Gas chromatographic analysis of myo-inositol in microgram samples of brain

Developmental control of inositol phosphate biosynthesis is altered in the brain of both curly and phenotypically normal straight tail mutant mice

BACKGROUND

Altered levels of inositol phosphate in the central nervous system (CNS) are hypothesized to produce distorted brain signaling and lead to numerous neurologic maladies. Little is known of mechanisms controlling the complex metabolic flux of inositol phosphate. Less is known of controls that regulate inositol-phosphate biosynthesis in the mammalian brain. The expression of 1L-myo-inositol-1 phosphate synthase (MIP), the only enzyme known to synthesize inositol phosphate, was studied in the brain of normal (CBA) and curly tail (CT) mutant mice. The CT strain exhibits a neural tube defect, spina bifida, responsive to inositol supplementation, but not to folic acid treatment.

METHODS

Utilizing enzyme assays to determine the specific activity of MIP, Western blotting to detect expression, gas chromatography/mass spectrometry to measure inositol concentration, and statistical analyses to evaluate quantitative data, MIP expression was analyzed in newborn, young, and adult brains of CBA and CT (curly tail [ct-CT] and straight tail [st-CT]) mutant mice.

RESULTS

Data analyses suggest there is a significant difference in MIP activity in the brain of CBA mice as compared to that of CT mutant mice and that temporal and spatial control of MIP expression and inositol concentrations are altered in the brain of both the ct-CT and phenotypically normal st-CT mutant. Moreover, two differentially expressed forms of MIP were identified in the adult mouse brain.

CONCLUSIONS

These findings implicate a role for MIP in the maturation of the CNS and evoke a hypothesis regarding the regulation of inositol phosphate biosynthesis in brain development.

Specific determination of myo-inositol in multivitamin pharmaceutical preparations by a flow injection system using a myo-inositol dehydrogenase reactor coupled with a glucose eliminating enzyme reactor

A flow injection system for myo-inositol determination in multivitamin pharmaceutical preparations using two enzyme reactors was developed. Myo-inositol was detected using a fluorophotometer, to measure the fluorescence of NADH produced from NAD+ by a myo-inositol dehydrogenase reactor (IDR) containing myo-inositol dehydrogenase immobilized on porous glass. Enhanced interference due to excess glucose included in a multivitamin pharmaceutical preparation as a sweetener was eliminated by a glucose eliminating reactor (GER) co-immobilized with three enzymes (glucose oxidase, mutarotase and catalase). The calibration coefficient for the standard curve was 0.9993 for myo-inositol detection in the range of 1-5 microg/ml. Myo-inositol was determined even in the presence of glucose concentrations of 140-420 microg/ml. The recovery of myo-inositol added to the multivitamin pharmaceutical preparation was 99.6% (n=9).

Differentiated human NT2-N neurons possess a high intracellular content of myo-inositol

myo-Inositol plays a key role in signal transduction and osmotic regulation events in the CNS. Despite the known high concentrations of inositol in the human CNS, relatively little is known about its distribution within the different cell types. In this report, inositol homeostasis was studied in NT2-N cells, a unique cell culture model of human CNS neurons. Differentiation of precursor NT2 teratocarcinoma cells into NT2-N neurons by means of retinoic acid treatment resulted in an increase in inositol concentration from 24 to 195 nmol/mg of protein. After measurement of intracellular water spaces, inositol concentrations of 1.6 and 17.4 mM were calculated for NT2 and NT2-N cells, respectively. The high concentrations of inositol in NT2-N neurons could be explained by (1) an increased uptake of inositol (3.7 vs. 1.6 nmol/mg of protein/h, for NT2-N and NT2 cells, respectively) and (2) a decreased efflux of inositol (1.7%/h for NT2-N neurons vs. 9.0%/h for NT2 cells). Activity of inositol synthase, which mediates de novo synthesis of inositol, was not detected in either cell type. The observation that CNS neurons maintain a high intracellular concentration of inositol may be relevant to the regulation of both phosphoinositide signaling and osmotic stress events in the CNS.

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.

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.

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.

Sample preparation for inositol measurement: Sep-Pak C18 use in detergent removal

The enzymatic-fluorometric method of myo-inositol quantitation by L.C. MacGregor and F.M. Matschinsky (1984, Anal. Biochem. 141, 382-389) has proved to be very useful in accurately measuring small amounts of myo-inositol. Although this procedure is quite satisfactory, relatively high concentrations of detergents, salts, NADH, and malate interfere. To extend the usefulness of the MacGregor and Matschinsky method we report here an extraction procedure which removed the interfering substances, yet allowed the recovery of close to 100% of the inositol. The procedure involved first passing the sample through a Sep-Pak C18 cartridge to remove detergent and then through a mixed-bed resin to remove the ionic constituents. The procedure with the Sep-Pak C18 cartridge is applicable to a wide variety of biological samples requiring detergent removal.

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.

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.