Oxidative injury to the locus coeruleus of rat brain: neuroprotection by melatonin

Melatonin Action in Type 2 Diabetic Parotid Gland and Dental Pulp: In Vitro and Bioinformatic Findings

Type 2 diabetes mellitus (T2DM) is associated with functional deterioration of the salivary gland and dental pulp, related to oxidative stress. The aim was to integrate experimental and bioinformatic findings to analyze the cellular mechanism of melatonin (MEL) action in the human parotid gland and dental pulp in diabetes. Human parotid gland tissue was obtained from 16 non-diabetic and 16 diabetic participants, as well as human dental pulp from 15 non-diabetic and 15 diabetic participants. In human non-diabetic and diabetic parotid gland cells (hPGCs) as well as in dental pulp cells (hDPCs), cultured in hyper- and normoglycemic conditions, glial cell line-derived neurotrophic factor (GDNF), MEL, inducible nitric oxide synthase (iNOS) protein expression, and superoxide dismutase (SOD) activity were measured by enzyme-linked immunosorbent assay (ELISA) and spectrophotometrically. Bioinformatic analysis was performed using ShinyGO (v.0.75) application. Diabetic participants had increased GDNF and decreased MEL in parotid (p < 0.01) and dental pulp (p < 0.05) tissues, associated with increased iNOS and SOD activity. Normoglycemic hDPCs and non-diabetic hPGCs treated with 0.1 mM MEL had increased GDNF (p < 0.05), while hyperglycemic hDPCs treated with 1 mM MEL showed a decrease in up-regulated GDNF (p < 0.05). Enrichment analyses showed interference with stress and ATF/CREB signaling. MEL induced the stress-protective mechanism in hyperglycemic hDPCs and diabetic hPGCs, suggesting MEL could be beneficial for diabetes-associated disturbances in oral tissues.

Melatonin: Potential avenue for treating iron overload disorders

Iron overload as a highly risk factor, can be found in almost all human chronic and common diseases. Iron chelators are often used to treat iron overload; however, patient adherence to these chelators is poor due to obvious side effects and other disadvantages. Numerous studies have shown that melatonin has a high iron chelation ability and direct free radical scavenging activity, and can inhibit the lipid peroxidation process caused by iron overload. Therefore, melatonin may become potential complementary therapy for iron overload-related disorders due to its iron chelating and antioxidant activities. Here, the research progress of iron overload is reviewed and the therapeutic potential of melatonin in the treatment of iron overload is analyzed. In addition, studies related to the protective effects of melatonin on oxidative damage induced by iron overload are discussed. This review provides a foundation for preventing and treating iron homeostasis disorders with melatonin.

Melatonin attenuates caspase-dependent apoptosis in the thoracic aorta by regulating element balance and oxidative stress in pinealectomised rats

The aim of this study was to explain the possible mechanisms by which melatonin deficiency results in cardiovascular injury and to investigate the effects of melatonin administration on important signalling pathways and element equilibrium in the thoracic aorta (TA). For this purpose, we analysed the cellular and molecular effects of melatonin deficiency or administration on oxidative stress, DNA damage, molecular chaperone response, and apoptosis induction in TA tissues of pinealectomised rats using ELISA, RAPD, qRT-PCR, and Western blot assays. The results showed that melatonin deficiency led to an imbalance in essential element levels, unfolded or misfolded proteins, increased lipid peroxidation, and selectively induced caspase-dependent apoptosis in TA tissues without significantly affecting the Bcl-2/BAX ratio (2.28 in pinealectomised rats, 2.73 in pinealectomised rats treated with melatonin). In pinealectomised rats, the genomic template stability (80.22%) was disrupted by the significantly increased oxidative stress, and heat shock protein 70 (20.96-fold), TNF-α (1.73-fold), caspase-8 (2.03-fold), and caspase-3 (2.87-fold) were markedly overexpressed compared with the sham group. Melatonin treatment was protective against apoptosis and inhibited oxidative damage. In addition, melatonin increased the survivin level and improved the regulation of element equilibrium in TA tissues. The results of the study indicate that melatonin deficiency induces TNF-α-related extrinsic apoptosis signals and that the administration of pharmacological doses of melatonin attenuates cardiovascular toxicity by regulating the increase in the rate of apoptosis caused by melatonin deficiency in TA tissue of Sprague–Dawley rats.

