Flow cytometric and optical microscopic evaluation of poly(D, L-lactide-co-glycolide) microspheres phagocytosis by pig alveolar macrophages

Adjuvants and delivery systems in veterinary vaccinology: current state and future developments

Modern adjuvants should induce strong and balanced immune responses, and it is often desirable to induce specific types of immunity. As an example, efficient Th1-immunity-inducing adjuvants are highly in demand. Such adjuvants promote good cell-mediated immunity against subunit vaccines that have low immunogenicity themselves. The development of such adjuvants may take advantage of the increased knowledge of the molecular mechanisms and factors controlling these responses. However, knowledge of such molecular details of immune mechanisms is relatively scarce for species other than humans and laboratory rodents, and in addition, there are special considerations pertaining to the use of adjuvants in veterinary animals, such as production and companion animals. With a focus on veterinary animals, this review highlights a number of approaches being pursued, including cytokines, CpG oligonucleotides, microparticles and liposomes.

5-Fluorouracil plasma levels and biodegradation of subcutaneously injected drug-loaded microspheres prepared by spray-drying poly(d,l-lactide) and poly(d,l-lactide-co-glycolide) polymers

Microspheres (MS) of 5-fluorouracil-loaded poly(D,L-lactide) (PLA), poly(D,L-lactide-co-glycolide) 75/25 (PLGA 75/25) and poly(D,L-lactide-co-glycolide) 50/50 (PLGA 50/50) prepared by the spray-drying technique were subcutaneously injected in the back of Wistar rats in order to evaluate the 5-fluorouracil (5-FU) release and the biodegradation characteristics. Determination of plasma 5-FU concentration by HPLC with analysis of data using a non-compartmental model showed drug in plasma between 9 and 14 days after administration of drug-loaded PLGA 50/50 or PLA and PLGA 75/25 microspheres, respectively, with a maximum drug concentration of 2.4+/-0.2microg/mL at 24h (5-FU-loaded PLGA 50/50 MS), 2.5+/-0.1microg/mL at 48h (5-FU-loaded PLGA 75/25 MS), and 2.3+/-0.1microg/mL at 24h (5-FU-loaded PLA MS). Pharmacokinetically, a significant increase of AUC (up to 50 times) and MRT (up to 196 times) of 5-FU with regard to the administration of the drug in solution was observed. Scanning electron microscopy and histological studies indicated that a small fibrous capsule was observed around the microspheres in the site of injection. One month after the injection of PLGA 50/50 MS and 2 months after the injection of PLGA 75/25 and PLA MS, masses of polymers, instead of single microspheres, were observed. Close to them, macrophagic cells were present, and blood vessels were observed in the connective tissue. Total absence of fibrous capsule and injected microspheres was observed after 2 (for PLGA 50/50 MS) or 3 (PLGA 75/25 and PLA MS) months.

In vitro and in vivo evaluation of the effects of PLA microparticle crystallinity on cellular response

Previous research suggests that crystallinity of poly(L-lactide) P(L)LA microparticles can influence surface free energy, which in turn might influence biocompatibility. This work studies the cellular response to P(L)LA microparticles of different crystallinity both in vitro and in vivo. Following incubation with P(L)LA microparticles, the in vitro production of reactive oxygen intermediates (ROI) was measured as a marker of cellular response. In both fluorescence and chemiluminescence experiments to measure ROI, a small effect of microparticle crystallinity on NR8383 AM response was observed. Microparticles of higher crystallinity elicited a smaller inflammatory response compared to lower crystallinity particles. Compared to the elevated inflammatory response induced by zymosan, the response to all P(L)LA microparticles tested was practically negligible. Results from in vivo experiments further supported conclusions that P(L)LA microparticles elicit minimal inflammatory response. Following acute exposure to P(L)LA microparticles in guinea-pig lungs, the inflammatory response was not significantly different from the response observed when sterile saline was administered. In contrast to the in vitro experiments, there were not apparent differences in cellular responses to microparticles of different crystallinity.

