Scavenging properties of metronidazole on free oxygen radicals in a skin lipid model system.

Reactive oxygen species (ROS) play a vital role in the pathophysiology of the skin disease rosacea, a chronic, genetically-determined and UV-triggered disease, leading to facial redness and blemishes and exhibiting a deep impact on a patient's self-esteem and quality of life. ROS can cause oxidative damage to nucleic acids, sugars, proteins and lipids, thereby contributing to adverse effects on the skin. Metronidazole has been the first-line topical agent therapy for many years; nevertheless the mechanism of action is still not well understood. The therapeutic efficacy of metronidazole has been attributed to its antioxidant effects, which can involve two pathways: decreased generation of ROS within tissues or scavenging and inactivation of existing ROS. Previous investigations have shown that metronidazole reduces ROS by decreasing ROS production in cellular in-vitro systems. The aim of the following study was to demonstrate that metronidazole additionally exhibits antioxidative properties in a cell-free system, by acting as an antioxidant scavenger. A simple skin lipid model (oxidative) system and a complex skin adapted lipid system in conjunction with thiobarbituric acid (TBA) test, a quantitative assay for the detection of malondialdehyde (MDA) and therefore lipid peroxidation, were used to determine the antioxidative properties of metronidazole after UV irradiation. Results clearly show that metronidazole has antioxidative properties in a cell-free environment, acting as a free radical scavenger. Simple skin lipid model: in the presence of 10, 100 and 500 microg mL(-1)metronidazole the MDA concentration was reduced by 25, 36 and 49%, respectively. Complex skin lipid system: in the presence of 100 and 500 microg mL(-1)metronidazole the MDA concentration was reduced by 19 and 34%, respectively. The results obtained in this study and from previous publications strongly suggest that metronidazole exhibits antioxidative effects via two mechanisms: decrease in ROS production through modulation of neutrophil activity and decrease in ROS concentration by exhibiting ROS scavenging properties. The remarkable clinical efficacy of metronidazole in the treatment of rosacea is probably due to its ability to decrease ROS via different mechanisms, thereby protecting skin components from induced damage.

Associations between two common variants C677T and A1298C in the methylenetetrahydrofolate reductase gene and measures of folate metabolism and DNA stability (strand breaks, misincorporated uracil, and DNA methylation status) in human lymphocytes in vivo.

OBJECTIVE: Homozygosity for variants of the methylenetetrahydrofolate reductase (MTHFR) gene is associated with decreased risk for colorectal cancer. We have investigated the relationships between two variants of the MTHFR gene (C677T and A1298C) and blood folate, homocysteine, and genomic stability (strand breakage, misincorporated uracil, and global cytosine methylation in lymphocytes) in a study of 199 subjects. RESULTS: The frequencies of homozygosity for the C677T and A1298C variants of the MTHFR gene were 12.6% and 14.6%, respectively. Plasma homocysteine, folate, vitamin B12, 5-methyltetrahydrofolate, and RBC folate were determined in the C677T genotypes. Plasma folate was significantly lower (P < 0.001) in the homozygous variants (6.7 +/- 0.6 ng/mL) compared with wild-types (8.8 +/- 0.4 ng/mL) and heterozygotes (9.1 +/- 0.5 ng/mL). Homocysteine was significantly higher (P < 0.05) in homozygous variants (13.2 +/- 1.1 micromol/L) compared with homozygous subjects (10.9 +/- 0.4 micromol/L). Homozygous variants had significantly lower (P < 0.05) RBC folate (84.7 +/- 6.3 ng/mL) compared with wild-types (112.2 +/- 5.2 ng/mL) and heterozygous individuals (125.1 +/- 6.6 ng/mL). No significant difference in RBC folate was observed between wild-types and heterozygotes. The A1298C variant did not influence plasma homocysteine, folate, 5-methyltetrahydrofolate, vitamin B12, or RBC folate. Lymphocyte DNA stability biomarkers (strand breaks, misincorporated uracil, and global DNA methylation) were similar for all MTHFR C677T or A1298C variants. CONCLUSION: Data from this study do not support the hypothesis that polymorphisms in the MTHFR gene increase DNA stability by sequestering 5,10-methylenetetrahydrofolate for thymidine synthesis and reducing uracil misincorporation into DNA.

Folate, DNA stability and colo-rectal neoplasia.