Diplomats' Mystery Illness and Pulsed Radiofrequency/Microwave Radiation

Importance: A mystery illness striking U.S. and Canadian diplomats to Cuba (and now China) "has confounded the FBI, the State Department and US intelligence agencies" (Lederman, Weissenstein, & Lee, 2017). Sonic explanations for the so-called health attacks have long dominated media reports, propelled by peculiar sounds heard and auditory symptoms experienced. Sonic mediation was justly rejected by experts. We assessed whether pulsed radiofrequency/microwave radiation (RF/MW) exposure can accommodate reported facts in diplomats, including unusual ones. Observations: (1) Noises: Many diplomats heard chirping, ringing or grinding noises at night during episodes reportedly triggering health problems. Some reported that noises were localized with laser-like precision or said the sounds seemed to follow them (within the territory in which they were perceived). Pulsed RF/MW engenders just these apparent "sounds" via the Frey effect. Perceived "sounds" differ by head dimensions and pulse characteristics and can be perceived as located behind in or above the head. Ability to hear the "sounds" depends on high-frequency hearing and low ambient noise. (2) Signs/symptoms: Hearing loss and tinnitus are prominent in affected diplomats and in RF/MW-affected individuals. Each of the protean symptoms that diplomats report also affect persons reporting symptoms from RF/MW: sleep problems, headaches, and cognitive problems dominate in both groups. Sensations of pressure or vibration figure in each. Both encompass vision, balance, and speech problems and nosebleeds. Brain injury and brain swelling are reported in both. (3) Mechanisms: Oxidative stress provides a documented mechanism of RF/MW injury compatible with reported signs and symptoms; sequelae of endothelial dysfunction (yielding blood flow compromise), membrane damage, blood-brain barrier disruption, mitochondrial injury, apoptosis, and autoimmune triggering afford downstream mechanisms, of varying persistence, that merit investigation. (4) Of note, microwaving of the U.S. embassy in Moscow is historically documented. Conclusions and relevance: Reported facts appear consistent with pulsed RF/MW as the source of injury in affected diplomats. Nondiplomats citing symptoms from RF/MW, often with an inciting pulsed-RF/MW exposure, report compatible health conditions. Under the RF/MW hypothesis, lessons learned for diplomats and for RF/MW-affected civilians may each aid the other.

Short- but not long-term melatonin administration reduces central levels of brain-derived neurotrophic factor in rats with inflammatory pain

OBJECTIVE

To evaluate the effect of short- and long-term administration of melatonin on central brain-derived neurotrophic factor (BDNF) levels in rats with acute and chronic inflammatory pain.

METHODS

The animals were allocated to one of two experiments: experiment 1 or experiment 2. In experiment 1, all animals were injected with complete Freund's adjuvant (CFA) to induce inflammation and were randomly allocated to receiving melatonin (60 mg/kg) or vehicle. Injections were administered 1 h after CFA and once daily for 2 more days (for a total of 3 days of melatonin administration). In experiment 2, fifteen days after CFA injection, the animals were treated with melatonin (50 mg/kg) or vehicle for 8 days. The animals were killed by decapitation 24 h after the last melatonin or vehicle administration, and an ELISA assay was performed to detect BDNF expression in the spinal cord, brainstem, and prefrontal cortex of the rats in both groups. Data were analyzed using Student's t test and the results are expressed as means ± SEM.

RESULTS

In the first experiment, the BDNF levels of the melatonin group were reduced in the prefrontal cortex (Student's t test, p = 0.01) and increased in the spinal cord (Student's t test, p = 0.04). In experiment 2, BDNF levels were similar in both groups for all structures (Student's t test, p > 0.00 for all). A two-way ANOVA reveled a significant effect of structures (p = 0.0001) but not of treatment (p > 0.05). The prefrontal cortex presented higher BDNF levels than other structures (ANOVA/Student-Newman-Keuls test, p = 0.0001). Considering the relationship between BDNF levels in all three structures, we found an effect of central nervous system structures (p = 0.01) and an interaction between treatment and structures (p = 0.04).

CONCLUSION

The high spinal cord BDNF levels and the low prefrontal cortical BDNF levels observed in rats with acute CFA-induced inflammation following short-term melatonin administration may be related to the pain-modulating and neuroprotective effects of this protein. Long-term melatonin administration did not alter BDNF levels in chronic inflammation.

