Cyclic PIP Research Articles

Activated Inositol Phosphate, Substrate for Synthesis of Prostaglandylinositol Cyclic Phosphate (Cyclic PIP)-The Key for the Effectiveness of Inositol-Feeding.

The natural cyclic AMP antagonist, prostaglandylinositol cyclic phosphate (cyclic PIP), is biosynthesized from prostaglandin E (PGE) and activated inositol phosphate (n-Ins-P), which is synthesized by a particulate rat-liver-enzyme from GTP and a precursor named inositol phosphate (pr-Ins-P), whose 5-ring phosphodiester structure is essential for n-Ins-P synthesis. Aortic myocytes, preincubated with [3H] myo-inositol, synthesize after angiotensin II stimulation (30 s) [3H] pr-Ins-P (65% yield), which is converted to [3H] n-Ins-P and [3H] cyclic PIP. Acid-treated (1 min) [3H] pr-Ins-P co-elutes with inositol (1,4)-bisphosphate in high performance ion chromatography, indicating that pr-Ins-P is inositol (1:2-cyclic,4)-bisphosphate. Incubation of [3H]-GTP with unlabeled pr-Ins-P gave [3H]-guanosine-labeled n-Ins-P. Cyclic PIP synthase binds the inositol (1:2-cyclic)-phosphate part of n-Ins-P to PGE and releases the [3H]-labeled guanosine as [3H]-GDP. Thus, n-Ins-P is most likely guanosine diphospho-4-inositol (1:2-cyclic)-phosphate. Inositol feeding helps patients with metabolic conditions related to insulin resistance, but explanations for this finding are missing. Cyclic PIP appears to be the key for explaining the curative effect of inositol supplementation: (1) inositol is a molecular constituent of cyclic PIP; (2) cyclic PIP triggers many of insulin's actions intracellularly; and (3) the synthesis of cyclic PIP is decreased in diabetes as shown in rodents.

Insulin Resistance Develops Due to an Imbalance in the Synthesis of Cyclic AMP and the Natural Cyclic AMP Antagonist Prostaglandylinositol Cyclic Phosphate (Cyclic PIP)

The reasons initiating insulin resistance are not identified. Various metabolic derailments have been characterized. These are the outcome and not the initiation of insulin resistance. In animal models of type 2 diabetes and hypertension, a decreased hormonal stimulation of the synthesis of the cyclic AMP antagonist prostaglandylinositol cyclic phosphate (cyclic PIP) was determined. The resultant imbalance of the action of cyclic AMP and cyclic PIP shifts metabolic regulation to the dominance of catabolism and a decrease in imperative anabolism. This dominance develops gradually since the more cyclic AMP dominates, the more the synthesis of cyclic PIP will be inhibited. Vanishing actions of cyclic PIP are its 10-fold activation of glucose uptake in adipocytes, its inhibition of insulin release from pancreatic β-cells, its inhibition of PKA and its 7-fold activation of protein ser/thr phosphatase. Reduced synthesis of cyclic PIP results from (a) decreased substrate availability, (b) long-time elevated cyclic AMP levels resulting from stress overloads and (c) aging and the gradual decrease in the synthesis of hormones which likely maintain mechanisms that stimulate cyclic PIP synthesis. The need is to discover which hormones, such as growth hormone, insulin-like growth factor-1, dehydroepiandrosterone, and testosterone, are involved in maintaining the stimulation of cyclic PIP synthesis.

Metformin's Mechanism of Action Is Stimulation of the Biosynthesis of the Natural Cyclic AMP Antagonist Prostaglandylinositol Cyclic Phosphate (Cyclic PIP).

Metformin is the leading drug for treating type 2 diabetics, but the mechanism of action of metformin, despite some suggested mechanisms such as the activation of the AMP-kinase, is largely unknown. Among its many positive effects are the reduction of blood glucose levels, the inhibition of cyclic AMP synthesis, gluconeogenesis and an increase in sensitivity to insulin. Recent studies have described the natural antagonist of cyclic AMP, prostaglandylinositol cyclic phosphate. Synthesis of cyclic PIP is stimulated in all organs by hormones such as insulin and also by drugs such as metformin. Its primary action is to trigger the dephosphorylation of proteins/enzymes, phosphorylated on serine/threonine residues. Cyclic PIP triggers many of the regulations requested by insulin. The parallels between the beneficial effects of metformin and the regulations triggered by cyclic PIP suggest that the mechanism of action of this key drug may well be explained by its stimulation of the synthesis of cyclic PIP.

