The Morphology of Islets within the Porcine Donor Pancreas Determines the Isolation Result: Successful Isolation of Pancreatic Islets can Now be Achieved from Young Market Pigs

Advancing Diabetes Research: A Novel Islet Isolation Method from Living Donors

Pancreatic islet isolation is critical for type 2 diabetes research. Although -omics approaches have shed light on islet molecular profiles, inconsistencies persist; on the other hand, functional studies are essential, but they require reliable and standardized isolation methods. Here, we propose a simplified protocol applied to very small-sized samples collected from partially pancreatectomized living donors. Islet isolation was performed by digesting tissue specimens collected during surgery within a collagenase P solution, followed by a Lympholyte density gradient separation; finally, functional assays and staining with dithizone were carried out. Isolated pancreatic islets exhibited functional responses to glucose and arginine stimulation mirroring donors' metabolic profiles, with insulin secretion significantly decreasing in diabetic islets compared to non-diabetic islets; conversely, proinsulin secretion showed an increasing trend from non-diabetic to diabetic islets. This novel islet isolation method from living patients undergoing partial pancreatectomy offers a valuable opportunity for targeted study of islet physiology, with the primary advantage of being time-effective and successfully preserving islet viability and functionality. It enables the generation of islet preparations that closely reflect donors' clinical profiles, simplifying the isolation process and eliminating the need for a Ricordi chamber. Thus, this method holds promises for advancing our understanding of diabetes and for new personalized pharmacological approaches.

Bioabsorption of Subcutaneous Nanofibrous Scaffolds Influences the Engraftment and Function of Neonatal Porcine Islets

The subcutaneous space is currently being pursued as an alternative transplant site for ß-cell replacement therapies due to its retrievability, minimally invasive procedure and potential for graft imaging. However, implantation of ß-cells into an unmodified subcutaneous niche fails to reverse diabetes due to a lack of adequate blood supply. Herein, poly (ε-caprolactone) (PCL) and poly (lactic-co-glycolic acid) (PLGA) polymers were used to make scaffolds and were functionalized with peptides (RGD (Arginine-glycine-aspartate), VEGF (Vascular endothelial growth factor), laminin) or gelatin to augment engraftment. PCL, PCL + RGD + VEGF (PCL + R + V), PCL + RGD + Laminin (PCL + R + L), PLGA and PLGA + Gelatin (PLGA + G) scaffolds were implanted into the subcutaneous space of immunodeficient Rag mice. After four weeks, neonatal porcine islets (NPIs) were transplanted within the lumen of the scaffolds or under the kidney capsule (KC). Graft function was evaluated by blood glucose, serum porcine insulin, glucose tolerance tests, graft cellular insulin content and histologically. PLGA and PLGA + G scaffold recipients achieved significantly superior euglycemia rates (86% and 100%, respectively) compared to PCL scaffold recipients (0% euglycemic) (* p < 0.05, ** p < 0.01, respectively). PLGA scaffolds exhibited superior glucose tolerance (* p < 0.05) and serum porcine insulin secretion (* p < 0.05) compared to PCL scaffolds. Functionalized PLGA + G scaffold recipients exhibited higher total cellular insulin contents compared to PLGA-only recipients (* p < 0.05). This study demonstrates that the bioabsorption of PLGA-based fibrous scaffolds is a key factor that facilitates the function of NPIs transplanted subcutaneously in diabetic mice.

Correction of Hyperglycemia in Diabetic Rats With the Use of Microencapsulated Young Market Pig Islets

OBJECTIVE

The aim of this work was to investigate the transplantation efficacy of microencapsulated young market pig islets in a diabetic rat model.

METHODS

Islets were isolated and purified from young market pigs obtained from a local slaughterhouse. The islets were encapsulated in barium alginate and subjected to a glucose-induced insulin release functional assay in culture. Microencapsulated islets were transplanted into diabetic Sprague-Dawley rats and removed after 30 days for histologic examination.

RESULTS

The mean islet equivalent (IEQ) yield per gram of digested tissue was 3,125 ± 617 IEQ/g after isolation and 2,618 ± 917 IEQ/g after purification, respectively. Host rats' blood glucose concentrations normalized (from 22.3 ± 2.7 mmol/L to 5.1 ± 0.67 mmol/L) following encapsulated islet transplantation. After graft removal, hyperglycemia recurred in the rats, indicating that the grafts were responsible for maintaining euglycemia. Histology revealed viable islets in the capsules 30 days after graft removal. Immunolabeling of insulin verified that β-cells within the capsules remained well granulated. No fibrosis or immune cells were found in histopathology.

CONCLUSIONS

Barium alginate encapsulation of young market pig islets can normalize glucose regulation in diabetic rats without fibrosis or an immunologic response.

Plasticity and Aggregation of Juvenile Porcine Islets in Modified Culture: Preliminary Observations

Diabetes is a major health problem worldwide, and there is substantial interest in developing xenogeneic islet transplantation as a potential treatment. The potential to relieve the demand on an inadequate supply of human pancreata is dependent upon the efficiency of techniques for isolating and culturing islets from the source pancreata. Porcine islets are favored for xenotransplantation, but mature pigs (>2 years) present logistic and economic challenges, and young pigs (3-6 months) have not yet proven to be an adequate source. In this study, islets were isolated from 20 juvenile porcine pancreata (~3 months; 25 kg Yorkshire pigs) immediately following procurement or after 24 h of hypothermic machine perfusion (HMP) preservation. The resulting islet preparations were characterized using a battery of tests during culture in silicone rubber membrane flasks. Islet biology assessment included oxygen consumption, insulin secretion, histopathology, and in vivo function. Islet yields were highest from HMP-preserved pancreata (2,242 ± 449 IEQ/g). All preparations comprised a high proportion (>90%) of small islets (<100 μm), and purity was on average 63 ± 6%. Morphologically, islets appeared as clusters on day 0, loosely disaggregated structures at day 1, and transitioned to aggregated structures comprising both exocrine and endocrine cells by day 6. Histopathology confirmed both insulin and glucagon staining in cultures and grafts excised after transplantation in mice. Nuclear staining (Ki-67) confirmed mitotic activity consistent with the observed plasticity of these structures. Metabolic integrity was demonstrated by oxygen consumption rates = 175 ± 16 nmol/min/mg DNA, and physiological function was intact by glucose stimulation after 6-8 days in culture. In vivo function was confirmed with blood glucose control achieved in nearly 50% (8/17) of transplants. Preparation and culture of juvenile porcine islets as a source for islet transplantation require specialized conditions. These immature islets undergo plasticity in culture and form fully functional multicellular structures. Further development of this method for culturing immature porcine islets is expected to generate small pancreatic tissue-derived organoids termed "pancreatites," as a therapeutic product from juvenile pigs for xenotransplantation and diabetes research.

