Effects of Combination of Carvedilol and Melatonin on Induced Metabolic Syndrome in Rats

Background: The prevalence of metabolic syndrome is increasing and it is considered one of the main threats to human health worldwide. Fructose feeding induces hyper-insulinemia, insulin resistance and hyper-triglyceridemia. The main objective of the present study is to evaluate the pharmacological effects of the single and combined administration of carvedilol and melatonin on fructose-induced metabolic syndrome in rats.

Methods: Male albino rats were fed a high fructose diet for ten weeks to induce metabolic syndrome. Oral administration of carvedilol (20 mg/kg/day), melatonin (10 mg/kg/day), carvedilol and melatonin (20 mg +10 mg/kg/day) or vehicle was conducted for six weeks after stopping the high fructose feeding.Indices of systolic blood pressure (SBP), Fasting Blood Glucose (FBG), Fasting Serum Insulin (FSI), serum lipid profiles, serum Nitric Oxide (NO), serum lipid peroxides as well as levels of total antioxidants were determined. Insulin resistance index were calculated from FBG and FSI using HOMA-IR (Homeostasis Model Assessment).

Results: A high-fructose diet was associated with hypertension, dyslipidemia, insulin resistance, decreased nitrite and increased oxidative stress. Carvedilol, melatonin or combination of carvedilol and melatonin was able to reverse features of metabolic syndrome in the six weeks. The intensity of changes produced by melatonin was of greater extent in insulin resistance and lipid profiles than produced by carvedilol but the effect of carvedilol was higher in hypertension. The combination of carvedilol plus melatonin was superior of the others.

Conclusion: A combination of both carvedilol (20 mg/kg/ day orally) and melatonin (10 mg/kg/ day orally) for 6 weeks revealed a statistical significant results in comparison to carvedilol (20 mg/kg/ day orally) or melatonin (10 mg/kg/ day orally) alone. A combination of carvedilol and melatonin may give an additive effect better than each of them alone.

Metabolic syndrome; Dyslipidemia; Insulin resistance; Carvedilol; Melatonin; Oxidative stress

Metabolic syndrome is characterized by a group of metabolic risk factors in one person. They include: abdominal obesity, abnormal blood lipids (increased low density lipoproteins-cholesterol and triglycerides and reduced high density lipoproteins-cholesterol), insulin resistance and hypertension [1,2]. Metabolic syndrome affects more than 25% of population in the developed and underdeveloped world and it is considered one of the main threats to human health worldwide. The epidemic correlates with pronounced changes in the environment, behavior and lifestyle [3].

High fructose diet increases free radicals production and advanced glycation end products [4]. Increased oxidative stress suppresses endothelium-derived vasodilatation by converting nitric oxide (NO•) into peroxynitrite. In addition, advanced glycation end products promote the development of inflammation and induce vascular cell adhesion molecule production, which enhances the interaction between the vascular endothelium and circulating monocytes [5]. Endothelial dysfunction, in the form of increased free radicals production and decreased NO• bioavailability, may contribute to the development of atherosclerosis [6].

The pineal hormone melatonin is secreted with a marked circadian rhythm with a peak at 2-4 a.m. The endogenous rhythm of secretion is generated by the suprachiasmatic nuclei, entrained to the light/dark cycle and conveys information concerning the daily cycle to body physiological functions such as sleep, immune system and glucose regulation [7]. The intimate relationship between circadian rhythms and metabolism is getting recognized and a link between the disruption of circadian rhythms and metabolic perturbations is suggested as one of the major causes of metabolic syndrome [8]. Sleep disorders such as insomnia and obstructive sleep apnea are very common in individuals with metabolic and endocrine pathologies [7]. Melatonin level was disturbed in many patients who have circadian-rhythm disorders caused by shift work also develop gastrointestinal and metabolic disorders such as glucose intolerance, diabetes and high blood pressure [9]. On this basis, the successful management of metabolic syndrome may require an ideal drug that besides antagonizing the trigger factors of metabolic syndrome could also correct the disturbed sleep-wake rhythm [10]. So we hypothesized that if we can correct disturbed circadian rhythm associated with metabolic syndrome by melatonin this may has a potential to improve glucose metabolism, energy balance and subsequently metabolic syndrome.

Carvedilol is a third-generation, vasodilating non-cardio selective β-blocker which lacks intrinsic sympathomimetic activity. In addition to its β-blocking effects, it has blocking effects at vascular α1-receptors, antioxidant, and calcium antagonist properties [11]. The lack of inverse agonist activity and intrinsic sympathomimetic activity reduces the side-effects and metabolic actions of traditional β-blocker therapy [12].

