Integrin mediated growth and apoptosis in human gastric adenocarcinoma

Integrins are important as the primary cell adhesion molecule providing information about the extracellular microenvironment to the interior of the cell to influence cellular behavior such as differentiation, proliferation and apoptosis. Apoptotic death due to loss of adhesion is termed anoikis. In this study we have obtained a parental human gastric adenocarcinoma cell line that yielded two variant lines that had differing responses to lack of adhesion. The STAD.APO cell line undergoes apoptosis when denied adherence and the STAD.ARR cell line enters into cell cycle arrest under the identical suspended conditions. We have shown that cyclin A and cyclin D mRNA and protein are down regulated when cells are denied adherence for 24 hours in tissue culture wells previously coated with poly-HEMA. To test whether cyclin A was able to rescue cells from cell cycle arrest and/or anoikis by overriding the cell cycle machinery we transfected the full length cDNA in to each cell type. Surprisingly we found that anoikis and cell cycle arrest due to suspended conditions was not affected by overexpression of cyclin A protein, but that growth under adhered conditions was reduced compared to vector alone control transfectants. Further, we transfected other cell lines; ST7, gastric cancer, MDA-MB-4.35, breast cancer, and HPB T-cell leukemic and in no case were suspended culturing conditions overcome by cyclin A. This result indicates an additional level of regulation for the cell cycle machinery. Additionally, soluble collagen was shown to be able to save from anoikis and also from cell cycle arrest while the β1 specific mAb 33B6 was only able to save from anoikis. Immunofluorescent studies show that soluble collagen creates clusters of β1 with FAK and also β1 with actin in the STAD.ARR cells but does not in the STAD.APO cells. This result indicates that the phenotypes under suspended conditions between these cell lines may diverge at their requirements for integrin ligation. Additionally we characterized the nature of anoikis by showing cytochrome c release, caspase 3, p21 and p53 activation in STAD.APO cells. Thus, our results have implications in the understanding of integrin biology and neoplastic progression. ^

beta-catenin interacts with and inhibits NF-kappaB in colon cancer

The β-catenin pathway plays an important role in the progression of colon cancer as well as many other cancer types. Almost all colorectal tumors show an upregulation of β-catenin activity either through mutations in the β-catenin regulator APC or through mutations in β-catenin itself. Upregulation of β-catenin leads to the transcription of many target genes involved in tumorigenesis. NF-κB is a transcription factor which activates many target genes, including both anti-apoptotic and pro-apoptotic molecules. Recently, it has been shown that GSK-3β, a negative regulator of β-catenin, is involved in the activation of NF-κB. However, the mechanism of this regulation of NF-κB by GSK-3β is unclear. As GSK-3β inhibits β-catenin we hypothesized that β-catenin may be responsible for the regulation of NF-κB by GSK-3β; i.e. β-catenin may inhibit NF-κB activity. In this study we show that β-catenin physically interacts with NF-κB leading to the inhibition of NF-κB transcriptional and DNA-binding activities. We also show that in colon cancer cells with high β-catenin expression there is a suppressed NF-κB activity and depletion of β-catenin increases NF-κB activity. Similarly, in colon cancer cells that have a low level of β-catenin NF-κB activity is high and introduction of β-catenin reduces NF-κB activity. Importantly, we show that this suppression of NF-κB by β-catenin leads to a reduction of NF-κB target gene Fas expression. Also Fas-mediated apoptosis is reduced in β-catenin overexpressing cells, which can be reversed upon depletion of β-catenin. Introduction of the NF-κB subunit p65 can restore Fas expression indicating that the effect of β-catenin on Fas is through NF-κB. Furthermore, β-catenin expression was found to inversely correlate with Fas expression in human colon and breast primary tumor tissues. As Fas downregulation is important for tumors to evade immune surveillance, β-catenin inhibition of NF-κB and Fas downregulation likely plays and important role for colon cancer progression. Additionally, we found that phosphoinositide 3-kinase plays a role in the regulation of β-catenin inhibition of NF-κB through the disruption of the β-catenin/NF-κB complex. This study provides a link between two important signal transduction pathways as well as another mechanism of β-catenin oncogenesis. ^

