S-sulfhydration/desulfhydration and S-nitrosylation/denitrosylation: a common paradigm for gasotransmitter signaling by H2S and NO.

Sulfhydryl groups on protein Cys residues undergo an array of oxidative reactions and modifications, giving rise to a virtual redox zip code with physiological and pathophysiological relevance for modulation of protein structure and functions. While over two decades of studies have established NO-dependent S-nitrosylation as ubiquitous and fundamental for the regulation of diverse protein activities, proteomic methods for studying H2S-dependent S-sulfhydration have only recently been described and now suggest that this is also an abundant modification with potential for global physiological importance. Notably, protein S-sulfhydration and S-nitrosylation bear striking similarities in terms of their chemical and biological determinants, as well as reversal of these modifications via group-transfer to glutathione, followed by the removal from glutathione by enzymes that have apparently evolved to selectively catalyze denitrosylation and desulfhydration. Here we review determinants of protein and low-molecular-weight thiol S-sulfhydration/desulfhydration, similarities with S-nitrosylation/denitrosylation, and methods that are being employed to investigate and quantify these gasotransmitter-mediated cell signaling systems.

Benzophenones and biflavonoids from Rheedia edulis.

Two new polyisoprenylated benzophenones, 32-hydroxy-ent-guttiferone M (1) and 6-epi-guttiferone J (2), along with seven known compounds, 6-epi-clusianone (3), guttiferone A (4), xanthochymol (5), guttiferone E (6), isoxanthochymol (7), (+)-volkensiflavone (8), and (+)-morelloflavone (9), were identified from the seeds and rinds of Rheedia edulis. Compounds 1-3 and 5-9 have been isolated and identified from this species for the first time. The structures of the new compounds were elucidated mainly by analysis of their 1D and 2D NMR spectroscopic data, and their absolute configurations were determined by comparison of their experimental optical rotation and electronic circular dichroism measurements with those values predicted by DFT calculations. Compound 1 showed significant antioxidant activity in both DPPH and ABTS free radical scavenging assays, whereas compound 2 was inactive.

Vitamin C selectively kills KRAS and BRAF mutant colorectal cancer cells by targeting GAPDH.

More than half of human colorectal cancers (CRCs) carry either KRAS or BRAF mutations and are often refractory to approved targeted therapies. We found that cultured human CRC cells harboring KRAS or BRAF mutations are selectively killed when exposed to high levels of vitamin C. This effect is due to increased uptake of the oxidized form of vitamin C, dehydroascorbate (DHA), via the GLUT1 glucose transporter. Increased DHA uptake causes oxidative stress as intracellular DHA is reduced to vitamin C, depleting glutathione. Thus, reactive oxygen species accumulate and inactivate glyceraldehyde 3-phosphate dehydrogenase (GAPDH). Inhibition of GAPDH in highly glycolytic KRAS or BRAF mutant cells leads to an energetic crisis and cell death not seen in KRAS and BRAF wild-type cells. High-dose vitamin C impairs tumor growth in Apc/Kras(G12D) mutant mice. These results provide a mechanistic rationale for exploring the therapeutic use of vitamin C for CRCs with KRAS or BRAF mutations.

Carbohydrate translocation determines the phenolic content of Populus foliage: a test of the sink-source model of plant defense.

• Here, we examine the influence of source-to-sink carbohydrate (CHO) flow on the development of constitutive and inducible levels of phenylpropenoids in hybrid poplar (Populus nigra × P. deltoides) foliage to determine if secondary metabolic processes in plant modules can be inhibited in a predictable manner by events such as herbivory and the development of new leaves and reproductive structures, which alter the path of phloem-borne resources. • Phenylpropenoid concentrations were determined for developing foliage after CHO flow, measured as the translocation of 13 C from labeled sources was manipulated. • Phenylpropenoid metabolism in both unwounded and induced sink leaves was directly and positively linked to rates of CHO import. Alterations in rates of translocation yielded different results, depending on how CHO import was affected: the removal of competing sinks rapidly and dramatically increased leaf phenolic contents, whereas phenolic levels (and their inducibility) tended to be reduced when import was interrupted. • High and inducible sink strength in developing poplar leaves provides resources for phenolic biosynthesis and, as a result, restrictions or re-directions of CHOs affect the foliar quality. Sink strength and the vascular architecture of plants, which confer upon them a modular nature, can determine the direction and magnitude of defense responses in trees.

