Inter- and intraspecific diversity of Salix bark phenolic profiles - A resource for the pharmaceutical industry

Due to their content of phenolic compounds, willow bark preparations are used as an herbal remedy. The large diversity of phenolic secondary metabolites in Salix still provides a resource for the identification of bioactive compounds in particular species, including species not yet in focus from a phytopharmaceutical perspective. The present study describes the bark phenolic profile of 13 Salix species analyzed by HPLC-MS: Salix alba, Salix babylonica, Salix daphnoides, Salix fragilis, Salix hastata, Salix myrsinifolia, Salix pentandra, Salix purpurea, Salix repens (including subspecies S. repens ssp. arenaria and S. repens ssp. repens), Salix rosmarinifolia, Salix sachalinensis, Salix triandra and Salix viminalis. The analyzed profiles comprised the chemical groups of salicylates, flavonoids, procyanidins, phenolic acid derivatives, and some unclassified phenolics. Particular compounds were detected in species where they have not been previously reported. Apart from interspecific diversity, qualitative variability within species was observed as certain components were detected only in some of the analyzed genotypes. The knowledge on specific phenolic profiles of species and genotypes is the basis for the selection of suitable willow bark material with certain desired bioactive properties. Furthermore, the high inter- and intraspecific variability points out the necessity for product standardization of willow bark raw material.

Hemp Waste as a Substrate for Hermetia illucens (L.) (Diptera: Stratiomyidae) and Tenebrio molitor L. (Coleoptera: Tenebrionidae) Rearing

The proper treatment of cannabis agricultural wastes can reduce the environmental impact of its cultivation and generate valuable products. This study aimed to test the potential of cannabis agricultural wastes as a substrate for the rearing of black soldier fly larvae (BSFL) and yellow mealworms (MW). In the case of BSFL, replacing the fibre component (straw) in the substrate with the hemp waste can increase the nutritional value of the substrate and led to bigger larvae. The bigger larvae had lower P and Mg, and higher Fe and Ca. Crude protein also varied based on the size of larvae and/or the content of protein in the initial substrate, which was boosted by replacing straw with hemp material. No other cannabinoids than cannabidiolic acid (CBDA), cannabigerolic acid (CBGA), and cannabidiol (CBD) were found in significant amounts in the larvae. In the case of MW, the larvae grew less on the hemp material in comparison to wheat bran. Replacing wheat bran with the hemp material led to smaller larvae with higher Ca, Fe, K, and crude protein content, but lower Mg and P values. No cannabinoids were detected in the MW fed with the hemp material.

Drug-Drug Interaction Potential, Cytotoxicity, and Reactive Oxygen Species Production of Salix Cortex Extracts Using Human Hepatocyte-Like HepaRG Cells

Herbal preparations of willow bark (Salix cortex) are available in many countries as non-prescription medicines for pain and inflammation, and also as dietary supplements. Currently only little information on toxicity and drug interaction potential of the extracts is available. This study now evaluated the effects of two Salix cortex extracts on human hepatocyte-like HepaRG cells, in view of clinically relevant CYP450 enzyme activity modulation, cytotoxicity and production of reactive oxygen species (ROS). Drug metabolism via the CYP450 enzyme system is considered an important parameter for the occurrence of drug-drug interactions, which can lead to toxicity, decreased pharmacological activity, and adverse drug reactions. We evaluated two different bark extracts standardized to 10 mg/ml phenolic content. Herein, extract S6 (S. pentandra, containing 8.15 mg/ml total salicylates and 0.08 mg/ml salicin) and extract B (industrial reference, containing 5.35 mg/ml total salicylates and 2.26 mg/ml salicin) were tested. Both Salix cortex extracts showed no relevant reduction in cell viability or increase in ROS production in hepatocyte-like HepaRG cells. However, they reduced CYP1A2 and CYP3A4 enzyme activity after 48 h at ≥25 μg/ml, this was statistically significant only for S6. CYP2C19 activity inhibition (0.5 h) was also observed at ≥25 μg/ml, mRNA expression inhibition by 48 h treatment with S6 at 25 μg/ml. In conclusion, at higher concentrations, the tested Salix cortex extracts showed a drug interaction potential, but with different potency. Given the high prevalence of polypharmacy, particularly in the elderly with chronic pain, further systematic studies of Salix species of medical interest should be conducted in the future to more accurately determine the risk of potential drug interactions.

