The use of iodixanol for the purification of rat pancreatic islets

Emerging Drug Delivery Vectors: Engineering of Plant-Derived Nanovesicles and Their Applications in Biomedicine

Extracellular vesicles can transmit intercellular information and transport biomolecules to recipient cells during various pathophysiological processes in the organism. Animal cell exosomes have been identified as potential nanodrugs delivery vehicles, yet they have some shortcomings such as high immunogenicity, high cytotoxicity, and complicated preparation procedures. In addition to exosomes, plant-derived extracellular vesicles (PDVs), which carry a variety of active substances, are another promising nano-transport vehicles emerging in recent years due to their stable physicochemical properties, wide source, and low cost. This work briefly introduces the collection and characterization of PDVs, then focuses on the application of PDVs as natural or engineered drug carriers in biomedicine, and finally discusses the development and challenges of PDVs in future applications.

Plant-Derived Vesicle-Like Nanoparticles as Promising Biotherapeutic Tools: Present and Future

Extracellular vesicles (EVs) are heterogeneous, phospholipid bilayer-enclosed biological particles that regulate cell communication by molecular cargo delivery and surface signaling. EVs are secreted by almost all living cells, including plant cells. Plant-derived vesicle-like nanoparticles (PDVLNs) is a generic term referring to vesicle-like nanostructure particles isolated from plants. Their low immunogenicity and wide availability make PDVLNs safer and more economical to be developed as therapeutic agents and drug carriers. Accumulating evidence indicates the key roles of PDVLNs in regulating interkingdom crosstalk between humans and plants. PDVLNs are capable of entering the human-body systemand delivering effector molecules to cells that modulate cell-signaling pathways. PDVLNs released by or obtained from plants thus have great influenceon human health and diseases. In this review, the biogenesis, detailed preparation methods, various physical and biochemical characteristics, biosafety, and preservation of PDVLNs are introduced, along with how these characteristics pertain to their biosafety and preservability. The potential applications of PDVLNs on different plant and mammalian diseases and PDVLN research standardization are then systematically discussed.

Isolation and Purification of Human Pancreatic Islets

Successful islet isolation is the key to islet transplantation in diabetic patients. However, islet isolation is a technically complex and time-consuming manual process. Optimizing the islet isolation process can improve islet yield and quality, reduce operators, and thus reduce costs.The isolation and purification of human islets include pancreas acquisition and preservation, pancreas digestion, islet purification, islet culture, and islet quality identification. Briefly, after the duodenum was removed, the pancreas was trimmed, the main pancreatic duct was intubated at the distal end of the pancreatic head, collagenase was injected into the pancreatic duct, and the perfused pancreatic tissue was cut and then digested in a Ricordi chamber. A digestion temperature of 37 °C was continuously used to assess the number of samples and the integrity of the lysed and released islets. At the end of the digestion process, collect the digested tissue in a 500 mL centrifuge tube prefilled with 25 mL of cold (4 °C) human serum albumin and centrifuge twice at 150 g for 3 min. After mixing with UW solution as islet storage solution, put it on ice (shake occasionally to prevent clumping) after 30 min. Digested pancreatic tissue was centrifuged at 2200 rpm for 5 min in a COBE 2991 cell processor to isolate islets from exocrine tissue using a continuous density gradient. The purified islet fractions were washed twice in HBSS supplemented with 10% human serum albumin and finally collected in CMRL1066 medium supplemented with the corresponding liquid. The purity of purified islets was calculated by DTZ staining, the survival rate of islets was calculated by FDA/PI staining, and islet function was determined by in vitro glucose-stimulated insulin secretion test.

Technology insight: Plant-derived vesicles-How far from the clinical biotherapeutics and therapeutic drug carriers?

Within the past decades, extracellular vesicles (EVs) have emerged as important mediators of intercellular communication in both prokaryotes and higher eukaryotes to regulate a diverse range of biological processes. Besides EVs, exosome-like nanoparticles (ELNs) derived from plants were also emerging. Comparing to EVs, ELNs are source-widespread, cost-effective and easy to obtain. Their definite activities can be utilized for potential prevention/treatment of an abundance of diseases, including metabolic syndrome, cancer, colitis, alcoholic hepatitis and infectious diseases, which highlights ELNs as promising biotherapeutics. In addition, the potential of ELNs as natural or engineered drug carriers is also attractive. In this review, we tease out the timeline of plant EVs and ELNs, introduce the arising separation, purification and characterization techniques, state the stability and transport manner, discuss the therapeutic opportunities as well as the potential as novel drug carriers. Finally, the challenges and the direction of efforts to realize the clinical transformation of ELNs are also discussed.

