Dietary folate protects against the development of macroscopic colonic neoplasia in a dose responsive manner in rats

BACKGROUND AND AIMS

Diminished folate status is associated with enhanced colorectal carcinogenesis. This study investigated the potential chemopreventive role of dietary folate in the dimethylhydrazine colorectal cancer model.

SUBJECTS AND METHODS

Sprague-Dawley rats were fed diets containing either 0, 2 (daily dietary requirement), 8 or 40 mg folate/kg diet for 20 weeks. After five weeks of diet, rats were injected with dimethyl-hydrazine (44 mg/kg) weekly for 15 weeks. Fifteen weeks after the first injection of dimethylhydrazine, all rats were killed. Folate status was determined, and the entire colorectum from each rat was analysed for macroscopic and microscopic neoplasms.

RESULTS

Plasma and colonic folate concentrations correlated directly with dietary folate levels (p < 0.005). The incidence of microscopic neoplasms was similar among the four groups. However, the incidence and the average number of macroscopic tumours per rat decreased progressively with increasing dietary folate levels up to 8 mg/kg diet (p < 0.05). In the strongly procarcinogenic milieu used in this study, folate supplementation at 20 times the basal requirement was associated with rates of macroscopic tumour development that were intermediate, and not statistically distinct, from rates observed at either 0 or 8 mg/kg diet.

CONCLUSIONS

These data indicate that in this rat model, (a) increasing dietary folate up to four times the basal requirement leads to a progressive reduction in the evolution of macroscopic neoplasms from microscopic foci; and (b) folate supplementation beyond four times the requirement does not convey further benefit.

Folate: effects on carcinogenesis and the potential for cancer chemoprevention

A provocative array of observations from both laboratory and clinical investigations indicates that alterations in folate status modulate the process of neoplastic transformation in selected epithelial tissues. Diminished folate status appears to promote carcinogenesis. Considerably more speculative is the concept that supraphysiologic folate status may afford some protection against cancer. Although observations to this effect support such a relationship in the uterine cervix, lung, stomach, and esophagus, present evidence clearly is most compelling for the colorectum. This article reviews these observations, particularly as they apply to the colorectum, and outlines some of the possible mechanisms by which these effects may be exerted.

Exon-specific DNA hypomethylation of the p53 gene of rat colon induced by dimethylhydrazine. Modulation by dietary folate

Folate deficiency enhances colorectal carcinogenesis in dimethylhydrazine-treated rats. Folate is an important mediator of DNA methylation, an epigenetic modification of DNA that is known to be dysregulated in the early stages of colorectal cancer. This study investigated the effect of dimethylhydrazine on DNA methylation of the colonic p53 gene and the modulation of this effect by dietary folate. Sprague-Dawley rats were fed diets containing 0, 2, 8, or 40 mg of folate/kg of diet. Five weeks after diet initiation, dimethylhydrazine was injected weekly for fifteen weeks. Folate-depleted and folate-replete control animals did not receive dimethylhydrazine and were fed the 0- and 8-mg folate diets, respectively. The extent of p53 methylation was determined by a quantitative HpaII-polymerase chain reaction. In exons 6 and 7, significant p53 hypomethylation was observed in all dimethylhydrazine-treated rats relative to controls (P < 0.01), independent of dietary folate. In exon 8, significant p53 hypomethylation was observed only in the dimethylhydrazine-treated folate-depleted rats compared with controls (P = 0.038) and was effectively overcome by increasing levels of dietary folate (P = 0.008). In this model, dimethylhydrazine induces exon-specific p53 hypomethylation. In some exons, this occurs independent of dietary folate, and in others, increasing levels of dietary folate effectively override the induction of hypomethylation in a dose-responsive manner. This may be a mechanism by which increasing levels of dietary folate inhibit colorectal carcinogenesis.

Setting and evaluating the energy content of emergency rations

This paper examines the setting and evaluation of emergency rations for refugees and displaced people. After defining the purpose for which rations are designed, the variables affecting their quantification are discussed. The debate concerning the use of one as opposed to a range of energy levels for different populations is highlighted in a review of recent proposals for ration levels. It is demonstrated that up to a twofold range occurs if different combinations of the main parameters are used. This has important implications for the large-scale provision of food. The use of one figure for the setting and evaluation of rations for all populations is inappropriate; figures should be set according to specific context and need. To achieve this, a practical two-stage approach is proposed. Stage 1, probably a desk exercise, uses pre-calculated 'look-up' tables which provide energy values for each country. These figures are for immediate use as 'rule-of-thumb' estimates, based on clearly defined parameters. The second stage involves refining the values using improved information on local conditions collected by field assessment.

