A comparative calorimetric and spectroscopic study of the effects of cholesterol and of the plant sterols β-sitosterol and stigmasterol on the thermotropic phase behavior and organization of dipalmitoylphosphatidylcholine bilayer membranes

• Published in: Biochimica et biophysica acta Vol. 1848; no. 8; pp. 1629 - 1638
• Main Authors: Mannock, David A., Benesch, Matthew G.K., Lewis, Ruthven N.A.H., McElhaney, Ronald N.
• Format: Journal Article
• Language: English
• Published: Netherlands Elsevier B.V 01.08.2015
• Subjects: 1,2-Dipalmitoylphosphatidylcholine - chemistry; 1,2-Dipalmitoylphosphatidylcholine - metabolism; Brassicasterol; Calorimetry, Differential Scanning; Campesterol; Cholestadienols - chemistry; Cholesterol; Cholesterol - analogs & derivatives; Cholesterol - chemistry; Cholesterol - metabolism; Lipid Bilayers; Molecular Structure; Phase Transition; Phytosterols - chemistry; Sitosterols - chemistry; Sitosterols - metabolism; Spectroscopy, Fourier Transform Infrared; Sterol-phospholipid interactions; Stigmasterol; Stigmasterol - chemistry; Stigmasterol - metabolism; Temperature; β-sitosterol; Chol; Brassicasterol; N-PSpM; ΔHp/ΔHm; Stigmasterol; Ergo; β-sitosterol; Sterol-phospholipid interactions; DSC; Sito; FTIR; POPC; Ld; ΔT1/2(p)/ΔT1/2(m); DMPC; DOPC; DPPC; DPPE; Pβ; Lo; ESR; Lα; Cholesterol; SpM; NMR; PC; Campesterol; Stig; Bras; Camp; Tp/Tm
• ISSN: 0005-2736; 0006-3002; 1879-2642
• DOI: 10.1016/j.bbamem.2015.04.009

We performed comparative DSC and FTIR spectroscopic measurements of the effects of β-sitosterol (Sito) and stigmasterol (Stig) on the thermotropic phase behavior and organization of DPPC bilayers. Sito and Stig are the major sterols in the biological membranes of higher plants, whereas cholesterol (Chol) is the major sterol in mammalian membranes. Sito differs in structure from Chol in having an ethyl group at C24 of the alkyl side-chain, and Stig in having both the C24 ethyl group and trans-double bond at C22. Our DSC studies indicate that the progressive incorporation of Sito and Stig decrease the temperature and cooperativity of the pretransition of DPPC to a slightly lesser and greater extent than Chol, respectively, but the pretransition persists to 10mol % sterol concentration in all cases. All three sterols produce essentially identical effects on the thermodynamic parameters of the sharp component of the DPPC main phase transition. However, the ability to increase the temperature and decrease the cooperativity and enthalpy of the broad component decreases in the order Chol>Sito>Stig. Nevertheless, at higher Sito/Stig concentrations, there is no evidence of sterol crystallites. Our FTIR spectroscopic studies demonstrate that Sito and especially Stig incorporation produces a smaller ordering of the hydrocarbon chains of fluid DPPC bilayers than does Chol. In general, the presence of a C24 ethyl group in the alkyl side-chain reduces the characteristic effects of Chol on the thermotropic phase behavior and organization of DPPC bilayer membranes, and a trans-double bond at C22 magnifies this effect. [Display omitted] •Sito and especially Stig disorder gel state DPPC bilayers more than does Chol.•Sito and especially Stig order fluid DPPC bilayers less than does Chol.•Sito and especially Stig are less miscible in gel and fluid DPPC bilayers than Chol.•An ethyl group at C24 and trans-double bond at C22 reduce the effects of Chol.•Sito and Stig are less “Chol-like” than their C24 methyl sterol analogs Camp and Bras.