The effect of moxonidine on feeding and body fat in obese Zucker rats: role of hypothalamic NPY neurones

Moxonidine ameliorates cardiac injury in rats with metabolic syndrome by regulating autophagy

AIMS

Reduced cardiac autophagy, ischemic injury, sympathetic overactivity, and apoptosis all contribute to metabolic syndrome (MetS)-associated cardiovascular risks. NR4A2, an orphan nuclear receptor NR4A family member, induces autophagy while suppressing apoptosis in myocardial infarction. Moxonidine, a sympathoinhibitor imidazoline1 receptor (I1R) agonist, has beneficial metabolic and hemodynamic effects; however, whether autophagy and/or NR4A2 signaling are involved in moxonidine's cardiovascular effects via I1R activation, is unknown, and is the aim of this study.

MATERIALS AND METHODS

To induce MetS, rats were fed 3 % salt in their diet and 10 % fructose in their drinking water for 12 weeks. MetS-rats were given either moxonidine (6 mg/kg/day, gavage), efaroxan (I1R antagonist, 0.6 mg/kg/day, i.p), both treatments, or vehicles for the last two weeks. Blood pressure, lipid profile, and glycemic control were evaluated. Histopathological examination, circulating cardiac troponin I (c-TnI), proinflammatory interleukin-6 (IL-6), apoptosis (active caspase-3 and Fas-immunostaining), interstitial fibrosis [transforming growth factor-β1 (TGF-β1), Mallory's trichrome staining], and extracellular matrix remodeling [matrix metalloproteinase-9 (MMP-9)], were used to assess cardiac pathology. Cardiac NR4A2 and its downstream factor, p53, as well as autophagic flux markers, SQSTM1/p62, LC3, and Beclin-1 were also determined.

KEY FINDINGS

Moxonidine significantly ameliorated MetS-induced metabolic and hemodynamic derangements and the associated cardiac pathology. Moxonidine restored NR4A2 and p53 myocardial levels and enhanced autophagic flux via modulating SQSTM1/p62, LC3, and Beclin-1. Efaroxan reversed the majority of the moxonidine-induced improvements.

SIGNIFICANCE

The current study suggests that autophagy modulation via I1R activation is involved in moxonidine-mediated cardiac beneficial effects in MetS.

Effects of Moxonidine Administration on Serum Neuropeptide Y Levels in Hypertensive Individuals: A Prospective Observational Study

Moxonidine is a centrally acting, anti-hypertensive medication that exerts additional metabolic properties. It is unknown whether its effects are mediated by neurotransmitters or sympathetic tone regulators, including Neuropeptide Y (NPY). In this study, we evaluated the effects of moxonidine administration on serum NPY in humans. Methods: Ninety individuals with mild or moderate arterial hypertension that required monotherapy were categorized in three age and gender-matched groups according to their Body Mass Index (BMI) as normal weight (n = 30), overweight (n = 30), and obese (n = 30). Moxonidine was administered in therapeutic doses of up to 0.6 mg daily for 12 weeks, and clinical, biochemical and hormonal parameters were recorded. Results: In all three groups, a decrease in systolic and diastolic blood pressure and heart rate was shown. After treatment, BMI, 24 h urine catecholamines and catecholamines’ metabolites, and serum total cholesterol were also reduced. Most importantly, we found a decrease in serum NPY levels in all study groups, with the largest mean decrease in the group of obese and overweight participants compared to normal weight. Conclusions: Moxonidine administration results in improvement in cardio-metabolic parameters, as well as a decrease in serum NPY levels, which therefore represents it being a potent agent against obesity-associated hypertension. Its involvement in energy balance regulation warrants further investigation.

Cystathionine-γ lyase-derived hydrogen sulfide mediates the cardiovascular protective effects of moxonidine in diabetic rats

