The Oxidation-Induced Autofluorescence Hypothesis: Red Edge Excitation and Implications for Metabolic Imaging

Endogenous autofluorescence of biological tissues is an important source of information for biomedical diagnostics. Despite the molecular complexity of biological tissues, the list of commonly known fluorophores is strictly limited. Still, the question of molecular sources of the red and near-infrared excited autofluorescence remains open. In this work we demonstrated that the oxidation products of organic components (lipids, proteins, amino acids, etc.) can serve as the molecular source of such red and near-infrared excited autofluorescence. Using model solutions and cell systems (human keratinocytes) under oxidative stress induced by UV irradiation we demonstrated that oxidation products can contribute significantly to the autofluorescence signal of biological systems in the entire visible range of the spectrum, even at the emission and excitation wavelengths higher than 650 nm. The obtained results suggest the principal possibility to explain the red fluorescence excitation in a large class of biosystems—aggregates of proteins and peptides, cells and tissues—by the impact of oxidation products, since oxidation products are inevitably presented in the tissue. The observed fluorescence signal with broad excitation originated from oxidation products may also lead to the alteration of metabolic imaging results and has to be taken into account

Dissection of the Deep-blue Autofluorescence Changes Accompanying Amyloid Fibrillation

Pathogenesis of numerous diseases is associated with the formation of amyloid fibrils. Extrinsic fluorescent dyes, including Thioflavin T (ThT), are used to follow the fibrillation kinetics. It has recently been reported that the so-called deep-blue autofluorescence (dbAF) is changing during the aggregation process. However, the origin of dbAF and the reasons for its change remain debatable. Here, the kinetics of fibril formation in model proteins were comprehensively analyzed using fluorescence lifetime and intensity of ThT, intrinsic fluorescence of proteinaceous fluorophores, and dbAF. For all systems, intensity enhancement of the dbAF band with similar spectral parameters (∼350 nm excitation; ∼450 nm emission) was observed. Although the time course of ThT lifetime (indicative of protofibrils formation) coincided with that of tyrosine residues in insulin, and the kinetic changes in the ThT fluorescence intensity (reflecting formation of mature fibrils) coincided with changes in ThT absorption spectrum, the dbAF band started to increase from the beginning of the incubation process without a lag-phase. Our mass-spectrometry data and model experiments suggested that dbAF could be at least partially related to oxidation of amino acids. This study scrutinizes the dbAF features in the context of the existing hypotheses about the origin of this spectral band

Hydrophobic Rose Bengal Derivatives Exhibit Submicromolar-to-Subnanomolar Activity against Enveloped Viruses

Rose Bengal (RB) is an anionic xanthene dye with multiple useful biological features, including photosensitization properties. RB was studied extensively as a photosensitizer, mostly for antibacterial and antitumor photodynamic therapy (PDT). The application of RB to virus inactivation is rather understudied, and no RB derivatives have been developed as antivirals. In this work, we used a synthetic approach based on a successful design of photosensitizing antivirals to produce RB derivatives for virus photoinactivation. A series of n-alkyl-substituted RB derivatives was synthesized and evaluated as antiviral photosensitizers. The compounds exhibited similar 1O2 generation rate and efficiency, but drastically different activities against SARS-CoV-2, CHIKV, and HIV; with comparable cytotoxicity for different cell lines. Submicromolar-to-subnanomolar activities and high selectivity indices were detected for compounds with C4-6 alkyl (SARS-CoV-2) and C6-8 alkyl (CHIKV) chains. Spectrophotometric assessment demonstrates low aqueous solubility for C8-10 congeners and a significant aggregation tendency for the C12 derivative, possibly influencing its antiviral efficacy. Initial evaluation of the synthesized compounds makes them promising for further study as viral inactivators for vaccine preparations