Encapsulation of Islets in Rough Surface, Hydroxymethylated Polysulfone Capillaries Stimulates VEGF Release and Promotes Vascularization after Transplantation

The transplantation of encapsulated islets of Langerhans is one approach to treat type 1 diabetes without the need of lifelong immunosuppression. Capillaries have been used for macroencapsulation because they have a favorable surface-to-volume ratio and because they can be refilled. It is unclear at present whether the outer surface of such capillaries should be smooth to prevent, or rough to promote, cell adhesions. In this study we tested a new capillary made of modified polysulfone (MWCO: 50 kDa) with a rough, open-porous outer surface for islet transplantation. Compared with free-floating islets, encapsulation of freshly isolated rat islets affected neither the kinetics nor the efficiency of glucose-induced insulin release in perifusion experiments. Free-floating islets maintained insulin secretion during cell culture but encapsulated islets gradually lost their glucose responsiveness and released VEGF. This indicated hypoxia in the capillary lumen. Transplantation of encapsulated rat islets into diabetic rats significantly reduced blood glucose concentrations from the first week of implantation. This hypoglycaemic effect persisted until explantation 4 weeks later. Transplantation of encapsulated porcine islets into diabetic rats reduced blood glucose concentrations depending on the islet purity. With semipurified islets a transient reduction of blood glucose concentrations was observed (2, 8, 18, 18 days) whereas with highly purified islets a sustained normoglycaemia was achieved (more than 28 days). Explanted capillaries containing rat islets were covered with blood vessels. Vascularization was also observed on capillaries containing porcine islets that were explanted from normoglycaemic rats. In contrast, on capillaries containing porcine islets that were explanted from hyperglycemic rats a fibrous capsule and lymphocyte accumulations were observed. No vascularization on the surface of transplanted capillaries was observed in the absence of islets. In conclusion, encapsulated islets can release VEGF, which appears to be an important signal for the vascularization of the capillary material. The rough, open-porous outer surface of the polysulfone capillary provides a site well suited for vascular tissue formation and may allow a prolonged islet function after transplantation.

The Use of Pancreas Biopsy Scoring Provides Reliable Porcine Islet Yields While Encapsulation Permits the Determination of Microbiological Safety

For clinical xenogenic islet transplantation to be successful, several requirements must be met. Among them is a sizeable and reliable source of fully functional and microbiologically safe islets. The inherent variability among porcine pancreases, with respect to islet yield, prompted us to develop a Biopsy Score technique to determine the suitability of each pancreas for islet isolation processing. The Biopsy Score consists of an assessment of five variables: warm ischemia time, pancreas color, fat content, islet size, and islet demarcation, each of which is assigned a value of −1 or +1, depending on whether or not the established criteria is met. For determination of islet size and demarcation, fresh biopsies of porcine pancreases are stained with dithizone (DTZ) solution and examined under a dissecting microscope. Based on the scoring of such biopsies in pancreases from 26—56-month-old sows, we report here that the presence of large (>100 μm diameter), well-demarcated islets in the pancreas biopsy is a reliable predictor of isolation success. Encapsulation of the isolated porcine islets within the inner layer of a 1.5% agarose and an outer layer of 5.0% agarose macrobead, containing 500 equivalent islet number (EIN), provides for extended in vitro functional viability (>6 months of insulin production in response to glucose), as well as for comprehensive microbiological testing and at least partial isolation of the xenogeneic islets from the host immune system. All microbiological testing to date has been negative, except for the presence of porcine endogenous retrovirus (PERV). Taken together, we believe that the Biopsy Score enhancement of our islet isolation technique and our agarose-agarose macroencapsulation methodology bring us significantly closer to realizing clinical porcine islet xenotransplantation for the treatment of insulin-dependent diabetic patients.

A Closed System for Islet Isolation and Purification Using the COBE2991 Cell Processor May Reduce the Need of Clean Room Facilities

During the isolation of human islets of Langerhans the digest has repeated direct contact with the ambient atmosphere. In order to fulfill GMP requirements in clinical applications, the entire cell preparation must be performed in clean room facilities. We hypothesized that the use of a closed system, which avoids the direct exposure of tissue to the atmosphere, would significantly ease the preparation procedure. To avoid the direct atmosphere exposure we tested a modification of the isolation and purification process by performing all islet preparation steps in a closed system. In this study we compared the isolation outcome of the traditional open preparation technique with the new closed system. Pancreata from 6-month-old hybrid pigs were procured in the local slaughterhouse. After digestion/filtration the digest was cooled, collected, and concentrated in centrifugation containers and purified thereafter in the COBE2991 by top loading (control). In the control group 502 ± 253 IEQ per gram pancreas were purified. The total preparation time amounted to 12 h. In the closed system the digest was cooled and directly pumped into the COBE2991 for centrifugation followed by supernatant expelling. Bag filling, centrifugation, and expelling were repeated several times. Islets in pellet form were than purified by adding a gradient (bottom loading). Using this closed system 1098 ± 489 IEQ per gram pancreas were purified with a total cell viability of 67 ± 10% and a β-cell viability of 41 ± 13%. The total preparation time reduced to 6 h. After 24 h of cell culture the viability of β-cells was still 56 ± 10% and was only reduced after the addition of proapoptotic IL-1 and TNF-α to 40 ± 4%, indicating that freshly isolated islets are not apoptotic. In conclusion, the closed system preparation is much faster, more effective, and less expensive than the traditional islet preparation. The closed system may be applicable for human islets preparations to restrict the need of clean room facilities for islet preparations to a minimum and may open the way for islet preparations without clean room demand.

Porcine Islet Graft Function is Affected by Pretreatment with a Caspase-3 Inhibitor

During the isolation procedure and after transplantation islets are subjected to numerous variables associated with the induction of apoptosis. The present study investigated the effect of transient pretreatment with caspase inhibitors on function and survival of transplanted pig islets. Isolated porcine islets (3000 IEQ) were incubated overnight in 200 μM of the caspase-3 inhibitor DEVD-CMK prior to transplantation into diabetic nude mice. Glucose-stimulated insulin release of pretreated islets was assessed during static incubation. DEVD-CMK successfully prevented the expression of capase-3 and DFF as demonstrated in heat-shocked pig islets. Nevertheless, transient pretreatment of freshly isolated pig islets with DEVD-CMK resulted in a significantly decreased final graft function of 50.0% (n = 16) compared to 85.7% (n = 14) in control islets (p < 0.05). Glucose-stimulated insulin release of porcine islets (n = 6) was not significantly effected by overnight culture with DEVD-CMK. Morphological assessment revealed that this caspase-3 inhibitor significantly increased the percentage of necrosis to a small, but nevertheless significant, extent in comparison to control islets (p < 0.05). The study demonstrates that short-time pretreatment with the caspase-3 inhibitor DEVD-CMK reduces the capacity of transplanted porcine islets to restore normoglycemia in diabetic nude mice.

A comprehensive microbiological safety approach for agarose encapsulated porcine islets intended for clinical trials

BACKGROUND

The use of porcine islets to replace insulin-producing islet β-cells, destroyed during the diabetogenic disease process, presents distinct challenges if this option is to become a therapeutic reality for the treatment of type 1 diabetes. These challenges include a thorough evaluation of the microbiological safety of the islets. In this study, we describe a robust porcine islet-screening program that provides a high level of confidence in the microbiological safety of porcine islets suitable for clinical trials.

