A balance and proprioception intervention programme to enhance combat performance in military personnel.

BACKGROUND: Optimal functioning of the lower extremities under repeated movements on unstable surfaces is essential for military effectiveness. Intervention training to promote proprioceptive ability should be considered in order to limit the risk for musculoskeletal injuries. The aim of this study was to assess the effect of a proprioceptive intervention programme on static and dynamic postural balance among Israel Defense Forces combat soldiers. METHODS: Twenty-seven male soldiers, aged 18-20 years, from a physical fitness instructor's course, were randomly divided into two groups matched by age and army unit. The intervention group (INT) underwent 4 weeks of proprioceptive exercises for 10 min daily; the control group underwent 4 weeks of upper body stretching exercises for 10 min daily. All participants were tested pre and postintervention for both static and dynamic postural balance. RESULTS: Significant interaction (condition*pre-post-test*group) was found for static postural balance, indicating that for the INT group, in condition 3 (on an unstable surface-BOSU), the post-test result was significantly better compared with the pretest result (p<0.05). Following intervention, the INT group showed significant correlations between static postural stability in condition 2 (eyes closed) and the dynamic postural stability (length of time walked on the beam following fatigue) (r ranged from 0.647 to 0.822; p<0.05). CONCLUSIONS: The proprioceptive intervention programme for combat soldiers improved static postural balance on unstable surfaces, and improved the correlation between static postural balance in the eyes closed condition and dynamic postural balance following fatigue. Further longitudinal studies are needed to verify the relationship between proprioception programmes, additional weight bearing and the reduction of subsequent injuries in combat soldiers.

Low protein and high-energy diet: a possible natural cause of fatty liver hemorrhagic syndrome in caged White Leghorn laying hens.

Fatty liver hemorrhagic syndrome (FLHS) is a metabolic condition of chicken and other birds caused by diverse nutritional, hormonal, environmental, and metabolic factors. Here we studied the effect of different diet composition on the induction of FLHS in single comb White Leghorn (WL) Hy-line laying hens. Seventy six (76) young WL (26 wks old) laying hens and 69 old hens (84 wks old) of the same breed were each divided into 4 treatment groups and provided 4 different diet treatments. The diet treatments included: control (C), 17.5% CP, 3.5% fat (F); normal protein, high fat (HF), 17.5% CP, 7% F; low protein, normal fat (LP), 13% CP, 3.5% F; and low protein, high fat (LPHF), 13% CP, 6.5% F. The diets containing high fat also had a higher ME of 3,000 kcal/kg of feed while the other 2 diets with normal fat had a regular lower amount of ME (2750 kcal/kg). Hen-day egg production (HDEP), ADFI, BW, egg weight, plasma enzymes indicating liver damage (alkaline phosphatase [ALP], aspartate aminotransferase [AST], gamma-glutamyl transferase [GGT]), liver and abdominal fat weight, liver color score (LCS), liver hemorrhagic score (LHS), liver fat content (LFC), liver histological examination, lipid peroxidation product in the liver, and genes indicating liver inflammation were evaluated. HDEP, ADFI, BW, and egg weight were significantly decreased in the LPHF diet group, while egg weight was also decreased in the LP diet group. In the young hens (LPHF group), ALP was found significantly higher at 30 d of diet treatment and was numerically higher throughout the experiment, while AST was significantly higher at 105 d of treatment. LCS, LHS, and LFC were significantly higher in young hens on the LPHF diet treatment. A liver histological examination shows more lipid vacuolization in the LPHF treatment diet. HF or LP alone had no significant effect on LFC, LHS, or LCS. We suggest that LP in the diet with higher ME from fat can be a possible natural cause for predisposing laying hens to FLHS.

Does Wearing Textured Insoles during Non-class Time Improve Proprioception in Professional Dancers?

