Cited by 70Pharmacogenetics and Drug MetabolismEstrogen and related hormone effectsSteroid Chemistry and Biochemistry

16Alpha-hydroxylation of estrone by human cytochrome P4503A4/5

Huang, Z·1998·Carcinogenesis

Abstract

The cytochrome P450 (P450) enzymes that catalyse metabolism of the estrogen, estrone (E1), to the putative carcinogen 16alpha-hydroxy E1 (16alpha-OHE1) in humans were determined. The potential of the most abundant circulating form of estrogen, estrone 3-sulfate (E1S), to be the substrate was also investigated. Human liver microsomal sulfatases convert E1S to E1, an essential prerequisite for formation of 16alpha-OHE1 from added E1S in this system. E1 metabolism to 16alpha-OHE1 in a panel of 15 human liver microsomal preparations correlated with total P450 concentrations (r2 = 0.63) and with activities associated with P450 forms CYP3A4 and 3A5 (r2 = 0.72). E1 16alpha-hydroxylase activity in human liver microsomes was inhibited by 75% by monoclonal anti human CYP3A4/5 antibodies at 4 mg antibody/nmol total P450, and by troleandomycin, a specific CYP3A4/5 inhibitor. Rates of E1 metabolism to 16alpha-OHE1 were 1.6-fold higher when E1 was generated in situ from E1S than when E1 was added. Microsomal preparations of cDNA expressed CYP3A4 or 3A5, with NADPH-P450-reductase co-expressed, both metabolized E1 to 16alpha-OHE1, and added cytochrome b5 increased the rates 5.1- and 7.5-fold, respectively. In these systems rates of E1 metabolism to 16alpha-OHE1 were 2.8-fold higher when E1 was generated in situ from E1S than when E1 was added. Kinetic values for E1 metabolism to 16alpha-OHE1 by human liver microsomes and for the expressed CYP3A4 system were Km 154 and 172 microM, respectively, and Vmax 238 pmol/min/nmol total P450 and 1050 pmol/min/nmol CYP3A4, respectively. Thus, formation of the putative carcinogen 16alpha-OHE1 is catalysed by CYP3A4 and 3A5 and stimulated by cytochrome b5. E1S is not a substrate but formation of E1 from E1S in situ stimulates formation of 16alpha-OHE1, possibly because E1S is more water soluble and in situ generation of E1 provides for facilitated exposure of E1 to the P450 substrate binding sites. Blocking of the pathway of E1 to 16alpha-OHE1 could provide a therapeutic approach for diminishing the risk of estrogen dependent breast cancer.

Integrity signals

Registry

Crossref · 10.1093/carcin/19.5.867

Cites

25 of 25 references verified0 citation errors · 0 not checkable

Statistics

Recomputing p-values needs the paper’s full text.

Claims the paper makes

This paper’s full text isn’t openly available, so its claims and self-check weren’t run. The registry and citation checks still apply.

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?

Cites

Flagged first, then by citations

Cited by

Sorted by citations

Authors
Huang, Z.
Affiliations
University at Albany, State University of New York (US)
Corresponding author
Huang, Z
Venue
Carcinogenesis
Published
1998-05-01
Volume
19
Issue
5
Pages
867-872
ISSN
  • 0143-3334 (ISSN-L)
  • 1460-2180
OpenAlex
W2170616524
Cited by
70
References
25
Citations by year
2025: 1 · 2022: 3 · 2021: 3 · 2019: 1 · 2018: 1 · 2017: 1 · 2016: 1 · 2015: 1 · 2014: 1 · 2013: 4 · 2012: 4
FWCI
3.63
Type
journal article
Language
en
Open access
closed
Locations
  • Carcinogenesis (publishedVersion)
  • PubMed (publishedVersion)
Topics
  • Life Sciences › Pharmacology, Toxicology and Pharmaceutics › Pharmacology › Pharmacogenetics and Drug Metabolism
  • Life Sciences › Biochemistry, Genetics and Molecular Biology › Genetics › Estrogen and related hormone effects
  • Life Sciences › Biochemistry, Genetics and Molecular Biology › Molecular Biology › Steroid Chemistry and Biochemistry
Keywords
estrone, 16α-hydroxylation, 16α-hydroxyestrone, CYP3A4, CYP3A5, human liver microsomes, estrone-3-sulfate, estrogen metabolism, cytochrome b5, monoclonal antibody inhibition
MeSH terms
Aryl Hydrocarbon Hydroxylases, Cytochrome P-450 Enzyme System, Enzyme Inhibitors, Estrone, Humans, Mixed Function Oxygenases, Microsomes, Liver, Steroid Hydroxylases, Substrate Specificity, Steroid 16-alpha-Hydroxylase, Cytochrome P-450 CYP3A, Cytochrome P-450 Enzyme Inhibitors, Cytochrome P-450 CYP2C8, Cytochrome P-450 CYP2C9

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.

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 ›

Are you an author, or do you see a problem with this page? Request a review