Activator protein-1 DNA binding activation by hydrogen peroxide in neuronal and astrocytic primary cultures of trisomy-16 and diploid mice

Melatonin Synthesis and Function: Evolutionary History in Animals and Plants

Melatonin is an ancient molecule that can be traced back to the origin of life. Melatonin's initial function was likely that as a free radical scavenger. Melatonin presumably evolved in bacteria; it has been measured in both α-proteobacteria and in photosynthetic cyanobacteria. In early evolution, bacteria were phagocytosed by primitive eukaryotes for their nutrient value. According to the endosymbiotic theory, the ingested bacteria eventually developed a symbiotic association with their host eukaryotes. The ingested α-proteobacteria evolved into mitochondria while cyanobacteria became chloroplasts and both organelles retained their ability to produce melatonin. Since these organelles have persisted to the present day, all species that ever existed or currently exist may have or may continue to synthesize melatonin in their mitochondria (animals and plants) and chloroplasts (plants) where it functions as an antioxidant. Melatonin's other functions, including its multiple receptors, developed later in evolution. In present day animals, via receptor-mediated means, melatonin functions in the regulation of sleep, modulation of circadian rhythms, enhancement of immunity, as a multifunctional oncostatic agent, etc., while retaining its ability to reduce oxidative stress by processes that are, in part, receptor-independent. In plants, melatonin continues to function in reducing oxidative stress as well as in promoting seed germination and growth, improving stress resistance, stimulating the immune system and modulating circadian rhythms; a single melatonin receptor has been identified in land plants where it controls stomatal closure on leaves. The melatonin synthetic pathway varies somewhat between plants and animals. The amino acid, tryptophan, is the necessary precursor of melatonin in all taxa. In animals, tryptophan is initially hydroxylated to 5-hydroxytryptophan which is then decarboxylated with the formation of serotonin. Serotonin is either acetylated to N-acetylserotonin or it is methylated to form 5-methoxytryptamine; these products are either methylated or acetylated, respectively, to produce melatonin. In plants, tryptophan is first decarboxylated to tryptamine which is then hydroxylated to form serotonin.

Iron and mechanisms of neurotoxicity

The accumulation of transition metals (e.g., copper, zinc, and iron) and the dysregulation of their metabolism are a hallmark in the pathogenesis of several neurodegenerative diseases. This paper will be focused on the mechanism of neurotoxicity mediated by iron. This metal progressively accumulates in the brain both during normal aging and neurodegenerative processes. High iron concentrations in the brain have been consistently observed in Alzheimer's (AD) and Parkinson's (PD) diseases. In this connection, metalloneurobiology has become extremely important in establishing the role of iron in the onset and progression of neurodegenerative diseases. Neurons have developed several protective mechanisms against oxidative stress, among them, the activation of cellular signaling pathways. The final response will depend on the identity, intensity, and persistence of the oxidative insult. The characterization of the mechanisms mediating the effects of iron-induced increase in neuronal dysfunction and death is central to understanding the pathology of a number of neurodegenerative disorders.

Iron in neuronal function and dysfunction

Iron (Fe) is an essential element for many metabolic processes, serving as a cofactor for heme and nonheme proteins. Cellular iron deficiency arrests cell growth and leads to cell death; however, like most transition metals, an excess of intracellular iron is toxic. The ability of Fe to accept and donate electrons can lead to the formation of reactive nitrogen and oxygen species, and oxidative damage to tissue components; contributing to disease and, perhaps, aging itself. It has also been suggested that iron-induced oxidative stress can play a key role in the pathogenesis of several neurodegenerative diseases. Iron progressively accumulates in the brain both during normal aging and neurodegenerative processes. However, iron accumulation occurs without the concomitant increase in tissue ferritin, which could increase the risk of oxidative stress. Moreover, high iron concentrations in the brain have been consistently observed in Alzheimer's disease (AD) and Parkinson's disease (PD). In this regard, metalloneurobiology has become extremely important in understanding the role of iron in the onset and progression of neurodegenerative diseases. Neurons have developed several protective mechanisms against oxidative stress, among them the activation of cellular signaling pathways. The final response will depend on the identity, intensity, and persistence of the oxidative insult. The characterization of the mechanisms involved in high iron induced in neuronal dysfunction and death is central to understanding the pathology of a number of neurodegenerative disorders.

