Sodium/myo-Inositol transporters: substrate transport requirements and regional brain expression in the TgCRND8 mouse model of amyloid pathology

Anti-Alzheimer Potential of a New (+)-Pinitol Glycoside Isolated from Tamarindus indica Pulp: In Vivo and In Silico Evaluations

Tamarindus indica Linn (tamarind, F. Leguminosae) is one of the most widely consumed edible fruits in the world. Phytochemical investigation of tamarind pulp n-butanol fraction yielded one new (+)-pinitol glycoside compound 1 (25% w/w), and 1D, 2D NMR, and HRESIMS investigation were used to confirm the new compound's structure. (+)-Pinitol glycoside showed anti-Alzheimer potential that was confirmed in prophylactic and treatment groups by decreasing time for the T-maze test; decreased TAO, brain and serum AChE, MDA, tau protein levels, and β amyloid peptide protein levels; and increasing GPX, SOD levels, and in vivo regression of the neurodegenerative features of Alzheimer's dementia in an aluminum-intoxicated rat model. The reported molecular targets for human Alzheimer's disease were then used in a network pharmacology investigation to examine their complex interactions and identify the key targets in the disease pathogenesis. An in silico-based analysis (molecular docking, binding free energy calculation (ΔG_Binding), and molecular dynamics simulation) was performed to identify the potential targets for compound 1. The findings of this study may lead to the development of dietary supplements for the treatment of Alzheimer's disease.

A native chemical chaperone in the human eye lens

Cataract is one of the most prevalent protein aggregation disorders and still the most common cause of vision loss worldwide. The metabolically quiescent core region of the human lens lacks cellular or protein turnover; it has therefore evolved remarkable mechanisms to resist light-scattering protein aggregation for a lifetime. We now report that one such mechanism involves an unusually abundant lens metabolite, myo-inositol, suppressing aggregation of lens crystallins. We quantified aggregation suppression using our previously well-characterized in vitro aggregation assays of oxidation-mimicking human γD-crystallin variants and investigated myo-inositol’s molecular mechanism of action using solution NMR, negative-stain TEM, differential scanning fluorometry, thermal scanning Raman spectroscopy, turbidimetry in redox buffers, and free thiol quantitation. Unlike many known chemical chaperones, myo-inositol’s primary target was not the native, unfolded, or final aggregated states of the protein; rather, we propose that it was the rate-limiting bimolecular step on the aggregation pathway. Given recent metabolomic evidence that it is severely depleted in human cataractous lenses compared to age-matched controls, we suggest that maintaining or restoring healthy levels of myo-inositol in the lens may be a simple, safe, and globally accessible strategy to prevent or delay lens opacification due to age-onset cataract.

New Drug Delivery Systems Developed for Brain Targeting

The blood-brain barrier (BBB) and the blood-cerebrospinal fluid barrier (B_CSF) are two of the most complex and sophisticated concierges that defend the central nervous system (CNS) by numerous mechanisms. While they maintain the neuro-ecological homeostasis through the regulated entry of essential biomolecules, their conservative nature challenges the entry of most of the drugs intended for CNS delivery. Targeted delivery challenges for a diverse spectrum of therapeutic agents/drugs (non-small molecules, small molecules, gene-based therapeutics, protein and peptides, antibodies) are diverse and demand specialized delivery and disease-targeting strategies. This review aims to capture the trends that have shaped the current brain targeting research scenario. This review discusses the physiological, neuropharmacological, and etiological factors that participate in the transportation of various drug delivery cargoes across the BBB/B_CSF and influence their therapeutic intracranial concentrations. Recent research works spanning various invasive, minimally invasive, and non-invasive brain- targeting approaches are discussed. While the pre-clinical outcomes from many of these approaches seem promising, further research is warranted to overcome the translational glitches that prevent their clinical use. Non-invasive approaches like intranasal administration, P-glycoprotein (P-gp) inhibition, pro-drugs, and carrier/targeted nanocarrier-aided delivery systems (alone or often in combination) hold positive clinical prospects for brain targeting if explored further in the right direction.

