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Biomedical subjects

D Lin

Publications and source records attributed to D Lin.

At least 217 records · Page 12Linked to original sources
PubMed1987

Ultrastructural and biochemical comparisons of nuclear matrices prepared by high salt or LIS extraction.

We have directly compared two independently published methods for isolating operationally defined nuclear matrices by studying EM ultrastructure, protein composition and distribution of replicating DNA. Nuclear matrices prepared by extraction with 2 M NaCl consisted of fibrous pore complex lamina, residual fibrillar and granular components of nucleoli and interchromatin granules, and an extensive anastomosing internal fibrous network. These matrices were enriched in high molecular weight nonhistone proteins but were virtually devoid of histones. Consistent with previously published data, newly-replicated DNA was resistant to this high salt extraction. Nuclear matrices prepared by extraction of nuclei with 25 mM lithium 3,5-diiodosalicylate, LIS, also contained fibrous pore complex lamina, but lacked morphologically distinct residual nucleoli and were markedly depleted in internal structure. The reduced amounts and complexity of proteins associated with the LIS matrix were consistent with the ultrastructural data. Moreover, much less newly-replicated DNA was recovered in LIS matrices. The data show that LIS dissociates nuclear ultrastructure and extracts both protein and DNA in proportion to the concentration used, regardless of whether nuclei or high salt nuclear matrices are used as starting material. While the data suggest that LIS may not necessarily be an optimal reagent for preparing nuclear matrices containing internal structural elements from all tissue sources, it may be useful for selectively solubilizing and analyzing components of the nuclear matrix.

Animals↗
PubMed1987

Increased levels of glycine tRNA associated with collagen synthesis.

Analysis of codon usage for chick Type I collagen indicates that 89% of glycine codons are GGU/C. Since collagens are one-third glycine, chick Type I collagen synthesis should require large amounts of tRNAGly with the anticodon GCC. Earlier chromatographic studies of chick tRNA had indicated that connective tissues showed altered tRNAGly isoacceptor profiles [P. J. Christner and J. Rosenbloom (1976) Arch. Biochem. Biophys. 172, 399-409; H. J. Drabkin and L. N. Lukens (1978) J. Biol. Chem. 253, 6233-6241]. We have therefore used both two-dimensional gel electrophoresis and hybridization analysis to investigate whether collagen synthesis in chick connective tissues is associated with expression of a novel tRNAGly. Liver and calvaria tRNAs produced qualitatively similar patterns when separated on 2-D gels. Northern blots of 2-D-separated tRNAs from liver and calvaria, when hybridized to genes for vertebrate tRNAGly isoacceptors with GCC or UCC anticodons, showed hybridization to the same tRNAs in both tissues. Quantitation of tRNA species by dot blot hybridization indicated an increase in levels of the tRNAGly isoacceptor with anticodon GCC. Tissues synthesizing Type I collagen had a two- to threefold increase in this tRNA while tissues synthesizing Type II collagen showed a more modest increase. We conclude that elevated tRNAGly levels associated with collagen synthesis are due to increased amounts of the same isoacceptor which is the major tRNAGly in other tissues.

Animals↗
PubMed1987

Effects of alpha-deuterium substitution on the tumorigenicity of 4-(methylnitrosamino)-1-(3-pyridyl)-1-butanone in F344 rats.

4-(Methylnitrosamino)-1-(3-pyridyl)-1-butanone (NNK) and its analogues substituted with deuterium at the methylene carbon, 4,4-dideutero-4-(methylnitrosamino)-1-(3-pyridyl)-1-butanone [4,4-D2)NNK], and the methyl carbon, 4-(trideuteromethylnitrosamino)-1-(3-pyridyl)-1-butanone [(CD3)NNK], adjacent to the N-nitroso group were tested for tumorigenicity in F344 rats. Each compound was administered by 60 s.c. injections over a 20-week period such that the total doses were either 1.0 or 0.33 mmol/kg. The experiment was terminated after 104 weeks. Survival of the rats treated with the higher dose of (4,4-D2)NNK was significantly less than survival in the groups treated with the same doses of NNK or (CD3)NNK. Target tissues were liver, lung and nasal cavity for all three compounds. The higher dose of (4,4-D2)NNK induced higher numbers of nasal tumors and malignant nasal tumors than did NNK. The lower dose of (4,4-D2)NNK induced a higher number of nasal tumors than did NNK. No other significant differences in tumor incidence were observed. The results suggest that 4-(3-pyridyl)-4-oxobutylation of DNA might be important in induction of nasal cavity tumors by NNK.

Animals↗
PubMed1987

Investigations on the molecular dosimetry of tobacco-specific N-nitrosamines.