METHODS

A four-checkpoint program systematically screens the donor herd (Large White - Yorkshire × Landrace F1 hybrid animals), individual sentinel and pancreas donor animals and, critically, the islet macrobeads themselves. Molecular assays screen for more than 30 known viruses, while electron microscopy and in vitro studies are employed to screen for potential new or divergent (emergent) viruses.

RESULTS

Of 1207 monthly samples taken from random animals over a 2-year period, only a single positive result for Transmissible gastroenteritis virus was observed, demonstrating the high level of biosecurity maintained in the source herd. Given the lack of clinical signs, positive antibody titers for Porcine reproductive and respiratory syndrome virus, Porcine parvovirus, and Influenza A confirm the efficacy of the herd vaccination program. Porcine respiratory coronavirus was found to be present in the herd, as expected for domestic swine. Tissue homogenate samples from six sentinel and 11 donor animals, over the same 2-year period, were negative for the presence of viruses when co-cultured with six different cell lines from four species. The absence of adventitious viruses in separate islet macrobead preparations produced from 12 individual pancreas donor animals was confirmed using validated molecular (n = 32 viruses), in vitro culture (cells from four species), and transmission electron microscopy assays (200 cell profiles per donor animal) over the same 2-year period. There has been no evidence of viral transmission following the implantation of these same encapsulated and functional porcine islets into non-immunosuppressed diabetic cynomolgus macaques for up to 4 years. Isolated peripheral blood mononuclear cells from all time points were negative for PCV (Type 2), PLHV, PRRSV, PCMV, and PERV-A, PERV-B, and PERV-C by PCR analysis in all six recipient animals.

CONCLUSION

The four-checkpoint program is a robust and reliable method for characterization of the microbiological safety of encapsulated porcine islets intended for clinical trials.

Comparative aspects of rodent and nonrodent animal models for mechanistic and translational diabetes research

The prevalence of diabetes mellitus, which currently affects 387 million people worldwide, is permanently rising in both adults and adolescents. Despite numerous treatment options, diabetes mellitus is a progressive disease with severe comorbidities, such as nephropathy, neuropathy, and retinopathy, as well as cardiovascular disease. Therefore, animal models predictive of the efficacy and safety of novel compounds in humans are of great value to address the unmet need for improved therapeutics. Although rodent models provide important mechanistic insights, their predictive value for therapeutic outcomes in humans is limited. In recent years, the pig has gained importance for biomedical research because of its close similarity to human anatomy, physiology, size, and, in contrast to non-human primates, better ethical acceptance. In this review, anatomic, biochemical, physiological, and morphologic aspects relevant to diabetes research will be compared between different animal species, that is, mouse, rat, rabbit, pig, and non-human primates. The value of the pig as a model organism for diabetes research will be highlighted, and (dis)advantages of the currently available approaches for the generation of pig models exhibiting characteristics of metabolic syndrome or type 2 diabetes mellitus will be discussed.

Pancreatic Islets: Methods for Isolation and Purification of Juvenile and Adult Pig Islets

The current situation of organ transplantation is mainly determined by the disbalance between the number of available organs and the number of patients on the waiting list. This obvious dilemma might be solved by the transplantation of porcine organs into human patients. The metabolic similarities which exist between both species made pancreatic islets of Langerhans to that donor tissue which will be most likely transplanted in human recipients. Nevertheless, the successful isolation of significant yields of viable porcine islets is extremely difficult and requires extensive experiences in the field. This review is focussing on the technical challenges, pitfalls and particularities that are associated with the isolation of islets from juvenile and adult pigs considering donor variables that can affect porcine islet isolation outcome.

Optimal pig donor selection in islet xenotransplantation: current status and future perspectives

Islet transplantation is an attractive treatment of type 1 diabetes mellitus. Xenotransplantation, using the pig as a donor, offers the possibility of an unlimited supply of islet grafts. Published studies demonstrated that pig islets could function in diabetic primates for a long time (>6 months). However, pig-islet xenotransplantation must overcome the selection of an optimal pig donor to obtain an adequate supply of islets with high-quality, to reduce xeno-antigenicity of islet and prolong xenograft survival, and to translate experimental findings into clinical application. This review discusses the suitable pig donor for islet xenotransplantation in terms of pig age, strain, structure/function of islet, and genetically modified pig.

Nonenzymatic Cryogenic Isolation of Therapeutic Cells: Novel Approach for Enzyme-Free Isolation of Pancreatic Islets Using In Situ Cryopreservation of Islets and Concurrent Selective Freeze Destruction of Acinar Tissue

Cell-based therapies, which all involve processes for procurement and reimplantation of living cells, currently rely upon expensive, inconsistent, and even toxic enzyme digestion processes. A prime example is the preparation of isolated pancreatic islets for the treatment of type 1 diabetes by transplantation. To avoid the inherent pitfalls of these enzymatic methods, we have conceptualized an alternative approach based on the hypothesis that cryobiological techniques can be used for differential freeze destruction of the pancreas (Px) to release islets that are selectively cryopreserved in situ. Pancreata were procured from juvenile pigs using approved procedures. The concept of cryoisolation is based on differential processing of the pancreas in five stages: 1) infiltrating islets in situ preferentially with a cryoprotectant (CPA) cocktail via antegrade perfusion of the major arteries; 2) retrograde ductal infusion of water to distend the acinar; 3) freezing the entire Px solid to lt; −160°C for storage in liquid nitrogen; 4) mechanically crushing and pulverizing the frozen Px into small fragments; 5) thawing the frozen fragments, filtering, and washing to remove the CPA. Finally, the filtered effluent (cryoisolate) was stained with dithizone for identification of intact islets and with Syto 13/PI for fluorescence viability testing and glucose-stimulated insulin release assessment. As predicted, the cryoisolate contained small fragments of residual tissue comprising an amorphous mass of acinar tissue with largely intact and viable (>90%) embedded islets. Islets were typically larger (range 50–500 μm diameter) than their counterparts isolated from juvenile pigs using conventional enzyme digestion techniques. Functionally, the islets from replicate cryoisolates responded to a glucose challenge with a mean stimulation index = 3.3 ± 0.7. An enzyme-free method of islet isolation relying on in situ cryopreservation of islets with simultaneous freeze destruction of acinar tissue is feasible and proposed as a new and novel method that avoids the problems associated with conventional collagenase digestion methods.