D-Pinitol-Active Natural Product from Carob with Notable Insulin Regulation

Carob is one of the major food trees for peoples of the Mediterranean basin, but it has also been traditionally used for medicinal purposes. Carob contains many nutrients and active natural products, and D-Pinitol is clearly one of the most important of these. D-Pinitol has been reported in dozens of scientific publications and its very diverse medicinal properties are still being studied. Presently, more than thirty medicinal activities of D-Pinitol have been reported. Among these, many publications have reported the strong activities of D-Pinitol as a natural antidiabetic and insulin regulator, but also as an active anti-Alzheimer, anticancer, antioxidant, and anti-inflammatory, and is also immune- and hepato-protective. In this review, we will present a brief introduction of the nutritional and medicinal importance of Carob, both traditionally and as found by modern research. In the introduction, we will present Carob’s major active natural products. The structures of inositols will be presented with a brief literature summary of their medicinal activities, with special attention to those inositols in Carob, as well as D-Pinitol’s chemical structure and its medicinal and other properties. D-Pinitol antidiabetic and insulin regulation activities will be extensively presented, including its proposed mechanism of action. Finally, a discussion followed by the conclusions and future vision will summarize this article.

Inositol depletion regulates phospholipid metabolism and activates stress signaling in HEK293T cells

Inositol plays a significant role in cellular function and signaling. Studies in yeast have demonstrated an "inositol-less death" phenotype, suggesting that inositol is an essential metabolite. In yeast, inositol synthesis is highly regulated, and inositol levels have been shown to be a major metabolic regulator, with its abundance affecting the expression of hundreds of genes. Abnormalities in inositol metabolism have been associated with several human disorders. Despite its importance, very little is known about the regulation of inositol synthesis and the pathways regulated by inositol in human cells. The current study aimed to address this knowledge gap. Knockout of ISYNA1 (encoding myo-inositol-3-P synthase 1) in HEK293T cells generated a human cell line that is deficient in de novo inositol synthesis. ISYNA1-KO cells exhibited inositol-less death when deprived of inositol. Lipidomic analysis identified inositol depletion as a global regulator of phospholipid levels in human cells, including downregulation of phosphatidylinositol (PI) and upregulation of the phosphatidylglycerol (PG)/cardiolipin (CL) branch of phospholipid metabolism. RNA-Seq analysis revealed that inositol depletion induced substantial changes in the expression of genes involved in cell signaling, including extracellular signal-regulated kinase (ERK), and genes controlling amino acid transport and protein processing in the endoplasmic reticulum (ER). This study provides the first in-depth characterization of the effects of inositol depletion on phospholipid metabolism and gene expression in human cells, establishing an essential role for inositol in maintaining cell viability and regulating cell signaling and metabolism.

Redox chemistry of lens crystallins: A system of cysteines

The nuclear region of the lens is metabolically quiescent, but it is far from inert chemically. Without cellular renewal and with decades of environmental exposures, the lens proteome, lipidome, and metabolome change. The lens crystallins have evolved exquisite mechanisms for resisting, slowing, adapting to, and perhaps even harnessing the effects of these cumulative chemical modifications to minimize the amount of light-scattering aggregation in the lens over a lifetime. Redox chemistry is a major factor in these damages and mitigating adaptations, and as such, it is likely to be a key component of any successful therapeutic strategy for preserving or rescuing lens transparency, and perhaps flexibility, during aging. Protein redox chemistry is typically mediated by Cys residues. This review will therefore focus primarily on the Cys-rich γ-crystallins of the human lens, taking care to extend these findings to the β- and α-crystallins where pertinent.

Neurometabolite mapping highlights elevated myo-inositol profiles within the developing brain in down syndrome

The neurodevelopmental phenotype in Down Syndrome (DS), or Trisomy 21, is variable including a wide spectrum of cognitive impairment and a high risk of early-onset Alzheimer's disease (AD). A key metabolite of interest within the brain in DS is Myo-inositol (mIns). The NA+/mIns co-transporter is located on human chromosome 21 and is overexpressed in DS. In adults with DS, elevated brain mIns was previously associated with cognitive impairment and proposed as a risk marker for progression to AD. However, it is unknown if brain mIns is increased earlier in development. The aim of this study was to estimate mIns concentration levels and key brain metabolites [N-acetylaspartate (NAA), Choline (Cho) and Creatine (Cr)] in the developing brain in DS and aged-matched controls. We used in vivo magnetic resonance spectroscopy (MRS) in neonates with DS (n = 12) and age-matched controls (n = 26) scanned just after birth (36-45 weeks postmenstrual age). Moreover, we used Mass Spectrometry in early (10-20 weeks post conception) ex vivo fetal brain tissue samples from DS (n = 14) and control (n = 30) cases. Relative to [Cho] and [Cr], we report elevated ratios of [mIns] in vivo in the basal ganglia/thalamus, in neonates with DS, when compared to age-matched typically developing controls. Glycine concentration ratios [Gly]/[Cr] and [Cho]/[Cr] also appear elevated. We observed elevated [mIns] in the ex vivo fetal cortical brain tissue in DS compared with controls. In conclusion, a higher level of brain mIns was evident as early as 10 weeks post conception and was measurable in vivo from 36 weeks post-menstrual age. Future work will determine if this early difference in metabolites is linked to cognitive outcomes in childhood or has utility as a potential treatment biomarker for early intervention.