This study sought to determine whether textured insoles inserted in the sports shoes of young dancers improved their inversion and eversion ankle movement discrimination. 26 ballet dancers (14 female, 12 male) from the Australian Ballet School, ages 14-19 years, were divided into 2 groups according to sex and class levels. During the first 4 weeks, the first intervention group (GRP1) was asked to wear textured insoles in their sports shoes during non-class periods, and the second intervention group (GRP2) followed standard practice. In the next 4 weeks, GRP2 was asked to wear the textured insoles and GRP1 did not wear the textured insoles. Participants were tested pre-intervention, after 4 weeks, and at 8 weeks for both inversion and eversion ankle discrimination. In both inversion and eversion testing positions, interaction was found between the 2 groups and the 3 testing times (p<0.001), with significant differences between the first testing and the second testing (p=0.038 and p=0.019, respectively), and between the third testing and the second testing (p=0.003 and p=0.029, respectively). In conclusion, the stimulation to the proprioceptive system arising from textured insoles worn for 4 weeks was sufficient to improve the ankle proprioception of ballet dancers, in both inversion and eversion movements.

Reactive aldehydes--second messengers of free radicals in diabetes mellitus.

Elevated levels of pro-oxidants and various markers of oxidative tissue damage were found in diabetic patients, indicating involvement of oxidative stress in the pathogenesis of diabetes mellitus (DM). On one side, physiological levels of reactive oxygen species (ROS) play an important role in redox signaling of various cells, while on the other, excessive ROS production can jeopardize the integrity and physiological functions of cellular macromolecules, in particular proteins, thus contributing to the pathogenesis of DM. Reactive aldehydes, especially 4-hydroxynonenal (HNE), are considered as second messengers of free radicals that act both as signaling molecules and as cytotoxic products of lipid peroxidation causing long-lasting biological consequences, in particular by covalent modification of macromolecules. Accordingly, the HNE and related reactive aldehydes may play important roles in the pathophysiology of DM, both in the development of the disease and in its progression and complications due to the following: (i) exposure of cells to supraphysiological levels of 4-hydroxyalkenals, (ii) persistent and sustained generation of 4-hydroxyalkenals that progressively affect vulnerable cells that lack an efficient bioactive aldehyde neutralization system, (iii) altered redox signaling influenced by reactive aldehydes, in particular by HNE, and (iv) induction of extracellular generation of similar aldehydes under secondary pathological conditions, such as low-grade inflammation.

Potentiation of Fas-mediated apoptosis by attenuated production of mitochondria-derived reactive oxygen species.

The role of reactive oxygen species (ROS) production in death receptor-mediated apoptosis is ill-defined. Here, we show that ROS levels play a role in moderating Fas-dependent apoptosis. Treatment of Jurkat T cells with oligomycin (ATP-synthase inhibitor) or (mitochondrial uncoupler) and Fas-activating antibody (CH11) facilitated rapid cell death that was not associated with decreased ATP production or increased DEVDase activity and cytochrome c release. However, a decrease in cellular ROS production was associated with CH11 treatment, and combinations of CH11 with oligomycin or FCCP further inhibited cellular ROS production. Thus, decreased ROS production is correlated with enhanced cell death. A transition from state 3 to state 4 mitochondrial respiration accounted for the attenuated ROS production and membrane potential. Similar observations were demonstrated in isolated rat liver mitochondria. These data show that ROS production is important in receptor-mediated apoptosis, playing a pivotal role in cell survival.

Mitochondrial control of inducible nitric oxide production in stimulated RAW 264.7 macrophages.

Addition of glucose to activated RAW 264.7 macrophages or addition of mitochondrial electron-transfer chain inhibitors enhanced the cellular nitric oxide production. An additive effect of rotenone or antimycin A and glucose on enhancing nitric oxide production was shown. Uncoupling the mitochondria by a chemical uncoupler decreased nitric oxide production. The mitochondria membrane potential was found to be important for cell viability. Although nitric oxide is the physiological inhibitor of mitochondrial respiration, this study indicates that mitochondria were not inhibited in the activated macrophages. Furthermore, a role of mitochondria in the rapid regulation of nitric oxide synthesis by the inducible nitric oxide synthase has been demonstrated.

