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PubMed1983

Protein phosphorylation and diglyceride production during serotonin release induced by epinephrine plus ADP in human platelets.

Epinephrine (1 microM) plus ADP (5 microM) induced serotonin release from human platelets although neither epinephrine nor ADP alone brought about such a release. During this release reaction, the phosphorylation of 40K-dalton protein was induced to an extent similar to that induced by 0.5 unit/ml thrombin. The amount of diglyceride (DG) produced by epinephrine plus ADP, however, was much smaller than that produced by thrombin. The reaction velocities of these reactions induced by epinephrine plus ADP were slower than those induced by thrombin. Epinephrine or ADP alone hardly produced any DG and induced 40K-dalton protein phosphorylation only slightly. Indomethacin (1 microgram/ml), a cyclooxygenase inhibitor, remarkably inhibited epinephrine plus ADP induced serotonin release, 40K-dalton protein phosphorylation and DG production although this agent had little effect on the same reactions induced by thrombin. These results suggest that prostaglandin endoperoxides or thromboxane A2 may be involved in serotonin release, 40K-dalton protein phosphorylation and DG production induced by epinephrine plus ADP.

Adenosine Diphosphate↗
PubMed2004

Isotropic medium chain mono-diglyceride/oil/water formulations for solubilization of lipophilic and hydrophilic drugs.

The aim of the study was to investigate isotropic mono- and diglyceride (MCMDG)/oil/water systems as vehicles for combinations of hydrophilic and lipophilic drugs. For two-component systems, MCMDG was mixed with various masses of water. For MCMDG/oily vehicles/water systems, mixtures were prepared by mixing oil and MCMDG prior to the addition of the appropriate masses of water. The isotropic region was examined by visual inspection and confirmed using polarized light microscopy. Viscosities of the systems were determined. Solubilities of hydrophilic (levamisole HCl) and lipopohilic (abamectin) drugs were determined in the isotropic formulations by HPLC analysis. The isotropic regions in the two-component and three-component systems had water contents of up to 18% at 25 degrees C. The isotropic formulations exhibited Newtonion flow. The viscosity of formulations having the same percentage of water increased with increasing ratio of MCMDG to oil in three-component systems. The solubilities of the levamisole HCl and abamectin were higher in the isotropic MCMDG/sesame oil/water formulations than in equivalent MCMDG/water formulations. In some formulations, the solubility of levamisole HCl was higher in the absence of abamectin than in combination with abamectin. Isotropic MCMDG/oil/water systems were obtained without the use of co-surfactants. Increasing water content in the system did not proportionally increase the solubility of hydrophilic drug. Solubilization of hydrophilic drug was affected by lipophilic drug in the presence or absence of SO and lipophilic drug solubility was affected by hydrophilic drug in the absence of SO. These systems are suitable vehicles to deliver both hydrophilic and lipophilic drugs and could be of interest for pharmaceutical formulations.

Benzoates↗
PubMed1986

Phospholipase C-diglyceride lipase is a major pathway for arachidonic acid release in macrophages.

Macrophages are a rich source of arachidonic acid oxygenated metabolites and play a remarkable role in a number of physiopathological situations. The synthesis and secretion of arachidonic acid metabolites are triggered at the cytoplasmic membrane level. The present study was outlined to further investigate the cellular mechanisms controlling arachidonic acid release in macrophages. The results presented here strongly suggest that the amount of arachidonic acid released in macrophages in response to phagocytic challenge could be accounted for by a phospholipase C-diglyceride lipase system being unnecessary the presence of phospholipase A2 whose activity, on the other hand, was found vanishingly small in macrophage homogenates.

Animals↗
PubMed2001

Resveratrol inhibits the formation of phosphatidic acid and diglyceride in chemotactic peptide- or phorbol ester-stimulated human neutrophils.