Neuroimaging and neuropathology studies of X-linked dystonia parkinsonism

X-linked Dystonia Parkinsonism (XDP) is a recessive, genetically inherited neurodegenerative disorder endemic to Panay Island in the Philippines. Clinical symptoms include the initial appearance of dystonia, followed by parkinsonian traits after 10-15 years. The basal ganglia, particularly the striatum, is an area of focus in XDP neuropathology research, as the striatum shows marked atrophy that correlates with disease progression. Thus, XDP shares features of Parkinson's disease symptomatology, in addition to the genetic predisposition and presence of striatal atrophy resembling Huntington's disease. However, further research is required to reveal the detailed pathology and indicators of disease in the XDP brain. First, there are limited neuropathological studies that have investigated neuronal changes and neuroinflammation in the XDP brain. However, multiple neuroimaging studies on XDP patients provide clues to other affected brain regions. Furthermore, molecular pathological studies have elucidated that the main genetic cause of XDP is in the TAF-1 gene, but how this mutation relates to XDP neuropathology still remains to be fully investigated. Hence, we aim to provide an extensive overview of the current literature describing neuropathological changes within the XDP brain, and discuss future research avenues, which will provide a better understanding of XDP neuropathogenesis.

Transcriptome Changes in the Alzheimer's Disease Middle Temporal Gyrus: Importance of RNA Metabolism and Mitochondria-Associated Membrane Genes

We used Illumina Human HT-12 v4 arrays to compare RNA expression of middle temporal gyrus (MTG; BA21) in Alzheimer's disease (AD = 97) and non-demented controls (ND = 98). A total of 938 transcripts were highly differentially expressed (adj p < 0.01; log2 FC ≥ |0.500|, with 411 overexpressed and 527 underexpressed in AD. Our results correlated with expression profiling in neurons from AD and ND obtained by laser capture microscopy in MTG from an independent dataset (log2 FC correlation: r = 0.504; p = 2.2e-16). Additionally, selected effects were validated by qPCR. ANOVA analysis yielded no difference between genders in response to AD, but some gender specific genes were detected (e.g., IL8 and AGRN in males, and HSPH1 and GRM1 in females). Several transcripts were associated with Braak staging (e.g., AEBP1 and DNALI1), antemortem MMSE (e.g., AEBP1 and GFAP), and tangle density (e.g., RNU1G2, and DNALI1). At the pathway level, we detected enrichment of synaptic vesicle processes and GABAergic transmission genes. Finally, applying the Weighted Correlation Network Analysis, we identified four expression modules enriched for neuronal and synaptic genes, mitochondria-associated membrane, chemical stimulus and olfactory receptor and non-coding RNA metabolism genes. Our results represent an extensive description of MTG mRNA profiling in a large sample of AD and ND. These data provide a list of genes associated with AD, and correlated to neurofibrillary tangles density. In addition, these data emphasize the importance of mitochondrial membranes and transcripts related to olfactory receptors in AD.

The Biomedical Uses of Inositols: A Nutraceutical Approach to Metabolic Dysfunction in Aging and Neurodegenerative Diseases

Inositols are sugar-like compounds that are widely distributed in nature and are a part of membrane molecules, participating as second messengers in several cell-signaling processes. Isolation and characterization of inositol phosphoglycans containing myo- or d-chiro-inositol have been milestones for understanding the physiological regulation of insulin signaling. Other functions of inositols have been derived from the existence of multiple stereoisomers, which may confer antioxidant properties. In the brain, fluctuation of inositols in extracellular and intracellular compartments regulates neuronal and glial activity. Myo-inositol imbalance is observed in psychiatric diseases and its use shows efficacy for treatment of depression, anxiety, and compulsive disorders. Epi- and scyllo-inositol isomers are capable of stabilizing non-toxic forms of β-amyloid proteins, which are characteristic of Alzheimer’s disease and cognitive dementia in Down’s syndrome, both associated with brain insulin resistance. However, uncertainties of the intrinsic mechanisms of inositols regarding their biology are still unsolved. This work presents a critical review of inositol actions on insulin signaling, oxidative stress, and endothelial dysfunction, and its potential for either preventing or delaying cognitive impairment in aging and neurodegenerative diseases. The biomedical uses of inositols may represent a paradigm in the industrial approach perspective, which has generated growing interest for two decades, accompanied by clinical trials for Alzheimer’s disease.

