Evidence for a direct stimulatory effect of cibenzoline on insulin secretion in rats

Combined sepsis- and renal dysfunction-induced hypoglycaemia in an older patient taking cibenzoline

Key Clinical Message

An 86-year-old geriatric patient with sepsis presented cibenzoline-induced hypoglycaemia, although within the boundary range of cibenzoline blood concentration.

Abstract

An 86-year-old geriatric patient taking cibenzoline for ametropic hypertrophic cardiac tendinopathy was admitted to our hospital for the treatment of sepsis. Upon admission, blood cibenzoline levels of 400.1 ng/mL were observed. Antibiotic therapy was initiated and cibenzoline was discontinued. On Day 16, cibenzoline was administered orally at a reduced dose of 50 mg/day. Several days after restarting cibenzoline, the patient developed hypoglycaemia (64 mg/dL), prompting the administration of 20% glucose. The present case demonstrates a rational timeline for cibenzoline administration, considering the patient's renal dysfunction and sepsis. Clinicians should exercise caution when managing older patients with severe infections who are receiving cibenzoline, and should consider the possibility of blood glucose fluctuations regardless of cibenzoline blood levels. Further research is warranted to better understand and address the potential side effects of cibenzoline administration in geriatric populations.

Cyclopropyl Scaffold: A Generalist for Marketed Drugs

In recent decades, much attention has been given to cyclopropyl scaffolds, which commonly exist in natural products and synthetic organic molecules. Clinical drug molecules with cyclopropyl rings are an area of focus in therapeutic research due to their interesting chemical properties and unique pharmacology activity. These molecular drugs against different targets are applicable in some therapeutic treatment fields including cancer, infection, respiratory disorder, cardiovascular and cerebrovascular diseases, dysphrenia, nervous system disorders, endocrine and metabolic disorders, skin disease, digestive disorders, urogenital diseases, otolaryngological and dental diseases, and eye diseases. This review is a guide for pharmacologists who are in search of valid preclinical/clinical drug compounds where the progress, from 1961 to the present day, of approved marketed drugs containing cyclopropyl scaffold is examined.

Pharmacodynamics of cibenzoline-induced hypoglycemia in rats

Hypoglycemia is one of the serious adverse effects induced by cibenzoline (CBZ), an antiarrhythmic agent. In order to clarify the pharmacodynamics of CBZ-induced hypoglycemia, CBZ was administered intravenously to conscious rats at a dose of 5, 10 or 20 mg/kg and serum samples were collected periodically to determine the concentrations of CBZ, insulin and glucose. The pharmacokinetics of CBZ showed nonlinear characteristics and could be described by a two-compartment model with Michaelis-Menten elimination kinetics. CBZ induced a rapid increase in the serum concentration of insulin. As the CBZ dose was increased, a greater hypoglycemic effect occurred. The indirect response model was applied to account for the CBZ-induced increase in insulin secretion and the subsequent decrease in serum glucose. A linear relationship was assumed between the serum concentration of CBZ and its stimulating effect on insulin secretion. A nonlinear relationship was assumed between the serum concentration of insulin and its stimulating effect on the elimination of serum glucose. The time courses of serum concentrations of CBZ, insulin and glucose after intravenous injection of CBZ could be described by the pharmacokinetic and pharmacodynamic model developed. This approach will be useful for the identification of variable factors related to CBZ-induced hypoglycemia.

