Emerging Therapeutic Potential of Polyphenols from Geranium sanguineum L. in Viral Infections, Including SARS-CoV-2.

The existing literature supports the anti-inflammatory, antioxidant, and antiviral capacities of the polyphenol extracts derived from Geranium sanguineum L. These extracts exhibit potential in hindering viral replication by inhibiting enzymes like DNA polymerase and reverse transcriptase. The antiviral properties of G. sanguineum L. seem to complement its immunomodulatory effects, contributing to infection resolution. While preclinical studies on G. sanguineum L. suggest its potential effectiveness against COVID-19, there is still a lack of clinical evidence. Therefore, the polyphenols extracted from this herb warrant further investigation as a potential alternative for preventing and treating COVID-19 infections.

Anti-COVID-19 Potential of Ellagic Acid and Polyphenols of Punica granatum L.

Pomegranate (Punica granatum L.) is a rich source of polyphenols, including ellagitannins and ellagic acid. The plant is used in traditional medicine, and its purified components can provide anti-inflammatory and antioxidant activity and support of host defenses during viral infection and recovery from disease. Current data show that pomegranate polyphenol extract and its ellagitannin components and metabolites exert their beneficial effects by controlling immune cell infiltration, regulating the cytokine secretion and reactive oxygen and nitrogen species production, and by modulating the activity of the NFκB pathway. In vitro, pomegranate extracts and ellagitannins interact with and inhibit the infectivity of a range of viruses, including SARS-CoV-2. In silico docking studies show that ellagitannins bind to several SARS-CoV-2 and human proteins, including a number of proteases. This warrants further exploration of polyphenol-viral and polyphenol-host interactions in in vitro and in vivo studies. Pomegranate extracts, ellagitannins and ellagic acid are promising agents to target the SARS-CoV-2 virus and to restrict the host inflammatory response to viral infections, as well as to supplement the depleted host antioxidant levels during the stage of recovery from COVID-19.

Preventive and Therapeutic Effects of Punica granatum L. Polyphenols in Neurological Conditions.

Pomegranate (Punica granatum L.) is a polyphenol-rich food and medicinal plant containing flavonols, anthocyanins, and tannins. Ellagitannins (ETs) are the most abundant polyphenols in pomegranate. A growing body of research shows that polyphenol-rich pomegranate extracts and their metabolites target multiple types of brain cell and support their redox balance, proliferation and survival, as well as cell signaling. Independent studies have demonstrated that the significant neuroprotective effects of ETs are mediated by their antioxidant and anti-inflammatory effects, their chelating properties, by their ability to activate various signaling pathways, as well as the ability to influence mitochondrial damage, thus regulating autophagy, apoptosis and neurotransmitter signaling. The multitude of in vitro and in vivo studies summarized in the present review suggest that pomegranate polyphenols act on both neuronal and glial cells directly, and also affect blood-brain barrier function, restoring redox balance in the blood and brain and increasing blood flow to the brain.

Temperature-dependent metabolic adaptation of Triticum aestivum seedlings to anoxia.

Wheat (Triticum aestivum) is considered anoxia intolerant but it shows variance in anoxia responses between genotypes and environmental treatments. We firstly examined 4 day old seedlings of five wheat genotypes in response to anoxia at 15 °C and 28 °C by assessing growth rate, tissue damage and changes in metabolite abundances. Significant genotypic variations in anoxia tolerance were observed, especially at 28 °C. Wheat seedlings grown at 15 °C appeared to be more anoxia tolerant and showed less genotypic variation than those at 28 °C. To minimize seedling size variations and define the temperature effects, we grew two contrasting genotypes at 15 °C for 3.5 d and adapted to 4 different temperatures for 0.5 d before exposing them to anoxia at each adapted temperature. Genotypic variation in abundance of anoxia induced metabolites occurred at 24 °C and 28 °C but not at 15 °C and 20 °C. Tissue- and temperature-dependent metabolic adaptations to anoxia were revealed. In roots, the ability to maintain sugar/sugar-phosphate and TCA cycle metabolite levels and the accumulation of amino acids when temperature was below 24 °C correlated with anoxia tolerance. Temperatures between 20 °C-24 °C are critical for metabolic adaptation and suggest that further assessment of waterlogging/flooding tolerance of wheat seedlings should consider the temperature-dependence of tolerance in evaluations.

