叶酸在人体内作用的研究进展

叶酸Floic Acid是维生素B族中的一种,也是人体不可缺少的维生素,但人体不能合成,需由食物中获取。研究表明,叶酸缺乏可导致畸形儿出生、儿童肾衰、癌症、心血管疾病、老年性痴呆等疾病的发病率增高,补充叶酸除能有效减少上述疾病外,还有提高男性生育率,增强记忆力,预防硝酸甘油耐药性等效用。开发叶酸产品的前景看好。     

叶酸与消化系统疾病

叶酸是一种生长因子,其缺乏会出现机体多系统受损。在消化系统中可发生慢性萎缩性胃炎、结肠炎,甚至会增加患消化道肿瘤的危险。而且叶酸缺乏与肝细胞受损及巨幼红细胞性贫血密切相关。本文就叶酸的来源、代谢、生理功能、与消化系统疾病中的关系、实验室检测及其机体需要量的探讨作一综述。     

叶酸与食管癌关系的研究进展

叶酸在DNA合成、修复和甲基化过程中有重要作用,可能与肿瘤的发生发展相关。目前国内外有关叶酸与食管癌关系的研究越来越多,研究的角度和方法有所不同,但有关叶酸与食管癌发生的内在机理研究较少,大部分研究集中在叶酸代谢关键酶亚甲基四氢叶酸还原酶（MTHFR）基因多态性与食管癌的关联性,目前研究结果存在不确定性,需要进一步的探讨。本文综述近年来国内外有关食管癌与叶酸关系的研究进展。     

叶酸缺乏对小鼠胚胎干细胞Nespas DMR 区甲基化修饰的影响

目的：探讨叶酸缺乏对小鼠胚胎干细胞（ESCs）中Nespas 差异甲基化区域（Differentially Methylated Region, DMR）甲基化修 饰的影响以及叶酸浓度与甲基化水平的关系。方法：多种不同浓度叶酸处理小鼠ESCs,化学发光免疫分析法检测ESCs 细胞内叶 酸浓度。利用MassARRAY 技术平台检测三种不同叶酸浓度处理后的ESCs中Nespas DMR 启动子区,外显子区和内含子区甲基 化修饰状态,并且分析Nespas DMR 启动子区,外显子区和内含子区甲基化水平与叶酸浓度之间的关系。结果：无叶酸组（FF）小鼠 ESCs 细胞内叶酸浓度显著低于低叶酸组（FD）与正常叶酸组（FN）（P<0.05）。Nespas DMR 中启动子区、外显子区以及内含子区甲 基化水平在FF组显著低于FD 和FN 组（P<0.05）,并且Nespas DMR中启动子区以及内含子区甲基化水平与叶酸浓度存在显著 的正相关（P<0.05）。结论：叶酸缺乏影响小鼠ESCs 中Nespas DMR 区甲基化修饰的建立。     

叶酸缺乏对小鼠胚胎干细胞Nespas DMR区甲基化修饰的影响

目的：探讨叶酸缺乏对小鼠胚胎干细胞（ESCs）中Nespas差异甲基化区域（Differentially Methylated Region,DMR）甲基化修饰的影响以及叶酸浓度与甲基化水平的关系。方法：多种不同浓度叶酸处理小鼠ESCs,化学发光免疫分析法检测ESCs细胞内叶酸浓度。利用MassARRAY技术平台检测三种不同叶酸浓度处理后的ESCs中Nespas DMR启动子区,外显子区和内含子区甲基化修饰状态,并且分析Nespas DMR启动子区,外显子区和内含子区甲基化水平与叶酸浓度之间的关系。结果：无叶酸组（FF）小鼠ESCs细胞内叶酸浓度显著低于低叶酸组（FD）与正常叶酸组（FN）（P〈0.05）。Nespas DMR中启动子区、外显子区以及内含子区甲基化水平在FF组显著低于FD和FN组（P〈0.05）,并且Nespas DMR中启动子区以及内含子区甲基化水平与叶酸浓度存在显著的正相关（P〈0.05）。结论：叶酸缺乏影响小鼠ESCs中Nespas DMR区甲基化修饰的建立。     

