Insight into the in vivo translocation of oral liposomes by fluorescence resonance energy transfer effect

Gastroretentive drug delivery systems: A holy grail in oral delivery

Gastroretentive drug delivery systems (GRDDSs) offer a promising strategy for enhancing oral drug bioavailability by prolonging gastric residence time and enabling site-specific drug release. This review examines the key materials used in GRDDSs, including polymers for controlled drug release, gas-generating agents for buoyancy, and mucoadhesive components for improved retention and stability. Advances in fabrication techniques, such as 3D printing, spray drying, and nanoparticle encapsulation, have enabled precise modulation of drug release kinetics and retention properties. However, challenges such as inter-subject variability, physiological constraints, and manufacturing scalability remain. Future research will focus on smart materials, multi-drug platforms, and expanding applications to biologics and nutraceuticals, paving the way for more effective and patient-compliant oral drug delivery systems.

FRET-based analysis on the fate of liposome and cyclodextrin@liposome nanocomposites from ocular surface to the posterior segment of the eye

Investigating the structural integrity of nanocarriers in vivo is vital for exploring the fate of nanocarriers from ocular surface to the posterior segment of the eye. Most of the published studies adopted the structural integrity ratio of nanocarriers to determine the fate of them, which lacked scientific support. In this study, two methods were used to explore the factors which affected the structural integrity of liposomes. A new method with the standard curve of FRET fluorescence intensity and carbocyanine 7 (Cy7) content was drawn for the first time. Secondly, we used the traditional method of drawing the standard curve of FRET fluorescence efficiency and structural integrity ratios. The results showed that liposomes with particle size about 120 nm, positively charged, polyethyleneglycol5000 (PEG5000) and glycine sarcosine (GS) modified had the highest Cy7 content in rabbit tissues. When the dosage of Cy7 was 25 μg, at 60 min, the content of Cy7 in intact liposomes and the structural integrity ratio of liposomes in sclera was 210.5 ± 14.9 ng and 19.8 ± 5.3 %, respectively. Compared with the structural integrity ratio, the Cy7 content in the intact carrier could better estimate the fate of nanocarriers in vivo scientifically. On this basis, the fate of dual-carrier nanocomposites and the inner cyclodextrin complexes in vivo was investigated. The intact cyclodextrin complexes could reach choroid-retina with the protection of outer liposomes. The structural integrity ratios of liposomes were also studied after crossing human conjunctival epithelial cells (HConEpiC) monolayer, but in vitro cellular experiments could not simulate the real situation in vivo. Finally, the tissue distribution of nanocomposites was studied in rabbit eyes. The concentration of dexamethasone (Dex) in choroid-retina was 158 ± 23 ng/g after 3 h, which exhibited better drug delivery ability compared with our previous study. Overall, the present study provides a new scientific method to estimate the structural integrity in vivo, which is beneficial for the rational design of drug delivery systems with more structural integrity in vivo and higher drug delivery efficiency.

Mesoporous silica nanoparticles: An emerging approach in overcoming the challenges with oral delivery of proteins and peptides

Proteins and peptides (PPs), as therapeutics are widely explored in the past few decades, by virtue of their inherent advantages like high specificity and biocompatibility with minimal side effects. However, owing to their macromolecular size, poor membrane permeability, and high enzymatic susceptibility, the effective delivery of PPs is often challenging. Moreover, their subjection to varying environmental conditions, when administered orally, results in PPs denaturation and structural conformation, thereby lowering their bioavailability. Hence, for effective delivery with enhanced bioavailability, protection of PPs using nanoparticle-based delivery system has gained a growing interest. Mesoporous silica nanoparticles (MSNs), with their tailored morphology and pore size, high surface area, easy surface modification, versatile loading capacity, excellent thermal stability, and good biocompatibility, are eligible candidates for the effective delivery of macromolecules to the target site. This review highlights the different barriers hindering the oral absorption of PPs and the various strategies available to overcome them. In addition, the potential benefits of MSNs, along with their diversifying role in controlling the loading of PPs and their release under the influence of specific stimuli, are also discussed in length. Further, the tuning of MSNs for enhanced gene transfection efficacy is also highlighted. Since extensive research is ongoing in this area, this review is concluded with an emphasis on the potential risks of MSNs that need to be addressed prior to their clinical translation.

FRET as the tool for in vivo nanomedicine tracking

Advanced drug delivery system utilizing a nanocarrier is the major application of nanotechnology on pharmacotherapeutics. However, despite the promising benefits and a leading trend in pharmaceutical research, nanomedicine development suffers from a poor clinical translation problem as only a handful of nanomedicine products reach the market yearly. The conventional pharmacokinetic study generally focuses only on monitoring the level of a free drug but ignores the nanocarrier's role in pharmacokinetics. One hurdle is that it is difficult to directly track intact nanocarriers in vivo to explore their pharmacokinetics. Although several imaging techniques such as radiolabeling, nuclear imaging, fluorescence imaging, etc., have been developed over the past few years, currently, one method that can successfully track the intact nanocarriers in vivo directly is by Förster resonance energy transfer (FRET). This review summarizes the application of FRET as the in vivo nanoparticle tracker for studying the in vivo pharmacokinetics of the organic nanocarriers and gives elaborative details on the techniques utilized.

The long-circulating effect of pegylated nanoparticles revisited via simultaneous monitoring of both the drug payloads and nanocarriers

The long-circulating effect is revisited by simultaneous monitoring of the drug payloads and nanocarriers following intravenous administration of doxorubicin (DOX)-loaded methoxy polyethylene glycol-polycaprolactone (mPEG-PCL) nanoparticles. Comparison of the kinetic profiles of both DOX and nanocarriers verifies the long-circulating effect, though of limited degree, as a result of pegylation. The nanocarrier profiles display fast clearance from the blood despite dense PEG decoration; DOX is cleared faster than the nanocarriers. The nanocarriers circulate longer than DOX in the blood, suggesting possible leakage of DOX from the nanocarriers. Hepatic accumulation is the highest among all organs and tissues investigated, which however is reversely proportionate to blood circulation time. Pegylation and reduction in particle size prove to extend circulation of drug nanocarriers in the blood with simultaneous decrease in uptake by various organs of the mononuclear phagocytic system. It is concluded that the long-circulating effect of mPEG-PCL nanoparticles is reconfirmed by monitoring of either DOX or the nanocarriers, but the faster clearance of DOX suggests possible leakage of a fraction of the payloads. The findings of this study are of potential translational significance in design of nanocarriers towards optimization of both therapeutic and toxic effects.

FRET Ratiometric Nanoprobes for Nanoparticle Monitoring

Fluorescence labelling is often used for tracking nanoparticles, providing a convenient assay for monitoring nanoparticle drug delivery. However, it is difficult to be quantitative, as many factors affect the fluorescence intensity. Förster resonance energy transfer (FRET), taking advantage of the energy transfer from a donor fluorophore to an acceptor fluorophore, provides a distance ruler to probe NP drug delivery. This article provides a review of different FRET approaches for the ratiometric monitoring of the self-assembly and formation of nanoparticles, their in vivo fate, integrity and drug release. We anticipate that the fundamental understanding gained from these ratiometric studies will offer new insights into the design of new nanoparticles with improved and better-controlled properties.

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

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