Establishment of a streptozotocin-induced diabetic domestic pig model and a systematic evaluation of pathological changes in the hard and soft tissue over a 12-month period

The effects of hyperglycaemia on peri-implant tissues after osseointegration

PURPOSE

We assessed the effects of hyperglycaemia induced by streptozotocin (STZ) on peri-implantitis developing after implant osseointegration.

METHODS

Thirty-six male Wistar rats (4 weeks old) were used. We placed titanium implants 4 weeks after extraction of the maxillary first molars. Healing abutments were attached 4 weeks later. After osseointegration was confirmed, the rats were divided into control, hyperglycaemia (STZ), and STZ with insulin (STZ+INS) groups. Hyperglycaemia was induced by a single injection of 50mg/kg STZ. Silk ligatures were placed on only the right sides (i.e. ligature sides), not on the left sides. Peri-implant tissues extracted at 4 weeks post-ligation were analysed both radiologically (via micro-computed tomography) and histologically (via toluidine blue staining). Total RNA was also extracted and analysed by quantitative PCR to detect TNF-α, IL-1β and the receptor of advanced glycation end products (RAGE). Additionally, advanced glycation end products (AGEs) were measured by ELISA.

RESULTS

Radiological and histological analyses showed that bone loss on the non-ligature sides was significantly greater in the STZ than the control group. However, on the ligature sides, bone loss was greater than on the non-ligature sides, and no significant difference was evident among the three groups. The levels of mRNAs encoding TNF-α, IL-1β, RAGE, and AGEs on the ligature sides were significantly upregulated (all P<0.05) in the STZ compared to the control group.

CONCLUSIONS

Although hyperglycaemia could be associated with bone loss around implants with increased AGE production and RAGE expression, hyperglycaemia does not become a triggering factor of ligature induced peri-implantitis.

Epidermal growth factor receptor genes are overexpressed within the periprosthetic soft-tissue around percutaneous devices: A pilot study

Epidermal downgrowth around percutaneous devices produce sinus tracts, which then accumulate bacteria becoming foci of infection. This mode to failure is epidermal-centric, and is accelerated by changes in the chemokines and cytokines of the underlying periprosthetic granulation tissue (GT). In order to more fully comprehend the mechanism of downgrowth, in this 28-day study, percutaneous devices were placed in 10 Zucker diabetic fatty rats; 5 animals were induced with diabetes mellitus II (DM II) prior to the surgery and 5 animals served as a healthy, nondiabetic cohort. At necropsy, periprosthetic tissues were harvested, and underwent histological and polymerase chain reaction (PCR) studies. After isolating GTs from the surrounding tissue and extracting ribonucleic acids, PCR array and quantitative-PCR (qPCR) analyses were carried-out. The PCR array for 84 key wound-healing associated genes showed a five-fold or greater change in 31 genes in the GTs of healthy animals compared to uninjured healthy typical skin tissues. Eighteen genes were overexpressed and these included epidermal growth factor (EGF) and epidermal growth factor receptor (EGFR). Thirteen genes were underexpressed. When GTs of DM II animals were compared to healthy animals, there were 8 genes overexpressed and 25 genes underexpressed; under expressed genes included EGF and EGFR. The qPCR and immunohistochemistry data further validated these observations. Pathway analysis of genes up-regulated 15-fold or more indicated two, EGFR and interleukin-10, centric clustering effects. It was concluded that EGFR could be a key player in exacerbating the epidermal downgrowth, and might be an effective target for preventing downgrowth.

Morphological and pharmacological characterization of the porcine popliteal artery: A novel model for study of lower limb arterial disease

OBJECTIVE

This study was undertaken to characterize structural and pharmacological properties of the pig popliteal artery in order to develop a novel system for the examination of lower limb blood flow regulation in a variety of cardiovascular pathologies, such as diabetes-induced peripheral artery disease.

METHODS

Popliteal arteries were isolated from streptozocin-induced diabetic pigs or age-matched saline-injected control pigs for morphological study using transmission electron microscopy and for examination of vasoreactivity to pharmacological agents using wire myography.

