Search PubMed⌕ Search

Biomedical subjects

L Zhao

Publications and source records attributed to L Zhao.

At least 199 records · Page 11Linked to original sources
PubMed1999

Cloning of Chlamydomonas p60 katanin and localization to the site of outer doublet severing during deflagellation.

Katanin, a heterodimeric microtubule-severing protein that localizes to sites of microtubule organization, can mediate in vitro the ATP-dependent disassembly of both taxol-stabilized microtubules and axonemal doublet microtubules. In the unicellular biflagellate alga Chlamydomonas, katanin has been implicated in deflagellation, a highly specific process that involves a Ca(2+)-signal transduction pathway starting at the plasma membrane and culminating in the severing of axonemal outer doublet microtubules and excision of both flagella from the cell body. Previously, we showed that the microtubule severing activity of deflagellation and katanin's 60 kD catalytic subunit (termed p60) purified with the flagellar basal body complex (FBBC). Additional evidence supporting the involvement of katanin in deflagellation came from the observation that an antibody against human p60 katanin significantly inhibited FBBC-associated microtubule-severing activity. Here we report the cloning of p60 katanin from Chlamydomonas reinhardtii. Immunogold electron microscopy places Chlamydomonas p60 at several locations within the basal body apparatus and associated structures. Importantly, we find a dense accumulation of colloidal gold labeling the distal end of the flagellar transition zone, the site of outer doublet severing during deflagellation. These results suggest that, in addition to a potential involvement in the deflagellation pathway, katanin-mediated microtubule-severing may be associated with multiple processes in Chlamydomonas.

Adenosine Triphosphatases↗
PubMed1999

Postictal blockade of ischemic hippocampal neuronal death in primates using selective cathepsin inhibitors.

This paper is to study the participation of cathepsin in ischemic neuronal death of the monkey hippocampal cornu ammonis (CA) 1 sector and also to clarify whether its selective inhibitor epoxysuccinyl peptides such as CA-074 and E-64c can inhibit the neuronal death or not. In the preceding reports, we demonstrated mu-calpain activation and subsequent rupturing of the lysosomal membrane of postischemic CA1 neurons and also increase of enzyme activity of cathepsins B and L in monkeys undergoing a complete 20-min whole brain ischemia. Here, morphological, immunohistochemical and enzymatical analyses were performed to examine the efficacy of two selective cathepsin inhibitors in the postictal blockade of delayed neuronal death in the monkey hippocampus. Both inhibitors could significantly decrease enzyme activities of cathepsins B and L in all hippocampal sectors. When CA-074 was intravenously administered immediately after the ischemic insult, approximately 67% of CA1 neurons were saved from delayed neuronal death on day 5 after ischemia. In contrast, when E-64c was similarly administered, approximately 84% of CA1 neurons were saved from delayed neuronal death on day 5. The surviving neurons showed mild central chromatolysis and negligible immunoreactivity for cathepsins B and L. These observations indicate that the use of cathepsin inhibitors may become novel strategy for prevention of ischemic delayed neuronal death in the primate hippocampus.

Animals↗
PubMed1999

Real-time adaptive functional MRI.

Adaptively limiting image acquisition to areas of interest will allow more efficient data acquisition time for in-depth characterization of areas of brain activation. We designed and implemented an adaptive image acquisition scheme that uses a multiresolution-based strategy to zoom into the regions of cortical activity. Real-time pulse prescription and data processing capabilities were combined with spatially selective radiofrequency encoding. The method was successfully demonstrated in volunteers performing simple sensorimotor paradigms for simultaneous activation of primary motor and cerebellar areas. We believe that real-time adaptation of spatial and temporal sampling to task-related changes will increase the efficiency and flexibility of functional mapping experiments. Contrast-to-noise analysis in selected regions-of-interest was performed to quantitatively assess the multiresolution adaptive approach.

Adult↗
PubMed1999

Environmental influence on gene expression and recovery from cerebral ischemia.

