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Mechanisms involved in the cytotoxic and cytoprotective actions of saturated versus monounsaturated long-chain fatty acids in pancreatic beta-cells.

Diakogiannaki E, Dhayal S, Childs CE, Calder PC, Welters HJ, Morgan NG - J. Endocrinol. (2007)

Bottom Line: It has been proposed that alterations in neutral lipid synthesis (particularly triacylglycerol (TAG) formation) might mediate the differential responses to saturated and unsaturated fatty acids and we have examined this proposition.By contrast, methyl-palmitoleate failed to influence TAG levels (0.25 mM methyl-palmitoleate alone: 0.95 +/- 0.06 nmol TAG/10(6) cells; methyl-palmitoleate plus palmitate: 1.5 +/- 0.05) or its fatty acid composition in beta-cells exposed to palmitate.The results suggest that monounsaturated fatty acids can promote cell viability and mitogenesis by a mechanism that does not require their metabolism and is independent of alterations in TAG formation.

View Article: PubMed Central - PubMed

Affiliation: Institute of Biomedical and Clinical Sciences, Peninsula Medical School, John Bull Building, Plymouth, Devon, UK.

ABSTRACT
Long-chain saturated and monounsaturated fatty acids differ in their propensity to induce beta-cell death in vitro with palmitate (C16:0) being cytotoxic, whereas palmitoleate (C16:1n-7) is cytoprotective. We now show that this cytoprotective capacity extends to a poorly metabolised C16:1n-7 derivative, methyl-palmitoleate (0.25 mM palmitate alone: 92 +/- 4% death after 18 h; palmitate plus 0.25 mM methyl-palmitoleate: 12 +/- 2%; P < 0.001). Palmitoleate and its methylated derivative also acted as mitogens in cultured beta-cells (5-bromo-2-deoxyuridine incorporation - control: 0.15 +/- 0.01 units; 0.25 mM palmitoleate: 0.22 +/- 0.01 units; P < 0.05). It has been proposed that alterations in neutral lipid synthesis (particularly triacylglycerol (TAG) formation) might mediate the differential responses to saturated and unsaturated fatty acids and we have examined this proposition. Palmitate and palmitoleate both promoted beta-cell phospholipid remodelling and increased TAG formation (control: 0.9 +/- 0.1 nmol TAG/10(6) cells; 0.25 mM palmitate: 1.55 +/- 0.07; 0.25 mM palmitoleate: 1.4 +/- 0.05; palmitate plus palmitoleate: 2.3 +/- 0.1). By contrast, methyl-palmitoleate failed to influence TAG levels (0.25 mM methyl-palmitoleate alone: 0.95 +/- 0.06 nmol TAG/10(6) cells; methyl-palmitoleate plus palmitate: 1.5 +/- 0.05) or its fatty acid composition in beta-cells exposed to palmitate. The results suggest that monounsaturated fatty acids can promote cell viability and mitogenesis by a mechanism that does not require their metabolism and is independent of alterations in TAG formation.

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Dose-dependent inhibition of palmitate-induced β-cell death by palmitoleate and methyl-palmitoleate. BRIN-BD11 cells were incubated with increasing concentrations of palmitoleate (squares) or methyl-palmitoleate (circles) in the presence of 0·25 mM palmitate for 18 h. The extent of cell death was estimated after staining with trypan blue. Significant inhibition (P<0·05) of palmitate-induced cytotoxicity was achieved with concentrations of 0·025 mM or greater for both palmitoleate and methyl-palmitoleate.
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fig8: Dose-dependent inhibition of palmitate-induced β-cell death by palmitoleate and methyl-palmitoleate. BRIN-BD11 cells were incubated with increasing concentrations of palmitoleate (squares) or methyl-palmitoleate (circles) in the presence of 0·25 mM palmitate for 18 h. The extent of cell death was estimated after staining with trypan blue. Significant inhibition (P<0·05) of palmitate-induced cytotoxicity was achieved with concentrations of 0·025 mM or greater for both palmitoleate and methyl-palmitoleate.

Mentions: Next, methyl-palmitoleate, an analogue of palmitoleate that cannot be esterified to Co-enzyme A, was employed. As expected, exposure of cells to methyl-palmitoleate alone, failed to influence their TAG content (Fig. 7a). More significantly, the co-presence of this fatty acid failed to alter the TAG content of palmitate-treated cells, suggesting that it did not alter the metabolic routing of palmitate into TAG (Fig. 7a). To confirm this result, additional studies were conducted in which the fatty acid composition of BRIN-BD11 cell TAG was analysed after incubation of cells with palmitate and methyl-palmitoleate. As predicted, the increased incorporation of palmitate into TAG seen under these conditions was not attenuated by the presence of methyl-palmitoleate (control cells: 1·77±0·04 μg palmitate in TAG/106 cells; 0·25 mM palmitate alone: 2·57±0·28 μg (P<0·01); 0·25 mM methyl-palmitoleate alone: 1·02±0·14 μg; palmitate plus methyl-palmitoleate: 2·39±0·11 μg (not significantly different from palmitate alone)). Despite this, methyl-palmitoleate abolished the cytotoxicity induced by palmitate as revealed by cell viability assays (Fig. 7b). Indeed, its protective actions were equipotent with palmitoleate (Fig. 8) and, like palmitoleate, it also promoted β-cell growth following co-incubation with palmitate (not presented). Thus, the cytoprotective and growth-promoting properties of methyl-palmitoleate and palmitoleate were equivalent even though these fatty acids exerted differential effects on the TAG content of palmitate-treated cells.


