Effects of melatonin treatment in septic newborns.

Free radicals have been implicated in the pathogenesis of neonatal sepsis and its complications. This study was conducted to determine the changes in the clinical status and the serum levels of lipid peroxidation products [malondialdehyde (MDA) and 4-hydroxylalkenals (4-HDA)] in 10 septic newborns treated with the antioxidant melatonin given within the first 12 h after diagnosis. Ten other septic newborns in a comparable state were used as "septic" controls, while 10 healthy newborns served as normal controls. A total of 20 mg melatonin was administered orally in two doses of 10 mg each, with a 1-h interval. One blood sample was collected before melatonin administration and two additional blood samples (at 1 and 4 h) were collected after melatonin administration to assess serum levels of lipid peroxidation products. Serum MDA + 4-HDA concentrations in newborns with sepsis were significantly higher than those in healthy infants without sepsis; in contrast, in septic newborns treated with melatonin there was a significant reduction (p < 0.05) of MDA + 4-HDA to the levels in the normal controls at both 1 and 4 h (p < 0.05). Melatonin also improved the clinical outcome of the septic newborns as judged by measurement of sepsis-related serum parameters after 24 and 48 h. Three of 10 septic children who were not treated with melatonin died within 72 h after diagnosis of sepsis; none of the 10 septic newborns treated with melatonin died. To our knowledge, this is the first study where melatonin was given to human newborns.

Individual and synergistic antioxidative actions of melatonin: studies with vitamin E, vitamin C, glutathione and desferrioxamine (desferoxamine) in rat liver homogenates.

The pharmacological effects of melatonin, vitamin E, vitamin C, glutathione and desferrioxamine (desferoxamine) alone and in combination on iron-induced membrane lipid damage in rat liver homogenates were examined by estimating levels of malondialdehyde and 4-hydroxyalkenals (MDA+4-HDA). Individually, melatonin (2.5-1600 microM), vitamin E (0.5-50 microM), glutathione (100-7000 microM) and desferrioxamine (1-8 microM) inhibited lipid peroxidation in a concentration-dependent manner. Vitamin C had both a pro-oxidative (25-2000 microM) and an antioxidative (2600-5000 microM) effect. The IC50 (concentration that reduces damage by 50%) values were 4, 10, 426, 2290 and 4325 microM for vitamin E, desferrioxamine, melatonin, glutathione and vitamin C, respectively. The synergistic actions of melatonin with vitamin C, vitamin E, and glutathione were systematically investigated. When melatonin was combined with vitamin E, glutathione, or vitamin C, the protective effects against iron-induced lipid peroxidation were dramatically enhanced. Even though melatonin was added at very low concentrations, it still showed synergistic effects with other antioxidants at certain concentrations. Furthermore, melatonin not only reversed the pro-oxidative effects of vitamin C, but its efficacy in reducing lipid peroxidation was improved when it was combined with pro-oxidative concentrations of vitamin C. The results provide new information in terms of the possible pharmacological use of the combination of melatonin and classical antioxidants to treat free radical-related conditions.

N-acetylserotonin suppresses hepatic microsomal membrane rigidity associated with lipid peroxidation.

N-acetylserotonin, the immediate precursor of melatonin in the tryptophan metabolic pathway in the pineal gland, has been reported to be an antioxidant. The aim of this work was to test the effect of N-acetylserotonin in stabilizing biological membranes against oxidative stress. Hepatic microsomal membranes from male adult rats were incubated with N-acetylserotonin (0.001-3 mM) before inducing lipid peroxidation using FeCl(3), ADP and NADPH. Control experiments were done by incubating microsomal membranes with N-acetylserotonin in the absence of lipid peroxidation-inducing drugs. Membrane fluidity was assessed by fluorescence spectroscopy and malonaldehyde plus 4-hydroxyalkenals concentrations were measured to estimate the degree of lipid peroxidation. Free radicals induced by the combination of FeCl(3)+ADP+NADPH produced a significant decrease in the microsomal membrane fluidity, which was associated with an increase in the malonaldehyde plus 4-hydroxyalkenals levels. These changes were suppressed in a concentration-dependent manner when N-acetylserotonin was added in the incubation buffer. In the absence of lipid peroxidation, N-acetylserotonin (0.001-3 mM) did not change membrane fluidity nor malonaldehyde plus 4-hydroxyalkenals levels. These results suggest that the protective role of N-acetylserotonin in preserving optimal levels of fluidity of the biological membranes may be related to its ability to reduce lipid peroxidation.

