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Biomedical subjects

M L Blank

Publications and source records attributed to M L Blank.

At least 37 records · Page 2Linked to original sources
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↗
PubMed1990

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↗
PubMed1990

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↗
PubMed1990

[Results of repeated coronary angiography in patients with unstable angina pectoris in a long-term follow-up].

A total of 27 patients with unstable angina pectoris were examined in the acute period of the disease and 3.4 years later (from 30 to 51 months). A group of patients with a favorable outcome of unstable angina comprised 13 patients who had displayed no recurrences of disease exacerbation, but that of patients with an unfavorable outcome of unstable angina consisted of 14 patients who had had recurrences of symptoms of progressive angina until myocardial infarction (in 6 patients). Coronary angiography made during the first hospitalization showed that 40% of the patients exhibited a "complicated lesion" of the symptom-related artery, which further transformed to an uncomplicated one (Type I stenosis according to the classification by J. Ambrose et al.), the remaining developed coronary occlusion. Comparison of the specific features of a course of the disease and coronary angiographic findings revealed no relationship between the degree of symptom-related artery stenosis and the long-term outcome of unstable angina.

Adult↗
PubMed1989

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↗
PubMed1989

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↗