Oxidation of hydroquinone by myeloperoxidase. Mechanism of stimulation by benzoquinone.

Myeloperoxidase (MPO) is a prime candidate for mediating the inflammatory tissue damage of neutrophils because it converts Cl- to the potent oxidant hypochlorous acid. It also oxidizes xenobiotics to reactive free radicals. We have found that the kinetics of oxidation of hydroquinone by myeloperoxidase are inadequately explained by the classical peroxidase mechanism. Peroxidation of hydroquinone displayed a distinct lag phase, which was practically abolished by excluding O2 and was eliminated by adding benzoquinone at the start of the reaction. Superoxide dismutase increased the rate of peroxidation by 40% but did not eliminate the lag phase. Spectral investigations revealed that during the initial phase of the reaction, MPO was converted to oxy-MPO, or compound III, by a mechanism that was not reliant on superoxide. Benzosemiquinone, however, was able to convert ferric-MPO to compound III. Both compound III and ferro-MPO reacted with benzoquinone to regenerate ferric-MPO. We propose that the lag phase occurs because benzosemiquinone reduces ferric-MPO to ferro-MPO, which rapidly binds O2 to form compound III. Since compound III is outside the peroxidation cycle, conversion of hydroquinone to benzoquinone is retarded. However, as benzoquinone accumulates, it oxidizes ferro-MPO and compound III to ferric-MPO, thereby increasing the rate of peroxidation. There is a minimal lag phase under an atmosphere of N2 because ferro-MPO would be rapidly oxidized by benzoquinone, without formation of compound III. We conclude that when substrates produce radicals capable of reducing ferric-MPO, they will be peroxidized efficiently only if oxy-MPO is readily recycled. Furthermore, these radicals will prevent MP3+ from reacting with H2O2, and thereby prevent the enzyme from oxidizing Cl- to hypochlorous acid. Thus, this mechanism could be exploited to prevent hypochlorous acid-mediated inflammatory tissue damage.     

Oxidation of hydroquinone, 2,3-dimethylhydroquinone and 2,3,5-trimethylhydroquinone by human myeloperoxidase

Myeloperoxidase is very susceptible to reducing radicals because the reduction potential of the ferric/ferrous redox couple is much higher compared with other peroxidases. Semiquinone radicals are known to reduce heme proteins. Therefore, the kinetics and spectra of the reactions of p-hydroquinone, 2,3-dimethylhydroquinone and 2,3,5-trimethylhydroquinone with compounds I and II were investigated using both sequential-mixing stopped-flow techniques and conventional spectrophotometric measurements. At pH 7 and 15 degrees C the rate constants for compound I reacting with p-hydroquinone, 2,3-dimethylhydroquinone and 2,3,5-trimethylhydroquinone were determined to be 5.6+/-0.4 x 10(7) M(-1)s(-1), 1.3+/-0.1 x 10(6) M(-1)s(-1) and 3.1+/-0.3 x 10(6) M(-1)s(-1), respectively. The corresponding reaction rates for compound II reduction were calculated to be 4.5+/-0.3 x 10(6) M(-1)s(-1), 1.9+/-0.1 x 10(5) M(-1)s(-1) and 4.5+/-0.2 x 10(4) M(-1)s(-1), respectively. Semiquinone radicals, produced by compounds I and II in the classical peroxidation cycle, promote compound III (oxymyeloperoxidase) formation. We could monitor formation of ferrous myeloperoxidase as well as its direct transition to compound II by addition of molecular oxygen. Formation of ferrous myeloperoxidase is shown to depend strongly on the reduction potential of the corresponding redox couple benzoquinone/semiquinone. With 2,3-dimethylhydroquinone and 2,3,5-trimethylhydroquinone as substrate, myeloperoxidase is extremely quickly trapped as compound III. These MPO-typical features could have potential in designing specific drugs which inhibit the production of hypochlorous acid and consequently attenuate inflammatory tissue damage.     

