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Biomedical subjects

C A Sanchez

Publications and source records attributed to C A Sanchez.

At least 19 recordsLinked to original sources
PubMed2005

Perchlorate and nitrate in leafy vegetables of North America.

In previous studies trace levels of perchlorate were found in lettuce (Lactuca sativa L.) irrigated with Colorado River water, which is contaminated with low levels of perchlorate from aerospace and defense related industries. In this paper, we report the results of a survey conducted across North America to evaluate the occurrence of perchlorate in leafy vegetables produced outside the lower Colorado River region, and evaluate the relative iodide uptake inhibition potential to perchlorate and nitrate in these leafy vegetables. Conventionally and organically produced lettuce and other leafy vegetable samples were collected from production fields and farmers' markets in the central and coastal valleys of California, New Mexico, Colorado, Michigan, Ohio, New York, Quebec, and New Jersey. Results show that 16% of the conventionally produced samples and 32% of the organically produced samples had quantifiable levels of perchlorate using ion chromatography. Estimated perchlorate exposure from organically produced leafy vegetables was approximately 2 times that of conventional produce, but generally less than 10% of the reference dose recommended by the National Academy of Sciences. Furthermore, the iodide uptake inhibition potential of perchlorate was less than 1% of that of the nitrate present. These data are consistent with those of other reported perchlorate survey work with lettuce, bottled water, breast milk, dairy milk, and human urine, and suggest a wide national presence of perchlorate.

Environmental Monitoring↗
PubMed2005

Accumulation and perchlorate exposure potential of lettuce produced in the Lower Colorado River region.

The Colorado River is contaminated with perchlorate concentrations of 1.5-8 microg/L, an anion linked to thyroid dysfunction. Over 90% of the lettuce (Lactuca sativa L.) consumed during the winter months in the United States is produced in the Lower Colorado River region. Studies were conducted in this region to survey the potential for lettuce perchlorate accumulation and estimate potential human exposure to perchlorate from lettuce. Total uptake of perchlorate in the above-ground plant of iceberg lettuce was approximately 5 g/ha. Exposure estimates ranged from 0.45 to 1.8 microg/day depending on lettuce types and trimming. For all lettuce types, hypothetical exposures were less than 4% of the reference dose recommended by the National Academy of Sciences. Results show the relative iodide uptake inhibition potential because of lettuce nitrate was 2 orders of magnitude greater than that associated with the corresponding trace levels of perchlorate. These data support the conclusion that potential perchlorate exposures from lettuce irrigated with Colorado River water are negligible relative to acute or long-term harmful amounts.

Arizona↗
PubMed2001

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.

Adenocarcinoma↗
PubMed1999

Clonal expansion and loss of heterozygosity at chromosomes 9p and 17p in premalignant esophageal (Barrett's) tissue.

BACKGROUND: Abnormalities involving the p16 (also known as cyclin-dependent kinase N2 [CDKN2], p16 [INK4a], or MTS1) and p53 (also known as TP53) tumor suppressor genes are highly prevalent in esophageal adenocarcinomas. Loss of heterozygosity (LOH) at 9p21 and 17p13 chromosomes (locations for p16 and p53 genes, respectively) is frequently observed in the premalignant condition, Barrett's esophagus. We studied extensively the distribution and heterogeneity of LOH at 9p and 17p chromosomes throughout the Barrett's segment in patients who have not yet developed esophageal adenocarcinoma. METHODS: We evaluated 404 samples from 61 consecutive patients enrolled in the Seattle Barrett's Esophagus Study from February 1995 through September 1998. All patients had high-grade dysplasia but no diagnosis of cancer. The samples were assayed for LOH at 9p and 17p chromosomes after amplification of genomic DNA by use of polymerase chain reaction and DNA genotyping. The cell fractions were purified by flow cytometry on the basis of DNA content and proliferation-associated antigen labeling. Association between LOH at 9p and LOH at 17p with flow cytometric abnormalities was determined by chi-squared test, and logistic regression models were used to model and test for the extent to which a particular genotype was found in 2-cm intervals. RESULTS AND CONCLUSIONS: LOH at 9p and 17p chromosomes are highly prevalent somatic genetic lesions in premalignant Barrett's tissue. LOH at 9p is more common than LOH at 17p in diploid samples and can be detected over greater regions of Barrett's epithelium. In most patients with high-grade dysplasia, the Barrett's mucosa contains a mosaic of clones and subclones with different patterns of LOH. Some clones had expanded to involve extensive regions of Barrett's epithelium. LOH at 9p and 17p chromosomes may be useful biomarkers to stratify patients' risk of progression to esophageal cancer.