An emerging concept in neurobiology is that the adult brain retains a capacity for plasticity and functional reorganization throughout the life span. Experimental data from electrophysiological, morphological and behavioral studies have documented experience dependent plasticity in the intact and injured adult brain. Neuroimaging clinical studies indicate altered post stroke functional activation patterns, usually including activation of the intact hemisphere. However, there is some disagreement regarding their functional significance and longitudinal studies correlating outcome and activation pattern are needed to solve some controversies. Postoperative housing of rats in activity stimulating environment after ligation of the middle cerebral artery significantly enhances outcome. Gene expression for brain derived neurotrophic factor and Ca2+/calmodulin-dependent protein kinase II, two substances with potential role in brain plasticity, show different patterns in animals housed in standard and in enriched environment. The functional significance of altered gene expression needs to be evaluated.

Animals↗
PubMed1999

Kinetics of tumor necrosis factor alpha in plasma and the cardioprotective effect of a monoclonal antibody to tumor necrosis factor alpha in acute myocardial infarction.

BACKGROUND: Inflammation plays a critical role in acute myocardial infarction (AMI) and tumor necrosis factor alpha (TNF-alpha) is a potent inflammatory trigger. This study was designed to examine the kinetics of TNF-alpha in plasma in patients with AMI and the potential benefit of inhibition of TNF-alpha monoclonal antibody in AMI. METHODS AND RESULTS: TNF-alpha levels in plasma were measured in 42 patients with AMI. TNF-alpha levels were elevated at 4 hours after onset of chest pain and declined to control values at 48 hours. TNF-alpha levels were higher in patients with Killip III and IV than in those with Killip I and II (P <.01). To examine the pathogenic role of TNF-alpha, New Zealand White rabbits were treated with buffer or a TNF-alpha monoclonal antibody before left anterior descending artery (LAD) ligation. Treatment with the TNF-alpha monoclonal antibody decreased area of necrosis, number of circulating endothelial cells, and lipid peroxidation product malonaldehyde bis(dimethyl acetal). There was a significant correlation of TNF-alpha levels with peak CK-MB in AMI patients, and area of necrosis, MDA, and circulating endothelial cells in rabbits (all P <.05). CONCLUSIONS: TNF-alpha release early in the course of AMI contributes to myocardial injury and dysfunction. Treatment with the monoclonal antibody against TNF-alpha can be cardioprotective, particularly in the setting of heart failure in patients with AMI.

Adult↗
PubMed1999

Environmental enrichment alters nerve growth factor-induced gene A and glucocorticoid receptor messenger RNA expression after middle cerebral artery occlusion in rats.

Housing rats in an enriched environment after focal brain ischemia improves functional outcome without changes in infarct volume, suggesting neuroplastic changes outside the lesion. In this study, permanent occlusion of the middle cerebral artery was followed by housing in an enriched or a standard environment. Nerve growth factor-induced gene A and glucocorticoid receptor messenger RNA expression were determined by in situ hybridization two to 30 days after middle cerebral artery occlusion. Stroke induced a decrease in nerve growth factor-induced gene A messenger RNA expression in cortical areas outside the ischemic lesion and in the CA1 subregion of the hippocampus two to three days after ischemia. This decrease was more prolonged with environmental enrichment, lasting until 20 days. However, 30 days after focal cerebral ischemia, environmental enrichment increased nerve growth factor-induced gene A expression compared to standard housing. A reduction of hippocampal glucocorticoid receptor (type II) messenger RNA two to 12 days after stroke in standard housed rats was restored by environmental enrichment. These data suggest that improved functional outcome induced by environmental enrichment after middle cerebral artery occlusion is associated with dynamically altered expression of nerve growth factor-induced gene A messenger RNA in brain regions outside the ischemic lesion, and sustained levels of hippocampal glucocorticoid receptor messenger RNA expression.

Animals↗
PubMed1999

Solubilization of fluasterone.

Solubilization of nonpolar drugs constitutes one of the most important tasks in parenteral formulations design. This study investigates and assesses the solubility enhancement of Fluasterone by various techniques including cosolvency, micellization, and complexation. Of the solubilizing agents used, the modified beta-cyclodextrins were found to be the most effective. The solubility of Fluasterone is 1.55 x 10(-4) mM, 3.13 mM, and 4.04 mM in water, 20% sulfobutyl ether-beta-cyclodextrin (SBEbetaCD), and 20% hydroxypropyl-beta-cyclodextrin (HPbetaCD), respectively.

