Anti-Inflammatory, Antibacterial, Anti-Biofilm, and Anti-Quorum Sensing Activities of the Diterpenes Isolated from Clinopodium bolivianum

This study reports for the first time the isolation of four diterpenoid compounds: 15-Hydroxy-12-oxo-abietic acid (<b>1</b>), 12<i>α</i>-hydroxyabietic acid (<b>2</b>), (-)-Jolkinolide E (<b>3</b>), and 15-Hydroxydehydroabietic acid (<b>4</b>) from <i>Clinopodium bolivianum</i> (<i>C. bolivianum</i>). The findings demonstrate that both the dichloromethane/methanol (DCMECB) extract of <i>C. bolivianum</i> and the isolated compounds exhibit significant anti-inflammatory (inhibition of NF-κB activation), antibacterial (primarily against Gram-positive bacteria), and anti-biofilm (primarily against Gram-negative bacteria) activities. Among the isolated diterpenes, compounds <b>3</b> and <b>4</b> showed notable anti-inflammatory effects, with IC₅₀ values of 17.98 μM and 23.96 μM for compound <b>3</b>, and 10.79 μM and 17.37 μM for compound <b>4</b>, in the HBEC3-KT and MRC-5 cell lines. Regarding their antibacterial activity, compounds <b>3</b> and <b>4</b> were particularly effective, with MIC values of 0.53-1.09 μM and 2.06-4.06 μM, respectively, against the <i>S. pneumoniae</i> and <i>S. aureus</i> Gram-positive bacteria. Additionally, these compounds demonstrated significant anti-biofilm and anti-quorum sensing activities, especially against Gram-negative bacteria (<i>H. influenzae</i> and <i>L. pneumophila</i>). We also explain how compound <b>3</b> (BIC = 1.50-2.07 μM, Anti-QS = 0.31-0.64 μM) interferes with quorum sensing due to its structural homology with AHLs, while compound <b>4</b> (BIC = 4.65-7.15 μM, Anti-QS = 1.21-2.39 μM) destabilises bacterial membranes due to the presence and position of its hydroxyl groups. These results support the traditional use of <i>C. bolivianum</i> against respiratory infections caused by both Gram-positive and Gram-negative bacteria. Furthermore, given the increasing antibiotic resistance and biofilm formation by these bacteria, there is a pressing need for the development of new, more active compounds. In this context, compounds <b>3</b> and <b>4</b> isolated from <i>C. bolivianum</i> offer promising potential for the development of a library of new, more potent, and selective drugs.