Effect of reproductive status on uptake of latex microparticles in rat small intestine

Natural sporopollenin microcapsules: biological evaluation and application in regulating hepatic toxicity of diclofenac sodium in vivo

Diclofenac sodium (DIC) is a pain reliever and anti-nociceptive medication. Significant limitations of DIC treatment stem from its adverse effects. This study investigates the feasibility of using natural Lycopodium clavatum sporopollenin (LCS) microcapsules loaded with DIC to mitigate the hepatotoxicity associated with DIC treatment. In addition, LCS microcapsules were tracked in the blood, stomach, small intestine, and feces of rats to demonstrate their morphological integrity and uptake behavior. Four groups (6 per group) of adult male albino rats were administered normal saline (control), empty LCS (30 mg kg-1), plain DIC (10 mg kg-1), and DIC-loaded LCS (40 mg kg-1) orally for seven consecutive days. The first comprehensive histological examination of the rat stomach demonstrated the robustness and bioadhesion ability of LCS under severe conditions. The findings suggested that these versatile microcapsules are unlikely to be digested in the gastrointestinal tract (GIT). The administration of DIC-loaded LCS was found to play a potential protective role in regulating DIC-induced substantially increased serum levels of transaminases, alkaline phosphatase, total bilirubin, and pro-inflammatory cytokines. In addition, DIC-loaded LCS restored the antioxidant enzymes, DNA damage, and liver histological architecture abnormalities caused by DIC. Microencapsulation of DIC into pollen-derived biomaterials could be employed as an efficient platform with enough safety coverage on rat liver, pending further clinical studies.

Mechanisms of uptake and transport of particulate formulations in the small intestine

Micro- and nano-scale particulate formulations are widely investigated towards improving the oral bioavailability of both biologics and drugs with low solubility and/or low intestinal permeability. Particulate formulations harnessing physiological intestinal transport pathways have recently yielded remarkably high oral bioavailabilities, illustrating the need for better understanding the specific pathways underpinning particle small intestinal absorption and the relative role of intestinal cells. Mechanistic knowledge has been hampered by the well acknowledged limitations of current in vitro, in vivo and ex vivo models relevant to the human intestinal physiology and the lack of standardization in studies reporting absorption data. Here we review the relevant literature and critically discusses absorption pathways with a focus on the role of specific intestinal epithelial and immune cells. We conclude that while Microfold (M) cells are a valid target for oral vaccines, enterocytes play a greater role in the systemic bioavailability of orally administrated particulate formulations, particularly within the sub-micron size range. We also comment on less-reported mechanisms such as paracellular permeability of particles, persorption due to cell damage and uptake by migratory immune cells.

A Children's Health Perspective on Nano- and Microplastics

BACKGROUND

Pregnancy, infancy, and childhood are sensitive windows for environmental exposures. Yet the health effects of exposure to nano- and microplastics (NMPs) remain largely uninvestigated or unknown. Although plastic chemicals are a well-established research topic, the impacts of plastic particles are unexplored, especially with regard to early life exposures.

OBJECTIVES

This commentary aims to summarize the knowns and unknowns around child- and pregnancy-relevant exposures to NMPs via inhalation, placental transfer, ingestion and breastmilk, and dermal absorption.

METHODS

A comprehensive literature search to map the state of the science on NMPs found 37 primary research articles on the health relevance of NMPs during early life and revealed major knowledge gaps in the field. We discuss opportunities and challenges for quantifying child-specific exposures (e.g., NMPs in breastmilk or infant formula) and health effects, in light of global inequalities in baby bottle use, consumption of packaged foods, air pollution, hazardous plastic disposal, and regulatory safeguards. We also summarize research needs for linking child health and NMP exposures and address the unknowns in the context of public health action.

DISCUSSION

Few studies have addressed child-specific sources of exposure, and exposure estimates currently rely on generic assumptions rather than empirical measurements. Furthermore, toxicological research on NMPs has not specifically focused on child health, yet children's immature defense mechanisms make them particularly vulnerable. Apart from few studies investigating the placental transfer of NMPs, the physicochemical properties (e.g., polymer, size, shape, charge) driving the absorption, biodistribution, and elimination in early life have yet to be benchmarked. Accordingly, the evidence base regarding the potential health impacts of NMPs in early life remains sparse. Based on the evidence to date, we provide recommendations to fill research gaps, stimulate policymakers and industry to address the safety of NMPs, and point to opportunities for families to reduce early life exposures to plastic. https://doi.org/10.1289/EHP9086.

