Stochastic model of ultrafine particle deposition and clearance in the human respiratory tract

Ultrafine particulate matter impairs mitochondrial redox homeostasis and activates phosphatidylinositol 3-kinase mediated DNA damage responses in lymphocytes

Particulate matter (PM), broadly defined as coarse (2.5-10 μm), fine (0.1-2.5 μm) and ultrafine particles (≤0.1 μm), is a major constituent of ambient air pollution. Recent studies have linked PM exposure (coarse and fine particles) with several human diseases including cancer. However, the molecular mechanisms underlying ultrafine PM exposure induced cellular and sub-cellular repercussions are ill-defined. Since mitochondria are one of the major targets of different environmental pollutants, we herein aimed to understand the molecular repercussion of ultrafine PM exposure on mitochondrial machinery in peripheral blood lymphocytes. Upon comparative analysis, a significantly higher DCF fluorescence was observed in ultrafine PM exposed cells that confirmed the strong pro-oxidant nature of these particles. In addition, the depleted activity of antioxidant enzymes, glutathione reductase and superoxide dismutase suggested the strong association of ultrafine PM with oxidative stress. These results further coincided with mitochondrial membrane depolarization, altered mitochondrial respiratory chain enzyme activity and decline in mtDNA copy number. Moreover, the higher accumulation of DNA damage response proteins (γH2AX, pATM, p-p53), suggested that exposure to ultrafine PM induces DNA damage and triggers phosphatidylinositol 3 kinase mediated response pathway. Further, the alterations in mitochondrial machinery and redox balance among ultrafine PM exposed cells were accompanied by a considerably elevated pro-inflammatory cytokine response. Interestingly, the lower apoptosis levels observed in ultrafine particle treated cells suggest the possibility that the marked alterations may lead to the impairment of mitochondrial-nuclear cross talk. Together, our results showed that ultrafine PM, because of their smaller size possesses significant ability to disturb mitochondrial redox homeostasis and activates phosphatidylinositol 3 kinase mediated DNA damage response pathway, an unknown molecular paradigm of ultrafine PM exposure. Our findings also indicate that maneuvering through the mitochondrial function might be a viable, indirect method to modulate lymphocyte homeostasis in air pollution associated immune disorders.

Theoretical and experimental approaches to the deposition and clearance of ultrafine carcinogens in the human respiratory tract

INTRODUCTION

  Although inhaled ultrafine particles (UFPs) represent serious lung burdens and are thus responsible for a remarkable number of respiratory diseases (including cancer), only limited information on their deposition and clearance in the lung compartments is available. The study presented here tries to overcome this deficit by using a detailed theoretical approach to UFP behavior in the lungs.

METHODS

  The deposition model used in this context is based upon a stochastic lung geometry and the generation of single-particle trajectories in the tracheobronchial tree according to the random walk algorithm. Simulation of UFP clearance is conducted with the help of a multi-compartment model that considers cellular/non-cellular sites of temporary particle storage as separate compartments.

RESULTS

  As predicted by the models and confirmed by experimental findings, deposition of UFPs by Brownian motion takes place in both the upper and lower compartments of the respiratory tract. Alveolar accumulation of particulate mass increases proportionally with the inhalative flow rate. Clearance of UFPs is chiefly dominated by slow mechanisms with respective half-times ranging from several days to months.

DISCUSSION

  Modeling of UFP behavior in the respiratory tract represents an appropriate tool for forthcoming medical studies on this particle class, but it needs to be subjected to further refinements. •  As outlined by this study, alveolar deposition of UFPs, correlating with a noticeable risk of malignant transformations and cancer development, is determined by a number of factors, including effective particle size and velocity of particle transport in the conducting airways. •  With the help of appropriately validated models, respective predictions on the pulmonary burdens of UFP after short-term or long-term exposure can be made. In the case of subjects suffering from bronchial and/or alveolar UFP overloads, respective clearance approaches may be applied to simulate particle removal scenarios.

Local lung deposition of ultrafine particles in healthy adults: experimental results and theoretical predictions

BACKGROUND

Ultrafine particles (UFP) of biogenic and anthropogenic origin occur in high numbers in the ambient atmosphere. In addition, aerosols containing ultrafine powders are used for the inhalation therapy of various diseases. All these facts make it necessary to obtain comprehensive knowledge regarding the exact behavior of UFP in the respiratory tract.

METHODS

Theoretical simulations of local UFP deposition are based on previously conducted inhalation experiments, where particles with various sizes (0.04, 0.06, 0.08, and 0.10 µm) were administered to the respiratory tract by application of the aerosol bolus technique. By the sequential change of the lung penetration depth of the inspired bolus, different volumetric lung regions could be generated and particle deposition in these regions could be evaluated. The model presented in this contribution adopted all parameters used in the experiments. Besides the obligatory comparison between practical and theoretical data, also advanced modeling predictions including the effect of varying functional residual capacity (FRC) and respiratory flow rate were conducted.

