Molecular Modeling, Synthesis, and Antihyperglycemic Activity of the New Benzimidazole Derivatives - Imidazoline Receptor Agonists

Introduction

The paper presents the results of a study on the first synthesized benzimidazole derivatives obtained from labile nature carboxylic acids. The synthesis conditions of these substances were studied, their structure was proved, and some components were found to have sugar-reducing activity on the model of alloxan diabetes in rats.

Methods

The study used molecular modeling methods such as docking based on the evolutionary model (igemdock), RP_HPLC method to monitor the synthesis reaction, and 1H NMR and 13C NMR, and other methods of organic chemistry to confirm the structures of synthesized substances.

Results & Discussion

The docking showed that the ursodeoxycholic acid benzimidazole derivatives have high tropics to all imidazoline receptor carriers (PDB ID: 2XCG, 2bk3, 3p0c, 1QH4). The ursodeoxycholic acid benzimidazole derivative and arginine and histidine benzimidazole derivatives showed the highest sugar-lowering activity in the experiment on alloxan-diabetic rats. For these derivatives, the difference in glucose levels of treated rats was significant against untreated control. Therefore, the new derivatives of benzimidazole and labile natural organic acids can be used to create new classes of imidazoline receptor inhibitors for the treatment of diabetes mellitus and hypertension.

Imidazoline ligand BU224 reverses cognitive deficits, reduces microgliosis and enhances synaptic connectivity in a mouse model of Alzheimer's disease

BACKGROUND AND PURPOSE

Activation of type 2 imidazoline receptors has been shown to exhibit neuroprotective properties including anti-apoptotic and anti-inflammatory effects, suggesting a potential therapeutic value in Alzheimer's disease (AD). Here, we explored the effects of the imidazoline-2 ligand BU224 in a model of amyloidosis.

EXPERIMENTAL APPROACH

Six-month-old female transgenic 5XFAD and wild-type (WT) mice were treated intraperitoneally with 5-mg·kg^-1 BU224 or vehicle twice a day for 10 days. Behavioural tests were performed for cognitive functions and neuropathological changes were investigated by immunohistochemistry, Western blot, elisa and qPCR. Effects of BU224 on amyloid precursor protein (APP) processing, spine density and calcium imaging were analysed in brain organotypic cultures and N2a cells.

KEY RESULTS

BU224 treatment attenuated spatial and perirhinal cortex-dependent recognition memory deficits in 5XFAD mice. Fear-conditioning testing revealed that BU224 also improved both associative learning and hippocampal- and amygdala-dependent memory in transgenic but not in WT mice. In the brain, BU224 reduced levels of the microglial marker Iba1 and pro-inflammatory cytokines IL-1β and TNF-α and increased the expression of astrocytic marker GFAP in 5XFAD mice. These beneficial effects were not associated with changes in amyloid pathology, neuronal apoptosis, mitochondrial density, oxidative stress or autophagy markers. Interestingly, ex vivo and in vitro studies suggested that BU224 treatment increased the size of dendritic spines and induced a threefold reduction in amyloid-β (Aβ)-induced functional changes in NMDA receptors.

CONCLUSION AND IMPLICATIONS

Sub-chronic treatment with BU224 restores memory and reduces inflammation in transgenic AD mice, at stages when animals display severe pathology.

The imidazoline receptors and ligands in pain modulation

Pain is an unpleasant experience and effects daily routine negatively. Although there are various drugs, many of them are not entirely successful in relieving pain, since pain modulation is a complex process involving numerous mediators and receptors. Therefore, it is a rational approach to identify the factors involved in the complex process and develop new agents that act on these pain producing mechanisms. In this respect, the involvement of the imidazoline receptors in pain modulation has drawn attention in recent years. In this review, it is aimed to focus on the imidazoline receptors and their ligands which contribute to the pain modulation. It is demonstrated that imidazoline-2 (I2) receptors are steady new drug targets for analgesics. Even if the mechanism of I2 receptor is not well known in the modulation of pain, it is known that it plays a role in tonic and chronic pain but not in acute phasic pain. Moreover, the I2 receptor ligands increase the analgesic effects of opioids in both acute and chronic pain and prevent the development of opioid tolerance. So, they are valuable for the chronic pain treatment and also therapeutic coadjuvants in the management of chronic pain with opiate drugs due to the attenuation of opioid tolerance and addiction. Thus, the use of the ligands which bind to the imidazoline receptors is an effective strategy for relieving pain. This educational forum exhibits the role of imidazoline receptors and ligands in pain process by utilizing experimental studies.

