title: Oxidative stress induced by palytoxin in human keratinocytes is mediated by a H+-dependent mitochondrial pathway.
abstract: In the last decades, massive blooms of palytoxin (PLTX)-producing Ostreopsis cf. ovata have been observed along Mediterranean coasts, usually associated to human respiratory and cutaneous problems. At the molecular level, PLTX induces a massive intracellular Na(+) influx due to the transformation of Na(+)/K(+) ATPase in a cationic channel. Recently, we have demonstrated that Na(+) overload is the crucial step in mediating overproduction of reactive oxygen species (ROS) and cell death in human HaCaT keratinocytes, tentatively explaining PLTX-induced skin irritant effects. In the present study the molecular mechanisms of ROS production induced by PLTX-mediated Na(+) intracellular overload have been investigated. In HaCaT cells, PLTX exposure caused accumulation of superoxide anion, but not of nitric oxide or peroxynitrite/hydroxyl radicals. Even if RT-PCR and western blot analysis revealed an early NOX-2 and iNOS gene and protein over-expressions, their active involvement seemed to be only partial since selective inhibitors did not completely reduce O(2)(-) production. A significant role of other enzymes (COX-1, COX-2, XO) was not evidenced. Nigericin, that counteracts Na(+)-mediated H(+)-imbalance, dissipating ΔpH across mitochondrial inner membrane, and the uncouplers DNP significantly reduced O(2)(-) production. These inhibitions were synergistic when co-exposed with complex-I inhibitor rotenone. These results suggest a novel mechanism of O(2)(-) production induced by PLTX-mediated ionic imbalance. Indeed, the H(+) intracellular overload that follows PLTX-induced intracellular Na(+) accumulation, could enhance ΔpH across mitochondrial inner membrane, that seems to be the driving force for O(2)(-) production by reversing mitochondrial electron transport.
authors.affiliation: Department of Life Science, University of Trieste, Via L. Giorgieri 7/9, 34127 Trieste, Italy. marco.pelin@phd.units.it
authors.forename: Marco
authors.initials: M
authors.lastname: Pelin
authors.forename: Cristina
authors.initials: C
authors.lastname: Ponti
authors.forename: Silvio
authors.initials: S
authors.lastname: Sosa
authors.forename: Davide
authors.initials: D
authors.lastname: Gibellini
authors.forename: Chiara
authors.initials: C
authors.lastname: Florio
authors.forename: Aurelia
authors.initials: A
authors.lastname: Tubaro
mesh_terms: D000178:Acrylamides / Q000494:pharmacology*; D002460:Cell Line; D003064:Cnidarian Venoms / Q000494:pharmacology*; D004305:Dose-Response Relationship, Drug; D006801:Humans; D015603:Keratinocytes / Q000187:drug effects / Q000378:metabolism*; D008928:Mitochondria / Q000187:drug effects / Q000378:metabolism*; D018384:Oxidative Stress / Q000187:drug effects / Q000502:physiology*; D011522:Protons; D017382:Reactive Oxygen Species / Q000378:metabolism; D015398:Signal Transduction / Q000187:drug effects / Q000502:physiology*; D013481:Superoxides / Q000378:metabolism; D000095702:Polyether Toxins
chemical_list: D000178:Acrylamides; D003064:Cnidarian Venoms; D011522:Protons; D017382:Reactive Oxygen Species; D013481:Superoxides; C010272:palytoxin; D000095702:Polyether Toxins