Effect of englitazone on KATP and calcium-activated non-selective cation channels in CRI-G1 insulin-secreting cells

Synthetic Strategies of Thiazolidine-2,4-dione Derivatives for the Development of New Anti-diabetic Agents: Compressive Review

BACKGROUND

Thiazolidine-2,4-dione (2,4-TZD) is a flexible pharmacophore and a privileged platform and contains a five-membered ring with a 2-oxygen atom with double bond 2,4- position and one nitrogen atom as well as sulphur containing in the heterocyclic compound. A famous electron-rich nitrogen transporter combines invigorating electronic properties with the prospective for elemental applications. Thiazolidine-2,4-dione analogues have been synthesized using a variety of methods, all of which have shown to have a strong biological effect.

OBJECTIVES

The study of the biological activity of Thiazolidine-2,4-dione derivatives has been a fascinating field of pharmaceutical chemistry and has many purposes. This derivative described in the literature between 1995 to 2023 was the focus of this study. Thiazolidine-2,4-diones have been discussed in terms of their introduction, general method, synthetic scheme and antidiabetic significance in the current review.

CONCLUSION

Thiazolidine-2,4-diones are well-known heterocyclic compounds. The synthesis of Thiazolidine-2,4-diones has been described using a variety of methods. Antidiabetic activity has been discovered in several Thiazolidine-2,4-dione derivatives, which enhance further research. The use of Thiazolidine-2,4-diones to treat antidiabetics has piqued researchers' interest in learning more about thiazolidine-2,4-diones.

Lipophilicity predicts the ability of nonsulphonylurea drugs to block pancreatic beta-cell KATP channels and stimulate insulin secretion; statins as a test case

AIMS

KATP ion channels play a key role in glucose-stimulated insulin secretion. However, many drugs block KATP as "off targets" leading to hyperinsulinaemia and hypoglycaemia. As such drugs are often lipophilic, the aim was to examine the relationship between drug lipophilicity (P) and IC 50 for KATP block and explore if the IC 50's of statins could be predicted from their lipophilicity and whether this would allow one to forecast their acute action on insulin secretion.

MATERIALS AND METHODS

A meta-analysis of 26 lipophilic, nonsulphonylurea, blockers of KATP was performed. From this, the IC 50's for pravastatin and simvastatin were predicted and then tested experimentally by exploring their effects on KATP channel activity via patch-clamp measurement, calcium imaging and insulin secretion in murine beta cells and islets.

RESULTS

Nonsulphonylurea drugs inhibited KATP channels with a Log IC 50 linearly related to their logP. Simvastatin blocked KATP with an IC 50 of 25 nmol/L, a value independent of cytosolic factors, and within the range predicted by its lipophilicity (21-690 nmol/L). 10 μmol/L pravastatin, predicted IC 50 0.2-12 mmol/L, was without effect on the KATP channel. At 10-fold therapeutic levels, 100 nmol/L simvastatin depolarized the beta-cell membrane potential and stimulated Ca2+ influx but did not affect insulin secretion; the latter could be explained by serum binding.

CONCLUSIONS

The logP of a drug can aid prediction for its ability to block beta-cell KATP ion channels. However, although the IC 50 for the block of KATP by simvastatin was predicted, the difference between this and therapeutic levels, as well as serum sequestration, explains why hypoglycaemia is unlikely to be observed with acute use of this statin.

Thiazolidinedione drugs promote onset, alter characteristics, and increase mortality of ischemic ventricular fibrillation in pigs

PURPOSE

Despite favorable metabolic and vascular effects, thiazolidinedione (TZD) drugs have not convincingly reduced cardiovascular mortality in clinical trials, raising the possibility of countervailing, off-target effects. We previously showed that TZDs block cardiac ATP-sensitive potassium (K(ATP)) channels in pigs. In this study, we investigated whether TZDs affect onset, spectral characteristics, and mortality of ischemic ventricular fibrillation (VF) and whether such effects are recapitulated by a non-selective K(ATP) blocker (glyburide) or a mitochondrial K(ATP) blocker (5-hydroxydecanoate).

METHODS

A total of 121 anesthetized pigs were pre-treated with TZD (pioglitazone or rosiglitazone, 1 mg/kg IV, resulting in clinically relevant plasma concentrations), glyburide (1 mg/kg IV), 5-hydroxydecanoate (5 mg/kg IV) or inert vehicle. Ischemia was produced by occlusion of the left anterior descending coronary artery. In a subset of pigs treated with rosiglitazone or vehicle, ischemic preconditioning was performed.

