Role of diacetyl metabolite in alcohol toxicity and addiction via electron transfer and oxidative stress

Evaluation of the cytotoxicity and genotoxicity potential of synthetic diacetyl food flavoring in silico, in vivo, and in vitro

Diacetyl is a common ingredient that creates a buttery flavor in baked goods and other food products. The cytotoxic impact of diacetyl on a normal human liver cell line (THLE2) indicated an IC₅₀ value of 41.29 mg/ml through MTT assay and a cell cycle arrest in the G₀/G₁ phase relative to the control. Administration of diacetyl at two-time points (acute-chronic) led to a significant increase in DNA damage indicated by the increase in tail length, tail DNA%, and tail moment. The mRNA and protein expression levels of genes in the rats' livers were then measured using real-time PCR and western blotting. The results showed an activation of the apoptotic and necrosis mechanism, with an upregulation of p53, Caspase 3, and RIP1 and a downregulation of Bcl-2 at the mRNA level. The ingestion of diacetyl disrupted the liver's oxidant/antioxidant balance, as evidenced by alterations in levels of GSH, SOD, CAT, GPx, GR, MDA, NO, and peroxynitrite. Additionally, heightened levels of inflammatory cytokines were shown. Histopathological examinations revealed necrotic foci and congested portal areas in the rats' liver cells after treatment with diacetyl. Diacetyl may interact moderately with Caspase, RIP1, and p53 core domain through In-silico, possibly resulting in upregulated gene expression.

Elevated levels of α-dicarbonyl compounds in the plasma of type II diabetics and their relevance with diabetic nephropathy

The presence of α‑dicarbonyl compounds (α-DCs) in vivo has been associated with the development of complications of diabetes mellitus (DM) and also with other chronic diseases. Therefore, quantitative analysis of α-DCs in body fluids is crucial to understand their roles in the formation of these chronic diseases. We established in this study a practical HPLC-UV method to measure 3‑deoxyglucosone (3-DG), glyoxal (GO), methylglyoxal (MGO), diacetyl (DA), and pentane‑2,3‑dione (PD) in blood plasma using 4‑(2,3‑dimethyl‑6‑quinoxalinyl)‑1,2‑benzenediamine (DQB) as a derivatizing reagent. The derivatizing reaction could be carried out quickly under mild conditions and the HPLC determination is simple, sensitive, and easy to operate. The recoveries of the α-DCs are between 85.26% and 110.20% (intra-day) and 87.25% and 103.18% (inter-day); the RSDs are between 1.28% and 5.69% (intra-day) and 2.26% and 6.34% (inter-day). We found the plasma levels of 3-DG, GO, and MGO in the diabetic patients are all significantly higher than those in healthy subjects. The results also show that the contents of GO and MGO in diabetic nephropathy (DN) patients are both significantly higher than those in simple T2DM patients. Moreover, it is found for the first time that the plasma level of GO might be a potential predictor of DN. The developed method would be useful for the measurements of the plasma α-DCs and the data acquired could be informative in the diagnosis of DM complications.

Platelet Endothelial Cell Adhesion Molecule-1 and Oligodendrogenesis: Significance in Alcohol Use Disorders

Alcoholism is a chronic relapsing disorder with few therapeutic strategies that address the core pathophysiology. Brain tissue loss and oxidative damage are key components of alcoholism, such that reversal of these phenomena may help break the addictive cycle in alcohol use disorder (AUD). The current review focuses on platelet endothelial cell adhesion molecule 1 (PECAM-1), a key modulator of the cerebral endothelial integrity and neuroinflammation, and a targetable transmembrane protein whose interaction within AUD has not been well explored. The current review will elaborate on the function of PECAM-1 in physiology and pathology and infer its contribution in AUD neuropathology. Recent research reveals that oligodendrocytes, whose primary function is myelination of neurons in the brain, are a key component in new learning and adaptation to environmental challenges. The current review briefly introduces the role of oligodendrocytes in healthy physiology and neuropathology. Importantly, we will highlight the recent evidence of dysregulation of oligodendrocytes in the context of AUD and then discuss their potential interaction with PECAM-1 on the cerebral endothelium.

