The in vivo fate of nanocrystals

Fabrication of ultra-small nanocrystals by formation of hydrogen bonds: In vitro and in vivo evaluation

Poor water solubility and low bioavailability hinder the clinical application of about 70% of newly synthesized compounds. Nanocrystal technology has become a preferred way to improve bioavailability by improving solubility. However, it remains challenging to produce nanocrystals with ultra-small particle sizes to further enhance the extent of bioavailability. Herein, we constructed ultra-small puerarin nanocrystals (Pue-NCs) (20-40 nm) via formation of hydrogen bond during HPH. We confirmed the formation of hydrogen bonds by ¹H NMR and FTIR, and observed the distribution of polymer chains by SEM and TEM. The absorption mechanisms were studied in Caco-2 cell monolayers, and the results showed that the major transport mechanism for puerarin was passive diffusion, meanwhile, for Pue-NCs, the passive transport and micropinocytosis-mediated endocytosis coexisted. The absolute bioavailability of Pue-NCs was 35.28%, which was 11.54 folds compared to that of puerarin. Therapeutic equivalence was demonstrated between Pue-NCs and puerarin injection at 50 mg/kg and 15 mg/kg, respectively, in isoproterenol-induced myocardial ischemia model. This study provides a novel strategy for preparing ultra-small nanocrystals by HPH to increase bioavailability of poorly soluble drugs.

Ionic liquids: green and tailor-made solvents in drug delivery

Beyond their traditional use as green solvents, new applications have become available for ionic liquids (ILs) in drug delivery. Their flexible tunability enables task-specific optimization of ILs at molecular level. Thus, ILs have been exploited to improve the solubility and permeability of drugs and relieve the polymorphic problems associated with crystalline active pharmaceutical ingredients (APIs). Controlled preparation of drug nanocarriers are also achieved by using ILs either as media or as functional agents. Here, we highlight the importance and advantages of ILs in pharmaceutics and look towards the future of IL-based drug delivery.

"Locked" cancer cells are more sensitive to chemotherapy

The treatment of metastatic cancer is a great challenging issue throughout the world. Conventional chemotherapy can kill the cancer cells and, whereas, would exacerbate the metastasis and induce drug resistance. Here, a new combinatorial treatment strategy of metastatic cancer was probed via subsequentially dosing dual nanomedicines, marimastat-loaded thermosensitive liposomes (MATT-LTSLs) and paclitaxel nanocrystals (PTX-Ns), via intravenous and intratumoral injection. First, the metastasis was blocked and cancer cells were locked in the tumor microenvironment (TME) by delivering the matrix metalloproteinase (MMP) inhibitor, MATT, to the tumor with LTSLs, downregulating the MMPs by threefold and reducing the degradation of the extracellular matrix. And then, the "locked" cancer cells were efficiently killed via intratumoral injection of the other cytotoxic nanomedicine, PTX-Ns, along with no metastasis and 100% inhibition of tumor growth. This work highlights the importance of the TME's integrity in the chemotherapy duration. We believe this is a generalized strategy for cancer treatment and has potential guidance for the clinical administration.

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.

Drug nanocrystals: Fabrication methods and promising therapeutic applications

The drug nanocrystals (NCs) with unique physicochemical properties are now considered as a promising drug delivery system for poorly water-soluble drugs. So far >20 formulations of NCs have been approved in the market. In this review, we summarized recent advances of NCs with emphasis on their therapeutic applications based on administration route and disease states. At the end, we present a brief description of the future perspectives of NCs and their potential role as a promising drug delivery system. As a strategy for solubilization and bioavailability enhancement, the NCs have gained significant success. Besides this, the function of NCs is still far from developed. The emerging NC-based drug delivery approach would widen the applications of NCs in drug delivery and bio-medical field. Their in vitro and in vivo fate is extremely unclear; and the development of hybrid NCs with environment-sensitive fluorophores may assist to extend the scope of bio-imaging and provide better insight to their intracellular uptake kinetics, in vitro and in vivo.

Novel redispersible nanosuspensions stabilized by co-processed nanocrystalline cellulose-sodium carboxymethyl starch for enhancing dissolution and oral bioavailability of baicalin

BACKGROUND

To improve the dissolution and bioavailability of poorly soluble drugs, novel nanosuspensions using co-processed nanocrystalline cellulose-sodium carboxymethyl starch (NCCS) as a synergetic stabilizer were first designed.