Blunted cystathionine-γ lyase (CSE) activity (reduced endogenous H2S-level) is implicated in hypertension and myocardial dysfunction in diabetes. Here, we tested the hypothesis that CSE derived H2S mediates the cardiovascular protection conferred by the imidazoline I1 receptor agonist moxonidine in a diabetic rat model. We utilized streptozotocin (STZ; 55mg/kg i.p) to induce diabetes in male Wistar rats. Four weeks later, STZ-treated rats received vehicle, moxonidine (2 or 6mg/kg; gavage), CSE inhibitor DL-propargylglycine, (37.5mg/kg i.p) or DL-propargylglycine with moxonidine (6mg/kg) for 3 weeks. Moxonidine improved the glycemic state, and reversed myocardial hypertrophy, hypertension and baroreflex dysfunction in STZ-treated rats. Ex vivo studies revealed that STZ caused reductions in CSE expression/activity, H2S and nitric oxide (NO) levels and serum adiponectin and elevations in myocardial imidazoline I1 receptor expression, p38 and extracellular signal-regulated kinase, ERK1/2, phosphorylation and lipid peroxidation (expressed as malondialdehyde). Moxonidine reversed these biochemical responses, and suppressed the expression of death associated protein kinase-3. Finally, pharmacologic CSE inhibition (DL-propargylglycine) abrogated the favorable cardiovascular, glycemic and biochemical responses elicited by moxonidine. These findings present the first evidence for a mechanistic role for CSE derived H2S in the glycemic control and in the favorable cardiovascular effects conferred by imidazoline I1 receptor activation (moxonidine) in a diabetic rat model.

Pharmacological benefit of I(1)-imidazoline receptors activation and nuclear factor kappa-B (NF-κB) modulation in experimental Huntington's disease

Huntington's disease (HD), a neurodegenerative disorder, is characterized by progressive motor dysfunction, emotional disturbances, dementia, weight loss and anxiety. The tremendous amount of research work is required to identify new pharmacological agents of therapeutic utility to combat this condition. This study investigates the effect of selective modulator of I1-imidazoline receptor (moxonidine) as well as nuclear factor kappa-B (NF-κB) (natrium diethyl dithio carbamate trihydrate-NDDCT) on 3-nitropropionic acid (3-NPA) induced experimental HD condition. 3-NPA was used to induce mitochondrial damage and associated HD symptoms in rats. Anxiety was assessed using Elevated plus maze-EPM and learning-memory was assessed using EPM and Morris water maze-MWM. Different biochemical estimations were used to assess brain striatum oxidative stress (lipid peroxide, superoxide dismutase and catalase), nitric oxide levels (nitrite/nitrate), cholinergic activity (brain striatum acetyl cholinesterase activity), and mitochondrial enzyme complex (I, II and IV) activities. 3-NPA has induced anxiety, impaired learning-memory with a reduction in body weight, locomotor activity, grip strength. It has increased brain striatum acetylcholinesterase-AChE activity, oxidative stress (lipid peroxide, nitrite/nitrate, superoxide dismutase and catalase) and impaired mitochondrial complex enzyme (I, II and IV) activities. Tetrabenazine-TBZ (monoamine storage inhibitor) was used as positive control. Treatment with moxonidine, NDDCT and TBZ significantly attenuated 3-NPA induced reduction in body weight, locomotor activity, grip strength, anxiety as well as impaired learning and memory. Administration of these agents attenuated 3-NPA induced various biochemical impairments. Therefore, modulation of I1-imidazoline receptor as well as NF-κB may be considered as potential pharmacological agents for the management of 3-NPA induced HD.

Decrease of Obesity by Allantoin via Imidazoline I 1 -Receptor Activation in High Fat Diet-Fed Mice

The activation of the imidazoline I₁-receptor (I₁R) is known to regulate appetite. Allantoin, an active ingredient in the yam, has been reported to improve lipid metabolism in high fat diet- (HFD-)fed mice. However, the effect of allantoin on obesity remains unclear. In the present study, we investigated the effects of allantoin on HFD-induced obesity. The chronic administration of allantoin to HFD-fed mice for 8 weeks significantly decreased their body weight, and this effect was reversed by efaroxan at a dose sufficient to block I₁R. The epididymal white adipose tissue (eWAT) cell size and weight in HFD-fed mice were also decreased by allantoin via the activation of I₁R. In addition, allantoin significantly decreased the energy intake of HFD-fed mice, and this reduction was associated with a decrease in the NPY levels in the brain. However, no inhibitory effect of allantoin on energy intake was observed in db/db mice. Moreover, allantoin lowered HFD-induced hyperleptinemia, and this activity was abolished by I₁R blockade with efaroxan. Taken together, these data suggest that allantoin can ameliorate energy intake and eWAT accumulation by activating I₁R to improve HFD-induced obesity.

