The measurement of myo-inositol, myo-inosose-2 and scyllo-inositol in mammalian tissues

MYO-Inositol In Fermented Sugar Matrix Improves Human Macrophage Function

SCOPE

Reactive oxygen species production by innate immune cells plays a central role in host defense against invading pathogens at wound-site. A weakened hos-defense results in persistent infection leading to wound chronicity. Fermented Papaya Preparation (FPP), a complex sugar matrix, bolstered respiratory burst activity and improved wound healing outcomes in chronic wound patients. The objective of the current study was to identify underlying molecular factor/s responsible for augmenting macrophage host defense mechanisms following FPP supplementation.

METHODS AND RESULTS

In depth LC-MS/MS analysis of cells supplemented with FPP led to identification of myo-inositol as a key determinant of FPP activity towards improving macrophage function. Myo-inositol, in quantities that is present in FPP, significantly improved macrophage respiratory burst and phagocytosis via de novo synthesis pathway of ISYNA1. Additionally, myo-inositol transporters, HMIT and SMIT1, played a significant role in such activity. Blocking these pathways using siRNA attenuated FPP-induced improved macrophage host defense activities. FPP supplementation emerges as a novel approach to increase intracellular myo-inositol levels. Such supplementation also modified wound microenvironment in chronic wound patients to augment myo-inositol levels in wound fluid.

CONCLUSION

These observations indicate that myo-inositol in FPP influences multiple aspects of macrophage function critical for host defense against invading pathogens. This article is protected by copyright. All rights reserved.

A review of the role of inositols in conditions of insulin dysregulation and in uncomplicated and pathological pregnancy

Inositols, a group of 6-carbon polyols, are highly bioactive molecules derived from diet and endogenous synthesis. Inositols and their derivatives are involved in glucose and lipid metabolism and participate in insulin-signaling, with perturbations in inositol processing being associated with conditions involving insulin resistance, dysglycemia and dyslipidemia such as polycystic ovary syndrome and diabetes. Pregnancy is similarly characterized by substantial and complex changes in glycemic and lipidomic regulation as part of maternal adaptation and is also associated with physiological alterations in inositol processing. Disruptions in maternal adaptation are postulated to have a critical pathophysiological role in pregnancy complications such as gestational diabetes and pre-eclampsia. Inositol supplementation has shown promise as an intervention for the alleviation of symptoms in conditions of insulin resistance and for gestational diabetes prevention. However, the mechanisms behind these affects are not fully understood. In this review, we explore the role of inositols in conditions of insulin dysregulation and in pregnancy, and identify priority areas for research. We particularly examine the role and function of inositols within the maternal-placental-fetal axis in both uncomplicated and pathological pregnancies. We also discuss how inositols may mediate maternal-placental-fetal cross-talk, and regulate fetal growth and development, and suggest that inositols play a vital role in promoting healthy pregnancy.

Myo-Inositol and Its Derivatives: Their Emerging Role in the Treatment of Human Diseases

Myo-inositol has been established as an important growth-promoting factor of mammalian cells and animals. The role of myo-inositol as a lipotropic factor has been proven, in addition to its involvement as co-factors of enzymes and as messenger molecules in signal transduction. Myo-inositol deficiency leads to intestinal lipodystrophy in animals and "inositol-less death" in some fungi. Of late, diverse uses of myo-inositol and its derivatives have been discovered in medicinal research. These compounds are used in the treatment of a variety of ailments from diabetes to cancer, and continued research in this direction promises a new future in therapeutics. In different diseases, inositols implement different strategies for therapeutic actions such as tissue specific increase or decrease in inositol products, production of inositol phosphoglycans (IPGs), conversion of myo-inositol (MI) to D-chiro-inositol (DCI), modulation of signal transduction, regulation of reactive oxygen species (ROS) production, etc. Though inositol pharmacology is a relatively lesser-known field, recent years of research has generated a critical mass of information on the subject. This review aims to summarize our current understanding on the role of inositol derivatives in ameliorating the symptoms of different diseases.

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.

Metabolic perturbations of kidney and spleen in murine cerebral malaria: (1)H NMR-based metabolomic study

A significant fraction of global population is under the threat of malaria. Majority of annual death is due to the more complicated form of the infection i.e. the cerebral form, also known as Cerebral Malaria (CM). Host parasite interaction is known to cause a cascade of events in various tissues like brain, liver, kidney, and spleen. We have employed (1)H NMR based metabolomics to understand the specific perturbations of various tissues in CM. In our previous paper we have delineated the differences between CM vis-a-vis non-cerebral malaria (NCM) mice in serum, liver and brain. In this paper we focus on their differences of metabolic profile in kidney and spleen as kidney dysfunction and splenomegaly are known to be associated to neurological outcome of the disease. Moreover we have also looked into how the biological compartments (kidney, spleen and serum) interact with each other. The various metabolites involved in such interactions and their correlational aspects across the compartments have been studied in CM, NCM and control mice. The idea was to find out the specific pathways that are altered in CM mice. Our results demonstrate that both the kidney as well as spleen metabolism are differentially perturbed in CM with respect to NCM. The results point out that glutamate levels are decreased in CM mice with respect to NCM mice both in case of spleen and kidney while creatine, myo-inositol and betaine levels are increased in kidney of CM mice with respect to NCM mice. From the analysis of Multiway Principal Component Analysis (MPCA) we see that lipid metabolism and TCA cycle is altered in kidney and spleen.

