Biomedical subjects

D A Lee

Publications and source records attributed to D A Lee.

At least 37 records · Page 2Linked to original sources

PubMed2001

Dynamic compression inhibits the synthesis of nitric oxide and PGE(2) by IL-1beta-stimulated chondrocytes cultured in agarose constructs.

Both mechanical loading and interleukin-1beta (IL-1beta) are known to regulate metabolic processes in articular cartilage through pathways mediated by nitric oxide ((*)NO) and PGE(2). This study uses a well-characterized model system involving isolated chondrocytes cultured in agarose constructs to test the hypothesis that dynamic compression alters the synthesis of (*)NO and PGE(2) by IL-1beta-stimulated articular chondrocytes. The data presented demonstrate for the first time that dynamic compression counteracts the effects of IL-1beta on articular chondrocytes by suppressing both (*)NO and PGE(2) synthesis. Inhibitor experiments indicated that the dynamic compression-induced inhibition of PGE(2) synthesis and stimulation of proteoglycan synthesis were (*)NO mediated, while compression-induced stimulation of cell proliferation was (*)NO independent. The inhibition of (*)NO and PGE(2) by dynamic compression is a finding of major significance that could contribute to the development of novel strategies for the treatment of cartilage-degenerative disorders.

Animals↗

PubMed2001

Effects of tissue transglutaminase on retinoic acid-induced cellular differentiation and protection against apoptosis.

Retinoic acid (RA) and its various synthetic analogs affect mammalian cell growth, differentiation, and apoptosis. Whereas treatment of the human leukemia cell line HL60 with RA results in cellular differentiation, addition of the synthetic retinoid, N-(4-hydroxyphenyl) retinamide (HPR), induces HL60 cells to undergo apoptosis. Moreover, pretreatment of HL60 cells as well as other cell lines (i.e. NIH3T3 cells) with RA blocks HPR-induced cell death. In attempting to discover the underlying biochemical activities that might account for these cellular effects, we found that monodansylcadaverine (MDC), which binds to the enzyme (transamidase) active site of tissue transglutaminase (TGase), eliminated RA protection against cell death and in fact caused RA to become an apoptotic factor, suggesting that the ability of RA to protect against apoptosis is linked to the expression of active TGase. Furthermore, it was determined that expression of exogenous TGase in cells exhibited enhanced GTP binding and transamidation activities and mimicked the survival advantage imparted by RA. We tested whether the ability of this dual function enzyme to limit HPR-mediated apoptosis was a result of the ability of TGase to bind GTP and/or catalyze transamidation and found that GTP binding was sufficient for the protective effect. Moreover, excessive transamidation activity did not appear to be detrimental to cell viability. These findings, taken together with observations that the TGase is frequently up-regulated by environmental stresses, suggest that TGase may function to ensure cell survival under conditions of differentiation and cell stress.

3T3 Cells↗

PubMed2001

Chondrocyte deformation within mechanically and enzymatically extracted chondrons compressed in agarose.

Within articular cartilage, the chondron microenvironment will influence chondrocyte behaviour and response to loading. Chondrons were extracted from intact cartilage using either mechanical homogenisation (MC) or enzymatic digestion (EC) and cell and matrix morphology in unstrained and compressed agarose constructs was examined. Isolated chondrocytes (IC) were used for comparison. Immunolocalisation of type VI collagen and keratan sulphate revealed differences in the structure of the pericellular microenvironment such that MC most closely resembled chondrons in situ. The unstrained cell diameters of IC and EC were larger than MC at day 1 and increased significantly over a 7 day culture period. In contrast, cell diameters for MC remained constant. Compression of constructs at day 1 resulted in cell deformation for IC and EC but not MC. The two chondron extraction methods yielded chondrons of differing matrix morphology and associated differences in cell size and cellular response to load. The results indicate that the pericellular microenvironment of MC initially possessed a greater mechanical integrity than that of EC. Although these differences may be reduced with time in culture, characterisation of mechanically isolated chondrons suggests that the stiffness of the chondrons in situ may be greater than previous estimates.

Animals↗

PubMed2001

Temporal changes in cytoskeletal organisation within isolated chondrocytes quantified using a novel image analysis technique.

