In vitro lipid metabolism in the rat pancreas. I. Basal lipid metabolism

Overall survival of pancreatic ductal adenocarcinoma is doubled by Aldh7a1 deletion in the KPC mouse

Rationale: The activity of aldehyde dehydrogenase 7A1 (ALDH7A1), an enzyme that catalyzes the lipid peroxidation of fatty aldehydes was found to be upregulated in pancreatic ductal adenocarcinoma (PDAC). ALDH7A1 knockdown significantly reduced tumor formation in PDAC. We raised a question how ALDH7A1 contributes to cancer progression. Methods: To answer the question, the role of ALDH7A1 in energy metabolism was investigated by knocking down and knockdown gene in mouse model, because the role of ALDH7A1 has been reported as a catabolic enzyme catalyzing fatty aldehyde from lipid peroxidation to fatty acid. Oxygen consumption rate (OCR), ATP production, mitochondrial membrane potential, proliferation assay and immunoblotting were performed. In in vivo study, two human PDAC cell lines were used for pre-clinical xenograft model as well as spontaneous PDAC model of KPC mice was also employed for anti-cancer therapeutic effect. Results:ALDH7A1 knockdown significantly reduced tumor formation with reduction of OCR and ATP production, which was inversely correlated with increase of 4-hydroxynonenal. This implies that ALDH7A1 is critical to process fatty aldehydes from lipid peroxidation. Overall survival of PDAC is doubled by cross breeding of KPC (KrasG12D; Trp53R172H; Pdx1-Cre) and Aldh7a1-/- mice. Conclusion: Inhibitions of ALDH7A1 and oxidative phosphorylation using gossypol and phenformin resulted in a regression of tumor formation in xenograft mice model and KPC mice model.

PLA2G16 is a mutant p53/KLF5 transcriptional target and promotes glycolysis of pancreatic cancer

PLA2G16 is a member of the phospholipase family that catalyses the generation of lysophosphatidic acids (LPAs) and free fatty acids (FFAs) from phosphatidic acid. In the current study, we explored the functional role of PLA2G16 in pancreatic adenocarcinoma (PAAD) and the genetic/epigenetic alterations leading to its dysregulation. Bioinformatic analysis was performed using data from The Cancer Genome Atlas (TCGA), Genotype‐Tissue Expression (GTEx) and the Human Protein Atlas (HPA). Then, PANC‐1 and MIA‐PaCa‐2 cells harbouring TP53 mutations were used for cellular and animal studies. Results showed that PL2G16 expression was significantly up‐regulated in PAAD tissue and was associated with unfavourable survival. PLA2G16 inhibition suppressed pancreatic cell growth in vitro and in vivo and also inhibited aerobic glycolysis. Bioinformatic analysis indicated that KLF5 was positively correlated with PLA2G16 expression in PAAD tumours with TP53 mutation. TP53 or KLF5 inhibition significantly reduced PLA2G16 expression at both mRNA and protein levels. Dual‐luciferase and chromatin Immunoprecipitation‐quantitative polymerase chain reaction assays showed that KLF5 directly bound to the PLA2G16 promoter and activated its transcription. Co‐immunoprecipitation assay indicated that mutant p53 had a physical interaction with KLF5. Inhibition of mutant p53 impaired the transcriptional activating effects of KLF5. In PAAD cases in TCGA, PLA2G16 expression was positively correlated with its copy number (Pearson's r = 0.51, P < 0.001), but was strongly and negatively correlated with the methylation level of cg09518969 (Pearson's r = −0.64, P < 0.001), a 5’‐cytosine‐phosphodiester bond‐guanine‐3’ site within its gene locus. In conclusion, this study revealed a novel mutant p53/KLF5‐PLA2G16 regulatory axis on tumour growth and glycolysis in PAAD.

Is Positron Emission Tomography Using 18F-Fluorodeoxyglucose and 11C-Acetate Valuable in Diagnosing Indeterminate Pancreatic Masses?

