Search PubMed⌕ Search

Biomedical subjects

H Li

Publications and source records attributed to H Li.

At least 1,441 records · Page 80Linked to original sources
PubMed1996

Repair of dGMP hydroxyl radical adducts by verbascoside via electron transfer: a pulse radiolysis study.

The repair activity of verbascoside (VER), isolated from Pedicularis spicata, towards the oxidizing hydroxyl radical adduct of dGMP and its reaction mechanism were studied using pulse radiolysis. Upon pulse radiolysis of nitrous oxide saturated aqueous solution of 2'-deoxyguanosine-5'-monophosphate (dGMP) and VER, it was found that the transient absorption spectrum of the hydroxyl adduct of dGMP decays with the formation of that of the phenoxyl radical of VER, several tens of microseconds after the electron pulse. From the formation kinetics of the phenoxyl radical of VER, the rate constant of the repair reaction was determined to be 1.12 x 10(9) dm(3) mol(-1) s(-1).

Antioxidants↗
PubMed1996

Properties and regulation of gap junctional hemichannels in the plasma membranes of cultured cells.

During the assembly of gap junctions, a hemichannel in the plasma membrane of one cell is thought to align and dock with another in an apposed membrane to form a cell-to-cell channel. We report here on the existence and properties of nonjunctional, plasma membrane connexin43 (Cx43) hemichannels. The opening of the hemichannels was demonstrated by the cellular uptake of 5(6)-carboxyfluorescein from the culture medium when extracellular calcium levels were reduced. Dye uptake exhibited properties similar to those of gap junction channels. For example, using different dyes, the levels of uptake were correlated with molecular size: 5(6)-carboxyfluorescein (approximately 32%), 7-hydroxycoumarin-3-carboxylic acid (approximately 24%), fura-2 (approximately 11%), and fluorescein-dextran (approximately 0.4%). Octanol and heptanol also reduced dye uptake by approximately 50%. Detailed analysis of one clone of Novikoff cells transfected with a Cx43 antisense expression vector revealed a reduction in dye uptake levels according to uptake assays and a corresponding decrease in intercellular dye transfer rates in microinjection experiments. In addition, a more limited decrease in membrane resistance upon reduction of extracellular calcium was detected in electrophysiological studies of antisense transfectants, in contrast to control cells. Studies of dye uptake in HeLa cells also demonstrated a large increase following transfection with Cx43. Together these observations indicate that Cx43 is responsible for the hemichannel function in these cultured cells. Similar dye uptake results were obtained with normal rat kidney (NRK) cells, which express Cx43. Dye uptake can be dramatically inhibited by 12-O-tetradeconylphorbol-13-acetate-activated protein kinase C in these cell systems and by a temperature-sensitive tyrosine protein kinase, pp60v-src in LA25-NRK cells. We conclude that Cx43 hemichannels are found in the plasma membrane, where they are regulated by multiple signaling pathways, and likely represent an important stage in gap junction assembly.

Alcohols↗
PubMed1996

Effects of the phytochemicals, curcumin and quercetin, upon azoxymethane-induced colon cancer and 7,12-dimethylbenz[a]anthracene-induced mammary cancer in rats.

Curcumin and quercetin were evaluated in rats for their ability to modulate the carcinogenic activity of azoxymethane (AOM) in the colon and 7,12-dimethylbenz[a]anthracene (DMBA) in the mammary gland. In the AOM-induced colon cancer model, male Fischer 344 rats at 8 weeks of age started to receive either curcumin (8 and 16 g/kg) or quercetin (16.8 and 33.6 g/kg) in the diet and 1 week later, were administered AOM (30 mg/kg body wt.) by subcutaneous injection. The animals continued to receive the two agents in the diet until sacrificed 45 weeks later. Curcumin mediated a dose-dependent inhibition of the incidence and multiplicity of adenomas from 47% and 0.58 +/- 0.12 adenomas/rat in the AOM-treated control group to 19% and 0.22 +/- 0.08 and 0.06% and 0.08 +/- 0.06 adenomas/rat for the low and high dose groups, respectively. A low yield of adenocarcinomas (0.06 +/- 0.04 adenocarcinomas/rat) was induced by AOM which was not significantly altered by curcumin. Treatment with quercetin caused a dose-dependent increase in the yield of AOM-induced tumors in the colon from 0.06 +/- 0.04 adenocarcinoma/rat to 0.64 +/- 0.12 and 1.14 +/- 0.17 for the low and high dose groups, respectively. In the DMBA-induced mammary cancer model, curcumin or quercetin was administered at either 10 or 20 g/kg diet, beginning 7 days prior to DMBA and continually throughout the remainder of the experiment. Neither curcumin nor quercetin significantly altered the incidence of animals with tumors or the tumor multiplicity, while the high concentration of both agents significantly increased tumor latency. These results demonstrate different responses to these agents in the two models. While curcumin was highly effective as a chemopreventive agent in the colon model, it was only weakly effective in the mammary model. In contrast, quercetin which was also only weakly effective in the mammary model, caused a dose-dependent enhancement of tumors induced by AOM in the colon model.

