Search PubMed⌕ Search

Biomedical subjects

X Hu

Publications and source records attributed to X Hu.

At least 523 records · Page 29Linked to original sources
PubMedDate not supplied

Investigation of the initial dip in fMRI at 7 Tesla.

In agreement with optical imaging studies, previous fMRI studies have reported an initial decrease (i.e. the initial dip) in the BOLD response, which is believed to arise from an increase in oxygen consumption and to be mostly microvascular. To date, experimental studies of the initial dip in humans have been performed at fields up to 4 T, with relatively low spatial resolution. Because the sensitivity to microvascular contribution is increased at high magnetic fields, the present study investigated the initial dip at 7 T. In addition, to reduce the partial volume effect, the study is conducted at a high spatial resolution. The initial dip was detected in all subjects studied and was found to reside mostly in the gray matter. The relative amplitude of the early response was found to be 0.6, higher than that at 4 T (0.3) and 1.5 T (0.11). In addition, based on the assumption that the initial dip is a result of increased oxygen utilization, the fractional change in oxygen utilization was estimated to be 40% of that of the fractional change in cerebral blood flow. These results are in agreement with the notion that the initial dip arises from an increase in oxygen consumption.

Adult↗
PubMedDate not supplied

Kinetic studies of the reaction of hydroxyl radicals with trichloroethylene and tetrachloroethylene.

Rate coefficients are reported for the gas-phase reaction of the hydroxyl radical (OH) with C2HCl3 (k(1)) and C2Cl4 (k2) over an extended temperature range at 740+/-10 Torr in a He bath gas. These absolute rate measurements were accomplished using a laser photolysis/laser-induced fluorescence (LP/LIF) technique under slow flow conditions. The simple Arrhenius equation adequately describes the low temperature data for k1 (<650 K) and the entire data set for k2 and is given by (in units of cm3 molecule(-1) s(-1)): k1(291 - 650 K) = (9.73+/-1.15) x 10(-13) exp (158.7+/-44.0)/T, k2(293 - 720 K ) = (1.53+/-0.14) x 10(-12) exp (-688.2+/-67.5)/T. Error limits are 2sigma values. The room temperature values for k1 and k2 are within +/-2sigma of previous data using different techniques. The Arrhenius activation energies for k1 and k2 are a factor of 2-3 lower than previously reported values. The experimental measurements for both k1 and k2 in conjunction with transition state and variation transition state theory calculations infer an OH addition mechanism. The lack of a measurable kinetic isotope effect for k1 is consistent with this mechanism. Insight into the subsequent reactions of the chemically activated intermediate are presented in the form of potential energy diagrams derived from ab initio calculations.

Journal Article↗
PubMedDate not supplied

Transcriptional repression by nuclear hormone receptors.

Repression by nuclear receptors plays important roles in acute promyelocytic leukemia and other diseases. Nuclear receptor corepressor (N-CoR) and SMRT (silencing mediator of retinoic acid and thyroid hormone receptor) are corepressor proteins whose modular structure facilitates receptor interaction as well as transduction of repression signals involving histone deacetylation, alterations in chromatin structure and direct interactions with the basal transcription machinery. Interactions between nuclear receptors and corepressor complexes have multiple determinants. This allows regulation, and potentially therapeutic manipulation, of receptor, corepressor, cell-type and target-gene specificity.

Humans↗
PubMedDate not supplied

A cDNA clone from the Duchenne/Becker muscular dystrophy gene.

Duchenne muscular dystrophy (DMD) is the most common of the muscular dystrophies affecting one in 3,000 live male births. Both DMD and the mild form, Becker muscular dystrophy (BMD), are X-linked. There are a number of females affected by the disease who all possess an X-autosome translocation, with the exchange point in the X always occurring within chromosome band Xp21. This, together with linkage and deletion data, has localized the gene at band Xp21. DNA fragments from this region have been cloned using a patient with a large Xp21 deletion and from a patient with a t(X:21) translocation. The former clones (pERT 87) comprise the DXS164 locus and the latter clones (XJ) the DXS206 locus. Subclones from both regions allow the detection of deletions in approximately 11% of DMD patients. A fetal muscle complementary DNA clone corresponding to exons in the DXS164 locus has been isolated and detects a 16-kilobase (kb) transcript. We present the isolation of an adult muscle cDNA clone from the DXS206 locus that detects a 16-kb mRNA in adult human muscle. The cDNA clone contains exons that map in the DXS206 locus, the DXS164 locus, and on the centromeric side of these cloned regions. The t(X;21) translocation exchange points occurs within a large intron of 105 kb or larger, indicating that the translocation has disrupted the DMD/BMD gene to cause the disease in this patient.