Background:

It can be impossible to differentiate a mass forming chronic pancreatitis from adenocarcinoma of the pancreas using standard anatomical imaging. Positron emission tomography using 2-[18F] fluoro-2deoxy-D-glucose (18FDG-PET) and 1-[11C]-acetate (11C-acetate-PET) are methods taking advantage of the metabolic differences between benign and malignant tissues.

Aims:

To determine the diagnostic accuracy of 18FDG-PET and 11C-acetate-PET in indeterminate pancreatic masses.

Methods:

Twenty patients with an indeterminate mass of the head of the pancreas were prospectively studied. All patients underwent 18FDG-PET and eighteen of them 11C-acetate-PET. Scans were evaluated qualitatively and quantitatively; the later by using regional standardised uptake value (SUV). Final diagnosis was established using histopathologic evaluation of resected specimen or biopsy.

Results:

Adenocarcinoma was diagnosed in twelve patients and chronic pancreatitis in eight. Qualitative evaluation of 18FDG-PET imaging revealed three false negative and one false-positive results. The sensitivity, specificity, and diagnostic accuracy were 75 %, 88 %, and 80 %, respectively. The cut-off SUV to differentiate malignant from benign disease was 3,5 demonstrating a sensitivity of 91.7 % and a specificity of 75 %.

Conclusion:

18FDG-PET imaging could not confirm or exclude malignancy in indeterminate masses of the head of the pancreas with high sensitivity and diagnostic accuracy. 11C-acetate-PET provided no additional diagnostic benefits.

Apolipoprotein A-II Plus Lipid Emulsion Enhance Cell Growth via SR-B1 and Target Pancreatic Cancer In Vitro and In Vivo

BACKGROUND

Apolipoprotein A-II (ApoA-II) is down regulated in the sera of pancreatic ductal adenocarcinoma (PDAC) patients, which may be due to increase utilization of high density lipoprotein (HDL) lipid by pancreatic cancer tissue. This study examined the influence of exogenous ApoA-II on lipid uptake and cell growth in pancreatic cancer (PC) both in vitro and in vivo.

METHODS

Cryo transmission electron microscopy (TEM) examined ApoA-II's influence on morphology of SMOFLipid emulsion. The influence of ApoA-II on proliferation of cancer cell lines was determined by incubating them with lipid+/-ApoA-II and anti-SR-B1 antibody. Lipid was labeled with the fluorophore, DiD, to trace lipid uptake by cancer cells in vitro by confocal microscopy and in vivo in PDAC patient derived xenograft tumours (PDXT) by fluorescence imaging. Scavenger receptor class B type-1(SR-B1) expression in PDAC cell lines and in PDAC PDXT was measured by western blotting and immunohistochemistry, respectively.

RESULTS

ApoA-II spontaneously converted lipid emulsion into very small unilamellar rHDL like vesicles (rHDL/A-II) and enhanced lipid uptake in PANC-1, CFPAC-1 and primary tumour cells as shown by confocal microscopy. SR-B1 expression was 13.2, 10.6, 3.1 and 2.3 fold higher in PANC-1, MIAPaCa-2, CFPAC-1 and BxPC3 cell lines than the normal pancreatic cell line (HPDE6) and 3.7 fold greater in PDAC tissue than in normal pancreas. ApoA-II plus lipid significantly increased the uptake of labeled lipid and promoted cell growth in PANC-1, MIAPaCa-2, CFPAC-1 and BxPC3 cells which was inhibited by anti SR-B1 antibody. Further, ApoA-II increased the uptake of lipid in xenografts by 3.4 fold.

CONCLUSION

Our data suggest that ApoA-II enhance targeting potential of lipid in pancreatic cancer which may have imaging and drug delivery potentialities.

Metabolism addiction in pancreatic cancer

Pancreatic ductal adenocarcinoma, an aggressively invasive, treatment-resistant malignancy and the fourth leading cause of cancer deaths in the United States, is usually detectable only when already inevitably fatal. Despite advances in genetic screening, mapping and molecular characterization, its pathology remains largely elusive. Renewed research interest in longstanding doctrines of tumor metabolism has led to the emergence of aberrant signaling pathways as critical factors modulating central metabolic networks that fuel pancreatic tumors. Such pathways, including those of Ras signaling, glutamine-regulatory enzymes, lipid metabolism and autophagy, are directly affected by genetic mutations and extreme tumor microenvironments that typify pancreatic tumor cells. Elucidation of these metabolic networks can be expected to yield more potent therapies against this deadly disease.