9,10-Dimethyl-1,2-benzanthracene↗
PubMed1996

Cytochromes P450 5: induction of cytochrome P4501A1: a model for analyzing mammalian gene transcription.

The induction of microsomal cytochrome P4501A1 by polycyclic aromatic hydrocarbons represents an interesting response by which mammalian cells adapt to xenobiotic exposure. Enzyme induction reflects increased transcription of the corresponding CYP1A1 gene. Analyses of the induction mechanism using genetic, biochemical, and molecular biological approaches have revealed a novel transcriptional regulatory pathway that involves ligand-dependent heterodimerization between two basic helix-loop-helix proteins (the Ah receptor and Arnt), interaction of the heterodimer with a xenobiotic-responsive enhancer, transmission of the induction signal from the enhancer to the CYP1A1 promoter, and alterations in chromatin structure. Current techniques permit examination of the induction mechanism in intact cells and analyses of the CYP1A1 gene in its native chromosomal configuration. Such experiments generate new insights into the control of mammalian transcription that are of relatively broad interest.

Animals↗
PubMed1996

Developmental regulation of collagen differential expression in the rabbit bladder.

PURPOSE: It has been suggested that the amount and relative ratios of different types of collagen influence bladder compliance. To understand the mechanisms regulating collagen synthesis and degradation in the bladder we investigated the gene expression of collagen types I and III in the rabbit bladder during normal development. MATERIALS AND METHODS: New Zealand white rabbits ages fetus to adult were used for this study. The mid portion of the bladder wall was harvested. Northern blot hybridization was performed to analyze quantitatively collagen types I and III messenger (m) ribonucleic acid (RNA), and in situ hybridization was done to localize the messages. Corresponding protein distributions were obtained by immunohistochemical staining. RESULTS: Types I and III collagen are developmentally regulated at the level of gene expression. The temporal and spatial distribution of the mRNA transcripts of alpha 1(I) and alpha 1(III) correlates with extracellular protein deposition. Differential distribution of the mRNA transcripts is also developmentally regulated. CONCLUSIONS: This study characterizes the relationship between collagen gene expression and normal rabbit bladder development. The expression of alpha 1(I) and alpha 1(III) alters as the bladder grows. High levels and nonconcordant up and down regulation of different types of collagen mRNA during early development demonstrate the complexity of the extracellular matrix in a young bladder. This observation may be important in our understanding of the injury response in a developing versus mature bladder.

Animals↗
PubMed1996

Development of a gene transfer system in Treponema denticola by electroporation.

Treponema denticola is strongly implicated in the etiology of periodontal diseases. However, genetic transformation of this organism has not been reported. We now demonstrate a gene transfer system in T. denticola by electroporation using a broad host plasmid pKT210 as a shuttle vector. Plasmid extraction, Southern blot hybridization as well as the polymerase chain reaction indicated the presence of the plasmid in T. denticola transformants. The restriction patterns of plasmid pKT210 rescued from the T. denticola transformants in Escherichea coli suggested that some of the rescued plasmids were identical to the original pKT210, but some of them had been modified. This transformation system could be a potentially useful tool for genetic manipulation of oral spirochetes.

DNA, Bacterial↗
PubMed1996

Verification of absorbed dose determined with plane-parallel chambers in clinical electron beams following AAPM Task Group 39 protocol using ferrous sulphate dosimetry.

