Effects of in Utero Exposure to Arsenic during the Second Half of Gestation on Reproductive End Points and Metabolic Parameters in Female CD-1 Mice

Abstract

Background: Mice exposed to high levels of arsenic in utero have increased susceptibility to tumors such as hepatic and pulmonary carcinomas when they reach adulthood. However, the effects of in utero arsenic exposure on general physiological functions such as reproduction and metabolism remain unclear.

Objectives: We evaluated the effects of in utero exposure to inorganic arsenic at the U.S. Environmental Protection Agency (EPA) drinking water standard (10 ppb) and at tumor-inducing levels (42.5 ppm) on reproductive end points and metabolic parameters when the exposed females reached adulthood.

Methods: Pregnant CD-1 mice were exposed to sodium arsenite [none (control), 10 ppb, or 42.5 ppm] in drinking water from gestational day 10 to birth, the window of organ formation. At birth, exposed offspring were fostered to unexposed dams. We examined reproductive end points (age at vaginal opening, reproductive hormone levels, estrous cyclicity, and fertility) and metabolic parameters (body weight changes, hormone levels, body fat content, and glucose tolerance) in the exposed females when they reached adulthood.

Results: Arsenic-exposed females (10 ppb and 42.5 ppm) exhibited early onset of vaginal opening. Fertility was not affected when females were exposed to the 10-ppb dose. However, the number of litters per female was decreased in females exposed to 42.5 ppm of arsenic in utero. In both 10-ppb and 42.5-ppm groups, arsenic-exposed females had significantly greater body weight gain, body fat content, and glucose intolerance.

Conclusion: Our findings revealed unexpected effects of in utero exposure to arsenic: exposure to both a human-relevant low dose and a tumor-inducing level led to early onset of vaginal opening and to obesity in female CD-1 mice.

Figure 1

Experimental design: Pregnant CD-1 females were exposed to 0 (control), 10 ppb, or 42.5 ppm sodium arsenite in drinking water from E10 to birth. At birth, pups were fostered to females that had not been not exposed to arsenic. Vaginal opening was checked daily starting at 18 days of age, and body weight was recorded weekly for 15 weeks. At 8 weeks of age, female pups were included in the fertility study or analyzed for metabolic end points. The sample size for each experiment is listed in Table 1.

Figure 2

Effects of in utero arsenic exposure on onset of vaginal opening and body weight. (A) The x-axis represents the day of vaginal opening. The y-axis represents the percentage of animals with open vaginas. (B) The y-axis represents the average age ± SE when vaginal opening was observed. (C) Average body weight at 21 days of age (average age ± SE); (D) lines represent correlations between body weight (BW) and onset of vaginal opening (VO). *p < 0.05.

Figure 3

Effects of in utero arsenic exposure on levels of serum LH (A,B) and FSH (C,D) at 21 and 28 days of age (mean ± SE). Abbreviations: LH, luteinizing hormone; FSH, follicle-stimulating hormone; *p < 0.05 compared with control group.

Figure 4

Effects of in utero arsenic exposure on (A) body weight from 3 to 15 weeks of age. *Indicates significant difference (p < 0.05) between the control and the 10-ppb group and + indicates significant difference (p < 0.05) between the control and the 42.5-ppm group. (B) Percentage body fat. *Indicates significant difference (p < 0.05) compared with the control. (C) Glucose tolerance analysis. The y-axis represents serum glucose levels (mean ± SE; *indicates p < 0.05 compared with the control).

Figure 5

Effects of in utero arsenic exposure on (A) body weight, (B) serum leptin, and (C) serum insulin level at 6 months of age (mean ± SE) *p < 0.05 compared with the control.