Control of mitochondrial beta-oxidation flux

The control of mitochondrial beta-oxidation, including the delivery of acyl moieties from the plasma membrane to the mitochondrion, is reviewed. Control of beta-oxidation flux appears to be largely at the level of entry of acyl groups to mitochondria, but is also dependent on substrate supply. CPTI has much of the control of hepatic beta-oxidation flux, and probably exerts high control in intact muscle because of the high concentration of malonyl-CoA in vivo. beta-Oxidation flux can also be controlled by the redox state of NAD/NADH and ETF/ETFH(2). Control by [acetyl-CoA]/[CoASH] may also be significant, but it is probably via export of acyl groups by carnitine acylcarnitine translocase and CPT II rather than via accumulation of 3-ketoacyl-CoA esters. The sharing of control between CPTI and other enzymes allows for flexible regulation of metabolism and the ability to rapidly adapt beta-oxidation flux to differing requirements in different tissues.

Dynamic changes in glucose metabolism accompanying the expression of the neural phenotype after differentiation in PC12 cells

To assess what properties of glucose metabolism are most closely related to expression of the neural phenotype, some parameters of glucose metabolism in PC12 cells before (tumor-type) and after differentiation (neuron-type) were investigated. Neuron-type cells exhibited a 2.7-fold higher level of [3H]DG retention than tumor-type cells, accompanied by a higher glucose transport rate and higher levels of hexokinase activity. [14C]CO2 production from [U-14C]glucose in neuron-type was also more than four-times greater than that in tumor-type cells. The levels of [14C]carbon in macromolecules from [14C]glucose in neuron-type cells were also much higher (10.6-fold) than those in tumor-type cells, and the levels of incorporation of [14C]carbon were almost as high as those of [14C]CO2. From the metabolite analysis, amino acids appeared to be the major compounds converted from glucose. On the other hand, the uptakes of [35S]methionine-[35S]cysteine and [3H]uridine in neuron-type cells were lower than those in tumor-type cells. Following depolarization with 50 mM potassium, [14C]CO2 production increased, but the retention of [14C]carbon was not changed in neuron-type cells. The largest change accompanied by acquisition of the neural phenotype was carbon incorporation into the macromolecules derived from glucose. This property may be important for the expression of the neural phenotype as well as the higher levels of both glucose uptake and oxygen consumption.

Characterization of acetate metabolism in tumor cells in relation to cell proliferation: acetate metabolism in tumor cells

To reveal the metabolic fate of acetate in neoplasms that may characterize the accumulation patterns of [1-(11)C]acetate in tumors depicted by positron emission tomography. Four tumor cell lines (LS174T, RPMI2650, A2780, and A375) and fibroblasts in growing and resting states were used. In uptake experiments, cells were incubated with[1-(14)C]acetate for 40 min. [(14)C]CO(2) was measured in the tight-air chamber, and the metabolites in cells were identified by thin layer chromatography and paper chromatography. The glucose metabolic rate of each cell line was measured with [2,6-(3)H]2-deoxy-glucose (DG), and the growth activity of each cell line was estimated by measuring the incorporation of [(3)H]methyl thymidine into DNA. Compared with resting fibroblasts, all four tumor cell lines showed higher accumulation of (14)C activity from [1-(14)C]acetate. These tumor-to-normal ratios of [1-(14)C]acetate were larger than those of DG. Tumor cells incorporated (14)C activity into the lipid-soluble fraction, mostly of phosphatidylcholine and neutral lipids, more prominently than did fibroblasts. The lipid-soluble fraction of (14)C accumulation in cells showed a positive correlation with growth activity, whereas the water-soluble and CO(2) fractions did not. These findings suggest that the high tumor-to-normal ratio of [1-(14)C]acetate is mainly due to the enhanced lipid synthesis, which reflects the high growth activity of neoplasms. This in vitro study suggests that [1-(11)C]acetate is appropriate for estimating the growth activity of tumor cells.

