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Biomedical subjects

W R Sherman

Publications and source records attributed to W R Sherman.

At least 19 recordsLinked to original sources
PubMed1996

A stereospecific myo-inositol/D-chiro-inositol transporter in HepG2 liver cells. Identification with D-chiro-[3-3H]inositol.

D-chiro-Inositol is an epimer of myo-inositol that is found in certain mammalian glycosylphosphatidylinositol protein anchors and inositol phosphoglycans possessing insulin-like bioactivity. In order to generate a probe for metabolic studies, D-chiro-[3-3H]inositol was synthesized by selective reduction of D-chiro-3-inosose at pH 6.5 with sodium borotritide. D-chiro-[3-3H]Inositol was taken up by HepG2 human liver cells through a saturable and stereospecific pathway in which D-chiro-inositol and myo-inositol competed equally but L-chiro-inositol was not recognized. Dd-Glucose, but not L-glucose, competed for D-chiro-[3-3H]inositol uptake over glucose concentrations of 4-28 mM. Maximum transport capacity was 717 pmol/mg cell protein/3 h with a Km value of 348 microM. Uptake was reduced by 76% when sodium was eliminated from the medium and by 94% when the experiment was performed at 0 degrees C. The new myo/D-chiro-inositol transporter is distinct from the sodium-myo-inositol co-transporter found in many tissues and accounts for all of the saturable D-chiro-inositol uptake and for a portion of the saturable low affinity myo-inositol uptake in HepG2 cells. It may allow D-chiro-inositol to be used by cells in the presence of a relatively large amount of competing myo-inositol.

Binding, Competitive↗
PubMed1995

Visualization and comparison of molecular dynamics simulations of leukotriene C4, leukotriene D4, and leukotriene E4.

Molecular dynamics simulations of leukotriene C4 (LTC4), leukotriene D4 (LTD4), and leukotriene E4 (LTE4) were carried out, and the data were visualized in an animated video format. Three-dimensional ghost images show the positions of the heavy atoms of all three molecules throughout the simulations. The ghost images can be superimposed to give a single three-dimensional image in which the shapes of the most populated conformers of each molecule are apparent and can be compared. Leukotriene D4 was found to occupy mostly T-shaped conformations, while LTC4 occupied mostly cup-shaped conformations, and LTE4 occupied a wide range of conformations spanning the LTD4 and LTC4 types. Digital filtering and graphing of the internal geometries of the molecules as a function of time revealed differences in dynamic behavior. The results are discussed in light of current knowledge about leukotriene receptors.

Computer Graphics↗
PubMed1994

Effects of glucose on sorbitol pathway activation, cellular redox, and metabolism of myo-inositol, phosphoinositide, and diacylglycerol in cultured human retinal pigment epithelial cells.

Sorbitol (aldose reductase) pathway flux in diabetes perturbs intracellular metabolism by two putative mechanisms: reciprocal osmoregulatory depletion of other organic osmolytes e.g., myo-inositol, and alterations in NADPH/NADP+ and/or NADH/NAD+. The "osmolyte" and "redox" hypotheses predict secondary elevations in CDP-diglyceride, the rate-limiting precursor for phosphatidylinositol synthesis, but through different mechanisms: the "osmolyte" hypothesis via depletion of intracellular myo-inositol (the cosubstrate for phosphatidylinositol-synthase) and the "redox" hypothesis through enhanced de novo synthesis from triose phosphates. The osmolyte hypothesis predicts diminished phosphoinositide-derived arachidonyl-diacylglycerol, while the redox hypothesis predicts increased total diacylglycerol and phosphatidic acid. In high aldose reductase expressing retinal pigment epithelial cells, glucose-induced, aldose reductase inhibitor-sensitive CDP-diglyceride accumulation and inhibition of 32P-incorporation into phosphatidylinositol paralleled myo-inositol depletion (but not cytoplasmic redox, that was unaffected by glucose) and depletion of arachidonyl-diacylglycerol. 3 mM pyruvate added to the culture medium left cellular redox unaltered, but stimulated Na(+)-dependent myo-inositol uptake, accumulation, and incorporation into phosphatidylinositol. These results favor myo-inositol depletion rather than altered redox as the primary cause of glucose-induced aldose reductase-related defects in phospholipid metabolism in cultured retinal pigment epithelial cells.

