Giyasettin Baydas

Comparative analysis of the protective effects of melatonin and vitamin E on streptozocin‐induced diabetes mellitus

There is a clearly documented link between diabetic complications and lipid peroxidation. Hyperglycemia causes a reduction in levels of protective endogenous antioxidants and increases generation of free radicals. The present study was carried out to compare the protective effects of melatonin and vitamin E against streptozocin (STZ)‐induced diabetes in rats. Melatonin was administered s.c. (100 μg/kg) whereas vitamin E was given i.p. (100 mg/kg) after induction of diabetes with STZ (60 mg/kg). Plasma total cholesterol, triglyceride and low density lipoprotein (LDL) levels were increased in STZ group while both melatonin and vitamin E injection caused a significant decrease in the levels of all these parameters. The lipid lowering effect of melatonin was greater than that of vitamin E. Melatonin caused a significant decrease in brain, liver and kidney tissue malondialdehyde (MDA) levels which were increased because of STZ‐induced diabetes. Vitamin E also reduced elevated MDA concentrations in diabetic rat tissues, but the effect of melatonin was more potent than that of vitamin E. Furthermore, treatment of diabetic rats with melatonin increased brain and kidney glutathione peroxidase (GSH‐Px) activity to the levels below that of control rats. Vitamin E was found to be less effective on GSH‐Px activity levels in brain and kidney than melatonin whereas it was more potent than melatonin in liver. In summary, melatonin prevents many diabetic complications by reducing oxidative stress and protects organisms from oxidative damage and dyslipidemia. Considering the much lower molar concentration of melatonin compared with vitamin E, melatonin seems to be a more potent antioxidant, especially in the brain and kidney.

Antioxidant vitamin levels in term and preterm infants and their relation to maternal vitamin status.

BACKGROUND Lipid peroxidation plays a vital role in the pathogenesis of many neonatal complications. Preterm babies are especially predisposed to lung diseases and retinopathy, probably due to a deficiency in their antioxidant systems. Vitamins E, A, and C are part of the natural antioxidant defense systems. We aimed to determine the levels of vitamins E, A, and C in maternal and cord blood plasma of term and preterm infants and to investigate the relationships between these levels. METHODS In the present study we determined vitamin E, A, and C levels in the umbilical cord blood of term (n = 30) and preterm (n = 22) infants and their mothers by HPLC. Blood samples were taken during delivery. RESULTS Levels of lipid soluble antioxidant vitamin E and A in cord blood were lower than maternal values (p <0.01, p <0.05, respectively). Conversely, the level of water-soluble vitamin C was higher in cord blood than in maternal level (p <0.05). Significantly higher levels of vitamins E, A, and C were found in term babies as compared with those born preterm (p <0.05). CONCLUSIONS There was a positive correlation between maternal and cord blood levels of vitamins E and A (r = 0.775, r = 0.725, respectively). In conclusion, preterm babies have fewer lipid-soluble antioxidant vitamins in their serum compared to term infants. Therefore, it is possible to postulate that preterm infants are more susceptible to oxidative stress.

Daily rhythm of glutathione peroxidase activity, lipid peroxidation and glutathione levels in tissues of pinealectomized rats

Melatonin is a component of the antioxidant defense system since it has radical scavenging and antioxidant activities. In the present study, we aimed to investigate the endogenous rhythm of antioxidant enzyme glutathione peroxidase (GSH-Px) activity, oxidized glutathione (GSSG) and lipid peroxidation levels in tissues of pinealectomized rats (PINX). Rats were sacrificed by decapitation at 4 h intervals. GSH-Px activity, GSSG and lipid peroxidation levels showed a daily rhythm both in controls and in PINX rats. GSH-Px and GSSG exhibited the peak levels after the peak time of melatonin which was determined previously by other groups. Lipid peroxidation levels increased progressively during the night and started to decline before the GSH-Px peak time. These findings suggest that endogenous melatonin is involved in the night time increase of GSH-Px activity and GSSG levels and modulates the daily rhythm pattern of GSH-Px. In conclusion, pinealectomy which eliminates the melatonin rhythm has a supressor effect on GSH-Px activity levels.

