Hypotension with intravenous immunoglobulin therapy: importance of pH and dimer formation

Therapy with intravenous immunoglobulin preparations has been used effectively in a wide range of conditions. Although generally well tolerated, intravenous immunoglobulin preparations may be associated with transient hypotension in some patients. This study examined the role of different immunoglobulin G fractions in the development of intravenous immunoglobulin-induced hypotension in an anaesthetized rat model and assessed the effects of a new liquid immunoglobulin prepared at a low pH on both the formation of immunoglobulin G dimers and the development of hypotension. The effects of this new preparation in an experimental autoimmune encephalomyelitis model were also evaluated.Results from the haemodynamic studies indicated that immunoglobulin G dimers in polyclonal immunoglobulin G are responsible for the hypotensive events associated with some immunoglobulin preparations. They also showed that adjustment to an acidic pH results in the rapid dissociation of immunoglobulin G dimers and prevents the development of hypotension. Additional experiments demonstrated that only immunoglobulin G dimers with a functional Fc fragment can bind to Fcgamma receptors on macrophages to induce the release of blood pressure-lowering mediators. Moreover, essentially monomeric Fc fragments can block the blood pressure-lowering effects of immunoglobulin G dimers.Preparation of a new liquid intravenous immunoglobulin with the pH adjusted to 4.3 prevents the formation of immunoglobulin G dimers even over long-term storage and does not significantly affect blood pressure in a rat model. This preparation is as effective as other intravenous immunoglobulin preparations in ameliorating symptoms of experimental autoimmune encephalomyelitis. These results, like those from previous studies, indicate that preparation of intravenous immunoglobulin at a low pH substantially reduces immunoglobulin G dimerization; this effect significantly decreases the potential for intravenous immunoglobulin to induce hypotension without reducing its clinically relevant biological activity.     

Phylogeny of the Cocculinoidea (Mollusca, Gastropoda)

Abstract. The superfamily Cocculinoidea is a group of marine, deep-water, limpet-like gastropods. Recent speculation surrounding their affinities has concentrated on their placement within the Gastropoda. However, phylogenetic relationships within the Cocculinoidea, especially the monophyly of families and genera within the group, remain poorly understood. Phylogenetic analysis of 31 morphological characters for 15 cocculinoidean taxa and 2 outgroups resulted in a single most parsimonious tree, length=70, CI=0.62, and RI=0.71. Monophyly of the Cocculinoidea, Cocculinidae, and the genera Cocculina and Coccopigya was supported; Paracocculina and Coccocrater were found to be paraphyletic. Character optimization demonstrates that many characters often cited as diagnostic of various taxa, are often homoplastic and/or synapomorphies at different hierarchical levels.     

Highly efficient uptake of phosphorus in epiphytic bromeliads

Background and Aims

Vascular epiphytes which can be abundant in tree crowns of tropical forests have to cope with low and highly intermittent water and nutrient supply from rainwater, throughfall and stem flow. Phosphorus rather than nitrogen has been suggested as the most limiting nutrient element, but, unlike nitrogen, this element has received little attention in physiological studies. This motivated the present report, in which phosphate uptake kinetics by leaves and roots, the subsequent distribution within plants and the metabolic fate of phosphate were studied as a step towards an improved understanding of physiological adaptations to the conditions of tree canopies.

Methods

Radioactively labelled [³²P]phosphate was used to study uptake kinetics and plant distribution of phosphorus absorbed from bromeliad tanks. The metabolism of low molecular phosphorus metabolites was analysed by thin-layer chromatography followed by autoradiography.

Key Results

Uptake of phosphate from tanks is an ATP-dependent process. The kinetics of phosphorus uptake suggest that epiphytes possess effective phosphate transporters. The K_m value of 1·05 µm determined for leaves of the bromeliad Aechmea fasciata is comparable with values obtained for the high affinity phosphate transporters in roots of terrestrial plants. In this species, young leaves are the main sink for phosphate absorbed from tank water. Within these leaves, phosphate is then allocated from the basal uptake zone into distal sections of the leaves. More than 80 % of the phosphate incorporated into leaves is not used in metabolism but stored as phytin.

