Biomedical subjects

L J Lis

Publications and source records attributed to L J Lis.

At least 19 recordsLinked to original sources

PubMed1998

Phase changes in membrane lipids in sickle red cell shed-vesicles and sickle red cells.

Lipid phase transformations may occur in the membranes of sickle red cell shed-vesicles and sickle red cells. The presence of such phase changes could be important in sickle cell disease since membrane phase changes appear to contribute to the generation of antiphospholipid antibodies that are thrombophilic and occur in sickle cell disease. In the present study, we have evaluated sickle red cell shed-vesicles and sickle red cells for the presence of non-bilayer lipid phases using 31P-NMR spectroscopy. Results show that the spectra of both the shed-vesicles and the sickle red cells are compatible with the occurrence of non-bilayer phases in the membrane bilayers. The findings support the concept that these membranes could contribute to the generation of antiphospholipid antibodies in sickle cell disease.

Anemia, Sickle Cell↗

PubMed1997

Digital ischemia and gangrene due to red blood cell aggregation induced by acquired dysfibrinogenemia.

Digital gangrene was observed in a patient who had angiographic findings of digital arterial occlusion. The patient's blood showed a marked red blood cell aggregation with rouleaux formation in long chains, which could not be dispersed at shear rates up to 200 sec-1. Studies of the patient's blood revealed the presence of an abnormal fibrinogen capable of aggregating normal red blood cells. This fibrinogen was found by Raman spectroscopy to have an increased alpha-helical content, whereas the beta-sheet content was decreased. Defibrinogenation therapy with ancrod resulted in a dramatic symptomatic relief. The disappearance of the abnormal fibrinogen 6 months later and an absence of a family history indicate that this dysfibrinogenemia was acquired.

Arterial Occlusive Diseases↗

PubMed1995

Real-time X-ray diffraction study at different scan rates of phase transitions for dipalmitoylphosphatidylcholine in KSCN.

Multibilayer arrays of dipalmitoylphosphatidylcholine (DPPC) in 1 M KSCN were characterized using real-time X-ray diffraction and differential scanning calorimetry. A phase transition sequence was observed as a function of increasing temperature which involved changes from the interdigitated subgel (Lc(inter)) to interdigitated gel (L beta(inter)) to disordered (L alpha) bilayer states. The phase transition mechanisms were unambiguously determined by comparison of results from fast and slow scans. The Lc(inter)-->L beta(inter) phase transition was shown to involve a continuous change in acyl chain spacing between the rectangular subgel acyl chain unit cell into an hexagonal gel acyl chain unit cell. The mechanism is similar to that for subgel to gel state transitions involving non-interdigitated DPPC bilayers.

1,2-Dipalmitoylphosphatidylcholine↗

PubMed1995

Sterols stabilize the ripple phase structure in dihexadecylphosphatidylcholine.

The presence of various sterols in mixtures with dihexadecylphosphatidylcholine (DHPC) was studied using static X-ray diffraction of temperature equilibrated samples, and real-time X-ray diffraction of samples undergoing temperature scans. It was found that these sterols eliminate the interdigitation of the alkyl chains in the DHPC sub-gel and gel-state bilayers while stabilizing the ripple gel-state at the expense of the gel-state bilayer phase. The ripple-ripple phase transition previously observed for dipalmitoylphosphatidylcholine in the presence of low molar concentrations of sterols (Wolfe et al. (1992) Phys. Rev. Lett. 68, 1085-1088) was also observed for similar DHPC-sterol mixtures. In addition, we show the first evidence that the presence of 5 alpha-cholestane-3 beta,5,6 beta-triol will cause the lipid mixtures to continue to adopt a ripple mesophase structure even after the DHPC alkyl chain becomes disordered.

Cholestanols↗

PubMed1994

Effects of fibrinogens on phase transitions in lipid model membrane systems.