Protection by thiols of the mitochondrial complexes from 4-hydroxy-2-nonenal.

In the present study, the effects of 4-hydroxy-2-nonenal (HNE) on highly purified pyruvate dehydrogenase complex (PDC) and its catalytic components in vitro and on PDC, alpha-ketoglutarate dehydrogenase complex (KGDC), and the branched-chain alpha-keto acid dehydrogenase complex (BCKDC) activities in cultured human HepG2 cells were investigated. Among the PDC components, the activity of the dihydrolipoamide acetyltransferase-E3-binding protein subcomplex (E2-E3BP) only was decreased by HNE. Dihydrolipoamide dehydrogenase (E3) protected the E2-E3BP subcomplex from HNE inactivation in the absence of the substrates. In the presence of E3 and NADH, when lipoyl groups were reduced, higher inactivation of the E2-E3BP subcomplex by HNE was observed. Purified PDC was protected from HNE-induced inactivation by several thiol compounds including lipoic acid plus [LA-plus; 2-(N,N-dimethylamine)ethylamidolipoate(.)HCl]. Treatment of cultured HepG2 cells with HNE resulted in a significant reduction of PDC and KGDC activities, whereas BCKDC activity decreased to a lesser extent. Lipoyl compounds afforded protection from HNE-induced inhibition of PDC. This protection was higher in the presence of cysteine and reduced glutathione. Cysteine was able to restore PDC activity to some extent after HNE treatment. These findings show that thiols, including lipoic acid, provide protection against HNE-induced inactivation of lipoyl-containing complexes in the mitochondria.

Inhibitory effect of alpha-lipoic acid and its positively charged amide analogue on nitric oxide production in RAW 264.7 macrophages.

The aim of this study was to investigate the effect of the mitochondrial cofactor alpha-lipoic acid [R (+) LA] or its lipoamide analogue, 2-(N,N-dimethylamine) ethylamido lipoate [R (+) LA-plus], on nitric oxide (NO) production in RAW 264.7 macrophages. NO production from RAW 264.7 cells stimulated with 10 microg/mL of lipopolysaccharide and 50 U/mL of interferon-gamma was measured directly by electron spin resonance using spin-trapping techniques. R (+) LA or R (+) LA-plus was found to inhibit NO production at pharmacologically relevant concentrations. However, in a cell-free chemical system, neither R (+) LA nor R (+) LA-plus was able to directly scavenge NO. Furthermore, in the presence of 2.5 or 25 mM glucose, the inhibitory effects of R (+) LA and R (+) LA-plus on NO production were decreased markedly, while they showed more potent inhibitory effects in the presence of 2 microM rotenone or 5 microg/mL of antimycin A, inhibitors of mitochondrial complex I and complex III, respectively. Glucose, rotenone, or antimycin A alone resulted in an increase of NO production. These results suggest that NO production in macrophages can be regulated by glucose and mitochondrial respiration, and that modulation of NO production by lipoic acid or lipoamide analogues in inflammatory situations is attributed not to their radical scavenging activity but to their redox properties.

Cellular and mitochondrial changes in glutamate-induced HT4 neuronal cell death.

