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Cited by 345Phytoestrogen effects and researchEstrogen and related hormone effectsFlavonoids in Medical Research

Molecular basis of the inhibition of human aromatase (estrogen synthetase) by flavone and isoflavone phytoestrogens: A site-directed mutagenesis study.

Open access
Kao, Y C, Zhou, C, Sherman, M, Laughton, C A, Chen, S·1998·Environmental Health Perspectives
DOI 10.1289/ehp.9810685PMC PMC1533021
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Abstract

Flavone and isoflavone phytoestrogens are plant chemicals and are known to be competitive inhibitors of cytochrome P450 aromatase with respect to the androgen substrate. Aromatase is the enzyme that converts androgen to estrogen; therefore, these plant chemicals are thought to be capable of modifying the estrogen level in women. In this study, the inhibition profiles of four flavones [chrysin (5, 7-dihydroxyflavone), 7,8-dihydroxyflavone, baicalein (5,6,7-trihydroxyflavone), and galangin (3,5,7-trihydroxyflavone)], two isoflavones [genistein (4,5,7-trihydroxyisoflavone) and biochanin A (5,7-dihydroxy-4-methoxyisoflavone)], one flavanone [naringenin (4, 5,7-trihydroxyflavanone)], and one naphthoflavone (alpha-naphthoflavone) on the wild-type and six human aromatase mutants (I133Y, P308F, D309A, T310S, I395F, and I474Y) were determined. In combination with computer modeling, the binding characteristics and the structure requirement for flavone and isoflavone phytoestrogens to inhibit human aromatase were obtained. These compounds were found to bind to the active site of aromatase in an orientation in which rings A and C mimic rings D and C of the androgen substrate, respectively. This study also provides a molecular basis as to why isoflavones are significantly poorer inhibitors of aromatase than flavones.

AI snapshot

Written from the paper’s full text.

TL;DR

This study combined inhibition kinetics, site-directed aromatase mutants, and computer modeling to examine how flavone and isoflavone phytoestrogens bind and inhibit human aromatase. It found that flavones generally inhibit more strongly than isoflavones, with α-naphthoflavone and chrysin most potent, and proposed a binding orientation in which the flavone A and C rings mimic the steroid D and C rings while the C4-keto group faces the heme.

Key findings

  • Among the tested compounds, α-naphthoflavone had the lowest Ki (2.2 ± 0.1 µM), followed by chrysin (2.6 ± 0.1 µM), naringenin (5.1 ± 0.2 µM), 7,8-dihydroxyflavone (10 ± 1 µM), biochanin A (12 ± 5 µM), galangin (95 ± 28 µM), and genistein (123 ± 8 µM); baicalein showed no inhibition up to 50 µM.
  • Isoflavones were poorer aromatase inhibitors than flavones; biochanin A inhibited better than genistein, which the authors attribute to its C4′-methoxy rather than C4′-hydroxy substituent.
  • Mutations altered inhibitor potency in ways that supported the proposed binding pose: for example, chrysin Ki fell from 2.6 ± 0.1 µM in wild type to 0.3 ± 0.1 µM in I133Y, 0.6 ± 0.1 µM in I395F, and 0.06 ± 0.02 µM in I474Y, but rose to 13 ± 3 µM in D309A.
  • Modeling and inhibition profiles indicated that flavones bind with rings A and C mimicking steroid rings D and C, respectively, and with the C4-keto group oriented toward the heme; 5-hydroxy, 3-hydroxy, and C6 substituents reduce binding, while the isoflavone 4′-hydroxy group also weakens aromatase inhibition.

Methods

  • Inhibition kinetics were measured for eight phytoestrogens on wild-type human aromatase and six mutants (I133Y, P308F, D309A, T310S, I395F, I474Y) expressed in Chinese hamster ovary cells, using a ³H₂O release assay with 100 nM radiolabeled androstenedione and Ki values derived from Dixon plots.
  • Mutants were generated by PCR-based site-directed mutagenesis, stably expressed in CHO cells, and confirmed by enzyme activity and western blot or immunoprecipitation analysis.
  • Computer modeling used a previously generated human aromatase homology model; compounds were placed in the active site and energy minimized first with a rigid pocket and then allowing active-site residue movement.

