Sodium/myo-inositol cotransporter-1 is essential for the development and function of the peripheral nerves

Impact of erythropoietin and myoinositol versus metformin on insulin resistance in a rat model of polycystic ovary syndrome

This study aimed to evaluate the therapeutic role of erythropoietin (EPO) or myoinositol versus metformin (MET) in improving the reproductive functions and glucose tolerance in a rat model of polycystic ovary (PCOS). Oral letrozole (LTZ) was used for induction of PCOS in wester rats for 21 days, after that, MET, EPO and myoinositol were administered for the following 21 days. The LTZ-induced PCOS rats have lost their oestrous cyclicity and become fixed at the diestrus phase, developed insulin resistance, abnormal sex and gonadotrophin hormone serum levels, increased cystic follicles, decreased number of the growing follicles and very little or no corpora lutea on microscopic examination, which were reversed by the three drugs, MET, EPO and myoinositol. MET and myoinositol were mostly equally effective in improving the reproductive manifestations of the disease. However, EPO was most effective in decreasing the insulin level observed in this LTZ-induced model of PCOS.

The role of myo-inositol supplement in assisted reproductive techniques

Assisted reproductive techniques can help many infertile couples conceive. Therefore, there is a need for an effective method to overcome the widespread problems of infertile men and women. Oocyte and sperm quality can increase the chances of successful in vitro fertilisation. The maturation environment in which gametes are present can affect their competency for fertilisation. It is well established that myo-inositol (MI) plays a pivotal role in reproductive physiology. It participates in cell membrane formation, lipid synthesis, cell proliferation, cardiac regulation, metabolic alterations, and fertility. This molecule also acts as a direct messenger of insulin and improves glucose uptake in various reproductive tissues. Evidence suggests that MI regulates events such as gamete maturation, fertilisation, and embryo growth through intracellular Ca2 + release and various signalling pathways. In addition to the in-vivo production of MI from glucose in the reproductive organs, its synthesis by in vitro-cultured sperm and follicles has also been reported. Therefore, MI is suggested as a therapeutic approach to maintain sperm and oocyte health in men and women with reproductive disorders and individuals of reproductive age.

High impacts of cultivar and home-cooking practice on the content of free myo-inositol, a bioavailable health-promoting cyclitol, in sweet potato

Free myo-inositol is a bioavailable form of a cyclitol having various health-promoting activities. The impact of cultivar and home-cooking practice on the content of free myo-inositol in sweet potatoes (12 cultivars grown in 2 different locations) was studied. A GC-MS/MS method following in situ trimethylsilylation was established and validated to determine free myo-inositol. The established analytical method was sensitive, precise, and accurate. It was found that free myo-inositol content in sweet potato varied greatly (sevenfolds) with cultivar, ranging from 377.1 to 2628.3 mg/kg dw. A cultivar Poongwon-mi was found to be an exceptionally rich source of free myo-inositol (2628.3 mg/kg dw). Home-cooking practice markedly increased free myo-inositol content (maximum 240%). Baking showed the highest impact on the increase in free myo-inositol, followed by steaming, microwave cooking, and boiling, in decreasing order. This represents the first report of the remarkably high impact of cultivar and home-cooking practice on the free myo-inositol content in sweet potato. PRACTICAL APPLICATION: The free myo-inositol content in sweet potato varied greatly with the cultivars. Poongwon-mi contained a surprisingly high content of free myo-inositol. Home-cooking dramatically increased the free myo-inositol content.

Pathogenesis of Distal Symmetrical Polyneuropathy in Diabetes

Distal symmetrical polyneuropathy (DSPN) is a serious complication of diabetes associated with significant disability and mortality. Although more than 50% of people with diabetes develop DSPN, its pathogenesis is still relatively unknown. This lack of understanding has limited the development of novel disease-modifying therapies and left the reasons for failed therapies uncertain, which is critical given that current management strategies often fail to achieve long-term efficacy. In this article, the pathogenesis of DSPN is reviewed, covering pathogenic changes in the peripheral nervous system, microvasculature and central nervous system (CNS). Furthermore, the successes and limitations of current therapies are discussed, and potential therapeutic targets are proposed. Recent findings on its pathogenesis have called the definition of DSPN into question and transformed the disease model, paving the way for new research prospects.

An In Vivo CRISPR Screening Platform for Prioritizing Therapeutic Targets in AML

CRISPR-Cas9-based genetic screens have successfully identified cell type-dependent liabilities in cancer, including acute myeloid leukemia (AML), a devastating hematologic malignancy with poor overall survival. Because most of these screens have been performed in vitro using established cell lines, evaluating the physiologic relevance of these targets is critical. We have established a CRISPR screening approach using orthotopic xenograft models to validate and prioritize AML-enriched dependencies in vivo, including in CRISPR-competent AML patient-derived xenograft (PDX) models tractable for genome editing. Our integrated pipeline has revealed several targets with translational value, including SLC5A3 as a metabolic vulnerability for AML addicted to exogenous myo-inositol and MARCH5 as a critical guardian to prevent apoptosis in AML. MARCH5 repression enhanced the efficacy of BCL2 inhibitors such as venetoclax, further highlighting the clinical potential of targeting MARCH5 in AML. Our study provides a valuable strategy for discovery and prioritization of new candidate AML therapeutic targets. SIGNIFICANCE: There is an unmet need to improve the clinical outcome of AML. We developed an integrated in vivo screening approach to prioritize and validate AML dependencies with high translational potential. We identified SLC5A3 as a metabolic vulnerability and MARCH5 as a critical apoptosis regulator in AML, both of which represent novel therapeutic opportunities.This article is highlighted in the In This Issue feature, p. 275.

SLC5A3-Dependent Myo-inositol Auxotrophy in Acute Myeloid Leukemia

An enhanced requirement for nutrients is a hallmark property of cancer cells. Here, we optimized an in vivo genetic screening strategy in acute myeloid leukemia (AML), which led to the identification of the myo-inositol transporter SLC5A3 as a dependency in this disease. We demonstrate that SLC5A3 is essential to support a myo-inositol auxotrophy in AML. The commonality among SLC5A3-dependent AML lines is the transcriptional silencing of ISYNA1, which encodes the rate-limiting enzyme for myo-inositol biosynthesis, inositol-3-phosphate synthase 1. We use gain- and loss-of-function experiments to reveal a synthetic lethal genetic interaction between ISYNA1 and SLC5A3 in AML, which function redundantly to sustain intracellular myo-inositol. Transcriptional silencing and DNA hypermethylation of ISYNA1 occur in a recurrent manner in human AML patient samples, in association with IDH1/IDH2 and CEBPA mutations. Our findings reveal myo-inositol as a nutrient dependency in AML caused by the aberrant silencing of a biosynthetic enzyme. SIGNIFICANCE: We show how epigenetic silencing can provoke a nutrient dependency in AML by exploiting a synthetic lethality relationship between biosynthesis and transport of myo-inositol. Blocking the function of this solute carrier may have therapeutic potential in an epigenetically defined subset of AML.This article is highlighted in the In This Issue feature, p. 275.

