Carbonyl Reductase Inactivation May Contribute to Mouse Lung Tumor Promotion by Electrophilic Metabolites of Butylated Hydroxytoluene: Protein Alkylation in Vivo and in Vitro

Establishment of compound database of emerging antioxidants and high-resolution mass spectrometry screening in lake sediment from Taihu Lake Basin, China

Antioxidants are ubiquitous in various environmental samples, leading to increasing concern regarding their potential risk to environments or humans. However, there is dearth of information regarding the environmental fate of antioxidants and unknown/unexpected antioxidants in the environment. Here, we established a compound database (CDB) containing 320 current-used antioxidants by collecting the chemicals from EPA's functional use database and published documents. Physical-chemical characteristics of these antioxidants were estimated, and 19 ones were considered as persistent and bioaccumulative (P&B) substances. This CDB was further coupled with high resolution mass spectrometry (HRMS) technique, which was employed for suspect screening of antioxidants in extracts of sediments (n = 88) collected from Taihu Lake basin. We screened 119 HRMS features that can match 135 chemical formulas in the CDB, and 20 out of them exhibited the detection frequencies ≥ 90%. The total concentrations of suspect antioxidants in sediments ranged from 6.41 to 830 ng/g dw. Statistical analysis demonstrated that concentrations of suspect antioxidants in Taihu Lake were statistically significantly lower than those in Shihu and Jiulihu Lake, but greater than those from other small lakes. Collectively, this study provided a CDB that could be helpful for further monitoring studies of antioxidant in the environments, and also provided the first evidence regarding the ubiquity of antioxidants in aquatic environment of Taihu Lake basin.

Determination of 2,6-di-tert-butyl-hydroxytoluene and its transformation products in indoor dust and sediment by gas chromatography-mass spectrometry coupled with precolumn derivatization

We developed an analytical method to simultaneously determine 2,6-di-tert-butyl-hydroxytoluene (BHT) and its four transformation products in indoor dust and sediment samples. BHT, 2,6-di-tert-butylcyclohexa-2,5-diene-1,4-dione (BHT-Q), and 3,5-di-tert-butyl-4-hydroxybenzaldehyde (BHT-CHO) were measured by gas chromatography-mass spectrometry (GC-MS) after ultrasonic extraction with hexane/dichloromethane (1:3), while 2,6-di-tert-butyl-4-(hydroxymethyl) phenol (BHT-OH) and 3,5-di-tert-butyl-4-hydroxybenzoic acid (BHT-COOH) were derivatized using N, O-bis (trimethylsilyl) trifluoroacetamide before GC-MS analysis. The limits of detection (LODs) and quantification (LOQs) of the developed method were 0.02-0.34 and 0.08-1.14ngg^-1. The recoveries for BHT and its transformation products were 71.1-118% with relative standard deviations <10.6% at different spiking levels. The method was applied to indoor dust and sediment samples, showing that BHT was found in all samples with concentrations being 0.22-47.37μgg^-1 in dust and 0.09-6.93μgg^-1 in sediment. BHT-Q was the dominant transformation product, followed by BHT-CHO, BHT-OH, and BHT-COOH. Different metabolite profiles for BHT indicated various transformation pathways, making it necessary to study their transformation mechanism and environmental behaviors in the future studies.

Synthetic Phenolic Antioxidants and Their Metabolites in Indoor Dust from Homes and Microenvironments

Synthetic phenolic antioxidants (SPAs), including 2,6-di-tert-butyl-4-hydroxytoluene (BHT), are extensively used in food, cosmetic and plastic industries. Nevertheless, limited information is available on human exposures, other than the dietary sources, to SPAs. In this study, occurrence of 9 SPAs and their metabolites/degradation products was determined in 339 indoor dust collected from 12 countries. BHT was found in 99.5% of indoor dust samples from homes and microenvironments at concentrations that ranged from < LOQ to 118 μg/g and 0.10 to 3460 μg/g, respectively. This is the first study to measure BHT metabolites in house dust (0.01-35.1 μg/g) and their concentrations accounted for 9.2-58% of the sum concentrations (∑SPAs). 3,5-di-tert-butyl-4-hydroxybenzaldehyde (BHT-CHO), 2,6-di-tert-butyl-4-(hydroxymethyl)phenol (BHT-OH), 2,6-di-tert-butyl-1,4-benzoquinone (BHT-Q) were the major derivatives of BHT found in dust samples. The concentrations of gallic acid esters (gallates) in dust from homes and microenvironments ranged from < LOQ to 18.2 and < LOQ to 684 μg/g, respectively. The concentrations and profiles of SPAs varied among countries and microenvironments. Significantly elevated concentrations of SPAs were found in dust from an e-waste workshop (1530 μg/g). The estimated daily intake (EDI) of BHT via house dust ingestion ranged from 0.40 to 222 ng/kg/d (95th percentile).

