A Specific Inhibitor of Cytosolic Phospholipase A2Activity, AACOCF3, Inhibits Glucose-Induced Insulin Secretion from Isolated Rat Islets

Loweth, Anne C.; Scarpello, J. H. B.; Morgan, Noel G.

doi:10.1006/bbrc.1996.0075

Cited by 32 publications

(16 citation statements)

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“…Thus, application of PLA 2 inhibitors to inhibit endogenous arachidonic acid generation significantly decreased the amplitude of the insulin secretory response to 20 mmol/l glucose. A similar inhibitory effect of AACOCF 3 on glucose-stimulated insulin secretion from rat islets has been reported previously (34), and these data are consistent with a stimulatory role for arachidonic acid or an arachidonic acid metabolite(s) in nutrient-regulated insulin secretion. The trifluoro methyl ketone arachidonic acid derivatives used in this study also stimulated basal insulin secretion from human islets.…”

Section: Discussionsupporting

confidence: 90%

The Role of Arachidonic Acid and Its Metabolites in Insulin Secretion From Human Islets of Langerhans

et al. 2007

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The roles played by arachidonic acid and its cyclooxygenase (COX)-generated and lipoxygenase (LOX)-generated metabolites have been studied using rodent islets and insulin-secreting cell lines, but very little is known about COX and LOX isoform expression and the effects of modulation of arachidonic acid generation and metabolism in human islets. We have used RT-PCR to identify mRNAs for cytosolic phospholipase A 2 (cPLA 2 ), COX-1, COX-2, 5-LOX, and 12-LOX in isolated human islets. COX-3 and 15-LOX were not expressed by human islets. Perifusion experiments with human islets indicated that PLA 2 inhibition inhibited glucose-stimulated insulin secretion, whereas inhibitors of COX-2 and 12-LOX enzymes enhanced basal insulin secretion and also secretory responses induced by 20 mmol/l glucose or by 50 mol/l arachidonic acid. Inhibition of COX-1 with 100 mol/l acetaminophen did not significantly affect glucose-stimulated insulin secretion. These data indicate that the stimulation of insulin secretion from human islets in response to arachidonic acid does not require its metabolism through COX-2 and 5-/12-LOX pathways. The products of COX-2 and LOX activities have been implicated in cytokine-mediated damage of ␤-cells, so selective inhibitors of these enzymes would be expected to have a dual protective role in diabetes: they would minimize ␤-cell dysfunction while maintaining insulin secretion through enhancing endogenous arachidonic acid levels. Diabetes 56:197-203, 2007 P hospholipases A 2 (PLA 2 ) constitute a large family of enzymes that hydrolyze the sn-2 position of membrane phospholipids to generate arachidonic acid. Secretory type I (1) and type II (1,2) PLA 2 enzymes have been identified in islets, as have the Ca 2ϩ -dependent type IV cytosolic PLA 2 (cPLA 2 ) (1-3) and the Ca 2ϩ -independent type VI isozymes (4), and it is well-established that insulin secretion from pancreatic ␤-cells is stimulated by arachidonic acid (5-7). Although arachidonic acid is known to exert direct functional effects in vitro, it is also further metabolized by cyclooxygenase (COX) enzymes to produce prostaglandins (rev. in 8) and lipoxygenases (LOX) to produce hydroxyeicosatetraenoic acids (HETEs) and leukotrienes (rev. in 9). Two COX genes have been cloned: the COX-1 gene codes for COX-1 and the COX-3 splice variant (10), and the COX-2 gene codes for the COX-2 isoform. Depending on the oxygenation site in arachidonic acid, the LOX enzymes are termed 5-, 12-, and 15-LOX.The roles played by COX and LOX enzymes in ␤-cells have not been fully established, but there is good evidence that both COX-2 (11-14) and 12-LOX (15,16) play roles in cytokine-mediated damage of ␤-cells. Furthermore, signaling through the 12-LOX pathway is reported to upregulate COX-2 gene expression (17).Although there are some contradictory reports about the effects of COX and LOX products on insulin secretion, the consensus view is that prostaglandins (particularly prostaglandin E 2 [PGE 2 ]) have inhibitory effects, whereas HETEs and leukotrienes are stimulator...

