Biomedical subjects

Z Li

Publications and source records attributed to Z Li.

At least 1,099 records · Page 61Linked to original sources

PubMed1997

Primer tRNA3Lys on the viral genome exists in unextended and two-base extended forms within mature human immunodeficiency virus type 1.

In human immunodeficiency virus type 1, tRNALys3 is placed upon the primer binding site, where it serves as the primer for reverse transcription. We show herein that genomic placement occurs independently of precursor protein processing and that the placed tRNALys3 exists in two major forms: unextended or in a form extended by the first two DNA bases incorporated, C and T. The two-base extended form of the tRNALys3 is absent in a protease-negative mutant, indicating a requirement for mature viral proteins to initiate reverse transcription within the virus.

Animals↗

PubMed1997

Localization of the labile disulfide bond between SU and TM of the murine leukemia virus envelope protein complex to a highly conserved CWLC motif in SU that resembles the active-site sequence of thiol-disulfide exchange enzymes.

Previous studies have indicated that the surface (SU) and transmembrane (TM) subunits of the envelope protein (Env) of murine leukemia viruses (MuLVs) are joined by a labile disulfide bond that can be stabilized by treatment of virions with thiol-specific reagents. In the present study this observation was extended to the Envs of additional classes of MuLV, and the cysteines of SU involved in this linkage were mapped by proteolytic fragmentation analyses to the CWLC sequence present at the beginning of the C-terminal domain of SU. This sequence is highly conserved across a broad range of distantly related retroviruses and resembles the CXXC motif present at the active site of thiol-disulfide exchange enzymes. A model is proposed in which rearrangements of the SU-TM intersubunit disulfide linkage, mediated by the CWLC sequence, play roles in the assembly and function of the Env complex.

Animals↗

PubMed1997

Animal model of mucosally transmitted human immunodeficiency virus type 1 disease: intravaginal and oral deposition of simian/human immunodeficiency virus in macaques results in systemic infection, elimination of CD4+ T cells, and AIDS.

Chimeric simian/human immunodeficiency virus (SHIV) consists of the env, vpu, tat, and rev genes of human immunodeficiency virus type 1 (HIV-1) on a background of simian immunodeficiency virus (SIV). We derived a SHIV that caused CD4+ cell loss and AIDS in pig-tailed macaques (S. V. Joag, Z. Li, L. Foresman, E. B. Stephens, L. J. Zhao, I. Adany, D. M. Pinson, H. M. McClure, and O. Narayan, J. Virol. 70:3189-3197, 1996) and used a cell-free stock of this virus (SHIV(KU-1)) to inoculate macaques by the intravaginal route. Macaques developed high virus burdens and severe loss of CD4+ cells within 1 month, even when inoculated with only a single animal infectious dose of the virus by the intravaginal route. The infection was characterized by a burst of virus replication that peaked during the first week following intravenous inoculation and a week later in the intravaginally inoculated animals. Intravaginally inoculated animals died within 6 months, with CD4+ counts of <30/microl in peripheral blood, anemia, weight loss, and opportunistic infections (malaria, toxoplasmosis, cryptosporidiosis, and Pneumocystis carinii pneumonia). To evaluate the kinetics of virus spread, we inoculated macaques intravaginally and euthanized them after 2, 4, 7, and 15 days postinoculation. In situ hybridization and immunocytochemistry revealed cells expressing viral RNA and protein in the vagina, uterus, and pelvic and mesenteric lymph nodes in the macaque euthanized on day 2. By day 4, virus-infected cells had disseminated to the spleen and thymus, and by day 15, global elimination of CD4+ T cells was in full progress. Kinetics of viral replication and CD4+ loss were similar in an animal inoculated with pathogenic SHIV orally. This provides a sexual-transmission model of human AIDS that can be used to study the pathogenesis of mucosal infection and to evaluate the efficacy of vaccines and drugs directed against HIV-1.

Acquired Immunodeficiency Syndrome↗

PubMed1997

The critical N-linked glycan of murine leukemia virus envelope protein promotes both folding of the C-terminal domains of the precursor polyprotein and stability of the postcleavage envelope complex.

