Evidence of niche partitioning among bacteria living on plastics, organic particles and surrounding seawaters

Plastic pollution is widespread in ocean ecosystems worldwide, but it is unknown if plastic offers a unique habitat for bacteria compared to communities in the water column and attached to naturally-occurring organic particles. The large set of samples taken during the Tara-Mediterranean expedition revealed for the first time a clear niche partitioning between free-living (FL), organic particle-attached (PA) and the recently introduced plastic marine debris (PMD). Bacterial counts in PMD presented higher cell enrichment factors than generally observed for PA fraction, when compared to FL bacteria in the surrounding waters. Taxonomic diversity was also higher in the PMD communities, where higher evenness indicated a favorable environment for a very large number of species. Cyanobacteria were particularly overrepresented in PMD, together with essential functions for biofilm formation and maturation. The community distinction between the three habitats was consistent across the large-scale sampling in the Western Mediterranean basin. 'Plastic specific bacteria' recovered only on the PMD represented half of the OTUs, thus forming a distinct habitat that should be further considered for understanding microbial biodiversity in changing marine ecosystems.

PCL–PEG graft copolymers with tunable amphiphilicity as efficient drug delivery systems

Efficient drug delivery systems are prepared, thanks to the fine-tuning of the amphiphilicity and architecture of PCL–PEG graft copolymers via a simple photochemical approach.

Self-assembly of well-defined triblock copolymers based on poly(lactic acid) and poly(oligo(ethylene glycol) methyl ether methacrylate) prepared by ATRP

Self-assembly of a series of amphiphilic poly(oligo(ethylene glycol) methyl ether methacrylate)-block-poly(lactic acid)-block-poly(oligo(ethylene glycol) methyl ether methacrylate) (P(OEGMA)-b-PLLA-b-P(OEGMA)) copolymers was investigated.

Microspheres from new biodegradable poly(ester amide)s with different ratios ofL- andD-alanine for controlled drug delivery

A series of biodegradable poly (ester amide)s composed of sebacic acid, dodecanediol and different ratios of the stereoisomers of L- and D-alanine were synthesized for applications in drug delivery systems. Microspheres loaded with diclofenac sodium salt, triclosan and clofazimine were prepared with the solvent evaporation technique. No influence of polymer constitution in the drug release rate was found in vitro and no degradation occurred during the period of drug release. It was shown that a sustained delivery of the hydrophilic diclofenac sodium salt in Sörensen media occurred and it was controlled by diffusion. However, exhaustion of microspheres was feasible only from the most porous matrices where channelling had an important contribution.

Novel Amphiphilic Poly(ε-caprolactone)-g-poly(l-lysine) Degradable Copolymers

As part of the search of novel degradable polymers, amphiphilic and cationic poly(epsilon-caprolactone)-g-poly(l-lysine) (PCL-g-PlL) copolymers have been synthesized following a grafting "onto" or a grafting "from" method both applied to a macropolycarbanionic PCL derivative. The first approach led to PCL-g-PZlL containing 36% of epsilon-caprolactone and 64% of N-epsilon-Z-l-lysine units, by reaction of activated poly(N-epsilon-Z-l-lysine) on the macropolycarbanion derived from PCL. The second route was based on the anionic ring opening polymerization of N-carboxyanhydride of N-epsilon-benzyloxycarbonyl-l-lysine initiated by the macropolycarbanion derived from PCL and led to a similar copolymer containing 45% of of epsilon-caprolactone and 55% of N-epsilon-Z-l-lysine units. After deprotection of the lysine units, PCL-g-PlL copolymers were obtained. These copolymers are water-soluble and form nanometric micelle-like objects with mean diameters between 60 and 500 nm in distilled water depending on the synthesis route.

