Dietary flavonoids protect human colonocyte DNA from oxidative attack in vitro

Summary Background & Aims: Epidemiological studies suggest that antioxidant polyphenols in the human diet may protect against diseases such as cancer. In this study we investigated the cytoprotective potential of the flavonoids, quercetin, myricetin, kaempferol and rutin against oxidative DNA damage in human colonocytes in vitro. Methods: Caco-2 cells, which display specialised enterocyte/colonocyte cell functions, were used as an in vitro model for human colonocytes. Hydrogen peroxide was employed as the oxidant. DNA damage (strand breakage, oxidised purines and oxidised pyrimidines) was determined using the alkaline single cell gel electrophoresis or comet assay. Cell growth and viability were measured. Results: Hydrogen peroxide caused a dose-dependent increase in DNA strand breakage in human colonocytes, presumably via oxygen free radical generation. Quercetin and myricetin protected Caco-2 cells against oxidative attack. In addition, quercetin decreased hydrogen peroxide-mediated inhibition of growth. Neither rutin nor kaempferol was effective. However, quercetin, while inhibiting DNA strand breakage, did not alter the levels of oxidised bases following peroxide treatment. The antifungal agent ketoconazole, prevented quercetin cytoprotection in Caco-2 cells, indicating that P450-mediated metabolism may alter the efficacy of the flavonoids against oxidative DNA damage. Conclusion: Flavonoids, particularly quercetin, the most abundant flavonoid in the human diet, are likely to be important in defending human colonocytes from oxidative attack. Received: 7 October 1998, Accepted: 5 November 1998     

Effect of complex polyphenols and tannins from red wine on DNA oxidative damage of rat colon mucosa in vivo

Summary Background: Dietary polyphenols have been reported to have a variety of biological actions, including anti-carcinogenic, antioxidant and anti-inflammatory activities. Aim of the study: In the present study we have evaluated the effect of an oral treatment with complex polyphenols and tannins from red wine and tea on DNA oxidative dammage in the rat colon mucosa. Methods: Isolated colonocytes were prepared from the colon mucosa of rats treated for ten days with either wine complex polyphenols (57.2 mg/kg/d) or thearubigin (40 mg/kg/d) by oral gavage. Colonocyte oxidative DNA damage was analysed at the single cell level using a modification of the comet assay technique. Results: These results show that wine complex polyphenols and tannins induce a significant decrease (−62% for pyrimidine and −57% for purine oxidation) in basal DNA oxidative damage in colon mucosal cells without affecting the basal level of single-strand breaks. On the other hand, tea polyphenols, namely a crude extract of thearubigin, did not affect either strand breaks or pyrimidine oxidation in colon mucosal cells. Conclusions Our experiments are the first demonstration that dietary polyphenols can modulate in vivo oxidative damage in the gastrointestinal tract of rodents. These data support the hypothesis that dietary polyphenols might have both a protective and a therapeutic potential in oxidative damage-related pathologies. Received: 17 April 2000, Accepted: 27 July 2000     

叶酸及DNA甲基化与神经管畸形关系的研究进展

神经管畸形(neural tube defects,NTDs)是早期胚胎发育过程中神经管闭合不全导致的严重出生缺陷,NTDs是遗传和环境因素共同作用的结果,给社会和家庭带来了沉重的负担。叶酸是人体必需的营养物质,其参与的一碳代谢涉及嘌呤和嘧啶合成、体内甲基化等重要反应,影响体内多种发育相关基因和通路的调控,对神经管发育过程至关重要。大量的流行病学研究证实补充叶酸可有效预防NTDs的发生,但是叶酸降低NTDs发病率的机制尚不完全清楚。DNA甲基化是目前广泛研究的表观遗传机制,研究表明DNA甲基化异常与NTDs发生关系密切。综述叶酸代谢过程、叶酸代谢关键酶与相关基因、DNA甲基化与NTDs的关系,以阐明叶酸及DNA甲基化在NTDs中的作用,为NTDs的发病机制和NTDs的防治提供新思路。     

