New Perspectives for Cancer Hazard Evaluation by the Report on Carcinogens: A Case Study Using Read-Across Methods in the Evaluation of Haloacetic Acids Found as Water Disinfection By-Products.

BACKGROUND: Due to the large number of chemicals not yet tested for carcinogenicity but to which people are exposed, the limited number of human and animal cancer studies conducted each year, and the frequent need for a timely response, mechanistic data are playing an increasingly important role in carcinogen hazard identification. OBJECTIVES: To provide a targeted approach to identify relevant mechanistic data in our cancer evaluation of haloacetic acids (HAAs), we used several approaches including systematic review, the 10 key characteristics of carcinogens (KCs), and read-across methods. Our objective in this commentary is to discuss the strengths, limitations, and challenges of these approaches in a cancer hazard assessment. METHODS: A cancer hazard assessment for 13 HAAs found as water disinfection by-products was conducted. Literature searches for mechanistic studies focused on the KCs and individual HAAs. Studies were screened for relevance and categorized by KCs and other relevant data, including chemical properties, toxicokinetics, and biological effects other than KCs. Mechanistic data were organized using the KCs, and strength of evidence was evaluated; this information informed potential modes of action (MOAs) and read-across-like approaches. Three read-across options were considered: evaluating HAAs as a class, as subclass(es), or as individual HAAs (analog approach). DISCUSSION: Because of data limitations and uncertainties, listing as a class or subclass(es) was ruled out, and an analog approach was used. Two brominated HAAs were identified as target (untested) chemicals based on their metabolism and similarity to source (tested) chemicals. In addition, four HAAs with animal cancer data had sufficient evidence for potential listing in the Report on Carcinogens (RoC). This is the first time that the KCs and other relevant data, in combination with read-across principles, were used to support a recommendation to list chemicals in the RoC that did not have animal cancer data. https://doi.org/10.1289/EHP5672.

Health consequences of electric lighting practices in the modern world: A report on the National Toxicology Program's workshop on shift work at night, artificial light at night, and circadian disruption.

The invention of electric light has facilitated a society in which people work, sleep, eat, and play at all hours of the 24-hour day. Although electric light clearly has benefited humankind, exposures to electric light, especially light at night (LAN), may disrupt sleep and biological processes controlled by endogenous circadian clocks, potentially resulting in adverse health outcomes. Many of the studies evaluating adverse health effects have been conducted among night- and rotating-shift workers, because this scenario gives rise to significant exposure to LAN. Because of the complexity of this topic, the National Toxicology Program convened an expert panel at a public workshop entitled "Shift Work at Night, Artificial Light at Night, and Circadian Disruption" to obtain input on conducting literature-based health hazard assessments and to identify data gaps and research needs. The Panel suggested describing light both as a direct effector of endogenous circadian clocks and rhythms and as an enabler of additional activities or behaviors that may lead to circadian disruption, such as night-shift work and atypical and inconsistent sleep-wake patterns that can lead to social jet lag. Future studies should more comprehensively characterize and measure the relevant light-related exposures and link these exposures to both time-independent biomarkers of circadian disruption and biomarkers of adverse health outcomes. This information should lead to improvements in human epidemiological and animal or in vitro models, more rigorous health hazard assessments, and intervention strategies to minimize the occurrence of adverse health outcomes due to these exposures.

Effects of genistein on expression of bone markers during MC3T3-E1 osteoblastic cell differentiation.

In this in vitro study, the hypothesis that the beneficial effects of dietary genistein on bone are through the modulation of the bone marker synthesis by osteoblastic MC3T3-E1 cells was tested, and the possible roles of estrogen receptors in the actions of genistein on osteoblastic cells were also examined. Interleukin-6 production was decreased 40% to 60% in osteoblastic cells treated with genistein from either day 8-16 or day 12-16, at dietarily achievable concentrations (10(-10) to 10(-8) M) (P<0.05). The mRNA expression of osteoprotegerin increased about 140% in cells treated from with genistein day 4-8 at a concentration of 10(-8) M (P<0.05). The ratio of estrogen receptor-alpha to beta expression increased 10-fold from day 0 to 12 of culture (P<0.05). Correlating with this time-dependent variation in estrogen receptor expression, treatments of 17beta-estradiol and genistein had opposite dose patterns on the ratio of estrogen receptor-alpha to beta expression following treatment from day 4 to 6 compared to from day 0 to 2. The addition of ICI-182,780, an estrogen receptor blocker, reduced the inhibitory effect of genistein on IL-6 production by 30-50%. In summary, these findings suggest that the beneficial skeletal effects of genistein, at dietarily achievable levels, appear to be mediated, at least in part, by interleukin-6 and osteoprotegerin, and estrogen receptors play important roles in the inhibition of interleukin-6 synthesis by genistein in osteoblastic MC3T3-E1 cells.

