PubMed Health⌕ Search

Biomedical subjects

T Ling

Publications and source records attributed to T Ling.

At least 19 recordsLinked to original sources
PubMed2001

Enantioselective synthesis of the antiinflammatory agent (-)-acanthoic acid.

An enantioselective synthesis of the potent antiinflammatory agent (-)-acanthoic acid (1) is described. The successful strategy departs from (-)-Wieland-Miescher ketone (10), which is readily available in both enantiomeric forms and constitutes the starting point toward a fully functionalized AB ring system of 1. Conditions were developed for a regioselective double alkylation at the C4 center of the A ring, which produced compound 32 as a single stereoisomer. Construction of the C ring of 1 was accomplished via a Diels-Alder reaction between sulfur-containing diene 43 and methacrolein (36), which after desulfurization and further functionalization yielded synthetic acanthoic acid. The described synthesis confirms the proposed stereochemistry of the natural product and represents a fully stereocontrolled entry into an underexplored class of biologically active diterpenes.

Anti-Inflammatory Agents, Non-Steroidal↗
PubMed2001

New fluorescent probes for the measurement of cell membrane viscosity.

BACKGROUND: Molecular rotors are fluorescent molecules that exhibit viscosity-dependent fluorescence quantum yield, potentially allowing direct measurements of cell membrane viscosity in cultured cells. Commercially available rotors, however, stain not only the cell membrane, but also bind to tubulin and migrate into the cytoplasm. We synthesized molecules related to 9-(dicyanovinyl)-julolidine (DCVJ), which featured hydrocarbon chains of different length to increase membrane compatibility. RESULTS: Longer hydrocarbon chains attached to the fluorescent rotor reduce the migration of the dye into the cytoplasm and internal compartments of the cell. The amplitude of the fluorescence response to fluid shear stress, known to decrease membrane viscosity, is significantly higher than the response obtained from DCVJ. Notably a farnesyl chain showed a more than 20-fold amplitude over DCVJ and allowed detection of membrane viscosity changes at markedly lower shear stresses. CONCLUSIONS: The modification of molecular rotors towards increased cell membrane association provides a new research tool for membrane viscosity measurements. The use of these rotors complements established methods such as fluorescence recovery after photobleaching with its limited spatial and temporal resolution and fluorescence anisotropy, which has low sensitivity and may be subject to other effects such as deformation.

Cell Membrane↗
PubMed2000

Stereoselective synthesis of (-)-acanthoic acid.

[reaction: see text] The first stereoselective synthesis of (-)-acanthoic acid (1) has been designed and accomplished. Our synthetic plan departs from (-) Wieland-Miesher ketone (7) and calls upon a Diels-Alder cycloaddition reaction for the construction of the C ring of 1. The described synthesis confirms the proposed stereochemistry of 1 and represents an efficient entry into an unexplored class of biologically active diterpenes.

Anti-Inflammatory Agents, Non-Steroidal↗
PubMed2000

Enantioselective synthesis of the [6,6] spiroketal core of reveromycin A.

[structure: see text] Reveromycin A (1) belongs to a family of microbial polyketides with unusual structural features and biological activities. The structure of 1 is composed of a [6,6] spiroketal core decorated with highly unsaturated side chains. As a prelude to the synthesis of 1, we present herein a short, efficient, and enantioselective synthesis of the C9-C21 fragment 5 (spiroketal core) of reveromycin A.

Antineoplastic Agents↗
PubMed2000

[Changes of cytokines secreted by human oral mucosa keratinocytes from oral submucous fibrosis in vitro].

OBJECTIVE: To assess the significance of oral mucosa keratinocytes (KCs) and cytokines in the development of oral submucous fibrosis (OSF). METHODS: KCs were obtained and cultured from the buccal mucosa of healthy subjects who did not chew areca nut and patients with OSF who chewed areca nut. Then radioimmunoassay and enzyme-linked immunosorbent assays were employed, and endothelin (ET) and transforming growth factor beta 1 (TGF beta 1) were quantified in culture supernatants. RESULTS: The mean levels of ET and TGF beta 1 secreted by OSF-KC were 96.983 +/- 17.802 pg/ml and 4661.641 +/- 783.893 pg/ml respectively, which were higher than these secreted by NM-KC (P < 0.05); There was a positive correlation between the levels of ET and TGF beta 1 secreted by OSF-KC. CONCLUSION: External stimuli such as areca nut components may induce the development of OSF by activating and stimulating the keratinocytes to secret a series of cytokines, including ET and TGF beta 1. It is speculated that ET and TGF beta 1 may be the contributing factors in the pathological features noted in OSF.

Endothelins↗
PubMed2000

[A study on the clinical classification of oral submucous fibrosis].

