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Biomedical subjects

C Lee

Publications and source records attributed to C Lee.

At least 739 records · Page 41Linked to original sources
PubMed1992

Cyclophosphamide-induced neutropenia: effect on postischemic skin-flap survival.

In a blinded study, 24 pigs were randomized to a 5-day preoperative treatment regimen of cyclophosphamide (n = 12) or placebo (n = 12). At operation, buttock cutaneous and latissimus dorsi myocutaneous flaps were created and then subjected to 6 hours of global ischemia. After 24 hours of reperfusion, flap skin and muscle survivals were determined. All cyclophosphamide-treated animals were rendered neutropenic (less than 500 neutrophils/mm3 of peripheral blood). The results show that neutropenia had no effect on postischemic buttock cutaneous flap survival. In contrast, cyclophosphamide-induced neutropenia demonstrated a significant protective effect on postischemic latissimus dorsi myocutaneous flap survival. This study further implicates the neutrophil as a significant factor in the mediation of ischemia/reperfusion injury of myocutaneous flaps.

Analysis of Variance↗
PubMed1992

Permeability of arachidonic acid metabolites through the round window membrane in chinchillas.

Our previous studies showed that samples of middle ear effusion contain high concentrations of arachidonic acid metabolites (AAMs); both prostaglandins (PGs) and leukotrienes (LTs). Since abnormal levels of AAMs in the perilymph seem to be associated with salicylate ototoxicity and the round window membrane (RWM) is the most likely route of entry from the middle ear to the inner ear, it would be important to know the permeability of AAMs through the RWM. Permeability of AAMs was determined by applying labeled and standard representatives AAMs on the RWM and counting radioactivity or measuring concentrations of AAMs in perilymph at different time intervals. Using chinchillas as experimental animals, samples of perilymph were obtained through a fenestration made at the helicotrema of the cochlea after 0.5, 1, 2, and 4, hours from placing tritiated or standard PGE2, 6-keto-PGF1 alpha, LTB4, LTC4 and 15-hydroxyeicosatetraenoic acid (HETE) over RWMs. Radioactivity in the perilymph was determined by a scintillation counter and concentrations of AAMs were measured by reverse phase high performance liquid chromatography (RP-HPLC) and radioimmunoassay. AAMs, which are twenty carbon fatty acids, were found to cross the RWM readily. Radioactivity and concentrations of AAMs in perilymph were detected in 30 minutes and peaked by one hour from the application of AAMs on the RWM. The results of this study suggest that AAMs such as PGs and LTs present in the middle ear fluid can cross the RWM readily and enter into the perilymphatic space of the cochlea. Sensorineural hearing loss observed in chronic otitis media could be mediated by PGs and LTs in the middle ear effusion crossing over to the inner ear through the RWM.

Adrenal Cortex Hormones↗
PubMed1991

Quantitative analysis of molecular species of diacylglycerol and phosphatidate formed upon muscarinic receptor activation of human SK-N-SH neuroblastoma cells.

