Content variability of bioactive secondary metabolites in Hypericum perforatum L.

St John's Wort (Hypericum perforatum L.; Hypericaceae) is a perennial medicinal herb widespread and largely used in folk medicine inside the Mediterranean basin. Many bioactive compounds have been identified within its extracts. Under a pharmacological point of view, the most important of them belong to the chemical classes of naphthodianthrones, phloroglucinols and polyphenols. Many factors have been claimed responsible for the phytochemical variability in Hypericum perforatum, such as genotype, geographical origin, harvesting stage and age of the plants. Yet, when harvested plant material is addressed to the industry, the standardization of the active ingredients over cultivation years is a crucial issue. With the aim to detect the stability over years and genotypes of several bioactive Hypericum compounds, seven Hypericum biotypes retrieved from different Italian geographical areas were cultivated in 2015 and 2016, and their aerial flowering parts were analyzed. Naphthodianthrones (hypericin and its biosynthetic precursors), phloroglucinols (hyperforin and adhyperforin), and main polyphenols were determined by HPLC-DAD analysis. The results were statistically evaluated through ANOVA, and the stability over cultivation years of the tested genotypes was assessed. In rather all the examined metabolites, the ANOVA revealed a remarkable effect of both factors "year" (Y) and "provenance" (P), but the occurrence of significant "Y x P" interactions evidenced that the effect of climatic variability was often different according to the genotype. The evaluation of the stability level between years evidenced that only one biotype out of seven exhibited constantly higher-than-average amounts of rather all identified metabolites.