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Biomedical subjects

T S Chang

Publications and source records attributed to T S Chang.

At least 37 records · Page 2Linked to original sources
PubMed1998

Effects of Brazilin on the phospholipase A2 activity and changes of intracellular free calcium concentration in rat platelets.

Brazilin (7,11b-dihydrobenz[b]indeno[1,2-d]pyran-3,6a,9,10 (6 H)-tetrol) inhibited thrombin-,collagen- and ADP-induced aggregation of washed rat platelets. Thrombin- and collagen-induced ATP release were also inhibited by brazilin in a concentration-dependent manner. Brazilin inhibited the formation of platelet thromboxane A2 caused by thrombin, whereas it had no effect on the prostaglandin D2 formation. Brazilin inhibited [3H]-arachidonic acid liberation from membrane phospholipids of thrombin-stimulated platelets. Brazilin inhibited the rise of intracellular free calcium caused by thrombin. These results indicate that the inhibition of phospholipase (PLA2) activity and [Ca2+]i elevation might be at least a part of antiplatelet mechanism of brazilin.

Adenosine Triphosphate↗
PubMed1998

Computed radiography versus screen-film mammography in detection of simulated microcalcifications: a receiver operating characteristic study based on phantom images.

RATIONALE AND OBJECTIVES: The authors compare a 43-micron computed radiographic system with a mammographic screen-film system for detection of simulated microcalcifications in an observer-performance study. MATERIALS AND METHODS: The task of detecting microcalcifications was simulated by imaging aluminum wire segments (200-500 microns in length; 100, 125, or 150 microns in diameter) that overlapped with tissue background structures produced by beef brisket. A total of 288 such simulations were generated and examined with both computed radiography and conventional screen-film mammography techniques. Computed radiography was performed with high-resolution plates, a 43-micron image reader, and a 43-micron laser film printer. Computed radiographic images were printed with simple contrast enhancement and compared with screen-film images in a receiver operating characteristic study in which experienced readers detected and scored the simulated microcalcifications. Observer performance was quantitated and compared by computing the area under the receiver operating characteristic curve. RESULTS: Although the resolution of the computed radiography system was better than that of commercial systems, it fell short of that of screen-film systems. For the 100-micron microcalcifications, the difference in the average area under the curve was not statistically significant, but it was significant for the larger simulated microcalcifications: the average area under the curve was 0.58 for computed radiography versus 0.76 for screen-film imaging for the 125-micron microcalcifications and 0.83 versus 1.00, respectively, for the 150-micron microcalcifications. CONCLUSION: Observer performance in the detection of small simulated microcalcifications (100-150 microns in diameter) is better with screen-film images than with high-resolution computed radiographic images.

Breast Diseases↗
PubMed1998

An acidic glutaryl-7-aminocephalosporanic acid acylase from Pseudomonas nitroreducens.

A glutaryl-7-aminocephalosporanic acid (GL-7-ACA) acylase was purified 58-fold from Pseudomonas nitroreducens in a two-step procedure involving osmotic shock and carboxymethyl-Sepharose chromatography with a yield of 26%. The molecular mass of the native enzyme was 58 kDa. SDS/PAGE revealed that it consisted of two non-identical subunits with molecular masses of 35 and 21 kDa. The isoelectric point of the purified enzyme was 5.3. The enzyme had an optimal pH of 5.5 and an optimal temperature of 43 degrees C. The purified enzyme exhibited not only GL-7-ACA acylase activity but also gamma-glutamyltranspeptidase activity. The Km values of the enzyme for GL-7-ACA and L-gamma-glutamyl p-nitroanilide were 10.41 mM and 5.92 microM respectively.

Amidohydrolases↗
PubMed1997

Thromboxane A2 synthase inhibition and thromboxane A2 receptor blockade by 2-[(4-cyanophenyl)amino]-3-chloro-1,4-naphthalenedione (NQ-Y15) in rat platelets.

