X-rays destroy the lamellar structure of model membranes

Anatomical and surgical characteristics correlate with pachymeningeal failure in patients with brain metastases after neurosurgical resection and adjuvant stereotactic radiosurgery

PURPOSE

Neurosurgery (NS) is an essential modality for large brain metastases (BM). Postoperative stereotactic radiosurgery (SRS) is the standard of care adjuvant treatment. Pachymeningeal failure (PMF) is a newly described entity, distinct from classical leptomeningeal failure (LMF), that is uniquely observed in postoperative patients treated with adjuvant SRS. We sought to identify risk factors for PMF in patients treated with NS + SRS.

METHODS

From a prospective registry (2009 to 2021), we identified all patients treated with NS + SRS. Clinical, imaging, pathological, and treatment factors were analyzed. PMF incidence was evaluated using a competing risks model.

RESULTS

144 Patients were identified. The median age was 62 (23-90). PMF occurred in 21.5% (31/144). Female gender [Hazard Ratio (HR) 2.65, p = 0.013], higher Graded Prognostic Assessment (GPA) index (HR 2.4, p < 0.001), absence of prior radiation therapy (HR N/A, p = 0.018), controlled extracranial disease (CED) (HR 3.46, p = 0.0038), and pia/dura contact (PDC) (HR 3.30, p = 0.0053) were associated with increased risk for PMF on univariate analysis. In patients with PDC, wider target volumes correlated with reduced risk of PMF. Multivariate analysis indicated PDC (HR 3.51, p = 0.0053), piecemeal resection (HR 2.38, p = 0.027), and CED (HR 3.97, p = 0.0016) independently correlated with PMF risk. PMF correlated with reduced OS (HR 2.90, p < 0.001) at a lower rate compared to LMF (HR 10.15, p < 0.001).

CONCLUSION

PMF correlates with tumor PDC and piecemeal resection in patients treated with NS + SRS. For unclear reasons, it is also associated with CED. In tumors with PDC, wider dural radiotherapy coverage was associated with a lower risk of PMF.

Biological effects of radiation on cancer cells

With the development of radiotherapeutic oncology, computer technology and medical imaging technology, radiation therapy has made great progress. Research on the impact and the specific mechanism of radiation on tumors has become a central topic in cancer therapy. According to the traditional view, radiation can directly affect the structure of the DNA double helix, which in turn activates DNA damage sensors to induce apoptosis, necrosis, and aging or affects normal mitosis events and ultimately rewires various biological characteristics of neoplasm cells. In addition, irradiation damages subcellular structures, such as the cytoplasmic membrane, endoplasmic reticulum, ribosome, mitochondria, and lysosome of cancer cells to regulate various biological activities of tumor cells. Recent studies have shown that radiation can also change the tumor cell phenotype, immunogenicity and microenvironment, thereby globally altering the biological behavior of cancer cells. In this review, we focus on the effects of therapeutic radiation on the biological features of tumor cells to provide a theoretical basis for combinational therapy and inaugurate a new era in oncology.

Membrane protein crystallization in lipidic mesophases. A mechanism study using X-ray microdiffraction

The membrane structural biologist seeks to understand how membrane proteins function at a molecular level. One of the most direct ways of accomplishing this requires knowing the structure of the protein, ideally at atomic resolution. To date, this can only be done by the method of macromolecular crystallography. Integral to the method is the need for three-dimensional crystals of diffraction quality and their production represents a major rate-limiting step in the overall process of structure determination. The in meso method is a novel approach for crystallizing membrane proteins. It makes use of lipidic mesophases, the cubic phase in particular. A mechanism for how the method works has been proposed. In this study, we set out to test one aspect of the hypothesis which posits that the protein migrates from the bulk mesophase reservoir to the face of the crystal by way of a lamellar conduit. Using a sub-micrometer-sized X-ray beam the interface between a growing membrane protein crystal and the bulk cubic phase was interrogated with micrometer spatial resolution. Characteristic diffraction from the lamellar phase was observed at the interface as expected. This result supports the proposal that the protein uses a lamellar portal on its way from the bulk mesophase up and into the face of the crystal.

