Anisotropic line tension of domains in lipid monolayers.

We formulate a simple effective model to describe molecular interactions in a lipid monolayer and calculate the line tension between coexisting domains. The model represents lipid molecules in terms of two-dimensional anisotropic particles on the plane of the monolayer. These particles interact through forces that are believed to be relevant for the understanding of fundamental properties of the monolayer: van der Waals interactions originating from lipid chains and dipolar forces between dipole groups in the molecular heads. The model stresses the liquid-crystalline nature of the ordered phase in lipid monolayers and explains coexistence properties between ordered and disordered phases in terms of molecular parameters. Thermodynamic and interfacial properties of the model are analyzed using density-functional theory. In particular, the line tension at the interface between ordered and disordered phases turns out to be highly anisotropic with respect to the angle between the nematic director and the interface separating the coexisting phases. This important feature mainly results from the tilt angle of lipid chains and, to a lesser extent, from dipolar interactions perpendicular to the monolayer. The role of the two dipolar components, parallel and perpendicular to the monolayer, is assessed by comparing with computer simulation results for lipid monolayers.

Molecular Ordering in Lipid Monolayers: An Atomistic Simulation.

We report on atomistic simulations of DPPC lipid monolayers using the CHARMM36 lipid force field (and also the Slipid force field as a control case), combined with a four-point OPC water model. The entire two-phase region where domains of the "liquid-condensed" (LC) phase coexist with domains of the "liquid-expanded" (LE) phase has been explored. The simulations are long enough that the complete phase-transition stage, with two domains coexisting in the monolayer, is reached in all cases. Also, system sizes used are larger than those in previous works. As expected, domains of the minority phase are elongated, emphasizing the importance of anisotropic van der Waals and/or electrostatic dipolar interactions in the monolayer plane. The molecular structure is quantified in terms of distribution functions for the hydrocarbon chains and the PN dipoles. In contrast to previous work, where average distributions are calculated, distributions are here extracted for each of the coexisting phases by first identifying lipid molecules that belong to either LC or LE regions. In the case of the CHARMM36 force field, the three-dimensional distributions show that the average tilt angle of the chains with respect to the normal outward direction is (39.0 ± 0.1)° in the LC phase and (48.1 ± 0.5)° in the LC phase. In the case of the PN dipoles, the distributions indicate a tilt angle of (110.8 ± 0.5)° in the LC phase and (112.5 ± 0.5)° in the LE phase. These results are quantitatively different from those in previous works, which indicated a smaller normal component of the PN dipole. Also, the distributions of the monolayer-projected chains and PN dipoles have been calculated. Chain distributions peak along a particular direction in the LC domains, while they are uniform in the LE phase. Long-range ordering associated with the projected PN dipoles is absent in both phases. These results strongly suggest that LC domains do not exhibit dipolar ordering in the plane of the monolayer, the effect of these components being averaged out at short distances. Therefore, the only relevant component of the molecular dipoles, with regard to both intra- and long-range interdomain interactions, is normal to the monolayer. Also, the local orientation of chain projections is almost constant in LC domains and points in the direction along which domains are elongated, suggesting that the line tension driving the phase transition might be anisotropic with respect to the interfacial domain boundary.

Factors associated with ATXN2 CAG/CAA repeat intergenerational instability in Spinocerebellar ataxia type 2.

Spinocerebellar ataxia type 2 (SCA2) is a neurodegenerative disorder caused by the unstable expansion of a cytosine-adenine-guanine (CAG)/cytosine-adenine-adenine (CAA) repeat in the ATXN2 gene, which normally encodes 22 glutamines (Q22). A large study was conducted to characterize the CAG/CAA repeat intergenerational instability in SCA2 families. Large normal alleles (Q24-31) were significantly more unstable upon maternal transmissions. In contrast, expanded alleles (Q32-750) were significantly more unstable during paternal transmissions, in correlation with repeat length. Significant correlations were found between the instability and the age at conception in paternal transmissions. In conclusion, intergenerational instability at ATXN2 locus is influenced by the sex, repeat length and age at conception of the transmitting parent. These results have profound implications for genetic counseling services.

Solid-solid transitions induced by repulsive interactions revisited.

