Chromatographic analysis of phospholipase reaction products.
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Chromatography, Gas↗
Biomedical subjects
F Snyder
Publications and source records attributed to F Snyder.
Metabolism of platelet activating factor in lung.
PAF is known to be produced by two independent enzymatic pathways. The remodeling route involves structural modification of a membrane phospholipid (1-alkyl-2-acyl-sn-glycero-3-phosphocholine) by substitution of an acetate for the acyl group at the sn-2 position. In contrast, the de novo pathway includes a sequence of acetylation, dephosphorylation, and phosphocholine addition, starting with the alkyl analog of lyso-phosphatidic acid. Hypersensitivity reactions with PAF as the autacoid are triggered by activation of the remodeling enzymes to produce excessive amounts of PAF. Inactivation of PAF occurs primarily by hydrolysis of the acetate group in a reaction catalyzed by acetylhydrolase. Results of our studies indicate that biosynthesis and catabolism of PAF by membrane preparations from both lung tissue and alveolar macrophages are qualitatively similar to that found in other cells. All of the enzymatic activities for both the remodeling and de novo pathways of PAF biosynthesis occur in the lung. Recent experiments indicate the initial reaction that produces lyso-PAF in the remodeling pathway of PAF biosynthesis is under the control of a CoA-independent transacylase that is capable of catalyzing both the hydrolysis of the acyl moiety of the alkylacylglycerophosphocholine precursor and its transfer to another lyso-phospholipid. The substrate specificity for the phospholipase A2 component of this reaction is for alkylacylglycerophosphocholines possessing arachidonate at the sn-2 position. Other polyunsaturated alkylacylglycerophosphocholines appear to be utilized as PAF precursors too, albeit to a lesser extent than the 20:4 species. The CoA-independent transacylase and its high affinity for the transfer of arachidonate to lyso-PAF appears to be a very prominent enzyme activity in rat lung membranes.
Animals↗
High affinity of ether-linked lipids for omega 3 fatty acids.
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Animals↗
An arachidonoyl (polyenoic)-specific phospholipase A2 activity regulates the synthesis of platelet-activating factor in granulocytic HL-60 cells.
Human promyelocytic leukemia cells (HL-60) were used as a cell model to determine how arachidonic acid stimulates the synthesis of platelet-activating factor (PAF) synthesized via the remodeling pathway. In these studies HL-60 cells were cultured over 30 passages in fatty acid-free medium to deplete them of arachidonic acid. Even though the phospholipid classes from these cells contained no arachidonate, they could still be differentiated into granulocytes by dimethyl sulfoxide (1.25%). When the differentiated HL-60 cells, depleted of arachidonic acid, were stimulated with calcium ionophore A23187 in the presence of Ca2+ and [3H]acetate, only minimal amounts of [3H]PAF were produced. In contrast, if the differentiated HL-60 cells were supplemented with 10 microM arachidonic acid for 24 h and then stimulated with the ionophore, there was a large amount of [3H]PAF formed. The increase in PAF synthesis depended on the length of time the cells were supplemented with arachidonic acid; only a small increase in PAF synthesis occurred during the early hours of supplementation whereas stimulation of PAF synthesis was maximal (3-5-fold) after a 24-h period of the 20:4 supplementation. Other polyenoic fatty acid supplements (20:5, 22:4, and 22:6 for 24 h) also stimulated PAF production in the ionophore-treated HL-60 cells depleted of 20:4, but the amount of PAF was significantly less than found for the supplements of 20:4 under identical experimental conditions. Also noteworthy is that undifferentiated cells supplemented with 20:4 or their unsupplemented controls could not be stimulated by the calcium ionophore to produce PAF. Addition of indomethacin (cyclooxygenase inhibitor), A63162 (5'-lipoxygenase inhibitor), or eicosatetraynoic acid (cyclooxygenase/lipoxygenase inhibitor) to the incubations caused little change in the production of [3H]PAF in the differentiated cells supplemented with 20:4 for 24 h. On the other hand, the addition of mepacrine, bromophenacyl bromide, or U26384 (phospholipase A2 inhibitors) resulted in very large decreases (80-90% lower than controls) in the amount of [3H]PAF produced under the same conditions. Analysis of the molecular species of [3H]alkylacyl-GroPCho (1-alkyl-2-acetyl-sn-glycero-3-phosphocholine, the precursor of PAF in the remodeling pathway) in 20:4-supplemented cells prelabeled with [3H]alkyl-lyso-GroPCho revealed that only the alkylarachidonoyl-GroPCho species were preferentially decreased after stimulation with the A23187 ionophore. These results demonstrate that arachidonate must be at the sn-2 position of alkylacyl-GroPCho in order for it to serve as a precursor of PAF.(ABSTRACT TRUNCATED AT 400 WORDS)
Arachidonic Acid↗
Regulation of the synthesis of platelet-activating factor and its inactive storage precursor (1-alkyl-2-acyl-sn-glycero-3-phosphocholine) from 1-alkyl-2-acetyl-sn-glycerol by rabbit platelets.
