Identification of Na+/H+ exchange as a new target for toxic polycyclic aromatic hydrocarbons.
The ubiquitous environmental pollutants polycyclic aromatic hydrocarbons are responsible for important carcinogenic and apoptotic effects, whose mechanisms are still poorly understood, owing to the multiplicity of possible cellular targets. Among these mechanisms, alterations of ionic homeostasis have been suggested. In this work, the effects of benzo(a)pyrene [B(a)P] on pHi were tested in the rat liver F258 epithelial cell line, using the fluoroprobe carboxy-SNARF-1. After a 48-h treatment, B(a)P (50 nM) induced an alkalinization, followed by an acidification after 72 h and the development of apoptosis. Determinations of pH(i) recovery following an acid load showed an increased acid efflux at 48 h. Cariporide inhibited both the early alkalinization and the increased acid efflux, thus suggesting the involvement of Na+/H+ exchanger 1 (NHE1). Besides, alpha-naphtoflavone (alpha-NF), an inhibitor of CYP1A1-mediated B(a)P metabolism, prevented all pH(i) changes, and NHE1 activation was blocked by the antioxidant thiourea, which inhibited CYP1A1 metabolism-dependent H2O2 production. Regarding B(a)P-induced apoptosis, this was prevented by alpha-NF and bongkrekic acid, an inhibitor of mitochondria-dependent apoptosis. Interestingly, apoptosis was significantly reduced by cariporide. Taken together, our results indicate that B(a)P, via H2O2 produced by CYP1A1-dependent metabolism, induces an early activation of NHE1, resulting in alkalinization; this appears to play a significant role in mitochondria-dependent B(a)P-induced apoptosis.
Huc
Laurence
L
INSERM U456, Détoxication et Réparation Tissulaire, Faculté de Pharmacie, Université Rennes 1, 35043 Rennes Cedex, France.
Sparfel
Lydie
L
Rissel
Mary
M
Dimanche-Boitrel
Marie-Thérèse
MT
Guillouzo
André
A
Fardel
Olivier
O
Lagadic-Gossmann
Dominique
D
D000818:Animals; D017209:Apoptosis / Q000187:drug effects; D001564:Benzo(a)pyrene / Q000494:pharmacology / Q000633:toxicity*; D061945:Caspase Inhibitors; D020169:Caspases / Q000378:metabolism; D002460:Cell Line; D019363:Cytochrome P-450 CYP1A1 / Q000037:antagonists & inhibitors / Q000378:metabolism; D004847:Epithelial Cells / Q000166:cytology / Q000187:drug effects; D006146:Guanidines / Q000494:pharmacology; D006861:Hydrogen Peroxide / Q000378:metabolism; D006863:Hydrogen-Ion Concentration; D008099:Liver / Q000166:cytology / Q000187:drug effects; D008954:Models, Biological; D051381:Rats; D017923:Sodium-Hydrogen Exchangers / Q000378:metabolism*; D013450:Sulfones / Q000494:pharmacology; D013890:Thiourea / Q000494:pharmacology
D061945:Caspase Inhibitors; D006146:Guanidines; D017923:Sodium-Hydrogen Exchangers; D013450:Sulfones; C069139:growth factor-activatable Na-H exchanger NHE-1; D001564:Benzo(a)pyrene; C093373:cariporide; D006861:Hydrogen Peroxide; D019363:Cytochrome P-450 CYP1A1; D020169:Caspases; D013890:Thiourea