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Biomedical subjects

Y M Li

Publications and source records attributed to Y M Li.

At least 109 records · Page 6Linked to original sources
PubMed1992

Phosphoryl group participation leads to peptide formation from N-phosphorylamino acids.

N-phosphorylated amino acids without a side chain functional group can transfer themselves into peptides after prolonged standing in solvents at warm temperatures. Seven N-phosphorylpeptides and free peptides were isolated and their structures determined. The phosphoryl group participation is the key to the peptide formation. An intramolecular mixed carboxylic-phosphoric anhydride intermediate was proposed for this type of reaction which might provide a clue to the function of the phosphoryl group in the phosphorylated enzymes and in the prebiotic synthesis of protein.

Amino Acid Sequence↗
PubMed1992

Pituitary epithelial cell implants reverse the accumulation of CD4-CD8- lymphocytes in thymus glands of aged rats.

Although implantation of GH3 pituitary epithelial cells has been shown to reverse thymic aging in rats, the differentiation pattern of T-lymphocytes within the reconstituted thymus glands has not been investigated. Syngeneic GH3 cells were implanted into 22-month-old female (old) Wistar-Furth rats. Eight weeks later, thymus glands and thymocyte subpopulations were compared to those in aged (24-month-old) and young (3-month-old) female Wistar Furth rats. We confirmed that implantation of GH3 cells increased (P less than 0.05) not only thymus size but also the number of thymocytes isolated from aged rats. Flow cytometric analysis using dual color direct immunofluorescence with fluorescein isothiocyanate-labeled anti-CD4 (W3/25) and phycoerythrin-labeled anti-CD8 (OX 8) monoclonal antibodies revealed that thymus glands from young rats had approximately 20% CD4-CD8- and 30% CD4+CD8+ cells. Thymus glands from old rats contained greater than 50% more CD4-CD8- cells and a reduced percentage of CD4+CD8+ lymphocytes compared to those of young rats (P less than 0.05). Moreover, both of these age-associated changes were reversed (P less than 0.05) by implanting GH3 cells. GH3-treated aged rats also had a significantly (P less than 0.05) greater proportion of CD4+CD8- thymocytes compared to aged control rats. There were no differences among the three groups of rats in the percentage of CD4-CD8+ thymocytes or in the percentage or intensity of cells expressing the T-cell markers CD3, T-cell receptor, or OX19. These results show that in aged rats, intrathymic maturation is inhibited at the key transitional stage where double negative cells differentiate into double positive cells, which may limit the diversity of the T-cell repertoire. The data also extend earlier results by demonstrating that GH3 epithelial cells promote not only growth, but also the differentiation of T-lymphocytes in the aging rat thymus.

Aging↗
PubMed1991

Effect of zinc upon cell attachment and proliferation on periodontally-diseased root surfaces.

The purpose of this study was to determine the effect of zinc ions on fibroblast attachment to periodontally-diseased root surfaces in vitro. Extracted periodontally-diseased teeth were treated with 0.5% ZnCl2 by iontophoresis at 0.5 mA for 2 to 6 minutes. Control groups were untreated diseased and untreated healthy teeth. Sections of the root underlying the pocket were cut from the diseased teeth. The specimens were incubated for 18 hours with L929 mouse fibroblasts, then transferred and incubated in cell-free medium for 48 hours. Cell attachment was evaluated by cell counts and scanning electron microscopy (SEM). Root surfaces were sampled with an acid-etch technique and zinc was measured with an atomic absorption spectrophotometer. Two samples from each group were examined for cell attachment with SEM. Data were analyzed using the appropriate statistical methods. The results showed that diseased, untreated root surfaces had significantly fewer cells attached; however, zinc iontophoresis did not significantly improve cell attachment to the diseased root surfaces. Zinc analysis showed that diseased, untreated root surfaces had a higher zinc content than healthy ones. SEM examination showed striking differences in cell attachment to healthy versus diseased root surfaces. The data indicated that zinc iontophoresis did not significantly enhance cell attachment to root surfaces of diseased teeth.

Cell Adhesion↗
PubMed1990

Detection of the target progenitor cells of granulomonopoietic enhancing activity.