The absorbed dose values determined with the Exradin and PTW-Markus plane-parallel chambers were compared to the values obtained with the ferrous sulphate dosimetry for a number of the Philips SL25 and the Therac 20 electron beams. For the plane-parallel chambers, the cavity-gas calibration factor Ngaspp, was derived by a direct comparison with a calibrated cylindrical chamber using the three different calibration methods as proposed by the newly published AAPM TG 39 protocol. For the ferrous sulphate dosimetry, an epsilon mG value of 352 x 10(-6) m-2 kg-1 Gy-1 was adopted from ICRU Report No. 35. The average ratio of the dose values determined with the plane-parallel chambers and the dose values determined with the Fricke dosimetry system was 1.001 +/- 1.4%. These measurements are consistent with the AAPM TG 39 protocol.

Biophysical Phenomena↗
PubMed1996

Gene inactivation in the oral spirochete Treponema denticola: construction of an flgE mutant.

Treponema denticola is implicated in the etiology of periodontal diseases. We now report the construction of a specific flgE mutant of T. denticola ATCC 35405 following electroporation utilizing an erythromycin resistance cassette inserted into an flgE DNA fragment. The resulting mutant displays no visible motility and lacks periplasmic flagella as would be predicted from inactivation of the gene for the flagellar hook protein.

Bacterial Proteins↗
PubMed1996

3pK, a new mitogen-activated protein kinase-activated protein kinase located in the small cell lung cancer tumor suppressor gene region.

NotI linking clones, localized to the human chromosome 3p21.3 region and homozygously deleted in small cell lung cancer cell lines NCI-H740 and NCI-H1450, were used to search for a putative tumor suppressor gene(s). One of these clones, NL1G210, detected a 2.5-kb mRNA in all examined human tissues, expression being especially high in the heart and skeletal muscle. Two overlapping cDNA clones containing the entire open reading frame were isolated from a human heart cDNA library and fully characterized. Computer analysis and a search of the GenBank database to reveal high sequence identity of the product of this gene to serine-threonine kinases, especially to mitogen-activated protein kinase-activated protein kinase 2, a recently described substrate of mitogen-activated kinases. Sequence identitiy was 72% at the nucleotide level and 75% at the amino acid level, strongly suggesting that this protein is a serine-threonine kinase. Here we demonstrate that the new gene, referred to as 3pK (for chromosome 3p kinase), in fact encodes a mitogen-activated protein kinase-regulated protein serine-threonine kinase with a novel substrate specificity.

Amino Acid Sequence↗
PubMed1996

Regulation of rat Na+/Pi cotransporter-1 gene expression: the roles of glucose and insulin.

Cytosolic inorganic phosphate (P(i)) is important for glucose metabolism. It plays a role in homeostatic regulation of glucose by insulin and glucagon. Recently, we isolated two cDNA clones for rat Na+/P(i) cotransporter-1 (rNaPi-1) and demonstrated that they are expressed primarily in the rat liver and kidney. We now report that the expression of rNaPi-1 in these tissues is regulated by fasting and streptozotocin-induced diabetes. Using rat hepatocytes in primary culture, we also demonstrate that glucose and insulin upregulate rNaPi-1 expression, whereas glucagon and elevated intracellular adenosine 3',5'-cyclic monophosphate levels downregulate its expression. Because 2-deoxyglucose exhibits no effect on rNaPi-1 gene expression, we suggest that some metabolite accumulated during glucose metabolism may be responsible for the effects of glucose and insulin on rNaPi-1 gene expression. Our data also reveal that other known Na+/P(i) cotransporter genes, NaPi-2 and Ram-1 (a receptor for amphotropic murine retrovirus), are not regulated by insulin and glucose. It is therefore proposed that various subtypes of Na+/P(i) cotransporters are differentially regulated and that each subtype may be involved in a specific cellular function, rNaPi-1 may be responsible for Pi uptake by liver and kidney for glucose metabolism, whereas NaPi-2 may play a key role in P(i) reabsorption in the kidney.

Animals↗
PubMed1996

Body temperature and sleep in intact and ovariectomized female rats.

