The distribution of porcine pancreatic beta-cells at ages 5, 12 and 24 weeks

Current state of clinical trials on xenograft

BACKGROUND

Xenotransplantation is a worth investing branch of science, since it aims to fulfil the demand on human cells, tissues and organs. Despite decades of consistent work in preclinical assessments, clinical trials on xenotransplantation are far from reaching the targeted goal. Our study aims to track the characteristics, assess the content and summarize the plan of each trial on skin, beta-island, bone marrow, aortic valve and kidney xenografts, leading to a clear sorting of efforts made in this field.

METHODS

In December 2022, we searched clinicaltrial.gov for interventional clinical trials related to xenograft of skin, pancreas, bone marrow, aortic valve and kidney. A total of 14 clinical trials are included in this study. Characteristics on each trial were gathered. Linked publications were searched using Medline/PubMed and Embase/Scopus. Content of trials was reviewed and summarized.

RESULTS

Only 14 clinical trials met our study's criteria. The majority were completed, and most of the trials' enrolment was between 11 and 50 participants. Nine trials used a xenograft of porcine origin. Six trials targeted skin xenotransplantation, four targeted β-cells, two targeted bone marrow and one trial targeted each of the kidney and aortic valve. The average length of trials was 3.38 years. Four trials were conducted in the United States and two trials in each of Brazil, Argentina and Sweden. Of all the included trials, none had any results provided and only three had published work. Phases I, III, and IV had only one trial each. A total of 501 participants were enrolled in these trials.

CONCLUSION

This study sheds the light on the current state of clinical trials on xenograft. Characteristically, trials on this field are of low number, low enrolment, short duration, few related publications and no published results. Porcine organs are the most used in these trials, and skin is the most studied organ. An extension of the literature is highly needed due to the variety of conflicts mentioned. Overall, this study sheds the light on the necessity of managing research efforts, leading to the initiation of more trials targeting the field of xenotransplantation.

Heterogenous expression of endocrine and progenitor cells within the neonatal porcine pancreatic lobes-Implications for neonatal porcine islet xenotransplantation

Neonatal porcine islets (NPIs) are a source of islets for xenotransplantation. In the pig, the pancreatic lobes remain separate, thus, when optimizing NPI isolation, the pancreatic lobes included in the pancreatic digest should be specified. These lobes are the duodenal (DL), splenic (SL) and connecting (CL) lobe that correspond to the head, body-tail, and uncinate process of the human pancreas. In this study we are the first to evaluate all three neonatal porcine pancreatic lobes and NPIs isolated from these lobes. We report, a significant difference in endocrine and progenitor cell composition between lobes, and observed pancreatic duct glands (PDG) within the mesenchyme surrounding exocrine ducts in the DL and CL. Following in vitro differentiation, NPIs isolated from each lobe differed significantly in the percent increase of endocrine cells and final cell composition. Compared to other recipients, diabetic immunodeficient mice transplanted with NPIs isolated from the SL demonstrated euglycemic control as early as 4 weeks (p < 0.05) and achieved normoglycemia by 6 weeks post-transplant (p < 0.01). For the first time we report significant differences between the neonatal porcine pancreatic lobes and demonstrate that NPIs from these lobes differ in xenograft function.

Hemorheological and Microcirculatory Relations of Acute Pancreatitis

Acute pancreatitis still means a serious challenge in clinical practice. Its pathomechanism is complex and has yet to be fully elucidated. Rheological properties of blood play an important role in tissue perfusion and show non-specific changes in acute pancreatitis. An increase in blood and plasma viscosity, impairment of red blood cell deformability, and enhanced red blood cell aggregation caused by metabolic, inflammatory, free radical-related changes and mechanical stress contribute to the deterioration of the blood flow in the large vessels and also in the microcirculation. Revealing the significance of these changes in acute pancreatitis may better explain the pathogenesis and optimize the therapy. In this review, we give an overview of the role of impaired microcirculation by changes in hemorheological properties in acute pancreatitis.

