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Biomedical subjects

L Shi

Publications and source records attributed to L Shi.

At least 37 records · Page 2Linked to original sources
PubMed2001

Haemoproteus and Schistosoma synthesize heme polymers similar to Plasmodium hemozoin and beta-hematin.

Many parasites digest hemoglobin as an amino acid source, but only a few produce heme polymer pigment instead of catabolizing heme via heme oxygenase. This work compares purified heme polymers produced by Haemoproteus columbae and Schistosoma mansoni to that of Plasmodium falciparum hemozoin and synthetic beta-hematin. Fourier-transform infrared spectroscopy identifies the signature peaks of the common iron-carboxylate bond characteristic in all four heme polymers. However, all pigments could be distinguished by quite different three-dimensional structure visualized by Field Emission Inlens Scanning Electron Microscopy. Both P. falciparum and H. columbae heme polymers had a symmetrical shape unlike the amorphous S. mansoni heme polymer and beta-hematin. All four heme pigments serve as templates for heme polymer extension, which was inhibitable by chloroquine and other quinoline antimalarials. The polymers showed different levels of resistance to hydrogen peroxide degradation. This work identifies another genus, Haemoproteus, capable of intracellular heme polymer formation. The different three-dimensional structures of each pigment implicate genus specific formation of heme polymer, variation of inhibition of polymer extension by the quinolines and degradation by hydrogen peroxide.

Animals↗
PubMed2001

The political context of social inequalities and health.

This analysis reflects on the importance of political parties, and the policies they implement when in government, in determining the level of equalities/inequalities in a society, the extent of the welfare state (including the level of health care coverage by the state), the employment/unemployment rate, and the level of population health. The study looks at the impact of the major political traditions in the advanced OECD countries during the golden years of capitalism (1945-1980) -- social democratic, Christian democratic, liberal, and ex-fascist -- in four areas: (1) the main determinants of income inequalities, such as the overall distribution of income derived from capital versus labor, wage dispersion in the labor force, the redistributive effect of the welfare state, and the levels and types of employment/ unemployment; (2) levels of public expenditures and health care benefits coverage; (3) public support of services to families, such as child care and domiciliary care; and (4) the level of population health as measured by infant mortality rates. The results indicate that political traditions more committed to redistributive policies (both economic and social) and full-employment policies, such as the social democratic parties, were generally more successful in improving the health of populations, such as reducing infant mortality. The erroneous assumption of a conflict between social equity and economic efficiency, as in the liberal tradition, is also discussed. The study aims at filling a void in the growing health and social inequalities literature, which rarely touches on the importance of political forces in influencing inequalities. The data used in the study are largely from OECD health data for 1997 and 1998; the OECD statistical services; the comparative welfare state data set assembled by Huber, Ragin and Stephens; and the US Bureau of Labor Statistics.

Adolescent↗
PubMed2001

The convergence of vulnerable characteristics and health insurance in the US.

This study defines vulnerability as a multi-dimensional construct, reflected in the convergence of predisposing, enabling, and need attributes of risk. Using race, income, and self-perceived health status as indicators and based on eight rounds of the US 1996 panel of the Medical Expenditure Panel Survey, the study examined how the interactions of these vulnerable characteristics affect insurance coverage, a critical measure of health care access. The results of the study demonstrate insurance coverage does vary with the extent of vulnerability. While race and income significantly influence insurance coverage, respectively, there was relatively little disparity in insurance due to health status. Between race and income, income was a more significant predictor of lack of insurance coverage since low-income people regardless of race and health were significantly more likely to be uninsured or partially insured. However, it is important to note that minorities were disproportionately over-represented in the low-income or bad health groups so that any adverse association between income, bad health, and insurance status would affect minorities significantly more than whites. Among those with insurance, the most vulnerable group, the minority-low-income-bad health group or those with all the three vulnerability indicators, were most likely to be publicly insured. A policy implication is to target limited resources on insurance coverage for the more vulnerable groups, those with a convergence or cluster of predisposing, enabling, and need attributes of risk.

Health Services Research↗
PubMed2001

Tbr1 regulates differentiation of the preplate and layer 6.

During corticogenesis, early-born neurons of the preplate and layer 6 are important for guiding subsequent neuronal migrations and axonal projections. Tbr1 is a putative transcription factor that is highly expressed in glutamatergic early-born cortical neurons. In Tbr1-deficient mice, these early-born neurons had molecular and functional defects. Cajal-Retzius cells expressed decreased levels of Reelin, resulting in a reeler-like cortical migration disorder. Impaired subplate differentiation was associated with ectopic projection of thalamocortical fibers into the basal telencephalon. Layer 6 defects contributed to errors in the thalamocortical, corticothalamic, and callosal projections. These results show that Tbr1 is a common genetic determinant for the differentiation of early-born glutamatergic neocortical neurons and provide insights into the functions of these neurons as regulators of cortical development.