Resveratrol (trans-3,5,4'-trihydroxystilbene, Res) is a naturally occurring antioxidant found in grape berry skins and red wine. It has anti-inflammatory effects. In this study, we examined the effect of Res on the formation of phosphatidic acid (PA) and diglyceride (DG), in human neutrophils stimulated by formyl-methionyl-leucyl-phenylalanine (fMLP) or by phorbol 12-myristate 13-acetate (PMA). We measured the masses of PA and DG by using a nonradioactive method. Our results showed that Res inhibited the formation of PA in a concentration dependent manner with an IC(50) value of 42.4 and 60.9 microM in fMLP- and PMA-stimulated cells, respectively. Res also suppressed the formation of phosphatidylethanol (PEt), thereby implying inhibition of phospholipase D (PLD) activity. In addition, Res inhibited the formation of both diacylglycerol (DAG) and ether-linked acylglycerol (EAG) induced by fMLP and by PMA. Our results suggest that Res inhibition of PLD activity may contribute to its anti-inflammatory effects.

Choline↗
PubMed2001

Low- and high-affinity phorbol ester and diglyceride interactions with protein kinase C: 1-O-alkyl-2-acyl-sn-glycerol enhances phorbol ester- and diacylglycerol-induced activity but alone does not induce activity.

Phorbol ester-induced conventional protein kinase C (PKCalpha, -betaIota/IotaIota, and -gamma) isozyme activities are potentiated by 1,2-diacyl-sn-glycerol. This has been attributed to a "cooperative" interaction of the two activators with two discrete sites termed the low- and high-affinity phorbol ester binding sites, respectively [Slater, S. J., Milano, S. K., Stagliano, B. A., Gergich, K. J., Ho, C., Mazurek, A., Taddeo, F. J., Kelly, M. B., Yeager, M. D., and Stubbs, C. D. (1999) Biochemistry 38, 3804-3815]. Here, we report that the 1-O-alkyl ether diglyceride, 1-O-hexadecyl-2-acetyl-sn-glycerol (HAG), like its 1,2-diacyl counterpart, 1-oleoyl-2-acetyl-sn-glycerol (OAG), also potentiated PKCalpha, -betaI/II, and -gamma activities induced by the phorbol ester 4beta-12-O-tetradecanoylphorbol-13-acetate (TPA). Similar to OAG, HAG was found to bind to the low-affinity phorbol ester binding site and to enhance high-affinity phorbol ester binding, and to decrease the level of Ca(2+) required for phorbol ester-induced activity, while being without effect on the Ca(2+) dependence of membrane association. Thus, similar to OAG, HAG may also potentiate phorbol ester-induced activity by interacting with the low-affinity phorbol ester binding site, leading to a reduced level of Ca(2+) required for the activating conformational change. However, HAG was found not to behave like a 1,2-diacyl-sn-glycerol in that alone it did not induce PKC activity, and also in that it enhanced OAG-induced activity. The results reveal HAG to be a member of a new class of "nonactivating" compounds that modulate PKC activity by interacting with the low-affinity phorbol ester binding site.

Animals↗
PubMed1992

Comparison of diglyceride production from choline-containing phosphoglycerides in human neutrophils stimulated with N-formylmethionyl-leucylphenylalanine, ionophore A23187 or phorbol 12-myristate 13-acetate.

The turnover of choline-containing phosphoglycerides (PC) in response to agonist stimulation is well documented in human neutrophils. We have now compared the enzymic pathways of N-formylmethionyl-leucylphenylalanine (fMLP)-, A23187- and phorbol-12-myristate 13-acetate (PMA)-induced diglyceride (DG) and phosphatidic acid (PA) generation in these cells. In order to distinguish between phospholipase C- and D-mediated PC breakdown, human neutrophils were radiolabelled with 1-O-[3H]alkyl-2-acyl-glycero-3-phosphocholine and stimulated in the presence of ethanol or propranolol. The addition of 0.5% ethanol to the incubation mixture resulted in the production of phosphatidylethanol, indicative of phospholipase D activation, in response to all three stimuli. Concomitant with phosphatidylethanol formation was a partial block of PA production. The production of DG was also partially blocked by addition of ethanol. Propranolol (200 microM) was also used to assess the contributions of phospholipases C and D toward DG generation. Inhibition of PA phosphohydrolase by propranolol resulted in the complete abolition of DG generation when neutrophils were stimulated with fMLP. In contrast, propranolol only partially inhibited DG generation in response to A23187 and PMA. These results suggested that DG production in response to fMLP stimulation is mediated via the activation of phospholipase D, whereas A23187- or PMA-induced DG generation may involve more than one pathway. However, examination of the water-soluble choline metabolites produced indicated that phospholipase D was responsible for the production of PA and DG in response to all three stimuli.