Selective Activation of Fyn/PI3K and p38 MAPK Regulates IL-4 Production in BMMC under Nontoxic Stress Condition

Mast cells have the ability to react to multiple stimuli, implicating these cells in many immune responses. Specific signals from the microenvironment in which mast cells reside can activate different molecular events that govern distinct mast cells responses. We previously demonstrated that hydrogen peroxide (H(2)O(2)) promotes IL-4 and IL-6 mRNA production and potentates FcepsilonRI-induced cytokine release in rat basophilic leukemia RBL-2H3 cells. To further evaluate the effect of an oxidative microenvironment (which is physiologically present in an inflammatory site) on mast cell function and the molecular events responsible for mast cell cytokine production in this environment, we analyzed the effect of H(2)O(2) treatment on IL-4 production in bone marrow-derived, cultured mast cells. Our findings show that nanomolar concentrations of H(2)O(2) induce cytokine secretion and enhance IL-4 production upon FcepsilonRI triggering. Oxidative stimulation activates a distinct signal transduction pathway that induces Fyn/PI3K/Akt activation and the selective phosphorylation of p38 MAP kinase. Moreover, H(2)O(2) induces AP-1 and NFAT complexes that recognize the IL-4 promoter. The absence of Fyn and PI3K or the inhibition of p38 MAPK activity demonstrated that they are essential for H(2)O(2)-driven IL-4 production. These findings show that mast cells can respond to an oxidative microenvironment by initiating specific signals capable of eliciting a selective response. The findings also demonstrate the dominance of the Fyn/p38 MAPK pathway in driving IL-4 production.

One molecule, many derivatives: a never-ending interaction of melatonin with reactive oxygen and nitrogen species?

Melatonin is a highly conserved molecule. Its presence can be traced back to ancient photosynthetic prokaryotes. A primitive and primary function of melatonin is that it acts as a receptor-independent free radical scavenger and a broad-spectrum antioxidant. The receptor-dependent functions of melatonin were subsequently acquired during evolution. In the current review, we focus on melatonin metabolism which includes the synthetic rate-limiting enzymes, synthetic sites, potential regulatory mechanisms, bioavailability in humans, mechanisms of breakdown and functions of its metabolites. Recent evidence indicates that the original melatonin metabolite may be N1-acetyl-N2-formyl-5-methoxykynuramine (AFMK) rather than its commonly measured urinary excretory product 6-hydroxymelatonin sulfate. Numerous pathways for AFMK formation have been identified both in vitro and in vivo. These include enzymatic and pseudo-enzymatic pathways, interactions with reactive oxygen species (ROS)/reactive nitrogen species (RNS) and with ultraviolet irradiation. AFMK is present in mammals including humans, and is the only detectable melatonin metabolite in unicellular organisms and metazoans. 6-hydroxymelatonin sulfate has not been observed in these low evolutionary-ranked organisms. This implies that AFMK evolved earlier in evolution than 6-hydroxymelatonin sulfate as a melatonin metabolite. Via the AFMK pathway, a single melatonin molecule is reported to scavenge up to 10 ROS/RNS. That the free radical scavenging capacity of melatonin extends to its secondary, tertiary and quaternary metabolites is now documented. It appears that melatonin's interaction with ROS/RNS is a prolonged process that involves many of its derivatives. The process by which melatonin and its metabolites successively scavenge ROS/RNS is referred as the free radical scavenging cascade. This cascade reaction is a novel property of melatonin and explains how it differs from other conventional antioxidants. This cascade reaction makes melatonin highly effective, even at low concentrations, in protecting organisms from oxidative stress. In accordance with its protective function, substantial amounts of melatonin are found in tissues and organs which are frequently exposed to the hostile environmental insults such as the gut and skin or organs which have high oxygen consumption such as the brain. In addition, melatonin production may be upregulated by low intensity stressors such as dietary restriction in rats and exercise in humans. Intensive oxidative stress results in a rapid drop of circulating melatonin levels. This melatonin decline is not related to its reduced synthesis but to its rapid consumption, i.e. circulating melatonin is rapidly metabolized by interaction with ROS/RNS induced by stress. Rapid melatonin consumption during elevated stress may serve as a protective mechanism of organisms in which melatonin is used as a first-line defensive molecule against oxidative damage. The oxidative status of organisms modifies melatonin metabolism. It has been reported that the higher the oxidative state, the more AFMK is produced. The ratio of AFMK and another melatonin metabolite, cyclic 3-hydroxymelatonin, may serve as an indicator of the level of oxidative stress in organisms.