Inositols Depletion and Resistance: Principal Mechanisms and Therapeutic Strategies

Inositols are natural molecules involved in several biochemical and metabolic functions in different organs and tissues. The term "inositols" refers to five natural stereoisomers, among which myo-Inositol (myo-Ins) is the most abundant one. Several mechanisms contribute to regulate cellular and tissue homeostasis of myo-Ins levels, including its endogenous synthesis and catabolism, transmembrane transport, intestinal adsorption and renal excretion. Alterations in these mechanisms can lead to a reduction of inositols levels, exposing patient to several pathological conditions, such as Polycystic Ovary Syndrome (PCOS), hypothyroidism, hormonal and metabolic imbalances, like weight gain, hyperinsulinemia, dyslipidemia, and metabolic syndrome. Indeed, myo-Ins is involved in different physiological processes as a key player in signal pathways, including reproductive, hormonal, and metabolic modulation. Genetic mutations in genes codifying for proteins of myo-Ins synthesis and transport, competitive processes with structurally similar molecules, and the administration of specific drugs that cause a central depletion of myo-Ins as a therapeutic outcome, can lead to a reduction of inositols levels. A deeper knowledge of the main mechanisms involved in cellular inositols depletion may add new insights for developing tailored therapeutic approaches and shaping the dosages and the route of administration, with the aim to develop efficacious and safe approaches counteracting inositols depletion-induced pathological events.

Blood myo-inositol concentrations in preterm and term infants

OBJECTIVE

To describe relationship between cord blood (representing fetal) myo-inositol concentrations and gestational age (GA) and to determine trends of blood concentrations in enterally and parenterally fed infants from birth to 70 days of age.

DESIGN/METHODS

Samples were collected in 281 fed or unfed infants born in 2005 and 2006. Myo-inositol concentrations were displayed in scatter plots and analyzed with linear regression models of natural log-transformed values.

RESULTS

In 441 samples obtained from 281 infants, myo-inositol concentrations varied from nondetectable to 1494 μmol/L. Cord myo-inositol concentrations decreased an estimated 11.9% per week increase in GA. Postnatal myo-inositol concentrations decreased an estimated 14.3% per week increase in postmenstrual age (PMA) and were higher for enterally fed infants compared to unfed infants (51% increase for fed vs. unfed infants).

CONCLUSIONS

Fetal myo-inositol concentrations decreased with increasing GA. Postnatal concentrations decreased with increasing PMA and were higher among enterally fed than unfed infants.

Gestational diabetes mellitus: Prevention, diagnosis and treatment. A fresh look to a busy corner

BACKGROUND

Gestational diabetes mellitus (GDM) is a common pregnancy complication characterized by hyperglycaemia with onset or first recognition during pregnancy. Risk factors include family history of diabetes, previous GDM, genetic predisposition for GDM/type 2 diabetes, insulin resistance conditions such as overweight, obesity and ethnicity. Women with GDM are at high risk for fetal macrosomia, small for gestational age, neonatal hypoglycaemia, operative delivery and caesarean delivery. The aim of this narrative review is to summarize the most recent findings of diagnosis and treatment of GDM in order to underline the importance to promote adequate prevention of this disease, especially through lifestyle interventions such as diet and physical activity.

METHODS

The research was conducted using the following electronic databases, MEDLINE, EMBASE, Web of Science, Scopus, ClinicalTrial.gov, OVID and Cochrane Library, including all published randomized and non-randomized studies as well as narrative and systematic reviews.

RESULTS

The lack of universally accepted criteria makes the definition of diagnosis and prognosis of this condition difficult. Early diagnosis and glucose blood level control may improve maternal and fetal short and long-term outcomes. Treatment strategies include nutritional interventions and exercise. Medical treatment can be necessary if these strategies are not effective. Moreover, novel non-pharmacologic agents such as myo-inositol seem to be effective and safe both in the prevention and the treatment of GDM.

CONCLUSIONS

It is important to promote adequate prevention of GDM. Further studies are needed in order to better define the most appropriate strategies for the clinical management of women affected by GDM.

Maternal Inositol Status and Neural Tube Defects: A Role for the Human Yolk Sac in Embryonic Inositol Delivery?

Supplementation with myo-inositol during the periconceptional period of pregnancy may ameliorate the recurrence risk of having a fetus affected by a neural tube defect (NTD; e.g., spina bifida). This could be of particular importance in providing a means for preventing NTDs that are unresponsive to folic acid. This review highlights the characteristics of inositol and describes the role of myo-inositol in the prevention of NTDs in rodent studies and the evidence for its efficacy in reducing NTD risk in human pregnancy. The possible reduction in NTD risk by maternal myo-inositol implies functional and developmentally important maternal-embryonic inositol interrelationships and also suggests that embryonic uptake of myo-inositol is crucial for embryonic development. The establishment of active myo-inositol cellular uptake mechanisms in the embryonic stages of human pregnancy, when the neural tube is closing, is likely to be an important determinant of normal development. We draw attention to the generation of materno-fetal inositol concentration gradients and relationships, and outline a transport pathway by which myo-inositol may be delivered to the early developing human embryo. These considerations provide novel insights into the mechanisms that may underpin inositol's ability to confer embryonic developmental benefit.

Effects of Myo-inositol Alone and in Combination with Seleno-Lmethionine on Cadmium-Induced Testicular Damage in Mice

BACKGROUND

Cadmium (Cd) impairs gametogenesis and damages the blood-testis barrier.

OBJECTIVE

As the primary mechanism of Cd-induced damage is oxidative stress, the effects of two natural antioxidants, myo-inositol (MI) and seleno-L-methionine (Se), were evaluated in mice testes.

METHODS

Eighty-four male C57 BL/6J mice were divided into twelve groups: 0.9% NaCl (vehicle; 1 ml/kg/day i.p.); Se (0.2 mg/kg/day per os); Se (0.4 mg/kg/day per os); MI (360 mg/kg/day per os); MI plus Se (0.2 mg/kg/day); MI plus Se (0.4 mg/kg/day); CdCl2 (2 mg/kg/day i.p.) plus vehicle; CdCl2 plus MI; CdCl2 plus Se (0.2 mg/kg/day); CdCl2 plus Se (0.4 mg/kg/day); CdCl2 plus MI plus Se (0.2 mg/kg/day); and CdCl2 plus MI plus Se (0.4 mg/kg/day). After 14 days, testes were processed for biochemical, structural and immunohistochemical analyses.

RESULTS

CdCl2 increased iNOS and TNF-α expression and Malondialdehyde (MDA) levels, lowered glutathione (GSH) and testosterone, induced testicular lesions, and almost eliminated claudin-11 immunoreactivity. Se administration at 0.2 or 0.4 mg/kg significantly reduced iNOS and TNF-α expression, maintained GSH, MDA and testosterone levels, structural changes and low claudin-11 immunoreactivity. MI alone or associated with Se at 0.2 or 0.4 mg/kg significantly reduced iNOS and TNF-α expression and MDA levels, increased GSH and testosterone levels, ameliorated structural organization and increased claudin-11 patches number.

CONCLUSION

We demonstrated a protective effect of MI, a minor role of Se and an evident positive role of the association between MI and Se on Cd-induced damages of the testis. MI alone or associated with Se might protect testes in subjects exposed to toxicants, at least to those with behavior similar to Cd.

Myo-inositol: its metabolism and potential implications for poultry nutrition-a review

Myo-inositol (MI) has gained relevance in physiology research during the last decade. As a constituent of animal cells, MI was proven to be crucial in several metabolic and regulatory processes. Myo-inositol is involved in lipid signaling, osmolarity, glucose, and insulin metabolism. In humans and rodents, dietary MI was assessed to be important for health so that MI supplementation appeared to be a valuable alternative for treatment of several diseases as well as for improvements in metabolic performance. In poultry, there is a lack of evidence not only related to specific species-linked metabolic processes but also about the effects of dietary MI on performance and health. This review intends to provide information about the meaning of dietary MI in animal metabolism as well as to discuss potential implications of dietary MI in poultry health and performance with the aim to identify open questions in poultry research.

