Protective effect of melatonin on beta-cell damage in streptozotocin-induced diabetes in rats

Potential therapeutic value of melatonin in diabetic nephropathy: improvement beyond anti-oxidative stress

Diabetic nephropathy (DN) is a common complication of diabetes, and it is also the main cause of chronic renal failure. Physiological/pathological changes mediated by high glucose are the main factors causing injury of DN, including the enhancement of polyol pathway, the accumulation of advanced glycation products (AGEs), and the activation of protein kinase C (PKC) and transforming growth factor-β (TGF-β) signals. In addition, the abnormal activation of renin-angiotensin system (RAS) and oxidative stress are also involved. Melatonin is a physiological hormone mainly secreted by the pineal gland which has been proved to be related to diabetes. Studies have shown that exogenous melatonin intervention can reduce blood glucose and alleviate high glucose mediated pathological damage. At the same time, melatonin also has a strong antioxidant effect, and can inhibit the activation of RAS. Therefore, it is of great significance to explore the therapeutic effect and value of melatonin on DN.

Melatonin ameliorates the adrenal and pancreatic alterations in streptozotocin-induced diabetic rats: Clinical, biochemical, and descriptive histopathological studies

Previous studies have demonstrated the beneficial effects of melatonin in diabetic rats. However, limited studies have been conducted on the potential effects of melatonin on the descriptive histopathological and morphometric findings in different compartments of the adrenal glands in diabetic animal models. In this study, using a streptozotocin (STZ)-induced diabetic rat model, we sought to examine histological alterations in the pancreas and adrenal glands and observe the effect of the administration of melatonin on the histopathology and morphology of the pancreas and the adrenal gland cortex and medulla that are altered by STZ-induced hyperglycemia. Rats were randomly assigned to four different groups: Group I, normal control; Group II, melatonin group (MT) (10 mg/kg/day); Group III, (diabetic STZ group), and Group IV, diabetic (STZ) + melatonin group (MT). Throughout the experiment, the animals' fasting blood sugar levels were measured. Blood was obtained to determine the animals' cumulative blood sugar levels after sacrification. For histological and morphometrical evaluations, the pancreatic and adrenal gland tissues were dissected and processed. Our results showed that diabetic rats receiving melatonin significantly (P < 0.05) improved their fasting blood sugar and cumulative blood sugar levels compared to the diabetic group not receiving melatonin. Furthermore, histopathological examinations of the pancreatic and adrenal tissues of the diabetic rats indicated the occurrence of severe histopathological and morphometric changes. Morphometric analysis of the adrenals indicated a significant increase (P < 0.05) in the thickness of the cortex zones [zona glomerulosa (ZG), zona fasciculata (ZF), and zona reticularis (ZR)] for the diabetic STZ group compared with other groups, and a significant decrease (P < 0.05) in the diameter of the in adrenal gland medullas in the diabetic STZ rats compared to the other groups. Furthermore, treatment with melatonin restored these changes in both the pancreatic and adrenal gland tissues and produced a significant (P < 0.05) improvement in the cortex and medulla thickness compared to the untreated diabetic rats. Overall, melatonin significantly reduced the hyperglycemic levels of glucose in diabetic rats and reversed the majority of histopathological alterations in the tissues of the pancreas and adrenals, demonstrating its anti-diabetic activity.

A novel therapeutic combination of sitagliptin and melatonin regenerates pancreatic β-cells in mouse and human islets

Autoimmune-led challenge resulting in β-cell loss is responsible for the development of type 1 diabetes (T1D). Melatonin, a pineal hormone or sitagliptin, a dipeptidyl peptidase IV (DPP-IV) inhibitor, has increased β-cell mass in various diabetic models and has immunoregulatory property. Both β-cell regenerative capacity and melatonin secretion decrease with ageing. Thus, we aimed to investigate the therapeutic potential of melatonin combined with sitagliptin on β-cell regeneration under glucotoxic stress, in the streptozotocin-induced young and old diabetic mouse models, and euglycemic humanized islet transplant mouse model. Our results suggest that combination therapy of sitagliptin and melatonin show an additive effect in inducing mouse β-cell regeneration under glucotoxic stress, and in the human islet transplant mouse model. Further, in the young diabetic mouse model, the monotherapies induce β-cell transdifferentiation and reduce β-cell apoptosis whereas, in the old diabetic mouse model, melatonin and sitagliptin induce β-cell proliferation and β-cell transdifferentiation, and it also reduces β-cell apoptosis. Further, in both the models, combination therapy reduces fasting blood glucose levels, increases plasma insulin levels and glucose tolerance and promotes β-cell proliferation, β-cell transdifferentiation, and reduces β-cell apoptosis. It can be concluded that combination therapy is superior to monotherapies in ameliorating diabetic manifestations, and it can be used as a future therapy for β-cell regeneration in diabetes patients.

Melatonin relieves diabetic complications and regenerates pancreatic beta cells by the reduction in NF-kB expression in streptozotocin induced diabetic rats

Melatonin, a pleiotropic hormone, has many regulatory effects on the circadian and seasonal rhythms, sleep and body immune system. It is used in the treatment of blind circadian rhythm sleep disorders, delayed sleep phase and insomnia. It is a potent antioxidant, anti-inflammatory, free radical scavenger, helpful in fighting infectious disease and cancer treatment. Decreased level of circulating melatonin was associated with an increased blood glucose level, losing the anti-oxidant protection and anti-inflammatory responses. We aimed to evaluate the effect of melatonin administration, in streptozotocin (STZ) induced diabetic rats, on blood glucose level and pancreatic beta (β) cells. Diabetes mellitus was induced in Sprague dawley male rats by the intravenous (i.v) injection of 65 mg/kg of STZ. Diabetic rats received melatonin at a dose of 10 mg/kg daily for 8 weeks by oral routes. The results showed, after 8 weeks of melatonin administration, a reduction in: 1- fasting blood glucose (FBG) and fructosamine (FTA) levels, 2- kidney and liver function parameters, 3- levels of serum triglycerides, cholesterol and LDL-C, 4- malondialdehyde (MDA), 5- NF-κB expression in treated group, 6- pro-inflammatory cytokines (IL-1β and IL-12) and immunoglobulins (IgA, IgE and IgG). Furthermore, an elevation in insulin secretion was noticed in melatonin treated group that indicated β cells regeneration. Therefore, melatonin administration, in STZ induced diabetic rats; reduced hyperglycemia, hyperlipidemia and oxidative stress. Melatonin acted as an anti-inflammatory agent that reduced pro-inflammatory cytokines (IL-1β and IL-12) and oxidative stress biomarkers (MDA). Melatonin succeeded in protecting β cells under severe inflammatory situations, which was apparent by the regeneration of islets of Langerhans in treated diabetic rats. Moreover, these results can open a gate for diabetes management and treatment.

Diabetes mellitus and melatonin: Where are we?