Determination of Diacetyl in Beer by a Precolumn Derivatization-HPLC-UV Method Using 4-(2,3-Dimethyl-6-quinoxalinyl)-1,2-benzenediamine as a Derivatizing Reagent

Diacetyl is an important flavoring compound in many foods, especially in beer. In the present study, we developed and validated a new precolumn derivatization HPLC-UV method for the determination of diacetyl using 4-(2,3-dimethyl-6-quinoxalinyl)-1,2-benzenediamine as a novel derivatizing reagent. After derivatization with the reagent at a pH value 4.0 at ambient temperature for 10 min, diacetyl was analyzed on an ODS column and detected at 254 nm. The results show that the correlation coefficient of the method is 0.9991 in the range of 0.10 to 100.0 μM diacetyl, and the limit of detection is 0.02 μM. The method was further evaluated in the analysis of beer samples with the recoveries ranging from 94.4 to 102.6% and RSDs from 1.36 to 3.33%. The concentrations of diacetyl in 8 beer samples were determined in the range of 0.19 to 0.42 μM. The method established in this study may be well suitable for the determination of diacetyl in beer.

Human dehydrogenase/reductase (SDR family) member 11 is a novel type of 17β-hydroxysteroid dehydrogenase

We report characterization of a member of the short-chain dehydrogenase/reductase superfamily encoded in a human gene, DHRS11. The recombinant protein (DHRS11) efficiently catalyzed the conversion of the 17-keto group of estrone, 4- and 5-androstenes and 5α-androstanes into their 17β-hydroxyl metabolites with NADPH as a coenzyme. In contrast, it exhibited reductive 3β-hydroxysteroid dehydrogenase activity toward 5β-androstanes, 5β-pregnanes, 4-pregnenes and bile acids. Additionally, DHRS11 reduced α-dicarbonyls (such as diacetyl and methylglyoxal) and alicyclic ketones (such as 1-indanone and loxoprofen). The enzyme activity was inhibited in a mixed-type manner by flavonoids, and competitively by carbenoxolone, glycyrrhetinic acid, zearalenone, curcumin and flufenamic acid. The expression of DHRS11 mRNA was observed widely in human tissues, most abundantly in testis, small intestine, colon, kidney and cancer cell lines. Thus, DHRS11 represents a novel type of 17β-hydroxysteroid dehydrogenase with unique catalytic properties and tissue distribution.

S-Glutathionylation and Redox Protein Signaling in Drug Addiction

Drug addiction is a chronic relapsing disorder that comes at a high cost to individuals and society. Therefore understanding the mechanisms by which drugs exert their effects is of prime importance. Drugs of abuse increase the production of reactive oxygen and nitrogen species resulting in oxidative stress. This change in redox homeostasis increases the conjugation of glutathione to protein cysteine residues; a process called S-glutathionylation. Although traditionally regarded as a protective mechanism against irreversible protein oxidation, accumulated evidence suggests a more nuanced role for S-glutathionylation, namely as a mediator in redox-sensitive protein signaling. The reversible modification of protein thiols leading to alteration in function under different physiologic/pathologic conditions provides a mechanism whereby change in redox status can be translated into a functional response. As such, S-glutathionylation represents an understudied means of post-translational protein modification that may be important in the mechanisms underlying drug addiction. This review will discuss the evidence for S-glutathionylation as a redox-sensing mechanism and how this may be involved in the response to drug-induced oxidative stress. The function of S-glutathionylated proteins involved in neurotransmission, dendritic spine structure, and drug-induced behavioral outputs will be reviewed with specific reference to alcohol, cocaine, and heroin.

Application of gas-diffusion microextraction to solid samples using the chromatographic determination of α-diketones in bread as a case study

For the first time, gas-diffusion microextraction was used for the direct analysis of solid samples (vicinal diketones in bread).

Methylglyoxal is associated with bacteriostatic activity of high fructose agave syrups

Three α-ketoaldehydes, potentially present in high fructose agave syrups (HFASs) as intermediates of the Maillard reaction, were determined. A previously reported HPLC-FLD procedure based on pre-column derivatisation with 4-methoxy-o-phenylenediamine was adopted, yielding the method quantification limits 0.11 mg/kg, 0.10mg/kg, 0.09 mg/kg for glyoxal, methylglyoxal (MGo) and diacetyl, respectively. The obtained results revealed high concentrations of methylglyoxal in HFASs (average 102 ± 91 mg/kg, range 15.6-315 mg/kg) as compared to commercial Mexican bee honeys or corn syrups. Hydrogen peroxide was generated in all HFASs upon dilution, yet to less extent than in bee honeys. HFASs presented bacteriostatic activity against Bacillus subtilis and Escherichia coli; catalase addition had minimum effect on the assay results in syrups with elevated MGo. Principal component analysis revealed direct association between growth inhibition and MGo. It is concluded that elevated concentration of MGo in HFASs is at least in part responsible for their non-peroxide bacteriostatic activity.