Calcimycin↗
PubMed1997

Induction of cytosolic phospholipase A2 activity by phosphatidic acid and diglycerides in permeabilized human neutrophils: interrelationship between phospholipases D and A2.

Relationships between phospholipases are poorly understood, but phosphatidic acid (PA) and diglycerides (DGs), produced by phospholipase D (PLD) and phosphatidate phosphohydrolase actions, might function as second messengers coupling cell stimulation to cellular responses. This study investigates the role of PLD-mediated PA and DG formation in inducing phospholipase A2 (PLA2) activity in intact human neutrophils (PMNs) and in PMNs permeabilized with Staphylococcus aureus alpha-toxin. PMNs were labelled with [3H]arachidonic acid (AA) to assess AA release and metabolism and diacylglycerol formation, or with [3H]1-O-hexadecyl-2-lyso-glycerophosphatidylcholine for the determination of platelet-activating factor (PAF), PA and alkylacylglycerol production. In intact PMNs primed with tumour necrosis factor alpha before stimulation with N-formyl-Met-Leu-Phe, AA release and metabolism and PAF formation increased in parallel with enhanced PA and DG formation, and inhibition of PA and DG production led to a decrease in both AA release and PAF accumulation. In alpha-toxin-permeabilized PMNs, AA release and PAF production result from the specific activation of cytosolic PLA2 (cPLA2). In this system, PA and DG formation were always present when cPLA2 activation occurred; blocking PA and DG production inhibited AA release and PAF accumulation. Adding either PA or DG back to permeabilized cells (with endogenous PA and DG formation blocked) led to a partial restoration of AA release and PAF formation; a combination of PA and DGs reconstituted full cPLA2 activity. These results strongly suggest that products of PLD participate in activating cPLA2 in PMNs.

Arachidonic Acid↗
PubMed1994

Monogalactosyl diglyceride, a marker for myelination, activates oligodendroglial protein kinase C.

Protein kinase C (PKC) is activated by 1,2-sn-diacylglycerol (DAG), the source of which can either be phosphatidylinositol bisphosphate or phosphatidylcholine. Here, we show that monogalactosyl diglyceride (MGDG), a minor galactolipid present in oligodendrocytes (OLs) and myelin, which is designated as a marker for myelination, can enhance OL PKC activity. Based on different calcium and substrate requirements we conclude that MGDG and DAG activate different isoforms of PKC group A: MGDG primarily stimulates PKC-alpha, and DAG primarily activates PKC-gamma. The presence of these PKC isoforms in OLs was confirmed by western blotting, whereas PKC-beta was only weakly stained, if at all. Addition of MGDG to the culture medium provided a higher density of regenerating OL fibers, which was not observed when membrane-permeable DAG was used. These findings indicate that MGDG can modulate the OL PKC activity and that PKC-alpha is the major PKC isoform involved in OL process formation.

Animals↗
PubMed1977

Biosynthesis of the covalently linked diglyceride in murein lipoprotein of Escherichia coli.

Biosynthesis of the diglyceride moiety of murein lipoprotein in Escherichia coli was studied by pulse-labeling with [2-3H]glycerol and subsequent chase. The evidence strongly suggests that the precursor of the glycerol moiety in lipoprotein is one of the major phospholipid species in E. coli. Studies of biosynthesis of lipoprotein in cerulenin-treated cells indicated that the nonacylated glycerol moiety of phosphatidylglycerol is the donor for the formation of a thioether linkage in the glycerylcysteine residue of the lipoprotein. This is supported by the observation that carbon 1 rather than carbon 3 of sn-glycerol is involved in this thioether linkage. We propose that the biosynthesis of lipoprotein proceeds as follows: apolipoprotein + phosphatidylglycerol or acyl phosphatidylglycerol leads to lipoprotein + phosphatidic acid.

