Biomedical subjects

Wei R Chen

Publications and source records attributed to Wei R Chen.

At least 19 recordsLinked to original sources

PubMed2007

Fluorescence resonance energy transfer analysis of bid activation in living cells during ultraviolet-induced apoptosis.

Ultraviolet (UV) irradiation is a DNA-damaging agent that triggers apoptosis through both the membrane death receptor and mitochondrial apoptotic signaling pathways. Bid, a pro-apoptotic Bcl-2 family member, is important in most cell types to apoptosis in response to DNA damage. In this study, a recombinant plasmid, YFP-Bid-CFP, comprised of yellow and cyan fluorescent protein and a full length Bid, was used as a fluorescence resonance energy transfer analysis (FRET) probe. Using the FRET technique based on YFP-Bid-CFP, we found that Bid activation was initiated at 9+/-1 h after UV irradiation, and the average duration of the activation was 75+/-10 min. Bid activation coincided with a collapse of the mitochondrial membrane potential with an average duration of 50+/-10 min. When cells were pretreated with Z-IETD-fmk (caspase-8 specific inhibitor) the process of Bid activation was completely inhibited, but the apoptosis was only partially affected. Z-DEVD-fmk (caspase-3 inhibitor) and Z-FA-fmk (non asp specific inhibitor) did not block Bid activation. Furthermore, the endogenous Bid activation with or without Z-IETD-fmk in response to UV irradiation was confirmed by Western blotting. In summary, using the FRET technique, we observed the dynamics of Bid activation during UV-induced apoptosis and found that it was a caspase-8 dependent event.

Apoptosis↗

PubMed2006

Viral tracing identifies distributed columnar organization in the olfactory bulb.

Olfactory sensory neurons converge onto glomeruli in the olfactory bulb (OB) to form modular information processing units. Similar input modules are organized in translaminar columns for other sensory modalities. It has been less clear in the OB whether the initial modular organization relates to a columnar structure in the deeper layers involved in local circuit processing. To probe synaptic connectivity in the OB, we injected a retrograde-specific strain of the pseudorabies virus into the rat OB and piriform cortex. The viral-staining patterns revealed a striking columnar organization that extended across all layers of the OB from the glomeruli to the deep granule cell layer. We hypothesize that the columns represent an extension of the glomerular unit. Specific patterning was observed, suggesting selective, rather than distance-dependent, center-surround connectivity. The results provide a previously undescribed basis for interpreting the synaptic connections between mitral and granule cells within the context of a columnar organization in the OB and have implications for olfactory coding and network organization.

Animals↗

PubMed2006

Dendritic calcium plateau potentials modulate input-output properties of juxtaglomerular cells in the rat olfactory bulb.

Understanding the intrinsic membrane properties of juxtaglomerular (JG) cells is a necessary step toward understanding the neural basis of olfactory signal processing within the glomeruli. We used patch-clamp recordings and two-photon Ca(2+) imaging in rat olfactory bulb slices to analyze a long-lasting plateau potential generated in JG cells and characterize its functional input-output roles in the glomerular network. The plateau potentials were initially generated by dendritic calcium channels. Bath application of Ni(2+) (250 microM to 1 mM) totally blocked the plateau potential. A local puff of Ni(2+) on JG cell dendrites, but not on the soma, blocked the plateau potentials, indicating the critical contribution of dendritic Ca(2+) channels. Imaging studies with two-photon microscopy showed that a dendritic Ca(2+) increase was always correlated with a dendritic but not a somatic plateau potential. The dendritic Ca(2+) conductance contributed to boosting the initial excitatory postsynaptic potentials (EPSPs) to produce the plateau potential that shunted and reduced the amplitudes of the following EPSPs. This enables the JG cells to act as low-pass filters to convert high-frequency inputs to low-frequency outputs. The low frequency (2.6 +/- 0.8 Hz) of rhythmic plateau potentials appeared to be determined by the intrinsic membrane properties of the JG cell. These properties of the plateau potential may enable JG cells to serve as pacemaker neurons in the synchronization and oscillation of the glomerular network.

Animals↗

PubMed2006

The olfactory glomerulus: a cortical module with specific functions.

