Mitochondrial-Targeted Catalase: Extended Longevity and the Roles in Various Disease Models.

The free-radical theory of aging was proposed more than 50 years ago. As one of the most popular mechanisms explaining the aging process, it has been extensively studied in several model organisms. However, the results remain controversial. The mitochondrial version of free-radical theory of aging proposes that mitochondria are both the primary sources of reactive oxygen species (ROS) and the primary targets of ROS-induced damage. One critical ROS is hydrogen peroxide, which is naturally degraded by catalase in peroxisomes or glutathione peroxidase within mitochondria. Our laboratory developed mice-overexpressing catalase targeted to mitochondria (mCAT), peroxisomes (pCAT), or the nucleus (nCAT) in order to investigate the role of hydrogen peroxide in different subcellular compartments in aging and age-related diseases. The mCAT mice have demonstrated the largest effects on life span and healthspan extension. This chapter will discuss the mCAT phenotype and review studies using mCAT to investigate the roles of mitochondrial oxidative stresses in various disease models, including metabolic syndrome and atherosclerosis, cardiac aging, heart failure, skeletal muscle pathology, sensory defect, neurodegenerative diseases, and cancer. As ROS has been increasingly recognized as essential signaling molecules that may be beneficial in hormesis, stress response and immunity, the potential pleiotropic, or adverse effects of mCAT are also discussed. Finally, the development of small-molecule mitochondrial-targeted therapeutic approaches is reviewed.

Image cytometry accurately detects DNA ploidy abnormalities and predicts late relapse to high-grade dysplasia and adenocarcinoma in Barrett's oesophagus following photodynamic therapy.

BACKGROUND AND AIMS: DNA ploidy abnormalities (aneuploidy/tetraploidy) measured by flow cytometry (FC) are strong predictors of future cancer development in untreated Barrett's oesophagus, independent of histology grade. Image cytometric DNA analysis (ICDA) is an optical technique allowing visualisation of abnormal nuclei that may be undertaken on archival tissue. Our aim was to determine the accuracy of ICDA vs FC, and evaluate DNA ploidy as a prognostic biomarker after histologically successful treatment with photodynamic therapy (PDT). METHODS: Nuclei were extracted from 40 mum sections of paraffin-embedded biopsies and processed for ICDA at UCL and FC at UW using standardised protocols. Subsequently, DNA ploidy was evaluated by ICDA on a cohort of 30 patients clear of dysplasia 1 year after aminolaevulinic acid PDT for high-grade dysplasia (HGD). The results were correlated with long-term outcome. RESULTS: In the comparative study, 93% (41 out of 44) of cases were classified identically. Errors occurred in the near-diploid region by ICDA and the tetraploid region by FC. In the cohort study, there were 13 cases of late relapse (7 cancer, 6 HGD) and 17 patients who remained free of dysplasia after a mean follow-up of 44 months. Aneuploidy post-PDT was highly predictive for recurrent HGD or cancer with a hazard ratio of 8.2 (1.8-37.8) (log-rank P=0.001). CONCLUSIONS: ICDA is accurate for the detection of DNA ploidy abnormalities when compared with FC. After histologically successful PDT, patients with residual aneuploidy are significantly more likely to develop HGD or cancer than those who become diploid. DNA ploidy by ICDA is a valuable prognostic biomarker after ablative therapy.

High-quality RNA and DNA from flow cytometrically sorted human epithelial cells and tissues.

Microarray technologies have made possible comprehensive analyses of nucleic acid sequence and expression. However, the technology to obtain efficiently high-quality RNA and DNA suitable for array analysis from purified populations of neoplastic cells from human tissues has not been well addressed. Microdissection can enrich for populations of cells present in various tumor tissues, but it is not easily automated or performed rapidly, and there are tissues in which cells of interest cannot be readily isolated based on morphologic criteria alone. Here we describe a protocol for efficient RNA and DNA isolation from flow cytometrically purified whole epithelial cells from primary tissue. The aqueous reagent, RNAlater, which preserves RNA, allows immunolabeling and purification of whole epithelial cells by flow sorting without special instrument preparation to reduce RNase activity. We used real-time PCR to determine RNA quality afterflow sorting. High-quality RNA and DNA suitable for expression and genotype analysis can be readily obtained from flow cytometrically purified populations of neoplastic cells from human tissues.

Predictors of progression in Barrett's esophagus II: baseline 17p (p53) loss of heterozygosity identifies a patient subset at increased risk for neoplastic progression.

