Interaction of hexadecylbetainate chloride with biological relevant lipids.

The present work investigates the interaction of hexadecylbetainate chloride (C(16)BC), a glycine betaine-based ester with palmitoyl-oleoyl-phosphatidylcholine (POPC), sphingomyelin (SM), and cholesterol (CHOL), three biological relevant lipids present in the outer leaflet of the mammalian plasma membrane. The binding affinity and the mixing behavior between the lipids and C(16)BC are discussed based on experimental (isothermal titration calorimetry (ITC) and Langmuir film balance) and molecular modeling studies. The results show that the interaction between C(16)BC and each lipid is thermodynamically favorable and does not affect the integrity of the lipid vesicles. The primary adsorption of C(16)BC into the lipid film is mainly governed by a hydrophobic effect. Once C(16)BC is inserted in the lipid film, the polar component of the interaction energy between C(16)BC and the lipid becomes predominant. Presence of CHOL increases the affinity of C(16)BC for membrane. This result can be explained by the optimal matching between C(16)BC and CHOL within the film rather by a change of membrane fluidity due to the presence of CHOL. The interaction between C(16)BC and SM is also favorable and gives rise to highly stable monolayers probably due to hydrogen bonds between their hydrophilic groups. The interaction of C(16)BC with POPC is less favorable but does not destabilize the mixed monolayer from a thermodynamic point of view. Interestingly, for all the monolayers investigated, the exclusion surface pressures are above the presumed lateral pressure of the plasma membranes suggesting that C(16)BC would be able to penetrate into mammalian plasma membranes in vivo. These results may serve as a useful basis in understanding the interaction of C(16)BC with real membranes.

Penetration behaviour of alkylbetainate chlorides into lipid monolayers.

In this paper, the penetration behaviour of the alkylbetainate chloride surfactants (C(n)BC, n=10-16) into lipid monolayers of dipalmitoylphosphatidylserine (DPPS), dipalmitoylphosphatidic acid (DPPA), dipalmitoylphosphatidylethanolamine (DPPE), palmitoyoleoylphosphatidylcholine (POPC) and cholesterol (CHOL) is investigated using the Langmuir trough technique. The penetration of C(n)BC is followed by measurement of the surface pressure increase (Δπ) at a constant surface area after the injection of C(n)BC into the aqueous phase, underneath the lipid monolayer previously spread at the air-water interface at 25°C and at different initial surface pressures (π(i)). The influence of both the lipid head group and the surfactant hydrocarbon chain length on the effectiveness of C(n)BC penetration into these monolayers is discussed. The results have shown that C(n)BC adsorb at the air-water interface giving evidence of their surface-active properties. The adsorption kinetics of C16BC into different lipid monolayers are lipid head charge and lipid head volume-dependent. The magnitude of the surface pressure increase (Δπ) arises in the following order: DPPA>DPPS≫CHOL≈DPPE>POPC. C(n)BC penetration into negatively-charged (DPPS and DPPA) monolayers does not seem to depend on surfactant alkyl-chain length compared to uncharged (CHOL) and zwitterionic (DPPE and POPC) monolayers for which Δπ increases with a larger alkyl-chain length. Electrostatic interactions are mainly involved in the affinity of C(n)BC with monolayers but the hydrophobic effect plays also a role.

Effect of cholesterol and fatty acids on the molecular interactions of fengycin with Stratum corneum mimicking lipid monolayers.

The combination of atomic force microscopy (AFM) and the Langmuir trough technique was used in this work to investigate the molecular interactions of fengycin with lipid monolayers constituted of the major lipid classes found in human stratum corneum (SC). AFM imaging o f spread SC lipids/fengycin monolayers showed that fengycin preferentially partitions into cholesterol-rich phases surrounding 2D domains mainly constituted of ceramide and fatty acid molecules. Penetration experiments of fengycin from the subphase into SC-mimicking monolayers clearly indicated that the lipopeptide insertion at the lipid interface is enhanced in the presence of cholesterol. AFM analysis of mixed SC lipids/fengycin monolayers obtained after lipopeptide penetration revealed that cholesterol strongly interacts with fengycin and undergoes specific molecular interactions with more disordered, loosely packed ceramide molecules. These results highlight the capacity of fengycin to interact with the lipid constituents of the extracellular matrix of SC and, in particular, with cholesterol.

