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R J Reiter

Publications and source records attributed to R J Reiter.

At least 145 records · Page 8Linked to original sources
PubMed1997

Inhibition of cerebellar nitric oxide synthase and cyclic GMP production by melatonin via complex formation with calmodulin.

Constitutive rat cerebellar nitric oxide synthase (NOS) activity is shown to be inhibited by physiological concentrations of the pineal hormone melatonin. The inhibition was dose-dependent and was coupled to an inhibition of the cyclic GMP production activated by L-arginine. Results also show that calmodulin appears to be involved in this process because its presence in the incubation medium was able to prevent the effect of melatonin on both NOS activity and cyclic GMP production. Moreover, polyacrylamide gel electrophoresis studies suggest that melatonin can interact with calmodulin modifying the binding of the peptide to the synthetic NOS peptide encompassing the calmodulin-binding domain of constitutive NOS from rat cerebellum, the natural mechanism by which calmodulin activates cerebellar NOS.

Animals↗
PubMed1997

Melatonin prevents changes in microsomal membrane fluidity during induced lipid peroxidation.

We tested the effect of melatonin on membrane fluidity in microsomes of a rat liver model in which lipid peroxidation was induced by the addition of FeCl3, ADP and NADPH. Membrane fluidity was monitored using fluorescence spectroscopy and lipid peroxidation was estimated by quantifying malonaldehyde (MDA)+4-hydroxyalkenals (4-HDA) concentrations following the induction of lipid peroxidation with and without pre-incubation with melatonin (1 microM-3 mM). Membrane rigidity increased during induced lipid peroxidation while melatonin reduced in a concentration-dependent manner both membrane rigidity and MDA+4-HDA generation. Melatonin's protective effect may relate to its known ability to scavenge free radicals and function as an antioxidant.

Adenosine Diphosphate↗
PubMed1997

Melatonin prevents death of neuroblastoma cells exposed to the Alzheimer amyloid peptide.

Studies from several laboratories have generated evidence suggesting that oxidative stress is involved in the pathogenesis of Alzheimer's disease (AD). The finding that the amyloid beta protein (Abeta) has neurotoxic properties and that such effects are, in part, mediated by free radicals has provided insights into mechanisms of cell death in AD and an avenue to explore new therapeutic approaches. In this study we demonstrate that melatonin, a pineal hormone with recently established antioxidant properties, is remarkably effective in preventing death of cultured neuroblastoma cells as well as oxidative damage and intracellular Ca2+ increases induced by a cytotoxic fragment of Abeta. The effects of melatonin were extremely reproducible and corroborated by multiple quantitative methods, including cell viability studies by confocal laser microscopy, electron microscopy, and measurements of intracellular calcium levels. The importance of this finding is that, in contrast to conventional antioxidants, melatonin has a proposed physiological role in the aging process. Secretion levels of this hormone are decreased in aging and more severely reduced in AD. The reported phenomenon may be of therapeutic relevance in AD.

Alzheimer Disease↗
PubMed1997

Daily time course of the contents in monoamines and their metabolites in the pineal gland of Syrian hamster.

Twenty-four h changes in endogenous tyrosine hydroxylase (TH) activity, monoamines and their metabolites as well as N-acetyltransferase (NAT) activity and melatonin content were investigated in the Syrian hamster pineal gland. Both NAT activity and melatonin content exhibited an expected rise 8 h (0400 h) after darkness onset. Pineal dopamine (DA) and 3,4-dihydroxyphenyl acetic acid (DOPAC) levels were highest during the dark phase reaching a peak at 0200 h, just prior to the rise in melatonin production. However no significant difference were found in both norepinephrine (NE) and TH activity levels during the 24 h period. However, in the present study, the rat pineal gland exhibited a clear day/night difference in its TH activity. These data suggest a possible role of pineal DA in the induction of melatonin synthesis in addition to its function as a NE precursor in the Syrian hamster pineal gland and also indicate that catecholamines may act on the hamster pineal in a different manner than in the rat.

