Mechanism Of Cell Damage Research Articles

Investigating the effect of cell repopulation on the tumor response to fractionated external radiotherapy.

In this work we study the descriptive power of the main tumor control probability (TCP) models based on the linear quadratic (LQ) mechanism of cell damage with cell recovery. The Poisson, binomial, and a dynamic TCP model, developed recently by Zaider and Minerbo are considered. The Zaider-Minerbo model takes cell repopulation into account. It is shown that the Poisson approximation incorporating cell repopulation is conceptually incorrect. Based on the Zaider-Minerbo model, an expression for the TCP for fractionated treatments with varying intervals between two consecutive fractions and with cell survival probability that changes from fraction to fraction is derived. The models are fitted to an experimental data set consisting of dose response curves that correspond to different fractionation regimes. The binomial TCP model based on the LQ mechanism of cell damage solely was unable to fit the fractionated response data. It was found that the Zaider-Minerbo model, which takes tumor cell repopulation into account, best fits the data.

TEM evidence of ultrastructural alteration on Pseudomonas aeruginosa by photocatalytic TiO 2 thin films

The antibacterial efficiency of longwave UV-irradiated TiO 2 thin films as well as the ultrastructural damage on bacterial cells was evaluated using Pseudomonas aeruginosa as a model. The quantitative antibacterial efficiency assays showed a bacterial inhibition in the range of 32–72% at different times of irradiation. Transmission electron microscopy (TEM) was used to detect the effect of irradiation of TiO 2 thin films on the ultrastructure of the bacterial cell in order to reveal possible cellular damage. After 40 min irradiation, an abnormal cellular division was observed: instead of a normal septum, an ‘elongated bridge’ was formed. At a longer irradiation time, wavy structures all around the outer cell membrane were observed, and also some bubble-like protuberances, which expelled inner material. The mechanism of irreversible bacterial cell damage caused by the photocatalytic effect of TiO 2 could be related to abnormal cell division, aside from the reported physicochemical alteration of the cell membrane.

Sca+CD34- murine side population cells are highly enriched for primitive stem cells.

The aim of this study was to characterize murine side population (SP) stem cells and SP cell subpopulations for primitive stem cell capacity. SP cells, characterized by a specific Hoechst dye efflux pattern, were isolated by flow cytometric analysis and sorting from murine adult whole bone marrow (WBM). Different subpopulations of SP cells were isolated by staining with anti-Sca and anti-CD34 antibodies. Primitive stem cell content of SP cells and SP subsets were determined by cobblestone area-forming cell (CAFC) frequencies. Measurement of CAFC frequencies revealed that SP cells are greatly enriched for both primitive stem cells (day-28-35 CAFC) and somewhat more mature hematopoietic cells (day-14-21 CAFC) compared to WBM. The day-28 and day-35 CAFC enrichments in SP cells vs WBM cells were 1065 and 471, respectively. Analysis of the subpopulations of SP cells revealed that SP(+)Sca(-)CD34(+) cells contained almost exclusively day-7 CAFC and had little day-28-35 CAFC activity. SP(+)Sca(+)CD34(+) cells had high day-7-14 CAFC frequencies, but lower day-35 CAFC frequencies compared to SP(+)Sca(+)CD34(-) cells. SP(+)Sca(+)CD34(-) cells contained very low day-7 CAFC activity, but nearly 2200 times the day-28-35 CAFC activity as normal bone marrow. To evaluate the influence of Hoechst dye efflux capacity, we divided the SP tail into four groups of cells. The SP cells with lowest efflux of Hoechst dye contained the highest progenitor activity (day-7-14 CAFC). The highest day-35 CAFC frequencies, nearly 6000 times those of normal marrow, were seen in the SP cells with the greatest efflux of the Hoechst dye. Murine SP cells contain both progenitor and primitive populations of hematopoietic stem cells. The most primitive stem cells measured in the in vitro CAFC assay mark for Sca(+) and CD34(-) and have a high ability to efflux Hoechst dye. Isolation of these cells may provide the means to directly study mechanisms of primitive stem cell damage.

