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Biomedical subjects

C W Chang

Publications and source records attributed to C W Chang.

At least 73 records · Page 4Linked to original sources
PubMed1995

Kinetic and crystallographic studies of thrombin with Ac-(D)Phe-Pro-boroArg-OH and its lysine, amidine, homolysine, and ornithine analogs.

The X-ray crystallographic structure of Ac-(D)Phe-Pro-boroArg-OH [DuP714, Ki = 0.04 nM; Kettner, C., Mersinger, L., & Knabb, R. (1990) J. Biol. Chem. 265, 18289] complexed with human alpha-thrombin shows the boron atom covalently bonded to the side-chain oxygen of the active site serine, Ser195. The boron adopts a nearly tetrahedral geometry, and the boronic acid forms a set of interactions with the protein that mimic the tetrahedral transition state of serine proteases. Contributions of the arginine side chain to inhibitor affinity were examined by synthesis of the ornithine, lysine, homolysine, and amidine analogs of DuP714. The basic groups interact with backbone carbonyl groups, water molecules, and an aspartic acid side chain (Asp189) located in the thrombin S1 specificity pocket. The variation in inhibition constant by 3 orders of magnitude appears to reflect differences in the energetics of interactions made with thrombin and differences in ligand flexibility in solution.(ABSTRACT TRUNCATED AT 250 WORDS)

Amidines↗
PubMed1995

Differential inhibition of reverse transcriptase and cellular DNA polymerase-alpha activities by lignans isolated from Chinese herbs, Phyllanthus myrtifolius Moon, and tannins from Lonicera japonica Thunb and Castanopsis hystrix.

Two lignans, phyllamycin B and retrojusticidin B isolated from Phyllanthus myrtifolius Moon have been demonstrated to have a strong inhibitory effect on human immunodeficiency virus-1 reverse transcriptase activity (HIV-1 RT), but much less inhibitory effect on human DNA polymerase-alpha (HDNAP-alpha) activity. Fifty percent inhibitory concentrations of phyllamycin B and retrojusticidin B were determined to be 3.5 and 5.5 microM for HIV-1 RT, and 289 and 989 microM for HDNAP-alpha, respectively. The mode of inhibition was found to be non-competitive inhibition with respect to template-primer and triphosphate substrate. Several tannins such as caffeoylquinates (CQs) isolated from Lonicera japonica Thunb, galloylquinates (GQs) and galloylshikimates (GSs) purified from Castanopsis hystrix were shown to have a much less selective inhibitory effect on HIV-1 RT.

DNA Polymerase II↗
PubMed1995

Factors affecting microbiological colony count accuracy for bioaerosol sampling and analysis.

The effects of the following variables on the occurrence of colony masking (the indistinguishable merging or overlap of sufficiently close colonies) were evaluated experimentally using the bacterium Bacillus subtilis: spore density on a collection surface, concentration of nutrients in the culture medium, sample incubation time, and ability of an observation system to distinguish overlapped colonies. Increasing spore surface density and incubation time increased colony masking, whereas lowering nutrient concentration decreased colony diameter and, therefore, masking but also limited spore germination and growth. Overall, full-strength medium was best for accurate counting of early microcolonies examined with the aid of a microscope, whereas half- or quarter-strength medium was better for counting older readily observable macrocolonies. Masking bias was determined for varying spore surface densities and colony diameters and was applied to two widely used slit-to-agar bioaerosol impactors. Appropriate collection times have been determined for these samplers to minimize colony masking for expected bioaerosol concentrations. It was found, for example, that 6-min samples collected from an environment with an air concentration of 10(3) CFU m-3 would result in colony surface densities, for 3-mm colonies, of 1.5 and 3.9 microorganisms cm-2 for the two samplers with respective masking biases of < 10% and < 20%.

Aerosols↗
PubMed1995

Status epilepticus.

Status epilepticus is defined as a condition characterized by epileptic seizure prolonged or repeated so as to produce a lasting epileptic state. It is estimated that status epilepticus occurs in 50,000 to 60,000 individuals in the United States, with one third to one half of episodes occurring in patients with established epilepsy.

Anticonvulsants↗
PubMed1994

Evaluation of counting error due to colony masking in bioaerosol sampling.