3,4-Dihydroxyphenylacetic Acid↗
PubMed1997

Melatonin is protective against MPTP-induced striatal and hippocampal lesions.

The in vivo effect of melatonin on MPTP-induced neurotoxicity in mouse brain was studied. Melatonin (10 mg/kg) or saline was administered intraperitoneally (i.p.) to mice 30 min prior to a s.c. injection of MPTP (20 mg/kg). After MPTP treatment, the animals received melatonin or saline injections every hour for three hours. Mice were killed 4 hours after the MPTP injection. Regionally-specific increases in lipid peroxidation were observed in corpus striatum and hippocampus (71% and 58%, respectively), but not in cerebral cortex, cerebellum or midbrain. Treatment with melatonin completely reversed the rises in lipid peroxidation products. MPTP-treated mice showed a significant decrease in the striatal tyrosine hydroxylase immunoreactive nerve terminals, an effect that was also prevented by melatonin. These data show that melatonin is neuroprotective in this MPTP model of Parkinson's disease and suggest that melatonin, an endogenous antioxidant and nontoxic compound, may have potential beneficial effects for this neurodegenerative disorder.

1-Methyl-4-phenyl-1,2,3,6-tetrahydropyridine↗
PubMed1997

High affinity of sigma 1-binding sites for sterol isomerization inhibitors: evidence for a pharmacological relationship with the yeast sterol C8-C7 isomerase.

1. The sigma-drug binding site of guinea-pig liver is carried by a protein which shares significant amino acid sequence similarities with the yeast sterol C8-C7 isomerase (ERG2 protein). Pharmacologically-but not structurally-the sigma 1-site is also related to the emopamil binding protein, the mammalian sterol C8-C7 isomerase. We therefore investigated if sterol C8-C7 isomerase inhibitors are high affinity ligands for the (+)-[3H]-pentazocine labelled sigma 1-binding site. 2. Among the compounds which bound with high affinity to native hepatic and cerebral as well as to yeast expressed sigma 1-binding sites were the agricultural fungicide fenpropimorph (Ki 0.005 nM), the antihypocholesterinaemic drugs triparanol (Ki 7.0 nM), AY-9944 (Ki, 0.46 nM) and MDL28,815 (Ki 0.16 nM), the enantiomers of the ovulation inducer clomiphene (Ki 5.5 and 12 nM, respectively) and the antioestrogene tamoxifen (Ki 26 nM). 3. Except for tamoxifen these affinities are essentially identical with those for the [3H]-ifenprodil labelled sterol C8-C7 isomerase of S. cerevisiae. This demonstrates that sigma 1-binding protein and yeast isomerase are not only structurally but also pharmacologically related. Because of its affiliations with yeast and mammalian sterol isomerases we propose that the sigma 1-binding site is localized on a sterol isomerase related protein, involved in postsqualene sterol biosynthesis.

Animals↗
PubMed1997

Suppressive effect of melatonin administration on ethanol-induced gastroduodenal injury in rats in vivo.