Oxidation of hydroquinone, 2,3-dimethylhydroquinone and 2,3,5-trimethylhydroquinone by human myeloperoxidase

Abstract

Myeloperoxidase is very susceptible to reducing radicals because the reduction potential of the ferric/ferrous redox couple is much higher compared with other peroxidases. Semiquinone radicals are known to reduce heme proteins. Therefore, the kinetics and spectra of the reactions of p-hydroquinone, 2,3-dimethylhydroquinone and 2,3,5-trimethylhydroquinone with compounds I and II were investi-gated using both sequential-mixing stopped-flow techniques and conventional spectrophotometric measurements. At pH 7 and 15°C the rate constants for compound I reacting with p-hydroquinone, 2,3-dimethylhydroquinone and 2,3,5-trimethylhydroquinone were determined to be 5.6±0.4×10⁷ M^-1s^-1, 1.3±0.1×10⁶ M^-1s^-1 and 3.1±0.3×10⁶ M^-1s^-1, respectively. The corresponding reaction rates for compound II reduction were calculated to be 4.5±0.3×10⁶ M^-1s^-1, 1.9±0.1×10⁵ M^-1s^-1 and 4.5±0.2×10⁴ M^-1s^-1, respectively. Semiquinone radicals, produced by compounds I and II in the classical peroxidation cycle, promote compound III (oxymyeloperoxidase) formation. We could monitor formation of ferrous myeloperoxidase as well as its direct transition to compound III by addition of molecular oxygen. Formation of ferrous myeloperoxidase is shown to depend strongly on the reduction potential of the corresponding redox couple benzoquinone/semiquinone. With 2,3-dimethylhydroquinone and 2,3,5-trimethylhydroquinone as substrate, myeloperoxidase is extremely quickly trapped as compound III. These MPO-typical features could have potential in designing specific drugs which inhibit the production of hypochlorous acid and consequently attenuate inflammatory tissue damage.     

Sulfation of flavonoids and other phenolic dietary compounds by the human cytosolic sulfotransferases

The protective effects of diet, especially soya products, tea, and many fruits, against a variety of human cancers, as suggested by epidemiological studies, has focused attention on flavonoids, isoflavonoids, and other phenolic dietary compounds as chemoprotectants. Among the mechanisms suggested for their chemoprotective action, their ability to inhibit the bioactivation of carcinogens by the human cytosolic sulfotransferases (STs) and the direct effects of their sulfoconjugates are being increasingly studied. We report here a systematic study on the sulfation of representative flavonoids, isoflavonoids, anti-oxidants, and other phenolic dietary compounds by all ten known human cytosolic STs. All ten recombinant human cytosolic STs were prepared in a pure form and tested for their sulfating activities with a variety of these compounds. P-form (SULT1A1) phenol ST (PST) showed high sulfating activity with most of these compounds. M-form (SULT1A3) PST showed high activity with the flavonoids but not with the isoflavonoids. SULT1C ST #2 showed high activity with the isoflavonoids and also sulfated most of the other compounds. Possible relevance of these results to the chemoprotective effects of these dietary compounds is discussed.     

Metabolism of volatile phenolic compounds from hydroxycinnamic acids byBrettanomyces yeast

The formation of 4-ethyl and 4-vinyl derivatives of guaiacol, phenol and syringol from ferulic acid,p-coumaric acid and sinapic acid, respectively, byBrettanomyces sp. in a synthetic medium was studied by gas chromatography-mass spectrometry. Some of these metabolites possess strong spicy, smoke-like, medicinal, clove-like, woody or phenolic odours and their role as spoilage compounds in wine is discussed. Their formation appears to be characteristic of this yeast genus and its sporulating formDekkera, suggesting these yeasts are Pof⁺. This paper attempts to clarify the distinctive and characteristic odours which have long been attributed toBrettanomyces yeast metabolism.     

Secretion of myeloperoxidase isoforms by human neutrophils.

The human neutrophil lysosomal enzyme, myeloperoxidase (MPO), exists in three major and chromatographically distinct forms, MPO I, MPO II, and MPO III. We used cation-exchange medium-pressure liquid chromatography and kinetic microenzyme assay (or spectrophotometric monitoring) to analyze the secretion of MPO isoforms by neutrophils exposed to N-formylmethionylleucylphenylalanine (FMLP), digitonin, the ionophore A23187, and serum-opsonized zymosan A (SOZ). All three MPO isomers were released into the fluid phase after neutrophils were exposed to these secretagogues. A significant proportional increase in MPO I was released when neutrophils were stimulated with SOZ. MPO I was released in higher proportions than found in the whole cell constituency when neutrophils were stimulated with FMLP + cytochalasin B, A23187, and digitonin, but this was not statistically significant.     

Utilization of complex phenolic compounds by Acinetobacter sp.

