RESUMEN
AIM: To determine whether folic acid supplementation will reduce the recurrence of colorectal adenomas, the precursors of colorectal cancer, we performed a double-blind placebo-controlled trial in patients with adenomatous polyps. METHODS: In the current double-blind, placebo-controlled trial at this VA Medical Center, patients with colorectal adenomas were randomly assigned to receive either a daily 5 mg dose of folic acid or a matched identical placebo for 3 years. All polyps were removed at baseline colonoscopy and each patient had a follow up colonoscopy at 3 years. The primary endpoint was a reduction in the number of recurrent adenomas at 3 years. RESULTS: Of 137 subjects, who were eligible after confirmation of polyp histology and run-in period to conform compliance, 94 completed the study; 49 in folic acid group and 45 in placebo group. Recurrence of adenomas at 3-year was compared between the two groups. The mean number of recurrent polyps at 3-year was 0.36 (SD, 0.69) for folic acid treated patients compared to 0.82 (SD, 1.17) for placebo treated subjects, resulting in a 3-fold increase in polyp recurrence in the placebo group. Patients below 70 years of age and those with left-sided colonic adenomas or advanced adenomas responded better to folic acid supplementation. CONCLUSION: High dose folic acid supplementation is associated with a significant reduction in the recurrence of colonic adenomas suggesting that folic acid may be an effective chemopreventive agent for colorectal neoplasia.
Asunto(s)
Adenoma/prevención & control , Neoplasias Colorrectales/prevención & control , Suplementos Dietéticos , Ácido Fólico/uso terapéutico , Recurrencia Local de Neoplasia/prevención & control , Anciano , Colonoscopía , Relación Dosis-Respuesta a Droga , Método Doble Ciego , Femenino , Estudios de Seguimiento , Humanos , Estudios Longitudinales , Masculino , Persona de Mediana Edad , Factores de Riesgo , Resultado del TratamientoRESUMEN
Mortality from colorectal cancer, a leading cause of death in the U.S.A. and other western countries, has remained unchanged over the past 45 years. Therefore, the search for strategies to prevent the development and progression of colorectal cancer has markedly intensified. Chemoprevention is one such strategy. Accumulating evidence suggests that folic acid, a water soluble vitamin, could be an effective chemopreventive agent for colorectal cancer. Results from several studies have demonstrated that a diet deficient in folic acid may be associated with an increased risk of colonic neoplasia, whereas dietary supplementation of this nutrient may be chemopreventive. Although the mechanisms by which folic acid exerts its chemopreventive role in colorectal carcinogenesis remain to be fully elucidated, supplemental folic acid has been shown to arrest the loss of heterozygosity (LOH) of the tumor suppressor gene DCC (deleted in colorectal cancer) and to stabilize its protein in normal appearing rectal mucosa of patients with colorectal adenomas. Data from in vitro studies utilizing colon cancer cell lines suggest that supplemental folic acid or its metabolite 5-methyltetrahydrofolate (5-MTF) attenuates the expression and activation of EGF-receptor (EGFR) as well as proliferation of cells. The folic acid mediated reduction of EGFR function could partly be the result of suppression of EGFR gene through increased methylation of CpG sequences within its promoter.
Asunto(s)
Neoplasias Colorrectales/metabolismo , Neoplasias Colorrectales/prevención & control , Ácido Fólico/farmacología , Animales , Línea Celular Tumoral , Proliferación Celular , Islas de CpG , Receptor DCC , Metilación de ADN , Receptores ErbB/metabolismo , Humanos , Pérdida de Heterocigocidad , Receptores de Superficie Celular/genética , Proteínas Supresoras de Tumor/genéticaRESUMEN
We hypothesize that ERRP (EGFR-related protein), a recently identified negative regulator of EGFR may modulate EGFR function in colorectal carcinogenesis. The expression of ERRP and EGFR in normal and neoplastic colorectal tissue was examined. ERRP was highly expressed in normal colonic mucosa and benign colorectal adenomas, but lower in colorectal cancer. Mean scores for ERRP expression decreased significantly across well differentiated, moderately well differentiated and poorly differentiated (P = 0.002) tumors, respectively. ERRP expression became more attenuated in polyps with increasing grades of dysplasia. In contrast, expression of EGFR was inversely related to ERRP in representative samples of normal and neoplastic tissues.
