Dissociation of Muscle Insulin Resistance from Alterations in Mitochondrial Substrate Preference.

Alterations in muscle mitochondrial substrate preference have been postulated to play a major role in the pathogenesis of muscle insulin resistance. In order to examine this hypothesis, we assessed the ratio of mitochondrial pyruvate oxidation (V) to rates of mitochondrial citrate synthase flux (V) in muscle. Contrary to this hypothesis, we found that high-fat-diet (HFD)-fed insulin-resistant rats did not manifest altered muscle substrate preference (V/V) in soleus or quadriceps muscles in the fasting state.

Leptin's hunger-suppressing effects are mediated by the hypothalamic-pituitary-adrenocortical axis in rodents.

Leptin informs the brain about sufficiency of fuel stores. When insufficient, leptin levels fall, triggering compensatory increases in appetite. Falling leptin is first sensed by hypothalamic neurons, which then initiate adaptive responses.

Dehydration and insulinopenia are necessary and sufficient for euglycemic ketoacidosis in SGLT2 inhibitor-treated rats.

Sodium-glucose transport protein 2 (SGLT2) inhibitors are a class of anti-diabetic agents; however, concerns have been raised about their potential to induce euglycemic ketoacidosis and to increase both glucose production and glucagon secretion. The mechanisms behind these alterations are unknown. Here we show that the SGLT2 inhibitor (SGLT2i) dapagliflozin promotes ketoacidosis in both healthy and type 2 diabetic rats in the setting of insulinopenia through increased plasma catecholamine and corticosterone concentrations secondary to volume depletion.

Leptin Mediates a Glucose-Fatty Acid Cycle to Maintain Glucose Homeostasis in Starvation.

The transition from the fed to the fasted state necessitates a shift from carbohydrate to fat metabolism that is thought to be mostly orchestrated by reductions in plasma insulin concentrations. Here, we show in awake rats that insulinopenia per se does not cause this transition but that both hypoleptinemia and insulinopenia are necessary. Furthermore, we show that hypoleptinemia mediates a glucose-fatty acid cycle through activation of the hypothalamic-pituitary-adrenal axis, resulting in increased white adipose tissue (WAT) lipolysis rates and increased hepatic acetyl-coenzyme A (CoA) content, which are essential to maintain gluconeogenesis during starvation.

Mechanisms by which a Very-Low-Calorie Diet Reverses Hyperglycemia in a Rat Model of Type 2 Diabetes.

Caloric restriction rapidly reverses type 2 diabetes (T2D), but the mechanism(s) of this reversal are poorly understood. Here we show that 3 days of a very-low-calorie diet (VLCD, one-quarter their typical intake) lowered plasma glucose and insulin concentrations in a rat model of T2D without altering body weight. The lower plasma glucose was associated with a 30% reduction in hepatic glucose production resulting from suppression of both gluconeogenesis from pyruvate carboxylase (V), explained by a reduction in hepatic acetyl-CoA content, and net hepatic glycogenolysis.

A suite of activity-based probes for human cytochrome P450 enzymes.

Cytochrome P450 (P450) enzymes regulate a variety of endogenous signaling molecules and play central roles in the metabolism of xenobiotics and drugs. We recently showed that an aryl alkyne serves as an effective activity-based probe for profiling mouse liver microsomal P450s in vitro and in vivo. However, individual P450s display distinct substrate and inhibitor specificities, indicating that multiple probe structures may be required to achieve comprehensive coverage of this large and diverse enzyme family.