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Biomedical subjects

Q Liu

Publications and source records attributed to Q Liu.

At least 577 records · Page 32Linked to original sources
PubMed1996

Bi-directional dideoxy fingerprinting (Bi-ddF): a rapid method for quantitative detection of mutations in genomic regions of 300-600 bp.

There is a great need for rapid screening methods that detect essentially all mutations. Dideoxy fingerprinting (ddF) is a highly sensitive screening method that is performed by electrophoresing one lane of a Sanger dideoxy termination reaction through a nondenaturing gel. Mutations may produce an extra segment or eliminate a segment from the termination products (informative dideoxy component). In addition, mutations can be detected by the altered mobility of one or more termination segments (informative SSCP component). To screen larger segments with virtually 100% sensitivity, bi-directional ddF (Bi-ddF) was developed. Bi-ddF is a 'second generation ddF' in which the dideoxy termination reaction is performed simultaneously with two opposing primers. Bi-ddF has two important advantages over ddF: (i) the dideoxy component can detect 10 of the 12 types of possible single-base substitutions; and (ii) the SSCP component is enhanced because alterations of mobility can be detected in either the downstream or upstream direction. As a result, Bi-ddF can screen larger regions of genomic DNA with virtually 100% sensitivity. Bi-ddF detected 100% of 28 single-base substitutions in a 494 bp segment containing exons B and C of the human factor IX gene and 100% of 42 single-base substitutions and one microdeletion present in a 577 bp region containing exon H. In a blinded analysis in which 39 wildtype samples were randomly mixed with 51 mutant samples, all mutations were detected with no false positives. Bi-ddF requires essentially the same effort as ddF, yet twofold more DNA sequence can be screened reliably per unit effort.

DNA↗
PubMed1996

Treatment of experimental cryptococcal meningitis with fluconazole: impact of dose and addition of flucytosine on mycologic and pathophysiologic outcome.

Fluconazole is effective in the therapy of cryptococcal meningitis in patients with AIDS. The optimal dosage of fluconazole and the impact of combination with flucytosine are not known. In this study, rabbits with experimental cryptococcal meningitis were given fluconazole at low, intermediate, or high dose or in combination with a low or intermediate dose of flucytosine. Serial cerebrospinal fluid (CSF) examinations showed that all three doses of fluconazole and low-dose fluconazole in combination with intermediate-dose flucytosine were effective in reducing CSF cryptococcal titer, lactate, white blood cell count, and cryptococcal antigen (CRAG) titers. The intermediate and high doses of fluconazole reduced CSF fungal (P < .05) and CRAG (P < .001) titers earlier than low-dose fluconazole alone or in combination with flucytosine. Only the highest dose of fluconazole reduced brain edema after 7 days. In this model of cryptococcal meningitis, there was evidence of a dose response with fluconazole but no in vivo synergism with flucytosine.

Animals↗
PubMed1996

Coronary effects of diadenosine tetraphosphate resemble those of adenosine in anesthetized pigs: involvement of ATP-sensitive potassium channels.

Diadenosine tetraphosphate (Ap4A) is an adenine nucleotide with vasodilatory properties. We examined the effects of Ap4A on coronary circulation in comparison with those of adenosine, its metabolite, in anesthetized pigs. Left atrial (LA) infusion of Ap4A at increasing doses of 100, 200, and 300 micrograms/kg/min increased coronary blood flow (CBF) and decreased systemic blood pressure (BP) and coronary vascular resistance (CVR). Ap4A had no effect on large epicardial coronary artery diameter (CoD). Likewise, LA infusion of adenosine at doses of 150 and 300 micrograms/kg/min increased CBF and decreased BP and coronary vascular resistance (CVR) but did not affect CoD. Therefore, the vasodilatory effects of Ap4A and adenosine were predominant in small coronary resistance vessels and negligible in large coronary arteries. Pretreatment with glibenclamide (2 mg/kg, intravenously, i.v.), a specific blocker of ATP-sensitive potassium channels (KATP), attenuated alterations of CBF, BP, and CVR induced by Ap4A and by adenosine. In contrast, treatment with cromakalim (0.5 microgram/kg/min i.v.), an activator of KATP, enhanced the coronary effects of Ap4A and adenosine. Therefore, the opening of KATP in the pig coronary circulation is involved in the in vivo vasodilatory effects of Ap4A and adenosine. Treatment with 8-phenyltheophylline (8-PT, 4 mg/kg i.v.), an adenosine receptor antagonist, suppressed CBF increases induced by Ap4A (20 micrograms/kg/min, intracoronarily, i.c.) and adenosine (5 micrograms/kg/min i.c.) by 68 and 90%, respectively. These findings suggest that the in vivo coronary effects of Ap4A are largely caused by the opening of KATP through rapid degradation to adenosine to activate adenosine receptors.

