Affiliations of authors: R. Z. Stolzenberg-Solomon, Cancer Prevention Studies Branch, Division of Clinical Sciences, National Cancer Institute, Bethesda, MD, and Department of Epidemiology, The Johns Hopkins University School of Hygiene and Public Health, Baltimore, MD; D. Albanes, T. J. Hartman, J. A. Tangrea, P. R. Taylor, Cancer Prevention Studies Branch, Division of Clinical Sciences, National Cancer Institute; F. J. Nieto, Department of Epidemiology, The Johns Hopkins University School of Hygiene and Public Health; M. Rautalahti, J. Virtamo, National Public Health Institute, Helsinki, Finland; J. Sehlub, U.S. Department of Agriculture, Jean Mayer U.S. Department of Agriculture Human Nutrition Research Center at Tufts University, Boston.
Correspondence to: Rachael Z. Stolzenberg-Solomon, Ph.D., M.P.H., R.D., National Institutes of Health, 6006 Executive Blvd., Suite 321, Bethesda, MD 20892-7058 (e-mail: RS221Z{at}NIH.GOV).
![]() |
ABSTRACT |
---|
![]() ![]() ![]() ![]() ![]() ![]() ![]() |
---|
![]() |
INTRODUCTION |
---|
![]() ![]() ![]() ![]() ![]() ![]() ![]() |
---|
Few risk factors for pancreatic cancer have been identified. Age and cigarette smoking are most consistently associated with greater risk (3,4) with a rapid and substantial reduction in risk following smoking cessation (5). Coffee consumption and alcohol consumption have been studied extensively with conflicting results, and recent reviews (4,6) have concluded that there is insufficient evidence to support either as a causal factor. There is evidence to support a protective role for diets high in fruits and vegetables, vitamin C, and fiber (6), although it remains unknown whether (or which) specific nutrients in fruits and vegetables may account for the association.
The methyl donors, methionine and choline, and the methyl cofactors, folate and vitamin B12, are nutritional components involved in methylation and synthesis of DNA. Imbalances in DNA methylation may affect chromosome stability and gene expression throughout carcinogenesis (7). DNA hypomethylation or hypermethylation may increase the susceptibility of genes to mutations (7,8). In addition, hypomethylation may increase oncogene expression, and hypermethylation may silence tumor suppressor gene expression (9,10). Methionine, in the form S-adenosyl methionine, is the principal methyl donor for methylation reactions. Although methionine is an essential amino acid required in the diet of humans, a substantial proportion can be regenerated from homocysteine via methionine synthase with methyltetrahydrofolate and vitamin B12 as cofactors. Methylenetetrahydrofolate is used to synthesize methyltetrahydrofolate via methylenetetrahydrofolate reductase, as well as to synthesize nucleotides (purines and thymidylate) for DNA synthesis. Cigarette smoke may influence methyl-group availability by affecting folate status and interfering with vitamin B12 metabolism (11,12). Diets having lower methyl-group availability (i.e., low intake of folate and methionine and high alcohol consumption) have been associated with colorectal cancer (13,14) and may likewise contribute to pancreatic cancer. The protective association between fruits and vegetables, the major dietary folate sources, and pancreatic cancer (4) suggests that factors influencing methylation might be related to the development of this cancer. To our knowledge, no study has examined this relationship.
We investigated concentrations of serum folate (methyltetrahydrofolate), total homocysteine, and vitamin B12 in relation to pancreatic cancer risk. To increase the precision around homocysteine's use as a marker for methylation reactions, we also measured serum creatinine and pyridoxal-5'-phosphate (PLP, the coenzyme form of vitamin B6 measured in serum), which have been positively and inversely associated with serum homocysteine, respectively (15,16). Our purpose was to determine whether nutritional and environmental factors known to influence methyl-group availability are associated with the development of pancreatic cancer.
![]() |
SUBJECTS AND METHODS |
---|
![]() ![]() ![]() ![]() ![]() ![]() ![]() |
---|
The study was approved by the institutional review boards of both the National Public Health Institute in Finland and the U.S. National Cancer Institute. All study participants provided written informed consent prior to the study's initiation. Details of the study rationale, design, and methods have been described previously (17).