Introducing a New Experimental Islet Transplantation Model using Biomimetic Hydrogel and a Simple High Yield Islet Isolation Technique

BACKGROUND

Islet transplantation could be an ideal alternative treatment to insulin therapy for type 1 diabetes Mellitus (T1DM). This clinical and experimental field requires a model that covers problems such as requiring a large number of functional and viable islets, the optimal transplantation site, and the prevention of islet dispersion. Hence, the methods of choice for isolation of functional islets and transplantation are crucial.

METHODS

The present study has introduced an experimental model that overcomes some critical issues in islet transplantation, including in situ pancreas perfusion by digestive enzymes through common bile duct. In comparison with conventional methods, we inflated the pancreas in Petri dishes with only 1 ml collagenase type XI solution, which was followed by hand-picking isolation or Ficoll gradient separation to purify the islets. Then we used a hydrogel composite in which the islets were embedded and transplanted into the peritoneal cavity of the streptozotocin-induced diabetic C57BL/6 mice.

RESULTS

As compared to the yield of the classical methods, in our modified technique, the mean yield of isolation was about 130-200 viable islets/mouse pancreas. In vitro glucose-mediated insulin secretion assay indicated an appropriate response in isolated islets. In addition, data from in vivo experiments revealed that the allograft remarkably maintained blood glucose levels under 400 mg/dl and hydrogel composite prevents the passage of immune cells.

CONCLUSION

In the model presented here, the rapid islet isolation technique and the application of biomimetic hydrogel wrapping of islets could facilitate islet transplantation procedures.

An optimized protocol for purification of functional islets of Langerhans

Islets of Langerhans and β-cell isolation constitute routinely used cell models for diabetic research, and refining islet isolation protocols and cell quality assessment is a high priority. Numerous protocols have been published describing isolate of islets, but often rigorous and systematic assessment of their integrity is lacking. Herein, we propose a new protocol for optimal generation of islets. Pancreases from mice and rats were excised and digested using a low-activity collagenase solution and islets were then purified by a series of sedimentations and a Percoll gradient. Islets were maintained in culture for 5 days, during which viability, pro/antiapoptotic, and islet-specific genes, glucose-stimulated calcium entry, glucose uptake, and insulin secretion were assessed. The commonly used islet isolation technique by collagenase injection through the common bile duct (CBD) was also performed and compared with the present approach. This new protocol produced islets that retained a healthy status as demonstrated by the yield of stable living cells. Furthermore, calcium oscillation, glucose uptake, and insulin secretion remained intact in the islet cultures. This was reproducible when many rodent species were used, and neither sex nor age affected the cells behavior. When compared with the CBD technique, islet physiology was similar. Finally, this approach was used to uncover new ion channel candidates implicated in insulin secretion. In conclusion, this study outlines an efficient protocol for islet preparation that may support research into new therapeutic targets in diabetes research.

Adipose- and muscle-derived Wnts trigger pancreatic β-cell adaptation to systemic insulin resistance

Wnt signaling molecules are associated with obesity, hyperlipidemia, and type 2 diabetes (T2D). Here, we show that two Wnt proteins, WNT3a and WNT4, are specifically secreted by skeletal muscle and adipose tissue during the development of insulin resistance and play an important role in cross-talk between insulin-resistant tissues and pancreatic beta cells. The activation of Frizzled receptor and Wnt signaling in pancreatic islets via circulating WNT3a in blood resulted in higher insulin secretion and an increase in beta cell proliferation, thus leading to islet adaptation in a pre-diabetic state. Interestingly, in fully developed T2D, the expression profiles of Wnt3a and Wnt4 in adipose tissue and muscle cells and blood plasma levels of these proteins were opposite to the pre-diabetic state, thus favoring the downregulation of Wnt signaling in beta cells and resulting in dysfunctional pancreatic islets. These results demonstrate that alterations in the secretion profile of a canonical Wnt activator (WNT3a) and inhibitor (WNT4) from insulin-resistant tissues during the development of T2D are responsible for triggering progression from a pre-diabetic to a diabetic state. We also show here that WNT3a and WNT4 are potent myokines, and their expression and secretion are regulated in response to nutritional and metabolic changes.

