Characterization of Complex Drug Formulations Using Cryogenic Scanning Electron Microscopy (Cryo-SEM).

The physicochemical properties of complex drug formulations, including liposomes, suspensions, and emulsions, are important for understanding drug release mechanisms, quality control, and regulatory assessment. It is ideal to characterize these complex drug formulations in their native hydrated state. This article describes the characterization of complex drug formulations in a frozen-hydrated state using cryogenic scanning electron microscopy (cryo-SEM). In comparison to other techniques, such as optical microscopy or room-temperature scanning electron microscopy, cryo-SEM combines the advantage of studying hydrated samples with high-resolution imaging capability. Detailed information regarding cryo-fixation, cryo-fracture, freeze-etching, sputter-coating, and cryo-SEM imaging is included in this article. A multivesicular liposomal complex drug formulation is used to illustrate the impact of different cryogenic sample preparation conditions. In addition to drug formulations, this approach can also be applied to biological samples (e.g., cells, bacteria) and soft-matter samples (e.g., hydrogels). © Published 2022. This article is a U.S. Government work and is in the public domain in the USA. Basic Protocol 1: Cryo-fixation to preserve the native structure of samples using planchettes Alternate Protocol: Cryo-fixation to preserve the native structure of biological samples on sapphire disks Basic Protocol 2: Sample preparation for cross-sectional cryo-SEM imaging Basic Protocol 3: Cryo-SEM imaging and microanalysis.

Pharmacokinetics and Toxicity Evaluation of a PLGA and Chitosan-Based Micro-Implant for Sustained Release of Methotrexate in Rabbit Vitreous.

The present research investigates the pharmacokinetics and toxicity of a chitosan (CS) and poly(lactic-co-glycolic) acid (PLGA)-based methotrexate (MTX) intravitreal micro-implant in normal rabbit eyes. PLGA and CS-based micro-implants containing 400 µg of MTX were surgically inserted in the vitreous of twenty-four New Zealand rabbits using minimally invasive procedures. The PLGA-coated CS-MTX micro-implant and the placebo micro-implant were inserted in the right eye and in the left eye, respectively, of each rabbit. The intravitreal MTX concentration was evaluated on Days 1, 3, 7, 14, 28 and 56. A therapeutic concentration of MTX (0.1-1.0 µM) in the rabbit vitreous was observed for 56 days. The release of MTX in the therapeutic release phase followed first-order kinetics. Histopathologic evaluation on Days 14, 28 and 56 of the enucleated eyes demonstrated no signs of toxicity or any anatomical irregularity in the vitreoretinal domain. Additionally, the micro-implants were stationary at the position of their implantation throughout the duration of the study. The PLGA-coated CS-MTX micro-implant can serve as a potential alternative to the current treatment modality of intravitreal MTX injections based on its performance, thereby avoiding associated complications and the treatment burden of multiple injections.

Non-invasive evaluation of toxicity in vitreoretinal domain following insertion of sustained release methotrexate micro-implant.

PURPOSE: To evaluate the safety and toxicity profile of a chitosan (CS) and poly(lactic-co-glycolic) acid (PLGA)-based sustained release methotrexate (MTX) intravitreal micro-implant in normal rabbit eyes using non-invasive testing that included electroretinography (ERG), ultrasound biomicroscopy (US), slit-lamp biomicroscopy (SLB), funduscopy, and intraocular pressure (IOP). METHODS: PLGA-coated CS-based micro-implants containing 400 µg of MTX and placebo (without drug) micro-implants were surgically-implanted in the vitreous of the right and the left eyes, respectively, in each of the thirty New Zealand rabbits. ERG, US, SLB, funduscopy, and IOP were assessed in both eyes at pre-determined time points (days: 1, 3, 7, 14, 28 and 56). The safety of micro-implants was assessed by analyzing the ERG data using different statistical models, to quantify and compare the functional integrity of the retina. Further, US, funduscopy, SLB and IOP determined the condition of the retina, the micro-implant and associated intraocular features. RESULTS: Statistical analyses of the ERG data showed unchanged functional integrity of retina between eyes with the PLGA-coated CS-based MTX micro-implant and the placebo micro-implant. US analysis showed that micro-implants were stationary throughout the study. SLB, funduscopy and IOP further confirmed that there were no abnormalities in the intraocular physiology. CONCLUSION: The findings from ERG, US, SLB, funduscopy, and IOP showed no detectable adverse effects caused by our biodegradable micro-implants. These non-invasive techniques appeared to show lack of significant ocular toxicity over time in spite of degradation and changes in morphology of the micro-implants following intraocular implantation.

