Folate deficiency induces a cell cycle-specific apoptosis in HepG2 cells

In vitrofolate supplementation alleviates oxidative stress, mitochondria-associated death signalling and apoptosis induced by 7-ketocholesterol

Folate has recently been proposed as a new antioxidant. Folate supplementation may have a protective effect in counteracting oxidant-induced apoptotic damage. The present studies were undertaken to examine whether there is a direct link between folate levels, antioxidant capability and reduced apoptotic damage. Using anin vitrocellular model of 7-ketocholesterol (KC)-induced apoptosis, U937 cells were pre-cultured with a folate-deficient medium supplemented with various levels of folate (2–1500μmol/l) before treatment with 7-KC. Apoptotic markers, mitochondria-associated death signals and levels of reactive oxygen species were assayed. After treatment with 7-KC for 30h, low and high levels of folate supplementation significantly (P<0.05) reduced nuclear DNA loss. Only high levels of folate supplementation (>1000μmol/l) were effective in counteracting 7-KC-promoted apoptotic membrane phosphatidylserine exposure and DNA laddering. The attenuation of 7-KC-induced apoptotic damage by high-dose folate supplementation coincided with a partial normalization of mitochondria membrane potential dissipation, a suppression of cytochromecrelease and an inhibition of procaspase 3 activation. The prevention of mitochondrial dysfunctions and apoptotic processes was associated with antioxidant actions of high-dose folate by a marked scavenging of intracellular superoxide. Collectively, our present results demonstrate thatin vitrofolate supplementation exerts differentially protective effects against 7-KC-induced damage. High-dose supplementation alleviates oxidative stress, mitochondria-associated death signalling and apoptosis induced by 7-KC. However, thein vivorelevance is not clear and requires further study.

In vitrofolate deficiency induces apoptosis by a p53, Fas (Apo-1, CD95) independent, bcl-2 related mechanism in phytohaemagglutinin-stimulated human peripheral blood lymphocytes

Invitrofolate deficiency is associated with S phase accumulation and apoptosis in various cell types. To investigate the role of p53 and two apoptosis-related molecules, bcl-2 and Fas antigen (Apo-1, CD95), in the mechanism whereby folate-deficient lymphocytes accumulate and undergo apoptosis in the S phase, normal human peripheral blood lymphocytes were cultured for 3–9 d in control medium or in specially ordered and formulated HAM’ F-10 medium lacking folic acid, thymidine and hypoxanthine. Cells were stimulated with phytohaemagglutinin for the final 72 h prior to harvesting. The results indicate that p53 expression was downregulated in folate-deficient lymphocytes when compared with the control lymphocytes during the relevant period of S phase accumulation and apoptosis. In addition, folate deficiency was also found to downregulate IL-2, Fas antigen and bcl-2 expression, in terms of either mRNA or protein levels. The downregulation of Fas antigen suggests that folate deficiency-induced apoptosis probably does not occur via the Fas pathway. As IL-2 is a known inducer of bcl-2, and the downregulation of bcl-2 induces apoptosis, the downregulation of IL-2 and bcl-2 is suggested to play an important role in apoptosis. The complete rescue of folate-deficient lymphocytes from apoptosis was achieved by folic acid, thymidine or hypoxanthine alone or thymidine and hypoxanthine in combination. These results suggest that IL-2 depletion by folate deficiency in lymphocytes reduces the bcl-2 level, thereby triggering deoxynucleoside triphosphate pool imbalance and p53-independent apoptosis.

Acute respiratory infections during pregnancy and congenital abnormalities: a population-based case-control study