Baseline Characteristics, Smoking, and Dietary Factors
The study participants completed questionnaires on general background characteristicsmedical, smoking, and dietary histories during their baseline visit. Diet was assessed with the use of a self-administered dietary history questionnaire that determined the frequency of consumption and usual portion size of 276 food items during the past year; a color picture booklet was used as a guide for food items and portion size (17). The questionnaire was linked to a food-composition database of the National Public Health Institute in Finland. The questionnaire was developed for the ATBC Study, and its correlation coefficients for validity and reliability ranged from .40 to .80 and from .56 to .88, respectively (14,18). The diet history questionnaire was completed by 93% of the ATBC Study participants (17) and by 92% of the pancreatic cancer case subjects.
Case Ascertainment and Control Selection
Cases were ascertained by linkage of the cohort participants to the Finnish Cancer Registry and death certificates. The Finnish Cancer Registry provides almost 100% case ascertainment in Finland (17,19,20). All relevant medical records were collected by ATBC Study personnel for reported incident pancreatic cancer cases and were reviewed independently by two study oncology experts (17). Histopathologic diagnosis was assigned centrally by the study pathology review group after examining pathology and cytology specimens (17). Only cases confirmed by the study physicians as incident primary malignant neoplasms of the exocrine pancreas (International Classification of Diseases, ninth revision [ICD-9] (21) code 157), during the period from January 1985 through December 1995, were used for the analysis. The follow-up time ranged from 7 to 10 years. Islet cell carcinomas (ICD-9 code 157.4) were excluded because their etiology may be different from that of the exocrine tumors. There were 130 confirmed exocrine pancreatic cancer cases.
Control subjects were selected from participants in the ATBC Study who were alive at the time the case subject was diagnosed and free from cancer except nonmelanoma skin cancer as of December 1995. Two control subjects were matched to each case subject by (a) age (±5 years); (b) baseline month of blood draw, to control for seasonal variation of nutrient intake and sample degradation; (c) completion of dietary history questionnaire, to maximize power for the dietary analysis; (d) study center, to control for potential differences in blood handling; and (e) intervention group assignment.
Of the 130 case subjects with pancreatic cancer and 260 matched control subjects, 126 case subjects and 247 control subjects were used for the statistical analyses of the serum analytes. The remaining individuals were excluded because of cracked vials and serum loss during the laboratory analyses. One hundred sixteen of the case subjects and their matched control subjects had complete dietary histories.
Assessment of Serum Biomarkers
Fasting serum samples were collected at the ATBC Study participants' prerandomization baseline visit, and samples were stored in the dark at -70 °C. The stored serum samples from the case and control subjects were sent on dry ice to the Vitamin Metabolism Laboratory at the Jean Mayer U.S. Department of Agriculture Human Nutrition Research Center at Tufts University, Boston, MA, for nutrient determination.
Serum samples from the case and control subjects were analyzed for total concentrations of homocysteine, vitamin B12, folate, PLP, and creatinine. Total homocysteine concentration was determined by use of high-performance liquid chromatography with fluorescence detection done as described by Araki and Sako (22). Serum folate and vitamin B12 (cobalamin) concentrations were determined by radioassay with a commercial kit from Bio-Rad Laboratories (Richmond, CA), and PLP concentration was determined by the tyrosine decarboxylase apoenzyme method as described by Shin-Buehring et al. (23). Measurement of serum creatinine levels was performed by use of the standard method (24).
Specimens from the case and control subjects were handled in the same standard manner. The laboratories were blinded to case and control status. Matched serum case and control samples were analyzed consecutively as triplets. Blinded replicate quality-control phantom samples from male volunteers aged 50-69 years were placed toward the beginning and the end of each batch. The quality-control sample size was approximately 10% of each batch and the study sample. Intra-batch and inter-batch coefficients of variation percent, respectively, were 10.1 and 13.8 for serum total homocysteine, 11.7 and 13.5 for serum PLP, 6.8 and 9.0 for serum folate, 7.6 and 11.3 for serum vitamin B12, and 4.3 and 4.6 for serum creatinine.