Asunto(s)
Transformación Celular Neoplásica/genética , Neoplasias Colorrectales/genética , Neoplasias Colorrectales/fisiopatología , Regulación Neoplásica de la Expresión Génica , Glicoproteínas/biosíntesis , Adenoma/genética , Diferenciación Celular , Colon/fisiología , Pólipos del Colon/genética , Factor de Crecimiento Epidérmico , Receptores ErbB , Humanos , Proteínas OncogénicasRESUMEN
Although accumulating evidence suggests a chemopreventive role for folic acid (FA) in colorectal carcinogenesis, the underlying mechanisms are largely unknown. Previously, we reported that supplemental FA inhibits the expression and activation of epidermal growth factor receptor (EGFR) in colon cancer cell lines. To determine the mechanism(s) by which FA affects EGFR function, we have examined whether and to what extent supplemental FA or its metabolites 5-methyltetrahydrofolate (MTF), dihydrofolate (DF), and tetrahydrofolate (TF) will modulate basal and serum-induced activation of the EGFR promoter in the HCT-116 colon cancer cell line. HCT-116 cells were preincubated with or without (control) FA or one of its metabolites (10 microg/ml) for 48 h, transfected with the EGFR promoter luciferase reporter construct, and incubated for 48 h with FA, DF, TF, or 5-MTF in the absence or presence of 10% FBS. Supplemental FA as well as its metabolites markedly inhibited EGFR promoter activity and its methylation status. Exposure of the cells to 10% FBS caused a marked stimulation of EGFR promoter activity and its expression, both of which were greatly abrogated by supplemental FA and 5-MTF. In contrast, serum-induced activation of c-fos promoter activity was unaffected by 5-MTF. The 5-MTF-induced inhibition of serum-mediated stimulation of EGFR promoter activity and EGFR expression was reversed when methylation was inhibited by 5-aza-2'-deoxycytidine. Our data suggest that FA and its metabolite 5-MTF inhibit EGFR promoter activity in colon cancer cells by enhancing methylation. This could partly be responsible for FA-mediated inhibition of growth-related processes in colorectal neoplasia.
Asunto(s)
Azacitidina/análogos & derivados , Neoplasias del Colon/genética , Receptores ErbB/genética , Ácido Fólico/farmacología , Regiones Promotoras Genéticas/efectos de los fármacos , Antimetabolitos Antineoplásicos/farmacología , Azacitidina/farmacología , Western Blotting , Línea Celular Tumoral , Células Cultivadas , Neoplasias del Colon/metabolismo , Medio de Cultivo Libre de Suero , Metilación de ADN , Cartilla de ADN , Decitabina , Humanos , Luciferasas/genética , Reacción en Cadena de la Polimerasa de Transcriptasa Inversa , Tetrahidrofolatos/farmacología , TransfecciónRESUMEN
We have demonstrated that folic acid inhibits cell proliferation and epidermal growth factor receptor (EGFR) activation in colon cancer cell lines. We examined the effect of one year supplemental folic acid (5 mg/day) on the rectal mucosal expression of beta-catenin and pGSK3beta, known to be affected by EGF-R, in patients with colorectal adenomas. Folic acid treatment significantly reduced nuclear expression of beta-catenin (P < 0.05) and cellular expression of pGSK3beta (P < 0.01) when compared to placebo. Folic acid may exert its chemopreventive effect, at least in part, through inhibition of nuclear translocation of beta-catenin.
Asunto(s)
Adenoma/metabolismo , Núcleo Celular/metabolismo , Neoplasias Colorrectales/metabolismo , Proteínas del Citoesqueleto/metabolismo , Ácido Fólico/administración & dosificación , Mucosa Intestinal/efectos de los fármacos , Transactivadores/metabolismo , Adolescente , Adulto , Suplementos Dietéticos , Receptores ErbB/metabolismo , Femenino , Glucógeno Sintasa Quinasa 3/metabolismo , Glucógeno Sintasa Quinasa 3 beta , Humanos , Masculino , Persona de Mediana Edad , Fosforilación , Proyectos Piloto , Placebos , beta CateninaRESUMEN
Loss of heterozygosity (LOH) and/or inactivation of tumor suppressor genes are implicated in the initiation and progression of many malignancies, including colorectal cancer. Although accumulating evidence suggests a chemopreventive role for folate in colorectal cancer, regulatory mechanisms are poorly understood. The primary objective of the current investigation was to determine whether folic acid would prevent LOH of the three tumor suppressor genes, deleted in colorectal cancer (DCC), adenomatous polyposis coli (APC) and p53 in macroscopically normal appearing rectal mucosa of patients with adenomatous polyps. In addition, the effect of folic acid on rectal mucosal proliferation was determined. Twenty patients were randomized in a double-blind study to receive either folic acid 5mg once daily or identical placebo tablets for 1 year. Genomic DNA and total protein were extracted from the rectal mucosa at baseline and after 1 year of treatment and analyzed for LOH and protein levels of APC, DCC and p53 genes. In addition, paraffin-embedded mucosal specimens were analyzed for proliferating cell nuclear antigen (PCNA) immunoreactivity, as a measure of cellular proliferative activity. Folate supplementation prevented LOH of DCC gene in five out of five (100%) patients who demonstrated baseline heterozygosity, whereas two out of four (50%) placebo-treated patients with baseline heterozygosity demonstrated allelic loss. Mucosal protein levels of DCC were also reduced in 7 of 10 (70%) placebo-treated patients compared to only 2 of 10 (20%) of patients treated with folate. Levels increased, however, in eight and three patients in the folic acid and placebo groups, respectively (P<0.02). Folic acid caused no change in allelic status of either APC or p53 gene. Folate supplementation caused a small, but not statistically significant, 16% reduction in mucosal proliferation, whereas placebo treatment resulted in a 88% (P<0.05) increase in this parameter, when compared with the corresponding baseline values. Our results indicate that folic acid prevents an increase in proliferation and arrests LOH of DCC gene and also stabilizes its protein in normal appearing rectal mucosa of patients with colorectal adenomas. Taken together, our data suggest that one of the ways folate may exert its chemopreventive effect is by stabilizing certain tumor suppressor gene(s) and preventing further increases in proliferation.