Diseases of respiratory system caused by acute infections are among the most common maternal diseases during pregnancy. The objective of the study was to estimate the association between congenital abnormalities and acute respiratory infections during the first trimester of pregnancy. The data set of the Hungarian Case-Control Surveillance of Congenital Abnormalities including 22 843 cases with congenital abnormalities, 38 151 population controls without congenital abnormalities and 834 malformed controls with Down syndrome between 1980 and 1996 was evaluated. 2118 cases with congenital abnormalities (9.3%), 3455 population controls (9.1%) and 92 malformed controls with Down syndrome (11.0%) had mothers with acute respiratory infections. Of 25 different congenital abnormality groups, esophageal atresia/stenosis showed a high adjusted prevalence odds ratios (POR) with 95% confidence interval (CI) for acute respiratory infections during the first trimester of pregnancy in case mothers compared with population controls (3.6, 1.4-9.1) and malformed controls (1.9, 1.0-3.5), respectively. In addition there was an association between medically recorded acute respiratory infections during the first trimester of pregnancy and a higher risk for some other congenital abnormalities, such as posterior cleft palate and multiple congenital abnormalities. In conclusion a possible association between some congenital abnormalities, particularly esophageal atresia/stenosis and maternal acute respiratory infections cannot be excluded due to the interactions of the microbial agents, related drug treatments and last but not least the indirect effect of maternal diseases, such as fever-hyperthermia, hypoxia and dietary deficiency. However, periconceptional multivitamin/folic acid supplementation during the early pregnancy was able to reduce the acute respiratory infection related risk for congenital abnormalities.

Newly constructed stable reporter cell lines for mechanistic studies on electrophile-responsive element-mediated gene expression reveal a role for flavonoid planarity

The electrophile-responsive element (EpRE) is a transcriptional enhancer involved in cancer-chemoprotective gene expression modulation by certain food components. Two stably transfected luciferase reporter cell lines were developed, EpRE(hNQO1)-LUX and EpRE(mGST-Ya)-LUX, based on EpRE sequences from the human NAD(P)H:quinone oxidoreductase (hNQO1) and the mouse glutathione-S-transferase Ya (mGST-Ya) gene, containing one and two tandem EpRE core sequences, respectively. The standard inducer tert-butylhydroquinone (tBHQ), the electrophile benzyl isothiocyanate (BITC), and the antioxidant flavonoid quercetin were found to induce luciferase expression, thereby validating these newly developed reporter cell lines. For tBHQ and BITC, but not for quercetin, higher maximum luciferase induction was found under control of the mGST-Ya EpRE as compared to the hNQO1 EpRE, pointing at different induction mechanisms. Furthermore, we investigated the structure-activity relationship for induction of luciferase expression by flavonoids in EpRE(mGST-Ya)-LUX cells, and also the relation between luciferase induction and flavonoid antioxidant potency. Five different flavonoids with a planar molecular structure were found to induce various levels of luciferase activity, whereas taxifolin, a non-planar flavonoid, did not induce luciferase activity. This suggests that a stereospecific molecular interaction may be important for EpRE-mediated gene activation, possibly with Keap1, a regulator of EpRE-controlled transcription, or with another effector or receptor protein. No consistent relation between luciferase induction level and flavonoid antioxidant potential was observed. Altogether, these results point to differences in induction mechanism between the various chemoprotective compounds tested. The newly developed stably transfected reporter cell lines provide a validated tool for future screening and mechanistic studies of EpRE-mediated gene transcription.

Mild folate deficiency induces a proatherosclerotic phenotype in endothelial cells

Low folate/high homocysteine (Hcy) is an established risk marker for cardiovascular disease (CVD). Some in vivo studies suggest low folate may independently contribute to CVD. To study the effects of mild folate deficiency on endothelial function, we adapted the EA.hy 926 endothelial cell line to growth in medium containing 23 nM folic acid (LO cells) or 9 microM folic acid (HI cells). Folate derivatives were substantially depleted in LO cells relative to HI cells. No differences were seen in intracellular homocysteine, S-adenosylmethionine (SAM), S-adenosylhomocysteine (SAH), the SAM:SAH ratio, or global DNA methylation, and there was no consistent difference in secreted homocysteine. A greater percentage of LO than HI cells were in S phase of the cell cycle; supplementation of LO cells with thymidine/hypoxanthine prevented this. LO cells were more elongated than HI cells and did not form tight monolayers. Stress fibers were very prominent in LO but not HI cells. Treatment of LO cells with rho kinase inhibitors abolished stress fibers and partially normalized cell shape. LO cell monolayers were more permeable than HI cell monolayers at confluence, and MCP-1 mRNA and protein expression was higher in LO than HI cells. Our results suggest that mild folate deficiency is proatherosclerotic.