alpha-Lipoic acid and N-acetyl cysteine prevent zinc deficiency-induced activation of NF-kappaB and AP-1 transcription factors in human neuroblastoma IMR-32 cells

This work investigated the capacity of alpha-lipoic acid (LA) and N-acetyl-L-cysteine (NAC) to reduce zinc deficiency-induced oxidative stress, and prevent the activation of nuclear factor-kappaB (NF-kappaB) and activator protein-1 (AP-1), and the cross-talk between both activated cascades through beta-Transducin Repeat-containing Protein (beta-TrCP). IMR-32 cells were incubated in control media or media containing variable concentrations of zinc, without or with 0.5 mM LA or 1 mM NAC. Relative to control and zinc supplemented (15 microM Zn) groups, Hydrogen peroxide (H(2)O(2)) and total oxidant cell concentrations were higher, and total glutathione concentrations were lower in the zinc deficient groups (1.5 and 5 microM Zn). Both, LA and NAC, markedly reduced the increase in cell oxidants and the reduction in glutathione concentrations in the zinc deficient cells. Consistent with this, LA and NAC prevented zinc deficiency-induced activation of the early steps of NF- kappaB (IkappaBalpha phosphorylation) and AP-1 [c-Jun-N-terminal kinase (JNK) and p38 phophorylation] cascades, and the high NF-kappaB- and AP-1-DNA binding activities in total cell extracts. Thus, LA and NAC can reduce the oxidative stress associated with zinc deficiency and the subsequent triggering of NF-kappaB- and AP-1-activation in neuronal cells.

Regulation of the human taurine transporter by oxidative stress in retinal pigment epithelial cells stably transformed to overexpress aldose reductase

In diabetes, overexpression of aldose reductase (AR) and consequent glucose-induced impairment of antioxidant defense systems may predispose to oxidative stress and the development of diabetic complications, but the mechanisms are poorly understood. Taurine (2-aminoethanesulfonic acid) functions as an antioxidant, osmolyte, and calcium modulator such that its intracellular depletion could promote cytotoxicity in diabetes. The relationships of oxidative stress and basal AR gene expression to Na+-taurine cotransporter (TT) gene expression, protein abundance, and TT activity were therefore explored in low AR-expressing human retinal pigment epithelial (RPE) 47 cells and RPE 47 cells stably transformed to overexpress AR (RPE 75). Changes in TT gene expression were determined using a 4.6-kb TT promoter-luciferase fusion gene. Compared with RPE 47 cells, in high AR-expressing RPE 75 cells, TT promoter activity was decreased by 46%, which was prevented by an AR inhibitor. TT promoter activity increased up to 900% by prooxidant exposure, which was associated with increased TT peptide abundance and taurine transport. However, induction of TT promoter activity by oxidative stress was attenuated in high AR-expressing cells and partially corrected by AR inhibitor. Finally, exposure of RPE 75 cells to high glucose increased oxidative stress, but down-regulated TT expression. These studies demonstrate for the first time that the TT is regulated by oxidative stress and that overexpression of AR and high glucose impair this response. Abnormal expression of AR may therefore impair antioxidant defense, which may determine tissue susceptibility to chronic diabetic complications.

