Poly(lactic acid) microspheres for the sustained release of a selective A1 receptor agonist

Antibacterial activity and biological performance of a novel antibacterial coating containing a halogenated furanone compound loaded poly(L-lactic acid) nanoparticles on microarc-oxidized titanium

Titanium implants have been widely used for many medical applications, but bacterial infection after implant surgery remains one of the most common and intractable complications. To this end, long-term antibacterial ability of the implant surface is highly desirable to prevent implant-associated infection. In this study, a novel antibacterial coating containing a new antibacterial agent, (Z-)-4-bromo-5-(bromomethylene)-2(5H)-furanone loaded poly(L-lactic acid) nanoparticles, was fabricated on microarc-oxidized titanium for this purpose. The antibacterial coating produced a unique inhibition zone against Staphylococcus aureus throughout a 60-day study period, which is normally long enough to prevent the infection around implants in the early and intermediate stages. The antibacterial rate for adherent S. aureus was about 100% in the first 10 days and constantly remained over 90% in the following 20 days. Fluorescence staining of adherent S. aureus also confirmed the excellent antibacterial ability of the antibacterial coating. Moreover, in vitro experiments showed an enhanced osteoblast adhesion and proliferation on the antibacterial coating, and more notable cell spread was observed at the early stage. It is therefore concluded that the fabricated antibacterial coating, which exhibits relatively long-term antibacterial ability and excellent biological performance, is a potential and promising strategy to prevent implant-associated infection.

Adenosine-associated delivery systems

Adenosine is a naturally occurring purine nucleoside in every cell. Many critical treatments such as modulating irregular heartbeat (arrhythmias), regulation of central nervous system (CNS) activity and inhibiting seizural episodes can be carried out using adenosine. Despite the significant potential therapeutic impact of adenosine and its derivatives, the severe side effects caused by their systemic administration have significantly limited their clinical use. In addition, due to adenosine's extremely short half-life in human blood (<10 s), there is an unmet need for sustained delivery systems to enhance efficacy and reduce side effects. In this article, various adenosine delivery techniques, including encapsulation into biodegradable polymers, cell-based delivery, implantable biomaterials and mechanical-based delivery systems, are critically reviewed and the existing challenges are highlighted.

Encapsulation of PROLI/NO in biodegradable microparticles

Biodegradable hydrophilic polymers poly-lactic-co-glycolic acid (PLGA) and polyethylene oxide-co-lactic acid (PELA) were used to encapsulate a small hydrophilic prodrug (PROLI/NO) as a strategy to deliver nitric oxide (NO) by inhalation. The microparticles were prepared using double emulsion and solvent evaporation, followed by freeze-drying. The NO release kinetics were characterized by three parameters: the maximum concentration of NO per unit weight of microparticles, C(max) (nM mg(-1)); the window of time for which the concentration exceeded 50% of C(max), W(50) (min); and the initial rate of release, R(i) (nM mg(-1) min(-1)). PLGA-based microparticles did not encapsulate PROLI/NO. PELA-based microparticles demonstrated an entrapment efficiency rate of 43%, a mass median diameter of 2.3 micro m, and NO release in a physiological buffer characterized by C(max) = 123, W(50) = 4.11, and R(i) = 78.7. Addition of gelatin as a hydrophilic binding moiety in the first emulsion allowed PLGA-based microparticles to encapsulate PROLI/NO; however, the mass median diameter was too large for inhalation (23.5 micro m). It is concluded that the hydrophilic polyethylene glycol-moiety in PELA allows for efficient encapsulation of PROLI/NO, and PELA-based microparticles might be a strategy to generate a stable inhalable form of NO.

Complementary use of flow and sedimentation field-flow fractionation techniques for size characterizing biodegradable poly(lactic acid) nanospheres

Poly(lactic acid) (PLA) nanoparticles were synthesized using a modified evaporation method, testing two different surfactants (sodium cholate and Pluronic F68) for the process. During their formulation the prodrug 5'-octanoyl-CPA (Oct-CPA) of the anti-ischemic N(6)-cyclopentyladenosine (CPA) was encapsulated. Three different purification methods were compared with respect to the influence of surfactant on the size characteristics of the final nanoparticle product. Flow and sedimentation field-flow fractionation techniques (FlFFF and SdFFF, respectively) were used to size characterize the five poly(lactic acid) particle samples. Two different combinations of carrier solution (mobile phase) were employed in the FlFFF analyses, while a solution of poly(vinyl alcohol) was used as mobile phase for the SdFFF runs. The separation performances of the two techniques were compared and the particle size distributions (PSDs), derived from the fractograms, were interpreted with the support of observations by scanning electron microscopy. Some critical aspects, such as the carrier choice and the channel thickness determination for the FlFFF, have been investigated. This is the first comprehensive comparison of the two FFF techniques for characterizing non-standard particulate materials. The two FFF techniques proved to be complementary and gave good, congruent and very useful information on the size distributions of the five poly(lactic acid) particle samples.

