Synthesis and Identification of FITC-Insulin Conjugates Produced Using Human Insulin and Insulin Analogues for Biomedical Applications

Comparison of virus-capsid mimicking biologic-shell based versus polymeric-shell nanoparticles for enhanced oral insulin delivery

Virus-capsid mimicking mucus-permeable nanoparticles are promising oral insulin carriers which surmount intestinal mucus barrier. However, the impact of different virus-capsid mimicking structure remains unexplored. In this study, utilizing biotin grafted chitosan as the main skeleton, virus-mimicking nanoparticles endowed with biologic-shell (streptavidin coverage) and polymeric-shell (hyaluronic acid/alginate coating) were designed with insulin as a model drug by self-assembly processes. It was demonstrated that biologic-shell mimicking nanoparticles exhibited a higher intestinal trans-mucus (>80%, 10 min) and transmucosal penetration efficiency (1.6-2.2-fold improvement) than polymeric-shell counterparts. Uptake mechanism studies revealed caveolae-mediated endocytosis was responsible for the absorption of biologic-shell mimicking nanoparticles whereas polymeric-shell mimicking nanoparticles were characterized by clathrin-mediated pathway with anticipated lysosomal insulin digestion. Further, in vivo hypoglycemic study indicated that the improved effect of regulating blood sugar levels was virus-capsid structure dependent out of which biologic-shell mimicking nanoparticles presented the best performance (5.1%). Although the findings of this study are encouraging, much more work is required to meet the standards of clinical translation. Taken together, we highlight the external structural dependence of virus-capsid mimicking nanoparticles on the muco-penetrating and uptake mechanism of enterocytes that in turn affecting their in vivo absorption, which should be pondered when engineering virus-mimicking nanoparticles for oral insulin delivery.

Polyampholyte-Based Polymer Hydrogels for the Long-Term Storage, Protection and Delivery of Therapeutic Proteins

Protein storage and delivery are crucial for biomedical applications such as protein therapeutics and recombinant proteins. Lack of proper protocols results in the denaturation of proteins, rendering them inactive and manifesting undesired side effects. In this study, polyampholyte-based (succinylated ε-poly-l-lysine) hydrogels containing polyvinyl alcohol and polyethylene glycol polymer matrices to stabilize proteins are developed. These hydrogels facilitated the loading and release of therapeutic amounts of proteins and withstood thermal and freezing stress (15 freeze-thaw cycles and temperatures of -80 °C and 37 °C), without resulting in protein denaturation and aggregation. To the best of our knowledge, this strategy has not been applied to the design of hydrogels constituting polymers, (in particular, polyampholyte-based polymers) which have inherent efficiency to stabilize proteins and protect them from denaturation. Our findings can open up new avenues in protein biopharmaceutics for the design of materials that can store therapeutic proteins long-term under severe stress and safely deliver them.

Recent progress on the development of fluorescent probes targeting the translocator protein 18 kDa (TSPO)

The translocator protein 18 kDa (TSPO) was first identified in 1997, and has now become one of the appealing subcellular targets in medicinal chemistry and its related fields. TSPO involves in a variety of diseases, covering neurodegenerative diseases, psychiatric disorders, cancers, and so on. To date, various high-affinity TSPO ligands labelled with single-photon emission computed tomography (SPECT)/positron emission tomography (PET) radionuclides have been reported, with some third-generation radioligands advanced to clinical trials. On the other hand, only a few number of TSPO ligands have been labelled with fluorophores for disease diagnosis. It is noteworthy that the majority of the TSPO fluorescent probes synthesised to date are based on visible fluorophores, suggesting that their applications are limited to in vitro studies, such as in vitro imaging of cancer cells, post-mortem analysis, and tissue biopsies examinations. In this context, the potential application of TSPO ligands can be broadened for in vivo investigations of human diseases by labelling with near-infrared (NIR)-fluorophores or substituting visible fluorophores with NIR-fluorophores on the currently developed fluorescent probes. In this review article, recent progress on fluorescent probes targeting the TSPO are summarised, with an emphasis on development trend in recent years and application prospects in the future.