Blockade of Na+ channels in pancreatic α-cells has antidiabetic effects

Pancreatic α-cells express voltage-gated Na(+) channels (NaChs), which support the generation of electrical activity leading to an increase in intracellular calcium, and cause exocytosis of glucagon. Ranolazine, a NaCh blocker, is approved for treatment of angina. In addition to its antianginal effects, ranolazine has been shown to reduce HbA1c levels in patients with type 2 diabetes mellitus and coronary artery disease; however, the mechanism behind its antidiabetic effect has been unclear. We tested the hypothesis that ranolazine exerts its antidiabetic effects by inhibiting glucagon release via blockade of NaChs in the pancreatic α-cells. Our data show that ranolazine, via blockade of NaChs in pancreatic α-cells, inhibits their electrical activity and reduces glucagon release. We found that glucagon release in human pancreatic islets is mediated by the Nav1.3 isoform. In animal models of diabetes, ranolazine and a more selective NaCh blocker (GS-458967) lowered postprandial and basal glucagon levels, which were associated with a reduction in hyperglycemia, confirming that glucose-lowering effects of ranolazine are due to the blockade of NaChs. This mechanism of action is unique in that no other approved antidiabetic drugs act via this mechanism, and raises the prospect that selective Nav1.3 blockers may constitute a novel approach for the treatment of diabetes.

Improved Islet Purity by the Hypertonic-Hypotonic Method

Introduction

Islet purification is usually performed using the density gradient separation method, but the purity of islets is low because exocrine cells and the embedded islets are hard to remove by using only the density gradient method. The aim of this study was to establish a new islet purification process comprising a hypertonic-hypotonic treatment step followed by a density gradient centrifugation step to improve the purity of islets.

Methods

The Plackett-Burman method was used to determine which factors had a significant influence on the purity of islets obtained after the hypertonic-hypotonic treatment step.

Results

The hypertonic solution concentration and the incubation time were both found to have a significant effect on islet purity. The purity of islets obtained using the modified purification process was significantly higher than that of islets obtained by density gradient alone (97% vs. 87.23%). Importantly, good cell viability and normal insulin secretion ability of islets were maintained following the modified purification.

Conclusions

The new purification process allows isolation of islets with improved purity and does not compromise the viability or function of the islets.

The PARK2 gene is involved in the maintenance of pancreatic β-cell functions related to insulin production and secretion

Several association studies have implicated the PARK2 gene that encodes parkin--the key molecule orchestrating the mitochondrial quality control system--as a candidate susceptibility gene for diabetes. A total of 7551 unrelated Korean KARE cohort subjects were analyzed to investigate the association between the PARK2 single nucleotide polymorphism (SNP) and quantitative glycemic traits. Two SNPs, rs10455889 and rs9365294, were significantly associated with fasting plasma glucose level (p=∼1.2×10(-4)) and insulin secretion indices (p=∼7.4×10(-5)) in male KARE subjects. Parkin was expressed predominantly in the rat pancreatic islets. Downregulation of the Park2 gene in rat INS-1 β-cells resulted in a significant decrease in the glucose-stimulated insulin secretion, intracellular insulin gene expression, and intracellular ATP level. The Park2-depleted β-cells also exhibited increased mitochondrial fragmentation and ROS production and decreased mitochondrial membrane potential. Both population-based statistical evaluation and experimental evidence demonstrated a fundamental role of the PARK2 gene in the maintenance of β-cell function.

Pancreatic islet derived stem cells can express co-stimulatory molecules of antigen-presenting cells

BACKGROUND

Antigen-presenting cells (APCs) are crucial intermediates in the generation of both innate and specific immune responses. It has long been understood that some APCs are resident in islets in situ as well as after isolation. Our aim was to investigate the presence of molecules involved in antigen presentation in rat pancreatic islet-derived stem cells (PI-SCs).

METHODS

We used immunocytochemistry and reverse transcription polymerization chain reaction to study immunophenotypic characteristics; pluripotent-related gene expressions; transcripts coding for antigen-presenting surface proteins CD40, CD80, CD86; and major histocompatibility complex class II in addition to genes with known antiapoptotic functions including mitogen-activated protein kinase-activated protein kinase 2 (MAPKAPK2), tumor necrosis factor alpha-induced protein 3 (TNFAIP3) interacting protein 1 (TNIP1) and BCL3 of the PI-SCs.

RESULTS

Rat PI-SCs were negative for CD45 as demonstrated by flow cytometry and for CD31, CD34, and CD71 as demonstrated by immunocytochemistry. Therefore, there was no evidence of hematopoietic precursors in the cultures. OCT4, SOX2, and REX1 were expressed by rat PI-SCs. We determined the expression of genes for antigen-presenting surface proteins CD40 and CD80, and genes with known antiapoptotic functions including MAPKAPK2, TNIP1 and BCL3, besides the surface protein, CD80, by flow cytometry.

