Fas/Fas ligand regulation mediates cell death in human Ewing's sarcoma cells treated with melatonin

Background:

Despite recent advances in cancer therapy, the 5-year survival rate for Ewing's sarcoma is still very low, and new therapeutic approaches are necessary. It was found previously that melatonin induces cell death in the Ewing's sarcoma cell line, SK-N-MC, by activating the extrinsic apoptotic pathway.

Methods:

Melatonin actions were analysed by metabolic viability/survival cell assays, flow cytometry, quantitative PCR for mRNA expression, western blot for protein activation/expression and electrophoretic mobility shift assay for transcription factor activation.

Results:

Melatonin increases the expression of Fas and its ligand Fas L, this increase being responsible for cell death induced by the indolamine. Melatonin also produces a transient increase in intracellular oxidants and activation of the redox-regulated transcription factor Nuclear factor-kappaB. Inhibition of such activation prevents cell death and Fas/Fas L upregulation. Cytotoxic effect and Fas/Fas L regulation occur in all Ewing's cell lines studied, and do not occur in the other tumour cell lines studied where melatonin does not induce cell death.

Conclusion:

Our data offers new insights in the study of alternative therapeutic strategies in the treatment of Ewing's sarcoma. Further attention deserves to be given to the differences in the cellular biology of sensitive tumours that could explain the cytotoxic effect of melatonin and the increase in the level of free radicals caused by this molecule, in particular cancer types.

Antioxidants do not prevent acrylonitrile-induced toxicity

Several reports have recently described that acrylonitrile (ACN) toxicity resides in its capacity for inducing oxidative stress. ACN can be conjugated with glutathione (GSH), diminishing its cellular content, or being metabolized to cyanide. In the present report, we determine the effect of ACN on the viability of primary-cultured astrocytes as well as the oxidative damage generated by ACN by measuring GSH levels in primary cultured astrocytes. We also analyzed whether the ACN (2.5mM) toxicity could be avoided by using antioxidants such as taurine (5mM), N-acetylcysteine (20 mM), trolox (100 microM), estradiol (10 microM) and melatonin (100 nM-1mM). In this cell culture model, antioxidants were not able to prevent ACN-induced cell damage, with the exception of NAC, confirming that only GSH seems to play a key role in ACN-derived toxicity. Additionally, we measured different parameters of oxidative stress such as catalase activity, lipid peroxidation and GSH concentration, as indicators of the potential oxidative stress mediated by the toxicity of ACN, after exposure of Wistar rats to a concentration of 200 ppm ACN for 14 days. At the concentration assayed, we did not find any evidence of oxidative damage in the brain of ACN-treated rats.

Molecular characterization of ciprofloxacin resistance of gonococcal strains in Spain

BACKGROUND

Over the past several years, the emergence of gonococcal isolates with intermediate or full resistance to fluoroquinolones has become a significant concern in several countries, including Spain.

GOAL

The goal was to determine the occurrence of ciprofloxacin resistance among Neisseria gonorrhoeae strains in Spain during 2000 to 2001 and determine the frequency and patterns of mutations at gyrA, gyrB, and parC genes in these isolates.

STUDY DESIGN

Eleven ciprofloxacin-resistant strains (with MICs ranging from 1 to 64 micrograms/mL) and two intermediate isolates (with MICs of 0.12 and 0.5 microgram/mL) were found. Mutations were identified by polymerase chain reaction and direct sequencing of the amplified products.

RESULTS AND CONCLUSIONS

Alterations at Ser-91 and Asp-95 in GyrA were detected in all strains except one, an isolate for which the MIC was 0.12 microgram/mL. Alterations in ParC were more variable, and there was no clear correlation between the number of parC mutations and the level of resistance. No alterations at gyrB gene associated with ciprofloxacin resistance were found. The resistance was distributed among different types of strains, suggesting that the increase in the incidence of ciprofloxacin-resistant strains in Spain was not exclusively due to the appearance of a single-strain outbreak.

