Artificially reprogrammed stem cells deliver transcytosable nanocomplexes for improved spinal cord repair

Stem cell transplantation holds great promise for restoring function after spinal cord injury (SCI), but its therapeutic efficacy heavily depends on the innate capabilities of the cells and the microenvironment at the lesion site. Herein, a potent cell therapeutic (NCs@SCs) is engineered by artificially reprogramming bone marrow mesenchymal stem cells (BMSCs) with oxidation-responsive transcytosable gene-delivery nanocomplexes (NCs), which endows cells with robust oxidative stress resistance and improved cytokine secretion. NCs@SCs can accumulate in the injured spinal cord after intravenous administration via chemotaxis and boost successive transcytosis to deliver NCs to neurons, augmenting ciliary neurotrophic factor (CNTF) production in both BMSCs and neurons in response to elevated ROS levels. Furthermore, NCs@SCs can actively sense and eliminate ROS and re-educate recruited M1-like macrophages into the anti-inflammatory M2 phenotype via a paracrine pathway, ultimately reshaping the inflammatory microenvironment. Synergistically, NCs@SCs exhibit durable survival and provide neuroprotection against secondary damage, enabling significant locomotor function recovery in SCI rats. Transcriptome analysis reveals that regulation of the ROS/MAPK signaling pathway is involved in SCI therapy by NCs@SCs. This study presents a nanomaterial-mediated cell-reprogramming approach for developing live cell therapeutics, showing significant potential in the treatment of SCI and other neuro-injury disorders.

Core-shell nanosystems designed for effective oral delivery of polypeptide drugs

The stomach acid degradation, mucus clearance and intestinal epithelial impermeability severely limit the oral delivery of polypeptide drugs. To simultaneously address the three major barriers, novel self-assembled core-shell nanosystems (CA-NPs) were designed. The fabricated shell of citric acid cross-linked carboxymethyl cellulose (CA-CMC) wrapped on core nanoparticles (HA-NPs) maintained the integrity of CA-NPs in the stomach. When CA-NPs passed through the stomach, the CA-CMC shell was gradually degraded to release the core HA-NPs in the intestine. HA-NPs with numerous hydrophilic groups and mannose side chains rapidly penetrated through the mucus layer and efficiently transcellular transported via the glucose transporter (GLUT)-mediated and paracellular transport through reversible opening of tight junctions (TJs) by CA-CMC. The oral bioavailability and therapeutic effects of CA-NPs-loaded polypeptide colistin against Escherichia coli (E. coli) bacteremia in mice were significantly increased compared with the native colistin, respectively. Good safety was observed following oral daily delivery for 14 consecutive days. Thus, CA-NPs may offer a promising strategy for the oral delivery of polypeptide drugs.

Autophagy responsive intra-intercellular delivery nanoparticles for effective deep solid tumor penetration

Deep tumor cells (cells in the center of solid tumors) play a crucial role in drug tolerance, metastasis, recurrence and microenvironment immune suppression. However, their deep location endows them with an untouched abdomen and makes them refractory to current treatments. Herein, we exploited the characteristic of higher autophagy in deep tumor cells than in superficial tumor cells and designed autophagy-responsive multifunctional nanoparticles (PGN) to enhance drug accumulation in deep tumor cells. PGNs were prepared by densely coating poly (lactic-co-glycolic acid) (PLGA) with cationic autophagy-responsive cell-penetrating peptide (GR9) and anionic 2,3-dimethylmaleic anhydride (DMA)-modified DSPE-PEG. The suitable nanoparticle size (122.4 nm) and charge-neutral surface (0.21 mV) of the NPs enabled long blood circulation. The hydrolysis of surface-anchored anionic DMA in the acidic microenvironment led to the exposure of the GR9 peptide and enhance tumor penetration. Once the PGN arrived in deep tumor cells with strong autophagy, GR9 was cut off by an autophagy shear enzyme, and the nanoparticles remained in the cells to undergo degradation. Furthermore, we prepared docetaxel (DTX) and chloroquine (CQ) loaded d-PGN. CQ inhibits autophagosome fusion with lysosomes, resulting in autophagosome accumulation, which further enhances the sensitivity of d-PGN to autophagy and their deep tumor retention. In vivo experiments showed that drug-loaded d-PGN achieved excellent antitumor efficacy with a peak inhibition rate of 82.1%. In conclusion, autophagy-responsive multifunctional nanoparticles provide a novel potential strategy for solid tumor treatment.

