Red blood cell adenine nucleotides abnormalities in Down syndrome

Meta-analysis of metabolites involved in bioenergetic pathways reveals a pseudohypoxic state in Down syndrome

Clinical observations and preclinical studies both suggest that Down syndrome (DS) may be associated with significant metabolic and bioenergetic alterations. However, the relevant scientific literature has not yet been systematically reviewed. The aim of the current study was to conduct a meta-analysis of metabolites involved in bioenergetics pathways in DS to conclusively determine the difference between DS and control subjects. We discuss these findings and their potential relevance in the context of pathogenesis and experimental therapy of DS. Articles published before July 1, 2020, were identified by using the search terms “Down syndrome” and “metabolite name” or “trisomy 21” and “metabolite name”. Moreover, DS-related metabolomics studies and bioenergetics literature were also reviewed. 41 published reports and associated databases were identified, from which the descriptive information and the relevant metabolomic parameters were extracted and analyzed. Mixed effect model revealed the following changes in DS: significantly decreased ATP, CoQ10, homocysteine, serine, arginine and tyrosine; slightly decreased ADP; significantly increased uric acid, succinate, lactate and cysteine; slightly increased phosphate, pyruvate and citrate. However, the concentrations of AMP, 2,3-diphosphoglycerate, glucose, and glutamine were comparable in the DS vs. control populations. We conclude that cells of subjects with DS are in a pseudo-hypoxic state: the cellular metabolic and bio-energetic mechanisms exhibit pathophysiological alterations that resemble the cellular responses associated with hypoxia, even though the supply of the cells with oxygen is not disrupted. This fundamental alteration may be, at least in part, responsible for a variety of functional deficits associated with DS, including reduced exercise difference, impaired neurocognitive status and neurodegeneration.

Mitochondrial and Redox Modifications in Huntington Disease Induced Pluripotent Stem Cells Rescued by CRISPR/Cas9 CAGs Targeting

Mitochondrial deregulation has gained increasing support as a pathological mechanism in Huntington’s disease (HD), a genetic-based neurodegenerative disorder caused by CAG expansion in the HTT gene. In this study, we thoroughly investigated mitochondrial-based mechanisms in HD patient-derived iPSC (HD-iPSC) and differentiated neural stem cells (NSC) versus control cells, as well as in cells subjected to CRISPR/Cas9-CAG repeat deletion. We analyzed mitochondrial morphology, function and biogenesis, linked to exosomal release of mitochondrial components, glycolytic flux, ATP generation and cellular redox status. Mitochondria in HD cells exhibited round shape and fragmented morphology. Functionally, HD-iPSC and HD-NSC displayed lower mitochondrial respiration, exosomal release of cytochrome c, decreased ATP/ADP, reduced PGC-1α and complex III subunit expression and activity, and were highly dependent on glycolysis, supported by pyruvate dehydrogenase (PDH) inactivation. HD-iPSC and HD-NSC mitochondria showed ATP synthase reversal and increased calcium retention. Enhanced mitochondrial reactive oxygen species (ROS) were also observed in HD-iPSC and HD-NSC, along with decreased UCP2 mRNA levels. CRISPR/Cas9-CAG repeat deletion in HD-iPSC and derived HD-NSC ameliorated mitochondrial phenotypes. Data attests for intricate metabolic and mitochondrial dysfunction linked to transcriptional deregulation as early events in HD pathogenesis, which are alleviated following CAG deletion.

Adenine and Pyridine Nucleotides in the Red Blood Cells of Subjects with Solid Tumors

The concentration of adenine (ATP, ADP, AMP) and pyridine (NADP+, NADPH, NAD+, NADH) nucleotides in the erythrocytes of subjects affected by solid tumors was evaluated using a method which allows their simultaneous extraction and reverse-phase high-performance liquid chromatographic analysis. The results showed a lower level of ATP in the erythrocytes of subjects affected by solid tumors, whereas no significant modifications were observed in the other compounds. In fact, the mean value of ATP in these subjects was 27 % lower than that of normal adults. This fact is discussed in relation to other enzymatic and metabolic modifications previously observed in red blood cells.

