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PubMed1982

Acetyl glycerylphosphorylcholine inhibition of prostaglandin I2-stimulated adenosine 3',5'-cyclic monophosphate levels in human platelets. Evidence for thromboxane A2 dependence.

Previous studies with AGEPC (1-O-hexadecyl/octadecyl-2-acetyl-sn-glyceryl-3-phosphorylcholine) stress the independence of the proaggregatory activity of AGEPC from the platelet cyclooxygenase. However, our dose response analyses in human platelet-rich plasma show distinct primary and secondary waves of aggregation in response to AGEPC. Second wave aggregation is inhibited completely by either 10 micro M indomethacin, a cyclooxygenase inhibitor, or 5.6 micro M 9,11-azoprosta-5,13-dienoic acid, a thromboxane A2 synthetase inhibitor. Simultaneous addition of AGEPC and prostaglandin I2 to platelet-rich plasma results in a marked increase in platelet cyclic AMP, which is not different from the prostaglandin I2 response alone. However, if prostaglandin I2 is added to AGEPC-stimulated platelets at a point where secondary aggregation is just beginning, AGEPC can attenuate prostaglandin I2-stimulated cyclic AMP accumulation. The inhibition by AGEPC is blocked by either cyclooxygenase or thromboxane A2 synthetase inhibitors, and radioimmunoassay of thromboxane B2 confirmed that the inhibition of prostaglandin I2-stimulated cyclic AMP accumulation is due to thromboxane A2 synthesis, and that AGEPC-stimulated secondary aggregation does not start until thromboxane A2 is synthesized. These data suggest that much of the bioactivity of AGEPC is attributable to thromboxane A2.

Blood Platelets↗
PubMed1980

Relative suitability of 1-palmitoyl and 1-stearoyl homologues of 1-acyl-sn-glycerylphosphorylcholine and different acyl donors for phosphatidylcholine synthesis via acyl-CoA:1-acyl-sn-glycero-3-phosphorylcholine acyltransferase in rat lung microsomes.

The relative suitability of the 1-palmitoyl and 1-stearoyl homologues of 1-acyl-sn-glyceryl-phosphorylcholine and different acyl donors were tested as substrates for phosphatidylcholine synthesis via the acyl-CoA:1-acyl-sn-glycero-3-phosphorylcholine acyltransferase in rat lung microsomes. The acyl acceptor was an almost equi-molar mixture of the [3H]palmitoyl plus [14C]stearoyl species of 1-acyl-sn-glycero-3-phosphorylcholine with palmitoyl-, stearoyl-, oleoyl-, linoleoyl-, or arachidonoyl-CoA serving as the acyl donor. At all concentrations of acyl acceptor, reaction velocities with 20:4-CoA greater than or equal to 18:2-CoA > 18:1-CoA > 16:0-CoA >18:0-CoA. Furthermore, the acyltransferase selectively utilized the 1-palmitoyl over the 1-stearoyl species of 1-acylglycerylphosphorylcholine by 4.2- to 5.7-fold under optimal assay conditions with the various acyl-CoA thiolesters. However, the degree of preference exhibited for the 1-palmitoyl-sn-glycero-3-phosphorylcholine, as acyl acceptor, versus the 1-stearoyl homologue with palmitoyl-CoA as the acyl donor was not significantly different from that obtained with the other acyl-CoA derivatives. Thus, the specificity of the acyl-CoA:1-acyl-sn-glycero-3-phosphorylcholine acyltransferase indicates an ability of this enzyme to produce dipalmitoyl phosphatidylcholine but it cannot independently explain the predominance of dipalmitoyl phosphatidylcholine in lung or the tendency of stearate at the 1-position to associate with fatty acids of increasing unsaturation at the 2-position.

1-Acylglycerophosphocholine O-Acyltransferase↗
PubMed1985

Acetyl glycerylphosphorylcholine aggregates human platelets through two distinct pathways, both dependent on arachidonic acid metabolism.

