Streptozotocin-induced diabetes mellitus in pigs

Modeling Wound Chronicity In Vivo: The Translational Challenge to Capture the Complexity of Chronic Wounds

In an aging society with common lifestyle-associated health issues such as obesity and diabetes, chronic wounds pose a frequent challenge that physicians face in everyday clinical practice. Therefore, nonhealing wounds have attracted much scientific attention. Several in vitro and in vivo models have been introduced to deepen our understanding of chronic wound pathogenesis and amplify therapeutic strategies. Understanding how wounds become chronic will provide insights to reverse or avoid chronicity. Although choosing a suitable model is of utmost importance to receive valuable outcomes, an ideal in vivo model capturing the complexity of chronic wounds is still missing and remains a translational challenge. This review discusses the most relevant mammalian models for wound healing studies and provides guidance on how to implement the hallmarks of chronic wounds. It highlights the benefits and pitfalls of established models and maps out future avenues for research.

Animal Models in Diabetic Research-History, Presence, and Future Perspectives

Diabetes mellitus (DM) is a very serious disease, the incidence of which has been increasing worldwide. The beginning of diabetic research can be traced back to the 17th century. Since then, animals have been experimented on for diabetic research. However, the greatest development of diabetes research occurred in the second half of the last century, along with the development of laboratory techniques. Information obtained by monitoring patients and animal models led to the finding that there are several types of DM that differ significantly from each other in the causes of the onset and course of the disease. Through different types of animal models, researchers have studied the pathophysiology of all types of diabetic conditions and discovered suitable methods for therapy. Interestingly, despite the unquestionable success in understanding DM through animal models, we did not fully succeed in transferring the data obtained from animal models to human clinical research. On the contrary, we have observed that the chances of drug failure in human clinical trials are very high. In this review, we will summarize the history and presence of animal models in the research of DM over the last hundred years. Furthermore, we have summarized the new methodological approaches, such as "organ-on-chip," that have the potential to screen the newly discovered drugs for human clinical trials and advance the level of knowledge about diabetes, as well as its therapy, towards a personalized approach.

Therapeutic Effects of Amnion-Conjugated Chitosan-Alginate Membranes on Diabetic Wounds in an Induced Diabetic Swine Model: An In Vitro and In Vivo Study

Background  Chitosan (CS) is a well-known antimicrobial dressing material. Moreover, widely used amniotic membranes contain growth factors beneficial for wound healing. Herein, we created a novel amnion-conjugated CS-alginate membrane dressing and tested its wound healing potency in a diabetic swine model.

Methods  The bovine amniotic powder growth factor contents were evaluated by protein assay, and the powder's wound healing effects were assessed in vitro by HaCaT cell scratch closure. In vivo, two minipigs developed streptozotocin-induced diabetes. Serial serum glucose measurements and intravenous glucose tolerance tests were performed to confirm their diabetic status. Twelve square-shaped wounds created on each pig's back were randomly divided into control ( n  = 4), CS ( n  = 4), and amnion-CS (AC; n  = 4) groups and treated accordingly with different dressings. Wound healing in each group was assessed by measuring wound contraction over time, capturing wound perfusion with indocyanine green (ICG) angiography, and histologically analyzing inflammatory markers.

Results  Amniotic powder elution promoted HaCaT cell migration in the scratch wound model, suggesting its beneficial in vitro wound healing effects. In vivo, the CS and AC groups showed earlier wound contraction initiation and reepithelialization and earlier wound perfusion improvement by ICG angiography than the control group. Additionally, the wound size of the AC group at week 3 was significantly smaller than those in the control group. There was no significant difference in the numbers of acute and chronic inflammatory cells between the groups.

Conclusion  The amnion-conjugated CS-alginate membrane, as well as CS dressing alone, could be a favorable dressing option for diabetic wounds.

Effect of Chemically-Induced Diabetes Mellitus on Phenotypic Variability of the Enteric Neurons in the Descending Colon in the Pig

Gastrointestinal neuropathy in diabetes is one of numerous diseases resulting in abnormal functioning of the gastrointestinal tract (GIT), and it may affect any section of the GIT, including the descending colon. In the gastrointestinal system, the neurons are arranged in an interconnecting network defined as the enteric nervous system (ENS) which includes the myenteric plexus and the submucosal plexuses: inner and outer. Regular functioning of the ENS is determined by normal synthesis of the neurotransmitters and neuromodulators. This paper demonstrates the effect of hyperglycaemia on the number of enteric neurons which are immunoreactive to: neural isoform of nitric oxide synthase (nNOS), vasoactive intestinal peptide (VIP), galanin (GAL), calcitonin generelated peptide (CGRP) and cocaine amphetamine-regulated transcript (CART) in the porcine descending colon. It was demonstrated that there was a statistically significant increase in the number of neurons within the myenteric plexus immunoreactive to all investigated substances. In the outer submucosal plexus, the CART-positive neurons were the only ones not to change, whereas no changes were recorded for nNOS or CART in the inner submucosal plexus. This study is the first study to discuss quantitative changes in the neurons immunoreactive to nNOS, VIP, GAL, CGRP and CART in the descending colon in diabetic pigs.

Long-term case study of a Wuzhishan miniature pig with diabetes

BACKGROUND

Miniature pigs are attractive animal models for exploring diabetes because they are similar to humans in terms of physiological structure and metabolism. However, little is known about the complications of diabetes in pigs.

METHODS

In this study, a 28-month observation of a Wuzhishan miniature pig with streptozotocin (STZ)-induced (120 mg/kg) diabetes was conducted, to investigate diabetes-related complications and the possibility of self-recovery in miniature pigs. Blood glucose, serum and urinary biochemistry was measured, and histopathologic examinations of eyes, kidney and pancreas were made.

RESULTS

During the observation, diabetic complications of eyes and kidney were observed. The eye complications included bilateral cataracts in the 15th month and degeneration of inner retina and microaneurysm in the 28th month. Kidney complications included glomerular mesangial expansion, focal segmental glomerular sclerosis, and renal tubular epithelial degeneration, but no proteinuria was observed. By 28 months after the application of STZ, with no treatment given, blood glucose had recovered and the number of pancreatic islet beta-cells had increased significantly.