The infectivity of Friend ecotropic murine leukemia virus was previously shown to be highly sensitive to modification in its envelope protein (Env) at only one of the eight signals for N-linked glycan attachment, the fourth from the N terminus (gs4). In the present study, a set of six single-amino-acid substitutions in or near gs4 was used to determine the function of this region of Env and the role played by the glycan itself. One mutant that lacked the gs4 glycan was fully infectious, while one that retained this glycan was completely noninfectious, indicating that the gs4 glycan per se is not required for Env function. Infectivity correlated with the level of mature Env complex incorporated into virus particles, which was determined by the severity of defects in transport of the envelope precursor protein (gPrEnv) from the endoplasmic reticulum into the Golgi apparatus, in cleavage of gPrEnv into the two envelope subunits (the surface protein [SU] and the transmembrane protein [TM]), and in the association of SU with cellular membranes. All of the mutants induced the wild-type level of superinfection interference, indicating that the gs4 region mutations did not interfere with proper folding of the N-terminal domain of SU. These results suggest that the gs4 region mediates folding of the C-terminal domains of gPrEnv and stability of the interaction between SU and TM. Although the gs4 glycan was not essential for infectivity, processing of all mutant Envs lacking this glycan was significantly impaired, suggesting that efficient folding of gPrEnv requires a glycan at this position. The conservation of a glycosylation site homologous to gs4 across a broad range of retroviruses suggests that this sequence may play a similar role in many retroviral Envs.

3T3 Cells↗

PubMed1997

A new member of the I kappaB protein family, I kappaB epsilon, inhibits RelA (p65)-mediated NF-kappaB transcription.

A novel member of the I kappaB family has been identified as a protein that associated with the p50 subunit of NF-kappaB in a yeast two-hybrid screen. Similar to previously known I kappaB proteins, this member, I kappaB epsilon, has six consecutive ankyrin repeats. I kappaB epsilon mRNA is widely expressed in different human tissues, with highest levels in spleen, testis, and lung. I kappaB epsilon interacts with different NF-kappaB proteins, including p65 (RelA), c-Rel, p50, and p52, in vitro and in vivo and inhibits the DNA-binding activity of both p50-p65 and p50-c-Rel complexes effectively. Endogenous and transfected NF-kappaB (RelA-dependent) transcriptional activation is inhibited by I kappaB epsilon. I kappaB epsilon mRNA is expressed at different levels in specific cell types and is synthesized constitutively in transformed B-cell lines. It also displays differential induction in response to tumor necrosis factor alpha, interleukin-1, or phorbol ester stimulation compared to I kappaB alpha in non-B-cell lines. Therefore, I kappaB epsilon represents a novel I kappaB family member which provides an alternative mechanism for regulation of NF-kappaB-dependent transcription.

Amino Acid Sequence↗

PubMed1997

Effects of fluid flow on intracellular calcium in bovine articular chondrocytes.

Fluid flow-induced shear stress results in a variety of morphological and metabolic changes in cultured bovine articular chondrocytes (BAC). However, the mechanism by which the flow signal is transduced into a biological response is unknown. Therefore, we investigated the effects of fluid flow on intracellular Ca2+ concentration ([Ca2+]i) in BAC. Cells loaded with fura 2 were exposed to steady and pulsatile (0.5 Hz) flow at 9, 18, and 34 ml/min in a parallel-plate flow chamber. In response to flow, there was a significant and flow rate-dependent increase in the percentage of cells showing a rise in [Ca2+]i, but no effect on the [Ca2+]i response amplitude. There was no significant difference between the [Ca2+]i responses to steady and pulsatile flow. Mean intracellular Ca2+ response values ranged between 26.2 +/- 1.6 (9 ml/min) and 38.0 +/- 6.8 nM (34 ml/min) above basal [Ca2+]i (81.3 +/- 24.1 nM, n = 90). Removal of extracellular Ca2+ or addition of Gd3+ significantly reduced the percentage of cells responding, suggesting that influx of Ca2+, possibly through mechanosensitive channels, contributes to the rise in intracellular Ca2+. Our data suggest fluid flow-induced mobilization of intracellular Ca2+ may contribute to the mechanism by which mechanical loads are transduced by chondrocytes.

Animals↗

PubMed1997

Age-related decreases in stimulatory G protein-coupled adenylate cyclase activity in osteoblastic cells.