Myo-inositol in the protection from cadmium-induced toxicity in mice kidney: An emerging nutraceutical challenge

Cadmium (Cd) induces functional and morphological changes in kidney. Therefore, the effects of a natural nutraceutical antioxidant, myo-inositol (MI), were evaluated in mice kidneys after Cd challenge. Twenty-eight C57 BL/6 J mice were divided into these groups: 0.9% NaCl; MI (360 mg/kg/day); CdCl₂ (2 mg/kg/day) plus vehicle; CdCl₂ (2 mg/kg/day) plus MI (360 mg/kg/day). After 14 days, kidneys were processed for structural, biochemical and morphometric evaluation. Treatment with CdCl₂ increased urea nitrogen and creatinine in serum and augmented tumor necrosis factor-α (TNF-α) and inducible nitric oxide synthase (iNOS) expression. Furthermore, monocyte chemoattractant protein-1 (MCP-1), kidney injury molecule-1 (KIM-1) and myo-inositol oxygenase (MIOX) immunoreactivity, and terminal deoxynucleotidyl transferase dUTP nick end labeling (TUNEL) positive cells number were significantly higher than control and MI groups. Glutathione (GSH) content and glutathione peroxidase (GPx) activity were reduced and structural changes were evident. The treatment with MI significantly lowered urea nitrogen and creatinine levels, TNF-α and iNOS expression, MCP-1, KIM-1 and MIOX immunoreactivity and TUNEL positive cells number, increased GSH content and GPx activity and preserved kidney morphology. A protection of MI against Cd-induced damages in mice kidney was demonstrated, suggesting a strong antioxidant role of this nutraceutical against environmental Cd harmful effects on kidney lesions.

Expression of myo-inositol cotransporters in the sciatic nerve and dorsal root ganglia in experimental diabetes

The transport of myo-inositol is the main mechanism for the maintenance of its high intracellular levels. We aimed to measure the mRNA and protein levels of myo-inositol cotransporters in the sciatic nerve (SN) and dorsal root ganglia (DRG) during experimental diabetes. Streptozotocin-induced (STZ; 4, 8, and 12 weeks; 65 mg/kg; ip) diabetic rats (DB) and age-matched euglycemic (E) rats were used for the analysis of mRNA and protein levels of sodium myo-inositol cotransporters 1, 2 (SMIT1, SMIT2) or H⁺/myo-inositol cotransporter (HMIT). There was a significant reduction in the mRNA levels for SMIT1 in the SN and DRG (by 36.9 and 31.0%) in the 4-week DB (DB4) group compared to the E group. SMIT2 was not expressed in SN. The mRNA level for SMIT2 was up-regulated only in the DRG in the DB4 group. On the other hand, the protein level of SMIT1 decreased by 42.5, 41.3, and 44.8% in the SN after 4, 8, and 12 weeks of diabetes, respectively. In addition, there was a decrease of 64.3 and 58.0% of HMIT in membrane and cytosolic fractions, respectively, in the SN of the DB4 group. In the DRG, there was an increase of 230 and 86.3% for SMIT1 and HMIT, respectively, in the DB12 group. The levels of the main inositol transporters, SMIT1 and HMIT, were greatly reduced in the SN but not in the DRG. SMIT-1 was selectively reduced in the sciatic nerve during experimental STZ-induced diabetes.

Myo-inositol Effects on the Developing Respiratory Neural Control System

Myo-inositol is a highly abundant stereoisomer of the inositol family of sugar alcohols and forms the structural basis for a variety of polyphosphate derivatives including second messengers and membrane phospholipids. These derivatives regulate numerous cell processes including gene transcription, membrane excitability, vesicular trafficking, intracellular calcium signaling, and neuronal growth and development. Myo-inositol can be formed endogenously from the breakdown of glucose, is found in a variety of foods including breastmilk and is commercially available as a nutritional supplement. Abnormal myo-inositol metabolism has been shown to underlie the pathophysiology of a variety of clinical conditions including Down Syndrome, traumatic brain injury, bronchopulmonary dysplasia (BPD), and respiratory distress syndrome (RDS). Several animal studies have shown that myo-inositol may play a critical role in development of both the central and peripheral respiratory neural control system; a notable example is the neonatal apnea and respiratory insufficiency that manifests in a mouse model of myo-inositol depletion, an effect that is also postnatally lethal. This review focuses on myo-inositol (and some of its derivatives) and how it may play a role in respiratory neural control; we also discuss clinical evidence demonstrating a link between serum myo-inositol levels and the incidence of intermittent hypoxemia (IH) events (a surrogate measure of apnea of prematurity (AOP)) in preterm infants. Further, there are both animal and human infant studies that have demonstrated respiratory benefits following supplementation with myo-inositol, which highlights the prospects that nutritional requirements are important for appropriate development and maturation of the respiratory system.

Chansporter complexes in cell signaling

Ion channels facilitate diffusion of ions across cell membranes for such diverse purposes as neuronal signaling, muscular contraction, and fluid homeostasis. Solute transporters often utilize ionic gradients to move aqueous solutes up their concentration gradient, also fulfilling a wide variety of tasks. Recently, an increasing number of ion channel-transporter ('chansporter') complexes have been discovered. Chansporter complex formation may overcome what could otherwise be considerable spatial barriers to rapid signal integration and feedback between channels and transporters, the ions and other substrates they transport, and environmental factors to which they must respond. Here, current knowledge in this field is summarized, covering both heterologous expression structure/function findings and potential mechanisms by which chansporter complexes fulfill contrasting roles in cell signaling in vivo.

Identification and Functional Implications of Sodium/Myo-Inositol Cotransporter 1 in Pancreatic β-Cells and Type 2 Diabetes

Myo-inositol (MI), the precursor of the second messenger phosphoinositide (PI), mediates multiple cellular events. Rat islets exhibit active transport of MI, although the mechanism involved remains elusive. Here, we report, for the first time, the expression of sodium/myo-inositol cotransporter 1 (SMIT1) in rat islets and, specifically, β-cells. Genetic or pharmacological inhibition of SMIT1 impaired glucose-stimulated insulin secretion by INS-1E cells, probably via downregulation of PI signaling. In addition, SMIT1 expression in INS-1E cells and isolated islets was augmented by acute high-glucose exposure and reduced in chronic hyperglycemia conditions. In corroboration, chronic MI treatment improved the disease phenotypes of diabetic rats and islets. On the basis of our results, we postulate that the MI transporter SMIT1 is required to maintain a stable PI pool in β-cells in order that PI remains available despite its rapid turnover.

Functional Analysis of the Coronary Heart Disease Risk Locus on Chromosome 21q22

Background. The coronary heart disease (CHD) risk locus on 21q22 (lead SNP rs9982601) lies within a “gene desert.” The aim of this study was to assess if this locus is associated with CHD risk factors and to identify the functional variant(s) and gene(s) involved. Methods. A phenome scan was performed with UCLEB Consortium data. Allele-specific protein binding was studied using electrophoretic mobility shift assays. Dual-reporter luciferase assays were used to assess the impact of genetic variation on expression. Expression quantitative trait analysis was performed with Advanced Study of Aortic Pathology (ASAP) and Genotype-Tissue Expression (GTEx) consortium data. Results. A suggestive association between QT interval and the locus was observed (rs9982601  p = 0.04). One variant at the locus, rs28451064, showed allele-specific protein binding and its minor allele showed 12% higher luciferase expression (p = 4.82 × 10⁻³) compared to the common allele. The minor allele of rs9982601 was associated with higher expression of the closest upstream genes (SLC5A3 1.30-fold increase p = 3.98 × 10⁻⁵; MRPS6 1.15-fold increase p = 9.60 × 10⁻⁴) in aortic intima media in ASAP. Both rs9982601 and rs28451064 showed a suggestive association with MRPS6 expression in relevant tissues in the GTEx data. Conclusions. A candidate functional variant, rs28451064, was identified. Future work should focus on identifying the pathway(s) involved.