Effects of folate deficiency on gene expression in the apoptosis and cancer pathways in colon cancer cells

Folate is a B vitamin, deficiency of which appears to increase the risk of developing several malignancies including colorectal cancer. In contrast to the cancer-promoting effect of folate deficiency in normal tissues, several lines of evidence indicate that folate depletion suppresses the progression of existing neoplasms and enhance the sensitivity of cancer cells to chemotherapy. Folate mediates the transfer of one-carbon necessary for the de novo biosynthesis of purines and thymidylate, and hence is an essential factor for DNA synthesis and repair, and the maintenance of DNA integrity and stability. Folate deficiency induces DNA strand breaks, increases uracil misincorporation into DNA, impairs DNA repair and appears to induce apoptosis. Although the effects of folate depletion on DNA integrity and apoptosis and on subsequent cancer development, progression and treatment in colonic epithelial cells have been well characterized, it is largely unknown at present how folate depletion modulates specific upstream genes in apoptosis and cancer pathways that regulate these processes. We therefore investigated the effects of folate depletion on expression of genes involved in apoptosis and cancer pathways in four human colon adenocarcinoma cell lines in an in vitro model of folate deficiency. Apoptosis and cancer pathway-specific mini-microarray were used to screen for differentially expressed genes in response to folate deficiency, and the expression of seven most notably and consistently affected genes was confirmed by real time RT-PCR. Our data suggest that folate deficiency affects the expression of key genes that are related to cell cycle control, DNA repair, apoptosis and angiogenesis in a cell-specific manner. Cell-specificity in gene expression changes in response to folate deficiency is likely due to significant differences in molecular and phenotypic characteristics, growth rates and intracellular folate concentrations among the four cell lines.

Tribromomethane exposure and dietary folate deficiency in the formation of aberrant crypt foci in the colons of F344/N rats

Folate and folic acid are forms of the B vitamin that are involved in the synthesis, repair, and functioning of DNA and are required for the production and maintenance of cells. Low levels of folate have been associated with several forms of cancer, including colon cancer. Aberrant crypt foci (ACF), identified as putative precursor lesions in the development of colon cancer, have been induced by the drinking water disinfection by-product, tribromomethane (TBM). To investigate whether ACF induced by TBM could be promoted by a diet devoid of dietary folate, male F344/N rats were exposed to 500 mg/l of TBM in drinking water and fed either a normal or no folate diet (NFD) for 26 weeks. At the conclusion of the study, colons were excised and examined for ACF. Rats exposed to TBM and fed a NFD, evident by significantly reduced serum folate concentrations and elevated serum homocysteine levels, had significant increases of ACF when compared to rats exposed to TBM and fed a normal diet. This study highlights the important role that diet, especially folate intake, represents in protecting the colon against TBM-induced ACF.

Folate deficiency inhibits the proliferation of primary human CD8+ T lymphocytes in vitro

Folate is required for one-carbon transfer reactions and the formation of purines and pyrimidines for DNA and RNA synthesis. Deficiency of folate can lead to many clinical abnormalities, including macrocytic anemia, cardiovascular diseases, birth defects, and carcinogenesis. The nucleotide imbalance due to folate deficiency causes cell cycle arrest in the S phase and uracil misincorporation into DNA, which may result in DNA double-strand breaks during repair. The role of folate in the immune system has not been fully characterized. We cultured PHA-activated human T lymphocytes in varying concentrations of folate, and measured proliferation, cell cycle, apoptosis, uracil misincorporation, and proportions of Th cells (CD4(+)) and cytotoxic T (CD8(+)) cells. Folate deficiency reduced proliferation of T lymphocytes, induced cell cycle arrest in the S phase, induced apoptosis, and increased the level of uracil in DNA. Folate deficiency also increased the CD4(+) to CD8(+) ratio due to a marked reduction of CD8(+) cell proliferation. Folate or nucleoside repletion of folate-deficient cells rapidly restored T lymphocyte proliferation and normal cell cycle, reduced the DNA uracil content, and lowered the CD4(+) to CD8(+) ratio. These data suggest that folate status may affect the immune system by reducing the capacity of CD8(+) cells to proliferate in response to activation.

