Soybean-derived phosphatidylinositol inhibits in vivo low concentrations of amyloid beta protein-induced degeneration of hippocampal neurons in V337M human tau-expressing mice

[Amyloid β hypothesis in Alzheimer's disease and Cl--ATPase-Neuronal cell death via PI4KIIα inhibition and recovery agents]

In the brains of patients with Alzheimer's disease, a decrease in phosphatidylinositol phosphate (PIP) requiring Cl^--ATPase activity was found. In cultured rat hippocampal neurons, pathophysiological concentrations of amyloid β proteins (Aβs≤10 nM) lowered PIP levels and Cl^--ATPase activity with an increase in intracellular Cl^- concentrations, resulting in Cl^--dependent enhancements in glutamate neurotoxicity and, ultimately, neuronal cell death. Pathophysiological concentrations of Aβs(0.1-10 nM) directly lowered phosphatidylinositol-4-kinase. Non-toxic peptide fragments of Aβ, such as Ile-Gly-Leu, recovered Aβ-induced inhibition of recombinant human phosphatidylinositol-4-kinase IIα (PI4KIIα) and the intrahippocampally administered Aβ-induced degeneration of hippocampal neurons and impairment of spatial memory in mice. Agents with the potential to block these neurotoxic mechanisms of Aβ were summarized herein as (1) Aβ antagonists, (2) substrates of PI4K, (3) PI4K product, (4) PI4K activators, and (5) GABAc receptor stimulants.

Dietary Plant Lectins Appear to Be Transported from the Gut to Gain Access to and Alter Dopaminergic Neurons of Caenorhabditis elegans, a Potential Etiology of Parkinson's Disease

Lectins from dietary plants have been shown to enhance drug absorption in the gastrointestinal tract of rats, be transported trans-synaptically as shown by tracing of axonal and dendritic paths, and enhance gene delivery. Other carbohydrate-binding protein toxins are known to traverse the gut intact in dogs. Post-feeding rhodamine- or TRITC-tagged dietary lectins, the lectins were tracked from gut to dopaminergic neurons (DAergic-N) in transgenic Caenorhabditis elegans (C. elegans) [egIs1(Pdat-1:GFP)] where the mutant has the green fluorescent protein (GFP) gene fused to a dopamine transport protein gene labeling DAergic-N. The lectins were supplemented along with the food organism Escherichia coli (OP50). Among nine tested rhodamine/TRITC-tagged lectins, four, including Phaseolus vulgaris erythroagglutinin (PHA-E), Bandeiraea simplicifolia (BS-I), Dolichos biflorus agglutinin (DBA), and Arachis hypogaea agglutinin (PNA), appeared to be transported from gut to the GFP-DAergic-N. Griffonia Simplicifolia and PHA-E, reduced the number of GFP-DAergic-N, suggesting a toxic activity. PHA-E, BS-I, Pisum sativum (PSA), and Triticum vulgaris agglutinin (Succinylated) reduced fluorescent intensity of GFP-DAergic-N. PHA-E, PSA, Concanavalin A, and Triticum vulgaris agglutinin decreased the size of GFP-DAergic-N, while BS-I increased neuron size. These observations suggest that dietary plant lectins are transported to and affect DAergic-N in C. elegans, which support Braak and Hawkes' hypothesis, suggesting one alternate potential dietary etiology of Parkinson's disease (PD). A recent Danish study showed that vagotomy resulted in 40% lower incidence of PD over 20 years. Differences in inherited sugar structures of gut and neuronal cell surfaces may make some individuals more susceptible in this conceptual disease etiology model.

Discovery of the inhibitory effect of a phosphatidylinositol derivative on P-glycoprotein by virtual screening followed by in vitro cellular studies

P-glycoprotein is capable of effluxing a broad range of cytosolic and membrane penetrating xenobiotic substrates, thus leading to multi-drug resistance and posing a threat for the therapeutic treatment of several diseases, including cancer and central nervous disorders. Herein, a virtual screening campaign followed by experimental validation in Caco-2, MDKCII, and MDKCII mdr1 transfected cell lines has been conducted for the identification of novel phospholipids with P-gp transportation inhibitory activity. Phosphatidylinositol-(1,2-dioctanoyl)-sodium salt (8∶0 PI) was found to significantly inhibit transmembrane P-gp transportation in vitro in a reproducible-, cell line-, and substrate-independent manner. Further tests are needed to determine whether this and other phosphatidylinositols could be co-administered with oral drugs to successfully increase their bioavailability. Moreover, as phosphatidylinositols and phosphoinositides are present in the human diet and are known to play an important role in signal transduction and cell motility, our finding could be of substantial interest for nutrition science as well.

Improving thermostability of phosphatidylinositol-synthesizing Streptomyces phospholipase D

Aimed to produce thermostable phosphatidylinositol (PI)-synthesizing phospholipase D (PLD), we initiated site-directed combinatorial mutagenesis followed by high-throughput screening. Previous site-directed combinatorial mutagenesis of wild-type Streptomyces PLD produced a mutant, DYR (W187D/Y191Y/Y385R) with PI-synthesizing ability. Deriving PI as a product of transphosphatidylation between phosphatidylcholine and myo-inositol, with myo-inositol in excess at high-temperature reaction conditions can increase yield due to enhanced solubility of this substrate. Thus, we improved DYR's thermostability by introduction of random mutations into selected amino acid positions having high B-factor. Screening of the libraries under restricted conditions yielded single-point mutants, specifically D40H, T291Y and R329G. Combinations of these point mutations yielded double (D40H/T291Y, D40H/R329G and T291Y/R329G) and triple (D40H/T291Y/R329G) mutants. PI synthesis at elevated temperatures pointed at D40H/T291Y as the most efficient enzyme. Circular dichroism analysis revealed D40H/T291Y to have increased melting temperature and postponed onset of thermal unfolding compared with DYR. Thermal tolerance study at 65°C confirmed D40H/T291Y's thermostability as its half-inactivation time was 8.7 min longer compared with DYR. This mutant had significantly less root-mean-square deviation change compared with DYR and showed no change in root-mean-square fluctuation when temperature shifts from 40 to 60°C, as determined by molecular dynamics analysis. Acquired different degrees of thermostability were also observed for several other DYR mutants.

Anti-obesity effect of phosphatidylinositol on diet-induced obesity in mice

The aim of this study is to investigate the biodistribution of phosphatidylinositol (PI) after oral administration and its anti-obesity effect. When a suspension of radiolabeled PI was orally administered to mice and the biodistribution was examined, PI radioactivity accumulated in the liver compared to myo-inositol radioactivity at 48 h or later after administration. Then, a PI suspension was orally administered to diet-induced obesity (DIO) mice every 4 days, and the anti-obesity effect of PI was examined. As a result, PI suppressed the body weight increase of DIO mice and significantly reduced the plasma levels of aspartate aminotransferase (AST) and cholesterol. Furthermore, PI regulated the expression of some genes in the liver involved in lipid synthesis and metabolism. The present study demonstrated that PI accumulated in the liver after oral administration and exerted its anti-obesity effect on DIO by regulating the expression of certain genes involved in lipid metabolism in the liver.