetate methyltransferase deficiency (GAMT-D) is an autosomal recessively inherited disorder of creatine biosynthesis. Creatine deficiency on cranial proton magnetic resonance spectroscopy, and elevated guanidinoacetate levels in body fluids are the biomarkers of GAMT-D. In 74 patients, 50 different mutations in the GAMT gene have been identified with missense variants being the most common. Clinical and biochemical features of the patients with missense variants were obtained from their physicians using a questionnaire. In 20 patients, 17 missense variants, 25% had a severe, 55% a moderate, and 20% a mild phenotype. The effect of these variants on GAMT enzyme activity was overexpressed using primary GAMT-D fibroblasts: 17 variants retained no significant activity and are therefore considered pathogenic. Two additional variants, c.22C>A (p.Pro8Thr) and c.79T>C (p.Tyr27His) (the latter detected in control cohorts) are in fact not pathogenic as these alleles restored GAMT enzyme activity, although both were predicted to be possibly damaging by in silico analysis. We report 13 new patients with GAMT-D, six novel mutations and functional analysis of 19 missense variants, all being included in our public LOVD database. Our functional assay is important for the confirmation of the pathogenicity of identified missense variants in the GAMT gene.

Experimental and theoretical investigation of [Al(PCr)(H2O)] complex in aqueous solution

Phosphocreatine is a phosphorylated creatine molecule synthesized in the liver and transported to muscle cells where it is used for the temporary storage of energy. In Alzheimer's disease, the capture of glucose by cells is impaired, which negatively affects the Krebs cycle, leading to problems with the generation of phosphocreatine. Furthermore, the creatine-phosphocreatine system, regulated by creatine kinase, is affected in the brains of Alzheimer's disease patients. Aluminum ions are associated with Alzheimer's disease. Al(III) decreases cell viability and increases the fluidity of the plasma membrane, profoundly altering cell morphology. In this study, one of the complexes formed by Al(III) and phosphocreatine in aqueous solution was investigated by potentiometry, (31)P and (27)Al NMR, Raman spectroscopy and density functional theory (DFT) calculations. The log KAlPCr value was 11.37±0.03. Phosphocreatine should act as a tridentate ligand in this complex. The (27)Al NMR peak at 48.92ppm indicated a tetrahedral molecule. The fourth position in the arrangement was occupied by a coordinated water molecule. Raman spectroscopy, (31)P NMR and DFT calculations (DFT:B3LYP/6-311++G(**)) indicated that the donor atoms are oxygen in the phosphate group, the nitrogen of the guanidine group and the oxygen of the carboxylate group. Mulliken charges, NBO charges, frontier molecular orbitals, electrostatic potential contour surfaces and mapped electrostatic potential were also examined.

A new multistep induction protocol for the transdifferentiation of bone marrow stromal stem cells into GABAergic neuron-like cells

BACKGROUND

Bone marrow stromal stem cells (BMSC) are appropriate source of multipotent stem cells that are ideally suited for use in various cell-based therapies. It can be differentiated into neuronal-like cells under appropriate conditions. This study examined the effectiveness of co-stimulation of creatine and retinoic acid in increasing the differentiation of BMSC into GABAergic neuron-like cells (GNLC).

METHODS

BMSC isolated from the femurs and tibias of adult rats were cultured in DMEM/F12 medium supplemented with 10% FBS, pre-induced using β-mercaptoethanol β-ME) and induced using retinoic acid (RA) and creatine. Immunostaining of neurofilament 200 kDa, neurofilament 160 kDa, nestin, fibronectin, Gamma-amino butyric acid (GABA) and glutamic acid decarboxylase (GAD) 65/67 were used to evaluate the transdifferentiation of BMSC into GNLC and to evaluate the effectiveness of pre-induction and induction assays. The expression of genes that encode fibronectin, octamer-binding transcription factor 4 (Oct-4), GAD 65/67 and the vesicular GABA transporter was examined in BMSC and GNLC by using RT-PCR assays during transdifferentiation of BMSC into GLNC.

RESULTS

Co-stimulation with RA and creatine during the induction stage doubled the rates of GABAergic differentiation compared with induction using creatine alone, resulting in a 71.6% yield for GLNC. RT-PCR showed no expression of Oct-4 and fibronectin after the induction stage.

CONCLUSION

The results of this study showed that the application of β-ME, RA, and creatine induced the transdifferentiation of BMSC into GLNC.