KCNQ-SMIT complex formation facilitates ion channel-solute transporter cross talk

Voltage-gated potassium channels formed by KCNQ2 and KCNQ3 are essential for normal neuronal excitability. KCNQ2/3 channel activity is augmented in vivo by phosphatidylinositol 4,5-bisphosphate (PIP₂), which is generated from myo-inositol, an osmolyte transported into cells by sodium-dependent myo-inositol transporters (SMITs). Here, we discovered that KCNQ2/3 channels isoform-specifically colocalize with SMIT1 and SMIT2 at sciatic nerve nodes of Ranvier and in axon initial segments, and form channel-transporter complexes in vitro and in vivo KCNQ2/3 coexpression protected SMIT1 activity from the otherwise inhibitory effects of cellular depolarization imposed by elevating extracellular [K⁺], and KCNQ2 was required for potentiation of SMIT activity by myo-inositol preincubation. Cytoskeletal disruption, which speeds PIP₂ dispersion, attenuated potentiation of KCNQ2/3 currents by SMIT1-mediated myo-inositol uptake, suggesting close channel-transporter juxtaposition ensures KCNQ2/3 exposure to locally high myo-inositol-derived PIP₂ concentrations. Thus, KCNQ2/3-SMIT1/2 coassembly permits cross talk via physical interaction, and may also be required for optimal, reciprocal indirect regulation via membrane potential and PIP₂, especially within the specialized architecture of axons.-Neverisky, D. L., Abbott, G. W. KCNQ-SMIT complex formation facilitates ion channel-solute transporter cross talk.

Pharmacodynamics and pharmacokinetics of inositol(s) in health and disease

INTRODUCTION

Inositol and its derivatives comprise a huge field of biology. Myo-inositol is not only a prominent component of membrane-incorporated phosphatidylinositol, but participates in its free form, with its isomers or its phosphate derivatives, to a multitude of cellular processes, including ion channel permeability, metabolic homeostasis, mRNA export and translation, cytoskeleton remodeling, stress response.

AREAS COVERED

Bioavailability, safety, uptake and metabolism of inositol is discussed emphasizing the complexity of interconnected pathways leading to phosphoinositides, inositol phosphates and more complex molecules, like glycosyl-phosphatidylinositols.

EXPERT OPINION

Besides being a structural element, myo-inositol exerts unexpected functions, mostly unknown. However, several reports indicate that inositol plays a key role during phenotypic transitions and developmental phases. Furthermore, dysfunctions in the regulation of inositol metabolism have been implicated in several chronic diseases. Clinical trials using inositol in pharmacological doses provide amazing results in the management of gynecological diseases, respiratory stress syndrome, Alzheimer's disease, metabolic syndrome, and cancer, for which conventional treatments are disappointing. However, despite the widespread studies carried out to identify inositol-based effects, no comprehensive understanding of inositol-based mechanisms has been achieved. An integrated metabolomics-genomic study to identify the cellular fate of therapeutically administered myo-inositol and its genomic/enzymatic targets is urgently warranted.

Ion channel-transporter interactions

All living cells require membrane proteins that act as conduits for the regulated transport of ions, solutes and other small molecules across the cell membrane. Ion channels provide a pore that permits often rapid, highly selective and tightly regulated movement of ions down their electrochemical gradient. In contrast, active transporters can move moieties up their electrochemical gradient. The secondary active transporters (such as SLC superfamily solute transporters) achieve this by coupling uphill movement of the substrate to downhill movement of another ion, such as sodium. The primary active transporters (including H(+)/K(+)-ATPases and Na(+)/K(+)-ATPases) utilize ATP hydrolysis as an energy source to power uphill transport. It is well known that proteins in each of these classes work in concert with members of the other classes to ensure, for example, ion homeostasis, ion secretion and restoration of ion balance following action potentials. More recently, evidence is emerging of direct physical interaction between true ion channels, and some primary or secondary active transporters. Here, we review the first known members of this new class of macromolecular complexes that we term "chansporters", explore their biological roles and discuss the pathophysiological consequences of their disruption. We compare functional and/or physical interactions between the ubiquitous KCNQ1 potassium channel and various active transporters, and examine other newly discovered chansporter complexes that suggest we may be seeing the tip of the iceberg in a newly emerging signaling modality.

Myo-Inositol Supplementation to Prevent Gestational Diabetes Mellitus

Gestational diabetes mellitus (GDM) is a common complication characterized by increased insulin resistance, and by increased risk for adverse pregnancy outcomes affecting both the mother and the fetus. International guidelines describe optimal ways to recognize it, and the recommended treatment of patients affected to reduce adverse outcomes. Improving insulin resistance could reduce incidence of GDM and its complications. Recently, a few trials have been published on the possible prevention of GDM. Inositol has been proposed as a food supplement that might reduce gestational diabetes incidence in high-risk pregnant women.

Myo-Inositol Safety in Pregnancy: From Preimplantation Development to Newborn Animals

Myo-inositol (myo-Ins) has a physiological role in mammalian gametogenesis and embryonic development and a positive clinical impact on human medically assisted reproduction. We have previously shown that mouse embryo exposure to myo-Ins through preimplantation development in vitro increases proliferation activity and blastocyst production, representing an improvement in culture conditions. We have herein investigated biochemical mechanisms elicited by myo-Ins in preimplantation embryos and evaluated myo-Ins effects on postimplantation/postnatal development. To this end naturally fertilized embryos were cultured in vitro to blastocyst in the presence or absence of myo-Ins and analyzed for activation of the PKB/Akt pathway, known to modulate proliferation/survival cellular processes. In parallel, blastocyst-stage embryos were transferred into pseudopregnant females and allowed to develop to term and until weaning. Results obtained provide evidence that myo-Ins induces cellular pathways involving Akt and show that (a) exposure of preimplantation embryos to myo-Ins increases the number of blastocysts available for uterine transfer and of delivered animals and (b) the developmental patterns of mice obtained from embryos cultured in the presence or absence of myo-Ins, up to three weeks of age, overlap. These data further identify myo-Ins as a possibly important supplement for human preimplantation embryo culture in assisted reproduction technology.

The betaine/GABA transporter and betaine: roles in brain, kidney, and liver

The physiological roles of the betaine/GABA transporter (BGT1; slc6a12) are still being debated. BGT1 is a member of the solute carrier family 6 (the neurotransmitter, sodium symporter transporter family) and mediates cellular uptake of betaine and GABA in a sodium- and chloride-dependent process. Most of the studies of BGT1 concern its function and regulation in the kidney medulla where its role is best understood. The conditions here are hostile due to hyperosmolarity and significant concentrations of NH₄Cl and urea. To withstand the hyperosmolarity, cells trigger osmotic adaptation, involving concentration of a transcriptional factor TonEBP/NFAT5 in the nucleus, and accumulate betaine and other osmolytes. Data from renal cells in culture, primarily MDCK, revealed that transcriptional regulation of BGT1 by TonEBP/NFAT5 is relatively slow. To allow more acute control of the abundance of BGT1 protein in the plasma membrane, there is also post-translation regulation of BGT1 protein trafficking which is dependent on intracellular calcium and ATP. Further, betaine may be important in liver metabolism as a methyl donor. In fact, in the mouse the liver is the organ with the highest content of BGT1. Hepatocytes express high levels of both BGT1 and the only enzyme that can metabolize betaine, namely betaine:homocysteine –S-methyltransferase (BHMT1). The BHMT1 enzyme removes a methyl group from betaine and transfers it to homocysteine, a potential risk factor for cardiovascular disease. Finally, BGT1 has been proposed to play a role in controlling brain excitability and thereby represents a target for anticonvulsive drug development. The latter hypothesis is controversial due to very low expression levels of BGT1 relative to other GABA transporters in brain, and also the primary location of BGT1 at the surface of the brain in the leptomeninges. These issues are discussed in detail.