Insulin in the saliva of pigs: Validation of an automated assay and changes at different physiological conditions

This study aimed to evaluate whether insulin could be measured in the saliva of pigs and if its concentration changes in some physiological conditions. For this purpose, a validation of an automated heterologous immunoassay for measuring insulin in the saliva of pigs was performed. In addition, the possible changes of salivary insulin concentration in sows after food intake and during gestation and lactation were studied. The evaluated immunoassay was able to detect insulin in the saliva of pigs in a precise and accurate way when species-specific calibrators were used. There was no correlation in insulin concentrations between serum and saliva. Insulin concentrations showed a significant increase in the saliva of sows after feeding. Sows at farrowing and lactation presented higher salivary insulin levels as compared with those in gestation. In conclusion, the results showed that insulin could be measured in the saliva of pigs, and changes in its concentration can be detected due to food intake and different physiological conditions.

Characterization of Insulin and Glucagon Genes and Their Producing Endocrine Cells From Pygmy Sperm Whale (Kogia breviceps)

Insulin and glucagon are hormones secreted by pancreatic β and α cells, respectively, which together regulate glucose homeostasis. Dysregulation of insulin or glucagon can result in loss of blood glucose control, characterized by hyperglycemia or hypoglycemia. To better understand the endocrine physiology of cetaceans, we cloned and characterized the insulin and glucagon genes from pygmy sperm whale (Kogia breviceps). We obtained the complete coding sequences of the preproinsulin and preproglucagon genes, which encodes the preproinsulin protein of 110 amino acid (aa) residues and encodes the preproglucagon protein of 179 aa residues, respectively. Sequence comparison and phylogenetic analyses demonstrate that protein structures were similar to other mammalian orthologs. Immunohistochemistry and immunofluorescence staining using insulin, glucagon, and somatostatin antibodies allowed analysis of pygmy sperm whale islet distribution, architecture, and composition. Our results showed the pygmy sperm whale islet was irregularly shaped and randomly distributed throughout the pancreas. The architecture of α, β, and δ cells of the pygmy sperm whale was similar to that of artiodactyls species. This is the first report about insulin and glucagon genes in cetaceans, which provides new information about the structural conservation of the insulin and glucagon genes. Furthermore, offers novel information on the properties of endocrine cells in cetacean for further studies.

Distributions of endocrine cell clusters during porcine pancreatic development

Background

Pancreatic islet xenotransplantation is a potential treatment for diabetes mellitus, and porcine pancreas may provide a readily available source of islets. Islets in juvenile pigs are smaller than those in young adult pigs, but the insulin content is very similar. In addition, as juvenile pigs are more easily reared in uncontaminated conditions, many researchers have conducted studies using pancreatic islets from juvenile pigs. We aimed to analyze the distributions of endocrine cell clusters by comprehensively evaluating juvenile porcine pancreatic development and to propose an appropriate age at which islets could be isolated from the juvenile porcine pancreas.

Methods

Splenic (SL) and duodenal lobe (DL) samples were collected from the pancreases of pigs aged 0–180 days (n = 3/day after birth). The chronological changes in endocrine cell clustering were analyzed in relation to morphological changes, cell characterization, numbers, islet areas, and gene expression.

Results

In juvenile pigs aged 0–21 days, the pancreas contained numerous endocrine cells, and compact islets appeared from 21 days of age. Well-defined small islets were seen at 28 days of age, and the clusters were denser in the SL than in the DL. At 35 days of age, the islets were morphologically similar to those observed at 180 days of age, and the greater number of islets was similar to that seen at 90 days of age. The differences in the islets’ cytoarchitecture between the lobes were negligible. The expression of β-cell-related genes was higher in the juvenile pancreas than in the adult pancreas, and the expression of neurogenin-3 decreased dramatically over time.

Conclusions

These findings may have implications for attempts to refine the most appropriate age for islet isolation from porcine donors. Focusing on porcine pancreatic islets isolated at around 35 days after birth may offer benefits regarding their xenotransplantation potential.

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.

