Fit-for-purpose characterization of air-liquid-interface (ALI) in vitro exposure systems for e-vapor aerosol.

Air-liquid-interface (ALI) exposure systems deliver aerosol to the apical surface of cells which mimics the in vivo inhalation exposure conditions. It is necessary, however, to quantify the delivered amount of aerosol for ALI-based in vitro toxicity assessment. In this study, we evaluated two commercially available ALI exposure systems, a Vitrocell® Ames 48 (Ames 48) and a Vitrocell® 24/48 (VC 24/48), and the Vitrocell® VC1/7 smoking machine using a cig-a-like cartridge-based e-vapor device with a prototype formulation (containing 4% nicotine by weight). We characterized aerosol particle-size distribution, aerosol mass, and major chemical components (nicotine, propylene glycol, and glycerol) at the generation source and verified the repeatability of the aerosol generation. We determined aerosol delivery at the ALI by gravimetric analysis of mass collected on Cambridge filter pads and analytical quantitation of the buffer medium which showed that both aerosol mass and nicotine to an exposure insert linearly increased up to 400 puffs. The delivered aerosol mass covered a wide range of 0.8-3.4 mg per insert in the Ames 48 with variability (relative standard deviation, RSD) up to 12% and 1.1-6.4 mg per insert in the VC 24/48 with variability up to 15%. The delivered nicotine ranged approximately up to 200 µg per insert in both exposure systems. These results provided operation and aerosol delivery information of these ALI exposure systems for subsequent in vitro testing of e-vapor aerosols.

Effect of variable power levels on the yield of total aerosol mass and formation of aldehydes in e-cigarette aerosols.

The study objective was to determine the effect of variable power applied to the atomizer of refillable tank based e-cigarette (EC) devices. Five different devices were evaluated, each at four power levels. Aerosol yield results are reported for each set of 25 EC puffs, as mass/puff, and normalized for the power applied to the coil, in mass/watt. The range of aerosol produced on a per puff basis ranged from 1.5 to 28 mg, and, normalized for power applied to the coil, ranged from 0.27 to 1.1 mg/watt. Aerosol samples were also analyzed for the production of formaldehyde, acetaldehyde, and acrolein, as DNPH derivatives, at each power level. When reported on mass basis, three of the devices showed an increase in total aldehyde yield with increasing power applied to the coil, while two of the devices showed the opposite trend. The mass of formaldehyde, acetaldehyde, and acrolein produced per gram of total aerosol produced ranged from 0.01 to 7.3 mg/g, 0.006 to 5.8 mg/g, and <0.003 to 0.78 mg/g, respectively. These results were used to estimate daily exposure to formaldehyde, acetaldehyde, and acrolein from EC aerosols from specific devices, and were compared to estimated exposure from consumption of cigarettes, to occupational and workplace limits, and to previously reported results from other researchers.

Electrochemical oxidation of ochratoxin A: correlation with 4-chlorophenol.

Ochratoxin A (OTA, 1A) is a mycotoxin implicated in human kidney carcinogenesis, in which oxidative activation is believed to play a key role. To gain an understanding of the oxidative behavior of the toxin, we have carried out an electrochemical study and have observed a direct correlation between the electrochemistry of OTA and 4-chlorophenol (4-ClPhOH). Cyclic voltammetry (CV) of OTA in acetonitrile (MeCN) showed that the toxin exhibits an irreversible oxidative half-peak potential (E(p/2)) of 1.81 V vs saturated calomel electrode (SCE); the corresponding value for 4-ClPhOH is 1.59 V. For both compounds, subsequent scans revealed the appearance of the respective hydroquinone/benzoquinone couple, which formed from the oxidation of the parent para-chlorophenol moiety. The hydroquinone of OTA (OTHQ, 2) exhibited E(p/2) = 1.21 V in MeCN. Deprotonation of OTA to form the phenolate (OTA(-)) lowered the potential to E(p/2) = 1.0 V in MeCN. However, from the oxidation of OTA(-), no evidence for the OTHQ(2)/OTQ(3) redox couple was found. In aqueous phosphate buffer (pH 6-8), the electrochemical behavior of OTA mimicked that observed for OTA(-) in MeCN; E(p/2) was approximately 0.8 V vs SCE and subsequent scans did not generate the OTHQ/OTQ redox couple. From capillary electrophoresis (CE), a diffusion coefficient (D) of 0.48 x 10(-5) cm(2) s(-1) was determined for OTA in phosphate buffer, pH 7.0. Combining this value with electrochemical data suggested that OTA undergoes a 1H(+)/1e oxidation in aqueous media. The biological implications of these findings with respect to the oxidative metabolism of OTA, and other chlorinated phenols, are discussed.

Oxidation of ochratoxin A by an Fe-porphyrin system: model for enzymatic activation and DNA cleavage.

Ochratoxin A (OTA, 1) is a fungal toxin that facilitates single-strand DNA cleavage, DNA adduction, and lipid peroxidation when metabolically activated. To model the enzymatic activation of OTA, we have employed the water-soluble iron(III) meso-tetrakis(4-sulfonatophenyl)porphyrin (FeTPPS) oxidation system. In its presence, OTA has been found to facilitate single-strand cleavage of supercoiled plasmid DNA through production of reactive oxygen species (ROS) (i.e., the hydroxyl radical, HO(*)). The reaction of OTA with the FeTPPS oxidation system also generated three hydroxylated products (chlorine atom still attached), which was taken as evidence for production of the known hydroxylated metabolites (2-4) of OTA. This result suggested that the FeTPPS system served as a reasonable model for the enzymatic activation of OTA. When the reaction of OTA with FeTPPS was carried out in the presence of excess hydrogen peroxide (H(2)O(2)) and sodium ascorbate, a hydroquinone species (OTHQ, 5) was detected in which an OH group has replaced the chlorine atom of OTA. The production of OTHQ (5) was dependent on the presence of the reducing agent, sodium ascorbate, which suggested that the oxidation catalyst furnished the quinone derivative OTQ (6) that was subsequently reduced to OTHQ (5) by ascorbate. Utilizing a synthetic sample of OTHQ (5), the hydroquinone was found to undergo autoxidation with a t(1/2) of 11.1 h at pH 7.4, and to possess a pK(a) value of 8.03 for the phenolic oxygen ortho to the carbonyl groups. Our findings imply that the hydroquinone (OTHQ) and quinone (OTQ) metabolites of OTA have the ability to cause alkylation/redox damage and have allowed us to propose a viable pathway for oxidative damage by OTA.