Gentamicin-loaded microspheres for reducing the intracellular Brucella abortus load in infected monocytes

Objectives: The intracellular antibiotic efficiency of gentamicin-loaded microspheres in the context of Brucella-infected murine monocytes was examined in vitro with a view to developing improved therapies for the treatment of brucellosis. Methods: Biodegradable microspheres made of end-group capped and uncapped poly(lactide-co-glycolide) 50:50 (PLGA 50:50 and PLGA 50:50H) and containing gentamicin sulphate were used to target Brucella abortus-infected J774 monocyte-macrophages. The infected cells were treated with 15 µg of free or microencapsulated gentamicin and the efficacy of the treatments was measured after 24 h. Results: The particle sizes were below 8 µm and in vitro release of gentamicin from the microspheres followed a continuous (PLGA 50:50H) or a multiphasic (PLGA 50:50) pattern over 50 days. Treatment with gentamicin microencapsulated into the end-group uncapped PLGA 50:50H microspheres, decreased significantly the number of intracellular bacteria (typically by 2 log10) in comparison with untreated infected cells. Addition of 2% poloxamer 188 to the microsphere dispersion medium further reduced the infection (3.5 log10). Opsonization of the particles with non-immune mouse serum had no effect on the antibacterial efficacy of the microspheres. End-group capped PLGA 50:50 type microspheres containing the antibiotic were less effective at reducing intracellular bacteria (∼1 log10 reduction), although addition of poloxamer 188 to the dispersion medium again enhanced their intracellular antibacterial activity. Placebo PLGA 50:50 and PLGA 50:50H microspheres had no bactericidal activity. Conclusions: The results indicate that PLGA 50:50-microencapsulated gentamicin sulphate may be suitable for efficient drug targeting and delivery to reduce intracellular Brucella infections

Importance of single or blended polymer types for controlled in vitro release and plasma levels of a somatostatin analogue entrapped in PLA/PLGA microspheres.

The aim of the work was to develop biodegradable microspheres for controlled delivery of the somatostatin analogue vapreotide and maintenance of sustained plasma levels over 2–4 weeks after a single injection in rats. Vapreotide was microencapsulated into end-group capped and uncapped low molecular weight poly(lactide) (PLA) and poly(lactide-co-glycolide) (PLGA) by spray-drying and coacervation. Microspheres were prepared from single and blended (1:1) polymer types. The microparticles were characterized for peptide loading, in vitro release and pharmocokinetics in rats. Spray-drying and coacervation produced microspheres in the size range of 1–15 and 10–70 μm, respectively, and with encapsulation efficiencies varying between 46% and 87%. In vitro release of vapreotide followed a regular pattern and lasted more than 4 weeks, time at which 40–80% of the total dose were released. Microspheres made of 14-kDa end-group uncapped PLGA50:50 or 1:1 blends of this polymer with 35 kDa end-group uncapped PLGA50:50 gave the best release profiles and yielded the most sustained plasma levels above a pre-defined 1 ng/ml over approximately 14 days. In vitro/in vivo correlation analyses showed for several microsphere formulations a linear correlation between the mean residence time in vivo and the mean dissolution time (r=0.958) and also between the amount released between 6 h and 14 days and the AUC6h–14d (r=0.932). For several other parameters or time periods, no in vitro/in vivo correlation was found. This study demonstrates that controlled release of the vapreotide is possible in vivo for a duration of a least 2 weeks when administered i.m. to rats. These results constitute a step forward towards a twice-a-month or once-a-month microsphere-formulation for the treatment of acromegaly and neuroendocrine tumors

In vitro and in vivo evaluation of a somatostatin analogue released from PLGA microspheres

The purpose of this study was to design poly(lactide-co-glycolide) (PLGA) microspheres for the continuous delivery of the somatostatin analogue, vapreotide, over 2–4 weeks. The microspheres were produced by spray-drying and the desired characteristics, i.e. high encapsulation efficiency and controlled release over 2–4 weeks, achieved through optimizing the type of polymer, processing solvent, and co-encapsulated additive. The in vitro release was tested in fetal bovine serum preserved with 0.02% of thiomersal. Furthermore, formulations were injected intramuscularly into rats to obtain pharmacokinetic profiles. Encapsulation efficiency was between 34 and 91%, depending on the particular formulation. The initial peptide release (within 6 h) was lowest, i.e. 1 ng/ml) over 21–28 days in rats was the one made with end-group uncapped PLGA 50:50, the solvent acetic acid and the additive polyethyleneglycol. In conclusion, the optimization of formulation parameters allowed us to produce vapreotide-loaded PLGA microspheres of suitable characteristics for therapeutic use

Ultrasonic atomization and subsequent polymer desolvation for peptide and protein microencapsulation into biodegradable polyesters.

