Interaction of chlordecone with biological membranes

Pollutants, including Organophosphorus and Organochloride Pesticides, May Increase the Risk of Cardiac Remodeling and Atrial Fibrillation: A Narrative Review

Atrial fibrillation (AF) is the most common type of cardiac rhythm disorder. Recent clinical and experimental studies reveal that environmental pollutants, including organophosphorus-organochloride pesticides and air pollution, may contribute to the development of cardiac arrhythmias including AF. Here, we discussed the unifying cascade of events that may explain the role of pollutant exposure in the development of AF. Following ingestion and inhalation of pollution-promoting toxic compounds, damage-associated molecular pattern (DAMP) stimuli activate the inflammatory response and oxidative stress that may negatively affect the respiratory, cognitive, digestive, and cardiac systems. Although the detailed mechanisms underlying the association between pollutant exposure and the incidence of AF are not completely elucidated, some clinical reports and fundamental research data support the idea that pollutant poisoning can provoke perturbed ion channel function, myocardial electrical abnormalities, decreased action potential duration, slowed conduction, contractile dysfunction, cardiac fibrosis, and arrhythmias including AF.

Evaluation of the ecotoxicological impact of the organochlorine chlordecone on soil microbial community structure, abundance, and function

The insecticide chlordecone applied for decades in banana plantations currently contaminates 20,000 ha of arable land in the French West Indies. Although the impact of various pesticides on soil microorganisms has been studied, chlordecone toxicity to the soil microbial community has never been assessed. We investigated in two different soils (sandy loam and silty loam) exposed to different concentrations of CLD (D0, control; D1 and D10, 1 and 10 times the agronomical dose) over different periods of time (3, 7, and 32 days): (i) the fate of chlordecone by measuring (14)C-chlordecone mass balance and (ii) the impact of chlordecone on microbial community structure, abundance, and function, using standardized methods (-A-RISA, taxon-specific quantitative PCR (qPCR), and (14)C-compounds mineralizing activity). Mineralization of (14)C-chlordecone was inferior below 1 % of initial (14)C-activity. Less than 2 % of (14)C-activity was retrieved from the water-soluble fraction, while most of it remained in the organic-solvent-extractable fraction (75 % of initial (14)C-activity). Only 23 % of the remaining (14)C-activity was measured in nonextractable fraction. The fate of chlordecone significantly differed between the two soils. The soluble and nonextractable fractions were significantly higher in sandy loam soil than in silty loam soil. All the measured microbiological parameters allowed discriminating statistically the two soils and showed a variation over time. The genetic structure of the bacterial community remained insensitive to chlordecone exposure in silty loam soil. In response to chlordecone exposure, the abundance of Gram-negative bacterial groups (β-, γ-Proteobacteria, Planctomycetes, and Bacteroidetes) was significantly modified only in sandy loam soil. The mineralization of (14)C-sodium acetate and (14)C-2,4-D was insensitive to chlordecone exposure in silty loam soil. However, mineralization of (14)C-sodium acetate was significantly reduced in soil microcosms of sandy loam soil exposed to chlordecone as compared to the control (D0). These data show that chlordecone exposure induced changes in microbial community taxonomic composition and function in one of the two soils, suggesting microbial toxicity of this organochlorine.

Na⁺,K⁺-ATPase as the Target Enzyme for Organic and Inorganic Compounds

This paper gives an overview of the literature data concerning specific and non specific inhibitors of Na⁺,K⁺-ATPase receptor. The immobilization approaches developed to improve the rather low time and temperature stability of Na⁺,K⁺-ATPase, as well to preserve the enzyme properties were overviewed. The functional immobilization of Na⁺,K⁺-ATPase receptor as the target, with preservation of the full functional protein activity and access of various substances to an optimum number of binding sites under controlled conditions in the combination with high sensitive technology for the detection of enzyme activity is the basis for application of this enzyme in medical, pharmaceutical and environmental research.

