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Biomedical subjects

Y K Li

Publications and source records attributed to Y K Li.

At least 37 records · Page 2Linked to original sources
PubMed1993

[Management of primary retroperitoneal tumors].

Of 78 patients with primary retroperitoneal tumors, 38 were male and 40 female on the average 41 years age. Twenty-seven patients (35%) had benign tumors, 51 (65%) malignant. The biggest tumor weighted 28.5 kg. Complete resection was performed in 57 patients (73.1%), palliative in (11.5%). 64.7% of the patients with malignant tumor underwent complete resection with 1, 3, 5 year survival rates of 84.9%, 72.6% and 62.2%, respectively. Our experience showed that CT not only detected the mass, but also clearly defined its relationship to the adjacent viscera and vessel. It is suggested that embloc resection of the entire tumor with involved organs and tissues be used to decrease local recurrence and enhance the survival rate. The importance of aggressive reoperation for recurrence was also emphasized.

Adolescent↗
PubMed1993

[Two new isoprenyl flavonoids from the leaves of Glycyrrhiza uralensis Fisch].

In previous papers, we reported flavonoids isolated from the leaves of Glycyrrhiza uralensis on the west of Inner Mongolia. Three of these flavonoids had the isoprenyl on the B ring, one was phenolic glucoside and six were flavonoidic glucosides. In the present paper, we report the isolation and identification of flavonoids from the leaves of this plant. The structures of these compounds have been identified as 5,7,3',4'-tetrahydroxy-3-methoxy-5'- isoprenylflavone(I),5,6,3',4'-tetrahydroxy-3-methoxy-6'-isopren ylfavone(II) and quercetin (III) by chemical method and spectroscopic analyses. I and II are new compounds and named uralenol-3-methylether and uralene, respectively. III was found for the first time in this species.

Flavonoids↗
PubMed1993

[Management of perirenal liposarcoma].

Eighteen cases of perirenal liposarcoma were treated from 1969 to 1991. The average age of patients was 49 years (range 32-66 years). The main clinical features were abdominal mass and compression symptoms. Eight tumors originated from the right side and ten from the left. Sixty seven percent of the patients previously underwent one to three surgical procedures (laparotomy 3 cases, recurrence 9 cases). Tumors were resectable in all patients. The smallest tumor was 14 x 12 x 10 cm in size, the largest was 65 x 45 x 24 cm and 24 kg in weight. Preserved kidney was found to be highly related with local recurrence. Therefore, enbloc resection of the tumor with the kidney should be the operation of choice.

Adult↗
PubMed1992

Partitioning of the chicken genome by microcell hybridization.

Chicken fibroblast cells isolated from 7-day-old White Leghorn S-line chicken embryos were used for microcell hybridization. Cells transfected with a pSV2-neo plasmid, which carries the Neor gene and confers resistance to geneticin (G418), were selected and maintained in medium containing G418 (350 micrograms/mL). Cells were micronucleated by colcemid arrest and hypotonic treatment. Enucleation was carried out by centrifugation in a Percoll gradient in the presence of cytochalasin B. Purified microcells and HeLa S3 cells were mixed and agglutinated by addition of phytohemagglutinin P, followed by polyethylene glycol fusion to generate microcell hybrids. Chicken by human microcell hybrids were selected in RPMI-1640 medium containing 1.4 mg/mL G418. Cloned hybrid cell lines were maintained in the same medium containing .7 mg/mL of G418. The presence of chicken chromosomes in hybrid cells was demonstrated by cytogenetic analysis and high-resolution nonisotopic chromosomal in situ hybridization. Three out of 28 hybrid cell lines analyzed retained single chicken chromosomes.

Animals↗
PubMed1992

[Effects of tetramethylpyrazine and ferulic acid alone or combined on vascular smooth muscle, blood viscosity and toxicity].

The experiments showed that both tetramethylpyrazine and ferulic acid relaxed the norepinephrine-induced spasmodic contraction of rabbit and rat aorta strips, increased the coronary flow of isolated guinea pig hearts and reduced the whole blood viscosity in rats. Evaluated with Burgi's equation, the combined effect of these 2 drugs was obviously potentiated, but the combined acute toxicity in mice was greatly reduced.

