5,5-Diphenylhydantoin antagonizes neurochemical and behavioral effects of p,p'-DDT but not of chlordecone

Effects of endocrine disruptors on the electrical activity of leptin receptor neurons in the dorsomedial hypothalamus and anxiety-like behavior in male mice

There is increasing concern about the effects of endocrine disrupting chemicals (EDCs) on human health. Recently, some EDCs are suggested to affect energy metabolism leading to increased risk of obesity. Obesogenic effects of some EDCs on adipogenesis have been reported, however, there is no study examining their potential actions on the brain circuits controlling feeding and metabolism. We have investigated effects of tributyltin (TBT) and dichlorodiphenyltrichloroethane (p,p'-DDT) on electrical activity on dorsomedial hypothalamic leptin receptor neurons (DMH^LepR), morphological adaptations in neuronal anatomy of DMH^LepR, locomotion, and anxiety-like behaviors in mice. Twenty-three Lep-Cre transgenic mice were intracranially injected with GFP virus. Control animals received intraperitoneal corn oil alone while group 2 and 3 received TBT (25 μg/kg) and p,p'-DDT (2 mg/kg) for one month. Locomotor activity and anxiety-like behavior of the animals were determined by open field test. Electrophysiological effects of TBT and p,p'-DDT on DMH^LepR neurons were determined by patch clamp method. Neuronal anatomy was determined by confocal microscopy. Spontaneous firing frequency of DMH^LepR neurons of TBT group of mice was significantly higher than both p,p'-DDT and control groups (p < 0.01). TBT and p,p'-DDT significantly decreased frequency of the spontaneous inhibitory post-synaptic currents to DMH^LepR neurons compared to the control group (p < 0.05). The time spent in the center and the number of entrances to the center by the TBT-administered mice were significantly lower than other groups (p < 0.01). The total distance traveled and mean speed of the control group of mice were significantly higher than the p,p'-DDT- and TBT-administered animals (p < 0.0001). c-Fos activity of the p,p'-DDT- and TBT-administered animals were significantly elevated compared to the control group (p < 0.001), while no change in the number of dendritic spines were observed. In conclusion, this study demonstrates that exposure to TBT and p,p'-DDT alters electrical activity in DMH^LepR neurons and behavioral state in mice.

Public health and chronic low chlordecone exposure in Guadeloupe, Part 1: hazards, exposure-response functions, and exposures

BACKGROUND

Inhabitants of Guadeloupe are chronically exposed to low dose of chlordecone via local food. The corresponding health impacts have not been quantified. Nevertheless the public authority implemented an exposure reduction program in 2003. We develop methods for quantifying the health impacts of chlordecone and present the results in 2 articles: 1. hazard identification, exposure-response functions (ERF) and exposure in Guadeloupe, 2. Health impacts and benefits of exposure reduction. Here is the first article.

METHODS

Relevant data are extracted from publications searched in Medline and Toxline. Available knowledges on mode of action and key-event hazards of chlordecone are used to identify effects of chlordecone that could occur at low dose. Then a linear ERF is derived for each possible effect. From epidemiological data, ERF is the delta relative risk (RR-1) divided by the corresponding delta exposure. From animal studies, ERF is the benchmark response (10 %) divided by the best benchmark dose modeled with BMDS2.4.0. Our goal is to obtain central values for the ERF slopes, applicable to typical human populations, rather than lower or upper bounds in the most sensitive species or sex.

RESULTS

We derive ERFs for 3 possible effects at chronic low chlordecone dose: cancers, developmental impairment, and hepatotoxicity. Neurotoxicity in adults is also a possible effect at low dose but we lack quantitative data for the ERF derivation. A renal toxicity ERF is derived for comparison purpose. Two ERFs are based on epidemiological studies: prostate cancer in men aged >44y (0.0019 per μg/Lblood) and altered neurodevelopment in boys (-0.32 QIpoint per μg/Lcord-blood). Two are based on animal studies: liver cancer (2.69 per mg/kg/d), and renal dysfunction in women (0.0022 per mg/kg/d).

CONCLUSION

The methodological framework developed here yields ERFs for central risk estimates for non-genotoxic effects of chemicals; it is robust with regard to models used. This framework can be used generally to derive ERFs suitable for risk assessment and for cost-benefit analysis of public health decisions.

