Megadose effects of vitamin C on vitamin B-12 status in the rat

Effects of ascorbic acid ingestion on the severity of vitamin B-12 deficiency were investigated by feeding weanling rats experimental diets containing 0-100 micrograms of vitamin B-12 activity per kg of diet, with or without 6.0 mg of ascorbic acid per ml supplied in drinking water for 15 wk. This daily consumption of up to 150 mg of ascorbic acid did not impair growth, but did result in significantly higher concentrations of ascorbic acid in plasma, liver, adrenal glands and feces. When rats were fed diets deficient or marginally deficient in vitamin B-12, liver concentrations of vitamin B-12 were markedly lower than in liver of rats fed adequate vitamin B-12. Ascorbic acid ingestion raised values significantly in the vitamin B-12-deficient diet group. Urinary methylmalonic acid was significantly elevated in the deficient rats. However, it was significantly reduced to more normal values by ascorbic acid in rats with both low and marginal vitamin B-12 status, as defined by dietary and liver concentrations of vitamin B-12 activity. Although coprophagy was not prevented, rats showed no increased consumption of feces with the higher ascorbic acid content. Thus, the results of this research indicate that vitamin C ingestion partially protects rats from vitamin B-12 deficiency.     

Vitamin B-6 deficiency prolongs the time course of evoked dopamine release from rat striatum

Vitamin B-6-deficient animals exhibit motor abnormalities. To investigate the possible physiologic alterations in the dopaminergic nervous system in vitamin B-6 deficiency, dopamine release in the striatum of vitamin B-6-deficient rats was determined using in vivo electrochemistry. Male Sprague-Dawley rats, 3 wk old, weighing 50-60 g, were randomly assigned to a control (7 mg pyridoxine HCl/kg diet), vitamin B-6-deficient (0 mg pyridoxine HCl/kg diet), or pair-fed (7 mg pyridoxine HCl/kg diet) group. After 8 wk of dietary treatment, plasma concentrations of pyridoxal 5'-phosphate as well as the striatal pyridoxal 5'-phosphate and pyridoxamine 5'-phosphate were significantly lower in the vitamin B-6-deficient group than in the control and pair-fed groups. The dopamine concentrations of the striatum and the magnitude of the dopamine release after local application of KCl did not differ among the groups. However, the time required for KCl-evoked dopamine release to reach its peak level was significantly longer for the vitamin B-6-deficient rats than for controls. In addition, the decay time from the peak to one-half of the KCl-evoked dopamine release was also significantly prolonged in vitamin B-6-deficient rats compared with the control group. The results indicate that the cellular content of dopamine does not reflect the functional state of dopaminergic neurons in vitamin B-6 deficiency. The time course for release of dopamine and decay of the released dopamine is prolonged by vitamin B-6 deficiency, which might contribute to the motor abnormalities of the deficient rats.     

Effect of vitamin B-6 deficiency on fasting plasma homocysteine concentrations.

The catabolism of homocysteine through cystathionine synthesis requires pyridoxal-5'-phosphate, thus the effect of vitamin B-6 deficiency on plasma homocysteine concentrations was evaluated. Total fasting plasma homocysteine concentrations were measured in 11 elderly subjects aged 64.4 +/- 1.7 y (mean +/- SE) who consumed a vitamin B-6-deficient diet for less than or equal to 20 d. Only 1 of the 11 subjects was found to have elevated homocysteine concentrations even though all subjects exhibited high urinary xanthurenic acid concentrations after a tryptophan load, a measure indicative of vitamin B-6 deficiency. In a supporting study, fasting plasma homocysteine concentrations were measured in 3- and 23-mo-old rats fed vitamin B-6-deficient diets and were compared with those of vitamin B-6-replete, pair-fed controls. There was no difference in homocysteine concentrations between deficient and pair-fed animals after 6 wk of the dietary regimen for either age group; after 9 wk a modest elevation was observed in the 3-mo-old deficient rats whereas no difference was observed for the 23-mo-old rats. It is concluded that fasting plasma homocysteine concentrations are not initially elevated in vitamin B-6 deficiency and therefore fasting plasma homocysteine concentrations are not a good indicator of vitamin B-6 status.     