RESULTS

VF developed in all but 6 pigs. In non-preconditioned pigs, onset of VF occurred sooner with pioglitazone (11±3 min, p<0.05) or rosiglitazone (14±3 min, p=0.06) than with vehicle (20±2 min). Defibrillation of VF was successful in 44% of pigs treated with vehicle, compared with 0% with pioglitazone (p=0.057) and 33% with rosiglitazone (NS). After ischemic preconditioning, defibrillation was successful in 62% of pigs treated with vehicle, compared with 26% treated with rosiglitazone (p=0.03). TZDs attenuated slowing of conduction due to ischemia and shifted ECG power spectra during VF toward higher frequencies. All effects of TZDs were recapitulated by glyburide, but not by 5-hydroxydecanoate, supporting an interaction of TZDs with the sarcolemmal K(ATP) channel.

CONCLUSION

In a porcine model, TZDs promote onset and increase mortality of ischemic VF, associated with alterations of conduction and VF spectral characteristics. Similar effects in a clinical setting might adversely impact cardiovascular mortality.

PPAR-γ as a therapeutic target in cardiovascular disease: evidence and uncertainty

Peroxisome proliferator-activated receptor γ (PPAR-γ) is a key regulator of fatty acid metabolism, promoting its storage in adipose tissue and reducing circulating concentrations of free fatty acids. Activation of PPAR-γ has favorable effects on measures of adipocyte function, insulin sensitivity, lipoprotein metabolism, and vascular structure and function. Despite these effects, clinical trials of thiazolidinedione PPAR-γ activators have not provided conclusive evidence that they reduce cardiovascular morbidity and mortality. The apparent disparity between effects on laboratory measurements and clinical outcomes may be related to limitations of clinical trials, adverse effects of PPAR-γ activation, or off-target effects of thiazolidinedione agents. This review addresses these issues from a clinician's perspective and highlights several ongoing clinical trials that may help to clarify the therapeutic role of PPAR-γ activators in cardiovascular disease.

Serine-385 phosphorylation of inwardly rectifying K+ channel subunit (Kir6.2) by AMP-dependent protein kinase plays a key role in rosiglitazone-induced closure of the K(ATP) channel and insulin secretion in rats

AIMS/HYPOTHESIS

Rosiglitazone, an insulin sensitiser, not only improves insulin sensitivity but also enhances insulin secretory capacity by ameliorating gluco- and lipotoxicity in beta cells. Rosiglitazone can stimulate insulin secretion at basal and high glucose levels via a phosphatidylinositol 3-kinase (PI3K)-dependent pathway. We hypothesised that regulation of phosphorylation of the ATP-sensitive potassium (K(ATP)) channel might serve as a key step in the regulation of insulin secretion.

METHODS

Insulin secretory responses were studied in an isolated pancreas perfusion system, cultured rat islets and MIN6 and RINm5F beta cells. Signal transduction pathways downstream of PI3K were explored to link rosiglitazone to K(ATP) channel conductance with patch clamp techniques and insulin secretion measured by ELISA.

RESULTS

Rosiglitazone stimulated AMP-activated protein kinase (AMPK) activity and induced inhibition of the K(ATP) channel conductance in islet beta cells; both effects were blocked by the PI3K inhibitor LY294002. Following stimulation of AMPK by 5-aminoimidazole-4-carboxamide ribonucleoside (AICAR), a pharmacological activator, both AICAR-stimulated insulin secretion and inhibition of K(ATP) channel conductance were unaffected by LY294002, indicating that AMPK activation occurs at a site downstream of PI3K activity. The serine residue at amino acid position 385 of Kir6.2 was found to be the substrate phosphorylation site of AMPK when activated by rosiglitazone or AICAR.

CONCLUSIONS/INTERPRETATION

Our data indicate that PI3K-dependent activation of AMPK is required for rosiglitazone-stimulated insulin secretion in pancreatic beta cells. Phosphorylation of the Ser(385) residue of the Kir6.2 subunit of the K(ATP) channel by AMPK may play a role in insulin secretion.