Limitations

  • The paper states that this is an in vitro study and that in vivo effects could differ because of metabolic conversion; cell culture and animal studies were described as initiated but not reported here.
  • The paper states that the biphasic inhibition profiles observed for galangin in wild-type and some mutants are not understood, and that possible interaction with other CHO proteins cannot explain why only some mutant forms showed this pattern.
  • The paper notes that naringenin Ki values may reflect a racemic mixture, so the S-configuration isomer may have lower actual Ki; evident from the text, the conclusions also depend on a homology-based computational model and a limited set of six mutants, and baicalein was not tested against mutants because it did not inhibit wild-type aromatase up to 50 µM.

Model-written summary. Check it against the paper before relying on it.

Integrity signals

Registry

Crossref · 10.1289/ehp.9810685

Cites

46 of 46 references verified0 citation errors · 0 not checkable

Statistics

Nothing to recompute.

Claims the paper makes

0 of 52 cited sources checked · 0 supported · 0 flagged

  • Findingown data
    § Abstract

    These compounds bind to the active site of aromatase in an orientation in which rings A and C mimic rings D and C of the androgen substrate, respectively.

    “These compounds were found to bind to the active site of aromatase in an orientation in which rings A and C mimic rings D and C of the androgen substrate, respectively.”
    Quote in the paperSubstantial claim
  • Findingown data
    § Discussion

    Among these compounds, the C4-keto group of genistein is the farthest from the heme as seen in the model.

    “Among these compounds, the C4-keto group of genistein is the far- thest from the heme as seen in the model (Fig. 2D)”
    Quote in the paperNot a substantial claim
    • Rests on an assumption: The computer model of the aromatase active site accurately represents the enzyme's active site and the binding orientations of the compounds.
  • Findingown data
    § Discussion

    The presence of a single bond between C-2 and C-3 slightly modifies the conformation of ring C.

    “However, the presence of a single bond between the C-2 and C-3 positions does slightly modify the conformation of ring C (as shown by the computer model- ing)”
    Quote in the paperSubstantial claim
    • Rests on an assumption: The computer model of the aromatase active site accurately represents the enzyme's active site and the binding orientations of the compounds.
  • Findingown data
    § Results and Discussion

    The C4-keto group of chrysin points towards the heme prosthetic group.

    “The C4-keto group of chrysin points towards the heme prosthetic group (Fig. 2C).”
    Quote in the paperSubstantial claim
  • Findingown data
    § Results and Discussion

    Computer modeling suggests another possible orientation for the binding of flavone to the active site of aromatase, in which rings A and C of flavone mimic rings A and B of a steroid and the p-phenyl substituent is directed towards Ile-133.

    “As indicated in Figure 4, com- puter modeling suggests another possible orientation for the binding of flavone to the active site of aromatase, an orientation in which rings A and C of flavone mimics rings A and B of a steroid and the p-phenyl substituent is directed towards Ile-133.”
    Quote in the paperNot a substantial claim
  • Classified as probably not a substantial claim. 16
  • May combine two claims. 19
  • The quote only partly states this claim. 1

  • Probably not a substantial claim: may not pass S3 (load-bearing).

    Findingcitation
    § Results and Discussion

    7-Hydroxyflavone is four times more potent than chrysin.

    “In a recently completed experiment, 7- hydroxyflavone was found to be four times more potent than chrysin (Kao et al., unpublished results).”
    Quote in the paperNot a substantial claim

  • May combine two claims.

    Findingreasoning
    § Results and Discussion

    The p-phenyl substituent (ring B) of chrysin is oriented similarly to the substrate's ring A and is directed towards Asp 309.

    “By doing so, the p-phenyl sub- stituent (i.e., ring B) of chrysin is oriented in a similar position to that of the substrate's ring A and is directed towards Asp 309.”
    Quote in the paperSubstantial claim

  • The quote only partly states this claim.

    Findingown data
    § Results and Discussion

    Baicalein did not inhibit wild-type aromatase at concentrations up to 50 μM.

    “No inhibi- tion by baicalein was observed with concen- trations up to 50 pM.”
    Quote in the paperNot a substantial claim

  • May combine two claims.

    Findingreasoning
    § Results and Discussion

    Because 7,8-dihydroxyflavone has the same p-phenyl substituent as chrysin, the relative responses to P308F, D309A, T310S, and I474Y were similar to chrysin.