叶酸与蛋白质合成

叶酸作为一碳单位携带分子,在机体内发挥着非常重要的作用,它所参与的甲基化作用与蛋白质的合成紧密相关,本文对叶酸影响蛋白质的合成过程做了比较全面的综述,旨在阐明叶酸在蛋白质合成各个阶段中的作用。     

叶酸缺乏对斑马鱼背主动脉发育的影响

目的观察叶酸缺乏斑马鱼胚胎的背主动脉（DA）发育情况,初步探讨叶酸缺乏后胚胎DA发育异常的机理。方法采用将二氢叶酸还原酶（DHFR）功能阻断的方法构建叶酸缺乏斑马鱼模型,分别应用DHFR抑制剂甲氨蝶呤（MTX）以及DHFR基因knock-down技术处理斑马鱼胚胎。在胚胎发育至48 hpf时在显微镜下观察胚胎的整体发育情况,在60 hpf时应用荧光显微造影的方法观察胚胎的背主动脉发育状况。利用胚胎整体原位杂交和real-time PCR的方法检测影响DA发育的关键因子ephrinB2、Ang-1和Radar的表达情况,利用TUNEL法检测胚胎底索的凋亡情况。结果MTX处理组胚胎以及DHFR knock-down组胚胎有相似的胚胎发育异常表型。荧光显微造影显示叶酸缺乏组胚胎的DA发育异常。叶酸缺乏组胚胎的ephrinB2、Ang-1和Radar表达减弱,底索凋亡增加。结论叶酸缺乏可导致斑马鱼胚胎背主动脉发育异常,其机理与ephrinB2、Ang-1和Radar的表达减弱以及底索凋亡增加有关。     

叶酸-阿霉素连接物的制备及其抗肿瘤活性研究

目的:合成具有酸敏特性的叶酸-氨基己酸-阿霉素连接物,并观察其抗肿瘤活性以及对肿瘤细胞的靶向性。方法:首先将叶酸与氨基己酸连接,然后利用腙键与阿霉素连接,采用核磁共振、质谱等方法鉴定其结构;采用MTT法观察连接物对叶酸受体表达阳性的口腔表皮样癌细胞KB细胞及叶酸受体表达阴性肺癌A549细胞的毒性作用。结果:在氮羟基琥珀酰亚胺和二环己基碳二亚胺的催化作用下,合成了叶酸-氨基己酸-阿霉素连接物,波谱分析提示为目标产物。与游离阿霉素相比,连接物对KB细胞具有更强的细胞毒性,而且细胞毒性作用可被外源性叶酸抑制;而连接物对A549细胞的毒性弱于游离阿霉素,而且外源性游离叶酸对其细胞毒性没有显著影响。结论:叶酸-氨基己酸-阿霉素连接物能经叶酸受体介导靶向于叶酸受体丰富的肿瘤细胞,是一种潜在的新型抗肿瘤药物。     

叶酸-阿霉素连接物的制备及其抗肿瘤活性研究

目的:合成具有酸敏特性的叶酸-氨基己酸-阿霉素连接物,并观察其抗肿瘤活性以及对肿瘤细胞的靶向性.方法:首先将叶酸与氨基己酸连接,然后利用腙键与阿霉素连接,采用核磁共振、质谱等方法鉴定其结构;采用MTT法观察连接物对叶酸受体袁达阳性的口腔表皮样癌细胞KB细胞及叶酸受体表达阴性肺癌A549细胞的毒性作用.结果:在氮羟基琥珀酰亚胺和二环己基碳二亚胺的催化作用下,合成了叶酸-氨基己酸-阿霉素连接物,波谱分析提示为目标产物.与游离阿霉素相比,连接物对KB细胞具有更强的细胞毒性,而且细胞毒性作用可被外源性叶酸抑制;而连接物对A549细胞的毒性弱于游离阿霉素,而且外源性游离叶酸对其细胞毒性没有显著影响.结论:叶酸-氨基己酸-阿霉素连接物能经叶酸受体介导靶向于叶酸受体丰富的肿瘤细胞,是一种潜在的新型抗肿瘤药物.     