Murine models for pharmacological studies of the metabolic syndrome

Metabolic syndrome has been described as the association of insulin resistance, hypertension, hyperlipidemia and obesity. Its prevalence increased dramatically, mainly in developed countries. Animal models are essential to understand the pathophysiology of this syndrome. This review presents the murine models of metabolic syndrome the most often used in pharmacological studies. The most common metabolic syndrome models exhibit a non-functional leptin pathway, or metabolic disorders induced by high fat diets. In a first part, and after a short introduction on leptin, its receptor and mechanism of action, we provide a detailed description of each model: SHROB, SHHF, JCR:LA-cp, Zucker, ZDF, Wistar Ottawa Karlsburg W, and Otsuka Long-Evans Tokushima Fatty rats, ob/ob, db/db, agouti yellow and Mc4R KO mice. The second part of this review is dedicated to metabolic syndrome models obtained by high fat feeding.

Effects of sympatholytic therapy with moxonidine on serum adiponectin levels in hypertensive women

We examined whether moxonidine influences lipid profile, insulin resistance, adiponectin levels, renal function and microalbuminuria in women with essential hypertension in a study of 55 non-diabetic hypertensive patients and 53 normotensive women. Hypertensive patients received moxonidine for 12 weeks. At baseline the hypertensive group had significantly higher mean blood pressure, low-density lipoprotein cholesterol, triglycerides, total cholesterol, fasting glucose, urinary albumin excretion and homeostasis model assessment of insulin resistance (HOMA-IR), together with significantly lower mean high-density lipoprotein cholesterol, creatinine clearance and serum adiponectin than the normotensive group. Moxonidine significantly decreased blood pressure, fasting glucose, triglycerides, total cholesterol, HOMA-IR and albumin excretion, but significantly increased serum adiponectin. The change in adiponectin level was negatively correlated with the change in HOMA-IR. Moxonidine treatment may improve unfavourable metabolic status related to insulin resistance by increasing adiponectin levels in patients with essential hypertension. Since it can improve adiponectin levels, it may be used in the antihypertensive treatment of patients at high risk of diabetes and cardiovascular disease.

Involvement of Supraspinal Imidazoline Receptors and Descending Monoaminergic Pathways in Tizanidine-Induced Inhibition of Rat Spinal Reflexes

The neuronal pathways involved in the muscle relaxant effect of tizanidine were examined by measurement of spinal reflexes in rats. Tizanidine (i.v. and intra-4th ventricular injection) decreased the mono- and disynaptic (the fastest polysynaptic) reflexes (MSR and DSR, respectively) in non-spinalized rats. Depletion of central noradrenaline by 6-hydroxydopamine abolished the depressant effect of tizanidine on the MSR almost completely and attenuated the effect on the DSR. Co-depletion of serotonin by 5,6-dihydroxytryptamine and noradrenaline resulted in more prominent attenuation of tizanidine-induced inhibition of the DSR. Supraspinal receptors were then studied using yohimbine- and some imidazoline-receptor ligands containing an imidazoline moiety. Idazoxan (I1, I2, I3, and alpha2), efaroxan (I1, I3, and alpha2), and RX821002 (I3 and alpha2), but not yohimbine, an alpha2-adrenergic receptor antagonist with no affinity for I receptors, antagonized the inhibitory effects of tizanidine. Thus, supraspinal I receptors (most likely I3) and descending monoaminergic influences are necessary for tizanidine-induced inhibition of spinal segmental reflexes.

Importance of imidazoline-preferring receptors in the cardiovascular actions of chronically administered moxonidine, rilmenidine and clonidine in conscious rabbits

OBJECTIVE

To determine the involvement of central imidazoline receptors in the cardiovascular actions of the chronically administered antihypertensive agents moxonidine, rilmenidine and clonidine.

DESIGN AND METHODS

In 21 rabbits with implanted fourth-ventricular catheters, we investigated the central effects of three cumulative doses of an I(1)-imidazoline/alpha(2)-adrenoceptor antagonist, efaroxan, and of an alpha(2)-adrenoceptor antagonist, 2-methoxyidazoxan (2-MI), on the changes in blood pressure and heart rate (HR) elicited by chronic subcutaneous administration of moxonidine, rilmenidine and clonidine, after 1 and 3 weeks of treatment. A low, medium and high dose of 2-MI was matched to three doses of efaroxan, such that each produced equal reversal of the hypotension induced by fourth-ventricular alpha-methyldopa and hence produced a similar degree of alpha(2)-adrenoceptor blockade.