Fabrication of chitosan-coated epigallocatechin-3-gallate (EGCG)-hordein nanoparticles and their transcellular permeability in Caco-2/HT29 cocultures

Epigallocatechin-3-gallate (EGCG) has gained appreciable attention because of its health benefits. However, the poor permeability across the intestine limits its use. In this study, we have fabricated chitosan-coated EGCG-hordein nanoparticles (Cs-EHNs), with the aim to enhance the intestinal permeability of EGCG. Cs-EHNs were fabricated by layer-by-layer electrostatic stacking method, and its uptake and transcellular permeability were studied in the Caco-2/HT29 co-culture model. The constructed Cs-EHNs had the average diameter of 296 nm, polymer dispersity index (PDI) of 0.30, zeta potential of 59.6 mV, and showed a spherical morphology. Encapsulation efficiency of EGCG was 87.3%. The transcellular permeability experiments indicated that the apparent permeability coefficient (P_app) of Cs-EHNs was higher than that of free EGCG. Furthermore, the cellular uptake of Cs-EHNs was studied by specific endocytosis inhibitors, and results showed that the uptake mechanisms of Cs-EHNs were through caveolae-mediated endocytosis and macropinocytosis. This study demonstrated that encapsulation of EGCG using chitosan-coated hordein nanoparticles could be a promising approach to improve the absorption of EGCG.

The digestive tract as an essential organ for water acquisition in marine teleosts: lessons from euryhaline eels

Adaptation to a hypertonic marine environment is one of the major topics in animal physiology research. Marine teleosts lose water osmotically from the gills and compensate for this loss by drinking surrounding seawater and absorbing water from the intestine. This situation is in contrast to that in mammals, which experience a net osmotic loss of water after drinking seawater. Water absorption in fishes is made possible by (1) removal of monovalent ions (desalinization) by the esophagus, (2) removal of divalent ions as carbonate (Mg/CaCO₃) precipitates promoted by HCO₃^- secretion, and (3) facilitation of NaCl and water absorption from diluted seawater by the intestine using a suite of unique transporters. As a result, 70-85% of ingested seawater is absorbed during its passage through the digestive tract. Thus, the digestive tract is an essential organ for marine teleost survival in the hypertonic seawater environment. The eel is a species that has been frequently used for osmoregulation research in laboratories worldwide. The eel possesses many advantages as an experimental animal for osmoregulation studies, one of which is its outstanding euryhalinity, which enables researchers to examine changes in the structure and function of the digestive tract after direct transfer from freshwater to seawater. In recent years, the molecular mechanisms of ion and water transport across epithelial cells (the transcellular route) and through tight junctions (the paracellular route) have been elucidated for the esophagus and intestine. Thanks to the rapid progress in analytical methods for genome databases on teleosts, including the eel, the molecular identities of transporters, channels, pumps and junctional proteins have been clarified at the isoform level. As 10 y have passed since the previous reviews on this subject, it seems relevant and timely to summarize recent progress in research on the molecular mechanisms of water and ion transport in the digestive tract in eels and to compare the mechanisms with those of other teleosts and mammals from comparative and evolutionary viewpoints. We also propose future directions for this research field to achieve integrative understanding of the role of the digestive tract in adaptation to seawater with regard to pathways/mechanisms including the paracellular route, divalent ion absorption, metabolon formation and cellular trafficking of transporters. Notably, some of these have already attracted practical attention in laboratories.

Type of culture medium determines properties of cultivated retinal endothelial cells: induction of substantial phenotypic conversion by standard DMEM

Contradictory behavior of microvascular retinal endothelial cells (REC) - a reliable in vitro model to study retinal diseases - have recently been reported which might result from cultivating the cells in standard DMEM not optimized for this cell type. Therefore, we studied DMEM's effects on phenotype and behavior of immortalized bovine REC. Cells were cultivated in endothelial cell growth medium (ECGM) until a confluent monolayer was reached and then further kept for 1-4 days in ECGM, DMEM, or mixes thereof all supplemented with 5% fetal bovine serum, endothelial cell growth supplement, 90 μg/ml heparin, and 100 nM hydrocortisone. Within hours of cultivation in DMEM, the cell index - measured to assess the cell layer's barrier function - dropped to ~5% of the initial value and only slowly recovered, not only accompanied by stronger expression of HSP70 mRNA and secretion of interleukin-6, but also by lower expressions of tight junction proteins claudin-5, claudin-1 or of the marker of cell type conversion caveolin-1. Altered subcellular localizations of EC-typic claudin-5, vascular endothelial cadherin and von Willebrand factor were also observed. Taken together, all experiments with (retinal) EC cultivated in common DMEM need to be interpreted very cautiously and should at least include phenotypic validation.