Mining the brain metabolome to understand behavioural disruptions induced in mouse fed Hypochoeris radicata (L.), a neurotoxic plant for horse

Mining the brain metabolome to understand behavioural disruptions induced in mouse fed Hypochoeris radicata (L.), a neurotoxic plant for horse. C57BL/6J mice orally exposed to 9% H. radicata (HR) are metabolically competent laboratory animals which can be used as model of Australian stringhalt, a neurological horse disease induced by HR ingestion. So, the present study was conducted to assess the brain metabolome and the behavioural performances of mice fed with a 9%-HR-based diet for 21 days. By the end of the period of exposure, mice were investigated for motor activity and coordination, anxiety level, learning and memory performances, social behaviour and rewarding properties of for the plant. Thus, the animals were sacrificed and the brain metabolome was studied using (1)H NMR spectroscopy. HR-exposed mice displayed a motor hyperactivity in several tasks, a less resignation in the forced swimming test, and paradigm place preference for the plant. A bootstrap-based regularized canonical analysis performed on merged behavioural and metabolic datasets showed a clear relationship in HR-treated mice between an increase in cerebral scyllo-inositol, an increased motor activity, and seemingly rewarding properties of HR. These results underlie the interest of such a dual approach to characterize functional end-points of a pathophysiological model of the Australian stringhalt in equine species.

GC-MS metabolomic analysis reveals significant alterations in cerebellar metabolic physiology in a mouse model of adult onset hypothyroidism

Although adult-onset hypothyroidism (AOH) has been connected to neural activity alterations, including movement, behavioral, and mental dysfunctions, the underlying changes in brain metabolic physiology have not been investigated in a systemic and systematic way. The current knowledge remains fragmented, referring to different experimental setups and recovered from various brain regions. In this study, we developed and applied a gas chromatography-mass spectrometry (GC-MS) metabolomics protocol to obtain a holistic view of the cerebellar metabolic physiology in a Balb/cJ mouse model of prolonged adult-onset hypothyroidism induced by a 64-day treatment with 1% potassium perchlorate in the drinking water of the animals. The high-throughput analysis enabled the correlation between multiple parallel-occurring metabolic phenomena; some have been previously related to AOH, while others implicated new pathways, designating new directions for further research. Specifically, an overall decline in the metabolic activity of the hypothyroid compared to the euthyroid cerebellum was observed, characteristically manifested in energy metabolism, glutamate/glutamine metabolism, osmolytic/antioxidant capacity, and protein/lipid synthesis. These alterations provide strong evidence that the mammalian cerebellum is metabolically responsive to AOH. In light of the cerebellum core functions and its increasingly recognized role in neurocognition, these findings further support the known phenotypic manifestations of AOH into movement and cognitive dysfunctions.

Elevated brain scyllo-inositol concentrations in patients with Alzheimer's disease

in vivo (1)H MRS reveals reduced N-acetylaspartate (NAA) and elevated myo-inositol (mI) in patients with mild Alzheimer's disease (AD) and patients with amnestic mild cognitive impairment (MCI). We are unaware of studies that have documented abnormal scyllo-inositol (sI) levels in patients with AD or patients with MCI, although a previous MRS study in older adults has indicated that sI is a peak of interest to measure in AD. Fifteen patients with mild AD, 26 patients with amnestic MCI, and 19 healthy older adults were recruited to this study. All underwent (1)H MRS of the posterior cingulate gyrus of the brain using a 3 T MRI scanner. Increases in the sI/creatine (Cr) ratio were observed in patients with mild AD (P < 0.05). The mI/Cr ratio was raised in patients with mild AD (P < 0.01) and MCI (P < 0.05). Reduced NAA/Cr was detected in patients with mild AD (P < 0.05). The sI/Cr ratio correlated negatively (r = -0.60, P < 0.05) with a measure of clock drawing in patients with mild AD, indicating that impaired cognitive ability in AD is associated with higher concentrations of sI/Cr. In vivo measurement of sI/Cr in the posterior cingulate gyrus of patients with mild AD revealed increases compared with cognitively healthy older adults. Further research on the mechanisms of sI increase in AD is needed. Future studies on the longitudinal course of sI/Cr in MCI and AD appear warranted.

Simultaneous determination ofmyo-inositol andscyllo-inositol by MEKC as a rapid monitoring tool for inositol levels

A simple and rapid MEKC method was developed for the simultaneous determination of myo-inositol, scyllo-inositol, and glucose. Prior to electrophoretic separation, the nonfluorescent inositols and glucose were derivatized by N-methylisatoic anhydride at 25 degrees C for 10 min so that they could be detected by a fluorescence detector during separation. The good separation with high efficiency by MEKC was achieved in 13 min with a glycine buffer containing SDS and PEG 4000. Several parameters affecting the separation were studied, including the pH of BGE, the concentrations of glycine, SDS, and PEG 4000, and the applied voltage. Using glycerol as an internal standard, the linear ranges of the method for myo-inositol, scyllo-inositol, and glucose were 0.03-10, 0.01-5, and 0.05-20 mM; the concentration LODs of myo-inositol, scyllo-inositol, and glucose were 0.020, 0.0078, and 0.026 mM, respectively. The method was applied to analyze extracellular myo-inositol and glucose in the microdialysates from rat brain cortex of ischemia animal model and intracellular myo-inositol and scyllo-inositol in the rat brain extract.

