Carbaryl-induced changes in indoleamine synthesis in the pineal gland and its effects on nighttime serum melatonin concentrations

Is exposure to chemical pollutants associated with sleep outcomes? A systematic review

Environmental exposures may influence sleep; however, the contributions of environmental chemical pollutants to sleep health have not been systematically investigated. We conducted a systematic review to identify, evaluate, summarize, and synthesize the existing evidence between chemical pollutants (air pollution, exposures related to the Gulf War and other conflicts, endocrine disruptors, metals, pesticides, solvents) and dimensions of sleep health (architecture, duration, quality, timing) and disorders (sleeping pill use, insomnia, sleep-disordered breathing)). Of the 204 included studies, results were mixed; however, the synthesized evidence suggested associations between particulate matter, exposures related to the Gulf War, dioxin and dioxin-like compounds, and pesticide exposure with worse sleep quality; exposures related to the Gulf War, aluminum, and mercury with insomnia and impaired sleep maintenance; and associations between tobacco smoke exposure with insomnia and sleep-disordered breathing, particularly in pediatric populations. Possible mechanisms relate to cholinergic signaling, neurotransmission, and inflammation. Chemical pollutants are likely key determinants of sleep health and disorders. Future studies should aim to evaluate environmental exposures on sleep across the lifespan, with a particular focus on developmental windows and biological mechanisms, as well as in historically marginalized or excluded populations.

Environmental disruption of reproductive rhythms

Reproduction is a key biological function requiring a precise synchronization with annual and daily cues to cope with environmental fluctuations. Therefore, humans and animals have developed well-conserved photoneuroendocrine pathways to integrate and process daily and seasonal light signals within the hypothalamic-pituitary-gonadal axis. However, in the past century, industrialization and the modern 24/7 human lifestyle have imposed detrimental changes in natural habitats and rhythms of life. Indeed, exposure to an excessive amount of artificial light at inappropriate timing because of shift work and nocturnal urban lighting, as well as the ubiquitous environmental contamination by endocrine-disrupting chemicals, threaten the integrity of the daily and seasonal timing of biological functions. Here, we review recent epidemiological, field and experimental studies to discuss how light and chemical pollution of the environment can disrupt reproductive rhythms by interfering with the photoneuroendocrine timing system.

Association between pesticide exposure and sleep health among a representative sample of US adults: evidence from NHANES 2009-2014

BACKGROUND

Data suggest that pesticides interact with the melatonin receptor, which may influence sleep. However, the link between pesticides and sleep remains unexplored among the general adult population. This study evaluated unstratified and sex-stratified associations between urinary pesticide exposure (N = 4,478) and self-reported acute household pesticide exposure (N = 14,956), with sleep health outcomes within a nationally representative sample of US adults.

METHODS

Data from the National Health and Nutrition Examination Surveys (NHANES) 2009-2014 were combined for analysis of aim 1 and aim 2. Urinary pesticide metabolite concentrations served as biomarkers of pesticide exposure. Acute household pesticide exposure (if any chemical products were used in the home in the past seven days to control pests) was self-reported (yes/no). Insufficient sleep duration (< 7 h/night) and trouble sleeping (yes/no) were self-reported. Log-binomial regression models that accounted for complex survey weights and adjusted for confounders were used to compute prevalence ratios and 95% CI.

RESULTS

Log urinary 3-phenoxybenzoic acid (3-PBA) was related to a higher probability of insufficient sleep [1.09 (95% CI: 1.00, 1.20), p = 0.04] and trouble sleeping [1.14 (95% CI: 1.02, 1.27), p = 0.02] among males. Self-reported acute household pesticide exposure was associated with a higher probability of insufficient sleep duration [1.16 (95% CI: 1.02, 1.32), p = 0.03] and trouble sleeping [1.20 (95% CI: 1.01, 1.44), p = 0.04] in the unstratified sample. Sex-stratified findings showed that associations between acute household pesticide exposure and trouble sleeping only persisted  among males [1.69 (95% CI: 1.27, 2.24), p < .001].

CONCLUSIONS

In summary, acute pesticide exposure may be detrimental to adult sleep health, particularly among US males.