METHODS

Co-processed NCCS was prepared by means of homogenization. Poorly soluble baicalin (BCA) was used as a model drug. BCA nanosuspension (BCA-NS/NCCS) using co-processed NCCS as a dispersant was prepared via homogenization and further converted into the dried BCA nanosuspension particle (BCA-NP/NCCS) via spray drying. The influence of NCCS on the dispersion efficiency of BCA-NS/NCCS was investigated. Morphology and crystal characteristic of NCCS and BCA-NP were analyzed. The dissolution and bioavailability evaluation were performed to investigate the feasibility of NCCS as a stabilizer for BCA-NS/NCCS and BCA-NP.

RESULTS

The optimum 50% concentration of NCCS (nanocrystalline cellulose [NCC]:sodium carboxymethyl starch [SCS]=60:40) could be mostly beneficial for formation and stability of BCA-NS/NCCS. NCCS could completely prevent aggregation of BCA-NP during spray drying and enhance the redispersibility as well as dissolution of spray-dried BCA-NP, which might be attributed to "brick-concrete"-based barrier effect of NCCS and the swelling capacity of superdisintegrant SCS. The crystal state of NCC and BCA presented in BCA-NP/NCCS remained unchanged during the homogenization. The BCA-NP/NCCS exhibited a fast dissolution rate and significantly enhanced bioavailability of BCA. The AUC(0-∞) of the BCA-NP/NCCS (8,773.38±718.18 µg/L·h) was 2.01 times (P<0.05) as high as that of the crude BCA (4,354.61±451.28 µg/L·h).

CONCLUSION

This study demonstrated that novel surfactant-free nanosuspensions could be prepared using co-processed NCCS as a synergetic stabilizer and also provided a feasible strategy to improve the dissolution and oral bioavailability of poorly soluble drug.

Nanocrystals: A perspective on translational research and clinical studies

Poorly soluble small molecules typically pose translational hurdles owing to their low solubility, low bioavailability, and formulation challenges. Nanocrystallization is a versatile method for salvaging poorly soluble drugs with the added benefit of a carrier-free delivery system. In this review, we provide a comprehensive analysis of nanocrystals with emphasis on their clinical translation. Additionally, the review sheds light on clinically approved nanocrystal drug products as well as those in development.

Development of carrier-free nanocrystals of poorly water-soluble drugs by exploring metastable zone of nucleation

There has been increasing interest in research and development of nanocrystals for the delivery of poorly water-soluble drugs that can be directly produced from solution. Compared with traditional carrier-based or encapsulation designs, drug nanocrystals circumvent possible side-effects due to carrier polymers and poor stability issues associated with encapsulation. The production of carrier-free nanocrystals requires careful control of nucleation and thus a thorough understanding of the relevant solution's metastable zone. A solution may stay supersaturated without forming any nuclei and become metastable. The maximal degree of supersaturation is known as the metastable zone width. When nucleation is triggered directly from the metastable zone, it helps to produce homogeneous nuclei leading to uniform nanocrystals. Herein, we report a study in which the solubility and metastable limit of paclitaxel (PTX) in ethanol aqueous solution were measured at 40 °C. A wide range of metastable compositions were studied to prepare carrier-free PTX nanocrystals with particle size smaller than 250 nm and PDI less than 0.25. Compared with the raw material, dissolution rate of PTX nanocrystals was significantly increased. The study enables production of high-quality drug nanocrystals for treating patients.

Novel breviscapine nanocrystals modified by panax notoginseng saponins for enhancing bioavailability and synergistic anti-platelet aggregation effect

