Purification and characterization of pentagalloylglucose, and alpha-glucosidase inhibitor/antibiotic from the freshwater green alga Spirogyra varians

Natural product 1,2,3,4,6-penta-O-galloyl-β-D-glucopyranose is a reversible inhibitor of glyceraldehyde 3-phosphate dehydrogenase

Aerobic glycolysis, also known as the Warburg effect, is a hallmark of cancer cell glucose metabolism and plays a crucial role in the activation of various types of immune cells. Glyceraldehyde 3-phosphate dehydrogenase (GAPDH) catalyzes the conversion of D-glyceraldehyde 3-phosphate to D-glycerate 1,3-bisphosphate in the 6th critical step in glycolysis. GAPDH exerts metabolic flux control during aerobic glycolysis and therefore is an attractive therapeutic target for cancer and autoimmune diseases. Recently, GAPDH inhibitors were reported to function through common suicide inactivation by covalent binding to the cysteine catalytic residue of GAPDH. Herein, by developing a high-throughput enzymatic screening assay, we discovered that the natural product 1,2,3,4,6-penta-O-galloyl-β-D-glucopyranose (PGG) is an inhibitor of GAPDH with K_i = 0.5 μM. PGG blocks GAPDH activity by a reversible and NAD⁺ and Pi competitive mechanism, suggesting that it represents a novel class of GAPDH inhibitors. In-depth hydrogen deuterium exchange mass spectrometry (HDX-MS) analysis revealed that PGG binds to a region that disrupts NAD⁺ and inorganic phosphate binding, resulting in a distal conformational change at the GAPDH tetramer interface. In addition, structural modeling analysis indicated that PGG probably reversibly binds to the center pocket of GAPDH. Moreover, PGG inhibits LPS-stimulated macrophage activation by specific downregulation of GAPDH-dependent glucose consumption and lactate production. In summary, PGG represents a novel class of GAPDH inhibitors that probably reversibly binds to the center pocket of GAPDH. Our study sheds new light on factors for designing a more potent and specific inhibitor of GAPDH for future therapeutic applications.

Activity-guided isolation of α-amylase, α-glucosidase, and pancreatic lipase inhibitory compounds from Rhus coriaria L

The leaves and fruits of Rhus coriaria are traditionally used in Turkey for the treatment of diabetes. The aim of the present study is to determine α-amylase, α-glucosidase, and pancreatic lipase inhibitory activities of R. coriaria leaf and fruit ethanol extracts (80%), and to isolate active compounds against these enzymes. As a result of the activity-guided isolation, the active compounds were determined as the amentoflavone, agathisflavone, and 1,2,3,4,6-penta-O-galloyl-β-glucopyranose. Agathisflavone, amentoflavone, and penta-O-galloyl-β-glucopyranose inhibited α-glucosidase with 11.4 ± 0.9, 11.3 ± 0.7, and 4.1 ± 0.1 µM IC₅₀ values, respectively. Furthermore, penta-O-galloyl-β-glucopyranose inhibited α-amylase with 6.32 ± 0.18 µM IC₅₀ . These three compounds also significantly inhibited (P < 0.05) pancreatic lipase. The results of high-performance liquid chromatography analysis showed that penta-O-galloyl-β-D-glycopyranose was one of the main compounds in both fruit and leaf extracts. Therefore, it may be considered that R. coriaria fruit and leaf extracts can be standardized on this substance and used in the development of both medicinal products and functional food for diabetes. PRACTICAL APPLICATION: Rhus coriaria (Sumac) is one of the plants that is well known and used around the world as a spice. It is also used against diabetes traditionally. The determination of effective compounds can lead to the standardization and development of both medicinal products and functional foods for diabetes. While the fruits of the plant are used as a spice all around the world, the leaves are generally throw away; therefore, the usage of the leaves to the food and medical industry can lead to beneficial effects on the economy.

