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Polyphenol tannic acid inhibits hydroxyl radical formation from Fenton reaction by complexing ferrous ions.
Biochim Biophys Acta. 1999 Oct 18; 1472(1-2):142-52.BB

Abstract

Tannic acid (TA), a plant polyphenol, has been described as having antimutagenic, anticarcinogenic and antioxidant activities. Since it is a potent chelator of iron ions, we decided to examine if the antioxidant activity of TA is related to its ability to chelate iron ions. The degradation of 2-deoxyribose induced by 6 microM Fe(II) plus 100 microM H2O2 was inhibited by TA, with an I50 value of 13 microM. Tannic acid was over three orders of magnitude more efficient in protecting against 2-deoxyribose degradation than classical *OH scavengers. The antioxidant potency of TA was inversely proportional to Fe(II) concentration, demonstrating a competition between H2O2 and AT for reaction with Fe(II). On the other hand, the efficiency of TA was nearly unchanged with increasing concentrations of the *OH detector molecule, 2-deoxyribose. These results indicate that the antioxidant activity of TA is mainly due to iron chelation rather than *OH scavenging. TA also inhibited 2-deoxyribose degradation mediated by Fe(III)-EDTA (iron = 50 microM) plus ascorbate. The protective action of TA was significantly higher with 50 microM EDTA than with 500 microM EDTA, suggesting that TA removes Fe(III) from EDTA and forms a complex with iron that cannot induce *OH formation. We also provided evidence that TA forms a stable complex with Fe(II), since excess ferrozine (14 mM) recovered 95-96% of the Fe(II) from 10 microM TA even after a 30-min exposure to 100-500 microM H2O2. Addition of Fe(III) to samples containing TA caused the formation of Fe(II)n-TA, complexes, as determined by ferrozine assays, indicating that TA is also capable of reducing Fe(III) ions. We propose that when Fe(II) is complexed to TA, it is unable to participate in Fenton reactions and mediate *OH formation. The antimutagenic and anticarcinogenic activity of TA, described elsewhere, may be explained (at least in part) by its capacity to prevent Fenton reactions.

Authors+Show Affiliations

Departamento de Biologia Celular, Universidade de Brasília, Brazil.No affiliation info availableNo affiliation info available

Pub Type(s)

Journal Article
Research Support, Non-U.S. Gov't

Language

eng

PubMed ID

10572935

Citation

Lopes, G K., et al. "Polyphenol Tannic Acid Inhibits Hydroxyl Radical Formation From Fenton Reaction By Complexing Ferrous Ions." Biochimica Et Biophysica Acta, vol. 1472, no. 1-2, 1999, pp. 142-52.
Lopes GK, Schulman HM, Hermes-Lima M. Polyphenol tannic acid inhibits hydroxyl radical formation from Fenton reaction by complexing ferrous ions. Biochim Biophys Acta. 1999;1472(1-2):142-52.
Lopes, G. K., Schulman, H. M., & Hermes-Lima, M. (1999). Polyphenol tannic acid inhibits hydroxyl radical formation from Fenton reaction by complexing ferrous ions. Biochimica Et Biophysica Acta, 1472(1-2), 142-52.
Lopes GK, Schulman HM, Hermes-Lima M. Polyphenol Tannic Acid Inhibits Hydroxyl Radical Formation From Fenton Reaction By Complexing Ferrous Ions. Biochim Biophys Acta. 1999 Oct 18;1472(1-2):142-52. PubMed PMID: 10572935.
* Article titles in AMA citation format should be in sentence-case
TY - JOUR T1 - Polyphenol tannic acid inhibits hydroxyl radical formation from Fenton reaction by complexing ferrous ions. AU - Lopes,G K, AU - Schulman,H M, AU - Hermes-Lima,M, PY - 1999/11/26/pubmed PY - 1999/11/26/medline PY - 1999/11/26/entrez SP - 142 EP - 52 JF - Biochimica et biophysica acta JO - Biochim Biophys Acta VL - 1472 IS - 1-2 N2 - Tannic acid (TA), a plant polyphenol, has been described as having antimutagenic, anticarcinogenic and antioxidant activities. Since it is a potent chelator of iron ions, we decided to examine if the antioxidant activity of TA is related to its ability to chelate iron ions. The degradation of 2-deoxyribose induced by 6 microM Fe(II) plus 100 microM H2O2 was inhibited by TA, with an I50 value of 13 microM. Tannic acid was over three orders of magnitude more efficient in protecting against 2-deoxyribose degradation than classical *OH scavengers. The antioxidant potency of TA was inversely proportional to Fe(II) concentration, demonstrating a competition between H2O2 and AT for reaction with Fe(II). On the other hand, the efficiency of TA was nearly unchanged with increasing concentrations of the *OH detector molecule, 2-deoxyribose. These results indicate that the antioxidant activity of TA is mainly due to iron chelation rather than *OH scavenging. TA also inhibited 2-deoxyribose degradation mediated by Fe(III)-EDTA (iron = 50 microM) plus ascorbate. The protective action of TA was significantly higher with 50 microM EDTA than with 500 microM EDTA, suggesting that TA removes Fe(III) from EDTA and forms a complex with iron that cannot induce *OH formation. We also provided evidence that TA forms a stable complex with Fe(II), since excess ferrozine (14 mM) recovered 95-96% of the Fe(II) from 10 microM TA even after a 30-min exposure to 100-500 microM H2O2. Addition of Fe(III) to samples containing TA caused the formation of Fe(II)n-TA, complexes, as determined by ferrozine assays, indicating that TA is also capable of reducing Fe(III) ions. We propose that when Fe(II) is complexed to TA, it is unable to participate in Fenton reactions and mediate *OH formation. The antimutagenic and anticarcinogenic activity of TA, described elsewhere, may be explained (at least in part) by its capacity to prevent Fenton reactions. SN - 0006-3002 UR - https://www.unboundmedicine.com/medline/citation/10572935/Polyphenol_tannic_acid_inhibits_hydroxyl_radical_formation_from_Fenton_reaction_by_complexing_ferrous_ions_ L2 - https://linkinghub.elsevier.com/retrieve/pii/S0304-4165(99)00117-8 DB - PRIME DP - Unbound Medicine ER -