Oral administration of TiO2 nanoparticles during early life impacts cardiac and neurobehavioral performance and metabolite profile in an age- and sex-related manner

Abstract

Background: Nanoparticles (NPs) are increasingly incorporated in everyday products. To investigate the effects of early life exposure to orally ingested TiO₂ NP, male and female Sprague-Dawley rat pups received four consecutive daily doses of 10 mg/kg body weight TiO₂ NP (diameter: 21 ± 5 nm) or vehicle control (water) by gavage at three different pre-weaning ages: postnatal day (PND) 2-5, PND 7-10, or PND 17-20. Cardiac assessment and basic neurobehavioral tests (locomotor activity, rotarod, and acoustic startle) were conducted on PND 20. Pups were sacrificed at PND 21. Select tissues were collected, weighed, processed for neurotransmitter and metabolomics analyses.

Results: Heart rate was found to be significantly decreased in female pups when dosed between PND 7-10 and PND 17-20. Females dosed between PND 2-5 showed decrease acoustic startle response and when dosed between PND 7-10 showed decreased performance in the rotarod test and increased locomotor activity. Male pups dosed between PND 17-20 showed decreased locomotor activity. The concentrations of neurotransmitters and related metabolites in brain tissue and the metabolomic profile of plasma were impacted by TiO₂ NP administration for all dose groups. Metabolomic pathways perturbed by TiO₂ NP administration included pathways involved in amino acid and lipid metabolism.

Conclusion: Oral administration of TiO₂ NP to rat pups impacted basic cardiac and neurobehavioral performance, neurotransmitters and related metabolites concentrations in brain tissue, and the biochemical profiles of plasma. The findings suggested that female pups were more likely to experience adverse outcome following early life exposure to oral TiO₂ NP than male pups. Collectively the data from this exploratory study suggest oral administration of TiO₂ NP cause adverse biological effects in an age- and sex-related manner, emphasizing the need to understand the short- and long-term effects of early life exposure to TiO₂ NP.

Keywords: Cardiac performance; Early life exposure; Metabolomic analysis; Neurobehavioral assessment; Neurotransmitters; Pre-weaning rats; TiO2 NP.

Fig. 1

A TEM of TiO₂ NP and B histogram of size distribution. C Characterization of the 2 mg/mL dosing solutions was conducted by DLS and NTA at 0 and 4 h after preparation

Fig. 2

Body weight (bw) (A–C), liver-to-bw ratio (D–F), and brain-to-bw ratio (G–I) were measured for male (n = 15) and female (n = 15) rat pups orally dosed with TiO₂ NP and vehicle control between PND 2–5 (A, D, G), PND 7–10 (B, E, H), and PND 17–20 (C, F, I). No changes in bw were observed as a result of TiO₂ NP administration. TiO₂ NP led to increased liver-to-bw ratio at PND 21 for female pups dosed between PND 7–10 and PND 17–20, while liver-to-bw ratio increased for male pups dosed between PND 17–20. Male pups dosed between PND 7–10 had significantly increased brain-to-bw ratio. Body weight is presented as mean ± standard deviation. Box and whisker plots of organ-to-bw ratio data where the box extends from the 25th to 75th percentile and shows the median value, while the whiskers show the minimum and maximum value. TiO₂ NP dose groups are shown in black and vehicle control in gray. Statistical analyses were conducted using Mann–Whitney U test: *P-value < 0.05, **P-value < 0.01, ***P-value < 0.005

Fig. 3

Cardiac assessment at PND 20 for male (n = 6–7) and female (n = 6–7) pups dosed between PND 2–5 (A–C), PND 7–10 (D–F), and PND 17–20 (G–I). Oral administration of TiO₂ NP between PND 7–10 and PND 17–20 resulted in significantly decreased heart rate for female pups, and significantly increased ST and RR intervals. No significant changes in cardiac performance were found for male pups dosed with TiO₂ NP. Box and whisker plots, where the box extends from the 25th to 75th percentile and shows the median value, while the whiskers show the minimum and maximum value. TiO₂ NP dose groups are shown in black and vehicle control in gray. Statistical analyses were conducted using Mann–Whitney U test: *P-value < 0.05, **P-value < 0.01, ***P-value < 0.005

Fig. 4

Locomotor activity was measured at PND 20 at two intervals: Interval 1 (0–5 min) and Interval 2 (> 5–10 min) for male (n = 8) and female (n = 8) pups dosed between PND 2–5 (A, D), PND 7–10 (B, E), and PND 17–20 (C, F). The locomotor activity was significantly increased for Interval 1 for female pups dosed between PND 7–10, while the locomotor activity was significantly decreased for male pups in Interval 2 dosed between PND 17–20. Box and whisker plots, where the box extends from the 25th to 75th percentile and shows the median value, while the whiskers show the minimum and maximum value. TiO₂ NP dose groups are shown in black and vehicle control in gray. Statistical analyses were conducted using Mann–Whitney U test: *P-value < 0.05, **P-value < 0.01, ***P-value < 0.005

Fig. 5

RotaRod performance (A–C) and acoustic startle response (D–F) where recorded on PND 20 for male (n = 8) and female (n = 8) pups dosed between PND 2–5 (A, D), PND 7–10 (B, E), and PND 17–20 (C, F). Female pups dosed with TiO₂ NP between PND 7–10 showed significantly decreased performance in the RotaRod test, while female pups dosed between PND 2–5 showed decreased response in the acoustic startle response test. Box and whisker plots where, the box extends from the 25th to 75th percentile and shows the median value, while the whiskers show the minimum and maximum value. TiO₂ NP dose groups are shown in black and vehicle control in gray. Statistical analyses were done using Mann–Whitney U test: *P-value < 0.05, **P-value < 0.01, ***P-value < 0.005

Fig. 6

OPLS-DA score plots using (R2X, R2Y, and Q2) plasma metabolite differentiating male (A, C, E) and female (B, D, F) pups orally administered TiO₂ NP from vehicle control. Rat pups were dosed between PND 2–5 (A, D), PND 7–10 (B, E), or PND 17–20 (C, F) and sacrificed on PND 21. OPLS-DA plots show a clear grouping of metabolites in male pups (A–C). However, for female pups OPLS-DA plots show a clear grouping of metabolites in female pups for PND 2–5 (D), but not for PND 7–10 (E) and PND 17–20 (F)