CONCLUSIONS

We showed that the STZ-induced diabetes model in miniature pigs could accurately mimic the pathological changes of human diabetes, and that pancreatic islet beta-cell regeneration did occur in an adult miniature pig, providing a new means for exploring diabetic complications and pancreatic islet beta-cell regeneration.

Enhanced skeletal muscle growth in myostatin-deficient transgenic pigs had improved glucose uptake in stretozotocin-induced diabetes

The size of skeletal muscle mass plays a significant role in glucose uptake in healthy and diabetic human subjects. Previously, we have generated myostatin-deficient (MSTN^-/-) transgenic pigs via animal cloning technology. MSTN^-/- pigs had dramatic phenotype with individual muscle mass increase by 100% over their wild-type controls, which provides a unique large animal model to investigate how enhanced skeletal muscles are beneficial to glucose update in diabetes. We employed intravenous administration of stretozotocin (STZ) to male MSTN^-/- and wild-type pigs (100 mg/kg body weight). One month later, blood glucose and insulin concentrations and pancreas histology were examined, STZ-induced diabetes occurred in both MSTN transgenic and wild-type pigs. Histology of pancreas, analysis of pAKT and Glut4 transporter proteins by Western blotting, and real-time qPCR for MSTN gene expression were used in the study. The STZ-treated pigs had increased levels of fasting plasma glucose and insulin levels in comparison with animals receiving sodium citrate buffer, their pancreas also had reduced beta cells and slight increases in lymphocyte. There are significant lower concentrations of fasting plasma glucose and insulin in MSTN^-/- pigs than that of wild-type pigs after STZ administration. Detections of pAKT and Glut4 transporter proteins by Western blotting in muscle tissue indicates significant elevations of both proteins in MSTN^-/- pigs compared with the wild-type pigs. The results from this pig model suggest that enhanced skeletal muscle by manipulation of myostatin function can improve glucose uptake even in the status of diabetes.

Large Animal Models of Diabetes

Safe and reliable large animal diabetes models are a key prerequisite for advanced preclinical studies on diabetes. Chemical induction is the standard model of diabetes in rodents but is often critiqued in higher animals due to reduced efficacy, relevant side effects, and inadequate mortality rate. In this chapter, we aim to describe both pharmacological and surgical approaches for reproducible and safe diabetes models in minipigs and primates. In addition, genetically modified pig models for diabetes research are described.

Amylase-Dependent Regulation of Glucose Metabolism and Insulin/Glucagon Secretion in the Streptozotocin-Induced Diabetic Pig Model and in a Rat Pancreatic Beta-Cell Line, BRIN-BD11

The current study was aimed at highlighting the role of blood pancreatic amylase in the regulation of glucose homeostasis and insulin secretion in a porcine model of streptozotocin- (STZ-) induced diabetes and in a rat pancreatic beta-cell line, BRIN-BD11. Blood glucose, plasma insulin, and glucagon levels were measured following a duodenal glucose tolerance test (IDGTT), in four pigs with STZ-induced type 2 diabetes (T2D pigs) and in four pigs with STZ-induced type 1 diabetes (T1D pigs). Four intact pigs were used as the control group. The effect of amylase supplementation on both acute and chronic insulin secretion was determined in a BRIN-BD11 cell line. The amylase infusion had no effect on the glucose utilization curve or glucagon levels in the healthy pigs. However, a significant lowering of insulin release was observed in healthy pigs treated with amylase. In the T2D pigs, the glucose utilization curve was significantly lowered in the presence of amylase, while the insulin response curve remained unchanged. Amylase also significantly increased glucagon release during the IDGTT in the T2D and T1D pigs, by between 2- and 4-fold. Amylase did not affect the glucose utilization curve in the T1D pigs. Amylase supplementation significantly decreased both acute and chronic insulin secretion in the BRIN-BD11 cells. These data confirm our previous observations and demonstrate the participation of pancreatic amylase in glucose absorption/utilization. Moreover, the present study clearly highlights the direct impact of pancreatic blood amylase on insulin secretion from pancreatic beta-cells and its interactions with insulin and glucagon secretion in a porcine model.

Effect of Hyperglycemia on Myocardial Perfusion in Diabetic Porcine Models and Humans

BACKGROUND

Diabetes mellitus (DM) causes macro- and microvasculopathy, but data on cardiac microvascular changes in large animals are scarce. We sought to determine the effect of DM on macro- and microvascular changes in diabetic pigs and humans.

METHODS

Eight domestic pigs (4 with type I diabetes and 4 controls) underwent coronary angiography with optical coherence tomography (OCT; at baseline and 1 and 2 months), coronary computed tomography angiography, cardiac magnet resonance (CMR) imaging, and histologic examination.

RESULTS

The diabetic pigs had more irregular capillaries with acellular capillaries and a smaller capillary diameter (11.7 ± 0.33 μm vs. 13.5 ± 0.53 μm; P < 0.001) than those of the control pigs. The OCT showed no significant epicardial stenosis in either group; however diabetic pigs had a greater intima-media thickness. CMR results showed that diabetic pigs had a lower relative upslope at rest (31.3 ± 5.9 vs. 37.9 ± 8.1; P = 0.011) and during stress (18.0 ± 3.0 vs. 21.6 ± 2.8; P = 0.007) than the control pigs, implying decreased myocardial perfusion. Among the 79 patients with ST elevation myocardial infarction, 25 had diabetes and they had lower myocardial perfusion on CMR as well.

CONCLUSION

DM causes microvascular remodeling and a decrease in myocardial perfusion in large animals at a very early stage of the disease course. Early and effective interventions are necessary to interrupt the progression of vascular complications in diabetic patients.

