Maria Manuela Gaspar

Formulation of L-asparaginase-loaded poly(lactide-co-glycolide) nanoparticles : influence of polymer properties on enzyme loading, activity and in vitro release

This paper describes the preparation and characterisation of poly(lactide-co-glycolide) (PLG) nanoparticles containing the enzyme L-asparaginase. L-Asparaginase was encapsulated in PLG nanospheres using a water-in-oil-in-water solvent evaporation technique. The effect of the copolymer molecular weight and the presence of carboxyl-end groups in the copolymer chain on the physicochemical and in vitro release properties of the nanoparticles was investigated. Results indicated that size, encapsulation efficiency and in vitro release properties (enzymatic activity retention and protein quantification) of the nanoparticles were affected by the PLG molecular weight. As expected, nanoparticles made of high-molecular-weight PLG had a larger size, a higher loading and la slower release rate than those made od a low-molecular-weight PLG. Nevertheless, the most relevant factor affecting the entrapment and release of L-asparaginase from PLG nanoparticles was the presence of free carboxyl-end groups in the PLG chain. The nanoparticles made of PLG with free carboxyl-end groups had a high protein loading (4.86%, w/w) and provided a continuous delivery of the active enzyme for 20 days. However, the enzyme loading was lower (2.65%, w/v) and no active enzyme was detected in the release medium after a 14-day incubation period when nanoparticles were made of PLG with carboxyl-end groups esterified. These results give evidence of the potential of PLG nanospheres for the continuous delivery of L-asparaginase for extended periods of time and show the effect of the PLG chain end-groups in the amount and activity of the enzyme loaded into the nanospheres.

Biological characterization of L-asparaginase liposomal formulations.

Abstract The biological properties of preselected liposomal formulations of L-asparaginase (L-ASNase) were studied. Pharmacokinetics studies showed that encapsulation in large liposomes (sDRV; median diameter 1,249 nm) decreased the circulation time of the enzyme, whereas encapsulation in small liposomes (VET: median diameter 158–180 nm) prolonged it by a factor of up to 10. Liposome encapsulation in either VET or sDRV prevents the induction of anti-asparaginase antibodies and mitigates the anaphylatic reaction, as no death occurred in animals presensitized and challenged with liposomal formulation, in contrast to animals treated with the free enzyme. The antitumor activity was also enhanced by liposome encapsulation. The survival of animals bearing P1534 tumors was prolonged by a factor of 2 after treatment with selected liposomal formulations as compared with free enzyme.

Developments on drug delivery systems for the treatment of mycobacterial infections.

The clinical management of tuberculosis and other mycobacterial diseases with antimycobacterial chemotherapy remains a difficult task. The classical treatment protocols are long-lasting; the drugs reach mycobacteria-infected macrophages in low amounts and/or do not persist long enough to develop the desired antimycobacterial effect; and the available agents induce severe toxic effects. Nanotechnology has provided a huge improvement to pharmacology through the designing of drug delivery systems able to target phagocytic cells infected by intracellular pathogens, such as mycobacteria. Liposomes and nanoparticles of polymeric nature represent two of the most efficient drug carrier systems that after in vivo administration are endocytosed by phagocytic cells and then release the carried agents into these cells. This article reviews the relevant publications describing the effectiveness of the association of antimycobacterial agents with liposomes or nanoparticles for the treatment of mycobacterioses, particularly for Mycobacterium tuberculosis and M. avium infections. The increased therapeutic index of antimycobacterial drugs; the reduction of dosing frequency; and the improvement of solubility of hydrophobic agents, allowing the administration of higher doses, have been demonstrated in experimental infections. These advantages may lead to new therapeutic protocols that will improve patient compliance and, consequently, lead to a more successful control of mycobacterial infections. The potential therapeutic advantages resulting from the use of non-invasive administration routes for nanoparticulate systems are also discussed.

Design and characterization of enzymosomes with surface-exposed superoxide dismutase

Superoxide dismutase (SOD) was chemically modified by covalent linkage of fatty acid chains to the accessible epsilon-amino groups of the enzyme. This acylation method gave rise to a different enzyme entity (Ac-SOD) as evidenced by different physicochemical properties such as octanol/water partition coefficient and isoelectric point (pI) as compared to SOD. Ac-SOD was incorporated in conventional and long-circulating liposomes (LCL) and characterized in terms of incorporation efficiency, protein to lipid ratio (Prot/Lip), enzymatic activity retention and zeta potential. The observation that Ac-SOD liposomes present enzymatic activity on their external surface indicates that these formulations can act independent of rate and extent of enzyme release as required in case of SOD liposomes. The decrease of superficial charge of liposomal formulations containing Ac-SOD, as compared to SOD liposomes, may be related to the negatively charged enzyme molecules localized on the liposome surface. The comparative characterization of Ac-SOD and SOD liposomal formulations evidenced that the two enzyme forms differ substantially regarding their intraliposomal location: SOD tends to be localized in the internal aqueous spaces, whereas Ac-SOD is expected to be localized in the lipid bilayers of the liposomes, partially buried into the outer surface and exposed to the external medium. These liposomal structures with surface-exposed SOD were designated as Ac-SOD enzymosomes. The properties of these enzymosomes may influence the therapeutic effect, as the release of the enzyme from extravasated vesicles is no longer a necessary requirement for achieving dismutating activity within the inflamed target site.