In this study we examined parathyroid hormone (PTH)-, forskolin (FSK)-, and cholera toxin (CTX)-stimulated adenosine 3',5'-cyclic monophosphate (cAMP) accumulation in rat osteoblastic cells (ROB) isolated from young (4 mo), mature (12 mo), and old (24-28 mo) male rats. Exposure to PTH increased cAMP accumulation in a concentration-dependent manner in all ROB cells examined. However, the maximum response in ROB from young rats was threefold greater than the maximum response in those from mature and old rats. Exposure to FSK also stimulated cAMP accumulation in a concentration-dependent manner, but there were no significant differences in responsiveness among ROB isolated from young, mature, and old rats. Exposure to CTX resulted in a dramatic concentration-dependent increase in cAMP in ROB from young rats but only a modest increase in ROB from mature and old rats. PTH binding kinetics were similar in ROB from rats in each age group. These data suggest an age-related defect in stimulatory G protein coupling to adenylate cyclase, which contributes to decreased osteoblastic responsiveness to PTH.

Adenylyl Cyclases↗

PubMed1997

Ovariectomy eliminates sex differences in rat tail artery response to adrenergic nerve stimulation.

The influence of gonadal hormones on vasoconstrictor responses to adrenergic nerve stimulation was investigated by comparing tail arteries from intact and gonadectomized male and female Fisher 344 rats. Arterial ring segments from females were significantly less responsive to transmural nerve stimulation (1-8 Hz) than arteries from age-matched males. Significant male-female differences persisted after correcting the contractile responses for sex-related differences in arterial mass, optimal resting tension, and maximal contractile force. Arteries were taken from cycling, intact females in either proestrus, estrus, metestrus, or diestrus, but no significant differences were found among the four stages for vasoconstrictor responses to either adrenergic nerve stimulation or exogenous norepinephrine. These data suggest adrenergic function in the artery is not affected by hormonal variations during the estrous cycle. After bilateral ovariectomy, however, contractile responses of female arteries to adrenergic nerve stimulation were increased to levels similar to those observed in male arteries. Orchidectomy of males, in contrast, had no effect on neural-evoked contraction. Low concentrations of norepinephrine also produced greater contractile responses in male compared with female arteries; however, this sex-related difference was eliminated by orchidectomy but not ovariectomy. Taken together, the results indicate that circulating gonadal hormones contribute to gender differences observed in rat tail artery. Vasoconstrictor responses to exogenous norepinephrine appear to be enhanced by testicular hormones. In contrast, vasoconstriction induced by adrenergic nerve stimulation appears to be influenced by chronic exposure to circulating ovarian hormones, resulting in a smaller vascular response in female arteries.

Animals↗

PubMed1997

Increased cardiomyocyte apoptosis during the transition to heart failure in the spontaneously hypertensive rat.

The transition from compensated hypertrophy to failure in spontaneously hypertensive rats (SHR) of advanced age is associated with a marked increase in collagen, a reduction in myocyte mass, and a reduction in maximum Ca(2+)-activated myofibrillar force. We hypothesized that the reduction in myocyte mass and associated functional loss may be due to increased cell death by apoptosis. To test this hypothesis, we studied hearts from failing (SHR-F) and nonfailing SHR (SHR-NF) and age-matched Wistar-Kyoto rats (WKY). In addition, hearts from SHR-F that had been treated with an angiotensin-converting enzyme inhibitor (captopril) for an average of 27 days were also studied. Apoptotic cells were quantified in cross sections of myocardium by the terminal deoxynucleotidyltransferase- mediated 2'-deoxyuridine 5'-triphosphate nick end labeling technique. To identify the type of the cells undergoing apoptosis, sections were also stained for alpha-sarcomeric actin. Apoptotic cells were significantly increased in the SHR-F (38.92 +/- 12.79 vs. 8.05 +/- 3.98 cells/100,000 nuclei in SHR-NF; P < 0.05 and vs. 2.21 +/- 1.4 cells/100,000 nuclei in WKY; P < 0.01). Captopril treatment of SHR-F reduced the number of apoptotic cells to the level in SHR-NF (9.17 +/- 1.53 cells/100,000 nuclei; P < 0.01 vs. SHR-F). Most apoptotic cells were of cardiac myocyte origin. There was no significant difference in Bcl-2 protein expressed by hearts among the three groups. WAF-1 mRNA levels were increased in both SHR groups vs. WKY; in SHR-F, the density of WAF-1 mRNA was higher than in SHR-NF. Thus increased numbers of apoptotic cells are present in failing SHR hearts, suggesting that apoptosis might be a mechanism involved in the reduction of myocyte mass that accompanies the transition from stable compensation to heart failure in this model. Administration of the angiotensin-converting enzyme inhibitor captopril, which ameliorates heart failure in this model, is associated with a reduction in the exaggerated apoptosis that accompanies heart failure.