The determination of in vitro release kinetics of peptides from poly(d,l-lactide-co-glycolide) (PLGA) microspheres generally requires optimization of the test conditions for a given formulation. This is particularly important when in vitro/in vivo correlation should be determined. Here, the somatostatin analogue vapreotide pamoate, an octapeptide, was microencapsulated into PLGA 50:50 by spray-drying. The solubility of this peptide and its in vitro release kinetics from the microspheres were studied in various test media. The solubility of vapreotide pamoate was approximately 20–40 μg/ml in 67 mM phosphate buffer saline (PBS) at pH 7.4, but increased to approximately 500–1000 μg/ml at a pH of 3.5. At low pH, the solubility increased with the buffer concentration (1–66 mM). Very importantly, proteins (aqueous bovine serum albumin (BSA) solution or human serum) appeared to solubilize the peptide pamoate, resulting in solubilities ranging from 900 to 6100 μg/ml. The release rate was also greatly affected by the medium composition. Typically, in PBS of pH 7.4, only 33±1% of the peptide were released within 4 days, whereas 53±2 and 61±0.9% were released in 1% BSA solution and serum, respectively. The type of medium was found critical for the estimation of the in vivo release. The in vivo release kinetics of vapreotide pamoate from PLGA microspheres following administration to rats were qualitatively in good agreement with those obtained in vitro using serum as release medium. Finally, sterilization by γ-irradiation had only a minor effect on the in vivo pharmacokinetics

Ultrasonic atomization and subsequent polymer desolvation for peptide and protein microencapsulation into biodegradable polyesters.

The determination of in vitro release kinetics of peptides from poly(d,l-lactide-co-glycolide) (PLGA) microspheres generally requires optimization of the test conditions for a given formulation. This is particularly important when in vitro/in vivo correlation should be determined. Here, the somatostatin analogue vapreotide pamoate, an octapeptide, was microencapsulated into PLGA 50:50 by spray-drying. The solubility of this peptide and its in vitro release kinetics from the microspheres were studied in various test media. The solubility of vapreotide pamoate was approximately 20–40 μg/ml in 67 mM phosphate buffer saline (PBS) at pH 7.4, but increased to approximately 500–1000 μg/ml at a pH of 3.5. At low pH, the solubility increased with the buffer concentration (1–66 mM). Very importantly, proteins (aqueous bovine serum albumin (BSA) solution or human serum) appeared to solubilize the peptide pamoate, resulting in solubilities ranging from 900 to 6100 μg/ml. The release rate was also greatly affected by the medium composition. Typically, in PBS of pH 7.4, only 33±1% of the peptide were released within 4 days, whereas 53±2 and 61±0.9% were released in 1% BSA solution and serum, respectively. The type of medium was found critical for the estimation of the in vivo release. The in vivo release kinetics of vapreotide pamoate from PLGA microspheres following administration to rats were qualitatively in good agreement with those obtained in vitro using serum as release medium. Finally, sterilization by γ-irradiation had only a minor effect on the in vivo pharmacokinetics

Gentamicin-loaded microspheres for reducing the intracellular Brucella abortus load in infected monocytes

Objectives: The intracellular antibiotic efficiency of gentamicin-loaded microspheres in the context of Brucella-infected murine monocytes was examined in vitro with a view to developing improved therapies for the treatment of brucellosis. Methods: Biodegradable microspheres made of end-group capped and uncapped poly(lactide-co-glycolide) 50:50 (PLGA 50:50 and PLGA 50:50H) and containing gentamicin sulphate were used to target Brucella abortus-infected J774 monocyte-macrophages. The infected cells were treated with 15 µg of free or microencapsulated gentamicin and the efficacy of the treatments was measured after 24 h. Results: The particle sizes were below 8 µm and in vitro release of gentamicin from the microspheres followed a continuous (PLGA 50:50H) or a multiphasic (PLGA 50:50) pattern over 50 days. Treatment with gentamicin microencapsulated into the end-group uncapped PLGA 50:50H microspheres, decreased significantly the number of intracellular bacteria (typically by 2 log10) in comparison with untreated infected cells. Addition of 2% poloxamer 188 to the microsphere dispersion medium further reduced the infection (3.5 log10). Opsonization of the particles with non-immune mouse serum had no effect on the antibacterial efficacy of the microspheres. End-group capped PLGA 50:50 type microspheres containing the antibiotic were less effective at reducing intracellular bacteria (∼1 log10 reduction), although addition of poloxamer 188 to the dispersion medium again enhanced their intracellular antibacterial activity. Placebo PLGA 50:50 and PLGA 50:50H microspheres had no bactericidal activity. Conclusions: The results indicate that PLGA 50:50-microencapsulated gentamicin sulphate may be suitable for efficient drug targeting and delivery to reduce intracellular Brucella infections

