Brenda V. Dawson

Cardiac teratogenesis of halogenated hydrocarbon—Contaminated drinking water☆

OBJECTIVES The purpose of this study was to test the hypothesis that administration of trichloroethylene and dichloroethylene to pregnant rats during organogenesis would produce a significant fetal cardiac teratogenic effect. It was also hypothesized that administration of these compounds only before pregnancy would not be associated with fetal cardiac teratogenesis. BACKGROUND Epidemiologic observations demonstrated an increased number of congenital cardiac defects in children whose mother resided in an area with drinking water contaminated by trichloroethylene and dichloroethylene. A prior provocative intrauterine exposure study in rats established a positive link between these contaminants and an increased number of fetal hearts with congenital cardiac defects. METHODS Sprague-Dawley rats were given pure tap drinking water (control subjects) or water contaminated with high or low dose of trichloroethylene or dichloroethylene (experimental groups) during prepregnancy only, prepregnancy and pregnancy or during pregnancy alone. RESULTS A total of 2,045 fetuses were examined. Trichloroethylene or dichloroethylene delivered exclusively in the period before pregnancy caused no increase in congenital cardiac malformations over the control level. Compared with the control group, rats exposed to these agents both before and during pregnancy, had a significantly greater number of fetuses with cogenital cardiac malformations. Trichloroethylene (high dose only) administered only during pregnancy produced a significant increase in cardiac defects. Other fetal variables, including noncardiac congenital abnormalities, showed no significant difference between control and treated groups. CONCLUSIONS Trichloroethylene and dichloroethylene administered during organogenesis are cardiac, but not general, teratogens. The data indicate that these agents administered in drinking water to pregnant rats caused an increased number of congenital cardiac defects in rat fetuses.

Cardiac teratogenicity of trichloroethylene metabolites

OBJECTIVES The hypothesis of this study was that metabolites of trichloroethylene (TCE), dichloroethylene (DCE) and related compounds were responsible for fetal cardiac teratogenic effects seen when TCE or DCE is consumed by pregnant rats during organogenesis. Identification of teratogenic metabolites would allow more accurate assessment of environmental contaminants and public health risks from contaminated water or possibly municipal water supplies which, when chlorinated, may produce these potentially dangerous chemicals. BACKGROUND Human epidemiologic studies and previous teratogenic studies using chick embryos and fetal rats have shown an increased incidence of congenital cardiac lesions in animals exposed to TCE and DCE. METHODS Metabolites and compounds studied in drinking water exposure included: trichloroacetic acid (TCAA), monochloroacetic acid (MCAA), trichloroethanol (TCEth), carboxy methylcystine (CMC), trichloroacetaldehyde (TCAld), dichloroacetaldehyde (DCAld), and dichlorovinyl cystine (DCVC). Compounds were administered to pregnant rats during fetal heart development. RESULTS Fetuses of rats receiving 2,730 ppm TCAA in drinking water were the only group that demonstrated a significant increase in cardiac defects (10.53%) compared with controls (2.15%) on a per fetus basis (p = 0.0001, Fischers exact test), and a per litter basis (p = 0.0004, Wilcoxon and p = 0.0015, exact permutation tests). Trichloroacetic acid also demonstrated an increased number of implantation and resorption sites (p < 0.05) over controls. Other maternal and fetal variables showed no statistically significant differences between treated and untreated groups. CONCLUSIONS Of the metabolites tested, only TCAA appeared to be a specific cardiac teratogen in the fetus when imbibed by the maternal rat.

Cardiac teratogenesis of trichloroethylene and dichloroethylene in a mammalian model