Uracil in DNA, determined by an improved assay, is increased when deoxynucleosides are added to folate-deficient cultured human lymphocytes

Folate deficiency leads to increased dUMP/dTMP ratios and uracil misincorporation into DNA, which may increase cancer risk. We improved a previously described gas chromatography-mass spectrometry (GC-MS) assay for uracil in DNA and validated the assay by analyzing the DNA-uracil content of normal, primary human lymphocytes that were cultured in 0-3000 nM folic acid. In addition, the effects of nucleoside mixtures T or TdCA (T, thymidine; A, adenosine; dC, deoxycytidine) were investigated. Over 4 consecutive days, the inter- and intraassay coefficients of variation (CVs) were 2.3-3.9 and 0.6-2.2%. Mean recovery was 99.4%. Oligonucleotides containing 100 pg of uracil yielded a mean uracil measurement of 110.1 pg (CV=2.7%). Cells grown in different concentrations of folate showed a bimodal response, with maximum DNA-uracil at 12 nM, and minima at 0 and 3000 nM folate. Extremely folate-deficient cells may incorporate less uracil because DNA synthesis is reduced. A wide response to folate deficiency was seen in cells from different donors, suggesting that genetic background plays a critical role in individual susceptibility to DNA damage and cancer risk. Unexpectedly, TdCA supplementation caused increased DNA-uracil (vs 3000 nM folate for 10 days, P > 0.05), probably due to the conversion of deoxycytidine to deoxyuridine by cytidine deaminase, leading to elevated dUMP/dTMP ratios. This improved uracil assay could serve as a useful tool in the study of the mechanism of uracil misincorporation into DNA. The assay requires 3 microg of DNA per folate-deficient sample, but more may be required for baseline DNA-uracil detection in healthy humans.

Folate deficiency, mismatch repair-dependent apoptosis, and human disease

The vitamin that is most commonly deficient in the American diet is folate. Severe folate deficiency in humans is known to cause megaloblastic anemia and developmental defects, and is associated with an increased incidence of several forms of human cancer. Although the exact mechanisms by which this vitamin deficiency may cause these diseases are not known at the present time, recent work has shown that folate deficiency also causes genomic instability and programmed cell death (or apoptosis). Additionally, it is known that the DNA mismatch repair pathway mediates folate deficiency-induced apoptosis. This review will first describe work suggesting that folate deficiency causes genomic instability and apoptosis, then discuss possible mechanisms by which the mismatch repair pathway could trigger folate deficiency-induced apoptosis, which has either protective or destructive effects on tissue.

Folate deficiency and ionizing radiation cause DNA breaks in primary human lymphocytes: a comparison

DNA double-strand breaks, the most serious DNA lesion caused by ionizing radiation, are also caused by several vitamin or mineral deficiencies, such as for folate. Primary human lymphocytes were either irradiated or cultured at different levels of folate deficiency to assess cell proliferation, apoptosis, cell cycle, DNA breaks, and changes in gene expression. Both radiation and folate deficiency decreased cell proliferation and induced DNA breaks, apoptosis, and cell cycle arrest. Levels of folate deficiency commonly found resulted in effects similar to those caused by 1 Gy of radiation, a relatively high dose. Though both radiation and folate deficiency caused DNA breaks, they affected the expression of different genes. Radiation activated excision and DNA double-strand break repair genes and repressed mitochondrially encoded genes. Folate deficiency activated base and nucleotide excision repair genes and repressed folate-related genes. No DNA double-strand break repair gene was activated by folate deficiency. These findings suggest that a diet poor in folate may pose a risk of DNA damage comparable to that of a relatively high dose of radiation. Our results also suggest that research on biological effects of low-dose radiation should take into account the nutritional status of the subjects, because folate deficiency could confound the effects of low-dose radiation.

N-Acetylcysteine, vitamin C and vitamin E diminish homocysteine thiolactone-induced apoptosis in human promyeloid HL-60 cells

We showed previously that homocysteine thiolactone (HcyT) is a potent inducer of apoptosis in HL-60 cells. In the present study, the role of some radical scavengers (N-acetylcysteine, vitamin C, vitamin E and folate) on the reduction of HcyT-induced apoptosis was investigated. Preincubation of HcyT-treated HL-60 cells with vitamin C (Vit C; 100 micro mol/L) or vitamin E (Vit E; 100 micro mol/L) for 2 h significantly reduced the proportion of apoptotic cells with hypodiploid DNA contents or with membrane phosphatidylserine exposure, and attenuated the apoptotic DNA fragmentation. Preincubation of cells with N-acetylcysteine (NAC; 5 mmol/L) for 2 h significantly reduced HcyT-promoted apoptosis measured by membrane phosphatidylserine exposure only. The reduction of HcyT-induced apoptosis by NAC, Vit C or Vit E occurred simultaneously with a significant decrease in intracellular H(2)O(2) levels and reduced caspase-3 enzymatic activity. In contrast, folate had no H(2)O(2) scavenging capacity and did not suppress caspase-3 activity 6 h after HcyT treatment, although folate exhibited antioxidant behavior toward superoxide anions, hydroxyl radicals and peroxynitrite. Preincubation of cells with folate (10 micro mol/L) for 3 d did not affect the extent of HcyT-promoted apoptotic damage. Taken together, our findings suggest that antioxidant pretreatment with NAC, Vit C or Vit E exerts more beneficial effects than folate on reducing apoptotic cell damage induced by homocysteine thiolactone.

