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Biomedical subjects

Y Bouligand

Publications and source records attributed to Y Bouligand.

13 recordsLinked to original sources
PubMed2001

Chromosome separation and segregation in dinoflagellates and bacteria may depend on liquid crystalline states.

The patterns characteristic of certain liquid crystals called 'twisted nematics' or 'cholesterics' have been observed in thin sections of both dinoflagellates and bacterial chromosomes. These liquid crystals have also been obtained in vitro in concentrated DNA solutions. A large part of DNA in prokaryotic chromosomes forms such a twisted liquid crystal, whilst the remainder consists of lateral loops and is less concentrated. These semi-ordered phases could help chromosome separation to occur during and after DNA replication. We suggest that, owing to chemical differences, one of the two replicated filaments is immiscible with the rest of DNA in this chromosome. This immiscibility occurs in the context of an ordered liquid, with the DNA closely layered by a regular twist, a situation proposed to strongly minimize entangling after replication and hence to facilitate segregation.

Animals↗
PubMed2001

Interfacial properties of amiodarone: the stabilizing effect of phosphate anions.

Amiodarone, a drug used in heart therapy, is poorly soluble in water at room temperature, but forms transparent phases much more concentrated than the critical micellar concentration (CMC), when crystals are heated (above 60 degrees C) in presence of water and cooled down to room temperature. These pseudosolutions were supposed to be made of a complex system of micelles. In order to better understand the effects of pH and ion species on the supramolecular organization of amiodarone, interfacial pressure measurements were performed at the air/water interface on a Langmuir trough. Monolayers spread from chloroformic solutions over non bufferered subphases were insoluble at basic pH (NaOH, pH 10) but soluble at acidic pH (HCl, pH 4). However, a higher ionic strength obtained by adding NaCl (0.15 N) or NaH(2)PO(4) (0.15 N) to the subphase stopped the amiodarone solubilization. On an acidic phosphate subphase (NaH(2)PO(4), pH 4.4, 0.15 N), abnormally high surface pressures (>1 mN/m) were measured for high molecular areas (80-200 Å(2)/molecule) suggesting a supramolecular organization of the surface film. Insoluble monolayers were also obtained when the amiodarone supramolecular pseudosolution was spread on neutral (NaH(2)PO(4), pH 6.25, 0.15 N) or acidic (NaH(2)PO(4), pH 4.4, 0.15 N) subphases. However, a great instability on basic subphase (phosphate buffer pH 8.8) indicated the breakage of the supramolecular structure during spreading. These results are discussed taking into account the amiodarone state of ionization and the electrostatic interactions with counterions. Combining the use of phosphate counterions and that of acidic pH opens new perspectives in the optimization of amiodarone intravenous formulations.

Journal Article↗
PubMed1997

Tensioactivity and supramolecular organization of the palmitoyl prodrug of timolol.

PURPOSE: To improve the bioavailability of the ocular drug timolol by facilitating its transport through the cornea, an amphiphilic prodrug was synthesized via the addition of a palmitic chain by esterification. The present study was undertaken to investigate the physicochemical and tensioactive properties of the prodrug. METHODS: The amphiphilic properties of the prodrug were firstly investigated by the Wilhelmy plate method. The textures generated by the supramolecular organizations of the ester were visualized by optical microscopy. RESULTS: The prodrug clearly decreased the surface tension. Optical microscopy provided excellent evidence for the existence of lyotropic liquid crystalline phases: two isotropic but organized phases and a birefringent lamellar phase. CONCLUSIONS: The results from the ensemble of studies undertaken to determine the amphiphilic properties of the prodrug were all in accord with its ability to form liquid crystalline phases. The liquid crystalline state of the prodrug is believed to introduce a delay in the drug pharmacological effect.

Adrenergic beta-Antagonists↗
PubMed1985

Twisted architectures in cell-free assembled collagen gels: study of collagen substrates used for cultures.

Reprecipitated fibrils from collagen solutions assemble into aggregates often showing a remarkable twisted structure. We first observed these aggregates in collagen gels prepared to facilitate culture of epithelial cells. We verified that these structures form in the absence of cells and correspond to a process of self-assembly. Studies on reconstructed fibrils of collagen are generally based on the examination of thin specimens mounted onto coated grids prepared for electron microscopy. We rather applied the classical methods of fixation, embedding and ultramicrotomy, which allowed us to analyze the structure of these aggregates, several microns in diameter. Our gels were prepared from 2.5 mg/ml tropocollagen solutions usually chosen for cell and organ cultures. The time required to obtain twisted architectures, in these aggregates, depends on temperature and the presence of factors such as fetal calf serum proteins. Twist is observed at two different levels of organization. Microfibrils are gathered into twisted bundles which condense into cross-striated fibrils. These fibrils themselves aggregate and show a mutual twist whose orientation is left-handed as is the twist observed within each microfibril bundle. Several models of these architectures are presented. Planar twist, cylindrical twist and toroidal twist are described and their relation to the structure of certain liquid crystals is considered. Examples of orthogonal packing also have been observed. These structures obtained in vitro are very close to patterns already described in vivo in numerous collagen matrices.