An abnormal fibrinogen that caused aggregation of red blood cells (RBC) in a patient with gangrene was examined by real-time X-ray diffraction to determine its effects on dipalmitoylphosphatidylcholine (DPPC) and 1-palmitoyl-2-oleoylphosphatidylethanolamine (POPE) phase transitions. Similar studies were done with normal fibrinogen and results were compared. Both types of fibrinogen slightly increased the L alpha-->HII phase transition temperature and the HII phase parameters for POPE, while neither fibrinogen significantly affected the order-disordered acyl chain transitions in the lipid bilayer phase. However, fibrinogen differentially influenced the bilayer unit cell parameter of the gel and disordered bilayer and the gel state ripple phase. These results can be interpreted as indicating that fibrinogen has little effect on the balance of gel and disordered acyl chains in the lipid bilayer, but may influence membrane functions dependent on non-bilayer phases.

1,2-Dipalmitoylphosphatidylcholine↗

PubMed1994

Inhibition of cytolytic T lymphocyte activity by oxysterols.

The objective of this study was to investigate the effects of oxysterols (OS), namely 5 alpha-hydroxy-6-ketocholestanol, 6-ketocholestanol and 25-hydroxycholesterol, on specific cell-mediated cytotoxicity by C57BL/6 spleen cells against P815-X2 (a DBA/2 mastocytoma) target cells. Cytolytic T lymphocytes (CTL) were generated by intraperitoneally injecting C57BL/6 mice with P815-X2 tumor cells 10 d prior to the cytotoxicity experiments. Preincubation of CTL with 10(-5) M 5 alpha-hydroxy-6-ketocholestanol and 6-ketocholestanol for 45 min in lipoprotein-depleted medium resulted in an inhibition of cytolytic activity (73 and 43%, respectively) as measured by 4-h 51Cr release. At a concentration of 5 x 10(-6) M, 5 alpha-hydroxy-6-ketocholestanol inhibited CTL activity by 65%, whereas 6-ketocholestanol did not elicit any inhibition. By contrast, 25-hydroxycholesterol did not inhibit CTL at either concentration, although it is known to be a potent inhibitor of 3-hydroxy-3-methyl-glutaryl-coenzyme A reductase, the rate-limiting enzyme in the cholesterol biosynthetic pathway. When CTL were preincubated with OS in lipoprotein-replete medium, there was no inhibition of CTL activity at the respective concentrations. The results suggest that the inhibition of CTL activity upon short-term incubation with OS is not due to the inhibition of cholesterol synthesis, but may be due to the insertion of OS into the plasma membrane to replace cholesterol and alteration of membrane physical properties.

Animals↗

PubMed1994

Synchrotron X-ray studies of lipids and membranes: a critique.

This review gives a description of techniques, suitable for the study of lipid dispersions and unorientated membranes, that are available at synchrotron facilities to determine either the kinetics of transitional phenomena in the time after a temperature or pressure jump is initiated, or the phases present while a sample undergoes a phase transition. Included in this description is information about synchrotron X-ray sources, sample holders and temperature controllers, detection systems, as well as data reduction. Examples involving lipid dispersions are provided to illustrate the application of these methods using synchrotron radiation.

Kinetics↗

PubMed1993

The effect of ice on membrane lipid phase behaviour.

The effects of ice on the lipid phase behaviour of di-18:1 PE and di-18:2 PE were studied by comparing the behaviour of these lipids in supercooled and frozen dispersions. The presence of ice raised the onset temperature of the L alpha--> L beta phase transition of di-18:1 PE from -10 degrees C to -6.5 degrees C and increased its molar enthalpy from 6.1 to 8.5 kcal/mol but had little effect on the co-operativity of the transition. Real-time X-ray diffraction measurements of the HII--> L alpha phase transition of di-18:2 PE suggested that this transition could take place in the presence of ice but that the corresponding L alpha--> HII phase transition could not take place until the ice melted. Measurements of the temperature dependence of the d-spacing of di-18:1 PE and di-18:2 PC in frozen dispersions indicated that the amounts of unfrozen water in such dispersions changes significantly with temperature. It was concluded that the increases in onset temperature and molar enthalpy seen for the L alpha--> L beta transition of di-18:1 PE probably reflected the effects of osmotic dehydration. The main effect of ice in the case of the HII--> L alpha phase transition, however, appeared to be to limit the ability of the lipid to undergo structural reorganisation.