The effects of 2-[(4-acetylphenyl)amino]-3-chloro-1,4-naphthalenedione (NQ-Y15), a synthetic 1,4-naphthoquinone derivative, on platelet activity and its mechanism of action were investigated. NQ-Y15 caused a concentration-dependent inhibition of the aggregation induced by thrombin, collagen, arachidonic acid (AA), and A23187. The IC50 values of NQ-Y15 on thrombin (0.1 U/mL)-, collagen (10 microg/mL)-, AA (50 microM)-, and A23187 (2 microM)-induced aggregation were 36.2 +/- 1.5, 6.7 +/- 0.7, 35.4 +/- 1.7, and 93.1 +/- 1.4 microM, respectively. NQ-Y15 also inhibited thrombin-, collagen-, AA-, and A23187-stimulated serotonin secretion in a concentration-dependent manner. However, a high concentration (100 microM) of NQ-Y15 showed no significant inhibitory effect on ADP-induced primary aggregation, which is independent of thromboxane A2 (TXA2) production in rat platelets. In fura-2-loaded platelets, the elevation of intracellular free calcium concentration stimulated by AA, thrombin, and 4-bromo-A23187 was inhibited by NQ-Y15 in a concentration-dependent manner. The formation of TXA2 caused by AA, thrombin, and collagen was inhibited significantly by NQ-Y15. NQ-Y15 inhibited TXA2 synthase in intact rat platelets, since this agent reduced the conversion of prostaglandin (PG) H2 to TXA2. Similarly, NQ-Y15 selectively inhibited the TXA2 synthase activity in human platelet microsomes, whereas it had no effect on activity of phospholipase A2, cyclooxygenase, and PGI2 synthase in vitro. NQ-Y15 inhibited platelet aggregation induced by the endoperoxide analogue U46619 in human platelets, indicating TXA2 receptor antagonism, possibly of a competitive nature. These results suggest that the antiplatelet effect of NQ-Y15 is due to a combination of TXA2 synthase inhibition with TXA2 receptor blockade, and that it may be useful as an antithrombotic agent.

Animals↗
PubMed1997

Effects of calcium on brazilin-induced glucose transport in isolated rat epididymal adipocytes.

Brazilin increased [3H]2-deoxyglucose uptake in isolated rat epididymal adipocytes. The fact that calcium may be required for the stimulatory effects of insulin on glucose transport suggests that brazilin might also require calcium for its glucose transport-stimulating action. Changes in the concentration of extracellular calcium had no significant effect on brazilin-induced glucose transport. Nifedipine and verapamil decreased brazilin-induced glucose transport, and quin2-AM abolished the effect of brazilin on glucose transport. A23187, however, showed no effect on brazilin action. 45Ca2+ uptake into adipocytes was not influenced by brazilin treatment, and trifluoperazine significantly inhibited the effect of brazilin on glucose transport. These data suggest that calmodulin and the maintenance of the intracellular calcium concentration, rather than an increase in it, may be essential for the stimulatory action of brazilin on glucose transport.

Adipocytes↗
PubMed1997

Central cloudy corneal dystrophy of Francois. A clinicopathologic study.

Central cloudy corneal dystrophy of Francois was first described in 1955 by J. Francois; its pathophysiology remains unknown. An 80-year-old woman with bilateral central cloudy corneal dystrophy of Francois was examined after having undergone a combined penetrating keratoplasty and cataract extraction. The corneal button was obtained. Light microscopy revealed stromal staining for acid mucopolysaccharide. Transmission electron microscopy revealed extracellular vacuoles, some of which had fibrillogranular material and electron-dense deposits. Fibrillogranular material was present in and around some keratocytes. Numerous endothelial vacuoles contained light-staining fibrillogranular material and round electron-dense granules. Our findings suggest that the opacities in patients with central cloudy corneal dystrophy of Francois are due to the extracellular accumulation of mucopolysaccharide and lipidlike material. Further studies are needed to elucidate the nature of these deposits.

Aged↗
PubMed1997

Comparison of single photon emission computed tomography findings in cases of healthy adults and solvent-exposed adults.

Single photon emission computed tomography (SPECT) is a useful tool in measuring dynamic brain functioning. Its potential to reveal the physiological mechanisms of neurotoxicity has not been fully explored. In the present study, the SPECT findings for 25 healthy control subjects were compared to the findings for 25 mixed organic solvent exposure subjects. Specific physiological abnormalities related to regional cerebral blood flow activity (rCBF) were revealed. In the early phase of uptake, significantly decreased uptake was found in the mixed organic solvent group; in the late phase of uptake, a significant increase in uptake was found in specific regions of interest. The discovery of this abnormality in brain functioning may be a significant step toward the creation of a biological marker of neurotoxicity. Early detection of neurotoxicity is important in occupational medicine to prevent neurotoxic illnesses in working populations.

