Surface engineering of silica nanoparticles for oral insulin delivery: characterization and cell toxicity studies

The present work aimed at studying the interaction between insulin and SiNP surfaced with mucoadhesive polymers (chitosan, sodium alginate or polyethylene glycol) and the evaluation of their biocompatibility with HepG2 and Caco-2 cell lines, which mimic in vivo the target of insulin-loaded nanoparticles upon oral administration. Thus, a systematic physicochemical study of the surface-modified insulin-silica nanoparticles (Ins-SiNP) using mucoadhesive polymers has been described. The surfacing of nanoparticle involved the coating of silica nanoparticles (SiNP) with different mucoadhesive polymers, to achieve high contact between the systems and the gut mucosa to enhance the oral insulin bioavailability. SiNP were prepared by a modified Stöber method at room temperature via hydrolysis and condensation of tetraethyl orthosilicate (TEOS). Interaction between insulin and nanoparticles was assessed by differential scanning calorimetry (DSC), X-ray and Fourier-transform infrared (FTIR) studies. The high efficiency of nanoparticles' coating resulted in more stable system. FTIR spectra of insulin-loaded nanoparticles showed amide absorption bands which are characteristic of α-helix content. In general, all developed nanoparticles demonstrated high biocompatible, at the tested concentrations (50-500 μg/mL), revealing no or low toxicity in the two human cancer cell lines (HepG2 and Caco-2). In conclusion, the developed insulin-loaded SiNP surfaced with mucoadhesive polymers demonstrated its added value for oral administration of proteins.

The transport and efflux of glycosylated luteinising hormone-releasing hormone analogues in caco-2 cell model: contributions of glucose transporters and efflux systems

Luteinising hormone-releasing hormone (LHRH) analogues have wide therapeutic applications in the treatment of prostate cancers and endocrine disorders. The structure of LHRH was modified using a glycosylation strategy to increase the permeability of the peptide across biological membranes. Lactose, galactose and glucose units were coupled to LHRH peptide, and the impact of glucose transporters, GLUT2 and SGLT1, was investigated in the transport of the analogues. Results showed the contribution of both transporters in the transport of all LHRH analogues. In the presence of glucose transporter inhibitors, reduction in the apparent permeability (Papp ) was greatest for compound 6, which contains a glucose unit in the middle of the sequence (Papp = 58.54 ± 4.72 cm/s decreased to Papp = 1.6 ± 0.345 cm/s). The basolateral to apical flux of the glycosylated derivatives and the impact of two efflux pumps was also examined in Caco-2 cell monolayers. The efflux ratios (ERs) of all LHRH analogues in Caco-2 cells were in the range of 0.06-0.2 except for compound 4 (galactose modified, ER = 8.03). We demonstrated that the transport of the glycosylated peptides was facilitated through glucose transporters. The proportion of glucose and lactose derivatives pumped out by efflux pumps did not affect the Papp values of the analogues.

Combined use of phospholipid complexes and self-emulsifying microemulsions for improving the oral absorption of a BCS class IV compound, baicalin

The aim of this study was to develop a formulation to improve the oral absorption of baicalin (BA) by combining a phospholipid complex (PC) and self-emulsifying microemulsion drug delivery system (SMEDDS), termed BA–PC–SMEDDS. BA–PC was prepared by a solvent evaporation method and evaluated by complexation percentage (CP). The physicochemical properties of BA–PC were determined. The synergistic effect of PC and SMEDDS on permeation of BA was studied in vitro with Caco-2 cells and in situ with a single pass intestinal perfusion model. The improved bioavailability of BA in BA–PC–SMEDDS was confirmed in an in vivo rat model. The CP of BA–PC reached 100% when the molar ratio of drug to phospholipid (PP) was ≥1:1. The solubility of BA–PC increased in both water and octanol, and the log P_o/w of BA–PC was increased significantly. BA–PC–SMEDDS could be dispersed more evenly in water, compared to BA and BA–PC. Both the Caco-2 cell uptake and single-pass intestinal perfusion models illustrated that transport of BA in BA–PC was lower than that of free BA, while improved significantly in BA–PC–SMEDDS. The relative bioavailability of BA–PC(1:2)–SMEDDS was 220.37%. The combination system of PC and SMEDDS had a synergistic effect on improving the oral absorption of BA.

