Search PubMed⌕ Search

Biomedical subjects

X Shan

Publications and source records attributed to X Shan.

8 recordsLinked to original sources
PubMed1992

Effect of chronic hypoxia on detoxication enzymes in rat liver.

Studies were performed to determine the effects of chronic hypoxia on enzymes that catalyze various detoxication reactions. Rats were exposed to room air or 10.5% O2 for 10 days, and microsomes and postmicrosomal supernatants were isolated from liver. Detoxication enzyme activities were measured by radiochemical and spectrophotometric assays, and immunoreactive protein amounts were measured by Western blot analysis. Total cytochrome P450, as measured by the CO-difference spectrum, and activities of superoxide dismutase (EC 1.15.1.1), epoxide hydrolase (EC 4.2.1.63), catalase (EC 1.11.1.6), glutathione disulfide reductase (EC 1.6.4.2), and glutathione (GSH) S-transferase (EC 2.5.1.18) were not affected by this extent of hypoxia. In contrast, 10 days of hypoxia decreased activities or immunoreactivities (% of aerobic) of GSH peroxidase (EC 1.11.1.9) (54%), cytochrome P450EtOH2 (42%), CYP3A1 (53%), sulfotransferase (EC 2.8.2.1) (77%) and UDP-glucuronosyltransferase (EC 2.4.1.17) (65%). Activity of glucose-6-phosphate dehydrogenase (EC 1.1.1.49), an important enzyme in NADPH production was also decreased to 56% of the aerobic value, but Western blot analysis showed that the amount of protein reactive with antibodies to glucose-6-phosphate dehydrogenase was not affected by hypoxia. Thus, hypoxia may decrease activity of enzymes by regulatory mechanisms even though the amount of immuno-detectable enzyme is unchanged. Liver cells isolated from rats exposed to hypoxia also gave lower GSH synthetic rates than cells from normoxic rats. This result, together with the effect of hypoxia on glucose-6-phosphate dehydrogenase, indicates that the GSH supply for GSH-dependent detoxication reactions may be limited due to chronic hypoxia. To test directly whether chronic hypoxia increased sensitivity to a compound normally detoxified by a GSH-dependent reaction, sensitivity to tert-butyl hydroperoxide (t-BuOOH) of hepatocytes from rats exposed to in vivo hypoxia was compared to that from normoxic rats. The results showed that the cells from the hypoxic rats were much more sensitive to injury. Taken together, these results suggest that decreases in amounts and/or activities of detoxication enzymes during chronic hypoxia may result in increased susceptibility of cells to chemical injury.

Animals↗
PubMed1992

Spectroscopic studies of lipids and biological membranes: carbon-13 and proton magic-angle sample-spinning nuclear magnetic resonance study of glycolipid-water systems.

We have obtained 1H and 13C magic-angle sample-spinning (MAS) nuclear magnetic resonance (NMR) spectra of three glycosyldiacylglycerol-water (1:1, weight ratio) mesophases, at 11.7 T, as a function of temperature, in order to probe lipid headgroup, backbone, and acyl chain dynamics by using natural-abundance NMR probes. The systems investigated were monogalactosyldiacyldiglyceride [MGDG; primarily 1,2-di[(9Z,12Z,15Z)octadec-9,12,15-trienoyl++ +]-3-beta-D-galactopyranosyl- sn-glycerol]; digalactosyldiacyldiglyceride [DGDG; primarily 1,2-di[(9Z,12Z,15Z)octadec-9,12,15-trienoyl++ +]-3- (alpha-D-galactopyranosyl-1-6-beta-D-glactopyranosyl)-sn-glycerol] ; and sulfoquinovosyldiacyldiglyceride [SQDG; primarily 1-[(9Z,12Z,15Z)octadec-9,12,15-trienoyl]-2 -hexadecanoyl-3-(6-deoxyl-6- sulfono-alpha-D-glucopyranosyl)-sn-glycerol]. At approximately 22 degrees C, all three lipid-water systems give well-resoled 13C and 1H MAS NMR spectra, characteristic of fluid, liquid-crystalline mesophases. 13C spin-lattice relaxation times of the headgroup and glycerol backbone carbons of all three materials give, within experimental error, the same NT1 values (approximately 400 ms), implying similar high-frequency motions, independent of headgroup size and charge. Upon cooling, pronounced line broadenings are observed, due to an increase in slow motional behavior. For each lipid, the onset of line broadening is seen with the glycosyl headgroup, glycerol backbone, and the first two or three carbons of the acyl chains. By approximately -20 degrees, all headgroup carbon resonances are broadened beyond detection. Both galactose moieties in DGDG "freeze out" together, implying a rigid-body motion of the disaccharide unit. Upon further cooling, the bulk polymethylene chain resonances in all three systems (in both 13C and 1H MAS) broaden greatly, followed by the olefinic and allylic carbon resonances.(ABSTRACT TRUNCATED AT 250 WORDS)

Carbohydrate Conformation↗
PubMed1992

[A molecular analysis of females with 46,XY or 47, XYY karyotype].

