Human aldo-keto reductases in polycyclic aromatic hydrocarbon activation / Michael E. Burczynski.

Format:

Book

Manuscript

Microformat

Thesis/Dissertation

Author/Creator:

Burczynski, Michael E.

Contributor:

Penning, Trevor M., 1951- advisor.

University of Pennsylvania.

Language:

English

Subjects (All):

Penn dissertations--Pharmacology.

Pharmacology--Penn dissertations.

Pharmacology.

Academic Dissertations as Topic.

Medical Subjects:

Pharmacology.

Academic Dissertations as Topic.

Local Subjects:

Penn dissertations--Pharmacology.

Pharmacology--Penn dissertations.

Physical Description:

xvii, 164 pages : illustrations ; 29 cm

Production:

1999.

Summary:

A novel pathway of polycyclic aromatic hydrocarbon (PAH) activation is catalyzed by the cytosolic aldo-keto reductase (AKR) isoform (AKR1C9) from rat liver, 3alpha-hydroxysteroid dehydrogenase/dihydrodiol dehydrogenase (3alphaHSD/DD). Rat 3alphaHSD/DD oxidizes PAH trans-dihydrodiol proximate carcinogens to reactive and redox-active PAH ortho-quinones. However, the relevance of this metabolic pathway to PAH carcinogenesis in humans, was unknown.

Cloning and expression of four human AKRs revealed that multiple human homologs of AKR1C9 also catalyze the oxidation of the trans-dihydrodiol of benzo[a]pyrene (B[a]P), trans -dihydrodiol 7,8-dihydroxy-7,8-dihydro-benzo[a]pyrene (B[a]P-diol). Importantly, the redox-cycling o-quinone benzo[a]pyrene-7,8-dione (BPQ) was identified as the product of these reactions. These studies demonstrate that oxidation of PAH trans-dihydrodiols to o-quinones can occur in human cells.

An AKR is overexpressed in human cells exposed to the electrophilic Michael acceptor ethacrynic acid. Since the human AKRs possess high nucleotide sequence similarity, the identity of the inducible AKR isoform was unknown. Development of an isoform-discriminating ribonuclease protection assay demonstrated that AKR1C1 is both the constitutive and inducible AKR isoform in multiple human cell types following exposure to electrophiles, ROS, and PAH. The mechanism of AKR1C1 induction by PAH appears to be via an antioxidant response element (ARE)-like pathway rather than the xenobiotic response element (XRE) pathway which regulates CYP1A1 BPQ, the product of the AKR1C1 reaction, also feedback stimulates AKR1C1 expression. Thus PAH o-quinone formation by AKR1C1 sets up both a chemical (redox-cycling) and genetic (AKR1C1 induction) amplification of ROS in human cells.

Additional studies revealed that BPQ not only induces AKR1C1 via the ARE, but also induces CYP1A1 via the XRE pathway. Thus PAH o-quinones represent a novel class of bifunctional inducers capable of inducing phase I and phase II enzymes without a requirement for further metabolism. Importantly BPQ induces CYP1A1 via the AhR. Thus it appears that the cytosolic colocalization of AKRs and the AhR ultimately results in the deleterious targeting of genotoxic PAH o-quinones into the nucleus. These studies demonstrate that redox-cycling PAH o-quinones are formed in human cells by AKR members, and provide a foundation for investigating these metabolites as carcinogens in future in vivo studies.

Notes:

Supervisor: Trevor M. Penning.

Thesis (Ph.D. in Pharmacology) -- University of Pennsylvania, 1999.

Includes bibliographical references and index.

Local Notes:

University Microfilms order no.: 99-37706.

OCLC:

187475210