Structural constraints and importance of caffeic acid moiety for anti-hyperglycemic effects of caffeoylquinic acids from chicory

SCOPE: Chicory (Cichorium intybus L.) is a perennial herb often consumed as a vegetable, whereas the ground and roasted roots are blended as a coffee substitute. Caffeoylquinic or chlorogenic acids (CQA), the abundant intermediates of lignin biosynthesis in chicory, have been reported to improve glucose metabolism in humans, but the functional group in their structure responsible for this effect has not been yet characterized.

METHODS AND RESULTS: Here, we showed that three di-O-caffeoylquinic acids suppressed hepatic glucose production in H4IIE rat hepatoma cells by reducing expression of glucose-6-phosphatase (G6Pase) and phosphoenolpyruvate carboxykinase (PEPCK), two key enzymes that regulate hepatic gluconeogenesis. Direct comparisons between CQAs and their metabolites (3-caffeoylquinic, caffeic, and quinic acids) revealed the caffeic acid moiety alone was responsible for the observed effects. Further analysis suggested the activation of PI3K and MAPK pathways as a method of controlling gene expression was shared between caffeoylquinic and caffeic acids. These compounds promoted increased mitochondrial respiration and cellular metabolism, in part by inducing oxidative phosphorylation and proton leak.

CONCLUSION: We concluded that the caffeic acid moiety was important for suppression of hepatic gluconeogenesis and hyperglycemia, ultimately strengthening the link between dietary interventions based on caffeic acid-containing plant foods and healthy glucose metabolism.