Effects of p,p'-DDE and some other chlorinated hydrocarbons on the formation of prostaglandins by the avian eggshell gland mucosa

Environmental exposure to non-steroidal anti-inflammatory drugs and potential contribution to eggshell thinning in birds

Abnormally thin eggshells can reduce avian reproductive success, and have caused rapid population declines. The best known examples of this phenomenon are the widespread population crashes in birds, mostly raptors, fish eating birds, and scavengers, caused by the pesticide DDT and its isomers in the 1960s. A variety of other chemicals have been reported to cause eggshell thinning. Non-steroidal anti-inflammatory drugs (NSAIDs), which are extensively and increasingly used in human and veterinary medicine, may be one particularly concerning group of chemicals that demonstrate an ability to impair eggshell development, based both on laboratory studies and on their known mechanism of action. In this review, we outline environmental and wildlife exposure to NSAIDs, describe the process of eggshell formation, and discuss pathways affected by NSAIDs. We list pharmaceuticals, including NSAIDs, and other compounds demonstrated to reduce eggshell thickness, and highlight their main mechanisms of action. Dosing studies empirically demonstrated that NSAIDs reduce eggshell thickness through cyclooxygenase inhibition, which suppresses prostaglandin synthesis and reduces the calcium available for the mineralization of eggshell. Using the US EPA's CompTox Chemicals Dashboard, we show that NSAIDs are predicted to strongly inhibit cyclooxygenases. NSAIDs have been observed both in the putative diet of scavenging birds, and we report examples of NSAIDs detected in eggs or tissues of wild and captive Old World vultures. We suggest that NSAIDs in the environment represent a hazard that could impair reproduction in wild birds.

Impacts of endocrine disrupting chemicals on reproduction in wildlife and humans

Endocrine disrupting chemicals (EDCs) are ubiquitous in aquatic and terrestrial environments. The main objective of this review was to summarize the current knowledge of the impacts of EDCs on reproductive success in wildlife and humans. The examples selected often include a retrospective assessment of the knowledge of reproductive impacts over time to discern how the effects of EDCs have changed over the last several decades. Collectively, the evidence summarized here within reinforce the concept that reproduction in wildlife and humans is negatively impacted by anthropogenic chemicals, with several altering endocrine system function. These observations of chemicals interfering with different aspects of the reproductive endocrine axis are particularly pronounced for aquatic species and are often corroborated by laboratory-based experiments (i.e. fish, amphibians, birds). Noteworthy, many of these same indicators are also observed in epidemiological studies in mammalian wildlife and humans. Given the vast array of reproductive strategies used by animals, it is perhaps not surprising that no single disrupted target is predictive of reproductive effects. Nevertheless, there are some general features of the endocrine control of reproduction, and in particular, the critical role that steroid hormones play in these processes that confer a high degree of susceptibility to environmental chemicals. New research is needed on the implications of chemical exposures during development and the potential for long-term reproductive effects. Future emphasis on field-based observations that can form the basis of more deliberate, extensive, and long-term population level studies to monitor contaminant effects, including adverse effects on the endocrine system, are key to addressing these knowledge gaps.

Investigation of mRNA expression changes associated with field exposure to DDTs in chickens from KwaZulu-Natal, South Africa

The objective of this study was to identify potential mRNA expression changes in chicken livers associated with environmental exposure to dichloro-diphenyl-trichloroethane (DDT) and its metabolites (DDTs). In particular, we focused on genes relating to the immune system and metabolism. We analyzed liver samples from free-ranging chickens in KwaZulu-Natal, South Africa, for contamination by DDTs. This area predominantly uses DDT in its malaria control program, and homes are sprayed annually with the pesticide. Genes relating to the immune system and metabolism were selected as potential genetic biomarkers that could be linked to higher contamination with DDTs. RT-qPCR analysis on 39 samples showed strong correlations between DDTs contamination and mRNA expression for the following genes: AvBD1, AvBD2, AvBD6 and AvBD7 (down-regulated), and CYP17, ELOVL2 and SQLE (up-regulated). This study shows for the first time interesting and significant correlations between genetic material collected from environmentally-exposed chickens and mRNA expression of several genes involved in immunity and metabolism. These findings show the usefulness of analysis on field samples from a region with high levels of environmental contamination in detecting potential biomarkers of exposure. In particular, we observed clear effects from DDT contamination on mRNA expression of genes involved in immune suppression, endocrine-disrupting effects, and lipid dysregulation. These results are of interest in guiding future studies to further elucidate the pathways involved in and clinical importance of toxicity associated with DDT exposure from contaminated environments, to ascertain the health risk to livestock and any subsequent risks to food security for people.