OBJECTIVES: Most patients with Barrett's esophagus do not progress to cancer, but those who do seem to have markedly increased survival when cancers are detected at an early stage. Most surveillance programs are based on histological assessment of dysplasia, but dysplasia is subject to observer variation and transient diagnoses of dysplasia increase the cost of medical care. We have previously validated flow cytometric increased 4N fractions and aneuploidy as predictors of progression to cancer in Barrett's esophagus. However, multiple somatic genetic lesions develop during neoplastic progression in Barrett's esophagus, and it is likely that a panel of objective biomarkers will be required to manage the cancer risk optimally. METHODS: We prospectively evaluated endoscopic biopsies from 325 patients with Barrett's esophagus, 269 of whom had one or more follow-up endoscopies, by a robust platform for loss of heterozygosity (LOH) analysis, using baseline 17p (p53) LOH as a predictor and increased 4N, aneuploidy, high-grade dysplasia, and esophageal adenocarcinoma as outcomes. RESULTS: The prevalence of 17p (p53) LOH at baseline increased from 6% in negative for dysplasia to 57% in high-grade dysplasia (p < 0.001). Patients with 17p (p53) LOH had increased rates of progression to cancer (relative risk [RR] = 16, p < 0.001), high-grade dysplasia (RR = 3.6, p = 0.02), increased 4N (RR = 6.1, p < 0.001), and aneuploidy (RR = 7.5, p < 0.001). CONCLUSIONS: Patients with 17p (p53) LOH are at increased risk for progression to esophageal adenocarcinoma as well as high-grade dysplasia, increased 4N, and aneuploidy. 17p (p53) LOH is a predictor of progression in Barrett's esophagus that can be combined with a panel of other validated biomarkers for risk assessment as well as intermediate endpoints in prevention trials.

Predictors of progression in Barrett's esophagus III: baseline flow cytometric variables.

OBJECTIVES: Barrett's esophagus develops in 5-10% of patients with gastroesophageal reflux disease and predisposes to esophageal adenocarcinoma. We have previously shown that a systematic baseline endoscopic biopsy protocol using flow cytometry with histology identifies subsets of patients with Barrett's esophagus at low and high risk for progression to cancer. In this report, we further examined cytometric variables to better define the characteristics that best enable DNA cytometry to help predict cancer outcome. METHODS: Patients were prospectively evaluated using a systematic endoscopic biopsy protocol, with baseline histological and flow cytometric measurements as predictors and with cancer as the outcome. RESULTS: A receiver operating curve analysis demonstrated that a 4N fraction cut point of 6% was optimal to discriminate cancer risk (relative risk [RR] = 11.7, 95% CI = 6.2-22). The 4N fractions of 6-15% were just as predictive of cancer as were fractions of >15%. We found that only aneuploid DNA contents of >2.7N were predictive of cancer (RR = 9.5, CI = 4.9-18), whereas those patients whose sole abnormality was an aneuploid population with DNA content of < or =2.7 had a low risk for progression. The presence of both 4N fraction of >6% and aneuploid DNA content of >2.7N was highly predictive of cancer (RR = 23, CI = 10-50). S phase was a predictor of cancer risk (RR = 2.3, CI = 1.2-4.4) but was not significant when high-grade dysplasia was accounted for. CONCLUSIONS: Flow cytometry is a useful adjunct to histology in assessing cancer risk in patients with Barrett's esophagus. Careful examination of cytometric variables revealed a better definition of those parameters that are most closely associated with increased cancer risk.

Simultaneous analysis of surface marker expression and cell cycle progression in human peripheral blood mononuclear cells.

One method for examining cell cycle kinetics by flow cytometry uses continuous DNA labeling with bromodeoxyuridine (BrdU), a thymidine analogue. Upon incorporation into DNA, BrdU causes stoichiometric quenching of the DNA fluorochrome Hoechst 33258. After counterstaining with a secondary DNA fluorochrome (e.g., ethidium bromide), the analyst can distinguish cells in different phases of the cell cycle over a number of mitotic cycles with flow cytometry. In this report, we describe a modification of the flow cytometric BrdU-Hoechst assay that allows combined analysis of cell proliferation and immunophenotyping at the single cell level. To demonstrate an application of this method, human peripheral blood mononuclear cells were stimulated with tetanus toxoid or interleukin-2 for up to 6 days in the presence of BrdU, harvested, and immunostained for the cell surface markers CD3, CD4, CD8, CD14, CD19, and the cytokine receptor, CCR5. We used four-color flow cytometry analyses to simultaneously measure cell proliferation and surface marker expression, for the purpose of immunophenotyping and identifying specific cell subsets responding to antigen stimulation. Our successful application of this method suggests that it may be used to study immune responses at the molecular and cellular level and to identify mechanisms of immune system modulation.