Diabetes mellitus (DM) and diabetes-related complications are amongst the leading causes of mortality worldwide. The international diabetes federation (IDF) has estimated 592 million people to suffer from DM by 2035. Hence, finding a novel biomolecule that can effectively aid diabetes management is vital, as other existing drugs have numerous side effects. Melatonin, a pineal hormone having antioxidative and anti-inflammatory properties, has been implicated in circadian dysrhythmia-linked DM. Reduced levels of melatonin and a functional link between melatonin and insulin are implicated in the pathogenesis of type 2 diabetes (T2D) Additionally, genomic studies revealed that rare variants in melatonin receptor 1b (MTNR1B) are also associated with impaired glucose tolerance and increased risk of T2D. Moreover, exogenous melatonin treatment in cell lines, rodent models, and diabetic patients has shown a potent effect in alleviating diabetes and other related complications. This highlights the role of melatonin in glucose homeostasis. However, there are also contradictory reports on the effects of melatonin supplementation. Thus, it is essential to explore if melatonin can be taken from bench to bedside for diabetes management. This review summarizes the therapeutic potential of melatonin in various diabetic models and whether it can be considered a safe drug for managing diabetic complications and diabetic manifestations like oxidative stress, inflammation, ER stress, mitochondrial dysfunction, metabolic dysregulation, etc.

Potential Protective Effect of Vitamin C on Qunalphos-Induced Cardiac Toxicity: Histological and Tissue Biomarker Assay

Insecticides and toxicants abound in nature, posing a health risk to humans. Concurrent exposure to many environmental contaminants has been demonstrated to harm myocardial performance and reduce cardiac oxidative stress. The purpose of this research was to study the protective effect of vitamin C (Vit C) on quinalphos (QP)-induced cardiac tissue damage in rats. Eighteen albino male rats were randomly categorised into three groups (n = 6). Control, QP group: rats received distilled water. QP insecticide treatment: an oral administration of QP incorporated in drinking water. QP + Vit C group: rats received QP and Vit C. All the experiments were conducted for ten days. Decline of cardiac antioxidant biomarkers catalase (CAT) and reduced glutathione (GPx) along with increased proinflammatory markers tumour necrosis factor-alpha (TNF-α) and interleukin 6 (IL-6) indicated oxidative and inflammatory damage to the heart following administration of QP when compared to control rats. The light microscopic and ultrastructure appearance of QP-treated cardiomyocytes exhibited cardiac damage. Administration of Vit C showed decreased oxidative and inflammatory biomarkers, confirmed with histological and electron microscopic examination. In conclusion, Vit C protected the heart from QP-induced cardiac damage due to decreased inflammation and oxidative stress.

Modulatory effect of zingerone against STZ-nicotinamide induced type-2 diabetes mellitus in rats

The objective of this research was to explore the role of zingerone on hyperglycemia, hyperlipidemia, insulin level, oxidative biochemical markers and histological alterations in β-cells of type-2 diabetic rats. The outcome of this study illustrates reduction in glucose and insulin levels significantly in zingerone-treated diabetic groups. Lipid parameters were resumed to normal in zingerone-treated diabetic group as demonstrated by significant reduction in triglycerides, cholesterols (total, low-density and very low-density) levels along with significant increase high-density cholesterols levels. Zingerone-treated diabetic groups exhibited significant reduction in LPO levels and restoration of GSH contents. Administration of zingerone to treated diabetic groups indicated improvement in antioxidant enzymes (GPx, GR, GST, SOD and CAT). Administration of zingerone to treated diabetic groups minimized degeneration of pancreatic β-cells as witnessed from histopathological studies. Our results demonstrate that zingerone modulates hyperglycaemia, hyperlipidaemia, oxidative biochemical markers and degenerative changes in β-cells of treated diabetic groups.

Therapeutic potential of melatonin as a chronobiotic and cytoprotective agent in diabetes mellitus

PURPOSE

Diabetes mellitus is a complex metabolic disorder characterized by hyperglycemia occurring as a result of dysregulation and balance of various metabolic pathways. In recent years, circadian misalignment (due to altered sleep/wake, feeding/fasting cycles), has been intimately linked with the development of diabetes mellitus. Herein, we review our knowledge of oxidative stress, circadian rhythms control of metabolism, and the effects of its disruption on homeostasis while emphasizing the importance of melatonin, a nocturnally peaking, pineal hormone, as a potential therapeutic drug for the prevention and treatment of diabetes.

METHODS

PubMed database was systematically searched for related articles and data from all types of studies, including clinical trials, review articles, and case reports were considered without limiting the study to one specific category.

RESULTS

Experimental and epidemiological evidence indicate melatonin's multifaceted effects in intermediary metabolism via resynchronization of the circadian rhythms and its deficiency is associated with metabolic derangements. As a chronobiotic, it cures insomnia and sleep disorders caused by shift work or jet lag. The antagonistic relationship between melatonin and insulin highlights its influence in regulating insulin secretion, its action, and melatonin treatment successfully improved glucose homeostasis, energy balance, and overall health in diabetes mellitus. Melatonin's cytoprotective role as an antioxidant and free radical scavenger, proved useful in combating oxidative stress, preserving beta-cell function, and influencing the development of diabetic complications.

CONCLUSION

The therapeutic application of melatonin as a chronobiotic and cytoprotective agent is of promising significance in diabetes mellitus. Future investigations are encouraged to fully explore the efficacy of this ubiquitous molecule in various metabolic disorders.

Melatonin promotes Schwann cell proliferation and migration via the shh signalling pathway after peripheral nerve injury

Peripheral nerve injury (PNI) is a common and incurable disease in the clinic, but the effects of available treatments are still not satisfactory. Therefore, it is necessary to explore new treatment methods. To explore the effect and mechanism of melatonin in peripheral nerve regeneration, we administered melatonin to mice with PNI by intraperitoneal injection. We applied microarray analysis to detect differentially expressed genes of mice with sciatic nerve injury after melatonin application. Then, we conducted gene ontology and protein-protein interactions to screen out the key genes related to peripheral nerve regeneration. Cell biology and molecular biology experiments were performed in Schwann cells in vitro to verify the key genes identified by microarray analysis. Our results showed that a total of 598 differentially expressed genes were detected after melatonin subcutaneously injecting into mice with sciatic nerve injury. Bioinformatics analysis showed that Shh may be the key gene for the promotion of peripheral nerve regeneration by melatonin. In vitro, the proliferation and migration abilities of schwann cells in the melatonin group were significantly higher than those of Schwann cells in the control group; while after treating with both melatonin and luzindole (a Shh signalling pathway inhibitor), the proliferation and migration abilities of Schwann cells decreased compared with the melatonin group. Our study suggests that melatonin might improve the proliferation and migration of Schwann cells via the Shh signalling pathway after PNI, thus promoting peripheral nerve regeneration. Our study provides a new approach and target for the clinical treatment of PNI.

Mesenchymal stem cells versus curcumin in enhancing the alterations in the cerebellar cortex of streptozocin-induced diabetic albino rats. The role of GFAP, PLC and α-synuclein

BACKGROUND

Diabetes mellitus is the disease, termed either by insulin paucity or resistance and hyperglycemia. The selection of the cerebellum was built on its specific functions. The aim of this study was to investigate a comparison between the possible therapeutic effects of MSCs and curcumin against fluctuations in the cerebellar cortex of STZ-induced diabetic albino rats.