RESULTS

Transmission electron microscopy of the porcine popliteal artery wall revealed the presence of endothelial cell-smooth muscle cell interactions (myoendothelial junctions) and smooth muscle cell-smooth muscle cell interactions, for which we have coined the term "myo-myo junctions." These myo-myo junctions were shown to feature plaques indicative of connexin expression. Further, the pig popliteal artery was highly responsive to a variety of vasoconstrictors including norepinephrine, phenylephrine, and U46619, and vasodilators including acetylcholine, adenosine 5'-[β-thio] diphosphate, and bradykinin. Finally, 2 weeks after streptozocin-induced diabetes, the normalized vasoconstriction of the pig popliteal artery to norepinephrine was unaltered compared to control.

CONCLUSIONS

The pig popliteal artery displays structural and pharmacological properties that might prove useful in future studies of diabetes-associated peripheral artery disease and other lower limb cardiovascular diseases.

Effect of Obesity or Metabolic Syndrome and Diabetes on Osseointegration of Dental Implants in a Miniature Swine Model: A Pilot Study

PURPOSE

The increasing prevalence of obesity or metabolic syndrome (O/MS) and type 2 diabetes mellitus (DM) remains a global health concern. Clinically relevant and practical translational models mimicking human characteristics of these conditions are lacking. This study aimed to demonstrate proof of concept of the induction of stable O/MS and type 2 DM in a Göttingen minipig model and validate both of these disease-adjusted Göttingen minipig models as impaired healing models for the testing of dental implants.

MATERIALS AND METHODS

Nine minipigs were split into 3 groups-control (normal diet), obese (cafeteria diet), and diabetic (cafeteria diet plus low-dosage streptozotocin)-followed by placement of dental implants. Inflammatory markers including tumor necrosis factor α, C-reactive protein, and cortisol were recorded for each study group. Removal torque was measured, and histomorphometric analysis (bone-to-implant contact and bone area fraction occupancy) was performed.

RESULTS

O/MS pigs showed, on average, a 2-fold increase in plasma C-reactive protein (P < .05) and cortisol (P < .09) concentrations compared with controls; DM pigs showed, on average approximately, a 40-fold increase in plasma tumor necrosis factor α levels (P < .05) and a 2-fold increase in cortisol concentrations (P < .05) compared with controls. The impact of O/MS and DM on implants was determined. The torque to interface failure was highest in the control group (200 N-cm) and significantly lower in the O/MS (90 N-cm) and DM (60 N-cm) groups (P < .01). Bone formation around implants was significantly greater in the control group than in the O/MS and DM groups (P < .02).

CONCLUSIONS

Both O/MS and DM minipigs express a human-like disease phenotype, and both presented bone-healing impairment around dental implants. Our finding of no significant difference between type 2 DM and O/MS in bone formation around implants provides evidence that further investigation of the impact of O/MS is warranted.

The influence of direct laser metal sintering implants on the early stages of osseointegration in diabetic mini-pigs

Background

High failure rates of oral implants have been reported in diabetic patients due to the disruption of osseointegration. The aim of this study was to investigate whether direct laser metal sintering (DLMS) could improve osseointegration in diabetic animal models.

Methods

Surface characterizations were carried out on two types of implants. Cell morphology and the osteogenic-related gene expression of MG63 cells were observed under conditions of DLMS and microarc oxidation (MAO). A diabetes model in mini-pigs was established by intravenous injection of streptozotocin (150 mg/kg), and a total of 36 implants were inserted into the mandibular region. Micro-computed tomography (micro-CT) and histologic evaluations were performed 3 and 6 months after implantation.

Results

The Ra (the average of the absolute height of all points) of MAO surface was 2.3±0.3 µm while the DLMS surface showed the Ra of 27.4±1.1 µm. The cells on DLMS implants spread out more podia than those on MAO implants through cell morphology analysis. Osteogenic-related gene expression was also dramatically increased in the DLMS group. Obvious improvement was observed in the micro-CT and Van Gieson staining analyses of DLMS implants compared with MAO at 3 months, although this difference disappeared by 6 months. DLMS implants showed a higher bone–implant contact percentage (33.2%±11.2%) at 3 months compared with MAO group (18.9%±7.3%) while similar results were showed at 6 months between DLMS group (42.8%±10.1%) and MAO group (38.3%±10.8%).