This paper examines temporal changes in the organisation of the cytoskeleton within isolated articular chondrocytes cultured for up to 7 days in agarose constructs. Fluorescent labelling and confocal microscopy were employed to visualise microtubules (MT), vimentin intermediate filaments (VIF) and actin microfilaments (AMF). To quantify the degree of cytoskeletal organisation within populations of cells, a novel image analysis technique has been developed and fully characterised. Organisation was quantified in terms of an Edge Index, which reflects the density of 'edges' present within the confocal images as defined by a Sobel digital filter. This parameter was shown to be independent of image intensity and, for all three cytoskeletal components, was validated statistically against a visual assessment of organisation. Both MT and VIF exhibited fibrous networks extending throughout the cytoplasm, while AMF appeared as punctate units associated with the cell membrane. The use of the Edge Index parameter revealed statistical significant temporal variation, in particular associated with VIF and AMF. These findings indicate the possibility of cytoskeletal mediated temporal variation in many aspects of cell behaviour following isolation from the intact tissue. Furthermore, the image analysis techniques are likely to be useful for future studies aiming to quantify changes in cytoskeletal organisation.

Animals↗

PubMed2001

Cyclophotocoagulation: a report by the American Academy of Ophthalmology.

OBJECTIVE: This document describes cyclophotocoagulation procedures for glaucoma and examines the evidence to answer key questions about patient selection, and efficacy of transscleral and endoscopic techniques. METHODS: A literature search conducted for the years 1968 to 2000 retrieved 130 citations. The author reviewed 34 of these articles and selected 19 for the panel methodologist to review and rate according to the strength of evidence. A Level I rating is assigned to properly conducted, well-designed, randomized clinical trials; a Level II rating is assigned to well-designed cohort and case-control studies; and a Level III rating is assigned to case series and poorly designed prospective and retrospective studies, including case-control studies. RESULTS: The predominant problem with all studies on cyclophotocoagulation is the lack of a uniform definition of success, which makes comparisons difficult. One randomized controlled trial (Level I evidence) compared the efficacy of transscleral cyclophotocoagulation with noncontact Nd:YAG and semiconductor diode laser. It found no significant difference between the two, although a significant problem was the variability allowed with laser parameters. Most of the literature consists of noncomparative case series that provide evidence that is limited and often not convincing. CONCLUSION: Cyclophotocoagulation is indicated for patients with refractory glaucoma who have failed trabeculectomy or tube shunt procedures, patients with minimal useful vision and elevated intraocular pressure, and patients who have no visual potential and need pain relief (based on Level III evidence). It may be useful for patients whose general medical condition precludes invasive surgery or who refuse more aggressive surgery (i.e., filter or tube). It is also useful in emergent situations, such as the acute onset of neovascular glaucoma. There is insufficient evidence to definitively compare the relative efficacy of the cyclophotocoagulation procedures for glaucoma. It is the panel's opinion, however, that semiconductor diode systems appear to possess the best combination of effectiveness (based on Level III evidence), portability, expense, and ease of use at this time.

Academies and Institutes↗

PubMed2001

Effectiveness and safety of brimonidine as adjunctive therapy for patients with elevated intraocular pressure in a large, open-label community trial.

PURPOSE: To determine the effectiveness and safety of brimonidine when used in combination with one or more glaucoma medications in patients with glaucoma or ocular hypertension. METHODS: Post hoc analysis of a multicenter, 2-month, open-label, prospective, clinical trial in which 2,335 patients received brimonidine as monotherapy, replacement therapy, or combination therapy. Patients who received brimonidine as combination therapy (n = 554) were examined in the current analysis. Efficacy was determined by the reduction in intraocular pressure (IOP) from baseline before the addition of brimonidine. Safety and tolerability parameters included adverse events and quality-of-life measures (e.g., ocular comfort, energy level, breathing ability, night vision). RESULTS: Addition of brimonidine to preexisting regimens resulted in an overall mean additional reduction in IOP of 17.9% (4.26 mm Hg) at month 2 (P < 0.001). Significant additional IOP lowering was provided by brimonidine in combination with each preexisting regimen evaluated (P < or = 0.061). When brimonidine was added to monotherapy with a nonselective beta-blocker, the mean additional IOP reduction was 15.5% (3.61 mm Hg, P < 0.001). Addition of brimonidine to latanoprost monotherapy provided a 32.2% (5.89 mm Hg) mean additional IOP reduction (P < 0.001). Addition of brimonidine to combination regimens that included latanoprost provided additional mean decreases in LOP ranging from 15.5% (3.63 mm Hg, P < 0.002) to 20.1% (6.62 mm Hg, P < 0.001). All quality-of-life parameters remained high or improved during the study. Mild to moderate adverse events were reported in 5.23% of patients (29 of 552); 98.1% of physicians rated brimonidine adjunctive therapy as good or excellent. CONCLUSIONS: Brimonidine, when added to existing glaucoma regimens, safely and effectively lowered IOP in this community-based trial.