Mammalian Solute Carrier (SLC)-like transporters of Legionella pneumophila

Acquisition of nutrients during intra-vacuolar growth of L. pneumophila within macrophages or amoebae is poorly understood. Since many genes of L. pneumophila are acquired by inter-kingdom horizontal gene transfer from eukaryotic hosts, we examined the presence of human solute carrier (SLC)-like transporters in the L. pneumophila genome using I-TASSER to assess structural alignments. We identified 11 SLC-like putative transporters in L. pneumophila that are structurally similar to SLCs, eight of which are amino acid transporters, and one is a tricarboxylate transporter. The two other transporters, LstA and LstB, are structurally similar to the human glucose transporter, SLC2a1/Glut1. Single mutants of lstA or lstB have decreased ability to import, while the lstA/lstB double mutant is severely defective for uptake of glucose. While lstA or lstB single mutants are not defective in intracellular proliferation within Acanthamoeba polyphaga and human monocyte-derived macrophages, the lstA/lstB double mutant is severely defective in both host cells. The two phenotypic defects of the lstA/lstB double mutant in uptake of glucose and intracellular replication are both restored upon complementation of either lstA or lstB. Our data show that the two glucose transporters, LstA and LstB, are redundant and are required for intracellular replication within human macrophages and amoebae.

A guanidine-appended scyllo-inositol derivative AAD-66 enhances brain delivery and ameliorates Alzheimer's phenotypes

Alzheimer's disease (AD) is a degenerative brain disease that destroys memory and other important mental functions but lacks efficient therapeutic agents. Blocking toxic amyloid β (Aβ) could be beneficial for AD and represents a promising therapeutic strategy for AD treatment. scyllo-Inositol (SI) is a potential therapeutic for AD by directly interacting with the Aβ peptide to inhibit Aβ42 fiber formation. Clinical studies of SI showed promising benefits on mild to moderate AD, however, with limitations on dosage regime. A new strategy to enhance the brain delivery of SI is needed to achieve the efficacy with minimum adverse effects. Herein, we report that a novel guanidine-appended SI derivative AAD-66 resulted in more effective reductions of brain Aβ and plaque deposits, gliosis, and behavioral memory deficits in the disease-established 5xFAD mice. Overall, our present study reveals the potential of AAD-66 as a promising therapeutic agent for AD.

Investigating the efficacy of a combination Aβ-targeted treatment in a mouse model of Alzheimer's disease

Amyloid-beta peptide (Aβ) plays a critical role in the pathogenesis of Alzheimer's disease (AD). Here, we explored the use of a combination treatment to reduce amyloid load through microglial phagocytosis in a mouse model of AD. We hypothesized that using an initial treatment of magnetic resonance image guided focused ultrasound (MRIgFUS) to transiently increase the blood-brain barrier (BBB) permeability and enhance the delivery of an Aβ-antibody (BAM-10), followed by scyllo-inositol treatment would result in accelerated clearance. TgCRND8 mice expressing both Swedish (KM670/671NL) and Indiana (V717F) APP mutations under the hamster prion (PrP) promoter at 5 months of age were either treated with scyllo-inositol or received an initial MRIgFUS treatment delivering BAM-10 prior to scyllo-inositol treatment for one month. Treated animals and untreated TgCRND8 littermates were then sacrificed at 6 months of age, and their brains were processed for immunohistochemistry and immunofluorescence. Amyloid load was quantified and analyzed through immunohistochemical staining. Astrocyte and microglial activation were quantified and analyzed through immunofluorescent staining. We found that both the scyllo-inositol treatment and combination treatment, MRIgFUS/BAM10+scyllo-inositol, significantly reduced amyloid load and astrocyte activation in the hippocampus and the cortex. Furthermore, in both treatment paradigms microglial activation and phagocytosis was increased in comparison to the untreated mice. There were no differences detected between the two treatment paradigms. We propose that the 30-day scyllo-inositol treatment saturated the early benefit of the MRIgFUS/BAM-10 treatment. In the future, multiple FUS treatments combined with BAM-10 throughout the duration of scyllo-inositol treatment may lead to more effective amyloid clearance.