Structure of drug delivery DPPA and DPPC liposomes with ligands and their permeability through cells

Dipalmitoylphosphatidylcholine (DPPC) and 1,2-palmitoyl-phosphatidic acid (DPPA) liposomes, prepared by conventional rotary evaporation method, have similar structural organization, though they have significant differences. The similarity is that both types of lipids create standard bilayer liposomes with strong hydrophobic forces between lipids tails and with homogeneous bonds of hydrogen and electrostatic nature between hydrophilic lipids heads. By the calorimetric method, it has been shown that hydrophobic bonds break but liposomes' destruction does not occur by heating till 150 °C. As for bonds between lipid heads in liposomes, their cooperative destruction takes place at 41 °C for DPPC and 66 °C for DPPA liposomes. In the case of thermal distraction of DPPC liposomes, two so-called pre transitions peaks were observed before the main transition peak, which indicates that DPPC liposomes' structure is multilamellar. DPPA liposomes have one cooperative heat absorption peak, which points to a unilamellar structure of such liposomes. Substances of hydrophobic/hydrophilic nature, incorporated into the liposomes, are placed in hydrophobic or hydrophilic parts of liposomes, which lead to a change in calorimetric peak shapes and thermodynamic parameters. It has been shown that gold nanoparticles, incorporated into the DPPC liposomes, are able to enter Caco-2 cells. In contrast, these nanoparticles do not enter red blood cells.

Transport characteristics of isorhamnetin across intestinal Caco-2 cell monolayers and the effects of transporters on it

Flavonoid isorhamnetin occurs in various plants and herbs, and demonstrates various biological effects in humans. This work will clarify the isorhamnetin absorption mechanism using the Caco-2 monolayer cell model. The isorhamnetin transport characteristics at different concentrations, pHs, temperatures, tight junctions and potential transporters were systemically investigated. Isorhamnetin was poorly absorbed by both passive diffusion and active transport mechanisms. Both trans- and paracellular pathways were involved during isorhamnetin transport. Active transport under an ATP-dependent transport mechanism was mediated by the organic anion transporting peptide (OATP); isorhamnetin's permeability from the apical to the basolateral side significantly decreased after estrone-3-sulfate was added (p<0.01). Efflux transporters, P-glycoproteins (P-gp), breast cancer resistance proteins (BCRP) and multidrug resistance proteins (MRPs) participated in the isorhamnetin transport process. Among them, the MRPs (especially MRP2) were the main efflux transporters for isorhamnetin; transport from the apical to the basolateral side increased 10.8-fold after adding an MRP inhibitor (MK571). This study details isorhamnetin's cellular transport and elaborates isorhamnetin's absorption mechanisms to provide a foundation for further studies.

Transport of active flavonoids, based on cytotoxicity and lipophilicity: an evaluation using the blood-brain barrier cell and Caco-2 cell models

This in vitro study aims to evaluate and compare transmembrane transport of eight cardio-cerebrovascular protection flavonoids including puerarin, rutin, hesperidin, quercetin, genistein, kaempferol, apigenin and isoliquiritigenin via the rat blood-brain barrier cell and Caco-2 cell monolayer models, based on the data of cytotoxicity and lipophilicity. The cytotoxicity of the flavonoids to rat brain microvessel endothelial cell was determined by the MTT assay. The apparent permeability coefficients (Papp) of the flavonoids were calculated from the unilateral transport assays in Transwell system with simultaneous determination using a high performance liquid chromatography. The results showed that the cytotoxicity and oil-water partition coefficient of the flavonoids modified by the number and position of the glycoside and hydroxyl group were the key determinant for the transmembrane transport. The Papp values of the flavonoids reduced adversely when the numbers of glycoside and hydroxyl groups of the flavonoids increased accordingly. The tested flavonoids exhibited time-dependent Papp values in these models. The efflux mechanism related with P-glycoprotein also existed with the polar flavonoids; verapamil could enhance the permeation of rutin and quercetin via inhibition of P-glycoprotein. We propose that genistein and isoliquiritigenin with the permeation priority in vitro Caco-2 and BBB cell model could be better as the drug candidates for cardio-cerebral vascular protection. These findings provided important information for establishing the transport relationship for the flavonoid compounds and evaluating the potential oral bioavailability and brain distribution of the flavonoids.

