Aggregation and inactivation of pancreatic cystatin by riboflavin-derived singlet oxygen and flavin triplet state: polyphenols as preventive agents

Caprine pancreatic thiol proteinase inhibitor (PTPI) a cystatin superfamily variant has high affinity for cysteine proteinases providing tight regulation of their proteolytic potential. Oxidative stress buildup in various pancreatic pathologies worsens the disease course often by disturbing the delicate balance between proteinases and their inhibitors. We aimed to study the effect of reactive oxygen species (ROS) on PTPI and to determine the potency of caffeic acid, curcumin and quercetin as agents against the inflicted damage. Fluorescence spectroscopy, polyacrylamide gel electrophoresis, and papain inhibitory assay revealed that photoilluminated riboflavin severely challenged the functional and structural integrity of the inhibitor. Three hundred and fifty micromolar affeic acid or quercetin prevented the damage. Curcumin, however, failed to reverse the changes completely. Conclusively, PTPI rendered dysfunctional by ROS may explain the increased necrotic damage to the host tissue. Also, dietary antioxidants can reverse the riboflavin-induced protein damage providing an economic and safe anti-ROS therapy.