Exosome-Mediated Insulin Delivery for the Potential Treatment of Diabetes Mellitus

Exosomes are extracellular nanovesicles between 30 and 150 nm that serve as essential messengers for different biological signaling and pathological processes. After their discovery, a wide range of applications have been developed, especially in therapeutic drug delivery. In this context, the aim of this work was to test the efficiency of exosome-mediated human insulin delivery using exosomes extracted from three different cell lines: hepatocellular carcinoma (HepG2); primary dermal fibroblasts (HDFa) and pancreatic β cells (RIN-m); all are related to the production and/or the ability to sense insulin and to consequently regulate glucose levels in the extracellular medium. The obtained results revealed that the optimal insulin loading efficiency was achieved by a 200 V electroporation, in comparison with incubation at room temperature. Moreover, the maximum in vitro exosome uptake was reached after incubation for 6 h, which slightly decreased 24 h after adding the exosomes. Glucose quantification assays revealed that exosome-mediated incorporation of insulin presented significant differences in HDFa and HepG2 cells, enhancing the transport in HDFa, in comparison with free human insulin effects in the regulation of extracellular glucose levels. No significant differences were found between the treatments in RIN-m cells. Hence, the results suggest that exosomes could potentially become a valuable tool for stable and biocompatible insulin delivery in diabetes mellitus treatment alternatives.

Synthesis, Characterization, and Specific Localization of Mitochondrial-Targeted Antioxidant Peptide SS31 Probe

The aim of this study is to investigate the targeting efficiency of FITC-SS31 to mitochondria in both normal and H2O2-induced oxidative damaged 661W cells, characterizing the properties of FITC-SS31 in the biological assays. The purity and molecular weight of FITC-SS31 were identified using HPLC and MS. MTT and LDH assays were used to evaluate the cytotoxicity and cell permeability. The binding ability of FITC-SS31 to cells was demonstrated by flow cytometry. The colocalization of FITC-SS31 and MitoTracker both in normal and oxidative cells was analyzed by a laser confocal microscope. We detected the DEGs between SS31+H2O2 and H2O2-alone-treated cells by RNA seq. GO and KEGG analyses were performed to predict the functional gene of SS31. The molecular weight of FITC-SS31 was 1142.2 with the 97.76% purity. The flow cytometry results showed that the MFI (mean fluorescence intensity) of FITC-SS31 in normal cells in the 4 h probe treatment group was higher than that in the 2 h and the 0 h group. The MFI in the 2 h probe treatment group was much higher than that in the 4 h and 0 h groups in damaged cells. The positive rate of 10 μM FITC-SS31 was higher than that of 1 μM and 5 μM. Fluorescein imaging analysis confirmed that FITC-SS31 was overlapped with MitoTracker. Through the analysis, DEGs were highly expressed in "localization, organelle, antioxidant activity, binding" functions and enriched in "AMPK signaling pathway, MAPK targets/nuclear events mediated by MAP kinase pathway and PI3K-Akt signaling pathway." It is speculated that SS31 exerts an antioxidant effect through one of these pathways. We hypothesized that SS31 could play a more efficient role in the pathological cells in the half-life period to avoid cell death due to oxidative damage. The functions of the DEGs in SS31+H2O2 and H2O2-alone samples are related to the localization and antioxidant activity of SS31. DEGs are mostly enriched in the AMPK signaling pathway, which needs further studies.

Injectable Silk Fibroin-Based Hydrogel for Sustained Insulin Delivery in Diabetic Rats

Diabetes is a chronic disease affecting over 400 million people worldwide. Inadequate production of insulin due to loss of beta cells or insulin resistance within the body imbalances the glucose homeostasis, resulting in an abrupt increase of blood glucose level. The conventional and last resort of treatment involves repeated subcutaneous insulin injections to maintain the physiological glucose homeostasis. However, continuous and multiple subcutaneous injections are associated with poor patient compliance and local amyloidosis of insulin, which can be overcome with controlled and sustained insulin delivery. In this context, we have designed and formulated an injectable silk fibroin hydrogel (iSFH) to realize sustained insulin delivery over a prolonged period under diabetic conditions. The specific composition of glycol additives (ethylene glycol and triethylene glycol) allowed the silk fibroin protein to form an injectable hydrogel within 50 min. The detailed characterization of iSFH by a field-emission scanning electron microscope displayed the desired mesoporous structures, which are appropriate for drug (insulin) encapsulation in its active form. Interestingly, the subcutaneous injection of iSFH-encapsulated insulin (insulin-iSFH) in diabetic T1DM Wistar rats showed controlled release of insulin and restored physiological glucose homeostasis up to 4 days. The biocompatible and biodegradable nature of iSFH makes it a potential drug delivery system for active storage, and controlled and sustained delivery of insulin in diabetic conditions to maintain the physiological glucose level.