Baseline serum -tocopherol, ß-carotene, and retinol concentrations were
determined in all participants during the trial by high-performance liquid chromatography (17,25) and used to evaluate for confounding of the main effects.
Statistical Analyses
Analyses were performed separately for nutrients from serum, foods, and supplements. Nutrients were analyzed both as continuous and as categorical variables. Variables were categorized on the basis of the distribution of the controls for the conditional logistic regression analyses. Trends of the categorical variables were tested by calculating a score variable based on the median values of each category. Categories for the smoking inhalation variable were defined as never/seldom, often, and always. Pack-years were estimated from baseline smoking history by multiplying the number of years of smoking by the average number of packs smoked per day. Smoking cessation was defined as having quit smoking for three or more consecutive follow-up visits during the trial or for 1 year.
Spearman correlations were performed to assess correspondence between the study variables. Linear regression models for serum folate, vitamin B12, PLP, and total homocysteine were created to determine which other factors, including dietary nutrient estimates, were predictive of the serum markers. Natural log-transformed serum nutrients were used as dependent variables in the linear regression models, if they were not normally distributed. Dietary nutrients that were highly correlated (statistically) with energy (data not shown) were energy adjusted by use of the residual method described by Willett and Stampfer (26). Log-transformed dietary nutrients were used for energy adjustment for those nutrients that were not normally distributed.
Because many of the variables had skewed distributions, the characteristics of the case and control subjects were compared by use of the nonparametric Wilcoxon rank sum test for continuous variables and chi-squared tests for proportions. Odds ratios (ORs) and 95% confidence intervals (CIs) were determined by use of conditional logistic regression. Multivariable models were developed separately for each serum nutrient and smoking variable by individually adding covariates to the model. Variables were considered confounders if they were associated with both the disease and the risk factor and if they changed the risk estimate by 10% or more. Effect modification was determined by the addition of interaction terms using the categorical trend variables to the multivariable models and by stratification. Attributable risk was estimated with Levin's formula (27) by determining the OR for serum folate and PLP with the most adequate serum tertile as the reference category.
All statistical analyses were performed with the use of Statistical Analytic Systems (SAS) software (SAS Institute, Inc., Cary, NC), and statistical tests were two-tailed. Because case subjects and control subjects were matched, the median values, proportions, and risk estimates (including those labeled as crude) should be interpreted as adjusted for the matching factors.
![]() |
RESULTS |
---|
![]() ![]() ![]() ![]() ![]() ![]() ![]() |
---|
|
Table 2 presents results from the multivariable conditional logistic
regression models predicting cancer risk by use of the baseline serum biomarkers categorized as
tertiles. Pancreatic cancer was inversely associated with both serum folate and PLP, with the
highest nutrient tertiles being at half the risk compared with the lowest tertiles, and both nutrients
demonstrated statistically significant trends. The addition of serum vitamin B12,
serum total homocysteine, and number of cigarettes smoked daily to the univariate model of
serum folate strengthened folate's inverse association. Serum folate attenuated the
association between serum PLP and pancreatic cancer. After we controlled for serum folate, the
highest tertile of serum total homocysteine and serum vitamin B12 suggested
nonsignificant inverse and positive associations, respectively, with pancreatic cancer. Exclusion
of case subjects diagnosed early during follow-up (i.e., in the first 1, 2, 3, or even 4 years; data
not shown) did not change the risk estimates. The attributable risk estimate for serum folate and
PLP (lowest tertile versus highest tertile) is 0.29 and 0.26, respectively.