In Vivo Rodent Models of Type 2 Diabetes and Their Usefulness for Evaluating Flavonoid Bioactivity

About 40% of the world’s population is overweight or obese and exist at risk of developing type 2 diabetes mellitus (T2D). Obesity is a leading pathogenic factor for developing insulin resistance (IR). It is well established that IR and a progressive decline in functional β-cell mass are hallmarks of developing T2D. In order to mitigate the global prevalence of T2D, we must carefully select the appropriate animal models to explore the cellular and molecular mechanisms of T2D, and to optimize novel therapeutics for their safe use in humans. Flavonoids, a group of polyphenols, have drawn great interest for their various health benefits, and have been identified in naturally occurring anti-diabetic compounds. Results from many clinical and animal studies demonstrate that dietary intake of flavonoids might prove helpful in preventing T2D. In this review, we discuss the currently available rodent animal models of T2D and analyze the advantages, the limitations of each T2D model, and highlight the potential anti-diabetic effects of flavonoids as well as the mechanisms of their actions.

Effects of Streptozotocin-Induced Diabetes on the Pineal Gland in the Domestic Pig

Several observations from experiments in rodents and human patients suggest that diabetes affects pineal gland function, including melatonin secretion; however, the accumulated data are not consistent. The aim of the present study was to determine the effects of streptozotocin-induced diabetes on the pineal gland in the domestic pig, a species widely used as a model in various biomedical studies. The study was performed on 10 juvenile pigs, which were divided into two groups: control and diabetic. Diabetes was evoked by administration of streptozotocin (150 mg/kg of body weight). After six weeks, the animals were euthanized between 12.00 and 14.00, and the pineal glands were removed and divided into two equal parts, which were used for biochemical analyses and for preparation of explants for the superfusion culture. The pineal contents (per 100 μg protein) of serotonin, 5-hydroxyindole acetic acid, 5-hydroxytryptophol, 5-methoxyindole acetic acid, 5-methoxytryptophol, and 5-methoxytryptamine were significantly lower in diabetic pigs than in control pigs. In contrast, the level of N-acetylserotonin was significantly higher in diabetic animals. No significant differences were found in the level of melatonin between control and experimental pigs. The amounts of 3,4-dihydroxyphenylalanine, dopamine, norepinephrine, and 3,4-dihydroxyphenylacetic acid were significantly lower in the pineal glands of diabetic animals. The level of vanillylmandelic acid was higher in diabetic pigs. No differences were observed in the level of basal and NE-stimulated release of N-acetylserotonin or melatonin between the pineal explants prepared from control and experimental animals. In vitro treatment with insulin was ineffective. In conclusion, streptozotocin-induced diabetes affects both indole metabolism and adrenergic neurotransmission in the pig pineal gland.

Large Animal Models: The Key to Translational Discovery in Digestive Disease Research

Gastrointestinal disease is a prevalent cause of morbidity and mortality and the use of animal models have been instrumental in studying mechanisms of digestive pathophysiology. As investigators attempt to translate the wealth of basic science information developed from rodent, models, large animal models provide a number of translational advantages. The pig, in particular, is arguably one of the most powerful models of human organ systems, including the gastrointestinal tract. The pig has provided important tools and insight into intestinal ischemia/reperfusion injury, intestinal mucosal repair, as well as new insights into esophageal injury and repair. Porcine model development has taken advantage of the size of the animal, allowing increased surgical and endoscopic access. In addition, cellular tools such as the intestinal porcine epithelial cell line and porcine enteroids are providing the methodology to translate basic science findings using in-depth mechanistic analyses. Further opportunities in porcine digestive disease modeling include developing additional transgenic pig strains. Collectively, porcine models hold great promise for the future of clinically relevant digestive disease research.

Expression of Cocaine and Amphetamine Regulated Transcript (CART) in the Porcine Intramural Neurons of Stomach in the Course of Experimentally Induced Diabetes Mellitus

In the present study, the effect of streptozotocin-induced diabetes on the cocaine- and amphetamine-regulated transcript-like immunoreactive (CART-LI) enteric nervous structures was investigated within the porcine stomach. To induce diabetes, the pigs were administered intravenously streptozotocin at a dose of 150 mg/kg of body weight. A significant decrease of the number of CART-LI perikarya was observed in the myenteric plexus of the gastric antrum, corpus, and pylorus in the experimental group. In contrast, submucous plexus was devoid of CART-positive neuronal cells both in control and experimental animals. In the control group, the highest densities of CART-LI nerve fibers were observed in the circular muscle layer of antrum and slightly less nerve fibers were present in the muscle layer of corpus and pylorus. In turn, submucous layer of all studied stomach regions revealed relatively smaller number of CART-positive nerve fibers. Diabetes caused statistically significant decrease in the expression of CART-LI nerve fibers only in the antrum circular muscle layer. Also, no changes in the CART-like immunoreactivity in the intraganglionic nerve fibers were observed. The obtained results suggest that acute hyperglycemia produced significant reduction of the CART expression in enteric perikarya throughout entire stomach as well as decrease of density the CART-LI fibers in circular muscle layer of the antrum. Additionally, we suggest that CART might be involved in the regulation of stomach function especially in the gastric motility.

Vulnerable carotid atherosclerotic plaque creation in a Swine model: evaluation of stenosis creation using absorbable and permanent suture in a diabetic dyslipidemic model

PURPOSE

To compare the creation of carotid atherosclerotic plaque after stenosis creation with absorbable or permanent suture in a diabetic dyslipidemic swine model.

MATERIALS AND METHODS

A high-cholesterol diet was fed to 15 Sinclair pigs. Diabetes was induced by intraarterial injection of streptozotocin. Stenosis creation in carotid arteries was performed with an absorbable or a permanent suture assigned randomly on both sides. After 20 weeks, Doppler ultrasound (US), angiography, and intravascular US examinations were performed before sacrifice. Carotid, coronary, and femoral arteries were analyzed by histology according to the American Heart Association (AHA) classification.