Summary Acinetobacter sp. utilized the [ring-¹⁴C]dehydropolymer of coniferyl alcohol (DHP) (sp. act. 1.4 × 10⁴ dpm/mg), ¹⁴C-labelled teakwood lignin (sp. act. 2.5 × 10⁴ dpm/mg), guaiacolglyceryl ether, 2-methoxy-4-formylphenoxyacetic acid, p-benzyloxyphenol, dehydrodivanillyl alcohol, dehydrodiisoeugenol, veratrylglycerol--guaiacyl ether, conidendrin, black liquor lignin and indulin as sole carbon sources. The bacterium produced p-coumaric acid, p-hydroxybenzoic acid, vanillic acid, protocatechuic acid and catechol as intermediates from lignins. Acinetobacter sp. produced catechol 1,2-dioxygenase and protocatechuate 3,4-dioxygenase during the degradation of lignins. Correspondence to: A. Mahadevan     

Kinetics of oxidation of serotonin by myeloperoxidase compounds I and II.

The oxidation of serotonin (5-hydroxytryptamine) by the myeloperoxidase intermediates compounds I and II was investigated by using transient-state spectral and kinetic measurements at 25.0 +/- 0.1 degrees C. Rapid scan spectra demonstrated that both compound I and compound II oxidize serotonin via one-electron processes. Rate constants for these reactions were determined using both sequential-mixing and single-mixing stopped-flow techniques. The second order rate constant obtained for the one-electron reduction of compound I to compound II by serotonin is (1.7 +/- 0.1) x 10(7) M(-1) x s(-1), and that for compound II reduction to native enzyme is (1.4 +/- 0.1) x 10(6) M(-1) x s(-1) at pH 7.0. The maximum pH of the compound I reaction with serotonin occurs in the pH range 7.0-7.5. At neutral pH, the rate constant for myeloperoxidase compound I reacting with serotonin is an order of magnitude larger than for its reaction with chloride, (2.2 +/- 0.2) x 10(6) M(-1) x s(-1). A direct competition of serotonin with chloride for myeloperoxidase compound I oxidation was observed. Our results suggest that serotonin may have a role to protect lipoproteins from oxidation and to prevent enzymes from inactivation caused by the potent oxidants HOCl and active oxygen species.     

Metabolism of aromatic compounds by Caulobacter crescentus.

Cultures of Caulobacter crescentus were found to grow on a variety of aromatic compounds. Degradation of benzoate, p-hydroxybenzoate, and phenol was found to occur via beta-ketoadipate. The induction of degradative enzymes such as benzoate 1,2-dioxygenase, the ring cleavage enzyme catechol 1,2-dioxygenase, and cis, cis-muconate lactonizing enzyme appeared similar to the control mechanism present in Pseudomonas spp. Both benzoate 1,2-dioxygenase and catechol 1,2-dioxygenase had stringent specificities, as revealed by their action toward substituted benzoates and substituted catechols, respectively.     

Laccase-mediated detoxification of phenolic compounds.

The ability of a polyphenoloxidase, the laccase of the fungus Rhizoctonia praticola, to detoxify phenolic pollutants was examined. The growth of the fungus could be inhibited by phenolic compounds, and the effective concentration was dependent on the substituents of the phenol. A toxic amount of a phenolic compound was added to a fungal growth medium in the presence or absence of a naturally occurring phenol, and half of the replicates also received laccase. The medium was then inoculated with R. praticola, and the levels of phenols in the medium were monitored by high-performance liquid chromatography analysis. The addition of the laccase reversed the inhibitory effect of 2,6-xylenol, 4-chloro-2-methylphenol, and p-cresol. Other compounds, e.g., o-cresol and 2,4-dichlorophenol, were detoxified only when laccase was used in conjunction with a natural phenol such as syringic acid. The toxicity of p-chlorophenol and 2,4,5-trichlorophenol could not be overcome by any additions. The ability of the laccase to alter the toxicity of the phenols appeared to be related to the capacity of the enzyme to decrease the levels of the parent compound by transformation or cross-coupling with another phenol.     