Asunto(s)
Adenoma/genética , Adenoma/prevención & control , Proteína de la Poliposis Adenomatosa del Colon/genética , Moléculas de Adhesión Celular/genética , Neoplasias Colorrectales/genética , Neoplasias Colorrectales/prevención & control , Ácido Fólico/farmacología , Genes p53/genética , Hematínicos/farmacología , Pérdida de Heterocigocidad , Proteínas Supresoras de Tumor/genética , Adenoma/etiología , Administración Oral , Anciano , División Celular , Neoplasias Colorrectales/etiología , Receptor DCC , ADN de Neoplasias , Método Doble Ciego , Femenino , Humanos , Mucosa Intestinal , Masculino , Persona de Mediana Edad , Placebos , Receptores de Superficie CelularRESUMEN
Aging and gastrointestinal malignancies, including that of the stomach are associated with increased activation of EGF-receptor (EGFR). Although the intracellular events that regulate this process are poorly understood, we hypothesize that loss of ERRP (EGFR-related protein; GenBank accession number AF187818), a recently identified negative regulator of EGFR, that possesses a substantial homology to the ligand binding extracellular domain of EGFR, may contribute to this event. In support of our hypothesis, we have observed that in Fischer-344 rats, whereas aging is associated with increased activation of EGFR in the gastric mucosa, expression of ERRP decreases inthis tissue during this period. The latter is accompanied by a concomitant reduction in the amount of TGF-alpha bound to ERRP. In contrast, the amount of TGF-alpha bound to EGFR is found to be higher in the gastric mucosa of aged than in young rats. This is accompanied by a concomitant rise in EGFR levels. In the gastric mucosa, EGFR and ERRP are found to be colocalized. Gastric adenocarcinoma in humans, which has been shown to be associated with increased activation of EGFR, shows a substantial reduction in ERRP expression, when compared with benign tissues. We conclude that increased activation of EGFR in the gastric mucosa during aging and carcinogenesis may partly be due to the loss of ERRP.
Asunto(s)
Envejecimiento/fisiología , Transformación Celular Neoplásica , Mucosa Gástrica/patología , Genes erbB-1/genética , Glicoproteínas/biosíntesis , Glicoproteínas/genética , Animales , Secuencia de Bases , Biopsia con Aguja , Western Blotting , Células Cultivadas , Receptores ErbB , Mucosa Gástrica/citología , Mucosa Gástrica/metabolismo , Regulación de la Expresión Génica , Inmunohistoquímica , Masculino , Modelos Animales , Datos de Secuencia Molecular , Probabilidad , Ratas , Ratas Endogámicas F344 , Receptor ErbB-2 , Medición de Riesgo , Sensibilidad y Especificidad , Neoplasias Gástricas/etiología , Neoplasias Gástricas/patologíaRESUMEN
The current study is based on the hypothesis that aging predisposes gastric mucosa to carcinogenesis through altered expression and/or mutations of genes involved in cell growth. To test this hypothesis, we investigated the age-associated changes in mutation of adenomatous polyposis coli (APC), deleted in colorectal cancer (DCC), p53, and K-ras genes in the gastric mucosa of 19 healthy subjects of varying ages (25-91 yr). Specifically, we studied the loss of heterozygosity (LOH) of these genes in cardia, body, and antrum of the stomach. We observed that 3 of 19 subjects (16%) over 60 yr of age show LOH of at least one of the tumor suppressor genes. Among the subjects over 60 yr of age, the incidence of LOH is 38% (3/8). Two of three subjects had mutations in more than one tumor suppressor gene. In all three affected subjects, mutation in APC, DCC, or p53 was located mainly in the body of the stomach, suggesting increased susceptibility of this region to neoplastic changes. However, no LOH of K-ras was observed in these subjects. Our observation that subjects over 60 yr of age show mutation in one or more of the tumor suppressor genes suggests an age-related increase in predisposition of the stomach to neoplasia.