Effect of Curcumin Addition on the Adsorption and Transport of a Cationic Dye across DPPG-POPG Liposomes Probed by Second Harmonic Spectroscopy

Abstract

The effect of addition of curcumin on the adsorption and transport characteristics of a cationic dye, LDS, across negatively charged bilayers composed of POPG and DPPG lipids were investigated by the interface selective second harmonic (SH) spectroscopic technique. Curcumin induced changes in the SH electric field signal of the LDS ions (E (LDS)) were observed to depend critically on the bilayer acyl chain saturation/unsaturation ratio (S/U). Following earlier works, the increase in the E (LDS) signal is attributed to the release of the Na counterions present in the head group region of the bilayer by curcumin and the decay of the E (LDS) signal is attributed to the bilayer intercalated state of curcumin. While the changes observed in the E (LDS) signal in the presence of POPG liposomes were consistent with our earlier study ( Varshney, G. K. et al. Langmuir , 2016 , 32 , 10415 - 10421 ), they were significantly different for DPPG liposomes, following curcumin addition. While the increase in the E (LDS) signal in the presence of POPG liposomes, is marginal (∼10-20%) and instantaneous (<1 s) followed by a rapid decay (completed within ∼100 s), in the presence of DPPG liposomes it was observed to increase slowly and at saturation shows a substantial increase (100-200%), following curcumin addition. When liposomes consisting of a mixture of POPG and DPPG lipids are used, curcumin induced kinetic characteristics of the E (LDS) signal showed a mixture of the individual kinetic characteristics observed for the unsaturated (POPG) and saturated (DPPG) liposomes. The observed kinetic trends of the E (LDS) signal following curcumin addition are explained on the basis of the relative strength of the Na-POPG and Na-DPPG interaction. Higher ordering of the lipid acyl chain region in DPPG liposome makes the Na-DPPG interaction much stronger than the Na-POPG interaction. Further, it is proposed that, in POPG-DPPG liposomes, individual domains of POPG and DPPG lipids exist at low temperature as suggested by the observed temperature dependent kinetic characteristics of the E (LDS) signal following curcumin addition. These domains are dependent on the S/U ratio and phase state of the bilayer. The gel phase was observed to be more conducive for individual domain formation. Results presented in this work not only support the notion that biological activity of curcumin is associated with its bilayer altering properties, but more interestingly it provides a qualitative insight about how bilayer phase separation can be achieved by modulating the hydrophobic interactions between the lipid acyl chains.

Influence of Temperature on Molecular Adsorption and Transport at Liposome Surfaces Studied by Molecular Dynamics Simulations and Second Harmonic Generation Spectroscopy

“…Our SHG results here are also in general agreement with previous SHG studies where increased temperature leads to faster transport times. 15 , 16 Additionally, the obtained rate constants from the fits are shown to vary linearly as a function of MG concentration for each temperature, 11 , 35 and these corresponding slopes are observed to vary linearly with temperature, as shown in the Supporting Information . The linear dependence of the rate constant with respect to temperature is analogous to the related process of temperature-dependent diffusion described by the Stokes–Einstein equation.…”

“…Recent work has investigated the effect of temperature on molecular transport of small molecules through the liposome membrane. 15 , 16 However, a complete characterization of molecular adsorption and transport in lipid bilayer systems, including the associated kinetics and thermodynamics, has not been studied in detail.…”

Unveiling the Molecular Dynamics in a Living Cell to the Subcellular Organelle Level Using Second-Harmonic Generation Spectroscopy and Microscopy

“…These methods mainly depend on the lysis of living cells for the detection of molecular uptake or investigating the emitted signal from molecules in the cell sap to evaluate their interactions with the cell membranes. On the other hand, surface-sensitive second-harmonic generation (SHG) spectra have been widely used to study molecular adsorption and cross-membrane transport in vesicles − and living cells. − For example, Eisenthal’s group first studied the adsorption and transport of a dye molecule (malachite green, MG) on phospholipid bilayers using the SHG technique in 1988 . Kumal and co-workers investigated the molecular adsorption and transport in liposomes under the different buffer and salt conditions.…”

Determination of Bacterial Surface Charge Density Via Saturation of Adsorbed Ions

“…Likewise, both Gram-positive and Gram-negative cells have an interior CM which hinders the passive uptake of purely hydrophilic compounds. As demonstrated previously in numerous liposome based studies, (12)(13)(14)(15)(16)(17)(18)(19)) the MG cation is readily able to passively diffuse across phospholipid membranes. It is therefore reasonable that the MG cation should likewise cross the bacterial CM's of both Gram-positive and Gram-negative cells and at a comparable rate.…”

“…This characteristic mechanism has previously been employed to monitor molecular adsorption and transport across phospholipid membranes in biomimetic model liposomes (12)(13)(14)(15)(16)(17)(18)(19) and living cells. (20)(21)(22)(23)(24)(25)(26)(27)(28) When SHG-active molecules adsorb onto the exterior surface of the membrane, they align with one another due to the similarity of the interaction driving the adsorption process.…”