Comparison of two functionalized fullerenes for antimicrobial photodynamic inactivation: Potentiation by potassium iodide and photochemical mechanisms

Abstract

A new fullerene (BB4-PPBA) functionalized with a tertiary amine and carboxylic acid was prepared and compared with BB4 (cationic quaternary group) for antimicrobial photodynamic inactivation (aPDI). BB4 was highly active against Gram-positive methicillin resistant Staphylococcus aureus (MRSA) and BB4-PPBA was moderately active when activated by blue light. Neither compound showed much activity against Gram-negative Escherichia coli or fungus Candida albicans. Therefore, we examined potentiation by addition of potassium iodide. Both compounds were highly potentiated by KI (1-6 extra logs of killing). BB4-PPBA was potentiated more than BB4 against MRSA and E. coli, while for C. albicans the reverse was the case. Addition of azide potentiated aPDI mediated by BB4 against MRSA, but abolished the potentiation caused by KI with both compounds. The killing ability after light decayed after 24 h in the case of BB4, implying a contribution from hypoiodite as well as free iodine. Tyrosine was readily iodinated with BB4-PPBA plus KI, but less so with BB4. We conclude that the photochemical mechanisms of these two fullerenes are different. BB4-PPBA is more Type 2 (singlet oxygen) while BB4 is more Type 1 (electron transfer). There is also a possibility of direct bacterial killing by electron transfer, but this will require more study to prove.

The Remarkable Effect of Potassium Iodide in Eosin and Rose Bengal Photodynamic Action against Salmonella Typhimurium and Staphylococcus aureus

“…Some research groups that studied the use of PSs with KI in aPDT stated that, when a PS is used in combination with KI, it is necessary to have lower PS concentration or lower light exposure than when used in non-combined strategies [15,36,[38][39][40][41][47][48][49]. The potentiated effect of RB by KI was studied in the photoinactivation of E. coli and S. aureus [36,41].…”

“…Some studies have shown that KI also enhances the effect of other PS classes [36,[38][39][40][47][48][49]. The potentiated effect of KI was observed for porphyrin-based PSs, Photofrin [40] and, for a formulation constituted by five cationic porphyrin derivatives [15], in the photoinactivation of gram-negative and gram-positive bacteria.…”

“…These reactions could produce free iodine ( pathway, as well as porphyrins. So, for these dyes this extra killing effect of KI is caused by several parallel reactions that initiates with the reaction of 1 O2 with KI [15,[36][37][38]40,41,49] (Figure 4). These reactions could produce free iodine (I2/I3 − ) and hydrogen peroxide (H2O2), that are stable species, as well as the short-lived reactive iodine radicals (I2 •− ).…”

An Insight Into the Potentiation Effect of Potassium Iodide on aPDT Efficacy

“…It has also been shown that different organic salts can improve the efficiency of aPDT against Gram-negative bacteria ( Huang et al, 2012 ; Kasimova et al, 2014 ). Recently, some studies have demonstrated that aPDT can be potentiated by addition of several different inorganic salts, such as sodium bromide ( Wu et al, 2016 ) sodium azide ( Huang et al, 2012 ; Kasimova et al, 2014 ), sodium thiocyanate ( St Denis et al, 2013 ) and potassium iodide ( Vecchio et al, 2015 ; Zhang et al, 2015 ; Freire et al, 2016 ; Huang et al, 2016 , 2017 , 2018a , c ; Hamblin, 2017 ; Reynoso et al, 2017 ; Wen et al, 2017 ). In fact, the addition of iodide has been shown to improve the efficiency of aPDT in several animal models of localized infection.…”

“…This approach was also efficient in aPDT of Gram-negative and Gram-positive bacteria mediated by Rose Bengal ( Wen et al, 2017 ) and fullerenes ( Huang et al, 2018b ). Interestingly, an anionic porphyrin in the presence of KI was able to photoinactivate E. coli ( Huang et al, 2018a ). The combination of MB and KI was also efficient to treat an urinary tract infection in a female rat model ( Huang et al, 2018c ).…”