Respiratory mechanics do not always mirror pulmonary histological changes in emphysema

Abstract

Objective: To verify the accordance of functional and morphometric parameters during the development of emphysema.

Methods: BALB/c mice received a nasal drop of either papain or saline solution and were studied after 1, 3, 15, 28, and 40 days. Functional parameters, such as airway resistance, tissue damping, and tissue elastance, were analyzed. To evaluate the structural changes and possible mechanisms involved in this disease, we measured the mean linear intercept, the volume proportions of elastic and collagen fibers, the number of macrophages, the numbers of cells expressing metalloprotease 12 and 8-isoprostane in lung parenchyma.

Results: We only observed decreases in tissue elastance and tissue damping on the 28th day, with a concomitant increase in the mean linear intercept, indicating the presence of emphysema. However, only the mean linear intercept values remained increased until the 40th day. The volume proportion of collagen fibers was increased from the 15th day to the 40th day, whereas the volume proportion of elastic fibers was only increased on the 40th day. The number of macrophages increased beginning on the 1st day. The expression of metalloproteinase 12 was increased from the 3rd day until the 40th day. However, 8-isoprostane expression was only increased on the 1st and 3rd days.

Conclusions: In this study, morphometric parameters were found to be more reliable for detecting the presence of emphysema than the functional parameters measured by respiratory mechanics. Further investigations are necessary to understand how the extracellular matrix remodeling observed in the lung parenchyma could be involved in this process.

Figure 1

The Htis, Gtis, and Raw for the papain and saline groups at each time point are represented in Figures 1A, 1B, and 1C. (A) The Htis results are separated into the 1^st, 3^rd, 15^th, 28^th, and 40^th days. When comparing the groups that received intranasal saline to the papain groups, a significant difference was found on the 28^th day (* p = 0.012). (B) Increases in the Gtis values were observed on the 1^st (* p = 0.09) and 28^th days (* p = 0.03) as compared with the groups that received the intranasal vehicle (saline). (C) No significant differences were found in the Raw values between the experimental groups over time. The values are expressed as means ± SD.

Figure 2

(A) Mean linear intercept values measured for the experimental groups. Increases in Lm were observed on the 28^th (* p≤0.001) and 40^th days (* p = 0.008). The values are expressed as means ± SD. (B) Increases in the volume proportion of collagen fibers in the parenchyma were observed on the 15^th (* p = 0.003), 28^th (* p = 0.003) and 40^th days (* p = 0.012). The values are expressed as means ± SD. (C) The volume proportion of elastic fibers in the parenchyma of the experimental groups was only increased on the 40^th day (* p =  0.009). The values are expressed as means ± SD.

Figure 3

(A) The density of macrophages (cells immunostained for MAC-2) was increased on the 1^st (* p = 0.007), 3^rd, 15^th, 28^th, and 40^th days (p≤0.005 for these groups). (B) MMP12-immunopositive cells in the lung alveolar tissue of the experimental groups, increases were observed on the 3^rd (* p = 0.034), 15^th, 28^th, and 40^th days (p≤0.005 for these groups). The values are expressed as means ± SD. (C) Expression of 8-isoprostane measured in the different groups revealed increases on the 1^st and 3^rd days (* p ≤0.05 for both groups).

Figure 4

Photomicrographs of lung parenchyma 15, 28, and 40 days after administering papain (P15, P28, and P40, respectively) or saline solution (S15, S28, and S40, respectively). (A) Lung tissue sections stained with H&E. Alveolar destruction and marked enlargement of the distal air spaces were observed in the papain group. (B) Lung parenchyma sections stained with Sirius red (to detect collagen fibers, which are red) illustrate an increased collagen fiber proportion starting on the 15^th day. (C) Lung parenchyma sections stained with resorcin-fuchsin (to detect elastic fibers, which are purple) illustrate an increase in their proportion starting on the 40^th day. (D) MMP12-immunopositive cells in the lung alveolar tissue, there was an increase in MMP12-positive cells in the papain groups. Original magnification, 200x.