|
|
|
![]() |
DISCUSSION |
---|
![]() ![]() ![]() ![]() ![]() ![]() ![]() |
---|
An important strength of our study lies in its large prospective nature, with a greater number of cases providing sufficient power to detect smaller differences in risk factors, compared with most previous studies (4). We eliminated recall bias by obtaining the biochemical sample and other risk factor exposure data at baseline, before pancreatic cancer was diagnosed. Our study also has internal consistency; both the case and the control subjects were derived from the same study cohort, thus eliminating control selection bias. Consistent with other studies and despite not having a nonsmoking comparison group, our study demonstrated increasing risk and a positive dose-response relationship for pancreatic cancer with greater smoking. Our measurement of serum nutrient concentrations better reflects absorption and biologically active dose than self-reported intake. Finally, the case subjects had statistically lower baseline dietary folate intake than the control subjects, which is in accordance with our serum folate results.
Mechanisms by which the methyl-group-related serum nutrients may influence carcinogenesis remain speculative. DNA hypomethylation, through epigenetic, nongenotoxic events (9), could result from folate inadequacy. Thus far, only transcriptional silencing of the wild-type p16 tumor suppressor gene through regional hypermethylation of the gene's 5'-CpG islands has been observed in 14%-21% of pancreatic tumors (32). Higher total homocysteine concentrations may prevent hypermethylation by less regeneration of methionine for methylation reactions and possibly account for our observed risk reduction with higher total homocysteine concentrations (after controlling for folate status). Hypermethylation could lead to decreased expression of tumor suppressor genes and increased susceptibility to carcinogens (7), possibly accounting for the positive association with serum vitamin B12 and its interaction with smoking dose. Cigarette smoke-related cyanide, organic nitrites, and nitrous oxide may inactivate vitamin B12 and methionine synthase and thus interfere with vitamin B12's function (12,33). Heavy smokers have higher serum concentrations of the coenzymatically inactive form of vitamin B12, cyanocobalamin (33), which could result in decreased remethylation of methionine, decreased levels of S-adenosyl methionine, and less DNA methylation in tissues.
Alternatively, inadequate folate or pyridoxine status could result in less
methylenetetrahydrofolate available for methylation of deoxyuridylate to deoxythymidylate,
misincorporation of uracil for thymine in DNA, and a greater potential for chromosome strand
breaks (34) and/or impaired DNA excision repair (35). PLP is required as a coenzyme for the synthesis of methylenetetrahydrofolate.
Studies that have demonstrated a protective association between the homozygous recessive
thermolabile methylenetetrahydrofolate reductase genotype, C (cytosine) T (thymine)
substitution at base pair 677 (alanine to valine) and colon cancer (36,37)
and our observed reduced risk associated with more adequate folate and PLP status may support
this mechanism.
Deficiencies in both folate and pyridoxine have been shown to impair pancreatic exocrine function in rats (38-42). This situation could theoretically lead to incomplete digestion of food, greater duodenal cholecystokinin release, and stimulation of pancreatic enzyme production, hypertrophy, and hyperplasia, thereby increasing the susceptibility of the pancreas to carcinogens. Chronic hypercholecystokininemia has been shown to enhance pancreatic carcinogenesis in animals (43-46). In addition, animals treated with an inhibitor of cellular methylation reactions, ethionine, develop acute hemorrhagic pancreatitis (47-49) as a consequence of autolytic destruction of the pancreas (50), and chronic pancreatitis has been associated with increased pancreatic cancer risk (51-54).
Our having studied male Finnish smokers raises the question of generalizability to other
populations. Smokers are a high-risk population for pancreatic cancer because cigarette smoke
contains chemicals that are likely pancreatic carcinogens (3).
Nitrosamines produced during cigarette smoking can induce G (guanosine) A (adenosine)
transitions at the second nucleotide of a GG pair, which is the most common alteration found in
pancreatic cancer K-ras mutations (55). The overwhelming effect of the
smoke-related carcinogens to which heavy smokers are exposed likely explains the lack of a
dose-response relationship observed with serum PLP among those with greater smoking dose
(Table 4
). Cigarette smoke, however, has been attributed to 29%
of pancreatic cancer deaths in males (56), such that other exposures must
contribute to the development of the disease.