    “Because 7,8- dihydroxyflavone has the same p-phenyl substituent as chrysin, the relative respons- es to P308F, D309A, T310S, and I474Y were found to be similar to chrysin.”
    Quote in the paperSubstantial claim

  • May combine two claims.

    Findingreasoning
    § Discussion

    α-Naphthoflavone, but not β-naphthoflavone, is a good inhibitor of aromatase.

    “a-Naphthoflavone, but not P-naph- thoflavone, is a good inhibitor of aromatase.”
    Quote in the paperSubstantial claim

  • May combine two claims.

    Findingown data
    § Results and Discussion

    Galangin binds relatively better to the mutant D309A than to the wild-type enzyme, suggesting that galangin fits better in the active site with an Asp-309 to Ala mutation.

    “Contrary to chrysin and other flavones, galangin binds relatively better to the mutant D309A than to the wild-type enzyme, sug- gesting that galangin fits better in the active site with a Asp-309 to Ala mutation.”
    Quote in the paperSubstantial claim

  • Probably not a substantial claim: may not pass S3 (load-bearing).

    Findingreasoning
    § Results and Discussion

    4'-Amino-6-hydroxyflavone is a very ineffective inhibitor of aromatase.

    “This may also explain why 4'- amino-6-hydroxyflavone is a very ineffec- tive inhibitor of aromatase (Kao et al., unpublished results).”
    Quote in the paperNot a substantial claim

  • May combine two claims.

    Findingown data
    § Results and Discussion

    For galangin, three mutants with changes located on the distal helix (P308F, D309A, and T310S) exhibited regular dose-dependent inhibition profiles, while the other three mutants and the wild-type enzyme exhibited unusual biphasic profiles.

    “Two types of inhibition profiles were observed for this compound; three mutants with changes located on the distal helix (P308F, D309A, and T310S) exhibited regular dose-dependent profiles, while the other three mutants as well as the wild-type enzymes exhibited unusual biphasic profiles (Fig. 5).”
    Quote in the paperSubstantial claim

  • Probably not a substantial claim: may not pass S3 (load-bearing).

    Premisecitation
    § Discussion

    For the estrogen receptor, isoflavones were found to be better ligands than flavones.

    “For ER, isoflavones were found to be better ligands than flavones”
    Quote in the paperNot a substantial claim0 of 2 sources checked
    • cites [40]

      Couldn’t be matched to a paper in Crossref, so it can’t be checked.

    • cites [41]

      Couldn’t be matched to a paper in Crossref, so it can’t be checked.

  • May combine two claims.

    Interpretationcitation
    § Results and Discussion

    Pro-308 to Phe and Asp-309 to Ala mutations modify the size of the active site pocket, preventing the binding of chrysin, as indicated by increases in Ki values.

    “As suggested previously (30), Pro-308 to Phe and Asp- 309 to Ala mutations modify the size of the active site pocket, thus preventing the bind- ing of chrysin as indicated by increases in the Ki values (Table 1).”
    Quote in the paperSubstantial claim0 of 1 sources checked
    • cites [30]

      Couldn’t be matched to a paper in Crossref, so it can’t be checked.

  • May combine two claims.

    Interpretationown data
    § Results and Discussion

    The 3-hydroxyl group of galangin points to the I-helix and affects the orientation of the phenyl substituent at the C-2 position and may also interfere with the interaction of the 4-keto group with the heme.

    “Computer modeling has revealed that the 3-hydroxyl group is pointing to the I-helix and affects the orientation of the phenyl substituent at the C-2 position and may also interfere with the interaction of the 4-keto group with the heme.”
    Quote in the paperSubstantial claim

  • May combine two claims.

    Interpretationown data
    § Discussion

    When superimposed over chrysin, α-naphthoflavone's C4-keto group points closer to the heme, implying a better fit in the aromatase active site.

    “When superimposed over the structure of chrysin, the C4-keto group of a-naphthoflavone points closer to the heme, implying a better fit in the active site of aromatase (see Fig. 2C).”
    Quote in the paperSubstantial claim
    • Rests on an assumption: The computer model of the aromatase active site accurately represents the enzyme's active site and the binding orientations of the compounds.

  • Probably not a substantial claim: may not pass S3 (load-bearing).

    Premisecitation
    § Discussion

    A 4'-hydroxy group is thought to be required to bind the estrogen receptor effectively.