Quantitative changes in the total mass and the molecular species of 1,2-diacyl-sn-glycerol (DAG) and phosphatidic acid (PA) formed upon muscarinic receptor activation were studied in cultured human SK-N-SH neuroblastoma cells. DAG was isolated from the total lipid extracts of carbachol (CCh)-stimulated and unstimulated cells and after benzoylation, was subjected to reverse phase high performance liquid chromatography to separate the component species. The molecular species of DAG were identified by analyzing the fatty acid composition of each separated fraction by gas chromatography, and their total and individual masses were quantified from the known amount of an internal standard, 1,2-distearoyl-sn-glycerol, added during the extraction of the lipid. Relatively high basal levels of DAG (1.5 nmol/mg protein) are present in these cells, and addition of CCh elicited a 50-60% increase in the total amounts of DAG within 5 min. The increase was biphasic: an initial major peak at 5 min was followed by a sustained increase that persisted for at least 30 min. An increase in DAG was elicited by both full and partial muscarinic agonists and was blocked by atropine. The presence of extracellular Ca2+ was necessary for muscarinic receptor-activated formation of DAG. To determine the source of the DAG, the molecular species of the major phospholipids present in SK-N-SH cells were also analyzed. The phospholipids were first enzymatically hydrolyzed to DAGs which were then analyzed as described above. A number of unusual fatty acids, the major one being 20:3 (n-9), were present in these lipids especially in the phosphoinositides and also in the DAG formed after CCh stimulation. Within 5 s of CCh stimulation there were transient increases in the DAG species representative of phosphoinositides. By 5 min the newly formed molecular species of DAG resembled a mixture of phosphoinositides and phosphatidylcholine (PC). Quantitative comparison of the molecular species compositions of phosphoinositides, PC, and newly formed DAGs indicated that at time periods up to 10 min, approximately 30% of the DAG originated from the phosphoinositides and the rest from PC. At longer intervals (greater than 20 min), most (85%) of DAGs originated from PC. Activation of muscarinic receptors in SK-N-SH cells also elicited an increase in PA (200% in 5 min). A quantitative molecular species analysis, using 1,2-distearoyl-sn-glycerol-3-P as internal standard, was performed by enzymatic (alkaline phosphatase) hydrolysis of PA to DAG and subsequent analysis.(ABSTRACT TRUNCATED AT 400 WORDS)

Calcium↗
PubMed1991

Profiles of antibacterial drug use in Australia and trends from 1987 to 1989. A report from the Drug Utilization Subcommittee of the Pharmaceutical Benefits Advisory Committee.

OBJECTIVE: To survey the use by Australian pensioners of orally administered antimicrobial agents supplied through the Pharmaceutical Benefits Scheme over the years 1987-1989. DATA SOURCES: Australian Pharmaceutical Benefits Scheme pensioner data for 1987-1989 and market research data from a private company. DATA EXTRACTION: The data were initially available as the number of prescriptions dispensed and were aggregated on a quarter year basis. These were converted to defined daily doses (DDDs) per 1000 pensioners per day (DDD/1000 per day). This conversion of the data allows comparisons across drug groups, and with prescribing patterns in other countries. The DDD/1000 per day also gives an indication of the proportion of individuals in the community receiving a drug at a particular time. DATA SYNTHESIS: There was a 26% increase in antibacterial drug use over this period. Comparison of prescribing profiles for particular indications with peer consensus guidelines revealed marked discrepancies, particularly for upper respiratory tract infections, urinary tract infections, otitis media and sinusitis. Upper respiratory tract infections accounted for 31% of instances of antibiotic prescribing. Dispensing of amoxycillin/potassium clavulanate relative to amoxycillin as a single agent, showed a marked increase in 1989 to the point where it represented 25% of all amoxycillin used. This could be considered excessive given the lack of evidence that amoxycillin resistance has substantially increased in infections presenting to general practice. The data presented here confirm previous suggestions that Australian antibiotic prescribing is heavily concentrated on the use of broad spectrum agents. By comparison with Norway or Sweden, there is a greater relative use of broad spectrum penicillins and tetracyclines and a lower relative use of phenoxymethylpenicillin and trimethoprim. CONCLUSIONS: Antibiotic prescribing practices in Australia continue to be often inappropriate and expensive, being directed too heavily towards the use of broad spectrum agents and newer more expensive drugs. Correction of such antibacterial drug use will require coordination of educational and regulatory activities that are sensitive to the context of general practice.

Anti-Bacterial Agents↗
PubMed1991

Myeloablative chemoradiotherapy and autologous bone marrow infusions for treatment of neuroblastoma: factors influencing engraftment.

