Biomedical subjects

K H Cheng

Publications and source records attributed to K H Cheng.

At least 19 recordsLinked to original sources

PubMed2007

Recognition and capture of breast cancer cells using an antibody-based platform in a microelectromechanical systems device.

Cancer is one of the most common diseases afflicting humans. The use of biomarkers specific for tumor cells has facilitated their identification. However, technology has not kept pace with the field of molecular biomarkers, leaving their potential unrealized. Here, we demonstrate the efficacy of recognizing and capturing cancer cells using an antibody-based, on-chip, microfluidic device. A cancer cell capture biochip consisting of microchannels of size 2.0 cm long and 500 microm wide and deep, was etched onto Polydimethylsiloxane. Epithelial membrane antigen (EMA) and Epithelial growth factor receptor (EGFR) were coated on the inner surface of the microchannels. The overall chip measured 2.0 cm x 1.5 cm x 0.5 cm. Normal and tumor breast cells in a phosphate buffered saline (PBS) suspension were flowed through the biochip channels at a rate of 15 microL/min. Breast cancer cells were preferentially captured and identified while most of normal cells passed through. The capture rates for tumor and normal cells were found to be >30% and <5%, respectively. This preliminary cancer cell capture biochip design supports our initial effort of moving a BioMEMS device, from the bench top to the clinic.

Animals↗

PubMed2005

Microfluidic-based diagnostics for cervical cancer cells.

The use of biomarkers has facilitated the detection of specific tumor cells. However, the technology to apply these markers in a clinical setting has not kept pace with their increasing availability. In this project, we use an antibody-based microfluidics platform to recognize and capture cervical cancer cells. Because HPV-16 infection of cervical cells and up-regulation of alpha6-integrin cell surface receptors are correlated, we utilized alpha6-integrin as a capture antibody bound to the channel surface. Normal human glandular epithelial cells (HGEC), human cervical stromal cells (HCSC) and cervical cancer cells (HCCC) were suspended in PBS and flowed through the system. Greater than 30% of the cancer cells were captured while the capture of the normal cell types was less than 5%. The technique is sensitive and accurate. It is potentially useful in the detection of cervical cancer at all stages, as well as other of cancers with similar characteristics of cell surface antigen expression.

Biomarkers, Tumor↗

PubMed2005

Mass spectra and time-resolved fluorescence spectroscopy of the reaction product of glycine with 1,2-indanedione in methanol.

The reaction products of 1,2-indanedione (a new fluorescent fingerprint reagent) with glycine in methanol, at room temperature have been studied using excitation and emission and time-resolved fluorescence spectroscopy. Gas chromatography-mass spectroscopy (GC/MS) has also been used to determine which compounds are formed. Reaction products were identified using GC/MS as 2-carboxymethyliminoindanone (MW=203 g) and 1,2-di(carboxymethylimino)indane (MW=260 g). Identified compounds show room temperature fluorescence lifetimes of tau(1)=7.69 ns and tau(2)=1.27 ns. It is not clear yet which compound is having fluorescence lifetime of 7.69 ns and which one is showing 1.27 ns.

Dermatoglyphics↗

PubMed2001

The effects of cidofovir on progressive multifocal leukoencephalopathy: an MRI case study.

MRI was used to study the effects of introducing cidofovir (HPMPC, Vistide) to the antiretroviral therapy of a 33-year-old white man diagnosed as having progressive multifocal leukoencephalopathy (PML) secondary to AIDS. In response to combined cidofovir and antiretroviral therapy he showed significant clinical improvement. MRI showed a decrease in extent of existing lesions, without new ones. Blood chemistry information obtained indicated some involvement of immunologic mechanisms: the CD4:8 ratio showed improvement from an average of 0.08 before treatment to 0.13 during therapy.

Adult↗

PubMed2001

Characteristics of pyrene phospholipid/gamma-cyclodextrin complex.

