Enhanced bone regeneration using porcine small intestinal submucosa

Structural bone allograft combined with genetically engineered mesenchymal stem cells as a novel platform for bone tissue engineering

The presence of live periosteal progenitor cells on the surface of bone autografts confers better healing than devitalized allograft. We have previously demonstrated in a murine 4 mm segmental femoral bone-grafting model that live periosteum produces robust endochondral and intramembraneous bone formation that is essential for effective healing and neovascularization of structural bone grafts. To the end of engineering a live pseudo-periosteum that could induce a similar response onto devitalized bone allograft, we seeded a mesenchymal stem cell line stably transfected with human bone morphogenic protein-2/beta-galactosidase (C9) onto devitalized bone allografts or onto a membranous small intestinal submucosa scaffold that was wrapped around the allograft. Histology showed that C9-coated allografts displayed early cartilaginous tissue formation at day 7. By 6 and 9 weeks, a new cortical shell was found bridging the segmental defect that united the host bones. Biomechanical testing showed that C9-coated allografts displayed torsional strength and stiffness equivalent to intact femurs at 6 weeks and superior to live isografts at 9 weeks. Volumetric and histomorphometric micro-computed tomography analyses demonstrated a 2-fold increase in new bone formation around C9-coated allografts, which resulted in a substantial increase in polar moment of inertia (pMOI) due to the formation of new cortical shell around the allografts. Positive correlations between biomechanics and new bone volume and pMOI were found, suggesting that the biomechanical function of the grafted femur relates to both morphological parameters. C9-coated allograft also exhibited slower resorption of the graft cortex at 9 weeks than live isograft. Both new bone formation and the persistent allograft likely contributed to the improved biomechanics of C9-coated allograft. Taken together, we propose a novel strategy to combine structural bone allograft with genetically engineered mesenchymal stem cells as a novel platform for bone tissue engineering.

Small Intestinal Submucosa Improves Islet Survival and Function in Vitro Culture

INTRODUCTION

Most centers maintain isolated human islet preparations in tissue culture to improve the safety as well as the practicality of islet transplantation. However, maintaining viability and recovery of islets remains a challenge. Extracellular matrix (ECM) is one of the most important components of the islet microenvironment. Reconstruction of the cell-matrix relationship seems to be necessary to sustain the structure and function of differentiated islets. Small intestinal submucosa (SIS), a natural ECM, is well known to promote wound healing, tissue remodeling, and cell growth. The purpose of this study was to evaluate recovery and function of isolated rat pancreatic islets during in vitro culture with SIS.

METHODS

Pancreatic islets isolated from Wistar rats following intraductal collagenase distension, mechanical dissociation, and EuroFicoll purification were cultured in plates coated with multilayer SIS (SIS-treated group) or without (standard cultured group) for 7 or 14 days in an islet culture media of RPMI 1640 (Gibco). The islets from both experimental groups were stained and counted with dithizone. Islet recovery following culture was determined by the ratio of counts after culture to the yield of islets immediately following islet isolation. The viability of the islets was assessed by a glucose challenge test with low glucose (2.7 mmol/L), high glucose (16.7 mmol/L), and high glucose solution supplemented with 50 micromol/L 3-isobutyl-1-methylxanthine solution. The apoptosis of islet cells was measured by relative quantification of histone-complexed DNA fragments by using enzyme-linked immunosorbent assay.

RESULTS

After 7 or 14 days of in vitro tissue culture, the recovery in SIS-treated islets group was about double of that cultured in the plates without SIS coating. In the SIS-treated group, there was no significant difference between the short- and the long-term periods of culture (95.8%+/-1.0% vs 90.8%+/-1.5%, P>.05). Following incubation with high glucose (16.7 mmol/L) solution, the insulin secretion in the SIS-treated group showed a greater increase than the control group after 14 days of culture (20.7+/-1.1 mU/L vs 11.8+/-1.1 mU/L, P<.05). When islets were placed in the high glucose solution containing IBMX, the stimulated insulin secretion was more increased in the SIS-treated than in the control group despite the duration of the culture. The calculated stimulation index of SIS-treated group was about two to three times greater than the control group. In addition, the stimulation index of the SIS-treated group remained constant regardless of short-term versus long-term culture (9.5+/-0.2 vs 10.2+/-1.2, P>.05). Much less apoptosis of islet cells occurred in the SIS-treated than in the control group.