Evaluation of PLGA microspheres as delivery system for antitumor agent-camptothecin

Camptothecin (CPT) and its analogues are a new class of anticancer agents that have been identified over the past several years. Camptothecin exists in two forms depending on the pH: An active lactone form at pH below 5 and an inactive carboxylate form at basic or physiological neutral pH. Poly(lactide-co-glycolide) (PLGA) microspheres have been considered good delivery vehicles for CPT because of acidic microenvironment formed through PLGA degradation. The objective of this study is to investigate antitumor activity of CPT after it is encapsulated in PLGA microspheres. In this study, PLGA microspheres containing various CPT loadings were prepared and characterized. Cytotoxicity of these microspheres to B16 melanoma cells was then evaluated, and uptake of microspheres by B16 cells was also studied. Analysis of drug stability revealed that CPT is released from the microspheres in its active lactone form over the entire release duration. It was also found that there was no interaction between CPT and PLGA matrix within microspheres through Differential Scanning Calorimetry (DSC) and Fourien Transform Infrared Spectroscopy (FT-IR) and hign performance liquid chromatography (HPLC) studies. Cytotoxicity assay showed that CPT encapsulated in PLGA microspheres still retained its antitumor potency. Uptake study revealed quick uptake of the microspheres by B16 cells, which was desirable. It was concluded that PLGA microspheres were suitable delivery vehicles to stabilize and deliver CPT for the treatment of cancer.

Analysis of individual acidic organelles by capillary electrophoresis with laser-induced fluorescence detection facilitated by the endocytosis of fluorescently labeled microspheres

Submicrometer-sized fluorescent microspheres were loaded into the acidic organelles of NS-1 mouse myeloma cells via endocytosis. Confocal microscopy imaging showed that microspheres colocalized nearly perfectly with LysoTracker Red, a probe that stains acidic organelles. Unlike LysoTracker dyes that seem to leak from acidic organelles upon cell disruption, microspheres are retained within these organelles, facilitating their analysis following isolation. Using capillary electrophoresis (CE) with laser-induced fluorescence detection (LIF), the electrophoretic mobilities of acidic organelles were individually calculated and fluorescence intensities individually measured. When cells were incubated for sufficient time to allow for endocytosis (48 h) with 3.9 x 10(3) microspheres/cell, replicate CE-LIF analyses of the corresponding isolated fraction indicated a dramatic increase in the number of detected events (n = 1990 +/- 234) and in the overall fluorescence intensity of the individual events (0.38 +/- 0.01 RFU; average +/- SD; n = 3) over the corresponding <10-min incubations (n = 60; 0.21 RFU, respectively). In addition, a treatment with 4-fold increase in microsphere density (1.6 x 10(4) microspheres/cell), increased the number of detected individual events (n = 3427 +/- 101) and altered only slightly the fluorescence intensity and electrophoretic mobility distributions. The individual electrophoretic mobility values ranged from -1.45 x 10(-)(4) to -3.0 x 10(-)(4) cm(2) V(-)(1) s(-)(1) while the individual fluorescence values ranged from 0.1 V to over 8 V, demonstrating the benefit of detecting organelles individually rather than averaging their properties over single cells or bulk homogenates.

The inhibition of phagocytosis of respirable microspheres by alveolar and peritoneal macrophages

Respirable poly(lactic co-glycolic acid) (PLGA) microspheres (2-3 microm diameter), were fabricated as a model drug delivery system whose uptake by macrophages could be quantified by fluorescent activated cell sorting. The microspheres exhibited minimal release of the entrapped flourophore (rhodamine B) and thus avoided possible fluid phase uptake of the flourophore. Externally bound microspheres were removed from the cell membrane by acid washing. The fluorescent intensity associated with the cells arose, therefore, from the internalised microspheres. NR8383 continuous culture alveolar macrophages were verified against primary cultures as a good model of alveolar phagocytosis. Peritoneal macrophages were also isolated and systemic and alveolar phagocytosis compared. Poloxamer 338 adsorbed at the microsphere surface did not reduce phagocytosis by NR8383 macrophages. It did, however, reduce the number of microspheres contained in primary alveolar macrophages but did not reduce the percentage of phagocytic cells. Poloxamer coatings did not reduce phagocytosis by peritoneal macrophages once the ratio of five microspheres per cell was exceeded. Dipalmitoylphosphatidylcholine (DPPC), the major component of lung surfactant, was added to cultures to model the alveolar environment where it was observed to reduce phagocytosis. In light of this finding, microspheres were coated in DPPC, which reduced their uptake by all cell types at all microsphere to cell ratios.