Interconverting flavanone glucosides and other phenolic compounds in Lippia salviaefolia Cham. ethanol extracts

Four interconverting flavanone glycosides [(2R)- and (2S)-3′,4′,5,6-tetrahydroxyflavanone 7-O-β-d-glucopyranoside, and (2R)- and (2S)-3′,4′,5,8-tetrahydroxyflavanone 7-O-β-d-glucopyranoside], in addition to eight known flavonoids [naringenin, asebogenin, sakuranetin, 6-hydroxyluteolin 7-O-β-d-glucoside, (2R)- and (2S)-eriodictyol 7-O-β-d-glucopyranoside, aromadendrin and phloretin], three phenylpropanoid glycosides [forsythoside B, alyssonoside and verbascoside] and the epoxylignan lariciresinol 4′-O-β-d-glucopyranoside were isolated and identified in the EtOH extract of the aerial parts of Lippia salviaefolia Cham. The phytochemical study herein was guided by preliminary antioxidant tests, namely, β-carotene protection and 2,2-diphenyl-1-picrylhydrazyl (DPPH) free radical scavenging activity. The crude extracts, their active fractions and the isolated compounds were assayed against intracellular reactive oxygen species (ROS) and human embryonic kidney HEK-293 and human melanoma M14 cancer cell growth. Aromadendrin and phloretin were able to counteract elevation of ROS induced by the oxidant t-butylhydroperoxide (t-BOOH) in HEK-293 cells, whereas phloretin strongly protected HEK-293 cells from ROS damage at 1 μM. Additionally, phloretin exhibited a significant growth inhibitory effect at 20–40 μM in both HEK-293 and M14 cells and induced a concentration dependent apoptosis at 20 μM in M14 cells, suggesting a selective action towards malignant cells. Due to their equilibria, the four interconverting flavanone glycosides were studied using 1D and 2D NMR, HPLC–CD–PDA and HRMS analyses.     

Degradation mechanisms of phenolic beta-1 lignin substructure model compounds by laccase of Coriolus versicolor

Phenolic beta-1 lignin substructure model compounds, 1-(3,5-dimethoxy-4-hydroxy-phenyl)-2-(3,5-dimethoxy-4-ethoxyphenyl)propa ne-1, 3-diol (I) and 1-(3,5-dimethoxy-4-ethoxyphenyl)-2-(3, 5-dimethoxy-4-hydroxyphenyl)propane-1,3-diol (II) were degraded by laccase of Coriolus versicolor. Substrate I was converted to 1-(3,5-dimethoxy-4-hydroxyphenyl)-2-(3,5-dimethoxy-4-ethoxyphenyl)-3- hydroxypropanone (III), 1-(3,5-dimethoxy-4-ethoxyphenyl)-2-hydroxyethanone (IV), syringaldehyde (V), 1-(3,5-dimethoxy-4-ethoxyphenyl)-3-hydroxypropanal (VI), 2,6-dimethoxy-p-hydroquinone (VII), and 2,6-dimethoxy-p-benzoquinone (VIII). Furthermore, incorporations of 18O of 18O2 into ethanone (IV) and 18O of H218O into hydroquinone (VII) and benzoquinone (VIII) were confirmed. Substrate II gave 1-(3,5-dimethoxy-4-hydroxyphenyl)ethane-1, 2-diol (IX), 1-(3,5-dimethoxy-4-hydroxyphenyl)-2-hydroxyethanone (X), and 3,5-dimethoxy-4-ethoxybenzaldehyde (XI). Also 18O of H218O was incorporated into glycol (IX) and ethanone (X). Based on the structures of the degradation products and the isotopic experiments, it was established that three types of reactions occurred via phenoxy radicals of substrates caused by laccase: (i) C alpha-C beta cleavage (between C1 and C2 carbons); (ii) alkyl-aryl cleavage (between C1 carbon and aryl group); and (iii) C alpha (C1) oxidation.     

A new flavanone sulfonate and other phenolic compounds from Fumana montana

The phytochemical study of ethyl acetate and n-butanol extracts of Fumana montana Pomel yielded a new flavanone sulfonate named naringenin-8-sulfonate (1), in addition to nine known compounds including two flavonols; tellimoside (2) and isoquercetrin (3), two flavanols; (−)-gallocatechin (4) and (−)-epigallocatechin (5), one benzophenone glucoside; iriflophenone-2-O-β-glucoside (6), one phenolic glucoside; (−)-rhododendrin (7) and three benzoic acid derivatives; p-hydroxybenzoic acid (8), gallic acid (9) and methyl gallate (10). It should be noted that this is the first report of compounds (2) and (6) in Cistaceae family. The structures of the isolated compounds were determined by comprehensive 1D and 2D NMR analysis, mass spectrometry, IR and by comparison with literature data.     

