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Biomedical subjects

O Gauthier

Publications and source records attributed to O Gauthier.

At least 19 recordsLinked to original sources
PubMed2002

In vitro characterization and in vivo properties of a carbonated apatite bone cement.

This study evaluated the in vivo behavior of an injectable calcium phosphate bone cement implanted in bone defects at the distal end of rabbit femora. After 3 weeks, samples were harvested and processed for undecalcified sectioning. Scanning electron microscopy, transmission electron microscopy, and Fourier transform infrared microspectroscopy showed direct contact of bone and cement without soft tissue interposition, biocompatibility, and bioactivity with osteoconductive properties.

Animals↗
PubMed2001

Scanning electron microscopic description of cellular activity and mineral changes in feline odontoclastic resorptive lesions.

The cellular activity and changes in mineral composition of dental tissues involved in feline odontoclastic resorptive lesions were investigated. Teeth with at least 1 lesion (n = 10) were extracted from 10 different cats that were presented primarily for chronic gingivostomatitis and/or severe periodontal disease. Scanning electron microscopic methods were used to determine the presence of resorptive cells in 8 teeth while 2 teeth were evaluated for pathologic changes in dental mineral composition. Observations were complicated by the presence of organic wear on the dental surfaces, however resorptive cells could be clearly identified in feline odontoclastic resorptive lesions. Resorptive cells had morphologic features indicative of "osteoclast-like" cells or odontoclasts. Resorptive cell activity created a resorption area of darker dentin continuous with physiologic dentin. The darker dentin area seemed poorly mineralized and showed a significantly lower calcium/phosphorous ratio compared with adjacent physiologic denting in 1 tooth. A significantly higher level of magnesium combined with available carbonate ions may have increased the solubility in areas of darker dentin.

Animals↗
PubMed1999

In vivo retrovirus-mediated gene transfer to the liver of dogs results in transient expression and induction of a cytotoxic immune response.

Gene transfer in regenerating dog liver using high-titer recombinant retroviral vectors carrying the E. coli beta-galactosidase gene was studied. Supernatants containing amphotropic or gibbon ape pseudotyped recombinant retroviruses were infused into a peripheral vein in beagle dogs after partial hepatectomy. The kinetics of liver regeneration were determined in the animals and daily infusions were carried out for 4 or 5 days during the regeneration period. Up to 2.8% of hepatocytes were beta-galactosidase positive at the end of the procedure. However, the number of positive cells declined rapidly and few positive hepatocytes were detected after 3 weeks. PCR demonstrated the disappearance of the provirus. Histologically, inflammatory lesions were observed in the transduced livers. Finally, we demonstrated the presence of a cytotoxic T lymphocyte immune response directed against beta-galactosidase-expressing cells, which could explain the disappearance of the transgene. This work suggests that the efficiency of in vivo gene delivery using high-titer retroviral vectors directly infused into the circulation may be hampered by a cytotoxic immune response against the infected cells.

Animals↗
PubMed1999

Leg ulcers and hydroxyurea: forty-one cases.

BACKGROUND: Hydroxyurea is an antitumor agent used to treat chronic myeloproliferative disorders. Leg ulcerations have been reported in patients undergoing long-term hydroxyurea therapy for myeloproliferative diseases. To better define this dermatological adverse effect of hydroxyurea therapy and to try to understand the pathophysiological process of this disease, we collected medical information for such patients in a multicenter retrospective study. OBSERVATIONS: Forty-one patients (mean age, 67 years) developed leg ulcerations while undergoing hydroxyurea therapy (mean therapy duration, 5 years). The sex ratio was 1, and there was no underlying vascular disease. Hematologic abnormalities were identified. Complete recovery from the ulcerations occurred quickly after withdrawal of treatment in 33 (80%) of the cases. CONCLUSIONS: This longest-reported series of patients confirms the role of hydroxyurea therapy in the onset of leg ulcerations. Healing or improvement requires cessation of treatment. Cutaneous atrophy and impaired wound healing may explain the relationship between hydroxyurea and leg ulcers. In addition, the megaloblastic erythrocytes resulting from the presence of hydroxyurea may circulate poorly through the capillary network. A prospective study in hematologic centers would be valuable.

