Melatonin enhances tamoxifen's ability to prevent the reduction in microsomal membrane fluidity induced by lipid peroxidation

Protective effects of melatonin against oxidation of guanine bases in DNA and decreased microsomal membrane fluidity in rat liver induced by whole body ionizing radiation

The aim of the study was to examine the potential protective effect of melatonin against whole body ionizing radiation (800 cGy). Changes in 8-hydroxy-2'-deoxyguanosine (8-OH-dG) levels, an index of DNA damage, and alterations in membrane fluidity (the inverse of membrane rigidity) and lipid peroxidation in microsomal membranes, as indices of damage to lipid and protein molecules in membranes, were estimated. Measurements were made in rat liver, 12 h after their exposure to radiation. To test the potential protective effects of melatonin, the indole was injected (i.p. 50 mg/kg b.w.) at 120, 90, 60 and 30 min prior to radiation exposure. Both 8-OH-dG levels and microsomal membrane rigidity increased significantly 12 h after radiation exposure. Melatonin completely counteracted the effects of ionizing radiation. Changes in 8-OH-dG levels and membrane fluidity are early sensitive parameters of DNA and microsomal membrane damage, respectively, induced by ionizing radiation and our findings document the protective effects of melatonin against ionizing radiation.

Melatonin and tryptophan derivatives as free radical scavengers and antioxidants

Several tryptophan derivatives function as free radical scavengers and antioxidants. The molecule that has been most widely investigated in this regard is N-acetyl-5-methoxytryptamine (melatonin); however, pinoline (6-methoxy-1,2,3,4-tetrahydro-beta-carboline) and N-acetylserotonin also possess free radical scavenging activity. Experimental studies have shown that melatonin directly scavenges the hydroxy radical, peroxyl radical, peroxynitrite anion, and singlet oxygen. Furthermore, this tryptophan derivative stimulates a number of antioxidative enzymes and stabilizes cell membranes; this latter action helps membranes to resist free radical damage. While the antioxidative actions of most molecules are limited by their specific intracellular distribution, e.g., vitamin E in lipid-rich membranes, melatonin's antioxidative actions include the protection of lipids in the cell membrane, proteins in the cytosol, and DNA in the nucleus. Furthermore, melatonin crosses all morphophysiological barriers and enters equally well all cells in the organism.

Synergistic approach to cancer therapy: exploiting interactions between anti-estrogens, retinoids, monoterpenes and tyrosine kinase inhibitors

Non-responsiveness and toxicity are large problems encountered during cancer treatment. Utilization of compounds that synergize should increase treatment efficacy while avoiding problems of toxicity. This review explores interactions between classes of compounds, including anti-estrogens, retinoids, monoterpenes and tyrosine kinase inhibitors, that are effective independent, and how their synergistic interaction could be exploited in cancer treatment. The effects of these compounds on insulin-like growth factors (IGF) and transforming-growth factor-beta (TGF-beta) will also be examined.

Melatonin as a pharmacological agent against neuronal loss in experimental models of Huntington's disease, Alzheimer's disease and parkinsonism

This review summarizes the experimental findings related to the neuroprotective role of melatonin. In particular, it focuses on research directed at models of Huntington's disease, Alzheimer's disease and Parkinsonism. Melatonin has been shown to be highly effective in reducing oxidative damage in the central nervous system; this efficacy derives from its ability to directly scavenge a number of free radicals and to function as an indirect antioxidant. In particular, melatonin detoxifies the highly toxic hydroxyl radical as well as the peroxyl radical, peroxynitrite anion, nitric oxide, and singlet oxygen, all of which can damage macromolecules in brain cells. Additionally, melatonin stimulates a variety of antioxidative enzymes including superoxide dismutase, glutathione peroxidase and glutathione reductase. One additional advantage melatonin has in reducing oxidative damage in the central nervous system is the ease with which to crosses the blood-brain barrier. This combination of actions makes melatonin a highly effective pharmacological agent against free radical damage. The role of physiological levels of melatonin in forestalling oxidative damage in the brain is currently being tested.

