MMP9 and periodontitis: Furthermore, in a ligation-induced periodontitis experiment in rats, Kuo Po-Jan et al. (2017) found that gingival TNF-α and IL-6, along with IL-1β, inducible nitric oxide synthase expression, and Matrix metallopeptidase 9 (MMP-9), were modulated by intragastrically administered carvacrol [37].