Biomedical subjects

M Tang

Publications and source records attributed to M Tang.

At least 19 recordsLinked to original sources

PubMed1998

Biochemical basis of SOS-induced mutagenesis in Escherichia coli: reconstitution of in vitro lesion bypass dependent on the UmuD'2C mutagenic complex and RecA protein.

Damage-induced SOS mutagenesis requiring the UmuD'C proteins occurs as part of the cells' global response to DNA damage. In vitro studies on the biochemical basis of SOS mutagenesis have been hampered by difficulties in obtaining biologically active UmuC protein, which, when overproduced, is insoluble in aqueous solution. We have circumvented this problem by purifying the UmuD'2C complex in soluble form and have used it to reconstitute an SOS lesion bypass system in vitro. Stimulated bypass of a site-directed model abasic lesion occurs in the presence of UmuD'2C, activated RecA protein (RecA*), beta-sliding clamp, gamma-clamp loading complex, single-stranded binding protein (SSB), and either DNA polymerases III or II. Synthesis in the presence of UmuD'2C is nonprocessive on damaged and undamaged DNA. No lesion bypass is observed when wild-type RecA is replaced with RecA1730, a mutant that is specifically defective for Umu-dependent mutagenesis. Perhaps the most noteworthy property of UmuD'2C resides in its ability to stimulate both nucleotide misincorporation and mismatch extension at aberrant and normal template sites. These observations provide a biochemical basis for the role of the Umu complex in SOS-targeted and SOS-untargeted mutagenesis.

Bacterial Proteins↗

PubMed1998

Liprins, a family of LAR transmembrane protein-tyrosine phosphatase-interacting proteins.

LAR family transmembrane protein-tyrosine phosphatases function in axon guidance and mammary gland development. In cultured cells, LAR binds to the intracellular, coiled coil LAR-interacting protein at discrete ends of focal adhesions, implicating these proteins in the regulation of cell-matrix interactions. We describe seven LAR-interacting protein-like genes in humans and Caenorhabditis elegans that form the liprin gene family. Based on sequence similarities and binding characteristics, liprins are subdivided into alpha-type and beta-type liprins. The C-terminal, non-coiled coil regions of alpha-liprins bind to the membrane-distal phosphatase domains of LAR family members, as well as to the C-terminal, non-coiled coil region of beta-liprins. Both alpha- and beta-liprins homodimerize via their N-terminal, coiled coil regions. Liprins are thus multivalent proteins that potentially form complex structures. Some liprins have broad mRNA tissue distributions, whereas others are predominately expressed in the brain. Co-expression studies indicate that liprin-alpha2 alters LAR cellular localization and induces LAR clustering. We propose that liprins function to localize LAR family tyrosine phosphatases at specific sites on the plasma membrane, possibly regulating their interaction with the extracellular environment and their association with substrates.

Adaptor Proteins, Signal Transducing↗

PubMed1998

Slow repair of bulky DNA adducts along the nontranscribed strand of the human p53 gene may explain the strand bias of transversion mutations in cancers.

Using UvrABC incision in combination with ligation-mediated PCR (LMPCR) we have previously shown that benzo(a)pyrene diol epoxide (BPDE) adduct formation along the nontranscribed strand of the human p53 gene is highly selective; the preferential binding sites coincide with the major mutation hotspots found in human lung cancers. Both sequence-dependent adduct formation and repair may contribute to these mutation hotspots in tumor tissues. To test this possibility, we have extended our previous studies by mapping the BPDE adduct distribution in the transcribed strand of the p53 gene and quantifying the rates of repair for individual damaged bases in exons 5, 7, and 8 for both DNA strands of this gene in normal human fibroblasts. We found that: (i) on both strands, BPDE adducts preferentially form at CpG sequences, and (ii) repair of BPDE adducts in the transcribed DNA strand is consistently faster than repair of adducts in the nontranscribed strand, while repair at the major damage hotspots (guanines at codons 157, 248 and 273) in the nontranscribed strand is two to four times slower than repair at other damage sites. These results strongly suggest that both preferential adduct formation and slow repair lead to hotspots for mutations at codons 157, 248 and 273, and that the strand bias of bulky adduct repair is primarily responsible for the strand bias of G to T transversion mutations observed in the p53 gene in human cancers.