Salivary cortisol, psychological stress and depressive symptoms among patients undergoing colon cancer screenings

As the second leading cause of cancer-related deaths in the United States, colon cancer has a high cure rate if detected early by a colonoscopy (U.S. Cancer Statistics Working Group, 2007). However, more than 41 million at-risk Americans are not properly receiving colonoscopy screenings according to the recommendations of the Center for Disease Control. This study provides insight into the physiological and psychological benefits of the colonoscopy procedure over and above cancer detection and prevention. Thirty-six patients receiving colonoscopic screening at the University of Connecticut Health Center participated in this study. A questionnaire battery that assessed perceived stress, depressive symptoms, colon cancer related worry, and social support, and optional saliva sampling was completed 2 weeks prior to and post colonoscopy. It was hypothesized that salivary cortisol concentrations, perceived stress, and self-reported depressive symptoms would show significant decreases from pre to post colonoscopy, and that these variables would all be positively correlated with one another. Results showed significant, positive correlations between depressive symptoms and both salivary cortisol (r (34)= .348, p< .05) and perceived stress (r (34)= .635, p< .01). Morning salivary cortisol levels decreased significantly from pre to post colonoscopy to levels below the population mean (t (16)=-3.711, p<. 01). No such differences were observed in either perceived stress or depressive symptoms. These results indicate that by decreasing cortisol concentrations to levels below that of the population mean, the colonoscopy provided physiological health benefits to patients beyond cancer screening. From a health psychology standpoint, this may encourage some of the 41 million Americans not receiving proper colon cancer screenings to adopt this potentially life-saving health behavior.

Jenny-Marguerite Colon, Hüftbild

Signatur des Originals: S 36/G02907

Léontine Fay, Hüftbild - Jenni-Vertpré, Hüftbild - Jenni-Colon, Hüftbild - Marie Thomase Amélie Dorval, Hüftbild - Alberr, Hüftbild - {[N.N.], Hüftbild

Signatur des Originals: S 36/G04476

High-resolution microarray analysis of chromosome 20q in human colon cancer metastasis model systems

Amplification of human chromosome 20q DNA is the most frequently occurring chromosomal abnormality detected in sporadic colorectal carcinomas and shows significant correlation with liver metastases. Through comprehensive high-resolution microarray comparative genomic hybridization and microarray gene expression profiling, we have characterized chromosome 20q amplicon genes associated with human colorectal cancer metastasis in two in vitro metastasis model systems. The results revealed increasing complexity of the 20q genomic profile from the primary tumor-derived cell lines to the lymph node and liver metastasis derived cell lines. Expression analysis of chromosome 20q revealed a subset of over expressed genes residing within the regions of genomic copy number gain in all the tumor cell lines, suggesting these are Chromosome 20q copy number responsive genes. Bases on their preferential expression levels in the model system cell lines and known biological function, four of the over expressed genes mapping to the common intervals of genomic copy gain were considered the most promising candidate colorectal metastasis-associated genes. Validation of genomic copy number and expression array data was carried out on these genes, with one gene, DNMT3B, standing out as expressed at a relatively higher levels in the metastasis-derived cell lines compared with their primary-derived counterparts in both the models systems analyzed. The data provide evidence for the role of chromosome 20q genes with low copy gain and elevated expression in the clonal evolution of metastatic cells and suggests that such genes may serve as early biomarkers of metastatic potential. The data also support the utility of the combined microarray comparative genomic hybridization and expression array analysis for identifying copy number responsive genes in areas of low DNA copy gain in cancer cells. ^