1. Melatonin protection against ethanol-induced gastroduodenal injury was investigated in duodenumligated rats. 2. Melatonin, injected i.p. 30 min before administration of 1 ml of absolute ethanol, given by gavage, significantly decreased ethanol-induced macroscopic, histological and biochemical changes in the gastroduodenal mucosa. 3. Ethanol-induced lesions were detectable as haemorrhagic streaks. Ethanol administration damaged 36% and 25% of the total gastric and duodenal surface, respectively. Melatonin treatment reduced ethanol-induced gastric and duodenal damage to 14% and 8%, respectively. When indomethacin was given together with ethanol, the gastric damaged area was 44% of the total surface, while the duodenal damaged area was 35%; melatonin administration reduced the damage to only 13% of the total gastric surface and to 12% of total duodenal surface. 4. Both stomach and duodenum of ethanol-treated animals showed polymorphonuclear leukocyte (PMN) infiltration. The number of PMN increased more than 600 and 200 times in stomach and duodenum, respectively, following ethanol administration. Melatonin treatment reduced ethanol-induced PMN infiltration by 38% in the stomach and 20% in the duodenum. In indomethacin-ethanol-treated rats, the number of PMN increased by 875% compared to control group in the stomach and by 264% in duodenum. Melatonin administration reduced the indomethacin-ethanol-induced PMN rise by 57% in the stomach and 40% in the duodenum. 5. Gastroduodenal total glutathione (tGSH) concentration and glutathione reductase (GSSG-Rd) activity were significantly reduced following ethanol and indomethacin-ethanol administration. Melatonin ameliorated both the decrease in tGSH concentration as well as the reduction of GSSG-Rd activity elicited by ethanol both in the stomach and duodenum; melatonin was effective against indomethacin-ethanol-induced damage only in the stomach. 6. Ethanol-induced gastroduodenal damage is believed to be mediated by the generation of free radicals. Recently, a number of in vivo and in vitro experiments have shown melatonin to be an effective antioxidant and free radical scavenger; thus, we conclude that the protection by melatonin against ethanol-induced gastroduodenal injury is due, at least in part, to its radical scavenging activity.

Animals↗
PubMed1997

Melatonin in relation to cellular antioxidative defense mechanisms.

Melatonin's actions in organisms are more widespread than originally envisaged. Over three decades ago, the changing pattern of nocturnal melatonin production was found to be the signal for the annual cycle of reproduction in photoperiodic species. Since then, melatonin's actions also have been linked to circadian rhythms, immune function, sleep, retinal physiology and endocrine functions in general. In recent years, however, the sphere of influence of melatonin was further expanded when the indole was found to be an effective free radical scavenger and antioxidant. Free radicals are toxic molecules, many being derived from oxygen, which are persistently produced and incessantly attack and damage molecules within cells; most frequently this damage is measured as peroxidized lipid products, carbonyl proteins, and DNA breakage or fragmentation. Collectively, the process of free radical damage to molecules is referred to as oxidative stress. Melatonin reduces oxidative stress by several means. Thus, the indole is an effective scavenger of both the highly toxic hydroxyl radical, produced by the 3 electron reduction of oxygen, and the peroxyl radical, which is generated during the oxidation of unsaturated lipids and which is sufficiently toxic to propagate lipid peroxidation. Additionally, melatonin may stimulate some important antioxidative enzymes, i.e., superoxide dismutase, glutathione peroxidase and glutathione reductase. In in vivo tests, melatonin in pharmacological doses has been found effective in reducing macromolecular damage that is a consequence of a variety of toxic agents, xenobiotics and experimental paradigms which induce free radical generation. In these studies, melatonin was found to significantly inhibit oxidative damage that is a consequence of paraquat toxicity, potassium cyanide administration, lipopolysaccharide treatment, kainic acid injection, carcinogen administration, carbon tetrachloride poisoning, etc., as well as reducing the oxidation of macromolecules that occurs during strenuous exercise or ischemia-reperfusion. In experimental models which are used to study neurodegenerative changes associated with Alzheimer's and Parkinson disease, melatonin was found to be effective in reducing neuronal damage. Its lack of toxicity and the ease with which melatonin crosses morphophysiological barriers and enters subcellular compartments are essential features of this antioxidant. Thus far, most frequently pharmacological levels of melatonin have been used to combat oxygen toxicity. The role of physiological levels of melatonin, which are known to decrease with age, is being investigated as to their importance in the total antioxidative defense capacity of the organism.

Animals↗
PubMed1997

Cataractogenesis and lipid peroxidation in newborn rats treated with buthionine sulfoximine: preventive actions of melatonin.