Maternal fever, multivitamin use, and selected birth defects: evidence of interaction?

BACKGROUND

Multivitamin use has been associated with lower risks for some birth defects. We evaluated whether multivitamin use modified birth defect risks associated with febrile illness, a common and possibly teratogenic exposure.

METHODS

From the population-based Atlanta Birth Defects Case-Control Study (1968-1980) we selected seven defects (neural tube defects, cleft lip and palate, cardiac outflow tract defects, ventricular septal defects, atrial septal defects, omphalocele, and limb deficiencies) because of their inverse relation with multivitamin supplement use documented in previous analyses. We defined four exposure categories from combinations of multivitamin use (periconceptional use compared with no use) and febrile illness (early pregnancy compared with no illness). The reference category was no multivitamin use and no illness.

RESULTS

Febrile illness with no multivitamin use was associated with generally increased risk for the seven defects and the combined group (odds ratio = 2.1, 1.7, 1.5, 1.9, 2.9, 4.4, 3.3, and 2.3, respectively). With multivitamin use, however, the risk estimates associated with febrile illness were generally lower (odds ratio = 0.6, 1.1, 0.0, 1.5, 0.0, 0.8, 0.0, and 0.8, respectively). Some of the associated 95% confidence intervals included one.

CONCLUSIONS

The pattern of findings suggests that multivitamin use might decrease the risk associated with febrile illness.

Involvement of DNA mismatch repair in folate deficiency-induced apoptosis small star, filled

Folate is a critical factor for DNA metabolism and its deficiency is associated with a number of human diseases and cancers. Although it has been shown that folate deficiency induces genomic instability and apoptotic cell death, the underlying mechanism is largely unknown. Given the role of mismatch repair in maintaining genomic integrity, mismatch repair was tested for its involvement in folate deficiency-induced genomic instability and cell death. Cells proficient in mismatch repair were highly sensitive to folate deficiency compared with cells defective in either hMutSalpha or hMutLalpha. Since wild-type cells but not mutant cells underwent apoptosis upon extensive folate depletion, the apoptotic response is dependent on a functional mismatch repair system. Our data also indicate that p53 is required for the folate depletion-induced apoptosis. In vitro biochemical studies demonstrated that hMutSalpha specifically recognized DNA damage induced by folate deficiency, suggesting a direct participation of mismatch repair proteins in mediating the apoptotic response. We conclude that while the mismatch repair-dependent apoptosis is necessary to protect damaged cells from tumorigenesis, it may damage a whole tissue or organ, as seen in patients with megaloblastic anemia, during extensive folate deficiency.

Occurrence of omphalocele in relation to maternal multivitamin use: a population-based study

OBJECTIVE

We evaluated the association between mothers' use of multivitamin supplements and their infants' risk for omphalocele, a congenital anomaly of the abdominal wall. Omphalocele can occur in certain multiple congenital anomaly patterns with neural tube defects, for which a protective effect of multivitamins with folic acid has been demonstrated.

METHODS

We used data from a population-based case-control study of infants born from 1968-1980 to mothers residing in metropolitan Atlanta. Case-infants with nonsyndromic omphalocele (n = 72) were actively ascertained from multiple sources. Control-infants (n = 3029), without birth defects, were selected from birth certificates by stratified random sampling.