7,8-Dihydro-7,8-dihydroxybenzo(a)pyrene 9,10-oxide↗

PubMed1998

Simultaneous determination of glucosamine and glucosamine 4-phosphate in Lipid A with high-performance anion-exchange chromatography (HPAEC).

A method for simultaneous determination of glucosamine (GlcN) and glucosamine 4-phosphate (GlcN-4-P) in Lipid A with high-performance anion-exchange chromatography (HPAEC) is described. Lipid A is hydrolyzed with 4 M HCl for 16 h at 100 degrees C, and the peaks of glucosamine and glucosamine 4-phosphate were measured. The true GlcN value can be computed from the GlcN value after correction for the incomplete hydrolysis of GlcN-4-P, or by the combined yield of GlcN and GlcN-4-P.

Chromatography, High Pressure Liquid↗

PubMed1998

The Home Infusion Therapy/Relative Benefit Index: summary of an analysis using insurance claims data.

OBJECTIVES: The cost of providing services is the traditional criteria used by payers in making selective contracting decisions regarding home care providers in general, and home infusion therapy (HIT) vendors specifically for this analysis. This approach assumes comparable health outcomes, for which adequate measures often are unavailable. In practice, poor quality can result in a need for remedial services. The objective of this research is to develop a method to use health insurance claims data to incorporate the hidden costs of adverse outcomes into an analysis of the costs of a vendor's HIT. METHODS: The Home Infusion Therapy/Relative Benefit Index (HIT/RBI) model incorporates measures of both the cost of providing HIT services as well as the cost of remedial treatment for the adverse outcomes that may result from HIT care, eg, emergency room visits. The data source for the analysis is the health care claims for a sample of managed care patients of national insurer for the period 1990 to 1994. RESULTS: The analysis confirms that adverse clinical outcomes can lead to additional demand for remedial health care with resultant negative financial consequences. When the cost of the adverse outcomes is incorporated into the analysis, vendors who appeared to be low cost on the basis of HIT services, in fact were higher cost vendors, whereas vendors with a high cost of services but with few adverse events were low cost vendors. CONCLUSIONS: Payers should consider both the clinical and economic consequences of providing care into account in selecting vendors. The HIT/RBI model is a useful tool for incorporating the cost of adverse outcomes into a comprehensive comparison of the cost multiple vendors of HIT services.

Bacterial Infections↗

PubMed1998

Molecular analysis of the human laminin alpha3a chain gene (LAMA3a): a strategy for mutation identification and DNA-based prenatal diagnosis in Herlitz junctional epidermolysis bullosa.

Mutations in the genes (LAMA3, LAMB3, and LAMC2) encoding the subunit polypeptides of the cutaneous basement membrane zone protein laminin 5 have been reported in different forms of junctional epidermolysis bullosa (JEB), an inherited blistering skin disease. In this study, we present the complete exon-intron organization of the "a" transcript of the laminin alpha3 chain gene, LAMA3a, which is expressed primarily in the skin. We have performed fine-resolution mapping of this gene on chromosome 18q11.2 using a human-hamster radiation hybrid panel. We have also developed a mutation-detection strategy based on the exon-intron structure of LAMA3a. This strategy, based on PCR amplification of genomic sequences, followed by heteroduplex scanning and automated nucleotide sequencing, was used for successful mutation screening in a family with the lethal (Herlitz) type of JEB, and two novel LAMA3 mutations were identified in the proband. The mutations consisted of a single-base pair deletion in LAMA3a exon A11 on the paternal allele, designated 1239delC, and a two-base pair deletion in LAMA3a exon A23 on the maternal allele, designated 2959delGG. This information was also used for DNA-based prenatal testing in a subsequent pregnancy in this family. Collectively, these results attest to our expanding capability to elucidate the genetic basis of various forms of epidermolysis bullosa using molecular techniques.