Breviscapine (BVP) is a flavonoid compound with strong neuroprotective and anti-platelet aggregation effect. The objective of this study is to design novel BVP nanocrystals modified by natural panax notoginseng saponins (PNS) for enhancing dissolution and anti-platelet aggregation effect of BVP. BVP nanocrystals modified by PNS (BVP-NC/PNS) were firstly prepared by coupling homogenization technology and freeze-drying technology, and BVP nanocrystals modified by RH40 (BVP-NC/RH40) as reference for comparison. The morphology, crystals characterization, dissolution behavior and anti-platelet aggregation effect of BVP-NC/PNS was systemically evaluated. The results demonstrated that the PNS could effectively maintain stability of BVP-NC at suspensions state dependent of its surface activity and the electrostatic repulsion effect. Combination of PNS and trehalose could prevent the aggregation of BVP-NC/PNS during freeze-drying. The PXRD and DSC results demonstrated that the BVP crystal state in BVP-NC/PNS was not changed owing to PNS modification and homogenization treatment. And the freeze-dried BVP-NC could easily recover back to BVP-NS and significantly improve the dissolution of BVP. The AUC_(0-∞) of the BVP-NC/PNS was 4.54 times as high as that of the coarse BVP, but not significantly different compared to that of BVP-NC/RH40 (p < 0.05). The anti-platelet aggregation results demonstrated that, BVP-NC/PNS group showed more effective inhibition on PAF-induced platelet aggregation compared with corresponding control groups, which might attribute to the enhanced bioavailability of BVP and synergistic effect of PNS with BVP. In conclusion, PNS could be used as an alternative stabilizer for preparation of BVP-NC, and BVP-NC modified by PNS is a promising formulation strategy for enhancing oral bioavailability and anti-platelet aggregation of BVP.

Amorphous Nanosuspensions Aggregated from Paclitaxel⁻Hemoglobulin Complexes with Enhanced Cytotoxicity

Amorphous nanosuspensions (ANSs) enable rapid release and improved delivery of a poorly water-soluble drug; however, their preparation is challenging. Here, using hemoglobin (Hb) as a carrier, ANSs aggregated from paclitaxel (PTX)⁻Hb complexes were prepared to improve delivery of the hydrophobic anti-cancer agent. An affinity study demonstrated strong interaction between Hb and PTX. Importantly, the complexes could aggregate into <300 nm ANSs with high drug loading, which acidic condition facilitated their formation. Furthermore, the ANSs possessed improved cytotoxicity against cancer cells over the crystalline nanosuspensions. Taken together, ANSs aggregated from PTX⁻Hb complexes were developed, which could kill cancer cells with high efficiency.

A drug-delivering-drug strategy for combined treatment of metastatic breast cancer

Treatment of metastatic cancer continues to be a huge challenge worldwide. Notably, drug nanocrystals (Ns) in nanosuspensions clearly belong to a type of nanoparticle. Therefore, a question arose as to whether these drug particles can also be applied as carriers for drug delivery. Here, we design a novel paclitaxel (PTX) nanocrystal stabilized with complexes of matrix metalloproteinase (MMP)-sensitive β-casein/marimastat (MATT) for co-delivering MATT and PTX and combined therapy of metastatic breast cancer. The prepared Ns (200 nm) with a drug-loading of >50% were potent in treatment of metastatic cancer, which markedly inhibited MMP expression and activity and greatly blocked the lung metastasis and angiogenesis. In conclusion, employing protein-drug complexes as stabilizers, Ns with dual payloads are developed and are a promising strategy for co-delivery. Furthermore, the developed Ns can target the tumor microenvironment and cancer cells and, as a result, enable efficient treatment for breast metastatic cancer.

Novel nanocrystal-based solid dispersion with high drug loading, enhanced dissolution, and bioavailability of andrographolide

Objective

The current study sought to design a quickly dissolving, high drug loading nanocrystal-based solid dispersion (NC-SD) in order to improve the dissolution of poorly soluble drugs.

Methods

The NC-SD was prepared by means of combination of homogenization and spray-drying. Polymer hydroxypropylmethylcellulose (HPMC) was used as baseline dispersant for NC-SD of the model drug – andrographolide (AG). Three superdisintegrants cohomogenized with HPMC were used as codispersant for AG-NC-SD and compared to common water-soluble dispersants – mannitol and lactose. The dissolution characterization and oral bioavailability of AG-NC-SD were evaluated.

Results

The AG-NC-SD with the higher concentration of HPMC exhibited fast dissolution due to the enhanced wettability of HPMC. The water-soluble codispersants (mannitol and lactose) did not completely prevent AG-NC from aggregation during spray-drying. To achieve much faster AG release, cohomogenized superdisintegrants at a level of 20% must be used along with 25% HPMC. Compared with water-soluble dispersants like mannitol and lactose, superdisintegrants with high swelling capacity were much more effective dispersants for enhancing fast redispersion/dissolution of AG-NC-SD via a swelling-triggered erosion/disintegration mechanism. Surfactant-free AG-NC-SD with 15% cohomogenized sodium carboxymethyl starch combined with 15% HPMC and 10% lactose enhanced the dissolution further, without comprising drug loading, exhibited a barely compromised dissolution rate compared to precursor NC suspensions (f₂>50), and possessed drug loading up to 67.83%±1.26%. The pharmacokinetics results also demonstrated that the AG-NC-SD significantly improved the bioavailability in vivo of AG (P<0.05), compared with to the coarse AG.