Glutathione levels and related enzyme activities in vitamin B-6-deficient rats fed a high methionine and low cystine diet

We examined the change in glutathione metabolism in vitamin B-6-deficient rats. Vitamin B-6-deficient rats were fed a vitamin B-6-deficient diet containing 0.56% methionine and 0.075% cystine for 8 wk. Controls were fed an identical diet supplemented with 10 mg pyridoxine hydrochloride/kg diet. Glutathione concentrations in each organ examined were similar in control and vitamin B-6-deficient rats, and the values were comparably lower after intraperitoneal injection of diethylmaleate. However, buthionine sulfoximine caused a significantly greater decrease in glutathione levels in the liver and lungs of vitamin B-6-deficient rats relative to controls. Glutathione peroxidase activity in the liver of vitamin B-6-deficient rats was higher than in control animals; however, glutathione transferase activity in tissues other than liver of vitamin B-6-deficient rats was higher than in the controls. The activities of gamma-glutamyl-transferase in the liver and spleen of vitamin B-6-deficient rats were significantly lower than control values. The holoenzyme activities of cystathionine beta-synthase and cystathionine gamma-lyase in the liver of vitamin B-6-deficient rats were markedly reduced. These findings indicate that although the activities of enzymes that synthesize cysteine from methionine were decreased by vitamin B-6 deficiency, the level of synthesis and supply of cysteine in vitamin B-6-deficient rats were sufficient to maintain the same glutathione level as in controls, and that glutathione utilization in the liver was accelerated by vitamin B-6 deficiency.     

Vitamin B-12 deficiency increases the specific activities of rat liver NADH- and NADPH-linked aquacobalamin reductase isozymes involved in coenzyme synthesis

Rat liver contains both NADH- and NADPH-linked aquacobalamin reductases, which are involved in the synthesis of the vitamin B-12 coenzymes and are distributed in both the mitochondrial and microsomal membranes. To clarify the physiological roles of these hepatic enzymes, vitamin B-12-deficient rats were used to study the effect of the deficiency on the enzyme activities. Male rats fed a vitamin B-12-deficient diet for 11 wk developed a severe vitamin B-12 deficiency with a high urinary methylmalonate excretion (214.3 +/- 115.2 mumol/d) and approximately 96% lower hepatic vitamin B-12 content. Tissues of the vitamin B-12-deficient rats were assayed for NADH- and NADPH-linked aquacobalamin reductase activities. The specific activities of both enzymes in homogenates of liver, kidney or upper intestine were shown to be three- to 20-fold greater in the vitamin-deficient rats than in the control rats. In liver, the vitamin deficiency specifically elevated the specific activities of the mitochondrial NADH-linked and microsomal NADPH-linked enzymes. These are likely the isozymes involved in vitamin B-12 coenzyme synthesis.     

Dietary folate and selenium affect dimethylhydrazine-induced aberrant crypt formation,global DNA methylation and one-carbon metabolism in rats

Several observations suggest a role for DNA methylation in cancer pathogenesis. Although both selenium and folate deficiency have been shown to cause global DNA hypomethylation and increased cancer susceptibility, the nutrients have different effects on one-carbon metabolism. Thus, the purpose of this study was to investigate the interactive effects of dietary selenium and folate. Weanling, Fischer-344 rats (n = 23/diet) were fed diets containing 0 or 2.0 mg selenium (as selenite)/kg and 0 or 2.0 mg folate/kg in a 2 x 2 factorial design. After 3 and 4 wk of a 12-wk experiment, 19 rats/diet were injected intraperitoneally with dimethylhydrazine (DMH, 25 mg/kg) and 4 rats/diet were administered saline. Selenium deficiency decreased (P < 0.05) colonic DNA methylation and the activities of liver DNA methyltransferase and betaine homocysteine methyltransferase and increased plasma glutathione concentrations. Folate deficiency increased (P < 0.05) the number of aberrant crypts per aberrant crypt foci, the concentration of colonic S-adenosylhomocysteine and the activity of liver cystathionine synthase. Selenium and folate interacted (P < 0.0001) to influence one-carbon metabolism and cancer susceptibility such that the number of aberrant crypts and the concentrations of plasma homocysteine and liver S-adenosylhomocysteine were the highest and the concentrations of plasma folate and liver S-adenosylmethionine and the activity of liver methionine synthase were the lowest in rats fed folate-deficient diets and supplemental selenium. These results suggest that selenium deprivation ameliorates some of the effects of folate deficiency, probably by shunting the buildup of homocysteine (as a result of folate deficiency) to glutathione.     

