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Biomedical subjects

W Cai

Publications and source records attributed to W Cai.

At least 91 records · Page 5Linked to original sources
PubMed1996

Time-resolved optical diffusion tomographic image reconstruction in highly scattering turbid media.

The image of an object hidden in highly scattering media was reconstructed using a fast, noise-resistant algorithm newly applied to diffusion tomography. A pulsed light source producing scattered and transmitted light is examined at multiple times. Multiple source detector pairs around the medium are used to obtain data in many different directions. An inverse scattering algorithm with nonuniform regularization achieves rapid inversion convergence.

Journal Article↗
PubMed1996

Identification of seven new human MHC class I region genes around the HLA-F locus.

Using cDNA hybridization selection techniques, we identified seven new genes in a 280 kilobase YAC covering the HLA-F locus. The new genes were mapped back to the YAC by a combination of optical restriction mapping and pulse field gel electrophoresis. Northern analysis of individual clones demonstrated the presence of either different mRNA sizes or different expression patterns. Two of the cDNA clones were expressed only in lymphoid cell lines: one in Jurkat cells (T cell) and another in JY cells (B cell). All the genes lacked sequence similarity to any known classical and non-classical major histocompatibility complex (MHC) class I genes, indicating that the MHC class I region has more functions than anticipated. Of the seven new genes, one is highly similar (97%) to mouse 60S ribosomal protein, and another is homologous to diubiquitin proteins. Of the two G-coupled receptor-like cDNAs, one was fully sequenced and found to be an olfactory receptor-like gene. The study strengthens evidence that the MHC complex not only plays a key role in the immune system, but also contributes to non-immunological functions.

Animals↗
PubMed1996

Sequence and transcription of Qa-2-encoding genes in mouse lymphocytes and blastocysts.

The protein product of the mouse preimplantation embryo development (Ped) gene, which controls the rate of preimplantation embryonic cleavage division and subsequent embryo survival, is the Qa-2 antigen. This major histocompatibility complex (MHC) class I b protein is encoded by four genes, Q6, Q7, Q8, and Q9. The present study was undertaken to begin to elucidate which of the four Qa-2-encoding genes are responsible for the Ped gene phenotype in the C57BL/6 mouse (H2(b)). First, restriction maps of the four genes, using 25 restriction enzymes, were created. The RE maps confirmed that Q6 is similar to Q8 and Q7 is similar to Q9, but that the Q6/Q8 gene pair differs from the Q7/Q9 gene pair. The genomic DNA sequences of Q6 and Q8 were determined, as well as the DNA sequences of exons 4 - 8 of Q9, and the 5' regulatory regions of Q6, Q8, and Q9. This DNA sequence information, combined with the published DNA sequence information for the entire Q7 gene and exons 1 - 3 of Q9, allowed us to design primers for reverse transcription-polymerase chain reaction that could distinguish which of the four genes were transcribed in mouse lymphocytes and embryos. It was found that all four genes are transcribed in lymphocytes, but only Q7 and Q9 are transcribed in mouse embryos. Thus, both Q7 and Q9 are candidates for the genes responsible for the Ped gene phenotype.

Amino Acid Sequence↗
PubMed1996

Transcription-modulating drugs: mechanism and selectivity.

Transcription-modulating drugs achieve their therapeutic effects through the modulation of gene transcription. To understand how selectivity is achieved, four groups of such drugs - including immunosuppressants, estrogen analogs, the antidiabetic thiazolidinediones, and the anti-inflammatory salicylates - will be discussed. The immunosuppressants cyclosporin A and FK506, when complexed with immunophilins, inactivate the protein phosphatase calcineurin, resulting in the inhibition of interleukin-2 gene activation. Another immunosuppressant, rapamycin, binds to the same immunophilin as FK506 but inactivates a protein kinase p70(s6k). Estrogen analogs tamoxifen and rolaxifene antagonize one estrogen receptor transactivation function (AF-2) and agonize another (AF-1). They modulate expression of a wide variety of genes, including transforming growth factor-alpha, insulin-like growth factor-1, and transforming growth factor-beta3, which are important for breast and endometrial cancer proliferation and bone maintenance respectively. The antidiabetic drugs thiazolidinediones bind and activate peroxisome proliferator-activated receptor gamma and suppress insulin resistance mediated by tumor necrosis factor-alpha. Salicylates inhibit transcription factor NFkappaB, which is important for immune and inflammatory responses. Continuing understanding of molecular mechanisms of such drugs not only helps to identify better drugs for these targets but should also provide an insight into developing future transcription-modulating drugs with better selectivity and reduced toxicity.