Chlorination of guanosine and other nucleosides by hypochlorous acid and myeloperoxidase of activated human neutrophils. Catalysis by nicotine and trimethylamine

Activated human neutrophils secrete myeloperoxidase, which generates HOCl from H2O2 and Cl(-). We have found that various (2'-deoxy)nucleosides react with HOCl to form chlorinated (2'-deoxy)nucleosides, including novel 8-chloro(2'-deoxy)guanosine, 5-chloro(2'-deoxy)cytidine, and 8-chloro(2'-deoxy)adenosine formed in yields of 1.6, 1.6, and 0.2%, respectively, when 0.5 mM nucleoside reacted with 0.5 mM HOCl at pH 7.4. The relative chlorination, oxidation, and nitration activities of HOCl, myeloperoxidase, and activated human neutrophils in the presence and absence of nitrite were studied by analyzing 8-chloro-, 8-oxo-7,8-dihydro-, and 8-nitro-guanosine, respectively, using guanosine as a probe. 8-Chloroguanosine was always more easily formed than 8-oxo-7,8-dihydro- or 8-nitro-guanosine. Using electrospray ionization tandem mass spectrometry, we show that several chlorinated nucleosides including 8-chloro(2'-deoxy)guanosine are formed following exposure of isolated DNA or RNA to HOCl. Micromolar concentrations of tertiary amines such as nicotine and trimethylamine dramatically enhanced chlorination of free (2'-deoxy)nucleosides and nucleosides in RNA by HOCl. As the G-463A polymorphism of the MPO gene, which strongly reduces myeloperoxidase mRNA expression, is associated with a reduced risk of lung cancer, chlorination damage of DNA /RNA and nucleosides by myeloperoxidase and its enhancement by nicotine may be important in the pathophysiology of human diseases associated with tobacco habits.     

Flavonolignans and other phenolic compounds from Sorghum halepense (L.) Pers.

Eight compounds (1-7b) were isolated from the aerial parts of S. halepense in present investigation and five of them (2, 5, 6, 7a, 7b) were firstly reported from this species. The two rare diastereomeric flavonolignans tricin-4'-O-(threo-β-guaiacylglyceryl) ether and tricin-4'-O-(erythro-β-guaiacylglyceryl) ether is from Sorghum genus for the first time. The chemotaxonomic significance of these compounds was summarized.     

Inhibition of aflatoxin biosynthesis by phenolic compounds

The phenolic compounds acetosyringone, syringaldehyde and sinapinic acid inhibited the biosynthesis of aflatoxin B1 (AFB1) by A. flavus. Acetosyringone was the most active among the three compounds, inhibiting aflatoxin level by 82% at 2 m moll-1. The synthesis and accumulation of norsolorinic acid, an aflatoxin biosynthetic intermediate, was also inhibited. These results suggest that at least one step early in the AFB1 biosynthetic pathway is inhibited by the phenolics.     

Distribution of quinic acid derivatives and other phenolic compounds in Brazilian propolis

The quinic acid derivatives (including 4-feruoyl quinic and 5-ferruoyl quinic acids characterized for first time in propolis samples) and other phenolic compounds were quantified in thirteen Brazilian propolis samples by HPLC analysis. For chemometrical analysis, the distribution of quinic acid derivatives and other phenolic compounds were considered. The results suggest that the Brazilian propolis with floral origin from Citrus sp. have the highest concentration of the quinic acid derivatives (between 11.0 to 58.4 mg/mg of the dried crude hydroalcoholic extract) and therefore would probably show a more effective hepatoprotective activity.     

Biotransformation of phenolic compounds by Bacillus aryabhattai

Bioprocess and Biosystems Engineering - Phenolic compounds could pose environmental problems if they are in excess, although they could be a renewable resource of substances with industrial...     

Bioactive phenolic compounds: production and extraction by solid-state fermentation. A review

Interest in the development of bioprocesses for the production or extraction of bioactive compounds from natural sources has increased in recent years due to the potential applications of these compounds in food, chemical, and pharmaceutical industries. In this context, solid-state fermentation (SSF) has received great attention because this bioprocess has potential to successfully convert inexpensive agro-industrial residues, as well as plants, in a great variety of valuable compounds, including bioactive phenolic compounds. The aim of this review, after presenting general aspects about bioactive compounds and SSF systems, is to focus on the production and extraction of bioactive phenolic compounds from natural sources by SSF. The characteristics of SSF systems and variables that affect the product formation by this process, as well as the variety of substrates and microorganisms that can be used in SSF for the production of bioactive phenolic compounds are reviewed and discussed.