Search PubMed⌕ Search

Biomedical subjects

H Cheng

Publications and source records attributed to H Cheng.

At least 271 records · Page 15Linked to original sources
PubMed1996

Molecular cloning of a Schizosaccharomyces pombe cDNA encoding lanosterol synthase and investigation of conserved tryptophan residues.

A Schizosaccharomyces pombe cDNA encoding lanosterol synthase was cloned by complementing a Saccharomyces cerevisiae lanosterol synthase mutant. The predicted 83-kDa protein is 54-58% identical to other lanosterol synthases. The previously known lanosterol synthases contain 229 conserved residues, which should encompass the catalytically essential amino acids. This number is decreased dramatically by including the Sc. pombe lanosterol synthase in the analysis; 42 residues are no longer conserved and therefore are catalytically nonessential. We have begun mutagenic studies to identify catalytic residues from the remaining conserved residues. Mutant Sa. cerevisiae lanosterol synthase genes were generated in which phenylalanine was specifically substituted for conserved tryptophan residues. All of the resultant mutant enzymes retained the ability to complement the Sc. cerevisiae lanosterol synthase mutant, suggesting that these conserved tryptophan residues are not catalytically essential.

Amino Acid Sequence↗
PubMed1996

Two mechanisms of quantized calcium release in skeletal muscle.

Skeletal muscle uses voltage sensors in the transverse tubular membrane that are linked by protein-protein interactions to intracellular ryanodine receptors, which gate the release of calcium from the sarcoplasmic reticulum. Here we show, by using voltage-clamped single fibres and confocal imaging, that stochastic calcium-release events, visualized as Ca2+ sparks, occur in skeletal muscle and originate at the triad. Unitary triadic Ca(2+)-release events are initiated by the voltage sensor in a steeply voltage-dependent manner, or occur spontaneously by a mechanism independent of the voltage sensor. Large-amplitude events also occur during depolarization and consist of two or more unitary events. We propose a 'dual-control' model for discrete Ca2+ release events from the sacroplasmic reticulum that unifies diverse observations about Ca(2+)-signalling in frog skeletal muscle, and that may be applicable to other excitable cells.

Animals↗
PubMed1996

Partial repression of human gamma-globin genes by LCR element HS3 when linked to beta-globin genes and LCR element HS2 in MEL cells.

Clues for overcoming fetal (gamma-) globin gene repression in adult human erythroid cells may come from understanding why repression of isolated gamma-globin genes has not previously been achieved in the adult erythroid environment of mouse erythroleukemia cells (MEL). Repression of human gamma-globin genes has been demonstrated in MEL cells when transferred as part of the entire beta-globin gene cluster packaged in chromatin. Major differences in these approaches are prior packaging into chromatin and the presence of additional sequences, notably from the locus control region (LCR). In this report we focus on the contribution to gamma-globin gene repression that multiple elements of the LCR may have. We first show preferential activation of beta-globin genes over gamma-globin genes in MEL cells when linked to each other and to LCR sequences containing the core elements of DNase I hypersensitive sites 4, 3, and 2. Removal of the HS4 element had no effect, however, removal of the 225 bp HS3 core element resulted in a five-fold increase in gamma-globin gene expression. The enhancer 3' to the A gamma-globin gene also had no apparent effect on gamma-globin gene expression. These results provide first evidence of gamma-globin gene repression involving the core region of HS3 in the presence of the core region of HS2 and a beta-globin gene. A mechanism for repression involving sequestration of the gamma-promoter away from the strong enhancer activity of HS2 is proposed.

Animals↗
PubMed1996

Patterns of gene expression along the crypt-villus axis in mouse jejunal epithelium.

BACKGROUND: There is considerable interest in gene expression along the crypt-villus axis of the small intestinal epithelium, particularly in the identification of genes expressed in intestinal crypts. METHODS: In an attempt to identify crypt-expressed genes, single-stranded cDNA made from normal mouse jejunal epithelium was used in subtractive hybridization against single-stranded cDNA from epithelium from which crypt cells were depleted by 2,000 rads of gamma irradiation. Partial DNA sequence and in situ hybridization of 72 resulting clones were determined. RESULTS: The sequence of 45 clones matched previously published genes. Gene expression patterns fell into three categories: expression throughout the crypt-villus axis, expression restricted to the villus, and expression restricted to the crypt. Clones in the first two categories could be further divided into three subgroups: those with uniform expression, those with an increasing gradient of expression, and those with a decreasing gradient of expression along the crypt-villus axis. Twenty two clones showed a stronger expression in crypt and lower villus cells, four of these were differentially localized to the crypt. Two of the crypt localized clones were uniformly expressed throughout the crypt, expression of one was stronger in the lower crypt, and expression of the remaining clone was enhanced Paneth cells. We report the full-length cDNA sequence of the Paneth-cell-enhanced clone. CONCLUSIONS: The screen isolated crypt-expressed genes that may prove useful tools in the study of crypt biology. In a companion report, we characterize one of the crypt clones.