Naringenin enhances intestinal barrier function through the expression and cytoskeletal association of tight junction proteins in Caco-2 cells

SCOPE

We have previously reported that naringenin promotes the tight junction (TJ) integrity in intestinal Caco-2 cells. This study investigated the naringenin-mediated effect in Caco-2 cells with a particular focus on the modulation of TJ structure and claudin-4 transcriptional regulation.

METHODS AND RESULTS

Naringenin (10~100 μM) dose-dependently enhanced TJ barrier integrity of Caco-2 cells, indicated by transepithelial electrical resistance and FITC-dextran flux. Immunoblot analysis showed that naringenin increased the cytoskeletal association of TJ proteins, zonula occludens-2, occludin, claudin-1, and claudin-4, simultaneously with increased occludin phosphorylation. The total expression of claudin-4 was also increased by naringenin. Quantitative RT-PCR and luciferase reporter assay revealed that naringenin transcriptionally increased the claudin-4 expression with activation of claudin-4 promoter. The mutation of the binding site of the transcriptional factor Sp1 in the claudin-4 promoter sequence and the pharmacological inhibition of Sp1 partially suppressed the naringenin-mediated activation of the claudin-4 promoter. Further, naringenin induced the heat shock protein 70 expression in the cells.

CONCLUSION

Naringenin enhances barrier integrity through the assembly and expression of TJ proteins in intestinal epithelial cells. Naringenin-mediated claudin-4 expression occurs, at least partially, through Sp1-dependent transcriptional regulation. The induction of heat shock protein 70 may be also involved in the increased claudin-4 expression.

Development and characterization of a new oral dapsone nanoemulsion system: permeability and in silico bioavailability studies

BACKGROUND

Dapsone is described as being active against Mycobacterium leprae, hence its role in the treatment of leprosy and related pathologies. Despite its therapeutic potential, the low solubility of dapsone in water results in low bioavailability and high microbial resistance. Nanoemulsions are pharmaceutical delivery systems derived from micellar solutions with a good capacity for improving absorption. The aim of this work was to develop and compare the permeability of a series of dapsone nanoemulsions in Caco-2 cell culture against that of effective permeability in the human body simulated using Gastroplus™ software.

METHODS AND RESULTS

The release profiles of the dapsone nanoemulsions using different combinations of surfactants and cosolvent showed a higher dissolution rate in simulated gastric and enteric fluid than did the dispersed dapsone powder. The drug release kinetics were consistent with a Higuchi model.

CONCLUSION

This comparison of dapsone permeability in Caco-2 cells with effective permeability in the human body simulated by Gastroplus showed a good correlation and indicates potential improvement in the biodisponibility of dapsone using this new system.

