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Biomedical subjects

X Jin

Publications and source records attributed to X Jin.

At least 163 records · Page 9Linked to original sources
PubMed1995

Comparison of base inclination of ribo-AU and deoxyribo-AT polymers.

The inclination angle between the base normal and the helix axis is measured for ribo-AU polymers by using flow linear dichroism (LD), and compared to measurements for deoxyribo-AT polymers under dehydrating conditions. The CD of the DNA polymers under the dehydrating conditions is not the same as the corresponding RNA polymers, which are presumed to be in the A form. However, the LD indicates that poly(dAdT)-poly(dAdT) can assume the A form in 80% 2,2,2-trifluoroethanol, although poly(dA)-poly(dT) retains B form structure in this dehydrating solvent. The inclination angles are similar for B form poly(dAdT)-poly(dAdT) and poly(dA)-poly(dT), and these parameters are also similar for A form poly(rArU)-poly(rArU) and poly(rA)-poly(rU). All inclination axes are similar.

Adenine↗
PubMed1995

Comparison of base inclination of ribo-GC and deoxyribo-GC polymers, and synthesis of poly(rGrC)-poly(rGrC).

The inclination angle between the base normal and the helix axis, and the axes around which the bases incline, are measured for ribo-GC polymers in buffer by using flow linear dichroism (LD), and compared to measurements for deoxyribo-GC polymers in buffer and under dehydrating conditions. A new method is designed to synthesize poly(rGrC)-poly(rGrC), which is not available commercially, in large quantities. The LD of this RNA reveals inclination angles that are similar to the B-form DNA in buffer, although the axes are different. The CD of poly(dGdC)-poly(dGdC) under the dehydrating conditions is similar to poly(rGrC)-poly(rGrC), indicating it is in the A form, and the LD gives larger inclination angles than either the B form or the corresponding RNA. Poly(dG)-poly(dC) is in the A form in buffer. Comparison among poly(rG)-poly(rC) in buffer, and poly(dG)-poly(dC) in buffer under dehydrating conditions, reveals similar inclination angles and axes, although the LD shows that the DNA has the largest inclination angles. Except for poly(rGrC)-poly(rGrC), which has a unique reduced dichroism, all the axes for G are similar, as are the axes for C.

Circular Dichroism↗
PubMed1995

A practical method for preparing peroxynitrite solutions of low ionic strength and free of hydrogen peroxide.

The reaction of ozone (approximately 5% in oxygen) with sodium azide (0.02-0.2 M in water) at pH 12 and 0-4 degrees C is shown to yield concentrated, stable peroxynitrite solutions of up to 80 mM. The product of this reaction is identified based on a broad absorption spectrum with a maximum around 302 nm and by its first-order rate of decomposition (k = 0.40 +/- 0.01 s-1 at pH 7.05 and 25 degrees C). These peroxynitrite solutions can be obtained essentially free of hydrogen peroxide (detection limit 1 microM) and only traces of azide (detection limit 0.1 mM). They are low in ionic strength and have a pH of about 12 but without buffering capacity; therefore, they can be adjusted to any pH by addition of buffer. These preparations of peroxynitrite frozen at -20 degrees C show negligible decomposition for about 3 weeks of storage and follow a first-order decomposition with a halflife of about 7 days at refrigerator temperatures (approximately 5 degrees C). These preparations give reactions that are characteristic of peroxynitrite. For example, at pH 7.0, they react with L-tyrosine to give a 7.3 mol % yield of nitrotyrosine(s), and with dimethyl sulfoxide to give a 8.2 mol % yield of formaldehyde, based on starting peroxynitrite concentration.

Azides↗
PubMed1995

Higher lung cancer risk for younger African-Americans with the Pro/Pro p53 genotype.