Differential Membrane Packing of Stereoisomers of Bis(monoacylglycero)phosphate

Bis(monoacylglycero)phosphate (BMP) reveals an unusual sn-1,sn-1' stereoconfiguration of glycerophosphate. We synthesized sn-(3-myristoyl-2-hydroxy)glycerol-1-phospho-sn-1'-(3'-myristoyl-2'-hydroxy)glycerol (1,1'-DMBMP) and characterized the thermotropic phase behavior and membrane structure, in comparison with those of the corresponding sn-3:sn-1' stereoisomer (3,1'-DMBMP), by means of differential scanning calorimetry (DSC), small- and wide-angle X-ray scattering (SAXS and WAXS, respectively), pressure-area (pi-A) isotherms, epifluorescence microscopy of monolayers, and molecular dynamics (MD) simulations. In DSC, these lipids exhibited weakly energetic broad peaks with an onset temperature of 9 degrees C for 1,1'-DMBMP and 18 degrees C for 3,1'-DMBMP. In addition, a highly cooperative, strongly energetic transition peak was observed at approximately 40 degrees C for 1,1'-DMBMP and approximately 42 degrees C for 3,1'-DMBMP. These results are supported by the observation that 1,1'-DMBMP exhibited a larger phase transition pressure (pi(c)) than 3,1'-DMBMP. Small- and wide-angle X-ray scattering measurements identified these small and large energetic transitions as a quasi-crystalline (L(c1))-quasi-crystalline with different tilt angle (L(c2)) phase transition and an L(c2)-L(alpha) main phase transition, respectively. X-ray measurements also revealed that these DMBMPs undergo an unbinding at the main phase transition temperature. The MD simulations estimated stronger hydrogen bonding formation in the 3,1'-DMBMP membrane than in 1,1'-DMBMP, supporting the experimental data.

Structure and thermal history dependant phase behavior of hydrated synthetic sphingomyelin analogue: 1,2-dimyristamido-1,2-deoxyphosphatidylcholine

The physical properties of hydrated multilamellar sample of 1,2-dimyristamido-1,2-deoxyphosphatidylcholine (DDPC) were investigated by means of differential scanning calorimetry (DSC), static X-ray diffraction, and simultaneous DSC and X-ray diffraction. The DDPC is a synthetic sphingomyelin analogue and has two amide bonds in its hydrophobic parts. This paper reports on metastable phase behavior of the hydrated DDPC sample. By cooling from a chain-melted state at the rates of greater than 4 degrees C min(-1), hydrated DDPC bilayers form a metastable gel phase. In the gel phase, the hydrophobic chains are tilted with respect to the bilayer normal, as like the gel phase of glycero-phosphatidylcholines. By heating, the metastable gel phase is transformed in to a stable phase associated with an exothermic heat event at 18.3 degrees C (DeltaH=14.6 kJ mol(-1)) and then the stable phase is transformed into a liquid-crystalline phase at 25.6 degrees C (DeltaH=42 kJ mol(-1)). The incubation at 17 degrees C for more than 1 h also induces the formation of the stable phase. In the stable phase, the hydrophobic chains are packed into highly ordered crystal-like structure. However, the X-ray diffraction pattern of the stable phase suggested that the entire DDPC molecules do not form a two-dimensional molecular ordered lattice, differing from normal subgel phase of glycero-phosphatidylcholines. The structure and phase behavior of DDPC revealed by the present study are discussed from the viewpoint of hydrogen bonds.

A simple mechanical mixer for small viscous lipid-containing samples

The construction and performance characteristics of a simple device for rapid and convenient hydration and mixing of small volumes (10-500 microliters) of viscous hydrated lipid samples for use in X-ray diffraction/scattering and other applications are described. The mixer has been used successfully over the past several years in studies of the equilibrium properties of lipid mesophases and of the kinetics and mechanism of phase transitions. It is a low dead-volume (3.6-11.2 microliters) device that was built to facilitate maximal transfer of homogeneously hydrated lipid from the mixer into 1 mm diameter X-ray capillaries with minimal loss of water during transfer and sample manipulation. The device consists of inexpensive, commercially available parts, the most important of which are two microsyringes joined by a small-bore coupling needle. Also described in this report is a technique for determining the water content of the small volume, hydrated samples prepared with the mixer and an accessory for conveniently heating and/or degassing samples during mixing. Inadvertent sample heating that occurs during mixing is described.