Macrophage-derived granulomonopoietic enhancing activity (GM-EA) is a novel mediator that amplifies colony formation of myeloid progenitor cells (CFU-GM) in conjunction with colony-stimulating factors (CSFs), and is distinct from other hematopoietic synergizing factors such as interleukin (IL)-1, IL-4, and IL-6. In the present study, we try to ascertain whether or not there is a GM-EA-specific responsive myeloid progenitor cell population. Human bone marrow cells deleted of adherent cells and T lymphocytes were separated by velocity sedimentation into three subpopulations with respective sedimentation rates (millimeters per hour) of 7.4 +/- 0.4, 6.0 +/- 0.6, and 4.7 +/- 0.3. These subpopulations corresponded to the day 7 CFU-GM, day 14 CFU-GM, and the earlier myeloid progenitor cells, pre-CFU-GM, respectively. Pre-CFU-GM failed to respond to the colony-inducing effect of GM-CSF but could be stimulated by GM-EA alone to generate small clusters (5 to 25 cells) in soft agar after 14 days of incubation. Correspondingly, suspension preculture of the fractionated bone marrow cells also showed that only the progenitor cells with low sedimentation rate (4.7 mm/h) could be activated by GM-EA to generate CFU-GM. Taken together, our results suggest that the specific target cell of GM-EA is the pre-CFU-GM, and that GM-EA acts on these cells as a growth/maturation factor, but on the day 7 and day 14 CFU-GM as a synergistic growth factor.

Bone Marrow↗
PubMed1990

Glutathione augments in vitro proliferative responses of lymphocytes to concanavalin A to a greater degree in old than in young rats.

The proliferative response of splenocytes to concanavalin A (Con A) is significantly lower in aged than in young rats. The addition of reduced (GSH) but not oxidized (GSSG) gamma-glutamylcysteinyl-glycine (glutathione) in vitro totally reverses the defective proliferative response of splenocytes from aged rats. The inhibitor of gamma-glutamylcysteine synthetase, buthionine sulfoximine, abrogates the in vitro proliferation of splenocytes from young rats activated with Con A, and this effect is significantly reversed by addition of GSH. The enhancing effects of GSH on proliferation of Con A-activated splenocytes of both young and old rats are apparent as early as 24 h and are still evident as late as 72 h in culture. Both cysteine and 2-mercaptoethanol are able to mimic the effect of GSH in causing a greater increase in Con A-induced proliferative responses of splenocytes from old rats (eightfold) as compared to young animals (threefold). Although 2-mercaptoethanol increases expression of membrane-bound transferrin receptors on both Con A-activated splenocytes and T lymphocytes, this alone does not account for the greater enhancement of Con A-induced proliferation of splenocytes from old as compared to young rats. These data are consistent with the hypothesis that the glutathione peroxidase-dependent detoxification system is defective in T lymphocytes of aged rats.

Aging↗
PubMed1989

Genotoxic evaluation of chronic fluoride exposure: sister-chromatid exchange study.

As part of a continuing investigation, this study was conducted to examine the genotoxic effects of chronic exposure to sodium fluoride (NaF) in drinking water on the frequency of sister-chromatid exchange (SCE) in the bone-marrow cells of male Chinese hamsters. Animals at about 3 weeks of age were randomly assigned to 6 groups, each with at least 3 hamsters, and were maintained on a low fluoride diet (less than 0.2 ppm F) throughout the experiment. At 4 weeks of age, the animals in groups I-V began to receive drinking water containing fluoride at concentrations of 0, 1, 10, 50 and 75 ppm, respectively. Group VI was treated with cyclophosphamide and served as the positive control. The animals were sacrificed at 24 weeks of age by cervical dislocation. The humeri and plasma were analyzed for fluoride content, which was found to increase with the increase in fluoride concentration in drinking water. Slides of chromosomes from bone-marrow cells were prepared and blindly examined for the frequency of SCE. The mean scores of SCE for the hamsters receiving drinking water containing F concentrations up to 75 ppm for 21 weeks ranged from 4.28 to 6.28 per cell, and were not significantly different from those of the negative controls (4.60-5.44/cell). The results indicated that chronic fluoride exposure had no effect on the frequency of SCE in Chinese hamster bone-marrow cells under the conditions of the present investigation.

Animals↗
PubMed1989

[Effect of Rheum tanguticum Maxim ex Balf on cAMP in the central nervous system].

Rabbit model of fever was produced by means of subcutaneous inoculation of pneumocci. Third ventricular intubation and irrigation were carried out in rabbits. Irrigation fluid was collected during the stage of normal temperature, at the peak of fever and when the temperature was lowered by rhubarb. cAMP was detected with RlA in each of the three portions of the irrigated CSF. The result showed that cAMP level was raised during fever and decreased after rhubarb administration. Irrigation of CSF without medication had no significant influence on cAMP level.

Animals↗
PubMed1989

[Pulmonary complications after radiotherapy in lung cancer].

The appearance of the pulmonary injury after irradiation using 60Co-gamma-ray was investigated for 574 cases with carcinoma of the lung. In 437 patients these (76.2% of the total cases) radiation pneumonitis was seen, and the late radiation fibrosis was observed in 197 cases (29.1%). In cases which more than 50 Gy was irradiated for the treatment of more than 75 cm2, the frequency and the grade of pulmonary complications increased rapidly.

