Biological activity and stability analyses of knipholone anthrone, a phenyl anthraquinone derivative isolated from Kniphofia foliosa Hochst

Rheum khorasanicum. Hydroalcoholic root extract induces cell death in human colorectal adenocarcinoma: An in vitro and in silico study

Colorectal cancer (CRC) is the second greatest cause of cancer-related death in the world and chemotherapy, as an important part of CRC treatment, has some drawbacks, including systemic toxicity. Therefore, it is crucial to discover new and more effective CRC treatment plans. Rheum khorasanicum (R. khorasanicum) is a medicinal plant with high flavonoids, stilbenes, and anthraquinone contents, so it can be a potential source of antioxidants and can be used for therapeutic purposes and trigger apoptosis in cancer cells. In this study, we investigated the effects of hydroalcoholic root extract of R. khorasanicum treatment on inducing mitochondrial apoptosis of HT-29 and Caco-2 human colorectal adenocarcinoma cells. Firstly, the total phenolic and flavonoid content was determined. Then, the cytotoxic effects of R. khorasanicum on cells of three different types, including HT-29 and Caco-2 colon cancer cells as well as normal 3T3 cells were assessed using the MTT assay. To investigate the characteristics of cellular death, flow cytometry, and western blotting were performed. The results of this study indicated considerable phenolic (356.4±9.4 GAE/gDW) and flavonoid (934.55±17.1 QE/gDW) contents in R. khorasanicum. MTT assay's finding indicated that 100, 60, and 30μg/mL concentrations of R. khorasanicum reduce cell viability in HT-29 and Caco-2 cell lines significantly (P<0.05). It has been also revealed that R. khorasanicum extract induces apoptosis rather than necrosis in these cell lines. Moreover, Bcl-2 expression was significantly reduced in both HT-29 and Caco-2 cell lines, while Bax and cleaved caspase-3 expression soared considerably in the groups under R. khorasanicum treatment (P<0.05). In conclusion, our findings have suggested that high phenol and flavonoid contents of R. khorasanicum root extract possibly play an important role in cell cytotoxicity and apoptosis induction in HT-29 and Caco-2 colon cancer cells.

Plant anthraquinones: Classification, distribution, biosynthesis, and regulation

Anthraquinones are polycyclic compounds with an unsaturated diketone structure (quinoid moiety). As important secondary metabolites of plants, anthraquinones play an important role in the response of many biological processes and environmental factors. Anthraquinones are common in the human diet and have a variety of biological activities including anticancer, antibacterial, and antioxidant activities that reduce disease risk. The biological activity of anthraquinones depends on the substitution pattern of their hydroxyl groups on the anthraquinone ring structure. However, there is still a lack of systematic summary on the distribution, classification, and biosynthesis of plant anthraquinones. Therefore, this paper systematically reviews the research progress of the distribution, classification, biosynthesis, and regulation of plant anthraquinones. Additionally, we discuss future opportunities in anthraquinone research, including biotechnology, therapeutic products, and dietary anthraquinones.

Potential medicinal plants to combat viral infections: A way forward to environmental biotechnology

The viral diseases encouraged scientific community to evaluate the natural antiviral bioactive components rather than protease inhibitors, harmful organic molecules or nucleic acid analogues. For this purpose, medicinal plants have been gaining tremendous importance in the field of attenuating the various kinds of infectious and non-infectious diseases. Most of the commonly used medicines contains the bioactive components/phytoconstituents that are generally extracted from medicinal plants. Moreover, the medicinal plants offer many advantages for the recovery applications of infectious disease especially in viral infections including HIV-1, HIV-2, Enterovirus, Japanese Encephalitis Virus, Hepatitis B virus, Herpes Virus, Respiratory syncytial virus, Chandipura virus and Influenza A/H1N1. Considering the lack of acceptable drug candidates and the growing antimicrobial resistance to existing drug molecules for many emerging viral diseases, medicinal plants may offer best platform to develop sustainable/efficient/economic alternatives against viral infections. In this regard, for exploring and analyzing large volume of scientific data, bibliometric analysis was done using VOS Viewer shedding light on the emerging areas in the field of medicinal plants and their antiviral activity. This review covers most of the plant species that have some novel bioactive compound like gnidicin, gniditrin, rutin, apigenin, quercetin, kaempferol, curcumin, tannin and oleuropin which showed high efficacy to inhibit the several disease causing virus and their mechanism of action in HIV, Covid-19, HBV and RSV were discussed. Moreover, it also delves the in-depth mechanism of medicinal with challenges and future prospective. Therefore, this work delves the key role of environment in the biological field.

