In vitro dopaminergic neurotoxicity of pesticides: a link with neurodegeneration?

Understanding role of pesticides in development of Parkinson's disease: Insights from Drosophila and rodent models

Parkinson's disease is a neurodegenerative illness linked to ageing, marked by the gradual decline of dopaminergic neurons in the midbrain. The exact aetiology of Parkinson's disease (PD) remains uncertain, with genetic predisposition and environmental variables playing significant roles in the disease's frequency. Epidemiological data indicates a possible connection between pesticide exposure and brain degeneration. Specific pesticides have been associated with important characteristics of Parkinson's disease, such as mitochondrial dysfunction, oxidative stress, and α-synuclein aggregation, which are crucial for the advancement of the disease. Recently, many animal models have been developed for Parkinson's disease study. Although these models do not perfectly replicate the disease's pathology, they provide valuable insights that improve our understanding of the condition and the limitations of current treatment methods. Drosophila, in particular, has been useful in studying Parkinson's disease induced by toxins or genetic factors. The review thoroughly analyses many animal models utilised in Parkinson's research, with an emphasis on issues including pesticides, genetic and epigenetic changes, proteasome failure, oxidative damage, α-synuclein inoculation, and mitochondrial dysfunction. The text highlights the important impact of pesticides on the onset of Parkinson's disease (PD) and stresses the need for more research on genetic and mechanistic alterations linked to the condition.

Effect of temperature and dietary pesticide exposure on neuroendocrine and olfactory responses in juvenile Chinook salmon (Oncorhynchus tshawytscha)

Projected water temperature increases based on predicted climate change scenarios and concomitant pesticide exposure raises concern about the responses of aquatic organisms. To better understand the effect of pesticide mixtures and influence of water temperature to fish, juvenile Chinook salmon (Oncorhynchus tshawytscha) were dietarily exposed to a mixture of legacy and current use pesticides (p,p'-DDE, bifenthrin, chlorpyrifos, esfenvalerate, and fipronil) at concentrations detected from field-collected prey items in the Sacramento-San Joaquin Delta, California (Delta) and exposed under current and predicted future water temperature scenarios, 11, 14, or 17 °C, for 14 days. The expression of a subset of genes (deiodinase 2-dio2, gonadotropin releasing hormone 2-gnrh2, and catechol-o-methyltransferase-comt) involved in neuroendocrine, dopaminergic, and olfactory function previously shown to be altered by individual pesticide exposures germane to this study were determined and olfactory function assessed using a Y-maze behavioral assay. When total body burdens of pesticides were measured, a significant decrease in dio2 expression was observed in Chinook salmon exposed at 14 °C compared to fish kept at 11 °C. Increases in gnrh2 expression were also observed in fish exposed to 14 °C. Similarly, increases in comt expression was noted at 14 and 17 °C. Additionally, altered expression of all transcripts was observed, showing interactions between temperature and individual pesticide concentrations. Chinook salmon spent significantly more time actively avoiding the odorant arm at baseline conditions of 11 °C in the Y-maze. At higher temperatures, Chinook spent significantly more time not making a choice between the odorant or clean arm following exposure to the low pesticide mixture, relative to 11 °C. These results suggest that dietary exposure to pesticide mixtures can potentially induce neuroendocrine effects and behavior. Impaired olfactory responses exhibited by Chinook salmon could have implications for predator avoidance in the wild under increased temperature scenarios and impact populations in the future.

Neurotoxicity of pesticides - A link to neurodegeneration

Parkinson's disease (PD) is a neurodegenerative disorder which mainly targets motor symptoms such as tremor, rigidity, bradykinesia and postural instability. The physiological changes occur due to dopamine depletion in basal ganglia region of the brain. PD aetiology is not yet elucidated clearly but genetic and environmental factors play a prominent role in disease occurrence. Despite of various environmental factors, pesticides exposure has been convicted as major candidate in PD pathogenesis. Among various pesticides 1-methyl-4-phenyl-1,2,3,6-tetrahydropyridine (MPTP) has been widely investigated in PD following with paraquat (PQ), maneb (MB), organochlorines (OC) and rotenone. Effect of these pesticides has been suggested to be involved in oxidative stress, alterations in dopamine transporters, mitochondrial dysfunction, α-synuclein (αSyn) fibrillation, and neuroinflammation in PD. The present review discusses the influence of pesticides in neurodegeneration and its related epidemiological studies conducted in PD. Furthermore, we have deliberated the common pesticides involved in PD and its associated genetic alterations and the probable mechanism of them behind PD pathogenesis. Hence, we conclude that pesticides play a prominent role in PD pathogenesis and advance research is needed to investigate the alterations in genetic and mechanistic aspects of PD.

Rutin Improves Cardiac and Erythrocyte Membrane-Bound ATPase Activities in Male Rats Exposed to Cadmium Chloride and Lead Acetate