Animals↗

PubMed1997

Determination of 2-keto-3-deoxyoctulosonic acid (KDO) with high-performance anion-exchange chromatography (HPAEC): survey of stability of KDO and optimal hydrolytic conditions.

A new method for 2-keto-3-deoxy-octulosonic acid (KDO) determination using high-performance anion-exchange chromatography was developed. KDO is well separated from Neu5Ac, and the response was linear from 20 pmol to 5 nmol. The method was used to examine the stability of KDO under various hydrolytic, conditions and to survey optimal hydrolytic conditions for release of KDO.

Chromatography, Ion Exchange↗

PubMed1997

Mortality from Parkinson disease.

BACKGROUND: Levodopa therapy for Parkinson disease (PD) has improved quality of life, but mortality rates remain high. Although the presence of dementia and severity of extrapyramidal signs (EPSs) influence morbidity in PD, it is not known whether these manifestations contribute to mortality. METHODS: Patients with PD were compared with nondemented and demented elderly subjects. Each underwent annual neurological and neuropsychological examinations. Dementia was diagnosed by Diagnostic and Statistical Manual of Mental Disorders, Third Edition, Revised criteria, and EPSs were rated with the Unified Parkinson's Disease Rating Scale. Survival rates were compared using Kaplan-Meier analysis and Cox proportional hazards models. RESULTS: The risk of mortality, when compared with nondemented elderly subjects, was highest among those with both PD and dementia (rate ratio, 4.9; 95% confidence interval, 3.4-7.1), but also was elevated in patients with PD only (rate ratio, 2.7; 95% confidence interval, 1.7-4.4). Dementia in the absence of PD also was associated with an increased risk of mortality (rate ratio, 1.6; 95% confidence interval, 1.1-2.3). A high baseline total EPS score was associated with significantly earlier mortality. CONCLUSIONS: Compared with nondemented elderly people in the same community, patients with PD have a 2- to 5-fold increased risk of mortality. The risk is strongly related to the presence of severe EPSs, especially bradykinesia. Despite the introduction of levodopa and other advances in the treatment of PD, these factors greatly increase mortality.

Aged↗

PubMed1997

Extracellular matrix heparan sulfate modulates endothelial cell susceptibility to Staphylococcus aureus.

The ability of extracellular matrix heparan sulfate to alter the susceptibility of human endothelial cells to S. aureus was investigated. Endothelial cells grown on extracellular matrix synthesized by S. aureus-infected endothelial cells were more susceptible to subsequent staphylococcal infection than endothelial cells grown on the extracellular matrix synthesized by untreated endothelial cells. Endothelial cells were more susceptible to S. aureus infection when 1) grown on heparitinase-treated extracellular matrix that removed heparan sulfate chains, 2) grown on extracellular matrix produced by chlorate-treated endothelial cells that reduced sulfation in the matrix heparan sulfate proteoglycans, 3) grown on heparan sulfate purified from extracellular matrix elaborated by infected endothelial cells, and 4) endothelial cells were chlorate-treated and therefore expressed desulfated cellular heparan sulfate proteoglycans. Extracellular matrix produced by S. aureus-infected endothelial cells contained heparan sulfate proteoglycans with reduced sulfation. The altered extracellular matrix with reduced sulfated heparan sulfate proteoglycans signalled the uninfected endothelial cells to produce under sulfated cellular heparan sulfate proteoglycans that increased S. aureus adherence to the endothelial cells.

Bacterial Adhesion↗

PubMed1997

ERG abnormalities in relation to histopathologic findings in vitiligo mutant mice.