CONCLUSION

Coculture of isolated rat islets with native sheetlike small intestinal submucosa seemed to build an ECM for islets providing possible biotrophic and growth factors that promote the recovery and subsequent function of islets.

Small intestinal submucosa improves islet survival and function during in vitro culture

AIM

To evaluate the recovery and function of isolated rat pancreatic islets during in vitro culture with small intestinal submucosa (SIS).

METHODS

Pancreatic islets were isolated from Wistar rats by standard surgical procurement followed by intraductal collagenase distension, mechanical dissociation and Euroficoll purification. Purified islets were cultured in plates coated with multilayer SIS (SIS-treated group) or without multilayer SIS (standard cultured group) for 7 and 14 d in standard islet culture media of RPMI 1640. After isolation and culture, islets from both experimental groups were stained with dithizone and counted. Recovery of islets was determined by the ratio of counts after the culture to the yield of islets immediately following islet isolation. Viability of islets after the culture was assessed by the glucose challenge test with low (2.7 mmol/L) and high glucose (16.7 mmol/L) solution supplemented with 50 mmol/L 3-isobutyl-1-methylxanthine (IBMX) solution. Apoptosis of islet cells after the culture was measured by relative quantification of histone-complexed DNA fragments using ELISA.

RESULTS

After 7 or 14 d of in vitro tissue culture, the recovery of islets in SIS-treated group was significantly higher than that cultured in plates without SIS coating. The recovery of islets in SIS-treated group was about twice more than that of in the control group. In SIS-treated group, there was no significant difference in the recovery of islets between short- and long-term periods of culture (95.8+/-1.0% vs 90.8+/-1.5%, P>0.05). When incubated with high glucose (16.7 mmol/L) solution, insulin secretion in SIS-treated group showed a higher increase than that in control group after 14 d of culture (20.7+/-1.1 mU/L vs 11.8+/-1.1 mU/L, P<0.05). When islets were placed in high glucose solution containing IBMX, stimulated insulin secretion was higher in SIS-treated group than in control group. Calculated stimulation index of SIS-treated group was about 23 times of control group. In addition, the stimulation index of SIS-treated group remained constant regardless of short- and long-term periods of culture (9.5+/-0.2 vs 10.2+/-1.2, P>0.05). Much less apoptosis of islet cells occurred in SIS-treated group than in control group after the culture.

CONCLUSION

Co-culture of isolated rat islets with native sheet-like SIS might build an extracellular matrix for islets and provide possible biotrophic and growth factors that promote the recovery and subsequent function of islets.

Porcine small intestine submucosa (SIS) is not an acellular collagenous matrix and contains porcine DNA: possible implications in human implantation

Porcine small intestinal submucosa (SIS) has been recommended as a cell-free, biocompatible biomaterial for the repair of rotator cuff tendon tear. However, we have observed noninfectious edema and severe pain in patients who have undergone SIS implantation for tendon repair. The aim of this study was to conduct an independent assessment of the safety and efficacy of Restore SIS membrane. The Restore orthobiologic implant was examined by histology and the nested PCR technique using porcine immunoreceptor DAP12 gene to examine if SIS membrane contained porcine cells or DNA, respectively. The material was also implanted into mice and rabbits for the evaluation of biological reaction and inflammatory response. Restore SIS was found to contain multiple layers of porcine cells. Chloroacetate esterase staining showed that some of these cells were mast cells. Nested PCR of the DAP12 gene demonstrated that Restore SIS contained porcine DNA material. Subcutaneous implantation of Restore SIS membrane in mice, and in rabbits for rotator cuff tendon repair, showed that the membrane caused an inflammatory reaction characterized by massive lymphocyte infiltration. In conclusion, Restore SIS is not an acellular collagenous matrix, and contains porcine DNA. Our results contradict the current view that Restore SIS is a cell-free biomaterial, and that no inflammatory response is elicited by its implantation. We suggest that further studies should be conducted to evaluate the clinical safety and efficacy of SIS implant biomaterials.

Use of porcine renal capsule matrix as a full-thickness dermal wound-healing material in rats

OBJECTIVE

To compare the utility of porcine renal capsule matrix (RCM) with porcine small intestinal mucosa (SIS) in a rat full-thickness skin wound model.

