Oral targeted drug delivery to post-gastrointestinal sites

As an essential branch of targeted drug delivery, oral targeted delivery is attracting growing attention in recent years. In addition to site-specific delivery for the treatment of locoregional diseases in the gastrointestinal tract (GIT), oral targeted delivery to remote sites beyond the GIT emerges as a cutting-edge research topic. This review aims to provide an overview of the fundamental concepts and most recent advances in this field. Owing to the physiological barriers existing in the GIT, carrier systems should be transported across the enteric epithelia to target remote sites. Recently, pioneer investigations have validated the transport of intact micro- or nanocarriers across gastrointestinal barriers and subsequently to various distal organs and tissues. The microfold (M) cell pathway is the leading mechanism underlying the oral absorption of particulates, but the contribution of the transcellular and paracellular pathways should not be neglected either. In addition to well-acknowledged physicochemical and biological factors, the formation of a protein corona may also influence the biological fate of carrier systems. Although in an early stage of conceptualization, oral targeted delivery to remote diseases has demonstrated promising potential for the treatment of inflammation, tumors, and diseases inflicting the lymphatic and mononuclear phagocytosis systems.

Glucans and applications in drug delivery

Glucan is a natural polysaccharide widely distributed in cereals and microorganisms that has various biological activities, including immunomodulatory, anti-infective, anti-inflammatory, and antitumor activities. In addition to wide applications in the broad fields of food, healthcare, and biomedicines, glucans hold promising potential as drug delivery carrier materials or ligands. Specifically, glucan microparticles or yeast cell wall particles are naturally enclosed vehicles with an interior cavity that can be exploited to carry and deliver drug payloads. The biological activities and targeting capacities of glucans depend largely on the recognition of glucan moieties by receptors such as dectin-1 and complement receptor 3, which are widely expressed on the cell membranes of mononuclear phagocytes, dendritic cells, neutrophils, and some lymphocytes. This review summarizes the chemical structures, sources, fundamental properties, extraction methods, and applications of these materials, with an emphasis on drug delivery. Glucans are utilized mainly as vaccine adjuvants, targeting ligands and as carrier materials for various drug entities. It is believed that glucans and glucan microparticles may be useful for the delivery of both small-molecule and macromolecular drugs, especially for potential treatment of immune-related diseases.

Yeast glucan particles: An express train for oral targeted drug delivery systems

As an emerging drug delivery vehicle, yeast glucan particles (YGPs) derived from yeast cells could be specifically taken up by macrophages. Therefore, these vehicles could rely on the recruitment of macrophages at the site of inflammation and tumors to enable targeted imaging and drug delivery. This review summarizes recent advances in the application of YGPs in oral targeted delivery systems, covering the basic structure of yeast cells, methods for pre-preparation, drug encapsulation and characterization. The mechanism and validation of the target recognition interaction of YGPs with macrophages are highlighted, and some inspiring cases are presented to show that yeast cells have promising applications. The future chances and difficulties that YGPs will confront are also emphasized throughout this essay. YGPs are not only the "armor" but also the "compass" of drugs in the process of targeted drug transport. This system is expected to provide a new idea about the oral targeted delivery of anti-inflammatory and anti-tumor drugs, and furthermore offer an effective delivery strategy for targeted therapy of other macrophage-related diseases.

Serum and lymph pharmacokinetics of nilotinib delivered by yeast glucan particles per os

Nilotinib is a selective tyrosine-kinase inhibitor approved for the treatment of chronic myeloid leukemia. It is poorly soluble in aqueous media and has a low oral bioavailability. Nilotinib encapsulation into yeast glucan particles (GPs) was investigated in this work as a means of increasing bioavailability. The amorphization of nilotinib in GPs resulted in an increased dissolution rate, which was confirmed by in vitro experiments using biorelevant dissolution media. Simultaneously, GPs containing nilotinib were effectively taken up by macrophages, which was quantified in vitro on cell cultures. The overall oral bioavailability in a rat model was approximately 39 % for nilotinib delivered in a reference formulation (Tasigna) and was almost doubled when delivered in GPs. The contribution of glucan particles to the lymphatic transport of nilotinib was quantified. When delivered by GPs, cumulative nilotinib absorption via the lymphatic system increased by a factor of 10.8 compared to the reference, but still represented arelative bioavailability of only 1.12 %. The cumulative uptake of GPs in the lymph was found to be 0.54 mg after a single dose of 50 mg. Yeast glucan particles can therefore serve as a drug delivery vehicle with a dual function: dissolution rate enhancement by amorphization, and, to asmaller extent, lymphatic delivery due to macrophage uptake.

Preparation of whey based savory beverage with enhanced bio-accessible zinc

Zinc is an essential micronutrient for numerous catalytic, structural and regulatory functions in human body. However, its direct fortification in the food matrix poses the challenges of decreased bio-accessibility by forming insoluble sediments. Complexing zinc with polysaccharides has been reported as a possible intervention to address this issue by keeping the zinc in soluble form. Present investigation was undertaken to transform paneer whey containing complexed zinc into a sensorially acceptable beverage by varying its pH from 3.5 to 5.5, common salt concentration from 0.5 to 1.5% and spices concentration at 0.2 and 0.4%. Changes in complexed zinc concentration, apparent viscosity, instrumental color parameters and sensory attributes were determined. Complexed zinc concentration increased (p < 0.05) with increasing pH, decreasing salt and increasing spices concentration. Whey beverage having 4.5 pH, 1.0% salt and 0.4% spices concentration was most preferred by the sensory panelists. In-vitro digestion of optimized whey beverage revealed that bio-accessibility of zinc was significantly higher (p < 0.05) in complex form than free from.

