An assay for uracil in human DNA at baseline: effect of marginal vitamin B6 deficiency

Measurement of deaminated cytosine adducts in DNA using a novel hybrid thymine DNA glycosylase

The hydrolytic deamination of cytosine and 5-methylcytosine drives many of the transition mutations observed in human cancer. The deamination-induced mutagenic intermediates include either uracil or thymine adducts mispaired with guanine. While a substantial array of methods exist to measure other types of DNA adducts, the cytosine deamination adducts pose unusual analytical problems, and adequate methods to measure them have not yet been developed. We describe here a novel hybrid thymine DNA glycosylase (TDG) that is comprised of a 29-amino acid sequence from human TDG linked to the catalytic domain of a thymine glycosylase found in an archaeal thermophilic bacterium. Using defined-sequence oligonucleotides, we show that hybrid TDG has robust mispair-selective activity against deaminated U:G and T:G mispairs. We have further developed a method for separating glycosylase-released free bases from oligonucleotides and DNA followed by GC-MS/MS quantification. Using this approach, we have measured for the first time the levels of total uracil, U:G, and T:G pairs in calf thymus DNA. The method presented here will allow the measurement of the formation, persistence, and repair of a biologically important class of deaminated cytosine adducts.

DNA damage is inversely associated to blood levels of DHA and EPA fatty acids in Brazilian children and adolescents

This study aimed to investigate the association between DNA damage and blood levels of docosahexaenoic acid (DHA), eicosapentaenoic acid (EPA), retinol, beta-carotene and riboflavin in Brazilian children and adolescents. Subjects (n = 140) were healthy boys and girls aged 9 to 13 years in Ribeirão Preto (SP, Brazil). Data collection included anthropometry, assessment of energy intake and blood sampling. DNA damage was evaluated by single-cell gel electrophoresis (comet assay). Principal component analysis (PCA) was used to verify associations between blood concentrations of vitamins, polyunsaturated fatty acids and DNA damage. Multiple regression analyses, k-means cluster, and analysis of covariance (ANCOVA), adjusted for confounding variables such as age, sex, energy intake, body mass index and total cholesterol (when needed), were applied to confirm the associations. PCA explained 69.4% of the inverse relationships between DNA damage and blood levels of DHA, EPA, retinol, and beta-carotene. Results were confirmed by ANCOVA and multiple regression analyses for DHA and EPA. In conclusion, omega-3-fatty acids were inversely associated with DNA damage in Brazilian children and adolescents and may be a protective factor against the development of future diseases.

Genetic variants of the dUTPase-encoding gene DUT increase HR-HPV infection rate and cervical squamous cell carcinoma risk