Animals↗
PubMed2001

Frequency and distribution in three ethnic populations of single nucleotide polymorphisms in the MICA gene.

The Homo sapiens major histocompatibility complex (MHC) class 1 chain related gene A (MICA) was scanned for novel single nucleotide polymorphisms (SNPs) using a panel of DNA samples from African-, Japanese- and Mexican-Americans. Overlapping primer-pairs were used to amplify products in the size range of 300 to 400 bp that were sequenced and scanned for SNPs using Phred, Phrap, Polyphred and Consed sequence analysis programs. A total of 16 SNPs were detected, six of which represent new variant nucleotides in the Homo sapiens MICA gene. Three of the variants also represent amino acid changes in the MICA protein. Differences among the three ethnic panels in the frequency of the variant nucleotides observed were inconsistent, but significant for seven of the SNPs detected. Though a small sample size, this study represents the first multi-population based analysis of the frequency and distribution of SNPs in the MICA gene, a locus that may be essential in the antigenic recognition by gammadelta T cells.

Alleles↗
PubMed2001

Inhibition of cervical ripening by local application of cyclooxygenase 2 inhibitor.

OBJECTIVE: Our goal was to test the hypothesis that the previously demonstrated progesterone-independent prolongation of pregnancy in rats treated with cervical application of the cyclooxygenase 2 inhibitor nimesulide is the result of inhibition of cervical ripening. STUDY DESIGN: Timed-pregnant Sprague-Dawley rats were randomly allocated to treatment with 50 mg nimesulide or vehicle, applied daily on the cervix for 5 days (days 14-18). On day 19 the animals were humanely killed and the cervices were removed. In the first series of experiments the cervices of animals treated with nimesulide (n = 10) or vehicle (n = 10) were examined with a cervimeter, which stretches the cervical tissues in incremental steps of 0.2 mm at 1-minute intervals. A steeper slope through the linear portion of the resulting force-versus-displacement curve indicates more resistance to stretch. In the second series of experiments the cervices of animals treated with nimesulide (n = 11) or vehicle (n = 11) were examined with the Collascope optical device. The cervical content of cross-linked collagen was measured with light-induced fluorescence. The fluorescence spectrum at 390 nm (peak wavelength of the collagen spectrum) was determined. For standardization, the ratio of counts of collagen peak over reference counts was used in the final analyses as an indicator of cross-linked collagen content. RESULTS: Animals treated with cervical application of nimesulide had significantly higher resistance to stretch than controls (slope: 0.2564 +/- 0.1213 vs 0.1387 +/- 0.0652; P =.019). The cervical content of cross-linked collagen was not significantly different between nimesulide-treated animals and controls (light-induced fluorescence ratios: 3.2134 +/- 0.7390 vs 2.7892 +/- 0.8518; P =.227). CONCLUSIONS: Treatment with cervical application of the cyclooxygenase 2 inhibitor nimesulide prevents the physiologic process of cervical ripening in late pregnancy. The inhibition is not the result of changes in cross-linked collagen content. Inhibition of cervical ripening with locally administered cyclooxygenase 2 inhibitor may be a potentially valuable treatment for patients at risk for preterm delivery.

Administration, Topical↗
PubMed2001

Use of membrane collectors in electrostatic precipitators.

Membrane collection surfaces, developed and patented by researchers at Ohio University, were used to replace steel plates in a dry electrostatic precipitator (ESP). Such replacement facilitates tension-based rapping, which shears the adhered particle layer from the collector surface more effectively than hammer-based rapping. Tests were performed to measure the collection efficiency of the membranes and to quantify the potential improvements of this novel cleaning technique with respect to re-entrainment. Results indicate that even semiconductor materials (e.g., carbon fibers) collect ash nearly as efficiently as steel plates, potentially indicating that collection surface resistivity is primarily dictated by the accumulated ash layer and not by the underlying plate conductivity. In addition, virtually all sheared particles separated from the collecting membranes fell within the boundary layer of the membrane, indicating extremely low potential for re-entrainment.

Air Pollution↗
PubMed2001

A review of studies on maternal occupational exposures and birth defects, and the limitations associated with these studies.

