Effect of polyvinylpyrrolidone on the interaction of chlorin e6 with plasma proteins and its subcellular localization

A photophysical study describing the effects of the polymer polyvinylpyrrolidone (PVP), on the binding interaction between chlorin e6 (Ce6) with bovine serum albumin (BSA) and human plasma proteins such as very low-density lipoprotein (VLDL), high-density lipoprotein (HDL) and low-density lipoprotein (LDL) was performed using a steady-state fluorescence technique. Combined Ce6–PVP was found to have very stable photostability at three different temperatures (4 °C, 21 °C and 37 °C) when dissolved in an aqueous solution containing 5% and 10% fetal calf serum. The partition coefficient of combined Ce6–PVP was relatively more hydrophilic than that of Ce6 alone. There was a marked increase in the emission profile of Ce6–PVP and the correlated bathochromic shift on the addition of proteins. These results also suggest that Ce6–PVP might have slightly greater association energy with VLDL in comparison to Ce6 alone. The co-localization of Ce6 and Ce6–PVP in cells was also assessed using confocal microscopy. The association of Ce6 with PVP resulted in an enhanced cellular uptake of Ce6 within the cytoplasmic compartment of cells. The present study supported the hypothesis that PVP improves the permeability of Ce6 through the biological membranes of cells.

MGH cells were incubated with PVP-FITC (green) and co-stained with (A) rhodamine phalloidin (red) and (B) DAPI (blue). Cells were also incubated with (C) Ce6 (red) and (D) Ce6-PVP (red) and co-stained with rhodamine phalloidin (yellow). Cellular uptake of Ce6-PVP was observed to be higher compared to that of Ce6, implying that PVP may increase the rate of membrane transport of Ce6 in the cells.