Recently, it was demonstrated that gamma-cyclodextrins (gamma-CDs) greatly accelerates transfer of hydrophobic pyrene-labeled and other fluorescent phospholipid derivatives from vesicles to cells in culture (). To understand better the characteristics of this process, we studied the interaction of gamma-CD with pyrene-labeled phosphatidylcholines (PyrPCs) using a variety of physical methods. Either one or both of the acyl chains of PC was labeled with a pyrene moiety (monoPyrPCs and diPyrPCs, respectively), and the length of the labeled chain(s) varied from 4 to 14 carbons. Fluorescent binding assays showed that the association constant decreases strongly with increasing acyl chain length. PyrPC/gamma-CD stoichiometry was 1:2 for the shorter chain species, but changed to 1:3 when the acyl chain length exceeded 8 (diPyrPCs) or 10 (monoPyrPCs) carbons. The activation energy for the formation of diPyr(10)PC/gamma-CD complex was high, i.e., +92 kJ/mol, indicating that the phospholipid molecule has to fully emerge from the bilayer before complex formation can take place. The free energy, enthalpy, and entropy of transfer of monoPyrPC from bilayer to gamma-CD complex were close to zero. The absorption, Fourier transform infrared, and fluorescence spectral measurements and lifetime analysis indicated that the pyrene moiety lies inside the CD cavity and is conformationally restricted, particularly when the labeled chain is short. The acyl chains of a PyrPC molecule seem to share a CD cavity rather than occupy different ones. The present data provide strong evidence that the ability of gamma-CD to enhance intermembrane transfer of pyrene-labeled phospholipids is based on the formation of stoichiometric complexes in the aqueous phase. This information should help in designing CD derivatives that are more efficient lipid carriers then those available at present.

Acylation↗

PubMed2000

Photoluminescent semiconductor nanocrystals for fingerprint detection.

The concept of utilizing photoluminescent semiconductor nanocrystals for latent fingerprint detection, especially in concert with phase-resolved imaging for background fluorescence suppression, is reduced to practice with CdS nanocrystals that are capped with dioctyl sulfosuccinate. The nanocrystals are dissolved in heptane or hexane and are applied in much the same way as staining with fluorescent dye, on articles that have been pre-fumed with cyanoacrylate ester and also on the sticky side of electrical tape without pre-fuming. Since CdS can form a photoluminescent nanocomposite with dendrimers, a feasibility examination of dendrimer tagging of fingerprints has also been conducted.

Crystallization↗

PubMed2000

Photoluminescent CdS/dendrimer nanocomposites for fingerprint detection.

CdS/dendrimer nanocomposites with a range of concentrations of the photoluminescent semiconductor nanocluster and the dendrimer are prepared in methanol and 1:9 methanol:water solutions. The solutions are utilized for detection of cyanoacrylate ester fumed and unfumed fingerprints on polyethylene and aluminum foil.

Crystallization↗

PubMed1999

Lateral organisation of membrane lipids. The superlattice view.

Most biological membranes are extremely complex structures consisting of hundreds or even thousands of different lipid and protein molecules. The prevailing view regarding the organisation of these membranes is based on the fluid-mosaic model proposed by Singer and Nicholson in 1972. According to this model, phospholipids together with some other lipids form a fluid bilayer in which these lipids are diffusing very rapidly laterally. The idea of rapid lateral diffusion implies that, in general, the different lipid species would be randomly distributed in the plain of the membrane. However, there are recent data indicating that the components tend to adopt regular (superlattice-like) distributions in fluid, mixed bilayers. Based on this, a superlattice model of membranes has been proposed. This superlattice model is intriguing because it allows only a limited certain number of 'critical' compositions. These critical compositions could play a key role in the regulation of the lipid compositions of biological membranes. Furthermore, such putative critical compositions could explain how compositionally distinct organelles can exist despite of rapid inter-organelle membrane traffic. In this review, these intriguing predictions are discussed along with the basic principles of the model and the evidence supporting it.

Membrane Lipids↗

PubMed1999

Incidence of contact-lens-associated microbial keratitis and its related morbidity.