Effects of bile salts on cholestan-3beta,5alpha,6beta-triol-induced apoptosis in dog gallbladder epithelial cells.

Oxysterols are cytotoxic agents. The gallbladder epithelium is exposed to high concentrations of oxysterols, and so elucidating the mechanisms of cytotoxicity in this organ may enhance our understanding of the pathogenesis of biliary tract disorders. We investigated the cytotoxic effects of the oxysterol cholestan-3beta,5alpha,6beta-triol (TriolC) on dog gallbladder epithelial cells. Apoptosis was the major form of cytotoxicity, as determined by analysis of nuclear morphologic changes and by multiparameter flow cytometry. Hydrophobic bile salts are known to have cytotoxic effects, whereas hydrophilic bile salts have cytoprotective effects. We therefore examined whether the hydrophobic bile acid taurodeoxycholic acid (TDC) and the hydrophilic bile acid tauroursodeoxycholic acid (TUDC) had modifying effects on oxysterol-induced cytotoxicity. TriolC caused an increase in the number of apoptotic cells from 14+/-11% (control) to 48+/-12% of total cells (P<0.01). After combining TriolC with TDC, cell apoptosis increased to 63+/-16% (P<0.05), whereas after addition of TUDC, the number of apoptotic cells decreased to 31+/-12% (P<0.05) of total cells. In summary, oxysterols such as TriolC induce apoptosis. Hydrophobic bile salts enhance TriolC-induced apoptosis, whereas hydrophilic bile salts diminish TriolC-induced apoptosis. These results suggest that interactions between oxysterols and bile salts play a role in the pathophysiology of biliary tract disorders.

Analysis of cell proliferation and cell survival by continuous BrdU labeling and multivariate flow cytometry.

Halogenated deoxyuridines such as BrdU incorporated into DNA in place of thymidine can be detected by virtue of their ability to quench the fluorescence of Hoechst dyes. This property is the basis for a simple and reliable method of enumerating cells which have incorporated BrdU. Counterstaining with another suitable DNA dye permits resolution of cells in G1, S, and G2 phases of three consecutive cell cycles. In addition to this basic technique, the authors present newer protocols for proliferative analysis of GFP-expressing or cell surface antigen expressing cells versus nonexpressing cells in culture as well as one to determine the absolute number of proliferating and nonproliferating cells by calibration for the volume analyzed. With this technique the proliferative survival of cells can be determined.

Measurement of intracellular calcium ions by flow cytometry.

Using flow cytometry, single-cell measurements of calcium can be made on isolated populations identified by one or more phenotypic characteristics. This unit describes the preparation of cells, including labeling with antibodies and with calcium probes, and discusses the principles of data analysis and interpretation.

The role of cyclooxygenase 2 in ulcerative colitis-associated neoplasia.

Cyclooxygenase 2 (COX-2) overexpression has been described in sporadic colonic neoplasia, but its role in ulcerative colitis (UC) neoplastic progression remains unexplored. Although the specific role of cyclooxygenase in colonic neoplasia is uncertain, its inhibition by nonsteroidal anti-inflammatory drugs decreases the risk of sporadic colonic adenocarcinoma and causes regression of adenomas in familial adenomatous polyposis. To investigate the role of COX-2 in UC-associated neoplasia, we assessed COX-2 protein and mRNA expression throughout the spectrum of UC-associated neoplastic lesions in four total colectomy specimens, using immunocytochemistry and a novel TaqMan reverse transcriptase-polymerase chain reaction assay. The findings were correlated with DNA ploidy and inflammatory activity. We found COX-2 overexpression throughout the neoplastic spectrum in UC (P: < 0.0001, R:(2)=0.53), even in diploid samples that were negative for dysplasia. Overall, neoplastic change explained 53% of the variation in COX-2 expression, whereas inflammatory activity explained only 11%. COX-2 was overexpressed in all aneuploid samples and in 38% of diploid samples (P: = 0.0074). cDNA representational difference analysis was also performed and revealed that COX-2 mRNA was an up-regulated cDNA representational difference analysis difference product. COX-2 overexpression occurs early in UC-associated neoplasia, and the increase cannot be explained by inflammatory activity alone. The data suggest that COX-2-specific inhibitors may have a chemopreventative role in UC but the possibility that they could exacerbate UC inflammatory activity needs to be tested.

