PCB11 Metabolite, 3,3'-Dichlorobiphenyl-4-ol, Exposure Alters the Expression of Genes Governing Fatty Acid Metabolism in the Absence of Functional Sirtuin 3: Examining the Contribution of MnSOD.

Sinthia Alam,Kimberly Krager,Nukhet Aykin-Burns,Hans-Joachim Lehmler,Xueshu Li,Gwendolyn Carter

doi:10.3390/antiox7090121

Abstract

Although the production of polychlorinated biphenyls (PCBs) is prohibited, the inadvertent production of certain lower-chlorinated PCB congeners still threatens human health. We and others have identified 3,3’-dichlorobiphenyl (PCB11) and its metabolite, 3,3’-dichlorobiphenyl-4-ol (4OH-PCB11), in human blood, and there is a correlation between exposure to this metabolite and mitochondrial oxidative stress in mammalian cells. Here, we evaluated the downstream effects of 4OH-PCB11 on mitochondrial metabolism and function in the presence and absence of functional Sirtuin 3 (SIRT3), a mitochondrial fidelity protein that protects redox homeostasis. A 24 h exposure to 3 μM 4OH-PCB11 significantly decreased the cellular growth and mitochondrial membrane potential of SIRT3-knockout mouse embryonic fibroblasts (MEFs). Only wild-type cells demonstrated an increase in Manganese superoxide dismutase (MnSOD) activity in response to 4OH-PCB11–induced oxidative injury. This suggests the presence of a SIRT3-mediated post-translational modification to MnSOD, which was impaired in SIRT3-knockout MEFs, which counters the PCB insult. We found that 4OH-PCB11 increased mitochondrial respiration and endogenous fatty-acid oxidation-associated oxygen consumption in SIRT3-knockout MEFs; this appeared to occur because the cells exhausted their reserve respiratory capacity. To determine whether these changes in mitochondrial respiration were accompanied by similar changes in the regulation of fatty acid metabolism, we performed quantitative real-time polymerase chain reaction (qRT-PCR) after a 24 h treatment with 4OH-PCB11. In SIRT3-knockout MEFs, 4OH-PCB11 significantly increased the expression of ten genes controlling fatty acid biosynthesis, metabolism, and transport. When we overexpressed MnSOD in these cells, the expression of six of these genes returned to the baseline level, suggesting that the protective role of SIRT3 against 4OH-PCB11 is partially governed by MnSOD activity.

Highlights

Polychlorinated biphenyls (PCBs) are synthetic organic chemicals consisting of a biphenyl and various numbers of chlorine atoms
When we overexpressed Manganese superoxide dismutase (MnSOD) in Sirtuin 3 (SIRT3)-KO mouse embryonic fibroblasts (MEFs) with and without 4OH-PCB11, we found no significant differences in the expression of the following six genes: Acot12, Acsl1, Gk2, Hmgs2, lipoprotein lipase (Lpl), and Oxct2a, suggesting increased MnSOD activity was able to revert the increased gene expression of genes associated with fatty acid biosynthesis, metabolism, and transport
Our results demonstrate that MnSOD activity plays a significant role in regulating mitochondrial function as well as the expression of genes involved in regulating fatty acid biosynthesis, metabolism, and transport during exposure to 4OH-PCB11

Summary

Introduction

Polychlorinated biphenyls (PCBs) are synthetic organic chemicals consisting of a biphenyl and various numbers of chlorine atoms. For more than 50 years, PCBs were produced commercially (Aroclors) and marketed for various industrial applications, including use in capacitors, transformers, plasticizers, surface coatings, inks, adhesives, and pesticides—until their adverse effects on health. Chronic exposure to mixtures of PCBs is associated with a wide range of toxic effects, including hepatotoxicity, carcinogenicity, hormonal disruption, and neurotoxicity [2]. The same group identified PCB11 and other PCB congeners (due to unintended production during yellow pigment manufacturing) in commercial paints, inks, textiles, paper, cosmetics, leather, plastics, and food. Marek et al, as well as Sethi et al, detected PCB11 in human samples [6,7], and our group reported measurable levels of hydroxylated PCB11 metabolites, including 4OH-PCB11, in human blood [8]. Understanding the PCB-induced health effects at a molecular level could help establish strategies to overcome the health effects of PCB exposure

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