Absorption and DNA protective effects of flavonoid glycosides from an onion meal

Summary Background. It is widely believed that antioxidant micronutrients obtained from fruit and vegetables afford significant protection against cancer and heart disease, as well as ageing. Flavonoids are potential antioxidants found in food such as onions; information on their effectiveness in vivo is so far lacking. Aims. To determine uptake as well as in vivo antioxidant effects of flavonoids from foods. Methods. Six healthy non-obese normocholesterolaemic female volunteers in the age range 20–44 years participated in a randomised two-phase crossover supplementation trial to compare the antioxidant effects associated with (a) a meal of fried onions and (b) a meal of fried onions and fresh cherry tomatoes. Plasma flavonoids, lymphocyte DNA damage, plasma ascorbic acid, tocopherols and carotenoids, urinary malondialdehyde and 8-hydroxy-2’-deoxyguanosine were determined to assess flavonoid absorption and antioxidant efficacy. Results. Flavonoid glucosides (quercetin-3-glucoside and isorhamnetin-4-glucoside) were significantly elevated in plasma following ingestion of the onion meal and the increases were associated with an increased resistance of lymphocyte DNA to DNA strand breakage. A significant decrease in the level of urinary 8-hydroxy-2’-deoxyguanosine was evident at 4 h following ingestion of the onion meal. After the combined tomato and onion meal, only quercetin was detected in plasma. Endogenous base oxidation was decreased but resistance to strand breakage was unchanged. There was no significant change in the excretion of urinary malondialdehyde following either meal. Conclusion. Both meals – onions, and onions together with tomatoes – led to transient decreases in biomarkers of oxidative stress, although the particular biomarkers affected differ. It is possible that the differences in patterns of response reflect the different uptakes of flavonoids but the underlying mechanism is not understood. Received: 1 April 2000, Accepted: 1 August 2000     

Recovery of human lymphocytes from oxidative DNA damage; the apparent enhancement of DNA repair by carotenoids is probably simply an antioxidant effect

Summary Background: Many epidemiological studies have identified a protection against cancer associated with consumption of fruit and vegetables. One factor is this protection may be the enhancement of cellular DNA repair activity by micronutrients, such as carotenoids, found in these foods. Aims of the study: To measure the capacity of lymphocytes isolated from volunteers supplemented with β-carotene, lutein or lycopene to recover from DNA damage induced in vivo by treatment with H₂O₂. Methods: Healthy volunteers were given supplements of lutein (15 mg/day), lycopene (15 mg/day) and βcarotene (15 mg/day), each for 1 week, the supplementation periods being separated by 3-week wash-out periods. Blood samples were taken at the beginning and end of each supplementation, and at 1 week and 3 weeks during the wash-out period. Carotenoid levels were measured in plasma. Lymphocytes were isolated and frozen. Subsequently, they were treated with 100 μM H₂O₂ and incubated for up to 24 h; DNA damage was measured with the comet assay (single cell gel electrophoresis) after 0, 2, 4, 8, and 24 h. Results: Increases of 2- to 3-fold in mean plasma lutein and β-carotene concentrations were seen at the end of the respective supplementation periods; they returned virtually to basal levels after wash-out. Lycopene concentrations were less affected by supplementation, and were more variable. H₂O₂-induced DNA strand breaks were apparently only slowly rejoined by the lymphocytes. The rejoining of breaks in the first few hours appeared substantially faster in lymphocytes following supplementation with β-carotene, but no such effect was seen with lutein. In those individuals who showed increases in lycopene concentrations, the recovery was significantly faster. Lymphocytes that were not treated with H₂O₂ showed a transient increase in DNA breakage to about double the background level in 2 h, presumably as a result of exposure to atmospheric oxygen; this effect, too, was relieved by supplementation with lycopene or β-carotene. Conclusions: While certain carotenoids appear to enhance recovery from oxidative damage, this is probably in fact an antioxidant protective effect against additional damage induced by atmospheric oxygen, rather than a stimulation of DNA repair. Received: 6 December 1999, Accepted: 22 March 2000     