Properties of scyllo–inositol as a therapeutic treatment of AD-like pathology

Inositol is a simple polyol with eight naturally occurring stereoisomers. myo-Inositol, D-chiro- and epi-inositol have been examined as potential therapeutic agents for various diseases, with favorable results, but treatment with scyllo-inositol has not been previously investigated. Our laboratory has shown that scyllo-inositol inhibits cognitive deficits in TgCRND8 mice and significantly ameliorates disease pathology, suggesting it might be effective in treating Alzheimer's disease (AD). In this paper, we show that scyllo-inositol has a sustained ability to treat animals at advanced stages of AD-like pathology. Significant decreases in insoluble Abeta40, Abeta42, and plaque accumulation were observed in the brains of treated versus untreated TgCRND8 mice. The growth of plaques of all sizes was inhibited by scyllo-inositol administration. To demonstrate that the scyllo-inositol effects were within the CNS, gas chromatography/mass spectrometry was used to examine myo- and scyllo-inositol concentrations after oral administration. Further, we examined how closely scyllo- and myo-inositol are inter-regulated in the CNS and whether scyllo-inositol, if elevated within the CNS, would incorporate into phosphatidylinositol lipids. Cerebral spinal fluid levels of scyllo-inositol increased after scyllo-inositol treatment but not myo-inositol treatment. scyllo-Inositol treatment also caused increased levels of scyllo-inositol in the brain. We further show that scyllo-inositol, even at elevated levels, does not incorporate into the phosphatidylinositol family of lipids. These combined results demonstrate that scyllo-inositol accumulates within the CNS up to tenfold endogenous levels and does not interfere with phosphatidylinositol lipid production.

Scyllo-inositol in normal aging human brain: 1H magnetic resonance spectroscopy study at 4 Tesla

The scyllo-inositol and myo-inositol concentrations of 24 normal human subjects were measured in vivo using 1H magnetic resonance spectroscopy at 4 T. Single-voxel short-echo (TE = 15 ms) metabolite spectra were collected from the white matter region of the corona radiata. Test-retest studies performed on 10 normal subjects demonstrated coefficient of variation for scyllo-inositol measurement of 37%, compared with 6% for N-acetyl aspartate. Comparisons between old and young subjects showed higher concentration of scyllo-inositol and myo-inositol in older subjects and a trend for a correlation between scyllo-inositol and myo-inositol levels across subjects.

High cerebral scyllo-inositol: a new marker of brain metabolism disturbances induced by chronic alcoholism

Cerebral metabolic changes that concur to motor and/or cognitive disorders in actively drinking alcoholics are not well established. We tested the hypothesis that chronic alcoholics exhibit profound alterations in the cerebral metabolism of scyllo-inositol. Brain metabolism was explored in nine actively drinking and 11 recently detoxified chronic alcoholics by in vivo brain (1)H-MRS and in vitro(1)H-MRS of blood serum and cerebrospinal fluid. The cohort was composed of individuals with acute, subacute or chronic encephalopathy or without any clinical encephalopathy. Chronic alcoholism is associated with a hitherto unrecognized accumulation of brain scyllo-inositol. Our results suggest that scyllo-inositol is produced within the central nervous system and shows a diffuse but heterogenous distribution in brain where it can persist several weeks after detoxification. Its highest levels were observed in subjects with a clinically symptomatic alcohol-related encephalopathy. When detected, brain scyllo-inositol takes part in a metabolic encephalopathy since it is associated with reduced N-acetylaspartate and increased creatine. High levels of cerebral scyllo-inositol are correlated with altered glial and neuronal metabolism. Our findings suggest that the accumulation of scyllo-inositol may precede and take part in the development of symptomatic alcoholic metabolic encephalopathy.

Stereo- and regiospecificity of yeast phytases-chemical synthesis and enzymatic conversion of the substrate analogues neo- and L-chiro-inositol hexakisphosphate

Phytases are enzymes that catalyze the hydrolysis of phosphate esters in myo-inositol hexakisphosphate (phytic acid). The precise routes of enzymatic dephosphorylation by phytases of the yeast strains Saccharomyces cerevisiae and Pichia rhodanensis have been investigated up to the myo-inositol trisphosphate level, including the absolute configuration of the intermediates. Stereoselective assignment of the myo-inositol pentakisphosphates (D-myo-inositol 1,2,4,5,6-pentakisphosphate and D-myo-inositol 1,2,3,4,5-pentakisphosphate) generated was accomplished by a new method based on enantiospecific enzymatic conversion and HPLC analysis. Via conduritol B or E derivatives the total syntheses of two epimers of myo-inositol hexakisphosphate, neo-inositol hexakisphosphate and L-chiro-inositol hexakisphosphate were performed to examine the specificity of the yeast phytases with these substrate analogues. A comparison of kinetic data and the degradation pathways determined gave the first hints about the molecular recognition of inositol hexakisphosphates by the enzymes. Exploitation of the high stereo- and regiospecificity observed in the dephosphorylation of neo- and L-chiro-inositol hexakisphosphate made it possible to establish enzyme-assisted steps for the synthesis of D-neo-inositol 1,2,5,6-tetrakisphosphate, L-chiro-inositol 1,2,3,5,6-pentakisphosphate and L-chiro-inositol 1,2,3,6-tetrakisphosphate.