Interactions of GRF(1–29)NH2 with plasma proteins and their effects on the release of the peptide from a PLAGA matrix

The administration of the GRF(1-29)NH2 Growth Hormone Releasing Hormone analog is known as relevant of the concept of drug delivery system using a bioresorbable matrix. However, the release of this peptide from poly(dl-lactic acid-co-glycolic acid) matrices is affected by its insolubility at neutral in salted media and in plasma as well. In order to investigate the origin and the nature of the insolubility in these media in more details, the precipitates collected when the peptide was set in contact with saline, isotonic pH=7.4 phosphate buffer and plasma were analyzed by various techniques, namely weighting, gel chromatography, 1D- and 2D-immunoelectrophoresis, and dialysis to discern the soluble from the insoluble or aggregated fractions. It is shown that precipitation in protein-free salted media is due to a salting out phenomenon complemented by the neutralization of the solubilizing electrostatic charges in the isotonic buffer. In contrast, the precipitation in plasma is due to inter polyelectrolyte-type complexation that involved polyanionic proteins having a rather low isoelectric point like albumin, transferin, haptoglobulin and IgG immunoglobulins. When a rather large quantity of GRF(1-29)NH2 was entrapped in bioresorbable pellets working at a percolating regime after subcutaneous implantation in rats, the peptide was slowly released despite the complexation with plasma proteins. However only a very small part of the peptide was found in blood, this small part being still large enough to cause a detectable increase of the circulating growth hormone concentration. Attempts made to increase the solubility of the peptide in plasma were successful when the peptide was combined with arginine, an amino acid known to promote the poor hormonal activity of injected GRF(1-29)NH2 solutions under clinical conditions.

Novel degradable polymers combining D-gluconic acid, a sugar of vegetal origin, with lactic and glycolic acids

To synthesize functionalized poly(lactic acid-co-glycolic acid)-based polyesters for biomedical and pharmaceutical applications such as controlled drug delivery, D-gluconic acid was considered as an interesting source of comonomer. Accordingly D-gluconic acid was used to synthesize novel 1,4-dioxane-2,5-diones with protected hydroxyl groups, namely 3-(1,2:3,4-tetraoxobutyl-di-O-isopropylidene)-dioxane-2,5-dione (5a) and 3-methyl-6-(1,2:3,4-tetraoxobutyl-di-O-isopropylidene)-dioxane-2,5-dione (5b). The ring-opening homopolymerization and copolymerization of these cyclic dilactones with DL-lactide provided novel degradable polyesters with higher glass transition temperatures than poly(lactic acid-co-glycolic acid) polymers.

Biodegradation of [(3)H]poly(epsilon-caprolactone) in the presence of active sludge extracts

Poly(epsilon-caprolactone), PCL, is a commercial biodegradable and biocompatible polyester that can be bioassimilated by outdoor microorganisms. For biomedical and environmental applications, monitoring the fate of degradation products in vivo or under environmental conditions is one of the critical steps to evaluate degradation characteristics. [(3)H] radiolabeling is the best method to monitor the fate of degradable polymer chains in contact with complex living systems and to show bioassimilation. Therefore, tritiated PCL was synthesized by chemical modification using anionic activation by reaction with lithium diisopropylamide. The resulting radioactive polymer was characterized and allowed to degrade at 37 degrees C under aerobic conditions in the presence of active sludge. Comparison was made with abiotic hydrolytic degradation in pH = 7.4, 0.13 M phosphate buffer at 37 degrees C. Water-soluble degradation products were assessed by measuring radioactivity in the solution phase. It was shown that biodegradation of PCL started after a few hours and proceeded up to the ultimate stage over ca. 72 days, giving tritiated water (80-90%) and biomass. Radioactivity detection appeared much more sensitive than measurement of CO(2) production or consumption to monitor degradation phenomena. In particular, it showed that the onset of biodegradation occurs earlier than that reported using respirometry.

