植物多酚的定量分析方法和生态作用研究进展

植物多酚是植物体内最重要的次生代谢物质.由于其特殊的结构特征和生物学活性,植物体中多酚潜在的生态学意义受到广泛关注.本文综述了植物多酚在生态领域的研究进展,并对其未来的研究方向进行了展望和预测;通过分析各种植物多酚的定性定量方法的优缺点,试图为研究植物多酚的非化学专业研究人员提供一些简单通用的分析方法.     

Design,synthesis and biological evaluation of new inhibitors of Bax/Bcl-xL interaction in cancer cells

We describe the synthesis of a series of new molecules containing phenol and triazoles moieties, compounds which have been evaluated for their ability to inhibit Bax/Bcl-xL interactions in cancer cells, by using BRET assays, and to induce cell death. Several derivatives exhibit a very promising activity, being more potent than the reference compounds acylpyrogallol A and ABT-737. These preliminary results demonstrate that derivatives of this family can be attractive to develop new molecules with potent anticancer activity.     

Monomeric and dimeric hydrolysable tannins of Tamarix nilotica

An ellagitannin monomer, nilotinin M1 (1), and three dimers, nilotinins D1 (2), D2 (3), and D3 (4), were isolated from leaves of Tamarix nilotica (Ehrenb.) Bunge. Structures were elucidated based on analysis of spectroscopic data and chemical correlations with known compounds. In addition, six known tannins, hirtellin A (5) (dimer), remurin A (6), remurin B (7), 1,3-di-O-galloyl-4,6-O-(S)-hexahydroxydiphenoyl-β-d-glucose (8), gemin D (9), and hippomanin A (10) (monomers), were isolated for the first time from this plant species. The reported ¹³C NMR assignments of the dehydrodigalloyl moiety and glucose cores of 5 are revised, and the ¹³C NMR spectroscopic data for 6 and 7 are also reported for the first time.     

Gene markers for grain polyphenol oxidase activity in common wheat

Polyphenol oxidase (PPO) in grain is regarded as a major factor resulting in time-dependent darkening of wheat end products, particularly for Asian noodles and steamed bread. Breeding wheat cultivars with low PPO activity using efficient and reliable markers is one of the best ways to reduce the undesirable darkening. In the present study, we developed a gene-specific marker (PPO05) for low PPO activity from the sequence AY515506. This marker detected double PCR fragments (<750 and >750 bp) in the cultivars with low PPO activity and a single PCR fragment (<750 bp) in the cultivars with high PPO activity. Screening of this marker on 235 Chinese wheat micro-core collections showed that the double fragments were present in 113 genotypes and the single fragments in the remaining 122 genotypes. Statistic analysis revealed that the cultivars with the double fragments had significantly lower mean PPO activity than those with single fragments. Through sequence analysis and blast search in NCBI, we found that the cultivars with the double fragments contained the PPO-2Ab allele, while the cultivars with the single fragments contained the PPO-2Aa allele. The PPO-2Ab and PPO-2Da alleles were associated with the low grain PPO activity and the PPO-2Aa and PPO-2Db alleles associated with the high PPO activity. The genotypes carrying both PPO-2Ab and PPO-2Da showed the lowest PPO activity, while the genotypes carrying both PPO-2Aa and PPO-2Db showed the highest PPO activity. Comparison of PPO05 and STS01 with the STS markers PPO18 and PPO29 showed that the larger and small fragments of PPO05 were equivalent to the 876- and 685-bp fragments of PPO18, respectively, and that STS01 was the complementary marker of PPO29. Thus, the STS markers PPO05 and STS01 along with PPO18 and PPO29 are the efficient and reliable markers for the evaluation of PPO activity and can be used in wheat breeding programs to improve the quality of noodles and other end products.     

Effect of Cu2+, Mn2+ and aromatic compounds on the production of laccase isoforms by Coprinus comatus

Six different extracellular laccase isoforms were identified in submerged cultures of the commercially important edible mushroom, Coprinus comatus. Although laccase activity (~55 IU/L) was readily detectable in unsupplemented control cultures containing 1.6 μM Cu²⁺ after 22-day incubation, mean enzyme levels (~150–185 IU/L) were 2.7–3.4-fold higher in cultures supplemented with 0.5–3.0 mM Cu²⁺. Laccase production was also stimulated by Mn supplementation over the range 0.05–0.8 mM Mn²⁺, and the peak value of ~225 IU/L recorded after 22 days in cultures containing 0.8 mM added Mn²⁺ was 4.5-fold higher compared with unsupplemented controls. Of 12 aromatic compounds tested for their effect on laccase isozyme production by C. comatus, highest laccase levels (~188 IU/L), equivalent to a 4.4-fold increase compared with unsupplemented controls (~43 IU/L), were recorded after 22 days in cultures supplemented with 3.0 mM caffeic acid. Other aromatic compounds tested all stimulated laccase production, with peak enzyme levels 1.3–3.3-fold higher compared with unsupplemented controls. Extracellular laccase levels in cultures supplemented with optimal concentrations of Mn²⁺ and caffeic acid together were 38% and 15% lower, respectively, compared with cultures containing the separate supplements. Lac1 was the most abundant laccase isoform produced under all the conditions tested, but marked differences were observed in the production patterns of Lac2–Lac6.     