Identification of Salicylates in Willow Bark (Salix Cortex) for Targeting Peripheral Inflammation

Salix cortex-containing medicine is used against pain conditions, fever, headaches, and inflammation, which are partly mediated via arachidonic acid-derived prostaglandins (PGs). We used an activity-guided fractionation strategy, followed by structure elucidation experiments using LC-MS/MS, CD-spectroscopy, and 1D/2D NMR techniques, to identify the compounds relevant for the inhibition of PGE2 release from activated human peripheral blood mononuclear cells. Subsequent compound purification by means of preparative and semipreparative HPLC revealed 2'-O-acetylsalicortin (1), 3'-O-acetylsalicortin (2), 2'-O-acetylsalicin (3), 2',6'-O-diacetylsalicortin (4), lasiandrin (5), tremulacin (6), and cinnamrutinose A (7). In contrast to 3 and 7, compounds 1, 2, 4, 5, and 6 showed inhibitory activity against PGE2 release with different potencies. Polyphenols were not relevant for the bioactivity of the Salix extract but salicylates, which degrade to, e.g., catechol, salicylic acid, salicin, and/or 1-hydroxy-6-oxo-2-cycohexenecarboxylate. Inflammation presents an important therapeutic target for pharmacological interventions; thus, the identification of relevant key drugs in Salix could provide new prospects for the improvement and standardization of existing clinical medicine.

Comparative Anti-Inflammatory Effects of Salix Cortex Extracts and Acetylsalicylic Acid in SARS-CoV-2 Peptide and LPS-Activated Human In Vitro Systems

The usefulness of anti-inflammatory drugs as an adjunct therapy to improve outcomes in COVID-19 patients is intensely discussed in this paper. Willow bark (Salix cortex) has been used for centuries to relieve pain, inflammation, and fever. Its main active ingredient, salicin, is metabolized in the human body into salicylic acid, the precursor of the commonly used pain drug acetylsalicylic acid (ASA). Here, we report on the in vitro anti-inflammatory efficacy of two methanolic Salix extracts, standardized to phenolic compounds, in comparison to ASA in the context of a SARS-CoV-2 peptide challenge. Using SARS-CoV-2 peptide/IL-1β- or LPS-activated human PBMCs and an inflammatory intestinal Caco-2/HT29-MTX co-culture, Salix extracts, and ASA concentration-dependently suppressed prostaglandin E2 (PGE₂), a principal mediator of inflammation. The inhibition of COX-2 enzyme activity, but not protein expression was observed for ASA and one Salix extract. In activated PBMCs, the suppression of relevant cytokines (i.e., IL-6, IL-1β, and IL-10) was seen for both Salix extracts. The anti-inflammatory capacity of Salix extracts was still retained after transepithelial passage and liver cell metabolism in an advanced co-culture model system consisting of intestinal Caco-2/HT29-MTX cells and differentiated hepatocyte-like HepaRG cells. Taken together, our in vitro data suggest that Salix extracts might present an additional anti-inflammatory treatment option in the context of SARS-CoV-2 peptides challenge; however, more confirmatory data are needed.

Chemoprofiling as Breeding Tool for Pharmaceutical Use of Salix

Willow bark is traditionally used for pharmaceutical purposes. Evaluation is so far based on the salicylate content, however, health promoting effects of extracts might be attributed to the interaction of those salicylates with other compounds, which support and complement their action. So far, only S. purpurea, S. daphnoides, and S. fragilis are included in pharmaceutical extracts. Crossing with other species could result in a more diverse secondary metabolite profile with higher pharmacological value. With the help of targeted inter- and intraspecific crossing, new chemotypes were generated, whereby nine different Salix genotypes (S. alba, S. daphnoides, S. humboldtiana, S. lasiandra, S. nigra, S. pentandra, S. purpurea, S. x rubens, S. viminalis) were included in the study. Based on substances known for their health promoting potential and characteristic for Salix (selected phenolic compounds including salicylates), a targeted metabolomics analysis and clustering of 92 generated Salix clones was performed revealing four different cluster/chemoprofiles. In more specific, one group is formed by S. daphnoides clones and inter- and intraspecific hybrids, a second group by S. viminalis clones and inter- and intraspecific hybrids, a third group generally formed by S. alba, S. pentandra, S. x rubens, and S. lasiandra clones and hybrids, and a fourth group by S. purpurea clones and inter- and intraspecific hybrids. Clustering on the basis of the selected phenolic compounds can be used for identifying Salix clones with a different compound profile. New combinations of secondary plant metabolites offer the chance to identify Salix crosses with improved effects on human health.