A novel route to poly(epsilon-caprolactone)-based copolymers via anionic derivatization

Poly(epsilon-caprolactone) (PCL) is known to biodegrade under composting or water sewage plant conditions. However, as compared with poly(alpha-hydroxy acids) derived from lactic and glycolic acids, PCL is much more resistant to chemical hydrolysis and is achiral, a feature that limits very much the possibility of property modulation through the configurational structure of polymer chains. For the sake of enlarging the family of PCL-type polymers, a novel method is proposed which is based on the anionic activation of PCL chain by the removal of a proton from the methylene group in alpha-position of the ester carbonyl present in the main chain, using a nonnucleophilic base such as lithium diisopropyl amide (LDA). This activation leads to a polycarbanion onto which various electrophile groups can be attached. The feasibility of the process was first shown on poly(methyl acrylate), (PMA), whose polyacrylic main chain is resistant to strong bases. The PMA polycarbanion was modified by various electrophiles, namely benzaldehyde, naphthoyl chloride, benzyl chloroformate, and iodomethane. In a second stage, the same reactions were performed successfully on PCL. The degree of substitution depended on the experimental conditions. PCL underwent main chain degradation during the formation of the polycarbanion whereas the reaction with the electrophiles did not cause any further main chain cleavages. The degradation of PCL chains can be limited enough to give access to novel functional PCL polymers.

Labile conjugation of a hydrophilic drug to PLA oligomers to modify a drug delivery system: cephradin in a PLAGA matrix

The physical entrapment of a hydrophilic drug within degradable microspheres is generally difficult because of poor entrapment yield and/or fast release, depending on the microsphere fabrication method. In order to counter the effects of drug hydrophilicity, it is proposed to covalently attach the drug to lactic acid oligomers, with the aim of achieving temporary hydrophobization and slower release controlled by the separation of the drug from the degradable link within the polymer matrix. This strategy was tested on microspheres of the antibiotic cephradin. As the prodrug form, the entrapment of the drug was almost quantitative. The prodrug did degrade in an aqueous medium, modelling body fluids, but cleavage did not occur at the drug-oligomer junction and drug molecules bearing two lactyl residual units were released. When the prodrug is entrapped within a PLAGA matrix, no release was observed within the experimental time period. However, data suggest that conjugation via a bond more sensitive to hydrolysis than the main chain PLA ester bonds should make the system work as desired.

Synthesis, characterisation and in vivo behaviour of a norfloxacin-poly(L-lysine citramide imide) conjugate bearing mannosyl residues

With the aim of promoting the targeting of macrophage mannose receptors and the internalisation of the norfloxacin antibiotic, which is active against some intracellular bacteria, a macromolecular prodrug was synthesised where the antibiotic and mannosyl moieties were coupled to a polymeric carrier, namely poly(L-lysine citramide imide). This carrier, which derived from two metabolites, citric acid and L-lysine, is known to be biocompatible and slowly degradable under slight acidic conditions. Norfloxacin was coupled onto the acid groups present along the polymer chains, and conjugates were characterised by UV, TLC and SEC. The mannosyl groups selected to promote the targeting of the mannose-specific lectin present on the outer membrane of macrophages were incorporated through a biodegradable glycolic spacer arm. Two different strategies were considered to synthesise the full conjugates, namely coupling norfloxacin onto mannosylated conjugates, and coupling mannose onto PLCAI/Nflx conjugates. The second pathway led to better results regarding mannosylation. The presence of norfloxacin and mannose caused chain aggregation, especially for conjugates with a high content of mannosyl residues. The targeting ability of the prodrug was investigated using a method based on the competition between the mannosylated macromolecules and glucose oxidase, a mannosyl-bearing non-human protein. This method showed that prodrug macromolecules competed effectively with glucose oxidase and thus should be able to bring the drug up to the mannosyl receptor-bearing membranes of macrophages infected by intracellular bacteria.