RESULTS

Compared with no use in the periconceptional period, periconceptional use of multivitamin supplements (regular use from 3 months before pregnancy through the first trimester of pregnancy) was associated with an odds ratio for nonsyndromic omphalocele of 0.4 (95% confidence interval [CI]: 0.2-1.0). For the subset comprising omphalocele alone or with selected midline defects (neural tube defects, hypospadias, and bladder/cloacal exstrophy), the odds ratio was 0.3 (95% CI: 0.1-0.9). These estimates were similar when the reference group also included women who began using multivitamins late in pregnancy (during the second or third month of pregnancy). The small number of participants limited the precision of subgroup analyses and translated into wide confidence intervals that included unity.

CONCLUSIONS

Periconceptional multivitamin use was associated with a 60% reduction in the risk for nonsyndromic omphalocele. These findings await replication from additional studies to confirm the findings, generate more precise estimates, and detail possible mechanisms of actions.

Sphingoid bases and ceramide induce apoptosis in HT-29 and HCT-116 human colon cancer cells

Complex dietary sphingolipids such as sphingomyelin and glycosphingolipids have been reported to inhibit development of colon cancer. This protective role may be the result of turnover to bioactive metabolites including sphingoid bases (sphingosine and sphinganine) and ceramide, which inhibit proliferation and stimulate apoptosis. The purpose of the present study was to investigate the effects of sphingoid bases and ceramides on the growth, death, and cell cycle of HT-29 and HCT-116 human colon cancer cells. The importance of the 4,5-trans double bond present in both sphingosine and C(2)-ceramide (a short chain analog of ceramide) was evaluated by comparing the effects of these lipids with those of sphinganine and C(2)-dihydroceramide (a short chain analog of dihydroceramide), which lack this structural feature. Sphingosine, sphinganine, and C(2)-ceramide inhibited growth and caused death of colon cancer cells in time- and concentration-dependent manners, whereas C(2)-dihydroceramide had no effect. These findings suggest that the 4,5-trans double bond is necessary for the inhibitory effects of C(2)-ceramide, but not for sphingoid bases. Evaluation of cellular morphology via fluorescence microscopy and quantitation of fragmented low-molecular weight DNA using the diphenylamine assay demonstrated that sphingoid bases and C(2)-ceramide cause chromatin and nuclear condensation as well as fragmentation of DNA, suggesting these lipids kill colon cancer cells by inducing apoptosis. Flow cytometric analyses confirmed that sphingoid bases and C(2)-ceramide increased the number of cells in the A(0) peak indicative of apoptosis and demonstrated that sphingoid bases arrest the cell cycle at G(2)/M phase and cause accumulation in the S phase. These findings establish that sphingoid bases and ceramide induce apoptosis in colon cancer cells and implicate them as potential mediators of the protective role of more complex dietary sphingolipids in colon carcinogenesis.

Nutrition in cancer prevention: an integrated approach

There is considerable evidence that the war on cancer is not being won. There is, however, strong evidence that a substantial fraction of cancer can be prevented by using existing nutritional knowledge. In this paper we discuss strategies for reducing cancer incidence by implementing this knowledge. The most obvious route for persuading large numbers to change their diets is by individual counseling in a health-care setting, public education campaigns and interventions at the worksite. However, such health promotion actions have met with only limited success. For efforts to change population diets to be successful, a vital component must include changes in govemment policies. Examples of the tools that need to be employed are restrictions on advertising and marketing. Effective action will likely require an economic dimension, namely the employment of taxation and subsidies, for instance, by taxing unhealthy food choices and by subsidizing fruit and vegetables.

Flow cytometric analysis of spontaneous and dexamethasone-induced apoptosis in thymocytes from severely malnourished rats

Severe malnutrition is widely distributed throughout the world, showing a high prevalence in developing countries. Experimental animal models have been useful to study the effects of malnutrition at different levels and ages. Apoptosis is a well recognised process of cell death occurring under several physiological and pathological conditions. It represents the principal mechanism involved in cell selection in the thymus. Thymocyte apoptosis induction by dexamethasone is one of the best characterised experimental models of programmed cell death. The aim of the present study was to determine whether severe malnutrition increased spontaneous and/or dexamethasone-induced apoptosis in vivo in thymocytes of experimentally malnourished rats during lactation. Thymocytes were obtained from malnourished rats at weaning (21d of age). Apoptosis frequency was estimated by the terminal transferase-mediated dUTP nick end labelling assay. Spontaneous apoptosis was 1.9 (sd 1.0) % in well nourished rats in contrast to 13.3 (sd 3.8) % in malnourished animals; this is seven times greater (P<0.001). Interestingly, the frequency of dexamethasone-induced apoptosis was similar in both groups of animals (47.9 (sd 10.1) % in well nourished rats and 53.8 (sd 8.0) % in malnourished rats). The results obtained in the present study indicate that malnutrition is associated with a significant increase of spontaneously apoptotic cells. In addition, the data showed that the fraction of thymocytes susceptible to dexamethasone-induced apoptosis was similar in well nourished and malnourished animals. The greater levels of spontaneously apoptotic cells associated with malnutrition could be related to alterations of the microenvironment of the thymus and/or to an obstruction of early thymocyte maturation.

