Room temperature two terminal tunnel magnetoresistance in a lateral graphene transistor

We investigate the behavior of both pure spin and spin-polarized currents measured with four-probe non-local and two probe local configurations up to room temperature and under an external gate voltage in a lateral graphene transistor, produced using a standard large-scale microfabrication process. The high spin diffusion length of pristine graphene in the channel, measured both directly and by the Hanle effect, and the tuning of the relationship between the electrode resistance areas present in the device architecture allowed us to observe local tunnel magnetoresistance at room temperature, a new finding for this type of device. The results also indicate that while pure spin currents are less sensitive to temperature variations, spin-polarized current switching by an external voltage is more efficient, due to a combination of the Rashba effect and a change in carrier mobility by a Fermi level shift.

Associations between birth size and later height from infancy through adulthood: An individual based pooled analysis of 28 twin cohorts participating in the CODATwins project

BACKGROUND

There is evidence that birth size is positively associated with height in later life, but it remains unclear whether this is explained by genetic factors or the intrauterine environment.

AIM

To analyze the associations of birth weight, length and ponderal index with height from infancy through adulthood within mono- and dizygotic twin pairs, which provides insights into the role of genetic and environmental individual-specific factors.

METHODS

This study is based on the data from 28 twin cohorts in 17 countries. The pooled data included 41,852 complete twin pairs (55% monozygotic and 45% same-sex dizygotic) with information on birth weight and a total of 112,409 paired height measurements at ages ranging from 1 to 69 years. Birth length was available for 19,881 complete twin pairs, with a total of 72,692 paired height measurements. The association between birth size and later height was analyzed at both the individual and within-pair level by linear regression analyses.

RESULTS

Within twin pairs, regression coefficients showed that a 1-kg increase in birth weight and a 1-cm increase in birth length were associated with 1.14-4.25 cm and 0.18-0.90 cm taller height, respectively. The magnitude of the associations was generally greater within dizygotic than within monozygotic twin pairs, and this difference between zygosities was more pronounced for birth length.

CONCLUSION

Both genetic and individual-specific environmental factors play a role in the association between birth size and later height from infancy to adulthood, with a larger role for genetics in the association with birth length than with birth weight.

Ligand-induced conformational changes in prolyl oligopeptidase: a kinetic approach

Most kinetic studies of prolyl oligopeptidase (PREP) were performed with the porcine enzyme using modified peptide substrates. Yet recent biophysical studies used the human homolog. Therefore, the aim of this study was to compare the kinetic behavior of human and porcine PREP, as well as to find a suitable method to study enzyme kinetics with an unmodified biological substrate. It was found that human PREP behaves identically to the porcine homolog, displaying a double bell-shaped pH profile and a pH-dependent solvent kinetic isotope effect of the kcat/Km, features that set it apart from the related exopeptidase dipeptidyl peptidase IV (DPP IV). However, the empirical temperature coefficient Q10, describing the temperature dependency of the kinetic parameters and the non-linear Arrhenius plot of kcat/Km are common characteristics between PREP and DPP IV. The results also demonstrate the feasibility of microcalorimetry for measuring turn-over of proline containing peptides.

Leben mit chronischer spinaler Muskelatrophie

Eines der höchsten Ziele der individuellen menschlichen Entwicklung ist es, erwachsen zu werden, sein Leben selbstständig und eigenverantwortlich in die Hand zu nehmen und vielleicht sogar seinen Beitrag für die Gemeinschaft zu leisten. Dies kann aufgrund einer schweren Körperbehinderung, z. B. wenn wegen einer Muskelerkrankung nicht einmal die Gabel zum Essen gehalten werden kann, als praktisch schwierig und für nicht umsetzbar angesehen werden. Ins Erwachsenenalter zu kommen und auch Erwachsen zu sein, d. h. eigenverantwortlich und selbstbestimmt zu leben, ist aber durchaus möglich, auch wenn die rein körperliche Kraft dazu fehlt.

Wir berichten über unser Leben mit einer spinalen Muskelatrophie (SMA) vom Typ II, 3 Survival-motor-neuron-2(SMN2)-Genkopien, ein Leben voller Herausforderungen und Abhängigkeiten und doch ein ganz normales Leben.

Chiral effects in adrenocorticolytic action of o,p'-DDD (mitotane) in human adrenal cells

Adrenocortical carcinoma (ACC) is a rare malignant disease with poor prognosis. The main pharmacological choice, o,p'-DDD (mitotane), produces severe adverse effects. Since o,p'-DDD is a chiral molecule and stereoisomers frequently possess different pharmacokinetic and/or pharmacodynamic properties, we isolated the two o,p'-DDD enantiomers, (R)-(+)-o,p'-DDD and (S)-(-)-o,p'-DDD, and determined their absolute structures. The effects of each enantiomer on cell viability and on cortisol and dehydroepiandrosterone (DHEA) secretion in the human adrenocortical cell line H295R were assessed. We also assayed the o,p'-DDD racemate and the m,p'- and p,p'-isomers. The results show small but statistically significant differences in activity of the o,p'-DDD enantiomers for all parameters tested. The three DDD isomers were equally potent in decreasing cell viability, but p,p'-DDD affected hormone secretion slightly less than the o,p'- and m,p'-isomers. The small chiral differences in direct effects on target cells alone do not warrant single enantiomer administration, but might reach importance in conjunction with possible stereochemical effects on pharmacokinetic processes in vivo.

Interindividual differences in o,p'-DDD enantiomer kinetics examined in Göttingen minipigs

Five minipigs were given a single oral dose of a racemic mixture of o,p'-DDD (30 mg kg(-1)b.w., EF=0.49). Blood plasma and subcutaneous adipose tissue were collected for analysis, at different time-points over 180 d. At the end of the experiment also liver, kidney and brain tissue were collected. Low concentrations of o,p'-DDD still remained after 180 d in plasma (mean 0.5+/-0.3 ng g(-1)f.w.) and in adipose tissue (mean 40+/-40 ng g(-1)f.w.). The mean concentrations in liver and kidney were 500+/-300 pg g(-1)f.w. and 90+/-50 pg g(-1)f.w., respectively. The enantiomers of o,p'-DDD were isolated by HPLC and the absolute configuration of the enantiomers were determined by X-ray crystallography and polarimetry as R-(+)-o,p'-DDD and S-(-)-o,p'-DDD. The enantiomer fractions (EFs) of o,p'-DDD were determined in plasma, adipose tissue and kidney using GC/ECD equipped with a chiral column. The EFs of o,p'-DDD in the individual minipigs showed large variability, ranging from 0.2 to 0.6 after 24h in plasma and from 0.2 to 0.7 after 90 d in adipose tissue. Hence in two of the minipigs, the S-(-)-o,p'-DDD enantiomer was dominating while the other enantiomer, R-(+)-o,p'-DDD was dominating in three minipigs. We propose that a yet not identified factor related to polymorphism, regulating the metabolism and/or elimination of the enantiomeric o,p'-DDD, is responsible for the differences in enantiomeric retention of the compound in the minipigs.