Aldehyde Reductase↗
PubMed1993

D-chiro-inositol metabolism in diabetes mellitus.

D-chiro-inositol is a rare inositol isomer present in inositol phosphoglycans which are proposed mediators of insulin action. To study D-chiro-inositol metabolism in diabetes mellitus, a sensitive and specific assay was developed using negative-ion chemical ionization gas chromatography/mass spectrometry. Median urinary D-chiro-inositol excretion, which was 2.1 mumol/day in nondiabetics, was substantially increased to 12 mumol/day in non-insulin-dependent diabetes (P < 0.0001) and to 74 mumol/day in insulin-dependent diabetes (P < 0.0001). Urinary D-chiro-inositol was strongly correlated with fasting plasma glucose (r = 0.568, P < 0.0001), glycated hemoglobin (r = 0.529, P < 0.0001), and urinary glucose (r = 0.368, P = 0.01). The renal clearance of D-chiro-inositol was selectively elevated in both non-insulin-dependent and insulin-dependent diabetes when compared with the clearances of L-chiro-inositol or myo-inositol and exceeded the glomerular filtration rate in 71% of the diabetics but in none of the nondiabetics. In poorly controlled diabetic patients insulin treatment reduced urinary D-chiro-inositol losses by 63% and increased plasma levels by 8.8-fold. The metabolism of D-chiro-inositol is abnormal in diabetes and appears to be influenced by short- and long-term metabolic control.

Adult↗
PubMed1993

Restoration of brain myo-inositol levels in rats increases latency to lithium-pilocarpine seizures.

Lithium pretreatment in rats potentiates the epileptogenic effects of pilocarpine and other cholinergic agonists. In order to determine if this effect of lithium could be reversed by myo-inositol, rats were pretreated with intracerebroventricular (ICV) injections of myoinositol, artificial CSF or L-chiro-inositol. Lithium chloride, 3 meq/kg was administered intraperitoneally 20-24 h prior to the subcutaneous injection of pilocarpine, 20 or 30 mg/kg. In both experiments, myo-inositol significantly prolonged the latency to the appearance of clonic seizures and lowered the pilocarpine seizure score. myo-Inositol prevented the development of clonic seizures in 50% of the rats receiving pilocarpine, 20 mg/kg. The levels of cortical myo-inositol in rats injected with myo-inositol were approximately double those of the CSF and L-chiro-inositol groups.

Animals↗
PubMed1992

Reevaluation of dioxin bioconcentration and bioaccumulation factors for regulatory purposes.

Bioconcentration factors (BCF) or bioaccumulation factors (BAF) reported for 2,3,7,8-tetrachlorodibenzo-p-dioxin (TCDD or dioxin) in aquatic environments encompass a wide range of values, from less than 1000 to 189,000 l/kg. These values are based on concentrations of TCDD in various environmental media including water, sediment, or food. Under the Federal Water Pollution Control Act and its enabling regulations (40 CFR 100-140, 400-470), point source discharge limits are established so that the nominal receiving water concentration will not exceed the water quality criterion. To be consistent with this regulatory process, the water quality criterion should also be calculated using an accumulation factor that is based on a nominal water concentration. The regulatory process for developing a water quality criterion for TCDD requires the selection of a BAF that describes the relationship between the source to be regulated and the fish tissue concentration.

Animals↗
PubMed1991

Readily synthesized calibration compounds for quadrupole and magnetic instruments for use over the mass range to 2000 daltons.