硅转化BALB/c-3T3细胞基因组DNA异常甲基化的研究

目的 对硅转化细胞基因组DNA异常甲基化进行研究，探讨硅的表遗传致癌机制。方法 从结晶型硅(Si)转化BALB/c-3T3细胞中提取基因组DNA，经Msel(甲基化非敏感性酶)单独消化或Msel和BstU1(甲基化敏感性酶)联合消化，消化产物用甲基化敏感性内切酶指纹法(MSRF)进行分析，差异显示出异常甲基化基因片段，进一步将异常甲基化DNA片段亚克隆和序列测定，再与基因文库中的基因进行类比分析。结果发现硅转化细胞存在6条异常甲基化DNA(其中1条为高甲基化，5条有低甲基化现象)，序列测定显示这些异常甲基化基因片段似乎来源于一些RNA转录和蛋白质翻译等基因家族。结论DNA异常甲基化会导致基因表达激活或抑制，因此硅转化细胞基因组某些功能基因DNA异常甲基化导致的异常表达，可能间接是硅诱导细胞转化及其致癌作用的一种表遗传机制。     

Beneficial role for folate in the prevention of colorectal and breast cancer

Summary Folate is involved in the synthesis of nucleotides and amino acid metabolism such as methylation of homocysteine to methionine. Methionine is activated by adenosine triphosphate (ATP) to produce S-adenosylmethionine (SAM), the primary intracellular methyl donor. Thus, folate is essential for the synthesis, methylation, and repair of DNA. With regard to its biochemical function it has been hypothesized that a diminished folate status may contribute to carcinogenesis by alteration of gene expression and increased DNA damage. Animal and human studies support this hypothesis, particularly with respect to colorectal cancer. Epidemiological evidence for the association between folate status and cancer was first observed among ulcerative colitis patients. Several case-control studies demonstrated reduction in colorectal cancer risk with better folate status. Two large, prospective cohort studies support the concept that high folate intake is protective against colon cancer. In contrast to colorectal cancer, the potential association of folate status and risk has been less investigated in breast cancer. Recently, convincing epidemiological data establishing a positive effect of folate status on breast cancer risk were published. This review summarizes the epidemiological evidence for the association between folate status and colorectal and breast cancer risk. In addition, a short overview is given on the discussed mechanism(s) by which folate might be involved in carcinogenesis. Received: 6 October 2000, Accepted: 13 June 2001     

DNA甲基化在子宫内膜异位症发病机制中的作用及地西他滨对其治疗的研究

目的探讨DNA甲基化在子宫内膜异位症发病机制中的作用以及DNA甲基转移酶抑制剂地西他滨在内异症治疗中的可行性。方法根据大鼠自体移植方法构建大鼠子宫内膜异位症模型,4周后2次开腹判断造模是否成功,用游标卡尺测量记录异位灶体积后将大鼠随机分为实验组(12只)、PBS组(12只)和对照组(11只)。同时选取未造模的正常大鼠作为空白组(10只)。实验组大鼠腹腔注射5-氮-2’-脱氧胞苷(2.5 mg/kg/d),PBS组注射等量PBS溶液,对照组未用药。应用免疫组织化学染色方法和Western Blot法检测各组异位灶内DNA甲基转移酶1的表达情况。收集腹腔冲洗液用Elisa法检测肿瘤坏死因子(tumor necrosis factor-α,TNF-α)含量。结果 50只大鼠根据大鼠子宫内膜自体移植方法成功35只,造模成功率为70%(35/50)。实验组大鼠经药物处理后异位灶体积明显缩小(P0.05),PBS组及对照组异位灶体积无明显改变(P0.05)。实验组用药后异位内膜组织上皮细胞体积缩小,腺体萎缩,囊液分泌减少;异位灶组织中DNA甲基转移酶1的表达低于PBS组及对照组(P0.05),PBS组及对照组间表达无明显差异(P0.05)。治疗后实验组大鼠腹腔冲洗液中TNF-α含量较PBS组及对照组降低,造模组(实验组、PBS组、对照组)较空白组均升高(P0.05)。结论 DNA甲基转移酶抑制剂能明显缩小异位灶体积,促进异位灶萎缩。DNA甲基转移酶抑制剂能抑制异位灶中DNA甲基转移酶表达,这可能是其抑制病灶生长的途径之一。DNA甲基转移酶抑制剂能抑制子宫内膜异位症大鼠模型腹腔环境中TNF-α的含量。     

Hyperhomocysteinemia,and low intakes of folic acid and vitamin B12 in urban North India