Platelet imidazoline receptors as state marker of depressive symptomatology

OBJECTIVE

Previous studies have shown that imidazoline receptors (IR-1) are increased in platelets and frontal cortex of depressed patients, and this up-regulation is normalized (down-regulated) after antidepressant drug treatments. It has been hypothesized that IR-1 up-regulation during the depressive episode may be a state marker for depressive symptomatology. The goal of the present study was to address the state versus trait question.

METHOD

Twelve healthy subjects (six males and six females) met stringent inclusion and exclusion criteria for physical and mental health. They received desipramine for 6 weeks in order to simulate the length of time and dosing used previously to obtain an IR-1 down-regulation and a therapeutic response in depressed patients. Outcome and safety measures included clinical, psychological, and cardiovascular assessments obtained throughout the study. Plasma concentrations of desipramine were measured throughout the 6 weeks of treatment and again after 2 weeks following tapered discontinuation of desipramine. Platelet receptors were assessed by Western blotting and radioligand binding assays.

RESULTS

Healthy subjects taking desipramine experienced mild dysphoric effects but there were no adverse events. The binding of 8 nM p-[(125)I]clonidine to IR-1 and alpha(2)-adrenoceptors in healthy subjects did not change during desipramine treatment. The immunodensity of the 33 kDa band associated with IR-1 gradually increased to a maximum, by week-6, of 26% higher than baseline (p < 0.01 compared to baseline). Two weeks after desipramine discontinuation, there was a decline in alpha(2)-adrenoceptor binding and 33 kDa band's immunodensity (p = 0.04).

CONCLUSIONS

The findings support the hypothesis that platelet IR-1 binding sites are a marker of mood state rather than of antidepressant-induced pharmacological regulation. By comparison, platelet alpha(2)-adrenoceptors appear to be regulated by desipramine as a pharmacological effect independent of mood state.

Effect of agmatine on locus coeruleus neuron activity: possible involvement of nitric oxide

1. To investigate whether agmatine (the proposed endogenous ligand for imidazoline receptors) controls locus coeruleus neuron activity and to elucidate its mechanism of action, we used single-unit extracellular recording techniques in anaesthetized rats. 2. Agmatine (10, 20 and 40 microg, i.c.v.) increased in a dose-related manner the firing rate of locus coeruleus neurons (maximal increase: 95 +/- 13% at 40 microg). 3. I(1)-imidazoline receptor ligands stimulate locus coeruleus neuron activity through an indirect mechanism originated in the paragigantocellularis nucleus via excitatory amino acids. However, neither electrolytic lesions of the paragigantocellularis nucleus nor pretreatment with the excitatory amino acid antagonist kynurenic acid (1 micromol, i.c.v.) modified agmatine effect (10 microg, i.c.v.). 4. After agmatine administration (20 microg, i.c.v.), dose-response curves for the effect of clonidine (0.625 - 10 microg kg(-1) i.v.) or morphine (0.3 - 4.8 mg kg(-1) i.v.) on locus coeruleus neurons were not different from those obtained in the control groups. 5. Pretreatment with the nitric oxide synthase inhibitors N(omega)-nitro-L-arginine (10 microg, i.c.v.) or N(omega)-nitro-L-arginine methyl ester (100 microg, i.c.v.) but not with the less active stereoisomer N(omega)-nitro-D-arginine methyl ester (100 microg, i.c.v.) completely blocked agmatine effect (10 and 40 microg, i.c.v.). 6. Similarly, when agmatine (20 pmoles) was applied into the locus coeruleus there was an increase that was blocked by N(omega)-nitro-L-arginine methyl ester (100 microg, i.c.v.) in the firing rate of the locus coeruleus neurons (maximal increase 53 +/- 11% and 14 +/- 10% before and after nitric oxide synthase inhibition, respectively). 7. This study demonstrates that agmatine stimulates the firing rate of locus coeruleus neurons via a nitric oxide synthase-dependent mechanism located in this nucleus.