Supplementary Information

The online version contains supplementary material available at 10.1007/s13197-022-05497-y.

Mucoadhesive carriers for oral drug delivery

Among the various dosage forms, oral medicine has extensive benefits including ease of administration and patients' compliance, over injectable, suppositories, ocular and nasal. Despite of extensive demand and emerging advantages, over 50% of therapeutic molecules are not available in oral form due to their physicochemical properties. More importantly, most of the biologics, proteins, peptide, and large molecular drugs are mostly available in injectable form. Conventional oral drug delivery system has limitation such as degradation and lack of stability within stomach due to presence of highly acidic gastric fluid, hinders their therapeutic efficacy and demand more frequent and higher dosing. Hence, formulation for controlled, sustained, and targeted drug delivery, need to be designed with feasibility to target the specific region of gastrointestinal (GI) tract such as stomach, small intestine, intestine lymphatic, and colon is challenging. Among various oral delivery approaches, mucoadhesive vehicles are promising and has potential for improving oral drug retention and controlled absorption to treat local diseases within the GI tract, as well systemic diseases. This review provides the overview about the challenges and opportunities to design mucoadhesive formulation for oral delivery of therapeutics in a way to target the specific region of the GI tract. Finally, we have concluded with future perspective and potential of mucoadhesive formulations for oral local and systemic delivery.

Yeast β-Glucans as Fish Immunomodulators: A Review

Simple Summary

The β-glucan obtained from yeast—a very important molecule for fish production—activates the immune system of fish by different mechanisms and induces protection against pathogens. However, most previous related studies have focused on the use of commercial β-glucan from the yeast Saccharomyces cerevisiae to understand the activation pathways. Experimental β-glucans extracted from other yeasts show other interesting biological activities even at lower doses. This review article analyzes the current information and suggests perspectives on yeast β-glucans.

Abstract

Administration of immunostimulants in fish is a preventive method to combat infections. A wide variety of these biological molecules exist, among which one of the yeast wall compounds stands out for its different biological activities. The β-glucan that forms the structural part of yeast is capable of generating immune activity in fish by cell receptor recognition. The most frequently used β-glucans for the study of mechanisms of action are those of commercial origin, with doses recommended by the manufacturer. Nevertheless, their immune activity is inefficient in some fish species, and increasing the dose may show adverse effects, including immunosuppression. Conversely, experimental β-glucans from other yeast species show different activities, such as antibacterial, antioxidant, healing, and stress tolerance properties. Therefore, this review analyses the most recent scientific reports on the use of yeast β-glucans in freshwater and marine fish.

Biological and Intracellular Fates of Drug Nanocrystals through Different Delivery Routes: Recent Development Enabled by Bioimaging and PK Modeling

Nanocrystals have contributed to exciting improvements in the delivery of poorly water-soluble drugs. The biological and intracellular fates of nanocrystals are currently under debate. Due to the remarkable commercial success in enhancing oral bioavailability, nanocrystals have originally been regarded as a simple formulation approach to enhance dissolution. However, the latest findings from novel bioimaging tools lead to an expanded view. Intact nanocrystals may offer long-term durability in the body and offer drug delivery capabilities like those of other nano-carriers. This review renews the understanding of the biological fates of nanocrystals administered via oral, intravenous, and parenteral (e.g., dermal, ocular, and pulmonary) routes. The intracellular pathways and dissolution kinetics of nanocrystals are explored. Additionally, the future trends for in vitro and in vivo quantification of nanocrystals, as well as factors impacting the biological and intracellular fates of nanocrystals are discussed. In conclusion, nanocrystals present a promising and underexplored therapeutic opportunity with immense potential.

Yeast as carrier for drug delivery and vaccine construction

Yeast has been employed as an effective derived drug carrier as a unicellular microorganism. Many research works have been devoted to the encapsulation of nucleic acid compounds, insoluble small molecule drugs, small molecules, liposomes, polymers, and various nanoparticles in yeast for the treatment of disease. Recombinant yeast-based vaccine carriers (WYV) have played a major role in the development of vaccines. Herein, the latest reports on the application of yeast carriers and the development of related research are summarized, a conceptual description of gastrointestinal absorption of yeast carriers, as well as the various package forms of different drug molecules and nanoparticles in yeast carriers are introduced. In addition, the advantages and development of recombinant yeast vaccine carriers for the disease, veterinary and aquaculture applications are discussed. Moreover, the current challenges and future directions of yeast carriers are proposed.