Animals↗
PubMed1996

Inhibition of restriction endonuclease activity by DNA binding fluorochromes.

Activity of type II restriction endonuclease is affected by many common factors including buffer composition and sequences flanking the recognition site (Brabec et al., Eur.J. Biochem. 216, 183, 1993). The successful development of Optical Mapping (Schwartz et al., Science, 262, 110, 1993; Meng et al., Nature Genet. 9, 432, 1995; Wang and Schwartz, PNAS, 1995 Cai et al., PNAS, 92, 5164, 1995) relied on optimization of light microscope-based imaging of fluorescently labeled DNA molecules during restriction endonuclease digestion. Little was known about the effects of commonly used DNA-fluorochromes on restriction endonuclease activity. Thus, we developed an enzyme activity assay using lambda bacteriophage DNA or adenovirus-2 DNA to evaluate the effects of five DNA binding fluorochromes (4'-6-daimidine-2-phenylindole (DAPI), ethidium bromide (EtdBr), ethidium bromide homodimer (EthD-1), bis-benzimide (H33258) and benzothiazolium-4-quinolinium dimer (TOTO-1)) on the enzymatic activities of eleven type II restriction endonucleases (Asc I, Csp I, Dra I, EcoR I, Hha I, Hind III, Not I, Rsr II, Sfi I, SgrA I and Sma I). We found that the minor groove binding fluorochrome, DAPI, did not measurably inhibit activity of this group, with the exception of Dra I. Similarly, another minor groove binding fluorochrome H33258 inhibited Dra I and Not I (slightly). The three intercalating fluorochromes EtdBr, EthD-1 and TOTO-1, however, variably inhibited the other enzymes. Since Beta-mercaptoethanol (Beta-ME) is used to discourage photodamage of stained DNA molecules, we also assessed its effect on restriction endonuclease activity. Interestingly, Dra I, Hind III, Sfi I and Sma I retained full activities at high concentration of Beta-ME (5%), but Asc I, Csp I, Not I, Rsr II and SgrA I showed varying sensitivities to the Beta-ME. Isoschizomers Csp I and Rsr II behaved differently to both fluorochromes and Beta-ME. The results presented here should provide a basis for further development of new Optical Mapping-based techniques requiring fluorescence labeling of other actively imaged enzymatic reactions.

Binding Sites↗
PubMed1996

The cost of coverage: rural health insurance in China.

China has undergone great economic and social change since 1978 with far reaching implications for the health care system and ultimately for the health status of the population. The Chinese Medical Reform of the 1980s made cost recovery a primary objective. The urban population is mostly protected by generous government health insurance. A high share government budget is allocated to urban health care. Rural cooperative health insurance reached a peak in the mid-1970s when 90% of the rural population were covered. In the 1980s rural cooperative health insurance collapsed and present coverage is less than 8%. The decline has been accompanied by reports of growing equity problems in the financing of and access to health care. This article is the first in a four-year study of the impact on equity of the changes in Chinese health care financing. The article examines the relationship between rural cooperative health insurance as the explanatory variable and health care expenditure, curative vs. preventive expenditure and tertiary curative care expenditure as dependent variables using a natural experimental design with a 'twin' county as a control. The findings support the hypothesis that cooperative health insurance will induce higher growth of health care expenditure. The findings also support the hypothesis that cooperative health insurance will lead to a shift from preventive medicine to curative medicine and to a higher level of tertiary curative care expenditure. The empirical evidence from the Chinese counties is contradicting World Bank health financing policies.

China↗
PubMed1996

Novel tetranucleotide repeat polymorphism in the human adenosine deaminase gene: interethnic comparison of three major human groups.

A new tetranucleotide repeat polymorphism was revealed at the human adenosine deaminase (ADA) locus by using the polymerase chain reaction and denaturing polyacrylamide gel electrophoresis. Allele frequencies were estimated in seven populations from three major ethnic groups. Heterozygosity values were calculated and found to differ significantly between Africans and non-Africans.

Adenosine Deaminase↗
PubMed1996

The cloning, sequence analysis, and expression in E. coli of coat protein gene of grapevine fanleaf virus Gh.