We have established previously that 1-alkyl-2-acetyl-sn-glycerol (alkylacetyl-G) can be converted into at least six metabolites by rabbit platelets, including alkylacetyl-sn-(glycero-3-phosphocholine) (-GPC), i.e. platelet-activating factor (PAF) and 1-alkyl-2-acyl-sn- (alkylacyl)-GPC. Since part of the biological functions of alkylacetyl-G can be explained by its metabolic conversion to PAF and also to alkylacyl-GPC as an inactive storage precursor of PAF, the present study focused on the regulation of the synthesis of PAF and alkylacyl-GPC from alkylacetyl-G. Our results document the presence of a specific dithiothreitol (DTT)-insensitive cholinephosphotransferase in saponin-permeabilized rabbit platelets and show that DTT potentiates the production of PAF from alkylacetyl-G but inhibits the formation of phosphatidylcholine from diolein. We also demonstrated that the availability of CDP-choline controls the generation of PAF from alkylacetyl-G. Furthermore, when CTP: phosphocholine cytidylyltransferase is activated to produce more CDP-choline through the translocation of this enzyme from the cytosol to membranes by incubating the rabbit platelets with 0.2 mM sodium oleate, the production of PAF from alkylacetyl-G is increased 5-fold. More importantly, our experiments reveal the presence of two metabolic pathways that are responsible for the synthesis of alkylacyl-GPC from alkylacetyl-G, with each producing a unique molecular species composition of the stored PAF precursor, alkylacyl-GPC. The latter is enriched in polyunsaturates (70.7-78.5% 20:4) when formed through the remodeling pathway of PAF cycle via alkylacetyl-G (DTT-insensitive cholinephosphotransferase)----alkylacetyl-GPC----alkyllyso-GPC---- alkylacyl-GPC . Alkylacyl-GPC containing saturated species (71.8% 16:0) is generated by the retroconversion/de novo pathway according to the reaction scheme of alkylacetyl-G----alkyl-G----alkyllyso-glycero-3-phosphate (-GP)----alkylacyl-GP----alkylacyl-G (DTT-sensitive cholinephosphotransferase)----alkylacyl-GPC. Inactivation of PAF through the remodeling/PAF cycle can generate alkylacyl-GPC at both low (1.75 x 10(-7) M) and high (10(-6) M) concentrations of PAF whereas the conversion of alkylacetyl-G to alkylacyl-GPC via PAF through the remodeling pathway only occurs at a low concentration (1.75 x 10(-7) M). At a high concentration (10(-6) M), alkylacetyl-G is converted to alkylacyl-GPC via the retroconversion/de novo route. These data suggest that the formation of PAF by the DTT-insensitive cholinephosphotransferase activity limits the amounts of alkylacyl-GPC produced from alkylacetyl-G through this remodeling pathway (PAF cycle).(ABSTRACT TRUNCATED AT 400 WORDS)
Animals↗
Thin-layer and high-performance liquid chromatographic separation of glycerolipid subclasses as benzoates. Derivatives of ether and ester analogues of phosphatidylcholine, phosphatidylethanolamine and platelet activating factor.
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Benzoates↗
Development of specific functionally active receptors for platelet-activating factor in HL-60 cells following granulocytic differentiation.