Folate deficiency-induced oxidative stress and apoptosis are mediated via homocysteine-dependent overproduction of hydrogen peroxide and enhanced activation of NF-kappaB in human Hep G2 cells

Folate coenzymes are critical for de novo synthesis of purine and thymidine, and for interconversion of amino acids. Folate deficiency inhibits cellular proliferation, disturbs cell cycling, causes genetic damage and eventually results in cell death. Previously, we demonstrated that the demise of human hepatoma Hep G2 cells mediated by folate deficiency proceeded via a p53-independent apoptosis, and the perturbation of intracellular calcium homeostasis was also shown to be involved. To further delineate the mechanism associated with this observed phenomenon, Hep G2 cells were cultivated in the control or folate-deficient media (control media lacking folate, glycine, thymidine and hypoxanthine) for 4 weeks. At the end of this cultivation period, we found that TBARS (an index of lipid peroxidation) concentrations in the folate-deficient cells were drastically increased as compared to the control cells (0.04 vs 0.01 nmole/10(6) cells), indicating that a severe oxidative stress of the former cells had occurred. This phenomenon was also shown to coincide with the ability of these folate-deficient cells to elaborate increased amounts of H2O2 as compared to its folate-supplemented cells (2.87 vs 0.98 nmole/10(5) cells/h). Furthermore, the accelerated production of H2O2 by the folate-deficient cells was also closely correlated with the elevated homocysteine concentrations released in the culture medium (15.37 +/- 2.4 vs 3.58 +/- 2.4 micromole/L; P< 0.001). Finally, we demonstrated that folate deficiency was indeed capable of activating a redox-sensitive transcription factor, NF-kappaB, which is crucial in the control of a reactive oxygen species-mediated apoptosis. In summary, we show that folate deficiency-induced apoptosis is proceeded via the enhanced activation of NF-kappaB, which is the resulting form of the homocysteine-mediated overproduction of hydrogen peroxide.

Congenital heart defects, maternal febrile illness, and multivitamin use: a population-based study

We assessed the relation between febrile illness during pregnancy and cardiac defects in the offspring in a population-based case-control study in metropolitan Atlanta. Case infants (905) with cardiac defects were actively ascertained from multiple sources. Control infants (3,029) were infants without birth defects who were selected from birth certificates by stratified random sampling. We compared those whose mothers reported febrile illness from 1 month before pregnancy through the third month of pregnancy with those whose mothers reported no illness during the same period. Febrile illness was positively associated with the occurrence of heart defects in the offspring (odds ratio [OR] = 1.8; 95% confidence interval = 1.4-2.4). When influenzalike illness was the reported febrile illness, the OR was 2.1 (95% confidence interval = 0.8-5.5). The association with febrile illness was strongest for tricuspid atresia (OR = 5.2), left obstructive defects (OR = 2.7), transposition of the great arteries (OR = 1.9), and ventricular septal defects (OR = 1.8). These ORs were generally lower among mothers who used multivitamins during the periconceptional period.

The effect of folate deficiency on the cytotoxic and mutagenic responses to ethyl methanesulfonate in human lymphoblastoid cell lines that differ in p53 status

