Alveolar size effects on nanoparticle deposition in rhythmically expanding-contracting terminal alveolar models

Significant differences in alveolar size exist in humans of different ages, gender, health, and among different species. The effects of alveolar sizes, as well as the accompanying breathing frequencies, on regional and local dosimetry of inhaled nanoparticles have not been sufficiently studied. Despite a well-accepted qualitative understanding of the advection-diffusion-sedimentation mechanism in the acinar region, a quantitative picture of the interactions among these factors remains inchoate. The objective of this study is to quantify the effects of alveolar size on the regional and local deposition of inhaled nanoparticles in alveolar models of varying complexities and to understand the dynamic interactions among different deposition mechanisms. Three different models were considered that retained 1, 4, and 45 alveoli, respectively. For each model, the baseline geometry was scaled by ¼, ½, 2, 4, and 8 times by volume. Temporal evolution and spatial distribution of particle deposition were tracked using a discrete-phase Lagrangian model. Lower retentions of inhaled nanoparticles were observed in the larger alveoli under the same respiration frequency, while similar retentions were found among different geometrical scales if breathing frequencies allometrically matched the alveolar size. Dimensional analysis reveals a manifold deposition mechanism with tantamount contributions from advection, diffusion, and gravitational sedimentation, each of which can become dominant depending on the location in the alveoli. Results of this study indicate that empirical correlations obtained from one sub-population cannot be directly applied to others, nor can they be simply scaled as a function of the alveolar size or respiration frequency due to the regime-transiting deposition mechanism that is both localized and dynamic.

Effects of Wharton's jelly-derived mesenchymal stem cells on chronic obstructive pulmonary disease

Objectives

Chronic obstructive pulmonary disease (COPD) is a fatal disease that shortens one's life expectancy and reduces the quality of life of patients. The current known treatments for COPD can only act to alleviate the symptoms. Recently, stem cells have demonstrated efficacy in various medical areas. The aim of this study was to investigate the possibility of using human Wharton's jelly-derived mesenchymal stem cells (MSC)s for lung recovery in a COPD mouse model.

Methods

Human Wharton's jelly was obtained during natural delivery or caesarean section from healthy women. Wharton's jelly-derived MSC was confirmed with expression of CD14, CD34, CD45, CD73, CD90, and CD105 using flow cytometry. Mice model (C57BL/6) of COPD were induced by injecting 10 μL elastase into the trachea and they were divided into three treatment groups (sham, vehicle, stem cell). The sham group was not induced COPD, nor provided any treatment; the vehicle group comprised of COPD-induced mice treated with normal saline; the stem cell group comprised of COPD-induced mice treated with Wharton's jelly-derived MSCs. The vehicle and mesenchymal stem cells (5 × 10⁴ cells) were injected in tail vein 7 days following COPD induction. Mice were euthanized 7 days after vehicle and stem cell injection, and pathologic findings were confirmed. Mean Linear Intercept (MLI) was measured after emphysema-induced alveoli were identified.

Results

Cell surface markers were positive for CD105, CD90, and CD73 and negative for CD45, CD34, and CD14. Pathological tests showed that COPD-induced mice had significantly increased emphysema volume as compared with that in the sham group. The degree of emphysema in the stem cell group was reduced based on pathologic findings. The mean MLI of the sham group was measured as 38.85 ± 6.45. The mean MLI of the vehicle and stem cell groups were 163.05 ± 48.94 and 123.59 ± 30.53, respectively, and there was a statistically significant difference between the two groups (p = 0.008).

Conclusions

Though the number of mice in the experiment was not large, human Wharton's jelly-derived MSCs showed pulmonary regenerative effects in the COPD mouse model. Although we cannot confirm the effects of Wharton's jelly-derived MSCs in COPD through this experiment, it can be used as a basis for a larger clinical experiment.