Biomedical subjects

V Vallyathan

Publications and source records attributed to V Vallyathan.

At least 37 records · Page 2Linked to original sources

PubMed2001

Transactivation of RARE and GRE in the cellular response to arsenic.

Arsenic compounds are a somewhat unique class of metals, which have been considered as both carcinogens and chemotherapeutic agents for cancers. Tumor promotion effects of arsenic are believed to be associated with its transactivational activities on transcription factors, such as AP-1 and NFkappaB, while the induction of cell apoptosis and differentiation by arsenic is considered to be a mechanism for the chemotherapeutic effects of arsenic. Here, we found that exposure of cells to arsenite and arsenate leads to transactivation of retinoic acid response elements (RARE) and glucocorticoid response elements (GRE) in mouse epidermal JB6 cells. These inductions occur in a time-dependent manner. Furthermore, induction of RARE activity by arsenic was synergistically enhanced by co-treatment of cells with retinoic acid, while GRE activation by arsenic was not affected by combined treatment of cells with fluocinolone acetonide (FA). In consideration of the important role of RARE and GRE in induction of cell differentiation, we speculate that transactivation of RARE and GRE by arsenic may be involved in its induction of cell differentiation and anti-cancer activities in addition to its induction of apoptosis.

Animals↗

PubMed2001

Cell apoptosis induced by carcinogenic metals.

Well-documented evidence suggests that environmental and occupational exposure of toxic metals or metal-containing compounds can cause a number of human diseases, including inflammation and cancer, through DNA damage, protein modifications, or lipid peroxidation. This mini-review addresses the mechanisms of cell death induced by some carcinogenic metals, including arsenic (III), chromium (VI) and vanadium (V). A possible contribution of reactive oxygen species to metal-induced cell death is also discussed.

Animals↗

PubMed2001

Arsenic-induced NFkappaB transactivation through Erks- and JNKs-dependent pathways in mouse epidermal JB6 cells.

Tumor promoting effects of arsenic are believed to be associated with its transactivation activity on transcription factors, such as AP-1 and NFkappaB. However, the results from different groups studying the effects of arsenic on NFkappaB activation are contradictory in different cell models. Since arsenic is a strong skin carcinogen, we have investigated the activation of NFkappaB by arsenic in a mouse skin epidermal cell line, JB6 cells. Exposure of cells to arsenite or arsenate led to NFkappaB transactivation in mouse epidermal JB6 NFkappaB-luciferase reporter stable transfectants, C141 NFkappaB mass1. This induction of NFkappaB activity by arsenic was dose- and time-dependent. The transactivation of NFkappaB by arsenic appeared to be through activation of Erks and JNKs pathways because increased NFkappaB activity by arsenic could be dramatically inhibited by either pre-treatment of cells with PD98059 or overexpression of dominant negative JNK1. That Erks activation is required for arsenic-induced NFkappaB transactivation was further supported by the findings that arsenic-induced NFkappaB transactivation was impaired in JB6 30.7b cells, which were deficient in Erks.

Animals↗

PubMed2001

Cr (VI) induces cell growth arrest through hydrogen peroxide-mediated reactions.

Cr (VI) compounds are widely used in industries and are recognized human carcinogens. The mechanism of carcinogenesis associated with these compounds is not well understood. The present study focused on Cr (VI)-induced cell growth arrest in human lung epithelial A549 cells, using flow cytometric analysis of DNA content. Treatment of the cells with Cr (VI) at 1 microM caused a growth arrest at G2/M phase. An increase in Cr (VI) concentration enhanced the growth arrest. At a concentration of 25 microM, Cr (VI)-induced apoptosis became apparent. Superoxide dismutase (SOD) or sodium formate did not alter the Cr (VI)-induced cell growth arrest. While catalase inhibited growth, indicating H2O2 is an important mediator in Cr (VI)-induced G2/M phase arrest. Electron spin resonance (ESR) spin trapping measurements showed that incubation of cells with Cr (VI) generated hydroxyl radical (*OH). Catalase inhibited the *OH radical generation, indicating that H2O2 was generated from cells stimulated by Cr (VI), and that H2O2 functioned as a precursor for *OH radical generation. The formation of H2O2 from Cr (VI)-stimulated cells was also measured by the change in fluorescence of scopoletin in the presence of horseradish peroxidase. The mechanism of reactive oxygen species generation involved the reduction of molecular oxygen as shown by oxygen consumption assay. These results support the following conclusions: (a) Reactive oxygen species are generated in Cr (VI)-stimulated A549 cells through reduction of molecular oxygen, (b) Among the reactive oxygen species generated, H2O2 played a major role in causing G2/M phase arrest in human lung epithelial cells.