We revisit a problem already studied 15 years ago by us in collaboration with Stell and Hemmer: the isostructural solid-solid transitions induced by repulsive particle interactions exhibited by classical systems interacting via the Stell-Hemmer potentials. The full phase diagram in the crystal region is obtained by applying a perturbation theory for classical solids used during our collaboration with Stell. Also, the performance of such a theory is now tested by comparing the perturbative phase diagram with that obtained from computer simulations. The latter was calculated using a recently refined method to obtain the free-energy of crystals by means of Monte Carlo simulations. The perturbation theory captures the correct topology and correctly identifies the stable, fcc and bcc, phases. In addition, the theory predicts the occurrence of special points: a point where the two stable structures coexist at the same density, and two critical points terminating the corresponding isostructural phase transitions for fcc and bcc phases. The location of some of these features in the phase diagram is predicted almost quantitatively. However, phase boundaries involving the non-compact bcc phase are much less accurate, a problem that can be traced to the poor representation used for the bcc phase of the reference, hard-sphere, system.

Role of glutathione S-transferases in the spinocerebellar ataxia type 2 clinical phenotype.

Spinocerebellar ataxia type 2 (SCA2) is a neurodegenerative and incurable hereditary disorder caused by a CAG repeat expansion mutation on ATXN2 gene. The identification of reliable biochemical markers of disease severity is of paramount significance for the development and assessment of clinical trials. In order to evaluate the potential use of glutathione-S-transferase (GST) activity as a biomarker for SCA2, a case-control study in 38 affected, presymptomatic individuals or healthy controls was conducted. An enlarged sample of 121 affected individuals was set to assess the impact of GST activity on SCA2 clinical expression. There was a significant increase in GST activity in affected individuals relative to controls, although sensibility and specificity were not high. GST activity was not significantly influenced by sex, age, disease duration or CAG repeat size and did not significantly influence disease severity markers. These findings show a disruption of in vivo GST activity in SCA2, suggesting a role for oxidative stress in the neurodegenerative process.

The Cuban program for predictive testing of SCA2: 11 years and 768 individuals to learn from.

Having reported the world's highest prevalence of spinocerebellar ataxia type 2 (SCA2), health professionals in Cuba developed a program for the predictive testing of this condition. Between February 2001 and December 2011, a total of 1050 individuals requested their inclusion in the presymptomatic testing (PST) program. Their medical records were retrospectively analyzed in the present descriptive study. A total of 768 participants completed the protocol, 204 withdrew and 78 were excluded. The PST uptake was 24.91%. Females predominated and 70.96% had negative test results. Their main motivations were risk assessment in their descendants, physical and psychological preparation to cope with the disease and planning for the future. The profile of Cuban participants in the predictive testing program is similar to the one reported for other programs all over the world, nevertheless the genetic counseling practice at the community level is a distinctive aspect, which is valuable in providing at-risk individuals with wide and proper knowledge before their testing inclusion request. The SCA2 predictive testing program has high uptake rates and is renowned in our population. Future research is needed to assess the long-term psychological impact in the participants, their partners and relatives.

Linfadenitis por mycobacterium incluyendo pacientes infectados por el virus de inmunodeficiencia humana / Mycobacterium lymphadenitis including patients infected with human inmunodefi

El género Mycobacterium provoca infecciones pulmonares y extrapulmonares, de estas últimas predomina la infección ganglionar. Mientras Mycobacterium tuberculosis es el agente causal más importante, en las últimas décadas aumenta la incidencia de otras especies micobacterianas que se han hecho prevalentes en los pacientes positivos al virus de la inmunodeficiencia humana (VIH +) tanto en países desarrollados como en vías de desarrollo. Durante el período enero 2007 hasta diciembre 2009 se procesó en nuestro laboratorio 6540 muestras, 210 muestras fueron obtenidas por biopsia ganglionar, precisamente este constituyó nuestro universo de estudio, 190 (90.4%) muestras se obtuvieron por exéresis quirúrgica, 20 (9.5%) por punción espirativa;17 procedían de pacientes VIH– (8.1%) y 193 procedentes de pacientes VIH+(91.9%). En solo 16 muestras (7.6%) el cultivo BAAR fue positivo; 4 procedentes de pacientes VIH– (25%) y 12 VIH+(75%). La clasificación e identificación micobacteriana demostró la presencia de Mycobacterium tuberculosis en 13 de los casos (81.25%), mientras Mycobacterium avium-intracellulare fue aislado en 3 (18.7%). En los pacientes inmunodeprimidos con linfadenopatía incluidos los pacientes VIH/sida, es muy importante la búsqueda activa de la presencia de BAAR como coinfección oportunista, donde Mycobacterium tuberculosis se mantiene como el agente infeccioso más frecuente, sin embargo la posibilidad de que otras especies micobacterianas también estén presentes no se debe descartar. Nuestro objetivo en este estudio como Laboratorio Nacional de Referencia de TB- Micobacterias fue lograr la caracterización etiológica de linfadenopatías en pacientes en que se sospechaba clínicamente la participación del género Mycobacterium.