Mild depletion of dietary folate combined with other B vitamins alters multiple components of the Wnt pathway in mouse colon

Preclinical and clinical studies suggest that diminished folate status increases the risk of colorectal carcinogenesis. However, many biochemical functions of folate are dependent on the adequate availability of other 1-carbon nutrients, including riboflavin, vitamin B-6, and vitamin B-12. Aberrations in the Wnt pathway are thought to play an important role in human colorectal cancers. This study therefore investigated if mild depletion of folate combined with depletion of riboflavin, vitamin B-6, and vitamin B-12 could induce alterations in the Wnt pathway in the colonic mucosa. Ninety-six mice were pair-fed diets with different combinations of B vitamin depletion for 10 wk. Genomic DNA methylation and uracil misincorporation were measured by LC/MS and GC/MS. Gene-specific methylation, strand breaks, and expressions were measured by real-time PCR and immunoblotting. Proliferation and apoptosis were determined by immunohistochemistry. DNA strand breaks within the Apc mutation cluster region were induced by folate depletion combined with inadequacies of riboflavin, vitamin B-6, and vitamin B-12 (P < 0.05), but such effects were not induced by folate depletion alone. Similarly, minor changes in the expression of Apc, beta-catenin, and cyclin D1 produced by mild folate depletion were significantly magnified by multiple vitamin depletion. Apoptosis, which can be suppressed by increased Wnt-signaling, was attenuated by the combined deficiency state (P < 0.05) but not by singlet or doublet deficiencies. These findings indicate that a mild depletion of folate that is of insufficient magnitude by itself to induce alterations in components of the Wnt pathway may produce such effects when present in conjunction with mild inadequacies of other 1-carbon nutrients.     

Effect of a vitamin B-12-deficient diet on lipid and fatty acid composition of spinal cord myelin in the fruit bat

The effects of vitamin B-12 deficiency on lipids and fatty acids of spinal cord myelin were studied in control and vitamin B-12-deficient fruit bats. Very low plasma and brain vitamin B-12 concentrations were present in animals fed the vitamin B-12-free, all fruit diet. Myelin was isolated from the spinal cord of control and vitamin B-12-deficient animals (n = 3 pools) by means of a flotation method in a discontinuous sucrose gradient. The molar concentration of cholineglycerophosphatide was significantly lower in the deficient bats than in the controls. The molar cholesterol: phospholipid ratio in the deficient bats was also significantly lower. The odd-chain fatty acid 15:1 was not detected in cholineglycerophosphatide from the controls, but comprised 1.4% of the total fatty acids in the deficient group. The odd-chain fatty acids 15:0, 17:1 and 19:0 were present in slightly higher amounts in cholineglycerophosphatide of deficient bats. Lipid and fatty acid differences were related to the vitamin B-12-requiring methionine synthetase and methylmalonyl CoA mutase reactions.     

Response of B-6 vitamers in plasma, erythrocytes and tissues to vitamin B-6 depletion and repletion in the rat