Diacetyl: occurrence, analysis, and toxicity

Diacetyl possesses a butter-like flavor and has been widely used as a flavoring agent. It forms from sugars and lipids via various bacteria and heat treatment in various foods and beverages, such as milk. The toxicity of diacetyl, especially when inhaled, has recently attracted the attention not only of consumers but also of regulatory agencies. Even though accurate quantitative analysis of diacetyl is extremely important in evaluating its possible adverse effects, precise quantitative analysis of diacetyl in foods and beverages, as well as in ambient air, is considerably difficult because it is highly reactive and soluble in water. Among the many analytical methods developed for measuring diacetyl, preparation of 2,3-dimethylquinoxaline followed by gas chromatography has been most commonly used in the analysis of various foods, beverages, and air samples. This mini-review summarizes the formation mechanisms, analytical methods, occurrence, and toxicity of diacetyl.

Radical acylation of L-lysine derivatives and L-lysine-containing peptides by peroxynitrite-treated diacetyl and methylglyoxal

Highly electrophilic α-dicarbonyls such as diacetyl, methylglyoxal, 3-deoxyglucosone, and4,5-dioxovaleric acid have been characterized as secondary catabolites that can aggregate proteins and form DNA nucleobase adducts in several human maladies, including Alzheimer's disease, rheumatoid arthritis, diabetes, sepsis, renal failure, and respiratory distress syndrome. In vitro, diacetyl and methylglyoxal have also been shown to rapidly add up the peroxynitrite anion (k2 ~ 10(4)-10(5) M(-1) s(-1)), a potent biological nucleophile, oxidant and nitrosating agent, followed by carbon chain cleavage to carboxylic acids via acetyl radical intermediate that can modify amino acids. In this study, we used the amino acid derivatives Ac-Lys-OMe and Z-Lys-OMe and synthesized the tetrapeptides H-KALA-OH, Ac-KALA-OH, and H-K(Boc)ALA-OH to reveal the preferential Lys amino group targeted by acyl radical generated by the α-dicarbonyl/peroxynitrite system. The pH profiles of the reactions are bell-shaped, peaking at approximately 7.5; hence, they are close to the pKa values of ONOOH and of the catalytic H2PO4(-) anion. RP-HPLC and ESI-MS analyses of reaction products confirmed (α)N- and (ϵ)N-acetylation of Lys by diacetyl as well as acetylation and formylation by methylglyoxal, with preference for the α-amino group. These data suggest the possibility of radical acylation of proteins in epigenetic processes, where enzymatic acetylation of these biomolecules is a well-documented event, recently reported to be as critical to the cell cycle as phosphorylation. Also noteworthy is the observed formylation of L-Lys containing peptides by methylglyoxal never reported to occur in amino acid residues of peptides and proteins.

High-performance liquid chromatography determination of glyoxal, methylglyoxal, and diacetyl in urine using 4-methoxy-o-phenylenediamine as derivatizing reagent

Bioanalytical relevance of glyoxal (Go) and methylglyoxal (MGo) arises from their role as biomarkers of glycation processes and oxidative stress. The third compound of interest in this work is diacetyl (DMGo), a component of different food products and alcoholic beverages and one of the small α-ketoaldehydes previously reported in urine. The original idea for the determination of the above compounds by reversed phase high-performance liquid chromatography (HPLC) with fluorimetric detection was to use 4-methoxy-o-phenylenediamine (4MPD) as a derivatizing reagent and diethylglyoxal (DEGo) as internal standard. Acetonitrile was added to urine for matrix precipitation, and derivatization reaction was carried out in the diluted supernatant at neutral pH (40 °C, 4 h); after acidification, salt-induced phase separation enabled recovery of the obtained quinoxalines in the acetonitrile layer. The separation was achieved within 12 min using a C18 Kinetex column and gradient elution. The calibration detection limits for Go, MGo, and DMGo were 0.46, 0.39, and 0.28 μg/L, respectively. Within-day precision for real-world samples did not exceed 6%. Several urine samples from healthy volunteers, diabetic subjects, and juvenile swimmers were analyzed. The sensitivity of the procedure proposed here enabled detection of differences between analyte concentrations in urine from patients at different clinical or exposure-related conditions.

