G. Biagini

Biological activity of chitosan: ultrastructural study

Reparative processes are reconstructive phenomena in which cellular elements and extracellular matrix glycoproteins interact to build the injured tissue. Biomaterials can be used to improve or stimulate reconstruction. In the present experimental investigation, tissue repair induced by chitosan, an 86.8% deacetylated poly(GlcNAc), was monitored by morphological analysis. To evaluate its biological role, chitosan was positioned in contact with dura mater or was used as a dura mater substitute. This polysaccharide, having structural characteristics similar to glycosaminoglycans, seems to mimic their functional behaviour. The inductive and stimulatory activity of chitosan on connective tissue-rebuilding is clearly demonstrated, and it is suggested that chitosan could be considered a primer on which a normal tissue architecture is organized.

Stimulatory effect on bone formation exerted by a modified chitosan

A novel modified chitosan carrying covalently linked imidazole groups (average molecular weight 700,000, degree of substitution 0.28, degree of acetylation 0.08) was used to stimulate bone formation in an animal model. Lesions (7 mm diameter) were surgically made in the femoral condyle of sheep and treated with the modified chitosan. Within 40 d after surgery, the neoformed tissue occluded the surgical hole and assumed a trabecular structure in the peripheral area of the lesion, while looking like a mineralization nodule in the central part in association with a fibrous component. In the control, no sign of osteoinduction or reparative process was observed and bone marrow was rich in adipocytes.

Reconstruction of parodontal tissue with chitosan

Chitosan ascorbate, obtained by mixing chitosan with ascorbic acid and sodium ascorbate, was produced in a gel form suitable for the treatment of periodontitis according to current dental surgery. While chitosan ascorbate underwent degradation in vitro, especially in the presence of atmospheric oxygen and at pH 6.0, the protection from oxygen offered by the surgical cements and the physiological pH value permitted chitosan ascorbate to play an important biological role in vivo, where it kept a honeycomb structure, as indicated by SEM on biopsies taken on 10 patients. The proliferation and organization of the cells were thus favoured with a subsequent enhanced capability of reconstructing a histoarchitectural tissue. Chitosan was progressively reabsorbed by the host, with very satisfactory clinical recoveries of the 52 defects treated, for which tooth mobility and pocket depths were significantly reduced.

Osteoconduction exerted by methylpyrrolidinone chitosan used in dental surgery.

Surgical wounds from wisdom tooth avulsions were medicated with freeze-dried methylpyrrolidinone chitosan, a gel-forming resorbable biopolymer obtained from crab chitosan by chemical modification. Methylpyrrolidinone chitosan promoted osteoconduction and the space left after avulsion was filled with newly formed bone tissue, which conferred desirable mechanical and physiological characteristics to the healed would site. Morphological evidence obtained from biopsies confirmed the radiographic data. Methylpyrrolidinone chitosan was progressively depolymerized by lysozyme and was no longer detected 6 months after surgery. None of the 10 patients reported adverse effects over one year of observation.

Desmin and actin in the identification of Ito cells and in monitoring their evolution to myofibroblasts in experimental liver fibrosis

SummaryIt has been reported that myofibroblasts contain actin and that Ito cells are positive for desmin. The distribution of desmin and actin detected by immunofluorescence, of vitamin A autofluorescence and of Sudan III staining of lipid droplets has been evaluated in sequential stages of experimental liver fibrosis induced in rats by intraperitoneal injections of swine serum. In the normal rat liver Ito cells were positive for desmin and weakly positive for actin. Prior to the development of hepatic fibrosis a clearcut increase in number and desmin staining of lobular Ito cells was observed in treated rats, but the overall actin pattern was unchanged. In the fibrotic rat livers, highly cellular septa contained large numbers of strongly desmin-positive, actin-weakly positive Ito cells and strongly desmin-and actin-positive myofibroblasts. These observations indicate that both Ito cells and myofibroblasts are positive for desmin, but only myofibroblasts contain large amounts of actin. Visualization of actin and desmin using relatively simple techniques, allows the monitoring of Ito cells proliferation, the accumulation of these cells in fibrous septa and their evolution into myofibroblasts as characterized by their increased desmin and actin content; it also allows an indirect evaluation of the process of fibrogenesis.

WOUND MANAGEMENT WITH N-CARBOXYBUTYL CHITOSAN

In patients undergoing plastic surgery, donor sites were treated with soft pads of freeze-dried N-carboxybutyl chitosan to promote ordered tissue regeneration. Compared to control donor sites, better histoarchitectural order, better vascularization and the absence of inflammatory cells were observed at the dermal level, whilst fewer aspects of proliferation of the malpighian layer were reported at the epidermal level. Accordingly, N-carboxybutyl chitosan leads to formation of regularly organized cutaneous tissue and reduces anomalous healing.

Osteoconductive properties of methylpyrrolidinone chitosan in an animal model

Bone defects were surgically produced in the tibiae of rabbits and medicated with freeze-dried methylpyrrolidinone chitosan. Histological observations 60 d after surgery showed a considerable presence of neoformed bone tissue, as opposed to controls, originating from the pre-existing bone as well as from the periosteum. The cationic nature and the chelating ability of the methylpyrrolidinone chitosan apparently favoured mineralization. Endosteal-periosteal and bone marrow osteoblast-like precursors, stimulated by growth factors entrapped in the coagulum-polysaccharide mixture, gave rise to intramembranous bone formation. The ultrastructural examination evidenced that bone osteoid was followed by mineralization of the tissue.

Vascular endothelial growth factor expression and capillary architecture in high-grade PIN and prostate cancer in untreated and androgen-ablated patients.

Recent studies have demonstrated that angiogenesis is a potent prognostic indicator for patients with prostate cancer (PCa) and have pointed out that the evaluation of vascular endothelial growth factor (VEGF) is useful in assessing the angiogenic phenotype in PCa. The aim of the study was to investigate immunohistochemically the expression of VEGF and its correlation with the pattern of capillary architecture in prostate cancer and high‐grade prostatic intraepithelial neoplasia (PIN), in untreated and androgen‐ablated patients.

N,N-dicarboxymethyl chitosan as delivery agent for bone morphogenetic protein in the repair of articular cartilage.

Bone morphogenetic protein (BMP), associated with N,N-dicarboxymethyl chitosan, is used to induce or facilitate the repair of articular cartilage lesions. This association is intended for the synergistic potentiation of the respective biological effects. Data show that BMP-7 enhances the in vivo proliferation of cells with chondrocytes phenotype in the articular environment, leading to partial healing of the articular surface of the lesions. N,N-dicarboxymethyl chitosan is found to be useful as a molecular carrier or drug delivery agent.

Involvement of E‐cadherin, β‐catenin, Cdc42 and CXCR4 in the progression and prognosis of cutaneous melanoma

Background  A key event in cancer metastasis is the migration of tumour cells from their original location to a secondary site. The development of melanoma may be viewed as a consequence of the disruption of homeostatic mechanisms in the skin of the original site.