ISSN:0959-8278    

出版商:OVID    

年代:1995

数据来源: OVID

摘要:

This article reviews the current knowledge on the cancer-preventive potential of β-carotene, a precursor of vitamin A, and plentiful in fruits and vegetables, which has been studied widely as a promising chemopreventive agent in reducing the risk of cancer in humans. Several retrospective and prospective epidemiological investigations have demonstrated that a diet rich in micronutrients such as vitamins, carotenoids and selenium, could prevent the arising, in ‘high-risk’ patients, of precancerous and neoplastic lesions of specific sites, particularly of the upper aerodigestive tract. Numerous in vitro experiments have been performed in order to verify the true role played by this agent on cell proliferation and differentiation; until now, findings have been very encouraging, uniformly showing that β-carotene can affect carcinogenesis, particularly in early stages, through an antigenotoxic action. Antioxidant functions, immunomodulatory effects and control of intercellular messages via gap junctions are possible action mechanisms of the ability of β-carotene to block the carcinogenetic process. In vivo animal studies partially confirm the results obtained in vitro showing that β-carotene is able to reduce the induced cancer development; moreover, the association of the carotenoid with other microelements, such as vitamins E, C and glutathione often appears to be more effective than each agent used alone. From a clinical point of view, β-carotene appears an ‘ideal’ agent to be used in chemoprevention trials in humans, although optimal doses and intake methods need to be better defined; its almost zero toxicity permits the long-term administration of the drug, a vital condition for its anti-cancer activity, with good patient compliance. Human intervention studies performed so far, both randomized and uncontrolled clinical trials, have showed positive findings in specific cancer sites such as oral cavity, head and neck and colon; less consistent or negative are results on skin, lung and oesophagus cancer. The ongoing studies will provide more answers on these issues. A definitive evaluation of the ability of β-carotene to prevent cancer in humans requires further controlled trials; studies on a larger spectrum of cancer sites and different stages of disease must be encouraged. In addition, further investigation on biomarkers related to cancer risk and cancer incidence are necessary, particularly focused on the measurements for genotoxic damage, eg micronuclei, that may provide a valid and ‘easy’ marker for early stage carcinogenesis.

ISSN:0959-8278    

出版商:OVID    

年代:1995

数据来源: OVID

摘要:

Concentrations of dioxins (PCDD) and dibenzofurans (PCDF) were analysed in adipose tissue from seven patients with malignant lymphoproliferative diseases and 12 surgical patients without a malignant disease. All cases in the first group had reported potential exposure to PCDD and PCDF. Of the analysed congeners significantly higher concentrations of 1, 2, 3, 7, 8-pentachlorodioxin, 1, 2, 3, 6, 7, 8-hexachlorodioxin, and 2, 3, 4, 7, 8-pentachlorodibenzofuran were found in the cases with lymphoproliferative diseases compared with the patients in the other group. Higher mean concentration of 2, 3, 7, 8-TCDD was also found in the first group but not significantly so. Toxic equivalents of PCDD and PCDF were significantly higher in the first group (mean 64.7 pg/g, range 19.9–187) than in the second group (mean 29.7 pg/g, range 12.9–53.4). Even if the cases with lymphoproliferative diseases in this case series were potentially exposed to PCDD/PCDF in contrast to the other group, the observed differences may be of interest in relation to the aetiology of these malignancies. Immunosuppression increases the risk for malignant lymphoproliferative diseases, and PCDD/PCDF have established immunotoxic properties.