Activation of I(2)-imidazoline receptors enhances supraspinal morphine analgesia in mice: a model to detect agonist and antagonist activities at these receptors

This work investigates the receptor acted upon by imidazoline compounds in the modulation of morphine analgesia. The effects of highly selective imidazoline ligands on the supraspinal antinociception induced by morphine in mice were determined. 2. Intracerebroventricular (i.c.v.) or subcutaneous (s.c.) administration of ligands selective for the I(2)-imidazoline receptor, 2-BFI, LSL 60101, LSL 61122 and aganodine, and the non selective ligand agmatine, increased morphine antinociception in a dose-dependent manner. Neither moxonidine, a mixed I(1)-imidazoline and alpha(2)-adrenoceptor agonist, RX821002, a potent alpha(2)-adrenoceptor antagonist that displays low affinity at I(2)-imidazoline receptors, nor the selective non-imidazoline alpha(2)-adrenoceptor antagonist RS-15385-197, modified the analgesic responses to morphine. 3. Administration of pertussis toxin (0.25 microg per mouse, i.c.v.) 6 days before the analgesic test blocked the ability of the I(2)-imidazoline ligands to potentiate morphine antinociception. 4. The increased effect of morphine induced by I(2)-imidazoline ligands (agonists) was completely reversed by idazoxan and BU 224. Identical results were obtained with IBI, which alkylates I(2)-imidazoline binding sites. Thus, both agonist and antagonist properties of imidazoline ligands at the I(2)-imidazoline receptors were observed. 5. Pre-treatment (30 min) with deprenyl, an irreversible inhibitor of monoamine oxidase B (IMAO-B), produced an increase of morphine antinociception. Clorgyline, an irreversible IMAO-A, given 30 min before morphine did not alter the effect of the opioid. At longer intervals (24 h) a single dose of either clorgyline or deprenyl reduced the density of I(2)-imidazoline receptors and prevented the I(2)-mediated potentiation of morphine analgesia. 6. These results demonstrate functional interaction between I(2)-imidazoline and opioid receptors. The involvement of G(i)-G(o) transducer proteins in this modulatory effect is also suggested.

Harmane produces hypotension following microinjection into the RVLM: possible role of I(1)-imidazoline receptors

The beta-carboline, harmane (0.1 - 1.0 nmol) produces dose dependent hypotension when microinjected unilaterally into the rostral ventrolateral medulla (RVLM) of the anaesthetized rat. The potency of harmane on blood pressure is similar to that of the imidazoline, clonidine. The hypotensive effects of both clonidine and harmane are reversed by microinjection of the relatively I(1)-receptor selective antagonist efaroxan (20 nmol). These results are consistent with harmane acting at an I(1)-receptor in the RVLM. This is the first report of an endogenous ligand for I(1)-receptors that has central effects on blood pressure.

Non-adrenergic binding of [3H]atipamezole in rat kidney--regional distribution and comparison to alpha2-adrenoceptors

1 Atipamezole (4-(2-ethyl-2,3-dihydro-1H-inden-2-yl)-1H-imidazole) was first introduced as a potent and specific alpha2-adrenoceptor antagonist, but in some tissues [3H]atipamezole identifies an additional population of binding sites, distinct from both classical alpha2-adrenoceptors and I1- and I2-imidazoline receptors identified with [3H]para-aminoclonidine or [3H]idazoxan. 2 In the present study we have characterized [3H]atipamezole binding sites in rat kidney by receptor autoradiography and membrane binding assays and determined whether they are pharmacologically identical with the previously described binding sites for [3H]para-aminoclonidine and [3H]idazoxan. [3H]RX821002 and [3H]rauwolscine were used to compare the regional distribution of alpha2-adrenoceptors to that of non-adrenergic binding sites of [3H]atipamezole. 3 Comparative autoradiographic experiments demonstrated the differential localisation of [3H]atipamezole, [3H]RX821002 and [3H]rauwolscine binding sites in rat kidney. The pattern of distribution of non-adrenergic [3H]atipamezole binding sites is clearly distinct from that of alpha2-adrenoceptors. 4 The non-adrenergic binding of [3H]atipamezole in rat kidney does not fall into any of the previously identified three classes of imidazoline receptors studied with [3H]para-aminoclonidine, [3H]idazoxan and [3H]RX821002. 5 Atipamezole had no inhibitory effect on MAO-A or MAO-B activity in renal membranes, which speaks against the involvement of MAOs in the observed radioligand binding.

