gms | German Medical Science

Introduction: Hyperbaric oxygen has been shown both in experimental and clinical settings to improve wound healing, particulary in cases where the tissue is compromised due to local injury, infection or systemic diseases like diabetis. In the present study, we measured the effects of hyperbaric oxygen therapy on wound epithelialization and neovascularization in an in-vivo hairless mouse ear wound model.

Materials and methods: Standardized full thickness dermal wounds (2.25 mm diameter, 0.125 mm depth) were created on the dorsum of the ears of 32 male hairless mice (n=8 per group). To impair wound healing, macrophages were depleted in 2 of the 4 groups studied by pretreatment with iota-carrageenan. One impaired healing group and control (non-impaired) group received hyperbaric oxygen therapy whereas their counterparts obtained no hyperbaric oxygen. Wound epithelialization and neovascularization were measured every third day until wounds were completely healed, using intravital microscopy and computerized planimetry. Metalloproteinase-2 (MMP-2), -9 (MMP-9), tissue inhibitor of metalloproteinase-1 (TIMP-1) and TNFα were measured on days 2 and 7 using immunohistochemistry of 40 male mice (n=5 per group).

Results: In non-impaired wound healing, the rate of epithelialization was significantly increased in the groups treated with hyperbaric oxygen as compared to controls (14.1 ± 1.6 days vs. 16.8 ± 0.5 days; p < 0.05). Furthermore, reduced macrophage levels significantly decelerated wound closure compared with controls (20.4 ± 1.3 days vs. 16.8 ± 0.5 days; p < 0.005). This negative effect was reversed nearly completely by the treatment with HBO (17.1 ± 1.5 days vs. 20.4 ± 1.3 days; p < 0.05). Similary to epithelialization, the treatment with HBO significantly accelerated neovascularization in impaired wound healing (17.5 ± 1.3 days vs. 21.5 ± 1.6 days; p < 0.05). Neither treatment with HBO nor macrophage depletion caused significantly alterations in wound expression of MMP-2. In contrast, MMP-9 was significantly upregulated on day 2 in the impaired healing group receiving HBO treatment compared with the macrophage depleted group without HBO therapy (1.67 ± 0.19 vs. 0.67 ± 0.19; p < 0.05). The treatment with HBO in the impaired healing group induces furthermore a significantly upregulation of the TIMP-1 expression compared with the macrophage depleted group without HBO therapy (1.67 ± 0.19 vs. 0.83 ± 0.15; p < 0.05). Equally, the TNFα expression was increased significantly on days 2 (1.83 ± 0.28 vs. 0.5 ± 0.2; p < 0.05) and 7 (2.17 ± 0.28 vs. 1.0 ± 0.24; p < 0.05) post wounding.

Conclusion: These results demonstrate that hyperbaric oxygen therapy effectively reserved the negative effect macrophage reduction has on wound epithelialization and neovascularization. This effect could be attributable to stimulation of TNFα production and to a lesser degree to the release of metalloproteinases.