Recent epidemiologic studies have demonstrated a greater than expected number of pediatric patients with congenital heart disease in areas where drinking water was contaminated by halogenated aliphatic hydrocarbons. Trichloroethylene, trichloroethane and dichlorethylene were the principal contaminants in the groundwater. A previous study of chick embryos demonstrated that when injected into the air sacs of fertilized eggs trichloroethylene produced more than three times the number of cardiac defects that are found in control embryos. This mammalian study demonstrates similar effects of trichloroethylene and dichloroethylene when applied under provocative circumstances (that is, solutions delivered through a catheter into the gravid uterus from an intraperitoneal osmotic pump) to the developing rat fetus in utero during the period of organ differentiation and development. Furthermore, the effect is dose dependent for both agents. Although only a very small number of congenital heart anomalies (3%) were found in the control group, 9% and 12.5% were found in the lower dose trichloroethylene and dichloroethylene groups and 14% and 21% in the higher dose groups, respectively (p less than 0.05). A variety of cardiac defects were found. Dichloroethylene appears to be at least as great a cardiac teratogen as trichloroethylene even though it was administered at a 10-fold lower concentration. These agents appear to be specific cardiac teratogens because only a single noncardiac anomaly was found. This study in a rat model demonstrates a dose-dependent relation between fetal exposure to trichloroethylene and dichloroethylene in utero during the period of organogenesis and the appearance of a variety of congenital cardiac defects.

Toxicologic studies of a superpotent α-melanotropin, [Nle4, D-Phe7]α-MSH

SummaryA toxicology study was performed in mice given a superpotent α melanocyte stimulating hormone (MSH) analog. This 13 amino acid derivative, [Nle4, D-Phe7]α-MSH or NDP-MSH, is a melanotropin which is very slowly biodegraded in vivo and is active at 1/1,000 the concentration of natural α-MSH. Mice were administered up to 2 mg/kg of the analog daily and weekly over 4 or 12 weeks by both topical application (in 90% DMSO) or by IP injections (in physiologic saline). At the end of this period, no toxic effects were observed in various organs, on hematologic indices, or on weight gain. A slight increase in triglyceride and platelet levels were noted in mice given the analog weekly for 12 weeks. There was no evidence of an effect on behavior nor ACTH-like endocrine actions such as elevated serum cortisol levels. Transdermal drug delivery studies performed in vitro showed reproducible diffusion of the NDP-MSH analog through full-thickness mouse skin. Approximately 0.002% to 0.05% of a 10−4M preparation was transdermally delivered using a DMSO/water solution or a PEG/alcohol cream base, respectively. This superpotent analog is now entering a Phase I clinical trial with possible therapeutic applications for the treatment of hypomelanotic disorders such as vitiligo and for pharmacologic tanning without the need for sunlight exposure.

Transdermal delivery of a melanotropic peptide hormone analogue

We previously reported that topical application of [Nle4,D-Phe7]alpha-MSH, a superpotent analogue of alpha-melanocyte stimulating hormone, to mice induces a darkening of follicular melanocytes throughout the skin. We now report that the melanotropin analogue can be delivered across mouse but not rat skin in an in vitro model system. Passage of the analogue from the topically applied vehicle (polyethylene glycol) across the skin into a subcutaneous receiving vessel was demonstrated by both bioassay as well as by radioimmunoassay. The bioassay data demonstrate that percutaneous absorption of the melanotropin did not result in loss of biological activity of the peptide. The differential penetration of the peptide across rodent skin reveals that one cannot predict percutaneous absorption of a substance across the stratum corneum from studies on a single species. The present results are the first to demonstrate, by direct quantitative measurements, that a bioactive peptide can be delivered across the vertebrate integument in vitro. These studies point out the potential of a topically applied melanotropin for tanning of the skin and possibly for treatment of certain hypopigmentary disorders.

Evaluation of potential health effects of 10 kHz magnetic fields: A short-term mouse toxicology study

A high-frequency inductive power distribution (HID) technology has been developed that generates sinusoidal magnetic fields at a frequency of 10 kHz. In typical industrial applications, field intensities in the order of 0.2 mT can be expected between the current-carrying coils. Because the possible health effects of 10 kHz sinusoidal magnetic fields of this type had never been investigated, a broad evaluation of possible effects on animal health was made in a preliminary 14 day acute study and in a 90 day subchronic study using male and female B6C3F1 mice. Exposures were at 0.08, 0.28, and 1.0 mT vs. a background exposure of 3.7 microT and were essentially continuous. These studies failed to demonstrate any health effects that can be clearly related to the magnetic field exposure. No changes in animal behaviour or indications of morbidity were detected during the initial exposure to the fields. There were no significant differences in body weight between exposed and unexposed (control) mice at any time in the study, and the clinical chemistry and hematology parameters were essentially unchanged. Although minor differences in some clinical chemistry and hematology parameters were seen between control and exposure groups, the lack of exposure dependence, the lack of consistency between sexes, and the lack of correspondence with the results of the two studies all suggest that these were chance associations. Even if the changes were real, the magnitude of the changes was very small and does not indicate serious biological effects. Finally, all organs were macroscopically and microscopically normal except for isolated, generally mild, histological lesions and lesions that were ascribed to fighting among males. There was no obvious association with field intensity.