Soy isoflavones: no effects on bone mineral content and bone mineral density in healthy, menstruating young adult women after one year.

BACKGROUND: The effects of isoflavone-enriched soy protein on human bone mineral content (mass) and density in healthy, menstruating young adult females have not been examined in a comparative prospective investigation. Peri- and post-menopausal women have been reported to show beneficial effects of isoflavones on bone measurements. Therefore, young women may also be able to improve their accrual of peak bone mineral content (BMC) and bone mineral density (BMD) during the early adult years of bone consolidation with an isoflavone-enriched diet. OBJECTIVES: In this controlled, double-blind intervention, we tested the hypothesis that an isoflavone-rich soy protein diet increases BMC and BMD in young adult females over a period of one year in comparison to a control group receiving soy protein that has isoflavones removed. DESIGN: Young healthy women of any ethnic background, 21 to 25 years of age, were divided into two groups, placebo (n = 13) and supplement (n = 15). The soy protein supplement was enriched with isoflavones ( approximately 90 mg of total isoflavones/day), whereas the control protein diet was isoflavone-deficient, even though it contained the same amount of soy protein and other ingredients as the isoflavone-rich diet. Dual-energy x-ray absorptiometric (DXA) measurements of BMC and BMD were made at baseline and at 6 and 12 months. DXA estimates of body composition, including fat mass and lean body mass, were generated from whole-body BMC measurements. BMI was calculated as weight (kg) over height (m) squared. Physical activity was assessed, and three-day dietary records were taken at entry (baseline) and at 6 and 12 months. RESULTS: No changes in BMD after 12 months were found in either the isoflavone-treated (treatment) group or the isoflavone-deficient (control) group. Other variables also remained essentially constant over the 12-month period, including normal menstrual patterns in both the treatment and control groups. CONCLUSIONS: The isoflavone-rich soy preparation had no effects on BMC and BMD over a 12-month period in young healthy adult females with normal menses. An isoflavone-rich supplement appears to have little or no effect on bone in young adult women with normal ovarian function, at least over this 12-month study period.

Anabolic effects of a G protein-coupled receptor kinase inhibitor expressed in osteoblasts.

G protein-coupled receptors (GPCRs) play a key role in regulating bone remodeling. Whether GPCRs exert anabolic or catabolic osseous effects may be determined by the rate of receptor desensitization in osteoblasts. Receptor desensitization is largely mediated by direct phosphorylation of GPCR proteins by a family of enzymes termed GPCR kinases (GRKs). We have selectively manipulated GRK activity in osteoblasts in vitro and in vivo by overexpressing a GRK inhibitor. We found that expression of a GRK inhibitor enhanced parathyroid hormone (PTH)/PTH-related peptide (PTHrP) receptor-stimulated cAMP generation and inhibited agonist-induced phosphorylation of this receptor in cell culture systems, consistent with attenuation of receptor desensitization. To determine the effect of GRK inhibition on bone formation in vivo, we targeted the expression of a GRK inhibitor to mature osteoblasts using the mouse osteocalcin gene 2 (OG2) promoter. Transgenic mice demonstrated enhanced bone remodeling as well as enhanced urinary excretion of the osteoclastic activity marker dexoypyridinoline. Both osteoprotegrin and OPG ligand mRNA levels were altered in calvaria of transgenic mice in a pattern that would promote osteoclast activation. The predominant effect of the transgene, however, was anabolic, as evidenced by an increase in bone density and trabecular bone volume in the transgenic mice compared with nontransgenic littermate controls.

A method for the determination of betaine in tissues using high performance liquid chromatography.

Betaine is a major metabolite of choline in liver and kidney and may be an important product of choline metabolism in other tissues. The available methods for assay of betaine, however, are time consuming and relatively insensitive. We describe a modification of published methods that provides a sensitive and specific assay for betaine by derivatization and HPLC separation with UV quantitation. Betaine and other water-soluble choline metabolites are extracted from biological samples and separated by HPLC based on mobility of 14C-labeled internal standards. The betaine fraction is collected and derivatized with 4'-bromo-phenacyl triflate. The betaine-triflate derivative is quantitated by UV absorbance and the result is corrected for possible losses due to incomplete extraction recovery and incomplete derivatization by simultaneous measurement of radioactivity from the derivatized 14C-betaine internal standard. Betaine concentrations determined with this procedure are reported for several adult and fetal rat tissues.