Gnetol: Uncovering the Therapeutic Potential of an Underexplored Natural Stilbenoid

Gnetol (trans-3,5,2′,6′-tetrahydroxystilbene) is a naturally occurring tetrahydroxylated stilbenoid found mainly in Gnetum species. Despite its structural similarity to resveratrol (trans-3,5,4′-trihydroxystilbene), gnetol remains comparatively underexplored, and its therapeutic potential has yet to be clearly defined. This review critically evaluates the current knowledge of its natural occurrence, chemistry, pharmacological activities, molecular mechanisms, pharmacokinetics, metabolism, and tissue distribution, with particular attention to the relationship between biological activity and in vivo exposure. Available studies suggest that gnetol has a broad pharmacological profile involving cardiovascular protection, inflammation, metabolic regulation, melanogenesis, neuroprotection, cancer-related processes, and bone remodeling. However, cardioprotective and bone-related effects currently have stronger experimental support from animal studies, whereas most other activities remain supported primarily by biochemical or cellular evidence. Recent mechanistic studies have further implicated redox regulation, ferroptosis, iron homeostasis, and direct enzyme modulation in its biological actions, with context-dependent effects on ferroptosis in cardiomyocytes and osteoclasts. Gnetol undergoes extensive glucuronidation and exhibits low systemic bioavailability as the unchanged compound following oral administration, although the contributions of incomplete absorption, luminal degradation, and microbial metabolism remain incompletely understood. A mouse study reported relatively high concentrations in gastrointestinal samples, but residual luminal contents may have contributed to these measurements. Moreover, measured tissue concentrations do not necessarily reflect pharmacologically available unbound concentrations, and exposure at effective doses remains poorly characterized. Future studies should therefore integrate molecular activity with target-site exposure, metabolite contributions, dose–response relationships, safety, and route of administration to identify the most plausible therapeutic applications of gnetol.