Melatonin reduces glial reactivity in the hippocampus, cortex, and cerebellum of streptozotocin-induced diabetic rats

Hyperglycemia plays a critical role in the development and progression of diabetic neuropathy. One of the mechanisms by which hyperglycemia causes neural degeneration is via the increased oxidative stress that accompanies diabetes. Metabolic and oxidative insults often cause rapid changes in glial cells. Key indicators of this response are increased synthesis of glial fibrillary acidic protein (GFAP) and S100B, both astrocytic markers. In the present study, we examined glial reactivity in hippocampus, cortex, and cerebellum of streptozotocin (STZ)-induced diabetic rats by determining the expression of GFAP and S-100B and we evaluated the effect of melatonin on the glial response. Western blot measurement of contents in brain regions after 6 weeks of STZ-induced diabetes indicated significant increases in these constituents compared with those in nondiabetic controls. Administration of melatonin prevented the upregulation of GFAP in all brain regions of diabetic rats. Using GFAP immunohistochemistry, we observed an increase in GFAP immunostaining in the hippocampus of STZ-diabetic rats relative to levels in the control brains. Treatment with melatonin resulted in an obvious reduction of GFAP-immunoreactive astrocytes in hippocampus. Like GFAP, S100B levels also were increased in all three brain areas of diabetic rats, an effect also reduced by melatonin treatment. Finally, the levels of lipid peroxidation products were elevated as a consequence of diabetes, with this change also being prevented by melatonin. These results suggest that diabetes causes increased glial reactivity possibly due to elevated oxidative stress, and administration of melatonin represents an achievable adjunct therapy for preventing gliosis.

Melatonin inhibits neural apoptosis induced by homocysteine in hippocampus of rats via inhibition of cytochrome c translocation and caspase-3 activation and by regulating pro- and anti-apoptotic protein levels.

In the present study, we examined the molecular mechanism by which homocysteine causes neuronal cell apoptosis. We further investigated the mechanisms of melatonins ability to reduce homocysteine-induced apoptosis. Consistent with its antioxidant properties, melatonin reduced homocysteine-induced lipid peroxidation and stimulated glutathione peroxidase enzyme activity in hippocampus of rats with hyperhomocysteinemia. Furthermore, melatonin treatment diminished cytochrome c release from mitochondria and reduced caspase 3 and caspase 9 activation induced by hyperhomocysteinemia. Chronic hyperhomocysteinemia also led to poly(ADP-ribose) polymerase cleavage and subsequently DNA fragmentation. Treatment with melatonin markedly inhibited poly(ADP-ribose) polymerase cleavage and reduced DNA damage. Hyperhomocysteinemia caused an elevation of pro-apoptotic Bax levels while reducing anti-apoptotic protein, Bcl-2, levels. Daily administration of melatonin up-regulated Bcl-2 and down-regulated Bax levels. We propose that, in addition to its antioxidant properties, melatonin has the ability to protect neuronal cells against apoptosis mediated homocysteine neurotoxicity by modulating apoptosis-regulatory proteins in the hippocampus of rats.

Increase of glial fibrillary acidic protein and S-100B in hippocampus and cortex of diabetic rats: effects of vitamin E

Glial interactions with neurones play vital roles during the ontogeny of the nervous system and in the adult brain. Physical and metabolic insults cause rapid changes in the glial cells and this phenomenon is called reactive gliosis. One of the important events during astrocyte differentiation is the increased expression of glial markers, glial fibrillary acidic protein (GFAP) and S-100B protein. Diabetes mellitus is the most common serious metabolic disorder, which is characterised by functional and structural changes in the peripheral as well as in the central nervous system. In the present study, we aimed to investigate glial reactivity in hippocampus, cortex and cerebellum of streptozotocin-induced diabetic rats by determining the expression of GFAP and S-100B and also to examine the protective effects of vitamin E against gliosis. Western blotting showed increases in total and degraded GFAP content and S-100B protein expression in brain tissues of diabetic rats compared with those of controls. In addition, there was a significant increase in lipid peroxidation in these brain regions of diabetic rats. Both glial markers and lipid peroxidation levels were reversed by vitamin E administration. These findings indicate that streptozotocin-induced diabetes alters degradation and production of GFAP and S-100B, which are markers of reactive astrocytosis. Thus, determination of GFAP and S-100B may provide a relevant marker in the central nervous system for studying neurodegenerative changes in experimental diabetes mellitus. This study also suggests that the gliosis that occurs in diabetes mellitus is mediated, at least indirectly, by free radical formation and antioxidants may prevent reactive gliosis possibly by reducing damaging effects of reactive oxygen species in the central nervous system.

Altered expression of NCAM in hippocampus and cortex may underlie memory and learning deficits in rats with streptozotocin-induced diabetes mellitus.