Structures of Saccharomyces cerevisiae D-arabinose dehydrogenase Ara1 and its complex with NADPH: implications for cofactor-assisted substrate recognition

Here, crystal structures of Ara1 in apo and NADPH-complexed forms are presented at 2.10 and 2.00 Å resolution, respectively.

The primary role of yeast Ara1, previously mis-annotated as a d-arabinose dehydrogenase, is to catalyze the reduction of a variety of toxic α,β-dicarbonyl compounds using NADPH as a cofactor at physiological pH levels. Here, crystal structures of Ara1 in apo and NADPH-complexed forms are presented at 2.10 and 2.00 Å resolution, respectively. Ara1 exists as a homodimer, each subunit of which adopts an (α/β)₈-barrel structure and has a highly conserved cofactor-binding pocket. Structural comparison revealed that induced fit upon NADPH binding yielded an intact active-site pocket that recognizes the substrate. Moreover, the crystal structures combined with computational simulation defined an open substrate-binding site to accommodate various substrates that possess a dicarbonyl group.

Respiratory and olfactory cytotoxicity of inhaled 2,3-pentanedione in Sprague-Dawley rats

Flavorings-related lung disease is a potentially disabling disease of food industry workers associated with exposure to the α-diketone butter flavoring, diacetyl (2,3-butanedione). To investigate the hypothesis that another α-diketone flavoring, 2,3-pentanedione, would cause airway damage, rats that inhaled air, 2,3-pentanedione (112, 241, 318, or 354 ppm), or diacetyl (240 ppm) for 6 hours were sacrificed the following day. Rats inhaling 2,3-pentanedione developed necrotizing rhinitis, tracheitis, and bronchitis comparable to diacetyl-induced injury. To investigate delayed toxicity, additional rats inhaled 318 (range, 317.9-318.9) ppm 2,3-pentanedione for 6 hours and were sacrificed 0 to 2, 12 to 14, or 18 to 20 hours after exposure. Respiratory epithelial injury in the upper nose involved both apoptosis and necrosis, which progressed through 12 to 14 hours after exposure. Olfactory neuroepithelial injury included loss of olfactory neurons that showed reduced expression of the 2,3-pentanedione-metabolizing enzyme, dicarbonyl/L-xylulose reductase, relative to sustentacular cells. Caspase 3 activation occasionally involved olfactory nerve bundles that synapse in the olfactory bulb (OB). An additional group of rats inhaling 270 ppm 2,3-pentanedione for 6 hours 41 minutes showed increased expression of IL-6 and nitric oxide synthase-2 and decreased expression of vascular endothelial growth factor A in the OB, striatum, hippocampus, and cerebellum using real-time PCR. Claudin-1 expression increased in the OB and striatum. We conclude that 2,3-pentanedione is a respiratory hazard that can also alter gene expression in the brain.

Development and validation of a high-performance liquid chromatography method for the determination of diacetyl in beer using 4-nitro-o-phenylenediamine as the derivatization reagent

Diacetyl is a natural byproduct of fermentation and known to be an important flavor compound in many food products. Because of the potential undesirable effects of diacetyl on health safety and beer flavor, determination of its concentration in beer samples is essential and its analytical methods have attracted close attention recently. The aim of the present work is to develop and validate a novel high-performance liquid chromatography method for the quantification of diacetyl in beer based on the derivatization reaction of diacetyl with 4-nitro-o-phenylenediamine (NPDA). After the derivatization with NPDA in pH 3.0 at 45 °C for 20 min, diacetyl was separated on a kromasil C(18) column at room temperature in the form of the resulting 6-nitro-2,3-dimethylquinoxaline and detected by the ultraviolet detector at 257 nm. The results showed that the correlation coefficient for the method was 0.9992 in the range of 0.0050-10.0 mg L(-1) and the limit of detection was 0.0008 mg L(-1) at a signal-to-noise ratio of 3. The applicability of the proposed method was evaluated in the analysis of beer samples with the recovery range of 94.0-99.0% and relative standard deviation range of 1.20-3.10%. The concentration levels of diacetyl detected in beer samples from 12 brands ranged from 0.034 to 0.110 mg L(-1). The proposed method showed efficient chromatographic separation, excellent linearity, and good repeatability that can be applied to quantification of diacetyl in beer samples.

