Background: Glycogen phosphorylase (GP) is a pharmaceutical target for the
discovery of new antihyperglycaemic agents. Punica granatum is a well-known plant for
its potent antioxidant and antimicrobial activities but so far has not been examined for antihyperglycaemic
Objective: The aim was to examine the inhibitory potency of eighteen polyphenolic extracts
obtained from Punica granatum fruits and industrial juicing byproducts against GP
and discover their most bioactive ingredients.
Method: Kinetic experiments were conducted to measure the IC50 values of the extracts
while affinity crystallography was used to identify the most bioactive ingredient. The inhibitory
effect of one of the polyphenolic extracts was also verified ex vivo, in HepG2 cells.
Results: All extracts exhibited significant in vitro inhibitory potency (IC50 values in the
range of low μg/mL). Affinity crystallography revealed that the most bioactive ingredients
of the extracts were chlorogenic and ellagic acids, found bound in the active and the inhibitor
site of GP, respectively.While ellagic acid is an established GP inhibitor, the inhibition
of chlorogenic acid is reported for the first time. Kinetic analysis indicated that chlorogenic
acid is an inhibitor with Ki=2.5 x 10-3Mthat acts synergistically with ellagic acid.
Conclusion: Our study provides the first evidence for a potential antidiabetic usage of
Punica granatum extracts as antidiabetic food supplements. Although, more in vivo studies
have to be performed before these extracts reach the stage of antidiabetic food supplements,
our study provides a first positive step towards this process.