Comparison of UVB effects on growth and induction of UVB screening compounds in isolates of metaphytic algae from temperate zone streams and ponds

Filaments in the surface layers of metaphytic mats are exposed to high photon flux densities of PAR and UVBR. We investigated the effect of UVBR exposure on growth of eight isolates of common metaphytic algae (Cladophora, Mougeotia, Oedogonium, Pithophora, Spirogyra, and Zygnema) acclimated to either high or low PAR levels prior to UVBR exposure. All isolates acclimated to low PAR exhibited significant reductions in growth rate caused by the UVBR exposure (P < 0.05). Acclimation to high PAR resulted in seven of the isolates being more tolerant of the UVB exposure. The two Zygnema isolates exhibited the most pronounced effect of high PAR acclimation with growth rates of UVB exposed treatments being equal to that of controls (P > 0.05). High PAR acclimation also protected chlorophyll a levels in the Zygnema isolates. Absorption of UVB by methanol extracts increased 322%-381% for the two Zygnema isolates when high PAR acclimated. The broad absorption peak at 270 nm suggests that phenolic compounds were responsible. Previous studies have shown that Zygnema isolates from extreme environments tolerate UVBR and contain UVB screening compounds, but our results extend these adaptions to Zygnema from typical temperate zone habitats. Although none of the other metaphytic algae produced UVB absorbing compounds, they all exhibited higher growth rates under UVBR exposure following high PAR acclimation. This suggests that the algae evaluated have inducible defenses against UVBR exposure that coupled with their mat structure would provide an adaption to the challenging light environment in shallow-water habitats.

Arctic, Antarctic, and temperate green algae Zygnema spp. under UV-B stress: vegetative cells perform better than pre-akinetes

Species of Zygnema form macroscopically visible mats in polar and temperate terrestrial habitats, where they are exposed to environmental stresses. Three previously characterized isolates (Arctic Zygnema sp. B, Antarctic Zygnema sp. C, and temperate Zygnema sp. S) were tested for their tolerance to experimental UV radiation. Samples of young vegetative cells (1 month old) and pre-akinetes (6 months old) were exposed to photosynthetically active radiation (PAR, 400-700 nm, 400 μmol photons m^-2 s^-1) in combination with experimental UV-A (315-400 nm, 5.7 W m^-2, no UV-B), designated as PA, or UV-A (10.1 W m^-2) + UV-B (280-315 nm, 1.0 W m^-2), designated as PAB. The experimental period lasted for 74 h; the radiation period was 16 h PAR/UV-A per day, or with additional UV-B for 14 h per day. The effective quantum yield, generally lower in pre-akinetes, was mostly reduced during the UV treatment, and recovery was significantly higher in young vegetative cells vs. pre-akinetes during the experiment. Analysis of the deepoxidation state of the xanthophyll-cycle pigments revealed a statistically significant (p < 0.05) increase in Zygnema spp. C and S. The content of UV-absorbing phenolic compounds was significantly higher (p < 0.05) in young vegetative cells compared to pre-akinetes. In young vegetative Zygnema sp. S, these phenolic compounds significantly increased (p < 0.05) upon PA and PAB. Transmission electron microscopy showed an intact ultrastructure with massive starch accumulations at the pyrenoids under PA and PAB. A possible increase in electron-dense bodies in PAB-treated cells and the occurrence of cubic membranes in the chloroplasts are likely protection strategies. Metabolite profiling by non-targeted RP-UHPLC-qToF-MS allowed a clear separation of the strains, but could not detect changes due to the PA and PAB treatments. Six hundred seventeen distinct molecular masses were detected, of which around 200 could be annotated from databases. These results indicate that young vegetative cells can adapt better to the experimental UV-B stress than pre-akinetes.