Pesticide induced changes of nitric oxide synthase in rat brain in vitro

Organic insecticides are well known neurotoxicants. Nitric oxide (NO) is a neurotransmitter formed stoicheometrically with citrulline from L-arqinine through mediation of the enzyme nitric oxide synthase (NOS). We measured NOS activity in rat brain in vitro in the presence of selected organic insecticides such as, 10-200 microM conc carbaryl, kepone and malathion. All these three compounds inhibited NOS activity of rat brain in vitro in a concentration dependent manner. In most cases the changes observed were statistically significant. The order of potency, based on IC50 values of these insecticides, to inhibit NOS activity of rat brain, is carbaryl (105 microM) > Kepone (144 microM) > malathion (170 microM). We further demonstrated that these insecticides inhibit calmodulin (CaM)-stimulated NOS activity without affecting the basal enzyme activity. It is reported that the observed inhibition of NOS by selected insecticides may be due to interaction of these insecticides with Ca2+/CaM on which the NOS activity is well known to be dependent. This ultimately may lead to neurotoxicity of rat brain.

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.

The effects of dietary calcium and chlordecone on cholinesterase, triglycerides, low density lipoproteins, and cholesterol in serum of rat

Male, Sprague-Dawley rats were treated with 0, 1, 10, 50, 100 ppm chlordecone (Cd) mixed in calcium-sufficient (Ca-S) or calcium-deficient (Ca-D) diet for 15 days. A significant decrease in body weight gain was observed in 100 ppm of Cd-treated rats. Cholinesterase (ChE) activity was significantly decreased in serum of Ca-D rats. Chlordecone did not alter serum ChE activity in both Ca-S and Ca-D rats. However, Cd decreases serum triglycerides, low density lipoproteins (LDL) and cholesterol in both Ca-S and Ca-D rats. Rats fed with Ca-S or Ca-D diet exhibited differential sensitivity to Cd-toxicity. Decreased levels of serum triglycerides, LDL and cholesterol suggest that Cd might interfere in lipid metabolism.

Effects of chlordecone and malnutrition on immune response in rats

Effect of Chlordecone (Cd) and malnutrition on total body and spleen weights, and plaque forming cells (PFC) were studied. Rats were fed on normal, calcium (Ca-D), protein (P-D) or Ca+P-deficient diets containing 0, 10 or 100 ppm of Cd for 2 or 4 weeks. High (95-100%) mortality was observed in malnourished rats treated with 100 ppm of Cd for 4 weeks. A slight decrease in body weight and an increase in spleen weight was observed in normal but not malnourished rats treated with 10 ppm of Cd for 4 weeks. PFC were significantly increased in both malnourished and Cd-treated rats. Similar increase in PFC was observed in rats fed on Ca-D but not P-D diet containing 10 or 100 ppm of Cd. Whereas, rats fed on Ca+P-D diet containing 100 ppm of Cd exhibited a significant decrease in PFC.

Triorganotin inhibition of rat cardiac adenosine triphosphatases and catecholamine binding