The Different Faces of the Pancreatic Islet

Type 1 diabetes (T1D) patients who receive pancreatic islet transplant experience significant improvement in their quality-of-life. This comes primarily through improved control of blood sugar levels, restored awareness of hypoglycemia, and prevention of serious and potentially life-threatening diabetes-associated complications, such as kidney failure, heart and vascular disease, stroke, nerve damage, and blindness. Therefore, beta cell replacement through transplantation of isolated islets is an important option in the treatment of T1D. However, lasting success of this promising therapy depends on durable survival and efficacy of the transplanted islets, which are directly influenced by the islet isolation procedures. Thus, isolating pancreatic islets with consistent and reliable quality is critical in the clinical application of islet transplantation.Quality of isolated islets is important in pre-clinical studies as well, as efforts to advance and improve clinical outcomes of islet transplant therapy have relied heavily on animal models ranging from rodents, to pigs, to nonhuman primates. As a result, pancreatic islets have been isolated from these and other species and used in a variety of in vitro or in vivo applications for this and other research purposes. Protocols for islet isolation have been somewhat similar across species, especially, in mammals. However, given the increasing evidence about the distinct structural and functional features of human and mouse islets, using similar methods of islet isolation may contribute to inconsistencies in the islet quality, immunogenicity, and experimental outcomes. This may also contribute to the discrepancies commonly observed between pre-clinical findings and clinical outcomes. Therefore, it is prudent to consider the particular features of pancreatic islets from different species when optimizing islet isolation protocols.In this chapter, we explore the structural and functional features of pancreatic islets from mice, pigs, nonhuman primates, and humans because of their prevalent use in nonclinical, preclinical, and clinical applications.

Data on morphometric analysis of the pancreatic islets from C57BL/6 and BALB/c mice

The endocrine portion of the pancreas, which is characterized by pancreatic islets, has been widely investigated among different species. The BALB/c and C57BL/6 mice are extensively used in experimental research, and the morphometric differences in the pancreatic islets of these animals have not been evaluated so far. Thus, our data have a comparative perspective related to the morphometric analysis of area, diameters, circularity, and density of pancreatic islets from BALB/c and C57BL/6 mice. The data presented here are focused to evaluate the differences in morphology of pancreatic islets of two common laboratory mouse strains.

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.

Histomorphology of the bottlenose dolphin (Tursiops truncatus) pancreas and association of increasing islet β-cell size with chronic hypercholesterolemia

Bottlenose dolphins (Tursiops truncatus) can develop metabolic states mimicking prediabetes, including hyperinsulinemia, hyperlipidemia, elevated glucose, and fatty liver disease. Little is known, however, about dolphin pancreatic histomorphology. Distribution and area of islets, α, β, and δ cells were evaluated in pancreatic tissue from 22 dolphins (mean age 25.7years, range 0-51). Associations of these measurements were evaluated by sex, age, percent high glucose and lipids during the last year of life, and presence or absence of fatty liver disease and islet cell vacuolation. The most common pancreatic lesions identified were exocrine pancreas fibrosis (63.6%) and mild islet cell vacuolation (47.4%); there was no evidence of insulitis or amyloid deposition, changes commonly associated with type 2 diabetes. Dolphin islet architecture appears to be most similar to the pig, where α and β cells are localized to the central or periphery of the islet, respectively, or are well dispersed throughout the islet. Unlike pigs, large islets (greater than 10,000μm(2)) were common in dolphins, similar to that found in humans. A positive linear association was identified between dolphin age and islet area average, supporting a compensatory response similar to other species. The strongest finding in this study was a positive linear association between islet size, specifically β-cells, and percent blood samples with high cholesterol (greater than 280mg/dl, R(2)=0.57). This study is the most comprehensive assessment of the dolphin pancreas to date and may help direct future studies, including associations between chronic hypercholesterolemia and β-cell size.