CONCLUSION

Expression of these genes by rat PI-SCs implied that they could be involved in the regulation of immunity in islets, highlighting the influence of protective role-playing antiapoptotic mechanisms on pancreatic islet cells. This study offers the potential to understand the molecular mechanisms of a devastating disease, type-1 diabetes mellitus.

Bone marrow-derived mesenchymal stem cells co-cultured with pancreatic islets display β cell plasticity

The direct co-culturing effect of rat bone-marrow-derived mesenchymal stem cells (rBM-MSCs) on the pancreatic-islets (PIs) was studied to obtain functional islet cells. MSCs were isolated from rat bone marrow and cultivated under standard conditions. Following their characterization, the rBM-MSCs were directly (with cell-islet contact) co-cultured with recovered PIs together with the single cell cultures of those cell cultures as a control. The effect of direct co-cultures of rBM-MSCs with the PIs of normal rats was investigated using immunophenotypical and functional methods. The change in the amount of insulin secretion was evaluated as an indicator for differentiation of rBM-MSCs. One approache for in vitro differentiation to achieve reprogramming for differentiation into suitable cell types by changing the microenvironment of the cells to provide signals that might activate metabolic pathways is to use co-cultures with the microenvironment of the specific cells of the desired cell type, tissue/organ extracts, extracellular matrix compounds or biologically absorbable materials. Differentiated rBM-MSCs were found to be immunopositive for the specific insulin-producing cell marker, insulin, but not in undifferentiated rBM-MSCs. The functionality tests by ELISA confirmed that insulin secretion of co-cultured MSCs with islets was higher than that of islets. These evidences indicated that PIs could be regarded as critical components of the stem cell niche, such that MSCs can be differentiated into insulin-producing cells (IPCs). Moreover, direct cell-to-cell contact might provide additional and independent support. This approach would circumvent the need for PI-stem cell co-culture and could potentially facilitate the production of functional IPCs for future clinical applications.

Induction of indoleamine 2,3-dioxygenase by gene delivery in allogeneic islets prolongs allograft survival

Indoleamine 2,3-dioxygenase (IDO), an enzyme that plays a critical role in fetomaternal tolerance, exerts immunoregulatory functions suppressing T-cell responses. The aims of this study were to promote IDO expression in rat islets using a nonviral gene transfer approach, and to analyze the effect of the in vivo induction of IDO in a model of allogeneic islet transplantation. The IDO cDNA was isolated from rat placenta, subcloned into a plasmid and transfected into rat islets using Lipofectamine. The efficiency of transfection was confirmed by qRT-PCR and functional analysis. The in vivo effect of IDO expression was analyzed in streptozotocin-induced diabetic Lewis rats transplanted with allogeneic islets under the renal capsule. Transplantation of IDO-allogeneic islets reversed diabetes and maintained metabolic control, in contrast to transplantation of allogeneic nontransfected islets, which failed shortly after transplantation in all animals. Graft survival of allograft islets transfected with IDO transplanted without any immunosuppression was superior to that observed in diabetic rats receiving nontransfected islets. These data demonstrated that IDO expression induced in islets by lipofection improved metabolic control of streptozotocin-diabetic rats and prolonged allograft survival.

Improved, low-cost methods for pancreatic islet purification in rats

OBJECTIVE

Density gradient separation of islets from exocrine tissue is usually performed using Ficoll. However, this reagent significantly increases the cost of isolation. The aim of the present study was to investigate the effects on islet preparations of purification methods using Lymphoprep and Iodixanol (OptiPrep) density gradients.

METHODS

Pancreata were procured from 46 Wistar rats, loaded with collagenase V (Sigma), and mechanically dissociated using standard procedures. After the digestion phase, the islets purified by 3 methods-Ficoll, Lymphoprep, and Iodixanol (OptiPrep)-were assessed for yields, purity, morphology, and in vitro function.

RESULT

We expressed the yields as islet equivalents (IEQ, diameter standardizing to 150 microm), showing no significant differences. Compared with the Ficoll group, the purity was significantly higher in the Lymphoprep (P = .005) and Iodixanol (OptiPrep) groups (P = .011). While the viability was >90% in all 3 groups, the viability in the Lymphoprep Group and OptiPrep groups was significantly higher than that of the Ficoll group (P < .001). In vitro islet function did not differ among the 3 experimental groups.

CONCLUSION

Lymphoprep and Iodixanol were as effective as Ficoll in terms of islet yield and in vitro function. High-purity and high-viability islet cells were obtained using improved Lymphoprep-based or Iodixanol (OptiPrep)-based density gradient methods, potential low-cost substitutes for Ficoll.