Neuroimaging of animal models of brain disease.

The main aim of this review is to describe some of the many animal models that have proved to be valuable from a neuroimaging perspective. This paper complements other articles in this volume, with a focus on animal models of the pathology of human brain disorders for investigations with modern non-invasive neuroimaging techniques. The use of animal model systems forms a fundamental part of neuroscience research efforts to improve the prevention, diagnosis, understanding and treatment of neurological conditions. Without such models it would be impossible to investigate such topics as the underlying mechanisms of neuronal cell damage and death, or to screen compounds for possible anticonvulsant properties. The adequacy of any one particular model depends on the suitability of information gained during experimental conditions. It is important, therefore, to understand the various types of animal model available and choose an appropriate model for the research question.

Ischemic preconditioning attenuates the oxidant-dependent mechanisms of reperfusion cell damage and death in rat liver.

In an in vivo rat model of liver ischemia followed by reperfusion a consistent appearance of necrosis and activation of biochemical pathways of apoptosis was reproduced and monitored after 30 minutes reperfusion. Preconditioning by application of a short cycle of ischemia-reperfusion (10 minutes + 10 minutes) positively conditioned recovery of the organ at reperfusion, attenuating both necrotic and apoptotic events. Preconditioning at least halved cell oxidative damage occurring early at reperfusion, and as a major consequence, the increase of cytolysis and apoptosis occurring at reperfusion was about 50% less. The attenuation of both pathways of cell death by preconditioning appeared at least partly related to its modulate action on H(2)O(2) and 4-hydroxy-2,3-trans-nonenal production. The overall data point to a marked diminished oxidant generation and oxidative reactions as one major possible mechanism through which ischemic preconditioning exerts protection against necrotic and apoptotic insult to the postischemic liver.

Regulation of Apoptosis in Endocrine Autoimmunity

Dysregulation of apoptosis is associated with the pathogenesis of organ-specific autoimmune diseases, through altered target organ susceptibility. Apoptosis signaling pathways can be initiated through activation of death receptors such as Fas. A comparative analysis of the expression of Fas and FasL, the antiapoptotic molecule Bcl-2, and apoptosis in both thyrocytes and thyroid-infiltrating lymphocytes (TILs) from patients with either Graves' disease (GD) or Hashimoto's thyroiditis (HT) was performed. GD thyrocytes expressed less Fas than HT thyrocytes, whereas GD TILs had higher levels of Fas and FasL than HT TILs. GD thyrocytes expressed higher levels of Bcl-2 compared with HT thyrocytes. The opposite pattern was observed in GD (low Bcl-2) and HT (high Bcl-2) TILs. Consistently, thyrocyte apoptosis was marked in HT and poor in GD thyroids, and TIL apoptosis was marked in GD and poor in HT. Our findings suggest that in GD thyroid the regulation of Fas/FasL/Bcl-2 favors apoptosis of infiltrating lymphocytes. Moreover, the reduced levels of Fas/FasL and increased levels of Bcl-2 should favor thyrocyte survival and hypertrophy associated with stimulatory thyroid-stimulating hormone receptor antibodies. In contrast, the regulation of Fas/FasL/Bcl-2 expression in HT can promote thyrocyte apoptosis via homophylic Fas-FasL interactions, and a gradual reduction in thyrocyte numbers leading to hypothyroidism. Fas-mediated apoptosis may be a general mechanism of cell damage in destructive organ-specific autoimmunity.

La maladie de Berger chez l’enfant

Berger’s disease or IgA nephropathy (NIgA) is the most common form of glomerulonephritis in the world. In children macroscopic haematuria is the first sign in about 80% of the patients. Renal failure appears in 20% of cases after twenty years of follow-up. The most important prognosis indicators are a nephrotic syndrome at the onset, a proteinuria > 1 g/24 hours, diffuse tubulo-interstitial lesions and extracapillary proliferation with crescents in more than 50% of the glomeruli. The pathogenic mechanisms are just emerging and involve a disrupted process of the systemic tolerance to mucosal antigen with abnormal mucosal γδT cell repertoire, abnormally glycosylated IgA1 molecules and a down-regulation of Fcα receptors on blood cells. After IgA deposition, the mechanisms of mesangial cell damage and activation involve vascular factors as endothelin/nitric oxide system, cytokines and growth factors such as interleukine-6, platelet derived growth factor and transforming growth factor β. There is no curative treatment but steroids are useful in diffuse proliferative extracapillary forms, when histological activity score is high with a short delay between diagnosis and treatment, or for moderately severe NIgA with normal renal function.

