Acute dipeptidyl peptidase-4 inhibition rapidly enhances insulin-mediated suppression of endogenous glucose production in mice.

Pharmacological approaches that enhance incretin action for the treatment of type 2 diabetes mellitus have recently been developed, i.e. injectable glucagon-like peptide-1 receptor (GLP-1R) agonists with prolonged plasma half-lives and orally available inhibitors of dipeptidyl peptidase (DPP)-4, the main enzyme responsible for the rapid degradation of circulating glucagon-like peptide-1 and glucose-dependent insulinotropic peptide. The mechanism(s) underlying the glucose-lowering effect of these two pharmacotherapies differs and is not yet fully understood. Here we investigated whether acute GLP-1R activation (exendin-4) or DPP-4 inhibition (des-F-sitagliptin) modulates insulin action in mice using a hyperinsulinemic euglycemic clamp. A single iv bolus of des-F-sitagliptin (11 mg/kg) was administered to mice 15 min after the start of the clamp, and its effect was compared with a 50-ng bolus of exendin-4 or the same volume of saline. Despite matched levels of plasma glucose and insulin, within 15 min the glucose infusion rate required to maintain euglycemia was significantly greater after des-F-sitagliptin compared with saline or exendin-4. This difference was entirely due to enhancement of insulin-mediated suppression of endogenous glucose production by des-F-sitagliptin, with no difference in glucose disposal rate. These findings illustrate that DPP-4 inhibition modulates glucose homeostasis through pathways distinct from those used by GLP-1R agonists in mice.

Evolution and future of preclinical testing for endovascular grafts.

The preclinical testing of endovascular grafts has evolved significantly since the creation and early testing of these devices; however, there are continued limitations in using preclinical testing to predict clinical performance. Early testing was conducted in the absence of standards and guidance specific to endovascular grafts, and references available for vascular grafts and stents did not adequately account for the complexity of endovascular graft systems. Failure of early-generation devices suggested that the testing being conducted was inadequate and that there was a lack of understanding of the in vivo environment. These concerns led to several efforts to improve preclinical testing. The Food and Drug Administration (FDA) sponsored a workshop to discuss the limitations inherent in testing of endovascular grafts, and an ISO standard for endovascular grafts was developed. Publication of the standard in 2003 succeeded in standardizing testing and reporting across device manufacturers; however, several clinical failure modes, such as migration and stent fractures, continued to be unpredicted by current preclinical testing. This, coupled with knowledge gained from additional clinical experience, led the FDA to hold a second workshop to discuss the benefits and limitations of current testing and propose future testing that may better predict device performance. This workshop was successful in accurately describing past testing, determining what has been learned, identifying issues that have not been adequately addressed, proposing modifications to address these limitations, and discussing how the proposed modifications should be implemented. While significant progress has been made in endovascular graft testing, continued collaboration among industry, academia, regulators, and clinicians will provide continued improvement in the predictability of device performance.

AMP kinase activation with AICAR simultaneously increases fatty acid and glucose oxidation in resting rat soleus muscle.

5-Amino-4-imidazolecarboxamide riboside (AICAR), a pharmacological activator of AMP-activated protein kinase (AMPK), acutely stimulates glucose uptake and fatty acid (FA) oxidation in skeletal muscle. However, it is not fully understood whether AICAR-induced changes in glucose oxidation are secondary to changes in FA oxidation (i.e. glucose fatty acid cycle), or what role AMPK may be playing in the regulation of intramuscular triacylglycerol (TAG) esterification and hydrolysis. We examined the acute (60 min) effects of AICAR (2 mm) on FA metabolism, glucose oxidation and pyruvate dehydrogenase (PDH) activation in isolated resting rat soleus muscle strips exposed to two different FA concentrations (low fatty acid, LFA, 0.2 mm; high fatty acid, HFA, 1 mm). AICAR significantly increased AMPK alpha2 activity (+192%; P<0.05) over 60 min, and simultaneously increased both FA (LFA: +33%, P<0.05; HFA: +36%, P<0.05) and glucose (LFA: +105%, P<0.05; HFA: +170, P<0.001) oxidation regardless of FA availability. While there were no changes in TAG esterification, AICAR did increase the ratio of FA partitioned to oxidation relative to TAG esterification (LFA: +15%, P<0.05; HFA: +49%, P<0.05). AICAR had no effect on endogenous TAG hydrolysis and oxidation in resting soleus. The stimulation of glucose oxidation with AICAR was associated with an increase in PDH activation (+126%; P<0.05) but was without effect on pyruvate, an allosteric activator of the PDH complex, suggesting that AMPK may stimulate PDH directly. In conclusion, AMPK appears to be an important regulator of both FA metabolism and glucose oxidation in resting skeletal muscle.