Reduction of Cr(VI) by immobilized cells of Desulfovibrio vulgaris NCIMB 8303 and Microbacterium sp. NCIMB 13776.

Hexavalent chromium, a carcinogen and mutagen, can be reduced to Cr(III) by Desulfovibrio vulgaris NCIMB 8303 and Microbacterium sp. NCIMB 13776. This study examined Cr(VI) reduction by immobilized cells of the two strains in a common solution matrix using various entrapment matrices. Chitosan and PVA-borate beads did not retain integrity and supported low or no reduction of Cr(VI) by the cells. A commercial preparation (Lentikats) was stable but also did not support Cr(VI) reduction. K-carrageenan beads were stable in batch suspensions but gel integrity was lost after only 5 h in a flow-through system in the presence of 100 microM Cr(VI). The best immobilization matrices were agar and agarose, where the initial rates of reduction of Cr(VI) (from 500 microM solution) for D. vulgaris NCIMB 8303 and Microbacterium sp. NCIMB 13776 were 127 (agar) and 130 (agarose), and 15 (agar) and 12 (agarose) nmol h(-1) mg dry cell wt(-1), respectively. The higher removal of Cr(VI) by D. vulgaris was also seen in 14-mL packed-bed flow-through columns, where, at a flow rate of 2.4 mL h(-1), the percentage removal of Cr(VI) was approximately 95% and 60% for D. vulgaris and Microbacterium sp., respectively (agar-immobilized cells). The Cr(VI) reducing activities of D. vulgaris and Microbacterium sp. were lost after 159 and 140 h, respectively. Examination of the beads for structural integrity within the columns in situ using magnetic resonance imaging after 24 and 100 h of continuous operation against Cr(VI) (with negligible Cr retained within the columns) showed that agar beads were more stable with time. The most appropriate system for development of a continuous bioprocess is thus the use of D. vulgaris NCIMB 8303 immobilized in an agar gel matrix.

Continuous removal of Cr(VI) from aqueous solution catalysed by palladised biomass of Desulfovibrio vulgaris.

Growth-decoupled cells of Desulfovibrio vulgaris NCIMB 8303 can be used to reduce Pd(II) to cell-bound Pd(0) (Bio-Pd(0)), a bioinorganic catalyst capable of reducing hexavalent chromium to less toxic Cr(III), using formate as the electron donor. Magnetic resonance imaging showed that Bio-Pd(0), immobilized in chitosan and agar beads, is distinguishable from the surrounding gel and is evenly dispersed within the immobilization matrix. Agar-immobilized Bio-Pd(0) and 'chemical Pd(0)' were packed into continuous-flow reactors, and challenged with a solution containing 100 microM Cr(VI) (pH 7) at a flow rate of 2.4 ml h(-1). Agar-immobilized chemical Pd(0) columns lost Cr(VI) reducing ability by 160 h, whereas columns containing immobilized Bio-Pd(0) maintained 90% reduction until 680 h, after which reduction efficiency was gradually lost.

Imaging mixed lipid monolayers by dynamic atomic force microscopy.

Phase imaging with tapping mode atomic force microscopy (AFM) and force modulation microscopy were used to probe the mechanical properties of phase-separated lipid monolayers made of a mixture (0.25:0.75) of the surface-active lipopeptide surfactin and of dipalmitoylphosphatidylcholine (DPPC). The pi-A isotherms and the result of a molecular modeling study revealed a loose, 2-D liquid-like organization for the surfactin molecules and a closely packed, 2-D solid-like organization for DPPC molecules. This difference in molecular organization was responsible for a significant contrast in height, tapping mode phase and force modulation amplitude images. Phase imaging at light tapping, i.e., with a ratio of the set-point tapping amplitude with respect to the free amplitude A(sp)/A(0) approximately 0.9, showed larger phase shifts on the solid-like DPPC domains attributed to larger Young's modulus. However, contrast inversion was observed for A(sp)/A(0)<0.7, suggesting that at moderate and hard tapping the image contrast was dominated by the probe-sample contact area. Surprisingly, force modulation amplitude images showed larger stiffness for the liquid-like surfactin domains, suggesting that the contrast was dominated by contact area effects rather than by Young's modulus. These data emphasize the complex nature of the contrast mechanisms of dynamic AFM images recorded on mixed lipid monolayers.