Triorganotins have been reported to affect heme metabolism as well as the cardiovascular system. Our recent studies indicated that these organotins inhibit cardiac sarcoplasmic reticulum Ca(2+)-transport and cAMP-stimulated phosphorylation of specific proteins involved in Ca2+ transport, suggesting their interference with cardiac adrenergic function. The present study determines the effect of three organotins--tributyltin bromide (TBT), triethyltin bromide (TET) and trimethyltin chloride (TMT)--on rat cardiac ATPases and catecholamine binding, since these phenomena are involved in cardiac function. Cardiac membrane fraction was prepared from heart ventricles of male Sprague-Dawley rats. All three organotins inhibited cardiac Na+,K(+)-ATPase, [3H]ouabain binding, K(+)-activated p-nitrophenyl phosphatase (K(+)-PNPPase) and oligomycin-sensitive (OS) and oligomycin-insensitive (OI) Mg(2+)-ATPase in a concentration-dependent manner. K(+)-PNPPase was less sensitive to these triorganotins when compared to Na+K(+)-ATPase, suggesting that triorganotins affect the Na(+)-pump activity by acting on the Na(+)-dependent phosphorylation process. OS Mg(2+)-ATPase was more sensitive to these organotins when compared to OI Mg(2+)-ATPase, confirming their potent effect on the enzymes of oxidative phosphorylation. The order of potency is TBT greater than TET greater than TMT. TET and TMT, but not TBT, inhibited [3H]norepinephrine and [3H]dopamine binding to cardiac membranes in a concentration-dependent manner, the effect being more with TET. These results suggest that triorganotins inhibit sodium pump activity as well as ATP synthesis. Since Na+,K(+)-ATPase is involved in the active transport of catecholamines, triorganotins not only inhibited the catecholamine transport but also to some extent affected catecholamine binding, thus interfering with cardiac function.

Combined effects of carbon tetrachloride and chlordecone on calmodulin activity in gerbil brain

The potentiation of carbon tetrachloride (CCl4) toxicity by chlordecone (CD) pretreatment in different animal models is well established. However, these studies have only dealt with hepatotoxicity. The present study was initiated to determine whether CD preexposure potentiates CCl4 neurotoxicity in gerbils. Gerbils were chosen for the reason that the metabolism of CD in gerbil is similar to that of humans. Gerbils (50-80 g), fed on diet without or with CD (10 ppm) for 15 d, were challenged with a single dose of CCl4 (15 microliters, ip). Ca(2+)-ATPase and calmodulin (CaM) activities were determined in gerbil brain P2 fraction and cytosol, respectively, at intervals of 0.5, 2, 6, 12, and 24 h after CCl4 administration. Ca(2+)-ATPase and CaM activities were decreased at 0.5 and 2 h in both CD-preexposed and CCl4-treated gerbils. However, CaM activity returned to normal levels after 6 h and Ca(2+)-ATPase activity showed 80% recovery after 2 h. In vitro experiments showed that CCl4 alone at 5 microM concentration inhibited Ca(2+)-ATPase activity up to 50%. Combination of CD (0.5 microM) and CCl4 (1 and 5 microM) on Ca(2+)-ATPase activity showed no additive effect in vitro. Interaction between CCl4 and CaM was studied in the presence and absence of CD by monitoring NPN fluorescence. The decrease in NPN fluorescence observed with CCl4 was not potentiated by CD preincubation. These data suggest that CD does not enhance CCl4-induced alterations of Ca(2+)-ATPase and CaM activities in gerbil brain.

In vivo and in vitro effects of aldrin on rat brain synaptosomal Mg2+ and Na+,K(+)-adenosine triphosphatase

Aldrin, a chlorinated hydrocarbon, inhibited rat brain synaptosomal membrane-bound Na+,K(+)-adenosine triphosphatase (ATPase) and Mg2(+)-ATPase activities under in vivo and in vitro conditions. Na+,K(+)-ATPase was non-competitively inhibited whereas Mg2(+)-ATPase was inhibited uncompetitively. Arrhenius plots of both these ATPases without aldrin under in vivo and in vitro conditions were found to be linear. In the presence of aldrin, on the other hand, Arrhenius plots of the same ATPases were nonlinear. Slopes of Arrhenius plots of both ATPases under in vivo and in vitro condition were changed with change in temperature with aldrin. The activation energy (AE) of Na+,K(+)-ATPase and Mg2(+)-ATPase activities were changed over the temperature range 15-40 degrees in the presence of aldrin. These results thus suggest that aldrin increases the lipid fluidity of the synaptosomal membrane which may be a cause of inhibition of neuronal membrane-bound Na+,K+ and Mg2(+)-ATPase activities.

