The female parts of hops (Humulus lupulus L.) show estrogenic effects as well as cancer chemopreventive potential. We analyzed the chemopreventive mechanism of hops by studying its antioxidative activities and its effect on the detoxification of a potentially toxic quinone (menadione). The detoxification enzyme quinone reductase [(NAD(P)H:quinone oxidoreductase, QR] protects against quinone-induced toxicity and has been used as a marker in cancer chemoprevention studies. Although the hop extract was only a weak quencher of free radicals formed from 1,1-diphenyl-2-picrylhydrazyl, it demonstrated strong QR induction in Hepa 1c1c7 cells. In addition, compounds isolated from hops including xanthohumol (XH) and 8-prenylnaringenin were tested for QR induction. Among these, XH was the most effective at inducing QR with a concentration required to double the specific activity of QR (CD value) of 1.7 +/- 0.7 microM. In addition, pretreatment of Hepa1c1c7 cells with XH significantly inhibited menadione-induced DNA single-strand breaks. The QR inhibitor dicumarol reversed the protective effect of XH against menadione-induced DNA damage. Because the expression of QR and other detoxifying enzymes is known to be upregulated by binding of the transcription factor Nrf2 to the antioxidant response element (ARE), the reporter activity mediated by ARE in HepG2-ARE-C8 cells was investigated after incubation with XH for 24 h. Under these conditions, XH increased ARE reporter activity in a dose-dependent manner. One mechanism by which XH might induce QR could be through interaction with Keap1, which sequesters Nrf2 in the cytoplasm, so that it cannot activate the ARE. Using LC-MS-MS, we demonstrated that XH alkylates human Keap1 protein, most likely on a subset of the 27 cysteines of Keap1. This suggests that XH induces QR by covalently modifying the Keap1 protein. Therefore, XH and hops dietary supplements might function as chemopreventive agents, through induction of detoxification enzymes such as QR.
In broad bean (Vicia faba L.), an apoplastic phloem loader, the sucrose concentration increases up to~2 mM in the leaf apoplast and up to~150 mM in the guard-cell apoplast during the photoperiod. This high concentration in the guard-cell apoplast results from transpiration and is sufficient osmotically to reduce stomatal aperture size by up to 3 mm or~25% of the maximum aperture size. In this paper, we investigated a parallel and required role for high bulkleaf apoplastic sucrose concentration, which correlates with high photosynthesis rate. An empirically determined combination of lowered light intensity and lowered CO2 concentration reduced the photosynthesis rate to nominally one-fifth of the control value without a significant change in transpiration. This reduction in photosynthesis caused the sucrose concentration in the leaf apoplast -the immediate source pool for guard cells -to decrease by 70% (to 0.4 mM). In turn, sucrose concentration in the guard-cell apoplast decreased by~80% (to~40 mM). These results complete the required evidence for a non-exclusive, transpiration-linked, photosynthesis-dependent passive mechanism for the modulation of stomatal aperture size. In an ancillary investigation, hexoses in the bulk-leaf apoplast decreased when photosynthesis was lowered, but their concentrations in the guard-cell apoplast of control plants indicated that their osmotic contribution was negligible.
A new butenylflavanone, (2S)-5-hydroxy-7-methoxy-8-[(E)-3-oxo-1-butenyl]flavanone (1), and a new rotenoid, 4',5'-dihydro-11,5'-dihydroxy-4'-methoxytephrosin (2), as well as three active flavonoids of previously known structure, isoliquiritigenin (3), genistein (4), and chrysoeriol (5), along with nine known inactive compounds, alpha-toxicarol (6), sumatrol, 6a,12a-dehydro-alpha-toxicarol, 11-hydroxytephrosin, obovatin, marmesin, lupenone, benzyl benzoate, and benzyl trans-cinnamate, were isolated from an ethyl acetate-soluble extract of the stems of Tephrosia toxicaria, using a bioassay based on the induction of quinone reductase (QR) in cultured Hepa 1c1c7 mouse hepatoma cells to monitor chromatographic fractionation. The structures of compounds 1 and 2 were elucidated by spectroscopic data interpretation. All isolates were evaluated for their potential cancer chemopreventive properties utilizing an in vitro assay to determine quinone reductase induction. Selected compounds were tested in a mouse mammary organ culture assay to evaluate the inhibition of 7,12-dimethylbenz[a]anthracene (DMBA)-induced preneoplastic lesions.
