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Biomedical subjects

Stephen Chen

Publications and source records attributed to Stephen Chen.

9 recordsLinked to original sources

Surgical treatment of infrabony defects with autologous platelet concentrate or bioabsorbable barrier membrane: a prospective case series.

BACKGROUND: Autologous platelet concentrate (APC) contains concentrated platelet-derived growth factors that promote wound healing and tissue regeneration. The purpose of this prospective case series was to compare the treatment effects of an intralesional graft of APC to guided periodontal regeneration (GPR) using a bioabsorbable barrier membrane (MEM) over a 52-week period. METHODS: Five patients were recruited for the study from two private periodontal practices. There were four females and one male having a mean age of 33 +/- 10.23 years. The five selected contralateral teeth had similar, but not identical, combinations of 1-, 2-, and 3-wall infrabony defects not involving furcations. Probing depths (PDs) of the defects were > or = 6 mm and had radiographic angular infrabony defects > or = 4 mm in depth. The patients had no local or systemic contraindications to minor oral surgical procedures and had not taken systemic antibiotics for > or = 6 months before the commencement of the study. All patients had completed cause-related periodontal therapy up to 6 months previously and had achieved a satisfactory level of oral hygiene. The selected teeth did not have purulent discharge from the pockets and responded normally to pulp sensibility testing. Patients were excluded if they smoked, were pregnant or lactating, or were allergic to any of the materials to be used in the treatment. At baseline and 8, 26, and 52 weeks after surgery, PDs, recession (REC), presence of plaque, and bleeding on probing were recorded, and standardized periapical radiographs were taken. At the time of surgery, the vertical distance to the deepest point of the infrabony defect was measured from the cemento-enamel junction (CEJ) to the buccal and lingual bone crests. The vertical distance to the base of the defect from the CEJ and defect angles were obtained from radiographs. The paired contralateral infrabony defects were treated with a graft APC or MEM after debridement and EDTA root surface conditioning. Surgical flaps were prepared and closed according to the papilla preservation method. Post-surgical care was provided at 1, 2, 8, 26, and 52 weeks after surgery. A mouthwash of 0.2% chlorhexidine gluconate was used twice daily for the first 3 weeks after surgery. Mean PD, REC, clinical attachment level (CAL), radiographic bone loss, and defect angle were computed and compared for each data collection point. RESULTS: From baseline to 52 weeks, a mean PD reduction of 3 +/- 1.41 mm (APC) and 3.6 +/- 1.67 mm (MEM), mean REC increase of 0.8 +/- 1.01 mm (APC) and 0.6 +/- 1.14 mm (MEM), mean CAL gain of 2.2 +/- 1.79 mm (APC) and 3 +/- 1 mm (MEM), mean radiographic bone fill of 3.24 +/- 2.85 mm (APC) and 2.7 +/- 1.9 mm (MEM), and mean defect-angle increase of 15.25 degrees +/- 18.21 degrees (APC) and 22.4 degrees +/- 27.3 degrees (MEM) were calculated. CAL gain was not related clearly to defect angle at baseline, although radiographic bone fill was slightly greater for defect angles <39.4 degrees +/- 7.88 degrees. CONCLUSIONS: This case series of five similar, but not identical, bilateral paired infrabony defects suggests that an APC graft achieves a similar CAL gain and PD reduction to GPR using an MEM over a 52-week period. A larger, controlled clinical trial is needed to evaluate further the efficacy of autologous platelet-rich plasma for the treatment of infrabony defects.

Absorbable Implants↗

Establishing efficient siRNA knockdown in mouse embryonic stem cells.

FAM-labeled oligo dT (FAMdT) was utilized as a means to gauge efficient transfection of small nucleic acids into mouse embryonic stem cell (mESC) colonies. Using colonies grown overnight, transfection was restricted largely to the periphery of the colonies with only a 40% decrease in Oct-3/4 RNA transcript levels following cognate Oct-3/4, small interfering RNA (siRNA) delivery. However, transfection of mESC 4 h after seeding gave greater than 90% cells being successfully transfected based on quantitative real-time PCR detection of approximately 90% Oct-3/4 RNA transcript knockdown. This method provides an economical and efficient means by which to determine effective transfection conditions, and establish efficient siRNA knockdown of reportedly difficult to transfect cell lines such as mESC.

Animals↗

In vivo molecular evolution reveals biophysical origins of organismal fitness.

In nature, evolution occurs through the continuous adaptation of a population to its environment. At the molecular level, adaptive changes in protein sequence and expression impact organismal fitness and, consequently, dictate population dynamics. Here, we have used a "weak link" method to favor variations in one gene, allowing adaptation to thermostability to be studied in molecular detail as bacteria were grown continuously for approximately 1500 generations. Surprisingly, only six mutant alleles, representing less than 1% of the possible missense mutations, were observed, suggesting a highly constrained molecular landscape during protein evolution. The changes in organismal fitness were linked directly to incremental increases in enzyme stability and activity maxima and corresponded to the narrow temperature ranges where each mutant enjoyed success within the overall population. Thus, continuous evolution of a single gene permits a quantitative approach that extends from the phenotypes of the microbial populations to their underlying biophysical basis.

