This study aimed at evaluating the antiproliferative, antibacterial, and anti-inflammatory properties of an ethanolic myrtle extract (Myrtacine®) in vitro, characterising its potential active compounds (myrtucommulones A and B') by structural analysis, and evaluating their biological activity. Antiproliferative activity was assessed by the BrdU incorporation assay in HaCat keratinocytes and inhibitory and bactericidal activities against P. ACNES strains by measuring the minimal inhibitory concentration (MIC) and D value. Anti-inflammatory effect was evaluated by measuring 6-keto-prostaglandin F1 α and [³H]-arachidonic acid metabolite production in keratinocytes stimulated for inflammation. Myrtacine® inhibited keratinocyte proliferation by 27 % and 76 % at 1 and 3 µg/mL, respectively (p < 0.001). A comparable effect, though less marked, was observed with 5 µg/mL myrtucommulones A and B' (-36 % and -28 %, respectively). Myrtacine® inhibited erythromycin-sensible and -resistant P. ACNES strains growth with MICs of 4.9 µg/mL and 2.4 µg/mL, respectively. Myrtucommulone B' and myrtucommulone A displayed a similar inhibitory activity against both strains (for both strains, MIC = 1.2 µg/mL and about 0.5 µg/mL, respectively). At 3 and 10 µg/mL, Myrtacine® significantly decreased all metabolite production from cyclooxygenase (81 % and 107 %, p < 0.0001) and lipoxygenase (52 % and 95 %, p < 0.001) pathways. Finally, Myrtacine® exhibited a concentration-dependent anti-lipase activity at 100 µg/mL and 1 mg/mL, as it decreased lipase activity by respectively 53 % and 100 % (p < 0.01 for both). In conclusion, in vitro, Myrtacine® demonstrated antiproliferative, antibacterial, and anti-inflammatory properties that may be of value to exert a global action in the treatment of acne lesions.
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