Inositol and higher inositol phosphates in neural tissues: homeostasis, metabolism and functional significance

Inositol phospholipids and inositol phosphates mediate well-established functions in signal transduction and in Ca2+ homeostasis in the CNS and non-neural tissues. More recently, there has been renewed interest in other roles that both myo-inositol and its highly phosphorylated forms may play in neural function. We review evidence that myo-inositol serves as a clinically relevant osmolyte in the CNS, and that its hexakisphosphate and pyrophosphorylated derivatives may play roles in such diverse cellular functions as DNA repair, nuclear RNA export and synaptic membrane trafficking.

Identification of a mammalian H(+)-myo-inositol symporter expressed predominantly in the brain

Inositol and its phosphorylated derivatives play a major role in brain function, either as osmolytes, second messengers or regulators of vesicle endo- and exocytosis. Here we describe the identification and functional characterization of a novel H(+)-myo- inositol co-transporter, HMIT, expressed predominantly in the brain. HMIT cDNA encodes a 618 amino acid polypeptide with 12 predicted transmembrane domains. Functional expression of HMIT in Xenopus oocytes showed that transport activity was specific for myo-inositol and related stereoisomers with a Michaelis-Menten constant of approximately 100 microM, and that transport activity was strongly stimulated by decreasing pH. Electrophysiological measurements revealed that transport was electrogenic with a maximal transport activity reached at pH 5.0. In rat brain membrane preparations, HMIT appeared as a 75-90 kDa protein that could be converted to a 67 kDa band upon enzymatic deglycosylation. Immunofluorescence microscopy analysis showed HMIT expression in glial cells and some neurons. These data provide the first characterization of a mammalian H(+)-coupled myo- inositol transporter. Predominant central expression of HMIT suggests that it has a key role in the control of myo-inositol brain metabolism.

Effects of inositol, LiCl, and heparin on the antibody responses to SRBC by normal and immunodeficient XID mice

Spleen cells from naïve adult immunocompetent and immunodeficient XID mice were cultured on agar containing sheep red blood cells (SRBC) with and without myo-inositol, scyllo-inositol, lithium chloride, or heparin, and after 1 or 2 days the number of colonies of antiSRBC antibody-forming cells (PFC) were determined. It was found that myo-inositol and scyllo-inositol at one-tenth the concentration were equally effective in increasing the number of specific PFC. Myo-inositol, scyllo-inositol, and lithium chloride accelerated the appearance of direct foci in cultures of spleen cells from normal and XID mice. When heparin was added to cultures of XID spleen cells, PFC were found to be increased on Day 1; however, PFC and foci were not increased in cultures of spleen cells from competent mice until 1 day later. The addition of combinations of these agents to cultures of spleen cells had no positive or negative effect on the generation of foci or PFC. Normal mice given heparin intraperitoneally with SRBC had increased splenic PFC on Days 3 and 4 but not on Day 7. The results suggest that these agents modulate B-cell responses by increasing the rate of proliferation and/or secretion through a signaling pathway(s) distal to, or more likely, independent of Bruton's tyrosine Kinase (BTK). It is not clear that the mechanism is the same with each agent.

Alternate splicing in human Na+-MI cotransporter gene yields differentially regulated transport isoforms

myo-Inositol is a ubiquitous intracellular organic osmolyte and phosphoinositide precursor maintained at millimolar intracellular concentrations through the action of membrane-associated Na+-myo-inositol cotransporters (SMIT). Functional cloning and expression of a canine SMIT cDNA, which conferred SMIT activity in Xenopus oocytes, predicted a 718-amino acid peptide homologous to the Na+-glucose cotransporter with a potential protein kinase A phosphorylation site and multiple protein kinase C phosphorylation sites. A consistent approximately 1.0- to 13.5-kb array of transcripts hybridizing with this cDNA are osmotically induced in a variety of mammalian cells and species, yet SMIT activity appears to vary among different tissues and species. An open reading frame on human chromosome 21 (SLC5A3) homologous to that of the canine cDNA (96.5%) is thought to comprise an intronless human SMIT gene. Recently, this laboratory ascribed multiply sized, osmotically induced SMIT transcripts in human retinal pigment epithelial cells to the alternate utilization of several 3'-untranslated SMIT exons. This article describes an alternate splice donor site within the coding region that extends the open reading frame into the otherwise untranslated 3' exons, potentially generating novel SMIT isoforms. In these isoforms, the last putative transmembrane domain is replaced with intracellular carboxy termini containing a novel potential protein kinase A phosphorylation site and multiple protein kinase C phosphorylation sites, and this could explain the heterogeneity in the regulation and structure of the SMIT.

Manganese-stimulated phosphatidylinositol headgroup exchange in rat liver microsomes

Manganese-dependent, CMP-independent incorporation of myo-[3H]inositol into phospholipids of rat liver microsomes was studied in an attempt to clarify the physiological significance of this headgroup-exchange reaction. The enzyme responsible worked best with Mn2+ as a co-factor, but Mg2+ at physiological concentrations supported a significant rate of incorporation. The K(m) for myo-inositol was around 11 microM, yet incorporation of myo-[3H]inositol was unaffected by as much as 5 mM choline, ethanolamine, glycerol or serine; as this is a reversible reaction, these data imply that phosphatidylinositol is the most likely lipid substrate. Similarly, other inositols showed an apparent affinity at least two orders of magnitude lower than myo-inositol. Glucosamine alpha 1-6 myo-inositol also had a low affinity for the enzyme, making it unlikely that this headgroup-exchange activity is part of a metabolic pathway for glycosyl phosphatidylinositols. The phosphatidylinositol radiolabelled by headgroup exchange was deacylated and deglycerated, and the resulting inositol phosphate headgroup cochromatographed on anion exchange HPLC with myo-inositol l-phosphate. The simplest interpretation of all the data is the apparent paradox that this enzyme functions at a slow rate under physiological conditions to remove the myo-inositol headgroup from phosphatidylinositol, only to replace it with another myo-inositol.

