Marie-Hélène Antoine

A potent diazoxide analogue activating ATP-sensitive K+ channels and inhibiting insulin release

Aims/hypothesis. To characterise the effects of BPDZ 73 (7-chloro-3-isopropylamino-4H-1,2,4-benzothiadiazine 1,1-dioxide), a newly synthesised diazoxide analogue, on insulin secretory cells.¶Methods. Measurements of 86Rb, 45Ca outflow, membrane potential, [Ca2+]i, insulin release in secretory cells as well as measurements of smooth muscle contractile activity and glycaemia were carried out.¶Results. The analogue BPDZ 73 induced a dose-dependent decrease in insulin output. The IC50 value averaged 0.73 ± 0.05 μmol/l. The drug increased the rate of 86Rb (42K substitute) outflow from perifused rat pancreatic islets. This effect was inhibited by glibenclamide, a KATP channel blocker. Measurements of DiBAC4(3) fluorescence further indicated that BPDZ 73 hyperpolarised the insulin secreting cells. It also decreased 45Ca outflow from pancreatic islets perifused throughout in the presence of 16.7 mmol/l glucose and extracellular Ca2+. By contrast, the drug did not affect the increase in 45Ca outflow mediated by K+ depolarisation. In single beta cells, BPDZ 73 inhibited the glucose-induced but not the K+-induced rise in [Ca2+]i. Moreover, in Wistar rats, i. p. injection of BPDZ 73 provoked a considerable increase in blood glucose concentration whereas diazoxide induced a modest rise in glycaemia. Lastly, the vasorelaxant properties of BPDZ 73 were slightly less pronounced than those of diazoxide.¶Conclusion/interpretation. The inhibitory effect of BPDZ 73 on the insulin-releasing process results from the activation of KATP channels with subsequent decrease in Ca2+ inflow and [Ca2+]i. The drug seems to be a KATP channel opener, more potent and more selective than diazoxide for insulin secreting cells. [Diabetologia (2000) 43: 723-732]

Probenecid prevents acute tubular necrosis in a mouse model of aristolochic acid nephropathy

Experimental aristolochic acid nephropathy is characterized by early tubulointerstitial injury followed by fibrosis, reproducing chronic lesions seen in humans. In vitro, probenecid inhibits aristolochic acid entry through organic anion transporters, reduces specific aristolochic acid-DNA adduct formation, and preserves cellular viability. To test this in vivo, we used a mouse model of aristolochic acid nephropathy displaying severe tubulointerstitial injuries consisting of proximal tubular epithelial cell necrosis associated to transient acute kidney injury followed by mononuclear cell infiltration, tubular atrophy, and interstitial fibrosis. Treatment with probenecid prevented increased plasma creatinine and tubulointerstitial injuries, and reduced both the extent and the severity of ultrastructural lesions induced by aristolochic acid, such as the loss of brush border, mitochondrial edema, and the disappearance of mitochondrial crests. Further, the number of proliferating cell nuclear antigen-positive cells and total aristolochic acid-DNA adducts were significantly reduced in mice receiving aristolochic acid plus probenecid compared with mice treated with aristolochic acid alone. Thus, we establish the nephroprotective effect of probenecid, an inhibitor of organic acid transporters, in vivo toward acute proximal tubular epithelial cell toxicity in a mouse model of aristolochic acid nephropathy.

Sodium nitroprusside inhibits glucose-induced insulin release by activating ATP-sensitive K+ channels

Sodium nitroprusside (SNP) has been reported to be a potent stimulator of cGMP formation in different tissues, including pancreatic islets. The present study aimed at comparing the effects of sodium nitroprusside and dibutyryl cGMP on 86Rb outflow, 45Ca outflow, short-term 45Ca uptake, cytosolic Ca2+ concentration and insulin release from rat pancreatic islet cells. The data indicate that cGMP potentiates whilst SNP inhibits the glucose-induced insulin release. This inhibitory effect appears to be mediated by the activation of ATP-sensitive K+ channels leading to a decrease in Ca2+ influx and subsequent reduction in cytosolic free Ca2+ concentration. Whatever the exact mechanism(s) underlying the capacity of sodium nitroprusside to enhance the K+ permeability of the B-cell membrane, the drug appears to be an inadequate pharmacological tool to characterize the involvement of cGMP in the insulin secretory process. The experimental results also suggest that cGMP potentiates glucose-induced insulin release without affecting ionic movements.

Synthesis and characterization of a quinolinonic compound activating ATP-sensitive K(+) channels in endocrine and smooth muscle tissues.

Original quinolinone derivatives structurally related to diazoxide were synthesized and their effects on insulin secretion from rat pancreatic islets and the contractile activity of rat aortic rings determined. A concentration‐dependent decrease of insulin release was induced by 6‐chloro‐2‐methylquinolin‐4(1H)‐one (HEI 713). The average IC50 values were 16.9±0.8 μM for HEI 713 and 18.4±2.2 μM for diazoxide. HEI 713 increased the rate of 86Rb outflow from perifused pancreatic islets. This effect persisted in the absence of external Ca2+ but was inhibited by glibenclamide, a KATP channel blocker. Inside‐out patch‐clamp experiments revealed that HEI 713 increased KATP channel openings. HEI 713 decreased 45Ca outflow, insulin output and cytosolic free Ca2+ concentration in pancreatic islets and islet cells incubated in the presence of 16.7 or 20 mM glucose and extracellular Ca2+. The drug did not affect the K+(50 mM)‐induced increase in 45Ca outflow. In aortic rings, the vasorelaxant effects of HEI 713, less potent than diazoxide, were sensitive to glibenclamide and to the extracellular K+ concentration. The drug elicited a glibenclamide‐sensitive increase in 86Rb outflow from perifused rat aortic rings. Our data describe an original compound which inhibits insulin release with a similar potency to diazoxide but which has fewer vasorelaxant effects. Our results suggest that, in both aortic rings and islet tissue, the biological effects of HEI 713 mainly result from activation of KATP channels ultimately leading to a decrease in Ca2+ inflow.