Generation of liposome aerosols with the Aeroneb Pro and the AeroProbe nebulizers

Background: Inhalation of therapeutic aerosols is a long-established means of drug delivery to the lungs or to the systemic circulation. In addition to solutions, suspensions, and particulates, liposomal formulations are being developed for aerosol administration. In this report, we investigated the membrane integrity of liposomes encapsulating the fluorescent model compound, calcein, after nebulization using two novel aerosolization devices, the Aeroneb Pro vibrating-mesh nebulizer (Aerogen, Dangan, Ireland) and the AeroProbe intracorporeal nebulizing catheter (Trudell Medical Corporation, London, Ontario, Canada). Materials and Methods: The influence of lipid composition and lamellarity on the stability of the vesicles was investigated by measuring changes in median diameter, ζ-potential, and calcein retention. Results: Both nebulizers were able to successfully aerosolise 1.5 mL of liposome suspension in a short period of time. The diameter and ζ-potential of the liposomes was preserved upon nebulization, and the calcein retention was above 70% in all cases. Conclusions: It can, hence, be concluded that both systems, the Aeroneb Pro and the AeroProbe, are well suited for the pulmonary delivery of liposomal formulations, with the AeroProbe having the additional advantage of allowing targeted delivery into the select regions of the lungs with a high degree of efficiency and control.

Therapeutic Efficacy of Liposomal Rifabutin in a Mycobacterium avium Model of Infection

ABSTRACT Liposomal formulations of rifabutin were developed, and the effects of some parameters on the incorporation efficiency were studied. The antimycobacterial activity of rifabutin incorporated into liposomes prepared with phosphatidylcholine and phosphatidylserine (molar ratio, 7:3) was evaluated in a murine model of infection with a virulentMycobacterium avium strain (strain P1581) and was compared with that of free rifabutin. The influences of the size of the liposomal rifabutin formulation, the administered doses, and the treatment schedules on the evolution of infection were studied. Two types of treatment schedules were assayed: therapeutic and prophylactic. The therapeutic treatment started 2 weeks after infection, while the prophylactic treatment began 1 day before the experimental infection with mycobacteria. Incorporation of rifabutin in liposomes resulted in a significant enhancement of activity againstM. avium infection compared to that of rifabutin in the free form in both schedules. These results demonstrate that liposomal formulations of antibiotics such as rifabutin may be effective for the treatment or prophylaxis of infectious diseases.

Targeted Delivery of Transferrin-Conjugated Liposomes to an Orthotopic Model of Lung Cancer in Nude Rats

BACKGROUND Lung cancer is the leading cause of cancer death worldwide. Pulmonary anticancer therapy might offer several advantages over systemic delivery, leading to an increased exposure of the lung tumor to the drug, while minimizing side effects, due to regional containment. Here, we studied if a combination of inhalation therapy and drug targeting holds potential as an even more efficient lung cancer therapy. METHODS Transferrin (Tf )-conjugated PEG liposomes loaded with doxorubicin (DOX) were administered using an intracorporeal nebulizing catheter to an orthotopic lung cancer model established in athymic Rowett nude rats. Different DOX formulations and doses (0.2 and 0.4 mg/kg) were tested and the influence on tumor progression and life span of rats was evaluated in comparison with the i.v. administration of Tf-PEG-liposomes loaded with DOX at a therapeutic dose of 2 mg/kg. RESULTS Rats in the untreated control group showed significant weight loss 2 weeks after tumor induction and died between days 19 and 29. Lungs of these animals showed multiple foci of neoplastic deposits, ranging up to 20 mm replacing the entire lobe. Empty Tf-liposomes showed a significant effect on survival time. This might be caused by the secondary cytotoxicity via stimulation of pulmonary macrophages. All animal treated intravenously also perished before the end of the study. No significant (p<0.05) improvement in survival was observed between the groups treated with aerosols of free drug, DOX encapsulated in plain and in Tf-modified liposomes. However, more animals survived in the Tf-liposome groups than in the other treatment regimes, and their lung tissue generally had fewer and smaller tumors. Nevertheless, the size of the groups, and the duration of the trial render it impossible to come to a definite conclusion. CONCLUSIONS Drug targeting demonstrated potential for improving the aerosol treatment of lung cancer.

