John Bondo Hansen

Phenylpiperidine selective serotonin reuptake inhibitors interfere with multidrug efflux pump activity in Staphylococcus aureus

Structural variants of phenylpiperidine selective serotonin reuptake inhibitors (P-SSRIs) inhibited the function of two unique Staphylococcus aureus multidrug efflux pumps. The most active compound was the paroxetine isomer NNC 20-7052, which had an IC(50) for ethidium, acriflavine, and pyronin Y efflux of 9, 53, and 18% of its MIC, respectively, against the NorA pump. The unbalanced effect of NNC 20-7052 on the efflux of different substrates suggests the possibility that P-SSRIs function by a physical interaction with NorA. Under the conditions employed pump inhibition partially extended to the resistance-nodulation-division (RND) pump AcrAB-TolC, but not to the Pseudomonas aeruginosa RND pumps MexAB-OprM or MexCD-OprJ.

Kir6.2-dependent high-affinity repaglinide binding to β-cell KATP channels

1 The β‐cell KATP channel is composed of two types of subunit – the inward rectifier K+ channel (Kir6.2) which forms the channel pore, and the sulphonylurea receptor (SUR1), which serves as a regulatory subunit. The N‐terminus of Kir6.2 is involved in transduction of sulphonylurea binding into channel closure, and deletion of the N‐terminus (Kir6.2ΔN14) results in functional uncoupling of the two subunits. In this study, we investigate the interaction of the hypoglycaemic agents repaglinide and glibenclamide with SUR1 and the effect of Kir6.2 on this interaction. We further explore how the binding properties of repaglinide and glibenclamide are affected by functional uncoupling of SUR1 and Kir6.2 in Kir6.2ΔN14/SUR1 channels. All binding experiments are performed on membranes in ATP‐free buffer at 37°C. 2 Repaglinide was found to bind with low affinity (KD=59±16 nM) to SUR1 alone, but with high affinity (increased ∼150‐fold) when SUR1 was co‐expressed with Kir6.2 (KD=0.42±0.03 nM). Glibenclamide, tolbutamide and nateglinide all bound with marginally lower affinity to SUR1 than to Kir6.2/SUR1. 3 Repaglinide bound with low affinity (KD=51±23 nM) to SUR1 co‐expressed with Kir6.2ΔN14. In contrast, the affinity for glibenclamide, tolbutamide and nateglinide was only mildly changed as compared to wild‐type channels. 4 In whole‐cell patch‐clamp experiments inhibition of Kir6.2ΔN14/SUR1 currents by both repaglinide and nateglinde is abolished. 5 The results suggest that Kir6.2 causes a conformational change in SUR1 required for high‐affinity repaglinide binding, or that the high‐affinity repaglinide‐binding site includes contributions from both SUR1 and Kir6.2. Glibenclamide, tolbutamide and nateglinide binding appear to involve only SUR1.

Inhibition of cisplatin-induced emesis in ferrets by the non-NMDA receptor antagonists NBQX and CNQX.

The excitatory amino acid (EAA) receptor antagonists, 2,3-dihydroxy-6-nitro-7-sulphamoylbenzo(f)quinoxaline (NBQX) and 6-cyano-7-nitroquinoxaline-2,3-dione (CNQX), which preferentially block non-N-methyl-D-aspartate (non-NMDA) subtypes of EAA receptors, effectively inhibit cisplatin-induced emesis in ferrets. A high dose of cisplatin (10 mg/kg i.v.) was used which induced emesis in all saline-treated control ferrets. At 10 mg/kg i.v., NBQX totally prevented cisplatin-induced emesis in 5 of 6 ferrets and CNQX totally prevented emesis in 3 of 5 ferrets. By comparison, each of the 5-HT3 inhibitors, zacopride and ondansetron, at 1.0 mg/kg i.v. (a dose considered in the high therapeutic range for controlling emesis by these compounds), totally prevented emesis in 2 of 5 ferrets. It is concluded that non-NMDA antagonists effectively inhibit cisplatin-induced emesis. They are potential antiemetic compounds, alone or in combination with 5-HT3 antagonists or other more conventional drugs of choice.

Bioisosteric replacement strategy for the synthesis of 1-azacyclic compounds with high affinity for the central nicotinic cholinergic receptors

Bioisosteric replacement of the isoxazole heterocycle in (3-methyl-5-isoxazolyl)methylene-azacyclic compounds with pyridine, oxadiazole, or an acyl group resulted in ligands with high to moderate affinity for the central nicotinic cholinergic receptors (IC50 = 2.0 to IC50 > 1000 nM) labeled by [3H]methylcarbamylcholine. Additionally, further support of an important distance parameter for high-affinity nicotinic compounds has been provided.