A human promyelocytic leukemia cell line (undifferentiated HL-60 cells) as well as a granulocyte form of HL-60 cells induced in vitro by exposure to dimethyl sulfoxide were examined for binding, metabolism, and biological responses to platelet-activating factor (PAF). Undifferentiated and differentiated HL-60 cells each exhibit a high capacity to incorporate and metabolize [3H]PAF at 37 degrees C; however, the amount of [3H]PAF that is assimilated by both cell populations is greatly reduced and its metabolism abolished at less than or equal to 4 degrees C. At 0 degrees C HL-60 granulocytes bind more [3H]PAF than their undifferentiated counterparts. Binding to differentiated cells reaches equilibrium within 80 min and is saturable, reversible and specific; PAF receptor antagonists WEB 2086, L-659,989, BN 52021, and kadsurenone abolish this specific [3H]PAF binding. In contrast, [3H]PAF uptake by undifferentiated HL-60 cells is neither saturable nor sensitive to specific receptor antagonists. Scatchard analyses reveal 5850 +/- 850 binding sites per differentiated HL-60 cell with a dissociation constant of 0.66 +/- 0.15 nM. In the presence of cytochalasin B, PAF (200 nM) induces degranulation only in differentiated cells and this response also is blocked by PAF receptor antagonists. Our results demonstrate that HL-60 cells develop specific and functionally active PAF receptors only after chemically induced differentiation into granulocytes.
Acetylglucosaminidase↗
Characterization of the enzymatic hydrolysis of acetate from alkylacetylglycerols in the de novo pathway of PAF biosynthesis.
This report describes the partial characterization of the enzymatic activity responsible for the hydrolysis of acetate from 1-alkyl-2-acetyl-sn-glycerol, the immediate precursor in the de novo synthesis of PAF (platelet-activating factor or 1-alkyl-2-acetyl-sn-glycero-3-phosphocholine) by Ehrlich ascites cells. The highest acetylhydrolase activity for this neutral lipid was associated with the membrane fractions from Ehrlich ascites cells (greater than 90% of total activity); only a minimal level of activity (less than 10%) was observed in the cytosol which contrasts with the cytosolic site of PAF acetylhydrolase in normal cells. Hydrolysis of 1-[3H]hexadecyl-2-acetyl-sn-glycerol by the membrane fraction at pH 7.5 and 37 degrees C gave apparent values for Km and Vmax of 45 microM and 179 nmol/min per mg protein, respectively. Hydrolysis of acetate from 1-[3H]hexadecyl-2-acetyl-sn-glycerol by the membrane fraction was not affected by 5 mM concentrations of Ca+2, Mg+2 or EDTA, but was significantly inhibited (80% reduction) by 10 mM NaF. Based on differences in both the subcellular distribution and response to inhibition by NaF, the neutral lipid acetylhydrolase does not appear to be the same enzyme that hydrolyzes acetate from platelet-activating factor. In contrast to inhibition of diacylglycerol lipase by p-chloromercuribenzoate and N-ethylmaleimide, we found no significant inhibition of acetate hydrolysis from 1-[3H]hexadecyl-2-acetyl-sn-glycerol by either of these compounds. Also, p-nitrophenyl acetate (a nonspecific esterase substrate) failed to inhibit acetate hydrolysis of 1-[3H]hexadecyl-2-acetyl-sn-glycerol. Our studies of this enzyme would indicate that it may play an important role in regulating the levels of platelet-activating factor synthesized by the de novo pathway via hydrolysis of the immediate precursor of PAF.
Acetates↗
Conversion of alkylacetylglycerol to platelet-activating factor in HL-60 cells and subcellular localization of the mediator.
A human promyelocytic leukemia (HL-60) cell line was used to investigate the conversion of 1-alkyl-2-acetyl-sn-glycerol (alkylacetyl-G) to platelet-activating factor (PAF; 1-alkyl-2-acetyl-sn-glycero-3-phosphocholine) by intact cells and in subcellular fractions in order to examine the fate of PAF synthesized de novo. Lipid extracts obtained from undifferentiated HL-60 cells incubated with [3H]alkylacetyl-G contained 2-4% of the label as [3H]PAF; several related metabolites were also detected. The yield of [3H]PAF could be dramatically increased by pretreating the cells with either oleic acid, an activator of CTP:phosphocholine cytidylyltransferase, or phenylmethylsulfonyl fluoride, an inhibitor of PAF acetylhydrolase. These results, together with a kinetic study of [3H]alkylacetyl-G metabolism, indicate the sequential participation of a cholinephosphotransferase for the conversion of [3H]-alkylacetyl-G to PAF and acetylhydrolase and transacylase activities in the remodeling pathway that metabolize the newly formed [3H]PAF to 1-[3H]alkyl-2-acyl(long chain)-sn-glycero-3-phosphocholine. The dithiothreitol-insensitive cholinephosphotransferase activity capable of converting alkylacetyl-G to PAF was localized in subcellular fractions that contain CDP-choline:1,2-dioleoyl-sn-glycerol cholinephosphotransferase (dithiothreitol-sensitive), as well as marker enzyme activities for the endoplasmic reticulum and Golgi membranes. Subcellular localization analyses also indicated that the majority of newly formed [3H]PAF and a large portion of its deacetylated metabolite were associated with the plasma membrane-containing fractions, whereas most of the 1-[3H]alkyl-2-acyl(long chain)-sn-glycero-3- phosphocholine was present in the intracellular organelles. Incubations of HL-60 cells with exogenous [3H]PAF produced a similar subcellular distribution of metabolites. Very little (less than 10%) of the [3H]PAF produced from [3H]alkylacetyl-G was released from intact cells under a variety of incubation conditions but 50% of the de novo-derived mediator was recovered in the medium of cells that were permeabilized with saponin. Our results indicate that PAF is rapidly translocated from its intracellular site of enzymatic synthesis to the plasma membrane where it is apparently sequestered in a pool that is not accessible to extracellular acceptors in contact with intact cells.