Metabolism of ethanol by rat pancreatic acinar cells

It has been postulated that ethanol-induced pancreatic injury may be mediated by the oxidation of ethanol within the pancreas with secondary toxic metabolic changes, but there is little evidence of pancreatic ethanol oxidation. The aims of this study were to determine whether pancreatic acinar cells metabolize significant amounts of ethanol and, if so, to compare their rate of ethanol oxidation to that of hepatocytes. Cultured rat pancreatic acinar cells and hepatocytes were incubated with 5 to 50 mmol/L carbon 14-labeled ethanol (25 dpm/nmol). Ethanol oxidation was calculated from the production of 14C-labeled acetate that was isolated by Dowex ion-exchange chromatography. Ethanol oxidation by pancreatic acinar cells was demonstrable at all ethanol concentrations tested. At an intoxicating ethanol concentration (50 mmol/L), 14C-labeled acetate production (227+/-20 nmol/10(6) cells/h) approached that of hepatocytes (337+/-61 nmol/10(6) cells/h). Phenanthroline (an inhibitor of classes I through III isoenzymes of alcohol dehydrogenase (ADH)) inhibited pancreatic ethanol oxidation by 90%, but 4-methylpyrazole (a class I and II ADH inhibitor), carbon monoxide (a cytochrome P450 inhibitor), and sodium azide (a catalase inhibitor) had no effect. This study has shown that pancreatic acinar cells oxidize significant amounts of ethanol. At intoxicating concentrations of ethanol, pancreatic acinar cell ethanol oxidation may have the potential to contribute to pancreatic cellular injury. The mechanism appears to involve the class III isoenzyme of ADH.

Carbachol stimulation of triacylglycerol lipase activity in pancreatic acinar cells

Carbachol (CCh) reduced the levels of [3H]arachidonic acid in triacylglycerol (TG) of pancreatic acinar cells. In cells prelabeled with [14C]glycerol, CCh reduced [14C]TG and increased [14C]diacylglycerol levels. Using [3H]triolein as exogenous substrate, CCh enhanced TG lipase activity 3-fold in a particulate fraction derived from intact acinar cells. These results portray a mechanism for generating diacylglycerol and arachidonic acid in exocrine pancreas involving agonist stimulation of TG hydrolysis.

Effects of various ginseng saponins on 5-hydroxytryptamine release and aggregation in human platelets

The effects of various ginseng saponins isolated from red ginseng roots, on aggregation and 5-hydroxytryptamine release (5-HT) human platelets have been investigated. Among the six saponins tested, only ginsenoside Rg1 inhibited adrenaline- and thrombin-induced platelet aggregation and 5-HT release dose-dependently, at concentrations of 5 to 500 micrograms ML-1. Ginsenoside Rg1 had no effect on adrenaline- and thrombin-induced arachidonic acid release and diacylglycerol production. But it did reduce the elevation of cytosolic free calcium concentration (Ca2+)i shown in the second phase induced by adrenaline and thrombin, at concentrations of 10 to 500 micrograms mL-1. Those data suggest that the inhibitory effects of ginsenoside Rg1 on 5-HT release from, and aggregation of, platelets might be due to the reduction of (Ca2+)i elevation at the second phase induced by adrenaline and thrombin. The results suggest that ginsenoside Rg1 in red ginseng roots may be active as a drug in the treatment of artheroscleorosis and thrombosis.

The alpha 1-adrenergic transduction system in hamster brown adipocytes. Release of arachidonic acid accompanies activation of phospholipase C