The use of additives to modulate the release of a sparingly water soluble drug entrapped in PLA50 microparticles: in vivo investigation

Sustained and total release of the sparingly water soluble compound, namely 1-[2-(4-fluorobenzoyl)aminoethyl]-4-(7-methoxynaphthyl) piperazine hydrochloride (FAM), from poly (DL-lactic acid) (PLA50) microparticles was previously shown to be feasible if the particles are obtained by grinding a solid mixture composed of the polymer and a percolating array of the compound mixed with an additive. Such microparticles, where the additive was poly (ethylene glycol) (PEG), dimyristoylphosphatidylcholine (DMPC), or Poloxamer 6800, were administrated subcutaneously to rats either as depot or using a liquid vehicle. The variations of the plasma concentration vs time determined by high pressure liquid chromatography and fluorometric detection, were plotted for the various microparticle systems, blood being taken twice from each animal and each measurement being triplicated. Data were analysed by non-compartmental analysis, in order to evaluate the elimination constant, the half-life, the area under the curve and the bioavailability for each system. Kinetics experiments were performed over 24h and also for 7 days. It was found that, for the selected formulations, the release of the sparingly water soluble compound depends on the dissolution rate in vivo and on the physicochemical characteristics of the additive, including solubility and micelle formation. Data correlated well with the results of previous in vitro investigation.

The use of additives to modulate the release of a sparingly water soluble drug entrapped in PLA50 microparticles

One of the major problems raised by the microencapsulation of drugs which are sparingly soluble in water is the difficulty to achieve a controlled and total release of the drug. It was previously shown that the microencapsulation of a model water insoluble drug, namely 1-[2-(4-fluorobenzoyl)aminoethyl]-4-(7-methoxynaphthyl) piperazine hydrochloride (FAMP) with a hydrophilic additive like low molar mass poly(ethylene glycol)s (PEG) can fulfil these requirements, provided all the drug + additive matter is in contact with the surrounding liquid medium via open pores and percolating channels. In this paper, PEG was replaced by other additives, selected because of their potential ability to increase the solubility of FAMP in pH = 7.4 isosomolar phosphate buffer (PBS). The idea was that increasing the solubility locally in microparticles could allow the drug to be released, despite its poor solubility in aqueous media like body fluids, and be absorbed before recrystallization. The solubility in PBS of FAMP mixed with additive, in the form of solid dispersions, was determined for various additives, namely citric acid, dimyristoyl DL-alpha-phosphatidyl choline (DMPC), poloxamer copolymers of different compositions and poly(dodecyl L-lysine citramidate) (PLCAC12(100)), an aggregate-forming hydrophilic polyelectrolyte containing 100%, hydrophobizing ester groups which can accommodate lipophilic compounds in hydrophobic pockets present in the aggregates. PEG was taken as a reference. It was found that DMPC, some poloxamers and the hydrophobized polyelectrolyte do increase the solubility of FAMP in PBS. Investigation was made of the release of FAMP from ground microparticles, whose loads were composed of FAMP combined with these solubilization-promoting additives. It was found that the release rate of FAMP from such systems can be increased and modulated to achieve an in vitro sustained release over a 20-30 day period and secure exhaustion of the particles at the end of this period.

In vitro delivery of a sparingly water soluble compound from PLA50 microparticles