The vitiligo, mivit, mutation has several prenatal and perinatal effects on development of the retinal pigment epithelium, and later, leads to extensive, progressive degeneration of photoreceptor cells in the neural retina of homozygous affected mice. The aim of the present study was to determine by functional criteria how early can abnormalities be detected in the neural retina. Electroretinograms (ERGs) were correlated with histopathological findings in the same animals. Congenic homozygous mutants, heterozygotes, and homozygous wild-type mice were studied at 2, 3, 6, 24 and 56 weeks of age, the same animals being tested serially at the three older time points. The nontested eye of each animal was embedded in Epon and sectioned at 1 micron for light microscopic study. ERG recordings from vitiligo homozygotes differed from heterozygous and wild-type mice, but the latter two groups did not differ from each other. As early as two weeks of age, homozygous mutants showed a significant reduction of rod dominated maximum ERG a-wave and b-wave amplitude. ERG b-wave sensitivity (sigma) was significantly reduced, and ERG implicit times were delayed for homozygous mutants at 3 (a-wave) and 6 (b-wave) weeks of age. This is the first study to report reduced and delayed ERG a-waves and b-waves in this animal model, like the early functional abnormalities in human retinitis pigmentosa, and also the first to show short and disoriented rod outer segments, beginning retinal separation from the pigment epithelium, and a few macrophage-like cells already present in the subretinal space at 2 weeks of age (in three of four homozygous mutant eyes examined). Given these early functional and structural abnormalities in the neural retina, it remains to be determined whether the mi gene targets the retinal pigment epithelial cell, the photoreceptor cell, or both.

Aging↗

PubMed1997

The effect of levobunolol hydrochloride on the calcium and potassium channels in isolated ventricular myocytes of guinea pig.

The effects of levobunolol hydrochlorid (Bun) on the type L calcium channel currents (ICA) and delayed rectifier potassium channel currents (IK) in isolated ventricular myocytes of guinea pig were studied by using patch clamp whole cell recording techniques. The results were showed that: 1) Bun caused a dose dependent decrease in ICA and a dose-dependent increase in IK of the ventricular myocytes. The threshold concentrations of Bun for ICA and IK were 10(-8) mol/L and 10(-7) mol/L respectively. The maximum effective concentration of Bun for bot ICA and IK was 3x10(-5) mol/L, and half-maximal concentration was 3x10(-6) mol/L; 2) IK was blocked by 2x100(-6) mol/L tetraethylammonium (TEA). A concentration of 3x10(-6) mol/L Bun showed a decreasing effect on the ICA as revealed by the current-voltage relationship curve, i.e., Bun caused an elevation of the curve;3) When ICA was blocked by 2x10(-6) mol/L Isoptin (Verapamil), at a concentration of 3x10(-6) mol/L Bun showed an increasing effect on IK and the effect could be blocked by TEA. The above-mentioned results indicated that Bun had an inhibitory effect on ICA and a fascilitatory effect on IK. The results suggested that the molecular mechanisms of antihypertensive, heart rate slowing the beta -receptor blocking effects of Bun might be due to decrease of ICA and increase of IK.

Adrenergic beta-Antagonists↗

PubMed1997

Mapping and retinal phenotype of the hugger mutation in the mouse.

Hugger, hug, is a recessively expressed mutation in mice that features mildly abnormal locomotion, not yet explained, and a unique combination of developmental and degenerative retinal abnormalities. Analysis with the efficient MEV linkage testing stock established that hug is on mouse Chr 19 about 14 cM from th centromere, between the microsatellite markers D19Mit28 and D19Mit14. An abnormal retinal phenotype was recognized on the day of birth, when some retinal ganglion cells already lie in abnormal positions in the inner plexiform layer. By postnatal day 18 the number of neurons is reduced in all three cellular layers of the retina. Rod photoreceptor cells develop only rudimentory outer segments, and by 9 months of age, about 75% of the photoreceptor cells have completely disappeared. Similar photoreceptor cell abnormalities are seen in prph2 (formerly rds) homozygotes, which lack the peripherin/rds protein of the rod outer segments, but a mating of the respective homozygotes yielded normal progeny. Rom1, which codes for an outer segment protein similar to peripherin/rds, maps to a more proximal position on Chr 19.