Pig-to-monkey islet xenotransplantation using multi-transgenic pigs

The generation of pigs with genetic modifications has significantly advanced the field of xenotransplantation. New genetically engineered pigs were produced on an α1,3-galactosyltransferase gene-knockout background with ubiquitous expression of human CD46, with islet beta cell-specific expression of human tissue factor pathway inhibitor and/or human CD39 and/or porcine CTLA4-lg. Isolated islets from pigs with 3, 4 or 5 genetic modifications were transplanted intraportally into streptozotocin-diabetic, immunosuppressed cynomolgus monkeys (n = 5). Immunosuppression was based on anti-CD154 mAb costimulation blockade. Monitoring included features of early islet destruction, glycemia, exogenous insulin requirement and histopathology of the islets at necropsy. Using these modified pig islets, there was evidence of reduced islet destruction in the first hours after transplantation, compared with two series of historical controls that received identical therapy but were transplanted with islets from pigs with either no or only one genetic modification. Despite encouraging effects on early islet loss, these multi-transgenic islet grafts did not demonstrate consistency in regard to long-term success, with only two of five demonstrating function beyond 5 months.

Pig-islet xenotransplantation: recent progress and current perspectives

Islet xenotransplantation is one prospective treatment to bridge the gap between available human cells and needs of patients with diabetes. Pig represents an ideal candidate for obtaining such available cells. However, potential clinical application of pig islet still faces obstacles including inadequate yield of high-quality functional islets and xenorejection of the transplants. Adequate amounts of available islets can be obtained by selection of a suitable pathogen-free source herd and the development of isolation and purification method. Several studies demonstrated the feasibility of successful preclinical pig-islet xenotransplantation and provided insights and possible mechanisms of xenogeneic immune recognition and rejection. Particularly promising is the achievement of long-term insulin independence in diabetic models by means of distinct islet products and novel immunotherapeutic strategies. Nonetheless, further efforts are needed to obtain much more safety and efficacy data to translate these findings into clinic.

Human islet mass, morphology, and survival after cryopreservation using the Edmonton protocol

The aim of this study was to assess recovery, cell death, and cell composition of post-thaw cultured human islets. Cryopreserved islets were provided by the Clinical Islet Transplant Program, Edmonton, Canada. Islets were processed using media prepared in accordance with Pre-Edmonton and Edmonton protocols. Cryopreserved islets were rapidly thawed and cultured for 24 h, 3 d, 5 d, and 7 d, following which they were processed for histology. Islet quantification, integrity, morphology and tissue turnover were studied via hematoxylin and eosin stained sections. Ultrastructure was studied by electron microscopy and endocrine cell composition by immunohistochemistry. Using the Pre-Edmonton protocol, islet recovery was 50.1% and islet survival was 50% at 24 h while for the Edmonton protocol, the islet recovery was 69.4% (p<0.001) and islet survival, 50% at ≈2.5 d. With an increasing culture duration although the physical integrity was retained there was an increasing loss of cohesivity both at light microscopic and at ultrastructure level regardless of the protocols used. Percentage islet survival and tissue turnover correlated negatively with culture duration in both protocols. The Edmonton protocol appears to preserve the islets better. However, culture duration adversely affects islet survival and quality, indicating the need for more optimal cryopreservation and culture techniques.

Histomorphometrical analysis of porcine islets of Langerhans

Xenotransplantation of pig islets of Langerhans may be an efficient method for treatment of type I diabetic patients. Considering the shortage of human pancreas donors, pigs offer readily available islet source. Unfortunately, their morphologic characteristics makes isolation of pig islets of Langerhans extremely difficult. The selection of a suitable donor may favorably affect the success of isolation. Therefore, we examined pig breeds and weights for their influence histomorphometric features of Langerhans islets. Pancreatic tissue biopsy specimens were obtained from Polish Large White pigs (n=5), Polish Landrace pigs (n=8), Pietrain pigs (n=4), and marked-weight pigs of 100 kg (n=8) or more than 200 kg (n=10). Biopsy specimens were fixed and stored in 4% formaldehyde. Tissue sections were stained with polyclonal guinea pig anti-insulin antibody. The number of islets per 1 cm2 was counted in each section. Mean diameters and areas of the islets were measured to calculate the percentage volume density. Differences were observed among the groups of pigs weighing 200 kg and 100 kg in islet mean diameter and area. The number of islets/cm2 was higher among Pietrain than Polish Landrace pigs (425.45±111.7 versus 315.33±36.59 islet/cm2, P<.05). Furthermore, Pietrain pigs showed the largest volume density (1.44%). Histological analysis revealed that Pietrain pigs of 100 kg and market-weight pigs of 200 kg were the best donors for islets of Langerhans.

PK11195, a specific ligand of the peripheral benzodiazepine receptor, may protect pancreatic beta-cells from cytokine-induced cell death

We cultured isolated islets from human or porcine origin in the presence or absence of IL1 and TNFα and studied cytoprotective effects of two structurally different PBR ligands. Storage of pig or human islets in the presence of cytokines significantly lowered the fraction of vital beta-cells. Compared with cytokine incubations PK11195 alone or in combination with cytokines was effective to prevent cytokine induced cell death. The data indicate that cold storage in the presence of PK11195 may further protect beta-cells from cytokine induced cell death. This ligand may be helpful to preserve beta-cell survival before transplantation.

The influence of porcine pancreas digestion parameters and islet histomorphology on islet isolation outcome

Transplantation of the pig islets of Langerhans is considered as the future treatment for patients suffering from type Idiabetes mellitus. Despite the adaptation of modified Ricordi method and highly purified collagenase, the results of pancreas digestions are precarious. Selection of proper donor and optimal digestion procedure are fundamental. The aim of this study was to assess the impact of pancreas procuring parameters on pig islets yield. The pancreata were harvested from 69 market sows weighting over 150 kg. After intraductal injection of cold collagenase solution pancreata were transported in UW solution or under conditions of two layer method (TLM). In laboratory pancreata were digested at 37°C according to Ricordi isolation method or stationary in the bottle. The particular parameters of isolation procedure were considered as substantial. Pig weight, volume of infused collagenase solution, TLM application and pancreas dividing before digestion positively affected islet yield. Additionally, the influence of pancreatic islet tissue histomorphology on isolation outcome was studied. Proper donor selection as well as adequate digestion parameters could improve pig islet recovery during islet isolation.

Rapid quantitative assessment of the pig pancreas biopsy predicts islet yield

BACKGROUND

The cost of islet procurement from donor pigs is increased by the use of organs that produce low yields. We developed an assessment system using dithizone-stained pig pancreas biopsies to enable the preselection of donor organs.

METHODS

Pig pancreas biopsy slices were soaked in dithizone solution. The islets were evaluated before islet isolation by converting the islet counts (IC) to islet equivalents (IE), and then determining the IE/cm(2), IE/IC, % islets >150 microm, and % islets >200 microm. These parameters were evaluated in 3 different areas of the pancreas (duodenal, splenic, and connecting lobe; n = 42 each). Stepwise multivariate linear regression analysis was performed to assess for correlations with islet yield and decide which area of the pancreas had the most predictive value. To identify other predictors, including donor and islet isolation variables, we performed binary logistic regression analysis with significant variables from the univariate analysis (n = 67). For this analysis, the pigs were categorized into high (n = 23) and low (n = 44) yield groups.

