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NAD(P)H:quinone oxidoreductase 1 (NQO1) activity threshold in intact pulmonary arterial endothelial cells (PAEC)
Author(s) -
Bongard Robert,
Krenz Gary,
Lindemer Brian,
Merker Marilyn
Publication year - 2009
Publication title -
the faseb journal
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 1.709
H-Index - 277
eISSN - 1530-6860
pISSN - 0892-6638
DOI - 10.1096/fasebj.23.1_supplement.1024.10
Subject(s) - sulforaphane , chemistry , biochemistry , cytosol , nad+ kinase , dehydrogenase , enzyme , enzyme assay , pharmacology , biology
One pulmonary endothelial metabolic function is reduction of blood borne redox compounds via NQO1, wherein phase II enzyme induction is a potential means to optimize this function. However, a threshold above which increases in NQO1 activity do not support increases in NQO1 substrate toxicity is seen in other cell types. The goal of this study was to use a kinetic approach to evaluate whether PAEC also exhibit an NQO1 activity threshold. PAEC NQO1 activity in cell cytosol fraction was induced ~6 fold (46.2±3.4 vs 268.1±28.5 nmol/min/mg protein) by exposure to sulforaphane (5 μM;24 hr). However, when intact cell NQO1 activity was measured by addition of duroquinone (DQ; 0‐50 μM) to the extracellular medium, the maximal reduction rate was only ~3 fold higher in sulforaphane than control cells (10.0±0.6 vs 32.2±1.3 nmol/min/mg protein). The possibility that NADPH availability was limiting NQO1 activity in sulforaphane exposed cells was suggested by the observation that glucose‐6‐phosphate dehydrogenase was induced only 1.2 fold (19.6 ± 1.2 vs 23.9 ± 1.6 nmol/min/mg protein). The study demonstrates a threshold effect for intact PAEC NQO1 activity and implies that the pulmonary endothelial NQO1 capacity to activate blood borne anticancer drugs or detoxify xenobiotics is limited by factors other than enzyme activity measured in cytosol fractions. Support: HL‐65537 and Dept. of Veterans Affairs.