Elevated levels of extracellular glutamate are neurotoxic. The cytotoxic property of extracellular glutamate is known to mediate two primary mechanisms, excitotoxicity and excitotoxicity-independent processes. The excitotoxicity-independent pathway was investigated in the current study in a mouse hippocampal-derived HT4 cell line. Exposure of HT4 cells to glutamate for 12h induced loss of cell viability preceded by rapid loss of intracellular reduced glutathione followed by accumulation of intracellular reactive oxygen species, elevation of intracellular Ca(2+), progressive loss of mitochondrial membrane potential swelling and loss of mitochondrial outer membrane integrity. Glutamate-induced loss of DNA integrity has been detected. The antioxidants alpha-tocopherol and trolox, mitochondrial calcium uniporter inhibitor Ruthenium Red and protein synthesis inhibitor cycloheximide all showed protection against glutamate-induced toxicity. None of the protective agents except for alpha-tocopherol controlled the glutamate-induced reactive oxygen species build-up. However, these cell death regulators prevented the glutamate-induced mitochondrial damage and regulated glutamate-induced increase in intracellular Ca(2+). Carbonyl cyanide p-trifluoromethoxyphenyl-hydrazone, a mitochondrial uncoupler, partially protected against glutamate-induced cell death and mitochondrial damage, while the mitochondrial ribosomal inhibitor chloramphenicol and extracellular Ca(2+) chelator ethylene glycol-bis(beta-aminoethyl ether)-N,N,N',N'-tetraacetic acid did not protect the cells against glutamate treatment. The results of this study demonstrated that mitochondrial dysfunction was a key event in the excitotoxicity-independent component of neuronal cell death. Reactive oxygen species accumulation and glutathione depletion were prominent in glutamate-treated cells; however, these events were not direct mediators of cell death.

Quantification of the overall reactive oxygen species scavenging capacity of biological fluids and tissues.

A method has been developed for measuring and evaluating the overall antioxidant activity derived from the low-molecular weight antioxidants (scavengers). The principle governing this method is based on a common chemical characteristic of the scavengers, their reducing properties. It was hypothesized and then demonstrated that an evaluation of the overall reducing power of a biological sample correlates with the overall scavenging activity of the sample. In order to quantify the total reducing power, the cyclic voltammetry methodology was applied. The resulting measurements correlated with the antioxidant activity of both hydrophilic and lipophilic scavengers. The method is suitable for use in biological fluids and in tissue homogenates, and can supply information concerning the type of antioxidants and their total concentration without having to determine specific compounds. A noninvasive procedure for determining skin overall scavenging activity is also described. This method is based on a well containing an extraction solution that is attached to the skin's surface. Following incubation time the extraction solution is analyzed using the cyclic voltammeter instrument and other methods. We have found these methods suitable for evaluating the reducing capacity status in various clinical conditions such as diabetes, ionizing and nonionizing irradiation, brain degenerative diseases, head trauma, and inflammatory bowel diseases. This method is also an efficient tool for evaluating the overall antioxidant capacity of mixtures of antioxidant preparations in vitro. The measurements themselves are simple and rapid. Furthermore, they do not require manipulation of the samples.

Comparison of the effect of alpha-lipoic acid and alpha-tocopherol supplementation on measures of oxidative stress.

In vitro studies have shown that alpha-lipoic acid (LA) is an antioxidant. There is a paucity of studies on LA supplementation in humans. Therefore, the aim of this study was to assess the effect of oral supplementation with LA alone and in combination with alpha-tocopherol (AT) on measures of oxidative stress. A total of 31 healthy adults were supplemented for 2 months either with LA (600 mg/d, n = 16), or with AT (400 IU/d, n = 15) alone, and then with the combination of both for 2 additional months. At baseline, after 2 and 4 months of supplementation, urine for F2-isoprostanes, plasma for protein carbonyl measurement and low-density lipoprotein (LDL) oxidative susceptibility was collected. Plasma oxidizability was assessed after incubation with 100 mM 2,2'-azobis (2-amidinopropane) hydrochloride (AAPH) for 4 h at 37 degrees C. LDL was subjected to copper- and AAPH-catalyzed oxidation at 37 degrees C over 5 h and the lag time was computed. LA significantly increased the lag time of LDL lipid peroxide formation for both copper-catalyzed and AAPH-induced LDL oxidalion (p < .05), decreased urinary F2-isoprostanes levels (p < .05), and plasma carbonyl levels after AAPH oxidation (p < .001). AT prolonged LDL lag time of lipid peroxide formation (p < .01 ) and conjugated dienes (p < .01) after copper-catalyzed LDL oxidation, decreased urinary F2-isoprostanes (p < .001), but had no effect on plasma carbonyls. The addition of LA to AT did not produce an additional significant improvement in the measures of oxidative stress. In conclusion, LA supplementation functions as an antioxidant, because it decreases plasma- and LDL-oxidation and urinary isoprostanes.