Summary Background and Aim An adverse coronary risk profile has been reported amongst rural-to-urban migrant population living in urban slums undergoing stressful socio-economic transition. These individuals are likely to have low intakes of folic acid and vitamin B12, which may have an adverse impact on serum levels of homocysteine (Hcy). To test this hypothesis, we studied serum levels of Hcy in subjects living in an urban slum of North India and healthy subjects from urban non-slum area. Methods Group I consisted of 46 subjects (22 males and 24 females) living in an urban slum, while group II consisted of healthy subjects (n = 26, 13 males and 13 females) living in the adjacent non-slum area. Anthropometric measurements, biochemical profile (fasting blood glucose, total cholesterol, serum triglycerides, low-density lipoprotein cholesterol, and high-density lipoprotein cholesterol) and fasting serum levels of Hcy were measured. Dietary intakes of folic acid, vitamin B12, vitamin B1, and iron were calculated by the 24-hour dietary recall method. Serum levels of Hcy were correlated with dietary intakes of nutrients, anthropometry, and metabolic variables. Results Sex-adjusted serum levels of Hcy in mmol/L (Mean ± SD) were high, though statistically comparable, in both the groups (group I: 20.8 ± 5.9 and group II: 23.2 ± 5.9). Overall, higher than normal serum levels of Hcy (> 15 μmol/L) were recorded in 84 % of the subjects. A substantial proportion of subjects in both groups had daily nutrient intakes below that recommended for the Asian Indian population (folic acid: 93.4 % in group I and 96.7 % in group II, vitamin B12: 76.1 % in group I and 88.4 % in group II). However, between the two groups, average daily dietary intakes of both the nutrients were statistically comparable. As compared to non-vegetarians, vegetarians showed lower intakes of folic acid (p < 0.01) and vitamin B12 (p < 0.01) in both groups. On multivariate linear regression analysis with serum Hcy as the response variable and vegetarian/non-vegetarian status and sex (male/female) as predictor variables, higher serum levels of Hcy were observed in vegetarians vs non-vegetarians (β = 4.6, p < 0.05) and males vs females (β = 5.3, p < 0.01). Conclusions Low intakes of folic acid and vitamin B12, and hyperhomocysteinemia, in both the healthy population living in urban slums and adjacent urban non-slum areas, are important observations for the prevention of nutritional and cardiovascular diseases in the Indian subcontinent. Received: 30 October 2001, Accepted: 14 January 2002     

Associations of plasma selenium with arsenic and genomic methylation of leukocyte DNA in Bangladesh

Background

Global hypomethylation of DNA is thought to constitute an early event in some cancers and occurs in response to arsenic (As) exposure and/or selenium (Se) deficiency in both in vitro and animal models. In addition, antagonism between As and Se, whereby each reduces toxicity of the other, has been well documented in animal models. Se status may therefore modify the health effects of As in As-exposed populations.

Objective

The primary objectives of our study were to test the hypothesis that Se deficiency is associated with genomic hypomethylation of lymphocyte DNA and to determine whether Se levels are associated with blood As (bAs) and urinary As (uAs) concentrations in adults exposed to As-contaminated groundwater in Bangladesh. A secondary objective was to explore the relationships between plasma Se and As metabolites.

Design

We assessed plasma Se concentrations, As metabolite profiles in blood and urine, and genomic methylation of leukocyte DNA in a cross-sectional study of 287 adults.

Results

After adjustment for potential confounders, we observed an inverse association between Se (micrograms per liter) and genomic DNA methylation (disintegrations per minute per 1-μg/L increase in Se): β = 345.6; 95% confidence interval (CI), 59–632. Se concentrations were inversely associated with total As concentrations (micrograms per liter) in blood (β = −0.04; 95% CI, −0.08 to −0.01) and urine (β = −20.1; 95% CI, −29.3 to −10.9). Se levels were negatively associated with the percentage of monomethylarsinic acid (β = −0.59; 95% CI, −1.04 to −0.13) and positively associated with the percentage of dimethylarsinic acid (β = 0.53; 95% CI, 0.04 to 1.01) in blood.