Antioxidants↗

PubMed2000

Induction of activator protein-1 through reactive oxygen species by crystalline silica in JB6 cells.

We reported previously that freshly fractured silica (FFSi) induces activator protein-1 (AP-1) activation through extracellular signal-regulated protein kinases (ERKs) and p38 kinase pathways. In the present study, the biologic activities of FFSi and aged silica (ASi) were compared by measuring their effects on the AP-1 activation and phosphorylation of ERKs and p38 kinase. The roles of reactive oxygen species (ROS) in this silica-induced AP-1 activation were also investigated. We found that FFSi-induced AP-1 activation was four times higher than that of ASi in JB6 cells. FFSi also caused greater phosphorylation of ERKs and p38 kinase than ASi. FFSi generated more ROS than ASi when incubated with the cells as measured by electron spin resonance (ESR). Studies using ROS-sensitive dyes and oxygen consumption support the conclusion that ROS are generated by silica-treated cells. N-Acetylcysteine (an antioxidant) and polyvinyl pyridine-N-oxide (an agent that binds to Si-OH groups on silica surfaces) decreased AP-1 activation and phosphorylation of ERKs and p38 kinase. Catalase inhibited phosphorylation of ERKs and p38 kinase, as well as AP-1 activation induced by FFSi, suggesting the involvement of H(2)O(2) in the mechanism of silica-induced AP-1 activation. Sodium formate (an ( small middle dot)OH scavenger) had no influence on silica-induced MAPKs or AP-1 activation. Superoxide dismutase enhanced both AP-1 and MAPKs activation, indicating that H(2)O(2), but not O(2), may play a critical role in silica-induced AP-1 activation. These studies indicate that freshly ground silica is more biologically active than aged silica and that ROS, in particular H(2)O(2), play a significant role in silica-induced AP-1 activation.

Animals↗

PubMed2000

Vanadate induces p53 transactivation through hydrogen peroxide and causes apoptosis.

Vanadium is a metal widely distributed in the environment. Although vanadate-containing compounds exert potent toxic effects on a wide variety of biological systems, the mechanisms controlling vanadate-induced adverse effects remain to be elucidated. The present study investigated the vanadate-induced p53 activation and involvement of reactive oxygen species (ROS) in p53 activation as well as the role of p53 in apoptosis induction by vanadate. Exposure of mouse epidermal JB6 cells to vanadate led to transactivation of p53 activity in a time- and dose-dependent manner. It also caused mitochondrial damage, apoptosis, and generated ROS. Scavenging of vanadate-induced H(2)O(2) by N-acetyl-l-cysteine (a general antioxidant) or catalase (a specific H(2)O(2) inhibitor), or the chelation of vanadate by deferoxamine, resulted in inhibition of p53 activation and cell mitochondrial damage. In contract, an increase in H(2)O(2) generation in response to superoxide dismutase or NADPH enhanced these effects caused by vanadate. Furthermore, vanadate-induced apoptosis occurred in cells expressing wild-type p53 (p53+/+) but was very weak in p53-deficient (p53-/-) cells. These results demonstrate that vanadate induces p53 activation mainly through H(2)O(2) generation, and this activation is required for vanadate-induced apoptosis.

Acetylcysteine↗

PubMed2000

Arsenic mediates cell proliferation and gene expression in the bladder epithelium: association with activating protein-1 transactivation.