β- blockers are considered the first choice or at least a good alternative to other drugs in many cardiovascular diseases including heart failure as well as non-cardiovascular conditions including renal dysfunction [13].

Each of melatonin and carvedilol is a potent scavenger of toxic free radicals and both stimulate antioxidants formation [14]. Metabolic syndrome is one of oxidative stress diseases [5]. However, there is a long term debate regarding the usefulness of these agents in diabetes and metabolic syndrome. Some studies reported β-blockers induced hyperglycaemia contradicting the ideas of its vasodilating property inducing hypoglycaemia by improving insulin sensitivity [15]. In spite of their well-known and evidence-proven protective effects and better prognostic outcomes in different disease conditions, β-blockers are still underused in diabetic and metabolic syndrome patients who in need of cardiovascular therapy [16].

To our knowledge no study has addressed the efficacy of combination of melatonin and carvedilol in metabolic syndrome. Therefore the objective of the present study was to examine further the effect of carvedilol administration, with or without melatonin in fructose induced metabolic syndrome.

Materials

Experimental animals

High Fructose Diet

Studied groups

Experimental Design

Table 1 showed the effect of fructose on the induced metabolic syndrome. Administration of carvedilol, melatonin or both induced a significant decrease in the SBP [P<0.05] in treated animals when compared with UHFD ones. There was no significant change of the SBP in the treated groups compared with the control group [P>0.05]. The intensity of changes produced by carvedilol was of greater extent than produced by melatonin.

Induction of metabolic syndrome by fructose diet-feeding for 10 weeks caused a significant increase of glucose, insulin and insulin resistance [HOMA2-IR and QUICKI] in the UHFD group when compared to control animals. However, administration of carvedilol, melatonin or carvedilol plus melatonin significantly attenuated these effects compared to UHFD group [P<0.05]. Normalization of HOMA2-IR and QUICKI values was observed only in the melatonin and carvedilol plus melatonin -treated group (Table 1).

Treatment of fructose induced metabolic syndrome animals with carvedilol, melatonin or carvedilol plus melatonin for six weeks resulted in a significant decrease of serum cholesterol, triglyceride, and LDL while, serum HDL was increased as compared with untreated high fructose diet group [P<0.05]. The intensity of changes produced by melatonin was of greater extent than produced by carvedilol and the combination is more effective than each one alone (Table 2).

Table 3 demonstrated that the induction of metabolic syndrome in rats was associated with enhanced oxidative stress as evidenced by a significant increase in the levels of lipid peroxide [P<0.05]. This was associated with a significant decrease in total antioxidant and NOx levels when compared to control animals [P<0.05].

Treatment with carvedilol, melatonin or both improved the metabolic syndrome-induced changes. This was evidenced by a significant decrease in lipid peroxide [P<0.05] in association with a significant increase in total antioxidant and NOx levels in treated rats [P<0.05]. The intensity of changes produced by melatonin was of greater extent than produced by carvedilol and the combination is more effective than each one alone.

Several important observations were detected in our present study. A high fructose [50%�60%] solid diet in male rats induces metabolic alterations similar to those found in metabolic syndrome, including insulin resistance and hypertension [30,31].

In the present study our results revealed a significant reduction in systolic blood pressure was observed in carvedilol treated group in comparison to UHFD group. These results are in agreement with Tedesco et al. [32]; Mancia et al. [33]; PolÃ?³nia et al. [34]; Xiaozhen et al. [35]; Erdogan et al. [36]. Reduction in arterial blood pressure by carvedilol may be attributed to it blocks norepinephrine binding to α1-adrenergic receptors in addition to both β1-adrenergic and β2-adrenergic receptors [37]. This results in a reduction in arterial blood pressure by maintaining cardiac output and decreasing total β-adrenergic vasoconstrictor tone [38]. The presence of β2-adrenoceptor antagonism may also be of importance because of a potential role in the presynaptic modulation of catecholamine release [37]. Finally, carvedilol stimulates NO• formation and displays antioxidant actions [14].

In the present study also our results revealed a statistically significant decreases in blood pressure in melatonin treated group in comparison to UHFD group. These data are in accordance with Hussain et al. [39]; Leibowitz et al. [40]; Kozirog et al. [41]; Huang et al. [42]. The hypotensive effect of melatonin might be mediated via melatonin receptors [M1 and M2]. The involvement of melatonin receptors in regulation of blood pressure was supported by the finding that the hypotensive effect of microinjection of melatonin into specific brain structures was almost completely prevented by luzindole, an antagonist of the melatonin receptors [43].

