The Natural Phloroglucinol α-Pyrone Arzanol Protects HaCaT Keratinocytes from Lipopolysaccharide and Polyriboinosinic-Polyribocytidylic Acid-Induced Damage and Promotes Reparative Mechanisms

The protective effect of arzanol, a natural prenylated phloroglucinol α-pyrone from the Helichrysum microphyllum subsp. tyrrhenicum, was investigated in HaCaT keratinocytes exposed to two inflammatory stimuli: lipopolysaccharide (LPS, 0.5–75 µg/mL), a component of gram-negative bacteria, and polyriboinosinic-polyribocytidylic acid (poly I:C, 0.5–50 µg/mL), a synthetic viral RNA analog. LPS and poly I:C significantly decreased HaCaT cell viability (18–93% reduction in the 5–75 μg/mL LPS range and 25% at 50 μg/mL poly I:C, MTT assay) and increased apoptosis and cell death (NucView 488 and propidium iodide assay) after 3 h and 24 h of exposure. Arzanol (1 h of pre-incubation, 5–25 μM) showed a significant protective effect against LPS and poly I:C-induced damage, preserving cell viability (25% of viability increase at 5 μg/mL LPS concentration, and 30% at 50 μg/mL of poly I:C) and decreasing apoptosis/cell death. Western blot analysis demonstrated the ability of arzanol (5 μM) to reduce the apoptotic protein Bax and the inflammatory cytokine IL-1β levels in HaCaT keratinocytes exposed for 3 h to 5 and 10 μg/mL LPS. Moreover, scratch assay showed the arzanol reparative effect on HaCaT cells. Our results qualified arzanol as a protective drug for dermatological applications in human skin diseases.