Exposure to benzene metabolites causes oxidative damage in Saccharomyces cerevisiae

Hydroquinone exposure accumulates neutral lipid by the activation of CDP-DAG pathway in Saccharomyces cerevisiae

Benzene metabolites (HQ and BQ) are toxic compounds and their presence in human cause alteration in cellular respiration and kidney damage. In the current study, Saccharomyces cerevisiae has been used as a model organism and acute exposure of hydroquinone (HQ) decreased cell growth and increased reactive oxygen species (ROS). The expression of apoptosis regulatory genes (YCA1, NUC1, YSP1 and AIF1) were increased with HQ exposure in the wild-type cells. HQ exposure in the wild-type cells altered both the phospholipid and neutral lipid levels. Phosphatidylcholine is a vital membrane lipid that has a vital role in membrane biogenesis and was increased significantly with HQ. The neutral lipid results were supported with lipid droplets data and mRNA expression study. The phospholipid knockouts (Kennedy pathway) accumulated neutral lipids via the CDP-DAG (cytidine-diphosphate-diacylglycerol) pathway genes both in the presence and absence of HQ.

Benzoquinone alters the lipid homeostasis in Saccharomyces cerevisiae

Objective: To elucidate the impact of benzoquinone (BQ) on lipid homeostasis and cytotoxicity in Saccharomyces cerevisiae. Methods: The impact of BQ exposure on wild-type and knockouts of PC biosynthesizing genes revealed the alterations in the lipids that were analyzed by fluorescence microscopy, thin layer chromatography, and gene expression studies. Results: In yeast, BQ exposure reduced the growth pattern in wild-type cells. The gene knockout strains of the phospholipid metabolism altered the mRNA expression of the apoptosis genes - both caspase-dependent and independent. The BQ exposure revealed an increase in both the phospholipids and neutral lipids via the CDP:DAG and the Kennedy pathway genes. The accumulation of both neutral lipids and phospholipids during the BQ exposure was discrete and regulated by different pathways. Conclusions: BQ exposure inhibited cell growth, increased the reactive oxygen species (ROS), and altered membrane proliferation. The CDP:DAG and Kennedy pathway lipids also discretely altered by BQ, which is required for the membrane functions and energy purposes of life.

Mechanism of Tolerance to the Lignin-Derived Inhibitor p-Benzoquinone and Metabolic Modification of Biorefinery Fermentation Strains

p-Benzoquinone (BQ) is a lignin-derived inhibitor of biorefinery fermentation strains produced during pretreatment of lignocellulose. Unlike the well-studied inhibitors furan aldehydes, weak acids, and phenolics, the inhibitory properties of BQ, the microbial tolerance mechanism, and the detoxification strategy for this inhibitor have not been clearly elucidated. Here, BQ was identified as a by-product generated during acid pretreatment of various lignocellulose feedstocks, including corn stover, wheat straw, rice straw, tobacco stem, sunflower stem, and corncob residue. BQ at 20 to 200 mg/liter severely inhibited the cell growth and fermentability of various bacteria and yeast strains used in biorefinery fermentations. The BQ tolerance of the strains was found to be closely related to their capacity to convert BQ to nontoxic hydroquinone (HQ). To identify the key genes responsible for BQ tolerance, transcription levels of 20 genes potentially involved in the degradation of BQ in Zymomonas mobilis were investigated using real-time quantitative PCR in BQ-treated cells. One oxidoreductase gene, one hydroxylase gene, three reductase genes, and three dehydrogenase genes were found to be responsible for the conversion of BQ to HQ. Overexpression of the five key genes in Z. mobilis (ZMO1696, ZMO1949, ZMO1576, ZMO1984, and ZMO1399) accelerated its cell growth and cellulosic ethanol production in BQ-containing medium and lignocellulose hydrolysates.IMPORTANCE This study advances our understanding of BQ inhibition behavior and the mechanism of microbial tolerance to this inhibitor and identifies the key genes responsible for BQ detoxification. The insights here into BQ toxicity and tolerance provide the basis for future synthetic biology to engineer industrial fermentation strains with enhanced BQ tolerance.

Application of cell-based assays for toxicity characterization of complex wastewater matrices: Possible applications in wastewater recycle and reuse

Exposure to pre-concentrated inlet or outlet STP wastewater extracts at different concentrations (0.001% to 1%) induced dose-dependent toxicity in MCF-7 cells, whereas drinking water extracts did not induce cytotoxicity in cells treated. GC-MS analysis revealed the occurrence of xenobiotic compounds (Benzene, Phthalate, etc.) in inlet/outlet wastewater extracts. Cells exposed to inlet/outlet extract showed elevated levels of reactive oxygen species (ROS: inlet: 186.58%, p<0.05, outlet, 147.8%, p<0.01) and loss of mitochondrial membrane potential (Δψm: inlet, 74.91%, p<0.01; outlet, 86.70%, p<0.05) compared to the control. These concentrations induced DNA damage (Tail length: inlet: 34.4%, p<0.05, outlet, 26.7%, p<0.05) in treated cells compared to the control (Tail length: 7.5%). Cell cycle analysis displayed drastic reduction in the G1 phase in treated cells (inlet, G1:45.0%; outlet, G1:58.3%) compared to the control (G1:67.3%). Treated cells showed 45.18% and 28.0% apoptosis compared to the control (1.2%). Drinking water extracts did not show any significant alterations with respect to ROS, Δψm, DNA damage, cell cycle and apoptosis compared to the control. Genes involved in cell cycle and apoptosis were found to be differentially expressed in cells exposed to inlet/outlet extracts. Herein, we propose cell-based toxicity assays to evaluate the efficacies of wastewater treatment and recycling processes.

Inhibition of autophagy enhances Hydroquinone-induced TK6 cell death

Hydroquinone (HQ), one of the metabolic products of benzene, is a carcinogen. It can induce apoptosis in lymphoma cells. However, whether HQ can induce autophagy and what roles autophagy plays in TK6 cells exposured to HQ remains unclear. In this study, we found that HQ could induce autophagy through techniques of qRT-PCR, Western blot, immunofluorescent assay of LC3 and transmission electron microscope. Furthermore, inhibiting autophagy using 3-methyladenine (3-MA) or chloroquine (CQ) significantly enhanced HQ-induced cell apoptosis, suggesting that autophagy may be a survival mechanism. Our study also showed that HQ activated PARP-1. Moreover, knockdown of PARP-1 strongly exhibited decreased autophagy related genes expression. In contrast, the absence of SIRT1 increased that. Altogether, our data provided evidence that HQ induced autophagy in TK6 cells and autophagy protected TK6 from HQ attack-induced injury in vitro, and the autophagy was partially mediated via activation of the PARP-1-SIRT1 signaling pathway.