Moderate ethanol ingestion, redox status, and cardiovascular system in the rat

Moderate intake of alcoholic beverages decreases the incidence of cardiovascular pathologies, but it is in dispute if cardioprotective effects are due to ethanol, to polyphenolic compounds present in beverages or to a combination of both. In humans, effects of high, moderate, and low doses of alcoholic beverages are widely studied, but effects of pure alcohol remain unclear. On the other hand, experiments with laboratory animals are centered on high toxicological doses of ethanol but not on low doses. In the present study, we have aimed to mimic in the rat the pattern of alcohol intake in Mediterranean population. Alcohol ingestion is spread along the day and not always related to solid food consumption. We tried to define the beneficial and harmful effects of pure ethanol ingestion without polyphenol's influence. Experimental rats were given 1% ethanol in their drinking water for 30 days, resulting in a daily ingestion of 0.27 mL of ethanol/rat/d. Ethanol ingestion did not cause deleterious effects on the general status of the animals, but it decreased cholesterol, triglycerides, and catecholamine stores' rate of utilization in peripheral sympathetic system. Moreover, ethanol lowered pulmonary arterial pressure and did not alter systemic arterial pressure. In the liver, the reduced glutathione/oxidized glutathione ratio was augmented and lipid peroxide, superoxide dismutase, and glutathione peroxidase activities were decreased. However, catalase activity was unaltered. Liver cytochrome P4502E1 distribution and protein level and activity were unchanged by ethanol ingestion. Data indicate a lack of harmful effects and underscore a set of potentially beneficial effects of this dose of ethanol.

Dermal toxicity and environmental contamination: electron transfer, reactive oxygen species, oxidative stress, cell signaling, and protection by antioxidants

Large numbers of chemicals are known to produce diverse types of skin injury, and these substances fit into a wide variety of both organic and inorganic chemical classes. Skin contact with toxins is difficult to avoid, because they are widely distributed, e.g., in industrial substances, agricultural chemicals, household products, and plants. Although various hypotheses have been advanced, there is no universal agreement as to how dermal toxins act to produce their effects. In this review, we provide evidence and numerous literature citations to support the view that oxidative stress (OS) and electron transfer (ET) comprise a portion of a key mechanism, and perhaps unifying theme that underlie the action of dermatotoxins. We apply the concept that ET and OS are key elements in the induction of dermatotoxic effects to all of the main classes of toxins, and to other toxins, as well. We believe it is not coincidental that the vast majority of dermatotoxic substances incorporate recurrent ET chemical functionalities (i.e., quinone, metal complexes, ArNO2, or conjugated iminium), either per se or as metabolites; such entities potentially give rise to reactive oxygen species (ROS) by redox cycling. However, in some categories, wherein agents cause dermal damage, e.g., peroxides and radiation, it appears that ROS are generated by non-ET routes. As expected, if ET and oxidative process do constitute the mechanistic framework by which most dermal toxins act, then antioxidants (AOs), if present, should prevent or mitigate effects. This is exactly what has been discovered to occur. Because ET and OS either cause or contribute to dermal toxicity, and AOs may offer protection therefrom, policy makers and researchers may be better positioned to prevent human dermatotoxicity.

Electron transfer as a potential cause of diacetyl toxicity in popcorn lung disease

Diacetyl, a butter-flavoring component, has recently attracted scientific and media attention because it has been implicated as an agent that induces popcorn lung disease in exposed plant workers. This disease, officially referred to as bronchiolitis obliterans, entails exposure-induced compromise to the lung's epithelial barrier function. In this review, we present a novel molecular mechanism (electron transfer, ET) designed to explain how diacetyl and its imine derivatives might interact to produce lung damage. We relate the fact that diacetyl and related compounds possess reduction potentials amenable to electron transfer (ET) in vivo. The electrochemical nature of these toxicants can potentially disrupt normal ET processes, generate reactive oxygen species (ROS), and participate in cell signaling events. Condensation of diacetyl with protein may also play a role in the toxicity caused by this compound. ET is a common feature of toxic substances, usually involving their metabolites which can operate per se or through reactions that generate ROS and oxidative stress (OS). Examples of agents capable of ET are quinone and metal compounds, aromatic nitro compounds, and iminium salts. Among compounds that generate ET, the alpha-dicarbonyl ET class, of which diacetyl is a member, is much less studied. This review emphasizes diacetyl as an agent that acts through oxidative processes to cause its effects. However, we also treat related substances that appear to act by a similar mechanism. This mechanism forms a theoretical framework capable of describing the mechanism by which diacetyl may induce its effects and is in accord with various physiological activities displayed by other alpha-dicarbonyl substances. Examples of substances that may act by mechanisms similar to that displayed by diacetyl include cyclohexane-1,2-dione, marinopyrroles, reactive carbonyl species, the bacterial signaling agent DPD, and advanced glycation end products.