Na+/K(+)-ATPase in rat brain and erythrocytes as a possible target and marker, respectively, for neurotoxicity: studies with chlordecone, organotins and mercury compounds

Due to the inaccessibility of human nerve tissue for direct biochemical evaluation, there appears to be a need to identify peripheral markers which will reflect toxicity to the central nervous system by relatively non-invasive means. The aim of this study was to investigate whether the enzyme Na+/K(+)-ATPase in erythrocytes could be used as a marker for effects on the same enzyme in brain tissue. The compounds chosen to test this hypothesis were the pesticide chlordecone, the organotin compounds triethyltin and tributyltin, mercuric chloride and methyl mercury. All compounds were found to inhibit in vitro Na+/K(+)-ATPase activity in rat brain (IC50s = 0.9-56 microM) and in rat erythrocytes (IC50s = 1.2-66 microM) with similar potencies. However, administration of these compounds in vivo at high doses produced no significant inhibition of either brain or erythrocyte Na+/K(+)-ATPase activity, despite observed symptoms of neurotoxicity. Dialysis experiments indicated that dissociation of the compounds by dilution during tissue preparation was not responsible for the lack of detectable in vivo inhibition. Measurements of metal concentrations in brain by atomic absorption spectrometry after in vivo administration of triethyltin, mercuric chloride and methyl mercury indicated that levels of these compounds were too low to inhibit significantly NA+/K(+)-ATPase activity. These results suggest that inhibition of Na+/K(+)-ATPase activity might not represent the mechanism responsible for the neurotoxicity of these compounds, and that erythrocyte Na+/K(+)-ATPase activity is not a useful marker for neurotoxicity following acute exposures.

Age-related changes in rat brain ATPases during treatment with chlordecone

Chlordecone was reported to produce neurotoxicity by modulating the Na+ pump in adult rat brain. The present in vitro and in vivo studies were initiated to investigate its effect on maturing rat brain ATPases. Neonates were exposed to chlordecone for 20 d indirectly through lactation by treating the mothers po and from 21 to 50 d as adults. Brain P2 fractions were prepared from treated and control rats. Na+,K+, oligomycin-sensitive (O.S.) and oligomycin-insensitive (O.I.) Mg2+-ATPase activities were increased with age up to d 20. Na+,K+- and O.S. Mg2+-ATPases were inhibited in both in vitro and in vivo treatment with chlordecone. Both these enzymes were more sensitive to chlordecone in the neonatal brains as compared to adult rats (20-50 d). The activity of Mg2+-ATPase but not of Na+,K+-ATPase was restored to normal activity after 20 d of withdrawal of chlordecone treatment. O.I. Mg2+-ATPase was insensitive to chlordecone treatment in all age groups. Ca2+-ATPase activity was not increased with age; however, it was more sensitive to chlordecone in neonates as compared to adults. These results suggest that the Na+ pump, Ca2+-ATPase, and ATP synthesizing enzymes are highly sensitive to chlordecone during early postnatal development.

The influence of chlordecone and oestrogen on the secretion of proteinaceous molecules of the mouse uterus

Ovariectomised mice were treated with sesame seed oil, oestradiol, or one of three different levels of the insecticide chlordecone (1, 1a, 3, 3a, 4, 5, 5a, 6-decachloro-octahydro-1, 3, 4-metheno-2H-cyclobuta[cd] pentalen-2-one). After 9 days of treatment, the uteri were injected with (35)S-methionine and radiolabelled proteins were flushed from uteri 4 h later. Reproductive tract weights and the total amount of radioactivity in uterine flushings were measured. Reproductive tract weights increased significantly only in animals treated with the highest dose of chlordecone tested and oestradiol-treated animals. Trichloroacetic acid (TCA) precipitated radioactivity was increased by all doses of insecticide chlordecone tested but increases were significant only at one level. The greatest stimulation of (35)S-methionine incorporation occurred in ovariectomised animals treated with oestradiol. Radioactive proteins were analysed by fluorography of two-dimensional gels. The fluorograms showed that the proteinaceous uterine secretions, as influenced by chlordecone, were greatly reduced in number as compared with those secreted under the influence of oestradiol. Chlordecone appears to cause the secretion of proteinaceous material from the uteri of mice in a qualitatively different manner than does oestradiol.