Free radical mediated x-ray damage of model membranes

The damaging effects of synchrotron-derived x rays on aqueous phospholipid dispersions have been evaluated. The effect of degree of lipid hydration, phospholipid chemical structure, mesophase identity, aqueous medium composition, and incident flux on the severity and progress of damage was quantified using time-resolved x-ray diffraction and chromatographic analysis of damage products. Electron spin resonance measurements of spin-trapped intermediates generated during irradiation suggest a free radical-mediated process. Surprisingly, radiation damage effects revealed by x-ray diffraction were imperceptible when the lamellar phases were prepared under water-stressed conditions, despite the fact that x-ray-induced chemical breakdown of the lipid occurred regardless of hydration level. Of the fully hydrated lipid systems studied, saturated diacyl-phosphatidylcholines were most sensitive to radiation damage compared to the ester- and ether-linked phosphatidylethanolamines and the ether-linked phosphatidylcholines. The inclusion of buffers or inorganic salts in the dispersing medium had only a minor effect in reducing damage development. A small inverse dose-rate effect was found when the x-ray beam intensity was changed 15-fold. These results contribute to our understanding of the mechanism of radiation damage, to our appreciation of the importance of monitoring both structure and composition when evaluating biomaterials radiation sensitivity, and to the development of strategies for eliminating or reducing the severity of damage due to an increasingly important source of x rays, synchrotron radiation. Because damage is shown to be free radical mediated, these results have an important bearing on age-related accumulation of free radicals in cells and how these might compromise membrane integrity, culminating in cell death.

Effects of cholesterol on the lamellar and the inverted hexagonal phases of dielaidoylphosphatidylethanolamine

Effects of cholesterol on the lamellar and the inverted hexagonal (HII ) phases of dielaidoylphosphatidylethanolamine (DEPE) were studied by means of not only differential scanning calorimetry (DSC) but also simultaneous X-ray diffraction and DSC (XDDSC). XDDSC shows that structural changes are related to thermotropic events of the mixtures. Addition of cholesterol to DEPE induces to broaden the transition from the lamellar gel (L beta) to lamellar liquid-crystalline (L alpha) phase. In fact, in the broad transition region, a coexistence of two lamellar X-ray diffraction peaks of the L beta and L alpha phases take place. In samples containing above 30 mol% cholesterol, no peak at the L beta-L alpha phase transition was observed in the DSC thermogram. On the other hand, cholesterol causes biphasic effects on the L alpha-HII phase transition: At low cholesterol concentrations below 20 mol%, the incorporation of cholesterol reduces the transition temperature and at high cholesterol concentrations about 30 mol%, the transition temperature increases by addition of cholesterol. Based upon the results of X-ray diffraction, the thermal expansion coefficients of lattice spacings, i.e., the temperature dependence of lattice spacings, were calculated in each phase. Addition of cholesterol reduces the thermal expansion coefficients of the lamellar phases and, in contrast, increases that of the HII phase. From the above results it is suggested that cholesterol in cell membranes works in keeping the bilayer membrane nature notwithstanding the change of external conditions.

Effects of plant sterols on the hydration and phase behavior of DOPE/DOPC mixtures

Freeze-induced injury of protoplasts of non-acclimated rye and oat is associated with the formation of the inverted hexagonal (HII) phase in regions where the plasma membrane and various endomembranes are brought into close apposition as a result of freeze-induced dehydration. The influence of lipid composition and hydration on the propensity of mixtures of DOPE:DOPC containing either sterols or acylated steryl glucosides to form the HII phase was determined by DSC, freeze-fracture electron microscopy and X-ray diffraction. The addition of plant sterols to a mixture of DOPE/DOPC (either 1:1:1 or 1:1:2 mole ratio of DOPE/DOPC/sterols) reduced the total hydration of the mixture (expressed as wt% water) after desorption over a range of osmotic pressures of 2.8 to 286 MPa. However, most or all of the water remaining in the dehydrated lipid mixtures was associated predominantly with the phospholipids. Both sterols and acylated steryl glucosides significantly promoted both the dehydration-induced and thermally induced L alpha-->HII phase transitions in DOPE/DOPC mixtures however, acylated steryl glucosides were much more effective. In mixtures containing plant sterols, the HII phase occurred after dehydration at 20 MPa (20 degrees C), which resulted in a water content of 11.7 wt%. In contrast, mixtures containing acylated steryl glucosides were in the HII phase in excess water, i.e., they did not require dehydration to effect the L alpha-->HII phase transition. The results indicate that genotypic differences in the lipid composition of the plasma membrane of rye and oat leaves have a significant influence on the propensity for formation of the HII phase during freeze-induced dehydration.