A fluorescent probe for diacetyl detection

A water-soluble fluorescent probe, rhodamine B hydrazide (RBH), was prepared and its properties for recognition of diacetyl were studied. The method employs the reaction of diacetyl with RBH, a colorless and non-fluorescent rhodamine B spiro form derivative to give a pink-colored fluorescent substance. In weakly acidic media, RBH reacts more selectively with diacetyl than with other carbonyls, causing a large increase in fluorescence intensity and thereby providing an easy assay for the determination of diacetyl.

Radical acetylation of 2'-deoxyguanosine and L-histidine coupled to the reaction of diacetyl with peroxynitrite in aerated medium

Diacetyl, like other alpha-dicarbonyl compounds, is reportedly cytotoxic and genotoxic. A food and cigarette contaminant, it is related with alcohol hepatotoxicity and lung disease. Peroxynitrite is a potent oxidant formed in vivo by the diffusion-controlled reaction of the superoxide radical anion with nitric oxide, which is able to form adducts with carbon dioxide and carbonyl compounds. Here, we investigate the nucleophilic addition of peroxynitrite to diacetyl forming acetyl radicals, whose reaction with molecular oxygen leads to acetate. Peroxynitrite is shown to react with diacetyl in phosphate buffer (bell-shaped pH profile with maximum at 7.2) at a very high rate constant ( k 2 = 1.0 x 10 (4) M (-1) s (-1)) when compared with monocarbonyl substrates ( k 2 < 10 (3) M (-1) s (-1)). Phosphate ions (100-500 mM) do not affect the rate of spontaneous peroxynitrite decay, but the H 2PO 4 (-) anion catalyzes the nucleophilic addition of the peroxynitrite anion to diacetyl. The intermediacy of acetyl radicals is suggested by a three-line spectrum ( a N = a H = 0.83 mT) obtained by EPR spin trapping of the reaction mixture with 2-methyl-2-nitrosopropane. The peroxynitrite reaction is accompanied by concentration-dependent oxygen uptake. Stoichiometric amounts of acetate from millimolar amounts of peroxynitrite and diacetyl were obtained under nonlimiting conditions of dissolved oxygen. In the presence of either l-histidine or 2'-deoxyguanosine, the peroxynitrite/diacetyl system afforded the corresponding acetylated molecules identified by HPLC-MS ( n ). These studies provide evidence that the peroxynitrite/diacetyl reaction yields acetyl radicals and raise the hypothesis that protein and DNA nonenzymatic acetylation may occur in cells and be implicated in aging and metabolic disorders in which oxygen and nitrogen reactive species are putatively involved.

Ototoxicity and noise trauma: electron transfer, reactive oxygen species, cell signaling, electrical effects, and protection by antioxidants: practical medical aspects

Ototoxins are substances of various structures and classes. This review provides extensive evidence for involvement of electron transfer (ET), reactive oxygen species (ROS) and oxidative stress (OS) as a unifying theme. Successful application is made to the large majority of ototoxins, as well as noise trauma. We believe it is not coincidental that these toxins generally incorporate ET functionalities (quinone, metal complex, ArNO(2), or conjugated iminium) either per se or in metabolites, potentially giving rise to ROS by redox cycling. Some categories, e.g., peroxides and noise, appear to operate via non-ET routes in generating OS. These highly reactive entities can then inflict injury via OS upon various constituents of the ear apparatus. The theoretical framework is supported by the extensive literature on beneficial effects of antioxidants, both for toxins and noise. Involvement of cell signaling and electrical effects are discussed. This review is the first comprehensive one based on a unified mechanistic approach. Various practical medical aspects are also addressed. There is extensive documentation for beneficial effects of antioxidants whose use might be recommended clinically for prevention of ototoxicity and noise trauma. Recent research indicates that catalytic antioxidants may be more effective. In addition to ototoxicity, a widespread problem consists of ear infections by bacteria which are demonstrating increasing resistance to conventional therapies. A recent, novel approach to improved drugs involves use of agents which inhibit quorum sensors that play important roles in bacterial functioning. Prevention of ear injury by noise trauma is also discussed, along with ear therapeutics.