Adrenergic alpha-Agonists↗

PubMed2001

Compressive deformation and damage of muscle cell subpopulations in a model system.

To study the effects of compressive straining on muscle cell deformation and damage an in vitro model system was developed. Myoblasts were seeded in agarose constructs and cultured in growth medium for 4 days. Subsequently, the cells were allowed to fuse into multinucleated myotubes for 8 days in differentiation medium, resulting in a population of spherical myoblasts (50%), spherical myotubes (35%), and elongated myotubes (15%) with an overall viability of 90%. To evaluate cell deformation upon construct compression half-core shaped constructs were compressed up to 40% strain and the resulting cell shape was assessed from confocal scans through the central plane of spherical cells. The ratio of cell diameters measured parallel and perpendicular to the axis of compression was used as an index of deformation (DI). The average DI of myoblasts decreased with strain level (0.99+/-0.03, 0.70+/-0.04, and 0.56+/-0.10 at 0%, 20%, and 40% strain), whereas for myotubes DI decreased up to 20% strain and then remained fairly constant (0.99+/-0.06, 0.55+/-0.06, 0.50+/-0.11). The discrepancy in DI between spherical myoblasts and myotubes at 20% strain was explained by the relative sensitivity of the cell membrane to buckling, which is more pronounced in the myotubes. Sustained compression up to 24 h at 20% strain resulted in a significant increase in cell damage with time as compared to unstrained controls. Despite differences in membrane buckling no difference in damage between myoblasts and spherical myotubes was observed over time, whereas the elongated myotubes were more susceptible to damage.

Animals↗

PubMed2001

Mechanical compression influences intracellular Ca2+ signaling in chondrocytes seeded in agarose constructs.

Ca2+ signaling forms part of a possible mechanotransduction pathway by which chondrocytes may alter their metabolism in response to mechanical loading. In this study, a well-characterized model system utilizing bovine articular chondrocytes embedded in 4% agarose constructs was used to investigate the effect of physiological mechanical compressive strain applied after 1 and 3 days in culture. The intracellular Ca2+ concentration was measured by use of the ratiometric Ca2+ indicator indo 1-AM and confocal microscopy. A positive Ca2+ response was defined as a percent increase in Ca2+ ratio above a preset threshold. A significantly greater percentage of cells exhibited a positive Ca2+ response in strained constructs compared with unstrained controls at both time points. In strained constructs, treatment with either Ga3+ or EGTA significantly reduced the number of positive Ca2+ responders compared with untreated controls. These results represent an important step in understanding the physiological role of intracellular Ca2+ in chondrocytes under mechanical compression.

Algorithms↗

PubMed2001

The role of shame and guilt in traumatic events: a clinical model of shame-based and guilt-based PTSD.

Post-traumatic stress disorder is currently classified as an anxiety disorder with fear as the predominant emotion. This has led to the development of treatment techniques such as exposure aimed at alleviating fear. This article highlights the need to address other emotional responses, in particular shame and guilt, when assessing and treating PTSD. Hence, it presents two clinical models of shame-based PTSD and guilt-based PTSD. These models are offered as aids to clinicians in assessing and formulating cases of PTSD where shame and guilt are salient issues. The models highlight the importance of assessing meaning in the context of pre-existing schemas and address two pathways to the development of shame and/or guilt: schema congruence and schema incongruence. Several treatment implications are drawn from the models.