We determined the response patterns of B-6 vitamers in blood and tissues to vitamin B-6 depletion and repletion. B-6 vitamers were measured in plasma, erythrocytes, liver, muscle, kidney, heart, brain, spleen and lung by reverse-phase high performance liquid chromatography in male rats pair-fed control or vitamin B-6-deficient diets for 2 or 4 wk, or for 4 wk followed by 1 wk of repletion with the control diet (n = 4/group). Food intake (15.6 +/- 0.3 g/d, mean +/- SEM; n = 28) and body weight (190 +/- 2 and 290 +/- 5 g at wk 0 and 5, respectively; n = 28) of control groups were not different from those of deficient groups throughout the study. After 2 wk of vitamin B-6 depletion, tissue concentrations of pyridoxal phosphate (PLP) and pyridoxamine phosphate (PMP) were about 50% and 10-40% lower, respectively, in the deficient than in the control group (except for spleen PMP); in plasma and erythrocytes, PLP and pyridoxal concentrations were about 90% lower in the deficient group. Differences in vitamer concentrations between control and deficient groups were not larger after 4 wk of depletion than after 2 wk. Vitamer concentrations in plasma, erythrocytes and all tissues returned to control levels after 1 wk of repletion with the control diet. These results demonstrate that B-6 vitamers in blood and tissues of the rat respond quickly and reversibly to changes in dietary vitamin B-6, with larger percentage changes occurring in plasma and erythrocytes than in tissues.     

Postweaning dietary folate deficiency provided through childhood to puberty permanently increases genomic DNA methylation in adult rat liver

Folate plays an important role in the pathogenesis of several chronic diseases by its potential ability to modulate DNA methylation. We hypothesized that the postweaning period might be a highly susceptible period to dietary folate intervention for DNA methylation patterning. We determined the effects of timing and duration of dietary folate intervention provided during the postweaning period on genomic DNA methylation in adult rat liver. In study 1, weanling rats were randomized to receive an amino acid-defined diet containing 0 (deficient), 2 (control), or 8 (supplemented) mg folic acid/kg until 8 wk of age, after which all the rats were fed the control diet until 30 wk of age. In study 2, weanling rats were fed the control diet until 8 wk of age and then randomized to receive the diet containing 0, 2, or 8 mg folic acid/kg until 30 wk of age. In study 3, weanling rats were randomized to receive these diets until 30 wk of age. Dietary folate deficiency, but not supplementation, provided during the postweaning period through childhood to puberty significantly increased genomic DNA methylation by 34-48% (P < 0.04) in rat liver that persisted into adulthood following a return to the control diet at puberty. In contrast, dietary folate deficiency or supplementation continually imposed at weaning or at puberty did not significantly affect genomic DNA methylation in adult rat liver. Our data suggest that early folate nutrition during postnatal development plays an important role in epigenetic programming that can have a permanent effect in adulthood.     

Biomarkers of nutrient exposure and status in one-carbon (methyl) metabolism

One-carbon metabolism is a network of interrelated biochemical reactions that involve the transfer of one-carbon groups from one compound to another. The coenzymes necessary for several of these reactions include the B-vitamins, folate, vitamin B-12, vitamin B-6 and riboflavin (vitamin B-2), whereas important intermediary compounds in this schema include methionine and choline. There has been renewed interest in one-carbon metabolism during the past several years, engendered by recent insights that indicate that modest dietary inadequacies of the abovementioned nutrients, of a degree insufficient to cause classical deficiency syndromes, can still contribute to important diseases such as neural tube defects, cardiovascular disease and cancer. Traditional means of assessing nutrient exposure with food frequency questionnaires, and nutrient status with plasma and urine vitamin assays, has some genuine validity and utility. Assessing the concentration of appropriate intermediary compounds, such as plasma homocysteine for folate and methylmalonic acid for vitamin B-12, provides further insights because they appear to add a degree of sensitivity that does not exist with the more traditional assays. There may also be value in developing measures that integrate the status of all these nutrients and express it as a functional "methylation capacity" of the individual. Plasma or tissue concentrations of S-adenosylmethionine and S-adenosylhomocysteine, and genomic DNA methylation are two potential candidates in this regard although much work is yet to be done to define the nature of these relationships.     