Nutrition chemoprevention of gastrointestinal cancers: a critical review

Various strategies utilizing specific dietary factors have been investigated for their ability to modulate the development of several cancers of the gastrointestinal tract. The effects of fat, red meat, fiber, fruits and vegetables, and alcohol on colorectal carcinogenesis have been reasonably well defined. Folate, selenium, and omega-3 fatty acids are rapidly emerging as important agents in nutrition chemoprevention, while the role of antioxidant vitamins and calcium is less certain. Although recent intervention studies from China have suggested a protective role of certain vitamins and minerals for esophageal and gastric cancers, further data from prospective randomized intervention studies are needed. Until more firm data are available, the dietary recommendations provided by the American Cancer Society and the National Cancer Institute are appropriate guidelines.

DNA hypomethylation in inflammatory arthritis: reversal with methotrexate

This study investigated whether methotrexate, by interrupting the methyl transfer function of folate, can induce genomic DNA hypomethylation in patients with inflammatory arthritis. Consecutive subjects with inflammatory arthritis (rheumatoid or psoriatic), who were taking methotrexate (n = 7) or other medications (n = 6), and control subjects, either healthy or with osteoarthritis and taking nonsteroidal anti-inflammatory agents only (n = 9) were recruited. The methylation status of genomic DNA from peripheral blood mononuclear cells was determined. Plasma levels of folate, B12, and pyridoxal-5'-phosphate (PLP), all of which are involved in biologic methylation, were also examined. The extent of genomic DNA methylation was lowest in subjects with inflammatory arthritis who were not taking methotrexate, highest in subjects with inflammatory arthritis who were taking methotrexate, and intermediate in control subjects (p < 0.05). Plasma levels of folate and B12 were similar among the three groups. The mean plasma PLP level in subjects with inflammatory arthritis was 33% lower than that in control subjects (p = 0.04). No significant correlation between genomic DNA methylation and folate, B12, and PLP levels was observed. These data do not support the hypothesis that methotrexate induces genomic DNA hypomethylation. However, these data indicate that inflammatory arthritis is associated with genomic DNA hypomethylation that is reversed with methotrexate. Future studies using a larger number of subjects are warranted to confirm these findings.

Folate synthesized by bacteria in the human upper small intestine is assimilated by the host

BACKGROUND & AIMS

Some intestinal flora are known to synthesize folate. The aim of this study was to determine whether folate synthesized by small intestinal flora is assimilated by the human host.

METHODS

Subjects with atrophic gastritis and healthy volunteers were studied before and after omeprazole administration. A double-lumen perfusion tube was placed in the duodenum. 3H-labeled P-aminobenzoic acid, a precursor substrate for bacterial folate synthesis, was perfused. Downstream intestinal aspirates and a 48-hour urine collection were obtained.

RESULTS

Atrophic gastritis and omeprazole administration were associated with increases in duodenal pH and in small intestinal flora. Bacterially synthesized folates were isolated from the intestinal aspirates. Tritiated 5-methyltetrahydrofolate, a major metabolite of folate, was isolated from the urine of omeprazole-treated subjects in greater quantities than from drug-free subjects (P<0.01); the quantity of tritiated 5-methyltetrahydrofolate in the urine of the subjects with atrophic gastritis was similarly elevated.

CONCLUSIONS

(1) Mild bacterial overgrowth caused by atrophic gastritis and administration of omeprazole are associated with de novo folate synthesis in the lumen of the small intestine; (2) the human host absorbs and uses some of these folates; and (3) the contribution to folate nutriture from this source remains unclear.

Total joint replacement and golf

Definitive characterization of the effects of golf on a total joint replacement remains elusive. However, from our study of active golfers and solicitation of the opinions of orthopedists who specialize in joint replacements, and from a careful review of the literature regarding exercise and total joint replacement, it appears possible for patients to remain active golfers with no significant increase in either symptoms or rates of revision of implants following total hip, knee, or shoulder replacement.