Folic acid deficiency acts synergistically with alkylating agents to increase genetic damage at the HPRT locus in Chinese hamster ovary cells in vitro and in rat splenocytes in vivo. The present studies extend these observations to human cells and, in addition, investigate the role of p53 activity on mutation induction. The human lymphoblastoid cell lines TK6 and WTK1 are derived from the same parental cell line (WI-L2), but WTK1 expresses mutant p53. Treatment of folate-replete or deficient WTK1 and TK6 cells with increasing concentrations (0-50microg/ml) of ethyl methanesulfonate (EMS) resulted in significantly different HPRT mutation dose-response relationships (P<0.01), indicating that folate deficiency increased the EMS-induced mutant frequency in both cell lines, but with a greater effect in TK6 cells. Molecular analyses of 152 mutations showed that the predominant mutation (65%) in both cell types grown in the presence or absence of folic acid was a G>A transition on the non-transcribed strand. These transitions were mainly at non-CpG sites, particularly when these bases were flanked 3' by a purine or on both sides by G:C base pairs. A smaller number of G>A transitions occurred on the transcribed strand (C>T=14%), resulting in 79% total G:C>A:T transitions. There were more genomic deletions in folate-deficient (15%) as compared to replete cells (4%) of both cell types. Mutations that altered RNA splicing were common in both cell types and under both folate conditions, representing 33% of the total mutations. These studies indicate that cells expressing p53 activity exhibit a higher rate of mutation induction but are more sensitive to the toxic effects of alkylating agents than those lacking p53 activity. Folate deficiency tends to reduce toxicity but increase mutation induction after EMS treatment. The p53 gene product did not have a major influence on the molecular spectrum after treatment with EMS, while folate deficiency increased the frequency of deletions in both cell types.

Apoptosis in megaloblastic anemia occurs during DNA synthesis by a p53-independent, nucleoside-reversible mechanism

Deficiency of folate or vitamin B12 (cobalamin) causes megaloblastic anemia, a disease characterized by pancytopenia due to the excessive apoptosis of hematopoietic progenitor cells. Clinical and experimental studies of megaloblastic anemia have demonstrated an impairment of DNA synthesis and repair in hematopoietic cells that is manifested by an increased percentage of cells in the DNA synthesis phase (S phase) of the cell cycle, compared with normal hematopoietic cells. Both folate and cobalamin are required for normal de novo synthesis of thymidylate and purines. However, previous studies of impaired DNA synthesis and repair in megaloblastic anemia have concerned mainly the decreased intracellular levels of thymidylate and its effects on nucleotide pools and misincorporation of uracil into DNA. An in vitro model of folate-deficient erythropoiesis was used to study the relationship between the S-phase accumulation and apoptosis in megaloblastic anemia. The results indicate that folate-deficient erythroblasts accumulate in and undergo apoptosis in the S phase when compared with control erythroblasts. Both the S-phase accumulation and the apoptosis were induced by folate deficiency in erythroblasts fromp53 null mice. The complete reversal of the S-phase accumulation and apoptosis in folate-deficient erythroblasts required the exogenous provision of specific purines or purine nucleosides as well as thymidine. These results indicate that decreased de novo synthesis of purines plays as important a role as decreased de novo synthesis of thymidylate in the pathogenesis of megaloblastic anemia.

Apoptosis in megaloblastic anemia occurs during DNA synthesis by a p53-independent, nucleoside-reversible mechanism

Deficiency of folate or vitamin B12 (cobalamin) causes megaloblastic anemia, a disease characterized by pancytopenia due to the excessive apoptosis of hematopoietic progenitor cells. Clinical and experimental studies of megaloblastic anemia have demonstrated an impairment of DNA synthesis and repair in hematopoietic cells that is manifested by an increased percentage of cells in the DNA synthesis phase (S phase) of the cell cycle, compared with normal hematopoietic cells. Both folate and cobalamin are required for normal de novo synthesis of thymidylate and purines. However, previous studies of impaired DNA synthesis and repair in megaloblastic anemia have concerned mainly the decreased intracellular levels of thymidylate and its effects on nucleotide pools and misincorporation of uracil into DNA. An in vitro model of folate-deficient erythropoiesis was used to study the relationship between the S-phase accumulation and apoptosis in megaloblastic anemia. The results indicate that folate-deficient erythroblasts accumulate in and undergo apoptosis in the S phase when compared with control erythroblasts. Both the S-phase accumulation and the apoptosis were induced by folate deficiency in erythroblasts fromp53 null mice. The complete reversal of the S-phase accumulation and apoptosis in folate-deficient erythroblasts required the exogenous provision of specific purines or purine nucleosides as well as thymidine. These results indicate that decreased de novo synthesis of purines plays as important a role as decreased de novo synthesis of thymidylate in the pathogenesis of megaloblastic anemia.