Coexistence of oil droplets and lipid vesicles in propofol drug products.

Propofol is intravenously administered oil-in-water emulsion stabilized by egg lecithin phospholipids indicated for the induction and maintenance of general anesthesia or sedation. It is generally assumed to be structurally homogenous as characterized by commonly used dynamic light scattering technique and laser diffraction. However, the excessive amount of egg lecithin phospholipids added to the propofol formulation may, presumably, give rise to additional formation of lipid vesicles (i.e., vesicular structures consisting of a phospholipid bilayer). In this study, we investigate the use of high-resolution cryogenic transmission electron microscopy (cryo-TEM) in morphological characterization of four commercially available propofol drug products. The TEM result, for the first time, reveals that all propofol drug products contain lipid vesicles and oil droplet-lipid vesicle aggregated structures, in addition to oil droplets. Statistical analysis shows the size and ratio of the lipid vesicles varies across four different products. To evaluate the impact of such morphological differences on active pharmaceutical ingredient (API)'s distribution, we separate the lipid vesicle phase from other constituents via ultracentrifuge fractionation and determine the amount of propofol (2,6-diisopropylphenol) using high performance liquid chromatography (HPLC). The results indicate that a nearly negligible amount of API (i.e., NMT 0.25% of labeled content) is present in the lipid vesicles and is thus primarily distributed in the oil phase. As oil droplets are the primary drug carriers and their globule size are similar, the findings of various lipid vesicle composition and sizes among different propofol products do not affect their clinical outcomes.

Probing the mechanism of bupivacaine drug release from multivesicular liposomes.

The mechanism of drug release from complex dosage forms, such as multivesicular liposomes (MVLs), is complex and oftentimes sensitive to the release environment. This challenges the design and development of an appropriate in vitro release test (IVRT) method. In this study, a commercial bupivacaine MVL product was selected as a model product and an IVRT method was developed using a modified USP 2 apparatus in conjunction with reverse-dialysis membranes. This setup allowed the use of in situ UV-Vis probes to continuously monitor the drug concentration during release. In comparison to the traditional sample-and-separate methods, the new method allowed for better control of the release conditions allowing for study of the drug release mechanism. Bupivacaine (BPV) MVLs exhibited distinct tri-phasic release characteristics comprising of an initial burst release, lag phase and a secondary release. Temperature, pH, agitation speed and release media composition were observed to impact the mechanism and rate of BPV release from MVLs. The size and morphology of the MVLs as well as their inner vesicle compartments were analyzed using cryogenic-scanning electron microscopy (cryo-SEM), confocal laser scanning microscopy and laser diffraction, where the mean diameters of the MVLs and their inner "polyhedral" vesicles were found to be 23.6 ±â€¯11.5 µm and 1.52 ±â€¯0.44 µm, respectively. Cryo-SEM results further showed a decrease in particle size and loss of internal "polyhedral" structure of the MVLs over the duration of release, indicating erosion and rearrangement of the lipid layers. Based on these results a potential MVL drug release mechanism was proposed, which may assist with the future development of more biorelevant IVRT method for similar formulations.

Improved design and characterization of PLGA/PLA-coated Chitosan based micro-implants for controlled release of hydrophilic drugs.