Defective craniofacial development and brain function in a mouse model for depletion of intracellular inositol synthesis

myo-Inositol is an essential biomolecule that is synthesized by myo-inositol monophosphatase (IMPase) from inositol monophosphate species. The enzymatic activity of IMPase is inhibited by lithium, a drug used for the treatment of mood swings seen in bipolar disorder. Therefore, myo-inositol is thought to have an important role in the mechanism of bipolar disorder, although the details remain elusive. We screened an ethyl nitrosourea mutant mouse library for IMPase gene (Impa) mutations and identified an Impa1 T95K missense mutation. The mutant protein possessed undetectable enzymatic activity. Homozygotes died perinatally, and E18.5 embryos exhibited striking developmental defects, including hypoplasia of the mandible and asymmetric fusion of ribs to the sternum. Perinatal lethality and morphological defects in homozygotes were rescued by dietary myo-inositol. Rescued homozygotes raised on normal drinking water after weaning exhibited a hyper-locomotive trait and prolonged circadian periods, as reported in rodents treated with lithium. Our mice should be advantageous, compared with those generated by the conventional gene knock-out strategy, because they carry minimal genomic damage, e.g. a point mutation. In conclusion, our results reveal critical roles for intracellular myo-inositol synthesis in craniofacial development and the maintenance of proper brain function. Furthermore, this mouse model for cellular inositol depletion could be beneficial for understanding the molecular mechanisms underlying the clinical effect of lithium and myo-inositol-mediated skeletal development.

Potential role and therapeutic interests of myo-inositol in metabolic diseases

Several inositol isomers and in particular myo-inositol (MI) and D-chiro-inositol (DCI), were shown to possess insulin-mimetic properties and to be efficient in lowering post-prandial blood glucose. In addition, abnormalities in inositol metabolism are associated with insulin resistance and with long term microvascular complications of diabetes, supporting a role of inositol or its derivatives in glucose metabolism. The aim of this review is to focus on the potential benefits of a dietary supplement of myo-inositol, by far the most common inositol isomer in foodstuffs, in human disorders associated with insulin resistance (polycystic ovary syndrome, gestational diabetes mellitus or metabolic syndrome) or in prevention or treatment of some diabetic complications (neuropathy, nephropathy, cataract). The relevance of such a nutritional strategy will be discussed for each context on the basis of the clinical and/or animal studies. The dietary sources of myo-inositol and its metabolism from its dietary uptake to its renal excretion will be also covered in this review. Finally, the actual insights into inositol insulin-sensitizing effects will be addressed and in particular the possible role of inositol glycans as insulin second messengers.

Expression Profiling of Solute Carrier Gene Families at the Blood-CSF Barrier

The choroid plexus (CP) is a highly vascularized tissue in the brain ventricles and acts as the blood-cerebrospinal fluid (CSF) barrier (BCSFB). A main function of the CP is to secrete CSF, which is accomplished by active transport of small ions and water from the blood side to the CSF side. The CP also supplies the brain with certain nutrients, hormones, and metal ions, while removing metabolites and xenobiotics from the CSF. Numerous membrane transporters are expressed in the CP in order to facilitate the solute exchange between the blood and the CSF. The solute carrier (SLC) superfamily represents a major class of transporters in the CP that constitutes the molecular mechanisms for CP function. Recently, we systematically and quantitatively examined Slc gene expression in 20 anatomically comprehensive brain areas in the adult mouse brain using high-quality in situ hybridization data generated by the Allen Brain Atlas. Here we focus our analysis on Slc gene expression at the BCSFB using previously obtained data. Of the 252 Slc genes present in the mouse brain, 202 Slc genes were found at detectable levels in the CP. Unsupervised hierarchical cluster analysis showed that the CP Slc gene expression pattern is substantially different from the other 19 analyzed brain regions. The majority of the Slc genes in the CP are expressed at low to moderate levels, whereas 28 Slc genes are present in the CP at the highest levels. These highly expressed Slc genes encode transporters involved in CSF secretion, energy production, and transport of nutrients, hormones, neurotransmitters, sulfate, and metal ions. In this review, the functional characteristics and potential importance of these Slc transporters in the CP are discussed, with particular emphasis on their localization and physiological functions at the BCSFB.

Fell Pony syndrome: characterization of developmental hematopoiesis failure and associated gene expression profiles

Fell Pony syndrome (FPS) is a fatal immunodeficiency that occurs in foals of the Fell Pony breed. Affected foals present with severe anemia, B cell lymphopenia, and opportunistic infections. Our objective was to conduct a prospective study of potential FPS-affected Fell Pony foals to establish clinical, immunological, and molecular parameters at birth and in the first few weeks of life. Complete blood counts, peripheral blood lymphocyte phenotyping, and serum immunoglobulin concentrations were determined for 3 FPS-affected foals, 49 unaffected foals, and 6 adult horses. In addition, cytology of bone marrow aspirates was performed sequentially in a subset of foals. At birth, the FPS-affected foals were not noticeably ill and had hematocrit and circulating B cell counts comparable to those of unaffected foals; however, over 6 weeks, values for both parameters steadily declined. A bone marrow aspirate from a 3-week-old FPS-affected foal revealed erythroid hyperplasia and concurrent erythroid and myeloid dysplasia, which progressed to a severe erythroid hypoplasia at 5 weeks of life. Immunohistochemical staining confirmed the paucity of B cells in primary and secondary lymphoid tissues. The mRNA expression of genes involved in B cell development, signaling, and maturation was investigated using qualitative and quantitative reverse transcriptase PCR (RT-PCR). Several genes, including CREB1, EP300, MYB, PAX5, and SPI1/PU.1, were sequenced from FPS-affected and unaffected foals. Our study presents evidence of fetal erythrocyte and B cell hematopoiesis with rapid postnatal development of anemia and B lymphopenia in FPS-affected foals. The transition between fetal/neonatal and adult-like hematopoiesis may be an important aspect of the pathogenesis of FPS.

myo-Inositol uptake is essential for bulk inositol phospholipid but not glycosylphosphatidylinositol synthesis in Trypanosoma brucei

myo-Inositol is an essential precursor for the production of inositol phosphates and inositol phospholipids in all eukaryotes. Intracellular myo-inositol is generated by de novo synthesis from glucose 6-phosphate or is provided from the environment via myo-inositol symporters. We show that in Trypanosoma brucei, the causative pathogen of human African sleeping sickness and nagana in domestic animals, myo-inositol is taken up via a specific proton-coupled electrogenic symport and that this transport is essential for parasite survival in culture. Down-regulation of the myo-inositol transporter using RNA interference inhibited uptake of myo-inositol and blocked the synthesis of the myo-inositol-containing phospholipids, phosphatidylinositol and inositol phosphorylceramide; in contrast, it had no effect on glycosylphosphatidylinositol production. This together with the unexpected localization of the myo-inositol transporter in both the plasma membrane and the Golgi demonstrate that metabolism of endogenous and exogenous myo-inositol in T. brucei is strictly segregated.

