Impact of the ingestion of titanium dioxide nanoparticles via breast milk on the respiratory health of young rabbits - 20/03/24

The perinatal period is critical for adequate maturation of the immune system, the microbiota and multiple organs, including the lungs. During this vulnerable phase of life, maternal exposure to environmental factors can potentially influence health trajectories of the offspring. Although banned from food applications in Europe since 2022, Titanium dioxide (TiO₂) nanoparticles (NPs) are still massively used in most industrial sectors and their release into the air, water and soil, makes the exposure of mammals by oral, respiratory or skin routes likely. Emerging literature shows the presence of Ti in the breastmilk of rodents exposed orally or by inhalation but the consequences on the offspring's lung development and its susceptibilities are unknown. The objective of our study was to evaluate the transfer of TiO₂NPs from orally exposed rabbit does, to the kits and the consequences on gut and lung microbiota and lung development.

From parturition, lactating does were exposed per os to 2 forms of TiO₂NPs giving three groups: Rutile TiO₂ (R), Anatase: Rutile TiO₂ (AR) and the vehicle group (E). Fluids (milk, blood) and tissues (lung, jejunum) were analysed for Ti and Ti-NPs content using inductively coupled plasma mass spectrometry (ICP-MS). Offspring's lung development and pathology was assessed by histology, bronchoalveolar lavage cell numeration and qPCR. Lung, fecal and caecal microbiota were analysed by sequencing the V3-V4 region of the 16SrRNA gene.

We observed an increase in Ti in the caeca and feces from the exposed offspring groups compared to control, suggesting a transfer of Ti via breastmilk and its elimination, at least partly, by the feces. Despite similar Ti levels in the lungs and jejunum between groups, histological analyses of the lungs showed increased severity of suppurative bronchopneumonia in TiO₂-NPs exposed groups. In 3 exposed kits, there were Cilia-Associated Respiratory Bacillus and multinucleated giant cells that were not detected in the controls. Moreover, in the R group, pro-inflammatory cytokines mRNA levels increased whereas AR NPs decreased anti-inflammatory cytokines, collagen and elastin messengers, potentially explaining the increased incidence and severity of pulmonary pathologies described histologically in the lungs. Finally, the transfer of NPs to kits did not modify the overall microbial composition of the caeca but altered the relative abundances of bacterial families in the lungs, in particular in the AR group compared to the control group. The differential analysis of the OTUs showed that 14 OTUs were significantly different in the lungs of the AR rabbit rabbits in comparison with the E group.

This study is the first to suggest an impact of TiO₂NPs, administered to mothers during breastfeeding, on lung defenses of the offspring, probably via alterations in the gut-lung axis.