The administration of a sparingly soluble drug is always problematic, especially when the drug has to be released from the degradable matrix of a polymeric drug delivery system. Attempts were made to achieve the complete release of 1-[2-(fluorobenzoyl) aminoethyl]-4-(7-methoxynaphtyl)piperazine (FAMP), a potential anxiolytic and antidepressor hydrophobic compound, from racemic poly(lactic acid) (PLA50)-based microparticles, 100% release was required at a low rate in order to allow monthly repeated S.C. or I.M. injections of this potent compound. FAMP-polymer combinations were made in the form of microspheres by the solvent evaporation technique. Release profiles were investigated under dynamic conditions by using a constant flow rate of pH 7.4 0.15 M phosphate buffer, used as a model of body fluids. Under these conditions, none of the microsphere compositions led to total release within a month, even when hydrophilic excipients, namely fructose and PEG were added. PLA50-FAMP microparticles with compositions and sizes similar to those of the microspheres, were then made by direct blending in dichloromethane, evaporation of the solvent, grinding and sieving. These formulations also failed in providing total drug release within 30 days, even at a high drug load. FAMP/PLA50/water-soluble additive, ternary grounded particles were finally prepared with fructose, PLA50 oligomers or poly(ethylene glycol) (PEG) as the additive. Only PLA50 grounded particles with percolating FAMP-PEG microdomains allowed 100% release of FAMP over a 30 day period, at a quasi constant rate which depended primarily on solubility and channelling provided the flow was slow enough. Data are discussed in terms of the accessibility of the entrapped drug to the aqueous medium.

Cephradin-plaga microspheres for sustained delivery to cattle

In the field of controlled drug delivery, most of the reported work is aimed at introducing new systems, or at providing basic information on the critical parameters which affect release profiles in vitro and occasionally in vivo. The situation is totally different when one wants to fulfil the specific requirements imposed by the marketing of a sustained release device to be used in humans or in animals eaten by human beings. The control of the release characteristics is then a difficult challenge. In this work, attempts were made to combine cephradin, a hydrophilic beta-lactam antibiotic, and bioresorbable polymeric matrices of a poly(alpha-hydroxy acid) in the form of microspheres with the aim of delivering the antibiotic to cattle at a dose rate of 4-5 mg/kg/day over a 3-4 days period after i.m. injection. PLAGA aliphatic polyesters were selected because they are already FDA approved as matrices. The solvent evaporation technique using PVA as the emulsion stabilizer was selected because it is efficient and can be extended to an industrial scale. Various experimental conditions were used in order to obtain the highest encapsulation yields compatible with the desired specifications. Decreasing the volume of the aqueous phase and adding a water-miscible organic solvent/non-solvent of cephradin failed. In contrast, microspheres containing up to 30% cephradin were prepared after addition of sodium chloride to the aqueous dispersing phase. The amount of entrapped drug was raised to 40% by decreasing the temperature and the pressure. Preliminary investigations using dogs showed that 20% cephradin microspheres prepared under these conditions extended the presence of cephradin in the blood circulation up to 48 h. Increasing the load led to higher blood concentrations but shorter sustained release. The fact that the microspheres were for cattle limited the volume of the injection and thus the amount of microspheres to be administered. The other limiting factors were related to microsphere morphology.

Something new in the field of PLA/GA bioresorbable polymers?

Polymers issued from glycolic acid and lactic acids (PLAGA) are now used worldwide as bioresorbable devices in surgery and in pharmacology. Their abiotic hydrolytic degradation has been shown to depend on diffusion-reaction phenomena and to proceed homogeneously or heterogeneously, depending on many factors. Two initiators are presently used industrially to make PLAGA polymers by ring opening polymerisation of lactide and/or glycolide in the bulk, namely Sn octanoate and zinc metal. In this contribution, attention is paid to the differences generated by the use of these two initiator systems in the case of the polymerisation of DL-lactide. Various poly(DL-lactide)s were prepared and characterised by size-exclusion chromatography (SEC), differential scanning calorimetry (DSC) and nuclear magnetic resonance spectroscopy (NMR). These polymers were allowed to age in pH=7.4 isoosmolar phosphate buffer at 37 degrees C. Under these conditions, polymers prepared by the two initiator systems showed dramatic differences when the fates of parallel sided specimens of rather large dimensions were considered. These differences were related to the esterification of some of the OH chain ends by octanoic acid and to the presence of rather hydrophobic low molecular weight by-products which were insoluble in the solvent generally used to purify the crude PLAGA polymers. These new findings should be of great interest in the case of PLAGA based matrices aimed at drug delivery.