Moderate folate deficiency does not cause global hypomethylation of hepatic and colonic DNA or c-myc-specific hypomethylation of colonic DNA in rats

Global and gene-specific DNA hypomethylation is considered to be an important early epigenetic event in several human neoplasms. A growing body of evidence has suggested that DNA methylation can be altered by dietary manipulation of methyl group donors. This study investigated whether moderate depletion of folate, a dietary component needed for the synthesis of methyl groups, would cause decreased hepatic and colonic S-adenosylmethionine concentrations, and thereby lead to global and/or protooncogene-specific DNA hypomethylation. Weanling rats were fed an amino acid-defined diet containing either 0 or 8 mg folate/kg diet for 15 or 24 wk. Significantly lower systemic, hepatic and colonic folate concentrations were observed in the moderately folate-depleted rats than in controls at both 15 and 24 wk (P < 0.005). Although hepatic S-adenosylmethionine was significantly lower in the moderately folate-depleted rats than in controls at the two time points (P < 0.03), colonic S-adenosylmethionine concentrations were not significantly different between the two groups at either time point. No significant differences between the folate-depleted and control animals could be detected with regard to global DNA methylation in the liver or colonic mucosa. Furthermore, c-myc protooncogene-specific DNA methylation in the colonic mucosa was not significantly different between these two groups of animals. These results indicate that moderate folate depletion does not cause a significant reduction in global DNA methylation in liver or colonic mucosa or in c-myc-specific colonic mucosal DNA methylation in this rat model.

DNA methylation as an intermediate biomarker in colorectal cancer: modulation by folic acid supplementation

Several studies have suggested that DNA hypomethylation is an early step in colorectal carcinogenesis. However, it is not clear at which stage in carcinogenesis this hypomethylation occurs, what promotes it, the extent to which it can be reversed and the consequences of such reversal in affecting tumour development. In an attempt to address some of these questions, we studied three groups of subjects with similar age and gender distributions: a group of 12 patients with colorectal carcinomas; a group of 12 patients with colorectal adenomas; and a group of eight healthy control subjects. Two experimental protocols were employed. In the first protocol, intrinsic DNA methylation was evaluated in neoplastic and in normal-appearing rectal mucosa of patients with colonic carcinomas or adenomas, compared with a group of healthy controls. In the second protocol, we examined, in a prospective and controlled fashion, the effect of folic acid supplementation (10 mg/day) on the degree of DNA methylation of rectal mucosa from those same patients after removal of the neoplasms. The degree of intrinsic DNA methylation was assessed on the basis of the capacity of the DNA isolates to serve as methyl acceptors in in vitro incubations that contained DNA methylase and [3H-methyl] S-adenosylmethionine. Intrinsic DNA methylation was significantly lower in carcinomas than in adenomas (P < 0.005). In addition, normal-appearing rectal mucosa from patients with carcinomas was significantly less methylated than in healthy controls (P < 0.005); the mean value found in the latter was also greater than the value observed in patients with adenomas, but not significantly so (P > 0.05).(ABSTRACT TRUNCATED AT 250 WORDS)

Severe folate deficiency causes secondary depletion of choline and phosphocholine in rat liver

It has previously been shown that choline deficiency causes depletion of hepatic folate concentration in rats. Two separate experiments were undertaken to investigate the converse phenomenon: whether folate deficiency would lead to depletion of hepatic choline. In Experiment 1, severe folate deficiency was induced in rats by feeding an amino acid-defined diet containing (per kg diet) 1.4 g choline, 0 mg folate and 10 g succinylsulfathiazole. Control rats were fed the same diet containing 8 mg folate/kg. After 4 wk, plasma and hepatic folate concentrations were significantly depleted in the severely folate-deficient rats compared with controls (P < 0.001), and hepatic choline and phosphocholine concentrations were 65 and 80% lower, respectively (P < 0.001). In Experiment 2, moderate folate deficiency was induced in rats by feeding the same diet as described above, but with the succinylsulfathiazole omitted. After 24 wk, significant systemic folate deficiency was present in the moderately folate-deficient rats compared with controls (P < 0.001). A modest reduction (36%, P = 0.087) in hepatic choline concentration was observed in the moderately folate-deficient rats compared with controls. No significant differences in hepatic phosphocholine concentrations were detected between the two groups. These results indicate that severe folate deficiency causes secondary hepatic choline deficiency in rats.

Global DNA hypomethylation increases progressively in cervical dysplasia and carcinoma

BACKGROUND

Global DNA hypomethylation has been observed in some human neoplasms and has been implicated as an important factor in carcinogenesis. The current study was designed to assess whether DNA hypomethylation occurs in cervical dysplasia and cancer, and to determine the relationship between the degree of DNA hypomethylation and the grade of neoplasia.