Endocrine disruption in the context of life cycles: perception and transduction of environmental cues

Environmental and social stresses have major impacts on the life cycles of organisms. Furthermore, habitat disturbance/destruction, global climate change, and existence of endocrine disrupting chemicals (EDCs) due to human activities are increasingly likely to pose additive and synergistic stresses that could have potential deleterious effects on physiological function in vertebrates. Central to an organism's life cycle is the ability to respond to environmental cues, physical and social. Environmental signals may act directly on endocrine tissues, but most act through neural pathways, and neuroendocrine and endocrine secretions that affect changes in morphology, physiology and behavior. While most investigations focus on endocrine secretions and their effects, we know much less about perception and transduction of environmental signals. Additionally, some populations of vertebrates, from fish to mammals, temporarily resist environmental and social stresses, and breed successfully. However, many show varying degrees of failure, sometimes resulting in marked population decline. There is potential for EDCs to act at all levels of the response systems to environmental cues. Because animals live in diverse habitats, there is variation in susceptibility to disruption of response systems to environmental cues. Although this may be partly due to genetic differences at a level of receptors and/or metabolism, fundamental differences in how species perceive environmental cues and respond to them may also be major factors. Here we discuss how EDCs may interact with the perception and transduction of environmental cues that are important for all organisms in their natural world. This may introduce a new perspective on the effects of environmental endocrine disruptors.

Avian transgenerational reproductive toxicity test with in ovo exposure

Ecological risk assessment of environmental pollutants requires effective laboratory assays and extrapolation of the resultant data to wild species. Because avian reproductive disorder and accumulation of persistent compounds in wild birds and their eggs have long been observed in polluted regions, we have developed an assay for investigating whether pollutants accumulated in eggs impair the reproduction of the exposed birds and the survival of the next generation using the Japanese quail. A typical estrogenic compound, diethylstilbestrol (DES), dissolved in olive oil was injected into the air-chamber of fertilized eggs on day 10 of incubation. After sexual maturation of hatched chicks, we mated pairs of male and female quails following an observation period of egg production and collected their eggs. The collected eggs were incubated and checked for the fertility and hatchability, and then the hatchlings were raised and observed in growth for 3 weeks. A dosage of 5 ng/g per egg of DES caused eggshell thinning in eggs laid by exposed females and reduction in eggshell strength. DES also induced shortening of the left oviduct and unexpected development of the right oviduct, while testis weight was reduced symmetrically. The ability of quail pairs to produce offspring was significantly diminished by exposure of females to DES independently of exposure of males, which mainly arose from production of abnormal and inviable eggs. Fertility of normal-shelled eggs and hatchability of fertilized eggs were unchanged regardless of treatments. External morphological abnormalities, which were mostly unopened toes of the foot, were frequently observed in hatchlings from exposed males independently of exposure of females. Additionally, we attempted to extrapolate the experimental results to the northern bobwhite and to predict population trends for quails in a polluted habitat using a population projection model composed of a combination of a Leslie matrix and the logistic equation. In the event of accumulation of an estrogenic compound equivalent to a dosage of 5 ng/g DES in quail eggs, the average population size was predicted to decrease by 20.2% after 1 year, to approximately half after 4 years, and to a fifth after 14 years. When observed weakening of individuals and the risk of egg breakage are taken into consideration, the decline in population was further accelerated. The proposed assay appears to be suitable not only for assessing adverse effects of chemicals on avian reproduction but for population projection of affected wild birds.

In ovo exposure quail assay for risk assessment of endocrine disrupting chemicals

Although there are in vivo assays using various organisms for the risk assessment of chemicals with endocrine disrupting properties, effective experimental methods for avian species are still under debate. We have developed an in ovo exposure assay using Japanese quail eggs, aimed at assessing disrupting effects on avian reproductive development and function. Hybrid eggs from Brazilian Brown male and White Egg female quails, which can be genetically sexed by their plumage color after hatching, were prepared, and test materials dissolved in olive oil were injected into the air-chamber on day 10 of incubation. After sexual maturation of hatched chicks, we observed egg production by females and the egg quality and male-typical reproductive behavior, and then examined reproductive system morphology and serum steroid concentrations in both sexes. Treatment with a synthetic estrogen, diethylstilbestrol (DES, 0.5-50 ng/g egg), dose-dependently reduced the eggshell thickness and strength of eggs. A few females treated with 5 ng/g DES per egg produced soft-shelled/ unmarked eggs, and all laying females treated with 50 ng/g egg produced eggs completely lacking shells. DES also induced shortening of the left oviduct and abnormal development of the right oviduct in a dose-dependent manner, while testis weight was reduced symmetrically. In addition, 2,2',4',6'-tetrachlorobiphenyl-4-ol (10-1,000 ng/g egg), which previously showed relatively high estrogenic activity in vitro, caused dose-dependent shortening of the left oviduct and reduction in testis weight. The methods for evaluating endocrine disrupting effects and preparing experimental birds proposed in the present study are expected to facilitate assays for avian reproductive toxicology.