RESULTS

Three animals died during the perioperative period, and three others died during follow-up. Diabetes was successfully induced in all surviving animals (9 of 15). On angiography, stenoses were estimated at 80.4%±12.4 in carotid arteries with permanent sutures and at 48.8%±39 with absorbable sutures (P = .03). With permanent suturing, carotid plaques were observed in all animals with five of nine manifesting an AHA stage IV or more. With absorbable suture, atherosclerosis developed in seven of nine carotid arteries including three animals with an AHA stage IV or more. Advanced coronary and femoral plaques were observed in four and one of the nine animals. A correlation between AHA classes of coronary plaques and cholesterol level was observed (P = .01), whereas for carotid arteries, AHA class correlated with the degree of stenosis (P = .045).

CONCLUSIONS

Creation of atheromatous lesions in carotid and coronary arteries was successful with this model despite a high mortality rate. Less severe carotid stenoses and advanced plaques were observed with absorbable sutures.

Establishment of a stringent large animal model of insulin-dependent diabetes for islet autotransplantation: combination of pancreatectomy and streptozotocin

OBJECTIVE

A stringent porcine islet autograft diabetes model was developed to enable the assessment of autoislet safety and efficacy in either portal vein or an extrahepatic site.

METHODS

A 95% pancreatectomy was performed preserving the pancreaticoduodenal arcade; however, glycemic control was still maintained at 3.3 ± 0.3 days (mean ± SEM), shown by euglycemic fasting blood glucose levels of 4.9 ± 0.8 mmol/L (mean ± SEM, n = 3). To reduce surgical complications and eliminate remaining islets, pigs were dosed intravenously after a modified 90% pancreatectomy, with 150-mg/kg streptozotocin, producing a diabetic state (18.9 ± 1.8 mmol/L [mean ± SEM], n = 8; P < 0.001) within 2.0 ± 0.9 days (mean ± SEM).

RESULTS

Animals presented with sustained hyperglycemia, failing a glucose challenge test 12 weeks after diabetic induction, and showed no stimulated C-peptide secretion compared to nondiabetic controls (baseline: 0.479 ± 0.080 ng/mL [mean ± SEM] vs after procedure: 0.219 ± 0.055 ng/mL [mean ± SEM], P = 0.02). Diabetic animals were maintained on daily insulin. Despite an initial decline in body weight acutely after pancreatectomy and streptozotocin administration, the mean body weight increased after induction over the approximately 88-day study, indicating that the animals were in good health.

CONCLUSION

This stringent porcine model of diabetic induction should be used to assess autograft transplantation safety and efficacy.

The use of animal models in diabetes research

Diabetes is a disease characterized by a relative or absolute lack of insulin, leading to hyperglycaemia. There are two main types of diabetes: type 1 diabetes and type 2 diabetes. Type 1 diabetes is due to an autoimmune destruction of the insulin-producing pancreatic beta cells, and type 2 diabetes is caused by insulin resistance coupled by a failure of the beta cell to compensate. Animal models for type 1 diabetes range from animals with spontaneously developing autoimmune diabetes to chemical ablation of the pancreatic beta cells. Type 2 diabetes is modelled in both obese and non-obese animal models with varying degrees of insulin resistance and beta cell failure. This review outlines some of the models currently used in diabetes research. In addition, the use of transgenic and knock-out mouse models is discussed. Ideally, more than one animal model should be used to represent the diversity seen in human diabetic patients.

Goettingen Minipigs (GMP): Comparison of Two Different Models for Inducing Diabetes

PURPOSE

Preclinical experiments on large animals are indispensable for evaluating the effectiveness of diabetes therapies. Miniature swine are well suited for such studies due to their physiological and pathophysiological responses.

METHODS

We compare two methods for inducing diabetes in Goettingen minipigs (GMP), in five with the beta cell toxin streptozotocin (STZ) and in five other GMP by total pancreatectomy (PE). Glucose homeostasis was assessed with the intravenous glucose-tolerance test (IVGTT) and continual monitoring of interstitial glucose levels. At conclusion of the observation period, the pancreata were examined histologically. Three non-diabetic GMP served as control group.

RESULTS

The IVGTT revealed markedly diabetic profiles in both GMP groups. STZ-GMP were found to harbor residual C-peptides and scattered insulin-positive cells in the pancreas. PE-GMP survived the total pancreatectomy only with intensive postoperative care.

CONCLUSIONS

Although both methods reliably induced diabetes in GMP, the PE-GMP clearly had more health problems and required a greater expenditure of time and resources. The PE-GMP model, however, was better at eliminating endogenous insulin and C-peptide than the STZ-GMP model.

Molecular characterization of the porcine TIM-3 gene

TIM-3 is a member of the TIM (T-cell immunoglobulin domain and mucin domain) family, which plays an important role in TH1 responses and autoimmune diseases. In this study, we cloned and characterized the porcine TIM-3 gene. Real-time PCR showed little expression of porcine TIM-3 in muscle and stomach, low expression in kidney, brain, stomach and muscle, moderate expression in liver, small intestine and lymph, and high expression in spleen and lung. Transient transfection indicated that porcine TIM-3 fusion protein was found to localize on the cell membranes or cytoplasm. Association analysis indicated that the SNP AccI in exon2 was significantly associated (P < 0.05) with red blood cell count mean corpuscular haemoglobin, packed cell volume, Lymphocyte percentage and Lymphocyte modulus. In conclusion, our results provide some information for conducting further studies on the functions of porcine TIM-3 gene in type I diabetes and suggest that SNP AccI in exon2 may be utilized as a marker for molecular-assisted selection in animal breeding.

Complex porcine model of atherosclerosis: induction of early coronary lesions after long-term hyperlipidemia without sustained hyperglycemia

BACKGROUND

The incidence of coronary artery disease (CAD) is still increasing in industrialized countries and it is even higher in diabetic patients. For experimental studies investigating the pathophysiology of CAD, the use of an animal model comparable with the pathological situation in patients is crucial.

OBJECTIVE

To develop a model of advanced coronary atherosclerosis with induction of hyperlipidemia and hyperglycemia in domestic pigs.