The fact that the majority of our study sample had less than adequate folate and pyridoxine status is likely relevant to our findings. Lower folate status has been associated with risk for neural tube defects (57). By contrast, Finland has a relatively low incidence of neural tube defects (five of 10 000 births), approximately half of that of the United States (10 of 10 000 births) (58). International differences in the incidence of neural tube defects are likely influenced by genetic predisposition and diet. Our population's low folate and PLP concentrations most likely reflect their smoking and/or dietary habits. Cigarette smokers tend to have poorer nutritional status for these vitamins (11,12, 29) and may have greater requirements for them than nonsmokers. In our study of smokers, 29% and 26% of the pancreatic cancer cases may have potentially been prevented by improving the folate and pyridoxine status of those in the lowest serum tertiles, respectively, based on the attributable risk estimates. In addition, the protective relationships of these nutrients tended to be greater among those who smoked less. Adequate folate and pyridoxine status appeared to decrease the susceptibility to pancreatic cancer in the present studya finding that should be confirmed in other smoking populations and in nonsmokers.
Other limitations of our study are that more adequate folate and pyridoxine status may reflect a healthier lifestyle or health status in general and the adjustment for serum folate in the other serum nutrient models. There could be other unmeasured correlates to more adequate nutritional status not controlled for in our analysis. In addition, poorer folate or pyridoxine status could be a marker for subclinical disease, particularly as the latency of pancreatic cancer is unknown and it is most often diagnosed at advanced stages; however, our observation of similar associations after excluding early case subjects argues against this. The potential confounding effect of other unmeasured health status-related risk factors needs further investigation. Finally, although serum folate may be interrelated with serum vitamin B12, total homocysteine, and PLP in the causal pathways for disease, adjustment for serum folate in these models (or for serum total homocysteine and vitamin B12 in the folate model) either strengthened or slightly attenuated the crude associations, suggesting independent associations and perhaps multiple mechanisms by which these factors may be contributing to our observed associations.
In conclusion, we found statistically significant reduced risks for cancer of the exocrine pancreas associated with more adequate folate and pyridoxine status in a prospective cohort of older male smokers. Dose-response relationships were evident. Level of cigarette smoking was also positively related to cancer risk. The level of folic acid grain fortification in the United States has been estimated to reduce the risk of neural tube defects by 22%-26% in women with marginal folate status (59) and, in view of our study findings, could conceivably have an impact on exocrine pancreatic cancer incidence in persons with marginal folate status. The results from this observational study support the hypothesis that maintaining adequate folate and pyridoxine status may reduce the risk of pancreatic cancer and confirm the risk associated with cigarette smoking. Additional studies are needed to determine if the observed associations reflect cause-and-effect relationships.
![]() |
NOTES |
---|
![]() |
REFERENCES |
---|
![]() ![]() ![]() ![]() ![]() ![]() ![]() |
---|
1 Ries LA, Kosary CL, Hankey BF, Miller BA, Harras A, Edwards BK, editors. SEER cancer statistics review, 1973-1994: tables and graphs. Bethesda (MD): National Institutes of Health, National Cancer Institute; 1997 Report No.: DHHS Publ No. (NIH)97-2789.
2 Fernandez E, La Vecchia C, Porta M, Negri E, Lucchini F, Levi F. Trends in pancreatic cancer mortality in Europe, 1955-1989. Int J Cancer 1994;57:786-92.[Medline]
3 Anderson KE, Potter JD, Mack TM. Pancreatic cancer. In: Schottenfeld D, Fraumeni JF Jr, editors. Cancer epidemiology and prevention. 2nd ed. New York (NY): Oxford University Press; 1996. p. 725-71.
4 Howe GR, Burch JD. Nutrition and pancreatic cancer. Cancer Causes Controls 1996;7:69-82.[Medline]
5 Harvard report on cancer prevention. Causes of human cancer. Smoking. Cancer Causes Control 1996;7 Suppl 1:S5-6.
6 World cancer research fund in association with the American Institute for Cancer Research. Food, nutrition and the prevention of cancer: a global prospective. Washington (DC): American Institute for Cancer Research; 1997. p. 176-97.
