A Generic Pharmacokinetic Model for Quantifying Mother-to-Offspring Transfer of Lipophilic Persistent Environmental Chemicals

Lipophilic persistent environmental chemicals (LPECs) can accumulate in a woman's body and transfer to her developing child across the placenta and via breast milk. To assess health risks associated with developmental exposures to LPECs, we developed a pharmacokinetic (PK) model that quantifies mother-to-offspring transfer of LPECs during pregnancy and lactation and facilitates internal dosimetry calculations for offspring. We parameterized the model for mice, rats, and humans using time-varying functions for body mass and milk consumption rates. The only required substance-specific parameter is the elimination half-life of the LPEC in the animal species of interest. We used the model to estimate whole-body concentrations in mothers and offspring following maternal exposures to hexachlorobenzene (HCB) and 2,2',4,4',5,5'-hexachlorobiphenyl (PCB 153) and compared these with measured concentrations from animal studies. We also compared estimated concentrations for humans to those generated using a previously published human LPEC PK model. Finally, we compared human equivalent doses (HEDs) calculated using our model and an allometric scaling method. Estimated and observed whole-body concentrations of HCB and PCB 153 in offspring followed similar trends and differed by less than 60%. Simulations of human exposure yielded concentration estimates comparable to those generated using the previously published model, with concentrations in offspring differing by less than 12%. HEDs calculated using our PK model were about 2 orders of magnitude lower than those generated using allometric scaling. Our PK model can be used to calculate internal dose metrics for offspring and corresponding HEDs and thus informs assessment of developmental toxicity risks associated with LPECs.

Tolerability and age-dependent toxicokinetics following perinatal hydroxyurea treatment in Sprague Dawley rats

Hydroxyurea (HU) is a valuable therapy for individuals with sickle cell anemia. With increased use of HU in children and throughout their lives, it is important to understand the potential effects of HU therapy on their development and fertility. Thus, studies were conducted to identify appropriate doses to examine long‐term effects of prenatal and early postnatal HU exposure and to understand kinetics of HU at various life stages. Pregnant Sprague Dawley dams were administered HU (0–150 mg/kg/day) via oral gavage from gestation days 17 to 21 and during lactation. Pups were dosed with the same dose as their respective dam starting on postnatal day (PND) 10 and up to PND 34. There was minimal maternal toxicity, and no significant effects on littering at any dose of HU. Starting on ~PND 16, offspring displayed skin discoloration and alopecia at doses ≥75 mg/kg/day and lower body weight compared to controls at doses ≥100 mg/kg/day. Gestational transfer of HU was observed, but there was minimal evidence of lactational transfer. Our toxicokinetic studies suggest that the internal dose in offspring may be altered due to age, but not due to sex. The plasma area under the curve, a measure of systemic exposure, at doses tolerated by offspring was threefold to sevenfold lower than the internal therapeutic dose in humans. Therefore, strategies to establish clinically relevant exposures in animal studies are needed. Overall, these data are useful for the design of appropriate nonclinical studies in the future to evaluate the consequences of long‐term HU treatment starting in childhood.

Increased use of hydroxyurea (HU) to treat sickle cell disease in children and throughout their lives augments the importance of understanding potential effects of HU on development and fertility. To inform the design of studies to evaluate long‐term safety of HU use in children, tolerability of prenatal and early postnatal HU treatment was evaluated in Sprague Dawley rats. Additionally, studies investigating gestational and lactational transfer of HU and how toxicokinetics of HU vary with age were conducted.

Transfer of Deoxynivalenol (DON) through Placenta, Colostrum and Milk from Sows to Their Offspring during Late Gestation and Lactation

Deoxynivalenol (DON) contamination of feed may result in reduced growth, feed refusal, immunosuppression, and health problems in swine. Piglets can be exposed to DON via placenta before birth and via milk during lactation. The extent of early-life exposure of piglets to DON is, however, not fully known. This study was therefore aimed at investigating DON uptake in sows fed with naturally contaminated diets, DON transfer across placenta during late gestation, and transfer of DON to piglets via colostrum and milk. Forty-four crossbred sows were evaluated from day 93 ± 1 of gestation until weaning of piglets and fed with feed made from naturally DON-contaminated oats at three concentration levels: (1) control (DON < 0.2 mg/kg), (2) DON level 1 (1.4 mg DON/kg), and (3) DON level 2 (1.7 mg DON/kg). The transfer of DON to the piglets was evaluated in 15 sows, with repeated sampling of blood and milk from the sows and blood samples from five piglets of each litter. The piglet/sow plasma DON ratio and milk/plasma (M/P) DON ratio in sows were calculated to estimate the degree of transfer. Piglet/sow plasma ratios were 2.14 at birth, 2.30 within 12–36 h after parturition, 0.08 on day 7, 0.16 on day 21, and 0.20 at weaning. M/P ratios were 0.92, 1.11, 0.94, 1.21, and 0.90, respectively. The results indicate that DON is efficiently transferred across placenta and into milk. However, the low piglet/sow plasma ratios at mid-lactation to weaning indicate that the piglets were most strongly exposed to DON in early life, despite the high M/P ratios and efficient secretion of DON in milk throughout the entire lactation.

Effect of PCBs on the lactational transfer of methyl mercury in mice: PBPK modeling

MeHg and PCB exposure to lactating mice were analyzed and a physiologically-based pharmacokinetic (PBPK) model was developed to describe the lactational transfer of MeHg in mice. The influence of albumin on the lactational transfer of MeHg was incorporated into the PBPK model. Experimental results with lactating mice and their pups showed that co-exposure with PCB congeners increased the lactational transfer of MeHg to the pups, which was associated with the rise of albumin levels in maternal blood. Observed results were matched with PBPK model simulations conducted under the assumptions that (1) MeHg bound to plasma albumin is transferred to maternal milk, and (2) PCB congeners may increase the lactational transfer of MeHg by escalating albumin levels in maternal blood. Further refinement of PBPK model quantitatively described the pharmacokinetic changes of MeHg by co-exposure with PCBs in pup's tissues.

Population physiologically based pharmacokinetic modeling for the human lactational transfer of PCB-153 with consideration of worldwide human biomonitoring results

BACKGROUND

One of the most serious human health concerns related to environmental contamination with polychlorinated biphenyls (PCBs) is the presence of these chemicals in breast milk.

OBJECTIVES

We developed a physiologically based pharmacokinetic model of PCB-153 in women, and predict its transfer via lactation to infants. The model is the first human, population-scale lactational model for PCB-153. Data in the literature provided estimates for model development and for performance assessment.

METHODS

We used physiologic parameters from a cohort in Taiwan and reference values given in the literature to estimate partition coefficients based on chemical structure and the lipid content in various body tissues. Using exposure data from Japan, we predicted acquired body burden of PCB-153 at an average childbearing age of 25 years and compared predictions to measurements from studies in multiple countries. We attempted one example of reverse dosimetry modeling using our PBPK model for possible exposure scenarios in Canadian Inuits, the population with the highest breast milk PCB-153 level in the world.

RESULTS

Forward-model predictions agree well with human biomonitoring measurements, as represented by summary statistics and uncertainty estimates.

CONCLUSION

The model successfully describes the range of possible PCB-153 dispositions in maternal milk, suggesting a promising option for back-estimating doses for various populations.