Comment on Shvedova et al. (2016), "gender differences in murine pulmonary responses elicited by cellulose nanocrystals"

Our plain-English summary of Comment on Shvedova et al. (2016), "gender differences in murine pulmonary responses elicited by cellulose nanocrystals", by J.A. Shatkin, G. Oberdörster (Particle and Fibre Toxicology, 2016).

The study

• Authors: J.A. Shatkin, G. Oberdörster
• Journal: Particle and Fibre Toxicology
• Published: 2016;13(1):59
• Type of article: Letter, Comment
• Cited by: 8 articles, as counted by NIH iCite
• Read it: PubMed · Publisher · Free full text

Abstract

A recent publication in "Particle and Fibre Toxicology" reported on the gender differences in pulmonary toxicity from oro-pharyngeal aspiration of a high dose of cellulose nanocrystals. The study is timely given the growing interest in diverse commercial applications of cellulose nanomaterials, and the need for studies addressing pulmonary toxicity. The results from this study are interesting and can be strengthened with a discussion of how differences in the weights of female and male C57BL/6 mice was accounted for. Without such a discussion, the observed differences could be partially explained by the lower body weights of females, resulting in higher doses than males when standardized to body weight or lung volume. Further, few conclusions can be drawn about the pulmonary toxicity of cellulose nanocrystals given the study design: examination of a single high dose of cellulose nanocrystals, administered as a bolus, without positive or negative controls or low dose comparisons, and at an unphysiological and high dose rate. Simulating the bolus type delivery by inhalation would require a highly unrealistic exposure concentration in the g/m3 range of extremely short duration. A discussion of these limitations is missing in the paper; further speculative comparisons of cellulose nanocrystals toxicity to asbestos and carbon nanotubes in the abstract are both unwarranted and can be misleading, these materials were neither mentioned in the manuscript, nor evaluated in the study.

In plain English

This is a letter to the editor, not a new experiment. The authors criticized an earlier study by Shvedova et al., which gave male and female C57BL/6 mice repeated doses of cellulose nanocrystals (CNCs) into the lungs and reported stronger lung responses in females. The authors argued that the smaller body weight of female mice might explain the difference. Scaling by lung surface area, they estimated that each 40 μg/mouse dose was 12 times the mouse-equivalent of one 8-hour worker day at the OSHA limit for respirable cellulose dust. They also objected to the earlier study's abstract comparing CNCs to asbestos and carbon nanotubes, because neither was tested. The authors concluded that the study showed only that very high doses of CNCs cause inflammation, which is common even to benign particles. The original study's authors replied in the same article. They disputed the dose comparison, attributed the female responses to sex differences in lung reactivity, and agreed the asbestos inference should have been left out. One letter author heads an advisory firm whose clients include organizations seeking to commercialize nanomaterials.

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: Letter to the editor (commentary) criticizing a published mouse study, with the authors' own dose-estimation calculation; followed by a response from the original study's authors
• Who was studied: No new subjects. The letter discusses Shvedova et al.'s experiment in male and female C57BL/6 mice.
• Exposure: Cellulose nanocrystals given by pharyngeal aspiration in the criticized study, 40 μg per mouse per dose, cumulative 240 μg per mouse. Asbestos was not tested.
• Main results:
  • Citing a reference source, the authors stated that at 7 to 8 weeks of age female C57BL/6 mice average 18 g and males 23 g, more than a 20% difference. They said this might give females a higher dose per unit body weight.
  • The authors' model estimated alveolar deposition of 5.1% in a 20 g mouse. For a human worker breathing 5 mg/m3 (the OSHA limit for respirable cellulose dust) for 8 hours, it estimated a deposited dose in the worker's lungs of 3,985 μg/day, or 6.3 ng per square centimeter of alveolar surface.
  • Scaling the worker's dose per unit of alveolar surface to the mouse lung, the authors estimated a mouse-equivalent of 3.3 μg/mouse for one 8-hour day, 12 times less than the 40 μg/mouse given in the criticized study.
  • By the authors' estimate, delivering 3.3 μg to a mouse over 8 hours of inhalation would need 3.6 mg/m3. Delivering it in one minute, as with a bolus dose, would need 1.73 g/m3, which the authors said nobody would consider realistic.
  • The authors stated that the CNCs studied were 158 nm long and are not classifiable as WHO fibers.
  • The authors stated that asbestos was not used as a comparison in the criticized study, and no negative benchmark was included either.
  • In their reply, the original study's authors disputed the letter's dose comparison. Under their own assumptions, they estimated the mouse lung burden was about 2.3 times a worker's 18-day burden, reached by a worker in about 42 days.
  • In their reply, the original study's authors maintained that the stronger female responses reflected sex differences in lung reactivity rather than body weight. They agreed that the inference about asbestos and carbon nanotubes should have been left out.
• The authors' conclusion: The letter's authors concluded that the only conclusion supported about CNC lung toxicity is that very high doses cause inflammation, an effect common even to benign fibrous and non-fibrous particles.
• Limitations the authors state:
  • The authors noted that their calculation did not consider unequal distribution of particles between aspiration and inhalation.

Related studies

• Gender differences in murine pulmonary responses elicited by cellulose nanocrystals — A.A. Shvedova, E.R. Kisin, et al. (2016)
• Fibrous nanocellulose, crystalline nanocellulose, carbon nanotubes, and crocidolite asbestos elicit disparate immune responses upon pharyngeal aspiration in mice — E.J. Park, T.O. Khaliullin, et al. (2018)
• In vivo pulmonary toxicity of cellulose in rats — E. Tátrai, M. Brozik, et al. (1996)
• Investigating the interaction of cellulose nanofibers derived from cotton with a sophisticated 3D human lung cell coculture — M.J. Clift, E.J. Foster, et al. (2011)
• Multiwalled carbon nanotube-induced pulmonary inflammatory and fibrotic responses and genomic changes following aspiration exposure in mice: A 1-year postexposure study — B.N. Snyder-Talkington, C. Dong, et al. (2016)
• Role of p53 in the chronic pulmonary immune response to tangled or rod-like multi-walled carbon nanotubes — K.S. Duke, E.A. Thompson, et al. (2018)

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