Pharmacological modification of tremor and enhanced acoustic startle by chlordecone and p,p'-DDT

Pretreatment of rats with phenoxybenzamine (5 mg/kg; SC), an alpha adrenergic antagonist, decreased the peak tremor power and startle magnitude of rats subsequently given DDT (75 mg/kg; PO) or chlordecone (60 mg/kg; IP), without having a significant effect on control animals. Pretreatment with an intracerebroventricular injection of calcium (3.75 microM in 5 microliters NaCl) decreased the peak tremor power due to subsequently administered DDT, while increasing the tremor response in rats later dosed with chlordecone. The effects of phenoxybenzamine are postulated to be due to a blockade of an excitatory influence of the adrenergic system. Calcium may decrease DDT-induced tremor by acting as a neuronal stabilizer. Potentiation of the tremorigenic effect of chlordecone by calcium may be due to increased levels of intracellular calcium, resulting in augmented release of neurotransmitters in chlordecone-exposed animals.

Effects of tricyclohexylhydroxytin on the kinetics of adenosine triphosphatase system and protection by thiol reagents

Tricyclohexylhydroxytin, commonly known as Plictran, inhibited Na+, K+-ATPase activity of rat brain synaptosomes in a concentration-dependent manner with median inhibitory concentration (IC-50) of 2 microM. Both K+-stimulated para-nitrophenylphosphatase and [3-H]-ouabain binding to synaptosomes were also inhibited by Plictran with IC-50 values of 11 and 30 microM, respectively. Altered pH and Na+, K+-ATPase activity curves demonstrated comparable inhibition in buffered neutral and alkaline pH ranges, and no inhibition was observed in acidic pH. The inhibition of Na+, K+-ATPase was independent of temperature. Kinetic studies of substrate (ATP) activation of Na+, K+-ATPase indicated uncompetitive inhibition. Results also showed noncompetitive inhibition for p-nitrophenylphosphate and uncompetitive inhibition for K+ activations of p-nitrophenylphosphatase. Preincubation of synaptosomes with dithiothreitol, a sulfhydryl (SH) agent, resulted in the complete protection of Plictran inhibition of Na+, K+-ATPase, K+-para-nitrophenylphosphatase, and [3-H]-ouabain binding. The protection was specific and concentration dependent since cysteine and glutathione did not afford protection. These results indicate that Plictran inhibited Na+, K+-ATPase by interacting with dephosphorylation of the enzyme-phosphoryl complex and exerted a similar effect to that of SH-blocking agents.

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

Rats were given 75 mg/kg of 5,5-diphenylhydantoin (phenytoin) or vehicle 30 min prior to 75 mg/kg of 1,1,1-trichloro-bis(p-chlorophenyl)ethane (p,p'-DDT) (p.o.) or chlordecone (i.p.) and tremor was measured 12 h later. Rats were then killed, and regional brain levels of biogenic amines and their acid metabolites and amino acids were determined. Pretreatment with phenytoin significantly attenuated the tremor produced by p,p'-DDT but enhanced that produced by chlordecone. p,p'-DDT had significant effects on the levels of aspartate, glutamate, 5-hydroxyindoleacetic acid (5-HIAA), and 3-methoxy-4-hydroxyphenylglycol (MHPG), whereas chlordecone increased glycine, 5-HIAA, and MHPG levels. Pretreatment with phenytoin blocked p,p'-DDT-induced increases of aspartate in the brainstem and spinal cord, 5-HIAA in the hippocampus, and MHPG in the brainstem and hypothalamus. Phenytoin significantly enhanced chlordecone-induced increases of MHPG in the brainstem. These data indicate that organochlorine-induced increases in noradrenergic activity in the brainstem and spinal cord may be directly related to the tremorigenic effects of these chemicals.