Although the mechanism of action has not yet been defined, epidemiological studies have demonstrated an association between elevated arsenic levels in drinking water and the incidence of urinary bladder transitional cell carcinomas. In the current studies, we demonstrate that mice exposed to 0.01% sodium arsenite in drinking water develop hyperplasia of the bladder urothelium within 4 weeks of exposure. This was accompanied by the accumulation of inorganic trivalent arsenic, and to a lesser extent dimethylarsinic acid, in bladder tissue, as well as a persistent increase in DNA binding of the activating protein (AP)-1 transcription factor. AP-1 transactivation by arsenic also occurred in bladders of transgenic mice containing an AP-1 luciferase reporter. Consistent with these in vivo observations, arsenite increased cell proliferation and AP-1 DNA binding in a human bladder epithelial cell line. Gene expression studies using RNase protection assays, reverse transcription-PCR, and cDNA microarrays indicated that arsenite alters the expression of a number of genes associated with cell growth, such as c-fos, c-jun, and EGR-1, as well as cell arrest, such as GADD153 and GADD45. The proliferation-enhancing effect of arsenic on uroepithelial cells likely contributes to its ability to cause cancer.

Animals↗

PubMed2000

Antioxidant properties of (-)-epicatechin-3-gallate and its inhibition of Cr(VI)-induced DNA damage and Cr(IV)- or TPA-stimulated NF-kappaB activation.

Electron spin resonance (ESR) spin trapping was utilized to investigate the scavenging effects on hydroxyl radicals (*OH) and superoxide radicals (O2*-) by (-)-epigallocatechin-3-gallate (EGCG), one of the major anticancer compounds in tea. The spin trap used was 5,5-dimethyl-pyrroline N-oxide (DMPO). The Fenton reaction (Fe2+ + H2O2-->Fe3+ + *OH + OH-) was used as a source of *OH radicals. EGCG efficiently scavenges *OH radicals with reaction rate of 4.62 x 10(11) M(-1)sec(-1), which is an order of magnitude higher than several well recognized antioxidants, such as ascorbate, glutathione and cysteine. It also scavenges O2*- radicals as demonstrated by using xanthine and xanthine oxidase system as a source of O2*- radicals. Through its antioxidant properties, EGCG exhibited a protective effect against DNA damage induced by Cr(VI). EGCG also inhibited activation of nuclear transcription factor NF-kappaB induced by Cr(IV) and 12-o-tetradecanoylphorbol-13-acetate (TPA). The present studies provide a mechanistic basis for the reported anticarcinogenic properties of EGCG and related tea products.

Antioxidants↗

PubMed2000

Impairment of NF-kappaB activation and modulation of gene expression by calpastatin.

To address the involvement of the calpain system in both basal and silica-induced nuclear factor (NF)-kappaB activation, several human bronchial epithelial cell lines were established in which an intracellular inhibitor of calpain, calpastatin, was stably expressed. Reduced basal and silica-induced inhibitor (IkappaBalpha) degradation and NF-kappaB activation were observed in cells stably overexpressing calpastatin. In addition, the cells in which calpain was constitutively inhibited by the overexpression of calpastatin exhibited a notable morphological change. Whereas empty vector-transfected cells displayed a morphology indistinguishable from that of parental cells, cells overexpressing calpastatin exhibited a mosaic morphological change with reduced formation of lamella 30 min after the cells were seeded. Genefilter microarray experiments, in which 3,965 human genes can be evaluated for their expression at the same time, showed that calpastatin downregulated genes encoding several membrane-associated proteins or nuclear proteins and upregulated genes of collagen alpha2, DAZ, and mitochondrial capsule selenoprotein. These results suggest that, in addition to their proteolytic activities on cytoskeletal proteins and other cellular regulatory proteins, calpain-calpastatin systems can also affect the expression levels of genes encoding structural or regulatory proteins.

Adrenergic beta-Agonists↗

PubMed2000

Effect of antioxidant protection by p-coumaric acid on low-density lipoprotein cholesterol oxidation.