Liposomal l-asparaginase: in vitro evaluation

Abstract The purpose of this work was the development of liposomal formulations of l -asparaginase ( l -ASNase) with the following characteristics: preservation of active enzyme, high entrapment efficiency, prolonged serum half-life and reduced toxicity compared with the free enzyme. Several liposome formulations were developed using simplified dehydration-rehydration vesicles (sDRV) or extruded vesicles (VET). The effect of lipid composition, vesicle size, ionic strength and osmolarity on enzyme encapsulation was investigated. Using a simplified dehydration-rehydration method (sDRV) we were able to achieve encapsulation efficiencies of up to 100% with full preservation (99%) of the specific activity of the encapsulated enzyme. The protein to lipid ratios of the liposomal formulations ranged from 5 to 27 μg/μmol, depending on the lipid composition. Extruded vesicles ranging from 85 to 250 nm in diameter were also tested. The encapsulation efficiency of extruded vesicles was lower than that of large vesicles and the range of preservation of specific activity was dependent on the lipid composition. Lipid combinations of phosphatidylcholine and cholesterol and either stearylamine, phosphatidylinositol or monosialoganglioside resulted in a high encapsulation efficiency (40 and 98% in VET and sDRV, respectively), high stability in saline and human serum (65–90% after 48 h) and considerable preservation of enzymatic activity (74–98%). The liposomal formulations were significantly less toxic than the free enzyme against normal CHO cells. In vivo toxicity, pharmacokinetics, biodistribution and antitumour activity studies are planned with the best formulations described in this paper.

What Makes Umbilical Cord Tissue-Derived Mesenchymal Stromal Cells Superior Immunomodulators When Compared to Bone Marrow Derived Mesenchymal Stromal Cells?

MSCs derived from the umbilical cord tissue, termed UCX, were investigated for their immunomodulatory properties and compared to bone marrow-derived MSCs (BM-MSCs), the gold-standard in immunotherapy. Immunogenicity and immunosuppression were assessed by mixed lymphocyte reactions, suppression of lymphocyte proliferation and induction of regulatory T cells. Results showed that UCX were less immunogenic and showed higher immunosuppression activity than BM-MSCs. Further, UCX did not need prior activation or priming to exert their immunomodulatory effects. This was further corroborated in vivo in a model of acute inflammation. To elucidate the potency differences observed between UCX and BM-MSCs, gene expression related to immune modulation was analysed in both cell types. Several gene expression profile differences were found between UCX and BM-MSCs, namely decreased expression of HLA-DRA, HO-1, IGFBP1, 4 and 6, ILR1, IL6R and PTGES and increased expression of CD200, CD273, CD274, IL1B, IL-8, LIF and TGFB2. The latter were confirmed at the protein expression level. Overall, these results show that UCX seem to be naturally more potent immunosuppressors and less immunogenic than BM-MSCs. We propose that these differences may be due to increased levels of immunomodulatory surface proteins such as CD200, CD273, CD274 and cytokines such as IL1β, IL-8, LIF and TGFβ2.

Activation of necroptosis in human and experimental cholestasis

Cholestasis encompasses liver injury and inflammation. Necroptosis, a necrotic cell death pathway regulated by receptor-interacting protein (RIP) 3, may mediate cell death and inflammation in the liver. We aimed to investigate the role of necroptosis in mediating deleterious processes associated with cholestatic liver disease. Hallmarks of necroptosis were evaluated in liver biopsies of primary biliary cholangitis (PBC) patients and in wild-type and RIP3-deficient (RIP3−/−) mice subjected to common bile duct ligation (BDL). The functional link between RIP3, heme oxygenase-1 (HO-1) and antioxidant response was investigated in vivo after BDL and in vitro. We demonstrate increased RIP3 expression and mixed lineage kinase domain-like protein (MLKL) phosphorylation in liver samples of human PBC patients, coincident with thioflavin T labeling, suggesting activation of necroptosis. BDL resulted in evident hallmarks of necroptosis, concomitant with progressive bile duct hyperplasia, multifocal necrosis, fibrosis and inflammation. MLKL phosphorylation was increased and insoluble aggregates of RIP3, MLKL and RIP1 formed in BLD liver tissue samples. Furthermore, RIP3 deficiency blocked BDL-induced necroinflammation at 3 and 14 days post-BDL. Serum hepatic enzymes, fibrogenic liver gene expression and oxidative stress decreased in RIP3−/− mice at 3 days after BDL. However, at 14 days, cholestasis aggravated and fibrosis was not halted. RIP3 deficiency further associated with increased hepatic expression of HO-1 and accumulation of iron in BDL mice. The functional link between HO-1 activity and bile acid toxicity was established in RIP3-deficient primary hepatocytes. Necroptosis is triggered in PBC patients and mediates hepatic necroinflammation in BDL-induced acute cholestasis. Targeting necroptosis may represent a therapeutic strategy for acute cholestasis, although complementary approaches may be required to control progression of chronic cholestatic liver disease.