Differential gene expression in the olfactory bulb following exposure to the olfactory toxicant 2,6-dichlorophenyl methylsulphone and its 2,5-dichlorinated isomer in mice

2,6-Dichlorophenyl methylsulphone and a number of structurally related chemicals are CYP-activated toxicants in the olfactory mucosa in mice and rats. This toxicity involves both the olfactory neuroepithelium and its subepithelial nerves. In addition, 2,6-dichlorophenyl methylsulphone induces glial acidic fibrillary protein expression (Gfap, a biomarker for gliosis) in the olfactory bulb, as well as long-lasting learning deficits and changes in spontaneous behavior in mice and rats. So far the 2,5-dichlorinated isomer has not been reported to cause toxicity in the olfactory system, although it gives rise to transient changes in spontaneous behavior. In the present study we used 15k cDNA gene arrays and real-time RT-PCR to determine 2,6-dichlorophenyl methylsulphone-induced effects on gene expression in the olfactory bulb in mice. Seven days following a single ip dose of 2,6-dichlorophenyl methylsulphone, 56 genes were found to be differentially expressed in the olfactory bulb. Forty-one of these genes clustered into specific processes regulating, for instance, cell differentiation, cell migration and apoptosis. The genes selected for real-time RT-PCR were chosen to cover the range of B-values in the cDNA array analysis. Altered expression of Gfap, mt-Rnr2, Ncor1 and Olfml3 was confirmed. The expression of these genes was measured also in mice dosed with 2,5-dichlorophenyl methylsulphone, and mt-Rnr2 and Olfml3 were found to be altered also by this isomer. Combined with previous data, the results support the possibility that the persistent neurotoxicity induced by 2,6-dichlorophenyl methylsulphone in mice represents both an indirect and a direct effect on the brain. The 2,5-dichlorinated isomer, negative with regard to CYP-catalyzed toxicity in the olfactory mucosa, may prove useful to resolve this issue.

Defective Reproductive Organ Morphology and Function in Domestic Rooster Embryonically Exposed to o,p′-DDT or Ethynylestradiol1

Environmental pollutants with estrogenic activity have a potential to disrupt estrogen-dependent developmental processes. The objective of this study was to investigate if embryonic exposure to the environmental estrogens o,p'-DDT (1-(2-chlorophenyl)-1-(4-chlorophenyl)-2,2,2-trichloroethane; 37, 75, 150 or 300 microg/g egg) and EE2 (17alpha-ethynyl estradiol; 60 ng/g egg) affects the reproductive system in domestic roosters. Following egg injection on Embryonic Day 4, the newly hatched chicks were sexed by cloacal inspection. A skewed phenotypic sex ratio with overrepresentation of chicks deemed as females was observed in the groups exposed to the three highest doses of o,p'-DDT but not in the EE2-exposed group. Normal sex ratios were observed in all groups at adulthood. However, a cloacal deformation seemed to remain in the adult roosters, causing an abnormal semen flow upon semen collection. Semen yield was significantly reduced in both o,p'-DDT-exposed and EE2- exposed birds, whereas semen quality was unaffected. When killed, deformations of the left testis were found in all treatment groups. Image analysis revealed a reduced seminiferous tubular area in the roosters exposed to the two highest doses of o,p'-DDT. Embryonic exposure to o,p'-DDT caused decreased comb weight and right-spur diameter, while EE2 only affected right-spur diameter. In conclusion, this study shows that embryonic exposure to estrogenic compounds can induce permanent effects in male birds. The effects of the two studied compounds were partly similar but o,p'-DDT also induced alterations not seen in the EE2-treated birds.

Embryonic exposure to oestrogen causes eggshell thinning and altered shell gland carbonic anhydrase expression in the domestic hen

Eggshell thinning among wild birds has been an environmental concern for almost half a century. Although the mechanisms for contaminant-induced eggshell thinning are not fully understood, it is generally conceived to originate from exposure of the laying adult female. Here we show that eggshell thinning in the domestic hen is induced by embryonic exposure to the synthetic oestrogen ethynyloestradiol. Previously we reported that exposure of quail embryos to ethynyloestradiol caused histological changes and disrupted localization of carbonic anhydrase in the shell gland in the adult birds, implying a functional disturbance in the shell gland. The objective of this study was to examine whether in ovo exposure to ethynyloestradiol can affect eggshell formation and quality in the domestic hen. When examined at 32 weeks of age, hens exposed to ethynyloestradiol in ovo (20 ng/g egg) produced eggs with thinner eggshells and reduced strength (measured as resistance to deformation) compared with the controls. These changes remained 14 weeks later, confirming a persistent lesion. Ethynyloestradiol also caused a decrease in the number of shell gland capillaries and in the frequency of shell gland capillaries with carbonic anhydrase activity. These data suggested that a disrupted carbonic anhydrase expression was involved in the mechanism for the oestrogen-induced eggshell thinning found in this study. The results support our hypothesis that eggshell thinning in avian wildlife can result from a structural and functional malformation in the shell gland, induced by xeno-oestrogen exposure during embryonic development.

Distribution of bisphenol A and tetrabromobisphenol A in quail eggs, embryos and laying birds and studies on reproduction variables in adults following in ovo exposure

In a previous study, we showed that bisphenol A (BPA) had oestrogen-like effects in bird embryos, causing malformations of the oviducts in Japanese quail (Coturnix japonica) and feminisation of the left testis in chicken (Gallus domesticus). In this study, uptake and distribution of BPA and tetrabromobisphenol A (TBBPA) in embryos and laying quail were examined as well as variables related to reproduction in adult quail following administration of the compounds into the yolk of embryonated eggs. The uptake of radiolabelled BPA, TBBPA and the reference compound diethylstilboestrol (DES) was studied in the embryos using beta-spectrometry. Autoradiography was employed to examine distribution in egg and embryo after yolk sac injection of BPA or TBBPA and in laying birds, following intravenous and oral administration. Following embryonic exposure to BPA or TBBPA, sexually mature male birds were examined for reproductive behaviour and testis morphology, and females were examined for egg laying and oviduct morphology. Neither BPA (200 microg/g egg) nor TBBPA (15 microg/g egg) caused any significant oestrogen-like effects on the variables studied, although effects on the female oviducts after BPA exposure were indicated. Embryonic exposure to DES is known to cause profound effects on male sexual behaviour and female oviduct morphology at doses 3-5 orders of magnitude lower than the BPA and TBBPA doses used in the present study. The proportions of BPA and TBBPA taken up by the embryos after yolk sac injection were similar to the proportion of DES taken up. Differences in bioavailability, therefore do not account for any major part of the potency differences between DES and the two bisphenol A compounds. The concentration of radioactivity in the embryo, as revealed by autoradiography, was low compared with that in the yolk at all stages studied (days 6, 10 and 15). Pronounced labelling of the bile and the allantoic fluid was observed, however, indicating that both compounds were readily metabolised and excreted. Radiolabelled BPA and TBBPA administered to laying quail were largely excreted via the bile and 9 days after oral dosing, only small amounts of the labelled compound remained within the body. Maternal transfer of labelled BPA and TBBPA to the egg was low.

Disrupted carbonic anhydrase distribution in the avian shell gland following in ovo exposure to estrogen

Eggshell thinning among wild birds has been an environmental concern for almost half a century and the underlying mechanisms are still not fully understood. Previously we showed that exposure of quail embryos to ethynylestradiol (EE2) caused disorganization of the tubular glands in the shell gland of adult birds. In this study, we have examined the effect of in ovo exposure to EE2 on carbonic anhydrase (CA) localization, especially in the shell gland, because CA is required for shell formation. In the control birds, CA was localized in the cell membranes of the tubular gland cells of the shell gland, whereas the surface epithelium was always devoid of CA. In ovo treatment with 20ng EE2/g egg resulted in a loss of CA activity in the tubular glands while the surface epithelium showed strong induction of both membrane bound and cytoplasmic CA activity in 49+/-1% of the cells. The dose 2ng EE2/g egg resulted in partial loss of tubular gland CA and strong induction of CA activity in 2.5+/-0.5% of the surface epithelial cells and weaker induction in 22+/-2% of the epithelial cells. In conclusion, this study shows that embryonic exposure to a xenoestrogen disrupts CA distribution in the adult shell gland. We propose that eggshell thinning in avian wildlife could reflect a functional malformation in the shell gland, already induced by xenoestrogen during embryonic development rather than being caused solely by exposure of the adult bird.

