Taurine recovers mice emotional learning and memory disruptions associated with fragile x syndrome in context fear and auditory cued-conditioning

Untargeted metabolomic, and proteomic analysis identifies metabolic biomarkers and pathway alterations in individuals with 22q11.2 deletion syndrome

INTRODUCTION

The chromosome 22q11.2 deletion syndrome (22q11.2DS) is characterized by a well-defined microdeletion and is associated with a wide range of brain-related phenotypes including schizophrenia spectrum disorders (SCZ), autism spectrum disorders (ASD), anxiety disorders and attention deficit disorders (ADHD). The typically deleted region in 22q11.2DS contains multiple genes which haploinsufficiency has the potential of altering the protein and the metabolic profiles.

OBJECTIVES

Alteration in metabolic processes and downstream protein pathways during the early brain development may help to explain the increased prevalence of the observed neurodevelopmental phenotypes in 22q11.2DS. However, relatively little is known about the correlation of dysregulated protein/metabolite expression and neurobehavioral impairments in individuals who developed them over time.

METHODS

In this study, we performed untargeted metabolic and proteomic analysis in plasma samples derived from 30 subjects including 16 participants with 22q11.2DS and 14 healthy controls (TD) enrolled in a longitudinal study, aiming to identify a metabolic and protein signature informing about the underlying mechanisms involved in disease development and progression. The metabolic and proteomic profiles were also compared between the participants with 22q11.2DS with and without various comorbidities, such as medical involvement, psychiatric conditions, and autism spectrum disorder (ASD) to detect potential changes among multiple specimens, collected overtime, with the aim to understand the basic underlying mechanisms involved in disease development and progression.

RESULTS

We observed a large number of statistically significant differences in metabolites between the two groups. Among them, the levels of taurine and arachidonic acid were significantly lower in 22q11.2DS compared to the TD group. In addition, we identified 16 proteins that showed significant changes in expression levels (adjusted P < 0.05) in 22q11.2DS as compared to TD, including those involved in 70 pathways such as gene expression, the PI3K-Akt signaling pathway and the complement system. Within participants with 22q11.2DS, no significant changes in those with and without medical or psychiatric conditions were observed.

CONCLUSION

To our knowledge, this is the first report on plasma metabolic and proteomic profiling and on the identification of unique biomarkers in 22q11.2DS. These findings may suggest the potential role of the identified metabolites and proteins as biomarkers for the onset of comorbid conditions in 22q11.2DS. Ultimately, the altered protein pathways in 22q11.2DS may provide insights of the biological mechanisms underlying the neurodevelopmental phenotype and may provide missing molecular outcome measures in future clinical trials to assess early-diagnosis treatment and the efficacy of response to targeted treatment.

Taurine-Derived Compounds Produce Anxiolytic Effects in Rats Following Developmental Lead Exposure

Lead (Pb2+) is a developmental neurotoxicant that disrupts the GABA-shift and subsequently causes alterations in the brain's excitation-to-inhibition (E/I) balance. Taurine is a well-established neuroprotective and inhibitory compound for regulating brain excitability. Since mechanistically taurine can facilitate neuronal inhibition through the GABA-AR, the present study examined the anxiolytic potential of taurine derivatives. Treatment groups consisted of the following developmental Pb2+-exposures: Control (0 ppm) and Perinatal (150 ppm or 1,000 ppm lead acetate in the drinking water). Rats were scheduled for behavioral tests between postnatal days (PND) 36-45 with random drug assignments to either saline, taurine, or taurine-derived compound (TD-101, TD-102, or TD-103) to assess the rats' responsivity to each drug in mitigating the developmental Pb2+-exposure and anxiety-like behaviors through the GABAergic system. Long-Evans hooded rats were assessed using an open field (OF) test for preliminary locomotor assessment. Twenty-four hours later, the same rats were exposed to the elevated plus maze (EPM) and were given an i.p. injection of 43 mg/Kg of the saline, taurine, or TD drugs 15 min prior to testing. Each rat was tested using the triple-blind random assignment method for each drug condition. The OF data revealed that Control female rats had increased locomotor activity over Control male rats, and the Pb2+-exposed males and females had increased locomotor activity when compared to the Control male and female rats. However, in the EPM, the Control female rats exhibited more anxiety-like behaviors over Control male rats, and the Pb2+-exposed male and female rats showed selective responsivity to TD drugs when compared to taurine. For Pb2+-exposed males, TD-101 showed consistent recovery of anxiety-like behaviors similar to that of taurine regardless of Pb2+ dose, whereas in Pb2+-exposed females TD-101 and TD-103 showed greater anxiolytic responses in the EPM. The results from the present psychopharmacological study suggests that taurine and its derivatives are interesting drug candidates to explore sex-specific mechanisms and actions of taurine and the associated GABAergic receptor properties by which these compounds alleviate anxiety as a potential behavioral pharmacotherapy for neurodevelopmental Pb2+ exposure.