Volatile mass calibration standards have been prepared by esterifying beta-cellobiose (4-beta-D-glucopyranosyl-D-glucose) with a mixture of heptafluorobutyric (HFB) anhydride and pentafluoropropionic (PFP) anhydride. The mixed esters produce spectra that are useful for mass spectrometer calibration with positive or negative ion methane chemical ionization and electron impact over the mass range 300-2000. The spectra contain prominent ions spaced at m/z 20 and m/z 50 intervals. Using the mixed ester with direct insertion probe introduction gives intense spectra that persist for tens of minutes. All signals above m/z 194 derived from these substances disappear rapidly upon withdrawal of the probe. The composition and exact masses are given for the positive and negative ion spectra of a mixed HFB/PFP ester of beta-cellobiose. Two other calibrants are described: one made from beta-cellobiose using a mixture of HFB, PFP and trifluoroacetic anhydrides, and another the HFB/PFP mixed ester of perseitol. These are examples of the flexibility of this approach with respect to mass range and ion composition.

Calibration↗
PubMed1991

Diacylglycerol accumulation and microvascular abnormalities induced by elevated glucose levels.

The present experiments were undertaken to examine the hypothesis that glucose-induced increased de novo synthesis of 1,2-diacyl-sn-glycerol (which has been observed in a number of different tissues, including retinal capillary endothelial cells exposed to elevated glucose levels in vitro) and associated activation of protein kinase C may play a role in mediating glucose-induced vascular functional changes. We report here that twice daily instillation of 30 mM glucose over 10 d in a rat skin chamber granulation tissue model induces approximately a 2.7-fold increase in diacylglycerol (DAG) levels (versus tissues exposed to 5 mM glucose) in association with marked increases in vascular clearance of albumin and blood flow. The glucose-induced increase in DAG levels as well as the vascular functional changes are prevented by addition of 3 mM pyruvate. Pharmacological activation of protein kinase C with the phorbol ester TPA in the presence of 5 mM glucose increases microvascular albumin clearance and blood flow, and similar effects are observed with 1-monoolein (MOG), a pharmacological inhibitor of the catabolism of endogenous DAG. A pharmacological inhibitor of protein kinase C (staurosporine) greatly attenuates the rise in microvascular albumin clearance (but not the rise in blood flow) induced by glucose or by MOG. These findings are compatible with the hypothesis that elevated concentrations of glucose increase tissue DAG content via de novo synthesis, resulting in protein kinase C activation, and that these biochemical events are among the factors that generate the increased microvascular albumin clearance.

Alkaloids↗
PubMed1990

Studies on the permethylation/dephosphorylation of inositol polyphosphates: an approach to a more sensitive assay.

Methods for the permethylation of inositol phosphates (i.e. the formation of the completely substituted C-O-methyl/P-O-methyl derivatives) have been studied as a precursor to preparing C-O-methyl inositols where the remaining inositol hydroxyl groups are at the positions originally occupied by the phosphomonoesters. Classical sodium-driven methylations, diazomethane methylations and methylation with methyl trifluoromethanesulfonate were studied and only the latter was found to produce completely alkylated inositol phosphates. Treatment of the permethylated substrates with methanolic HCl removed the dimethylphosphate groups to produce C-O-methyl inositols which are candidates for negative ion chemical ionization gas chromatographic/mass spectrometric analysis as heptafluorobutyryl C-O-methyl inositols. As an example, gas chromatographic/mass spectrometric analysis of myo-inositol 1,2,6-trisphosphate was carried out by methylation, dephosphorylation and conversion to the tris(heptafluorobutyryl) derivative. Detection at the low-femtomole level was achieved by this means. A limitation of the method may be that the methylation procedure appears to produce a variable degree of phosphate positional isomerization, with resulting loss of specificity. If stable isotope internal standards were available for the inositol polyphosphates of interest, this limitation could be compensated for.

Gas Chromatography-Mass Spectrometry↗
PubMed1990

Characterization of soluble vs membrane-bound human placental 5'-nucleotidase.