Conclusions

Tank epiphytes are adapted to low and intermittent nutrient supply by different mechanisms. They possess an effective mechanism to take up phosphate, minimizing dilution and loss of phosphorus captured in the tank. Available phosphorus is taken up from the tank solution almost quantitatively, and the surplus not needed for current metabolism is accumulated in reserves, i.e. plants show luxury consumption. Young, developing leaves are preferentially supplied with this nutrient element. Taken together, these features allow epiphytes the efficient use of scarce and variable nutrient supplies.Key words: Epiphytic bromeliads, phosphorus uptake, forest canopies, luxury consumption, phytotelms, plant nutrition, Aechmea fasciata     

Synthesis and antitumor-evaluation of cyclopropyl-containing combretastatin analogs

Several derivatives of combretastatin have been prepared bearing a cyclopropyl unit instead of the natural occurring cis-double bond. Final products and synthetic intermediates were evaluated for their cytotoxic properties in two human cancer cell lines.     

Viral and Flagellate Control of Prokaryotic Production and Community Structure in Offshore Mediterranean Waters

A dilution and size fractionation approach was used to study the separate and combined effects of viruses and flagellates on prokaryotic production ([³H]leucine incorporation) and community composition (16S rRNA gene PCR and denaturing gradient gel electrophoresis [DGGE]) in the upper mixed layer and the deep chlorophyll maximum in the offshore Mediterranean Sea. Four experiments were established using differential filtration: a resource control without predators (C treatment), treatment in the presence of viruses (V treatment), treatment in the presence of flagellates (F treatment), and treatment in the presence of both predators (VF treatment). The V and VF treatments increased prokaryotic abundance (1.4- to 2.3-fold) and the number of DGGE bands (by up to 43%) and decreased prokaryotic production compared to the level for the C treatment (by 22 to 99%). For the F treatment, significant differences compared to the level for the C treatment were found as well, but trends were not consistent across experiments. The relative abundances of the high-nucleic-acid subgroups of prokaryotes with high scatter (HNAhs) in flow cytometer settings were lower in the V and VF treatments than in the C and F treatments. These differences were probably due to lysis of very active HNA prokaryotes in the V and VF treatments. Our results indicate that the presence of viruses or viruses plus flagellates sustains prokaryotic diversity and controls prokaryotic production by regulating the proportion of the highly active members of the community. Our data also suggest that lysis and grazing control influences the relationship between bacterial community composition and prokaryotic production.During the last 3 decades, a wealth of information on the mechanisms controlling prokaryotic production in the ocean has been accumulated (26). It is commonly accepted that inorganic nutrients, composition and bioavailability of dissolved organic matter (DOM), and predation are the major factors shaping the spatiotemporal variability of prokaryotic production. Protistan grazing might result in the formation of grazing-resistant prokaryotic cell types (16, 23) and in a stimulation of specific growth rates (39) by recycling nutrients (45, 48). Viruses, considered here to be another type of predator, cause a mortality of prokaryotes that is highly variable but, on average, as important as protistan grazing (summarized in references 56 and 63).A modeling approach suggested that viral lysis reduces the carbon flow to higher trophic levels and stimulates prokaryotic production (10). Support for this “stimulation of production” hypothesis comes from experimental data showing that viral lysis increases bacterial production and respiration (34) at the food web level. However, in experimental studies with the viral community either present or absent, a negative effect of viruses on bacterial production was typically found (6, 35, 65). It has also been argued that grazing should have a negative effect on viral production, since grazers consume infected cells (5, 58). However, in a set of experiments performed with freshwater systems, viral infection was stimulated in the presence of grazers, suggesting synergistic interactions (41, 54, 55).Prokaryotic community composition can vary during phytoplankton blooms (4, 40), probably due to changing DOM composition and bioavailability, as suggested by the covariation in the types of ß-glucosidases (4). It has also been suggested that phages control competitive dominants for resource acquisition, thus sustaining diversity (10). This idea has been mathematically described in the “killing the winner” hypothesis (53) and is also applicable to flagellates (52). In a general model, diversity shows a hump-shaped distribution along gradients of increasing resource as well as consumer control (64). However, this relationship can vary for different taxonomic groups of bacteria. In an in situ study conducted in the North Sea, the number of bacterial phylotypes was negatively related to viral abundances and prokaryotic production and respiration (42, 62). Others have shown for the open ocean a positive relationship between the number of phylotypes and productivity (18) and predictability of bacterial community structure over annual cycles (11). Differences in such relationships between environments were also detected (19). Moreover, a latitudinal diversity gradient has been demonstrated for bacterioplankton (12). In a study with coastal water, in the presence of viruses, flagellates, or both types of predators, bacterial production decreased and the number of phylotypes detected by a genetic community fingerprint increased compared to the levels for predator-free controls (65). Overall, there is evidence that protistan grazing (e.g., references 24, 48, and 49) and viral lysis (e.g., references 21, 44, and 61) can affect prokaryotic community composition.Experimental tests of the effect of grazing versus that of viral lysis on prokaryotic production are scarce for the open ocean. Moreover, the links between bacterial production and respiration have mostly been studied for freshwater and coastal marine waters (e.g., references 1, 22, 28, 42, and 62). During an offshore experimental study, in the frame of a mesoscale iron fertilization experiment, changes were detectable in bacterial production, bulk ectoenzymatic activity, and types of β-glucosidase expressed, whereas the number of detectable bacterial phylotypes was remarkably stable (3). This suggests that bacterial production parameters and bacterial community composition were only weakly related. Such observations have also been made in experimental freshwater studies (28).In the present study, we investigated the relative and combined effects of viral lysis and protistan grazing on prokaryotic production and community composition in offshore Mediterranean waters and compared the findings to those for predator-free incubations (resource control). The types of predators had distinct effects on community composition and production and altered the resource control of prokaryotic diversity. When both types of predators were present, prokaryotic production was consistently reduced and diversity likely sustained, probably by controlling the more-active members of the community.     