Deoxyuridine 5′-triphosphate nucleotidohydrolase (dUTPase) is involved in the repair and prevention of uracil misincorporations into DNA. Maintenance of DNA integrity is critical for cancer prevention. Many studies have identified susceptibility loci and genetic variants in cervical cancer. The aim of this study was to explore the distribution frequency of six single nucleotide polymorphisms (SNPs) in the dUTPase-encoding gene DUT in a case-control study to identify the relationship between DUT genetic variants and cervical cancer susceptibility. Six DUT intronic SNPs (rs28381106, rs3784619, rs10851465, rs28381126, rs3784621 and rs11637235) were genotyped by mismatch amplification-PCR in 400 cervical squamous cell carcinomas (CSCCs), 400 precursor cervical intraepithelial neoplasia (CIN) III lesions and 1,200 normal controls. No correlations were found between four DUT SNPs (rs3784621, rs10851465, rs28381106 and rs28381126) and CIN III and CSCC risk. However, the homozygous GG allele of rs3784619 and TT allele of rs11637235 correlated significantly with increased risk of CIN III and CSCC (OR = 2.29, 2.05; OR = 3.15, 3.15, respectively). Individuals with the G allele or G carrier allele (AG + GG) at rs3784619 and with the T allele or T carrier allele (CT + TT) at rs11637235 were at higher risk for CIN III and CSCC (OR = 1.26, 1.30; OR = 1.41, 1.65, respectively). Similarly, in the human papillomavirus (HPV)-positive groups, we found that the homozygous GG alleles of rs3784619 and TT alleles of rs11637235 markedly increased the risk of CIN III and CSCC (OR = 2.44, 2.71; OR = 3.32, 4.04, respectively). When performing a stratified analysis of sexual and reproductive histories, we found that the GG genotype of rs3784619 had a particularly high level of enrichment in the group of patients with > one sexual partner in CIN III (P = 0.043) and CSCC (P = 0.007). Meanwhile, the TT genotype of rs11637235 was enriched for in the high risk HPV (HR-HPV)-positive cases of CIN III (P = 0.033) and CSCC (P = 0.022). Analysis of the haplotype between rs3784619 (A/G) and rs11637235 (C/T) revealed that the genotypes with AA-TT (OR = 2.59), AG-TT (OR = 2.29), GG-CC (OR = 2.72), GG-CT (OR = 3.01 (1.83–4.96)) were significantly associated with increased risk of CIN III. More notably, this risk was much greater for CSCC (AA-TT (OR = 3.62), AG-TT (OR = 5.08), GG-CC (OR = 5.28), and GG-CT (OR = 4.23). Additionally, most GG genotypes of rs3784619 were linkage GG-CT, while most TT genotypes of rs11637235 were linkage AA-TT. In conclusion, these findings suggested that the homozygous GG allele of rs3784619 and the TT allele of rs11637235 in the DUT gene significantly increased the risk of CIN III and CSCC. Most GG genotypes of rs3784619 and TT genotypes of rs11637235 were linkage GG-CT and AA-TT, respectively. The TT genotype of rs11637235 was enriched in the HR-HPV-positive cases. These two SNPs of the DUT gene can be early predictive biomarkers of CIN III and CSCC, and may be involved in HR HPV infection.

Association of SMUG1 SNPs in Intron Region and Linkage Disequilibrium with Occurrence of Cervical Carcinoma and HPV Infection in Chinese Population

Background and Aims: This study was aim to investigate the relationship between the four intron SNPs (rs3087404, rs2029167, rs2029166 and rs7296239) of SMUG1 and the susceptibility of cervical squamous cell carcinoma. Methods: Four SMUG1 intron SNPs (rs3087404, rs2029167, rs2029166 and rs7296239) were genotyped by MA-PCR in 400 CSCCs, 400 CIN III and 1200 controls. qRT-PCR and Western blot were used to detect the SMUG1 mRNA and protein expression. Results: Interestingly, we found that the homozygous GG of rs3087404 had a significantly increased risk of CIN III [OR=1.78(1.27-2.51), P= 0.001] and CSCCs [OR=4.04(2.94-5.55), P=0.000]. The individuals with G allele or G carrier (AG +GG) at rs3087404 were at higher risk for CSCCs [OR=1.34 (1.04-1.71), P= 0.022]. Similarly, the homozygous GG of rs2029167 also had an increased risk of CIN III [OR=2.56 (1.91-3.43), P= 0.000] and CSCCs [OR=4.05(3.02-5.44), P=0.000]. The individuals with G allele or G carrier (AG +GG) at rs2029167 were at higher risk for CINIII [OR=1.41(1.10-1.80), P= 0.006] and CSCCs [OR=1.91 (1.48-2.47), P= 0.000]. In HR-HPV positive group, both the homozygous GG of rs3087404 and the homozygous GG of rs2029167 had an increased risk to CIN III and CSCC. Stratified analysis of the number of sexual partners and the age of first sexual intercourse found that the rs3087404 (A/G) had a particularly high level of enrichment in the CIN III or CSCCs groups. About the rs2029167 (A/G), we only found a particularly high level of enrichment grouping by the number of sexual partners in the CIN III and CSCCs groups. Meanwhile, we also found that there is a correlation between the SNPs of SMUG1 rs3087404 (A/G) and rs2029167 (A/G) with tumor cell differentiation and family heredity. But we didn't find that there was an association between the deferent genotypes of SMUG1 rs2029166 and rs7296239 with SMUG1 gene mRNA or protein expression. During the linkage disequilibrium analysis between rs3087404 (A/G) and rs2029167 (A/G), the genotype with AA-GG [OR=3.14(1.95-5.05)], AG-GG [OR=2.45(1.58-3.89)], GG-AA [OR=2.24(1.28-3.90)] and GG-AG [OR=2.58(1.54-4.32)] significantly increased the risk of CIN III. More notably, this risk is much greater in CSCCs: AA-GG [OR=7.13(4.03-12.61)], AG-GG [OR=7.22(4.21-12.38)], GG-AA [OR=8.60(4.73-15.63)], GG-AG [OR=9.64(5.43-17.13)]. Additionally, most GG (rs3087404) genotypes were linkage GG-AG (44/77, 80/140) in the CIN III and CSCCs, while most GG (rs2029167) genotypes were linkage genotype AG-GG (79/145, 112/184) in the CIN III and CSCCs, respectively. Conclusions: These findings suggested that there was association between the two genetic polymorphisms of SMUG1 rs3087404(A/G) and rs2029167(A/G) with the susceptibility of CIN III and CSCCs, and there was a linkage disequilibrium between the rs3087404 with the rs2029167 in CIN III and CSCCs. This particular linkage disequilibrium can be used as predictive biomarkers of CIN III and CSCC.