MATERIALS AND METHODS

Forty rats were divided into five groups: control, sham control, streptozotocin-induced diabetes, diabetes and MSCs administered and diabetes and curcumin administered. Light microscopic (H&E), immune-histochemical; Glial fibrillary acidic protein (GFAP), real-time PCR; phospholipase-C (PLC) and α-synuclein, histomorphometric analysis, oxidative / anti-oxidatants; malondialdehyde (MDA)/ superoxide dismutase (SOD) glutathione (GSH) and were made.

RESULTS

The histopathological examination of the STZ-induced diabetic rats revealed alterations in the molecular, purkinje and granular layers. Abnormal organizations, vacuolation, patchy loss of purkinje cells were detected. Some purkinje cells migrated into the granular layer.Hemorrhage in pia mater outspreading to cerebellar layers is discerned. Purkinje cells showed karyorrhexis. The mean value of area percentage for GFAP immune- reactivity revealed 360 % significant increase compared to that of the control group. Also, MDA level was significantly increased while the SOD and GSH levels were significantly lower when compared to the control group. Meanwhile, mean values of PLC demonstrated significant decrease, while α-synuclein levels displayed a significant increment in the diabetic group. Administration of curcumin and MSCs extremely ameliorated the previous alterations.

CONCLUSION

the deleterious alterations on the cerebellar cortex induced by diabetes were obviously improved when treated with either MSCs or curcumin.

Melatonin regulates the expression of inflammatory cytokines, VEGF and apoptosis in diabetic retinopathy in rats

The present study analyzed whether melatonin could mediate the expression of VEGF, IL-6 and TNF-α, as well as the apoptotic index in rats with diabetic retinopathy. Fifty Wistar albino rats were divided into the following groups: GC: rats without induction of diabetes by streptozotocin; GD: rats induced to diabetes by streptozotocin and treated with placebo; GDM: rats induced to diabetes by streptozotocin and after confirmation treated with melatonin at a dose of 10 mg/kg for 20 days; GDMS: rats induced to diabetes by streptozotocin and treated simultaneously with melatonin at a dosage of 10 mg/kg for 20 days; GDI: rats induced to diabetes by streptozotocin and after confirmation treated with insulin for 20 days. Diabetes was induced by intraperitoneal injections of streptozotocin (60 mg/kg), and insulin (5 U/day) was administered subcutaneously. For apoptosis TUNEL was used, while for the analysis of VEGF, IL-6 and TNF-α. The results showed that the groups that were treated with melatonin decreased the expression of cytokines and VEGF, in addition to apoptosis. Thus, it is concluded that melatonin can regulate the expression of these factors by improving the condition of the retina in diabetic retinopathy.

Dietary Melatonin Protects Against Behavioural, Metabolic, Oxidative, and Organ Morphological Changes in Mice that are Fed High-Fat, High- Sugar Diet

BACKGROUND

Metabolic syndrome is a complex pattern of disorders that occur jointly and is associated with an increased risk of cardiovascular and cerebrovascular disease. Therefore the need for more-efficient options of treatment has become imperative.

OBJECTIVE

This study examined the effect of dietary-melatonin in the management of behavioural, metabolic, antioxidant, and organ changes due to high-fat/high-sugar (HFHS) diet-induced metabolic syndrome in mice.

METHODS

Mice were randomly assigned into five groups of ten animals each. Groups were normal control [fed standard diet (SD)], HFHS control, and 3 groups of melatonin incorporated into HFHS at 2.5, 5, and 10 mg/kg of feed. Mice were fed for seven weeks, and body weight was assessed weekly. Open-field behaviours, radial-arm, and Y-maze spatial memory were scored at the end of the experimental period. Twenty-four hours after the last behavioural test, blood was taken for estimation of blood glucose levels after an overnight fast. Animals were then euthanised, and blood was taken for estimation of plasma insulin, leptin, and adiponectin levels, and serum lipid profile. The liver, kidneys, and brain were excised and processed for general histology, while homogenates of the liver and whole brain were used to assess oxidative stress parameters.

RESULTS

Results showed that dietary melatonin (compared to HFHS diet) was associated with a decrease in body weight, food intake, and novelty-induced behaviours; and an increase in spatial-working memory scores. A decrease in glucose, insulin, leptin, and malondialdehyde levels; and an increase in adiponectin levels and superoxide dismutase activity were also observed. Histomorphological/ histomorphometric examination revealed evidence of organ injury with HFHS diet, and varying degrees of amelioration with melatonin-supplemented diet.

CONCLUSION

In conclusion, dietary melatonin supplementation may have beneficial effects in the management of the metabolic syndrome.

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

Background

Melatonin is a well-known free radical scavenger. The present study aimed to investigate the effects of melatonin treatment on the antioxidant status in the lenticular tissue of streptozotocin (STZ)-induced diabetic rats.

Methods

Thirty-four male rats were randomly divided into four groups as follows: healthy control rats (group 1, n = 10); diabetic control rats (group 2, n = 10); melatonin-treated (5 mg/kg·day) diabetic rats (group 3, n = 10) and melatonin-treated (5 mg/kg·day) healthy rats (group 4, n = 4). Diabetes was induced by injection of streptozotocin (50 mg/kg, ip). Following 8-weeks of melatonin treatment, all rats were killed and the blood plasma and their lenses were stored at -70 °C for antioxidant enzyme activities assay and biochemical determination.

Results

The plasma glucose and lens malondialdehyde (MDA) increased significantly in the rats of group 2 as compared to the group 1. Also, a significant decrease in the levels of catalase (CAT) and glutathione reductase (GR) activities in the lenses and plasma reduced glutathione (GSH) was found. However, the levels of lenticular MDA (not significant) and the plasma glucose significantly decreased in the rats of group 3 compared to the group 2. Besides, the levels of CAT, GR in the rats lens and plasma GSH increased significantly.

Conclusion

Diabetes mellitus induced hyperglycemia and oxidative stress, whereas melatonin decreased the blood glucose levels and lipid peroxidation and increased the activities of antioxidant enzymes in diabetic rat lenses.

Melatonin and/or rowatinex attenuate streptozotocin-induced diabetic renal injury in rats

The study aimed to explore the prophylactic effect of melatonin, rowatinex; a naturally occurring renal drug, and its combination on diabetic nephropathy in type 2 diabetic rats. Diabetes was induced by intraperitoneal injection of a single dose of streptozotocin (50 mg/g body weight). Three days before diabetes induction, rats were daily treated with melatonin, rowatinex and their combination continuously for 8 weeks. Evaluation was done through measuring blood urea nitrogen (BUN), serum uric acid, serum creatinine, urine creatinine, creatinine clearance, nitric oxide (NO), malondialdehyde (MDA), superoxide dismutase (SOD), glutathione (GSH), total antioxidant capacity (TAC), kidney injury molecule-1 (KIM-1), heat shock protein-70 (HSP-70), caspase-3, transforming growth factor β1 (TGFβ1), DNA degradation by the comet assay and total protein contents. Histopathologic study was also done for the kidney and the pancreas. Drastic changes in all measured parameters of the diabetic rats were observed. Treatment with melatonin and rowatinex showed amelioration to variable degrees. In conclusion, melatonin showed the most potent effect on protecting rats from deleterious action of diabetic nephropathy followed by its combination with rowatinex.

