Tetrahydrocurcumin (THC) is one of the major metabolites of curcumin (CUR), an ancient bioactive natural polyphenolic compound. This research article describes both the solid and liquid state characterization of THC using advanced spectroscopic and thermo-analytical techniques. Anti-inflammatory, anti-oxidant, and neuroprotective activities of THC were investigated using in vitro cell lines. Liquid chromatography-mass spectrometry analysis revealed that our sample comprised 95.15% THC, 0.51% tetrahydrodemethoxycurcumin (THDC), 3.40% hexahydrocurcumin, and 0.94% octahydrocurcumin. Gas chromatography-mass spectrometry analysis indicated the presence of 96.68% THC and 3.32% THDC. THC in solution existed as keto-enol tautomers in three different forms at different retention time, but the enol form was found to be dominant, which was also supported by nuclear magnetic resonance analysis. THC was thermally stable up to 335.55 °C. THC exhibited more suppression of cytokines (TNF-α, IL-1β, and MIP-1α) than CUR in a concentration-dependent manner in mouse splenocytes, while NK-cell and phagocytosis activity was increased in macrophages. THC showed a significant reduction of free radicals (LPO) along with improved antioxidant enzymes (SOD and catalase) and increased free radical scavenging activity against ABTS⁺ radicals in HepG2 cells. THC displayed higher protection capability than CUR from oxidative stress and neuronal damage by improving cell viability against H₂O₂ induced HepG2 cells and MPP⁺ induced SH-SY5Y cells, respectively, in a concentration-dependent manner. Thus, a variation of the biological activities of THC might rely on its keto-enol form and the presence of other THC analogs as impurities. The present study could be advantageous for further research on THC for better understanding its physicochemical properties and biological variation.

四氢姜黄素 (THC) 是姜黄素 (CUR) 的主要代谢物之一，姜黄素是一种古老的生物活性天然多酚化合物。这篇研究文章使用先进的光谱和热分析技术描述了 THC 的固态和液态表征。使用体外研究了 THC 的抗炎、抗氧化和神经保护活性细胞系。液相色谱-质谱分析表明，我们的样品包含 95.15% THC、0.51% 四氢去甲氧基姜黄素 (THDC)、3.40% 六氢姜黄素和 0.94% 八氢姜黄素。气相色谱-质谱分析表明存在 96.68% THC 和 3.32% THDC。溶液中的四氢大麻酚在不同的保留时间以三种不同形式的酮-烯醇互变异构体存在，但发现烯醇形式占优势，这也得到核磁共振分析的支持。THC 在高达 335.55 °C 时具有热稳定性。THC 在小鼠脾细胞中表现出比 CUR 更多的细胞因子（TNF-α、IL-1β 和 MIP-1α）抑制，且呈浓度依赖性，而巨噬细胞中 NK 细胞和吞噬活性增加。⁺ HepG2 细胞中的自由基。THC 通过分别以浓度依赖性方式提高对 H ₂ O ₂诱导的 HepG2 细胞和 MPP ⁺诱导的 SH-SY5Y 细胞的细胞活力，显示出比 CUR 更高的氧化应激和神经元损伤保护能力。因此，THC 生物活性的变化可能取决于其酮-烯醇形式和其他 THC 类似物作为杂质的存在。本研究可能有利于进一步研究四氢大麻酚，以更好地了解其理化性质和生物学变异。