MRI phase mapping of temperature distributions induced in food by microwave heating.

A range of temperature-sensitive MRI parameters of water (T2, T1, diffusion coefficient, and chemical shift) were evaluated to map in three dimensions the non-uniform temperature distributions induced by microwave heating in both model and real food systems. Phase mapping was found to be the most robust method, and evaluations of possible experimental errors were based on semi-quantitative studies of homogeneous and heterogeneous systems. The MRI protocol provides complementary phase and magnitude data, which are related to the sample temperature and structural heterogeneity, respectively. Used together, they relate the temperature changes to the differential thermal properties of the various components within a heterogeneous sample. The potential applications of this technique to microwave and other forms of heating is discussed.

Nature and consequences of stressful life events in homosexual HIV-positive men: a review.

A great deal of research has been conducted into the stressful experiences that befall HIV-infected individuals. In this review we have focused on the work that has been conducted with HIV-positive homosexual males and have examined issues concerning the measurement, nature and consequences of stressful life events. It is apparent that, in consort with most other life events research, the measurement of events in this patient group is affected by methodological difficulties. Such difficulties may have, in particular, led to the observation by some investigators that HIV-positive homosexual men experience greater numbers of such events than their HIV-negative counterparts. It is also evident that, while some of these events are typical of those faced by individuals with other life threatening conditions, others are peculiar to this patient group. Research into the consequences of these events for emotional and behavioural functioning indicate that the effects are far-reaching. Similarly, data on the consequences of stressful events for immune function suggest that they may play a role in the progression of the disease, although these data are equivocal.

Quantitative magnetic resonance imaging of fresh and frozen-thawed trout.

Magnetic resonance imaging (MRI) has been used to visualise the major organs and muscular-skeletal frame-work of fresh rainbow trout (Salmo gairdneri) in two dimensions, and to identify the spatial distribution of lipid- and collagen-rich tissues. Quantitative MRI provides the MR parameters (T1, T2, M0, T1sat, Msat/M0, and the Magnetisation Transfer (MT) rate) for the tissue water; variations in those parameters enable distinction to be made between a freshly killed trout and one which has been frozen-thawed. The effects of freezing method, repeat freeze-thawing, and storage time on the MR parameters are discussed.

Measurement of textural changes of food by MRI relaxometry.

This article summarises the current status of, and future prospects for, the use of magnetic resonance imaging (MRI) to evaluate the texture of a range of foods, and changes therein which accompany pathogen infection, natural ageing, damage, ripening and processing. The basic concept is that the magnetic resonance parameters of water are sufficiently sensitive to the texture of the food matrix, that magnetic resonance images of the spatial distribution of those parameters are effectively maps of the structural status of the foodstuff. This is illustrated in the context of the effects of pathogen infection in cucumbers, internal necrosis of melons, bruising in peaches, ripening of pineapples, and the effect of freeze-thawing on meat and fish.

An exploration into occupational stress experienced by HIV health care professionals who work within genitourinary medicine settings.

The present study investigates the occupational stress of health care workers involved with HIV care in genitourinary medicine (GUM) outpatient departments. Sixteen nursing and 14 medical staff completed the P. Gray-Toft and J. G. Anderson (1981) occupational stress inventory. This assesses 7 potential sources of stress (death and dying, uncertainty regarding treatment, inadequate preparation, lack of support, conflict with others, conflict with physicians, and workload). The mean scores obtained revealed a preponderance of low-stress scores for both medical and nursing staff. Analyses of variance and covariance further demonstrated that, in general, levels of stress did not differ within or between the occupational groups. However, sources and characteristics of stress were different between nurses and doctors. In this group of health care professionals, their work with HIV-positive patients within the GUM outpatient setting may be instrumental in limiting levels of stress.

The role of disclosure in coping with HIV infection.