Predictors of progression to cancer in Barrett's esophagus: baseline histology and flow cytometry identify low- and high-risk patient subsets.

OBJECTIVE: Barrett's esophagus develops in 5-20% of patients with gastroesophageal reflux disease and predisposes to esophageal adenocarcinoma. The value of endoscopic biopsy surveillance is questioned because most patients do not develop cancer. Furthermore, observer variation in histological diagnosis makes validation of surveillance guidelines difficult because varying histological interpretations may lead to different estimated rates of progression. Thus, objective biomarkers need to be validated for use with histology to stratify patients according to their risk for progression to cancer. METHODS: We prospectively evaluated patients using a systematic endoscopic biopsy protocol with baseline histological and flow cytometric abnormalities as predictors and cancer as the outcome. RESULTS: Among patients with negative, indefinite, or low-grade dysplasia, those with neither aneuploidy nor increased 4N fractions had a 0% 5-yr cumulative cancer incidence compared with 28% for those with either aneuploidy or increased 4N. Patients with baseline increased 4N, aneuploidy, and high-grade dysplasia had 5-yr cancer incidences of 56%, 43%, and 59%, respectively. Aneuploidy, increased 4N, or HGD were detected at baseline in all 35 patients who developed cancer within 5 yr. CONCLUSIONS: A systematic baseline endoscopic biopsy protocol using histology and flow cytometry identifies subsets of patients with Barrett's esophagus at low and high risk for progression to cancer. Patients whose baseline biopsies are negative, indefinite, or low-grade displasia without increased 4N or aneuploidy may have surveillance deferred for up to 5 yr. Patients with cytometric abnormalities merit more frequent surveillance, and management of high-grade dysplasia can be individualized.

Disruption of redox homeostasis in tumor necrosis factor-induced apoptosis in a murine hepatocyte cell line.

Tumor necrosis factor (TNF) is a mediator of the acute phase response in the liver and can initiate proliferation and cause cell death in hepatocytes. We investigated the mechanisms by which TNF causes apoptosis in hepatocytes focusing on the role of oxidative stress, antioxidant defenses, and mitochondrial damage. The studies were conducted in cultured AML12 cells, a line of differentiated murine hepatocytes. As is the case for hepatocytes in vivo, AML12 cells were not sensitive to cell death by TNF alone, but died by apoptosis when exposed to TNF and a small dose of actinomycin D (Act D). Morphological signs of apoptosis were not detected until 6 hours after the treatment and by 18 hours approximately 50% of the cells had died. Exposure of the cells to TNF+Act D did not block NFkappaB nuclear translocation, DNA binding, or its overall transactivation capacity. Induction of apoptosis was characterized by oxidative stress indicated by the loss of NAD(P)H and glutathione followed by mitochondrial damage that included loss of mitochondrial membrane potential, inner membrane structural damage, and mitochondrial condensation. These changes coincided with cytochrome C release and the activation of caspases-8, -9, and -3. TNF-induced apoptosis was dependent on glutathione levels. In cells with decreased levels of glutathione, TNF by itself in the absence of transcriptional blocking acted as an apoptotic agent. Conversely, the antioxidant alpha-lipoic acid, that protected against the loss of glutathione in cells exposed to TNF+Act D completely prevented mitochondrial damage, caspase activation, cytochrome C release, and apoptosis. The results demonstrate that apoptosis induced by TNF+Act D in AML12 cells involves oxidative injury and mitochondrial damage. As injury was regulated to a larger extent by the glutathione content of the cells, we suggest that the combination of TNF+Act D causes apoptosis because Act D blocks the transcription of genes required for antioxidant defenses.

Effect of segment length on risk for neoplastic progression in patients with Barrett esophagus.