Pharmacological Actions of Carbamate Insecticides at Mammalian Melatonin Receptors

Integrated in silico chemical clustering and melatonin receptor molecular modeling combined with in vitro 2-[125I]-iodomelatonin competition binding were used to identify carbamate insecticides with affinity for human melatonin receptor 1 (hMT1) and human melatonin receptor 2 (hMT2). Saturation and kinetic binding studies with 2-[125I]-iodomelatonin revealed lead carbamates (carbaryl, fenobucarb, bendiocarb, carbofuran) to be orthosteric ligands with antagonist apparent efficacy at hMT1 and agonist apparent efficacy at hMT2 Furthermore, using quantitative receptor autoradiography in coronal brain slices from C3H/HeN mice, carbaryl, fenobucarb, and bendiocarb competed for 2-[125I]-iodomelatonin binding in the suprachiasmatic nucleus (SCN), paraventricular nucleus of the thalamus (PVT), and pars tuberalis (PT) with affinities similar to those determined for the hMT1 receptor. Carbaryl (10 mg/kg i.p.) administered in vivo also competed ex vivo for 2-[125I]-iodomelatonin binding to the SCN, PVT, and PT, demonstrating the ability to reach brain melatonin receptors in C3H/HeN mice. Furthermore, the same dose of carbaryl given to C3H/HeN mice in constant dark for three consecutive days at subjective dusk (circadian time 10) phase-advanced circadian activity rhythms (mean = 0.91 hours) similar to melatonin (mean = 1.12 hours) when compared with vehicle (mean = 0.04 hours). Carbaryl-mediated phase shift of overt circadian activity rhythm onset is likely mediated via interactions with SCN melatonin receptors. Based on the pharmacological actions of carbaryl and other carbamate insecticides at melatonin receptors, exposure may modulate time-of-day information conveyed to the master biologic clock relevant to adverse health outcomes. SIGNIFICANCE STATEMENT: In silico chemical clustering and molecular modeling in conjunction with in vitro bioassays identified several carbamate insecticides (i.e., carbaryl, carbofuran, fenobucarb, bendiocarb) as pharmacologically active orthosteric melatonin receptor 1 and 2 ligands. This work further demonstrated that carbaryl competes for melatonin receptor binding in the master biological clock (suprachiasmatic nucleus) and phase-advances overt circadian activity rhythms in C3H/HeN mice, supporting the relevance of circadian effects when interpreting toxicological findings related to carbamate insecticide exposure.

Carbaryl-induced ototoxicity in rat postnatal cochlear organotypic cultures

Carbaryl, a widely used carbamate-based insecticide, is a potent anticholinesterase known to induce delayed neurotoxicity following chronic exposure. However, its potential toxic effects on the cochlea, the sensory organ for hearing that contains cholinergic efferent neurons and acetylcholine receptors on the hair cells (HC) and spiral ganglion neurons has heretofore not been evaluated. To assess ototoxic potential of carbaryl, cochlear organotypic cultures from postnatal day 3 rats were treated with doses of carbaryl ranging from 50 to 500 μM for 48 h up to 96 h. Carbaryl damaged both the sensory HC and spiral ganglion neurons in a dose- and duration-dependent manner. HC and neuronal damage was observed at carbaryl concentrations as low as 50 μM after 96-h treatment and 100 μM after 48-h treatment. Hair cell was greatest in the high frequency basal region of the cochlea and progressively decreased towards the apex consistent with the majority of ototoxic drugs. In contrast, damage to the spiral ganglion neurons was of similar magnitude in the basal and apical regions of the cochlea. Carbaryl damage was characterized by soma shrinkage, nuclear condensation and fragmentation, and blebbing, morphological features of programmed cell death. Carbaryl upregulated the expression of executioner caspase-3 in HC and spiral ganglion neurons indicating that cellular damage occurred primarily by caspase-mediated apoptosis. These results suggest that chronic exposure to carbaryl and other carbamate anticholinesterases may be ototoxic. © 2016 Wiley Periodicals, Inc. Environ Toxicol 32: 956-969, 2017.

