Light Emission Accompanies Oxygen Uptake During the Peroxidative Metabolism of Tetracyclines

Ve, Gilio; Cilento, Giuseppe

doi:10.1111/j.1751-1097.1993.tb09588.x

Cited by 10 publications

(5 citation statements)

References 24 publications

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“…These observations are consistent with a reaction between O 2 and the phenoxyl radicals formed by TPO-catalyzed oxidation that diverts the inactivating radical to a pathway leading to turnover of the suicide substrate and not enzyme inactivation (see Scheme 2). Similar reactions have been proposed for light emission that accompanies peroxidase-mediated metabolism of tetracycline and oxicams under aerobic conditions (26).…”

Section: Discussionsupporting

confidence: 54%

Inhibition of Thyroid Peroxidase by Dietary Flavonoids

Divi

Doerge

1996

Chem. Res. Toxicol.

204

114

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Flavonoids are widely distributed in plant-derived foods and possess a variety of biological activities including antithyroid effects in experimental animals and humans. A structure-activity study of 13 commonly consumed flavonoids was conducted to evaluate inhibition of thyroid peroxidase (TPO), the enzyme that catalyzes thyroid hormone biosynthesis. Most flavonoids tested were potent inhibitors of TPO, with IC50 values ranging from 0.6 to 41 microM. Inhibition by the more potent compounds, fisetin, kaempferol, naringenin, and quercetin, which contain a resorcinol moiety, was consistent with mechanism-based inactivation of TPO as previously observed for resorcinol and derivatives. Other flavonoids inhibited TPO by different mechanisms, such as myricetin and naringin, showed noncompetitive inhibition of tyrosine iodination with respect to iodine ion and linear mixed-type inhibition with respect to hydrogen peroxide. In contrast, biochanin A was found to be an alternate substrate for iodination. The major product, 6,8-diiodo-biochanin A, was characterized by electrospray mass spectrometry and 1H-NMR. These inhibitory mechanisms for flavonoids are consistent with the antithyroid effects observed in experimental animals and, further, predict differences in hazards for antithyroid effects in humans consuming dietary flavonoids. In vivo, suicide substrate inhibition, which could be reversed only by de novo protein synthesis, would be long-lasting. However, the effects of reversible binding inhibitors and alternate substrates would be temporary due to attenuation by metabolism and excretion. The central role of hormonal regulation in growth and proliferation of thyroid tissue suggests that chronic consumption of flavonoids, especially suicide substrates, could play a role in the etiology of thyroid cancer.

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Section: Discussionsupporting

confidence: 54%

Inhibition of Thyroid Peroxidase by Dietary Flavonoids

Divi

Doerge

1996

Chem. Res. Toxicol.

204

114

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“…Since the absorption maximum at 355 nm is due to the BCD chromophore, changes in absorbance at this wavelength can be attributed to modification of functional groups in the BCD chromophore by components of the root exudates. The phenolic group in the D-ring and the enol group in the B-ring provide possible sites of oxidation (18); therefore oxidation of the BCD chromophore at these sites is a strong possibility. The A-ring has only one possible site of oxidation, which is the OH group (18).…”

Section: W T Wmentioning

confidence: 99%

“…The phenolic group in the D-ring and the enol group in the B-ring provide possible sites of oxidation (18); therefore oxidation of the BCD chromophore at these sites is a strong possibility. The A-ring has only one possible site of oxidation, which is the OH group (18). Thus, in the case of limited availability of oxidants, the modification at the BCD chromophore may be expected to exceed that at the A chromophore, depending on the reduction potentials of functional groups at the two locations.…”

Section: W T Wmentioning

confidence: 99%

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Hairy Roots of Helianthus annuus: A Model System to Study Phytoremediation of Tetracycline and Oxytetracycline

Gujarathi

Haney

Park

et al. 2008

Biotechnol Progress

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The release of antibiotics to the environment has to be controlled because of serious threats to human health. Hairy root cultures of Helianthus annuus (sunflower), along with their inherent rhizospheric activity, provide a fast growing, microbe-free environment for understanding plant-pollutant interactions. The root system catalyzes rapid disappearance of tetracycline (TC) and oxytetracycline (OTC) from aqueous media, which suggests roots have potential for phytoremediation of the two antibiotics in vivo. In addition, in vitro modifications of the two antibiotics by filtered, cell- and microbe-free root exudates suggest involvement of root-secreted compounds. The modification is confirmed from changes observed in UV spectra of exudate-treated OTC. Modification appears to be more dominant at the BCD chromophore of the antibiotic molecule. Kinetic analyses dismiss direct enzyme catalysis; the modification rates decrease with increasing OTC concentrations. The rates increase with increasing age of cultures from which root exudates are prepared. The decrease in modification rates upon addition of the antioxidant ascorbic acid (AA) suggests involvement of reactive oxygen species (ROS) in the antibiotic modification process.

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“…Oxygen, hydroxyl radical, and hydrogen peroxide oxidize tetracyclines (Gilio and Cilento, 1993;Lau et al, 2004). Oxidation of OTC is expected to yield quinone derivatives (Lau et al, 2004).…”

Section: Introductionmentioning

confidence: 99%

Oxytetracycline inactivation by putative reactive oxygen species released to nutrient medium ofHelianthus annuus hairy root cultures

Gujarathi

Linden

2005

Biotechnol. Bioeng.

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When subjected to stress, plants produce reactive oxygen species (ROS) as a part of the defense response. The oxidative response is also used to degrade organic pollutants. Hairy roots of Helianthus annuus (sunflower) are shown to oxidize oxytetracycline (OTC) through the action of the ROS released to the nutrient medium by the hairy root cultures. Methyl jasmonate (MeJA) elicits ROS formation in the hairy root cultures. The activities of the antioxidant enzymes, ascorbate peroxidase (APX), catalase (CAT), and guaiacol peroxidase (GPX), are reported for hairy root cultures treated with increasing concentrations of MeJA. A bioassay using Enterococcus hirae as the test microorganism demonstrates the root-catalyzed oxidation process results in conversion of OTC into product(s) devoid of antibiotic activity. Direct evidence for putative ROS oxidation of OTC is obtained by mass spectrometry (MS) and HPLC/MS showing first quinone formation followed possibly by ring cleavage, which disrupts UV absorption and destroys antibiotic activity. ß

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Light Emission Accompanies Oxygen Uptake During the Peroxidative Metabolism of Tetracyclines

Cited by 10 publications

References 24 publications

Inhibition of Thyroid Peroxidase by Dietary Flavonoids

Inhibition of Thyroid Peroxidase by Dietary Flavonoids

Hairy Roots of Helianthus annuus: A Model System to Study Phytoremediation of Tetracycline and Oxytetracycline

Oxytetracycline inactivation by putative reactive oxygen species released to nutrient medium ofHelianthus annuus hairy root cultures

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