Approaches for assessing molecular dosimetry of 4-(N-nitrosomethylamino)-1-(3-pyridyl)-1-butanone (NNK) and N'-nitrosonornicotine (NNN) in humans by measurement of haemoglobin or DNA adducts are discussed. NNK and NNN form haemoglobin adducts in Fischer 344 rats. Acid or base hydrolysis of the globin gives 4-hydroxy-1-(3-pyridyl)-1-butanone, which can be detected in rat blood up to six weeks after injection of NNK; it may be a useful marker for assessing uptake and metabolic activation of NNK and NNN in tobacco consumers. NNK and its major metabolite, 4-(N-nitrosomethylamino)-1-(3-pyridyl)-1-butanol (NNAI), methylated DNA of rat liver, lung and nasal mucosa to similar extents. NNAI is formed in human tissues from NNK, but immunoassays for O6-methyldeoxyguanosine (O6-medGuo) in exfoliated oral cells from snuff-dippers have been negative. NNK is also expected to form pyridyloxobutyl adducts in DNA; 32P-postlabelling assays for these adducts are being developed and appear to hold promise for detecting NNK- or NNN-DNA adducts in vivo.

Animals↗
PubMed1986

Absorption of cholesterol and beta-sitosterol from cigarette smoke in Macaca mulatta.

When smoke from single cigarettes containing [4-14C]cholesterol or beta-[4-14C]sitosterol was delivered to the lungs of Rhesus macaques, plasma contained radiolabeled sterols up to 50 days later. Since cholesterol, as well as plant sterols (campesterol, stigmasterol and beta-sitosterol), are normally present in cigarette smoke, our observations suggest that protracted absorption of sterols occurs after cigarette smoking.

Animals↗
PubMed1986

Comparative mutagenicity of 4-(carbethoxynitrosamino)-4-(3-pyridyl)butanal and 4-(carbethoxynitrosamino)-1-(3-pyridyl)-1-butanone, model compounds for alpha-hydroxylation of N'-nitrosonornicotine.

4-(Carbethoxynitrosamino)-1-(3-pyridyl)butanal, a stable precursor to the putative diazohydroxide formed by 5'-hydroxylation of the tobacco-specific nitrosamine, N'-nitrosonornicotine, was synthesized in six steps from nicotinaldehyde. Its mutagenicity toward S. typhimurium was compared to that of 4-(carbethoxynitrosamino)-1-(3-pyridyl)-1-butanone, a precursor to the diazohydroxide formed by 2'-hydroxylation of N'-nitrosonornicotine. At equimolar doses, 4-(carbethoxynitrosamino)-1-(3-pyridyl)-1-butanone was a potent mutagen, but 4-(carbethoxynitrosamino)-1-(3-pyridyl)butanal was inactive toward strains TA 100 and TA 1535. The results of this study indicate that the putative diazohydroxide formed by 2'-hydroxylation of N'-nitrosonornicotine has higher inherent mutagenicity toward S. typhimurium than does the corresponding diazohydroxide formed by 5'-hydroxylation.

Magnetic Resonance Spectroscopy↗
PubMed1984

A study of a Caucasian family with variant von Willebrand's disease in association with vascular telangiectasia and haemoglobinopathy.

A family was identified which carries multi-haematological disorders including Type IIA von Willebrand's disease, vascular telangiectasia, and a haemoglobinopathy (haemoglobin S trait). In the affected individuals, the von Willebrand's disease varies in its expression from an asymptomatic form to a severe form especially in those patients with telangiectasia. Some patients have vascular telangiectasia in the mucous membranes of the mouth and lips. In two patients endoscopy disclosed telangiectasia in the mucous membranes of the gastrointestinal tract. All of the patients who had telangiectasia also had von Willebrand's disease. An incidental finding was the presence of an abnormal haemoglobin (haemoglobin S) in some family members. The pattern of inheritance of the haemoglobinopathy was unrelated to the inheritance pattern of von Willebrand's disease. The presence of haemoglobin S did not interfere with the aggregation of platelets in response to ristocetin.

Adult↗
PubMed1983

Effects of alpha-deuterium substitution on the mutagenicity of 4-(methyl-nitrosamino)-1-(3-pyridyl)-1-butanone (NNK).