Mucus Penetrating and Cell-Binding Polyzwitterionic Micelles as Potent Oral Nanomedicine for Cancer Drug Delivery

Orally administrable anticancer nanomedicines are highly desirable due to their easy and repeatable administration, but are not yet feasible because the current nanomedicine cannot simultaneously overcome the strong mucus and villi barriers and thus have very low bioavailability (BA). Herein, this work presents the first polymeric micelle capable of fast mucus permeation and villi absorption and delivering paclitaxel (PTX) efficiently to tumors with therapeutic efficacy even better than intravenously administered polyethylene glycol based counterpart or free PTX. Poly[2-(N-oxide-N,N-diethylamino)ethyl methacrylate] (OPDEA), a water-soluble polyzwitterion, is highly nonfouling to proteins and other biomacromolecules such as mucin but can weakly bind to phospholipids. Therefore, the micelle of its block copolymer with poly(ε-caprolactone) (OPDEA-PCL) can efficiently permeate through the viscous mucus and bind to villi, which triggers transcytosis-mediated transepithelial transport into blood circulation for tumor accumulation. The orally administered micelles deliver PTX to tumors, efficiently inhibiting the growth of HepG2 and patient-derived hepatocellular carcinoma xenografts and triple-negative breast tumors. These results demonstrate that OPDEA-based micelles may serve as an efficient oral nanomedicine for delivering other small molecules or even large molecules.

Oral delivery of proteins and peptides: Challenges, status quo and future perspectives

Proteins and peptides (PPs) have gradually become more attractive therapeutic molecules than small molecular drugs due to their high selectivity and efficacy, but fewer side effects. Owing to the poor stability and limited permeability through gastrointestinal (GI) tract and epithelia, the therapeutic PPs are usually administered by parenteral route. Given the big demand for oral administration in clinical use, a variety of researches focused on developing new technologies to overcome GI barriers of PPs, such as enteric coating, enzyme inhibitors, permeation enhancers, nanoparticles, as well as intestinal microdevices. Some new technologies have been developed under clinical trials and even on the market. This review summarizes the history, the physiological barriers and the overcoming approaches, current clinical and preclinical technologies, and future prospects of oral delivery of PPs.

An update on oral drug delivery via intestinal lymphatic transport

Orally administered drug entities have to survive the harsh gastrointestinal environment, penetrate the enteric epithelia and circumvent hepatic metabolism before reaching the systemic circulation. Whereas the gastrointestinal stability can be well maintained by taking proper measures, hepatic metabolism presents as a formidable barrier to drugs suffering from first-pass metabolism. The pharmaceutical academia and industries are seeking alternative pathways for drug transport to circumvent problems associated with the portal pathway. Intestinal lymphatic transport is emerging as a promising pathway to this end. In this review, we intend to provide an updated overview on the rationale, strategies, factors and applications involved in intestinal lymphatic transport. There are mainly two pathways for peroral lymphatic transport-the chylomicron and the microfold cell pathways. The underlying mechanisms are being unraveled gradually and nowadays witness increasing research input and applications.

The effect of curcumin encapsulation into yeast glucan particles on antioxidant enzyme expression in vitro

Glucan particles (GPs) from Saccharomyces cerevisiae consist mainly of β-1,3-d-glucan. Curcumin is a phenolic compound of plant origin. A 24 h incubation with a mixture of GPs and curcumin increased the expression of the Nrf2 protein and increased the activation of the Nrf2-ARE system significantly.

Polysaccharide dual coating of yeast capsules for stabilization of anthocyanins

The dual coated yeast capsules for anthocyanin encapsulation and stabilization were fabricated. Anthocyanins were preloaded in hollow yeast capsules, and then the dual coating was performed by deposition of opposite charged polysaccharides using layer-by-layer technique. The combination of positively charged chitosan and negatively charged chondroitin sulfate was found to confer the yeast capsules with the highest encapsulation efficiency and retention rate of anthocyanins. Additionally, the coated yeast capsules featured high tolerance to environmental stresses (i.e., oxygen, ascorbic acid, and heat) and therefore effectively inhibited the degradation of anthocyanins. These stabilizing effects were related to the formation of high penetration barrier provided by the double layers of polysaccharides, as well as the enhanced hydrophobic microenvironment in the capsules. Further development of the polysaccharide-coated yeast capsules may hold promise for the controlled delivery of other water-soluble bioactive components.

Targeting strategies of oral nano-delivery systems for treating inflammatory bowel disease

Inflammatory bowel disease (IBD) is a chronic relapsing inflammatory disorder of gastrointestinal tract with rising incidence. Established treatments of IBD are characterized by significantly adverse effects, insufficient therapeutic efficacy. Employing the oral nano-drug delivery systems for targeted therapy is capable of effectively avoiding systematic absorption and increasing local drug concentration, consequently leading to decreased adverse effects and improved therapeutic outcomes. This review gives a brief profile of pathophysiological considerations in terms of developing disease-directed drug delivery systems, then focuses on mechanisms and strategies of current oral nano-drug delivery systems, including size-, enzyme-, redox-, pH-, ligand-receptor-, mucus-dependent systems, and proposes the future directions of managements for IBD.