Chromosome Deletion↗
PubMedDate not supplied

Sequence variations of the late upstream region of HPV16 in cervical intraepithelial neoplasm and invasive carcinoma.

HPV16 is the most common type of human papillomavirus (HPV) seen in cervical squamous cell carcinoma. A 78-bp promotor element at nt 4118-4196 called late upstream region (LUR), critical for the expression of late genes, has been identified recently. Late genes encode viral capsid proteins that coat viral DNA to form particles and serve as antigen. To elucidate whether there are any sequence variations within LUR of HPV16 and any difference of these sequence variations between cervical invasive squamous cell carcinoma (CIC) and cervical intraepithelial neoplasia (CIN), we sequenced HPV16 LUR from 50 cases of HPV16-positive CIC and CIN. We found that variation frequency in the late upstream region ranged from 0 to 4.2 except for two cases in which variation frequency was as high as 22.8%. Eight of 24 CINs and 17 of 26 CICs contained two or more variations (33% vs. 65%, P < 0.025). The results suggested that the sequence variations occurred more often in LUR of HPV16 than in other regions of HPV16 and the variations in HPV16 LUR might play a role in the process of carcinogenesis of cervical carcinoma.

Base Sequence↗
PubMedDate not supplied

Ovarian toxicity of 4-vinylcyclohexene diepoxide: a mechanistic model.

Female mammals are born with a finite number of ovarian primordial follicles that cannot be regenerated; thus, chemicals that destroy oocytes contained in these follicles can produce premature ovarian failure (early menopuase in women). Exposure of women to known ovotoxicants, such as contaminants in cigarette smoke, is associated with early menopause. Thus, the potential risks posed by ovotoxic chemicals is of concern. Our studies have focused on the environmental chemical 4-vinylcyclohexene (VCH), which is produced during the manufacture of rubber tires, flame retardants, insecticides, plasticizers, and antioxidants. Dosing of female rats and mice with the ovotoxic diepoxide metabolite of VCH, 4-vinylcyclohexene diepoxide (VCD), for 30 days destroyed the majority of ovarian primordial follicles. Using VCD in rats as a generalized model for ovotoxicity, we determined that 1) repeated daily dosing is required, 2) cell death is via apoptosis, and 3) altered expression of specific genes is involved. An integrated approach at the morphologic, biochemical, and molecular level was used to support these conclusions. Studies in isolated rat small preantral follicles (targeted for VCD-induced ovotoxicity) focused on the role of cell death genes, mitochondrion-associated events, and VCD metabolism. We also evaluated how this information relates to human risk for early menopause. These animal research results provide a better understanding of the potential risk of human exposure to environmental ovarian toxicants and greater insight as to the impact of these toxicants on reproductive health in women.

Animals↗
PubMedDate not supplied

Clinical significance of anti-glomerular basement membrane antibodies in a cohort of Chinese patients with lupus nephritis.

OBJECTIVES: To evaluate the clinical and laboratory features of patients with lupus nephritis (LN) in the presence and absence of anti-glomerular basement membrane antibodies (anti-GBM) and to establish whether the characteristics of the disease correlate with anti-GBM. METHODS: We performed a retrospective study of 157 hospitalised patients with systemic lupus erythematosus (SLE), 91 of whom had LN. The test for anti-GBM used an enzyme-linked immunosorbent assay (ELISA). Clinical and laboratory data were collected and assessed in LN patients with and without anti-GBM. RESULTS: Anti-GBM was detected in 14 (8.9%) of 157 patients with SLE. All of the 14 patients developed LN; of these, 10 reached the criteria for crescentic glomerulonephritis (CGN) and five were diagnosed as Goodpasture's disease. Serum anti-GBM levels were correlated with the presence of both anti-double-stranded DNA antibodies (anti-dsDNA) and anti-nucleosome antibodies (anti-NuA). Significant differences in extrarenal clinical manifestations were found between anti-GBM-positive and -negative LN patients, with regard to pleuritis, pulmonary haemorrhage, sinusitis, and anaemia in particular. CONCLUSIONS: LN with anti-GBM is not rare in Chinese patients. Anti-GBM, together with the additional nephritogenic potential of anti-dsDNA and anti-NuA, may play an essential role in the pathogenesis of the anti-GBM disease in LN. Therefore, in addition to routine anti-GBM assay, anti-dsDNA and anti-NuA measurements should be performed early to ensure a prompt diagnosis and immediate treatment in patients with anti-GBM-mediated disease.