The axons of many olfactory receptor cells converge on an individual glomerulus in the olfactory bulb, where they make contacts with the distal dendrites of mitral and tufted cells. Each glomerulus is targeted by olfactory receptor neurons expressing a single type of olfactory receptor protein. The glomerulus provides a unique model in which the function of a cortical module can be unambiguously established. Here we review the increasing evidence that a key functional operation of the glomerulus is to act as a signal-to-noise enhancing device in the processing of sensory input and that this function is critical across vertebrate and invertebrate species for the ability to detect specific odor stimuli within "noisy" odor environments and to carry out discriminations between odor molecules that are structurally closely related.

Animals↗

PubMed2006

Treatment of volatile organic chemicals on the EPA Contaminant Candidate List using ozonation and the O3/H2O2 advanced oxidation process.

Seven volatile organic chemicals (VOCs) on the EPA Contaminant Candidate List together with 1,1-dichloropropane were studied for their reaction kinetics and mechanisms with ozone and OH radicals during ozonation and the ozone/ hydrogen peroxide advanced oxidation process (O3/H2O2 AOP) using batch reactors. The three aromatic VOCs demonstrated high reactivity during ozonation and were eliminated within minutes after ozone addition. The high reactivity is attributed to their fast, indirect OH radical reactions with k(OH,M) of (5.3-6.6) x 10(9) M(-1) s(-1). Rates of aromatic VOC degradation are in the order 1,2,4-trimethylbenzene > p-cymene > bromobenzene. This order is caused by the selectivity of the direct ozone reactions (k(O3,M) ranges from 0.16 to 304 M(-1) s(-1)) and appears to be related to the electron-donating or -withdrawing ability of the substituent groups on the aromatic ring. The removal rates for the five aliphatic VOCs are much lower and are in the order 1,1-dichloropropane > 1,3-dichloropropane > 1,1-dichloroethane > 2,2-dichloropropane > 1,1,2,2-tetrachloroethane. The second-order indirect rate constants for the aliphatic VOCs range from 0.52 x 10(8) to 5.5 x 10(8) M(-1) s(-1). The relative stability of the carbon-centered intermediates seems to be related to the relative reactivity of the aliphatic VOCs with OH radicals. Except for 1,3-dichloropropane, ozonation and the O3/H2O2 AOP are not effective for the removal of other aliphatic VOCs. Bromide formation during the ozonation of bromobenzene indicates that bromate can be formed, and thus, ozonation and O3/H2O2 AOP may not be suitable for the treatment of bromobenzene.

Hydrocarbons↗

PubMed2006

Simultaneous compensation for spatial and temporal dispersion of acousto-optical deflectors for two-dimensional scanning with a single prism.

The dispersive nature of the acousto-optical deflector (AOD) presents a challenge to applications of two sequential orthogonal AODs (a two-dimensional AOD) as XY scanners in multiphoton microscopy. Introducing a prism before the two-dimensional (2D) AOD allows both temporal and spatial dispersion to be compensated for simultaneously. A 90 fs laser pulse was broadened to 572 fs without compensation, and 143 fs with compensation. The ratio of long axis to short axis of the exiting laser beam spot was 3.50 without compensation and 1.14 with compensation. The insertion loss was 37%. Two-photon fluorescence microscopy used the compensated 2D AOD scanner to image a fluorescent microsphere, which improves signal intensity -15-fold compared with the uncompensated scanner.

Artifacts↗

PubMed2006

Single cell FRET imaging for determination of pathway of tumor cell apoptosis induced by photofrin-PDT.

Apoptosis is an important cellular event that plays a key role in pathogeny and therapy of many diseases. Apoptosis has been associated with photodynamic therapy (PDT) and its pathway is important in the mechanistic study of PDT. We show that single cell fluorescent imaging can be used to determine the pathway of PDT-induced tumor cell apoptosis. In this study, ASTC-a-1 tumor cells transfected by plasmid DNA SCAT3 were treated by Photofrin-PDT. The intracellular distribution of Photofrin was observed using a confocal microscope. The activations of caspase-3 and caspase-8 were dynamically observed using fluorescence resonance energy transfer (FRET). Our experimental results show that the Photofrin molecules are localized in cell mitochondria, and that after PDT caspase-3 was activated rapidly while caspase-8 remained inactive. These results demonstrate that the tumor cell apoptosis induced by Photofrin-PDT was directly initiated from the mitochondrial pathway.

Apoptosis↗

PubMed2006

Dendritic excitability and calcium signalling in the mitral cell distal glomerular tuft.