Tannic acid inhibits in vitro iron-dependent free radical formation

The antioxidant activity of tannic acid (TA), a plant polyphenol claimed to possess antimutagenic and anticarcinogenic activities, was studied by monitoring (i) 2-deoxyribose degradation (a technique for OH detection), (ii) ascorbate oxidation, (iii) ascorbate radical formation (determined by EPR analysis) and (iv) oxygen uptake induced by the system, which comprised Fe(III) complexes (EDTA, nitrilotriacetic acid (NTA) or citrate as co-chelators), ascorbate and oxygen. TA removes Fe(III) from the co-chelators (in the case of EDTA, this removal is slower than with NTA or citrate), forming an iron-TA complex less capable of oxidizing ascorbate into ascorbate radical or mediating 2-deoxyribose degradation. The effectiveness of TA against 2-deoxyribose degradation, ascorbate oxidation and ascorbate radical formation was substantially higher in the presence of iron-NTA (or iron-citrate) than with iron-EDTA, which is consistent with the known formation constants of the iron complexes with the co-chelators. Oxygen uptake and 2-deoxyribose degradation induced by Fe(II) autoxidation were also inhibited by TA. These results indicate that TA inhibits OH formation induced by Fe(III)/ascorbate/O(2) mainly by arresting Fe(III)-induced ascorbate oxidation and Fe(II) autoxidation (which generates Fe(II) and H(2)O(2), respectively), thus limiting the production of Fenton reagents and OH formation. We also hypothesize that the Fe(II) complex with TA exhibits an OH trapping activity, which explains the effect of TA on the Fenton reaction.     

Preliminary characterisation of the blue-green pigment “marennine” from the marine tychopelagic diatom Haslea ostrearia (Gaillon/Bory) Simonsen

Haslea ostrearia is a common marine tychopelagic diatom which has the particularity of synthesizing a blue-green hydrosoluble pigment called “marennine”. This pigment, when released into the external medium, is known to be responsible for the colour of oyster gills. Here we present results for main biophysical and biochemical characteristics of pure intra- and extracellular marennine. Tests for chemical determination show that the nature of the two forms of marennine cannot be distinguished and could be related to a polyphenolic compound. Nevertheless, based on spectral properties and the molecular weight, which is about 10751 ± 1 and 9893 ± 1 Da, for the intracellular and extracellular forms respectively, we assess that the pigment accumulated in the apex of the cell and the one released in the external medium have probably distinct molecular structures.     

Improving the oral bioavailability of beneficial polyphenols through designed synergies

A substantial and growing consumer demand exists for plant-based functional foods that improve general health and wellbeing. Amongst consumed phytochemicals, the polyphenolic compounds tend to be the most bioactive. Many commonly consumed polyphenols have been shown to have specific and potent health-promoting activities when assessed by high-throughput in vitro assays and when administered to experimental animals by injection. However, very few have been shown to have any beneficial effects in animals or man when orally consumed, because of the poor bioavailability exhibited by most polyphenols following the ingestion. Consumed polyphenols, like most pharmaceuticals, are regarded as xenobiotics by the body and must overcome many barriers, including extensive enzymatic and chemical modification during digestion and absorption, to reach their site(s) of action. This is especially true for polyphenols targeting the brain, which is protected by the tightly regulated blood–brain barrier. Interestingly, many polyphenols are also known to specifically modify some of the metabolic and transport processes that govern bioavailability. Therefore, the opportunity exists to increase the bioactivity of beneficial polyphenols by designing specific synergistic interactions with polyphenols that improve their oral bioavailability. This hypothesis and review paper will discuss some of the endogenous systems that limit the bioavailability of ingested polyphenols to the body and the brain, and the means by which bioavailability may be improved by specifically designing synergies between orally consumed polyphenols.     

Characterization of a Novel Class of Polyphenolic Inhibitors of Plasminogen Activator Inhibitor-1

Plasminogen activator inhibitor type 1, (PAI-1) the primary inhibitor of the tissue-type (tPA) and urokinase-type (uPA) plasminogen activators, has been implicated in a wide range of pathological processes, making it an attractive target for pharmacologic inhibition. Currently available small-molecule inhibitors of PAI-1 bind with relatively low affinity and do not inactivate PAI-1 in the presence of its cofactor, vitronectin. To search for novel PAI-1 inhibitors with improved potencies and new mechanisms of action, we screened a library selected to provide a range of biological activities and structural diversity. Five potential PAI-1 inhibitors were identified, and all were polyphenolic compounds including two related, naturally occurring plant polyphenols that were structurally similar to compounds previously shown to provide cardiovascular benefit in vivo. Unique second generation compounds were synthesized and characterized, and several showed IC₅₀ values for PAI-1 between 10 and 200 nm. This represents an enhanced potency of 10–1000-fold over previously reported PAI-1 inactivators. Inhibition of PAI-1 by these compounds was reversible, and their primary mechanism of action was to block the initial association of PAI-1 with a protease. Consistent with this mechanism and in contrast to previously described PAI-1 inactivators, these compounds inactivate PAI-1 in the presence of vitronectin. Two of the compounds showed efficacy in ex vivo plasma and one blocked PAI-1 activity in vivo in mice. These data describe a novel family of high affinity PAI-1-inactivating compounds with improved characteristics and in vivo efficacy, and suggest that the known cardiovascular benefits of dietary polyphenols may derive in part from their inactivation of PAI-1.     

Glutathione and Cinnamic Acid: Natural Dietary Components Used in Preventing the Process of Browning by Inhibition of Polyphenol Oxidase in Apple Juice

Consumer demands for ‘freshness’ in processed foods has been given increasing attention by food processing industries by searching for minimally processed products. Polyphenol Oxidase (PPO) mediated browning is a major cause of undesirable flavors and nutritional losses in fruit juices. Here the anti-browning efficiency of glutathione (GSH, reduced form) and cinnamic acid (CA) in apple juice is evaluated. It was observed that the rate of the browning reaction could be efficiently delayed using GSH and CA, which act as inhibitors of PPO. Kinetic studies confirm that GSH and CA are non-competitive and competitive inhibitors of PPO respectively.