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M L Blank

Publications and source records attributed to M L Blank.

At least 19 recordsLinked to original sources
PubMed1992

Contributing factors in the trafficking of [3H]arachidonate between phospholipids.

Cultured human promyelocytic leukemia cells (HL-60), depleted of arachidonic acid by continued growth in serum-free media, were used as a model system to examine various factors that control the incorporation and distribution of [3H]arachidonic acid into classes and subclasses of cellular lipids. Increasing the culture media concentration of [3H]arachidonic acid from 1 x 10(-8) M to 1 x 10(-5) M caused a greater percentage of the cellular tritium to be distributed into triacylglycerols (from less than 1% at 1 x 10(-8) M to 38% at 1 x 10(-5) M) with a corresponding decrease in cellular [3H]diradylglycerophosphoethanolamine (from 53% at 1 x 10(-8) M to 12% at 1 x 10(-5) M) during 2 h incubations. A greater proportion of the tritium present in diradylglycerophosphoethanolamine and diradylglycerophosphocholine, at the higher media concentration of [3H]arachidonic acid (1 x 10(-5) M), was found in the diacyl subclasses of these two lipids than was observed at the lower concentrations (less than 1 x 10(-6) M) of [3H]arachidonic acid. Significant amounts of diarachidonoyl molecular species were found in the phosphatidylethanolamine (10%) and phosphatidylcholine (15%) of HL-60 cells that were labeled for 2 h with 1 x 10(-5) M [3H]arachidonic acid. This was the only molecular species of phosphatidylcholine to completely disappear when prelabeled cells were placed in arachidonate-free media for 22 h. Prelabeling-chase experiments with 1 x 10(-5) M [3H]arachidonic acid were consistent with movement of [3H]arachidonate from triacylglycerols into diradylglycerophosphatides and from diacylphospholipids into ether-linked phospholipids. Increasing the concentration of HL-60 cells in the incubations influenced the distribution of [3H]arachidonic acid in cellular lipid classes in a manner analogous to decreasing the concentration of [3H]arachidonic acid in the media. Increasing the endogenous level of cellular arachidonate in phospholipid classes with supplements of unlabeled arachidonic acid changed the subsequent lipid class distribution of a low concentration (1 x 10(-8) M) of [3H]arachidonic acid to resemble results obtained with a much higher mass level of [3H]arachidonate in arachidonate depleted cells. HL-60 cells differentiated into granulocytes by treatment with dimethyl sulfoxide incorporated less [3H]arachidonic acid but had a greater proportion associated with alkylacylglycerophosphocholine and alk-1-enylacylglycerophosphoethanolamine than undifferentiated HL-60 cells.

Arachidonic Acid↗
PubMed1992

Meats and fish consumed in the American diet contain substantial amounts of ether-linked phospholipids.

The primary goal of this study was to determine the amounts of ether-containing phospholipids, along with their concentration of certain polyunsaturated acyl groups, from selected, commonly consumed foods of animal origin (salmon, catfish, pork, beef, turkey and chicken). Levels of ether-linked glycerolipids in the samples were of particular interest, because ingestion of ether lipids could contribute to the production of platelet-activating factor (PAF; 1-alkyl-2-acetyl-sn-glycero-3-phosphocholine), one of the most potent biological mediators known. Alkylacyl-sn-glycero-3-phosphocholine was found in all of the meats, with pork loin having the highest levels (0.9 mumol/g tissue) and chicken breasts the lowest (0.1 mumol/g tissue). Although choline plasmalogens were not as evident as the ubiquitous ethanolamine plasmalogens, substantial amounts (1.0 mumol/g tissue) of alk-1-enylacyl-sn-glycero-3-phosphocholine were found in tissues from beef and turkey. Triacylglycerols contained greater proportions of saturated fatty acids than phospholipids, and the ether-linked phospholipids were generally more unsaturated than diacyl species of the same phospholipid. Our data indicate that in addition to the phospholipid fraction of commonly eaten animal tissues supplying substantial amounts of polyunsaturated fatty acids, they are also a rich source of ether-linked lipids. Dietary ether-linked phospholipids could influence the lipid composition of host tissues to the extent that biological responses produced by ether lipid mediators would be affected.

Animals↗
PubMed1991

Acylation of alkyllysophospholipids by Fischer sarcoma microsomes.

Acylation of alkyllysophospholipids in most cells occurs by: (a) CoA-independent transacylation, (b) CoA-dependent transacylation, and (c) acyl-CoA-dependent acylation. Using a recently developed high-performance liquid chromatography method, we have investigated the factors that influence the molecular species composition of the acylated products formed via these pathways with 1-hexadecyl-2-lyso-sn-glycero-3-phosphocholine (alkyllyso-GPC) or 1-hexadecyl-2-lyso-sn-glycero-3-phospho-ethanolamine (alkyllyso-GPE) as substrates for the enzymes in Fischer R-3259 sarcoma microsomes. We found that short incubation times and low substrate concentrations favored the formation of polyunsaturated molecular species, i.e., 16:0-22:6, 16:0-22:5 (n - 3), and 16:0-20:4. Also, in agreement with results from other systems, CoA-independent transacylation produced a high percentage of polyunsaturated molecular species; acyl-CoA-dependent acylations generated the least polyunsaturated molecular species and CoA-dependent transacylation gave intermediate values. Furthermore, no substrate selectivity occurred with respect to alkyl chain lengths of alkyllyso-GPE; similar molecular species composition was obtained with either hexadecyllyso-GPE or octadecyllyso-GPE as substrates. Responses to N-ethylmaleimide inhibition and heat inactivation as well as pH optima suggest the same enzyme catalyzes the CoA-independent transacylation of both alkyllyso-GPC and alkyllyso-GPE.