Inhibition of HIV replication by neuroleptic agents and their potential use in HIV infected patients with AIDS related dementia

A series of neuroleptic agents and their structural isomers have been tested as inhibitors of HIV-replication. At non-toxic concentrations, cis (Z)- and trans (E)-flupentixol and several derivatives of the 5HT-uptake-inhibitors paroxetine and femoxetine, inhibit HIV-1 replication. The findings indicated that these compounds could be used in combination with other anti-retroviral therapy in HIV-1 infected patients with AIDS-related dementia.

Imidazoline NNC77-0074 stimulates insulin secretion and inhibits glucagon release by control of Ca2+-dependent exocytosis in pancreatic α- and β-cells

We have investigated the effects of the novel imidazoline compound (+)-2-(2-(4,5-dihydro-1H-imidazol-2-yl)-thiopene-2-yl-ethyl)pyridine (NNC77-0074) on stimulus-secretion coupling in isolated pancreatic alpha- and beta-cells. NNC77-0074 stimulated glucose-dependent insulin secretion in intact mouse pancreatic islets. No effect was observed at less than or equal to 2.5 mM glucose and maximal stimulation occurred at 10-15 mM glucose. NNC77-0074 produced a concentration-dependent stimulation of insulin secretion. Half-maximal (EC50) stimulation was observed at 24 muM and at maximally stimulatory concentrations insulin release was doubled. The stimulatory action of NNC77-0074 on insulin secretion was not associated with membrane depolarisation or a change in the activity of ATP-sensitive K+ channels. Using capacitance measurements, we found that NNC77-0074 stimulated depolarisation-induced exocytosis 2.6-fold without affecting the whole-cell Ca2+ current when applied via the extracellular medium. The concentration dependence of the stimulatory action was determined by intracellular application of NNC77-0074 through the recording pipette. NNC77-0074 stimulated exocytosis half-maximal at 44 nM and at maximally stimulatory concentrations the rate of exocytosis was increased twofold. NNC77-0074 stimulated depolarised-induced insulin secretion from islets exposed to diazoxide and high external KCl (EC50 = 0.45 muM). The stimulatory action of NNC77-0074 was dependent on protein kinase C activity. NNC77-0074 potently inhibited glucagon secretion from rat islets (EC50 = I I nM). This was not associated with a change in spontaneous electrical activity and ATP-sensitive K channel activity but resulted from a reduction of the rate of Ca2+-dependent exocytosis in single rat alpha-cells (EC50=9 nM). Inhibition of exocytosis by NNC77-0074 was pertussis toxin-sensitive and mediated by activation of the protein phosphatase calcineurin. In rat somatotrophs, PC12 cells and mouse cortical neurons NNC77-0074 did not stimulate Ca2+-evoked exocytosis, whereas the other imidazoline compounds phentolamine and efaroxan produced 2.5-fold stimulation of exocytosis. Our data suggest that the imidazoline compound NNC77-0074 constitutes a novel class of antidiabetic compounds that stimulates glucose-dependent insulin release while inhibiting glucagon secretion. These actions are exclusively exerted by modulation of exocytosis of the insulin- and glucagon-containing granules

The Actions of a Novel Potent Islet β-Cell–Specific ATP-Sensitive K+ Channel Opener Can Be Modulated by Syntaxin-1A Acting on Sulfonylurea Receptor 1

Islet β-cell–specific ATP-sensitive K+ (KATP) channel openers thiadiazine dioxides induce islet rest to improve insulin secretion, but their molecular basis of action remains unclear. We reported that syntaxin-1A binds nucleotide binding folds of sulfonylurea receptor 1 (SUR1) in β-cells to inhibit KATP channels. As a strategy to elucidate the molecular mechanism of action of these KATP channel openers, we explored the possibility that 6-chloro-3-(1-methylcyclobutyl)amino-4H-thieno[3,2-e]-1,2,4-thiadiazine 1,1-dioxide (NNC55-0462) might influence syntaxin-1A–SUR1 interactions or vice versa. Whole-cell and inside-out patch-clamp electrophysiology was used to examine the effects of glutathione S-transferase (GST)-syntaxin-1A dialysis or green fluorescence protein/syntaxin-1A cotransfection on NNC55-0462 actions. In vitro pull-down binding studies were used to examine NNC55-0462 influence on syntaxin-1A–SUR1 interactions. Dialysis of GST–syntaxin-1A into the cell cytoplasm reduced both potency and efficacy of extracellularly perfused NNC55-0462 in a HEK cell line stably expressing Kir6.2/SUR1 (BA8 cells) and in rat islet β-cells. Moreover, inside-out membrane patches excised from BA8 cells showed that both GST–syntaxin-1A and its H3 domain inhibited KATP channels previously activated by NNC55-0462. This action on KATP channels is isoform-specific to syntaxin-1A because syntaxin-2 was without effect. Furthermore, the parent compound diazoxide showed similar sensitivity to GST–syntaxin-1A inhibition. NNC55-0462, however, did not influence syntaxin-1A–SUR1 binding interaction. Our results demonstrated that syntaxin-1A interactions with SUR1 at its cytoplasmic domains can modulate the actions of the KATP channel openers NNC55-0462 and diazoxide on KATP channels. The reduced levels of islet syntaxin-1A in diabetes would thus be expected to exert a positive influence on the therapeutic effects of this class of KATP channel openers.