According to numerous cadaveric, radiographic, and clinical studies, ankle and knee joints differ in susceptibility to osteoarthritis. To test for biochemical differences in susceptibility to damage, a chondrocytic chondrolysis system has been utilized. In this system, fibronectin fragments are added to cultured cartilage explants, resulting in enhanced release of catabolic cytokines, induction of matrix metalloproteinases, temporary suppression of proteoglycan synthesis, and consequently, severe loss of cartilage proteoglycan. We found that the addition of an amino-terminal thrombin-generated 29-kDa fibronectin fragment to cultured knee cartilage from 14 donors (average age: 53 years) usually caused a 30-50% decrease in proteoglycan content by day 7. However, of the ankle cartilage specimens examined from 21 donors (average age: 50 years), only three showed damage by day 7, one by day 14, and six by day 21, and 11 were not damaged until day 28. For eight of the donors (average age: 44 years), both knee and ankle cartilages were obtained: this allowed comparison between tissues from the same donor. The analysis showed that the ankle cartilage was much more refractory to damage than was the knee cartilage from the same donor. These data clearly show differences between ankle and knee cartilage in susceptibility to the fibronectin fragments and suggest the feasibility of use of these fragments for discerning differences in homeostasis of the ankle and knee cartilage.
European elderberry (Sambucus nigra), recognized in Europe for its health-promoting properties for many generations, is known to contain a range of anthocyanins, flavonoids, and other polyphenolics that contribute to the high antioxidant capacity of its berries. American elderberry (Sambucus canadensis), on the other hand, has not been cultivated, bred, and promoted as a medicinal plant like its better-characterized European counterpart. In this study, aqueous acetone extracts of the berries from these two species were fractionated and tested in a range of assays that gauge anticarcinogenic potential. Both cultivated S. nigra and wild S. canadensis fruits demonstrated significant chemopreventive potential through strong induction of quinone reductase and inhibition of cyclooxygenase-2, which is indicative of anti-initiation and antipromotion properties, respectively. In addition, fractions of S. canadensis extract showed inhibition of ornithine decarboxylase, an enzyme marker related to the promotion stage of carcinogenesis. Analysis of active fractions using mass spectrometry and liquid chromatography-mass spectrometry revealed, in addition to flavonoids, the presence of more lipophilic compounds such as sesquiterpenes, iridoid monoterpene glycosides, and phytosterols.
Apoplastic phloem loaders have an apoplastic step in the movement of the translocated sugar, prototypically sucrose, from the mesophyll to the companion cell-sieve tube element complex. In these plants, leaf apoplastic sucrose becomes concentrated in the guard cell wall to nominally 150 mM by transpiration during the photoperiod. This concentration of external sucrose is sufficient to diminish stomatal aperture size in an isolated system and to regulate expression of certain genes. In contrast to apoplastic phloem loaders and at the other extreme, strict symplastic phloem loaders lack an apoplastic step in phloem loading and mostly transport raffinose family oligosaccharides (RFOs), which are at low concentrations in the leaf apoplast. Here, the effects of the phloem-loading mechanism and associated phenomena on the immediate environment of guard cells are reported. As a first step, carbohydrate analyses of phloem exudates confirmed basil (Ocimum basilicum L. cv. Minimum) as a symplastic phloem-loading species. Then, aspects of stomatal physiology of basil were characterized to establish this plant as a symplastic phloem-loading model species for guard cell research. [(14)C]Mannitol fed via the cut petiole accumulated around guard cells, indicating a continuous leaf apoplast. The (RFO+sucrose+hexoses) concentrations in the leaf apoplast were low, <0.3 mM. Neither RFOs (<10 mM), sucrose, nor hexoses (all, P >0.2) were detectable in the guard cell wall. Thus, differences in phloem-loading mechanisms predict differences in the in planta regulatory environment of guard cells.
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