Mitochondrial permeability transition as the critical target of N-acetyl perfluorooctane sulfonamide toxicity in vitro.
Perfluorooctanyl compounds with active functional groups have been shown to disrupt mitochondrial bioenergetics by three distinct mechanisms: protonophoric uncoupling of mitochondrial respiration, induction of the mitochondrial permeability transition (MPT), or a nonselective increase in membrane permeability. The purpose of this investigation was to identify the initial target and specific sequence of events associated with the N-acetyl substituted perfluorooctanesulfonamides induced MPT. N-acetyl-perfluorooctanesulfonamide (FOSAA), N-ethyl-N-acetyl-perfluorooctanesulfonamide (N-Et FOSAA), perfluorooctanoic acid (PFOA), perfluorooctanesulfonate (PFOS), and N-ethyl-N-(2-ethoxy)-perfluorooctanesulfonamide (N-Et FOSE) were added individually to liver mitochondria freshly isolated from Sprague-Dawley rats. Mitochondrial swelling and cytochrome c release were recorded spectrophotometrically, oxygen uptake was monitored with a Clark-type oxygen electrode, and reactive oxygen species (ROS) were monitored by dichlorodihydrofluorescein diacetate (H(2)DCFDA) fluorescence. FOSAA (45 microM) and N-Et FOSAA (7.5 microM) induced calcium-dependent mitochondrial swelling, the release of cytochrome c, inhibition of uncoupled mitochondrial respiration, and ROS generation, all of which were inhibited by cyclosporin-A (CsA). PFOA (200 microM) displayed slight CsA sensitive activity, but neither PFOS (10 microM) nor N-Et FOSE (70 microM) induced the MPT. Results of this investigation demonstrate two important findings: (1) MPT induction is specific to the N-acetyl substituted perfluorooctanesulfonamides and, (2) the sequence of events is initiated by induction of the MPT, which causes the release of cytochrome c as well as other cofactors leading to inhibition of respiration and ROS generation. The toxicity of N-acetyl perfluorooctanyl compounds may therefore reflect the mitochondrial dysfunction, which is compounded by the ensuing oxidative injury.
Department of Biochemistry and Molecular Biology, Toxicology Graduate Program, University of Minnesota School of Medicine, 1035 University Drive, Duluth, MN 55812, USA.
Timothy M
TM
O'Brien
Kendall B
KB
Wallace
D000818:Animals; D002210:Caprylates / Q000737:chemistry / Q000633:toxicity; D045304:Cytochromes c / Q000378:metabolism; D005466:Fluorocarbons / Q000737:chemistry / Q000633:toxicity*; D066298:In Vitro Techniques; D008297:Male; D008930:Mitochondria, Liver / Q000187:drug effects* / Q000378:metabolism; D008933:Mitochondrial Swelling / Q000187:drug effects; D010539:Permeability / Q000187:drug effects; D051381:Rats; D013329:Structure-Activity Relationship; D013449:Sulfonamides / Q000737:chemistry / Q000633:toxicity*
D002210:Caprylates; D005466:Fluorocarbons; D013449:Sulfonamides; C063900:perfluorooctanesulfonamide; D045304:Cytochromes c; C023036:perfluorooctanoic acid