Three forms of 5'-nucleotidase purified from human placenta (two membrane-bound forms, one sensitive and one resistant to cleavage by phosphatidylinositol-specific phospholipase C, as well as a soluble form) had the same molecular weight before (73,000 Da) and after (56,000 Da) digestion with N-glycosidase F and showed similar amino acid compositions, N-terminal amino acid sequences, and KMs for IMP (9.6 to 11.9 microM). Thus, these three forms of 5'-nucleotidase appear to have very similar structures. The form sensitive to phosphatidylinositol-specific phospholipase C contained nearly 1 mol myo-inositol/mol of protein as determined by mass spectrometry, indicating a glycosyl phosphatidylinositol membrane anchor. Soluble 5'-nucleotidase contained a similar quantity of myo-inositol, suggesting that it was previously membrane-anchored via glycosyl phosphatidylinositol. The form resistant to phosphatidylinositol-specific phospholipase C contained less myo-inositol, leaving open the possibility of a third form of 5'-nucleotidase with a conventional transmembrane anchor.

5'-Nucleotidase↗
PubMed1990

Thermospray liquid chromatographic/mass spectrometric studies with inositol phosphates.

Thermospray mass spectrometry of inositol mono- and polyphosphates, separated by ion-exchange chromatography, was evaluated for its potential as a general method for quantitative analysis of these substances. The only ions of significant abundance that are produced by the thermospray ionization process result from the total loss of phosphate from inositol. Thus inositol mono-, tris- and hexakisphosphate each gave mass spectra consisting solely of [MH]+ and [MNH4]+ of inositol. When the chromatographic eluates are passed through a heated reactor prior to the thermospray source maximal yields of these ions are obtained. The sensitivity of the technique falls short of that needed for a general method for biological applications, because the lower limit of detection is about 100 pmol microliter-1. Inositol phosphates peracetylated on C-hydroxyls were also studied, with separation by ion-exchange chromatography. Again, thermospray ionization produces totally dephosphorylated species, with the highest-mass ions retaining all of the acetyl groups, even when using the thermal reactor. Losses of acetate were also observed. Sensitivity with the acetyl derivative was comparable to that with the underivatized inositol phosphates.

Gas Chromatography-Mass Spectrometry↗
PubMed1990

Evidence that phosphoinositide metabolism in rat cerebral cortex stimulated by pilocarpine, physostigmine, and pargyline in vivo is not changed by chronic lithium treatment.

The effect of chronic versus acute administration of lithium on receptor-linked phosphoinositide metabolism was assessed by comparing the change in the cerebral cortex levels of myo-inositol 1-phosphate in response to pilocarpine, physostigmine, or pargyline in rats. Rats were exposed to either 29 consecutive days of LiCl injections or 27 and 39 days of dietary Li2CO3, followed by injected LiCl at the end of the diet to insure a constant level of exposure to the drug. In each experiment, an acute group received a single injection of LiCl 20-24 h before they were killed. One hour before being killed, some of the animals acutely exposed to lithium and some of the animals chronically exposed to lithium each received pilocarpine, physostigmine, or pargyline. At the conclusion of the experiment, the rats were killed and brain levels of myo-inositol 1-phosphate and lithium were determined. A differential production of myo-inositol 1-phosphate in groups receiving acute versus chronic lithium would provide evidence of a change in receptor-linked phosphoinositide metabolism due to the chronic administration of lithium. Brain levels of myo-inositol 1-phosphate are dependent on tissue lithium concentrations; consequently, significant differences observed in brain lithium levels between the groups receiving acute versus chronic lithium prevented a meaningful assessment of the effect of the mode of lithium administration on the production of myo-inositol 1-phosphate in those groups. Stepwise multiple regression analysis and the measured brain lithium levels were used to assess the response of myo-inositol 1-phosphate levels to stimulation in animals receiving acute or chronic lithium treatment.(ABSTRACT TRUNCATED AT 250 WORDS)

Animals↗
PubMed1990

Glucose-induced microvascular functional changes in nondiabetic rats are stereospecific and are prevented by an aldose reductase inhibitor.