BACKGROUND: The incidence of contact-lens-associated microbial keratitis is uncertain and its related morbidity in the general population of contact-lens wearers is not known. We examined these issues in a prospective epidemiological study. METHODS: We surveyed all practising ophthalmologists in the Netherlands to identify all new cases of microbial keratitis reported during a 3-month period in 1996. Follow-up telephone calls were made to examine ocular morbidity. We undertook annual nationwide telephone surveys between 1994 and 1997 to estimate the prevalence of contact-lens wear. FINDINGS: Of 440 ophthalmologists contacted, 379 provided information. There were 92 cases of microbial keratitis; 17 used daily-wear rigid gas-permeable lenses, 63 daily-wear soft lenses, and 12 extended-wear soft lenses. The estimated annualised incidence of microbial keratitis was 1.1 per 10,000 (95% CI 0.6-1.7) users of daily-wear rigid gas-permeable lenses, 3.5 per 10,000 (2.7-4.5) users of daily-wear soft lenses, and 20.0 per 10,000 (10.3-35.0) users of extended-wear soft lenses (p<0.00001 for comparison between all groups), Five of the 92 patients achieved a final visual acuity of 20/70 or less. Pseudomonas and Serratia spp were the organisms most commonly isolated. Pseudomonas keratitis accounted for the largest mean diameter of corneal ulcers, the highest mean number of days in hospital, the greatest number of mean outpatients visits, and the poorest visual acuity outcome. INTERPRETATION: The incidence of microbial keratitis among users of extended-wear soft contact lenses in the Netherlands is similar to that reported in the USA during 1989. Awareness of risk factors and improvement in contact-lens materials have not led to a decrease in incidence. Overnight wear should be strongly discouraged.

Adolescent↗

PubMed1999

Fluorescence studies of dehydroergosterol in phosphatidylethanolamine/phosphatidylcholine bilayers.

Our previous fluorescence study has provided indirect evidence that lipid headgroup components tend to adopt regular, superlattice-like lateral distribution in fluid phosphatidylethanolamine/phosphatidylcholine (PE/PC) bilayers (, Biophys. J. 73:1967-1976). Here we have further studied this intriguing phenomenon by making use of the fluorescence properties of a sterol probe, dehydroergosterol (DHE). Fluorescence emission spectra, fluorescence anisotropy (r), and time-resolved fluorescence intensity decays of DHE in 1-palmitoyl-2-oleoyl-PC (POPC)/1-palmitoyl-2-oleoyl-PE (POPE) mixtures were measured as a function of POPE mole fraction (X(PE)) at 23 degrees C. Deviations, including dips or kinks, in the ratio of fluorescence peak intensity at 375 nm/fluorescence peak intensity at 390 nm (I(375)/I(390)), fluorescence decay lifetime (tau), or rotational correlation time (rho) of DHE versus PE composition plots were found at X(PE) approximately 0.10, 0.25, 0.33, 0.65, 0.75, and 0.88. The critical values at X(PE) approximately 0.33 and 0.65 were consistently observed for all measured parameters. In addition, the locations, but not the depth, of the dips for X(PE) < 0.50 did not vary significantly over 10 days of annealing at 23 degrees C. The observed critical values of X(PE) coincide (within +/-0.03) with some of the critical mole fractions predicted by a headgroup superlattice model proposing that the PE and PC headgroups tend to be regularly distributed in the plane of the bilayer. These results agree favorably with those obtained in our previous fluorescence study using dipyrenylPC and Laurdan probes and thus support the proposition that 1) regular arrangement within a domain exists in fluid PE/PC bilayers, and 2) superlattice formation may play a significant role in controlling the lipid composition of cellular membranes (, Proc. Natl. Acad. Sci. USA. 95:4964-4969). The present data provide new information on the physical properties of such superlattice domains, i.e., the dielectric environment and rotational motion of membrane sterols appear to change abruptly as the lipid headgroups exhibit regular superlattice-like distributions in fluid bilayers.

Biophysical Phenomena↗

PubMed1998

Phospholipid composition of the mammalian red cell membrane can be rationalized by a superlattice model.