Apolipoproteins↗
PubMed2001

Hormone-sensitive lipase deficiency in mice causes diglyceride accumulation in adipose tissue, muscle, and testis.

Hormone-sensitive lipase (HSL) is expressed predominantly in white and brown adipose tissue where it is believed to play a crucial role in the lipolysis of stored triglycerides (TG), thereby providing the body with energy substrate in the form of free fatty acids (FFA). From in vitro assays, HSL is known to hydrolyze TG, diglycerides (DG), cholesteryl esters, and retinyl esters. In the current study we have generated HSL knock-out mice and demonstrate three lines of evidence that HSL is instrumental in the catabolism of DG in vivo. First, HSL deficiency in mice causes the accumulation of DG in white adipose tissue, brown adipose tissue, skeletal muscle, cardiac muscle, and testis. Second, when tissue extracts were used in an in vitro lipase assay, a reduced FFA release and the accumulation of DG was observed in HSL knock-out mice which did not occur when tissue extracts from control mice were used. Third, in vitro lipolysis experiments with HSL-deficient fat pads demonstrated that the isoproterenol-stimulated release of FFA was decreased and DG accumulated intracellularly resulting in the essential absence of the isoproterenol-stimulated glycerol formation typically observed in control fat pads. Additionally, the absence of HSL in white adipose tissue caused a shift of the fatty acid composition of the TG moiety toward increased long chain fatty acids implying a substrate specificity of the enzyme in vivo. From these in vivo results we conclude that HSL is the rate-limiting enzyme for the cellular catabolism of DG in adipose tissue and muscle.

Adipose Tissue↗
PubMed1994

Retinoids inhibit protein kinase C-dependent transduction of 1,2-diglyceride signals in human colonic tumor cells.

1,2-Diglycerides with long-chain fatty acid residues related to nutritional fat (LCDGs) specifically affect growth and urokinase secretion in human colonic tumor cells, but not in normal mucosa. This allows them to advance and enhance carcinogenesis in the colon and rectum. SW480 colon carcinoma cells are LCDG sensitive in the same way as primary colonic tumor cells and have therefore been used as a model system to study the mechanism of LCDG action and to search for inhibitors of tumor development in the colon. Using this model system, we have shown that the effects of LCDGs are transmitted by protein kinase C and abolished by downregulation of the enzyme. Retinol, retinoic acid, and beta-carotene in nanomolar concentrations inhibit LCDG-induced growth and urokinase secretion and block stimulation of protein kinase C. Although retinol and retinoic acid at higher concentrations also display stimulatory activity, beta-carotene does not. At 100 nM, a concentration that can easily be reached in the plasma of humans, beta-carotene reduces LCDG-induced urokinase secretion about 50%. Inasmuch as beta-carotene does not have side effects due to intrinsic activities and storage effects, beta-carotene and foods rich in carotenes could be useful in the prevention of colorectal cancer.

Carotenoids↗
PubMed2004

Isotropic systems of medium-chain mono- and diglycerides for solubilization of lipophilic and hydrophilic drugs.

