Chronic exposure of rats to the liver tumor promoter phenobarbital (PB) significantly reduces the ability of normal hepatocytes, but not of initiated hepatocytes, to respond to mitogenic stimuli. This reduced proliferative ability of normal hepatocytes was correlated with a marked elevation in hepatic concentration of the potent mito-inhibitory factor, transforming growth factor-beta 1 (TGF-beta 1). PB also increased the mannose 6-phosphate/insulin-like growth factor-II (M6P/IGF-II) receptor concentration in hepatocytes, with a concomitant up-regulation in gene expression. Since the M6P/IGF-II receptor facilitates the proteolytic activation of TGF-beta 1, this suggests that PB increases the capacity of normal hepatocytes to activate TGF-beta 1. In contrast, a subset of preneoplastic lesions induced with N-nitrosodiethylamine did not demonstrate elevated levels of the M6P/IGF-II receptor or TGF-beta 1 in response to PB. These findings emphasize the potential importance of TGF-beta 1 during liver tumor promotion with PB and suggest that reduction of M6P/IGF-II receptor levels in liver tumors may provide the tumor cells with an important selective growth advantage.
The Cosmetic Ingredient Review Expert Panel (Panel) assessed the safety of talc for use in cosmetics. The safety of talc has been the subject of much debate through the years, partly because the relationship between talc and asbestos is commonly misunderstood. Industry specifications state that cosmetic-grade talc must contain no detectable fibrous, asbestos minerals. Therefore, the large amount of available animal and clinical data the Panel relied on in assessing the safety of talc only included those studies on talc that did not contain asbestos. The Panel concluded that talc is safe for use in cosmetics in the present practices of use and concentration (some cosmetic products are entirely composed of talc). Talc should not be applied to the skin when the epidermal barrier is missing or significantly disrupted.
The Cosmetic Ingredient Review Expert Panel (Panel) reviewed the safety of methylisothiazolinone (MI), which functions as a preservative. The Panel reviewed relevant animal and human data provided in this safety assessment and in a previously published safety assessment of MI and concluded that MI is safe for use in rinse-off cosmetic products at concentrations up to 100 ppm and safe in leave-on cosmetic products when they are formulated to be nonsensitizing, which may be determined based on a quantitative risk assessment.
BACKGROUND:The toxicity of arsenic compounds is highly dependent on the valence and methylation state of the compound. Although there is extensive published literature on the potential developmental toxicity of inorganic arsenic compounds, little exists on organic arsenic compounds and, in particular, studies conducted in accordance with conventional regulatory guidelines appropriate for risk assessment are rare. The organic arsenic compounds, monomethylarsonic acid (MMA V ) and dimethylarsinic acid (DMA V , also called cacodylic acid), are the active ingredients in pesticide products that are used mainly for weed control. MMA V and DMA V are also metabolites of inorganic arsenic formed intracellularly by most living organisms (animals, plants and bacteria). In mammals, this occurs predominantly in liver cells. METHODS: Conventional developmental toxicity studies of orally administered MMA V and DMA V in the Sprague-Dawley rat and New Zealand White rabbit were conducted in commercial contract laboratories in the late 1980s for regulatory compliance. The results of these studies are summarized and presented to broaden the data available in the public domain. RESULTS: In both species, data shows an absence of dose-related effects at organic arsenic exposures that were not maternally toxic. MMA V doses of 0, 10, 100, and 500 mg/kg/day (rat) and 0, 1, 3, 7, and 12 mg/kg/day (rabbit) and DMA V doses of 0, 4, 12, and 36 mg/kg/day (rat) and 0, 3, 12, and 48 mg/kg/day (rabbit) were administered by oral gavage daily during organogenesis (Gestation Day [GD] 6-15, rat; GD 7-19, rabbit) and the litters examined at maternal sacrifice (GD 20, rat; GD 29, rabbit). After treatment with MMA V , maternal and fetal toxicity were observed at the highest doses of 500 mg/kg/day (rat) and 12 mg/kg/day (rabbit), but no treatment-related developmental toxicity at the lower doses, even in the presence of minimal maternal toxicity in the rat at 100 mg/kg/d. There was no evidence of teratogenicity associated with MMA V treatment. With DMA V , maternal and developmental toxicity were observed in the rat at 36 mg/kg/day, with a higher than spontaneous incidence of fetuses with diaphragmatic hernia. In the rabbit at 48 mg/kg/day, there was marked maternal toxicity, culminating for most females in abortion and with no surviving fetuses for evaluation. There was no treatment-related maternal or developmental toxicity in the rat or rabbit at 12 mg/kg/day. Based on pregnancy outcome, the developmental toxicity no observed adverse effect level (NOAEL) for orally administered MMA V were 100 and 7 mg/kg/day in the rat and rabbit, respectively, and for DMA V were 12 mg/kg/day in both species. CONCLUSIONS: Margins of exposure estimated based on conservative estimates of daily intakes of arsenic in all of its forms indicate that exposure to MMA V or DMA V at environmentally relevant exposure levels, by the oral route (the environmentally relevant route of exposure) is unlikely to pose a risk to pregnant women and their offspring. Birth Defects Res (Par...
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