Effect of chymase activity on skin thickness in the Clawn miniature pig hypertrophic scarring model

Objective: The female red Duroc pig, a heavy and cumbersome animal, is routinely used as an animal model for hypertrophic scarring. Chymase, a chymotrypsin-like serine protease, plays an important role in skin fibrosis. This study aimed to create a lightweight pig hypertrophic scarring model using Clawn miniature pigs, and to investigate the role of chymase in hypertrophic scarring.

Methods: After creating four skin wounds (7.5?×?7.5?cm, depth?=?0.15?cm) in each pig, skin biopsies were performed after 15, 30, 60, 90, 120, and 150?days. Skin thickness, water content, hydroxyproline percentage, chymase activity, and transforming growth factor-beta 1 concentration were measured, and pathological analyses were performed.

Results and conclusions: Both tissue thickness and chymase activity were increased in scar tissue, peaked on day 90 after injury, and then gradually decreased. Peripheral scar tissue showed higher chymase activity than central scar tissue. Neither chymase activity nor transforming growth factor-beta 1 was detected in the surrounding normal skin, whereas central scar tissue showed a high transforming growth factor-beta 1 concentration, peaking on day 15, and decreasing to normal by day 120. We found the Clawn miniature pig to be a useful model for hypertrophic scarring. Chymase activity and skin thickness were well-correlated, suggesting that scars thicken when chymase activity is high.