Acylation↗
PubMed1991

Occurrence of ether-containing inositol phospholipids in bovine erythrocytes.

Several proteins including bovine erythrocyte acetylcholinesterase are anchored in the membrane through glycoinositol phospholipids containing an alkyl linkage at the sn-1 position of the glycerol. However, the existence of 1-alkyl-2-acyl-sn-glycero-3-phosphoinositol (alkylacyl-GPI) in biological systems has not been demonstrated. In this study, we identified the presence of alkylacyl-GPI in bovine erythrocytes by the following criteria: (1) TLC-Rf value, (2) radyllyso-GPI was produced after phospholipase A2 treatment of the diradyl-GPI, and (3) benzoate derivatives of alkylacylglycerols produced by phospholipase C hydrolysis of diradyl-GPI had the same retention time as that of authentic alkylacylglycerobenzoates on normal-phase HPLC. Diradyl-GPI consisted of 5-10% alkylacyl-GPI. Reverse-phase HPLC analysis of alkylacylglycerobenzoates derived from bovine erythrocyte alkylacyl-GPI showed a multiplicity of species with 18:0-20:4 (11.7%), 16:0-18:1 + 18:0-18:2 (34.9%), and 18:0-18:1 (19.4%) being the major components. Composition of alkyl chains of alkylacyl-GPI from bovine erythrocytes was similar to the reported value for alkylacylglycerols isolated from the glycoinositol phospholipid anchor of bovine erythrocyte acetylcholinesterase. Based on these results, we suggest that alkylacyl-GPI serves as a precursor for the glycoinositol phospholipid of the anchored proteins.

Acetylcholinesterase↗
PubMed1991

Chemical synthesis and physiological activity of sulfonium analogues of platelet activating factor.

Phosphatidylsulfocholine (PSC), the sulfonium analogue of phosphatidylcholine (PC), occurs naturally in some diatoms. The replacement of the [formula; see text] group by a [formula; see text] results in an increase in the polar head group size in PSC relative to that of PC, consistent with the observed increase in permeability of PSC bilayers towards urea. It was of interest to see whether replacement of the [formula; see text] group in platelet activating factor (PAF) by an [formula; see text] group leads to any change in platelet aggregation or other physiological activity. Synthesis of the sulfonium analogue of PAF was carried out by suitable modifications of known procedures. The PAF-sulfonium analogue was found to have almost the same platelet aggregating activity as PAF itself, in the concentration range 1-20 microM, but a much lower activity in the range 0.01-1 microM. The analogue had little or no effect on the platelet aggregation activity of PAF when added in the concentration range 0.01-1 microM and had about half the hypotensive activity of PAF towards hypertensive CDF male rats. The sulfonium analogue, however, was much more cytotoxic to HL-60 cells than PAF itself, in the concentration range 0-15 microM; replacement of the acetate group by a benzyl group increased the cytotoxicity to the level of that of the methoxy analogue of PAF. Thus, replacement of the [formula; see text] group by a [formula; see text] group in the polar head group region of PAF results in a relatively small change in its platelet aggregation activity and a decrease in its hypotensive activity, but greatly increases its antitumor activity.

Animals↗
PubMed1991

Dietary supplementation with ether-linked lipids and tissue lipid composition.

The goal of this investigation was to determine the effect of an alkylglycerol dietary supplement on the lipid composition of several major organs. Lipids from kidney, liver, and lung tissues of rats on a laboratory chow diet (controls) were compared to lipids from the same tissues of rats that had received oral supplements (300-600 mg/day) of 1-O-alkyl-2,3-diacetyl-sn-glycerol (alkyl groups were 65% 18:1 and 17% 16:1) for six days. Incorporation of the alkylglycerol into tissue lipids was indicated by both the presence of a neutral lipid in liver that had the same chromatographic migration as alkyldiacylglycerols and by a substantial increase (approximately 150% of controls) in the octadecenyl group of the alk-1-enyl- and alkyl-glycerol side chains derived from total phospholipids of all three tissues. Compared to controls, there was a significant increase in the amount of alkylacylglycerophosphocholine in all three tissues of the alkylglycerol supplemented group. Total lipids, total phospholipid phosphorus, or the distribution of phospholipid classes (except for small differences in lung tissue) were not affected by the dietary supplement. The increase in ether lipids was offset by a corresponding decrease in the diacyl subclass in tissues from animals on the alkyldiacetylglycerol supplement. Our results indicate that the amount of ether-linked glycerolipids in rat tissues can be easily increased with dietary supplements of alkylglycerols.

Animals↗
PubMed1991

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↗
PubMed1991

[Addition to the article by Iu. E. Dubrova et al. "Influence of heterozygosity on the variation of anthropometric traits in newborns." Determination of intersample differences by covariation and correlation statistics].

Relationships between heterozygosity of 13 polymorphic loci and variation of the set of anthropometric traits were studied in 302 singleton newborns (174 boys, 128 girls). Statistically significant correlation between heterozygosity and all traits were not found. Variances of four traits--body weight, body length, circumference of head and breast measured by first principal component decrease with increase of heterozygosity in boys and girls. At the same time, variance of body proportions (second principal component) increase significantly in boys only. The highest values of correlation between four traits were found in the group of low heterozygous boys. The groups of newborns with different level of heterozygosity are characterized by different combinations of first principal component and the number of minor deviations from development (stigma). It is concluded from the whole set of data that newborn boys with the average level of heterozygosity have the highest level of viability.

Anthropometry↗
PubMed1990

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↗
PubMed1990

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↗