PubMed Health⌕ Search

Biomedical subjects

C Bernstein

Publications and source records attributed to C Bernstein.

At least 19 recordsLinked to original sources
PubMed2006

Deoxycholate induces mitochondrial oxidative stress and activates NF-kappaB through multiple mechanisms in HCT-116 colon epithelial cells.

Nuclear factor kappa B (NF-kappaB) is a redox-associated transcription factor that is involved in the activation of survival pathways. We have previously shown that deoxycholate (DOC) activates NF-kappaB in hepatocytes and colon epithelial cells and that persistent exposure of HCT-116 cells to increasing concentrations of DOC results in the constitutive activation of NF-kappaB, which is associated with the development of apoptosis resistance. The mechanisms by which DOC activates NF-kappaB in colon epithelial cells, and whether natural antioxidants can reduce DOC-induced NF-kappaB activation, however, are not known. Also, it is not known if DOC can generate reactive oxygen species within mitochondria as a possible pathway of stress-related NF-kappaB activation. Since we have previously shown that DOC activates the NF-kappaB stress-response pathway in HCT-116 cells, we used this cell line to further explore the mechanisms of NF-kappaB activation. We found that DOC induces mitochondrial oxidative stress and activates NF-kappaB in HCT-116 cells through multiple mechanisms involving NAD(P)H oxidase, Na+/K+-ATPase, cytochrome P450, Ca++ and the terminal mitochondrial respiratory complex IV. DOC-induced NF-kappaB activation was significantly (P < 0.05) inhibited by pre-treatment of cells with CAPE, EGCG, TMS, DPI, NaN3, EGTA, Ouabain and RuR. The NF-kappaB-activating pathways, induced by the dietary-related endogenous detergent DOC, provide mechanisms for promotion of colon cancer and identify possible new targets for chemoprevention.

Antioxidants↗
PubMed2006

Esophageal acid exposure at pH < or = 2 is more common in Barrett's esophagus patients and is associated with oxidative stress.

Barrett's esophagus (BE) patients demonstrate a higher distal esophageal acid exposure profile than other gastroesophageal reflux disease patients. Cellular oxidative stress has been proposed to contribute to the development of BE and esophageal adenocarcinoma. However, a relationship between low esophageal pH and oxidative stress has yet to be elucidated. The aim of this study was to determine the duration of low pH exposure in the esophagus of BE patients compared to those with erosive esophagitis (EE) and to test if brief exposure to low pH leads to the induction of reactive oxygen species (ROS). Seventy-three patients with BE or EE were evaluated by 24-hour esophageal pH monitoring and the percentage of time during which there was exposure to pH < or = 4 and pH < or = 2 was recorded. In vitro, Seg-1 and Het-1A cells were evaluated after brief exposure to pH4 or pH2 by flow cytometry and fluorescent microscopy for the production of ROS. BE patients demonstrated a significantly higher exposure to low pH values (pH < or = 2) than EE patients. The mean percent total time, duration and mean number of reflux episodes at pH < or = 2 were 2.8 +/- 0.53%, 28.8 +/- 3.6 seconds and 79 +/- 11.4 episodes in BE patients, whereas in EE patients they were significantly less, 1.16 +/- 0.3%, 15.6 +/- 1.2 seconds and 48.3 +/- 8.8 episodes, respectively (P < 0.05). In vitro experiments indicate that esophageal cells, when exposed to pH 2, produce ROS. In vitro studies using brief pH 2 exposure are biologically relevant to the clinical situation. Our studies indicate that such exposure induces oxidative stress. This stress may cause DNA damage, mutations and progression to cancer.

Adenocarcinoma↗
PubMed2005

Bile acids as carcinogens in human gastrointestinal cancers.

Bile acids were first proposed to be carcinogens in 1939 and 1940. On the basis of later work with rodent models, bile acids came to be regarded as cancer promoters rather than carcinogens. However, considerable indirect evidence, obtained more recently, supports the view that bile acids are carcinogens in humans. At least 15 reports, from 1980 through 2003, indicate that bile acids cause DNA damage. The mechanism is probably indirect, involving induction of oxidative stress and production of reactive oxygen species that then damage DNA. Repeated DNA damage likely increases the mutation rate, including the mutation rate of tumor suppressor genes and oncogenes. Additional reports, from 1994 through 2002, indicate that bile acids, at the increased concentrations accompanying a high fat diet, induce frequent apoptosis. Those cells within the exposed population with reduced apoptosis capability tend to survive and selectively proliferate. That bile acids cause DNA damage and may select for apoptosis-resistant cells (both leading to increased mutation), indicates that bile acids are likely carcinogens. In humans, an increased incidence of cancer of the laryngopharyngeal tract, esophagus, stomach, pancreas, the small intestine (near the Ampulla of Vater) and the colon are associated with high levels of bile acids. The much larger number of cell generations in the colonic (and, likely, other gastrointestinal) epithelia of humans compared to rodents may allow time for induction and selection of mutations leading to cancer in humans, although not in rodents.