Activation of osmolyte pathways in inflammatory myopathy and Duchenne muscular dystrophy points to osmoregulation as a contributing pathogenic mechanism

Alongside well-known nuclear factor κB (NFκB) and its associated cytokine networks, nuclear factor of activated T cells 5 (NFAT5), the master regulator of cellular osmoprotective programs, comes forward as an inflammatory regulator. To gain insight into its yet unexplored role in muscle disease, we studied the expression of NFAT5 target proteins involved in osmolyte accumulation: aldose reductase (AR), taurine transporter (TauT), and sodium myo-inositol co-transporter (SMIT). We analyzed idiopathic inflammatory myopathy and Duchenne muscular dystrophy muscle biopsies and myotubes in culture, using immunohistochemistry, immunofluorescence, and western blotting. We report that the level of constitutive AR was upregulated in patients, most strongly so in Duchenne muscular dystrophy. TauT and SMIT expression levels were induced in patients' muscle fibers, mostly representing regenerating and atrophic fibers. In dermatomyositis, strong staining for AR, TauT, and SMIT in atrophic perifascicular fibers was accompanied by staining for other molecular NFAT5 targets, including chaperones, chemokines, and inducible nitric oxide synthase. In these fibers, NFAT5 and NFκB p65 staining coincided, linking both transcription factors with this important pathogenic hallmark. In sporadic inclusion body myositis, SMIT localized to inclusions inside muscle fibers. In addition, SMIT was expressed by a substantial subset of muscle-infiltrating macrophages and T cells in patient biopsies. Our results indicate that osmolyte pathways may contribute to normal muscle functioning, and that activation of AR, TauT, and SMIT in muscle inflammation possibly contributes to the tissue's failing program of damage control.

Evidence of TAF1 dysfunction in peripheral models of X-linked dystonia-parkinsonism

The molecular dysfunction in X-linked dystonia-parkinsonism is not completely understood. Thus far, only noncoding alterations have been found in genetic analyses, located in or nearby the TATA-box binding protein-associated factor 1 (TAF1) gene. Given that this gene is ubiquitously expressed and is a critical component of the cellular transcription machinery, we sought to study differential gene expression in peripheral models by performing microarray-based expression profiling in blood and fibroblasts, and comparing gene expression in affected individuals vs. ethnically matched controls. Validation was performed via quantitative polymerase chain reaction in discovery and independent replication sets. We observed consistent downregulation of common TAF1 transcripts in samples from affected individuals in gene-level and high-throughput experiments. This signal was accompanied by a downstream effect in the microarray, reflected by the dysregulation of 307 genes in the disease group. Gene Ontology and network analyses revealed enrichment of genes involved in RNA polymerase II-dependent transcription, a pathway relevant to TAF1 function. Thus, the results converge on TAF1 dysfunction in peripheral models of X-linked dystonia-parkinsonism, and provide evidence of altered expression of a canonical gene in this disease. Furthermore, our study illustrates a link between the previously described genetic alterations and TAF1 dysfunction at the transcriptome level.

The "Other" Inositols and Their Phosphates: Synthesis, Biology, and Medicine (with Recent Advances in myo-Inositol Chemistry)

Cell signaling via inositol phosphates, in particular via the second messenger myo-inositol 1,4,5-trisphosphate, and phosphoinositides comprises a huge field of biology. Of the nine 1,2,3,4,5,6-cyclohexanehexol isomers, myo-inositol is pre-eminent, with "other" inositols (cis-, epi-, allo-, muco-, neo-, L-chiro-, D-chiro-, and scyllo-) and derivatives rarer or thought not to exist in nature. However, neo- and d-chiro-inositol hexakisphosphates were recently revealed in both terrestrial and aquatic ecosystems, thus highlighting the paucity of knowledge of the origins and potential biological functions of such stereoisomers, a prevalent group of environmental organic phosphates, and their parent inositols. Some "other" inositols are medically relevant, for example, scyllo-inositol (neurodegenerative diseases) and d-chiro-inositol (diabetes). It is timely to consider exploration of the roles and applications of the "other" isomers and their derivatives, likely by exploiting techniques now well developed for the myo series.

