Extrapulmonary transport of MWCNT following inhalation exposure

Abstract

BackgroundInhalation exposure studies of mice were conducted to determine if multi-walled carbon nanotubes (MWCNT) distribute to the tracheobronchial lymphatics, parietal pleura, respiratory musculature and/or extrapulmonary organs. Male C57BL/6 J mice were exposed in a whole-body inhalation system to a 5 mg/m3 MWCNT aerosol for 5 hours/day for 12 days (4 times/week for 3 weeks, lung burden 28.1 ug/lung). At 1 day and 336 days after the 12 day exposure period, mice were anesthetized and lungs, lymph nodes and extrapulmonary tissues were preserved by whole body vascular perfusion of paraformaldehyde while the lungs were inflated with air. Separate, clean-air control groups were studied at 1 day and 336 days post-exposure. Sirius Red stained sections from lung, tracheobronchial lymph nodes, diaphragm, chest wall, heart, brain, kidney and liver were analyzed. Enhanced darkfield microscopy and morphometric methods were used to detect and count MWCNT in tissue sections. Counts in tissue sections were expressed as number of MWCNT per g of tissue and as a percentage of total lung burden (Mean ± S.E., N = 8 mice per group). MWCNT burden in tracheobronchial lymph nodes was determined separately based on the volume density in the lymph nodes relative to the volume density in the lungs. Field emission scanning electron microscopy (FESEM) was used to examine MWCNT structure in the various tissues.ResultsTracheobronchial lymph nodes were found to contain 1.08 and 7.34 percent of the lung burden at 1 day and 336 days post-exposure, respectively. Although agglomerates account for approximately 54% of lung burden, only singlet MWCNT were observed in the diaphragm, chest wall, liver, kidney, heart and brain. At one day post exposure, the average length of singlet MWCNT in liver and kidney, was comparable to that of singlet MWCNT in the lungs 8.2 ± 0.3 versus 7.5 ± 0.4 um, respectively. On average, there were 15,371 and 109,885 fibers per gram in liver, kidney, heart and brain at 1 day and 336 days post-exposure, respectively. The burden of singlet MWCNT in the lymph nodes, diaphragm, chest wall and extrapulmonary organs at 336 days post-exposure was significantly higher than at 1 day post-exposure.ConclusionsInhaled MWCNT, which deposit in the lungs, are transported to the parietal pleura, the respiratory musculature, liver, kidney, heart and brain in a singlet form and accumulate with time following exposure. The tracheobronchial lymph nodes contain high levels of MWCNT following exposure and further accumulate over nearly a year to levels that are a significant fraction of the lung burden 1 day post-exposure.

Assessment of Extrapulmonary Toxicity Induced by Carbon Nanomaterials Following Intra-Tracheal Instillation in Rats

“…Translocation to the blood circulation could provide a mechanism for a direct particle effect on the cardiovascular system as an explanation for epidemiological findings of cardiovascular effects associated with inhaled ambient ultra fine particles [24][25][26]. All these above studies were supported our results for translocation and extrapulmonary toxicity induced by the test CNMs.…”

Identification of Metal Oxide Nanoparticles in Histological Samples by Enhanced Darkfield Microscopy and Hyperspectral Mapping

“…Others, such as the semi-metallic oxides investigated in this study and carbon-based nanomaterials 24,27 , may be more challenging due to their elemental composition, shape, and depending on the matrix. In two murine inhalation studies by Mercer et al, a similar system to the one employed in this study was used in order to locate carbon nanotubes in the lung and in secondary organs based on their remarkably high contrast with surrounding tissues.…”

Long‐term retention of pristine multi‐walled carbon nanotubes in rat lungs after intratracheal instillation

“…Therefore, well‐dispersed MWCNTs might be more toxic and show more widespread organ distribution than aggregated MWCNTs, although published data have not indicated that dispersion affected the toxicity of TiO 2 nanoparticles (Kobayashi et al ., 2009). However, there are a few previous studies that have investigated the biodistribution of well‐dispersed MWCNTs for observation periods of over 6 months (Mercer et al ., 2013; Czarny et al . 2014,).…”

“…After inhalation exposure and intratracheal instillation to original and functionalized MWCNTs, no clearance was observed within 21 days (Silva et al ., 2014). After inhalation exposure, 25% and 35% cleared at 168 and 336 days post‐exposure compared with the burden at 1 day post‐exposure in rats (Mercer et al ., 2013). In contrast, spherical C 60 nanoparticles were cleared from the lungs much faster than MWCNTs [half‐life < 1 month (Shinohara et al ., 2010)] although C 60 and CNTs are both carbon allotropes, and both have a graphene structure.…”