Effect of amiodarone on Na+-, K+-ATPase and Mg2+-ATPase activities in rat brain synaptosomes

Amiodarone hydrochloride is a diiodinated antiarrhythmic agent widely used in the treatment of cardiac disorders. With the increasing use of amiodarone, several untoward effects have been recognized and neuropathy following amiodarone therapy has recently been reported. The present studies were carried out to study the effect of amiodarone on rat brain synaptosomal ATPases in an effort to understand its mechanism of action. Na+, K+-ATPase and oligomycin sensitive Mg2+ ATPase activities were inhibited by amiodarone in a concentration dependent manner with IC50 values of 50 microM and 10 microM respectively. [3H]ouabain binding was also decreased in a concentration dependent manner with an IC50 value of 12 microM, and 50 microM amiodarone totally inhibited [3H]ouabain binding. Kinetics of [3H]ouabain binding studies revealed that amiodarone inhibition of [3H]ouabain binding is competitive. K+-activated p-nitrophenyl phosphatase activity showed a maximum inhibition of 32 per cent at 200 microM amiodarone. Synaptosomal ATPase activities did not show any change in rats treated with amiodarone (20 mg kg-1 day-1) for 6 weeks, when compared to controls. The treatment period may be short, since the reported neurological abnormalities in patients were observed during 3-5 years of treatment. The present results suggest that amiodarone induced neuropathy may be due to its interference with sodium dependent phosphorylation of Na+, K+-ATPase reaction, thereby affecting active ion transport phenomenon and oxidative phosphorylation resulting in low turnover of ATP in the nervous system.

Increased susceptibility to mouse hepatitis virus 3 of peritoneal macrophages exposed to dieldrin

Interaction of a single dose (36 mg/kg body wt) of the organochlorine pesticide dieldrin with mouse peritoneal macrophages was examined in C57Bl/6, (C57Bl/6 X A/J)F1, and A/J strains of different genetic resistance to mouse hepatitis virus 3 (MHV3) infection. In vivo studies showed increased susceptibility to MHV3 acute disease of C57Bl/6 and (C57Bl/6 X A/J)F1 animals challenged with the pesticide. Significant decrease of mean time of death in dieldrin-exposed, MHV3-infected susceptible C57Bl/6 mice was observed similarly upon po or ip administration of a single, sublethal dose of dieldrin. In addition, decrease of humoral response to the virus was quantified by determination of anti-MHV3 IgG antibodies in spleen cell supernatant fractions and in blood sera of dieldrin-exposed C57Bl/6 mice. A single dose of dieldrin did not alter the in vivo resistance of A/J animals to acute MHV3 disease. The resistant A/J mice, however, showed increased mortality upon two subsequent exposures to dieldrin followed by infection with high lethal doses of MHV3. Phagocytic activity, cell adherence capacity, and attachment and uptake of 3H-radiolabeled MHV3 by C57Bl/6 peritoneal macrophages were determined by in vitro studies. These affector activities of peritoneal macrophages were slightly decreased or unchanged in cells originating from animals exposed to the pesticide. However, the intrinsic activity of MHV3 restriction appeared to be affected in macrophages derived from dieldrin-treated animals: (i) peritoneal C57Bl/6 macrophages collected from the early phase of acute MHV3 disease contained increased MHV3 antigen and (ii) increased cytolysis was observed after in vitro MHV3 infection of macrophages originating from dieldrin-exposed C57Bl/6 mice.