Enhancing insulin action: from chemical elements to thiazolidinediones

Type 2 diabetes is characterized by two fundamental biological defects: a reduced glucose-dependent insulin secretion and an increased resistance to the action of insulin at the level of various target tissues. While the use of agents to improve the insulin secretory activity of the islets of Langerhans has witnessed the flourishing of several new drugs over the years, a much greater difficulty has been experienced in the search for insulin-sensitizing drugs. The aim of this article is to critically review this topic, and to emphasize the importance of providing alternative strategies for the management of Type 2 diabetes.

Sensitivity of Kir6.2-SUR1 currents, in the absence and presence of sodium azide, to the K(ATP) channel inhibitors, ciclazindol and englitazone

Two electrode voltage clamp and single channel recordings were used to investigate the actions of various ATP-sensitive K(+) (K(ATP)) channel inhibitors on cloned K(ATP) channels, expressed in Xenopus oocytes and HEK 293 cells. Oocytes expressing Kir6.2 and SUR1 gave rise to inwardly rectifying K(+) currents following bath application of 3 mM sodium azide. Inside-out recordings from non-azide treated oocytes demonstrated the presence of K(ATP) channels which were activated by direct application of 3 mM azide and 0.1 mM Mg-ATP. Tolbutamide inhibited azide-induced macroscopic Kir6.2-SUR1 currents, recorded from Xenopus oocytes, with an IC(50) value similar to native K(ATP) channels. Ciclazindol and englitazone also inhibited these currents in a concentration-dependent manner, but with relative potencies substantially less than for native K(ATP) channels. Single channel currents recorded from inside-out patches excised from oocytes expressing Kir6.2-SUR1 currents were inhibited by tolbutamide, Mg-ATP, englitazone and ciclazindol, in the absence of azide, with potencies similar to native K(ATP) channels. In the presence of azide, Kir6.2-SUR1 currents were inhibited by englitazone and tolbutamide but not ciclazindol. Single channel currents derived from Kir6.2Delta26, expressed in HEK 293 cells, were inhibited by ciclazindol and englitazone irrespective of the absence or presence of SUR1. In conclusion, heterologously expressed Kir6.2 and SUR1 recapitulate the pharmacological profile of native pancreatic beta-cell K(ATP) channels. However, currents induced by azide exhibit a substantially reduced sensitivity to ciclazindol. It is likely that ciclazindol and englitazone inhibit K(ATP) currents by interaction with the Kir6.2 subunit.

Cyclic AMP stimulates the gene expression of a non-selective cation channel, mNSC1, in pancreatic beta-cell line, MIN6

Mouse non-selective cation channel 1 (mNSC 1) cDNA from mouse pancreatic beta-cell line, MIN6, have recently been cloned. Since the number of non-selective cation channel in pancreatic duct cells has been reported to increase 9-fold in 5 h incubation with cAMP, the effect of cAMP on the gene expression of mNSC1 in MIN6 cells was examined. Dibutyryl cAMP (db-cAMP) was shown to increase the level of the mRNA by reverse transcription-polymerase chain reaction (RT-PCR). The copy number of the mRNA was increased 4-fold in 6 h incubation with db-cAMP by competitive PCR. Western blot analysis also indicated a 4-fold increase in the quantity of the newly synthesized protein in 9 h incubation with db-cAMP. Experiments with 5'-flanking region and with a transcriptional inhibitor suggested that db-cAMP affected transcription, and protected the mRNA from its degradation as well. It is concluded that the expression of mNSC1 is indeed increased by cAMP in the pancreatic beta-cells.

Adenosine triphosphate-sensitive potassium channels are involved in insulin-mediated glucose transport in humans

We investigated the influence of treatment with nicorandil, a K-channel opener currently used for angina, on glucose homeostasis in patients with non-insulin-dependent diabetes mellitus (NIDDM) and coronary artery disease (CAD). Adenosine triphosphate (ATP)-sensitive K (K-ATP) channels are present in various tissues, including pancreatic B cells and skeletal muscle, and are the putative targets of this agent. Nine NIDDM patients with CAD and five healthy subjects participated in the study. Fasting plasma levels (mean+/-SEM) of glucose (144+/-11 to 180+/-22 mg/dL, P<.05) and insulin (5.8+/-1.6 to 7.0+/-1.8 microU/mL, P<.05) and hemoglobin A1c (7.54+/-0.47 to 8.11+/-0.55%, P<.01) increased significantly in nine NIDDM patients after treatment with nicorandil at a dose of 5 mg three times daily for 2 to 8 months. Glucose tolerance as examined by an identical meal test deteriorated (P<.001), but the insulin response did not change significantly. A washout of nicorandil for 1 to 4 months restored glucose tolerance almost to pretreatment levels in four patients. A 5- to 7-day trial of nicorandil (5 mg three times daily) in five healthy subjects resulted in a marginal to twofold increase in fasting plasma insulin, reflecting the progression of insulin resistance. In addition, three healthy subjects showed a substantial reduction in the glucose infusion rate (GIR) required in the euglycemic-hyperinsulinemic clamp study. Since the therapeutic dose of nicorandil did not affect pancreatic B-cell function but caused insulin resistance in both healthy and NIDDM subjects, we conclude that K-ATP channels play a regulatory role in insulin-mediated glucose transport in humans.

