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Biomedical subjects

M Cheng

Publications and source records attributed to M Cheng.

At least 73 records · Page 4Linked to original sources
PubMed1984

A path probability model for sister-chromatid exchanges induced by alkylating agents.

A path probability model is described for evaluation of sister-chromatid exchanges (SCEs) induced by alkylating agents following treatment of G1 cells at the beginning of the first or second cycles of BrdUrd incorporation, or during G1 corresponding to an exact cell-cycle interval preceding BrdUrd incorporation. Algebraic expressions are derived for calculations of expected induced SCE frequencies (over baseline levels) in second and third (reciprocal and nonreciprocal SCEs) division cells for the described treatment protocols. The derivations take into consideration: p, the probability of a specific lesion inducing an SCE; rn, the extent of repair within the nth post-treatment cycle; and X, the number of lesions induced. Expressions are also derived for expected ratios of single: twin exchanges in endoreduplicated or tetraploid cells.

Alkylating Agents↗
PubMed1984

Evaluation of the genotoxicity of cresols using sister-chromatid exchange (SCE).

o-, m- and p-Cresols were evaluated in both an in vitro and in vivo SCE assay. Dose-dependent SCE increases were not observed in cultured human fibroblasts with any of the isomers at concentrations up to 8 mM. There was a small but significant increase in SCE frequency compared to control at 8 mM o-cresol. A significant decrease in cell-cycle progression as measured by average generation time (AGT), was seen for all isomers at a concentration of 8 mM. Furthermore, no increase in SCE frequencies was observed in bone marrow, alveolar macrophages, and regenerating liver cells of male DBA/2 mice treated with a single i.p. injection of either o-cresol (200 mg/kg), m-cresol (200 mg/kg), or p-cresol (75 mg/kg) 21.5 h prior to sacrifice.

Animals↗
PubMed1983

Long-term cell culture of adult mammalian cardiac myocytes: electron microscopic and immunofluorescent analyses of myofibrillar structure.

Adult rat heart was dissociated into a single-cell suspension by a retrograde perfusion technique with collagenase and hyaluronidase in Krebs-Ringer phosphate buffer. Long-term culture of these isolated single cardiac muscle cells was established for up to 45 days. Transmission electron microscopy and immunofluorescence analysis with monoclonal antibodies to cardiac myosin were used to examine sequentially the external and internal structural organization of the cardiac myocytes. Most of the cardiac myocytes exhibited prominent alterations in their external and internal structural organization during the first two weeks of culture. As they attached to the substrate and spread out, the myocytes assumed various shapes and sizes, with the exception of a few which maintained their original cylindrical shape. Electron microscopy of 2 to 4-day cultures revealed that most of the muscle cells contained disorganized myofibrils and surface blebs with enclosed mitochondria and myofilaments, which were eventually extruded from the cytoplasm. With progressive culture, the cardiac myocytes appeared to lose myofibrillar material; fewer myofilaments or sacromere fragments with interfibrillar mitochondria were observed in the sarcoplasm. Such cells resembled cultured embryonic or neonatal cardiac myocytes. However, some muscle cells retained closely packed, well organized myofibrils characteristic of freshly dissociated or in vivo cardiac myocytes. Immunofluorescence microscopy demonstrated that the cultured cardiac myocytes were strongly myosin positive throughout their morphological changes and subsequent maintenance in culture. Two patterns of fluorescence were observed in these cells in correlation with the fine structural evidence for myofibrillar distribution. One pattern exhibited bright fluorescence near the central region of the cell with a more weakly diffuse fluorescence throughout the cytoplasm; the other pattern was characterized by bright fluorescence throughout the sarcoplasm. Most of the myocytes retained their contractility throughout the culture period excepting the initial 24 to 48 h of cell attachment and flattening. These studies demonstrate the feasibility of maintaining contractile cardiac muscle cells from adult rats for at least 1 1/2 months in monolayer culture, although some variability in myofibrillar organization has been observed.

Animals↗
PubMed1983

DNA synthesis in rat heart cells after injury and the regeneration of myocardia.