Hypotonic activation of the myo-inositol transporter SLC5A3 in HEK293 cells probed by cell volumetry, confocal and super-resolution microscopy

Swelling-activated pathways for myo-inositol, one of the most abundant organic osmolytes in mammalian cells, have not yet been identified. The present study explores the SLC5A3 protein as a possible transporter of myo-inositol in hyponically swollen HEK293 cells. To address this issue, we examined the relationship between the hypotonicity-induced changes in plasma membrane permeability to myo-inositol P_ino [m/s] and expression/localization of SLC5A3. P_ino values were determined by cell volumetry over a wide tonicity range (100–275 mOsm) in myo-inositol-substituted solutions. While being negligible under mild hypotonicity (200–275 mOsm), P_ino grew rapidly at osmolalities below 200 mOsm to reach a maximum of ∼3 nm/s at 100–125 mOsm, as indicated by fast cell swelling due to myo-inositol influx. The increase in P_ino resulted most likely from the hypotonicity-mediated incorporation of cytosolic SLC5A3 into the plasma membrane, as revealed by confocal fluorescence microscopy of cells expressing EGFP-tagged SLC5A3 and super-resolution imaging of immunostained SLC5A3 by direct stochastic optical reconstruction microscopy (dSTORM). dSTORM in hypotonic cells revealed a surface density of membrane-associated SLC5A3 proteins of 200–2000 localizations/μm². Assuming SLC5A3 to be the major path for myo-inositol, a turnover rate of 80–800 myo-inositol molecules per second for a single transporter protein was estimated from combined volumetric and dSTORM data. Hypotonic stress also caused a significant upregulation of SLC5A3 gene expression as detected by semiquantitative RT-PCR and Western blot analysis. In summary, our data provide first evidence for swelling-mediated activation of SLC5A3 thus suggesting a functional role of this transporter in hypotonic volume regulation of mammalian cells.

The expression of apoptosis inducing factor (AIF) is associated with aging-related cell death in the cortex but not in the hippocampus in the TgCRND8 mouse model of Alzheimer's disease

BACKGROUND

Recent evidence has suggested that Alzheimer's disease (AD)-associated neuronal loss may occur via the caspase-independent route of programmed cell death (PCD) in addition to caspase-dependent mechanisms. However, the brain region specificity of caspase-independent PCD in AD-associated neurodegeneration is unknown. We therefore used the transgenic CRND8 (TgCRND8) AD mouse model to explore whether the apoptosis inducing factor (AIF), a key mediator of caspase-independent PCD, contributes to cell loss in selected brain regions in the course of aging.

RESULTS

Increased expression of truncated AIF (tAIF), which is directly responsible for cell death induction, was observed at both 4- and 6-months of age in the cortex. Concomitant with the up-regulation of tAIF was an increase in the nuclear translocation of this protein. Heightened tAIF expression or translocation was not observed in the hippocampus or cerebellum, which were used as AD-vulnerable and relatively AD-spared regions, respectively. The cortical alterations in tAIF levels were accompanied by increased Bax expression and mitochondrial translocation. This effect was preceded by a significant reduction in ATP content and an increase in reactive oxygen species (ROS) production, detectable at 2 months of age despite negligible amounts of amyloid-beta peptides (Aβ).

CONCLUSIONS

Taken together, these data suggest that AIF is likely to play a region-specific role in AD-related caspase-independent PCD, which is consistent with aging-associated mitochondrial impairment and oxidative stress.

scyllo-Inositol promotes robust mutant Huntingtin protein degradation

Huntington disease is characterized by neuronal aggregates and inclusions containing polyglutamine-expanded huntingtin protein and peptide fragments (polyQ-Htt). We have used an established cell-based assay employing a PC12 cell line overexpressing truncated exon 1 of Htt with a 103-residue polyQ expansion that yields polyQ-Htt aggregates to investigate the fate of polyQ-Htt-drug complexes. scyllo-Inositol is an endogenous inositol stereoisomer known to inhibit accumulation and toxicity of the amyloid-β peptide and α-synuclein. In light of these properties, we investigated the effect of scyllo-inositol on polyQ-Htt accumulation. We show that scyllo-inositol lowered the number of visible polyQ-Htt aggregates and robustly decreased polyQ-Htt protein abundance without concomitant cellular toxicity. We found that scyllo-inositol-induced polyQ-Htt reduction was by rescue of degradation pathways mediated by the lysosome and by the proteasome but not autophagosomes. The rescue of degradation pathways was not a direct result of scyllo-inositol on the lysosome or proteasome but due to scyllo-inositol-induced reduction in mutant polyQ-Htt protein levels.