Respiratory distress syndrome in the newborn: role of oxidative stress.

Reactive oxygen and nitrogen species are generated by several inflammatory and structural cells of the airways. These oxidant species have important effects on a variety of lung cells as regulators of signal transduction, activators of key transcription factors and modulators of gene expression and apoptosis. Thus, increased oxidative stress accompanied by reduced endogenous antioxidant defenses may play a role in the pathogenesis of a number of inflammatory pulmonary diseases, including respiratory distress syndrome (RDS) in the newborn. There obviously are conflicting reports on the effect of oxygen, ventilation and nitric oxide (NO) on RDS and, thus, the question arises as what the neonatologist should do when confronted with a newborn with RDS. Clearly, utilizing lung protective strategies requires compromises between gas exchange goals and potential toxicities associated with over-distension, derecruitment of lung units and high oxygen concentrations. The results discussed in this brief review suggest rigorous clinical tests with antioxidants which may help to define the mechanisms associated with RDS and which could lead to new treatment strategies.

Induction of lipid peroxidation in hamster organs by the carcinogen cadmium: melioration by melatonin.

Cadmium is a well-known human carcinogen. Lipid peroxidation is involved in cadmium-related toxicity and carcinogenesis. Melatonin is an effective antioxidant and free radical scavenger. The potential protective effects of melatonin against cadmium-induced lipid peroxidation in hamster brain, heart, kidney, testes, lung, and liver were examined. Lipid peroxidation was induced by intraperitoneal injection of cadmium chloride [single dose of 1 mg/kg body weight (bw)]. To test whether melatonin would protect against the toxicity of the carcinogen, the melatonin was injected peritoneally at a dose of either 15 mg/kg bw or 5 mg/kg bw, 0.5 h before cadmium treatment and thereafter at 8 h intervals during the day in the 48 h interval following the cadmium injection. One group of hamsters received only a single melatonin injection (a dose of 15 mg/kg bw, 30 min prior to cadmium). Forty-eight hours after cadmium injection, lipid peroxidation increased in brain, heart, kidney, testes, and lung. Either multiple injections of melatonin at both the 5 and 15 mg/kg bw doses, or a single injection of 15 mg/kg bw, prevented the cadmium-related increases in lipid peroxidation in brain, heart and lung. Cadmium-induced lipid peroxidation in kidney was prevented by melatonin when it was given as a single dose of 15 mg/kg bw. Melatonin slightly, but not significantly, reduced cadmium-induced lipid peroxidation in testes. It is concluded that cadmium toxicity, at least with regard to the resulting lipid peroxidation, is reduced by administering melatonin.

Carcinogen-induced, free radical-mediated reduction in microsomal membrane fluidity: reversal by indole-3-propionic acid.

Chromium (Cr) is a well established carcinogen, with Cr(III) accounting for much of the intracellular oxidative damage that this transition metal induces. Indole-3-propionic acid (IPA), a melatonin-related molecule, is a reported antioxidant and free radical scavenger. Concentration (1, 10, 100, 500, or 1000 microM) and time (15, 30, 45, 60, or 90 min)-dependent effects of Cr(III) in the presence of H2O2 (0.5 mM), as well as the protective effect of IPA on Cr(III)-induced alterations in membrane fluidity (the inverse of membrane rigidity), as an index of membrane damage, were estimated by fluorescence spectroscopy. Cr(III), in a concentration- and a time-dependent manner, decreased membrane fluidity, with marked effects at a concentration of 500 microM and 60 min of incubation. IPA (5, 3, or 1 mM) prevented the Cr(III)-induced decrease in membrane fluidity. It is concluded that the carcinogen Cr(III), in the presence of H202, generates free radicals, which decrease membrane fluidity in rat microsomal membranes. Membrane alterations are pharmacologically prevented by the antioxidant IPA.

Melatonin attenuates estradiol-induced oxidative damage to DNA: relevance for cancer prevention.