A comprehensive review of the ethnomedicine, phytochemistry, pharmacological activities of the genus Kniphofia

CONTEXT

Kniphofia (Asphodelaceae) is found mainly in South Africa and Tropical Africa. Malaria, hepatitis B, blood purifier, cancer, eczema, and female infertility have all been traditionally treated using this genus.

OBJECTIVE

The current review provides a complete and up-to-date compilation of documented traditional medicinal uses, phytochemicals, and pharmacological activities of the genus.

METHOD

Relevant literature was collected by searching the major electronic scientific databases including PubMed, Science Direct, Web of Science, and Google Scholar using appropriate keywords ethnomedicinal studies, phytochemical investigations, and pharmacological activities of Kniphofia species. The search strategy included all articles with descriptors that were available until November 30, 2021. Only published works in English were used for this study. The data were collected using textual descriptions of the studies, tabulation, grouping, and figures.

RESULT

At present, more than 40 compounds have been isolated from different parts of Kniphofia species. The major compounds isolated from the Kniphofia species are monomeric anthraquinones and dimeric anthraquinones. Pharmacologically the extracts and isolated compounds showed antioxidant, antimalarial, antiproliferative, anti-HIV-1, anti-leukotriene, and cytotoxic activity. The genus afforded exemplary drug leads such as knipholone and knipholone anthrone with anti-HIV-1, antimalarial and cytotoxicity activity.

CONCLUSIONS

Kniphofia species have traditionally been used to treat a variety of diseases. Pharmacological actions of phytochemicals were shown to be promising. Despite this, considering the genus's inclusion on the red data list of South Africa, it deserves more attention. In order to find novel drug candidates, more studies on promising crude extracts and compounds are needed.

Endemic medicinal plants of Ethiopia: Ethnomedicinal uses, biological activities and chemical constituents

ETHNOPHARMACOLOGICAL RELEVANCE

Around 80% of Ethiopians rely on traditional medicinal plants to treat a variety of ailments, and the country is home to a number of endemic plants, making it part of East Africa's hotspot of biodiversity. Despite widespread acceptance of endemic medicinal plants among the local community, comprehensive documentation of their therapeutic uses and phytochemistry is lacking. This review thus provides the first comprehensive appraisal of traditional use, pharmacological properties and phytochemistry of Ethiopian endemic medicinal plants. By storing and preserving indigenous and scientific knowledge about the medicinal benefits of the plants, such documentation generates information database for the future. It also aids the conservation of key medicinal plants along with translational research to accelerate the development of pharmaceuticals.

AIM OF THE REVIEW

The aims of this review are to collect and document current information on the ethnopharmacological uses, phytochemistry, and biological activities of Ethiopian endemic medicinal plants, identify research gaps, and provide perspectives and suggestions for future research on the plants as potential sources of pharmaceuticals.

MATERIALS & METHODS

A comprehensive literature review using electronic databases such as Medline, Web of Science, Google Scholar, ScienceDirect, SpringerLink, and Wiley Online Library was conducted for collecting relevant information. The World Flora Online (WFO) database and the International Plant Names Index (IPNI) were utilized to authenticate the taxonomic information of the plants. Chemical structures were drawn using ChemBioDraw Ultra 12.1 and verified via PubChem.