Lower levels of dietary folate are associated with the development of epithelial cell tumours in man, particularly colo-rectal cancer. In the majority of epidemiological studies blood folate or reported folate intake have been shown to be inversely related to colo-rectal cancer risk. Folate, via its pivotal role in C1 metabolism, is crucial both for DNA synthesis and repair, and for DNA methylation. This function is compromised when vitamin B12 is low. Vitamin B12 deficiency has been shown to increase biomarkers of DNA damage in man but there is no evidence directly linking low vitamin B12 with cancer. Disturbingly, folate and vitamin B12 deficiencies are common in the general population, particularly in the underprivileged and the elderly. How folate and/or vitamin B12 deficiency influence carcinogenesis remains to be established, but it is currently believed that they may act to decrease DNA methylation, resulting in proto-oncogene activation, and/or to induce instability in the DNA molecule via a futile cycle of uracil misincorporation and removal. The relative importance of these two pathways may become clear by determining both DNA stability and cytosine methylation in individuals with different polymorphic variants of key folate-metabolising enzymes. 5,10-Methylenetetrahydrofolate reductase converts 5,10-methylenetetrahydrofolate to 5-methyltetrahydrofolate and thereby controls whether folate is employed for DNA synthesis or DNA methylation. Colo-rectal cancer risk is decreased in subjects homozygous for a common variant (C677T) of the gene coding for this enzyme, suggesting that DNA synthesis and repair may be 'enhanced' in these individuals. Evidence from animal and human studies is presented here in support of folate acting to maintain genomic stability through both these mechanisms.

Colon cancer and genetic variation in folate metabolism: the clinical bottom line.

So far, evidence for the relation between folate intake and colorectal cancer has been insufficient to lead to specific public health interventions. In principle, data on the relation between genetic variation in folate metabolism and colorectal neoplasia could be used to corroborate the data on the relation between folate intake or status and the disease, strengthening the evidence base for primary prevention. Issues in considering the relation between a health outcome and genetic variation in metabolism of nutrients or other food components include knowledge of gene function, linkage disequilibrium, population stratification, study size and quality, and gene-environment interaction. Overall homozygosity for MTHFR variant genotypes is associated with a reduced risk of colorectal cancer, the opposite of what might have been expected a priori. This has led investigators to place greater emphasis on the functions of folate and methylenetetrahydrofolate reductase in DNA synthesis. Folate and related nutrients may be important after adenoma formation. A challenge for the future is to characterize the effects of multiple genes influencing folate metabolism. Limited data for colorectal cancer suggest that the effect of a low folate diet overrides the effect of genotype, but two studies of adenomas suggested the opposite. Another potential role of information on genetic variation in folate metabolism is in the management of colorectal cancer but most studies have been small, have included selected patient groups, and have made limited adjustment for potentially important factors.

Impact of folate deficiency on DNA stability.

Convincing evidence links folate deficiency with colorectal cancer incidence. Currently, it is believed that folate deficiency affects DNA stability principally through two potential pathways. 5,10-Methylenetetrahydrofolate donates a methyl group to uracil, converting it to thymine, which is used for DNA synthesis and repair. If folate is limited, imbalances in the DNA precursor pool occur, and uracil may be misincorporated into DNA. Subsequent misincorporation and repair may lead to double strand breaks, chromosomal damage and cancer. Moreover, folate affects gene expression by regulating cellular S-adenosylmethionine (SAM) levels. 5-Methyltetrahydrofolate serves as methyl donor in the remethylation of homocysteine to methionine, which in turn is converted to SAM. SAM methylates specific cytosines in DNA, and this regulates gene transcription. As a consequence of folate deficiency, cellular SAM is depleted, which in turn induces DNA hypomethylation and potentially induces proto-oncogene expression leading to cancer. Data from several model systems supporting these mechanisms are reviewed here. There is convincing evidence that folate modulates both DNA synthesis and repair and DNA hypomethylation with altered gene expression in vitro. The data from in vivo experiments in rodents is more difficult to interpret because of variations in the animal and experimental systems used and the influence of tissue specificity and folate metabolism. Most importantly, the confounding effects of nutrient-gene interactions, together with the identification of polymorphisms in key enzyme systems and the influence that these have on folate metabolism and DNA stability, must be considered when interpreting evidence from human studies.