Conclusion

This study illustrates that a quickly dissolving, high drug load, surfactant-free NC-SD can be prepared by using a superdisintegrant as codispersant, and provides a feasible strategy to improve the oral bioavailability of poorly soluble drugs.

Drug-delivering-drug platform-mediated potent protein therapeutics via a non-endo-lysosomal route

Protein therapeutics is playing an increasingly critical role in treatment of human diseases. However, current vectors are captured by the digestive endo-lysosomal system, which results in an extremely low fraction (<2%) of protein being released in the cytoplasm. This paper reports a drug-delivering-drug platform (HA-PNPplex, 200 nm) for potent intracellular delivery of protein and combined treatment of cancer.

Methods: The platform was prepared by loading functional protein on pure drug nanoparticles (PNPs) followed by hyaluronic acid coating and was characterized by dynamic light scattering, transmission electron microscopy, and gel electrophoresis. In vitro, cellular uptake, trafficking, and cytotoxicity were evaluated by flow cytometry and confocal laser microscopy. Protein expression was assayed by western blot. In vivo, blood circulation and biodistribution were studied using a fluorescence imaging system, antitumor efficacy was assessed in a caspase 3-deficient tumor model, and biocompatibility was determined by comparison of hemolytic activity and proinflammatory cytokines and tissue histology.

Results: HA-PNPplex delivered the functional protein, caspase 3, to cells via bypassing endo-lysosomes and raised the caspase-3 level 6.5-fold in caspase 3-deficient cells. Promoted tumor accumulation (1.5-fold) and penetration were exhibited, demonstrating a high tumor-targeting ability of HA-PNPplex. HA-PNPplex rendered a 7-fold increase in caspase 3 in tumor and allowed for a 100% tumor growth inhibition and >60% apoptosis, implying significant antitumor activities.

Conclusions: This platform gains cellular entry without entrapment in the endo-lysosomes and enables efficient intracellular protein delivery and resultant profound cancer treatment. This platform, with extremely high drug-loading, is a valuable platform for combined cancer therapy with small-molecule drugs and proteins. More importantly, this work offers a robust and safe approach for protein therapeutics and intracellular delivery of other functional peptides, as well as gene-based therapy.

Tracking translocation of self-discriminating curcumin hybrid nanocrystals following intravenous delivery

Nanocrystals hold great potential as parenteral delivery carrier systems for poorly water-soluble drugs. Elucidation of the in vivo fate of parenteral nanocrystals is of pharmacological, toxicological and mechanistic significance. However, it is of tremendous difficulty to monitor real-time translocation of nanocrystals in vivo owing to progressive dissolution of nanocrystals and a lack of workable tools to probe nanocrystals. In this study, self-discriminating hybrid nanocrystals (SDHNs) of a model drug curcumin (CUR) were developed by embedding traces of environment-responsive fluorescent dyes into the crystalline lattices of CUR. The SDHNs glow, but the released dyes aggregate and quench spontaneously due to the aggregation-caused quenching (ACQ) effect. Following intravenous administration into rats, a large fraction of CUR nanocrystals are cleared from blood rapidly and accumulate mainly in liver and lung. A small fraction circulate in blood for at least 48 h. Long circulating might be attributable to the surface coating with poloxamer 188, a stabilizer used during preparation; nevertheless, the ultimate fate of nanocrystals ends in reticulo-endothelial organs and tissues. It is implied that parenteral delivery provide sustained release and prolonged pharmacological efficacy, but concomitantly raise concerns of local toxicity in vital organs and tissues, especially when the active ingredients are highly toxic.

Nanocrystal-based drug delivery system of risperidone: lyophilization and characterization

OBJECTIVE

In the present work nanocrystal-based formulation of risperidone (RIS) was proposed to overcome solubility issue of RIS, while lyophilization technique was used effectively, for conversion of RIS nanosuspension to solid state.

SIGNIFICANCE

RIS nanosuspension was developed and stabilized with a combination of polycaprolactone and Pluronic^® F-68 as stabilizers. With focus on critical parameters like nature of cryoprotectants and effect of eutectic temperature on properties of nanosuspension, the suitability of lyophilization technique in improving the physical stability of prepared nanosuspension was also evaluated. Additionally, the developed nanocrystals were also assessed for their solid states properties.

