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


  • Accepted for Podium Presentation at the Combined Otolaryngology Spring Meeting; American Laryngological Association, Las Vegas, NV, April 2010.

  • The authors have no financial interests to disclose for this article.

  • §

    The authors have no conflicts of interest to declare.



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.

Study Design:

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. Laryngoscope, 2011