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Abstract from Krister Grønliens lecture at symposium PDT-4. Human antimicriobial PDT. ESP-IUPB World Congress, Light & Life, Barcelona, Spain. August 25-30. 2019.

Natural deep eutectic solvents (NADES) is a group of eutectics that is based solely on environmental-friendly (“Green”) components. These solvents have unique solubilizing properties; i.e. they are more polar than water but can still dissolve highly lipophilic compounds such as aromatic heterocycles like porphyrins. Further, certain NADES possess antimicrobial properties and increase the phototoxicity of porphyrins against e.g. Gram -negative bacteria. Selected NADES are thereby suitable as solvents in antimicrobial photodynamic therapy (aPDT).

We have previously demonstrated that NADES can potentiate the phototoxic effect of the anionic porphyrin TCPP (4, 4’, 4’’, 4’’’-(porphine-5, 10, 15, 20-tetrayl) tetrakis benzoic acid) towards Gram-negative bacteria (1). The potentiating effect was dependent on the type of NADES. The present work includes a photostability study on TCPP in two relevant NADES of different pH but with comparable polarity and viscosity; choline chloride – xylitol (5:1) and malic acid – glucose – fructose (1:1:1).

The photodegradation was studied in undiluted NADES and in NADES diluted (1:1) in MilliQ water or PBS, respectively. The following parameters were investigated: reaction order, reaction rate constant, shelf-life, absorption and emission characteristics, and the relative potential to generate singlet oxygen.

The results demonstrate that the photoreactivity of TCPP was dependent on the type of NADES, the dilution factor and type of dilution medium. This emphasizes that a small modification of the formulation; e.g. change in dilution medium from water to PBS, can have an impact on the photochemical behavior of the drug molecule. The observed effects constitute essential information in the development of consumer products.

Reference:

Wikene, K.O., Rukke, H.V, Bruzell, E, Tønnesen, H.H.

Physicochemical characterisation and antimicrobial phototoxicity of an anionic porphyrin in natural deep eutectic solvents.

Eur. J. Pharm. Biopharm., 105, 75-84 (2016)

Grønlien was per August 2019 a Doctoral Research Fellow at Section for Pharmaceutics and Social Pharmacy at the University of Oslo, and collaborated with NIOM researchers Bruzell and Valen.