title: Failure of MTT as a toxicity testing agent for mesoporous silicon microparticles.
abstract: In this work, it is shown that the common toxicity indicator, MTT (3-[4,5-dimethylthiazol-2-yl]-2,5-diphenyltetrazolium bromide), will fail to predict the toxicity of porous silicon (PSi) microparticles. This is due to the spontaneous redox reactions where the MTT is reduced and the PSi particle surfaces are oxidized simultaneously. MTT was shown to even react with thermally oxidized and carbonized forms of PSi particles, although the treatment did give an enhanced protection against the unwanted reactions as compared to as-anodized PSi particles. The observed levels of cellular viability with the MTT assay were much higher than expected in the presence of Caco-2 cells, even considering the spontaneous reduction of MTT at PSi surfaces. The results indicate that the redox reaction is further enhanced inside living cells. Thus, we recommend that MTT should not be used to test the cytotoxicity of drug formulations containing PSi microparticles. The study also shows that since PSi particles are capable of reducing the MTT, they will also be able to reduce other species as well. This should be taken into account when considering future applications for the porous silicon particles. The completely oxidized SiO2 particles (MCM-41 and SBA-15) were shown to work as expected with the MTT assay and showed no inherent oxidation/reduction.
authors.affiliation: Division of Pharmaceutical Technology P.O. Box 56 (Viikinkaari 5 E), FI-00014 University of Helsinki, Finland. timo.laaksonen@helsinki.fi
authors.forename: Timo
authors.initials: T
authors.lastname: Laaksonen
authors.forename: Hélder
authors.initials: H
authors.lastname: Santos
authors.forename: Henna
authors.initials: H
authors.lastname: Vihola
authors.forename: Jarno
authors.initials: J
authors.lastname: Salonen
authors.forename: Joakim
authors.initials: J
authors.lastname: Riikonen
authors.forename: Teemu
authors.initials: T
authors.lastname: Heikkilä
authors.forename: Leena
authors.initials: L
authors.lastname: Peltonen
authors.forename: Narendra
authors.initials: N
authors.lastname: Kumar
authors.forename: Dmitry Yu
authors.initials: DY
authors.lastname: Murzin
authors.forename: Vesa-Pekka
authors.initials: VP
authors.lastname: Lehto
authors.forename: Jouni
authors.initials: J
authors.lastname: Hirvonen
mesh_terms: D018938:Caco-2 Cells; D002470:Cell Survival / Q000187:drug effects; D004396:Coloring Agents / Q000032:analysis* / Q000737:chemistry; D004337:Drug Carriers / Q000737:chemistry / Q000633:toxicity*; D006801:Humans; D010084:Oxidation-Reduction; D010316:Particle Size; D016062:Porosity; D012680:Sensitivity and Specificity; D012825:Silicon / Q000737:chemistry / Q000633:toxicity*; D013499:Surface Properties; D013778:Tetrazolium Salts / Q000032:analysis* / Q000737:chemistry; D013844:Thiazoles / Q000032:analysis* / Q000737:chemistry; D018675:Toxicity Tests / Q000379:methods / Q000592:standards
chemical_list: D004396:Coloring Agents; D004337:Drug Carriers; D013778:Tetrazolium Salts; D013844:Thiazoles; C022616:thiazolyl blue; D012825:Silicon