Structural similarities and differences between the human and the mouse pancreas

Mice remain the most studied animal model in pancreas research. Since the findings of this research are typically extrapolated to humans, it is important to understand both similarities and differences between the 2 species. Beside the apparent difference in size and macroscopic organization of the organ in the 2 species, there are a number of less evident and only recently described differences in organization of the acinar and ductal exocrine tissue, as well as in the distribution, composition, and architecture of the endocrine islets of Langerhans. Furthermore, the differences in arterial, venous, and lymphatic vessels, as well as innervation are potentially important. In this article, the structure of the human and the mouse pancreas, together with the similarities and differences between them are reviewed in detail in the light of conceivable repercussions for basic research and clinical application.

In Vitro Maturation of Viable Islets from Partially Digested Young Pig Pancreas

Isolation of islets from market-sized pigs is costly, with considerable islet losses from fragmentation occurring during isolation and tissue culture. Fetal and neonatal pigs yield insulin unresponsive islet-like cell clusters that become glucose-responsive after extended periods of time. Both issues impact clinical applicability and commercial scale-up. We have focused our efforts on a cost-effective scalable method of isolating viable insulin-responsive islets. Young Yorkshire pigs (mean age 20 days, range 4–30 days) underwent rapid pancreatectomy (<5 min) and partial digestion using low-dose collagenase, followed by in vitro culture at 37°C and 5% CO2 for up to 14 days. Islet viability was assessed using FDA/PI or Newport Green, and function was assessed using a glucose-stimulated insulin release (GSIR) assay. Islet yield was performed using enumeration of dithizonestained aliquots. The young porcine (YP) islet yield at dissociation was 12.6 ± 2.1 × 103 IEQ (mean ± SEM) per organ and increased to 33.3 ± 6.4 × 103 IEQ after 7 days of in vitro culture. Viability was 97.3 ± 7% at dissociation and remained over 90% viable after 11 days in tissue culture ( n = ns). Glucose responsiveness increased throughout maturation in culture. The stimulation index (SI) of the islets increased from 1.7 ± 2 on culture day 3 to 2.58 ± 0.5 on culture day 7. These results suggest that this method is both efficient and scalable for isolating and maturing insulin-responsive porcine islets in culture.

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.

Improvement of pig islet function by in vivo pancreatic tissue remodeling: a "human-like" pig islet structure with streptozotocin treatment

Pig islets demonstrate significantly lower insulin secretion after glucose stimulation than human islets (stimulation index of ∼12 vs. 2 for glucose 1 and 15 mM, respectively) due to a major difference in β- and α-cell composition in islets (60% and 25% in humans and 90% and 8% in pigs, respectively). This leads to a lower rise in 3',5'-cyclic adenosine monophosphate (cAMP) in pig β-cells. Since glucagon is the major hormonal effector of cAMP in β-cells, we modified pig islet structure in vivo to increase the proportion of α-cells per islet and to improve insulin secretion. Selected doses (0, 30, 50, 75, and 100 mg/kg) of streptozotocin (STZ) were intravenously injected in 32 young pigs to assess pancreatic (insulin and glucagon) hormone levels, islet remodeling (histomorphometry for α- and β-cell proportions), and insulin and glucagon secretion in isolated islets. Endocrine structure and hormonal content of pig islets were compared with those of human islets. The dose of STZ was significantly correlated with reductions in pancreatic insulin content (p< 0.05, r(2) = 0.77) and the proportion of β-cells (p < 0.05, r(2) = 0.88). A maximum of 50 mg/kg STZ was required for optimal structure remodeling, with an increased proportion of α-cells per islet (26% vs. 48% α-cells per islet for STZ <50 mg/kg vs. >75 mg/kg; p < 0.05) without β-cell dysfunction. Three months after STZ treatment (30/50 mg/kg STZ), pig islets were isolated and compared with isolated control islets (0 mg/kg STZ). Isolated islets from STZ-treated (30/50 mg/kg) pigs had a higher proportion of α-cells than those from control animals (32.0% vs. 9.6%, respectively, p < 0.05). After in vitro stimulation, isolated islets from STZ-treated pigs demonstrated significantly higher glucagon content (65.4 vs. 21.0 ng/ml, p < 0.05) and insulin release (144 µU/ml) than nontreated islets (59 µU/ml, p < 0.05), respectively. Low-dose STZ (<50 mg/kg) can modify the structure of pig islets in vivo and improve insulin secretion after isolation.

