Organochlorine Insecticides Induce NADPH Oxidase-Dependent Reactive Oxygen Species in Human Monocytic Cells via Phospholipase A₂/Arachidonic Acid

Abstract

Bioaccumulative organohalogen chemicals, such as organochlorine (OC) insecticides, have been increasingly associated with disease etiology; however, the mechanistic link between chemical exposure and diseases, such as atherosclerosis, cancer, and diabetes, is complex and poorly defined. Systemic oxidative stress stemming from OC exposure might play a vital role in the development of these pathologies. Monocytes are important surveillance cells of the innate immune system that respond to extracellular signals possessing danger-associated molecular patterns by synthesizing oxyradicals, such as superoxide, for the purpose of combating infectious pathogens. We hypothesized that OC chemicals can be toxic to monocytes because of an inappropriate elevation in superoxide-derived reactive oxygen species (ROS) capable of causing cellular oxidative damage. Reactive oxyradicals are generated in monocytes in large part by NADPH oxidase (Nox). The present study was conducted to examine the ability of two chlorinated cyclodiene compounds, trans-nonachlor and dieldrin, as well as p,p′-DDE, a chlorinated alicyclic metabolite of DDT, to stimulate Nox activity in a human monocytic cell line and to elucidate the mechanisms for this activation. Human THP-1 monocytes treated with either trans-nonachlor or dieldrin (0.1–10 μM in the culture medium) exhibited elevated levels of intracellular ROS, as evidenced by complementary methods, including flow cytometry analysis using the probe DCFH-DA and hydroethidine-based fluorometric and UPLC-MS assays. In addition, the induced reactive oxygen flux caused by trans-nonachlor was also observed in two other cell lines, murine J774 macrophages and human HL-60 cells. The central role of Nox in OC-mediated oxidative stress was demonstrated by the attenuated superoxide production in OC-exposed monocytes treated with the Nox inhibitors diphenyleneiodonium and VAS-2870. Moreover, monocytes challenged with OCs exhibited increased phospho-p47phox levels and enhanced p47phox membrane localization compared to that in vehicle-treated cells. p47phox is a cytosolic regulatory subunit of Nox, and its phosphorylation and translocation to the NOX2 catalytic subunit in membranes is a requisite step for Nox assembly and activation. Dieldrin and trans-nonachlor treatments of monocytes also resulted in marked increases in arachidonic acid (AA) and eicosanoid production, which could be abrogated by the phospholipase A2 (PLA2) inhibitor arachidonoyltrifluoromethyl ketone (ATK) but not by calcium-independent PLA2 inhibitor bromoenol lactone. This suggested that cytosolic PLA2 plays a crucial role in the induction of Nox activity by increasing the intracellular pool of AA that activates protein kinase C, which phosphorylates p47phox. In addition, ATK also blocked OC-induced p47phox serine phosphorylation and attenuated ROS levels, which further supports the notion that the AA pool liberated by cytosolic PLA2 is responsible for Nox activation. Together, the results suggest that trans-nonachlor and dieldrin are capable ...

A Critical Review of Methodologies to Detect Reactive Oxygen and Nitrogen Species Stimulated by NADPH Oxidase Enzymes: Implications in Pesticide Toxicity

“…Consequently, these chemicals tend to bioaccumulate in fatty tissues and release slowly with time, causing oxidative stress. Recent reports suggest that these chemicals activate Nox complex through activation of phospholipases A 2 /arachidonic acid (PLA 2 /AA) in monocyte/macrophages (Mangum et al 2015). Monocytes treated with organochlorinated compounds enhanced Nox assembly and activation (Mangum et al 2015).…”

“…Recent studies have shown that organochlorine insecticides ( trans -nonachlor, dieldrin, and DDE) induced enhanced expression of phospho-p47 phox and enhanced its membrane localization (Mangum et al 2015). Mechanistically, this was attributed to (PLA 2 ) activation, leading to increased arachidonic acid and eicosanoid production in monocytes treated with organochlorinated compounds (Mangum et al 2015).…”

“…The two major sources of ROS proposed to be responsible for the toxicity observed are mitochondria and NADPH oxidase enzymes (Nox) (Finkle 2011). In this article, we focus mainly on Nox enzymes, especially Nox2, due to their role in the molecular mechanisms of pesticide toxicity (Mangum et al 2015). …”

Amelioration of oxidative stress-induced phenotype loss of parvalbumin interneurons might contribute to the beneficial effects of environmental enrichment in a rat model of post-traumatic stress disorder

“…Since PV interneurons are susceptible to oxidative stress in response to adverse stimulation [15] and nicotinamide adenosine dinucleotide phosphate (NADPH) oxidases 2 (NOX2) mediates excessive reactive oxygen species (ROS) production [16,17], we further hypothesized that NOX2-induced excessive oxidative stress can lead to phenotype loss of PV interneurons and consequent behavioral impairments in rats with PTSD.…”

Lipoproteomics Environmental and Genetic Factors Affecting High-Density Lipoprotein (HDL)

“…Another OCP, trans-nonachlor, has been demonstrated to promote the production of intracellular reactive oxygen species by increasing the activity of NADPH oxidase in human monocytes. Interestingly, DDE did not cause a similar effect [Mangum et al 2015], indicating that these compounds could have different target cells and/or modes of action.…”