Oncologic outcomes in diabetic patients with colon cancer

Type II diabetes mellitus is a growing problem worldwide and although its association with increased cardiovascular morbidity and mortality is well known, its role in the development of cancer is now being further elucidated. Recently, there has been increasing evidence that not only are diabetics more susceptible towards development of particular types of cancer, but also have worse oncologic outcomes. This retrospective chart review investigates whether diabetics with colon cancer have a poorer prognosis than their nondiabetic counterparts. Patients with high risk Stage II and Stage III colon cancer who were diagnosed and/or treated at The University of Texas M.D. Anderson Cancer Center from 1/1/2000 till 12/1/2004 were included in our study. We carried out a survival analysis using Kaplan-Meier method and multivariable analysis to assess differences in outcomes of the two population groups. We found that the decreased overall survival in diabetics did not reach statistical significance but this could be due to a lower event rate in our study. Larger studies are required to investigate this further. ^

Retrospective cohort study to determine the effect of metformin on survival of diabetic patients with pancreatic adenocarcinoma

Background: Pancreatic cancer is the fourth most common cause of cancer death in the United States. Despite advances in cancer treatment, prognosis of pancreatic cancer remains extremely poor with survival rates of 24% and 5% in 1 and 5 years, respectively. Many patients with pancreatic cancer have a history of diabetes and are treated with various antidiabetic regimens including metformin. In multiple retrospective studies, metformin has been associated with decreased risk of cancer and cancer-related mortality. Metformin has also been reported to inhibit the growth of cancer cells, both in vitro and in vivo.^ Methods: We conducted a retrospective cohort study to examine the survival benefit of metformin in diabetic patients with pancreatic cancer at MD Anderson Cancer Center (MDACC). A dataset of 397 patients who carried the diagnosis of "Diabetes Mellitus" and "Pancreatic Cancer" at MD Anderson were screened for this study. ^ Results: Mean age of patients at diagnosis of cancer was 64.0 ± 8.7 years (range 37-84). The majority of the patients were male (65.6%) and of Caucasian race (78.5%). The most common antidiabetic regimen used were insulin and metformin (in 39.1% and 38.7%, respectively). Patients' cancer were staged as resectable in 34.1%, locally advanced unresectable in 29.1%, and disseminated disease in 36.7% of cases. Overall 1-year and 3-year survival rates for all stages combined were 51.8% and 7.6%, respectively. Earlier stage, metformin use, low CA19-9 level, better ECOG performance status, surgical intervention, negative surgical margins, and smaller tumor size were associated with longer survival. Metformin use was associated with a 33% decrease in risk of death (HR: 0.67; 95% CI: 0.51-0.88). Multivariate Cox proportional hazard regression showed hazard ratio of 1.77 (95% CI 1.49-2.10) for cancer stage, 0.65 (95% CI 0.49-0.86) for metformin use, and 1.68 (95% CI 1.26-2.23) for CA 19-9 level above population median. ^ Conclusion: Our study suggests that metformin may improve the outcome in diabetic patients with pancreatic cancer independently of other known prognostic factors. Pancreatic cancer carries extremely poor prognosis; metformin may provide a suitable adjunct therapeutic option for pancreatic cancer in patients with and without diabetes mellitus.^