4-(Methylnitrosamino)-1-(3-pyridyl)-1-butanone (NNK), a carcinogenic tobacco specific nitrosamine, can be converted to electrophilic diazohydroxide intermediates by metabolic hydroxylation of either the methylene carbon (carbon 4) or the methyl carbon attached to the nitrosamine group. To investigate the relative importance of these two processes in NNK mutagenesis, we synthesized 4,4-dideutero-4-(methylnitrosamino)-1-(3-pyridyl)-1-butanone([4,4,-D2]NNK) and 4-(trideuteromethylnitrosamino)-1-(3-pyridyl)-1-butanone ([CD3] NNK), and evaluated their mutagenic activities in Salmonella typhimurium tester strains. In the presence of Aroclor induced rat liver 9000 g supernatant, NNK and [4,4-D2]NNK had comparable mutagenic activities towards S. typhimurium TA 1535 and TA 100, but [CD3]NNK was inactive in both strains. These results suggest that hydroxylation of the methyl group of NNK is more important than hydroxylation of carbon 4 in its activation to a mutagen. To test the inherent mutagenicity of 4-oxo-4-(3-pyridyl)butyldiazohydroxide and methyldiazohydroxide which would be formed by methyl hydroxylation or carbon 4 hydroxylation, respectively, we compared the mutagenicities, without activation, of the corresponding model compounds, 4-(carbethoxynitrosamino)-1-(3-pyridyl)-1-butanone and carbethoxynitrosaminomethane (methylnitrosourethane). Both compounds were highly mutagenic toward S. typhimurium TA 1535 and TA 100, but at doses of 4 x 10(-3) to 4 x 10(-4) mumol/plate, only 4-(carbethoxynitrosamino)-1-(3-pyridyl)-1-butanone was mutagenic. These results are consistent with those obtained with the deuterium substituted compounds and indicate the importance of 4-oxo-4-(3-pyridyl)butylation of DNA in NNK mutagenesis.

Deuterium↗
PubMed1982

Metabolism of N'-nitrosonornicotine by cultured rat esophagus.

The metabolism of N'-nitrosonornicotine (NNN), an esophageal carcinogen, by organ cultured F-344 rat esophagus was investigated. The major metabolites were separated by h.p.l.c. and were identified by comparison to standards as 4-hydroxy-1-(3-pyridyl)-1-butanone, 4-hydroxy-4-(3-pyridyl)-1-butanol and 4-oxo-4-(3-pyridyl)butyric acid from 2'-hydroxylation of NNN and 4-hydroxy-4-(3-pyridyl)-butyric acid from 5'-hydroxylation of NNN. These results demonstrate that alpha-hydroxylation, which leads to electrophilic diazohydroxides, is the major pathway of metabolism of NNN in cultured F-344 rat esophagus. The extents of formation of the metabolites increased with time and the ratio of products resulting from 2'-hydroxylation to those resulting from 5'-hydroxylation was 4.3 after 1 h, 3.9 after 6 h, 3.4 after 24 h and 3.1 after 48 h. F-344 rat liver slices from the same animals produced metabolites of NNN with a 2'/5'-hydroxylation ratio of 1.4. The 2'/5'-hydroxylation ratio in cultured Syrian golden hamster esophagus was 0.3. These results, together with those of parallel studies of NNN metabolism in A/J mouse lung and Syrian golden hamster trachea indicate that among these tissues, F-344 rat esophagus has a unique ability to preferentially hydroxylate the 2'-position of NNN. The results suggest that 2'-hydroxylation is the key step in the metabolic activation of NNN in rat esophagus.

Animals↗
PubMed1981

Comprehensive analysis of urinary metabolites of N'-nitrosonornicotine.

A detailed study of the urinary metabolites of N'-nitrosonornicotine has been performed, employing a simple high pressure liquid chromatographic method. The percentage excretion of the principal urinary metabolites was determined over a dose range of 3-300 mg/kg in the F-344 rat, as follows: 4-hydroxy-4-(3-pyridyl)butyric acid (37.1-53.3%, respectively, of the dose), N'-nitrosonornicotine-I-N-oxide (6.7-10.7%), norcotinine (3.2-5.1%), 4-oxo-4-(3-pyridyl)butyric acid (31.1-12.8%), N'-nitrosonornicotine (3.3-5.2%). In the strain A mouse and Syrian golden hamster, the urinary metabolites were qualitatively similar to those observed in the F-344 rat. The interrelationships of the various metabolites of N'-nitrosonornicotine which have been observed in vitro and in vivo were established. The in vitro metabolites resulting from 2'-hydroxylation by liver microsomes, myosmine and 4-hydroxy-I-(3-pyridyl)-1-butanone were converted, by the F-344 rat, primarily to 4-oxo-4-(3-pyridyl)butyric acid as a urinary metabolite. The in vitro metabolite resulting from 5'-hydroxylation by liver microsomes, 2-hydroxy-5-(3-pyridyl)tetrahydrofuran, gave 4-hydroxy-4-(3-pyridyl)butyric acid as its major urinary metabolite, apparently via 5-(3-pyridyl)-tetrahydrofuran-2-one. N'-nitrosonornicotine-I-N-oxide, the remaining major in vitro metabolite, was excreted to a large extent unchanged in F-344 rat urine. The urinary metabolites from 2'-hydroxylation and 5'-hydroxylation of N'-nitrosonornicotine, 4-oxo-4-(3-pyridyl)butyric acid and 4-hydroxy-4-(3-pyridyl)butyric acid, respectively, were not formed from the in vivo metabolite norcotinine and were ot interconverted significantly by the F-344 rat. Thus, these metabolites appear to be reliable indicators for the two possible in vivo alpha-hydroxylations of N'-nitrosonornicotine.

Animals↗