Amino Acid Sequence↗
PubMed1996

CRP-ductin: a gene expressed in intestinal crypts and in pancreatic and hepatic ducts.

BACKGROUND: A subtraction screen isolated CRP-ductin (CRP), a gene expressed in intestinal crypts. METHODS: DNA sequencing, in situ hybridization, immunostaining, Western and Northern blotting were used to characterize murine CRP. RESULTS: CRP is restricted to the intestine and its associated glands. In the small intestine, CRP mRNA is expressed in crypt cells at all stages of differentiation from the stem cells to the terminally differentiating cells of the crypt top, but not in the mature cells of the villus. In the colon, CRP mRNA is most heavily expressed in the mid-crypt. Expression is also seen in the pancreas and pancreatic ducts, and in the epithelium lining larger hepatic ducts, but not in the liver parenchyma or stomach. CRP protein is localized to the lumenal aspect of crypt cells in the small intestine. In the colon, the protein is seen in the lumenal aspect of surface epithelial cells. CRP protein is similarly found in the lumenal aspect of epithelial cells lining the pancreatic duct system and the larger hepatic ducts. Two cDNA variants, CRP-alpha and CRP-beta, were cloned from mouse jejunal epithelium. Their 3'-sequence differs in an 82-bp domain unique to CRP-beta. CONCLUSIONS: The CRP-alpha sequence predicts a protein with a short cytoplasmic region, a transmembrane domain, and a large extracellular region composed of many repeats (8 scavenger receptor domains, 5 CUB-domains, 1 ZP-domain, and 6 copies of a previously unreported domain which we call the CRP-domain). The structure of the CRP protein suggests a role in ligand interaction; possible functions are discussed.

Amino Acid Sequence↗
PubMed1996

Pharmacokinetics and food interaction of MK-462 in healthy males.

A study was conducted to assess the safety, tolerability, and pharmacokinetics of single intravenous (IV) doses of 5-90 micrograms kg-1 of MK-462, and the effect of food on the pharmacokinetics of MK-462 administered orally to healthy males. Results of this study indicate that IV doses of MK-462 from 5 to 90 micrograms kg-1 are well tolerated. The disposition kinetics of MK-462 were linear for IV doses up to and including 60 micrograms kg-1. The values of the plasma clearance (CL), steady-state volume of distribution (Vss), plasma terminal half-life (t1/2), and mean residence time in the body (MRT) of MK-462 averaged 1376 mL min-1, 140 L, 1.8 h, and 1.7 h, respectively, and remained essentially constant over the dosage range of 10-60 micrograms kg-1 of IV MK-462. However, as the dose increased from 60 to 90 micrograms kg-1, the mean value of the apparent CL decreased from 1376 to 807 mL min-1. Thus, elimination of MK-462 was dose dependent in this dosage range. Based on the disposition decomposition analysis (DDA), it was shown that the Vss value of MK-462 remained essentially constant over the dosage range of 10-90 micrograms kg-1 of IV MK-462. The following values of two dose-independent parameters were also calculated by using DDA: distribution clearance (CLd) = 2028 mL min-1, and mean transit time in the peripheral tissues (MTTT) = 0.74 h. The mean values of AUC, Cmax, tmax, and apparent t1/2 of MK-462 in 12 subjects each receiving a 40 mg tablet of MK-462 without breakfast were 330 ng.h mL-1, 77 ng mL-1, 1.6 h, and 1.8 h, respectively. Although administration of a standard breakfast prior to dosing increased the AUC value (by approximately 20%) of MK-462 and delayed its absorption, there were no significant effects of the meal on the values of Cmax and apparent t1/2 of MK-462.

Absorption↗
PubMed1996

Disposition decomposition analysis for pharmacodynamic modeling of the link compartment.

An approach based on disposition decomposition analysis (DDA) and the hysteresis minimization principle has been developed for pharmacodynamic modeling. It allows calculation of the mean transit time and the ratio of distribution clearance to biophase distribution volume of drug, and determination of the drug concentration-time function at the biophase (Cb(t)). The proposed method extends the DDA approach to drug distribution to a possibly heterogeneous effect compartment of a generalized pharmacokinetic/pharmacodynamic model. The application of this DDA-dynamics method is demonstrated using published data for pancuronium.