Adult weight gain and risk of colon cancer in men

Previous research supports the hypothesis that a "rich" diet (i.e., high in fat and low in fiber) increases the risk of colon cancer. Previous research also supports the hypothesis that physical inactivity increases the risk of colon cancer, perhaps because physical inactivity decreases gut motility, thereby increasing tee time that carcinogens are in contact with the intestinal mucosa. Habitual physical inactivity, combined with rich diet, ordinarily results in chronic energy imbalance and gain in weight, except when energy balance is modified by disease or factors such as cigarette smoking. Cigarette smokers typically stay lean because of effects of smoking on the resting metabolic rate as well as on efficiency of caloric intake and storage. Therefore, if physical inactivity and rich diet do increase the risk of colon cancer, then weight gain during young adulthood should be positively associated with incidence of colon cancer during later life, especially in nonsmokers.^ This hypothesis was investigated in a cohort of 2,059 randomly selected middle-aged men who were employed at the Western Electric Company in Chicago and were free of clinically diagnosed cancer at initial examination in 1958. Body mass index (BMI) in middle age was calculated from measured height and weight at the initial examination. BMI at age 20 was estimated from weight at age 20 as recalled at the initial examination and height as measured at the initial examination. Change in BMI between age 20 and middle age was estimated by subtracting the BMI at 20 from the BMI in middle age. Forty-nine incident cases of colon cancer were detected during 25 years (43,326 person-years) at risk. When stratified by level of change in BMI from age 20 to middle age ($\le$1.9, 2.0-3.9, 4.0-5.9, $\ge$6.0 kg/m$\sp2$), age-adjusted relative hazards of colon cancer in never-smokers were 1.00, 1.22, 2.31, and 5.01, respectively (p for trend = 0.008); corresponding values in ever-smokers were 1.00, 0.95, 0.77, and 0.87, These associations did not change appreciably after further adjustment for BMI at age 20, subscapular-triceps skinfold ratio, cigarette smoking, consumption of alcohol, energy, fat, and calcium.^ We also investigated the hypothesis that the risk of colon cancer was higher in men who were lean at age 20 and became fat by middle age (lean-to-fat) than in men who were fat at age 20 and stayed fat in middle-age (fat-to-fat). "Lean" was defined as BMI $<$24 kg/m$\sp2$ at age 20 and as BMI $<$27.0 kg/m$\sp2$ in middle age. Among never-smokers, in comparison to men who were lean at age 20 and in middle age (lean-to-lean), the age-adjusted relative hazard of colon cancer was 1.43 in the fat-to-fat group (95% confidence interval (CI) 0.37-5.52) and 3.36 in the lean-to-fat group (95% CI 1.21-9.37). This investigation provides new results on the magnitude of risk of colon cancer associated with weight gain during adulthood (from age 20 to middle age). This relation was obscured or underestimated in previous studies due to effect-modification by cigarette smoking. Finally, the result supports the idea that a life-style characterized by chronic energy imbalance during young adulthood increases risk of colon cancer. ^

Fibulin-2 stabilizes tumor extracellular matrix and drives malignant progression of lung adenocarcinoma

The ECM of epithelial carcinomas undergoes structural remodeling during periods of uncontrolled growth, creating regional heterogeneity and torsional stress. How tumors maintain ECM integrity in the face of dynamic biophysical forces is still largely unclear. This study addresses these deficiencies using mouse models of human lung adenocarcinoma. Spontaneous lung tumors were marked by disorganized basement membranes, dense collagen networks, and increased tissue stiffness. Metastasis-prone lung adenocarcinoma cells secreted fibulin-2 (Fbln2), a matrix glycoprotein involved in ECM supra-molecular assembly. Fibulin-2 depletion in tumor cells decreased the intra-tumoral abundance of matrix metalloproteinases and reduced collagen cross-linking and tumor compressive properties resulting in inhibited tumor growth and metastasis. Fbln2 deposition within intra-tumoral fibrotic bands was a predictor of poor clinical outcome in patients. Collectively, these findings support a feed-forward model in which tumor cells secrete matrix-stabilizing factors required for the assembly of ECM that preferentially favors malignant progression. To our knowledge, this is the first evidence that tumor cells directly regulate the integrity of their surrounding matrix through the secretion of matrix-stabilizing factors such as fibulin-2. These findings open a new avenue of research into matrix assembly molecules as potential therapeutic targets in cancer patients.