Mechanical and ionic response of rat aorta to diazoxide.

Diazoxide provoked concentration-dependent and endothelium-independent relaxations of the mechanical responses evoked by low concentrations of KCl. Glibenclamide, tolbutamide and tetraethylammonium shifted the concentration-response curve for diazoxide to the right. The drug also caused a dose-dependent stimulation of 86Rb outflow which was inhibited by glibenclamide and tolbutamide. Diazoxide (10(-4) and 10(-3) M) inhibited the contractions elicited by 10(-1) M K+ and provoked a concentration-dependent reduction in the contractile responses to Ca2+. Diazoxide also reduced the KCl (8 x 10(-2) M)-induced increase in 45Ca outflow. These data indicate that the vasorelaxant properties of diazoxide are probably related to an inhibition of Ca2+ entry into smooth muscle cells. The reduction in Ca2+ entry appears to result from K+ channel activation. At high concentrations, diazoxide also exhibited antagonistic actions on voltage-sensitive Ca2+ channels.

Nephroprotective effects of ferulic acid, Z-ligustilide and E-ligustilide isolated from Angelica sinensis against cisplatin toxicity in vitro

Cisplatin (CisPt), a chemotherapeutic drug applied against solid tumors, is highly detrimental to the kidney. The risk of acute kidney injury implies adequate patient hydration to ensure sufficient diuresis; this strategy, now implemented in clinical practice, remains however incompletely satisfactory. New pharmacological approaches relying on the discovery of bioactive compounds need to be developed. Based on previous studies reporting renoprotective activities for extracts of Angelica sinensis (Oliv.) Diels roots, three of its major active compounds, ferulic acid, Z-ligustilide and E-ligustilide, were investigated for possible alleviation of CisPt-induced nephrotoxicity. Five phenomena involved in acute kidney injury and subsequent fibrosis were investigated: (i) modulation of cell survival via reduction of the apoptosis rate; (ii) reduction of oxidative stress; (iii) improvement of tubular regeneration capacities through proliferation and migration; (iv) limitation of extracellular matrix and collagen deposition; and (v) prevention of the dedifferentiation processes via the β-catenin pathway. Ferulic acid emerged as the most potent compound for alleviating cell death and collagen deposition, and for enhancing cell regeneration capacities. It also partially inhibited the β-catenin pathway, but was ineffective in lowering oxidative stress. Z- and E-ligustilides, however, were effective for limiting the oxidative stress, but only moderately affected other parameters. Ferulic acid appears to be a promising nephroprotective drug lead deserving further preclinical investigation.

Protective effects of schizandrin and schizandrin B towards cisplatin nephrotoxicity in vitro.

Renal proximal tubular epithelial cells are the main targets of toxic drugs such as cisplatin (CisPt), an alkylating agent indicated for the treatment of solid organ tumors. Current techniques aiming at reducing nephrotoxicity in patients receiving CisPt are still not satisfactory as they can only partially prevent acute kidney injury. New nephroprotective strategies remain to be developed. In the present in vitro study, schizandrin (Schi) and schizandrin B (Schi B), major phytochemicals from Schisandra chinensis (Turcz.) Baill. fruits, were tested on HK‐2 cells along four processes that could help alleviate CisPt toxicity. Results indicated that: (i) both Schi and Schi B enhanced cell survival via reducing apoptosis rate; (ii) only Schi showed moderate effects towards modulation of regeneration capacities of healthy cells; (iii) both Schi and Schi B limited extracellular matrix deposition; and (iv) both compounds could help preventing dedifferentiation processes via the β‐catenin pathway. Schi and Schi B present promising activities for future development of protective agents against CisPt nephrotoxicity. Copyright

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].

Hypoglycemic Sulfonylureas Antagonize the Effects of Cromakalim and Pinacidil on 86Rb Fluxes and Contractile Activity in the Rat Aorta

Cromakalim, pinacidil and nitroprusside provoked concentration-dependent relaxations of K(+)-depolarized rat aortae. Glibenclamide, tolbutamide and to a lesser extent tetraethylammonium antagonized the vasorelaxant action of cromakalim and pinacidil. Cromakalim, pinacidil but not nitroprusside elicited a marked increase in 86Rb outflow from preloaded and perifused aortic rings. These increases in 86Rb outflow were inhibited in a concentration-dependent manner by glibenclamide and tetraethylammonium. Our data extend previous observations indicating the involvement of K+ channels in the vasorelaxant properties of cromakalim and pinacidil. Moreover, the present findings suggest that both compounds could interfere with a vascular type of ATP-sensitive K+ channels.

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.