Conclusion

The three-dimensional environment of implant surfaces with highly porous and fully interconnected channel and pore architectures can improve cell spreading and accelerate the progress of osseointegration in diabetic mini-pigs.

Wound Healing Delay in the ZDSD Rat

Animal models of diabetic delayed wound healing are essential to the development of strategies to improve clinical approaches for human patients. The Zucker diabetic Sprague Dawley (ZDSD) rat has proved to be an accurate model of diet-induced obesity and diabetes and we evaluated the utility of the ZDSD rat as a model for delayed wound healing associated with diabetes and obesity. Groups of ZDSD and Sprague Dawley (SD) rats were placed on a diabetogenic diet and evaluated two weeks later for hyperglycemia, as a sign of diabetes. Rats with blood glucose levels of >300 mg/dl were considered diabetic and those with blood glucose of <180 mg/dl were considered non-diabetic. All SD rats were non-diabetic. A full-thickness excisional skin wound was created in anesthetized rats using a punch biopsy and wound diameter measured on days 1, 4, 7, 9 and 11. Blood glucose levels and body weights were measured periodically before and after wounding. Diabetic ZDSD rats had significantly greater blood glucose levels than non-diabetic ZDSD and SD rats within 10 days of being placed on the diabetogenic diet. Furthermore, diabetic ZDSD rats initially weighed more than non-diabetic ZDSD and SD rats, however, by the end of the study there was no significant difference in body weight between the ZDSD groups. By day nine, wounds in ZDSD rats were significantly larger than those in SD rats and this persisted until the end of the study at day fourteen. Wounds from all groups were characterized histologically by abundant fibroblast cells, collagen deposition and macrophages. These results demonstrate delayed wound healing in both diabetic and non-diabetic ZDSD rats and suggest that obesity or metabolic syndrome are important factors in wound healing delay.

Peri-implant defect regeneration in the diabetic pig: A preclinical study

OBJECTIVES

The study aims to establish a peri-implant dehiscence-type bone defect in a diabetic animal model of human bone repair and to quantify the influence of diabetes on peri-implant bone regeneration.

MATERIAL AND METHODS

Experimental diabetes was induced in three domestic pigs by streptozotocin. Three animals served as healthy controls. After 12 months four standardized peri-implant dehiscence bone defects were surgically created in the ramus mandibulae. The animals were sacrificed after 90 days. Samples were histologically analyzed to quantify new bone height (NBH), bone-to-implant-contact (BIC), area of newly formed bone (NFB), bone-density (BD), and bone mineralization (BM) in the prepared defect (-D) and in a local control region (-L).

RESULTS

After 90 days, diabetic animals revealed a significantly lower BIC (p = 0.037) and BD (p = 0.041) in the defect area (-D). NBH and BM-D differences within the groups were not significant (p > 0.05). Significant more NFB was measured in the healthy control group (p = 0.046). In the region of local bone BIC-L was significant less in the diabetic group (p = 0.028). In the local control region BD-L and BM-L was lower in the diabetic group compared to the healthy control animals (p > 0.05).

CONCLUSION

Histological evidence indicates impaired peri-implant defect regeneration in a diabetic animal model.

Effect of targeted delivery of bone morphogenetic protein-2 on bone formation in type 1 diabetes

PURPOSE

Bone formation and healing are diminished in experimental type 1 diabetes. The present study investigated whether controlled local release of recombinant human bone morphogenetic protein 2 (rhBMP-2) stimulates bone defect healing in diabetes as a consequence of its anabolic effects on bone.

MATERIALS AND METHODS

Bilateral experimental circular bone defects were created in the temporal bones of 64 BALB/cByJ mice. Defects were treated with acellular collagen sponge plus 0.4 or 1.8 μg of rhBMP-2 per defect, and untreated defects served as controls. The healing of the defects over a 14-day period in diabetic and nondiabetic mice was analyzed histomorphometrically.

RESULTS

Diabetes inhibited bone formation in both untreated and BMP-treated bone defects. Controlled local release of rhBMP-2 significantly stimulated bone formation in diabetic animals, bringing it nearly to normal levels, and enhanced bone regeneration in normal animals.