METHODS

Various process parameters affecting average particle size and polydispersity index (PDI), viz. drug to surfactant ratio, solvent to anti-solvent ratio, stirring speed, type of stabilizer were optimized. Assessment of lyophilization as a suitable solidification technique (for conversion to powder form) was done with selective cryoprotectants (trehalose dihydrate and sorbitol).

RESULTS

The formulation was found to be stable at 4 °C for 3 months with size, PDI and zeta potential of 214 ± 3.4 nm, 0.120, and -10.2 ± 0.90 mV, respectively. Release profile of developed nanosuspension showed cumulative % release of ∼90% in initial 10 h whereas the value for the unprocessed drug was ∼11% in same time frame.

CONCLUSIONS

These findings suggest that developed formulation was able to enhance water solubility of the drug effectively and can be potentially used in the management of psychotic disorders.

A Smart Paclitaxel-Disulfiram Nanococrystals for Efficient MDR Reversal and Enhanced Apoptosis

PURPOSE

A multidrug resistance (MDR) modulator, disulfiram (DSF), was incorporated into pure paclitaxel (PTX) nanoparticles to construct a smart paclitaxel-disulfiram nanococrystals (PTX-DSF Ns) stabilized by β-lactoglobulin (β-LG), with the aim to reverse MDR and therefore enhnce cytotoxicity towards Taxol-resistant A549 cells (A549/TAX).

METHOD

PTX-DSF Ns was prepared by antisolvent precipitation method. Flow cytometry was used to determine the cell uptake, drug efflux inhibition, cell cycle phase arrest and apoptosis. MDR-1 gene expression level was detected by real time quantitative PCR and gel electrophoresis.

RESULTS

PTX-DSF Ns prepared from the optimized formulation had an optimum diameter of 160 nm, was stable and had a high drug-loading capacity. Importantly, the uptake of PTX-DSF Ns in A549/TAX cells was 14-fold greater than the uptake of PTX Ns. Furthermore, PTX-DSF Ns promoted 5-folds increase in apoptosis, enabled 7-folds reduction in the IC₅₀, and rendered 8.9-fold decrease in the dose compared with free PTX.

CONCLUSION

PTX-DSF Ns with a precise mass ratio offer efficient cytotoxicity against Taxol-resistant cells and a novel approach for codelivery and sensitizing MDR cancer to chemotherapy. In addition, the use of nanosuspensions as a combined treatment provides a new research avenue for nanosuspensions.

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.

Enhanced transdermal delivery of meloxicam by nanocrystals: Preparation, in vitro and in vivo evaluation

Meloxicam (MLX) is efficient in relieving pain and inflammatory symptoms, which, however, is limited by the poor solubility and gastrointestinal side effects. The objective of this study is to develop a nanocrystal formulation to enhance transdermal delivery of MLX. MLX nanocrystals were successfully prepared by the nanoprecipitation technique based on acid-base neutralization. With poloxamer 407 and Tween 80 (80/20, w/w) as mixed stabilizers, MLX nanocrystals with particle size of 175 nm were obtained. The crystalline structure of MLX nanocrystals was confirmed by both differential scanning calorimetry and X-ray powder diffractometry. However, the nanoprecipitation process reduced the crystallinity of MLX. Nanocrystals increased both in vitro and in vivo transdermal permeation of MLX compared with the solution and suspension counterparts. Due to the enhanced apparent solubility and dissolution as well as the facilitated hair follicular penetration, nanocrystals present a high and prolonged plasma MLX concentration. And 2.58- and 4.4-fold increase in AUC_0→24h was achieved by nanocrystals comparing with solution and suspension, respectively. In conclusion, nanocrystal is advantageous for transdermal delivery of MLX.