Adenosine↗
PubMed1996

Simultaneous characterization of glutathione S-transferase M1 and T1 polymorphisms by polymerase chain reaction in American whites and blacks.

Human glutathione S-transferase (GST) M1 and T1 enzymes exhibit genetic polymorphism, with a percentage of normal individuals exhibiting a homozygous deletion of the relevant genes. We established a differential polymerase chain reaction (PCR) technique to simultaneously characterize inactivating mutations responsible for the null alleles of GSTM1 and GSTT1. Primers for GSTM1,GSTT1,and for beta-globin (as a positive control) were used to simultaneously amplify all three gene products from leukocyte DNA from 416 normal healthy human volunteers. Identical GSTM1 and CSTT1 genotypes were obtained using nine samples processed either separately or simultaneously for GSTM1 and GSTT1. The frequency of the null genotype for GSTM1 was higher in whites (114/213 or 53.5% vs 56/203 or 27.6%, p < 0.001) and for GSTT1 was higher in blacks (49/203 or 24.1% vs 32/213 or 15.0%, p = 0.019). The observed frequency of the 'double null' genotype for both GSTM1 and GSTT1 was not significantly different from that predicted if both polymorphisms were independent (p = 0.102) and did not differ by race (p = 0.120) or sex (p = 0.800). There was a higher frequency of the GSTM1 null genotype among females than males (92/202 or 45.5% vs 78/214 or 36.4%, p = 0.049). These results demonstrate that this PCR method is a simple and reliable tool to simultaneously characterize both GSTM1 and GSTT1 null genotypes.

Adolescent↗
PubMed1996

Sequence variation in the 18S rRNA gene, a target for PCR-based malaria diagnosis, in Plasmodium ovale from southern Vietnam.

Field surveys of malaria were performed in southern Vietnam by using an acridine orange staining method for rapid diagnosis and a PCR-based, microtiter plate hybridization method for accurate diagnosis. A total of three patients of Plasmodium ovale infection were detected, but PCR-amplified DNA of the P. ovale isolates from two of the patients did not hybridize with the P. ovale-specific probe. Analysis of the target sequence in the 18S rRNA gene indicated that in the DNA of isolates from both patients three nucleotides in the probe region from the typical P. ovale sequence were different, with deletions of two nucleotides and the substitution of one nucleotide. These results may suggest that in addition to molecular biological methods, careful microscopic examination of stained thin blood films is still required in studies of the prevalence of different malaria species.

Animals↗
PubMed1996

Sex-linkage of glucosephosphate isomerase-B and mapping of the sex-determining gene in channel catfish.

Sex-linkage of glucosephosphate isomerase-B (GPI-B) was observed in five experimental matings between heterozygous male and homozygous female channel catfish (Ictalurus punctatus). Offspring phenotypes for GPI-B were 40.8% heterozygous male and 43.0% homozygous female, while recombinant offspring were 7.4% homozygous male and 8.8% heterozygous female. Thus, GPI-B and the sex-determining gene (SDG) were linked and had a recombination rate of 16.2%. This linkage was designated I. punctatus linkage group XXIX. The gene-centromere distance (1.66 cM) of SDG, estimated in six gynogenetic families derived from XY females, indicated that SDG resides very close to the centromere. Based on estimates of these genetic distances, a chromosomal order of GPI-B-centromere-SDG was proposed. Additionally, joint segregation of GPI-A and SDG in two experimental matings indicated no genetic linkage between GPI-A and sex. These genetic relationships were compared to those reported in other teleost taxa with regard to evolutionary conservation of ancestral gene arrangements.

Animals↗
PubMed1996

Growth hormone, growth factors and hematopoiesis.

