Discovery of non-covalent dipeptidyl peptidase IV inhibitors which induce a conformational change in the active site.

A series of non-covalent inhibitors of the serine protease dipeptidyl peptidase IV (DPP-IV) were found to adopt a U-shaped binding conformation in X-ray co-crystallization studies. Remarkably, Tyr547 undergoes a 70 degrees side-chain rotation to accommodate the inhibitor and allows access to a previously unexposed area of the protein backbone for hydrogen bonding.

Dipeptidyl peptidase-IV inhibitors can restore glucose homeostasis in type 2 diabetics via incretin enhancement.

Incretin levels approach normal physiological values following treatment with dipeptidyl peptidase (DPP)-IV inhibitors. This is in contrast to incretin levels resulting from the exogenous administration of glucagon-like peptide (GLP)-1 and its analogs, which can reach super-physiological values. This review describes the role of DPP-IV inhibitors as incretin enhancers in the regulation of glucose homeostasis in type 2 diabetic patients. The roles of incretins and the effect of DPP-IV on their actions are described, as are new therapeutic interventions based on the restoration of impaired incretin secretion in type 2 diabetic patients and obese individuals. In addition, the relevance of DPP-IV inhibition for weight control, its potential influence on beta-cell mass, and possible new indications are discussed, as are the implications of the currently available clinical data.

Structure activity studies of the serine-AIB dipeptide domain in 2,3-dihydroisothiazole based growth hormone secretagogues.

A series of growth hormone secretagogues (GHSs) based on 2,3-dihydroisothiazole has been synthesized in the search for a potential treatment of growth hormone deficiency or frailty in the elderly. This paper describes the evaluation of the SAR of the benzyl-D-Ser-aminoisobutyric acid dipeptide fragment. Introduction of substituents in the peptide backbone and in the phenyl ring has been investigated, as well as replacements for the benzyl group and for the AIB residue. A number of modifications resulted in enhanced potency over the parent benzyl-D-Ser-AIB derivative.

A buffer temperature controlled perifusion system to study temperature dependence and kinetics of insulin secretion in MIN6 pseudoislets.

INTRODUCTION: The perifusion of pancreatic islets is a well-known method to investigate the kinetics of insulin secretion. Nevertheless, little interest has been attributed to a precise temperature control in perifusion systems. Insulin secretion from MIN6 cells, cultured as monolayers, differs substantially from pancreatic islets, at least partly due to missing beta-to-beta cell contacts. These cellular contacts are abundant in MIN6 pseudoislets, which show a more pronounced glucose-induced insulin release. Here, a perifusion system that directly and dynamically controls the perifusion buffer temperature inside the reaction chamber is described. Additionally, the influence of small temperature changes, glucagon-like peptide 1 (GLP-1) and tolbutamide on insulin release from MIN6 pseudoislets is examined. METHODS: MIN6 cells were cultured in suspension culture dishes to generate MIN6 pseudoislets. The pseudoislets were perifused using a newly developed 12-channel perifusion system. The buffer temperature inside the reaction chambers was dynamically controlled by a programmable proportional plus integral plus differential (PID) controller. Insulin was determined by radioimmunoassay. RESULTS: After adjusting the PID controller, the temperature inside the reaction chambers was constant in a very narrow range. The first phase of the glucose-induced insulin secretion was enhanced from 1.0+/-0.1 to 2.8+/-0.2 ng insulin/ml and the second phase from 5.4+/-0.9 to 17.8+/-1.3 ng insulin/ml, when the temperature was elevated by 1 degrees C, from 37 to 38 degrees C. GLP-1 concentration dependently increased insulin release at 15.0 mM and was ineffective at 0.0 mM glucose. Tolbutamide induced a concentration-dependent increase in both phases of the insulin secretion. DISCUSSION: MIN6 pseudoislets are a useful tool to study insulin secretion from beta-cells, which are arranged in clusters like pancreatic beta-cells in the islet. The strong influence of temperature on insulin release from these pseudoislets requires a perifusion system, which precisely controls the buffer temperature.

Pertussis toxin converts hyperpolarizations caused by alpha(2)-adrenoceptor agonists containing an imidazoline moiety into depolarizations in MIN 6 cells.

Several alpha(2)-adrenoceptor agonists containing an imidazoline moiety inhibit insulin secretion when applied to beta cells. In the present study we investigated such imidazolines in regard to membrane potential effects in MIN 6 cells. We confirmed the inhibition of insulin release as reported in previous studies and showed an additional hyperpolarizing activity of the imidazolines using bisoxonol for membrane potential measurements. Pertussis toxin pre-incubation of MIN 6 cells converted the inhibitory imidazoline activity with regard to insulin release into a stimulatory effect. In addition, the marked hyperpolarization caused by the alpha-adrenoceptor agonists containing an imidazoline moiety was converted into a depolarizing effect after pertussis toxin pre-incubation. Adrenaline, an alpha-adrenoceptor agonist lacking an imidazoline moiety, also inhibited insulin release and hyperpolarized MIN 6 cells. Pertussis toxin pre-incubation led only to a loss of the inhibitory adrenaline effect and of the hyperpolarization but not to the stimulatory effects observed with the imidazolines. Thus a stimulatory effect of alpha-adrenoceptor agonists containing an imidazoline moiety was demasked by PTX in this study. It remains to be clarified to which extent a blockade of K(ATP) channels is responsible for this effect.

Insulinotropic activity of the imidazoline derivative RX871024 in the diabetic GK rat.

The insulinotropic activity of the imidazoline derivative RX871024 was compared in pancreatic islets from nondiabetic Wistar rats and spontaneously diabetic Goto-Kakizaki (GK) rats. RX871024 significantly stimulated insulin secretion in islets from both animal groups. The insulinotropic activity of RX871024 was higher than that of the sulfonylurea glibenclamide. This difference was more pronounced in islets from GK rats compared with Wistar rat islets. More importantly, RX871024 substantially improved glucose sensitivity in diabetic beta-cells, whereas glibenclamide stimulated insulin secretion about twofold over a broad range of glucose concentrations in nondiabetic and diabetic rats. RX871024 induced a faster increase in cytosolic free Ca(2+) concentration and faster inhibition of ATP-dependent K(+) channel activity in GK rat islets compared with Wistar rat islets. RX871024 also induced a more pronounced increase in diacylglycerol concentration in GK rat islets. These data support the idea that imidazoline compounds can form the basis for the development of novel drugs for treatment of type 2 diabetes, which can restore glucose sensitivity in diabetic beta-cells.