Glutamate induces oxidative stress not mediated by glutamate receptors or cystine transporters: protective effect of melatonin and other antioxidants

Glutamate is responsible for most of the excitatory synaptic activity and oxidative stress induction in the mammalian brain. This amino acid is increased in the substantia nigra in parkinsonism due to the lack of dopamine restraint to the subthalamic nucleus. Parkinson's disease also shows an increase of iron levels in the substantia nigra and a decrease of glutathione, the antioxidant responsible for the ascorbate radical recycling. Considered together, these facts could make the antioxidant ascorbate behave as a pro-oxidant in parkinsonism. Since both glutamate and ascorbate are present in the synaptosomes and neurons of substantia nigra, we tested 1) if glutamate is able to induce oxidative stress independently of its excitatory activity, and 2) if ascorbate may have synergistic effects with glutamate when these two molecules co-exist. Brains were homogenized in order to disrupt membranes and render membrane receptors and intracellular signaling pathways non-functional. In these homogenates glutamate induced lipid peroxidation, indicating that this amino acid also may cause oxidative stress not mediated by its binding to glutamate receptors or cystine transporters. Ascorbate also induced lipid peroxidation thus behaving as a pro-oxidant. Both substances together produced an additive effect but they did not synergize. Given that melatonin is a potent physiological antioxidant with protective effects in models of neurotoxicity, we tested the role of this secretory product on the pro-oxidant effect of both compounds given separately or in combination. We also checked the protective ability of several other antioxidants. Pharmacological doses of melatonin (millimolar), estrogens, pinoline and trolox (micromolar) prevented the oxidant effect of glutamate, ascorbate, and the combination of both substances. Potential therapeutic application of these results is discussed.

Ultrastructural confirmation of neuronal protection by melatonin against the neurotoxin 6-hydroxydopamine cell damage

6-Hydroxydopamine (6-OHDA) is a neurotoxin used in the induction of experimental Parkinson's disease in both animals and cultured neuronal cells. Biochemical and molecular approaches showed previously that low doses of 6-OHDA induced apoptosis in PC12 cells, while high doses of this neurotoxin induced necrosis. Melatonin has been shown to protect against the neuronal programmed cell death induced by 6-OHDA, although it was not able to prevent the massive necrotic cellular death occurring after the addition of high doses of the neurotoxin. In the present work, we demonstrate by ultrastructural analysis that although low doses of 6-OHDA induced apoptosis in PC12 cells, it also damaged the non-apoptotic cells, morphologically corresponding this damage to incipient and reversible necrotic lesions. When the doses of the neurotoxin increase, there are still apoptotic cells, although most of the cells show necrotic irreversible lesions. We also found that melatonin partially prevents the incipient necrotic lesions caused by low doses of 6-OHDA. The fact that melatonin was shown in previous work to prevent apoptosis caused by low doses of 6-OHDA, but not necrosis induced by high doses of the neurotoxin, seemed to indicate that this agent is only able to protect against apoptosis. However, our present results, melatonin preventing also the incipient necrotic neuronal lesions, suggest that this hormone may provide a general protection against cell death, suggesting that higher doses should be tried in order to prevent the necrotic cell death induced by high doses of the neurotoxin.

Melatonin decreases mRNA for histone H4 in thymus of young rats

The antiproliferative properties of melatonin have been previously demonstrated for several normal and tumoral tissues. In a recent report we have shown that melatonin is able to inhibit programmed cell death in thymus both, in vivo and in vitro. Given that other authors have related programmed cell death and cell proliferation and that no previous reports on melatonin and cell division exist on thymus, we decide to study the possible antiproliferative effect of melatonin in this organ measured as the levels of mRNA for the histone H4. We found that melatonin inhibits cell division on thymus when administered chronically both, at high (500 microg/body weight) and low (50 microg/body weight) dose. We also found a circadian rhythm of the mRNA for histone H4, opposed to the one previously described for melatonin, supporting the negative regulation by this hormone of cell division on thymus. A single dose of melatonin (50 microg/body weight) was not able to decrease the levels of mRNA for H4 in the time-points studied but after two hours of its administration. Finally, we report the inhibitory effect of melatonin in the cell proliferation of Harderian gland, brain, lung and kidney.