Identification of a high concentration of scyllo-inositol in the brain of a healthy human subject using 1H- and 13C-NMR

The peak at 3.35 ppm in the 1H-NMR spectrum characteristic for scyllo-inositol may be a marker for cerebral pathology, although it has a well-known constant concentration relative to myo-inositol. Such a peak was observed with an intensity at least 300% above normal in the brain of a healthy volunteer. The scyllo-inositol signal was assigned based on the detection of a corresponding peak at 74.5 ppm in the 13C-NMR spectrum and on the demonstration of singlet characteristics of the proton signal. The presence of substantial brain concentrations of scyllo-inositol suggests that scyllo-inositol metabolism may be regulated independently from myo-inositol and that such concentrations are compatible with normal health.

Quantitative and qualitative characterization of 1H NMR spectra of colon tumors, normal mucosa and their perchloric acid extracts: decreased levels of myo-inositol in tumours can be detected in intact biopsies

Sixteen colonic tumours and 10 normal mucosa biopsies have been examined by 1H NMR spectroscopy at 9.4 T. A complete characterization and quantification of the aliphatic region of PCA extract spectra and the analysis of the two-dimensional COSY spectra of five pairs of intact biopsies (tumor and control mucosa) has been carried out. The analysis of the PCA extracts demonstrated a significant increase in the concentration of the endogenous compounds: lactate, glutamate, aspartate, taurine, spermine, glutathione and glycerophosphoethanolamine, and a significant decrease of myo- and scyllo-inositol, in tumours with respect to mucosae. Among these metabolites, the high myo-inositol and taurine levels and the reciprocal changes found between them in tumours and mucosae make their resonances interesting as possible malignancy markers if they are detectable in vivo. In contrast to the easy observation of taurine in one-dimensional spectra of intact biopsies, the difficulty of observing myo-inositol prompted us to use two-dimensional COSY spectra for the detection and quantification of both these metabolites. In the two-dimensional spectra, the use of a ratio between the cross-peak volumes of both metabolites permits an excellent differentiation between tumours and normal mucosa and suggests its potential to detect malignant changes in the healthy tissue, provided a two-dimensional approach is used.

The development of a sensitive myo-inositol analyser using a liquid chromatograph with a post-label fluorescence detector

A sensitive liquid chromatographic analysis for myo-inositol was developed using glycocyamine as the post-labelling reagent. The sensitivity was 500 pmol/injection. The system was applied to analyse myo-inositol in sera from eight patients with chronic renal failure. The average concentration of serum myo-inositol was 498.6 +/- 257.0 mumol/L before haemodialysis, and 244.0 +/- 131.1 mumol/L after haemodialysis. These results indicated that the kidney is the main site of myo-inositol metabolism.

The human osmoregulatory Na+/myo-inositol cotransporter gene (SLC5A3): molecular cloning and localization to chromosome 21

A human Na+/myo-inositol cotransporter (SLC5A3) gene was cloned; sequencing revealed a single intron-free open reading frame of 2157 nucleotides. Containing 718 amino acid residues, the predicted protein is highly homologous to the product of the canine osmoregulatory SLC5A3 gene. The SLC5A3 protein is number 3 of the solute carrier family 5 and was previously designated SMIT. Using fluorescence in situ hybridization, the human SLC5A3 gene was localized to band q22 on chromosome 21. Many tissues including brain demonstrate gene expression. The inability of a trisomic 21 cell to downregulate expression of three copies of this osmoregulatory gene could result in increased flux of both myo-inositol and Na+ across the plasma membrane. The potential consequences include perturbations in the cell membrane potential and tissue osmolyte levels. The SLC5A3 gene may play a role in the pathogenesis of Down syndrome.

Scyllo-inositol depletion in hepatic encephalopathy

Cerebral myo-inositol depletion is found in patients with hepatic encephalopathy and can be implicated in the pathogenesis of hepatic encephalopathy. We measured scyllo-inositol, a stereoisomer of myo-inositol, in brain extracts from patients dying in hepatic coma using HPLC and high resolution 1H MRS. The cerebral scyllo-inositol concentration, determined by both methods, in patients without hepatic encephalopathy was 0.41 +/- 0.11 mmol/kg wet weight. It decreased by 73% and 76%, respectively, as measured by HPLC and 1H MRS, in patients with hepatic encephalopathy. These findings indicate that myo-inositol depletion in patients with hepatic encephalopathy is not due to enhanced conversion of myo-inositol to scyllo-inositol or inhibition of myo-inositol transport by scyllo-inositol, but rather to the reduced biosynthesis or transport of both inositols.