Oxidative stress, age-dependent [correction of age-related] cell damage and antioxidative mechanisms

Cellular oxidative stress is due to the production of reactive oxygen species (ROS), on the one hand, and weaknesses of the antioxidative defence, on the other. This is particularly true for cells with an active metabolism such as neurons and muscle cells, but it is also relevant for all other cell types. Hydrogen peroxide is an important member of ROS and is generated predominantly by mitochondria. In combination with reduced trace metals such as iron or copper, hydrogen peroxide is transformed into the highly reactive hydroxyl radical which causes damage to virtually all macromolecules. Oxidation of nucleic acids results in mutations while protein denaturation leads to enzyme defects and impairment of the cytoskeleton. Lipid peroxidation in cell membranes is strongly involved in the perturbation of ion homeostasis. Because this cell damage ultimatively causes cell death, oxidative stress initiates several diseases. Mitochondria play a major role in this context because they are the main source of endogenous oxidative stress and additionally function as an inducer of programmed cell death (apoptosis). Several strategies of antioxidative defence exist: While transition metals can be inactivated by chelating proteins (e.g., ferritin), ROS can be reduced enzymatically (e.g., by the glutathione peroxidase) or non-enzymatically by antioxidants (e.g., by vitamin E, vitamin C and glutathione). Stress proteins are implicated in the repair and transport of denatured proteins as well as in the inhibition of apoptosis.

5-s-Cysteinyl-conjugates of catecholamines induce cell damage, extensive DNA base modification and increases in caspase-3 activity in neurons.

A decrease in reduced glutathione levels in dopamine containing nigral cells in Parkinson's disease may result from the formation of cysteinyl-adducts of catecholamines, which in turn exert toxicity on nigral cells. We show that exposure of neurons (CSM 14.1) to 5-S-cysteinyl conjugates of dopamine, L-DOPA, DOPAC or DHMA causes neuronal damage, increases in oxidative DNA base modification and an elevation of caspase-3 activity in cells. Damage to neurons was apparent 12-48 h of post-exposure and there were increases in caspase-3 activity in neurons after 6 h. These changes were paralleled by large increases in pyrimidine and purine base oxidation products, such as 8-OH-guanine suggesting that 5-S-cysteinyl conjugates of catecholamines are capable of diffusing into cells and stimulating the formation of reactive oxygen species (ROS), which may then lead to a mechanism of cell damage involving caspase-3. Indeed, intracellular ROS were observed to rise sharply on exposure to the conjugates. These results suggest one mechanism by which oxidative stress may occur in the substantia nigra in Parkinson's disease.

The influence of calcium channel blockers on the brain free fatty acid level and glutathione peroxidase activity in rats with lithium and pilocarpine‐induced status epilepticus

AbstractThe aim of this study was to investigate possible therapeutic approach to neuronal damage caused by status epilepticus. The effects of the L‐type voltage‐sensitive calcium channel blockers (nimodipine, nicardipine) and NMDA blockers (ifenprodil and MK‐801) on the brain free fatty acid (FFA) level and glutathione peroxidase (GPX) activity in rats with lithium and pilocarpine (LiPi) ‐ induced status epilepticus were examined. Vehicle or various doses of calcium channel and NMDA blockers had been injected i.p. 30 min after the pilocarpine application. Tested doses of nicardipine and MK‐801 did not influence the increase in the brain FFA level. Nimodipine and ifenprodil revealed a tendency to reduce FFA level. The inhibition of L‐type voltage‐sensitive Ca2+ channels or NMDA receptor ‐ associated channels was not sufficient for significant attenuation of an increase in the rat brain FFA content and a decrease GPX activity associated with LiPi ‐ induced status epilepticus. Individual compounds have shown to prevent FFA increase, suggesting some alternative or additional mechanism of action. The prevention of FFA accumulation was not followed by the prevention of GPX decrease indicating the activation of non FFA‐related mechanisms of cell damage.