Hypocellularity of primary lymphoid organs is a distinctive and reproducible characteristic of aged humans and animals. Similar changes have been reported in both hypophysectomized and dwarf rodents. In the bone marrow of these animals, there is an associated reduction in the number of erythroid, lymphoid and myeloid elements. Implantation of growth hormone (GH)-secreting GH3 pituitary cells or infusion of growth hormone into aged rodents dramatically improves cellularity of both the thymus gland and bone marrow. At present it is unknown whether these effects are due to direct effects of growth hormone on hematopoietic cells or if they are caused by the induction of insulin-like growth factor-1 (IGF-1) synthesis. We recently discovered that colony-stimulating factor-1 (CSF-1) and interleukin-3 (IL-3) induce expression and synthesis of the IGF-1 peptide in murine bone marrow cells. Transcripts for IGF-1 increase approximately 50-fold during differentiation over the negligible levels that are expressed in freshly isolated bone marrow cells. Two potential functions of macrophage-derived IGF-1 are to: (a) increase the proliferation of early or committed bone marrow progenitors and (b) reduce their rate of cell death. In support of the first possibility, IGF binding protein-3 significantly inhibits the proliferation of CSF-1-treated bone marrow cells and this inhibition can be reversed by addition of exogenous IGF-1. In support of the second possibility, we have induced apoptosis of both nonadherent bone marrow cells and a myeloid progenitor cell line by depriving these cells of CSFs. Preliminary results indicate that addition of IGF-1 to these cells reduces apoptotic cell death by 50%. These data establish that two different CSFs, CSF-1 and IL-3, induce abundant expression of IGF-1 as these cells differentiate into more mature hematopoietic cells. This model offers a novel approach for investigating the developmental expression of IGF-1 during defined differentiation pathways of hematopoietic cells. If IGF-1 is indeed proven to act as a survival factor for hematopoietic progenitors, these data would support the idea that the hypocellularity of primary lymphoid tissues in aged animals is related to the limited availability to these cells of either growth hormone or IGF-1.

Aging↗
PubMed1996

Insulin-like growth factor II induces DNA synthesis in fetal ventricular myocytes in vitro.

Insulin-like growth factor II (IGF2) belongs to a family of growth factors that includes insulin and insulin-like growth factor I (IGF1). Although the accumulating evidence indicates that IGF1 is involved in regulating proliferation of ventricular myocytes, the role of IGF2 is less clear. To gain more insight into the functions of IGF2, rat ventricular expression of IGF2 mRNA at four developmental stages was examined by Northern analysis. An abundant IGF2 mRNA of approximately 3.8 kb was detected in fetal ventricles. It was dramatically decreased in neonatal ventricles and became undetectable in juvenile and adult ventricles. Similar expression patterns of the mRNA encoding IGF1 receptor and IGF2 receptor were observed. Since the results of Northern analysis strongly suggest the importance of IGF2 in regulating proliferation of fetal rat ventricular myocytes, the effects of an exogenous IGF2 on DNA synthesis in cultured rat ventricular myocytes were determined. DNA synthesis, which was monitored by measuring 5-bromo-2'-deoxyuridine (BrdU) and [3H]thymidine incorporation, was increased by twofold to threefold in IGF2-stimulated fetal ventricular myocytes, whereas no change in BrdU or [3H]thymidine incorporation was observed in neonatal ventricular myocytes. Instead, IGF2 seemed to induce hypertrophy in neonatal ventricular myocytes. An antisense oligonucleotide against rat IGF2 mRNA was able to significantly reduce BrdU incorporation, and this effect was quantitatively reversed by the addition of exogenous IGF2. Reversion by exogenous IGF2 was abolished by a monoclonal antibody against IGF1 receptor. In conclusion, our results suggest that IGF2 directly regulates proliferation of fetal rat ventricular myocytes in a paracrine/autocrine fashion.

Animals↗
PubMed1996

Near-infrared spectroscopy in experimental pneumococcal meningitis in the rabbit: cerebral hemodynamics and metabolism.

Near-infrared spectroscopy is a noninvasive technique which measures oxidized cytochrome aa3, oxygenated Hb, and deoxygenated Hb and calculates total Hb in tissue. This technique, in conjunction with measurement of cerebral blood flow, was used in rabbits with experimental bacterial meningitis to determine whether there was evidence for cerebral energy depletion and alterations in the cerebral vascular bed with infection. Rabbits with meningitis had a significant reduction in cerebral blood flow, cerebral oxidized cytochrome aa3 and a relative increase in the deoxygenated Hb fraction and a decrease in the oxygenated Hb fraction compared with uninfected controls. Total Hb was not significantly different between the two groups. These findings may help clarify the mechanism for some of the intracranial pathophysiologic abnormalities in meningitis.