Mycobacterium tuberculosis is the most important etiological agent producing pulmonary as well as extrapulmonary infection. During these last decades, the increase in the incidence of infection due to other mycobacteria species is evident. Lymphadenopathy is the most frequent extrapulmonary presentation form of Mycobacterium Genera infection among HIV positive patients either in developed or underdeveloped countries. The aim of this work is to analyze the results obtained during January 2007 - December 2009 in our laboratory. Two hundred ten tissue samples were studied; 190 (90.4%) samples were lymph node biopsied tissues and 20 (9.5%) samples were obtained by fine needle aspiration; 17 were from HIV - patients (8.1%) and 193 from HIV + (91.9%). A total of 16 (7.6%) samples produced a positive culture for BAAR, 4 VIH- (25%) and 12 VIH+ (75%). Classification and identification for mycobacteria confirmed Mycobacterium tuberculosis in 13 of the cases (81.25%), and Mycobacterium avium-intracellulare in three patients (18.7%). The present study once again confirms that BAAR culture has more sensitivity and specificity than histopathologhic studies have. Lymphadenopathy in immunosuppressed patients should by studied for the presence of an BAAR coinfection where M. tuberculosis is still the agent most frequently found, nevertheless, other species of Mycobacteria may be causing infection and should be searched for. Our objective as National Reference Laboratory of Tuberculosis and Mycobacterial was to obtain the etiological characterization of Mycobacterium lymphadenopathy in clinically suspect patients.

Estimation of the age at onset in spinocerebellar ataxia type 2 Cuban patients by survival analysis.

Previous studies have investigated the close association that exists between CAG repeat number and the age at onset in SCA2 = spinocerebellar ataxia type 2. These studies have focused on affected individuals. To further characterize this association and estimate the risk of a carrier developing SCA2 at a particular age as a function of a specific CAG repeat size, we have analyzed a large group of 924 individuals, including 394 presymptomatic and 530 affected individuals with a CAG repeat length of 32-79 units. Using a Kaplan-Meier survival analysis, we obtained cumulative probability curves for disease manifestation at a particular age for each CAG repeat length in the 34-45 range. These curves were significantly different (p < 0.001) and showed small overlap. All these information may be very valuable in predictive-testing programs, in the planning of studies for the identification of other genetic and environmental factors as modifiers of age at onset, and in the design of clinical trials for people at enlarged risk for SCA2.

Topological defects in a two-dimensional liquid crystal confined in a circular nanocavity.

Using a microscopic theory based on excluded-volume interactions, we analyze the structure and thermodynamic stability of configurations in a two-dimensional liquid crystal confined into a (small) circular nanocavity. Weak homeotropic anchoring conditions are considered, and topological defects of total charge k=+1 are discussed. It is found that, for small cavity radii, the cavity is free of defects at the expense of surface free energy not being optimized. For larger cavities, a configuration with two repulsive k=+1/2-charge point defects is always stable. The two configurations are equally stable thermodynamically (structural or Frederiks transition) on a curve in the chemical potential-cavity radius plane. This curve ends for chemical potential and cavity radius below some critical values. Elastic-theory arguments are used to explain the stability of the defected structure compared with the one free of defects. Our results indicate that the two-defect structure is always more stable than the one with a single point defect of charge k=+1 at the cavity center, which, in agreement with computer simulation, is never found to be stable. Finally, the relation with the bulk behavior of the fluid is discussed.

Saccade velocity is reduced in presymptomatic spinocerebellar ataxia type 2.

OBJECTIVE: A characteristic feature of spinocerebellar ataxia type 2 (SCA2) is saccadic slowing at early disease stages. We sought to determine whether this sign is detectable before clinical manifestation and quantifies the disease progression throughout life in linear fashion. METHODS: In a specialized ataxia clinic, 54 presymptomatic carriers of SCA2 polyglutamine expansions and 56 relatives without mutation were documented with regard to their maximal saccade velocity (MSV). RESULTS: Among the control individuals, a significant effect of aging on MSV was observed. After elimination of this age influence through a matched-pair approach, a presymptomatic decrease of MSV could be shown. The MSV reduction was stronger in carriers of large expansions. In the years before calculated disease manifestation, the MSV impairment advanced insidiously. CONCLUSION: Saccade velocity is a sensitive SCA2 endophenotype that reflects early pontine degeneration and may be a useful diagnostic parameter before the onset of ataxia. SIGNIFICANCE: Future neuroprotective therapies of polyglutamine neurodegeneration may be assessed by MSV from earliest to prefinal disease stages.