Bone marrow harvested from cancer patients for autologous bone marrow reinfusion (ABMR) after myeloablative treatment may be injured, in both its proliferating and stromal cell pools, by either previous treatment or manipulation at the time of harvest. We have examined the relative effects of seven covariates on hematologic recovery after ABMR in children with neuroblastoma (NBL) using univariate and step-up analysis. We measured recovery by times to achieve (1) white blood cell counts greater than 1,000/microL; (2) absolute neutrophil counts greater than 500/microL; and (3) platelet counts greater than 20,000/microL without transfusion. In univariate analysis, recovery was significantly associated with the amount of prior chemotherapy and the interval between last chemotherapy and marrow harvest. Patient sex, the number of granulocyte-macrophage colonies infused, harvest-to-freeze interval, and use of purging were marginally associated. After adjusting for potential confounders in a multivariate model, the amounts of chemotherapy and granulocyte-macrophage colonies infused were independently significant predictors of time to total white blood cell count recovery; chemotherapy courses and chemo-to-harvest interval were predictors of neutrophil count recovery; and sex, use of purging, and harvest-to-freeze interval were marginal predictors of platelet recovery. The speed of hematologic recovery after ABMR seems to depend mainly on pre-existing factors and marginally on manipulation of the marrow after harvest. These factors may affect both proliferating and stromal cell pools.

Antineoplastic Combined Chemotherapy Protocols↗
PubMed1991

Recent trends in the prescribing of cholesterol lowering drugs in Australia. A report from the Drug Utilization Subcommittee of the Pharmaceutical Benefits Advisory Committee.

OBJECTIVE: To determine the recent pattern of use of hypolipidaemic drugs in the Australian community. DESIGN: Drug utilisation study employing prescription data collected during the operation of the Australian Pharmaceutical Benefits Scheme (PBS). SETTING: Non-hospital drug use in Australia. PATIENTS: All patients, pensioners and non-pensioners, who received prescriptions for hypolipidaemic agents under the PBS between January 1987 and December 1989. MAIN OUTCOME MEASURES: The total number of prescriptions, average quantity dispensed with each prescription, defined daily doses (DDD) and Australian population figures for pensioners and non-pensioners were used to express the consumption of hypolipidaemic agents as DDD/1000 individuals/day. RESULTS: Between the March quarter 1987 and the December quarter 1989 prescribing of hypolipidaemics for the Australian community increased from 68,120 to 304,760 prescriptions per quarter, which translates to a rise in use from 1.2 to 5.2 DDD/1000 inhabitants/day. This included a rise in the use of clofibrate from 0.6 to 2.6 DDD/1000 inhabitants/day, and of cholestyramine from 0.6 to 1.9 DDD/1000 inhabitants/day. Prescribing of hypolipidaemics for pensioners increased from 29,569 to 123,440 prescriptions per quarter. This translated into a rise in use from 3.7 to 14.8 DDD/1000 pensioners/day. Notable rises were seen for clofibrate, 1.9 to 8.1 DDD/1000 pensioners/day, and cholestyramine, 1.6 to 4.7 DDD/1000 pensioners/day. In comparison published data from the Nordic countries and the United States showed a lower overall use of hypolipidaemics and declining consumption of clofibrate. CONCLUSIONS: The trend in Australia was unusual in that the use of clofibrate increased to a greater extent than that of the resins, cholestyramine and colestipol which are generally preferred for treatment of hypercholesterolaemia. Possible reasons for this include: the better tolerability of clofibrate; its readier availability during the study period; the recommendation by the Pharmaceutical Benefits Advisory Committee that clofibrate was the preferred drug when triglyceride levels were also elevated and the limited availability of newer hypolipidaemic agents.

Aged↗
PubMed1991

Accurate prediction of the stability and activity effects of site-directed mutagenesis on a protein core.