Vitamin B-6 deficiency in rats reduces hepatic serine hydroxymethyltransferase and cystathionine beta-synthase activities and rates of in vivo protein turnover, homocysteine remethylation and transsulfuration

Vitamin B-6 deficiency causes mild elevation in plasma homocysteine, but the mechanism has not been clearly established. Serine is a substrate in one-carbon metabolism and in the transsulfuration pathway of homocysteine catabolism, and pyridoxal phosphate (PLP) plays a key role as coenzyme for serine hydroxymethyltransferase (SHMT) and enzymes of transsulfuration. In this study we used [(2)H(3)]serine as a primary tracer to examine the remethylation pathway in adequately nourished and vitamin B-6-deficient rats [7 and 0.1 mg pyridoxine (PN)/kg diet]. [(2)H(3)]Leucine and [1-(13)C]methionine were also used to examine turnover of protein and methionine pools, respectively. All tracers were injected intraperitoneally as a bolus dose, and then rats were killed (n = 4/time point) after 30, 60 and 120 min. Rats fed the low-PN diet had significantly lower growth and plasma and liver PLP concentrations, reduced liver SHMT activity, greater plasma and liver total homocysteine concentration, and reduced liver S-adenosylmethionine concentration. Hepatic and whole body protein turnover were reduced in vitamin B-6-deficient rats as evidenced by greater isotopic enrichment of [(2)H(3)]leucine. Hepatic [(2)H(2)]methionine production from [(2)H(3)]serine via cytosolic SHMT and the remethylation pathway was reduced by 80.6% in vitamin B-6 deficiency. The deficiency did not significantly reduce hepatic cystathionine-beta-synthase activity, and in vivo hepatic transsulfuration flux shown by production of [(2)H(3)]cysteine from the [(2)H(3)]serine increased over twofold. In contrast, plasma appearance of [(2)H(3)]cysteine was decreased by 89% in vitamin B-6 deficiency. The rate of hepatic homocysteine production shown by the ratio of [1-(13)C]homocysteine/[1-(13)C]methionine areas under enrichment vs. time curves was not affected by vitamin B-6 deficiency. Overall, these results indicate that vitamin B-6 deficiency substantially affects one-carbon metabolism by impairing both methyl group production for homocysteine remethylation and flux through whole-body transsulfuration.     

Vitamin B-6 deficiency and renal function and structure in chronically uremic rats

In preliminary studies, rats with chronic renal failure (CRF) demonstrated worsening renal function, as measured by urea clearance, when fed vitamin B-6-deficient diets. However, urea clearance is not a precise measure of glomerular filtration rate (GFR) and these studies did not indicate the mechanism for the reduced GFR. To measure renal function more precisely and to assess whether B-6 deficiency augments renal injury, we examined [14C]inulin clearance, urine oxalate excretion, and renal histopathology in rats with CRF pair fed to receive a pyridoxine-replete or -deficient diet for 3 or 6 wk. After 3 or 6 wk, pyridoxine-deficient rats had significantly lower [14C]inulin clearances and increased urine oxalate excretion. Histological evaluation indicated increased renal damage in kidneys from pyridoxine-deficient rats as compared with tissue from pyridoxine-replete rats. These findings suggest that in rats with CRF, vitamin B-6 deficiency reduces the GFR and increases renal scarring.     

Effect of vitamin B-6 deficiency on plasma amino acid levels in chronically azotemic rats

Chronic renal failure is associated with many abnormalities in plasma amino acids. Since patients with renal failure are frequently deficient in vitamin B-6, this study examined whether vitamin B-6 deficiency may be a cause of any of the abnormal plasma amino acid concentrations observed in chronic renal failure. Sham-operated and chronically azotemic rats were pair-fed diets deficient in or replete with vitamin B-6 for 21 d. By the end of 21 d, the EGOT index rose significantly in the B-6-deficient rats but not in the B-6-replete animals. There were several differences in plasma amino acid concentrations between azotemic and control rats. Azotemia and B-6 deficiency each lowered the plasma serine concentration and raised the glycine-to-serine ratio. Plasma glycine was affected by a two-way interaction between azotemia and vitamin B-6 deficiency whereby the highest values were found in the sham-operated vitamin B-6-deficient animals. Plasma alanine and asparagine were reduced by B-6 deficiency and unchanged by azotemia. These results suggest that vitamin B-6 deficiency may contribute to several of the abnormalities in the plasma aminograms observed in chronic renal failure.     