Passerine migration strategies and body mass variation along geographic sectors across East Africa, the Middle East and the Arabian Peninsula

Using the body mass estimates of 12 long-distance migrating Palearctic passerine species monitored at successive sites across the Eastern Africa flyway, we tested whether birds modulate their body mass according to specific seasonal demands across different geographic sectors. We compared body mass estimates across latitudinal distances and geographic sectors in Europe, the desert, Northeast Africa and East Africa. Our results show that, depending on the species and season considered, the average body mass increase or decrease is variable at and among different geographic sectors. By comparing the variation in body mass between different ecological sectors, we were able to show when and where migrants accumulate their migratory fuel reserves during migration.     

DFT and MP2 studies on the C2C2α bond cleavage in thiamin catalysis

Thiamin diphosphate (ThDP), the biologically active derivative of vitamin B₁, is an important cofactor of several enzymes that catalyze the oxidative and non-oxidative conversion of α-keto acids. The final step of non-oxidative decarboxylation of pyruvate by pyruvate decarboxylase – the liberation of acetaldehyde – requires deprotonation of the α-hydroxyl group and cleavage of the C2–C2α bond of the transitory 2-(1-hydroxyethyl)-ThDP intermediate. It has been proposed that the cofactor 4′-amino/imino function is essentially involved in the deprotonation of the α-hydroxyl group. Proton transfer and C2–C2α cleavage may occur in a stepwise manner, or, alternatively in a concerted mechanism. Here, density functional theory (DFT) calculations as well as second order Møller–Plesset perturbation theory (MP2) studies were performed on a simple model for the enzyme using the program package Gaussian 03. Calculations favor a stepwise mechanism with initial formation of the C2α alkoxide, followed by C2–C2α bond cleavage.     

Nonflowers near the base of extant angiosperms? Spatiotemporal arrangement of organs in reproductive units of Hydatellaceae and its bearing on the origin of the flower

Reproductive units (RUs) of Trithuria, the sole genus of the early-divergent angiosperm family Hydatellaceae, are compared with flowers of their close relatives in Cabombaceae (Nymphaeales). Trithuria RUs combine features of flowers and inflorescences. They differ from typical flowers in possessing an "inside-out" morphology, with carpels surrounding stamens; furthermore, carpels develop centrifugally, in contrast to centripetal or simultaneous development in typical flowers. Trithuria RUs could be interpreted as pseudanthia of two or more cymose partial inflorescences enclosed within an involucre, but the bractlike involucral phyllomes do not subtend partial inflorescences and hence collectively resemble a typical perianth. Teratological forms of T. submersa indicate a tendency to fasciation and demonstrate that the inside-out structure-the primary feature that separates RUs of Hydatellaceae from more orthodox angiosperm flowers-can be at least partially modified, thus producing a morphology that is closer to an orthodox flower. The Trithuria RU could be described as a "nonflower", i.e., a structure that contains typical angiosperm carpels and stamens but does not allow recognition of a typical angiosperm flower. The term nonflower could combine cases of secondary loss of flower identity and cases of a prefloral condition, similar to those that gave rise to the angiosperm flower. Nonhomology among some angiosperm flowers could be due to iterative shifts between nonfloral construction and flower/inflorescence organization of reproductive organs. Potential testing of these hypotheses using evolutionary-developmental genetics is explored using preliminary data from immunolocalization of the floral meristem identity gene LEAFY in T. submersa, which indicated protein expression at different hierarchical levels.