Fragments of 5' end and 3' end of the coat protein gene of a Chinese strain grapevine fanleaf virus (GFLV-Gh) were separately amplified through RT-PCR. The two products were cloned and ligated into a complete full-length coat protein gene via an inherent BgIII restriction site. The entire gene contains 1512 nucleotides which encode a 504 amino acids coat protein, molecular weight approximately 56 kDa. Comparison with GFLV F-13 shows 88.4% homology in nucleotides and 95.8% similarity in deduced amino acid residues. Also this coat protein gene was expressed in E. coli DH 5 alpha.

Amino Acid Sequence↗
PubMed1996

[Effect of 5-HT and somatostatin on SP and chronic pain initiated electrical activity of neurons in spinal dorsal horn].

The effects of SP on the electric activities of neurons of spinal dorsal horn and the influence of 5-HT, somatostatin (SOM) on the effects of SP were observed in anesthetized rats with multimicropipete and iontophoresis techniques. It was found that: (1) The microiontophoretically administrating of SP could increase spinal dorsal horn unit discharge. (2) The noxious electrical activity of neurons induced by formalin could be inhibited by microiontophoretically applied SP. (3) The microiontophoretically administrating of 5-HT and SOM could inhibit the SP and formalin evoked unit discharge of neurons in spinal dorsal horn. It was suggested that SP took a double-effect part in modulation of pain transmission and analgesia in spinal cord, 5-HT and SOM inhibited the effect of SP and participated in pain modulation of SP.

Animals↗
PubMed1995

Ordered restriction endonuclease maps of yeast artificial chromosomes created by optical mapping on surfaces.

We have developed a surface mounting technology for the rapid construction of ordered restriction maps from individual DNA molecules. Optical restriction maps constructed from yeast artificial chromosome DNA molecules mounted on specially derivatized glass surfaces are accurate and reproducible, and the technology is amenable to automation. The mounting procedures described here should also be useful for fluorescence in situ hybridization studies. We believe these improvements to optical mapping will further stimulate the development of nonelectrophoretic approaches to genome analysis.

Automation↗
PubMed1995

Bovine adrenal cortex transformations of mitotane [1-(2-chlorophenyl)-1-(4-chlorophenyl)-2,2-dichloroethane; o,p'-DDD] and its p,p'- and m,p'-isomers.

The adrenalytic activity of mitotane (o,p'-DDD) has made it useful in the treatment of adrenocortical carcinoma and Cushing's syndrome. In support of a study to develop mitotane analogs as more effective therapeutic agents and as a basis for understanding the toxicity of related compounds in the adrenals, the biotransformations of o,p'-DDD in adrenocortical homogenate preparations have been studied and compared with those of its m,p'- and p,p'-isomers. Aliphatic oxidation to the corresponding acetic acid derivative, o,p'-, m,p'- or p,p'-DDA, was the major transformation for all the preparations. In the comparisons of the DDD isomers, the order of both DDA formation and apparent covalent binding was o,p'- > m,p'- > p,p'-DDD. There was also evidence for alpha-hydroxylation at the benzylic carbon with subsequent loss of water to form ethylene derivatives. This was a minor pathway for o,p'-DDD, but was the major pathway for the other two isomers. Thus, while the total yields of metabolites of o,p'- and m,p'-DDD were similar and at least twice that of the p,p'-isomer, their distribution of metabolites differed significantly. The effects of the three isomers on cell growth and cortisol production with the human adrenocortical carcinoma cell line, NCI H-295, followed the same order as their DDA formation and tissue binding. It is proposed that hydroxylation by the adrenal cortex at the beta-carbon leads to an adrenalytic effect, whereas hydroxylation at the alpha-carbon would represent an alternate deactivation pathway.

Adrenal Cortex↗
PubMed1995

Immobilization of heparin oligosaccharides onto radiofrequency plasma modified pyrolytic carbon-coated graphite.