Although the phospholipid composition of the erythrocyte membrane has been studied extensively, it remains an enigma as to how the observed composition arises and is maintained. We show here that the phospholipid composition of the human erythrocyte membrane as a whole, as well as the composition of its individual leaflets, is closely predicted by a model proposing that phospholipid head groups tend to adopt regular, superlattice-like lateral distributions. The phospholipid composition of the erythrocyte membrane from most other mammalian species, as well as of the platelet plasma membrane, also agrees closely with the predictions of the superlattice model. Statistical analyses indicate that the agreement between the observed and predicted compositions is highly significant, thus suggesting that head group superlattices may indeed play a central role in the maintenance of the phospholipid composition of the erythrocyte membrane.

Animals↗

PubMed1997

Evidence for superlattice arrangements in fluid phosphatidylcholine/phosphatidylethanolamine bilayers.

Recently, evidence for cholesterol and phosphatidylcholine (PC) molecules to adapt superlattice arrangements in fluid lipid bilayers has been presented. Whether superlattice arrangements exist in other biologically relevant lipid membranes, such as phosphatidylethanolamine (PE)/PC, is still speculative. In this study, we have examined the physical properties of fluid 1-palmitoyl-2-oleoyl-PC (POPC) and 1-palmitoyl-2-oleoyl-PE (POPE) binary mixtures as a function of the POPE mole fraction (X(PE)) using fluorescence and Fourier transform infrared spectroscopy. At 30 degrees C, i.e., above the Tm of POPE and POPC, deviations, or dips, as well as local data scattering in the excimer-to-monomer fluorescence intensity ratio of intramolecular excimer forming dipyrenylphosphatidylcholine probe in POPE/POPC mixtures were detected at X(PE) approximately 0.04, 0.11, 0.16, 0.26, 0.33, 0.51, 0.66, 0.75, 0.82, 0.91, and 0.94. The above critical values of X(PE) coincide (within +/-0.03) with the critical mole fractions X(HX,PE) or X(R,PE) predicted by a headgroup superlattice model, which assumes that the lipid headgroups form hexagonal or rectangular superlattice, respectively, in the bilayer. Other spectroscopic data, generalized polarization of Laurdan and infrared carbonyl and phosphate stretching frequency, were also collected. Similar agreements between some of the observed critical values of X(PE) from these data and the X(HX,PE) or X(R,PE) values were also found. However, all techniques yielded critical values of X(PE) (e.g., 0.42 and 0.58) that cannot be explained by the present headgroup superlattice model. The effective cross-sectional area of the PE headgroup is smaller than that of the acyl chains. Hence, the relief of "packing frustration" of PE in the presence of PC (larger headgroup than PE) may be one of the major mechanisms in driving the PE and PC components to superlattice-like lateral distributions in the bilayer. We propose that headgroup superlattices may play a significant role in the regulation of membrane lipid compositions in cells.

Biophysical Phenomena↗

PubMed1997

An experimental method for measuring aerosol deposition efficiency in the human oral airway.

An experimental technique was developed to measure the oral deposition of aerosols by successively drawing them passively through (1) the nasal and oral passage in series, and (2) the nose and an oral bypass "extension tube" inserted into the oral cavity just anterior to the uvula. To test this technique, a replicate human upper airway cast was challenged with monodisperse aerosols ranging in diameter from 3.6 to 150.0 nm at constant flow rates ranging from 7.5 to 30 L/min. For the inhalation study, test aerosols were drawn into the nasal cavity and directed either through the laryngeal-tracheal (L-T) section or the oral passage with/without the oral extension tube. The flow was reversed for the exhalation study. Deposition fractions of aerosols in the main oral cavity were found approximately equal to those in the L-T section for both inhalation and exhalation. Following this phase of the study, experimental measurements of total particle deposition fraction for the oral inlet-tracheal outlet path were performed. The results of these measurements agreed well with the calculated oral deposition fractions based on the initial measurements. This technique has application for measuring oral deposition of larger particles encountered in occupational environments.

Aerosols↗

PubMed1997

Measurements of airway dimensions and calculation of mass transfer characteristics of the human oral passage.

