532-nanometer potassium titanyl phosphate (KTP) laser-induced expression of selective matrix metalloproteinases (MMP) in the rat larynx.

Abstract

The 532-nm KTP laser is clinically useful to induce benign vocal fold lesion regression without a fibrotic response. Previously, we described an in vivo model for KTP-induced injury in the rat larynx. This study uses this model to correlate the KTP-induced histologic and biochemical changes with the absence of long-term vocal fold fibrosis seen in clinical scenarios. In vivo. Unilateral vocal fold injury was induced via KTP laser at 10W (20mS pulse width) as described by our laboratory previously. Animals were subjected to serial endoscopic imaging from postoperative days 1 through 3. Animals were euthanized at 1 day, 4 weeks, and 12 weeks posttreatment and subjected to histologic analyses via hematoxylin and eosin and trichrome staining, as well as RT-PCR analyses for MMP-3, 9, transforming growth factor-beta (TGF-β), and COX-2 mRNA expression. Uninjured vocal folds were used as controls. Our study revealed gross healing of the vocal fold mucosa by 3 days posttreatment, and an immediate, moderate inflammatory infiltrate with no subsequent ultrastructural changes on histology. MMP-3 and COX-2 expression increased transiently, although no changes were seen in expression of MMP-9, an MMP involved in extracellular matrix remodeling, or TGF-β, a profibrotic cytokine. These data suggest that the KTP laser induces a modest inflammatory response, selective MMP expression, and no long-term fibrotic processes in a clinically relevant simulation.