Angiotensin II↗

PubMed1997

Expression of functional gap junctions in cultured pulmonary alveolar epithelial cells.

Recent observations suggest that cell-cell interactions may modulate the response of the alveolar epithelium to injury. Expression and function of gap junctions were thus evaluated in isolated alveolar type II cells. Freshly isolated (day 0) type II cells expressed mRNAs for gap junctional connexins 26, 32, and 43. Whereas connexin 26 mRNA declined approximately 40% in cultured cells, connexin 32 message decreased rapidly and was not detectable on day 1. In contrast, connexin 43 expression increased 10-fold by day 3 compared with day 0. Western blot confirmed a 30-fold elevation in connexin 43 protein. Connexin 45 mRNA was not detected. Functional gap junction-mediated calcium signal propagation was monitored using fura 2, a calcium-sensitive dye. Membrane deformation in a single type II cell increased intracellular calcium; the signal spread rapidly to neighboring cells by octanol-sensitive pathways. Transfer of Lucifer yellow between cells also was inhibited by octanol. These observations demonstrate functional gap junctions between cultured alveolar epithelial cells and suggest that gap junctional expression and gap junction-mediated cell-cell coupling are regulated with time in culture.

Animals↗

PubMed1997

Tamoxifen inhibits arterial accumulation of LDL degradation products and progression of coronary artery atherosclerosis in monkeys.

Estrogen replacement therapy reduces the risk of coronary heart disease in postmenopausal women and inhibits progression of coronary artery atherosclerosis in monkeys. Tamoxifen is a nonsteroidal compound with mixed estrogen agonist and antagonist properties. Its antagonist activity is useful in chemotherapy of breast cancer and may have protective effects on plasma lipid concentrations, but its effects on atherogenesis have not been defined. The goal of this study was to examine the effect of tamoxifen on plasma lipids, arterial and hepatic LDL metabolism, and progression of coronary artery atherosclerosis in surgically postmenopausal female monkeys. Thirty-five monkeys were fed an atherogenic diet containing 1.3 mg.kg-1.d-1 tamoxifen (equivalent to the usual dose of 20 mg/d given to women). Thirty-one monkeys were fed the same atherogenic diet with no tamoxifen. Ten monkeys from each treatment group were fed the test diets for 12 weeks to examine the short-term effects of tamoxifen on arterial LDL metabolism. The rest of the monkeys were fed the test diets for 3 years to study the long-term effects of tamoxifen on development of atherosclerosis. In the short term, tamoxifen inhibited the rate of arterial accumulation of LDL degradation products overall (P = .03) and decreased hepatic cholesterol content (P = .003). In the long term, tamoxifen increased plasma concentrations of triglycerides (0.60 +/- 0.67 versus 0.23 +/- 0.02 mmol/L, P = .001) and reduced average LDL molecular weight (5.3 +/- 0.2 versus 4.8 +/- 0.1 g/mumol, P = 0.004) but had no effects on plasma total, LDL, or HDL cholesterol concentrations. Coronary artery atherosclerosis (intimal area, mean +/- SEM) was 0.25 +/- 0.06 mm2 in control monkeys and 0.12 +/- 0.03 mm2 in tamoxifen-treated monkeys (P = .057). We conclude that tamoxifen has antiatherogenic effects that may be modulated in part through direct effects on arterial LDL metabolism.

Animals↗

PubMed1997

Inhibitory effects of hypercholesterolemia and ox-LDL on angiogenesis-like endothelial growth in rabbit aortic explants. Essential role of basic fibroblast growth factor.

