Haisheng He

Environment-responsive aza-BODIPY dyes quenching in water as potential probes to visualize the in vivo fate of lipid-based nanocarriers

UNLABELLED Environment-responsive near-infrared (NIR) aza-BODIPY dyes capable of fluorescence quenching in water were explored to visualize the in vivo fate of model lipid-based nanocarriers, solid lipid nanoparticles (SLNs). The water-quenching effect of the dyes was confirmed to be sensitive and remained stable for at least 24h. In vitro lipolysis measured by fluorescence quenching completed within 20min, which was in correlation with alkaline compensation results. In vivo live imaging indicated predominant digestion of SLNs within 2h and complete digestion within 4h, which correlated well to in vitro data. Rekindling of quenched dyes by mixed micelles was observed in vitro, but not in vivo. In sharp contrast, SLNs encapsulating another NIR dye DiR showed persistent fluorescence both in vitro and in vivo despite significant lipolysis. It was envisaged that water-quenching fluorescence dyes can be used as probes to monitor the in vivo fate of lipid-based nanocarriers. FROM THE CLINICAL EDITOR Lipid-based drug delivery systems can provide an excellent nanocarrier platform for the delivery of poorly water-soluble drugs. Nonetheless, the mechanism of oral absorption and subsequent kinetics is poorly understood. In this article, the authors studied the novel use of near-infrared (NIR) aza-BODIPY dyes to visualize the fate of these lipid-based nanocarriers. The positive finding means that this approach may be useful for in-vivo monitoring of lipid-based nanocarriers.

Tracking translocation of glucan microparticles targeting M cells: implications for oral drug delivery

Taking advantage of its ability to deal with exogenous pathogens, the M cell passage has proven to be the most reliable pathway for entry of particulates, thus creating opportunities for oral immunization and delivery of biomacromolecules. Albeit a well-known story, the underlying mechanisms of this pathway are not yet well understood, especially concerning direct evidence of translocation of particulates. Herein, model glucan microparticles (GMs) targeting M cells are employed to track translocation through M cell pathways as well as to various organs via the systemic circulation. GMs were first labeled with a novel kind of near-infrared fluorescent water-quenching probe through encapsulation and locking by stearin. In vivo live imaging indicates prolonged residence of GMs in the gastrointestinal tract for as long as 12 h. GMs are found to be gradually absorbed from the ligated ileum segment but little from the jejunum. Histological examination using confocal laser scanning microscopy (CLSM) confirms distribution of GMs to the basolateral side of the ileum through Peyers patches. However, no detectable fluorescence can be observed in any other organs or tissues until 12 h after administration. After 12 h, GMs can be found in the liver, spleen and lung. At 24 h, GMs accumulate in these organs with approximately 2.3% of the total amount. Repeated administration for three consecutive days augments total accumulation to as high as 4.5%. By tracking GM-bound fluorescence, the particles can be accurately located in these organs. GMs can be transported across Caco-2/Raji and Caco-2/Raji/J774A.1 co-culture monolayers, but not Caco-2 monolayers, in a time-dependent manner. As observed by CLSM, GMs can be voraciously engulfed with as many as 10-15 particles per cell. Evidence of translocation of GMs indicates that GMs can be absorbed through the M cell pathway located at Peyers patches, especially in the ileum, and translocated to reticulo-endothelial organs.

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 Peyers 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.

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.

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.

In vivo fate of lipid-silybin conjugate nanoparticles: Implications on enhanced oral bioavailability

Lipid-drug conjugates (LDCs) of a poorly soluble and poorly permeable drug silybin (SB) and lipids with different chain lengths (6C, 12C, 18C) are synthesized and formulated into solid lipid nanoparticles (SLNs). The in vivo fate of LDCs as well as SLNs is investigated by tracking either SB or LDCs or SLNs. LDCs are prone to be hydrolyzed by lipases either in simulated gastrointestinal media or in Caco-2 cell lines in a lipid chain length-dependent mode. The oral bioavailability of SB is enhanced by 5-7-fold in comparison with a fast-release formulation. No integral LDCs are detected in plasma confirms the readily degradable nature of LDCs. The absorption of LDCs by enteric epithelia and subsequent transportation into circulation might play a leading role in absorption enhancement, whereas the contribution of then M-cell pathway is not as remarkable. A shorter lipid chain favors earlier lipolysis and faster absorption along the intestine-to-circulation path.

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.

An update on the role of nanovehicles in nose-to-brain drug delivery

A quantitative analysis has cast doubt over the limited advantages provided by particles for nose-to-brain (NTB) drug delivery. Thus, it is imperative to identify the role of nanovehicles in NTB drug delivery. If nanocarriers are used merely as an option to improve various properties of the drugs or the formulations, it is difficult for them to outperform conventional formulations, such as solutions or gels. However, nanovehicles bring about special features, such as maintenance of the solubilized state of drugs, sustained or delayed release, and enhanced penetration because of surface modifications, all of which lead to enhanced NTB delivery efficiency.

Adapting liposomes for oral drug delivery

Liposomes mimic natural cell membranes and have long been investigated as drug carriers due to excellent entrapment capacity, biocompatibility and safety. Despite the success of parenteral liposomes, oral delivery of liposomes is impeded by various barriers such as instability in the gastrointestinal tract, difficulties in crossing biomembranes, and mass production problems. By modulating the compositions of the lipid bilayers and adding polymers or ligands, both the stability and permeability of liposomes can be greatly improved for oral drug delivery. This review provides an overview of the challenges and current approaches toward the oral delivery of liposomes.

Visual validation of the measurement of entrapment efficiency of drug nanocarriers

Graphical abstract Figure. No caption available. ABSTRACT 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.