Tilapia (Oreochromis mossambicus) brain cells respond to hyperosmotic challenge by inducing myo-inositol biosynthesis

This study aimed to determine the regulation of the de novo myo-inositol biosynthetic (MIB) pathway in Mozambique tilapia (Oreochromis mossambicus) brain following acute (25 ppt) and chronic (30, 60 and 90 ppt) salinity acclimations. The MIB pathway plays an important role in accumulating the compatible osmolyte, myo-inositol, in cells in response to hyperosmotic challenge and consists of two enzymes, myo-inositol phosphate synthase and inositol monophosphatase. In tilapia brain, MIB enzyme transcriptional regulation was found to robustly increase in a time (acute acclimation) or dose (chronic acclimation) dependent manner. Blood plasma osmolality and Na(+) and Cl(-) concentrations were also measured and significantly increased in response to both acute and chronic salinity challenges. Interestingly, highly significant positive correlations were found between MIB enzyme mRNA and blood plasma osmolality in both acute and chronic salinity acclimations. Additionally, a mass spectrometry assay was established and used to quantify total myo-inositol concentration in tilapia brain, which closely mirrored the hyperosmotic MIB pathway induction. Thus, myo-inositol is a major compatible osmolyte that is accumulated in brain cells when exposed to acute and chronic hyperosmotic challenge. These data show that the MIB pathway is highly induced in response to environmental salinity challenge in tilapia brain and that this induction is likely prompted by increases in blood plasma osmolality. Because the MIB pathway uses glucose-6-phosphate as a substrate and large amounts of myo-inositol are being synthesized, our data also illustrate that the MIB pathway likely contributes to the high energetic demand posed by salinity challenge.

Tumour cells can employ extracellular Ins(1,2,3,4,5,6)P6 and multiple inositol-polyphosphate phosphatase 1 (MINPP1) dephosphorylation to improve their proliferation

InsP6 [Ins(1,2,3,4,5,6)P6; phytate] is the most abundant inositol phosphate in mammalian cells with cytosolic/nuclear concentrations of up to 50 μM. We noticed that InsP6 in culture medium at a concentration of ≤50 μM significantly stimulates H1299 tumour cell growth, whereas larger concentrations of InsP6 inhibit growth. A detailed study of the fate of 30 μM InsP6 added to H199 cells revealed a major fraction of InsP6 initially precipitates as cell-surface metal complexes, but becomes slowly re-solubilized by extracellular dephosphorylation first to InsP3 isomers and subsequently to free myo-inositol. The precipitated metal–InsP6 complex is endocytosed in a receptor-independent but intact-glycocalyx-dependent manner and appears in lysosomes, where it is immediately dephosphorylated to Ins(1,2,4,5,6)P5 and very slowly to free inositol. By RNA knockdown, we identified secreted and lysosome targeted MINPP1 (multiple inositol-polyphosphate phosphatase 1), the mammalian 3-phytase, to be essentially involved both in extracellular and in lysosomal InsP6 dephosphorylation. The results of the present study indicate that tumour cells employ this enzyme to utilize the micronutrients myo-inositol and metal-phosphate when encountering extracellular InsP6 and thus to enhance their growth potential.

Protection against the synaptic targeting and toxicity of Alzheimer's-associated Aβ oligomers by insulin mimetic chiro-inositols

Alzheimer's disease (AD) is a progressive dementia that correlates highly with synapse loss. This loss appears due to the synaptic accumulation of toxic Aβ oligomers (ADDLs), which damages synapse structure and function. Although it has been reported that oligomer binding and toxicity can be prevented by stimulation of neuronal insulin signaling with PPARγ agonists, these agonists have problematic side effects. We therefore investigated the therapeutic potential of chiro-inositols, insulin-sensitizing compounds safe for human consumption. Chiro-inositols have been studied extensively for treatment of diseases associated with peripheral insulin resistance, but their insulin mimetic function in memory-relevant central nervous system (CNS) cells is unknown. Here we demonstrate that mature cultures of hippocampal neurons respond to d-chiro-inositol (DCI), pinitol (3-O-methyl DCI), and the inositol glycan INS-2 (pinitol β-1-4 galactosamine) with increased phosphorylation in key upstream components in the insulin-signaling pathway (insulin receptor, insulin receptor substrate-1, and Akt). Consistent with insulin stimulation, DCI treatment promotes rapid withdrawal of dendritic insulin receptors. With respect to neuroprotection, DCI greatly enhances the ability of insulin to prevent ADDL-induced synapse damage (EC(50) of 90 nM). The mechanism comprises inhibition of oligomer binding at synapses and requires insulin/IGF signaling. DCI showed no effects on Aβ oligomerization. We propose that inositol glycans and DCI, a compound already established as safe for human consumption, have potential as AD therapeutics by protecting CNS synapses against Aβ oligomers through their insulin mimetic activity.