Conclusions

Our results suggest that Se is inversely associated with genomic DNA methylation. The underlying mechanisms and implications of this observation are unclear and warrant further investigation. In addition, Se may influence bAs and uAs concentrations, as well as relative proportions of As metabolites in blood.     

Nutrition, acid-base status and growth in early childhood

Summary Optimal growth is only possible in a well-balanced “inner milieu”. Premature infants are especially vulnerable for disturbances of acid-base metabolism with a predisposition to metabolic acidosis due to a transient disproportion between age-related low renal capacity for net acid excretion (NAE) and an unphysiologically high actual renal NAE on nutrition with standard formulas. During a 50 month period, 452 low birth-weight infants were screened for spontaneous development of incipient late metabolic acidosis (ILMA), an early stage during the development of retention acidosis, characterized by maximum renal acid stimulation (MRAS, urine-pH < 5.4) on two consecutive days but still compensated systemic acid-base status. Compared with controls, patients with ILMA showed higher serum creatinine values, an increased urinary excretion of sodium, aldosterone and nitrogen, but only slightly lower blood pH (7.38 vs 7.41) and base excess (−2.8 vs. 0.2 mmol/l) with respiratory compensation (PCO₂ 35 vs 37 mm Hg). Patients with altogether 149 episodes of ILMA were subsequently randomly allocated to either treatment with NaHCO₃ 2 mmol/kg/d for 7 days or no special therapy in protocol I, or NaHCO₃ vs NaCl each 2 mmol/kg/d for 7 days in protocol II. Patients of protocol I with persistent MRAS for 7 days showed lowest weight gain and a tendency for a further increase in urinary aldosterone and nitrogen excretion. NaCl supplementation (protocol II) seemed to promote weight gain without affecting either impaired mineralization or suboptimal nitrogen retention. Patients with alkali therapy under both protocols showed normal weight gain and normalization of hormonal stimulation, mineralization (protocol II) and nitrogen assimilation. Modification of the mineral content of a standard preterm formula decreased renal NAE to the low level seen on alimentation with human milk and reduced the incidence of ILMA in preterm and small-for-gestational-age infants to 1 %. The data show that ILMA is associated with impaired growth. Activation of secondary homeostatic mechanisms (extracellular volume contraction, depletion of disposable net base pools) might be important for impaired growth. Production of new formulas for reduced renal NAE could be an effective general preventive measure to reduce the clinical importance of one component of mixed acid-base disorders in early childhood. Received: 26 February 2001, Accepted: 7 March 2001     

Spinach and tomato consumption increases lymphocyte DNA resistance to oxidative stress but this is not related to cell carotenoid concentrations

Summary Background The increased consumption of fruit and vegetables has been linked to protection against different chronic diseases, but the dietary constituents responsible for this association have not been clearly identified. Aim of the study We evaluated the effect of spinach and spinach+tomato puree consumption on cell DNA resistance to an oxidative stress. Methods To this aim, in a dietary controlled intervention study, 9 healthy female volunteers consumed a basal diet low in carotenoids (< 600 μg/day) enriched with daily portions (150 g) of spinach (providing about 9 mg lutein, 0.6 mg zeaxanthin, 4 mg β-carotene) for 3 weeks (from day 0 to day 21) followed by a 2 week wash-out period (basal diet) and finally another 3 weeks (from day 35 to day 56) of diet enriched with daily portions of spinach (150 g) + tomato puree (25 g, providing about 7 mg lycopene, 0.3 mg β-carotene). At the beginning and the end of each period of vegetable intake, blood samples were collected for lymphocyte separation. Carotenoid concentrations of lymphocytes were determined by HPLC and DNA damage was evaluated by the comet assay following an ex vivo treatment with H₂O₂. Results During the first period of spinach consumption, lymphocyte lutein concentration did not increase significantly (from 1.6 to 2.2 μmol/10¹² cells) while lycopene and β-carotene concentrations decreased significantly (from 1.0 to 0.1 μmol/10¹² cells, P < 0.001, and from 2.2 to 1.2 μmol/10¹² cells, P < 0.05, respectively). Lutein and lycopene concentrations increased after spinach+tomato puree consumption (from 1.2 to 3.5 μmol/10¹² cells, P < 0.01, and from 0.1 to 0.7 μmol/10¹² cells, P < 0.05, respectively). The increase may be attributed to the addition of tomato puree to spinach; however, the different concentrations of carotenoids in lymphocytes registered at the beginning of the two intervention periods may have affected the results. DNA resistance to H₂O₂ insult increased significantly after both the enriched diets (P < 0.01); however, no “additive effect” was seen after spinach + tomato puree consumption. In the spinach + tomato intervention period an inverse correlation was observed between lymphocyte lycopene concentration and DNA damage, but this seems not able to explain the protection observed. Conclusions The consumption of carotenoid-rich foods even for a short period of time gives protection against oxidative stress. The results obtained seem to suggest that this protective role is not specifically related to carotenoids. However they may contribute together with other substances present in vegetables to lymphocyte resistance to oxidative damage. Received: 20 September 2001, Accepted: 18 February 2002     