The processing of odour information starts at the level of the olfactory glomerulus, where the mitral cell distal dendritic tuft not only receives olfactory nerve sensory input but also generates dendrodendritic output to form complicated glomerular synaptic circuits. Analysing the membrane properties and calcium signalling mechanisms in these tiny dendritic branches is crucial for understanding how the glomerular tuft transmits and processes olfactory signals. With the use of two-photon Ca2+ imaging in rat olfactory bulb slices, we found that these distal dendritic branches displayed a significantly larger Ca2+ signal than the soma and primary dendrite trunk. A back-propagating action potential was able to trigger a Ca2+ increase throughout the entire glomerular tuft, indicative of the presence of voltage-gated Ca2+ conductances in all branches at different levels of ramification. In response to a train of action potentials evoked at 60 Hz from the soma, the tuft Ca2+ signal increased linearly with the number of action potentials, suggesting that these glomerular branches were able to support repetitive penetration of Na+ action potentials. When a strong olfactory nerve excitatory input was paired with an inhibition from mitral cell basal dendrites, a small spike-like fast prepotential was revealed at both the soma and distal primary dendrite trunk. Corresponding to this fast prepotential was a Ca2+ increase confined locally within the glomerular tuft. In summary, the mitral cell distal dendritic tuft possesses both Na+ and Ca2+ voltage-dependent conductances which can mediate glomerular Ca2+ responsiveness critical for dendrodendritic output and synaptic plasticity.

Action Potentials↗

PubMed2006

Photoimmunotherapy for cancer treatment.

Phototherapy, with its effective dose control and light delivery, has become a promising modality for treating malignant and nonmalignant diseases. Photochemical interaction, specifically photodynamic therapy (PDT), and photothermal interaction have been the primary mechanisms for direct cell destruction in the treatment of cancers. Preclinical studies demonstrate that, in addition to direct local cytotoxicity, PDT can also induce systemic immune responses, which may enhance therapeutic effects on primary tumors and on metastases at distant sites. Selective photothermal therapy, using an in situ application of light-absorbing dye, has also proven to be an effective method for local treatment of tumors. When combined with immunotherapy, the effects of phototherapy can be amplified, potentially making the photoimmunotherapy a systemic treatment modality. This phototherapy-immunotherapy combination, particularly in conjunction with immunoadjuvant, has been used in preclinical studies. The efficacy and long-term effects of such a combination are summarized and the recent experimental results are presented. A new immunoadjuvant, glycated chitosan (GC), has been used to enhance photochemical and photothermal therapies. The PDT-GC combination in the treatment of mammary tumors and lung tumors in mice provided significant improvement in the long-term survival of tumor-bearing animals. The use of GC in dye-assisted laser photothermal therapy also provided long-term curative effects and antitumor immune responses in the treatment of metastatic tumors in rats. The immune responses induced by phototherapy and enhanced by immunotherapy could become important mechanism in the control of metastatic tumors.

Adjuvants, Immunologic↗

PubMed2004

Voltage imaging from dendrites of mitral cells: EPSP attenuation and spike trigger zones.

To obtain a more complete description of individual neurons, it is necessary to complement the electrical patch pipette measurements with technologies that permit a massive parallel recording from many sites on neuronal processes. This can be achieved by using voltage imaging with intracellular dyes. With this approach, we investigated the functional structure of a mitral cell, the principal output neuron in the rat olfactory bulb. The most significant finding concerns the characteristics of EPSPs at the synaptic sites and surprisingly small attenuation along the trunk of the primary dendrite. Also, the experiments were performed to determine the number, location, and stability of spike trigger zones, the excitability of terminal dendritic branches, and the pattern and nature of spike initiation and propagation in the primary and secondary dendrites. The results show that optical data can be used to deduce the amplitude and shape of the EPSPs evoked by olfactory nerve stimulation at the site of origin (glomerular tuft) and to determine its attenuation along the entire length of the primary dendrite. This attenuation corresponds to an unusually large mean apparent "length constant" of the primary dendrite. Furthermore, the images of spike trigger zones showed that an action potential can be initiated in three different compartments of the mitral cell: the soma-axon region, the primary dendrite trunk, and the terminal dendritic tuft, which appears to be fully excitable. Finally, secondary dendrites clearly support the active propagation of action potentials.

Action Potentials↗

PubMed2003

Induced antitumor immunity against DMBA-4 metastatic mammary tumors in rats using laser immunotherapy.