    “Furthermore, a 4'-hydroxy group is thought to be required to bind ER effec- tively (see Fig. 6).”
    Quote in the paperNot a substantial claim0 of 2 sources checked
    • cites [40]

      Couldn’t be matched to a paper in Crossref, so it can’t be checked.

    • cites [41]

      Couldn’t be matched to a paper in Crossref, so it can’t be checked.

  • Probably not a substantial claim: may not pass S3 (load-bearing).

    Premisecitation
    § Discussion

    For the estrogen receptor, rings A and C of isoflavones were thought to mimic rings A and B of estrogen.

    “rings A and C of isoflavones were thought to mimic rings A and B of estrogen.”
    Quote in the paperNot a substantial claim0 of 2 sources checked
    • cites [40]

      Couldn’t be matched to a paper in Crossref, so it can’t be checked.

    • cites [41]

      Couldn’t be matched to a paper in Crossref, so it can’t be checked.

  • Probably not a substantial claim: may not pass S3 (load-bearing).

    Study design and conductcitation
    § Materials and Methods

    The 3H2O release assay for human aromatase expressed in CHO cells was previously validated by the product isolation assay.

    “This 3H20 release assay for human aromatase expressed in CHO cells was previously vali- dated by the product isolation assay (33).”
    Quote in the paperNot a substantial claim0 of 1 sources checked
    • cites [33]

      Couldn’t be matched to a paper in Crossref, so it can’t be checked.

  • May combine two claims.

    Interpretationown data
    § Discussion

    The opposite side of the pocket is comparatively spacious, allowing the benzopyranone rings of these compounds relatively free movement.

    “In contrast, the opposite side of the pocket is compara- tively spacious (e.g., a-naphthoflavone binds stronger in the active site of aro- matase) and therefore allows the benzopyra- none rings of these compounds relatively free movement.”
    Quote in the paperSubstantial claim
    • Rests on an assumption: The computer model of the aromatase active site accurately represents the enzyme's active site and the binding orientations of the compounds.

  • May combine two claims.

    Interpretationown data
    § Results and Discussion

    This alternative binding orientation is unfavorable because mutant I133Y is more resistant to 7,8-dihydroxyflavone than wild-type, whereas the same mutant is more sensitive to chrysin than wild-type.

    “However, this binding orientation is thought to be unfavorable because the mutant I133Y has been found to be more resistant to 7,8-dihydroxyflavone than the wild-type aromatase, whereas the same mutant is more sensitive to chrysin than the wild-type aromatase.”
    Quote in the paperSubstantial claim

  • May combine two claims.

    Interpretationreasoning
    § Discussion

    The observed Ki values for naringenin might originate from a racemic mixture, and the actual Ki values for the S-configuration isomer may be lower than those shown in Table 1.

    “Therefore, the observed Ki values might originate from a racemic mixture and the actual Ki values for the S-configuration isomer may be lower than those shown in Table 1.”
    Quote in the paperNot a substantial claim

  • Classified as probably not a substantial claim. May combine two claims.

    Premisecitation
    § Introduction

    Estrogen synthesized by tumor aromatase stimulates breast tumor growth in both an autocrine and a paracrine manner.

    “Estrogen synthesized by the tumor aromatase was shown to stimulate breast tumor growth in both an autocrine and a paracrine manner (15).”
    Quote in the paperSubstantial claim0 of 1 sources checked
    • cites [15]

      Couldn’t be matched to a paper in Crossref, so it can’t be checked.

  • Classified as probably not a substantial claim.

    Premisecitation
    § Introduction

    In estrogen-dependent breast tumors, estrogens induce the expression of peptide growth factors that are responsible for the proliferative responses of cancer cells.

    “In estrogen-dependent breast tumors, estrogens induce the expression of peptide growth factors that are responsible for the proliferative responses of cancer cells (11,12).”
    Quote in the paperSubstantial claim0 of 2 sources checked
    • cites [11]

      Couldn’t be matched to a paper in Crossref, so it can’t be checked.

    • cites [12]

      Couldn’t be matched to a paper in Crossref, so it can’t be checked.

  • May combine two claims.

    Interpretationreasoning
    § Discussion

    The presence of a 5-hydroxy group reduces binding affinity, probably by forming a hydrogen bond with the 4-keto group.