Animals↗
PubMed1992

Inhibitory effect of rhynchophylline on platelet aggregation and thrombosis.

Rhynchophylline (Rhy) inhibited rabbit platelet aggregation induced by arachidonic acid (AA), collagen, and ADP. The values of IC50 were 0.72, 0.74, and 0.67 mmol.L-1, respectively. Rhy reduced the thromboxane B2 (TXB2) generation in PRP induced by collagen but failed to reduce that induced by AA. Rhy suppressed malondialdehyde (MDA) formation in platelet suspension stimulated by thrombin, inhibited the platelet factor 4 (PF4) release. It did not alter intraplatelet cAMP concentration. Rhy 10-20 mg.kg-1 iv showed a significant inhibition of venous thrombosis and cerebral thrombosis in rats.

Alkaloids↗
PubMed1991

Facile formation of a crosslinked adduct between DNA and the daunorubicin derivative MAR70 mediated by formaldehyde: molecular structure of the MAR70-d(CGTnACG) covalent adduct.

MAR70 is a synthetic derivative of the anticancer drug daunorubicin that contains an additional sugar, attached to the O4' of daunosamine. When MAR70 was crystallized with the DNA hexamer d(CGTnACG), where nA is 2-aminoadenine, a covalent methylene bridge was formed between the N3' of daunosamine and the N2 of 2-aminoadenine. This spontaneous reaction occurred through the crosslinking action of formaldehyde. The crosslink was demonstrated by the three-dimensional structure of the 2:1 adduct between MAR70 and d(CGTnACG) solved at 1.3-A resolution by x-ray diffraction analysis. The perfect juxtaposition of the two amino groups in the complex provides a template for efficient addition of formaldehyde. This adduct structure is compared with the analogous structure at 1.5-A resolution of the complex of MAR70-d(CGTACG), in which no formaldehyde addition was observed. In both complexes, two MAR70 molecules bind to the DNA hexamer double helix; the elongated aglycon chromophore is intercalated between the CpG steps and spans the G.C Watson-Crick base pairs. The disaccharides occupy nearly the entire minor groove of the distorted B-DNA hexamer double helix. The second sugar is in contact with the sugar-phosphate backbone and does not affect the binding interactions of the daunorubicin portion to DNA. The structure allows us to model the binding to DNA of drugs having more extensive oligosaccharides. In addition, it suggests that placing a reactive (e.g., alkylating) functional group at the N3' amino position of daunorubicin might be a fruitful route for designing anticancer drugs.

Antineoplastic Agents↗
PubMed1991

Alkylation of glyceraldehyde-3-phosphate dehydrogenase with haloacetylphosphonates. An unusual pH-dependence.

Two new alkylating reagents, chloro- and bromo-acetylphosphonate, were found to be very effective thiol-blocking reagents. The pH-dependence of the reaction of BAP with 2,4-dinitrothiophenol (25 degrees C, I 0.5) shows a tailing bell-shaped curve (with a plateau at high pH) characteristic of two ionizing groups: the thiol group (pKa 3.2) and the phosphonate group (pKa2 4.6). The rate constant for the reaction of the monoanionic inhibitor with dinitrothiophenolate (k2 = 7 M-1.s-1) is 120 times larger than that of the dianionic species. The haloacetylphosphonates were found to be irreversible inhibitors of glyceraldehyde-3-phosphate dehydrogenase from a variety of sources. They react with the active-site thiol group (Cys-149) and are half-site reagents with yeast glyceraldehyde-3-phosphate dehydrogenase. Thus, when two of the identical four subunits are modified the enzyme is catalytically inactive. The effects of pH (7-10), 2H2O and NAD+ on the reaction with the yeast enzyme were examined in detail. NAD+ enhances the alkylation rates. The second-order rate constant does not show a simple sigmoidal dependence on pH but rather a tailing bell-shaped curve (pKa 7.0 and 8.4) qualitatively similar to that obtained with dinitrothiophenol. There is no significant solvent isotope effect on the limiting rate constants and a normal isotope effect on the two pKa values. The results are consistent with the more reactive enzyme species containing a thiolate and an acidic group that may either donate a proton to the dianionic haloacetylphosphonate or orient the inhibitor.