Gastrointestinal Transit↗
PubMed1996

Volumes of distribution and mean residence time of drugs with linear tissue distribution and binding and nonlinear protein binding.

Based on a generalized model, equations for calculating the mean residence time in the body at single dose (MRT) and at steady state (MRTss), apparent steady-state volume of distribution (Vss), and steady-state volume of distribution (Vss) are derived for a drug exhibiting nonlinear protein binding. Interrelationships between Vss and Vss as well as between MRT and MRTss are also discussed and illustrated with simulated data. In addition, a method for estimating the central volume of distribution of the bound drug and the sum of the central volume of distribution of the unbound drug and the area under the first moment curve of distribution function for drugs with nonlinear protein binding is proposed and illustrated with both simulated and published data.

Humans↗
PubMed1996

Psychiatric symptomatology and the recall of positive and negative personality information.

Various studies from the cognitive information processing tradition have shown that neuroticism is particularly associated with the preferential processing of negative information about the self. Just over 60 'normal' subjects completed the Langner (1962, Journal of Health and Human Behaviour, 3, 269-276) 22 measure of minor psychiatric symptoms. Later, they were presented with a list of positive, neutral and negative trait words for self-rating. After 1 hr, subjects were asked to recall all the trait words. As predicted, the Langner (1962) score was associated with an increased probability of recalling negative self-referent information (r = 0.36). Implications for therapy are considered.

Adult↗
PubMed1996

Isolated lung perfusion with melphalan for the treatment of metastatic pulmonary sarcoma.

OBJECTIVE: Isolated lung perfusion allows the delivery of high-dose chemotherapy to the perfused lung and is an efficacious modality in the treatment of pulmonary metastases in the rat. Melphalan activity in this model was investigated. METHODS: TOXICITY STUDY: Maximum tolerated dose of melphalan delivered by means of isolated lung perfusion was determined by survival after contralateral pneumonectomy. PHARMACOKINETICS STUDY: Nineteen rats were treated with melphalan administered either by isolated lung perfusion (2 mg) or intravenously (2 mg or 1 mg). Lung, pulmonary effluent, and serum melphalan were analyzed by high-pressure liquid chromatography. EFFICACY STUDY: On day 0, 41 rats received an intravenous injection of 5 x 10(6) methylcholanthrene induced sarcoma cells. On day 7, rats either received intravenous melphalan (2 mg [n = 10]; 1 mg [n = 8]) or underwent left isolated lung perfusion with 2 mg of melphalan (n = 12). Isolated lung perfusion with buffered hetastarch in sodium chloride (Hespan, n = 11) was used as control. On day 14, pulmonary nodules were counted. RESULTS TOXICITY: Maximum tolerated dose of melphalan delivered buy means of isolated lung perfusion was 2 mg. PHARMACOKINETICS: Left lung melphalan level was significantly higher in the isolated lung perfusion group (62.2 +/- 34.3 microg/gm lung) than in the intravenous treatment groups (6.9 +/- 1.9 microg/gm lung and 3.3 +/- 0.9 microg/gm lung, respectively) (p = 0.0002). EFFICACY: Significantly fewer left lung nodules were found in animals receiving melphalan by means of isolated lung perfusion (7 +/- 10) than in the groups receiving intravenous melphalan (60 +/- 21) or buffered hetastarch by isolated lung perfusion (84 +/- 52) (p = 0.01 and p = 0.0001, respectively). CONCLUSION: Isolated lung perfusion with melphalan is safe and effective in the treatment of pulmonary sarcoma metastases in the rat.

Animals↗
PubMed1996

Excitation-contraction coupling in heart: new insights from Ca2+ sparks.