Evaluation of the DNA Alkylation Properties of a Chlorambucil-Conjugated Cyclic Pyrrole-Imidazole Polyamide.

Hairpin pyrrole-imidazole polyamides (hPIPs) and their chlorambucil (Chb) conjugates (hPIP-Chbs) can alkylate DNA in a sequence-specific manner, and have been studied as anticancer drugs. Here, we conjugated Chb to a cyclic PIP (cPIP), which is known to have a higher binding affinity than the corresponding hPIP, and investigated the DNA alkylation properties of the resulting cPIP-Chb using the optimized capillary electrophoresis method and conventional HPLC product analysis. cPIP-Chb conjugate 3 showed higher alkylation activity at its binding sites than did hPIP-Chb conjugates 1 and 2. Subsequent HPLC analysis revealed that the alkylation site of conjugate 3, which was identified by capillary electrophoresis, was reliable and that conjugate 3 alkylates the N3 position of adenine as do hPIP-Chbs. Moreover, conjugate 3 showed higher cytotoxicity against LNCaP prostate cancer cells than did conjugate 1 and cytotoxicity comparable to that of conjugate 2. These results suggest that cPIP-Chbs could be novel DNA alkylating anticancer drugs.

Prostaglandylinositol cyclic phosphate, the natural antagonist of cyclic AMP.

While searching for a counterpart to cyclic AMP, a new compound was found to inhibit adenylate cyclase. It was identified as prostaglandyl-(15-4')-myo-inositol (1':2'-cyclic)-phosphate (cyclic PIP). The substrates for its biosynthesis are prostaglandin E (PGE) and the novel inositol phosphate, guanosine diphospho-4-myo-inositol 1:2-cyclic phosphate (n-IP). The basic regulatory properties of cyclic PIP are to inhibit dose-dependently protein kinase A (PKA) and to seven-fold activate protein ser/thr phosphatase holoenzyme. These regulations occur as rapidly as the activation of PKA by cyclic AMP. Such regulatory properties are essential for the meticulous regulation of the equilibrium between the phospho- and de-phospho-form of interconvertible enzymes. The synthesis of cyclic PIP is stimulated by insulin and noradrenaline (α-receptor action). The insulin-stimulated cyclic PIP synthase is active in a tyrosine-phosphorylated state. A comparable characterization of the adrenaline-stimulated cyclic PIP synthase is still incomplete. In streptozotocin-diabetic rats, the hormonal stimulation of cyclic PIP synthesis decreases with time. Cyclic PIP synthesis is activated by biguanides as metformin two to four-fold and by antihypertensive drugs two-fold. Inhibition of cyclic PIP synthesis leads to a metabolic state as observed in early-stage type-2 diabetes. In summary, all living cells synthesize cyclic PIP, which switches on anabolism, whereas cyclic AMP triggers catabolism.

Preparation and Properties of Cf/SiC-ZrC Ultrahigh Temperature Ceramic Matrix Composites

Ultra-high temperature materials have many excellent properties, such as high melting point, high specific strength, high thermal conductivity, high conductivity, corrosion resistance and good chemical stability, which make them become high temperature structural materials for aircraft in extreme environments.Cf/SiC-ZrC ultra-high temperature ceramic matrix composites were fabricated by the combined process of chemical vapor deposition and precursor infiltration pyrolysis (CVI-PIP) in this study. The phase composition and microstructure features of the composites were characterized using X-ray diffraction, scanning electron microscopy. A PyC layer was observed as the interfacial layer between carbon fiber and the ultrahigh temperature ceramic matrix. It can protect the carbon fiber from damage during the cyclic PIP process. Nano crystalline ZrC particles were observed in the composites. The ablation mechanisms of the composites were tested in arc-jet wind tunnel and it exhibited good ablation-resistant properties. The ablation mechanism of composite materials in wind tunnel environment is discussed.

