Currently, type II diabetes mellitus, has reached epidemic levels in the world. Moreover, the prediction for the year 2030 is even more alarming. Insulin resistance, characterized by a depressed cellular sensitivity to insulin in insulin-sensitive organs, is a central feature of the metabolic syndrome and a risk factor for type 2 diabetes. Its appearance may precede the diagnosis of true diabetes several years. Insulin resistance results in decreased membrane translocation of GLUT-4, whole the molecular mechanism remains unclear. Currently, there is no simple tool to measure insulin resistance. The gold standard technique remains the hyperinsulinemic euglycemic clamp. However, the complexity and length of this technique render it unsuitable for routine clinical use. Many methods or index have been proposed to assess insulin resistance in human, but none have shown enough relevance to be used in clinical use. Moreover, all these clinical measurements focus on whole-body glucose uptake, however an accurate and convenient procedure for insulin resistance measurement by organ would be interesting. Indeed there are increasingly evidences to insulin resistance as a primary etiologic factor in the development of nonischemic heart failure (HF), another growing public health problem.
Nuclear imaging provides interesting methods to measure insulin resistance using Positron Emission Tomographic (PET) tracer. Two glucose analogs \[18F\]2-fluoro-2-deoxy-D-glucose (FDG) and \[11Cl-30methyl-n-glucose (3-OMG) have been used to evaluate noninvasively the cellular uptake of glucose using PET techniques for several organs like heart, skeletal muscle blood-brain barrier, and liver. \[18F\] 2-fluoro-2-deoxy-D-glucose (FDG), the most commonly used to study glucose metabolism in humans, allows the estimation of glucose transport and its phosphorylation. A number of kinetic modeling approaches have been used for the quantitation of glucose utilization rates using FDG. FDG is transported and phosphorylated as native glucose, but calculation of glucose uptake and metabolism requires the use of correction factors for each process merged into a lumped constant. The major limitation of these approaches is that quantification of glucose metabolism requires the knowledge of the lumped constant, a factor, which relates the kinetic behavior of FDG to naturally occurring glucose in terms of the relative affinity of each molecule for the trans-sarcolemmal transporter and for hexokinase. Unfortunately, the value of the lumped constant in humans under different physiological and pathophysiological conditions varies, and metabolic imaging with PET need standardization of metabolic conditions by hyperinsulinaemic euglycaemic clamp. 3-OMG appears as an ideal glucose analog to probe transmembrane transport. However, due to the short half-life of the 11C (t1/2 = 20 min), this analog can be used only in clinical institutions in close proximity of a cyclotron and which have access to PET devices.
According to these knowledge, the investigators have developed an original compound, \[123I\] 6-deoxy-6-iodo-D-glucose (6DIG), as a tracer of glucose transport equivalent to 3-OMG, the reference tracer. 6-DIG has previously been exploited to measure IR in vivo and the investigators transfer to human this measurement technique, perfectly validated in animal. Previous, they have reported the first use a potential single-photon emission computed tomography (SPECT) tracer to study basal and insulin-stimulated glucose transport non-invasively. In a phase I of development, they use a new nuclear probe using an iodinated tracer of glucose transport for clinical application and specific imaging processing to assess cardiac insulinoresistance in healthy or diabetic subjects. The results in human subjects show that this technique rapidly provides insulinoresistance index (ratio scintigraphy measurement of glucose transport in heart before and after infusion of insulin) in a simple procedure, opening up new opportunities for screening for pre-diabetic patients.
