Current Status of Experimental Animal Skin Flap Models: Ischemic Preconditioning and Molecular Factors

Abstract

Skin flaps are necessary in plastic and reconstructive surgery for the removal of skin cancer, wounds, and ulcers. A skin flap is a portion of skin with its own blood supply that is partially separated from its original position and moved from one place to another. The use of skin flaps is often accompanied by cell necrosis or apoptosis due to ischemia-reperfusion (I/R) injury. Proinflammatory cytokines, such as nuclear factor kappa B (NF-κB), inhibitor of kappa B (IκB), interleukin-6 (IL-6), tumor necrosis factor-α (TNF-α), and oxygen free radicals are known causative agents of cell necrosis and apoptosis. To prevent I/R injury, many investigators have suggested the inhibition of proinflammatory cytokines, stem-cell therapies, and drug-based therapies. Ischemic preconditioning (IPC) is a strategy used to prevent I/R injury. IPC is an experimental technique that uses short-term repetition of occlusion and reperfusion to adapt the area to the loss of blood supply. IPC can prevent I/R injury by inhibiting proinflammatory cytokine activity. Various stem cell applications have been studied to facilitate flap survival and promote angiogenesis and vascularization in animal models. The possibility of constructing tissue engineered flaps has also been investigated. Although numerous animal studies have been published, clinical data with regard to IPC in flap reconstruction have never been reported. In this study, we present various experimental skin flap methods, IPC methods, and methods utilizing molecular factors associated with IPC.

Keywords: biomaterial; inflammatory cytokine; ischemic preconditioning; skin flap; skin flap animal model; stem cell.

Figure 1

Skin flap procedure in rats. (A) Hair from the dorsal side of the rat was removed. (B) A 9 cm long red line originating at the level of the base of the scapulae was drawn on the dorsal midline. A rectangular area was drawn with its long edges parallel to and 1.5 cm away from the midline. (C) The skin was incised along the cranial and lateral lines of the rectangular area. (D) The skin flap was immediately re-attached in its original position and sutured with 4-0 nylon single stitches at 0.5 cm intervals. All experimental procedures were approved by the Institutional Animal Care and Use Committee of Seoul National University Bundang Hospital (BA1612-213/075-01).

Figure 2

The nuclear factor kappa B (NF-κB) signal and Inflammatory Factors in I/R injury. I/R injury factors enter the cytoplasm. Activated inhibitor of kappa B (IκB) kinase separates the NF-κB/IκB complex into NF-κB and IκB. Separated IκB is degraded in the cytoplasm, and the NF-κB dimer (RelA/p50) translocates to the nucleus. Within the nucleus, the NF-κB dimer (RelA/p50) binds to the DNA promoter of pro-inflammatory genes. Finally, pro-inflammatory transcription induces the expression of inflammatory cytokines such as tumor necrosis factor-α (TNF-α), interleukin (IL)-1, and IL-6.

Figure 3

Non-invasive ischemic preconditioning (IPC) in rats. Hind limb blood flow was occluded using a tourniquet at the inguinal level.