Guilt↗

PubMed2001

Eye conditions among 5- to 7-year-old Asian-Pacific Islander schoolchildren in Southern California.

BACKGROUND: The prevalence rates and specific risk factors for development of eye conditions among Asian-Pacific Islander schoolchildren are unknown. This information is necessary to understand their eye care needs and to improve access to eye care for this rapidly growing population. METHODS: Data obtained from a computer database of vision screening examinations conducted by the UCLA Mobile Eye Clinic from October 1987 through December 1996 were analyzed for 2,687 Asian-Pacific Islander schoolchildren between 5 and 7 years of age. RESULTS: Myopia (8.9%) and astigmatism (15.8%) represented the majority of visual disorders. Mean myopic refractive error was -1.21 +/- 0.83 D among bilateral myopes. Color-vision deficiency was prevalent among 2.8% of male children, extraocular muscle imbalance among 3.0% of children, and amblyopia among 1.0% of children. All other conditions were present in less than 4% of children screened. CONCLUSIONS: Asian-Pacific Islander schoolchildren may be at higher risk for development of juvenile myopia than white, Hispanic, and African-American children. Prevalence rates of other disorders are comparable to those obtained for other ethnic groups. This information can be used in planning to meet the eye care needs of Asian-Pacific Islander schoolchildren.

Asia↗

PubMed2000

The effect of integrin antibodies on the attachment and proliferation of human Tenon's capsule fibroblasts.

The integrins are protein heterodimers consisting of noncovalently associated alpha and beta subunits. The adhesive interactions mediated by integrins are necessary for cellular survival and proliferation. In this study we investigated the effects of three different integrin antibodies on the proliferation of human Tenon's capsule fibroblasts in tissue culture. Human Tenon's capsule fibroblasts were cultured into 96 well plates and treated with different concentrations (ranging from 10(-6) to 1 microg ml(-1)) of three different integrin antibodies: human integrin alpha-2 antibody, human integrin alpha-3 antibody and human integrin alpha-5/FnR (fibronectin receptor) antibody. Coulter counter, hexosaminidase, and 3H-thymidine assays were used to determine the inhibitory effects of these integrin antibodies on ocular fibroblasts on days 0 (attachment), 1,3 and 7 following antibody treatment. The concentration of each antibody required to produce a proliferation 50% less than the control (ID50) was calculated for each assay. With respect to attachment, all three antibodies studied displayed some inhibitory activity. All three antibodies also displayed dose-dependent antiproliferative properties, especially at the highest concentration tested after 7 days of exposure. The integrin alpha-2 antibody was the most potent of the inhibitors, followed by the integrin alpha-3 antibody, with the integrin alpha-5 antibody being the least potent antibody tested. In addition, the anti-proliferative activities of the integrin alpha-2 and integrin alpha-3 antibodies increased with increasing incubation time. In conclusion, these integrin antibodies demonstrated some inhibitory effects on the attachment and proliferation of human Tenon's capsule fibroblasts in culture. Further investigation will be required to determine whether integrin antibodies can significantly limit scar formation in vivo without significant toxicity.

Antibodies↗

PubMed2000

Chondrocyte deformation within compressed agarose constructs at the cellular and sub-cellular levels.

Mechanotransduction events in articular cartilage may be resolved into extracellular components followed by intracellular signalling events, which finally lead to altered cell response. Cell deformation is one of the former components, which has been examined using a model involving bovine chondrocytes seeded in agarose constructs. Viable fluorescent labels and confocal laser scanning microscopy were used to examine cellular and sub-cellular morphology. It was observed that cell size increased up to day 6 in culture, associated with an increase in the contents of proteoglycan and collagen. In addition, the organisation of the cytoskeleton components, described using a simple scoring scale, revealed temporal changes for actin fibres, microtubules and vimentin intermediate filaments. The constructs on day 1 were also subjected to unconfined compressive strains. A series of confocal scans through the centre of individual cells revealed a change from a spherical to an elliptical morphology. This was demonstrated by a change in diameter ratio, from a mean value of 1.00 at 0% strain to 0.60 at 25% strain. Using simple equations, the volume and surface areas were also estimated from the scans. Although the former revealed little change with increasing construct strain, surface area appeared to increase significantly. However further examination, using transmission electron microscopy to reveal fine ultrastructural detail at the cell periphery, suggest that this increase may be due to an unravelling of folds at the cell membrane. Cell deformation was associated with a decrease in the nuclear diameter, in the direction of the applied strain. The resulting nuclear strain in one direction increased in constructs compressed at later time points, although its values at all three assessment times were less than the corresponding values for cell strain. It is suggested that the nuclear behaviour may be a direct result of temporal changes observed in the organisation of the cytoskeleton. The study demonstrated that the chondrocyte-agarose model provides a useful system for the examination of compression events at both cellular and sub-cellular levels.

