Browsing by Author "Reis, Salette"
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- Assessment of immunoglobulin capture in immobilized protein A through automatic bead injectionPublication . Ramos, Inês I.; Marques, Sara S.; Magalhães, Luís M.; Barreiros, Luisa; Reis, Salette; Lima, José L.F. C.; Segundo, Marcela A.The repeatable immobilization of molecular recognition elements onto particle surfaces has a strong impact on the outcomes of affinity-based assays. In this work, an automatic method for the immobilization of immunoglobulin G (IgG) onto protein A-Sepharose microbeads was established through the flow programming features of the portable lab-on-valve platform using micro-bead injection spectroscopy. The reproducible packing of protein A-microbeads between two optic fibers was feasible, allowing on-column probing of IgG retention. The automation of solutions handling and the precise control of time of IgG interaction with the beads rendered repeatable immobilization cycles, within a short timeframe (<2 min). The proposed method featured the preparation of disposable immunosorbents for downstream analytical applications, such as immunosensing or microenrichment of target analytes. In-situ quantification of IgG@protein A-microbeads was carried out using a horseradish peroxidase-labeled detection IgG. The colorimetric oxidation of 3,3',5,5'-tetramethylbenzidine was monitored on-column. Quantitation of mouse and human IgG immobilized@protein A-microbeads was achieved for loading masses between 0.1 and 0.4 μg per ca. 5.5 mg of sorbent. The implemented detection strategy allowed the quantification of human IgG in certified human serum (ERM®- DA470k/IFCC) and spiked saliva, yielding recoveries of 102-108% and requiring minimal volume (1-15 μL) from serum and saliva.
- Chromatographic method for the simultaneous quantification of dapsone and clofazimine in nanoformulationsPublication . Machado, Sandia; Fernandes, Sara; Chaves, Luise L.; Lima, Sofia A. C.; Silva, Eduarda M. P.; Barreiros, Luisa; Reis, Salette; Segundo, Marcela A.The low bioavailability and nonspecific distribution of dapsone and clofazimine, commonly applied in combination for the treatment of leprosy, can produce toxic effects. Nanotechnological approaches enhance the delivery of these drugs. Therefore, a high-performance liquid chromatography method was developed for the simultaneous determination of dapsone and clofazimine loaded in nanoformulations for quality control purposes. Chromatographic separation was achieved on a reversed-phase Kinetex core-shell C18 column, followed by spectrophotometric detection at 280 nm. Considering the different physicochemical properties of dapsone and clofazimine, elution was performed in gradient mode using an aqueous acetate buffer (50 mmol/L, pH 4.8) and an increasing acetonitrile content from 27 to 63% v/v at a flow rate of 1.0 mL/min with retention times of 6.2 and 14.0 min, respectively. The method was validated according to the European Medicines Agency guideline and it was found to be specific, accurate (99.6-114.0%), and precise for intra- (RSD ≤ 1.8%) and interday assays (RSD ≤ 12.5%). Both drugs showed stability after 24 h at room temperature and over three freeze-thaw cycles with recoveries ≥86.2%. Low temperature (4°C) in the autosampler caused the precipitation of clofazimine and must be avoided. The validated method was successfully applied in the quantification of both drugs in nanoformulations.
- Effects of novel triple-stage antimalarial ionic liquids on lipid membrane modelsPublication . Ferraz, Ricardo; Pinheiro, Marina; Gomes, Ana; Teixeira, Cátia; Prudêncio, Cristina; Reis, Salette; Gomes, PaulaPrimaquine-based ionic liquids, obtained by acid-base reaction between parent primaquine and cinnamic acids, were recently found as triple-stage antimalarial hits. These ionic compounds displayed significant activity against both liver- and blood-stage Plasmodium parasites, as well as against stage V P. falciparum parasites. Remarkably, blood-stage activity of the ionic liquids against both chloroquine-sensitive (3D7) and resistant (Dd2) P. falciparum strains was clearly superior to those of the respective covalent (amide) analogues and of parent primaquine. Having hypothesized that such behaviour might be ascribed to an enhanced ability of the ionic compounds to permeate into Plasmodium-infected erythrocytes, we have carried out a differential scanning calorimetry-based study of the interactions between the ionic liquids and membrane models. Results provide evidence, at the molecular level, that the primaquine-derived ionic liquids may contribute to an increased permeation of the parent drug into malaria-infected erythrocytes, which has relevant implications towards novel antimalarial approaches based on ionic liquids.