RESULTS

Validation of the UFP deposition model shows that highest deposition fractions occur in those volumetric lung regions corresponding to the small and partly alveolated airways of the tracheobronchial tree. Particle deposition proximal to the trachea is increased in female probands with respect to male subjects. Decrease of both the FRC and the respiratory flow rate results in an enhancement of UFP deposition.

CONCLUSIONS

The study comes to the conclusion that deposition of UFP taken up via bolus inhalation is influenced by a multitude of factors, among which lung morphometry and breathing conditions play a superior role.

Total deposition of ultrafine particles in the lungs of healthy men and women: experimental and theoretical results

BACKGROUND

Inhaled ultrafine particles (UFP) may induce greater adverse respiratory effects than larger particles occurring in the ambient atmosphere. Due to this potential of UFP to act as triggers for diverse lung injuries medical as well as physical research has been increasingly focused on the exact deposition behavior of the particles in lungs of various probands. Main purpose of the present study was the presentation of experimental and theoretical data of total, regional, and local UFP deposition in the lungs of men and women.

METHODS

Both experiments and theoretical simulations were carried out by using particle sizes of 0.04, 0.06, 0.08, and 0.10 µm [number median diameters (NMD)]. Inhalation of UFP took place by application of predefined tidal volumes (500, 750, and 1,000 mL) and respiratory flow rates (150, 250, 375, and 500 mL·s(-1)). For male subjects a functional residual capacity (FRC) of 3,911±892 mL was measured, whereas female probands had a FRC of 3,314±547 mL. Theoretical predictions were based on (I) a stochastic model of the tracheobronchial tree; (II) particle transport computations according to a random walk algorithm; and (III) empirical formulae for the description of UFP deposition.

RESULTS

Total deposition fractions (TDF) are marked by a continuous diminution with increasing particle size. Whilst particles measuring 0.04 µm in size deposit in the respiratory tract by 40-70%, particles with a size of 0.10 µm exhibit deposition values ranging from 20% to 45%. Except for the largest particles studied here TDF of female probands are higher than those obtained for male probands. Differences between experimental and theoretical results are most significant for 0.10 µm particles, but never exceed 20%. Predictions of regional (extrathoracic, tracheobronchial, alveolar) UFP deposition show clearly that females tend to develop higher tracheobronchial and alveolar deposition fractions than males. This discrepancy is also confirmed by airway generation-specific deposition, which is permanently higher in women than in men.

CONCLUSIONS

From the experimental data and modeling predictions it can be concluded that females bear a slightly higher potential to develop lung insufficiencies after exposure to UFP than males. Besides higher deposition fractions occurring in female subjects, also total lung deposition dose is noticeably enhanced.

Spatial visualization of theoretical nanoparticle deposition in the human respiratory tract

BACKGROUND

Although nanoparticles and their hazardous effects on human health are well elucidated meanwhile, inhalation and distribution of these materials in the human respiratory tract still represent partly enigmatic phenomena. Main objective of the present study was the detailed description of a mathematical method, with the help of which spatial distributions of nanoparticles deposited in the tracheobronchial tree may be visualized appropriately.

METHODS

The technique is founded on a stochastic model of the bronchial network, within which inhaled particles follow individual, randomly selected trajectories. The lengths of these random paths depend on the airway-specific deposition probabilities calculated for the particles and the duration of the breath cycle. Positions of the deposited material were determined by computation of the exact lengths of individual particle trajectories and the orientation of single path segments within a Cartesian coordinate system, where the z-direction corresponds with the trachea. For a better quantification of the particle distribution and its eventual comparison with experimental data particle coordinates were fitted into a voxel grid [1 voxel = (0.467 cm)(3)]. Particle deposition is chiefly controlled by diffusive processes, whereas deposition mechanisms associated with inertia or gravity play a subordinate role.

RESULTS

Deposition patterns were visualized for particles with sizes of 1, 10, and 100 nm. As clearly demonstrated by the results obtained from the modeling procedure, under normal breathing conditions 1-nm particles tend to deposit in the upper airways, whilst 10- and 100-nm particles are preferably accumulated in the airways of the central and peripheral lung. The particle dose deposited in the extrathoracic and thoracic airways within one breath cycle significantly declines with increasing particle size.

CONCLUSIONS

Based on the predictions presented in this study possible consequences of nanoparticle inhalation to the health of subjects increasingly exposed to these airborne materials were discussed.