Endogenously generated DNA nucleobase modifications source, and significance as possible biomarkers of malignant transformation risk, and role in anticancer therapy

The DNA of all living cells undergoes continuous structural and chemical alteration, which may be derived from exogenous sources, or endogenous, metabolic pathways, such as cellular respiration, replication and DNA demethylation. It has been estimated that approximately 70,000 DNA lesions may be generated per day in a single cell, and this has been linked to a wide variety of diseases, including cancer. However, it is puzzling why potentially mutagenic DNA modifications, occurring at a similar level in different organs/tissue, may lead to organ/tissue specific cancers, or indeed non-malignant disease - what is the basis for this differential response? We suggest that it is perhaps the precise location of damage, within the genome, that is a key factor. Finally, we draw attention to the requirement for reliable methods for identification and quantification of DNA adducts/modifications, and stress the need for these assays to be fully validated. Once these prerequisites are satisfied, measurement of DNA modifications may be helpful as a clinical parameter for treatment monitoring, risk group identification and development of prevention strategies.

Functions and Malfunctions of Mammalian DNA-Cytosine Deaminases

The AID/APOBEC family enzymes convert cytosines in single-stranded DNA to uracils, causing base substitutions and strand breaks. They are induced by cytokines produced during the body's inflammatory response to infections, and they help combat infections through diverse mechanisms. AID is essential for the maturation of antibodies and causes mutations and deletions in antibody genes through somatic hypermutation (SHM) and class-switch recombination (CSR) processes. One member of the APOBEC family, APOBEC1, edits mRNA for a protein involved in lipid transport. Members of the APOBEC3 subfamily in humans (APOBEC3A, APOBEC3B, APOBEC3C, APOBEC3D, APOBEC3F, APOBEC3G, and APOBEC3H) inhibit infections of viruses such as HIV-1, HBV, and HCV, and retrotransposition of endogenous retroelements through mutagenic and nonmutagenic mechanisms. There is emerging consensus that these enzymes can cause mutations in the cellular genome at replication forks or within transcription bubbles depending on the physiological state of the cell and the phase of the cell cycle during which they are expressed. We describe here the state of knowledge about the structures of these enzymes, regulation of their expression, and both the advantageous and deleterious consequences of their expression, including carcinogenesis. We highlight similarities among them and present a holistic view of their regulation and function.

A Vitamin B-6 Antagonist from Flaxseed Perturbs Amino Acid Metabolism in Moderately Vitamin B-6-Deficient Male Rats

BACKGROUND

Pyridoxal 5'-phosphate (PLP) plays a crucial role as a cofactor in amino acid metabolism. There is a prevalence of moderate vitamin B-6 deficiency in the population that may be exacerbated through the ingestion of 1-amino d-proline (1ADP), a vitamin B-6 antagonist found in flaxseed.

OBJECTIVE

Given prior evidence of the impact of synthetic 1ADP on indexes of pyridoxine metabolism, the current study was designed to investigate the effects of 1ADP derived from flaxseed on amino acid metabolism in moderately vitamin B-6-deficient rats.

