Reactions of the putative neurotoxin tryptamine-4,5-dione with L-cysteine and other thiols

Elevation of the serotonin-derived quinone, tryptamine-4,5-dione, in the intestine of ICR mice with dextran sulfate-induced colitis

Inflammatory bowel diseases, including Crohn's disease and ulcerative colitis, are chronic inflammatory disorders associated with oxidative stress. The intestines produce 5-hydroxytryptamine that may negatively affect disease state under inflammatory conditions when overproduced. 5-Hydroxytryptamine is a substrate for myeloperoxidase and is converted into reactive tryptamine-4,5-dione. Here, an experimental colitis model was established through oral administration of 5% dextran sulfate sodium to ICR mice for 7 days. Furthermore, the formation of tryptamine-4,5-dione in the colorectal mucosa/submucosa and colorectal tissue was analyzed by chemical and immunochemical methodologies. First, free tryptamine-4,5-dione in the homogenate was chemically trapped by o-phenylenediamine and analyzed as the stable phenazine derivative. Tryptamine-4,5-dione localization as adducted proteins in the colorectal tissue was immunohistochemically confirmed, and as demonstrated by both methods, this resulted in the significant increase of tryptamine-4,5-dione in dextran sulfate sodium-challenged mice compared with control mice. Immunohistochemical staining confirmed tryptamine-4,5-dione-positive staining at the myeloperoxidase accumulation site in dextran sulfate sodium-challenged mice colorectal tissue. The tryptamine-4,5-dione locus in the mice was partly matched with that of a specific marker for myeloperoxidase, halogenated tyrosine. Overall, the results possibly indicate that tryptamine-4,5-dione is generated by neutrophil myeloperoxidase in inflammatory tissue and may contribute to the development of inflammatory bowel disease.

Covalent adduction of endogenous and food-derived quinones to a protein: its biological significance

There are many chemically reactive compounds, including quinone, in living systems and also food. Even after the ingestion of food polyphenols, quinones derived from catechol moieties could form endogenously in the body. Dopaquinone, dopamine quinone, estrogen-derived quinones, tryptamine-4,5-dione, and ubiquinone are examples of an endogenous quinone. These indicate that quinone is ubiquitously formed or present in living systems and food. Quinones can induce a variety of hazardous effects and also could have beneficial physiological effects. This review focuses on the chemical reactivity of quinone toward a biomolecule and its biological action.

Cytotoxic and cytoprotective effects of tryptamine-4,5-dione on neuronal cells: a double-edged sword

Serotonin (5-hydroxytryptamine) is a putative substrate for myeloperoxidase, which may convert it into the reactive quinone tryptamine-4,5-dione (TD). In this study, we found that the viability of human SH-SY5Y neuroblastoma cells treated with 25 μM TD was increased to approximately 117%. On the other hand, the cell viability was significantly decreased by exposure to TD (150-200 μM), with an increase in intracellular reactive oxygen species (ROS). Interestingly, pre-treatment of SH-SY5Y cells with 100 μM TD prevented cell death and suppressed intracellular ROS generation evoked by the addition of hydrogen peroxide (H₂O₂). Expression of the phase-II antioxidant enzyme NAD(P)H: quinone oxidoreductase 1 and haem oxygenase 1 were upregulated by TD at a concentration of 50-100 μM. Nuclear factor erythroid 2-related factor 2 (Nrf2), the regulator of these enzyme, was translocated from the cytosol to the nucleus by 100 μM TD. In summary, moderate concentrations of TD may increase the self-defence capacity of neuronal cells against oxidative stress.

A novel quinone derived from 5-hydroxyindoleacetic acid reacts with protein: Possible participation of oxidation of serotonin and its metabolite in the development of atherosclerosis

The modification of 5-hydroxyindoleacetic acid (5HIAA) by myeloperoxidase with a xanthine oxidase system was investigated by chromatographic analyses. Two major products were identified as a dimer and quinone (indoleacetate dione) of 5HIAA. The formation of a quinone moiety was also confirmed by chemical trapping with o-phenylenediamine. In the presence of N-acetyl-cysteine (NAC), a quinone-NAC adduct was formed. When glyceraldehyde 3-phosphate dehydrogenase was exposed to the myeloperoxidase system with 5HIAA, quinone adducts were formed on the protein molecule. A monoclonal antibody was prepared using a quinone-modified protein as an immunogen to immunochemically detect the quinone on a protein. The established antibody recognized the quinone-NAC adduct, quinone-modified poly-L-lysine, and quinone-modified low-density lipoprotein. Quinone-modified proteins in human atherosclerotic lesions were immunohistochemically observed using the established antibody to the quinone and also a monoclonal antibody to tryptamine dione-modified protein, suggesting an occurrence of in vivo oxidation of serotonin and 5HIAA, accompanied by covalent adduction to biomolecules.