OBJECTIVE: To increase the positive rate and sensitivity of the diagnosis for oral submucous fibrosis (OSF). METHODS: A general oral survey of 11,046 persons was carried out in Xiangtan, Hunan. According to Pindborg's diagnostic standard to epidemiological studies of OSF, 335 cases of OSF were found. The prevalence was 3%. According to different clinical manifestations, 335 cases of OSF were divided into two types: diffuse type and localized type. The cases with typical features of OSF, such as burning pain and discomfort, dryness of the mucosa, progressive inability to open the mouth and presence of palpable bands in the oral mucosa and so on, were in the diffuse type. Those with non-typical features, only having presence of palpable bands in the oral mucosa, were in the localized type. 72 cases were followed-up for ten years. RESULTS: 335 cases of OSF were divided into two types. 13 cases (3.9%) were in the diffuse type, and 322 cases (96.1%) were in the localized type. Most of the OSF in this region belonged to the localized type. It was also discovered that without proper treatment, the subjects sticked to one type of OSF without changing from one type to another after ten years of follow-up. CONCLUSION: Localized type of OSF is the major type of OSF in Xiangtan. It is an independent clinical type. To classify OSF, it is good for the clinicians to pay attention to non-typical OSF. If the non-typical OSF cases are taken into consideration, the prevalence of OSF will increase considerably.

China↗
PubMed1999

Enantioselective Total Synthesis of Avarol and Avarone.

Formation of the C11-C1' bond through application of Barton's radical decarboxylation and quinone addition is the cornerstone of a new convergent and concise synthesis of the marine metabolites avarol (1) and avarone (2; see scheme), for which antimitotic, antileukemic, and antiviral effects have been reported.

Journal Article↗
PubMed1999

[Research on inhibition of areca nut extract on human buccal keratinocytes].

OBJECTIVE: To culture human oral mucosa epithelial cells in vitro and study the mechanism of changes in the epithelia of oral submucous fibrosis (OSF). METHODS: The keratinocytes were obtained from normal buccal mucosa (NM-KC) and OSF buccal mucosa (OSF-KC) with dispase trypsine and cultured in vitro. Then the cell proliferation of keratinocytes incubated with or without areca nut extract in the presence of 10% fetal calf serum for 48 hours at 37 degrees C in 5% CO2 and air were monitored by use of thiazolyl blue (MTT) assay. RESULTS: Primary culture grew in small islands that coalesced at confluency. Ultrastructurally the cells contained a large of tonofilament and microvilli. Immunohistochemistry demonstrated uniform staining of the cells with antibodies to keratins. There was no difference in cell proliferation between OSF-KC and NM-KC, and areca nut extract inhibited keratinocyte proliferation in a concentration-dependent manner. CONCLUSION: The results suggested that utilizing dispase II can establish fibroblast-free culture for growing of human oral mucosa keratinocytes and areca nut extract is a cytotoxic agent to human buccal keratinocytes.

Areca↗
PubMed1997

[Expression of transforming growth factor beta 1 in keratinocytes of oral submucous fibrosis tissue].

To explore significance of transforming growth factor beta 1 (TGF beta 1) in the pathogenesis of oral submucous fibrosis (OSF), TGF beta 1 mRNAs in keratinocytes of the paraffin embeded tissues of 25 OSF cases, 5 normals (NOR) and 10 oral lichen planus (OLP) were determined by the in situ hybridization technique. The result showed that there was an expression of TGF beta 1 mRNA in keratinocytes of 15 OSFs (60%). The positive expression of TGF beta 1 mRNA was mainly in kerationcytes of early and middle stage OSF. There was no expression in that of 5 NORs and 10 OLPs. The study suggests that keratinocytes of OSF tissue may synthesize and release TGF beta 1 which may play an important role in the pathogenesis of OSF and participate as a mediator in the pathogenetic process of OSF.

Humans↗
PubMed1997

[Experimental study on aqueous areca nut extracts inducing oral submucous fibrosis in rats. I. Observation of histomorphology].

The purpose of this study was to establish the animal model of oral submucous fibrosis (OSF) in buccal mucosa of SD rats by submucosa injecting and surface painting aqueous areca nut extracts (AANE). The animals of all groups were killed randomly in the 12th, 16th, 22nd and 28th week. The buccal mucosae were collected, and were detected by light microscope and transmission electron microscope. The results were obtained: at different stages, the OSF-like lesions appeared in different degrees among some animals of the model groups, including atrophic epithelium with loss or partial loss of rate pegs, inflammation, accumulation and disorder of collagen fibre in juxta-epithelial region, along with concomitant muscle degeneration. The lesions didn't reverse obviously themselves after the authors stopped using AANE. Histomorphologic changes didn't appear in any animal of the control groups. The results indicated that the typical and stable OSF animal model were induced rapidly by submucosa injecting and surface painting AANE.