BACKGROUND: The increased risk for esophageal adenocarcinoma associated with long-segment (> or =3 cm) Barrett esophagus is well recognized. Recent studies suggest that short-segment (<3 cm) Barrett esophagus is substantially more common; however, the risk for neoplastic progression in patients with this disorder is largely unknown. OBJECTIVE: To examine the relation between segment length and risk for aneuploidy and esophageal adenocarcinoma in patients with Barrett esophagus. DESIGN: Prospective cohort study. SETTING: University medical center in Seattle, Washington. PATIENTS: 309 patients with Barrett esophagus. MEASUREMENTS: Patients were monitored for progression to aneuploidy and adenocarcinoma by repeated endoscopy with biopsy for an average of 3.8 years. Cox proportional hazards analysis was used to calculate adjusted relative risks and 95% Cls. RESULTS: After adjustment for histologic diagnosis at study entry, segment length was not related to risk for cancer in the full cohort (P > 0.2 for trend). When patients with high-grade dysplasia at baseline were excluded, however, a nonsignificant trend was observed; based on a linear model, a 5-cm difference in segment length was associated with a 1.7-fold (95% CI, 0.8-fold to 3.8-fold) increase in cancer risk. Among all eligible patients, a 5-cm difference in segment length was associated with a small increase in the risk for aneuploidy (relative risk, 1.4 [CI, 1.0 to 2.1]; P = 0.06 for trend). A similar trend was observed among patients without high-grade dysplasia at baseline. CONCLUSIONS: The risk for esophageal adenocarcinoma in patients with short-segment Barrett esophagus was not substantially lower than that in patients with longer segments. Although our results suggest a small increase in risk for neoplastic progression with increasing segment length, additional follow-up is needed to determine whether the patterns of risk occurred by chance or represent true differences. Until more data are available, the frequency of endoscopic surveillance should be selected without regard to segment length.

Pancolonic chromosomal instability precedes dysplasia and cancer in ulcerative colitis.

Patients with long-standing ulcerative colitis (UC) are at increased risk for colon cancer. These cancers are thought to arise from preexisting dysplasia in a field of abnormal cells that often exhibits aneuploidy and p53 abnormalities. Using dual color fluorescence in situ hybridization with centromere probes and locus-specific arm probes for chromosomes 8, 11, 17, and 18, we demonstrate that chromosomal instability (CIN) is present throughout the colon of UC patients with high-grade dysplasia or cancer. In rectal biopsies that were negative for dysplasia, abnormalities in chromosomal arms, especially losses, were most common, whereas centromere gains were most common in dysplasia and cancer. The frequency and type of abnormalities varied between the chromosomes examined; chromosome 8 was the least affected, and 17p loss was found to be an early and frequent event. Chromosomal arm instability showed 100% sensitivity and specificity for distinguishing control biopsies from histologically negative rectal biopsies from these UC patients, raising the possibility that a screen for CIN might detect the subset of UC patients who are at greatest risk for development of dysplasia and cancer. These results suggest that dysplasia and cancer in UC arise from a process of CIN that affects the entire colon; this may provide the mutator phenotype that predisposes to loss of tumor suppressor genes and evolution of cancer.

Evolution of neoplastic cell lineages in Barrett oesophagus.

It has been hypothesized that neoplastic progression develops as a consequence of an acquired genetic instability and the subsequent evolution of clonal populations with accumulated genetic errors. Accordingly, human cancers and some premalignant lesions contain multiple genetic abnormalities not present in the normal tissues from which the neoplasms arose. Barrett oesophagus (BE) is a premalignant condition which predisposes to oesophageal adenocarcinoma (EA) that can be biopsied prospectively over time because endoscopic surveillance is recommended for early detection of cancer. In addition, oesophagectomy specimens frequently contain the premalignant epithelium from which the cancer arose. Neoplastic progression in BE is associated with alterations in TP53 (also known as p53) and CDKN2A (also known as p16) and non-random losses of heterozygosity (LOH). Aneuploid or increased 4N populations occur in more than 90-95% of EAs, arise in premalignant epithelium and predict progression. We have previously shown in small numbers of patients that disruption of TP53 and CDKN2A typically occurs before aneuploidy and cancer. Here, we determine the evolutionary relationships of non-random LOH, TP53 and CDKN2A mutations, CDKN2A CpG-island methylation and ploidy during neoplastic progression. Diploid cell progenitors with somatic genetic or epigenetic abnormalities in TP53 and CDKN2A were capable of clonal expansion, spreading to large regions of oesophageal mucosa. The subsequent evolution of neoplastic progeny frequently involved bifurcations and LOH at 5q, 13q and 18q that occurred in no obligate order relative to each other, DNA-content aneuploidy or cancer. Our results indicate that clonal evolution is more complex than predicted by linear models.

Apoptotic human lymphocytes have diminished CD4 and CD8 receptor expression.