Carcinoma, Squamous Cell↗
PubMed1988

Genotoxic effects of fluoride: a controversial issue.

Fluoride is an element which is widely distributed in our environment. Its cariostatic efficacy has been well documented, and numerous studies indicate that at a concentration of 1 ppm in water, fluoride is beneficial for caries prevention and does not appear to exacerbate any diseases. Currently, more than half the American population is consuming naturally or artificially fluoridated water and efforts are being made to increase this proportion significantly. In addition, the multiple use of fluoride for dental caries prevention is clearly increasing. It is a common practice to use fluoride in a variety of delivery systems, including dentifrices, mouthrinses, pediatric supplements, and professional or self-applied topical solutions or gels as well as dental restorative materials. These dental products may contain fluoride in concentrations as high as 12,300 ppm. Increasing exposure of the population to fluoride has raised questions about the safety of this measure and has established the need for objective reappraisal. In particular, interest has developed regarding the genotoxic effects of fluoride. Unfortunately, there is, at present, only a limited amount of information available concerning the potential genotoxic effects of fluoride, and the results that have been published are contradictory and often very confusing. A review of the literature clearly indicates the importance of, and necessity for, clarifying the conflicts and controversies regarding this important issue.

Animals↗
PubMed1987

Genotoxic effects of fluoride evaluated by sister-chromatid exchange.

The purpose of this investigation was to study the genotoxic potential of fluoride (in the form of sodium fluoride, NaF) using in vitro and in vivo sister-chromatid exchange (SCE) assays with Chinese hamster cells. The NaF concentrations used in cultures of Chinese hamster ovary (CHO) cells ranged from 0 to 6.3 mM, both with and without S9 activation. Fluoride analysis of the culture medium demonstrated that it contained little indigenous fluoride, and the concentration of added fluoride was not affected by the components of the medium or the S9 mix. The CHO cells cultured in 6.3 mM NaF almost vanished, and at the concentration of 5.3 mM NaF in cultures without S9 microsome, only M1 cells were observed. In in vivo studies, Chinese hamsters were intubated with NaF dosages of 0, 0.1, 1.0, 10, 60 and 130 mg/kg, and the bone marrow (CHBM) cells were examined for SCE frequencies. Bone fluoride data showed that the intubated NaF was effectively absorbed. Death occurred in 3 of the 8 animals given 130 mg NaF/kg. The results indicated that NaF, in dosages up to 5.3 mM in CHO cell cultures and 130 mg/kg in in vivo CHBM cells, did not significantly increase the SCE frequencies over those observed in the negative (distilled water) controls. However, examination of the cell cycle revealed an inhibitory effect of NaF on cell proliferation with doses of NaF at or greater than 1.0 mM in cultured CHO cells and at or greater than 60 mg NaF/kg in in vivo CHMB cells. The results of the present study indicated an inhibition of the cell cycle and death of the cells with increasing concentrations of fluoride but not effect of fluoride on SCE frequency in CHO and CHBM cells.

Animals↗
PubMed1987

Cancer of esophagus and esophagogastric junction: analysis of results of 1,025 resections after 5 to 20 years.

Resection was carried out in 1,025 of 1,654 patients with cancer of the esophagus or esophagogastric junction at the Peking Medical College Hospitals in China from 1953 through 1973. All cancers of the esophagus were squamous cell carcinomas except for five adenocarcinomas. A lesion localized within the esophageal wall was found in 55% and lymph node metastasis in 41.3% of the patients undergoing resection. All cancers of the esophagogastric junction were adenocarcinomas. The tumor had invaded beyond the boundaries of the stomach in 76.7% of these patients, and positive nodes were found in 61% of the patients. The rate of resectability was 81.2% for esophageal cancer and 74% for cancer of the esophagogastric junction. Surgical mortality after resection was 4.9% (50/1,025). The 5-year survival after resection was 20.9% (214/1,025). Better results were found following complete resection: 24% (210/875) for all patients, 28.2% (162/575) for patients with cancer of the esophagus, and 16% (48/300) for patients with cancer of the esophagogastric junction. Late survival at 10, 15, and 20 years after resection of esophageal cancer was 20%, 12%, and 7.4%, respectively. The favorable prognostic factors after resection of esophageal cancer were tumor of the lower third of the esophagus, the absence of lymph node involvement, and the presence of a localized lesion. The 5-year survival for patients with cancer of the lower third of the esophagus was 32.7%. It was 64.2% for patients with a localized lesion with negative nodes in this subgroup.

Esophageal Neoplasms↗