Effect of chlordecone (Kepone) on the rat brain concentration of 3-methoxy-4-hydroxyphenylglycol: evidence for a possible involvement of the norepinephrine system in chlordecone-induced tremor

3-Methoxy-4-hydroxyphenylglycol (MHPG) is the major metabolite of norepinephrine (NE) in the rat brain. A single injection of tremorigenic doses of chlordecone to adult male Fischer-344 rats resulted in significant increases in MHPG concentrations in hypothalamus, brain stem, cerebellum, and caudate nucleus. The increase in MHPG was accompanied by a decrease in NE in the hypothalamus, suggesting that chlordecone treatment caused an increase in the turnover of NE in the brain. There was a dose- and time-related correlation between the increases in the concentrations of MHPG in hypothalamus, brain stem, and cerebellum and tremor in rats. The increase in MHPG in hypothalamus and brain stem occurred as early as 1 hr postdosing; this preceded the earliest measurable sign of tremor and initial hypothermia. Whether the alterations in the brain NE system are involved in the expression of the tremor and the initial hypothermia induced by chlordecone or whether they are merely associated with these changes is not clear.

Chlordecone inhibition of calmodulin activated calcium ATPase in rat brain synaptosomes

The effect of chlordecone on Ca2+-ATPase of rat brain synaptosomes in the absence and presence of calmodulin was determined in vitro and in vivo. A 50% activation of Ca2+-ATPase was obtained at 5 micrograms calmodulin per 1.5 ml reaction mixture containing 50 micrograms synaptosomal protein. Chlordecone inhibited Ca2+-ATPase in the absence of calmodulin with an IC50 of 10 microM, whereas chlordecone at 1.0 microM, which had no effect on the basal enzyme activity, completely inhibited the calmodulin activated Ca2+-ATPase. Chlordecone-treated rats showed a significant reduction in calmodulin levels in brain P2 fraction. Brain synaptosomal Ca2+-ATPase in chlordecone-treated rats showed a 50% reduction, which was restored by exogenously added calmodulin. These results suggest that chlordecone may be altering calmodulin-regulated synaptic processes in the brain.

On the neurotoxicity of chlordecone: a role for gamma-aminobutyric acid and serotonin

Rats receiving the chlorinated insecticide, chlordecone (80 mg/kg i.p.), exhibit hyperexcitability, exaggerated startle response and tremors within a few hours after the injection. Since the chlordecone-elicited tremors are relieved by injections of muscarinic receptor blockers, acetylcholine has been implicated indirectly in the mechanism of chlordecone toxicity. Our studies on acetylcholine steady-state levels and turnover in several brain structures failed to detect evidence for an involvement of cholinergic presynaptic mechanisms in the chlordecone toxicity. We then investigated whether GABA is involved by measuring the rate of its accumulation following intraventricular injection of gabaculine. Chlordecone reduced the rate of GABA accumulation in striatum, but not in cerebellum, brainstem or hippocampus. Such inhibition appeared 4 h after drug injection thereby preceding the onset of tremors. Since tremors elicited by chlordecone are attenuated by the administration of serotonin receptor blockers and since chlordecone increases serotonin (5-HT) turnover, we studied whether 5-HT recognition sites are modified following chlordecone administration. We have found a reduction of the Bmax of 5-HT1 receptors in striatum and hippocampus without any modification in the kinetic characteristics of 5-HT2 receptors. We have also shown that the temporal relationship between down regulation of 5-HT1 recognition sites, reduction of striatal GABA turnover and tremors caused by chlordecone allows one to consider these 3 phenomena as reciprocally dependent. In conclusion our results favor the possibility that tremors may result from a decrease in the striatal GABergic tone which probably is elicited by an increase of serotonergic activity caused by chlordecone by a yet unknown mechanism.