Hemolysis of human red blood cells induced by the combination of diethyldithiocarbamate (DDC) and divalent metals: modulation by anaerobiosis, certain antioxidants and oxidants.

The objective of the present communication is to describe the role played by combinations between diethydithiocarbamate (DDC) and divalent metals in hemolysis of human RBC. RBC which had been treated with DDC (10-50 microM) were moderately hemolyzed (about 50%) upon the addition of subtoxic amounts of Cu2+ (50 microM). However, a much stronger and a faster hemolysis occurred either if mixtures of RBC-DDC were immediately treated either by Co2+ (50 microM) or by a premixture of Cu2+ and Co2+ (Cu:Co) (50 microM). While Fe2+ and Ni2+, at 50 microM, initiated 30-50% hemolysis when combined with DDC (50 microM), on a molar basis, Cd2+ was at least 50 fold more efficient than any of the other metals in the initiation of hemolysis by DDC. On the other hand, neither Mn2+ nor Zn2+, had any hemolysis-initiating effects. Co2+ was the only metal which totally blocked hemolysis if added to DDC prior to the addition of the other metals. Hemolysis by mixtures of DDC + (Cu:Co) was strongly inhibited by anaerobiosis (flushing with nitrogen gas), by the reducing agents glutathione, N-acetyl cysteine, mercaptosuccinate, ascorbate, TEMPO, and alpha-tocopherol, by the PLA2 inhibitorbromophenacylbromide (BrPACBr), by tetracycline as well as by phosphatidyl choline, cholesterol and by trypan blue. However, TEMPO, BrPACBr and PC were the only agents which inhibited hemolysis induced by DDC: Cd2+ complexes. On the other hand, none of the classical scavengers of reactive oxygen species (ROS) employed e.g dimethylthiourea, catalase, histidine, mannitol, sodium benzoate, nor the metal chelators desferal and phenanthroline, had any appreciable inhibitory effects on hemolysis induced by DDC + (Cu:Co). DDC oxidized by H2O2 lost its capacity to act in concert either with Cu2+ or with Cd2+ to hemolyze RBC. While either heating RBC to temperatures greater than 37 degrees C or exposure of the cells to glucose-oxidase-generated peroxide diminished their susceptibility to hemolysis, exposure to the peroxyl radical from AAPH, enhanced hemolysis by DDC + (Cu:Co). The cyclovoltammetry patterns of DDC were drastically changed either by Cu2+, Co2+ or by Cd2+ suggesting a strong interaction of the metals with DDC. Also, while the absorbance spectrum of DDC at 280 nm was decreased by 50% either by Co2+, Cd2+ or by H2O2, a 90% reduction in absorbance occurred if DDC + H2O2 mixtures were treated either by Cu2+ or by Co2+, but not by Cd2+. Taken together, it is suggested that DDC-metal chelates can induce hemolysis by affecting the stability and the integrity of the RBC membrane, and possibly also of the cytoskeleton and the role played by reducing agents as inhibitors might be related to their ability to deplete oxygen which is also supported by the inhibitory effects of anaeobiosis.

Neuroprotective effects of alpha-lipoic acid and its positively charged amide analogue.