Colony counting error due to indistinguishable colony overlap (i.e., masking) was evaluated theoretically and experimentally. A theoretical model to predict colony masking was used to determine colony counting efficiency by Monte Carlo computer simulation of microorganism collection and development into CFU. The computer simulation was verified experimentally by collecting aerosolized Bacillus subtilis spores and examining micro- and macroscopic colonies. Colony counting efficiency decreased (i) with increasing density of collected culturable microorganisms, (ii) with increasing colony size, and (iii) with decreasing ability of an observation system to distinguish adjacent colonies as separate units. Counting efficiency for 2-mm colonies, at optimal resolution, decreased from 98 to 85% when colony density increased from 1 to 10 microorganisms cm-2, in contrast to an efficiency decrease from 90 to 45% for 5-mm colonies. No statistically significant difference (alpha = 0.05) between experimental and theoretical results was found when colony shape was used to estimate the number of individual colonies in a CFU. Experimental colony counts were 1.2 times simulation estimates when colony shape was not considered, because of nonuniformity of actual colony size and the better discrimination ability of the human eye relative to the model. Colony surface densities associated with high counting accuracy were compared with recommended upper plate count limits and found to depend on colony size and an observation system's ability to identify overlapped colonies. Correction factors were developed to estimate the actual number of collected microorganisms from observed colony counts.(ABSTRACT TRUNCATED AT 250 WORDS)

Aerosols↗
PubMed1993

Oligomers of 4-chloroaniline are intermediates formed during its biodegradation by Phanerochaete chrysosporium.

Lignin peroxidase H2 (LP-H2) from Phanerochaete chrysosporium oxidized 4-chloroaniline to form several oligomers. Included among the compounds identified were: 4,4'-dichloroazobenzene, 2-(4-chloroanilino)-5-hydroxybenzoquinone-di-4-chloroanil and 2-amino-5-(4-chloroanilino) benzoquinone-di-4-chloroanil. In contrast to results by others, we showed that oligomers of 4-chloroaniline were also formed by the fungus in vivo. It was also demonstrated that, although these potentially toxic intermediates are made, they are also degraded.

Aniline Compounds↗
PubMed1993

Positron emission tomographic studies on aromatic L-amino acid decarboxylase activity in vivo for L-dopa and 5-hydroxy-L-tryptophan in the monkey brain.

The regional brain kinetics following 5-hydroxy-L-(beta-11 C)tryptophan and L-(beta-11 C)DOPA intravenous injection was measured in twelve Rhesus monkeys using positron emission tomography (PET). The radiolabelled compounds were also injected together with various doses of unlabelled 5-hydroxy-L-tryptophan or D-DOPA. The radioactivity accumulated in the striatal region and the rate of increased utilization with time was calculated using a graphical method with back of the brain as a reference region. The rate constants for decarboxylation were 0.0070 +/- 0.0007 (S. D) and 0.0121 +/- 0.0010 min-1 for 5-hydroxy-L-(beta-11 C)tryptophan and L-(beta-11 C)DOPA, respectively. After concomitant injection with unlabelled 5-hydroxy-L-tryptophan, the rate constant of 5-hydroxy-L-(beta-11 C)tryptophan decreased dose-dependently and a 50 percent reduction was seen with a dose of about 4 mg/kg of unlabelled compound. A decreased utilization rate of L-(beta-11 C)DOPA was seen only after simultaneous injection of 30 mg/kg of either L-DOPA or 5-hydroxy-L-tryptophan. This capacity limitation was most likely interpreted as different affinity of the striatal aromatic amino acid decarboxylase for L-DOPA and 5-hydroxy-L-tryptophan, respectively.

5-Hydroxytryptophan↗
PubMed1993

Temperature effects on nerve conduction studies in patients with carpal tunnel syndrome.

This study was done to evaluate the effect of rising temperature on nerve conduction parameters in 22 patients with carpal tunnel syndrome (CTS). We wanted to find out whether diseased nerves responded to temperature rise in a different manner from normal controls. For this purpose a group of 20 healthy individuals were also tested. With rising temperature motor nerve conduction velocities increased, whereas latencies, amplitudes and duration of the compound muscle action potential decreased in both groups. These changes were not statistically significant between the two groups. Sensory nerve conduction parameters yielded basically similar findings except for a significantly smaller reduction in amplitude of the compound nerve action potential (CNAP) in the CTS group (p < 0.005). We conclude that there is a different response in the sensory CNAP amplitude between normal and CTS groups, but the same nerve conduction correction formulae for temperature can be used in CTS patients as in normal individuals in the event of low skin temperature.

Adult↗
PubMed1993

Management of windshield facial injuries.