Irreversible binding and adrenocorticolytic activity of the DDT metabolite 3-methylsulfonyl-DDE examined in tissue-slice culture

The persistent adrenocorticolytic DDT metabolite 3-methylsulfonyl-DDE (MeSO(2)-DDE) was originally identified in Baltic grey seals, a population suffering from adrenocortical hyperplasia. In mice, MeSO(2)-DDE induces mitochondrial degeneration and cellular necrosis in the adrenal zona fasciculata. In this study, we used precision-cut tissue slice culture to examine local CYP11B1-catalyzed irreversible binding of MeSO(2)-DDE in the murine adrenal cortex. We also examined effects on steroid hormone secretion, histology, and ultrastructure. As determined by microautoradiography, selective binding occurred in zona fasciculata of slices exposed to MeSO(2)-[(14)C]-DDE. Quantification of binding by phosphorautoradiography revealed a 3-fold reduction of binding in slices co-exposed to the CYP11B1 inhibitor metyrapone. As measured by HPLC, corticosterone and 11-deoxycorticosterone secretion to the medium increased linearly for at least 24 hr. Addition of the ACTH analog tetracosactide caused an 8-fold increase in corticosterone secretion. Addition of metyrapone reduced corticosterone secretion 4-fold. Exposure of slices to MeSO(2)-DDE (50 microM) reduced the rate of corticosterone secretion by 90% after 24 hr of incubation. As determined by electron microscopy, vacuolated mitochondria were present in zona fasciculata of slices exposed to MeSO(2)-DDE (50 microM) for 24 hr. Our findings show that all effects of MeSO(2)-DDE previously reported in vivo could be reproduced in adrenal slice culture ex vivo. This test system allows analysis of zone-specific irreversible binding and effects on steroid hormone secretion and target cell ultrastructure. We propose adrenal slice culture as a simple ex vivo test system with which to examine the adrenocorticolytic activity of xenobiotics in human and wild animal tissue.

Anatomical and histological changes in the oviducts of Japanese quail, Coturnix japonica, after embryonic exposure to ethynyloestradiol

Oestrogen is needed for normal oviductal development in female birds, but excessive early exposure to oestrogen can cause oviductal abnormalities and impair egg-laying ability. In this study, the anatomical and histological effects of in ovo exposure to the synthetic oestrogen ethynyloestradiol on the oviducts of immature and adult female Japanese quail, Coturnix japonica, were investigated. A series of abnormalities was observed after injection of ethynyloestradiol (2 or 20 ng g(-1) egg) into the yolk on day 3 of incubation. Ethynyloestradiol induced precocious differentiation of the luminal epithelium and tubular glands in immature chicks. Right-side oviduct retention occurred at all the ages studied, whereas certain other effects were not evident until sexual maturity. The left oviduct was reduced in size and tubular gland density in the uterus (shell gland) was reduced in sexually mature birds that had been treated with ethynyloestradiol. The utero-vaginal junction was longer than in control birds and had a higher tubular gland density. The epithelial cells in the magnum were taller in birds treated with ethynyloestradiol. Embryonic exposure to the environmental contaminant ethynyloestradiol may cause persisting structural malformations in oviducts of quails, which can impair fertility. As oviductal malformations are indicative of embryonic exposure to exogenous oestrogen, they are potentially useful as biomarkers of xenooestrogen exposure in wild bird populations.

Cytochrome P450-dependent binding of 7,12-dimethylbenz[a]anthracene (DMBA) and benzo[a]pyrene (B[a]P) in murine heart, lung, and liver endothelial cells

Autoradiography was used to investigate the cellular sites of irreversible binding of 3H-labelled 7,12-dimethylbenz[a]anthracene (DMBA) and benzo[a]pyrene (B[a]P) in mice. Autoradiograms obtained from solvent-extracted tape-sections revealed an even distribution of DMBA- and B[a]P-derived radioactivity in control mice lacking sites of selective binding in the tissues. In mice pretreated with a cytochrome P4501A (CYP1A) inducer, beta-naphthoflavone (BNF) or 3,3',4,4', 5-pentachlorobiphenyl (PCB 126), a noticeable accumulation of bound radioactivity was observed in the pulmonary alveolar region. Increased labelling was also observed in heart tissue of induced mice. As demonstrated by microautoradiography of tissues from CYP1A-induced mice treated with 3H-DMBA or 3H-B[a]P in vivo, irreversible binding in lung tissue was present in endothelial cells of arteries and veins, in the alveolar septal walls, and in type 2 pneumocytes. In heart tissue, binding was confined to endothelial cells of arteries, capillaries and veins. In liver, binding was found in the hepatocytes as well as in endothelial cells of the portal veins, whereas no binding was seen in endothelial cells of the sinusoids, central veins, or arteries. These findings were confirmed in vitro using 3H-DMBA-exposed precision-cut slices, indicating that reactive intermediates of DMBA and B(a)P were formed in situ. The addition of the CYP1A inhibitor ellipticine abolished binding in the target endothelial cells. Increased endothelial binding in the lungs and liver of CYP1A-induced mice was concomitant with increased 7-ethoxyresorufin O-deethylase (EROD) and DMBA hydroxylase activity. In heart, endothelial binding was positively correlated with EROD, but not with DMBA hydroxylase. The results suggest that endothelial cells may be targets for CYP-dependent activation of such toxicants as polycyclic aromatic hydrocarbons. Consequently, the possibility that chemically induced endothelial dysfunction is a risk factor in the aetiology of cardiovascular disease demands consideration.

Target cells for methylsulphonyl-2,6-dichlorobenzene in the olfactory mucosa in mice

Previously we reported that methylsulphonyl-2,6-dichlorobenzene, 2, 6-(diCl-MeSO(2)-B), was irreversibly bound to the olfactory mucosa of mice and induced necrosis of the Bowman's glands with subsequent neuroepithelial degeneration and detachment. In this study, autoradiography and histopathology were used to determine tissue-localization and toxicity of 2,6-(diCl-MeSO(2)-B) in the olfactory mucosa of control mice and animals pretreated with cytochrome P450 (CYP) and glutathione (GSH) modulators. The Bowman's glands of the olfactory mucosa were the major target sites of non-extractable binding of 2,6-(diCl-(14)C-MeSO(2)-B), whereas the olfactory neuroepithelium and nerve bundles showed only background levels of silver grains. Metyrapone pretreatment slightly decreased binding in the Bowman's glands and markedly decreased toxicity in the olfactory mucosa after 2,6-(diCl-MeSO(2)-B) administration. These results support that a CYP-mediated activation of 2, 6-(diCl-MeSO(2)-B) takes place in the Bowman's glands giving rise to toxic reactive intermediates. In mice pretreated with the GSH-depleting agent phorone, a marked increase of irreversible binding of 2,6-(diCl-(14)C-MeSO(2)-B) in the Bowman's glands was observed. Tape-section autoradiograms also revealed a significant increase of uptake of radioactivity in the olfactory bulb. As determined by histopathology, GSH-depletion increased both the extent and severity of the lesion in the mucosa. These results imply that 2,6-(diCl-MeSO(2)-B)-reactive intermediates are conjugated with GSH. The amount of irreversible binding and toxicity in the olfactory mucosa seems to be associated with the level of 2, 6-(diCl-MeSO(2)-B)-reactive intermediates.