The proportion of pregnant women who work during pregnancy is increasing as more women move into previously male-dominated occupations. With this move, occupational exposure to chemical or physical factors during pregnancy could be further increased. In the last decade, there have been many reports on the causes of birth defects. Unfortunately, most reported associations between occupational exposures and adverse reproductive outcomes in epidemiological studies are equivocal and often controversial. Many reported associations are only suggestive. More information is needed before firm conclusions can be drawn. The major reasons for ambiguous findings are due to limitations of study methodology, e.g. inappropriate endpoints, multiple confounders, low study power and inadequate analysis methods. It must also be noted that maternal work, and therefore exposure, may also differ greatly from country to country.

Bias↗
PubMed2001

Xenopus eggs express an identical DNA methyltransferase, Dnmt1, to somatic cells.

In mouse, an oocyte-specific short isoform of DNA methyltransferase-1 (Dnmt1) lacking amino terminal 118 amino acid residues exists and plays a crucial role in maintaining the methylation state of imprinted genes during early embryogenesis [Howell et al. (2001) Cell 104, 829-838]. To address the question of whether or not Xenopus oocyte expresses such a short isoform, we raised monoclonal antibodies against the amino-terminal portion of Xenopus Dnmt1. Two of the isolated monoclonal antibodies, 3C6 and 4A8, were determined to recognize (1-32) and (115-126) of Xenopus Dnmt1, respectively. The amounts of Dnmt1 in Xenopus eggs were determined to be similar, 10.0 2.5, 8.0 0.8, and 8.2 0.2 ng per egg with monoclonal antibodies 3C6 and 4A8, and polyclonal antibodies, respectively. This indicated that Dnmt1 in Xenopus mature eggs had an identical amino-terminal sequence to the amino acid sequence deduced from the cDNA. Together with the fact that Dnmt1 in A6 cells immuno-reacted with all the monoclonal antibodies isolated and with the polyclonal antibodies, we concluded that Dnmt1 expressed in Xenopus mature eggs possesses an identical amino-terminal sequence to that in somatic cells. Immuno-purified Xenopus Dnmt1 in mature eggs showed similar specific activity to that in proliferating A6 cells and that of mouse recombinant Dnmt1.

Amino Acid Sequence↗
PubMed2001

Expressed sequence tags for the chicken genome from a normalized, ten-day-old white leghorn whole embryo cDNA library. 2. Comparative DNA sequence analysis of guinea fowl, quail, and turkey genomes.

Accelerated efforts to develop a high-utility chicken genome map have resulted in the development of resources that may be useful for genetic analysis in other economically important poultry species. Here we describe a total of 26 comparative genomic DNA sequences (CGS) for the guinea fowl, Japanese quail, and domestic turkey developed using 10 primer pairs specific for 10 previously reported, unique, chicken expressed sequence tags (EST). The total length of CGS developed for each of the three species was 4,193, 4,597, and 6,057 bp in quail, turkey, and guinea fowl, respectively. About 70% of the CGS showed significant sequence similarity to reference database sequences, including the reference chicken EST and other avian and nonavian genes. A majority of the between-species comparisons of the CGS from all but two primer pairs were significant and ranged from 81 to 99%. The percentage similarity of the CGS appears to be a function of phylogenetic relatedness and was generally higher for comparisons between the chicken, quail, and turkey and lower between the guinea fowl and chicken, quail, or turkey. Maximum likelihood estimation of the phylogenetic relationships using CGS from two primer pairs also showed a closer relationship, as expected, among chicken, quail, and turkey than between guinea fowl and either chicken, quail, or turkey. Within the guinea fowl, quail, and turkey CGS developed, the total number of single nucleotide polymorphisms detected was 28, 17, and 14, respectively. Together, these resources represent tools that will facilitate genetic analysis of species that have been studied very little and our understanding of their genomes and genome evolution.

Animals↗
PubMed2001

The impact of managed care on the mix of vulnerable populations served by community health centers.

This article examined the impact of managed care involvement on vulnerable populations served by community health centers (CHCs), while controlling for center rural-urban location and size, and found that centers involved in managed care have served a significantly smaller proportion of uninsured patients but a higher proportion of Medicaid users than those not involved in managed care. The results suggest that the increase in Medicaid managed care patients may lead to a reduced capacity to care for the uninsured, thus hampering CHCs from expanding access to health care for the medically indigent.

Analysis of Variance↗
PubMed2001

A profile of women medical directors in community and migrant health centers.

This article looks at the nation's community and migrant health centers, where substantial numbers of female physicians are medical directors, the second highest executive position, in search of insights for managed care organizations for recruiting and retaining women medical directors. This paper provides the first comparative national profile of women and men community and migrant health center (C/MHC) medical directors in terms of their personal and work characteristics, as well as job satisfaction. The study findings indicate that, for the most part, female medical directors do not differ much from their male colleagues in issues of work characteristics or job satisfaction.