A review of metal-catalyzed molecular damage: protection by melatonin

Metal exposure is associated with several toxic effects; herein, we review the toxicity mechanisms of cadmium, mercury, arsenic, lead, aluminum, chromium, iron, copper, nickel, cobalt, vanadium, and molybdenum as these processes relate to free radical generation. Free radicals can be generated in cells due to a wide variety of exogenous and endogenous processes, causing modifications in DNA bases, enhancing lipid peroxidation, and altering calcium and sulfhydryl homeostasis. Melatonin, an ubiquitous and pleiotropic molecule, exerts efficient protection against oxidative stress and ameliorates oxidative/nitrosative damage by a variety of mechanisms. Also, melatonin has a chelating property which may contribute in reducing metal-induced toxicity as we postulate here. The aim of this review was to highlight the protective role of melatonin in counteracting metal-induced free radical generation. Understanding the physicochemical insights of melatonin related to the free radical scavenging activity and the stimulation of antioxidative enzymes is of critical importance for the development of novel therapeutic strategies against the toxic action of these metals.

Comparison of the beneficial effect of melatonin on recovery after cut and crush sciatic nerve injury: a combined study using functional, electrophysiological, biochemical, and electron microscopic analyses

PURPOSE

Following tissue injury, melatonin is known to reduce detrimental effects of free radicals by stimulating antioxidant enzymes and also to inhibit posttraumatic polymorphonuclear infiltration. Beneficial effects after peripheral nerve injury have been suggested, but not studied in detail. Therefore, we aimed to elucidate the effects of melatonin on the recovery of the lesioned rat sciatic nerve by means of combined analysis.

METHODS

A total number of 90 rats were randomly distributed into six groups: control (group 1), sham-operated (group 2), sciatic nerve cut (group 3), sciatic nerve cut + melatonin treatment (group 4), sciatic nerve crush (group 5), and sciatic nerve crush + melatonin treatment (group 6). Melatonin was administered intraperitoneally at a dose of 50 mg/kg/day for 6 weeks. Recovery of function was analyzed by assessment of the sciatic functional index based on walking track analysis, somatosensory evoked potentials, biochemical quantification of malondialdehyde, antioxidant enzymes levels, and ultrastructural analysis.

RESULTS

Our data showed the beneficial effect of melatonin on sciatic nerve recovery. Rats treated with melatonin demonstrated better structural preservation of the myelin sheaths compared to the nontreated group. The biochemical analysis confirmed the beneficial effects of melatonin displaying lower lipid peroxidation and higher superoxide dismutase, catalase, and glutathione peroxidase activities in sciatic nerve samples in comparison to nontreated groups.

CONCLUSIONS

The beneficial effects of melatonin administration on the recovery of the cut and crush injured sciatic nerve may be attributed to its antioxidant properties. Based on these investigations, we think that our data would be helpful for clinicians who deal with peripheral nerve injuries.

Chronically lowering sympathetic activity protects sympathetic nerves in spleens from aging F344 rats

In the present study, we investigated how increased sympathetic tone during middle-age affects the splenic sympathetic neurotransmission. Fifteen-month-old (M) F344 rats received rilmenidine (0, 0.5 or 1.5mg/kg/day, i.p. for 90 days) to lower sympathetic tone. Controls for age were untreated 3 or 18M rats. We report that rilmenidine (1) reduced plasma and splenic norepinephrine concentrations and splenic norepinephrine turnover, and partially reversed the sympathetic nerve loss; and (2) increased β-adrenergic receptor (β-AR) density and β-AR-stimulated cAMP production. Collectively, these findings suggest a protective effect of lowering sympathetic tone on sympathetic nerve integrity, and enhanced sympathetic neurotransmission in secondary immune organs.

Melatonin improves 3-nitropropionic acid induced behavioral alterations and neurotrophic factors levels

OBJECTIVE

This study sought to determine whether melatonin causes changes in neurotrophic factors and it protects against the mycotoxin 3-nitropropionic acid (3-NP) in brain tissue.

METHODS

Rats were given 3-NP over four consecutive days (20 mg/kg BW), while melatonin was administered over 21 days (1 mg/kg/BW), starting after the last injection of 3-NP.

RESULTS

Rats treated with 3-NP displayed significant changes in neurotrophic factor (BDNF and GDNF) levels, together with alterations in behavior; they also displayed extensive oxidative stress and a massive neuronal damage.