METHODS

Male weanling rats (n = 8/treatment) consumed a semipurified diet containing either 7 mg pyridoxine hydrochloride/kg diet [optimum vitamin B-6 (OB)] or 0.7 mg pyridoxine hydrochloride/kg diet [moderately vitamin B-6 deficient (MB)], each with 0 or 10 mg vitamin B-6 antagonist/kg diet, in either a synthetic form (1ADP) or as a flaxseed extract (FE), for 5 wk. At the end of the experiment, plasma vitamin B-6 and amino acid concentrations and the activities of hepatic PLP-dependent enzymes were analyzed.

RESULTS

Compared with the MB control group, plasma PLP concentrations were 26% and 69% lower, respectively, in the MB+FE and MB+1ADP rats (P ≤ 0.001). In the MB+FE group, the plasma cystathionine concentration was 100% greater and the plasma α-aminobutyric acid and glutamic acid concentrations were 59% and 30% lower, respectively, than in the MB control group. Both synthetic 1ADP and FE significantly (P < 0.001) inhibited the in vitro hepatic activities of 2 PLP-dependent enzymes, cystathionine β-synthase (up to 44%) and cystathionine γ-lyase (up to 60%), irrespective of vitamin B-6 concentrations. Because of vitamin B-6 antagonist exposure, observed perturbations in plasma biomarkers and hepatic enzyme activities were not evident or of lesser magnitude in rats consuming adequate vitamin B-6.

CONCLUSION

The current data from a rat model provide evidence that a vitamin B-6 antagonist now prevalent in the human food supply may pose challenges to individuals of moderate vitamin B-6 status.

Biomarkers of Nutrition for Development-Folate Review

The Biomarkers of Nutrition for Development (BOND) project is designed to provide evidence-based advice to anyone with an interest in the role of nutrition in health. Specifically, the BOND program provides state-of-the-art information and service with regard to selection, use, and interpretation of biomarkers of nutrient exposure, status, function, and effect. To accomplish this objective, expert panels are recruited to evaluate the literature and to draft comprehensive reports on the current state of the art with regard to specific nutrient biology and available biomarkers for assessing nutrients in body tissues at the individual and population level. Phase I of the BOND project includes the evaluation of biomarkers for 6 nutrients: iodine, iron, zinc, folate, vitamin A, and vitamin B-12. This review represents the second in the series of reviews and covers all relevant aspects of folate biology and biomarkers. The article is organized to provide the reader with a full appreciation of folate's history as a public health issue, its biology, and an overview of available biomarkers (serum folate, RBC folate, and plasma homocysteine concentrations) and their interpretation across a range of clinical and population-based uses. The article also includes a list of priority research needs for advancing the area of folate biomarkers related to nutritional health status and development.

Genome instability biomarkers and blood micronutrient risk profiles associated with mild cognitive impairment and Alzheimer's disease

Successful maintenance of metabolic systems relating to accurate DNA replication and repair is critical for optimal lifelong human health. Should this homeostatic balance become impaired, genomic instability events can arise, compromising the integrity of the genome, which may result in gene expression and human disease. Both genome instability and micronutrient imbalance have been identified and implicated in diseases associated with accelerated ageing which potentially leads to an increased risk for the future development of clinically defined neurodegenerative disorders. Cognitive decline leading to the clinical diagnosis of mild cognitive impairment (MCI) has been shown to predict an increased risk in later life of developing Alzheimer's disease (AD). Knowledge on the impact of dietary factors in relation to MCI and AD risk is improving but incomplete; in particular the role of nutrient combinations (i.e. nutriomes) has not been thoroughly investigated. Currently, there is a need for preventative strategies as well as the identification of robust and reproducible diagnostic biomarkers that will allow identification of those individuals with increased risk for neurodegenerative diseases. Growing evidence suggests cells originating from different somatic tissues derived from individuals that have been clinically diagnosed with neurodegenerative disorders exhibit elevated frequencies of DNA damage compared to tissues of cognitively normal individuals which could be due to malnutrition. The objective of this review is to discuss current evidence and identify knowledge gaps relating to genome instability biomarkers and blood micronutrient profiles from human studies of MCI and AD that may be specific to and contribute to the increased risk of these diseases. This is a vital step in order to create research strategies for the future development of diagnostics that are indicative of dementia risk and to inform preventative therapies.

