Detection of Oxidant Producing-sites in Glutaraldehyde-fixed Human Neutrophils and Eosinophils Stimulated with Phorbol Myristate Acetate

The aim of the present study was to detect oxidant-producing sites, and to elucidate their dynamic reorganization in human polymorphonuclear leukocytes (PMNs) fixed with glutaraldehyde which preserves cell structure. In biochemical analyses, the detectable O2– generation in unfixed PMNs upon stimulation with phorbol 12-myristate 13-acetate (PMA) in the presence of cytochalasin B was characterized by a lag period of approximately 10sec followed by O2– production. The maximal rate reached was 3.18±0.07nmol/min/1×106 cells (mean±S.D.; n=4) after 30sec of stimulation. PMNs exposed to PMA and cytochalasin B followed by fixation with glutaraldehyde generated O2– without a lag period at a rate of 0.35±0.05nmol/min/1×106 cells (mean±S.D.) by the addition of NADPH as substrate to the cell suspension. In the cytochemical assays, we employed both cells exposed to PMA and cytochalasin B, and then fixed with glutaraldehyde followed by incubation in the cytochemical reaction medium (pre-fixed cells) and cells incubated in the medium containing PMA and cytochalasin B followed by fixation with glutaraldehyde (post-fixed cells). Oxidant reaction in the pre-fixed cells was detected by the addition of NADPH and FAD to the reaction medium. No oxidant-reaction product was seen in pre-fixed cells stimulated for 10sec whereas the oxidant reaction was visualized in intracellular compartments of pre-fixed PMNs stimulated for 20sec. The fact that the pre-fixed PMNs stimulated for 30sec showed increased numbers of oxidant-producing structures compared to those seen in the pre-fixed cells stimulated for 20sec, demonstrates that the amount of the reaction product and the number of oxidant-producing intracellular compartments increases between 20 and 30sec after start of stimulation with PMA. These cytochemical results using the pre-fixed cells coincided with the findings obtained from the biochemical assays in the pre-fixed cells exposed to PMA and cytochalasin B. The oxidant reaction was observed in elongated tubular structures that were arranged in a radial fashion, and were associated with the plasma membrane in the pre-fixed PMNs, whereas post-fixed PMNs exhibited slender spherical or rod-shaped structures of various lengths. The present results indicate that the pre-fixed PMNs can be employed for elucidating the dynamic reorganization of oxidant-producing sites in human PMNs.     

Ecto-ATPase activity in the rat cardiac muscle: biochemical characteristics and histocytochemical localization

We used a combined biochemical and histocytochemical approach to study ecto-ATPase in the rat cardiac muscle. The reaction medium employed for histocytochemical detection was optimized in biochemical assays to achieve the highest enzyme activity and lowest inhibition by the capture agent used for visualization of the reaction product. Approximately 70% of the enzyme activity was retained in samples after the fixation procedure. Divalent cations stimulated ecto-ATPase. High activity was detectable within a wide pH range. Histocytochemical reaction was observed at sites at which extracellular ATP can potentially exert its actions on the cardiac muscle: nerve endings, plasma membranes of cardiac myocytes and capillary endothelial cells, and T-tubules. Product of the reaction was found exclusively at the outer surface of the cells. In controls, enzyme activity was abolished by diethyl pyrocarbonate and slightly stimulated by digitonin and concanavalin A, whereas sodium orthovanadate, N-ethylmaleimide, and sodium azide yielded no effect. Our results support the view that cardiac ecto-ATPase is involved in important physiological functions and suggest that its activity may be regulated by the release of ATP from nerve endings.     

p38alpha mitogen-activated protein kinase plays a critical role in cardiomyocyte survival but not in cardiac hypertrophic growth in response to pressure overload

The molecular mechanism for the transition from cardiac hypertrophy, an adaptive response to biomechanical stress, to heart failure is poorly understood. The mitogen-activated protein kinase p38alpha is a key component of stress response pathways in various types of cells. In this study, we attempted to explore the in vivo physiological functions of p38alpha in hearts. First, we generated mice with floxed p38alpha alleles and crossbred them with mice expressing the Cre recombinase under the control of the alpha-myosin heavy-chain promoter to obtain cardiac-specific p38alpha knockout mice. These cardiac-specific p38alpha knockout mice were born normally, developed to adulthood, were fertile, exhibited a normal life span, and displayed normal global cardiac structure and function. In response to pressure overload to the left ventricle, they developed significant levels of cardiac hypertrophy, as seen in controls, but also developed cardiac dysfunction and heart dilatation. This abnormal response to pressure overload was accompanied by massive cardiac fibrosis and the appearance of apoptotic cardiomyocytes. These results demonstrate that p38alpha plays a critical role in the cardiomyocyte survival pathway in response to pressure overload, while cardiac hypertrophic growth is unaffected despite its dramatic down-regulation.     

Bioconcentration mechanism of selenium by a coccolithophorid, Emiliania huxleyi

We investigated the uptake and bioconcentration of the essential element selenium by a coccolithophorid, Emiliania huxleyi, using [75Se]selenite. The time course of 75Se uptake showed a biphasic pattern, namely a primary phase and a subsequent secondary phase. The primary and secondary phases are due to a rapid selenite uptake process that attained a stationary level within 2 min and a slow Se-accumulation process that continued at a constant rate for 4 h or longer, respectively. Kinetic analysis revealed that the selenite uptake process consists of two components, one saturable and one linearly related to substrate concentration. The Km of the saturable component was 29.8 nM selenite; the uptake activity of this component was suppressed by inhibitors of ATP biogenesis, suggesting that selenite uptake is driven by a high-affinity, active transport system. During a 6-h incubation of cells with [75Se]selenite, 70% of the intracellular 75Se was incorporated into low-molecular-mass compounds (LMCs), and 17% was incorporated into proteins, but [75Se]selenite was barely detectable. A pulse-chase experiment demonstrated that the 75Se that had accumulated in LMCs was transferred into proteins. When the syntheses of amino acids and proteins were each separately inhibited, 75Se incorporation into LMCs and proteins was decreased. These results suggest that E. huxleyi rapidly absorbs selenite, filling a small intracellular pool. Then, Se-containing LMCs are immediately synthesized from the selenite, creating a pool of LMCs that are then metabolized to selenoproteins.     