Animals↗
PubMed2004

Prolonged diapause and the stability of host-parasitoid interactions.

We investigated the effect on host-parasitoid dynamics of prolonged diapause, a feature of the life history of many animals living in unpredictable environments, by modifying the classical May (J. Anim. Ecol. 47 (1978) 833) host-parasitoid model. We considered three patterns of development of host and parasitoid: (a) prolonged parasitoid diapause controlled by host physiology, (b) parasitoid interference in host development, preventing parasitized hosts from prolonging diapause, and (c) host diapause independent of parasitoid attack. We found that single-year prolonged diapause shifted the boundaries of the May model towards a slight increase in stability. Longer periods of diapause prolongation had a stronger influence, but this influence remained modest if we considered realistic parameter values. In contrast to other recent studies, our results suggest that prolonged diapause does not necessarily compensate for the destabilizing effects of time lags on the influence of parasitoids on population dynamics.

Animals↗
PubMed2003

Caspase-6 mediated cleavage of guanylate cyclase alpha 1 during deoxycholate-induced apoptosis: protective role of the nitric oxide signaling module.

Hydrophobic bile acids such as deoxycholate are known tumor promoters in the gastrointestinal tract. We have previously shown that deoxycholate induces apoptosis in colon epithelial cells and that these cells can be made resistant to deoxycholate-induced apoptosis. We now show that the nitric oxide synthase/nitric oxide/guanylate cyclase/cyclic guanosine monophosphate/cGMP-activated protein kinase (NOS/NO/GC/cGMP/PKG) signaling module contributes, in part, to the observed resistance of the cultured DOC-resistant colon epithelial cells (HCT-116R) using pharmacological inhibitors/antagonists (NS2028, Rp-8pCPT-cGMP, KT5823) of members of this signaling module. A novel finding from this study is the caspase-6 mediated cleavage of guanylate cyclase alpha 1 during deoxycholate-induced apoptosis of deoxycholate-sensitive HCT-116SA cells and the absence of guanylate cyclase alpha 1 cleavage in deoxycholate-treated HCT-116R resistant cells using Western blot analyses. This cleavage was specific to caspases as lysosomal, proteasomal, serine protease, cathepsin and calpain inhibitors failed to prevent the cleavage, whereas a general caspase inhibitor and a specific caspase-6 inhibitor did prevent guanylate cyclase alpha 1 cleavage.

Animals↗
PubMed2002

Activation of the metallothionein IIA promoter and other key stress response elements by ursodeoxycholate in HepG2 cells: relevance to the cytoprotective function of ursodeoxycholate.

Ursodeoxycholate, used to treat a variety of pathologies, has the ability to reverse cytotoxic and hepatotoxic conditions. We examined HepG2, a hepatic cell line, treated with increasing levels of ursodeoxycholate, for responses of a range of promoters/response elements responsive to DNA damage, heavy metal ions, protein denaturants, aromatic hydrocarbons, retinoids, changes in intracellular AMP levels, end endoplasmic reticulum stress. The metallothionein IIA promoter was the most highly activated by ursodeoxycholate. Since ursodeoxycholate protects against the cytotoxic effects of deoxycholate, our data, combined with observations made by others, implicate metallothionein IIA as being important in this protective pathway.

Cell Survival↗
PubMed2001

The specific NOS2 inhibitor, 1400W, sensitizes HepG2 cells to genotoxic, oxidative, xenobiotic, and endoplasmic reticulum stresses.

We tested the hypothesis that the constitutive activity of the inducible form of nitric oxide synthase (NOS2) serves to protect cells against numerous endogenous stresses. To accomplish this, we treated HepG2 cell lines that were individually transfected with 13 different promoter/response element (RE) chloramphenicol acetyl transferase (CAT) reporter constructs, with a highly selective NOS2 inhibitor, 1400W [N-(3-(aminomethyl)benzyl) acetamidine)]. HepG2 cells were incubated for 6 h with 0, 1, 10, 50, 100, and 200 microM 1400W, and the activation of the promoter/RE CAT reporter constructs was simultaneously determined. The highest fold inductions occurred at 200 microM 1400W, a concentration that had no effect on overall cell viability, as determined by the MTT assay. Twelve of the 13 promoter/RE CAT reporter constructs were significantly activated by 200 microM 1400W. These results indicate the extensive protective role of constitutive NOS2 against genotoxic, oxidative, and endoplasmic reticulum stresses. The mechanism of this protection may involve the complexing of iron by nitric oxide (NO) to reduce hydroxyl radical formation, NO inhibition of electron transport and the generation of reactive oxygen species within mitochondria, NO inhibition of cyclooxygenase, lipoxygenase, and cytochrome P450 enzyme activity, and the scavenging of superoxide anions by NO to form peroxynitrite.