Evaluation of self-emulsifying drug delivery systems for oral insulin delivery using an in vitro model simulating the intestinal proteolysis

The gentle preparation and the functionalization potential of self-emulsifying drug delivery systems (SEDDS) make them an interesting formulation strategy for oral administration of peptide and protein (p/p) drugs. A series of Kolliphor® RH40 (RH40) and Labrasol® (LAB)-based SEDDS containing either long-chain (LC) or medium-chain (MC) glycerides were formulated and characterized with regard to their rheological behavior, as well as the size distribution and zeta potential of the generated emulsions. Insulin, in order to be incorporated in SEDDS, was complexed with soybean phosphatidylcholine. The ability of different SEDDS to protect the incorporated insulin against enzymatic hydrolysis was evaluated by an in vitro model simulating the intestinal proteolysis. SEDDS were incubated in simulated intestinal fluids in the presence of α-Chymotrypsin (α-CT), and HPLC was used to quantify the remaining insulin. Principal component analysis (PCA) was applied to identify the relations between different excipients and properties of SEDDS that describe the SEDDS protective effect on insulin during in vitro proteolysis. The RH40-SEDDS behaved Newtonian in the presence of ethanol (EtOH) and non-Newtonian in the absence of EtOH, which generated emulsion with droplets between 30 to 300 nm. The LAB-SEDDS always behaved Newtonian and generated polydisperse emulsions with broad size distribution (190-4000 nm). During the in vitro proteolysis, insulin can be effectively protected against α-CT (> 60% remaining insulin after 60 min in vitro proteolysis). According to PCA analysis, insulin was better protected in MC-SEDDS compared to LC-SEDDS, and better in LAB-SEDDS compared to RH40-SEDDS. Monoacyl phosphatidylcholine and Capmul® MCM C8 were recognized as excipients favored for SEDDS protection on insulin. However, SEDDS viscosity and the addition of EtOH in SEDDS played insignificant roles on the remaining insulin after in vitro proteolysis. In summary, an in vitro proteolysis model with increased physiological relevance was applied to enable the optimal design of SEDDS for oral p/p drug delivery.

Cholesterol moieties as building blocks for assembling nanoparticles to achieve effective oral delivery of insulin

The amphiphilic cholesterol-phosphate conjugate can fabricate into cholesterol-coated nanoparticles by reverse emulsion method. The nanoparticles generated a rapid-onset and long-lasting hypoglycemic effect following gavage in T1DM rats.

FITC labeling of human insulin and transport of FITC-insulin conjugates through MDCK cell monolayer

Fluorescein isothiocyanate-labeled insulin (FITC-insulin) has been widely used for bioanalytical applications. Due to the high cost of commercial FITC-insulin and tedious labeling procedures described in the literature, there is still a need to develop a cost effective, reliable and quick labeling method for insulin. The purpose of the present work was to develop a quick and affordable method for FITC labeling of human insulin and to determine the effect of different conjugations of FITC to human insulin on its permeability through the MDCK cell monolayer. FITC labeling of insulin gives mono-, di- or tri-conjugates depending on the reaction time and the molar ratio of FITC:insulin. Mono-conjugate with unlabeled insulin, mixture of di- and tri-conjugate, and tri-conjugate with very little amount of di-conjugate were synthesized in less than 4 h. Degree of conjugation had an effect on the permeability of insulin through the MDCK cell monolayer. Mono-conjugate had higher permeability than the unlabeled insulin due to increase in partition coefficient. However, tri-conjugate showed lower permeability than the unlabeled insulin due to the increase in molecular weight.

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Quick and simple labeling method for FITC labeling of insulin.

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First report on the effect of different conjugation on the permeability of FITC-insulin across a biological membrane.

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FITC conjugation changes the partition coefficient of insulin.

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FITC conjugation affects the permeability of insulin.

[Synthesis of amphiphilic block copolymer of PLGA-b-(PEI-co-PEG) and characterization of the self-assembled cationic micelles]

OBJECTIVE

To synthesize a biodegradable and minimally cytotoxic amphiphilic block copolymer of PLGA-b-(PEI-co- PEG) and study its micellization behavior.