Uptake and transport of a novel anticancer drug-delivery system: lactosyl-norcantharidin-associated N-trimethyl chitosan nanoparticles across intestinal Caco-2 cell monolayers

In this paper, novel liver-targeting nanoparticles (NPs), lactosyl-norcantharidin (Lac-NCTD)-associated N-trimethyl chitosan (TMC) NPs (Lac-NCTD-TMC-NPs), were prepared using ionic cross-linkage. The physical properties, particle size, and encapsulation efficiency of the nanoparticles were then investigated. The continuous line of heterogeneous human epithelial colorectal adenocarcinoma cells (Caco-2) cell monolayer model was used to study the transport mechanism of Lac-NCTD, and the effects of factors such as time, temperature, pH level, drug concentration, enhancers, and inhibitors. This model was also used to indicate the differences among Lac-NCTD, Lac-NCTD-associated chitosan NPs (Lac-NCTD-CS-NPs), and Lac-NCTD-TMC- NPs in the absorption and transportation of membranes. Drug concentration levels were measured using high-performance liquid chromatography. Active transport and paracellular transport were suggested to be both the primary and secondary mechanisms for Lac-NCTD absorption, respectively. Lac-NCTD uptake and absorption were not controlled by pH levels, but were positively correlated to uptake time, and negatively correlated to temperature. The basolateral to apical apparent permeability coefficients (Papps) were higher than those of the apical to basolateral values. The inhibitor of P-glycoprotein and the multidrug resistance-associated protein 2 significantly enhanced the uptake amount of Lac-NCTD. Compared with Lac-NCTD, Lac-NCTD-CS-NPs and Lac-NCTD-TMC-NPs significantly enhanced drug absorption. Additionally, the latter exhibited stronger action. Lac-NCTD-NPs could penetrate the plasma membrane of Caco-2 cells and translocate into the cytoplasm and even into the nucleus. Nanoparticles were uptaken into Caco-2 cells through the endocytosis pathway.

In-vitro Cellular Uptake and Transport Study of 9-Nitrocamptothecin PLGA Nanoparticles Across Caco-2 Cell Monolayer Model

The uptake and transport of 9-nitrocamptothecin (9-NC), a potent anticancer agent, across Caco-2 cell monolayers was studied as a free and PLGA nanoparticle loaded drug. Different sizes (110 to 950 nm) of 9-nitrocamptothecin nanoparticles using poly (lactic-glycolic acid) were prepared by via the nanoprecipitation method. The transport of nanoparticles across the Caco-2 cell monolayer as a function of incubation time and concentration was evaluated for each different nanoparticle formulation. The amount of 9-NC transported from the apical to the basolateral side and the uptake of the drug into the cells was determined by HPLC. The uptake of intact nanoparticles into Caco-2 cells was visualized by confocal laser scanning microscopy using 6-coumarin as a fluorescent marker. The study demonstrated that Caco-2 cell uptake and transport of encapsulated 9-nitrocamptothecin is significantly affected by the diameter of the carrier and incubation time. In addition it was shown to be independent of concentration. The results indicated a significant accumulation of the drug in the cell membrane and an enhanced diffusion across the cell membrane. There was also a sustained release of characteristics pertaining to polymeric carriers that provided prolonged drug availability for absorptive cells.

Tumor necrosis factor-α increases the paracellular permeability of Caco-2 cell monolayers in vitro

AIM: To investigate the effects of tumor necrosis factor-α (TNF-α) on the paracellular permeability of Caco-2 cell monolayers and to explore potential mechanisms involved.

METHODS: Caco-2 cells were cultured in vitro to establish a model of intestinal epithelial barrier and divided randomly into two groups: control group and TNF-α treatment group. The TNF-α treatment group was further divided into four subgroups for testing at 3, 6, 12 and 24 h after TNF-α treatment. The changes in transepithelial electrical resistance (TEER) of Caco-2 cells were measured using an electrical resistance system. The changes in cytoskeleton were observed by direct staining with rhodamine-phalloidin. The activation of nuclear factor-κB (NF-κB) was determined by luciferase reporter gene assay.

RESULTS: The TEER significantly decreased in all four treatment subgroups compared to the control group (all P < 0.05). The TEER was significantly lower in the 24-h treatment subgroup than in other subgroups (all P < 0.05). The activation level of NF-κB was significantly raised in 3-, 6- and 12-h treatment subgroups compared to the control group (all P < 0.05). The activation level of NF-κB in 12-h treatment subgroup was significantly higher than those in other subgroups (all P < 0.05). In the control group, rhodamine-phalloidin staining showed that F-actin was visualized around the cell membrane and exhibited a honeycomb pattern of fluorescent staining. After treatment with TNF-α, the fluorescence signals were weakened and distributed in a serrated pattern.