Amidines↗
PubMed2000

Increased susceptibility of cells to inducible apoptosis during growth from early to late log phase: an important caveat for in vitro apoptosis research.

The physiologic mode of cell death known as apoptosis has become a major focus of scientific research due to its biologic importance. Much of this research involves cells grown in culture, where induction of apoptosis is achieved through a variety of agents. We report that cell cultures in late log growth phase exhibit an increased susceptibility to apoptosis compared with cultures in early log growth phase when apoptosis is induced by sodium deoxycholate (NaDOC), anti-Fas antibody and cytosine-b-D-arabino-furanoside (Ara-C), three agents which induce apoptosis through different upstream mechanisms. We show that this phenomenon occurs in Jurkat lymphocytes, HT-29 and HCT-116 colon epithelial cells. We also present evidence that cell density alone does not affect NaDOC-induced apoptosis, but rather that the growth media plays a key role in increased susceptibility of cells in late log growth phase to NaDOC-induced apoptosis. These results indicate that growth phase is a variable that must be controlled in order to obtain reliable apoptosis data.

Apoptosis↗
PubMed2000

Influence of parasitized adult reproduction on host-parasitoid dynamics: an age-structured model.

In this work, we develop an age-structured model (based on delay-differential equations) to investigate the dynamics of host-parasitoid systems in which adults are the target of parasitism. The rare previous work dealing with such interactions assumes that hosts are functionally dead as soon as they are attacked. We relax this assumption and show that low reproduction rates of parasitized hosts can promote stability at the expense of cyclic behavior (either long term or generation cycles). Higher reproduction rates make the regulation of the host population by parasitoids impossible. As it is the case in models in which adults are subjected to attacks but do not reproduce, our model generates generation cycles for a larger set of parameter values than in models in which juveniles are attacked.

Aging↗
PubMed2000

The NAD+ precursors, nicotinic acid and nicotinamide protect cells against apoptosis induced by a multiple stress inducer, deoxycholate.

The bile salt, sodium deoxycholate (NaDOC), is a natural detergent that promotes digestion of fats. At high physiologic levels, NaDOC activates many stress-response pathways and induces apoptosis in various cell types. NaDOC induces DNA damage and activates poly(ADP-ribose) polymerase (PARP), an enzyme that utilizes NAD+ as a substrate to repair DNA. NaDOC also induces oxidative stress, endoplasmic reticulum (ER) stress and contributes to protein malfolding. The NAD+ precursors, nicotinic acid (NA) and nicotinamide (NAM) were found to protect cells against NaDOC-induced apoptosis. NA and NAM also decreased constitutive levels of both activated NF-kappaB and GRP78, two proteins that respond to oxidative stress. However, the mechanism by which NA and NAM protects cells against apoptosis does not involve a reduction in constitutive levels of oxidative stress. NA or NAM treatment increased the protein levels of glyceraldehyde-3-phosphate dehydrogense (GAPDH), a multi-functional enzyme, in the nucleus and cytoplasm, respectively. NAM did not activate the promoter/response elements of 13 stress response genes nor reduce intracellular non-protein thiols, suggesting that it is non-toxic to cells. NAM thus has promise as a dietary supplement to help prevent disorders involving excessive apoptosis.

Apoptosis↗
PubMed1999

Activation of the promoters of genes associated with DNA damage, oxidative stress, ER stress and protein malfolding by the bile salt, deoxycholate.

Toxic bile salts, retained within the liver because of impaired biliary excretion, are considered to play a major role in liver injury during cholestasis. Bile salts cause cellular stresses that may result in apoptosis. To better understand such cellular stresses, the effect of the bile salt sodium deoxycholate (NaDOC) on activation of 13 specific gene promoters or response elements associated with different cellular stresses was measured in the transformed human hepatoma line, HepG2. NaDOC was found to activate transcription factors and induce or activate the promoters of genes that respond to protein malfolding (grp78 and hsp70), DNA damage (gadd153, hsp70 and c-fos), oxidative stress (NF-kappaB, c-fos, hsp70 and gadd153), ER stress (grp78) and Ca++ imbalance (grp78).

Bile Acids and Salts↗
PubMed1999

A bile acid-induced apoptosis assay for colon cancer risk and associated quality control studies.

