Release of salbutamol sulphate and ketoprofen enantiomers from matrices containing HPMC and cellulose derivatives

We studied the release of salbutamol and ketoprofen enantiomers from HPMC K100M matrices containing two types of cellulose derivatives: cellulose tris (3,5-dimethylphenylcarbamate) and cellulose tris (2,3-dichlorophenylcarbamate), chiral excipients used as stationary phases for liquid chromatography. These matrices provided an extended release of both drugs. Ketoprofen release from formulations elaborated with cellulose tris (2,3-dichlorophenylcarbamate) was by anomalous transport, because the value of n (release exponent of the diffusion equation) ranged between 0.60-0.68, whereas for all other formulations the value of exponent n ranged from 0.50-0.54. The drug thus diffuses through the matrix and is released following a quasi-Fickian diffusion mechanism (stereoselective process). The matrices preferentially retained R-salbutamol and S-ketoprofen and cellulose tris (3,5-dimethylphenylcarbamate) showed more capacity of chiral discrimination for both drugs than cellulose tris (2,3-dichlorophenylcarbamate). Moreover, we observed that stereoselectivity is dependent on the amount of chiral excipient in the formulation. Diffusion tests confirmed the chiral interaction between drugs and cellulose derivatives observed in the dissolution assays except for matrices elaborated with ketoprofen and cellulose tris (2,3-dichlorophenylcarbamate), where the low stereoselectivity observed with the matrices is due to the presence of HPMC K100M. We conclude that the inclusion of these cellulose derivatives in HPMC matrices does not result in a relevant stereoselectivity with respect to the two drugs studied.     

Influence of the red fox (<Emphasis Type="Italic">Vulpes vulpes</Emphasis>, Linnaeus 1758) on the distribution and number of breeding birds in an intensively used farmland

This study tested the hypothesis that small birds at their nest sites avoid areas around dens of the red fox (Vulpes vulpes, Linneaus 1758) in an intensively used farmland. Birds were counted at 18 points (radius 100m) located near dens, as well as at 18 control points that were located at least 600m away from the nearest den. These two types of points did not differ with respect to the number of recorded bird species. However, a negative effect of the proximity of fox dens on the total density of the bird community was observed. This effect was also recorded for the most abundant bird species, the skylark (Alauda arvensis, Linneaus 1758). In agreement with our expectations, these results indicate a negative impact of fox presence on a breeding bird community in an open farmland.     

His-859 is an essential residue for the activity and pH dependence of Escherichia coli RTX toxin alpha-hemolysin

Escherichia coli alpha-hemolysin (HlyA) is a toxin protein that, in common with other members of the RTX family, contains a calcium-binding domain consisting of a number of Gly- and Asp-rich nonapeptides (17 in this case) repeated in tandem. Amino acid number 6 in these nonapeptides is almost invariably Asp, and occasionally Asn, but HlyA contains a His residue (number 859 in the chain) in position 6 of the last-but-one nonapeptide. HlyA mutants have been prepared, by site-directed mutagenesis, in which His-859 has been replaced by an Asn (H859N) or by Asp (H859D). HlyA exists in aqueous media in an aggregate-monomer equilibrium, but only the monomer containing bound Ca(2+) (HlyA.Ca) appears to be competent to achieve target membrane insertion and subsequent lysis. In mutant H859N, equilibrium appears to be shifted toward the aggregate, therefore the protein does not exchange Ca(2+) with the aqueous environment, no HlyA.Ca monomers are detected, and the protein lacks any membrane lytic activity. Mutant H859D in turn is almost indistinguishable from the wild-type regarding its calcium binding and membrane lytic activity, however, it differs significantly in its pH dependence. Wild-type HlyA activity decreases sigmoidally with pH, following rather closely the protonation curve of a His residue (apparent pK(a) approximately 6.5). With mutant H859D activity decreases almost linearly with pH and to a smaller extent. It can be concluded that His-859 plays a critical role in several aspects of HlyA activity, namely self-aggregation properties, calcium binding, hemolysis, and pH dependence.     

Denitrification in a seashore sandy deposit influenced by groundwater discharge

The chemical compositions of ground water and organic matter in sediments were investigated at a sandy shore of Tokyo Bay, Japan to determine the fate of ground water NO₃ ^–. On the basis of Cl^– distribution in ground water, the beach was classified into freshwater (FR)-, transition (TR)-, and seawater (SW)-zones from the land toward the shoreline. The NO₃ ^– and N₂O did not behave conservatively with respect to Cl^– during subsurface mixing of freshwater and seawater, suggesting NO₃ ^– consumption and N₂O production in the TR-zone. Absence of beach vegetation indicated that NO₃ ^– assimilation by higher plants was not as important as NO₃ ^– sink. Low NH₄ ⁺ concentrations in ground water revealed little reduction of NO₃ ^– to NH₄ ⁺. These facts implied that microbial denitrification and assimilation were the likely sinks for ground water NO₃ ^–. The potential activity and number of denitrifiers in water-saturated sediment were highest in the low-chlorinity part of the TR-zone. The location of the highest potential denitrification activity (DN-zone) overlapped with that of the highest NO₃ ^– concentration. The C/N ratio and carbon isotope ratio (¹³C) of organic matter in sediment (< 100 -m) varied from 12.0 to 22.5 and from –22.5 to –25.5, respectively. The ¹³C value was inversely related to the C/N ratio (r ² = 0.968, n = 11), which was explained by the mixing of organic matters of terrestrial and marine origins. In the DN-zone, the fine sediments were rich in organic matters with high C/N ratios and low ¹³C values, implying that dissolved organic matters of terrestrial origin might have been immobilized under slightly saline conditions. A concurrent supply of NO₃ ^– and organic matter to the TR-zone by ground water discharge probably generates favorable conditions for denitrifiers. Ground water NO₃ ^– discharged to the beach is thus partially denitrified and fixed as microbial biomass before it enters the sea. Further studies are necessary to determine the relative contribution of these processes for NO₃ ^– removal.     

Dead-ended autologous connective tissue chambers in peripheral nerve repair--early observations

The effects of the repair of nerve gap injuries are still unsatisfactory, despite the great progress in microsurgery. Until now, there is no effective method to induce the regeneration of the transected peripheral nerve when its distal stump is missing. The aim of this work was to examine whether the implantation of dead-ended connective tissue chambers can promote the outgrowth of injured peripheral neurites. This method differs from all previous nerve guides because it totally eliminates the distal part of the nerve and restricts the influence of surrounding tissues. We have also tried to establish whether some neurotrophic factors can be applied by means of these chambers. The results of this work show that dead-ended autologous connective tissue chambers can be a useful tool in peripheral nerve injuries treatment, even when the distal part of the nerve is missing.