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R Bittman

Publications and source records attributed to R Bittman.

135 records · Page 8Linked to original sources
PubMed1972

Fluorescence studies of the binding of the polyene antibiotics filipin 3, amphotericin B, nystatin, and lagosin to cholesterol.

The interactions of filipin III, amphotericin B, nystatin, and lagosin with sterols in aqueous suspension and in vesicles were followed by fluorescence excitation spectra and by measurement of polarized fluorescence intensities. The equilibrium constants for association of the polyene antibiotics with aqueous suspensions of cholesterol follow the order filipin III > amphotericin B > nystatin > lagosin, in agreement with the order reported for the extent of damage these antibiotics cause in natural and model membranes. Fluorescence polarization measurements show that hydrophobic forces are primarily responsible for the formation of the complexes. Filipin III undergoes a large enhancement in fluorescence polarization on binding to aqueous suspensions of cholesterol and epi-cholesterol, and to vesicles of lecithin-cholesterol, lecithin-beta-cholestanol, and lecithinergosterol. Small increases in polarization occur on interaction of filipin III with vesicles derived from lecithin and epi-cholesterol, thiocholesterol, and androstan-3beta-ol. Amphotericin B undergoes a relatively constant enhancement in fluorescence polarization on interaction with the various lecithin-sterol vesicles used and does not display the selectivity exhibited by filipin III. It is suggested that filipin III serves as a probe of lecithin-sterol interaction.

Amphotericin B↗
PubMedDate not supplied

1-O-hexadecyl-2-O-methyl-sn-glycero-3-phosphocholine inhibits diacylglycerol kinase in WEHI-3B cells.

The effects of 1-O-hexadecyl-2-O-methyl-sn-glycero-3-phosphocholine (ET-16-OCH3-GPC) and its metabolite 1-O-hexadecyl-2-O-methyl-sn-glycerol (AMG) on the activity of diacylglycerol kinase (DGK) in WEHI-3B cells were investigated. Treatment of WEHI-3B cells with 200 nM 12-O-tetradecanoylphorbol-13-acetate (TPA) for 5 min leads to the activation of cytosolic DGK without significant effect on microsomal DGK. When these cells were first exposed to 50 microM ET-16-OCH3-GPC for 30 min prior to activation with TPA, the activity of DGK was inhibited by about 70%, as measured by the ability of enzyme to form [32P]phosphatidic acid ([32P]PA). Addition of either ET-16-OCH3-GPC or AMG to the preparation of enzyme in vitro also inhibited 1,2-dioleoyl-sn-glycerol (DG) phosphorylation in the presence of [gamma-32P]ATP. The IC50 value for inhibition of cytosolic DGK by ET-16-OCH3-GPC and AMG were about 8.5 and 15 microM, respectively. ET-16-OCH3-GPC also inhibited the ability of guanosine 5'-O-(3-thiophosphate) (GTP-gamma S) to activate DGK in vitro. The potency of ET-16-OCH3-GPC at 10 microM in inhibiting DGK was greater than that of sphingosine at 50 microM, but less than that of R59022 (a specific DGK inhibitor) at 10 microM.(ABSTRACT TRUNCATED AT 250 WORDS)

Animals↗
PubMedDate not supplied

A comparison of the lytic properties of two ether-linked lipids, one with and one without antineoplastic activity.

We have synthesized two ether lipids: 2'-(trimethylammonio)ethyl 4-(hexadecyloxy)-3(S)-methoxybutanephosphonate (compound 1) with antineoplastic activity and a maltosyl derivative (compound 2) without antineoplastic activity. We have compared the antineoplastic activity of these two compounds against WEHI-3B cells with their ability to disrupt the membranes of erythrocytes or neutrophils. Since ether lipids are highly hydrophobic molecules, it is possible that they may exert their cytotoxic action by inducing the nonspecific perturbation of cellular membranes, causing lysis and cell death. Membrane disruption was monitored by the lysis of cells or the change in erythrocyte membrane microviscocity and compared with the effect of detergents (known nonspecific lytic agents). Both compounds 1 and 2 caused the lysis of erythrocytes and neutrophils. The rate of lysis of erythrocytes was comparable to the rate of change of erythrocyte membrane microviscosity caused by both compounds 1 and 2. Both compounds caused the lysis of erythrocytes via a noncolloid osmotic mechanism that displayed features of the lysis caused by detergents at high concentrations.

Antineoplastic Agents↗
PubMedDate not supplied

Fusion of Semliki Forest virus with cholesterol-containing liposomes at low pH: a specific requirement for sphingolipids.

Semliki Forest virus (SFV) utilizes a membrane fusion strategy to introduce its genome into the host cell. After binding to cell-surface receptors, virus particles are internalized through receptor-mediated endocytosis and directed to the endosomal cell compartment. Subsequently, triggered by the acid pH in the lumen of the endosomes, the viral envelope fuses with the endosomal membrane. As a result of this fusion reaction the viral RNA gains access to the cell cytosol. Low-pH-induced fusion of SFV, in model systems as well as in cells, has been demonstrated previously to be strictly dependent on the presence of cholesterol in the target membrane. In this paper, we show that fusion of SFV with cholesterol-containing liposomes depends on sphingomyelin (SM) or other sphingolipids in the target membrane, ceramide representing the sphingolipid minimally required for mediating the process. The action of the sphingolipid is confined to the actual fusion event, cholesterol being necessary and sufficient for low-pH-dependent binding of the virus to target membranes. The 3-hydroxyl group on the sphingosine backbone plays a key role in the SFV fusion reaction, since 3-deoxy-sphingomyelin does not support the process. This, and the remarkably low levels of sphingolipid required for half-maximal fusion (1-2 mol%), suggest that the sphingolipid does not play a structural role in SFV fusion, but rather acts as a cofactor, possibly through activation of the viral fusion protein. Domain formation between cholesterol and sphingolipid, although it may facilitate SFV fusion, is unlikely to play a crucial role in the process.