METHOD

Groups of rats had surgically-created wounds filled with either SIS or RCM. On each rat a contralateral wound was left unfilled (RCM-U or SIS-U). Wound diameter was measured 3, 7, 12, 17, 26 and 30 days after creation. Wound sites sampled 3, 7, 14, 28, 42 and 56 days after wound creation were numerically graded for degree of histologic change and for collagen content, based on intensity of trichrome staining.

RESULTS

Wounds in all groups rapidly contracted to less than 50% of the original diameter within 12 days. There were no differences in wound diameter between RCM- and SIS-treated wounds at any time point, but these wounds had significantly greater (p < 0.001) diameters than their unfilled counterparts on days 7, 12 and 17. There were no differences in histologic scores or trichrome-staining scores between RCM- and SIS-treated wounds and their unfilled counterparts at any time point, except for a greater (p < 0.05) histologic score in SIS-treated wounds compared with unfilled controls on day 14. In both treatment groups an acute inflammatory response at the wound site was soon replaced by an influx of macrophages and fibroblasts.

CONCLUSION

The results show that RCM is equivalent to SIS for the treatment of full-thickness wounds and that these materials may enhance wound healing in terms of wound-tissue collagenisation and maturation. These materials therefore merit further study in other wound-care models.

Xenogeneic extracellular matrix as a scaffold for tissue reconstruction

Bioscaffolds derived from xenogeneic extracellular matrix (ECM) have been used in numerous tissue engineering applications. The safety and efficacy of such scaffolds when used for the repair and reconstruction of numerous body tissues including musculoskeletal, cardiovascular, urogenital and integumentary structures has been shown in both preclinical animal studies and in human clinical studies. More than 200,000 human patients have been implanted with xenogeneic ECM scaffolds. These ECM scaffolds are typically prepared from porcine organs such as small intestine or urinary bladder, which are subjected to decellularization and terminal sterilization without significant loss of the biologic effects of the ECM. The composition of these bioscaffolds includes the structural and functional proteins that are part of native mammalian extracellular matrix. The three-dimensional organization of these molecules distinguishes ECM scaffolds from synthetic scaffold materials and is associated with constructive tissue remodeling instead of scar tissue. The biologic response to these xenogeneic bioscaffolds, including the immune response, is discussed herein.

Development and transplantation of a mineralized matrix formed by osteoblasts in vitro for bone regeneration

The use of extracellular matrix materials as scaffolds for the repair and regeneration of tissues is receiving increased attention. The current study was undertaken to test whether extracellular matrix formed by osteoblasts in vitro could be used as a scaffold for osteoblast transplantation and induce new bone formation in critical size osseous defects in vivo. Human osteoblasts derived from alveolar bone were cultured in six-well plates until confluent and then in mineralization media for a further period of 3 weeks to form an osteoblast--mineralized matrix complex. Histologically, at this time point a tissue structure with a "connective tissue"-like morphology was formed. Type I collagen was the major extracellular component present and appeared to determine the matrix macrostructure. Other bone-related proteins such as alkaline phosphatase (ALP), bone morphogenetic protein (BMP)-2 and -4, bone sialoprotein (BSP), osteopontin (OPN), and osteocalcin (OCN) also accumulated in the matrix. The osteoblasts embedded in this matrix expressed mRNAs for these bone-related proteins very strongly. Nodules of calcification were detected in the matrix and there was a correlation between calcification and the distribution of BSP and OPN. When this matrix was transplanted into a critical size bone defect in skulls of immunodeficient mice (SCID), new bone formation occurred. Furthermore, the cells inside the matrix survived and proliferated in the recipient sites, and were traceable by the human-specific Alu gene sequence using in situ hybridization. It was found that bone-forming cells differentiated from both transplanted human osteoblasts and activated endogenous mesenchymal cells. This study indicates that a mineralized matrix, formed by human osteoblasts in vitro, can be used as a scaffold for osteoblast transplantation, which subsequently can induce new bone formation.

Small intestinal submucosa does not promote PAIII tumor growth in Lobund-Wistar rats

BACKGROUND

Site-specific remodeling and angiogenesis are two observations associated with the use of small intestinal submucosa (SIS) as a tissue repair graft. Its angiogenic capacity has raised questions concerning its effect on tumor growth and metastasis in clinical tumor resection cases. The effect of SIS on the ability of neoplastic (prostate adenocarcinoma) cells to establish, grow, and metastasize was examined in Lobund-Wistar (L-W) rats.