The present study examined intact and ovariectomized adult rats to assess the effects of removal of sex hormones on body temperature (Tb) and sleep. Subjects were 12 female rats, aged 5-8 mo, half of which were bilaterally ovariectomized (OVX). Sleep or waking and Tb were recorded under a 12:12-h light-dark cycle. There was a strong coupling between level of Tb and the three conditions of waking, slow-wave sleep (SWS), and rapid eye movement sleep (REMS): Tb was significantly positively correlated with waking and significantly negatively correlated with SWS and REMS. These correlations were even higher in OVX rats. In the light, OVX rats had more SWS and stayed awake less than did the intact rats. OVX rats had more REMS than did intact rats in both light and dark. Mean Tb and daily Tb amplitude were the same in both groups. These results suggest that ovariectomy increases and, by extension, gonadal steroids decrease, the coupling between Tb and sleep.

Animals↗
PubMed1996

Brainstem gliomas in children. A Children's Cancer Group review of 119 cases.

Brainstem gliomas (BSG) with intrinsic and extensive brainstem involvement continue to have a poor outlook despite current treatment approaches. Neuroimaging studies have aided in the differentiation of malignant brainstem tumors from more 'benign' subgroups. A Children's Cancer Group protocol evaluating outcome in children with BSG after treatment with hyperfractionated radiotherapy (7,200-7,800 cGy) was recently completed. The clinical aspects of 119 children entered into this study were reviewed in an attempt to determine risk groups and prognostic indicators. The overall survival of this group was very poor and there was no statistically significant correlation of survival with age, sex, clinical symptoms and signs, or tumor grade. Longer survival was only associated with prolonged duration of brainstem symptoms and signs greater than 1 month prior to diagnosis of the tumor. Improved outlook for children with BSG will require further research in tumor biology and newer therapeutic modalities.

Adolescent↗
PubMed1996

Immunoblot analysis of IgE and IgG binding antigens in extracts of mosquitos Aedes vexans, Culex tarsalis and Culiseta inornata.

Extracts of one globally distributed mosquito species (Aedes vexans) and two North American species (Culex tarsalis and Culiseta inornata) were prepared from heads and thoraxes. Proteins of the three extracts were separated by 12% SDS-PAGE and transferred to nitrocellulose membranes for immunoblotting. Immunoblotting was completed by sequential incubations of the membranes with a pooled human serum from subjects allergic to mosquito bites, monoclonal antibodies to human IgE or IgG, and goat antimouse IgG conjugate. Twelve to sixteen antigens with molecular masses ranging from 18.5 to 160 kDa were found in each extract. Nine antigens were shared by 3 species and 6 were shared by 2 species. Only 3 were species-unique. Most antigens bound to both IgE and IgG antibodies. IgE and IgG antibodies against A. vexans were studied by immunoblotting using individual serum from subjects with or without skin reactions to A. vexans bites. All 3 subjects with severe skin reactions had strong IgE and IgG antibodies to 32.5, 40, and 50 kDa proteins. The patterns and magnitudes of IgE and IgG antibodies to the antigens varied among individuals. Very faint IgE antibodies to these antigens were found in the 2 subjects with no skin reactions, suggesting that IgE plays a role in the development of mosquito allergy.

Aedes↗
PubMed1996

Picture resembling hemicentral retinal vein occlusion in the acquired immunodeficiency syndrome: is it related to cytomegalovirus?

Three HIV-seropositive subjects presented with diffuse inferior retinal hemorrhages. The first patient had an inferior hemicentral vein occlusion with subsequent development of an inferior cytomegalovirus retinitis. Two other patients had an inferior 'hemorrhagic' cytomegalovirus retinitis mimicking a venous occlusion, with the retinitis being subtle in 1 patient. We speculate that: (1) venous occlusion may predispose to cytomegalovirus infection of the retina by stasis and ischemic loss of endothelium; (2) early cytomegalovirus infection of the large retinal veins may give the picture of a hemorrhagic retinopathy in a subset of patients with cytomegalovirus retinitis. The differential diagnoses of hemorrhagic retinopathy in HIV-seropositive subjects include: cytomegalovirus retinitis, retinal vein occlusion, syphilitic retinitis and retinopathy of severe anemia.

AIDS-Related Opportunistic Infections↗
PubMed1996

Purification, properties, sequencing, and cloning of a lipoprotein-associated, serine-dependent phospholipase involved in the oxidative modification of low-density lipoproteins.