Between Jan. 1986 and Dec. 1990, 99 patients with automobile windshield facial injuries were hospitalized in Kaohsiung Medical College hospital. All patients were injured by old type windshields in car accidents. Seventy-three patients (74%) were male and twenty-six (26%) were female. Ages ranged from 6 to 62 years (mean age 31 years). Fifty-seven patients (58%) were car drivers and forty-two (42%) were front seat passengers. All patients had typical multiple U-shaped lacerations on the face. The major injury sites were localized to the upper one third of the face. The wounds were repaired immediately after careful debridement. A total of 21 facial bone fractures were noted. All were open fractures with large, deep avulsion wounds. Displaced and comminuted fractures received reduction and fixation before wound closure. Three patients had cranial bone fracture with no displacement. Brain edema and subarachnoid hemorrhage were found by brain CT scan in two and one patients respectively. They were treated conservatively. In one patient with frontal sinus fracture the glass pieces penetrated into the brain. The foreign bodies were removed from the brain and frontal sinus. Eyeball rupture was found in 16 patients, including two patients in whom both eyes were involved. Eight eyeballs needed immediate evisceration and ten eyeballs received reparation. Blindness occurred in all these patients. Of the 99 patients in this study, 15% sustained additional injury. Most were wounds on the extremities. Because serious injuries can be caused by the old type of windshields, it should be abandoned. Driving with the seat belt fastened is the best way to insure safety.

Accidents, Traffic↗
PubMed1992

Microskin autograft with pigskin xenograft overlay: a preliminary report of studies on patients.

Split-thickness pigskin graft (STPSG) was used to replace allograft skin for microskin grafting in 16 patients, nine of whom were burn patients, five suffered from traumatic defects and two from diabetic ulcers. The expansion ratios used in these patients ranged from 8:1 to 12:1. The STPSG preparation described was found to be safe for clinical application. The autogenous donor skin was excised from the inguinal area, and the donor site was primarily closed. There were no instances of donor site morbidity. The majority of the STPSG overlays adhered to the wound firmly. Histological examination showed that the microskin grafts proliferated actively immediately beneath the STPSG overlay. The time for the wound to be fully resurfaced varied from 13 to 21 days depending on the expansion ratio employed. There were only two episodes of pseudomonas infection and no further grafting was required in any of the patients. In this study the pigskin xenograft was found to provide a suitable environment for the epithelialization of microskin autografts. When allograft is not available, this is an alternative way of ensuring successful microskin grafting.

Adolescent↗
PubMed1991

Fourier transform infrared spectroscopic study on retinochrome and its primary photoproduct, lumiretinochrome.

Structural studies of retinochrome, and its photoproduct, lumiretinochrome, were done by Fourier transform infrared difference spectroscopy. The absorption bands in the carbonyl stretching region which shift in D2O show the changes in the protein part during the photoreaction. Strong absorption bands in the finger-print region show that the all-trans-retinal chromophore in retinochrome isomerizes to the 11-cis-retinal chromophore in lumiretinochrome upon illumination with yellow-green light at 83K.

Animals↗
PubMed1991

Platelet-induced expression of Fc gamma RIII (CD16) on human monocytes.

Monocytes constitutively express Fc receptor (FcR) for IgG type I (CD64) and type II (CD32), but not type III (CD16). Prior studies have indicated that in vitro culture of monocytes results in spontaneous induction of CD16, but this phenomenon has been variable and the mechanism unexplained. Here, we demonstrate that activated platelets are responsible for induction of CD16 on monocytes, as a consequence of TGF-beta release. Local release of TGF-beta by activated platelets at sites of tissue damage may induce CD16 on infiltrating or resident monocytes that in turn facilitate the function of these effector cells. The FcR on these CD16+ monocytes is functionally competent, and enables the monocytes to kill murine anti-CD16 hybridoma cells. CD16 expressed on platelet-activated monocytes is structurally similar to the transmembrane-anchored CD16-II polypeptide expressed on natural killer (NK) cells. However, whereas CD16-II on NK cells is co-associated with CD3 zeta, we were unable to detect CD3 zeta transcript or protein in monocytes. Transcripts for the gamma subunit of the high-affinity IgE FcR (Fc epsilon RI-gamma) were detected in monocytes, and presumably gamma proteins are co-associated with CD16-II in these cells. Nucleotide sequence analysis of Fc epsilon RI-gamma cDNA derived from both NK cells and cultured monocytes indicated identity with the structure previously cloned from basophils. Since CD16+ monocytes can kill anti-CD16 hybridoma cell targets in the absence of CD3 zeta, these results indicate that CD3 zeta is not essential for signal transduction in CD16-II-mediated cytotoxicity.

Antibody-Dependent Cell Cytotoxicity↗
PubMed1991

Estimate of motor conduction in human spinal cord: slowed conduction in spinal cord injury.

By using motor evoked potential (MEP) created by transcranial electric stimulation over the motor cortex and F-wave measurement from the peripheral nerve stimulation, it is possible to estimate the spinal cord motor conduction velocity (SCMCV) in the diseased state. Twenty-four patients with spinal cord injury (SCI) between T1 and T11 neurological levels participated in this study. MEP in leg muscle was absent in all neurologically complete paraplegics. In 16 patients with neurologically incomplete SCI, MEP was obtained in 13 patients. The SCMCV estimated from C7 to T12 spinal levels was 32.1 (SD = 9.4) m/s. This was significantly slower than 63.3 (SD = 8.6) m/s in 40 normal controls. This noninvasive, indirect method is measurable, and can provide valuable electrophysiological data in the assessment of motor function in patients with SCI.