7 Baylin SB, Herman JG, Graff JR, Vertino PM, Issa JP. Alterations in DNA methylation: a fundamental aspect of neoplasia. Adv Cancer Res 1998:72:141-96.[Medline]
8 Chen RZ, Pettersson U, Beard C, Jackson-Grusby L, Jaenisch R. DNA hypomethylation leads to elevated mutation rates. Nature 1998;395:89-93.[Medline]
9 Counts JL, Goodman JI. Hypomethylation of DNA: a nongenotoxic mechanism involved in tumor promotion. Toxicol Lett 1995;82-3:663-72.
10 Jones PA. DNA methylation errors and cancer. Cancer Res 1996;56:2463-7.[Medline]
11 Feinman L, Lieber CS. Nutrition and diet in alcoholism. In: Shils M, Olson J, Shike M, editors. Modern nutrition in health and disease. 8th ed. Baltimore (MD): Lea & Febiger; 1994. p. 1081-97.
12 Piyathilake CJ, Macaluso M, Hine RJ, Richards EW, Krumdieck CL. Local and systemic effects of cigarette smoking on folate and vitamin B-12. Am J Clin Nutr 1994;60:559-66.[Abstract]
13 Giovannucci E, Stampfer MJ, Colditz GA, Rimm EB, Trichopoulos D, Rosner BA, et al. Folate, methionine, and alcohol intake and risk of colorectal adenoma. J Natl Cancer Inst 1993;85:875-84.[Abstract]
14 Glynn SA, Albanes D, Pietinen P, Brown CC, Rautalahti M, Tangrea JA, et al. Colorectal cancer and folate status: a nested case-control study among male smokers. Cancer Epidemiol Biomarkers Prev 1996;5:487-94.[Abstract]
15 Ubbink JB, Vermaak WJ, van der Merwe A, Becker PJ. Vitamin B-12, vitamin B-6, and folate nutritional status in men with hyperhomocysteinemia. Am J Clin Nutr 1993;57:47-53.[Abstract]
16 Brattstrom L, Lindgren A, Isrealsson B, Andersson A, Hultberg B. Homocysteine and cysteine: determinants of plasma levels in middle-aged and elderly subjects. J Intern Med 1994;236:633-41.[Medline]
17 The ATBC Cancer Prevention Study Group. The alpha-tocopherol, beta-carotene lung cancer prevention study: design, methods, participant characteristics, and compliance. Ann Epidemiol 1994;4:1-10.[Medline]
18 Pietinen P, Hartman AM, Haapa E, Rasanen L, Haapakoski J, Palmgren J, et al. Reproducibility and validity of dietary assessment instruments. I. A self-administered food use questionnaire with a portion size picture booklet. Am J Epidemiol 1988;128:655-66.[Abstract]
19 Kyllonen LE, Teppo L, Lehtonen M. Completeness and accuracy of registration of colorectal cancer in Finland. Ann Chir Gynaecol 1987;76:185-90.[Medline]
20 Pukkala E. Use of record linkage in small-area studies. In: Elliott P, Cuzick J, English D, Stern R, editors. Geographical and environmental epidemiology: methods for small-area studies. Oxford (U.K.): Oxford University Press; 1992. p. 125-31.
21 Physician ICD-9-CM; Vols. 1 and 2. Salt Lake City (UT): Medicode, Inc.; 1997.
22 Araki A, Sako Y. Determination of free and total homocysteine in human plasma by high-performance liquid chromatography with fluorescence detection. J Chromatogr 1987;422:43-52.[Medline]
23 Shin-Buehring Y, Rasshofer R, Endres W. A new enzymatic method for pyridoxal-5' phosphate determination. J Inherit Metab Disorders 1981;4:123-24.
24 Larsen K. Creatinine assay by a reaction-kinetic principle. Clin Chim Acta 1972;41:209-17.[Medline]
25
Milne DB, Botnen J. Retinol, alpha-tocopherol, lycopene, and
alpha- and beta-carotene simultaneously determined in plasma by isocratic liquid
chromatography. Clin Chem 1986;32:874-6.
