In response to the World Health Organization’s (WHO) call to develop alternative antibacterial methods, we investigate endogenous compounds and biopolymers. Lumichrome (LC) is an endogenous, lipophilic degradation product of riboflavin (vitamin B2) that can act as a photosensitizer for antimicrobial applications. LC is also a photocrosslinker of collagen. Crosslinked collagen hydrogels were prepared with two types of cyclodextrins (CDs), namely (2-hydroxypropyl)-β-CD (HPβCD) and -γ-CD (HPγCD), to improve the aqueous solubility of LC. The release of LC from the collagen gels and the phototoxic effect of UVA-irradiated LC against planktonic Staphylococcus (S.) aureus were investigated. Irradiation of LC hydrogels complexed with either CD resulted in similar levels of bacterial death despite the HPγCD gels containing half the LC concentration of the HPβCD gels. This effect may be explained by the higher complexation efficiency and stability of the LC-HPβCD complex, slowing down the LC release. Following treatment, small colony variants of S. aureus were observed. The study is a proof of concept of the release and phototoxic effects of an endogenous photocrosslinker embedded in a biopolymer as a sustainable antibacterial alternative to conventional therapy of, e.g., infected wounds.

Bacterial phototoxicity of lumichrome photocrosslinked collagen hydrogels
Grønlien KG, Valen H, Pain M, Bruzell E, Tønnesen HH.
Sustainable Chemistry and Pharmacy, Volume 31