Imidazoline-induced amplification of glucose- and carbachol-stimulated insulin release includes a marked suppression of islet nitric oxide generation in the mouse

Iodine-catalyzed convergent aerobic dehydro-aromatization toward benzazoles and benzazines

An iodine-catalyzed aerobic dehydro-aromatization has been developed, providing straightforward and efficient access to various benzoazoles and benzoazines. The present transition-metal-free protocol enables the dehydro-aromatization of tetrahydrobenzazoles and tetrahydroquinolines with molecular oxygen as the green oxidant, along with some other N-heterocycles. Hence, a broad range of heteroaromatic compounds are generated in moderate to good yields under facile reaction conditions.

An iodine-catalyzed aerobic dehydro-aromatization has been developed, providing a straightforward and efficient access to various benzoazoles and benzoazines.

Activation of imidazoline receptor I2, and improved pancreatic β-cell function in human islets

AIM

The impact of BL11282, an imidazoline receptor (NISCH) agonist, on potentiation of glucose-stimulated insulin secretion (GSIS) from isolated human non-diabetic (ND) and type 2 diabetic (T2D) islets was investigated.

METHODS

Analysis of mRNA was performed by RNA-sequencing and qPCR. Insulin and cAMP by RIA and ELISA respectively.

RESULTS

RNA-sequencing data revealed that NISCH is highly expressed in fat tissues, islets, liver and muscles, with eight detectable splice variants of transcripts in islets. NISCH had a positive correlation with GLP-1 (GLP1R) and GIP (GIPR) receptor transcripts. The expression of NISCH was confirmed by qPCR in human islets. NISCH and GLP1R were comparably higher expressed in mouse islets compared to human islets. GSIS was dose-dependently potentiated by BL11282 from incubated islets of ND and T2D human islet donors. The insulinotropic action of BL11282 was associated with increased cAMP. While the harmful effect of high glucose on reductive capacity of islet cells was enhanced by glibenclamide during long-term culture, it was counteracted by BL11282 or Bt2-cAMP. BL11282 also increased proliferation of INS-1 cells during long-time culture.

CONCLUSION

Our data suggest that BL11282 potentiates GSIS by an action involving cAMP/PKA system and BL11282 could be an attractive insulinotropic and β-cell protective agent.

Dissection of mechanisms that account for imidazoline-induced lowering of blood glucose in mice

Multiple mechanisms have been suggested to be responsible for the insulinotropic and blood glucose lowering effects of imidazoline compounds. This study was to unravel which mechanism predominantly accounts for glucose lowering by the prototypical imidazolines idazoxan and phentolamine. To this end, an α2-adrenoceptor agonist (UK14,304) and a KATP channel opener (diazoxide) were used to inhibit insulin release from isolated perifused mouse islets and to induce hyperglycaemia in conscious mice. Potentials of idazoxan and phentolamine to counteract these effects were examined in a comparative manner. In perifused islets, idazoxan increased insulin release only in the presence of the α2-agonist, whereas phentolamine strongly counteracted both inhibitors of insulin release. In vivo, a lower dose of idazoxan was necessary to ameliorate hyperglycaemia induced by the α2-agonist than by the KATP channel opener, indicating α2A-antagonism as the predominant mechanism of action (decrease in incremental area under the glucose curve induced by 0.1mg/kg idazoxan: under diazoxide, -3±7%, vs. under UK14,304, -34±9%, P<0.02). In contrast, identical doses of phentolamine were required to counteract hyperglycaemia induced by the two inhibitors of insulin release, implicating involvement of another mechanism beside α2A-antagonism (2mg/kg phentolamine: diazoxide, -11±8%, vs. UK14,304, -15±9%, ns; 4mg/kg phentolamine: diazoxide, -48±6%, vs. UK14,304, -48±8%, ns). The results show that imidazolines can lower blood glucose via more than one mechanism of action, with the relative contributions of the mechanisms varying considerably between individual compounds. Dissection of the involved mechanisms could help to develop imidazoline drugs for the treatment of type 2 diabetes.

Mechanisms of antihyperglycaemic action of efaroxan in mice: time for reappraisal of α2A-adrenergic antagonism in the treatment of type 2 diabetes?

AIMS/HYPOTHESIS

Inspired by recent speculation about the potential utility of α(2A)-antagonism in the treatment of type 2 diabetes, the study examined the contribution of α(2)-antagonism vs other mechanisms to the antihyperglycaemic activity of the imidazoline (±)-efaroxan.

METHODS

Effects of the racemate and its pure enantiomers on isolated pancreatic islets and beta cells in vitro, as well as on hyperglycaemia in vivo, were investigated in a comparative manner in mice.

RESULTS

In isolated perifused islets, the two enantiomers of efaroxan were equally potent in counteracting inhibition of insulin release by the ATP-dependent K(+) (K(ATP)) channel-opener diazoxide but (+)-efaroxan, the presumptive carrier of α(2)-antagonistic activity, was by far superior in counteracting inhibition of insulin release by the α(2)-agonist UK14,304. In vivo, (+)-efaroxan improved oral glucose tolerance at 100-fold lower doses than (-)-efaroxan and, in parallel with observations made in vitro, was more effective in counteracting UK14,304-induced than diazoxide-induced hyperglycaemia. The antihyperglycaemic activity of much higher doses of (-)-efaroxan was associated with an opposing pattern (i.e. with stronger counteraction of diazoxide-induced than UK14,304-induced hyperglycaemia), which implicates a different mechanism of action.

CONCLUSIONS/INTERPRETATION

The antihyperglycaemic potency of (±)-efaroxan in mice is almost entirely due to α(2)-antagonism, but high doses can also lower blood glucose via another mechanism. Our findings call for reappraisal of the possible clinical utility of α(2A)-antagonistic compounds in recently identified subpopulations of patients in which a congenitally higher level of α(2A)-adrenergic activation contributes to the development and pathophysiology of type 2 diabetes.

Reactive oxygen and nitrogen species generation, antioxidant defenses, and β-cell function: a critical role for amino acids

Growing evidence indicates that the regulation of intracellular reactive oxygen species (ROS) and reactive nitrogen species (RNS) levels is essential for maintaining normal β-cell glucose responsiveness. While long-term exposure to high glucose induces oxidative stress in β cells, conflicting results have been published regarding the impact of ROS on acute glucose exposure and their role in glucose stimulated insulin secretion (GSIS). Although β cells are considered to be particularly vulnerable to oxidative damage, as they express relatively low levels of some peroxide-metabolizing enzymes such as catalase and glutathione (GSH) peroxidase, other less known GSH-based antioxidant systems are expressed in β cells at higher levels. Herein, we discuss the key mechanisms of ROS/RNS production and their physiological function in pancreatic β cells. We also hypothesize that specific interactions between RNS and ROS may be the cause of the vulnerability of pancreatic β cells to oxidative damage. In addition, using a hypothetical metabolic model based on the data available in the literature, we emphasize the importance of amino acid availability for GSH synthesis and for the maintenance of β-cell function and viability during periods of metabolic disturbance before the clinical onset of diabetes.