Genomic uracil homeostasis during normal B cell maturation and loss of this balance during B cell cancer development

Activation-induced deaminase (AID) converts DNA cytosines to uracils in immunoglobulin genes, creating antibody diversification. It also causes mutations and translocations that promote cancer. We examined the interplay between uracil creation by AID and its removal by UNG2 glycosylase in splenocytes undergoing maturation and in B cell cancers. The genomic uracil levels remain unchanged in normal stimulated B cells, demonstrating a balance between uracil generation and removal. In stimulated UNG(-/-) cells, uracil levels increase by 11- to 60-fold during the first 3 days. In wild-type B cells, UNG2 gene expression and enzymatic activity rise and fall with AID levels, suggesting that UNG2 expression is coordinated with uracil creation by AID. Remarkably, a murine lymphoma cell line, several human B cell cancer lines, and human B cell tumors expressing AID at high levels have genomic uracils comparable to those seen with stimulated UNG(-/-)splenocytes. However, cancer cells express UNG2 gene at levels similar to or higher than those seen with peripheral B cells and have nuclear uracil excision activity comparable to that seen with stimulated wild-type B cells. We propose that more uracils are created during B cell cancer development than are removed from the genome but that the uracil creation/excision balance is restored during establishment of cell lines, fixing the genomic uracil load at high levels.

A robust, sensitive assay for genomic uracil determination by LC/MS/MS reveals lower levels than previously reported

Considerable progress has been made in understanding the origins of genomic uracil and its role in genome stability and host defense; however, the main question concerning the basal level of uracil in DNA remains disputed. Results from assays designed to quantify genomic uracil vary by almost three orders of magnitude. To address the issues leading to this inconsistency, we explored possible shortcomings with existing methods and developed a sensitive LC/MS/MS-based method for the absolute quantification of genomic 2'-deoxyuridine (dUrd). To this end, DNA was enzymatically hydrolyzed to 2'-deoxyribonucleosides and dUrd was purified in a preparative HPLC step and analyzed by LC/MS/MS. The standard curve was linear over four orders of magnitude with a quantification limit of 5 fmol dUrd. Control samples demonstrated high inter-experimental accuracy (94.3%) and precision (CV 9.7%). An alternative method that employed UNG2 to excise uracil from DNA for LC/MS/MS analysis gave similar results, but the intra-assay variability was significantly greater. We quantified genomic dUrd in Ung(+/+) and Ung(-/-) mouse embryonic fibroblasts and human lymphoblastoid cell lines carrying UNG mutations. DNA-dUrd is 5-fold higher in Ung(-/-) than in Ung(+/+) fibroblasts and 11-fold higher in UNG2 dysfunctional than in UNG2 functional lymphoblastoid cells. We report approximately 400-600 dUrd per human or murine genome in repair-proficient cells, which is lower than results using other methods and suggests that genomic uracil levels may have previously been overestimated.

Single nucleotide polymorphisms in uracil-processing genes, intake of one-carbon nutrients and breast cancer risk

BACKGROUND/OBJECTIVES

The misincorporation of uracil into DNA leads to genomic instability. In a previous study, some of us identified four common single nucleotide polymorphisms (SNPs) in uracil-processing genes (rs2029166 and rs7296239 in SMUG1, rs34259 in UNG and rs4775748 in DUT) that were associated with significantly altered levels of uracil in human DNA. We investigated whether any of these SNPs are associated with an altered risk of developing breast cancer and if one-carbon nutrients intake can modify their effects.

SUBJECTS/METHODS

We genotyped the four SNPs in 1077 cases of incident breast cancer and 1910 age and race-matched controls in the Western New York Exposures and Breast Cancer (WEB) Study and examined associations with breast cancer risk and interactions with intake of folate, vitamins B6 and B12.

RESULTS

After adjustment for known risk factors for breast cancer, there was increased risk of breast cancer among postmenopausal women who were heterozygous for either of the two SMUG1 SNPs (odds ratio (OR) 1.29, 95% confidence interval (CI) 1.07-1.56) and OR 1.29, 95% CI 1.07-1.55, respectively). Among premenopausal women, increased risk associated with the SMUG1 rs2029166 genotype was limited to those with low folate intake. There were no other interactions with vitamins B(6) or B(12) intake.

CONCLUSIONS

Our study suggests that the four selected SNPs are not robust determinants of breast cancer risk, but that the two SNPs in SMUG1 might modestly alter the risk of breast cancer. However, the increase in risk among heterozygotes in the two SNPs in SMUG1, which is thought to be the most active glycosylase in vivo, raises the possibility that subtle 'heterosis' effects on cancer risk might be produced by these SNPs.