    “The presence of a 5-hydroxy group reduces the binding affinity, probably by forming a hydrogen bond with the 4-keto group.”
    Quote in the paperSubstantial claim

  • Probably not a substantial claim: may not pass S3 (load-bearing), S4 (based).

    Interpretationnone given
    § Results and Discussion

    Ile-133 is situated close to the heme in the current model.

    “Ile-133 has been proposed to be sit- uated close to the heme in the current model.”
    Quote in the paperNot a substantial claim

  • Probably not a substantial claim: may not pass S3 (load-bearing).

    Interpretationreasoning
    § Results and Discussion

    The increased potency of galangin for I474Y may be due to a favorable aromatic-aromatic interaction between the p-phenyl substituent and the mutated residue.

    “As predict- ed from the computer model, the increased potency of galangin for I474Y may be due to a favorable aromatic-aromatic interac- tion between the p-phenyl substituent and the mutated residue.”
    Quote in the paperNot a substantial claim

  • May combine two claims.

    Interpretationcitation
    § Results and Discussion

    The 5-hydroxy group probably forms an intramolecular hydrogen bond with the 4-keto group, weakening the interaction of the 4-keto group with the heme.

    “The 5-hydroxy group probably forms an intramolecular hydrogen bonding with the 4-keto group [indicated by nuclear magnetic resonance (NMR) analysis (39)], weakening the inter- action of the 4-keto group with the heme.”
    Quote in the paperNot a substantial claim0 of 1 sources checked
    • cites [39]

      Couldn’t be matched to a paper in Crossref, so it can’t be checked.

  • Classified as probably not a substantial claim.

    Premisecitation
    § Introduction

    Cell culture and nude mouse studies using aromatase-transfected MCF-7 and T-47D cells have demonstrated that tumor aromatase can play a role in breast cancer maintenance and progression.

    “Cell culture and nude mouse studies using aromatase-transfected MCF-7 and T-47D cells (13-15) have demonstrated that tumor aromatase can play a role in breast cancer maintenance and progression.”
    Quote in the paperSubstantial claim0 of 3 sources checked
    • cites [13]

      Couldn’t be matched to a paper in Crossref, so it can’t be checked.

    • cites [14]

      Couldn’t be matched to a paper in Crossref, so it can’t be checked.

    • cites [15]

      Couldn’t be matched to a paper in Crossref, so it can’t be checked.

  • May combine two claims.

    Interpretationreasoning
    § Results and Discussion

    Ile-395 lies at the far end of the hydrophobic pocket, and an aromatic-aromatic interaction may explain the increased potency of the I395F mutation.

    “Ile-395 is assigned to lie at the far end of the hydrophobic pocket, and an aromatic-aro- matic interaction may also explain the increased potency by the mutation Ile-395 to Phe.”
    Quote in the paperNot a substantial claim

  • Probably not a substantial claim: may not pass S3 (load-bearing).

    Premisecitation
    § Results and Discussion

    5-Hydroxyflavone is a less potent inhibitor of aromatase than flavone.

    “It has been reported that 5-hydrox- yflavone is a less potent inhibitor of aro- matase than flavone (19).”
    Quote in the paperNot a substantial claim0 of 1 sources checked
    • cites [19]

      Couldn’t be matched to a paper in Crossref, so it can’t be checked.

  • Probably not a substantial claim: may not pass S3 (load-bearing). May combine two claims.

    Premisecitation
    § Introduction

    Phytoestrogens are plant chemicals that bind to the estrogen receptor and induce many components of estrogen action.

    “Phytoestrogens are plant chemicals that bind to the estrogen receptor and induce many components of estrogen action (2-10).”
    Quote in the paperNot a substantial claim0 of 9 sources checked
    • cites [2]

      Couldn’t be matched to a paper in Crossref, so it can’t be checked.

    • cites [3]

      Couldn’t be matched to a paper in Crossref, so it can’t be checked.

    • cites [4]

      Couldn’t be matched to a paper in Crossref, so it can’t be checked.

    • cites [5]

      Couldn’t be matched to a paper in Crossref, so it can’t be checked.

    • cites [6]

      Couldn’t be matched to a paper in Crossref, so it can’t be checked.

    • cites [7]

      Couldn’t be matched to a paper in Crossref, so it can’t be checked.

    • cites [8]

      Couldn’t be matched to a paper in Crossref, so it can’t be checked.