Redox state alteration modulates astrocyte glucuronidation

We have investigated the effects of mild oxidative conditions on drug-metabolizing enzyme activity in rat cultured astrocytes. These experimental conditions promoting an oxidative environment were obtained by short exposure to a low concentration of menadione (5 microM) for a short duration (15 min). This resulted in the rapid and transient production of reactive oxygen species (+130%), associated with a decrease in GSH cellular content (-24%), and an increase in total protein oxidation (+26%), but promoted neither PGE(2) nor NO production. This treatment induced a rapid and persistent decrease in astrocyte glucuronidation activities, which was totally prevented by N-acetyl-l-cysteine. These oxidative conditions also affected the specific UGT1A6 activity measured in transfected V79-1A6 cells. Finally, the subsequent recovery of astrocyte glucuronidation activity may result from upregulation of UGT1A6 expression (+62%) as shown by RT-PCR and gene reporter assay. These results show that the catalytic properties and expression of cerebral UGT1A6 are highly sensitive to the redox environment. The protective effect of N-acetyl-l-cysteine suggests both a direct action of reactive oxygen species on the protein and a more delayed action on the transcriptional regulation of UGT1A6. These results suggest that cerebral metabolism can be altered by physiological or pathological redox modifications.

Heparin-binding epidermal growth factor-like growth factor and intestinal ischemia-reperfusion injury

Intestinal ischemia/reperfusion (I/R) injury affects patients of different ages, especially premature babies and the elderly. The outcome after intestinal I/R is often dismal, which may be attributed to loss of the barrier and immune functions of the intestines, as well as development of secondary injury in remote organs. The available treatment for advanced gut ischemia mandates extensive resection, which may cause growth retardation in infants and nutritional problems in the elderly. Throughout the past decade we have been investigating the potential therapeutic role of heparin-binding epidermal growth factor-like factor (HB-EGF) in intestinal I/R. The mitogenic and chemoattractant functions of HB-EGF formed the initial rationale for our investigations. In addition, HB-EGF is a potent antiapoptotic protein that enables cells and tissues exposed to different apoptotic stimuli to survive hypoxic, oxidative, and nutritional stresses. HB-EGF is known to have a vital role in wound healing and postischemic regeneration in different organs. In the current review, we summarize the results of our findings of the beneficial effects of HB-EGF in intestinal I/R, supported by additional evidence from the literature and an explanation of different possible mechanisms of its actions. Collectively, the data strongly suggest a potential therapeutic role for the use of HB-EGF to treat intestinal ischemic diseases such as I/R and necrotizing enterocolitis.

Sp1 and Sp3 are oxidative stress-inducible, antideath transcription factors in cortical neurons

Neuronal cell death in response to oxidative stress may reflect the failure of endogenous adaptive mechanisms. However, the transcriptional activators induced by oxidative stress in neurons that trigger adaptive genetic responses have yet to be fully elucidated. We report that basal DNA binding of the zinc finger transcription factors Sp1 and Sp3 is unexpectedly low in cortical neurons in vitro and is significantly induced by glutathione depletion-induced or hydrogen peroxide-induced oxidative stress in these cells. The increases in Sp1/Sp3 DNA binding reflect, in part, increased levels of Sp1 and Sp3 protein in the nuclei of cortical neurons. Similar induction of Sp1 and Sp3 protein is also observed in neurons in vivo in a chemical or a genetic model of Huntington's disease, two rodent models in which neuronal loss has been attributed to oxidative stress. Sustained high-level expression of full-length Sp1 or full-length Sp3, but not the Sp1 zinc finger DNA-binding domain alone, prevents death in response to oxidative stress, DNA damage, or both. Taken together, these results establish Sp1 and Sp3 as oxidative stress-induced transcription factors in cortical neurons that positively regulate neuronal survival.