Adult↗
PubMed1997

Nitric oxide modulates human chorionic gonadotropin-induced ovulation in the rabbit.

OBJECTIVE: To examine the potential role of the L-arginine:nitric oxide pathway in hCG-induced ovulation in the rabbit. DESIGN: Randomized, controlled animal study. SETTING: University research laboratory. INTERVENTION(S): Nitric oxide synthase, the enzyme that produces nitric oxide (NO), was immunohistochemically localized in the ovary. NG-nitro-L-arginine methyl ester (L-NAME), an analogue of L-arginine, which inhibits the enzyme NO synthase, and the inactive D-enantiomer were administered in vivo and/or in vitro via an isolated, perfused ovary preparation during the periovulatory period. MAIN OUTCOME MEASURE(S): Rate of follicular rupture (ovulatory efficiency). RESULT(S): Immunohistochemical staining for NO synthase was localized specifically to the granulosa cell layer of the follicle and the endothelium and adventitia of ovarian blood vessels. In vivo administration of L-NAME significantly reduced the percentage of large follicles that ovulated in response to hCG (treated 24.6%, control 68.1%). Similarly, exposure of the in vitro-perfused ovary to L-NAME significantly reduced follicular rupture (treated 32.8%, control 64.2%). In contrast, addition of an equimolar concentration of D-NAME to the perfusion medium had no significant effect on the rate of ovulation (treated 83.3%, control 61.3%). CONCLUSION(S): The stereospecific inhibition of follicular rupture by the arginine analogue suggests that NO production by the ovary is an important feature of the normal physiologic processes of the periovulatory period.

Animals↗
PubMed1997

Brazilin modulates immune function mainly by augmenting T cell activity in halothane administered mice.

Previously we reported that brazilin, the main principle of Caesalpinia sappan, was able to improve the altered immune functions caused by halothane administration in mice. To elucidate the mechanisms of its immunomodulating activities, the effects of brazilin on the functions of T cells and splenic cellularity were investigated. Brazilin decreased splenic cellularity and IL-2 production which had been augmented in mice treated with halothane (21.5% in olive oil, 10 mmol/kg) for 4 consecutive days whereas the reduced expression of IL-2 receptors by ConA or standard IL-2 was increased by brazilin treatment. These data indicate that halothane induced a dysfunction of T cells resulting in abnormal immune responses and these altered immune functions might be improved mainly by affecting the function of T cells.

Animals↗
PubMed1997

Preliminary clinical evaluation of a high-resolution telemammography system.

RATIONALE AND OBJECTIVES: The authors designed, assembled, tested, and clinically evaluated a high-quality, fast, and relatively inexpensive telemammography system. METHODS: The authors designed a telemammography system that uses a high-resolution film digitizer and high data compression (> or = 40:1) to send images over regular telephone lines to a high-resolution laser printer that produces images with the look and feel of the original image and can operate in a hub and spokes mode. The authors then evaluated the system's performance. In a preliminary clinical study, interpretations of the laser-printed system's output of 119 cases were compared with the original interpretations, followed by a review of any clinically significant differences. RESULTS: With the exception of the laser printer, which is a modified off-the-shelf product, all hardware components of the system are commercially available products. The system digitizes (50 microns pixel size), compresses, transmits, receives, decompresses, and prints a 30 MB mammography file in less than 4 minutes. In the clinical study, there were 13 differences (in 13 cases) in the level of concern or recommendations. Seven were found to be clinically insignificant by a third-party review. The remaining six were reviewed by the original interpreter, and three were determined to be significant enough for further action. All were found to result from intra-reader variability rather than differences in visualization of possible abnormalities. CONCLUSIONS: Almost real-time, high-quality telemammography without geographic boundaries is possible with the use of high-level data compression. Telemammography with laser-printed film as the display may make it possible to offer mammographic services in remote locations while using commercially available technology.

Evaluation Studies as Topic↗
PubMed1997

Treatment of capillary vascular malformation (port-wine stains) with photochemotherapy.