CONCLUSIONS

Melatonin improved behavioral alterations, reduced oxidative damage, lowered neurotrophic factor levels and neuronal loss in 3-NP-treated rats. These results suggest that melatonin exerts a neuroprotective action.

Fibroblast growth factor 9 prevents MPP+-induced death of dopaminergic neurons and is involved in melatonin neuroprotection in vivo and in vitro

Oxidative stress and down-regulated trophic factors are involved in the pathogenesis of nigrostriatal dopamine(DA)rgic neurodegeneration in Parkinson's disease. Fibroblast growth factor 9 (FGF9) is a survival factor for various cell types; however, the effect of FGF9 on DA neurons has not been studied. The antioxidant melatonin protects DA neurons against neurotoxicity. We used MPP(+) to induce neuron death in vivo and in vitro and investigated the involvement of FGF9 in MPP(+) intoxication and melatonin protection. We found that MPP(+) in a dose- and time-dependent manner inhibited FGF9 mRNA and protein expression, and caused death in primary cortical neurons. Treating neurons in the substantia nigra and mesencephalic cell cultures with FGF9 protein inhibited the MPP(+)-induced cell death of DA neurons. Melatonin co-treatment attenuated MPP(+)-induced FGF9 down-regulation and DA neuronal apoptosis in vivo and in vitro. Co-treating DA neurons with melatonin and FGF9-neutralizing antibody prevented the protective effect of melatonin. In the absence of MPP(+), the treatment of FGF9-neutralizing antibody-induced DA neuronal apoptosis whereas FGF9 protein reduced it indicating that endogenous FGF9 is a survival factor for DA neurons. We conclude that MPP(+) down-regulates FGF9 expression to cause DA neuron death and that the prevention of FGF9 down-regulation is involved in melatonin-provided neuroprotection.

Melatonin inhibits arsenite-induced peripheral neurotoxicity

In this study, the effect of melatonin on sodium arsenite (arsenite)-induced peripheral neurotoxicity was investigated using dorsal root ganglion (DRG) explants. After 24-hr incubation, arsenite (30 microm) consistently elevated the expression of heat shock protein 70 and haeme oxygenase-1, two well-known stress proteins, in the treated DRG explants. Co-incubation with melatonin (4 and 20 mm) concentration-dependently attenuated arsenite-induced elevation in stress proteins. Furthermore, melatonin inhibited arsenite-induced phosphorylation of p38 and DNA fragmentation. Inhibition by melatonin of arsenite-induced apoptosis was mediated via inactivating both endoplasmic reticulum (ER) and mitochondrial pathways. In the ER pathway, melatonin suppressed arsenite-induced elevation in activating transcription factor-6 and CCAAT/enhancer-binding protein homologous protein in the nuclear fraction of the treated DRG explants. Moreover, melatonin attenuated arsenite-induced activation of caspase 12, an ER-specific enzyme. In the mitochondrial pathway, arsenite-induced increases in Bcl-2 levels and cytosolic cytochrome c were reduced by melatonin. At the same time, melatonin inhibited arsenite-induced activation of caspase 3 in the treated DRG explants. Compared with glutathione and N-acetyl cysteine, melatonin was more potent than either in inhibiting arsenite-induced elevation in stress proteins. Taken together, our study demonstrates that melatonin is protective against arsenite-induced neurotoxicity in DRG explants. In addition, melatonin prevented arsenite-induced apoptosis via suppression of ER and mitochondrial activation. Our data suggest that melatonin is potentially a therapy for arsenite-induced peripheral neuropathy.

Epigenetic targets for melatonin: induction of histone H3 hyperacetylation and gene expression in C17.2 neural stem cells