Targeted analysis of polyphenol metabolism during development of hop (Humulus lupulus L.) cones following treatment with prohexadione-calcium.

Hops (Humulus lupulus), a main ingredient in beer, are valued as a source of bitter flavour and biologically active polyphenols. We treated immature hop cones with prohexadione-calcium (Pro-Ca), a flavanone-3-hydroxylase (F3H) inhibitor, to perturb the flavonoid pathway, and conducted a targeted analysis of 29 compounds from the phenolic acid, flavonoid, and terpenophenolic pathways, using photodiode array (UHPLC-PDA), and time of flight mass spectrometry (LC-TOF-MS) analysis. Hop cones were analysed over four stages of development spanning 22days following Pro-Ca treatment. The content of terpenophenolics as well as metabolic precursors upstream from F3H significantly increased, and levels of flavonoid products downstream from F3H decreased. The methods developed here serve to compliment flavour analysis of polyphenol rich foods, and our results suggest ways to improve upon traditional agricultural methods to produce hops with altered chemical profiles.

Metabolic profiling of Actaea species extracts using high performance liquid chromatography coupled with electrospray ionization time-of-flight mass spectrometry.

Despite persistent questions about the safety of black cohosh (Actaea racemosa L., syn. Cimicifuga racemosa L.), its products continue to be one of the most popular botanical supplements in the United States market. Black cohosh products have been associated with cases of liver toxicity, but subsequent evaluation found some products to be adulterated with other related plants from the same genus. US FDA regulations require that black cohosh products be unadulterated, and correct identification of different species of Actaea is a key first step for their good manufacturing practice. We have developed a phytochemical method to distinguish four different groups of Actaea, including: species other than A. racemosa, Asian species, A. racemosa, and North American species other than A. racemosa. Using HPLC-TOF-ESI-MS technique and principal component analysis, we identified 15 chemical markers (1-3, 5-6, 8-10, 12, 16-21). Three marker compounds were unambiguously identified using authentic standards, and 12 marker compounds were tentatively identified by comparison of fragmentation patterns with previously reported data. The presence of these marker compounds is critical for discrimination among the four groups of closely related plants. The use of metabolic profiling to distinguish black cohosh from related species of Actaea has broader implications in the identification of markers to help authenticate other important medicinal plants.

Increase in cone biomass and terpenophenolics in hops ( Humulus lupulus L.) by treatment with prohexadione-calcium.

Humulus lupulus L. (hop), a specialty crop bred for flavor characteristics of the inflorescence, is an essential ingredient in beer. Hop inflorescences, commonly known as hop cones, contain terpenophenolic compounds, which are important for beer flavoring and of interest in biomedical research. Hop breeders focus their efforts on increasing cone biomass and terpenophenolic content. As an alternative to traditional breeding, hops were treated with prohexadione-calcium (Pro-Ca), a growth inhibitor previously shown to have positive agronomic effects in several crops. Application of Pro-Ca to hop plants during cone maturation induced increases in cone biomass production by 1.5-19.6% and increased terpenophenolic content by 9.1-87.3%; however, some treatments also induced significant decreases in terpenophenolic content. Induced changes in cone biomass production and terpenophenolic accumulation were most dependent on cultivar and the developmental stage at which plants were treated.

Saponins from the traditional medicinal plant Momordica charantia stimulate insulin secretion in vitro.