Host Microbe Interactions in the Lactating Mammary Gland

The bacteria present in human milk constitute the human milk microbiome (hMM). Both the older culture-based work and the more recent studies using molecular detection of bacterial DNA have reached similar conclusions: the hMM mostly consists of commensal staphylococci such as Staphylococcus epidermidis, and streptococci. The prevalence of other bacterial groups such lactobacilli varies widely, while the abundance and prevalence of bifidobacteria is generally low. Recently, the hMM became accepted as a part of a physiologically normal state with suggested potential health benefits. Most research on the hMM has focused on its composition and potential effect on the breastfed infant. A major role as a microbiome inoculum for the infant gut has been proposed, but remains to be clearly demonstrated. Herein, we also discuss the emerging connection between the hMM and mammary gland physiology and lactation. Similarities between the mammary gland and mucosal interfaces are considerable, and in particular mucosal-like immune attributes of mammary gland. The potential role of hMM-host interactions in the mammary gland in maternal health is explored with a primary focus on lactational mastitis.

Alginate Microencapsulation for Oral Immunisation of Finfish: Release Characteristics, Ex Vivo Intestinal Uptake and In Vivo Administration in Atlantic Salmon, Salmo salar L

This study examined the feasibility of alginate microcapsules manufactured using a low-impact technology and reagents to protect orally delivered immunogens for use as immunoprophylactics for fish. Physical characteristics and protein release kinetics of the microcapsules were examined at different pH and temperature levels using a microencapsulated model protein, bovine serum albumin (BSA). Impact of the microencapsulation process on contents was determined by analysing change in bioactivity of microencapsulated lysozyme. Feasibility of the method for oral immunoprophylaxis of finfish was assessed using FITC-labelled microcapsules. These were applied to distal intestinal explants of Atlantic salmon (Salmo salar) to investigate uptake ex vivo. Systemic distribution of microcapsules was investigated by oral administration of FITC-labelled microcapsules to Atlantic salmon fry by incorporating into feed. The microcapsules produced were structurally robust and retained surface integrity, with a modal size distribution of 250-750 nm and a tendency to aggregate. Entrapment efficiency of microencapsulation was 51.2 % for BSA and 43.2 % in the case of lysozyme. Microcapsules demonstrated controlled release of protein, which increased with increasing pH or temperature, and the process had no significant negative effect on bioactivity of lysozyme. Uptake of fluorescent-labelled microcapsules was clearly demonstrated by intestinal explants over a 24-h period. Evidence of microcapsules was found in the intestine, spleen, kidney and liver of fry following oral administration. Amenability of the microcapsules to intestinal uptake and distribution reinforced the strong potential for use of this microencapsulation method in oral immunoprophylaxis of finfish using sensitive immunogenic substances.

Gold nanoparticles as localization markers for direct and live imaging of particle absorption through a Caco-2 cell monolayer using dark-field microscopy

Recently, efforts have been made to reduce the size of food particles containing functional ingredients, since reducing the size is expected to improve intestinal absorption. However, the absorption mechanisms have yet to be fully clarified. Therefore, a microscopy-based method for studying interactions between the particles and intestinal cells is required. We optimized the experimental conditions for observing gold nanoparticles (AuNPs) on the surface of an unfixed Caco-2 cell using dark-field microscopy (DFM). Tight junctions were clearly visible with AuNPs on the cells, producing intense scattered light under DFM. This suggests that AuNPs could be used as localization markers to visualize particle absorption through Caco-2 cells.

Bimodal visualization of colorectal uptake of nanoparticles in dimethylhydrazine-treated mice

AIM: To investigate colorectal uptake of solid lipid nanoparticles (SLNs) in mice receiving different doses of 1,2-dimethylhydrazine (DMH) using magnetic resonance (MR) and laser-scanning confocal fluorescence microscope (LSCFM) imaging.

METHODS: Eight mice were sacrificed in a pilot study to establish the experimental protocol and to visualize colorectal uptake of SLNs in normal mice. Gadopentetate dimeglumine and fluorescein isothiocyanate (FITC)-loaded SLN (Gd-FITC-SLN) enemas were performed on mice receiving DMH for 10 wk (group 1, n = 9) or 16 wk (group 2, n = 7) and FITC-SLN enema was performed on 4 DMH-treated mice (group 3). Pre- and post-enema MR examinations were made to visualize the air-inflated distal colorectum. Histological and LSCFM examinations were performed to verify colorectal malignancy and to track the distribution of SLNs.

