In Vivo Evaluation of the Pulmonary Toxicity of Cellulose Nanocrystals: A Renewable and Sustainable Nanomaterial of the Future

Our plain-English summary of In Vivo Evaluation of the Pulmonary Toxicity of Cellulose Nanocrystals: A Renewable and Sustainable Nanomaterial of the Future, by N. Yanamala, M.T. Farcas, M.K. Hatfield, et al (ACS Sustainable Chemistry & Engineering, 2014).

The study

• Authors: N. Yanamala, M.T. Farcas, M.K. Hatfield, E.R. Kisin, V.E. Kagan, C.L. Geraci, A.A. Shvedova
• Journal: ACS Sustainable Chemistry & Engineering
• Published: 2014;2(7):1691-1698
• Cited by: 95 articles, as counted by NIH iCite
• Read it: PubMed · Publisher · Free full text

Abstract

The use of cellulose as building blocks for the development of novel functional materials is rapidly growing. Cellulose nanocrystals (CNC), with advantageous chemical and mechanical properties, have gained prominence in a number of applications, such as in nanofillers in polymer composites, building materials, cosmetics, food, and the drug industry. Therefore, it becomes critical to evaluate the potential health effects associated with CNC exposures. The objective of this study was to compare pulmonary outcomes caused by exposure of C57BL/6 mice to two different processed forms of CNC derived from wood, i.e., CNCS (10 wt %; gel/suspension) and CNCP (powder), and compare to asbestos induced responses. Pharyngeal aspiration with CNCS and CNCP was found to facilitate innate inflammatory response assessed by an increase in leukocytes and eosinophils recovered by bronchoalveolar lavage (BAL). Biomarkers of tissue damage were elevated to a higher extent in mice exposed to CNCP. Compared to CNCP, CNCS caused a significant increase in the accumulation of oxidatively modified proteins. The up-regulation of inflammatory cytokines was higher in the lungs after CNCS treatments. Most importantly, CNCP materials were significantly longer than CNCS. Taken together, our data suggests that particle morphology and nanosize dimensions of CNCs, regardless of the same source, may be critical factors affecting the type of innate immune inflammatory responses. Because various processes have been developed for producing highly sophisticated nanocellulose materials, detailed assessment of specific health outcomes with respect to their physical-structural-chemical properties is highly warranted.

In plain English

This was an animal experiment. The authors tested two forms of cellulose nanocrystals (CNC), tiny rod-shaped particles made from wood pulp. One was a 10 percent gel or suspension (CNCS) and the other a freeze-dried powder (CNCP). Female mice received a single dose of 50, 100 or 200 micrograms, placed at the back of the throat so it was breathed into the lungs. For comparison, other mice received 50 micrograms of crocidolite asbestos, and control mice received water. Lung fluid and blood were examined 24 hours later. Both CNC forms increased inflammatory cells, a marker of cell damage (LDH) and inflammatory signaling proteins. At 50 micrograms, one type of inflammatory white cell (PMNs) rose about 480-fold after the powder and 143-fold after the gel, compared with 57-fold after asbestos. Asbestos produced slightly more eosinophils than the low CNC doses. Protein carbonyls, a marker of oxidative damage, stayed similar to controls after asbestos. The authors concluded that the short-term responses to CNC were more prominent than those to crocidolite asbestos, and that small changes in production can cause different lung responses. Only short-term effects after one dose were measured.

We wrote this plain-English summary from the full article with the help of AI, and a second AI model checked each sentence against the article. It is not the authors' wording; the abstract and the article are their own account.

What the study did and found

• Design: Animal experiment: a single dose given by pharyngeal aspiration (placed at the back of the throat and breathed in), with short-term effects measured 24 hours later
• Who was studied: Specific pathogen-free adult female C57BL/6 mice, 7 to 8 weeks old, from Jackson Laboratories, housed in NIOSH animal facilities. The figure legends give 5 mice per group (Figure 2: at least 5). No study dates are given.
• Exposure: Wood pulp-derived cellulose nanocrystals given as an unmodified 10 wt % suspension (CNCS) or as a freeze-dried powder (CNCP), at 50, 100 or 200 micrograms per mouse. Crocidolite asbestos was given at 50 micrograms per mouse as a positive control. Control mice received sterile water.
• Main results:
  • Particle size by TEM: CNCS particles had a length of 90.2 ± 3.0 nm and a width of 7.2 ± 2.1 nm. CNCP particles had a length of 207.9 ± 49.0 nm and a width of 8.2 ± 2.3 nm.
  • Total cells in lung lavage fluid compared with controls: 1.44-fold, 1.40-fold and 1.56-fold increases for 50, 100 and 200 micrograms of CNCP, and 1.22-fold, 1.33-fold and 1.63-fold increases for the same doses of CNCS.
  • At 50 micrograms per mouse, PMNs (a type of inflammatory white cell) increased about 480-fold with CNCP and 143-fold with CNCS, compared with 57-fold with asbestos.
  • At 200 micrograms per mouse, eosinophils increased up to 47-fold with CNCS and 181-fold with CNCP. At the low dose (50 micrograms), asbestos caused a slightly higher eosinophil increase (48-fold) than CNCS or CNCP (19-fold or 36-fold).
  • LDH activity (a marker of lung cell damage) increased up to 1.63-fold with CNCS and 1.57-fold with CNCP compared with controls. The levels after CNC were similar to those after asbestos.
  • Protein carbonyls (a marker of oxidative damage) rose up to 2.1-fold with CNCP and up to 2.6-fold with CNCS compared with controls. In mice given 50 micrograms of asbestos, protein carbonyl levels remained similar to controls.
  • Twelve cytokines were significantly raised compared with control mice after both CNCS and CNCP.
  • In blood, CNCS or CNCP at 200 micrograms per mouse caused a significant increase in white blood cell counts.
• The authors' conclusion: The authors concluded that wood pulp-derived CNC caused dose-dependent oxidative stress, tissue damage and strong inflammatory responses in mouse lungs, and that the size of these responses differed between the gel and powder forms. They also concluded that acute responses to CNC were more prominent than those to crocidolite asbestos, and that even slight changes in how CNC is produced can lead to distinct respiratory responses.
• Limitations the authors state:
  • The authors described their idea that IL-13 may play a role in lung inflammation after asbestos and CNCP as speculation, and said further studies are needed to support it.

Topics

Medical terms in this study, explained in our Lexicon: Bronchoalveolar Lavage (BAL), Biomarker, Cytokine.

Related studies

• Gender differences in murine pulmonary responses elicited by cellulose nanocrystals — A.A. Shvedova, E.R. Kisin, et al. (2016)
• In vivo pulmonary toxicity of cellulose in rats — E. Tátrai, M. Brozik, et al. (1996)
• Comment on Shvedova et al. (2016), "gender differences in murine pulmonary responses elicited by cellulose nanocrystals" — J.A. Shatkin, G. Oberdörster (2016)
• Toxicity evaluations of various carbon nanomaterials — M. Uo, T. Akasaka, et al. (2011)
• Potential toxicity and safety evaluation of nanomaterials for the respiratory system and lung cancer — T. Vlachogianni, K. Fiotakis, et al. (2013)
• Risk Analysis of Cellulose Nanomaterials by Inhalation: Current State of Science — J.D. Ede, K.J. Ong, et al. (2019)

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