Drug-Induced Endocrine and Metabolic Disorders

Complex interactions exist amongst the various components of the neuroendocrine system in order to maintain homeostasis, energy balance and reproductive function. These components include the hypothalamus-pituitary- adrenal and -gonadal axes, the renin-angiotensin-aldosterone system, the sympathetic nervous system and the pancreatic islets. These hormones, peptides and neurotransmitters act in concert to regulate the functions of many organs, notably the liver, muscles, kidneys, thyroid, bone, adrenal glands, adipocytes, vasculature, intestinal tract and gonads, through many intermediary pathways. Endocrine and metabolic disorders can arise from imbalance amongst numerous hormonal factors. These disturbances may be due to endogenous processes, such as increased secretion of hormones from a tumour, as well as exogenous drug administration. Drugs can cause endocrine abnormalities via different mechanisms, including direct alteration of hormone production, changes in the regulation of the hormonal axis, effects on hormonal transport, binding, and signalling, as well as similar changes to counter-regulatory hormone systems. Furthermore, drugs can affect the evaluation of endocrine parameters by causing interference with diagnostic tests. Common drug-induced endocrine and metabolic disorders include disorders of carbohydrate metabolism, electrolyte and calcium abnormalities, as well as drug-induced thyroid and gonadal disorders. An understanding of the proposed mechanisms of these drug effects and their evaluation and differential diagnosis may allow for more critical interpretation of the clinical observations associated with such disorders, better prediction of drug-induced adverse effects and better choices of and rationales for treatment.

Effect of levofloxacin on serum glucose concentration in rats

To clarify the mechanism of fluoroquinolone-induced abnormalities in blood glucose, the effect of levofloxacin on serum glucose concentration was investigated in rats. Rats received an intravenous injection of levofloxacin and their arterial blood was sampled periodically. The serum glucose concentration decreased after an injection of 100 mg/kg of levofloxacin, while it increased at levofloxacin 300 mg/kg. The serum immunoreactive insulin concentration increased as the dose of levofloxacin increased. The serum epinephrine concentration was rapidly elevated by levofloxacin at 300 mg/kg. The serum histamine concentration increased after injections of levofloxacin, 200 and 300 mg/kg. Diphenhydramine (1 mg/kg) antagonized the hyperglycemia induced by 300 mg/kg of levofloxacin. In an in vitro study, the release of epinephrine from the adrenal medulla in the presence of levofloxacin was determined. Levofloxacin (300 microg/ml) did not affect epinephrine release from the adrenal medulla. Levofloxacin can induce hypoglycemia and hyperglycemia in rats. Levofloxacin can promote histamine release, leading to an increased serum epinephrine concentration and hyperglycemia.

Design and synthesis of novel imidazoline derivatives with potent antihyperglycemic activity in a rat model of type 2 diabetes

Imidazoline derivatives have been reported to show antihyperglycemic activity in vivo. In the present study, we first showed that there was no correlation between the in vivo antidiabetic activity and the in vitro affinities for the I1/I2 binding sites for several substituted aryl imidazolines. Among these compounds, 2-(alpha-cyclohexyl-benzyl)-4,5-dihydro-1H-imidazole 2 exhibited potent antihyperglycemic properties. It was then chosen as lead compound. Thirty-six new derivatives were synthesized by replacing the cyclohexyl/benzyl group by various cyclic systems or the imidazoline ring by isosteric heterocycles. These compounds were evaluated in vivo for their antihyperglycemic activity using an oral glucose tolerance test (OGTT) in a rat model of type-2 diabetes obtained by giving a single intravenous (iv) injection of a low dose of streptozotocin to rats (STZ rats) and in normal rats. Nine compounds with an imidazoline moiety, possibly substituted by a methyl group, had a potent effect on the glucose tolerance in normal or STZ-diabetic rats, after an oral (po) administration of the test compound at a dose of 30 or 10 mg kg(-1), without any hypoglycemia. Replacement of the imidazoline ring by isosteric heterocycles resulted in a total loss of activity.

Pathways in beta-cell stimulus-secretion coupling as targets for therapeutic insulin secretagogues

Physiologically, insulin secretion is subject to a dual, hierarchal control by triggering and amplifying pathways. By closing ATP-sensitive K+ channels (KATP channels) in the plasma membrane, glucose and other metabolized nutrients depolarize beta-cells, stimulate Ca2+ influx, and increase the cytosolic concentration of free Ca2+ ([Ca2+]i), which constitutes the indispensable triggering signal to induce exocytosis of insulin granules. The increase in beta-cell metabolism also generates amplifying signals that augment the efficacy of Ca2+ on the exocytotic machinery. Stimulatory hormones and neurotransmitters modestly increase the triggering signal and strongly activate amplifying pathways biochemically distinct from that set into operation by nutrients. Many drugs can increase insulin secretion in vitro, but only few have a therapeutic potential. This review identifies six major pathways or sites of stimulus-secretion coupling that could be aimed by potential insulin-secreting drugs and describes several strategies to reach these targets. It also discusses whether these perspectives are realistic or theoretical only. These six possible beta-cell targets are 1) stimulation of metabolism, 2) increase of [Ca2+]i by closure of K+ ATP channels, 3) increase of [Ca2+]i by other means, 4) stimulation of amplifying pathways, 5) action on membrane receptors, and 6) action on nuclear receptors. The theoretical risk of inappropriate insulin secretion and, hence, of hypoglycemia linked to these different approaches is also envisaged.