Effects of inulin-type fructans of different chain length and type of branching on intestinal absorption and balance of calcium and magnesium in rats

Summary. Background: Inulin-type fructans or chains with mainly β[2–1] linked fructose molecules escape the ingestion procedure in the small intestine and are fermented by the microflora, and are known to increase colonic absorption of minerals in animals. The fermentation rate in the large bowel into short-chain fatty acids depends on the molecular mass and the structure of these food ingredients. It is thought that this colonic fermentation is the basis for the reported increase in mineral absorption. Aim of the study: The purpose of the present study was twofold: a) to compare different types of fructans that differ in the sugar chain length and in chain branching; b) to determine the potential synergistic effect of a combination of inulin-type fructans with different chain lengths. Methods: For this purpose, 50 adult male Wistar rats weighing 170 g each were used in this study. The rats were distributed into 5 groups and fed for 28 days a fiber-free basal purified diet or diet containing 10 % oligofructose (OF) (DP_av 4), or 10 % HP-inulin (DP_av 25), a blend of 50 % OF and 50 % HP-inulin, or a branched-chain inulin. Results: During the first period, the rats went into a gradual adaptation, during which the rats received 2.5 % for 1 week and then 5 % for 1 week of the tested products. During the last 4 days of the experiment, feces and urine were monitored for mineral balance study. The animals were then sacrificed and blood, cecum and tibia were sampled for mineral status assessment. Our results showed that the ingestion of all the tested fructans led to a considerable cecal fermentation. All tested compounds increased the intestinal absorption and balance of Mg significantly. Interestingly, in the present experimental set-up, all tested compounds increased the intestinal absorption and balance of Ca numerically, but only the blend OF + HP-inulin increased apparent intestinal absorption and balance of Ca significantly. Conclusions: The different types of fructans studied in the present experiment seem to have similar activity on mineral absorption. However, the combination of OF and HP-inulin showed synergistic effects on intestinal Ca absorption and balance in rats. Further studies with other combinations of fructans need to be done to extend these findings. Received: 5 August 2002, Accepted: 4 November 2002 Correspondence to: Charles Coudray     

Effect of lactobacilli, bifidobacteria and inulin on the formation of aberrant crypt foci in rats

Summary Background Our studies were aimed at investigating the effect of lactic acid producing bacteria (LAB) or inulin, a natural source of non-digestible oligosaccharides derived from chicory, on the induction by carcinogens of aberrant crypt foci (ACF) in the colon, which are considered to be early precursor lesions of neoplasia. Methods Strains of Bifidobacterium longum, Lactobacillus casei and Lactobacillus acidophilus were administered to rats fed a purified high starch diet, under a variety of treatment protocols including daily gavage, via the drinking water and in the diet. The rats were treated with methyl-N-nitrosourea, 1,2-dimethylhydrazine, or azoxymethane (AOM) to induce ACF. Results In general, no consistent significant changes in ACF numbers were detected in these experiments. In one study, the basal diet of the rats was changed to one containing a higher level of fat (corn oil). Under these conditions, a significant decrease in AOM-induced colonic ACF was seen in rats given L. acidophilus or inulin. In a concurrent group of animals fed a low fat diet, no significant decrease in ACF was observed. Conclusions The results indicate that the type of diet fed can influence the detection of protective effects of LAB and oligosaccharides and that against the background of a diet with a level of fat typical of a Western diet, evidence for a protective effect of L. acidophilus and inulin towards colon cancer was obtained Received: 26 July 2001, Accepted: 26 November 2001     