P-79: Cyclic PIP synthetase, activated by tyrosine phosphorylation, combines prostaglandin E with activated inositol phosphate to cyclic PIP, a mediator of insulin action

P-79: Cyclic PIP synthetase, activated by tyrosine phosphorylation, combines prostaglandin E with activated inositol phosphate to cyclic PIP, a mediator of insulin action

Direct comparison of inositol phosphoglycan with prostaglandylinositol cyclic phosphate, two potential mediators of insulin action.

Though insulin signalling is thought by many groups to function without second messenger action, others have provided evidence for the existence and action of such regulators. Chemically quite different compounds, however, have been proposed as mediators, such as various inositol phosphoglycans and prostaglandylinositol cyclic phosphate (cyclic PIP). In spite of marked structural differences, these compounds are reported to have the same regulatory properties, i.e. to activate protein ser/thr phosphatases and to inhibit protein kinase A. In order to clarify this discrepancy, the regulatory potency of these different compounds was assayed under identical conditions. It was found that in contrast to cyclic PIP, the synthetic inositol phosphoglycan PIG41 neither directly inhibited protein kinase A nor activated protein ser/thr phosphatases. However, when added to intact cells, such as primary adipocytes, PIG41 inhibited isoproterenol-stimulated lipolysis. This effect most likely results from tyrosine phosphorylation of insulin receptor substrates (IRSs) by PIG41. This tyrosine phosphorylation is not carried out by the insulin receptor tyrosine kinase but by cytosolic tyrosine kinases. This indicates that cyclic PIP, an intracellular regulator, which primarily acts on protein kinase A and on protein ser/thr phosphatases, operates more downstream in the signal transduction cascade as compared to the inositol phosphoglycan PIG41. Thus, cyclic PIP appears to be a suitable candidate to close the gap between IRSs and the protein kinases/phosphatases involved in the signal transduction of insulin.

Phosphatidylinositol 3-kinase and prostaglandylinositol cyclic phosphate (cyclic PIP), a mediator of insulin action, in the signal transduction of insulin.

It has been suggested that downstream signaling from the insulin receptor to the level of the protein kinases and protein phosphatases is accomplished by prosta-glandylinositol cyclic phosphate (cyclic PIP), a proposed second messenger of insulin. However, evidence points also to both phosphatidylinositol 3-kinase, which binds to the tyrosine phosphorylated insulin receptor substrate-1, and the Ras complex in insulin's downstream signaling. We have examined whether a correlation exists between these various observations. It was found that wortmannin, a specific inhibitor of phosphatidylinositol 3-kinase, prevented insulin-induced, as well as cyclic PIP-induced activation of glucose transport, indicating that PI 3-kinase action on glucose transport involves downstream signaling of both insulin and cyclic PIP. Wortmannin has no effect on cyclic PIP synthase activity nor on the substrate production for cyclic PIP synthesis either, indicating that the functional role of PI 3-kinase is exclusively downstream of cyclic PIP.

Prostaglandin deficiency promotes sensitization of adenylyl cyclase.

Inhibition of prostaglandin synthesis by the drug indomethacin suppresses the synthesis of the cyclic AMP antagonist, prostaglandylinositol cyclic phosphate (cyclic PIP), and leads to a metabolic state comparable to type II diabetes. It was of interest whether prostaglandin-deficiency likewise causes sensitization of adenylyl cyclase, as this has been reported for the diabetic state. In liver plasma membranes of indomethacin-treated male rats, basal and forskolin-stimulated cyclic AMP synthesis remained unchanged when compared to untreated control rats. In control rats, stimulation of cyclic AMP synthesis by fluoride (2.2-fold) or glucagon (3.5-fold) was much lower than stimulation by forskolin (6.6-fold). In contrast, in indomethacin-treated rats, stimulation of cAMP synthesis by fluoride (4.6-fold) or glucagon (5.2-fold) nearly matched the stimulation by forskolin (6.4-fold). The level of alpha1-adrenergic receptors was slightly reduced, from 450 to 320 fmol/mg protein, by the indomethacin treatment. Independent of the treatment by indomethacin, stimulation of cyclic AMP synthesis by adrenaline failed, in agreement with the low density of adrenergic beta-receptors. In conclusion, PGE deficiency sensitizes adenylyl cyclase in rat liver for G protein-coupled receptors (glucagon) and also for fluoride.