Adult↗
PubMedDate not supplied

Retrospective fusion of radiographic and MR data for localization of subdural electrodes.

Prior to epilepsy surgery, subdural electrodes are often implanted and monitored for a few days to identify the focus of abnormal electrical activity. During the implantation and subsequent brain resection, there may be uncertainty about the exact location of the electrodes with respect to features of brain anatomy such as specific gyral convolutions or lesions. In experiments with a phantom and patients, implanted electrodes were imaged with multiplanar skull radiographs (or CT scans). After retrospective registration with preimplantation MR data, the electrodes were mapped from these studies onto an MR-derived three-dimensional brain model. The resulting multimodality displays showed the relationship of the electrodes to brain anatomy. In one patient the position of each electrode with respect to a metabolic lesion was also displayed by mapping preimplantation PET data onto the same brain model. This new display of electrode positions may strengthen the interpretation of subdural electrical recordings and thereby reduce uncertainty in planning the resection of epileptic tissue.

Adult↗
PubMedDate not supplied

Does P-glycoprotein play a pivotal role in the drug resistance of an MDR variant, K562/Dox?

A multidrug-resistant (MDR) variant, K562/Dox, was selected from repeated exposure of human erythroleukemia cell line K562 to doxorubicin (Dox). K562/Dox displayed typical MDR features with respect to its cross-resistance to a variety of functionally and structurally unrelated compounds: vincristine (Vin), Dox, mitomycin C, reduced steady-state intracellular anthracycline accumulation, and elevated P-glycoprotein expression/mdr1 mRNA transcription/mdr1 gene amplification. Nevertheless, by incubation of cells with Dox/epirubicin (Epi)/daunorubicin (Dau) (5-80 micrograms/ml), the initial drug uptake was similar (p > 0.05) in K562/Dox and K562 cells, suggesting P-glycoprotein-mediated drug efflux would not occur unless a relatively high cellular drug concentration was reached. After 8 h incubation of cells with 50 ng/ml Dox (5 times higher than its IC50 to K562 cells), there were only slight differences (p > 0.05) in intracellular drug levels between K562/Dox and K562 cells, clearly indicating that K562/Dox, circumventing drug toxicity in this case, was irrelevant to reduced drug accumulation caused by P-glycoprotein. Similar results were obtained when Epi or Dau was applied. Despite complete restoration of anthracycline accumulation in K562/Dox cells in the presence of 6 mumol/l verapamil, the reversal of their drug resistance was incomplete. These results suggest that P-glycoprotein-mediated drug efflux possibly did not play a primary role in the drug resistance of K562/Dox cells.

ATP Binding Cassette Transporter, Subfamily B, Mem↗
PubMedDate not supplied

Immunohistochemical and DNA sequencing analysis on human mismatch repair gene MLH1 in cervical squamous cell carcinoma with LOH of this gene.

BACKGROUND: The human MLH1 gene (hMLH1) is one of the DNA mismatch repair genes. Defects in these genes are believed to be the underlying cause of microsatellite instability (MSI). MSI has been demonstrated in many human cancers such as colon cancer and some female-specific tumors. The hMLH1 gene can be inactivated by genetic mutation or by hypermethylation of its promoter region, which often causes cessation of hMLH1 protein production. We were prompted by our previous finding of 43% of cervical cancers and their precursors with a loss of heterozygosity (LOH) of the hMLH1 gene to investigate whether it is inactivated during the carcinogenesis of cervical cancer. MATERIALS AND METHODS: hMLH1 protein production was assessed by immunohistochemistry, and nucleotide sequence analysis were performed on all exons of the hMLH1 gene. RESULTS: In 11 cases of invasive cervical cancer, among which 7 had LOH of the hMLH1 gene, immunohistochemistry provided no evidence for cessation of hMLH1 protein production. In addition, no mutations were found in any of the 19 hMLH1 gene exons. CONCLUSIONS: The activity of hMLH1 gene might not be disturbed in the development of cervical cancer although a proportion of the cases had lost one of its hMLH1 gene copies.

Adaptor Proteins, Signal Transducing↗
PubMedDate not supplied

Non-Hodgkin's lymphoma in women with breast cancer.

