Efficacy of melatonin in restoring the antioxidant status in the lens of diabetic rats induced by streptozotocin

Melatonin increases AKT and SOD gene and protein expressions in diabetic rats

Diabetes mellitus (DM) is a chronic metabolic disease marked by hyperglycemia due to insulin deficiency or insulin resistance leading to many chronic complications. It is thus important to manage diabetes effectively in order to prevent and or delay these complications. Melatonin is produced by the pineal gland and regulates the wake-sleep circadian rhythm. Existing evidence suggests that melatonin may be effective in the management of DM. However, the evidence on the mechanism of the beneficial effect melatonin as a treatment for DM is limited. In this study, we investigated the effect of melatonin treatment on blood glucose, insulin (INS), AKT and superoxide dismutase (SOD) gene levels in diabetic rats. Non-diabetic and diabetic rats were treated orally for 4 weeks with either 25 mg or 50 mg/kg body weight of melatonin. At the end of the study, pancreatic and liver tissues morphology, glucose homeostasis, serum insulin and SOD levels, hepatic gene and protein expression of SOD as protecting antioxidant enzyme and AKT as central element involved in PI3K/AKT insulin signaling pathway were estimated. Melatonin treated diabetic rats showed reduced hyperglycemia, and increased serum insulin and SOD levels. In addition, melatonin induced an increased gene and protein expression of SOD and AKT. In conclusion, melatonin may play a role in treating diabetic rats via stimulation of insulin secretion, insulin signaling and reduction in oxidative stress.

Selenium and Resveratrol Attenuated Diabetes Mellitus-Mediated Oxidative Retinopathy and Apoptosis via the Modulation of TRPM2 Activity in Mice

Diabetes mellitus induces optic nerve injury via the excessive generation of mitochondria reactive free oxygen radical (mitROS). TRPM2 channel is activated by mitROS, although it is inhibited by selenium (Se) and resveratrol (RSV). The activation of TRPM2 induces apoptosis and oxidative injury in the optic nerve. The inhibition of TRPM2 may decrease the optic nerve injury action of diabetes mellitus after the treatments of Se and RSV. Present study aimed to investigate the protective actions of Se and RSV on the excessive Ca²⁺ influx and mitROS generation-mediated optic nerve oxidative injury via the modulation of TRPM2. Fifty-six C57BL/6j male mice were divided into seven groups as control, Se, RSV, streptozotocin (STZ), STZ + Se, STZ + RSV, and STZ + Se + RSV. The STZ-mediated stimulation of TRPM2 increased the cytosolic Ca²⁺, lipid peroxidation, mitROS, cytosolic ROS, apoptosis, caspase-3, caspase-8, and caspase-9 concentrations in the mice, although their concentrations were decreased in the optic nerve by the treatments of Se and RSV. The STZ-induced decrease of optic nerve viability, glutathione, glutathione peroxidase, vitamin A, and vitamin E concentrations was also upregulated by the treatments of Se and RSV. The STZ-induced increase of TRPM2, PARP-1, caspase-3, and caspase-9 protein band expressions was diminished by the treatments of Se and RSV. In conclusion, STZ induced the optic nerve oxidative injury and apoptosis via the upregulation of TRPM2 stimulation, although the treatments of Se and RSV decreased the injury and apoptosis via the downregulation of TRPM2 activity.

Effect of oligosaccharides on the antioxidant, lipid and inflammatory profiles of rats with streptozotocin-induced diabetes mellitus

Prebiotics, gut microbiota-fermentable substances, delay the development of type I diabetes. In the present study, we investigated the effect of two prebiotics (galacto-oligosaccharides and xylo-oligosaccharides) on the antioxidant protection, lipid profile, and inflammatory activity of rats with streptozotocin-induced diabetes. The following markers were studied - malondialdehyde, 8-hydroxy-2'-deoxyguanosine, ferric reducing ability of plasma (FRAP), triacylglycerols, total cholesterol (TC), high-density lipoproteins, C-reactive protein (CRP), and interleukin-6. Diabetes was induced in male Wistar experimental rats by streptozotocin injection, while the non-diabetic controls were injected with saline. Afterward the oligosaccharides were administered orally to the experimental animals. The blood collected following the decapitation was analyzed by ELISA. A modified protocol was used only for measuring the FRAP values. The galacto-oligosaccharides and xylo-oligosaccharides lowered the malondialdehyde levels in the diabetic rats (p < 0.05). The galacto-oligosaccharides decreased the serum levels of 8-hydroxy-2'-deoxyguanosine (p = 0.01), while the xylo-oligosaccharides increased the FRAP (p < 0.05) in the experimental animals. None of the oligosaccharides affected triacylglycerol and interleukin-6 concentrations, but the galacto-oligosaccharides decreased the TC and CRP levels in the diabetic animals. Both oligosaccharides exert a beneficial effect on the antioxidant protection of the diabetic rats, but have a minor effect on their lipid and inflammatory profiles.