The dual face of endogenous alpha-aminoketones: pro-oxidizing metabolic weapons

Amino metabolites with potential prooxidant properties, particularly alpha-aminocarbonyls, are the focus of this review. Among them we emphasize 5-aminolevulinic acid (a heme precursor formed from succinyl-CoA and glycine), aminoacetone (a threonine and glycine metabolite), and hexosamines and hexosimines, formed by Schiff condensation of hexoses with basic amino acid residues of proteins. All these metabolites were shown, in vitro, to undergo enolization and subsequent aerobic oxidation, yielding oxyradicals and highly cyto- and genotoxic alpha-oxoaldehydes. Their metabolic roles in health and disease are examined here and compared in humans and experimental animals, including rats, quail, and octopus. In the past two decades, we have concentrated on two endogenous alpha-aminoketones: (i) 5-aminolevulinic acid (ALA), accumulated in acquired (e.g., lead poisoning) and inborn (e.g., intermittent acute porphyria) porphyric disorders, and (ii) aminoacetone (AA), putatively overproduced in diabetes mellitus and cri-du-chat syndrome. ALA and AA have been implicated as contributing sources of oxyradicals and oxidative stress in these diseases. The end product of ALA oxidation, 4,5-dioxovaleric acid (DOVA), is able to alkylate DNA guanine moieties, promote protein cross-linking, and damage GABAergic receptors of rat brain synaptosome preparations. In turn, methylglyoxal (MG), the end product of AA oxidation, is also highly cytotoxic and able to release iron from ferritin and copper from ceruloplasmin, and to aggregate proteins. This review covers chemical and biochemical aspects of these alpha-aminoketones and their putative roles in the oxidative stress associated with porphyrias, tyrosinosis, diabetes, and cri-du-chat. In addition, we comment briefly on a side prooxidant behaviour of hexosamines, that are known to constitute building blocks of several glycoproteins and to be involved in Schiff base-mediated enzymatic reactions.

Unifying mechanism for bacterial cell signalers (4,5-dihydroxy-2,3-pentanedione, lactones and oligopeptides): Electron transfer and reactive oxygen species. Practical medical features

Cell signaling has attracted much attention involving higher organisms, and more recently is of considerable interest concerning involvement in the bacterial realm. Many aspects can apply, including quorum sensing. Of the participating molecules, designated autoinducers, 4,5-dihydroxy-2,3-pentanedione (DPD) is one of the most important. It is in equilibrium with a furanone and a furanosyl-borate diester (AI-2). A prior hypothesis for cell signaling in higher organisms invoked a key role for electron transfer (ET) and reactive oxygen species (ROS), as well as conduits, relays and electrical effects. The principal ET functionalities are quinones, metal complexes, ArNO(2), and iminium species. A lesser known type is the alpha-dicarbonyl class. Diacetyl, a member, as well as its imine derivatives, can serve as a model for DPD, since the parent possesses a reduction potential amenable to ET in the biological domain. Hence, it is conceivable that DPD and its imine derivatives may be involved in ET-ROS processes. Presence of hydroxy groups should facilitate ET by DPD vs. diacetyl. Extensive prior literature supports participation of ET functionalities in action of therapeutic drugs, toxins and various illnesses. This biochemical behavior also applies to the alpha-dicarbonyl parent models. A second important bacterial autoinducer is the lactone category. Although ET functionality is lacking, the presence of the 1,3-dicarbonyl structure can provide a site for avid chelation with redox metal, e.g., iron or copper, followed by ET-ROS. Findings with added iron furnish support for the proposal. Oligopeptides comprise the third principal type of bacterial signaling agent. A prior review incorporates these within the theoretical framework based on ET by redox amino acids and redox enzymes. In recent years there has been a rapid increase in resistance to antibiotics by pathogenic bacteria. Infectious diseases are the leading cause of death worldwide and the third leading cause in the US. An alternate approach to antibiotics that are becoming less and less effective is to attenuate bacterial virulence. Bacterial infections appear to be importantly associated with biofilm formation. Since quorum sensors play a crucial role in this connection, they provide attractive targets for much-needed, novel approaches. Two of the main autoinducers investigated are the AHL and AI-2 systems. This review summarizes the literature, mostly recent, on this topic. Leads are provided by higher organisms that appear to have evolved means for disrupting bacterial cell communication and, hence, escape colonization. The main types in this category are the furanones, for which both natural and synthetic types have been investigated with promising results.