Melatonin reduces oxidative neurotoxicity due to quinolinic acid: in vitro and in vivo findings

The in vivo and in vitro effects of melatonin on quinolinic acid-induced oxidative damage in rat brain were determined. The concentrations of malonaldehyde and 4-hydroxyalkenals were assayed as an index of oxidatively damaged lipid. In in vitro experiments, the increase in malonaldehyde and 4-hydroxyalkenals concentrations induced by quinolinic acid were concentration-dependent and time-dependent. The accumulation of products of lipid peroxidation induced by quinolinic acid were very significantly reduced by melatonin in a concentration-dependent manner. Additionally, at the highest concentrations of melatonin used in quinolinic acid treated homogenates, it reduced the levels of oxidatively damaged lipid products below those measured in control homogenates (no quinolinic acid or melatonin). When quinolinic acid (200 mg/kg) was intraperitonally injected into 11-day-old rats, lipid peroxidation in the brain was significantly increased 24 hours later compared to levels in control rats. When melatonin (10 mg/kg) was injected i.p. 30 min before and 4 and 20 hours after the administration of quinolinic acid, the increased lipid peroxidation induced by quinolinic acid was significantly reduced. Likewise, neurobehavioral signs associated with quinolinate administration were attenuated by melatonin. These results show that both in vitro and in vivo pharmacological levels of melatonin confer protection against quinolinic acid-induced oxidative toxicity in the brain. The findings also indicate that melatonin may be pharmacologically useful in combatting quinolinic neurotoxicity which is associated with several acute and chronic neurodegenerative neurological diseases.

5-methoxytryptophol preserves hepatic microsomal membrane fluidity during oxidative stress

Lipid peroxidation is a degenerative chain reaction in biological membranes that may be initiated by exposure to free radicals. This process is associated with changes in the membrane fluidity and loss of several cell membrane-dependent functions. 5-methoxytryptophol (ML) is an indole isolated from the mammalian pineal gland. The purpose of this study was to investigate the effects of ML (0. 01mM-10mM) on membrane fluidity modulated by lipid peroxidation. Hepatic microsomes obtained from rats were incubated with or without ML (0.01-10 mM). Then lipid peroxidation was induced by FeCl(3), ADP, and NADPH. Membrane fluidity was determined using fluorescence spectroscopy. Malonaldehyde (MDA) +4-hydroxyalkenals (4-HDA) concentrations were estimated as an indicator of the degree of lipid peroxidation. With oxidative stress, membrane fluidity decreased and MDA+4-HDA levels increased. ML (0.01-3 mM) reduced membrane rigidity and the rise in MDA+4-HDA formation in a concentration-dependent manner. 10 mM ML protected against lipid peroxidation but failed to prevent the membrane rigidity. In the absence of oxidative reagents, ML (0.3-10 mM) decreased membrane fluidity whereas MDA+4-HDA levels remained unchanged. This indicates that ML may interact with membrane lipids. The results presented here suggest that ML may be another pineal indoleamine (in addition to melatonin) that resists membrane rigidity due to lipid peroxidation.

Augmentation of indices of oxidative damage in life-long melatonin-deficient rats

The chief pineal secretory product, melatonin, is an efficient free radical scavenger and antioxidant. The current study tested whether the life-long reduction of endogenous melatonin levels due to pinealectomy would influence the accumulation of oxidatively damaged products as the animals aged. Rats were either pinealectomized or sham operated when they were 2-months-old. At 25 months of age these animals were killed along with 2-month-old controls. Aging in the pineal-intact animals was associated with increased levels of lipid peroxidation products (malondialdehyde and 4-hydroxyalkenals in the lung, kidney and skin), rises in an oxidatively damaged DNA product (8-hydroxy-deoxyguanosine in liver, kidney and pancreas), and in the levels of protein carbonyls (in the liver). Likewise, advanced age was associated with a significant decrease in membrane fluidity (increased membrane rigidity) of hepatic microsomes in pineal-intact rats. For all of these parameters and in a number of organs, pinealectomy caused further increases in the indices of oxidative damage. Consistent with previous suggestions, the implications of these findings is that aging is associated with the augmented accumulation of oxidatively damaged macromolecules and that these increases are exaggerated when a relative melatonin deficiency is induced by pinealectomy. The findings are consistent with the idea that the accelerated accumulation of oxidatively damaged products after pinealectomy was due to reduction in melatonin since it functions as a free radical scavenger and antioxidant. On the other hand, other pineal secretory products that were reduced as a consequence of pineal removal may have also been responsible for some of the observed changes.