A mass spectrometry and 1H NMR study of hypoglycemic and antioxidant principles from a Castanea sativa tannin employed in oenology

The ethanol extract of the commercial tannin Tan'Activ C, (from Castanea sativa wood), employed in oenology, was subjected to chromatography on XAD-16 affording fractions X1-X5, evaluated for total phenols content (GAE), antioxidant activity (DPPH, ORAC), and hypoglycemic activity (α-glucosidase inhibition). Fraction X3 showed GAE, radical scavenging activity, and α-glucosidase inhibition higher than those of the Castanea sativa extract, and was subjected to chromatography on Sephadex LH-20 to obtain fractions S1-S7, analyzed by HPLC/ESI-MS/MS and ¹H NMR to identify the main active constituents. In fractions with higher antioxidant activity, gallic acid (4), grandinin (5), valoneic acid dilactone (9), 1,2,3-tri-O-galloyl-β-glucose (14), 3,4,6-tri-O-galloyl-β-glucose (15) and galloyl derivative of valoneic acid dilactone (21) were identified as the major constituents. The highest hypoglycemic activity was found in fractions S6 and especially S7; the major constituents of these fractions are valoneic acid dilactone (9), three tetragalloyl glucose isomers (16-18) and 1,2,3,4,6-penta-O-galloyl-β-glucose (23), previously reported as α-glucosidase inhibitors.

Abiotic Stress Tolerance of Charophyte Green Algae: New Challenges for Omics Techniques

Charophyte green algae are a paraphyletic group of freshwater and terrestrial green algae, comprising the classes of Chlorokybophyceae, Coleochaetophyceae, Klebsormidiophyceae, Zygnematophyceae, Mesostigmatophyceae, and Charo- phyceae. Zygnematophyceae (Conjugating green algae) are considered to be closest algal relatives to land plants (Embryophyta). Therefore, they are ideal model organisms for studying stress tolerance mechanisms connected with transition to land, one of the most important events in plant evolution and the Earth's history. In Zygnematophyceae, but also in Coleochaetophyceae, Chlorokybophyceae, and Klebsormidiophyceae terrestrial members are found which are frequently exposed to naturally occurring abiotic stress scenarios like desiccation, freezing and high photosynthetic active (PAR) as well as ultraviolet (UV) irradiation. Here, we summarize current knowledge about various stress tolerance mechanisms including insight provided by pioneer transcriptomic and proteomic studies. While formation of dormant spores is a typical strategy of freshwater classes, true terrestrial groups are stress tolerant in vegetative state. Aggregation of cells, flexible cell walls, mucilage production and accumulation of osmotically active compounds are the most common desiccation tolerance strategies. In addition, high photophysiological plasticity and accumulation of UV-screening compounds are important protective mechanisms in conditions with high irradiation. Now a shift from classical chemical analysis to next-generation genome sequencing, gene reconstruction and annotation, genome-scale molecular analysis using omics technologies followed by computer-assisted analysis will give new insights in a systems biology approach. For example, changes in transcriptome and role of phytohormone signaling in Klebsormidium during desiccation were recently described. Application of these modern approaches will deeply enhance our understanding of stress reactions in an unbiased non-targeted view in an evolutionary context.

Phylogenetic position of Zygogonium ericetorum (zygnematophyceae, charophyta) from a high alpine habitat and ultrastructural characterization of unusual aplanospores

Characeae (Charophyceae, Charophyta) contains two tribes with six genera: tribe Chareae with four genera and tribe Nitelleae, which includes Tolypella and Nitella. This paper uses molecular and morphological data to elucidate the phylogeny of Tolypella species in North America. In the most comprehensive taxonomic treatment of Characeae, 16 Tolypella species worldwide were subsumed into two species, T. intricata and T. nidifica, in two sections, Rothia and Tolypella respectively. It was further suggested that Tolypella might be a derived group within Nitella. In this investigation into species diversity and relationships in North American Tolypella, sequence data from the plastid genes atpB, psbC, and rbcL were assembled for a broad range of charophycean and land plant taxa. Molecular data were used in conjunction with morphology to test monophyly of the genus and species within it. Phylogenetic analyses of the sequence data showed that Characeae is monophyletic but that Nitelleae is paraphyletic with Tolypella sister to a monophyletic Nitella + Chareae. The results also supported the monophyly of Tolypella and the sections Rothia and Tolypella. Morphologically defined species were supported as clades with little or no DNA sequence differences. In addition, molecular data revealed several lineages and a new species (T. ramosissima sp. nov.), which suggests greater species diversity in Tolypella than previously recognized.