In this paper, 4 females of 46,XY and one of 47,XYY karyotype were studied by Southern blotting using 10 Y-DNA probes. The results showed that 3 cases of 46,XY and the one 47,XYY had not lost any Y-specific fragment, while one 46, XY had lost a 15 kb Y-specific fragment, as detected by pDP34. The cause of these 46,XY and 47,XYY karyotypes could not be explained by the theory of X-Y unequal exchange in meiosis. It was postulated that an alternative genetic mechanism, such as gene mutation or defective gonad receptor, might be related to sex reversion in these patients.

Adult↗
PubMed1991

[Loss of Ha-ras alleles in DNA from gastric carcinoma tissue of Chinese individuals].

In this study, a human c-Ha-ras-1 6 kilobase recombinant clone (EcoRI fragment) was used as a probe, DNA from 13 gastric carcinoma patients heterozygous for the Ha-ras locus contained two Ha-ras-related BamHI restriction fragments. Southern blotting results showed similar patterns of allelic restriction fragments between gastric carcinoma and normal gastric tissue DNA in 12 cases. But one heterozygous patient (6.3kb/7.8kb) lost a 6.3kb allelic restriction fragment in the gastric carcinoma tissue. We also examined the RFLPs of the Ha-ras oncogene in one pedigree of a heterozygous gastric carcinoma patient. The results showed that one daughter had lost one Ha-ras allele in WBC DNA. This Ha-ras allele loss may have resulted from a mitotic nondisjunction or a mitotic recombination event.

Alleles↗
PubMed1990

[Study on Ha-ras RFLPs in gastric carcinoma and normal tissue DNAs of Chinese individuals].

By using recombinant plasmid PHS-49 as a probe, BamHI restriction fragment length polymorphisms (RFLPs) was studied in tumour DNAs of 36 gastric carcinoma patients and normal tissue DNAs of 25 unaffected Chinese individuals. Ten alleles and eighteen genotypes for Ha-ras gene were found. Four "rare" restriction fragments of size less than 6 kilobase pairs (kb) are first reported for Ha-ras locus in present paper, we inferred that these alleles might be one of the characteristics of genetic polymorphisms in Chinese population. Moreover, the frequency of some "rare" alleles and genotypes occurred in gastric carcinoma samples is significantly higher than that occurred in normal individuals. The results of pedigree analysis for two patients showed that some heterozygotes carried three or four alleles. It suggested that there may be more than one copy of Ha-ras gene sequence existed in a chromosome. The possible causes of the phenomenon mentioned above were discussed.

Alleles↗
PubMed1990

[Saccadic sinusoidal tracking test].

This paper introduces a new method of ENG-Saccadic sinusoidal tracking test (SSTT). In 4 of the 55 cases with peripheral vestibular lesions, the results were abnormal. But among 50 cases with central lesions, 40 cases were abnormal. In 50 control cases, no abnormalities were found. The results showed that SSTT might be of great value in differential diagnosis of central Lesions.

Adult↗
PubMed1989

Oxygen dependence of glutathione synthesis in hepatocytes.

The O2 dependence of glutathione (GSH) synthesis was studied in freshly isolated hepatocytes of white male rats. The rate of synthesis with methionine as the sulfur-containing amino acid precursor was decreased at hypoxic O2 concentrations and was half-maximal at 5 microM O2. ATP-dependent formation of S-adenosylmethionine was the rate-limiting step in GSH synthesis under these hypoxic conditions as shown by studies of S-adenosylmethionine concentrations and effects of compounds that inhibit mitochondrial ATP production. GSH synthesis with cysteine as the sulfur-containing precursor amino acid was relatively resistant to O2 deficiency. The rate under anoxia was 48% of the aerobic rate and the O2-dependent rate was half-maximal at 0.9 microM O2. These results indicate that GSH synthesis from methionine is likely to be impaired under physiological and pathological conditions involving hypoxia, but synthesis from cysteine is not likely to be greatly affected except during anoxia. In addition, the sensitivity of the cystathionine pathway to hypoxia suggests that other products of the pathway, such as choline, creatine, epinephrine, and methylated tRNA's, may also be decreased by hypoxia.

Adenosine Triphosphate↗