Animals↗

PubMed2000

Efficacy of brimonidine as replacement therapy in patients with open-angle glaucoma or ocular hypertension.

BACKGROUND: Patients with glaucoma or ocular hypertension may have inadequately controlled intraocular pressure (IOP) or experience adverse effects with their current medication regimens. OBJECTIVE: This post hoc reanalysis determined the effectiveness and tolerability of brimonidine used as replacement therapy in a real-life clinical practice setting. METHODS: In this multicenter, open-label, observational, 2-month study, 460 patients received brimonidine 0.2% as a 1:1 replacement for another antiglaucoma medication in their current regimen. Effectiveness was assessed by calculating the mean additional reduction in IOP from the treated baseline measurement (before the switch to brimonidine) to 2 months postbaseline, and by determining physicians' opinions of treatment effectiveness. Tolerability was determined based on quality-of-life assessments and recorded adverse events. RESULTS: Overall, brimonidine replacement significantly reduced mean (+/- SEM) IOP by an additional 2.33 +/- 0.17 mm Hg (9.8% +/- 0.9%; P < 0.001). Significant additional reductions in IOP were seen when brimonidine replaced an agent used either as monotherapy or adjunctive therapy, regardless of the drug class of the agent replaced. However, particularly good hypotensive effectiveness and additional lowering of IOP were observed when brimonidine replaced certain medications, including latanoprost (12.44%; P < 0.003) and betaxolol (13.56%; P < 0.001) monotherapy, and latanoprost (16.08%; P < 0.010) adjunctive therapy. The effectiveness of brimonidine was rated as good or excellent by 92.4% of physicians. All quality-of-life variables remained favorable or improved throughout the study, and brimonidine treatment was well tolerated. CONCLUSIONS: Brimonidine 0.2% used as a 1:1 replacement for monotherapy or adjunctive therapy with other antiglaucoma drugs significantly lowered IOP from that produced by previous therapy and was well tolerated. Brimonidine offers a useful treatment option in patients who require replacement therapy.

Adrenergic alpha-Agonists↗

PubMed2000

A system for monitoring the response of uniaxial strain on cell seeded collagen gels.

The success of cell seeded constructs for the repair of collagenous tissues may be improved by the use of mechanical stimulation in vitro. A mechanical loading apparatus, termed the cell straining system, was developed according to a set of design criteria, to enable cell seeded constructs to be cyclically loaded in tension. A suitable cell seeded collagen gel model system was used to characterise the apparatus. These gels were subjected to a cyclic strain of 10% superimposed on two separate tare loads of 2 and 10 mN, while being maintained in cell culture conditions. The computer controlled apparatus was shown to be capable of monitoring the individual loads on six specimens simultaneously, to an accuracy of 0.02 mN. Results indicated a wide variability between individual specimens. Following cyclic loading, the cell seeded collagen gels exhibited an increase in structural stiffness compared with the unloaded controls. This novel and versatile apparatus will provide a means of enhancing structural and mechanical integrity of tissue engineered repair systems.

Biomechanical Phenomena↗

PubMed2000

Confocal analysis of cytoskeletal organisation within isolated chondrocyte sub-populations cultured in agarose.