Carboxymethyl cellulose protects algal cells against hydrodynamic stress

The harmful effect of direct air sparging on Phaeodactylum tricornutum microalgal cultures was investigated in bubble columns and airlift photobioreactors with various superficial air velocities and two types of spargers which generated different sizes of bubbles. Small bubbles bursting at the surface of the culture were apparently the main cause of cell damage in batch cultures in laboratory-scale bubble columns. Other mechanisms of cell damage also were a contributing factor to the observed cell loss in outdoor pilot-scale bubble columns. Supplementation of the microalgal culture medium with carboxymethyl cellulose at concentrations of 0.02% and greater is shown to protect the algal cells against aeration-induced hydrodynamic stress.

Differential Effects of Caspase-1/Interleukin-1β–Converting Enzyme on Acinar Cell Necrosis and Apoptosis in Severe Acute Experimental Pancreatitis

There is recent experimental evidence that inhibition of caspase-1/interleukin-1β converting enzyme (ICE) significantly ameliorates overall severity and survival in severe acute experimental pancreatitis. However, little is known about the effects of this approach on the dynamics and mechanisms of local acinar cell damage, which we aimed to investigate in the present study. Severe acute pancreatitis (SAP) was induced by retrograde infusion of 4% sodium taurocholate in rats treated with isotonic saline or a highly selective, irreversible inhibitor of ICE. After 3, 6, and 24 hours, 3 and 7 days, acinar cell death by necrosis and apoptosis, as well as intrapancreatic and systemic interleukin-1β (IL-1β) and tumor necrosis factor-α (TNF-α) expression, was assessed. Treatment with the ICE inhibitor significantly reduced the extent of acinar cell necrosis accounting for major parenchymal destruction. In contrast, apoptosis was confined to the postacute course of the disease and was closely related to tubular complex formation, both remaining unchanged. Whereas intrapancreatic IL-1β mRNA expression was highly up-regulated in both treated and untreated animals, active IL-1β protein expression and subsequent neutrophil tissue infiltration was dramatically decreased in the ICE-inhibited group. Parallel to the onset of enhanced apoptotic acinar cell death and tubular complex formation, TNF-α mRNA and protein expression was up-regulated, with levels being lower in ICE inhibitor-treated rats. We conclude that activation of caspase-1/ICE plays a central role in the progression of acinar cell death by necrosis in SAP. Herein, IL-1β–mediated neutrophil infiltration seems to be a crucial step in enhanced cellular destruction. In contrast, acinar cell apoptosis contributes to ductal transformation and is independent of this mechanism, but may be influenced by TNF-α

Glutamine synthelase in the mechanism of ammonia-induced gastric mucosal cell damage

Glutamine synthelase in the mechanism of ammonia-induced gastric mucosal cell damage

Glutamine synthelase in the mechanism of ammonia-induced gastric mucosal cell damage

Glutamine synthelase in the mechanism of ammonia-induced gastric mucosal cell damage