Calorimetry, Differential Scanning↗

PubMed1993

Phase behaviour of membrane lipids containing polyenoic acyl chains.

The low-temperature thermal behaviour of di-18:2 phosphatidylethanolamine (di-18:2 PE) is shown to be characterized by similar broad low-enthalpy transitions to those previously reported for polyenoic samples of phosphatidylcholines (Keough and Kariel (1987) Biochim. Biophys. Acta 902, 11-18), and monogalactosyldiacylglycerol (Sanderson and Williams (1992) Biochim. Biophys. Acta. 1107, 77-85). Real-time X-ray diffraction measurements indicate that these transitions correspond to transitions between the gel (L beta) and liquid-crystal (L alpha) phases of the lipids. The gel phase of these lipids is, however, much more loosely packed than the corresponding phases of membrane lipids containing monoenoic or fully-saturated acyl chains. The low enthalpy and reduced co-operativity of the L alpha--> L beta phase transitions of the polyenoic lipids is attributed to the reduced contribution of van der Waals interactions between their acyl chains in the gel-state of these lipids. Comparison with the earlier results obtained for MGDG suggest that the acyl chains of polyenoic lipids can form well-ordered lattices but require the additional energy input associated with the formation of a hydrogen bond network between the lipid headgroups in order to do so.

Calorimetry, Differential Scanning↗

PubMed1993

Antiphospholipid antibodies in sickle cell disease.

Antiphospholipid antibody formation can be induced in mice by phospholipid in a hexagonal II phase but not by phospholipid in a bilayer phase. Since sickle red cell membranes have increased hexagonal II phase content, we have measured serum antiphospholipid antibody levels in 25 patients with sickle cell disease to determine whether anti-phospholipid antibody may similarly be induced in these patients. Seventeen of the 25 patients (68%) had increased levels of antiphospholipid antibodies. Eleven patients (65%) had IgG and six each (35%) had IgM and IgA isotypes. Antiphosphatidylethanolamine, antiphosphatidylserine, antiphosphatidylinositol, and antiphosphatidic acid were the most frequently increased antibodies. The finding of increased antiphospholipid antibodies in these patients is compatible with the concept that antiphospholipid antibody formation is associated with structural changes in the red cell membrane and that such structural changes occur in the red cells of patients with sickle cell disease.

Antibodies, Antiphospholipid↗

PubMed1992

The effects of cholesterol oxidation products in sickle and normal red blood cell membranes.

The oxysterol content in normal and sickle red blood cell (RBC) membranes was assessed using thin-layer chromatography and capillary gas chromatography/mass spectrometry. Several more oxysterols were present in sickle RBCs compared to normal RBCs. Sickle RBC membranes had a higher concentration of 5 alpha,6 alpha-epoxycholesterol, 5 alpha-cholestane-3 beta,5,6 beta-triol, 7-ketocholesterol and 19-hydroxycholesterol than normal RBC membranes. The increased oxysterols in sickle RBC may be an effect of the increased oxidative stress which occurs in sickle RBC membranes. Physical characteristics of normal and sickle RBC membrane ghosts with and without inserted oxysterols were examined by Fourier transform infrared spectroscopy. The data are consistent with a greater sterol content in sickle cells compared to normal RBC membranes, and a possible oxysterol-cholesterol synergism.

Cholesterol↗

PubMed1992

Inhibition of NK cell-mediated cytotoxicity by oxysterols.