Cardiovascular effects of rilmenidine, moxonidine and clonidine in conscious wild-type and D79N alpha2A-adrenoceptor transgenic mice

1. We investigated the cardiovascular effects of rilmenidine, moxonidine and clonidine in conscious wild-type and D79N alpha2A-adrenoceptor mice. The in vitro pharmacology of these agonists was determined at recombinant (human) alpha2-adrenoceptors and at endogenous (dog) alpha2A-adrenoceptors. 2. In wild-type mice, rilmenidine, moxonidine (100, 300 and 1000 microg kg(-1), i.v.) and clonidine (30, 100 and 300 microg kg(-1), i.v.) dose-dependently decreased blood pressure and heart rate. 3. In D79N alpha2A-adrenoceptor mice, responses to rilmenidine and moxonidine did not differ from vehicle control. Clonidine-induced hypotension was absent, but dose-dependent hypertension and bradycardia were observed. 4. In wild-type mice, responses to moxonidine (1 mg kg(-1), i.v.) were antagonized by the non-selective, non-imidazoline alpha2-adrenoceptor antagonist, RS-79948-197 (1 mg kg(-1), i.v.). 5. Affinity estimates (pKi) at human alpha2A-, alpha2B- and alpha2C-adrenoceptors, respectively, were: rilmenidine (5.80, 5.76 and 5.33), moxonidine (5.37, <5 and <5) and clonidine (7.21, 7.16 and 6.87). In a [35S]-GTPgammaS incorporation assay, moxonidine and clonidine were alpha2A-adrenoceptor agonists (pEC50/intrinsic activity relative to noradrenaline): moxonidine (5.74/0.85) and clonidine (7.57/0.32). 6. In dog saphenous vein, concentration-dependent contractions were observed (pEC50/intrinsic activity relative to noradrenaline): rilmenidine (5.83/0.70), moxonidine (6.48/0.98) and clonidine (7.22/0.83). Agonist-independent affinities were obtained with RS-79948-197. 7. Thus, expression of alpha2A-adrenoceptors is a prerequisite for the cardiovascular effects of moxonidine and rilmenidine in conscious mice. There was no evidence of I1-imidazoline receptor-mediated effects. The ability of these compounds to act as alpha2A-adrenoceptor agonists in vitro supports this conclusion.

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.

The involvement of pertussis toxin-sensitive G proteins in the post receptor mechanism of central I1-imidazoline receptors

1. To elucidate the possible involvement of pertussis toxin (PTX)-sensitive G proteins in the post receptor mechanism of alpha 2-adrenoceptors and imidazoline receptors, we examined the effect of pretreatment of the central nervous system with PTX on the antidysrhythmic effect of dexmedetomidine, a selective alpha 2-adrenoceptor agonist, and rilmenidine, a selective I1-imidazoline receptor agonist on halothane-adrenaline dysrhythmias in rats. 2. Dexmedetomidine (0, 1.0, 2.0, 5.0 micrograms kg-1 min-1.i.v.) and rilmenidine (0, 1.0, 3.0, 10, 20 micrograms kg-1, i.v.) prevented the genesis of halothane-adrenaline dysrhythmias in a dose-dependent fashion. Both idazoxan (10, 20 micrograms kg-1, intracerebroventricularly (i.c.v.)), an alpha 2-adrenoceptor antagonist with high affinity for imidazoline receptors, and rauwolscine, (40 micrograms kg-1, i.c.v.), an alpha 2-adrenoceptor antagonist with low affinity for imidazoline receptors inhibited the action of dexmedetomidine (5.0 micrograms kg-1, min-1, i.v.), but the inhibitory potency of idazoxan was much greater than that of rauwolscine. While the pretreatment with PTX (0.1, 0.5, 1.0 micrograms kg-1, i.c.v.) did not change the dysrhythmogenecity of adrenaline, this treatment completely blocked the antidysrhythmic property of rilmenidine (20 micrograms kg-1, i.v.) as well as dexmedetomidine (5.0 micrograms kg-1 min-1, i.v.). 3. It is suggested that central I1-imidazoline receptors as well as alpha 2-adrenoceptors may be functionally coupled to PTX-sensitive G proteins.

