Behavioral and monoaminergic changes after lindane exposure in developing rats

Identifying childhood pesticide exposure trajectories and critical window associated with behavioral problems at 10 years of age: Findings from SMBCS

BACKGROUND

Pesticides may impact children's neurodevelopment. As children's metabolic function and neural plasticity change throughout their growth and development, the effects of pesticide exposure may also vary.

OBJECTIVES

We aimed to identify the trajectories of combined pesticide exposure during childhood, and to examine the associations of the exposure trajectories with children's neurobehavior at the age of 10.

METHODS

We involved repeated measurements of three pesticide metabolites [Pentachlorophenol (PCP), 3,5,6-Trichloro-2-pyridinol (TCPy), and Carbofuran phenol (CFP)], in urine samples collected from children in a cohort study at ages 1, 2, 3, 6, 7, 8, 9, and 10 years. The group-based multi-trajectory model (GBMT) and latent class analysis (LCA) were separately utilized to describe the distinct trajectories and patterns of pesticide mixture exposure during childhood. Meanwhile, the Strengths and Difficulties Questionnaire (SDQ) and attention deficit hyperactivity disorder (ADHD) Criteria of Diagnostic and Statistical Manual of Mental Disorders, Fourth Edition (DSM-IV) list were applied to assess behavioral disorders in children. The associations between exposure trajectories and behavioral problem scores were then examined.

RESULTS

The GBMT model delineated three distinct trajectories of combined pesticide exposure among children: consistently low, higher levels in early childhood transitioning to lower levels during pre-school age, and lower levels in early childhood followed by higher levels in the middle childhood. The LCA model identified three similar longitudinal exposure patterns. Further, the children in the second trajectory group identified by GBMT, characterized by higher early childhood exposure levels, exhibited significantly elevated hyperactivity/inattention scores of the SDQ compared to the other two groups (β = 0.46, 95 %CI: 0.11, 0.81; β = 0.44, 95 %CI: 0.02, 0.86).

CONCLUSIONS

Our study revealed that exposure to pesticides during early childhood (especially before the age of two), rather than other age periods, was linked to hyperactivity/inattention problems in children aged 10 years. We also provided a novel perspective on characterizing the fluctuation in repeated measurements of multiple environmental chemicals and identifying the potential critical windows.

β-Hexachlorocyclohexane triggers neuroinflammatory activity, epigenetic histone post-translational modifications and cognitive dysfunction

Persistent organic pollutants (POPs), which encompass pesticides and industrial chemicals widely utilized across the globe, pose a covert threat to human health. β-hexachlorocyclohexane (β-HCH) is an organochlorine pesticide with striking stability, still illegally dumped in many countries, and recognized as responsible for several pathogenetic mechanisms. This study represents a pioneering exploration into the neurotoxic effects induced by the exposure to β-HCH specifically targeting neuronal cells (N2a), microglia (BV-2), and C57BL/6 mice. As shown by western blot and qPCR analyses, the administration of β-HCH triggered a modulation of NF-κB, a key factor influencing both inflammation and pro-inflammatory cytokines expression. We demonstrated by proteomic and western blot techniques epigenetic modifications in H3 histone induced by β-HCH. Histone acetylation of H3K9 and H3K27 increased in N2a, and in the prefrontal cortex of C57BL/6 mice administered with β-HCH, whereas it decreased in BV-2 cells and in the hippocampus. We also observed a severe detrimental effect on recognition memory and spatial navigation by the Novel Object Recognition Test (NORT) and the Object Place Recognition Task (OPRT) behavioural tests. Cognitive impairment was linked to decreased expression of the genes BDNF and SNAP-25, which are mediators involved in synaptic function and activity. The obtained results expand our understanding of the harmful impact produced by β-HCH exposure by highlighting its implication in the pathogenesis of neurological diseases. These findings will support intervention programs to limit the risk induced by exposure to POPs. Regulatory agencies should block further illicit use, causing environmental hazards and endangering human and animal health.

Correlation between Lindane Use and the Incidence of Thyroid Cancer in the United States: An Ecological Study

The increasing rate of thyroid cancer may be attributable to endocrine disruptive chemicals. Lindane is a persistent organochlorine pesticide with endocrine disruptive properties that has been classified as carcinogenic to humans. The aim of this ecological study was to evaluate potential correlation between lindane exposure and thyroid cancer incidence in the United States (US). Data on statewide age-adjusted thyroid cancer incidence rate (per 100,000 people) was obtained from the Centers for Disease Control and Prevention for all US states for 2019. Lindane use estimates per cropland (kg/acres cropland) were then overlaid on the map of age-adjusted thyroid cancer incidence rate using ArcGIS. The trend of lindane use in the US between 1992 and 2007 was calculated using the Mann Kendall correlation test. The correlation between statewide lindane use and age-adjusted thyroid cancer incidence rates was calculated using Spearman correlation. Lindane use in the US decreased significantly between 1992 and 2007 (T = -0.617; p < 0.001). There was no statistically significant correlation between lindane use in 1992 and thyroid cancer incidence rate for any of the years between 1999 and 2019. Our results suggest that restrictions clearly seem to be effective in reducing lindane use, however, more research is needed for individual pesticides and thyroid cancer.