METHODS

Six pigs were fed a standard pig chow (controls), two were fed a 2% cholesterol and 17% coconut fat diet (Chol group), and two pigs received a 4% cholesterol and 17% coconut fat diet combined with streptozotocin (STZ) injections to induce diabetes (High Chol+STZ group). Serum lipid and plasma glucose values were analyzed, and histochemical staining for morphometric analysis and immunohistochemistry were performed.

RESULTS

Pigs on the hyperlipidemic diet had elevated mean (+/- SD) serum lipid levels (total cholesterol 5.05+/-1.45 mmol/L [Chol] and 5.03+/-2.41 mmol/L [High Chol+STZ] versus 2.09+/-0.23 mmol/L [controls]). Histopathological evaluation revealed an initial stage of coronary atherosclerosis. None of the STZ-treated pigs showed a sustained elevation of plasma glucose (mean glucose before STZ injection was 5.11+/-0.94 mmol/L and thereafter was 6.03+/-2.39 mmol/L) or a decline in pancreatic beta cells.

CONCLUSIONS

The current data suggest that the domestic porcine model is not suitable to create severe CAD using an atherogenic diet in combination with STZ injections for experimental interventional vascular research. This may be due to different STZ sensitivities among species. However, hyperlipidemia induced early pathological lesions in coronary arteries resembling initial stages of atherosclerosis without severe luminal narrowing.

Effects of mitemcinal (GM-611), an orally active erythromycin-derived prokinetic agent, on delayed gastric emptying and postprandial glucose in a new minipig model of diabetes

AIMS

This study was conducted to evaluate the suitability of a new minipig model for investigating aspects of diabetes such as delayed gastric emptying and glucose metabolism abnormalities, and to test the effects of mitemcinal (GM-611), an orally active erythromycin-derived motilin receptor agonist, on gastric emptying and postprandial glucose in normal and diabetic minipigs.

METHODS AND RESULTS

Intravenous injection of 300 mg/kg streptozotocin (STZ) to 5-week-old minipigs induced moderate hyperglycemia (about 200 mg/dl) for >80 weeks without insulin treatment. Decreased insulin production (P<.05), increased area under the glucose curve (P<.05), and slower glucose disappearance (P<.05) were demonstrated, and there was no severe inhibition of body weight gain, liver failure, or renal failure. Gastric emptying was significantly delayed in diabetic minipigs (P<.05) at 80 weeks, but not at 40 weeks, post-STZ. Oral administration of mitemcinal (5 mg/kg) at 80 weeks accelerated gastric emptying and induced a similar postprandial glucose profile in normal and diabetic minipigs with delayed gastric emptying.

CONCLUSIONS

The new diabetic minipig model showed suitability for investigating diabetes, gastric emptying, and plasma glucose excursions. Since delayed gastric emptying and irregular plasma glucose excursions are characteristic of diabetic gastroparesis, the accelerating and regulating effects of mitemcinal on this model add to the existing evidence that mitemcinal is likely to be useful for treating diabetic gastroparesis.

Impaired wound healing in an acute diabetic pig model and the effects of local hyperglycemia

Diabetic wounds result in significant morbidity, prolonged hospitalization, and enormous health-care expenses. Pigs have been shown to have wound healing resembling that in humans. The aim of this study was to develop a large-animal model for diabetic wound healing. Diabetes was induced by streptozotocin injection in Yorkshire pigs. Full-thickness wounds were created and dressed with a sealed chamber. Nondiabetic pigs with or without high glucose wound fluid concentration served as controls. Glucose concentration in serum and wound fluid was measured and collected. Wound contraction was monitored, and biopsies were obtained for measurement of reepithelialization. Wound fluid was analyzed for insulin-like growth factor-1 (IGF-1), platelet-derived growth factor, and transforming growth factor. Glucose concentration in wound fluid initially followed serum levels and then decreased to undetectable on day 9. Reepithelialization was significantly delayed in diabetic pigs. In nondiabetic pigs, wounds treated in a local hyperglycemic environment, and thus excluding the effects of systemic hyperglycemia, showed no difference in wound closure compared with controls. This suggests that delayed wound healing in diabetes is not induced by local high-glucose concentration itself. Analysis of growth factor expression showed a marked reduction in IGF-1 in the diabetic wounds. Diabetic pigs have impaired healing that is accompanied by a reduction of IGF-1 in the healing wound and is not due to the local hyperglycemia condition itself.

Mechanisms and outcomes of drug- and toxicant-induced liver toxicity in diabetes

Increase dincidences of hepatotoxicity have been observed in diabetic patients receiving drug therapies. Neither the mechanisms nor the predisposing factors underlying hepatotoxicity in diabetics are clearly understood. Animal studies designed to examine the mechanisms of diabetes-modulated hepatotoxicity have traditionally focused only on bioactivation/detoxification of drugs and toxicants. It is becoming clear that once injury is initiated, additional events determine the final outcome of liver injury. Foremost among them are two leading mechanisms: first, biochemical mechanisms that lead to progression or regression of injury; and second, whether or not timely and adequate liver tissue repair occurs to mitigate injury and restore liver function. The liver has a remarkable ability to repair and restore its structure and function after physical or chemical-induced damage. The dynamic interaction between biotransformation-based liver injury and compensatory tissue repair plays a pivotal role in determining the ultimate outcome of hepatotoxicity initiated by drugs or toxicants. In this review, mechanisms underlying altered hepatotoxicity in diabetes with emphasis on both altered bioactivation and liver tissue repair are discussed. Animal models of both marked sensitivity (diabetic rats) and equally marked protection (diabetic mice) from drug-induced hepatotoxicity are described. These examples represent a remarkable species difference. Availability of the rodent diabetic models offers a unique opportunity to uncover mechanisms of clinical interest in averting human diabetic sensitivity to drug-induced hepatotoxicities. While the rat diabetic models appear to be suitable, the diabetic mouse models might not be suitable in preclinical testing for potential hepatotoxic effects of drugs or toxicants, because regardless of type 1 or type2 diabetes, mice are resistant to acute drug-or toxicant-induced toxicities.