Suppression of both basal and antigen-induced lipid peroxidation in ring dove heterophils by melatonin

There have been several findings recently concerning melatonin as a free radical scavenger and general antioxidant. For instance, in bird heterophils we found that 100 microM of melatonin decreases superoxide anion levels and modulates superoxide dismutase activity. This paper sought to study the effect of melatonin upon induced oxidative damage in heterophils of the ring dove (Streptopelia risoria). The concentration of malonaldehyde (MDA) as an index of induced oxidative damage to lipid membranes was tested by colorimetric assay. A heterophil suspension was co-incubated with and without inert particles (latex beads) as material to be phagocytosed, both alone and in combination with 100 microM of melatonin. Measurements were made at the basal time (0 min), as well as at 15, 30, 45, and 60 min. Protein concentrations were determined by a standardized method using bovine serum albumin as standard. Results are expressed as nmol MDA/mg prot. Melatonin clearly reduced the production of MDA, an index of lipid peroxidation. It also annulled the enhancement of MDA levels produced by latex beads. Both effects were observed at all the times studied. In conclusion, our findings again show that the neurohormone melatonin could be useful as an effective pharmacological antioxidant.

Protective effect of melatonin on indomethacin-induced gastric injury in rats

The gastric injury associated with nonsteroidal anti-inflammatory drug (NSAID) therapy has been linked to the detrimental effects of the agents on the processes of prostaglandin synthesis, neutrophil (PMN) activation. and oxygen free radical generation. In the present study, we investigated the in vivo protective effects of melatonin on indomethacin-induced gastric lesions in the rat. Peroxidation of lipids and changes in the activities of related enzymes such as glutathione peroxidase (GSH-px) and myeloperoxidase (MPO), as a marker of PMNs infiltration, were also studied. Intraperitoneal (i.p.) injection of melatonin (0.25. 0.5, 1 mg kg(-1)) 30 min before indomethacin administration prevented gastric injury. The mean ulcer indices significantly (P < 0.05) decreased. Thiobarbituric acid (TBA) reactive substances in the gastric mucosa as an index of peroxidation, was increased after indomethacin administration and this increase was inhibited by melatonin. In addition, pretreatment with melatonin resulted in a significant increase of the enzymatic GSH-px activity up to the control levels; however, inhibition of ulceration by melatonin was not associated with a significant reduction in PMN infiltration. These results suggest that the protection afforded by the pineal hormone against indomethacin-induced gastric injury may be, in addition to other possible mechanisms, to its radical scavenging activity.

Interactions of melatonin with membrane models: portioning of melatonin in AOT and lecithin reversed micelles

The interaction of melatonin with water containing either sodium bis (2-ethylhexyl) sulfosuccinate (AOT) or soybean phosphatidylcholine (lecithin) reversed micelles has been investigated by UV absorption spectroscopy, at a molar ratio of melatonin:surfactant 1:800 for AOT and 1:400 for lecithin reversed micelles, and by varying the water:surfactant molar ratio (R). Our results suggest that in the presence of domains from apolar organic solvent to surfactant and to water, melatonin positions itself in the micellar phase, with a preferential location in the surfactant polar head group domain, independent of the nature of the surfactant and the amount of water encapsulated into the micellar core. Effects are due to the hydrophilic and lipophilic moieties of melatonin. The effectiveness of melatonin as an electron donor and free radical scavenger has been recently recognized. While supporting the hypothesis that melatonin may provide antioxidant protection without the benefit of receptors, present findings may suggest that the molecule could easily scavenge aqueous as well as lipophilic radicals.

