Ricerc@Sapienza

Background: Polyphenolic compounds isolated from pomegranate fruit possess several pharmacological
activities including anti-inflammatory, hepatoprotective, antigenotoxic and anticoagulant activities. The
present work focuses the attention on PDIA3 interaction with punicalagin and ellagic acid, the most
predominant components of pomegranate extracts. PDIA3, a member of the protein disulfide isomerase
family involved in several cellular functions, is associated with different human diseases and it has the
potential to be a pharmacological target.
Methods: The interaction of polyphenols with PDIA3 purified protein was explored by fluorescence
quenching and calorimetric techniques and their effect on PDIA3 activity was investigated.
Results: A higher affinity was observed for punicalagin which also strongly affects PDIA3 reductase activity
in vitro as a non-competitive inhibitor. Isothermal titration calorimetry confirmed the high affinity
of punicalagin for PDIA3. Considering the PDIA3 involvement in oxidative cellular stress response
observed in neuroblastoma cells after treatment with hydrogen peroxide, a comparative study was
conducted to evaluate the effect of punicalagin on wild type and PDIA3-silenced cells. Punicalagin increases
the cell sensitivity to hydrogen peroxide in neuroblastoma cells, but this effect is drastically
reduced in PDIA3-silenced cells treated in the same experimental conditions.
Conclusions: Punicalagin binds PDIA3 and inhibits its redox activity. Comparative experiments conducted
on unsilenced and PDIA3-silenced neuroblastoma cells suggest the potential of punicalagin to modulate
PDIA3 reductase activity also in a biological model.
General significance: Punicalagin can be used as a new PDIA3 inhibitor and this can provide information
on the molecular mechanisms underlying the biological activities of PDIA3 and punicalagin.