Nanocomplex formation between riboflavin and β-lactoglobulin: Spectroscopic investigation and biological characterization

• We investigate the interaction between β-lactoglobulin (βlg) and riboflavin (RF).
• We demonstrate the formation of the βlg/RF nanocomplex.
• The interaction causes minor impact on the structure of βlg.
• The βlg/RF nanocomplex can be used in photodynamic therapy.
• The βlg/RF nanocomplex has potential in food industry and biomedical sciences.

Light activated drug delivery systems with the use of photosensitizers are attracting increasing interest in both the medical and non-medical fields. Riboflavin (RF) is an endogenous photosensitizer that interacts with proteins located in the cell membrane and induces damages to biological systems including tumor tissues. Spectroscopic methods were used to demonstrate interaction and energy transfer between β-lactoglobulin (βlg), the major bovine milk protein, and RF. The findings reveal the formation of a ground-state nanocomplex between βlg and RF with minor impact on the structure of the protein. βlg can bind and transport RF, which has great implications for the food industry in terms of food fortification. The impact of these interactions on RF was determined by assessing the anti-proliferative activity of the βlg/RF nanocomplex by irradiating skin melanoma cancer cell lines with UV-A light according to the NCI/NIH Developmental Therapeutics Program. The βlg/RF nanocomplex exhibited important anti-proliferative activity in the micromolar range. The cytotoxicity is likely due to the generation of reactive radical and oxygen species as the result of the interaction between RF and βlg. This study provides important information on the potential use of the βlg/RF nanocomplex in photodynamic therapy, which is applied in the medical field against tumor cells as well as in the food industry against food-borne pathogens.