Adult↗
PubMed1999

Kinetic study of bone ingrowth and ceramic resorption associated with the implantation of different injectable calcium-phosphate bone substitutes.

This study investigated the in vivo performance of two composite injectable bone substitutes (IBS), each with different calcium-phosphate particles granulometries [40-80 (IBS 40-80) and 200-500 microm (IBS 200-500)]. These biomaterials were obtained by associating a biphasic calcium-phosphate (BCP) ceramic mineral phase with a 3% aqueous solution of a cellulosic polymer (hydroxy-propyl-methyl-cellulose). Both materials were injected for periods of 2, 3, 8, or 12 weeks into bone defects at the distal end of rabbit femurs. Quantitative results on new bone formation, BCP resorption, and staining for tartrate-resistant acid phosphatase (TRAP) activity were studied for statistical purposes. Measurements with scanning electron microscopy and image analysis showed that the final rates of newly formed bone were similar for both tested IBS after 12 weeks of implantation. Bone colonization occurred more extensively during early implantation times for IBS 40-80 than for IBS 200-500. For the latter, BCP degradation occurred regularly throughout the implantation period, whereas it was very intensive during the first 2 weeks for IBS 40-80. Positive TRAP-stained degradation cells were significantly more numerous for IBS 40-80 than for IBS 200-500 regardless of implantation time. With the granulometry of either mineral phase, both tested IBS supported extensive bone colonization, which was greater than that previously reported for an equivalent block of macroporous BCP. The resorption-bone substitution process seemed to occur earlier and faster for IBS 40-80 than for IBS 200-500. Both tested IBS expressed similar biological efficiency, with conserved in vivo bioactivity and bone-filling ability.

Animals↗
PubMed1999

Biphasic calcium phosphate/hydrosoluble polymer composites: a new concept for bone and dental substitution biomaterials.

Calcium phosphate materials have been increasingly employed in orthopedic and dental applications in recent years and are now being developed for use in noninvasive surgery or as carriers for drug delivery systems. We developed an injectable bone substitute (IBS) constituted of biphasic calcium phosphate and a hydrosoluble polymer as a carrier. In vivo biocompatibility and biofunctionality of IBS were tested in rabbits using implants in osseous and nonosseous areas. The results obtained demonstrated that the concept of IBS, a filler without initial mechanical properties but able to be rapidly resorbed and replaced by newly formed bone, can be applied to new surgical applications in orthopedic surgery, maxillofacial surgery, and dentistry for pulp capping and root filling.

Animals↗
PubMed1999

Short-term effects of mineral particle sizes on cellular degradation activity after implantation of injectable calcium phosphate biomaterials and the consequences for bone substitution.

This in vivo study investigated the influence of two calcium phosphate particle sizes (40-80 microm and 200-500 microm) on the cellular degradation activity associated with the bone substitution process of two injectable bone substitutes (IBS). The tested biomaterials were obtained by associating a biphasic calcium phosphate (BCP) ceramic mineral phase and a 3% aqueous solution of a cellulosic polymer (hydroxypropylmethylcellulose). Both were injected into osseous defects at the distal end of rabbit femurs for 2- and 3-week periods. Quantitative results for tartrate-resistant acid phosphatase (TRAP) cellular activity, new bone formation, and ceramic resorption were studied for statistical purposes. Positive TRAP-stained degradation cells were significantly more numerous for IBS 40-80 than IBS 200-500, regardless of implantation time. BCP degradation was quite marked during the first 2 weeks for IBS 40-80, and bone colonization occurred more extensively for IBS 40-80 than for IBS 200-500. The resorption-bone substitution process occurred earlier and faster for IBS 40-80 than IBS 200-500. Both tested IBS displayed similar biological efficiency, with conserved in vivo bioactivity and bone-filling ability. Differences in calcium phosphate particle sizes influenced cellular degradation activity and ceramic resorption but were compatible with efficient bone substitution.

Acid Phosphatase↗
PubMed1999

Injectable bone substitute using a hydrophilic polymer.