Previous studies of brown adipocytes identified an increased breakdown of phosphoinositides after selective alpha 1-adrenergic-receptor activation. The present paper reports that this response, elicited with phenylephrine in the presence of propranolol and measured as the accumulation of [3H]inositol phosphates, is accompanied by increased release of [3H]arachidonic acid from cells prelabelled with [3H]arachidonic acid. Differences between stimulated arachidonic acid release and formation of inositol phosphates included a requirement for extracellular Ca2+ for stimulated release of arachidonic acid but not for the formation of inositol phosphates and the preferential inhibition of inositol phosphate formation by phorbol 12-myristate 13-acetate. The release of arachidonic acid in response to phenylephrine was associated with an accumulation of [3H]arachidonic acid-labelled diacylglycerol, and this response was not dependent on extracellular Ca2+ but was partially prevented by treatment with the phorbol ester. The release of arachidonic acid was also stimulated by melittin, which increases the activity of phospholipase A2, by ionophore A23187, by lipolytic stimulation with forskolin and by exogenous phospholipase C. The arachidonic acid response to phospholipase C was completely blocked by RHC 80267, an inhibitor of diacylglycerol lipase, but this inhibitor had no effect on release stimulated with melittin or A23187 and inhibited phenylephrine-stimulated release by only 40%. The arachidonate response to forskolin was additive with the responses to either phenylephrine or exogenous phospholipase C. These data indicate that brown adipocytes are capable of releasing arachidonic acid from neutral lipids via triacylglycerol lipolysis, and from phospholipids via phospholipase A2 or by the sequential activities of phospholipase C and diacylglycerol lipase. Our findings also suggest that the action of phenylephrine to promote the liberation of arachidonic acid utilizes both of these reactions.

The interaction of lithium with thyrotropin-releasing hormone-stimulated lipid metabolism in GH3 pituitary tumour cells. Enhancement of stimulated 1,2-diacylglycerol formation

Treatment of GH3 cells with thyrotropin-releasing hormone (TRH) for periods up to 60 min resulted in a prolonged reduction in the cellular content of phosphatidylinositol (PtdIns) with no lasting change in the levels of the other inositol-containing phospholipids. Accompanying this was a maintained increase in the GH3 cell 1,2-diacylglycerol content and a slower decline in the level of cellular triacylglycerol. When the cells were suspended in lithium-containing balanced salt solution for 30 min (in the absence of exogenous myo-inositol), there was a 15% decrease in GH3 cell inositol levels. This was associated with a small, but significant, increase in the cellular content of phosphatidylinositol 4,5-bisphosphate (PtdIns4,5P2) and 1,2-diacylglycerol. Addition of TRH to cells suspended in lithium-containing medium depleted cellular inositol levels by around 65% within 30 min. By this time, there was also a 50% reduction in the cellular content of PtdIns and a 20% reduction in phosphatidylinositol 4-phosphate (PtdIns4P). Control levels of PtdIns4,5P2 were maintained in the combined presence of TRH and lithium. Under those conditions, TRH no longer depleted cellular triacylglycerol and there was a marked increase in the ability of TRH to elevate the GH3 cell content of 1,2-diacylglycerol. The effect of TRH on the cellular content of phosphatidic acid was not altered by the presence of lithium. The results show, firstly, that when PtdIns resynthesis is inhibited by lithium-induced inositol depletion, its glycerol backbone accumulates, at least in part, in 1,2-diacylglycerol and, secondly, that GH3 cells preserve their cellular levels of PtdIns4,5P2 in the face of a considerable reduction in the cellular content of PtdIns.

Prostaglandin F2 alpha stimulates phosphatidylinositol turnover and increases the cellular content of 1,2-diacylglycerol in confluent resting Swiss 3T3 cells

Prostaglandin F2 alpha (PGF2 alpha); which stimulates DNA synthesis in resting 3T3 cells, also stimulates the incorporation of [32P]PO4 into phosphatidylinositol. The effect is selective for PGF2 alpha when compared with PGE1, PGE2, and PGF2 beta. Epidermal growth factor (EGF) also stimulates DNA synthesis but does not affect phosphatidylinositol turnover. PGE1, which acts synergistically with PGF2 alpha to enhance DNA synthesis, does not affect the ability of PGF2 alpha, to enhance the incorporation of [32P]PO4 into phosphatidylinositol. PGF2 alpha, also causes a small increase in the cellular content of 1,2-diacylglycerol. This effect is not shared by EGF or PGE1. Stimulation of phosphatidylinositol metabolism resulting in an increase in the cellular content of 1,2-diacylglycerol may thus constitute an event in the pathway leading to the initiation of DNA synthesis in which PGF2 alpha differs in its action from EGF.