26 Willett W, Stampfer MJ. Total energy intake: implications for epidemiologic analyses. Am J Epidemiol 1986;124:17-27.[Abstract]
27 Levin ML. The occurrence of lung cancer in man. Acta Intern Cancer 1973;9:531.
28 Gibson RS. Assessment of the status of folate and vitamin B12. In: Gibson RS, editor. Principles of nutritional assessment. New York (NY): Oxford University Press; 1990. p. 461-86.
29 Leklem JE. Vitamin B6. In: Shils ME, Olson JA, Shike M, editors. Modern nutrition in health and disease. Philadelphia (PA): Lea & Febiger; 1994. p. 383-401.
30 Gibson RS. Assessment of the status of vitamin B6 status. In: Gibson RS, editor. Principles of nutritional assessment. New York (NY): Oxford University Press; 1990. p. 445-60.
31 Green R, Jacobsen DW. Clinical implications of hyperhomocysteinemia. In: Bailey LB, editor. Folate in health and disease. New York (NY): Marcel Dekker; 1995. p. 75-122.
32 Schutte M, Hruban RH, Geradts J, Maynard R, Hilgers W, Rabindran SK, et al. Abrogation of the Rb/p16 tumor-suppressive pathway in virtually all pancreatic carcinomas. Cancer Res 1997;57:3126-30.[Abstract]
33 Herbert V. Vitamin B12. In: Ziegler EE, Filer LJ, editors. Present knowledge in nutrition. 7th ed. Washington (DC): ILSI Press; 1996. p. 191-205.
34
Blount BC, Mack MM, Wehr CM, MacGregor JT, Hiatt RA,
Wang G, et al. Folate deficiency causes uracil misincorporation into human DNA and
chromosome breakage: implications for cancer and neuronal damage. Proc Natl Acad Sci
U S A 1997;94:3290-5.
35 Choi SW, Kim YI, Weitzel JN, Mason JB. Folate depletion impairs DNA excision repair in the colon of the rat. Gut 1998;4:93-9.
36 Ma J, Stampfer MJ, Giovannucci E, Artigas C, Hunter DJ, Fuchs C, et al. Methylenetetrahydrofolate reductase polymorphism, dietary interactions, and risk of colorectal cancer. Cancer Res 1997;57:1098-102.[Abstract]
37 Chen J, Giovannucci E, Kelsey K, Rimm EB, Stampfer MJ, Colditz GA, et al. A methylenetetrahydrofolate reductase polymorphism and the risk of colorectal cancer. Cancer Res 1996;56:4862-4.[Abstract]
38 Balaghi M, Horne DW, Woodward SC, Wagner C. Pancreatic one-carbon metabolism in early folate deficiency in rats. Am J Clin Nutr 1993;58:198-203.[Abstract]
39 Balaghi M, Wagner C. Folate deficiency inhibits pancreatic amylase secretion in rats. Am J Clin Nutr 1995;61:90-6.[Abstract]
40 Capdevila A, Decha-Umphai W, Song KH, Borchardt RT, Wagner C. Pancreatic exocrine secretion is blocked by inhibitors of methylation. Arch Biochem Biophys 1997;345:47-55.[Medline]
41 Dubick MA, Gretz D, Majumdar AP. Overt vitamin B-6 deficiency affects rat pancreatic digestive enzyme and glutathionine reductase activities. J Nutr 1995;125:20-5.[Medline]
42 Singh M. Effect of vitamin B6 deficiency on pancreatic acinar cell function. Life Sci 1980;26:715-24.[Medline]
43 Chu M, Rehfeld JF, Borch K. Chronic endogenous hypercholecystokininemia promotes pancreatic carcinogenesis in the hamster. Carcinogenesis 1997;18:315-20.[Abstract]
44 Howatson AG, Carter DC. Pancreatic carcinogenesis-enhancement by cholecystokinin in the hamster-nitrosamine model. Br J Cancer 1985;51:107-14.[Medline]
45 Satake K, Mukai R, Kato Y, Umeyama K. Effects of cerulein on the normal pancreas and on experimental pancreatic carcinoma in the Syrian golden hamster. Pancreas 1986;1:246-53.[Medline]
46 Roebuck BD, Kaplita PV, Edwards BR, Praissman M. Effects of dietary fats and soybean protein on azaserine-induced pancreatic carcinogenesis and plasma cholecystokinin in the rat. Cancer Res 1987;47:1333-8.[Abstract]
47 Farber E, Pappas H. Production of acute pancreatitis with ethionine and its prevention by methionine. Proc Soc Exp Biol Med 1950;74:838-40.