We studied a new injectable biomaterial for bone and dental surgery consisting of a hydrophilic polymer as matrix and bioactive calcium phosphate (CaP) ceramics as fillers. This material is composed of complex fluids whose flow is determined by the laws of rheology. We investigated the macromolecular effects on this composite in a tube. The stability of the polymer and the mixture is essential to the production of a ready-to-use injectable biomaterial. These flow properties are necessary to obtain CaP bioactivity in a dental canal or bone defect during percutaneous surgery. Macromolecules provide spaces between CaP ceramic granules and facilitate the role of the biological agents of bone substitution.

Animals↗
PubMed1999

A new injectable calcium phosphate biomaterial for immediate bone filling of extraction sockets: a preliminary study in dogs.

BACKGROUND: Many different bone substitutes, such as autografts, allografts or synthetic biomaterials have been proposed to restore alveolar bone loss and support efficient placement of dental implants. This experimental study evaluated the osteoconductive properties of an injectable bone substitute (IBS) composed of a polymeric carrier and a calcium phosphate mineral phase, used to fill mandibular and maxillary canine extraction sockets. METHODS: The polymer was a cellulose derivative (methyl-hydroxy-propyl-cellulose, MHPC), and the mineral phase consisted of granules of biphasic calcium phosphate (BCP) ceramics 200 to 500 microm in diameter. Mandibular and maxillary premolars extracted from 3 dogs (a total of 60 extraction sites) were immediately treated with the IBS or left unfilled as control sites. Animals were sacrificed 3 months after implantation and all extraction sockets were prepared for histological evaluation. RESULTS: Qualitative histological studies showed that the IBS was able to support the extensive apposition of well-mineralized newly formed lamellar bone over the entire socket surface and appeared to prevent alveolar ridge bone loss in treated extraction sites. Quantitative evaluation showed that the amount of newly formed bone was significantly higher in mandibular than maxillary extraction sockets for both treated and control sites. CONCLUSIONS: An injectable bone substitute composed of a polymeric carrier and calcium phosphate was effective in enhancing the bone fill of extraction sockets. This approach may prove promising for periodontal lesions. The material expressed osteoconductive capacities, and the biological properties of the mineral phase were conserved.

Animals↗
PubMed1998

Growth hormone-loaded macroporous calcium phosphate ceramic: in vitro biopharmaceutical characterization and preliminary in vivo study.

Calcium phosphate ceramics recently have been used for administering therapeutic agents in bone. The present work investigated the efficacy of macroporous biphasic calcium phosphate (MBCP) implants as a matrix for local delivery of human growth hormone (hGH). An initial study showed that the release of 5 microg of hGH loaded onto MBCP cylinders was rapid during the first 48 h and sustained for a total of 11 days. The biological integrity of hGH (88.2%) was checked using a specific bioassay (cellular proliferation of hGH-sensitive Nb2 cells) in comparison with a radioimmunoassay to calculate the proportion of bioactive hGH released. MBCP cylinders then were loaded with 1, 10, and 100 microg of hGH and implanted into rabbit femurs (n = 16) to determine hGH effects on bone ingrowth and ceramic resorption, as evaluated by scanning electron microscopy and image analysis. Results indicated that hGH increased bone ingrowth and ceramic resorption significantly in comparison with contralateral and control implants. Biochemical parameters monitored in rabbit plasma showed that hGH did not produce detectable systemic effects. Thus the use of MBCP appears to be effective for local delivery of hGH and for increasing bone ingrowth.

Absorption↗
PubMed1998

Transmission FT-IR microspectroscopy of mineral phases in calcified tissues.

Fourier-transform infrared microspectroscopy (FT-IRM) was used to study bone mineralization processes in an in vivo model and in enamel in osteogenesis imperfecta. Finally, the ability of FT-IRM to map new bone formed in implanted macroporous calcium phosphate biomaterial from sections was reported for the first time. FT-IRM allowed the correlation of the microstructure of bone formation in the in vivo model with modifications in carbonate and phosphate environments of the mineral phases during maturation. FR-IRM analysis on enamel sections revealed changes in the mineral environment of carbonate and phosphate ions and probably in the size of enamel crystals. These modifications contributed to the fragility of enamel in osteogenesis imperfecta. The infrared functional group imaging of a part of implanted biomaterial and the bone ingrowth provided the visualization of chemical modifications occurring in biomaterial implants at 20 microns spatial resolution. The use of FT-IRM, in conjunction with appropriate sampling methods and data analysis should provide further insight into the molecular structure of mineral phases of calcified tissues and help to elucidate mineralization processes, skeletal disorders and properties of the biomaterials used as bone substitute.