Cell Line↗
Synthesis and antineoplastic properties of ether-linked thioglycolipids.
Ether-linked glycero-alpha- and beta-D-glucopyranosides and glycero-1-thio-alpha- and beta-D-glucopyranosides have been synthesized by modifications of the Königs-Knorr procedure, and their antitumor activities have been evaluated. The bioactivities of these compounds have been evaluated in five different cell lines (WEHI 3B, C653, X63/OMIL3, R6X-B15, and HL-60) and compared with the activities of 1-O-hexadecyl-2-O-methyl-sn-3-glycerophosphocholine (GPC) and its enantiomer, 3-O-hexadecyl-2-O-methyl-sn-1-GPC. The results indicate that a alpha-D-thioglucopyranoside [1-O-hexadecyl-2-O-methyl-3-S-(alpha-D-1'- thioglucopyranosyl-sn-glycerol)] is selective with respect to its action on target cells, with high activity for killing of WEHI 3B and C653 cells as determined by inhibition of [3H]thymidine incorporation into DNA and HL-60 cell cytotoxicity, but unable to induce aggregation of rabbit platelets at 10(-5) M. The corresponding beta-linked thioglycolipid was ineffective with respect to cytotoxicity against each cell line tested, indicating the importance of configuration at the anomeric position; the beta-thioglycoside was also ineffective with respect to inducing platelet aggregation. 1-O-Hexadecyl-2-O-methyl-sn-3-GPC and 3-O-hexadecyl-2-O-methyl-sn-1-GPC were potent inhibitors of growth of each cell line tested but also caused rabbit platelet aggregation at concentrations greater than or equal to 10(-7) M. Thus, 3-S-(alpha-thioglycopyranosyl)-sn- glycerols bearing a long-chain O-alkyl group at the sn-1 position and a methoxy group at the sn-2 position of glycerol appear to be a promising class of antineoplastic agents with lower risk of inducing thrombosis than the widely studied platelet activating factor analogue, 1-O-octadecyl-2-O-methyl-rac-3-GPC.
Animals↗
Platelet-activating factor and related acetylated lipids as potent biologically active cellular mediators.
Platelet-activating factor (PAF or 1-alkyl-2-acetyl-sn-glycero-3-phosphocholine) is the most potent lipid mediator yet discovered. It is known to stimulate a wide span of biological responses ranging from aggregation and degranulation of platelets and neutrophils to a variety of cellular effects involving the stimulation of chemotaxis; chemokinesis; superoxide formation; protein phosphorylation; activation of protein kinase C, arachidonic acid, and phosphoinositide metabolites; glycogenolysis; and tumor necrosis factor production. Obviously, with such a diversity of biological activities, it is not surprising that PAF has been considered to be a key component in numerous diseases related to hypersensitivity and inflammatory responses. Evidence has also been presented for the role of PAF in physiological processes, particularly those involving reproduction and fetal development. Furthermore, because of its potent hypotensive action, PAF has been implicated as a contributing factor in blood pressure regulation. PAF is produced by two independent enzymatic pathways. The remodeling route involves the structural modification of a membrane lipid (1-alkyl-2-acyl-sn-glycero-3-phosphocholine) by replacement of the acyl moiety with an acetate group. An alternate route is the de novo synthesis of PAF from an O-alkyl analogue of a lysophosphatidic acid that requires a reaction sequence of acetylation, dephosphorylation, and phosphocholine addition steps. Hypersensitivity and other pathophysiological reactions are thought to be caused by activation of the remodeling pathway, whereas the de novo route is believed to be the source of endogenous levels of PAF required for physiological functions. Inactivation of PAF occurs when the acetate group is hydrolyzed by an acetylhydrolase that is present in both extra- and intracellular compartments, although the catalytic activity of the two forms of acetylhydrolase are identical, some of their properties differ. The control of PAF metabolism is very complex, but acetylhydrolase, Ca2+, phosphorylation/dephosphorylation of enzymes, and fatty acids (especially polyunsaturates) appear to be important regulatory factors. Specific PAF receptors have clearly been demonstrated on several different types of cells, and although the mechanism of PAF actions is poorly understood, it appears that the PAF/receptor-induced responses are closely associated with the signal transduction process; both G proteins and adenyl cyclase appear to be involved. Because significant quantities of PAF are often retained within certain cells, the possibility of PAF serving as an intracellular mediator has also been proposed.