- Fast monolith-based chromatographic method for determination of methotrexate in drug delivery studiesPublication . Barbosa, Ana Isabel; Fernandes, Sara; Machado, Sandia; Sousa, Patrícia; Sze, Ong Yong; Silva, Eduarda M.P.; Barreiros, Luisa; Lima, Sofia A.C.; Reis, Salette; Segundo, Marcela A.Methotrexate (MTX) is a derivative of aminopterin, used as an anticancer or an anti-inflammatory agent. The development of suitable drug delivery systems containing MTX is an active area of research, requiring suitable analytical methods. Therefore, a high-throughput HPLC method is proposed for determination of MTX in the delivery system and permeation studies. Chromatographic separation was achieved on a reversed phase monolithic C18 column using isocratic elution (phosphate buffer (pH 7.0, 10 mM)-ACN (91:9, v/v)) and spectrophotometric detection at 302 nm. Total run time was 3.5 min, with MTX retention time of 2.1 min, providing 17 determinations per hour. The method was found to be specific, accurate (99.2–110%) and precise for intra-day (RSD ≤ 3.5%) and inter-day assays (RSD ≤ 3.4%). MTX showed stability after 24 h at room temperature or in the autosampler (4 °C) and over three freeze-thaw cycles with recoveries ≥94.2%. The validated method was successfully applied to establish in vitro drug release profile of MTX delivered by lipid nanoparticles. Application to pig skin permeation media provided mean recovery values ranging from 94.1 to 101.6% (RSD ≤ 1.1%).
- Insights on Ultrafiltration-Based Separation for the Purification and Quantification of Methotrexate in NanocarriersPublication . Marques, Sara S.; Ramos, Inês I.; Fernandes, Sara; Barreiros, Luisa; Lima, Sofia A. C.; Reis, Salette; Domingues, M. Rosário M.; Segundo, Marcela A.The evaluation of encapsulation efficiency is a regulatory requirement for the characterization of drug delivery systems. However, the difficulties in efficiently separating nanomedicines from the free drug may compromise the achievement of accurate determinations. Herein, ultrafiltration was exploited as a separative strategy towards the evaluation of methotrexate (MTX) encapsulation efficiency in nanostructured lipid carriers and polymeric nanoparticles. The effect of experimental conditions such as pH and the amount of surfactant present in the ultrafiltration media was addressed aiming at the selection of suitable conditions for the effective purification of nanocarriers. MTX-loaded nanoparticles were then submitted to ultrafiltration and the portions remaining in the upper compartment of the filtering device and in the ultrafiltrate were collected and analyzed by HPLC-UV using a reversed-phase (C18) monolithic column. A short centrifugation time (5 min) was suitable for establishing the amount of encapsulated MTX in nanostructured lipid carriers, based on the assumption that the free MTX concentration was the same in the upper compartment and in the ultrafiltrate. The defined conditions allowed the efficient separation of nanocarriers from the free drug, with recoveries of >85% even when nanoparticles were present in cell culture media and in pig skin surrogate from permeation assays.
- Micro-bead injection spectroscopy for label-free automated determination of immunoglobulin G in human serumPublication . Ramos, Inês I.; Magalhães, Luís M.; Barreiros, Luisa; Reis, Salette; Lima, José L. F. C.; Segundo, Marcela A.Immunoglobulin G (IgG) represents the major fraction of antibodies in healthy adult human serum, and deviations from physiological levels are a generic marker of disease corresponding to different pathologies. Therefore, screening methods for IgG evaluation are a valuable aid to diagnostics. The present work proposes a rapid, automatic, and miniaturized method based on UV-vis micro-bead injection spectroscopy (μ-BIS) for the real-time determination of human serum IgG with label-free detection. Relying on attachment of IgG in rec-protein G immobilized in Sepharose 4B, a bioaffinity column is automatically assembled, where IgG is selectively retained and determined by on-column optical density measurement. A "dilution-and-shoot" approach (50 to 200 times) was implemented without further sample treatment because interferences were flushed out of the column upon sample loading, with minimization of carryover and cross-contamination by automatically discarding the sorbent (0.2 mg) after each determination. No interference from human serum albumin at 60 mg mL-1 in undiluted sample was found. The method allowed IgG determination in the range 100-300 μg mL-1 (corresponding to 5.0-60 mg mL-1 in undiluted samples), with a detection limit of 33 μg mL-1 (1.7 mg mL-1 for samples, dilution factor of 50). RSD values were < 9.4 and < 11.7%, for intra and inter-assay precision, respectively, while recovery values for human serum spiked with IgG at high pathological levels were 97.8-101.4%. Comparison to commercial ELISA kit showed no significant difference for tested samples (n = 8). Moreover, time-to-result decreased from several hours to < 5 min and analysis cost decreased 10 times, showing the potential of the proposed approach as a point-of-care method. Graphical abstract Micro-Bead Injection Spectroscopy method for real time, automated and label-free determination of total serum human Immunoglobulin G (IgG). The method was designed for Lab-on-Valve (LOV) platforms using a miniaturised protein G bioaffinity separative approach. IgG are separated from serum matrix components upon quantification with low non-specific binding in less than 5 min.