Red blood cell metabolism in Down syndrome: hints on metabolic derangements in aging

Red blood cells (RBCs) are the most abundant cell in the human body. During their ∼120-day life span in the circulatory system, RBCs release oxygen to all human tissues while being exposed to tissue metabolic activity. Owing to the relative simplicity of their intrinsic metabolism and the abundance of metabolite transporters in RBC membranes, the metabolism of mature erythrocytes indirectly mirrors systemic metabolic homeostasis and its alterations as a function of physiological factors, such as aging. Trisomy 21 (T21), the etiological factor of Down syndrome (DS), has been shown to cause chronic autoinflammation, promoting alterations in RBC life span, size (macrocytosis), and redox homeostasis. Here, we provide the first mass spectrometry-based relative and absolute quantitative metabolomic description of human RBCs from volunteer disomic and trisomic donors (n = 97). The results indicate a widespread deregulation of T21 RBC metabolism, including significant intracellular accumulation of lactate, amino acids (except methionine), purine catabolites, glutathione metabolites, carboxylic acids, bile acids (especially conjugated ones), and acyl-conjugated carnitines. These changes may underlie some of the well-established comorbidities in DS. Finally, we identify sex- and/or T21-specific metabolic signatures of aging.

Uncoupling Protein 2 Inhibition Exacerbates Glucose Fluctuation-Mediated Neuronal Effects

Though glucose fluctuations have been considered as an adverse factor for the development of several diabetes-related complications, their impact in the central nervous system is still not fully elucidated. This study was conducted to evaluate the responses of neuronal cells to different glycemic exposures alongside to elucidate the role of uncoupling protein 2 (UCP2) in regulating such responses. To achieve our goals, primary cortical neurons were submitted to constant high (HG)/low (LG) or glucose level variations (GVs), and the pharmacological inhibition of UCP2 activity was performed using genipin. Results obtained show that GV decreased neuronal cells' viability, mitochondrial membrane potential, and manganese superoxide dismutase activity and increased reactive oxygen species (ROS) production. GV also caused an increase in the glutathione/glutathione disulfide ratio and in the protein expression levels of nuclear factor E2-related factor 2 (NRF2), UCP2, NADH-ubiquinone oxidoreductase chain 1 (ND1), and mitochondrially encoded cytochrome c oxidase I (MTCO1), both mitochondrial DNA encoded subunits of the electron transport chain. Contrariwise, genipin abrogated all those compensations and increased the levels of caspase 3-like activity, potentiated mitochondrial ROS levels, and the loss of neuronal synaptic integrity, decreased the protein expression levels of NRF1, and increased the protein expression levels of UCP5. Further, in the control and LG conditions, genipin increased mitochondrial ROS and the protein expression levels of UCP4, postsynaptic density protein 95 (PSD95), ND1, and MTCO1. Overall, these observations suggest that UCP2 is in the core of neuronal cell protection and/or adaptation against GV-mediated effects and that other isoforms of neuronal UCPs can be upregulated to compensate the inhibition of UCP2 activity.

Adenosine A1 receptor antagonist rolofylline alleviates axonopathy caused by human Tau ΔK280

Accumulation of Tau is a characteristic hallmark of several neurodegenerative diseases but the mode of toxic action of Tau is poorly understood. Here, we show that the Tau protein is toxic due to its aggregation propensity, whereas phosphorylation and/or missorting is not sufficient to cause neuronal dysfunction. Aggregate-prone Tau accumulates, when expressed in vitro at near-endogenous levels, in axons as spindle-shaped grains. These axonal grains contain Tau that is folded in a pathological (MC-1) conformation. Proaggregant Tau induces a reduction of neuronal ATP, concomitant with loss of dendritic spines. Counterintuitively, axonal grains of Tau are not targeted for degradation and do not induce a molecular stress response. Proaggregant Tau causes neuronal and astrocytic hypoactivity and presynaptic dysfunction instead. Here, we show that the adenosine A₁ receptor antagonist rolofylline (KW-3902) is alleviating the presynaptic dysfunction and restores neuronal activity as well as dendritic spine levels in vitro. Oral administration of rolofylline for 2-wk to 14-mo-old proaggregant Tau transgenic mice restores the spatial memory deficits and normalizes the basic synaptic transmission. These findings make rolofylline an interesting candidate to combat the hypometabolism and neuronal dysfunction associated with Tau-induced neurodegenerative diseases.

Pathogenesis of mental deficiency in trisomy 21

In trisomy 21, pathogenesis of mental retardation is still poorly understood although the knowledge of the genic content of chromosome 21 is steadily increasing. Short of discovering how to silence selectively one of the 3 chromosomes 21, no rational medication can be envisaged before pathogenesis has been unraveled, at least partially. A biochemical scheme of impairment of mental efficiency is presented. Secondarily, the possible deleterious effects of a given gene overdose are discussed. Cu/Zn SOD, cystathionine beta synthase, S 100 beta protein, phosphofructokinase, purine synthesis and adenosine pharmacology, thyroid disturbance, and elevated TSH with low rT3 as well as biopterine metabolism interferences are reviewed. It is observed that the metabolic paths controlled by these genes, although unrelated at first glance, are in fact tightly related by their effects, just as if synteny was in some way related to biochemical cooperation or mutually controlled regulation. Experiments in vitro have demonstrated a peculiar sensitivity of trisomic 21 lymphocytes to methotrexate. From this starting point, systematic research of special sensitivities has begun. Clinical observations and relevant statistical methods allow study of the speed of mental development under various medications. The interest of regulating thyroid metabolism, when needed, is exemplified. Reequilibration of monocarbon metabolism is discussed and the seemingly favourable effect of folinic acid medication in pseudo-Alzheimer complication is presented.