KATP Channels and Pancreatic Islet Blood Flow in Anesthetized Rats: Increased Blood Flow Induced by Potassium Channel Openers

K(ATP) channels are important for insulin secretion and depolarization of vascular smooth muscle. In view of the importance of drugs affecting K(ATP) channels in the treatment of diabetes, we investigated the effects of these channels on splanchnic blood perfusion in general and pancreatic islet blood flow in particular. We treated anesthetized Sprague-Dawley rats with the K(ATP) channel openers diazoxide or NNC 55-0118 or the K(ATP) channel closer glipizide. Both diazoxide and NNC 55-0118 dose-dependently increased total pancreatic and islet blood flow in the presence of moderate hyperglycemia, but had no effects on the blood perfusion of other splanchnic organs. Diazoxide markedly lowered the mean arterial blood pressure and thus increased vascular conductance in all organs studied. NNC 55-0118 had much smaller effects on the blood pressure. Glipizide did not affect total pancreatic blood flow, but decreased islet blood flow by 50% in the presence of hypoglycemia. We conclude that K(ATP) channels actively participate in the blood flow regulation of the pancreatic islets and that substances affecting such channels may also influence islet blood flow.

Possible role of an ischemic preconditioning-like response mechanism in KATP channel opener-mediated protection against streptozotocin-induced suppression of rat pancreatic islet function

Potassium channel openers (KCOs) decrease insulin secretion from beta-cells. Some KCOs also protect against damage to beta-cell function and type 1 diabetes in animal models. Previously we have found that the KCO NNC 55-0118 counteracted islet cell dysfunction, and this was associated with a lowering of the mitochondrial membrane potential (Deltapsi). Presently we aimed to explore whether inhibition of insulin secretion per se or rather inhibition of mitochondrial function correlates to counteraction of beta-cell suppression. For this we used two novel KCOs (NNC 55-0321 and NNC 55-0462), which at certain concentrations have different actions regarding insulin secretion and the Deltapsi, with NNC 55-0321 being a potent inhibitor of Deltapsi and NNC 55-0462 being a potent inhibitor of insulin secretion. At 10 microM NNC 55-0321, but not with NNC 55-0462, the islet ATP content and ATP/ADP ratio was acutely decreased. This was accompanied by a complete protection against streptozotocin-induced suppression of islet insulin secretion using the former KCO. In cardiac research KCOs have been used to induce an ischemic preconditioning (IPC) response. In line with an IPC-like mechanism we found that NNC 55-0321 induced an initial free oxygen radical formation, PKC-epsilon isoform activation and a subsequent phosphorylation of the survival promoting factor Akt. Thus, KCOs may elicit mitochondrial events that resemble classical IPC seen in cardiomyocytes, and this could explain the enhanced islet cell function observed. KCOs with this property may be particularly interesting compounds to study as a rescue therapy during acute episodes of beta-cell suppression/destruction.

NNC 19-1228 and NNC 22-0031, novel neuroleptics with a “mesolimbic-selective” behavioral profile

Abstract NNC 19-1228 [1-(3(6-benzothiazolylcarbamoyloxy)propyl)-4-(6-flouro-1,2-benzisoxazol-3-yl)piperidine] and NNC 22-0031 [4-(6-flouro-1,2-benzisoxazol-3-yl)-1-(3-(3,4-methylenedioxyphenylcarbamoyloxy)propyl)piperidine] are newly developed compounds with an in vitro pharmacologic profile similar to that of clozapine, i.e., mixed dopamine (DA), 5-hydroxytryptamine (5-HT)2 and α1-adrenergic antagonist action. In pharmacological experiments in mice, the compounds inhibited DA D2 receptor binding in vivo at doses that produced only moderate antagonism of methylphenidate (MPD)-induced stereotyped gnawing. However, the compounds were markedly more potent in blocking MPD-induced motility, a model which showed a high degree of sensitivity to α1-adrenergic antagonism, but not 5-HT2 antagonism. In rats, the NNC-compounds blocked conditioned avoidance responding and attenuated the discriminative stimulus effects of amphetamine, but failed to induce catalepsy. These results are discussed in terms of adrenergic, serotonergic and dopaminergic interactions which suggest that the NNC compounds may act as DA antagonists with mesolimbic selectivity, and thus may have efficacy as antipsychotics without coincident extrapyramidal side effects.