Temporal development of the barley leaf metabolic response to Pi limitation.

The response of plants to Pi limitation involves interplay between root uptake of Pi , adjustment of resource allocation to different plant organs and increased metabolic Pi use efficiency. To identify potentially novel, early-responding, metabolic hallmarks of Pi limitation in crop plants, we studied the metabolic response of barley leaves over the first 7 d of Pi stress, and the relationship of primary metabolites with leaf Pi levels and leaf biomass. The abundance of leaf Pi , Tyr and shikimate were significantly different between low Pi and control plants 1 h after transfer of the plants to low Pi . Combining these data with 15 N metabolic labelling, we show that over the first 48 h of Pi limitation, metabolic flux through the N assimilation and aromatic amino acid pathways is increased. We propose that together with a shift in amino acid metabolism in the chloroplast a transient restoration of the energetic and redox state of the leaf is achieved. Correlation analysis of metabolite abundances revealed a central role for major amino acids in Pi stress, appearing to modulate partitioning of soluble sugars between amino acid and carboxylate synthesis, thereby limiting leaf biomass accumulation when external Pi is low.

Specific global responses to N and Fe nutrition in toxic and non-toxic Microcystis aeruginosa.

The bloom-forming cyanobacteria species Microcystis aeruginosa includes toxic and non-toxic (microcystin-producing) strains. Certain stress conditions stimulate synthesis of microcystin (MCYST) and enhance the binding of the MCYST molecule to proteins. In this quantitative proteomic study, we compared the response of a wild-type toxic strain PCC 7806, an mcyH(-) knockout non-toxic strain, and a naturally occurring non-toxic strain, PCC 7005, after 8 days in low iron (Fe) and nitrogen (N) starvation in order to assess the benefit of MCYST synthesis in non-optimal conditions. Fe limitation increased MCYST synthesis and caused an accumulation of phycobilisome proteins and the ferric iron transporter FutA only in the toxic PCC 7806 but not the non-toxic strains. In N starvation, photosynthetic, C and N metabolism proteins were more abundant in the non-toxic strains, as were chaperones and proteases. Significant interaction between nutrient availability and toxicity existed for thioredoxin peroxidase and several thioredoxin-regulated proteins. We propose a competition of MCYST for binding sites in thioredoxin-regulated proteins during oxidative stress (low Fe) but not in growth-limiting conditions (low N). This then leads to differences in the regulation of C:N metabolism in toxic and non-toxic M. aeruginosa in nutrient-replete and nutrient-limited conditions.

Exposure of barley plants to low Pi leads to rapid changes in root respiration that correlate with specific alterations in amino acid substrates.

The majority of inorganic phosphate (Pi ) stress studies in plants have focused on the response after growth has been retarded. Evidence from transcript analysis, however, shows that a Pi -stress specific response is initiated within minutes of transfer to low Pi and in crop plants precedes the expression of Pi transporters and depletion of vacuolar Pi reserves by days. In order to investigate the physiological and metabolic events during early exposure to low Pi in grain crops, we monitored the response of whole barley plants during the first hours following Pi withdrawal. Lowering the concentration of Pi led to rapid changes in root respiration and leaf gas exchange throughout the early phase of the light course. Combining amino and organic acid analysis with (15) N labelling we show a root-specific effect on nitrogen metabolism linked to specific substrates of respiration as soon as 1 h following Pi withdrawal; this explains the respiratory responses observed and was confirmed by stimulation of respiration by exogenous addition of these respiratory substrates to roots. The rapid adjustment of substrates for respiration in roots during short-term Pi -stress is highlighted and this could help guide roots towards Pi -rich soil patches without compromising biomass accumulation of the plant.

Proteins with high turnover rate in barley leaves estimated by proteome analysis combined with in planta isotope labeling.