    • cites [9]

      Couldn’t be matched to a paper in Crossref, so it can’t be checked.

    • cites [10]

      Couldn’t be matched to a paper in Crossref, so it can’t be checked.

  • Probably not a substantial claim: may not pass S3 (load-bearing), S4 (based).

    Interpretationnone given
    § Results and Discussion

    The 3-hydroxyl group of galangin and Thr-310 of the enzyme are on the same side of the beta-face of the flavone's ring-C.

    “The 3-hydroxyl group of galangin and Thr-310 of the enzyme are thought to be on the same side of the beta-face of the flavone's ring-C.”
    Quote in the paperNot a substantial claim

  • May combine two claims.

    Interpretationown data
    § Discussion

    It is unlikely that flavones inhibit NADPH-cytochrome P450 reductase, or at least such inhibition does not play a major role, because inhibition profiles vary for different aromatase mutants.

    “However, we feel that this possibility is unlikely, or at least the cytochrome P450 reductase inhibition does not play a major role here because the inhibition profiles do vary for different aromatase mutants.”
    Quote in the paperSubstantial claim

  • May combine two claims.

    Premisecitation
    § Discussion

    The IC50 values for coumestrol, genistein, biochanin A, chrysin, and naringenin for binding to recombinant human estrogen receptor were 0.01 pM, 2.0 pM, 6.0 pM, 33 pM, and 45 pM, respectively.

    “The IC50 values (i.e., the con- centration of the ligand competitor at which the binding of radiolabeled 17p- estradiol to the hER was reduced to 50%) for coumestrol, genistein, biochanin A, chrysin, and naringenin were determined as 0.01 pM, 2.0 pM, 6.0 pM, 33 pM, and 45 pM, respectively (42).”
    Quote in the paperSubstantial claim0 of 1 sources checked
    • cites [42]

      Couldn’t be matched to a paper in Crossref, so it can’t be checked.

  • Probably not a substantial claim: may not pass S3 (load-bearing). May combine two claims.

    Interpretationnone given
    § Discussion

    The present study is an in vitro study, and the effects could be different in vivo due to metabolic conversion processes.

    “The present study is an in vitro study. The effects could be different in vivo due to metabolic conversion processes.”
    Quote in the paperNot a substantial claim

  • Probably not a substantial claim: may not pass S3 (load-bearing).

    Premisecitation
    § Discussion

    Flavones are known to be competitive inhibitors of NAD(P)H:quinone acceptor oxidoreductase with respect to NAD(P)H.

    “Since we have found that flavones are known to be competitive inhibitors of NAD(P)H: quinone acceptor oxidoreductase with respect to NAD(P)H (43)”
    Quote in the paperNot a substantial claim0 of 1 sources checked
    • cites [43]

      Couldn’t be matched to a paper in Crossref, so it can’t be checked.

33 of 33

  • The paper relies on this without support.

    The molecular basis of phytoestrogen inhibition of aromatase is not known.

    “While phytoestrogens have been reported to be inhibitors of aromatase, the molecular basis of their inhibition of aromatase is not known.”

  • The authors state this as an assumption.

    The active site pocket of aromatase is rigid during initial modeling.

    “assuming that the pocket was rigid.”

  • The authors state this as an assumption.

    Residues within the active site can move to better accommodate inhibitors (induced fit).

    “assuming that residues within the active site can move to better accommodate the inhibitors (induced fit theory of molecular interaction)”

  • The paper relies on this without support.

    The computer model of the aromatase active site accurately represents the enzyme's active site and the binding orientations of the compounds.

    “Our computer modeling has revealed that only the S-configuration isomer can bind to the active site.”
    “Computer modeling suggests that the pocket on the distal helix side may be more compact or rigid so that ring B of chrysin and the two isoflavones have to be held at about the same position.”

  • The paper relies on this without support.

    The inhibition profiles and Ki values measured in the assay directly reflect the binding affinity of the compounds to aromatase.

    “The results obtained from inhibition profile studies indicate that the binding of genistein is improved by conformational changes upon mutations in the region Pro-308 to Thr-310.”

  • The paper relies on this without support.

    The site-directed mutations alter the active site pocket in the intended way without grossly disrupting the enzyme's overall structure.