Effect of different obesogenic diets on pancreatic histology in Ossabaw miniature swine

OBJECTIVE

Obesity is a factor in the outcome and severity of pancreatic conditions. We examined the effect of hypercaloric diets on the pancreata of Ossabaw swine, a large animal model of metabolic syndrome and obesity.

METHODS

Swine were fed with 1 of 4 diets: high-fructose (n = 9), atherogenic (n = 10), modified atherogenic (n = 6), or eucaloric standard diet (n = 12) for 24 weeks. Serum chemistries were measured, and pancreata were examined for histological abnormalities including steatosis, inflammation or fibrosis, insulin content, and oxidative stress.

RESULTS

The fructose, atherogenic, and modified atherogenic diet groups exhibited obesity, metabolic syndrome, islet enlargement, and significantly increased pancreatic steatosis (22.9% ± 7.5%, 19.7% ± 7.7%, and 38.7% ± 15.3% fat in total tissue area, respectively) compared with controls (9.3% ± 1.9%; P < 0.05). The modified atherogenic diet group showed significantly increased oxidative stress levels as evidenced by elevated serum malondialdehyde (3.0 ± 3.3 vs 1.5 ± 0.3 μmol/L in controls; P = 0.006) and pancreatic malondialdehyde (0.1 ± 0.12 vs 0.04 ± 0.01 nmol/mg protein in controls; P = 0.01). None of the swine exhibited pancreatitis or cellular injury.

CONCLUSIONS

Ossabaw swine fed with a modified atherogenic diet developed significant pancreatic steatosis and increased oxidative stress, but no other histological abnormalities were observed.

Pancreatic islet plasticity: interspecies comparison of islet architecture and composition

The pancreatic islet displays diverse patterns of endocrine cell arrangement. The prototypic islet, with insulin-secreting beta-cells forming the core surrounded by other endocrine cells in the periphery, is largely based on studies of normal rodent islets. Recent reports on large animals, including humans, show a difference in islet architecture, in which the endocrine cells are randomly distributed throughout the islet. This particular species difference has raised concerns regarding the interpretation of data based on rodent studies to humans. On the other hand, further variations have been reported in marsupials and some nonhuman primates, which possess an inverted ratio of beta-cells to other endocrine cells. This review discusses the striking plasticity of islet architecture and cellular composition among various species including changes in response to metabolic states within a single species. We propose that this plasticity reflects evolutionary acquired adaptation induced by altered physiological conditions, rather than inherent disparities between species.

Islet isolation from juvenile porcine pancreas after 24-h hypothermic machine perfusion preservation

