Oscillations in growth of multicellular tumour spheroids: a revisited quantitative analysis

Objectives: Multicellular tumour spheroids (MTS) provide an important tool for study of the microscopic properties of solid tumours and their responses to therapy. Thus, observation of large‐scale volume oscillations in MTS, reported several years ago by two independent groups ( 1 , 2 ), in our opinion represent a remarkable discovery, particularly if this could promote careful investigation of the possible occurrence of volume oscillations of tumours ‘in vivo’. Materials and methods: Because of high background noise, quantitative analysis of properties of observed oscillations has not been possible in previous studies. Such an analysis can be now performed, thanks to a recently proposed approach, based on formalism of phenomenological universalities (PUN). Results: Results have provided unambiguous confirmation of the existence of MTS volume oscillations, and quantitative evaluation of their properties, for two tumour cell lines. Proof is based not only on quality of fitting of the experimental datasets, but also on determination of well‐defined values of frequency and amplitude of the oscillations for each line investigated, which would not be consistent with random fluctuation. Conclusions: Biological mechanisms, which can be directly responsible for observed oscillations, are proposed, which relates also to recent work on related topics. Further investigations, both at experimental and at modelling levels, are also suggested. Finally, from a methodological point of view, results obtained represent further confirmation of applicability and usefulness of the PUN approach.     

Archaeal lipids and their biotechnological applications

The lipids of Archaea, based on glycerol isopranoid ethers, can be used taxonomically to distinguish between phenotypic subgroups of the domain to delineate them clearly from all other organisms. This review is a general survey of the structural features of archaeal lipids and how they relate to survival in the harsh environments in which the Archaea live. The molecular organization of archaeal lipids in monolayers, artificial black membranes and vesicles and the unique properties and possible biotechnological applications of liposomes of the lipids are presented. The results with these liposomes are compared with similar data obtained with synthetic compounds which mimic the structure of archaeal lipids. Studies on computer simulation are also reported.A. Gambacorta is with the istituto per la Chimica di Molecole di interesse Biologico, CNR via Toiano 6, 80072 Arco Felice, Napoli, Italy; A Gliozzi is with the Dipartimento di Fisica, Università di Genova, via Dodecanneso 33, 16146 Genova, Italy. M. De Rosa is with the Istituto di Biochimica delle Macromolecole. Seconda Università di Napoli, via Costantinopoli 16, 80132 Napoli, Italy.     

Transport properties of charged membranes undergoing conformational transitions

Summary The permeability and reflection behavior of cross-linked collagen films in dilute salt solutions have been investigated by measurements of net volume flow, isotopic exchange of THO and of Ca⁴⁵, and osmotic pressure. Complementary measurements of swelling, membrane resistance, membrane potential, and streaming potential are presented. Measurements were performed in the pH range of 5 to 1.5, at temperatures between 25 and 52 °C, and in the presence of KCl, 10^–2 m or CaCl₂, 10^–3 m. Under the conditions adopted, the membrane carries a net positive charge and undergoes large changes in degree of swelling (Donnan effect) and structure (crystal amorphous transition). The results indicate that when pH is lowered the filtration coefficientL _p decreases in the crystalline state (pH 5 to 3), increases during the conformational transition (pH 3 to 2), and decreases in the amorphous state (pH<2). It appears thatL _p is affected more by such properties as structure and porosity (i.e., mechanical resistance to flow) than properties related to the charged character of the membrane. The reflection coefficient increases when pH is lowered until pH 3, and decreases upon further lowering of pH. Such behavior is described in terms of the competition between swelling (due to both the Donnan effect and the melting transition) and fixed-charge density. Values of fixed-charge density derived on the basis of a theoretical expression for were found to be in good agreement with independent titration data.     