A systematic approach to the amplified expression, functional characterization and purification of inositol transporters from Bacillus subtilis

Abstract A systematic approach was used for the cloning and amplified expression in Escherichia coli of the genes for each of three inositol transport proteins (IolF, IolT, YfiG) from Bacillus subtilis that are evolutionarily-related to human transporters. Inducible amplified expression of each was achieved to levels of ∼ 10-15% of total protein in E. coli inner membrane preparations. The functional integrity of each heterologously-expressed protein was demonstrated by measuring the kinetics of (3)H-myo-inositol transport into energized whole cells; this confirmed that IolT is the major inositol transporter, IolF is an inefficient transporter of this substrate and demonstrated that YfiG is an inositol transport protein for the first time. Competition for (3)H-myo-inositol transport by 17 unlabelled compounds revealed all three proteins to be highly specific in recognizing inositols over sugars. IolT was confirmed to be highly specific for both myo- and D-chiro-inositol and IolF was confirmed to prefer D-chiro-inositol over myo-inositol. YfiG selectively recognized myo-inositol, D-chiro-inositol and, uniquely, L-chiro-inositol. All three proteins were successfully solubilized and purified in milligram quantities from inner membrane preparations and their suitability for inclusion in crystallization trials was assessed by analysis of structural integrity and thermal stability using circular dichroism spectroscopy followed by examination for monodispersity using gel filtration chromatography.

Clinical utility of neuroprotective agents in neurodegenerative diseases: current status of drug development for Alzheimer's, Parkinson's and Huntington's diseases, and amyotrophic lateral sclerosis

INTRODUCTION

According to the definition of the Committee to Identify Neuroprotective Agents in Parkinson's Disease (CINAPS), "neuroprotection would be any intervention that favourably influences the disease process or underlying pathogenesis to produce enduring benefits for patients" [Meissner W, et al. Trends Pharmacol Sci 2004;25:249-253]. Preferably, neuroprotective agents should be used before or eventually during the prodromal phase of the diseases that could start decades before the appearance of symptoms. Although several symptomatic drugs are available, a disease-modifying agent is still elusive.

AREAS COVERED

The aim of the present review is to give an overview of neuroprotective agents being currently investigated for the treatment of AD, PD, HD and ALS in clinical phases.

EXPERT OPINION

Development of effective neuroprotective therapies resulting in clinically meaningful results is hampered by several factors in all research stages, both conceptual and methodological. Novel solutions might be offered by evaluation of new targets throughout clinical studies, therapies emerging from drug repositioning approaches, multi-target approaches and network pharmacology.

Contributions in astrocytes of SMIT1/2 and HMIT to myo-inositol uptake at different concentrations and pH

myo-Inositol is important for cell signaling both in cytoplasm and in intracellular organelles. It is required in the plasma membrane and cytoplasm for maintained synthesis of the second messengers, inositoltrisphosphate (IP(3)) and diacylglycerol (DAG) from phosphatidylinositol bisphosphate (PIP(2)), and in organelles as precursor for synthesis of complex signaling phospholipids and inositolphosphates from IP(3) and PIP(2). myo-Inositol must be taken up into the cell where its is used, because neither neurons nor astrocytes synthesize it. It is also an osmolyte, taken up in response to surrounding hyperosmolarity and released during hypo-osmolarity. There are three myo-inositol transporters, the Na(+)-dependent SMIT1 and SMIT2, and HMIT, which co-transports myo-inositol with H(+). Their relative expressions in astrocytes and neurons are unknown. Uptake kinetics for myo-inositol in astrocytes has repeatedly been determined, but always on the assumption of only one component, leaving kinetics for the individual transporters unknown. This paper demonstrates that astrocytes obtained directly from the brain express SMIT1 and HMIT, but little SMIT2, and that all three transporters are expressed in neurons. Cultured mouse astrocytes show a high-affinity/low-capacity myo-inositol uptake (V(max): 60.0 ± 3.0 pmol/min per mg protein; K(m): 16.7 ± 2.6 μM), mediated by SMIT1 and perhaps partly by SMIT2. It was determined in cells pre-treated with HMIT-siRNA and confirmed by specific inhibition of SMIT. However at physiologically relevant myo-inositol concentrations most uptake is by a lower-affinity/higher-capacity uptake, mediated by HMIT (V(max): 358 ± 60 pmol/min per mg protein; K(m): 143 ± 36 μM) and determined by subtraction of SMIT-mediated from total uptake. At high myo-inositol concentrations, its uptake is inhibited by incubation in medium with increased pH, and increased during intracellular acidification with NH(4)Cl. This is in agreement with literature data for HMIT alone. At low concentration, where SMIT1/2 activity gains importance, myo-inositol uptake is reduced by ammonia-induced intracellular acidification, consistent with the transporter's pH sensitivity reported in the literature.