In vitro α-glucosidase inhibitory activity of Tamarix nilotica shoot extracts and fractions.

α-glucosidase inhibitors represent an important class of type 2 antidiabetic drugs and they act by lowering postprandial hyperglycemia. Today, only three synthetic inhibitors exist on the market, and there is a need for novel, natural and more efficient molecules exhibiting this activity. In this study, we investigated the ability of Tamarix nilotica ethanolic and aqueous shoot extracts, as well as methanolic fractions prepared from aqueous crude extracts to inhibit α-glucosidase. Both, 50% ethanol and aqueous extracts inhibited α-glucosidase in a concentration-dependent manner, with IC50 values of 12.5 µg/mL and 24.8 µg/mL, respectively. Importantly, α-glucosidase inhibitory activity observed in the T. nilotica crude extracts was considerably higher than pure acarbose (IC50 = 151.1 µg/mL), the most highly prescribed α-glucosidase inhibitor on the market. When T. nilotica crude extracts were fractionated using methanol, enhanced α-glucosidase inhibitory activity was observed in general, with the highest observed α-glucosidase inhibitory activity in the 30% methanol fraction (IC50 = 5.21 µg/mL). Kinetic studies further revealed a competitive reversible mechanism of inhibition by the plant extract. The phytochemical profiles of 50% ethanol extracts, aqueous extracts, and the methanolic fractions were investigated and compared using a metabolomics approach. Statistical analysis revealed significant differences in the contents of the crude extracts and fractions and potentially identified the molecules that were most responsible for these observed variations. Higher α-glucosidase inhibitory activity was associated with an enrichment of terpenoids, fatty acids, and flavonoids. Among the identified molecules, active compounds with known α-glucosidase inhibitory activity were detected, including unsaturated fatty acids, triterpenoids, and flavonoid glycosides. These results put forward T. nilotica as a therapeutic plant for type 2 diabetes and a source of α-glucosidase inhibitors.

A review of alpha-glucosidase inhibitors from plants as potential candidates for the treatment of type-2 diabetes.

Diabetes mellitus is a multifactorial global health disorder that is rising at an alarming rate. Cardiovascular diseases, kidney damage and neuropathy are the main cause of high mortality rates among individuals with diabetes. One effective therapeutic approach for controlling hyperglycemia associated with type-2 diabetes is to target alpha-amylase and alpha-glucosidase, enzymes that catalyzes starch hydrolysis in the intestine. At present, approved inhibitors for these enzymes are restricted to acarbose, miglitol and voglibose. Although these inhibitors retard glucose absorption, undesirable gastrointestinal side effects impede their application. Therefore, research efforts continue to seek novel inhibitors with improved efficacy and minimal side effects. Natural products of plant origin have been a valuable source of therapeutic agents with lesser toxicity and side effects. The anti-diabetic potential through alpha-glucosidase inhibition of plant-derived molecules are summarized in this review. Eight molecules (Taxumariene F, Akebonoic acid, Morusin, Rhaponticin, Procyanidin A2, Alaternin, Mulberrofuran K and Psoralidin) were selected as promising drug candidates and their pharmacokinetic properties and toxicity were discussed where available. Supplementary Information: The online version contains supplementary material available at 10.1007/s11101-021-09773-1.

A metabolomics approach to evaluate the effect of lyophilization versus oven drying on the chemical composition of plant extracts.

Lyophilization is the "gold standard" for drying plant extracts, which is important in preserving their quality and extending their shelf-life. Compared to other methods of drying plant extracts, lyophilization is costlier due to equipment, material and operational expenses. An alternative method is post-extraction oven-drying, but the effects of this process on extract quality are unknown. In this study, crude extracts from Arthrocnemum macrostachyum shoots were compared using three post-extraction drying methods (lyophilization and oven drying at 40 and 60 °C) and two extraction solvents (water and aqueous 50% ethanol). Untargeted metabolomics coupled with chemometrics analysis revealed that post extraction oven-drying resulted in the loss of up to 27% of molecular features when compared to lyophilization in water extracts only. In contrast, only 3% of molecular features were lost in aqueous 50% ethanol extracts when subjected to oven drying. That is to say, ethanol used as a solvent has a stabilizing effect on metabolites and enhances their resistance to thermal transformation in the oven. Collectively, oven-drying of extracts was as effective as lyophilization in preserving metabolites in extracts only when 50% ethanol was used as a solvent. The results presented in this paper demonstrate the value of selecting solvent-appropriate post-extraction drying methods.

Agronomic assessment of pyrolysed food waste digestate for sandy soil management.