Polymorphism, mesomorphism, and metastability of monoelaidin in excess water

The polymorphic and metastable phase behavior of monoelaidin dry and in excess water was studied by using high-sensitivity differential scanning calorimetry and time-resolved x-ray diffraction in the temperature range of 4 degrees C to 60 degrees C. To overcome problems associated with a pronounced thermal history-dependent phase behavior, simultaneous calorimetry and time-resolved x-ray diffraction measurements were performed on individual samples. Monoelaidin/water samples were prepared at room temperature and stored at 4 degrees C for up to 1 week before measurement. The initial heating scan from 4 degrees C to 60 degrees C showed complex phase behavior with the sample in the lamellar crystalline (Lc0) and cubic (Im3m, Q229) phases at low and high temperatures, respectively. The Lc0 phase transforms to the lamellar liquid crystalline (L alpha) phase at 38 degrees C. At 45 degrees C, multiple unresolved lines appeared that coexisted with those from the L alpha phase in the low-angle region of the diffraction pattern that have been assigned previously to the so-called X phase (Caffrey, 1987, 1989). With further heating the X phase converts to the Im3m cubic phase. Regardless of previous thermal history, cooling calorimetric scans revealed a single exotherm at 22 degrees C, which was assigned to an L alpha+cubic (Im3m, Q229)-to-lamellar gel (L beta) phase transition. The response of the sample to a cooling followed by a reheating or isothermal protocol depended on the length of time the sample was incubated at 4 degrees C. A model is proposed that reconciles the complex polymorphic, mesomorphic, and metastability interrelationships observed with this lipid/water system. Dry monoelaidin exists in the lamellar crystalline (beta) phase in the 4 degrees C to 45 degrees C range. The beta phase transforms to a second lamellar crystalline polymorph identified as beta* at 45 degrees C that subsequently melts at 57 degrees C. The beta phase observed with dry monoelaidin is identical to the LcO phase formed by monoelaidin that was dispersed in excess water and that had not been previously heated.

Kinetics of lipid phase changes

In the past two years, the kinetics of transitions involving the assorted lamellar and inverted hexagonal and cubic phases in bulk hydrated lipid systems have been established using a variety of physical techniques. In several cases, the kinetic data have lead to a transition mechanisms being deciphered.

Thermodynamic, thermomechanical, and structural properties of a hydrated asymmetric phosphatidylcholine

1-Behenyl-2-lauryl-sn-glycero-3-phosphocholine (22/12 PC) belongs to a unique group of phospholipids in which the molecule has one acyl chain almost twice as long as the other. The temperature-composition phase diagram for this lipid in the range of 25-65 degrees C, and 0 to 84.3% (w/w) water has been constructed by using the isoplethal method in the heating direction and x-ray diffraction for phase identification and structure characterization. At water contents between 10.3 and 34% (w/w) and at temperatures below 43 degrees C, a single mixed interdigitated lamellar gel phase (Lm beta, [symbol: see text]) of the type described by Hui et al. (1984. Biochemistry. 23:5570-5577) and McIntosh et al. (1984. Biochemistry. 23:4038-4044) was found. A second phase consisting of bulk aqueous solution coexists with the Lm beta phase at hydration levels above 34% (w/w) water in the temperature range between 25 and 43 degrees C. Above 43 degrees C, a partially interdigitated lamellar liquid crystalline (Lp alpha) phase ([symbol: see text]) is seen in the water concentration range extending from 0 to 84.3% (w/w). The pure Lp alpha phase is found below 43% (w/w) water, while coexistence of the Lp alpha phase and the bulk aqueous solution is observed above this water concentration which marks the hydration boundary. Interestingly, the latter boundary for both Lm beta and Lp alpha phases is nearly vertical in the temperature range studied. Furthermore, the lamellar chain-melting transition temperature appears to be relatively insensitive to hydration in the range 0-85% (w/w) water. We have confirmed the identify of the Lm beta phase by constructing a 5.7-A resolution electron density profile on oriented samples by the swelling method. Temperature-induced chain melting effects an increase in lipid bilayer thickness suggesting that the Lp alpha phase has chains packed in the partially as opposed to the mixed interdigitated configuration. Unlike the symmetric phosphatidylcholines a ripple (P beta') phase was not found as an intermediate between the low and high temperature lamellar phases of 22/12 PC. The specific volume of 22/12 PC is 940 (+/- 1) microliter/g and 946 (+/- 1) microliter/g in the hydrated lamellar gel state at 28 (+/- 2) and 40 (+/- 2) degrees C, respectively, from neutral buoyancy experiments. Based on measurements of the temperature dependence of the various lattice parameters of the different phases encountered in this study the corresponding lattice thermal expansion coefficients have been measured. These are discussed and their dependence on lipid hydration is reported.