Melatonin strongly interacts with zwitterionic model membranes—evidence from Fourier transform infrared spectroscopy and differential scanning calorimetry

Abstract

Interactions of melatonin with zwitterionic dipalmitoyl phosphatidylcholine (DPPC) multilamellar liposomes (MLVs) were investigated as a function of temperature and melatonin concentration (1-30 mol%) by using two noninvasive techniques, namely Fourier transform infrared (FTIR) spectroscopy and differential scanning calorimetry (DSC). The investigation of the C-H, CO, and PO2- antisymmetric double stretching modes in FTIR spectra and DSC studies reveal that melatonin changes the physical properties of the DPPC bilayers by decreasing the main phase transition temperature, abolishing the pretransition, ordering the system in the gel phase, and increasing the dynamics of the system both in the gel and liquid crystalline phases. It also causes significant decrease in the wavenumber for the CO stretching and PO2- antisymmetric double bond stretching bands, which indicates strong hydrogen bonding The results imply that melatonin locates in the interfacial region of the membrane. Furthermore, in the DSC curve, more than one signal is observed at high melatonin concentrations (24 and 30 mol%), which indicates melatonin-induced phase separation in DPPC membranes.

Effects of the non-steroidal anti-inflammatory drug celecoxib on cholesterol containing distearoyl phosphatidylcholine membranes

“…This kind of disconcerted behavior has been previously reported for interactions of model membranes with melatonin [26], progesterone [17], vitamin D 2 [15], vitamin E [30] and cholesterol [29]. This controversial effect of high celecoxib concentrations on membrane order and dynamics may reflect the presence of more than one phase in the bilayer [30].…”

“…This band arises from the stretching vibrations of ester carbonyl groups of phospholipids and is conformationally sensitive to the level of hydration at the membrane interface [17,26]. Therefore any effect seen in the spectra of this region (C=O stretching) can be attributed to an interaction of celecoxib or cholesterol with the polar/apolar interfacial region of the membrane.…”

“…An increase in the bandwidth is an indication of an increase in the dynamics and therefore the fluidity of the membrane system [4,17,18,25,26]. In the interpretation of the results in FTIR spectra, extra care was taken in distinguishing between structural parameters (frequency) describing molecular order and dynamical parameters (bandwidth) describing molecular mobility, as suggested previously by us and others [26,29]. The variations in the bandwidth of the CH 2 antisymmetric stretching mode of DSPC:Chol MLVs for 6 and 18 mol% celecoxib at 30 and 65 • C, are given in Fig.…”

“…In this study, FTIR spectroscopy was used to determine the changes in membrane structure and dynamics in response to low and high concentrations of CLX by analyzing the frequency and bandwidth of different vibrational modes which represent the acyl chains, head group and interfacial region of lipid molecules [5,26].…”

“…MLVs were prepared according to the procedure reported previously [17,26]. Briefly, 5 mg of DSPC and 0.82 mg cholesterol (to have a DSPC:Chol molar ratio of 3:1) was dissolved in 150 µl chloroform and excess chloroform was evaporated by using a gentle stream of nitrogen.…”