A restriction fragment length polymorphism in codon 72 of the p53 gene has been implicated in lung cancer risk, although the functional significance of the polymorphism has not been determined. This association was examined in 109 lung cancer cases (67 African-American and 42 Mexican-American) and 114 controls (74 African-American and 40 Mexican-American) identified from a molecular epidemiological study of lung cancer. The susceptible Pro/Pro genotype was associated with a 1.56-fold higher risk of lung cancer in African-Americans and a 1.95-fold in Mexican-Americans, although neither estimate was statistically significant. In fact, the prevalence of the Pro/Pro genotype was only 2.5% in Mexican-American controls, compared with 20.3% for African-American controls. Patients with the susceptible genotype appeared to have earlier age at diagnosis and lower mean cigarette pack-year exposures than did patients with the Arg/Arg or Arg/Pro genotypes. Risk estimates for the susceptible genotype were 11.29 (1.1, 111.3) for patients < 53 years of age and 14.1 (1.5, 130.6) for patients who reported < 30 pack-years of smoking. The Pro/Pro genotype was not associated with elevated risk in older patients, nor with heavier smokers. If Pro/Pro is a susceptible genotype, the lower prevalence evident in Mexican-Americans may partly explain their lower rates of lung cancer.

Aged↗
PubMed1995

[Captopril in improving vascular structure and lowering blood pressure].

SHRs were given captopril 20 mg/kg/day (group A, n = 13) and 100 mg/kg/day (group B, n = 17) from intrauterus period to 16 weeks of age, then the treatment was removed. Experiments were carried out at 40 weeks. SBP, left ventricular mass/body weight ratio, wall/lumen ratio of branch III mesenteric and renal artery were determined. The perfusion pressure response to alpha 1 adrenergic agonist (phenylephrine) of resistance blood vessels in a hindquarter model in the presence of Nw-nitro-1-arginine-methyl ester (LNAME) or L-arginine were examined. Untreated SHR (n = 16) and untreated WKY (n = 17) served as controls. Both doses of captopril treatment completely prevented hypertrophy of vascular vessels to some extent comparable to that of the untreated WKY. But their SBP was still significantly higher than that of the untreated WKY. The curves of perfusion pressure responding to incremental doses of phenylephrine shifted rightward in the captopril treatment groups in a dose dependent manner. The curves of high dose group were almost identical to those of WKY, markedly different from that of the untreated SHR. Captopril decreased the over enhanced vasoconstrictor effect of LNAME in SHR. The attenuated vasoconstrictor effect by L-arginine was greatly augmented by captopril, suggesting that captopril improves the function of resistance of vessels by mediating endothelial cells. Captopril-induced alteration in vascular structure and function may be separated from its hypotensive effect. Clinically, continuing administration of captopril may be beneficial to the improvement of the vascular system in those blood pressure unresponsive patients.

Animals↗
PubMed1995

[Amylopsin activator in the decoction of fried malt].

From the decoction of fried malt (Fructus Hordei Germinatus) a kind of amylopsin activator was extracted and distinguished as calcium nitrate (with small amount of sodium chloride). The existence of this activator may can be explain properly why the decoction is helpful to digestion.

Calcium Compounds↗
PubMed1995

[Accumulation sites of kanamycin in cochlear basal membrane cells].

The dissection technique of cochlear basal membrane, the fractional technique of tissular homogenization, and the radiometry technique were used to study the toxicity of kanamycin on the hair cells. It was found that after the cochlea was perfused with a 0.25% perilymph solution of kanamycin, there were 3.14 fg KM in a nucleus, 7.61 fg KM in a mitochondria and 21.16 fg KM in a lysosome. It showed that after entering the cell, KM mainly accumulated with in the mitochondria. Simultaneously the lysosome also phagocytized a lot of kanamycin. The germicidal mechanism of kanamycin is to inhibit the synthesis of protein in bacteria and the mitochondria has the same way of protein synthesis, the mitochondria can combine with kanamycin specifically; the drug in lysosome may be related to its phagocytic function.

Animals↗
PubMed1994

One- and two-electron oxidations of methionine by peroxynitrite.