Residential exposure to pesticides as risk factor for childhood and young adult brain tumors: A systematic review and meta-analysis

BACKGROUND

Accumulating evidence suggests a positive association between exposure to non-agricultural pesticides and childhood brain tumors (CBT).

OBJECTIVE

(1) To conduct a systematic review and meta-analysis of published studies on the association between residential/household/domestic exposure to pesticides and childhood brain tumors. (2) To clarify variables that could impact the results.

METHODS

Publications in English were identified from a MEDLINE search through 28 February 2017 and from the reference list of identified publications. Risk estimates were extracted from 18 case-control studies published between 1979 and 2016 and study quality assessments were performed. Summary odds ratios (mOR) were calculated according to fixed and random-effect meta-analysis models. Separate analyses were conducted after stratification for study quality, critical exposure period, exposure location, specific exposures, pesticide category, application methods, type of pest treated, type of CBT, child's age at diagnosis and geographic location.

RESULTS

Statistically significant associations were observed with CBT after combining all studies (mOR: 1.26; 95% CI: 1.13-1.40) without evidence of inconsistency between study results or publication bias. Specifically, increased risks were observed for several groupings and more particularly for gliomas and exposure involving insecticides. Statistical significance was also reached for high quality studies, for all exposure periods, for indoor exposure and, more particularly, during the prenatal period for all stratifications involving insecticides (except for outdoor use), for pet treatments, for flea/tick treatment, for studies from USA/Canada and studies from Europe (borderline) as well as for data from studies including children of up to 10years at diagnosis and of up to 15years.

CONCLUSIONS

Our findings support an association between residential exposure to pesticides and childhood brain tumors. Although causality cannot be established, these results add to the evidence leading to recommend limiting residential use of pesticides and to support public health policies serving this objective.

Developmental neurotoxicity of succeeding generations of insecticides

Insecticides are by design toxic. They must be toxic to effectively kill target species of insects. Unfortunately, they also have off-target toxic effects that can harm other species, including humans. Developmental neurotoxicity is one of the most prominent off-target toxic risks of insecticides. Over the past seven decades several classes of insecticides have been developed, each with their own mechanisms of effect and toxic side effects. This review covers the developmental neurotoxicity of the succeeding generations of insecticides including organochlorines, organophosphates, pyrethroids, carbamates and neonicotinoids. The goal of new insecticide development is to more effectively kill target species with fewer toxic side effects on non-target species. From the experience with the developmental neurotoxicity caused by the generations of insecticides developed in the past advice is offered how to proceed with future insecticide development to decrease neurotoxic risk.

Responsiveness of cerebral and hepatic cytochrome P450s in rat offspring prenatally exposed to lindane

Prenatal exposure to low doses of lindane has been shown to affect the ontogeny of xenobiotic metabolizing cytochrome P450s (CYPs), involved in the metabolism and neurobehavioral toxicity of lindane. Attempts were made in the present study to investigate the responsiveness of CYPs in offspring prenatally exposed to lindane (0.25 mg/kg b. wt.; 1/350th of LD(50); p. o. to mother) when challenged with 3-methylcholanthrene (MC) or phenobarbital (PB), inducers of CYP1A and 2B families or a sub-convulsant dose of lindane (30 mg/kg b. wt., p. o.) later in life. Prenatal exposure to lindane was found to produce an increase in the mRNA and protein expression of CYP1A1, 1A2, 2B1, 2B2 isoforms in brain and liver of the offspring at postnatal day 50. The increased expression of the CYPs in the offspring suggests the sensitivity of the CYPs during postnatal development, possibly, to low levels of lindane, which may partition into mother's milk. A higher increase in expression of CYP1A and 2B isoenzymes and their catalytic activity was observed in animals pretreated prenatally with lindane and challenged with MC (30 mg/kg, i. p. x 5 days) or PB (80 mg/kg, i. p. x 5 days) when young at age (approx. 7 weeks) compared to animals exposed to MC or PB alone. Further, challenge of the control and prenatally exposed offspring with a single sub-convulsant dose of lindane resulted in an earlier onset and increased incidence of convulsions in the offspring prenatally exposed to lindane have demonstrated sensitivity of the CYPs in the prenatally exposed offspring. Our data assume significance as the subtle changes in the expression profiles of hepatic and cerebral CYPs in rat offspring during postnatal development could modify the adult response to a later exposure to xenobiotics.

