The combined effects of ascorbic acid and bovine serum albumin on phototransformations of hematoporphyrin derivative in aquaeous medium: Absorption and EPR spectroscopy study

Abstract

There is a constant interest to increase the efficacy of photosensitized therapy by combining it with other modalities in order to boost the oxidative stress in tumour tissues, and L-ascorbic acid (AscA) could serve as a potential candidate. The photoinduced transformations of a hematoporphyrin-type photosensitizer (HpDiA) were chosen as a model system to monitor the effects of AscA on oxygen-dependent photoreactions in aqueous model solutions of different pH. Additional data on the role of the ascorbate radical in photoreactions initiated by HpDiA, as well as on the mutual activity in samples containing bovine serum albumin (BSA), including participation in Type I reactions, were obtained performing electron paramagnetic resonance (EPR) spectroscopy measurements, done on the mixed aqueous solutions poured into capillary tubes of a carefully selected diameter, both in the dark and under illumination with a laser beam in the absence of additional trapping molecules. A strong interaction between BSA and porphyrins was determined as a main factor in the observed photoreactions, not only boosting the photooxidation and photoreduction pathways, but also leading to the enhanced photoactivity in combination with AscA, especially, in the acidic medium.