Inhibition of cell proliferation: a mechanism likely to mediate the prevention of neuronal cell death by melatonin

In a previous work we demonstrated that melatonin is able to prevent apoptosis induced by low doses of 6-hydroxydopamine (6-OHDA) in undifferentiated and neuronal PC12 cells. We also reported how this neurohormone was able to prevent the decrease in the mRNA for antioxidant enzymes caused by 6-OHDA. Although the antioxidant capability of melatonin seems to be clearly implicated in its antiapoptotic activity, literature suggests that its antiproliferative property could also be involved in its prevention of apoptosis. In the present work we demonstrated that melatonin is able to inhibit cell proliferation in undifferentiated PC12 cells, decreasing cell number and the total amount of DNA, and the mRNA for the histone H4, which are known to increase during DNA synthesis. Melatonin does not decrease the number of cells in nonproliferating PC12 cells, indicating that it does not cause cell death. Additionally, we demonstrate that other inhibitors of cell proliferation, as well as other antioxidants, are able to mimic the antiapoptotic effect of melatonin. This is interpreted to mean that melatonin acts by both mechanisms to inhibit apoptosis caused by 6-OHDA and the findings support the hypothesis of a relationship between oxidative stress and regulation of the cell cycle.

Melatonin increases gene expression for antioxidant enzymes in rat brain cortex

During the last years several reports have demonstrated that melatonin is a efficient free radical scavenger and general antioxidant. In addition, it has been shown that this neurohormone is able to increase the activity of glutathione peroxidase in rat brain cortex as well as the gene expression for some antioxidant enzymes in the Harderian gland of female Syrian hamster. Also, it is well known that brain cells are particularly exposed to free radicals, with antioxidant enzymes as the major defense mechanism that the brain uses to neutralize reactive oxygen species. The aim of the present study was to examine the influence of melatonin on gene expression for antioxidant enzymes in rat brain cortex. Our results clearly demonstrate that exogenously administered melatonin increases the levels of mRNA for glutathione peroxidase, copper-zinc superoxide dismutase, and manganese superoxide dismutase in this tissue. These stimulatory effects are observed after both acute and chronic treatment with this hormone, producing in the latter case the more marked increase. We therefore conclude that melatonin exerts an important role in providing indirect protection against free radical injury by stimulating gene expression for antioxidant enzymes. Consequently, melatonin could be considered as a potential therapeutic agent in some age-related neurodegenerative diseases where excessive free radical production has been implicated.

Antioxidative protection in a high-melatonin organism: the dinoflagellate Gonyaulax polyedra is rescued from lethal oxidative stress by strongly elevated, but physiologically possible concentrations of melatonin

Lethal oxidative stress was investigated in the dinoflagellate Gonyaulax polyedra by measuring the dying-peak of bioluminescence during circadian phases of low physiological light emission, low bioluminescence capacity, and low sensitivity to stimulatory agents. Measurements were carried out in constant darkness after transfer of cells from light at CT 6 (circadian time, 0600 hr). H2O2 (0.08 mM), when administered 1 hr after transfer of cells, led to a multifold, long-lasting enhancement of light emission, which is typical for lethal cell damage. At the circadian phases of investigation, melatonin did not substantially stimulate bioluminescence up to concentrations of 0.5 mM. At this concentration, addition of melatonin prevented the dying-peak and reduced bioluminescence to almost basal values. The high concentration of melatonin applied is not unphysiological in Gonyaulax, because the indoleamine can increase to levels of several millimolar, e.g., in response to temperature signals. These protective effects of melatonin seem to be caused mainly by the direct action of melatonin as an antioxidant, because the major enzymes of antioxidative protection were not stimulated by melatonin, although some of them responded to H2O2. The activities of neither superoxide dismutase, hemoperoxidase/catalase, glutathione peroxidase, nor haloperoxidase were enhanced under the influence of melatonin; glutathione S-transferase activity increased only slightly.

