Mn2+ and Ca2+ ATPases in lobster axon plasma membranes and their inhibition by pesticides

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.

Effects of lead on Na(+)-K(+) ATPase and Ca(+2) ATPase activities and lipid peroxidation in blood of workers

Lead is considered one of the major environmental toxicants that causes hematological, neurological, and gastrointestinal dysfunction. In this study, the authors examined the relationship between lead and lipid peroxidation, lead and Na(+)-K(+) ATPase activity, and lead and Ca(+2) ATPase activity in blood of workers. The working group consisted of 30 male workers occupationally exposed to lead at least for 10 years. The control group consisted of 20 healthy male individuals not involved with job-related lead exposures. Blood lead content of the control group and the working group were 10.0 +/- 1.8 microg/dl and 317.3 +/- 47.6 microg/dl, respectively. Malondialdehyde (MDA) value of the working group (0.57 +/- 0.30 nmol MDA/ml) was significantly greater than MDA value of the control goup (0.17 +/- 0.02 nmol MDA/ml). In the working group, both Na(+)-K(+) ATPase activity (105.0 +/- 47.0 nmol Pi. mg protein(-1) x h(-1)) and Ca(+2) ATPase activity (58.0 +/- 40.0 nmol Pi. mg protein(-1) x h(-1)) were lower compared with the corresponding values of Na(+)-K(+) ATPase activity (247.0 +/- 41.0 nmol Pi. mg protein(-1) x h(-1)) and Ca(+2) ATPase activity (230.0 +/- 41.0 nmol Pi. mg protein(-1) x h(-1)) of normal controls. The results show that lead exposure causes inhibition of Na(+)-K(+) ATPase and Ca(+2) ATPase activities and also results in increased lipid peroxidation.

Inhibition of Na+,K+-ATPase in Penaeus indicus postlarvae by lead

The plasma membrane/mitochondrial fractions of Penaeus indicus postlarvae contain Mg2+-dependent ATPase, Na+,K+-stimulated ATPase, Na+-stimulated ATPase and K+-stimulated ATPase. The Na+,K+-activated, Mg2+-dependent ATPase was investigated further in relation to different pH and temperature conditions, and at various concentrations of protein, ouabain, ATP and ions in the incubation medium. In vitro and in vivo effects of lead were studied on the enzyme activity. In vitro lead inhibited the enzyme activity in a concentration-dependent manner with an IC50 value of 204.4 microM. In correlation with in vitro studies, in vivo investigations (both concentration and time dependent) of lead also indicated a gradual inhibition in enzyme activity. A maximum decrease of 85.3% was observed at LC50 (7.2 ppm) of lead for concentration-dependent experiments. In time-dependent studies, the decrease was maximal (81.7%) at 30 days of sublethal exposure (1.44 ppm). In addition, the substrate- and ion-dependent kinetics of Na+,K+-ATPase was studied in relation to in vitro exposure of lead; these studies suggest a non-competitive type of inhibition.

Modulation of Mn2+ accumulation in cultured rat neuronal and astroglial cells

The effects of physiological concentrations of K+ on Mn2+ accumulation were compared in rat glial cells and neurons in culture. Increasing the K+ concentration in growth medium increased significantly the Mn2+ level of the cultivated cells, with glial cells more affected than neurons. Ethanol markedly increased the Mn2+ accumulation within glia but not within neurons while ouabain caused inhibition of Mn2+ uptake with neurons and glial cells. A modulation of the total protein synthesis by Mn2+ and ethanol level in the growth medium was observed with glial cells. These data suggest that the mechanisms involved in Mn2+ accumulation in glial cells are different from those present in neurons. Moreover, the results are consistent with the hypothesis that Mn2+ plays a regulatory role in glial cell metabolism.

Neurotoxicological effects and the mode of action of pyrethroid insecticides

Neuroexcitatory symptoms of acute poisoning of vertebrates by pyrethroids are related to the ability of these insecticides to modify electrical activity in various parts of the nervous system. Repetitive nerve activity, particularly in the sensory nervous system, membrane depolarization, and enhanced neurotransmitter release, eventually followed by block of excitation, result from a prolongation of the sodium current during membrane excitation. This effect is caused by a stereoselective and structure-related interaction with voltage-dependent sodium channels, the primary target site of the pyrethroids. Near-lethal doses of pyrethroids cause sparse axonal damage that is reversed in surviving animals. After prolonged exposure to lower doses of pyrethroids axonal damage is not observed. Occupational exposure to pyrethroids frequently leads to paresthesia and respiratory irritation, which are probably due to repetitive firing of sensory nerve endings. Massive exposure may lead to severe human poisoning symptoms, which are generally treated well by symptomatic and supportive measures.

Effects of chlordecone and chlordecone alcohol on isolated ovine erythrocytes

Chlordecone (CHLO, 14-30 microM) and chlordecone alcohol (CHLO ALC, 10-23 microM) altered the permeability of isolated ovine erythrocytes as evidenced by a concentration- and time-dependent induction of K+ efflux and hemolysis. Hemolysis, but not K+ efflux, was markedly delayed when the erythrocytes were suspended in isotonic sucrose. CHLO-induced and CHLO ALC-induced hemolysis and K+ efflux were dependent on the pH of the external media. Raising the pH from 6.5 to 9.4 inhibited CHLO-induced K+ efflux and hemolysis, whereas CHLO ALC-induced K+ efflux and hemolysis were increased. Low concentrations of both compounds (1-4 microM) protected erythrocytes against hypotonic hemolysis. Neither CHLO (30 microM) nor CHLO ALC (23 microM) induced the release of trapped K+ from KSCN-loaded unilamellar liposomes made from erythrocyte lipids. It is postulated that CHLO and CHLO ALC interact with membrane proteins and increase the permeability of the membrane to cations. This interaction leads to colloid-osmotic hemolysis.