Showing papers by "Barbara D. Abbott published in 2003"

Methoxychlor-induced alterations in the histological expression of angiogenic factors in pituitary and uterus.

Abstract: Within the reproductive system, oestrogenic stimulation of uterine and pituitary tissue typically causes a proliferative response accompanied by an angiogenic induction of new blood vessels from existing ones, thereby providing nutrients and oxygen to the growing tissue. The pro-oestrogenic pesticide methoxychlor (MXC), however, has shown a differential effect on proliferative activity. An increase in uterine growth is present, while the pituitary undergoes a decrease in size, even though the effect is accompanied by a characteristic oestrogen-induced elevation in pituitary prolactin concentration. The focus of the current study was whether the observed differences in tissue growth between uterus and pituitary in response to MXC administration were paralleled by a corresponding disparity in the expression of those growth factors (members of the vascular endothelial growth factor (VEGF) and angiopoietin families and their receptors) that are involved in the angiogenic cascade. Ovariectomized adult Sprague–Dawley female rats were administered MXC (0–200 mg/kg, oral) for 1 or 3 weeks. Immunohistochemical staining of uteri and pituitaries was performed under strictly controlled conditions for VEGF and its receptor VEGFR2, Angiopoietin-1 (Ang1) and angiopoietin-2 and their tyrosine kinase receptor Tie2, and platelet endothelial adhesion factor (as an index of vascularity). Image acquisition and densitometric assessments of staining intensity were conducted under blind conditions. The results showed uterine MXC-induced increases in the expression of VEGFR2 and Ang1, changes consistent with a normal proliferative response to oestrogenic stimulation. For VEGF, staining tended to be most pronounced in the stromal region, although there did not appear to be a progressive increase with dose. VEGFR2 expression showed significant dose-related trends in luminal and glandular epithelia by 1 week. Similar effects at 1 week were evident for Ang1 in glandular epithelium. In the anterior pituitary, a dose-related increase in VEGF was present for the 1 and 3 week treatments, and the number of pituitary vessels per unit area was also increased after 3 weeks. The effects indicate that even though the insecticide has not been found to cause an augmentation in pituitary growth, a dose-related rise in the expression of at least one principal angiogenic factor is present that may be associated with an increase in vascular density.

TOXICOLOGICAL HIGHLIGHT In Vitro Screening for Developmental Toxicity of Tobacco Smoke Constituents

Abstract: Cigarette smoking is unrivaled among developmental toxicants in terms of total adverse impact on the human population. According to the American Lung Association, smoking during pregnancy is estimated to account for 20–30% of low-weight babies, up to 14% of preterm deliveries, and about 10% of all infant deaths (http://www.lungusa.org/tobacco/pregnancy_ factsheet99.html). Both active (Stillman et al., 1986) and passive smokers (Martin and Bracken, 1986) have babies with lower than normal birthweights. The long-term consequences associated with low birthweight are just beginning to come to light, and they are many. Risks of childhood and adult morbidity, including—but not limited to—diabetes, cardiovascular disease, obesity, and cancer, are inversely related to birthweight (for review, see Godfrey and Barker, 2001; Slikker and Schwetz, 2003). It has been estimated that 12–24% of pregnant women smoke, with the lower figure coming from surveys based on self-reporting. Smoking is the single largest preventable risk factor for pregnancy-related morbidity and mortality in the US (Dempsey and Benowitz, 2001), and the Surgeon General’s Report (USDHHS, 2001) states that the known adverse women’s health effects of smoking “compels the Nation to make reducing and preventing smoking one of the highest contemporary priorities for women’s health.” Vasculogenesis and angiogenesis are essential for embryonic development (Drake, 2003), and disruption of these processes can be a powerful mechanism of teratogenesis. In fact, thalidomide, the most notorious of human teratogens, may work at least in part through its known antiangiogenic properties (Ng et al., 2003; Stephens et al., 2000). In this issue, Melkonian and coworkers present another in a series of papers from their group demonstrating that constituents of tobacco smoke are developmentally toxic and antiangiogenic in the chick chorioallantoic membrane (CAM) assay. The use of the CAM to study effects on angiogenesis is well established, if not yet well standardized (Ribatti and Vacca, 1999; Richardson and Singh, 2003), and the signaling pathways controlling vasculogenesis and angiogenesis are highly conserved across species (Drake, 2003). The type of screening done in this paper demonstrates the advantages of screening systems when used appropriately in a mechanism or mode of action framework. Previous papers from the same group presented CAM assay results for pyridines identified in tobacco smoke (Ji et al., 2002) as well as for mainstream and sidestream tobacco smoke solutions (Melkonian et al., 2000, 2002). Pyridine derivatives with single methyl or ethyl substitutions were the most potent, inhibiting CAM growth down to picomolar concentrations. Both mainstream and sidestream cigarette smoke solutions caused abnormal pattern formation of CAM blood vessels and altered the composition of the extracellular matrix in the CAM mesoderm. In the paper highlighted here, the effects of pyrazine and derivatives previously identified in tobacco smoke are examined. Pyrazine itself was found to be a more potent inhibitor of CAM and embryo growth (picomolar concentrations) than any of the six derivatives tested. Effects on growth were apparently due to inhibition of cell proliferation, as DNA synthesis was inhibited by pyrazine. While higher concentrations inhibited angiogenesis and blood vessel pattern formation, these parameters were not affected at the lowest concentration that affected CAM and embryo growth. Since they previously demonstrated that tobacco smoke extracts were antiangiogenic, the authors speculate that there may be other, as yet untested, compounds in cigarette smoke that are more strongly antiangiogenic than is pyrazine. Yet the potency of pyrazine in this developmental assay is important, particularly in light of its inclusion on a list of chemicals that are generally regarded as safe additives for human foods and consumer products (Adams et al., 2002; Smith et al., 2001). Further work on its developmental toxicity is certainly merited. Given the immense deleterious health effects of cigarette 1 To whom correspondence should be addressed at rogers.john@epa.gov.

Organ culture of midfacial tissue and secondary palate.

Abstract: Palatal organ culture provides an in vitro model for the study of the formation of the secondary palate, which forms the roof of the mouth in the developing fetus. The protocol describes the steps for culture of the mid-facial region of the fetal mouse or rat. In culture the secondary palatal shelves proceed through stages of growth, elevation and fusion in a manner analogous to that occurring in utero. This model provides a tool for studies of mechanisms of normal and abnormal palatogenesis and has applications for developmental biology and toxicology. Keywords: cleft palate; palatogenesis; palate organ culture