Heparin oligosaccharides with different anticoagulant activities were prepared and immobilized onto pyrolytic carbon coated graphite (PC) heart valve materials commonly used in mechanical heart valve prostheses. Prior to immobilization, PC surfaces were modified by radiofrequency plasma polymerized N-vinyl-2-pyrrolidone (PPNVP) thin films (approximately 100 nm) and derivatized to provide surface hydroxyl groups. Cleaved, low affinity heparin (C-heparin) with factor Xa inhibition activity of 107 to 130 IU/mg, was prepared by partial deaminative cleavage of commercial crude heparin, and high-affinity heparin (HA-heparin) with factor Xa inhibition activity of 550 to 1000 IU/mg was prepared by fractionation of C-heparin using agarose-ATIII affinity chromatography. C-heparin and HA-heparin were immobilized to surface modified PC by reductive amination. Anticoagulant activity of the heparin immobilized surfaces was determined by chromogenic assay for the inhibition of factor Xa. Highest surface anticoagulant activity was measured on C-heparin immobilized surfaces (64.0 +/- 7.3 mIU/cm2) compared with HA-heparin immobilized surfaces (27.2 +/- 12.2 mIU/cm2), suggesting higher binding of C-heparin than HA-heparin on the modified PC surfaces. Immobilized surfaces were evaluated under dynamic flow conditions, by subjecting samples to shear stress of up to 206 dyn/cm2 in the presence of 5% albumin solution or human plasma. Anticoagulant activity of the immobilized heparin was retained, although reduced, and the modified surfaces showed evidence for protein resistance.

Anticoagulants↗
PubMed1995

Metabolic activation and binding of mitotane in adrenal cortex homogenates.

Mitotane [1-(2-chlorophenyl)-1-(4-chlorophenyl)-2,2-dichloroethane, o,p'-DDD] is an adrenocorticolytic agent of value in the treatment of adrenocortical carcinoma and Cushing's syndrome. In support of a program to develop agents superior to mitotane, it is the purpose of this study to explore the relationship of the metabolism of mitotane to its binding to adrenal cortex tissue from several sources. The objective was to detect the mitotane moiety responsible for its covalent binding in various test systems. Studies were conducted with an 125l-labeled analog of mitotane, 1-(2-chlorophenyl)-1-(4-iodophenyl)-2,2-dichloroethane, prior to a comparison to results with lower specific activity [14C]mitotane. With dog adrenal cortical whole homogenates, the majority of covalent binding was to proteins with an additional one-sixth of the total bound radioactivity associated with a phospholipid fraction. No radioactivity was associated with DNA. The rank order of species in regard to metabolism and protein binding was bovine > dog > rat adrenal homogenates > human normal adrenal or tumor homogenates. The percentage of radioactivity recovered from the hydrolysates of those fractions was uniformly high. In addition, the only metabolite present in the hydrolysates corresponded to 1-(2-chlorophenyl)-1-(4-iodophenyl)acetic acid from the iodo analog of o,p'-DDD and the corresponding o,p'-dichlorodiphenylacetic acid (o,p'-DDA) from o,p'-DDD. Our results are consistent with an acyl chloride being the reactive intermediate formed from the dichloromethyl moiety of mitotane, which leads to both DDA metabolite formation and binding to adrenal cortical bionucleophiles.

Adrenal Cortex↗
PubMed1995

Evaluation of a thin-film peripheral nerve cuff electrode.

This is a study of the reaction of large nerves to implantation using a flexible, thin-film cuff electrode. Cuff electrodes were implanted on the sciatic nerve of three cats. An implantation period of six weeks allowed sufficient time for any injury responses in the nerve and connective tissue sheath around the cuff to develop. The electrode came off the nerve in one of the cats. In the remaining two cats, gross observation following explantation of the electrodes revealed encapsulation of the cuffs without swelling of nerve tissue. Histological evaluation did not demonstrate nerve injury. The nerve cuff electrodes, which are comprised of titanium and iridium coatings on a fluorocarbon polymer substrate, appeared unaffected by the implantation, and connective tissue encapsulation did not adhere to either the polymer substrate or metallization. Evaluation of the electrodes using activated iridium oxide charge injection sites in more extended studies is now being undertaken.

Animals↗
PubMed1995

Direct bladder stimulation with percutaneous electrodes and impedance monitoring of volume in an SCI animal model.

Bladder responses to percutaneous electrodes were investigated with stimulation in three male spinal cats. The animals had been spinalized (T1 level lesion) 10 weeks prior to these studies and had been instrumented with chronic bladder had been spinalized (T1 level lesion) 10 weeks prior to these studies and had been instrumented with chronic bladder wall electrodes and suprapubic bladder catheters for filling and pressure recording. percutaneous stimulation in tethered animals was conducted wit hook electrodes inserted with a needle in the abdomen bilaterally adjacent to the bladder trigone. Stimulation was conducted with 40 Hz pulse trains of 10 to 30 mA for three seconds. Stimulation with both percutaneous and chronic electrodes induced high bladder pressures and voiding. In addition, with chronically implanted electrodes, impedance monitoring of bladder volume was found to be an effective recording technique.

Animals↗