Identification of Scyllo-inositol in proton NMR spectra of human brain in vivo

Scyllo-inositol has been identified in proton NMR spectra of mammalian brain in vitro and in vivo. In contrast to myo-inositol this isomer comprises six equivalent CH protons that yield a singlet resonance at a chemical shift of 3.35 ppm. 1-D and 2-D J-resolved proton NMR studies (7.0 T) of perchloric acid extracts of brain tissues revealed different amounts of scyllo-inositol in man, sheep, cow and rat. Absolute quantification of localized short-echo time proton NMR spectra (2.0 T) of human brain in vivo resulted in scyllo-inositol concentrations of 0.35 +/- 0.06 mM for white matter (n = 25), 0.43 +/- 0.11 mM for grey matter (n = 23) and 0.57 +/- 0.14 mM for cerebellum (n = 10). Evidence for a tight metabolic link to myo-inositol was supported by a simultaneous variation of myo- and scyllo-inositol in patients with various brain diseases.

Mass measurement of inositol phosphates

This review summarises the methods available for the mass measurement of inositol phosphates, i.e., use of radioactive inositol lipid precursors, optical techniques, gas chromatography, mass spectrometry, nuclear magnetic resonance, fast atom bombardment and assays specific for Ins(1,4,5)P3. Examples of the use of each method, its sensitivity, advantages and drawbacks are given.

Mechanism of glucose-induced (Na+, K+)-ATPase inhibition in aortic wall of rabbits

Hyperglycaemia decreases (Na+, K+)-ATPase activity in specific tissues by a mechanism whose effects are prevented by aldose reductase inhibitors and by raising plasma myo-inositol. This mechanism was activated and studied in vitro in normal rabbit aortic intima-media. Raising medium glucose to 10 mmol/l for 60 min inhibited a major component of (Na+, K+)-ATPase-mediated 86Rb+/K+ uptake normally operative in resting aortic intima-media in medium containing normal plasma levels of glucose (5 mmol/l) and myo-inositol (70 mumol/l); 20 or 30 mmol/l glucose had no greater effect. This effect occurred under conditions in which the aortic intima-media's normal myo-inositol content is not detectably decreased. The inhibition was prevented by sorbinil (10 mumol/l) and by raising medium myo-inositol from 70 to 500 mumol/l, which had no effect on (Na+, K+)-ATPase activity when the medium glucose remained at 5 mmol/l. Raising medium glucose selectively inhibited a component of (Na+, K+)-ATPase activity that requires medium myo-inositol, because it is maintained by a regulatory system through rapid basal phosphatidylinositol turnover in a discrete pool, which is replenished by a fraction of basal de novo phosphatidylinositol synthesis that is selectively dependent on myo-inositol uptake. Medium myo-inositol at a normal plasma level became inadequate to maintain this fraction of basal de novo phosphatidylinositol synthesis [( 1,3-14C]glycerol incorporation) when the medium glucose was raised. When sorbinil was added raising medium glucose did not alter the ability of 70 mumol/l medium myoinositol to maintain the (Na+, K+)-ATPase activity that requires medium myo-inositol.(ABSTRACT TRUNCATED AT 250 WORDS)

High-resolution proton magnetic resonance spectroscopy of rabbit brain: regional metabolite levels and postmortem changes

The changes in 16 cerebral metabolites produced by cardiac arrest and subsequent room temperature autolysis were studied using high-resolution proton nuclear magnetic resonance spectroscopy. Biopsies of rabbit cerebral cortex, cerebral white matter, and cerebellum were quantitatively analyzed for acetate, alanine, gamma-aminobutyric acid, creatine, glutamate, glycine, inositol, lactate, N-acetylaspartate, phosphocreatine, succinate, taurine, and threonine. Of these, N-acetylaspartate and the total creatine pool are the best candidates for use as concentration reference standards linking in vitro to in vivo 1H nuclear magnetic resonance measurements. Both changed little immediately after death, and they varied in a distinctive way among cortex, white matter, and cerebellum.

Differential effect of progesterone on the labeling of phosphatidylinositol with [3H]inositol and [32P]phosphate in the uterus of the estrogen-treated ovariectomized rat

In rat uterine mince incubated in vitro [3H]inositol was found to be incorporated into phosphatidylinositol (PI) predominantly via a pathway which could be markedly and dose dependently activated with Mn2+ (0.1-10 mM) and inhibited by Ca2+ (1-10 mM). These ions had no effect on the incorporation of [32P]phosphate (32P) into PI indicating a distinct inositol-exchange mechanism for the labeling of PI with [3H]inositol. Treatment of ovariectomized rats for 5 days with 2 micrograms estradiol dipropionate (EDP) increased about 3-fold (when measured in the presence of 1 mM Mn2+) and 4-5-fold (when measured in the presence of 1 mM Ca2+) the inositol-exchange activity in the rat uterus, and these effects were suppressed by 40 and 30% respectively by the concomitant administration of 2 mg progesterone (P). EDP alone or in combination with P increased to the same extent (by a factor of 2-3) the rate of labeling with 32P of phosphatidylcholine (PC), phosphatidylethanolamine (PE) and plasmenylethanolamine (PmE). The labeling rate of PI was increased 1.5-1.7-fold by treatment with EDP and this increase was selectively augmented further to about 2.5-fold by the simultaneous administration of P. Treatment with P alone had no significant effect on the incorporation of either labeled precursor. Steroid hormone treatments had no effect on the amount of these phospholipids in 100 mg uterine tissue, but they increased about 1.7-fold the rate of labeling of ATP with 32P. We conclude that P, when administered together with estradiol, regulates differentially the turnover of the inositol and phosphate moieties of PI with possible physiological consequences.