METHODS

Cervical biopsy specimens were obtained from colposcopically identifiable lesions in 41 patients with abnormal Pap smear results. The extent of global DNA methylation was assessed by incubating the extracted DNA with [3H]-S-adenosylmethionine and Sss1 methyltransferase, an enzyme that specifically catalyzes the transfer of methyl groups to cytosine residues in the cytosine-guanine doublet. The degree of exogenous 3H-methyl group incorporation into the DNA therefore is related reciprocally to the extent of endogenous DNA methylation. These data were compared with the histopathologic classification of the lesions.

RESULTS

The extent of 3H-methyl group incorporation was increased threefold and sevenfold in the DNA from cervical dysplasia and cancer, respectively, compared with the DNA from normal cervical tissue (P = 0.006, analysis of variance). Significant incremental increases in DNA hypomethylation were observed in the progression from normal and low grade squamous intraepithelial lesions (SIL) to high grade SIL and to cancer (P < 0.0001, trend).

CONCLUSIONS

These data show that global DNA hypomethylation is a significant epigenetic event in cervical carcinogenesis and that the degree of DNA hypomethylation increases with the grade of cervical neoplasia. These data suggest that global DNA methylation may serve as a biochemical marker of cervical neoplasia.

Measurement of zinc bioavailability from beef and a ready-to-eat high-fiber breakfast cereal in humans: application of a whole-gut lavage technique

We measured zinc absorption in humans from two different foods, using a whole-gut lavage technique. Healthy adults (n = 8) were given test foods containing approximately 4 mg (61.2 mumol) Zn as either beef or a high-fiber, ready-to-eat breakfast cereal. Basal zinc loss in the gut was measured after giving only 200 mL water alone after an overnight fast. Mean polyethylene glycol (PEG) recovery, a nonabsorbable fecal marker, was 95 +/- 2% (mean +/- SE). There was no significant difference of PEG recoveries with the various treatments. True absorption of zinc was 11.0 +/- 5.4 mumol (716.3 +/- 355.9 micrograms) for breakfast cereal and 34.8 +/- 3.5 mumol (2274.1 +/- 230.2 micrograms) for beef. Fractional zinc absorption was significantly lower for breakfast cereal compared with beef, 14.7 +/- 6.7% vs 55.1 +/- 4.6%, respectively. Our findings demonstrate that zinc absorption can be measured in humans from single foods containing a physiological dose of zinc by using the whole-gut lavage absorption technique and that zinc bioavailability from beef is about fourfold greater than from a high-fiber breakfast cereal.

The vitamin K content of intravenous lipid emulsions

Commercially available intravenous lipid emulsions are largely derived from vegetable oils, a natural source of phylloquinone (vitamin K1). We therefore examined the concentration of vitamin K1 in two widely used intravenous lipid emulsions by using a previously validated high performance liquid chromatography technique. The vitamin K1 concentrations of 10% emulsions of Intralipid and Liposyn II were 30.8 and 13.2 micrograms/dL, respectively. The concentration of vitamin K1 in the 20% emulsions of these products was essentially double that in the 10% emulsions. The coefficients of variation between the vitamin K1 content in three different lots of each product were consistently less than 7.0%. The observed concentrations of the vitamin in these lipid emulsions paralleled the predicted content on the basis of the type of vegetable oil(s) used to make the product. The type of vegetable oil used for production therefore seems to be a major determinant of the final vitamin K1 content. The vitamin K1 contained in these intravenous lipid emulsions is substantial and may have great impact on the vitamin K status of the recipient.

The effects of vitamins B12, B6, and folate on blood homocysteine levels

The interaction between plasma homocysteine levels and vitamins B6, B12, and folate is an exciting field and one that has gathered great momentum over the past few years, with the recognition that homocysteine probably plays an important role in occlusive vascular disease. Our understanding in this field is greatly advanced compared to just a few years ago. There are a number of important issues, however, that will need to be addressed in the future if we are to develop a sufficient knowledge base to effectively minimize the risk of occlusive vascular disease ascribable to hyperhomocysteinemia. These include (1) definitive evidence that homocysteine is the actual agent that mediates accelerated occlusive vascular disease and the mechanism by which this occurs; (2) an understanding of what constitutes a pathologic elevation in homocysteine (is there a threshold concentration in the plasma below which no vascular injury occurs? is the peak concentration achieved the critical determinant of injury, or is the area under the curve, or some other feature, more important?); (3) understanding what synergies might exist by adding B6 or B12 to a regimen of folate supplementation (what doses are most appropriate? will toxologic issues limit the utility of supplementation?); and (4) determining the circumstances where reduction of plasma homocysteine will retard or reverse the process of occlusive vascular disease.