Incorporating natural anti-inflammatory compounds into yeast glucan particles increases their bioactivity in vitro

Yeast glucan particles (GPs) are promising agents for the delivery of biologically active compounds as drugs. GPs possess their own biological activities and can act synergistically with their cargo. This study aimed to determine how incorporating artemisinin, ellagic acid, (-)-epigallocatechin gallate, morusin, or trans-resveratrol into GPs affects their anti-inflammatory and antioxidant potential in vitro. Two different methods - slurry evaporation and spray drying - were used to prepare composites (GPs + bioactive compound) and the anti-inflammatory and antioxidative properties of the resultant products were compared. Several of the natural compounds showed the beneficial effects of being combined with GPs. The materials prepared by spray drying showed greater activity than those made using a rotary evaporator. Natural compounds incorporated into yeast GPs showed greater anti-inflammatory potential in vitro than simple suspensions of these compounds as demonstrated by their inhibition of the activity of transcription factors NF-κB/AP-1 and the secretion of the pro-inflammatory cytokine TNF-α.

Beta-d-glucan-based drug delivery system and its potential application in targeting tumor associated macrophages

Use of polysaccharides as carriers in drug delivery system is a hot topic, especially those with specific recognition of immune cells, enabling them to be applied in targeting delivery system. β-d-glucans are naturally occurring non-digestible polysaccharides with immunomodulatory activities that have attracted increasing attention to serve as therapeutic agents or immune-adjuvants. Being able to be specifically recognized by immune cells like macrophages, β-d-glucans can be developed as promising carriers for targeting delivery with stability, biocompatibility and specificity when applied in immunotherapy. Targeting tumor associated macrophages (TAMs) is an emerging strategy for cancer immunotherapy since it exerts anti-cancer effects based on modulating body immunity in tumor microenvironment (TME). This new strategy does not require high concentration of drugs to kill cancer cells directly and lessen tumor recurrence by creating unique immune memory for malignant cells. In this review, construction strategies of polysaccharide-based drug delivery system of three types of β-d-glucan including non-yeast and yeast β-d-glucans as well as hyper-branched β-d-glucan are discussed with reference to their branching characteristics and conformation. The applications of these β-d-glucans as nano-carrier for drug delivery targeting TAMs are also discussed.

Bioinspired β-glucan microcapsules deliver FK506 to lymph nodes for treatment of cardiac allograft acute rejection

Lymph node (LN)-targeted delivery exhibits enormous potential to improve the treatment efficacy of immunosuppressants for transplantation. However, current strategies are still limited by the inefficiency of delivery by passive targeting, the high cost of antibody-mediated active targeting, as well as poor patient compliance by parenteral delivery. Herein, bioinspired β-glucan microcapsules (GM) was used to load and transfer low dose FK506 into LNs via oral administration, which may relieve cardiac allograft acute rejection with low nephrotoxicity. The LN distribution study showed that both DiR and FK506 were delivered into the LNs effectively via GM-mediated transport after 24 h and were present in the LNs for at least 48 h. The FK506-loaded GM (GM-FK506) significantly prolonged allograft survival compared with the PBS group (mean survival time, 17.8 ± 1.9 versus 7.3 ± 1.0 days; P < 0.01), and marked decreased the acute rejection grade. Furthermore, T cell infiltration, and secretion of IL-2 and IFN-γ were dramatically reduced in the GM-FK506 group. As expected, no nephrotoxicity was observed after five consecutive administrations of GM-FK506. Our results demonstrate that GM-FK506 is a promising strategy for the treatment of cardiac allograft acute rejection, indicating that GM mediated LNs targeting may provide a potential opportunity for managing immune-related diseases.

Glucan particles as suitable carriers for the natural anti-inflammatory compounds curcumin and diplacone - Evaluation in an ex vivo model

Natural compounds offer a wide spectrum of potential active substances, but often they have a poor bioavailability. To increase the bioavailability and bioactivity of the natural anti-inflammatory molecules curcumin and diplacone, we used glucan particles (GPs), hollow shells from Saccharomyces cerevisiae composed mainly of β-1,3-d-glucan. Their indigestibility and relative stability in the gut combined with their immunomodulatory effects makes them promising carriers for such compounds. This study aimed to determine how curcumin and diplacone, either alone or incorporated in GPs, affect the immunomodulatory activity of the latter by assessing the respiratory burst response and the secretion of pro-inflammatory cytokines by primary porcine innate immune cells. Incorporating curcumin and diplacone into GPs by controlled evaporation of the organic solvent substantially reduced the respiratory burst response mediated by GPs. Incorporated curcumin in GPs also reduced GPs mediated secretion of IL-1β and TNF-α by innate immune cells. The obtained results indicate a potentially beneficial effect of the incorporation of curcumin or diplacone into GPs against inflammation.

A Novel Strategy for Treating Inflammatory Bowel Disease by Targeting Delivery of Methotrexate through Glucan Particles

Therapy of inflammatory bowel disease (IBD) has been a difficult task in the medical field. There is a great clinical need for more effective treatments for IBD. Herein, a targeted oral delivery system of yeast glucan particles (YGPs) carrying a clinically used anti-inflammatory drug methotrexate (MTX) to the inflamed sites in IBD mice for therapy is reported. In the findings, MTX is effectively loaded into YGPs through re-precipitation followed by gelation reaction of alginate to obtain the composite YGPs/MTX, which are internalized into RAW264.7 macrophage cells through dectin-1 and CR3 receptors. Furthermore, YGPs/MTX can suppress the proliferation of macrophage cells efficiently, leading to down-regulation of pro-inflammatory cytokines induced by lipopolysaccharides. Additionally, YGPs accumulate in the inflammation site of colitis mice, enabling YGPs/MTX to target the inflammatory site, significantly improve the efficacy of MTX, and reduce the cytotoxicity of MTX. Therefore, the YGPs-based drug delivery system provides a new strategy for MTX application in the clinical treatment of IBD.

