R. Ouedraogo

Hydroxylamine, a nitric oxide donor, inhibits insulin release and activates K+ATP channels

The present study was undertaken to assess the effects of hydroxylamine, a nitric oxide (NO) donor, on ionic and secretory events in rat pancreatic islets. Hydroxylamine provoked a concentration-dependent inhibition of the glucose-induced insulin release. This inhibitory action was counteracted by glibenclamide. Moreover, hydroxylamine increased the rate of 86Rb outflow from perifused islets. This effect persisted in the absence of external Ca2+ but was impaired by glibenclamide. Hydroxylamine decreased 45Ca outflow, [Ca2+]i and insulin output from islets exposed to 16.7 mM glucose and extracellular Ca2+. By contrast, hydroxylamine did not affect the increase in 45Ca outflow and [Ca2+]i evoked by K+ depolarization. These experimental results suggest that the negative insulinotropic action of the NO donor results, at least in part, from the activation of ATP-sensitive K+ channels leading to a decrease in Ca2+ influx and [Ca2+]i. Additional mechanisms, however, could also be involved in the NO donor modulation of the secretory process.

Verapamil, a phenylalkylamine Ca2 + channel blocker, inhibits ATP-sensitive K + channels in insulin-secreting cells from rats

Summary Radioisotopic and electrophysiological techniques were used to assess the effects of verapamil, a phenylalkylamine Ca2 + channel blocker, on K + permeability of insulin-secreting cells. Verapamil provoked a concentration-dependent inhibition of 86Rb (42K substitute) outflow from prelabelled and perifused rat pancreatic islets. This property appears to be inherent to the phenylalkylamine Ca2 + channel blockers since gallopamil, a methoxyderivative of verapamil, but not nifedipine, a 1,4-dihydropyridine Ca2 + channel blocker, inhibited 86Rb outflow. The experimental data further revealed that verapamil interacted with a Ca2 + -independent, glucose- and glibenclamide-sensitive modality of 86Rb extrusion. Moreover, verapamil prevented the increase in 86Rb outflow brought about by BPDZ 44; a potent activator of the ATP-sensitive K + channel. Single-channel current recordings by the patch clamp technique confirmed that verapamil elicited a dose-dependent inhibition of the ATP-dependent K + channel. Lastly, under experimental conditions in which verapamil clearly inhibited the ATP-sensitive K + channels, the drug did not affect 45Ca outflow, the cytosolic free Ca2 + concentration or insulin release. It is concluded that the Ca2 + entry blocker verapamil inhibits ATP-sensitive K + channels in pancreatic beta cells. This effect was not associated with stimulation of insulin release [Diabetologia (1997) 40: 1403–1410].

Preparation and pharmacological evaluation of the R- and S-enantiomers of 3-(2'-butylamino)-4H- and 3-(3'-methyl-2'-butylamino)-4H-pyrido[4,3-e]-1,2,4-thiadiazine 1,1-dioxide, two tissue selective ATP-sensitive potassium channel openers

The preparation and the pharmacological evaluation of the R- and S-isomers of 3-(2-butylamino)-4H-pyrido[4,3-e]-1,2,4-thiadiazine 1,1-dioxide (BPDZ 42) and 3-(3-methyl-2-butylamino)-4H-pyrido[4,3-e]-1,2,4-thiadiazine 1,1-dioxide (BPDZ 44), two potassium channel openers, is described. Their optical purity was estimated by means of capillary electrophoresis (R- and S-BPDZ 42) and chiral HPLC (R- and S-BPDZ 44). The absolute configuration of each isomer of BPDZ 44 was deduced from crystallographic data. Pharmacological assays performed with the R- and S-isomers of BPDZ 44 revealed only slight differences in their activity on pancreatic B-cells but significant differences in their activity on vascular smooth muscle cells: the R-isomer being sixfold more potent than its corresponding S-isomer. The R-isomer of BPDZ 42 was shown to be more potent than its corresponding S-isomer on the endocrine pancreas. S-BPDZ 44 as well as R- and S-BPDZ 42 were found to exhibit tissue selectivity for the pancreatic versus the vascular smooth muscle tissue.

