Biological and phytochemical variation with pre- and post-harvest conditions for the Acanthus mollis L. leaf

Abstract

This study investigated for the first time the temporal variation of compounds and biological activities in Acanthus mollis leaves harvested during different seasons. Variables like the harvest date, edaphic-climatic conditions, storage, drying process, and extraction methods can potentially affect phytochemicals content, potentially influencing its safety and efficacy. The study was conducted over two consecutive years, and leaves were harvested at three different vegetative stages: early vegetation, pre-flowering, and flowering. The main non-volatile compounds in the harvested leaves' ethanol extracts were quantified using HPLC-PDA (High-Performance Liquid Chromatography with Photodiode Array Detection). Additionally, the antioxidant capacity of the extracts was evaluated using the DPPH (2,2-diphenyl-1-picrylhydrazyl) assay. Finally, the anti-inflammatory activity of the extracts on RAW 264.7 murine macrophages stimulated with LPS (lipopolysaccharide) was studied. Phytochemical analysis revealed different compounds crucial for identifying the most favorable harvesting season for Acanthus mollis. These compounds included DIBOA (2,4-dihydroxy-1,4-benzoxazin-3-one), HBOA (2-hydroxy-1,4-benzoxazin-3-one), and verbascoside. The concentration of these compounds varied depending on the vegetative state, with lower levels observed during the flowering season. During the initial vegetation stage, DIBOA emerged as the primary compound, gradually diminishing as the plant advanced through its vegetative state. Notably, the concentrations of both DIBOA and verbascoside exhibited a reverse correlation with temperature, rising as temperatures declined. Under elevated temperatures, humidity, and sun exposure, DIBOA is prone to degradation, while verbascoside, a phenylpropanoid, remains relatively stable in these conditions. It was found that the antioxidant activity of the leaves depends mainly on the amount of verbascoside, while the anti-inflammatory potential is primarily attributed to DIBOA. Verbascoside also showed a protective function against the cytotoxicity of the extracts in this study. Tyrosinase activity was affected by the levels of total benzoxazinoids and phenylpropanoids. Overall, this study elucidates the temporal variation of compounds in Acanthus mollis leaves harvested during different seasons, highlighting the importance of the quantification of specific compounds, such as DIBOA, HBOA, and verbascoside, for the selection of the most favorable harvesting season, and providing insights into the effects of temperature and environmental factors on the concentration of these compounds as well as their biological activities.