Mechanisms in which p-coumaric acid (CA) acts as an antioxidant are not well understood. This study investigated whether CA can act as a direct scavenger of reactive oxygen species (ROS) and whether it minimizes the oxidation of low-density lipoprotein (LDL). Rats were administered CA in drinking water at low or high doses for 10, 21, and 30 days (uptakes were 29 and 317 mg/day, respectively). Blood levels of 8-epiprostaglandin F(2alpha) were monitored as a marker of LDL oxidation. Oral administration of CA (317 mg/day) for 30 days significantly inhibited LDL oxidation. CA also reduced LDL cholesterol levels in serum but had no effect on levels of high-density lipoprotein cholesterol. In vitro studies that used electron spin resonance in combination with spin trapping techniques were used to determine the ability of CA to scavenge ROS and alter LDL oxidation. CA effectively scavenged.OH in a dose-dependent manner. IC(50) and maximum velocity for CA scavenging of.OH were 4. 72 microM and 1.2 microM/s, respectively, with a rate constant of 1. 8 x 10(11) M(-1). s(-1). Our studies suggest that the antioxidant properties of CA may involve the direct scavenging of ROS such as.OH.

Animals↗

PubMed2000

Mast cell basic fibroblast growth factor in silicosis.

To investigate the role of mast cells (MC) and their fibrogenic growth factors in silicosis, we performed quantitative immunohistochemistry for MC tryptase and for basic fibroblast growth factor (bFGF) in lung tissue from silicotic and control subjects. Anti-bFGF antibody was bound to lung MC, basement membrane, endothelial cells, and smooth-muscle cells. Morphometric analysis revealed that the volume density (V(v)) of MC was increased in silicotic lung and that the V(v) of bFGF-positive (bFGF(+)) cells was significantly higher than normal in silicotic lung. Most MC contained bFGF (rho = 0.88, p < 0.001). The V(v) of collagen/reticulin fibers was increased in silicosis and correlated with the V(v) of bFGF(+) cells (rho = 0.81, p < 0.001). Immature silicotic nodules contained bFGF(+) MC throughout the loose array of collagen/reticulin fibers. In large, mature nodules, the density of collagen/reticulin fibers was higher, and bFGF(+) MC were found only in the nodule periphery. Because of this circumferential MC alignment in silicotic nodules, we observed a negative correlation between the V(v) of bFGF(+) MC and the density of collagen/reticulin fibers in silicotic nodules (rho = -0.80, p < 0.001) and between the V(v) of all other nodule-associated cells and the density of collagen/reticulin fibers in the hypocellular nodule centers (rho = -0.84, p < 0.001). We conclude that MC that produce bFGF may play an important role in the development of silicosis.

Aged↗

PubMed2000

Changes in bronchoalveolar lavage indices associated with radiographic classification in coal miners.

Previous studies on symptomatic coal miners have shown that alveolar macrophages, recovered by bronchoalveolar lavage (BAL), release excessive amounts of reactive oxygen species (ROS) and inflammatory cytokines. It has been proposed that these secretions may mediate cell injury and initiate the disease process. We hypothesized that acellular bronchoalveolar lavage fluid (BALF) indices in coal miners chronically exposed to coal dust may reflect the status of important homeostatic modulations in the lung that lead to the development of coal workers' pneumoconiosis (CWP). To test this hypothesis, we measured inflammatory status, oxidant burden, antioxidant defenses, cytokines, growth factors, fibronectin, and alpha(1)-antitrypsin (alpha(1)-AT) in the BALF of healthy never-smoker control subjects, never-smoker underground coal miners with negative radiographs (ILO 0/0-1/0), and two miners with moderate changes in the chest radiographs (ILO 2/2). Interestingly, indices of injury and inflammation increased with the progression of disease in coal miners. Antioxidant enzymes, such as catalase, glutathione peroxidase, and superoxide dismutase, showed a 19-fold, 22-fold, and 6-fold increase above control, respectively, in coal miners with category 2/2 CWP. Significant increases in the secretion of IL-1, IL-6, TNF-alpha, TGF-beta, fibronectin, and alpha(1)-AT also were evident in coal miners with disease. This up-regulation of antioxidant defenses and cytokines was not evident in coal miners in the absence of clinically evident radiographic disease. In addition, the concentration of lipid peroxidation by products in the BALF of coal miners without evidence of radiographic disease showed a moderate 3-fold increase, whereas, in coal miners with category 2/2 CWP it showed a 59-fold increase compared to control subjects. These results are in good agreement with our hypothesis that development of CWP and its progression may be correlated with an oxidative stress and up-regulation of cytokines and mediators of growth.