RESULTS

The present review has identified 412 Ethiopian endemic plants. Out of the 412 endemic plants species recorded for Ethiopia 44 are medicinally valuable to mitigate a myriad of diseases, and nine (27.3%) of them are endangered. Our literature survey also found out that a total of 74 compounds were isolated and characterized from the endemic plants, with phenolics accounting for the majority of them (66.2%). The plants exhibited antimalarial, antimicrobial, anticancer, anthelmintic, mosquitocidal, antidiabetic, antioxidant, and anti-inflammatory properties.

CONCLUSION

The work has resulted in an up-to-date inventory of Ethiopia's endemic flora, as well as the identification of species with traditional medicinal uses. The pharmacological activity and phytochemistry of numerous endemic plants with various traditional therapeutic claims are yet to be researched scientifically. Scientific validation of the herbal remedies, including evidence-based safety and efficacy studies are, therefore, crucial. The endangered medicinal plants must be conserved in order for local communities to have access to them in the future.

Effect of Substitution of Hydrogen Atoms in the Molecules of Anthrone and Anthraquinone

The geometry of anthrone and anthraquinone-natural substances of plant origin-was investigated under the substitution of hydrogen atoms in side aromatic ring and, for anthrone, also in the central ring. A significant influence of substitution on geometry expressed by the angle between the side rings was shown. The geometry changes are connected with the changes of electron density and aromaticity of the anthrone and anthraquinone rings. The flexibility of the investigated compounds was confirmed by comparison of the optimized molecules and the molecules in the crystal state where the packing forces can influence the molecular geometry.

Modulation of CYP3A4 and CYP2C9 activity by Bulbine natalensis and its constituents: An assessment of HDI risk of B. natalensis containing supplements

BACKGROUND

Bulbine natalensis is an African-folk medicinal plant used as a dietary supplement for enhancing sexual function and muscle strength in males by presumably boosting testosterone levels, but no scientific information is available about the possible herb-drug interaction (HDI) risk when bulbine-containing supplements are concomitantly taken with prescription drugs.

PURPOSE

This study was aimed to investigate the HDI potential of B. natalensis in terms of the pregnane X receptor (PXR)-mediated induction of major drug-metabolizing cytochrome P450 enzyme isoforms (i.e., CYP3A4 and CYP2C9) as well as inhibition of their catalytic activity.

RESULTS

We found that a methanolic extract of B. natalensis activated PXR (EC₅₀ 6.2 ± 0.6 µg/ml) in HepG2 cells resulting in increased mRNA expression of CYP3A4 (2.40 ± 0.01 fold) and CYP2C9 (3.37 ± 0.3 fold) at 30 µg/ml which was reflected in increased activites of the two enzymes. Among the constituents of B. natalensis, knipholone was the most potent PXR activator (EC₅₀ 0.3 ± 0.1 µM) followed by bulbine-knipholone (EC₅₀ 2.0 ± 0.5 µM), and 6'-methylknipholone (EC₅₀ 4.0 ± 0.5 µM). Knipholone was also the most effective in increasing the expression of CYP3A4 (8.47 ± 2.5 fold) and CYP2C9 (2.64 ± 0.3 fold) at 10 µM. Docking studies further confirmed the unique structural features associated with knipholones for their superior inductive potentials in the activation of PXR compared to other anthraquinones. In a CYP inhibition assay, the methanolic extract as well as the anthraquinones strongly inhibited the catalytic activity of CYP2C9 while, inhibition of CYP3A4 was weak.

CONCLUSIONS

These results suggest that consumption of B. natalensis may pose a potential risk for HDI if taken with conventional medications that are substrates of CYP3A4 and CYP2C9 and may contribute to unanticipated adverse reactions or therapeutic failures. Further studies are warranted to validate these findings and establish their clinical relevancy.