Immunohistochemical staining and enzyme activity measurements show myo-inositol-1-phosphate synthase to be localized in the vasculature of brain

Rabbit anti-bovine myo-inositol-1-phosphate synthase was used to examine the distribution of that enzyme in perfused and immersion-fixed bovine brain and testis. In brain, intense and specific staining was found in the walls of all the vascular elements including cerebral capillaries. The remainder of brain parenchyma exhibited only low levels of background staining. In testis, an organ rich in the enzyme, blood vessels showed no specific staining. Instead, the enzyme was found in the seminiferous epithelium of the seminiferous tubules, perhaps localized in spermatozoa. To confirm the brain finding, the activity of myo-inositol-1-phosphate synthase was measured in bovine brain microvessel preparations and brain pial vessels. In these preparations the activity of the enzyme was found on average to be 7 and 22 times enriched over that in whole brain, respectively. The activities of two other enzymes of inositol metabolism, myo-inosose reductase and myo-inositol-1-phosphatase, were also examined for their distribution in brain. Those enzymes were found to be generally distributed. The surprising finding of a vascular localization of myo-inositol-1-phosphate synthase in brain raises new questions about the mechanism by which myo-inositol is concentrated to such high cellular levels in the principal substance of that organ.

Profiling of organic acids and polyols in nerves of uraemic and non-uraemic patients

Organic acids, polyols and lipid-bound polyols in the cauda equina nerves of uraemic patients and non-uraemic patients were analysed with high-resolution gas chromatography-mass spectrometry. In the uraemic nervous tissue, the concentrations of myoinositol and 4-hydroxyphenylacetic acid were increased. Levulinic acid was first detected in the nervous tissue as a normal component. 1-Deoxyglucose and free and lipid phosphatide scylloinositol were detected in the nervous tissue as normal components.

Experimental diabetes mellitus impairs the function of the retinal pigmented epithelium

The retinal pigmented epithelium (RPE), which influences the composition of the retinal extracellular fluid, is significantly affected in diabetes. Changes in RPE morphology, permeability, and electrophysiology in experimentally diabetic animals have been described. To facilitate the study of diabetes-related changes in RPE metabolism, we applied the techniques of quantitative histochemistry to pure samples of RPE and individual retinal layers from eyes of normal and alloxan-diabetic rabbits. Glucose within the RPE approximated serum levels in both normal and diabetic animals. Other changes in diabetics included increased sorbitol, decreased myo-inositol, elevated total Na, and loss of measurable Na+-K+-ATPase activity within the RPE. The altered ion metabolism was associated with a progressive decrease in the amplitude of the RPE-generated c-wave of the electroretinogram. The deterioration of the c-wave was arrested by treatment of the diabetic animals with either myo-inositol supplementation or with sorbinil, an inhibitor of aldose reduction. Diabetic alterations in the RPE might impair the ability of the tissue to maintain normal transport functions. The subsequently altered composition of the extracellular environment of the retina may play an important role in the pathogenesis of diabetic retinopathy.

An enzymatic fluorimetric assay for myo-inositol

An enzymatic assay for myo-inositol (MI) is described. The method is based on the oxidation of MI by NAD+-dependent myo-inositol dehydrogenase, coupled to reoxidation of NADH with oxalacetate and malate dehydrogenase. The resultant malate is measured fluorimetrically. Several variations of the assay are described for measuring MI in serum and in tissues in amounts ranging from 0.2 pmol to 8 nmol. Highest sensitivity is achieved by applying an oil-well technique for handling small droplets, and by using the principle of enzymatic cycling. The potential of the technique is illustrated by MI measurements in several tissues of normal and diabetic rats and Chinese hamsters.

Characterization of a scyllo-inositol-containing sialyloligosaccharide from normal human urine

Three inositol-containing sialyloligosaccharides were isolated from normal human urine. Structural studies including gas-liquid chromatography of mono- and disaccharide derivatives, methylation analysis, mass spectrometry and glycosidase treatments indicated the structure NeuAc (alpha 2-3)Gal(beta 1-0)scyllo-inositol for one of the oligosaccharides isolated. This provides the first evidence for the natural occurrence of a scyllo-inositol glycoside in biological material. The two other oligosaccharides isolated were identified as two isomers of NeuAc(alpha 2-3)Gal(beta 1-0)myo-inositol, which have not been identified in normal urine before.

The composition of animal cells: solutes contributing to osmotic pressure and charge balance

The cytoplasmic solutes of vertebrates and invertebrates, other than Na, K and Cl, are surveyed in relation to their influence on ionic regulation through osmolality and charge balance. The most abundant include MgATP, phosphagens, amino acids, various other nitrogen and phosphorus compounds and sometimes anaerobic end products and antifreeze agents. Differences in muscle osmolality, e.g. between marine and non-marine animals, affect mainly nitrogenous solutes of no net charge, such as certain amino acids, taurine, betaine, trimethylamine oxide and urea. The high osmolality of axoplasm in marine invertebrates is due more to anions such as aspartate, glutamate and isethionate.