A peptide for transcellular cargo delivery: Structure-function relationship and mechanism of action

The rate of transport of small molecule drugs across biological barriers, such as the blood-brain barrier, is often a limiting factor in achieving a therapeutic dose. One proposed strategy to enhance delivery across endothelial or epithelial monolayers is conjugation to cell-penetrating peptides (CPPs); however, very little is known about the design of CPPs for efficient transcellular transport. Here, we report on transcellular transport of a CPP, designated the CL peptide, that increases the delivery of small-molecule cargoes across model epithelium approximately 10-fold. The CL peptide contains a helix-like motif and a polyarginine tail. We investigated the effect of cargo, helix-like motif sequence, polyarginine tail length, and peptide stereochemistry on cargo delivery. We showed that there is an optimal helix-like motif sequence (RLLRLLR) and polyarginine tail length (R₇) for cargo delivery. Furthermore, we demonstrated that the peptide-cargo conjugate is cleaved by cells in the epithelium at the site of a two-amino acid linker. The cleavage releases the cargo with the N-terminal linker amino acid from the peptide prior to transport out of the epithelium. These studies provide new insight into the sequence requirements for developing novel CPPs for transcellular delivery of cargo.

HIV-1 Tat and opioids act independently to limit antiretroviral brain concentrations and reduce blood-brain barrier integrity

Poor antiretroviral penetration may contribute to human immunodeficiency virus (HIV) persistence within the brain and to neurocognitive deficits in opiate abusers. To investigate this problem, HIV-1 Tat protein and morphine effects on blood-brain barrier (BBB) permeability and drug brain penetration were explored using a conditional HIV-1 Tat transgenic mouse model. Tat and morphine effects on the leakage of fluorescently labeled dextrans (10-, 40-, and 70-kDa) into the brain were assessed. To evaluate effects on antiretroviral brain penetration, Tat+ and Tat- mice received three antiretroviral drugs (dolutegravir, abacavir, and lamivudine) with or without concurrent morphine exposure. Antiretroviral and morphine brain and plasma concentrations were determined by LC-MS/MS. Morphine exposure, and, to a lesser extent, Tat, significantly increased tracer leakage from the vasculature into the brain. Despite enhanced BBB breakdown evidenced by increased tracer leakiness, morphine exposure led to significantly lower abacavir concentrations within the striatum and significantly less dolutegravir within the hippocampus and striatum (normalized to plasma). P-glycoprotein, an efflux transporter for which these drugs are substrates, expression and function were significantly increased in the brains of morphine-exposed mice compared to mice not exposed to morphine. These findings were consistent with lower antiretroviral concentrations in brain tissues examined. Lamivudine concentrations were unaffected by Tat or morphine exposure. Collectively, our investigations indicate that Tat and morphine differentially alter BBB integrity. Morphine decreased brain concentrations of specific antiretroviral drugs, perhaps via increased expression of the drug efflux transporter, P-glycoprotein.

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.

Fluid and ion transfer across the blood-brain and blood-cerebrospinal fluid barriers; a comparative account of mechanisms and roles