Plasma S-adenosylhomocysteine is a better biomarker of atherosclerosis than homocysteine in apolipoprotein E-deficient mice fed high dietary methionine

Homocysteine (Hcy) and S-adenosylhomocysteine (AdoHcy) are critical intermediates of methionine metabolism. To investigate which, if either, of these compounds is more closely related to atherosclerosis, we fed 5 groups of apolipoprotein E (apoE)-deficient mice different diets for 8 wk to induce changes in their plasma Hcy and AdoHcy concentrations. These included an AIN-93G control diet (C), this C diet supplemented with methionine (M), the M diet deficient in folates, vitamin B-6, and vitamin B-12 (M-V), this M diet supplemented with these B vitamins (M+V), and a C diet deficient in B vitamins (C-V). Compared with controls, mice fed the C-V diet had a moderate elevation in their plasma total Hcy (tHcy) levels; however, their plasma AdoHcy concentration and atherosclerotic lesion areas were not different. In contrast, the mice fed the M+V diet had larger atherosclerotic lesion areas and elevated plasma AdoHcy concentrations but their plasma tHcy concentration did not differ from that of the group C mice. The plasma AdoHcy concentration and aortic sinus lesion areas were positively correlated (r = 0.866; P < 0.001). We observed a negative correlation between the plasma AdoHcy concentration and both the DNA methyltransferase activity (r = -0.792; P < 0.001) and global DNA methylation status (r = -0.824; P < 0.001) in the aortic tissue. Hence, our study suggests that plasma AdoHcy is a better biomarker of atherosclerosis than Hcy and may accelerate the development of atherosclerotic lesions in apoE-deficient mice that have been fed a high methionine diet. The mechanisms underlying this effect may be related to the AdoHcy-mediated inhibition of DNA methylation in the aortic tissue.     

Influence of vitamin B-6 upon reproduction and upon plasma and egg cholesterol in chickens.

Vitamin B-6 deficiency in the laying hen causes an immediate anorexia, loss of body weight, greatly reduced body fat stores and severe effects upon primary and secondary sex characteristics resulting in severely reduced hatchability culminating in complete cessation of egg production. While inanition may have been largely responsible for involution of the ovaries and oviducts in the vitamin B-6 deficient hens, regression of combs and wattles appears to be a more specific sign of vitamin B-6 deficiency. Serum cholesterol levels of vitamin B-6-deficient hens were lower than those of hens receiving an adequate diet. Egg cholesterol values remained relatively constant regardless of dietary B-6 levels or of alterations in serum cholesterol. No ataxia or mortality was observed in vitamin B-6-deficient hens or roosters. The effects of vitamin B-6 deficiency were almost completely reversed upon repletion of the hens with adequate dietary vitamin B-6.     

Extremely low activity of methionine synthase in vitamin B-12-deficient rats may be related to effects on coenzyme stabilization rather than to changes in coenzyme induction

Severely vitamin B-12 (B-12)-deficient rats were produced by feeding a B-12-deficient diet. The status of B-12 deficiency was confirmed by an increase in urinary methylmalonate excretion and decreases in liver B-12 concentrations and cobalamin-dependent methionine synthase activity. Rat liver methionine synthase existed almost exclusively as the holoenzyme. In B-12-deficient rats, the level of methionine synthase protein was lower, although the mRNA level was not significantly different from that of control rats. When methylcobalamin, the coenzyme for methionine synthase, was administered to the B-12-deficient rats, growth, liver B-12 concentrations and urinary excretion of methylmalonate were reversed although not always to control (B-12-sufficient) levels in a short period. During this recovery process, methionine synthase activity and its protein level increased, whereas the mRNA level was unaffected. We reported previously that rat apomethionine synthase is very unstable and is stabilized by forming a complex with methylcobalamin. Thus, the extremely low activity of methionine synthase in B-12-deficient rats may be related to effects on "coenzyme stabilization" (stabilization of the enzyme by cobalamin binding) rather than to changes in "coenzyme induction."     

Chronic alcohol consumption induces genomic but not p53-specific DNA hypomethylation in rat colon.