Biomimetic and bioinspired strategies for oral drug delivery

Oral drug delivery remains the most preferred approach due to its multiple advantages. Recently there has been increasing interest in the development of advanced vehicles for oral delivery of different therapeutics. Among them, biomimetic and bioinspired strategies are emerging as novel approaches that are promising for addressing biological barriers encountered by traditional drug delivery systems. Herein we provide a state-of-the-art review on the current progress of biomimetic particulate oral delivery systems. Different biomimetic nanoparticles used for oral drug delivery are first discussed, mainly including ligand/antibody-functionalized nanoparticles, transporter-mediated nanoplatforms, and nanoscale extracellular vesicles. Then we describe bacteria-derived biomimetic systems, with respect to oral delivery of therapeutic proteins or antigens. Subsequently, yeast-derived oral delivery systems, based on either chemical engineering or bioengineering approaches are discussed, with emphasis on the treatment of inflammatory diseases and cancer as well as oral vaccination. Finally, bioengineered plant cells are introduced for oral delivery of biological agents. A future perspective is also provided to highlight the existing challenges and possible resolution toward clinical translation of currently developed biomimetic oral therapies.

Curcumin encapsulation in yeast glucan particles promotes its anti-inflammatory potential in vitro

Glucan particles (GPs) from Saccharomyces cerevisiae are hollow shells that are composed mainly of β-1,3-d-glucan, which has demonstrated immunomodulatory and anti-inflammatory potential both in vitro and in vivo. Curcumin is a natural hydrophobic phenolic compound, which possesses a significant anti-inflammatory effect and is used as supportive therapy in the treatment of many inflammatory diseases. The aim of this study is to evaluate the possible synergic effect and other benefits of the co-application of GPs and curcumin in the form of pharmaceutical composites. GP/curcumin composites were prepared using controlled evaporation of the organic solvent and their anti-oxidative effect and anti-inflammatory potential were tested on THP1‑XBlue™‑MD2‑CD14 human monocytes cell line. The anti-oxidative effect was measured on pyocyanin-stimulated cells in vitro and the NF-κB/AP-1 signaling pathway on lipopolysaccharide pre-treated monocytes was chosen for anti-inflammatory assays. The secretion of pro-inflammatory cytokines TNF-α and IL-1β was evaluated as well. Results mostly showed a pro-oxidative activity of empty GPs, however, pharmaceutical composites demonstrated an anti-oxidative effect. The activity of NF-κB/AP-1 was substantially decreased by the tested GP/curcumin composites, which also caused the attenuation of cytokines secretion. The obtained results indicate a beneficial effect of the incorporation of curcumin into GPs.

Towards more accurate bioimaging of drug nanocarriers: turning aggregation-caused quenching into a useful tool

One of the current challenges in the monitoring of drug nanocarriers lies in the difficulties in discriminating the carrier-bound signals from the bulk signals of probes. Environment-responsive probes that enable signal switching are making steps towards a solution to this problem. Aggregation-caused quenching (ACQ), a phenomenon generally regarded as unfavorable in bioimaging, has turned out to be a promising characteristic for achieving environment-responsiveness and eliminating free-probe interference. So-called ACQ probes emit fluorescence when dispersed molecularly within the carrier matrix but quench immediately and absolutely once they are released into the ambient aqueous environment upon the degradation of the nanocarriers. Therefore, the fluorescence observed represents integral nanocarriers. Based on this rationale, the in vivo fates of various nanocarriers have been explored using live imaging equipment, with very interesting findings revealing the role of the particles. The current applications are however restricted to nanocarriers with highly hydrophobic matrices (lipid or polyester nanoparticles) or with a hydrophobic core-hydrophilic shell structure (micelles). The ACQ-based bioimaging strategy is emerging as a promising tool to achieve more accurate bioimaging of drug nanocarriers. This review article provides an overview of the ACQ phenomenon and the rationale for and examples of applications, as well as the limitations of the ACQ-based strategy, with a focus on improving the accuracy of bioimaging of nanoparticles.

Hybrid drug nanocrystals

Nanocrystals show promise to deliver poorly water-soluble drugs to yield systemic exposure. However, our knowledge regarding the in vivo fate of nanocrystals is in its infancy, as nanocrystallization is simply viewed as an approach to enhance the dissolution of drug crystals. The dying crystal phenomenon inspired the development of hybrid nanocrystals by physically embedding fluorophores into the crystal lattice. This approach achieved concurrent therapy and bioimaging and is well-established to study pharmacokinetics and nanocrystal dissolution in vivo. Nanocrystals also offer the advantage of long-term durability in the body for interacting with biological tissues and cells. This review introduces the hybrid nanocrystal technique, including the theoretical concepts, preparation, and applications. We also discuss the latest development in self-discriminative hybrid nanocrystals utilizing environment-responsive probes. This review will stimulate further development and application of nanocrystal-based drug delivery systems for theranostic strategies.