Acetyl glyceryl ether phosphorylcholine (AGEPC) is a mediator of inflammation and anaphylaxis, released from IgE-sensitized basophils when exposed to antigens. Convincing evidence shows that AGEPC is synthesized by inflammatory cells, and its mechanism of action has been extensively studied with particular interest focusing on platelet stimulation, the key event initiating the inflammatory cascade. However, widely different results have been reported so that the mode of action of AGEPC in activating platelets is still largely obscure. The objective of this investigation was to elucidate whether AGEPC stimulates human platelets independently from arachidonate metabolism, as previously suggested, and to define the role of nonsteroidal antiinflammatory drugs in inhibiting AGEPC-mediated platelet activation. Irreversible platelet aggregation in vitro occurred at low AGEPC concentrations, was dose dependent, and was accompanied by thromboxane A2 formation. Aspirin inhibited irreversible aggregation induced by low AGEPC concentrations. A thromboxane inhibitor, UK-37, 248-01, failed to affect AGEPC aggregation, suggesting a crucial role for cyclic endoperoxides in AGEPC's mechanism of action. A thromboxane/endoperoxide receptor antagonist 13-azaprostanoic acid prevented irreversible platelet aggregation induced by low AGEPC concentrations. The inhibiting effect of aspirin on AGEPC aggregation could be overcome by increasing the concentration of the agonist by a factor of 10, unless a lipoxygenase inhibitor, nordihydroguaiaretic acid, or 5,8,11,14-eicosatetraynoic acid was previously added to platelet-rich plasmas. The phospholipase inhibitor, mepacrine, completely suppressed human platelet aggregation induced by AGEPC. These results indicate that AGEPC induces irreversible aggregation in human platelets by two distinct pathways, both dependent upon arachidonic acid metabolism: a cyclooxygenase-dependent one at low AGEPC concentrations and a cyclooxygenase-independent one, possibly mediated through the formation of lipoxygenase products, at high AGEPC concentrations.

5,8,11,14-Eicosatetraynoic Acid↗
PubMed1974

The mechanism of intestinal absorption of phosphatidylcholine in rats.

1. The mechanism of absorption of phosphatidylcholine was studied in rats by injecting into the intestine phosphatidylcholine specifically labelled either in the fatty acid or in the glycerol moiety or with (32)P, when considerable amounts of 1-acyl-lysophosphatidylcholine were found in the intestinal lumen. 2-([(14)C]Acyl)phosphatidylcholine gave markedly more radioactive unesterified fatty acids in the lumen, compared with the 1-([(14)C]acyl) derivative. Some of the radioactivity from either the fatty acid or the glycerol moiety of the injected phosphatidylcholine appeared in the mucosal triacylglycerols. 2. Injection of (32)P-labelled phosphatidylcholine or (32)P-labelled lysophosphatidylcholine led to the appearance of radioactive glycerylphosphorylcholine, glycerophosphate and P(i) in the mucosa. 3. Rat mucosa was found to contain a highly active glycerylphosphorylcholine diesterase. 4. It was concluded that the dietary phosphatidylcholine is hydrolysed in the intestinal lumen by the pancreatic phospholipase A to 1-acylglycerylphosphorylcholine, which on entering the mucosal cell is partly reacylated to phosphatidylcholine, and the rest is further hydrolysed to glycerylphosphorylcholine, glycerophosphate, glycerol and P(i). The fatty acids and glycerophosphate are then reassembled to give triacylglycerols via the Kennedy (1961) pathway.

Animals↗
PubMed1997

Novel phosphoserine phosphatase inhibitors.

Phosphoserine phosphatase (EC 3.1.1.3) catalyzes the final step in the major pathway of L-serine biosynthesis in brain. This enzyme may also regulate the levels of glycine and D-serine, the known and putative co-agonists for the glycine site of the N-methyl-D-aspartate receptor in caudal and rostral brain regions, respectively. Using L-phosphoserine as substrate, the rank order potency for inhibition of phosphoserine phosphatase was p-chloromercuriphenylsulfonic acid (CMPSA) > glycerophosphorylcholine >> hexadecylphosphocholine > or = phosphorylcholine > N-ethylmaleimide > or = L-serine > fluoride > D-2-amino-3-phosphonopropionic acid (D-AP3). Glycerylphosphorylcholine (IC50 18 microM) was found to be an uncompetitive inhibitor of phosphoserine phosphatase. Glycerylphosphorylcholine probably binds a novel site on the enzyme since the known allosteric inhibitor L-serine is highly selective for its feedback regulatory site, indicated by the inactivity of 25 L-serine analogs. Fluoride ion (IC50 770 microM) may bind the active site as has been shown for other Mg2+-dependent enzymes. The sulfhydryl reagent CMPSA is a potent, noncompetitive inhibitor of the enzyme using L-phosphoserine as substrate (IC50 9 microM) but is > 300-fold less potent using D-phosphoserine as substrate. Substrate-dependent differences are also observed with the sulfhydryl alkylator N-ethylmaleimide, which inhibits L-phosphoserine, but stimulates D-phosphoserine hydrolysis. These sulfhydryl reagents may dissociate multimeric forms of the enzyme to form monomers; the multimeric forms and monomers may preferentially cleave L- and D-phosphoserine, respectively. Phosphorylcholine esters and sulfhydryl reagents may prove useful in determining the contribution of phosphoserine phosphatase to the biosynthesis of glycine and D-serine in neuronal tissue in vitro.