Carbamate Insecticides Target Human Melatonin Receptors

Carbaryl (1-naphthyl methylcarbamate) and carbofuran (2,3-dihydro-2,2-dimethyl-7-benzofuranyl methylcarbamate) are among the most toxic insecticides, implicated in a variety of diseases including diabetes and cancer among others. Using an integrated pharmacoinformatics based screening approach, we have identified these insecticides to be structural mimics of the neurohormone melatonin and were able to bind to the putative melatonin binding sites in MT₁ and MT₂ melatonin receptors in silico. Carbaryl and carbofuran then were tested for competition with 2-[¹²⁵I]-iodomelatonin (300 pM) binding to hMT₁ or hMT₂ receptors stably expressed in CHO cells. Carbaryl and carbofuran showed higher affinity for competition with 2-[¹²⁵I]-iodomelatonin binding to the hMT₂ compared to the hMT₁ melatonin receptor (33 and 35-fold difference, respectively) as predicted by the molecular modeling. In the presence of GTP (100 μM), which decouples the G-protein linked receptors to modulate signaling, the apparent efficacy of carbaryl and carbofuran for 2-[¹²⁵I]-iodomelatonin binding for the hMT₁ melatonin receptor was not affected but significantly decreased for the hMT₂ melatonin receptor compatible with receptor antagonist/inverse agonist and agonist efficacy, respectively. Altogether, our data points to a potentially new mechanism through which carbamate insecticides carbaryl and carbofuran could impact human health by altering the homeostatic balance of key regulatory processes by directly binding to melatonin receptors.

Assessment of the toxicological interaction of sertraline with cholinesterase inhibiting insecticides in aquatic insects using the black fly, Simulium vittatum IS-7

Sertraline is a selective serotonin reuptake inhibitor (SSRI) prescribed as an antidepressant. Although SSRIs are known to block serotonin reuptake sites on cell membranes, they also have been shown to inhibit acetylcholinesterase (AChE) activity. Thus, the interaction of these chemicals with other AChE inhibitors, namely, organophosphate and carbamate insecticides, is of interest. In addition, these insecticides have been shown to interact with serotonergic neuronal pathways creating questions as to how these chemicals might interact. In this study, the interactive effect of sertraline (SSRI) in binary combinations with carbaryl (carbamate insecticide) and diazinon (organophosphate insecticide) was assessed using a 48-h acute toxicity test with black fly larvae, Simulium vittatum IS-7. Results showed that observed mortality was bracketed by the independent action model and concentration addition model with the independent action model slightly underestimating mortality and the concentration addition model slightly overestimating mortality. Varying the concentration of the chemicals in the mixture did not indicate that sertraline was interacting with the insecticides to make them more toxic or vice versa. These results indicate that sertraline and the insecticides are likely eliciting toxicity at separate neuronal pathways since no interaction was observed.

Effects of naphthalene, beta-naphthoflavone and benzo(a)pyrene on the diurnal and nocturnal indoleamine metabolism and melatonin content in the pineal organ of rainbow trout, Oncorhynchus mykiss

Polycyclic aromatic hydrocarbons (PAHs) have deleterious effects on neuroendocrine systems in teleost fish affecting, among other processes, reproductive function or stress responses. The hormone melatonin, mainly produced in the pineal organ of vertebrates, is involved in the regulation of biological rhythms as well as other important functions, and may also act as an antioxidant molecule. The effects of environmental pollutants on the endocrine and metabolic activity of the pineal organ have been studied only in mammals. We here evaluate the effects of the PAHs naphthalene (NAP) and benzo(a)pyrene (BaP) and the flavonoid beta-naphthoflavone (BNF) on the pineal organ of rainbow trout by quantifying the diurnal and nocturnal pineal content of some indoles and methoxyindoles, including melatonin. NAP mainly induced diurnal increases in the pineal content of melatonin and other methoxyindoles like 5-methoxytryptamine (5-MT), 5-methoxyindole-3-acetic acid (5-MIAA) or 5-methoxytryptophol (5-MTOL). Those increases did not occur at night, when even occasional decreases were observed compared with controls. NAP also induced some diurnal and nocturnal decreases in the levels of indolic compounds like serotonin (5-HT) and 5-hydroxyindole-3-acetic acid (5-HIAA), while pineal content of 5-hydroxytryptophan (5-HTP) was first decreased (few hours after injection) and then increased (few days after injection) during the day. BaP and BNF induced strong increases in diurnal levels of melatonin, whereas other pineal compounds were unaffected. It seems that an increase of the methylation capacity of the pineal organ takes place during the day, and a decrease occurs at night. Those effects could be mediated by changes in the activity of key enzymes involved in pineal melatonin biosynthesis, maybe as a result of the alteration of the cellular phototransduction mechanisms involved in the light-induced inhibition of melatonin synthesis in the pineal photoreceptor cells. These results demonstrate for the first time that environmental pollutants can disrupt the activity of the pineal organ of teleost fish. This disruption could be a threat for the survival of the animals in their natural environment, although the increases observed in melatonin levels could play a relevant role as a toxicity-protection factor.