Insulin protects against hepatocyte ultrastructural damage induced by type 1 diabetes mellitus in rats

Diabetic complications that affect vital organs such as the heart and liver represent a major public health concern. The potential protective effects of the hormone insulin against hepatocyte ultrastructural alterations induced secondary to type 1 diabetes mellitus (T1DM) in a rat model of the disease have not been investigated before. Therefore, rats were injected once with 65 mg/kg streptozotocin (T1DM group) and the protection group (T1DM+Ins) received a daily injection of insulin 48 h post diabetic induction by streptozotocin and continued until being sacrificed at week 8. The harvested liver tissues were examined using transmission electron microscopy (TEM) and blood samples were assayed for biomarkers of liver injury enzyme, glycemia, lipidemia, inflammation, and oxidative stress. TEM images showed that T1DM induced profound hepatocyte ultrastructural alterations as demonstrated by pyknotic nucleus, condensation of chromatin, irregular nuclear membrane, swollen mitochondria, dilated rough endoplasmic reticulum, damaged intercellular space, and accumulation of few lipid droplets inside the hepatocyte cytoplasm, which were substantially protected with insulin. In addition, the blood chemistry profile complements the TEM data as demonstrated by an increase in serum levels of alanine aminotransferase (ALT), dyslipidemia, C-reactive protein (CRP), tumor necrosis factor-alpha (TNF-α), interleukin-6 (IL-6), and malondialdehyde (MDA) by T1DM that were significantly (p < 0.05) reduced with insulin injections. Thus, we conclude that insulin effectively protects against T1DM-induced liver injury in rats for a period of 8 weeks, possibly due to the inhibition of inflammation, oxidative stress, and dyslipidemia.

Potential therapeutic role of melatonin on STZ-induced diabetic central neuropathy: A biochemical, histopathological, immunohistochemical and ultrastructural study

The aim of the present study was to assess the therapeutic potential of melatonin (Mel) in diabetic central neuropathy in a rat model of streptozotocin (STZ)-induced diabetes. The rats were injected with 60 mg/kg STZ and diabetes was confirmed by blood glucose levels (BGL) ≥ 250 mg/dL. Mel treatment (50 mg/kg) was started 72 h before the STZ injection and continued for 45 days. In addition, normal control, vehicle (5% ethanol) control, and Mel-treated non-diabetic control were also included. STZ induced a diabetic phenotype with persistent hyperglycemia and elevated oxidative stress in the brain, liver, and kidneys compared to the control groups. In addition, the diabetic rats showed severe β-cell necrosis with reduced insulin levels, cerebral neuronopathy, myelinopathy, axonopathy, microglial and astroglial activation, and vascular damage. While Mel treatment did not prevent the development of STZ-induced diabetes mellitus and had no significant effect on the BGLs of the diabetic rats, it significantly ameliorated the diabetes-induced oxidative stress and neurodegeneration. Taken together, Mel showed potent therapeutic effects against the neurological complications of hyperglycemia and therefore can be used to treat diabetic neuropathy.

Ameliorative effects of bone marrow derived pancreatic progenitor cells on hyperglycemia and oxidative stress in diabetic rats

The present study aimed to investigate the effects of Bone marrow derived pancreatic progenitor cells (BM- PPCs) in diabetic rats. It was conducted on 30 adult male Sprague-Dawley rats weighing 200-220 g. They were divided into three groups: (a) Group 1 was the control group; (b) Group 2 was the diabetic (induced diabetic by a single intraperitoneal (IP) injection of streptozotocin (STZ) (60 mg/kg) and (c) Group 3 was the treated (received injection of 2.5 X 10⁶ BM- PPCs via the tail vein twice with a 21-day time interval). The blood glucose level was estimated weekly, the oxidative stress and insulin gene expression were evaluated at the end of the experiment. Pancreatic tissue histopathology was performed. The insulin immuno-histochemical reaction was applied to the islets. The blood glucose level was reduced in the treated group over time till reaching its acceptable level whereas it was increased in the diabetic group. The oxidative stress was decreased in the treated group compared to the diabetic one. The treated group showed increased expression of the insulin gene compared to the diabetic group. The immune-histochemical analysis of insulin showed an increased number and size of pancreatic islets in the treated group compared to the diabetic one. Thus, the twofold injection of BM- PPCs could restore the normal beta-cell morphology and function.

Improvement in Serum Biochemical Alterations and Oxidative Stress of Liver and Pancreas following Use of Royal Jelly in Streptozotocin-Induced Diabetic Rats

OBJECTIVE

This study aimed to evaluate the effects of royal jelly (RJ) on serum biochemical alterations and oxidative stress status in liver and pancreas of streptozotocin (STZ)- induced diabetic rats.

MATERIALS AND METHODS

In this experimental study, thirty two male Wistar rats were divided into the following four groups (n=8/group): i. Control (C), ii. Diabetic (D), iii. Royal jelly (R), and iv. Royal jelly-treated diabetic (D/R) groups. Diabetes was induced by single intraperitoneal (IP) injection of STZ (60 mg/kg). The RJ [100 mg/kg body weight (BW)] was administered orally for 42 days. Blood samples were used to determine serum levels of insulin, high density lipoprotein cholesterol (HDL-c), total protein (TP), albumin, alanine aminotransferase (ALT), aspartate aminotransferase (AST), alkaline phosphatase (ALP), and fasting blood glucose (FBG). Also, the antioxidant status was evaluated by determining the levels of malondialdehyde (MDA), catalase (CAT) and ferric reducing antioxidant power (FRAP) in liver and pancreas. Data were analyzed by one-way analysis of variance (ANOVA) with P<0.05 as the significant level.

RESULTS

STZ-induced diabetic rats showed a significant elevation in the serum levels of AST, ALT, ALP and FBG, whereas there was a significant decrease in serum levels of insulin, albumin, HDL-c and TP (P<0.05). Treatment of the diabetic rats with RJ restored the changes of the above parameters to their normal levels (P<0.05). In addition, RJ significantly improved reduced levels of FRAP and CAT as well as high MDA level in liver and pancreas (P<0.05).

CONCLUSION

RJ improves oxidative damage induced by STZ in the liver and pancreas of rats; therefore, it can be considered as an effective and alternative treatment for diabetes.

