The prevalence of diabetes mellitus has grown to staggering numbers, and its incidence is expected to rise in the next 2 decades. The need for novel approaches to treat hyperglycemia cannot be ignored. Current agents have been shown to modestly improve glycemia and in some cases prevent complications of diabetes, but they become less effective over time and are often accompanied by undesirable adverse effects. Dapagliflozin is the lead agent in a new class of oral antidiabetic agents known as sodium-glucose cotransporter type 2 (SGLT2) inhibitors, which represent a novel approach to the management of type 2 diabetes mellitus. By selectively and reversibly blocking the SGLT2 receptor, dapagliflozin prevents the reabsorption of glucose at the renal proximal tubule. Phase II and III clinical trials have demonstrated that dapagliflozin is a safe and effective method for treating type 2 diabetes. Dapagliflozin produces a sustained, dose-dependent reduction in plasma glucose levels while simultaneously improving insulin secretion and sensitivity. Over 12-24 weeks, reductions in hemoglobin A(1c) ranged from 0.54-0.89% when dapagliflozin was administered once/day (either as monotherapy or add-on therapy to oral antidiabetic drugs with or without insulin) to patients with type 2 diabetes. Therapy with dapagliflozin also results in a mild osmotic-diuretic effect that may account for decreases in total body weight (~2-3 kg) and blood pressure (systolic 2-5 mm Hg, diastolic 1.5-3 mm Hg), and increases in hematocrit (1-2%). Dapagliflozin has a favorable safety profile, with the rates of hypoglycemia similar to those of placebo. Genital and urinary tract infections were more commonly reported in patients taking dapagliflozin (2-13%) than those taking placebo (0-8%). Dapagliflozin does not appear to cause electrolyte disturbances, hepatotoxicity, or nephrotoxicity. Results from clinical trials have been promising, and well-designed clinical programs that address the long-term safety and efficacy of dapagliflozin are under way.

Compared with the sc depot, omental (om) adipose tissue is relatively resistant to the metabolic actions of insulin. Protein-tyrosine phosphatases (PTPases) modulate receptor kinase activation and signal transduction in insulin-sensitive tissues, and their activity is dependent on the reduced state of the cysteine thiol required for catalysis. Using a novel anaerobic technique to avoid air oxidation, we found that the mean endogenous PTPase activity was 2.1-fold higher in om compared with paired samples of sc adipose tissue (P < 0.003). The specific activity of PTP1B isolated under anaerobic conditions was also 41% higher in om adipose tissue (P < 0.001). Interestingly, the total PTPase activity from both adipose depots and the specific activity of PTP1B was increased by 42-71% after reduction in vitro with dithiothreitol, indicating that a major fraction of the cellular PTPase activity can be reactivated by sulfhydryl reduction. The mass of the insulin receptor beta-subunit and the PTPases PTP1B and leukocyte antigen related was not significantly different between the two adipose depots. These studies provide the first demonstration that endogenous PTPase activity, including PTP1B, is increased in om adipose tissue and may contribute to the relative insulin resistance of this fat depot. The finding that a substantial fraction of PTPase activity in human adipose tissue is present in a latent, oxidized form also suggests a potential means of in vivo regulation of these important cellular enzymes that modulate the insulin signaling cascade.

Protein-tyrosine phosphatases (PTPases) have a common cysteine residue whose reduced state is integral to their phosphocysteine-mediated reaction mechanism. The catalytic cysteine thiol can be oxidized or conjugated during cellular redox reactions, which provides an important means of PTPase regulation in vivo. Because exposure to air can artifactually oxidize this reactive thiol, PTPase assays have typically used potent reducing agents such as dithiothreitol to reactivate the enzymes present. However, this approach does not allow for the measurement of endogenous PTPase activity as directly isolated from the in vivo cellular environment. Here we show that sample processing and assay in an anaerobic chamber by using deoxygenated buffers can preserve the overall activity of PTPases in subcellular fractions of 3T3-L1 adipocytes, HepG2 hepatoma cells, and human adipose tissue, as well as with PTP1B, specifically isolated by immunoprecipitation. Cell lysis into air reduced the PTPase activity to as low as 20% of the level observed with sample handling in the anaerobic environment, which was variably restored towards the activity in the anaerobic samples by treatment with dithiothreitol. The approach reported here provides a new framework for characterizing the activity of PTPases as isolated from the intracellular milieu, which more closely reflects the endogenous reactivity and potential impact of these PTPases on signal transduction pathways involving reversible protein-tyrosine phosphorylation.