- Serine-based surfactants as effective antimicrobial agents against multiresistant bacteriaPublication . Silva, Sandra G.; Pinheiro, Marina; Pereira, Rui; Dias, Ana Rita; Ferraz, Ricardo; Prudêncio, Cristina; Eaton, Peter J.; Reis, Salette; Vale, M. Luísa C. doThe antimicrobial activity of two serine derived gemini cationic surfactants, amide (12Ser)2CON12 and ester (12Ser)2COO12, was tested using sensitive, E. coli ATCC 25922 and S. aureus ATCC 6538, and resistant, E. coli CTX M2, E. coli TEM CTX M9 and S. aureus ATCC 6538 and S. aureus MRSA ATCC 43300 Gram-positive and Gram-negative bacteria strains. Very low MIC values (5 μM) were found for the two resistant strains E.coli TEM CTX M9 and S. aureus MRSA ATCC 43300, in the case of the amide derivative, and for S. aureus MRSA ATCC 43300, in the case of the ester derivative. The interaction of the serine amphiphiles with lipid-model membranes (DPPG and DPPC) was investigated using Langmuir monolayers. A more pronounced effect on the DPPG than on the DPPC monolayer was observed. The effect induced by the surfactants on bacteria membrane was explored by Atomic Force Microscopy. A clear disruption of the bacteria membrane was observed for E. coli TEM CTX M9 upon treatment with (12ser)2CON12, whereas for the S. aureus MRSA few observable changes in cell morphology were found after treatment with either of the two surfactants. The cytotoxicity of the two compounds was assessed by hemolysis assay on human red blood cells (RBC). The compounds were shown to be non-cytotoxic up to 10 μM. Overall, the results reveal a promising potential, in particular of the amide derivative, as antimicrobial agent for two strains of antibiotic resistant bacteria.
- Simultaneous determination of dapsone and clofazimine in nanoformulations by HPLCPublication . Fernandes, Sara R.; Fernandes, Sara; Chaves, Luíse L.; Lima, Sofia A. C.; Silva, Eduarda M. P.; Barreiros, Luísa; Reis, Salette; Segundo, Marcela A.The multidrug therapy with dapsone (DAP) and clofazimine (CLZ) is known as an effective treatment against Mycobacterium leprae. However, the low bioavailability and non-specific distribution can reduce therapy efficacy and produce side effects. The use of nanotechnological approaches was explored as a promising carrier for delivery enhancement of these drugs. Therefore, a simple and precise highperformance liquid chromatography (HPLC) method with UV/Vis detection has been developed and validated for the simultaneous determination of DAP and CLZ loaded in solid dispersion and poly(D,L-lactide-co-glycolic acid) nanoparticles, respectively, targeting therapy improvement. A reversed phase Kinetex core-shell C18 column at room temperature followed by UV/Vis detection at 280 nm was used for chromatographic separation. The elution was performed in gradient mode using aqueous acetate buffer (50 mol L-1, pH 4.8) and an increasing acetonitrile content from 27 to 63% (v/v), at a flow rate of 1.0 mL min-1. The injection volume was fixed at 20 µL and total run time was 23.0 min, with a retention time of 6.0 min for DAP and 14.0 min for CLZ. The method was validated according to EMA guideline and showed specificity, accuracy (between 99.6 and 114.0% of nominal values) and precision for intra-day (RSD ≤1.8%) and inter-day assays (RSD ≤12.5%). Calibration curves were linear (r2 >0.9979) and LOD ≤0.03 and LOQ ≤0.06 mg L-1 were obtained. Stability was studied after 24 h at room temperature and over three freeze-thaw cycles, and recovery values ≥86.2% were obtained. Precipitation of CLZ was observed at low temperatures (4 °C). Entrapment efficiency in nanoformulations was evaluated as 54.8 ± 0.1% for DAP and 24.9 ± 0.2% for CLZ. The developed method was successfully validated for the simultaneous determination of DAP and CLZ in nanoparticles.