Mechanisms involved in the cytotoxic and cytoprotective actions of saturated versus monounsaturated long-chain fatty acids in pancreatic beta-cells.

Diakogiannaki E, Dhayal S, Childs CE, Calder PC, Welters HJ, Morgan NG - J. Endocrinol. (2007)

Dose-dependent inhibition of palmitate-induced β-cell death by palmitoleate and methyl-palmitoleate. BRIN-BD11 cells were incubated with increasing concentrations of palmitoleate (squares) or methyl-palmitoleate (circles) in the presence of 0·25 mM palmitate for 18 h. The extent of cell death was estimated after staining with trypan blue. Significant inhibition (P<0·05) of palmitate-induced cytotoxicity was achieved with concentrations of 0·025 mM or greater for both palmitoleate and methyl-palmitoleate.
© Copyright Policy - open-access
Related In: Results  -  Collection

License
Show All Figures
getmorefigures.php?uid=PMC1994570&req=5

fig8: Dose-dependent inhibition of palmitate-induced β-cell death by palmitoleate and methyl-palmitoleate. BRIN-BD11 cells were incubated with increasing concentrations of palmitoleate (squares) or methyl-palmitoleate (circles) in the presence of 0·25 mM palmitate for 18 h. The extent of cell death was estimated after staining with trypan blue. Significant inhibition (P<0·05) of palmitate-induced cytotoxicity was achieved with concentrations of 0·025 mM or greater for both palmitoleate and methyl-palmitoleate.
Mentions: Next, methyl-palmitoleate, an analogue of palmitoleate that cannot be esterified to Co-enzyme A, was employed. As expected, exposure of cells to methyl-palmitoleate alone, failed to influence their TAG content (Fig. 7a). More significantly, the co-presence of this fatty acid failed to alter the TAG content of palmitate-treated cells, suggesting that it did not alter the metabolic routing of palmitate into TAG (Fig. 7a). To confirm this result, additional studies were conducted in which the fatty acid composition of BRIN-BD11 cell TAG was analysed after incubation of cells with palmitate and methyl-palmitoleate. As predicted, the increased incorporation of palmitate into TAG seen under these conditions was not attenuated by the presence of methyl-palmitoleate (control cells: 1·77±0·04 μg palmitate in TAG/106 cells; 0·25 mM palmitate alone: 2·57±0·28 μg (P<0·01); 0·25 mM methyl-palmitoleate alone: 1·02±0·14 μg; palmitate plus methyl-palmitoleate: 2·39±0·11 μg (not significantly different from palmitate alone)). Despite this, methyl-palmitoleate abolished the cytotoxicity induced by palmitate as revealed by cell viability assays (Fig. 7b). Indeed, its protective actions were equipotent with palmitoleate (Fig. 8) and, like palmitoleate, it also promoted β-cell growth following co-incubation with palmitate (not presented). Thus, the cytoprotective and growth-promoting properties of methyl-palmitoleate and palmitoleate were equivalent even though these fatty acids exerted differential effects on the TAG content of palmitate-treated cells.

Bottom Line: It has been proposed that alterations in neutral lipid synthesis (particularly triacylglycerol (TAG) formation) might mediate the differential responses to saturated and unsaturated fatty acids and we have examined this proposition.By contrast, methyl-palmitoleate failed to influence TAG levels (0.25 mM methyl-palmitoleate alone: 0.95 +/- 0.06 nmol TAG/10(6) cells; methyl-palmitoleate plus palmitate: 1.5 +/- 0.05) or its fatty acid composition in beta-cells exposed to palmitate.The results suggest that monounsaturated fatty acids can promote cell viability and mitogenesis by a mechanism that does not require their metabolism and is independent of alterations in TAG formation.

View Article: PubMed Central - PubMed

Affiliation: Institute of Biomedical and Clinical Sciences, Peninsula Medical School, John Bull Building, Plymouth, Devon, UK.

ABSTRACT
Long-chain saturated and monounsaturated fatty acids differ in their propensity to induce beta-cell death in vitro with palmitate (C16:0) being cytotoxic, whereas palmitoleate (C16:1n-7) is cytoprotective. We now show that this cytoprotective capacity extends to a poorly metabolised C16:1n-7 derivative, methyl-palmitoleate (0.25 mM palmitate alone: 92 +/- 4% death after 18 h; palmitate plus 0.25 mM methyl-palmitoleate: 12 +/- 2%; P < 0.001). Palmitoleate and its methylated derivative also acted as mitogens in cultured beta-cells (5-bromo-2-deoxyuridine incorporation - control: 0.15 +/- 0.01 units; 0.25 mM palmitoleate: 0.22 +/- 0.01 units; P < 0.05). It has been proposed that alterations in neutral lipid synthesis (particularly triacylglycerol (TAG) formation) might mediate the differential responses to saturated and unsaturated fatty acids and we have examined this proposition. Palmitate and palmitoleate both promoted beta-cell phospholipid remodelling and increased TAG formation (control: 0.9 +/- 0.1 nmol TAG/10(6) cells; 0.25 mM palmitate: 1.55 +/- 0.07; 0.25 mM palmitoleate: 1.4 +/- 0.05; palmitate plus palmitoleate: 2.3 +/- 0.1). By contrast, methyl-palmitoleate failed to influence TAG levels (0.25 mM methyl-palmitoleate alone: 0.95 +/- 0.06 nmol TAG/10(6) cells; methyl-palmitoleate plus palmitate: 1.5 +/- 0.05) or its fatty acid composition in beta-cells exposed to palmitate. The results suggest that monounsaturated fatty acids can promote cell viability and mitogenesis by a mechanism that does not require their metabolism and is independent of alterations in TAG formation.

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