The isolation of secondary metabolites from Rheum ribes L. and the synthesis of new semi-synthetic anthraquinones: Isolation, synthesis and biological activity

Rheum ribes L. (Rhubarb) is one of the most important edible medicinal plants in the Eastern Anatolia region and is called "Işkın" by local people. Resveratrol and 6-O-methylalaternin were isolated from the Rhubarb for the first time in addition to well-known secondary metabolites including emodin, aloe-emodin, β-sitosterol and rutin. The new semi-synthetic anthraquinone derivatives with the N^αFmoc-l-Lys and ethynyl group were synthesized from the isolated anthraquinones emodin and aloe-emodin of Rhubarb to increase the bioactivities. Aloe-emodin derivative with N^αFmoc-l-Lys shows the highest inhibition values by 94.11 ± 0.12 and 82.38 ± 0.00% against HT-29 and HeLa cell lines, respectively, at 25 µg/mL. Further, modification of the aloe-emodin with both the ethynyl and the N^αFmoc-l-Lys groups showed an antioxidant activity-enhancing effect. From molecular docking studies, the relative binding energies of the emodin and aloe-emodin derivatives to human serum albumin ranged from -7.30 and -10.62 kcal/mol.

The African natural product knipholone anthrone and its analogue anthralin (dithranol) enhance HIV-1 latency reversal

A sterilizing or functional cure for HIV is currently precluded by resting CD4⁺ T cells that harbor latent but replication-competent provirus. The "shock-and-kill" pharmacological ap-proach aims to reactivate provirus expression in the presence of antiretroviral therapy and target virus-expressing cells for elimination. However, no latency reversal agent (LRA) to date effectively clears viral reservoirs in humans, suggesting a need for new LRAs and LRA combinations. Here, we screened 216 compounds from the pan-African Natural Product Library and identified knipholone anthrone (KA) and its basic building block anthralin (dithranol) as novel LRAs that reverse viral latency at low micromolar concentrations in multiple cell lines. Neither agent's activity depends on protein kinase C; nor do they inhibit class I/II histone deacetylases. However, they are differentially modulated by oxidative stress and metal ions and induce distinct patterns of global gene expression from established LRAs. When applied in combination, both KA and anthralin synergize with LRAs representing multiple functional classes. Finally, KA induces both HIV RNA and protein in primary cells from HIV-infected donors. Taken together, we describe two novel LRAs that enhance the activities of multiple "shock-and-kill" agents, which in turn may inform ongoing LRA combination therapy efforts.

1-Hydroxyanthraquinones Containing Aryl Substituents as Potent and Selective Anticancer Agents

A series of 1,2-, 1,4-disubstituted or 1,2,4-trisubstituted anthraquinone-based compounds was designed, synthesized, characterized and biologically evaluated for anticancer efficacy. 2- or 4-arylated 1-hydroxy-9,10-antraquinones (anthracene-9,10-diones) were prepared by Suzuki–Miyaura cross-coupling reaction of 1-hydroxy-2-bromoanthraquinone, 1-hydroxy-4-iodoanthraquinone or 1-hydroxy-2,4-dibromoanthraquinone with arylboronic acids. The cross-coupling reaction of 2,4-dibromo-9,10-anthraquinone with arylboronic acids provide a convenient approach to 2,4-bis arylated 1-hydroxyanthraquinones with a variety of aryl substituent in the 2 and 4 position. The cytotoxicity of new anthraquinone derivatives was evaluated using the conventional MTT assays. The data revealed that six of the aryl substituted compounds among the entire series 3, 15, 16, 25, 27, 28 were comparable potent with the commercially available reference drug doxorubicin on the human glioblastoma cells SNB-19, prostate cancer DU-145 or breast cancer cells MDA-MB-231 and were relatively safe towards human telomerase (h-TERT)immortalized lung fibroblasts cells. The results suggested that the in vitro antitumor activity of synthesized 2-aryl, 4-aryl- and 2,4-diaryl substituted 1-hydroxyanthraquinones depends on the nature of the substituent within the cyclic backbone. Docking interaction of 2-, 4-substituted and 2,4-disubstituted 1-hydroxyanthraquinones indicates intercalative mode of binding of compounds with DNA topoisomerase. The interaction with the DNA of 4-aryl-13, 15, 16 and 4-(furan-3-yl)-23 1-hydroxyanthraquinones was experimentally confirmed through a change in electroforetic mobility. Further experiments with 1-hydroxy-4-phenyl-anthraquinone 13 demonstrated that the compound induced cell cycle arrest at sub-G1 phase in DU-145 cells in the concentration 1.1 μM, which is probably achieved by inducing apoptosis. 4-Arylsubstituted 1-hydroxyanthraquinones 13 and 16 induced the enhancement of DNA synthesis on SNB19 cell lines.