ISSN:0959-8278    

出版商:OVID    

年代:1995

数据来源: OVID

摘要:

Several studies have indicated dietary fish oil (FO) as a protective agent in colon carcinogenesis. Rectal cell proliferation as an intermediate biomarker of cancer risk was shown to be reduced by dietary FO in patients with adenomatous polyps and healthy subjects consuming a low-fat diet. Because the synthesis of prostaglandins (PC) which seem to be involved in this process is dependent on the ratio of n-3:n-6 fatty acids in the diet, the present study was designed to investigate whether this FO effect is also detectable in volunteers eating a high-fat diet (50% of energy) with a low n-3:n-6 ratio of 0.25. Twelve healthy volunteers received in addition to a controlled basal diet either FO (4.4 g n-3 fatty acids/day) or corn oil supplements (double-blind, crossover) for two 4-week periods. No significant differences between the two study periods were found for rectal cell proliferation as assessed by bromodeoxyuridine immunohistochemistry and ornithine decarboxylase activity, as well as for mucosal PGE2release and mucosal membrane fatty acid composition. The results emphasize the importance of dietary n-3:n-6 ratio in determining the effects of FO on rectal cell proliferation.

ISSN:0959-8278    

出版商:OVID    

年代:1995

数据来源: OVID

摘要:

In this case-control study we compared dietary habits among 108 patients with small (≤ 5 mm, n = 26), medium (5–9 mm, n = 48) or large (≥ 10 mm, n = 34) colorectal polyps with 35 healthy age- and gender-matched controls. A food record by weighing during 5 consecutive days was performed. The intake of fat was significantly higher among the patients, in contrast to a significantly lower intake of carbohydrate, dietary fibre and iron, compared with controls. The intake of vitamin C and calcium was shown to be lower among the patients, but this was significant only for women. There was a tendency among the patients to consume a lower-antioxidant, fibre and cereal fibre diet, and a calcium-rich and more cholesterol-rich diet with increasing size of polyps. The patients with the smallest polyps tended to consume less starch. Our results are too preliminary to draw conclusions with regard to the influence of nutritional factors on the size and growth of polyps. However, our results on risk factors for the presence of polyps are in agreement with previous studies. Further studies taking into account the size of the polyp are needed to corroborate our findings.

ISSN:0959-8278    

出版商:OVID    

年代:1995

数据来源: OVID

摘要:

Calcium is purported to prevent colorectal cancer by forming insoluble complexes with bile acids and long-chain fatty acids in the large bowel. Therefore, a method for analysing calcium-lipid complexes in faeces has been developed to investigate this. The calcium soaps of a long-chain fatty acid (calcium palmitate) and bile acids (calcium deoxycholate, chenodeoxycholate, cholate and lithocholate) were obtained by organic synthesis. Studies with the authentic soaps reveal that they exist in an empirical ratio of calcium-to-lipid of 1:2. On addition to lipidfree faeces, approximately 30% of calcium palmitate could be recovered and quantified in the authentic state by extraction with 72% ethanol and overnight precipitation at 0° C. In contrast, the calcium soaps of the bile acids could not be recovered in the authentic state but were quantified entirely as the free acids. The method was applied to the analyses of calcium-lipid complexes in the faeces of adenoma patients partaking in a placebo-controlled calcium-intervention study. The results show that human faeces contain appreciable amounts of calcium long-chain fatty acid soaps predominantly in the form of calcium palmitate and stearate. The faecal concentration of long-chain fatty acid soaps was increased significantly (P = 0.005) during calcium intervention but this did not have a statistically significant effect on the excretion of free long-chain fatty acids (P = 0.4). Calcium long-chain fatty acid soap formation was found by multiple regression to be equally dependent on stool long-chain fatty acid and calcium concentration. Calcium soaps of the bile acids were not detected by this method. Studies with EDTA revealed that the ability of this divalent cation chelator to solubilize bile acids is independent of an association with calcium because free bile acids and bile acid soaps were solubilized to a similar extent. The solubilization of faecal bile acids was found to be significantly dependent on both total and primary bile acid concentration. The method needs further development before faecal bile acid soaps (if they exist) can be adequately evaluated.

ISSN:0959-8278    

出版商:OVID    

年代:1995

数据来源: OVID

ISSN:0959-8278    

出版商:OVID    

年代:1995

数据来源: OVID

ISSN:0959-8278    

出版商:OVID    

年代:1995

数据来源: OVID

ISSN:0959-8278    

出版商:OVID    

年代:1995

数据来源: OVID