An RNA-dependent protein kinase is involved in tunicamycin-induced apoptosis and Alzheimer's disease

Various types of stress, such as disruption of calcium homeostasis, inhibition of protein glycosylation and reduction of disulfide bonds, result in accumulation of misfolded proteins in the endoplasmic reticulum (ER). The initial cellular response involves removal of such proteins by the ER, but excessive and/or long-term stress results in apoptosis. In this study, we used a randomized ribozyme library and ER stress-mediated apoptosis (tunicamycin-induced apoptosis) in SK-N-SH human neuroblastoma cells as a selective phenotype to identify factors involved in this process. We identified a double-stranded RNA-dependent protein kinase (PKR) as one of the participants in this process. The level of nuclear PKR was elevated, but the level of cytoplasmic PKR barely changed in tunicamycin-treated SK-N-SH cells. Furthermore, tunicamycin also raised levels of phosphorylated PKR in the nucleus. We also detected the accumulation of phosphorylated PKR in the nuclei of autopsied brain tissues in Alzheimer's disease. Thus, PKR might play a role in ER stress-induced apoptosis and in Alzheimer's disease.     

Imidazole derivatives as new potent and selective 20-HETE synthase inhibitors

In a previous paper, we reported that an imidazole derivative 1 exhibited a potent inhibitory activity of 20-HETE synthase (1; IC(50) value of 5.7 nM), but this compound also exhibited little selectivity for cytochrome P450s (CYPs). We examined some derivatives of imidazole 1 which had an amino group on the side chain, and found that a dimethylaminohexyloxy derivative (3g; IC(50) value of 8.8 nM) showed potent and selective inhibitory activity.     

GRP94 reduces cell death in SH-SY5Y cells perturbated calcium homeostasis

The endoplasmic reticulum (ER) resident-94 kDa glucose-regulated protein (GRP94), plays a pivotal role in cell death due to ER stress. In our study expression of GRP94 was increased in human neuroblastoma SH-SY5Y cells due to exposure to calcium ionophore A23187. A23187-mediated cell death was associated with activation of the major cysteine proteases, caspase-3 and calpain. Pretreatment with adenovirus-mediated antisense GRP94 (AdGRP94AS) reduced viability of SH-SY5Y cells subjected to A23187 treatment compared with wild type cells or cells with adenovirus-mediated overexpression of GRP94 (AdGRP94S). These results indicated that suppression of GRP94 is associated with accelerated cell death. Moreover, expression of GRP94 suppressed A23187-induced cell death and stabilized calcium homeostasis.     

Localized compliance of small airways in excised rat lungs using microfocal X-ray computed tomography.

Airway compliance is a key factor in understanding lung mechanics and is used as a clinical diagnostic index. Understanding such mechanics in small airways physiologically and clinically is critical. We have determined the "morphometric change" and "localized compliance" of small airways under "near"-physiological conditions; namely, the airways were embedded in parenchyma without dehydration and fixation. Previously, we developed a two-step method to visualize small airways in detail by staining the lung tissue with a radiopaque solution and then visualizing the tissue with a cone-beam microfocal X-ray computed tomography system (Sera et al. J Biomech 36: 1587-1594, 2003). In this study, we used this technique to analyze changes in diameter and length of the same small airways ( approximately 150 microm ID) and then evaluated the localized compliance as a function of airway generation (Z). For smaller (<300-microm-diameter) airways, diameter was 36% larger at end-tidal inspiration and 89% larger at total lung capacity; length was 18% larger at end-tidal inspiration and 43% larger at total lung capacity than at functional residual capacity. Diameter, especially at smaller airways, did not behave linearly with V(1/3) (where V is volume). With increasing lung pressure, diameter changed dramatically at a particular pressure and length changed approximately linearly during inflation and deflation. Percentage of airway volume for smaller airways did not behave linearly with that of lung volume. Smaller airways were generally more compliant than larger airways with increasing Z and exhibited hysteresis in their diameter behavior. Airways at higher Z deformed at a lower pressure than those at lower Z. These results indicated that smaller airways did not behave homogeneously.     

Potent and orally active ET(A) selective antagonists with 5,7-diarylcyclopenteno[1,2-b]pyridine-6-carboxylic acid structures

The synthesis and structure-activity relationships of a series of 5,7-diarylcyclopenteno[1,2-b]pyridine-6-carboxylic acids are described. Our efforts have been focused on modification of the aryl ring at the 5-position and the alkyl substituent at the 2-position of the bottom 4-methoxyphenyl ring in an effort to develop orally available ET(A) selective antagonists with safer profiles in terms of the P-450 enzyme inhibitory activity. Incorporation of a hydroxymethyl group as an alkyl substituent in methylenedioxyphenyl and 6-dihydrobenzofuran derivatives led to the identification of orally bioavailable ET(A) selective antagonists 1f and 7f. These compounds also showed not only excellent binding affinity (IC(50) < 0.10nM, more than 800-fold selectivity for the ET(A) receptor over the ET(B) receptor) but also sufficient oral bioavailability, 48% and 56%, respectively, in rats. Furthermore, these compounds did not exhibit either competitive or mechanism-based inhibition of human cytochrome P450 enzymes.