Ascorbic acid pre-treated quartz stimulates TNF-alpha release in RAW 264.7 murine macrophages through ROS production and membrane lipid peroxidation.
BACKGROUND
Inhalation of crystalline silica induces a pulmonary fibrotic degeneration called silicosis caused by the inability of alveolar macrophages to dissolve the crystalline structure of phagocytosed quartz particles. Ascorbic acid is capable of partially dissolving quartz crystals, leading to an increase of soluble silica concentration and to the generation of new radical sites on the quartz surface. The reaction is specific for the crystalline forms of silica. It has been already demonstrated an increased cytotoxicity and stronger induction of pro-inflammatory cyclooxygenase-2 (COX-2) by ascorbic acid pre-treated quartz (QA) compared to untreated quartz (Q) in the murine macrophage cell line RAW 264.7.


METHODS
Taking advantage of the enhanced macrophage response to QA as compared to Q particles, we investigated the first steps of cell activation and the contribution of early signals generated directly from the plasma membrane to the production of TNF-alpha, a cytokine that activates both inflammatory and fibrogenic pathways.


RESULTS
Here we demonstrate that TNF-alpha mRNA synthesis and protein secretion are significantly increased in RAW 264.7 macrophages challenged with QA as compared to Q particles, and that the enhanced response is due to an increase of intracellular ROS. Plasma membrane-particle contact, in the absence of phagocytosis, is sufficient to trigger TNF-alpha production through a mechanism involving membrane lipid peroxidation and this appears to be even more detrimental to macrophage survival than particle phagocytosis itself.


CONCLUSIONS
Taken together these data suggest that an impairment of pulmonary macrophage phagocytosis, i.e. in the case of alcoholic subjects, could potentiate lung disease in silica-exposed individuals.
Scarfì
Sonia
S
Department of Experimental Medicine, Section of Biochemistry, University of Genova, Genova, Italy. soniascarfi@unige.it
Magnone
Mirko
M
Ferraris
Chiara
C
Pozzolini
Marina
M
Benvenuto
Federica
F
Benatti
Umberto
U
Giovine
Marco
M
D000818:Animals; D000975:Antioxidants / Q000494:pharmacology; D001205:Ascorbic Acid / Q000737:chemistry*; D002084:Butylated Hydroxytoluene / Q000494:pharmacology; D002460:Cell Line; D002462:Cell Membrane / Q000187:drug effects* / Q000276:immunology / Q000378:metabolism; D002470:Cell Survival / Q000187:drug effects; D003571:Cytochalasin B / Q000494:pharmacology; D016264:Dextran Sulfate / Q000494:pharmacology; D004305:Dose-Response Relationship, Drug; D015227:Lipid Peroxidation / Q000187:drug effects*; D008264:Macrophages / Q000187:drug effects* / Q000276:immunology / Q000378:metabolism; D016676:Macrophages, Alveolar / Q000187:drug effects / Q000276:immunology / Q000378:metabolism; D008297:Male; D051379:Mice; D010587:Phagocytosis / Q000187:drug effects*; D011791:Quartz / Q000737:chemistry / Q000633:toxicity*; D012333:RNA, Messenger / Q000378:metabolism; D051381:Rats; D017207:Rats, Sprague-Dawley; D017382:Reactive Oxygen Species / Q000378:metabolism*; D051116:Receptors, Scavenger / Q000187:drug effects / Q000378:metabolism; D012995:Solubility; D013499:Surface Properties; D013997:Time Factors; D014409:Tumor Necrosis Factor-alpha / Q000235:genetics / Q000378:metabolism*
D000975:Antioxidants; D012333:RNA, Messenger; D017382:Reactive Oxygen Species; D051116:Receptors, Scavenger; D014409:Tumor Necrosis Factor-alpha; D011791:Quartz; D002084:Butylated Hydroxytoluene; D003571:Cytochalasin B; D016264:Dextran Sulfate; D001205:Ascorbic Acid