Saccade velocity is reduced in presymptomatic spinocerebellar ataxia type 2

A characteristic feature of spinocerebellar ataxia type 2 (SCA2) is saccadic slowing at early disease stages. We sought to determine whether this sign is detectable before clinical manifestation and quantifies the disease progression throughout life in linear fashion. In a specialized ataxia clinic, 54 presymptomatic carriers of SCA2 polyglutamine expansions and 56 relatives without mutation were documented with regard to their maximal saccade velocit Spinocerebellar ataxia type 2 Among the control individuals, a significant effect of aging on MSV was observed. After elimination of this age influence through a matched-pair approach, a presymptomatic decrease of MSV could be shown. The MSV reduction was stronger in carriers of large expansions. In the years before calculated disease manifestation, the MSV impairment advanced insidiously.Saccade velocity is a sensitive SCA2 endophenotype that reflects early pontine degenerationPolyglutamine expansion and may be a useful diagnostic parameter before the onset of ataxia. Significance: Future neuroprotective therapies of polyglutamine neurodegeneration may be assessed by MSV from earliest to prefinal disease stages...(AU)

New variants of polar glycopeptidolipids detected in Mycobacterium simiae, including 'habana' strains, as evidenced by electrospray ionization-ion trap-mass spectrometry.

AIMS: To determine the composition of polar glycopeptidolipids (pGPLs) of Mycobacterium simiae and, particularly, those of 'habana' strains, in a search for specific markers given the immunogenic potential of 'habana' TMC 5135 in experimental tuberculosis. METHODS AND RESULTS: pGPLs were determined in free lipid extracts using electrospray ionization-ion trap-mass spectrometry (ESI-IT-MS), working in both negative- and positive-ion mode. In the case of TMC 5135, the presence of the previously characterized GPL-II (containing 2,4-di-O-CH(3) glucuronic acid as distal sugar in the oligosaccharide antigenic moiety) and GPL-III (containing 4-O-CH(3) glucuronic acid as distal sugar) was confirmed using MS/MS and MS/MS/MS approaches. Interestingly, some 'habana' strains presented variants of GPL-II, designated GPL-II'-A and GPL-II'-B. A di-O-CH(3)-deoxy-hexose (tentatively, 2,3-di-O-CH(3)-fucose) was identified as the penultimate sugar in the oligosaccharide moiety of GPL-II'-A, whereas in GPL-II'-B the penultimate sugar was fucose (tentative identification). On the contrary, the distal sugar of the oligosaccharide chain of pGPLs of Myco. simiae ATCC 25275(T) was identified as tri-O-CH(3)-glucuronic acid (designated GPL-sim(T)-I, with two variants: GPL-sim(T)-I-A and GPL-sim(T)-I-B), O-CH(3)-glucuronic acid (designated GPL-sim(T)-II) and di-O-CH(3)-glucuronic acid (GPL-II'-A and GPL-II'-B). The penultimate sugar of the oligosaccharide chain of GPL-sim(T)-I-A and GPL-sim(T)-II was identified as di-O-CH(3)-deoxy-hexose (tentatively, 2,3-di-O-CH(3) fucose), and that of GPL-sim(T)-I-B as deoxy-hexose (tentatively, fucose). In all strains studied, each [M-H](-) and [M+Na](+) ion was revealed as a mixture of homologous compounds varying in the number of -O-CH(3) groups present in the oligosaccharide moiety and in the length of the fatty acyl linked to the peptide. CONCLUSIONS: The present work indicates that, within a similar general pattern of pGPLs, different strains of Myco. simiae present some variations, so that new compounds (GPL-II'-A, GPL-II'-B, GPL-sim(T)-I-A, GPL-sim(T)-I-B and GPL-sim(T)-II) were defined. Noteworthy was the fact that the 'habana' strains clearly differed from the type strain of Myco. simiae. SIGNIFICANCE AND IMPACT OF THE STUDY: The data obtained can be used in the delineation of the 'habana' group of Myco. simiae, including the quality control of the immunogenic strain 'habana' TMC 5135.

Antigliadin antibodies in Cuban patients with spinocerebellar ataxia type 2.