Combination of melatonin and certain drugs for treatment of diabetic nephropathy in streptozotocin-induced diabetes in rats

Diabetic nephropathy is a major complication of diabetes and a leading cause of end-stage renal failure in many developed countries. The study aimed to evaluate the efficiency of certain drugs and melatonin in the treatment of nephropathy secondary to diabetes. Diabetes was induced in rats by a single intraperitoneal injection of streptozotocin (50 mg/kg body weight). Three days after induction of diabetes (460-500 mg/dl), rats were treated daily for 60 days with Rowatinex, melatonin, Rowatinex + melatonin, Amosar (Losartan Potassium) (LSP) and LSP + melatonin. The evaluations were made by measuring blood urea nitrogen (BUN), serum uric acid, serum creatinine, urine creatinine, creatinine clearance, nitric oxide, malondialdehyde, superoxide dismutase, glutathione, total antioxidant capacity, kidney injury molecule-1, heat shock protein-70, caspase-3, transforming growth factor β1, and DNA degradation by comet assay and total protein contents. The histopathological picture of the kidneys and pancreases was confirmed in our results. Diabetic rats showed drastic changes in all the measured parameters. Treatment with melatonin and the selected drugs revealed amelioration levels with variable degrees. In conclusion, the combination of LSP and melatonin had the most potent effect on treating the deleterious action of diabetes on rat kidney.

Genetic variation in MTNR1B is associated with gestational diabetes mellitus and contributes only to the absolute level of beta cell compensation in Mexican Americans

AIMS/HYPOTHESIS

MTNR1B is a type 2 diabetes susceptibility locus associated with cross-sectional measures of insulin secretion. We hypothesised that variation in MTNR1B contributes to the absolute level of a diabetes-related trait, temporal rate of change in that trait, or both.

METHODS

We tested rs10830963 for association with cross-sectional diabetes-related traits in up to 1,383 individuals or with rate of change in the same phenotypes over a 3-5 year follow-up in up to 374 individuals from the family-based BetaGene study of Mexican Americans.

RESULTS

rs10830963 was associated cross-sectionally with fasting glucose (p = 0.0069), acute insulin response (AIR; p = 0.0013), disposition index (p = 0.00078), glucose effectiveness (p = 0.018) and gestational diabetes mellitus (OR 1.48; p = 0.012), but not with OGTT 30 min Δinsulin (the difference between the 30 min and fasting plasma insulin concentration) or 30 min insulin-based disposition index. rs10830963 was also associated with rate of change in fasting glucose (p = 0.043), OGTT 30 min Δinsulin (p = 0.01) and AIR (p = 0.037). There was no evidence for an association with the rate of change in beta cell compensation for insulin resistance.

CONCLUSIONS/INTERPRETATION

We conclude that variation in MTNR1B contributes to the absolute level of insulin secretion but not to differences in the temporal rate of change in insulin secretion. The observed association with the rate of change in insulin secretion reflects the natural physiological response to changes in underlying insulin sensitivity and is not a direct effect of the variant.

Melatonin prevents pancreatic β-cell loss due to glucotoxicity: the relationship between oxidative stress and endoplasmic reticulum stress

Prolonged hyperglycemia results in pancreatic β-cell dysfunction and apoptosis, referred to as glucotoxicity. Although both oxidative and endoplasmic reticulum (ER) stresses have been implicated as major causative mechanisms of β-cell glucotoxicity, the reciprocal importance between the two remains to be elucidated. The aim of this study was to evaluate the differential effect of oxidative stress and ER stress on β-cell glucotoxicity, by employing melatonin which has free radical-scavenging and antioxidant properties. As expected, in β-cells exposed to prolonged high glucose levels, cell viability and glucose-stimulated insulin secretion (GSIS) were significantly impaired. Melatonin treatment markedly attenuated cellular apoptosis by scavenging reactive oxygen species via its plasmalemmal receptor-independent increase in antioxidant enzyme activity. However, treatments with antioxidants alone were insufficient to recover the impaired GSIS. Interestingly, 4-phenylbutyric acid (4-PBA), a chemical chaperone that attenuate ER stress by stabilizing protein structure, alleviated the impaired GSIS, but not apoptosis, suggesting that glucotoxicity induces oxidative and ER stress independently. We found that cotreatment of glucotoxic β-cells with melatonin and 4-PBA dramatically improved both their survival and insulin secretion. Taken together, these results suggest that ER stress may be the more critical mechanism for prolonged high-glucose-induced GSIS impairment, whereas oxidative stress appears to be more critical for the impaired β-cell viability. Therefore, combinatorial therapy of melatonin with an ER stress modifier may help recover pancreatic β-cells under glucotoxic conditions in type 2 diabetes.

Effects of Brown Seaweed (Sargassum polycystum) Extracts on Kidney, Liver, and Pancreas of Type 2 Diabetic Rat Model

The edible seaweed Sargassum polycystum (SP) is traditionally used against several human diseases. This investigation evaluated the effects of two dietary doses of SP ethanolic and aqueous extracts on the pancreatic, hepatic, and renal morphology of type 2 diabetic rats (T2DM). T2DM was induced by feeding rats on high calorie diet followed by a low dose streptozotocin. Changes in the diabetic rat organs in SP treated groups with different doses of extracts were compared with normal rats, diabetic control rats, and metformin treated rats. After 22 days of treatment, the pathological lesions of the livers and kidneys in the diabetic rats were quantitatively and qualitatively alleviated (P < 0.05) by both the SP extracts at 150 mg/kg body weight and by metformin. All the treated diabetic groups revealed marked improvement in the histopathology of the pancreas compared with the control diabetic group. Oral administration of 300 mg/kg body weight of aqueous and ethanolic extracts of SP and metformin revealed pancreas protective or restorative effects. The seaweed extracts at 150 mg/kg body weight reduced the liver and kidney damages in the diabetic rats and may exert tissue repair or restoration of the pancreatic islets in experimentally induced diabetes to produce the beneficial homeostatic effects.

Role of dietary and endogenous antioxidants in diabetes

Diabetes affects different people of all ages, race, and sex. This is a condition characterized by a state of chronic hyperglycaemia that leads to an increase of intracellular oxidative stress linked to the overproduction of free radicals. In the present review, we focus our attention on the molecular mechanisms leading to oxidative stress-mediates complications with particular regard to central nervous system (CNS). Furthermore, the present review reports the effects of different kind of antioxidants with enzymatic and nonenzymatic action that may significantly decrease the intracellular free radicals' overproduction and prevents the hyperglycaemia-mediated complications.

Protective effects of melatonin against spinal cord injury induced oxidative damage in rat kidney: A morphological and biochemical study

Spinal cord injury (SCI) induced oxidative stress affects multiple organ systems including the kidney. We studied the possible protective effects of melatonin on SCI-induced oxidative damage in renal tissues of rats. Wistar albino rats (n = 24) were exposed to SCI and divided into vehicle- or melatonin-treated SCI groups. Melatonin was administred intraperitoneally at a dose of 10 mg/kg for seven days. Renal tissues were investigated by light and electron microscopy. Furthermore, tissue malondialdehyde (MDA) and glutathione (GSH) levels and myeloperoxidase (MPO) and superoxide dismutase (SOD) activities were also determined. In the vehicle-treated SCI group, the renal histology was disturbed compared to controls, whereas the melatonin-treated SCI group showed significantly reduced degeneration of renal tissue as seen by both light and electron microscopy. MDA levels, MPO and SOD activities were increased and GSH levels were decreased in the vehicle-treated SCI group compared to controls. On the other hand, decreased MDA levels and MPO activities and increased GSH levels were observed in the melatonin-treated SCI group compared to vehicle-treated SCI group. These results showed that experimentally induced SCI caused oxidative stress in the rat kidney, whereas melatonin treatment reduced oxidative stress, suggesting that it may be used as a complementary therapy of renal problems occurring following SCI.