Estrogens exert pro-oxidative effects and have been shown to damage DNA, potentially leading to cancer. Melatonin is a well-known antioxidant, free radical scavenger, and oncostatic agent. Changes in the levels of 8-oxo-7,8-dihydro-2'-deoxyguanosine (8-oxodGuo), an index of DNA damage, and the levels of malondialdehyde + 4-hydroxyalkenals, an index of lipid peroxidation, were measured in kidneys, liver, and testes from hamsters treated with E2 (75 mg/kg body wt) and were collected 3 or 5 hr later. Other animals were treated with melatonin (15 mg/kg body wt, 30 min before and 120 min after E2 treatment) or were given both compounds. Additionally, lipid peroxidation was measured in liver homogenates exposed to ferrous sulfate (15 microM) in vitro. E2 treatment caused an increase in 8-oxodGuo levels in kidneys collected 5 hr after E2 administration, and in liver 3 hr after estrogen treatment. Melatonin completely prevented E2-induced DNA damage in both organs. Melatonin alone or when given with E2 and examined 3 hr later decreased the base level of 8-oxodGuo in testes. A tendency for a reduction in in vivo lipid peroxidation was observed after treatment of hamsters with either melatonin, E2, or both compounds, with a statistically significant decrease being measured in the liver following E2 administration. In vitro exposure to iron significantly enhanced lipid peroxidation in hepatic homogenates from untreated, melatonin-treated, or E2-injected hamsters; in the hepatic homogenates of hamsters given both E2 and melatonin, ferrous sulfate failed to augment lipid peroxidation. Our results confirm the dual actions of estrogens relative to oxidative damage, i.e., estrogen increases oxidative destruction of DNA while reducing lipid peroxidation. Melatonin had antioxidative actions in reducing oxidative damage to both DNA and to membrane lipids. Melatonin completely prevented the damaging action of E2 on DNA and synergized with the steroid to reduce lipid peroxidation.

Anticarcinogenic actions of melatonin which involve antioxidative processes: comparison with other antioxidants.

The complex processes of carcinogenesis often involve oxidative stress. Numerous indicators of oxidative damage are enhanced as the result of the action of carcinogens. Several antioxidants, with different efficacies, protect against oxidative abuse caused by carcinogens. Recently, melatonin (N-acetyl-5-methoxytryptamine) and related indoleamines have attracted attention because of their high antioxidant and anticarcinogenic activity. Some antioxidants, e.g. ascorbic acid, play an ambivalent role in antioxidative defense, since, under specific conditions, they are strongly prooxidant. Among known antioxidants, melatonin has been an often investigated experimental agent in reducing cancer initiation and inhibiting the growth of established tumors. The indoleamine has been shown to protect macromolecules from oxidative mutilation induced by carcinogens. In these studies, a variety of in vitro and in vivo models were used and numerous indices of oxidative damage were evaluated. The protective effects of melatonin and several other indoleamine antioxidants against cellular damage caused by carcinogens make them potential supplements in the treatment or co-treatment at several stages of cancer.

DNA oxidatively damaged by chromium(III) and H(2)O(2) is protected by the antioxidants melatonin, N(1)-acetyl-N(2)-formyl-5-methoxykynuramine, resveratrol and uric acid.

Chromium (Cr) compounds are widely used industrial chemicals and well known carcinogens. Cr(III) was earlier found to induce oxidative damage as documented by examining the levels of 8-hydroxydeoxyguanosine (8-OH-dG), an index for DNA damage, in isolated calf thymus DNA incubated with CrCl(3) and H(2)O(2). In the present in vitro study, we compared the ability of the free radical scavengers melatonin, N(1)-acetyl-N(2)-formyl-5-methoxykynuramine (AFMK), resveratrol and uric acid to reduce DNA damage induced by Cr(III). Each of these scavengers markedly reduced the DNA damage in a concentration-dependent manner. The concentrations that reduced 8-OH-dG formation by 50% (IC(50)) were 0.10 microM for both resveratrol and melatonin, and 0.27 microM for AFMK. However, the efficacy of the fourth endogenous antioxidant, i.e. uric acid, in terms of its inhibition of DNA damage in the same in vitro system was about 60--150 times less effective than the other scavengers; the IC(50) for uric acid was 15.24 microM. These findings suggest that three of the four antioxidants tested in these studies may have utility in protecting against the environmental pollutant Cr and that the protective effects of these free radical scavengers against Cr(III)-induced carcinogenesis may relate to their direct hydroxyl radical scavenging ability. In the present study, the formation of 8-OH-dG was likely due to a Cr(III)-mediated Fenton-type reaction that generates hydroxyl radicals, which in turn damage DNA. Once formed, 8-OH-dG can mutate eventually leading to cancer; thus the implication is that these antioxidants may reduce the incidence of Cr-related cancers.

