Superior Glycemic Control With a Glucose-Responsive Insulin Analog: Hepatic and Nonhepatic Impacts.

We evaluated the hepatic and nonhepatic responses to glucose-responsive insulin (GRI). Eight dogs received GRI or regular human insulin (HI) in random order. A primed, continuous intravenous infusion of [3-3H]glucose began at -120 min. Basal sampling (-30 to 0 min) was followed by two study periods (150 min each), clamp period 1 (P1) and clamp period 2 (P2). At 0 min, somatostatin and GRI (36 ± 3 pmol/kg/min) or HI (1.8 pmol/kg/min) were infused intravenously; basal glucagon was replaced intraportally. Glucose was infused intravenously to clamp plasma glucose at 80 mg/dL (P1) and 240 mg/dL (P2). Whole-body insulin clearance and insulin concentrations were not different in P1 versus P2 with HI, but whole-body insulin clearance was 23% higher and arterial insulin 16% lower in P1 versus P2 with GRI. Net hepatic glucose output was similar between treatments in P1. In P2, both treatments induced net hepatic glucose uptake (HGU) (HI mean ± SEM 2.1 ± 0.5 vs. 3.3 ± 0.4 GRI mg/kg/min). Nonhepatic glucose uptake in P1 and P2, respectively, differed between treatments (2.6 ± 0.3 and 7.4 ± 0.6 mg/kg/min with HI vs. 2.0 ± 0.2 and 8.1 ± 0.8 mg/kg/min with GRI). Thus, glycemia affected GRI but not HI clearance, with resultant differential effects on HGU and nonHGU. GRI holds promise for decreasing hypoglycemia risk while enhancing glucose uptake under hyperglycemic conditions.

Engineering Glucose Responsiveness Into Insulin.

Insulin has a narrow therapeutic index, reflected in a small margin between a dose that achieves good glycemic control and one that causes hypoglycemia. Once injected, the clearance of exogenous insulin is invariant regardless of blood glucose, aggravating the potential to cause hypoglycemia. We sought to create a "smart" insulin, one that can alter insulin clearance and hence insulin action in response to blood glucose, mitigating risk for hypoglycemia. The approach added saccharide units to insulin to create insulin analogs with affinity for both the insulin receptor (IR) and mannose receptor C-type 1 (MR), which functions to clear endogenous mannosylated proteins, a principle used to endow insulin analogs with glucose responsivity. Iteration of these efforts culminated in the discovery of MK-2640, and its in vitro and in vivo preclinical properties are detailed in this report. In glucose clamp experiments conducted in healthy dogs, as plasma glucose was lowered stepwise from 280 mg/dL to 80 mg/dL, progressively more MK-2640 was cleared via MR, reducing by ∼30% its availability for binding to the IR. In dose escalations studies in diabetic minipigs, a higher therapeutic index for MK-2640 (threefold) was observed versus regular insulin (1.3-fold).

Glucagon receptor antagonism induces increased cholesterol absorption.

Glucagon and insulin have opposing action in governing glucose homeostasis. In type 2 diabetes mellitus (T2DM), plasma glucagon is characteristically elevated, contributing to increased gluconeogenesis and hyperglycemia. Therefore, glucagon receptor (GCGR) antagonism has been proposed as a pharmacologic approach to treat T2DM. In support of this concept, a potent small-molecule GCGR antagonist (GRA), MK-0893, demonstrated dose-dependent efficacy to reduce hyperglycemia, with an HbA1c reduction of 1.5% at the 80 mg dose for 12 weeks in T2DM. However, GRA treatment was associated with dose-dependent elevation of plasma LDL-cholesterol (LDL-c). The current studies investigated the cause for increased LDL-c. We report findings that link MK-0893 with increased glucagon-like peptide 2 and cholesterol absorption. There was not, however, a GRA-related modulation of cholesterol synthesis. These findings were replicated using structurally diverse GRAs. To examine potential pharmacologic mitigation, coadministration of ezetimibe (a potent inhibitor of cholesterol absorption) in mice abrogated the GRA-associated increase of LDL-c. Although the molecular mechanism is unknown, our results provide a novel finding by which glucagon and, hence, GCGR antagonism govern cholesterol metabolism.

Effect of creatine supplementation and a lacto-ovo-vegetarian diet on muscle creatine concentration.

The purpose of this investigation was to examine the effects of preceding oral creatine monohydrate with a lacto-ovo-vegetarian diet on muscle creatine concentration. Thirty-two healthy men, who regularly consumed an omnivorous diet, were randomly assigned to consume a weight maintaining, lacto-ovo-vegetarian (LOV; n = 16) or omnivorous (Omni; n = 16) diet for 26 days. In addition to their assigned diet, on day 22 of the study, subjects were assigned in a double-blind manner to receive either creatine monohydrate (CM; 0.3 g kg d 1 + 20 g Polycose) or an equivalent dose of placebo (PL) for 5 days. There were no significant differences between the LOV and Omni groups at baseline with respect to age, height, and weight. The results demonstrated that consuming a LOV diet for 21 days was an effective procedure to decrease muscle creatine concentration (p <.01) in individuals who normally consume meat and fish in their diet. However, muscle total creatine (TCr) following creatine supplementation did not differ statistically between LOV and Omni diet groups (148.6 4.5 vs. 141.7 4.5 mmol kg-1 d.m.).