We have reported the induction of glial cell line-derived neurotrophic factor, a potent survival factor for dopaminergic neurons, in the C17.2 neural stem cell line following in vitro treatment with melatonin. Furthermore, we have detected the melatonin MT(1) receptor in these cells. Given these findings and recent evidence that melatonin may play a role in cellular differentiation, we examined whether this indoleamine induces morphological and transcriptional changes suggestive of a neuronal phenotype in C17.2 cells. Moreover, in order to extend preliminary evidence of a potential role for melatonin in epigenetic modulation, its effects on the mRNA expression of several histone deacetylase (HDAC) isoforms and on histone acetylation were examined. Physiological concentrations of melatonin (nanomolar range) increased neurite-like extensions and induced mRNA expression of the neural stem cell marker, nestin, the early neuronal marker beta-III-tubulin and the orphan nuclear receptor nurr1 in C17.2 cells. The indoleamine also significantly increased mRNA expression for various HDAC isoforms, including HDAC3, HDAC5, and HDAC7. Importantly, treatment with melatonin for 24 hr caused a significant increase in histone H3 acetylation, which is associated with chromatin remodeling and gene transcription. Since the melatonin MT(2) receptor was not detected in C17.2 cells, it is likely that the MT(1) receptor is involved in mediating these physiological effects of melatonin. These findings suggest novel roles for melatonin in stem cell differentiation and epigenetic modulation of gene transcription.

Driving GDNF expression: the green and the red traffic lights

Glial cell line-derived neurotrophic factor (GDNF) is widely recognized as a potent survival factor for dopaminergic neurons of the nigrostriatal pathway that degenerate in Parkinson's disease (PD). In animal models of PD, GDNF delivery to the striatum or the substantia nigra protects dopaminergic neurons against subsequent toxin-induced injury and rescues previously damaged neurons, promoting recovery of the motor function. Thus, GDNF was proposed as a potential therapy to PD aimed at slowing down, halting or reversing neurodegeneration, an issue addressed in previous reviews. However, the use of GDNF as a therapeutic agent for PD is hampered by the difficulty in delivering it to the brain. Another potential strategy is to stimulate the endogenous expression of GDNF, but in order to do that we need to understand how GDNF expression is regulated. The aim of this review is to do a comprehensive analysis of the state of the art on the control of endogenous GDNF expression in the nervous system, focusing mainly on the nigrostriatal pathway. We address the control of GDNF expression during development, in the adult brain and after injury, and how damaged neurons signal glial cells to up-regulate GDNF. Pharmacological agents or natural molecules that increase GDNF expression and show neuroprotective activity in animal models of PD are reviewed. We also provide an integrated overview of the signalling pathways linking receptors for these molecules to the induction of GDNF gene, which might also become targets for neuroprotective therapies in PD.

Neuroprotective effects of high-dose vs low-dose melatonin after blunt sciatic nerve injury

INTRODUCTION

Melatonin, the secretory product of the pineal gland, has potent antioxidant properties. The aim of this study was to compare the effects of low-dose (10 mg/kg) vs high-dose (50 mg/kg) melatonin on early lipid peroxidation levels and ultrastructural changes in experimental blunt sciatic nerve injury (SNI). We believe this to be the first study to assess the dose-dependent neuroprotective effects of melatonin after a blunt peripheral nerve injury.

MATERIALS AND METHODS

Rats were randomly allocated into 5 groups of 10 animals each. The SNI only rats underwent a nerve injury procedure. The SNI plus vehicle group received SNI and intraperitoneal injection of vehicle (diluted ethanol) as a placebo. The SNI plus low-dose or high-dose melatonin groups received intraperitoneal melatonin at doses of 10 mg/kg or 50 mg/kg, respectively. Controls had no operation, melatonin or vehicle injection. SNI was induced by clamping the sciatic nerve at the upper border of the quadratus femoris for 2 min.

RESULTS

Sciatic nerve samples were harvested 6 h after nerve injury and processed for biochemical and ultrastructural analysis. Trauma increased the lipid peroxidation of the sciatic nerve by 3.6-fold (153.85 +/- 18.73 in SNI only vs 41.73 +/- 2.23 in control rats, P < 0.01). Low (P = 0.02) and high (P < 0.01) doses of melatonin attenuated the nerve lipid peroxidation by 25% and 57.25%, respectively (65.76 +/- 2.47 in high-dose vs 115.08 +/- 7.03 in low-dose melatonin groups).

DISCUSSION

Although low-dose melatonin reduced trauma-induced myelin breakdown and axonal changes in the sciatic nerve, high-dose melatonin almost entirely neutralized any ultrastructural changes.

CONCLUSION

Our results suggest that melatonin, especially at a dose of 50 mg/kg, has a potent neuroprotective effect and can preserve peripheral neural fibers from lipid peroxidative damage after blunt trauma. With further investigations, we hope that these data may prove useful to clinicians who treat patients with nerve injuries.