Transient abnormal neurologic signs (TANS) in a longitudinal study of very low birth weight preterm infants

OBJECTIVE AND METHODS

In the Bonn Longitudinal Study (BLS), the course of neurologic development was analysed with regard to transient abnormal neurologic signs (TANS). Abnormal neurologic signs (ANS) are defined when present in at least one developmental area at one examination. From birth to adulthood (mean 23 years) 108 preterm infants, 81% of very low birth weight (VLBW) were examined with regard to their psychological, neurologic and physical development: 62 appropriate for gestational age (AGA), 46 small for gestational age (SGA), 27 with postnatal catch-up growth of head circumference (group A) and 19 without catch-up (group B); 73 full terms served as controls. The dropout rate was 7.6%.

RESULTS

ANS showed a great inter- and intraindividual variability. Episodes of neurologic abnormalities changed with those of normality. ANS reappeared when new abilities developed. ANS were observed mainly during the first year. The incidence was higher in preterms (AGA 49%, SGA A 63%, SGA B 61%) than in full terms (15%). Transient ANS (TANS) were diagnosed in 42% of AGA, 63% of SGA A, 33% of SGA B preterms and 12% of full terms. The recovery rate, i.e., the TANS to ANS percentage, was higher in AGA (86%), SGA A (100%) and full terms (82%) than in SGA B (55%) preterms.

CONCLUSION

It is impossible to predict early on whether ANS will be transient, i.e. TANS. Longitudinal analyses are needed. The outcome depends on recovery from or persistence in ANS.

Persistent olfactory mucosal metaplasia and increased olfactory bulb glial fibrillary acidic protein levels following a single dose of methylsulfonyl-dichlorobenzene in mice: comparison of the 2,5- and 2, 6-dichlorinated isomers

Histopathology was used to characterize long-term toxic effects in the olfactory system following a single ip dose (4-65 mg/kg) of methylsulfonyl-2,6-dichlorobenzene, (2,6-(diCl-MeSO(2)-B)), in female NMRI mice. The effects of 2,6-(diCl-MeSO(2)-B) and its 2, 5-chlorinated isomer, (2,5-(diCl-MeSO(2)-B)), on the levels of glial fibrillary acidic protein (GFAP; a biomarker for neurotoxicity) in different brain regions were examined by an enzyme-linked immunosorbent assay (ELISA). The histopathologic effects of 2, 6-(diCl-MeSO(2)-B) were dose-, time-, and tissue-dependent. At the highest doses (16-65 mg/kg), the initial effect of 2, 6-(diCl-MeSO(2)-B) was necrosis of the Bowman's glands, followed by a sequence of secondary events including degeneration of the olfactory neuroepithelium, repopulation of the basement membrane by a ciliated respiratorylike epithelium, fibrosis and ossification in the lamina propria, formation of bilateral polyps, angiogenesis, and disappearance of nerve bundles. Remodeling was most pronounced in the dorsal meatus of the olfactory mucosa and persisted for the duration of the experiment (46 weeks). A dose-dependent induction of GFAP in the olfactory bulb of mice treated with 2,6-(diCl-MeSO(2)-B) was observed at all doses examined (16-65 mg/kg). GFAP levels were highest 2 weeks after treatment (eightfold induction at 65 mg/kg) and then gradually decreased to normal within 26 weeks. The 2, 5-substituted isomer (65 mg/kg) did not induce GFAP in the olfactory bulb and or toxicity in the olfactory mucosa. In conclusion, a single dose of 2,6-(diCl-MeSO(2)-B) results in persistent metaplasia and remodeling of the olfactory mucosa, and a long-lasting but transient induction of GFAP in the olfactory bulb. It is proposed that methylsulfonyl-2,6-dichlorobenzene may serve as an experimental tool with a unique ability to produce persistent primary and/or secondary lesions in the olfactory system of mice.

Health effects of endocrine-disrupting chemicals on wildlife, with special reference to the European situation

Many wildlife species may be exposed to biologically active concentrations of endocrine-disrupting chemicals. There is strong evidence obtained from laboratory studies showing the potential of several environmental chemicals to cause endocrine disruption at environmentally realistic exposure levels. In wildlife populations, associations have been reported between reproductive and developmental effects and endocrine-disrupting chemicals. In the aquatic environment, effects have been observed in mammals, birds, reptiles, fish, and mollusks from Europe, North America, and other areas. The observed abnormalities vary from subtle changes to permanent alterations, including disturbed sex differentiation with feminized or masculinized sex organs, changed sexual behavior, and altered immune function. For most reported effects in wildlife, however, the evidence for a causal link with endocrine disruption is weak or nonexisting. Crucial in establishing causal evidence for chemical-induced wildlife effects appeared semifield or laboratory studies using the wildlife species of concern. Impaired reproduction and development causally linked to endocrine-disrupting chemicals are well documented in a number of species and have resulted in local or regional population changes. These include: Masculinization (imposex) in female marine snails by tributyltin, a biocide used in antifouling paints, is probably the clearest case of endocrine disruption caused by an environmental chemical. The dogwhelk is particularly sensitive, and imposex has resulted in decline or extinction of local populations worldwide, including coastal areas all over Europe and the open North Sea. DDE-induced egg-shell thinning in birds has caused severe population declines in a number of raptor species in Europe and North America. Endocrine-disrupting chemicals have adversely affected a variety of fish species. In the vicinity of certain sources (e.g., effluents of water treatment plants) and in the most contaminated areas is this exposure causally linked with the effects on reproductive organs that could have implications for fish populations. However, there is also a more widespread occurrence of endocrine disruption in fish in the U.K., where estrogenic effects have been demonstrated in freshwater systems, in estuaries, and in coastal areas. In mammals, the best evidence comes from the-field studies on Baltic gray and ringed seals, and from the Dutch semifield studies on harbor seals, where both reproduction and immune functions have been impaired by PCBs in the food chain. Reproduction effects resulted in population declines, whereas impaired immune function has likely contributed to the mass mortalities due to morbillivirus infections. Distorted sex organ development and function in alligators has been related to a major pesticide spill into a lake in Florida, U.S.A. The observed estrogenic/antiandrogenic effects in this reptile have been causally linked in experimental studies with alligator eggs to the DDT complex. Although most observed effects currently reported concern heavily polluted areas, endocrine disruption is a potential global problem. This is exemplified by the widespread occurrence of imposex in marine snails and the recent findings of high levels of persistent potential endocrine-disrupting chemicals in several marine mammalian species inhabiting oceanic waters.

Basal and induced EROD activity in the chorioallantoic membrane during chicken embryo development

The chorioallantoic membrane (CAM) is a highly vascularized tissue that takes part in the respiratory exchange of gases through the eggshell. Although the CAM may be exposed to environmental contaminants, its response to pollutants has not been studied. We examined the cytochrome P4501A (CYP1A)-catalyzed deethylation of 7-ethoxyresorufin (EROD) in the CAM during chicken embryo development. EROD was constitutively present and was inducible by the aryl hydrocarbon (Ah) receptor agonist 3,3',4,4',5-pentachlorobiphenyl (PCB 126). Our results suggest the CAM as a first line of defence of the avian embryo against toxic compounds, but also as a target for CYP1A-activated chemicals.