The digestate (DFW) of an industrial food waste treatment plant was pyrolysed for production of biochar for its direct application as bio-fertilizer or soil enhancer. Nutrient dynamics and agronomic viability of the pyrolysed food waste digestate (PyD) produced at different temperatures were evaluated using germination index (GI), water retention/availability and mineral sorption as indicators when applied on arid soil. The pyrolysis was found to enrich P, K and other micronutrients in the biochar at an average enrichment factor of 0.87. All PyD produced at different temperatures indicated significantly low phytotoxicity with GI range of 106-168% and an average water retention capacity of 40.2%. Differential thermogravimetric (DTG) thermographs delineated the stability of the food waste digestate pyrolysed at 500 °C (PyD500) against the degradation of the digestate food waste despite the latter poor nutrient sorption potential. Plant available water in soil is 40% when treated with 100 g of digestate per kg soil, whereas PyD500 treated soil indicated minimal effect on plant available water, even with high application rates. However, the positive effects of PyD on GI and the observed enrichment in plant macro and micronutrients suggest potential agronomic benefits for PyD use, in addition to the benefits from energy production from DFW during the pyrolysis process.

Global transcriptome analysis of salt acclimated Prochlorococcus AS9601.

Molecular processes leading to salt stress acclimation in the model cyanobacterium Prochlorococcus are not known. To address this, we used RNA sequencing (RNAseq) to compare the global transcriptome of two exponential-phase populations of Prochlorococcus AS9601 cells - acclimated to high salt (5%, w/v) and normal seawater salt (3.8%, w/v). Experiments showed that salt acclimated cells exhibit slower growth rates with a doubling time almost twice as controls. Approximately 1/3 of the genome was found to be differentially expressed (p-value <0.05), but a considerably large number of these genes are "hypothetical proteins" with unknown function. Transcript abundance were higher for genes involved in respiratory electron flow, carbon fixation, osmolyte/compatible solute biosynthesis and inorganic ion transport. Many of the highly expressed genes are 'high light inducible proteins' believed to be part of the general Prochlorococcus stress response. Transcript abundance were lower for genes involved in photosynthetic electron transport and cell division. The relative reduction in transcript abundance for genes encoding proteins containing heme groups and iron transporters suggests cellular iron requirements in salt acclimated cells maybe lower. The results presented here provide the first glimpse into global gene expression changes in Prochlorococcus cells due to salt stress.

Stigmasterol and cholesterol regulate the expression of elicitin genes in Phytophthora sojae.

Sterol acquisition by soilborne plant pathogens of the genus Phytophthora is presumed to involve extracellular proteins belonging to class-I elicitins. However, little is known about the relationship between sterol availability and elicitin secretion. The objective of this study was to determine the expression of class-I elicitin genes in Phytophthora sojae when grown in a medium containing stigmasterol or cholesterol. P. sojae growth was stimulated by nanomolar concentrations of stigmasterol and cholesterol, which also resulted in the down-regulation of its elicitin genes over time when expression profiles were monitored using real time Reverse Transcription Polymerase Chain Reaction (RT-PCR). The down-regulation of elicitin genes in response to the two sterols also coincided with a reduction in the amount of elicitins detected in spent filtrates. Our study is the first to show the influence of sterols on elicitin gene expression in Phytophthora, which is important with respect to the ecology of elicitin secretion as sterol carrier proteins in the environment.

In vitro metabolism of ginsenosides by the ginseng root pathogen Pythium irregulare.

The role of ginseng saponins (ginsenosides) as modulators or inhibitors of disease is vague, but our earlier work supports the existence of an allelopathic relationship between ginsenosides and soilborne microbes. Interestingly, this allelopathy appears to significantly promote the growth of the important ginseng pathogen, Pythium irregulare while inhibiting that of an antagonistic non-pathogenic fungus, Trichoderma hamatum. Herein we report on the apparent selective metabolism of 20(S)-protopanaxadiol ginsenosides by an extracellular glycosidase from P. irregulare. Thus, when P. irregulare was cultured in the presence of a purified (> 90%) ginsenoside mixture, nearly all of the 20(S)-protopanaxadiol ginsenosides (Rb1, Rb2, Rc, Rd, and to a limited extent G-XVII) were metabolized into the minor ginsenoside F2, at least half of which appears to be internalized by the organism. No metabolism of the 20(S)-protopanaxatriol ginsenosides (Rg1 and Re) was evident. By contrast, none of the ginsenosides added to the culture medium of the non-pathogenic fungus T. hamatum were metabolized. The metabolism of 20(S)-protopanaxadiol ginsenosides by P. irregulare appears to occur through the hydrolysis of terminal monosaccharide units from disaccharides present at C-3 and/or C-20 of ginsenosides Rb1, Rc, Rb2, Rd and G-XVII to yield one major product, ginsenoside F2 and one minor product (possibly G-III). A similar transformation of ginsenosides was observed using a crude protein preparation isolated from the spent medium of P. irregulare cultures.