OBJECTIVE-Insulin secretion involves complex events in which the mitochondria play a pivotal role in the generation of signals that couple glucose detection to insulin secretion. Studies on the mitochondrial generation of reactive oxygen species (ROS) generally focus on chronic nutrient exposure. Here, we investigate whether transient mitochondrial ROS production linked to glucose-induced increased respiration might act as a signal for monitoring insulin secretion.RESEARCH DESIGN AND METHODS-ROS production in response to glucose was investigated in freshly isolated rat islets. ROS effects were studied using a pharmacological approach and calcium imaging.RESULTS-Transient glucose increase from 5.5 to 16.7 mmol/l stimulated ROS generation, which was reversed by antioxidants. Insulin secretion was dose dependently blunted by antioxidants and highly correlated with ROS levels. The incapacity of ␤-cells to secrete insulin in response to glucose with antioxidants was associated with a decrease in ROS production and in contrast to the maintenance of high levels of ATP and NADH. Then, we investigated the mitochondrial origin of ROS (mROS) as the triggering signal. Insulin release was mimicked by the mitochondrial-complex blockers, antimycin and rotenone, that generate mROS. The adding of antioxidants to mitochondrial blockers or to glucose was used to lower mROS reversed insulin secretion. Finally, calcium imaging on perifused islets using glucose stimulation or mitochondrial blockers revealed that calcium mobilization was completely reversed using the antioxidant trolox and that it was of extracellular origin. No toxic effects were present using these pharmacological approaches. CONCLUSIONS-Altogether, these complementary results demonstrate that mROS production is a necessary stimulus for glucose-induced insulin secretion. Diabetes 58:673-681, 2009 E lucidating the mechanisms by which pancreatic ␤-cells couple glucose sensing to insulin secretion, a vital process in energy homeostasis, is of prime importance. Although ATP production is considered the main mitochondrial signal, detailed studies show that insulin secretion cannot be restricted to ATP synthesis, and numerous experimental clues show that additional mitochondrial factors involved in glucose-secretion coupling are necessary, although not yet identified (1).Transient increases in glucose metabolism generate NADH and FADH 2 , leading rapidly to increased superoxide anion (O 2 ⅐ ) production; obligatorily associated with the respiratory chain function, superoxide anion will be converted into H 2 O 2 (2). This production of mitochondrial reactive oxygen species (mROS)-transient because H 2 O 2 -inactivating enzymes rapidly quench it before a damage to the physiological conditions of the cell occurs-is now recognized as an intracellular messenger (3,4). These features make mROS a good candidate for rapidly regulating pathways that depend directly on metabolic fluxes. Based on such a view, we recently demonstrated that mROS production is required for hypothalamic...

Goto-Kakizaki (GK) rats are a well characterized model for non-insulin dependent diabetes mellitus (NIDDM). We have used a combination of physiological and genetic studies to identify quantitative trait loci (QTLs) responsible for the control of glucose homeostasis and insulin secretion in a F2 cohort bred from spontaneously diabetic GK rats. The genetic dissection of NIDDM allowed us to map up to six independently segregating loci predisposing to hyperglycaemia, glucose intolerance or altered insulin secretion, and a seventh locus implicated in body weight. QTLs implicated in glucose tolerance and adiposity map to the same region of rat chromosome 1, and may indicate the influence of a single locus. Our study demonstrates that distinct combinations of genetic loci are responsible for different physiological characteristics associated with the diabetic phenotype in the GK rat, and it constitutes an important step for directing the search for the genetic factors involved in human NIDDM.

Plasma metabolite concentrations reflect the activity of tissue metabolic pathways and their quantitative determination may be informative about pathogenic conditions. We searched for plasma lipid species whose concentrations correlate with various parameters of glucose homeostasis and susceptibility to type 2 diabetes (T2D). Shotgun lipidomic analysis of the plasma of mice from different genetic backgrounds, which develop a pre-diabetic state at different rates when metabolically stressed, led to the identification of a group of sphingolipids correlated with glucose tolerance and insulin secretion. Quantitative analysis of these and closely related lipids in the plasma of individuals from two population-based prospective cohorts revealed that specific long-chain fatty-acid-containing dihydroceramides were significantly elevated in the plasma of individuals who will progress to diabetes up to 9 years before disease onset. These lipids may serve as early biomarkers of, and help identify, metabolic deregulation in the pathogenesis of T2D.

We investigated the specific and associated effects of insulin and glucose on beta-cell growth and function in adult rats. By combining simultaneous infusion either of glucose and/or insulin or glucose and diazoxide, three groups of rats were constituted: hyperglycemic-hyperinsulinemic rats (high glucose-high insulin), hyperglycemic-euinsulinemic rats (high glucose), and euglycemic-hyperinsulinemic rats (high insulin). All the infusions lasted 48 h. Control rats were infused with 0.9% NaCl (saline controls). In all groups, beta-cell mass was significantly increased, compared with controls (by 70% in high glucose-high insulin rats, 65% in high glucose rats, and 50% in high insulin rats). The stimulation of neogenesis was suggested by the high number of islets budding from pancreatic ducts in high glucose-high insulin and high glucose rats and by the presence of numerous clusters of few beta-cells within the exocrine pancreas in high insulin rats. beta-Cell hypertrophy was observed only in high glucose-high insulin rats. The rate of beta-cell proliferation was similar to that of controls in high glucose-high insulin rats after a 48-h glucose infusion, dropped dramatically in high insulin rats, and dropped to a lesser extent in high glucose rats. In high glucose-high insulin and high glucose rats, beta-cell mass increase was related to a higher beta-cell responsiveness to glucose in vitro as measured by islet perifusion studies, whereas in high insulin rats, no significant enhancement of glucose induced insulin secretion could be noticed. The data show that glucose and insulin may have specific stimulating effects on beta-cell growth and function in vivo in adult rats independently of the influence they exert each other on their respective plasma concentration.