RESULTS: Homogeneous enhancement and dense fluorescence (FITC) deposition in colorectal wall were observed in normal mice and 1 DMH-treated mouse (group 1) on fluid attenuated inversion recovery (FLAIR) and LSCFM images, respectively. Heterogeneous mural enhancement was found in 6 mice (4 in group 1; 2 in group 2). No visible mural enhancement was observed in the other mice. LSCFM imaging revealed linear fluorescence deposition along the colorectal mucosa in all groups. Nine intraluminal masses and one prolapsed mass were detected by MR imaging with different enhancement modes and pathologies. Interstitial FITC deposition was identified where obvious enhancement was observed in FLAIR images. Bladder imaging agent accumulations were observed in 11 of 16 DMH-treated mice of groups 1 and 2.

CONCLUSION: There are significant differences in colorectal uptake and distribution of SLNs between normal and DMH-treated mice, which may provide a new mechanism of contrast for MR colonography.

Macrophages increase microparticle uptake by enterocyte-like Caco-2 cell monolayers

Caco-2 cells form an enterocyte-like monolayer that has been used to explore small intestinal microparticle uptake. They are a useful functional model for the investigation of in vivo drug delivery systems and the uptake of particulate environmental pollutants. The aim of this paper was to determine if the previously reported decrease in Caco-2 transepithelial resistance following exposure to macrophages was matched by increased microparticle uptake, especially as macrophage phagocytosis simulates removal of particles from the subepithelial compartment. Caco-2 cells were grown as a monoculture for 21 days on insert membranes. A compartmentalised model involved Caco-2 cells in the upper compartment, with THP-1-derived macrophages adhering to the base of the underlying well, the two cell populations communicating only through the shared culture medium. Caco-2 cells were also cultured in macrophage-conditioned medium and all groups were exposed apically to 2 μm latex particles for 5 or 60 min. Parameters measured were: transepithelial resistance; cytokine levels; cell dimensions and the distribution of nuclei, actin and junctional proteins. Subepithelial particle numbers, defined as those located below the insert membrane, were also counted and were significantly increased in the Caco-2/macrophage model, with over 90% associated with the macrophages. Other changes induced by the presence of macrophages included decreased transepithelial resistance levels, diffuse localisation of some junctional proteins, higher proinflammatory cytokine levels, disorganisation of cell shape and decreased cell height associated with actin reorganisation. Macrophage-conditioned medium produced a smaller transepithelial resistance decrease than the Caco-2/macrophage model and there were few other changes. In conclusion, culture of Caco-2 cells with underlying macrophages produced a lower, less organised epithelium and greater microparticle uptake.

Culture conditions and treatments affect Caco-2 characteristics and particle uptake

Small intestinal microparticle uptake via a paracellular route is relevant to oral drug delivery and environmental pollution. In vitro investigation uses latex microparticle passage across a confluent Caco-2 cell epithelium. This paper examines the influence of culture conditions on transepithelial resistance (TER); cell dimensions from confocal microscopy; and number of particles below the epithelium. Variables investigated include level of initial TER; multiple TER measurements; involvement of medium; cell source; and pretreatment with ethanol or a range of temperatures. Data were collected after exposure to 2 microm latex particles for 5-120 min: sham groups were exposed to pretreatment but not particles. The results highlight the importance of very precise control of the experimental environment; confirm the pattern of sequential-TER increase/decrease in groups exposed only to particles and show accompanying increases in cell dimensions. Greater particle uptake was associated with ethanol-induced decreased TER, decreased cell height and increased intercellular spaces, similar to previous findings for external irradiation. Low temperatures raised TER but, despite this, cooling did not alter particle uptake. In conclusion, culture microenvironment and sham treatment are crucial considerations in studies of epithelial microparticle uptake in vitro.

Biodegradable polymer nanoparticles that rapidly penetrate the human mucus barrier