叶酸缺乏孕鼠子代脑组织DNA甲基化变化

目的: 从分子水平探讨叶酸缺乏(FD)对胎鼠脑发育的影响。方法: 雌性SD大鼠实验组30只、对照组20只,分别饲以不含叶酸和含叶酸2 mg/kg的纯合饲料,2w后与雄鼠交配,于孕D20将孕鼠剖腹取胎,观察FD对胎鼠发育的影响,HPLC法检测孕鼠妊晚期末血清叶酸、胎鼠血清叶酸及胎鼠脑组织DNA甲基化水平。结果: (1)实验组孕鼠交配前及妊晚期末血清叶酸均明显低于对照组(P<0.01),外周血出现多分叶核粒细胞。实验组胎鼠血清叶酸也明显低于对照组(P<0.01),出现巨幼红细胞,RBC和Hb均低于对照组(P<0.01),且伴宫内生长迟缓。(2)实验组胎鼠脑组织DNA甲基化水平低于对照组(P<0.05),且与孕鼠及胎鼠的血清叶酸浓度呈正相关。结论: 母体FD时胎鼠的脑组织DNA甲基化水平降低,可能是胎鼠脑发育障碍的机制之一,受孕前后增补叶酸宜延长至妊娠结束。     

Effect of high-fat diet on lypolisis in isolated adipocytes from visceral and subcutaneous WAT

Variations in total energy intake and composition of daily food play an important role in the regulation of metabolic processes and so, in the control of body weight. This study was designed in order to investigate the effect of a high-fat diet on lipolysis in isolated adipocytes. For this purpose, fourteen Wistar rats were divided into two groups and fed either a standard-fat diet or a high-fat diet ad libitum for 7 weeks. Adipocytes were prepared from fat pads by collagenase digestion and incubated in vitro in the absence or presence of various lipolytic agents. Lipolysis was measured by the release of glycerol into the medium during 90 min of incubation. We observed that a high amount of fat in the diet induced an enlargement of adipose tissue, which was accompanied by a reduction of β-adrenergic agonist-induced lipolysis, that could be due to a loss of β₁ and β₃-adrenoceptor number or to alterations of their coupling to adenylate-cyclase through the guanine nucleotide regulatory protein. New data about regional differences were provided by comparing two adipose locations (subcutaneous and visceral). Received: 30 January 1999, Accepted: 23 June 1999     

Lipolysis induced by leptin in rat adipose tissue from different anatomical locations

Summary. The aim of the present work is to compare the lipolytic response of three fat depots (subcutaneous, epididymal and perirenal) to leptin under in vitro conditions in rats. Moreover an assessment of the potential differences between young and mature rats in terms of the response of these tissues to leptin is made. Adipocytes from 6- and 20-wk-old rats were isolated by collagenase digestion and incubated in vitro both in the absence and the presence of either leptin (10⁻¹²–10⁻⁶ M) or isoproterenol (10⁻⁶ M). Lipolysis was measured by the release of glycerol into the incubation medium over 2 hours of incubation. Adipocytes responded in a dose-dependent manner to leptin concentrations ranging from 10⁻¹² M to 10⁻⁶ M. The lowest leptin concentration inducing a significant lipolytic effect was 10⁻⁹ M in all tissues. No significant differences in the effect of the maximal concentration of leptin (10⁻⁶ M) were observed among tissues for either age. The lipolytic effect of isoproterenol (10⁻⁶ M) was significantly reduced in adipose tissues from mature rats; in contrast no significant differences in the effect of leptin (10⁻⁶ M) were observed between young and mature rats. In summary, no anatomical-specific differences exist in the response of rat adipose tissue to lipid mobilization induced by leptin. Furthermore, this leptin action is not decreased in mature rats compared with young ones. Received: 25 January 2002, Accepted: 16 December 2002 Correspondence to: Dra. María del Puy Portillo     