Prevention of mutation, cancer, and other age-associated diseases by optimizing micronutrient intake

I review three of our research efforts which suggest that optimizing micronutrient intake will in turn optimize metabolism, resulting in decreased DNA damage and less cancer as well as other degenerative diseases of aging. (1) Research on delay of the mitochondrial decay of aging, including release of mutagenic oxidants, by supplementing rats with lipoic acid and acetyl carnitine. (2) The triage theory, which posits that modest micronutrient deficiencies (common in much of the population) accelerate molecular aging, including DNA damage, mitochondrial decay, and supportive evidence for the theory, including an in-depth analysis of vitamin K that suggests the importance of achieving optimal micronutrient intake for longevity. (3) The finding that decreased enzyme binding constants (increased Km) for coenzymes (or substrates) can result from protein deformation and loss of function due to an age-related decline in membrane fluidity, or to polymorphisms or mutation. The loss of enzyme function can be compensated by a high dietary intake of any of the B vitamins, which increases the level of the vitamin-derived coenzyme. This dietary remediation illustrates the importance of understanding the effects of age and polymorphisms on optimal micronutrient requirements. Optimizing micronutrient intake could have a major effect on the prevention of cancer and other degenerative diseases of aging.

Uracil in DNA--its biological significance

Uracil may arise in DNA as a result of spontaneous cytosine deamination and/or misincorporation of dUMP during DNA replication. In this paper we will review: (i) sources of the origin of uracil in DNA; (ii) some properties of the enzymes responsible for the excision of uracil and their role in the Ig diversification process, which comprises somatic hypermutation and class switch recombination; and (iii) consequences of cytosine deamination in other than the Ig loci, in cell types different than B lymphocytes. Furthermore, the issue concerning the basal level of uracil in DNA and consequences of the presence of U:A pairs for DNA stability and cell functions will be discussed. Finally, we will discuss the clinical significance of aberrant uracil incorporation into DNA and possible involvement of aberrantly expressed AID and the enzyme-induced presence of uracil, in carcinogenesis. Based on the literature data we conclude/hypothesize that the non-canonical base uracil may be present and well tolerated in DNA mostly as U:A pairs, likely in quantities of 10(4) per genome. Although a role of uracil in DNA is not fully defined, it is possible that an ancestral system which once used uracil in primordial genetic material (uracil-DNA), may have evolved to use this molecule in regulatory processes such as: (i) meiotic cell division to facilitate chromatid exchange during crossing-over (in spermatocytes); (ii) it is possible that uracil present in DNA may be a signaling molecule during metamorphosis of Drosophila melanogaster; and (iii) during transcription since some regulatory proteins (Escherichia coli lac repressor) and GCN4 can recognize uracil versus thymine in specific DNA regulatory sequences. Moreover, recent data suggest that in transcriptionally active chromatin the dUTP/dTTP pool may be significantly increased, which in turn may lead to massive uracil incorporation into DNA.

Optimal micronutrients delay mitochondrial decay and age-associated diseases

Three of our research efforts are reviewed, which suggest that optimizing metabolism will delay aging and the diseases of aging in humans. (1) Research on delay of the mitochondrial decay of aging by supplementing rats with lipoic acid and acetyl carnitine. (2) The triage theory, which posits that modest micronutrient deficiencies (common in much of the population) accelerate molecular aging, including mitochondrial decay, and supportive evidence, including an analysis in depth of vitamin K, that suggests the importance of achieving optimal micronutrient intake for longevity. (3) The finding that decreased enzyme binding constants (increased Km) for coenzymes (or substrates) can result from protein deformation and loss of function due to loss of membrane fluidity with age, or to polymorphisms or mutation. The loss of enzyme function can be ameliorated by high doses of a B vitamin, which raises coenzyme levels, and indicates the importance of understanding the effects of age, or polymorphisms, on micronutrient requirements.

Uracil misincorporation into DNA and folic acid supplementation

BACKGROUND

Folate deficiency decreases thymidylate synthesis from deoxyuridylate, which results in an imbalance of deoxyribonucleotide that may lead to excessive uracil misincorporation (UrMis) into DNA during replication and repair.