METHODS

PLGA was synthesized by ring-opening polymerization. The cross-linked copolymer of PEI-co-PEG was synthesized from the low-molecular-weight polyethyleneimine (PEI, 1800 D) and hydrophilic poly(ethylene glycol) (PEG, 2000 D). PLGA-b-(PEI-co-PEG) was synthesized by dehydration condensation reaction of PLGA and water soluble PEI-co-PEG. The biodegradability of PEI-co-PEG was evaluated according to the molecular weight change after incubation at 37 ℃ for different time. The cytotoxicity of PLGA- b-(PEI-co-PEG) and PEI-co-PEG in MCF-7 cells was determined by MTT assay. The cationic PLGA-b-(PEI-co-PEG) micelles were prepared by standard dialysis method. The particle size and Zeta potential of the micelles were measured by a Malvern laser particle size analyzer. Micelle/insulin complexes were prepared by simple mixing method and their morphology were characterized by transmission electron microscopy (TEM). The fluorescence quenching method was used to determine the stability of the micelle/insulin complexes at different salt concentrations.

RESULTS

Amphiphilic block copolymer of PLGA-b-(PEI-co-PEG) was successfully synthesized. The half-life of PEI-co-PEG degradation in PBS at 37 ℃ was about 48 h. The 50% cell inhibiting concentration (IC₅₀) of PLGA-b-(PEIco- PEG) and PEI-co-PEG in MCF-7 cells were 1375.7 μg/mL and 425.1 μg/mL, respectively. The micelles of PLGA-b-(PEI-co- PEG) (particle size: 99.5±2.61 nm, Zeta potential: 52.9±2.38 mV) were complexed with insulin via electrostatic interaction and formed nanoscale micelle/insulin complexes. The dissociation rate of micelle/insulin complexes in 150 mmol/L NaCl solution was 27.6%.

CONCLUSIONS

The synthesized PEI-co-PEG shows good degradability in vitro. The cytotoxicity of PLGA-b-(PEI-co- PEG) is significantly lower than PEI-co-PEG, and PLGA-b-(PEI-co-PEG) micelle/insulin complexes have good salt- resistant stability in physiological condition.

The function and mechanism of preactivated thiomers in triggering epithelial tight junctions opening

As a unique macromolecular permeation enhancer, thiolated polymers (thiomers), especially the preactivated thiomers, have demonstrated great merits in oral delivery of protein/peptide drugs by triggering epithelial tight junctions (TJs) opening. However, the underlying molecular mechanism remains unclear. To clarify this issue, preactivated thiomers were synthesized and their TJs opening function as well as signaling pathways on MDCK and Caco-2 cell monolayers was investigated. The results showed that preactivated thiomers could reduce TEER and increase the permeation of Na-Flu and FITC-Insulin over 2-fold and 4-fold on MDCK monolayers, respectively, indicating their huge potential as macromolecular permeation enhancers. The signaling pathway study showed that intracellular PTK Src but not FAK, involved in the TJs opening by claudin-4 disruption. Src activation was based on interaction between thiol group of thiomers and cysteine-riched Src upstream membrane receptors, EGFR and IGFR. The deep comprehension of the thiomers-mediated TJs opening mechanisms provides goodness in application of protein/peptide drugs for the oral delivery.

Insulin adsorption onto zinc oxide nanoparticle mediates conformational rearrangement into amyloid-prone structure with enhanced cytotoxic propensity

BACKGROUND

Injection localized amyloidosis is one of the most prevalent disorders in type II diabetes mellitus (TIIDM) patients relying on insulin injections. Previous studies have reported that nanoparticles can play a role in the amyloidogenic process of proteins. Hence, the present study deals with the effect of zinc oxide nanoparticles (ZnONP) on the amyloidogenicity and cytotoxicity of insulin.

METHODS

ZnONP is synthesised and characterized using XRD, Zeta Sizer, UV-Visible spectroscope and TEM. The characterization is followed by ZnONP interaction with insulin, which is studied employing fluorescence spectroscopes, isothermal titration calorimetry and molecular dynamics simulations. The interaction leads insulin conformational rearrangement into amyloid-like fibril, which is studied using thioflavin T dye binding assay, circular dichroism spectroscopy and TEM, followed by cytotoxicity propensity using Alamar Blue dye reduction assay.

RESULTS

Insulin has very weak interaction with ZnONP interface. Insulin at studied concentration forms amorphous aggregates at physiological pH, whereas in presence of ZnONP interface amyloid-like fibrils are formed. While the amyloid-like fibrils are cytotoxic to MIN6 and THP-1 cell lines, insulin and ZnONP individual solutions and their fresh mixtures enhance the cells proliferation.

CONCLUSIONS

The presence of ZnONP interface enhances insulin fibrillation at physiological pH by providing a favourable template for the nucleation and growth of insulin amyloids.