It is well recognized that conventional β-blockers exert negative effects on glucose control and insulin sensitivity, while also increasing the risk of new-onset diabetes in hypertensive patients [38]. Our data in the present study revealed a significant decrease in blood glucose level, serum insulin and a significant improvement in insulin sensitivity in carvedilol treated group in comparison to UHFD group. These data are in accordance with Wilson et al. [44]; Stefania et al. [45]; Kveiborg et al. [46]; Fonseca, [47]. In contrast to our results Bakriset al. [48] found that carvedilol did not affect glycemic control but improves some components of the metabolic syndrome relative to metoprolol in patients with DM and hypertension. This may be explained by the effects of the 2 β-blockers on clinical outcomes need to be compared in long-term clinical trials. Carvedilol prevents norepinephrine binding to α1-adrenegric receptors, which decreases peripheral vascular resistance and increases peripheral blood flow and glucose uptake [49].

Also our data revealed a statistically significant reduction in the blood glucose level, serum insulin and a significant improvement in insulin sensitivity in melatonin treated group in comparison to UHFD group. These data were previously proved by Sartori et al. [50]; Sheih et al. [51]; Peschke et al. [52]; Srivastava and Krishna [53]; Kitagawa et al. [54].

In the present study a statistically significant improvement was observed in lipid profiles, NO• and total antioxidant and statistically significant decrease of free radicals levels of carvedilol treated group in comparison to UHFD group. These data coincide with Fonarow et al. [55]; Fonseca [47]; Deedwania [56]; Gastone and Colin [57]. Carvedilol reduces peripheral vascular resistance, have little or no effect on cardiac output, and improve endothelial function through anti-oxidative and free radical scavenger properties [56].

Carvedilol also promote endothelial-dependent vasodilatation via enhanced NO• synthesis [58]. It possesses antioxidant properties, including the ability to scavenge free oxygen radicals, suppress free radical generation, and prevent ferric ion-induced oxidation [59]. The antioxidant activity of carvedilol may also be related to stimulation of endothelial NOâÂ?¢ production or a reduction in NO• inactivation [38].

In the present study our results revealed a statistically significant improvement in the lipid profiles of melatonin treated group in comparison to UHFD. These data coincide with previous findings of Nduhirabandif et al. [60]; Rios-Lugo et al. [61]; Hussain et al. [39]; Kozirog et al. [41]; Nishida et al. [62]; Agil et al. [63]; Huang et al. [42]; Kitagawa et al. [54]; She et al. [64].

In the present study our results revealed a statistically significant improvement in the total antioxidants and a statistically significant decrease in the free radicals level of melatonin treated group in comparison to UHFD. These findings go with previous findings of Achike et al. [65]; Kitagawa et al. [54]; Srinivasan et al. [43]; She et al. [64].

Melatonin has significant anti-oxidant activities and also plays a role in circadian rhythm regulation. In addition to this, melatonin is important to regulate various metabolic activities in the body [66].

Melatonin exerts a beneficial effect in various experimental models of obesity, hyperglycemia, hypo-insulinemia and hypertension by its action on glucose homeostasis [53], by reducing body weight, visceral fat, hyper-insulinemia, plasma levels of lepton, TG, VLDL, and C-reactive protein, endothelial dysfunction, insulin resistance and fasting blood glucose, and by increasing plasma levels of HDL cholesterol and adiponectin, as well as hepatic and muscular glycogen contents [43]. Besides all these metabolic actions, which are exerted through melatonin receptors, melatonin being an efficient anti-oxidant, anti-hyper-lipidemic action, anti-inflammatory action, modulatory action on insulin�s synthesis and release is helpful in reducing the oxidative stress involved in the pathophysiology ofmetabolic syndrome [43,54,65,67,68].

Melatonin scavenges hydroxyl, carbonate, and various organic radicals as well as a number of reactive nitrogen species [68]. Melatonin also enhances the antioxidant potential of the cell by stimulating the synthesis of antioxidant enzymes including superoxide dismutase, glutathione peroxidase, and glutathione reductase, and by augmenting glutathione levels [68,69]. Melatonin preserves mitochondrial homeostasis, reduces free radical generation and protects mitochondrial ATP synthesis by stimulating complexes I and IV activities [68].

A significant improvement in hypertension, insulin resistance, lipid peroxide, total antioxidants, lipid profiles and NOx was observed in carvdolol plus melatonin treated group in comparison to carvidolol treated group and melatonin treated group alone.

Having the same properties antioxidants, free radicals scavengers and increased of NO•, a combination of carvedilol and melatonin may give an additive effect on fructose induced metabolic syndrome.

The authors report no conflicts of interest. The authors alone are responsible for the content and writing of the paper.

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