Animals↗
PubMed1984

The liquid crystalline nature of the cytoskeleton in epidermal cells of the chaetognath Sagitta.

The chaetognaths have a multilayered epidermis, which is not covered by cuticle, except in the head region. Two kinds of cells are found in the epidermis: the filament-rich cells, adjacent to the basement membrane, and superficial cells, which are filament poor. The filament-rich cells, which are linked by gap junctions and columnar junctions, are highly developed in the collarette region, which joins the head and the trunk. As elsewhere in the epidermis these cells are covered by the filament poor cells which are linked by zonulae adhaerentes, gap junctions and septate junctions. The filaments present in the inner cells of the collarette form a twisted fibrous arrangement, which shows parallel series of nested arcs when observed in oblique section. Such systems are well known in numerous skeletal materials and correspond to polymerized analogues of certain liquid crystals. The amount of connective tissue is extremely reduced in Sagitta. One can hypothesize that filament-rich cells are abundant in regions which undergo strong deformations. This is the case in the collarette, in contact with the basement membrane of the epidermis (which in turn is in contact with a myotendinous system), in a region where ingested prey must go through the general cavity where there is high internal pressure.

Animals↗
PubMed1978

The fibrous structure of coelacanth scales: a twisted 'plywood'.

Isopedin is a network of collagen bundles present in the scales of most fishes. The scales of coelacanths show a remarkable three-dimensional arrangement of this network which is similar to a regularly twisted plywood. The successive fibrous layers cross at an angle which differs slightly from a right angle. It results that the whole system is twisted. The progressive rotation of the fibril direction is right-handed. Certain preferential orientations of fibrils have been observed, namely parallel to the growth rings. Such arrangments also exist in the embryonic cornea of birds and in the cuticle of certain insects, but do not present such an extensive and regular development.

Animals↗
PubMed1975

Studies on the fine structure of the cuticle of Porcellidium, crustacea copepoda.

Two species of Porcellidium have been studied by scanning and transmission electron microscopy: P. viride from Banyuls-sur-mer, Mediterranian Sea and P. fimbriatum from Roscoff, English Channel. Both species live on green Algae of the genus Ulva. We confirmed previous descriptions of the cuticular ultrastructure in the main groups of Copepods. Four new characteristics however were shown to occur in the backcuticle of Porcellidium: 1. The presence of a system of highly differentiated external microvilli showing electron dense basal portions and less electron dense tips, from which thin filaments project towards a large population of Bacteria associated with the Copepod. 2. The surface of the cuticle resembles a lunar landscape with craters. The sheet of microvilli closely follows the contour of the cuticle. 3. The presence of branched cytoplasmic canals with swollen extremities (beneath the epicuticle) extending from the epidermal cells. 4. Systems of vesicles lying between the bases of the microvilli and the expansions (ampullae) at the tip of the cytoplasmic canals. The association of Bacteria with the cuticle is constant and many of these are apparently undergoing cytolysis; The system of microvilli and of cytoplasmic canals are apparently related to the presence of the bacterial microflora.

Animals↗
PubMedDate not supplied

Hypothesis: hyperstructures regulate bacterial structure and the cell cycle.

A myriad different constituents or elements (genes, proteins, lipids, ions, small molecules etc.) participate in numerous physico-chemical processes to create bacteria that can adapt to their environments to survive, grow and, via the cell cycle, reproduce. We explore the possibility that it is too difficult to explain cell cycle progression in terms of these elements and that an intermediate level of explanation is needed. This level is that of hyperstructures. A hyperstructure is large, has usually one particular function, and contains many elements. Non-equilibrium, or even dissipative, hyperstructures that, for example, assemble to transport and metabolize nutrients may comprise membrane domains of transporters plus cytoplasmic metabolons plus the genes that encode the hyperstructure's enzymes. The processes involved in the putative formation of hyperstructures include: metabolite-induced changes to protein affinities that result in metabolon formation, lipid-organizing forces that result in lateral and transverse asymmetries, post-translational modifications, equilibration of water structures that may alter distributions of other molecules, transertion, ion currents, emission of electromagnetic radiation and long range mechanical vibrations. Equilibrium hyperstructures may also exist such as topological arrays of DNA in the form of cholesteric liquid crystals. We present here the beginning of a picture of the bacterial cell in which hyperstructures form to maximize efficiency and in which the properties of hyperstructures drive the cell cycle.

Bacteria↗