Animals↗
PubMedDate not supplied

Transbilayer distribution of sterols in mycoplasma membranes: a review.

The polyene antibiotic, filipin, binds to 3 beta-hydroxysterols. The initial rate of filipin-sterol association, monitored in a stopped-flow spectrophotometer, was first order in each reacting partner. The ratio of rate constants in intact mycoplasma cells relative to isolated, unsealed membranes provides an estimate of sterol distribution in the membrane bilayer. Cholesterol is distributed symmetrically in the bilayer of M. gallisepticum cells from the early exponential phase. However, in the M. capricolum membrane two-thirds of the unesterified cholesterol is localized in the outer leaflet; alkyl-sterols are distributed predominantly in the external monolayer. Cholesterol is translocated rapidly in the bilayer of M. capricolum cells. Exogenous phospholipids incorporated into the membrane had no effect on the cholesterol distribution in M. capricolum.

Cell Membrane↗
PubMedDate not supplied

Synthesis of ether-linked analogues of lysophosphatidate and their effect on the proliferation of human epithelial cancer cells in vitro.

To investigate whether lysophosphatidate analogues of alkyllysophospholipids were antiproliferative we synthesized three new ether-linked analogues of lysophosphatidic acid and investigated their antiproliferative activity on epithelial cancer cell lines derived from different tissues. The antiproliferative effects of the compounds on MCF-7 and T47D (breast), A549 and A427 (lung), A498 (kidney), SK-N-SH and SK-N-MC (neuroblastoma), and DU145 (prostate) cells were compared with the ability of 1-O-octadecyl-2-O-methyl-glycero-3-phosphocholine, the archetypic alkyllysophospholipid, to inhibit the proliferation of all the cell lines. 1-O-Hexadecyl-2-O-methyl-sn-glycero-3-phosphate and 4-thiohexadecyl-3(S)-O-methoxybutane-4-phosphate were unable to inhibit the proliferation of any of the cells to any degree, while slightly enhancing the proliferation of DU145 cells. In contrast 4-O-hexadecyl-3(S)-O-methoxybutanephosphonate was a potent antiproliferative agent that was on the whole more active than 1-O-octadecyl-2-O-methyl-glycero-3-phosphocholine. Since 1-Oleoyl-2-lyso-phosphatidate (LPA) was non-mitogenic in all the cell lines except the neuroblastoma line SK-N-SH, it is unlikely that the inhibition of cell proliferation by 4-O-hexadecyl-3(S)-O-methoxybutanephosphonate was a consequence of perturbation of cellular response to the mitogenic effects of LPA.

Antineoplastic Agents↗
PubMedDate not supplied

Glycosylated antitumor ether lipids are more effective against oncogene-transformed fibroblasts than alkyllysophospholipids.

We have investigated the antiproliferative effects of different types of antitumor ether lipids (AELs) against non-transformed and transformed fibroblasts. The compounds examined were choline phosphate-containing alkyllysophospholipids (1-O-octadecyl-2-O-methyl glycerophosphocholine (ET18-OCH3), 2'-(trimethylammonio)ethyl 3-(hexadecyloxy)-2-(methoxymethyl)propylphosphate (oxo-BM 41.440), 2'-(triethylammonio)ethyl 4-(hexadecyloxy)-3-methoxybutane phosphonate (ET16-OCH3-phosphonocholine)), and glycosylated ether-linked diglycerides (1-O-hexadecyl-2-O-methyl-3-S-(beta-D-1'-thioglucopyranosyl-sn-gly cerol) [ET16-OCH3-beta-thio-Glc] and 1-O-hexadecyl-2-O-methyl-3-O-(2'amino-2'-deoxy-beta-D-glucopyranosyl)-sn -glycerol (ET16-OCH3-Gln)). The choline phosphate-containing alkyllysophospholipids (ALPs) had little or moderate effect on the proliferation and none on the viability of NIH 3T3 clone 7, and sublines transformed by raf (NIH/9IV #5), fes (Fes 1), src (Src 1) and mos (Mos 1) oncogenes. The glycosylated ether-linked diglycerides were more effective than the choline phosphate-containing ALPs. Of the two ether-linked diglycerides, ET16-OCH3-beta-thio-Glc did not affect the viability of the cells at any of the concentrations examined while ET16-OCH3-Gln was cytotoxic to all the transformed cell lines at concentrations equal to or greater than 9 microM. The IC50 for ET16-OCH3-Gln was 6.4 microM for Mos 1, 6.5 microM for NIH/9IV #5, 7.5 microM for Src 1, 8.2 microM for Fes 1 and 8.4 microM for NIH 3T3 clone 7. These results suggest that the ether-linked diglycerides may be more effective against fibrosarcomas than the cholinephosphate containing ALPs. Also, with the exception of ET16-OCH3-Gln there was no significant difference in the effect of the compounds on the transformed and untransformed cell lines, suggesting that the selectivity displayed by AELs may depend on both the type of compound and transformation in the cell.

3T3 Cells↗