This study reports the cytoskeletal organisation within chondrocytes, isolated from the superficial and deep zones of articular cartilage and seeded into agarose constructs. At day 0, marked organisation of actin microfilaments was not observed in cells from both zones. Partial or clearly organised microtubules and vimentin intermediate filaments cytoskeletal components were present, however, in a proportion of cells. Staining for microtubules and vimentin intermediate filaments was less marked after 1 day in culture however than on initial seeding. For all three cytoskeletal components there was a dramatic increase in organisation between days 3 and 14 and, in general, organisation was greater within deep zone cells. Clear organisation for actin microfilaments was characterised by a cortical network and punctate staining around the periphery of the cell, while microtubules and vimentin intermediate filaments formed an extensive fibrous network. Cytoskeletal organisation within chondrocytes in agarose appears, therefore, to be broadly similar to that described in situ. Variations in the organisation of actin microfilaments between chondrocytes cultured in agarose and in monolayer are consistent with a role in phenotypic modulation. Vimentin intermediate filaments and microtubules form a link between the plasma membrane and the nucleus and may play a role in the mechanotransduction process.

Actin Cytoskeleton↗

PubMed2000

The effectiveness and safety of brimonidine as mono-, combination, or replacement therapy for patients with primary open-angle glaucoma or ocular hypertension: a post hoc analysis of an open-label community trial. Glaucoma Trial Study Group.

The purpose of this study was to determine the effectiveness and safety of brimonidine 0.2% (Alphagan, Allergan Inc., Irvine, CA) as mono-, combination, or replacement therapy for reducing intraocular pressure (IOP) in patients with primary open-angle glaucoma or ocular hypertension. The study method was an open-label, comparative clinical evaluation involving 2335 patients. During the 2-month trial, data were collected at baseline (visit 1), month 1 (visit 2), and month 2 (visit 3). Various parameters were evaluated, including glaucoma medications (visit 1), IOP (visit 1-visit 3), and adverse events. A subset cohort of 1254 patients was selected that met specific study criteria. Data from these 1254 patients were used to evaluate adverse events and the change in IOP from visit 1 to visit 3. Patient data were grouped according to specific drug regimen, and drug regimens were categorized into supergroups of mono-, combination, and replacement therapy. The results of the study revealed that the overall mean change in IOP for 1) monotherapy (n = 240) was -5.07 mm Hg (-20.2%), 2) combination therapy (n = 554) was -4.01 mm Hg (-16.9%), 3) replacement therapy (n = 460) was -2.33 mm Hg (-9.8%), and 4) overall (n = 1254) was -3.59 mm Hg (-14.9%) (p < 0.001 for all changes). Overall, 6.0% of the subjects reported adverse events, with no hypersensitivity or unexpected systemic or ocular adverse events. Eighty-five percent (85%) of clinicians rated brimonidine as "good" to "excellent". In conclusion, brimonidine is safe and effectively lowers IOP when used as mono-, combination, or replacement therapy as observed in a large community population.

Adrenergic alpha-Agonists↗

PubMed2000

Reduced nerve growth factor in Rett syndrome postmortem brain tissue.

To determine whether reduced nerve growth factor (NGF) and/or its high affinity receptor, trkA, play a role in the pathophysiology of Rett syndrome (RS), we used immunohistochemistry in paraffin-embedded human autopsy brain tissue, to quantify NGF and trkA levels within the frontal cortex of 9 RS females and 10 female controls of similar age. The results showed a significant reduction of NGF expression in RS patients (p < 0.001). Specifically, all RS brains exhibited NGF levels at or below the minimum level observed in controls. In 3 RS brains there was no NGF detected. TrkA expression was also reduced in the RS group (p = 0.035). Interestingly, the expression of NGF in the RS group was significantly related to the presence of cortical astrogliosis (r = 0.91) as indicated by immunostaining for glial fibrillary acidic protein (GFAP). This suggests that while the signals for NGF production during injury remain intact, the critical developmental signals required for early NGF production are impaired.

Adult↗

PubMed2000

Collagen degradation in glaucoma: will it gain a therapeutic value?

The extracellular matrix is in a constant state of turnover, and several studies suggest that this homeostasis is out of balance in open-angle glaucoma. Recent evidence suggests that matrix metalloproteinases, which are the enzymes primarily responsible for degradation, play a role in numerous modern glaucoma therapies, including topical prostaglandin analogues, topical steroids, and argon laser trabeculoplasty. Additionally, direct and indirect regulation of this system has been shown to increase aqueous humor outflow facility. It is possible that therapies directed at modulating specific enzymes represent the next generation of glaucoma therapy.

Animals↗