Animals↗
PubMed1998

Human growth hormone locally released in bone sites by calcium-phosphate biomaterial stimulates ceramic bone substitution without systemic effects: a rabbit study.

Calcium-phosphate bone replacement biomaterial has been used as a drug carrier for therapeutic agents. This study investigated the efficacy of local administration of human growth hormone (hGH) by macroporous biphasic calcium phosphate (MBCP) implants in improving the bone substitution qualities of ceramics. hGH release from MBCP implants loaded with 1 microg of hGH was rapid during the first 48 h and then sustained for a total of 9 days. Immunolocalization of hGH in vitro and in vivo by transmission electron microscopy showed its presence inside the material, indicating that it was able to penetrate within the porosity of the ceramic during the adsorption process. MBCP cylinders (6 x 6 mm) were loaded with 0.1, 1, and 10 microg of hGH and implanted into rabbit femurs (n = 40). The effects of locally released hGH on bone ingrowth and ceramic resorption were evaluated by scanning electron microscopy and image analysis. The results indicated that hGH increased bone ingrowth (+65%) and ceramic resorption (+140%) significantly in comparison with control implants and that the increase was dose dependent. Biochemical parameters monitored in rabbit plasma and urine, as well as the absence of any significant difference between contralateral implants and the control, indicated that hGH did not produce detectable systemic effects. Thus, the use of MBCP appears to be effective for local delivery of hGH, resulting in improved bone substitution.

Animals↗
PubMed1996

[Atrophic collodion-like skin in long-term treatments with hydroxyurea].

INTRODUCTION: Despite good general and hematological tolerance, hydroxyurea frequently causes polymorphous skin lesions when given as long-term therapy. Distal skin atrophy, pseudodermatomyositis, pseudolichen and ulcerations have been observed. CASE REPORT: We report three cases of diffuse atrophic collodion skin in patients given long-term hydroxyurea. Histology findings demonstrated atrophy and the same signs located at the dermo-epidermal junction as seen in acute toxidermia due to hydroxyurea. Examination of the ultrastructure showed abnormalities in the proliferative epidermal layer which was disrupted by edema and a multiple, irregular basal membrane. DISCUSSION: The chronology of the lesions and partial resolution after treatment withdrawal together with clinical and histological signs demonstrating hydroxyurea impregnation would implicate hydroxyurea as the cause of this case of diffuse atrophic collodion skin. Cells in the epidermal layer of the skin, the most external layer in the organism, have a high turnover rate and would be more vulnerable to the cytostatic action of hydroxyurea than other tissues. The effect of hydroxyurea on keratinocytes implicated in the production and maintenance of the basal membrane would be one of the causes.

Aged↗
PubMed1978

[Hypomelanosis of the skin and malignant melanoma (author's transl)].

8 patients suffering from malignant melanoma have been found to have various degrees of hypomelanoses of the skin. Depigmentation of the skin and/or hair associated with malignant melanoma may take several forms. Schematically six clinical types are described: - vitiligo-like hypomelanoses distant from cutaneous tumors; - vitiligo-like depigmentation associated with uveitis (incomplete Vogt-Koyanagi); - hypomelanoses in the primary tumor and/or its metastases; - "halo melanoma" in which the hypomelanoses encircles the primary tumor and/or its metastases; - halo nevi around preexisting benign nevocellular nevi; - "non-specific depigmentary phenomen" distant from the primary tumor or its metastases. Histological and ultrastructural studies of the depigmented skin show an absence of melanocytes. The association of hypomelanoses of the skin with malignant melanoma is probably not coincidental. Various hypothesis are discussed as well as the prognostic significance of such an association.

Adult↗