Geographic variation in the utilization and survival associated with oxaliplatin chemotherapy in patients with stage III colon cancer

Background: Overall objectives of this dissertation are to examine the geographic variation and socio-demographic disparities (by age, race and gender) in the utilization and survival of newly FDA-approved chemotherapy agents (Oxaliplatin-containing regimens) as well as to determine the cost-effectiveness of Oxaliplatin in a large nationwide and population-based cohort of Medicare patients with resected stage-III colon cancer. Methods: A retrospective cohort of 7,654 Medicare patients was identified from the Surveillance, Epidemiology and End Results – Medicare linked database. Multiple logistic regression was performed to examine the relationship between receipt of Oxaliplatin-containing chemotherapy and geographic regions while adjusting for other patient characteristics. Cox proportional hazard model was used to estimate the effect of Oxaliplatin-containing chemotherapy on the survival variation across regions using 2004-2005 data. Propensity score adjustments were also made to control for potential bias related to non-random allocation of the treatment group. We used Kaplan-Meier sample average estimator to calculate the cost of disease after cancer-specific surgery to death, loss-to follow-up or censorship. Results: Only 51% of the stage-III patients received adjuvant chemotherapy within three to six months of colon-cancer specific surgery. Patients in the rural regions were approximately 30% less likely to receive Oxaliplatin chemotherapy than those residing in a big metro region (OR=0.69, p=0.033). The hazard ratio for patients residing in metro region was comparable to those residing in big metro region (HR: 1.05, 95% CI: 0.49-2.28). Patients who received Oxalipaltin chemotherapy were 33% less likely to die than those received 5-FU only chemotherapy (adjusted HR=0.67, 95% CI: 0.41-1.11). KMSA-adjusted mean payments were almost 2.5 times higher in the Oxaliplatin-containing group compared to 5-FU only group ($45,378 versus $17,856). When compared to no chemotherapy group, ICER of 5-FU based regimen was $12,767 per LYG, and ICER of Oxaliplatin-chemotherapy was $60,863 per LYG. Oxaliplatin was found economically dominated by 5-FU only chemotherapy in this study population. Conclusion: Chemotherapy use varies across geographic regions. We also observed considerable survival differences across geographic regions; the difference remained even after adjusting for socio-demographic characteristics. The cost-effectiveness of Oxaliplatin in Medicare patients may be over-estimated in the clinical trials. Our study found 5-FU only chemotherapy cost-effective in adjuvant settings in patients with stage-III colon cancer.^

Risk factors for surgical site infections among patients undergoing major colon surgery in the United States 2007-2009

Background: Surgical site infections (SSIs) after abdominal surgeries account for approximately 26% of all reported SSIs. The Center for Disease Control and Prevention (CDC) defines 3 types of SSIs: superficial incisional, deep incisional, and organ/space. Preventing SSIs has become a national focus. This dissertation assesses several associations with the individual types of SSI in patients that have undergone colon surgery. ^ Methods: Data for this dissertation was obtained from the American College of Surgeons' National Surgical Quality Improvement Program (NSQIP); major colon surgeries were identified in the database that occurred between the time period of 2007 and 2009. NSQIP data includes more than 50 preoperative and 30 intraoperative factors; 40 collected postoperative occurrences are based on a follow-up period of 30 days from surgery. Initially, four individual logistic regressions were modeled to compare the associations between risk factors and each of the SSI groups: superficial, deep, organ/space and a composite of any single SSI. A second analysis used polytomous regression to assess simultaneously the associations between risk factors and the different types of SSIs, as well as, formally test the different effect estimates of 13 common risk factors for SSIs. The final analysis explored the association between venous thromboembolism (VTEs) and the different types of SSIs and risk factors. ^ Results: A total of 59,365 colon surgeries were included in the study. Overall, 13% of colon cases developed a single type of SSI; 8% of these were superficial SSIs, 1.4% was deep SSIs, and 3.8% were organ/space SSIs. The first article identifies the unique set of risk factors associated with each of the 4 SSI models. Distinct risk factors for superficial SSIs included factors, such as alcohol, chronic obstructive pulmonary disease, dyspnea and diabetes. Organ/space SSIs were uniquely associated with disseminated cancer, preoperative dialysis, preoperative radiation treatment, bleeding disorder and prior surgery. Risk factors that were significant in all models had different effect estimates. The second article assesses 13 common SSI risk factors simultaneously across the 3 different types of SSIs using polytomous regression. Then each risk factor was formally tested for the effect heterogeneity exhibited. If the test was significant the final model would allow for the effect estimations for that risk factor to vary across each type of SSI; if the test was not significant, the effect estimate would remain constant across the types of SSIs using the aggregate SSI value. The third article explored the relationship of venous thromboembolism (VTE) and the individual types of SSIs and risk factors. The overall incidence of VTEs after the 59,365 colon cases was 2.4%. All 3 types of SSIs and several risk factors were independently associated with the development of VTEs. ^ Conclusions: Risk factors associated with each type of SSI were different in patients that have undergone colon surgery. Each model had a unique cluster of risk factors. Several risk factors, including increased BMI, duration of surgery, wound class, and laparoscopic approach, were significant across all 4 models but no statistical inferences can be made about their different effect estimates. These results suggest that aggregating SSIs may misattribute and hide true associations with risk factors. Using polytomous regression to assess multiple risk factors with the multiple types of SSI, this study was able to identify several risk factors that had significant effect heterogeneity across the 3 types of SSI challenging the use of aggregate SSI outcomes. The third article recognizes the strong association between VTEs and the 3 types of SSIs. Clinicians understand the difference between superficial, deep and organ/space SSIs. Our results indicate that they should be considered individually in future studies.^