Collagen plays an active role in the aggregation of beta2-microglobulin under physiopathological conditions of dialysis-related amyloidosis

Dialysis-related amyloidosis is characterized by the deposition of insoluble fibrils of beta(2)-microglobulin (beta(2)-m) in the musculoskeletal system. Atomic force microscopy inspection of ex vivo amyloid material reveals the presence of bundles of fibrils often associated to collagen fibrils. Aggregation experiments were undertaken in vitro with the aim of reproducing the physiopathological fibrillation process. To this purpose, atomic force microscopy, fluorescence techniques, and NMR were employed. We found that in temperature and pH conditions similar to those occurring in periarticular tissues in the presence of flogistic processes, beta(2)-m fibrillogenesis takes place in the presence of fibrillar collagen, whereas no fibrils are obtained without collagen. Moreover, the morphology of beta(2)-m fibrils obtained in vitro in the presence of collagen is extremely similar to that observed in the ex vivo sample. This result indicates that collagen plays a crucial role in beta(2)-m amyloid deposition under physiopathological conditions and suggests an explanation for the strict specificity of dialysis-related amyloidosis for the tissues of the skeletal system. We hypothesize that positively charged regions along the collagen fiber could play a direct role in beta(2)-m fibrillogenesis. This hypothesis is sustained by aggregation experiments performed by replacing collagen with a poly-L-lysine-coated mica surface. As shown by NMR measurements, no similar process occurs when poly-L-lysine is dissolved in solution with beta(2)-m. Overall, the findings are consistent with the estimates resulting from a simplified collagen model whereby electrostatic effects can lead to high local concentrations of oppositely charged species, such as beta(2)-m, that decay on moving away from the fiber surface.     

Palaeoenvironmental analysis of Early Pleistocene brackish marshes in the Rieti and Tiberino intrapenninic basins (Latium and Umbria, Italy) using ostracods (Crustacea)

Recent palaeontological and sedimentological studies on the Upper Pliocene–Lower Pleistocene continental deposits of the Rieti and Tiberino basins (Latium and Umbria, Italy) showed the existence of brackish marshes influenced by the Early Pleistocene Tyrrhenian sea. The micropaleontological analyses carried out on five sections cropping out in the northern sector of the Rieti Basin and on one section cropping out in the southwestern branch of the Tiberino Basin showed the repeated alternance of two ostracod assemblages. The first is characterized by a very abundant ostracod association dominated by Cyprideis torosa, typical of brackish waters; the second one is less rich in specimens and dominated by several species of freshwater Candoninae. This alternance allowed the recognition of several changes in the water salinity that could be related to many Early Pleistocene sea-level changes. Palaeosalinities were estimated for both the Tiberino and the Rieti Basin using the morphological analysis of the shell of Cyprideis torosa (ornamentation, nodosities and percentages of sieve-type pore canals). The obtained palaeosalinity values, ranging from freshwater to oligohaline, show slightly higher salinities for the Tiberino Basin, located nearer the ancient coastline, than for the Rieti Basin.     

Morphometric analysis and taxonomic revision of the Vriesea paraibica complex (Bromeliaceae)

The species related to Vriesea paraibica (Bromeliaceae, Tillandsioideae) have controversial taxonomic limits. For several decades, this group has been identified in herbarium collections as V. × morreniana, an artificial hybrid that does not grow in natural habitats. The aim of this study was to assess the morphological variation in the V. paraibica complex through morphometric analyses of natural populations. Two sets of analyses were performed: the first involved six natural populations (G1) and the second was carried out on taxa that emerged from the first analysis, but using material from herbarium collections (G2). Univariate ANOVA was used, as well as discriminant analysis of 16 morphometric variables in G1 and 18 in G2. The results of the analyses of the two groups were similar and led to the selection of diagnostic traits of four species. Lengths of the lower and median floral bracts were significant for the separation of red and yellow floral bracts. Vriesea paraibica and V. interrogatoria have red bracts; these two species are differentiated by the widths of the lower and median portions of the inflorescence and by scape length. These structures are larger in the former and smaller in the latter. Of the species with yellow floral bracts, V. eltoniana is distinguished by longer leaf blades and scapes and V. flava is characterized by its shorter sepal lengths. © 2009 The Linnean Society of London, Botanical Journal of the Linnean Society, 2009, 159 , 163–181.