Elevated levels of extracellular glutamate have been linked to reactive oxygen species mediated neuronal damage and brain disorders. Lipoic acid is a potent antioxidant that has previously been shown to exhibit neuroprotection in clinical studies. A new positively charged water soluble lipoic acid amide analog, 2-(N,N-dimethylamine) ethylamido lipoate HCl (LA-plus), with a better cellular reduction and retention of the reduced form was developed. This novel antioxidant was tested for protection against glutamate induced cytotoxicity in a HT4 neuronal cell line. Glutamate treatment for 12 h resulted in significant release of LDH from cells to the medium suggesting cytotoxicity. Measurement of intracellular peroxides showed marked (up to 200%) increase after 6 h of glutamate treatment. Compared to lipoic acid, LA-plus was more effective in (1) protecting cells against glutamate induced cytotoxicity, (2) preventing glutamate induced loss of intracellular GSH, and (3) disallowing increase of intracellular peroxide level following the glutamate challenge. The protective effect of LA-plus was found to be independent of its stereochemistry. The protective function of this antioxidant was synergistically enhanced by selenium. These results demonstrate that LA-plus is a potent protector of neuronal cells against glutamate-induced cytotoxicity and associated oxidative stress.

Noninvasive in vivo evaluation of skin antioxidant activity and oxidation status.

The method described here allows noninvasive quantification of reducing LMWA or the lipid hydroperoxide present on the surface of the skin. Quantification of reducing antioxidants can be achieved because they are secreted from the skin surface into a well containing an extraction solution. Analysis of the reducing equivalents released indicates the presence of uric acid and ascorbic acid. Other LMWA released from the skin are as yet unidentified. The secretion of the LMWA reaches a plateau following 20-30 min of incubation. Therefore, a 30-min incubation period was chosen as the optimal time for the extraction solution to be present in the well and in contact with the skin. This extraction procedure can be repeated after 24 hr. This period of time is needed for regeneration of the LMWA to their initial levels. Direct measurement allows continuous determination of the release of LMWA and their interaction with the iron chelate. The reaction is completed after 25-35 min, at which time the final potential can be recorded. When organic peroxides on the surface of the skin are determined, it is important that the glassy carbon electrode be in close contact with the skin, since the reaction occurs on the surface of the electrode and the bound peroxide on the outer layer of the skin. Furthermore, close contact is needed to avoid interference of reducing equivalents secreted from the skin into the well.

Low-density lipoprotein oxidation and its prevention by amidothionophosphate antioxidants.

Amidothionophosphates (AMTPs) are a novel group of antioxidants that are lacking in pro-oxidant activity. In this paper, we compare two different amidothionophosphates: 2-hydroxy-ethyl amido, diethyl thionophosphate (AMTP-B), which contains a single primary amido group, and N,N',N-tripropylamidothionophosphate (AMTP-3A), which contains three primary amido groups. The lipoprotein/medium partition coefficients of AMTP-3A and AMTP-B are 74 and 38, respectively. Both protected isolated human low density lipoprotein (LDL) against oxidative damage induced by copper sulfate. Oxidative damage to polyunsaturated acyl chains was determined by gas chromatography (GC), and oxidation kinetics were monitored by following the accumulation of conjugated dienes spectrophotometrically at 234 nm. The AMTP antioxidants significantly protected the LDL against Cu2+-induced oxidation. However, if the LDLs were already partially oxidized, protection against oxidation by the AMTPs was reduced. AMTP-3A was more effective in protecting LDL than was AMTP-B. The difference in antioxidant activity was attributed to the 15-fold higher reactivity of AMTP-3A toward peroxides. Oxidizability of plasma lipoproteins from guinea pigs injected with AMTPs was strongly reduced.

A positively charged alpha-lipoic acid analogue with increased cellular uptake and more potent immunomodulatory activity.

alpha-Lipoic acid (LA) is taken up by cells and reduced to its potent dithiol form, dihydrolipoate(DHLA), much of which is rapidly effluxed out from cells. To improve retention in cells, the LA molecule was modified to confer a positive charge at physiological pH. N,N-dimethyl,N'-2-amidoethyl-lipoate was synthesized. The protonated form of the new molecule is referred to as LA-Plus. The uptake of LA-Plus by human Wurzburg T cells was higher compared to that of LA. Several-fold higher amounts of DHLA-Plus, the corresponding reduced form of LA-Plus, were detected in LA-Plus treated cells compared to the amount of DHLA found in cells treated with LA. At 100 microM, LA did not but LA-Plus inhibited H2O2 induced NF-kappaB activation and NF-kappaB directed IL-2 receptor expression. Both LA and LA-Plus synergised with selenium in inhibiting H2O2 induced NF-kappaB activation. At 150 microM LA-Plus, but not LA, inhibited TNFalpha induced NF-kappaB activation. At 5 microM LA-Plus, but not LA, protected against both spontaneous and etoposide induced apoptosis in rat thymocytes. LA-Plus is thus an improved form of LA with increased therapeutic potential.