Protein turnover is a key component in cellular homeostasis; however, there is little quantitative information on degradation kinetics for individual plant proteins. We have used (15)N labeling of barley (Hordeum vulgare) plants and gas chromatography-mass spectrometry analysis of free amino acids and liquid chromatography-mass spectrometry analysis of proteins to track the enrichment of (15)N into the amino acid pools in barley leaves and then into tryptic peptides derived from newly synthesized proteins. Using information on the rate of growth of barley leaves combined with the rate of degradation of (14)N-labeled proteins, we calculate the turnover rates of 508 different proteins in barley and show that they vary by more than 100-fold. There was approximately a 9-h lag from label application until (15)N incorporation could be reliably quantified in extracted peptides. Using this information and assuming constant translation rates for proteins during the time course, we were able to quantify degradation rates for several proteins that exhibit half-lives on the order of hours. Our workflow, involving a stringent series of mass spectrometry filtering steps, demonstrates that (15)N labeling can be used for large-scale liquid chromatography-mass spectrometry studies of protein turnover in plants. We identify a series of abundant proteins in photosynthesis, photorespiration, and specific subunits of chlorophyll biosynthesis that turn over significantly more rapidly than the average protein involved in these processes. We also highlight a series of proteins that turn over as rapidly as the well-known D1 subunit of photosystem II. While these proteins need further verification for rapid degradation in vivo, they cluster in chlorophyll and thiamine biosynthesis.

Proteomics of phosphate use and deprivation in plants.

Phosphate is an essential element for plants and is involved in the composition of sugar phosphates, nucleic acids, membrane lipids, and energy metabolism via the generation of ATP. Crop farming requires the application of large amounts of phosphate fertilizer, but the fossilized rock deposits used as a commercial source of phosphate fertilizer are a nonrenewable resource that is predicted to reach a peak within the next century and drive plant production costs up as the global demand for food increases. Recent progress in the identification of key molecular regulators of the plant response to phosphate deprivation has highlighted differences in the response of the model plant Arabidopsis compared to economically important crops. This review focuses on the potential of proteomics to unravel the common and specific biochemical changes that contribute to phosphate use efficiency in cultivars of rice, maize, and oilseed rape. Proteome studies reveal a wide scope of species-specific metabolic strategies that lead to changes in root morphology and metabolism, driven by secretion of specific proteins and alteration of energy metabolism, carbon, and nitrogen assimilation inside the root cells. Understanding of the mechanisms underlying plant phosphate use efficiency in crops is critical for developing sustainable agriculture practices.

Comparative protein expression in different strains of the bloom-forming cyanobacterium Microcystis aeruginosa.

Toxin production in algal blooms presents a significant problem for the water industry. Of particular concern is microcystin, a potent hepatotoxin produced by the unicellular freshwater species Microcystis aeruginosa. In this study, the proteomes of six toxic and nontoxic strains of M. aeruginosa were analyzed to gain further knowledge in elucidating the role of microcystin production in this microorganism. This represents the first comparative proteomic study in a cyanobacterial species. A large diversity in the protein expression profiles of each strain was observed, with a significant proportion of the identified proteins appearing to be strain-specific. In total, 475 proteins were identified reproducibly and of these, 82 comprised the core proteome of M. aeruginosa. The expression of several hypothetical and unknown proteins, including four possible operons was confirmed. Surprisingly, no proteins were found to be produced only by toxic or nontoxic strains. Quantitative proteome analysis using the label-free normalized spectrum abundance factor approach revealed nine proteins that were differentially expressed between toxic and nontoxic strains. These proteins participate in carbon-nitrogen metabolism and redox balance maintenance and point to an involvement of the global nitrogen regulator NtcA in toxicity. In addition, the switching of a previously inactive toxin-producing strain to microcystin synthesis is reported.

Characterization of a unique conformational epitope on free immunoglobulin kappa light chains that is recognized by an antibody with therapeutic potential.

The murine mAb, K-1-21, recognizes a conformational epitope expressed on free Ig kappa light chains (FκLCs) and also on cell membrane-associated FκLCs found on kappa myeloma cells. This has led to the development of a chimeric version of K-1-21, MDX-1097, which is being assessed in a Phase II clinical trial for the treatment of multiple myeloma. The epitope recognized by K-1-21 is of particular interest, especially in the context that it is not expressed on heavy chain-associated light chains such as in an intact Ig molecule. Using epitope excision techniques we have localized the K-1-21 epitope to a region spanning residues 104-110 of FκLC. This short strand of residues links the variable and constant domains, and is a flexible region that adopts different conformations in FκLC and heavy chain-associated light chain. We tested this region using site-directed mutations and found that the reactivity of K-1-21 for FκLC was markedly reduced. Finally, we applied in silico molecular docking to generate a model that satisfied the experimental data. Given the clinical potential of the Ag, this study may aid the development of next generation compounds that target the membrane form of FκLC expressed on the surface of myeloma plasma cells.