Assessment of DNA damage and lipid peroxidation in diabetic mice: effects of propolis and epigallocatechin gallate (EGCG)

There is growing recognition that polyphenolic compounds present in many plants and natural products may have beneficial effects on human health. Propolis - a substance produced by honeybees - and catechins in tea, in particular (-)-epigallocatechin gallate (EGCG), are strong antioxidants that appear to have anti-obesity and anti-diabetic effects. The present study was designed to elucidate the anti-diabetic effect of the water-soluble derivative of propolis (WSDP), which contains phenolic acids as the main compounds, and EGCG in alloxan-induced (75mg/kg, iv) diabetes in mice. Intraperitoneal administration of EGCG or propolis at doses of 50mg/kg body weight (bw) to diabetic mice for a period of 7 days resulted in a significant increase in body weight and in haematological/immunological blood parameters, as well as in 100% survival of the mice. A significant decrease in lipid peroxidation in liver, kidney and brain tissue was also observed in diabetic mice treated with these two agents. Additionally, EGCG and propolis clearly reduced DNA damage in peripheral lymphocytes of diabetic mice. Our studies demonstrate the anti-oxidative and anti-inflammatory potential of WSDP and EGCG, which could exert beneficial effects against diabetes and the associated consequences of free-radical formation in kidney, liver, spleen and brain tissue. The results suggest that dietary supplementation with WSDP or EGCG could potentially contribute to nutritional strategies for the prevention and treatment of diabetes mellitus.

Mitochondria and chloroplasts as the original sites of melatonin synthesis: a hypothesis related to melatonin's primary function and evolution in eukaryotes

Mitochondria and chloroplasts are major sources of free radical generation in living organisms. Because of this, these organelles require strong protection from free radicals and associated oxidative stress. Melatonin is a potent free radical scavenger and antioxidant. It meets the criteria as a mitochondrial and chloroplast antioxidant. Evidence has emerged to show that both mitochondria and chloroplasts may have the capacity to synthesize and metabolize melatonin. The activity of arylalkylamine N-acetyltransferase (AANAT), the reported rate-limiting enzyme in melatonin synthesis, has been identified in mitochondria, and high levels of melatonin have also been found in this organelle. From an evolutionary point of view, the precursor of mitochondria probably is the purple nonsulfur bacterium, particularly, Rhodospirillum rubrum, and chloroplasts are probably the descendents of cyanobacteria. These bacterial species were endosymbionts of host proto-eukaryotes and gradually transformed into cellular organelles, that is, mitochondria and chloroplasts, respectively, thereby giving rise to eukaryotic cells. Of special importance, both purple nonsulfur bacteria (R. rubrum) and cyanobacteria synthesize melatonin. The enzyme activities required for melatonin synthesis have also been detected in these primitive species. It is our hypothesis that mitochondria and chloroplasts are the original sites of melatonin synthesis in the early stage of endosymbiotic organisms; this synthetic capacity was carried into host eukaryotes by the above-mentioned bacteria. Moreover, their melatonin biosynthetic capacities have been preserved during evolution. In most, if not in all cells, mitochondria and chloroplasts may continue to be the primary sites of melatonin generation. Melatonin production in other cellular compartments may have derived from mitochondria and chloroplasts. On the basis of this hypothesis, it is also possible to explain why plants typically have higher melatonin levels than do animals. In plants, both chloroplasts and mitochondria likely synthesize melatonin, while animal cells contain only mitochondria. The high levels of melatonin produced by mitochondria and chloroplasts are used to protect these important cellular organelles against oxidative stress and preserve their physiological functions. The superior beneficial effects of melatonin in both mitochondria and chloroplasts have been frequently reported.

Effects of topiramate on diabetes mellitus induced by streptozotocin in rats

Topiramate currently approved for marketing as antiepileptic drug also possesses anti-diabetic activity. The aim of this study was to determine the antidiabetic effect of topiramate in a rat model of diabetes mellitus. Diabetes was induced by a single injection of streptozotocin to fasted rats. Diabetic animals were divided into untreated; insulin treated; topiramate treated with 25, 50 and 100 mg/kg; and combined insulin plus topiramate treatment in the previous doses. All medications were given once daily started after the rise of blood glucose for three weeks. Control rats were divided into untreated; vehicle treated and rats given topiramate in the previous doses. Body weight, blood-glucose and insulin levels were measured. Histopathological examination, immunohistochemical and morphometric studies of islets of the pancreas were done. Topiramate 50 and 100mg/kg resulted in a significant decrease in the blood glucose and increase in the insulin levels as well as the number of islets and the count and mass of beta cells. Combined treatment to diabetic rats with insulin and topiramate induced a better response than either alone. Further experimental and clinical studies are needed to explore the different mechanisms of action of topiramate as antidiabetic both in insulin dependent and non-insulin-dependent diabetes mellitus.

Metabolic disorders and adipose tissue insulin responsiveness in neonatally STZ-induced diabetic rats are improved by long-term melatonin treatment

Diabetes mellitus is a product of low insulin sensibility and pancreatic β-cell insufficiency. Rats with streptozotocin-induced diabetes during the neonatal period by the fifth day of age develop the classic diabetic picture of hyperglycemia, hypoinsulinemia, polyuria, and polydipsia aggravated by insulin resistance in adulthood. In this study, we investigated whether the effect of long-term treatment with melatonin can improve insulin resistance and other metabolic disorders in these animals. At the fourth week of age, diabetic animals started an 8-wk treatment with melatonin (1 mg/kg body weight) in the drinking water at night. Animals were then killing, and the sc, epididymal (EP), and retroperitoneal (RP) fat pads were excised, weighed, and processed for adipocyte isolation for morphometric analysis as well as for measuring glucose uptake, oxidation, and incorporation of glucose into lipids. Blood samples were collected for biochemical assays. Melatonin treatment reduced hyperglycemia, polydipsia, and polyphagia as well as improved insulin resistance as demonstrated by constant glucose disappearance rate and homeostasis model of assessment-insulin resistance. However, melatonin treatment was unable to recover body weight deficiency, fat mass, and adipocyte size of diabetic animals. Adiponectin and fructosamine levels were completely recovered by melatonin, whereas neither plasma insulin level nor insulin secretion capacity was improved in diabetic animals. Furthermore, melatonin caused a marked delay in the sexual development, leaving genital structures smaller than those of nontreated diabetic animals. Melatonin treatment improved the responsiveness of adipocytes to insulin in diabetic animals measured by tests of glucose uptake (sc, EP, and RP), glucose oxidation, and incorporation of glucose into lipids (EP and RP), an effect that seems partially related to an increased expression of insulin receptor substrate 1, acetyl-coenzyme A carboxylase and fatty acid synthase. In conclusion, melatonin treatment was capable of ameliorating the metabolic abnormalities in this particular diabetes model, including insulin resistance and promoting a better long-term glycemic control.