Epithelia transmembrane transport of orally administered ultrafine drug particles evidenced by environment sensitive fluorophores in cellular and animal studies

Little is known about the in vivo fate of drug particles taken orally, in particular, the drug release kinetics and interaction with the gastrointestinal (GI) membrane. Lacking is analytical means that can reliably identify the integrity of drug particles under the complexity of biological environment. Herein, we explored fluorescent probes whose signals become quenched upon being released from drug carriers. Taking advantage of so-called the aggregation caused quenching (ACQ), particles may be identified by the integrated fluorophores, which are "turned off" when the particles become destructed and dyes are released. In the current study, ultrafine amorphous particles (UAPs) of cyclosporin A (CsA) were prepared with synthesized ACQ dyes physically entrapped. The fluorescence intensity of suspension of these UAPs was found correlated well with the dissolution of the particles. When given to rats orally, it was found that some of the administered UAPs could survive the animal's GI tracts for as long as 18h. Whole-body fluorescence imaging detected fluorescent signals in the liver and lungs. Particularly noticed in sections of jejunum and ileum, the detection suggested the possibility of direct absorption of UAPs through epithelial membranes. Moreover, 250nm particles were absorbed faster via transepithelia than larger ones (550nm), while the latter were preferably taken up by M cells in the follicle-associated epithelium (FAE) region of Peyer's patches. In vitro permeation studies with Caco-2 cells confirmed the transmembrane transport of the dye-integrated UAPs. Our study supports the idea of using ACQ fluorophores for imaging and characterizing the fate of intact particles in a biological environment.

Apolipoproteins adsorption and brain-targeting evaluation of baicalin nanocrystals modified by combination of Tween80 and TPGS

To help baicalin pass across BBB and improve its targeting in brain, we designed a novel formulation strategy of baicalin nanocrystals that preferentially adsorbing apolipoprotein E (ApoE) and repelling protein adsorption of opsonins. Intravenous baicalin nanocrystals suspensions (BCL-NS) modified by different surfactant were prepared by high-pressure homogenization. The targeting potential of surface-modified BCL-NS with mean particles size of about 250nm was assessed by in vitro protein adsorption studies using two-dimensional polyacrylamide gel electrophoresis (2-D PAGE), and further evaluated in vivo pharmacokinetics. The protein adsorption results showed that BCL-NS/TPGS, BCL-NS/TW80 and BCL-NS/TPGS+TW80 adsorbed very high amounts of apolipoproteins (ApoA-I, ApoA-Ⅱ, ApoA-IV, ApoC-III, ApoE, ApoJ) and relative low amounts of opsonins (fibrinogen, immunoglobulin heavy chain gamma, immunoglobulin light chain). The pharmacokinetics results demonstrated the AUC _(0-∞) in brain of the BCL-NS/TW80+TPGS was 6.67 times as high as that of the BCL solution, and 2.59 times as high as that of the BCL-NS/TW80. It could be attributed to the most ApoE and Apo J adsorption indicative of strong BBB penetration, and least IgG γ and fibrinogen loading minimizing the risk of hepatic uptake. Combination of TW80 and TPGS can be rational choice of surfactants of baicalin nanocrystals for brain-targeting mediated by ApoE adsorption.

Zebrafish as a visual and dynamic model to study the transport of nanosized drug delivery systems across the biological barriers

With the wide application of nanotechnology to drug delivery systems, a simple, dynamic and visual in vivo model for high-throughput screening of novel formulations with fluorescence markers across biological barriers is desperately needed. In vitro cell culture models have been widely used, although they are far from a complimentary in vivo system. Mammalian animal models are common predictive models to study transport, but they are costly and time consuming. Zebrafish (Danio rerio), a small vertebrate model, have the potential to be developed as an "intermediate" model for quick evaluations. Based on our previously established coumarin 6 nanocrystals (C6-NCs), which have two different sizes, the present study investigates the transportation of C6-NCs across four biological barriers, including the chorion, blood brain barrier (BBB), blood retinal barrier (BRB) and gastrointestinal (GI) barrier, using zebrafish embryos and larvae as in vivo models. The biodistribution and elimination of C6 from different organs were quantified in adult zebrafish. The results showed that compared to 200nm C6-NCs, 70nm C6-NCs showed better permeability across these biological barriers. A FRET study suggested that intact C6-NCs together with the free dissolved form of C6 were absorbed into the larval zebrafish. More C6 was accumulated in different organs after incubation with small sized NCs via lipid raft-mediated endocytosis in adult zebrafish, which is consistent with the findings from in vitro cell monolayers and the zebrafish larvae model. C6-NCs could be gradually eliminated in each organ over time. This study demonstrated the successful application of zebrafish as a simple and dynamic model to simultaneously assess the transport of nanosized drug delivery systems across several biological barriers and biodistribution in different organs, especially in the brain, which could be used for central nervous system (CNS) drug and delivery system screening.