48 Goldberg RC, Chaikoff IL, Dodge AH. Destruction of pancreatic acinar tissue by D,L-ethionine. Proc Soc Exp Biol Med 1950;74:869-72.
49 Lombardi B, Estes LW, Longnecker DS. Acute hemorrhagic pancreatitis (massive necrosis) with fat necrosis induced in mice by DL-ethionine fed with a choline-deficient diet. Am J Pathol 1975;79:465-80.[Abstract]
50 Steer ML, Meldolesi J. The cell biology of experimental pancreatitis. N Engl J Med 1987;316:144-50.[Medline]
51
Lowenfels AB, Maisonneuve P, DiMagno EP, Elitsur Y, Gates
LK Jr, Perrault J, et al. Hereditary pancreatitis and the risk of pancreatic cancer. International
Hereditary Pancreatitis Study Group. J Natl Cancer Inst 1997;89:442-6.
52
Lowenfels AB, Maisonneuve P, Cavallini G, Ammann RW,
Lankisch PG, Andersen JR, et al. Pancreatitis and the risk of pancreatic cancer. International
Pancreatitis Study Group. N Engl J Med 1993;328:1433-7.
53 Ekbom A, Mclaughlin JK, Karlsson BM, Nyren O, Gridley G, Adami Ho, et al. Pancreatitis and pancreatic cancer; a population-based study. J Natl Cancer Inst 1994;86:625-7.[Abstract]
54 Fernandez E, La Vecchia C, Porta M, Negri E, d'Avanzo B, Boyle P. Pancreatitis and the risk of pancreatic cancer. Pancreas 1995;11:185-9.[Medline]
55 Hruban RH, van Mansfeld AD, Offerhaus GJ, van Weering DH, Allison DC, Goodman SN, et al. K-ras oncogene activation in adenocarcinoma of the human pancreas. A study of 82 carcinomas using a combination of mutant-enriched polymerase chain reaction analysis and allele-specific oligonucleotide hybridization. Am J Pathol 1993;143:545-54.[Abstract]
56 U.S. Department of Health and Human Services. The health consequences of smoking. 25 years of progress. A report of the Surgeon General. Washington (DC): U.S. Department of Health and Human Services, Public Health Service, Centers for Disease Control, Center of Chronic Disease Prevention and Health Promotion, Office on Smoking and Health; 1989 Report No. (PHS)89-8411.
57 Daly LE, Kirke PN, Molloy A, Weir DG, Scott JM. Folate levels and neural tube defects, implications for prevention. JAMA 1995;274:1696-702.
58 Mills JL, Tuomilehto J, Yu KF, Colman N, Blaner WS, Koskela P, et al. Maternal vitamin levels during pregnancies producing infants with neural tube defects. J Pediatr 1992;120:863-71.[Medline]
59 Daly S, Mills JL, Molloy AM, Conley M, Lee YJ, Kirke PN, et al. Minimal effective dose of folic acid for food fortification to prevent neural-tube defects. Lancet 1997;350:1666-9.[Medline]
Manuscript received July 6, 1998; revised December 29, 1998; accepted January 11, 1999.
This article has been cited by other articles in HighWire Press-hosted journals:
![]() |
||||
|
Oxford University Press Privacy Policy and Legal Statement |