Lanosterol is the biosynthetic precursor of cholesterol and ergosterol, sterols that predominate in the membranes of mammals and lower eukaryotes, respectively. These three sterols are structurally quite similar, yet their relative effects on membranes have been shown to differ. Here we study the effects of cholesterol, lanosterol, and ergosterol on 1-palmitoyl-2-oleoyl-sn-glycero-3-phosphatidylcholine lipid bilayers at room temperature. Micropipette aspiration is used to determine membrane material properties (area compressibility modulus), and information about lipid chain order (first moments) is obtained from deuterium nuclear magnetic resonance. We compare these results, along with data for membrane-bending rigidity, to explore the relationship between membrane hydrophobic thickness and elastic properties. Together, such diverse approaches demonstrate that membrane properties are affected to different degrees by these structurally distinct sterols, yet nonetheless exhibit universal behavior.

The phase behavior and lipid mixing properties of an equimolar mixture of nonhydroxylated palmitoyl ceramide (Cer16), palmitic acid (PA), and cholesterol have been investigated using 2H NMR and vibrational spectroscopy. This mixture is formed by the three main classes of lipids found in the stratum corneum (SC), the top layer of the epidermis, and provides an optimized hydrophobic matching. Therefore, its behavior highlights the role played by hydrophobic matching on the phase behavior of SC lipids. We found that, below 45 degrees C, the mixture is essentially formed of coexisting crystalline domains with a small fraction of lipids (less than 20%) that forms a gel or fluid phase, likely ensuring cohesion between the solid domains. Upon heating, there is the formation of a liquid ordered phase mainly composed of PA and cholesterol, including a small fraction of Cer16. This finding is particularly highlighted by correlation vibrational microspectroscopy that indicates that domains enriched in cholesterol and PA include more disordered Cer16 than those found in the Cer16-rich domains. Solubilization of Cer16 in the fluid phase occurs progressively upon further heating, and this leads to the formation of a nonlamellar self-assembly where the motions are isotropic on the NMR time scale. It is found that the miscibility of Cer16 with cholesterol and PA is more limited than the one previously observed for ceramide III extracted from bovine brain, which is heterogeneous in chain composition and includes, in addition to Cer16, analogous ceramide with longer alkyl chains that are not hydrophobically matched with cholesterol and PA. Therefore, it is inferred that, in SC, the chain heterogeneity is a stronger criteria for lipid miscibility than chain hydrophobic matching.

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Purpose:To describe what, if any, specific long T 2 -related abnormalities occur in the white matter of subjects with either phenylketonuria (PKU) or multiple sclerosis (MS). Materials and Methods:The 48-echo T 2 relaxation data (maximum TE ϭ 1.12 sec) were acquired from 15 PKU subjects, 20 MS subjects, and 15 healthy volunteers. Regions of interest were drawn in diffuse white matter hyperintensities (DiffWM), lesions, normal-appearing white matter (NAWM), and normal white matter. Long T 2 maps (200 msec Ͻ T 2 Ͻ 800 msec) were created for each subject. Results:A new water reservoir with a markedly prolonged T 2 peak was identified in DiffWM and NAWM in 12 out of 15 subjects with PKU and a long T 2 signal was also seen in 23/97 lesions in 50% of subjects with MS. Additionally, a long T 2 component was observed in the corticospinal tracts of 10 healthy volunteers. The characteristics of the long T 2 signal were unique for each subject group. Potential sources of this signal include vacuolation and increases in extracellular water. Conclusion:This study supports the usefulness of increasing the data acquisition window of the multiecho T 2 relaxation sequence to better characterize the T 2 decay from pathological brain. MAGNETIC RESONANCE T 2 relaxation measurements in white matter have the potential to provide specific information about the pathological damage that occurs in the brains of people with neurodegenerative diseases. Multiecho T 2 relaxation measurements in healthy human brain can separate the water signal into three components: 1) a very long T 2 component (Ͼ2 sec) attributed to cerebral spinal fluid (CSF), 2) an intermediate T 2 component (Ϸ80 msec) attributed to intra-and extracellular water, and 3) a short T 2 component (Ϸ20 msec) assigned to water trapped between the myelin bilayers (labeled myelin water) (1,2). Such multiecho experiments have been used extensively to characterize myelin water and total water content in both healthy and diseased white matter (2-9). Previous T 2 relaxation work in phenylketonuria (PKU) and multiple sclerosis (MS) have suggested abnormalities in brain water content and myelin water fraction (MWF) for both normal-appearing white matter (NAWM) and lesions (3-5,7,9,10).Accurate multiecho measurement and analysis of the T 2 decay curve has the potential to identify other water reservoirs and characterize additional signal arising from white matter pathology such as edema or inflammation. To better define the intermediate and long T 2 components, important for the characterization of abnormal white matter, the total acquisition time of our multiecho T 2 relaxation sequence was lengthened from 320 msec to 1.120 sec (11,12). The purpose of this study was to describe what, if any, specific long T 2 -related abnormalities occur in the white matter of subjects with PKU and MS. MATERIALS AND METHODS Subject InformationFifteen subjects with PKU (6 male, 9 female; mean age ϭ 27 years; range 18 -40 years), 20 subjects with clinically definite MS (14 relapsing-remitting, 3 secondary...