Animals↗

PubMed1997

Association of estrogens with human plasma lipoproteins: studies using estradiol-17beta and its hydrophobic derivative.

Estrogen replacement therapy is widely used to combat symptoms of menopause, but factors influencing the transport of estrogen in plasma and its cellular uptake have been explored only to a limited extent. In this study, labeled estradiol-17beta (E2) was compared with its hydrophobic derivative (estradiol-3,17-diacetate, E2AA) in terms of (1) distribution within various lipoproteins and lipoprotein-free fractions of human plasma by ultracentrifugation and (2) uptake by human endothelial cells. Although added E2 was predominantly bound to HDL and lipoprotein-free fractions, E2AA was associated to some degree with VLDL and LDL but was still present in significant amounts in HDL and lipoprotein-free fractions. Significant associations of E2 with lipoproteins were also confirmed by polyacrylamide gel electrophoretic separation of E2-labeled plasma. In normal plasma, however, <10% of E2 was associated with lipoproteins when measured by radioimmunoassay. Incubation of E2AA and E2 with human dermal capillary endothelial cells showed similar uptake by 24 hours. A significant portion of E2AA was hydrolyzed to estradiol-17-monoacetate both in plasma and in cells. The addition of HDL and LDL to medium containing lipoprotein-deficient serum significantly reduced labeled E2 and E2AA uptake, respectively, by endothelial cells. These studies suggest that (1) although the association of E2 with HDL under normal conditions may be small, it increases significantly with higher estrogen concentrations of E2; (2) the hydrophobic ester of E2 shows increased binding to VLDL and LDL; and (3) this approach may be useful in manipulating the delivery of selected E2 derivatives to cells.

Endothelium, Vascular↗

PubMed1997

Use of the intestinal bile acid transporter for the uptake of cholic acid conjugates with HIV-1 protease inhibitory activity.

PURPOSE: To investigate the ability of the human intestinal bile acid transporter to transport cholic acid conjugates with potential HIV-1 protease inhibitory activity. METHODS: Cholic acid was conjugated at the 24 position of the sterol nucleus with various amino acids and amino acid analogs. The CaCo-2 cell line was used as a model to investigate the interaction of these bile acid conjugates with the human intestinal bile acid transporter. Interaction between the carrier and the conjugates was quantified by inhibition of taurocholic acid transport and confirmed by transport of radiolabelled conjugates in this cell line. RESULTS: The highest interaction with the transporter, as quantified by inhibition of taurocholic acid transport, occurred when a single negative charge was present around the 24 to 29 region of the sterol nucleus. A second negative charge or a positive charge significantly reduced the interaction. Transport of radiolabelled cholyl-L-Lys-epsilon-tBOC ester and cholyl-D-Asp-beta-benzyl ester was inhibited by taurocholic acid. Of all tested compounds, only cholyl-D-Asp-beta-benzyl ester showed modest HIV-1 protease inhibitory activity with an IC50 of 125 microM. CONCLUSIONS: Cholic acid-amino acid conjugates with appropriate stereochemistry are recognized and transported by the human bile acid transporter and show modest HIV-1 protease inhibitory activity. Transport of these conjugates by the bile acid carrier is influenced by charge and hydrophobicity around the 24 position of the sterol nucleus.

Amino Acids↗

PubMed1997

Molecular defects in Hb H hydrops fetalis.

The molecular defect in two unique cases of Hb H hydrops fetalis has been characterized. Both cases are due to co-inheritance of a 'non-deletion' defect affecting the alpha2 gene: at codon 30 delta GAG, Glu) and codon 59 (G --> A, Gly --> Asp) respectively, and a zeta-alpha thalassaemia (thal) 1 or alpha thal 1 genotype. These two non-deletion defects, unlike previously described cases, resulted in severe anaemia of the fetuses and emphasize the importance of performing prenatal diagnosis for these families.