Algorithms↗
PubMed1999

Combined effect of cosolvent and cyclodextrin on solubilization of nonpolar drugs.

Solubility enhancement has broad implications in parenteral formulation design. A simple mathematical model has been developed to describe the combined effect of cosolvency and complexation on nonpolar drug solubilization. The total drug solubility is determined by the summation of three drug species present in the solution: free drug [D], drug-ligand binary complex [DL], and drug-ligand-cosolvent ternary complex [DLC]. The proposed model established the dependencies of these three species upon the intrinsic drug solubility, [D(u)], the cosolvent solubilizing power, sigma, the binary and ternary intrinsic complexation constants, K(b)(int) and K(t)(int), and the cosolvent destabilizing powers for the binary and the ternary complexes, rho(b) and rho(t). A nonpolar solute, Fluasterone, is used to evaluate the newly generated equation. The model explains the decline in drug solubility produced by low cosolvent concentrations as well as the increase in the solubility produced by high cosolvent concentrations that are observed at all cyclodextrin concentrations.

2-Hydroxypropyl-beta-cyclodextrin↗
PubMed1999

Morphological and functional changes in the colonic epithelial cells in a rabbit model of colitis.

A rabbit model of TNBS-colitis was used to study the effect of intestinal inflammation on epithelial cell function. Epithelial cells were isolated using a non-enzymatic isolation method without any apparent contamination with infiltrating immune cells. The isolated cells were found to be viable using dye exclusion studies, unidirectional Na+ -fluxes, proliferation assays and morphological studies. The cells, however, showed morphological changes that suggested the presence of increased number of secretory vesicles. This increase correlated well with the increase observed in ion and water secretion as measured by the short-circuit current. Finally, in the colitic tissue the number of PGE2 receptors was greatly reduced with no changes observed in the affinity of PGE2 to its receptor. The reduced number of PGE2 receptors might be due to sensitization of the receptor. In conclusion, we have demonstrated that morphologically and functionally normal epithelial cells can be isolated from the rabbit inflamed distal colon.

Animals↗
PubMed1999

Comparative analysis of three genetic modifications designed to inhibit human serum-mediated cytolysis.

Hyperacute rejection (HAR) remains a critical immunologic hurdle in the development of xenogeneic organs for human transplantation. Strategies that simultaneously eliminate both natural antibody reactivity and complement activation on the xenogeneic cell surface may be the best approach to achieve clinical application of xenogeneic vascularized organ transplantation. We have developed multiple lines of genetically manipulated mice to evaluate the combination of different genetic approaches aimed at inhibiting antibody and complement-mediated cell lysis. We utilized transgenic mice expressing the human complement inhibitor, CD59, the human 1,2-fucosyltransferase (H-transferase, HT) and the alpha1,3-galactosyltransferase (alpha1,3-GT) knock-out mouse line (Gal KO). Our data show that expression of hCD59 in combination with HT expression or the null phenotype of alpha1,3-GT are equally effective at preventing human serum-mediated cytolysis. Interestingly, the triple combination affords no additional protective effect. Therefore, coexpression of HT and a complement inhibitor is the most immediate strategy to genetically engineer transgenic pigs to be used as xenogeneic donors.

Animals↗
PubMed1999

c-Rel and p65 trans-activate the monocyte chemoattractant protein-1 gene in interleukin-1 stimulated mesangial cells.

BACKGROUND: The chemokine monocyte chemoattractant protein-1 (MCP-1) is secreted by human glomerular mesangial cells in response to interleukin-1 (IL-1) and has a central role in amplifying the inflammatory response during glomerulonephritis. However, the mechanism by which IL-1 regulates its transcription is not understood. Specific members of the nuclear factor kappaB/rel (NF-kappaB) proteins may regulate MCP-1 expression in a stimulus- and tissue-specific manner. METHODS: Electrophoretic mobility shift assays and Western blot analysis characterized the members of the NF-kappaB family that bound the two NF-kappaB sites of the MCP-1 enhancer (A1 and A2) in vitro. Trans-activation of the MCP-1 gene was investigated by transfer of the MCP-1 enhancer DNA to mesangial cells. RESULTS: Primary human mesangial cells contained in addition to p50 (NF-kappaB1) and p65 (Rel A) NF-kappaB proteins, the oncoprotein c-rel, and Rel B, but not p52 (NF-kappaB2). IL-1 induced c-rel to form a complex with p65, which bound the MCP-1 A2 site but not the A1 or IL-6 NF-kappaB sites in vitro. IL-1 up-regulated transfected MCP-1 enhancer activity. Cotransfer of the MCP-1 enhancer together with individual members of the NF-kappaB family showed that the heterodimer c-relp65 or (p65)2 can selectively trans-activate the MCP-1 gene via its A1 and A2 sites in mesangial cells. CONCLUSIONS: This study demonstrates for the first time that the c-rel oncoprotein can enhance MCP-1 transcription in mesangial cells and suggests that it may have an important role in amplifying gene expression in the inflamed glomerulus.