The role and regulation of adenosine in the central nervous system

Adenosine is a modulator that has a pervasive and generally inhibitory effect on neuronal activity. Tonic activation of adenosine receptors by adenosine that is normally present in the extracellular space in brain tissue leads to inhibitory effects that appear to be mediated by both adenosine A1 and A2A receptors. Relief from this tonic inhibition by receptor antagonists such as caffeine accounts for the excitatory actions of these agents. Characterization of the effects of adenosine receptor agonists and antagonists has led to numerous hypotheses concerning the role of this nucleoside. Previous work has established a role for adenosine in a diverse array of neural phenomena, which include regulation of sleep and the level of arousal, neuroprotection, regulation of seizure susceptibility, locomotor effects, analgesia, mediation of the effects of ethanol, and chronic drug use.

Differences in purine metabolism in patients with Down's syndrome

Three enzymes intervening in de novo purine synthesis, as well as cystathionine B-synthetase, have been mapped to chromosome 21. In order to gain a better understanding of purine synthesis anomalies in Down's syndrome, the present authors studied the variations in mitotic index of lymphocyte cultures to which various inhibitors or metabolites of purine synthesis had been added. In spite of common gene dosage effects, unexpected and highly significant differences were noted between Down's syndrome patients without complications and those presenting with additional psychotic features. In Down's syndrome patients without complications, a highly significant decrease in mitotic index was noted in the presence of exogenous inosine. A significant decrease in the presence of adenosine and guanosine was also noted. These findings are in keeping with the expected metabolic repercussions of genes mapped to chromosome 21. In Down's syndrome patients with psychotic complications, the in vitro reactions were quite different. A paradoxal increase in mitotic index was noted in the presence of inosine and of adenosine, but the response to guanosine did not differ from that observed in normal controls. These findings were unexpected and seem to indicate that, in spite of the gene dosage effect, psychotic Down's syndrome patients are unable to compensate abnormal purine synthesis and resulting imbalances. Furthermore, a marked difference in purine metabolic reactions was noted between Down's syndrome patients receiving supplemental folic/folinic acid and those on no therapy. This suggests that some modulation of the gene dosage effect may be possible.

The levels of adenine nucleotides and pyridine coenzymes in red blood cells from the newborn, determined simultaneously by HPLC

The concentrations of ATP, ADP, AMP; NADP and NADPH; NAD and NADH were determined in erythrocytes from healthy newborns and compared with those obtained in healthy adults. No significant differences were found for the adenine nucleotide concentrations, but NADH levels were reduced in newborn erythrocytes, with a consequent increase in the NAD/NADH ratio. Moreover, in newborn erythrocytes increased levels of NADP were observed, with a consequent increase in the NADP/NADPH ratio and a decrease in the NAD/NADP ratio. These results indicate the need to use reference values of the ratios NAD/NADH, NADP/NADPH and NAD/NADP from healthy newborns in the study of syndromes affecting the metabolism of erythrocytes in the newborn.

A very fast ion-pair reversed-phase HPLC method for the separation of the most significant nucleotides and their degradation products in human red blood cells

A simple and fast ion pair reversed-phase high-performance liquid chromatographic method has been developed for the simultaneous determination of ATP, ADP, AMP, GTP, GDP, IMP, NADP+, NADPH+, NAD+, NADH, ADP-ribose, inosine, adenosine, hypoxanthine, and xanthine. This method allows us to have a complete picture of the most important nucleotides present in fresh human erythrocytes. Furthermore it is particularly useful in the study of the erythrocyte adenine nucleotide catabolism allowing the detection of degradation products such as IMP, inosine, adenosine, hypoxanthine, and xanthine. The separation of the compounds under investigation is achieved in less than 15 min using a reversed-phase 3-micron Supelcosil LC-18 column and adding tetrabutylammonium, as ion-pair agent, to the buffers. The short time of analysis, the high reproducibility of the system, and the accurate evaluation of the compounds of interest make this method particularly suitable for routine analysis. Finally it is possible to use this assay as an alternative method of measuring activities of enzymes which catalyze reactions involving some of these compounds, as in the case of Na+-K+ ATPase, AMP deaminase, and adenosine deaminase.