CONCLUSION

Recombinant human BMP-2 may be beneficial in treating deficient intramembranous bone formation in diabetes.

Bone formation in peri-implant defects grafted with microparticles: a pilot animal experimental study

AIM

This study aimed to evaluate the healing of peri-implant defects grafted with microparticles (MPs).

MATERIAL AND METHODS

Six domestic pigs received nine standardized defects at the calvaria, and an implant was inserted in the middle of each defect. The space between the implant and lateral bone portion was filled with MP pellets (n = 18) or MP supernatant (n = 18) or left unfilled (n = 18). After 14 and 28 days, three animals were sacrificed and specimens removed for further processing. Samples were microradiographically and histologically analysed. In addition, we immunohistochemically stained for anti-vWF as a marker of angiogenesis.

RESULTS

In the case of bone regeneration and vessel formation, the null hypothesis can be partially rejected. After 14 and 28 days, no significant difference was observed within groups regarding de novo bone formation, bone density and osseointegration. However, superior vessel formation was found at both time points.

CONCLUSION

Microparticles represent a promising treatment option to accelerate peri-implant vessel formation. Further studies are needed to investigate the regenerative properties of MPs more precisely.

Establishing a critical-size mandibular defect model in growing pigs: characterization of spontaneous healing

PURPOSE

A large animal model is desired for preclinical studies aimed at reconstructing severe mandibular skeletal defects using tissue engineering techniques. To identify the size and location requirements for a mandibular critical-size bone defect in growing pigs, the present study investigated the spontaneous healing of surgically created mandibular defects.

MATERIALS AND METHODS

Six 4-month-old domestic pigs were used. In pigs 1 and 2, a 3-, 5-, or 7-cm(3) subperiosteal mandibular defect was created. In pigs 3 to 6, 3- to 5-cm(3) bilateral defects were randomly created at the anterior (apical to the molars) and posterior (mandibular angle) mandibular regions. Spontaneous healing of these defects was assessed by serial computed tomography scans (postoperative week 1, 6, and 12) and histologic analyses.

RESULTS

In pigs 1 and 2, regardless of defect size, the anterior, but not posterior, defects had largely healed. Systematic analyses of pigs 3 to 6 revealed, first, the extent of defect regeneration from spontaneous healing was significantly less in the posterior than in the anterior defects, with about two thirds and one third of the original defect volume remaining, respectively. Second, histologically, the posterior defects had considerably less regeneration and more evident tapering of the new bone than did the anterior defects. Finally, the buccal periosteum had completely regenerated in the anterior defects, but had only partially done so in the posterior defects. Also, the buccal surface contour was moderately concave in the anterior defects, but it was severely concave in the posterior defects.

CONCLUSIONS

Despite robust spontaneous healing of mandibular defects in growing pigs, 5-cm(3) defects in the mandibular angle region without buccal periosteum would be a reasonable critical-size defect model relevant to mandibular defects in adolescent humans.

Scaffold-based delivery of autologous mesenchymal stem cells for mandibular distraction osteogenesis: preliminary studies in a porcine model

Purpose

Bone regeneration through distraction osteogenesis (DO) is promising but remarkably slow. To accelerate it, autologous mesenchymal stem cells have been directly injected to the distraction site in a few recent studies. Compared to direct injection, a scaffold-based method can provide earlier cell delivery with potentially better controlled cell distribution and retention. This pilot project investigated a scaffold-based cell-delivery approach in a porcine mandibular DO model.

Materials and Methods

Eleven adolescent domestic pigs were used for two major sets of studies. The in-vitro set established methodologies to: aspirate bone marrow from the tibia; isolate, characterize and expand bone marrow-derived mesenchymal stem cells (BM-MSCs); enhance BM-MSC osteogenic differentiation using FGF-2; and confirm cell integration with a gelatin-based Gelfoam scaffold. The in-vivo set transplanted autologous stem cells into the mandibular distraction sites using Gelfoam scaffolds; completed a standard DO-course and assessed bone regeneration by macroscopic, radiographic and histological methods. Repeated-measure ANOVAs and t-tests were used for statistical analyses.