微生物分析法测定保健食品中叶酸

1942年,STOKSTAD首次成功地合成了叶酸,并阐明了叶酸的化学结构。半个世纪过去了,叶酸一直是学术界的研究热点。叶酸的化学名称为蝶酰谷氨酸,又叫维生素B11,通常意义上,叶酸指的是一组具有蝶酰谷氨的结构和相关生物活性的同效维生素,广泛存在于绿叶蔬菜中。其英文名称包括folic ac id,folate,folates,folac in,一般可以互用,近几十年来人们逐渐认识到它的重要性。由于叶酸参与体内高半胱氨酸的转化,因而其对防止血管硬化和阻塞有益;另外还发现叶酸可大量提供游离碳原子,是制造神经末梢和构成传递神经冲动的重要化学物质的原料。2000年F…     

Production of natural folates by lactic acid bacteria starter cultures isolated from artisanal Argentinean yogurts

Folate is a B-group vitamin that cannot be synthesized by humans and must be obtained exogenously. Although some species of lactic acid bacteria (LAB) can produce folates, little is known about the production of this vitamin by yogurt starter cultures. Lactobacillus delbrueckii subsp. bulgaricus and Streptococcus thermophilus strains were isolated from artisanal Argentinean yogurts and were grown in folate-free culture medium (FACM) and nonfat milk after which intracellular and extracellular folate production were evaluated. From the initial 92 isolated LAB strains, 4 L. delbrueckii subsp. bulgaricus and 32 S. thermophilus were able to grow in the absence of folate. Lactobacillus delbrueckii subsp. bulgaricus CRL 863 and S.?thermophilus CRL 415 and CRL 803 produced the highest extracellular folate levels (from 22.3 to 135?μg/L) in FACM. In nonfat milk, these strains were able to increase the initial folate concentrations by almost 190%. This is the first report where native strains of L. delbrueckii subsp. bulgaricus were shown to produce natural folate. The LAB strains identified in this study could be used in developing novel fermented products bio-enriched in natural folates that could in turn be used as an alternative to fortification with the controversial synthetic chemical folic acid.     

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.     

Folate biofortification in food plants

Folate deficiency is a global health problem affecting many people in the developing and developed world. Current interventions (industrial food fortification and supplementation by folic acid pills) are effective if they can be used but might not be possible in less developed countries. Recent advances demonstrate that folate biofortification of food crops is now a feasible complementary strategy to fight folate deficiency worldwide. The genes and enzymes of folate synthesis are sufficiently understood to enable metabolic engineering of the pathway, and results from pilot engineering studies in plants (and bacteria) are encouraging. Here, we review the current status of investigations in the field of folate enhancement on the eve of a new era in food fortification.     

Folate status in various pathophysiological conditions

Folate is the generic term for compounds that have vitamin activity similar to that of pteroylglutamic acid. Folate acts as a coenzyme in several single carbon transfers involved in biosynthesis of purine nucleotides and deoxythymidylic acid essential for DNA and RNA synthesis. In addition, folate provides one-carbon unit for methylation of a wide variety of biological substances including DNA, proteins, phospholipids, and neurotransmitters, thereby regulating their function. Recent epidemiological-clinical and experimental studies suggest the association of folate deficiency with the risk of various cancers, birth defects, and cardiovascular diseases. Thus, it is important to consider the conditions that are associated with altered folate status and their consequences. The impairment in folate status has been found in number of pathophysiological conditions like inflammatory bowel disease, cancer, alcoholism, pregnancy, neonatal growth, and during administration of some drugs. The recent advances dealing with mechanistic aspects of impaired folate status in these conditions have been discussed in this review.     

Recent update on lactic acid bacteria producing riboflavin and folates: application for food fortification and treatment of intestinal inflammation

Lactic acid bacteria (LAB), widely used as starter cultures for the fermentation of a large variety of food, can improve the safety, shelf life, nutritional value and overall quality of the fermented products. In this regard, the selection of strains delivering health-promoting compounds is now the main objective of many researchers. Although most LAB are auxotrophic for several vitamins, it is known that certain strains have the capability to synthesize B-group vitamins. This is an important property since humans cannot synthesize most vitamins, and these could be obtained by consuming LAB fermented foods. This review discusses the use of LAB as an alternative to fortification by the chemical synthesis to increase riboflavin and folate concentrations in food. Moreover, it provides an overview of the recent applications of vitamin-producing LAB with anti-inflammatory/antioxidant activities against gastrointestinal tract inflammation. This review shows the potential uses of riboflavin and folates producing LAB for the biofortification of food, as therapeutics against intestinal pathologies and to complement anti-inflammatory/anti-neoplastic treatments.     