A computer model for the simulation of nanoparticle deposition in the alveolar structures of the human lungs

BACKGROUND

According to epidemiological and experimental studies, inhalation of nanoparticles is commonly believed as a main trigger for several pulmonary dysfunctions and lung diseases. Concerning the transport and deposition of such nano-scale particles in the different structures of the human lungs, some essential questions are still in need of a clarification. Therefore, main objective of the study was the simulation of nanoparticle deposition in the alveolar region of the human respiratory tract (HRT).

METHODS

Respective factors describing the aerodynamic behavior of spherical and non-spherical particles in the inhaled air stream (i.e., Cunningham slip correction factors, dynamic shape factors, equivalent-volume diameters, aerodynamic diameters) were computed. Alveolar deposition of diverse nanomaterials according to several known mechanisms, among which Brownian diffusion and sedimentation play a superior role, was approximated by the use of empirical and analytical formulae. Deposition calculations were conducted with a currently developed program, termed NANODEP, which allows the variation of numerous input parameters with regard to particle geometry, lung morphometry, and aerosol inhalation.

RESULTS

Generally, alveolar deposition of nanoparticles concerned for this study varies between 0.1% and 12.4% during sitting breathing and between 2.0% and 20.1% during heavy-exercise breathing. Prolate particles (e.g., nanotubes) exhibit a significant increase in deposition, when their aspect ratio is enhanced. In contrast, deposition of oblate particles (e.g., nanoplatelets) is remarkably declined with any reduction of the aspect ratio.

CONCLUSIONS

The study clearly demonstrates that alveolar deposition of nanoparticles represents a topic certainly being of superior interest for physicists and respiratory physicians in future.

Brain cytokine and chemokine mRNA expression in mice induced by intranasal instillation with ultrafine carbon black

Ambient air ultrafine particles (UFPs) have gained enormous attention to many researchers with recent evidence showing them to have more hazardous effects on human health than larger ambient particles. Studies focusing the possibility of effects on brain are quite limited. To examine the effect of ultrafine carbon black (ufCB) on mice brain, we instilled 125 microg of 14 nm or 95 nm CB into the nostrils of 8-week-old male BALB/c mice, once a week for 4 weeks. Four hours after the last instillation, we collected olfactory bulb and hippocampus and detected the expression of cytokine and chemokine mRNA by quantitative real-time PCR method. In this study, we found the induction of proinflammatory cytokines (interleukin-1 beta and tumor necrosis factor-alpha and chemokines (monocyte chemoattractant protein-1/CCL2, macrophage inflammatory protein-1 alpha/CCL3), and monokine induced interferon-gamma/CXC chemokine ligand (CXCL9) mRNA in brain olfactory bulb, not in the hippocampus of mice instilled with 14 nm ufCB intranasally. We suggest that the intranasal instillation of ufCB may influence the brain immune function depending on their size. To our knowledge, this is the first study to demonstrate region-specific brain cytokine and chemokine mRNA-induction in mice triggered by intranasal instillation of specific-sized ufCB, in a physiologically relevant condition.

Effect of intratracheal instillation of ultrafine carbon black on proinflammatory cytokine and chemokine release and mRNA expression in lung and lymph nodes of mice

Our understanding of how ultrafine particles, which are constituents of particulate matter, affect immunological response is poor. To investigate the size-specific effect of ultrafine particles on pulmonary immune responses, translocation to lymph nodes, and chemokine mRNA expressions in lung and lymph nodes, we performed three experiments in 8-week-old male BALB/c mice. In experiment 1, we instilled 25 microg, 125 microg, or 625 microg of 14 nm carbon black (CB) particles intratracheally, once weekly for 4 weeks, and in experiment 2, we instilled 95 nm CB. For detection of total and differential cell counts and cytokine and chemokine protein release, we collected bronchoalveolar lavage (BAL) fluid 24 h after the last instillation of CB. Experiments 1 and 2 showed that 125 microg was the suitable dose for experiment 3, which we then performed on the same schedule and 4 h after the last instillation, we harvested the lung and mediastinal lymph node to detect chemokine mRNA expression by real-time RT-PCR. The total cell count as well as the differential cell counts such as macrophages, lymphocytes, and neutrophils in BAL fluid increased significantly in mice exposed to 14 nm CB in a dose-dependent manner. Release of cytokines such as interleukin (IL)-1beta, IL-6, and tumor necrosis factor-alpha increased significantly in BAL fluid in mice instilled with 14-nm CB. Macrophage inflammatory protein 1 alpha/CCL-3 protein and mRNA expression were increased significantly in the lungs and lymph nodes of mice given 14 nm CB. Histologically, deposition of CB was observed greater in the mediastinal lymph nodes of mice given 14 nm than in 95 nm CB. These findings indicate that repeated intratracheal instillation of ultrafine carbon black in mice leads to pulmonary inflammation, their translocation to mediastinal lymph nodes and increased chemokine mRNA expression in lung and lymph nodes size-specifically.