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

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.

The toxicological profile of polychlorinated naphthalenes (PCNs)

“…Comparatively, 1,2,3,4-T 4 CN and 1,2,3,4,5-P 5 CN showed a lower level of retention in the liver (Kilanowicz et al, 2004). Interestingly, all analyzed tissues showed varying levels of decrease in the level of 1,2,3,5,6,7-H 6 CN during the measurement interval, except for the brain and sciatic nerve, in which there was an increase or a sustained value, respectively, over a period of 24-120 h. This data indicates that 1,2,3,5,6,7-H 6 CN passes through the blood/brain barrier and suggests that the nervous system may be an important target for the higher chlorinated PCNs congeners (Kilanowicz et al, 2012;Lisek et al, 2020;, especially in terms of long-term toxicity resulting from hexa-CN exposure. Successive elimination of moderately to higher chlorinated congeners from the liver and adipose tissue was observed in Sprague-Dawley rats, following the order: tetra-, penta-and also hepta-CNs and octa-CN, but this was after much longer retention of up to 32 days (Asplund et al, J o u r n a l P r e -p r o o f 1986).…”

“…The historical observations of anorectic behaviour in occupationally exposed workers and in later animal studies have not been fully explored, but some of the most recent neurotoxicity studies (Lisek et al, 2020(Lisek et al, , 2022 suggest that some PCN congeners (e.g. 1,2,3,5,6,7-H 6 CN) appear to affect dopaminergic transmission (dopamine is associated in the regulation of food intake) by altering tyrosine hydroxylation, reducing VMAT1 expression and impairing antioxidant protection.…”

“…Impaired function of mitochondria and neurite damage may be connected with cognitive defects or even some diseases such as schizophrenia and Alzheimer's disease (Lisek et al, 2020). PC12 cells were also used to investigate the effects of a 1,2,3,5,6,7-H 6 CN (0.025 to 0.35 μg mL -1 ) on the dopamine biosynthesis and secretion pathway (Lisek et al, 2022).…”

Strategies for Biomaterial-Based Spinal Cord Injury Repair via the TLR4-NF-κB Signaling Pathway

“…It includes demyelination, axon and neuron necrosis and cellular tissue damage ( Xing et al, 2021 ; Kiyotake et al, 2020 ; Berry et al, 2016 ). Neurons are highly specialized for intercellular communication through axons and dendrites in the spinal cord of CNS, thus it’s crucial to maintain neuronal integrity throughout their life cycle ( Lisek et al, 2020 ). Traumatic impairment of normal function of central and peripheral axons results in molecular and progressive morphological changes in stress response ( Schellino et al, 2019 ).…”