Some of the oxidation products of cholesterol (oxysterols) have profound effects on plasma membrane structure and function. The present studies were undertaken to determine the effects of oxysterols on NK cell-mediated cytotoxicity. When mouse spleen cells were preincubated with certain oxysterols, NK cell cytotoxicity was inhibited without loss of effector cell viability. The strongest inhibition was observed with oxysterols that are oxidized at the C-5, C-6, or C-7 positions of the sterol nucleus. Among these, 7 beta-hydroxycholesterol caused more inhibition than 7 alpha-hydroxycholesterol suggesting that the spatial orientation of the hydroxyl group in the beta-position results in a greater perturbation in plasma membrane structure than that oriented in the alpha-position. In contrast, oxysterols that are oxidized at the C-20 and C-25 positions that are located on the C-17 acyl chain had little or no inhibitory effect, suggesting that oxidation in the cholesterol nucleus which is situated closer to the phospholipid headgroups at the lipid bilayer-aqueous interface results in a more profound effect on the plasma membrane physical structure. These results suggest that the lytic function of NK cell is sensitive to alterations in the physical state of its plasma membrane induced by oxysterols.

Animals↗

PubMed1991

Effect of inserted oxysterols on phospholipid packing in normal and sickle red blood cell membranes.

Fourier transform infrared (FTIR) spectroscopy was used to examine the effect of oxysterol insertion into normal and sickle RBC membranes and the total lipid extracts of the membranes. Examination of the FTIR C-H stretch and fingerprint regions reveal that the insertion of 7 alpha- and 7 beta-hydroxycholesterol has the greatest effect on the fluidity of RBC membranes and lipid extracts. The results confirm the observation that sterol molecules are oriented in the membrane so that the 7 position is located in the phospholipid head group region at the lipid/water interface. The substitution of a keto for a hydroxy group at the number seven position decreases the effect of the sterol on membrane packing.

Anemia, Sickle Cell↗

PubMed1991

The Hofmeister effect in relation to membrane lipid phase stability.

The phase behaviour of L-alpha-1-palmitoyl-2-oleoyl-phosphatidylethanolamine (POPE) was examined in aqueous dispersions containing a range of sodium salts. The phase properties of the lipid exhibited a graded response to the presence of simple anions analogous to that of the Hofmeister series encountered in the study of the solution properties of proteins. Salts early in the series (such as Na2SO4 and NaCl) gave rise to substantial decreases in the temperature (Th) of the transition from the lamellar liquid-crystal to inverted hexagonal phase (L alpha----HII) and small increases in the temperature (Tm) of the transition from the lamellar gel to lamellar liquid-crystal phase (L beta----L alpha). Salts towards the end of this series (such as NaI and NaSCN) led to increases in Th and decreases in Tm. Similar effects were seen in lipid dispersions containing a series of non-ionic co-solutes. In both cases, the relative efficiency of perturbation of the lipid phase properties reflected the relative ability of the anion or co-solute to influence the structure of the bulk water. X-ray diffraction measurements indicated that these effects were probably mediated through the ability of the co-solutes to bring about changes in the extent of the lipid/water interface.

Calorimetry, Differential Scanning↗

PubMed1990

Phase structures and transitions in fully hydrated diacyltrehalose.

Real time X-ray diffraction was used to examine the gel bilayer to disordered bilayer phase transition in fully hydrated dipalmitoyltrehalose. The L beta to L alpha phase transition was shown to proceed via a second-order thermodynamic process involving incommensurate mesophase bilayer repeat structures and the formation of an intermediate rectangular acyl chain packing subcell. This phenomenon has only been previously shown to occur for dihexadecylphosphatidylcholine (DHPC) and dipalmitoylphosphatidylcholine (DPPC) dihydrates undergoing stepwise (i.e., noncontinuous) temperature changes. It can thus be inferred that the presence of trehalose-trehalose intra-bilayer interactions is a sufficient condition to modify the acyl chain structural rearrangements within the bilayer as a function of temperature.

1,2-Dipalmitoylphosphatidylcholine↗

PubMed1989

Membrane fusion and inverted phases.