Association between maternal serum concentration of the DDT metabolite DDE and preterm and small-for-gestational-age babies at birth

BACKGROUND

DDT (1,1,1-trichloro-2,2-bis(p-chlorophenyl)ethane) is highly effective against most malaria-transmitting mosquitoes and is being widely used in malaria-endemic areas. The metabolite, DDE (1,1-dichloro-2,2-bis(p-chlorophenyl)ethylene), has been linked to preterm birth in small studies, but these findings are inconclusive. Our aim was to investigate the association between DDE exposure and preterm birth.

METHODS

Our study was based on the US Collaborative Perinatal Project (CPP). From this study we selected a subset of more than 44000 eligible children born between 1959 and 1966 and measured the DDE concentration in their mothers' serum samples stored during pregnancy. Complete data were available for 2380 children, of whom 361 were born preterm and 221 were small-for-gestational age.

FINDINGS

The median maternal DDE concentration was 25 mg/L (range 3-178)-several fold higher than current US concentrations. The adjusted odds ratios (OR) of preterm birth increased steadily with increasing concentrations of serum DDE (ORs=1, 1.5, 1.6, 2.5, 3.1; trend p<0.0001). Adjusted odds of small-for-gestational-age also increased, but less consistently (ORs=1, 1.9, 1.7, 1.6, 2.6; trend p=0.04). After excluding preterm births, the association of DDE with small-for-gestational-age remained.

INTERPRETATION

The findings strongly suggest that DDT use increases preterm births, which is a major contributor to infant mortality. If this association is causal, it should be included in any assessment of the costs and benefits of vector control with DDT.

DDE-induced eggshell thinning in birds: effects of p,p'-DDE on the calcium and prostaglandin metabolism of the eggshell gland

1. The focus of this review is the effects and mechanism of action of p,p'-DDE on eggshell formation in birds. Inhibition of prostaglandin synthesis in the eggshell gland mucosa is a probable mechanism for p,p'-DDE-induced eggshell thinning. 2. The duck is sensitive to p,p'-DDE-induced eggshell thinning but the domestic fowl is not, and studies comparing the two species in regard to the calcium and prostaglandin metabolism of the eggshell gland have shown that eggshell thinning induced by p,p'-DDE in ducks is accompanied by reduced activity of prostaglandin synthetase, reduced levels of prostaglandin E2, and reduced uptake of 45Ca by the eggshell gland mucosa. The content of calcium, bicarbonate, chloride, sodium, and potassium are also reduced in the eggshell gland lumen in ducks exhibiting eggshell thinning. None of these effects are seen in the domestic fowl. 3. Inhibition of prostaglandin synthesis is a specific effect of p,p'-DDE. The detrimental effects of p,p'-DDE on the eggshell gland seem to be unique when comparing the compound with structurally related substances, i.e., similar treatment regimens with o,p'-DDE, p,p'-DDT, o,p'-DDT, and p,p'-DDD do not cause eggshell thinning in ducks. Neither do they inhibit prostaglandin synthesis in the eggshell gland mucosa. 4. Administration of other compounds that do inhibit prostaglandin synthesis, e.g., indomethacin, does cause the same effects as those seen with p,p'-DDE, i.e., eggshell thinning and the described effects on the calcium and prostaglandin metabolism of the eggshell gland.

Characterisation of the effects of cadmium on the release of calcium and on the activity of some enzymes from neonatal mouse calvaria in culture