Modulatory effect of resveratrol and melatonin on natural killer cell activity and adrenomedullin in diabetic rats

BACKGROUND

Epidemiological evidence suggests that diabetes poses a high risk for many chronic diseases, especially cardiovascular diseases, and cancer by stimulating many inflammatory and immunological pathogenic mediators and affecting natural killer (NK)-cell activity. In this study, the effects of melatonin and resveratrol on IL-6, TNF-alpha, oxidant/antioxidant capacity, NK-cell activity, and mid-regional proadrenomedullin (MR-proADM) levels of diabetic rats were investigated.

METHODS

In the study, 28 Sprague Dawley rats were randomly divided into the control group (group I) and 3 streptozotocininduced diabetes mellitus (DM) groups (group II, III, and IV), each group consisting of 7 rats. Five mg/kg/day melatonin to group III and 5 mg/kg/day resveratrol (intraperitoneal) to group IV was given. At the end of 3 weeks, NK-cell activity, total antioxidant/oxidant capacity, MR-proADM, IL-6, and TNF-alpha levels were measured in intracardiac blood taken under anesthesia.

RESULTS

NK-cell activity of group II was found lower than group I, group III, and group IV (7.4 ± 2.0 vs. 22.5 ± 11.9, 30.6 ± 22.5 and 20.4 ± 9.1 pg/mL; p = 0.0018, respectively). The difference was more prominent in diabetic rats receiving melatonin (p < 0.01). TNF-alpha levels of group II were higher than the group I (p < 0.05). The MR-proADM levels of group II were found to be lower than the group I and group III (6.4 ± 3.6 vs. 14.4 ± 3.2 and 14.0 ± 4.2 ng/L; p < 0.05, respectively). In addition, NK-cell activity was moderately correlated with MR-proADM (r = 0.5618, p = 0.0019).

Melatonin ameliorates diabetes-induced brain injury in rats

Diabetic brain is a serious complication of diabetes, and it is associated with oxidative stress and neuronal injury. This study investigated the protective effect of melatonin (MLT) on diabetes-induced brain injury. A rat model of type 2 diabetes mellitus was produced by intraperitoneal injection of nicotinamide 100 mg/kg, followed by intraperitoneal injection of streptozotocin 55 mg/kg. The diabetic rats were orally administered MLT 10 mg/kg of body weight for 15 days. MLT remarkably downregulated serum glucose levels. It also improved levels of the lipid peroxidation product 4-hydroxynonenal, improved levels of antioxidants including glutathione, glutathione peroxidase and glutathione reductase in the brains of the diabetic rats, and this is indicative of the antioxidant potential of MLT. MLT also prevented increase in homocysteine, amyloid-β42 and tau levels in diabetic rats, and this suggests that it can reduce the risk of dementia. This is associated with reduction in the levels of the dopamine, serotonin, and glutamate and is indicative of the regulatory effect of MLT on neurotransmitters. Treatment with MLT improved diabetes-induced structural alteration in the hippocampus and cerebral cortex. MLT significantly reduced caspase-3 and Bax as well as significantly increase Bcl-2 protein and GFAP-positive astrocytes indicating its anti-apoptotic effect. MLT showed remarkable ameliorative effect against biochemical and molecular alterations in the brains of diabetic rats most likely through its antioxidant property.

Levosimendan Prevents Memory Impairment Induced by Diabetes in Rats: Role of Oxidative Stress

BACKGROUND

Levosimendan is a calcium sensitizer and phosphodiesterase inhibitor that has potent antioxidant and anti-inflammatory activities.

OBJECTIVES

The aim of the current study is to investigate the potential protective effect of levosimendan on learning and memory impairment induced by diabetes.

