Abstract
Cyanine fluorescent dyes are attractive diagnostic or therapeutic agents due to their excellent optical properties. However, in free form, their use in biological applications is limited due to the short circulation time, instability, and toxicity. Therefore, their encapsulation into nano-carriers might help overcome the above-mentioned issues. In addition to indocyanine green (ICG), which is clinically approved and therefore the most widely used fluorescent dye, we tested the structurally similar and cheaper alternative called IR-820. Both dyes were encapsulated into liposomes. However, due to the synthetic origin of liposomes, they can induce an immunogenic response. To address this challenge, we proposed to use erythrocyte membrane vesicles (EMVs) as “new era” nano-carriers for cyanine dyes. The optical properties of both dyes were investigated in different biological relevant media. Then, the temperature stability and photo-stability of dyes in free form and encapsulated into liposomes and EMVs were evaluated. Nano-carriers efficiently protected dyes from thermal degradation, as well as from photo-induced degradation. Finally, a hemotoxicity study revealed that EMVs seem less hemotoxic dye carriers than clinically approved liposomes. Herein, we showed that EMVs exhibit great potential as nano-carriers for dyes with improved stability and hemocompatibility without losing excellent optical properties.
Highlights
Cyanine fluorescent dyes are widely used as diagnostic or therapeutic agents
Due to the limited solubility of dyes in phosphate-buffered saline (PBS), 0.9% saline, and blood plasma, Indocyanine green (ICG) and IR-820 were first dissolved in ultrapure water to obtain a dye concentration pf 0.5 mg/mL and diluted further with PBS, 0.9% saline, or blood plasma to reach working solutions in the concentration range of 1–50 μg/mL
Control (PBS only), dyes in PBS (1–50 μg/mL), empty liposomes, empty erythrocyte membrane vesicles (EMVs), and dye-loaded liposomes and EMVs were incubated with 5 vol.% of erythrocytes in PBS for 3 h at 37 ◦C with constant orbital shaking in 1.5 mL tubes (Eppendorf, Germany; volume of samples 1 mL; all samples in triplicate)
Summary
Cyanine fluorescent dyes are widely used as diagnostic or therapeutic agents. Indocyanine green (ICG) is a tricarbocyanine dye that absorbs and emits in the near-infrared (NIR) region of the spectrum (peak spectral absorption at about 800 nm) and has small absorption in the visible range [1]. Due to its optical properties, ICG is a contrast agent commonly used for in vivo cardiovascular fluorescence imaging and NIR optical imaging for intervention in cases of lymphatic abnormalities [3,4] It was clinically approved in 1959 by the Food and Drug Administration but was widely used during the Second World War for fluorescence-aided surgery [5,6]. Despite excellent imaging and clearance properties (ICG follows an almost entirely bile juice route for clearance and has no known metabolites [10]), there are some concerns about its safety in limited applications The latter is the case of retinal toxicity [11] arising from decreased mitochondrial activity while exposed to a light source, while increasing DNA synthesis. Omer peak position for ICG and IR-820 in plasma was 794 and 840 nm, respectively
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