This paper presents measurements of the geometric shape, perimeter, and cross-sectional area of the human oral passage (from oral entrance to midtrachea) and relates them through dimensionless parameters to the depositional mass transfer of ultrafine particles. Studies were performed in two identical replicate oral passage models, one of which was cut orthogonal to the airflow direction into 3 mm elements for measurement, the other used intact for experimental measurements of ultrafine aerosol deposition. Dimensional data were combined with deposition measurements in two sections of the oral passage (the horizontal oral cavity and the vertical laryngeal-tracheal airway) to calculate the dimensionless mass transfer Sherwood number (Sh). Mass transfer theory suggests that Sh should be expressible as a function of the Reynolds number (Re) and the Schmidt number (Sc). For inhalation and exhalation through the oral cavity (O-C), an empirical relationship was obtained for flow rates from 7.5-30.0 1 min-1: Sh = 15.3 Re0.812 Sc-0.986 An empirical relationship was likewise obtained for the laryngeal-tracheal (L-T) region over the same range of flow rates: Sh = 25.9 Re0.861 Sc-1.37 These relationships were compared to heat transfer in the human upper airways through the well-known analogy between heat and mass transfer. The Reynolds number dependence for both the O-C and L-T relationships was in good agreement with that for heat transfer. The mass transfer coefficients were compared to extrathoracic uptake of gases and vapors and showed similar flow rate dependence. For gases and vapors that conform to the zero concentration boundary condition, the empirical relationships are applicable when diffusion coefficients are taken into consideration.

Absorption↗

PubMed1996

Detection of membrane packing defects by time-resolved fluorescence depolarization.

Packing defects in lipid bilayer play a significant role in the biological activities of cell membranes. Time-resolved fluorescence depolarization has been used to detect and characterize the onset of packing defects in binary mixtures of dilinoleoylphosphatidylethanolamine/1-palmitoyl-2- oleoylphosphatidylcholine (PE/PC). These PE/PC mixtures exhibit mesoscopic packing defect state (D), as well as one-dimensional lambellar liquid crystalline (L alpha) and two-dimensional inverted hexagonal (HII) ordered phases. Based on previous electron microscopic investigations, this D state is characterized by the presence of interlamellar attachments and precursors of HII phase between the lipid layers. Using a rotational diffusion model for rod-shaped fluorophore in a curved matrix, rotational dynamics parameters, second rank order parameter, localized wobbling diffusion, and curvature-dependent rotational diffusion constants of dipyenylhexatriene (DPH)-labeled PC (DPH-PC) in the host PE/PC matrix were recovered from the measured fluorescence depolarization decays of DPH fluorescence. At approximately 60% PE, abrupt increases in these rotational dynamics parameters were observed, reflecting the onset of packing defects in the host PE/PC matrix. We have demonstrated that rotational dynamics parameters are very sensitive in detecting the onset of curvature-associating packing defects in lipid membranes. In addition, the presence of the D state can be characterized by the enhanced wobbling diffusional motion and order packing of lipid molecules, and by the presence of localized curvatures in the lipid layers.

Cell Membrane↗

PubMed1996

Effects of unsaturation and curvature on the transverse distribution of intramolecular dynamics of dipyrenyl lipids.

The roles of acyl chain unsaturation and curvature in the excimer formation efficiency (EFE) of site-specific conjugated pyrene molecules in lipid membranes have been investigated by steady-state and time-resolved fluorescence spectroscopy. Six 1-2-(pyrenyl-n-acyl)-phosphatidylcholine (dipy(n)PC) probes, with pyrenyl chains of varying methylene units n from 4 to 14 carbons, were incorporated separately into dioleoylphosphatidylcholine (DOPC) or dioleoylphosphatidylethanolamine (DOPE) lipid membranes at 0.1 mol%. Both the excimer-to-monomer fluorescence intensity ratio and association-to-dissociation rate constant ratio of conjugated pyrenes were used to quantify EFE. At all temperatures (T = 0-30 degrees C) and for n = 4 and 6, the EFE for DOPE was always smaller than EFE for DOPC. At T < 10 degrees C (where DOPE and DOPC are in the liquid crystalline L alpha phase) and for n > 8, the EFE for curvature frustrated DOPE was significantly greater than EFE for nonfrustrated DOPC (control), and the difference increased gradually with n. At T> 18 degrees C (where DOPE is in the inverted hexagonal H(II) phase and DOPC is in the L alpha phase) and for n > 8, EFE for the curvature-relaxed DOPE was again smaller than the EFE for DOPC control. The contributions of splay conformation and internal dynamics of pyrenyl chains to EFE were examined separately using a lattice model. Our results suggest that i) the cis double bonds of the host lipid matrix strongly perturb both the conformation and dynamics of conjugated pyrenes at the specific location around n = 8, and ii) the lateral stress at the upper part (n < 8) of the curvature frustrated bilayer membranes (DOPE) may be significantly relaxed once the membrane surface adopts a favorable negative interfacial curvature.