Peroxynitrite is stable, but its acid, HOONO, either rearranges to form nitrate or oxidizes nearby biomolecules. We report here the reactions of HOONO with methionine and the methionine analog 2-keto-4-thiomethylbutanoic acid (KTBA). These oxidations proceed by two competing mechanisms. The first yields the sulfoxide; the second-order rate constants, k2, for this process for methionine and KTBA are 181 +/- 8 and 277 +/- 11 M-1.s-1, respectively, at pH 7.4 and 25 degrees C. In the second mechanism, methionine or KTBA undergoes a one-electron oxidation that ultimately gives ethylene. We propose that the one-electron oxidant is an activated form of peroxynitrous acid, HOONO*, that is formed in a steady state mechanism. The ratios of the second-order rate constants for the ethylene-producing reaction (k*2) and the first-order rate constant to produce nitric acid (kN) for methionine and KTBA, k*2/kN, are 1250 +/- 290 and 6230 +/- 1390 M-1, respectively. Both ceric and peroxydisulfate ions also oxidize KTBA to ethylene, confirming a one-electron transfer mechanism. The yields of neither MetSO nor ethylene are affected by several hydroxyl radical scavengers, suggesting that a unimolecular homolysis of HOONO to HO. and .NO2 is not involved in these reactions. HOONO* gives hydroxyl radical-like products from various substrates but displays more selectivity than does the hydroxyl radical; thus, HOONO* is incompletely trapped by typical HO. scavengers. However, a mechanism involving dissociation of HOONO* to caged radicals cannot be ruled out at this time.

Chelating Agents↗
PubMed1994

Lung cancer among tin miners in southeast China: silica exposure, silicosis, and cigarette smoking.

The Dachang Tin Mine is an industrial facility with high rates of lung cancer compared to the resident population in Guangxi province in southern China. Historically, exposure to silica dust was very high in the 1950s, falling in recent years to levels in keeping with international standards. Radon levels in the mine are low. We report the findings of a case-control study nested into a cohort study on miners working in Dachang. Cases of lung cancer among miners incident from 1973-1989 were obtained from local comprehensive medical records covering workers employed at the mine. These were matched approximately 3 to 1 with miners randomly chosen from the district surrounding the mine within the same birth decade. Matched odds ratios of 2.42 (95% confidence limit [CL] 1.3, 4.4) for underground employment, 3.52 (95% CL 1.7, 7.5) for smoking, and 2.04 (95%) CL 1.2, 3.7) for silicosis as determined on chest film were noted. Multifactor analysis of unconditional logistic regression showed that among the risk factors for excess mortality from lung cancer only the years spent drilling underground and the cumulative smoking index (product of daily cigarette consumption and number of years smoking) were independent contributors to risk and there was no interaction observed. The presence of silicosis did not contribute to predicting risk independently of the years spent underground.

Case-Control Studies↗
PubMed1994

An epidemiological study on the relationship of ectopic pregnancy and the use of contraceptives in Beijing--the incidence of ectopic pregnancy in the Beijing area. Beijing Collaborating Study Group for Ectopic Pregnancy.

The incidence of ectopic pregnancy (EP) was studied through a 3-level monitoring network of maternal and child health care (MCH) in the entire Beijing area, including 82 hospitals, 19 MCH centers and 2 institutes for family planning. A total of 1,420 cases of EP were collected in a sample of 2.7 million women of reproductive age (15-49) during a one-year period from January 1 to December 31, 1990. The cases were confirmed by pathological examination or laparoscopy. In addition, epidemiological surveillance method was used. The results showed that the overall incidence of EP was 0.52 per thousand women of reproductive age (W = Women of reproductive age (15-49)) in the Beijing area, 0.6/1000W in the urban districts and 0.41/1000 in the rural area; 0.67/1000W married women, and 0.05/1000W in the unmarried. For married women, 0.54/1000W for those women using various contraceptive measures and 1.80/1000W for women using no contraceptives. The incidence of EP varies with different contraceptive methods. Female sterilization had the lowest incidence (0.18/1000W) and natural contraceptive measures (rhythm or withdrawal method) had the highest (2.43/1000W). It was 0.65/1000W in IUD users, 0.21/1000W in OC users and 0.57/1000W in couples using condoms or spermicides.

Adolescent↗