Mechanisms of multidrug resistance: Differences between natural and acquired adriamycin -resistant human colon carcinoma cells

Mechanisms of multidrug resistance (MDR) were studied in two independent MDR sublines (AdR1.2 and SRA1.2) derived from the established human colon carcinoma cell line LoVo. AdR1.2 was developed by long-term continuous exposure of the cells to adriamycin (AdR) in stepwise increments of concentration, while SRA1.2 was selected by repetitive pulse treatments with AdR at a single concentration. In this dissertation, the hypothesis that the mechanism of drug resistance in SRA1.2 is different than that in AdR1.2 is tested. While SRA1.2 demonstrated similar biological characteristics when compared to the parental LoVo, AdR1.2 exhibited remarkable alterations in biological properties. The resistance phenotype of AdR1.2 was reversible when the cells were grown in the drug-free medium whereas SRA1.2 maintained its resistance for at least 10 months under similar conditions. Km and Vmax of carrier-mediated facilitated diffusion AdR transport were similar among the three lines. However, both resistant sublines exhibited an energy-dependent drug efflux. AdR1.2 appeared to possess an activated efflux pump, and a decreased nucleus-binding of AdR, whereas SRA1.2 showed merely a lower affinity in binding of AdR to the nuclei. Southern blot analysis showed no amplification of the MDR1 gene in either of the two resistant subclones. However, Western blot analysis using the C219 monoclonal antibody against P170 glycoprotein detected a Mr 150-kDa plasma protein (P150) in AdR1.2 but not in SRA1.2 or in the parental LoVo. In vitro phosphorylation studies revealed that P150 was a phosphoprotein; its phosphorylation was Mg$\sp{2+}$-dependent and could be enhanced by verapamil, an agent capable of increasing intracellular AdR accumulation in AdR1.2 cells. The phosphorylation studies also revealed elevated phosphorylation of a Mr 66-kDa plasma membrane protein that was detectable in the AdR1.2 revertant and in AdR1.2 when verapamil was present, suggesting that hyperphosphorylation of the Mr 66-kDa protein may be related to the reversal of MDR. SDS-PAGE of the plasma membrane protein demonstrated overproduction of a Mr 130-kDa, MDR-related protein in both the resistant sublines. The Mr 130-kDa, MDR-related protein in both the resistant sublines. The Mr 130-kDa protein was not immunoreactive with C219, but its absence in the AdR1.2 revertant and the parental LoVo suggests that it is an MDR-related plasma membrane protein. In conclusion, the results from this study support the author's hypothesis that the mechanisms responsible for "Acquired" and "Natural" MDR are not identical. ^

