Behavioural phenotyping of sodium-myo-inositol cotransporter heterozygous knockout mice with reduced brain inositol.

Inositol plays a key role in dopamine, serotonin, noradrenaline and acetylcholine neurotransmission, and inositol treatment is reported to have beneficial effects in depression and anxiety. Therefore, a reduction in brain intracellular inositol levels could be a cause of some psychiatric disorders, such as depression or anxiety. To determine the behavioural consequences of inositol depletion, we studied the behaviour of sodium-dependent myo-inositol cotransporter-1 heterozygous knockout mice. In heterozygous mice, free inositol levels were reduced by 15% in the frontal cortex and by 25% in the hippocampus, but they did not differ from their wild-type littermates in cholinergic-mediated lithium-pilocarpine seizures, in the apomorphine-induced stereotypic climbing model of dopaminergic system function, in the Porsolt forced-swimming test model of depression, in amphetamine-induced hyperactivity, or in the elevated plus-maze model of anxiety. Reduction of brain inositol by more than 25% may be required to elicit neurobehavioural effects.

Sugar nucleotide concentrations in red blood cells of patients on protein- and lactose-limited diets: effect of galactose supplementation.

Uridine diphosphate (UDP) galactose, a pivotal compound in the metabolism of galactose, is the obligate donor of galactose in the formation of complex glycoconjugates. The cellular UDPgalactose concentration has been thought to be maintained by the interconversion of UDPglucose and UDPgalactose by UDPgalactose-4-epimerase. However, recent findings of lower average red blood cell (RBC) UDPgalactose concentrations in galactose-1-phosphate uridyltransferase-deficient patients suggest that other factors play a role in determining its concentration. To test the hypothesis that the amount of galactose traversing the Leloir pathway contributes to the cellular UDPgalactose pool, we determined RBC UDPgalactose in patients with maple syrup urine disease (MSUD), phenylketonuria (PKU), and other metabolic diseases who were treated with a low-protein, and consequently, low-lactose diet. Six patients with MSUD were also supplemented with 19 g galactose/d and their UDPhexose concentrations were measured at intervals. We show that young patients with MSUD or PKU have decreased average RBC UDPgalactose concentrations when compared with similarly aged healthy subjects. Galactose supplementation of MSUD patients significantly increased their UDPgalactose concentrations in both RBCs and white blood cells (WBCs) from 29.5 +/- 1.5 to 42.3 +/- 5.8 nmol/g hemoglobin and from 69.0 +/- 7.5 to 193.0 +/- 49.0 nmol/g protein, respectively. Discontinuation of supplementation was associated with a return to basal values in RBCs and a reattainment of the pretreatment ratio of UDPglucose to UDPgalactose in WBCs. These observations demonstrate that dietary galactose is a factor in establishing the steady state concentrations of the uridine sugar nucleotides and imply that galactose metabolism modulates the achievement of an epimerase-mediated equilibrium.

The 21q22.1 STS marker, VN02 (EST00541 cDNA), is part of the 3' sequence of the human Na+/myo-inositol cotransporter (SLC5A3) gene.

The human osmoregulatory Na+/myo-inositol cotransporter gene (SLC5A3) was recently cloned and localized to the region of 21q22. Fine mapping of this gene was accomplished by identifying YAC clones that contain SLC5A3 and utilizing known STS markers for 21q22.1 and 21q22.2 sub-bands that map to the positive YAC clones. Two bacteriophage P1 clones containing the SLC5A3 gene gave a positive PCR product when screened with the 21q22.1 marker VN02, an expressed sequence tag (EST00541). Through DNA sequence analysis, it was determined that this STS marker if part of the 3' untranslated region of the SLC5A3 gene.

The effect of glucose and galactose toxicity on myo-inositol transport and metabolism in human skin fibroblasts in culture.

Myo-inositol transport and metabolism were studied in cultured human skin fibroblasts exposed to potentially toxic levels of glucose or galactose. Although variable among 11 different cell lines, the myo-inositol level in confluent cells, ranging from 10-50 nmol/mg protein, was constant with passage. A high-affinity transport system for myo-inositol had an apparent Kt of 55 microM and Vmax of 16 pmol/min/mg protein. No obvious relationship existed between cellular levels and transport capacity. Dependency on sodium was complex. When medium sodium was lowered to 23 mM, myo-inositol uptake ceased after about 1 h. However, the initial rate of myo-inositol uptake only showed a sodium dependence at low myo-inositol concentrations. Both phloretin and phloridzin inhibited myo-inositol uptake. Phloridzin had a Ki of 60 microM, and phloretin was either a noncompetitive or uncompetitive inhibitor. Glucose and galactose were only weak competitive inhibitors, with a Ki of 30 mM and 65 mM, respectively. After 24 h of incubation with myo-[2-3H]inositol, only 10% of the total cell label was incorporated into phospholipid. Compared with control media with 5 mM glucose, the incubation of confluent cells in media with 20 mM glucose had little effect on intracellular glucose and sorbitol, whereas cells incubated in control media supplemented with 5 mM galactose showed a large increase in galactose and polyol levels. In media with more than 200 microM of myo-inositol, neither treatment had an effect on myo-inositol levels after 24 h.(ABSTRACT TRUNCATED AT 250 WORDS)

myo-inositol transport and metabolism in fetal-bovine aortic endothelial cells.