2,4-Dinitrophenol↗
PubMed1991

Formaldehyde cross-links daunorubicin and DNA efficiently: HPLC and X-ray diffraction studies.

Formaldehyde (HCHO) cross-links the anticancer drug daunorubicin (DAU) to DNA efficiently. When DAU is mixed with DNA hexamers, d(CGCGCG) and d(CGTDCG), in the presence of HCHO, stable covalent adducts of DNA are formed, as shown by the HPLC analyses. The major adducts are identical with the materials in the respective crystals which can be readily obtained from the 1:1 mixture of DAU-d(CGCGCG) and DAU-d(CGTDCG) plus HCHO, but not from the solution without HCHO. The high-resolution (1.5 A) X-ray crystal structure of those adducts shows unambiguously that they contain a covalent methylene bridge between the N3' of daunosamine and the N2 of the guanine or 2-aminoadenine. The perfect juxtaposition of the two amino groups in the minor groove of the complex provides a template for an efficient addition of HCHO. The methylene bridge does not perturb the conformation of the drug-DNA complex, when compared to the structure of DAU-d(CGTACG). The results suggest new approaches for synthesizing a new type of potential anticancer drug by attaching a reactive (e.g., alkylating) functional group at the N3' amino position of daunorubicin/doxorubicin. The stable drug-DNA adduct may be useful as probes for other biological studies.

Base Sequence↗
PubMed1991

[Effect of rhyncophylline on platelet aggregation and experimental thrombosis].

Rhyncophylline (Rhy) produced a potent inhibition of rat platelet aggregation in ex vivo. TXA2 generation in platelet rich plasma from rats treated with Rhy obviously decreased in the collagen-induced group, but was not altered in the AA-induced group. These results suggest that Rhy suppressed the release of AA from platelet phospholipids stimulated by collagen, and this may be one of the mechanisms related to its action on platelet aggregation. Pretreatment with ASA, but not Rhy, reduced plasma PGI2 in rats. In the in vitro system, the PGI2 synthesis in rat aorta was shown to be inhibited by ASA but was not by Rhy. Rhy significantly reduced the number of mice died due to thrombosis by platelet aggregates. ASA prevented collagen plus adrenaline induced thrombotic death while Rhy prevented both ADP and collagen plus adrenaline induced thrombotic death.

6-Ketoprostaglandin F1 alpha↗
PubMed1989

Inhibition of beta-glucosidase by imidazoles.

Over 25 nitrogen-containing heterocycles were tested as inhibitors of sweet almond beta-glucosidase (EC 3.2.1.21). Among the most potent of these are some imidazole derivatives. The pH dependence indicates that the unprotonated inhibitor binds most tightly to the catalytically active species of the enzyme. This is analogous to the situation with 1-deoxynojirimycin where the permanently cationic species, N,N-dimethyl-1-deoxynojirimycin, binds at least two orders of magnitude less tightly to the enzyme than does the unprotonated 1-deoxynojirimycin. The binding of imidazole derivatives show a general tendency of increasing affinity with increasing basicity (beta approximately 0.4). One derivative which shows a significant positive deviation from this correlation (- log Ki vs. pKa) is 4-phenylimidazole. 4-Phenylimidazole is one of the most potent reversible inhibitors of beta-glucosidase with a pH-independent Ki = 0.8 microM. It is also fairly specific for beta-glucosidase, binding at least three orders of magnitude less tightly to any of the other exoglycosidases tested. This inhibitor combines, in a mono-molecular species, the binding affinities of benzene, which binds at the hydrophobic aglycone binding site, and imidazole, which binds at the sugar binding site of beta-glucosidase. The binding energy of 4-phenylimidazole can be attributed to the sum of the intrinsic binding energies of the phenyl and imidazole moieties. Thus, there is no significant entropic advantage of combining the component parts of phenylimidazole in a single species. This indicates that there is no significant uncompensated entropy loss upon binding of either benzene or imidazole to the enzyme. Nevertheless, the additivity of binding energy, even in the absence of an entropic advantage, results in the most powerful known inhibitor of the enzyme.

1-Deoxynojirimycin↗