Monitoring the Health Status of Mice with Bleomycin-induced Lung Injury by Using Body Condition Scoring

Abstract

Well-defined, humane endpoints aid in monitoring animal health status during disease development. Body condition scoring (BCS) is a method for assessing health status in mouse studies where wasting and death are potential endpoints. Whether BCS is useful in monitoring animals with bleomycin-induced lung injury has not been reported. Body weight (BW) is a common humane endpoint for this model, but because the lungs increase in weight as BW decreases, the animal's true physical condition could be masked when using BW as the sole endpoint criterion. Therefore, our goal here was to assess the usefulness of BCS in monitoring health status in a mouse model of lung injury. Lung injury was caused by acute instil- lation of the fibrogenic antibiotic bleomycin into the lungs through the trachea. Male C57BL/6 mice received bleomycin (0.075 U) dissolved in saline or saline alone. Bleomycin instillation led to a doubling of lung weight and decreases in both BW and BCS, compared with saline instillation. The changes in BW and BCS were significantly correlated with lung weight. When the adjusted BW was used (corrected for the increase in lung weight), the correlation was unchanged, suggesting that the increase in lung weight did not significantly mask the decrease in BW. Bleomycin instillation caused decreases in both soleus and visceral epididymal fat masses. The change in BCS was significantly correlated with both soleus and VEF mass, suggesting that BCS is reflective of the systemic loss of muscle and fat mass. Our findings suggest that BW and BCS are significantly correlated to lung injury in the bleomycin model of lung fibrosis and that BCS is an appropriate alternative humane endpoint in this mouse model.

Figure 1.

Tracheal instillation of bleomycin causes lung injury and increases lung weight. (A) Gross morphology and histology of right lung of a saline-treated mouse (left) and bleomycin-treated animal (right). Bleomycin instillation causes multifocal lesions on the lung, which are associated with infiltration of inflammatory cells, disruption of alveoli, thickening of the alveoli walls, and increased deposition of collagen. Note that gross lung images are not to scale. Hematoxylin, eosin, and picrosirius red staining; magnification, 400×. (B) Bleomycin instillation leads to doubling of lung wet weight, even when (C) expressed relative to body weight (BW). §, P < 0.0001.

Figure 2.

Tracheal instillation of bleomycin causes decreases in body weight (BW) and body condition score (BCS). (A) Bleomycin instillation causes decreased BW. §, P < 0.0001. (B) Bleomycin instillation causes decreased BCS. §, P < 0.0001. (C) Representative changes in BW and BCS in a bleomycin-treated mouse and a saline control animal. Bleomycin causes an initial drop in BW that is stable until day 5, after which a precipitous drop in BW occurs. Decreases in BCS closely follow the decreases in BW. Saline instillation does not affect BCS, whereas BW slightly increases. (D) Decreases in BW and BCS are strongly correlated with each other.

Figure 3.

Decreases in body weight (BW) and body condition score (BCS) are correlated with lung weight. (A) The change in BW is highly correlated with lung weight (r = –0.54, P = 0.0001). (B) The change in BCS is highly correlated with lung weight (r = –0.63, P < 0.0001). (C) Adjusted BW (corrected for the increase in lung weight) is significantly decreased by bleomycin instillation (§, P < 0.0001). (D) The change in adjusted BW is highly correlated with lung weight (r = –0.54, P = 0.0001).

Figure 4.

Tracheal instillation of bleomycin causes decreases in muscle and fat mass. (A) Bleomycin instillation causes a significant decrease in soleus mass (‡, P < 0.001). (B) There is no effect of bleomycin instillation on soleus mass when expressed relative to body weight (BW). (C) Bleomycin instillation causes a significant decrease in visceral epididymal fat (VEF) mass (†, P < 0.01). (D) Bleomycin instillation causes a significant decrease in VEF mass when expressed relative to BW (*, P < 0.05).

Figure 5.

Tracheal instillation of bleomycin causes a disproportionate loss of visceral epididymal fat (VEF) compared with soleus mass. Soleus and VEF masses were normalized to the average weight of the saline-treated control group (Saline). When normalized soleus and VEF masses are correlated with BW (% of initial), the slope of the VEF mass compared with BW (% of initial) is significantly steeper (P = 0.001).

Figure 6.

Decreases in body condition score (BCS) are correlated with soleus and visceral epididymal fat (VEF) masses. (A) The change in BCS is highly correlated with soleus mass (r = 0.48, P = 0.0009). (B) The change in BCS is highly correlated with VEF mass (r = 0.70, P = 0.0002).