Animals↗
O-alkyl-O-methylglycerophosphocholine, an antineoplastic lipid, undergoes spontaneous redistribution between biological membranes prepared from HL-60 cells.
Cytotoxic actions of the unnatural phospholipid 1-O-alkyl-2-O-methyl-sn-glycero-3-phosphocholine (alkylmethyl-GPC) appear to be targeted to the plasma membrane of sensitive cells. We analyzed the distribution of [3H]alkylmethoxy-GPC in subcellular membranes isolated from human promyelocytic leukemia (HL-60) cells. [3H]Alkylmethyl-GPC added to intact cells selectively labels plasma membrane-enriched fractions of the postnuclear supernatant, but the labeling profile is independent of the temperature and duration of the incubation, and concentration of the molecule. Also, an identical distribution pattern is obtained when [3H]alkylmethyl-GPC is directly added to postnuclear supernatants. Moreover, [3H]alkylmethyl-GPC translocates between subcellular membranes in a manner that does not depend on membrane-adsorbed or cytosolic transfer proteins. These results indicate that the subcellular localization studies reported for alkylmethyl-GPC and structurally-related molecules must be interpreted with caution.
Antineoplastic Agents↗
Renal necrosis and the involvement of a single enzyme of the de novo pathway for the biosynthesis of platelet-activating factor in the rat kidney inner medulla.
2-Bromoethylamine hydrobromide (BEA), when administered to rats, induces a highly specific papillary necrosis associated with the inner medulla. PAF levels in the blood were lowered by 50% and of the three enzymes that comprise the de novo route for PAF in the cortex/medulla, only the cholinephosphotransferase activity in the inner medulla microsomes was reduced (33%) by the BEA treatment. Moreover, BEA did not affect phosphatidylcholine synthesis in either the cortex or inner medulla. Our studies indicate that the de novo pathway for PAF synthesis in the renal inner medulla is responsible for the secretion of newly formed PAF into the blood stream and that a single enzyme in the de novo route accounts for the decreased rate of PAF synthesis during the development of renal necrosis.
Animals↗
Identification of 1-alkyl-2-acyl-3-(2',3'-diacylglycerol)glycerols, a new type of lipid class, in harderian gland tumors of mice.
A new class of alkyl glycerolipids, 1-alkyl-2-acyl-3-(2',3'-diacylglycerol)glycerols, was identified in lipid extracts prepared from harderian gland tumors of mice. After saponification, this lipid class yielded 1-alkyl-3-(1'-glycerol)glycerols. Identification was based on mass spectrometry, proton nuclear magnetic resonance spectroscopy, infrared spectroscopy, and chromatography of various derivatives and appropriate standards that were synthesized. The alkyl moieties of this unique lipid class consisted of saturated aliphatic chains with chain lengths of 14 to 20 carbon atoms. The acyl moieties were mostly saturated and monounsaturated aliphatic chains ranging from 14 to 24 carbon atoms. The alkyl and acyl moieties of 1-alkyl-2-acyl-3-(2',3'-diacylglycerol)glycerols were similar to those of alkyldiacylglycerols present in the same tissue, except for the presence of monounsaturated alkyl moieties in the latter. 1-Alkyl-2-acyl-3-(2', 3'-diacylglycerol)glycerols were only found in trace amounts in the normal harderian glands of mice. The total quantity of the alkyl and acyl moieties with a chain length greater than 20 carbon atoms in the alkyldiacylglycerols from tumors were considerably lower than those found in normal harderian glands of mice. This is the first report of the presence of bisglyceryl ether lipids in mammalian tissue; its unique chemical structure is consistent with the type of ether-linked lipid products that could be synthesized in the reaction catalyzed by alkyldihydroxyacetone-P synthase.