Folate deficiency enhances the development of colonic neoplasia in dimethylhydrazine-treated rats

In patients with ulcerative colitis, epidemiological work has suggested an association between low folate status and an increased risk of colonic neoplasia. The aim of the present study was to determine if experimental folate deficiency increases the likelihood of developing neoplasia in rats treated with the carcinogen dimethylhydrazine. Weanling male Sprague-Dawley rats were fed with an amino acid-defined diet containing either 8 or 0 mg/kg folic acid. After 5 weeks of defined diet, weekly s.c. injections of dimethylhydrazine (20 mg/kg) were administered to both groups. Serum, whole blood, liver, and colonic folate concentrations at the time of sacrifice were significantly lower in folate-depleted animals (P less than 0.001). There were significant differences in the incidence of colonic neoplasia between the two groups after 20 weeks of dimethylhydrazine exposure: folate-deficient rats had a greater incidence of dysplasia (6 of 7 versus 2 of 7 animals; P less than 0.05) and carcinoma (6 of 7 versus 1 of 7 animals; P less than 0.01). Furthermore, a significantly greater proportion of folate-replete rats than folate-deficient rats were free of neoplastic lesions (5 of 7 versus 0 of 7 animals; P less than 0.05). These results suggest that, in this animal model, folate deficiency increases the risk of malignancy when there is an underlying predisposition to colorectal cancer.

Vitamin E deficiency and impaired cellular immunity related to intestinal fat malabsorption

This report describes a patient in whom a severe vitamin E deficiency developed secondary to an intestinal malabsorptive disorder. In vivo and in vitro impairment of T-cell function, as well as a polyneuropathy, were observed in conjunction with this vitamin deficiency. Repletion of the vitamin deficiency was associated with marked improvement in the T-cell functions and modest improvement in the neuropathy. Observations in this patient suggest that severe vitamin E deficiency in humans may impair T-cell activity and that correction of the deficient state may reverse these T-cell abnormalities. Further studies will need to be performed to confirm these findings.

Use of the deoxyuridine suppression test to evaluate localized folate deficiency in rat colonic epithelium

In this study the deoxyuridine suppression test (dUST) was performed on isolated rat colonocytes to establish its value as an indicator of folate status in the colonic epithelium. [3H]thymidine incorporation into DNA was suppressed greater than 90% by deoxyuridine (dU) concentrations greater than 2.5 mumol/L. Preincubation of cells with 5-fluorouracil (1-100 mumol/L) but not methotrexate (10-100 mumol/L) resulted in a significant decrease in the degree of suppression. The dUST performed on colonocytes from folate-deficient animals displayed less suppression than on colonocytes from folate-replete animals (P less than 0.05). The abnormal degree of suppression was corrected by adding 100 mumol folinic acid/L. There was a negative correlation between the degree of suppression and the folate concentration of the colonic epithelium (P less than 0.001). These data indicate that the dUST is useful for detecting folate deficiency in the colonic epithelium and may therefore be valuable in assessing a deficiency state localized to that epithelium.

Comparison of two growth charts in Lesotho: health workers' ability to understand and use them for action

BACKGROUND

Two growth monitoring charts widely used for growth monitoring in Africa (the Road-to-Health (RTH) and the Growth Surveillance (GS] were compared in order to assist the Government of Lesotho to decide on an appropriate national growth chart.

METHODS

Thirty-four health workers were taught and tested on the RTH during a first week of training and on the GS during a second week (the RTH-GS group), while the order was reversed for another 25 trainees (the GS-RTH group). The health workers were trained and tested on their ability not only to use and interpret the two charts, but also to make the right decisions about specific actions to be taken when growth faltering occurs.

RESULTS

There was no difference between scores to the RTH and GS charts after one week of training. After the second week of training, the scores to the RTH chart improved and became better than those to the GS chart. The scores to the GS test did not increase with previous knowledge of the RTH chart.

CONCLUSIONS

For this reason and others discussed in the paper, the RTH chart was recommended for nationwide use in Lesotho. The adoption of this recommendation was facilitated by the close involvement in this research of public and private agencies responsible for growth monitoring in Lesotho.