The regenerative responses of the myocardia of post-natal rats of different age groups (1, 2, 3 and 4 weeks old) to an injury made by a clinical electricator were studied. DNA synthesis and the ultrastructural organization of the cardiac myocytes of the injured myocardia were examined for an evaluation of the potential for regeneration of the developing myocardia. The maximum labeling index of cardiac myocytes was observed in 1-week-old rats showing 8% labeled myocytes 3 days after injury as opposed to 3.2, 2.2 and 0.2% indices in 2-, 3- and 4-week-old rats respectively, 3 days after injury . In subsequent days after injury the labeling indices declined considerably in all age group hearts, and attained values less than 1% labeled myocytes 30 days after injury with the lowest labeling index in the oldest age group heart. When DNA synthesis in uninjured myocardial tissue adjacent to the injured tissue was examined, it was found to be significantly lower than it was in the injured tissue. However, both injured and adjacent uninjured tissue attained a peak in the labeling indices 3 days after injury, with the exception of 3- and 4-week-old uninjured tissue. The overall incorporation of 3H-thymidine into the DNA of heart cells as revealed by scintillation counts showed that the rate of incorporation of the isotope in younger hearts was significantly higher than in the older hearts. Non-muscle cells contributed significantly to the rise of scintillation counts in hearts of all age groups. Ultrastructural analyses of 1- to 4-week-old hearts showed that 24 hr after injury, injured areas of myocardia were heavily crowded with macrophages that surrounded damaged myocytes. Later on, fibroblasts and other non-muscle cells predominated the injury sites along with fibrous connective tissue. Scattered regenerating cardiac myocytes were frequently observed in the injury sites of 1- and 2-week-old hearts 3 days after injury. Myocytes were rare in the corresponding regions of 3- and 4-week-old hearts. Instead abundant non-muscle cells and fibrous connective tissue were predominant. In the fourth and final week of this study, the repaired areas of myocardia in 1- and 2-week-old rats contained more myocytes than those of the 3- and 4-week-old rats, and the repaired zone of the 1-week-old heart contained more myocytes than the repaired areas of the other age groups. These findings suggest that the mammalian myocardia possess an age-dependent potential for regeneration that involves the healing of injury sites with contractile and connective tissues.

Animals↗
PubMed1983

Persistence of ethyl carbamate-induced DNA damage in vivo as indicated by sister chromatid exchange analysis.

Various treatment protocols were designed to investigate sister chromatid exchanges (SCEs) induced over successive posttreatment cell cycles in bone marrow and alveolar macrophage cells following treatment of C57BL/6J X DBA/2J F1 mice by i.p. injection of ethyl carbamate (3.3 mmol/kg). The same initial extent of alkylation in bone marrow and alveolar macrophages was suggested by identical SCE frequencies produced in both cell types by a one-cycle exposure protocol. The relatively lower responses in bone marrow cells by all other protocols may be a result of its faster mean population-cycling time. Second- and third-division cell SCE data produced by the various protocols indicate persistence of SCE-inducing lesions with no evidence of repair. In spite of the demonstrated lack of repair, first-cycle ethyl carbamate treatment was less effective than was second-cycle treatment in inducing SCEs. These results could not be attributed to selection of less-damaged cells over 2 cycles or to enhanced bromodeoxyuridine sensitivity in the second-cycle treatment protocol. It is speculated that the apparent cancellation of SCEs occurring over two successive cycles in the two-cycle exposure protocol may indicate the transient presence of ethyl carbamate-induced DNA interstrand cross-links. A possible mechanism of action of ethyl carbamate involving the formation of a transient cross-link and a persistent DNA monoadduct is postulated.

Animals↗
PubMed1982

Purification and physicochemical characterization of human alpha 2-HS-glycoprotein.

A large-scale purification method for alpha 2 HS-glycoprotein from normal human pooled serum is presented. 130 mg of alpha 2 HS was obtained from 21 of normal serum and the yield was 13.6%. Charge heterogeneity on isoelectrofocusing of this protein is mainly due to sialic acid. By the measurement of the circular dichroism spectrum, the alpha-helix content was calculated as 11% and the beta-structure content was calculated as 21 to 33%. alpha 2HS consists of a single polypeptide chain (Mr 49,000) of which the N-terminal amino acid is alanine. The N-terminal sequence of 31 amino acids contains 19 hydrophobic residues.

Amino Acid Sequence↗
PubMed1982

Ribonucleic acid metabolism in rat liver during long-term adaptation to malnutrition.

Ornithine decarboxylase (ODC) and nucleolar DNA-dependent RNA polymerase (RNA polymerase I) activities increased in the liver of young adult male rats fed a 6% casein diet (malnourished) for 1 week when compared with rats fed a 25% casein diet (control). ODC activity increased progressively and reached a peak after 3 weeks of malnutrition and then decreased to control values by 5 weeks. RNA polymerase I reached peak activity 1 week after malnutrition was imposed, decreasing thereafter to control values by 3 weeks. At 4 and 5 weeks, RNA polymerase I activity in malnourished animals was lower than control. Nucleoplasmic DNA-dependent RNA polymerase activity remained unchanged in the first 2 weeks of malnutrition and decreased thereafter to values significantly lower than control. The data confirm our previous observations of cyclical changes during prolonged malnutrition and suggests a process of "biochemical adaptation" to malnutrition in which the organism enhances essential metabolic processes to maintain cellular homeostasis to the detriment of less essential functions like systemic growth.