Identification of a mutation associated with fatal Foal Immunodeficiency Syndrome in the Fell and Dales pony

The Fell and Dales are rare native UK pony breeds at risk due to falling numbers, in-breeding, and inherited disease. Specifically, the lethal Mendelian recessive disease Foal Immunodeficiency Syndrome (FIS), which manifests as B-lymphocyte immunodeficiency and progressive anemia, is a substantial threat. A significant percentage (∼10%) of the Fell ponies born each year dies from FIS, compromising the long-term survival of this breed. Moreover, the likely spread of FIS into other breeds is of major concern. Indeed, FIS was identified in the Dales pony, a related breed, during the course of this work. Using a stepwise approach comprising linkage and homozygosity mapping followed by haplotype analysis, we mapped the mutation using 14 FIS–affected, 17 obligate carriers, and 10 adults of unknown carrier status to a ∼1 Mb region (29.8 – 30.8 Mb) on chromosome (ECA) 26. A subsequent genome-wide association study identified two SNPs on ECA26 that showed genome-wide significance after Bonferroni correction for multiple testing: BIEC2-692674 at 29.804 Mb and BIEC2-693138 at 32.19 Mb. The associated region spanned 2.6 Mb from ∼29.6 Mb to 32.2 Mb on ECA26. Re-sequencing of this region identified a mutation in the sodium/myo-inositol cotransporter gene (SLC5A3); this causes a P446L substitution in the protein. This gene plays a crucial role in the regulatory response to osmotic stress that is essential in many tissues including lymphoid tissues and during early embryonic development. We propose that the amino acid substitution we identify here alters the function of SLC5A3, leading to erythropoiesis failure and compromise of the immune system. FIS is of significant biological interest as it is unique and is caused by a gene not previously associated with a mammalian disease. Having identified the associated gene, we are now able to eradicate FIS from equine populations by informed selective breeding.

Foal Immunodeficiency Syndrome (FIS) is a genetic disease that affects two related British pony breeds, namely the Fell and the Dales. Foals with FIS appear to be normal at birth but within a few weeks develop evidence of infection such as diarrhoea, pneumonia, etc. The infections are resistant to treatment, and the foals die or are euthanized before three months of age. The foals also suffer from a severe progressive anemia. Being a recessive condition, the disease is difficult to control without a diagnostic DNA test to identify symptom-free carrier parents. Within the last few years the horse genome has been sequenced, and this has allowed the development of tools to identify genetic mutations in the horse at high resolution. In this article we demonstrate the use of these new tools to identify the location of the FIS mutation. The presumptive causal lesion was then identified by sequencing this region. This has enabled us to develop a test that can be used to identify carrier ponies, allowing breeders to avoid FIS in their foal crop.

Is prenatal myo-inositol deficiency a mechanism of CNS injury in galactosemia?

Classic Galactosemia due to galactose-1-phosphate uridyltransferase (GALT) deficiency is associated with apparent diet-independent complications including cognitive impairment, learning problems and speech defects. As both galactose-1-phosphate and galactitol may be elevated in cord blood erythrocytes and amniotic fluid despite a maternal lactose-free diet, endogenous production of galactose may be responsible for the elevated fetal galactose metabolites, as well as postnatal CNS complications. A prenatal deficiency of myo-inositol due to an accumulation of both galactose-1- phosphate and galactitol may play a role in the production of the postnatal CNS dysfunction. Two independent mechanisms may result in fetal myo-inositol deficiency: competitive inhibition of the inositol monophosphatase1 (IMPA1)-mediated hydrolysis of inositol monophosphate by high galactose-1- phosphate levels leading to a sequestration of cellular myo-inositol as inositol monophosphate and galactitol-induced reduction in SMIT1-mediated myo-inositol transport. The subsequent reduction of myo-inositol within fetal brain cells could lead to inositide deficiencies with resultant perturbations in calcium and protein kinase C signaling, the AKT/mTOR/ cell growth and development pathway, cell migration, insulin sensitivity, vescular trafficking, endocytosis and exocytosis, actin cytoskeletal remodeling, nuclear metabolism, mRNA export and nuclear pore complex regulation, phosphatidylinositol-anchored proteins, protein phosphorylation and/or endogenous iron "chelation". Using a knockout animal model we have shown that a marked deficiency of myo-inositol in utero is lethal but the phenotype can be rescued by supplementing the drinking water of the pregnant mouse. If myo-inositol deficiency is found to exist in the GALT-deficient fetal brain, then the use of myo-inositol to treat the fetus via oral supplementation of the pregnant female may warrant consideration.

Sodium/myo-inositol cotransporter 1 and myo-inositol are essential for osteogenesis and bone formation

myo-Inositol (MI) plays an essential role in several important processes of cell physiology, is involved in the neural system, and provides an effective treatment for some psychiatric disorders. Its role in osteogenesis and bone formation nonetheless is unclear. Sodium/MI cotransporter 1 (SMIT1, the major cotransporter of MI) knockout (SMIT1(-/-)) mice with markedly reduced tissue MI levels were used to characterize the essential roles of MI and SMIT1 in osteogenesis. SMIT1(-/-) embryos had a dramatic delay in prenatal mineralization and died soon after birth owing to respiratory failure, but this could be rescued by maternal MI supplementation. The rescued SMIT1(-/-) mice had shorter limbs, decreased bone density, and abnormal bone architecture in adulthood. Deletion of SMIT1 resulted in retarded postnatal osteoblastic differentiation and bone formation in vivo and in vitro. Continuous MI supplementation partially restored the abnormal bone phenotypes in adult SMIT1(-/-) mice and strengthened bone structure in SMIT1(+/+) mice. Although MI content was much lower in SMIT1(-/-) mesenchymal cells (MSCs), the I(1,4,5)P(3) signaling pathway was excluded as the means by which SMIT1 and MI affected osteogenesis. PCR expression array revealed Fgf4, leptin, Sele, Selp, and Nos2 as novel target genes of SMIT1 and MI. SMIT1 was constitutively expressed in multipotential C3H10T1/2 and preosteoblastic MC3T3-E1 cells and could be upregulated during bone morphogenetic protein 2 (BMP-2)-induced osteogenesis. Collectively, this study demonstrated that deficiency in SMIT1 and MI has a detrimental impact on prenatal skeletal development and postnatal bone remodeling and confirmed their essential roles in osteogenesis, bone formation, and bone mineral density (BMD) determination.

Chronic treatment with D-chiro-inositol prevents autonomic and somatic neuropathy in STZ-induced diabetic mice

AIM

D-chiro-inositol (DCI) has been shown to prevent and reverse endothelial dysfunction in diabetic rats and rabbits. The present study evaluates the preventive effect of DCI on experimental diabetic neuropathy (DN).

METHODS

Streptozotocin-induced (STZ) diabetic mice were treated by oral gavage for 60 days with DCI (20 mg/kg/12 h) or saline (NaCl 0.9%; 0.1 ml/10 g/12 h; Diab) and compared with euglycaemic groups treated with saline (0.1 ml/10 g/12 h; Eugly). We compared the response of the isolated sciatic nerve, corpora cavernosa or vas deferens to electrical stimulation.

RESULTS

The electrically evoked compound action potential of the sciatic nerve was greatly blunted by diabetes. The peak-to-peak amplitude (PPA) was decreased from 3.24 ± 0.7 to 0.9 ± 0.2 mV (p < 0.05), the conduction velocity (CV) of the first component was reduced from 46.78 ± 4.5 to 26.69 ± 3.8 ms (p < 0.05) and chronaxy was increased from 60.43 ± 1.9 to 69.67 ± 1.4 ms (p < 0.05). These parameters were improved in nerves from DCI-treated mice (p < 0.05). PPA in the DCI group was 5.79 ± 0.8 mV (vs. 0.9 ± 0.2 mV-Diab; p < 0.05) and CV was 45.91 ± 3.6 ms (vs. 26.69 ± 3.8 ms-Diab; p < 0.05). Maximal relaxation of the corpus cavernosum evoked by electrical stimulation (2-64 Hz) in the Diab group was 36.4 ± 3.8% compared to 65.4 ± 2.8% in Eugly and 59.3 ± 5.5% in the DCI group (p < 0.05). Maximal contraction obtained in the vas deferens was 38.0 ± 9.2% in Eugly and 11.5 ± 2.6% in Diab (decrease of 69.7%; p < 0.05), compared to 25.2 ± 2.3% in the DCI group (p < 0.05 vs. diabetic). Electron microscopy of the sciatic nerves showed prevention of neuronal damage.