Two different mechanisms for activation of cyclic PIP synthase: by a G protein or by protein tyrosine phosphorylation.

The biosynthesis of the functional, endogenous cyclic AMP antagonist, prostaglandylinositol cyclic phosphate (cyclic PIP) is performed by the plasma membrane-bound enzyme cyclic PIP synthase, which combines prostaglandin E (PGE) and activated inositol phosphate (n-IP) to cyclic PIP. The Km values of the enzyme for the substrates PGE and n-IP are in the micromolar range. The plasma membrane-bound synthase is activated by fluoride, by the stable GTP analog GMP-PNP, by protamine or biguanide, by noradrenaline, and by insulin. The activation by protamine or biguanide and fluoride (10 mM) is additive, which may indicate the presence of two different types of enzyme, comparable to phospholipase Cbeta and phospholipase Cgamma. Plasma membrane-bound cyclic PIP synthase is inhibited by the protein tyrosine kinase inhibitor tyrphostin B46 with an IC50 of 1.7 microM. However, the solubilized and gel-filtrated enzyme is no longer inhibited by tyrphostin, indicating that the activity of cyclic PIP synthase is connected with the activity of a membrane-bound protein tyrosine kinase. Cyclic PIP synthase activity of freshly prepared plasma membranes is unstable. Upon freezing and rethawing of liver plasma membranes, this instability is increased about 2-fold. Protein tyrosine phosphatase inhibitors [vanadate, fluoride (50-100 mM)] stabilize the enzyme activity, but protease inhibitors do not, indicating that inactivation of the enzyme is connected with protein tyrosine dephosphorylation. Cyclic PIP synthase is present in all tissues tested, like brain, heart, intestine, kidney, liver, lung, skeletal muscle, spleen, and testis. Apart from liver, cyclic PIP synthase activity in most tissues is rather low, but it can be increased up to 5-fold when protein tyrosine phosphatase inhibitors like vanadate are present in the homogenization buffer. Preincubation of cyclic PIP synthase of liver plasma membranes with the tyrosine kinase src kinase causes a 2-fold increase of cyclic PIP synthase activity, though this is certainly not the physiological role played by src kinase in intact cells. The data indicate that cyclic PIP synthase can be activated by two separate mechanisms: by a G protein or by protein tyrosine phosphorylation.

Degradation of the cyclic AMP antagonist prostaglandylinositol cyclic phosphate (cyclic PIP) by dephosphorylation.

The cAMP antagonist, prostaglandylinositol cyclic phosphate (cyclic PIP), is synthesized from prostaglandin E and activated inositol phosphate. From various tissues only that amount of cyclic PIP can be isolated that constitutes the difference between synthesis and degradation. In order to overcome this drawback, the cyclic PIP degrading enzyme or enzymes had to be characterized prior to searching for inhibitors. Cyclic PIP degrading activities have been found in all rat tissues tested, and are lowest in brain (380 pmol x min(-1) x g(-1) wet weight) and highest in liver (1460 pmol x min(-1) x g(-1) wet weight). They are associated primarily with particulate structures of the cells, but not with the plasma membrane. There appear to be at least two different enzymatic activities involved in the degradation of cyclic PIP, because there are two pH-optima, one between pH 7 and 8 and another between pH 4 and 5. It is assumed that these activities are located in microsomes and lysosomes. Because prostaglandylinositol is the final product obtained in the degradation of cyclic PIP, a phosphodiesterase and a phosphatase should be involved, which could not yet be identified individually. Like alkaline phosphatase, cyclic PIP-degrading enzymes require Mg2+ and they are inhibited by heavy metal ions such as mercuric and copper chloride, by sodium fluoride and interestingly, by prostaglandins.