Adenocarcinoma↗
PubMed1999

p53-mutant clones and field effects in Barrett's esophagus.

Previous studies have demonstrated multifocal neoplasia in Barrett's esophagus. We evaluated 213 mapped, flow-purified, endoscopic biopsies to determine the distribution of p53-mutant clones in the Barrett's segments of 58 patients who had high-grade dysplasia without cancer. Twenty-nine patients (50%) had p53 mutations in their Barrett's segments, including 3 patients with multiple distinct p53 mutations. p53-mutant clones, including diploid cell populations, underwent expansion from 1 to 9 cm in the Barrett's segment. In 12 of 29 patients (41%) with a p53 mutation, the same mutation was found at every evaluated level of the metaplastic epithelium. This extensive p53-mutant clonal expansion suggests a somatic genetic basis for previous observations of field effects in Barrett's esophagus.

Adenocarcinoma↗
PubMed1999

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.

Adenocarcinoma↗
PubMed1996

Allelic loss of 9p21 and mutation of the CDKN2/p16 gene develop as early lesions during neoplastic progression in Barrett's esophagus.

High frequency allelic loss of chromosome 9p21 has been reported in a number of human cancers, including those of the esophagus. The CDKN2 gene on chromosome 9p21 that encodes the p16 inhibitor of cyclinD/Cdk4 complexes is a target of allelic loss and inactivation in a variety of human cancers and cell lines. However, the roles of 9p21 allelic losses and CDKN2 mutations in human neoplastic progression in vivo remain controversial. We determined the prevalence of allelic loss at 9p21 and mutations in CDKN2 in esophageal adenocarcinomas and investigated the order in which they occurred relative to the development of aneuploidy and cancer during neoplastic progression. Aneuploid cell populations from 32 patients with Barrett's esophagus who had premalignant epithelium, cancer, or both, were purified by DNA content flow cytometric cell sorting and evaluated by polymerase chain reaction. Twenty-four of 32 informative patients (75%) had allelic loss at 9p21 in aneuploid cell populations. Premalignant epithelium was available for seven of the patients who had 9p21 allelic losses in cancer; allelic loss of 9p21 was detected before cancer in all seven (100%). Allelic loss of 9p21 preceded the development of aneuploidy in 13 of 15 patients (87%) who had aneuploid cell populations detected in premalignant epithelium, and the two events were detected simultaneously in the remaining two patients. Five of 22 aneuploid populations (23%) with 9p21 loss had somatic mutations in the remaining CDKN2 allele. The same mutations and 9p21 allelic losses were also found in the corresponding diploid cells from premalignant epithelium in all three cases that were evaluable. However, there was no evidence for mutation or homozygous deletion of p16 in the other 17 patients with 9p21 allelic loss. Our results indicate that 9p21 allelic losses and CDKN2 mutations develop as early lesions in diploid cells before aneuploidy and cancer during neoplastic progression in Barrett's esophagus.

Adenocarcinoma↗
PubMed1996

17p (p53) allelic losses, 4N (G2/tetraploid) populations, and progression to aneuploidy in Barrett's esophagus.

Increased 4N (G2/tetraploid) cell populations have been postulated to be genetically unstable intermediates in the progression to many cancers, but the mechanism by which they develop and their relationship to instability have been difficult to investigate in humans in vivo. Barrett's esophagus is an excellent model system in which to investigate the order in which genetic and cell cycle abnormalities develop relative to each other during human neoplastic progression. Neoplastic progression in Barrett's esophagus is characterized by inactivation of the p53 gene, the development of increased 4N (G2/tetraploid) cell fractions, and the appearance of aneuploid cell populations. We investigated the hypothesis that patients whose biopsies have increased 4N (G2/tetraploid) cell fractions are predisposed to progression to aneuploidy and determined the relationship between inactivation of p53 and the development of 4N abnormalities in Barrett's epithelium. Our results indicate that increased 4N (G2/tetraploid) populations predict progression to aneuploidy and that the development of 4N abnormalities is interdependent with inactivation of the p53 gene in Barrett's esophagus in vivo.