Animals↗
PubMed1996

In vivo vasodilatory action of atrial natriuretic peptides in canine coronary circulation.

To investigate the role that atrial natriuretic peptides (ANP) play in regulating coronary circulation in vivo, we examined the effects of intravenous (iv) ANP and/or HS-142-1 (HS), a specific ANP receptor antagonist, in chronically instrumented dogs on circumflex coronary artery diameter (CoD) and coronary blood flow (CBF). At ANP plasma levels of 366.7, 785.0, and 1850.0 pg/ml, which were induced by continuous iv infusion of ANP at 25, 50, and 100 ng/kg per min respectively, ANP increased CoD by 1.2 +/- 0.3%*, 2.2 +/- 0.5%*, and 2.9 +/- 0.5%*, and decreased mean systemic blood pressure by 2.3 +/- 1.0%, 4.3 +/- 1.5%* and 5.3 +/- 1.8%* (*p < 0.05), respectively. A significant increase in the plasma cGMP level was also observed. However, neither CBF nor heart rate changed significantly. Pretreatment with HS (3 mg/kg) almost completely suppressed these hemodynamic effects of ANP along with inhibiting the increases in the plasma cGMP level. However, under control conditions, HS itself (3 mg/kg, iv) produced no significant changes in coronary parameters. Thus, ANP significantly increased CoD at plasma levels 10- to 20-fold higher than those in the control. These findings suggest that in patients under pathological conditions such as severe congestive heart failure increased endogenous ANP may contribute to the regulation of coronary circulation as a compensatory mechanism. It may also have direct vasodilatory effects on epicardial vessels, since HS suppressed both its coronary effects and the increase in plasma cGMP levels. However, in normal subjects, endogenous ANP may have little direct effect on coronary circulation.

Animals↗
PubMed1996

Technical note: a simplified procedure for vitamin E determination in beef muscle.

A simplified method for the determination of alpha-tocopherol concentration in beef muscle was developed and evaluated. The method consists of a saponification step applied to 1-g samples of intact, fresh muscle, followed by a single isooctane extraction of the saponified samples. alpha-Tocopherol in the extract was separated by normal phase chromatography and quantified by fluorescence detection. A single extraction with the simplified method accounted for 95% of the total muscle alpha-tocopherol concentration obtained by two extractions with the Arnold et al. (J. Food Sci. 58:28, 1993) method. Recovery of added alpha-tocopherol standard after two extractions of a saponified muscle sample was 91% for the simplified method, which was not different (alpha = .78) from recovery using the Arnold method, and the efficiency of the single extraction in the simplified method was 89%. The coefficients of variation for the simplified and Arnold methods were both 3.1%. This method should permit the duplicate analysis of 100 fresh muscle samples within 24 h.

Animals↗
PubMed1996

Color coordinates for assessment of dietary vitamin E effects on beef color stability.

Color stability was investigated in longissimus lumborum (LL), semimembranosus (SM), and gluteus medius (GM) muscles from Holstein steers fed diets including doses of alpha-tocopheryl acetate that were 0 (EO), 250 (E250), 500 (E500), and 2,000 (E2000) mg.steer-1.d-1 for 42 or 126 d. Longissimus lumborum was aged for 14, 28, and 56 d and GM and SM were aged for 14 d. Effects of vitamin E dose on retention of redness (a*), yellowness (b*), color saturation (chroma), and proportions of redness and yellowness (hue angle) following an aging period of 14 d were E2000 > E500 = E250 > EO (P < .01). Effectiveness of dose duration on the color parameters was 126 d > 42 d (P < .01). Dietary vitamin E supplementation stabilized redness and color saturation, decreased yellowness, and extended color display life of fresh beef. A technique for estimation of color display life based on hue angle measurements of fresh beef is described. Color display life estimates based on hue angle measurements were more consistent with vitamin E supplementation effects on metmyoglobin percentage and hue angle than were estimates obtained from the metmyoglobin threshold method. Color display life across LL, SM, and GM stored until d 14 and then displayed under simulated retail conditions was extended (P < .01) 2.0 (E250) to 5.0 d (E2000). Coefficients of determination for regressions of color display life on muscle alpha-tocopherol concentration were .81, .64, and .63 in LL, SM, and GM muscles aged 14 d, respectively. Supplementation of 500 mg of alpha-tocopheryl acetate per steer daily improved (P < .01) the mean color display life of these three muscles by 2.3 d, or 100%.