Relative efficacies of indole antioxidants in reducing autoxidation and iron-induced lipid peroxidation in hamster testes.

Increased iron stores are associated with free radical generation and carcinogenesis. Lipid peroxidation is involved in DNA damage, thus indirectly participating in the early steps of tumor initiation. Melatonin and structurally related indoles are effective in protecting against oxidative stress. The aim of the study was to compare the relative efficacies of melatonin, N-acetylserotonin (NAS), indole-3-propionic acid (IPA), and 5-hydroxy-indole-3-acetic acid (5HIAA) in altering basal and iron-induced lipid peroxidation in homogenates of hamster testes. To determine the effect of the indoles on the autoxidation of lipids, homogenates were incubated in the presence of each agent in concentrations of 0.0, 0.01, 0.05, 0.1, 0.25, 0.5, 0.75, 1.0, 2.0, 2.5, or 5.0 mM. To study their effects on induced lipid peroxidation, homogenates were incubated with FeSO(4) (30 microM + H(2)O(2) (0.1 mM) + each of the indoles in the same concentrations as above. The degree of lipid peroxidation was expressed as concentrations of malondialdehyde + 4-hydroxyalkenals (MDA + 4-HDA) per mg protein. The indoles decreased both basal and iron-related lipid peroxidation in a concentration-dependent manner. Melatonin reduced basal MDA + 4-HDA levels when used at the concentrations of 0.25 mM or higher, and prevented iron-induced lipid peroxidation at concentrations of 1.0, 2.0, 2.5, or 5.0 mM. The lowest effective concentrations of NAS required to lower basal and iron-related lipid peroxidation were 0.05 mM and 0.25 mM, respectively. IPA, only when used in the highest concentrations of 2.5 mM or 5 mM inhibited basal lipid peroxidation levels and it was ineffective on the levels of MDA + 4-HDA due to iron damage. 5HIAA reduced basal lipid peroxidation when used at concentrations of 0.25 mM or higher, and it prevented iron-induced lipid peroxidation only at the highest applied concentration (5 mM). In conclusion, melatonin and related indoles at pharmacological concentrations protect against both the autoxidation of lipids as well as induced peroxidation of lipids in testes. In doing so, these agents would be expected to reduce testicular cancer that is initiated by products of lipid peroxidation.

Influence of hemithyroidectomy on bromodeoxyuridine incorporation into DNA of rat thyroid follicular cells.

OBJECTIVE: To examine the bromodeoxyuridine (BrdU) incorporation into DNA of thyroid follicular cells (TFC) in the remaining thyroid lobe after hemithyroidectomy (hemiTx) in 1, 2, 3 and 4 weeks time after surgery. METHODS: The experiment was performed on male Wistar rats. The Cell Proliferation Kit (Amersham, UK) was used in order to detect the incorporated BrdU. The BrdU incorporation was expressed as a BrdU labeling index (BrdULI; a number of BrdU-immunopositive TFC per 1000 TFC). RESULTS: 1. No statistically significant changes of BrdULI were observed between the particular groups of sham-operated (shamTx)-rats in 1, 2, 3 and 4 weeks time after surgery, and in comparison of each of them to the controls (at time "0"); 2. In the first 2-week period after hemiTx, an increasing effect of that surgical procedure on BrdULI value was observed (the highest BrdULI value was detected 2 weeks after hemiTx); 3. In the third and fourth week after hemiTx, a decrease of BrdULI value was observed, as compared to BrdULI groups (in 1- and 2-week time after hemiTx), and to the controls (at time "0"); 4. An increase of weight of contralateral lobe was shown in 1, 2, 3 and 4 weeks after hemiTx in comparison to thyroid lobe weight in intact rats. CONCLUSIONS: During the first 2 weeks after hemiTx, the thyroid growth in the remaining thyroid lobe seems to ensue by hyperplasia mechanisms. The thyroid growth processes during subsequent 2 weeks (3rd and 4th) could result from other mechanisms - for example, from hypertrophy.

Indole-3-propionic acid, a melatonin-related molecule, protects hepatic microsomal membranes from iron-induced oxidative damage: relevance to cancer reduction.