Bioimaging of Intact Polycaprolactone Nanoparticles Using Aggregation-Caused Quenching Probes: Size-Dependent Translocation via Oral Delivery

The limited information on biological fate impedes the development of more efficient polymeric nanoparticles for oral delivery of bio-macromolecules. In this study, the in vivo fate as well as the trans-epithelia transport of polycaprolactone (PCL) nanoparticles is explored by labeling with aggregation-caused quenching probes, which is capable of identifying intact nanoparticles. Live imaging and confocal laser scan microscopy confirm size-dependent absorption of PCL nanoparticles. In general, reducing particle size favors a faster and more oral absorption. Nanoparticles larger than 200 nm, such as 600 and 2000 nm, cannot be efficiently transported across the intestinal membrane. The absorbed nanoparticles (50 and 200 nm) mainly accumulate in the liver. Lymph may be the main absorption route for PCL nanoparticles, transporting 2.39 ± 1.81% and 0.98 ± 0.58% of administered 50 and 200 nm nanoparticles, respectively. Cellular uptake and transportation of PCL nanoparticles are also size dependent. Both enterocytes and M cells mediated transcytosis are involved in the transport of 50 nm PCL nanoparticles, while the M cell pathway is dominative for other nanoparticles. In conclusion, the study provides a valuable tool for bioimaging of intact polymeric nanoparticles as well as solid evidence supporting size-dependent translocation of the nanoparticles via oral delivery.

Loss of integrity of doxorubicin liposomes during transcellular transportation evidenced by fluorescence resonance energy transfer effect

The aim of this work was to elucidate the influence of liposome characteristics on the transcellular process by in vitro studies that would enable designing more efficient oral formulations. Various liposomes with different properties were prepared, including 100-500 nm, anionic, cationic and PEGylated liposomes. All liposomes were labeled by fluorescence resonance energy transfer (FRET) probes to evaluate their integrity in cellular uptake and transport. The FRET fluorescent intensity is proportional to the amount of intact liposomes, which was used to calculate the amount of intact liposomes in cellular uptake and transport. The liposomal structures were found to lose their integrity during or after uptake and only about 20% intact liposomes were detected in cells. However, more cationic liposomes were transported integrally across cell monolayer and accounted for 40.49% of total transport by triple culture models of Caco-2/HT29-MTX/Raji B. These results suggest that liposomes could improve cellular uptake and transport of the payloads significantly, but only a small fraction of liposomes are transported integrally across epithelial monolayer. The study is therefore helpful to rationally fabricate more efficient oral liposomes for poorly water-soluble drugs or biomacromolecules.

Reassessment of long circulation via monitoring of integral polymeric nanoparticles justifies a more accurate understanding

Monitoring of payloads results in a biased perception of long circulation of nanoparticles. Instead, herein, the long-circulation effect was re-confirmed by monitoring integral nanoparticles, but circulation was not found to be as long as generally perceived. In contrast, disparate pharmacokinetics were obtained by monitoring a model drug, paclitaxel, highlighting the bias of the conventional protocol.

Visual validation of the measurement of entrapment efficiency of drug nanocarriers

Entrapment efficiency (EE) is a crucial parameter for the evaluation of nanocarriers. The accurate measurement of EE demands clear separation of nanocarriers from free drugs, which so far has not been clearly validated due to a lack of functional tools to identify nanocarriers. Herein, an environment-responsive water-quenching fluorophore was employed to label and identify model nanocarriers, polycaprolactone nanoparticles (PN), methoxy polyethylene glycol-poly(d,l-lactic acid) polymeric micelles (PM) and solid lipid nanoparticles (SLN). The separation process of three commonly used methods (centrifugation, ultrafiltration and gel permeation chromatography) was visualized by live imaging. The separation efficiency of the centrifugation method is very poor, especially for PM (40 nm), SLN (100 nm) and PN (100 nm); only PN (200 nm) can be efficiently separated but at a consumption of enormous energy. The ultrafiltration method shows the best separation efficiency with only 0.32-0.93% of leakage of the nanocarriers. Gel permeation chromatography exhibits good separation as well but suffers from low recovery, a potential factor that might compromise the accuracy of EE measurement. In conclusion, the ultrafiltration method is the method of choice for efficient separation and accurate measurement of EE.

Biomimetic thiamine- and niacin-decorated liposomes for enhanced oral delivery of insulin

Biomimetic nanocarriers are emerging as efficient vehicles to facilitate dietary absorption of biomacromolecules. In this study, two vitamins, thiamine and niacin, are employed to decorate liposomes loaded with insulin, thus facilitating oral absorption via vitamin ligand-receptor interactions. Both vitamins are conjugated with stearamine, which works to anchor the ligands to the surface of liposomes. Liposomes prepared under optimum conditions have a mean particle size of 125-150 nm and an insulin entrapment efficiency of approximately 30%-36%. Encapsulation into liposomes helps to stabilize insulin due to improved resistance against enzymatic disruption, with 60% and 80% of the insulin left after 4 h when incubated in simulated gastric and intestinal fluids, respectively, whereas non-encapsulated insulin is broken down completely at 0.5 h. Preservation of insulin bioactivity against preparative stresses is validated by intra-peritoneal injection of insulin after release from various liposomes using the surfactant Triton X-100. In a diabetic rat model chemically induced by streptozotocin, both thiamine- and niacin-decorated liposomes showed a comparable and sustained mild hypoglycemic effect. The superiority of decorated liposomes over conventional liposomes highlights the contribution of vitamin ligands. It is concluded that decoration of liposomes with thiamine or niacin facilitates interactions with gastrointestinal vitamin receptors and thereby facilitates oral absorption of insulin-loaded liposomes.