RESULTS

Stepwise multivariate linear regression analysis revealed that IE/cm(2) of the splenic lobe significantly predicted islet yield. Binary logistic regression analysis indicated that the IE/mm(2) of the splenic lobe was the only parameter that significantly correlated with successful pig islet isolations (P = .01; odds ratio 3.605). Variables associated with donor and islet isolation, such as age, gender, ischemic time, or enzyme lot, were not significantly correlated with islet yield.

CONCLUSION

Our study suggests that the islet distribution of splenic lobe biopsies can be a reliable predictor of islet yield from pig pancreata.

Isolation and purification of islet cells from adult pigs

We used in situ perfusion and a multiple-organ harvesting technique to collect islets from adult pig pancreata. The tissues were digested with collagenase P followed by purification in a lympholyte discontinuous gradient using a COBE2991 cell separator. The yield and purity of isolated islets were evaluated with a light microscope after dithizone (DTZ) staining. Islet function was assessed using an in vitro insulin release assay. The results showed that before purification 275,000 +/- 20,895 islet equivalents (IEQ) were obtained from 1 digested pancreas. After purification with gradient centrifugation, the islet yield was 230,350 +/- 26,679 IEQ/pancreas. Each gram of the purified pancreatic tissues yielded 2710 +/- 229 IEQ with an average purity of 50.2 +/- 2.0%. The purified islet cells responded to stimulation with high glucose concentrations (16.7 mmol/L), namely, 4.74-fold greater than the insulin secretion with exposure to the basal level of glucose (3.3 mmol/L; P < .001). These results suggested that the established isolation method can be applied to large-scale purification of fully functional islets from pig pancreata.

Use of iodixanol self-generated density gradients to enrich for viable urothelial cells from nonneurogenic and neurogenic bladder tissue

Suspensions of viable urothelial cells (UC) isolated from patient bladder biopsies often contain considerable amounts of extraneous materials comprised of cellular debris, dead and dying UC, and red blood cells. We have consistently observed an inversely proportional relationship between UC attachment efficiency and the amount of extraneous materials in the suspension; viable UC cell attachment efficiency decreases as the amount of extraneous materials in the cell suspension increases. Processing the initial cell isolate to reduce the amount of extraneous materials can enrich for viable UC capable of attaching and proliferating in ex vivo cultures. In this report, we describe the isolation of an enriched population of viable UC from nonneurogenic and neurogenic bladder tissue biopsies using iodixanol self-generated density gradients (OptiPrep), and characterization by trypan blue exclusion, fluorescence-activated cell sorting, immunofluorescence, and growth kinetics.

Enhanced prediction of porcine islet yield and posttransplant outcome using a combination of quantitative histomorphometric parameters and flow cytometry

Prediction of islet yield and posttransplant outcome is essential for clinical porcine islet xenotransplantation. Although several histomorphometric parameters of biopsied porcine pancreases are predictive of islet yield, their role in the prediction of in vivo islet potency is unknown. We investigated which histomorphometrical parameter best predicts islet yield and function, and determined whether it enhanced the predictive value of in vitro islet function tests for the prediction of posttransplant outcome. We analyzed the histomorphometry of pancreases from which 60 adult pig islet isolations were obtained. Islet function was assessed using the beta-cell viability index based on flow cytometry analysis, oxygen consumption rate, ADP/ATP ratio, and/or concurrent transplantation into NOD/SCID mice. Receiver operating characteristic (ROC) analysis revealed that only islet equivalent (IEQ)/cm(2) and the number of islets >200 microm in diameter significantly predicted an islet yield of >2000 IEQ/g (p < 0.001 for both) and in vivo islet potency (p = 0.024 and p = 0.019, respectively). Although not predictive of islet yield, a high proportion of large islets (>100 microm in diameter) best predicted diabetes reversal (p = 0.001). Multiple regression analysis revealed that the beta-cell viability index (p = 0.003) and the proportion of islets >100 microm in diameter (p = 0.048) independently predicted mean posttransplant blood glucose level (BGL). When BGL was estimated using both these parameters [area under the ROC curve (AUC), 0.868; 95% confidence interval (CI), 0.730-1.006], it predicted posttransplant outcome more accurately than the beta-cell viability index alone (AUC, 0.742; 95% CI, 0.544-0.939). In conclusion, we identified the best histomorphometric predictors of islet yield and posttransplant outcome. This further enhanced the predictive value of the flow cytometry analysis. These parameters should be useful for predicting islet yield and in vivo potency before clinical adult porcine islet xenotransplantation.

Parameters for successful pig islet isolation as determined using 68 specific-pathogen-free miniature pigs

BACKGROUND

Islet cell transplantation is a novel therapeutic modality for the cure of diabetes. Pig islet cells are an attractive substitute for human islet cells; however, they are known to be particularly difficult to isolate because of a weak islet capsule and a tendency to be fragmented during enzymatic digestion. Therefore, parameters favoring successful pig islet isolation were investigated using specific-pathogen-free (SPF) miniature pigs.

METHODS

Sixty-eight SPF miniature pigs were used for islet isolation. Birth weight, body weight, age, sex, pregnancy history, and the fasting blood glucose levels of each pig were determined. Each pig's general condition was assessed with regard to feeding status and physical activity. Pancreas procurement was performed by one surgical team. Anesthesia duration, operation duration, procedure quality, and perfusate type were recorded. After pancreatectomy, a biopsy was performed for islet density analysis. Decapsulation, cannulation duration, degree of distension, and cold ischemic time were assessed. During islet isolation, pancreas weight, digestion time, and digested tissue proportion were recorded. Isolation results were evaluated by total islet equivalents (IEQ), islet equivalents per gram of pancreas (IEQ/g), isolation index, islet recovery rate, purity, and visual grade. To identify the predictors of higher islet isolation yield, we performed binary logistic regression analysis with significant (P < 0.05) variables from the univariate analysis.

RESULTS

The pigs were categorized into high (n = 34) and low yield (n = 34) groups according to the median IEQ/g or total IEQ values. Body weight and age were significantly different between the two groups. Being male or a positive history of pregnancy in females was factors favoring successful islet isolation. General condition assessments failed to estimate islet isolation results. Long anesthesia duration, which might have caused ischemic injury to the pancreas, negatively affected islet isolation results. Decapsulation, cannulation duration, and subsequent pancreas distension were significantly important in successful islet isolation. Inter-lot variability of Liberase was not observed because of screening processes performed before purchase. Isolation index and islet recovery rate correlated well with islet yields.

CONCLUSIONS

Multivariate analysis using total IEQ and IEQ/g as outcome variables indicated that age older than 2, being male and moderate distension by Liberase injection are major determinants influencing successful islet isolation.

