Supporting Information. Evaluating the Cell Membrane Penetration Potential of Lipid- Soluble Compounds using Supported Phospholipid Bilayers

Transcription

1 Supporting Information Evaluating the Cell Membrane Penetration Potential of Lipid- Soluble Compounds using Supported Phospholipid Bilayers ANDREAS WARGENAU *, SEBASTIAN SCHULZ, ARSHAM HAKIMZADEH, and NATHALIE TUFENKJI Department of Chemical Engineering, McGill University, Montreal, Quebec H3A 0C5, Canada * Corresponding Author. Phone: (514) ; Fax: (514) ; andreas.wargenau@mail.mcgill.ca S-1

2 Materials and Methods 1. SUV Production Chloroform solutions of 1,2-dimyristoyl-sn-glycero-3-phosphocholine (DMPC) were purchased from Avanti Polar Lipids (Alabaster, AL) and stored at -20 C. 1.5 mg DMPC were dried under a stream of nitrogen and placed in a vacuum desiccator for 3 h. Dried lipids were subsequently suspended in 1.5 ml of 10 mm Tris buffer (ph 7.5, 100 mm NaCl) and allowed to hydrate for 1 h at 40 C. SUVs were obtained by extruding the resultant vesicle suspensions using a Mini-Extruder from Avanti Polar Lipids. Vesicles were extruded for 11 cycles through polycarbonate membranes of 100 nm and 30 nm pore diameter (Whatman Nuclepore Track-Etched Membranes, GE Healthcare, Little Chalfont, UK). During this process, the sample temperature was consistently maintained at ~ 40 C. Final SUV suspensions were stored at 4 C and used within 7 days. 2. QCM-D Experiments QCM-D experiments were performed with a Q-Sense E1 QCM-D (Biolin Scientific, Gothenburg, Sweden) and silica-coated QCM-D crystals (QSX303, Q-Sense). The QCM-D crystals were cleaned using the following three steps: (i) 20 min of sonication in 2 % sodium dodecyl sulfate (SDS), (ii) 20 min of sonication in ethanol, and (iii) 20 min of UV treatment in a UV/ozone cleaner. After the cleaning, crystals were placed inside the QCM-D flow module and temperature equilibrated in the presence of stagnant Tris (10 mm, 100 mm NaCl). 10 mm Tris buffer containing 100 mm NaCl was used as a reference and background medium in all QCM-D experiments. The buffer was adjusted to ph 7.5 and filtered through a pre-rinsed Millex-VV 0.1 µm syringe filter (MilliporeSigma, Burlington, MA). Dissolution of 20 mm gallic acid, vanillin, and protocatechualdehyde in the Tris buffer resulted in ph values of 3.2, 6.2, and 6.1, respectively. Under these conditions, ~ 90 % of the phenolic compounds were present in their protonated forms. SPBs were formed and exposed to the phenolic compounds as described in the results and discussion section of the main article. During both steps, the fluid flow was kept constant at 0.2 ml/min. Temperature scans were performed under stagnant conditions. In the course of a full cooling/heating cycle, the temperature inside the QCM-D chamber was decreased from 28 C to 15 C (-0.3 C/min), maintained at 15 C for 30 min, and then increased back to 28 C (0.3 C/min). To convert the measured dissipation changes into SPB temperatures, we recorded temperature dissipation calibration curves in the absence of a SPB. To this end, cleaned crystals were exposed to gradual temperature changes between 18 C and 28 C in steps of 2 C and allowed to equilibrate for 45 min after each temperature variation. An exemplary calibration curve is shown in Figure S1. 3. Data Analysis All QCM-D experiments were consistently analyzed using the 11th harmonic of the quartz crystal resonator, i.e., the normalized resonance frequency f 11 and the corresponding energy dissipation factor D 11. Energy dissipation values recorded during the calibration procedure were plotted as a function of the controlled QCM-D temperature and fitted by a second order polynomial. The polynomial was used to assess the SPB temperature during temperature cycling (T SPB ) and to calculate main phase transition temperatures (T m ). For the precise detection of the phase transitions, we plotted the first-order time derivative of the resonance frequency as a function of the temperature scan time and subjected the df/dt traces to linear baseline correction. The resultant peak optima were then fitted with Gaussian functions to determine their center positions on the time axis. All phase transition temperatures were calculated based on the recorded energy dissipation changes between the beginning of the temperature cycle (i.e., at thermal equilibrium) and the points in time at which the peak optima occurred. S-2

3 Figure S1. Representative temperature dissipation calibration curve. Energy dissipation shifts were recorded in 10 mm Tris buffer (ph 7.5, 100 mm NaCl) and fitted by a second order polynomial (red line). Figure S2. SPB formation process with visible enforced vesicle collapse. The collapse of the adsorbed vesicles was induced by the injection of a hypoosmotic Tris buffer (10 mm Tris, ph 7.5, no added NaCl; arrow 2) 15 min after the injection of the SUV suspension (arrow 1). The subsequent change to the reference medium (10 mm Tris, ph 7.5, 100 mm NaCl; arrow 3) reveals a significant decrease in energy dissipation ( D 11 = ) and an increase in the normalized resonance frequency. The final energy dissipation shift obtained after thermal equilibration under stagnant conditions (arrow 4) suggests a minimum amount of stably-adsorbed vesicles on the silica surface of the QCM-D ( D 11 = ). S-3

4 Figure S3. Phase transition behavior of a DMPC SPB in the presence of gallic acid. The diagram compares the first-order time derivatives of the normalized resonance frequency during the cooling (between 5 min and 48 min) and heating (between 78 min and 122 min) of a DMPC SPB before and during its exposure to 20 mm gallic acid. The baseline-corrected heating traces indicate a reduction in the phase transition temperature by ~ 2 C and a significant broadening of the phase transition peak (see inset). Figure S4. QCM-D responses during SPB exposures to vanillin and protocatechualdehyde. 20 mm of vanillin (a) and protocatechualdehyde (b) were injected for 20 min (arrow 1) and subsequently replaced by the reference medium (10 mm Tris, ph 7.5, 100 mm NaCl; arrow 2). The final frequency values after thermal equilibration of the QCM-D under stagnant conditions (arrow 3) indicate no significant variations in the surface mass density of the SPB. S-4

5 Figure S5. Phase transition behavior of a protocatechualdehyde treated DMPC SPB. The diagram compares the first-order time derivatives of the normalized resonance frequency during the cooling (between 5 min and 48 min) and heating (between 78 min and 122 min) of a DMPC SPB before and after its exposure to 15 mm protocatechualdehyde. At this concentration, the presence of the phenolic compound resulted in a visible phase separation with an additional melting peak occurring at a temperature of 20.9 C (see inset). Figure S6. Phase transition behavior of a vanillin treated DMPC SPB. The diagram compares the firstorder time derivatives of the normalized resonance frequency during the cooling (between 5 min and 48 min) and heating (between 78 min and 122 min) of a DMPC SPB before and after its exposure to 20 mm vanillin. As can be seen from the baseline-corrected heating traces in the inset of the diagram, the exposure of the SPB to vanillin resulted in a detectable increase in the melting temperature of the SPB ( T m = 0.3 C). S-5