Sexual behavior in Japanese quail as a test end point for endocrine disruption: effects of in ovo exposure to ethinylestradiol and diethylstilbestrol

Chemicals having a capacity to disturb the endocrine system have attracted considerable interest during recent years. There is a shortage of well-characterized in vivo tests with which to study such disturbances in different classes of vertebrates. In the present study, test end points related to reproduction in the Japanese quail were used to examine the estrogenic activity of chemicals. The synthetic estrogens ethinylestradiol (EE(2)) and diethylstilbestrol (DES), used as model compounds, were injected into the yolk of embryonated eggs. After the birds had been raised to sexual maturity, we examined sexual behavior, plasma testosterone concentrations, and testis morphology in adult males. The lowest doses resulting in a significantly depressed male sexual behavior were 6 ng/g egg for EE(2) and 19 ng/g egg for DES. Testis weight asymmetry was increased at 6 ng EE(2)/g egg, but DES had no effect at any treatment level. The area of the androgen-dependent cloacal gland was significantly reduced at 57 ng DES/g egg. No effects on plasma testosterone concentration or body weight following exposure to EE(2) or DES were observed at any dose level. Depressed male sexual behavior was the most sensitive of the end points studied, and we suggest that this ecologically relevant end point be included in avian in vivo testing for neuroendocrine disruptors.

The avian egg as a test system for endocrine disrupters: effects of diethylstilbestrol and ethynylestradiol on sex organ development

Many environmental contaminants are known or suspected to interfere with hormonal function in animals. In vivo test methods to detect and characterize chemicals that disrupt the endocrine system are therefore urgently needed. In this study, we assessed the usefulness of abnormalities of the reproductive organs as test endpoints for estrogenic activity of xenobiotics in Japanese quail embryos. Two synthetic estrogens, diethylstilbestrol (DES) and ethynylestradiol (EE2), were injected into the yolks of embryonated eggs. At a dose as low as 2 ng EE2/g egg, all male embryos became feminized, containing ovary-like tissue in the left testis. The extent of feminization of the testes was determined by measuring the relative area of the ovary-like component. Persistent Müllerian ducts (oviducts) in male embryos, and malformations of the Müllerian ducts in females occurred at 2 ng EE2/g egg and higher doses. DES was approximately one-third to one-tenth as potent as EE2. The morphological changes studied were dose-dependent, indicating that they are useful as test endpoints for estrogenic activity. Feminization of the left testis in males proved to be the most sensitive endpoint. We propose the quail egg as a simple in vivo test system for estrogenic compounds.

Localization and comparative toxicity of methylsulfonyl-2,5- and 2,6-dichlorobenzene in the olfactory mucosa of mice

Several methylsulfonyl (MeSO2) metabolites formed from chlorinated aromatic hydrocarbons have been identified in human milk, lung, and body fat, as well as in the tissues of Baltic grey seals and arctic polar bears. The tissue localization and nasal toxicity of two methylsulfonyl-substituted dichlorobenzenes (diCl-MeSO2-B), with the chlorine atoms in the 2,5-, and 2,6- positions, were investigated in female NMRI and C57B1 mice. Using tape-section autoradiography, animals dosed i.v. with 14C-labeled 2,5-, or 2,6-(diCl-MeSO2-B) showed a preferential uptake of radioactivity in the olfactory mucosa and the tracheobronchial epithelium. Histopathology showed that 2,6-(diCl-MeSO2-B) is a potent toxicant that induces necrosis in the olfactory mucosa following a single dose as low as 4 mg/kg (i.p. injection), whereas 2,5-(diCl-MeSO2-B) induced no signs of toxicity in the olfactory mucosa at doses as high as 130 mg/kg (i.p. injection). Necrosis of the Bowman's glands was the first sign of 2,6-(diCl-MeSO2-B)-induced toxicity followed by degeneration of the neuroepithelium, which implies that the Bowman's gland may be the primary site of toxicity and degeneration of the neuroepithelium may be a secondary effect. Administration of the parent compounds, 1,3-dichlorobenzene and 1,4-dichlorobenzene, or the chlorinated analog 1,2,3-trichlorobenzene (85, 85, and 105 mg/kg, respectively; i.p. injection), induced no signs of toxicity in the olfactory mucosa. These and previous results suggest that 2,6-positioned chlorine atoms and an electron withdrawing substituent in the primary position is an arrangement that predisposes for toxicity in the olfactory mucosa.

Methods for studying xenoestrogenic effects in birds

The embryonated bird egg provides a simple whole organism test system that allows examination of xenoestrogenic effects at different levels of biological organisation. Test compounds are injected into the yolk, the albumen or the air chamber at defined stages of embryonic development. Bioavailability and embryonic exposure may be determined by autoradiography and image analysis. Females represent the heterogametic sex (ZW) and estrogens determine differentiation into the female phenotype in birds. Xenoestrogenic effects can be examined by markers of gene expression and anatomical or histological characterization of the gonads and tubular sex organs. Chicks may be raised to sexual maturity and examination of sexual behaviour and reproductive physiology performed. The Japanese quail is a suitable test organism due to its small size and early sexual maturation.

Controlling persistent organic pollutants-what next?

Within the context of current international initiatives on the control of persistent organic pollutants (POPs), an overview is given of the scientific knowledge relating to POP sources, emissions, transport, fate and effects. At the regional scale, improvements in mass balance models for well-characterised POPs are resulting in an ability to estimate their environmental concentrations with sufficient accuracy to be of help for some regulatory purposes. The relevance of the parameters used to define POPs within these international initiatives is considered with an emphasis on mechanisms for adding new substances to the initial lists. A tiered approach is proposed for screening the large number of untested chemical substances according to their long-range transport potential, persistence and bioaccumulative potential prior to more detailed risk assessments. The importance of testing candidate POPs for chronic toxicity (i.e. for immunotoxicity, endocrine disruption and carcinogenicity) is emphasised as is a need for the further development of relevant SAR (structure activity relationship) models and in vitro and in vivo tests for these effects. Where there is a high level of uncertainty at the risk assessment stage, decision-makers may have to rely on expert judgement and weight-of-evidence, taking into account the precautionary principle and the views of relevant stake-holders. Close co-operation between the various international initiatives on POPs will be required to ensure that assessment criteria and procedures are as compatible as possible.

Induction of ethoxyresorufin O-deethylase (EROD) and endothelial activation of the heterocyclic amine Trp-P-1 in bird embryo hearts

The xenobiotic-metabolizing activity of avian heart was investigated in chicken and Eider duck embryos exposed to aryl hydrocarbon (Ah) receptor agonists in ovo. Both beta-naphthoflavone (BNF) and 3,3',4,4',5-pentachlorobiphenyl (PCB 126) induced 7-ethoxyresorufin O-deethylase (EROD) activities in chicken embryo hearts whereas Eider duck embryos only responded to BNF. The differential responses of chicken and Eider duck embryos were used to examine the involvement of Ah receptor-mediated enzyme induction in the activation of the environmental and food mutagen 3-amino- 1,4-dimethyl-5H-pyrido[4,3-b]indole (Trp-P-1). As determined by light microscopic autoradiography, there was a highly selective binding of non-extractable 3H-Trp-P-1-derived radioactivity in endothelial cells of large vessels and capillaries in hearts of BNF- and PCB 126-treated chicken embryos. No binding occurred at these sites in vehicle-treated controls. There was also a strong endothelial binding of 3H-Trp-P-1 in hearts of BNF-treated Eider duck embryos whereas no binding occurred in hearts of PCB 126-treated Eider duck embryos. A positive correlation between induction of EROD activity and covalent binding of 3H-Trp-P-1 to protein in heart homogenates from BNF- and PCB 126-treated chicken and Eider duck embryos was also observed. The results suggest a cytochrome P450 1A (CYP1A)-mediated activation of Trp-P-1 in avian heart endothelial cells although involvement of other Ah receptor-regulated enzymes is also possible. We propose that heart endothelial cells may be targets for bioactivation and toxicity of environmental contaminants in birds exposed to Ah receptor agonists.

