Fullerol in human lens and retinal pigment epithelial cells: time domain fluorescence spectroscopy and imaging

Abstract

Fullerol is a fullerene derivative that is extensively hydroxylated [nano-C₆₀(OH)₂₄] and this makes it water-soluble. These fullerene derivatives have shown promise as drug carriers that bypass ocular barriers but fullerols are also potentially phototoxic to human lens and retinal tissues. Fluorescence imaging is a powerful and non-invasive means of probing nanoparticles in biological systems. However, fullerol nanoparticles have a very low level of fluorescence and have not as yet been imaged in vitro and in vivo. Using specialized measurements including time-correlated single photon counting (TCSPC), fullerol fluorescence was determined in aqueous solutions and detected in both human lens and retinal pigment epithelial cells. Time-resolved fluorescence of fullerol (5–200 μM) was characterized in aqueous environment, where the fluorescence decay is best fitted with three lifetimes (3 ns, 0.7–0.9 ns and 0.2 ns). Time-resolved microspectrofluorimetry and time-gated fluorescence imaging were performed on both human lens and retinal pigment epithelial cells incubated with increasing fullerol doses (5–500 μM and 5–50 μM, respectively). Upon increasing concentration, we observe some shortening of the lifetimes, a reduction in the relative amplitude of the shortest-living component and a corresponding increase in the weight of the intermediate-living species. Time-gated imaging of fullerol fluorescence provided information on its intracellular distribution that correlates with progressive cell damage. Therefore time-gated imaging may potentially be used as a means to investigate fullerol distribution and toxicity in the human lens and retina in vivo.