RESULTS

Clonidine and moxonidine, at doses of 1 mg/kg per day, and rilmenidine at 5 mg/kg per day, produced sustained reductions in mean arterial pressure of 13 +/- 3, 15 +/- 2 and 13 +/- 2 mmHg, respectively over the 3-week treatment period, but did not alter HR. Central administration of efaroxan on day 9 and day 23 of treatment produced a greater increase in blood pressure than did 2-MI with all three antihypertensive agents. Blood pressure reached levels that were significantly above the original control values. By contrast, the alpha(2)-adrenoceptor antagonist 2-MI only induced a rebound blood pressure effect in clonidine- and to a lesser extent in rilmenidine-treated rabbits. Both efaroxan and 2-MI produced a similar degree of tachycardia in moxonidine-, rilmenidine- and clonidine-treated animals.(2)

CONCLUSIONS

The greater effect of efaroxan compared to the alpha(2)-adrenoceptor antagonist 2-MI suggests that the hypotension induced by chronic subcutaneous administration of moxonidine, rilmenidine and clonidine is mediated predominantly via an action on central imidazoline receptors. Furthermore, all agents showed a propensity to produce rebound hypertension with imidazoline receptor blockade. However, only clonidine showed a rebound phenomenon when challenged by acute central alpha(2)-adrenoceptor blockade

Sibutramine reduces feeding, body fat and improves insulin resistance in dietary-obese male Wistar rats independently of hypothalamic neuropeptide Y

We studied the effects of the novel noradrenaline and serotonin (5-HT) reuptake inhibitor sibutramine on feeding and body weight in a rat model of dietary obesity, and whether it interacts with hypothalamic neuropeptide Y (NPY) neurones. Chow-fed and dietary-obese (DIO) male Wistar rats were given sibutramine (3 mg kg(-1) day(-1) p.o.) or deionized water for 21 days. Sibutramine decreased food intake throughout the treatment period in both dietary-obese rats (P<0.0001) and lean rats (P<0.0001). Weight gain was reduced so that final body weight was 10% lower in dietary-obese (P<0.005) and 8% lower in lean (P<0.05) rats versus their untreated controls. Plasma leptin concentration was lower in sibutramine-treated dietary-obese rats (P<0.05), and in treated lean rats (P<0.05). Using the homeostasis model assessment (HOMA) as a measure of insulin resistance, untreated DIO rats were significantly more insulin resistant than controls (P<0.005), and this was corrected by sibutramine treatment (P<0.05). Neither hypothalamic NPY mRNA nor NPY peptide levels in a number of hypothalamic nuclei were significantly altered by sibutramine compared to untreated controls. The hypophagic and anti-obesity effects of sibutramine in dietary-obese Wistar rats appear not to be mediated by inhibition of ARC NPY neurones.

Moxonidine: some controversy

Initially it was considered that moxonidine, like clonidine, acted at central (2)-adrenoceptors to reduce blood pressure. With the characterisation of imidazoline binding sites distinct from (2)-adrenoceptors, the consensus became that moxonidine was acting predominantly at imidazoline I(1) receptors in the rostral ventrolateral medulla to lower blood pressure. Moxonidine acts at prejunctional (2)-adrenoceptors on sympathetic nerve endings to decrease noradrenaline release and this may contribute to its ability to lower blood pressure. The predominant site of action of moxonidine may also depend on route of administration, with imidazoline I(1) receptors being predominant after central, and (2)-adrenoceptors predominant after systemic administration. The controversy over the mechanism and site of action with moxonidine is ongoing. In animal models, moxonidine lowers blood pressure, reduces cardiac hypertrophy and remodelling, reduces cardiac arrhythmias and increases blood flow in cerebral ischaemia. Moxonidine also has beneficial effects in animal models of diabetes and kidney disease. Moxonidine increases sodium and water excretion in rats, but not humans. Animal studies indicate that moxonidine may be useful in the treatment of glaucoma by reducing intra-ocular pressure. Animal studies show that moxonidine may also be effective in pain and in ethanol withdrawal. In humans, the pharmacokinetics of moxonidine are of the one-compartment model with first-order absorption. Renal elimination is the major route of elimination and individual titration of moxonidine is needed in patients with renal impairment. There is overwhelming evidence that moxonidine is a safe and effective antihypertensive. A large clinical trial of moxonidine in heart failure, MOXCON, was stopped because of excessive deaths in the moxonidine group. Moxonidine should not be used in patients with heart failure, but there are no obvious reasons to stop its use as an antihypertensive, or its development for other clinical uses.