Iron uptake and toxin synthesis in the bloom-forming Microcystis aeruginosa under iron limitation.

Toxin production during cyanobacterial blooms poses a significant public health threat in water bodies globally and requires the development of effective bloom management strategies. Previously, synthesis of the hepatotoxin microcystin has been proposed to be regulated by iron availability, but the contribution of the toxin to the adaptation of cyanobacteria to environmental stresses, such as changing light intensity and nutrient limitation, remains unclear. The aim of this study was to compare the iron stress response in toxic and non-toxic strains of Microcystis aeruginosa subjected to moderate and severe iron limitation. The transcription of a number of genes involved in iron uptake, oxidative stress response, toxin synthesis and transcriptional control of these processes was accessed by quantitative real-time PCR (qRT-PCR). The process of adaptation of M. aeruginosa to iron stress was found to be highly dynamic and strain-specific. Toxin production in PCC 7806 increased in an iron-dependent manner and appeared to be regulated by FurA. The inability to produce microcystin, either due to natural mutations in the mcy gene cluster or due to insertional inactivation of mcyH, affected the remodelling of the photosynthetic machinery in iron-stressed cells, the transport of Fe(II) and transcription of the Fur family of transcriptional regulators. The presence of the toxin appears to give an advantage to microcystin-producing cyanobacteria in the early stages of exposure to severe iron stress and may protect the cell from reactive oxygen species-induced damage.

Assessment of salinity-induced photorespiratory glycolate metabolism in Anabaena sp. PCC 7120.

This paper reports an investigation of salinity-induced glycolate metabolism in the cyanobacterium Anabaena sp. PCC 7120 (hereafter Anabaena PCC 7120). Quantitative analysis of transcripts for the photosynthesis-associated genes encoding ribulose-1,5-bisphosphate carboxylase oxygenase (Rubisco), phosphoribulokinase and transketolase, as well as those involved in glycolate metabolism (phosphoglycolate phosphatase, glycolate oxidase, alanine-glyoxylate aminotransferase and serine hydroxymethyltransferase) was performed. The expression of all investigated photosynthesis-associated genes except Rubisco was downregulated after 24 h NaCl treatment. However, under the same conditions, the transcripts encoding enzymes involved in glycolate metabolism were overexpressed. This was further confirmed by the quantitative analysis of the intermediates involved in glycolate metabolism. The intracellular levels of organic acids (glyceric, glycolic and glyoxylic acids) and amino acids (glycine and serine) were elevated in salt-treated cells as compared to those in the control cells. Transcriptional inhibition of photosynthesis-associated genes, and upregulation of genes and enhanced synthesis of intermediates associated with glycolate metabolism, indicate the occurrence of this photorespiratory metabolic pathway metabolism in Anabaena PCC 7120 under salt stress.

Functional analysis of PilT from the toxic cyanobacterium Microcystis aeruginosa PCC 7806.

The evolution of the microcystin toxin gene cluster in phylogenetically distant cyanobacteria has been attributed to recombination, inactivation, and deletion events, although gene transfer may also be involved. Since the microcystin-producing Microcystis aeruginosa PCC 7806 is naturally transformable, we have initiated the characterization of its type IV pilus system, involved in DNA uptake in many bacteria, to provide a physiological focus for the influence of gene transfer in microcystin evolution. The type IV pilus genes pilA, pilB, pilC, and pilT were shown to be expressed in M. aeruginosa PCC 7806. The purified PilT protein yielded a maximal ATPase activity of 37.5 +/- 1.8 nmol P(i) min(-1) mg protein(-1), with a requirement for Mg(2+). Heterologous expression indicated that it could complement the pilT mutant of Pseudomonas aeruginosa, but not that of the cyanobacterium Synechocystis sp. strain PCC 6803, which was unexpected. Differences in two critical residues between the M. aeruginosa PCC 7806 PilT (7806 PilT) and the Synechocystis sp. strain PCC 6803 PilT proteins affected their theoretical structural models, which may explain the nonfunctionality of 7806 PilT in its cyanobacterial counterpart. Screening of the pilT gene in toxic and nontoxic strains of Microcystis was also performed.