THE USE OF HYDROGEN PEROXIDE TO ENHANCE THE EFFICACY OF DOXORUBICIN HYDROCHLORIDE IN A MURINE BLADDER TUMOR CELL LINE

We determined whether the cytotoxicity of doxorubicin hydrochloride would be enhanced by adding hydrogen peroxide as a source of oxygen free radicals. Mouse bladder tumor cells (MBT-2) were grown in RPMI 1640 medium and treated with various concentrations of doxorubicin hydrochloride for 2 hours. Protein content was assayed as a measure of cell growth. A similar set of experiments was done with cells exposed to hydrogen peroxide only and combined doxorubicin and hydrogen peroxide. Protein content was again assayed as a measure of cell growth. Cells were also assayed for glutathione peroxidase and malonyl dialdehyde, a product of lipid peroxidation, to determine the mechanism of cell damage. Furthermore, MBT-2 cells were incubated with 100 M. alpha-tocopherol, a free radical scavenger, before exposure to hydrogen peroxide to determine whether the effects of hydrogen peroxide could be reversed. We observed a dose dependent inhibition of MBT-2 cell growth after exposure to doxorubicin hydrochloride. Exposure to doxorubicin and hydrogen peroxide resulted in greater cell growth inhibition than exposure to either agent alone. The effects of hydrogen peroxide on cell proliferation were reversed by pre-incubation with alpha-tocopherol. As a source of oxygen free radicals, hydrogen peroxide enhances the antiproliferative effect of doxorubicin hydrochloride on a mouse bladder tumor cell line. Thus, hydrogen peroxide may be a relatively inexpensive, nontoxic method of augmenting the cytotoxicity of doxorubicin hydrochloride. Further studies are warranted to determine whether these observations may have clinical application.

The cytotoxic effects of diesel exhaust particles on human pulmonary artery endothelial cells in vitro: role of active oxygen species

Diesel exhaust particles (DEP) have been proved to induce serious pulmonary injury, among which lethal pulmonary edema has been assumed to be mediated by vascular endothelial cell damage. In the present study, we investigated the cytotoxic mechanism of DEP on human pulmonary artery endothelial cells focusing on the role of active oxygen species. Endothelial cell viability was assessed by WST-8, a novel tetrazolium salt. Nitric oxide (NO) production was measured by using a new fluorescence indicator, diaminofluorescein-2 (DAF-2). Organic compounds in DEP were extracted by dichloromethane and methanol. DEP-extracts damaged endothelial cells under both subconfluent and confluent conditions. The DEP-extract-induced cytotoxicity was markedly reduced by treatment with SOD, catalase, N-(2-mercaptopropionyl)-glycine (MPG), or ebselen (a selenium-containing compound with glutathione peroxidase-like activity). Thus superoxide, hydrogen peroxide, and other oxygen-derived free radicals are likely to be implicated in DEP-extract-induced endothelial cell damage. Moreover, L-NAME and L-NMA, inhibitors of NO synthase, also attenuated DEP-extract-induced cytotoxicity, while sepiapterin, the precursor of tetrahydrobiopterin (BH 4, a NO synthase cofactor) interestingly enhanced DEP-extract-induced cell damage. These findings suggest that NO is also involved in DEP-extract-mediated cytotoxicity, which was confirmed by direct measurement of NO production. These active oxygen species, including peroxynitrite, may explain the mechanism of endothelial cell damage upon DEP exposure during the early stage.

Identification of a peptide sequence in albumin that potentiates superoxide production by microglia.

Microglial activation has recently been recognized as a cause of damage in various neurodegenerative diseases. A possible mechanism underlying this damage is the activation of microglia by serum factors leaked through a disruption of the blood-brain barrier, which in turn trigger microglial cell proliferation and the release of various substances toxic to neurons, such as superoxide (O(2)(-)). We recently reported that serum albumin enhanced O(2)(-) production in cultured rat microglia stimulated by phorbol ester. In the present report, we identify the active site of this enhancement within the albumin molecule. We purified an active subfragment from trypsin-treated bovine serum albumin that was composed of 12-mer and 33-mer peptides connected by a disulfide bond. The chemically synthesized 12-mer peptide showed activity within a concentration range ( approximately 10(-7) M:) equivalent to that of albumin. The activities of a series of synthesized peptides conclusively indicated that the minimum active sequence was Leu-His-Thr-Leu. The present study may shed light on the mechanism of neuronal cell damage in various neurodegenerative diseases.