Androgen-dependent mast cell degranulation in the Harderian gland of female Syrian hamsters: in vivo and organ culture evidence

In previous articles we have reported the "disappearance" of Harderian gland mast cells (HGMC) after treatment with testosterone. In the present work we study: (a) if the apparent decrease in the number of mast cells caused by this androgen is real or is due to the fact that testosterone induces mast cell degranulation that avoids its recognition by toluidine blue staining; (b) if testosterone acts through its receptor directly on the Harderian gland (HG). In order to give an answer to the first question, we observed HG of female Syrian hamsters treated with testosterone under the electron microscope to find the possible degranulated mast cells not recognizable with the aid of the toluidine blue staining. We also studied in vivo and in vitro the effects of the beta-agonists isoproterenol and salbutamol, given that they increase cAMP and can therefore prevent degranulation of mast cells. Finally we have used cytocalasin B, which inhibits degranulation by blocking actin depolimerization. Both the beta-agonists and cytochalasin B were able to prevent the decrease of mast cells, as recognized by staining with toluidine blue after treatment with testosterone. Indeed, when observed under the electron microscope, abundant degranulated mast cells were found after treatment with testosterone. For solving the second issue we analyzed the effect of the antiandrogen cyproterone acetate in vivo and in vitro. Our results demonstrate that testosterone is able to induce degranulation of HGMC in the Syrian hamster Mesocricetus auratus and that this effect is achieved directly through its receptor on the Harderian gland.

Isolation and identification of sex-specific cDNA clones from the Syrian hamster harderian gland

Syrian hamster Harderian glands show a typical sexual dimorphism, with males having two secretory cell types and females having one cell type and intraluminal porphyrin accretions, among other differences. Since these differences may be due to the expression of specific genes, our interest is to identify those genes and their role on the development and control of the sexual dimorphism. The experimental approach was to construct cDNA libraries for male and female Syrian hamster Harderian glands and then subtracted libraries for male vs. female and for female vs. male. By this method, cDNA libraries enriched either in male-specific or in female-specific clones were obtained. Clones from those libraries were checked for differential expression by using double colony hybridization with [32P]-cDNA from male and female glands. Then, the selected clones were checked again for expression in Harderian glands by Northern hybridization, using poly(A+) RNA from males, castrated males, and females. Finally, the clones were sequenced and compared to search for significant homologies. One of the male-specific clones showed strong homology with rat cytochrome p450b/e. Among the female-specific clones, homologies were found to the complement C3 fragment from several species, to sequences from the mouse mammary tumor virus, and to the subunits C1 and C2 of the rat prostatic steroid binding protein. Several other clones showed no significant homologies and need further characterization.

Neurohormone melatonin prevents cell damage: effect on gene expression for antioxidant enzymes

It is well known that porphyrins cause a toxic light-mediated effect due to their capability to generate free radicals. Several reports have proved that melatonin is a potent free radical scavenger. The aim of this work has been to study the ability of melatonin to prevent the cell damage caused by porphyrins in the Harderian gland of female Syrian hamsters. Cell injury was evaluated estimating the percentage of damaged cells found in the gland and analyzing the degree of this damage at ultrastructural level. To explain the mechanism by which this hormone could prevent the cell damage caused by porphyrins, its capability to both decrease porphyrin synthesis and increase the mRNA levels for antioxidant enzymes was evaluated. Our results demonstrate that melatonin administration decreases the percentage of damaged cells, porphyrin synthesis, and aminolevulinate synthase (ALA-S) mRNA levels and increases the mRNA levels for manganese superoxide-dismutase and copper-zinc superoxide dismutase. When observed under an electron microscope, the lesions in the clear cells of the treated females were much less severe than in the corresponding cells of the control animals. Melatonin exerts a cytoprotective effect by inhibiting the ALA-S gene expression (and so porphyrin synthesis) and by raising the mRNA levels for several antioxidant enzymes.

Castration increases cell damage induced by porphyrins in the Harderian gland of male Syrian hamster. Necrosis and not apoptosis mediates the subsequent cell death

It is known that the Harderian gland of male Syrian hamster synthesizes a much smaller amount of porphyrins than the gland of the female and that castration greatly increases this synthesis. We have studied in this experimental model the behavior of the different classes of secretory cells and their role in the synthesis of porphyrins, attempting to clarify the participation of these compounds in the cell damage leading to the formation of clear cells previously described in the gland of females. We have also investigated the mechanism underlying the death of these secretory cells after porphyrin accumulation (necrosis vs apoptosis). To achieve this, we have utilized the following techniques: (a) morphometrical; (b) ultrastructural; (c) biochemical (fluorescence spectrophotometry); and (d) molecular (DNA nick-end labeling in methacrylate sections and dot blot analysis). The glands from male hamsters (serving as control) present a very low rate of damaged cells that progressively rises after castration. This rise runs parallel to that of porphyrin synthesis, porphyrin deposits, and the decrease of Type II secretory cells. The damage and subsequent death of the secretory cells in the gland is produced by the deposit of porphyrins in the mitochondrial membrane. This porphyrin accumulation leads to a complete mitochondrial destruction that finally results in cell death and its secretion into the lumen. We finally conclude that this event is not a physiological cell death (apoptosis) but the consequence of the toxic accumulation of porphyrins (necrosis).