The purpose of this study was to examine the influence of exogenously administered melatonin on cataract formation and lipid peroxidation in newborn rats treated with buthionine sulfoximine (BSO), a drug which inhibits the rate-limiting enzyme in glutathione (GSH) synthesis, gamma-glutamylcysteine synthase, thereby depleting animals of their stores of the important intracellular antioxidant, GSH. BSO (3 mmol/kg BW) was given for three consecutive days beginning on postnatal day 2; melatonin (4 mg/kg) was injected daily beginning on postnatal day 2 and continuing until the animals were killed (either day 9 or day 17 after birth). None of the control animals (rats treated with neither BSO nor with melatonin) developed lenticular opacification during the observation period. In the BSO-treated rats, 16 of 18 animals (89%) had observable cataracts when they were examined. In rats that received both BSO and melatonin, the incidence of cataracts was highly significantly decreased, i.e., only 3 of 18 rats (7%) had observable cataracts. In addition to cataracts, the level of lipid peroxidation products (malondialdehyde (MDA) and 4-hydroxyalkenals (4-HDA)) was examined in the lens, brain, liver, lung, and kidney of control and experimental animals. In BSO-treated rats, the lens, kidney, and lung exhibited increased levels of MDA plus 4-HDA relative to those measured in the control rats; these increases were reversed in the BSO-treated rats who were injected with melatonin daily. While BSO administration did not increase basal levels of MDA plus 4-HDA in either the brain or liver, melatonin reduced levels of lipid peroxidation products below those measured in the control rats (at 17 days after birth). The changes induced by melatonin are consistent with the free-radical scavenging and antioxidative properties of this indole.

Animals↗
PubMed1997

Melatonin prevents increases in neural nitric oxide and cyclic GMP production after transient brain ischemia and reperfusion in the Mongolian gerbil (Meriones unguiculatus).

While nitric oxide (NO) has been implicated as a mediator of glutamate excitotoxicity after cerebral ischemia/reperfusion, melatonin has been reported to inhibit brain NO production by suppressing nitric oxide synthase. The purpose of the present studies was to determine the effect of exogenous melatonin administration on NO-induced changes during brain ischemia/reperfusion. Indicators of cerebral cortical and cerebellar NO production [nitrite/nitrate levels and cyclic guanosine monophosphate (cGMP)] were used to estimate neural changes after transient bilateral carotid artery ligation followed by reperfusion in adult Mongolian gerbils (Meriones unguiculatus). Results show for the first time that melatonin prevents the increases in NO and cGMP production after transient ischemia/reperfusion in frontal cerebral cortex and cerebellum of Mongolian gerbils. The inhibitory effect of melatonin on NO production and its ability to scavenge free radicals and the peroxynitrite anion may be responsible for the protective effect of melatonin on neuronal structures during transient ischemia followed by reperfusion.

Animals↗
PubMed1997

Utility of high doses of melatonin as adjunctive anticonvulsant therapy in a child with severe myoclonic epilepsy: two years' experience.

Recent data indicate that melatonin inhibits brain glutamate receptors and nitric oxide production, thus suggesting that it may exert a neuroprotective and antiexcitotoxic effect. Melatonin has been seen to prevent seizures in several animal models and to decrease epileptic manifestations in humans. The lack of response to conventional anticonvulsants in an epileptic child led us to use melatonin in this case. A female child who began to have convulsive seizures at the age of 1.5 months and was diagnosed as having severe myoclonic epilepsy was unsuccessfully treated with different combinations of anticonvulsants, including valproic acid, phenobarbital, clonazepam, vigabatrin, lamotrigin, and clobazam. Melatonin was thus added to the treatment. Imaging studies (CT, SPECT, and MNR), EEG recordings, blood biochemical, and hematological analyses, including measures of the circadian rhythm of melatonin, were made. The child was initially treated with various anticonvulsants. Severe neurological and psychomotor deterioration combined with increased seizure activity showed a lack of response to the treatment. At the age of 29 mon the patient was in a pre-comatose stage at which time melatonin was added to treatment. After 1 month of melatonin plus phenobarbital therapy and for a year thereafter, the child's seizures were under control. On reducing the melatonin dose after this time, however, seizures resumed and the patient's condition was re-stabilized after restoring melatonin. Prior to our attempts to reduce melatonin, all analyses, including EEG recordings and SPECT, were normal. As far as the results of neurological examination are concerned, only mild hypotony without focalization remained. Changes in the therapeutic schedules during the second year of melatonin treatment, including the withdrawal of phenobarbital, did not result in the same degree of seizure control, although progressively the child became satisfactorily controlled. At the present moment the child continues to have mild hypotony and shows attention disorder and irritability. Melatonin has proven to be useful as adjunctive therapy in the clinical control of this case of severe infantile myoclonic epilepsy. The results suggest that melatonin may have a useful role in mechanisms of neuroprotection and also indicate its use in other cases of untreatable epilepsy. Further studies using more patients and placebo-treatment would be beneficial in understanding the potential use of melatonin as a co-therapy in some cases of seizures.