Adult↗
PubMed1991

Comparison of sensory nerve conduction in the palmar cutaneous branch and first digital branch of the median nerve: a new diagnostic method for carpal tunnel syndrome.

Comparison of sensory nerve conductions in palmar cutaneous branch (PCB) and digit I nerves was applied in 50 patients suspected of having carpal tunnel syndrome (CTS) and 40 healthy persons. The abnormalities were defined as the differences in latencies and sensory nerve conduction velocities (SNCVs) of more than mean plus 2.5 SD of controls. Comparing these 2 sensory nerves, statistical differences were seen in 83.7% (36 of 43 patients) of their sensory latencies and 76.7% (33 of 43 patients) of their SNCVs. This excluded 7 patients who had unobtainable sensory nerve action potentials in digit I nerves. This method may serve as an adjunctive technique in the diagnosis of CTS. Its diagnostic sensitivity was high in comparison with other testing methods.

Adult↗
PubMed1991

Plasma lysosomal enzymes after liver transplantation in the pig.

During liver transplantation in the pig, the plasma activities of beta-galactosidase, beta-glucuronidase and beta-glucosidase were elevated as early as 15 min after establishing the hepatic circulation. The enzyme activities peaked at 3 h and returned to the initial level within 2-3 days. However, such substantial alterations were not observed in other enzymes, alpha-mannosidase and alpha-glucosidase. Similar reactions to those of the first three enzymes were found in aspartate aminotransferase and lactate dehydrogenase but with later peaks and slower eliminations. In light of the current study, the serial estimation of acid hydrolases may be useful to discover the extent of tissue injury and also to evaluate the effectiveness of various organ-preservation methods.

Animals↗
PubMed1991

The response of 21-hydroxylase messenger ribonucleic acid levels to adenosine 3',5'-monophosphate and 12-O-tetradecanoylphorbol-13-acetate in bovine adrenocortical cells is dependent on culture conditions.

The regulation of 21-hydroxylase mRNA and enzyme activity by cAMP and 12-O-tetradecanoylphorbol-13-acetate (TPA) was studied as a function of different culture conditions in bovine adrenocortical cells. Induction of 21-hydroxylase mRNA and enzyme activity was assessed after cultures were incubated with cAMP analogs. Basal 21-hydroxylase mRNA and enzyme activities were high; cAMP addition resulted in some increase in the level of mRNA, but little increase in enzyme activity. When cultures were made mitotically quiescent by using a higher starting cell density or by allowing cells to grow for a longer period before incubation with cAMP, basal mRNA and enzyme activity were low and increased greatly in response to cAMP. Other agents that raise intracellular cAMP (ACTH, prostaglandin E1, cholera toxin, and forskolin) increased 21-hydroxylase mRNA in quiescent cultures. As previously demonstrated for 11 beta-hydroxylase,21-hydroxylase mRNA induction by cholera toxin or cAMP analogs was dependent on the presence of insulin-like growth factor-I or insulin in the culture medium. When cultures were not quiescent, 21-hydroxylase mRNA and enzyme activity were highly variable, but characterized by 1) high basal levels, 2) small increases or actual decreases in response to cAMP, and 3) variable increases in response to TPA, not observed in quiescent cultures. This last effect was observed within a very narrow range of TPA concentrations (0.3-3 nM); at higher concentrations 21-hydroxylase activity decreased to values below those in the control culture. The protein kinase inhibitor staurosporine at 1-5 nM inhibited basal 21-hydroxylase enzyme activity in nonquiescent cultures by up to 80%. The probable existence of controlling factors for 21-hydroxylase expression other than cAMP suggests that the regulation of this gene differs substantially from that of the other steroid hydroxylases.

8-Bromo Cyclic Adenosine Monophosphate↗
PubMed1991

An improved method for isolation and culture of pigment epithelial cells from rat retina.

An improved method for isolation and culture of pigment epithelial cells from normal rat retinas is described. Following a brief incubation in the neutral protease Dispase, large epithelial sheets can be harvested rapidly. The separation of the choroid from the pigment epithelium prior to retinal detachment greatly reduces the risk of contamination of the cultures with choroidal cells. Growth of pigment epithelial cells on Matrigel-coated microporous filters in hormonally-defined medium allows for development of high levels of transepithelial electrical resistance as well as for preservation of the differentiated pigment epithelial cell phenotype. This method should be useful for studies of pigment epithelial cell permeability and structural differentiation in vitro.

Animals↗