L-Methionine Protects against Oxidative Stress and Mitochondrial Dysfunction in an In Vitro Model of Parkinson's Disease

Methionine is an aliphatic, sulfur-containing, essential amino acid that has been demonstrated to have crucial roles in metabolism, innate immunity, and activation of endogenous antioxidant enzymes, including methionine sulfoxide reductase A/B and the biosynthesis of glutathione to counteract oxidative stress. Still, methionine restriction avoids altered methionine/transmethylation metabolism, thus reducing DNA damage and possibly avoiding neurodegenerative processes. In this study, we wanted to study the preventive effects of methionine in counteracting 6-hydroxydopamine (6-OHDA)-induced injury. In particular, we analyzed the protective effects of the amino acid L-methionine in an in vitro model of Parkinson's disease and dissected the underlying mechanisms compared to the known antioxidant taurine to gain insights into the potential of methionine treatment in slowing the progression of the disease by maintaining mitochondrial functionality. In addition, to ascribe the effects of methionine on mitochondria and oxidative stress, methionine sulfoxide was used in place of methionine. The data obtained suggested that an L-methionine-enriched diet could be beneficial during aging to protect neurons from oxidative imbalance and mitochondrial dysfunction, thus preventing the progression of neurodegenerative processes.

Mechanisms underlying auditory processing deficits in Fragile X syndrome

Autism spectrum disorders (ASD) are strongly associated with auditory hypersensitivity or hyperacusis (difficulty tolerating sounds). Fragile X syndrome (FXS), the most common monogenetic cause of ASD, has emerged as a powerful gateway for exploring underlying mechanisms of hyperacusis and auditory dysfunction in ASD. This review discusses examples of disruption of the auditory pathways in FXS at molecular, synaptic, and circuit levels in animal models as well as in FXS individuals. These examples highlight the involvement of multiple mechanisms, from aberrant synaptic development and ion channel deregulation of auditory brainstem circuits, to impaired neuronal plasticity and network hyperexcitability in the auditory cortex. Though a relatively new area of research, recent discoveries have increased interest in auditory dysfunction and mechanisms underlying hyperacusis in this disorder. This rapidly growing body of data has yielded novel research directions addressing critical questions regarding the timing and possible outcomes of human therapies for auditory dysfunction in ASD.

Preclinical testing of the ketogenic diet in fragile X mice

The ketogenic diet is highly effective at attenuating seizures in refractory epilepsy, and accumulating evidence in the literature suggests that it may be beneficial in autism. To our knowledge, no one has studied the ketogenic diet in any fragile X syndrome (FXS) model. FXS is the leading known genetic cause of autism. Herein, we tested the effects of chronic ketogenic diet treatment on seizures, body weight, ketone and glucose levels, diurnal activity levels, learning and memory, and anxiety behaviors in Fmr1^KO and littermate control mice as a function of age. The ketogenic diet selectively attenuates seizures in male but not female Fmr1^KO mice and differentially affects weight gain and diurnal activity levels dependent on Fmr1 genotype, sex and age.

Taurine and its analogs in neurological disorders: Focus on therapeutic potential and molecular mechanisms

Taurine is a sulfur-containing amino acid and known as semi-essential in mammals and is produced chiefly by the liver and kidney. It presents in different organs, including retina, brain, heart and placenta and demonstrates extensive physiological activities within the body. In the several disease models, it attenuates inflammation- and oxidative stress-mediated injuries. Taurine also modulates ER stress, Ca2+ homeostasis and neuronal activity at the molecular level as part of its broader roles. Different cellular processes such as energy metabolism, gene expression, osmosis and quality control of protein are regulated by taurine. In addition, taurine displays potential ameliorating effects against different neurological disorders such as neurodegenerative diseases, stroke, epilepsy and diabetic neuropathy and protects against injuries and toxicities of the nervous system. Several findings demonstrate its therapeutic role against neurodevelopmental disorders, including Angelman syndrome, Fragile X syndrome, sleep-wake disorders, neural tube defects and attention-deficit hyperactivity disorder. Considering current biopharmaceutical limitations, developing novel delivery approaches and new derivatives and precursors of taurine may be an attractive option for treating neurological disorders. Herein, we present an overview on the therapeutic potential of taurine against neurological disorders and highlight clinical studies and its molecular mechanistic roles. This article also addresses the neuropharmacological potential of taurine analogs.