Results

From aspirated bone marrow, multi-potent, heterogeneous BM-MSCs purified from hematopoietic stem cell contamination were obtained. FGF-2 significantly enhanced pig BM-MSC osteogenic differentiation and proliferation, with 5 ng/ml determined as the optimal dosage. Pig BM-MSCs integrated readily with Gelfoam and maintained viability and proliferative ability. After integration with Gelfoam scaffolds, 2.4–5.8×10⁷ autologous BM-MSCs (undifferentiated or differentiated) were transplanted to each experimental DO site. Among 8 evaluable DO sites included in the final analyses, the experimental DO sites demonstrated less interfragmentary mobility, more advanced gap obliteration, higher mineral content and faster mineral apposition than the control sites, and all transplanted scaffolds were completely degraded.

Conclusion

It is technically feasible and biologically sound to deliver autologous BM-MSCs to the distraction site immediately after osteotomy using a Gelfoam scaffold to enhance mandibular DO.

Bone response to biomimetic implants delivering BMP-2 and VEGF: an immunohistochemical study

This animal study evaluated bone healing around titanium implant surfaces biomimetically coated with bone morphogenic protein-2 (BMP-2) and/or vascular endothelial growth factor (VEGF) by examining bone matrix proteins and mineralisation. Five different implant surfaces were established: acid-etched surface (AE), biomimetic calcium phosphate surface (CAP), BMP-2 loaded CAP surface, VEGF loaded CAP surface and dual BMP-2 + VEGF loaded CAP surface. The implants were inserted into calvariae of adult domestic pigs. For the comparison of osteoconductive capacity of each surface, bone mineral density and expression of bone matrix proteins (collagen I, BMP-2/4, osteocalcin and osteopontin) inside defined chambers around the implant were assessed using light microscopy and microradiography and immunohistochemical analysis at 1, 2 and 4 weeks. In the both groups delivering BMP-2, the bone mineral density was significantly enhanced after 2 weeks and the highest value was measured for the group BMP + VEGF. In the group VEGF, collagen I and BMP-2/4 expressions were significantly up-regulated at the first and second weeks. The percentage of BMP-2/4 positive cells in the group BMP + VEGF was significantly enhanced compared with the groups AE and CAP at the second week. Although the highest osteocalcin and osteopontin expression values were observed for the group BMP + VEGF after 2 weeks, no statistically significant difference in osteocalcin and osteopontin expressions was found between all groups at any time. It was concluded that combined delivery of BMP-2 and VEGF favoured bone mineralisation and expression of important bone matrix proteins that might explain synergistic interaction between both growth factors.

Implants in bone: part II. Research on implant osseointegration: material testing, mechanical testing, imaging and histoanalytical methods

PURPOSE

In order to determine whether a newly developed implant material conforms to the requirements of biocompatibility, it must undergo rigorous testing. To correctly interpret the results of studies on implant material osseointegration, it is necessary to have a sound understanding of all the testing methods. The aim of this overview is to elucidate the methods that are used for the experimental evaluation of the osseointegration of implant materials.

DISCUSSION

In recent decades, there has been a constant proliferation of new materials and surface modifications in the field of dental implants. This continuous development of innovative biomaterials requires a precise and detailed evaluation in terms of biocompatibility and implant healing before clinical use. The current gold standard is in vivo animal testing on well validated animal models. However, long-term outcome studies on patients have to follow to finally validate and show patient benefit.

CONCLUSION

No experimental set-up can provide answers for all possible research questions. However, a certain transferability of the results to humans might be possible if the experimental set-up is carefully chosen for the aspects and questions being investigated. To enhance the implant survival rate in the rising number of patients with chronic diseases which compromise wound healing and osseointegration, dental implant research on compromised animal models will further gain importance in future.