Melatonin attenuates arsenite-induced apoptosis in rat brain: involvement of mitochondrial and endoplasmic reticulum pathways and aggregation of alpha-synuclein

In the present study, the protective effect of melatonin on sodium arsenite (arsenite)-induced apoptosis was investigated. Local infusion of arsenite elevated lipid peroxidation and depleted glutathione content in the infused substantia nigra (SN), as well as reduced striatal dopamine content. Systemic administration of melatonin diminished arsenite-induced oxidative injury. Furthermore, melatonin attenuated arsenite-induced increases in heat shock protein 70 and heme oxygenase-1 as well as phosphorylation of p38 mitogen-activated protein kinase and elevations in cyclooxygenase II and inducible nitric oxide synthase expression. Inhibition by melatonin of arsenite-induced apoptosis was determined by its attenuation of DNA fragmentation and terminal deoxytransferase-mediated dUTP-nick end labeling's positive cells in the infused SN of melatonin-treated rats. Melatonin reduced arsenite-induced apoptosis through mitochondrial and endoplasmic reticulum (ER) pathways. In the mitochondrial pathway, systemic melatonin inhibited arsenite-induced elevations in Bcl-2 and cytosolic cytochrome c as well as arsenite-induced reductions in procaspase-3 levels and elevations in active caspase-3 levels in the infused SN. Regarding the ER pathway, melatonin attenuated arsenite-induced elevations in activating transcription factor-4, CCAAT/enhancer binding protein (C/EBP) homologues protein, X-bon binding protein (XBP-1) and cytosolic immunoglobulin binding protein (BIP) as well as reductions in procaspase 12 levels. Moreover, aggregation of alpha-synuclein was reduced in the arsenite-infused SN of melatonin-treated rats. Our in vitro data showed that melatonin ameliorated arsenite-induced lipid peroxidation. Taken together, our data suggest that melatonin is neuroprotective against arsenite-induced oxidative injury in the nigrostriatal dopaminergic system of rat brain. Furthermore, the neuroprotective effects by melatonin on arsenite-induced apoptosis were mediated via inhibiting both mitochondrial and ER pathways. Accordingly, melatonin may be therapeutically useful for the treatment of arsenite-induced apoptosis in central nervous system.

Melatonin and 6-hydroxymelatonin protect against iron-induced neurotoxicity

Oxidative damage of biological macromolecules is a hallmark of most neurodegenerative disorders such as Alzheimer, Parkinson and diffuse Lewy body diseases. Another important phenomenon involved in these disorders is the alteration of iron homeostasis, with an increase in iron levels. The present study investigated whether 6-hydroxymelatonin (6-OHM) can reduce Fe2+-induced lipid peroxidation and necrotic cell damage in the rat hippocampus in vivo. It was found that 6-OHM administration proved successful in reducing Fe2+-induced neurotoxicity in rat hippocampus. This study provides some evidence of the neuroprotective effects of 6-OHM.

Melatonin potentiates flavone-induced apoptosis in human colon cancer cells by increasing the level of glycolytic end products

Melatonin is a natural compound synthesized by a variety of organs. It has been described to possess cell protecting activity in normal cells but was shown to induce apoptotic cell death in cancer cells. We determined to which extent and based on which molecular mechanisms melatonin is able to cause apoptosis in HT-29 human colon cancer cells. Induction of apoptosis was assessed by caspase-3-like activity, nuclear fragmentation and chromatin condensation. Melatonin, when given alone at a concentration of 1 mM, did not affect any of the apoptosis markers. It potentiated apoptosis induced by the flavonoid flavone significantly. Whereas flavone alone at a concentration of 150 microM led to a 8-fold increase in caspase-3-like activity associated with around 40% of cells displaying DNA-fragmentation, a combination of flavone and melatonin increased caspase-3-like activity 30-fold and 80% of cells exhibited fragmentation of DNA when compared to untreated controls. Melatonin caused an increase in cytosolic lactate levels that most likely allows the flavone-induced activation of the mitochondrial pyruvate/lactate importer to deliver more substrates to mitochondrial respiration. The subsequent increased production of mitochondrial O2-* in the presence of flavone was further increased by melatonin. Scavenging mitochondrial O2-* by benzoquinone or blocking the lactate/pyruvate transporter by 5-nitro-2-(3-phenylpropylamino) benzoate inhibited mitochondrial O2-* -generation and apoptosis execution mediated by flavone and melatonin. Our study provides evidence that melatonin potentiates flavone-induced apoptosis in HT-29 human colon cancer cells by enhancing the level of oxidizable substrates that can be transported into mitochondria in the presence of flavone.