The two major interfaces separating brain and blood have different primary roles. The choroid plexuses secrete cerebrospinal fluid into the ventricles, accounting for most net fluid entry to the brain. Aquaporin, AQP1, allows water transfer across the apical surface of the choroid epithelium; another protein, perhaps GLUT1, is important on the basolateral surface. Fluid secretion is driven by apical Na+-pumps. K+ secretion occurs via net paracellular influx through relatively leaky tight junctions partially offset by transcellular efflux. The blood-brain barrier lining brain microvasculature, allows passage of O2, CO2, and glucose as required for brain cell metabolism. Because of high resistance tight junctions between microvascular endothelial cells transport of most polar solutes is greatly restricted. Because solute permeability is low, hydrostatic pressure differences cannot account for net fluid movement; however, water permeability is sufficient for fluid secretion with water following net solute transport. The endothelial cells have ion transporters that, if appropriately arranged, could support fluid secretion. Evidence favours a rate smaller than, but not much smaller than, that of the choroid plexuses. At the blood-brain barrier Na+ tracer influx into the brain substantially exceeds any possible net flux. The tracer flux may occur primarily by a paracellular route. The blood-brain barrier is the most important interface for maintaining interstitial fluid (ISF) K+ concentration within tight limits. This is most likely because Na+-pumps vary the rate at which K+ is transported out of ISF in response to small changes in K+ concentration. There is also evidence for functional regulation of K+ transporters with chronic changes in plasma concentration. The blood-brain barrier is also important in regulating HCO3- and pH in ISF: the principles of this regulation are reviewed. Whether the rate of blood-brain barrier HCO3- transport is slow or fast is discussed critically: a slow transport rate comparable to those of other ions is favoured. In metabolic acidosis and alkalosis variations in HCO3- concentration and pH are much smaller in ISF than in plasma whereas in respiratory acidosis variations in pHISF and pHplasma are similar. The key similarities and differences of the two interfaces are summarized.

The apparent permeabilities of Caco-2 cells to marketed drugs: magnitude, and independence from both biophysical properties and endogenite similarities

We bring together fifteen, nonredundant, tabulated collections (amounting to 696 separate measurements) of the apparent permeability (P_app) of Caco-2 cells to marketed drugs. While in some cases there are some significant interlaboratory disparities, most are quite minor. Most drugs are not especially permeable through Caco-2 cells, with the median P_app value being some 16 ⋅ 10⁻⁶ cm s⁻¹. This value is considerably lower than those (1,310 and 230 ⋅ 10⁻⁶ cm s⁻¹) recently used in some simulations that purported to show that P_app values were too great to be transporter-mediated only. While these values are outliers, all values, and especially the comparatively low values normally observed, are entirely consistent with transporter-only mediated uptake, with no need to invoke phospholipid bilayer diffusion. The apparent permeability of Caco-2 cells to marketed drugs is poorly correlated with either simple biophysical properties, the extent of molecular similarity to endogenous metabolites (endogenites), or any specific substructural properties. In particular, the octanol:water partition coefficient, logP, shows negligible correlation with Caco-2 permeability. The data are best explained on the basis that most drugs enter (and exit) Caco-2 cells via a multiplicity of transporters of comparatively weak specificity.

Vitamin D-enhanced duodenal calcium transport. Vitam Horm. 2015;98:407-440. [PMID: 25817876 DOI: 10.1016/bs.vh.2014.12.010]

For humans and rodents, duodenum is a very important site of calcium absorption since it is exposed to ionized calcium released from dietary complexes by gastric acid. Calcium traverses the duodenal epithelium via both transcellular and paracellular pathways in a vitamin D-dependent manner. After binding to the nuclear vitamin D receptor, 1,25-dihydroxyvitamin D3 [1,25(OH)2D3] upregulates the expression of several calcium transporter genes, e.g., TRPV5/6, calbindin-D9k, plasma membrane Ca(2+)-ATPase1b, and NCX1, thereby enhancing the transcellular calcium transport. This action has been reported to be under the regulation of parathyroid-kidney-intestinal and bone-kidney-intestinal axes, in which the plasma calcium and fibroblast growth factor-23 act as negative feedback regulators, respectively. 1,25(OH)2D3 also modulates the expression of tight junction-related genes and convective water flow, presumably to increase the paracellular calcium permeability and solvent drag-induced calcium transport. However, vitamin D-independent calcium absorption does exist and plays an important role in calcium homeostasis under certain conditions, particularly in neonatal period, pregnancy, and lactation as well as in naturally vitamin D-impoverished subterranean mammals.