Serotonin as a putative scavenger of hypohalous acid in the brain

Neurodegenerative disorders represent the culmination of numerous insults including oxidative stress. The long etiology of most of these disorders suggests that lessening the effects of one or more of the insults could significantly delay disease onset. Antioxidants have been tested as possible therapeutics for neurodegenerative disorders, but with little success. Here we report that serotonin acts as a scavenger of hypochlorous acid (HOCl) in the brain. Serotonin was shown to prevent the oxidation of 2-thio-5-nitrobenzoate by HOCl in a biphasic manner. The first phase was a partial scavenging that occurred at concentrations of serotonin that exceeded those of HOCl. (1)H-NMR studies indicated that HOCl chlorinates both the aryl and akyl nitrogen atoms of serotonin. Thus, the oxidation of 2-thio-5-nitrobenzoate that occurred during the first phase of scavenging is likely due to the formation of serotonergic chloramines. A second phase of scavenging occurred at concentrations of HOCl that exceeded those of serotonin. Under these conditions, the chlorinated serotonin polymerized and formed inert aggregates. Serotonin was further shown to prevent the loss of cells and cellular α-ketoglutarate dehydrogenase complex activity caused by HOCl. Extracellular concentrations of serotonin in the brain can be elevated with selective serotonin reuptake inhibitors and suggests that such compounds could be used to increase the cerebral antioxidant capacity. Acute administration of selective serotonin reuptake inhibitors to mice treated with endotoxin partially mitigated sickness behavior and protein chlorination in the brain. These observations suggest that serotonin may act to suppress chlorinative stress in the brain.

Covalent modification of cytoskeletal proteins in neuronal cells by tryptamine-4,5-dione

Serotonin, 5-hydroxytryptamine, is a systemic bioactive amine that acts in the gut and brain. As a substrate of myeloperoxidase in vitro, serotonin is oxidized to tryptamine-4,5-dione (TD), which is highly reactive with thiols. In this work, we successively prepared a monoclonal antibody to quinone-modified proteins and found that the antibody preferentially recognizes the TD–thiol adduct. Using the antibody, we observed that the chloride ion, the predominant physiological substrate for myeloperoxidase in vivo, is not competitive toward the enzyme catalyzed serotonin oxidation process, suggesting that serotonin is a plausible physiological substrate for the enzyme in vivo. Immunocytochemical analyses revealed that TD staining was observed in the cytosol of SH-SY5Y neuroblastoma cells while blot analyses showed that some cellular proteins were preferentially modified. Pull-down analyses confirmed that the cytoskeletal proteins tubulins, vimentin, and neurofilament-L were modified. When pure tubulins were exposed to micromolar levels of synthetic TD, self-polymerization was initially enhanced and then suppressed. These results suggest that serotonin oxidation by myeloperoxidase or the action of other oxidants could cause functional alteration of cellular proteins, which may be related to neurodegeneration processes or irritable bowel syndrome.

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Antibody to quinone-modified protein was established and characterized.

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Modification of protein by quinone was dependent on myeloperoxidase but independent of chloride ion concentration.

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We immunochemically found that cellular proteins were preferentially modified.

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Quinone modulated polymerization of tubulins in vitro.

Amphetamine toxicities: classical and emerging mechanisms

The drugs of abuse, methamphetamine and MDMA, produce long-term decreases in markers of biogenic amine neurotransmission. These decreases have been traditionally linked to nerve terminals and are evident in a variety of species, including rodents, nonhuman primates, and humans. Recent studies indicate that the damage produced by these drugs may be more widespread than originally believed. Changes indicative of damage to cell bodies of biogenic and nonbiogenic amine-containing neurons in several brain areas and endothelial cells that make up the blood-brain barrier have been reported. The processes that mediate this damage involve not only oxidative stress but also include excitotoxic mechanisms, neuroinflammation, the ubiquitin proteasome system, as well as mitochondrial and neurotrophic factor dysfunction. These mechanisms also underlie the toxicity associated with chronic stress and human immunodeficiency virus (HIV) infection, both of which have been shown to augment the toxicity to methamphetamine. Overall, multiple mechanisms are involved and interact to promote neurotoxicity to methamphetamine and MDMA. Moreover, the high coincidence of substituted amphetamine abuse by humans with HIV and/or chronic stress exposure suggests a potential enhanced vulnerability of these individuals to the neurotoxic actions of the amphetamines.