PURPOSE: The purpose of this study was to describe a series of patients with breast cancer and non-Hodgkin's lymphoma and to determine the usual sequence of the diagnoses. Therapy for both neoplasms and its relationship to the development of the second neoplasm were also evaluated. PATIENTS AND METHODS: Patients were identified primarily from cancer registries at various institutions. The observed proportion of women diagnosed with breast cancer first, after, or simultaneously with non-Hodgkin's lymphoma was compared with the expected proportion by employing New York State and Surveillance, Epidemiology, and End Results program cancer incidence rates. RESULTS: The expected number of lymphoma cases that were diagnosed after or simultaneously with breast cancer was 31.6 (New York state data) to 39.1 (New York State and Surveillance, Epidemiology, and End Results data), and 78 such cases were identified from a total group of 87 (P < or = .001). There was no evidence that in this study, lymphoma as a second neoplasm was therapy induced. DISCUSSION: Anecdotal case reports suggest a relationship between breast cancer and non-Hodgkin's lymphoma. Mouse mammary tumor virus induces breast cancer and, in some circumstances, lymphoma in mice. The mouse mammary tumor virus ENV gene has been identified in approximately one third of human breast cancers. Women with both breast cancer and lymphoma are diagnosed first with breast cancer or simultaneously with both cancers more frequently than expected, and the lymphoma is not therapy induced. In some women with both breast cancer and lymphoma, the two neoplasms may have a common etiology, perhaps viral.

Adult↗
PubMedDate not supplied

Two-body wear of dental composites under different loads.

PURPOSE: Although dental composites are excellent for restoring the appearance of natural tooth tissues, their relatively poor resistance to wear, especially in approximal and occlusal contact areas, is still a major source of concern. The aim of this research was to study a basic wear mechanism, under 2-body wear conditions, that may be integrated into our understanding of the in vitro and in vivo wear behavior of dental composites. MATERIALS AND METHODS: An in vitro 2-body wear test was conducted on 2 selected ultrafine compact-filled dental composites under different magnitudes of sinusoidal cyclic load. The wear surfaces and cross sections of the wear layers were assessed using scanning electron microscopy (SEM) to explore the nature of the wear pattern of the dental composites under cyclic loading conditions. RESULTS: The wear losses of both composites increased with load. SEM analysis of wear surfaces and subsurface sections indicated that the composites tested displayed different wear mechanisms from low to high loads. An explanation for the wear pattern is proposed based on the observed wear behavior. CONCLUSION: The in vitro wear pattern of the ultrafine compact-filled dental composites tested is closely related to the applied load. Although the wear loss increased in a roughly linear relationship with applied load, the underlying wear mechanism involved may experience a significant change from low to high load conditions during wear.

Bisphenol A-Glycidyl Methacrylate↗
PubMedDate not supplied

[Cervical carcinoma progression-associated genetic alterations on chromosome 6].

To identify the loci associated with progression of cervical carcinoma, chromosome 6 regions were tested for loss of heterozygosity. Detailed analysis with 28 microsatellite markers revealed a high frequency of allelic deletions for several loci of the short (6p25, 6p22, 6p21.3) and long (6q14, 6q16-21, 6q23-24, 6q25, 6q27) arms of chromosome 6. Examination of 37 microdissected carcinoma and 22 cervical dysplasia specimens revealed allelic deletions from the HLA class I-III genes (6p22-21.3) and subtelomeric locus 6p25 were found in more than 40% dysplasia specimens. With multiple microdissection of cryosections, genetic heterogeneity of squamous cervical carcinoma was analyzed, and clonal and subclonal allelic deletions from chromosome 6 were identified. Half of the tumors had clonal allelic deletion of D6S273 (6p21.3), which is in a Ly6G6D (MEGT1) intron in the HLA class III gene locus. The frequency of allelic deletions from the chromosome 6 long arm was no more than 20% in dysplasias. Allelic deletions from two loci, 6q14 and 6q16-21, were for the first time associated with invasion and metastasis in cervical carcinoma.

Chromosomes, Human, Pair 6↗
PubMedDate not supplied

Comparison of sufentanil, bupivacaine, and their combination for epidural analgesia in obstetrics.