Reversal of lindane-induced impairment of step-down passive avoidance and oxidative stress by neurosteroids in rats

Neurosteroids (NS) are recognized as important modulators of functioning of the nervous system. Lindane, an organochlorine pesticide has been shown to adversely affect memory and induce oxidative stress on both acute and chronic exposure. The present study was designed to explore the modulation of effects of lindane over cognitive function by progesterone (PROG), pregnenolone sulfate (PREG-S) and 4'-chlorodiazepam (4CD). Cognitive function was assessed using step-down latency (SDL) on a passive avoidance apparatus and transfer latency (TL) on a plus maze. Oxidative stress was assessed by examining brain malondialdehyde (MDA) and non-protein thiol (NP-SH) levels. A significant reduction in SDL was found for the lindane treated group at weeks 6 and 7 as compared to control (p<0.001). One-week treatment by PREG-S or 4CD antagonized the effect of lindane on SDL. PROG failed to modulate the effect of lindane on SDL. Lindane caused a significant prolongation of TL as compared to control (p<0.001) from second week onwards. One-week administration of PROG, PREG-S or 4CD was unable to reverse this prolongation of TL. Lindane produced a statistically significant increase in the brain MDA levels (p<0.001) and significant decrease in the brain NP-SH levels (p<0.001). Treatment with PREG-S and 4CD attenuated the effect of lindane on MDA (p<0.001) and NP-SH levels. PROG failed to influence oxidative stress induced by lindane. Results of the present study thus show that some NS have potential in reversing cognitive dysfunction and oxidative stress induced by toxicants like lindane in the brain.

Developmental exposure to pesticides zineb and/or endosulfan renders the nigrostriatal dopamine system more susceptible to these environmental chemicals later in life

Several epidemiological studies have suggested a role for environmental pesticide exposures in idiopathic Parkinson's disease. The purpose of this study was to test the hypothesis that exposure to pesticides such as endosulfan and/or zineb during critical periods of postnatal development could result in neuronal dysfunction and enhance the impact of these pesticides during exposure as adults. C57BL/6 mice, exposed daily to each of the pesticides or their mixtures from postnatal days 5 to 19, exhibited insignificant changes in striatal dopamine, acetylcholinesterase and alpha-synuclein levels. However, mice exposed to these pesticides as juveniles and re-exposed at 8 months of age had significantly altered striatum and brain cortex neurotransmitter levels. Thus, mice re-exposed during adulthood to zineb, endosulfan and their mixtures showed a significantly depleted striatal dopamine levels, to 22, 16 and 35% of control, respectively. Acetylcholinesterase activity in the cerebral cortex was significantly increased in all pesticide treated groups (rho< or =0.05) upon repeated exposure, and pesticide mixture treatment also significantly increased levels of normal and aggregated alpha-synuclein. Collectively, these findings support our hypothesis that exposure to pesticides such as endosulfan and zineb during critical periods of postnatal development contributes to neurotransmitter changes upon re-challenge in adulthood.

Neurochemical targets and behavioral effects of organohalogen compounds: an update

Organohalogen compounds (OHCs) have been used and still are used extensively as pesticides, flame retardants, hydraulic fluids, and in other industrial applications. These compounds are stable, most often lipophilic, and may therefore easily biomagnify. Today these compounds are found distributed both in human tissue, including breast milk, and in wildlife animals. In the late 1960s and early 1970s, high levels of the polychlorinated biphenyls (PCBs) and the pesticide dichlorodiphenyl trichloroethane (DDT) were detected in the environment. In the 1970s it was discovered that PCBs and some chlorinated pesticides, such as lindane, have neurotoxic potentials after both acute and chronic exposure. Although the use of PCBs, DDT, and other halogenated pesticides has been reduced, and environmental levels of these compounds are slowly diminishing, other halogenated compounds with potential of toxic effects are being found in the environment. These include the brominated flame retardants, chlorinated paraffins (PCAs), and perfluorinated compounds, whose levels are increasing. It is now established that several OHCs have neurobehavioral effects, indicating adverse effects on the central nervous system (CNS). For instance, several reports have shown that OHCs alter neurotransmitter functions in CNS and Ca2+ homeostatic processes, induce protein kinase C (PKC) and phospholipase A2 (PLA2) mobilization, and induce oxidative stress. In this review we summarize the findings of the neurobehavioral and neurochemical effects of some of the major OHCs with our main focus on the PCBs. Further, we try to elucidate, on the basis of available literature, the possible implications of these findings on human health.