Role of hexose monophosphate shunt in parathyroid hormone secretion

The metabolism of labeled glucose by collagenase-dispersed bovine parathyroid cells was examined. When the medium calcium ion concentration was increased to 2.0 mM, the rate of 14CO2 release from [1-14C]glucose was increased 169 +/- 45% compared with the rate of 0.5 mM calcium. There was no significant change in the rate of 14CO2 release from [6-14C]glucose by this maneuver. The greatest increase in 14CO2 release and decrease in parathyroid hormone secretion occurred between medium calcium ion concentrations of 0.5-1.5 mM. This difference in the metabolism of glucose represents a true increase in hexose shunt activity because the incorporation of label from either [1-14C]- or [6-14C]glucose into parathyroid tissue lipids was equal. This suggests equilibration of label at the level of triose-phosphates. The increase in hexose shunt activity was not due to a calcium-mediated increase in glucose uptake because calcium changes did not affect 2-[3H]deoxyglucose transport by the cells. Phenazine methosulfate added to cells incubated at 0.5 mM calcium selectively increased hexose shunt activity in a dose-dependent manner (91 +/- 33% overall) and concomitantly inhibited parathyroid hormone secretion 65% overall at 0.5 mM calcium. The compound 6-aminonicotinamide inhibited hexose shunt activity but could not overcome the inhibition of hormone secretion at 2.0 mM calcium. A decrease in protein biosynthesis cannot fully explain the inhibition of hormone secretion by calcium or phenazine methosulfate because [3H]-leucine incorporation into total cell protein was not as affected as secretion.(ABSTRACT TRUNCATED AT 250 WORDS)

Nonoxidative ethanol metabolism: formation of fatty acid ethyl esters by cholesterol esterase

The recent identification of myocardial metabolites of ethanol--fatty acid ethyl esters--suggests that some of the pathophysiological derangements associated with alcohol-induced heart muscle disease may be a consequence of products of myocardial ethanol metabolism. The donor of the fatty acid moiety in the formation of fatty acid ethyl esters has been identified as nonesterified fatty acid. Fatty acid esterification with ethanol is shown to be mediated by cholesterol esterase (sterol-ester acylhydrolase, EC 3.1.1.13), a finding that identifies a singular nonoxidative ethanol metabolism by an enzyme. A potential basis for the protective effect of ethanol ingestion on atherogenesis is also suggested because fatty acid ethyl esters inhibit cholesterol esterification catalyzed by pancreatic cholesterol esterase and hepatic and aortic microsomal fatty acyl-CoA:cholesterol O-acyltransferase (EC 2.3.1.26).

In vitro effects of ethanol and ethanol metabolism in the rat pancreas

1. Ethanol provoked no effect on basal and carbamylcholine-stimulated secretion of amylase from rat pancreatic fragments incubated for 1 h. 2. Ethanol enhanced in vitro synthesis of fatty acids from [1-14C]acetate and from 3H2O by 110 and 166%, respectively. The spectrum of fatty acids labelled with [1-14C]acetate in the presence of ethanol pointed to a stimulation of the malonic acid pathway, whereas the elongation of polyenoic fatty acids was unaltered. The in vitro metabolism of [1-14C]ethanol indicates that ethanol itself contributed carbon atoms to lipogenesis dose-dependently. 3. The conversion of [U-14C]glucose into sn-glycero 3-phosphate and the esterification of fatty acids into phosphatidic acids and triacylglycerols was stimulated whereas net lipolysis was unaffected. The oxidation of [U-14C]-glucose and of [1-14C]acetate to 14CO2 and the beta-oxidation of [1-14C]palmitate was reduced by 24--26%. 4. Maximal effects were produced by a 100--200 mM ethanol concentration and the concentration of ethanol evoking a similar half-maximal alteration of most processes was 20--30 mM. A 10--20 min lag period was required for the full development of these effects. 5. It is concluded that ethanol at low concentration alters the redox state of pancreatic fragments therefore favoring de novo lipogenesis and triacylglycerol formation and depressing glucose uptake and fatty acid oxidation.