Phenolic compound abundance in Pak choi leaves is controlled by salinity and dependent on pH of the leaf apoplast

Onset of salinity induces the pH of the leaf apoplast of Pak choi transiently to increase over a period of 2 to 3 hr. This pH event causes protein abundances in leaves to increase. Among them are enzymes that are key for the phenylpropanoid pathway. To answer the questions whether this short-term salt stress also influences contents of the underlying phenylpropanoids and for clarifying as to whether the apoplastic pH transient plays a role for such a putative effect, Pak choi plants were treated with 37.5 mM CaCl2 against a non-stressed control. A third experimental group, where the leaf apoplast of plants treated with 37.5 mM CaCl2, was clamped in the acidic range by means of infiltration of 5 mM citric acid/sodium citrate (pH 3.6), enabled validation of pH-dependent effects. Microscopy-based live cell imaging was used to quantify leaf apoplastic pH in planta. Phenolics were quantified shortly after the formation of the leaf apoplastic pH transient by means of HPLC-DAD-ESI-MS. Results showed that different phenolic compounds were modulated at 150 and 200 min after the onset of chloride salinity. A pH-independent reduction in phenolic acid abundance as well as an accumulation of phenolic acid:malate conjugates was quantified after 200 min of salt stress. However, at 150 min after the onset of salt stress, flavonoids were significantly reduced by salinity in a pH-dependent manner. These results provided a strong indication that the pH of the apoplast is a relevant component for the short-term metabolic response to chloride salinity.

Compound-specific responses of phenolic metabolites in the bark of drought-stressed Salix daphnoides and Salix purpurea

The bark of willows (Salix spp.) is rich in bioactive phenolic compounds from different compound classes and is therefore used as an herbal remedy. The accumulation of these secondary plant metabolites is influenced by environmental factors, including the availability of water. To analyze the influence of drought stress on the profile of phenolic metabolites in willow bark, a pot experiment with Salix daphnoides Vill. and Salix purpurea L. was conducted. Plants were subjected to three irrigation treatments for four and ten weeks: 65-75% field capacity (well-watered), 33-38% field capacity (moderate drought), and 17-22% field capacity (severe drought). Shoot biomass and proline content were assessed as drought-sensitive traits. Contents of phenolic compounds were analyzed by high-performance liquid chromatography. Drought stress reduced shoot biomass and led to an increase of the bark proline content. The particular effects on phenolics depended on the individual compound, Salix species and drought stress duration. Whereas salicylates were not affected, some flavonoids and phenolic acid derivatives, as well as salireposide indicated treatment effects. The effects comprised decreasing as well as increasing contents. However, beyond the impact of drought stress, the observed responses are assumed to be superimposed by seasonal changes in the content of phenolics. Regarding the yield of willow shoots, the impairment of growth under water shortage seems to be more decisive than drought-induced changes of the bark metabolite content.

Characteristic single glucosinolates from Moringa oleifera: Induction of detoxifying enzymes and lack of genotoxic activity in various model systems