Islet transplantation and antioxidant management: A comprehensive review

Islet transplantation as a promising treatment for type 1 diabetes has received widespread attention. Oxidative stress plays an essential role in cell injury during islet isolation and transplantation procedures. Antioxidants have been used in various studies to improve islet transplantation procedures. The present study reviews the role of oxidative stress and the benefits of antioxidants in islet transplantation procedures. The bibliographical databases Pubmed and Scopus were searched up to November 2008. All relevant human and animal in-vivo and in-vitro studies, which investigated antioxidants on islets, were included. Almost all the tested antioxidants used in the in-vitro studies enhanced islet viability and insulin secretion. Better control of blood glucose after transplantation was the major outcome of antioxidant therapy in all in-vivo studies. The data also indicated that antioxidants improved islet transplantation procedures. Although there is still insufficient evidence to draw definitive conclusions about the efficacy of individual supplements, the benefits of antioxidants in islet isolation procedures cannot be ignored.

Modified method for isolation of langerhans islets from mice

Successful isolation of Langerhans islets is a crucial prerequisite for their experimental or possible clinical use such as transplantation. Centrifugation in a Ficoll gradient is a common step used for separation of Langerhans islets from exocrine tissue. However, islets have been reported to be negatively affected by employing Ficoll gradients. Therefore, the aim of this study was to modify the isolation procedure by excluding Ficoll gradient centrifugation to obtain a similar or better yield of viable, functional islets. In our modification of the isolation procedure, the separation of islets from exocrine tissue was based on their sedimentation rate combined with their differential ability to attach to the surface of culture dishes for suspension cells. The resulting purity of islets facilitated their handpicking from the suspension. The mean yield was 900 viable, insulin-producing islets per mouse, which was comparable to or even higher than the yield in commonly used protocols. Our modification of the isolation method may be useful when centrifugation in Ficoll gradient is undesirable due to potential toxicity.

Adhesive growth of pancreatic islet cells on a polyglycolic acid fibrous scaffold

BACKGROUND

The use of cultured pancreatic islet cells for diabetes treatment offers several advantages. In theory, cultured cells show greater purity and lower immunogenicity. However, cultured islet cells display a low survival rate in vitro. In the present study we grew islet cells on a polyglycolic acid (PGA) fibrous scaffold to promote cell adhesion, growth, and viability during prolonged culture.

METHODS

Islets isolated from Wistar rat pancreata were digested with collagenase and purified by the Ficoll method. Cells were grown in culture with or without PGA scaffolds. Islet cell purity was determined using a dithizone stain; viability and survival rates were determined using an AO-PI stain. The insulin-secretion index was detected using radioimmunodetection and the growth on an adhesive scaffold analyzed using an inverted microscope and scanning electron microscope (SEM).

RESULTS

In contrast to the scaffold-free control group, cells cultured on PGA scaffolds exhibited improved morphology, less cell death, and prolonged survival times. Cell viability and survival rates were significantly increased in scaffolded cells when compared to control cells (P < .05). Increased insulin secretion was observed in the culture solution of scaffolded cells following stimulation with low glucose (5.6 mmol/L) versus high glucose (16.7 mmol/L). The secretion indices of the two groups were significantly different (P < .05). Islet cell growth, as observed under SEM, was tightly circumvolute, adhesive, and three-dimensional.

CONCLUSIONS

The present results demonstrated that islet cells can successfully grow and survive in culture on a PGA scaffold. These cells exhibited enhanced viability, survival, and insulin secretion.

Efficacy comparison of rat islet purification between iodixanol and Ficoll density gradient method

AIM: To compare the yield, purity, quality and function of rat islets after purification by iodixanol or Ficoll-400 density gradient method.

METHODS: Twenty Sprague Dawley rats were randomly divided into iodixanol and Ficoll group according to the corresponding purification methods. Rat pancreas was isolated by collagenase P digestion, and the rat islets of two groups were purified by iodixanol or Ficoll-400 density gradient method. After isolation, the islet yield and purity were evaluated by DTZ staining and the islet function was assessed by insulin release assays in vitro and islet allotransplantation in vivo.

RESULTS: There were no marked differences in the yield and purity of islets between both groups. The survival rate of islets in iodixanol group was significantly higher than that in Ficoll group (93.3% ± 3.5% vs 84.8% ± 3.8%, P < 0.01), and the time of hyperglycemia reversal in diabetic rat was also longer (11.4 ± 2.1 d vs 7.0 ± 1.6 d, P < 0.05).

CONCLUSION: Iodixanol density gradient method is superior to Ficoll-400 method in improving the quality and function of purified rat islets.