The pineal neurohormone melatonin prevents in vivo and in vitro apoptosis in thymocytes

Recently, melatonin was found to be the most potent physiological free radical scavenger known to date. In this work, we attempted to define the role this neurohormone plays in the regulation of apoptosis, since the effect of bcl-2, the main gene implicated in its inhibition, acts via an antioxidant mechanism. We investigated the role of melatonin in cell death of thymus, a well known model for the study of apoptosis. Two sets of experiments were carried out: in vivo experiments, performed with Wistar rats, and in vitro experiments, performed with primary cultures of young Wistar rat thymocytes treated with glucocorticoids in order to induce apoptosis. Morphometrical studies in semithin sections of thymus and analysis of DNA fragmentation by gel electrophoresis show that physiological apoptosis occurring in thymus of 65 days old rats, is prevented by the daily administration of melatonin beginning when the rats were 25 days old. Also, we found that at a concentration of 10(-7) M, melatonin decreases by 35% the percentage of apoptotic cells induced by glucocorticoids in cultured thymocytes of 25 day old rats. 10(-9) M melatonin decreases cell death by 20%. Finally, melatonin at 10(-11) M did not have any effect. Several hypothesis are discussed to explain this effect: direct interaction of melatonin with glucocorticoid receptors in the thymus; induction of interleukin-4 release; direct genomic action modulating the expression of apoptosis-inhibiting genes; an effect on nitric oxide synthase; and finally, the antioxidant action of melatonin. Since apoptosis is a possible mechanism involved in neuronal death shown in several neurodegenerative diseases such as Parkinson or Alzheimer's diseases, investigative efforts should be directed to the possible role of melatonin in inhibiting cell death in tissues other that the thymus. Melatonin might be a potent therapeutic agent in some of these conditions.

Androgen regulation of gene expression in the Syrian hamster Harderian gland

The androgenic control of sexual dimorphism has been studied in the Harderian gland from Syrian hamster and compared to rat Harderian gland, a system without dimorphism. Hybridization in situ with a rat cDNA clone has revealed the presence of androgen receptor mRNA in all secretory cells from male and female hamster glands. Testosterone or 5-alpha-dihydrotestosterone administration to females both caused a 60% decrease in the levels of 5-aminolevulinate synthase mRNA after 1 day of treatment, but the resulting patterns of in vitro translation using RNA from glands treated with the two androgens are different. Testosterone alters the mRNA levels for androgen receptor and 5-aminolevulinate synthase in the glands only 6 h after its implantation in females, and the action is maintained up to 10 days of treatment. Finally, androgen administration to females or deprivation in males alter androgen receptor but not 5-aminolevulinate synthase mRNA levels in rat Harderian glands. Our results suggest that the androgen receptor from Harderian glands is responsible for the sexual dimorphism found in Syrian hamsters, whereas the lack of sexual dimorphism in rat seems to be due to a restricted effect of androgens in the glands.

Porphyrin accumulation in the harderian glands of female Syrian hamster results in mitochondrial damage and cell death

BACKGROUND

The Harderian glands of female Syrian hamsters contain very high concentrations of protoporphyrin (in the range of micrograms per mg of tissue) which accumulate in the tubulo-alveoli of the gland. We have studied the process of synthesis, accumulation, and secretion of this cyclic compound by the secretory cells of the hamster Harderian glands.

METHODS

The animals used were female Syrian hamster of 15, 35, 75, 180, and 360 days of age. Items first examined were (1) percentage of the "clear cells," (2) area occupied by intraluminal porphyrins, and (3) histological characteristics of "clear cells" by light and transmission electron microscopy (TEM). In a second study the total content of porphyrins was determined. Finally, the levels of mRNA for the enzyme aminolevulinate synthase (ALV-S) were measured.