Transplacental toxicity of 3-methylsulphonyl-DDE in the developing adrenal cortex in mice

The transplacental transfer, irreversible binding, and ultrastructural lesions in the fetal adrenal cortex were studied following single injections of the persistent DDT-metabolite 3-methylsulphonyl-DDE (MeSO2-DDE) in pregnant C57B1 mice. Tape-section autoradiograms of fetuses on gestation days 12 to 17 revealed a high and tissue-specific accumulation of MeSO2-DDE-14C-derived radioactivity in the fetal adrenal gland. On gestation day 12 the adrenal radioactivity could be extracted with organic solvents, whereas on days 13 to 17 the radioactivity in the adrenal was irreversibly bound and could not be extracted from the tissue. As determined by computer-assisted image analysis of autoradiograms, the uptake of radioactivity in the fetal adrenals increased continuously with gestational age. Electron microscopy revealed mitochondrial degeneration and vacuolation in fetal adrenal cortex cells following injection of MeSO2-DDE (25 mg/kg b.w.) to the pregnant dam. The lesions were clearly visible on days 14 to 15 but most pronounced on days 16 to 17. Administration of the cytochrome P450(11 beta) inhibitor metyrapone to pregnant dams (gestation day 17) reduced the mitochondrial toxicity induced by MeSO2-DDE in the fetal adrenal cortex. In conclusion, the adrenocorticolytic DDT metabolite MeSO2-DDE is transformed to a reactive, cytotoxic metabolite in the fetal adrenal cortex from its earliest stage of development. Hence, the activating cytochrome P450 form, previously proposed to be P450(11 beta), seems to be expressed during gestation days 12 to 13 in the adrenal cortex in the mouse fetus.

Metabolic activation of the food mutagen 3-amino-1,4-dimethyl-5H-pyrido-[4,3-b]indole (Trp-P-1) in endothelial cells of cytochrome P-450-induced mice

3-Amino-1,4-dimethyl-5H-pyrido[4,3-b]indole (Trp-P-1) is a carcinogen which is metabolically activated by cytochrome P4501A. This microautoradiographic study showed that there was a highly selective solvent-resistant binding of radioactive substance in endothelial cells of the pulmonary and hepatic portal vascular system and of the vena cava and type 2 pneumocytes 1 day following i.p. or i.v. injection of [3H]Trp-P-1 (100 micrograms/kg) in NMRI mice treated with the cytochrome P4501A-inducing agent beta-naphthoflavone (BNF). In mice treated with indole-3-carbinol, a dietary cytochrome P4501A-inducing factor, a similar binding was observed in the liver but not in the lung. No binding in endothelial cells occurred in vehicle-treated control mice given injections of [3H]Trp-P-1. At incubation of tissues with [3H]Trp-P-1 (0.75 microM) there was also a selective binding of radioactive substance in endothelial cells of the lung and liver and in the vena cava from BNF-treated mice but not from vehicle-treated control mice. Ellipticine but not alpha-naphthoflavone inhibited the endothelial binding in BNF-treated mice exposed to [3H]Trp-P-1 in vivo or in vitro. No binding of radioactive substance occurred in hepatic central veins or in the aorta of BNF-treated mice exposed to [3H]Trp-P-1 in vivo or in vitro. Our data suggest an in situ metabolism of [3H]Trp-P-1 to a reactive species, catalyzed by an BNF-inducible P450 form, possibly 1A1, in endothelial cells. The results of this study and reported heterocyclic amine-induced tumors in the rodent vascular system suggest that endothelial cells are targets for food-derived mutagens.

Secondary combined resistance to the multidrug-resistance-reversing activity of cyclosporin A in the cell line F4-6RADR-CsA

Multidrug-resistant tumor cells can be resensitized by combined application of the selecting cytostatic drug and a chemosensitizer, such as cyclosporin A (CsA) or a calcium channel blocker. Since clinical trials on the circumvention of multidrug resistance (MDR) with chemosensitizers report disparate results, we investigated whether tumor cells of the MDR phenotype can develop additional resistance to the cytostatic chemosensitizer combination. Thus, the Adriamycin(ADR)-selected, P-glycoprotein-positive MDR Friend leukemia cell line F4-6RADR was exposed to stepwise increased concentrations of CsA at a constant level of 0.05 microgram/ml ADR. The initial CsA concentration (plus 0.05 microgram/ml ADR) to inhibit cell growth of F4-6RADR cells by 50% (IC50) was 0.04 microgram/ml. By continuous incubation for more than 6 months, the IC50 for CsA (at constant ADR) was elevated to 3.6 micrograms/ml (90-fold), thus generating the variant F4-6RADR-CsA. The F4-6RADR-CsA cells were cross-resistant for cyclosporin H (CsH), a non-immunosuppressive derivative of CsA. As shown by immunocytochemistry as well as by the polymerase chain reaction and by Western blotting including densitometry, P-glycoprotein was preserved in the F4-6RADR-CsA variant and was expressed at a 4-fold higher level than in F4-6RADR cells. Sodium dodecyl sulfate/polyacrylamide gel electrophoresis analysis could detect no new proteins in F4-6RADR-CsA as compared to F4-6RADR. Interestingly, resistance of F4-6RADR-CsA cells remained reversible for the calcium antagonists verapamil and dihydropyridine B859-35 (dexniguldipine-HCl), indicating that CsA and these compounds interfere with the P glycoprotein function by different pharmacodynamic mechanisms. Transport studies with [14C]ADR, performed in the presence and absence of chemosensitizers, confirmed the good correlation of P-glycoprotein function with the pattern of resistance found in proliferation assays. Cellular accumulation of [3H]cyclosporin was reduced to 71% of that of the F4-6 controls in F4-6RADR-CsA cells, but remained at the level of controls in F4-6RADR cells. Results indicate that increased amounts of the P-glycoprotein--besides other, perhaps more important mechanisms that are as yet unknown--partially mediate CsA resistance in F4-6RADR-CsA cells. We have designated this new form of resistance "secondary combined resistance" (SCR). The results suggest that at least some clinical cases of insensitivity to chemosensitizers or of relapse after reversing therapy could be explained by SCR, and that resensitizing treatment of tumor patients should be based on the consideration of several chemosensitizers of different pharmacodynamics.

Liver accumulation of 2,3,7,8-tetrachloro-[3H]dibenzofuran in mice: modulation by treatments with polychlorinated biphenyls

The distribution of 2,3,7,8-tetrachloro-[3H]dibenzofuran ([3H]TCDF; 40 micrograms/kg) resembled that earlier reported for 2,3,7,8-tetrachlorodibenzo-p-dioxin, with a strong accumulation in the liver and a selective uptake in the nasal olfactory mucosa of adult and fetal mice. Pretreatments with a series of selected congeners of polychlorinated biphenyls (PCBs), i.e.. I (IUPAC)-77, I-105, I-118, I-126, I-153, I-156, I-169, and a commercial preparation, Aroclor 1254 (25-100 mg/kg body wt. i.p.), were found to modulate the hepatic uptake of [3H]TCDF (24 h post-3H-injection). At a short pretreatment time (4 h), non-ortho-chlorinated congeners decreased the uptake of [3H]TCDF equivalents in the liver (e.g., I-126 = 3,3',4,4',5-pentachlorobiphenyl: 34% of control), while several mono- and di-ortho PCB congeners and Aroclor 1254 increased the hepatic uptake of [3H]TCDF (e.g., I-156 = 2,3,3',4,4',5-hexachlorobiphenyl: 183% of control). At a longer pretreatment time (48 h), both a non-ortho (I-169 = 3,3',4,4',5,5'-hexachlorobiphenyl) and mono-ortho PCB congener(s) (e.g. I-156) markedly increased the hepatic 3H-uptake (190%), a probable effect of an induction of hepatic binding sites for TCDF. Ethoxyresorufin-O-deethylase activities, regarded to mirror the metabolic activity of cytochrome P-450 IA1 (CYP IA1), were strongly and time-dependently induced after I-169, but not after I-156, pretreatment (25 mg/kg). The initial liver concentrations of the two PCB congeners were similar and increased for I-169 but not for I-156 at later time points. In conclusion, the results show a selective uptake of [3H]TCDF in the mouse liver and nasal olfactory mucosa of both dam and fetus. The uptake of [3H]TCDF in the liver is influenced both by dose and pre-exposure with PCBs. The presence of a PCB-sensitive, but CYP IA1-independent, hepatic binding site for TCDF is suggested. Consequently, pharmacokinetic interactions with PCBs complicate the toxicity assessment of TCDF in complex mixtures.