Protective mucus coatings typically trap and rapidly remove foreign particles from the eyes, gastrointestinal tract, airways, nasopharynx, and female reproductive tract, thereby strongly limiting opportunities for controlled drug delivery at mucosal surfaces. No synthetic drug delivery system composed of biodegradable polymers has been shown to penetrate highly viscoelastic human mucus, such as non-ovulatory cervicovaginal mucus, at a significant rate. We prepared nanoparticles composed of a biodegradable diblock copolymer of poly(sebacic acid) and poly(ethylene glycol) (PSA-PEG), both of which are routinely used in humans. In fresh undiluted human cervicovaginal mucus (CVM), which has a bulk viscosity approximately 1,800-fold higher than water at low shear, PSA-PEG nanoparticles diffused at an average speed only 12-fold lower than the same particles in pure water. In contrast, similarly sized biodegradable nanoparticles composed of PSA or poly(lactic-co-glycolic acid) (PLGA) diffused at least 3,300-fold slower in CVM than in water. PSA-PEG particles also rapidly penetrated sputum expectorated from the lungs of patients with cystic fibrosis, a disease characterized by hyperviscoelastic mucus secretions. Rapid nanoparticle transport in mucus is made possible by the efficient partitioning of PEG to the particle surface during formulation. Biodegradable polymeric nanoparticles capable of overcoming human mucus barriers and providing sustained drug release open significant opportunities for improved drug and gene delivery at mucosal surfaces.

Changes produced by external radiation in parameters influencing intestinal permeability and microparticle uptake in vitro

PURPOSE

To determine the interaction between X-irradiation and in vitro intestinal microparticle uptake through Caco-2 epithelial cells.

METHODS

Caco-2 cells were cultured on 3 microm porous membranes for 21 days, X-irradiated with 2 Gy or sham-irradiated, then incubated for 5 or 30 min and exposed apically for 30 min to 2 microm latex microparticles. Measurements included cell dimensions, from confocal microscope 'optical slices'; transepithelial resistance (TER) for tight junction (TJ) permeability; particle aggregation; and particle numbers on (adsorbed), in (intraepithelial) and through (submembranous) the epithelium.

RESULTS

Irradiation alone reduced TJ permeability more than sham-treatment, more so 5 min than 30 min after treatment. Irradiated epithelia were more permeable to particles than the equivalent sham-irradiated or previously untreated (particle only) groups: the latter two were similar. Irradiation altered adsorbed particle numbers and increased submembranous counts: particle uptake correlated best with cell height.

CONCLUSIONS

2 Gy X-irradiation increased particle uptake and translocation through the epithelium. This correlated well with the TJ opening seen after particle exposure in irradiated samples and changes in cell morphology. New data on cell dimensions underlined the similarity in particle uptake between this in vitro epithelium and that in an in vivo model, highlighting the translational significance of the work.

Parameters influencing intestinal epithelial permeability and microparticle uptake in vitro

The hypothesis that, in vivo in situ, villous uptake of 2 microm latex microparticles involves changes at enterocyte tight junctions (TJs) was tested using Caco-2 cells on porous membranes. Epithelial permeability was measured by transepithelial resistance (TER) and particle numbers in surface, intraepithelial and sub-epithelial compartments by microscopy. Apical particle or medium addition initially closed TJs, but this was subsequently reversed in particle-treated groups. Peristaltic onward movement of a bolus was simulated by removing apical particles after an exposure period and leaving the remaining particles to interact with the epithelium: this produced marked TJ loosening during the interaction period. For particle exposure groups, the early similarity with particle numbers in vivo taken up in young adult rats became less marked with time, although bolus removal counteracted this tendency. The TJ response to vasoactive intestinal polypeptide (VIP) was time-dependent. Adsorbed and intraepithelial particle numbers increased with particle exposure time; epithelial-associated microparticle aggregation varied with treatment and submembranous particles were seen in all groups. Correlation between TER changes and particle numbers suggests TJ loosening may be important in microparticle uptake. This Caco-2 model gives epithelial particle numbers that approximate well to published figures for microparticle uptake in vivo and allows effective microenvironmental manipulation.

Factors influencing intestinal microparticle uptake in vivo

The aim of this study is to compare microparticle uptake in animals of different ages, gender and species and at different time points. The 2mum latex/in vivo in situ model uses the observation of animal responses or post-mortem changes and also particle identification by fluorescence microscopy in nine sequential intestinal segments and secondary sites. The wide size range of animals studied requires particle numbers in tissue compartments to be related to intestinal tissue section area through a circumference measurement. Area under the curve (AUC) data for particles in intestinal tissue are plotted against measurements of intestinal length, allowing comparisons to be made across different ages and species and between males and females. The percentage uptake of administered dose and particle numbers in macerated tissue are also reported. Some parameters, in particular species, do not appear to affect the extent of microparticle uptake, which ranges from 0.12 to 0.32% of the administered dose. Particle uptake does, however, vary with age, being significantly greater in young adult males (7 weeks) than in younger (3 weeks) and older (17 and 52 weeks) age groups. It is concluded that age is more important in determining the extent of uptake than gender or species.