The I1-imidazoline receptor: from binding site to therapeutic target in cardiovascular disease

OBJECTIVE

To review previous work and present additional evidence characterizing the I1-imidazoline receptor and its role in cellular signaling, central cardiovascular control, and the treatment of metabolic syndromes. Second-generation centrally-acting antihypertensives inhibit sympathetic activity mainly via imidazoline receptors, whereas first-generation agents act via alpha2-adrenergic receptors. The I1 subtype of imidazoline receptor resides in the plasma membrane and binds central antihypertensives with high affinity.

METHODS AND RESULTS

Radioligand binding assays have characterized I1-imidazoline sites in the brainstem site of action for these agents in the rostral ventrolateral medulla. Binding affinity at I1-imidazoline sites, but not at other classes of imidazoline binding sites, correlates closely with the potency of central antihypertensive agents in animals and in human clinical trials. The antihypertensive action of systemic moxonidine is eliminated by the I1/alpha2-antagonist efaroxan, but not by selective blockade of alpha2-adrenergic receptors. Until now, the cell signaling pathway coupled to I1-imidazoline receptors was unknown. Using a model system lacking alpha2-adrenergic receptors (PC12 pheochromocytoma cells) we have found that moxonidine acts as an agonist at the cell level and I1-imidazoline receptor activation leads to the production of the second messenger diacylglycerol, most likely through direct activation of phosphatidylcholine-selective phospholipase C. The obese spontaneously hypertensive rat (SHR; SHROB strain) shows many of the abnormalities that cluster in human syndrome X, including elevations in blood pressure, serum lipids and insulin. SHROB and their lean SHR littermates were treated with moxonidine at 8 mg/kg per day. SHROB and SHR treated with moxonidine showed not only lowered blood pressure but also improved glucose tolerance and facilitated insulin secretion in response to a glucose load. Because alpha2-adrenergic agonists impair glucose tolerance, I1-imidazoline receptors may contribute to the multiple beneficial effects of moxonidine treatment.

CONCLUSION

The I1-imidazoline receptor is a specific high-affinity binding site corresponding to a functional cell-surface receptor mediating the antihypertensive actions of moxonidine and other second-generation centrally-acting agents, and may play a role in countering insulin resistance in an animal model of metabolic syndrome X.

New therapeutic agents for hypertension

1. Over the last 40 years a range of therapeutic strategies has been introduced for the long term treatment of hypertension. 2. Although safe effective agents are available a significant number of patients are unable or unwilling to take these drugs as long term treatment. 3. Both insufficient efficacy and adverse effects justify the search for new antihypertensive strategies. 4. Recent developments include orally active angiotensin (AT1) receptor antagonists (ARA) which appear to offer the benefits of prevention of angiotensin II effects without the adverse effects of bradykinin potentiation, such as cough, which limit the usefulness of angiotensin converting enzyme (ACE) inhibitors. 5. Imidazoline receptor agonists offer the potential of centrally active antihypertensives without the adverse effects of sedation and dry mouth. Further clinical experience is necessary to confirm whether the clinical efficacy and good tolerability are confirmed with long term use. 6. Both ARA and imidazoline preferring substances offer the bonus of a desirable haemodynamic profile in patients with heart failure and may open new therapeutic avenues in the management of cardiac failure.