Hypercholesterolemic (HC) rabbits exhibit suppressed compensatory vascular growth after restriction of arterial supply. However, neovascularization is commonly found in atheromas containing inflammatory cells. We used an in vitro model to determine the effects of hypercholesterolemia on angiogenesis in the absence or presence of inflammatory cells. HC rabbit aortic explants (1 mm2) with or without (n = 90 each) lesion-forming inflammatory cells were cultured in a collagen matrix with serum-free medium. Explant-derived endothelial cell growth was organized into capillary-like microtubes (CLM) that could be videomicroscopically quantified. CLM growth from lesion-free HC explants was significantly reduced to 13 +/- 4% of the value in explants (n = 90) from normocholesterolemic (NC, n = 15) rabbits (P < .001). In contrast, in lesion-containing HC explants, the matrix was invaded by foam cells, and CLM growth was not inhibited. Immunoassayable basic fibroblast growth factor (bFGF, in pg/mL) in the culture medium was significantly lower in lesion-free HC (< 5) than NC explants (11 +/- 2, P < .01) or HC explants with lesions (14 +/- 3). In addition, CLM growth was reduced in NC explants incubated with oxidized LDL (ox-LDL, 50-100 micrograms/mL). Exogenous bFGF (10 ng/mL) reversed the inhibitory effects of hypercholesterolemia and ox-LDL, whereas bFGF-neutralizing antibody (10 micrograms/mL) abolished CLM growth in all groups. In cultured rabbit aortic endothelial cells, ox-LDL reduced DNA synthesis, but this inhibition was reversed by bFGF. We conclude that hypercholesterolemia and ox-LDL inhibit angiogenesis like endothelial growth because of a suppressed availability of endogenous bFGF. Retained responsiveness to exogenous bFGF suggests that inducing bFGF expression at targeted sites may improve collateral growth in hyperlipidemic arterial disease.

Animals↗

PubMed1997

Expression of connexin 43 in rat mandibular bone and periodontal ligament (PDL) cells during experimental tooth movement.

Bone remodeling in response to force requires the coordinated action of osteoblasts, osteoclasts, osteocytes, and periodontal ligament cells. Coordination among these cells may be mediated, in part, by cell-to-cell communication via gap junctions. This study tests the hypothesis that the regulation of expression of connexin 43, a gap junction protein, is part of the transduction mechanism between force as applied to bone during orthodontic tooth movement and bone remodeling. To test this hypothesis, we examined connexin 433 expression in a rat model system of experimental tooth movement. To establish the model, we extracted maxillary first molars to initiate supra-eruption of opposing mandibular molars. The rats were killed at 0, 6, 12, 24, and 48 hrs post-extraction. The mandibles were removed, demineralized, and embedded in paraffin. To localize connexin 43 protein and mRNA, we used a specific antibody for immunohistochemistry and a specific cDNA probe for in situ hybridization. Western and Northern blot analyses were used to assess the specificity of the connexin 43 antibody and cDNA probe, respectively. We found connexin 43 protein expressed by osteoclasts (++ ++) and periodontal ligament cells (++ +) in compression zones, and by osteoblasts (++ ++) and osteocytes (++ ++) in tension zones of the periodontal ligament. In addition, connexin 43 mRNA was found in some bone and periodontal ligament cells. Connexin 43 protein was found, by densitometric analysis, to be higher in the periodontal ligament after exposure to force compared with controls (P < 0.001). The number of osteocytes expressing connexin 43 48 hrs after molar extraction was also significantly greater in bone subjected to tension when compared with controls (P < 0.001). The results of this study support the hypothesis that connexin 43 plays a role in the coordination of events during experimentally induced alveolar bone remodeling.

Animals↗

PubMed1997

The impact of payor/provider type on health care use and expenditures among the frail elderly.

OBJECTIVES: This study examined whether health care expenditures and usage by the frail elderly differ under three payor/provider types: Medicare fee for service, Medicare health maintenance organization (HMO), and dual Medicare-Medicaid enrollment. METHODS: In-home interviews were conducted among 450 frail elderly patients of a San Diego, Calif, health care system. Cost and use data were collected from providers. RESULTS: Analyses revealed no difference in total expenditures between fee-for-service and HMO enrollees, but Medicare-Medicaid beneficiaries' expenditures were 46.8% higher than those for HMO enrollees and 52.2% higher than those for the fee-for-service group. Fee-for-service participants were less than half as likely as HMO enrollees to have two or more hospital admissions, but hospital usage rates between those two payor/provider groups did not differ. Not were there payor/provider differences in access to home health care, but HMO home health care users received significantly fewer services than the others. CONCLUSIONS: The care provided to these HMO beneficiaries resulted in a combination of restricted home health use and higher multiple hospitalizations. This raises compelling questions for future research. For the dually enrolled, stronger cost containment may be required.