OBJECTIVE

We evaluated the relation between UrMis in different tissues and the effect of folate supplementation on UrMis.

DESIGN

We analyzed UrMis concentrations in rectal mucosa (n = 92) and white blood cells (WBCs; n = 60) among individuals randomly assigned to receive supplementation with 1 mg folate/d or placebo, who were then evaluated for colorectal adenoma recurrence.

RESULTS

As expected, total homocysteine was significantly lower among the study participants who received active folate treatment (Wilcoxon's P = 0.003) than among those in the placebo group. The median UrMis concentration in rectal mucosa and WBCs among individuals treated with folate was not significantly lower than that in those who received placebo (Wilcoxon's P = 0.17). UrMis concentrations in both rectal mucosa and WBCs did not correlate significantly with folate measured in plasma and red blood cells. UrMis in rectal mucosa was marginally associated with an increased risk of adenoma recurrence (odds ratio per SD: 1.43; 95% CI: 0.91, 2.25).

CONCLUSIONS

UrMis measurements in WBCs are not a robust surrogate for UrMis measurements in the rectal mucosa (Spearman correlation coefficient = 0.23, P = 0.08). Furthermore, folate supplementation in an already replete population (half treated with folic acid supplements and all exposed to folic acid fortification of the food supply) was not significantly associated with reduced UrMis in rectal mucosa cells or WBCs. Large-scale studies are needed to evaluate whether excessive UrMis concentrations are an important risk factor for colorectal neoplasia. This trial was registered at clinicaltrials.gov as NCT00272324.

Crystallization and crystal-packing studies of Chlorella virus deoxyuridine triphosphatase

The 141-amino-acid deoxyuridine triphosphatase (dUTPase) from the algal Chlorella virus IL-3A and its Glu81Ser/Thr84Arg-mutant derivative Mu-22 were crystallized using the hanging-drop vapor-diffusion method at 298 K with polyethylene glycol as the precipitant. An apo IL-3A dUTPase with an amino-terminal T7 epitope tag and a carboxy-terminal histidine tag yielded cubic P2(1)3 crystals with unit-cell parameter a = 106.65 A. In the presence of dUDP, the enzyme produced thin stacked orthorhombic P222 crystals with unit-cell parameters a = 81.0, b = 96.2, c = 132.8 A. T7-histidine-tagged Mu-22 dUTPase formed thin stacked rectangular crystals. Amino-terminal histidine-tagged dUTPases did not crystallize but formed aggregates. Glycyl-seryl-tagged dUTPases yielded cubic P2(1)3 IL-3A crystals with unit-cell parameter a = 105.68 A and hexagonal P6(3) Mu-22 crystals with unit-cell parameters a = 132.07, c = 53.45 A, gamma = 120 degrees . Owing to the Thr84Arg mutation, Mu-22 dUTPase had different monomer-to-monomer interactions to those of IL-3A dUTPase.

Ultratrace analysis of uracil and 5-fluorouracil by molecularly imprinted polymer brushes grafted to silylated solid-phase microextraction fiber in combination with complementary molecularly imprinted polymer-based sensor

Main inborn errors of metabolism diagnosable through uracil (Ura) analysis and the therapeutic monitoring of toxic 5-fluorouracil (5FU) in dihydro pyrimidine dehydrogenase (DPD) deficient patients require a sensitive, reproducible, selective and accurate method. In this work, an artificial receptor in the format of molecularly imprinted polymer (MIP) brush 'grafted to' the surface of sol-gel immobilized on cost-effective homemade solid-phase microextraction (SPME) fibers, individually imprinted with either of Ura and 5FU, was used in combination with a voltammetric sensor duly modified with the same MIP. This combination provided up to 10- and 8.4-fold preconcentrations of Ura and 5FU, respectively, which was more than sufficient for achieving stringent detection limits in the primitive diagnosis of uracil disorders and fluoropyrimidine toxicity in DPD-deficient patients. The proposed method permits the assessment of Ura and 5FU plasma concentrations with detection limits pf 0.0245 and 0.0484 ng mL(-1) (RSD = 1.0-2.5%, S/N = 3), respectively, without any problems of non-specific false-positives and cross-reactivities in complicated matrices of biological samples.