GENERAL SIGNIFICANCE

The studied protein-nanoparticle system from protein conformational dynamics point of view throws caution over nanoparticle use in biological applications, especially in vivo applications, considering the amyloidosis a very slow but non-curable degenerative disease.

Insulin uptake and action in microvascular endothelial cells of lymphatic and blood origin

Whereas the blood microvasculature constitutes a biological barrier to the action of blood-borne insulin on target tissues, the lymphatic microvasculature might act as a barrier to subcutaneously administrated insulin reaching the circulation. Here, we evaluate the interaction of insulin with primary microvascular endothelial cells of lymphatic [human dermal lymphatic endothelial cells (HDLEC)] and blood [human adipose microvascular endothelial cells (HAMEC)] origin, derived from human dermal and adipose tissues, respectively. HDLEC express higher levels of insulin receptor and signal in response to insulin as low as 2.5 nM, while HAMEC only activate signaling at 100 nM (a dose that blood vessels do not normally encounter). Low insulin acts specifically through the insulin receptor, while supraphysiological insulin acts through both the IR and insulin growth factor-1 receptor. At supraphysiological or injection site-compatible doses pertinent to lymphatic microvessels, insulin enters HAMEC and HDLEC via fluid-phase endocytosis. Conversely, at physiologically circulating doses (0.2 nM) pertinent to blood microvessels, insulin enters HAMEC through a receptor-mediated process requiring IR autophosphorylation but not downstream insulin signaling. At physiological doses, internalized insulin is barely degraded and is instead released intact to the extracellular medium. In conclusion, we document for the first time the mechanism of interaction of insulin with lymphatic endothelial cells, which may be relevant to insulin absorption during therapeutic injections. Furthermore, we describe distinct action and uptake routes for insulin at physiological and supraphysiological doses in blood microvascular endothelial cells, providing a potential explanation for previously conflicting studies on endothelial insulin uptake.

Insulin transport into the brain

While there is a growing consensus that insulin has diverse and important regulatory actions on the brain, seemingly important aspects of brain insulin physiology are poorly understood. Examples include: what is the insulin concentration within brain interstitial fluid under normal physiologic conditions; whether insulin is made in the brain and acts locally; does insulin from the circulation cross the blood-brain barrier or the blood-CSF barrier in a fashion that facilitates its signaling in brain; is insulin degraded within the brain; do privileged areas with a "leaky" blood-brain barrier serve as signaling nodes for transmitting peripheral insulin signaling; does insulin action in the brain include regulation of amyloid peptides; whether insulin resistance is a cause or consequence of processes involved in cognitive decline. Heretofore, nearly all of the studies examining brain insulin physiology have employed techniques and methodologies that do not appreciate the complex fluid compartmentation and flow throughout the brain. This review attempts to provide a status report on historical and recent work that begins to address some of these issues. It is undertaken in an effort to suggest a framework for studies going forward. Such studies are inevitably influenced by recent physiologic and genetic studies of insulin accessing and acting in brain, discoveries relating to brain fluid dynamics and the interplay of cerebrospinal fluid, brain interstitial fluid, and brain lymphatics, and advances in clinical neuroimaging that underscore the dynamic role of neurovascular coupling.

Selective lysine modification of native peptides via aza-Michael addition

N-Phenylvinylsulfonamides were developed as applicable reagents for site-selective lysine functionalization in native peptides with a free N-terminus.

Fabrication of biodegradable composite microneedles based on calcium sulfate and gelatin for transdermal delivery of insulin

To reduce the inconvenience and pain of subcutaneous needle injection, the calcium sulfate and gelatin biodegradable composite microneedle patches with high aspect-ratio microneedles (MNs) and a flexible substrate have been developed. The microneedles with an aspect-ratio approximate 6:1 exhibit excellent mechanical property which can achieve 0.4N for each needle. The cross-section views show the inside of microneedles that have abundant pores and channels which offer potential for different drug-release profiles. The preparation procedures, degradable property for the biodegradable composite microneedle patches are described in the paper. Insulin, the drug to control blood glucose levels in diabetic patients, has been embedded into the biodegradable composite MNs. The hypoglycemic effect for transdermal delivery of insulin is studied using diabetic Sprague-Dawley (SD) rats as models in vivo. After transdermal administration to the diabetic rats, the released insulin from biodegradable composite MNs exhibit an obvious and effective hypoglycemic effect for longer time compared with that of subcutaneous injection route. This work suggests that biodegradable composite MNs containing of insulin have a potential application in diabetes treatment via transdermal ingestion.