Glucose: a vital toxin and potential utility of melatonin in protecting against the diabetic state

The molecular mechanisms including elevated oxidative and nitrosative reactants, activation of pro-inflammatory transcription factors and subsequent inflammation appear as a unified pathway leading to metabolic deterioration resulting from hyperglycemia, dyslipidemia, and insulin resistance. Consistent evidence reveals that chronically-elevated blood glucose initiates a harmful series of processes in which toxic reactive species play crucial roles. As a consequence, the resulting nitro-oxidative stress harms virtually all biomolecules including lipids, proteins and DNA leading to severely compromised metabolic activity. Melatonin is a multifunctional indoleamine which counteracts several pathophysiologic steps and displays significant beneficial effects against hyperglycemia-induced cellular toxicity. Melatonin has the capability of scavenging both oxygen and nitrogen-based reactants and blocking transcriptional factors which induce pro-inflammatory cytokines. These functions contribute to melatonin's antioxidative, anti-inflammatory and possibly epigenetic regulatory properties. Additionally, melatonin restores adipocyte glucose transporter-4 loss and eases the effects of insulin resistance associated with the type 2 diabetic state and may also assist in the regulation of body weight in these patients. Current knowledge suggests the clinical use of this non-toxic indoleamine in conjunction with other treatments for inhibition of the negative consequences of hyperglycemia for reducing insulin resistance and for regulating the diabetic state.

The insulin-melatonin antagonism: studies in the LEW.1AR1-iddm rat (an animal model of human type 1 diabetes mellitus)

AIMS/HYPOTHESIS

It is well documented that melatonin influences insulin secretion mediated by G-protein-coupled melatonin receptor isoforms MT1 and MT2, which are present in rat and human pancreatic islets, as well as in rat insulinoma cells. Recent investigations have proven that hyperinsulinaemic Goto-Kakizaki (GK) rats, which are a rat model of type 2 diabetic rats, and humans have decreased melatonin plasma levels, whereas a streptozotocin-induced rat model of diabetes developed reduced insulin levels combined with increased melatonin levels.

METHODS

Plasma levels of glucose, insulin and melatonin as well as RNA expression of pineal Aanat, Hiomt (also known as Asmt), insulin receptor, adrenoceptor β1 and the clock genes Per1 and Bmal1 (also known as Arntl) were determined in male and female LEW.1AR1-iddm rats as well as in insulin-substituted LEW.1AR1-iddm rats.

RESULTS

Severe hypoinsulinaemia in diabetic LEW.1AR1-iddm rats was associated with decreased body weight and increased melatonin plasma levels combined with mainly elevated expression of Aanat, Hiomt, pineal insulin receptor and adrenoceptor β1. The changes were normalised by insulin substitution. Diurnal profiles of plasma melatonin and of antagonistic clock genes Per1 and Bmal1 were maintained in diabetic and insulin-substituted rats.

CONCLUSIONS/INTERPRETATION

The assumed causal relation between elevated melatonin and reduced insulin levels in LEW.1AR1-iddm rats is supported by the observation that insulin substitution normalised these changes. Further support for this interpretation comes from the observation that in GK rats an increase of plasma insulin was combined with a decrease of plasma noradrenaline (norepinephrine), the most important activator of melatonin synthesis. These relationships between the noradrenergic and insulin pathway support the existence of melatonin-insulin antagonism.

Taurine is more effective than melatonin on cytochrome P450 2E1 and some oxidative stress markers in streptozotocin-induced diabetic rats

Melatonin and taurine have alleviative effects in streptozotocin (STZ)-induced diabetic rats. Male Wistar rats were divided into nondiabetic, diabetic, diabetic melatonin supplemented and diabetic taurine supplemented groups. At the end of the study, both blood and liver were collected for determination of some oxidative stress parameters, and hepatic cytochrome P450 2E1 (CYP2E1) enzyme activity and gene expression. An increased CYP2E1 activity and expression level with a concomitant significant change in oxidative stress parameters were found in STZ-induced diabetic rats. Taurine or melatonin supplementation to the diabetic rats alleviated these experimental parameters with a more significant effect for taurine than that of melatonin. Suppression of β-hydroxybutyrate (β-HB) production by taurine can be one of the mechanisms of a reduction in CYP2E1. Taurine was effective more than melatonin in reducing CYP2E1 activity and expression; therefore antioxidants might prove beneficial in type 1 diabetes associated with manifestations of liver injury.

Central nervous system complications of diabetes in streptozotocin-induced diabetic rats: a histopathological and immunohistochemical examination

Diabetes mellitus is a common, potentially serious metabolic disorder. Over the long term, diabetes leads to serious consequences in a number of tissues, especially those that are insulin insensitive (retina, neurons, kidneys). It also causes a variety of functional and structural disorders in the central and peripheral nervous systems. We investigated whether neurodegenerative changes were observable in the hippocampus, cortex, and cerebellum after 4 weeks of streptozotocin (STZ)-induced diabetes in rats and the effect(s) of melatonin. Male Wistar rats (n = 32) were divided into four groups (n = 8 each): untreated controls, melatonin-treated controls, untreated diabetics, and melatonin-treated diabetics. Experimental diabetes was induced by a single dose of STZ (60 mg/kg, intraperitoneal (ip)). For 3 days before the administration of STZ, melatonin (200 microg/kg/day, ip) was injected and continued for 4 weeks. Sections of hippocampus, cortex, and cerebellum were stained with hematoxylin and eosin and examined using light microscopy. In addition, brain tissues were examined immunohistochemically for the expression of glial and neuronal markers, including glial fibrillary acidic protein (GFAP), neuron-specific enolase (NSE), and heat shock protein-70 (HSP-70). No neurodegenerative changes were observed in the hippocampus, cortex, or cerebellum of the untreated diabetic group after 4 weeks compared with the other groups. We did not observe any change in GFAP, NSE, or HSP-70 immunostaining in the brain tissues of STZ-induced diabetic rats. In summary, after 4 weeks of STZ-induced diabetes in rats, no degenerative or immunohistochemical changes were detected in the hippocampus, cortex, or cerebellum.

