Involvement of Semiquinone Radicals in the in Vitro Cytotoxicity of Cigarette Mainstream Smoke

Abstract

Free radicals in cigarette smoke have attracted a great deal of attention because they are hypothesized to be responsible in part for several of the pathologies related to smoking. Hydroquinone, catechol, and their methyl-substituted derivatives are abundant in the particulate phase of cigarette smoke, and they are known precursors of semiquinone radicals. In this study, the in vitro cytotoxicity of these dihydroxybenzenes was determined using the neutral red uptake (NRU) assay, and their radical-forming capacity was determined by electron paramagnetic resonance (EPR). All of the dihydroxybenzenes studied were found to generate appreciable amounts of semiquinone radicals when dissolved in the cell culture medium employed in the NRU assay. Hydroquinone exhibited by far the highest capacity to form semiquinone radicals at physiological pH, even though it is not the most cytotoxic dihydroxybenzene. Methyl-substituted dihydroxybenzenes were found to be more cytotoxic than either hydroquinone or catechol. The formation of semiquinone radicals via auto-oxidation of the dihydroxybenzenes was found to be dependent on the reduction potential of the corresponding quinone/semiquinone radical redox couple. The capacity to generate semiquinone radicals was found to be insufficient to explain the variance in the cytotoxicity among the dihydroxybenzenes in our study; consequently, other mechanisms of toxicity must also be involved. The observed interactions between 2,6-dimethylhydroquinone and hydroquinone in the cytotoxicity assay and EPR analysis suggest that care needs to be taken when the bioactivity of cigarette smoke constituents is evaluated, i.e., the effect of the cigarette smoke complex matrix on the activity of the single constituent studied must be taken into consideration.

Effects of Different Phases of Cigarette Smoke on Lipid Peroxidation and Membrane Structure in Liposomes

“…[16][17][18]24,26,27] The tar contains diverse persistent radicals that can be observed directly by ESR. [16,17,19,21,25] However, the effects of the smoke tar on the LPO development remain unclear. [16,17,26,27] In the present work, addition of tar extracts to liposomes provoked a slight decrease in the DB level as compared with the control samples during the first 20 min after LPO initiation (Fig.…”

“…[6,[15][16][17][18][19][20][21][22][23] Cigarette smoke is a complex chemical conglomerate that contains high concentrations of two distinctly different fractions of free radicals, one in its gas phase (GP) and another one in the particulate matter (tar). [16,17,[24][25][26][27] The GP of the smoke predominantly contains reactive carbon-and oxygencentred radicals, as well as a rather sizable amount of nitric oxide. [16,19] Tar contains, most prominently, polycyclic hydrocarbons, polyphenols, and quinones.…”

Phenolic compound formation from the low temperature pyrolysis of tobacco

“…The most abundant phenolic compounds identified in cigarette smoke are phenol, dihydroxybenzenes, and their respective methyl-substituted derivatives. Hydroquinone, catechol, and their methyl derivatives have been shown to be toxic [15][16][17][18][19][20].…”

Activated charcoal filter effectively reduces p-benzosemiquinone from the mainstream cigarette smoke and prevents emphysema

“…It has been reported that the semiquinone of CS is cytotoxic (Chouchane et al 2006;Pryor et al 1998). Here we show that a charcoal fi lter, which effectively reduces the p-BSQ of mainstream smoke, also causes a marked reduction in the cytotoxicity of CS.…”

“…Once identifi ed, removal of that chemical entity could effectively reduce smokers' risk. Earlier, it was indicated that long-lived semiquinone radical(s) present in an aqueous extract of CS (AECS) is cytotoxic and causes protein and DNA damage (Pryor et al 1983(Pryor et al , 1986(Pryor et al , 1998Panda et al 1999Panda et al , 2000Panda et al , 2001Chouchane et al 2006;Banerjee et al 2008). Protein damage and DNA fragmentation are hallmarks of emphysema (Tuder et al 2003).…”