Cibenzoline, an ATP-sensitive K(+) channel blocker, binds to the K(+)-binding site from the cytoplasmic side of gastric H(+),K(+)-ATPase

1. Cibenzoline, (+/-)-2-(2,2-diphenylcyclopropyl-2-imidazoline succinate, has been clinically used as one of the Class I type antiarrhythmic agents and also reported to block ATP-sensitive K(+) channels in excised membranes from heart and pancreatic beta cells. In the present study, we investigated if this drug inhibited gastric H(+),K(+)-ATPase activity in vitro. 2. Cibenzoline inhibited H(+),K(+)-ATPase activity of permeabilized leaky hog gastric vesicles in a concentration-dependent manner (IC(50): 201 microM), whereas no effect was shown on Na(+),K(+)-ATPase activity of dog kidney (IC(50): >1000 microM). Similarly, cibenzoline inhibited H(+),K(+)-ATPase activity of HEK-293 cells (human embryonic kidney cell line) co-transfected with rabbit gastric H(+),K(+)-ATPase alpha- and beta-subunit cDNAs (IC(50): 183 microM). 3. In leaky gastric vesicles, inhibition of H(+),K(+)-ATPase activity by cibenzoline was attenuated by the addition of K(+) (0.5 - 5 mM) in a concentration-dependent manner. The Lineweaver-Burk plot of the H(+),K(+)-ATPase activity shows that cibenzoline increases K(m) value for K(+) without affecting V(max), indicating that this drug inhibits H(+),K(+)-ATPase activity competitively with respect to K(+). 4. The inhibitory effect of H(+),K(+)-ATPase activity by cibenzoline with normal tight gastric vesicles did not significantly differ from that with permeabilized leaky gastric vesicles, indicating that this drug reacted to the ATPase from the cytoplasmic side of the membrane. 5. These findings suggest that cibenzoline is an inhibitor of gastric H(+),K(+)-ATPase with a novel inhibition mechanism, which inhibits gastric H(+),K(+)-ATPase by binding its K(+)-recognition site from the cytoplasmic side.

Effect of the new imidazoline derivative S-22068 (PMS 847) on insulin secretion in vitro and glucose turnover in vivo in rats

We have investigated the possible mechanisms underlying the antihyperglycaemic effect of the imidazoline derivative S-22068. In vitro, in the presence of 5 mmol/l glucose, S-22068 (100 micromol/l) induced a significant and sustained increase in insulin secretion from isolated, perifused, rat islets and a marked sensitization to a subsequent glucose challenge (10 mmol/l). S-22068 (100 micromol/l was able to antagonize the stimulatory effect of diazoxide on 86Rb efflux from preloaded islets incubated in the presence of 20 mmol/l glucose. Experiments were also performed to investigate whether S-22068 can alter glucose turnover and peripheral insulin sensitivity in vivo in mildly diabetic rats and obese, insulin resistant, Zucker rats. Neither glucose production nor individual tissue glucose utilization was modified by S-22068 in either group of rats. Similar results were obtained whether the studies were performed under basal conditions or during euglycaemic/hyperinsulinemic clamps. The results suggest that S-22068 exerts part of its antihyperglycaemic effect by promoting insulin secretion without alteration of peripheral insulin sensitivity.