The genetic background of the curly tail strain confers susceptibility to folate‐deficiency‐induced exencephaly

BACKGROUND : Suboptimal maternal folate status is considered a risk factor for neural tube defects (NTDs). However, the relationship between dietary folate status and risk of NTDs appears complex, as experimentally induced folate deficiency is insufficient to cause NTDs in nonmutant mice. In contrast, folate deficiency can exacerbate the effect of an NTD‐causing mutation, as in splotch mice. The purpose of the present study was to determine whether folate deficiency can induce NTDs in mice with a permissive genetic background which do not normally exhibit defects. METHODS : Folate deficiency was induced in curly tail and genetically matched wild‐type mice, and we analyzed the effect on maternal folate status, embryonic growth and development, and frequency of NTDs. RESULTS : Folate‐deficient diets resulted in reduced maternal blood folate, elevated homocysteine, and a diminished embryonic folate content. Folate deficiency had a deleterious effect on reproductive success, resulting in smaller litter sizes and an increased rate of resorption. Notably, folate deficiency caused a similar‐sized, statistically significant increase in the frequency of cranial NTDs among both curly tail (Grhl3 mutant) embryos and background‐matched embryos that are wild type for Grhl3. The latter do not exhibit NTDs under normal dietary conditions. Maternal supplementation with myo‐inositol reduced the incidence of NTDs in the folate‐deficient wild‐type strain. CONCLUSIONS : Dietary folate deficiency can induce cranial NTDs in nonmutant mice with a permissive genetic background, a situation that likely parallels gene‐nutrient interactions in human NTDs. Our findings suggest that inositol supplementation may ameliorate NTDs resulting from insufficient dietary folate. Birth Defects Research (Part A), 2010. © 2009 Wiley‐Liss, Inc.     

Formation of folates by microorganisms: towards the biotechnological production of this vitamin

Folates (vitamin B₉) are essential micronutrients which function as cofactors in one-carbon transfer reactions involved in the synthesis of nucleotides and amino acids. Folate deficiency is associated with important diseases such as cancer, anemia, cardiovascular diseases, or neural tube defects. Epidemiological data show that folate deficiency is still highly prevalent in many populations. Hence, food fortification with synthetic folic acid (i.e., folic acid supplementation) has become mandatory in many developed countries. However, folate biofortification of staple crops and dairy products as well as folate bioproduction using metabolically engineered microorganisms are promising alternatives to folic acid supplementation. Here, we review the current strategies aimed at overproducing folates in microorganisms, in view to implement an economic feasible process for the biotechnological production of the vitamin.

     

The effect of folic acid and/or methionine deficiency on deoxyribonucleotide pools and cell cycle distribution in mitogen-stimulated rat lymphocytes

Abstract. Folate deficiency will induce abnormal deoxynucleoside triphosphate (dNTP) metabolism because folate-derived one-carbon groups are essential for de novo synthesis of purines and the pyrimidine, thymidylate. Under conditions of methionine deprivation, a functional folate deficiency for deoxynucleoside triphosphate synthesis is induced as a result of the irreversible diversion of available folates toward endogenous methionine resynthesis from homocysteine. The purpose of the present study was to examine the effect of nutritional folate and/or methionine deprivation in vitro on intracellular dNTP pools as related to DNA synthesis activity and cell cycle progression. Primary cultures of mitogen-stimulated rat splenic T-cells were incubated in complete RPMI 1640 medium or in custom-prepared RPMI 1640 medium lacking in folic acid and/or methionine. Parallel cultures, initiated from the same cell suspension, were analysed for deoxyribonucleotide pool levels and for cell proliferation. The distribution of cells within the cell cycle was quantified by dual parameter flow cytometric bromodeoxyuridine/propidium iodide DNA analysis which allows more accurate definition of DNA synthesizing S-phase cells than the traditional DNA-specific staining with propidium iodide alone. Relative to cells cultured in complete RPMI 1640 media, the cells cultured in media deficient in folate, methionine or in both nutrients manifested increases in the deoxythymidylate pool and an apparent depletion of the deoxyguanosine triphosphate pool. Both adenosine triphosphate and nicotinamide adenine diphosphate levels were significantly reduced with single or combined deficiencies of folate and methionine. These nucleotide pool alterations were associated with a decrease in the proportion of cells actively synthesizing DNA and an increase in cells in G₂+ M phase of the cell cycle. Folate deprivation in the presence of adequate methionine produced a moderate decrease in DNA synthesizing cells over the 68 h incubation. However, methionine deprivation, in the presence or absence of folate, severely compromised DNA synthesis activity. These results are consistent with the established ‘methyl trap’ diversion of available folates towards the resynthesis of methionine from homocysteine and away from nucleotide synthesis. The data confirm the metabolic interdependence of folic acid and methionine and emphasize the pivotal role of methionine on the availability of folate one-carbon groups for deoxynucleotide synthesis. The decrease in DNA synthesis activity under nutrient conditions that negatively affect nucleotide biosynthesis suggest a possible role for abnormal dNTP metabolism in the regulation of cell cycle progression and DNA synthesis.     

