Yves Bouligand

New lipid nanocapsules exhibit sustained release properties for amiodarone

Amiodarone is widely used in heart diseases but also provokes severe adverse effects due to its accumulation in other tissues than the heart. In order to circumvent side effects colloidal drug carriers have been designed to deliver the drug specifically to the site of action. Many preparation methods have been described and most have been reported to involve a high initial drug loss when introduced in an aqueous environment. Lipid nanocapsules (LNC) were prepared by a new phase inversion procedure and characterized in terms of size, surface potential, encapsulation efficiency, and drug release pattern. The encapsulation rate was varying between 92 and 94%. LNC did not display a distinct initial burst effect while the drug release of amiodarone can be prolonged over a significant period. Acceptor phase interfaces such as liposomes or blank LNC were applied to the release medium to enable a drug release to larger extents. The release was triggered by the pH of the release medium showing a faster release for lower pH; t(50%) values vary from 25.6 h (pH 2) to 236.3 h (pH 7.4). Moreover, LNC were prepared of different sizes (24.7+/-2.0 to 102.5+/-0.9 nm) showing only slight influences on their drug release profiles. It was concluded that the LNC surface is able to retain amphiphilic drugs. Such properties could allow drug delivery to the site of action without high initial drug loss.

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.

New observations on the twisted arrangement of Dinoflagellate chromosomes

The Dinoflagellate Prorocentrum micans has been studied in classical and high voltage transmission electron microscopy, with the help of a goniometric stage. The general structure of the nucleus is analysed with special reference to the links observed between chromosomes and the nuclear envelope, the nucleoplasm and the nucleolus. The chromosomes present stacked series of nested arcs which are studied in detail. The sense of the arcs can be changed by a simple tilt of the section. These arcs do not correspond to DNA filaments with a genuine bend but to an illusion created by the overlap of layers of filaments whose orientation turns along the chromosome axis. — The transversal orientation of DNA and the examination of defects allow to rule out the polytenic hypothesis. It is clear that this hypothesis does not apply to bacterial nucleoids, which however can form series of nested arcs as in Dinoflagellate chromosomes. — The twisted arrangement of Dinoflagellate chromosomes is that of a liquid crystal of the cholesteric type. DNA is known to self assemble into cholesteric phases and this affords informations on the origin of the elongated shape of chromosomes and on the mechanisms of condensation and aggregation observed in this particular chromatin.

Chemists and the school of nature

The term biomimicry first appeared in 1962 as a generic term including both cybernetics and bionics. It referred to all sorts of imitation of one form of life by another one, while the term “bionics”, defined as “an attempt to understand sufficiently well the tricks that nature actually uses to solve her problems”, is closer to the meaning of “biomimicry” as it has been used by materials scientists since the 1980s. Biomimetism is an umbrella covering a variety of research fields ranging from the chemistry of natural products to nanocomposites, via biomaterials and supramolecular chemistry. It is an informal movement and the concept itself is so loose that one might wonder whether biomimetism is more than a slogan forged by chemists in order to hop on the “green” bandwagon. Or could it bring a revolution into chemistry with a profound transformation of its practices? It is too early to judge, but a historical perspective helps to highlight some trends and tendencies.

Double helical arrangement of spread dinoflagellate chromosomes

Dinoflagellate chromosomes observed in thin section show regular patterns which have been shown to correspond to a liquid crystalline helicoidal arrangement of DNA. Peripheral DNA filaments form a system of loops in the surrounding nucleoplasm. When such chromosomes (studied in Prorocentrum micans) are in presence of water, they extend considerably and form a double helical bundle. At the periphery of these bundles, one observes numerous filaments, which are smooth and devoid of nucleosomes; their diameter is constant.This study, in phase contrast and in electron microscopy, allows statistical measurements. A geometrical model is proposed and shows the simplest way to pass from the intact to the extended form. The liquid crystalline character of the chromosome is probably involved in the extension mechanisms.

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 hyperstructures 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.

Theory of microtomy artefacts in arthropod cuticle.

Arthropod cuticles observed in section generally present alternating clear and dark bands. These have often been interpreted in terms of superimposed layers of different structure or composition. It has been shown, however that this material is homogeneous, and is formed by a twisted arrangement of microfibrils. The dense bands correspond actually to a microtomy artefact and they form dark single spirals in certain distorted areas of the cuticle. A model was proposed, involving the interaction between knife motion and microfibrils; it will be referred to as the stepped model, since the proposed mechanism results in the formation of steps at the surface of sections, on both faces. These steps are limited by structures resembling crests or cliffs, whose regular distribution produces alternating thick and thin bands in the section. This explains the observed contrast (Bouligand, (1972)). Two very interesting models were proposed later (Gordon and Winfree, (1978)) and are referred to as the cos F model and the sand model, but steps and crests are absent in these models. However, Giraud-Guille ((1986)), has shown very clearly the existence of these crests, which seem to be quite essential in this microtomy artefact. To clarify the debate, the texts defining the initial and the two new models are reproduced here and the difficulties encountered by each model are discussed. A mathematical formulation of this artefact is presented in an appendix to the present article; this leads to a more complete discussion of the possible models. Other factors are also taken into consideration: microfibril orientation and staining. The main factor of contrasts is undoubtedly the variation in thickness over a single section, as proposed in the stepped model.

Freeze-Fractures in Cholesteric Mesophases of Polymers

Abstract Freeze-fracture techniques were used to study the cholesteric liquid crystalline phases of three polymer solutions (PBLG, Xanthan, HPC). All fracture surfaces showed a regular stratification corresponding to the half-helical pitch, P/2. Electron microscopy permits very small helical pitches (P/2 < 300 A) to be observed and defects and textures previously analyzed in the polarizing microscope can be easily recognized: edge dislocations, +π and −π disclinations etc. Fractures oblique with respect to the cholesteric stratification present a regular distribution of parallel series of nested arcs whose nature is directly related to the cholesteric organization but the shape of the arcs can be modified by the presence of steps in the fracture surface. The position of these steps is related to the fracture direction with respect to the cholesteric stratification. Fractures through polygonal fields are very different from the classical patterns observed in the polarizing microscope since we are observing...

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.

Hyperstructures, genome analysis and I-Cells

New concepts may prove necessary to profit from the avalanche of sequence data on the genome, transcriptome, proteome and interactome and to relate this information to cell physiology. Here, we focus on the concept of large activity-based structures, or hyperstructures, in which a variety of types of molecules are brought together to perform a function. We review the evidence for the existence of hyperstructures responsible for the initiation of DNA replication, the sequestration of newly replicated origins of replication, cell division and for metabolism. The processes responsible for hyperstructure formation include changes in enzyme affinities due to metabolite-induction, lipid-protein affinities, elevated local concentrations of proteins and their binding sites on DNA and RNA, and transertion. Experimental techniques exist that can be used to study hyperstructures and we review some of the ones less familiar to biologists. Finally, we speculate on how a variety of in silico approaches involving cellular automata and multi-agent systems could be combined to develop new concepts in the form of an Integrated cell (I-cell) which would undergo selection for growth and survival in a world of artificial microbiology.