Alcohol consumption has been implicated as an etiologic agent in colorectal carcinogenesis, but the mechanism by which alcohol enhances the development of colorectal cancer is not yet known. Recent reports indicate that alcohol consumption can diminish cellular S-adenosylmethionine levels, thus possibly altering normal patterns of DNA methylation, a phenomenon that is mediated by S-adenosylmethionine and whose abnormalities are observed in colonic neoplasia. This study investigated the effect of chronic alcohol consumption on genomic DNA methylation of rat colonic epithelium and methylation of the p53 tumor suppressor gene, abnormalities of which have been implicated in colonic carcinogenesis. Two groups of rats (n = 10/group) were pair-fed either an alcohol-containing or an isocaloric control Lieber-DeCarli diet for 4 wk. The extent of genomic DNA methylation was assessed by incubating the extracted DNA with [(3)H]S-adenosylmethionine and Sss1 methyltransferase. Gene-specific methylation was assessed by using semiquantitative polymerase chain reaction (PCR). Tritiated methyl uptake by colonic DNA (which is inversely correlated with genomic methylation) from alcohol-fed rats was 57% less than that in control DNA (P < 0.05). However, gene-specific DNA methylation, both in the p53 gene (exons 5-8) and in the beta-actin gene, a control gene, did not differ between the two groups. In conclusion, this study indicates that chronic alcohol consumption produces genomic DNA hypomethylation in the colonic mucosa. This may constitute a means by which carcinogenesis is enhanced, although further studies are required to establish causality.     

Cystathionine excretion in relation to vitamin B-6 nutriture of rats: strain differences and effects of DL- or L-methionine supplementation.

Wistar and Long-Evans rats excreted significantly more cystathionine during days 27 to 31 of a vitamin B-6 deficiency than did Spague-Dawley rats. Wistar rats were therefore chosen for experiments designed to test the effects of dietary DL- and L-methionine supplementation upon cystathionine excretion of vitamin B-6-deficient and control rats. Methionine supplementation did not significantly affect mean daily food consumption or weight gain of the control animals. L-Methionine-supplemented, deficient rats gained significantly more during the first 15 days of the experiment and less during the last 11 days than did the other deficient groups. No cystathionine was detected in the urine of methionine-supplemented or unsupplemented control rats between days 8 and 26 of the experiment; but measurable quantities of cystathionine were present in the urine of all deficient groups by days 8 to 12. Deficient animals fed DL-methionine excreted up to 2.33 mg more cystahionine per 4-day period than did the unsupplemented deficient rats, whereas rats fed L-methionine excreted up to 7.44 mg more per 4-day period than did the unsupplemented ones. This difference in cystathionine response was highly significant and indicates that the L supplement stressed the vitamin B-6-deficient rats more than did the DL supplement. An explanation for this may be that the D isomer in the DL supplement was not as efficiently absorbed and/or metabolized as the L form.     

Response of vitamin B-6 content of muscle to changes in vitamin B-6 intake in men

Previous reports indicated that in growing rats the vitamin B-6 pool in muscle was relatively stable during deficiency but increased in response to increased vitamin B-6 intake. To determine whether human muscle would show a similar response 10 college-aged males received a low vitamin B-6 diet (1.76 mumol/d) for 6 wk followed by 6 wk on a self-selected diet supplemented with 0.98 mmol pyridoxine HCl/d. During depletion, excretion of pyridoxic acid rapidly adjusted to approximate the intake. Plasma pyridoxal phosphate concentrations at the end of the baseline, depletion, and supplementation periods were 81 +/- 51, 9 +/- 3, and 455 +/- 129 nmol/L, respectively, whereas muscle concentrations were 21 +/- 9, 20 +/- 4, and 25 +/- 7 nmol/g, respectively and total vitamin B-6 in muscle was 28 +/- 10, 27 +/- 4, and 35 +/- 10 nmol/g, respectively. These data provide further confirmation that the vitamin B-6 pools in skeletal muscle are resistant to depletion. They also demonstrate that in humans with constant body weight, vitamin B-6 supplementation is not associated with marked increases in vitamin B-6 in muscle.