Animals↗
PubMed1997

[Experimental study on aqueous areca nut extracts inducing oral submucous fibrosis in rats. II. Effection of mast cells on collagen metabolism].

The effection of mast cells (MC) on collagen metabolism of oral submucous fibrosis (OSF) induced by aqueous areca nut extracts (AANE) in rats was studied by transmission electron microscope, histochemical and biochemical analyses. The results revealed that there was a close relationship between MC and fibroblats (FB) in the pathogensis of OSF; MC which appeared in the buccal mucosa in the model groups increased significantly and became more active in the function. A great deal of collagen compacted in the buccal mucosa in the model groups. The contents of tissue hydroxyproline (Hyp) in the model groups were obviously higher than those in the control groups. Moreover, the longer the time of irritation continued, the higher the contents were. The number of MC had a higher positive correlation with the contents of tissue Hyp at the same time. Total serum Hyp had no significant difference among all the groups and any stages. The results indicated that some aqueous components of areca nuts might disturb collagen metabolism by accumulation and activation of MC.

Animals↗
PubMed1993

High-level expression of porcine fructose-1,6-bisphosphatase in Escherichia coli: purification and characterization of the enzyme.

A cDNA encoding porcine fructose-1,6-bisphosphatase was isolated from total pig liver RNA. The enzyme's coding sequence was fused to the bacteriophage T7 gene 10 promoter and transcription terminator sequence and expressed in E. coli under control of the T7 RNA polymerase. Induced cells contain elevated levels of fructose-1,6-bisphosphatase enzymatic activity and an abundant 37,000 dalton protein. The enzyme was purified to apparent homogeneity and judged identical to wild-type porcine fructose-1,6-bisphosphatase. The kinetic parameters are similar to those reported for the pig kidney enzyme. The N-terminal amino acid sequence is identical to the predicted sequence and the kinetic parameters are consistent with freedom from proteolysis. As estimated from enzymatic activity and visual inspection of coomassie blue-stained SDS-PAGE gels, porcine fructose-1,6-bisphosphatase constitutes as much as 20% of the soluble protein from the over-expressing E. coli strain.

Amino Acid Sequence↗
PubMed1990

Effects of various granulating systems on the bioavailability of naproxen sodium from polymeric matrix tablets.

Naproxen sodium and a cellulose ether derivative were granulated with either water or a poly(meth)acrylic acid ester copolymer aqueous dispersion to make three controlled-release matrix dosage forms. The different polymeric matrix systems contained hydroxypropyl methylcellulose (formulation A), hydroxypropyl cellulose:poly(meth)acrylic acid ester copolymer (formulation B), and hydroxypropyl methylcellulose:poly(meth)acrylic acid ester copolymer (formulation C). All three hydrophilic matrix tablets demonstrated identical in vitro dissolution rates. The three controlled-release formulations were compared with a marketed immediate-release naproxen sodium dosage form (formulation D) in a single-dose crossover study in six healthy volunteers. The AUC values for controlled-release dosage forms A and C were larger than those for formulations B and D. However, the reasons why the AUC for formulations A and C is larger than that for formulations B versus D can be explained differently. Formulations A and C more effectively maintain naproxen plasma levels than formulation D by reducing the amount of naproxen unbound to plasma proteins, therefore reducing naproxen available for urinary excretion. Naproxen sodium delivered from formulations A and C is also probably much better absorbed than from that from formulation B, possibly due to less drug entrapment. More importantly, although all three CR formulations had identical in vitro dissolution profiles, naproxen sodium plasma levels were better maintained (based on AUC) in subjects taking formulations A and C, which contained a lower polymer content and did not use hydroxypropyl cellulose. The tmax values were larger for the three controlled-release dosage forms. Also, the Cmax value for the conventional dosage form was nearly twofold higher than that observed for the controlled-release dosage forms.

Adult↗
PubMed1990

Outbreaks of infection with methicillin-resistant Staphylococcus aureus on neonatal and burns units of a new hospital.

Multiple introductions of methicillin-resistant Staphylococcus aureus (MRSA) strains occurred to a new hospital in Hong Kong. Two years of clinical microbiological surveillance of the resulting outbreaks was combined with laboratory investigation by phage and antibiogram typing, and plasmid profiling. The outbreaks on the special care baby (SCBU) and burns (BU) units were studied in detail, and colonization of staff and contamination of the environment were investigated. MRSA were spread by the hands of staff on the SCBU, where long-term colonization of dermatitis was important, but were probably transmitted on the BU by a combination of the airborne, transient hand-borne and environmental routes. Simple control measures to restrict hand-borne spread on the SCBU were highly effective, but control was not successful on the BU.

Burn Units↗