Description: <p><b>Usnic Acid</b></p>
<p><b>Recommended Abbreviation:</b> UA</p>
<p><b>Type:</b> Natural product / lichen secondary metabolite / dibenzofuran derivative</p>
<p><b>Source:</b> Usnic acid is a secondary metabolite produced by several lichen genera, including <i>Usnea</i>, <i>Cladonia</i>, <i>Lecanora</i>, and related species. It occurs naturally as (+)- and (-)-usnic acid enantiomers.</p>
<p><b>Function:</b> Usnic acid exhibits antimicrobial, anti-inflammatory, antioxidant, antiviral, antiparasitic, photoprotective, and experimental anticancer activities. Its biological effects involve mitochondrial function, oxidative stress, apoptosis, inflammatory signaling, and cellular metabolism.</p>
<p><b>Cancer:</b> Usnic acid has demonstrated preclinical anticancer activity in multiple cancer models, including proliferation ↓, tumor-cell viability ↓, apoptosis ↑, mitochondrial dysfunction ↑, and modulation of oxidative-stress and survival pathways. Its anticancer activity remains predominantly experimental, and toxicity may limit systemic therapeutic use.</p>
<p><b>Neuroprotection:</b> Experimental studies indicate antioxidant and neuroprotective activity, including Nrf2-associated cytoprotective responses and protection against oxidative and ischemic neuronal injury. Direct evidence for Alzheimer's disease is not sufficiently established to assign a specific Alzheimer's disease direction.</p>
<p><b>Safety:</b> Usnic acid has a significant hepatotoxicity concern, particularly with systemic or oral exposure at higher doses. Human cases of severe liver injury, including acute liver failure requiring transplantation, have been reported with usnic-acid-containing weight-loss supplements. Mitochondrial dysfunction and oxidative stress are important mechanisms implicated in its hepatotoxicity.</p>