The antidiabetic activity of Momordica charantia (L.), Cucurbitaceae, a widely-used treatment for diabetes in a number of traditional medicine systems, was investigated in vitro. Antidiabetic activity has been reported for certain saponins isolated from M. charantia. In this study insulin secretion was measured in MIN6 ß-cells incubated with an ethanol extract, saponin-rich fraction, and five purified saponins and cucurbitane triterpenoids from M. charantia, 3ß,7ß,25-trihydroxycucurbita-5,23(E)-dien-19-al (1), momordicine I (2), momordicine II (3), 3-hydroxycucurbita-5,24-dien-19-al-7,23-di-O-ß-glucopyranoside (4), and kuguaglycoside G (5). Treatments were compared to incubation with high glucose (27 mM) and the insulin secretagogue, glipizide (50 µM). At 125 µg/ml, an LC-ToF-MS characterized saponin-rich fraction stimulated insulin secretion significantly more than the DMSO vehicle, p=0.02. At concentrations 10 and 25 µg/ml, compounds 3 and 5 also significantly stimulated insulin secretion as compared to the vehicle, p≤0.007, and p=0.002, respectively. This is the first report of a saponin-rich fraction, and isolated compounds from M. charantia, stimulating insulin secretion in an in vitro, static incubation assay.

Phytochemical and morphological characterization of hop (Humulus lupulus L.) cones over five developmental stages using high performance liquid chromatography coupled to time-of-flight mass spectrometry, ultrahigh performance liquid chromatography photodiode array detection, and light microscopy techniques.

Hop (Humulus lupulus L.) inflorescences, commonly known as "hop cones", are prized for their terpenophenolic contents, used in beer production and, more recently, in biomedical applications. In this study we investigated morphological and phytochemical characteristics of hop cones over five developmental stages, using liquid chromatography coupled to time-of-flight mass spectrometry (LC-TOF-MS), and ultrahigh performance liquid chromatography photodiode array detection (UHPLC-PDA) methods to quantitate 21 polyphenolics and seven terpenophenolics. Additionally, we used light microscopy to correlate phytochemical quantities with changes in the morphology of the cones. Significant increases in terpenophenolics, concomitant with glandular trichome development and associated gross morphological changes, were mapped over development to fluctuations in contents of polyphenolic constituents and their metabolic precursor compounds. The methods reported here can be used for targeted metabolic profiling of flavonoids, phenolic acids, and terpenophenolics in hops, and are applicable to quantitation in other crops.

White and green teas (Camellia sinensis var. sinensis): variation in phenolic, methylxanthine, and antioxidant profiles.

Recent investigations have associated white teas with anti-carcinogenic, immune-boosting, and antioxidative properties that may impact human health in a manner comparable to green teas. An in-depth chemical analysis of white tea types was conducted to quantify polyphenols and antioxidant potential of 8 commercially available white teas, and compare them to green tea. Extraction and HPLC protocols were optimized and validated for the quantification of 9 phenolic and 3 methylxanthine compounds to examine inter- and intra-variation in white and green tea types and subtypes. A sampling strategy was devised to assess various subtypes procured from different commercial sources. Variation in antioxidant activity and total phenolic content (TPC) of both tea types was further assessed by the 1-1-diphenyl-2-picrylhydrazyl (DPPH) and Folin-Ciocalteau (F-C) assays, respectively. Total catechin content (TCC) for white teas ranged widely from 14.40 to 369.60 mg/g of dry plant material for water extracts and 47.16 to 163.94 mg/g for methanol extracts. TCC for green teas also ranged more than 10-fold, from 21.38 to 228.20 mg/g of dry plant material for water extracts and 32.23 to 141.24 mg/g for methanol extracts. These findings indicate that statements suggesting a hierarchical order of catechin content among tea types are inconclusive and should be made with attention to a sampling strategy that specifies the tea subtype and its source. Certain white teas have comparable quantities of total catechins to some green teas, but lesser antioxidant capacity, suggesting that white teas have fewer non-catechin antioxidants present. Practical Application: In this investigation white and green teas were extracted in ways that mimic common tea preparation practices, and their chemical profiles were determined using validated analytical chemistry methods. The results suggest certain green and white tea types have comparable levels of catechins with potential health promoting qualities. Specifically, the polyphenolic content of green teas was found to be similar to certain white tea varieties, which makes the latter tea type a potential substitute for people interested in consuming polyphenols for health reasons. Moreover, this study is among the first to demonstrate the effect subtype sampling, source of procurement, cultivation, and processing practices have on the final white tea product, as such analysis has previously been mostly carried out on green teas.