Repetitive intravitreal injections of Methotrexate (MTX), a hydrophilic chemotherapeutic drug, are currently used to treat selected vitreoretinal (VR) diseases, such as intraocular lymphoma. To avoid complications associated with the rapid release of MTX from the injections, a Polylactic acid (PLA) and Chitosan (CS)-based MTX micro-implant prototype was fabricated in an earlier study, which showed a sustained therapeutic release rate of 0.2-2.0 µg/day of MTX for a period ∼1 month in vitro and in vivo. In the current study, different combinations of Poly(lactic-co-glycolic) acid (PLGA)/PLA coatings were used for lipophilic surface modification of the CS-MTX micro-implant, such as PLGA 5050, PLGA 6535 and PLGA 7525 (PLA: PGA - 50:50, 65:35, 75:25, respectively; M.W: 54,400 - 103,000) and different PLA, such as PLA 100 and PLA 250 (MW: 102,000 and 257,000, respectively). This improved the duration of total MTX release from the coated CS-MTX micro-implants to ∼3-5 months. With an increase in PLA content in PLGA and molecular weight of PLA, a) the initial burst of MTX and the mean release rate of MTX can be reduced; and b) the swelling and biodegradation of the micro-implants can be delayed. The controlled drug release mechanism is caused by a combination of diffusion process and hydrolysis of the polymer coating, which can be modulated by a) PLA content in PLGA and b) molecular weight of PLA, as inferred from Korsmeyer Peppas model, Zero order, First order and Higuchi model fits. This improved micro-implant formulation has the potential to serve as a platform for controlled release of hydrophilic drugs to treat selected VR diseases.

Noninvasive Electroretinography Assessment of Intravitreal Sustained-Release Methotrexate Microimplants in Rabbit Eyes.

PURPOSE: The purpose of this study is to noninvasively evaluate the safety and toxicity of a chitosan (CS) and polylactic acid (PLA)-based sustained-release methotrexate (MTX) intravitreal microimplant in normal rabbit eyes using electroretinography (ERG). METHODS: PLA-coated CS-based microimplants containing 400 µg of MTX and placebo microimplants (without drug) were surgically implanted in the vitreous of the right and the left eyes, respectively, in each of the 8 New Zealand rabbits using minimally invasive technique. At each predetermined time points (days 5, 12, 19, and 33), ERG was conducted on 2 rabbits to evaluate the safety of the microimplants administered in each eye. ERG was carried out using 2 protocols, scotopic and photopic, on each eye prior to surgery (PS) and prior to euthanasia (PE) conditions. The safety of the microimplants was assessed using statistical analysis of the ERG data (B/A ratio analysis, oscillatory potential analysis, and Naka-Rushton analysis) and subsequently quantifying and comparing functional integrity of the retina between the PS and PE conditions of each eye. RESULTS: Statistical analysis of the ERG data showed no change in retinal functional integrity because of the PLA-coated CS-based MTX microimplant and the placebo microimplant. ERG analysis also revealed absence of any evident bioelectrical dysfunction caused by the microimplants. CONCLUSION: ERGs were performed to determine whether the microimplants containing MTX and the placebo microimplants were associated with any profound retinal bioelectrical dysfunction that might be attributable to toxicity not apparent on histological studies of such eyes. The results shown in this report indicate that there were no such evident adverse effects of the microimplants or contained drug.

Ultrasonographical assessment of implanted biodegradable device for long-term slow release of methotrexate into the vitreous.

Our group has developed a biodegradable drug delivery device (micro-implant) for long-term slow intraocular release of methotrexate (MTX) that can be implanted in the peripheral vitreous. The purpose of this study was to assess the position of the implanted devices and the status of the adjacent vitreous and peripheral retina over time using B-scan ocular ultrasonography (US). In each of the eight New Zealand rabbits used in this study, a chitosan (CS) and poly-lactic acid (PLA)-based micro-implant containing approximately 400 µg of MTX and a placebo micro-implant without MTX were inserted into the peripheral vitreous of the right and left eyes, respective, employing minimally invasive surgery. B-scan US imaging was performed on all of the rabbits immediately after implant insertion and on two rabbits at each of several pre-determined time points post-insertion (post-insertion days 5, 12, 19, and 33) to evaluate the position of the micro-implants and identify any evident morphological changes in the micro-implants and in the peripheral retina and vitreous during treatment. US imaging revealed stable positioning of the PLA-coated CS-based MTX micro-implant and the placebo micro-implant in the respective eyes throughout the study and lack of any changes in size, shape or sonoreflectivity of the micro-implants or abnormalities of the peripheral vitreous or retina in any of the study eyes. In summary, US did not show any evident morphological changes in the micro-implants, shifts in post-insertion position of the micro-implants, or identifiable changes in the micro-implants or peripheral vitreous and retina of the study eyes.