Animals↗
Effects of eicosapentaenoic and docosahexaenoic acid supplements on phospholipid composition and plasmalogen biosynthesis in P388D1 cells.
This investigation describes the influence of n-3 fatty acid supplements on the phospholipid composition and the metabolism of plasmalogens in P388D1 cells. The cellular content of phospholipid classes and subclasses was unchanged in P388D1 cells (a macrophage-like cell) grown for 24 h in media supplemented with 10 microM sodium eicosapentaenoate or sodium docosahexaenoate. However, phospholipids from these cells were highly enriched in acyl groups of the corresponding fatty acid supplement, with the largest increases occurring in the ethanolamine plasmalogens (e.g., 46% of the ethanolamine plasmalogens from cells supplemented with docosahexaenoate contained this acyl group at the sn-2 position). Eicosapentaenoate supplements lowered the levels of oleate in phosphatidylinositol/serine, diacyl-sn-glycero-3-phosphoethanolamine (GroPEtn), and alk-1-enylacyl-GroPEtn in the P388D1 cells but had little or no effect on the amounts of arachidonate in the cellular phospholipids. In contrast, supplementation of the cells with docosahexaenoic acid not only reduced the level of oleate but also decreased the amount of arachidonate by one-third in the alk-1-enylacyl-GroPEtn. When P388D1 cells were incubated for 1 h with [3H]alkyllyso-GroPEtn both [3H]alkylacyl-GroPEtn and [3H]alk-1-enylacyl-GroPEtn were formed. The sn-2 acyl composition of these two ether-containing GroPEtn lipids reflected the fatty acid supplement that the cells had received (e.g., 68% of the [3H]alk-1-enylacyl-GroPEtn from cells supplemented with docosahexaenoate contained this acyl group at the sn-2 position). Cells from both the controls and supplemented groups contained greater amounts of docosahexaenoate in the [3H]alk-1-enylacyl-GroPEtn (plasmalogen) than in the [3H]alkylacyl-GroPEtn subclass. Analysis of molecular species from pulse-chase experiments with intact cells and examination of the molecular species of [3H]alk-1-enylacyl-GroPEtn produced by the delta 1-desaturase system in cell-free membrane fractions suggest that the docosahexaenoate-containing species of [3H]alk-1-enylacyl-GroPEtn have a higher turnover rate than other molecular species. Possible biological implications of our findings are also discussed.
Animals↗
Platelet-activating factor and related ether lipid mediators. Biological activities, metabolism, and regulation.
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Humans↗
Biochemistry of platelet-activating factor: a unique class of biologically active phospholipids.
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Animals↗
HL-60 cells become resistant towards antitumor ether-linked phospholipids following differentiation into a granulocytic form.
1-0-Alkyl-2-0-methyl-sn-glycero-3-phosphocholine (alkylmethoxy-GPC) exerts a highly selective cytotoxic activity towards a variety of tumor cells that is not seen in normal cells. Human promyelocytic leukemia (HL-60) cells are particularly sensitive to this cytotoxic action. In this report we show that when HL-60 cells are differentiated into a granulocytic form by dimethylsulfoxide (Me2SO)they become resistant toward the cytotoxic effects of alkylmethoxy-GPC. Also, after short-term exposures of the HL-60 cells to alkylmethoxy-GPC, the uptake of [methyl-3H]choline is inhibited in the undifferentiated cells, but not in those differentiated with Me2SO. Thus, cellular choline uptake appears to be a useful index for assessing the susceptibility of cells to the cytotoxic effects of antitumor phospholipids. [3H]Alkylmethoxy-GPC is poorly metabolized by both cell populations as is evident by the trace quantities of labeled metabolites formed; also, alkylmethoxyglycerols do not exert any cytotoxic activity toward undifferentiated cells. These results demonstrate that differences in the cytotoxic response of sensitive (undifferentiated) and resistant (differentiated) cells to alkylmethoxy-GPC are not due to differences in their ability to metabolize alkylmethoxy-GPC or to a phospholipase C-generated toxic metabolite. Instead the data support our earlier hypothesis that the antitumor action of alkylmethoxy-GPC is, at least in part, caused by an impaired transport of small molecules across the membrane of sensitive cells.
Antineoplastic Agents↗