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Section: Discussionsupporting

confidence: 90%

The Role of Arachidonic Acid and Its Metabolites in Insulin Secretion From Human Islets of Langerhans

et al. 2007

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“…When islets were incubated for 4 h in 100 mol/l fatty acid-free BSA in the presence and absence of 50 mol/l AACOCF3, a specific inhibitor of phospholipase A 2 (23), no inhibition of the biphasic response to 16.7 mmol/l glucose was seen. When 100 nmol/l wortmannin was used there was no inhibition of glucosestimulated insulin secretion under control (10 mol/l fatty acid-free BSA) or augmented (100 mol/l fatty acid-free BSA) conditions.…”

Section: Resultsmentioning

confidence: 97%

Massive Augmentation of Stimulated Insulin Secretion Induced by Fatty Acid–Free BSA in Rat Pancreatic Islets

Straub

Sharp

2004

Diabetes

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Incubation of rat pancreatic islets for 4 -6 h with 100 mol/l fatty acid-free BSA induced a 3-to 10-fold enhancement of insulin release to a subsequent challenge with 16.7 mmol/l glucose, without changing the typical biphasic pattern of the response. A similar enhancement was observed with other stimuli, such as leucine, depolarizing concentrations of KCl and tolbutamide, pointing to a general phenomenon and common mechanism for the augmentation. Norepinephrine completely blocked the stimulated response. The protein kinase C (PKC) inhibitor Ro 31-8220, which acts at the ATP-binding site and inhibits all PKC isoforms, strongly inhibited the enhancement of a subsequent glucose challenge when present during the BSA pretreatment period. In contrast, Go 6976, an inhibitor of conventional PKC isoforms, was without effect, even at the high concentration of 1 mol/l. Preincubation with calphostin C, which competes for the diacylglycerol (DAG)-binding site, therefore inhibiting conventional, novel, and PKC isoforms of the PKD type, completely abolished the enhancing effect of the BSA but did not affect secretion in islets treated with 10 mol/l fatty acid-free BSA. We conclude that the remarkable enhancement of insulin release is due to a change in glucose signaling and activation of a novel PKC isoform or a DAG-binding protein.

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“…A series of signals that result from glucose-induced ATP production and alterations of intracellular redox potentials trigger insulin secretion via a rise in cytosolic [Ca 2ϩ ], and Ca 2ϩ /calmodulin-dependent protein kinase II (CaMKII) is an important ␤-cell [Ca 2ϩ ] sensor and mediator of Ca 2ϩ -dependent events in insulin secretion (6 -11). Much evidence (12)(13)(14)(15)(16)(17)(18)(19)(20)(21)(22) suggests that iPLA 2 ␤ also participates in insulin secretion, including the facts that the mechanism-based bromoenol lactone (BEL) inhibitor of iPLA 2 ␤ suppresses glucose-induced hydrolysis of arachidonate from islet membrane phospholipids, the rise in ␤-cell cytosolic [Ca 2ϩ ], and insulin secretion (19 -22).…”

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confidence: 99%

Group VIA Phospholipase A2 Forms a Signaling Complex with the Calcium/Calmodulin-dependent Protein Kinase IIβ Expressed in Pancreatic Islet β-Cells

