Hexachloronaphthalene Induces Mitochondrial-Dependent Neurotoxicity via a Mechanism of Enhanced Production of Reactive Oxygen Species.

Malwina Lisek,Joanna Stragierowicz,Ludmila Zylinska,Tomasz Boczek,Feng Guo,Bozena Ferenc,Magdalena Wiktorska,Anna Kilanowicz,Philipp P Prosseda

doi:10.1155/2020/2479234

Abstract

Hexachloronaphthalene (PCN67) is one of the most toxic among polychlorinated naphthalenes. Despite the known high bioaccumulation and persistence of PCN67 in the environment, it is still unclear to what extent exposure to these substances may interfere with normal neuronal physiology and lead to neurotoxicity. Therefore, the primary goal of this study was to assess the effect of PCN67 in neuronal in vitro models. Neuronal death was assessed upon PCN67 treatment using differentiated PC12 cells and primary hippocampal neurons. At 72 h postexposure, cell viability assays showed an IC50 value of 0.35 μg/ml and dose-dependent damage of neurites and concomitant downregulation of neurofilaments L and M. Moreover, we found that younger primary neurons (DIV4) were much more sensitive to PCN67 toxicity than mature cultures (DIV14). Our comprehensive analysis indicated that the application of PCN67 at the IC50 concentration caused necrosis, which was reflected by an increase in LDH release, HMGB1 protein export to the cytosol, nuclear swelling, and loss of homeostatic control of energy balance. The blockage of mitochondrial calcium uniporter partially rescued the cell viability, loss of mitochondrial membrane potential (ΔΨm), and the overproduction of reactive oxygen species, suggesting that the underlying mechanism of neurotoxicity involved mitochondrial calcium accumulation. Increased lipid peroxidation as a consequence of oxidative stress was additionally seen for 0.1 μg/ml of PCN67, while this concentration did not affect ΔΨm and plasma membrane permeability. Our results show for the first time that neuronal mitochondria act as a target for PCN67 and indicate that exposure to this drug may result in neuron loss via mitochondrial-dependent mechanisms.

Highlights

Polychlorinated naphthalenes (PCNs) were included in 2015 into the Stockholm Convention on Persistent Organic Pollutants to protect human health and the environment from highly dangerous, long-lasting chemicals by the elimination of their production and reduction of their unintentional release [1]
To assess in vitro neurotoxicity of PCN67, differentiated PC12 cells were exposed to a concentration ranging from 0.001 μg/ml to 25 μg/ml (Figures 1(a)– 1(c))
The expression level of neurofilament L (NF-L) measured at the same time point (Figure 2(e)) was reduced by 72% (F(2,6), P < 0:01). These results demonstrate that PCN67 in a dosedependent manner may interfere with the gene expression of NF-L and neurofilament M (NF-M) associated with the differentiation of PC12 cells into neuronal phenotype

Summary

Introduction

Polychlorinated naphthalenes (PCNs) were included in 2015 into the Stockholm Convention on Persistent Organic Pollutants to protect human health and the environment from highly dangerous, long-lasting chemicals by the elimination of their production and reduction of their unintentional release [1]. The main sources of PCNs are not old technical formulations used previously (e.g., Halowax) but high-temperature industrial processes that contribute to global environmental contamination [6,7,8,9,10]. The evidence of their ubiquity in the environment is their detection in sediments, soil, water, and air [11,12,13,14,15,16,17,18]. This is confirmed by their persistent presence in various biological materials collected from the general population such as serum [20, 21], liver [22], adipose tissue [23], human milk [24, 25], and umbilical cord blood [26]

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