Effects of troglitazone and pioglitazone on the action potentials and membrane currents of rabbit ventricular myocytes

The effects of the antidiabetic thiazolidinediones troglitazone and pioglitazone on action potentials and membrane currents were studied in rabbit ventricular myocytes. Troglitazone (10 microM) reversibly reduced excitability of the myocytes and modified their action potential configuration. It significantly increased the stimulation threshold required to elicit action potentials and decreased action potential amplitude and the maximum upstroke velocity of the action potentials. The Inhibition of the maximum upstroke velocity by troglitazone was also significant at 1 microM. Voltage-clamp experiments revealed that troglitazone (10 microM) reversibly inhibited both the slow inward Ca2+ current and the steady-state K+ current. In contrast to troglitazone, pioglitazone (1-10 microM) had no significant effect on the excitability, action potential configuration, or membrane currents of myocytes. These results suggest that troglitazone, but not pioglitazone, modulates Na+, Ca2+ and K+ currents, leading to the changes in excitability and action potential configuration of ventricular myocytes.

Diazoxide- and leptin-activated K(ATP) currents exhibit differential sensitivity to englitazone and ciclazindol in the rat CRI-G1 insulin-secreting cell line

1. The effects of the antidiabetic agent englitazone and the anorectic drug ciclazindol on ATP-sensitive K+ (K(ATP)) channels activated by diazoxide and leptin were examined in the CRI-G1 insulin-secreting cell line using whole cell and single channel recording techniques. 2. In whole cell current clamp mode, the hyperglycaemic agent diazoxide (200 microM) and the ob gene product leptin (10 nM) hyperpolarised CRI-G1 cells by activation of K(ATP) currents. K(ATP) currents activated by either agent were inhibited by tolbutamide, with an IC50 for leptin-activated currents of 9.0 microM. 3. Application of englitazone produced a concentration-dependent inhibition of K(ATP) currents activated by diazoxide (200 microM) with an IC50 value of 7.7 microM and a Hill coefficient of 0.87. In inside-out patches englitazone (30 microM) also inhibited K(ATP) channel currents activated by diazoxide by 90.8+/-4.1%. 4. In contrast, englitazone (1-30 microM) failed to inhibit K(ATP) channels activated by leptin, although higher concentrations (> 30 microM) did inhibit leptin actions. The englitazone concentration inhibition curve in the presence of leptin resulted in an IC50 value and Hill coefficient of 52 microM and 3.2, respectively. Similarly, in inside-out patches englitazone (30 microM) failed to inhibit the activity of K(ATP) channels in the presence of leptin. 5. Ciclazindol also inhibited K(ATP) currents activated by diazoxide (200 microM) in a concentration-dependent manner, with an IC50 and Hill coefficient of 127 nM and 0.33, respectively. Furthermore, application of ciclazindol (1 microM) to the intracellular surface of inside-out patches inhibited K(ATP) channel currents activated by diazoxide (200 microM) by 86.6+/-8.1%. 6. However, ciclazindol was much less effective at inhibiting KATP currents activated by leptin (10 nM). Ciclazindol (0.1-10 microM) had no effect on K(ATP) currents activated by leptin, whereas higher concentrations (> 10 microM) did cause inhibition with an IC50 value of 40 microM and an associated Hill coefficient of 2.7. Similarly, ciclazindol (1 microM) had no significant effect on K(ATP) channel activity following leptin addition in excised inside-out patches. 7. In conclusion, K(ATP) currents activated by diazoxide and leptin show different sensitivity to englitazone and ciclazindol. This may be due to differences in the mechanism of activation of K(ATP) channels by diazoxide and leptin.