Hydration of polyethylene glycol-grafted liposomes.

This study aimed to characterize the effect of polyethylene glycol of 2000 molecular weight (PEG2000) attached to a dialkylphosphatidic acid (dihexadecylphosphatidyl (DHP)-PEG2000) on the hydration and thermodynamic stability of lipid assemblies. Differential scanning calorimetry, densitometry, and ultrasound velocity and absorption measurements were used for thermodynamic and hydrational characterization. Using a differential scanning calorimetry technique we showed that each molecule of PEG2000 binds 136 +/- 4 molecules of water. For PEG2000 covalently attached to the lipid molecules organized in micelles, the water binding increases to 210 +/- 6 water molecules. This demonstrates that the two different structural configurations of the PEG2000, a random coil in the case of the free PEG and a brush in the case of DHP-PEG2000 micelles, differ in their hydration level. Ultrasound absorption changes in liposomes reflect mainly the heterophase fluctuations and packing defects in the lipid bilayer. The PEG-induced excess ultrasound absorption of the lipid bilayer at 7.7 MHz for PEG-lipid concentrations over 5 mol % indicates the increase in the relaxation time of the headgroup rotation due to PEG-PEG interactions. The adiabatic compressibility (calculated from ultrasound velocity and density) of the lipid bilayer of the liposome increases monotonically with PEG-lipid concentration up to approximately 7 mol %, reflecting release of water from the lipid headgroup region. Elimination of this water, induced by grafted PEG, leads to a decrease in bilayer defects and enhanced lateral packing of the phospholipid acyl chains. We assume that the dehydration of the lipid headgroup region in conjunction with the increase of the hydration of the outer layer by grafting PEG in brush configuration are responsible for increasing thermodynamic stability of the liposomes at 5-7 mol % of PEG-lipid. At higher PEG-lipid concentrations, compressibility and partial volume of the lipid phase of the samples decrease. This reflects the increase in hydration of the lipid headgroup region (up to five additional water molecules per lipid molecule for 12 mol % PEG-lipid) and the weakening of the bilayer packing due to the lateral repulsion of PEG chains.

Oxidative stress effect on the integrity of lipid bilayers is modulated by cholesterol level of bilayers.

Large unilamellar vesicles (120-160 nm) composed of egg phosphatidylcholine (egg PC) containing approximately 22 wt% of polyunsaturated fatty acids (PUFA) and various mol% (0, 10, 22, or 45) of cholesterol were exposed to oxidative stress. The hydrophilic azo compound 2,2'-azobis-(2-amidinopropane)2HCl (AAPH) which was thermally decomposed to produce a constant flux of peroxy radicals was the source of the oxidative stress (< or = 48 h incubation at 37 degrees C). Cholesterol loss following the oxidation was up to 33%, while PUFA were more extensively damaged; loss was up to 52, 88, and 100% for C-18:2, C-20:4, and C-22:6, respectively. (ii) Oxidizability of cholesterol when quantified in absolute amount was three-fold higher when its level was 45 mol%. The interrelationship between bilayer structure, especially its lateral organization and free volume, and lipid peroxidation are discussed. Differential scanning calorimetry of oxidized multilamellar vesicles lacking cholesterol revealed that a high level of oxidative damage to egg phosphatidylcholine PUFA resulted in the loss of the gel to liquid-crystalline phase transition of egg PC (broad peak at around -8 degrees C).