The potential of anti-malarial compounds derived from African medicinal plants: a review of pharmacological evaluations from 2013 to 2019

Background

African Traditional Medicine (ATM) is used for the healthcare of about 80% of the rural populations of the continent of Africa. The practices of ATM make use of plant-products, which are known to contain plant-based secondary metabolites or natural products (NPs), likely to play key roles in drug discovery, particularly as lead compounds. For various reasons, including resistance of strains of Plasmodium to known anti-malarial drugs, local African populations often resort to plant-based treatments and/or a combination of this and standard anti-malarial regimens. Emphasis has been laid in this review to present the anti-malarial virtue of the most recently published phytochemicals or natural products, which have been tested by in vitro and in vivo assays.

Methods

The data was based on the current version of the African Compound Libraries, which are constantly being updated based on inputs from journal articles and student theses (M.Sc/Ph.D) from African University libraries. Emphasis was laid on data published after 2012. In order to carry out the original data collection, currently being included in the African Compounds Database, individual journal websites were queried using the country names in Africa as search terms. Over 40,000 articles “hits” were originally retrieved, then reduced to about 9000 articles. The retained articles/theses was further queried with the search terms “malaria”, “malarial”, “plasmodium”, “plasmodial” and a combination of them, resulting in over 500 articles. Those including compounds with anti-malarial activities for which the measured activities fell within the established cut off values numbered 55, which were all cited in the review as relevant references.

Results and discussion

Pure compounds derived from African medicinal plants with demonstrated anti-malarial/antiplasmodial properties with activities ranging from “very active” to “weakly active” have been discussed. The majority of the 187 natural products were terpenoids (30%), followed by flavonoids (22%), alkaloids (19%) and quinones (15%), with each of the other compound classes being less than 5% of the entire compound collection. It was also observed that most of the plant species from which the compounds were identified were of the families Rubiaceae, Meliaceae and Asphodelaceae. The review is intended to continue laying the groundwork for an African-based anti-malarial drug discovery project.

Anti-amebic effects of Chinese rhubarb (Rheum palmatum) leaves' extract, the anthraquinone rhein and related compounds

Entamoeba histolytica infects 50 million people worldwide and causes 55 thousand fatalities every year. Current anti-amebic drugs (e.g. paromomycin) work either at the level of the intestinal lumen (where trophozoites proliferate via cell divisions) or on the invasive trophozoites that have penetrated the gut or colonized internal organs (e.g. metronidazole). Some of these drugs are highly toxic to patients, have generated trophozoite resistance, or caused mutations and cancer in laboratory animals. Thus, alternative anti-amebic compounds need to be identified to minimize the side effects (on patients) or resistance (by amebas) to current treatments. The literature suggests that anthraquinones (chemicals found in medicinal plants) have antibacterial, antiparasitic, anti-inflammatory and antioxidant properties. Here we provide experimental evidence that Chinese rhubarb (Rheum palmatum) leaves' extract (rich in the anthraquinone rhein) inhibits E. histolytica trophozoite growth in vitro. In addition, from a set of ten isolated/synthetic anthraquinones (which we suspected to have anti-amebic properties), four analogs (rhein; AHHDAC = 1-amino-4-hydroxy-9, 10-dioxo-9, 10-dihydro-anthracene-2-carboxylic acid; unisol blue AS; and sennoside B) efficiently inhibited amebic growth at EIC50 concentrations comparable to metronidazole. The mechanism of action of these compounds still needs to be determined, although anthraquinones might enhance the production of toxic oxygen metabolites as it has been suggested for various protists (e.g. Leishmania, Plasmodium, Trypanosoma). Our research is the first to explore anti-amebic effects of Chinese rhubarb leaves' extract and isolated/synthetic anthraquinones on pathogenic Entamoeba.