AP-1 activation through endogenous H(2)O(2) generation by alveolar macrophages

Reactive oxygen species released during the respiratory burst are known to participate in cell signaling. Here we demonstrate that hydrogen peroxide produced by the respiratory burst activates AP-1 binding. Stimulation of the macrophage cell line NR8383 with respiratory burst agonists ADP and C5a increased AP-1 binding activity. Importantly, this increase in binding was blocked by catalase, confirming mediation by endogenous H(2)O(2). Moreover, exogenously added H(2)O(2) mimicked the agonists, and also activated AP-1. Antibodies revealed that the activated AP-1 complex is composed predominantly of c-Fos/c-Jun heterodimers. Treatment of the cells with ADP, C5a and H(2)O(2) (100 microM) all increased the phosphorylation of c-Jun. c-Fos protein was increased in cells treated with C5a or high dose (200 microM) H(2)O(2), but not in cells treated with ADP. The MEK inhibitor, PD98059, partially blocked the C5a-mediated increase in AP-1 binding. A novel membrane-permeable peptide inhibitor of JNK, JNKi, also inhibited AP-1 activation. Together these data suggest that C5a-mediated AP-1 activation requires both the activation of the ERK and JNK pathways, whereas activation of the JNK pathway is sufficient to increase AP-1 binding with ADP. Thus, AP-1 activation joins the list of pathways for which the respiratory burst signals downstream events in the macrophage.

Therapeutic effect of dimethyl sulfoxide on ICAM-1 gene expression and activation of NF-kappaB and AP-1 in septic rats

BACKGROUND

Dimethyl sulfoxide (DMSO) is a potent antioxidant which protects against endotoxemia and septic shock in animal models. We investigated the therapeutic effect of DMSO on intercellular adhesion molecule 1 (ICAM-1) gene expression and activation of nuclear factor-kappaB (NF-kappaB) and activating protein-1 (AP-1) in a rat model of peritonitis sepsis. This postchallenge model simulates the clinical treatment of ruptured viscus peritonitis.

MATERIALS AND METHODS

Peritonitis was produced by subjecting rats to laparotomy, followed by a 1-cm cecal incision (CI) to produce fecal soilage of the peritoneum. Rats were subjected to laparotomy only for the sham-operated group. For the protection study, DMSO (6 ml/kg) was injected ip at 30, 60, or 90 min post-CI surgery. The levels of ICAM-1 mRNA expression and activation of NF-kappaB and AP-1 in livers were determined at 3 and 6 h post-CI.

RESULTS

At 3 h post-CI surgery (early sepsis), DMSO treatment at 30 and 60 min post-CI surgery significantly inhibited sepsis-induced ICAM-1 mRNA expression and activation of NF-kappaB and AP-1. DMSO has no effect on ICAM-1 gene expression and activation of NF-kappaB and AP-1 when administered at 90 min post-CI surgery. At 6 h post-CI surgery (late sepsis), DMSO administered at 30, 60, or 90 min post-CI surgery significantly inhibited ICAM-1 mRNA expression and NF-kappaB activation but not AP-1 activation.

CONCLUSIONS

Therapeutic treatment of DMSO inhibited sepsis-induced activation of NF-kappaB and AP-1, resulting in the suppression of ICAM-1 gene expression in the livers of peritonitis septic rats. This finding suggests that reactive oxidants are involved in the signal transduction pathways for activation of NF-kappaB and AP-1. Thus, antioxidants which inhibit NF-kappaB and AP-1 activation may be beneficial in treating sepsis and septic shock.