Excessive free iron and the associated oxidative damage are commonly related to carcinogenesis. Among the antioxidants known to protect against iron-induced oxidative abuse and carcinogenesis, melatonin and other indole compounds recently have received considerable attention. Indole-3-propionic acid (IPA), a deamination product of tryptophan, with a structure similar to that of melatonin, is present in biological fluids and is an effective free radical scavenger. The aim of the study was to examine the effect of IPA on experimentally induced oxidative changes in rat hepatic microsomal membranes. Microsomes were preincubated in presence of IPA (10, 3, 2, 1, 0.3, 0.1, 0.01 or 0.001 mM) and, then, incubated with FeCl(3) (0.2 mM), ADP (1.7 mM) and NADPH (0.2 mM) to induce oxidative damage. Alterations in membrane fluidity (the inverse of membrane rigidity) were estimated by fluorescence spectroscopy and lipid peroxidation by measuring concentrations of malondialdehyde+4-hydroxyalkenals (MDA+4-HDA). IPA, when used in concentrations of 10, 3 or 2 mM, increased membrane fluidity, although at these concentrations it did not influence lipid peroxidation significantly. The decrease in membrane fluidity due to Fe(3+) was completely prevented by preincubation in the presence of IPA at concentrations of 10, 3, 2 or 1 mM. The enhanced lipid peroxidation due to Fe(3+) was prevented by IPA only at the highest concentration (10 mM). It is concluded that Fe(3+)-induced rigidity and, to a lesser extent, lipid peroxidation in microsomal membranes may be reduced by IPA. However, IPA in high concentrations increase membrane fluidity. Besides melatonin, IPA may be used as a pharmacological agent to protect against iron-induced oxidative damage to membranes and, potentially, against carcinogenesis.

Comparison of the protective effect of melatonin with other antioxidants in the hamster kidney model of estradiol-induced DNA damage.

17beta-Estradiol (E(2)) is a known carcinogen. Estrogen induction of tumors in hamster kidney is a model of estrogen-related carcinogenesis. Melatonin is a well-known antioxidant, free radical scavenger and oncostatic agent. Changes in the levels of 8-oxo-7,8-dihydro-2'-deoxyguanosine (8-oxodGuo), an index of DNA damage, were measured in kidneys, liver and testes from hamsters treated with E(2) (75mg/kg b.w.) and collected 5h later. Potential protective effects of melatonin, N-acetylserotonin (NAS), indole-3-propionic acid (IPA) and ascorbic acid (AA) against E(2)-induced DNA damage were tested. The antioxidants were applied in equimolar doses of 64.5 micromol/kg b.w., 2 and 0.5h before and 2 and 4h after E(2) treatment. E(2) treatment caused a significant increase in 8-oxodGuo levels in kidneys, but did not influence significantly the oxidation of guanine bases in liver and testes. Melatonin, IPA and AA, but not NAS, completely prevented E(2)-induced DNA damage in hamster kidneys. It is concluded that melatonin, IPA and AA may be effective in protecting against E(2)-related DNA damage and, consequently, carcinogenesis.

A programme of iodine supplementation using only iodised household salt is efficient--the case of Poland.

BACKGROUND: Iodine prophylaxis in Poland started in 1935 and has been interrupted twice: by World War II and in 1980 for economic reasons. Epidemiological surveys carried out after the Chernobyl accident in 1989 as well as in 1992/1993 and in 1994 as a 'ThyroMobil' study, revealed increased prevalence of goitre in children and adults. Ninety per cent of Poland was classified as an area of moderate iodine deficiency, and 10%, in the seaside area, as mild iodine deficiency territory. Iodine prophylaxis based on iodisation of household salt was introduced again in 1986 as a voluntary model and in 1997 as a mandatory model with 30+/-10 mg KI/kg salt. OBJECTIVE: The evaluation of the obligatory model of iodine prophylaxis in schoolchildren from the same schools in 1994 and 1999. METHODS: Thyroid volume was determined by ultrasonography. Ioduria in casual morning urine samples was measured using Sandell-Kolthoff's method, within the framework of the ThyroMobil study. RESULTS: Goitre prevalence decreased from 38.4 to 7% and urinary iodine concentration increased from 60.4 to 96.2 microg/l mean values between 1994 and 1999. In four schools the prevalence of goitre diminished below 5%. In 1999, 70% of children excreted over 60 microg I/l, and 36% over 100 microg I/l, whereas in 1994 the values were 44 and 13% respectively. CONCLUSION: The present findings indicate that iodine prophylaxis based only on iodised household salt is highly effective.