In vitro and in vivo evaluation of a somatostatin analogue released from PLGA microspheres

The purpose of this study was to design poly(lactide-co-glycolide) (PLGA) microspheres for the continuous delivery of the somatostatin analogue, vapreotide, over 2–4 weeks. The microspheres were produced by spray-drying and the desired characteristics, i.e. high encapsulation efficiency and controlled release over 2–4 weeks, achieved through optimizing the type of polymer, processing solvent, and co-encapsulated additive. The in vitro release was tested in fetal bovine serum preserved with 0.02% of thiomersal. Furthermore, formulations were injected intramuscularly into rats to obtain pharmacokinetic profiles. Encapsulation efficiency was between 34 and 91%, depending on the particular formulation. The initial peptide release (within 6 h) was lowest, i.e. 1 ng/ml) over 21–28 days in rats was the one made with end-group uncapped PLGA 50:50, the solvent acetic acid and the additive polyethyleneglycol. In conclusion, the optimization of formulation parameters allowed us to produce vapreotide-loaded PLGA microspheres of suitable characteristics for therapeutic use

Importance of the test medium for the release kinetics of a somatostatin analogue from poly(D,L-lactide-co-glycolide) microspheres

The determination of in vitro release kinetics of peptides from poly(d,l-lactide-co-glycolide) (PLGA) microspheres generally requires optimization of the test conditions for a given formulation. This is particularly important when in vitro/in vivo correlation should be determined. Here, the somatostatin analogue vapreotide pamoate, an octapeptide, was microencapsulated into PLGA 50:50 by spray-drying. The solubility of this peptide and its in vitro release kinetics from the microspheres were studied in various test media. The solubility of vapreotide pamoate was approximately 20–40 μg/ml in 67 mM phosphate buffer saline (PBS) at pH 7.4, but increased to approximately 500–1000 μg/ml at a pH of 3.5. At low pH, the solubility increased with the buffer concentration (1–66 mM). Very importantly, proteins (aqueous bovine serum albumin (BSA) solution or human serum) appeared to solubilize the peptide pamoate, resulting in solubilities ranging from 900 to 6100 μg/ml. The release rate was also greatly affected by the medium composition. Typically, in PBS of pH 7.4, only 33±1% of the peptide were released within 4 days, whereas 53±2 and 61±0.9% were released in 1% BSA solution and serum, respectively. The type of medium was found critical for the estimation of the in vivo release. The in vivo release kinetics of vapreotide pamoate from PLGA microspheres following administration to rats were qualitatively in good agreement with those obtained in vitro using serum as release medium. Finally, sterilization by γ-irradiation had only a minor effect on the in vivo pharmacokinetics

Importance of the test medium for the release kinetics of a somatostatin analogue from poly(D,L-lactide-co-glycolide) microspheres

The determination of in vitro release kinetics of peptides from poly(d,l-lactide-co-glycolide) (PLGA) microspheres generally requires optimization of the test conditions for a given formulation. This is particularly important when in vitro/in vivo correlation should be determined. Here, the somatostatin analogue vapreotide pamoate, an octapeptide, was microencapsulated into PLGA 50:50 by spray-drying. The solubility of this peptide and its in vitro release kinetics from the microspheres were studied in various test media. The solubility of vapreotide pamoate was approximately 20–40 μg/ml in 67 mM phosphate buffer saline (PBS) at pH 7.4, but increased to approximately 500–1000 μg/ml at a pH of 3.5. At low pH, the solubility increased with the buffer concentration (1–66 mM). Very importantly, proteins (aqueous bovine serum albumin (BSA) solution or human serum) appeared to solubilize the peptide pamoate, resulting in solubilities ranging from 900 to 6100 μg/ml. The release rate was also greatly affected by the medium composition. Typically, in PBS of pH 7.4, only 33±1% of the peptide were released within 4 days, whereas 53±2 and 61±0.9% were released in 1% BSA solution and serum, respectively. The type of medium was found critical for the estimation of the in vivo release. The in vivo release kinetics of vapreotide pamoate from PLGA microspheres following administration to rats were qualitatively in good agreement with those obtained in vitro using serum as release medium. Finally, sterilization by γ-irradiation had only a minor effect on the in vivo pharmacokinetics