Gene Deletion↗

PubMed1997

New-onset bronchospasm or recrudescence of asthma associated with cocaine abuse.

OBJECTIVE: To determine whether the occurrence of new-onset bronchospasm or the recrudescence of asthma is associated with the use of cocaine. METHODS: A consecutive sample of patients presenting to an inner-city adult ED with new-onset bronchospasm or recrudescence of bronchospasm after > 5 years were prospectively enrolled in a case-control prevalence study. The bronchospasm patients were queried as to their exposure to illicit drugs, and urine was obtained to screen for cocaine and its metabolite, benzoylecgonine. An age- and sex-matched control group was composed of randomly chosen subjects without respiratory complaints or a history of asthma. The control group was also screened by urine toxicology for cocaine and its metabolite, benzoylecgonine. RESULTS: In the asthma group, 21/59 (36%) had a urine toxicologic screen positive for cocaine metabolite (benzoylecgonine). Of the 21 with a positive screen for cocaine, 8 denied illicit drug abuse. Among the 13 patients reporting drug use, 10 said that they smoked crack and 3 snorted cocaine. In the control group, 8/53 (15%) were positive. Multivariate logistic regression analysis, with adjustment for age and sex, indicated that the use of cocaine was associated with a 3-fold higher prevalence of new-onset bronchospasm or recrudescence of asthma (OR = 3.28, 95% CI: 1.26 to 8.50). CONCLUSIONS: There appears to be an association between cocaine use and new-onset bronchospasm or recrudescence of asthma in this inner-city ED population. Further study is necessary to determine the basis for this association.

Adult↗

PubMed1997

Alzheimer's disease after remote head injury: an incidence study.

OBJECTIVE: To evaluate a history of remote head injury as a risk factor for subsequent dementia due to Alzheimer's disease. METHODS: 271 participants of a community based longitudinal study of aging in north Manhattan without evidence of significant cognitive impairment were interrogated for a history of head injury on two occasions at entry into the study. The examining physician sought a history of head injury with loss of conciousness. Independently, a risk factor interviewer inquired about a history of head injury with loss of consiousness or amnesia, the duration of any loss of consiousness, and the date of the head injury. Patients were followed up with standardised annual evaluations for up to five years to determine the first occurrence of dementia. RESULTS: Over the course of the study incident dementia due to probable or possible Alzheimer's disease was diagnosed in 39 patients. Cox proportional hazards modelling showed that a history of head injury with loss of consiousness reported to the physician was associated with earlier onset of dementia due to Alzheimer's disease (relative risk (RR) = 4.1, 95% confidence interval (95% CI) 1.3-12.7). head injury with loss of consiousness or amnesia reported to the risk factor interviewer was not significantly associated with earlier onset of Alzheimer's disease overall (RR 2.0, 95% CI 0.7-6.2), but those who reported loss of consiousness exceeding five minutes were at significantly increased risk (RR 11.2, 95% CI 2.3-59.8). Incident Alzheimer's disease was significantly associated with head injury which occurred within the preceding 30 years (RR 5.4, 95% CI 1.5-19.5). CONCLUSION: The results of this cohort study are consistent with the findings of several case-control studies suggesting that head injury may be a risk factor for Alzheimer's disease.

Age of Onset↗

PubMed1997

[The genetical effects of degUS gene in Bacillus subtilis Ki-2-132].

Using the methods of recombination and gene disruption, the effects of degUS gene in Bacillus subtilis Ki-2-132 were studied. The results showed that the gene could affect all protease-producing, competence formation, cell mobility and repression effects of glucose on protease-production. This implies that it is a pleitropic gene in Bacillus subtilis Ki-2-132. The disruption of the gene caused morphological changes and repressed the expression of aprE in vectors.

Bacillus subtilis↗