PLGA microspheres phagocytosis by pig alveolar macrophages: influence of poly(vinyl alcohol) concentration, nature of loaded-protein and copolymer nature

The study aimed to investigate on a pig alveolar macrophage culture model the influence of: (1) poly(D,L-lactide-co-glycolide) characteristics, (2) the residual poly(vinyl alcohol) (PVA) and (3) the nature of encapsulated proteins, immunoglobulin Y (IgY) or bovine serum albumin, on the microspheres phagocytosis efficiency. The phagocytosis evaluation was performed by flow cytometry and has allowed a screening of microspheres formulations. The hydrophilicity of microspheres resulting from the nature of the polymer and/ or from the residual hydrophilic surface agent (PVA) led to a decrease of phagocytosis intensity. The phagocytosis results of IgY-loaded microspheres strongly suggested that the phagocytosis was increased when the phagocytic cell possessed a receptor for this protein on its surface.

Ex vivo and in situ PLGA microspheres uptake by pig ileal Peyer's patch segment

We investigated the ability of pig ileal Peyer's patch segments to transport intestinal poly (D,L-lactide-co-glycolide) microspheres (PLGA MS) from intestinal lumen across the mucosae using in situ and ex vivo segments with confocal laser scanning microscopy (CLSM) and transmission electronic microscopy (TEM). From a global aspect, CLSM suggested that PLGA MS were translocated by M cells labelled with a FITC-conjugated anti-cytokeratin peptide 18, and transported through the follicle-associated epithelium (FAE) in the dome area in both types of experiments. At the ultrastructural level, TEM showed the traffic of PLGA MS throughout M cells, their transport into the basolateral invaginations of the M cells and their subsequent migration into the dome area and the follicular area in contact with macrophages and lymphatic vessels. Although in situ experiments allowed following the migration of PLGA MS until mesenteric lymph nodes, an ex vivo model could be used as a useful tool to study the targeting ability of PLGA MS formulations to the gut-associated lymphoid tissue (GALT).

Microcalorimetry does not predict the cellular phagocytosis of latex microspheres

Current literature highlights the potential suitability of microcalorimetry for the investigation of cell-drug interactions. Previous work using bacteria or antigens derived from infectious organisms yielded conclusions that heat production is a quantitative means of measuring phagocytosis. In this study we evaluated the potential of flow-through microcalorimetry as a method of quantifying the phagocytosis of microsphere particulates. The technique avoids the need to incorporate radioactive or fluorescent markers into the particulate formulation, and would be widely applicable in biopharmaceutical research. Using the monocyte cell line Mono Mac 6 a power output of 9.00 microW per million cells was increased significantly on addition of zymosan, lipopolysaccaride (LPS) and phorbol myristate acetate but not following exposure to FITC labelled latex microspheres (LM). TNFalpha production increased on exposure to zymosan, LPS and LPS-phorbol myristate acetate, though not on exposure to LB. An assay was developed which allowed the quantification of internalised particulates in phagocytic cells using fluorescent activated cell sorting (FACS). In contrast to the microcalorimetric and TNFalpha data FACS revealed that 20% of the MM6 population phagocytosed a mean of 1.35 LM. Microcalorimetry and measurements of TNFalpha production are assays of cellular activation a phenomenon not necessarily associated with phagocytosis. FACS, however, serves as a specific and quantitative measure of phagocytosis. Microcalorimetry may not be a suitable technique for the quantitative assessment of the phagocytosis of drug delivery particulates.