Theoretical prediction of the structure, stability and activity of proteins, an important unsolved problem in molecular biology, would be of use for guiding site-directed mutagenesis and other protein-engineering techniques. X-ray diffraction studies have provided extensive structural information for many proteins, challenging theorists to develop reliable techniques able to use such knowledge as a base for prediction of mutants' characteristics. Here we report theoretical calculation of stabilization energies for 78 triple-site sequence variants of lambda repressor characterized experimentally by Lim and Sauer. The calculated energies correlate with the mutants' measured activities; active and inactive mutations are discriminated with 92% reliability. They correlate even more directly with the mutants' thermostabilities, correctly identifying two of the mutants to be more stable than the wild type.

Chemical Phenomena↗
PubMed1991

Autonomous growth of androgen-independent human prostatic carcinoma cells: role of transforming growth factor alpha.

The androgen-independent prostatic carcinoma cell line PC3 is known to exhibit autonomous growth in vitro and in vivo. The purpose of the present study was to investigate the role of transforming growth factor alpha (TGF-alpha) and its receptor, the epidermal growth factor (EGF) receptor, in the regulation of PC3 cell proliferation. Results showed that PC3 cells secrete factors into conditioned medium that are mitogenic for the less aggressive prostatic carcinoma lines DU145 and LNCaP. Gel filtration chromatography of PC3-conditioned medium revealed a major peak of mitogenic activity at a molecular weight of 5,000 to 10,000 which was inhibited by the addition of antibody to TGF-alpha. The synthesis and secretion of TGF-alpha by PC3 cells were further demonstrated by immunoblotting and radioimmunoassay. Radioreceptor analysis showed a single class (Kd 5.3 nM) of EGF receptors on PC3 cells. The presence of Mr 170,000 EGF receptors on PC3 cells was further demonstrated by immunoprecipitation of metabolically labeled proteins. TGF-alpha was effective in stimulating the growth of low-density, but not high-density, PC3 cultures. In addition, the proliferation of PC3 cells under serum-free defined conditions was inhibited by antibodies to TGF-alpha and/or the EGF receptor. These data indicate that TGF-alpha/EGF receptor interactions are partially responsible for autonomous growth of the PC3 cell line and may explain one mechanism of escape from androgen-dependent growth in human prostatic carcinoma.

Cell Division↗
PubMed1991

Switching substrate preference of thermophilic xylose isomerase from D-xylose to D-glucose by redesigning the substrate binding pocket.

The substrate specificity of thermophilic xylose isomerase from Clostridium thermosulfurogenes was examined by using predictions from the known crystal structure of the Arthrobacter enzyme and site-directed mutagenesis of the thermophile xylA gene. The orientation of glucose as a substrate in the active site of the thermophilic enzyme was modeled to position the C-6 end of hexose toward His-101 in the substrate-binding pocket. The locations of Met-87, Thr-89, Val-134, and Glu-180, which contact the C-6-OH group of the substrate in the sorbitol-bound xylose isomerase from Arthrobacter [Collyer, C.A., Henrick, K. & Blow, D. M. (1990) J. Mol. Biol. 212, 211-235], are equivalent to those of Trp-139, Thr-141, Val-186, and Glu-232 in the thermophilic enzyme. Replacement of Trp-139 with Phe reduced the Km and enhanced the kcat of the mutant thermophilic enzyme toward glucose, whereas this substitution reversed the effect toward xylose. Replacement of Val-186 with Thr also enhanced the catalytic efficiency of the enzyme toward glucose. Double mutants with replacements Trp-139----Phe/Val-186----Thr and Trp-139----Phe/Val-186----Ser had a higher catalytic efficiency (kcat/Km) for glucose than the wild-type enzyme of 5- and 2-fold, respectively. They also exhibited 1.5- and 3-fold higher catalytic efficiency for D-glucose than for D-xylose, respectively. These results provide evidence that alteration in substrate specificity of factitious thermophilic xylose isomerases can be achieved by designing reduced steric constraints and enhanced hydrogen-bonding capacity for glucose in the substrate-binding pocket of the active site.

Aldose-Ketose Isomerases↗