Unusual phenolic compounds contribute to ecophysiological performance in the purple-colored green alga zygogonium ericetorum (zygnematophyceae, streptophyta) from a high-alpine habitat

The filamentous green alga Zygogonium ericetorum (Zygnematophyceae, Streptophyta) was collected in a high-alpine rivulet in Tyrol, Austria. Two different morphotypes of this alga were found: a purple morph with a visible purple vacuolar content and a green morph lacking this coloration. These morphotypes were compared with respect to their secondary metabolites, ultrastructure, and ecophysiological properties. Colorimetric tests with aqueous extracts of the purple morph indicated the presence of soluble compounds such as phenolics and hydrolyzable tannins. High-performance liquid chromatography-screening showed that Z. ericetorum contained several large phenolic peaks with absorption maxima at ∼280 nm and sometimes with minor maxima at ∼380 nm. Such compounds are uncommon for freshwater green microalgae, and could contribute to protect the organism against increased UV and visible (VIS) irradiation. The purple Z. ericetorum contained larger amounts (per dry weight) of the putative phenolic substances than the green morph; exposure to irradiation may be a key factor for accumulation of these phenolic compounds. Transmission electron microscopy of the purple morph showed massive vacuolization with homogenous medium electron-dense content in the cell periphery, which possibly contains the secondary compounds. In contrast, the green morph had smaller, electron-translucent vacuoles. The ecophysiological data on photosynthesis and desiccation tolerance indicated that increasing photon fluence densities led to much higher relative electron transport rates (rETR) in the purple than in the green morph. These data suggest that the secondary metabolites in the purple morph are important for light acclimation in high-alpine habitats. However, the green morph recovered better after 4 d of rehydration following desiccation stress.

Changes in phenolic compounds and cellular ultrastructure of arctic and antarctic strains of Zygnema (Zygnematophyceae, Streptophyta) after exposure to experimentally enhanced UV to PAR ratio

Ultraviolet (UV) radiation has become an important stress factor in polar regions due to anthropogenically induced ozone depletion. Although extensive research has been conducted on adaptations of polar organisms to this stress factor, few studies have focused on semi-terrestrial algae so far, in spite of their apparent vulnerability. This study investigates the effect of UV on two semi-terrestrial arctic strains (B, G) and one Antarctic strain (E) of the green alga Zygnema, isolated from Arctic and Antarctic habitats. Isolates of Zygnema were exposed to experimentally enhanced UV A and B (predominant UV A) to photosynthetic active radiation (PAR) ratio. The pigment content, photosynthetic performance and ultrastructure were studied by means of high-performance liquid chromatography (HPLC), chlorophyll a fluorescence and transmission electron microscopy (TEM). In addition, phylogenetic relationships of the investigated strains were characterised using rbcL sequences, which determined that the Antarctic isolate (E) and one of the Arctic isolates (B) were closely related, while G is a distinct lineage. The production of protective phenolic compounds was confirmed in all of the tested strains by HPLC analysis for both controls and UV-exposed samples. Moreover, in strain E, the content of phenolics increased significantly (p = 0.001) after UV treatment. Simultaneously, the maximum quantum yield of photosystem II photochemistry significantly decreased in UV-exposed strains E and G (p < 0.001), showing a clear stress response. The phenolics were most probably stored at the cell periphery in vacuoles and cytoplasmic bodies that appear as electron-dense particles when observed by TEM after high-pressure freeze fixation. While two strains reacted moderately on UV exposure in their ultrastructure, in strain G, damage was found in chloroplasts and mitochondria. Plastidal pigments and xanthophyll cycle pigments were investigated by HPLC analysis; UV A- and UV B-exposed samples had a higher deepoxidation state as controls, particularly evident in strain B. The results indicate that phenolics are involved in UV protection of Zygnema and also revealed different responses to UV stress across the three strains, suggesting that other protection mechanisms may be involved in these organisms.