Exposure to cadmium (Cd) causes skeletal impairments, such as osteoporosis and osteomalacia, in many mammalian species, including humans. There is, however, some controversy about the mechanism of action of these Cd-induced skeletal effects, although both a direct influence on bone cells and effects that are secondary to renal damage caused by the metal have been demonstrated. In the present study, we cultured calvarial bones from neonatal mice and exposed them to Cd to study the effects of the metal on calcium release and on the activity of some enzymes of importance for bone resorption and bone formation. Cd dose-dependently stimulated calcium release from the bones. Maximal release was noted at Cd concentrations of 0.4-0.8 microM, which was similar to the level of release in the presence of maximal stimulatory concentrations of parathyroid hormone (10 nM) and prostaglandin E2 (10 microM). Cykloheximide (1 microM) inhibited calcium release elicited by Cd, prostaglandin E2 and parathyroid hormone. Cd-induced calcium release was linearly increased from 24 to 72 hr of culture. Production of prostaglandin E2 by the bone specimens was dose-dependently stimulated by Cd and inhibited by 1 microM indomethacin. Cd-induced calcium release was inhibited by acetazolamide (100 microM), indomethacin (1 microM) and ibuprofen (10 microM). Prostaglandin E2-stimulated calcium release was not inhibited by indomethacin. Exposure to 32 microM Cd, present during a 48-hr incubation period, significantly decreased prostaglandin E2-stimulated calcium release from 38.9% to 29.8%. Calcium release induced by parathyroid hormone was more sensitive to inhibition by the metal (i.e., Cd concentrations of 0.2 and 32 microM decreased the release from 37.7% to 31% and 19%, respectively). Cd present in the culture medium during a 48-hr incubation dose-dependently inhibited the activity of alkaline phosphatase and tartrate-resistant acid phosphatase in the bones but did not influence the activity of carbonic anhydrase. We conclude that Cd has a direct stimulatory effect on bone resorption, and this effect is dependent on prostaglandin production and also on protein synthesis. On the other hand, Cd also has an inhibitory effect on bone resorption (i.e., resorption is inhibited by higher concentrations of the metal). Moreover, Cd may impair bone formation by impeding the activity of alkaline phosphatase.

Effects of methyl mercury at different dose regimes on eggshell formation and some biochemical characteristics of the eggshell gland mucosa of the domestic fowl

Eggshell formation and egg production in domestic fowl were studied following the administration of methyl mercury (two dose regimes: 5 mg daily for 6 consecutive days and 1 mg daily for 50 consecutive days). A daily oral dose of 5 mg of methyl mercury for 6 consecutive days induced significant eggshell thinning and deformation and inhibited egg production. Uptake of 45Ca and synthesis of prostaglandins by a homogenate of eggshell gland mucosa from methyl-mercury-treated birds were significantly reduced, as was the calcium content of blood plasma. A daily oral dose of 1 mg of methyl mercury administered for 50 consecutive days also induced eggshell deformation and thinning and reduced egg production. This dose did not, however, have significant effects on the following: 45Ca uptake and prostaglandin synthesis by a homogenate of the eggshell gland mucosa; 45Ca uptake by a homogenate of duodenal mucosa; the Ca content of the blood plasma, shell gland mucosa or shell gland lumen; the HCO3- content of the shell gland lumen or the specific gravity of tibia. Methyl mercury added in vitro to a homogenate of eggshell gland mucosa significantly stimulated the synthesis of prostaglandins PGF2 alpha and PGE2. Addition of mercury chloride to the same type of preparation stimulated the synthesis of PGF2 alpha at the expense of thromboxane (TxB2) synthesis. Administration of 5 mg methyl mercury for 6 consecutive days seemed to reduce the availability of calcium for eggshell formation. This effect could have been due to a direct inhibitory effect of methyl mercury on calcium uptake from the gastrointestinal tract and/or to mobilization of medullary bone.(ABSTRACT TRUNCATED AT 250 WORDS)

Inhibition of eggshell formation in domestic fowl by indomethacin: Relation to calcium and prostaglandin metabolism in the eggshell gland mucosa

1. The involvement of prostaglandins in eggshell formation in the domestic fowl was investigated by considering the effects of the drug indomethacin on the calcium metabolism on the eggshell gland. Egglaying birds were given a single dose (100 mg) of indomethacin at the beginning of shell calcification. Fourteen hours later the birds were sacrificed and the effects of the drug were determined. There was a 21% reduction in the shell thickness of the egg present in the shell gland at the time of slaughter (P < 0.01). The calcium content of the eggshell gland mucosa was increased to 153% (P < 0.01) of the controls. In the treated birds, there was 43% more calcium (P < 0.05) present in the shell gland lumen (recovered by rinsing with Tris buffer) than in the gland lumen of control birds. Total calcium in blood plasma was decreased by 15% (P < 0.05). In homogenate and three subcellular fractions (MIII, FI and FIII) of eggshell gland mucosa, 45Ca uptake was significantly reduced (i.e. by 29%, 25%, 17% and 35%, respectively). A significant reduction (62-66%) was also observed in the synthesis of PGF2 alpha, PGE2 and TxB2 by eggshell gland mucosa homogenate. 2. The effects of indomethacin treatment on the calcium metabolism of the avian eggshell gland are discussed and compared with p,p-DDE-induced alterations in calcium metabolism and prostaglandin synthesis by the eggshell gland.