RESULTS

In the glands of female hamsters, both the tissue concentration and the intraluminal area occupied by protoporphyrin correlate with the appearance of a special type of cell (clear cells) which show signs of cell degeneration. In addition, the expression of the gene for ALV-S, which is the limiting enzyme in porphyrin production, also parallels the relative number of clear cells. Analyzed under TEM, these clear cells display dilated mitochondria and short and swollen endoplasmic reticulum cisternae. In a late phase of necrosis, the nuclear envelope appears disorganized with scarce chromatin. The mitochondria undergo complete destruction, resulting in electron-dense bacillary formations which progressively coalesce in large and dense areas of protoporphyrin. The cell dies after this accumulation, being secreted by a "cytogen" mechanism.

CONCLUSIONS

In view of our results, the Harderian gland of female Syrian hamster may provide a useful model for the study of the mechanism by which the anomalous accumulation of protoporphyrin induces cell damage in human protoporphyria.

Development and androgen regulation of the secretory cell types of the Syrian hamster (Mesocricetus auratus) Harderian gland

The secretory cell types of the hamster Harderian glands were studied in both male and female Syrian hamsters. As previously demonstrated, female hamsters showed a single secretory cell type (type I), while male hamsters displayed two secretory cell types (type I and type II). Type-II cells were observed after the first month of age correlating with the increase in testosterone levels. The administration of testosterone to adult female hamsters resulted in a marked increase in the percentage of type-II cells without a significant increase in the number of mitotic figures. Very low levels of serum testosterone were able to maintain the percentage of type-II cells. Castration of male hamsters produced a decrease in the percentage of type-II cells. This drop correlated with the reduction in serum testosterone levels. The chronic administration of a luteinizing hormone-releasing hormone agonist to male Syrian hamsters induced a significant reduction in both serum luteinizing hormone and testosterone. However, the percentage of type-II cells was similar to that of control hamsters suggesting that very low levels of circulating testosterone are able to maintain the percentage of type-II cells. In a final experiment male Syrian hamsters were treated with the antiandrogen cyproterone acetate. No changes were observed in the percentage of type-II cells, whereas serum luteinizing hormone and testosterone levels were significantly modified. We concluded that (1) type-II cells differentiate from type-I cells; (2) gonadal androgens are the major factor controlling this differentiation; and (3) the disappearance of type-II cells after androgen deprivation occurs through holocrine and apocrine mechanisms.(ABSTRACT TRUNCATED AT 250 WORDS)

Lymphoid cells in the harderian gland of the rodent Octodon degus

The Harderian gland of the degu (Octodon degus) is composed of tubulo-alveolar secretory units that share most of morphological features found in the Harderian glands of other rodents. However, a peculiar characteristic observed in the glands of female degus is the existence of lymphoid cell clusters within the connective tissue surrounding the secretory adenomeres. Lymphocytes and lymphoblasts are found associated with blood vessels and especially with nerve bundles in the medullary region of the gland. Occasionally, macrophages and plasma cells are also observed. Although the Golgi apparatus appears well developed, the ultrastructural characteristics of most of these lymphoid elements correspond to those of inactive lymphocytes. Unmyelinated fibers containing clear and dense-core vesicles are found closely related to lymphocytes. On some occasions, lymphocytes present extensive areas of apposition with structures resembling intercellular junctions. The analogy of the lymphoid clusters reported in this study with those described in the avian Harderian gland is discussed.

The pineal gland of the trumpet-tailed rat (Octodon degus)

The structure and ultrastructure of the pineal gland of the degu or trumpet-tailed rat (Octodon degus), a rodent inhabiting tropical-equatorial areas, was examined under light and electron microscopy. On the basis of its form, size, and location, the pineal gland of the degu is classified as a proximal or "A" type. The connective tissue appeared poorly developed and the gland contained non-fenestrated capillaries. A single population of typical pinealocytes was found. In addition, a small number of glial cells and cells with electron dense bodies appeared scattered throughout the gland. Cells with dense granules were found isolated or forming small groups always in close proximity to blood vessels. Numerous sympathetic nerve fibers with small dense-core vesicles were found. Also, some myelinated nerve fibers were observed. The physiological significance of the presence of large electron-dense granules in some pineal cells and their particular location around the blood vessels in discussed.