Pig pancreas anatomy: implications for pancreas procurement, preservation, and islet isolation

BACKGROUND

Islet transplantation is emerging as a treatment option for selected patients with type 1 diabetes. The limited human islet supply from cadavers and poor islet yield and quality remain substantial impediments to progress in the field. Use of porcine islets holds great promise for large-scale application of islet transplantation. Consistent isolation of porcine islets is dependent on advances in pancreas procurement, pancreas preservation, and islet isolation, requiring detailed knowledge of the porcine pancreatic anatomy. The primary aim of this study was to describe the vascular and ductal anatomy of the porcine pancreas to guide and improve organ preservation and enzyme perfusion.

METHODS

Pancreata were removed by en bloc viscerectomy from 65 female Landrace pigs.

RESULTS

Fifteen percentage of organs exhibited inconsistent vascular branching from the celiac trunk. All organs showed uniform patterns of branching at the superior mesenteric artery. The superior and inferior mesenteric veins merged to become the portal vein in all but one case in which the inferior mesenteric vein drained into the splenic vein. Ninety-seven percent of pancreata had three lobes: duodenal lobe (DL), connecting lobe (CL), and splenic lobe (SL); 39% demonstrated ductal communication between the CL and the other two lobes; 50% had ductal communication only between the CL and duodenal lobe; and 11% presented other types of ductal delineation.

CONCLUSIONS

Accounting for the variations in vascular and ductal anatomy, as detailed in this study, will facilitate development of protocols for preservation, optimal enzyme administration, and pancreas distention and digestion, and will ultimately lead to substantial improvements in isolation outcomes.

Nutrient control of insulin secretion in perifused adult pig islets

OBJECTIVES

Xenotransplantation of pig islets is a potential solution to the shortage of human islets, but our knowledge of how these islets secrete insulin in response to nutrients is still fragmentary. This was the question addressed in the present study.

METHODS

After 24 h culture adult pig islets were perifused to characterize the dynamics of insulin secretion. Some responses were compared to those in human islets.

RESULTS

Increasing glucose from 1 to 15 mM weakly (approximately 2x) stimulated insulin secretion, which was potentiated (approximately 12x) by the cAMP-producing agent, forskolin. The effect of glucose was concentration-dependent (threshold at 3-5 mM and maximum at approximately 10 mM). The pattern of secretion was biphasic with a small first phase and an ascending second phase, and a paradoxical increase when the glucose concentration was abruptly lowered. Diazoxide abolished glucose-induced insulin secretion and tolbutamide reversed the inhibition. Glucose also increased secretion when islets were depolarized with tolbutamide or KCl. Insulin secretion was increased by leucine+glutamine, arginine, alanine or a mixture of amino acids, but their effect was significant only in the presence of forskolin. Upon stimulation by glucose alone, human islets secreted approximately 10x more insulin than pig islets, and the kinetics was characterized by a large first phase, a flat second phase, and rapid reversibility.

CONCLUSIONS

Compared with human islets, in vitro insulin secretion by adult pig islets is characterized by a different kinetics and a major quantitative deficiency that can be corrected by cAMP.

Influence of strain and age differences on the yields of porcine islet isolation: extremely high islet yields from SPF CMS miniature pigs

BACKGROUND

Porcine pancreas is a potential source of material for islet xenotransplantation. However, the difficulty in isolating islets, because of their fragility and the variability of isolation outcome in donor age and breed, represents a major obstacle to porcine islet xenotransplantation. In this study, we compared the islet isolation yield of specific pathogen-free (SPF) Chicago Medical School (CMS) miniature pigs with that of another miniature pig breed and market pigs from a local slaughterhouse.

METHODS

Nine adult CMS miniature (ACM) pigs (>12 months), six young CMS miniature (YCM) pigs (6-7 months), four adult Prestige World Genetics (PWG) miniature (APM) pigs (>12 months), and 13 adult market (AM) pigs from a local slaughterhouse were used for islet isolation.

RESULTS

The islet yield per gram of pancreas from ACM pigs (9589 +/- 2823 IEQ/g) was significantly higher than that from APM pigs (1752 +/- 874 IEQ/g, P < 0.05), AM pigs (1931 +/- 947 IEQ/g, P < 0.05), or YCM pigs (3460 +/- 1985 IEQ/g, P < 0.05). Isolated islets from ACM pigs were significantly larger than those from AM pigs or YCM pigs. The in vitro and in vivo function of isolated islets showed no difference among experimental groups. The pancreases of ACM pigs contained higher mean islet volume density percentages and larger size of islets than those of AM or APM pigs.

CONCLUSIONS

We isolated extremely high yields of well-functioning islets from ACM pigs bred under SPF conditions. SPF CMS miniature pigs should be one of the best porcine islet donors for clinical porcine islet xenotransplantation.

Isolation outcome and functional characteristics of young and adult pig pancreatic islets for transplantation studies

INTRODUCTION

Pig islets have been proposed as an alternative to human islets for clinical use, but their use is limited by rejection. The availability of genetically modified pigs devoid of alpha1,3-galactosyltransferase might provide islets more suitable for xenotransplantation. To limit the costs involved in the logistics and health care of pigs for clinical xenotransplantation, we have studied whether younger, rather than older, pigs that are typically preferred can be used as islet donors.

METHODS

We utilized pancreases from Yorkshire and White Landrace wild-type pigs and alpha1,3-galactosyltransferase gene-knockout pigs of three main different age and size groups: (i) <6 months, (ii) 6 to 12 months, and (iii) >2 yr of age, inclusive of retired breeders. We compared isolation yield and in vitro and in vivo function of islet cells obtained from these groups.

RESULTS

Islets from adult pigs (>2 yr) offered not only higher islet yields, but retained the ability to preserve intact morphology during the isolation process and culture, in association with high functional properties after transplantation. Following isolation, islet cells from young (<6 m) and young-adult (6 to 12 m) pigs dissociated into small aggregates and single cells, and exhibited inferior functional properties than adult islets both in vitro and in vivo.

CONCLUSIONS

These data support the conclusion that, in view of the large number of islets needed to maintain normoglycemia after xenotransplantation, organ-source pigs need to reach adult age (>2 yr) before being considered optimal islet donors, in spite of the higher costs involved.

Parameters favouring successful adult pig islet isolations for xenotransplantation in pig-to-primate models

BACKGROUND

In the near future, adult porcine islets of Langerhans appear as an unlimited source of insulin-producing cells which could play a major role for treating diabetes mellitus. There is, however, an obvious lack of pre-clinical results and data in the pig-to-primate model. One of the main hurdles of this model is certainly related to the difficulty of reproducing regularly successful porcine islet isolation. This experimental work was designed to provide guidelines applicable in pig pancreas procurement and islet isolation for successful islet xenotransplantation into primates.

METHODS

Pancreases were harvested from adult Belgium Landrace pigs (n = 79) in a single centre. The impact on islet yield of (1) pancreas procurement (blood exsanguination and warm ischaemia time (WIT)), (2) cold storage solutions (classic UW and modified UW (without hydroxyethyl starch and inverse K+/Na+ concentration)), (3) a dynamic or static method of pancreas digestion, and (4) the endotoxin content and enzymatic activity from five different batches of Liberase PI was studied. In addition, pancreatic biopsies (n = 18), performed before isolation, were retrospectively analyzed to study the impact of histomorphometry on porcine islet yield. Finally, two diabetic cynomolgus monkeys were transplanted without immunosuppression with 15,000 pig islet equivalents/kg body weight of recipient to assess in vivo the function of freshly isolated islets. Univariate and multivariate analyses were performed.