Animals↗
PubMed1999

The mechanisms of action of interleukin-1 on rabbit intestinal epithelial cells.

Interleukin-1 (IL-1) is an inflammatory mediator that increases Cl- secretion in intestinal epithelial cells. To identify the signal transduction pathway(s) involved in IL-1's action, cells were treated with IL-1 and the levels of cyclooxygenase (COX) enzymes, prostaglandin E2 (PGE2) and phospholipase A2-activating protein (PLAP), and the activity of phospholipase A2 (PLA2) were measured. IL-1 caused concentration- and time-dependent increases in the levels of PLA2 activity, and/or in the levels of PLAP, COX-2 and PGE2. The IL-induced increase in PGE2 levels was biphasic, with the first peak due to the increase in PLAP levels, and the second peak due to the increase in COX-2 levels. This increase in PGE2 levels may provide a mechanism for acute and chronic inflammation in the intestine.

Animals↗
PubMed1999

Construction, expression, and characterization of anticarcinoma sFv fused to IL-2 or GM-CSF.

Local production of cytokines by genetically engineered tumor cells decreases their tumorigenicity and elicits protective immune responses against the parental tumor cells. An alternative approach to elicit a therapeutic immune response is to use fusion proteins that can target tumor cells and simultaneously activate effector cells. Fusion proteins between human IL-2, murine or human GM-CSF, and sFv of antihuman carcinoma antibody L6 have been constructed, expressed in both COS and Chinese hamster ovary (CHO) cells, and purified by affinity chromatography. The biologic activity of L6 sFV-hIL-2, L6 sFv-mGM-CSF, and L6 sFv-hGM-CSF was tested on human T cell blasts, factor-dependent FDCP-1, and TF-1 cells, respectively. The ability of soluble L6 sFv-hIL-2, L6 sFv-mGM-CSF, and L6 sFv-hGM-CSF to stimulate the proliferation of the indicator cells was found to be comparable to that of recombinant hIL-2, mGM-CSF, or hGM-CSF. Tumor cells coated with L6 sFV-mGM-CSF or L6 sFv-hGM-CSF were also tested in this way and were found to be potent stimulators, indicating that the cytokines were functionally active when bound to the tumor cell surface. This work demonstrates the feasibility of targeting sFv-cytokine fusion proteins for the activation of effector cells as an alternative to cytokine gene therapy.

Animals↗
PubMed1999

Studies on the mechanism of cancer protection by wheat bran: effects on the absorption, metabolism and excretion of the food carcinogen 2-amino-3-methylimidazo[4,5-f]quinoline (IQ).

We examined ways in which dietary supplements of wheat bran may protect against colon cancer. The effects of supplementing the diet of female Wistar rats with 10% wheat bran on the disposition and metabolism of the dietary carcinogen 2-amino-3-methylimidazo[4,5-f]quinoline (IQ) labelled with (14)C was determined. Our data show that the wheat bran had a major effect on both the distribution and metabolism of IQ. At a low dose of IQ (1 mg/kg), we unexpectedly found that up to 2 h after gavage there were higher concentrations of radioactivity in the plasma of rats fed wheat bran compared with the controls, but there were lower concentrations of radioactivity after 2 h. At a high dose of IQ (50 mg/kg), there were always lower concentrations of radioactivity in the plasma of rats fed wheat bran compared with the control rats. One of the most marked effects of wheat bran was apparently to significantly retard the metabolism of IQ in the plasma when this was fed at either dose. There were also differences between the rats fed wheat bran and the control in the concentrations and types of IQ metabolites in the urine.