Adult↗

PubMed2000

Distribution of particulate matter and tissue remodeling in the human lung.

We examined the relationship between intrapulmonary particle distribution of carbonaceous and mineral dusts and remodeling of the airways along anatomically distinct airway paths in the lungs of Hispanic males from the central valley of California. Lung autopsy specimens from the Fresno County Coroner's Office were prepared by intratracheal instillation of 2% glutaraldehyde at 30 cm H(2)O pressure. Two distinct airway paths into the apico-posterior and apico-anterior portions of the left upper lung lobe were followed. Tissue samples for histologic analysis were generally taken from the intrapulmonary second, fourth, sixth, and ninth airway generations. Parenchymal tissues beyond the 12th airway generation of each airway path were also analyzed. There was little evidence of visible particle accumulation in the larger conducting airways (generations 2-6), except in bronchial-associated lymphoid tissues and within peribronchial connective tissue. In contrast, terminal and respiratory bronchioles arising from each pathway revealed varying degrees of wall thickening and remodeling. Walls with marked thickening contained moderate to heavy amounts of carbonaceous and mineral dusts. Wall thickening was associated with increases in collagen and interstitial inflammatory cells, including dust-laden macrophages. These changes were significantly greater in first-generation respiratory bronchioles compared to second- and third-generation respiratory bronchioles. These findings suggest that accumulation of carbonaceous and mineral dust in the lungs is significantly affected by lung anatomy with the greatest retention in centers of lung acini. Furthermore, there is significant remodeling of this transitional zone in humans exposed to ambient particulate matter.

Adolescent↗

PubMed2000

Silicosis and coal workers' pneumoconiosis.

Exposure to coal mine dust and/or crystalline silica results in pneumoconiosis with initiation and progression of pulmonary fibrosis. This review presents characteristics of simple and complicated coal workers' pneumoconiosis (CWP) as well as pathologic indices of acute and chronic silicosis by summarizing results of in vitro, animal, and human investigations. These results support four basic mechanisms in the etiology of CWP and silicosis: a) direct cytotoxicity of coal dust or silica, resulting in lung cell damage, release of lipases and proteases, and eventual lung scarring; b) activation of oxidant production by pulmonary phagocytes, which overwhelms the antioxidant defenses and leads to lipid peroxidation, protein nitrosation, cell injury, and lung scarring; c) activation of mediator release from alveolar macrophages and epithelial cells, which leads to recruitment of polymorphonuclear leukocytes and macrophages, resulting in the production of proinflammatory cytokines and reactive species and in further lung injury and scarring; d) secretion of growth factors from alveolar macrophages and epithelial cells, stimulating fibroblast proliferation and eventual scarring. Results of in vitro and animal studies provide a basis for proposing these mechanisms for the initiation and progression of pneumoconiosis. Data obtained from exposed workers lend support to these mechanisms.

Air Pollutants, Occupational↗

PubMed2000

Role of molecular oxygen in the generation of hydroxyl and superoxide anion radicals during enzymatic Cr(VI) reduction and its implication to Cr(VI)-induced carcinogenesis.

Electron spin resonance (ESR) spin trapping measurements provide evidence for the generation of hydroxyl radicals (*OH) in the reduction of Cr(VI) by glutathione reductase (GSSG-R) in the presence of NADPH as a cofactor. Catalase inhibited the *OH generation, while the addition of H2O2 enhanced it, indicating that the *OH radical generation involves a Fenton-like reaction. The metal chelator, deferoxamine, inhibited the *OH generation with a concomitant generation of a deferoxamine nitroxide radical. EDTA and 1,10-phenanthroline also inhibited the *OH generation. Experiments performed under argon atmosphere decreased the yield of the *OH formation, showing that molecular oxygen plays a critical role. ESR spin trapping and measurements of fluorescence change of scopoletin in the presence of horseradish peroxidase show that reduction of Cr(VI) by GSSG-R/NADPH generates superoxide anion radicals (O2*-) as well as H2O2. It can be concluded that *OH radical is generated by the reaction of H2O2 with Cr(V), which is produced by enzymatic one-electron reduction of Cr(VI). H2O2 is produced by the reduction of molecular oxygen via O2*- as an intermediate. The *OH radicals generated by these reactions are capable of causing DNA strand breaks, which can be inhibited by catalase, formate, and experiments performed under argon.