MATERIALS AND METHODS

In one study, SIS, expanded polytetrafluoroethylene (ePTFE), or human cadaveric dermis was placed in a subcutaneous pocket on the flank of L-W rats and immediately inoculated with PA-III cell suspension. Tumors were allowed to establish and metastasize for 5 weeks prior to sacrifice. Rate of tumor growth, tumor weight, and frequency of lung metastases were assessed. In a second study, SIS was placed in a resected tumor bed and tumors were allowed to recur. Rate of tumor growth, tumor weight, and frequency of lung metastases were assessed after 3 weeks.

RESULTS

ePTFE hastened the rate of formation of palpable tumors compared to controls and other materials; cadaveric dermis and SIS did not. No differences between materials were noted in final tumor weight nor in the frequency of metastasis to the lungs. Following surgical tumor resection, residual tumor cells led to recurrence of same-site tumors in all animals, but in the defects augmented with SIS, the tumors were significantly smaller than those which regrew in the resected, unaugmented group.

CONCLUSIONS

This study demonstrates that SIS does not enhance tumor establishment, growth, or metastasis in de novo tumors. Furthermore, SIS appears to reduce the rate of tumor growth, but not metastasis, when applied in direct contact with a residual tumor bed in a rat model of prostate-related tumors.

Host protection against deliberate bacterial contamination of an extracellular matrix bioscaffold versus Dacron mesh in a dog model of orthopedic soft tissue repair

The resistance of two biomaterials, one synthetic and one biologic in origin, to deliberate bacterial infection was compared in a dog model of orthopedic soft tissue reconstruction. Twenty-four adult female dogs were randomly divided into two equal groups and a 2.0-cm-round full-thickness defect was created on the lateral surface of the stifle joint, leaving only the synovium and skin intact. The defect was surgically repaired with either Dacron trade mark mesh or a porcine derived extracellular matrix (ECM) scaffold material. The repair site was inoculated with 1 x 10(8) Staphylococcus aureus at the time of surgery and the dogs were survived for 28 days. Results showed a chronic pyogranulomatous inflammatory response at the Dacron trade mark implant sites versus a constructive tissue-remodeling response without residual inflammation at the ECM implant site. Three dogs in the group receiving the Dacron trade mark mesh were treated with Keflex trade mark (500 mg bid x 7 days) for signs of septicemia. A quantitative bacterial count of the implant sites at the time of sacrifice showed 6.52 x 10(5) +/- 1.2 x 10(6) and 6.5 x 10(2) +/- 1.8 x 10(3) bacteria per gram of tissue for the Dacron trade mark and ECM scaffold sites, respectively (P <.03). The ECM implant material was more resistant than the synthetic implant material to persistent infection following deliberate bacterial contamination and the ECM scaffold supported constructive tissue remodeling.

Preformed grafts of porcine small intestine submucosa (SIS) for bridging segmental bone defects

Previous studies suggest that fresh, morselized porcine small intestine submucosa (SIS) may have promise in the treatment of large bone defects. This study evaluated the bone regenerative potential of preformed tubular SIS grafts, designed to provide a scaffold for regeneration of diaphyseal bone. Critical length segmental defects in the femurs of male rats were either left unfilled (n = 11) or filled with morselized cancellous bone (n = 12), or spanned with intramedullary tubes (n = 12) or periosteal sleeves (n = 12) fabricated from SIS. All of the animals were euthanized 12 weeks postoperatively. Healing was assessed with biweekly radiographs, routine histology, and mechanical testing. Copious new bone formed in the defects of all of the animals treated with cancellous bone; 10 of the 12 animals in that group had healed their defects. In contrast, no new bone was formed in the defects left unfilled or treated with SIS; only fibrous tissue was found. In both of the SIS-treated groups, the SIS persisted at twelve weeks. The cellular response to the SIS involved a mild mononuclear infiltrate in the loose or delaminated superficial layers of the tubes and sleeves, with few cells in the deeper layers. The results of this study cast doubt on the ability of SIS to support or stimulate growth of bone across a critical length segmental bone defect. Additional work will be required to determine whether our results reflect the protocols used to prepare and fabricate the SIS grafts used in the study or the inherent inability of SIS to support new bone growth.

