Theoretical approach to the hit probability of lung-cancer-sensitive epithelial cells by mineral fibers with various aspect ratios

Our plain-English summary of Theoretical approach to the hit probability of lung-cancer-sensitive epithelial cells by mineral fibers with various aspect ratios, by R. Sturm (Thoracic Cancer, 2010).

The study

• Author: R. Sturm
• Journal: Thoracic Cancer
• Published: 2010;1(3):116-125
• Cited by: 8 articles, as counted by NIH iCite
• Read it: PubMed · Publisher

Abstract

Background: Inhalation of fibers may lead to the damage and, as a further consequence, to the malignant transformation of specific (most of all non-ciliated) cells of the bronchial and bronchiolar airway epithelium. In order to accurately estimate the cancer risk induced by inhaled fibers, hit probabilities of non-ciliated (secretory) cells by mineral fibers (asbestos and chrysotile) were computed.

Methods: Besides the use of a stochastic lung geometry and a particle transport/deposition model being based upon the random-walk algorithm, histological data of cell distributions in the human lungs were applied for the theoretical calculations. Diameters of computer-generated fibers ranged from 0.1 µm to 10 µm, whilst two values (3 and 100) were selected for the aspect ratios (ratios of fiber length to fiber diameter), thereby simulating the behavior of short and very long fibrous particles.

Results: According to the modeling results, the highest regional hit probabilities (up to 10%) are available for fibers with a diameter of 1.0 µm, whereby cells of the bronchiolar compartment represent a preferential target of these particles. For fibers with a diameter of 0.1 µm, bronchiolar hit probabilities reach 2-3%, whereas fibers with a diameter of 10 µm penetrate to the peripheral lung parts with only low amounts (<0.1%). A change of the inhalation conditions from sitting to light-work breathing enhances the extrathoracic and bronchial filtering of large particles (diameter ≥1 µm), whilst penetration of small particles towards distal lung airways is subject to a reinforcement. Further refinement of hit probabilities by considering single airway generations results in the circumstance that fibers with diameters ≤1.0 µm preferably collide with cancer-sensitive cells of airway generations 12-15. In contrast, fibers with a diameter of 10 µm mainly represent a hazard for cancer-sensitive cells being located in the uppermost airways. A change of breathing conditions both supports the effect of short fibers and enhances the filtering of long ones.

Conclusion: Based upon the results of this contribution it can be concluded that highest cancer risk is generated by the inhalation of mineral fibers with diameters ≤1.0 µm, whereby fiber length has to be classified as a parameter with lower importance.

© Tianjin Lung Cancer Institute and Blackwell Publishing Asia Pty. Ltd.

In plain English

This was a theoretical computer-modeling study by a single author; no people or animals were studied, and cancer itself was not measured. The author used a simulated human lung and a random-walk (Monte Carlo) model of particle deposition, combined with published counts of airway cells. The model calculated how likely inhaled fibers were to hit non-ciliated (secretory) airway cells, which the author treated as the cells sensitive to lung cancer. Simulated fibers were 0.1, 1.0 or 10 micrometres thick, with length-to-diameter ratios of 3 or 100, and had densities for 'asbestos' and 'chrysotile', under sitting and light-work breathing. Fibers 1.0 micrometre thick had the highest hit probabilities: for long asbestos fibers during sitting breathing, 3.2% in the bronchi and 10.4% in the bronchioles. For 0.1-micrometre fibers, hits peaked in airway generations 12 to 15. Fibers 10 micrometres thick reached the lower airways only in very low amounts. The author concluded that the bronchiolar airways may be the main targets, and that fiber length matters less for deposition but greatly for fiber-tissue interaction. The model assumed airway mucus did not block fibers.

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: Theoretical computer modeling study: a stochastic lung geometry and a random-walk (Monte Carlo) particle transport and deposition model, combined with published histological cell-distribution data
• Who was studied: No human or animal subjects. A simulated human lung (functional residual capacity 3300 mL) with at least 10,000 computer-generated particles per run. Ciliated and non-ciliated cell numbers came from a published histological study (Mercer et al.).
• Exposure: Simulated inhaled fibers 0.1 to 10 micrometres in diameter (0.1, 1.0 and 10 in the results), with aspect ratios of 3 and 100. Densities were those typical for chrysotile (2.6 g/cm3) and 'asbestos' fibers (3.0 g/cm3); the article does not name a specific asbestos type for the latter. Breathing was modeled as sitting (tidal volume 750 mL, 12 breaths per minute) and light work (1250 mL, 20 per minute).
• Main results:
  • Long asbestos fibers (aspect ratio 100) under sitting breathing had their highest hit probabilities at 1.0 micrometre diameter: 3.2% in the bronchi and 10.4% in the bronchioles (Table 2: 3.1545 and 10.4344).
  • Fibers 10 micrometres in diameter reached the respiratory tract only in very low amounts, and the author judged them negligible for fiber-induced lung cancer. Under sitting breathing, the bronchiolar hit probability was 0.0007% for both long asbestos and long chrysotile fibers.
  • Compared with asbestos, chrysotile fibers 0.1 and 1.0 micrometre thick had hit probabilities 5 to 10% lower. Chrysotile fibers 10 micrometres thick had hit probabilities 20 to 50% higher.
  • By airway generation, under sitting breathing, 0.1-micrometre fibers had hit probabilities of 0.01% to 0.2%, highest in airway generations 12 to 15.
  • For 10-micrometre fibers, hit probabilities by airway generation declined steadily from the upper (proximal) to the deeper (distal) airways, whatever the aspect ratio.
  • Moving from sitting to light-work breathing raised bronchial and bronchiolar hit probabilities by up to 25% for short fibers of 1.0 micrometre or less. For short 10-micrometre fibers it lowered them by up to 60%.
• The authors' conclusion: The author concluded that bronchiolar airways may be regarded as the main targets of carcinogenic mineral fibers. Carcinogenic efficiency was highest for fibers whose aerodynamic diameters allow two or three deposition forces to act at once. Fiber length plays a less remarkable role in transport and deposition but a highly significant role in particle-tissue interaction. The abstract states that the highest cancer risk comes from fibers 1.0 micrometre or less in diameter.
• Limitations the authors state:
  • As the main simplification, the model assumed the airways are not covered by a continuous mucus layer, or that this layer is easily penetrated by fibers. Allowing for mucociliary clearance would reduce hit probabilities in the uppermost airways practically to zero.
  • For lack of morphometric data, ciliated and non-ciliated cells were assumed to have equal mean surface areas.
  • For simplification, cells were divided only into ciliated and non-ciliated secretory cells.

Topics

Medical terms in this study, explained in our Lexicon: Mineral Fiber, Aspect Ratio (Length-to-diameter ratio), Malignant Transformation, Epithelium, Chrysotile, Deposition, Fiber Length.

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