Proline oxidase inhibition by free fatty acids of rat pancreas

Proline oxidase activity was not measurable in pancreas homogenate but was measurable in pancreas slices. Moreover, added pancreas homogenate inhibited proline oxidase activity in rat liver mitochondria and several other tissues. The partially purified inhibitor from pancreas also inhibited the activity of glutamate, glucose 6-phosphate, NADH and succinate dehydrogenases. The inhibition was reversed by the addition of bovine serum albumin. Further studies to identify the inhibitor indicated that it consisted of free fatty acids that were enzymatically released after homogenization of pancreas. The free fatty acids released appeared to be derived primarily from triglycerides.

In vitro lipid metabolism in the rat pancreas. III. Effects of carbamylcholine and pancreozymin on the turnover of phosphatidylinositols, 1,2-diacylglycerols and phosphatidylcholines

1. The turnover of phosphatidylinositols and other glycerolipids was examined in rat pancreatic fragments incubated in the presence of carbamylcholine and pancreozymin used at a concentration inducing maximal alpha-amylase hypersecretion. 2. In stimulated tissue, [1-14C]acetate-labeled fatty acids were incorporated into phosphatidylinositols, 1,2-diacylglycerols, and phosphatidic acids in preference to phosphatidylcholines, phosphatidylethanolamines, triacylglycerols, monoacylglycerols, and free fatty acids. Variations in the percent distribution of 14C among fatty acids and in specific activity of individual fatty acids in each lipid class suggested that the secretagogues reduced selection of newly synthesized 1,2-diacylglycerols which occurred in the resting state before their incorporation into phosphatidylinositols. Secretagogues also promoted recycling of endogenous 1,2-diacylglycerols (produced from hydrolysis of unlabeled glycerolipids) for the biosynthesis of phosphatidylinositols. 3. Increased rate of incorporation of [1-14C]palmitate, [1-14C]linoleate, [1-14C]arachidonate and [1(3)(n)-3H]glycerol into phosphatidylinositols was detrimental to phosphatidylcholines. 4. The lipolytic effects of carbamylcholine and pancreozymin as illustrated by the release of 1,2-diacylglycerols and free fatty acids, were markedly inhibited in calcium-free medium enriched with 1 mM EGTA but increased turnover of phosphatidylinositols as determined from incorporation of radioactive precursors was only moderately affected.

In vitro lipid metabolism in the rat pancreas. II. Effects of secretagogues on fatty acid metabolism, net lipolysis and ATP levels

1. The concentration of carbamylcholine, bombesin, pancreozymin, pentagastrin and secretin evoking a similar 4--5-fold maximal increase in amylase secretion from rat pancreatic fragments were 3.10(-6), 10(-7), 10(-8), 3.10(-6), and 3.10(-6) M, respectively. The maximal concentration of vasoactive intestinal peptide tested (3.10(-6) M) increased amylase secretion by 250%. The six secretagogues could be separated into two groups according to their effects on lipid metabolism and ATP levels. 2. When used at their optimal concentrations, carbamylcholine, bombesin, pancreozymin, and pentagastrin lowered pancreatic ATP levels by 18-26% and increased net release of free fatty acids by 68-105%. 3. The effects of 3.10(-6) M carbamylcholine and 10(-8) M pancreozymin on the metabolism of 3H2O, D-[U-14C]glucose and [1-14C]acetate were similar; the incorporation of radioactivity in the fatty acid moiety of glycerolipids decreased by 20--50% whereas the incorporation of 3H from 3H2O and of 14C from [U-14C]glucose increased by 20--35% in the glycerol moiety. In addition, the oxidation of [U-14C]glucose, [1-14C]acetate and [1-14C]palmitate to 14CO2 increased by 15--32% while the esterification of [1-14C]palmitate, [1-14C]-linoleate, and [1-14C]arachidonate was inhibited by 14--23%. The spectrum of fatty acids labeled with [1-14C]acetate indicated an inhibition of the malonic acid pathway whereas the elongation of polyenoic fatty acids was unaltered.