Glucuronidation and methylation of procyanidin dimers b2 and 3,3″-di-o-galloyl-b2 and corresponding monomers epicatechin and 3-o-galloyl-epicatechin in mouse liver

PURPOSE

The 3,3″-di-O-galloyl ester of procyanidin B2 (B2G2) is a component of grape seed extract that inhibits growth of human prostate carcinoma cell lines. In preparation for studies in mice, its hepatic metabolism was examined in vitro and compared to B2 and the corresponding monomers, epicatechin (EC) and 3-O-galloyl-epicatechin (ECG).

METHODS

Compounds were incubated with liver microsomes or cytosol containing cofactors for glucuronidation, sulfation or methylation, and products analyzed by liquid chromatography-mass spectrometry (LC-MS). B2G2 was administered orally to mice and plasma analyzed by LC-MS for unmodified procyanidin and metabolites.

RESULTS

Glucuronides and methyl ethers of B2 and B2G2 were formed in small amounts. In contrast, EC and ECG were largely or completely converted to glucuronides, sulfates and methyl ethers under the same incubation conditions. B2G2 given orally to mice was partially absorbed intact; no significant metabolites were detected in plasma.

CONCLUSIONS

Glucuronidation and methylation of procyanidins B2 and B2G2 occurred but were minor processes in vitro. B2G2 was partially absorbed intact in mice after oral dosing and did not undergo significant metabolism. Unlike the flavanol monomers EC and ECG, therefore, B2G2 bioavailability should not be limited by metabolism. These results paved the way for ongoing pharmacokinetic and efficacy studies.

Protein damage from electrophiles and oxidants in lungs of mice chronically exposed to the tumor promoter butylated hydroxytoluene

The food additive butylated hydroxytoluene (BHT) promotes tumorigenesis in mouse lung. Chronic BHT exposure is accompanied by pulmonary inflammation and several studies indicate that elevated levels of reactive oxygen species (ROS) are involved in its promoting activity. The link between BHT and elevated ROS involves formation of quinone methide (QM) metabolites; these electrophiles form adducts with a variety of lung proteins including several enzymes that protect cells from oxidative stress. Studies in vitro demonstrated that QM alkylation of cytoprotective enzymes is accompanied by inactivation, so an objective of the present investigation was to determine if inactivation also occurs in vivo. Two groups of mice were exposed to BHT by intraperitoneal injection, one for 10 days and the other for 24 days, and proteins from lung cytosols were examined for damage. Analysis by Western blotting demonstrated that BHT treatment caused substantial increases in protein carbonylation, nitration and adduction by 4-hydroxynonenal, confirming the occurrence of sustained oxidative and nitrosative stress over the treatment period required for tumor promotion. Effects of BHT on the activities and/or levels of a representative group of antioxidant/protective enzymes in mouse lung also were assessed; NAD(P)H:quinone reductase and glutathione reductase were unaffected, however carbonyl reductase activity decreased 50-60%. Superoxide dismutase and glutathione peroxidase activities increased 2- and 1.5-fold, respectively, and glutamate-cysteine ligase catalytic subunit expression increased 32-39% relative to untreated mice. Glutathione S-transferase (GST) activity decreased 50-60% but concentrations of the predominant isoforms, GSTM1 and P1, were not affected. GSTP1 was substantially more susceptible than M1 to adduction and inhibition by treatment with BHT-QM in vitro, suggesting that lower GST activity in mice after BHT treatment is due to adduction of the P1 isoform. The results of this study provide additional insight into mechanisms of BHT-induced oxidative damage and further support a link between inflammation and tumor promotion in mouse lung.