Glucokinase activation repairs defective bioenergetics of islets of Langerhans isolated from type 2 diabetics

Doliba NM, Qin W, Najafi H, Liu C, Buettger CW, Sotiris J, Collins HW, Li C, Stanley CA, Wilson DF, Grimsby J, Sarabu R, Naji A, Matschinsky FM. Glucokinase activation repairs defective bioenergetics of islets of Langerhans isolated from type 2 diabetics. Am J Physiol Endocrinol Metab 302: E87-E102, 2012. First published September 27, 2011; doi:10.1152/ajpendo.00218.2011.-It was reported previously that isolated human islets from individuals with type 2 diabetes mellitus (T2DM) show reduced glucose-stimulated insulin release. To assess the possibility that impaired bioenergetics may contribute to this defect, glucose-stimulated respiration ((V) over dotO(2)), glucose usage and oxidation, intracellular Ca2+, and insulin secretion (IS) were measured in pancreatic islets isolated from three healthy and three type 2 diabetic organ donors. Isolated mouse and rat islets were studied for comparison. Islets were exposed to a "staircase" glucose stimulus, whereas IR and (V) over dotO(2) were measured. (V) over dotO(2) of human islets from normals and diabetics increased sigmoidally from equal baselines of 0.25 nmol/100 islets/min as a function of glucose concentration. Maximal (V) over dotO(2) of normal islets at 24 mM glucose was 0.40 +/- 0.02 nmol.min(-1).100 islets(-1), and the glucose S-0.5 was 4.39 +/- 0.10 mM. The glucose stimulation of respiration of islets from diabetics was lower, V-max of 0.32 +/- 0.01 nmol.min(-1).100 islets(-1), and the S-0.5 shifted to 5.43 +/- 0.13 mM. Glucose-stimulated IS and the rise of intracellular Ca2+ were also reduced in diabetic islets. A clinically effective glucokinase activator normalized the defective (V) over dotO(2), IR, and free calcium responses during glucose stimulation in islets from type 2 diabetics. The body of data shows that there is a clear relationship between the pancreatic islet energy (ATP) production rate and IS. This relationship was similar for normal human, mouse, and rat islets and the data for all species fitted a single sigmoidal curve. The shared threshold rate for IS was similar to 13 pmol.min(-1).islet(-1). Exendin-4, a GLP-1 analog, shifted the ATP production-IS curve to the left and greatly potentiated IS with an ATP production rate threshold of similar to 10 pmol.min(-1).islet(-1). Our data suggest that impaired beta-cell bioenergetics resulting in greatly reduced ATP production is critical in the molecular pathogenesis of type 2 diabetes mellitus.