Possible involvement of beta-adrenergic receptors in the enhancement of nocturnal pineal N-acetyltransferase activity due to parathion administration

The purpose of the present study was to examine the effects of administration of sublethal doses of O,O-diethyl-O-p-nitrophenyl phosphorothioate (parathion) on serum epinephrine (EPI) and norepinephrine (NE), as well as on night-time rat pineal melatonin synthesis, both in the presence and absence of propranolol, a beta-adrenergic receptor antagonist. In the first experiment, two groups of adult albino rats were administered parathion orally (1.08 and 2.17 mg/kg/day; the total received by each animal was 6.5 and 13.0 mg/kg body weight over 6 days); another two groups received corn oil only. Animals were killed at 23:00 and 01:00 h by decapitation. Serum EPI was augmented at 01:00 h, but NE was increased at 01:00 and 23:00 h due to administration of the high dose of parathion (13 mg/kg). In the second experiment, two groups of adult male albino rats were administered parathion orally (13 mg/kg); another two groups received an intraperitoneal injection of propranolol (20 mg/kg body weight, 1 h before the lights were turned off). In addition, two groups were given a saline injection. Four hours after darkness onset, pineal N-acetyltransferase (NAT) activity as well as pineal and serum melatonin levels were measured. Parathion by itself significantly augmented nocturnal pineal NAT activity and serum melatonin levels in otherwise untreated rats; the insecticide was ineffective in reference to this enzyme when it was given in conjunction with the beta-adrenergic receptor antagonist propranolol. The augmentation of NAT activity by parathion also caused significant reduction in pineal serotonin (5-HT); again, this response was blocked by propranolol treatment. The results are consistent with the idea that parathion influences pineal 5-HT metabolism either at the level of the beta-adrenergic receptor or via the sympathetic innervation to the pineal gland.

Changes in nocturnal pineal indoleamine metabolism in rats treated with parathion are prevented by beta-adrenergic antagonist administration

Parathion, an organophosphorous insecticide, was previously shown to enhance the nighttime rise in pineal N-acetyltransferase (NAT) activity and serum melatonin levels. The purpose of the present study was to test whether parathion acts on the pineal gland by means of a beta-adrenergic receptor mechanism. Whereas parathion (total dose 6.5 mg/kg body wt over 6 days) by itself significantly augmented nocturnal pineal NAT activity and serum melatonin levels in otherwise untreated rats, the insecticide was ineffective in reference to this enzyme when it was given in conjunction with the beta-adrenergic receptor antagonist propranolol (20 mg/kg body wt, 1 h before lights off). The augmentation of NAT activity by parathion also caused significant reductions in pineal serotonin (5-HT); again, this response was blocked by propranolol treatment. Neither pineal hydroxyindole-O-methyltransferase (HIOMT) activity nor pineal levels of 5-hydroxytryptophan or hydroxyindole acetic acid (5-HIAA) were significantly changed as a result of either parathion or propranolol treatment. The results are consistent with the idea that parathion influences pineal 5-HT metabolism either at the level of the beta-adrenergic receptor or via the sympathetic innervation to the pineal gland.