One-hundred and thirty patients (85 female, 45 male) with port-wine stains were treated with photodynamic therapy, also called photochemotherapy, which recently has become acknowledged as effective for a variety of malignant tumors. Probably based on the photochemical reaction with the generation of toxic species, photochemotherapy results in endothelial cell injury and death of abnormal capillaries under overlying epidermis. A retrospective review of 118 available patients with port-wine stains reveals that 98.3 percent responded to photochemotherapy with varying degrees of success after one-time treatment. Results were reported under a simple classification system ranging from ordinary to dilated to posttreatment type. In the ordinary group, the results evaluated as excellent, good, fair, and poor were 37.8, 53.7, 8.5, and 0 percent, respectively, before a second treatment; the treated area was an average of 9.8 (range 7 to 13) cm in diameter. In addition, hypertrophic scars, permanent hyperpigmentation, and hypopigmentation were not seen based on proper parameters. Photochemotherapy offers a potentially efficient and promising choice based on a completely different mechanism from that of selected photothermal therapy with the pulsed-dye laser.

Adolescent↗
PubMed1996

Conjunctival intraepithelial neoplasia. A possible marker for human immunodeficiency virus infection?

BACKGROUND: Conjunctival intraepithelial neoplasia has traditionally been found at the limbus in elderly individuals. Recently, this ocular tumor has been observed in younger patients. OBJECTIVE: To investigate the potential association of human immunodeficiency virus infection with the emergence of this atypical presentation of conjunctival intraepithelial neoplasia. DESIGN, SETTING, AND PARTICIPANTS: Records of patients at the Bascom Palmer Eye Institute (Miami, Fla) in whom conjunctival intraepithelial neoplasia was diagnosed between January 1, 1991, and December 31, 1993, were reviewed. Attempts were made to contact those patients younger than 50 years for clinical evaluation and human immunodeficiency virus serologic testing. RESULTS: Conjunctival intraepithelial neoplasia was diagnosed in 73 patients during the study period. Of the nine patients younger than 50 years, six were available for serologic testing. Three (50%) of these individuals were found to be positive for human immunodeficiency virus. CONCLUSION: Human immunodeficiency virus testing and counseling should be considered in patients younger than 50 years in whom conjunctival intraepithelial neoplasia is diagnosed.

Adult↗
PubMed1996

Echographic findings in benign reactive lymphoid hyperplasia of the choroid.

BACKGROUND: Benign reactive lymphoid hyperplasia is an uncommon uveal tumor. Misdiagnosis may lead to unnecessary enucleations. Clinical evaluation alone is usually not sufficient to diagnose this tumor. OBJECTIVE: To evaluate the utility of standardized echography in the recognition of this disease. METHODS: Retrospective review of the medical and echographic records of 6 patients with choroidal involvement of benign reactive lymphoid hyperplasia. RESULTS: Extraocular episcleral lymphoid nodules were present in 5 of the 6 patients and were usually seen as a late manifestation of the disease. Two patients had repeated echography after treatment of the tumor and showed marked regression of the episcleral nodules. CONCLUSIONS: A combination of clinical and echographic findings can assist in the accurate diagnosis of this rare uveal tumor. The presence of episcleral nodules on standardized echography supports the diagnosis.

Aged↗
PubMed1996

Subjective quality assessment of computed radiography hand images.

To evaluate the sensitivity of a non-receiver-operating characteristic (ROC) study in assessing small differences of perceived image quality of hand images acquired by computed radiography (CR) and conventional screen-film systems, hand images were acquired on 12 patients with both conventional screen-film and CR. Each CR image was then processed with three different edge-enhancement algorithms. One conventional film and four CR images were then viewed side by side by five radiologists. Observers rated perceived image quality of each radiograph using a 10-category discrete scale. The study was repeated after 6 weeks using a different block randomization scheme. Despite the small sample size, significant differences (P < .05) in assigned image quality were detected among CR images acquired at low, medium, and high resolutions. Image processing routines did not fully compensate for differences in quality between conventional film and CR-acquired images. The quality rating of the reference conventional image was found to be dependent on the quality of images with which it was compared. Small, highly sensitive study designs can be used to identify radiologists' perceived differences in image quality. "Reference" or "gold standard" quality are important in such studies. Edge-enhancement schemes cannot fully compensate for perceived image quality degradations because of reduced image resolution.

Algorithms↗
PubMed1996

Microwave heating in the management of postmastectomy upper limb lymphedema.

The results of treating chronic lymphedema using microwave heating are described in 45 patients with postmastectomy lymphedema of the upper extremity. Forty-five patients showed a significant (p < 0.01) reduction in the amount of peripheral edema after two courses of treatment. The incidence and severity of secondary acute inflammation (erysipelas) were also sharply reduced (p < 0.01). The elasticity of the soft tissue was restored.

Adult↗