The aim of this study was to investigate isotropic mono- and diglyceride-based (MCMDG) systems, which are potential vehicles for injectable products containing both hydrophilic and lipophilic drugs. For two-component systems, MCMDG was mixed with various masses of water. For three-component systems, the samples were prepared by mixing propylene glycol or glycerol formal or short-chain alcohols with MCMDG prior to the addition of water. The isotropic region was examined by visual inspection and confirmed using polarized light microscopy. Viscosities of formulations were measured. Solubilities of levamisole phosphate (hydrophilic) and abamectin (lipophilic) were determined in the isotropic formulations using high-performance liquid chromatography assay. The isotropic region in the two-component systems had a water content of up to 18% at 25 degrees C. Solvents such as propylene glycol (PG), glycerol formal (FG), and ethyl alcohol increased the isotropic region. The area of isotropic region in these three-component systems increased with increasing temperature. The area of the isotropic region became larger with decreasing dielectric constant and solubility parameter of the series of short-chain alcohols, except n-butyl alcohol, at 25 degrees C. The systems exhibited Newtonian behavior. The solubility of both hydrophilic and lipophilic drugs was high in formulations at 25 degrees C. It was concluded that more water was solubilized in MCMDG/short-chain alcohols/water systems, and the isotropic region in the short-chain alcohol systems enlarged compared with MCMDG/PG/water or MCMDG/GF/water systems, except the n-butyl alcohol system. Hydrophilic and lipophilic drugs solubilize in the systems. The isotropic formulations containing MCMDG may represent an alternative to more traditional formulations for injectable formulations containing both lipophilic and hydrophilic drugs.

Chemistry, Pharmaceutical↗
PubMed1986

Comparison of the activity of phorbol 12-myristate 13-acetate and the diglyceride glycerol 1-myristate 2-acetate.

Diglycerides function as analogs of the phorbol ester tumor promoters. We compare here the activity of glycerol 1-myristate 2-acetate (GMA) with the corresponding phorbol 12-myristate 13-acetate (PMA). GMA inhibited phorbol ester binding to reconstituted protein kinase C, stimulated protein kinase C enzymatic activity, and, upon addition to intact 3T3 cells, inhibited [125I]EGF binding. Its potency was much less than that of PMA, however (2.9 X 10(4)-fold less for phorbol ester binding, greater than 1.2 X 10(5)-fold less for inhibition of EGF binding), and its activity on the intact cells was more transient. The marked difference in potency contrasts with the much smaller differences found previously for the corresponding pairs of dilaurate and dioleate derivatives.

Animals↗
PubMed1976

Solubilization of diglyceride acyltransferase from the membrane of Mycobacterium smegmatis.

Diglyceride acyltransferase [acyl-CoA : 1,2-diacylglycerol O-acyltransferase, EC 2.3.1.20] was found to be localized in the membrane of Mycobacterium smegmatis, and this enzyme could be solubilized from the membrane by treatment with aqueous acetone. The solubilized enzyme required either 1,2-diolein or 1, 3-diolein as an acceptor for palmitoyl-CoA. The apparent Km value for 1,2- or 1,3-diolein and that for palmitoyl-CoA were about 1.4 X 10(-5) M and 6 X 10(-6) M, respectively. Several sulfhydryl reagents were inhibitory to the enzyme activity, suggesting the existence of a thiol group(s) in its active site. The solubilized enzyme, which was more labile than that membrane-bound one, could be stabilized to some extent with antichaotropic salts such as phosphate, pyrophosphate, and sulfate.

Acyltransferases↗
PubMed1996

The consequences of engineering an extra disulfide bond in the Penicillium camembertii mono- and diglyceride specific lipase.

The extracellular lipase from Penicillium camembertii has unique substrate specificity restricted to mono- and diglycerides. The enzyme is a member of a homologous family of lipases from filamentous fungi. Four of these proteins, from the fungi Rhizomucor miehei, Humicola lanuginosa, Rhizopus delemar and P. camembertii, have had their structures elucidated by X-ray crystallography. In spite of pronounced sequence similarities the enzymes exhibit significant differences. For example, the thermostability of the P. camembertii lipase is considerably lower than that of the H. lanuginosa enzyme. Since only the P. camembertii enzyme lacks the characteristic long disulfide bridge, corresponding to Cys22-Cys268 in the H. lanuginosa lipase, we have engineered this disulfide into the former enzyme in the hope of obtaining a significantly more stable fold. The properties of the double mutant (Y22C and G269C) were assessed by a variety of biophysical techniques. The extra disulfide link was found to increase the melting temperature of the protein from 51 to 63 degrees C. However, no difference is observed under reducing conditions, indicating an intrinsic instability of the new disulfide. The optimal temperature for catalytic activity decreased by 10 degrees C and the optimum pH was shifted by 0.7 units to more acidic.