Melatonin protects hippocampal neurons in vivo against kainic acid-induced damage in mice

In this investigation, 40 mg/kg of the excitatory neurotoxin kainic acid (KA) was subcutaneously administered to CD2-F1 mice. In this mouse strain morphological damage induced by KA in the hippocampus was markedly concentrated in the CA3 pyramidal neurons. Neuronal injury was accompanied by several pathological neurobehavioral activities including arching of tail, tremors and seizures, and by certain biochemical changes, i.e., increased lipid peroxidation products (LPO) in the brain. When melatonin was injected intraperitoneally at a single dose of 5 mg/kg 10 min before KA administration, it significantly reduced these pathological neurobehavioral changes and almost completely attenuated the increase in LPO and morphological damage induced by KA. The neuroprotective effect of melatonin against KA-induced brain damage in mice is believed to be in part related to its oxygen radical scavenging properties as well as its antiepileptic and GABA receptor regulatory actions. Considering melatonin's relative lack of toxicity and ability to enter the brain, these results along with previous evidence suggest that melatonin, which is a natural substance, may be useful in combating free radical-induced neuronal injury in acute situations such as stroke and brain trauma as well as neurodegenerative diseases such as Alzheimer's disease and Parkinson's disease that have free radicals as causative factors.

Oxidative damage in the central nervous system: protection by melatonin

Melatonin was recently reported to be an effective free radical scavenger and antioxidant. Melatonin is believed to scavenge the highly toxic hydroxyl radical, the peroxynitrite anion, and possibly the peroxyl radical. Also, secondarily, it reportedly scavenges the superoxide anion radical and it quenches singlet oxygen. Additionally, it stimulates mRNA levels for superoxide dismutase and the activities of glutathione peroxidase, glutathione reductase and glucose-6-phosphate dehydrogenase (all of which are antioxidative enzymes), thereby increasing its antioxidative capacity. Also, melatonin, at least at some sites, inhibits nitric oxide synthase, a pro-oxidative enzyme. In both in vivo and in vitro experiments melatonin has been shown to reduce lipid peroxidation and oxidative damage to nuclear DNA. While these effects have been observed primarily using pharmacological doses of melatonin, in a small number of experiments melatonin has been found to be physiologically relevant as an antioxidant as well. The efficacy of melatonin in inhibiting oxidative damage has been tested in a variety of neurological disease models where free radicals have been implicated as being in part causative of the condition. Thus, melatonin has been shown prophylactically to reduce amyloid beta protein toxicity of Alzheimer's disease, to reduce oxidative damage in several models of Parkinson's disease (dopamine auto-oxidation, 1-methyl-4-phenyl-1,2,3,6-tetrahydropyridine and 6-hydroxydopamine), to protect against glutamate excitotoxicity, to reduce ischemia-reperfusion injury, to lower neural damage due to gamma-aminolevulinic acid (phorphyria), hyperbaric hyperoxia and a variety of neural toxins. Since endogenous melatonin levels fal 1 markedly in advanced age, the implication of these findings is that the loss of this antioxidant may contribute to the incidence or severity of some age-associated neurodegenerative diseases.

2-Nitropropane-induced lipid peroxidation: antitoxic effects of melatonin

The degree of lipid peroxidation (LPO) as indicated by the levels of thiobarbituric acid reactive substances, malondialdehyde (MDA) and 4-hydroxyalkenals (4-HDA), and the activity of sorbitol dehydrogenase (SDH) in serum as parameters of hepatotoxicity were studied in rats treated with a single intraperitoneal (i.p.) injection of the hepatocarcinogen 2-nitropropane (2-NP). Since melatonin, the main secretory product of the pineal gland, has been shown to protect against a number of toxic agents, it was given 30 min before 2-NP to test its protective effect against 2-NP toxicity. Significant increases in LPO in liver (P<0.0001), lung (P<0.05) and kidney (P<0.0001) were observed 24 h after 4 mmol/kg 2-NP while serum SDH activity was increased 470-fold. All parameters showed time (0, 4, 8, 24 h) and dose (0, 1, 2, 3, 4 mmol/kg) dependency. The induction of LPO by 2-NP was significantly reduced in lung and kidney when melatonin (2.5, 5 or 10 mg/kg) was given prior to 2-NP administration. The elevation in serum SDH caused by 2-NP was also reduced when melatonin was given. These findings show that 2-NP induces LPO and that pharmacological levels of melatonin can reduce the toxicity of this hepatocarcinogen.