Kinetics↗

PubMed1996

Immunoglobulin A antibodies against Pseudomonas aeruginosa in the tear fluid of contact lens wearers.

PURPOSE: Pseudomonas aeruginosa is the most important cause of contact lens-associated ulcerative keratitis, especially for those who use extended-wear lenses. Until now, the presence of specific anti-P. aeruginosa immunoglobulin A (IgA) antibodies in the tears of contact lens wearers has not been investigated and is the purpose of the current study. METHODS: The levels of specific IgA antibodies against P. aeruginosa and total secretory IgA (s-IgA) concentrations were measured in tears of various groups of contact lens and non-contact lens wearers using enzyme-linked immunosorbent assays. Contact lens groups were divided into the following categories: daily-wear rigid gas-permeable lenses (n = 23), daily-wear soft lenses (n = 22), extended-wear soft lenses (n = 17), and non-contact lens wearers (n = 23). As a positive control group, we tested tears obtained from patients with cystic fibrosis (n = 5) because the respiratory tract of these persons often are colonized by P. aeruginosa. RESULTS: The percentage of nonresponders (< 15 U/ml) varied between 9% in daily-wear rigid gas-permeable contact lens users to 23% in daily-wear soft contact lens users. The percentage of nonresponders in controls was 13%. The frequency of nonresponders was not significantly different among the different groups tested. All patients with cystic fibrosis showed a very high anti-P. aeruginosa IgA response in their tears. When analyzing the mean anti-P. aeruginosa IgA response, a significantly lower level was found in extended-wear contact lens users (38 U/ml) compared to non-contact lens wearers (82 U/ml). Total s-IgA levels in the tears of the various groups tested were not significantly different. CONCLUSIONS: A substantial number of persons in the population of contact lens wearers tested lack detectable IgA antibodies against P. aeruginosa in their tears and may be susceptible to P. aeruginosa keratitis if the physiological condition of their cornea is compromised.

Adolescent↗

PubMed1995

Sidestream tobacco smoke exposure acutely alters human nasal mucociliary clearance.

Nasal mucociliary clearance (NMC) is a biomarker of nasal mucosal function. Tobacco smokers have been shown to have abnormal NMC, but the acute effect of environmental tobacco smoke (ETS) on nonsmokers is unknown. This study evaluated acute tobacco smoke-induced alterations in NMC in 12 healthy adults. Subjects were studied on 2 days, separated by at least 1 week. Subjects underwent a 60-min controlled exposure at rest to air or sidestream tobacco smoke (SS) (15 ppm CO) in a controlled environmental chamber. One hour after the exposure, 99mTc-sulfur colloid was aerosolized throughout the nasal passage and counts were measured with a scintillation detector. Six out of 12 subjects showed more rapid clearance after smoke exposure than after air exposure, and 3/12 had rapid clearance on both days. However, substantial decreases in clearance occurred in 3/12 subjects, all of whom had a history of ETS rhinitis. In two subjects, more than 90% of the tracer remained 1 hr after tracer administration (2 hr after smoke exposure). Understanding the basis for biologic variability in the acute effect of tobacco smoke on NMC may advance our understanding of pathogenesis of chronic effects of ETS.

Adult↗