Reprogramming the Metabolome of Centella asiatica (L.) Urban Callus: Profiling of Newly Synthesized Cryptic Anthocyanins Triggered by LED Light Exposure

Centella asiatica L., a medicinal herb, has attracted substantial interest in research as well as commercial domains due to its bioactive compounds which include the pentacyclic triterpenoid centellosides, and in addition, hydroxy. In addition, hydroxycinnamic acid conjugates as well as flavonoids. The latter is the major class of secondary plant metabolites and comprises various subclasses, including anthocyanidins. Anthocyanins are rarely reported in extracts from C. asiatica and differ structurally due to a flavylium (2-phenylchromenylium) ion that carries a positive charge at the oxygen atom of the C-ring of the basic flavonoid structure. Callus of C. asiatica was initiated and propagated on synthetic media and subjected to different light regimes. White callus resulted from white fluorescent illumination, while purple callus developed in response to white light emitting diode (LED) illumination. To profile the metabolites responsible for the intense purple coloration, methanolic extracts were prepared from the two cell lines. Total phenolic, flavonoid, and anthocyanin content were determined and indicated (i) very low levels of flavonoids and anthocyanins in white callus and (ii) that anthocyanins dominate the flavonoid content of the purple callus. Extracts were subjected to untargeted ultra-high-performance liquid chromatography coupled to high-definition mass spectrometry (UHPLC–MS) to profile newly synthesized anthocyanins. Metabolite annotation was based on accurate mass determination and characteristic fragmentation patterns. Here, the reprogramming of the metabolome of white C. asiatica callus due to LED illumination is reported and the profiles of cryptic anthocyanins as well as putative flavonoid and caffeoylquinic acid co-pigments in purple callus are described.