Evidence for the presence of N-formyl-methionyl-leucyl-phenylalanine (fMLP) receptor ligands in human amniotic fluid and fMLP receptor modulation by physiological labour

OBJECTIVES

The presence of amniotic binding sites for N-formyl-methionyl-leucyl-phenylalanine (fMLP), an inflammatory peptide, and its ability to induce prostaglandin E2 synthesis in the human amnion prompted us to investigate for: (1) the presence of fMLP receptor ligands (fMLPRL) in the amniotic fluid; (2) expression of the fMLP receptor in amniotic tissue; (3) the effect of amniotic fMLPRL on neutrophil cyclic AMP (cAMP) level and calcium concentration ([Ca2+]i) during physiological pregnancy and labour.

METHODS

Binding assays were performed on neutrophils to determine the presence of fMLRL in the amniotic fluid at the 17th week of pregnancy, as well as at term, before and after the onset of labour. The expression of fMLP receptor mRNA was evaluated by RT-PCR, the cAMP level by a radiochemical assay, and the calcium concentration by Fura-2 AM fluorescence measurement.

RESULTS

fMLPRLs were detectable in amniotic fluid throughout pregnancy, and their levels did not vary during gestation. Labour significantly increased both the amniotic fMLPRL level and the expression of fMLP receptor in amnion tissue. The increased amniotic fMLPRL concentration noted during labour significantly increased neutrophil cAMP level and [Ca2+]i.

CONCLUSIONS

These findings demonstrate for the first time the presence of fMLP receptor ligands in amniotic fluid, and indicate a modulation of the fMLP system by the events of physiological labour.

Development and characterization of biodegradable nanospheres as delivery systems of anti-ischemic adenosine derivatives

We report a preliminary study concerning the encapsulation modalities in nanoparticles of the anti-ischemic drug N6-cyclopentyladenosine (CPA) and its pro-drug 5'-octanoyl-CPA (Oct-CPA). The release of these compounds and the related pro-drug stability effects in human whole blood have been tested. Moreover, the influence of the delivery systems on CPA interaction toward human adenosine A1 receptor has been analysed. The nanospheres were prepared by nanoprecipitation or double emulsion solvent evaporation method using poly(lactic acid) and recovered by gel filtration or ultracentrifugation or dialysis. Free and encapsulated Oct-CPA was incubated in fresh blood and its stability was analysed with HPLC. Quite spherical nanoparticles with mean diameters ranging between 210+/-50 and 390+/-90 nm were obtained. No encapsulation occurred when CPA was used. Satisfactory results concerning drug content (0.1-1.1% w/w) and encapsulation efficiency (6-56%) were achieved when Oct-CPA was employed. The controlled release of the pro-drug was achieved, being released within a range of 1-4 h, or very slowly, depending on nanoparticle preparations. The hydrolysis rate of Oct-CPA in human whole blood appeared stabilized in human whole blood with modalities related to the release patterns. The presence of all nanoparticle preparations did not interfere with CPA interaction at its action site.

Poly(lactic acid) microspheres for the sustained release of antiischemic agents

We report a preliminary study evaluating the encapsulation modalities in microparticles of the antiischemic drug N(6)-cyclopentyladenosine (CPA). The effects of release systems have been evaluated on the stability in human whole blood of CPA and its affinity toward human adenosine A(1) receptors. The microspheres were prepared by an emulsion-solvent evaporation method (different CPA amounts and two stirring rates were employed) using poly(lactic acid). Free and encapsulated CPA was incubated in human blood and the drug stability was analyzed. The affinity of CPA to human A(1) receptor was also obtained in the presence and in the absence of unloaded microspheres. The microspheres obtained using 1200 rpm showed a broad size distribution and a mean diameter value of 21+/-9 microm. Using 1700 rpm the mean diameter decreased to 5+/-2 microm and a more homogeneous size distribution was obtained. The CPA release changed with the particle size and the different amounts of drug employed during the preparation of the microspheres. The degradation in human whole blood of CPA encapsulated in the microspheres was negligible, with respect to that of free CPA. Affinity values of CPA obtained in the absence and in the presence of unloaded microspheres were the same.