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Biomedical subjects

M C Ng

Publications and source records attributed to M C Ng.

8 recordsLinked to original sources
PubMed1992

Maturation-associated changes in the cellular composition of mouse calvariae and in the biochemical characteristics of calvarial cells separated into subclasses on Percoll density gradients.

The effects of tissue maturation on the cellular composition and biochemical characteristics of bone were studied in neonatal, young adult, and aging mice. Osteoblast subclasses were isolated on Percoll density gradients. Neonatal calvariae consisted almost exclusively of cells banding at low and intermediate buoyant density. High buoyant density cells constituted 5-10% of total cells at 10 days of age but increased to 50-60% by 5 weeks of age. These latter cells were released late during collagenase digestion. This indicates that they arise from the deeper layer of bone. For this reason, we consider them putative osteocytes. We established that constitutive secretion of IGF-I and TGF-beta and activities of cellular alkaline phosphatase paralleled those of the tissue of origin in all cell groups and was highest in cells of intermediate buoyant density. These activities declined rapidly after cessation of growth at 5 weeks of age in both bone and isolated cells. Between 5 and 8 weeks of age, the hormonal response to PTH also declined dramatically. The maximum cAMP induced by PTH declined by about 70% in highly responsive cells of intermediate buoyant density and fell to insignificant levels in cells of high buoyant density. We found that a cyclic AMP response to PTH was positively correlated with stimulated secretion of IGF-I by this hormone in cells from animals of all ages. Despite their inability to respond to PTH with increases in cAMP and IGF-I, adult bone cells of high buoyant density continued to respond to PTH with increases in the secretion of TGF-beta.(ABSTRACT TRUNCATED AT 250 WORDS)

Age Factors↗
PubMed1991

Characterization of bone cells isolated on discontinuous Percoll gradients: distribution in sequentially derived populations.

Bone cell populations obtained by sequential digestion of newborn mouse calvariae remain morphologically heterogeneous despite well-documented biochemical differences. Fractionation of these populations on Percoll gradient reveal three major cell groups of low, intermediate, and high buoyant density (1.056, 1.070, and 1.095 g/ml) that are present in different ratios in early and late released populations. Cells of low and intermediate density dominate in early released populations. In contrast, late released populations contain mostly high-density cells. Basal levels of alkaline phosphatase are highest in cells of intermediate buoyant density. All cells respond to PTH with cAMP production and morphologic transformation, but biochemical responses to PTH, such as secretion of insulin-like growth factor I (IGF-I) and stimulation of alkaline phosphatase activity, occur mostly in cells of intermediate density. These data suggest that (1) subclasses of osteoblasts can be further separated by density and (2) PTH effects on alkaline phosphatase activity and IGF-I secretion are probably expressed by osteoblasts of a certain subclass and/or stage of development.

Alkaline Phosphatase↗
PubMed1989

Peroxisomal palmityl CoA oxidase activity in ocular tissues and cultured ciliary epithelial cells.

The activity of palmityl CoA oxidase, a peroxisomal enzyme, was determined in bovine ocular tissues. Significant levels of activity were found in the iris, ciliary body and pigmented epithelium-choroid but little or no activity was detected in the corneal epithelium, lens capsule-epithelium and retina. Treatment of bovine ciliary epithelial cells with clofibric acid for 72 hours in culture resulted in a several fold enhancement of palmityl CoA oxidase activity. These results suggest that peroxisomal enzymes can be induced in uveal tissues when peroxisome proliferation is stimulated by certain drugs in these tissues.

Animals↗
PubMed1988

Bovine non-pigmented and pigmented ciliary epithelial cells in culture: comparison of catalase, superoxide dismutase and glutathione peroxidase activities.

Non-pigmented epithelial (NPE) cells and pigmented epithelial (PE) cells were dissociated from bovine ciliary processes by brief digestion with pronase and grown in a culture medium containing high fetal bovine serum for at least 25 generations. Both types of cells grown to confluence showed the presence of intermediate junctions with associated tonofilaments. PE cells were distinguished from NPE cells by pigmentation during the early passages. Gamma-glutamyl transpeptidase activity was associated almost exclusively with NPE cells and proved to be a useful enzymatic marker to distinguish NPE from PE. A comparison was made between NPE and PE cells as to the levels of enzymes involved in the detoxification of active oxygen species. Catalase, Se-dependent glutathione peroxidase and superoxide dismutase activities were significantly higher in NPE than in PE cells. The results suggest that NPE cells play the major role in detoxification of active oxygen species during aqueous humor formation.