The myo-inositol transport system in confluent fetal-bovine aortic endothelial cells was characterized after 7-10 days in subculture, at which time the myo-inositol levels and rates of myo-[2-3H]-inositol uptake and incorporation into phospholipid had reached steady state. Kinetic analysis indicated that the uptake occurred by both a high-affinity transport system with an apparent Kt of 31 microM and Vmax. of 45 pmol/min per mg of protein, and a non-saturable low-affinity system. Uptake was competitively inhibited by phlorhizin, with a Ki of 50 microM; phloretin was a non-competitive inhibitor, with half-maximal inhibition between 0.2 and 0.5 mM. Glucose was a weak competitive inhibitor, with a Ki of 37 mM; galactose failed to inhibit uptake. A weak dependence on Na+ for the initial rate of uptake was observed at 11 microM myo-inositol. When fetal-bovine-serum (FBS)-supplemented medium, which contained 225 microM myo-inositol, was used, the cells contained about 200 nmol of myo-inositol/mg of DNA. With adult-bovine-serum (ABS)-supplemented medium, which contained 13 microM myo-inositol, the cells contained about 110 nmol/mg of DNA. Transport of 11 microM myo-[2-3]inositol was 18 and 125 pmol/min per mg of DNA for cells grown in FBS and ABS respectively. Kinetic analysis showed that for the cells grown in FBS the Vmax. of the high-affinity system was decreased by 64%, whereas the Kt remained essentially unchanged. Increased cell myo-inositol levels were not associated with an increased rate of phosphatidylinositol synthesis. After prolonged exposure of fetal endothelial cells to a myo-inositol concentration which approximated to a high fetal as opposed to a low adult blood level, cell myo-inositol levels doubled and high-affinity transport underwent down-regulation.

Acrodermatitis enteropathica-like syndrome secondary to isoleucine deficiency during treatment of maple syrup urine disease.

We describe a patient with maple syrup urine disease in whom an acrodermatitis enteropathica-like syndrome developed while he was receiving a branched-chain amino acid-free formula. Iatrogenically induced isoleucine deficiency developed and resulted in a decreased protein accretion and persistent increase in the plasma concentrations of leucine. A rapid clinical response to isoleucine supplementation was noted. This observation underscores the risks of using amino acid-free formulas without adequate supplementation of deficient amino acids.

31P NMR analysis of red blood cell UDPGlucose and UDPGalactose: comparison with HPLC and enzymatic methods.

The levels of uridine diphosphogalactose (UDPGal) and uridine diphosphoglucose (UDPGlu) in trichloroacetic acid extracts of human red blood cells (RBC) were measured by 31P NMR spectroscopy. Individual determinations were compared to results obtained by enzymatic and high-pressure liquid chromatographic (HPLC) methods. The characteristic doublet of the P beta resonance signals of both UDPGal and UDPGlu were detected in proton-decoupled spectra of extracts. Quantitative analyses were obtained by employing a standard, methylene diphosphonate, in an external capillary tube during data acquisition for periods of 14 to 24 h using an "inverse-gated" pulse sequence. The ratio of the integrated area of each of the uridine sugar nucleotide doublets to the area of the external reference peak was linear with concentrations between 0.03 and 0.50 mM. There was no difference between the mean value obtained by 31P NMR of 6.6 +/- 1.4 mumol UDPGlu/100 g Hgb or 2.1 +/- 0.6 mumol UDPGal/100 gHgb and the corresponding levels determined enzymatically or by HPLC in identical RBC extracts. When analyzed as paired data, only UDPGlu by NMR was found to be lower than the value obtained by HPLC. As a quantitative analytical tool, NMR spectrometry validated both the enzymatic and HPLC methods used for measurement of uridine sugar nucleotides in our laboratories.

Isovaleric acidemia: medical and neurodevelopmental effects of long-term therapy.

Nine patients with isovaleric acidemia were treated with a low-protein diet and supplemental glycine for up to 10 years. Carnitine was added to the therapy in four patients. Overall, the treatment was well tolerated, resulting in no significant side effects other than persistent hyperglycinemia. Normal growth was observed in all patients. Of four patients with the chronic phenotype, three, whose treatment was delayed beyond the first year of life, are mentally retarded. Two of five patients with the acute phenotype are retarded. The outcome in these two was complicated in one by neonatal intraventricular hemorrhage and in the other by therapeutic noncompliance. In our patients, only those who were treated successfully from early infancy and had no complications did not develop mental retardation. After initiation of therapy, there was a significant decrease in ketoacidotic attacks requiring hospitalization. Glycine is indicated for the treatment of acute ketoacidosis in these patients; none of the catastrophically ill newborn who received glycine died. The aim of treatment is to reduce the isovaleric acid burden to a minimum. Therapy consisting of leucine restriction with supplemental glycine and carniline should be started as soon as possible after birth.