The antiarrhythmic agent cibenzoline inhibits KATP channels by binding to Kir6.2

We reported previously that cibenzoline, an antiarrhythmic agent, inhibits the ATP-sensitive K+ (KATP) channels of pancreatic beta-cells through a binding site distinct from that for glibenclamide. In the present study, we have determined the locus of the action of cibenzoline on KATP channels reconstituted with mutant Kir6.2 and SUR1. We expressed a C-terminal truncated Kir6.2 (Kir6. 2DeltaC26) with and without SUR1 in COS7 cells. Both Kir6.2DeltaC26 and Kir6.2DeltaC26 + SUR1 formed functional KATP channels. Glibenclamide inhibited Kir6.2DeltaC26 + SUR1 channels but failed to inhibit Kir6.2DeltaC26. In contrast, cibenzoline inhibited equally Kir6.2DeltaC26 and Kir6.2DeltaC26 + SUR1 channels, in a dose-dependent manner, the half-maximal concentrations of channel inhibition being 22.2 +/- 6.1 and 30.9 +/- 9.4 microM, respectively. Furthermore, we determined also that [3H]cibenzoline bound to Kir6. 2DeltaC26. These findings confirm that cibenzoline inhibits KATP channels by a novel inhibitory mechanism in which cibenzoline directly affects the pore-forming Kir6.2 subunit rather than the SUR1 subunit.

Potent antihyperglycaemic property of a new imidazoline derivative S-22068 (PMS 847) in a rat model of NIDDM

Recent data suggest that some imidazoline derivatives can lower plasma glucose in experimental animal models of diabetes. We studied the activity of an imidazoline S-22068, in rat model of non-insulin-dependent diabetes mellitus (NIDDM) produced with a low dose of streptozotocin (35 mg kg(-1), i.v.) in the adult. The respective increase over basal value in glucose (deltaG) and insulin (deltaI), and the rate of glucose disappearance (K), were measured during a 30 min intravenous glucose tolerance test. After an intraperitoneal injection of S-22068 (24 mg kg(-1)), deltaG (mM min(-1)) was decreased (91.67+/-5.83 vs 120.5+/-3.65; P<0.001), whereas K was increased (1.74+/-0.09 vs 1.18+/-0.05; P<0.001). Although insulinaemia was increased at time-point 0 of the test, deltaI was unchanged. During oral glucose tolerance tests (OGTT), S-22068 (24 mg kg(-1), p.o.) improved glucose tolerance, and its efficiency was potentiated after chronic treatment (15 days). Basal glycaemia was unaffected by the treatment. Under the same conditions, a higher dose of S-22068 (40 mg kg(-1)) further improved glucose tolerance without causing hypoglycaemia. Binding experiments revealed that S-22068 displays no affinity for either adrenoceptors or the two imidazoline receptors I1 or I2. These results demonstrate that S-22068 improves glucose tolerance without causing hypoglycaemia. Thus S-22068 represents a new potential option in the treatment of NIDDM.

Metabolic inhibition impairs ATP-sensitive K+ channel block by sulfonylurea in pancreatic beta-cells

The effect of metabolic inhibition on the blocking of beta-cell ATP-sensitive K+ channels (KATP channels) by glibenclamide was investigated using a patch-clamp technique. Inhibition of KATP channels by glibenclamide was attenuated in the cell-attached mode under metabolic inhibition induced by 2,4-dinitrophenol. Under a low concentration (0.1 microM) of ATP applied in the inside-out mode, KATP channel activity was not fully abolished, even when a high dose of glibenclamide was applied, in contrast to the dose-dependent and complete KATP channel inhibition under 10 microM ATP. On the other hand, cibenzoline, a class Ia antiarrhythmic agent, inhibits KATP channel activity in a dose-dependent manner and completely blocks it, even under metabolic inhibition. In sulfonylurea receptor (SUR1)- and inward rectifier K+ channel (Kir6.2)-expressed proteins, cibenzoline binds directly to Kir6.2, unlike glibenclamide. Thus, KATP channel inhibition by glibenclamide is impaired under the condition of decreased intracellular ATP in pancreatic beta-cells, probably because of a defect in signal transmission between SUR1 and Kir6.2 downstream of the site of sulfonylurea binding to SUR1.