Animals↗
PubMed1996

Titration of fresh meat color stability and malondialdehyde development with Holstein steers fed vitamin E-supplemented diets.

Pigment and lipid oxidations were investigated in longissimus lumborum (LL), semimembranosus (SM), and gluteus medius (GM) from Holstein steers fed four doses of vitamin E (64 [control], 295, 550, or 2,173 IU/d) for two durations (42 or 126d). Vitamin E dose did not affect (P = .30) carcass quality or yield characteristics. The LL was stored in vacuum packages at 4 degrees C for 14, 28, and 56 d, and GM and SM were stored for 14 d. Increments of dose and duration of vitamin E supplementation increased (P < .001) alpha-tocopherol concentration in blood plasma and in these muscles. During simulated retail display, accumulations of metmyoglobin (METMB) and thiobarbituric acid reactive substances (TBARS) were greater (P < .01) in beef from control than in beef from supplemented steers. In cubic models, muscle alpha-tocopherol accounted for 79% of the variation in TBARS and 66% of the variation in METMB. Color display life, calculated by the METMB threshold method, revealed fewer dose and duration effects of vitamin E than were evident following analysis of variance of the METMB responses. Across durations and muscles, color display-life of fresh beef calculated by the METMB threshold method was extended (P < .05) .9 to 1.8 d by vitamin E supplementation (P < .05). Storage for 28 or 56 d caused only a slight decline (P < .001) in LL alpha-tocopherol concentration but diminished (P < .05) vitamin E effects on color display-life. Although the ranking of alpha-tocopherol accumulation was GM > SM > LL, the color display-life ranking of these muscles across vitamin E treatments was LL > SM > GM.

Aging↗
PubMed1996

NIRCA: a rapid robust method for screening for unknown point mutations.

We describe a method for screening for dispersed point mutations, based on the observation that RNase frequently cleaves both strands of base pair mismatches in duplex RNA targets. The mismatched substrates are generated by in vitro transcription of wild-type and mutant templates amplified by the PCR or reverse transcription (RT)-PCR; bacteriophage promoters are incorporated into the PCR primers to permit both strands of the products to be transcribed into RNA. Complementary wild-type and mutant transcripts are hybridized and treated with RNase, and the cleavage products are separated on agarose gels and detected by visualization of the ethidium-stained sample under UV light. The method is thus non-isotopic, and since the cleavage products remain double-stranded during analysis, the labor-intensive RNase inactivation steps required in the original procedure can be eliminated. Also, nonspecific background cleavage is reduced so that longer target regions (1 kb) can be screened in a single step. The Non-Isotopic RNase Cleavage Assay (NIRCA) achieved a detection rate of 88%-90% in blind studies in a Factor IX model system, and it was also used to detect unknown p53 mutations in breast tumor samples. NIRCA provides a rapid method for sensitive, non-isotopic, high-throughput genetic screening.

Base Sequence↗
PubMed1996

Field evaluation of the QBC technique for rapid diagnosis of vivax malaria.

The QBC (quantitative buffy coat) technique was compared with that of the Giemsa-stained thick blood film (GTF) under field conditions in Junlian and Mingshan counties, Sichuan, China, for rapid diagnosis of vivax malaria. Blood samples were collected from 364 volunteer villagers, and each sample was examined with both the QBC and GTF techniques. For each GTF sample (10 microliters of blood), as many as 300 oil-immersion fields were examined; each QBC tube was inspected for up to 5 minutes. The GTF technique resulted in 86 positive blood samples and 278 negative; the QBC technique indicated 89 positive and 275 negative samples. Relative to the results obtained with GTF, the QBC technique had a sensitivity and specificity of 87.2% and 95.0%, respectively; concordance between the tests was 93.1%. The median time-to-positive diagnosis with the QBC technique (1.12 min) was 11% of that with GTF. The distribution of different developmental stages of Plasmodium vivax parasites was also examined in the centrifuged QBC tubes: all stages except schizonts could be found in the lower part of the platelet zone (the interphase between the monocyte and platelet layers), especially ring forms.

Azure Stains↗