Characterization of the protective effects of melatonin and related indoles against alpha-naphthylisothiocyanate-induced liver injury in rats.

The protective effect of melatonin, 6-hydroxymelatonin and N-acetylserotonin against alpha-naphthylisothiocyanate (ANIT)-induced liver injury was investigated and compared in rats injected once with the hepatotoxicant (75 mg/kg body weight). In rats injected with ANIT alone, liver injury with cholestasis developed within 24 h, as indicated by both serum levels of alanine aminotransferase (SGPT) and aspartic acid aminotransferase (SGOT) activities and serum total bilirubin concentration. The administration of melatonin or 6-hydroxymelatonin (10 mg/kg body weight) to ANIT-injected rats reduced significantly the serum levels of both SGPT and SGOT and the serum total bilirubin concentration. For all hepatic biochemical markers, melatonin was more effective that 6-hydroxymelatonin. By comparison, the administration of N-acetylserotonin (10 mg/kg body weight) to ANIT-injected rats did not reduce the serum levels of either hepatic enzymes or the serum total bilirubin concentration. In ANIT-injected rats, hepatic lipid peroxidation (LPO) was significantly higher than in control animals and this increase was significantly reduced by either melatonin, 6-hydroxymelatonin or N-acetylserotonin. Furthermore, ANIT treatment caused a significant reduction in liver microsomal membrane fluidity and this reduction was completely reversed by the three indoles. The liver from ANIT-injected rats showed several histopathological alterations; above all there was an acute infiltration of polymorphonuclear neutrophils and an increase in the number of apparent apoptotic hepatocytes. The concurrent administration of melatonin reduced the severity of all morphological alterations, specially the neutrophil infiltration and the number of presumed apoptotic cells. On the contrary, the administration of 6-hydroxymelatonin or N-acetylserotonin did not provide any protective effect in terms of the histopathological alterations. These results indicate that melatonin protects against ANIT-induced liver injury with cholestasis in rats, and suggests that this protective effect is likely due to its antioxidant properties and above all to its capacity to inhibit liver neutrophil infiltration, a critical factor in the pathogenesis of ANIT-induced liver injury. 6-hydroxymelatonin, although able to provide partial protection against the ANIT-induced hepatic injury, probably through its antioxidant properties by mechanisms that are unclear, was unable to reduce neutrophil infiltration. Finally, N-acetylserotonin in the experimental conditions of this study, only exhibited some antioxidant protection but had no protective effect against ANIT-induced hepatic damage.

Autoxidation and toxicant-induced oxidation of lipid and DNA in monkey liver: reduction of molecular damage by melatonin.

Melatonin, the main secretory product of the pineal gland, is a free radical scavenger and antioxidant which protects against oxidative damage due to a variety of toxicants. However, there is little information regarding melatonin's antioxidative capacity in tissues of primates. In this study we examined the protective effects of melatonin in monkey liver homogenates against lipid damage that occurred as a result of autoxidation or that induced by exogenous addition of H202 and ferrous iron (Fe2+). Additionally, we tested melatonin's protective effect against oxidative damage to DNA induced by chromium(III) (CrIII) plus H202. The levels of malondialdehyde and 4-hydroxyalkenals were assayed as an index of lipid peroxidation, and the concentrations of 8-hydroxydeoxyguanosine (8-OHdG) as an endpoint of oxidative DNA damage. The increases in malondialdehyde+4-hydroxyalkenals concentrations as a consequence of autoxidation or after the addition of H202 plus Fe2+ to the homogenates were time-dependent. The accumulation of these damaged products due to either auto-oxidative processes or induced by H202 and Fe2+ were significantly reduced by melatonin in a concentration-dependent-manner. The levels of 8-OHdG were elevated in purified monkey liver DNA incubated with a combination of CrCl3 plus H2O2. This rise in oxidatively damaged DNA was prevented by 10 microM concentration of melatonin. Also, melatonin reduced the damage to DNA that was caused by auto-oxidative processes. These findings in monkey liver tissue document the ability of melatonin to protect against oxidative damage to both lipid and DNA in primate tissue, as observed previously in rodent tissue. The findings provide support for the use of melatonin as suitable agent to reduce damage inflicted by free radical species in primates.