Base Sequence↗
PubMed1990

Bradykinin induces phosphoinositide turnover, 1,2-diglyceride formation, and growth in cultured adult human keratinocytes.

The effects of bradykinin on activation of phosphoinositide turnover, 1,2-diglyceride formation, and growth of cultured adult human keratinocytes were investigated. Keratinocytes specifically bound [3H]bradykinin with high affinity (kd = 3.4 nM) and displayed 1.5 X 10(5) binding sites/cell. Bradykinin caused a rapid dose-dependent increase in inositol trisphosphate (IP3) inositol bisphosphate, and inositol monophosphate. IP3 was maximally increased (fivefold) at 30 s and remained elevated for at least 10 min. Half maximal stimulation of IP3 formation was observed at 27 nM bradykinin. IP3 accumulation was equally elevated by bradykinin and lys-bradykinin but was not stimulated by des-Arg9-bradykinin, indicating that phospholipase C in cultured keratinocytes is coupled to B2 bradykinin receptors. Treatment of keratinocytes with active phorbol ester (TPA) caused a significant inhibition (50%) of bradykinin-induced IP3 accumulation, suggesting negative regulation of phospholipase C by protein kinase C. Bradykinin also caused a significant elevation in 1,2-diacylglycerol (DAG) content. DAG content was maximally elevated (twofold) at 1 min and remained elevated for at least 10 min. Bradykinin also caused a significant (twofold, p less than 0.02) increase in keratinocyte growth. These data demonstrate that bradykinin is a potent agonist of the phospholipase C/protein kinase C signal transduction system in cultured adult human keratinocytes and that activation of this pathway by bradykinin is associated with increased keratinocyte growth.

Adult↗
PubMed1979

Diglyceride kinase from Escherichia coli. Purification in organic solvent and some properties of the enzyme.

The diglyceride kinase activity of membranes from Escherichia coli was extracted into acidic butan-1-ol. The enzyme was purified in organic solvent by precipitation at -20 degrees C, chromatography on DEAE-cellulose and repeated chromatography on Sephadex LH-60. The final 1460-fold purified enzyme preparation gave a single protein band upon isoelectric focusing in the presence of Triton X-100 (pI, 4.0) and upon polyacrylamide-gel electrophoresis in the presence of sodium dodecylsulphate. The latter method as well as gel chromatography on Sephadex LH-60 indicated a molecular weight of about 15400. The purified enzyme was devoid of lipid, and it required re-addition of lipid for activity. sn-1,2-Dipalmitate and ceramide were phosphorylated, whereas the C55-isoprenoid alcohol, ficaprenol, did not serve as a substrate under the same conditions. Conversely, the butanol-soluble C55-isoprenoid-alcohol kinase from Staphylococcus aureus did not phosphorylate sn-1,2-dipalmitate.

Cell Membrane↗
PubMed1981

Properties of a CDP-diglyceride hydrolase from guinea pig brain.

Enzymatic hydrolysis of the pyrophosphate bond of CDP-diglyceride (CDP-DG), previously shown to occur in bacteria, is demonstrable in mammalian tissues. Activity was enriched in a lysosomal fraction obtained from guinea pig cerebral cortex and was purified 92-fold relative to the homogenate by a combination of XM-300 ultrafiltration and DEAE-cellulose column chromatography. When incubated with CDP-dipalmitin, the purified enzyme produced stoichiometric amounts of CMP and phosphatidate. dCDP-DG served as a substrate, while ADP-DG was an inhibitor, as were 5'-AMP and 5'-dAMP. CDP-DG hydrolysis was not affected by the presence of excess amounts of CDP-choline, CDP-glycerol, sodium pyrophosphate, or cyclic 3',5'-AMP.

Animals↗