Wang

Ramanadham

Alex

et al. 2005

Journal of Biological Chemistry

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Insulin-secreting pancreatic islet ␤-cells express a Group VIA Ca 2؉ -independent phospholipase A 2 (iPLA 2 ␤) that contains a calmodulin binding site and protein interaction domains. We identified Ca 2؉ /calmodulindependent protein kinase II␤ (CaMKII␤) as a potential iPLA 2 ␤-interacting protein by yeast two-hybrid screening of a cDNA library using iPLA 2 ␤ cDNA as bait. Cloning CaMKII␤ cDNA from a rat islet library revealed that one dominant CaMKII␤ isoform mRNA is expressed by adult islets and is not observed in brain or neonatal islets and that there is high conservation of the isoform expressed by rat and human ␤-cells. Binary two-hybrid assays using DNA encoding this isoform as bait and iPLA 2 ␤ DNA as prey confirmed interaction of the enzymes, as did assays with CaMKII␤ as prey and iPLA 2 ␤ bait. His-tagged CaMKII␤ immobilized on metal affinity matrices bound iPLA 2 ␤, and this did not require exogenous calmodulin and was not prevented by a calmodulin antagonist or the Ca 2؉ chelator EGTA. Activities of both enzymes increased upon their association, and iPLA 2 ␤ reaction products reduced CaMKII␤ activity. Both the iPLA 2 ␤ inhibitor bromoenol lactone and the CaMKII␤ inhibitor KN93 reduced arachidonate release from INS-1 insulinoma cells, and both inhibit insulin secretion. CaMKII␤ and iPLA 2 ␤ can be coimmunoprecipitated from INS-1 cells, and forskolin, which amplifies glucose-induced insulin secretion, increases the abundance of the immunoprecipitatable complex. These findings suggest that iPLA 2 ␤ and CaMKII␤ form a signaling complex in ␤-cells, consistent with reports that both enzymes participate in insulin secretion and that their expression is coinduced upon differentiation of pancreatic progenitor to endocrine progenitor cells.Phospholipases A 2 (PLA 2 ) 1 are a diverse group of enzymes that catalyze hydrolysis of sn-2 fatty acid substituents from glycerophospholipid substrates to yield a free fatty acid and a 2-lysophospholipid (1). The Group VIA PLA 2 designated iPLA 2 ␤ has a molecular mass of 84 -88 kDa and does not require Ca 2ϩ for catalysis (2). Various splice variants of iPLA 2 ␤ are expressed at high levels in testis (3), brain (4), and pancreatic islet ␤-cells (5), among other tissues.Certain nutrients, hormones, neurotransmitters, and pharmacologic agents stimulate insulin secretion from ␤-cells, and the dominant physiologic insulin secretagogue is D-glucose. A series of signals that result from glucose-induced ATP production and alterations of intracellular redox potentials trigger insulin secretion via a rise in cytosolic [Ca 2ϩ ], and Ca 2ϩ /calmodulin-dependent protein kinase II (CaMKII) is an important ␤-cell [Ca 2ϩ ] sensor and mediator of Ca 2ϩ -dependent events in insulin secretion (6 -11). Much evidence (12-22) suggests that iPLA 2 ␤ also participates in insulin secretion, including the facts that the mechanism-based bromoenol lactone (BEL) inhibitor of iPLA 2 ␤ suppresses glucose-induced hydrolysis of arachidonate from islet membrane phospholipids, the rise in ␤-cell cytosolic...

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A Specific Inhibitor of Cytosolic Phospholipase A2Activity, AACOCF3, Inhibits Glucose-Induced Insulin Secretion from Isolated Rat Islets

Cited by 32 publications

References 0 publications

The Role of Arachidonic Acid and Its Metabolites in Insulin Secretion From Human Islets of Langerhans

The Role of Arachidonic Acid and Its Metabolites in Insulin Secretion From Human Islets of Langerhans

Massive Augmentation of Stimulated Insulin Secretion Induced by Fatty Acid–Free BSA in Rat Pancreatic Islets

Group VIA Phospholipase A2 Forms a Signaling Complex with the Calcium/Calmodulin-dependent Protein Kinase IIβ Expressed in Pancreatic Islet β-Cells

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