Fast and Effective Photodynamic Inactivation of Multiresistant Bacteria by Cationic Riboflavin Derivatives

Abstract

Photodynamic inactivation of bacteria (PIB) proves to be an additional method to kill pathogenic bacteria. PIB requires photosensitizer molecules that effectively generate reactive oxygen species like singlet oxygen when exposed to visible light. To allow a broad application in medicine, photosensitizers should be safe when applied in humans. Substances like vitamin B2, which are most likely safe, are known to produce singlet oxygen upon irradiation. In the present study, we added positive charges to flavin derivatives to enable attachment of these molecules to the negatively charged surface of bacteria. Two of the synthesized flavin derivatives showed a high quantum yield of singlet oxygen of approximately 75%. Multidrug resistant bacteria like MRSA (Methicillin resistant Staphylococcus aureus), EHEC (enterohemorrhagic Escherichia coli), Pseudomonas aeruginosa, and Acinetobacter baumannii were incubated with these flavin derivatives in vitro and were subsequently irradiated with visible light for seconds only. Singlet oxygen production in bacteria was proved by detecting its luminescence at 1270 nm. After irradiation, the number of viable bacteria decreased up to 6 log10 steps depending on the concentration of the flavin derivatives and the light dosimetry. The bactericidal effect of PIB was independent of the bacterial type and the corresponding antibiotic resistance pattern. In contrast, the photosensitizer concentration and light parameters used for bacteria killing did not affect cell viability of human keratinocytes (therapeutic window). Multiresistant bacteria can be safely and effectively killed by a combination of modified vitamin B2 molecules, oxygen and visible light, whereas normal skin cells survive. Further work will include these new photosensitizers for topical application to decolonize bacteria from skin and mucosa.

New photosensitizers for photodynamic therapy

“…Riboflavin has two peaks in the UVA (360 nm) and blue (440 nm) regions. Maisch et al [68] have synthesized a cationic version of riboflavin designed as an antimicrobial PS.…”

Antimicrobial photodynamic inactivation: a bright new technique to kill resistant microbes

“…Notable examples of the synthetic high activity compounds are the cationic zinc phthalocyanine RLP068 [30], the cationic phenalenone derivative known as SAPYR [31], and the porphyrin known as Sylsens B [32]. Examples of compounds derived from natural products are a cationic hypericin compound derived from St John's Wort [33], a cationic riboflavin compound derived from vitamin B2 [34], and a cationic derivative of curcumin (a yellow spice found in turmeric) known as SACUR-3 [35]. …”

Strategies to optimize photosensitizers for photodynamic inactivation of bacteria

“…Such a combination is used for photochemical inactivation of pathogens present in blood components like platelets concentrates [60]. To avoid the application of harzard UV new Vitamin B2 derivatives were synthesized to design safe (no broad UV irradiation) and effective photosensitizer to kill superbugs [61] (Fig. 5A).…”

“…These new synthesized flavin derivatives showed a high quantum yield of singlet oxygen of approximately 75%. Light-activation of these riboflavin-derivatives decreased the viable number of bacteria up to 6 log 10 steps of multi-resistant Superbugs (MRSA, EHEC, P. aeruginosa and A. baumanii) [61]. This new class of photosensitizer is considered safe in humans showing a great potential of bacterial killing without harming the adjacent tissue ('therapeutic window'), because decomposition of flavin [56]; and (C) (2-((4-pyridinyl)methyl)-1Hphenalen-1-one (SAPyR) [19].…”

“…(A) Riboflavin derivative FLASH-01a[61]. (B) Curcumin (1,7-bis-(4-hydroxy-3-methoxyphenyl)-hepta-1,6-dien-3,5-dione) existing in tautomeric forms, including a 1,3-diketo form (left) and two equivalent enol form (right, only one enol form is pointed)[66,68].…”