Animals↗
PubMed1999

Forgotten mysteries in the early history of vitamin D.

In the early 1920s, workers in both England and the US had discovered that rats on a rachitic diet would remain healthy if irradiated with ultraviolet light. However, they also found, to their surprise, that "control" rats too would recover if either their jar was irradiated without the rat in it or if a cage-mate was removed for irradiation and then returned. The ideas that either air or material objects that had been irradiated continued themselves to convey healthful secondary radiations were investigated but not confirmed. There was then the commercially important finding that with irradiation, some rachitic diets would become anti-rachitic. However, this effect did not explain all the previous findings. Consumption of either small irradiated fecal particles or of feces from irradiated rats was the likely explanation for the recovery of nonirradiated rats, but this was not tested by direct experiment, and it now appears unlikely that feces from irradiated rats would show significant antirachitic activity. It is suggested that an alternative possibility--activity of grease from irradiated fur--deserves investigation.

Animals↗
PubMed1999

Characterization of a cytokinesis defective (cyd1) mutant of Arabidopsis.

Although several mutations and genes affecting plant cytokinesis have been identified, mutant screens are not yet saturated and knowledge about gene function is still limited. A novel Arabidopsis mutation, cytokinesis defective1 (cyd1), was identified by partial or missing cell walls in stomata. Stomata with incomplete or no cytokinesis still differentiate and some contain swellings of the outer wall not found in the wild type. The incomplete walls are correctly placed opposite stomatal wall thickenings suggesting that the mutation interferes with the execution of cytokinesis rather than with the placement of the division site. Cytokinesis defects are also detectable in other cell types throughout the plant, defects which include cell wall protrusions, two or more nuclei in one cell, and reduced cell number. The extent of cytokinetic partitioning correlates with nuclear number in abnormal stomata. Many cyd1 epidermal cells, stomata and pollen are larger, and trichomes have more branches. cyd1 is partially lethal with poor seed set and some defective ovules, but many plants are fertile despite abnormalities in vegetative and reproductive development such as missing, reduced, fused or misshapen leaves and floral organs. cyd1 appears to be the only cytokinesis mutant described where defects are known to occur in both mature vegetative and reproductive organs. Thus, the CYD1 gene product appears to be necessary for the execution of cytokinesis throughout the shoot. The examination of stomata by microscopy may be a useful screen for the directed isolation of additional cytokinesis mutations that are not embryo or seedling lethal

Arabidopsis↗
PubMed1999

Expression of the human alpha1,2-fucosyltransferase in transgenic pigs modifies the cell surface carbohydrate phenotype and confers resistance to human serum-mediated cytolysis.

Hyperacute rejection (HAR) is the first critical immunological hurdle that must be addressed in order to develop xenogeneic organs for human transplantation. In the area of cell-based xenotransplant therapies, natural antibodies (XNA) and complement have also been considered barriers to successful engraftment. Transgenic expression of human complement inhibitors in donor cells and organs has significantly prolonged the survival of xenografts. However, expression of complement inhibitors without eliminating xenogeneic natural antibody (XNA) reactivity may provide insufficient protection for clinical application. An approach designed to prevent XNA reactivity during HAR is the expression of human alpha1, 2-fucosyltransferase (H-transferase, HT). H-transferase expression modifies the cell surface carbohydrate phenotype of the xenogeneic cell, resulting in the expression of the universal donor O antigen and a concomitant reduction in the expression of the antigenic Galalpha1,3-Gal epitope. We have engineered various transgenic pig lines that express HT in different cells and tissues, including the vascular endothelium. We demonstrate that in two different HT transgenic lines containing two different HT promoter constructs, expression can be differentially regulated in a constitutive and cytokine-inducible manner. The transgenic expression of HT results in a significant reduction in the expression of the Galalpha1,3-Gal epitope, reduced XNA reactivity, and an increased resistance to human serum-mediated cytolysis. Transgenic pigs that express H-transferase promise to become key components for the development of xenogeneic cells and organs for human transplantation.

ABO Blood-Group System↗