RESULTS

By multiple linear regression, the most significant variables that significantly improved islet yield were, firstly, the presence of <30 EU (endotoxin units) of endotoxin in Liberase batches, followed by a WIT under 10 min and the use of blood exsanguination before pancreas harvesting (P < 0.005). In contrast, isolation method (dynamic vs. static) and the solution used for storage (short-term) (UW vs. modified UW) did not significantly influence islet yield. The correlation of retrospective histomorphometry analysis of native pancreas and extemporaneous biopsy before isolation clearly determined a positive relationship between isolated islet number and the number of islets/cm2 (r = 0.708, P < 0.01) or with the percentage of large islets (r = 0.680, P < 0.01) found in pancreas biopsies. Pig pancreases containing more than 82 islets/cm2 and more than 42% of large islets (>100 microm) thus enabled more than 120,000 islet equivalents to be obtained in 90% of the cases, which is an ideal amount of islets to transplant into a primate of 4 to 5 kg. In vivo, a reduction of blood glucose (<200 mg/dl), associated with porcine C-peptide production, was observed in two primates after transplantation with adult pig islets. At day 7 post-transplantation, however, loss of islet function was associated with graft destruction and immune reaction.

CONCLUSIONS

Morphological screening of the pig pancreas before isolation, optimal blood exsanguination, WIT <10 min, and an endotoxin content <30 EU/mg in Liberase PI batches determine successful pig islet isolation for xenotransplantation in primates.

Suitability of human juvenile pancreatic islets for clinical use

AIMS/HYPOTHESIS

The limited availability of deceased donor pancreases suitable for pancreas and islet transplantation calls for a broader utilisation of donor tissue for transplantation purposes. Young donors, representing, fortunately, a minor but significant pool of individuals, have been largely under-employed, mainly because of anatomical and functional incompatibilities with potential recipients. For islet transplantation, the isolation of pancreatic islets from young donors rarely occurs, because of technical problems. As a result of the peculiar characteristics of young donor pancreases, the standard isolation procedure does not allow efficient separation of the islets from the surrounding exocrine tissue, and favours the generation of mantled islets. Nonetheless, young donor islets offer high qualitative and clinically appealing characteristics.

SUBJECTS AND METHODS

We standardised a modified methodology to obtain purified and mantle-free human islets from young donors. This method principally involves efficient delivery of isolation enzyme with reduced mechanical disruption of the pancreas combined with additional filtration steps.

RESULTS

We were able to obtain purified and mantle-free human islets from donors as young as 6 months of age with good morphological and functional properties. The good qualitative characteristics of the islets, evidenced in vitro, were proven in vivo, as they were qualitatively superior to islets of older donors in transplantation studies.

CONCLUSIONS/INTERPRETATION

This study justifies the utilisation of islets derived from young donors for islet transplantation.

Pig-to-nonhuman primate islet xenotransplantation: a review of current problems

Islet allotransplantation has been shown to have potential as a treatment for type 1 diabetic patients. Xenotransplantation, using the pig as a donor, offers the possibility of an unlimited number of islets. This comprehensive review focuses on experience obtained in pig-to-nonhuman primate models, particularly with regard to the different types of islets (fetal, neonatal, adult) and isolation procedures used, and the methods to determine islet viability. The advantages and disadvantages of the methods to induce diabetes (pancreatectomy, streptozotocin) are discussed. Experience in pig-to-nonhuman primate islet transplantation studies is reviewed, including discussion of the possible mechanisms of rejection and the immunosuppressive regimens used. The research carried out to date has led to workable animal models to study islet xenotransplantation, but several questions regarding methodology remain unanswered, and details of these practicalities require to be adequately addressed. The encouraging porcine islet survival reported recently provides an indicator for future immunosuppressive regimens.

Small rat islets are superior to large islets in in vitro function and in transplantation outcomes

Barriers to the use of islet transplantation as a practical treatment for diabetes include the limited number of available donor pancreata. This project was designed to determine whether the size of the islet could influence the success rate of islet transplantations in rats. Islets from adult rats were divided into two groups containing small (diameter <125 microm) or large (diameter >150 microm) islets. An average pancreas yielded three times more small islets than large. Smaller islets were approximately 20% more viable, with large islets containing a scattered pattern of necrotic and apoptotic cells or central core cell death. Small islets in culture consumed twice as much oxygen as large islets when normalized for the same islet equivalents. In static incubation, small islets released three times more insulin under basal conditions than did large islets. During exposure to high glucose conditions, the small islets released four times more insulin than the same islet equivalencies of large islets, and five times more insulin was released by the small islets in response to glucose and depolarization with K+. Most importantly, the small islets were far superior to large islets when transplanted into diabetic animals. When marginal islet equivalencies were used for renal subcapsular transplantation, large islets failed to produce euglycemia in any recipient rats, whereas small islets were successful 80% of the time. The results indicate that small islets are superior to large islets in in vitro testing and for transplantation into the kidney capsule of diabetic rats.

Persistent normoglycemia in the streptozotocin-diabetic rat by syngenic transplantation of islets isolated from a single donor with Liberase

OBJECTIVES

Enzymatic digestion of donor pancreas is a vital step in islet isolation process. Recently, human and large mammalian islet isolation has been improved by Liberase. However, there are no data to show the improvement of rat islet isolation with Liberase. We hypothesized that commercially available Liberase has variable activities from batch to batch and that a short culture period might improve the function of isolated islets in vivo. We therefore isolated islets with Liberase and cultured them for a short period before transplantation to reverse diabetes in a syngenic rat model.

METHODS

Islets of high inbred Lewis rats were isolated with Liberase, purified by discontinuous density gradients, hand-picked, and cultured at 37 degrees C for 24 hours. The same batch of Liberase was used for all experiments in this study. Freshly isolated and cultured islets were implanted intraportally into rats rendered diabetic by streptozotocin.

RESULTS

In this study, we were not able to reverse diabetes by syngenic transplantation of freshly isolated islets from 2 donors with Liberase in the rat model. Surprisingly, for the first time, we successfully achieved normoglycemia for more than 100 days in the diabetic rats by syngenic transplantation of the cultured islets isolated with Liberase. These normoglycemic diabetic rats showed normal glucose tolerance curves. Histologic examination of the livers of the islet recipients revealed intact islets, with numerous well-granulated insulin-containing cells and only few glucagon-expressing cells. In islets of the recipients' pancreata, the remaining native islets consisted mainly of glucagon-expressing cells, with few insulin-expressing cells in the center.

CONCLUSIONS

We conclude that Liberase isolation followed by a short culture period may be a good substitute for collagenase in rats. Islet culture before transplantation can promote the success of single-donor-single-recipient islet transplantation to reverse diabetes in the rat model.