We have found a correlation between liposome fusion kinetics and lipid phase behavior for several inverted phase forming lipids. N-Methylated dioleoylphosphatidylethanolamine (DOPE-Me), or mixtures of dioleoylphosphatidylethanolamine (DOPE) and dioleoylphosphatidylcholine (DOPC), will form an inverted hexagonal phase (HII) at high temperatures (above TH), a lamellar phase (L alpha) at low temperatures, and an isotropic/inverted cubic phase at intermediate temperatures, which is defined by the appearance of narrow isotropic 31P NMR resonances. The phase behavior has been verified by using high-sensitivity DSC, 31P NMR, freeze-fracture electron microscopy, and X-ray diffraction. The temperature range over which the narrow isotropic resonances occur is defined as delta TI, and the range ends at TH. Extruded liposomes (approximately 0.2 microns in diameter) composed of these lipids show fusion and leakage kinetics which are strongly correlated with the temperatures of these phase transitions. At temperatures below delta TI, where the lipid phase is L alpha, there is little or no fusion, i.e., mixing of aqueous contents, or leakage. However, as the temperature reaches delta TI, there is a rapid increase in both fusion and leakage rates. At temperatures above TH, the liposomes show aggregation-dependent lysis, as the rapid formation of HII phase precursors disrupts the membranes. We show that the correspondence between the fusion and leakage kinetics and the observed phase behavior is easily rationalized in terms of a recent kinetic theory of L alpha/inverted phase transitions. In particular, it is likely that membrane fusion and the L alpha/inverted cubic phase transition proceed via a common set of intermembrane intermediates.

Calorimetry, Differential Scanning↗

PubMed1989

Physiological levels of diacylglycerols in phospholipid membranes induce membrane fusion and stabilize inverted phases.

In the preceding paper (Ellens et al., 1989), it was shown that liposome fusion rates are substantially enhanced under the same conditions which induce isotropic 31P NMR resonances in multilamellar dispersions of the same lipid. Both of these phenomena occur within the same temperature interval, delta TI, below the L alpha/HII phase transition temperature, TH. TH and delta TI can be extremely sensitive to the lipid composition. The present work shows that 2 mol% of diacylglycerols like those produced by the phosphatidylinositol cycle in vivo can lower TH, delta TI, and the temperature for fast membrane fusion by 15-20 degrees C. N-Monomethylated dioleoylphosphatidylethanolamine is used as a model system. These results show that physiological levels of diacylglycerols can substantially increase the susceptibility of phospholipid membranes to fusion. This suggests that, in addition to their role in protein kinase C activation, diacylglycerols could play a more direct role in the fusion event during stimulus-exocytosis coupling in vivo.

Chemical Phenomena↗

PubMed1988

Structural rearrangements during crystal-liquid-crystal and gel-liquid-crystal phase transitions in aqueous dispersions of dipalmitoylphosphatidylethanolamine. A time-resolved X-ray diffraction study.

The mechanism and kinetics of the crystal-liquid-crystal (Lc----L alpha) and gel-liquid-crystal (L beta----L alpha) transitions of the L-enantiomer and racemic dipalmitoylphosphatidylethanolamine have been examined in temperature scans and jumps using time-resolved X-ray diffraction methods. The Lc----L alpha transformations (at 66 degrees C for L-dipalmitoylphosphatidylethanolamine and 82 degrees C for DL-dipalmitoylphosphatidylethanolamine) were found to be two-state (first-order) processes characterised by co-existence of the initial Lc and final L alpha states during the transition with the absence of any detectable intermediates states. The transition mechanism involves firstly, disordering of the hydrocarbon chains which makes a major contribution to the transition enthalpy and secondly by a transition in the lamellar repeat spacing. The overall relaxation time of the Lc----L alpha transition of L-dipalmitoylphosphatidylethanolamine during temperature jumps of 4.5 degrees C/s was about 10 s. A gradual increase in the gel-state interchain spacing during the L beta----L alpha transitions of L- and DL-dipalmitoylphosphatidylethanolamine preceded a broadening of the wide-angle diffraction peak. There was a concomitant and continuous increase of the lamellar repeat spacing to values typical of the L alpha phase with increasing temperature. This sequence of events is completely reversible on cooling with a temperature hysteresis of 5-6 degrees C. The relaxation times of the L beta---L alpha transitions during jumps of 4.5 degrees C/s were about 2 s in both the heating and cooling directions.

Crystallization↗