Sodium- and energy-dependent uptake of myo-inositol by rabbit peripheral nerve. Competitive inhibition by glucose and lack of an insulin effect

Experimental diabetes consistently reduces the concentration of free myo-inositol in peripheral nerve, which usually exceeds that of plasma by 90-100-fold. This phenomenon has been explicitly linked to the impairment of nerve conduction in the acutely diabetic streptozocin-treated rat. However, the mechanism by which acute experimental diabetes lowers nerve myo-inositol content and presumably alters nerve myo-inositol content and presumably alters nerve myo-inositol metabolism is unknown. Therefore, the effects of insulin and elevated medium glucose concentration of 2-[3H]myo-inositol uptake were studied in a metabolically-defined in vitro peripheral nerve tissue preparation derived from rabbit sciatic nerve, whose free myo-inositol content is reduced by experimental diabetes. The results demonstrate that myo-inositol uptake occurs by at least two distinct transport systems in the normal endoneurial preparation. A sodium- and energy-dependent saturable transport system is responsible for at least 94% of the measured uptake at medium myo-inositol concentrations approximating that present in plasma. This carrier-mediated transport system has a high affinity for myo-inositol (Kt = 63 microM), and is not influenced acutely by physiological concentrations of insulin; it is, however, inhibited by hyperglycemic concentrations of glucose added to the incubation medium in a primarily competitive fashion. Thus, competitive inhibition of peripheral nerve myo-inositol uptake by glucose may constitute a mechanism by which diabetes produces physiologically significant alterations in peripheral nerve myo-inositol metabolism.

Estimation of free myo-inositol in milks of various species and its source in milk of rats (Rattus norvegicus)

Free myo-inositol content of milk of rats and other rodents fed standard laboratory chow is 80 mg/100 g as compared to about 4 mg/100 g for cow milk. Feeding experiments with graded amounts of myo-inositol demonstrated that the myo-inositol content of milk is strongly influenced by dietary intake. Radioactivity from either [carbon-14] glucose or [hydrogen-3] myo-inositol injected intraperitoneally was incorporated rapidly into milk myo-inositol. Thus, both mammary biosynthesis and active transport contribute to the high myo-inositol in rat milk, but the latter is quantitatively the more important.

Distribution of myo-inositol in the cat cochlear nucleus

The distribution of myo-inositol, a substance that has been implicated in synaptic transmission, has been mapped within sections of the cat cochlear nucleus as well as some nearby regions. Highest values in the cochlear nucleus were found in regions of granule cells along the periphery of the anteroventral subdivision of the nucleus. Highest values overall were found in the molecular layer of the cerebellar flocculus. A fairly good correlation was found between myo-inositol levels and activities of the enzymes of acetylcholine metabolism in the cat cochlear nucleus, supporting the possibility that myo-inositol may be involved in cholinergic synaptic transmission. No positive correlation was found between myo-inositol levels and the levels of glutamate, aspartate, glycine, or gamma-aminobutyric acid (GABA). The most striking gradient of myo-inositol levels within a region was found in the auditory nerve, where different myo-inositol levels might be related to nerve fibers innervating different parts of the cochlea. The distribution of scyllo-inositol, a stereoisomer of myo-inositol, was also examined, and found to parallel closely the distribution of myo-inositol, with levels 4--5% as high.

The nutritional significance, metabolism, and function of myo-inositol and phosphatidylinositol in health and disease

Recent advances in nutritional and biochemical research have substantiated the importance of inositol as a dietary and cellular constituent. The processes involved in the metabolism of inositol and its derivatives in mammalian tissues have been characterized both in vivo and at the enzyme level. Biochemical functions elucidated for phosphatidylinositol in biological membranes include the mediation of cellular responses to external stimuli, nerve transmission, and the regulation of enzyme activity through specific interactions with various proteins. Inositol deficiency in animals has been shown to produce an accumulation of triglyceride in liver, intestinal lipodystrophy, and other abnormalities. The metabolic mechanisms giving rise to these latter phenomena have been extensively studied as a function of dietary inositol. Altered metabolism of inositol has been documented in patients with diabetes mellitus, chronic renal failure, galactosemia, and multiple sclerosis. A moderate increase in plasma and nerve inositol levels by dietary supplementation has been suggested as a means of treating diabetic neuropathy, although excessively high levels, such as are found in uremic patients, may be neurotoxic. A thorough consideration of the biochemical functions of inositol and a further characterization of various diseases with the aid of appropriate animal models may suggest a possible role for inositol and other dietary components in their prevention and treatment

Myo-inositol turnover in the intact rat brain: increased production after d-amphetamine

Apparent turnover of myo-inositol in the brain of urethane-anesthetized rats was estimated in vivo from the rate of appearance of endogenous myo-inositol in the cerebroventricular compartment. Ventricular-cisternal perfusion technique combined with isotope dilution of [14C]myo-inositol was used to determine the rate of appearance of brain-produced myo-inositol and its modification by d-amphetamine. A mean value of 0.75 nmol/min was obtained for the rate of appearance in the cerebroventricular system. A dose-dependent increase in this rate was seen after the administration of d-amphetamine. The endogenous removal of myo-inositol from the perfusate was also studied and found to be mediated in part by a saturable transport system that was not influenced by d-amphetamine. The rate of entry of myo-inositol from blood to the cerebroventricular system was very low and accounted for only 2% of the total rate of appearance, indicating that the majority of myo-inositol in the rat cerebroventricular fluid originates in the brain.

Estimation of neutral sugars and sugar alcohols in biological fluids by gas-liquid chromatography

Gas-liquid chromatographic procedures for measuring sugar and polyol concentrations in biological fluids are reviewed. Such methods require the preparations of derivatives such as methyl ethers, trimethylsilyl ethers or acetyl esters. Prior to derivatisation samples must be deproteinised and dried. Complex mixtures of sugars and sugar alcohols may be resolved. Quantitative analyses are precise, sensitive and linear. If internal standardisation is used recoveries approaching 100% are obtained.