Leaves of Moringa oleifera are used by tribes as biological cancer medicine. Scientific investigations with M. oleifera conducted so far have almost exclusively used total plant extracts. Studies on the activity of single compounds are missing. Therefore, the biological effects of the two main aromatic multi-glycosylated glucosinolates of M. oleifera were investigated in the present study. The cytotoxic effects of M. oleifera glucosinolates were identified for HepG2 cells (NRU assay), for V79-MZ cells (HPRT assay, SCE assay), and for two Salmonella typhimurium strains (Ames test). Genotoxic effects of these glucosinolates were not observed (Ames test, HPRT assay, and SCE assay). Reporter gene assays revealed a significant increase in the ARE-dependent promoter activity of NQO1 and GPx2 indicating an activation of the Nrf2 pathway by M. oleifera glucosinolates. Since both enzymes can also be induced via activation of the AhR, plasmids containing promoters of both enzymes mutated in the respective binding sites (pGL3enh-hNQO1-ARE, pGL3enh-hNQO1-XRE, pGL3bas-hGPX2-mutARE, pGL3bas-hGPX2-mutXRE) were transfected. Analyses revealed that the majority of the stimulating effects was mediated by the ARE motif, whereas the XRE motif played only a minor role. The stimulating effects of M. oleifera glucosinolates could be demonstrated both at the transcriptional (reporter gene assay, real time-PCR) and translational levels (enzyme activity) making them interesting compounds for further investigation.

Ecotype variability in growth and secondary metabolite profile in Moringa oleifera: impact of sulfur and water availability

Moringa oleifera is widely cultivated in plantations in the tropics and subtropics. Previous cultivation studies with M. oleifera focused primarily only on leaf yield. In the present study, the content of potentially health-promoting secondary metabolites (glucosinolates, phenolic acids, and flavonoids) were also investigated. Six different ecotypes were grown under similar environmental conditions to identify phenotypic differences that can be traced back to the genotype. The ecotypes TOT4880 (origin USA) and TOT7267 (origin India) were identified as having the best growth performance and highest secondary metabolite production, making them an ideal health-promoting food crop. Furthermore, optimal cultivation conditions-exemplarily on sulfur fertilization and water availability-for achieving high leaf and secondary metabolite yields were investigated for M. oleifera. In general, plant biomass and height decreased under water deficiency compared to normal cultivation conditions, whereas the glucosinolate content increased. The effects depended to a great extent on the ecotype.

Development of a reliable extraction and quantification method for glucosinolates in Moringa oleifera

Glucosinolates are the characteristic secondary metabolites of plants in the order Brassicales. To date the common DIN extraction 'desulfo glucosinolates' method remains the common procedure for determination and quantification of glucosinolates. However, the desulfation step in the extraction of glucosinolates from Moringa oleifera leaves resulted in complete conversion and degradation of the naturally occurring glucosinolates in this plant. Therefore, a method for extraction of intact Moringa glucosinolates was developed and no conversion and degradation of the different rhamnopyranosyloxy-benzyl glucosinolates was found. Buffered eluents (0.1 M ammonium acetate) were necessary to stabilize 4-α-rhamnopyranosyloxy-benzyl glucosinolate (Rhamno-Benzyl-GS) and acetyl-4-α-rhamnopyranosyloxy-benzyl glucosinolate isomers (Ac-Isomers-GS) during HPLC analysis. Due to the instability of intact Moringa glucosinolates at room temperature and during the purification process of single glucosinolates, influences of different storage (room temperature, frozen, thawing and refreezing) and buffer conditions on glucosinolate conversion were analysed. Conversion and degradations processes were especially determined for the Ac-Isomers-GS III.

Factors influencing the variability of antioxidative phenolic glycosides in Salix species

Phenolic glycosides, especially the salicylates, are important secondary metabolites in the bark of willows (Salix spp.). Because of their anti-inflammatory, analgesic, and fever-reducing properties, they are of particular interest to society. Compared to the fabrication of synthetic salicylacetylic acid, the commercial production of willow bark extracts with adequate amounts of salicylate is very difficult due to several biological and technical reasons. Therefore, one of the objectives was to identify salicylate-rich clones from three species, Salix daphnoides , Salix purpurea , and Salix pentandra , with potentially high amounts of phenolic glycosides. Three hundred different Salix clones were collected, and the chemical profiles of their bark were analyzed by HPLC. Overall, S. daphnoides clones showed the highest phenolic glycoside contents, followed by S. purpurea and S. pentandra. Second, seasonal changes of secondary compounds in willow bark were analyzed to determine the optimal harvesting time. The phenolic glycoside levels decreased over the growing season, with highest contents detected during plant dormancy. The effects of different cultivation conditions were also examined, and none of these treatments were found to have a significant effect on the phenolic glycoside content in willow bark. Biomass accumulation in the clones with grass competition was significantly lower than in the other three treatments.