Characterization of an UV- and VIS-absorbing, purpurogallin-derived secondary pigment new to algae and highly abundant in Mesotaenium berggrenii (Zygnematophyceae, Chlorophyta), an extremophyte living on glaciers

Mesotaenium berggrenii is one of few autotrophs that thrive on bare glacier surfaces in alpine and polar regions. This extremophilic alga produces high amounts of a brownish vacuolar pigment, whose chemical constitution and ecological function is largely unknown until now. Field material was harvested to isolate and characterize this pigment. Its tannin nature was determined by photometric methods, and the structure determination was carried out by means of HPLC-MS and 1D- and 2D-NMR spectroscopy. The main constituent turned out to be purpurogallin carboxylic acid-6-O-β-d-glucopyranoside. This is the first report of such a phenolic compound in this group of algae. Because of its broad absorption capacities of harmful UV and excessive VIS radiation, this secondary metabolite seems to play an important role for the survival of this alga at exposed sites. Attributes and abundances of the purpurogallins found in M. berggrenii strongly suggest that they are of principal ecophysiological relevance like analogous protective pigments of other extremophilic microorganisms. To prove that M. berggrenii is a true psychrophile, photosynthesis measurements at ambient conditions were carried out. Sequencing of the 18S rRNA gene of this alpine species and of its arctic relative, the filamentous Ancylonema nordenskiöldii, underlined their distinct taxonomic position within the Zygnematophyceae.

Anti-cancer, anti-diabetic and other pharmacologic and biological activities of penta-galloyl-glucose

1, 2, 3, 4, 6-penta-O-galloyl-beta-D-glucose (PGG) is a polyphenolic compound highly enriched in a number of medicinal herbals. Several in vitro and a handful of in vivo studies have shown that PGG exhibits multiple biological activities which implicate a great potential for PGG in the therapy and prevention of several major diseases including cancer and diabetes. Chemically and functionally, PGG appears to be distinct from its constituent gallic acid or tea polyphenols. For anti-cancer activity, three published in vivo preclinical cancer model studies with PGG support promising efficacy to selectively inhibit malignancy without host toxicity. Potential mechanisms include anti-angiogenesis; anti-proliferative actions through inhibition of DNA replicative synthesis, S-phase arrest, and G(1) arrest; induction of apoptosis; anti-inflammation; and anti-oxidation. Putative molecular targets include p53, Stat3, Cox-2, VEGFR1, AP-1, SP-1, Nrf-2, and MMP-9. For anti-diabetic activity, PGG and analogues appear to improve glucose uptake. However, very little is known about the absorption, pharmacokinetics, and metabolism of PGG, or its toxicity profile. The lack of a large quantity of highly pure PGG has been a bottleneck limiting in vivo validation of cancer preventive and therapeutic efficacies in clinically relevant models.

The screening and isolation of an effective anti-endotoxin monomer from Radix Paeoniae Rubra using affinity biosensor technology

Lipopolysaccharide (LPS) is a known trigger in the pathogenesis of sepsis, lipid A being the toxic component. One of several adjuvant therapeutic approaches for severe sepsis is currently focusing on the neutralization of LPS. In order to obtain the components from traditional Chinese herbs that can neutralize the endotoxin, aqueous extractions were tested using affinity biosensor technology. From amongst 42 herbs, eight were found to possess lipid A-binding abilities. Radix Paeoniae Rubras had the highest lipid A-binding ability; therefore an aqueous extraction from this plant was investigated further. After preparation using standard methods, including silica gel chromatography and HPLC, we obtained 1, 2, 3, 4, 6-beta-d-pentagalloylglucose (PGG), with lipid A-binding ability. It was found that in vitro, PGG directly bound to lipid A, with a Kd of 32 microM, and that it neutralized the endotoxin both in the Limulus Amebocyte Lysate (LAL) assay and in a TNF-alpha release experiment, in a dose-dependent manner. In in vivo experiments, PGG was found to protect mice from a lethal challenge by LPS, and significantly decreased the plasma endotoxin level both in endotoxemic mice and rats, the reduction of the endotoxin level in rats being tightly associated with the TNF-alpha level. In conclusion, we demonstrate the effectiveness of affinity biosensor technology in discovering useful agents amongst traditional Chinese herbs and using this approach we found a new anti-endotoxin agent.