Impact of porcine islet size on cellular structure and engraftment after transplantation: adult versus young pigs

OBJECTIVES

To study the impact of porcine islet size on structural properties and cellular engraftment.

METHODS

The endocrine structure and collagen/vascular localization in pig islets were studied before and after enzymatic isolation on the pancreas from 6 young and 6 adult Landrace pigs. Isolated islets from both pig types were transplanted under the kidney capsula of diabetic nude rats to assess cellular engraftment.

RESULTS

In comparison with adult pig pancreata, a significantly greater number of small beta cells (<100 microm) were observed before and after isolation (82% vs. 32%, respectively, P < 0.005) from young pig pancreata. Small islets (<100 microm) showed a peripheral vascular structure, whereas large islets showed a more centralized vascular organization, thereby providing protection during the enzymatic digestion procedure. The islet endocrine structure was not affected by the islet size, but a loss of glucagon cells (-7.9%, P < 0.005) was observed in large isolated islets. The purity of islet preparation was better with pancreata from adult than young donors (86% vs. 64%, respectively, P < 0.05). A lack of engraftment was observed for small islets from young pig donors as compared with large islets from adult donors.

CONCLUSIONS

Large and well-structured islets, mainly found in adult pig pancreata, probably possess a better potential for cellular engraftment due to centralized vascularization and collagen distribution.

Influence of Collagenase Loading on Long-Term Preservation of Pig Pancreas by the Two-Layer Method for Subsequent Islet Isolation

BACKGROUND

The introduction of the two-layer method (TLM) for long-term human pancreas preservation revealed the enormous potential of TLM to improve graft function of isolated islets. It is still unclear whether pig islets can be successfully isolated from pancreases after prolonged cold ischemia. To clarify this question, pig pancreases were subjected to 7-hour preservation by University of Wisconsin solution (UWS) storage or TLM. Another aim was to verify whether TLM can be synergistically combined with intraductal collagenase injection before cold storage.

METHODS

After intraductal flush with UWS, organs were distended with 4.4 PZ-U/g of UWS-dissolved collagenase NB-8 and neutral protease adjusted to respectively 1.1, 0.2, 0.5, or 0.8 DMC-U/g for pancreases freshly procured (n=6) or distended with enzymes before (TLM preloaded, n=7) or after cold storage (UWS storage, n=4; TLM postloaded, n=10).

RESULTS

Purified islet yield decreased from 429,200+/-86,700 islet equivalents (IEQ) in unstored pancreases to respectively 37,670+/-19620, 210,400+/-22900 and 238,000+/-26600 IEQ in UWS-stored (P<0.01), TLM-preloaded, or postloaded organs (P<0.05). Purity (>90%), viability (>95%), and insulin content were not different between groups. Islets from UWS-stored pancreases fragmented extensively, preventing further assessment of in vivo function. Compared with other experimental groups, islets from TLM-preloaded organs were characterized by enhanced basal and stimulated insulin release. Sustained normoglycemia was observed in diabetic nude mice transplanted with islets from TLM-postloaded or unstored pancreases in contrast with transient function in TLM-preloaded islets.

CONCLUSIONS

This study demonstrates that significant amounts of intact pig islets can be isolated after prolonged pancreas preservation by TLM. Enzyme administration before TLM preservation decreases islet graft function.

Experimental islet isolation in porcine pancreas with new enzyme Liberase PI

The aim of this study was to investigate the results of 20 consecutive porcine islet isolations using a new enzyme Liberase PI. Twenty pancreata were procured for islet isolation, which was performed using modified Ricordi's method with Liberase PI. Quantitation of islet viability staining, insulin stimulation assay, intracellular insulin content/DNA, and in vivo transplantability into diabetic nude mice were examined for quality control. The results were compared between a high-yield group (>2500 IEQ/g pancreas) and a low-yield group (<2500 IEQ/g pancreas). Sufficient amount of purified islets (3000 IEQ/g pancreas) were obtained using the new brand enzyme Liberase PI. These islets showed good quality in structure and functions, which were demonstrated by in vitro and in vivo standard assays. Isolation index (IEQ/number) of the low-yield group was lower than that of high-yield group (0.75 vs 0.86), which means more fragmentation of islets in the low-yield group. There were no differences in function between the two groups. In conclusion, we obtained sufficient numbers of viable, functional islets from porcine pancreas using a new brand enzyme Liberase PI and low-temperature isolation technique. However, overdigestion of islets during the isolation remains to be overcome. Advance in porcine islet isolation technique will in the future make the porcine islet xenotransplantation a reality for the cure of diabetes mellitus.

Use of the Gottingen Minipig as a Model of Diabetes, with Special Focus on Type 1 Diabetes Research

Animal models of type 1 diabetes remain essential tools for investigation of the etiology and pathogenesis of the disease and, importantly, for the development of effective new treatments. Although a range of well-characterized and widely used models of type 1 diabetes in rodents are currently available, large animal models are a valuable complement to rodent models for both physiological and practical reasons. The pig is very useful in many aspects as a model for human physiology and pathophysiology because many organ systems of this species, as well as physiological and pathophysiological responses, resemble those of the human. The Göttingen minipig is particularly suitable for long-term studies because of its inherent small size and ease of handling, even at full maturity. Of particular relevance to the field of type 1 diabetes are the many similarities evident between humans and pigs with regard to pharmacokinetics of compounds after subcutaneous administration, structure and function of the gastrointestinal tract, morphology of the pancreas, and the overall metabolic status of the two species. Because spontaneous type 1-like diabetes is very rare in pigs, a model of the condition must be induced experimentally, either surgically or chemically. This process is discussed, and the use of the pig as a model in islet transplantation and diabetic complications is briefly summarized.

Assessment of some porcine strains as donors of islets of langerhans

Mass isolation of viable porcine islets is a difficult task because of their fragility, and because of donor variability with respect to strain, age, sex, feeding, and methods of slaughtering. Not all strains are equally suitable for islet separation. The aim of this study was to evaluate porcine pancreata as an alternative source of islets for clinical transplantation. Pancreata were digested from pig strains available in Poland: 248 market weight slaughterhouse pigs and 42 pigs, belonging to the Polish Large White (WBP, 14 sows and 3 males), Polish White Pendant-Ears (PBZ; 16 sows), Pietrain (8 sows), and Yorkshire (1 sow) races. Prepurification data of recoverable islets/g and islet equivalents/g were considered as representative for the number of recoverable islets. Acceptable results namely, islet and/or islet-equivalent (IE) number of at least 1000/g, were obtained from only 56 of 248 slaughterhouse pigs, namely 2073 +/- 137.4 SE (median 1767/g) islets with values of IE of 2994 +/- 303 SE (median 1874/g). Our data support Krickhahn et al suggesting that only pancreata with an average islet size exceeding 199 microm should be digested and that only from 1 of 3 to 5 porcine pancreata is an adequate amount of islets generated.