Self-discriminating fluorescent hybrid nanocrystals: efficient and accurate tracking of translocation via oral delivery

The in vivo fate of nanocrystals is a controversial topic, i.e. dissolving versus integral absorption through the intestinal membrane. This is due to the lack of functional strategies to identify integral nanocrystals. In this study, the in vivo fate of quercetin hybrid nanocrystals (QT-HNCs) via the oral route is explored by physically embedding an environment-responsive probe in the crystal lattices of quercetin. The specific property of the probe is the water-initiated aggregation-caused quenching (ACQ) ability, by which integral QT-HNCs can be self-discriminated. Instead of dissolving instantly, QT-HNCs can be retained in the gastrointestinal tract for 12-16 h, and can then be absorbed and distributed into various organs with the liver as the primary terminal. The ileum provides better absorption than the jejunum. Cellular studies prove that both trans-epithelial and M cell-mediated routes are involved in the absorption of integral QT-HNCs, which may be impeded by the mucous layer. Moreover, the particle size affects the in vivo behavior and the ex vivo cellular interaction of QT-HNCs, with moderate size, such as 550 nm, being preferred. The results not only validate the idea of using ACQ fluorophores for bioimaging of integral nanocrystals but also support the intestinal absorption of nanocrystals.

Influence of Particle Geometry on Gastrointestinal Transit and Absorption following Oral Administration

Geometry has been considered as one of the important parameters in nanoparticle design because it affects cellular uptake, transport across the physiological barriers, and in vivo distribution. However, only a few studies have been conducted to elucidate the influence of nanoparticle geometry in their in vivo fate after oral administration. This article discloses the effect of nanoparticle shape on transport and absorption in gastrointestinal (GI) tract. Nanorods and nanospheres were prepared and labeled using fluorescence resonance energy transfer molecules to track the in vivo fate of intact nanoparticles accurately. Results demonstrated that nanorods had significantly longer retention time in GI tract compared with nanospheres. Furthermore, nanorods exhibited stronger ability of penetration into space of villi than nanospheres, which is the main reason of longer retention time. In addition, mesenteric lymph transported 1.75% nanorods within 10 h, which was more than that with nanospheres (0.98%). Fluorescent signals arising from nanoparticles were found in the kidney but not in the liver, lung, spleen, or blood, which could be ascribed to low absorption of intact nanoparticles. In conclusion, nanoparticle geometry influences in vivo fate after oral delivery and nanorods should be further investigated for designing oral delivery systems for therapeutic drugs, vaccines, or diagnostic materials.

Size-Dependent Translocation of Nanoemulsions via Oral Delivery

The in vivo translocation of nanoemulsions (NEs) was tracked by imaging tools with an emphasis on the size effect. To guarantee the accurate identification of NEs in vivo, water-quenching environment-responsive near-infrared fluorescent probes were used to label NEs. Imaging evidence confirmed prominent digestion in the gastrointestinal tract and oral absorption of integral NEs that survive digestion by enteric epithelia in a size-dependent way. In general, reducing particle size leads to slowed in vitro lipolysis and in vivo digestion, a prolonged lifetime in the small intestine, increased enteric epithelial uptake, and enhanced transportation to various organs. Histological examination revealed a pervasive distribution of smaller NEs (80 nm) into enterocytes and basolateral tissues, whereas bigger ones (550, 1000 nm) primarily adhered to villi surfaces. Following epithelial uptake, NEs are transported through the lymphatics with a fraction of approximately 3-6%, suggesting a considerable contribution of the lymphatic pathway to overall absorption. The majority of absorbed NEs were found 1 h post administration in the livers and lungs. A similar size dependency of cellular uptake and transmonolayer transport was confirmed in Caco-2 cell lines as well. In conclusion, the size-dependent translocation of integral NEs was confirmed with an absolute bioavailability of at least 6%, envisioning potential applications in oral delivery of labile entities.

Size-dependent penetration of nanoemulsions into epidermis and hair follicles: implications for transdermal delivery and immunization

Nanoemulsions have been widely applied to dermal and transdermal drug delivery. However, whether and to what depth the integral nanoemulsions can permeate into the skin is not fully understood. In this study, an environment-responsive dye, P4, was loaded into nanoemulsions to track the transdermal translocation of the nanocarriers, while coumarin-6 was embedded to represent the cargoes. Particle size has great effects on the transdermal transportation of nanoemulsions. Integral nanoemulsions with particle size of 80 nm can diffuse into but not penetrate the viable epidermis. Instead, these nanoemulsions can efficiently fill the whole hair follicle canals and reach as deep as 588 μm underneath the dermal surfaces. The cargos are released from the nanoemulsions and diffuse into the surrounding dermal tissues. On the contrary, big nanoemulsions, with mean particle size of 500 nm, cannot penetrate the stratum corneum and can only migrate along the hair follicle canals. Nanoemulsions with median size, e.g. 200 nm, show moderate transdermal permeation effects among the three-size nanoemulsions. In addition, colocalization between nanoemulsions and immunofluorescence labeled antigen-presenting cells was observed in the epidermis and the hair follicles, implying possible capture of nanoemulsions by these cells. In conclusion, nanoemulsions are advantageous for transdermal delivery and potential in transcutaneous immunization.

