SUMMARY Obesity is a highly heritable disease driven by complex interactions between genetic and environmental factors. Human genome-wide association studies (GWAS) have identified a number of loci contributing to obesity; however, a major limitation of these studies is the inability to assess environmental interactions common to obesity. Using a systems genetics approach, we measured obesity traits, global gene expression, and gut microbiota composition in response to a high-fat/high-sucrose (HF/HS) diet of more than 100 inbred strains of mice. Here we show that HF/HS feeding promotes robust, strain-specific changes in obesity that is not accounted for by food intake and provide evidence for a genetically determined set-point for obesity. GWAS analysis identified 11 genome-wide significant loci associated with obesity traits, several of which overlap with loci identified in human studies. We also show strong relationships between genotype and gut microbiota plasticity during HF/HS feeding and identify gut microbial phylotypes associated with obesity.

Efforts to further elucidate structure-activity relationships (SAR) within our previously disclosed series of beta-quaternary amino acid linked l-cis-4,5-methanoprolinenitrile dipeptidyl peptidase IV (DPP-IV) inhibitors led to the investigation of vinyl substitution at the beta-position of alpha-cycloalkyl-substituted glycines. Despite poor systemic exposure, vinyl-substituted compounds showed extended duration of action in acute rat ex vivo plasma DPP-IV inhibition models. Oxygenated putative metabolites were prepared and were shown to exhibit the potency and extended duration of action of their precursors in efficacy models measuring glucose clearance in Zucker(fa/fa) rats. Extension of this approach to adamantylglycine-derived inhibitors led to the discovery of highly potent inhibitors, including hydroxyadamantyl compound BMS-477118 (saxagliptin), a highly efficacious, stable, and long-acting DPP-IV inhibitor, which is currently undergoing clinical trials for treatment of type 2 diabetes.

DPP-4 (dipeptidyl peptidase-4) degrades the incretin hormones GLP-1 (glucagon-like peptide-1) and GIP (gastric inhibitory polypeptide), decreasing their stimulatory effects on beta-cell insulin secretion. In patients with Type 2 diabetes, meal-related GLP-1 secretion is reduced. DPP-4 inhibitors (alogliptin, saxagliptin, sitagliptin and vildagliptin) correct the GLP-1 deficiency by blocking this degradation, prolonging the incretin effect and enhancing glucose homoeostasis. DPP-4 is a member of a family of ubiquitous atypical serine proteases with many physiological functions beyond incretin degradation, including effects on the endocrine and immune systems. The role of DPP-4 on the immune system relates to its extra-enzymatic activities. The intracytosolic enzymes DPP-8 and DPP-9 are recently discovered DPP-4 family members. Although specific functions of DPP-8 and DPP-9 are unclear, a potential for adverse effects associated with DPP-8 and DPP-9 inhibition by non-selective DPP inhibitors has been posed based on a single adverse preclinical study. However, the preponderance of data suggests that such DPP-8 and DPP-9 enzyme inhibition is probably without clinical consequence. This review examines the structure and function of the DPP-4 family, associated DPP-4 inhibitor selectivity and the implications of DPP-4 inhibition in the treatment of Type 2 diabetes.

We report the purification of two peptides, called "imperatoxin inhibitor" and "imperatoxin activator," from the venom of the scorpion Pandinus imperator targeted against ryanodine receptor Ca2+-release channels. Imperatoxin inhibitor has a Mr of 10,500, inhibits [3Hjryanodine binding to skeletal and cardiac sarcoplasmic reticulum with an EDso of 10 nM, and blocks openings of skeletal and cardiac Ca2+-release channels incorporated into planar bilayers. In whole-cell recordings of cardiac myocytes, imperatoxin inhibitor decreased twitch amplitude and intracellular Ca2+ transients, suggesting a selective blockade of Ca2+ release from the sarcoplasmic reticulum. Imperatoxin activator has a Mr of -8700, stimulates [3H]ryanodine bind in skeletal but not cardiac sarcoplasmic reticulum with an ED50 of -6 nM, and activates skeletal but not cardiac Ca2+-release channels. These ligands may serve to selectively "turn on" or "turn off" ryanodine receptors in fragmented systems and whole cells.Activation of muscle, neurons, and secretory cells by voltage, neurotransmitters, or hormones can evoke a release of Ca2+ from intracellular Ca2+ stores (1). Two types of Ca2+ channels, namely ryanodine receptors and inositol 1,4,5-trisphosphate (InsP3) receptors, have been shown to control the intracellular Ca2+ permeability of many cells. In striated muscle, these channels transduce membrane voltage, sarcolemmal Ca2+ entry, and other external stimuli into an increase in the Ca2+ permeability of the sarcoplasmic reticulum (SR) (2). Elucidation of the mechanism of Ca2+ release from intracellular stores depends critically on the specificity of pharmacological agents to selectively alter a single intracellular Ca2+ channel type. The alkaloid ryanodine is presently the only ligand available to dissect the contribution of ryanodine receptors to intracellular Ca2+ release in situ. However, the usefulness of this compound is limited by the fact that it has an extremely slow association and dissociation kinetics that makes the onset of the pharmacological effect slow and essentially irreversible (3). To accelerate the onset, micromolar instead of nanomolar levels of ryanodine are used, but at micromolar concentrations the alkaloid inhibits other Ca2+ channels (4). Furthermore, certain concentrations of ryanodine may open the Ca2+-release channel while others may block it (5), leading to ambiguous results (6). Alternative ligands that act fast, reversibly, and in a simple manner should be more helpful in establishing the contribution of ryanodine receptors to intracellular Ca2+ signals.Scorpion venoms have traditionally represented an invaluable source ofpeptide toxins specific for a single channel type (7). In the present report, we screened venom from several genera of scorpions with the hope of finding peptides specific for ryanodine receptors. We purified two peptides from the venom of Pandinus imperator that selectively blocked [imperatoxin inhibitor (IpTxi)] or activated [imperatoxin activator (IpTxa)] ryanodine receptors of skel...

ABSTRACT:Saxagliptin is a potent, selective, reversible dipeptidyl peptidase 4 (DPP4) inhibitor specifically designed for extended inhibition of the DPP4 enzyme and is currently under development for the treatment of type-2 diabetes. The pharmacokinetics of saxagliptin were evaluated in rats, dogs, and monkeys and used to predict its human pharmacokinetics. Saxagliptin was rapidly absorbed and had good bioavailability (50-75%) in the species tested. The plasma clearance of saxagliptin was higher in rats (115 ml/min/kg) than in dogs (9.3 ml/min/kg) and monkeys (14.5 ml/min/kg) and was predicted to be low to moderate in humans. The plasma elimination half-life was between 2.1 and 4.4 h in rats, dogs, and monkeys, and both metabolism and renal excretion contributed to the overall elimination. The primary metabolic clearance pathway involved the formation of a significant circulating, pharmacologically active hydroxylated metabolite, M2. The volume of distribution values observed in rats, dogs, and monkeys (1.3-5.2 l/kg) and predicted for humans (2.7 l/kg) were greater than those for total body water, indicating extravascular distribution. The in vitro serum protein binding was low (<30%) in rats, dogs, monkeys, and humans. After intra-arterial administration of saxagliptin to Sprague-Dawley and Zucker diabetic fatty rats, higher levels of saxagliptin and M2 were observed in the intestine (a proposed major site of drug action) relative to that in plasma. Saxagliptin has prolonged pharmacodynamic properties relative to its plasma pharmacokinetic profile, presumably due to additional contributions from M2, distribution of saxagliptin and M2 to the intestinal tissue, and prolonged dissociation of both saxagliptin and M2 from DPP4.