BACKGROUND AND OBJECTIVES: We postulated that epidural sufentanil alone would provide adequate analgesia for labor and delivery. We also considered the possibility that a combination of epidural sufentanil and bupivacaine would demonstrate superior analgesia and fewer side effects when compared with either agent alone. METHODS: Using a randomized, double-blind design, parturients were prospectively assigned to receive intermittent 10-ml doses of 3 micrograms/ml sufentanil in saline (Group S), 1.5 micrograms/ml sufentanil in 0.125% bupivacaine (Group SB), or 0.25% bupivacaine (Group B). Lumbar epidural catheters were placed during the first stage of labor, and a test dose (3 ml 2% lidocaine with 15 micrograms epinephrine) was given, followed by coded study solution. Subsequent doses of study solution were given at the patient's request. Those parturients who remained uncomfortable after 30 minutes were given 10 ml 2% lidocaine and were designated efficacy failures. Patients were evaluated for quality and duration of analgesia for each dose. Neonates were assessed using Apgar scores and the neonatal behavioral assessment scale. Maternal and umbilical venous sufentanil concentrations were measured at the time of delivery. RESULTS: All patients received satisfactory analgesia of similar duration after the first epidural dose. After subsequent doses, women in Group S experienced more efficacy failures (Groups S, SB, and B, respectively, 12 of 26, 5 of 22, and 1 of 25; p less than 0.005) and received briefer, less intense analgesia compared to the other groups. Instrumental delivery was performed more frequently for women in Group B (Groups S, SB, and B, respectively, 0 of 14, 2 of 17, and 7 of 24; p = 0.04). No serious maternal side effects occurred. Apgar and neurobehavioral scores were comparable for all groups, with the exception that Group B infants had higher irritability scores at 1 hour of age (p = 0.003). Neither maternal nor umbilical venous sufentanil concentrations bore a consistent relationship to clinical outcomes. CONCLUSIONS: Epidural sufentanil alone does not reliably provide satisfactory analgesia for labor and delivery. Addition of small amounts of local anesthetic to bolus doses of sufentanil enhances and prolongs the analgesic effect.

Adult↗
PubMedDate not supplied

Hepatic adenoma: report of three cases and review of the literature.

Pathologically confirmed hepatic adenoma (HA) was observed in two women who were not using contraceptives and one 60-year-old man. All three cases had a mass in the right lobe of the liver and almost normal laboratory results. One case that had a movable pedunculated mass mimicked an extrahepatic tumor preoperatively, and two cases associated with acute abdominal pain resulting from intratumor hemorrhage were misdiagnosed as hepatoma and given interventional therapy prior to liver biopsy. In hepatic arterial DSA of two cases, the tumor appeared as hypervascular with peripheral blood supply and regularly parallel branches coursing centrally. On CT scans, the tumor appeared to be surrounded by a low-density ring in two cases, and an intratumor hyperdense area of fresh blood was noted in one case. Analysis of the three cases in this series and a review of the literature indicated that if the DSA and CT findings described above were revealed in a patient, particularly a young woman, with a mass of the right lobe of the liver (with or without acute abdominal pain) and normal laboratory results, HA should be strongly suspected, and CT-guided biopsy should be performed for pathological diagnosis, particularly when an equivocal diagnosis is made.

Adenoma, Liver Cell↗
PubMedDate not supplied

Fatal and non-fatal childhood injuries in Metropolitan Toronto, 1986-1991.

The distribution of the cause, rate and nature of fatal and major non-fatal injuries in children living in Metropolitan Toronto and their trends from 1986 to 1991 were systematically reviewed from hospital discharge records and coroner's records. A total of 11,024 non-fatal injuries, of which falls were the leading cause (45%), and 133 fatal injuries, of which intentional injury (21%) was the principal cause, occurred during the six-year study period. The non-fatal injury rate dropped 23%, from 567 to 436 per 100,000 children. Mortality rates also fell during the study period. However, injuries to motor vehicle occupants and drownings increased considerably. Fractures of various kinds were the most common clinical diagnosis. Protecting children in motor vehicles by promoting the use of proper restraints and preventing injuries caused by falls and drowning should be high priorities for childhood injury prevention in Metropolitan Toronto.

Adolescent↗
PubMedDate not supplied

Current bicycle helmet ownership, use and related factors among school-aged children in metropolitan Toronto.

A random digit dialing telephone survey was conducted to examine bicycle helmet ownership, use and related factors among 707 children in Metropolitan Toronto. The ownership rate was 22% and use rate 12%. Although ownership was similarly distributed by age and sex, helmet use varied considerably across age strata among boys; only about one fifth of teenaged boys who owned a helmet wore it regularly. Both parental education and annual family income were significantly associated with ownership and use. Past bicycle injuries, although increasing helmet ownership, had no positive impact on use. The strength of a parental role model was reflected in the fact that when parents owned and used a helmet, 93% of their children had a helmet and more than 80% of them always wore it. Since about half of parents are cyclists themselves, helmet promotion activities are likely to maximize their effect if they target both parents and children.

Adolescent↗