Alleles↗
PubMed1996

Determination of the frequency of loss of heterozygosity in esophageal adenocarcinoma by cell sorting, whole genome amplification and microsatellite polymorphisms.

It is well established that the progression to human cancer is characterized by the evolution of clones of cells with accumulated genetic abnormalities. However, technical difficulties limit the ability to study this process in some premalignant and malignant conditions. For example, the progression to esophageal adenocarcinoma in the premalignant condition Barrett's esophagus is characterized by the evolution of genetic and cell cycle abnormalities, but it has been difficult to characterize this process completely because of the small size of biopsies and the relative abundance of genetically normal stromal cells in some esophageal adenocarcinomas and premalignant mucosa. We have combined flow cytometric cell sorting to obtain purified populations of neoplastic cells with whole genome amplification and analysis of microsatellite polymorphisms to determine the frequency of allelic loss on every nonacrocentric autosomal arm in 20 esophageal adenocarcinomas and two high-grade dysplasias. DNA samples of purified flow-sorted aneuploid and corresponding normal tissue were amplified with a degenerate 15mer primer. Aliquots of these reactions were then screened with forty-three highly polymorphic simple sequence repeat markers in PCR-based assays. Allelic losses were observed at polymorphic loci in 38 of the 40 chromosome arms that were analysed and the median fractional allelic loss (FAL) observed in the samples was 0.28. The background allelic loss frequency was estimated at 0.23 with the highest rates of loss observed at 17p (100%), 5q (80%), 9p (64%), 13q (43%), 18q (43%) and 1p (41%). These data represent the first comprehensive allelotype of esophageal adenocarcinoma and show the feasibility of multiloci analyses with small highly purified human biopsy material.

Adenocarcinoma↗
PubMed1995

A p53-dependent mouse spindle checkpoint.

Cell cycle checkpoints enhance genetic fidelity by causing arrest at specific stages of the cell cycle when previous events have not been completed. The tumor suppressor p53 has been implicated in a G1 checkpoint. To investigate whether p53 also participates in a mitotic checkpoint, cultured fibroblasts from p53-deficient mouse embryos were exposed to spindle inhibitors. The fibroblasts underwent multiple rounds of DNA synthesis without completing chromosome segregation, thus forming tetraploid and octaploid cells. Deficiency of p53 was also associated with the development of tetraploidy in vivo. These results suggest that murine p53 is a component of a spindle checkpoint that ensures the maintenance of diploidy.

Animals↗
PubMed1995

Comparative genomic analysis of tumors: detection of DNA losses and amplification.

We demonstrate the use of representational difference analysis for cloning probes that detect DNA loss and amplification in tumors. Using DNA isolated from human tumor cell lines to drive hybridization against matched normal DNA, we were able to identify six genomic regions that are homozygously deleted in cultured cancer cells. When this method was applied in the reverse way, using normal DNA to drive hybridization against tumor cell DNA, we readily isolated probes detecting amplification. Representational difference analysis was also performed on DNAs derived from tumor biopsies, and we thereby discovered a probe detecting very frequent homozygous loss in colon cancer cell lines and located on chromosome 3p.

Animals↗
PubMed1995

Inactivation of p53 and the development of tetraploidy in the elastase-SV40 T antigen transgenic mouse pancreas.

Human pancreatic cancer develops in association with an acquired genomic instability, but the events that lead to instability are difficult to investigate because they occur sporadically and unpredictably. The elastase-SV40 T antigen transgenic mouse model of pancreatic adenocarcinoma reproducibly proceeds through a diploid --> tetraploid --> multiple aneuploid sequence of genetic abnormalities. We investigated the relationship between inactivation of p53 and development of tetraploidy in this model. Because T antigen inactivates p53 by forming a stable complex with it, we used multiparameter flow cytometry to assess p53 expression in pancreatic samples of transgenic and control mice between 8 and 24 days of age. On day 18, a cell cycle-specific inactivation of p53 developed between diploid G, and S phase and was associated with the appearance of a cycling tetraploid cell population that had p53 protein overexpression in both G1- and S-phase cells. Cytogenetic analysis of pancreatic samples confirmed the development of a tetraploid cell population. Inactivation of p53 in diploid cells of the transgenic pancreas is followed by the development of a tetraploid cell population. We have shown previously that this tetraploid intermediate is predisposed to progression to aneuploidy because it has abnormal mitotic poles. Therefore, our results suggest that inactivation of p53 by T antigen leads to formation of a tetraploid cell intermediate that is predisposed to chromosome segregation abnormalities and the development of multiple aneuploid cell populations.