Genome instability quantified in constitutive tissues as well as putatively stable tumor tissue in hereditary non -polyposis colon cancer patients by small pool PCR

Microsatellite instability (MSI) is a hallmark of the mutator phenotype associated with Hereditary Non-Polyposis Colon Cancer (HNPCC). The MSI-High (MSI-H) HNPCC population has been well characterized, but the microsatellite low and stable (MSI-L/MSS) HNPCC population is much less understood. We hypothesize there are significant levels of MSI in HNPCC DNA classified as MSI-L/MSS, but no single variant allele makes up a sufficient population in the tumor DNA to be detected by standard analysis. Finding variants would suggest there is a mutator phenotype for the MSI-L/MSS HNPCC population that is distinct from the MSI-H HNPCC populations. This study quantified and compared MSI in HNPCC patients previously shown to be MSI-H, MSI-L/MSS and an MSI-H older, sporadic colorectal cancer patient. Small-pool Polymerase Chain Reactions (SP-PCRs) were conducted where the DNAs from each sample and controls are diluted into multiple pools, each containing approximately single genome equivalents. At least 100 alleles/sample were studied at six microsatellite loci. Mutant fragments were identified, quantified, and compared using Poisson statistics. Most of the variants were small deletions or insertions, with more mutants being deletions, as has been previously described in yeast and transgenic mice. SP-PCR, where most of the pools contained only 3 or less fragments, enabled identification of variants too infrequent to be detected by large pool PCR. Mutant fragments in positive control MSI-H tumor samples ranged from 0.26 to 0.68 in at least 4 of the 6 loci tested and were consistent with their MSI-H status. In the so called MSS tumors and constitutive tissues (normal colon tissue, and PBLs) of all the HNPCC patients, low, but significant levels of MSI were seen in at least two of the loci studied. This phenomenon was not seen in the sporadic MSI constitutive tissues nor the normal controls and suggests haploinsufficiency, gain-of-function, or a dominant/negative basis of the instability in HNPCC patients carrying germline mutations for tumor suppressor genes. A different frequency and spectrum of mutant fragments suggests a different genetic basis (other than a major mutation in MLH1 or MSH2) for disease in MSI-L and MSS HNPCC patients. ^

Transporte electrogénico en el colon de ratas privadas de sodio : bloqueo de canales epiteliales versus inhibición de la NA, K-ATPASA

La privación dietaria de sodio estimula la secreción de aldosterona. En el colon de rata, la aldosterona elevada aumenta la absorción de Na+, pero además torna electrogénico el mecanismo de absorción (normalmente electroneutro). Dicho transporte electrogénico puede suprimirse mediante el bloqueo de los canales epiteliales de Na+ en la membrana apical o la inhibición de la Na, KATPasa de la membrana basolateral. La absorción electrogénica de sodio está estrechamente acoplada al metabolismo aerobio, pero se desconoce si el bloqueo de los canales de Na+ reduce el consumo de oxígeno en igual medida que la inhibición de la Na, K-ATPasa. Se obtuvieron preparados de mucosa aislada del colon distal de ratas alimentadas con una dieta hiposódica por 10 días. Se determinó simultáneamente la corriente de cortocircuito y el consumo de oxígeno en condición basal y luego del bloqueo de canales de Na+ con amilorida (n=12) o de la Na, K-ATPasa con uabaína (n=12). Ambos tratamientos redujeron la corriente de cortocircuito en igual medida (>80%), pero la reducción en el consumo de oxígeno fue mayor con uabaína que con amilorida (p<0.03). Esto se debe probablemente a que la Na, KATPasa cumple otras funciones, además del transporte transepitelial de Na+, que son suprimidas por la uabaína pero no por la amilorida.