CONCLUSION: TNF-α increases the paracellular permeability of Caco-2 cell monolayers perhaps by inducing NF-κB activation and actin reorganization.

Expression and metabolic activity of carboxylesterases in human colorectal carcinoma Caco-2 cells

AIM: To investigate the expression of carboxylesterases (CEs) in human colorectal carcinoma Caco-2 cells and evaluate their catalytic activity for hydrolysis of ester-containing drugs.

METHODS: The hydrolytic capacity of Caco-2 cells were evaluated using two substrates, imidapril and irinotecan (CPT-11), the specific substrates of human CE-1 and human CE-2, respectively. After co-incubation of the two substrates with Caco-2 cell 9 000 g supernatant (S9 fraction), the two drugs and their metabolic products were assayed by high-performance liquid chromatography (HPLC). Furthermore, the major CE isoforms expressed in Caco-2 cells were detected by reverse transcription-polymerase chain reaction (RT-PCR).

RESULTS: Compared with the human small intestinal microsomes, Caco-2 cells tend to hydrolyze imidapril instead of CPT-11. RT-PCR results indicated that hCE-1 was highly expressed in Caco-2 cells. In contrast, the expression of hCE-2 mRNA was hardly detected in Caco-2 cells.

CONCLUSION: The expression pattern of CEs in Caco-2 cells is completely different from that in human small intestine and colon. Therefore, caution should be exercised in predicting human intestinal absorption of ester-containing drugs based on transport results obtained using Caco-2 cells.

Effect of tumor necrosis factor-α on protein expression of tight junction protein in intestinal epithelial cells

AIM: To explore the mechanism of intestinal epithelial barrier disruption induced by tumor necrosis factor alpha (TNF-α). We detected the expression of the tight junction protein claudin-1 in Caco-2 cells with TNF-α treatment.

METHODS: Caco-2 cells between passages 20 and 30 were cultured with DMEM including 20% fetal bovine serum and 2 mmol/L glutamine for 7 d. Cells were then treated with different concentrations of TNF-α (0, 10, and 100 μg/L) for 24 h when they became fused. Protein was extracted from cells to prepare NP-40 detergent-soluble and insoluble protein fractions. Western blot was used to measure the protein levels of phosphorylated and unphosphorylated claudin-1. Indirect immunofluorescence was applied to the localization of claudin-1. Real-time quantity polymerase-chain reaction (RQ-PCR) was used to detect the mRNA expression of claudin-1.

RESULTS: Immunofluorescence showed that claudin-1 was distributed around the cell membrane and presented scrobiculate linear fluorescence. A 10 μg/L concentration of TNF-α caused weakened fluorescence signals that were abnormally distributed dentately. Claudin-1 has two molecular forms: one is the nonphosphorylated form (20 kDa) that primarily exists in NP-40 soluble proteins; the other is the phosphorylated form (25 kDa) that only exists in NP-40 insoluble proteins. TNF-α did not affect the protein expression of 65-kDa claudin-1 but decreased 80-kDa claudin-1 protein expression in a concentration-dependant manner compared with the control (10, 100 μg/L: 0.31 ± 0.02, 0.24 ± 0.05 vs 0.43 ± 0.09, P > 0.05, P < 0.05). Real time PCR demonstrated that the mRNA expression of claudin-1 in TNF-α treatment groups with different concentrations (10 and 100 μg/L) for 24 h, or a different reacting time (4, 8, 24 h), was not significantly different from the corresponding time normal groups (P > 0.05).

CONCLUSION: TNF-α does not affect the mRNA expression of the tight junction protein claudin-1 but decreases the expression of functional claudin-1 in Caco-2 cells.