Induced antitumor immunity is a highly effective and long-term cure for cancer, particularly for metastatic tumors. Laser immunotherapy was developed to induce such an immunologic response. It involves intratumoral administration of a light-absorbing dye and a specially formulated immunoadjuvant, followed by noninvasive irradiation of a near-infrared laser. Treatment of DMBA-4 metastatic mammary tumors in rats with this approach has resulted in local control of primary tumors and eradication of untreated distant metastases. After laser immunotherapy, rats were resistant to tumor rechallenge and developed immunity, which could be adoptively transferred. To better understand the immunity induced in this tumor model, immunization using freeze-thaw DMBA-4 cell lysates was performed, followed by tumor challenge 21 days later. Tumor cell lysate immunization delayed the emergence of metastases but did not provide immunity against the tumor challenge. Also performed was surgical resection of primary tumors before the observation of metastatic tumors. Removal of primary tumors was unsuccessful at changing the course of tumor progression. Tumors re-emerged at the primary sites, and metastases developed at multiple remote sites. In contrast, tumor-bearing rats successfully treated by laser immunotherapy experienced tumor regression and eradication and developed strong resistance to repeated challenges by tumor cells of the same type. Our results show that laser immunotherapy could have potential for the treatment of metastatic tumors by inducing tumor-specific, long-lasting immunity.

9,10-Dimethyl-1,2-benzanthracene↗

PubMed2003

Synergistic effect of sequential administration of mitoguazone (MGBG) and gemcitabine in treating tissue cultured human breast cancer cells and mammary rat tumors.

Modulation of cancer chemotherapeutic drugs has been attempted to increase efficacy and overcome resistance to the chemotherapeutic agent. Studies have shown schedule-dependent interactions in combined use of chemotherapeutic drugs. Mitoguazone (MGBG), an old drug with possible modulating activity, was used in combination with gemcitabine, a relatively new cancer drug, in treating tissue cultured human breast cancer cells and mammary rat tumors. Tissue cultured BOT-2 cancer cells were first treated with varying concentrations of gemcitabine and MGBG, independently. Combinations of the two drugs were then used with different scheduled administrations. Marked synergistic activity was found between gemcitabine and MGBG when the MGBG was given first, followed by gemcitabine 24 hours later. A non-toxic dose of MGBG enhanced the toxicity of gemcitabine by eight orders of magnitude using MTT assays in the tissue cultured human breast cancer cell study. The sequential administration of MGBG and gemcitabine also increased the survival rate of rats bearing mammary tumors in our pilot animal study.

Animals↗

PubMed2003

A phase I human trial of mitoguazone and gemcitabine sequential bi-weekly treatment of cancer patients.

Our previous studies have demonstrated the existence of synergism in a combination therapy using mitoguazone and gemcitabine when the mitoguazone is administered 24 hours before gemcitabine. Based on the cell culture and animal experimental results, a phase I clinical trial was performed in order to determine the toxicity of the combined treatment. Mitoguazone and gemcitabine were administered sequentially: mitoguazone on day 1 and gemcitabine on day 2. This cycle was repeated every 2 weeks. The dosages of these two drugs were varied between patients. Ten patients were enrolled in the study. Six patients began treatment at dose level 1 (mitoguazone 500 mg/m2, gemcitabine 1500 mg/m2), three at dose level 2 (mitoguazone 500 mg/m2, gemcitabine 2000 mg/m2), and one at dose level 3 (mitoguazone 600 mg/m2, gemcitabine 2000 mg/m2). Dose-limiting toxicity (DLT) was only observed in two patients treated at dose level 1 and one patient treated at dose level 3, while all the other patients only experienced nonhematologic toxicity, such as asthenia and mucositis. Two melanoma patients showed responses (one partial and one minor) to the treatment. One lymphoma patient also showed a brief partial response. This phase I trial indicated that the combination of mitoguazone and gemcitabine had limited but noticeable activity for treatment of cancer patients. Further study on the toxicity and on the effect of the scheduled mitoguazone-gemcitabine combination is needed.

Aged↗

PubMed2003

Laser immunotherapy: a novel treatment modality for metastatic tumors.

Laser immunotherapy is a novel approach for the treatment of metastatic tumors. It combines a selective photothermal laser-tissue interaction for direct tumor destruction and an immunoadjuvant-directed simulation for immune responses. In experiments using a rat metastatic tumor model, laser immunotherapy resulted in the eradication of both treated primary tumors and untreated metastases at remote sites. It also induced anti-tumor resistance.