Community Health Centers↗
PubMed2001

Methods and devices for the management of term and preterm labor.

In this review, we outline studies showing that the uterus (myometrium) and cervix pass through a conditioning step in preparation for labor. This step is not easily identifiable with present methods designed to assess the uterus or cervix. In the uterus, this seemingly irreversible step consists of changes in the electrical properties that make muscle more excitable and responsive and produce forceful contractions. In the cervix, the step consists of softening of the connective tissue components. Progesterone and nitric oxide appear to have important roles in these processes. The progress of labor can be assessed noninvasively using electromyographic (EMG) signals from the uterus (the driving force for contractility) recorded from the abdominal surface. Uterine EMG bursts detected in this manner characterize uterine contractile events during human and animal pregnancy. A low uterine EMG activity, measured transabdominally throughout most of pregnancy, rises dramatically during labor. EMG activity also increases substantially during preterm labor in humans and rats and may be predictive of preterm labor. A quantitative method for assessing the cervix is also described. A collascope estimates cervical collagen content from a fluorescent signal generated when collagen crosslinks are illuminated with an excitation light of about 340 nm. The system has proved useful in rats and humans at various stages of pregnancy and indicates that cervical softening occurs progressively in the last one-third of pregnancy. In rats, collascope readings correlate with resistance measurements made in the isolated cervix, which may help to assess cervical function during pregnancy and indicate controls and treatments.

Delivery, Obstetric↗
PubMed2001

The PPP-family protein phosphatases PrpA and PrpB of Salmonella enterica serovar Typhimurium possess distinct biochemical properties.

Salmonella enterica serovar Typhimurium requires Mn(2+), but only a few Mn(2+)-dependent enzymes have been identified from bacteria. To characterize Mn(2+)-dependent enzymes from serovar Typhimurium, two putative PPP-family protein phosphatase genes were cloned from serovar Typhimurium and named prpA and prpB. Their DNA-derived amino acid sequences showed 61% identity to the corresponding Escherichia coli proteins and 41% identity to each other. Each phosphatase was expressed in E. coli and purified to near electrophoretic homogeneity. Both PrpA and PrpB absolutely required a divalent metal for activity. As with other phosphatases of this class, Mn(2+) had the highest affinity and stimulated the greatest activity. The apparent K(a) of PrpA for Mn(2+) of 65 microM was comparable to that for other bacterial phosphatases, but PrpB had a much higher affinity for Mn(2+) (1.3 microM). The pH optima were pH 6.5 for PrpA and pH 8 for PrpB, while the optimal temperatures were 45 to 55 degrees C for PrpA and 30 to 37 degrees C for PrpB. Each phosphatase could hydrolyze phosphorylated serine, threonine, or tyrosine residues, but their relative specific activities varied with the specific substrate tested. These differences suggest that each phosphatase is used by serovar Typhimurium under different growth or environmental conditions such as temperature or acidity.

Amino Acid Sequence↗
PubMed2001

Inequality in America: the contribution of health centers in reducing and eliminating disparities in access to care.

Reducing and eliminating health status disparities by providing access to appropriate health care is a goal of the nation's health care delivery system. This article reviews the literature that demonstrates a relationship between access to appropriate health care and reductions in health status disparities. Using comprehensive site-level data, patient surveys, and medical record reviews, the authors present an evaluation of the ability of health centers to provide such access. Access to a regular and usual source of care alone can mitigate health status disparities. The safety net health center network has reduced racial/ethnic, income, and insurance status disparities in access to primary care and important preventive screening procedures. In addition, the network has reduced low birth weight disparities for African American infants. Evidence suggests that health centers are successful in reducing and eliminating health access disparities by establishing themselves as their patients' usual and regular source of care. This relationship portends well for reducing and eliminating health status disparities.

Community Health Centers↗
PubMed2001

Proliferation stage-dependent expression of DNA methyltransferase (Dnmt1) in mouse small intestine.

In cultured cells, the maintenance-type DNA methyltransferase (Dnmt1) is highly expressed during the proliferation stage. In the present study, we detected significant expression of Dnmt1 protein in the nuclear fraction of mouse small intestine. From its mobility in SDS polyacrylamide gel electrophoresis and the specific antibodies against the somatic cell-type Dnmt1, Dnmt1 was determined as a somatic cell type. Immunofluorescence study revealed that the Dnmt1 was highly expressed in the proliferating stem cells in crypts, and was localized in the nuclei. The present results indicate that the expression of Dnmt1 in vivo is also under the control of cell proliferation as in cultured cells.

Animals↗