Neurological and structural changes are paralleled by cognitive deficits in diabetes mellitus. The present study was designed to evaluate the expression of neural cell adhesion molecules (NCAM) in the hippocampus, cortex and cerebellum and to examine cognitive functions in diabetic rats. Diabetes was induced in male albino rats via intraperitoneal streptozotocin injection. Learning and memory behaviors were investigated using a passive avoidance test and a spatial version of the Morris water maze test. NCAM expression was detected in the hippocampus, cortex and cerebellum by an immunoblotting method. The diabetic rats developed significant impairment in learning and memory behaviours as indicated by deficits in passive avoidance and water maze tests as compared to control rats. Expression of NCAM 180 and 120 kDa were found to be higher in hippocampus and cortex of diabetic rat brains compared to those of control, whereas expression of NCAM 140 kDa decreased in these brain regions. Our findings suggest that streptozotocin-induced diabetes impairs cognitive functions and causes an imbalance in expression of NCAM in those brain regions involved in learning and memory. Altered expression of NCAM in hippocampus may be an important cause of learning and memory deficits that occur in diabetes mellitus.

Melatonin protects the central nervous system of rats against toluene-containing thinner intoxication by reducing reactive gliosis

Neuroprotective effects of melatonin against free radical damage have been studied extensively. Thinner containing 60-70% toluene is a neurotoxic mixture which is widely used as an aromatic industrial solvent. This product has been shown to cause functional and structural changes in the central nervous system. Toluene generates reactive oxygen species (ROS) and the toxic effects relating to these reactants. In the present study we investigated glial reactivity in hippocampus, cortex and cerebellum and the expression of glial fibrillary acidic protein (GFAP) after exposure of rats to toluene vapor (3000 ppm) for 45 days. We also examined the protective effects of melatonin against gliosis. Western blots demonstrated a marked elevation in total GFAP, a specific marker for astrocytes, by thinner fume inhalation in the hippocampus (P<0.001), cortex (P<0.01) and cerebellum (P<0.05) of rats. Melatonin administration prevented the increase of total GFAP induced by thinner fume inhalation. Thinner exposure caused a significant increase of lipid peroxidation products (malondialdehyde and 4-hydroxyalkenals) in all brain regions (P<0.01 for each region), and this elevation was also was inhibited by melatonin. Furthermore, melatonin augmented glutathione levels in all brain regions (P<0.05 for each region) investigated. In conclusion, melatonin treatment may provide neuroprotection against toluene neurotoxicity by increasing the survival of glial cells possibly by directly scavenging ROS and by indirectly augmenting their antioxidant capacity.

Inhibitory effects of melatonin on neural lipid peroxidation induced by intracerebroventricularly administered homocysteine

Abstract: Melatonin, the main secretory product of the pineal gland, has been shown to be potentially effective in prevention of numerous types of neurodegenerative disorders in which free radical processes are involved. Homocysteine (Hcy), an independent risk factor for atherosclerosis, undergoes auto‐oxidation and generates reactive oxygen species. The purpose of this study was to test whether intracerebroventricular (ICV) injection of Hcy leads to neural lipid peroxidation and also to investigate the protective effects of melatonin on the brain tissue from oxidative stress of Hcy. Adult male Wistar rats under anaesthesia were injected ICV with Hcy at a dose of 143 μg/kg. Melatonin was administered intraperitoneally to a group of rats for three consecutive days before Hcy injection. The rats were decapitated and brain tissues were removed and hippocampus, cortex and cerebellum were dissected. There was a significant development of oxidative stress as indicated by an increase in malondialdehyde in hippocampus, cortex and cerebellum of rats injected with Hcy, whereas melatonin prevented the elevation of lipid peroxidation. Furthermore, melatonin significantly increased glutathione levels and glutathione peroxidase activity in all brain regions. The present study demonstrates that Hcy, in high levels, may be a causal factor in generation of free radicals in the brain and it may be one of the mechanisms which cause neurodegeneration in elderly people. It also shows that melatonin could potentially be beneficial in prevention of neurodegeneration caused by hyperhomocysteinemia.

Effects of pinealectomy and exogenous melatonin on serum leptin levels in male rat

The effects of pinealectomy and exogenous melatonin (N-acetyl-5-methoxytryptamine) on serum leptin levels were investigated in rats. Exogenous administration of melatonin to intact rats resulted in significant decreases in serum leptin levels (P < 0.05) compared to those of the intact control group. Serum leptin levels were significantly elevated in the pinealectomised rats in comparison to the sham-pinealectomised animals (P < 0.001) and were significantly suppressed by exogenous administration of melatonin compared to those of non-treated pinealectomised rats (P < 0.001). Hormone concentrations in the melatonin-treated pinealectomised group were found to be similar to those seen in the sham-pinealectomised group. These results suggest that pineal gland has an effect on leptin release.