Using porcine small intestinal submucosa in intestinal regeneration

Small intestinal submucosa (SIS) is an unusual tissue that promotes constructive tissue remodeling when applied as a xenogeneic material. The aim of our experimental study was to assess its effectiveness in intestinal regeneration. Twenty white New Zealand rabbits were anesthetized and underwent celiotomy. A 6-cm antimesenteric incision was created at the jejunal segment. An elliptical SIS graft measuring 6 cm long and 2 cm wide was sutured to the jejunal defect as a patch graft. Thirteen living rabbits were divided into groups of three and the grafts were harvested at postoperative weeks 2, 4, and 6. The obtained specimens were evaluated for gross and histologic appearance. In morphometric examination, in the 2, 4, and 6 weeks groups, the diameters of grafted intestines were larger than preoperatively by 50%, 25%, and 25% respectively; also the grafts had contracted to 0%, 25%, and 50% of their original sizes respectively. At the end of 2 weeks, the grafts were intact without evidence of epithelial regeneration. By 4 weeks, intestinal tissue regeneration was started, and epithelial coverage of the grafts was detected. The grafts were covered with a complete intestinal mucosa at 6 weeks. Remarkable regeneration marked fibroplasia, angiogenesis, and mild mononuclear cell infiltration had also occurred throughout the grafts at 6 weeks. Porcine SIS appeared an effective biodegradable scaffold, facilitating regeneration of intestinal tissue. These results suggest that SIS may be useful to increase the mucosal surface of intestine and may provide a new substance for short gut syndrome in the future.

Evaluation of small-intestinal submucosa implants for repair of meniscal defects in dogs

OBJECTIVE

To assess the effects of porcine small intestinal submucosa (SIS) implants on the healing of meniscal lesions in dogs.

ANIMALS

16 adult Greyhounds of both sexes.

PROCEDURE

Unilateral osteotomy was performed at time 0 to disrupt the medial collateral ligament attachment, and two (1 cranial and 1 caudal) 4-mm circular defects were created in the avascular portion of the medial meniscus. One defect was filled with an SIS graft, and the other defect remained empty (control). Three months later, the identical procedure was performed on the contralateral limb. Three months after the second surgery, dogs were euthanatized, and meniscal tissue specimens from both stifle joints were collected for gross, histologic, biomechanical, and biochemical evaluations.

RESULTS

Regenerative tissue was evident in 4 (2 SIS-implanted and 2 control) of 16 defects examined histologically. In 3 defects, this thin bridge of tissue was composed of immature haphazardly arranged fibrous connective tissue with a relatively uniform distribution of fibroblasts. Aggregate modulus, Poisson ratio, permeability, and shear modulus were not significantly different between control and SIS-implanted defects either 3 or 6 months after surgery. Hydroxyproline content also did not differ between SIS-implanted and control defects at 3 or 6 months.

CONCLUSIONS AND CLINICAL RELEVANCE

Implantation of porcine SIS into experimentally induced meniscal lesions in dogs did not promote tissue regeneration.

Small intestinal submucosa covered expandable Z stents for treatment of tracheal injury: an experimental pilot study in swine

PURPOSE

To evaluate efficacy of small intestinal submucosa (SIS) as a stent covering in healing experimentally created tracheal defects and to explore the trachea's reaction to placement of SIS-covered stents.

MATERIAL AND METHODS

A tracheal defect with a diameter of approximately 10 mm was created in six swine with use of a blade or electrocauterization. A double-body, self-expandable SIS-covered Gianturco Rösch Z stent was placed into the trachea to cover the defect. The animals were observed, and were killed when they developed respiratory problems. Autopsy and histologic studies were performed.

RESULTS

The SIS-covered stents were accurately placed without immediate complications related to placement. All animals developed respiratory problems on follow-up. One animal died 9 days after procedure because of pneumonia, the others five were killed at 12, 17, 18, 28, and 56 days because of stridor, wheezing, and cough. At autopsy and histology, the tracheal defects were found to be completely healed, with epithelial lining and regeneration of submucosal glands. Animals whose defects were created with a blade demonstrated cartilage remodeling between 9 and 18 days, and apparent deposition of new cartilage at 28 days after SIS placement. The defects made by electrocauterization showed only fibrous tissue with no cartilage regeneration. The tracheal lumen was narrowed by overgrowth of granulation tissue, particularly at the end wires of the stents. In three animals, polypoid masses caused 60%, 70%, and 80% tracheal obstruction, respectively.

CONCLUSION

Placement of SIS-covered stents contributed to rapid and effective healing of large tracheal defects. Rigidity and oversizing of Gianturco Rösch Z stents led to secondary changes of the tracheal wall, causing significant airway obstructions. Smaller size and flexible stents should be selected for future work.