Animals↗
PubMed1966

Histochemical demonstration of phospholipase B (lysolecithinase) activity in rat tissues.

A method has been developed for the histochemical demonstration of phospholipase B (lysolecithinase) of rat tissues. The enzyme attacks lysolecithin with liberation of 1 mole of glycerylphosphorylcholine and 1 mole of fatty acid. The recommended procedure involves use of 6-10 micro frozen sections, fixed in cold calcium-formol and incubated at 37 degrees C in Tris buffered medium at pH 6.6 containing 2.2 X 10(-3) M lysolecithin and 1% cobalt acetate. The fatty acid liberated by enzymatic hydrolysis is trapped as a cobalt precipitate and is then converted to a black-brown precipitate by treatment with dilute ammonium sulfide in cold isotonic saline. Equivalent amounts of fatty acid and glycerylphosphorylcholine are recovered by extraction and analysis of the incubated sections and of the incubation medium, thus proving that lysolecithin hydrolysis occurs under the proposed reaction conditions. Staining is reduced by treating the sections with copper ions, mercury compounds, alcohols, acetone and by heating at 60 degrees C prior to incubation with substrate. Lowering of the pH of the incubation medium has similar effect. These findings are interpreted as evidence of the enzymatic nature of the reaction. Cells exhibiting a positive staining are found in the lamina propria of the intestinal villi and crypts, in the red pulp of the spleen and in the interstitial tissue of lung, liver and thymus. Similar elements are present in bone marrow smears and in leukocyte preparations obtained by peritoneal lavage. The morphologic and staining characteristics of these cells correspond to those of the eosinophilic leukocytes. Physical and chemical agents (x-irradiation, corticosteroids) which sharply decrease the number of eosinophils also reduce the number of cells shown histochemically to hydrolyze lysolecithin. A correspondent diminution of phospholipase B activity of homogenates of the same tissues can be shown in vitro. Differences in tissue distribution and chemical properties distinguish the phospholipase B from less specific esterases and lipases.

Acetone↗
PubMed1977

Functional maturation of the epididymis in rabbit and rhesus monkey.

The changes in the weight, histology and biochemical composition of the epididymis (caput, corpus and cauda segments) in prepuberal rabbit and rhesus monkey in response to testosterone treatment were investigated. The increase in the weight of the organ was accompanied by increased levels of RNA and DNA. Androgen therapy caused an increase in the concentration of sialic acid, phospholipids and glycerylphosphorylcholine and activities of alkaline phosphatase, acid phosphatase and hyaluronidase. The cauda region of the epididymis exhibited relatively higher levels of sialic acid and glycerylphosphorylcholine. These findings are discussed in relation to the functional maturation of the organ and the role of androgen in this process.

Acid Phosphatase↗
PubMedDate not supplied

Semen biochemistry of leprosy patients.

Studies have been made on the semen of three categories (borderline, borderline tuberculoid and lepromatous) of leprosy patients to evaluate the seminal biochemical constituents viz. fructose, glycerylphosphorylcholine and acid phosphatase besides the physical properties viz. volume, pH, liquefaction time, sperm density and sperm motility. In all categories of leprosy patients, seminal pH, liquefaction time and sperm density underwent significant decline. The decline in the seminal volume and sperm motility was significant only in borderline leprosy. It was observed that seminal glycerylphosphorylcholine (GPC) concentration and acid phosphatase activity declined in all categories of leprosy patients but GPC showed a significant decline only in borderline tuberculoid and acid phosphatase declined significantly only in borderline and lepromatous leprosy.

Acid Phosphatase↗