CONCLUSIONS

DCI has a neuroprotective action in both autonomic and somatic nerves in STZ-induced DN.

An NGF-responsive element targets myo-inositol monophosphatase-1 mRNA to sympathetic neuron axons

mRNA localization is an evolutionary conserved mechanism that underlies the establishment of cellular polarity and specialized cell functions. To identify mRNAs localized in subcellular compartments of developing neurons, we took an original approach that combines compartmentalized cultures of rat sympathetic neurons and sequential analysis of gene expression (SAGE). Unexpectedly, the most abundant transcript in axons was mRNA for myo-inositol monophosphatase-1 (Impa1), a key enzyme that regulates the inositol cycle and the main target of lithium in neurons. A novel localization element within the 3' untranslated region of Impa1 mRNA specifically targeted Impa1 transcript to sympathetic neuron axons and regulated local IMPA1 translation in response to nerve growth factor (NGF). Selective silencing of IMPA1 synthesis in axons decreased nuclear CREB activation and induced axonal degeneration. These results provide insights into mRNA transport in axons and reveal a new NGF-responsive localization element that directs the targeting and local translation of an axonal transcript.

Investigation of the H+–myo-inositol transporter (HMIT) as a neuronal regulator of phosphoinositide signalling

Phosphoinositide signalling regulates a series of important neuronal processes that are thought to be altered in mood disorders. Furthermore, mood-stabilizing drugs inhibit key enzymes that regulate phosphoinositide production and alter neuronal growth cone morphology in an inositol-reversible manner. Inositol is taken up by neurons from the extracellular fluid, presumably via membrane transporters; it can also be synthesized by the enzyme MIP-synthase (myo-inositol-1-phosphate synthase) and, in addition, it is generated by inositol phospholipid hydrolysis. The neuronal-specific HMIT (H+–myo-inositol transporter) represents a potential regulator of inositol signalling in neurons that warrants further investigation.

Characterization of the null murine sodium/myo-inositol cotransporter 1 (Smit1 or Slc5a3) phenotype: myo-inositol rescue is independent of expression of its cognate mitochondrial ribosomal protein subunit 6 (Mrps6) gene and of phosphatidylinositol levels in neonatal brain

Ablation of the murine Slc5a3 gene results in severe myo-inositol (Ins) deficiency and congenital central apnea due to abnormal respiratory rhythmogenesis. The lethal knockout phenotype may be rescued by supplementing the maternal drinking water with 1% Ins. In order to test the hypothesis that Ins deficiency leads to inositide deficiencies, which are corrected by prenatal treatment, we measured the effects of Ins rescue on Ins, phosphatidylinositol (PtdIns) and myo-inositol polyphosphate levels in brains of E18.5 knockout fetuses. As the Slc5a3 gene structure is unique in the sodium/solute cotransporter (SLC5) family, and exon 1 is shared with the mitochondrial ribosomal protein subunit 6 (Mrps6) gene, we also sought to determine whether expression of its cognate Mrps6 gene is abnormal in knockout fetuses. The mean level of Ins was increased by 92% in brains of rescued Slc5a3 knockout fetuses (0.48 versus 0.25 nmol/mg), but was still greatly reduced in comparison to wildtype (6.97 nmol/mg). The PtdIns, InsP(5) and InsP(6) levels were normal without treatment. Mrps6 gene expression was unaffected in the E18.5 knockout fetuses. This enigmatic model is not associated with neonatal PtdIns deficiency and rescue of the phenotype may be accomplished without restoration of Ins. The biochemical mechanism that both uniformly leads to death and allows for Ins rescue remains unknown. In conclusion, in neonatal brain tissue, Mrps6 gene expression may not be contingent on function of its embedded Slc5a3 gene, while inositide deficiency may not be the mechanism of lethal apnea in null Slc5a3 mice.

Homozygote inositol transporter knockout mice show a lithium-like phenotype

OBJECTIVE

Lithium inhibits inositol monophosphatase and also reduces inositol transporter function. To determine if one or more of these mechanisms might underlie the behavioral effects of lithium, we studied inositol transporter knockout mice. We previously reported that heterozygous knockout mice with reduction of 15-37% in brain inositol had no abnormalities of pilocarpine sensitivity or antidepressant-like behavior in the Porsolt forced swim test. We now report on studies of homozygous inositol transporter knockout mice.

METHODS

Homozygote knockout mice were rescued by 2% inositol supplementation to the drinking water of the dam mice through pregnancy and lactation. Genotyping was carried out by polymerase chain reaction followed by agarose electrophoresis. Brain free myo-inositol levels were determined gas-chromatographically. Motor activity and coordination were assessed by the rotarod test. Behavior of the mice was studied in lithium-pilocarpine seizure models for lithium action and in the Porsolt forced swim test model for depression.

RESULTS

In homozygote knockout mice, free inositol levels were reduced by 55% in the frontal cortex and by 60% in the hippocampus. There were no differences in weight or motor coordination by the rotarod test. They behaved similarly to lithium-treated animals in the model of pilocarpine seizures and in the Porsolt forced swimming test model of depression.

CONCLUSIONS

Reduction of brain inositol more than 15-37% may be required to elicit lithium-like neurobehavioral effects.

IMPA1 is essential for embryonic development and lithium-like pilocarpine sensitivity

Lithium has been the standard pharmacological treatment for bipolar disorder over the last 50 years; however, the molecular targets through which lithium exerts its therapeutic effects are still not defined. We characterized the phenotype of mice with a dysfunctional IMPA1 gene (IMPA1-/-) to study the in vivo physiological functions of IMPA1, in general, and more specifically its potential role as a molecular target in mediating lithium-dependent physiological effects. Homozygote IMPA1-/- mice died in utero between days 9.5 and 10.5 post coitum (p.c.) demonstrating the importance of IMPA1 in early embryonic development. Intriguingly, the embryonic lethality could be reversed by myo-inositol supplementation via the pregnant mothers. In brains of adult IMPA1-/- mice, IMPase activity levels were found to be reduced (up to 65% in hippocampus); however, inositol levels were not found to be altered. Behavioral analysis of the IMPA1-/- mice indicated an increased motor activity in both the open-field test and the forced-swim test as well as a strongly increased sensitivity to pilocarpine-induced seizures, the latter supporting the idea that IMPA1 represents a physiologically relevant target for lithium. In conclusion the IMPA1-/- mouse represents a novel model to study inositol homeostasis, and indicates that genetic inactivation of IMPA1 can mimic some actions of lithium.

SMIT2 mediates all myo-inositol uptake in apical membranes of rat small intestine

This study presents the characterization of myo-inositol (MI) uptake in rat intestine as evaluated by use of purified membrane preparations. Three secondary active MI cotransporters have been identified; two are Na(+) coupled (SMIT1 and SMIT2) and one is H(+) coupled (HMIT). Through inhibition studies using selective substrates such as d-chiro-inositol (DCI, specific for SMIT2) and l-fucose (specific for SMIT1), we show that SMIT2 is exclusively responsible for apical MI transport in rat intestine; rabbit intestine appears to lack apical transport of MI. Other sugar transport systems known to be present in apical membranes, such as SGLT1 or GLUT5, lacked any significant contribution to MI uptake. Functional analysis of rat SMIT2 activity, via electrophysiological studies in Xenopus oocytes, demonstrated similarities to the activities of SMIT2 from other species (rabbit and human) displaying high affinities for MI (0.150 +/- 0.040 mM), DCI (0.31 +/- 0.06 mM), and phlorizin (Pz; 0.016 +/- 0.007 mM); low affinity for glucose (36 +/- 7 mM); and no affinity for l-fucose. Although these functional characteristics essentially confirmed those found in rat intestinal apical membranes, a unique discrepancy was seen between the two systems studied in that the affinity constant for glucose was approximately 40-fold lower in vesicles (K(i) = 0.94 +/- 0.35 mM) than in oocytes. Finally, the transport system responsible for the basolateral efflux transporter of glucose in intestine, GLUT2, did not mediate any significant radiolabeled MI uptake in oocytes, indicating that this transport system does not participate in the basolateral exit of MI from small intestine.