DNA甲基化与衰老研究进展

DNA甲基化与衰老的研究是近20a来分子生物学研究的热点之一。本文综述了近年来国内外文献，概括DNA甲基化理论研究进展，探讨影响甲基化与衰老的主要因素，以揭示两者之间可能存在的联系，并分析了与甲基化和衰老相关疾病的发生机制。     

Antioxidant and radical scavenging properties in vitro of polyphenolic extracts from red wine

Summary Background & Aims Red wine polyphenols inhibit chemically-induced oxidative DNA damage in vivo in experimental animals through a mechanism which is still unclear. On this basis, we tried to clarify the mechanisms of inhibition of DNA oxidation in vitro by wine extracts containing monomeric and polymeric phenols (WE) and monomer-free complex polyphenols and tannins (WCPT) from red wine. Methods Oxidative DNA damage was induced by incubating DNA with GSH/Fe³⁺ or cumene hydroperoxide (CumOOH) in vitro and using 8-OH–2-deoxyguanosine (8-OHdG) levels as a measure of DNA oxidation. Levels of 8-OHdG were determined by HPLC coupled with electrochemical detector (ESA). Results and conclusions WCPT and WE, at μM concentrations, reduced concentration-dependently oxidative DNA damage induced by GSH/Fe³⁺. WCPT and WE also reduced DNA oxidation by CumOOH. In conclusion, complex polyphenols and tannin extracts from red wine, with or without small molecular phenols, prevent oxidative DNA damage through a dual mechanism, iron binding and direct free radical scavenging. Received: 27 November 2000 / Accepted: 11 April 2001     

The status of plasma homocysteine and related B-vitamins in healthy young vegetarians and nonvegetarians

Summary. Background: Exclusion of animal products and having only plant protein in vegetarian diets may affect the status of certain B-vitamins, and further cause the elevation of plasma homocysteine concentration. Aim: The purpose of this study was to assess the status of homocysteine and related B-vitamins in vegetarians and nonvegetarians. The effects of biochemical parameters of B-vitamins and dietary protein on plasma homocysteine were also examined. Methods: The study was performed at the Chung Shan Medical University, Taichung, in the central part of Taiwan. Thirty-seven vegetarians (28.9 ± 5.5 y) and 32 nonvegetarians (22.9 ± 1.6 y) were recruited. Nutrient intake was recorded using 3-day dietary records. Fasting venous blood samples were obtained. Plasma homocysteine, folate and vitamin B-12 were measured. Vitamin B-6 status was assessed by direct measures [plasma pyridoxal 5'-phosphate (PLP) and urinary 4-pyridoxic acid (4-PA)] and indirect measures [erythrocyte alanine (EALT-AC) and aspartate (EAST-AC) aminotransaminase activity coefficient]. Results: There was no significant difference in vitamin B-6 intake between the two groups, although the vegetarian group had a significantly lower vitamin B-12 intake than the nonvegetarian group. Vegetarian subjects had significantly lower mean plasma PLP and vitamin B-12 concentrations than did nonvegetarian subjects (p < 0.05); however, a significantly higher mean plasma folate concentration was found in the vegetarian group. Vegetarian subjects had a significantly higher mean plasma homocysteine concentration than nonvegetarian subjects (13.2 ± 7.9 vs. 9.8 ± 2.2 μmol/L). Negative correlations were seen between plasma homocysteine and vitamin B-12 concentrations in the vegetarian (p = 0.004), nonvegetarian (p = 0.026), and pooled (p < 0.001) groups. From best subsets regression analyses, the plasma homocysteine concentration could be significantly predicted by total protein intake (p = 0.027) and plasma vitamin B-12 concentration (p = 0.005) in the pooled group. When the intake of protein is not considered, vitamin B-12 concentration is still a strong predictor of plasma homocysteine concentration (p = 0.012). Conclusions: Vitamin B-12 intake and mean plasma vitamin B-12 concentration were lower for vegetarian subjects than for nonvegetarian subjects, leading to an increase in plasma homocysteine concentration. Vitamin B-6 and folate had little effect on plasma homocysteine concentration when individuals had adequate vitamin B-6 and folate status. Received: 15 July 2002, Accepted: 24 October 2002 The study was supported by National Science Council (NSC 89–2320-B-040–046), Taiwan. Correspondence to: Y. C. Huang