Association of insulin resistance with hyperglycemia in streptozotocin-diabetic pigs: effects of metformin at isoenergetic feeding in a type 2-like diabetic pig model

Insulin-mediated glucose metabolism was investigated in streptozotocin (STZ)-treated diabetic pigs to explore if the STZ-diabetic pig can be a suitable model for insulin-resistant, type 2 diabetes mellitus. Pigs (approximately 40 kg) were meal-fed with a low-fat (5%) diet. Hyperinsulinemic (1, 2, and 8 mU kg(-1) min(-1)) clamps and/or 6,6-(2)H-glucose infusion studies were performed in 36 pigs. Diabetic (slow, 30-minute infusion of 130 mg STZ/kg) vs normal pigs were nonketotic, showed fasting hyperglycemia (21.7 +/- 1.1 vs 5.3 +/- 0.2 mmol/L), comparable plasma insulin (9 +/- 7 vs 5 +/- 1 mU/L), and elevated triglyceride concentrations (1.0 +/- 0.3 vs 0.2 +/- 0.1 mmol/L). After a standard meal, plasma triglycerides, cholesterol, and nonesterified fatty acid concentrations were significantly higher in diabetic vs normal pigs (1.2 +/- 0.3 vs 0.3 +/- 0.1, 2.3 +/- 0.2 vs 1.7 +/- 0.1, and 1.5 +/- 0.5 vs 0.2 +/- 0.1 mmol/L, respectively, P < .05). Fasting whole-body glucose uptake, hepatic glucose production, and urinary glucose excretion were increased (P < .01) in diabetic vs normal pigs (9.1 +/- 0.6 vs 4.8 +/- 0.4, 11.4 +/- 0.6 vs 4.8 +/- 0.4, and 2.3 +/- 0.2 vs 0.0 +/- 0.0 mg kg(-1) min(-1)). During hyperinsulinemic euglycemia (approximately 6 mmol/L), whole-body glucose uptake was severely reduced (P < .01) and hepatic glucose production was moderately increased (P < .05) in diabetic vs normal pigs (6.7 +/- 1.3 vs 21.1 +/- 2.2 and 1.7 +/- 0.5 vs 0.8 +/- 0.3 mg kg(-1) min(-1)) despite plasma insulin concentrations of 45 +/- 5 vs 24 +/- 5 mU/L, respectively. Metformin vs placebo treatment of diabetic pigs (twice 1.5 g/d) for 2 weeks during isoenergetic feeding (1045 kJ/kg body weight(0.75)) resulted in a reduction in both fasting and postprandial hyperglycemia (14.7 +/- 1.5 vs 19.4 +/- 0.6 and 24.9 +/- 2.2 vs 35.5 +/- 4.9 mmol/L), a reduction in daily urinary glucose excretion (approximately 250 vs approximately 350 g/kg food), and an increase in insulin-stimulated glucose disposal (9.4 +/- 2.2 vs 5.8 +/- 1.7 mg kg(-1) min(-1); P < .05), respectively. In conclusion, a slow infusion of STZ (130 mg/kg) in pigs on a low-fat diet induces the characteristic metabolic abnormalities of type 2 diabetes mellitus and its sensitivity to oral metformin therapy. It is therefore a suitable humanoid animal model for studying different aspects of metabolic changes in type 2 diabetes mellitus. Insulin resistance in STZ-diabetic pigs is most likely secondary to hyperglycemia and/or hyperlipidemia and therefore of metabolic origin.

Streptozotocin-induced diabetes in large animals (pigs/primates): role of GLUT2 transporter and beta-cell plasticity

BACKGROUND

To induce irreversible diabetes in large animals, the efficiency of streptozotocin (STZ) was evaluated in pigs, primates and compared to the gold standard model in rats.

METHODS

Low (50 mg/kg) and high (150 mg/kg) doses of STZ were tested. Hepatic/renal function, glucose metabolism (intravenous glucose tolerance tests, fasting blood glucose) and histomorphometry were evaluated prior to, 1, and 4 weeks after STZ treatment.

RESULTS

In rats and primates, expressing a high level of GLUT2 expression on beta cells, a dose of 50 mg/kg STZ induced irreversible diabetes (due to the 97% destruction of beta cell mass) without provoking liver or renal failure. In pigs, despite the use of high STZ dose, partial correction of hyperglycaemia was observed four weeks after STZ injection (decreased fasting blood glucose and intravenous glucose tolerance tests; increased insulin production). The correction of hyperglycaemia was associated with significant hypertrophy of immature pig beta-cell clusters (+30%, P<0.05), whereas no hypertrophy was observed in rats/primates.

CONCLUSION

These results demonstrated that STZ might be used to induce irreversible diabetes in rats and primates. In contrast, the low STZ sensitivity in pigs related to a low expression of GLUT2, higher number of immature beta cells and compensatory beta-cell hypertrophy, renders STZ-induced diabetes inappropriate for studying islet allografts in swine.

Effects of Syzygium cordatum (Hochst.) [Myrtaceae] leaf extract on plasma glucose and hepatic glycogen in streptozotocin-induced diabetic rats