VII. Topical application of a melanotropic peptide induces systemic follicular melanogenesis

We determined the relative effectiveness of alpha-MSH and a highly potent melanotropin analogue, [Nle4, D-Phe] - alpha-MSH, in stimulating a shift from pheomelanogenesis to eumelanogenesis within hair bulbs of mice. The analogue proved to be at least a hundred times more effective than the native hormone when injected subcutaneously. The two melanotropins were then incorporated into an ointment base and topically applied to a shaved area of the skin on the back of a yellow strain of mice (C57BL/6JAY). Within 24-48 hours eumelanin production was visible within hair bulb melanocytes in both treated and untreated areas of animals. The presence of melanized organelles (eumelanosomes) within melanocytes was confirmed by electron microscopy. These results document the delivery of a peptide hormone through the skin and into the systemic circulation. This is the first demonstration of the delivery of a peptide hormone by percutaneous absorption and may provide a model for a similar route of delivery of other peptide hormones. The hormone analogue has also been delivered across human skin in vitro. Delivery of a melanotropin by a transdermal route may prove to be clinically useful in the treatment of some integumental hypopigmentary disorders in humans.

Administration of melanotropic peptides during gestation in the rodent

A potent analogue of alpha-MSH (alpha-melanocyte stimulating hormone, S-alpha-melanotropin), [Nle4,D-Phe7] alpha-MSH, induces darkening of follicular melanocytes when injected or applied topically to the skin of mice [1]. This analogue also results in increased pigmentation when injected subcutaneously (s.c.) in humans. Toxicological studies have been performed on rodent models with administration topically or by intraperitoneal (i.p.) injection. No toxicity was observed and no pathological or significant biochemical changes were found. However there has been some controversy in the literature revolving around whether or not alpha-MSH is trophic for fetal growth and whether the hormone affects fetal adrenal development. These questions have been addressed in this study. All previous studies on the possible reproductive function of alpha-MSH have involved use of the natural hormone only. This is first to demonstrate the effects of the more potent analogue. The rat was used as the animal model to determine if the potent analogue of alpha-MSH affects events in gestation and embryonic fetal development and to determine if the analogue was a developmental toxicant. This study also examines the effect of a melanotropic peptide delivered directly to the conceptus in utero during organogenesis. No changes were found in the parameters examined (sex ratio, weight, morphology or histology, etc.) between treated and control fetuses. There was no evidence of premature parturition or pigmentation changes in the fetuses. The work reported in this study is of relevance if such a melanotropic peptide is to be used in women of childbearing age to induce pigmentation of the skin. Although the present results cannot necessarily be extrapolated to humans, indications are that, in rodents at least, [Nle4,D-Phe7] alpha-MSH and natural alpha-MSH have no adverse effects when administered during gestation and fetal development.

The iliopubic tract: an important anatomical landmark in surgery

A band of fascial thickening, termed the iliopubic tract, lies on the posterior aspect of the inguinal region and has been described in the surgical literature as playing an important role during herniorraphy. This study was undertaken to examine the gross and microscopic anatomy of the iliopubic tract in 12 cadavers. The results confirmed that the iliopubic tract can be readily identified as a thickening of the transversalis fascia running deep and parallel to the inguinal ligament. It attaches to the superomedial part of the pubic bone medially, but laterally its fibres fan out within the fascia transversalis and fascia iliaca without bony attachment to the iliac spines. In contrast to the inguinal ligament, the histological analysis of the iliopubic tract shows a high elastin to collagen ratio. The functional signficance of this structure merits further study, but there is no doubt that it is important in many approaches to inguinal herniorraphy. For this reason it is considered that the iliopubic tract deserves greater emphasis in the anatomy teaching of the inguinal region.