Metabolism of D-[1,2-13C]glucose and alpha-D-[1,2-13C]glucose pentaacetate in tumoral pancreatic islet cells

Tumoral pancreatic islet cells of the RINm5F line were incubated, in groups of 25x106 cells each, for 120 min at 37 degrees C in media (5. 0 ml) containing either alpha-D-1,2-13C]glucose pentaacetate (1.7 mM) or both D-1,2-13C]glucose (1.7 mM) and acetate (8.5 mM). In both cases, the amounts of 13C-enriched metabolites (D-glucose, L-lactate and acetate) and non-enriched metabolites (acetate) recovered in the incubation medium after incubation were close to the initial amount of esterified or non-esterified D-1, 2-13C]glucose and acetate, respectively. The 13C-enriched metabolites corresponded mainly to double-labelled D-1, 2-13C]glucose, L-2,3-13C]lactate and 1,2-13C]acetate. The output of L-2,3-13C]lactate and 1,2-13C]acetate was about 3-4 times lower in the cells exposed to alpha-D-1,2-13C]glucose pentaacetate than in those incubated with unesterified D-1,2-13C]glucose. These findings indicate that, despite extensive hydrolysis of alpha-D-1, 2-13C]glucose pentaacetate in the RINm5F cells, the hexose moiety of the ester is less efficiently metabolized than unesterified D-1, 2-13C]glucose tested at the same molar concentration (1.7 mM) in the presence of 8.5 mM acetate. Thus, a higher utilization of the hexose moiety of alpha-D-glucose pentaacetate than that of unesterified D-glucose, as previously documented in isolated pancreatic islets, represents a far-from-universal situation.