The present study investigates the hypoglycaemic effect of Syzygium cordatum (Hochst.) [Myrtaceae] leaf extract in non-diabetic and streptozotocin (STZ)-induced diabetic rats. Oral glucose tolerance tests (OGGT) were conducted in non-diabetic and STZ-diabetic rats using orally administered glucose (1.4 g 100 g(-1) body weight) followed by either the leaf extract (6 mg 100 g(-1) body weight) or subcutaneous (sc) injection of metformin (50 mg 100 g(-1)). Weekly plasma glucose and terminal hepatic glycogen concentrations were recorded in control STZ-diabetic rats and diabetic rats orally treated with the leaf extract once every third day for 4 weeks. Administration of the leaf extract decreased plasma glucose from 7.7+/-0.9 mmol l(-1) to 3.7+/-0.6 mmol l(-1) (n = 6), and 21.1+/-2.2 mmol l(-1) to 12.5+/-1.8 mmol l(-1) (n = 7) by 2 1/2 h in non-diabetic and STZ-diabetic rats, respectively. OGTT data in metformin-treated rats were similar at the corresponding time in all groups, except for significant blood glucose reduction by the drug in non-diabetic rats between 1 and 1 1/2 h after treatment. Oral administration of the extract did not affect plasma glucose concentration in STZ-diabetic rats after 4 weeks, although it significantly increased hepatic glycogen content by comparison with untreated STZ-diabetic rats (28+/-5 mg 100 g(-1) body weight, n = 7, versus 16+/-3 mg 100 g(-1) body weight, n = 6). We conclude that Syzygium cordatum leaf extract contains compounds that could be effective in mild diabetes mellitus or in cases of glucose tolerance impairment. The possible mechanism(s) involved in the short-term hypoglycaemic effect of the extract could not be established by the current study.

Development of a porcine model of type 1 diabetes by total pancreatectomy and establishment of a glucose tolerance evaluation method

PURPOSE

To develop and evaluate the efficacy of diabetes-targeted cell therapies in humans, a reliable model in larger animals is highly desirable. This article reports the surgical technique of total pancreatectomy in pigs and the biochemical analysis of the characteristics of totally pancreatectomized pigs.

METHODS

Surgical total pancreatectomy was conducted in 23 pigs. Blood glucose, insulin, biochemistries, activity index, and intravenous glucose tolerance test (IVGTT) were examined to assess the pathophysiological profiles of diabetic pigs.

RESULTS

A total of 14 pigs successfully underwent total pancreatectomy without requiring biliary reconstruction and were analyzed in the present study. Activity index was decreased from day 5 on and the mean survival of totally pancreatectomized pigs was 7.6 +/- 2.7 days. No endogenous insulin secretion was confirmed in these pigs. Pigs which received total pancreatectomy demonstrated significantly higher levels of ketone bodies. IVGTT performed within 4 days after total pancreatectomy showed a spontaneous decrease in blood glucose levels despite an absence of endogenous insulin secretion. IVGTT on day 5 or later showed continued hyperglycemia in pigs with total pancreatectomy. Histological examination showed atrophy of hepatocytes and decreased glycogen storage in the liver and decreased mucus production of the small intestine.

CONCLUSION

This article describes a porcine model of diabetes created by total pancreatectomy and it analyzes the pathophysiological profiles in the animals. The present study has suggested that IVGTT on day 5 or later after total pancreatectomy is a reliable method to evaluate the efficacy of cell therapies.

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.

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.

Effects of Opuntia megacantha leaves extract on renal electrolyte and fluid handling in streptozotocin (STZ)-diabetic rats

We previously demonstrated that Opuntia megacantha leaves' extracts can reduce blood glucose levels in diabetes mellitus. For O. megacantha leaves' extracts to have potential in the management of diabetes mellitus, it is necessary to establish its detailed effects on renal function since diabetes is associated with renal fluid and electrolyte disturbances. Therefore, the current study was designed to investigate the influence of the extracts on renal function in male diabetic Sprague-Dawley rats. Rats were made diabetic by an i.p. injection of streptozotocin (STZ, 60 mg/kg in citrate buffer). Vehicle injected animals acted as controls. Separate groups of nondiabetic and diabetic rats were orally administered O. megacantha leaves extracts (20 mg/100 g bw) or normal saline (0.1 ml x 100 g(-1) bw) daily for 5 weeks. Urine volume and total urinary outputs of Na+ and K+ were determined from 24 h samples. O. megacantha leaves' extracts significantly (p < 0.01) increased urinary Na+ output in diabetic and nondiabetic rats resulting in significantly (p < 0.01) low plasma concentration by comparison with untreated animals. Treatment with the extract significantly increased FE(Na+) and GFR in all groups. The urinary K+ outputs in nondiabetic was slightly lowered, but did not reach statistically significance. O. megacantha leaves' extracts did not alter plasma aldosterone and AVP concentrations in diabetic and nondiabetic rats in nondiabetic animals. It is concluded that O. megacantha leaves extracts modulate renal water and sodium handling. The mechanisms are not clear.

Effects of Opuntia megacantha on blood glucose and kidney function in streptozotocin diabetic rats

The purpose of the study was to investigate the effects of Opuntia megacantha leaf extracts on blood glucose concentrations and kidney function in normal and streptozotocin (STZ)-diabetic rats. STZ-diabetic and non-diabetic rats were orally administered extracts of O. megacantha leaves (20 mg/100 g body weight) daily for 5 weeks and respective control rats were administered normal saline (0.1 ml/100 mg body weight). Urine volume, urinary outputs of Na+, K+ and creatinine were monitored daily over the 5-week period. Plasma concentrations of Na+, K+, urea and creatinine and the glomerular filtration rate (GFR) as assessed by creatinine clearance were determined after 5 weeks. Plasma glucose concentrations in STZ-diabetic and non-diabetic rats were reduced by the administration of leaf extracts of O. megacantha. However, leaf extracts increased urinary Na+ output in STZ-diabetic and non-diabetic rats, concomitantly with a reduction in plasma concentration of the ion. O. megacantha leaf extracts significantly increased plasma creatinine and urea concentrations in non-diabetic and STZ-diabetic rats. Administration of the leaf extract was also associated with an increased GFR in STZ-diabetic rats (from 1.8 +/- 0.3 ml/min to 2.8 +/- 0.3 ml/min, n = 8) although the rate was unaltered in non-diabetic rats. The results suggest that leaf extracts of O. megacantha not only reduce blood glucose levels, but may be toxic to the kidney as shown by the elevation in plasma urea and creatinine concentrations and the reduction of plasma Na+ concentration.

