Endocrine Abstracts

Background: Cyclo-oxygenase-2 (COX-2), the enzyme responsible for converting arachidonic acid to prostanoids such as PGE₂, has been reported to play an anti-apoptotic role in invasive breast cancers. We have now examined whether COX-2 and PGE₂ protect against apoptosis in the MIN6 insulin-secreting cell line.

Methods: Serum-deprived MIN6 cells were exposed to an inhibitor of COX-2 (NS-398) and/or PGE₂ for 48 hours and the degree of apoptosis was assessed by measuring increases in caspase 3 activity. COX-2 mRNA levels were measured by quantitative Lightcycler RT-PCR.

Results: Glucose caused a concentration-dependent inhibition of MIN6 cell apoptosis (caspase activity, OD₄₀₅: glucose, 2.5mM: 178.3 plus/minus 13.0; 11mM: 96.7 plus/minus 2.9; 17mM: 76.0 plus/minus 1.0; 25mM: 68.0 plus/minus 2.6, n=3, P<0.001) and COX-2 mRNA levels were increased 3-fold by incubation for 48 hours at 25mM glucose (copies COX-2/100,000 copies beta-actin: glucose, 2.5mM: 2,400 plus/minus 91; 25mM: 7,288 plus/minus 459, n=3, P<0.01). NS-398 (10 microM) increased apoptosis by (22-32%) at all glucose concentrations and higher concentrations of NS-398 produced larger increases in apoptosis (% increase in apoptosis by 100 microM NS-398: glucose, 2.5mM: 208 plus/minus 17; 17mM 253 plus/minus 15, n=3, P<0.01 vs absence of NS-398). The increased apoptosis at high concentrations of NS-398 was reversed by exogenous PGE₂ (caspase activity, OD₄₀₅: 2.5mM glucose + 50 microM NS-398: 172.7 plus/minus 41.9; plus PGE₂, 0.2 microM:153.7 plus/minus 15.2; 1 microM: 119.3 plus/minus 18.7; 5 microM: 110.3 plus/minus 21.2; 2.5mM glucose: 97.7 plus/minus 14.6, n=3). PGE₂ alone (1 microM) decreased apoptosis by 26% at both 2.5 and 11mM glucose (P<0.05), but did not further protect against apoptosis at 25mM glucose.

Conclusion: These data indicate that glucose exerts anti-apoptotic effects in MIN6 cells and, in parallel, it elevates COX-2 levels. However, although COX-2 protects against MIN6 cell apoptosis, most likely through the generation of PGE₂, the anti-apoptotic effects of glucose are not solely a result of elevations in COX-2 since glucose still exerted anti-apoptotic effects in the presence of the COX-2 inhibitor NS-398.