Pancreas procurement for islet isolation and transplantation is limited by concerns for the detrimental effects of postmortem ischemia. Hypothermic machine perfusion (HMP) preservation technology has had a major impact in circumventing ischemic injury in clinical kidney transplantation and is applied here to the preservation and procurement of viable islets after hypothermic perfusion preservation of porcine pancreata because pigs are now considered the donor species of choice for xenogeneic islet transplantation. Pancreases were surgically removed from young (<6 months) domestic Yorkshire pigs (25-32 kg), either before or after 30 min of warm ischemia time (WIT), and cannulated for perfusion. Each pancreas was assigned to one of six preservation treatment groups: fresh controls-processed immediately (cold ischemia <1 h) (G1, n = 7); static cold storage-flushed with cold UW-Viaspan and stored in UW-Viaspan at 2-4 degrees C for 24 h with no prior WIT (G2, n = 9); HMP perfused on a LifePort(R) machine at 4-6 degrees C and low pressure (10 mmHg) for 24 h with either KPS1 solution (G3, n = 7) or Unisol-UHK (G4, n = 7). Additional treatment groups to evaluate the effects of prior warm ischemia examined islet isolation after 30 min WIT in situ without (G5, n = 6) or with subsequent 24-h HMP with KPS1 (G6, n = 7). The pancreas was intraductally distended with Liberase PI enzyme and normothermically digested. The isolated islets were purified by a continuous density-gradient centrifugation. Perfusion-induced glandular edema was G3 = 138 +/- 19%, G4 = 160 +/- 16%, and G6 = 127 +/- 22%. Islet yield (IEQ/g of pancreas) varied between the groups: G1 = 1,425 +/- 610, G2 = 1,002 +/- 262, G3 = 2,242 +/- 449 (p < 0.05 vs. G2), G4 = 1,901 +/- 420 (p < 0.05 vs. G2), G5 = 1,756 +/- 329, and G6 = 1,396 +/- 243. Islet stimulation indices were equivalent between the groups and similar to controls (G1). Insulin content (ng/IE) was different between the treatment groups with the highest insulin content in islets harvested from HMP pancreata. Dithizone staining for islets consistently showed more uniform digestion of the perfused organs, with greater separation of the tissue, less entrapped islets, and higher islet yield and purity. The salutary effects of HMP for 24 h were also manifest after 30-min prior warm ischemia. We conclude that 24 h of HMP is well tolerated, leading to moderate edema but no loss of function of the harvested islets. The edema appears to aid in enzymatic digestion, producing a greater yield and purity of islets compared with pancreas subjected to 24 h of static cold storage.

Pig islets for clinical islet xenotransplantation. Curr Opin Nephrol Hypertens. 2009;18:495-500. [PMID: 19726985 DOI: 10.1097/MNH.0b013e328331a8e3]

PURPOSE OF REVIEW

Allogeneic islet transplantation faces difficulties because organ shortage is recurrent; several pancreas donors are often needed to treat one diabetic recipient; and the intrahepatic site of islet implantation may not be the most appropriate one. Another source of insulin-producing cells, therefore, would be of major interest, and pigs represent a possible and serious source for obtaining such cells.

RECENT FINDINGS

Pig islet grafts may appear difficult because of the species barrier, but recent studies demonstrate that pig islets may function in diabetic primates for at least 6 months.

SUMMARY

Pig islet xenotransplantation, however, must still overcome the selection of a suitable pig donor to translate preclinical findings into clinical applications. This review summarizes the actual acquired knowledge of pig islet transplantation in primates to select the 'ideal' pig donor.

Pig islet xenotransplantation into non-human primate model

Allogeneic islet transplantation faces difficulties because (1) organ shortage is recurrent; (2) several pancreas donors are often needed to treat one diabetic recipient; and (3) the intrahepatic site of islet implantation may not be the most appropriate site. Another source of insulin-producing cells, therefore, would be of major interest, and pigs represent a possible and serious source for obtaining such cells. Pig islet grafts may seem difficult because of the species barrier, but recent reports demonstrate that pig islets may function in primates for at least 6 months. Pig islet xenotransplantation, however, must still overcome several hurdles before becoming clinically applicable. The actual consensus is to produce more preclinical data in the pig-to-primate model as a necessary requirement to envisage any pig-to-human transplantation of islets; therefore, a summary of the actual acquired knowledge of pig islet transplantation in primates seemed useful and is summarized in this overview.

Size distribution of mouse Langerhans islets

Pancreatic beta-cells are clustered in islets of Langerhans, which are typically a few hundred micrometers in a variety of mammals. In this study, we propose a theoretical model for the growth of pancreatic islets and derive the islet size distribution, based on two recent observations: First, the neogenesis of new islets becomes negligible after some developmental stage. Second, islets grow via a random process, where any cell in an islet proliferates with the same rate regardless of the present size of the islet. Our model predicts either log-normal or Weibull distributions of the islet sizes, depending on whether cells in an islet proliferate coherently or independently. To confirm this, we also measure the islet size by selectively staining islets, which are exposed from exocrine tissues in mice after enzymatic treatment. Indeed revealed are skewed distributions with the peak size of approximately 100 cells, which fit well to the theoretically derived ones. Interestingly, most islets turned out to be bigger than the expected minimal size (approximately 10 or so cells) necessary for stable synchronization of beta-cells through electrical gap-junction coupling. The collaborative behavior among cells is known to facilitate synchronized insulin secretion and tends to saturate beyond the critical (saturation) size of approximately 100 cells. We further probe how the islets change as normal mice grow from young (6 weeks) to adult (5 months) stages. It is found that islets may not grow too large to maintain appropriate ratios between cells of different types. Our results implicate that growing of mouse islets may be regulated by several physical constraints such as the minimal size required for stable cell-to-cell coupling and the upper limit to keep the ratios between cell types. Within the lower and upper limits the observed size distributions of islets can be faithfully regenerated by assuming random and uncoordinated proliferation of each beta-cell at appropriate rates.

