Gender differences in murine pulmonary responses elicited by cellulose nanocrystals

Our plain-English summary of Gender differences in murine pulmonary responses elicited by cellulose nanocrystals, by A.A. Shvedova, E.R. Kisin, N. Yanamala, et al (Particle and Fibre Toxicology, 2016).

The study

• Authors: A.A. Shvedova, E.R. Kisin, N. Yanamala, M.T. Farcas, A.L. Menas, A. Williams, P.M. Fournier, J.S. Reynolds, D.W. Gutkin, A. Star, R.S. Reiner, S. Halappanavar, V.E. Kagan
• Journal: Particle and Fibre Toxicology
• Published: 2016;13(1):28
• Cited by: 62 articles, as counted by NIH iCite
• Read it: PubMed · Publisher · Free full text

Abstract

Background: Cellulose-based materials have been used for centuries to manufacture different goods derived from forestry and agricultural sources. In the growing field of nanocellulose applications, its uniquely engineered properties are instrumental for inventive products coming to competitive markets. Due to their high aspect ratio and stiffness, it is speculated that cellulose nanocrystals (CNC) may cause similar pulmonary toxicity as carbon nanotubes and asbestos, thus posing a potential negative impact on public health and the environment.

Methods: The present study was undertaken to investigate the pulmonary outcomes induced by repeated exposure to respirable CNC. C57BL/6 female and male mice were exposed by pharyngeal aspiration to CNC (40 μg/mouse) 2 times a week for 3 weeks. Several biochemical endpoints and pathophysiological outcomes along with gene expression changes were evaluated and compared in the lungs of male and female mice.

Results: Exposure to respirable CNC caused pulmonary inflammation and damage, induced oxidative stress, elevated TGF-β and collagen levels in lung, and impaired pulmonary functions. Notably, these effects were markedly more pronounced in females compared to male mice. Moreover, sex differences in responses to pulmonary exposure to CNC were also detected at the level of global mRNA expression as well as in inflammatory cytokine/chemokine activity.

Conclusions: Overall, our results indicate that there are considerable differences in responses to respirable CNC based on gender with a higher pulmonary toxicity observed in female mice.

In plain English

This was an animal experiment in mice testing cellulose nanocrystals (CNC), a wood-pulp-derived nanomaterial that, the authors noted in their background, has been speculated to cause pulmonary toxicity similar to carbon nanotubes and asbestos because of its high aspect ratio and stiffness. Male and female C57BL/6 mice received CNC (40 micrograms per mouse) by pharyngeal aspiration twice a week for three weeks (cumulative 240 micrograms), with sterile water controls; lungs were examined three months after the last exposure. CNC caused lung damage, inflammation, oxidative stress, raised TGF-beta1 and collagen, and histological chronic peribronchial and perivascular inflammation with multi-nucleated giant cells in both sexes, but most measures were greater in females: LDH rose 67 percent in females versus 21 percent in males, protein 31 versus 13 percent, TGF-beta1 was 3.2-fold higher in females, and airway responsiveness to methacholine rose about 1.7-fold only in females. Gene expression differed by sex, with only 68 differentially expressed genes shared. The authors concluded responses to respirable CNC differ considerably by gender, with higher pulmonary toxicity in female mice.

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: controlled animal experiment (repeated-dose pharyngeal aspiration study in mice, with gene expression microarray analysis)
• Who was studied: Specific pathogen-free adult male and female C57BL/6 mice, 7–8 weeks old, about 10 mice per group (5 per group for microarray), housed at the NIOSH animal facility, USA
• Exposure: Wood pulp derived cellulose nanocrystals (CNC), 40 micrograms per mouse by pharyngeal aspiration twice weekly for three weeks, cumulative dose 240 micrograms per mouse; controls received USP sterile water
• Main results:
  • Lung damage markers rose more in females than males: LDH 67 percent versus 21 percent and total protein 31 percent versus 13 percent above control
  • CNC-exposed females had higher fold increases in BAL polymorphonuclear leukocytes and lymphocytes than males
  • Multi-nucleated giant cells in BAL were 2.8-fold more frequent in females than males; none were found in controls
  • Oxidative stress markers: total antioxidant reserve fell 2.8-fold in females versus 1.4-fold in males; vitamin E fell 2.2-fold versus 1.4-fold; protein carbonyls rose 1.4-fold in females with no significant change in males; 4-HNE rose 1.2-fold in females and 1.1-fold in males
  • TGF-beta1 in BAL fluid was 3.2-fold higher in females than in males, and lung collagen increase was also greater in females
  • Airway responsiveness to methacholine (50 mg/ml) increased about 1.7-fold versus controls only in females; no significant change in males
  • Microarray: 845 of 22,486 probes differentially expressed in males and 794 in females, with 68 genes commonly regulated
  • Cytokine fold-increases over control (Table 1) were significantly greater in females than males for IL-1beta (2.21 ± 0.12 versus 1.68 ± 0.08), KC (4.16 ± 0.56 versus 2.33 ± 0.18), MCP-1 (8.15 ± 1.7 versus 2.35 ± 0.26) and MIP-1alpha (13.43 ± 1.63 versus 6.51 ± 0.64)
• The authors' conclusion: The authors concluded that pulmonary responses to respirable CNC, including inflammation and oxidative stress, were more pronounced in female than male mice, and raised the possibility of increased or earlier allergic responses in females
• Limitations the authors state:
  • The authors stated that the contribution of sex differences in pro-inflammatory cytokines to the sex difference in oxidative damage needs further investigation
  • The authors stated it remains to be understood whether acute or sub-chronic exposure is required for these gender-based differences to appear, and that inhalation and in vitro studies are still underway
  • The authors did not validate the microarray data by RT-qPCR
  • The authors stated further studies are needed on the mechanisms by which estrogen may drive the inflammatory outcomes seen

Topics

Medical terms in this study, explained in our Lexicon: Aspect Ratio (Length-to-diameter ratio), Inflammation, Oxidative Stress, Collagen, Cytokine.

Related studies

• Comment on Shvedova et al. (2016), "gender differences in murine pulmonary responses elicited by cellulose nanocrystals" — J.A. Shatkin, G. Oberdörster (2016)
• An in vitro testing strategy towards mimicking the inhalation of high aspect ratio nanoparticles — C. Endes, O. Schmid, et al. (2014)
• 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)
• In Vivo Evaluation of the Pulmonary Toxicity of Cellulose Nanocrystals: A Renewable and Sustainable Nanomaterial of the Future — N. Yanamala, M.T. Farcas, et al. (2014)
• Inhalation of rod-like carbon nanotubes causes unconventional allergic airway inflammation — E.M. Rydman, M. Ilves, et al. (2014)
• 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)

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