Animals↗
PubMed1994

17p allelic losses in diploid cells of patients with Barrett's esophagus who develop aneuploidy.

Inactivation of the p53 gene, located on chromosome 17p, leads to genetic instability and aneuploidy in vitro. Aneuploid cell populations from Barrett's adenocarcinomas have a high prevalence of 17p allelic losses, and there is substantial evidence that the target of these losses is the p53 gene. If 17p allelic losses lead to aneuploidy in Barrett's esophagus, then they should be present in diploid cells from patients who develop aneuploidy. We detected 17p allelic losses in diploid cells from 10 of 11 patients (91%) with Barrett's esophagus who developed aneuploid cell populations. Our data strongly suggest that 17p allelic losses precede the development of aneuploidy during neoplastic progression in Barrett's esophagus in vivo and, therefore, support in vitro evidence for the role of p53 in genetic instability.

Adenocarcinoma↗
PubMed1994

p53 mutations in Barrett's adenocarcinoma and high-grade dysplasia.

BACKGROUND/AIMS: Allelic losses of chromosome 17p and overexpression of p53 protein have been reported in Barrett's adenocarcinomas. This study aimed to determine the stage in which p53 mutations arise in neoplastic progression in Barrett's esophagus and their relationship to the clonal evolution of cancer. METHODS: Fourteen patients with high-grade dysplasia, adenocarcinoma, or both arising in Barrett's esophagus were evaluated. Flow cytometric cell sorting was used to obtain purified populations of neoplastic cells for analysis of p53 mutations. DNA was extracted, and exons 5 through 9 of the p53 gene were amplified by polymerase chain reaction. Amplified DNA was sequenced and analyzed by automated sequencing. RESULTS: Nine of the 14 patients had p53 mutations. Six of the 9 patients had regions of high-grade dysplasia that could be evaluated; all 6 had p53 mutations in high-grade dysplasia. In 3 patients, the same p53 mutations were found in both high-grade dysplasia and adenocarcinoma. All 14 patients had aneuploidy. In 4 patients, diploid cell populations could also be evaluated for p53 mutations; 3 of the 4 patients had p53 mutations in diploid cell populations. In 2 patients, the same p53 mutation was found in multiple aneuploid cell populations within a cancer. CONCLUSIONS: p53 mutations occur frequently in Barrett's adenocarcinomas. They develop in diploid cell populations. The same p53 mutations are then found in aneuploid cell populations in high-grade dysplasia, in cancer, and in multiple aneuploid cell populations in cancer.

Adenocarcinoma↗
PubMed1994

Critical thinking disposition as a measure of competent clinical judgment: the development of the California Critical Thinking Disposition Inventory.

Assessing critical thinking skills and disposition is crucial in nursing education and research. The California Critical Thinking Disposition Inventory (CCTDI) uses the Delphi Report's consensus definition of critical thinking as the theoretical basis to measure critical thinking disposition. Item analysis and factor analysis techniques were used to create seven disposition scales, which grouped the Delphi dispositional descriptions into larger, more unified constructs: open-mindedness, analyticity, cognitive maturity, truth-seeking, systematicity, inquisitiveness, and self-confidence. Cronbach's alpha for the overall instrument, the disposition toward critical thinking, is .92. The 75-item instrument was administered to an additional sample of college students (N = 1019). The alpha levels in the second sample remained relatively stable, ranging from .60 to .78 on the subscales and .90 overall. The instrument has subsequently been used to assess critical thinking disposition in high school through the graduate level but is targeted primarily for the college undergraduates. Administration time is 20 minutes. Correlation with its companion instrument, the California Critical Thinking Skills Test, also based on the Delphi critical thinking construct, was measured at .66 and .67 in two pilot sample groups.

Adult↗