Carcinogenicity Tests↗

PubMed2000

Predisposing factors in occupational lung cancer: inorganic minerals and chromium.

Reactive oxygen species (ROS) have been implicated in the pathogenesis of cancer. Inhalation of inorganic minerals such as asbestos and crystalline silica, and metals such as arsenic, beryllium, chromium, nickel, and vanadium, may promote directly and indirectly enhanced generation of ROS at a persistent level in concert with chronic inflammation. Perpetual ROS generation can cause specific molecular changes resulting in the activation or inactivation of transcription factors that may alter gene expression leading to cell proliferation, differentiation, and carcinogenesis. The mechanisms involved in the signal transduction leading to these processes are the subject of intense investigation. In this review, some of the recent findings from our laboratories concerning key molecular events elicited by asbestos, crystalline silica, and chromium are presented. These include genotoxicity, DNA damage, lipid peroxidation, activation of transcription factors activator protein-1 (AP-1) or nuclear factor kappa B (NF-kappaB), and p53 or k-ras gene alterations. From these studies, it is evident that ROS signaling is critical for the responses of cytokines, growth factors, and activation or inactivation of transcription factors that promote carcinogenesis.

Asbestos↗

PubMed2000

Participation of MAP kinase p38 and IkappaB kinase in chromium (VI)-induced NF-kappaB and AP-1 activation.

Epidemiological studies demonstrate that environmental and occupational exposure of chromium(VI) [Cr(VI)] or Cr(VI)-containing particles can cause a number of human diseases, including inflammation and cancer. The biological mechanisms responsible for the initiation and progression of diseases resulting from exposure to Cr(VI) are not fully understood. The present studies evaluated the ability of Cr(IV) to induce activation of NF-kappaB and AP-1, two important transcription factors governing the expression of many early response genes involved in inflammation and carcinogenesis. The activation of NF-kappaB and AP-1 by Cr(IV) was dose dependent. Aspirin, a well-established antioxidant, substantially inhibited Cr(VI)-induced activation of both NF-kappaB and AP-1. SB202190, a specific inhibitor for p38, attenuated AP-1 activation induced by Cr(IV), whereas PD98059, a specific inhibitor for Erk, exhibited no effect on Cr(IV)-induced AP-1 activation. Blockage of NF-kappaB signaling pathway by a transient transfection of a dominant negative expressing vector for IkappaB kinase beta resulted in inhibition of Cr(IV)-induced NF-kappaB, but not AP-1 activation. These data suggest that the activation of AP-1 or NF-kappaB by Cr(IV) is through the involvement of MAP kinase or IKK pathway, respectively.

Animals↗

PubMed1999

Involvement of 5'-flanking kappaB-like sites within bcl-x gene in silica-induced Bcl-x expression.

The present study investigated the involvement of the transcription factor NF-kappaB in the expression of an anti-apoptotic gene, bcl-x, using a murine macrophage cell line and peritoneal macrophages from both wild type (p50(+/+)) and NF-kappaB p50 gene knockout (p50(-/-)) mice. Increased expression of Bcl-x protein was observed in native and silica-exposed p50(-/-) macrophages in which the NF-kappaB p65-containing complex was predominantly induced. Co-transfection experiment using a bcl-x promoter reporter construct and an expression vector for NF-kappaB p50 or p65 indicates that p65, but not p50, up-regulates the promoter activity of the bcl-x gene. DNA sequence analysis revealed that there are several kappaB-like sites within the 5'-flanking region of the bcl-x gene. Electrophoretic mobility shift assay suggested differences in binding of the NF-kappaB complexes to these putative NF-kappaB binding sites of the bcl-x gene.

Animals↗