Cognitive, visual, and motor development of 7-month-old Guadeloupean infants exposed to chlordecone

BACKGROUND

The insecticide chlordecone was extensively used in the French West Indies to control banana root borer. Its persistence in soils has led to the widespread pollution of the environment, and human beings are still exposed to this chemical. Chlordecone has been shown to impair neurological and behavioural functions in rodents when exposed gestationally or neonatally.

OBJECTIVES

The aim of the study was to evaluate the impact of prenatal and postnatal exposure to chlordecone on the cognitive, visual, and motor development of 7-month-old infants from Guadeloupe.

METHODS

Infants were tested at 7 months (n=153). Visual recognition memory and processing speed were assessed with the Fagan Tests of Infant Intelligence (FTII), visual acuity with the Teller Acuity Card, and fine motor development with the Brunet-Lezine. Samples of cord blood and breast milk at 3 months (n=88) were analyzed for chlordecone concentrations. Postnatal exposure was determined through breast feeding and frequency of contaminated food consumption by the infants.

RESULTS

Cord chlordecone concentrations in tertiles were associated with reduced novelty preference on the FTII in the highly exposed group (β=-0.19, p=0.02). Postnatal exposure through contaminated food consumption was marginally related to reduced novelty preference (β=-0.14, p=0.07), and longer processing speed (β=0.16, p=0.07). Detectable levels of chlordecone in cord blood were associated with higher risk of obtaining low scores on the fine motor development scale (OR=1.25, p<0.01).

CONCLUSION

These results suggest that pre- and postnatal low chronic exposure to chlordecone is associated with negative effects on cognitive and motor development during infancy.

DDT and Other Chlorinated Insecticides

The use of organochlorine insecticides such as DDT, lindane and cyclodieneshas declined markedly worldwide over the last decades. Most are now banned or not used. At an acute toxicity level they have been relatively safe in use for humans. However, the greatest concerns are their persistence in people, wildlife and the environment due to their slow metabolism. Although their carcinogenicity for humans has not been supported by strong epidemiological evidence, their potential to be modulators of endocrine and immune function at levels remaining in the environment or associated with residual spraying of DDT continue to be of concern. At present, DDT is still allowed by the United Nations for combating malaria, with continual monitoring and assessment where possible. The toxicological consequences of exposure of animals and people to DDT is discussed as well as some analogues and other insecticides such as lindane, dieldrin and chlordecone that, although little used, continue to persist in surroundings and people. Because of circumstances of world health brought about by climate change or human activities that have yet to develop, there may come a time when the importance of some may re-emerge.

Determination of a tolerable daily intake of DDT for consumers of DDT contaminated fish from the lower Yakima River, Washington

DDT, DDE, and DDD have been detected at elevated concentrations in sediments and fish of the Yakima River, its tributaries and drainages. An assessment was conducted to evaluate the public health significance of eating fish from the river. This was accomplished by establishing a daily intake level of DDT for the population of greatest concern, and comparing this level to a tolerable daily intake. The most sensitive and highly exposed group was determined to be breastfeeding infants. Infant daily intakes of DDT, based on estimated mother's DDT-breast milk levels, were compared to a recommended tolerable daily intake. Results indicate that mothers who frequently consume Yakima River bottom-feeding fish could have breast milk DDT concentrations sufficiently high to expose their infants to levels above the tolerable daily intake.

ATSDR evaluation of health effects of chemicals. II. Mirex and chlordecone: health effects, toxicokinetics, human exposure, and environmental fate

This document provides public health officials, physicians, toxicologists, and other interested individuals and groups with an overall perspective of the toxicology of mirex and chlordecone. It contains descriptions and evaluations of toxicological studies and epidemiological investigations and provides conclusions, where possible, on the relevance of toxicity and toxicokinetic data to public health. Additional substances will be profiled in a series of manuscripts to follow.

Blockade of only spinal alpha 1 adrenoceptors is insufficient to attenuate DDT-induced alterations in motor function