Evidence of nose-to-brain delivery of nanoemulsions: cargoes but not vehicles

The nose-to-brain pathway has been proven to be a shortcut for direct drug delivery to the brain. However, whether and to what extent nanoparticles can be delivered through this passage is still awaiting validation with evidence. In this study, nose-to-brain transportation of nanoparticles is tracked via fluorescence bioimaging strategies using nanoemulsions (NEs) as model carriers. Identification of NEs in biological tissues is based on the on → off signal switching of a new type of environment-responsive embedded dyes, P2 and P4, and two conventional probes, DiR and coumarin-6 (C6), are embedded to represent the cargoes. Evidence for the translocation of NEs was collected either via live imaging or ex vivo histological examination in rats after nasal administration. Results suggest that NEs with a particle size of about 100 nm, either naked or coated with chitosan, have longer retention duration in nostrils and slower mucociliary clearance than larger ones. P2 signals, representing integral NEs, can be found in mucosa and trigeminal nerves for all size groups, whereas only weak P2 signals are detected in the olfactory bulb for chitosan-coated NEs of 100 nm. Confocal microscopy further confirms the translocation of integral 100 nm NEs in nasal mucosa and along the trigeminal nerve in decremental intensity. Weak signals of the P4 probe, also representing integral NEs, can be detected in the olfactory bulb but few in the brain. NEs as large as 900 nm cannot be transported to the olfactory bulb. However, the DiR or C6 signals that represent the cargoes can be found in significant amounts along the nose-to-brain pathway and finally reach the brain. Evidence shows that integral NEs can be delivered to the olfactory bulb, but few to the brain, whereas the cargoes can be released and permeated into the brain in greater amounts.

Uptake of intraperitoneally administrated triple helical β-glucan for antitumor activity in murine tumor models

Triple helical β-glucan (THG) was captured by macrophages and degraded into small fragments to activate neutrophils, leading to apoptosis of tumor cells.

Bioimaging of nanoparticles: the crucial role of discriminating nanoparticles from free probes

The biological fate of nanocarriers has yet to be fully explored, mainly because of the lack of functional tools like probes to identify integral nanocarriers in the body. Understanding their in vivo fate remains as the bottleneck to the development of nanomedicines. Bioimaging results based on conventional fluorescent or radioactive probes should be judged critically because images merely reflect bulk signals of an admixture of the nanoparticles and free probes. It is crucial to discriminate between nanocarrier-bound and free signals. This review analyzes the state-of-the-art of bioimaging of nanoparticles in vivo and highlights directions for future endeavours.

Glucan microparticles thickened with thermosensitive gels as potential carriers for oral delivery of insulin

Although glucan microparticles (GMs) can be efficiently taken up and transported by M cells, their subsequent accumulation in lymphatic tissues of sub-follicle-associated epithelia (FAE) in Peyer's patches might present a barrier to the oral delivery of insulin by GMs into the systemic circulation. The goal of this study is to weigh the potential of GMs as carriers for oral delivery of systemic therapeutics using insulin (INS) as a model drug. INS is encapsulated into the inner cavities of GMs by repeated soaking in INS solution at acidic pH values and switching to an isoelectric pH of 5.6 to precipitate INS. To immobilize INS, a thermosensitive poloxamer 407 (P407) gel is introduced into the interior of GMs. Interiorly thickened GMs show significantly decreased in vitro release and well protected INS stability against enzyme-enriched media, highlighting the importance of thickening with P407 gels. A mild and prolonged hypoglycaemic effect is achieved in both normal and diabetic rats for a duration of at least 20 h with pharmacological bioavailability as high as about 9-10%. Lymphatic transportation of GMs is investigated by labelling with a near-infrared water-quenching fluorescent probe in a conscious mesentery lymphatic duct cannulation rat model following oral administration. GMs appear in lymph within the first 2 h, peak at around 6 h and slow down after 10 h with a cumulative amount of over 8% in 24 h. The high correlation between lymphatic transportation and pharmacological bioavailability implies that GMs are principally absorbed via the lymphatic route. An in vitro study on phagocytosis by macrophages confirms the easy and fast uptake of GMs by J774A.1 cell lines with as many as over 10 particles within the cytoplasm of a single cell. Intracellular pharmacokinetics indicates robustness and persistent residence of GMs within the cells. Little effect on cell viability and tight junctions was observed in Caco-2 cell models. It is concluded that GMs are mainly absorbed via the lymphatic route and show potential as carriers for oral delivery of labile therapeutics, though with limited bioavailability due to the sub-FAE residence barriers.