Serotonin as a physiological substrate for myeloperoxidase and its superoxide-dependent oxidation to cytotoxic tryptamine-4,5-dione

During inflammatory events, neutrophils and platelets interact to release a variety of mediators. Neutrophils generate superoxide and hydrogen peroxide, and also discharge the haem enzyme myeloperoxidase. Among numerous other mediators, platelets liberate serotonin (5-hydroxytryptamine), which is a classical neurotransmitter and vasoactive amine that has significant effects on inflammation and immunity. In the present study, we show that serotonin is a favoured substrate for myeloperoxidase because other physiological substrates for this enzyme, including chloride, did not affect its rate of oxidation. At low micromolar concentrations, serotonin enhanced hypochlorous acid production by both purified myeloperoxidase and neutrophils. At higher concentrations, it almost completely blocked the formation of hypochlorous acid. Serotonin was oxidized to a dimer by myeloperoxidase and hydrogen peroxide. It was also converted into tryptamine-4,5-dione, especially in the presence of superoxide. This toxic quinone was produced by stimulated neutrophils in a reaction that required myeloperoxidase. In plasma, stimulated human neutrophils oxidized serotonin to its dimer using the NADPH oxidase and myeloperoxidase. We propose that myeloperoxidase will oxidize serotonin at sites of inflammation. In doing so, it will impair its physiological functions and generate a toxic metabolite that will exacerbate inflammatory tissue damage. Consequently, oxidation of serotonin by myeloperoxidase may profoundly influence inflammatory processes.

Causes and consequences of methamphetamine and MDMA toxicity

Methamphetamine (METH) and its derivative 3,4-methylenedioxymethamphetamine (MDMA; ecstasy) are 2 substituted amphetamines with very high abuse liability in the United States. These amphetamine-like stimulants have been associated with loss of multiple markers for dopaminergic and serotonergic terminals in the brain. Among other causes, oxidative stress, excitotoxicity and mitochondrial dysfunction appear to play a major role in the neurotoxicity produced by the substituted amphetamines. The present review will focus on these events and how they interact and converge to produce the monoaminergic depletions that are typically observed after METH or MDMA administration. In addition, more recently identified consequences of METH or MDMA-induced oxidative stress, excitotoxicity, and mitochondrial dysfunction are described in relation to the classical markers of METH-induced damage to dopamine terminals.

Unifying mechanism for toxicity and addiction by abused drugs: electron transfer and reactive oxygen species

Abused drugs are of grave concern throughout the world for a variety of reasons. Although impressive advances have been made, there are many unknown mechanistic aspects. This report presents a novel hypothesis based on a unifying theme for action of the major classes of abused drugs, in addition to commonly abused therapeutic drugs. The approach is based on electron transfer (ET), reactive oxygen species (ROS), and oxidative stress (OS). It is significant that physiologically active substances generally incorporate ET functionalities, either per se, or more usually in their metabolites. In order to achieve ET in vivo, the reduction potential must be more positive than -0.5 V, which is the case for metabolites of abused drugs, except for special cases. Since the ET process is catalytic, only small quantities of agent are needed for generation of large amounts of ROS during redox cycyling. Bioaction with cellular materials could entail ET alone or participation of ROS. In the abused category, among the main classes of ET functionalities are quinones and iminiums, with alpha-dicarbonyl and nitroxyl radical being rarer. Nicotine yields nicotine iminium, myosmine iminium, and DNA base iminium via alkylation by a metabolic nitrosamine. In the case of alcohol, diacetyl (an alpha-dicarbonyl) is formed, which can lead to conjugated imine (or iminium) by condensation with pri-amine of protein. Phencyclidine is unusual since the iminium product is non-conjugated. However, data indicate that the conformation present at the binding site can accommodate delocalization of the derived radical. For cocaine, various metabolites may play a role: iminium, nitroxyl radical, nitrosonium and formaldehyde. Dealkylation of the ether moiety of ecstasy provides a catechol function capable of redox cycling with the o-quinone partner. Amphetamine and methamphetamine also appear to function by way of the catechol route, as well as morphine and heroin. Tetrahydrocannabinol produces an epoxide, a functionality capable of DNA base alkylation accompanied by ROS. LSD undergoes oxidation to a phenol which may be a quinone precursor. Therapeutic drugs display the indicated metabolic relationships: benzodiazepines, iminium; phenytoin, quinone; phenobarbital, catechol; aspirin, catechol and hydroquinone; acetaminophen, iminoquinone. Extensive evidence exists for formation of ROS, organ injury by OS, depletion of AOs, and protection by AOs for the various drugs. There is also discussion of computational approaches, addiction mechanism and prevention, and health promotion.