Synthesis and structural studies of 3-alkylamino-pyrido[4,3-e]-1,2,4-thiadiazine 1,1-dioxides: a new class of heterocyclic compounds with therapeutical promises

Abstract 3-Alkylamino-pyrido[4,3-e]-1,2,4-thiadiazine 1,1-dioxide represents a new class of heterocyclic compounds expressing important pharmacological properties. According to the position of the CN double bond in the thiadiazine ring, this heterocyclic ring system may exist under three different tautomeric forms. By means of spectral and X-ray data collected from selected compounds, the most favourable tautomeric form adopted by 3-alkylamino-pyrido[4,3-e]-1,2,4-thiadiazine 1,1-dioxides devoid of an alkyl substituent in the 2- or in the 4-position was determined. The present study giving new insights in the geometrical and conformational aspects of pyridothiadiazinedioxides is important considering the pharmacological potentialities of this class of heterocyclic compounds.

Synthesis and biological evaluation of sulfonylcyanoguanidines and sulfonamidonitroethylenes as bioisosteres of hypoglycemic sulfonylureas

Summary Sulfonylcyanoguanidines and sulfonamidonitroethylenes are bioisosteres of hypoglycemic sulfonylureas and were prepared and evaluated for their insulin release potency from rat pancreatic islets. At 25 μM, both bioisosteres of glibenclamide, sulfonylcyanoguanidine 22 and sulfonamidonitroethylene 23 , were as potent as their parent on insulin secretion.

3-Morpholinosydnonimine as instigator of a glibenclamide-sensitive reduction in the insulin secretory rate☆

The nitric oxide (NO) donor SIN-1 (3-morpholinosydnonimine) induced a concentration-dependent inhibition of the secretory response to glucose. The negative insulinotropic action of SIN-1 was attenuated by the hypoglycemic sulfonylurea glibenclamide. Moreover, the NO donor enhanced 86Rb outflow from perfused islets and reduced the glucose-induced increase in 45Ca outflow. The present data provide further evidence that NO donors impair the secretory response to glucose, at least in part, by activating the ATP-sensitive K+ channels.

2-alkyl-3-Alkylamino-2H-Benzo- and pyridothiadiazine 1,1-dioxides: from K+ATP channel openers to Ca++ channel blockers?

Abstract A series of 2-alkyl-3-alkylamino-2Hbenzo and 2-alkyl-3-alkylamino-2Hpyrido[4,3-e]-1,2,4-thiadiazine 1,1-dioxides, structurally related to BPDZ 44 and BPDZ 73, two potent pancreatic Bcells K+ ATP channel openers, were synthesized and tested on rat pancreatic islets (endocrine tissue) as well as on rat aorta rings (vascular smooth muscle tissue). Alkylation of the 2-position led to double bond tautomerization and formation of compounds with a 2Hconformation. In contrast to the previously described pyridothiadiazine dioxides, such as BPDZ 44, and 7-chlorobenzothiadiazine dioxides, such as BPDZ 73, the 2-alkylsubstituted analogs were found to be poorly active on the insulin releasing process although most drugs exhibited a vasorelaxant activity. As a result, the new 2-alkylsubstituted pyridinic compounds expressed a selectivity profile (vascular smooth muscle tissue vs pancreatic tissue) opposite to that of their nonalkylsubstituted counterparts, i.e. BPDZ 44. Additional investigations revealed that, in contrast to their non 2-alkylsubstituted analogs, the most interesting 2-methylsubstituted derivatives did not express the pharmacological profile of classical K+ATP channel openers. The pharmacological results rather suggest that alkylation of the 2-position of the thiadiazine ring led to drugs that could act as Ca2+ channel blockers rather than as potassium channel openers.

Effects of 3-alkylamino-7-chloro-4H-pyrido[2,3-e]-1,2,4-thiadiazine 1,1-dioxides on smooth muscle contractile activity

New 3-alkylaminopyridothiadiazine dioxides have been synthesized and characterized in a search for more efficient and selective KATP-channel activators. The new compounds induced concentration-dependent relaxation of vascular (aorta) and gastrointestinal (ileum) smooth muscle. The pharmacological profiles of the new compounds were different from those of diazoxide or pinacidil but similar to that of verapamil. The results suggest that the myorelaxant properties of the new compounds depend on their capacity to reduce calcium inflow into smooth muscle cells.

3-Alkylamino-pyrido[4,3-e]-1,2,4-thiadiazine 1,1-dioxides as potent KATP-channel activators: structural study and influence of stereochemistry

Pyrido[4,3-e]-1,2,4-thiadiazine 1,1-dioxides bearing a short and branched alkylamino side chain in the 3 position, appear to be powerful and tissue selective pancreatic KATP-channel activators. In order to confirm the pharmacophoric model for the activation of pancreatic KATP channels, a structural study was undertaken on representative 3-alkyl-aminopyridothiadiazines. The influence on the biological activity of the stereochemistry associated to the first carbon atom of the 3-alkylamino chain was also examined.