Bile acids are important in the etiology of colorectal cancer. Bile acids induce apoptosis in colonic goblet cells at concentrations comparable to those found in fecal water after high-fat meals. Preliminary evidence indicated that cells of the normal-appearing (nontumorous) portion of the colon epithelium of colon cancer patients are more resistant to bile salt-induced apoptosis than are cells from normal individuals. In the present study, 68 patients were examined, and biopsies were taken at 20 cm from the anal verge, cecum, and descending colon. The patients included 17 individuals with a history of colorectal cancer, 37 individuals with adenomas, and 14 individuals who were neoplasia free. The mean bile salt-induced apoptotic index among normal individuals was 57.6 +/- 3.47 (SE), which differed significantly (P < 0.05) from the mean value of 36.41 +/- 3.12 in individuals with a history of colon cancer. The correlation between independent observers was 0.89 (P < 0.001), indicating good interobserver reliability. Components of variance comparing interindividual versus intraindividual sources of variation suggested that site-to-site variability, both between regions of the colon and for adjacent biopsies, was larger than the interpatient variability for individuals with a history of neoplasia. Therefore, there was "patchiness" of the susceptibility of regions of the colon to bile acid-induced apoptosis in individuals with a history of neoplasia (a patchy field effect). There was no obvious correlation of low-apoptotic index regions with regions in which previous neoplasias had been found and removed. On the other hand, for normal, i.e., neoplasia-free, individuals, there was relatively less intraindividual variation compared to interindividual variation. Our assay shows an association between resistance to bile acid-induced apoptosis, measured at 20 cm from the anal verge, and colon cancer risk. Thus, this assay may prove useful as a biomarker of colon cancer risk.

Adenoma↗
PubMed1999

The NAD+ precursors, nicotinic acid and nicotinamide upregulate glyceraldehyde-3-phosphate dehydrogenase and glucose-6-phosphate dehydrogenase mRNA in Jurkat cells.

To better understand the role of nicotinic acid and nicotinamide in the regulation of the oxidative stress response, we measured the levels of glyceraldehyde-3-phosphate dehydrogenase (GAPDH) and glucose-6-phosphate dehydrogenase (G6PD) mRNA in Jurkat cells treated with these NAD+ precursors. We used a modified nonradioactive Northern blot method and detected the mRNA using 18-mer digoxigenin (DIG)-labeled oligonucleotides as probes. We observed increased levels of the mRNAs for the two enzymes in treated cells. Our findings suggest that the NAD+ precursors may protect against oxidative stress and DNA damage by up-regulating the stress response genes GAPDH and G6PD.

Gene Expression Regulation, Enzymologic↗
PubMed1999

Bile salt activation of stress response promoters in Escherichia coli.

Bile salts are prevalent in the mammalian intestine, a natural habitat of Escherichia coli. The bile salts deoxycholate, chenodeoxycholate, ursodeoxycholate, and glycocholate were tested for their effect on induction of 13 specific stress response genes. The most consistently activated E. coli promoters were those for genes micF, osmY, and dinD. MicF and osmY gene products are associated with membrane functions and are responsive to oxidative stress. DinD is induced by DNA damage as part of the SOS response. These results indicate that bile acids, to which E. coli are naturally exposed, induce expression of specific stress response genes, possibly in response to membrane perturbation, oxidative stress, and DNA damage. Altered expression of stress-response genes may also promote interaction of E. coli with cells of the colonic epithelium.

Bacterial Proteins↗
PubMed1999

Reactive nitrogen species in colon carcinogenesis.

The role of reactive nitrogen species (RNS) in colon carcinogenesis is multifactorial and affects diverse processes, such as proliferation, apoptosis, differentiation, tumorigenesis, and metastases. This review describes the stages in colon carcinogenesis where nitric oxide (NO) and inducible NO synthase (NOS2) may influence the progression of a normal mucosa to overt metastatic cancer. Overexpression of NOS2 and an increase in the generation of NO and other RNS may lead to apoptosis resistance, DNA damage, mutation, up-regulation of COX-2, increased proliferation, an increase in oxidative stress and an increase in tumor vascularity and metastatic potential. Therefore, future goals are to establish mechanistically based biomarkers to assess individuals at risk for colon cancer and to implement chemopreventive and dietary strategies that reduce colon cancer risk. An understanding of NO signaling pathways in colon epithelial cells should provide the basis for novel biomarker development. Colon cancer prevention may be achieved effectively by chemically interfering with key components of the NO signaling pathways, changing dietary habits to reduce fat and increase antioxidant-containing vegetables, and dietary supplementation to increase DNA repair.

Animals↗
PubMed1999

Measuring the primary care experiences of low-income and minority patients.

This article describes a community-based survey of patients' experiences in community and migrant health centers that was designed to (1) develop a method to measure patients' experiences and (2) create a national database of patient experiences. The project succeeded in surveying the most difficult-to-reach poor and minority populations (mainly Medicaid and uninsured populations) in medically underserved areas, although more than 10% lack ready access to a telephone, another 22% do not speak English well enough to be interviewed in English, and many have limited literacy. We analyzed the responses from 3 perspectives: (1) demographics and health status, (2) dimensions of care, and (3) patient progress through the community and migrant health center system.

Community Health Centers↗