The effect of venous drainage on glucose homeostasis after experimental pancreas transplantation

In this canine study, glucose homeostasis after clinical pancreas transplantation is complex, with the relative effect of systemic versus portal delivery of insulin remaining unresolved. Thirty-two pancreatectomized dogs received either systemic venous drainage (SVD) with bladder exocrine drainage (n = 16), or portal venous drainage (PVD) with gastric exocrine drainage (n = 16). Cyclosporine (CsA) based immunosuppression was commenced on day -7. The effect of immunosuppression was a significant increase in fasting blood glucose (FBGL) (P = 0.002), fasting insulin (P = 0.024), AUC for insulin (P = 0.009), and K values decreased (P = 0.009). FBGL and K values remained abnormal after transplantation with no significant difference seen between SVD and PVD. However, fasting insulin became significantly lower after PVD and AUC insulin fell in both groups. CsA levels fell in both groups after transplantation, mirroring the fall in AUC insulin, and implicating CsA as a major cause of peripheral resistance to insulin. In conclusion, PVD did not demonstrate a significant advantage over SVD in handling an intravenous glucose challenge. The need for pancreatectomy in large animals may make them an unsatisfactory experimental model to evaluate the glucoregulatory effects of pancreas allotransplantation.

Day-night differences in the kinetics and dynamics of insulin: diabetic versus normal Yucatan minipigs

Time-dependent variations in the pharmacokinetics and pharmacodynamics of insulin were studied at two times, 10:30 and 20:30 during the same day in normal and streptozotocin (STZ)-induced diabetic minipigs housed in L(06:00):D(18:00) using the intravenous insulin tolerance test. Following intravenous insulin (0.1 IU/kg) administration in normal minipigs, the time for the glucose level to reach nadir (tnadir) was significantly longer in the evening than the morning [(A.M.; 30.4 (+/- 2.4) vs. P.M.: 38.5 (+/- 3.3) min] (p < 0.01), although maximum reduction of glucose level (nadir) in the morning and evening was not significantly different [A.M.: (-70 (+/- 2) vs. P.M.: -65 (+/- 5) %]. The rate of glucose decline (Kin) was significantly decreased in the evening [A.M.: 5.33 (+/- 0.71) vs. P.M.: 4.44 (+/- 0.54) %dBG/min] (p < 0.01), and the integrated glucose-lowering response (ABCB) was significantly higher in the evening than the morning [A.M.: 3.18 (+/- 0.38) vs. P.M.: 4.52 (+/- 0.30) (g/dl)* min] (p < 0.01). The area under the plasma insulin concentration curve was increased significantly in the evening [A.M.: 2.26 (+/- 0.174) vs. P.M.: 2.74 (+/- 0.18) (mU/ml)* min], while the morning plasma insulin half-life did not differ significantly from that in the evening [A.M.: 4.79 (+/- 0.36) vs. P.M.: 5.47 (+/- 0.47) min]. After induction of diabetes by intravenous STZ injections, minipigs became diabetic, baseline blood glucose was observed to increase from the range of 45-55 to 200-250 mg/dl while plasma insulin levels decreased from 7-12 to 3-5 uU/ml. In the STZ-induced diabetic minipigs, a higher dose (0.2 IU/kg) was used in the intravenous insulin tolerance test in an attempt to normalize the high glucose levels. Following intravenous administration of insulin, the evening Kin and ABCB were significantly higher than they were in the morning [Kin = A.M.: 0.99 (+/- 0.25) vs. P.M.: 1.75 (+/- 0.44) %dBG/min (p < 0.01); ABCB = A.M.: 12.63 (+/- 1.91) vs. P.M.: 19.09 (+/- 5.43) (g/dl)* min (p < 0.01)]. However, there was no significant difference between tnadir and nadir values obtained in the morning and evening [tnadir = A.M.: 81.4 (+/- 9.2) vs. P.M.: 92.8 (+/- 13.7) min; nadir = A.M.: 39.6 (+/- 5.2) vs P.M.: 48.0 (+/- 9.0) %]. The pharmacodynamics and pharmacokinetics of IV insulin both were found to be highly dose-dependent (r > 0.90).

Renal fluid and electrolyte handling in streptozotocin-diabetic rats

Male Sprague-Dawley rats (300-400 g) were made diabetic by an i.p. injection of streptozotocin (STZ, 60 mg/kg in citrate buffer, n = 8) to examine renal function in well-established diabetes mellitus. Vehicle-injected animals (n = 8) acted as controls. The mean weekly total amounts of food taken by control and STZ-diabetic rats did not differ, but diabetic rats exhibited diarrhea and drank more water. STZ-diabetic rats progressively lost weight from the first to the third week but gained weight in the fourth week. At 5 weeks the weight stabilized, plasma glucose concentration was elevated, and this was associated with increased kidney weight. The weekly urine volume from STZ-diabetic rats was elevated throughout the 5-week period of study and this was associated with significantly lower urinary outputs of Na+ and higher outputs of K+ than those of control animals. After 5 weeks of STZ diabetes, plasma corticosterone and aldosterone concentrations in unanesthetized rats did not differ significantly from values seen in controls. To examine renal function in more detail, groups of Inactin-anesthetized 5-week STZ-diabetic rats (n = 7) and control rats (n = 7) were placed on continuous jugular infusion of 0.077 M NaCl at 150 microL/min for 8.5 h. Following a 3.5-h equilibration period, urine flow and Na+, K+, and Cl- outputs were determined for the subsequent 5-h period, with mean arterial pressure and glomerular filtration rate (GFR). STZ-diabetic rats voided significantly less of the infused fluid and the urinary excretions of Na+ and K+ were lower than those of controls. Mean arterial blood pressure and GFR values in STZ-diabetic rats did not differ statistically from those seen in controls. Following hypotonic saline infusion for 8.5 h the levels of aldosterone were elevated significantly (p < 0.01) in STZ-diabetic rats by comparison with control animals (5.36 +/- 1.58 nmol/L, n = 7 vs. 2.36 +/- 0.12 nmol/L, n = 7). It is concluded that a challenge of hypotonic saline load to rats with 5 weeks of STZ diabetes mellitus elevates plasma aldosterone to reduce the ability to excrete Na+.