Block of pancreatic ATP-sensitive K+ channels and insulinotrophic action by the antiarrhythmic agent, cibenzoline

1. We investigated the effect of cibenzoline (a class Ia antiarrhythmic drug) on basal insulin secretory activity of rat pancreatic islets and ATP-sensitive K+ channels (KATP) in single pancreatic beta cells of the same species, using radioimmunoassay and patch clamp techniques. 2. Micromolar cibenzoline had a dose-dependent insulinotrophic action with an EC50 of 94.2 +/- 46.4 microM. The compound inhibited the activity of the KATP channel recorded from a single beta-cell in a concentration-dependent manner. The IC50 was 0.4 microM in the inside-out mode and 5.2 microM in the cell-attached mode, at pH 7.4. 3. In the cell-attached mode, alkalinization of extracellular solution increased the inhibitory action of cibenzoline and the IC50 was reduced from 26.8 microM at pH 6.2 to 0.9 microM at pH 8.4. On the other hand, the action of cibenzoline in the excised inside-out mode was acute in onset with a small IC50, indicating that the drug attains its binding site from the cytoplasmic side of the cell membrane. 4. In the inside-out mode, micromolar ADP reactivated the cibenzoline-blocked KATP channels in a manner similar to that by which ADP restored ATP-dependent block of the channel. 5. The binding of [3H]-glibenclamide to pancreatic islets was inhibited by glibenclamide but not by cibenzoline. In contrast, the [3H]-cibenzoline binding was displaced by unlabelled cibenzoline but not by glibenclamide. It is concluded that cibenzoline blocks pancreatic KATP channels via a binding site distinct from the sulphonylurea receptor.

Developmental alteration and neuron-specific expression of bone morphogenetic protein-6 (BMP-6) mRNA in rodent brain

Bone morphogenetic proteins (BMPs) are a group of proteins which induce bone formation from mesenchymal cells. The existence of BMPs in the nervous system as well as in bone tissue has recently been reported. In this study, we show that BMP-6 is neuron-specific, and describe the temporal and spatial expression patterns of BMP-6 mRNA in the developing rat and gerbil brain. Northern blot analysis showed that the BMP-6 transcript level was specifically high from newborn to 3 weeks after birth compared with those in fetal and adult rats. In situ hybridization showed that most of the neurons possessed high levels of BMP-6 mRNA in the neonatal brain, while in the adult brain, BMP-6 mRNA level was significantly decreased in most of the neurons except those in hippocampus which retained high levels. Furthermore, to show that the BMP-6 expression was specific to neurons, we induced delayed neuronal cell death and compensative glial cell proliferation in the gerbil hippocampus by transient ischemia. Our findings collectively suggest that BMP-6 is neuron-specific and may play important roles in neuronal maturation and synapse formation.

Inhibition of the ATP-sensitive potassium channel by class I antiarrhythmic agent, cibenzoline, in rat pancreatic beta-cells

1. Cibenzoline, a class I antiarrhythmic agent, was investigated for its effect on the ATP-sensitive K+ channel of pancreatic beta-cells by the patch clamp technique. 2. In perforated patch clamp experiments, cibenzoline depolarized the membrane of single beta-cells and thereafter, caused firing of action potentials in the presence of 2.8 mM glucose. 3. Cibenzoline inhibited the activity of the ATP-sensitive K+ channel in cell-attached recordings in the presence of 2.8 mM glucose and evoked repetitive fluctuations of the baseline current, apparently reflecting the action potentials of the beta-cell. 4. In whole-cell clamp experiments, time-independent outward current was induced by depleting cytoplasmic ATP with 0.1 mM ATP and 0.1 mM ADP in the solution contained in the pipette. The outward current was inhibited by cibenzoline in a dose-dependent manner in the concentration range of 1 microM to 100 microM and half maximum inhibition occurred at 1.5 microM. 5. Cibenzoline blocked substantially the ATP-sensitive K+ channel current when applied at the inner side of the membrane in isolated inside-out membrane patches. 6. It is concluded that cibenzoline blocks the ATP-sensitive K+ channel of pancreatic beta-cells and, thereby, stimulates insulin secretion at sub-stimulatory levels of glucose.