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.

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.

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.

Functional and immunohistochemical evaluation of porcine neonatal islet-like cell clusters

Porcine neonatal islet-like cell clusters (NICCs) may be an attractive source of insulin-producing tissue for xenotransplantation in type I diabetic patients. We examined the functional and immunohistochemical outcome of the islet grafts in vitro during long-term culture and in vivo after transplantation to athymic nude mice. On average we obtained 29,000 NICCs from each pancreas. In a perifusion system, NICCs responded poorly to a glucose challenge alone, but 10 mmol/L arginine elicited a fourfold increase in insulin secretion and 16.7 mmol/L glucose + 10 mmol/L arginine caused a sevenfold increase in insulin section indicating some sensitivity towards glucose. Hormone content as well as the number of hormone-containing cells increased for the first 14 days of culture. When NICCs were stained for hormones, proliferation (Ki67), and duct cells (CK7), some insulin- and glucagon-positive cells co-stained for proliferation. However no co-staining was observed between insulin- and glucagon-positive cells or between hormone-and CK-positive cells. Following transplantation of 2000 NICCs under the renal capsule of diabetic nude mice, BG levels were normalized within an average of 13 weeks. Oral and IP glucose tolerance tests revealed a normal or even faster clearance of a glucose load compared with normal controls. Immunohistochemical examination of the grafts revealed primarily insulin-positive cells. In summary, in vitro, NICCs responded to a challenge including glucose and arginine. There was a potential for expansion of the beta-cell mass of NICCs in vitro as well as in vivo where NICCs eventually may normalize blood glucose of diabetic mice.

Mild streptozotocin diabetes in the Göttingen minipig. A novel model of moderate insulin deficiency and diabetes

Nonrodent models of diabetes are needed for practical and physiological reasons. Induction of mild insulin-deficient diabetes was investigated in male Göttingen minipigs by use of streptozotocin (STZ) alone (75, 100, and 125 mg/kg) or 125 mg/kg combined with pretreatment with nicotinamide (NIA; 0, 20, 67, 100, 150, and 230 mg/kg). Use of NIA resulted in a less steep slope of the regression line between fasting plasma glucose and changing doses compared with STZ [-7.0 +/- 1.4 vs. 29.7 +/- 7.0 mM. mg(-1). kg(-1), P < 0.0001]. Intermediate NIA doses induced moderate changes of glucose tolerance [glucose area under the curve increased from 940 +/- 175 to 1,598 +/- 462 mM. min, P < 0.001 (100 mg/kg) and from 890 +/- 109 to 1,669 +/- 691 mM. min, P = 0.003 (67 mg/kg)] with reduced insulin secretion [1,248 +/- 602 pM. min after 16 days and 1,566 +/- 190 pM. min after 60 days vs. 3,251 +/- 804 pM. min in normal animals (P < 0.001)] and beta-cell mass [5.5 +/- 1.4 mg/kg after 27 days and 7.9 +/- 4.1 mg/kg after 60 days vs. 17.7 +/- 4.7 mg/kg in normal animals (P = 0.009)]. The combination of NIA and STZ provided a model characterized by fasting and especially postprandial hyperglycemia and reduced, but maintained, insulin secretion and beta-cell mass. This model holds promise as an important tool for studying the pathophysiology of diabetes and development of new pharmacological agents for treatment of the disease.