In patients with PKU, NAWM and diffuse WM lesions have altered RWC and MWF relative to normal WM, and diffuse WM lesions show a redistribution of water into an extracellular reservoir with a long T2 time.

T2 of NAA, creatine and choline-containing compounds were measured in posterior frontal white matter and occipital grey matter in 10 healthy human volunteers. Decay curves comprised signals from eight TE times ranging from 30 to 800 ms with TR 2000 ms acquired with a PRESS sequence on a 1.5 T clinical scanner. Simulations were conducted to assess the precision of T2 estimates from decay curves comprising varying numbers and ranges of TE points. Mean and standard errors for T2s of NAA, creatine and choline-containing compounds were 300(8), 169(3) and 239(4) ms in posterior frontal white matter and 256(6), 159(8) and 249(8) ms in occipital grey matter. In vivo T2s found for choline and NAA were shorter than the T2s in the literature. The elevation of literature T2s is accounted for by the simulation results, which demonstrated that there is a bias towards lengthened T2s when T2 is measured with a maximum TE approximately T2. Concentration estimates are at risk of being underestimated if previously reported T2 corrections are used.

Saturation recovery spectra (STEAM) were acquired at 1.5 T with 7 TRs ranging from 530 to 5000 ms and a constant TE of 30 ms in voxels (7.2 ml) located in occipital grey, parietal white and frontal white matter (10 subjects each location). Spectra were also acquired at 7, 21 and 37 degrees C from separate 100 mm solutions of inositol (Ins), choline-containing compounds (Cho), N-acetyl-aspartate (NAA) and creatine. Simulations of T(1) fits with 2, 3 and 7 TRs demonstrated that at typical SNR there is potential for both inaccurate and biased results. In vivo, different metabolites had significantly different T(1)s within the same brain volume. The same order from shortest to longest T(1) (Ins, Cho, NAA, creatine) was found for all three brain regions. The order (Ins, NAA, creatine, Cho) was found in the metabolite solutions and was consistent with a simple model in which T(1) is inversely proportional to molecular weight. For all individual metabolites, T(1) increased from occipital grey to parietal white to frontal white matter. This study demonstrates that, in spectra acquired with TR near 1 s, T(1) weightings are substantially different for metabolites within a single tissue and also for the same metabolites in different tissues.

Ethanol is used in a variety of topical products. It is known to enhance the permeability of the skin by altering the ability of the stratum corneum (SC) intercellular membranes to form an effective barrier. In addition, ethanol and other alcohols are key components of antiseptic gels currently used for hand wash. Using infrared and deuterium NMR spectroscopy as well as calorimetry, we have investigated the effect of ethanol on a model membrane composed of lipids representing the three classes of SC lipids, an equimolar mixture of N-palmitoylsphingosine (ceramide), palmitic acid and cholesterol. Ethanol is found to influence the membrane in a dose dependent manner, disrupting packing and increasing lipid motion at low concentrations and selectively extracting lipids at moderate concentrations.