Ca2+ sparks, the elementary units of sarcoplasmic reticulum (SR) Ca2+ release in cardiac, smooth and skeletal muscle are localized (2-4 microns ) increases in intracellular Ca2+ concentration, [Ca2+]i, that last briefly (30-100 ms). These Ca2+ sparks arise from the openings of a single SR Ca2+ release channel (ryanodine receptor, RyR) or a few RyRs acting in concert. In heart muscle, Ca2+ sparks can occur spontaneously in quiescent cells at a low rate (100 s-1 per cell). Identical Ca2+ sparks are also triggered by depolarization because the voltage-gated sarcolemmal L-type Ca2+ channels (dihydropyridine receptors, DHPRs) locally increase [Ca2+]i and thereby activate the RyRs by Ca(2+)-induced Ca2+ release (CICR). The exquisite responsiveness of this process, reflected by the ability of even a single DHPR to activate a Ca2+ spark, is perhaps due to the large local increase in [Ca2+]i in the vicinity of the RyR that is a consequence of the close apposition of the DHPRs and the RyRs. In this review we examine our current understanding of cardiac excitation-contraction (EC) coupling in light of recent studies on the elementary Ca2+ release events or Ca2+ sparks. In addition, we further characterized Ca2+ spark properties in rat and mouse heart cells. Specifically we have determined that: (i) Ca2+ sparks occur at the junctions between the transverse-tubules and the SR in both species; (ii) Ca2+ sparks are asymmetric, being 18% longer in the longitudinal direction than in the transverse direction; and (iii) Ca2+ sparks individually do not produce measurable sarcomere shortening (< 1%). These results are discussed with respect to local activation of the RyRs, the stability of CICR, Ca2+ diffusion, and the theory of EC coupling.

Animals↗
PubMed1996

Pharmacokinetics, bioavailability, and safety of montelukast sodium (MK-0476) in healthy males and females.

PURPOSE: The safety, tolerability, and pharmacokinetics of intravenous *i.v.) montelukast sodium (Singulair, MK-0476), and the oral bioavailability of montelukast sodium in healthy males and healthy females were studied. METHODS: This was a two-part study. Part I was a four-period study in males of rising i.v. doses of montelukast sodium (3, 9, and 18 mg) administered as 15-minute constant-rate i.v. infusions (Periods 1-3), followed by a 10-mg oral tablet dose of montelukast sodium (Period 4) under fasting conditions. Part II was a four-period study in females of i.v. montelukast sodium (9 mg) infused over 15 and 5 minutes (Periods 5 and 6, respectively) or injected as a bolus over 2 minutes (Period 7), followed by a 10-mg oral tablet dose of montelukast sodium (Period 8). Plasma samples were collected and analyzed by HPLC. RESULTS: In males (N = 6), as the i.v. dose of montelukast sodium increased from 3 to 18 mg, the area under the plasma concentration-time curve of montelukast sodium from time 0 to infinity (AUC) increased proportionately. The mean values of plasma clearance (CL), steady-state volume of distribution (Vss), plasma terminal half-life (t1/12), and mean residence time in the body (MRTi.v.) of montelukast sodium were 45.5 ml/min, 10.5 1, 5.1 hr, and 3.9 hr, respectively, and remained essentially constant over the i.v. dosage range. Following oral administration of a 10-mg tablet of montelukast sodium, the AUC, maximum plasma concentration (Cmax), time when Cmax occurred (Tmax), apparent t1/12, mean absorption time (MAT), and bioavailability (F) of montelukast sodium averaged 2441 ng.hr/ml, 385 ng/ml. 3.7 hr, 4.9 hr, 3.4 hr, and 66%, respectively. Following i.v. administration of 9 mg of montelukast sodium to females (N = 6), the values of CL, Vss, t1/2, and MRT i.v. averaged 47.6 ml/min, 9.6 1, 4.5 hr, and 3.6 hr, respectively. Following oral administration of a 10-mg tablet to females, the mean AUC, Cmax, Tmax, apparent t1/2, MAT and F were 2270 ng.hr/ml, 350 ng/ml, 3.3 hr, 4.4 hr, 2.6 hr, and 58%, respectively. These parameter values were similar to or slightly smaller than those in healthy males receiving the same i.v. and oral doses. CONCLUSIONS: The disposition kinetics of montelukast sodium were linear. Gender had little or no effect on the kinetics of montelukast sodium. Safety results from this study indicate that intravenous doses of montelukast sodium from 3 to 18 mg and a 10-mg oral dose are well tolerated.

Acetates↗
PubMed1996

Risk factors for initiation of drug use among young males in southwest China.

To identify risk factors for drug use among young males in southwest China a cross-sectional survey and a non-concurrent cohort study were conducted. Demographic, behavioral and drug-use information was collected from young males aged 18-29 years. The non-concurrent cohort included the period 1 January 1991 to 1 August 1994. A total of 1548 subjects were interviewed. The cumulative incidence increased between 1991 and 1993. Multivariate analysis identified the following significant risk factors for drug use: being divorced/widowed/separated, having been encouraged by friends/others to try drugs, smoking cigarettes, belonging to the Jingpo ethnic group, and having a family member who used drugs in 1991. More than 6 years of education was a protective factor for drug use. Drug use in the community was associated with having been encouraged by friends or others to try drugs (71%), to smoking cigarettes (50%), and to belonging to the Jingpo group (24%). The results are consistent with community based prevention approaches which should be studied carefully because of the unique cultural and epidemiological situation in China.