Anticonvulsants↗
PubMed1997

Acutely administered melatonin reduces oxidative damage in lung and brain induced by hyperbaric oxygen.

Hyperbaric oxygen exposure rapidly induces lipid peroxidation and cellular damage in a variety of organs. In this study, we demonstrate that the exposure of rats to 4 atmospheres of 100% oxygen for 90 min is associated with increased levels of lipid peroxidation products [malonaldehyde (MDA) and 4-hydroxyalkenals (4-HDA)] and with changes in the activities of two antioxidative enzymes [glutathione peroxidase (GPX) and glutathione reductase (GR)], as well as in the glutathione status in the lungs and in the brain. Products of lipid peroxidation increased after hyperbaric hyperoxia, both GPX and GR activities were decreased, and levels of total glutathione (reduced+oxidized) and glutathione disulfide (oxidized glutathione) increased in both lung and brain areas (cerebral cortex, hippocampus, hypothalamus, striatum, and cerebellum) but not in liver. When animals were injected with melatonin (10 mg/kg) immediately before the 90-min hyperbaric oxygen exposure, all measurements of oxidative damage were prevented and were similar to those in untreated control animals. Melatonin's actions may be related to a variety of mechanisms, some of which remain to be identified, including its ability to directly scavenge free radicals and its induction of antioxidative enzymes via specific melatonin receptors.

Aldehydes↗
PubMed1997

Differential adrenergic regulation of rat pineal cyclic AMP production and N-acetyltransferase activity during postnatal development: involvement of G alpha s and G alpha i1-2 proteins.

We have studied why rat pineal N-acetyltransferase (NAT) activity is relatively insensitive to isoproterenol in young rats when compared with adult rats. We report that activation by isoproterenol of pineal cyclic AMP production and NAT activity is higher in adult than in 2-week-old rats. However, the effect of dibutyryl cyclic AMP, which enters the pinealocyte and duplicates the effect of cyclic AMP, on NAT activity was similar at both ages. Moreover, we found that both alpha- and beta-adrenergic receptors are highly specific at both ages, since the binding of the specific radioligands used to their receptors could be displaced only by their corresponding agonists and antagonists. However, we observed differences between pineals from young and adult rats when several families of the alpha subunit of G-proteins were studied in cell membranes. ADP-ribosylation and immunoblot studies have shown clear differences in both 42 and 45 kDa forms of the Gs alpha Both forms exhibit low values in pineals from 2-week-old animals when compared with 6-week-old. We also show that the later appearance of both Gs alpha forms is roughly similar to the potent activation of cyclic AMP production and NAT activity in adult rats when compared with young rats. In conclusion, the results presented suggest that the relative lack of sensitivity of rat pineal gland to beta-adrenergic receptor agonists early in the postnatal development may be explained by the low levels of membrane Gs alpha, rather than postreceptor-mediated mechanisms or changes in the characteristics of the beta-adrenergic receptors on the pinealocyte membrane.

Adrenergic alpha-Agonists↗
PubMed1996

Yeast sterol C8-C7 isomerase: identification and characterization of a high-affinity binding site for enzyme inhibitors.