Melatonin reduces phenylhydrazine-induced oxidative damage to cellular membranes: evidence for the involvement of iron.

Phenylhydrazine and iron overload result in augmented oxidative damage and an increased likelihood of cancer. Melatonin is a well known antioxidant and free radical scavenger. The aim of this study was to determine whether melatonin would protect against phenylhydrazine-induced oxidative damage to cellular membranes and to evaluate the possible role of iron in this process. Changes in lipid peroxidation and microsomal membrane fluidity were estimated after the treatment of rats with phenylhydrazine (15 mg/kg body weight, daily, 7 days) alone and melatonin or ascorbic acid (15 mg/kg body weight, two times daily, 8 days), or their combination. Additionally, lipid peroxidation was measured in liver homogenates from untreated and melatonin or ascorbic acid-treated rats in vivo and exposed to iron in vitro. Melatonin, but not ascorbic acid, reduced phenylhydrazine-induced lipid peroxidation in vivo in spleen (3.16+/-0.06 vs. 3.83+/-0.12 nmol/mg protein, P<0.05) and plasma (7. 73+/-0.52 vs. 9.96+/-0.71 nmol/ml, P<0.05) and attenuated the decrease in hepatic microsomal membrane fluidity (1/polarization, 3. 068+/-0.007 vs. 3.027+/-0.008, P<0.05). In vitro exposure to iron significantly enhanced the lipid peroxidation in liver homogenates from untreated (3.34+/-0.75 vs. 1.25+/-0.28, P<0.05) or ascorbic acid-treated rats (2.72+/-0.39 vs. 0.88+/-0.06, P<0.05) but not from melatonin-treated rats (1.49+/-0.55 vs. 0.68+/-0.20, NS). It is concluded that free radical mechanisms are involved in the toxicity of phenylhydrazine and that the antioxidant melatonin, but not ascorbic acid, reduces the toxic affects of phenylhydrazine in vivo and of iron in vitro in cell membranes. Therefore, melatonin co-treatment in conditions of iron overload may prove beneficial.

Renal toxicity of the carcinogen delta-aminolevulinic acid: antioxidant effects of melatonin.

An increased incidence of cancer in patients suffering from acute intermittent porphyria (AIP) is thought to be related to delta-aminolevulinic acid (ALA) accumulation. Chronic treatment with ALA augmented 8-oxo-7,8-dihydro-2'-deoxyguanosine levels, decreased microsomal and mitochondrial membrane fluidity and increased lipid peroxidation in blood serum. Co-treatment with melatonin completely counteracted the effects of ALA. Melatonin effectively protects DNA and microsomal and mitochondrial membranes in rat kidney from oxidative damage due to ALA. Because of its low toxicity and anticarcinogenic properties, melatonin could be tested as an agent to reduce oxidative damage in patients with AIP.

Melatonin reduces rat hepatic macromolecular damage due to oxidative stress caused by delta-aminolevulinic acid.

Delta-aminolevulinic acid, precursor of heme, accumulates in a number of organs, especially in the liver, of patients with acute intermittent porphyria. The potential protective effect of melatonin against oxidative damage to nuclear DNA and microsomal and mitochondrial membranes in rat liver, caused by delta-aminolevulinic acid, was examined. Changes in 8-hydroxy-2'-deoxyguanosine (8-OHdG) levels, an index of DNA damage, and alterations in membrane fluidity (the inverse of membrane rigidity) and lipid peroxidation in microsomal and mitochondrial membranes, as indices of damage to lipid and protein molecules in membranes, were estimated. Measurements were made in rat liver after a 2 week treatment with delta-aminolevulinic acid (40 mg/kg b.w., every other day). To test the potential protective effects of melatonin, the indole was injected (i.p. 10 mg/kg b.w.) 3 times daily for 2 weeks. 8-OHdG levels and lipid peroxidation in microsomal membranes increased significantly whereas microsomal and mitochondrial membrane fluidity decreased as a consequence of delta-aminolevulinic acid treatment. Melatonin completely counteracted the effects of delta-aminolevulinic acid. Melatonin was highly effective in protecting against oxidative damage to DNA as well as to microsomal and mitochondrial membranes in rat liver and it may be useful as a cotreatment in patients with acute intermittent porphyria.