OBJECTIVE: To evaluate the significance of antigliadin antibodies (AGA) levels for spinocerebellar ataxia type 2. METHODS: We determined AGA levels in 64 patients with spinocerebellar ataxia type 2 and in 65 healthy matched controls. The clinical assessment was carried out using the International Cooperative Ataxia Rating Scale and CAG repeat number was assessed by PCR. RESULTS: Antibodies were positive in 23.4% of the ataxia patients and 9.09% of the controls. Statistical comparison using chi2 test with Yates's correction reveals significant differences between these two groups (chi2 = 3.94; p = 0.047). The same was obtained for strongly positive AGA (chi2 = 4.62; p = 0.032). There were no significant differences between AGA positive and AGA negative patients in age at onset, disease duration, ataxia score or CAG repeat number, neither in the prevalence of gastrointestinal symptoms, prevalence of wheat intolerance or body weight. CONCLUSIONS: These results demonstrate an association between antigliadin antibodies serum levels and SCA2. However, more work has to be done to clarify the clinical consequences of such an association.

Depletion effects in smectic phases of hard-rod-hard-sphere mixtures.

It is known that when hard spheres are added to a pure system of hard rods the stability of the smectic phase may be greatly enhanced, and that this effect can be rationalised in terms of depletion forces. In the present paper we first study the effect of orientational order on depletion forces in this particular binary system, comparing our results with those obtained adopting the usual approximation of considering the rods parallel and their orientations frozen. We consider mixtures with rods of different aspect ratios and spheres of different diameters, and we treat them within Onsager theory. Our results indicate that depletion effects, and consequently smectic stability, decrease significantly as a result of orientational disorder in the smectic phase when compared with corresponding data based on the frozen-orientation approximation. These results are discussed in terms of the tau parameter, which has been proposed as a convenient measure of depletion strength. We present closed expressions for tau, and show that it is intimately connected with the depletion potential. We then analyse the effect of particle geometry by comparing results pertaining to systems of parallel rods of different shapes (spherocylinders, cylinders and parallelepipeds). We finally provide results based on the Zwanzig approximation of a fundamental-measure density-functional theory applied to mixtures of parallelepipeds and cubes of different sizes. In this case, we show that the tau parameter exhibits a linear asymptotic behaviour in the limit of large values of the hard-rod aspect ratio, in conformity with Onsager theory, as well as in the limit of large values of the ratio of rod breadth to cube side length, d, in contrast to Onsager approximation, which predicts tau approximately d (3). Based on both this result and the Percus-Yevick approximation for the direct correlation function for a hard-sphere binary mixture in the same limit of infinite asymmetry, we speculate that, for spherocylinders and spheres, the tau parameter should be of order unity as d tends to infinity.

Capillary effects in a confined smectic phase of hard spherocylinders: influence of particle elongation.

A system of hard rods confined into a pore with slit geometry (two parallel planar substrates) is studied theoretically in the regime of high packing fraction. In this regime the bulk system exhibits a nematic phase as well as a smectic-A (spatially layered) phase. When the system is confined, strong commensuration effects between the layer spacing and the pore width bring about a rich phenomenology, with a phase diagram showing layering and capillary transitions. The latter include capillary smectization transitions whereby a confined smectic phase occurs at conditions of saturation different from those of the corresponding bulk fluid. These transitions are seen to be intimately connected with layering transitions involving discontinuous changes in the number of layers inside the pore. This rich phenomenology is obtained by use of a sophisticated density-functional, Onsager-theory-based approach, especially suited to deal with strongly inhomogeneous fluids. The theory allows for a unified description of ordering and phase behavior of the fluid in confined geometry, and permits us to correlate the above behavior with the wetting properties of the fluid on a single substrate.

Lipids of 'Mycobacterium habana', a synonym of Mycobacterium simiae with vaccine potential.

'Mycobacterium habana' was proposed as a distinct species within the genus Mycobacterium; however, it is actually a synonym of Mycobacterium simiae and included in the serotype I of this species. The potential use of 'M. habana' as a vaccine in both leprosy and tuberculosis has led to the analysis of its lipid composition in an attempt to define distinctive markers that could be used in the quality control of true strains of this bacterium. Lipids of taxonomic value (fatty and mycolic acids) are similar in 'M. habana' and M. simiae; nevertheless, they clearly differ on the basis of glycopeptidolipid (GPL) composition. Thus, contrary to M. simiae, most strains of 'M. habana' can be defined by the presence of three polar compounds, designated GPL-I, GPL-II and GPL-III, easily determined by thin-layer chromatography, and characterized, respectively, by the content of l-fucose, 2,4-di-O-Me-d-glucuronic acid, and 4-O-Me-d-glucuronic acid, as epitopes.