Early Neurodevelopmental Exposure to Low Lead Levels Induces Fronto-executive Dysfunctions That Are Recovered by Taurine Co-treatment in the Rat Attention Set-Shift Test: Implications for Taurine as a Psychopharmacotherapy Against Neurotoxicants

Lead (Pb²⁺) is a developmental neurotoxicant that causes lifelong cognitive dysfunctions. In particular, Pb²⁺-induced frontoexecutive dysfunctions emerge later in life when the cortex is fully myelinated, thereby permitting the ability to assess the extent to which Pb²⁺ has developmentally impacted higher order cognitive and behavioral systems. The present study evaluated the effects of developmental Pb²⁺-exposure (150 ppm lead acetate in the drinking water) in Long Evans Hooded rats through the Attention Set-Shift Test (ASST) between postnatal days (PND) 60-90. Treatment groups were comprised of Control (0 ppm), Perinatal (150 ppm), and Perinatal+Taurine (150 ppm + 0.05% Taurine in the drinking water) rats (N = 36; n = 6 per treatment group for each sex). Frontoexecutive functions were evaluated based on trials-to-criterion (TTC) and errors-to-criterion (ETC) measures for simple and complex discriminations (SD & CD), intradimensional and extradimensional shifts (ID & ED), as well as reversals (Rev) of the CD, I-, and ED stages, respectively. Post-testing, the prelimbic (PrL), infralimbic (IL), orbital ventral frontal (OV), orbital ventro-lateral (OVL), and hippocampal (HP) brain regions were extracted and processed through Liquid Chromatography/Mass Spectrophotometry (LC/MS) for determining the GABA and Taurine ratios relative to Glutamate, Dopamine, Norepinephrine, Epinephrine, and Serotonin. The ASST data revealed that Perinatal rats are negatively impacted by developmental Pb²⁺-exposures evidenced by increased TTC and ETC to learn the SD, ID, and ID-Rev with unique sex-based differences in frontoexecutive dysfunctions. Moreover, Perinatal+Taurine co-treated rats exhibited a recovery of the frontoexecutive dysfunctions observed in Perinatal rats to levels equivalent to Control rats across both sexes. The LC/MS data revealed altered brain sub-region specific patterns across the PrL, IL, OV, OVL, and HP in response to developmental Pb²⁺-exposure that produced an altered neurochemical signaling profile in a sex-dependent manner, which may underlie the observed frontoexecutive dysfunctions, cognitive inflexibility, and associated motivation deficits. When taurine co-treatment was administered concurrently for the duration of developmental Pb²⁺-exposure, the observed frontoexecutive dysfunctions were significantly reduced in both ASST task performance and neurochemical ratios that were comparable to Control levels for both sexes. Altogether, the data suggest that taurine co-treatment may facilitate neuroprotection, mitigate neurotransmitter excitability balancing, and perhaps ameliorate against neurotoxicant exposures in early development as a potential psychopharmacotherapy.