EVALUATION OF A TWO-GENERATION REPRODUCTION TOXICITY STUDY ADDING ENDOPOINTS TO DETECT ENDOCRINE DISRUPTING ACTIVITY USING LINDANE

A two-generation reproduction toxicity study in rats adding extra endpoints to detect endocrine disrupting activity was conducted using lindane by dietary administration at 0, 10, 60, and 300 ppm, for investigation of its utility. The extra endpoints included anogenital distance (AGD), nipple development, sexual maturation (vaginal opening and preputial separation), estrous cycle, spermatogenesis, sex organ weights, and blood hormone concentrations (thyroid and sex hormones). F1 offspring were examined for emotionality (open field test), motor coordination (rotarod test), as well as learning and memory (pole-climbing test). Hepatic drug-metabolizing enzyme activities were also measured. The results revealed general toxicological effects on parental animals, influence on reproductive function, and altered development of offspring; however, they did not demonstrate any distinct changes in the extra endpoints for detection of endocrine disrupting activity. Adult toxicity was observed in both F0 and F1 animals, including suppressed body weight gain and reduced food consumption in both sexes, and deaths of females at 300 ppm. Convulsions and irritability were observed during the perinatal period in pregnant F1 females given 300 ppm. Pathological examination revealed increased liver weights and centrilobular hepatocellular hypertrophy in both sexes and generations at 10 or 60 ppm and above; in addition, increased kidney weights and increased hyaline droplets in the proximal tubule epithelium, and basophilic renal tubules in males were noted at 10 ppm and above. Pituitary weights were decreased in F0 females and in F1 males and females and adrenal weights were increased in F1 males and females at 300 ppm; however, no histological changes were observed, and manifestations suggesting endocrine disrupting activity related to these changes were lacking. Hypertrophy of the thyroid follicular epithelium in F0 females at 300 ppm and in F1 males at 60 and 300 ppm, and decreases in T3 and/or T4 in both sexes and generations at 300 ppm were presumed to be secondary changes associated with the induction of hepatic drug-metabolizing enzymes. Blood hormone analysis revealed no changes in sex hormones attributable to lindane in males or females. Hepatic drug-metabolizing enzyme activities were increased dose-dependently from 10 ppm in both sexes and generations, with the rise in BROD activity being the most prominent. There were also increases in MROD, EROD, T-6beta-OH, and T4-UDP-GT activities (BROD >> EROD > MROD, T-6beta-OH, T4-UDP-GT). This suggests that while lindane most strongly induces CYP2B, it also upregulates a number of other drug metabolizing enzymes, such as CYP1A, CYP3A, and UDP-GT. As for effects on reproductive function, lack of maternal behavior, including lactation and retrieval behavior, and consequent total litter loss were observed in F1 dams at 300 ppm. There were no effects of lindane on the estrous cycle, spermatogenesis, mating, fertility, pregnancy, or parturition. Neonatal toxicity was observed in both sexes and generations, including suppressed body weight gain at 60 and 300 ppm, and decreased thymus and spleen weights without histological change at 300 ppm. The postnatal survival rate in F2 offspring was decreased due to lack of maternal behavior in dams at 300 ppm.

Pharmacotherapy of ectoparasitic infections

Epizoonoses such as scabies, lice and cimicosis are common, vexing disorders that occur worldwide. Historically, many treatment modalities have been employed in the management of these disorders, and most of the drugs described in this review are of historical interest and no longer recommended or in widespread use because of their wide spectrum of adverse effects. More recently, reports documenting resistance against various antiectoparasite drugs, complicated and severe courses of the diseases, and adverse effects of drug therapy have prompted the development of new treatment strategies and drugs for optimal disease management. Because the strategies currently recommended for the treatment of ectoparasites differ worldwide, this review proposes a rational approach to selecting the best therapeutic agent by comparing the pharmacokinetics, pharmacodynamics, drug efficacy and adverse effects. A literature search of the currently Internet accessible libraries PubMed, Medline and Ideal library, of citations of articles found there, and from communications with the Federal Institute for Drugs and Medical Devices, Germany, was conducted based on this approach. One major observation of this literature search is that permethrin is the treatment of choice for lice and scabies in the US and in Great Britain, whereas lindane is still recommended for scabies in most other European countries because of its longer-standing record of effectiveness. Although permethrin has not yet been proven to be more effective than lindane in treating infections with these ectoparasites, it currently appears to have the best efficacy versus safety profile of topical treatments for scabies and lice. Ivermectin is a newer oral drug for the treatment of ectoparasites, which has been used with great success in the treatment of onchocercosis and other endoparasites. Although ivermectin appears to be a promising drug, its role in the treatment of ectoparasitic infections will be clarified as more study data become available. Finally, it is important to emphasise the clinical aspects of ectoparasite therapy and that providing the patient with optimal instructions on the use of topical therapeutics is of great importance in avoiding adverse effects and assuring complete removal of the ectoparasite, thereby avoiding the development of drug-resistance.