We used quantitative multiparameter flow cytometric assays to simultaneously detect viable, apoptotic, and necrotic human peripheral blood mononuclear cells (PBMC) and immunophenotyped lymphocyte subsets within the PBMC. Apoptosis was induced by a spectrum of treatments, including camptothecin, cisplatin, dexamethasone, hyperthermia, staurosporine, and etoposide in anti-CD3 mAb-stimulated cells and by cyclohexamide in both quiescent and stimulated cells; apoptosis in the latter was augmented by anti-fas mAb. We found that CD4(+) and CD8(+) cells were significantly underrepresented in the apoptotic PBMC and that the percentage of CD4(+) and CD8(+) PBMC each markedly decreased as apoptosis increased. This suggested that surface expression of these receptors was lessened on apoptotic CD4(+) and CD8(+) cells. This was directly confirmed by observation of sorted CD4(+) PBMC. This analysis of a wide variety of apoptotic stimuli demonstrates that diminished CD4 and CD8 surface receptor expression is a common feature of human T lymphocyte apoptosis.

Werner syndrome lymphoblastoid cells are sensitive to camptothecin-induced apoptosis in S-phase.

Werner Syndrome (WRN) is an autosomal recessive disorder showing an endogenous mutator phenotype in combination with an elevated risk of predominantly mesenchymal cancer. The gene mutated in WRN patients codes for 3'-->5' DNA helicase and 3'-->5' exonuclease activities. We have found similar S-phase arrest in both WRN and control cells after treatment with the DNA-topoisomerase-I-trapping drug camptothecin; this may be responsible for the drug-exposure-related growth inhibition seen in both cell types. A clearer phenotypic difference between WRN and control immortalized B-cell lines (LCLs) is obtained by examining cell death. The mechanism of camptothecin-induced cell death in WRN-deficient LCLs appears to be through apoptosis, a phenotype that strongly differentiates WRN-deficient from wild-type LCLs. We hypothesize that, in cells deficient for WRN function, a topoisomerase-I-DNA intermediate persists. Conflict with DNA replication may lead to apoptosis, increased mutation rates, and cancer in WRN.

Genetic analysis of long-term Barrett's esophagus epithelial cultures exhibiting cytogenetic and ploidy abnormalities.

BACKGROUND & AIMS: Progression to cancer in Barrett's esophagus occurs through an accumulation of cell cycle and genetic abnormalities that have been documented in vivo. To better study neoplastic evolution in Barrett's esophagus, the aim of this study was to establish in vitro cultures from preneoplastic tissues. METHODS: Mechanical and enzymatic dissociation methods were used to initiate Barrett's epithelial cultures from endoscopic biopsy specimens, and the cells were characterized using flow-cytometric, cytogenetic, and molecular genetic analyses. RESULTS: Four long-term cultures were established from 39 attempts. All cultures contain cytogenetic abnormalities and elevated flow-cytometric 4N DNA content fractions. Molecular genetic abnormalities detected include the following: 9p and/or CDKN2/p16 abnormalities in 4 of 4 cultures, 17p loss of heterozygosity and p53 mutation in 3 of 4 cultures, and 5q loss of heterozygosity in 1 of 4 cultures. Inactivation of p53 was statistically associated with successful long-term culture. CONCLUSIONS: These cultures contain cell cycle and molecular genetic abnormalities that closely parallel those previously documented to occur early in cancer development in Barrett's esophagus in vivo. These alterations also appear to be associated with successful growth in vitro. The cultures may provide a premalignant in vitro system in which to test potential therapies for Barrett's esophagus as well as to examine etiologic factors and genetic intermediates important in neoplastic progression.

Cultured renal epithelial cells from birds and mice: enhanced resistance of avian cells to oxidative stress and DNA damage.

Current mechanistic theories of aging would predict that many species of birds, given their unusually high metabolic rates, body temperatures, and blood sugar levels, should age more rapidly than mammals of comparable size. On the contrary, many avian species display unusually long life spans. This finding suggests that cells and tissues from some avian species may enjoy unusually robust and/or unique protective mechanisms against fundamental aging processes, including a relatively high resistance to oxidative stress. We therefore compared the sensitivities of presumptively homologous epithelial somatic cells derived from bird and mouse kidneys to various forms of oxidative stress. When compared to murine cells, we found enhanced resistance of avian cells from three species (budgerigars, starlings, canaries) to 95% oxygen, hydrogen peroxide, paraquat, and gamma-radiation. Differential resistance to 95% oxygen was demonstrated with both replicating and quiescent cultures. Hydrogen peroxide was shown to induce DNA single-strand breaks. There were fewer breaks in avian cells than in mouse cells when similarly challenged.