Biodegradable chitosan and polylactic acid-based intraocular micro-implant for sustained release of methotrexate into vitreous: analysis of pharmacokinetics and toxicity in rabbit eyes.

PURPOSE: The purpose of this study was to evaluate the pharmacokinetics and toxicity of a chitosan (CS) and polylactic acid (PLA) based methotrexate (MTX) intravitreal micro-implant in an animal model using rabbit eyes. METHODS: CS- and PLA-based micro-implants containing 400 µg of MTX were fabricated using lyophilization and dip-coating techniques. The micro-implants were surgically implanted in the vitreous of eight New Zealand rabbits employing minimally invasive technique. The PLA-coated CS-MTX micro-implant was inserted in the right eye and the placebo micro-implant in the left eye of each rabbit. Two rabbits were euthanized at each pre-determined time point post-implantation (days 5, 12, 19, and 33) for pharmacokinetics and histopathology evaluation. RESULTS: A therapeutic concentration of MTX (0.1-1.0 µM) in the vitreous was detected in the rabbit eyes studied for 33 days. The MTX release from the coated micro-implants followed a first order kinetics (R (2) ~ 0.88), implying that MTX release depends on the concentration of MTX in the micro-implant. Histopathological analysis of the enucleated eyes failed to show any signs of infection or tissue toxicity in any of the specimens. CONCLUSION: The PLA-coated CS-MTX micro-implants were able to deliver therapeutic release of MTX for a period of more than 1 month without detectable toxicity in a rabbit model. The micro-implants can be further investigated as a prospective alternative to current treatment protocols of repeated intravitreal MTX injections in intraocular disorders such as primary intraocular lymphoma, and selected cases of non-microbial intraocular inflammation.

Development of chitosan and polylactic acid based methotrexate intravitreal micro-implants to treat primary intraocular lymphoma: an in vitro study.

Primary intraocular lymphoma (PIOL) is an uncommon but clinically and pathologically distinct form of non-Hodgkin's lymphoma. It provides a therapeutic challenge because of its diverse clinical presentations and variable clinical course. Currently available treatments for PIOL include intravenous multiple drug chemotherapy, external beam radiation therapy, and intravitreal methotrexate (MTX) injection. Each intravitreal injection of MTX is associated with potentially toxic peaks and subtherapeutic troughs of intraocular MTX concentration. Repetitive injections are required to maintain therapeutic levels of MTX in the eye. A sustained release drug delivery system is desired for optimized therapeutic release (0.2-2.0 µg/day) of MTX for over a period of 1 month to achieve effective treatment of PIOL. This study reports development of a unique intravitreal micro-implant, which administers therapeutic release of MTX over a period of 1 month. Chitosan (CS) and polylactic acid (PLA) based micro-implants are fabricated for different MTX loadings (10%, 25%, and 40% w/w). First, CS and MTX mixtures are prepared for different drug loadings, and lyophilized in Tygon® tubing to obtain CS-MTX fibers. The fibers are then cut into desired micro-implant lengths and dip coated in PLA for a hydrophobic surface coating. The micro-implant is characterized using optical microscopy, scanning electron microscopy (SEM), time of flight-secondary ion mass spectroscopy (ToF-SIMS), and differential scanning calorimetry (DSC) techniques. The release rate studies are carried out using a UV-visible spectrophotometer. The total release durations for 10%, 25%, and 40% w/w uncoated CS-MTX micro-implants are only 19, 29, and 32 h, respectively. However, the therapeutic release durations for 10%, 25%, and 40% w/w PLA coated CS-MTX micro-implants significantly improved to 58, 74, and 66 days, respectively. Thus, the PLA coated CS-MTX micro-implants are able to administer therapeutic release of MTX for more than 50 days. The release kinetics of MTX from the coated micro-implants is explained by (a) the Korsmeyer-Peppas and zero order model fit (R2 ∼ 0.9) of the first 60% of the drug release, which indicates the swelling of polymer and initial burst release of the drug; and (b) the first order and Higuchi model fit (R2 ∼ 0.9) from the tenth day to the end of drug release, implying MTX release in the therapeutic window depends on its concentration and follows diffusion kinetics. The PLA coated CS-MTX micro-implants are able to administer therapeutic release of MTX for a period of more than 1 month. The proposed methodology could be used for improved treatment of PIOL.