Biosynthesis of the endogenous cyclic adenosine monophosphate (AMP) antagonist, prostaglandylinositol cyclic phosphate (cyclic PIP), from prostaglandin E and activated inositol polyphosphate in rat liver plasma membranes

Biosynthesis of the endogenous cyclic adenosine monophosphate (AMP) antagonist, prostaglandylinositol cyclic phosphate (cyclic PIP), from prostaglandin E and activated inositol polyphosphate in rat liver plasma membranes

Biosynthesis of the endogenous cyclic adenosine monophosphate (AMP) antagonist, prostaglandylinositol cyclic phosphate (cyclic PIP), from prostaglandin E and activated inositol polyphosphate in rat liver plasma membranes.

The endogenous cyclic adenosine monophosphate (AMP) antagonist, cyclic PIP, has been identified as a prostaglandylinositol cyclic phosphate. It inhibits protein kinase A 100% and activates protein serine phosphatase about sevenfold. It is biosynthesized by an enzyme of the plasma membrane when the assay mixture contains adenosine triphosphate (ATP), Mg2+, prostaglandin E and a novel inositol polyphosphate, which cannot be substituted by commercially available inositol phosphates. This novel inositol polyphosphate is a very labile compound. On anion exchange chromatography it elutes in the range of ATP, which may indicate the presence of three phosphate groups. It adsorbs on charcoal, which suggests the presence of a hydrophobic component, possibly a guanosine. Pyrophosphates obtained from inositol 1,4- and inositol 2,4-bisphosphate are accepted by cyclic PIP synthetase for the synthesis of cyclic PIP. The biosynthesis is characterized by enzyme kinetic parameters like dependence on time, enzyme and substrate concentration. The pH optimum of the enzyme is in the range 7.5-8. The enzyme functions optimally with prostaglandin E and poorly with prostaglandin A as the substrate. The presence of fluoride in the assay causes a three- to fourfold increase in cyclic PIP synthesis, which may be correlated with activation via G proteins. These data support previous reports on the chemical structure and action of cyclic PIP. With respect to the possible isomers of cyclic PIP, these indicate that it is most likely the C4-hydroxyl group of the inositol which binds the C15-hydroxyl group of prostaglandin E. A model of hormone-stimulated synthesis of cyclic PIP is proposed: phospholipase A2 and phospholipase C, activated by G proteins upon alpha-adrenergic stimulation, liberate either unsaturated fatty acids or inositol phosphates, which are transformed to prostaglandins and to novel inositol polyphosphate with an energy-rich bond. The cyclic PIP synthetase combines these two substrates to cyclic PIP.

The endogenous cyclic AMP antagonist, cyclic PIP: its ubiquity, hormone-stimulated synthesis and identification as prostaglandylinositol cyclic phosphate

This report shows that the cyclic AMP antagonist cyclic PIP is present in all organs and tissues of the rat so far examined: brain, heart, lung, intestine, kidney, liver, spleen, skeletal muscle and fat. The synthesis of cyclic PIP is stimulated by insulin or noradrenaline (alpha-adrenergic action) in a dose-dependent fashion. Increasing cyclic PIP synthesis with increasing insulin concentrations matches the insulin receptor binding curves. Cyclic PIP levels in blood serum remain low after hormonal stimulation and no cyclic PIP can be detected in urine. As an indication of its ubiquity, cyclic PIP was even detected in yeast. Prostaglandin E (as shown by incorporation of [3H]PGE into cyclic PIP and demonstration of a constant specific activity), myo-inositol (as shown by acid hydrolysis of the dephosphorylated cyclic PIP and mass spectrometric identification of the products) and one phosphate (as shown by the ionic nature of cyclic PIP and its inactivation by phosphodiesterase plus phosphatase) are components of cyclic PIP. Chemical derivatization experiments of cyclic PIP suggest the phosphate to be bound to myo-inositol and the myo-inositol phosphate to the prostaglandin E by its C15-hydroxyl group.