α,β-dicarbonyl reduction by Saccharomyces d-arabinose dehydrogenase

An alpha,beta-dicarbonyl reductase activity was purified from Saccharomyces cerevisiae and identified as the cytosolic enzyme D-Arabinose dehydrogenase (ARA1) by MALDI-TOF/TOF. Size exclusion chromatography analysis of recombinant Ara1p revealed that this protein formed a homodimer. Ara1p catalyzed the reduction of the reactive alpha,beta-dicarbonyl compounds methylglyoxal, diacetyl, and pentanedione in a NADPH dependant manner. Ara1p had apparent Km values of approximately 14 mM, 7 mM and 4 mM for methylglyoxal, diacetyl and pentanedione respectively, with corresponding turnover rates of 4.4, 6.9 and 5.9 s(-1) at pH 7.0. pH profiling showed that Ara1p had a pH optimum of 4.5 for the diacetyl reduction reaction. Ara1p also catalyzed the NADP+ dependant oxidation of acetoin; however this back reaction only occurred at alkaline pH values. That Ara1p was important for degradation of alpha,beta-dicarbonyl substrates was further supported by the observation that ara1-Delta knockout yeast mutants exhibited a decreased growth rate phenotype in media containing diacetyl.

Novel electrochemical approach to enhanced toxicity of 4-oxo-2-nonenal vs. 4-hydroxy-2-nonenal (role of imine): Oxidative stress and therapeutic modalities

Reactive oxygen species (ROS) and oxidative stress (OS) have received increasing attention in connection with illness, disease, and aging. The OS results in widespread attack of body constituents, with unsaturated lipids, leading to hydroperoxides, being a focus of research. Subsequent decomposition yields various functionalized aldehydes, including 4-hydroxy-2-nonenal (HNE). OS linked to HNE is associated with various illnesses. Recently, much attention has been devoted to 4-oxo-2-nonenal (ONE), also a product from lipid hydroperoxide decomposition. ROS and OS are increasingly implicated in the mode of action of drugs and toxins. The preponderance of bioactive substances or their metabolites incorporate electron transfer (ET) functionalities, among which are imines or iminiums. Also, in this category are the less well-known alpha-dicarbonyls. ET moieties undergo redox cycling accompanied by generation of ROS. Electrochemistry, a neglected area, can provide valuable insight. If the reduction potential is more positive than -0.5 V, then ET reactions are a possibility in vivo. Both HNE and ONE participate in Michael addition reactions with protein nucleophiles. The process occurs at a faster rate with ONE due mainly to the high reactivity toward His and Cys. The greater toxicity of ONE vs. HNE may partly reflect this difference. Also, ONE forms Schiff base (imine) at a faster rate than HNE, which also may contribute to the difference in toxicity. Electrochemistry of alpha-dicarbonyls and their imine derivatives can elucidate basic mechanisms. Methylglyoxal possesses a reduction potential of -0.18 V, amenable to ET in vivo. Since ONE is a vinylog of methylglyoxal, redox cycling should be even more facile. Another model is diacetyl whose reduction potential is also favorable. In contrast, crotonaldehyde, a model for the HNE vinylog, is characterized by a quite negative reduction potential, unsuitable for ET; acrolein is included. Imines of alpha-dicarbonyls serve as models for Schiff bases from ONE. The diimines in acid have reduction potentials of -0.45 to -0.49 V. Diacetyl monoxime, an oximino analog of the vinylogous ONE mono Schiff base, possesses a similar value. The ONE vinylogs should exhibit even better electrochemical characteristics. Thus, these neglected electrochemical properties can help rationalize the greater toxicity of ONE vs. HNE. Toxicity of the aldehydes may be countered by various approaches: formation of non-toxic imines, carboxylic acids, and Michael adducts. Genetic methods and AO therapy are treated.

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.