Cadmium-induced changes in the histoenzymatic activity in liver, kidney and duodenum of pregnant rats

Cadmium was administered in drinking water at a concentration of 50 ppm to female Wistar rats for 5 months before mating, and then continued during gestation. The histochemical evaluation revealed a relative decrease in succinic dehydrogenase (SDH) and Mg+2-stimulated ATPase activities in duodenum, liver and kidney in the exposed rats. It is suggested that the resulting decrease in metabolic efficiency in maternal organs would be expected to exert an indirect, inhibitive effect on maternal-fetal transfer of nutrients, as reflected by fetal growth retardation.

Effect of chlordecone on pH and temperature dependent substrate activation kinetics of rat brain synaptosomal ATPases

Chlordecone, a polycyclic chlorinated insecticide known as Kepone, inhibited the activities of (Na+-K+)ATPase and Mg2+-ATPase in rat brain synaptosomes. Altered pH and specific activity curves for both enzymes demonstrated significant inhibition by chlordecone in buffered acidic, neutral and alkaline pH ranges. Noncompetitive inhibition with respect to activation by ATP in the case of (Na+-K+)ATPase was indicated by altered Vmax values with no significant change in Km values at any pH studied, except at pH 9.5. Mg2+-ATPase was inhibited uncompetitively as evidenced by altered Vmax and Km values. The activities of both ATPase were decreased in the presence of chlordecone at higher temperatures. Activation energy (delta E) values were found to be decreased significantly in the presence of chlordecone at 37 degrees. Arrhenius plots of both ATPases preincubated with chlordecone were found to be nonlinear. In the presence of chlordecone, Vmax was decreased without significant change in Km values for (Na+-K+)ATPase at all temperatures, suggesting a noncompetitive type of inhibition. In the case of Mg2+-ATPase, similar noncompetitive type inhibition was obtained at 27 degrees but not at 32 and 37 degrees. The kinetic data in general suggest that the chlordecone inhibited (Na+-K+)ATPase noncompetitively and Mg2+-ATPase uncompetitively at all pHs and temperatures studied. The present data suggest that inhibition of (Na+-K+)ATPase and Mg2+-ATPase, the two membrane-bound enzymes in synaptosomes, by chlordecone is temperature dependent and pH independent.

Alterations in tissue distribution of chlordecone (kepone) in the rat following phenobarbital or SKF-525A administration

Phenobarbital (PB) or SKF-525A were injected ip into adult male rats prior to administration of 1.6 microCi [14C] chlordecone (CD) by gavage. Effects of these liver function modulators on tissue distribution of CD was assessed. In all cases, animals were sacrificed at 24 h following [14C]CD gavage. The timing and number of injections of PB or of SKF-525A were varied. Doses of PB (65 mg/kg) or of SKF-525A (75 mg/kg) were used except as noted, and controls received saline. Specific radioactivities of major tissues were assayed by scintillation counting. Rats pre-treated with a single dose of SKF-525A at 6, 12, or 24 h prior to [14C]CD distribution. Similarly, PB administered at 6 h prior to [14C]CD gavage was without effect on distribution. Rats pretreated 12 or 14 h before [14C]CD with PB appeared to have increased liver specific activities and had reduced [14C]CD levels in several other tissues. These trends were more marked in a second study, in which multiple doses of PB (3 consecutive daily doses of 65 mg/kg, the final dose 24 h prior to [14C]CD or SKF-525A (1 dose of 75 mg/kg 90 min prior to [14C]CD, followed by a second dose of 38 mg/kg at 6.5 h after [14C]CD) were given. Tissue [14C]CD levels were assayed as before; urine and feces samples were also counted and reported as percent of [14C]CD administered. SKF-525A animals had significantly high [14C] levels in digestive system, while fecal and urinary levels were significantly low. No other significant alterations were observed in these animals, except that testes levels were reduced. Livers of rats receiving multiple doses of PB had significantly elevated [14C]CD levels, and all other tissues examined had levels significantly below controls. Fecal and urinary excretion of [14C]CD was significantly depressed. Studies indicate that an inducer of hepatic metabolism can dramatically alter the distribution and hence the relative toxicity of CD.