Improved connective integration of a degradable 3D-nano-apatite/agarose scaffold subcutaneously implanted in a rat model.

In this work, we evaluate the tissue response and tolerance to a designed 3D porous scaffold composed of nanocrystalline carbonate-hydroxyapatite and agarose as a preliminary step in bone repair and regeneration. These scaffolds were subcutaneously implanted into rats, which were sacrificed at different times. CD4+, CD8+ and ED1+ cells were evaluated as measurements of inflammatory reaction and tolerance. We observed some inflammatory response early after subcutaneous implantation. The 3D interconnected porosity increased scaffold integration via the formation of granulation tissue and the generation of a fibrous capsule around the scaffold. The capsule is initially formed by collagen which progressively invades the scaffold, creating a network that supports the settlement of connective tissue and generating a compact structure. The timing of the appearance of CD4+ and CD8+ cell populations is in agreement with the resolved inflammatory response. The appearance of macrophage activity evidences a slow and gradual degradation activity. Degradation started with the agarose component of the scaffold, but the nano-apatite was kept intact for up to 30 days. Therefore, this apatite/agarose scaffold showed a high capacity for integration by a connective network that stabilizes the scaffold and results in slow nano-apatite degradation. The fundamental properties of the scaffold would provide mechanical support and facilitate bone mobilization, which is of great importance in the masticatory system or large bones.

Streptozotocin is responsible for the induction and progression of renal tumorigenesis in diabetic Wistar-Furth rats treated with insulin or transplanted with agarose encapsulated porcine islets.

Streptozotocin (STZ), a nitrosourea with DNA alkylating properties, has been widely used to induce hyperglycemia by specifically destroying the insulin-producing ß-cells of the islets of Langerhans in experimental models of Type I diabetes. STZ's known carcinogenic properties, however, raise concerns about its suitability for long-term studies. We conducted a formal study of STZ's carcinogenic effects in long-term surviving diabetic Wistar-Furth rats. To determine if insulin therapy or islet transplantation exacerbated tumorigenesis, rats were randomly assigned to one of four experimental groups: normal animals with no treatment (Group 1, n=12); normal animals that underwent peritoneal implantation of porcine islets encapsulated in a double layer of agarose to form islet macrobeads (normal + islets; group 2, n=12); STZ treatment followed by daily exogenous insulin (STZ + insulin; group 3, n=18) and STZ treatment followed by the intraperitoneal implantation of porcine islet macrobeads (STZ + islets; group 4, n=14). At 215 days post-STZ induction, no renal proliferative lesions were observed in animals that did not receive STZ (group 1 and group 2) whereas adenoma incidences of 57% for group 3 and 34% for group 4 were observed. By terminal necropsy at day 351, the incidence and severity of renal proliferative lesions increased with tubular carcinoma observed in 67% of group 3 and 60% of group 4 animals. We conclude that the STZ-induced diabetic rat model is not suitable for long-term studies because of progressive renal tumorigenesis. Our experiments also demonstrate the safety and effectiveness of porcine islet macrobeads for the treatment of diabetes.

Transient stasis of pancreatic fluid flow together with mild injury of the pancreatic duct cause chronic pancreatitis.

BACKGROUND: Little is known about the etiopathogenesis of chronic pancreatitis, due mainly to the lack of simple animal models suitable to study inflammatory and fibrogenetic processes in the pancreas. AIMS: The purpose of this study was to examine whether transient congestion of pancreatic fluid flow alone or slight ductal injury alone is sufficient, or where both are required, to induce chronic pancreatic injury. METHODS: Three different models of pancreatitis were tested in rats induced by retrograde intraductal infusion of 40 µl/100 g body weight of 0.01% agarose (group A), 40 µl/100 g body weight of 0.1% sodium taurocholate (group T), or a mixture of the two solutions (group M). Histological alterations of the pancreas were examined by hematoxylin-eosin staining, changes in type IV collagen structure were studied by immunostaining, and the gelatinolytic activity of latent and active matrix metalloproteinase-2 (MMP-2) was analyzed by zymography. RESULTS: In group A and T rats, histological alterations of the pancreas and the gelatinolytic activity of MMP-2 returned to baseline levels by day 14, and immunoreactivity for type IV collagen appeared as continuous lines along the basement membrane. In group M rats, however, acinar damage, fibrosis and fatty degeneration were observed even on day 56, and type IV collagen was detected as discontinuous lines until day 56. MMP-2 was significantly elevated from day 5 to day 42. CONCLUSIONS: Co-existence of transient stasis of pancreatic fluid flow, together with mild damage to the pancreatic duct and acinar cells, exert synergistic effects on the development of persistent pancreatic injury with continuous disorganization of type IV collagen in the basement membrane of the ducts.

Inflammatory reaction induced by agarose implants reduced by adding adrenal cells to the polymer.

Microencapsulation of adrenal cells is proposed for reducing the non-specific inflammatory reaction observed around polymer implants. This hypothesis was tested by comparing both host cellular reaction and the surrounding graft cell populations that appeared when either agarose embedded cells or empty agarose beads were implanted. The authors' results showed that the fibrotic material that surrounded the implanted empty agarose microbeads was not as severe when adrenal cells were present. Similarly, the T lymphocyte population surrounding the graft was considerably reduced, along with the percentage of CD4 and CD8 positive cell subpopulations. The activation macrophage marker IaD disappeared. The authors' results support the hypothesis that embedded adrenal cells may be a suitable solution for reducing early inflammatory events due to microcapsule implantation.