Genetically modified pigs for biomedical research

During the last two decades, pigs have been used to develop some of the most important large animal models for biomedical research. Advances in pig genome research, genetic modification (GM) of primary pig cells and pig cloning by nuclear transfer, have facilitated the generation of GM pigs for xenotransplantation and various human diseases. This review summarizes the key technologies used for generating GM pigs, including pronuclear microinjection, sperm-mediated gene transfer, somatic cell nuclear transfer by traditional cloning, and somatic cell nuclear transfer by handmade cloning. Broadly used genetic engineering tools for porcine cells are also discussed. We also summarize the GM pig models that have been generated for xenotransplantation and human disease processes, including neurodegenerative diseases, cardiovascular diseases, eye diseases, bone diseases, cancers and epidermal skin diseases, diabetes mellitus, cystic fibrosis, and inherited metabolic diseases. Thus, this review provides an overview of the progress in GM pig research over the last two decades and perspectives for future development.

Diabetes mellitus negatively affects peri-implant bone formation in the diabetic domestic pig

AIM

Diabetes mellitus is classified as a relative contraindication for implant treatment, and higher failure rates have been seen in diabetic patients. The aim of the present study was to investigate the effect of diabetes on peri-implant bone formation in an animal model of human bone repair.

MATERIALS AND METHODS

Diabetes was induced by an intra-venous application of streptozotocin (90 mg/kg) in 15 domestic pigs. Implants were placed after significant histopathological changes in the hard and soft tissues were verified. The bone-implant contact (BIC), peri-implant bone mineral density (BMD), and expression of collagen type-I and osteocalcin proteins were qualitatively evaluated 4 and 12 weeks after implantation. Fifteen animals served as healthy controls.

RESULTS

Diabetes caused pathological changes in the soft and hard tissues. The BIC and BMD were significantly reduced in the diabetic group after 4 and 12 weeks. Collagen type-I was increased in the diabetic group at both time points, whereas osteocalcin was reduced in the diabetic group.

CONCLUSIONS

Poorly controlled diabetes negatively affects peri-implant bone formation and bone mineralization. These findings have to be taken into consideration for diabetic patients with an indication for implant therapy.

Osseointegration of SLActive implants in diabetic pigs

OBJECTIVES

Diabetes mellitus is currently classified as a relative contraindication for implant treatment because of microangiopathies with the consequence of impaired bone regeneration and higher rates of implant failure. The study aim was to investigate peri-implant bone formation in a diabetic animal model in comparison to healthy animals and to evaluate the differences between conventional (SLA(®) ) and modified (SLActive(®) ) titanium implant surfaces on osseointegration.

MATERIAL AND METHODS

Each six implants were placed in the calvaria of 11 diabetic and 4 healthy domestic pigs. At 30 and 90 days after implant placement, the bone-to-implant contact (BIC) and bone density (BD) were appraised. Additionally, the expression of the bone-matrix proteins collagen type I and osteocalcin was evaluated at both points in time by using immunohistochemical staining methods.

RESULTS

Overall, BIC was reduced in the diabetic group at 30 and 90 days. After 90 days, the SLActive(®) implants showed significantly higher BICs compared with the SLA(®) implants in diabetic animals. Peri-implant BD was higher in the SLActive(®) group at 30 and 90 days in healthy and diabetic animals. Collagen type I protein expression was higher using SLA(®) implants in diabetic pigs at 30 days. Values for osteocalcin expression were not consistent.

CONCLUSIONS

The results indicate the negative effect of untreated diabetes mellitus on early osseointegration of dental implants. The modified SLA(®) surface (SLActive(®) ) elicited an accelerated osseointegration of dental implants, suggesting that a better prognosis for implant treatment of diabetic patients is possible.

Contribution of large pig for renal ischemia-reperfusion and transplantation studies: the preclinical model

Animal experimentation is necessary to characterize human diseases and design adequate therapeutic interventions. In renal transplantation research, the limited number of in vitro models involves a crucial role for in vivo models and particularly for the porcine model. Pig and human kidneys are anatomically similar (characterized by multilobular structure in contrast to rodent and dog kidneys unilobular). The human proximity of porcine physiology and immune systems provides a basic knowledge of graft recovery and inflammatory physiopathology through in vivo studies. In addition, pig large body size allows surgical procedures similar to humans, repeated collections of peripheral blood or renal biopsies making pigs ideal for medical training and for the assessment of preclinical technologies. However, its size is also its main drawback implying expensive housing. Nevertheless, pig models are relevant alternatives to primate models, offering promising perspectives with developments of transgenic modulation and marginal donor models facilitating data extrapolation to human conditions.