A qualitative investigation was conducted to explore the role of disclosure in HIV infection. Forty homosexual and bisexual men completed a short demographic questionnaire and participated in a one-to-one, semi-structured interview. The interview was designed to address a variety of personal, interpersonal and organizational issues related to their HIV status and participants were invited to talk about their personal experiences from immediately prior to their diagnosis to the time of the interview. The results from the interviews are presented in three sections: immediately post-diagnosis, asymptomatic phase and symptomatic/AIDS phases. The data revealed that disclosing one's HIV status was an acute and recurrent stressor. Immediately post-diagnosis, individuals were more likely to adopt a policy of non-disclosure and this provided them with an opportunity to come to terms with their diagnosis before having to contend with the reactions of others. After this phase, there was evidence that individuals increasingly used disclosure as a mechanism for coping with the disease. Disclosure of one's status was used to increase both practical and emotional support, share responsibility for sex and to facilitate self-acceptance of one's condition. The results from this investigation revealed that disclosure has a dual role in HIV infection acting as both a stressor and a mechanism by which individuals contend with their infection.

Greater emotional distress is associated with accelerated CD4+ cell decline in HIV infection.

An investigation was conducted to explore the relationship between emotional distress and HIV progression. One hundred twenty-five homosexual, HIV-positive males participated in a 12-month longitudinal investigation. Psychosocial data were collected at 6-month intervals and CD4+ data were collected from diagnosis to the end of the investigation. Principal component analyses were performed initially to identify factors of emotional distress and health status. In addition, CD4+ reliability assessments were performed to ensure the validity of the prognostic assessments made. As a result of these analyses, 47 individuals were eligible for the main analyses. The results from a stepwise regression revealed that disease progression was significantly predicted by CD4+ count at diagnosis (32% of variance) and emotional distress (17% of variance), but was unrelated to subjective perceptions of health. The data suggest that some of the variability in HIV progression can be attributed to emotional distress.

The assessment of the emotional and immunological consequences of examination stress.

Sixteen final-year students and 14 nonstudents were recruited into a pilot study exploring the utility of the Merieux Multitest CMI in identifying stress-related immune impairment. The results of the investigation revealed that the examination group reported greater stress than the nonexamination group. The relationship between stress and immune impairment was explored using two widely held definitions of stress (i.e., stimulus and response). When stress was defined as the stimulus (i.e., examination versus nonexamination groups), reactions to the skin test were not significantly different. However, when stress was defined as the response (i.e., high stress versus low stress scores), the high-stress individuals were found to have poorer reactions to the skin test than the low-stress subjects. The results of the study highlight the need for greater precision in the definition of the term stress and, also, suggest that Multitest CMI can provide a rapid and reproducible means of assessing stress-related immune dysfunction.

Psychosocial vulnerability to stress: a study of HIV-positive homosexual men.

Sixty-one homosexual men with HIV infection participated in a 12-month investigation into the role of stressful life events and mediating variables in the stress process. The results revealed that frequency of stressful life events and psychosocial resilience (a factor indexing levels of support, worry, personal self-esteem, and effective coping efforts) significantly predicted levels of emotional distress in this sample. The combined influence of these variables accounted for 53% (Phase 2) and 55% (Phase 3) of the variance in levels of emotional distress. The data point to a need to incorporate measures of life event frequency and several, rather than single, mediating variables in studies investigating the stress process.

A technique for accurate use of CD4+ cell counts.

Despite uncertainty over their reliability, CD4+ cell counts are used extensively in both clinical and research settings to document progression in HIV infection. We examined, therefore, whether the performance of a simple statistical test would facilitate greater accuracy in the use of this marker. CD4+ cell count data were collected from a cohort of deceased (N = 60) and living HIV-positive gay men (N = 100). Pearson's product moment correlation coefficients were calculated for each individual in order to examine the association between CD4+ counts and time since diagnosis. Correlations of 0.7 or greater were obtained in approximately 50 percent of cases in each cohort. For these individuals, CD4+ cell counts were deemed to be a reliable indicator of rate of progression. The results suggest that the proposed technique ensures greater precision in the use of CD4+ cell counts and that the technique cna be used in individuals with either complete (deceased patients) or partial (living patients) CD4+ data.

The role of social support in HIV infection.

A study was carried out in a group of 91 HIV positive gay men to investigate the relationship between social support, measures of affect and health; the changing nature of support over time; and the causal direction of this relationship. Overall levels of support for this group were found to be moderately high and consistent over 6 months and were associated with greater psychological well-being. Individuals in receipt of quantitatively different levels of support were found to differ on measures of depression, stress, coping efficacy and self-esteem, while individuals in receipt of deficient levels of support were found to be more depressed. However, initial support levels were found to be the most powerful predictors of subsequent support levels. The implications of these findings are discussed.