A novel LDL-associated phospholipase A2 (LDL-PLA2) has been purified to homogeneity from human LDL obtained from plasma apheresis. This enzyme has activity toward both oxidized phosphatidylcholine and platelet activating factor (PAF). A simple purification procedure involving detergent solubilization and affinity and ion exchange chromatography has been devised. Vmax and Km for the purified enzyme are 170 micromol.min-1.mg-1 and 12 micromol/L, respectively. Extensive peptide sequence from LDL-PLA2 facilitated identification of an expressed sequence tag partial cDNA. This has led to cloning and expression of active protein in baculovirus. A lipase motif is also evident from sequence information, indicating that the enzyme is serine dependent. Inhibition by diethyl p-nitrophenyl phosphate and 3,4-dichloroisocoumarin and insensitivity to EDTA, Ca2+, and sulfhydryl reagents confirm that the enzyme is indeed a serine-dependent hydrolase. The protein is extensively glycosylated, and the glycosylation site has been identified. Antibodies to this LDL-PLA2 have been raised and used to show that this enzyme is responsible for >95% of the phospholipase activity associated with LDL. Inhibition of LDL-PLA2 before oxidation of LDL reduces both lysophosphatidylcholine content and monocyte chemoattractant ability of the resulting oxidized LDL. Lysophosphatidylcholine production and monocyte chemoattractant ability can be restored by addition of physiological quantities of pure LDL-PLA2.

Amino Acid Sequence↗
PubMed1996

Effect of endogenously produced parathyroid hormone-related peptide on growth of a human hepatoma cell line (Hep G2).

A well differentiated human hepatoma cell line (Hep G2) was used to explore potential roles for PTH-related peptide (PTHrP) as an autocrine/paracrine growth factor. Using Northern analysis or reverse transcription-PCR, Hep G2 cells were found to express messenger RNAs for both PTHrP and the cloned PTH/PTHrP receptor, and the cells exhibited specific binding for [125I]PTHrP(1-36). Hep G2 growth medium was found to contain relatively large amounts of immunoreactive PTHrP (30 vs. 1-2 pM in medium not exposed to cells), and the PTHrP in growth medium (conditioned medium) was shown to contain N-terminal PTHrP biological activity, as assessed by the ability of the medium to stimulate cAMP production in rat osteosarcoma cells (ROS 17/2.8). Conditioned medium produced a dose-dependent severalfold increase in ROS cell cAMP that could be blocked by the PTHrP receptor antagonist [Asn10,Leu11,DTrp12]PTHrP-(7-34). PTHrP in Hep G2 cells also was detected by immunocytochemistry using antiserum to either synthetic PTHrP-(1-34) or recombinant PTHrP-(-5 to 139). Furthermore, these antisera were found to inhibit the ability of PTHrP-(1-34) to stimulate ROS cell cAMP production. When either antiserum (1:800-1:100 dilution) was added to subconfluent Hep G2 cells in medium containing 5% FBS for 3 days, a dose-related 40-50% increase in cell number occurred that could be inhibited by concurrent addition of 10 microM synthetic PTHrP-(1-36). The results show that Hep G2 cells synthesize and secrete both immunoreactive and biologically active PTHrP. As neutralization of PTHrP secreted by these cells by the addition of antiserum to PTHrP resulted in increased cell growth, the findings suggest that PTHrP can function as an autocrine or paracrine growth factor to suppress the growth of these human hepatoma cells.

Animals↗
PubMed1996

Western blotting using recombinant Hantaan virus nucleocapsid protein expressed in silkworm as a serological confirmation of hantavirus infection in human sera.

Recombinant Hantaan virus nucleocapsid protein expressed in silkworm larvae was applied as a serological diagnostic antigen in Western blots (WB) of human sera. The sensitivity of this method was similar to that of the IFA test. Hemorrhagic fever with renal syndrome (HFRS) and nephropathia epidemica diagnosed by their cross-reactivity in WB. The specificity of this method was higher than that of IFA test because the background was low. Sera that exhibited high background staining in the IFA test were readily diagnosed with this method. We recommended WB using recombinant Hantaan virus nucleocapsid antigen as a confirmatory procedure for the serodiagnosis of hantavirus.

Animals↗