Exposure of skin chamber granulation tissue vessels in nondiabetic rats to 11 or 15 mM D-glucose (but not L-glucose or 3-O-methylglucose) twice daily for 10 d induces vascular functional changes (increased albumin permeation and blood flow) identical to those in animals with mild or severe streptozotocin diabetes, respectively. These vascular changes are strongly linked to increased metabolism of glucose via the sorbitol pathway and are independent of nonenzymatic glycosylation as well as systemic metabolic and hormonal imbalances associated with the diabetic milieu. (J. Clin. Invest. 1990. 85:1167-1172.)

Aldehyde Reductase↗
PubMed1990

Modulation of hemodynamic and vascular filtration changes in diabetic rats by dietary myo-inositol.

To assess the potential of myo-inositol-supplemented diets to prevent diabetes-induced vascular functional changes, we examined the effects of diets supplemented with 0.5, 1, or 2% myo-inositol on blood flow and vascular filtration function in nondiabetic control rats and rats with streptozocin-induced diabetes (STZ-D). After 1 mo of diabetes and dietary myo-inositol supplementation, 1) 131I-labeled bovine serum albumin (BSA) permeation of vessels was assessed in multiple tissues, 2) glomerular filtration rate (GFR) was estimated as renal plasma clearance of 57Co-labeled EDTA, 3) regional blood flows were measured with 15-microns 85Sr-labeled microspheres, and 4) endogenous albumin and IgG urinary excretion rates were quantified by radial immunodiffusion assay. In STZ-D rats, 131I-BSA tissue clearance increased significantly (2- to 4-fold) in the anterior uvea, choroid-sclera, retina, sciatic nerve, aorta, new granulation tissue, diaphragm, and kidney but was unchanged in skin, forelimb muscle, and heart. myo-Inositol-supplemented diets reduced diabetes-induced increases in 131I-BSA clearance (in a dose-dependent manner) in all tissues; however, only in new granulation tissue and diaphragm did the 2% myo-inositol diet completely normalize vascular albumin permeation. Diabetes-induced increases in GFR and in urinary albumin and IgG excretion were also substantially reduced or normalized by dietary myo-inositol supplements. Increased blood flow in anterior uvea, choroid-sclera, kidney, new granulation tissue, and skeletal muscle in STZ-D rats also was substantially reduced or normalized by the 2% myo-inositol diet. myo-Inositol had minimal if any effects on the above parameters in control rats. These observations indicate that diabetes-induced increases in regional blood flow, 131I-BSA permeation, GFR, and urinary protein excretion can be markedly reduced or normalized by consumption of myo-inositol-supplemented diets that raise plasma myo-inositol levels approximately fivefold. The failure of the 2% myo-inositol diet to normalize GFR and blood flow and albumin permeation in several tissues despite markedly elevated plasma myo-inositol levels and normal or elevated tissue myo-inositol levels indicates that if vascular functional changes in these tissues are linked to altered myo-inositol levels, they are resistant to normalization by elevation of plasma myo-inositol levels. These results suggest that other factors independent of changes in relative or absolute tissue myo-inositol levels may play an important role in the pathogenesis of diabetes-induced vascular functional changes in these tissues.(ABSTRACT TRUNCATED AT 400 WORDS)

Animals↗
PubMed1989

Rapid analysis of sorbitol, galactitol, mannitol and myoinositol mixtures from biological sources.

The three commonly found hexitols mannitol, sorbitol and galactitol are well separated from each other and from myoinositol by gas chromatography as their butylboronate derivative on Dexsil-400, on a 1:1 mixture of OV-1 and OV-17, or on a DB-17 fused-silica capillary column. The method allows all four substances to be measured by autosampling electron ionization gas chromatography-mass spectrometry (GC-MS) in small tissue samples at organ concentrations as small as 5 mumol/kg wet mass in less than 4 min. Comparisons were made to determine the relative sensitivity of GC-MS and other detection methods. The order of sensitivity was electron ionization GC-MS greater than chemical ionization GC-MS greater than flame photometric detection using a boron-selective filter greater than hydrogen flame ionization detection.

Animals↗