Male Fischer 344N rats were chronically implanted with an intrathecal cannula and gavaged with p,p'-DDT (1,1,1-trichloro-2,2-bis[p-chlorophenyl]ethane; 30 or 45 mg/kg) or corn oil. Seven hours later, subjects were intrathecally infused with vehicle, 15, 30, 60, or 120 micrograms of prazosin (an alpha 1-adrenergic antagonist). Spectral analysis of bodily movements was performed 7.5, 8, and 10 hr after DDT administration. In control rats, 15 micrograms of prazosin reduced the spectral profiles of spontaneous movements. A 30-micrograms dose produced motor impairments, without significantly changing the spectral profiles. Tremulous movements induced by DDT were unaffected by 15 or 30 micrograms, whereas 60 or 120 micrograms of intrathecal prazosin significantly reduced the spectral profiles of rats pretreated with 45 mg/kg of DDT. Other subjects were administered vehicle or DDT (45 mg/kg), intrathecally infused with 15 or 60 micrograms of prazosin (7 hr), and sacrificed (7.5 hr). Noncannulated rats were gavaged with 60 mg/kg of DDT, injected subcutaneously (sc) with 0.5 mg/kg of prazosin (5.5 hr), and sacrificed (8 hr). Cortical and spinal tissues were used in ex vivo binding assay utilizing [3H]prazosin. Fifteen or sixty micrograms of intrathecal prazosin occupied similar percentages of spinal [3H]prazosin binding sites, but produced a dose-related increase in cortical prazosin equivalents. Sixty micrograms of intrathecal or 0.5 mg/kg of sc prazosin resulted in similar concentrations of cortical prazosin equivalents. Together, these data indicate that while intrathecal prazosin will attenuate DDT-induced motor dysfunction, this effect requires blockade of alpha 1 adrenoceptors in regions other than solely the spinal cord.

Milacemide increases 5-hydroxytryptamine and dopamine levels in rat brain--possible mechanisms of milacemide antimyoclonic property in the p,p'-DDT-induced myoclonus

Milacemide, a glycine prodrug that is able to enter the brain readily, has been shown to have an antimyoclonic property in the p,p'-DDT-induced myoclonus syndrome. Milacemide increased regional 5-HT and dopamine and decreased 5-HIAA, DOPAC and HVA levels in naive rats. In p,p'-DDT-treated rats, 5-HT levels were unchanged at the time the rats experienced spontaneous myoclonus in all brain regions except in the striatum, where it increased. 5-HIAA levels increased but did not reach significant levels except in the striatum. Dopamine, DOPAC, HVA and norepinephrine were unchanged. When rats were treated concurrently with both p,p'-DDT and milacemide, regional 5-HT levels were increased and NE levels in the brainstem and cerebellum decreased. Depletion of brain serotonin by pretreatment with PCPA or with 5,7-DHT, or blocking 5-HT receptors with different 5-HT antagonists, failed to eliminate the antimyoclonic property of milacemide. This antimyoclonic effect of milacemide may be mediated through other mechanisms besides its ability to increase brain 5-HT levels. Possible mechanisms to be considered are its antiepileptic property, and its ability to increase brain glycine levels. Milacemide may have potential for therapeutic trials in patients with myoclonus.

The effects of lindane, DDT, and chlordecone on avoidance responding and seizure activity

Male adult Fischer-344 rats were given various doses of lindane (0, 15, and 30 mg/kg, po), chlordecone (0, 25, 50, or 100 mg/kg, ip), or p,p'-dichlorodiphenyltrichloroethane (p,p'-DDT) (0, 25, 50, or 100 mg/kg, po) and tested for their ability to perform a two-way shuttle box task or to learn and retain a step-through passive avoidance response. Administration of p,p'-DDT or chlordecone 3 hr prior to acquisition did not affect the number of shuttle box avoidance responses made during a 60-trial training task, while responses during the intertrial interval (ITI) were decreased. Rats receiving 15 or 30 mg/kg of lindane made fewer avoidance responses, but did not differ from controls in terms of the number of responses during the ITI. When 30 mg/kg lindane was given 3 hr prior to passive avoidance acquisition, retention was impaired 7 days later; the lower dose of lindane, and all doses of chlordecone or p,p'-DDT had no effect under these conditions. When these chemicals were given immediately after passive avoidance training, animals treated with lindane were not affected. Animals receiving 100 mg/kg of p,p'-DDT or chlordecone displayed marked signs of toxicity and animals tested 7 days after training showed an impaired retention. Pretreatment with anticonvulsants such as phenobarbital and chlordiazepoxide, which may enhance GABA-mediated responses, blocked the disruptive effects of lindane (30 mg/kg) on shuttle box avoidance. The seizure-related activity produced by a higher dose of lindane (60 mg/kg) and kainic acid, a hippocampal excitotoxin, was also blocked by phenobarbital and chlordiazepoxide. Pretreatment with phenytoin, which is thought to bind to the inactivation gates of sodium, had no effect on the effects produced by lindane or kainic acid. These data suggest that treatment with nonconvulsant doses of lindane can interfere with the ability to acquire and use new information and that these effects may be associated with alterations in GABA.