Activities of Daily Living↗

PubMed1997

Effect of milk fat content on flavor perception of vanilla ice cream.

The effects of milk fat concentration on flavor perception of vanilla ice cream (with 0.5 to 10% fat) were studied by sensory analyses. The percentage of free vanillin in the ice cream was determined by HPLC. The HPLC data showed that the amount of free vanillin decreased when fat content increased. Perceptions of vanilla flavor and sweetness were evaluated by a trained panel using time-intensity methodology. No significant difference was found in sweetness perception. Among 11 time-intensity parameters for vanilla flavor perception, the panel found a significant difference only in the time required to reach maximum vanilla intensity. However, free-choice profiling and a consumer preference panel showed, respectively, that, as fat content was increased, sensory quality improved, and overall preference increased.

Animals↗

PubMed1997

[A simple nitric oxide exposure system for small animals].

A nitric oxide exposing system was designed for experimental research, which consist of equipments such as plexiglass chamber, blower, flowmeter, NO/N2 cylinder, pure O2 cylinder, NOx analyzer, and O2/CO2 monitor. The efficacy of the whole system has been verified through our practice as shown by the following results: measured NO inside the chamber were close to designed NO concentration, measured O2 concentrations in the chamber were similar to that of the atmosphere, and the highest nitrogen dioxide (NO2) and carbon dioxide (CO2) concentrations were lower than 3 ppm and 0.3% respectively. The experimental facility is simple in construction, easy to be operated and convenient for research on effects and toxicity of long-term inhaled nitric oxide in small animals.

Administration, Inhalation↗

PubMed1997

[The effect of endurance training and exhaustive exercise on metallothionein in rats].

To understand physiological role of metallothionein (MT) during exercise, MT levels in liver, brain, heart, lung, blood vessel, skeletal muscle and serum were observed in rats. The results showed that the levels of MT were decreased by 13-34% in lung, liver, heart and skeletal muscle of rats trained by swimming for 10 weeks and were increased by 21%-75% in skeletal muscle, heart, brain, lung and liver of rats after exhaustive swimming respectively, compared with normal control rats. (P < 0.05 and P < 0.01). But the levels of MT in blood vessel and serum were not changed in two groups of rats by swimming for 10 weeks and acute exhaustive swimming (P > 0.05). It is suggested that the different changes of MT levels under physical training and acute exhaustive exercise may be of importance in protection against oxygen free radicals.

Animals↗

PubMed1997

[DNA typing for HLA-DR and HLA-DQ alleles in Chinese patients with rheumatoid arthritis].

We analysed the associations of DR and DQ alleles with rheumatoid arthritis (RA) in Han nationality of China. PCR-RFLP technique was used to determine DRB1, DQA1 and DQB1 alleles in 35 unrelated patients with RA and 100 healthy controls from the Hans. The frequency of DR4 was 51.4% in RA patients and 24.0% in the healthy controls (P < 0.01, RR = 3.30). Subtyping of DR4 revealed no differences in the relative distributions of the DR4 alleles between the RA group and the controls, which both were predominated by DRB1 * 0405 allele, but there was a significant increase in the absolute frequency of DRB1 * 0405 in RA patients compared with the healthy controls (31.4% vs 12.0%, P < 0.01). DQ4 (DQB1 * 04) was also increased both in the RA patients compared with the healthy controls (37.1% vs 10.0%, P < 0.001) and in DR4+ RA patients compared with DR4+ healthy ones (72.2% vs 41.6%, P = 0.0376). Further analysis showed that the haplotype DR4-DQ4 was associated with RA (RR = 5.17, P < 0.001), and that the DR4(+)-DQ4+ patients had more severe disease than the DR4- patients. These results suggest that DR4, mainly the DRB1 * 0405, is associated with RA in Han nationality, and DQ4 may play a role in DR4 conferring susceptibility to RA. The DR4-DQ4 haplotype could be taken as a predictive marker for disease severity.

Alleles↗