Increased melatonin synthesis in pineal glands of rats in streptozotocin induced type 1 diabetes

It is well-documented that melatonin influences insulin secretion. The effects are mediated by specific, high-affinity, pertussis-toxin-sensitive, G protein-coupled membrane receptors (MT(1) as well MT(2)), which are present in both the pancreatic tissue and islets of rats and humans, as well as in rat insulinoma cells (INS1). Via the Gi-protein-adenylatecyclase-3',5'-cyclic adenosine monophosphate (cAMP) and, possibly, the guanylatecyclase-cGMP pathways, melatonin decreases insulin secretion, whereas, by activating the Gq-protein-phospholipase C-IP(3) pathway, it has the opposite effect. For further analysis of the interactions between melatonin and insulin, diabetic rats were investigated with respect to melatonin synthesis in the pineal gland and plasma insulin levels. In this context, recent investigations have proven that type 2 diabetic rats and humans display decreased melatonin levels, whereas type 1 diabetic IDDM rats or those with diabetes induced by streptozotocin (STZ) of the present study show increased plasma melatonin levels and elevated AA-NAT-mRNA. Furthermore, the mRNA of pineal insulin receptors and beta1-adrenoceptors, including the clock genes Per1 and Bmal1 and the clock-controlled output gene Dbp, increases in both young and middle-aged STZ rats. The results therefore indicate that the decreased insulin levels in STZ-induced type 1 diabetes are associated with higher melatonin plasma levels. In good agreement with earlier investigations, it was shown that the elevated insulin levels observed in type 2 diabetes, are associated with decreased melatonin levels. The results thus prove that a melatonin-insulin antagonism exists. Astonishingly, notwithstanding the drastic metabolic disturbances in STZ-diabetic rats, the diurnal rhythms of the parameters investigated are maintained.

Melatonin, endocrine pancreas and diabetes

Melatonin influences insulin secretion both in vivo and in vitro. (i) The effects are MT(1)-and MT(2)-receptor-mediated. (ii) They are specific, high-affinity, pertussis-toxin-sensitive, G(i)-protein-coupled, leading to inhibition of the cAMP-pathway and decrease of insulin release. [Correction added after online publication 4 December 2007: in the preceding sentence, 'increase of insulin release' was changed to 'decrease of insulin release'.] Furthermore, melatonin inhibits the cGMP-pathway, possibly mediated by MT(2) receptors. In this way, melatonin likely inhibits insulin release. A third system, the IP(3)-pathway, is mediated by G(q)-proteins, phospholipase C and IP(3), which mobilize Ca(2+) from intracellular stores, with a resultant increase in insulin. (iii) Insulin secretion in vivo, as well as from isolated islets, exhibits a circadian rhythm. This rhythm, which is apparently generated within the islets, is influenced by melatonin, which induces a phase shift in insulin secretion. (iv) Observation of the circadian expression of clock genes in the pancreas could possibly be an indication of the generation of circadian rhythms in the pancreatic islets themselves. (v) Melatonin influences diabetes and associated metabolic disturbances. The diabetogens, alloxan and streptozotocin, lead to selective destruction of beta-cells through their accumulation in these cells, where they induce the generation of ROS. Beta-cells are very susceptible to oxidative stress because they possess only low-antioxidative capacity. Results suggest that melatonin in pharmacological doses provides protection against ROS. (vi) Finally, melatonin levels in plasma, as well as the arylalkylamine-N-acetyltransferase (AANAT) activity, are lower in diabetic than in nondiabetic rats and humans. In contrast, in the pineal gland, the AANAT mRNA is increased and the insulin receptor mRNA is decreased, which indicates a close interrelationship between insulin and melatonin.

Antioxidative enzyme and glutathione S-transferase activities in diabetic rats exposed to long-term ASA treatment

Low-dose acetylsalicylic acid (ASA) treatment is a standard therapeutic approach in diabetes mellitus for prevention of long-term vascular complications. The aim of the present work was to investigate the effect of long-term ASA administration in experimental diabetes on activities of some liver enzymes: glutathione peroxidase (GSHPx), catalase, glucose-6-phosphate dehydrogenase (G6PDH) and glutathione S-transferase (GST). Blood glucose, glycated hemoglobin, as well as plasma ALT and AST activities increased in rats with streptozotocin-induced experimental diabetes. The long-term hyperglycemia resulted in decreased activities of GSHPx (by 26%), catalase (by 34%), GST (by 38%) and G6PDH (by 27%) in diabetic animals. We did not observe increased accumulation of membrane lipid peroxidation products or altered levels of reduced glutathione in livers. The linear correlation between blood glucose and glycated hemoglobin in diabetic animals was distorted upon ASA treatment, which was likely due to a chemical competition between nonenzymatic protein glycosylation and protein acetylation. The long-term ASA administration partially reversed the decrease in GSHPx activity, but did not influence the activities of catalase and GST in diabetic rats. Otherwise, some decrease in these parameters was noted in ASA-treated nondiabetic animals. Increased ASA-induced G6PDH activity was recorded in both diabetic and nondiabetic rats. While both glycation due to diabetic hyperglycemia and ASA-mediated acetylation had very similar effects on the activities of all studied enzymes but G6PDH, we conclude that non-enzymatic modification by either glucose or ASA may be a common mechanism of the observed convergence.

Effects of melatonin on streptozotocin-induced diabetic liver injury in rats

This study investigated the possible protective effects of melatonin as an antioxidant against streptozotocin (STZ)-induced diabetic liver injury in rats. Wistar rats were divided into four groups: untreated control (UC), melatonin-treated control (MC), untreated diabetic (UD), and melatonin-treated diabetic (MD). Experimental diabetes was induced by a single-dose (60 mg/kg, intraperitoneally (ip)) STZ injection, and melatonin was injected (200 microg/kg/day, ip) for 4 weeks. Upon light and electron microscopic examination, we observed that melatonin improved the morphological and histopathological changes of the liver caused by diabetes. Malondialdehyde levels in the liver homogenates of UD rats were higher than those of controls and were markedly reduced after melatonin treatment. Although no significant difference was observed with respect to antioxidant status, the superoxide dismutase activity tended to be higher in the UD rats than in the treated rats. Our findings showed that melatonin administration partially reduced liver injury in STZ-induced diabetic rats.

Metabolic effects of melatonin on oxidative stress and diabetes mellitus

Melatonin, which is synthesized in the pineal gland and other tissues, has a variety of physiological, immunological, and biochemical functions. It is a direct scavenger of free radicals and has indirect antioxidant effects due to its stimulation of the expression and activity of antioxidative enzymes such as glutathione peroxidase, superoxide dismutase and catalase, and NO synthase, in mammalian cells. Melatonin also reduces serum lipid levels in mammalian species, and helps to prevent oxidative stress in diabetic subjects. Long-term melatonin administration to diabetic rats reduced their hyperlipidemia and hyperinsulinemia, and restored their altered ratios of polyunsaturated fatty acid in serum and tissues. It was recently reported that melatonin enhanced insulin-receptor kinase and IRS-1 phosphorylation, suggesting the potential existence of signaling pathway cross-talk between melatonin and insulin. Because TNF-alpha has been shown to impair insulin action by suppressing insulin receptor-tyrosine kinase activity and its IRS-1 tyrosine phosphorylation in peripheral tissues such as skeletal muscle cells, it was speculated that melatonin might counteract TNF-alpha-associated insulin resistance in type 2 diabetes. This review will focus on the physiological and metabolic effects of melatonin and highlight its potential use for the treatment of cholesterol/lipid and carbohydrate disorders.