Adenylate Kinase↗

TGF-beta2 allows pluripotent human embryonic stem cell proliferation on E6/E7 immortalized mouse embryonic fibroblasts.

In this study we report observations that mouse embryonic fibroblasts (MEF) capable of supporting expansion of pluripotent, human embryonic stem cells (hESC) fail to support after immortalization using E6/E7 oncogenes in serum conditions; however this can be reversed following addition of exogenous TGF-beta2. Microarray analysis of immortalized and non-immortalized MEF revealed differential gene expression of several TGF-beta related genes. By supplementing TGF-beta2 into E6/E7 immortalized MEF cultures, this enabled proliferation of undifferentiated, pluripotent hESC as demonstrated by marker expression (Oct-4, SSEA-4, alkaline phosphatase) and teratoma formation representing three germ layers following hESC injection into immuno-deficient mice. Subsequent investigation using quantitative real-time PCR highlighted differential gene expression of several extracellular matrix related transcripts in primary and immortal (+/-TGF-beta2) feeder cells including the induction of osteopontin following addition of TGF-beta2. Our results demonstrate that TGF-beta2 and its related genes in MEF play a role in the support of pluripotent hESC expansion.

Animals↗

A rare presentation of tuberculosis.

Primary involvement of the musculoskeletal system with tuberculosis is rare. We present a case of a young, immunocompetent woman with primary sternal tuberculosis. The disease led to destruction of the manubrium and a portion of the gladiolus and required extensive debridement and partial sternectomy, followed by musculocutaneous flap closure. Long-term postoperative management included four-drug antitubercular therapy.

Adult↗

A cyclosporine-sensitive psoriasis-like disease produced in Tie2 transgenic mice.

Psoriasis is a common, persistent skin disorder characterized by recurrent erythematous lesions thought to arise as a result of inflammatory cell infiltration and activation of keratinocyte proliferation. Unscheduled angiogenic growth has also been proposed to mediate the pathogenesis of psoriasis although the cellular and molecular basis for this response remains unclear. Recently, a role for the angiopoietin signaling system in psoriasis has been suggested by studies that demonstrate an up-regulation of the tyrosine kinase receptor Tie2 (also known as Tek) as well as angiopoietin-1 and angiopoietin-2 in human psoriatic lesions. To examine temporal expression of Tie2, we have developed a binary transgenic approach whereby expression of Tie2 can be conditionally regulated by the presence of tetracycline analogs in double-transgenic mice. A psoriasis-like phenotype developed in double-transgenic animals within 5 days of birth and persisted throughout adulthood. The skin of affected mice exhibited many cardinal features of human psoriasis including epidermal hyperplasia, inflammatory cell accumulation, and altered dermal angiogenesis. These skin abnormalities resolved completely with tetracycline-mediated suppression of transgene expression, thereby illustrating a complete dependence on Tie2 signaling for disease maintenance and progression. Furthermore, the skin lesions in double-transgenic mice markedly improved after administration of the immunosuppressive anti-psoriatic agent cyclosporine, thus demonstrating the clinical significance of this new model.

Angiopoietins↗

Perturbation of B-cell development in mice overexpressing the Bcl-2 homolog A1.

Decisions about cell survival or death are central components of adaptive immunity and occur at several levels in immune system development and function. The Bcl-2 family of homologous proteins plays an important role in these decisions in lymphoid cells. Bcl-2, Bcl-xL, and A1 are differentially expressed during B- and T-cell development, and they have shared and distinct roles in regulating cell death. We sought to gain insight into the role of A1 in immune system development and function. A murine A1-a transgene was expressed under the control of the Emu enhancer, and mice with A1 overexpression in B- and T-cell lineages were derived. Thymocytes and early B cells in Emu-A1 mice showed extended survival. B-lineage development was altered, with expansion of the pro-B cell subset at the expense of pre-B cells, suggesting an impairment of the pro- to pre-B-cell transition. This early B-cell phenotype resembled Emu-Bcl-xL mice but did not preferentially rescue cells with completed V(D)J rearrangements of the immunoglobulin heavy chain. In contrast to Emu-Bcl-2 transgenes, A1 expression in pro-B cells did not rescue pre-B-cell development in SCID mice. These studies indicate that A1 protects lymphocytes from apoptosis in vitro but that it has lineage- and stage-specific effects on lymphoid development. Comparison with the effects of Bcl-2 and Bcl-xL expressed under similar control elements supports the model that antiapoptotic Bcl-2 homologs interact differentially with intracellular pathways affecting development and apoptosis in lymphoid cells.

Animals↗