METHODS

Adult Wister rats were randomly divided into four groups (n=15 rats/group): control, levosimendan, streptozotocin (STZ) induced diabetes, and levosimendan-STZ diabetes. Upon confirmation of the success of the STZ diabetic model, intraperitoneal levosimendan (100µg/kg/week) was administrated to the assigned groups for 4 weeks. Then, the radial arm water maze was used to evaluate spatial learning and memory. Oxidative stress biomarkers and brain-derived neurotrophic factor were evaluated in hippocampal tissues.

RESULTS

The results showed that Diabetes Mellitus (DM) impaired both short- and long- term memory (P<0.01), while levosimendan protected the animals from memory impairment. In addition, levosimendan prevented DM-induced reduction in the hippocampal levels of superoxide dismutase and glutathione peroxidase (P<0.05). Moreover, the administration of levosimendan prevented DM-induced increases in hippocampal thiobarbituric acid reactive substances level (P<0.05). Furthermore, levosimendan restored the ratio of reduced/oxidized glutathione (GSH/GSSG) in DM rats to that observed in the control group (P<0.05).

CONCLUSIONS

In summary, DM induced learning and memory impairment, and treatment with levosimendan impeded this impairment probably through preventing alterations in the antioxidant system in the hippocampus.

Melatonin prevents deterioration of erectile function in streptozotocin-induced diabetic rats via sirtuin-1 expression

A review of the literature indicated that sirtuin-1 expression, a regulator of nitric oxide bioavailability in erectile dysfunction (ED) after melatonin therapy, has not yet been investigated. The objective of this study was to evaluate the protective effects of melatonin for erectile function with sirtuin-1 protein expression in type 1 diabetic rat models. Fifty male Sprague Dawley rats were placed into five groups. Except for those in the control group (C), each animal received a single dose (60 mg/kg) of streptozotocin to induce diabetes. The animals were placed into the diabetes (D) group, insulin (I) group (6 U/kg/day), melatonin (Mel) group (10 mg kg^-1  day^-1 ) and combined treatment (I + Mel) group. Ten weeks later, the serum testosterone levels, intracavernosal pressure (ICP), mean arterial pressure (MAP), malondialdehyde (MDA), cyclic guanosine monophosphate (c-GMP), 8-hydroxydeoxyguanosine (8-OHdG), nitric oxide synthase (NOS), caspase-3 activity, sirtuin-1 and endothelial nitric oxide synthase (eNOS) protein expression and histological findings were assessed. The mean ICP/MAP ratio for the D group was lower than the mean ratios for the other groups. The treatment groups, particularly the I + Mel group, exhibited lower 8-OHdG and MDA levels and caspase-3 activity than the D group. The sirtuin-1 and eNOS expression and cavernosal tissue (CT) histology seemed to have been preserved by the melatonin and/or insulin therapy. These results were indicative of a profound protective effect of melatonin by the activation of sirtuin-1 protein expression against hyperglycemia-induced oxidative CT injury.

Melatonin alleviates cardiac fibrosis via inhibiting lncRNA MALAT1/miR-141-mediated NLRP3 inflammasome and TGF-β1/Smads signaling in diabetic cardiomyopathy

Melatonin is a hormone produced by the pineal gland, and it has extensive beneficial effects on various tissue and organs; however, whether melatonin has any effect on cardiac fibrosis in the pathogenesis of diabetic cardiomyopathy (DCM) is still unknown. Herein, we found that melatonin administration significantly ameliorated cardiac dysfunction and reduced collagen production by inhibiting TGF-β1/Smads signaling and NLRP3 inflammasome activation, as manifested by downregulating the expression of TGF-β1, p-Smad2, p-Smad3, NLRP3, ASC, cleaved caspase-1, mature IL-1β, and IL-18 in the heart of melatonin-treated mice with diabetes mellitus (DM). Similar beneficial effects of melatonin were consistently observed in high glucose (HG)-treated cardiac fibroblasts (CFs). Moreover, we also found that lncRNA MALAT1 (lncR-MALAT1) was increased along with concomitant decrease in microRNA-141 (miR-141) in DM mice and HG-treated CFs. Furthermore, we established NLRP3 and TGF-β1 as target genes of miR-141 and lncR-MALAT1 as an endogenous sponge or ceRNA to limit the functional availability of miR-141. Finally, we observed that knockdown of miR-141 abrogated anti-fibrosis action of melatonin in HG-treated CFs. Our findings indicate that melatonin produces an antifibrotic effect via inhibiting lncR-MALAT1/miR-141-mediated NLRP3 inflammasome activation and TGF-β1/Smads signaling, and it might be considered a potential agent for the treatment of DCM.