Animals↗

PubMed2003

Detection of anti-tumor immunity induced by laser immunotherapy.

Metastatic mammary tumors in rats were treated by laser immunotherapy. Tumors injected by a laserabsorbing dye and an immunoadjuvant were irradiated non-invasively by a near-infrared laser. The successfully cured rats developed a long-term resistance to repeated tumor challenges. Using the sera from cured rats as the source of primary antibodies, immune responses induced by laser immunotherapy were observed in both cellular and molecular levels using histochemical assays and Western blot analysis.

Animals↗

PubMed2002

Effect of different components of laser immunotherapy in treatment of metastatic tumors in rats.

Induction of a long-term tumor-specific immunity is the ultimate cure of metastatic cancers. Laser immunotherapy is a novel approach that aims at the tumor-directed stimulation of the immune system of the host. It involves an intratumor administration of a laser-absorbing dye and an immunoadjuvant, followed by noninvasive laser irradiation. Previous studies using glycated chitosan (GC) as immunoadjuvant and indocyanine green (ICG) as laser-absorbing dye have shown positive effects of the treatment on metastatic breast tumors in rats. In vivo experiments showed promising results such as: (a) eradication of treated primary tumors; (b) regression of untreated metastases; (c) induced antitumor immune response; and (d) long-term resistance to tumor rechallenge. In this study, rats bearing metastatic breast tumors and metastatic prostate tumors were treated with various combinations of the three components of laser immunotherapy. The rat survival rates and profiles of primary and metastatic tumors, after treatment by individual components and various combinations of the components, were analyzed. In the treatment of breast tumors, all of the experimental groups without immunoadjuvant showed little or no positive effect. The use of GC, either by itself or in combination with other components, had a noticeable impact on the survival rate of tumor-bearing rats. However, it was the combination of all of the three components that resulted in the highest cure rate. Three different concentrations of GC, 0.5, 1, and 2%, were also used to treat the metastatic breast tumors. The results showed that 1% GC was most effective in laser immunotherapy. In the treatment of metastatic prostate tumors, both the laser-ICG and laser-ICG-GC treatments significantly reduced the growth of primary tumors and lung metastases. Long-term survival of the rats bearing the prostate tumors was also observed after the laser immunotherapy treatment in our preliminary studies. These results revealed the important function of the immunoadjuvant in laser immunotherapy.

Adjuvants, Immunologic↗

PubMed2002

Characterization of a CCD-based digital x-ray imaging system for small-animal studies: properties of spatial resolution.

A digital x-ray imaging system was designed for small-animal studies. This system is a fiber-optics taper-coupled imaging system with two CCD arrays uniquely jointed. The x-ray source of the system has a small focal spot of 20 microm. This digital imaging system contains specially designed shelves to provide magnification levels, ranging from 1.5x to 5x. The system is characterized in terms of its properties of spatial resolution. An observer-based spatial resolution measurement was conducted with a line-pair target and a sector test pattern. The modulation transfer function of the system, with different magnifications, was studied by use of a 10-microm lead slit. The average resolutions at 50% and 5% modulations at 1x magnification were measured as 3.9 and 8.4 lp/mm, respectively, where lp indicates line pairs. With 5x magnification, the 50% and the 5% modulations provided 13.2- and 29.9-lp/mm, respectively, average spatial resolutions. The measurements showed consistency between the two individual CCD arrays; the difference in resolution between the two CCDs is less than 1%, even at high magnifications.

Animals↗

PubMed2002

Dynamic gating of spike propagation in the mitral cell lateral dendrites.

A unique feature of the olfactory bulb circuit is the long projection of the mitral cell lateral dendrites. Through dendrodendritic reciprocal synapses, these dendrites connect one olfactory glomerular module to hundreds of others; but the functional principles governing these extensive lateral interactions remain largely unknown. Here we report that the spatial extent of action potential propagation in these dendrites is dynamically regulated by inhibitory synapses distributed along the dendrites. The extent of propagation determines the spatial pattern of Ca(2+) influx and thus the range and number of dendrodendritic synapses to be activated. Accordingly, network control of spike traffic in the mitral cell lateral dendrites can mediate dynamic interaction with different combinations of glomerular modules in response to different odorants.

Action Potentials↗