Animals↗
PubMed1987

Enzymes of mercapturate pathway in cultured bovine ciliary epithelial cells.

Relative enzyme activities of the mercapturate pathway were determined in bovine ciliary pigmented (PE) and nonpigmented (NPE) epithelial cells in culture. Glutathione S-transferase activity was greater in PE cells than in NPE cells. Gamma-glutamyl transpeptidase activity appeared to be exclusively associated with NPE cells; the enzyme activity was virtually absent in PE cells. The level of cystine aminopeptidase activity was about the same in NPE and PE cells. N-acetyl transferase was predominantly found in NPE cells. If a similar enzyme distribution should exist in vivo in the bicellular layer of ciliary epithelium, the present result suggests that both NPE and PE cells are involved in the detoxification of xenobiotics via the mercapturate pathway, glutathione conjugation occurring primarily in the PE cells and the reactions catalyzed by the membrane-bound enzymes gamma-glutamyl transpeptidase and N-acetyl transferase taking place mainly in the NPE cells.

Acetylcysteine↗
PubMed1987

Effect of prolactin on galactose cataractogenesis.

Prolactin has been known to affect the water and electrolyte balance. Because increased lens hydration has been shown to be a common phenomenon in most, if not all types of cataracts, we have been interested in investigating a possible role of prolactin in sugar cataract induction and progression. For this study, we have used morphological and biochemical approaches. The prolactin delivery method involved intraperitoneal implantation of one or more pellets in Sprague-Dawley female rats. Following implantation of the desired number of prolactin or control (nonprolactin) pellets, animals were either fed galactose and lab chow, or lab chow diet. Gross morphological observations of whole lenses, slit-lamp examination of lenses and light microscopic analysis of lens sections showed that in the galactose-fed prolactin group, galactose associated alteration progressed faster and total opacification (mature cataract development) was achieved earlier than in the nonprolactin group. The levels of galactose and dulcitol were higher in the lenses of galactose-fed prolactin treated rats as compared to lenses from nonprolactin (control) rats. No significant difference in lens Na+-K+ ATPase activity between the prolactin and nonprolactin group was observed. Our results indicate that prolactin accelerates galactose-induced cataractogenesis in rats.

Animals↗
PubMed1986

Purification and properties of glutathione reductases from bovine ciliary body.

Two glutathione reductases, designated GR-I and GR-II, were purified from bovine ciliary body to apparent homogeneity by ion-exchange chromatography on DEAE-agarose and gel filtration on Sephacryl S-200. The two enzymes were isolated whether protease inhibitors were included or not in the medium during tissue homogenization. GR-I was found to have a molecular weight of about 140,000 by gel filtration and be composed of two identical subunits. On the other hand, GR-II was shown to exist as aggregates with molecular weights larger than 670,000. The subunit molecular weight of GR-II was estimated to be about 45,000 by SDS-polyacrylamide gel electrophoresis. The high molecular aggregate dissociated into smaller species by treatment with mercaptoethanol. The isoelectric points of GR-I and GR-II were determined to be 5.8 and 6.4, respectively. The K'm values for NADPH and oxidized glutathione (GSSG) were 22- and 84 microM for GR-I and 11- and 98 microM for GR-II. Coenzyme A-glutathione disulfide served as a substrate, though it was much less reactive than oxidized glutathione, for both enzymes. S-alkyl glutathiones were inactive as substrates. Nitrofurantoin was a non-competitive inhibitor of the enzymes. 1,3-bis(2 chloroethyl)-1-nitrosourea (BCNU) inhibited GR-I and GR-II irreversibly. The two enzymes are similar, if not identical, in their amino-acid composition. The two enzymes are also very similar on the basis of the relative position of tryptic peptides separated in two-dimensional peptide maps. From the tissue content and turnover numbers of these enzymes it is concluded that bovine ciliary body has a sufficient capability for rapid reduction of oxidized glutathione produced in the tissue during glutathione-dependent peroxide detoxification.

Amino Acids↗