Nephrotoxicity and covalent binding of 1,1-dichloroethylene in buthionine sulphoximine-treated mice

Autoradiography of mice injected i.p. with 14C-labelled 1,1-dichloroethylene (vinylidene chloride, VDC) in C57B1/6 mice revealed a selective covalent binding of radioactivity in the proximal tubules, in the midzonal parts of the liver lobules and in the mucosa of the upper and lower respiratory tract. Since VDC is a renal carcinogen in male mice the effects of compounds modulating biotransformation and glutathione (GSH) levels on the renal covalent binding were examined following a single i.p. dose of 14C-VDC. Most pretreatments did not influence the level of binding but treatment with buthionine sulphoximine (BSO), an irreversible inhibitor of gamma-glutamylcysteine synthetase and glutathione (GSH)-depleting agent, increased the renal covalent binding of VDC three-fold. Histopathological examination of kidneys in BSO-pretreated male mice given single i.p. injections of subtoxic doses of VDC (25 and 50 mg/kg) showed necrosis in the proximal tubules (S1 and S2 segments) 24 h following administration. In mice given VDC only, no significant lesions in the kidneys were observed. The severe renal toxicity of VDC in BSO-pretreated mice is suggested to be related to metabolic activation of VDC in the proximal tubules, resulting in further GSH depletion and covalent binding.

Adrenocorticolytic DDT-metabolites: studies in mink, Mustela vison and otter, Lutra lutra

: The irreversible binding and toxicity of the DDT metabolites p,p'-DDD and o,p-DDD in the adrenal cortex of female mink Mustela vison were studied. Histological examination of adrenals from mink given a single i.p. injection of p,p'-DDD or o,p'-DDD (125 mg per kg body weight) showed vacuolation, necrosis and focal bleedings in the zonae fasciculata and reticularis. Autoradiograms of solvent-extracted tissue sections of minks given a single i.v. injection of p,p'-[(14)C]DDD (0.7 mg per kg body weight) revealed a high level of irreversibly bound radio-activity in the adrenal cortex. Microautoradiography showed that the irreversibly bound radio-activity was confined to the zonae fasciculata and reticularis. Incubation of p,p'-[(14)C]DDD and o,p'-[(14)C]DDD with mink or otter, Lutra lutra, adrenal homogenate (300 x g supernatant) resulted in an irreversible binding of radioactivity to protein from both species. The irreversible protein binding of the DDD isomers in mink and otter was decreased by addition of the cytochrome P450 inhibitors metyrapone and carbon monoxide, indicating a cytochrome P450 dependent metabolic activation. In contrast, 3-methylsulfonyl-[(14)C]DDE, a potent adrenocortical toxicant in mice, does not appear to be metabolized to a reactive metabolite in the adrenal cortex of mink or otter. In conclusion, both p,p'-DDD and o,p'-DDD are toxic to the mink adrenal zona fasciculata and reticularis following activation in situ to reactive, tissue-binding metabolites. The results suggest that p,p'-DDD and o,p'-DDD are adrenocortical toxicants also in otter. The involvement of environmental pollutants in the generation of the adrenocortical hyperplasia observed among Baltic seals is discussed.

Enrichment of metabolites in the cerebrospinal fluid of cod (Gadus morhua) following oral administration of hexachlorobenzene and 2,4',5-trichlorobiphenyl

The disposition of 14C-labelled hexachlorobenzene (HCB) and 2,4',5-trichlorobiphenyl (triCB) was studied in cod (Gadus morhua) and rainbow trout (Oncorhynchus mykiss). For both compounds tape section autoradiography revealed substantial amounts of radiolabelled material in the central nervous system (CNS) of cod, whereas only traces of radioactivity were observed in the CNS of rainbow trout. Furthermore, an enrichment of radiolabelled compound in the cerebrospinal fluid (CSF) was observed in the cod, whereas no radioactivity could be detected in the CSF of rainbow trout. According to autoradiography, the CNS of cod dosed with HCB contained the parent compound, whereas the major part of radioactivity in CSF was due to HCB metabolites. Thin-layer chromatography of extracts from cod dosed with triCB showed the presence of parent compound in the CNS, whereas part of the radioactivity in the CSF was due to triCB metabolites. The activities of cytochrome P-450 and UDP-glucuronosyltransferase in the CNS of cod and rainbow trout were determined in microsomal and mitochondrial fractions. Both species expressed activities which were in the same order of magnitude as those reported for the corresponding fractions from rat brain. Incubation of triCB with cod brain mitochondria and microsomes resulted in the formation of two polar metabolites. It is suggested that cod may be more vulnerable than rainbow trout regarding neurotoxicological effects of HCB, triCB and related environmental pollutants.

Tissue-binding and toxicity of compounds structurally related to the herbicide dichlobenil in the mouse olfactory mucosa

The herbicides dichlobenil (2,6-dichlorobenzonitrile), chlorthiamid (2,6-dichlorothiobenzamide) and their environmental degradation product 2,6-dichlorobenzamide are irreversibly bound and toxic to the olfactory mucosa following single injections in mice (Brandt et al., Toxicology and Applied Pharmacology 1990, 103, 491-501; Brittebo et al., Fundamental and Applied Toxicology 1991, 17, 92-102). In the present study, autoradiography showed an irreversible binding of radioactivity in the olfactory mucosa (preferentially in the Bowman's glands) in C57Bl/6 mice treated with the 14C-labelled analogues [14C]2,6-difluorobenzonitrile ([14C]DFBN) and [14C]2,6-difluorobenzamide ([14C]DFBA). Therefore the toxicity of DFBN, DFBA and of some structurally related compounds including benzonitrile (BN) and the herbicides bromoxynil (3,5-dibromo-4-hydroxybenzonitrile) and ioxynil (3,5-diiodo-4-hydroxybenzonitrile) in the mouse olfactory mucosa was examined. No histopathological changes in the olfactory mucosa or in the liver were observed following a single ip dose of any of these compounds [0.145 mmol/kg (all compounds); 0.58 mmol/kg (DFBN, DFBA and BN)]. Also in mice treated with the glutathione-depleting agent phorone, none of these compounds induced any histopathological changes in the olfactory mucosa. The covalent binding of [14C]DFBN in the olfactory mucosa was 16 times lower than an equimolar toxic dose of [14C]dichlobenil, suggesting a low rate of metabolic activation of DFBN in the olfactory mucosa or a low reactivity of the DFBN metabolites formed. The results of this study thus show that single doses of DFBN, DFBA, BN, IX and BX, compounds structurally related to the potent olfactory toxicant dichlobenil, do not elicit acute toxicity in the olfactory mucosa of mice.