Attenuation in the evolution of experimental spinal cord trauma by treatment with melatonin

Melatonin is the principal secretory product of the pineal gland and its role as an immuno-modulator is well established. Recent evidence shows that melatonin is a scavenger of oxyradicals and peroxynitrite and exerts protective effects in septic shock, hemorrhagic shock and inflammation. In the present study, we evaluated the effect of melatonin treatment, in a model of spinal cord injury (SCI). SCI was induced by the application of vascular clips (force of 50 g) to the dura via a four-level T5-T8 laminectomy. SCI in rats resulted in severe trauma characterized by edema, neutrophil infiltration and apoptosis (measured by terminal deoxynucleotidyl transferase-mediated dUTP nick-end-labeling staining). Infiltration of spinal cord tissue with neutrophils (measured as increase in myeloperoxidase activity) was associated with enhanced lipid peroxidation (increased tissue levels of malondialdehyde). Immunohistochemical examination demonstrated a marked increase in immunoreactivity for nitrotyrosine and Poly(ADP-ribose) (PAR) in the spinal cord tissue. In contrast, the degree of (a) spinal cord inflammation and tissue injury (histological score), (b) nitrotyrosine and PAR formation, (c) neutrophils infiltration and (d) apoptosis was markedly reduced in spinal cord tissue obtained from rats treated with melatonin (50 mg/kg i.p., 30 min before SCI, 30 min, 6 hr, 12 hr and 24 hr after SCI). In a separate set of experiment we have clearly demonstrated that melatonin treatment significantly ameliorated the recovery of limb function (evaluated by motor recovery score). Taken together, our results demonstrate that treatment with melatonin reduces the development of inflammation and tissue injury events associated with spinal cord trauma.

Analysis of the human locus coeruleus in perinatal and infant sudden unexplained deaths. Possible role of the cigarette smoking in the development of this nucleus

We investigated the immunohistochemical expression of the tyrosine hydroxylase (TH) enzyme and the morphometric parameters of the human locus coeruleus (LC) in the brainstems of 32 subjects aged from 17 gestational weeks to 12 postnatal month, died of unknown (sudden unexplained perinatal and infant deaths) and known causes. The goals of this study were: (1) to obtain basic information about the structure and physiology of the LC during the first phases of human nervous system development; (2) to evaluate whether there is altered expression of TH and/or structural alterations of the LC in cases of sudden perinatal and infant death; and (3) to verify if morphological and/or physiological abnormalities of the LC could be related to maternal cigarette smoking. Morphometric analysis showed homogeneous data in cases of sudden perinatal and infant death and in age-matched controls who had died of known aetiology. However, immunohistochemistry demonstrated in a wide subset of sudden and unexplained deaths a negativity or low positivity of TH. High distribution of TH protein were instead detectable in the LC neurons of foetuses aged 17-18 gestational weeks who had died of known causes. Therefore, we postulate the functional importance of the LC in the early phases of central nervous system development. Besides, the observation of a significant correlation between sudden unexplained death, negativity of TH staining and maternal smoking, prompted us to suppose a close relation between smoking in utero and a decrease of the noradrenergic activity of the LC, leading to sudden death in the last part of pregnancy and in the first year of life.

Pharmacological but not physiological concentrations of melatonin reduce iron-induced neuronal death in rat cerebral cortex

Iron-mediated oxidative stress occurs in a wide variety of neurological disorders. The present study has investigated whether melatonin can alter the proportion of neurons that die in the 24 h period following 1.0 microl intracortical injections of 1.0 mM ferric ammonium citrate (FAC) or 0.9% saline. Rats which received systemic infusions of melatonin (5 mg/kg body weight per day) displayed a 40% reduction (P = 0.019) in the proportion of neurons killed by FAC. By contrast, reduction of endogenous melatonin by continuous light exposure did not significantly affect the extent of neuronal death. Furthermore, elevated or reduced melatonin levels did not alter the number of neurons killed by saline injections. We conclude that pharmacological concentrations of melatonin protect neurons against iron-induced injury.