Taurine Recovery of Learning Deficits Induced by Developmental Pb2+ Exposure

Lead (Pb2+) is a historically well-documented environmental neurotoxin that produces developmental cognitive learning and memory impairments. These early neurodevelopmental impairments cause increased brain excitability via disruption of Ca2+ mediated signaling during critical periods of synaptogenesis inducing competition with Ica2+ through NMDARs resulting in altered brain development and functioning across the lifespan. Interestingly, Pb2+ has been shown to decrease GABA transport and uptake, decrease spontaneous and depolarization-evoked GABA neurotransmission and lower the expression of glutamic acid decarboxylase (GAD); thereby, limiting excitatory GABAergic influences that regulate early developmental brain excitability and reducing inhibition across mature GABAergic networks. Taurine has been shown to regulate brain excitability in the mature brain through GABAAR mediated inhibition, thereby attenuating improper brain excitability. Mechanistically, taurine is developmentally a potent neuromodulator that acts as a GABAAR agonist and more recently has been reported as a partial agonist for NMDARs through glycine sites. We investigated the effects of developmental Pb2+ exposure on the rat's mature inhibitory cognitive control abilities pharmacologically through anxiety and emotional learning-related behaviors and whether taurine could recover Pb2+ induced neurodevelopmental behavioral deficits later in life. Results showed that Pb2+ increased anxiety symptoms in the open field and hole board test, increased sensitivity to context fear training with cognitive deficits in both acquisition and extinction learning while producing learning deficits and inabilities in acquiring inhibitory learned associations through the acoustic startle response and pre-pulse inhibition (ASR-PPI) test. Interestingly, taurine recovered Pb2+ developmentally induced behavioral deficits in the open field and hole board test evidenced by decreased freezing and increased exploration behaviors and facilitated inhibitory dependent ASR-PPI learning to levels higher than controls. In contrast, Baclofen, a GABABR agonist, dose dependently showed no interaction with Pb2+ effects on ASR-PPI learning. Thus, taurine may work as an important neuromodulator at both GABAARs and NMDARs glycine sites, thereby increasing inhibition, enhancing Ca2+-mediated signaling, and decreasing the altered brain excitability, which impedes learning and memory from early Pb2+ exposure. Taken together our data suggests that GABAAR dependent inhibitory learning is altered by early Pb2+ exposure and taurine was able to recover these Pb2+ induced deficits through neuromodulation of GABAARs and potentially NMDARs later in life. These findings may pave the way for further exploration of taurine as a pharmacotherapy for neurodevelopmental lead poisoning in both animal and clinical models.

Effects and Mechanisms of Taurine as a Therapeutic Agent

Taurine is an abundant, β-amino acid with diverse cytoprotective activity. In some species, taurine is an essential nutrient but in man it is considered a semi-essential nutrient, although cells lacking taurine show major pathology. These findings have spurred interest in the potential use of taurine as a therapeutic agent. The discovery that taurine is an effective therapy against congestive heart failure led to the study of taurine as a therapeutic agent against other disease conditions. Today, taurine has been approved for the treatment of congestive heart failure in Japan and shows promise in the treatment of several other diseases. The present review summarizes studies supporting a role of taurine in the treatment of diseases of muscle, the central nervous system, and the cardiovascular system. In addition, taurine is extremely effective in the treatment of the mitochondrial disease, mitochondrial encephalopathy, lactic acidosis, and stroke-like episodes (MELAS), and offers a new approach for the treatment of metabolic diseases, such as diabetes, and inflammatory diseases, such as arthritis. The review also addresses the functions of taurine (regulation of antioxidation, energy metabolism, gene expression, ER stress, neuromodulation, quality control and calcium homeostasis) underlying these therapeutic actions.

Taurine Administration Recovers Motor and Learning Deficits in an Angelman Syndrome Mouse Model

Angelman syndrome (AS, MIM 105830) is a rare neurodevelopmental disorder affecting 1:10–20,000 children. Patients show moderate to severe intellectual disability, ataxia and absence of speech. Studies on both post-mortem AS human brains and mouse models revealed dysfunctions in the extra synaptic gamma-aminobutyric acid (GABA) receptors implicated in the pathogenesis. Taurine is a free intracellular sulfur-containing amino acid, abundant in brain, considered an inhibiting neurotransmitter with neuroprotective properties. As taurine acts as an agonist of GABA-A receptors, we aimed at investigating whether it might ameliorate AS symptoms. Since mice weaning, we orally administered 1 g/kg/day taurine in water to Ube3a-deficient mice. To test the improvement of motor and cognitive skills, Rotarod, Novel Object Recognition and Open Field tests were assayed at 7, 14, 21 and 30 weeks, while biochemical tests and amino acid dosages were carried out, respectively, by Western-blot and high-performance liquid chromatography (HPLC) on frozen whole brains. Treatment of Ube3a^m−/p+ mice with taurine significantly improved motor and learning skills and restored the levels of the post-synaptic PSD-95 and pERK1/2-ERK1/2 ratio to wild type values. No side effects of taurine were observed. Our study indicates taurine administration as a potential therapy to ameliorate motor deficits and learning difficulties in AS.