    “Its binding was also improved by Ile-474 to Tyr, Ile- 133 to Tyr, and Ile-395 to Phe mutations.”
6 of 6

Claims other papers make about this one

Each is checked against this paper’s own text: does it say what the citing paper says it does?

  • Several studies demonstrated that components of alcoholic beverages such as procyanidin B and phytoestrogens could bind the active site of aromatase, leading to functional dysregulations.

    “several studies demonstrated that some component of alcoholic beverages, such as procyanidin B and phytoestrogens (i.e., flavones and isoflavones) could bind the active site of aromatase, leading to functional dysregulations.[133][134][135]”

    From The chronic alcohol consumption influences the gonadal axis in men: Results from a meta‐analysis (2024) · cites this paper as [135]

    The Results and Discussion report that flavone and isoflavone phytoestrogens bind the active site of aromatase and inhibit its activity. The paper does not establish that these compounds are components of alcoholic beverages, and it does not address procyanidin B (searched: procyanidin B, alcoholic beverages, wine, ethanol). (LLM, conf=0.88)

    Experimental — accuracy not yet measured

Self-check

Percentages, sums and reported differences re-computed from the paper’s own numbers.

  • Genistein's reported ER-binding advantage exceeds the stated range

    Minor

    The stated IC50 values are 2.0 pM for genistein and 33 pM for chrysin. Their ratio is 16.5, outside the stated 5-10-fold range.

    Reported 10 · recomputed 16.5

1 of 1

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Authors
Kao, Y. C., Zhou, C., Sherman, M., Laughton, C. A., & Chen, S.
Affiliations
Beckman Research Institute (US)
ORCID
Laughton, C A
Venue
Environmental Health Perspectives
Publisher
American Chemical Society (ACS)
Published
1998-02
Volume
106
Issue
2
Pages
85-92
ISSN
  • 0091-6765 (ISSN-L)
  • 1552-9924
DOI
10.1289/ehp.9810685
PMC
PMC1533021
OpenAlex
W2008151923
Cited by
338
References
46
Citations by year
2026: 5 · 2025: 3 · 2024: 5 · 2023: 9 · 2022: 5 · 2021: 14 · 2020: 11 · 2019: 5 · 2018: 7 · 2017: 11 · 2016: 9 · 2015: 7 · 2014: 9 · 2013: 17 · 2012: 10
FWCI
9.12
Type
journal article
Language
en
Open access
Licence
public-domain
Locations
  • Environmental Health Perspectives (publishedVersion, public-domain)
  • PubMed (publishedVersion)
Funders
  • National Cancer Institute (R01CA044735, CA 44735)
  • National Institute of Environmental Health Sciences (ES-08258, R01ES008258)
Topics
  • Health Sciences › Medicine › Pathology and Forensic Medicine › Phytoestrogen effects and research
  • Life Sciences › Biochemistry, Genetics and Molecular Biology › Genetics › Estrogen and related hormone effects
  • Health Sciences › Medicine › Pharmacology › Flavonoids in Medical Research
Keywords
phytoestrogens, flavones, isoflavones, flavanones, naphthoflavone, competitive inhibition, chrysin, baicalein, galangin, genistein, biochanin A, naringenin, active site binding, structure-activity relationship, estrogen synthesis
MeSH terms
Animals, Aromatase, Binding Sites, Enzyme Inhibitors, Estrogens, Non-Steroidal, Flavonoids, Cricetinae, Isoflavones, Models, Molecular, Plants, Mutagenesis, Site-Directed, CHO Cells, Reverse Transcriptase Polymerase Chain Reaction, Plant Preparations, Aromatase Inhibitors, Phytoestrogens

About these checks

Registry, retraction, Cites and statistics results are computed, not judged, with one exception: a printed reference that no index lists is read once by a model before it counts as a citation error. Claims are extracted by a model and kept only when their quote appears verbatim in the text; each cited source is then checked, with a model’s help, for whether it says what the claim relies on. Those verdicts can be wrong — read the claim’s quote and the cited source before relying on one.

Claims read by deepseek-v4.1-flash under definition version 3 (extract-v3) on 2026-11-02.

Classified by jev-1.13-20260917 (gold-guideline-v0.2) on 2026-11-02.

Statistics and arithmetic are recomputed, not judged.

Confidence bands are shown only for fields calibrated on our annotated test set. None is calibrated yet, so no band is shown.

What counts as a claim ›How we measure confidence ›How we check this ›

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