Effects of glutathione-modulating agents on the covalent binding and toxicity of dichlobenil in the mouse olfactory mucosa

Twenty-four hours following injection of a single dose of the herbicide dichlobenil (2,6-dichlorobenzonitrile) in C57Bl/6 mice a steep dose-response curve for the histopathological toxicity in the olfactory mucosa was observed. Four hours following injection of a toxic dose of [ring-14C]dichlobenil (12 mg/kg) the covalent binding in the olfactory mucosa was 26 times higher than that in the liver. A dose-dependent decrease of nonprotein sulfhydryls (mainly glutathione, GSH) in the olfactory mucosa was observed 2.5 hr following injection of dichlobenil (6, 12, 25 mg/kg). The synthetic GSH precursor N-acetyl-L-cysteine decreased both the dichlobenil-induced toxicity and the covalent binding, whereas N-acetyl-D-cysteine had no effect. No protective effects of the cyanide antidotes nitrite, thiosulfate, or superoxide dismutase on the dichlobenil-induced toxicity were observed. In mice given the GSH-depleting agent phorone and a subtoxic dose of dichlobenil (6 mg/kg), an extensive toxicity and an increased covalent binding in the olfactory mucosa were demonstrated. Autoradiography showed no change in the distribution of covalent [14C]dichlobenil binding to nontarget tissues of phorone-treated mice. In conclusion, the results demonstrate a relationship between the degrees of covalent binding, GSH depletion, and toxicity of dichlobenil in the olfactory mucosa. Hence, the level of GSH appears to be of importance for the dichlobenil-induced toxicity in the olfactory mucosa.

Adrenocortical toxicity of 3-methylsulphonyl-DDE; 3: Studies in fetal and suckling mice

Irreversible binding and toxicity of the DDT metabolite 3-methylsulphonyl-DDE (MeSO2-DDE) were examined in fetuses and suckling pups following administration to pregnant or lactating C57Bl mice. Tape-section autoradiography showed a high and tissue-specific accumulation and binding of MeSO2-DDE-14C-derived radioactivity in the late gestational fetal adrenal cortex. According to microautoradiography an irreversibly bound residue was confined to the zona fasciculata. Similarly, there was a high concentration of irreversibly bound 14C-labelled material in the adrenal zona fasciculata of suckling pups. Intraperitoneal injection of MeSO2-DDE-14C to lactating mice resulted in higher concentrations of radioactivity in the liver and stomach contents (milk) of the suckling pups than in the maternal liver. This treatment also resulted in a higher level of radioactivity in the adrenals of the pups than in the maternal adrenals, both at a subtoxic and at a toxic dose. Histopathologic examination of adrenals from suckling pups revealed extensive vacuolation and necrosis of the zona fasciculata 2 days following a single dose of MeSO2-DDE (25 mg/kg) to the dam. In the fetal adrenal zona fasciculata, slight degenerative changes were observed following a maternal dose of 50 mg/kg. In conclusion, the study shows that MeSO2-DDE is a highly tissue-specific toxicant to the fetal and postnatal adrenal zona fasciculata in mice. Based on the present data and on previous results in adult mice, we propose that a tissue-specific activation to a reactive metabolite in the fetal and postnatal adrenal cortex is mediated by cytochrome P-450 (11 beta).

Toxicity of 2,6-dichlorothiobenzamide (chlorthiamid) and 2,6-dichlorobenzamide in the olfactory nasal mucosa of mice

The toxic effects of the herbicide chlorthiamid (2,6-dichlorothiobenzamide) and its major environmental metabolite 2,6-dichlorobenzamide (DCBA) were examined in the nasal passages of C57Bl mice following single ip injections. Chlorthiamid (12.25, and 50 mg/kg) induced an extensive destruction of the olfactory region, similar to that previously observed with the analogue dichlobenil (2,6-dichlorobenzonitrile). Necrosis of Bowman's glands was evident first, whereas degeneration and necrosis of the olfactory neuroepithelium developed less rapidly. The lesions were most severe in the dorsomedial region of the nasal cavity. At longer post-treatment intervals, the olfactory epithelium was replaced by a respiratory-like epithelium, and there was fibrosis of the lamina propria. DCBA was also toxic to the olfactory region (100 mg/kg), inducing necrosis of the Bowman's glands and the neuroepithelium in the dorsomedial region of the nasal cavity. No lesions were observed in other parts of the nasal cavity or in the liver after administration of chlorthiamid or DCBA. Chlorthiamid (IC50 = 51 microM), but not DCBA, inhibited the covalent binding of 14C-labeled dichlobenil in the olfactory mucosa in vitro. It is proposed that the toxic effects of chlorthiamid and dichlobenil in the olfactory mucosa are mediated by common or closely related metabolites.

Metabolic activation of halogenated hydrocarbons in the conjunctival epithelium and excretory ducts of the intraorbital lacrimal gland in mice

Autoradiographic studies were performed to determine the localization of irreversibly bound radioactivity in the eyes and accessory structures of mice exposed to 14C-labelled organic solvents in vivo or in vitro. A selective localization of bound radioactivity was observed in the conjunctival epithelium of mice given i.v. injections of 1,2-dibromoethane, chloroform, carbon tetrachloride or bromobenzene. Similar results were observed after instillation of chloroform or carbon tetrachloride in the conjunctival sac and after incubation of eyelids with the labelled compounds in vitro. A high level of irreversibly bound radioactivity was also observed in the excretory ducts of the intraorbital lacrimal glands of mice exposed to 1,2-dibromoethane in vivo and in vitro. After incubation of 14C-labelled 1,2-dibromoethane or chloroform with homogenates prepared from rat conjunctiva, the presence of irreversibly protein-bound radioactivity was detected. The results indicate that the conjunctival epithelium can metabolically activate halogenated organic solvents into products that bind to the tissue. The significance of a metabolic activation of chemicals in the pathogenesis of chemically induced lesions in the conjunctiva merits further attention.

Adrenocortical toxicity of 3-methylsulfonyl-DDE in mice. II. Mitochondrial changes following ecologically relevant doses

Transmission electron microscopy was used to characterize early ultrastructural lesions in the adrenal zona fasciculata of female C57BL mice given a single ip injection of the adrenocorticolytic DDT-metabolite 3-methylsulfonyl-DDE (MeSO2-DDE). Following 3 mg/kg, mitochondrial changes were observed 6 hr after dosing. At 12 and 24 hr the mitochondrial changes were conspicuous, with disorganization and disappearance of central cristae. At doses of 6, 12, and 25 mg/kg body wt initial (6 hr) mitochondrial vacuolization was observed, followed by disappearance of mitochondria (6-12 mg/kg) or cellular necrosis (25 mg/kg). The metabolic activation and binding of MeSO2-[14C]DDE in adrenal homogenates were determined in vitro. The irreversible binding of MeSO2-[14C]DDE to the mitochondria-containing adrenal S-9 pellet fraction was 50 times higher than that to the postmitochondrial S-12 supernatant fraction. The apparent Km was 2.1 microM and the apparent Vmax was 104 pmol/mg protein/30 min for the binding of MeSO2-[14C]DDE to S-0.3 supernatants. The irreversible protein binding was inhibited by metyrapone (Ki = 1 microM) and 11-deoxycorticosterone (Ki = 3 microM). In conclusion, the adrenal metabolic activation of MeSO2-DDE is suggested to be mediated by a mitochondrial cytochrome P450 form, presumably P450 (11 beta). A primary mitochondrial lesion develops and subsequently leads to degeneration and necrosis of the zona fasciculata.