Adolescent↗
PubMed1996

Pilot study of MK-462 in migraine.

MK-462 is a potent, selective 5HT1D receptor agonist which may be useful in treating acute migraine. We conducted a double-blind placebo-controlled inpatient study to assess the preliminary efficacy and safety of oral doses of MK-462 20 mg (n = 8) and 40 mg (n = 36) vs placebo (n = 21), administered to 65 male and post-menopausal female migraine patients aged 22-51 with moderate or severe migraine headache. Headache severity and functional disability were measured at 0.5, 1, 1.5, and 2 h post-dose. The 20 mg dose was well tolerated and 4/8 patients obtained relief in headache severity at the 2 h time point. The 40 mg dose was well tolerated and was significantly (p < 0.05) superior to placebo at the 1.5 and 2 h time points (with 27/36 or 75% obtaining relief at 2 h compared to 7/21 or 33% for placebo). Adverse events occurred in 50% of patients on 20 mg MK-462, 72% of those on 40 mg MK-462, and in 52% of placebo-treated subjects. The most common adverse events associated with MK-462 were drowsiness (20 mg 12%; 40 mg 44%; placebo 24%), dry mouth (40 mg 36%; placebo 19%), and lightheadedness/dizziness (40 mg 17%; placebo 10%). Based on these preliminary results, MK-462 appears worthy of continued study for the treatment of acute migraine.

Adult↗
PubMed1996

Risk factors for intravenous drug use and sharing equipment among young male drug users in Longchuan County, south-west China.

OBJECTIVES: To identify the risk factors for intravenous drug use and sharing of equipment in Longchuan County in south-west China. METHODS: Demographic information and sexual and drug-use-related behavior between 1 January 1991 and 1 August 1994 were collected retrospectively from a cohort of young male drug users aged 18-29 years in 82 villages. RESULTS: A total of 433 drug users were identified. The cumulative incidence of intravenous drug use was 40.0% during the 3.7-year study period. The annual incidence increased from 10% in 1991 to over 30% in 1994. Risk factors for intravenous drug use among drug users, according to the multivariate model, included having had premarital/extramarital sex [odds ratio (OR), 1.5; 95% confidence interval (CI), 1.01-2.3], having a family member who used drugs in 1991 (OR, 1.8; 95% CI, 1.1-2.9), and currently not married (OR, 1.6; 95% CI, 0.98-2.7). Being Buddhist protected against intravenous drug use (OR, 0.4; 95% CI, 0.2-0.9). The population attributable fraction was 30% for not being currently married, 17% for having had premarital/extramarital sex and 14% for having a family member who used drugs. The risk factor for sharing of equipment was being of Jingpo ethnicity (OR, 5.8; 95% CI, 2.5-13.8). The average incidence of sharing equipment was 19.6% per year. The population attributable fraction for sharing equipment was 58.5% for being Jingpo. CONCLUSIONS: The incidence of intravenous drug use and sharing equipment is increasing. Therefore, it is urgent that vigorous, effective intervention programs be initiated in southern Yunnan. Unmarried, sexually promiscuous Jingpo drug users with a family history of drug use should be especially targeted. Given the problems of transport and communication in this remote area of China, intervention programs which use existing social, governmental and community networks should be implemented.

Adolescent↗
PubMed1996

Single-parent segregant pools for allocation of markers to a specified chromosomal region in outcrossing species.

Bulked co-segregant analysis is a method of rapidly allocating unmapped genetic markers to a specific chromosomal region. Although originally developed for utilization in populations derived from crosses between fully inbred lines, it has been proposed that co-segregant pools could also serve the same purpose in outbreeding populations, if individuals from only a single large family are pooled. Large, fully mapped, single-sire backcross and half-sib families are presently available as part of the international chicken and bovine reference family panels respectively. In this study, power and tests of significance for single-parent co-segregant analysis are derived for full-sib, single-parent back-cross and single-parent half-sib families, as a function of proportion of recombination between index marker and linked marker, pro-portion of single-parent alleles among the mates, number of individuals in each segregant pool and technical error variance. Power was found to be greater than 0.80 for many reasonable parameter combinations. The method is illustrated using microsatellite markers and a large single-sire bovine family, part of the international bovine reference family panel.

Alleles↗