Adaptation, Physiological↗
PubMed1982

Organization of head injury service in Beijing.

Beijing, the capital of the People's Republic of China, is a city with a population of over 10 million. The incidence of head injuries is increasing yearly and the government pays much attention to this social and medical problem. This is evidenced in both county and big city hospitals by the organization of neurosurgeons and general surgeons to serve the victim, by the training of some general surgeons in primary hospitals to handle emergency head injury care, and by the education of the citizens in accident prevention.

Brain Injuries↗
PubMed1982

Comparison of sister chromatid exchange induction and known carcinogenic activities of vinyl and allyl carbamates.

In vivo sister chromatid exchange (SCE) induction by vinyl and allyl carbamates was examined in alveolar macrophage, bone marrow, and regenerating liver cells of C57BL/6J x DBA/2J F1 mice. Allyl carbamate was effective in producing increases in SCE frequencies (relative to base-line SCE) over a dose range of 220 mumol/kg (approximately 2 times base line) to 2.2 mmol/kg (3 times base line). In general, alveolar macrophage and regenerating liver cells had higher responses, although not significantly, than did bone marrow. Vinyl carbamate produced significant increases in SCE frequencies over a dose range of 10 mumol/kg (2 times base line) to 75 mumol/kg (8 to 10 times base line). At the highest dose, SCE frequencies in extrahepatic tissues of hepatectomized mice were significantly higher than in intact mice and, within hepatectomized mice, alveolar macrophage and regenerating liver cell responses were greater than were bone marrow responses. Vinyl carbamate was approximately 30 times as potent a SCE inducer than we reported previously for ethyl carbamate. To date, our studies of six different carbamate esters have indicated a striking similarity in relative potencies for SCE induction and their known tumorigenic potencies.U

Animals↗
PubMed1982

Differentiation of fibre types in an extraocular muscle of the rat.

Mammalian extraocular muscles possess greater variation in structural and physiological properties than any other muscle. The superior rectus muscle of the adult rat contains five morphological fibre types. The differentiation of the muscle into these fibre types in embryonic and postnatal rats were studied by light and electron microscopy, and the distribution of each developing fibre type with its distinctive features was mapped. The muscle of the 18-day embryos did not display the specific structural fibre types that were observed in the adult muscle. Newborn rat muscle exhibited some differentiation that included scattered small-diameter fibres with large myofibrils (fibre type 'B'). As development proceeded, another small-diameter fibre type with small myofibrils (fibre type 'A') appeared in the 6-day postnatal rat muscle. By the end of the first week of development neuromuscular junctions were in evidence in these two fibre types. Postsynaptic folds were rare in the large-fibril fibre, and folds were extensive in the small-fibril fibre. The medium- (fibre type 'C') and large-diameter (fibre type 'D') fibres were fully differentiated with small myofibrils and abundant sarcoplasmic reticulum (SR) by the second week of the development. SR was most abundant in the large-diameter fibre, which constituted the predominant global fibre type in the adult muscle. The postsynaptic folds in the neuromuscular junctions of these two fibre types were highly developed, although the innervation did not extend widely in the global region of the muscle. The last fibre type (fibre type 'E') was fully differentiated with the largest myofibrils, a small amount of SR, and simple neuromuscular junction by the third week of the postnatal development. The superior rectus muscle of the four-week-old rat was differentiated with all fibre types present in the adult muscle. During the third to sixth, and final, week of development, the other types described above exhibited extensive differentiation of characteristic structural features.

Animals↗
PubMed1981

Adult mammalian cardiac muscle cells in culture.

Adult rat cardiac muscle cells were isolated from the ventricle by a retrograde perfusion technique through the aorta (Nag and Zak, 1979). These single, isolated cardiac muscle cells were cultured for 4 weeks. Throughout the culture period, a small number of muscle cells retained their cylindrical shape, while the rest exhibited alterations in shape and size assuming a flattened body of irregular shape with pseudopodia-like processes and thereby resembling embryonic/neonatal cardiac muscle cells in culture. Transmission electron microscopy revealed that the cylindrical muscle cells contained compactly arranged myofibrils and cellular organelles, similar to those of freshly isolated and in vivo cells. A few irregularly shaped cardiac muscle cells were similar to the cylindrical cells in their internal structural organization. Most of the irregular cells exhibited less myofibrillar content than that of the freshly dissociated and in vivo cells. Myofibrils in the irregular cells were widely spaced and myofilament of some of the myofibrils were loosely bunched. In addition, scattered patches of myofibrils and free myofilaments were observed in many of these cells. The internal structural organization of these irregularly shaped cardiac muscle cells closely resembled the embryonic and neonatal cardiac muscle cells in vitro and in vivo. Most of the muscle cells in culture continued to contract spontaneously, and electron microscope studies clearly indicated that they underwent dedifferentiation. Autoradiography studies demonstrated that the cylindrical and irregularly shaped cardiac muscle cells underwent DNA synthesis and cell division in culture.