The yeast gene ERG2 encodes a sterol C8-C7 isomerase and is essential for ergosterol synthesis and cell proliferation. Its striking homology with the so-called sigma1 receptor of guinea pig brain, a polyvalent steroid and drug binding protein, suggested that the yeast sterol C8-C7 isomerase (ERG2) carries a similar high affinity drug binding domain. Indeed the sigma ligands [3H]haloperidol (Kd = 0.3 nM) and [3H]ifenprodil (Kd = 1.4 nM) bound to a single population of sites in ERG2 wild type yeast microsomes (Bmax values of 77 and 61 pmol/mg of protein, respectively), whereas binding activity was absent in strains carrying ERG2 gene mutations or disruptions. [3H]Ifenprodil binding was inhibited by sterol isomerase inhibitors such as fenpropimorph (Ki = 0.05 nM), tridemorph (Ki = 0.09 nM), MDL28,815 (Ki = 0.44 nM), triparanol (Ki = 1.5 nM), and AY-9944 (Ki = 5.8 nM). [3H]Haloperidol specifically photoaffinity-labeled a protein with an apparent molecular weight of 27400, in agreement with the molecular mass of the sterol C8-C7 isomerase (24900 Da). 9E10 c-myc antibodies specifically immunoprecipitated the c-myc tagged protein after [3H]haloperidol photolabeling, unequivocally proving that the drug binding site is localized on the ERG2 gene product. Haloperidol, trifluperidol, and ifenprodil inhibited the growth of Saccharomyces cerevisiae and reduced the ergosterol content of cells grown in their presence. Our results demonstrate that the yeast sterol C8-C7 isomerase has a polyvalent high-affinity drug binding site similar to mammalian sigma receptors and that in yeast sigma ligands inhibit sterol biosynthesis.

Animals↗
PubMed1996

Melatonin and radioprotection from genetic damage: in vivo/in vitro studies with human volunteers.

Peripheral blood samples were collected from human volunteers at 0 (5-10 min before), and at 1 and 2 h after a single oral dose of 300 mg of melatonin. At each time point, (i) the concentration of melatonin in the serum and in the leukocytes was determined, and (ii) the whole blood was exposed in vitro to 150 cGy of 137Cs gamma radiation, and the lymphocytes were cultured with mitogenic stimulation to determine the extent of radiation-induced genetic damage, viz, chromosome aberrations and micronuclei. For each volunteer, the results showed a significant increase in the concentration of melatonin in the serum and in the leukocytes at 1 h after the oral dose of melatonin, as compared to the sample collected at 0 h. The lymphocytes in the blood samples collected at 1 and 2 h after melatonin ingestion and exposed in vitro to 150 cGy gamma radiation exhibited a significant decrease in the incidence of chromosome aberrations and micronuclei, as compared with similarly irradiated lymphocytes from the blood sample collected at 0 h; the frequencies observed in the cells sampled at 2 h after the ingestion of melatonin were consistently lower when compared with those collected at 1 h. The data may have important implications for the protection of human lymphocytes from the genetic damage induced by free radical-producing mutagens and carcinogens.

Chromosome Aberrations↗
PubMed1996

Effect of calcium on melatonin secretion in chick pineal gland I.

Melatonin is the neurohormone which is synthesized by the pineal gland and secreted rhythmically. The role of calcium in the activation of melatonin production remains unknown. In this study, we demonstrated that calcium input participates in the regulation of chick pineal gland. Pineal glands from Gallus domesticus were perifuse with Krebs medium (controls) or with Krebs medium plus drugs (ethylene glycol tetraacetic acid (EGTA) or calcium ionophore A23187). When EGTA was added to the perifusion medium, free extracellular calcium concentrations were dramatically decreased and melatonin synthesis was decreased. On the other hand, when the calcium ionophore A23187 was added to the perifusion medium, chick pineal glands exhibited a marked increase in secretion of melatonin. No effects were observed when chick pineal glands were treated with drugs during or after the time of the natural peak levels. We propose that calcium input from extracellular medium and output from intracellular calcium reserves are primary mechanisms in the activation of melatonin synthesis in the chick pineal gland.

Animals↗