Characterization of the intestinal absorption of inorganic mercury in Caco-2 cells

The main form of mercury exposure in the general population is through food. Intestinal absorption is therefore a key step in the penetration of mercury into the systemic circulation, and should be considered when evaluating exposure risk. Many studies have investigated the transport of mercury species in different cell lines, though the mechanisms underlying their intestinal absorption are not clear. This study evaluates the accumulation and transport of Hg(II), one of the mercury species ingested in food, using Caco-2 cells as intestinal epithelium model with the purpose of clarifying the mechanisms involved in its absorption. Hg(II) shows moderate absorption, and its transport fundamentally takes place via a carrier-mediated transcellular mechanism. The experiments indicate the participation of an energy-dependent transport mechanism. In addition, H(+)- and Na(+)-dependent transport is also observed. These data, together with those obtained from inhibition studies using specific substrates or inhibitors of different transporter families, suggest the participation of divalent cation and amino acid transporters, and even some organic anion transporters, in Hg(II) intestinal transport. An important cellular accumulation of up to 51% is observed - a situation which in view of the toxic nature of this species could affect intestinal mucosal function. This study contributes new information on the mechanisms of transport of Hg(II) at intestinal level, and which may be responsible for penetration of this mercurial form into the systemic circulation.

In vitro characterization of ABC transporters involved in the absorption and distribution of liensinine and its analogs

ETHNOPHARMACOLOGICAL RELEVANCE

Lotus plumule, the dried young cotyledon and radicle of the Nelumbo nucifera Gaertn. (Fam. Nymphaeaceae) ripe seed, is a famous Traditional Chinese Medicine to remove heat from the heart, anchor the mind, improve seminal emission, and arrest bleeding for centuries in China. Liensinine and its analogs neferine and isoliensinine are the major active components in lotus plumule. Aim of the study is to investigate the association of liensinine, neferine, and isoliensinine with efflux transporters.

MATERIALS AND METHODS

Caco-2, MDCK, MDCK-MDR1, and MDCK-MRP2 were used as cell models for the transcellular transport and accumulation studies.

RESULTS

The results obtained in Caco-2 cells suggested that P-glycoprotein (P-gp) might be involved in transcellular transport. Cellular accumulation and transport experiments were further performed in MDCK-MDR1 cells. GF120918 and cyclosporine A were found to completely inhibit the efflux, and the net efflux ratios of these alkaloids exhibited saturation over the concentration range. No significant differences in liensinine accumulation and transport were observed between MDCK and MDCK-MRP2 cells.

CONCLUSIONS

These results demonstrated that liensinine, neferine, and isoliensinine are substrates of P-gp, whereas MRP2 is not involved in the transport process, suggesting that P-gp might be responsible for the absorption and distribution of the 3 alkaloids.

Fibroblast growth factor-23 negates 1,25(OH)2D3-induced intestinal calcium transport by reducing the transcellular and paracellular calcium fluxes. Arch Biochem Biophys. 2013;536:46-52. [PMID: 23747333 DOI: 10.1016/j.abb.2013.05.009]

The calciotropic hormone 1,25-dihydroxyvitamin D3 [1,25(OH)2D3] has been known to stimulate intestinal calcium transport via both transcellular and paracellular pathways. Recently, we reported that the 1,25(OH)2D3-enhanced calcium transport in the mouse duodenum could be abolished by fibroblast growth factor (FGF)-23, but the targeted calcium transport pathway has been elusive. Herein, the 1,25(OH)2D3-enhanced calcium transport was markedly inhibited by FGF-23 and inhibitors of the basolateral calcium transporters, NCX1 and PMCA1b, suggesting the negative effect of FGF-23 on the transcellular calcium transport. Similar results could be observed in the intestinal epithelium-like Caco-2 monolayer. Although the Arrhenius plot indicated that FGF-23 decreased the potential barrier (e.g., activation energy) of the paracellular calcium movement, FGF-23 was found to modestly decrease the 1,25(OH)2D3-enhanced paracellular calcium transport and calcium permeability. Moreover, FGF-23 affected the 1,25(OH)2D3-induced change in duodenal water permeability as determined by tritiated water, but both 1,25(OH)2D3 and FGF-23 were without effects on the transepithelial fluxes of paracellular markers, (3)H-mannitol and (14)C-polyethylene glycol. It could be concluded that FGF-23 diminished the 1,25(OH)2D3-enhanced calcium absorption through the transcellular and paracellular pathways. Our findings have thus corroborated the presence of a bone-kidney-intestinal axis of FGF-23/vitamin D system in the regulation of calcium homeostasis.