Expression and functionality of the Na+/myo-inositol cotransporter SMIT2 in rabbit kidney

Myo-inositol (MI) is involved in several important aspects of cell physiology including cell signaling and the control of intracellular osmolarity i.e. by serving as a "compatible osmolyte". Currently, three MI cotransporters have been identified: two are Na(+)-dependent (SMIT1 and SMIT2) and one is H(+)-dependent (HMIT) and predominantly expressed in the brain. The goal of this study was to characterize the expression of SMIT2 in rabbit kidney and to compare it to SMIT1. First, we quantified mRNA levels for both transporters using quantitative real-time PCR and found that SMIT1 was predominantly expressed in the medulla while SMIT2 was mainly in the cortex. This distribution of SMIT2 was confirmed on Western blots where an antibody raised against a SMIT2 epitope specifically detected a 75 kDa protein in both tissues. Characterization of MI transport in brush-border membrane vesicles (BBMV), in the presence of d-chiro-inositol and l-fucose to separately identify SMIT1 and SMIT2 activities, showed that only SMIT2 is expressed at the luminal side of proximal convoluted tubules. We thus conclude that, in the rabbit kidney, SMIT2 is predominantly expressed in the cortex where it is probably responsible for the apical transport of MI into the proximal tubule.

Phenotype of the Taurine Transporter Knockout Mouse

This chapter reports present knowledge on the properties of mice with disrupted gene coding for the taurine transporter (taut-/- mice). Study of those mice unraveled some of the roles of taurine and its membrane transport for the development and maintenance of normal organ functions and morphology. When compared with wild-type controls, taut-/- mice have decreased taurine levels in skeletal and heart muscle by about 98%, in brain, kidney, plasma, and retina by 80 to 90%, and in liver by about 70%. taut-/- mice exhibit a lower body mass as well as a strongly reduced exercise capacity compared with taut+/- and wild-type mice. Furthermore, taut-/- mice show a variety of pathological features, for example, subtle derangement of renal osmoregulation, changes in neuroreceptor expression, and loss of long-term potentiation in the striatum, and they develop clinically relevant age-dependent disorders, for example, visual, auditory, and olfactory dysfunctions, unspecific hepatitis, and liver fibrosis. Taurine-deficient animal models such as acutely dietary-manipulated foxes and cats, pharmacologically induced taurine-deficient rats, and taurine transporter knockout mouse are powerful tools allowing identification of the mechanisms and complexities of diseases mediated by impaired taurine transport and taurine depletion (Chapman et al., 1993; Heller-Stilb et al., 2002; Huxtable, 1992; Lake, 1993; Moise et al., 1991; Novotny et al., 1991; Pion et al., 1987; Timbrell et al., 1995; Warskulat et al., 2004, 2006b). Taurine, which is the most abundant amino acid in many tissues, is normally found in intracellular concentrations of 10 to 70 mmol/kg in mammalian heart, brain, skeletal muscle, liver, and retina (Chapman et al., 1993; Green et al., 1991; Huxable, 1992; Timbrell et al., 1995). These high taurine levels are maintained by an ubiquitous expression of Na(+)-dependent taurine transporter (TAUT) in the plasma membrane (Burg, 1995; Kwon and Handler, 1995; Lang et al., 1998; Liu et al., 1992; Ramamoorthy et al., 1994; Schloss et al., 1994; Smith et al., 1992; Uchida et al., 1992; Vinnakota et al., 1997; Yancey et al., 1975). Taurine is not incorporated into proteins. It is involved in cell volume regulation, neuromodulation, antioxidant defense, protein stabilization, stress responses, and via formation of taurine-chloramine in immunomodulation (Chapman et al., 1993; Green et al., 1991; Huxtable, 1992; Timbrell et al., 1995). On the basis of its functions, taurine may protect cells against various types of injury (Chapman et al., 1993; Green et al., 1991; Huxtable, 1992; Kurz et al., 1998; Park et al., 1995; Stapleton et al., 1998; Timbrell et al., 1995; Welch and Brown, 1996; Wettstein and Häussinger, 1997). In order to examine the multiple taurine functions, murine models have several intrinsic advantages for in vivo research compared to other animal models, including lower cost, maintenance, and rapid reproduction rate. Further, experimental reagents for cellular and molecular studies are widely available for the mouse. In particular, mice can be easily genetically manipulated by making transgene and knockout mice. This chapter focuses on the phenotype of the TAUT-deficient murine model (taut-/-; Heller-Stilb et al., 2002), which may help researchers elucidate the diverse roles of taurine in development and maintenance of normal organ functions and morphology.

Micronutrient and urate transport in choroid plexus and kidney: implications for drug therapy

With application of molecular biology techniques, there has been rapid progress in understanding how many drugs and micronutrients (e.g., vitamins) are transferred across the choroid plexus (CP), the main transport locus of the blood-cerebrospinal fluid (CSF) barrier, and the renal tubular epithelial cells. In many cases, these molecules are transported by separate, specific carriers or receptors on the apical and/or basal side of the CP or renal epithelial cells. This commentary focuses on four micronutrient transport systems in CP (ascorbic acid, folate, inositol, and riboflavin), all of which have been recently cloned, expressed and for which knockout mice models were developed and transporter localization studies performed. Also reviewed is the recently cloned uric acid transport system in human kidney in which there exists a human "knockout" model. The implications of these transport systems for drug therapy of central nervous system and renal disorders are discussed, especially with regard to methods to circumvent the blood-brain and blood-CSF barriers to deliver drugs to the brain.

Localization and ontogeny of damage-induced neuronal endopeptidase mRNA-expressing neurons in the rat nervous system

Neuropeptides are crucial mediators in nervous and endocrine systems. Processing and degradation, the major regulatory mechanisms, of enzymes are essential for the control of these peptidergic intercellular signaling systems. Damage-induced neuronal endopeptidase (or endothelin converting enzyme-like1), a member of the neprilysin family, has recently been identified as an M13 zinc metalloprotease. Damage-induced neuronal endopeptidase mRNA expression is strikingly restricted to neurons, and is remarkably induced in response to various types of neuronal injuries, although its function and substrate remain unknown. To clarify the role of damage-induced neuronal endopeptidase, we examined the localization and ontogeny of damage-induced neuronal endopeptidase mRNA expression in the rat nervous system using in situ hybridization. Damage-induced neuronal endopeptidase mRNA was detected at embryonic day 12, and its expression restricted to the ventral region of the neural tube. Subsequently, expression was also apparent in primordia of the striatum, hypothalamus, and cranial motor nuclei during neural development. This specific distribution was relatively maintained in the adult brain, although expression levels became weaker. Expression of damage-induced neuronal endopeptidase was absent in the cerebral cortex, hippocampus, and cerebellum. In addition to prominent expression in CNS, intestinal and sensory ganglia and retina demonstrated transient intense damage-induced neuronal endopeptidase mRNA expression during the embryonic period that then declined, and disappeared after birth. The results indicated that damage-induced neuronal endopeptidase might play an important role in embryonic neural development, in particular in peripheral ganglia derived from the neural crest, and in some neurons originating from the basal plate such as the hypothalamus and cranial motor neurons.