Investigating a novel hepatoprotective substance from ume extract (heated Japanese apricot juice concentrate). Part 1: Finding an active substance using a liver injury rat model

Background: The Japanese apricot (Prunus mume Sieb. et Zucc.) is popularly known as ume in Japan, and the heated concentrate of ume juice, called ume extract, is commonly consumed as food. A neutralized, diluted ume extract (dUE) reported as MK615 solution exhibits hepatoprotective properties. However, the active substance contributing to its hepatoprotective efficacies has not been explored. We aimed to identify and characterize the active substance underlying the hepatoprotective potential of ume extract. Our results are described in two parts and whereas the objective of this part (Part 1) was to identify the active substance, in Part 2, we elucidated its chemical structure. Methods: The components of ume extract were fractionated stepwise, and their hepatoprotective activities were evaluated using a D-galactosamine-induced liver injury rat model. The fractionated components were characterized qualitatively and quantitatively using high-performance liquid chromatography (HPLC) analysis and were dosed to rats, equalizing the content of the main components. Finally, a purified active substance was isolated by crystallization, and its hepatoprotective activity was verified. The molecular mass and formula of the active substance were elucidated by high-resolution mass spectrometry. Results: The dUE, but not the components from unheated ume juice concentrate, showed hepatoprotective activity. Focusing on the components peculiar to the ume extract, a fraction rich in a water-soluble substance, tentatively named unknown 1 (UK1), was found to have hepatoprotective activity. It was observed that both the UK1-rich fraction and dUE suppressed the hepatic expression of nitric oxide synthase 2 (Nos2). Furthermore, the purified UK1 (≥93.88% purity, containing 6.11% hydrate water) was demonstrated to have hepatoprotective activity comparable to that of dUE. UK1 has the molecular formula C10H11NO9, with a molecular weight of 289, corresponding to a novel compound. Conclusions: Our findings revealed that UK1, which is likely to be a previously unknown, bioactive component in ume extract, is the major hepatoprotective substance in dUE.