Cardiovascular diseases have been associated with cadmium (Cd) and lead (Pb). Impaired Ca²⁺ and Na⁺/K⁺-ATPase activities have also been linked to hemolytic and cardiovascular disorders. This study investigated the effect of rutin on Cd and/or Pb-induced cardiac and erythrocyte disorders in male rats. Twenty-five (25) male Wistar rats were treated as (n=5): Control, Pb (60 mg/kg, p.o), Cd (5 mg/kg, p.o), Pb + Cd, Rutin + Pb + Cd (50 mg/kg Rt, 60 mg/kg Pb, 5 mg/kg Cd, p.o). Plasma electrolyte and Ca²⁺- and Na⁺/K⁺-ATPase activities in the erythrocyte and heart of the rats were assayed. There was an increased and decreased activity of cardiac and erythrocyte Na⁺/K⁺-ATPase in Pb- (172%) and Cd- (33.7%) treated groups, respectively. However, rutin increased erythrocyte Na⁺/K⁺-ATPase activity in Cd + Pb when compared with Cd and Cd + Pb groups. Erythrocyte Ca²⁺-ATPase activity was decreased in the Pb (68%), Cd (68%) and Cd + Pb (55.3%) groups. Cardiac Na⁺/K⁺-ATPase activity was not altered in Pb and Cd groups while it decreased in Cd + Pb. Rutin increased the activity of the pump in Cd +Pb-treated rats compared to the Cd+Pb group. Therefore, rutin reversed cadmium- and lead-induced impaired cardiac and erythrocyte membrane Ca²⁺- and Na⁺/K⁺-ATPase activities. Graphical Abstract Dotted lines-decrease activity, curved lines-increased activity (created with BioRender.com ).

Agricultural work and reduced circulating uric acid are both associated with initial hospital admission for Parkinson's disease

Monoamine oxidase type B inhibitors act in Parkinson's disease (PD) via potentiation of dopamine, but may also have neuroprotective effects by reducing oxidative damage. Oxidative damage is also a feature of environmental toxins, including pesticides, that are an established risk factor for PD. Another risk factor is low circulating uric acid (UA), which may relate to UA being the major endogenous antioxidant in the human body. We have undertaken a study of 192 initial admissions for PD in a general hospital neurology department in a partly rural region of Southern China to determine if there is an increased rate of PD in agricultural workers who have a high risk of exposure to pesticides, and how it may relate to deficits in UA. We found a disproportionately high number of agricultural workers admitted with PD (66.7% vs. 54.3% of all neurology admissions) and that PD subjects have a substantial reduction in UA. This is further reduced in agricultural workers and thus may contribute to the increased vulnerability of this group to PD.

Isorhynchophylline Attenuates MPP+-Induced Apoptosis Through Endoplasmic Reticulum Stress- and Mitochondria-Dependent Pathways in PC12 Cells: Involvement of Antioxidant Activity

Endoplasmic reticulum stress (ERS) and mitochondrial dysfunctions are thought to be involved in the dopaminergic neuronal death in Parkinson's disease (PD). In this study, we found that isorhynchophylline (IRN) significantly attenuated 1-methyl-4-phenylpyridinium (MPP⁺)-induced apoptotic cell death and oxidative stress in PC12 cells. IRN markedly reduced MPP⁺-induced-ERS responses, indicative of inositol-requiring enzyme 1 (IRE1) phosphorylation and caspase-12 activation. Furthermore, IRN inhibits MPP⁺-triggered apoptosis signal-regulating kinase 1 (ASK1)/c-Jun N-terminal Kinase (JNK) signaling-mediated mitochondria-dependent apoptosis pathway. IRN-mediated attenuation of endoplasmic reticulum modulator caspase-12 activation was abolished by diphenyleneiodonium (DPI) or IRE-1α shRNA, but not by SP600125 or pifithrin-α in MPP⁺-treated PC12 cells. Inhibitions of MPP⁺-induced both cytochrome c release and caspase-9 activation by IRN were blocked by pre-treatment with DPI or pifithrin-α, but not by IRE-1α shRNA. IRN blocks the generation of reactive oxygen species upstream of both ASK1/JNK pathway and IRE1/caspase-12 pathway. Altogether, our in vitro findings suggest that IRN possesses potent neuroprotective activity and may be a potential candidate for the treatment of PD.

Alterations in mitochondrial dynamics induced by tebufenpyrad and pyridaben in a dopaminergic neuronal cell culture model

Tebufenpyrad and pyridaben are two agro-chemically important acaricides that function like the known mitochondrial toxicant rotenone. Although these two compounds have been commonly used to kill populations of mites and ticks in commercial greenhouses, their neurotoxic profiles remain largely unknown. Therefore, we investigated the effects of these two pesticides on mitochondrial structure and function in an in vitro cell culture model using the Seahorse bioanalyzer and confocal fluorescence imaging. The effects were compared with rotenone. Exposing rat dopaminergic neuronal cells (N27 cells) to tebufenpyrad and pyridaben for 3h induced dose-dependent cell death with an EC50 of 3.98μM and 3.77μM, respectively. Also, tebufenpyrad and pyridaben (3μM) exposure induced reactive oxygen species (ROS) generation and m-aconitase damage, suggesting that the pesticide toxicity is associated with oxidative damage. Morphometric image analysis with the MitoTracker red fluorescent probe indicated that tebufenpyrad and pyridaben, as well as rotenone, caused abnormalities in mitochondrial morphology, including reduced mitochondrial length and circularity. Functional bioenergetic experiments using the Seahorse XF96 analyzer revealed that tebufenpyrad and pyridaben very rapidly suppressed the basal mitochondrial oxygen consumption rate similar to that of rotenone. Further analysis of bioenergetic curves also revealed dose-dependent decreases in ATP-linked respiration and respiratory capacity. The luminescence-based ATP measurement further confirmed that pesticide-induced mitochondrial inhibition of respiration is accompanied by the loss of cellular ATP. Collectively, our results suggest that exposure to the pesticides tebufenpyrad and pyridaben induces neurotoxicity by rapidly initiating mitochondrial dysfunction and oxidative damage in dopaminergic neuronal cells. Our findings also reveal that monitoring the kinetics of mitochondrial respiration with Seahorse could be used as an early neurotoxicological high-throughput index for assessing the risk that pesticides pose to the dopaminergic neuronal system.