Coumarin 6 as a fluorescent model drug: How to identify properties of lipid colloidal drug delivery systems via fluorescence spectroscopy?

Abstract

In the development of colloidal lipid drug delivery systems (DDS), the localization of the drug within the DDS, the protective potential of the DDS as well as the compatibility of the drug with the excipients are of special interest. In this study, Coumarin 6 (C6), a fluorescent dye frequently used to facilitate the traceability of DDS in vitro, is demonstrated as a tool to gain insight into the aforementioned properties by fluorescence spectroscopy. Both ways of loading C6 to solid colloidal DDS (pre‐loading to the lipid matrix or post‐loading to the ready DDS after its processing) led to a localization of C6 in the interfacial layer between solid lipid nanoparticles (SLN) and aqueous medium. In the case of pre‐loading, C6 is homogenously distributed in emulsion droplets and expelled from the lipid matrix due to crystallization. Nanoemulsions distributed C6 in the liquid lipid matrix itself and cause a hypsochromic shift of fluorescence spectra. Larger surface areas of emulsion droplets due to smaller droplet sizes displayed more interaction of C6 with the aqueous phase as a bathochromic shoulder in fluorescence spectra. Measured fluorescence intensity was linearly dependent on light scattering of colloidal DDS of the same excipients. A simple method to evaluate the protective properties of DDS was presented and displayed that (i) nanoemulsions provide more protection compared with SLN and (ii) higher phospholipid concentration improve the protection within SLN. Practical applications: In the development of colloidal DDS, it is important to identify the localization and distribution of a (model) drug in compartments within the disperse system. The simple approach by fluorescence spectroscopy presented in this study supplies information about the localization of drug substances with properties comparable with the fluorescent probe used. The results assist formulation development as a quick screening tool to elucidate (i) the localization of the probe, (ii) the microenvironment of the probe (e.g., differentiation of the physical state of the disperse phase), and (iii) the protection of the probe against damaging agents from the aqueous phase. The fluorescent dye Coumarin 6 was applied as model drug in colloidal lipid drug delivery systems. Fluorescence spectroscopy proved able to identify the localization of the model compound, the physical state of the dispersed phase, and the protective potential of the DDS, especially dependent on phospholipid concentration.

Nanoemulsions as Delivery Systems for Poly-Chemotherapy Aiming at Melanoma Treatment

“…Despite the different fluorescence intensities of the formulations under study, in comparison to untreated cells, significantly higher integrated mean fluorescence intensity (iMFI) values were measured in both the cell lines, indicating a fast internalization of lipid droplets and loaded drugs. 6-Coumarin was chosen as fluorescent probe for the IL lipid matrix [19,20]. Instead, internalization of RAP and BVZ loaded in IL was investigated, after fluorescent labelling, because of their different physico-chemical properties.…”

Synthesis of 2-Alkenyl-2H-indazoles from 2-(2-Carbonylmethyl)-2H-indazoles

“…Recently, 2-aryl-2 H -indazoles have been identified as a new class of fluorescent compounds [15]. In addition, coumarin derivatives have been widely studied and utilized as fluorescent probes in living cells [23,24,25,26]. We envisioned that coumarin-substituted 2 H -indazoles 6 (Scheme 4, Equation (2)) possessing a planar, rigid π-conjugated system might display interesting luminescent behavior.…”

Coumarins into Polyurethanes for Smart and Functional Materials

“…Coumarin 6 (C6) dye was also used as a fluorescent probe for monitoring the drug entrapping and delivery efficiency of enzyme azo-polyurethane nanoparticles [97]. Coumarin 6 (C6) is frequently used as a fluorescent hydrophobic drug model to trace drug delivery systems via fluorescence spectroscopy [98]. Besides, efficient colon-specific drug delivery systems as effective mechanisms to treat inflammatory bowel disease (IBD) are a challenging objective that is gaining increased importance [99][100][101].…”