Animals↗
PubMed1981

Multicellular in vivo sister-chromatid exchanges induced by urethane.

Following urethane inhalation exposure, clear dose--response relationships were apparent in all cell types examined in hepatectomized and intact mice. At concentrations of 0.1 mg/l and higher, induced SCE frequencies were linearly related to log urethane concentrations. No significant differences in SCE response between like cell types of hepatectomized and intact mice were apparent. In hepatectomized mice, there was no significant difference in the SCE response of regenerating liver and alveolar macrophage cells. However, bone-marrow response was significantly lower (p = 0.01). Likewise, in intact mice bone marrow response was significantly lower than in alveolar macrophages (p = 0.01). Inhalation and intravenous infusions of the same total dose of urethane (193 mg/kg) administered over a 4-h period produced comparable SCE responses in all cell types. However, a single intraperitoneal injection of 193 mg/kg just prior to BrdU infusion produced significantly higher SCE frequencies in bone marrow (alpha = 0.01), and alveolar macrophages (alpha = 0.05) of intact mice than did the equivalent inhalation dose. Intraperitoneal injections produced similar results in 2-month-old mice as in 4-month-old mice. However, regardless of the route of administration SCE frequencies in regenerating liver and/or alveolar macrophages were significantly higher than in bone marrow.

Aerosols↗
PubMed1981

Competence of embryonic mammalian heart cells in culture: DNA synthesis, mitosis and differentiation.

The competence for DNA synthesis, mitosis and differentiation of cardiac muscle and non-muscle cells of 14- and 18-day rat embryos was studied in vivo. The heart cells of 14-day embryos were relatively more competent in DNA synthesis and mitosis than those of 18-day embryos. These in vitro findings conformed with those of the in vivo studies. Cardiac muscle and non-muscle cells of the younger age group showed higher labelling indices than those of the other age group during 7 days of culture. The general profile of DNA synthesis was similar in both age group during 7 days of culture. The general profile of DNA synthesis was similar in both age group cells. Maximum labelling indices in muscle and non-muscle cells were observed after 24 h of culture. The number of labelled cells was always higher in non-muscle cells than in muscle cells. As the culture continued, the labelling indices declined in both cell types of the two age groups. On day seven, 10% labelled cardiac muscle cells and 45% labelled non-muscle cells were observed in the 14-day embryonic group, in comparison with 5% cardiac muscle cells and 35% non-muscle cells of the 18-day embryonic group. When the rate of in vitro differentiation of myofibrils, intercellular junctions and some cellular organelles, were compared between cells of two different age group hearts, no significant difference was observed. During the first week of culture, a considerable number of muscle cells contained myofibrils throughout the length and girth of the cells. The intercalated discs differentiate over a period of 3 weeks of culture. As the culture proceeded, adjoining cardiac muscle cells differentiated desmosomes and gap junctions. Cardiac muscle cells retained these structural specializations and did not undergo dedifferentiation in long-term culture. Overgrowth of one cell type by another was the regular occurrence in all heart cell cultures studied.

Animals↗
PubMed1981

Potency of some carbamates as multiple tissue sister chromatid exchange inducers and comparison with known carcinogenic activities.

The ethyl, ethyl N-hydroxy, isopropyl, and methyl esters of carbamic acid were examined for their abilities to induce sister chromatid exchanges (SCEs) in alveolar macrophages, bone marrow, and regenerating liver cells of C57BL/6J X DBA/2J F1 mice. The relative potencies in inducing SCE, ethyl greater than ethyl N-hydroxy- greater than isopropyl, paralleled previously described activities for induction of lung adenomas in strain A mice. The noncarcinogenic methyl carbamate was inactive in the SCE assay. Relative to bone marrow, regenerating liver and alveolar macrophage cells demonstrated increased susceptibility to carbamate-induced SCE. Of all carbamates studied, only the directly active compound, ethyl N-hydroxycarbamate, produced distinctly different responses in extrahepatic tissues of hepatectomized and intact mice. In intact mice, SCE levels induced by ethyl carbamate in bone marrow and alveolar macrophage cells were not significantly different whether assay followed the last of 12 (three times weekly) serial injections of 2.2 mmol/kg each or after a single injection of 2.2 mmol/kg. Linear regression relationships of log ethyl carbamate versus log SCE or log adenoma response were found to be parallel with the two assays having similar sensitivities.

Animals↗