Folate concentrations and folic acid supplementation among women in their first trimester of pregnancy in a rural area with a high prevalence of neural tube defects in Shanxi, China

BACKGROUND: Although an information campaign concerning periconceptional folic acid supplementation was launched in 1998 in Shanxi Province, China, the prevalence of neural tube defects in rural areas was reported as high as 140 per 10,000 births in 2002. The blood folate concentrations and the practice of folic acid supplementation among pregnant women in rural areas of the province are described. METHODS: A total of 483 pregnant women (mean gestation, 8.1 weeks) in a rural area of Shanxi were interviewed. Nonfasting blood samples and information on folic acid supplementation were collected. Folate concentrations in plasma and erythrocytes were determined by a microbiological assay. RESULTS: The mean concentrations of plasma and erythrocyte folate for pregnant women was 10.4 nmol/liter and 375.8 nmol/liter, respectively. Deficiencies of plasma and erythrocyte folate were observed in 20.9% and 47.6% of women, respectively. Seasonal variations were noted in the prevalence of folate deficiency, with significantly lower plasma folate concentrations in spring and summer and lower erythrocyte folate concentrations in seasons other than summer. Among pregnant women, <10% reported having taken or currently taking folic acid, and virtually no women (0.6%) took folic acid as recommended. CONCLUSIONS: Women in rural areas had low plasma and erythrocyte folate levels, and folate deficiency was highly prevalent in the area. Few women followed the recommendations regarding folic acid supplementation, and the information campaign in Shanxi was unsuccessful. These findings suggest the urgent need for combined strategies in rural areas to fortify grain with folic acid and promote folic acid supplements for childbearing-age women.     

Evaluation of the kinetic properties of the folate transport system in intestinal absorptive epithelium during experimental ethanol ingestion

Folate plays a critical role in maintaining normal metabolic, energy, differentiation and growth status of all mammalian cells. The disturbances in body folate homeostasis such as intestinal malabsorption in alcoholism are well-known contributor to folate deficiency associated disorders. The study was sought to delineate the kinetic features of folate transport in intestinal absorptive epithelium that could highlight insights of malabsorption during alcoholism. We studied [³H]-folic acid transport in intestinal brush border membrane (BBM) after 3 months of ethanol administration at 1 g/kg body weight/day to rats. The results showed that the folate transport exhibited saturable kinetics and was pH, Na⁺, temperature, divalent cation sensitive, besides –SH group(s) was/were found important in the folate transport system to be efficiently operative. Importantly, the decreased intestinal BBM folate transport in chronic alcoholism was associated with increased K _m and decreased V _max during alcoholism. In addition, S–S group status of the transporter and presence of Na⁺ at the absorptive site seems to be perturbed during ethanol ingestion. However, H⁺/folate⁻ coupled transport provided the driving force for transport as pH optimum in acidic range was not altered during alcoholism. The inhibition constants of methotrexate and unlabelled folic acid revealed that the two analogues are handled differently by the folate transport system. In addition, the low activity of folate transport system during chronic ethanol exposure was associated with low RBC folate levels. Overall, these findings suggest that the deregulated folate transport kinetics might contribute to intestinal folate malabsorption in alcoholism.