Induction of G1 arrest and apoptosis in human jurkat T cells by pentagalloylglucose through inhibiting proteasome activity and elevating p27Kip1, p21Cip1/WAF1, and Bax proteins

Pentagalloylglucose, which is found in many medicinal plants, can arrest the cell cycle at G(1) phase through down-regulation of cyclin-dependent kinases 2 and 4 and up-regulation of the cyclin-dependent kinase inhibitors p27(Kip1) and p21(Cip1/WAF1) in human breast cancer cells. Pentagalloylglucose also induces apoptosis in human leukemic cells. However, the mechanisms by which pentagalloylglucose induces these effects is unclear. We now show that pentagalloylglucose inhibits the activities of purified 20 and 26 S proteasomes in vitro, the 26 S proteasome in Jurkat T cell lysates, and chymotrypsin-like activity of the 26 S proteasome in intact Jurkat T cells. The turnover of p27(Kip1) and p21(Cip1/WAF1), which is necessary for cell cycle progression mediated by proteasome degradation, was disrupted by treatment of human Jurkat T cells with pentagalloylglucose. This was shown by cycloheximide treatment and in vivo pulse-chase labeling experiments, and this effect correlated with the arrest of proliferation of Jurkat T cells at G(1). Inhibition of the proteasome by pentagalloylglucose and by the proteasome inhibitor MG132 caused accumulation of ubiquitin-tagged proteins in Jurkat T cells. The addition of pentagalloylglucose to Jurkat T cells enhanced the stability of the proteasome substrate Bax and increased cytochrome c release and apoptosis. Our findings suggest a mechanism for the effect of pentagalloylglucose on the cell cycle in human leukemic cells: that pentagalloylglucose down-regulates proteasome-mediated pathways because it is a proteasome inhibitor.

In vitro anti-proliferative effect of 1,2,3,4,6-penta-O-galloyl-beta-D-glucose on human hepatocellular carcinoma cell line, SK-HEP-1 cells

The root of Paeonia suffruticosa ANDREWS is an important Chinese crude drug used in many traditional prescriptions. 1,2,3,4,6-penta-O-galloyl-beta-D-glucose (PGG), a major component of this crude drug, was found to exhibit in vitro growth-inhibiting effect on human hepatocellular carcinoma cell line, SK-HEP-1 cells. The growth-inhibitory effect was related to the ability of PGG not only to cause a G(0)/G(1) phase arrest but also to suppress the activation of nuclear factor-kappa B. Neither apoptosis nor necrosis was observed in the cells treated with PGG. These findings suggest that PGG could be a candidate for developing a low-toxic anticancer agent.

Alpha-glucosidase inhibitors from clove (Syzgium aromaticum)

The ellagitannins, casuarictin and eugeniin, were isolated as rat intestinal maltase inhibitors from methanol extracts of clove (Syzgium aromaticum). Eugeniin showed inhibitory activity with an IC50 value of 10(-3) M. A structure-activity relationship study among the isolates and their related compound, penta-O-galloyl-beta-D-glucose, indicates that an increasing number of galloyl units in the molecule might lead to an increase in the inhibitory activity. Eugeniin also inhibited maltase activity toward the human intestinal epithelial cell line, Caco-2.

Algal biotechnology

The review gives a general outline of macro- and microalgal biotechnology. The main methods by which algae are cultivated and harvested are described. The first section deals with the environmental factors affecting mass culture and the principles governing the design and operation of mass cultivation systems. The second section gives the main current and potential uses of algae: in wastewater treatment, a source of food and feed, an energy source, and in the production of common and fine chemicals, such as polysaccharides, lipids, glycerol, pigments, and enzymes. Pharmaceutical uses of algae are described, and their potential as a source of novel biologically-active compounds is discussed. Future developments and the great potential of algae are considered.