Astroglial cell death induced by excessive influx of sodium ions

Na + influx has been implicated to play an important role in the mechanisms of neuronal cell damage under ischemia as well as in neurodegenerative disorders. Thus far, however, the effects of Na + influx on astrocytic damage have not been studied extensively. In the present study, we have examined the effects of Na + influx induced by veratridine (Na + channel opener), monensin (Na + ionophore), and glutamate (co-transportation with Na +) on rat cultured astroglial damage. Cells were incubated with bicarbonate buffer with 25 mM glucose containing either 100 μM veratridine, 10 μM monensin, or 1 mM glutamate with or without 1 mM ouabain for 20 h. Cellular damage was evaluated quantitatively by lactate dehydrogenase (LDH) release or 3-(4,5-dimethylthiazol-2-yl)-2,5-diphenyltetrazolium bromide (MTT) reduction. Veratridine, monensin, or glutamate alone did not induce significant astroglial damage. Veratridine and monensin co-incubated with ouabain, which inhibits active extrusion of Na + by Na +,K +-ATPase, thereby enhances intracellular Na + accumulation, caused significant cell death ( P<0.001, approximately 50% cell damage), whereas glutamate did not. Na +-free solution substituted by choline (impermeable cation) attenuated cell damage induced by veratridine and monensin markedly, while Li + substitution (permeable cation) rather exacerbated. Nifedipine (100 μM), a blocker of l-type Ca 2+ channel, reduced veratridine-induced glial damage by 50%. Neither bepridil nor benzamil, a blocker of Na +–Ca 2+ exchanger, had any protection. Cyclosporin A (1 or 10 μM), an inhibitor of mitochondrial permeability transition or 10 μM N-benzyloxycarbonyl-Val-Ala-Asp-( O-methyl)fluoromethyl ketone (zVAD-fmk), which inhibits a broad range of caspases, did not show protective effects.

Motor neuron cell death in a mouse model of FALS is not mediated by the p53 cell survival regulator

Mutant Cu/Zn superoxide dismutase (SOD1) associated with familial amyotrophic lateral sclerosis (FALS) causes selective motor neuron loss through unknown mechanisms of cell damage. Damaged neurons frequently undergo apoptosis mediated by the p53 cell survival regulator. We therefore studied whether motor neuron disease (MND) in mice expressing the human SOD1 mutant G93A is dependent on p53 by crossing G93A mice with p53-knockout mice. Since p53−/− mice’s life expectance is usually shorter (160±49 days, n=11) than the time at which the G93A mice die from MND (212±50 days, n=7), only a few of the G93A/p53−/− double transgenics were expected to live to experience MND. Nevertheless, four of the 22 G93A/p53−/− mice succumbed to MND after 160±28 days, as expected under these conditions of competing death risks if the absence of p53 fails to protect from MND. Thus, MND in mice expressing G93A does not require p53. This conclusion is supported by histology: pre-symptomatic G93A mice display disease-associated vacuoles within the dendrites of motor neurons regardless of p53 status.

Hypomethylation as a cause of homocysteine-induced cell damage in human cell lines

Despite the growing evidence that plasma homocysteine is a cardiovascular risk factor, the mechanism behind the vascular injuries is still unknown. In the present study we have investigated the possible role of hypomethylation as a cause of homocysteine-induced cell damage in two human cell lines. A significant growth retardation was observed in HeLa cell cultures in the combined presence of homocysteine and adenosine, but first at concentrations of 250 μmol/l of each. A significant decrease of intracellular glutathione concentration was noted both in the presence of homocysteine (250 μmol/l) alone and in the presence of the combination of homocysteine and adenosine (250 μmol/l). Intracellular concentration of homocysteine was increased to a similar extent both in the presence of homocysteine alone and in the presence of a combination of homocysteine and adenosine. Similar findings to those described for HeLa cell cultures were observed in endothelial cell cultures. Furthermore, in the presence of copper ions together with 100 μmol/l of adenosine and homocysteine a significantly retarded cell growth was observed in HeLa cell cultures. This finding shows that a combination of two potentially cell-damaging mechanisms (formation of oxygen radicals and hypomethylation) aggravated the retardation of cell growth compared to only one of these mechanisms being present. Thus, it is likely that several mechanisms of homocysteine-induced cell damage contribute to the increased rate of the atherogenic process observed in hyperhomocysteinemia.